Design and development of an optical encoder with sub-micron accuracy using a multiple-tracks analyser grating.

In this paper, an optimized optical encoder based on generalized grating imaging is presented. A multiple-tracks analyser grating is proposed to eliminate the second and third harmonic signals, and a photodiodes array with optimized cell width is used to suppress the fifth harmonic signal. The photodiodes array also guarantees the consistency and stability of the encoder signals benefiting from single-field photoelectric scanning. High-quality encoder signals are expected to be obtained from the above optimization, thereby ensuring high encoder accuracy. In the experiment, measured encoder signals with the approximately ideal Lissajous figure are obtained. FFT analysis of the encoder signals shows that the second, third, and fifth harmonic distortions are smaller than 0.3%, 0.5%, and 0.1%, respectively. The calibration results of the optical encoder show that the positioning error within one signal period is ±0.12 μm, and the positioning error over 150 mm measuring range is within ±0.2 μm.