Piezo-based nanopositioning systems are known for their high precision. However, this is not self-evident since the motion characteristics of piezo actuators are by no means linear. This must be compensated by suitable control.
In this case, digital controllers are usually the best choice, especially since high-performance devices are now available on the market that do not cost any more than an analog controller. They are just as fast, but at the same time, they offer advanced servo algorithms. An example of this is the new E-727 three-channel digital controller from PI (Physik Instrumente).
The high-resolution AD/DA converter and piezo amplifier can be considered as a genuine "People's Controller" for all piezo actuator nanopositioning systems, irrespective of whether these work with capacitive, piezo-resistive or strain sensors.
A PI controller with two notch filters optimized for piezo operation allows a high control bandwidth (25 kHz). Intelligent servo algorithms minimize the settling times, which allows repeatability into the subnanometer range. Further highlights of the digital controller include 4th order polynomial linearization for the mechanics and electronics, an integrated data recorder, an ID chip for fast start-up and quick exchange of the system components as well as subordinate, programmable drift compensation.
In addition, there is the option of dynamic digital linearization. This DDL function lowers phase shift and trajectory errors in the case of dynamic-periodic applications to an indiscernible level.
This is particularly important for scanning applications, where a specific position needs to be identified and then approached with high precision. The piezo controller is commanded via the digital SPI, USB and RS-232 interfaces. In addition, there are four respective analog inputs and outputs for set-point values, sensor signals or external amplifier as well as four respective digital inputs and outputs. The extensive software package also includes drivers for LabVIEW as well as libraries for Windows and Linux.