Precision Position Measurement of PMSLM Based on ApFFT and Temporal Sinusoidal Fringe Pattern Phase Retrieval

To improve the accuracy of the mover position detection with longer measurement range, a linear motor displacement measurement method is proposed based on digital image measurement and temporal sinusoidal fringe pattern phase retrieval. A simple computer-generated sinusoidal fringe pattern is designed as the target image, and sequences of fringe signals are recorded by a line scan camera that moves with the linear motor. Fourier phase analysis is employed to extract the initial phase of each signal curve, and then temporal phase unwrapping is applied to reconstruct the mover displacement evolution according to the system magnification parameter and fringe width. This method removes the phase ambiguity problem of traditional temporal phase analysis, and can be used in complex motion of permanent magnet synchronous linear motors. To suppress the spectrum leakage of fast Fourier transform (FFT), all-phase FFT with double Hanning windows is used to improve the detection accuracy of initial phase and fringe width. Simulation and experimental results demonstrate that the proposed method can estimate the mover position with longer measurement range precisely and robustly under different working conditions.