The mechatronics laboratory at Politecnico di Torino

Pergamon

Plh S0957-4158(97)00007-X

.~elhotrmncs Vol 7, INo 5. pp 413 -427, Iqq7 1997 Elsevier Science Ltd All rights rese~ed

Printed in Great Britain 0957 ,1158'97 $17 I )0- t),09

REVIEW ARTICLE

THE MECHATRONICS LABORATORY AT POLITECNICO DI TORINO

B. BONA,* E. BRUSA, S. CARABELLi, M. CHIABERGE, C. DELPRETE, G. GENTA, F. MADDALENO and A. TONOLI

Corso Duca degli Abruz~i 24, 1-10129 Torino. Italy

(Received 9 February 1996: revised 6 March 1997; accepted 24 March 1997)

Abstract--The scientific activity of the Mechatronics Laboratory (LIM) founded in 1993 at the Politecnico di Torino is described. LIM is an interdepartmental structure founded by the Departments of Control and Computer Sciences, Electronics and Mechanics and the Mechanics Workshop. LIM's mission is the establishment of common ground where researchers and postgraduate students working in the mechatronics field can perform theoretical and experimental research and exchange experiences in a true interdisciplinary environment. LIM's activity is basically organized in terms of projects concerning preliminary investigation of advanced and integrated technologies and, successively, their transfer to industrial products. LIM actively cooperates with other technological and scientific institutions and with the local system of small and medium enterprises..~') 1997 Elsevier Science Ltd

INTRODUCTION

Recently, a technical committee on mechatronics adopted the following definition: Mechatronics is the synerqistic combination of precision mechanical enqineering, eh, ctronic

control and system thinkin# in the design of products and manufacturin9 processes. Pragmatically, Japanese engineers call mechatronics The way of designiny subsystems of electromechanical products to ensure optimum system

performance. The Mechatronics Laboratory (LIM) at the Politecnico di Torino is an interdepartmental

structure founded in 1993 by the Departments of Control and Computer Sciences, Elec- tronics and Mechanics and the Mechanics Workshop. its main aim is the establishment of a common ground where researchers and postgraduate students working in the mech-

*E-mail: lim(q!polito.it

413

414 B. I~()N,\ , / a /

atronics field can perform theoretical and expenmcnlal research and exchange experiences in a true interdisciplinary en,,ironmenl.

LIM is steered h', a Scientific ( 'ommittec and can provide expcrimcnt:d facilities in it~ wan laboratory ,a here a small, open and moli~.atcd research group is v,.orking on some aspecls c,f mechatronJcs and also in cooperation with other areas o1' the ]='O]ilecnico and some industries in Piemonle and l.omhardia

LIM activity is organized in terms of "'pr{uecls'" established on the basis of a shared ~,cientific and technological interest by at least a pair of different groups or institutions to guarantee the real interdiscipIinar3 nature of" the research. A number of pr~!jects concern experimental investigations about thc integration oI" advanced technologies and meth- odologies, l"hese projects are supported by internal or public funds and usually lead to the construction o1" small test rigs or demonstrators. A growing number of projects arc commissioned by private enterprises and lead to the construction and testing of" protot} pc.,, of industrial products.

I.IM was at lirst linanciall.v .,,upporled b\ the Politccnico di I o r i no and sincc then it has been self financing From research and consulting conlracls. Most of the initial LIM grants have becn invested in general pt,rposc instrumentation, such as a time and frequent) multichannel dynamic ~,nal.vzer and a mulliprocessor rapid protolypmg system for digital control. Specialized instrumentation such as a digital vector tiller Ibr rotordynamic analysis is also available, together with the basic instrumentation li"u vibration analysis (shakers. accelerometers, displacement sensors, instrumented hammers, etc.). Special instrumentation linked vdth the specific needs of research fields of intcrest has been built in co-operation ~,,ithin the lab or with several Ioct, l industries. 1he full co-operation of all the Mechanics Workshop staff, which represents a key feature of the laboratory, should also be emphas- ized: a number of test rigs and precision machines indispensable for the cxperin|enlal research could not have been realized without them.

LIM's present research projects stem l'rom the l 'ollowing main themes.

• Magne[ic SLlspcrlMon..'~c[i~.c lllaglletic- hearil]g~ I'or rotaiJllg machmcr',, magnetic le',i- tation I i v contactless transportalh.m ~ehiclcs. and precision balances are examples of active projects. I-:EM modeling, I'orce actuator,,, position sensors, power amplifiers, and modal control arc clcarl', all key features o1" a proper].,, working machine and their interaction is carefull,, investigaled at ever) design stage. Several lest rigs and prototypes SilO, V, the achieved results and enable further stud,, c,f related phenomenu.

