Piezo · Nano · Positioningnews

In medical engineering, modern PILine® ultrasonic piezo motor drives are

opening up applications which were impossible using classic electric motor

leadscrew systems. Due to the piezoelectric effect and the direct creation of

linear motion, PILine® drives are not only faster, lighter and more compact

than conventional motorized drives, but they can also be made non-magnetic.

They achieve resolutions of 20 nm (0.02 µm) and velocities of up to 1 m/s.

Their travel range is basically unlimited, and they are available in a number of

different integration levels to match the desired (OEM) application. Medical

engineering provides an up-to-date example.

Issue 37

Continued on page 2

OCT: Piezo Motors in Medical DesignUltrasonic piezo linear drives—new application in non-invasive medical technology

Contents: Page

Piezo Motors for OCT Scanner 1, 2

NEXACT® Controller 3

P-726 – High-power Nanopositioner 4

Mercury™DC Motor Controllers 4

High-Load Hexapod 5

E-712 – New Multi-Axis Piezo Controller 6

Increased presence in local markets 6

P-653 – Tiny UltrasonicLinear Motor Drive 7

Tradeshows, Publisher 8

Piezo technologyenables fast, com-

pact, high-resolutionOCT scanner

In addition to the clas-sic, invasive, punchbiopsy technique, there

are a number of only par-tially satisfactory non-invasive

procedures in clinical and cos-metic research for properly cate-gorizing skin changes. Those basedon ultrasound do not provide goodresolution, and confocal microscopycannot penetrate sufficiently belowthe epidermis. Now, however, thereis a practical alternative: the newSkinDex scanner – developed by ISISOptronics in Mannheim, Germany –combines the advantages of ultra-sound and confocal microscopy.

2

The SkinDex scanner is based on the technology of optical coherencetomography (OCT) and examines thetissue on and under the skin surfacenon-invasively. The results obtainedare extraordinary. The informationcontained in the 2-D and 3-D sectionalimages is comparable to that of a histological examination.

OCT uses the basic transparency ofskin together with the interferencefringes obtainable with white light.The optical paths are made up ofoptical fibers.

Exact positioning for precise results

To enable creation of 2- and 3-dimen-sional images from interferencepatterns, the optical fibers must bemoved both axially and laterallyduring the scan. This task requirespositioners capable of the highestprecision. Ultimately, it is the perfor-mance of the drives which determinethe system resolution and hence thequality of the images.

A PILine® P-661 OEM motor is usedto position the reference-arm mirror(depth parameter). This motor waschosen primarily because of its com-pact design and, considering its size,its high force capacity of 2 newtons(0.5 lbf). Total travel is 2 mm, the po-sition resolution in this application30 nm (0.03 µm, 1.18 micro-inch).

As the images are recorded sequen-tially, the high speed and excellentdynamic response of the drive is agreat advantage. As a result, theSkinDex needs only a few seconds to generate its highly informativeimages. The lateral motions of theoptical fibers in the sensing arm executing the surface scan are alsoperformed by a PI drive.

In this case it is a PIHera® P-622.2CD,

a flexure-guided, 2-axis, piezo nano-

positioning system, which provides

a resolution of 1 nm (0.001 µm, 0.04

µ-inch) and covers an area of 250 x

250 µm. Piezo-motor drives have thus

again contributed to an innovation

from which many people will benefit

in the future.

Continued from page 1

Integration levels in PILine® ultrasonicpiezo motor technology: from 8-mmdrives, through the successful Rod-Drive linear drive, to integrated multi-axis systems.

The SkinDex scanner based on OCTtechnology for non-invasive but reliableexamination of the tissue on and underthe skin surface (photo ISIS Optronics).

A look under the skin of the ball of thethumb. Even the untrained eye canrecognize the spiral-shaped sweat-gland ducts.

3-D OCT image: Individual laminar and cylindrical structures such as largerblood vessels are visible under therough skin surface.

White-light interferometry is the basis of OCT. Using optical fibers, light isdivided into a sensing and a referencebeam. After being reflected by the target(i.e., a cutaneous structure) and thereference mirror respectively, the beamsare recombined and enter the detector. An interference signal pattern results(photo: ISIS Optronics).

Working principle of an ultrasonicpiezo motor drive.

