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Bell & Hawell Information and Lmrning 300 North Zeeb Road, Ann Arbor, Ml 481-1 346 USA
Design of a Composite Link for the Freedom-7 Haptic Hand Controuer
by
John McDougall
Department of Mechanical Enginee~g
McGiU University, Montreal
A Thesis Submitted to the Facaiîty of Gtaduate Studies and Research
in Partial Fulnllment of the Requirements of the De- of
Master of Engineering
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A bstract
The Fnedom-7 Haptic H h d Ccmtroiicr is a high pafbmmœ hapic device &velopd
jointly bctween McG'ï and MPB Tcchnologies. This thesis diScusses previous wœk in
the field of haptic devices. the rrsearch into the bcmâing of mctils to Compdsites,
optimization procedures f a Composite hmhtcs, snd iiiclucks a bief ovav*w of human
haptic capabilities. The disassicm imludes the anal* procas d to design a
composite box-kem structure to replace one linL of tbe translation stage of tbc head
controlier, and to &termine the opcimil bond chatacteristics fa tbe joining of a smaU
diameter composite tube to a mail end fitting. Iterative finite element anaiysis as welï as
failure and vibration testing wae u d to dttcrmine tbc efficicncy of the designs. and to
measure the improvemcnts in the dynamic propcrties of the haptic device's structure.
Though certain clifficultics w a e eacountcred during tbe manufktwhg of the prototype
that lead to disappointing physical test d t s . th simulations p v e that a haptic device
such as the Frtedom-7 cuuid grcaîiy benefit !km the inclusion of composite materials
into the structure.
Résumé
Le contrôleur haptique Eieadam-7 est un aispositif de haute @OC~B~MX dévelappé
conjointement entre l'Université McGiU et MPB tachnologit~. Cette Ceac tbtse les
travaux existants sur les dispositif& haptiqucs, les mCthodcs d'dhaaia entre lu
matériaux composés et les métaux, les proddiins pour optimiser la structure des laminés
ainsi que les recherches sur les capacités du système haptique humain. L. discussion fait
part de l'analyse d'une sa~cbrie mcmocoque en fibre de carbanc utilisée pour remplacer
un joint d'alruninium dans k dispositif. De plus, l'opthhtion de la géométrie d'un
joint adhésif entre un tube ai fibre de a&mc et une garniture m aluminium est
expérimentée. L'efficacité du design a Cté Cvaluée par une analyse empirique ainsi que
differents tests mesurant la résistance et la vibration. C a demiers sement aussi a Cvaluer
les am6liorations des amcté&icpes dynamiques dc la stn~cture du dispositif. Cer<ams
problèmes de fabrication nuisent L 1. paf~rmzt~lce du dispositif lm des tests physiques,
mais les simulations par adinatau prouvent qw la possibiiité existe d'accroître
considérablement la penormance avec l'utilisation de matériaux avancés.
This work is dedicated to sevaal p p s ofpeop1e, without wh- SU- it neva
wouid have ban completed To my parmts, fa @ng me hat. To my fiends for
supporting me. To Rof. Lamy Lessard fœ ptting up with m. And to Emilie fa king
them for me.
Thanks must also p to Rof. V i t ILyward fa initiating the Freedom- 7
project. Also, to the peopie at MPB Tdmolqks, Dr. Ln Sinciair, Smdcr Boclm, a d
Jean Pouiin for ali thtir help in the initiai stages of the projcct. S@d thanlu must a h
go to Dr. Diao Xiaoxue for his invaluable help at th end of the pmjcct-
Table of Contents ............................................................................................... 1 . I.ntroduction to M o m - 7 1
1.1 Haptic Devices .......................................................................................................... 1
1.2 Requircmcnts for Haptic Devices . ................. ............................................................ 2
1.3 Advanced Matcrial Advantages .................... ............................................................ 4
1.4 F d ~ m - 7 ................................................................................................................. 5
. 1 5 Objectives of this thesis ........................................................................................... 11
. ....................*....*......*..*.*......................................................*............. 2 Litcrame Review 12
....................................................................................................... 2.1 General Haptics 12
........................................................................ 2.2 Literaûuc Review of Bonded Joints 17 . . . 2.3 fiterature Review of Iamhate Optimur mm. ......................................................... 23
............................................................................................... . 3 Design of Bonded ni- 29
3.1 Introduction ............................................................................................................. 29
3.2 Material Survey of Composite Tbbes ...................................................................... 29
3.3 Geometry and Parameter Variation of B4aded Inscrt~ .......................O...................e 33
3.4 Axisymmetric Fmite Element Modcls .................................................................... 34
............................................................................... 3.5 Results of Parameter Variath 36
3.6 Three Dimensional Finite Element Mode1 ............................................................ 43
4 . Bonding Tests .............. ..................................................................... ................. 4 9
4.1 Three-Point Bend Test ................... ....................................................... 49
4.2 Calcuiaîions for Bending Moment Load Case ........................................................ 51
4.3 Test R d t s ............................................................................................................. 53
5 . Design of Box Beam ..................................................................................................... 56
5.1 Introduction ............................................................................................................. 56
5.2 Dimensionai Requirrments f a the Box Bcrm .................................................... 56
5.3 Finite Element Mode1 of the Disral Stage Lhkage ............................................... 58
5.4 Results of Fite Eletnent Modd ............................................................................. 60 6 . Box Beam Prototype ..................................................................................................... 61
.......................................................................................... 6.1 Carbon Fiber Box Bcam 61
6.2 End Fittings ........................................................................................................... 65
.......................................................................................... 6.3 Bondhg of End Fittings 66
................................................................................ 6.4 TCSU an Fnedam-7 67
6.5 Frequtncy Respawc ofTransiatio(1 Stage .............................................................. 68 6.6 Refied Fite Element Mode1 of Distal Style Linkagc ......................................... 71
6.7 Maximum Acctlaati011 test^^^^^^.^^^.^^.^^^^^^^^^^^^^^^^^^^^^^^^^^^ 76
6.8 Summary for Box Berm Protdyping and Testing .................................................. 77
7 . CO~C~US~OLIS and R ~ C O ~ T T I S ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - ~ ~ ~ * ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ * ~ * ~ ~ ~ ~ ~ ~ ~ * ~ ~ ~ ~ * ~ ~ ~ ~ * 79
7.1 Rccommendaticms fbr Futme W d . . ...................................................................... 80
8 . Bibliogxaphy ............. ..................................................................................................... 81
1 . Appendix A ................................................................................................................... 9-i
2 . Appendix B ............................................................................................................... 10-ix
McGiii University Depamxms of MacbraicJ h g b u h g
Table of Figures Rgun 1.4.1 . PHANTOM .................................................................................................. 5
......................................................................................... Figure 1.4.2 O PER-Force device 6
Figure 1.4.3 O SARCOS dcxtcrais mn ................................................................... 6
Figurt 1.4.4 . Large W- IIud m&ok (LWHC) ................................................ 7
............................................................................ Figure 1.4.5 O S W S Hand Controller 8
Figure 1.4.6 . Frredom-7 Translation Stage ........................................................................ 9
. fi gui^ 1.4.7 O M m - 7 Distd St-6 ........................................................................ 10
...................................................... Figure 1.4.8 . The Frecdom-7 Haptic Hand conar~Uet 10
.............................................................................. Figure 3.2.1 O High-tech Arrow Shifts 30
Figure 3.3.1 . Bond Geometry for Parameter V a 0 1 1 .. ............................................ 33
Figure 3.4.1 . Axisymmtnc Fuite Elcmcnt Mode1 of Baided Geometry ....................... 34
Figure 3.4.2 . Rcfercnce Locations on Bond Geometry .................................................... 35
Figure 3.5.1 . Variation of Peak Rincipai Stress with Ad- Wail Thiclmess ............ 37
........................ Figure 3.5.2. Variation of Peak Rincipal Stress with Axial Engagement 37
Figure 3.5.3. Variation of Peak Principal Stress due to Bood Linc 'Ihickness ................. 38
Figure 3.5.4 . Maximum Principal Stress Contours in Epoxy Matairil fol
Test 1.4 (Bond AD Broken) ..................................................................................... 38
Figure 3.5.5 . Maximum Rincipal Stress Contours in Epxy Materhl for
Test 1.1 (Bond AD Exists) ...................................................................................... 39
Figure 3.5.6 . Maximum Rincipal Stress Contours in Epoxy Material with
Epoxy Fiet for Test 1.3 (Bond BAD Exists) .......................................................... 39
Figure 3.5.7 . Variation of Rincipal Sûes Along Bond due to Adberend
Thickncss (a) ................... ......................... .............................................................. 4 0 Figure 3-58 . Variation of Rincipai Stress Along Bond due to Bond Lise
Thichess (i) ................................. ....... ...................................................................... 41
Figure 3.6.1 . Three Dimens id Fite Element Mode1 of Bonded Tube
Geometry ................................................................................................................... 43
McGiii University Deputment of Mtchnicrl pjimmcnnr . .
Figure 3.62 . Maximum Rmcqioi S c r ~ Ccmtaars in Compaitc Tiibe
Close to Bondcd Region *..............**.~.....~.*~.......*.*~.*.....................*...*......................... 45
Figure 3.6.3 . Maximum Phcipal S m Coafouft fa B o d d F~ce of
....................................................................................................... Aluminm IIISCrt 46
Fiw 3.6.4 - Maxim- Principal Stress Con- in Epoxy Bond M.rcri.l .................. 47
Figure 4.1.1 - Sketch of thme-point buxi test wtup .......................................................... 49
Figure 4.1.2 . The-point bcnding test sprçimen ............................................................. 50
Figure 4.1.3. Variation of dimensions f a t h point bcnding tests ................................ 51 Figure 4.2.1- Shear and bading mmicnt diagrmm fa ibrrapoint kadmg tests ............ 5 1
Figure 4.3.1 . Graph of piston f a a va centexpoint displaccmcnt .................................. 54
Figure 4.3.2 O Broken thte~point bad rprcimm ............................................................ 54
Fi- 5.2.1 . Clearance area foi the distal stage driving Sazags ................... ... ............ 57
Figure 5.2.2 . Exploded view of cabon f i k distal stage assembly ................................. 57 Figure 6.1.1 . Time-tempcraturie Profile fa LTM25 Cure Cycle .................................... 62
Figure 6.1.2 . Lay-up Rocedurt for Composite Box-Sectim ........................................... 64
Figure 6.6.1 . Rcfined modcl of dist.l iinkagt for vibration simulati 011 ........................... 71
Figure 6.6.2 . Renned finite elemait modcl of distai linlrage with addd
cover for vibration simulah'011 ........................... ........... ........................................ 72
Figure 6.6.3 . Normal mode vibration in x direction of disîai stage with an
added cover ..................... ... ............................................................................... 73
Figure 6.6.4 œ Normal mode vibration in x direction fa u n c o v d distal stage .............. 73
Figure 6.6.5 . Stress contours in u n c o v d pilky btock base ...................................... 75
Fi- 6.6.6 . Stress contours in covasd puilcy block base .................... .................... 75
McGiU University Dcpucmnt ofbfdmid- . .
active DOF - eny DOF that can ex- r face or tmpc cm tbe usa's haad / body
uctuation dime1csio114Jity - tbc n u m k of active &pcs-of-- in the &via
adherend - the part of a bonded joint thaî b bejag glued
adhesive - the glue holdmg the two adhemds togetber
actzutor - any systcm to c01lvty torQuc a fcrce to a part of th mbatic device
buckdn'veuble - the abiLity to move a M c structpre by applying fara to tbe end
effector without any aiding joint torques
bucklash - small movcments in btMngs aad otba joints
bi-directional - a &ta Stream that fiows in two directions, i.t. rcad and w r i ~
bond Iine thickss - the distance betwccn two a d h d that is fillexi with adhesive
construined impedrutce - innnitc stifhess contact
crispness - subjective tam m f e g to the quality of a sensation felt through a haptic
interface
cure - the process of hcating, prrsourizing ancl then cooling an cpoxy to change the stnte
fkom liquid to soiid
degrees-of-fieedom (DOFI - the numbcr of dircctiolls in which a device is fkcc to move in
either translation or rotation
device intrusion - physical prcscnce of the haptic device in the operator's W-
engagement - the length of the adbesive bonâ
fidelity - the ability of a haptic intcdkc to accurately rrprerient a vlla>al aivuomSnent
fiber ~ r i e ~ o n - the direction almg which the fibcrs in the composite matcrial arc
aligned
haptics - the branch of study derLUig with tbe human sense of touch
marter robot - a robotic structure that controis through teieopcraticm motha robot
m o u - a rigid tool used to fam the imaMd composite rmPBii1 into a useabk sbripc
siàve robot - a robotic structure that is controiied by anotba robot or hand amtroUcr
teleoperution - action transmittcd ova a distance by an electronic signal
1. Introduction to Freedom-7
1.1 Haptic Devices
In the short span of twenty yr03, the computcr has gone fran an expensive.
novelty item to an essential tool that can be famd in ail walks of lifc. 'Lbe gains in
computing powcr have ban aiormous: early gcnerations of cornputers wcrc the sizc of a
r o o m a n c o u l d d o l e s s t h a n w b a t m o s t ~ a f c h c a l ~ d o ~ y . Thisquantum
Ieap in speed and capability. as weU as an mcrtrsmg danand foc hi@ s p d pcass to
idonnation, has contributcd to the incursion of the cornputer into every aspect of our
lives.
With the inCrrascd spssd of compufas. users can exist and interrt witû virtual
environments that woald have aai impossible to imagine only a dccde rgo. A viiai91
environment is a amputer quivalent of the reai world It can bc anything from a flight
simulation to a museum, w h m the user can browse thraugh thmszl~lds of rare painthgs.
The one thing about the vutual environment that remains constant is that it does not
physically exist anywherc except as a coiiection of 1's and 0's in the b ' i memory of a
computer.
Where btfote p p l e couid d y expaiare th*re m a l environmcnts ihrough
sight and sound, with the intmcluction of a varicty of haptic devices they c m now explore
with the sense of touch also. Hhptics is th branch of psych010gy that deals with the
cutaneous sense data, in otha words the data tbat is transmitted to the brai. by the
pressure receptors in the skin. 'Ibmfm, a @tic device is a &vice that will translate
cornputer signals into prwsun a face on the usa. The slan prwwirr that the user feeLp
fkom the device, wmbined with the visuaï and auditory inputs fmm the vir&uai
environment, crcate a -ter sense of bcing inside the envinrnmcat gc11eratcd by the
cornputer.
The haptic device is a bi-dircctional interface [l] between the human user and the
computer. It has to k able to accept usa @ut as welï as deliva its own àata output
back to the user. Ibe &CC~~VCIICSS oftfiU delivay % what udl dintraia'str! a "good"
haptic &vice h m a "badn au. HOWCVQ, detumining the qculity of this delRmy is not
assirnpleasitseems. T h c ~ t s f a h r p i c & ~ r r r d i t f i a e D t ~ o t h a
robotic applications. For clarity, a set of texms wiii be urtd to describe the gencrai
attributcd of ai i hand ~~~~trol îcrs:
DOF - & m f - f i e e d ~ m
hand controller - MY &vice thit â~ ui htafsce the US^ rnd
virtud enviranmcnt that is htcnded to be uscd by an operator's hand
a ~~~riveDOF-&~f-fi.eedomaiwbichthachfaaaatsdbythW
controller
a octuam - my focce or toque applicator
end-ejJiector - point at which the interfact bttwcc~l hwnan operator and hand
controilcr occurs
FFB - force ftedback
1.2 Requirernents for Haptic Devices
The earliest &tic devices wac designcd to give i a f d o n to the usas about
force states in the rai environment that they wert conttolling. Thcse k t FFB devices
were connectai physidy ta the remdt environmcnts by mechanical IinJcagcs such as
wires. For instance, in the bippluvs of Wodd War I, the pilots d d feel the faces on
their control surfaces tnulsmitted tbrough Qu flight control sticks, making the wntrol
stick into a haptic dtvicc [2]. The first genaiPon of -tic d e v i a ~onneard
electronidy to a nmote cnvvOnment t a c deviscd fa use in the nuclcar industry, to
enable operations to be carricd out in extttmtly hazadous enviraamcnts [1,2]. TheSe
devices consisted of dymmicaiiy identicai nuaster and s h robots, since the comp~ting
power at the time was not mfficicnt to calcuiatc extensive trandormatio~ls bctwœn the
two. The master =fers to the contmiihg device, and the slave refcts ta the mate
device.
In a virtual d t y application, the most important conccm is whctûcr th opnta
fbels lilre hdshe is r d i y inside tbe enviraimmt [3-'11. Ifthe virtuai cnviromneiit sccms
resolution of the device Cl], due to the limitai capacity of the human scnsory sygan to
absolutely locate a given point in space. Resolution is the maximm defiection about a
stationary point that the &vice genartes at an upilibrium statc. A vibratory dcflcction
caused by the conml systcm, irtuua ined#luacies or structurai Wts kreascs the
transparcncy of the hand colltroilcr.
To achieve transparency in a haptic device like a hand cuntrollet, tbae arc several
key requirements that need to be met. Fust, the structure of the hand contdler mua have
a very low inertia If the opaata is moving h g h h c s p x h i d e the cornputer, they
should not feel a large mass of the hrad cunaolla rcsisting h i . rnotiolls. Tbe low
inertia of the coatro11cr must k couplal with an almost constant and diagonal inertia
tensor. Achieving an inat* tcnsor that is constant and d i a g d wil l aiiow the inertia felt
by the operator to be equd in alï configurations of the hand controller mechanism. 1t wiîi
not seem heavier or lighter towards the edgcs of the wodcppw than it does in the middle.
