Encoder fault tolerance method based on angle residual observer

In high-precision position servo systems, damage to the absolute photoelectric encoder disk can cause faults in the angle bit signals, adversely affecting system performance and leading to current distortion. To address the issue in traditional correction strategies where angle differentiation includes normal variations caused by rotational speed—thereby reducing the effectiveness of fault correction —an encoder fault-tolerant method based on an angle residual observer is proposed in this paper. Firstly, the angular variations under three typical bit fault modes are analyzed, and correction value expressions are derived. Secondly, an angle residual observer is designed to reduce the normal variation component in estimation errors. Finally, by compensating the differential value using the residual, a fault correction method is developed. Simulation and prototype experimental results demonstrate that the proposed method effectively corrects encoder bit faults under various rotational speeds and suppresses motor current distortion. The proposed approach enhances the adaptability of fault tolerance and is conducive to online real-time implementation.