• Vibrat ion control. The problem of vibrat ion control ix approached either b): passive techniques and materials tconstrained laver danlpers) or by active techniques using piezoelectric sensors and actuators. The self-sensing operation of piezoelectric devices is currently under extcnsi',c investigation with a number of simple test rigs. Attitude control systems for satellite applications are also investigated by means of electrostatic suspension.

• Neural controllers and walking machincs. Ncural controllers are used in connection with walking machine control. A hexapod prototype ~aith motion control based on dedicated neural chips is currently under development.

• [)SP-based rapid prototyping and development tools. ( 'onventional and advanced control algorithms arc rapidly lesled on the real plant under the Matlab.Simulink computing cnvironment interfaced w.ith a number of DSP based and I.O equipped boards. l h c sol'tware and hardware modularit\ of the ~',stem is meant to be attractive for its sub-

The Mechatronics Laboratory at Politecnico di Torino 415

sequent easy adaptation to a number of industrial applications, in particular for dedicated or small series productions.

In the following sections a brief outline of several research projects currently worked on at LIM is presented.

MAGNETIC SUSPENSION

tfigh-speed spindle on A M B

The driving idea of the project is that of obtaining a flexible research tool for basic research in the field of magnetic bearings and their control systems, for testing new ideas and control strategies on the rigid-body or flexible-body dynamics of the system and for the development of practical design of components. The device is also intended for teaching purposes, mainly to demonstrate the principles of active magnetic suspension to mechanical and electronic engineering students and to show them the effects of the various control parameters on the stability and the dynamic behavior of the magnetic suspension.

The machine, with a total rotor mass of about 5.3 kg, has been tested in the speed range up to the third critical speed (25 000 rpm), corresponding to the first deformation mode of the shaft [1-4]. The test rig was successively modified to carry a tool holder and investigate the dynamic behavior under working conditions (Fig. 1).

Orbital tube Orbital view

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50

E ~ o

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YO (~m)

50

~ o

~ ..----"~ 50 -50 0

% (~m) -50 0 50 x o (~m)

Deceleration view for x axis Deceleration view for y axis

50

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-50

4000 6000 8000 4000 6000 CO (rpm) m (rpm)

Fig. I. Dynamic behavior of the rotor on AM B with PID control.

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lu rbomolccu la r punlp,, opcral ing on con\cn l lona l hall hcarings arc nm~ considered illadequale for some applications, nl~.lilll\ o~ving to the conlall l i l lalion or x.acutim due to ~apors of the he:irillg hlbricalll, and the ad',allhlges of a nlagllelic suspension are well eslablished.

AlllOlig lhe complelc line el ltiiholllOlCCtilLil ptllllp~, ~.ilt~ con~cnlional hall hearings a model with ,i pumping speed oI" 18001 s has been chosen Io build a pro to lype wilh a li~e active-axes suspcnsiori. The basic la,,oul o1" the converliional machines buih b,,. Eleltror;.p,n S.p.A. is inaintahled ~a. ith the mininltnll oI" adil_lstnlenls required by the introduction of the ne~ Icchnology, consisicn! ,,vilh Ihc cosl and lh'nc constraints hllposed on the v, tlole project. A dcdicaled difl'ereniial inductive sensol has been buih [5].

Marl \ lesls have been performcd on lhc pn~lolypes in order Io verify the thcorctical predictions [6. 7J. Thc~ ha~c given ~crv satisl'aclor~ resulls: vibration and powcr consumption arc very 1o~ compared v~ith zi convenlional t t i rbomolecular pump with ball bearings, and lhe agreement between iheorclical prediclions and actual behavior is very good [g. g]. The relevant phenonlcna due to the n{m-colocalion of sensors and LICIULIIt)I'S ha~.e been lhcorelicall,, investigated and expermlenlall)validated [10. I1 i.

Hi.qh-.vwed xpimlle <m conicu/ .I . l ib

In a conxcntional li~c-axi~, magnetic ",u.~pcnsion tin.' thrust hcaling can cause peculiar problems, m a i n h duc Io the periphcral xclocil\ ofi l~ rolat ing disk, which can hc a limiting l'aclor in high-speed operat ion. Also. Ihc bulk and ~eighl o1" lhc dc\ icc is incrcascd.

