Indexed optical encoder, method for indexing an optical encoder, and method for dynamically adjusting gain and offset in an optical encoder

Abstract

An optical encoder may include an encoder disk, an illumination system, and a detector to detect light diffracted from the encoder disk. The encoder disk may include a signal track comprising a diffraction grating, and an index track comprising a reflective index mark, wherein a width of the index mark is larger than a pitch of the diffraction grating. An indexing method may include providing an encoder disk, providing an illumination system to direct light to the encoder disk, providing a detector structured to detect light diffracted from the encoder disk, calculating an estimated count of quadrature states from a rising edge of an index pulse to a middle of the index interval, and calculating the quadrature state at an approximate center of the index pulse. A dynamic parameter correction method may include calculating a target gain and offset and correcting values based on the target gain and offset.

What is claimed is: 
     
         1 . An encoder disk for use in an optical encoder, the encoder disk comprising:
 a signal track comprising a diffraction grating formed as a ring on the encoder disk;   an index track comprising a reflective index mark, wherein a width of the index mark is larger than a pitch of the diffraction grating;   a glass substrate;   a low reflective layer provided on the substrate; and   a high reflective layer provided on the low reflective layer, wherein the high reflective layer is formed in a pattern such that a portion of the low reflective layer is visible.   
     
     
         2 . The encoder disk of  claim 1 , wherein the low reflective layer comprises a low reflective chrome layer. 
     
     
         3 . The encoder disk of  claim 1 , wherein the high reflective layer comprises a high reflective chrome layer. 
     
     
         4 . The encoder disk of  claim 1 , wherein the low reflective layer has a reflectivity of approximately 5% on a side opposite the glass substrate. 
     
     
         5 . The encoder disk of  claim 1 , wherein the high reflective layer has a reflectivity of approximately 59% on a side face the glass substrate and a reflectivity of approximately 65% on a side opposite the glass substrate. 
     
     
         6 . The encoder disk of  claim 1 , wherein the glass substrate comprises an optical absorption material applied to a face of the glass substrate. 
     
     
         7 . An optical encoder comprising:
 an encoder disk comprising:   a signal track comprising a diffraction grating formed as a ring on the encoder disk;   an index track comprising a reflective index mark, wherein a width of the index mark is larger than a pitch of the diffraction grating;   a glass substrate;   a low reflective layer provided on the substrate; and   a high reflective layer provided on the low reflective layer, wherein the high reflective layer is formed in a pattern such that a portion of the low reflective layer is visible;   an illumination system structured to direct light to the encoder disk; and   a detector structured to detect light diffracted from the encoder disk.   
     
     
         8 . The optical encoder of  claim 7 , wherein the low reflective layer comprises a low reflective chrome layer. 
     
     
         9 . The optical encoder of  claim 7 , wherein the high reflective layer comprises a high reflective chrome layer. 
     
     
         10 . The optical encoder of  claim 7 , wherein the low reflective layer has a reflectivity of approximately 5% on a side opposite the glass substrate. 
     
     
         11 . The optical encoder of  claim 7 , wherein the high reflective layer has a reflectivity of approximately 59% on a side facing the glass substrate and a reflectivity of approximately 65% on a side opposite the glass substrate. 
     
     
         12 . The optical encoder of  claim 7 , wherein the glass substrate comprises an optical absorption material applied to a face of the glass substrate. 
     
     
         13 . The optical encoder of  claim 7 , wherein the illumination system comprises a light-emitting diode. 
     
     
         14 . The optical encoder of  claim 7 , wherein the illumination system comprises:
 a multimode VCSEL laser structured to emit laser light.