Furthermore, a low linlt inertia will incrase the crispllcss of such FFB sensations as
impact with an immovblc wall- Minimizing the link inatia wil l incruise the maximum
acceleration that a given actuators can aeate at the end effcctorr. The s a m d requircrnent
of the structure of the hand controiler W link stiffiiess. The sti&r the links, the grtater
the dynamic benefits. The ramant iutursl fiequcncy of a sûuctun is depmdmt on its
stiffiiess: the higher the stiffiress the gMta the naairal fiqucncy. With stifftr links
comprising the structure of the hand conîmiier, hi* frcqucncy phcnomcnon such as
working a drill or scratchhg a mugh surface Mth a pencil can k simulrtcd without the
danger of rcaching a nsaiant frcquency of the stmcturc and inducing vihtion- As the
vimial pointer wmcs into contact with a solid wali, tbe cornputer QC&S to sample the
pointer location and calculate a joint face consistent with the proximity to the walL To
achieve thefidelity of such a simulation, the rrspaisc of the controller must be at a vay
high frcquency, on the order of #)O Hz.
McGill University Deputmcnt of Mechrnicrl- 3
1.3 Advanced Material Advantages
ïhge arc -y advmtagcs to the incapoiriion of dvmced Compogite mmeruls
into the dcsign and COIlSfNctioa of a haptic hand controiicr. Whm designers rcstrict
themselvestotraditidmstn;als,tbaeisaIunittoth~gnc~~ttUtc~ibermide
to op* lhk stifnie9p to wcight d o s . Fbr ( n d i t i d mrta.lr such u rtrel rid
duminum, the stinness and dcnsity aze constant. liaevitaôly, c o m p m k h a hu be made
in one of the design arcas.
With the in- utic of dvraced composite muaiils in mauy areas of
industry, the design toob fot applying Uvst matcri& arc becoming m a c avulrble. As
designers becorne more dortab le w&g with tkoc materiais, mon advantages
btcome apparent The ability to tailor the mataiai m e s of a laminate f a a spccific
task is unique to this type of matairl. A designer a n optimize the rmtcri.l in a iobotic
link for tcnsile moddus a d damping [8-141, two propcrties which are arasslrily nxed
in traditional matenalS. Designers are no longer rcstricted to madifications in the 1uiL
cross sections to obtain dcsmd results fa l ia dynamics.
1.4 Freedom-7 mm alnady e* scvctal makis of h;ipic &vice5 that are u!Bd specifically fa
vilaial nality applicaticms. Thy cm be divided into thcc categdcs- Tbe &st is the low
W F (dtp-of-frieed~m) dence$. 'Lbcse ae haptic devices thubm bi-diractid data
flow on three DOF's or less. They includt th PHANTOM (13.S. 15.1q &via
1.4. l), which is active in the thme trauslatid modcs aad has a thriee DOF rotationai
gimbai attached to a thimble that can k woni on tht user's index tinger. The Pantograph
[1,16,17] hasonlytwoactivettanslatidmades. WorkhaskcndcmeatUBCto
include a third active rotational mode to the Pantogmph [l]. As weU, severai haptic
applications have used muiitple Pantogmph uni& simdtancously to obtain mcrecised
active DOFs [lq. Th- arc scvcxal FFB joysticks on the market such as the immersion
Corporation's line of Irnpuise Sticks [18]- Tbtoe devices can d y provide an eshate of
the cask that the operator @onas in the vixtuai mvllanmcnt. Tbey am not sufficieat to
fully simuiate a reai system.
Figure 1.4.2 - PER-Force &vice
McGill University De- of Mechrnicrl E q m a m g . .
in the case of tbe PHANTOM &vice, the simuhW eavirainrent j8 siniilm to a
point probe. The user can invcstigatc the vimul mvinrmuiit in the thcc C M c s h
directions, but hPS w active rototicmai DOFs. This limits th vrricty and b of tbc
interactions that the user can have witb tbc mmote mvirarment,
The high DOF devices have enough compiexity to M y .imulra an interaction
with a virbal environnacnt. lhey do nut nœd to appmximate a ta& but cm rcpmcnt it
Mly . Examples of these high DOF devices am the Texas 9-string and the SPIDAR-I&
both stringed haptic i n t e r f ~ [lq. the PER-Fm joystick h m Cybcrntt Systcms Co.
[lq (figure 1.4.2). mt SARCOS tkxtawis a m masta (figure 1.4.3). and the FREFLEX
Figure 1.4.4 - Large Worksptace H4nd C ~ o l k r (LWHC)
McGiU University Deputment of Mechrnicrl Engmemg . . 7
exoskeleton mastem, among many others. T'hcsc FFB devices ail have several
drawbacks, the most cornmon of which is high complexity anâ inmision into the user's
workspace [la. Revious work by MPB anci Maiill d t e d in two high DOF hand contmiiers.
Tht first was a large worlcPprce h a d wntroller (LWHC) [6,19]. It comistd of a 3-DûF
rotational wrist mounted on a 3-WF translational stage (sec figwe 1.4.4). Large fiction
loads consistent with cxtrrmely ovcr1CIIYlCA bearings war dctrimcntal to the patimnance
of the LWHC. Another device caosc~cted at McGiîi was the cantilevd HC d e d the
STYLUS 119 1. The distal stage of this mode1 was surpendcd from the end of a jointed
aiutilever arm(figurt 1.4.5). The major drawback to this coz~troiîa was the static load on
the driving strings gentratecl by the gravity vecta. nie high moduius polymeric strings
required to drive the force feedback of the ccmtroiîa are prone to CL~CCQ. 'Ihis
configuration would themfoct k macccpW1e foi a production model
e 'TbeFreedom-7~~0lltro~irtbrlaerrhi~DOFhnd~odlatoemage
from the coqmation ktwœm MPB d Maiill [l9]. Xt has si% active DOF in the
translation and r o t a î ï d modes as weU as an o p t i d active scvmth DOF at the d
effcctor to simulate a plimgcr a a pir of sehom. 'Lht ttat paaypc, which exists in
an aii aluminum forni, solves the p b l c ~ l l s with th previous two prototypes.
The paraiiel design of the ttruislatim stsge (fi- 1.4.6) d œ ~ not rsquirc the hi&
modulus fibers for actuation, and they arc d c t e d to the ricbidtim of the distal stage
only. Low fiction, bush-1ess DC matcm m used as dinctLdiive acmitas on the
translation stage and aiiow fa -g of the grivicy f- vectar. An Mpn,ved
design of the distai stage ( f i p 1.4.7) IC~UCCS the incrtia felt by the opera-. Simple
tendon paths make assemb1y easiet md d o w for zero faa on the fibas at a@i'btium.
eliminating any creq d e f d m . A schematic of thc ursmibly of tht Fntdom-7
hand conttroiicr can bc sœn in figure 1.4.8.
1.5 Objectives of this thesis
niere exists two avauer f a improvcmcnt to this design thrt will be imdaraLen
in this work The f h t h to replact tbe stage 3 hbgc (figure 1.4.6) by a srmll diameter,
commerciaiiy avaiiable carbon f i k tube with boidcd mail insats. Second, the distaï
stage linlrage (figure 1.4.6) udi be rrplwd by 8 composite box-btam stnicbre. ?he
purpose of both these hclusions is to hcmaw the stühcss of tbe d t i n g sûucture while
decreasing the iink mas and inatu Howevcr, incranentai impovements of the
dynamic chanictenstics of hsptic devices need to be mcppurrd bascd <ni Specinc
pe~ormance criterion that do not correspoad neccssarily to those used fot traditional
robotic applications. As mch, propet mawmmmts have to be made to detam.int the
overall efféct the incorporation of advmced mstaiils hto the structure has on the
performance of the haptic device.
The foiiowing nsurch topics arc assocbd with the design and inclusion of
these two parts in the F d o m - 7 hsptic hanci controllcc
nieory and application of pmpcr end fixtures, i.e. propa design of composite
metal interfaces wiU k addrcssad. The design of the mral imerts wiU k optimjzcd fa
several basic geometric crittr ia
ïay-up choicc far the opthhtion of a bax. beam stnicturc will bc examined.
The choice of a lay-up fot composite parts can be @y af5cctcd by the applied loed
conditiolls.
optimization of composite parts for hi@ natunl frcquency and high damping
wiU be performed. The haptic hand controlk iaquins a vay high bandwidth, likc many
other potential applications for composite materials.
,Testhg of bonded joint strengîhs in bending wii l bc @annad. This testing is
m l y scen in the literaturc, whac the most cornmon foms of losding for a c m cross
section joint art torsion and axial.
Application of pmpcr test methods to dctcrmine prfamance characteristics of
haptic devices wii l be performcd. Thae is vay litilc in the way of serious pafbmmce
criterion for heptic devices, a d this topic shouid be ddrrsscd in ada to simpiify fiuther
work in this field.
M a University De-& Mecbrnicrl- . . 11
2. Literature Review
Before any action h taken to optimize the construction of a haptic devia, several
questions nttd to be auswctcd, F i of di, what factars wil l contri'butc most to the
improvcment of the devia? In [Il, Hayward md Strmg plnpose s c v d d i m t
performance muwns that can k usai to qyantitativcly detamirie the sUndard of a
haptic device. These measurcs include degrces of fieedom associated with the device
(actuated and non-actuatd), the type of device-body intcniiot, the range of motion of the
device. peaL force, incrtia and damping d pcak acce1eraticm. Howevcr, many of meSc
characteristics can be subject to M i t inttrpretatio~ls; ffa hstancc shodd the incrtia be
measured h m the point of view of the actuatars a the user, a d does the peak fora
mean the maximum actuator fofct, the hi- transient foife that can felt by the user, or
the maximum continuous fonx that can be applicd by the end efféctor? 1t becornes vay
important to &termine which factor wiU most af5ect the cvcntuai ~~a of a device
because expensive incremcntal improvcmcnts to nmdt ica i factors wili not serve to
increast the feel of the device.
The authors of [l]. H a y w d and Astley, suggest that the most important
characteristic of a haptic interface is bidimctiomlity. Tbe haptic chamel, as a human
sense, wiii both rcccive input fnnn and give output to the cnviranmcnt, Thercfort, any
device that sceks to use this sensory c h e l mua k b i d i r c c t i d as weU Achieving
both re!ading and writing of haptic M ' i o n by a mechanid dena rrquircs a design
that accounts for the inhacnt Limitations and capabbilies of the human haptic organs such
as the fïngertips, han&, and arms. In [2]. Durlach and Mavor d e w a p a t d d of woaE
that has been done to measme the sc~lsing capabilitics and limits of the human saisc of
touch, including both the hand and the arm. Though a full c-cm of the humui
sense of touch is weil beyond the scope of this work, certain clcments of prcviais wark
can be used to help detexmine rneaningfbi criterion fa the pafbrmmce muuns and
design goals of aie haptic inftnace. The human haad has 22 de- of fiaedom of
McGili University Deputmnt of M d m k d Eqummg - . 12
locatcd under the surfsce of the aLia Haptk opaatiocls arc divided into two ategorics.
ezphation and muùprrcetion. Exploration is dominrted by thc scmmy systcm located in
the skin, and serves to detamine the rmtcrkl and texturai pr0Peatic.s of the objea king
exploreci. Manipulation is a motor d o m h t d aperation tbat c01lsiscs of modifying the
environment thmugh the exa<im of faccs ai an objcct, and quires bi-directcmality of
the data seeam for succcssM ta& completion. Iae haptk data strecim itself can à
transmittcd by the neme endings under the skin and dominat#l the exploration ta&. The
kinesthetic data refas to the positionhg sauie derived by the I~CNOUS systcm from
information on joint angles and tendon faaa This data strcam wji l obviously dominate
the manipulation tasls. and is the most inîeresthg f a tbe purposes of this w& Any
mechanical design of a haptic intuface wii i be bavily dcpen&nt on the limitaticms of tbe
kinesthetic data nsolution. Of the w& that the authora [2] revicwed, the foiiowhg data
was providd for the ltinestbctic data rcsolution fa the average human:
1. It is possible to dctect joint rotatio~ls of a fiaction of a degree over the time
interval of seconds 121.
2. The kinesthetic saise had a bandwidth on the ada of 20-30 Hz. but goa up to
1 kHz for the tactual data stream [2].
3. The fartber the joint is 6rom the -ter of the body (th more distai the joint)
the lower the sensitivity to absolute joint rotations. 'Ibe methad for dctcrmining this is
caiied the jwt-mticeuûk-differcllce (JND). The JND for the fingcr joints is 2.5
degrees, for the wrist and elbow joint is 2 &grce and f a the shdder joint is 0.8
desces VI* 4. The Liaesthetic sense can detenaine to within 8 patent the différences in
position of a fixai point in space or a repeattcd movement [2].
5. A stiffness of at ltrst 25 N/mm h n c d d for a surface to be paoeived as rigid
Pl
--
McGill University Depurnrent of Mrcbrnicrl bguwamg . . 13
h [ 2 O ] , H a y w a r d ~ p ~ e v i 0 ~ w ~ t h a t w a s d a n e t o ~ t b t e n ~ ~ t o f
these haptic parameters an an eventuai design of a haptic i a t d b . ?be tests w a r
performed in a s u DOF simutrta on various subjacts- The conclusions of these tests
w m that the sensitivity of the subjbns to dUcrctc motions vaKd much 6 t h tbe subjoft's
training. A surgeon had tbc best s a m q discretization. ' I ky .Ira ccmcIuded tht, as the
most demancihg senses wac involved with high fhquency mations, the actuation of the
haptic &vice is much more hportant than its o v d pxecision in absolutt positionïng.
This conclusion is contrary to ~~~tvcntional robotic practice where the end e f f m
positioning is normally of the utmost h p t a m x , evca mae m thm avaiïable joint
toques and Linlc specds. Thus hi@ frcqucncy nsolutioa kfanes an important design
criteria for haptic &vices.
Other rt~earchers in the haptic design a m have come up with rcquirements for
haptic devices. In [3], Massic defiaes the ultimate feedback &vice as a "device . . . able
to apply forces, toques and dermai stimulation to m y part of the hnd" This is
obviously an imwnscly complu ta&. JU81 tbc degrces of hedom of mechanical motion
in the hand, 22 in all, w d d malrc this kmd of haptic &vice ptohibitively cornplex.
Massie goes on to list thrœ s u b m v e munas of a potcntiaiïy z d h b l t haptic device.
They are device intrusion, actuution dimc~lswnuiity andjMeiity. Device intrusion is
simpiy an ergonomic fiuiction of the design. and mliy has littie to do with the dynamic
behavior of the haptic &vice. Actuation dimcnsiOIllility refers to the active numbcr of
DOF's in the &vice. Fidelity is the ability of the haptic device to accurately simulate the
vittual event. To achieve sufncient fidclity in a dcvice, it should ncccwdy k ground
refercnd. If the device is mountcd to a fixed winace such as the floa or a rigid
tabletop, the forces that it will excrt on the operator will cause a teaction farçe on the
ground, not on anothcr part of the aperato~'s body as would k felt fa a body rcfcrenccd
device. This will allow fa a mat nalistic impression of the viraul environment.
However, Massie States thrit a gn>uad based device with long linlrages to a i l w f a a
greater range of motion WU duce the fidelity of the sirnufah'n.
In [21], Lawrence and Chape1 de- the ideai hand umtrolk in terms of
mechanical impbdance, and use this to detcmllae a range within which a non-idcal hand
McGill University Dcparmmt ofhkhmial Enpinacnnp - . 14
controllercanfunctionasanidcllhradccm~Ila. ' ï h c y ~ u e t û a î . ~ t h t h c i d a l ~
controlIer, whtn thcre is no contact crcaîcd in the virtual environment, the user should
feel no force, and that when in contact with 8 v i a w u a ob#r immovab1e obw the
stiffiiess should be infinite. 'Ibey SU- that t h ~ t r m s p i c l l ~ y of th^ tynnn will bê
improved by incrcasing structural stifnwsr rad toqse output of the h.ad ~tro l i cr , while
decreasing link stifhess. Lawrence d Chspel propose two mechanical hpdmces, the
constrained impedunce and the ~~~:onstraillCd inipcdonce, which coaespoad to infinite
stifbess contact and fkœ motion respectively, as two muair# of pdbnmxe for the
hand controllcr. Th unwmtmhd impedaiwr U afimctioa of thc f a a senshg
threshold of the human haptic syJtcm, md the mU-off frcquency above which a human
operator is unable to foilow a sinusoidal input to the h.ad coatrollc~, as well as the
amplitude of this input. 'Ibe simple sinusmidal input b a method of mwwcmcnt that can
be constant for alI haptic &vice$. The value for th imptdrnce required by
any haptic device wiil thcrefoct be vay sensitive the abilitics and training of individual
operators. nie constraincd impedancc for a low kqyency antact situation is a fbncticm
of the maximum masonable f- exerted by the user divided by the kineshetic nsoluticm
of the human operator. At high ficquency, the low hpency f k U x into a mae
complex equation including the same 20Ui)ff fiquency and amplitude for the sinusoida1
input to the human operator. nicrcfm, the constrainad irnpedana for the ideal heptic
device is also very dcpcndent on the Qualitits rad tnining of th aperatat, exoept in ihe
low Çcquency case. A device that bas enough fidelity fa use by a -do11 wodra
would not necessarily f e l good to a surgc011. ït Q possible to detetmint genaally the
haptic scnsing abilitics of the targeted usa population, but to do so Mth ciny &&LEC of
accuracy is almost impossible. Howevcr, we cm assurne fa the p p ê ~ of the Fradom-
7 pmject that, as the target user population for this devia is surgical training [22], the
structurai impedances on the mcchanism wili be v e y demanding.