1o inxesiigate the possihilit 3 of 'el iminating the thrust hearing, a small electric high-speed spindle based Oil two conical actixc nlagnelic bearings ~as built (Fig. 2). The machine has been designed to simulate lilt lOloP OJ" LI SlII~III tu rbo-compressor l'or tile air condit ioning unil o1" a small h igh-performance aircral'l. In oi'dcr I(~ comply with the requiremenl.s of this possible application, the whole machine ~as opiinli /cd with the aim of reducing the mass oI" the bearings. Both lhe pov¢cr ,tmplilier and Ihc clmlroller are analogic and tile I~o

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I i,_,. 2. Schcrn.:ltic drav, m.~ ~.H the H3indle ~m a corneal \ M B . I: rotor: ": enmrgenc~ beurings: 3 magnetic acluators; 4 nlolor: 5: inductive sensors: 6: center point: 7: velocit\ probe.


radial--axial bearings are controlled by a conventional five-axis decentralized compensator [121.

Power ampl(fier.['or A MB

Linear power amplifiers may still represent a suitable solution, in comparison with switching amplifiers, for very high-speed and low-weight rotating machinery on active magnetic bearings. Moreover, their low noise emission may be very useful for use in connection with colocated inductive sensors or self-sensing AMB. In order to improve the overall efficiency of a transconductance amplifier loaded by the high inductance and low resistance typical of the magnetic bearing coils, a modified class G amplifier has been developed. A couple of power Darlington pairs is connected on the same load but supplied with different voltages: the higher to deal with the inductive transient and the lower with the resistive steady state. A third transistor, connected to the ground, allows for the negative output voltage swing necessary for a rapid current decay. Particular attention has been devolved to assure flicker-free commutation between the two transistor pairs (Fig. 3).

A simple theoretical characterization has been developed to provide diagrams to optimize the power efficiency as a function of a varying load such as that caused by the rotor unbalance [13, 14]. A test rig for experiments on a single axis of an active magnetic bearing was built and has been used to test the modified class G linear power amplifier and to validate the optimization curves.

Theoretically, switching power amplifiers are the limiting case of class G amplifiers with an infinite number of supply voltages, in practice, they are commonly used due to their high efficiency compared to linear amplifiers. Significant noise on output and consequent

v,O t,,

LI Iv,,

(x~ /'~' > y ~ - ' x > ~ - I,~, :~ ~ t f f ~ . ~ A

" e, , P.

Fig. 3. Power fluxes in the modified class G linear amplifier. Dark areas indicate savings with respect to standard class A and class G amplifiers.

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higher command activity' are their main drawback,,,. With this as a main specilication, a full bridgc with two active switches and two diodes has been designed and tested [15J.

.S'ensorh'.s.~ ..I M B

Position sensorless magnetic suspension sound,,, attractive, mainly because it does not

employ expensive eddy current sensors, but il is no t cas~. to obtain in practice. When the observer approach is considered, that is the use of current or flux measures to estimate the position and velocity needed to stabilize the plant, the interactions between the power electronics, the coils and the mechanical parts must be correctly modeled to bc exploited for control. Moreover, the intrinsic redundancy assured bv a dedicated position sensor must be replaced with accurate construction of the aforementioned parts. The power amplifier must be as ideal as possible to drive the impedance with the minirnum amount of noise and distortion to enable the observer to work properly.

in order to investigate thc subject, a test rig was built with a complete industrial magnetic bearing constrained in such a wa~ as to allm~ a single radial degree of freedom. The rig is fully instrumented to compare "'sensorless'" measurements of position, velocity and f'orce with reference ones. A preliminary set of cxperimcnts has been accomplished and proved the feasibility of the proposed approach even if" not vet suited t'or practical use[I 6].

t'Tnile oh'men! modelhgl o/ .4 ..lib

The aim of the research is to develop a "'tini[c element" able to simulate active radial magnetic bearings together with their control systems and to implement the solution routines Io plot the eigenloci and the unbalance responsc of rotating machinery employing such bearings. The AMB element is implemented in ,i Matlab finite element code specialized for rotordynamic analysis, developed at the Department of Mechanics of the Politecnico di Torino [I 7]. The research work allm~ s st udv of the effects of the x arious design parameters of control systems, actuators and sensors on the d~namic behavior of the system. The possibilit} of introducing an accurate modeli?'ation of complex rotors allows one to obtain accurate results for practical case,,.

