Position Self-Sensing for Electrostatic Motors Under Amplitude-Modulated AC Operation

In a previous study, displacement self-sensing using driving current has been proposed for a synchronous-type macroscale electrostatic motor under alternating current (ac) operation; however, it cannot be used in practice due to its low noise immunity. This work improves the position self-sensing method for electrostatic motors under amplitude-modulated ac operation, in which the driving signal is amplitude-modulated using a high-frequency carrier signal. The modulation transfers the signal frequency to a higher region, which results in a much larger driving current and high noise immunity. In the modified self-sensing method discussed in this work, the high-frequency signal is demodulated, and then the slider displacement information is distilled through Clarke and Park transformations. The systematic error of the method is discussed to show that it depends on the performance of the cutoff frequency of the low-pass filter (LPF) in demodulation. Theoretical analysis shows that the accuracy is possibly improved by decreasing the cutoff frequency of the LPF. Simulation results confirmed that the noise immunity of this modified self-sensing method is much higher than that of the previous method, which means it can be used in practice. Verification experiments have been done under various conditions by using prototype electrostatic motors, which validated that the modified self-sensing method realizes a high accuracy/resolution of around
$20\,\mu$
m in practical situations.