Performance and Applications of L1B2 Ultrasonic Motors
actuators
Review Performance and Applications of L1B2 Ultrasonic Motors
Gal Peled, Roman Yasinov * and Nir Karasikov
Nanomotion Ltd., 3 Hayetsira St., Yokneam 20692, Israel; [email protected] (G.P.); [email protected] (N.K.) * Correspondence: [email protected]; Tel.: +972-073-249-8023
Academic Editor: Kenji Uchino Received: 13 April 2016; Accepted: 25 May 2016; Published: 1 June 2016
Abstract: Piezoelectric ultrasonic motors offer important advantages for motion applications where high speed is coupled with high precision. The advances made in the recent decades in the field of ultrasonic motor based motion solutions allow the construction of complete motion platforms in the fields of semiconductors, aerospace and electro-optics. Among the various motor designs, the L1B2 motor type has been successful in industrial applications, offering high precision, effective control and operational robustness. This paper reviews the design of high precision motion solutions based on L1B2 ultrasonic motors—from the basic motor structure to the complete motion solution architecture, including motor drive and control, material considerations and performance envelope. The performance is demonstrated, via constructed motion stages, to exhibit fast move and settle, a repeatability window of tens of nanometers, lifetime into the tens of millions of operational cycles, and compatibility with clean room and aerospace environments. Example stages and modules for semiconductor, aerospace, electro-optical and biomedical applications are presented. The described semiconductor and aerospace solutions are powered by Nanomotion HR type motors, driven by a sine wave up to 80 V/mm rms, having a driving frequency of 39.6 kHz, providing a maximum force up to 4 N per driving element (at 5 W power consumption per element) and a maximum linear velocity above 300 mm/s. The described electro-optical modules are powered by small Nanomotion Edge motors driven by voltages up to 11 V AC, providing stall forces up to 0.35 N (power consumption up to 0.75 W) and maximum linear velocity above 200 mm/s.
Keywords: ultrasonic motor; applications of piezoelectrics; precise motion
1. Introduction Compact ultrasonic motors, first suggested in the 1970s [1], were developed during subsequent decades [1,2] in response to the semiconductor industry’s increasing demand for precise nonmagnetic positioners; this development was supported by the increasing availability of high quality lower cost piezoelectric ceramics. The basic principle of their operation lies in transferring electrical energy into mechanical momentum by frictionally coupling a vibrating elastic stator to a moving stage. While the efficiency of an electromagnetic motor is size-dependent (making electromagnetic motors smaller than 1 cm3 barely efficient in principle), the efficiency of the piezoelectric motor does not change with size, making small piezoelectric motors prime candidates for use in small mechanical systems. The advantages of small piezoelectric ultrasonic motors, as compared to the standard electromagnetic ones with the same size and weight, include high power density and efficiency (both of which are not size sensitive), high torque at low speeds and low power, non-magnetic properties (leading to no generation of electromagnetic noise and no dependence on external electromagnetic fields), quiet drive, no gear mechanism (thereby saving space and reducing complexity), quick response and short settling times, hard brake, no backlash and no energy consumption while holding position.
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At present, those advantages allow successful competition with standard electromagnetic solutions in those high-end market segments where a combination of small size, high positioning accuracy and high torque is required. The offered products had evolved from a standalone motor to a complete motion solution consisting of a motor, a moving stage, a closed loop feedback circuit, a driver and a motion controller with programming support, all attuned to provide optimal motion and positioning performance [3]. The typical design of an ultrasonic motor takes advantage of the coupling between the mechanical resonance of a vibrating piezo-ceramic stator and the electrical resonance of an AC driving circuit, which allows for relatively high vibration amplitude while using low supply voltages. This approach allows the otherwise large voltage amplifiers to be reduced, essentially, to the size of a battery. The progress in the fields of materials and compact electronics allows manufacturers to provide compact motion solutions, tailor-made to meet specific demands of size, stiffness, force-velocity profile, shock resistance, temperature range, environmental conditions, outgassing and particle contamination, making ultrasonic motors viable candidates for semiconductor manufacturing and space applications [4]. The types of ultrasonic motor design can be subdivided according to the type of vibration, into standing or travelling wave, and according to the type of motion, into linear or rotary [5,6]. All designs must consider the sensitive aspects of resonant high voltage drive, frequency matching between the driving circuit and stator resonances, the quality factor of the resonance, the material and geometrical properties of a suitable friction pair (to achieve high force on one hand and low wear on the other) as well as other environmental conditions, such as low outgassing for space applications. Among the various design possibilities, the standing wave linear motor based on the combination of first longitudinal and second bending modes [7,8] (the L1B2 motor) is well suited to industrial production, combining a robust design with a high dynamic range in velocity, high positioning accuracy and low wear, with a correspondingly long life. Nanomotion Ltd. (Yokneam, Israel) has been developing L1B2 motor based motion solutions since 1992 [9,10]. In this paper we review the structure and characteristics of L1B2 motors along with the performance characteristics of the precise motion solutions, where L1B2 ultrasonic motors had been utilized by Nanomotion during the last decade. To complement the existing literature, which focuses mainly on the subject of basic element design, generally not treating the broader system aspects (e.g., [7,8,11–13]), this paper deals with the complete L1B2 motor-based motion solution, including the piezo-ceramic element, motor design, motor drive, motion control, material and thermal aspects, as well as positioning accuracy, to provide end user performance (also in demanding environments). We begin by reviewing the general design of an L1B2 motor based motion solution (Section2), continue with the aspects of operational conditions (Section3) and positioning accuracy (Section4) and conclude with examples of existing industrial motion solutions (Section5). The discussed applications come from the high-end solutions in the fields of aerospace, semiconductors, biomedical and electro-optics.
