Piezoelectrics in Positioning - PZT & Piezo Actuators: Sub ...

Piezo • Nano • PositioningOperating Characteristics of Piezoelectric ActuatorsOperating VoltageTwo types of piezo actuators havebecome established. Monolithicsintered,low-voltage actuators(LVPZT) operate with potential differencesup to about 100 V and aremade from ceramic layers from 20to 100 μm in thickness. Classicalhigh-voltage actuators (HVPZT),on the other hand, are made fromceramic layers of 0.5 to 1 mmthickness and operate with potentialdifferences of up to 1000 V.High-voltage actuators can bemade with larger cross-sections,making them suitable for largerloads than the more-compact,monolithic actuators.a casing with integrated preloador an external preload spring isrequired. Adequate measuresmust be taken to protect the piezoceramicfrom shear and bendingforces and from torque.Travel RangeTravel ranges of Piezo Actuatorsare typically between a few tensand a few hundreds of μm (linearactuators). Bender actuators andlever amplified systems canachieve a few mm. Ultrasonicpiezomotors and Piezo-Walk ®drives can be used for longer travelranges.concerning the sensor, actuatorand preload can induce micro-frictionwhich limits resolution andaccuracy.PI offers piezo actuators and positioningsystems that provide subnanometerresolution and stability.For more information, seep. 2-183 ff.Linear Actuators & MotorsNanopositioning / PiezoelectricsPiezo Flexure Stages /High-Speed Scanning SystemsLinearVertical & Tip/Tilt2- and 3-Axis6-AxisFast Steering Mirrors /Active OpticsPiezo Drivers /Servo ControllersSingle-ChannelMulti-ChannelModularAccessoriesStiffness, Load Capacity, ForceGenerationTo a first approximation, a piezoactuator is a spring-and-mass system.The stiffness of the actuatordepends on the Young’s modulusof the ceramic (approx. 25 % thatof steel), the cross-section andlength of the active material and anumber of other non-linearparameters (see p. 2-189). Typicalactuators have stiffnessesbetween 1 and 2,000 N/μm andcompressive limits between 10and 100,000 N. If the unit will beexposed to pulling (tensile) forces,ResolutionPiezoceramics are not subject tothe “stick slip” effect and thereforeoffer theoretically unlimitedresolution. In practice, the resolutionactually attainable is limitedby electronic and mechanical factors:a) Sensor and servo-control electronics(amplifier): amplifier noiseand sensitivity to electromagneticinterference (EMI) affect the positionstability.b) Mechanical parameters: designand mounting precision issuesFig. 2b. Custom linear drivewith integratedNEXLINE ® Piezo-Walk ® piezomotorPiezoelectrics in PositioningNanometrologyMicropositioningIndexFig. 2a. Ultrasonic piezo linear motorsFig. 3. Example of a compact piezonanopositioning and scanning systemwith integrated flexure guidance,sensor and motion amplifier2-179