Two types of magnetic bearings have been introduced in the code: an isotropic and an asymmetric active magnetic bearing [I 8]. The latter can be used also for bearings which are geometrically symmetrical but operate with constant radial loads with a class A approach. As no assumption on the relative positions of actuators and sensors is made, it is possible It) stud,, also thc dynarnic effects duc to the rclati'~e position of the sensors and the actuators (colocation problem). The controller is a linear filter and can be specified as a Pl[) structure or by a user delined transfer function. Procedures lbr computing the steady-state response to both static and unbalance forces are available, based on a modal approach in which the number of retained modes is controlled b~ the uscr

("o/lltl('l/~',~.s Ir~llL~[7orl¢ll/oll

When studying magic,, vehicles t,~so ~,olut,ons arc usually considered: active dec- tromagnetic suspension and electrodynamic levitation. The first one, developed mainly in Germany. was applied in the tratt.srapid ss.stem. Fhc vehicle is suspended under ferromagnetic rails by the magnetic tield generated b', electromagnets while other electro-

The Mechatronics Laboratory at Politecnico di q-orino 419

magnets perform the guiding task. The stability is assured by the active control of the magnetic fields, so the system can be considered as a five active-axes magnetic suspension. The main disadvantage of the system lies in the bulk and mass of the electromagnets, which add up to two-thirds of the mass of the vehicles.

The second solution, developed mainly in Japan, is based on the repulsive forces acting between the magnetic field generated on the moving vehicle by very powerful superconducting coils, and that generated in stationary coils located in the guideway by the eddy currents induced by the superconducting coils. This levitation mechanism has the advantage of being passively stable but also has a number of disadvantages, for example the need for superconductors (low-temperature, liquid helium superconductors are used in the applications), the very strong magnetic fields, which need shielding, the higher electromagnetic drag and finally the high cost of the whole system.

The solution here tested, sometimes referred to as the synthesis solution, is a three passive-axes levitation layout, in which the forces supporting the vehicle are supplied by the repulsion acting between permanent magnets located under the vehicle and on the guideway. This solution is passively stable in heave, roll and pitch while it is unstable in lateral directions and yaw. An active system, based on the attraction forces between guiding electromagnets and ferromagnetic rails, is used to control the unstable modes. Note that the active system is used only to render the system stable, while transversal forces are supplied directly by the suspension permanent magnets whose repulsive force can have a component in the horizontal plane. The advantages are mainly in the low mass of the onboard magnets and electromagnets and the possibility of supporting the vehicle along its whole length, resulting in a much lower structural weight.

The control design is aimed at stabilizing the plant and achieving a so-called zero power consumption configuration. The error with a zero current reference is integrated to give the command that allows one to achieve zero power consumption under static force load on the levitating system. In practice, the regulated system finds a new equilibrium position that allows one to produce the magnetic force to counterbalance the external load without augmenting the required current but diminishing the magnetic gap.

A platform, which constitutes a reduced scale model of the actual vehicle and has a mass of about 200 kg, is levitated on a section of guideway with a length of about 1 m by a set of ferrite permanent magnets [19, 20]. The test rig constitutes the first step towards a reduced scale demonstration model, in which the levitating platform will be free to translate on a short track to study the dynamic behavior of the system when moving along the sixth, uncontrolled, axis.

VIBRATION CONTROL

Free rotors with "skyhook" dampers

In the present research a new approach of active stabilization of free rotating machines is developed, dealing with the physical simulation of the non-rotating damping benefits of fixed suspensions, through the application of the so-called automotive "skyhook" dampers, which act following the inertial and non-rotating reference frame.

The research is linked to the space mission "Galileo Galilei" (GG), a flight experiment of the equivalence principle, which will fly in 2000, and developed in co-operation with the

42(I B. BONA ~'/al.

Italian Space Agency and the Space Mechanics Group of the Univcrsitfi di Pisa. The outlines of the theoretical analysis and of the G G program are summarized in [21]. The aims are the dynamic analysis of the stabilization of free spinning bodies, the development of the skyhook damping technology and the design of the electrostatic active dampers.

"'Pro-phase A'" of the whole pro.jecl has already been performed. The G G satellite consists of a spacecraft, a picogravity box and one pair of lest masses (each of l0 kg), a total weight of about 200kg, external diameter I m and length 70cm; the supercritical operating spin speed is 300 rpm. The picogravily box and the test masses arc connected by soft mechanical springs. A simplified rnalhematical model of the satellite has been produced to investigate the role of the mechanical suspensions on the attitude stability of the semi-rigid body dynamics. The application of active non-rolating damping between the picogravity box and the lest masses ,~lnd between the spacecrafl and the picogravity box assures system stabilit.~. The design of a single electrostatic actuator, based on a sinlplilied electromechanical model, investigates tile feasibility of tile stabilization s.vstem.

Beam.5 nith piu:oe/('('lri( dericc.~

In recent years there has been a growing interest in active control of structures, performed using a number of different materials. Anlong them piezonlatcrials appear to be very promising in short-term applications due to their lightness, their conlpatibility wilh large slructures, and their relativel} lov, cost.