2. General Design of a Motion Solution The complete architecture of a motion solution consists of an ultrasonic motor, motor driver, motion controller with a closed loop position encoder feedback and a moving stage. A schematic representation is shown in Figure1. The controller uses a pre-programmed control algorithm to accomplish the prescribed (stage) motion profile by applying a suitable voltage command level to the motor driver, which in turn applies a suitable AC drive voltage to the motor, which moves the stage. The position of the stage is continuously corrected, according to the position feedback signal provided to the controller by a position encoder, to minimize the position error between the prescribed and the actual positions. Thus, the magnitude of the position error depends on the motor motional resolution, the motor dynamic response, the encoder resolution and the controller bandwidth. Actuators 2016, 5, 15 3 of 19 Actuators 2016, 5, 15 3 of 19
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Figure 1. 1.Schematic Schematic representation representation of of the the architecture architecture of ofa aprecise precise motionmotion solution,solution, basedbased onon anan L1B2 ultrasonic motor. ultrasonicFigure motor. 1. Schematic representation of the architecture of a precise motion solution, based on an L1B2 ultrasonic motor. 2.1. The L1B2 Motor 2.1. The L1B2 Motor The2.1. The basic L1B2 motor Motor design utilizes the length to width ratio of a rectangular piezoelectric bar, poled The basic motor design utilizes the length to width ratio of a rectangular piezoelectric bar, poled along the thickness direction, to excite a simultaneous vibration of the first longitudinal and the along theThe thickness basic motor direction, design to utilizes excite the a simultaneous length to widt vibrationh ratio of a of rectangular the first longitudinal piezoelectric andbar, thepoled second secondalong bending the thickness resonance direction, modes to (both excite dependent a simultan eouson the vibration bar’s length) of the (seefirst Figurelongitudinal 2a). The and vibration the bending resonance modes (both dependent on the bar’s length) (see Figure2a). The vibration is excited is excitedsecond in bending the length-width resonance modes bar mid-plane (both dependent (a plane on perpendicular the bar’s length) to (see the Figure thickness 2a). The direction), vibration using in theis length-widthexcited in the length-width bar mid-plane bar mid-plane (a plane perpendicular (a plane perpendicular to the thicknessto the thickness direction), direction), using using the d31 the d31 piezoelectric coefficient. piezoelectricthe d31 piezoelectric coefficient. coefficient.
Figure 2. Basic design of an L1B2 piezoelectric ultrasonic motor: (a) Schematic representation of a Figure 2. Basic design of an L1B2 piezoelectric ultrasonic motor: (a) Schematic representation of simultaneous excitation of longitudinal and bending modes. (b) Schematic drawing of the preloading aFigure simultaneous 2. Basic excitationdesign ofof an longitudinal L1B2 piezoelectric and bending ultrasonic modes; motor: (b) Schematic (a) Schematic drawing representation of the preloading of a of a piezoelectric element onto a moving stage. (c) Example drawing of a Nanomotion HR1 type simultaneous excitation of longitudinal and bending modes. (b) Schematic drawing of the preloading of a piezoelectricmotor, based on element a single onto L1B2 a moving(Nanomotion stage; HR (c )type) Example piezoelectric drawing element, of a Nanomotion implementing HR1 the type of a piezoelectric element onto a moving stage. (c) Example drawing of a Nanomotion HR1 type motor,element based preloading on a single scheme L1B2 that (Nanomotion is schematically HR shown type) in (b piezoelectric). (d) Image ofelement, a linear stage implementing driven by a the elementmotor,Nanomotion based preloading on HR1 a single scheme motor. L1B2(e that) Image (Nanomotion is schematically of a rotary axis HR showndriven type) by inpiezoelectric a (Nanomotionb); (d) Image element, HR1 of motor. a linearimplementing stage driven the byelement a Nanomotion preloading HR1 scheme motor; that (e )is Image schematically of a rotary shown axis driven in (b). by(d) aImage Nanomotion of a linear HR1 stage motor. driven by a NanomotionThe simultaneous HR1 motor. vibration (e) Image can of bea rotary produced axis drivenby two by methods. a Nanomotion The first HR1 method motor. is selectively driving a chosen part of the element, using either one or two driving sources [8–13]. The second is The simultaneous vibration can be produced by two methods. The first method is selectively Theadapting simultaneous the element vibration geometry tocan produce be produced mode coup byling two [7]. methods. In this paper The we first treat method the first is method selectively driving a chosen part of the element, using either one or two driving sources [8–13]. The second is drivingonly, a sincechosen it is part the oneof the prevalent element, in industrial using either applications. one or two driving sources [8–13]. The second is adapting the element geometry to produce mode coupling [7]. In this paper we treat the first method adapting Thethe elementtwo modes geometry are excited to produce together modevia the coup appliclingation [7]. of In an this AC paper electric we fieldtreat over the firstthe barmethod only, since it is the one prevalent in industrial applications. only,thickness, since it is using the one a set prevalent of rectangular in industrial electrodes applications. applied to the two largest bar faces: four quadrant The two modes are excited together via the application of an AC electric field over the bar thickness, using a set of rectangular electrodes applied to the two largest bar faces: four quadrant
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The two modes are excited together via the application of an AC electric field over the bar thickness, using a set of rectangular electrodes applied to the two largest bar faces: four quadrant electrodes (of the same size) over one face and a single large electrode over the other. Applying the field between the bottom electrode and one of the pairs of diagonally positioned electrodes on the top face (so only half of the piezoelectric volume is excited) excites both bending and extension in the bar midplane. Choosing the proper length-to-width ratio, attuned to a suitable excitation field frequency, leads to a constant phase difference between the extension and bending modes (at resonance frequency) where, as a result, each of the smallest bar faces traverses an elliptical trajectory (in the bar midplane). To produce motion, the vibrating element is preloaded onto a moving stage (linear or rotary) using back and side springs, which are chosen to provide required motor force and side stiffness, respectively (Figure2b). An example of such design is shown in Figure2c. The choice of one or the other pair of diagonally positioned electrodes on the top face determines the direction of the bar’s elliptical trajectory and hence the direction of stage motion. Thus two-directional motion of the stage can be obtained from a single-phase electrical drive by simply changing the excitation quadrants. To prevent wear of the piezoelectric element during motor operation, preloading is done through a wear resistant hard ceramic tip, which is attached at the center of the bar’s face that is facing the stage (Figure2b). The tip can also be attached at other locations on the element; these designs are less common and are not treated in this paper (for example see [11]). A complementary wear-resistant strip is attached on the stage side. The type of motion—either linear or rotary—is determined by choosing, accordingly, either a linear or a rotary stage (Figure2d,e). The force-velocity performance of the moving stage is determined by the amplitude and frequency of the tip’s elliptical motion, the element preloading forces, and the frictional properties of the tip-strip friction couple. The amplitude of the tip’s motion is proportional to the product of the electric field’s amplitude, the d31 piezoelectric coefficient, bar length and the mechanical resonance quality factor. Note that the resonance quality is much lower than that of a free body, due to damping caused by the preloading and the frictional energy losses of motor operation. The resonance frequency of motor operation is determined by the geometry, density and the elastic properties of the piezoelectric element. The electric field driving the piezoelectric element (the motor) is produced via a resonance circuit, which converts a low voltage DC input into a high voltage AC output applied across the element. Thus when compared to a typical, DC voltage-driven, piezoelectric actuator, the displacement obtained at the tip of the ultrasonic motor’s element, operating at resonance, is enhanced by two quality factors: that of the geometric mechanical resonance and that of the driving circuit electrical resonance. The typical displacements are in the micrometer range, which allows the input DC voltages to be lowered to the level of several tens of volts. The use of multilayer elements [14] allows the required DC input voltages to be further reduced to the level of several volts, allowing the use of batteries as the power source.
