Patent ID: 8227744

Claim:
An absolute position length measurement type encoder comprising: a light-emitting element; a scale which has an absolute pattern based on a pseudorandom code and forms bright and dark patterns by the absolute pattern with respect to projection light from the light-emitting element; a light-receiving element for receiving the bright and dark patterns; a binarization circuit for dividing a digital signal in accordance with a signal output from the light-receiving elements into a mode having high brightness and a mode having lower brightness, carrying out a binarization process by a threshold value where dispersion with regard to the two modes is maximized, and decoding the pseudorandom code at the unit of minimum line width of the absolute pattern from the binarized values, wherein the binarization circuit obtains the respective total numbers of the binarization values at a cycle of the minimum line width of the absolute pattern, and determines and decodes the code of the minimum line width by the value the total number of which is greater; and a position detection circuit for calculating the absolute position of the scale with respect to the light-receiving element by acquiring the correlation between the decoded pseudorandom code and the design value of the pseudorandom code; wherein the scale comprises an absolute pattern and an incremental pattern.