A self-compensation algorithm for Electromagnetic Rotary Encoder with unbalanced installation

An electromagnetic rotary encoder (ERE) is a kind of angular sensors using magnetic effects to measure angular positions. It is widely used in many industrial control systems because it has many advantageous characteristics: low cost, simple structure, work in a harsh environment, and high reliability. However, the output signal of ERE is always disturbed by magnetic leakage caused by the inappropriate installation of ERE. To address this problem, the paper proposed a self-compensation algorithm for induced signal which contains two parts: the first part is determining the angle positions apart from 180 electrical-degree each other by constructing the ideal output signal by the difference between the sensor output signals of the two adjacent positions, and establishing the equations of the induced voltage at both positions to obtain the residual signal induced by the electromotive force generated by the leakage flux. The second part is employing the least square method for estimating the amplitude, phase, and offset of the residual voltage. In order to verify the algorithm, the experiments of the sensor in the unbalanced installation situation are carried out, and the signal compensation algorithm is then implemented based on ERE and the high accuracy optical encoder. The experimental results show that the unbalanced installation produces a systematic error of the rotation angle and the proposed algorithm can effectively reduce the systematic errors.