Composite Filter Design and Application to Piezo-driven Stage Systems

This paper presents a design approach for composite filters based on the displacement and acceleration sensor signals to cover the entire frequency range of motion in the plant. A target piezo-driven stage is installed the capacitive sensor to detect the accurate stage displacement, while the sensing system generally includes the phase delay due to the data conversion process and the lowpass filters in the amplifier to remove the sensor noise. In this paper, MEMS accelerometer signal is integrated into the displacement signal detected by capacitive sensor to improve the phase characteristic at high frequency range, where the composite filters for integrating two sensor outputs are generally designed considering a summation result as 1. According to the sensor characteristic, however, a simple filter design approach causes the deterioration of the output characteristic by the interference. In order to solve the problem, PQ method as a filter design guideline is adopted to compensate for the interference between the sensor outputs. The effectiveness of the design approach has been verified by experiments using the piezo-driven stage system.