PURPOSE: To obtain a less-distortion sine wave even if the light and dark part ratio of a stripe pattern on a scale is not 1:1, by providing a means of regulating the gap between the scale and a photodetecting means having a mask plate.
CONSTITUTION: Light from an infrared light emitting diode 2 is reflected by a scale 1 having a light and dark stripe pattern with pitch L and detected by a phototransistor 3. Said diode 2 and phototransistor 3 are constituted by using a united photoreflector, and a mask plate 4 having a slit of L/2 is provided on the photodetection surface. The gap between the mask plate 4 and scale 1 is adjusted by turning an adjusting screw 11 provided to an encoder moving means 10 to control the level of light incidents to the phototransistor, thus obtaining a less-distortion sine wave.
WAKABAYASHI NORIAKI
ONODERA HIROMI
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