Control of Piezo Act u ators an d Stages

Position Servo-Control

Piezo actuators Piezo Actuators Nanopositioning & Scanning Systems Nanopositioning & Scanning Systems Active Optics / Steering Mirrors Active Optics / Steering Mirrors Tutorial: Piezo- electrics in Positioning
Tutorial: Piezo- electrics in Positioning Capacitive Position sensors Capacitive Position Sensors Piezo Drivers & Nano- positioning controllers Piezo Drivers & Nano- positioning Controllers Hexapods / Micropositioning Hexapods / Micropositioning Photonics Alignment Solutions Photonics Alignment Solutions Motion controllers Motion Controllers Ceramic Linear motors & Stages Ceramic Linear Motors & Stages
Fig. 27. Variety of digital piezo controllers. Index Index

Position servo-control elimi-nates nonlinear behavior of piezoceramics such as hystere- sis and creep and is the key to highly repeatable nanometricmotion.PI offers the largest selection ofclosed-loop piezo mechanisms and control electronics world- wide. The advantages of posi- tion servo-control are: High linearity, stability, repeatability and accuracy Automatic compensation for varying loads or forces Virtually infinite stiffness (within load limits) Elimination of hysteresis and creep effectsPI closed-loop piezo actuatorsand systems are equipped with position measuring systems providing sub-nanometer reso-lution, linearity to 0.01 %, and bandwidths up to 10 kHz. A servo-controller (digital or ana- log) determines the output voltage to the PZT ceramics by comparing a reference signal (commanded position) to theactual sensor position signal(see Fig. 28).For maximum accuracy, it isbest if the sensor measures the motion of the part whose posi- tion is of interest (direct metrol-ogy). PI offers a large variety ofpiezo actuators with integrated direct-metrology sensors. Capacitive sensors provide the best accuracy (see section 5, “Capacitive Position Sensors”). Simpler, less accurate systemsmeasure things like strain indrive elements.

Fig. 29. Closed-loop position servo-control. For optimum performance, the sensoris mounted directly on the object to be positioned (direct metrology). Fig. 28. Block diagram of a typical PI closed-loop piezo positioning system.

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