When choosing the controller which best fits your application, first consider the number of axes that the piezo stage will have. A controller must be selected with an equal amount of channels to axes of the stage. For example, an XYZ stage would require a three channel controller while a tip/tilt stage a two channel. Each channel of the controller is used to communicate the necessary details to one axis of the stage. nPoint controllers are available with up to three channels in the LC.400 series and six with the C.400 series.
LC.400 Series Closed-loop Controllers
A controller is necessary for closed-loop control. It provides different feedback to the piezo every 24 microseconds, at the same time the sensor provides position data to ensure the stage is moving to the commanded position. A piezo driver can be used for applications where only open-loop control is required. Open-loop control can be used for applications where the user “closes the loop” or in applications where accuracy and hysteresis are not an issue. Piezos can experience creep and hysteresis, therefore commanded position could be off 10% or more without closed-loop control. During the production process, calibration of the piezo stage with the controller ensures linearization better than 99.97% over the entire range of travel. This helps ensure precision scanning and sample positioning.
C.400 Series Closed-loop Controllers
PC software can be used with the DSP controller to get the most out of a nanopositioning system. PID controls along with advanced control software allow a reduction in settling time and with a load necessary to the application. If you are interested in learning more about advanced control settings please watch this video on control loop tuning. In the video you can see the advanced control settings that include two notch filters per axis as well as a 2nd integrator. Certain applications that include high speed scanning may require greater current outputs to ensure the scanning speeds are not current limiting. The current required can vary by scan speed and stage design and is a factor to consider when determining what controller package is the best fit for your application.
The nanopositioning controller is an important piece of the nanopositioning system. It provides closed-loop control, powers the stage, and allows an interface for system integration. Advanced control electronics can help scan at high speeds and with custom loads. By connecting the correct controller and piezo stage it is possible to get a high spec nanopositioning system that enables today’s advanced applications.
