Importance

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Abstract

A photoelectric displacement detecting apparatus for measuring a length from a repeated number of bright and dark portions of light formed by the repetitions of overlappings of slits in respective slit rows during a relative movement between a main scale and an index scale, the apparatus comprising reference marks provided on the main scale at suitable intervals, a mark detecting device provided on the index scale, identification marks provided in spaces between the reference marks for identifying these spaces, and an identification mark reading device actuated by the mark detecting device. An identification mark ascertaining device is provided for comparing the identification mark read by the identification mark reading device with the identification mark preset by a mark selecting-setting device and ascertaining whether both identification marks coincide with each other or not. The apparatus further comprises an origin setting device for making the position of the detected reference mark to be the length measuring origin on condition of a coincidence signal from the identification mark ascertaining device and the mark detection signal from the mark detecting device immediately after the input of the coincidence signal.

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First Claim