Encoder with a combined position and index track
View Patent ↗An optical encoder. The encoder includes a coding element, an emitter, and a detector. The coding element has a track with a track pattern. The track pattern includes a plurality of optically distinguishable sections, which include a plurality of position sections and an index section. The emitter generates a light signal incident on the track of the coding element. The detector includes a combined position and index photodetector array. The combined position and index photodetector array includes a plurality of position photodetectors and an index photodetector. Embodiments of this type of optical encoder implement position and index sections in a single track on the coding element.
1. An optical encoder comprising:
a coding element having a track with a track pattern, the track pattern comprising a plurality of optically distinguishable sections, wherein the plurality of optically distinguishable sections comprises a plurality of position sections and an index section;
an emitter configured to generate a light signal incident on the track of the coding element; and
a detector comprising a combined position and index photodetector array, wherein the combined position and index photodetector array comprises a plurality of position photodetectors, an index photodetector, and an index-bar photodetector.
2. The optical encoder of claim 1 wherein the detector comprises a three-channel, single-track photodiode detector integrated circuit.
3. The optical encoder of claim 1 wherein the plurality of optically distinguishable sections further comprises an index-bar section, wherein the track pattern forms a ring.
4. The optical encoder of claim 3 wherein the combined position and index photodetector array forms a ring.
5. The optical encoder of claim 4 wherein the index photodetector has a smaller surface area than the index-bar photodetector.
6. The optical encoder of claim 5 wherein a circumferential width dimension of the index photodetector is approximately equal to a circumferential width dimension of the index-bar photodetector, and a radial height dimension of the index photodetector is smaller than a radial height dimension of the index-bar photodetector, wherein the circumferential width dimensions of the index and index-bar photodetectors are integral multiples of circumferential width dimensions of a pair of the position photodetectors, and the radial height of the index-bar photodetector is approximately equal to a radial height of the plurality of position photodetectors.
7. The optical encoder of claim 4 wherein the index-bar section is diametrically opposed to the index section within the ring, and the index-bar photodetector is diametrically opposed to the index photodetector in the photodetector array.
8. The optical encoder of claim 1 wherein the coding element comprises a reflective coding element, and the plurality of optically distinguishable sections comprises a plurality of reflective sections and a plurality of non-reflective sections.
9. The optical encoder of claim 1 wherein the coding element comprises a code wheel.