High resolution processing of position sensor with amplitude modulated signals of servo drive
M. G. Tiapkin, A. P. Balkovoi · 2017
An integral part of modern servo drive is a position measuring system. This article is focused on processing of resolvers and capacitive sensors signals, whose quadrature output signals are the modulated in double-sideband amplitude modulation. Well known, the disadvantage of the amplitude modulation is low noise immunity. One of the sources of the noise is switching of power transistors of inverter. This noise can leads to reduction of position feedback resolution and bandwidth. The article presents the high resolution and high bandwidth signal processing algorithm. The proposed algorithm suggests the choice of the sensor excitation frequency, based on the analyze of the noise spectrum of the inverter pulse-width modulation frequency, and includes fast synchronous demodulation and adaptive observer-based converter to estimate the feedback position. The proposed demodulation method allows sampling and demodulating of sensor signals with frequency limited only by conversion and processing time of analog-to-digital converter. The adaptive observer-based digital part of measuring system compensates the phase lag of demodulated signals and increases position feedback resolution for a given system dynamics. The proposed method was implemented in the planar servo drive with the capacitive position measuring system. The result demonstrates the 15 bit resolution into 640 μm signal period and 1 kHz bandwidth of position feedback with excitation frequency of 12 kHz.