2.2. Motor Drive The motor is driven by an AC sine wave produced using a voltage source resonant converter. The typical motor driver is constructed from several consecutive stages (see Figure3a): (1) a DC converter, which is fed by an external DC power source; (2) an amplifier circuit which produces a PWM signal and (3) an LC resonant circuit (including the motor element as the capacitor) which produces the final AC sine wave on the element. Either two drive channels or a single channel, with a direction switch, are used to control the direction of motion, being connected to a different set of diagonal electrodes on the top face of the element (see Figure3b). ActuatorsActuators 20162016,, 55,, 15 15 5 of 19
Figure 3.3. SchematicSchematic representation representation of of an an ultrasonic ultrasonic motor motor driver driver design design (Nanomotion (Nanomotion AB1A AB1A driver driver [15]): ([15]):a) Main (a) driverMain driver stages; stages. (b) Diagram (b) Diagram of the of output the output stage stage with anwith internal an internal LC card LC (singlecard (single channel channel with awith direction a direction switch). switch).
Due to thethe stagestage staticstatic frictionfriction an inherent minimumminimum level of AC motor voltage rms is required toto initiateinitiate stagestage motionmotion (this(this isis thethe deaddead zonezone motor/drivermotor/driver voltage rms), after whichwhich thethe maximummaximum attainable stagestage velocityvelocity increasesincreases linearlylinearly withwith increasingincreasing thethe motormotor voltagevoltage rms.rms. The aboveabove drive drive configuration configuration exhibits exhibits high high efficiency efficiency in converting in converting low voltagelow voltage DC input DC powerinput intopower a highinto a voltage high voltage AC drive, AC drive, allowing allowing the usethe us ofe a of small a small sized sized driver driver to to power power a a largelarge numbernumber of ultrasonicultrasonic elements in parallel, either in a singlesingle motor or in aa numbernumber ofof motorsmotors connectedconnected inin parallel.parallel. This is especially beneficial beneficial for large scale motion solutions, such as the ones used in thethe semiconductorsemiconductor industry.industry.
2.3. Motion Control The motionmotion controllercontroller providesprovides aa commandcommand voltage,voltage, typicallytypically between ´−1010 V V and and 10 10 V, to thethe driver’s amplifieramplifier circuit. The driver translates the command voltage into a high voltagevoltage ACAC signalsignal applied toto thethe motor; motor; thus thus a a constant constant controller controller command command voltage voltage leads leads to a to constant a constant motor motor voltage voltage rms. Therms. minimum The minimum driver rmsdriver voltage rms voltage to produce to motionproduce (dead motion zone (dead driver zone voltage) driver translates voltage) accordingly translates intoaccordingly a minimum into controller a minimum command controller value command to produce value motion to produce (dead zone motion controller (dead command zone controller value). Thecommand velocity value). as a function The velocity of time as (ofa function an initially of time idle stage)(of an ininitially response idle to stage) a step in function response of constantto a step controllerfunction of command, constant controller which is higher command, than the which dead is zone higher controller than the command dead zone value, controller can be command described value, can be described by a first order differential equation in velocity. The solution yields a
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Actuators 2016, 5, 15 6 of 19 by a first order differential equation in velocity. The solution yields a conversion to a maximum velocity valueconversion as function to a maximum of time (for velocity the corresponding value as functi commandon of time level) (for the (see corresponding Figure4) and acommand linear inverse level) relationship(see Figure 4) between and a stagelinear velocity inverseand relationship available between force (see stage Section velocity 3.3 below). and available Hence, for force a given (see constantSection 3.3 command below). levelHence, (above for a deadgiven zone) constant a stage command with a movinglevel (above mass, deadm, can zone) apply a stage a maximum with a forcemoving (for mass, that command , can apply level), a maximumFC , at zero force velocity (for that or command achieve a level), maximum velocity,, at zero VvelocityC , with or max max zeroachieve available a maximum force. Thevelocity, values of maximum, with zero force available and maximum force. The velocity values increaseof maximum with increasingforce and maximum velocity increase with increasing command level, where the absolute maximum force (the command level, where the absolute maximum force (the stall force), Fmax, and the absolute maximum stall force), , and the absolute maximum velocity, , values are achieved at a maximum velocity, Vmax, values are achieved at a maximum command of 10V. The velocity time dependence, Vcommandptq, can be of well10V. described The velocity by thetime relationship: dependence, ( ), can be well described by the relationship: ( ) = C ∙ 1− ´ t (1) V ptq “ Vmax¨ 1 ´ e τ (1) where = is a time constant relating to motor´ dynamics.¯ The values of and are mV max where τ “ is a time constant relating to motor dynamics. The values of Vmax and Fmax are determined byFmax the piezoelectric properties, the resonance quality and the amplitude and frequency determined´ by the¯ piezoelectric properties, the resonance quality and the amplitude and frequency of of the motor drive signal. also depends on: (1) the value of the normal force at the contact point thebetween motor the drive hard signal. ceramicFmax tipalso and dependsthe drive on:strip, (1) wh theich value is mainly of the determined normal force by atthe the preload contact applied point betweenby the back the spring; hard ceramic (2) the tipnumber and the of driveL1B2 elements strip, which operated is mainly in parallel determined (in a single by the motor preload or applied several bymotors the back operating spring; on (2) the the same number motion of L1B2 axis). elements An ex operatedample of instage parallel dynamics (in a single in response motor or to several a step motorsfunction operating of a constant on thecontroller samemotion command axis). is shown An example in Figure of 4, stage which dynamics shows the in response response of to a alinear step functionstage with of a moving constant weight controller of 235 command g, driven is shownby a Nanomotion in Figure4, whichHR2 motor, shows containing the response two of L1B2 a linear HR stage with a moving weight of 235 g, driven by a Nanomotion HR2 motor, containing two L1B2 HR type driving elements (each providing a stall force ( ) of 4 N), driven by a Nanomotion AB1A typedriver driving (see Figure elements 3). Figure (each providing5a shows an a stall example force dependence (Fmax) of 4 N), of driven on by the a Nanomotioncommand level AB1A for C driverNanomotion (see Figure HR motors.3). Figure 5a shows an example dependence of Vmax on the command level for NanomotionNanomotion HR motors. has also developed a proprietary driver (AB5 driver) which eliminates the minimumNanomotion motor hasvoltage also developed(and hence a proprietarythe minimum driver command (AB5 driver) level) which requirement eliminates to theinitiate minimum stage motormotion voltage [16] and (and yields hence a thelinear minimum relationship command between level) controller requirement command to initiate and stage stage motion velocity [16] and(see yieldsFigure a 5b). linear relationship between controller command and stage velocity (see Figure5b).
FigureFigure 4.4. Stage velocity as function of time for severalseveral values of constant controllercontroller command appliedapplied toto thethe driver;driver; thethe motormotor isis NanomotionNanomotion HR2,HR2, movingmoving aa horizontalhorizontal linearlinear stagestage withwith aa movingmoving massmass ofof 235235 g.g. The driverdriver isis NanomotionNanomotion AB1A.AB1A.
