Patent ID: 7034948

Claim:
A displacement pickup comprising: a first reading means for emitting a beam of light to diffraction gratings and reading a return component of light from the diffraction gratings; a first phase detecting means for detecting a first phase on the basis of the return component of light detected by the first reading means; a second reading means for emitting a beam of light to diffraction gratings and reading a return component of light from the diffraction gratings; a second phase detecting means for detecting a second phase on the basis of the return component of light detected by the second reading means; a phase comparing means for making a comparison between the first and second phases; an origin signal generating means for producing an origin signal on the basis of the result of comparison from the phase comparing means; and a scale having defined thereon a first area in which diffraction gratings are recorded with a predetermined pitch and from which the return component of light from the diffraction gratings is read by the first reading means, and a second area in which diffraction gratings are recorded at a predetermined pitch different from the diffraction grating pitch in the first area and from which the return component of light from the diffraction gratings is read by the second reading means, the scale being displaceable in a direction in which the return component of light from the diffraction gratings is read by the first and second reading means, the first and second areas being defined on the scale to be displaceable an equal distance in the same measuring direction; and a position for reading, by the first reading means, the positional information recorded in the first area and a position for reading, by the second reading means, the positional information recorded in the second area being in line with each other in the measuring direction.