Embedded Position Detecting Method for Permanent Magnet Linear Motor Systems

Abstract

An embedded position detecting method for permanent magnet linear motors was proposed. The pair of magnetoresistance sensors was employed as a position detector for sensing the periodical magnetic induction intensity from built-in permanent magnets. A composited travelling wave signal, whose phase shift was proportional to the measured displacement, was produced by adding two induced standing wave signals. The series of clock pulses with equal spatial equivalent were employed to dynamically interpolate the phase difference between the reference signal and the travelling wave signal. Differing from the arctangent calculation for sine and cosine signals of traditional displacement sensors, the proposed embedded position detecting method could reach dynamically high resolution using the interpolation technique. Furthermore, sensing parameters were optimized to obtain much finer induced displacement signals, and the error analysis was discussed. The experiment results prove that after the error correction, the measuring accuracy reached -49.8 μm~43.8 μm within the travelling range of 120 mm, and the resolution reached 0.15 μm. Compared with some traditional displacement sensors and various sensorless methods, the proposed embedded position detecting method had simple implementation and reasonable accuracy with the most cost-effective hardware, which had shown a significant promise in permanent magnet linear motors.