Coding element with integrated limit switch
View Patent ↗An optical encoder. The optical 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. The plurality of optically distinguishable sections includes a limit switch section. The emitter generates a light signal incident on the track of the coding element. The detector includes a limit switch photodetector positioned to detect the light signal from the emitter. The detector generates a limit switch output signal in response to the detected light signal above a limit switch threshold at the limit switch photodetector. Embodiments of this type of optical encoder implement limit switches into 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 limit switch section;
an emitter configured to generate a light signal incident on the track of the coding element; and
a detector comprising a limit switch photodetector positioned to detect the light signal from the emitter, the detector configured to generate a limit switch output signal in response to the detected light signal above a limit switch threshold at the limit switch photodetector.
2. The optical encoder of claim 1 wherein the coding element comprises a reflective coding element, and the plurality of optically distinguishable sections comprise a plurality of reflective sections and a plurality of non-reflective sections.
3. The optical encoder of claim 1 wherein the coding element comprises a transmissive coding element, and the plurality of optically distinguishable sections comprise a plurality of transmissive sections and a plurality of non-transmissive sections.
4. The optical encoder of claim 1 wherein the coding element comprises a code wheel.
5. The optical encoder of claim 1 wherein the coding element comprises a code strip.
6. The optical encoder of claim 1 wherein the detector further comprises a monitor photodetector positioned to detect the light signal from the emitter, the detector configured to generate a monitor output signal in response to the detected light signal at the monitor photodetector, wherein the limit switch threshold is based on the monitor output signal.
7. The optical encoder of claim 1 wherein the limit switch section is located at one end of the plurality of optically distinguishable sections, the plurality of optically distinguishable sections comprising a second limit switch section located at an opposite end of the plurality of optically distinguishable sections.
8. The optical encoder of claim 1 wherein the plurality of optically distinguishable sections comprises a plurality of position sections, and wherein the plurality of position sections and the limit switch section are in the same track of the coding element.
9. A system to control a range of motion for a device, the system comprising:
an encoder comprising a coding element coupled to a moving part of the device, the coding element comprising a track with a track pattern of a plurality of optically distinguishable sections, wherein the plurality of optically distinguishable sections comprises a limit switch section, the encoder configured to generate a periodic channel signal indicative of movement of the moving part of the device and a limit switch output signal indicative of a boundary position of the moving part of the device;
a decoder coupled to the encoder, the decoder to generate a count signal corresponding to the periodic channel signal and to generate a limit signal corresponding to the limit switch output signal; and
a microprocessor coupled to the decoder, the microprocessor to control the movement of the moving part and to alter the movement of the moving part in response to the limit signal from the decoder.
10. The system of claim 9 wherein the moving part of the device comprises a focusing element.
11. The system of claim 10 wherein the device comprises a camera.
12. The system of claim 10 wherein the device comprises a projector.
13. The system of claim 9 wherein the moving part comprises a motor shaft, and the coding element comprises a code wheel coupled to the motor shaft.
14. The system of claim 9 , wherein the coding element comprises a code strip.
15. The system of claim 9 , wherein the encoder comprises an optical imaging encoder.
16. The system of claim 9 wherein the encoder comprises:
a light source to generate a light signal incident on the track of the coding element, wherein the light source comprises a light emitting diode (LED);
a photodetector array comprising a plurality of photodiodes to detect the light signal from the track of the coding element, wherein the plurality of photodiodes comprises:
an A-signal photodiode to generate an analog A signal;
a B-signal photodiode adjacent to the A-signal photodiode, the B-signal photodiode to generate an analog B signal;
an A/-signal photodiode to generate an analog A/ signal;
a B/-signal photodiode adjacent to the A/-signal photodiode, the B/-signal photodiode to generate an analog B/ signal;
a monitor photodiode between the B-signal photodiode and the A/-signal photodiode, the monitor photodiode to generate a monitor signal;
a first limit switch photodiode at an end of the photodetector array, the first limit switch photodiode to generate the limit switch output signal indicative of the boundary position of the moving part of the device; and
a second limit switch photodiode at an opposite end of the photodetector array, the second limit switch photodiode to generate a second limit switch output signal indicative of an opposite boundary position of the moving part of the device; and
signal processing circuitry to process the analog signals from the photodiodes of the photodetector array to generate digital A and B signals, and to transmit the digital signals to the decoder.
17. A method for controlling a range of motion for a device, the method comprising:
coupling a coding element to a moving part of the device, wherein the coding element comprises a track with a track pattern of a plurality of optically distinguishable sections, wherein the plurality of optically distinguishable sections comprises a limit switch section;
generating a light signal incident on the track of the coding element;
detecting the light signal;
generating a limit switch output signal in response to the detected light signal above a limit switch threshold; and
stopping movement of the moving part in response to the limit switch output signal.
18. The method of claim 17 further comprising:
generating a monitor output signal in response to the detected light; and
establishing the limit switch threshold based on the monitor output signal.
19. The method of claim 17 wherein detecting the light signal from the emitter comprises detecting the light signal through a transmissive section of the track, wherein the plurality of optically distinguishable sections comprises a plurality of transmissive sections and a plurality of non-transmissive sections.
20. The method of claim 17 wherein detecting the light signal from the emitter comprises detecting the light signal from a reflective section of the track, wherein the plurality of optically distinguishable sections comprises a plurality of reflective sections and a plurality of non-reflective sections.