Integration of a grating-image-type encoder is proposed and the sensor for the encoder has been fabricated using Si micromachining technology. The sensor consists of the Si grids with line photodiodes, light emitting diode (LED) and signal amplifier. The Si grids works as the photodetectors as well as the object and index gratings. The incoherent light emission through the Si grids and the light detection with the grids make the optical system compact. Phase change of the signal is caused by the translation of the grating image on the Si grids. Two phase-shifted signals are generated by installing two sets of photodiodes on the Si substrate with a corresponding spatial displacement. Two types of grating structures are fabricated for the practical sensors. The signal contrast is high enough for the displacement measurements at a large air gap.
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