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Figure 5. Linear stage maximum velocity as function of controller command voltage applied to the FigureFigure 5. 5.Linear Linear stage stage maximum maximum velocityvelocity as function of of controller controller command command voltage voltage applied applied to tothe the driver. The values are for L1B2 motors (Nanomotion HR-Type [17]) driven by Nanomotion drivers driver.driver. The The values values are are for for L1B2 L1B2 motorsmotors (Nanomotion(Nanomotion HR-Type HR-Type [17]) [17]) driven driven by by Nanomotion Nanomotion drivers drivers AB1AAB1A ( a )( a and) and AB5 AB5 (b ().b ).The The The motors motorsmotors operate operateoperate horizontally horizontally atat at roomroom room temperature temperature and and and low low duty duty cycle cycle (<10%).(<10%). The The The motor motor motor interface interface interface is is is with with with a aa ceramic ceramicceramic stripstrip and and aa a cross-rollercross-roller cross-roller high high quality quality slide. slide.
The typical closed loop motor control is executed using a high bandwidth PIV controller with a TheThe typical typical closed closed loop loop motormotor control is is execut executeded using using a high a high bandwidth bandwidth PIV PIV controller controller with with a nonlinearnonlinear mechanism. mechanism. Figure Figure 66 showsshows anan example blockblock diagramdiagram ofof a acontroller controller servo servo loop loop a nonlinear mechanism. Figure6 shows an example block diagram of a controller servo loop (Nanomotion(Nanomotion XCD XCD [18]), [18]), utilizing utilizing the the following following mechanisms to to increase increase the the precision precision of of stage stage motion: motion: (Nanomotion XCD [18]), utilizing the following mechanisms to increase the precision of stage motion: (1)(1) Offset Offset mechanism—provides mechanism—provides an an initialinitial commandcommand startingstarting valuevalue to to overcome overcome the the inherent inherent dead dead (1) Offset mechanism—provides an initial command starting value to overcome the inherent dead zone; zone;zone; (2) (2) Zero Zero Feed Feed Forward Forward mechanism—improves mechanism—improves thee stagestage settling settling time time by by stopping stopping the the velocity velocity (2) Zero Feed Forward mechanism—improves the stage settling time by stopping the velocity control controlcontrol loop loop (typically (typically 30 30 to to 50 50 µm µm before before targettarget position) andand therebythereby reducing reducing the the speed speed at atwhich which loop (typically 30 to 50 µm before target position) and thereby reducing the speed at which the stage thethe stage stage approaches approaches its its target target position position and and elimeliminating overshoot;overshoot; (3) (3) Dead Dead Zone Zone mechanism—takes mechanism—takes approaches its target position and eliminating overshoot; (3) Dead Zone mechanism—takes advantage advantageadvantage of of the the motor motor intrinsic intrinsic friction friction toto preventprevent jitter andand improveimprove settling settling time. time. It Itis isrealized realized by by of the motor intrinsic friction to prevent jitter and improve settling time. It is realized by defining two definingdefining two two position position ranges ranges around around the the targettarget position. TheThe smallersmaller range range (DZMIN) (DZMIN) defines defines a small a small position ranges around the target position. The smaller range (DZMIN) defines a small position range positionposition range range around around the the target.target. WhenWhen thethe motor entersenters thisthis range,range, the the controller controller drops drops the the around the target. When the motor enters this range, the controller drops the command to zero but commandcommand to tozero zero but but continues continues to to monitor monitor position.position. Only ifif thethe position position leaves leaves a acertain certain (desired) (desired) continues to monitor position. Only if the position leaves a certain (desired) predefined higher range predefinedpredefined higher higher range range (the (the required required accuracy)accuracy) around thethe targettarget (DZMAX) (DZMAX) does does the the control control loop loop (therestart required to correct. accuracy) around the target (DZMAX) does the control loop restart to correct. restart to correct.
Figure 6. Motion controller servo loop block diagram (Nanomotion XCD controller [18]). Figure 6. Motion controller servo loop block diagram (Nanomotion XCD controller [18]). Figure 6. Motion controller servo loop block diagram (Nanomotion XCD controller [18]). 3. Operational Conditions 3. Operational Conditions 3. Operational Conditions 3.1. Temperature Range 3.1. Temperature Range 3.1. TemperatureSince many Range of the piezoelectric materials suitable for use in high power piezoelectric motors Since many of the piezoelectric materials suitable for use in high power piezoelectric motors have have Curie temperatures above 300 °C, the Curie temperature itself usually does not serve as a Curie temperatures above 300 ˝C, the Curie temperature itself usually does not serve as a temperature temperatureSince many limit of tothe motor piezoelectric operation materials (from a purely suitable piezoelectric for use in properties high power point piezoelectric of view, as a motors rule have Curie temperatures above 300 °C, the Curie temperature itself usually does not serve as a temperature limit to motor operation (from a purely piezoelectric properties point of view, as a rule
Actuators 2016, 5, 15 8 of 19 limit to motor operation (from a purely piezoelectric properties point of view, as a rule of thumb, the motor should not be operated above half the Curie temperature (in degrees Celsius) to ensure minimal change in the piezo properties). With respect to both high and low temperature operation limits one needs to account for: (1) the changes in the material properties of the piezoelectric element, which may affect the resonance frequency as well as the magnitude of the piezoelectric coefficient; (2) thermal expansion mismatch between the different motor parts and the resulting thermal stress; (3) the change in the mechanical properties of motor components, such as the glass transition temperatures of adhesives and engineering plastics and the solidus temperatures of solder joints. Currently L1B2 motors operating between ´20 ˝C and 50 ˝C are available (Nanomotion HR motors), where with the use of special materials this range can be expanded further to cover from ´55 ˝C to 80 ˝C (Nanomotion Edge and Edge4X motors) and more.
3.2. Vacuum Operation Due to the inherently low outgassing properties of piezoelectric ceramics, piezoelectric ultrasonic motors are well suited to operate in high vacuum. The design of a vacuum motor needs to account for the vacuum outgassing of all motor parts exposed to vacuum conditions, typically employing low outgassing metals and engineering plastics, as well as vacuum compatible adhesives (for example see [19]). In high vacuum motors, it is generally a good practice to limit the use of plastics and adhesives to a minimum. Table1 shows an example breakdown by weight of a high vacuum compatible L1B2 motor (Nanomotion HR4-1-U-1.5 UHV) into material types. Note that the combined weight of adhesives and elastomers is only 0.14% of the total motor weight. To further increase vacuum compatibility, special cleaning and vacuum baking techniques should be employed.
Table 1. Example breakdown of a high vacuum compatible L1B2 motor (Nanomotion HR4-1-U-1.5 UHV) into material types by weight.