In [23], Fasse and Hogan a#cmpted to measurc tbe hriptic paaption of a group of
subjects in a methodical statistical way. lbeir rrailts show that thzc is much marc work
to bc done in orda to modcl and mepsure the @tic prception of hunrsns. Two
experimcnts w e n pafcmncd to gage the subjects' ability to ducmmak . . . betwœn
McGili University Depurmmt of Mechrnrrl h g b m b g 15
lengths and angles in virmil rectangles and trhglcs rtspectively. The abjects all M
similar- . . . 'ai ptcms, kit th patterns tbemselves did not fit into a physid
Reimannian rcpre~c~ltation of sprc 'Ibac cicans to bc liak quantifiable l i e between
the traditional methuds of mechanics and human hrptic peEcepti011, and a ~~t
approach is rcquircd if detcrministic CntCrja are to be introduccd into this facet of
engineering.
In gentral, the design gorls of the @tic hanci controUer fa control and stability
in an interface with a hurmm operrtor are summed up by Kucrwai and Snydcr in [24].
The haptic &vice must be h ~ C 4 6 k . the opaua miut k able to mwe the systcm's
end effaiun M t h t any aiding toques applied to the actuators. Thc joints shouM have
very iow friction and b a c b h 1221. The structure must be v a y rigid, and designal with
the minimum numba of stia lightweight components.
nie industry leader for haptic hand controî.ias, the PHANTOM [3.4.6,8.16]
device (sec figure 1.4.1) h m SensAble devices, addtesses some but not al1 of the
requkrnents set out in this d o n . Accading to [SI, th designers of the PHANTOM
device consider that the most hportant haptic interactions involve ody the positioning
and forcing of a virtuaî point in thrcc dimensions. The PHANTOM &vice provides thme
active DOFs in the translation of a fingcr thimble rnountad on a univasal joint. The
thimble allows the user's fïnger to assume any orientation, but has no &ve DOFs to
provide haptic simulation. The translation stage is designcd out of lightweight aluminwn
tubing with the direct-drive actuators providing f a the WC mterbalancing. The
translation structure tbenfon aiiows for the low inaiio and low friction, rrqulltd of a
haptic device. 1 e . g to a v e y low free mechanical impedance. Howeva, the
Lightweight structure of aluminum t u b and the light actwtom do not provide a very high
level of constrained mechanical impcdanct. The incorporation of composite matcrials
into the structure of a haptic device ha9 the obvious aâvrntage of simultancously meeting
the design goals of stiffiness and light weight while inmeashg structurai dampinp. as weil
as providing for imaginative uscs of matdais to pmtect sensitive COmpoLlents while
acting as primary structural members.
McGill Ukrsity Dtpirtmcat of Mscbrnicrl Eagb&ng 16
2.2 Literature Review of Bonded Joints
nK arca of study of aühesivclybadedjoiuts is vayimparfint to the
development of the use of composite muniils in mechanid structures. 'Lbe adhesively
bonded joint comprises th most effective methd ofjoining compo~ite nuteriais to
met& and to other materials. The field of study of the bondeci joint includes matahi
selection for both the uàken&, a the boadcd entities, anâ the a k s i v e , or the glue
mattrial that bonds the adbuxb to@crt Aaotha area of infaiest is the stress in the
bonded joint, and the effect that the joint gcometry has on the stress distribution. It is this
second field within the grieatet study of boaded joints that wilï be of patest interest to
this work, as the mstnisii selccîion far the nrihcimuin (Md adhcrcnt arc somewhat m m
limited by other factors, includmg availability and compzttibility with aha mua*ls in
the F d o m - 7 stmcairt.
Th- arc several design problems zlssocia!ed with adhcsively bcmdcû joints that
are unlilre other types of mechanical joints. kr [25], k sctb to acqunint mgineas
unfamiiiar to adhesively bonded joints with the particular mquiremcnts of this type of
fastening. Lees lists seven problem arcas with dbcsivcs in joints thu mua be addrcsscd
in the final choice of a joint dcsign:
adhesives tend to have poor impact behavioz
O failurc ocaus easily f a a peel a cleaving face
material properties are very sensitive to surr0ulldi.g mvircmmmtd conditions
there exists liak accurate a usefal design data
a there is Little data n f d g to environmcntal cffects
a k k of codes fa implemmtation of standad & s i p
a poor communication b a n manufktwus and engbœm
Of these sevai factors, th most impatmt for the eventuai choie of the joint gtomctry
are the h t two, those that dcterminc the zlcccptable loading d o s of the adhesive
joint Lees goes on to say tbat the design of the joint s h d d be made such that the
adhesive is not exposed to high tcnsile lodk The prcfmed l o d case f a a ôondedjoiat
is in shcar. For a lap joint, the m m impatiint gaometry detail waitd have to be the
design of the dgc. with ôcmd fillets and tapacd dbaeods amtributhg patïy to the
overaii sîrcngth of the bonded &in.
The typicai joint gcomeûy that bcs examines in [25] is the single lap jomt This
can give several good indications about p f d desi@ aiterion f a otbcr types of
bonded joints. Fmt, the maximum l o d supportcd by a pint is dcbmiined by the sbear
ana of the adhesive. Howeva, as the majority of the adhtsives rire polymcric, they can
be subjected to ~t rep &formation. As such, at lcast part of the joint should be essc~ltiaüy
unstressedfortbatmbtnoaeepdefdanmidaa~ca~lod. Ibe
thickness of the adhercnds a f k t the distn'bution of stresses almg the adhcsive bon6 By
reducing the thicknss of the adh-d near to the adge of the bond arcs, there is a
reduction in the stress wncentration near the exige of the bond. Howevcr, by rcûucing the
adherend thichess in a s i a g k lap joint, then exists the pasii'biiity of inducing plastic
deformation in the a d h t t ~ ~ ~ d s , rcsulting in peel and fensile sûesses applied to the
adhesive. Adhesives should, at ail timcs, be k c from thesc peel Jtnsses. At worst. any
non-shear stresses expcricnccd by the adhesive s h d d be compressive in nature, and
certain design changes in the bond geomefiy could casily allow this to occur.
The final recommc11dation by Lets coma in the choice of the adhaive. A ductile
adhesive allows for the stress in the joint to be more cvenly distributcd ovcr the bond
area. For this reason, a more ductile adhcsive will o h d t in a stmnger bond than the
use of a vexy stiff? britîie adhesive.
in [2q. Adams and Hams examine in detaiî tbe double hp joint for the h d i n g
of unidirectional carbon film reinforccd plastic (CFRP) to a steel adhaend. The ovcrall
recommendation is that the failurc in an -1y dcsigntd joint should occur in the
adhesive and not in the adhaend. Adams and Hauis use finite dement methods ta
accuratcly determine the locations of the stressa in the joint, and the effacts that the
different geometry parameters have on the joint strength. The thickness of the adhesive.
caiied the bond line thickicss, is not modifi4 ncitber is the tbickncss of eithcr adhercnd.
The parameters that are examined arc: the effècts of the bond fillet at the edge of the
joint, and the effkct of the tapcring of the steel dbacad. Using the finite elemat mcthod
to examine both the sliear and tmmv~gt strwses in tbe amponents of the joint, Adams
andHarrisdrawsevdcoircllusi~aboutt&naaldesignofabondedjamt Fust,the
pcak traamerst stresses in the adbcsive, which would cause peeling Mure in the
adhesive, occur near the conier of tbe steel cdhgends. Tbey also canclude that tbc
tapering of the steel dhamds has v a y little effect cm this uadesllablt loading of the
adhesive whcn the adhesive mitmil ends rbniptly at tbe d g e of the steel dhamd The
reduction in the tranmetsc stress in the &esive is obtahd by adding a fillet to the
adhesivc bcyond the steel adherend. Furthermart. the introduction of an intemal taper to
tht steel adhercnd in combination with the dbcoive fillet gocg evcn Emba towards
reducing the peehg stress in the idhesive matcriaL F d y , the two modes of failue
predicted by Adams and Harris with the fiaite elcmcnt model shown in [26] h the inter-
Iaminar failurc of the CFRP due to the increased transverse - in the adbesive cl-
to the material bounciary, and cobesivc Wure in the adhtsive due to the ~ ~ ( ~ ~ t l t r a t i o n of
s t r e s s a in the adhcsive mrtaial almg the h c edge of the adbesive fillet. Fa a q a k
situation, the f b t failme mode is undesirab1e. as an inter-laminat fiiilure of the CFRP is
not easy to sec or to fix.
Much of the work associateci Mth the bonding of mctal composites is in the
field of composite aircran wing rcpair [17,27,28]. In [27. Xi0118 a d Raizenne dcvelop
an analytical model to &tcrm.int the strcngth of a compositdmetal patch joint. The
overall geometry of the joint considncd is that of a composite matcrial patch, adhesively
bonded to a metal s u b s a a or base matcrial, f a patching and fitigue tnhancing of the
metal par^ The model is capable of takhg into account the tapering of tbe composite
patchcs and calculates the adhesive &car strrsscs as weli as the interface p l stresses
between the composite and the sdhsive marerial, and the inter-laminat transverse
stresses in the composite. The model takes into account tbe differential thermal
coefficients of expansion of the differing matcrhb that rrwùt in thamally induccd
stresses and is used to prtdict joint failm.
Xiong and Raizcnae draw five ~ ~ I u s i o i w about the joint geomctry and matcrial
propertics for this type of patch joint:
McGill University Depumwit of Mtchrnid 19
T h e m o s t d t i d r i r e a f a t h e W ~ ~ t o f ~ m c t a l ~ b 9 a . s t e u n d e r
compression is the taperhg of the composite pich, which cui cause miaix shcaring in
the patch.
The pmiictions of the Mure I d and mode arc heavily depeadent an the
choice of matcrial pmpcrtits f a the différent amqmmts of the joints, so mataial choice
and envin,nmcntal f w arc a vay impatint consideration in the design of a composite
patch joint.
The most critical area of the bonded joint far a tcnsile load case is near the
center of the patch, by the edge of the crack in the mP1 wibsoate-
The tapering of the composite patch is uscfhi to &ce the stress in the adhesive
near the cdge of the patch, but am r d t in excessive omosts building up in the plies of
the composite material ncar to the adhaive boundary.
AU stresses necd to be collsidcred, rather than just the shcar area for the
adhesive as is cornmon, for proper design of a patch joint
Further work suggested by the authors is the investigation of the plrrticity eff-
of the bond matcrial, the bcnding effects an the joint due to I d ecccntricity and the
effect of de-bonding at the exa~mitics of the j o k
In [28], Charalambides e t PL use finite elanent anaiysis and physical testing
methods to determ.int failwc Cntena on enviranmentally trcatd patch joints- The main
conclusions werc that the environmental trtamient of the patch joints, cach test specimcn
was immcrsed in a 50° C wata bath for 16 maths, had vay îittle effkct on the s t m g t h
of the joint in tension or fatigue. Howeva, th fuiguc @ormance of the patchcd
specimens is much worse than thet of the whole. untouchecl specimens. Joint failw
criteria bascd on maximum aiticai stress a strain did not producc rcSuIts consistent with
the test specimens- It is their cociclusion that this methd of prcdicting th strcngth of the
joint is not adcquate due to the edge effets of the finite elcment mesh, and instcad
propose a fracturc-mechanics bwd mcthod that yielâs bettcr results.
In [29], Ricc and Moulds &der the variables govcming the design of a boodcd
interface between a composite pmpshaft and a mtal end fitting fa the p q of
transmitting toque. The goals of this design arc the reductim of o v d weight rad mst,
reàuction of whirling prob1ems causcû ôy tbe unbahces genenued by mechanimi
fasteners, the potcntial eIimirintion of an inmmahtc beaning, the rcdllctin of noise and
vibration and a lower part count fm the assembly. Ria and M d d s use an anaiytical
program based on continuum mechanics to evduatc the eEkt of proghssively modifyiag
certain joint geomcûy variables such as d k m d wall thickness, bond line tbichiess and
matenal properties. 'Ibe program determines the stress àistri'bution h g a single lap
joint and compares it to an elastic limit f a the cpoxy mrmiaL The c&a of dissimila+
materials in the joint with a hcat curcd adhesive is vay high, and not rmmmadd The
choice of a cold currd adhcsive is beneficïai to thejoint wlaietb, m that it does not rcsuit
in high residual su esse^ in the bond that wiil aggravate any m e r loading on the joint.
The cffect of changhg one adheread to GRP (glass reinforcd plastic) causes an Uicrease
in the stress in the bond ncar the dgc due to the difféxmtiai d e f d c m of the
adherends. To d u c c the stress concentration, the thicknss of the composite adhcrad
must be inctcased, to king the stiffiiess close to that of the duminum. and the h d line
thickness must be incrtased to ailow far mort m a t d in which to distrifite the stress.
The final joint mafiguration for the single lap joint is a 5 mm thick aluminum adhaend, a
3 mm thick GRP adhaend and a 0.2 mm bond line thickness of a two part, ductile, cold
cured epoxy. These amclusions arc used in the design of the bonded intcrf' between a
metal end fitting and a composite tube. The first geometry considercd is a simple plug-
tube joint, that causes exccs~ively high loads near the end of the plu& whüe the -ter of
bnded area is unloaded. A bore hole added to the center of the plug, mnlring a partiai
nght cylinder of the insert sucacds in Kstcibuting the more of the stress towards the
inner part of the bond fhxn the dg=, but docs not s u d in lowering the stress in the
adhesive bclow the elastic lirnit everywhcrc. Therie still txists a stress concentration near
the edges of the bondcd arek By -ring the dgcs of the insert, the stress in the bond
can be reduad fiirthcr ncar the tapend edge, but it rcmains high at the o<ha end of the
bonded region, near the end of the fuk. This stress concentration can be redud by
increasing the bond iinc thickncss, nt the ri& of causing a#p deformatcm in the bond.
The final conclusion by Ria and Mouids is that, if it is possible to bond both the inside
and the outside of the tube to the metal end fitfing, the iaaerse in the ovedi strength of
A wedrer, but dude &haive is prefcrable to strcmger yct brittle m.
Twghened adbtsives will work bcst.
The joint design must take into recamt eirviranmeatal degracW011 of the
adhsive mrtcn;il propeities.
'Ibemgaganrntoftbeboad,tbc~oftbc~vebocd,shddbcLept
assho~aspo~~~1e i fah~cwdadhes ive i sused . Thiswillrcducetùe
diffmtial expansion ww~er m mntti-matcrilll joint*
The bond line thickness s h d d as gmat as possible without allowing the joint
to expericnce awp fatigue.
Thcrc must k no con m o n of the composite part by mold reIcasc agents.
Composite s u r f i cari bc prcpand by chernical solvent wiping, foiiowd by
light abrasion end dust rcmovlil A h , ôcmbg prc-treatnments cm k used to
reduce wmsion and inciuise the wetting of a surface by the adhesive.
The use of bondcd joints in various h of design has a g m t potcntial f01
growth. The bonded tu- joint has the kaefit of rcâucing parts count by eliminathg
mechanical fastcners, and by incolpaating mstaial tûat b alrcady available in industcy, it
has thc potential of nducing manufktwhg costs as weL Tbae L somc difncuity
inherent in the bonding prauss, but 4 t h propa jig design in an n b l y liii. pmduction
method, thtsc problems are easily surmantable.
2.3 Literature Review of Laminate Optimization
One of the most attmctive rraums f a using composite nucaiain in a robotic
smicturc is the ability to precisely Pila matairil Propercics such as S i f f b s and muai.l
damping. The material propenies of a part made h m a cOmpOQitt miiai.l ut highly
dependent on the sequcnce that tbe individuai plies cire laid-up. and on the orientation of
the fibers embedded in the plies By varying tk n u m k of pl*s in a lay-up, md the f i k
orientation9 a base matcrial such as unidiribctioaal carbon fibers embcddd in an p x y
matrix uin exhibit mataiPl Propcrtics o v e a vecy large range. 'Lbac hm bccn much work
donc on meth& of optimizing the lay-up fa various Ptoparics. includhg severai linea
progmmming schemcs fot determining the optimum iay-up f a muimituig a parti&
material property such as damping. T1iW section wi l i se& to ovcntiew S O ~ C of the WC&
already done in implcmenting composite compo~c~lts far robutic systcms, as weli as
detailing some of the existiag lay-up optimi7ntion mcthods.