Mountingplattform

Bearing

Gluedfrictionbar

Friction tip Piezo Actuator(stationary)

exitationelectrodes

Miniaturized Technology

Displacement pumps are used world-wide in many diverse branches of in-dustry. Increasing miniaturizationmeans the market for their smaller“relatives“ is also growing: Micro-dispensers take on distribution anddosing tasks where small volumes inthe milliliter or microliter range haveto be controlled

Wide Range of Applicationsfor Promising Technology

In laboratory and medical engineer-ing, biotechnology or chemical analy-sis, tiny dispensers accurately doseactive substances or medicines.Micropumps take care of the removalof reaction gases in closed processes.Industrial machines benefit from thepossibility of using micro-valves toapply lubricants such as oils or greasein a decentralized way at the pointwhere they are required – in an eco-nomical, precise and automated way.

Piezo is the Driving Force

The design is based on the familiarprinciples of diaphragm pumps andvalves and also makes use of theperistaltic principle. The miniaturizeddrives are based on piezoelectricactuators in various shapes anddegrees of integration.

Adapted for Precision & Force

The properties of the pump media –viscosity and drop size, for example –determine the different forces whichhave to be applied and hence the sizeof the piezo actuator used. The piezodisplacement is a variable parameterwhich controls the dosing volume.With micropumps, the frequency alsodetermines the flow rate that can beachieved.

Actuators for Micro Pumps & ValvesPrecision Dosing of Small Volumes

The principle of peristaltic pumping makesdirectional valves obsolete; the pumpingdirection in this case is specified by the orderin which the individual actuator elementsare driven.

Micro-diaphragm pumps operate in a similarway to piston pumps, but the medium to betransported is separated from the drive by adiaphragm. Passive inlet and outlet valvescontrol the pumping direction. Piezo elementsin disk form which are mounted directly ontoa metal disk make ideal drive systems formicro-diaphragm pumps: This drive solutionoccupies extremely little space, and the piezodisplacement can be very finely adjusted,allowing the pumped volumes to be veryprecisely defined.

Working principle of a diaphragm valve.Usually, valve applications require higherforces than pumps.

Variety of piezoactuators and lever-amplified systems

Piezo • Nano • Positioning

Reliable and Fast

The special properties of the piezoceramics permit flexible flow rates of afew tenths of a microliter to severalhundred milliliters per minute at pump-ing frequencies up to the kilohertzrange accompanied by high dosingaccuracy. The switching times of a fewmicroseconds are significantly fasterthan those of magnetic designs. Thepiezo drives have the power and stiff-ness values required to also workagainst pressures of up to tens of barsand are thus also suitable for use withmore viscous media.

Piezo ceramics are fundamentally verysimple to use and integrate; their com-pact size even makes them suitablefor integration into so-called labs-on-a-chip.

Variable Shapes, Different Forces

Simple piezo ceramic disks or rings aremounted onto a metal or silicon diskand, as the most compact benderelement, thus control the opening orclosing of diaphragm pumps or valves.

An alternative is to use piezo benderelements, which PI Ceramic canmanufacture in almost all shapes andforms.

Small piezoelectric tubes have alsobeen used for a long time for the drop-

on-demand method as used in ink-jet-printing, for example. Piezo patchesor, for greater forces, piezo stack actu-ators operate peristaltic pumps.

The corresponding drive electronicsare compact and can even be used inportable instruments – for dosingmedication, for example.

In micro-valves, particularly where viscousliquids are processed with higher pressures,translational actuators with and without prestresscan be used. Where larger strokes of the valvetappet are required, the actuator stroke can beamplified by levers.

Piezo Actuators: Fast, Reliableand Easy to Integrate

Piezo actuators convert electricalenergy directly into mechanical energyand vice versa. Travel ranges of up toone millimeter can typically beachieved with resolutions down to thenanometer range. High dynamics withfrequencies of up to several kilohertzare also achievable. The movement isbased on crystalline effects and sothere are no rotating parts and no fric-tion; piezo actuators are thereforemaintenance-free and non-wearingand, because no lubrication is required,they are vacuum compatible. They canmove large loads and have a very com-pact design.

Piezo Advantage: Fast, Compact, Long LifePiezoceramic Elements Drive Micropumps

PI offers a large selection of different piezoelectric components: disks, tubes, benders, patches…

Piezo • Nano • Positioning

The continuing miniat urization in medical engineer ing places ev er in-

creasing demands on the components. Piezo drives are the solution for many

motion control applications; the piezo ef fect ef ficiently generates fast

and precise motion while requiring very little space.