Material/Part Weight Percent of the Motor Low outgassing metals 49.57 Plastic 2.71 Wiring (insulation + copper strands) 18.14 Adhesive 0.06 Elastomer 0.08 Ceramics 29.44
3.3. Envelope of Performance The ergonomic nature of the L1B2 solution allows several L1B2 elements to be combined in a single motor to increase the driving force and motor stiffness in the direction of motion. Nanomotion HR type motors employ this feature, offering 4 N of stall force per a single L1B2 HR type drive element (HR1 motor), 8 N for two elements (HR2 motor), 16 N for four (HR4 motor) and 32 N for eight (HR8 motor) [17]. Their envelope of performance, explained in the following paragraph, is shown in Figure7. Actuators 2016, 5, 15 9 of 19 Actuators 2016, 5, 15 9 of 19
Figure 7. Envelope of performance of L1B2 motors fr fromom Nanomotion HR motor series, when driven by AB1A driver [17]: [17]: ( a) Force—velocity curves, for Nanomotion HR-type motors; (b)) maximal duty duty cycle forfor operationoperation inin air air and and vacuum, vacuum, for for operating operatin atg force-velocityat force-velocity combinations, combinations, located located below below each eachof the of force the force velocity velocity curves curves shown shown in (a). in (a).
The duration of the motor’s continuous operation is limited by the need to balance the rate of The duration of the motor’s continuous operation is limited by the need to balance the rate of heat generation by the element, while it operates, with the rate of heat dissipation to the environment; heat generation by the element, while it operates, with the rate of heat dissipation to the environment; the dissipation rate depends on the element temperature, the environmental temperature and the the dissipation rate depends on the element temperature, the environmental temperature and the heat conductivity of motor and stage components. The resulting motor operation temperature must heat conductivity of motor and stage components. The resulting motor operation temperature must not exceed the material limitations of motor components. When those limits are approached (to not exceed the material limitations of motor components. When those limits are approached (to within a given safety factor) motor operation must be stopped and the motor given time to cool down. within a given safety factor) motor operation must be stopped and the motor given time to cool As a result, for each set of operational conditions, consisting of a combination of force, velocity and down. As a result, for each set of operational conditions, consisting of a combination of force, velocity environment type, there exists a maximal duty cycle, which is defined as a maximal percent of and environment type, there exists a maximal duty cycle, which is defined as a maximal percent of operational time out of the total (operational plus idle) time. An example maximal allowable duty operational time out of the total (operational plus idle) time. An example maximal allowable duty cycle, cycle, for Nanomotion HR type motors driven by AB1A driver, is shown in Figure 7b: for air for Nanomotion HR type motors driven by AB1A driver, is shown in Figure7b: for air environment at environment at 25 °C and 50 °C, and for high vacuum at 25 °C. The complementing operational 25 ˝C and 50 ˝C, and for high vacuum at 25 ˝C. The complementing operational conditions are shown conditions are shown in Figure 7a. in Figure7a.
3.4. Friction and Wear Considerations The use of friction drive by the L1B2 motor imposesimposes stringent requirements on the material properties of the friction pair. A high stiffness for both the tip and strip is required to facilitate high positioning precision with a fast move and settle. The friction coefficient coefficient must be high enough to provide the forces required by the intendedintended application.application. It must remain constant to within a small tolerance throughout the lifetime of the application,application, to facilitate smooth motor operation. The wear rate of both the the tip tip and and strip strip must must remain remain low low to to ne negligiblegligible throughout throughout the the lifetime lifetime of of the the application. application. The combinationcombination of of the the above above requirements requirements is not is straightforwardnot straightforward and typically and typically requires requires a research a researchand development and development effort into effort the into tribological the tribological aspects aspects of the tip-strip of the tip-strip contact. contact. For example For example the use the of uselubricants of lubricants to obtain to lowobtain wear low is wear typically is typically limited bylimited the friction by the coefficientfriction coefficient requirement. requirement. This increases This increasesthe importance the importance of the bulk of material the bulk parameters material parame in wearters prevention. in wear prevention. The value ofThe the value friction of the coefficient friction coefficientmight also might be affected also be by affected the chemistry by the chemistry of the environment of the environment the motor the is operatingmotor is operating in (e.g., ambient, in (e.g., ambient,high vacuum, high vaporvacuum, deposition vapor deposition chamber, chamber,etc.). etc.). In view of the above, the optimization of L1B2 motor operation must be supported by a base of tribological knowledge, gathered gathered through through a dedicated research and development effort, focused on the material material and and environmental environmental aspects aspects of of the the intended intended application. application. To To ensure ensure reliability, reliability, each chosen chosen friction pair should be tested by motor operation under under the the conditions conditions of of the the intended intended application. application. Nanomotion has gathered hu hundredsndreds of months of operating motors motors,, optimizing friction pairs to be used at various environments and operating conditions.conditions. The suitable materials are typically chosen from the family of hard ceramics.
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Actuators 2016, 5, 15 10 of 19 4. Positioning Accuracy 4. Positioning Accuracy LetLet us us consider consider a a linear linear stage stage coupledcoupled toto an L1B2 motor as as shown shown in in Figure Figure 2b.2b. The The stage stage moving moving massmass is is coupled coupled to to the the stationary stationary motormotor casingcasing through the elastic elastic components components housing housing the the L1B2 L1B2 elementselements (see (see for for example example Figure Figure2 c).2c). Thus Thus the the stagestage movingmoving mass effectively acts acts as as a a mass mass on on spring spring alongalong the the direction direction of of motion, motion, with with aa correspondingcorresponding resonance frequency frequency prop proportionalortional to to the the square square ofof the the effective effective stiffness stiffness of of the the elements’elements’ housing.housing. On On one one hand hand this this setup setup produces produces a low a low pass pass filter, filter, which,which, for for a a typical typical stage, stage, does does not not allowallow stagestage motionmotion frequencies in in the the ultrasonic ultrasonic range. range. Thus, Thus, the the positionposition error error during during motion motion does does notnot directlydirectly dependdepend on a single single ultrasonic ultrasonic vibration. vibration. On On the the other other handhand this this resonance resonance frequencyfrequency puts an upper upper limit limit on on stage stage dynamics. dynamics. As Asa result, a result, a high a high stiffness stiffness of ofelement element housing housing (the (the