In [8], Lee et. ai. dcvelop an antfvopomorpbic robot using composite matcripls to
construct the Linlrs. ïhey state that the specific siifnrtss of the links has to be high and
the materid damping has to be. in any robotic structure. high aiough to ~ I O W fot hi-
positional accuracy and dynamic @&mance. Ibe high specific stiffiicss of the linLs
will d o w lighter links to carry the same payload. IIence the Pcaiaton can be made
comspondingly SrnaUcr and less expensive. Tbe high mataial damping of the links wiU
allow for the daqing out of vi'brations induced in the st~~ctum by high acaleratio~ls. and
create a grrater end point accuracy fm the manipuiator. Lee ea ai. show that the
longitudinal stiffiiess of an mrgk pl& individuai plies that are placed with the f i k
direction at an angle to the part direction, deops off sharply at 15'. and they ch006e a lay-
up stacking sequaice of i1S0 for the composite nn with a box-type scctim. The robot
in [8] also used filament wound drive transmissicm dm&, ma& h m carbcm-fiber
matcrial. The interfaces betwecn the links and betwœn the drive iphllftp and the motars
were made using bonded end fittings on the composite m. A choice of bond line
thickness of 0.lmm was made. with an engagement length of lWmm fa the box-bcam
forcarm, and Sûmm for the drive trarismissian shsfts. Tbt shear erw ribquùed by the logd
case expected for the robot would dictate a minimum bond engagement of Uhnm, but L#
et. al. suggest that the longer bond lengths makc f a an euia joining process, anâ the
forearm joint might became unstable in baiding if a shortcc bond engagement w a e
chosen. The end fittmgs ae msehinrA as a double-lap joint Both th inside and the
outside of the composite parts are bcmded to the mtai sdberends. Hybrid jomts ue ustd
for the pivots on the composite fmcann. The joints ccmsist of a metal plate bonded oa the
outside of the box section, with P bolted reinfimcing plate on the Wde. Such a joint can
b t t x p t c t e d t o p c r f ~ n n w e U i n s h u r r ~ w e U a s h ~ o n d c o m p n # s s i ~ ~ ~ Tht
composite ami was cornparcd to an quivalent steel a m f a a variety of static anci
dynamic Cntcna The nindsmentai natural neqUency of the composite arm was mare
than twice that of the steel a m , anci the inhrrnt damping ratio was s e v a times as much
for the composite arm than for the stccl atm. The mass of the composite arm was lcss
than one quartet that of the steel ann. Overaii, the inclusion of the composite materials in
the robotic stmcture, while involving some complicstrA boading techniques. S C C ~ S to k
very advantageous to the dynamic perf6muncc of the device.
For accurate control of robots including composite matcri& in the structure.
accurate modeling of the dynamic charact&stics of the composite matcrial has to k
perfonned In [30], Gordaninejad et aL tak as a base assumpticm for the dynamic model
of a composite robot arm that ait rigid and flexible motions of the um must k couplai.
The basis of this assumption is that, for modem high s p d robot manipulatas, the
vibrations inducad in the structure arc not sa small as to be ntgiigible in the d-c
modeling of the robot structure, as is traditiodly the case fm large, low speed
manipulators. By applying their model of coupled dynamic tams to a simul.trd
composite box bcam made of ande plies, they show tht an inacasc in defldcticm for
angle plies up to about lSO of ply angle is negligible cornparcd to th unidirectional plies
(the highest obtainable spccif~c stiffiiess). Howeva, the marrimm nonnal bcnding stress
in the part shows P minimum fot the angle plies at lSO. This wiggtsts a masonable fimt
assumption for an ideal ply angk for the mata*l of the box bcam. Gordaninejad e t al.
show conclusively that the couphg of the dynamic tams in the caiculation of end point
defltction is rcquired f a accurate modehg of a ro&tîc systnn. BI (311, Gordaninejad e t
al. dcvelop a similat coup1ed dynamic modehg of a rcvo1ute-prismatic beam mrde of
composite matcrialS.
To design for specific matmial c-CS such as matai.l -hg, a methad
for predicting the value of the propaty is riequiricd, Ni and Adams, in [9], attcmpt to
formulate a predictive damping equati011 ôascd on the stmin encrgy in a symmctricaiiy
laminated composite bcam vibrating at a natuai fbqyency in fret flemrc. The damping
calcuiations arc functions of thr# measuted paramctcrs of the base material, the
longitudinal. txansvase and &car spccific damphg crpacity. The values fa the thnt
specific h p i n g coefficients f a the laminatad kam are calculated as s u m ~ of the
material properties and orientatins ovcr the tbiclmess of the iaminatca. The results of the
theoretical calculations arc vcry close to the values thai Ni and Adams meunirrd f a the
f?cc flexural damping of the symmetridy laminated bcams.
In [13], Adams and Bacon alsa attcmpt ta evaluatc both thcofcticaiiy and
experimentally the dpmpiag asociated with a composite mucri.l iay-up. Specifîcaiîy,
they evaiuatc the effect of the fiba orientation and the laminate gcometry on the damping
produced in a composite specimen. In general, the darnping in an mgic ply i4minritc
reaches its maximum at a fiber orientation of 3S0, and the dominant dissipation term is
the shear stress term. The majority of the damping that can k associateci with a
composite part is due t4 the rcsin systern use& more so than the fibers. This is shown by
the in- in the damping for a decrcast in the fiber moduius, The lowcr the fiber
moduius. the grrater tbe s t n i n mergy in the miau matcriaï, and the hi* th dampimg
wil l be for the laminate.
The same authors as [13] suggcst in [IO] somc mthodp f a increasing the
damping in a multi-laycr, unidirectional laminate specimen. Adams and Bacon show that
the prtsence of imperfections in a laminatr?, such as min poor amas, voids a even smaü
cracks can lead to grcater values of Asmping in the laminate. ' Ihy a h say that the
majority of the damping occurs with the strain aiasy in the mMix in the longitudinal, or
fiber, direction. The strain enagy s t o n d in the mmix mamiaï as a diîation will
contribute linle to the o v d damping of th lamime. Finally, as the modulus of the
f i k r s i s r e d ~ c c d , t h m c r g y s t m d h t b e r m r r i x ~ ~ TbtdamphgurociiodMth
the &car deformatim of an off-axis iaiiiun is esscntially unchangai, bit the
longitudinal damping incrrrres. Tkrefort the ovaaU dimping rorociPted wiih the
laminate wiU show an incIieasc. Whik the prrrare of voidr d cracks c;ia bc v a y
detrimental to the life of a irminatr, a similsr &kt of increaSing th Iiminitc damping
beyond the p d c t e d leveIs can be obtained by a slight deviation in the straighbness of the
fibers during manufiicturingœ For parts made unidirectid rna<airl, this caild k
very helpfil in improving the dynamic charactcristics of the composite parti
Extensive imowlcûgc of the rsquaed @amuice criterion f a any mnipulator is
needed to be able to acaurtely specify the mataiil pararncters that will be obaiaed with
the optimization of the iziminntE. In [ll], Lee et. al. constmct a SCARA type direct drive
robot with composite mrtcri.l linlrnpcs. A SCARA robot is a saudy. pick-and phcc
robot. Two revolute ihkagts fam a two dimcnsid pianar workspacc, through which a
prismatic k h g e can be moved in orda to @am the rrquvcd task~. Tbc hy-up of the
composite materiais was detennined by the static deflcction caldations of the end
effector. The oum a m of the SCARA robot is subjected to vay littk torsion l d , so a
filament winding angle boundary of betwt~~l S0 and lSO was chosen for this îinkage. nie
end effector deflection was calcuIated ova the wodrspacc joint angles fa a range of
winding angles for the inner a m . The winding angies choscn were 2ûO for the inna arm
and 10° for the outcr ann, while the matimum deflection of the end effectot ovcr the
entire workspace did not excecd 30 microns for 10 N of p a y l d Only the stifhess
material parameter was chosen for the o p ~ t i o n of these parts. and no cauideratians
other than the static load dcfîcction wert takcn into accuunt.
h [14], Sung a d Thompson propose a systcmatic mcthod foi optimizing the lay-
up of a robotic structure for maximum wonnance bcnefits. They show the influence
that material propcrtics of a laminatc can have ova the pdormancc of a robot with a
simple schematic. The fiber orientations and cbanrctaistics combineci with the matrix
characteristics, lay-up and stacmg scquencc have a dirrct effcct on the dcnsity. the
strength and the damping of the matcrial. The mataial density combined with the Iuik
gcometry detenaines the maap of the structure. The saagth of the mita*l and the linL
gcometry determine the Itifnuar of the structure. Howeva. the muairl damping b the
only f ~ r that contn'butes to th strucûd damping if the dculatedpints err
anisiderd ideal. F i y , the the ancl s t i f b a of the tbecûne i n b w iatdth tk
damping propercies of the matainl wii l detumine the aamacy, tbe wlt W. tbc
workspacc, payload and repeatability of the robotic xmnipulaîcx. ki m m y the Iinlr
geometry will bc fixed for rt.sans of interfkmcc, a drive syDtcm muting. For thh
m o n , it becornes neces~vy to provide a means to oprimiot .11 thsec materhi propcrties,
density, strength and âamping. simultaneously to obt.in a fully optiaiirrrt robotic
structure. The iinw programmïng techniques usrd m th* rrriclcr~t d e r i p d to
optirnue the properties of thin lamhatc bcamsT tht wül subsupcntly be boadrd togethcr
to form a box-section stnicturc. The opthhtion mutine dclaminer th hy-up tbt
obtains the maximum metcriai dmiping subjeacd to catam wmstmhts on the fiber
angle, maximum laminatlr tbickncss and knce ïink weight, fi- volume fiaction and
bending stiffiiess terms for the Carttsian diredions x and z (the axis of the link is
consideml to be the y direction). Ilie laminate gcometry obtained h m the optimizing
routine showed significantly improved dampiag over tbe arbittarily chosen initial design
for the composite part . The optimization mutine propooed in (141 is fiirthcr nfïned by Sung aad Shyl in
[12] to determine the optimum lay-up for a cornpletc box-section, rathcr than a box-
section made h m bonded i.minete plates. The pmposd optimizcd box bc8m could be
manufacture by bag molding cmwmd an intcrml mold as a single part. Sung a d Shyl
propose severiii iiiustrative exampks to show the fltxibiïity of the opbhatian mutine.
The first is a simple saial manipuiator. whrr the magnitude of th mdpoint viôraîion is
to be minimiird. The resuits of the opthh ion routine show that the waU thickness of
the laminates incrrase to the maximum vilue pumittad by the comtrahts as the routine is
dependent mon upon the &ess of the links than the o v d linlr weight. The secund
example. using the same manipuiatorT sœks to have the shortest settïing tim for a
pTeScribed maneuver. The same m t s on the box-section wae imposai as f a the
first example, but the optimum hy-up wrs @te dine~~~lt. For the shortest sctthg time,
the fiber-volume fiaction tcndcd to be minunilrA . t . .astbedrmpingoftbcmuairlwrs
heavily dcpendcnt on the mmix content of the iay-up. The potential fa ôphmmg . . . the
matcrial ptopeaies is extensive* 'Lbe pins mde iu thme two simple txamplcs arc
testimony to the impartanœ of a carefbi choice of all the mrtcn'ai chsnictenstics fot
optimuing a laminatc* Howeva, detailad critenon are q u i r d fa a opthbtion
to be possible. The srme manipuiator, subjcctcd to two slightly di&rrnt opthhtion
criteria rchinied two very din~~tnt Iiyspa 'Ibt breaw in the rmtrix W o n
for the second opthkation of the manipdator would k contrary to tht requihments of
the first optimization of the manipuiator* A h , ncitber case multed in a minimum
wtight far the manipulator lintrn. Bottr Optimizptiolls ~ ~ w e ~ t t o t h e b g i c f i t
of the material properties ofthe hminatc.
Unfortunatdy, the &tailed daaminrton of the performance cxitcaia fa a haptic
device is beyond the scape of this w a l c Subsequciltly, a fuii w o n of the i a m i ~ ~
for the box-section linkagcs carmot k prformd. As a p r r h h r y ophhaticm
technique, an iterative finite elexnent modtling of the lay-up in question will be usai
instead of the more rigorous non-lincar p r o ~ ~ g c o v d in this sccticm.
McGill University Deputment of- - . 28
3. Design of Bonded Tubes
3.1 Introduction
Small diameter commacislly availAhIe composite tubhg wu considercd as a
bais for the constniction of the h b g e s of the tninslation stage kfuue it pamits
several intmsting options. For an load scenario, such as that faiad in the
links of the translation stage of the hrrptic -, the most enicmt cross section fot
dealing with multi-axis I d is circulnr. A h , rclativcly inexpensive commctcially
available cylindncal tubes made nOm cacbau-fibcr rmtai.l pmmt a viable altemative to
the heavy machining costs usoCi.tai with compltx aluminum parts.
3.2 Material Survey of Composite Tubes
Anextcilsivesurchwumadctonnddequucmtcrialintbef~~fsrmll
diameter carbon-fiber mbcs rtadily availaôle fhm the commercial scctor. The choice of
puitruded carbon-fibcr tubes was made basai on üie design gmîs f a the Freedom-7
project: decrtasc the linL weight and incrcasc the link stiffness. Unidirectid carbon-
fiber tubing provides the highest stifniws to weight d o f a any materid. Howevcr, it
tumed out to k no easy ta& to find this mataiil cm the maLet Puitrusioa of carbon
fibers r e q u k special dies and vay expensive setups. The qoxy matrix matmcil
cornmonly uscd in conjunction with carbon fibers does not lend itself casily to the
pulltnision proass, as the cure tim f a this matenpl is normally quite long.
Several market s~nar wac targetbd as potcatial suppliers: the COIIStnrCtion
industry, the amonautics hdustry .nd î k sprts equîpment h c h s t ~ ~ . It was discovercd
thar,in thc~~~l~t~ctiiai~,th~jorifyofihe~ttmitai.ltnbhgUmrdeof
glass fibers. nK diameter of this tubhg was llso too large to k uscfiil in the translation
stage of the Fradom-7. A seirch in the acmmutics uidustry turned up s c v d candidates
for the Li& matcrial. 'Lbe most promlnig came from tbe Aa0Sp.a Composite Roducts
[32] a Company in rafironiia Th muairil obtainui b m thcm was originaily intendcd
for the construction of spars and contml aufre puah rods in mode1 ahplanes. 'Ik tubes
wcrcpar~carbcmfiibcr,partgîasafibcrrratcrial. 'Lhrtw~sonetypoftubingmadeof
w o v e n c a r b o n f i b e r ~ t h c R H - 2 . 'Lbtspatsindustryhsümanymaematairrl
options avaüable. The hunting industry manubures carbon f i k (vltows for high tcch
sport huntm, and composite ski poles can be found aU ova îhc market. 'Ihra spmples
of arrows w m obtained h m varias hunting stores in the Montrd uea. Thcsc arc
show in figure 3.2.1. 'Iëc top arrow, an aü aluminum shafk, is the XX75. the middle
shaft is the all-composite unidirectionai shaft, the V-Max, anà the boaom is the Easton
ACC. an a l h u m shaft sumwdcd by a wovm crrbon f i k shcath. F l y , the aoss
country sk i pole industry turned up the most ptomising materid in the form of
unidirectional pultruded csrban-fiber polyester ski pole bianks, bought fmn Top Sports
[33], a sports equipment man- in Mmtrcal.
In order to &termine the bcst d d a t e foc the iinlr matMial from all the available
tubes, a thrte-point knd test was pafomwd to &tamine the effketivt longitudinal
moduius of the material. The effectve mryiUtus was divided by the density of the tube to
determine the cffcctive speQfic lcmgihldilllt modulus ofthe tub. This wu done
according to the following caicuiatio~ls:
EIais the effective longitudinal moduius times the moment of inertia of the
tube (flexural stiffhcss)
El, is the e f f d v e speçific lungitudinal modilus times tbe mament of jncrtia of
the tube (specific flexurai stiffIicss)
A summary of the d t s of the three-point beidiag tests an the dBércnt tubes
can be found in table 3.2.1. The desircd propaty fot the optimizaticm of the structure is
the maximm E&, as that dctcrmines th f i e x ~ y stïf5est tube mamiaï and geometry foi
the lightest weight. The ski pole matMial, the unîâircctid carbon-fi& polyester, is
therefore the prcferrcü matcrial for the constmctioo of the stage 3 Linltage.
T d k 3.2.1 - Swnmaty of Composite T h Propcrn0es
McGill University Depumncnt of h&&nial . . 32
1
0.006
0.00384
0.00618
0.0058
0.00864
RH-2
Vmax
ACC
TU06
XX7S
TU-07 1 0.148 1 0.00384
0.768
0.838
0.870
0.287
0.850
0.008
0.00644
0.0076
0.0071
0.00956
0.0074
0.0218
0.0246
0.0203
0.0059
0.û294
0.0152
1.247~10'~
9.278~10'~
8.036x10"j
3.997~10-'
7 . 0 8 7 ~ 1 ~ ~
9.662~ 106
6.635~10"
5.293~10~
2.561~10"
2.531~10~
7.145x10-~ 2.186~10~
3 3 Geometry and Parameter Varintion of Bonded IiiseftS
The composite tubes raquirr baaded mul hsczts to aUow fa bcaring fitîhgs. A
choice was made to use extaior cylinAiid fittings. Ibe tube cnws d a n did n a aUow
for the more acsthetic intanrl fittings duc to SIMU b e r tube diametm. The extemal
fittings wue &Cr to ïmplemc~~t
As show prtviously, tbis type of boildtd joint hr bcm studiaï fa
loading, such as is f d in mqmite püp-sbaff design [29]. HOWCVC~~ littlt aûdysis
had becn done on this type of joint fa threcdhmsicmai beading and taisile Io& that
are consistent with the hand controilcr I d cases.
