Patent ID: 7227125

Claim:
An encoder device comprising: a first array that includes first through fourth photodiodes adjacent to each other in an X direction, each of the first through fourth photodiodes having a length of X 1 in the X direction; a second array that includes fifth through eighth photodiodes adjacent to each other in the X direction, and is adjacent to the first array in a Y direction perpendicular to the X direction but displaced by X 1 /2 in the X direction relative to the first array, each of the fifth through eighth photodiodes having a length of X 1 in the X direction; a slit member that includes light transmitting sections and light shielding sections alternately arranged, and is movable in the X direction, each of the light transmitting sections and the light shielding sections having a length of 2×X 1 in the X direction; and a logic circuit that generates a first detection signal from output signals of the first through fourth photodiodes that have received lights passing through the light transmitting sections, and a second detection signal from output signals of the fifth through eighth photodiodes that have received the lights passing through the light transmitting sections, a phase of the second detection signal being shifted by a ¼ period of the first detection signal relative to the first detection signal.