effective effective motor motor stiffness stiffness in in th thee direction direction of of motion) motion) is isan an important important factor factor in in achievingachieving fast fast move move and and settle settle dynamics dynamics withwith highhigh positioning precision. precision. TheThe positioning positioning accuracy accuracy ofof stages,stages, drivendriven by L1B2 ultrasonic ultrasonic motors motors via via a aclosed closed loop loop control, control, dependsdepends on on several several factors: factors: the the effective effective motor/smotor/s stiffness stiffness in in the the direction direction of of motion, motion, the the gains gains and and the the frequencyfrequency of of the the close close loop loop control control algorithm,algorithm, thethe position resolution resolution of of the the feedback feedback mechanism mechanism and and thethe magnitude magnitude of of ultrasonic ultrasonic vibrations.vibrations. In In the the next next example example we we show show that that for fora typical a typical 0.5 kg 0.5 stage kg stage an anaccuracy accuracy of of several several tens tens of ofnanometers nanometers is readily is readily available. available. InIn addition addition to to stage stage motion motion generatedgenerated byby ultrasonicultrasonic vibrations vibrations (AC (AC mode mode motion) motion) the the L1B2 L1B2 elementselements can can be be used used in in actuator actuator mode—wheremode—where af afterter switching switching off off the the ultrasonic ultrasonic resonance resonance mode, mode, the final position is attained and held by a close loop controlled DC voltage that is applied across the the final position is attained and held by a close loop controlled DC voltage that is applied across the element causing it to bend (DC mode motion), thereby moving the stage in a sub-micron range [20]. element causing it to bend (DC mode motion), thereby moving the stage in a sub-micron range [20]. This mode allows reaching a sub-nanometer resolution given a suitable resolution of position This mode allows reaching a sub-nanometer resolution given a suitable resolution of position feedback. feedback. Figures8 and9 show examples of linear stage motion via an L1B2 motor—a Nanomotion HR8 Figures 8 and 9 show examples of linear stage motion via an L1B2 motor—a Nanomotion HR8 motor, with a motor stiffness of 3.5 N/µm. Figure8 shows an example of a high accuracy AC mode motor, with a motor stiffness of 3.5 N/µm. Figure 8 shows an example of a high accuracy AC mode positioningpositioning of of a a 0.5 0.5 kg kg stage. stage. TheThe systemsystem performedperformed repetitive repetitive back back and and forth forth 10 10 mm mm movements, movements, repeatablyrepeatably settling settling within within 90 90 ms, ms, to to aa 5050 nmnm window. Figure 9 shows an example example DC DC mode mode actuation actuation ofof horizontal horizontal stage stage having having aa 22 kgkg movingmoving weight,weight, within a a maximum maximum actuation actuation range range of of 600 600 nm nm (Figure(Figure9a) 9a) as as well well as as an an example example of of a a 4 4 nm nm step step (Figure(Figure9 9b)b) with with thethe positionposition held to within 1 1 nm nm accuracyaccuracy before before and and after after the the step. step. TheThe measurementsmeasurements were were taken taken on on a a very very rudimentary rudimentary vibration vibration suppressionsuppression table, table, the the environmental environmental vibrations vibrations areare suppressedsuppressed by the the high high motor motor damping. damping. OperatingOperating an an L1B2 L1B2 motormotor over a drive ring ring equi equippedpped with with a high a high resolution resolution encoder encoder allows allows a a rotaryrotary axis to be constructed with with a a very very high high an angulargular accuracy. accuracy. An An example example is isshown shown in inFigure Figure 10, 10 , whichwhich details details the the position position error error of of a a NMNM FBR60FBR60 rotaryrotary stage stage (driven (driven by by two two Nanomotion Nanomotion HR2 HR2 vacuum vacuum motors)motors) over over more more than than 42,000 42,000 steps steps of of 9090°.˝. A typica typicall position position error, error, 10 10 seconds seconds after after the the end end of of motion motion isis less less than than 1 1 micro-radian. micro-radian.
Figure 8. Cont.
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FigureFigure 8. 8.Example Example of of high high accuracy accuracy fastfast positioning,positioning, using an, an, L1B2 L1B2 motor motor based, based, linear linear motion motion stage, stage, withwith a movinga moving weight weight of of 0.5 0.5 kg.kg. TheThe performance shown shown is is of of a aNM NM stage stage FB75-100-HR8 FB75-100-HR8 driven driven by a by a NMNM HR8-VHR8-V vacuumvacuum motor (containing eight eight L1B2 L1B2 elements) elements) and and equipped equipped with with an an optical optical encoder encoder positionposition feedback feedback (encoder (encoder resolution resolution is is 10 10 nm).nm). TheThe red colored graphs graphs are are all all taken taken with with an an external external reference encoder having a resolution of 0.1 nm. (a) An image of the FB75-100-HR8 stage. (b) Stage reference encoder having a resolution of 0.1 nm. (a) An image of the FB75-100-HR8 stage; (b) Stage position and velocity as function of time, showing a typical 10 mm motion step, accomplished within position and velocity as function of time, showing a typical 10 mm motion step, accomplished within 300 ms. (c) Feedback position during break, showing a (complete break) settling to a window less than 300 ms; (c) Feedback position during break, showing a (complete break) settling to a window less than 50 nm from target within 100 ms, followed by a landing drift of less than 15 nm during the next 3 s. 50 nm from target within 100 ms, followed by a landing drift of less than 15 nm during the next 3 s; (d) Position as function of time during sequential back and forth 10 mm moves. The graph focuses (d) Position as function of time during sequential back and forth 10 mm moves. The graph focuses around the landing position at one of the two motion ends, showing a landing repeatability window around the landing position at one of the two motion ends, showing a landing repeatability window of of less than 50 nm. less than 50 nm.
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Figure 9. The use of an L1B2 motor in actuator (DC) mode. (a) The motion of a linear stage with a Figure 9. The use of an L1B2 motor in actuator (DC) mode. (a) The motion of a linear stage with movingFigure 9. weight The use of 2of kg, an drivenL1B2 motor by a NM in actuator HR8 moto (DC)r (containing mode. (a) Theeight motion L1B2 elements) of a linear operating stage with in a a moving weight of 2 kg, driven by a NM HR8 motor (containing eight L1B2 elements) operating in DCmoving mode: weight position of 2 and kg, controllerdriven by commanda NM HR8 level moto asr function(containing of time. eight ( bL1B2) Example elements) of a operating4 nm position in a a DC mode: position and controller command level as function of time; (b) Example of a 4 nm position step,DC mode: performed position with and a Nanomotion controller command FB75-100-HR8 level as st agefunction operating of time. in DC (b) mode,Example equipped of a 4 nm with position a NM step, performed with a Nanomotion FB75-100-HR8 stage operating in DC mode, equipped with a NM HR8step, motor.performed The withresolution a Nanomotion of the feedback FB75-100-HR8 position st encoderage operating is 0.4 nm. in DC mode, equipped with a NM HR8 motor. The resolution of the feedback position encoder is 0.4 nm. HR8 motor. The resolution of the feedback position encoder is 0.4 nm.
