| 摘要 |
An encoder for accurately determining the position of one body relative to another consists of an optical mask carried by one body which moves through the focal point of a concave reflector carried by the other body. The reflector produces an image of the mask in the same plane of the mask and the mask and its image together produce positional information which is utilized by a photo-sensitive detector. The optical pattern of the mask is arranged such that the detector receives constant variations in the levels of illumination as the mask moves.
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