Patent ID: 7480060
Filing Date: 2009-01-20
Classification: G01D

Abstract:
1. An optical position encoder, comprising: a light source operative to generate a source light beam having a beam width; a scale including a diffractive scale pattern extending in a direction of relative motion of the scale with respect to the light source; an optical detector adjacent to the scale; and first and second spaced-apart diffraction gratings between the light source and the scale, the first diffraction grating having a location at which the source light beam is incident; wherein the diffraction gratings and scale are mutually configured and cooperative to spatially separate +/− 1st diffraction orders from other diffraction orders and to direct the +/− 1st diffraction orders as respective optical beams along respective optical paths, the optical paths (i) diverging from the location of the first diffraction grating to respective locations of the second diffraction grating, the respective locations being separated by more than the beam width, (ii) converging from the respective locations on the second diffraction grating to an area of the scale adjacent to the optical detector, and (iii) extending from the area of the scale to the optical detector to create an interference pattern at the optical detector as a function of the relative position between the scale and the light source.