Patent ID: 7319526
Filing Date: 2008-01-15
Classification: G01D

Abstract:
1. A displacement detection apparatus, comprising: a main scale having a main diffraction grating; and a detection head adapted to move relative to the main scale, the detection head detecting a displacement amount relative to the main scale, the detection head comprises: a light emission/reception unit that has a light source emitting coherent light, and photodetectors receiving light diffracted by the main scale; a first diffraction grating that diffracts and splits the light from the light source into at least two diffracted light beams of different orders; a second diffraction grating that diffracts and deflects the light beams diffracted by the first diffraction grating such that the light beams are projected on a first spot of the main scale; a third diffraction grating that diffracts and reflects the diffracted light beams from the first spot of the main scale such that the light beams are projected a second time onto a second spot of the main scale; and a multiplexing section that multiplexes the diffracted light beams from the second spot of the main scale, such that the multiplexed light beams interfere with each other.