Patent ID: 6407378
Filing Date: 2002-06-18
Classification: G01D

Abstract:
An encoder device comprising:a main scale with a plurality of slit-like openings at regular intervals; light-emitting means for emitting and directing light toward the main scale; light-receiving means including four light receiving members for receiving light emitted from the light-emitting means via the slit-like openings in the main scale; and means for obtaining information concerning displacement of the main scale by using output signals output from the light-receiving means, the first light-receiving member and the second light-receiving member disposed with respect to the slit-like openings of the main scale so as to have substantially the same phase, the third light-receiving member and the fourth light-receiving member disposed with respect to the slit-like openings of the main scale so that a first differential output signal, obtained by differentially amplifying an output signal output from the first light-receiving member and an output signal output from the third light-receiving member, and a second differential output signal, obtained by differentially amplifying an output signal output from the second light-receiving member and an output signal output from the fourth light receiving member, have the same period, and further, the first differential output signal and the second differential output signal have a predetermined phase difference wherein the light-emitting means has a lens for emitting light in substantially parallel beams, a central axis of the lens being positioned along a line midway between the first light-receiving member and the second light-receiving member.