For the mode1 consi- in thW wod. s e v d pammctczs wae ch- rad
varied in diffcrcnt finite elemnt modcis to gaugt tbek eff- on the ccmcmtration of
principal stresses in the bond mrtaiil Figure 3.3.1 shows a scbernatic chgram of the
bonded geomeûy, with the parameters a. e, and 1 am. rcspcctivcly. the dbaead
thichess, the axial engagement anci the bond linc thiclaiess. In edi model, the
diameter of the composite tube. the aâhesive f'iilet and the fillet an the inside adherend
surface remain constant.
Figure 33.1 - Band Geowutry for Pcvamctc~ Vorirrtion
- -
McGill University Dep~rtmnt of h k d d c d . . 33
3.4 AxSsgmmetric Finite Element ModeIs
ThefinitcelaaentmOdclsdtodctamiaethe&cooftbe~
parametcrs on the k m d saaigtâ w a r comtmcW using uioymmeaic elcxtmts. nie fht
i~mtionofthettsting~~doae~mcsberrimilPtothu~hfi~3.4~1. 'Ibe
Figure 3.4.1 - Axisymmctn*~ Finite E k n t M& of Bondcd Geonutry
elements composing the composite tube arc of an orthotropic muaial having the
propertis of unidirectional carbon fiber material [34]. The matcrbl axis for these
elements was set to be the same as the axiai direction of the tube. 'Ibe matcrial Properties
of the isotropie epoxy bond were dctcmiined frrnn fiterature. The elements of the
metallic insert w a e assignai isotmpic mntai.l propercies umsistent with duminuma061
PSI *
The elcments of the tube ut jomed (they have coincident nodes) with the
elements of the epoxy bond dong the bottom fkc (CW in fi- 3.3.2). nK elements of
epoxy and aluminum are wnnected h g the entire intahce fa test 1 and 2 for each
model, and the bond DAB in figure 5.3.2 is bmlaa in tests # 3 and #.4 in cach modd
This discontinuity is consistent with a bond th.t is going to be lodtd purcly in shear. As
the results will show in th next sections. the brt.lr is rlpo consistent with a pottntial first
failure mode.
Tests 3.1-3.4
Tests 4.14.4
Ttsts 5.1-5.4 2.0 0.05 5.0
Test Number r
Tests 1.1-1.4
A total of scven finite ekment m&ls wac cunstructed to anaiyze the of
the dinerent parametcm on the maximum principai stress in the bonci . E r h of the sevcn
models had four tests paf~~med. The fht and fair(h test w a c w i t b t the bcmd fillet at
the extreme end of the composite tub (lïnc PB in figure 3.4.2). The second and third
tests both have this fiilet. As mentioncd befort, the fbt and second tests have a bond
between the aluminum and the cpoxy on 1 . DAB in figure 3.4.2 whcrt in the third and
fourth tests, this bond has been broka. Table 3.4.1 shows the test numbers and the
patameter variations for each m a l . Tests 1.1-1.4 arc the arbitrarily choscn bw tests.
Tests 2.1-2.4 and 3.1-3.4 vary the adherend thickness u h m 0.5 mm to 4.0 mm. Tests
Figute 3.4.2 - Rcfe~encc Loc4tion.s on Bond Geomctry
a (mm)
2.0
1 (mm)
0.25
e (mm)
5.0
4.1-44and5.1-5.4varythebandlincthi- lfiam0.05 mmto 1.Omm. Tbeiasttwo
sets of tests, namc1y 6.1-6.4 and 7.1-7.4, v w the axial engagement e from 3.0 mm to 10
mm.
3.5 Results of Parameter Variation
To propcrly interprct the d t s that will be shown in this Secfion, the purpose of
the optimization must be msde clcar. As was staîd prcviou~ly, the design goal of the
Freedom-7 is to provide 8 h a d ccmtroUcr structure thit WU d n i m b the link weight and
inertia fclt by the opcrator, whik at the sam time meeting aii the design aiterion such as
minimum rcquircd smmgth and lowest mmant nrninl fkqcncy. To obcim this goal,
the links, and s u b s e q d y the boaded inserts, have to k designai with tbc following
purpose in mind: minimize the weight and muaial witbait sacrificing minimum strcngth
requirements. In our case, ifrcmoving maraiai fnni the intaf.ce inmeases the
maximum principal stress in the bond, then this b a desirable effect, so long as th final
geometry is able to withstand a minimum nquircd loaci. Howevcr, if incrcasing the
materiai in the bonded interface (such as incrcasing bond liae thickntss and adhercnd
thickncss) ingeases the maximum principal s~CSS in the bond, thn this ôaomcs a very
undesirable effecf countcring both design goals of minimum weight and minimum
required strength. Figure 3.5.1 shows the variation of the pcak maximum principal stress
with respect to the variation of a, th adbermd waü thickaess. Ibe maximum priacipi
stress concentration in the epoxy bond darrates Mth an iacrrape in the adhcrcnd wdl
thickness. F i e 3.5.2 shows the variaîiop of the peak maximum principaï stress Mth
the variation of e, the axial engagement of the tube hto the metil h c r ~ The stress
concentration dccmscs with the incrase of the axial engagement of the b d c d aitities.
Figure 3.5.3 shows the variation of the pcak maximum principal stress in the epoxy bond
material with the variation of the bond line thicknes 1. Tbac is a minimum fa the p&
principal stress in the bond mstn;al near a bond line thichiess of 0.25 mm.
~ c G i I l univmity Deparment of ~echriiicrl ~aghœhg 36
Figure 35.1- Vorlolon of P d P n n c i ' Stress with &Uaerd
W d mckrcss
Figure 3.5.2- Viwùation of Peak Principal Stress wirh AxhL
Engagement
Figure 35.3- VàrMon of P d Principal Stress dur to Bond fine
mckuss
Figure 3.5.4 - Màxiwuun Principal
Sacss Contents in E , M '
for Test 1.4 (Bond AD Broken)
Figure 3.5.5 - Maximum Pn'mipul Figwe 35.6 - M m Principal Stress
Sîress Contours in E'q Material Contours in E ' M W with E m
for Test I .l (Bond AD Ekists) Fillèt for Test 1.3 (Bond BAD Exwts)
Figures 3.5.4 and 3.5.5 show the effcct of brcaking th W h g the DA
interface. The stresses become much mozc distributed throughout tbe ôond lke
thickncss, and the pcak principai s t m s is also reducd. This situation is advantagcous, as
more of the bond is now loaded. As weli, ri& of &ieminat;on in the carbon fiber
material is reduccd, as the stress concentration is movcd to the ngian of the bond in
contact with the metal. Ibe e f f a of ddmg a fïiict in the Compogite tube is hÜly small.
Figure 3.5.6 shows the stress umtours of th 1.2 test, whcrc a band exists ktwan the
epoxy and the metai dong DAB and a met is dded in the composite tube to hacase the
bond line near the end of the joint (PB in figure 3.4.2). lbae is a lrge stxess
concentration at point B on figure 35.6 and thrr is little decrase in the maximum
principal stress betwccn test 1.1 and 1.2. The diaerc~lce in the band sîrcngth due to the
fiilet is considcred negligible ancl, fot mmufktming mamus, it wil i k lefk out of the
final geametry. L grnetal, the e f f a of kaoag the bond dcmg lise DB in figure 3.5.5
has the effcct of ducing the kge stress concentration in the epoxy at eitbcr A a B
dependhg on whethcr the epmy fillet exists a not.
Figure 3.5.7 - Variation of Priacipal Sirus Abng Bond due to Adhcrend TAIckss (a)
Figure 3.5.8 - VCUiQtion of Principal Stress Along Bond Civr to Bond Line Tliickness ( I )
McGiU University DcputnrwtofkCbcbrnicrlEagummg . . 41
The variation of the priaciple stress with tbc parameteft a and 1 b show11 in
figures 3.5.7 and 3.5.8 respeçtively. Figure 35.7 shows the variation of the priacipai
stress in the bond dong the s d h œ of the arbon fikr aibe (AC) due to the variation of
the adhercnd thickncss, a. As the adhermd decrieescs in thicbiess, the maximum
principal stress in the h d inncases. Thcrtf~~it, vrading to the design gorls stotcd
previously. to optimh the bond f a this geomctcy parameter involves decrtasing the
adherend thickness to the limit of sûuctural strcngth. The aptimizcû mode1 wiLt use a
value of a of 1.0 mm. Figure 3.5.7 shows tblt thC mainmm principal stxcmcs in the
bond are only weakly deperdcnt on a.
Figure 3 5.8 shows the variation of th maximum principal stress due to boad line
thicknss, 2. As the bond line t h i c b iacrtascs, ~~ICSS is distributed more e v d y ova
the bond. 'Ihe optimum line thickness &aiM be somewhat in ktwem 0.05 mm and
0.25 mm. According to the literaSutt [3q, tbe bond line thiclaiess should rcmain
between 0.01 and O. 1 mm for stabiity rrrisans. As such. a bond Line thiclaiess of O. 1 mm
was chosen for the optimized model
Obviously, in the interest of wcight savings cm the part, the &ai engagement
should be as short as possible. This factor wiU not be as critical in a puely tcnsile
application. However, as the stage thrre iinkagc can be subjocted to high trausvcrse
bending loads, the length of the uial engagement WU be critical in the rcsulting strcngth
of the bondcd joint 181. This f a ~ o r M11 kcam vay apparcnt lata cm during the testing
phase of the optimized joint As such, the value of e chosen for the optimizcd bond
geometry is 10.0 mm.
Appendix A shows the maximum principle stress contours for the whole range of
parameter variations. A 1 shows the maximum principal strcss contours fa the epoxy
material of the base instance, namcly test 1.4. A2 shows the effect of the band betwec~l
the aluniinum and the cpoxy dong DB in figure 3.4.2 cm the entire bcmd rcgicm, showing
the maximum principal stress contours in the epoxy material fa test 1.1. A.3 shows th
effet of the adhcrend thickncss on the maximum principai stress umtours and iacludes
the stress contours for the epoxy muairl fa tests 2.4 md 3.4. A 4 shows tk e f fa of
the bond line thickness on tbe muimum principal ;md incl* the stress contaas fa the
epoxy matcrial for tests 5.4 Md 4.4. Finally, A5 shows the effact of the axial
engagement on the maximum pincipal stress caîtouft. and ~ C ~ U ~ C S th stnac c01ltours
for the epoxy material for tests 6.4 and 74.
Thus fot optimum weight and aâupmtc st i f fhs. th o~mmuy of the d t s of the
study art:
makc a as small as possible within the sbnictural stability
malrc e as short as possible within the sîn~ctural stability
makc 1 such that it lies betwan 0.05 and 0.25 mm
3.6 Three Dimensional Finite Element Mode1
The strucbrt of the ~rnslation stage expaiemes two d imens id beading loads
as weli as Ioads in tension and compression. Therefw, we can not assume the bond
geometry is properly dtsigned without subjectllig it to off axis loads. ACCOCdiLlgly, a
th- dimensional M t e elemmt mode1 wu, ccmstructed to evaluak the design safety of
the optimized bond geometry. Values fa a, e. d 2. w a e obtaincd by the axisymmctric
parameter variation perfonncd in th prcvious scdoa: 1 .O mm, 10.0 mm. and O. 1 mm
respectively. Because of symmetry. only one haif of thé îube I insat was modeled,
significanùy rcducing computaticm tirne. Tht tbree dimensionai finite eicmcnt mode1 can
be seen in figure 3.6.1. 'Lbe blue composite tube elemcnts are thin sheiï elcments. with
Figure 3.6.1 - l k e e Diwaenswd Fink EkiKnt Modrl of Bondcd Tube Geometty
- - - - --
McGill University Deputmcnt of 43
a the mataial proPatics of unidireciid clrboi, nba mrterirL The yeilow aluminum
elements arc linear brick ekmmts and have tbe mrtairl -CS of botrupic
aluminum. The light blue cpoxy elcments have rmter*l propaties of isotqic cpoxy and
arc also linear bnck elcmcnîs. The load is M b u t e d ova seven nodes on the fhcc of the
aluminum insert, and the baiadry coaditions arc ruch tht the eid of tbc t u b is clamped
while the symmetric &&ce is rcstrictcd to move dong the phne of symmetry.
According to [SI, the typical maximum lard applicable by a h g e r is 40 N. If we
consider a hand grasping the end effkctor, mon than one fhga will k in a position to
apply force to the M m - 7 stnicturt. Thus, it is mmzmblt to assume a worst load case
scenario of 80 N on the end effectot. This l d is obvious1y b e y d the limits of the
actuators, but can be obtauied whn the sûuctaue cnc0~11tcrs a physicai limit stop ncar the
edge of the workspace. For the stage 3 Jinkage, thc mommt am is 150 mm. Ibe total
bending moment on the interface is therefm 12x1d N-mm. The offkt f a the eid of the
duminum insert is 10 mm, thcreforc, the rcquircù face fa the womt l d case scenario,
distributcd over sevai nodes. is 85.714 N pcr node. The units for IDMS-Mucr's Series
V. 2.0 [31] is mN, thertfort. the load rppiicd to cach node W 85 714 mN.
Figures 3.6.2.3.6.3 anâ 3.6.4 show the maximum principal stress amtours in the
various components of the bond gcometry. Figure 3.6.2 shows th maximum principal
stress contours in the composite tube, Mth the bonded region outlinal. Figure 3.6.3
shows the maximum principai stress contours on the bonded fke of the aluminwn imea
Figure 3.6.4 shows the maximum principai stress contours in the epoxy bond m a W .
The locations for the stress mncentrations en not in the same place on the txmd for cach
of the entities. The maximum stnss comtration fa the composite tube occurs near the
edge of the bonded region. The fibers in this ana arc in tension due to the kadiiig load
The stress concentration for the aluminum end fitting, howevcr, seans to be an lrrtifaa of
themesh,asitdoesnotcamspoad~,mydsoeasri~. 'Ibepcakprincipplstxessinthe
epoxy matcrial is on the fLict face of the band fillet, which is one of the Mure modes thaî
was observed in [W. As the stress is not conccntrated near the intdllct with the
composite tub, WC can wume that thae wiil be no delamination in the composite tube
due to the bond.
McGiii University Deputmmt of Macbrnical J h g h d a g 44
Boaded ~itgim
Outer surface of composite tube
Badedhgifnl
Iana swfacc of composite tube
Figure 3.6.2 - Maximum P n ' n c i ' Stress Contours in Composite Tùbe Close îo Bonded
Region
McGill University De- of Mbchrnicrl- . . 45
Figure 3-63 - Muxirmun Principal Stress Contows for Bondcd Face of Aluminwn
Insert
Figure 3.6.4 - M i h u m P r i n c i ' Sirus Co- in E ' Bond Mat&
McGiiï University Dcputn#it of Mecbrnicrl- . . 47
In figure 3.6.2, the maximum stxcm in tbe amp&c tube occ~rs m tcnsim mar
the end of the bondcd ricgiom niir stress ccmcentration is due to the transfa of the
~ i o n s ~ s e s g ~ b y t b e ~ o d t h e c p b e f r o m ~ b e U m i n u m a a d e p o x y t o c b e
composite tube, and is unavoidablt. Howevcr, the stressa kgin befw the end of the
cpoxy bond, which co~ltriôutts to a gradwl m a of the 1 4 aad rcduces the ovcraii
stress concentration. This graâual trrilisfi is thercason fa designhg the metil eiid
fitting with a fillet, and fa d g a Wt with the epony rmitairl nie composite tube
is not in danger of f&iling from this peak principal stress.
Figure 3.63 shows the imvr aima of the aluminum mSar The pcak principal
stress is locatcd right at the camer of the metal insat This stress at this point is fat
below the yield stress of aluminum, so tbac is no danger of M u e in thh part.
Figure 3.6.4 shows the epoxy m0tCri.l. 'Ibe maximum principal stxess is locatcd
near the top of the fillet on the metil insert. The maximum prhcipai stress is 16.7 MPa.
The value of the stress at this point is close to th yidd stxcngth of the cpoxy. The yield
strcngth of the epoxy is 20.3 MPa [38]. The factor of safety for the opcEnurd lxmd
subjected to the worst case l d scenario described above is b r e f - 1.22. The actual
hand load on the end effcctor could be 1.22 times greatcr, or 97.2 N, btfm a Wm
would occur at the bonded joint. It would wt be advisable to try to fiirther optimi7r! the
geometry of the bond, as this w d d jeoperdue the safcty of the bond fa the postulatcd
worst case loading scenario. W e can assume that the bond, as it stands, is optimbd for
this application.
McGiU University Depument of Mechaid . . 48
4. Bonding Tests
4.1 Three-Point Bend Test
It was proposed to @orm a tbra-point bend test to ev.hua the thrce
Composite tube
\
Figwc 4.1.1 - SActcR of thne-pint bend e s t se-
dimensional finite elment mode1 and the chosen optimai ~ g u r i t i o n of the boaded
interface. The thrcc-point bend test was paformed accordkg to Figure 4.1.1. A thr#-
point bend test, rather than a fouf-point bend test, was chosen for feat that the composite
materiai might fail localiy due to the applied pressme. 'Ibe thrcc-point *fixain above
d o w s loading on the duminwn inoar. 'Ibe aluminum irurar rsqiiirrd a double bond
configuration, with the load applied in the enter, to aIiow fa the maximum beading load
applied during the test ta be in the region of intacst, and ta allaw far the test to be
performed in a symmetric fashion.
