Patent ID: 8022354

Claim:
An absolute position length measurement type encoder, comprising: a light-emitting element; a scale having an absolute pattern based on a pseudorandom code and forming bright and dark patterns by the absolute pattern on the projection light from the light-emitting element; a light-receiving element for receiving the bright and dark patterns; an edge position detection circuit for obtaining a position, at which an after-differentiated absolute value of a binarized value is locally maximized, for each of the minimum line width zones of the absolute pattern by binarizing a digital signal in accordance with a signal output from the light-receiving element; a peak position detection circuit for preparing a histogram for the position where the absolute position is locally maximized in the minimum line width zone and for obtaining the peak position from the histogram; a decoding circuit for decoding pseudorandom codes based on the binarized value; a position detection circuit for calculating the absolute position of the scale in regard to the light-receiving element by referencing the decoded pseudorandom code with respect to the design value of the pseudorandom code; and a position data synthesizing circuit for correcting the absolute position of the scale, which has been obtained by the position detection circuit, by the peak position.