Custom piezo disks precisely dose liquidsand gases in the ThinXXS micropump.(source: thinXXS Microtechnology AG)

Efficient Aerosol Generation with

Piezo Elements

The treatment of respiratory diseasesoften in volves medications beingadministered directly with atomizers.One method of atomization is togenerate very fine droplets with theaid of ultrasonic piezo ceramics.

Specially shaped piezo disks excite a stainless steel diaphragm withseveral thousand holes to executeultrasonic oscillations at more than100 kiloher tz: this produces par-ticularly homogenous aerosols,allowing the medications to be dosedaccurately and administered in amore targeted way.

An annular piezo disk serves as an ultra-sonic transducer to produce the aerosolin the atomizer head of the eFlow® rapidElectronic Nebulizer series.(source: Pari Pharma GmbH)

Piezo elements from PI Ceramic. The broad spectrum of standard products issupplemented by custom engineered products, with the shortest-possible time-to-market

Moreover, the piez o tec hnologyreduces the time required to atomizemedications by up to 50 % comparedto conventional systems increasingthe quality of life for patients withchronic diseases.

Piezo ceramics meet the specialhygiene requirements in medicalengineering; the aerosol generatorscan be steriliz ed at high tem-peratures, even in autoclaves. Theultrasonic operation is soundless for humans, and the low powerconsumption of the piez o com-ponents allows battery operation.

Piezoelectric Drives in Microfluidics

Piezo-driven microdispenser s, i.e.micropumps and microvalves, candose minute volumes down to themicroliter range with very high ac-curacy. Disk-shaped piezo elementsmounted directly onto a metal micro-diaphragm pro vide the highly dy -namic drive for precision miniatureliquid or g as pumps. Due to theseparation of dri ve and mediumthrough the diaphragm, interferencewith the pumped media is completelyavoided.

Lab-on-a-chip applications are madepossible by the minute dimensions.

Medical Engineering News:Driven by Piezo

pi_091227_news40_uk.qxp 19.11.2009 9:13 Uhr Seite 6

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Piezo • Nano • Positioning

Othodontic Research: Hexapod Speeds up Biomechanical Test & MeasurementFrom Christoph Bourauel and Ludger

Keilig–Department for Orthodontics at

the Rheinischen Friedrich-Wilhelms-

Universität, Bonn.

Dental biomechanics deals with theinteractions between dental materi-als, treatment instruments or den-tures and the reaction of teeth, bio-logical tissues, etc. to mechanicalstresses. A wide spectrum of forcesystems occur here with masticatoryforces exerting loads to 380 N andtorques to several Nm.

At the same time, movements of several orders of magnitude areinvolved: orthodontic equipment canchange the position of teeth by up toseveral mm, whereas—during masti-cation—teeth are deflected by lessthan 100 µm and implants by as littleas a few microns or less. These com-binations of small forces with largedeflections, on the one hand, andlarge forces and extremely smalldeflections on the other , represent achallenge with respect to the biome-chanical metrology.

To deal with this challenge, theDental Clinic of the University ofBonn designed the HexMeS (Hexa-pod Measuring System) based on theM-850.50 Hexapod. The ability tomove in 6 degrees of freedom andthe combination of small dimensions,very high stiffness and resolution ofless than 1 µm (1 arcsec) were the keyreasons for choosing the M-850 sys-tem.

HexMeS also features two 6-compo-nent force/torque sensors for theHexapod with measuring ranges of12 N (120 Nmm) and 130 N (10 Nm)respectively and an optical detectionsystem equipped with 3 CCD cam-eras.

Because of its high stiffness (100N/µm), sample deflections can usual-ly be calculated directly from theHexapod motion.

For high-load testing—simulations of mastication in the 100 N range—the optical portion of the HexMeS is used. It resolves sample deflectionsto 0.7 µm / 0.2 arcsec.

The M-850-based HexMeS currentlyrepresents one of the most flexiblemeasuring systems in the field ofdental biomechanics. Its efficiencyand the broad spectrum of its appli-cation have been demonstrated in awhole series of experimental investi-gations into dental implants, tele-scope crowns and orthodontic pros-theses.

Load testing of a double crown.

Piezo • Nano • Positioning

3D position sensing PC(CCD cameras)

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HexMeS block diagram.

