Patent ID: 8110792

Claim:
An absolute position length measurement encoder comprising: a scale in which an absolute (ABS) pattern based on a pseudorandom code is provided; a light-receiving element for receiving bright and dark patterns formed by the scale, the light receiving element including an ABS light-receiving element array having an array interval P PDA ; and a signal processing circuit for processing signals sublected to output of the light-receiving element and measuring an absolute position of the scale to the light-receiving element; wherein the signal processing circuit includes a space-dividing number conversion circuit that obtains a smaller interval D than the array interval P PDA of the ABS light-receiving element array of the light-receiving element, and simultaneously obtains and outputs a digital value for each interval D sublected to output of the ABS light-receiving element array; wherein the signal processing circuit further includes a correlation circuit for executing arithmetic operations for correlation between the digital value subjected to output of the space-dividing number conversion circuit and a design value of the pseudorandom code; wherein a digital value subjected to arithmetic operations for correlation by the correlation circuit is made into a value binarized by a unit of a minimum line width P ABS of the ABS pattern; and wherein the signal processing circuit comprising; in an input side of the correlation circuit, an edge position detection circuit for first binarizing a signal output from the space-dividing number conversion circuit; a peak position detection circuit for preparing a histogram with respect to a position where a value obtained from a signal differentiated and made into an absolute value after being binarized becomes a local maximum value, for each of the minimum line width P ABS of the ABS pattern and for obtaining a peak position PK from the histogram; and a decoding circuit for processing the peak position PK based on the binarized value of a signal as the position where the pseudorandom code to be decoded is changed over; and in an output side of the correlation circuit, a position data synthesizing circuit for obtaining an accurate absolute position, with respect to a before-ABS-correction position signal output from the correlation circuit, through position correction by shifting the absolute position only by the peak position PK by means of a peak position signal obtained by the peak position detection circuit.