Vernier index position sensor
AssigneeMicroE, Inc.
InventorBruce A. Horwitz
Life of this patent
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Abstract
An index structure and method are disclosed which employ, in addition to a main diffractive grating track of an encoder, a short diffractive grating track (the vernier or index track) having a different frequency than that of the main track. The phase of the index track is used to provide windows for the main track in a manner so that a preselected phase condition of the main track occurs in only one of the windows provided by the index track.
Claims23
Apparatus for generating an index mark in a position sensor of the type which includes a main diffraction grating having a first frequency, a light source of quasi-monochromatic, spatially collimated light, and a main track detector positioned to detect interference fringes between diffraction orders from a portion of the main diffraction grating which has been positioned to be illuminated by the light source, the apparatus comprising
- a vernier diffraction grating having a second frequency which is different from the first frequency and which is positioned at a selected location along the main diffraction grating;
- a binary optic track having a cylindrical lens function and which is positioned along the vernier diffraction grating;
- vernier track and binary optic track detectors positioned adjacent the main track detector so that, upon illumination of the selected location of the main diffraction grating by the light source, interference fringes between diffraction orders from the illuminated portion of the vernier diffraction grating impinge upon the vernier track detector, and a near diffraction limited spot from the binary optic track impinges upon the binary optic track detector;
- and
- processing circuitry which generates an index signal when predetermined conditions are present in signals received from the main track, the vernier track, and the binary optics track detectors.
A method of generating an index track in a position sensor of the type which includes a main diffraction grating having a first frequency, a light source of quasi-monochromatic, spatially collimated light, the method comprising the steps of
- detecting the phase of interference fringes from a portion of the main diffraction grating which has been positioned to be illuminated by the light source;
- detecting the phase of interference fringes from a vernier diffraction grating having a second frequency which is different from the first frequency, and which is positioned at a selected location along the main diffraction grating, when the selected location is illuminated by the light source;
- detecting light formed by a binary optic track having a cylindrical lens function and which is positioned along the vernier diffraction grating, when the selected location is illuminated by the light source;
- generating an index signal when predetermined phase conditions are present in the interference fringes the main track and the vernier track, and the light formed by the binary optic track satisfies a predetermined condition.
Apparatus for generating an index mark in a position sensor of the type which includes a main track which periodically varies along an axis between a first attribute and a second different attribute at an approximate first frequency, and a main track detector which provides signals indicative of the periodic variation of the main track, the apparatus comprising
- a vernier track which periodically varies along an axis between the first attribute and the second different attribute at an approximate second frequency which is different from the first frequency, and which vernier track is positioned at a selected location along the main track;
- a gate track which is positioned along the vernier track and which has a varying selected attribute;
- vernier track and gate track detectors positioned along the main track detector so that when the selected location of the main track is positioned to be detected by the main track detector, the vernier and the gate tracks are positioned to be detected by the vernier and gate track detectors, wherein the vernier track detector provides signals indicative of the periodic variation of the vernier track, and the gate track detector provides signals indicative of the variation of the selected attribute of the gate track;
- and
- processing circuitry which generates an index signal when predetermined conditions are present in the signals received from the main track, the vernier track, and the gate track detectors.
Dependencies are inferred from the claim text.