Total error compensation of non-ideal signal parameters for Moiré encoders

Abstract Non-ideal encoder signal parameters generally include amplitude imbalance error, quadrature phase error, dc-offset error and harmonic distortion. These non-ideal signal parameters are the main cause of nonlinear interpolation errors for Moire encoders. In this paper, a total error compensation strategy for correcting these non-ideal signal parameters is presented. The compensation strategy consists of a passive compensation stage and an active compensation stage, which are realized through hardware and software means, respectively. In the passive compensation stage, an optimized scanning grating with specified micro-pattern is employed to suppress the harmonic distortion. In the active compensation stage, an adaptive compensation algorithm is proposed to compensate the remained amplitude imbalance error, quadrature phase error and dc-offset error. In the experiment, a Moire encoder using the optimized scanning grating is developed, and a digital circuit is designed by implementing the adaptive compensation algorithm into a field-programmable gate array (FPGA). The effectiveness of the total error compensation strategy has been validated by experimental results.