Position detection device

A position detection device for detecting an absolute position based on an image signal converted by a light-receiving element for receiving light irradiated from a light source toward a scale having a code pattern, the position detection device comprising:

• an edge detection unit for detecting edges by binarizing the image signal converted by the light-receiving element;
• an edge evaluation unit for performing a validity determination based on a comparison between a bit period, which is a width corresponding to one bit of the code pattern marked on the scale, and a position of each of the edges detected by the edge detection unit;
• a code string generation unit for generating a code string from the edges determined as being valid based on results of the validity determination performed by the edge evaluation unit;
• a coarse position calculation unit for calculating a position in bit period units as coarse position data by comparing and performing a correlation calculation between the code string generated by the code string generation unit and the code pattern;
• a phase calculation unit for calculating, based on the results of the validity determination performed by the edge evaluation unit, a phase, which is a relative deviation of the bit period or less, as phase data based on a distance between the positions of the edges determined as being valid and a bit period position, which is a reference position in bit period units generated based on the bit period;
• and
• an absolute position calculation unit for calculating the absolute position by adding the coarse position data calculated by the coarse position calculation unit and the phase data calculated by the phase calculation unit.