Dynamic Range Control for Optical Encoders

• US 20160061636A1
• Filed: 07/10/2015
• Published: 03/03/2016
• Est. Priority Date: 08/27/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Westerman, Wayne C., Gowreesunker, Baboo V., Holenarsipur, Prashanth S.
• Granted Patent: US 10,066,970 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01D 5/34715 Scale reading or illumination devices
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders

Abstract

Embodiments of the present disclosure provide a method and system for dynamically controlling a current that is applied to a light source of an optical encoder.

Claims

1. A method for dynamically adjusting output of a light source of an optical encoder, the method comprising:

receiving a first output current from a first photodiode of a plurality of photodiodes, wherein the first output current is associated with a first input current that was applied to the light source at a first time period;

receiving a second output current from a second photodiode of the plurality of photodiodes, wherein the second output current is associated with the first input current that was applied to the light source at the first time period;

comparing the first output current to the second output current to obtain a dynamic current value;

comparing the dynamic current value to a target current value; and

estimating, using the comparison between the dynamic current value and the target current value, an input current for the light source, wherein the input current is applied to the light source at a second time period.

2. The method of claim 1, wherein the input current is configured to change an intensity of the light source.

3. The method of claim 1, wherein the first output current and the second output current are received at a first sample time.

4. The method of claim 1, wherein comparing the first output current to the second output current to obtain a dynamic current value comprises finding the mean of the first output current and the second output current.

5. The method of claim 1, wherein at least one of the first output current and the second output current vary based on an alignment of an optical encoder with respect to the light source.

6. The method of claim 1, further comprising determining whether the dynamic current value is below a minimum current threshold.

7. The method of claim 1, further comprising determining whether the dynamic current value is above a maximum current threshold.

8. A computer-readable storage medium encoding computer executable instructions which, when executed by a processor, performs a method for dynamically adjusting a light source of an optical encoder, the method comprising:

receiving a first output current from a first photodiode of a plurality of photodiodes, wherein the first output current is associated with a first input current that was applied to the light source at a first time period;

receiving a second output current from a second photodiode of the plurality of photodiodes, wherein the second output current is associated with the first input current that was applied to the light source at the first time period;

comparing the first output current to the second output current to obtain a dynamic current value;

comparing the dynamic current value to a target current value; and

estimating, using the comparison between the dynamic current value and the target current value, an input current for the light source, wherein the input current is applied to the light source at a second time period.

9. The computer-readable storage medium of claim 8, wherein the input current is configured to change the intensity of the light source at the second time period.

10. The computer-readable storage medium of claim 8, wherein the first output current and the second output current are received at a first sample time.

11. The computer-readable storage medium of claim 8, wherein comparing the first output current to the second output current to obtain a dynamic current value comprises finding the mean of the first output current and the second output current.

12. The computer-readable storage medium of claim 8, wherein at least one of the first output current and the second output current vary based on an alignment of an optical encoder with respect to the light source.

13. The computer-readable storage medium of claim 8, further comprising determining whether the dynamic current value is below a minimum current threshold.

14. The computer-readable storage medium of claim 8, further comprising determining whether the dynamic current value is above a maximum current threshold.

15. An optical encoder for an electronic device, the optical encoder comprising:

a light source;

a plurality of photodiodes;

a shaft having an encoding pattern disposed thereon, wherein the shaft is configured to reflect light from the light source into the plurality of photodiodes; and

a dynamic range module, wherein the dynamic range module is configured to;

receive a first output current from a first photodiode of the plurality of photodiodes;

receive a second output current from a second photodiode of the plurality of photodiodes;

compare the first output current to the second output current to obtain a dynamic current value;

compare the dynamic current value to a target current value; and

estimating an input current for the light source, wherein the input current is based, at least in part, on the comparison between the dynamic current value and the target current value and wherein the input current is applied to the light source to dynamically adjust an intensity of the light source.

16. The optical encoder of claim 15, wherein the light source is an LED light source.

17. The optical encoder of claim 15, wherein the input current is provided to a digital to analog converter prior to being applied to the light source.

18. The optical encoder of claim 15, further comprising position sensing module configured to determine a position and a rotation of the shaft.

19. The optical encoder of claim 15, wherein at least one of the first output current and the second output current vary based on an alignment of the shaft with respect to the light source.

20. The optical encoder of claim 15, wherein the dynamic range module is further configured to determine whether the dynamic current value is below a minimum current threshold or above a maximum current threshold.