1 Stepper Motor Linear ActuatorsClassical Motor -Leadscrew / Ballscrew Linear Actuators FORCE Physik Instrumente (PI) GmbH & Co. KG 2008. Subject to change without Inspirations2009 08 & Drives FundamentalsClassic Drive Systems ( Stepper & Servo Motors)ActiveDrive DC Motorbecause no external driverdrives are good dynamic per-steps, without the need of posi-Some of the advantages of DC-and cabling are requiredformance, fast response, hightion sensor or servo-loop. torque at low rpm, low heatStepper motors have very longmotor drives are good dynam-Elimination of PWM amplifi-dissipation and low and are especiallyic performance, fast response,er noise radiation by mount-suited for applications wherehigh torque at low rpm, lowing the amplifier and motorDC- Motor / Gearhead Drivepredictablepositioningisheat dissipation and low vibra-together in a single electri-required as opposed totion.
2 The cost of a high-per-A few advantages of DC-fastcally shielded caseformance amplifier, however, Motor /gearheaddrivesareresponse and extreme acceler-Positioning accuracy isation. Another advantage liesis generally higher than that for very high angular resolution,a Stepper with either rotarysmall form factor and lowin the simple control electron-or optical Linear consumption with highics. Compared to closed-looptorque. They can be operatedDC motors of the same size,The ActiveDrive system re-DC Servo-Motorby PC controller boards suchstepper motors provide poorerduces this cost considerably,as the C-843 without an exter-dynamic performance and dis-by integrating a PWM (pulseA direct current Motor that isnal amplifier.)
3 PI uses varioussipate more heat, especially inwidth modulation) driver andoperated in a closed-loop sys-types with maximum power insteady state operation. PIamplifier in the Motor (servo-loop). Characteris-the 2 to 3 watt range and opti-offers microstepped 2-phaseThis design provides severaltics of DC servo-motors arecal rotary encoders with up tomotors, which are very cost-advantages:lack of vibration, smooth run-4000 counts per , wide speed range andMost models use preloaded Increased efficiency, byvery good low-speed to eliminate back-For optimum performance, aeliminating power Motor controller with PIDbetween the amplifier and(proportional, integral, deriva- Motor Reduced cost, more- Stepper Motortive) algorithm and filter set-compact system, andtings is mandatory.
4 Some ofAn electric Motor providingimproved reliability,the advantages of DC motormotion in discrete angularLeadscrewsLeadscrews can provide veryhigh resolutions and verysmooth motion. A leadscrewdrive consists of a Motor -driv-en screw with a nut coupled tothe sled of the stage. The nutcan be spring preloaded toreduce backlash. Leadscrewsare self-locking but exhibithigher friction than recirculat-ing ballscrews, with the pre-dictable effect on velocity,required Motor power, andlifetime. Typical leadscrewshave a pitch between mm/revolution, or upto1 mm/ revolution for longertravel BallscrewsRecirculating ballscrews havesignificantly less friction thanleadscrews, because they re-place sliding friction withrolling recirculating ballscrew driveconsists of a Motor -drivenscrew with a nut (ball housing)coupled to the sled of thestage, and a number of ballsriding between the screw andthe nut in a closed-circuit pas-sage.
5 Backlash can be eliminat-ed by selecting the proper ball-to-thread-diameter ratio. Ball-screws are not self-locking, butare maintenance free, very effi-cient and offer high speeds andlong lifetime in continuousoperation. Standard PI ball-screws have pitches of , 1 or2 screw type is noted in thedata sheet of each ScrewsPiezo DrivesIt is important to distinguishbetween different types ofpiezo drives: classical piezoactuators (direct acting), flex-ure amplified Actuators , andUltrasonic PiezomotorsUltrasonic piezomotors aredirect-drivesystems; they donot use leadscrews or gear-heads and are backlash-free. Inaddition, they neither create,nor are influenced by, magnet-ic fields.
6 The drive consists of astator, containing a piezoce-ramic oscillator and a slider(friction bar), which is attachedto the moving part of the PI ultrasonic piezomotorsspeeds of up to 500 mm/s andresolutions of m in closed-loop are possible. They arealso extremely compact, self-locking and have lifetimes ofover 20,000 hours. PI piezo-motors are used in miniaturepiezo Linear motors. Direct-drivepiezo Actuators offeringresolutions of under one nano-meter can be combined withclassical motorized actuatorsand stages to form coarse/finesystems or the more advancedhybrid systems (p. 4-132).Piezo Linear motors provideWorking principle of an ultrasonic Linear piezomotor drivebasicallyunlimitedtravelranges.
7 PI offers two types:Ultrasonic (high-speed) motorstranslation stages like theics, albeit with relatively lowand PiezoWalk (high-force,M-661, M-662, M-663 andholding force. They are usedhigh resolution) motors. PiezoM-664 series, and in XY stagesprimarily in scanning applica- Actuators can achieve extreme-like the with travel ranges in thely high accelerations of manymillimeter to low centimeterthousands of g s, are friction-Voice-Coil Linear Drivesrange. PI offers voice coilless and friction-free electromag-drives in the V-106 stages, asnetic Linear drives are charac-well as in custom-designedterized by their good Drives (Coarse / Fine)Classic Combinationsbecoming activated after theCombinations of different drivemotorized positioner has comeconcepts are called hybridto a complete stop.
8 Becausedrives. PI s micropositioningseparate position sensors aresystems realize stacked sys-used. the absolute accuracy (nottems of piezo and manual orthe resolution) is limited by themotorized stages, where aprecision of the motorized long- Motor /screw drive combina-range provides a long travelrange and a piezo drive addsNovel Hybrid Conceptfine positioning accuracy andexceptionalresponsivenessA novel concept is implement-over small ranges. For exam-ed in the and M-714ple, PI offers a fiber-scanningHybrid Translation Stages andand coupling system compris-C-702 Hybrid Controllers, thatDifferent types of combined motorized and piezo positioning systems.
9 Ing a 6-DoF micropositionerevaluate a nanometer-preci-a) Serially stacked drives with individual integrated position sensors(F-206) mounted beside asion, long-range, sensor andb) PI Hybrid drive with integrated, internal, high-resolution sensor,for use with highly specialized controllermulti-axis piezo system (P-611provide nanometer accuracyNanocube ) with high positionover the whole travel Motor -leadscrew and thetages of both the motorizedmakes hybrid systems ideal forpiezo actuator are fully inte- actuator and the piezo actuatorapplications where the positionThe servo-control algorithmsgrated to form one motion sys-from startup to an incident needs to be readwith stacked systems like thesetem, and act simultaneously atresult is immediate starting,and repositioned precisely, orgenerally operate independent-all times.
10 Thus every move be-smoothness of motion, and awhere an externally specifiedly, with the piezo system onlynefits from the specific advan-highly constant velocity. Thistarget position needs to be hit Physik Instrumente (PI) GmbH & Co. KG 2008. Subject to change without Inspirations2009 08 few a nanometers, suchas in surface inspection the mechanical side, this isaccomplished by decouplingthe motion platform of thehybrid positioning stage fromthe micropositioner s Motor -spindle-drive by frictionlessflexures and stiff, fast responsepiezo Actuators . The piezo actu-ators actively smooth out theirregularities in the motion ofthe platform caused by themotorized drive train to pro-vide full move capability downto the sensor control algorithms treatthe Motor and piezo combina-tion as one single drive unitand continuously compare theactual platform position (byreading the integrated linearencoder) with a calculated,smooth principle of the The platform is decou-pled from the Motor drive train by the piezo actuator andthe flexure guides.