The test was paformed on tbe MT'S machine 1391. Four simples w a e usai
(figure 4.1.2), tach with a diffcrc~lt bond gmmebry. The ccmsûuction of the samples went
as folIows:
. . McGiii University Deputnvnt OTMcchnicJ 49
1. Aluminum inacit?9 w a c machird with two bond in-
according to the dimmsicms shown in pble 4.1.1. (mfinaad
dimensions arc rccading to fi- 3.2.1)
2. Unidirectid cartxm-fiber / polyester tubing was ait into eight
loomm lcngths.
3. The inside bcmding s&bœ of the aluminum inrat was
roughcnd with a small file to iecreart the shcaring stmgth of the
bond.
Figure 4. I .2 - TIvee-point brnding tut spcciwaen
4. As suggested in [3q. the surfnce of the c ~ m p ~ s i t e tube thpt was
to be bondcd was a h sanded with cmery cl& to remove any
rclcast agent and extra min that might have bœn pmsat b the
manufacairing process.
5. The duminum iwrts w e n clampai in such a way as to be
vertical and couial with th composite tubes.
6. nie bond volume was fully filleci with Mbcmd epoxy [4û] md a
bond fillet was &a@ by heid to approximately 45 degras.
7. The set-up was leh 24 hours at m m temperaturr to nue.
McGill University Depsrcnwnt of Medunid &@e&g 50
Design of a Compogtie Link fa dw PIssQat7 Hirpric H a d
Test # The sampks were mounted in a
&me-point testins jig that ailowed fa
0.1 10.0 3.0 simp1y suppcxtcü conditions. 'Lbe l od F wu atppiicd by a cyiinâricai appliclltoc ai a
daBtsurfkcmachinadintothc
aluminum in!wrts at C an figure 4.1.1 to Figure 4.13- Variation of diwunswu
assure a point 1d conditicm. The for three point bmding ~ c s t s horizontal distances AC and CB art the
displacement rate for the position control was chosen to k 0.095 mmlsec, d t i n g in a
quasi-static loading case.
4.2 Calcuiations for Bending Moment Load Case
The ideal shear force (V) and bcnding mommt (M) &gram for the simply
Figure 4.2.1- S k and bedng inoment diograms for thme-point
benàïng tesu
supported threc-point knd test is show in fi- 4.Z 1. Tbe maximum bndbg moment
on the sample is at point C. The maxjmum kadiag moment on tk boided mgion is at
D e s i g n o f a C o m p o J i t e L i a L f d t t h t ~ 7 5 @ ~ ~ ~
pointsDandE. nrstfailurcwjllawthacductothefmsi011coDIcdb~thb~0f
the sample. Due to the na -honqpmw nature of the test samples, the pure bending
formula for the caiculation of tbe ItSUltant stress in tbe sdlllple dœs not hold 'Iae
individual wmponcnts have MCICII~ moduli ofclasticity a d dinirient rdii for
the same load. The ideai caldations f a the stress in a prismatic beam unda pue
bending qui re that the riuiius of curvature for the bcam is constant and that the cross
sections of the kam remain udefOllILtd and papendicular to the laigitudinai pris. an
assumption that d a s not hold hem.
To provide a design der ion fa the bondcd gcomcîry, th remrl l d canditicms
have bcen repmduccd as closcly as possible. 'Ibe bcnding mode is the load case that wïli
bcsecnintheactualpn>tot~pehriid~~~ltrollet,sadamuimum~~ldcmbe
calculated as follows:
M- is maximum ômding moment expeaed in h c e (case of usct hitting a
physical limit stop)
Fiihmd is maximum user hand force. In out case we take this to bc 40 N [3]
23 is the Iength of the stage 3 iinkage (sec figure 1.4.3). 1H)mm.
EB is the distance fmn the simply supportai sdge to the end of the bondeci
area (sec figure 4.1. 1). 90mm.
F , is the maximum f a a the sample is requirrd to withstand without failurc
Applyhg the nimnt values to the above equatim, we gct a minimum Mure load
of 133.33 N of force to be applied to the sample befae finit Mure If we takc a
minimum safety factor of 2.0. thc load that wiii need to be suppatcd by the sample is
266.67 N,
McGill University Departmcnt of Mechrnicrl- . . 52
The piston fixce vs. dispiaccment curves fœ the fam samples a shown in figm
4.3.1. The curvts for tests 1.2 .nd 3 show two definite filllult modes. Figure 4.3.2 shows
a failcd speciwn. niese a causcd by cracking in the epoxy bond. h the third ~gim cm
the curve, the bond is nùly M e 4 and the to the bcnding of the uaiplê hi due
entirely to the friction bctwecn the aluminum intchœ and the epoxy bond. The cur~e
for test 4 shows d y one Um. the -C MIKC. foiîowed by a simila Woii dominated by the fiction fora ktwœn the bond end th ioughencü dumin- insert.
The initiac f 0 Z w (IF) is what wïii be dealt with in thc campariscm bttwœn the bond
geometnts.
ceaterpoht dîspJaaHnent [mm]
Figure 4.3.I - Gr@ of pismn fom vs. cmtmpoint displrutement
Figure 43.2 - Broken the-point knd specimcn --
McGilï University Deputnrnt of Mocbraicrt . .
The sccond -le, with an .dbmnd waU thiclurnn of 3.0 mm, shows the highest
value of piston force for the IF. nie IF occurs at 600 N. The third sample shows a IF at
560 N. The fïrst sample's IF occurs at 540 N. Finally the fouah samp1e's IF occurs at
220 N.
Fmmthecurvcs, wecanseetheffktthatcachpuimctabas aitbeIiCSUIting
strength of the bonded joint. As prcdicted in the axiSymmetnc model in chaptcr 3,
incrtasing the bond line thickncss and increasing the adhacnd thickncss in effect
strengthen the joint. Howeva, it is obvious that the inaease in saiength is vay slight
cornparcd to the hacase in mamial in the joint. I k m s b g the axial engagement of the
joint decreastd the o v d strcngth of the joint. This coincides with the conclusions
drawn h m the finite elacmt modeling p a f d in chaptcr 3. Howeva. the e f f ' on
the overall strcngth of the joint is very pst. Thc lod thet the joint can su- befolt
catastrophic failurc is 4.7% of the nominil specimcn (test sample #1). The joint in this
case does not meet the safcty requircments f a use in structure.
It is intcrcsting to note that the physical specimens showcd a much higha failme
load than predicted by the finite clement model. 'Ibc maximum piston facc that should
have b e n sustainable by the nRt sample, bascd ai the fînïtc elment analysis, is 292.8 N.
The actual value for the piston force at IF for the first sample was 1.91 times this
theoretical value. However? the finite elcmcnt model did not nccessady predict
catastrophic failurc. The physical test of the bonded sample may not have measund
some initial cracking in the bond marcnpl that marc closcly matchcd the filllurc critcrion
obtained h m aie £initc elemcnt model of the h d e d joint The physical test provides a
factor of safety for the bond in bending of 2.33 o v a the worst load case scenario
considemi for a haptic devia.
Rom these tests, WC can see that the nominal joint COIIfiguration is vay close to
the optimizcd value. No gzat gains would k made in inmeashg the adhercnd wall
thickness or the bond liae thickncss, and decrrasing the axhi engagement of the
composite tube would jeopardLc the o v d streagth of the bondecl joint.
5. Design of Box Beam
The construction of a composite box bcam to bc usaï both as a stnictural member
and as a wver for the dista1 stage strings wu> made f a production and marketing rasons.
A less expensive structure w d d ccmsists entrly of the btmded composite tubCs as
describeci in the prrceding chpcas. Howmver, the polymaic Piriag that m usai to
actuate the distal stage of the hand controila arc fairly deliate. and shaild not bc left
exposed in a marketable product. Iastcd of usîng a tu- structure as the structural
entity, and fixing a protective covering over if tbacby grcatiy iwumg the link weight,
the carbon fiber box-section was pmposd as bot. a structural m c m k .ad a cover to
pro- the distal stage strings.
5.2 Dimensional Requirements for the Box Beam
The cross sectional dimensions of the box section fa use as the distal linhge and
the cover for the distal stage strings w a e detcrmined by the intcrfkcnce rcquirtments of
the pulleys caqhg the distal stage strings. The puiieys at dK intersection of the stage 2
linkage and the distal stage h h g e and the puiïeys out at tbe distnl stage arc 23.75 mm in
diameter and 6 mm in height. The puiieys at the distai stage rlso rotate k45" about an
axis that is 3.25 mm bclow the centcr of the N e y . The centers of rotation of the distal
stage puileys arc 32 mm .part, vcrticaliy. nirough simple trigcmometqr, the clcamnce
area for the box bcam c m k detennined as 23.75 mm widc and 53.5 mm high. A
cushion ne& to be added aiound this minimum clearance to pvent intcrfbcnce
between the bondcd inserts that WU be rcqumd for mounting the box-section u> the other
links in the translation stage and the dWal strings. Figure 5.2.1 shows the cl-a a m
for the strings at the distal stage end of the box section.
The box section rsquirrs a methoci of m g to the rrst of the translation stage
stmcnirt. As with the bonded tubes, it was chosen to machine aluminum ïma%s to bc
McGiU University Deportnwit of Mecbrnicrl- - . 56
Figure 5.2.1 - CIccuollce orea for the dis@ stage driving stdngs
adhwively bonded to the cadnm maicrial îhaî waild thcn bamme attacbment points foc
the other aluminum parts requirrd for tbt structure.
Figure 5.2.2 shows an explodtd view of the assembly of thc new crubon f i k
distal stage assembly. Ibe pullcy block base mecl as a mounting point f a tbc h f b
connectingthedistallinltapetothcstageZd3liolages. Thediralstagemamt
providcd the interface with the h c a a a i direil stage.
5.3 Finite Element Mode1 of the Distal Stage Linkage
The design criterion for the tmwIati011 stage of the hmd mtroUer is not kxd
upon a traditional failme critaion, a even a displacemnt &criai as is ofta the case in
robotics applications. The humsn haptic kinesthetic sense is not fine tuneci en- to
accurately disaiminatc kwai two points m spre. hstead the lowcst nmml structural
fkquency of the assembly is the design g d .
To simulate a viriual contact with a soiid wall with acceptable fidelity. th rate at
which the signal is modifled during the simulation is ncar 200 &. If the structurai
natural fiequency is nau or below 2ûû HZ, tben nsomnces can be set up in tbe structurit.
rcducing the fidclity of the sirnuiation.
Threc finite element modeh wae consaucted using 1-DEAS Miicn Series V2.O
of thne separate distal lintsge assemblies. 'Ibe first h i t e elemait mode1 was of the
composite box-bernn structure discussrd hue (figure 5.3.1). Th second modd
corresponded b the proposed shcct-mctai c o v d linlrngc (figure 5.3.2). An itcrative
process was used to determine the lay-up requited fa the composite part f a it to have an
quivalent defltction stifhess to the duminum c o v d linlrage. A iay-up of thme woven
layers (0/9û) was chosen. for a lay-up of [(0/90h Ir. Unfortuoately. due to the excessive
cost associatcd with a filament winding machine. the d y option f a fabncating the box
beam was hand lay-up. For this reason a more rigo~ous ophhation of the hlhatc.
hcluding prccise angle plies to in~rt8se mrrtciial damping. was not possible within the
=ope of this work. Such an optimhtion proccss, howeva. is a suggestion fot fbturc
work on this project.
- - --
McGill University Departnmt of Mcchrnicrl . . 58
Aluminum brick
Figure 53.1 - Fin& riement mesh of conpositc box-section ünbge
Aluminum elements
Aluminum brick elements
5.4 ResuIts of Finite Element Mode1
The finite elemcnt modeh wert solved far a test I d case of 10 N in static
bending to detexmine the e f f i v e s t i f b s s of th Linlcape. Ibc makis wac citso solved
ushg a normal mode dynamiccs iterative solva to dotermine the lowest rescrnant natural
frequencies for the first thrcc modes. Thrc w a e no bouodricy conditions placaï on the
models for planar motion during th normal mode dynamics solution because it vas
1 Max. Deflection
Table 5.4.1 S- of Coniplrrion Between Box B a Finite E k n t Modcls
Vetticaîly Vertical Natural Frq.
, Horizontal Naturaï Frcq. Total Estima- Weight
desircd to h d the rcwnant fiequencies in dl thrrc primPy directions.
Table 5.4.1 summarizes the most impaaat rrsults of the modehg. h m table
5.4.1, it is obvious that the composite h b g e cnnperrs fivorably to the aluminum
covered linkage. Then is a gain in vatical bcnding stifniess of the hkage of 8.67% for
the composite linlcage over the duminum mercd linkage. The vertical natural fnrluaicy of the composite linkage hacrises 31.89% ovcr the aiuminum c o v d linlrage. The
horizontal naturai fhpency of the aluminum linirage does not mœt the design critaion
of 200 Hz, while the composite Iinlrage does. F i y , it is expe*ed that a deatuc in
total weight of the lintage hm the aluminum covercd to thc composite of 35.43% wii i
occur. From these d t s , it is obvious that a composite box-secticm in p h of an
a1uminu.m sheet-metd cova is a vcry advmtagcous design choice.
AhmiinmCovcrcd
15h10-2 mm
McGill University Deparînmt of i k b a i d 60
' Composite Lkkagc
I
1.37xlû-2 mm
552 Hz [l86R'zJ
127 g
l
728 Hz 221 Hz
82 R
6. Box Beam Protoope
6.1 Carbon Fiber Box Beam
The actual co~~~truction of the box beam prototype rcqpbd s e v d steps. The
fint step was the constnicticm of an extcmal mold f a the carban fiber matdal. The
mold was d e in two halves. The stock mstniat for the mold was exbruded aluminuxu
channel. The use of the cbaaael allowed for conrers with Cansistent cumature of M y
large radius. It is important to avoid sharp COWR whcn w&g with an extemol mold
The channel sizc was chosen to have the same intenial dimmsians as the extemal
dimensions of the composite box-beam sbnictme. Ibe inncr mfke of the mold WU
polished to provide for a good surface finish for the composite picce. Holes wem drillecl
and tapptd in the w& of the channe1 to provide clamping points f a the two halva of
the mold. The purpose of the mold is to ptoviâc a rigid surf.ee on which to pbce the
carbon-fiber material to give it shape. The mw carbon-fiber materiai cornes in the farm
of long sheets of woven or unidirectid fibers pre-imprcgnated with an epoxy resin.
The epoxy resin holds the nbeR together in the finished piea while the fibers, being
much stronger than the epoxy, arc respoasible fot caxrying the l& applied to the part.
The @-up refers to the procas by whkh loyers of the cadxm f i k material rue placcd in
succession, one on top of the other, to neatt a waU t h i c b f a the composite part. The
materid for the layers can bc cut dinctcllt wiys to obtriii diffhntfibcr orientcrtions.
ailowing customizaticm of laya propaiies as explaineci in Chaptcr 2.
The choice of an extemai mold was ma& fa tum L~CBSOIIS: first, the cross-section
had to be hoiiow to allow the passing of the distd stage strings, and second, a marketable
product would nquire a superior s u a finish to be acceptable. Whik the fht condition
could bc met with an internai. rcmovable mol& the SeCoad rrquind the extcrnal mold to
prevent material wrinlüag during the c m .
To cure a composite part, the carbnnkr muai.l has to k subjectcd to
prolonged periods of hest and prrssuit in ada to hrrdm th^ epxy miin. l k sue cycle
BkGiU University Depattme~t of ~ c c h r n i ~ r l ~nghmkg 61
refers to the controlied changes in pssme and a ~ ~ l i t d to tk pt
duringthehardeningprocessoftbeepoxyresin. AUcOmpOSitemrta.lrrrgiiircanne
cycle. However, some resmS cure at much lowa tcaiparturw than otbas. Ibe cure
cycle that is used for the rmtmcil chosai [37] foe the cumpo&c box-section is the
Revious attempts at a lay-up with the split mold wen unsuccesJful b- of the
choice of a thin tefion sheet as a reieuscfih. 'Lbe rcleasc film is nquirrd so that the
epoxy min does not stick to the mold during the cure cycle- S e v d pr0bl.m~ ocaimd
with this technique. Fust, the mold had to be closed fimm the start of the iay-up process
to d o w for the insertion of the tcflon film. Not only did this mak the lay-up technique
more difficult but didn't aUow SuffiCient pressure to be applied to the corners of tk box
beam during curing. The teflcm film had a tmchcy to strctch away Ibn the corners of
the molci, causing gaps bctwccn the pazt and th mold mufkc thai, afta -8, d t e d
in excessive dry spots on the outer SUrf~ce.
Amisol. a Company that produces Fretkote liquid nlares, aras approached and
they provided a combination of BIS liquid seahnt and Ftetkde 7ûûNC releuv agent to
treat the inside of the mold [42]. This solution wodrtd v a y well. Application of the
seaiant and release agent took 20 minutes plus po1yrileriPng tim (24 h m ) and the
dtingSUrfacefinishwa9muchbaia~thtori~ypropoecdttfl0~tnIm. The
McGiU University Departmnt of Mecbinicrl Engmœnog . . 62
release agent on the mold riirnce .Ilowed thc lay-up to k stazted with the mold rpa.
which made the lay-up techaique much d e r .
