Matsushita Electric Industrial Co., Ltd.

Yutaka Masuda

Norio Okutani

A method and apparatus for simultaneously detecting and comparing a plurality of upper patterns indicative of Gray code patterns and having greater pattern pitches and a plurality of lower patterns indicative of pure binary code patterns and having smaller pattern pitches to correct the upper pattern detection data and thereby detect an absolute position. An absolute position detecting apparatus includes a code plate formed with a plurality of upper patterns and a plurality of lower patterns which are arranged radially along the periphery of a rotating body; a mask arranged at a position opposite to the code disc and having a plurality of upper slits and a plurality of first slits and a plurality of second slits which are formed to correspond to the lower patterns and having a 90-degree phase difference therebetween; a laser light source arranged at a position on the opposite side of the code plate to the mask to illuminate the code plate to form pattern projection images on the mask; a light detector for detecting the pattern projection images to detect positional alignment between the patterns and the slits; and data processing circuit for correcting detected data of the upper patterns by referring to those of the lower patterns.

Absolute position detecting method and apparatus therefor

A reference signal generation apparatus for a position detector is disclosed in which a plurality of signals having peaks at predetermined intervals are produced from the light transmitted through slit rows of random patterns and a plurality of light detectors for detecting the same light, thereby producing a reference signal in the vicinity of maximum and minimum values of the difference signal between the output signals of the light detectors.

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Hirakata, Japan

Yutaka Masuda