Improved Angle Calculation Method of Magnetic Absolute Encoder with Different Magnetic Flux Densities

Abstract

This paper proposes an angle calculation method to improve the accuracy of a magnetic absolute encoder with different magnetic flux densities (MAE-DMFD). Magnetic encoders have a conflicting relationship between the absolute angle calculation and high resolution. The MAE-DMFD is a magnetic absolute encoder that is proposed to solve the relationship. It can achieve both multipolarity and absolute angle calculation by using a magnet with magnetic force difference inside the encoder to characterize the magnetic force signal. However, the angle calculated with a magnetic force difference by the characterized magnetic force signals is greatly affected by external disturbances such as harmonics and observation noise. Additionally, the conventional angle calculation system of the MAE-DMFD uses second-order phase-locked loops (SO-PLLs) based on orthogonal signals. To use SO-PLLs, the steady-state estimation error should occur when the operating velocity changes. Therefore, this paper proposes an improved angle calculation method that considers disturbances, noise, and estimation error. The proposed method uses a higher-order PLL to compensate for the steady-state error and applies an adaptive filter to the orthogonal signal to consider the effects of noise and harmonics. The proposed method can efficiently remove noise, harmonics, and angle estimation errors. The effectiveness of the proposed method is demonstrated on an actual MAE-DMFD.