A lirst objective of the project has been thai of developing a theoretical model of beam structures provided vdth piezoelectric transducers linked to a generic electric network. This has been accomplished by developing a beam tinile element prmided with surface mounted piezoelectric devises having bol h mechanical and electrical degrees of freedom.

The model is based on a standard t~,vo-nodc Thnoshenko beam finite elenlcnt having a rectangular cross section and surface mountcd piezoelcctric layers: :ill rnaterials sire assumed to be orthotropic. A I.agrangian approach has been adopted to obtain the element consistent matrices starting from tile expressions of tile kinetic, potential and electric energies and coenergies. The assumptions at the base of the analysis arc thai the energy exchange between piezoelectric and structure is conservative, thai the frequencies involved sire low enough 1o jt,stify the quasi-electrostatic assumption vdthin the piezoelectric and that both the mechanical and the electrical constraints acting on the svstern are of hohmomic type. This approach leads to tile definition of a model in which tile piezoelectric transducers can be distinguished in sensors or in an ;.tCttl4tors depending.just c,n thc type of connected electric circuits+

An experimental '~ahdation of Ihis approach ha~, hccn carried Ol.l[ Oll se',,Cl;.ll aluminum alloy bearer, provided with both surface bonded piezoelectric transducers connected tO

charge and voltage amplitiers. Ill :ill tile cases lhe theoretically predicted input output transfer functions between the voltage input ill Ihe voltage ampliticrs and the output from tile charge anlplitiers have shown it, be in good agreement with the measured ones. at least in a frequency range involving the tirst live to six modes of the bealns [22].

In a second step a single piezoelectric transducer has been installed on the surface of a beam and connected to a "'sensing" bridge netw.ork. The output of the system is not given b,, a sensor device explicitly. nlounted on the structure but by an electric network devised with the objective to make somc of the rncchanical states of the structurc observable controllable (Fig. 4).


c~

V t ]

Fig. 4. Piezoelectric test rig tbr self-sensing operation.

Considering an aluminum alloy cantilever beam 250 mm long, 1.5 mm thick and 32 mm wide, equipped with a surface bonded 25 mm side piezoceramic transducer 0.3 mm thick, an observability/controllability analysis demonstrates that all the modal mechanical states of the beam are observable and controllable [23]. This result suggests the possibility to perform the vibration control of a structure without using transducers. Apart from the technological aspects, the main advantage of using the same transducer as sensing and actuating device is that the system becomes intrinsically colocated. A controller based on a modal observer and eigenstructure assignment is under development with the aim of increasing the damping of the first modes of the above mentioned beam.

Passive vibration control

Passive control is a valuable alternative active control when a structure is subject to vibrations in resonance conditions. Its main advantages are the intrinsically stable behavior, the low costs and weights, but conversely its effectiveness is usually poor in the case of structures affected by broadband vibrations.

Particular attention has been devoted to the analysis of the well known "constrained layer dampers", constituted by a layer of viscoelastic material sandwiched between the structure to be damped and a constraining layer.

The research has addressed both the measurement of the damping and the elastic proper-

422 B. BONA ('I ol

ties of viscoelastic material itself, and the damping of the vibrations affecting a commercial washing machine. Both tasks have been accomplished in co-operation with 3M and ZEROWATT S.p.A.

The characteristics of the viscoelastic laver illC >dent>lied by rain>hazing Ihc error between the experimentally nleasurect natural frequencies modal damping e l a clanlped free beam completely covered hx. the darrlpirlg treatment and the "values predicted b~. the theoretical model of the same beam. ( ' lamped free boundar \ conditions have been choscri as they lead to a xer~ simple experimental setup and can he performed ushlg the standard vibration lneasl.iremenl instrumentation a~ ailable al 1.1 M.

The potentialities of lhe consti.:iined laver ircalnlenl in the reduclion of the noisc pro- dated by a washing machine htl~.e been ilhcstigatcd bv damping the vibrations of its two side panels. First of" all acoustic and vibration incasurcments have been performed on the undamped machine to determine the I'requenc 5 l-illlgC where the acoustic intensity and the acceleration are n'lorc relevant. l h i s analysis cxidences thai the noise is lnainlv clue to the vibrations of the side panels in resonance conditions.

Two different damping treatments haxc been designed and inaplemented using 3M 1SD 113 viscoelastic sheets of 0. 127 mm thickness. -Ihe tir<q treatment addresses an increase in the danlping of the four modes in the frequent.,, range of interest. It is constituted by four patches covering aboul 30°, of the side panel area and leads to a 44°;, reduction of the acoustic intensity emitted b) the panel. The seconct treatment is obtained by covering about 70% of the area by two big patches and leads to a reduction of the acoustic intensity of about 58%.