Figure 10. Positioning accuracy of a rotary stage (Nanomotion FBR60 stage, shown in the inset) FigureoperatedFigure 10. 10.Positioning by Positioning two L1B2 accuracy accuracymotors of(Nanomotionof aa rotaryrotary stage HR2 (Nanomotion vacuum motors). FBR60 FBR60 The stage, stage,stage shown shownwas inoperated the in theinset) in inset) consecutive 90° steps (each four steps completing a rotation cycle). The angular position error for each operatedoperated by by two two L1B2 L1B2 motors motors (Nanomotion (Nanomotion HR2HR2 vacuumvacuum motors). motors). The The stage stage was was operated operated in in stepconsecutive was recorded 90° steps 10 s(each after four the endsteps of completing motion and a isro representedtation cycle). by The a pointangular on positionthis graph error that for shows each consecutive 90˝ steps (each four steps completing a rotation cycle). The angular position error for each thestep recorded was recorded position 10 serrors after thefor end42,000 of steps.motion and is represented by a point on this graph that shows step was recorded 10 s after the end of motion and is represented by a point on this graph that shows the recorded position errors for 42,000 steps. the recorded position errors for 42,000 steps.
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Actuators 2016, 5, 15 13 of 19 5. Examples of Motion Solutions 5. Examples of Motion Solutions 5.1. Vacuum Stages for Space Applications 5.1. Vacuum Stages for Space Applications The use of L1B2 motors holds several advantages for space applications. Having a direct drive The use of L1B2 motors holds several advantages for space applications. Having a direct drive allows L1B2 motors to provide high force/torque at low speeds, eliminating the need for gear (which allows L1B2 motors to provide high force/torque at low speeds, eliminating the need for gear (which is typically used in combination with DC motors to obtain high torque at low speeds), freeing up is typically used in combination with DC motors to obtain high torque at low speeds), freeing up design weight and volume and eliminating backlash. The zero power consumption when holding design weight and volume and eliminating backlash. The zero power consumption when holding position eases the power requirements, while low outgassing reduces the risk of contamination. position eases the power requirements, while low outgassing reduces the risk of contamination. FigureFigure 11 11 shows shows an an example example L1B2L1B2 motormotor based mi miniatureniature scanning scanning stage, stage, for for use use in in low low earth earth orbitorbit (LEO) (LEO) conditions. conditions. TheThe motormotor is an HR2 vacuum motor, motor, driven driven and and controlled controlled by by an an XCD XCD controllercontroller driver driver [21 [21].]. The The motor motor drives drives a a linear linear stage stage having having a movinga moving weight weight of of 230 230 g. gram. The system The ´6 hassystem been has tested been in tested a high in vacuum a high (10vacuumTorr) (10− while6 Torr) continuously while continuously performing performing a periodical a periodical motion profilemotion at aprofile frequency at a frequency of 8 Hz (Figure of 8 Hz 11 (Figureb). The 11b). profile The presents profile presents a high duty a high cycle duty operation cycle operation including 2 accelerationsincluding accelerations of 2 m/s . Theof 2 averagem/s2. The position average error position rms error during rms the du constantring the velocityconstant phasevelocity of phase motion hasof remainedmotion has below remained 4 µm below during 4 µm 50 millionduring 50 cycles million of operationcycles of operation in vacuum in vacuum (Figure 11(Figurec). This 11c). test simulatesThis test 3simulates years of space3 years operation of space operation in high vacuum. in high vacuum.
FigureFigure 11. 11.Vacuum Vacuum operation operation of ofa ascanning scanning stage:stage: (a) Image of of the the setup setup including including an an HR2 HR2 vacuum vacuum motormotor and and a a linear linear stage stage having having aa movingmoving massmass of 230 g. g; ( (bb)) Motion Motion profile profile during during a asingle single scanning scanning cycle. (c) Position error rms, as function of the number of performed scanning cycles. cycle; (c) Position error rms, as function of the number of performed scanning cycles.
To ensure negligible molecular outgassing, all of the motor and stage components need to pass stringentTo ensure vacuum negligible cleaning molecular procedures. outgassing, As an example, all of theFigure motor 12 presents and stage a residual components gas analysis need to scan pass stringentof a Nanomotion vacuum cleaning FBR60-U procedures. stage idle in As a an high example, vacuum Figure (with 12 active presents pumping). a residual The gasscan analysis was scanperformed of a Nanomotion on an as cleaned FBR60-U stage, stage 60 idleh after in a the high start vacuum of vacuum (with pumping. active pumping). A comparison The scan of the was
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Actuators 2016, 5, 15 14 of 19 performed on an as cleaned stage, 60 h after the start of vacuum pumping. A comparison of the obtained spectrum to that of the chamber baseline does not indicate the presence of any gasgas partialpartial pressure lines,lines, having a partial pressure above thatthat of test sensitivity (5E-11 Torr), whichwhich may be attributable to the stage outgassing.outgassing.
Figure 12.12. Nanomotion FBR60-U rotary stage based on two HR2 vacuumvacuum motors:motors: (a) Image of thethe stage without the encapsulating case;case. (b)) ImageImage ofof thethe stagestage withwith thethe encapsulatingencapsulating case;case. ((c)) ResidualResidual gas analysis analog scan of an FBR60-UFBR60-U high vacuum rotary stage idle in active vacuum (30 L vacuum chamber pumped via a turbomolecularturbomolecular vacuum pump).pump). The scan was performed on an as cleanedcleaned stage, 6060 hh afterafter thethe startstart ofof vacuumvacuum pumping.pumping.
5.2. Semiconductor Market L1B2 motorsmotors can can successfully successfully address address the requirementsthe requirements for clean for room clean wafer room handling, wafer operatinghandling, insideoperating production inside production and analytical and analytical instruments. instruments. The use The of use a resonant of a resonant drive drive method method allows allows the operationthe operation of multipleof multiple elements elements in in parallel, parallel, thereby thereby increasing increasing the the available available forces forces toto drivedrive heavy loads.loads. For example, a Nanomotion AB1B driver can drive up to 64 elements (or 8 HR8 type motors) per drive axis, reaching a combined stall force of 256 N. Compound multi-axis solutions provide fast move and settle moves over large distances and arbitrary orientations. Examples shown in Figure 13 includeinclude stagesstages forfor metrologymetrology andand microscopy.microscopy.
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Figure 13. The use of L1B2 motors for metrology and microscopy applications: ( a) Four axis stage for ion beam etching; ((b) threethree axisaxis stagestage forfor waferwafer handling;handling; ((cc)) fivefive axisaxis stagestage forfor Nanolithography.Nanolithography.
