APC vs. PID Servo Control Algorithm
An alternative control concept to PID is available for the modular E-712 controller for nanopositioning systems: Advanced Piezo Control. It is based on a state controller which, in turn, is based on a model of the positioning system. Advanced Piezo Control actively damps the resonance frequency, in contrast to conventional PID controllers with notch filter where the mechanical resonance is cut out of the excitation spectrum.
Advanced Piezo Control provides faster settling times and lower sensitivity with respect to interferences from the outside. The phase trueness is significantly improved compared to the damping with one or even two notch filters. This has immediate effects on the trajectory trueness and the settling response.
Limitations: If the mechanical system has too many resonances close together, or if the resonance frequency to be damped is about 1 kHz or more, the state controller in this form no longer has any advantage over conventional PID controllers. Learn more on advanced control algorithms
The operating limits of a linear piezo amplifier depend on the amplifier power, the amplifier design, and last but not least, the electrical capacitance of the piezo mechanism. For dynamic applications, piezo mechanisms require high charge and discharge currents. Those requirements are best met by power amplifiers that can source and sink high peak currents. The average current is usually of secondary importance. For exact information on maximum operating frequency with a given piezo load refer to the individual operating limits graphs in the PI product spec sheets.
Open-loop operating limits data for PI piezo power amplifiers are tested 15 minutes of continuous operation at room temperature. At power up, (cold conditions) the maximum operating frequency can be higher.
The indicated capacitance values for piezo actuators and mechanisms in PI datasheets are small-signal values (measured at 1 V, 1000 Hz, 20 °C, no load). The capacitance of piezo ceramics changes significantly with amplitude, temperature, and load, up to approximately 200% of the unloaded small-signal capacitance at room temperature. Therefore, the operating limits graphs actually reflect a significantly higher load to the amplifier compared to what a standard capacitor of the same value would represent.
More information is available in the tutorial on the PI Ceramic website