ANGULAR POSITION SENSOR WITH SEMICIRCULAR SHIELDING PLATE

摘要

An angular position sensor, especially for use in a galvanometric scanning system, and including a sectorized photodetector with an illumination shielding plate attached to a shaft whose rotation is to be sensed. The photodetector has two opposed sectors, preferably disposed diametrically opposite each other, such that incident illumination from a source is differentially modulated by rotation of the shielding plate. In addition, at least a third sector is provided which is always illuminated by the source regardless of the rotational position of the shielding plate. The output from the diametrically opposed sectors is used to determine the rotational angle of the shaft, while the output from the third sector is used to stabilize the illumination source, such that the output of the two opposed sectors of the detector is insensitive to changes in temperature.