5.3. Biomedical Applications 5.3. Biomedical Applications The unique advantages of L1B2 motors make them attractive for use in biomedical devices. The The unique advantages of L1B2 motors make them attractive for use in biomedical devices. extremely low magnetic signature (0.1 nT and a recovery time of less than 3 ms) allows operation The extremely low magnetic signature (0.1 nT and a recovery time of less than 3 ms) allows operation inside MRI instruments. Figure 14a,b shows an example application where two Nanomotion HR2-V inside MRI instruments. Figure 14a,b shows an example application where two Nanomotion HR2-V motors are used to rotate a shaft operating inside an MRI instrument with a magnetic field of 3 Tesla. motors are used to rotate a shaft operating inside an MRI instrument with a magnetic field of 3 Tesla. The high torque to size ratio and short response times allow solutions to be designed for moving The high torque to size ratio and short response times allow solutions to be designed for moving small medical and electro-optical devices. An example of a miniature zoom module for endoscopy small medical and electro-optical devices. An example of a miniature zoom module for endoscopy tool is shown in Figure 14c. This module is based on a small, 6.3 mm long L1B2 element, designed to tool is shown in Figure 14c. This module is based on a small, 6.3 mm long L1B2 element, designed to operate at a low motor voltage of 10 V rms, enabling operation in vivo. Maximum rotation torque is operate at a low motor voltage of 10 V rms, enabling operation in vivo. Maximum rotation torque is 0.5 mN·m. Maximum angular velocity is 30 rad/s. This zoom module has a total weight of 1.4 g and 0.5 mN¨ m. Maximum angular velocity is 30 rad/s. This zoom module has a total weight of 1.4 g and is equipped with a miniature camera with a diameter of 1.2 mm. is equipped with a miniature camera with a diameter of 1.2 mm.
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Figure 14.14. Examples of L1B2 motor use inin biomedicalbiomedical applications:applications: (a,b) Two NanomotionNanomotion HR2-VHR2-V motors are usedused toto rotaterotate aa shaftshaft inin aa tumortumor ablationablation instrumentinstrument operatingoperating insideinside anan MRIMRI instrumentinstrument having aa magneticmagnetic field field of of 3 Tesla;3 Tesla. (c) ( Schematicc) Schematic drawing drawing of a of rotary a rotary module module designed designed to provide to provide zoom capabilitieszoom capabilities for endoscopy for endoscopy tools; (tools.d) An ( imaged) An image of the moduleof the module that is that schematically is schematically shown shown in (c). in (c).
5.4. Electro-Optics Modules When used inin smallsmall electro-opticalelectro-optical modulesmodules L1B2L1B2 motorsmotors provideprovide fastfast accurateaccurate motionmotion whilewhile providingproviding favorablefavorable sizesize weightweight and power (SWaP) characteristicscharacteristics (small(small sizesize andand weight along with lowlow powerpower consumption).consumption). Example applications—Nonapplications—Non Uniformity Correction (NUC) shutters, for uncooled IR camera and laser applications—are shownshown in the figuresfigures below. All of thethe shuttersshutters are based on a Nanomotion EdgeEdge typetype motormotor [[22],22], which is based on a 9 mm long L1B2 element providing a maximummaximum velocityvelocity aboveabove 200200 mm/s,mm/s, a a maximum (stall) force above 0.35 N and a motormotor stiffnessstiffness above 0.060.06 N/N/µm.µm. An An example example linear linear shutter shutter is is show shownn in in Figure 15.15. It It has has a a total weight of 15 g 2 (moving(moving weightweight equalsequals 1.51.5 g),g), anan apertureaperture areaarea of of 14.7 14.7ˆ × 17.017.0 mmmm2 andand aa strokestroke (open/close)(open/close) time of 150150 ms.ms. Rotary shutter modules are shown in Figure 1616.. A single axis module, shown in Figure 16a,16a, weighsweighs 2 gram g in total in total and and has has the the ability ability to performto perform a 90a 90°˝ turn turn in in less less than than 50 50 ms. ms. AA twotwo axisaxis module, shownshown in Figure 1616bb can independently rotate each of the two shutter leafs, each weighing about 2 g, performingperforming aa 6060°˝ turn within 100 ms.ms.
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Figure 15. Linear NUC shutter based on Nanomotion Edge L1B2 motor: (a) Schematic drawing of the FigureFigure 15. 15.Linear LinearNUC NUC shutter based based on on Nanomotion Nanomotion Edge Edge L1B2 L1B2 motor: motor: (a) Schematic (a) Schematic drawing drawing of the of Edge motor preloaded onto the drive strip. (b) Schematic drawing of the leaf motion mechanism. theEdge Edge motor motor preloaded preloaded onto onto the the drive drive strip. strip; (b ()b Schematic) Schematic drawing drawing of ofthe the leaf leaf motion motion mechanism. mechanism; (c)( c Image) Image of of the the linear linear NUCNUC NUC shutter.shutter. shutter.
FigureFigure 16. 16. (a ()a Image) Image of of a a rotaryrotary rotary NUCNUC NUC shutter shuttershutter basedbased on a 9 mm mm longlong L1B2 L1B2L1B2 element. element.element. The The length length of of the the unit is 20 mm. (b) An image of a shutter module with two rotary axes. unit is 20 mm;mm. (b) An image of a shutter modulemodule withwith twotwo rotaryrotary axes.axes.
6. Summary 6. Summary Summary The precise motion solutions based on L1B2 ultrasonic motors are able to provide a positioning The precise motion solutions based on L1B2 ultrasonic motors are able to provide a positioning accuracy in the nm range, while offering high forces and large dynamic ranges in velocity, thereby accuracy in the nm range, while offering high fo forcesrces and large dynamic ranges in velocity, thereby accomplishing a fast move and settle throughput, over large travels, in a single mechanism. The accomplishing a a fast fast move move and and settle settle throughput, throughput, over over large large travels, travels, in a insingle a single mechanism. mechanism. The complete motion solution consists of a motor, a driver, a moving platform, and a motion controller complete motion solution consists of a motor, a driver, a moving platform, and a motion controller operating a closed servo loop using a position feedback sensor. All of these parts can be adapted to operating a closed servo loop using a position feedback sensor. All of these parts can be adapted to
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The complete motion solution consists of a motor, a driver, a moving platform, and a motion controller operating a closed servo loop using a position feedback sensor. All of these parts can be adapted to meet a specific application in the fields of semiconductor metrology, aerospace, biomedical and electro-optics. In the metrology field, the advantage of a high throughput is key, based on a fast move and settle and an unlimited travel. In multiple motion axes employed to meet 3D positioning requirements, the L1B2 motor yields significant weight benefits. Clean room environmental conditions are feasible, as the core piezo element is UHV compatible and no lubrication is required. The system UHV compatibility is met by using verified materials in combination with advanced cleaning techniques. In the fields of aerospace and electro-optics, the advantages of inherently high power density, energy efficiency at small size and low power consumption, coupled with ergonomic design and the absence of gear, allow favorable SWaP parameters (size weight and power) to be preserved. For biomedical applications, low magnetic signature allows operation in medical devices with high magnetic fields, while a small footprint is favorable for endoscopy applications. Ongoing work on the L1B2 motors at Nanomotion is aimed to broaden the performance envelope and the realm of applications.
Acknowledgments: The authors acknowledge partial support by the Office of the Israeli Chief Scientist and specifically the MAGNET Metro450 consortium. Conflicts of Interest: The authors declare no conflict of interest.
References
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