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Digital Controllers Provide Precision, Dynamics and Ease of Operation

Digital Controllers Provide Precision, Dynamics and Ease of Operation
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Digital Controllers Provide Precision, Dynamics and Ease of Operation Digital piezo controllers have several advantages over analog servo circuits: Linearity and settling behavior can be specifically influenced by digital algorithms allowing much greater flexibility than analog circuits. The result is higher precision and better dynamic performance. Linearization of the Electronics With digital servo controllers it is possible to upload calibration data quickly and remotely. PI piezo stages can store optimized parameters in an ID chip. With this combination, controllers and mechanics can be swapped without performance losses, because the controller recognizes the mechanics and reads specific linearization and calibration data when it is powered up. Modular, digital multi-axis controls with integrated coordinate transformation simplify the operation of complex parallelkinematics systems, such as this Hexapod with NEXLINE® piezo stepping drives Controllers and Servo Techniques The task of a servo loop is to correct deviations between the actual position and the target position. Commonly, this is done with P-I (proportional-integral) controllers. Depending on the application, however, advanced control techniques in combination with linearization algorithms can yield better results. Digital filters avoid undesired mechanical excitation, suppress noise and, with that, increase the resolution and system bandwidth. Linearization of the Mechanical System Target Value + Slew Rate Block diagram of a digital piezo servo controller Low-Pass Filter The linearity of the entire system is one criterion for its positioning accuracy. Piezo actuators typically show a nonlinearity of 10 to 15%, which has to be compensated by the control loop. Digital controllers use higher-order polynomials to reduce the motion nonlinearity to values below 0.001%, which, for a typical travel range of 100 μm, corresponds to an accuracy of one nanometer and better. Band-Stop Filter Sensor Electronics

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Digital Controllers Provide Precision, Dynamics and Ease of Operation - 2

Dynamic·Linearization: Following a Moving Target Elliptical scan (for laser micro bore applications) with an XY piezo scanning stage and conventional PID controller. The outer curve shows the desired position, the inner curve shows the actual motion The same scan as before but with a DDL controller. The tracking error is reduced to a few nanometers, target and actual position cannot be distinguished in the graph Dynamic digital linearization (DDL) reduces the dynamic tracking errors of periodic trajectories. This is relevant for scanning applications, where a specific position must be...

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Digital Controllers Provide Precision, Dynamics and Ease of Operation - 3

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