These results can be considered as an assessment of a dcsign procedure based mainly on the experimental measurement of the mode shapcs of a structure and also as an example of the efl'ectiveness of constrained layers for the damping of structures subject to vibrations in resonance Collditions.

NEURAl, CONI'ROLi~ERS AND WAI,KING MACHINES

H e x a p o d machine brith neural II~'l iior]~ .~

l h e aim of the research is to design, buikt and lest a small hexapod ~.alking machine controlled by purposel~ developed neural chips. ~hich can be used as a remotely controlled observation device and can evolve as a truc mobile rebel (Fig. 5). The machine can also be used as an experimental test rig for different control strategies to inx.estigate the possibilities of small s,,alking ,,oh>ties on diffcrenl types of terrain.

[ he main characteristics of Ihc nlachinc ,ire; simple ~,tlld l ighiweighl mechanical arch>- lecture to conlain overall cOsls, modularit,, [o use Ihe machine as a research tool. itexibilit~ leading to the possibilit.v of adapt>rig the gait it> a variety of terrains, and the possibility of ~orking as all alllcinomotls svstein wilhotl t the need of tin umbilical cord for either energy' supply or control.

In the initial parl of the project no rcql.iirenlenl:,, regarding the possibility of walking at high speed were stated. ]h is allovcs the use of low-cost permanent magnet electric motors in connectiori with rechargeable batteries and ttle adoption of a gait in which the vehicle is al~.'a.'v's irl conditions of stable static equilibrium. A "'reptilian" stance is adopted as its energetic disadvantages are of small importance in the present case. The design chosen


Fig. 5. The hexapod machine when used in a "'reptilian" stance,

allows it assume an "insect" stance and even to switch to a quadruped "'mammalian" configuration. The mass of the mechanical components, including the electric motors, is 24.3 kg. The mechanical subassembly is completed at present and the first tests on the completed machine are due in the near future.

The numerical simulation demonstrates the ability of the neural networks to control the machine not only in steady-state straight walking but also to manage changes of speed and of trajectory without major slipping of the feet on the ground [24].

A smaller machine is also under study: a robotic walking machine for planetary explo- ration complying with the specifications for the ESA Micro-Rosa-M project. To comply with the size, cost and, above all, low energy consumption constraints a different mechanical layout has been chosen, particularly suited to very low speed operation on rough terrain. The machine is made with two triangular frames, which can move in a longitudinal direction with respect to each other and rotate about a vertical axis. Each frame is provided with three legs, each one with a single degree of freedom (vertical translation). The machine therefore has a total of eight degrees of freedom.

Neural architectures

Real-time control of non-linear plants is often a hard and computationally intensive task. Neural networks and fuzzy systems (neuro-fuzzy systems, in general) are raising more and more interest in the field of real-time control thanks to their superior performance. Advantages of neuro-fuzzy techniques are their non-linear characteristics, the capability of learning from examples, the adaptation capability, etc.

Furthermore, the availability of dedicated neuro-fuzzy processors permits a very fast implementation of neuro-fuzzy algorithms, and therefore it allows the use of these methods in real-time applications, where a quite high sampling rate ( > i kHz) is required. The proposed control system, DAN 1ELA (Digital Analog Neuro-fuzzy Interface for Enhanced

424 B. i}()N.a, ('/a/.

l,carning Applications), is a real-time neuro-fu/zy controller that implements intelligent control algorithms mixing neuro-fuzzy paradigms with a Finite State Automata controllcr FSA) [25].

This mixing allows to the system to change the control strategy according It) the actual slate of the plant (the I=SA chooses one of the possible controllers). Applied to a six legged walking robot, it uses spccializcd controllers for every different plant state (ror instance forward and backward steps, curve~,, etc. }.

In order to build an experimental board of thi,s system, a custom neuro-fuzz,~ processor called AM INAH has been developed 126], ~hich implements several neural paradigms and or fuzzy systems. This new chip, which is the evolution of the previous ( ' INTIA neural processor, uses Cohercnt Pulse Width Modulation (CPWM) for low-power computation [27] and also for interfacing the controller with sensors and actuators of the system.

I)SP-BASED RAPID PROI"OI'YPIN(i AND C()i)E I)EVEI,OPMENT Ol" Dl( ; r rAl . CONTROl.

today. digital signal processors, (I)SP) represent a standard fool in mechatronics. ]llev are RIS('-Iikc microprocessors very v, vll suited for rapid signal processing, and may easily' be found on a variet\ of boards also equipped with some sort of A D I ) A interface for almost any computing platform and operating system. For research and development purposes lloating-point DSP are usually chosen to be programmed in C or (" + + high level languages which make it easy to write both the algorithmic (for loops) and the exception handling (if then .jumps) sections of code (diagnosis. error treatment, etc.).

