Positioning stages using piezoelectric stack actuators (PEA) have very high resolution. However, it is difficult to achieve precise dynamic motion tracking using traditional linear controllers such as PID due to the inherent hysteresis nonlinearity of piezoelectric materials and the phase lag associated with such controllers. Capacitance Sensors are ideal for measuring the actual piezo stage position and correcting for the inherent nonlinearity through closed loop feedback. They have the stability, bandwidth and high resolution needed to do the job.
Several of MTI’s capacitive products are available depending on the type of interface needed. All the amplifiers use similar type probes. Select range needed from the probe brochure.
MTI Accumeasure 9000 has up to two channels of analog positioning measurement capability. The amplifier has a built in universal power supply. Select loop bandwidth filters at the time of order.
MTI AS-500 is a multi channel rack system with up to 6 channels of measurement capability using the AS-563 PA amplifier boards. It has a built in universal power supply Select loop bandwidth filters at the time of order.
MTI Microcap boards are a small OEM style board with 1 channel of analog measurement capability. No power supply is included (±15VDC needed).
MTI’s New Digital Accumeasure is also capable of measuring the actuator position and using its digital output to directly communicate with a digital PID control loop (National Instruments or equivalent ) and HV amp to position the stage. The Digital Accumeasure has digitally controlled filters (5kHz through 1Hz ) and digitally controlled measuring ranges to fine tune the system and adjust the closed loop bandwidth. Presently the inherent latency is 1 ms but MTI is working to further reduce this.