Encoder Calibration Method for High Precision Servo Systems with a Sinusoidal Encoder

Abstract

The sinusoidal encoder is used as an absolute position (velocity) transducer to implement the position (velocity) of actuators in many industrial applications. However, the performance of the position (velocity) may be degraded due to non-ideal factors such as differential amplitudes of the encoder signals, offset, and phase shift. To analyze this problem, we formulate the relationship between the coefficients of ideal signals and the non-ideal signals characteristic, which is an ellipse formed by plotting the encoder signals versus each other. In this paper, we propose non-ideal signal calibration for the imperfect components of existing sinusoidal signals to improve position (velocity) regulation performance. The fictitious cosine function is used to detect the phase shift between the sine and cosine signals, and it can be designed by using the frequency of sinusoidal signals. The proposed method is validated by simulation and experimental implementation, showing noticeable improvement in estimating non-ideal signal components, Lissajous error curve, phase distribution, and the position (velocity) error signal. Experimental results show that the proposed method is able to obtain the components of the non-ideal signals and the accurate position (velocity) with a small error in real-time, while other calibration methods are difficult to apply to fast motion.