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Click here for Article on Hexapods in Spine Surgery

5

Movement in Micropositioning Technology

Low Cost PI Drives for M-228 StepperMikes offer a low-

Automation and Handling cost alternative.

Setting valves, adjusting components, pick and place ...

The specifications for these types of These requests have led to the de-motion control applications dif fer velopment of the M-228 and M-229 M-228 and M-229 are character-

ized by the following data:from those PI is used to dealing with linear actuators. These have travelin only two respects: Not one nano- ranges of 10 or 25 mm and use classic ■ bi-directional repeatability:meter but 10 micrometers and more stepper motors – with either a com- 5 µmare suf ficient for the positioning pact (motor + gearbox) or cubic (direct ■ unidirectional repeatability: accuracy. The price plays a muc h drive) configuration. Despite the low 2 µmmore important role, however. prices, the user need not forego

■ resolution 80 nm (with C-663useful features such as mechanicalGood quality and good service are Mercury™ Step controller) position display, a non-rotating spindletwo things which customers do not ■ backlash: 5 µmor safety limit switches.want to forego, which is why PI has

■ speed: 2 mm/secrecently received many requests from

■ positioning accuracy: 10 µmthe market segments mentioned.

Piezo Dispenser Drive for Bio-Handling

Small and fast is not only a require-ment in classical micropositioningtechnology, however. Piezo ultrasonicmotors are also extremely well suitedto applications where the accuracyrequirements are not quite so demand-ing – in the range between 5 and 100 micrometers for example, whichis usually suf ficient for industrialautomation and handling tasks.

PI has developed the low cost M-664KCEP dispenser dri ve withPILine® piezo ultrasonic motors forthis kind of application. Eight or moreof these dri ves stac ked together can mo ve pipet tes ver tically and

independently of each other in orderto dispense liquids into well plates. A single actuator is only 9 millimeterswide to matc h the standardized sample holder.

The M-664KCEP co vers the travelrange of 50 millimeters in less than250 milliseconds and generates forcesof up to 4 N. The resolution of thepositioning sensor is matched to theapplication and amounts to 5 micro-meters.

PI is increasingly employing PILine® piezo ultrasonic drives in its positioning

stages as an alternative to motor/leadscrew designs – particularly when the

stages must be small and fast.They achieve positioning accuracies of up to

0.1 µm and speeds of up to several 100 mm/s.

Stack of 8 M-664KCEP linear actuators,shown with well plate. The integrated

ceramic piezomotor provides highspeeds of more than 200 mm/sec.

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Piezo • Nano • Positioning

Nevertheless, control is 100 % com-patible to previous standard PIHexapods.

As with other parallel-kinematicspositioners from PI, the six high-resolution actuators are connecteddirectly to a single moving platform.The user is able to define the centerof rotation (pivot point) independentof platform motion with a simple soft-ware command.

In contrast to conventional, stacked,multi-axis systems, there is no accu-mulation of guiding and lever -armerrors.

The compact M-810 is smaller in diameter than a CD, but offers long travel ranges in six axes with excellent position resolution

Six Degrees of Freedom in a Small PackageNew Ultra-Compact Miniature Hexapod

The new M-810 miniature Hexapodcombines all advantages of PI’s otherproven parallel-kinematic systems inthe smallest of packages. With a dia-meter of only 10 cm and a height of

11.8 cm, the M-810 offers travelranges of up to 40 mm in the XY plane and 13 mm in the Z-

direction. Despite of its small size, the hexapod canreliably position loads of up to 5 kg at velocities of

10 mm/s.

The limited space necessitated the usage of new tec hnologies for encoders, motors and limit switches.

Piezo • Nano • Positioning

Physik Instrumente (PI) GmbH & Co. KG

Auf der Römerstraße 1D-76228 Karlsruhe

Tel. +49 721 4846-0Fax +49 721 4846-100info@pi.wswww.pi.ws

PI Ceramic GmbH

LindenstraßeD-07589 Lederhose

Tel. +49 36604 882-0Fax +49 36604 882-25info@piceramic.dewww.piceramic.de

PI USA

PI (Physik Instrumente) L.P.16 Albert St.Auburn, MA 01501Tel: +1 (508) 832 3456Fax: +1 (508) 832 0506info@pi-usa.uswww.pi-usa.us

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Hexapods in Spine Surgery