At the same time, as a computing environment. Matlab,Simulmk represents a standard de facto m the scientific community. Several collections of functions (toolboxes) cover most of the analysis and design needs in the field of signal processing and automatic control. It was then natural to try to integrate DSP systems and the Matlab environment in the simplest possible way (Fig. 6).

A new toolbox called Matl)SP is the result of Ibis efl'ort [28]. It may be used to acquire data and process them both in the frequency and in the time domain for plant identification, to design a suitable filter or controller and to rapidly test it. The capacity of working within the same environment greatly helps in the unavoidable cycling through the aforementioned tasks [29, 30].

( ' O N ( I , USION

The Interdepartmental Mechatromcs Laboratory of the Politecnico di Torino's experience has demonstrated the possibility to realize a useful interdisciplinary co-operation between the automatic, mechanics and electronics fields. The value of the adopted design approach with its main aim of" integrating the technical and scientific competencies of different engineering fields has been proved in practice with the realization of prototypes and test-rigs.

The LIM is also an important and useful experience for all the researchers involved, facing problems and experimental situations very 131-from their specific activity fields. The LIM activity is fully located in the solid engineering tradition of the Politecuico di Torino


Fig. 6. Matlab interface to DSP systems.

and enriches it with a modern interdisciplinary guideline that is frequently called upon but is rarely put in practice.

The methodological approach developed and the results obtained have raised an industrial interest, quantified in a number of research and development contracts. It is the authors' opinion that this kind of activity will find many more followers in the Engineering and Technical Universities of Italy.

REFERENCES

1. Delprete, C., Carabelli, S. and Genta, G., Design, construction, and testing of a five active axes magnetic bearing system. In Proceedings of 2nd International Symposium on Ma#netic Suspension Technology', Seattle, WA, 1993, pp. 5.a.21-5.a.35.

2. Carabelli, S., Deiprete, C. and Genta, G,, Control strategies for decentralized control of active magnetic bearings. In Proceedings of the 4th International Symposium on Magnetic Bearings, Zurich, 1994, pp. 29-34.

3. Argondizza, A., Carabelli, S., Cardascia, L. and Delprete, C., Rotor on active magnetic suspension part I I: Experimental characterization. European Journal of Mechanical and Environmental Engineering, accepted for publication.

4. Carabelli, S., Delprete, C. and Genta, G., Orbital tubes. Under final review for Mec- canica.

426 B. BONA ¢'/a/

5. Carabelli, S., Cerruti, F., Delprete. C. and Gcnta, G., High efficiency and low cost power amplifier and transducers for active magnetic bearings. In Proceedings of the 4th lnternationl Symposium on Magnetic" Bearings, Zurich, 1994, pp. 365 370.

6. Gcnta. G. and Tonoli, A.. A harmonic finite element for the analysis of flexural, torsional and axial rotordynamic behaviour of discs. Journal of Sound and Vibration, 1996, 196(1). 19-43.

7. Genta. G. and Tonoli, A., A harmonic tinite element for the analysis ot" flexural, torsional and axial rotordynamic behaviour of blade arrays. Submitted to Journal ¢~l Sound and Vibration, 1997.

8. Genta, G., Delprete. ('.. Tonoli. A.. Rava. 15. and Mazzocchetti, L., Study of the geometry of a passive radial magnetic bearing for application to a turbomolecular pump. In Proceedings ~[ MAG'92 Magnetic Bearings, Magnetic Drivers and Dry Gas Seals Conference & Exibition, Alexandria, VA, 1992, pp. 61-70.

9. Mazzocchetti. k.. Rava, E., Delprete, C.. Genta, G. and Carabelli, S., Design, construction and testing of a turbomolecular pump with five axes magnetic suspension. In Proceedings q/" the 4th International Symposium on Magnetic Bearings, Zurich, 1994, pp. 505- 510.

10. Bona, B., Calafiore, G., Carabelli, S. and Tonoli, A., Computation and physical interpretation of multivariate transmission zeros tbr lumped parameters colocated systems. In 13th Worm Congress IFAC, San I-rancisco, CA, 1996, pp. 7 12.

1 I. Calafiore, G., Carabelli, S. and Bona, B., Structural interpretation of transmission zero tor matrix second order systems. Automatica, 1997, 33(4), 745 -748.

12. Carabelli, S., Delprete, C.. Genta, G. and Moretto. I., A spindle running on a fivc axes magnetic suspension based on conical bearings. In Proceedings of 4th Industrial ConJ~,rence on Application of Magnetic Bearings, Alexandria, VA, 1995.