'Lhe first laya of the carôm-fiber matcriai wu put in phcc with the mold spart.
Two picces of the (W9û) woven carbcm nba maîdal4Smm x 175mm werc pisceci inside
one half of the mold with the cùgcs flush with th split edga of the mol& %O otba
pieces 60mm x 175 mm wcrc placcd in the ocha h.lf with m ovahrng of approxUnately
15mrn. The layers also ovaiap on the middlt of the large face of the box b m by
approximately Smm. Part of the second layg of woven niritaipl is addcd kfae to mold
is joined to ailow for beücr placement and cornplesai011 ofthe layem. 'NO picces of
60mm x 175mm are cut of the [W90] wovcp mntmal and arc p W f i t the lege
surf'acc of the mold, with a small overhp of a p p r o ~ t t l y 5mm k y d the midpoint of
the corner cwaturc. This mail overlap is essential fa goai bonding of tbe full laya to
the srnalier 30mm x 175mm pieces thrt arc addcd aice tbe mold b c l d A cornpletc
third layer consisting of two pieoc9 of 6ûmm x 175 mm. and two of 3<)mm x 175 mm are
put in place with the mold closcd nie f h i nsult is a loyYp comisthg of threc layen,
[(0/9ûhlr, where the (W90) grwp repmsats the woven graphite matuiai. In the mgions
of overlap near the corners, the lay-up is actually [(0/9û)SJT, and h g the middlt of the
large fafe of the box-beam, [(W90)4]r. The Iiy-up is show step by step in figure
6.1.2.
Two pieces of the teflon rcIease film were applied to the insi& of the composite
part, foUowed by a layer of brcather motenPl fa the even application of the vacuum to the
whole piece. The teflon film in this case pvents the brcather mptmel hm sticking to
the cured epoxy. The vucuwn h g is a seaicd plastic shea that wmpktely covers the
part By drawing a vacuum inside this bg. the composite mataial is presscd up against
the waii of the mold, cornpressing the layas togethcr and faming a much stmnger p i e .
The reason it is necessary to avoid sharp wmas in an extanal mol& as was mentioncd
above, is that the vacuum ôag cannot i n f i l m a shup radius to qply an evai prrsauc on
the composite material. It is the leck of vacuum pmsurc cm the mamiaï that causa dry
spots to occur.
~ c ~ i l l University ~cpertmnt of Mecbrnicrl ~ n g b e h g 63
layer 1 Aluminum mold
layer 2
1
1
Figue 6.12 - Luy-up P10ccdrve for Coni;posi& Box-Section
McGiU University Dcputmcnt OdMechrnicrl Piiarrwrnp . . 64
Design of a Composite Liuk for bit -7 Haptk Hlir;r-
The vacuum brgging t~chnique was slightly diffiicnnt tht is t m d i t ï d fa an
extcrnal mold applicaîiom The oven to be used did rmt hm a prtraimbag pump, d y a
vacuum pump attachmmt Thcrcfm, instcad of an innarshle i n t d b l d d a tù tpply
pressure to the part, a cyiindricai arrangement of tbc vacuum bag was dtvised. Two
cyhders of vacuum bagging mrtaipl, sedeci h g the side, wat piaced inside and
outside the mold. The ends w u c tha, d e d to each athcr aicmg the c v c u m f ~ c e . Th*
allowed for aîmospheric pressure to bc applied to the ni1l intemai sufbx of the molcl,
without the added expense of an Maiable bladdcr.
'I%ecurcdpiecehadgaodsurface~0ilb03hthcoutsjrlr!andinffiALsun8ces.
There was no wrinLling on the inside SULf'acc of the box bcam k a u s c the motaiPl WU,
slightly under tension. It was difficult to gct evcn p s s u c into the ~ ~ ~ Q C X S , anâ &y
ended up slightly min rich. It was obvious by looking u the thicbress of the waUs
throughout the cross section. me best comprtssion occuucd on the lPpe hct of the box
beam. This leads to a slight prob1em with dimensionai to1eranœs. It is diîflcuit to
control the final interior dimensions of the box kam since tbey pe v a y depeadent the
compression that could be obtained on the f&cs of the part d the guality of the vacuum
pressure in the corners. For the casc of the Ereedom-7 projcct, good dimensional canml
was quired on the inside d a c e of the box beam siafe machincd md fiüings an to be
bonded to this inside SUfact.
6.2 End Fittings
The nnai design of the end fittings was detcmhcd aRer siflcant pro-s had
a l d y bcen made on the consûuction of the box beam. Onginilly, small plPtes fixed cm
the exterior surface of the box bcam w a c inttnded u> bt uscd as mounting points fa th
various aluminum parts nquirrd for the ksriag mounts and joint shafts of the hand
wntroller. Last minute design cimages led to a modification of this i d u to d o w for
precisely machined, end fittings to be bonded to the inside waiî of the box section. As
discusseù in the previous section, the intcrior dimensions of the box bcam are not weli
controlled and can seriously affect the bond lim thiclaiess and, co~lsc~uently, the tbesemgth
of the bonded joint As weU, due to the close clcarance seleeted f a the distai stape
McGill University Depararuot of Mechinicrl- 65
strings, the wall thiclwss of the mctal inoar miut neccssdy be v a y rmrll. which pores
machining difficulties- A ampmmhe was mde betwecn thsc vdous -ts,
and the piece was designcd
The material selection for the end fitiiog was rnotba problem area. One of the
design goals of the Frcedom-7 was d u c c d link inatia. To achieve this goal, parts of
minimum weight werc rcqumd fot alî amas. Th existing metal pmtotyp it made
entkly of aluminum-6061. To avoid using two di&rmt mctals and mcoiinging gaivanic
wmsion among the metallic parts, it would k logicai to choolie aluminm 6061 as the
material for the bonded insgts. Howcver, almninum f m an &de v g y d y in au and
this aluminum oxide is highly anodic. In the pnsence of an eleca~lyte such as sca water,
there can be signincant corrosion of the contact surfaces bttwccll aiuminum and a
cathodic material such as graphite. As a resuit, the aluminum d fittings rcquire etchmg
to remove the aluminum oxide iaycr on the baading sudacc befoft the bonding opcrati011,
The West-Systcm's aiuminum etching kit (431 wu uscd to pnpsn tûe boading
surface of the aluminum hscrts. The portions of the bat not subjea to dhesive
bonding were maskd with tapc, and the etching process was Camed out accordhg to the
directions on the etching Lit. With the carcful ptcpatatim of the aluminum and
composite surfaces the galvanic corrosion of these purp should be kcpt to a minimum-
6.3 Bonding of End Fittings
The bonding of the aluminum end fittings roquirrd the collsf~cticm of a jig to
keep the two planes of the end fittings paraIlel. The jig coasisted of two acaratcly
machined right angle L's mounted on magnetic bases. The mgnetic bvles k themselves
to the top of a metai level table. nie right angk maire use of the mounting holes on the
end-fiaings to hold the end-fitthgs in p h . A dial-gauge wu, uscd to mepsun the
deviation of the end-fittings and the box-section from parallcl.
As sated before. the internai dimensions of the box-section wcm poaly contn,iied
with the rnanufacbg me- Thc min rich arcas in the comas of tk box-section hd
to be filed d o m to aliow the end-firtings to fit inside.
McGiil University Depatmitot of Mecbrnicrl- - . 66
One standard pmdurc f a casuriag evm boncl liiu thickncss ova a iargc
bonduigaruiistoursmrll~gearireembeddadhchcboadmaa*ltortuaspra
during the adhesive bonding [36]. nieSe wires normrlly ovc~Iap the bondcd region md
are cut flush with the adge once the adhcsive is curcd, Tbese wirw arc not necded in this
case to maintain the bond line thicloless as the corners of the metal insats art in contact
with the resin rich areas in the comas of the box-section. The mah &car camying amas
of the bonded interface, the 5 t fhccs of the boadtd region. have a gcmd, u d o m i bond
line thickness without the discontinuities and potential stress concentration points that
could bc caused by the incluskm of the sPndsrd wirc m tbc boadcd region.
Due to the long cure time (24 hours) of the Adbond epoxy [W. thac was ~ome
seepage around the interface with the end fittiag and the composite maîcd. Ibe
strength of the bond was not comproaiised. as the bonci lcngth was dcsigncd with a iarge
factor of safety. However, for friture production, an epoxy with a much lowa cure timc
should be considemi.
6.4 Structural Tests on Fkedom-7
The existing aluminum prototype at MPB Technologies was COIlfigurcd in such a
way as to be able to accept bath a distai stage linlcage and a stage tbrse linluge in the
form of a box beam. nienfore, a second box bum was constructed using ihe J I M ~
technique as for the ht, and substituted for the stage thrce linkage (inrttsd of using the
bonded composite tubes). This was a marketing design change. and will not the
continuhg research inta the propcr design of bonded intufbces fbr smaU diaiiaetcr
composite tubing that continues in the next chptns.
-
Table 6.4.1- Weight Dmbwion for BOX-Bccun Ports
Distal Stage Link
Stage 3 Link
McGill University Depattmcnt of hkhmid 67
Fittings 17.5 g x 2
17.5 g x 2
Flber 23.7 g
28.0 g
Composite 101.5 g
106.6 g
luluumiaumuminum 103.2 g
98.2 g
The weights of the iadividiial parts of thc box krm assemblics arc shown in pble
6.4.1. as weii as the overail weights of the asanbled mes md the aarespoidiiig
duminum linlrages. They do not match with thc dmaîcd weights fiom tabic 5.4-1. It is
obvious fkom the weight brtakdown that the aluminum bats f a the comp0site box
beams arc significantly ovadcsigned. As mentioncd kfae. the machin*tr have
difficulties working with aluminum of vay thin wall thichicrs. Thcrcf-, to facilitate
the machinhg process, the wail thicknesses were increased and more matujaî was lefk in
the center for mounting of the intcrface parts- The weights of the enâ fittings s~count f a
34.4% and 32.8% of the overail weights of the dïstd .nd stage 3 linlrnges rcspd.ve1y. It
is by no means unreasonable to consider that a design of the ad fittings could d u c e
their weight by 50%. malaiig the overail weight of the link assembiics 84s fa the distai
stage linkage and 89.1 g for the stage 3 bkage, which w d d be much closa to the
original estimateci weights. This des ign wodd COIlStitute a weight savings of 19.2
grams, or 18.6%. in the distd stage, wbich is the major contributor to the o v d inertia
of the translation stage.
6.5 Frequency Response of Translation Stage Two dynamic rcspoase tests wae pcrfamed on the translation stage of the
Freedom-7 hand controiier. 'Lhc first consistecl of sading a fiequency varying sine wave
individually to each of the thrte motors and mtasuring the end tffcctot accelledon in the
nominal direction g o v e d by each motor. Tht pur- of this test was to determint the
resonant frequencies of the structure in each direction. If we consider the translation
stage to be planar, with the positive xdirection paralle1 to the stage 1 and 3 iinkagcs
pointing towards the motor mounts 6Rnn the distd stage, the positive ydirccticm paralle1
to the distal stage linkage pointing out towards the usa. the right hanà ruic gives us the
positive z-dirrction as downwards perpendidar to the plrae of the brsnslation stage (sec
figure 1 A.6). A small magnitude rotation of the stage 3 motor about the centcd
position provides an instantancous movcmmt dong the x-axis. 'Lbe sznail mapitude
rotation of the stage 2 motor provides movemmt dong the y-axis. The smaU magnitude
rotation of the stage 1 motm govcms the disphcement a h g the the-axis. It is imparmt to
note that, as the stage 1 and 3 motors arc co-plmir, their effkts ai the disphœmcnt of
McGiII University Dep~rcme~lt of MechrnicJ Equrumg - . 68
Dtsign of a Composite Link fa dK Frtuîom-7 HIptic W rrribakr
the distal stage are coupled. Thrrfoee, the hdcpmdmt axes d y M d for smaU
magnitudes of joint displacement around tbe neutraï position. 'Ihc neutd position has ail
the joint angies at 9û0. The second SCLics of dynamic tests to be pcrformed on the
translation stage consisted of inducing an impulse in the motas ofa set amplitude auci
duration and measuring the maximum aac1eration of the end effcctot. This test was
perfonned in order to mcasurt the overail inertia of the stnicîurc in each of the three
motor directions.
Ideally, the resonant 6nquency for the structure in cach of the thee directions
should be greater that 200 Hz. This is an adequate mIution to simUlnlr_ contact with a
solid surf'ace in a virtual environment, The maximum acœleratïon at the end e f f w far
the motor impuise test should be as hïgh as possible, yct alupl ia aU directions. The
higher the maximum a~cclaation at the end effanoi, the greatcr the Mispness of tbe
device. Haptic sensations wiil fccl more rtaliStic and 1- sluggish. Howevcr, if tùe
maximum acceieration is not the same for each link, the apaata may acnac a change in
the response of the device bascd upon the devices orientation. 'Ih* is undesirable, as the
Freedom-7 is intended to be able to bc orientad in any direction.
For convenience, the fhquency rrspoase NVCS have becn gtouped in Appcndix
B. Figures B 1 through B5 show the acceleromcter output vs. the excitation frcquency of
the stage 1 motor (z-dirrction) for the five configurations of tbe translation stage links.
B1 shows the response of the aluminum st~~caire af<er a very carcfbl assembly, wiîh
proper pre-tensionhg of the bcarings and alignment of the shafts. B2 shows the nspoase
of the aluminum structure aAct a somcwhat lcss colltrolled, less expaicnced asscmbly
procedure. B3 shows the ~cspomc for the translation stage wich the two carbon f i k
links included in the structure. B4 shows the rrspanse with only the carbon fiber distal
stage hkage and BS, with only the stage 3 linkage. Similsr tests wae p a f ~ ~ n e d for
each of the other two motors, with figures B6 through BI0 nf-g to the stage 2 motors
@-direction) and figures BI1 through B15 rrfcning to the stage 3 (x-direction) motor. A
summary of the first nsonant fresuency for the translation stage in each Connguration can
be found in table 6.5.1.
-
~ c G i l l University ~cpartmnt of ~ac l iu i i~r l E n g k u h g 69
Second Aluminum Assembbly 103.9 Hz 95.6 Hz 94.2 Hz 1
Two Carban Lïnkagcs 128.0 Hz 127.8 Hz 102.9 Hz
Carbon Distal Stage Lïnkage 115.9 Eh 91.9 Hz 91.9 Hz
Original Aluminum Assembly
Table 65.1- Svnv~ly of First Reso~nt Ftequenciw for the Fretdom-7
Transhtion Stage
Several concIusions may drawn frwi these tests about the fkequmcy rrspaise of
the translation stage. First, the fkquency rcsponse of the translation stage is hcavily
dependent on the assembly proctdurc. F a the stage 1 mode, the aluminum pmiotype
experienced a drop of the naairal fkpency of 7.75% ôctwecn the cucful and
inexperienced assemblies. Second, the stage 1 mode was not afkckd by the inclusion of
tbe carbon linkages, as the frtqucncy rcspomc is dependent on the stifniess in bcnding of
the stage 2 linkage (which was not modined) and the mars of the distai stage, which as
discussed before, suEercd h m ciifTicultics in the mrchhing of the end fittings. 'ïbird,
the incorporation of the carbon linlrs improved the h p c ~ l c y f a the stage 2
mode. With the inclusion of the two composite linltp the naturai fiequency rose 12.2%
over the original assembly and 20.6% ovcr the incxpaiend asscmbly. Tbe stage 3
linkage was the greatest contributor to this impmvement, and f a the test with it slow. the
natural fkequency was 22.4% higher than the iaexperienccd assembly of tbe aluminum
prototype. Fourth, the inexperienct of the asembly contributai to the damping of the
translation stage. In every case th magnitude of the signai from the accelerometct was
higher for the original assembly of the aiuminum structure than fm the inexpcxienced
assembly of the aluminum structure Finally, th- was a problem with the design of the
puiiey block base (sec figure 5.2.2). 'Ibe inclusion of tbe carbcm distal stage was v a y
detrimental to the penormanct of the stage 3 mode. The naturrl fhquency dropped by
34.0% and the magnitude of the signai was vcry high. The rsoembly with only the stage 3
x ~ c m
189.9 Hz
McGill University Departmcnt of MechPniccil- . . 70
y-dllaction
1 15.0 IIz
zdirection
100.1 Hz
linlrage out of carbon ôehaved similady to tbe ahimmum prototype. lu, it's co(1~'kitim to
this m d e is cotlsidered limitai
6.6 Refbed Finite Element Mode1 of Distai Stage Linkage FurthcrinvcstigationwasrcquircdtodaecmMtbeaurtofthtpoa
pafomance. Mon refïncd finitc elaium mOdeIs than tbt one ccmstcuctcd m chiper 5
were uscd to detcrmine specifïcaiiy the rn0d.l v i i a m in the xdirectim fathe displ
stage linkage. 'Lbt author was wispicious of the strmgth in kiding of the pulley block
base. as the weight rcducing atouts wuld significantly compromise the stiffiiess of the
par^ For tbis m. two models w a t usai. The fht mode1ed distal stage iinkagc as
it was for the physicai tests (figure 6.6.1). The d dded a miaforculg cova tbst
exwided h m the carbon fiber nmtdai brk over the piiiey block base (figue 6.6.2).
simiiar to the configuration sem in the sketch in figure 1.4.6-
Figure 6.6.1 - Rrfned &l of d i s d linAuge for vibration simUlCJtiOn
Figure 6.6.2 - Rcfinedjîmk elanrnt d l of distal linkage with a d cmer
for vibran'on simulan'on
The two modcls werr sulved using the itcrative namrl mode vibration solva in
1-DEAS Masters Saies V2.0. Thcy w a c constdned to move dong the x-z plane, in
order to simulate the vibrationai modes that would occur for the stage 3 excitation. The
shafts were considemi as pin connections with the axis of rotation dong the y-axis. The
fïrst normal mode vibration d t fa rbc uncovcmî distal stage is shown in figure 6.6.3.
