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

Piezo • Nano • PositioningControl of Piezo Actuators and StagesPosition Servo-ControlPosition servo-control eliminatesnonlinear behavior ofpiezoceramics such as hysteresisand creep and is the key tohighly repeatable nanometricmotion.PI offers the largest selection ofclosed-loop piezo mechanismsand control electronics worldwide.The advantages of positionservo-control are:Fig. 27. Variety of digital piezo controllers High linearity, stability,repeatability and accuracy Automatic compensation forvarying loads or forces Virtually infinite stiffness(within load limits) Elimination of hysteresisand creep effectsPI closed-loop piezo actuatorsand systems are equipped withposition measuring systemsproviding sub-nanometer resolution,linearity to 0.01 %, andbandwidths up to 10 kHz. Aservo-controller (digital or analog)determines the outputvoltage to the PZT ceramics bycomparing a reference signal(commanded position) to theactual sensor position signal(see Fig. 28).For maximum accuracy, it isbest if the sensor measures themotion of the part whose positionis of interest (direct metrology).PI offers a large variety ofpiezo actuators with integrateddirect-metrology sensors.Capacitive sensors provide thebest accuracy (see “Nanometrology”p. 3-1 ff ). Simpler,less accurate systems measurethings like strain in drive elements.Linear Actuators & MotorsNanopositioning / PiezoelectricsPiezo Flexure Stages /High-Speed Scanning SystemsLinearVertical & Tip/Tilt2- and 3-Axis6-AxisFast Steering Mirrors /Active OpticsPiezo Drivers /Servo ControllersSingle-ChannelMulti-ChannelModularAccessoriesPiezoelectrics in PositioningNanometrologyMicropositioningIndexFig. 28. Block diagram of a typical PI closed-loop piezo positioning systemFig. 29. Closed-loop position servo-control. For optimum performance, the sensoris mounted directly on the object to be positioned (direct metrology)2-199