13. Carabelli. S., Delprete. C.. Genta, G.. Maddaleno, F., Mittino, M. and Ugazio, M.. High efficiency linear powcr amplificr for active magnetic bearings. Presented at 4th hldustrial Conlerence on Applications o/ Magm, tic Bearhlys, Alexandria. VA, August 1995.

14. Carabelli. S., Delprete, ('., Maddaleno, I.., Mittino, M., Muzzarelli, M. and Ugazio, M., High efficiency linear power amplifier for active magnetic bearings. In Proceedings ~[5th Internationl ,S~vmposium on Magnetic Bearings, Kanazawa, Japan, 1996, pp. 503 508.

15. Carabelli, S.. Crivelli. A., Maddaleno, t". and Muzzarelli, M.. A switching power amplifier tbr active magnetic suspensions. 7 th European Con/~,rence on Power Eh, ctronics and Applications, Trondheim. Norway. 8 10 September 1997, accepted.

16. Carabelli, S.. Delprete, C., Muzzarelli, M. and Poggi, C., Experiments on sensorless magnctic bearings. Infbrmally presented at 5th International ~vmposium on Magnetic Bearhtgs, Kanasawa. Japan, August 1996.

17. Genta, G.. Bassani, D. and Delprcte, ('., i)ynrot: a finite clemcnt codc for rotordynamic analysis based on complex coodinates. Enqineering Computations, 1996, 13(6), 86--119.

18. Delprete, C., Carabelli. S. and Genta. G., Active magnetic bearing control loop modeling for a finite clement rotordynamics code. In Proceedings oflnternational Symposium on Magnetic Suspension Technology. NASA. Seattle, WA, 1993, pp. 319 333.

19. Carabelli, S., Cerruti, F., Delpretc, C . Majo, F. D., Genta, G. and Zanolli. S.. A two active-axes suspension for maglev vehicles. In Proceedings of 5th International Symposium on Magnetic Bearings, Kanazawa, Japan, 1996, pp. 357 362.

20. Carabelli. S.. Delprete, C., Genta, G. and Zanolli, S., Control of a two active-axes suspension lbr maglev vehicles. Proceedings ~?/'A CC 1997, Albuquerque, New Mexico, 4--.6 June 1997, Vol. 6, pp. 3962 3966.

21. Nobili, A.. Bramanti. D., Gcnta. G., Brusa, 15. eta/.. Galileo galilei flight experiment


on the equivalence principle with field emission electric propulsion. The Journal of Astronautical Sciences, 1995, 43, 1-2.

22. Bona, B., Brusa, E., Canestre[li, P., Genta, G. and Tonoli, A., Finite element modeling and experimental validation of an elastic beam with surface bonded piezoelectric devices. In Proceedings International ConJbrence on Robotics and Automation, IEEE, San Diego, CA, 1994.

23. Brusa, E., Carabelli, S. and Tonoli, A., Self-sensing colocated structures with dis- tribuited piezoelectric transducers. In Proceedings of 7th International Conference on Adaptive Structures and Technology, Rome, 1996.

24. Bassani, D., Chiaberge, M., Corso, D. D., Genta, G. and Zanetti, F., Simulation of a hexapode walking machine controlled by neural network. In Proceedings ISMCR 1993, Torino, 1993.

25. Reyneri, M. C. L. M. and Zocca, L., Cintia: a neuro-fuzzy real time controller for low power embedded systems. IEEE MICRO, Special Issue on Hardware for Artificial Neural Networks, June 1995, pp. 40-47.

26. Chiaberge, E. M. M. and Reyneri, L., A pulse stream system for low-power neuro- fuzzy computation. IEEE Transactions on Circuits and Systems, 1995, 42, 946-954.

27. Reyneri, L. and Chiaberge, M., Cintia: a neuro-fuzzy real time controller for low power embedded systems. Special Issue of lEEE MICRO on MICRONEURO 94, June 1995.

28. Carabelli, S. MatDSP--Matlab and Simulink interface to floating point DSP systems. In Matlab Connections. The MathWorks Inc., 1996, p. 43, http://www.mathworks. com/connections/toc.html.

29. Carabeili, S., Greco, C. and Mannino, F., MatDSP: a DSP-based Matlab toolbox for rapid prototyping of digital control systems. In International Workshop on Algorithms and Architecture in Real-Time Control, IFAC/IFIP, Ostend, Belgium, 1995, pp. 317- 322.

30. Carabeili, S., MatDSP line: a DSP-based real-time development system, 1996, http://po- limage.polito.it/~ iim/activity/matdsp/welcome.

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The mechatronics laboratory at Politecnico di Torino