Multi-bit absolute position optical encoder with reduced number of tracks

• US 20070278392A1
• Filed: 06/02/2006
• Published: 12/06/2007
• Est. Priority Date: 06/02/2006
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Toh, Kheng Hin, Thor, Chung Min, Teh, Lee Ling, Tan, Boon Keet
• Granted Patent: US 7,521,669 B2
• Time in Patent Office: Days
• US Class Current: 250/231.130
• CPC Class Codes: H03M 1/26 with weighted coding, i.e. the weight given to a digit depends on the position of the digit within the block or code word, e.g. there is a given radix and the weights are powers of this radix
• CPC Class Codes: H03M 1/28 with non-weighted coding

Abstract

An optical encoder includes a coding element having a track with a track pattern that comprises multiple optically distinguishable sections. The optical encoder compares photodetector outputs with transition-specific thresholds that correspond to transitions between the optically distinguishable sections of the track. The comparisons are used to determine when the transition between two optically distinguishable sections of the track has passed the photodetector. Knowledge of the transition between two optically distinguishable sections is then translated into digital position information.

Claims

1. An optical encoder comprising:

a coding element having a track with a track pattern, the track pattern comprising multiple optically distinguishable sections;

a light source configured to output light to the track;

a photodetector positioned to detect light from the light source that is associated with the track, the photodetector generating an output signal in response to detected light;

threshold logic configured to indicate the magnitude of the output signal relative to at least one transition-specific threshold, wherein the at least one transition-specific threshold corresponds to a transition between optically distinguishable sections of the track; and

position logic configured to generate digital position information in response to the indication from the threshold logic.

2. The optical encoder of claim 1 further comprising:

a second track with a track pattern, the track pattern comprising multiple optically distinguishable sections;

a second photodetector positioned to detect light from the light source that is associated with the second track, the second photodetector generating an output signal in response to the detected light;

wherein the threshold logic is further configured to indicate the magnitude of the output signal from the second photodetector relative to at least one transition-specific threshold, wherein the at least one transition-specific threshold corresponds to a transition between optically distinguishable sections of the second track; and

wherein the position logic is further configured to generate the digital position information in response to the indications related to the second track.

3. The optical encoder of claim 1 wherein the optically distinguishable sections of the track pattern have width dimensions that are greater than the width dimension of the photodetector.

4. The optical encoder of claim 1 wherein the optically distinguishable sections of the track pattern have height dimensions that are less than the height dimension of the photodetector.

5. The optical encoder of claim 1 further comprising a threshold source configured to provide the transition-specific threshold.

6. The optical encoder of claim 5 wherein the threshold source comprises a photodetector positioned to detect light from the light source that is associated with the track.

7. The optical encoder of claim 1 wherein the threshold logic includes a transition-specific comparator to indicate the magnitude of the output signal relative to the at least one transition-specific threshold.

8. An optical encoder comprising:

a coding element having first and second tracks, the first and second tracks both having a track pattern comprising multiple optically distinguishable sections;

a light source configured to output light to the first and second tracks;

a first photodetector positioned to detect light from the light source that is associated with the first track, the first photodetector generating a first output signal in response to the detected light;

a second photodetector positioned to detect light from the light source that is associated with the second track, the second photodetector generating a second output signal in response to the detected light;

threshold logic configured to indicate the magnitude of the output signals from the first and second photodetectors relative to transition-specific thresholds, wherein the transition-specific thresholds correspond to transitions between optically distinguishable sections of the first and second tracks; and

position logic configured to generate digital position information in response to the indications from the threshold logic.

9. The optical encoder of claim 8 wherein the digital position information generated by the position logic is UVW information.

10. The optical encoder of claim 8 wherein the first track includes a repeating pattern of two optically distinguishable sections and the second track includes a repeating pattern of three optically distinguishable sections.

11. The optical encoder of claim 10 wherein the threshold logic includes three transition-specific comparators for comparing the output signals to the transition-specific thresholds.

12. The optical encoder of claim 11 wherein:

a first one of the transition-specific comparators compares the first output signal with a first transition-specific threshold;

a second one of the transition-specific comparators compares the second output signal with a second transition-specific threshold; and

a third one of the transition-specific comparators compares the second output signal with a third transition-specific threshold.

13. The optical encoder of claim 12 wherein the digital position information generated by the position logic is UVW information.

14. The optical encoder of claim 8 further comprising at least one threshold photodetector configured to provide a transition-specific threshold, wherein the threshold source comprises a photodetector positioned to detect light from the light source that is associated with the track.

15. The optical encoder of claim 8 wherein the optically distinguishable sections of the track pattern have width dimensions that are greater than the width dimension of the photodetector.

16. The optical encoder of claim 8 wherein the optically distinguishable sections of the track pattern have height dimensions that are less than the height dimension of the photodetector.

17. A method for generating absolute position information using an optical encoder, the method comprising:

applying light to a track of a coding element, the track having a track pattern comprising multiple optically distinguishable sections;

detecting the light that is applied to the track and generating an output signal in response to detected light;

comparing the output signal to at least one transition-specific threshold, wherein the at least one transition-specific threshold corresponds to a transition between optically distinguishable sections of the track; and

generating digital position information in response to the comparison of the output signal to the at least one transition-specific threshold.

18. The method of claim 17 further comprising:

applying light to a second track of the coding element, the second track having a track pattern comprising multiple optically distinguishable sections;

detecting the light that is applied to the second track and generating a second output signal in response to detected light;

comparing the second output signal to another transition-specific threshold, wherein the another transition-specific threshold corresponds to a transition between optically distinguishable sections of the second track; and

generating digital position information in response to the comparison of the second output signal to the another transition-specific threshold.

19. The method of claim 18 further comprising generating UVW digital position information from the comparisons.

20. The method of claim 18 further comprising converting the results of the comparison to digital position information.