The biack outline shows the vibration mo&, which is about the stage 2 linkagt
axis. The fkqutncy of vibration is shown at 127.93 Hz. which is very close to the
measured frtquency of the vibratian in the x-directiou with d y the carbon distai stage
shown in Appendix B. figure BI4 of 139 Hz. Tht mode1 seems to be a littïe less stiff
than the physical structure, anâ tends to vibrate at a slightly lowcr fLequ~~~cy. 'Ibis might
&O be accounted for by the lack of matcrial damping in the h i t e elexnent modcl as well
as the inaccuracy of modcling the bcarbg and 0 t h intafre khaviors as describeci in
section 6.5. The iack of matenil dampiag d d cause emws up to 5% and the intanice
effects wuld m u n t for an a d d i t i d lm ema in the naturaï fhpencics, based on the
vibration tests pafomied cm the duminum prototype.
Figure 6.6.4 - Normal d vibroiion in x direction for wu:overed distol stogc
Figure 6.6.3 - Norrrml ww& vibration in x direction of dis@ stage with M cddcd cmer
McGill University De- of Mecbiiricrl Eapmamg . . 73
The solution of the c o v d madcl fa the modal n i o n s is sbown in figure
6.6.4. The fkquency of vi'bration is 202.28 Hz fa tbc fmt rn0d.l frrqueacy in the x-
direction. Even if we do not take into ucomit the slightly lowcr value f a the naîurai
frtquency of vibration in th hite ctmem modcl, h m p m t h g thïs design mto the
translation stage structure would rcsult in an inatpoe in îbc naturai mmcy of 5.9%
over the aluminum box kam prototype. Obviously, the assumptim thir the iack of
stifhess in the pulley block base was the d t of the poor mmcy mponsc is Corna,
and the inclusion of a composite cova ova the Wey block base is an exallent solution.
In order to&tcnninctbcp~jb1eminthepiilley blockûascthatcauscdtbe
wealrness in the x-direction w'btation, the two modeis wcre soLved fa the static l d case
where a load of 10 N was applied to the stage 3 lïnkage SM in the xdircctiun and the
distal stage mount was ciamped in place. The maximum principle stress contours in the
puilcy block base for this load case are displaymi in fi- 6.65 for the u~lcovercd distai
linkage and in figure 6.6.6 f a the w v d distal lhWge.
h m the contours, it is obvious that the weak point in the pilley block base
cornes form the weight reduction cutouts around the shaft that j o b the distal d the
stage 2 linltages. The cutouts create non-rigid sections in thut arcas becau= thcy arc tut
right through instead of having a small flange as would an 1-bcam. F a th covercd distal
stage Linkage, the magnitude of the stress in the wealra region around the shaft holcs is
much less than for the unwvcred case. It is also apparent thu some of the l a d is
transfemd through the standoff bctwecn the two shpA holes to the wmposite covcr.
This rrdistribution of the l d explains the gains in structurai stiffiicss obtained by rddirig
a composite cover to this piece.
--
McGiii University Departmcnt of Mechrnicrl Equsmag . . 74
Figurc 6.6.6 - Stress contours in covcredpul@ b l d &se
McGill University DeprrÉment of MachiMcil . . 75
6.7 Maximum Acceleration Test In orâer to muwnthehecti~~~inlinkmatir. atcstwaspaiOLmddtomcasurc
the maximum acceleratim of the end e&da f a a givm impulse fiinctiaa It is &sirable
to have the highest end enaCtor acceleration possible. A higher end e&cta acœleratîon
capability wiU d o w a grriter aiqmcss of the haptic ~ 0 ~ 1 s féd bak to tbe user
through the device-
The physical test for the maximum üaL rceleration oonsirtcd of sending a single
10 ms pulse of 10 V peak to each of the motors in tum, and measuring the instantantous
output of the acce1erometcr rnouned at the end e f f i pogiticm on the translation stage
in each case. This test will be r e f d to as the k e p test, as the signal sent ta the motors
is a short voltage beep. The signal was gencratcd by a polynomial wavrfam synthesizer,
mode1 20U) by ANALOGIC. The wavcfam synthesiza was to a sq-
wave of pend 10 seconds, amplitude 10 V peak and a duty cycle of 0.1%. The pulse
was used to trigger a single sampling display f a a digitai OSCiUoscopt, which mu3 the
output of the accelemmttcr.
The beep test was pcrformed on each configuration of the translation stage (except
for the original alumùium assembly) for each motor direction. 'Ih output of th
acce1erometer had becn calibrate- to 10.20 mVfg accordbg to [44]. Table 6.7.1
summarizes the resuits of the maximum accelcration tests.
I Composite stage 3 linkage 1 3.43 g 1 2.54 g 1 2.94g 1
Alilminiim assembly
Two composite 1 i . c ~
Composite distal stage iïnkage
The results of this test show tht. fa the mcst part, the inc1usion of the composite
links have a beneficial e&ct on thc maximum ad e f f î a c c e l d o n Ibc giuast
3.43 g
3.92 g
3.92 g
2.94 g
2-94 g
3.92 g
2.94 g
3.92 g
3.92 g
gains are made in the x md z directicms fa the inc1usi01~ of boch CampoBite links.
However, with the design of the metailïc end fittings? the gains in maximum
acceleration shouid be highcr, as the linL weights rad t h d m t b ~ C O U H ~ ~
weights should dtcrcasc dong with the structurai iriertia.
6.8 Summary for Box Beam Rototyping and Testing The hand Lay-up method for fkbricating a composite box h m is time consamhg
and inappropriate for a pioductiou mode1 of the haptic hand controlier. A m a t suicable
manufacniring method would be filamait winding. Accurate f ï k orientations, almg
with good dimensional tolerances could be obtamed fot a much longer box section, that
couid thcn be cut to the rrquirrd lcngths for the linlugcr. Howevcr, fa pmtatyping
purposa, the hand lay-up in the extemal mold providcd a good sdhcc finish and wur
l a s expensive than obtaining a filament winding machine.
The design of the metal end fitiings was not carricd out rigaaisly mou@. An
overly cautious design couplcd with the iaberent difEiculties in machiiriiig duminum parts
with small waU thiclmcss crcatcd a part that was too hcavy fa the design rrquiricments.
By simply revising the part to be have one half the bond engagement would decruise the
weight of the end fitting by 50% and approach the rcquired design critaion.
The bonding of the aluminum end fiühgs to the composite box bcam was
accomplished without difficulty using a bondhg jig to hold the parts in place during the
epoxy cure. A s h o w cure epoxy could be substituted to allow for a quicker acsmibly
timc for the linkage.
The inclusion of composite mataials has koefits kyond w h t wu mersurrd in
the physical tests on the translation stage. The vibration charactcristics of the translation
stage are very heavily dcpcndent on the asscmbly pmccss. and the inexpience of the
author resulted in assembly dominated vaiues f a the lowest naturai hquency of
vibration in some modes for the translation stage.
The vibration modes tbat took advantage of the composite matcr*l showd sow
improvement over the alumulum prototype. Then was little gain in the maximum
acceleration of the end effcctor due to the ovcrdcsign of tbe bondcd bats thit
the weight of the composite links. Roblems assxiatcü with thc design of the alumin~m
Design of a Composite T,inC fa the Fxœdom7 H@c Hami rmkrJtr
interface parts such as tbe puiiey block base fa the disPl stage .Ir0 ccmtributed to the
poor penormance of the composite iinkages. niaha f i t e elcmnt analysis mnfhed
the wealmess of the pulley block base part, and showd that the simple inclusicm of a
composite cover to reinfo~ict this part wouid @y imPn,vt the dynimic respoase of tbe
composite distal stage ïinkage.
It is clear that the composite mataials show bcnefitr fa the dypanic
performance, however more carc has ta be t aka with the corMnaction of the metal
interface parts that are needed for the incorporation of the advanceci mataiils hto the
structure.
McGill University Deparmnent of Mtchirnicll- . . 78
7. Conclusions and Recommendations
This thesis has undatalrcn to r e h e and improve the design of the Rrcdom-7
haptic hand controkr f a dynamic and structurai rcpmse. Analysis was p a f d to
determine the optimum rncthod for incluskm of c011lpositc muaials in the translation
stage of îhe hand wntrok. Improvements hpve kai made in the 8nalysis and design of
composite parts for robotic applications:
An optimized bond geometry is proposcd fa the joining of smrll diameter mmposite
tubes to metallic W. Thc finite element modeling predicts a fiUlm that b slightly
lower than the muisurcd fail- of the test specimens. lhis d g u W a n ir ppd
as a repiacement for machineci aluminum iinkagges in the ûmdati011 stage of the had
controlier, such as the stage 3 iinkage.
Physical testing of the optimized bondcd gcometry cOIlfilmed the d y t i d e&cg
obtained through finitc element analysis. T b strength of tbe bond in bcnding is d y
weakly dependent on the adhercnd wali thichss and the bond Line thiclaiess, but is
very dependent on the axial engagement of the t u b and the duminum insaL The
overall strength of the physid spccimen was hi* than that of the finite el-t
model. suggesting an overly cowrvative modcling of the joint.
The distal stage linkage of the translation stage of the Frdom-7 is replsccd by a box
beam structure that is at once a structural elemeat of the translation stage and a
protective covering for the distai stage strings. 'Ibe iay-up lad box-bePm structure of
the carbon fiber is beneficial to the dy-c pdonnaiice of the translation stage.
However, insufficient sangth in the machincû duminum inscrts arc rwpoasible for a
drop in the lowest n a d resonant frcqucncy of the translatjon stage.
Swept sine tests were pcrformed on the translation stage, ushg an 8ccclcromta to
measure the resonant pcak w'brations at the end effcctot. This aiiowcd fa a separaticm
of the modal vibrations for the excitation of cach motor individdy.
- -
McGill University Dcpartmcnt of Mechanid Engbc&q 79
a Maximum link accelerations weric masurcd wing an acœlerometer maunted at the
end cffcctor for a voltage pulse to e r h motor. 'Ih rcspnsê of tbe translation stage to
this excitation depends on the link weighto rad inatirr â~ m ~ c h â~ W rcautor
capabilities.
7.1 Recommendations for Future Work The Freedom-7 haptic hand contr011cr could -y -fit hm the inclusion of
composite materials in the strucau~ of the translation stage. Howevu, more wodE is
requcd to narrow the design rtQuircments to d o w for prapa exploitation of the
potentials of the composite material pacts. The foliowing att samt suggestions f a fiiture
work on the Freedom-7 projcct, based on the obsemations and conclusions drawn fmm
this work:
hplement the addition of a reinforcing cuver over the puiiey block base. The addition
of a reinforcing covcr of carbon f ikr matcriai o v a the pulley block bPse of the duul
stage has bcen shown, by M t c element analysis to i m p v e the dynamic @'ce of the distal stage linkage.
Redesign the bondcd aluminwn insais on the distal stage box barn f a r e d u d
weighî.
Perfonn an extensive analysis on the human haptic systcm to determine Specinc
requirements of a haptic manipulator, such as maximum allowable end point
deflection, sensory bandwidth. etc..
Perfom a complete lay-up optimization routine on the linlrages of the translation stage
to detcnnine the optimum fiber orientations foi the opegfic haptic rcqhments and
proâuce filament wound box sections ushg this layiip.
McGili University Departmcnt of Mechrnid E n g b e i q 80
Design of a Composite Li& fœ bw Frrsdoat7 Hkptk Had
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Research: the 7L Intematid SympaSium, Springs Vctlag, pp.195-Un.
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McGill University Departumt of Mechanid 81
Design of a Composite Li& fa the Freedom-7 Hqtk WmA Cmîmlk
12. Sung, C.K. 6 Shyl, S.S., "A Composite raminatui BoxSection Beam Wgn for
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Robots Fabricated with Optimally Tailorcd Composite hmht&"' Tramadons of
the ASME, VoL109, Mar. 1987, pp-74-86-
15. Rosenberg et al., '4ElectromecMd Human-Computer Iiiterf- Mth Facc
Feedback", United States Patent # 5 576 727, Nov. 19,1996.
16. Burdea, Gngore C., "Force and Touch Fdhack for V i Reality", John W i y and
Sons, NY, 1996.
17. Laschet, G., "Numerical Strength Prcdictions of Adbcsively Boaded Multinratcrial
Joints", AGARD-CP-590, No. 12, Jan. 1997.
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McGilI University Deparment of Mechauid E n g h h n g 82
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590, No. 1 1, Jan.1997.
29. Rice, A. & Molds, J., "Bondecl Ropshnftr: design and Asscmbty of Com@te I'ubes
and Metal End Fittings", Matcriaïs Science and Tcchnoloey, VoL9, June 1993,
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30. Gordaninejad, F. et al., "Noniincar Deformation of a Shear-DefOLIIlZLble LambW
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McGiii University Department of Mccbrnicrl- - * 83
Design of a Composite Link fa the Fr#dom-7 H@c Hhad C m î m k
38. CIBA-GEIGY Selectot Guide, Furane Aerospace Adhesives, 5121 San FananQ Rd.,
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Dec. 24,1996.
46. Kazerooni, H, Bi Her, MG., 'She Dynamics and Control of a Haptic In-
Device", IEEE Transactions on Robotics and Automation, VoL10, No.4, Aug.1994,
pp. 453-464.
47. Choi. S.B, e t al., "Modeling and Control of a Single-Li& Flexible M'puiatOt
Featuring a Graphite-Epoxy Composite Arm", IEEE 1990, pp. 1450- 1455.
48. Papadopoulos, E. & Abu-Abcd, A., "Design and Motion Planning for a Zero-Rcaciton
Manipulatoi', IEEE 1994, pp. 1554- 1559.
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Jm, 1995, pp.88-89.
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pp.308- 3 14.
5 1. Thompson, B. S, & Sung, CJC, "An Analytical anci Expcrimental Investigation of
High-Speed Mechanisms FabriutrA with Composite Lar&aW"' J d of Sound
and Vibration, Vo1.I 11, N0.3.1986, pp.399428.
52. Bryfogle, M.D. et al., "Kinematics and Ccmtml of a M y Paralle1 Force-Reflecting
Hand Controller for Manipulator Telcopcration", Joumai of Robotic Systcms, Vol.10,
NOS, 1993, pp.745-766.
McGifl University Departnmt of hidmaid E- - . 84
Figure A 1 - Test 1.4
l
Figure A 2 - Test I . 1
, University Departmnt of Mechanid 9-ii
Figure A 3- Test 2.4
Figure A 4 - Test 3.4
pue A 5 - Test 4.4
ity Departmnt of Mechanid Eo@eubg 9-v
Figure A 6 - Tcst 5.4
- . McGiU University Depertnient of M c d m ï d 9 4
iof aCompositeLmkfordreh#dom-7
1
Figure A 8 - Test 7.4
IO. Appendk B
Vibration in z-àirecüon (Stage 1) - Alnminiim prototype orblnil-b
Figure B 1
McGïU University Departmnt of Mechrnicrl . * 10-ix
Figure B 2
McGiïï University Depiutment of Mechrnicrl- S . Io-x
Design of a Composite Link for the -7 &rptic Had
Vibration in z-dlrraion (Stage 1) - two fubon Jhbges lodudd
Figure B 3
McGiIl University Departmat of hhhaa id Enpmrimnp * .
Vibration in z-dirrction (Stage 1) - carbon disfPl stage
Figure B 4
Figure B 5
McGill University Dep~rrmnt of Macbaaicll- . . 1exiii
Figure B 6
McGill University De- of M d a n i d Engummg . - 10lxiv
Figure B 7
Vibration in y-direcüoa (Stage 2) - fwMmbIy with two carboa -
Figure B 8
McGill University De- of Mcdmaid WXV~
Figure B 9
McGill University Deputnient of bkhmid l & d
Vibration in y-direcüon (Stage 2) - arbon stage 3 k h g e
Figure B 10
McGili University De- of Ibkdmid Engmumg . . 10-xviii
Vibration in s-diroetion (Stage 3) - aiaminom prototype o r i g i d -Y
Figure B I I
McGill University Deputment of Mechrnicrl- . .
Vibration in xldirection (Stage 3) - .Inminom praotJpc 2ad asmnbly
Figure B 12
M O University Depmmnt of Mechinicrl - . 10-xx
Vibration in x-âûecüon (Stage 3) - assembly with two arbm -
Figure B 13
McGill University Deputment of I u k h i d b g m c m g . .
Design of a Composite Li& fol tbc F e 7 HIptic RMA Coatrollca
Figure B 14
Vibraüon in s -dhdon (Stages) - carbon a#age 3 Wmge
350E-02 -
3.ûûE-02 - -
Figure B I S
McGill University Department of Mechraicrl- . -
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