Method for determining motion using a velocity predictor

• US 20070165207A1
• Filed: 01/03/2006
• Published: 07/19/2007
• Est. Priority Date: 01/03/2006
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Silicon Light Machines Corporation (SCREEN Holdings Co., Ltd.)
• Inventors: Xu, Yansun, Todoroff, Brian
• Granted Patent: US 7,298,460 B2
• Time in Patent Office: Days
• US Class Current: 356/28
• CPC Class Codes: G01P 3/36 Devices characterised by the use of optical means, e.g. using infrared, visible, or ultraviolet light G01P3/68 takes precedence; gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams G01C19/64
• CPC Class Codes: G06F 3/0317 in co-operation with a patterned surface, e.g. absolute position or relative movement detection for an optical mouse or pen positioned with respect to a coded surface

Abstract

A method is provided for determining motion of an optical sensor including a periodic photo-diode array relative to a surface. The method includes steps of (i) generating sets of quasi-sinusoidal signals responsive to motion along first and second directions; (ii) combining the sets of signals to generate a wrapped phase angle value for each direction at a first time; (iii) combining the sets of signals at a second time to generate a second wrapped phase angle value for each direction; (iv) computing wrapped phase angle changes for each direction between the first time and the second time; (v) computing velocity predictors for each direction using corrected average phase angle changes from a number of preceding successive frames; (vi) calculating the number of full 27π rotations needed to unwrap the phase angle changes for each direction using the velocity predictors; and (vii) computing the unwrapped or corrected phase angle changes.

Claims

1. A method for detecting movement of a surface relative to an optical sensor having an array of photosensitive elements, the method comprising steps of:

generating at least one set of quasi-sinusoidal signals responsive to motion of light received on the array in at least a first direction;

combining said at least one set of quasi-sinusoidal signals to generate a phase angle value for said first direction at a first time;

combining said at least one set of quasi-sinusoidal signals at a second time to generate a phase angle value for said first direction at the second time;

computing wrapped phase angle changes for said first direction;

computing the unwrapped phase angle changes for said first direction; and

determining a value of distance moved in the first direction.

2. A method according to claim 1, wherein the step of computing the unwrapped phase angle changes for said first direction comprises the step of computing velocity predictors for said first direction using average velocity values from a number, K, of preceding successive frames, where K is a whole number greater than or equal to two.

3. A method according to claim 2, wherein the step of computing velocity predictors for the said first direction using average velocity values comprises the step of computing average phase angle changes along the said first direction using K sets of unwrapped phase angle changes from the preceding successive K frames.

4. A method according to claim 2, wherein the step of computing wrapped phase angle changes comprises the step of computing changes in phase angles between two successive sample frames, calculated from an inverse tangent function using at least one set of quasi-sinusoidal signals responsive to motion.

5. A method according to claim 1, wherein the step of generating at least one set of quasi-sinusoidal signals comprises the step of generating at least two sets of quasi-sinusoidal signals, the first set related to motion in the first direction and a second set related to motion in a second direction.

6. A method according to claim 5, wherein the step of determining a value of distance moved comprises the step of determining a value of distance moved in two-dimensions.

7. A method according to claim 1, further comprising the step of computing radius values in addition to phase angle values at each sample frame as an indication of the quality of the at least two sets of quasi-sinusoidal signals related to motion in the first direction and in the second direction.

8. A method according to claim 7, wherein the computed radius values are used as weighting factors in computing velocity predictors for the first direction and the second direction using unwrapped average phase angle changes from a number, K, of preceding successive frames.

9. A signal processing circuit for detecting movement of a surface relative to an optical sensor having an array of photosensitive elements, the circuit comprising:

means for generating at least one set of quasi-sinusoidal signals responsive to motion of light received on the array in at least a first direction;

means for combining said at least one set of quasi-sinusoidal signals to generate a phase angle value for said first direction at a first time, and combining said at least one set of quasi-sinusoidal signals at a second time to generate a phase angle value for said first direction at the second time;

means for computing wrapped phase angle changes for said first direction from the phase angle values generated at said first and second times;

means for computing the unwrapped phase angle changes for said first direction; and

means for determining a value of distance moved in the first direction.

10. A circuit according to claim 9, wherein the means for computing the unwrapped phase angle changes comprises means for computing velocity predictors for said first direction using average velocity values from a number, K, of preceding successive frames, where K is a whole number greater than or equal to two.

11. A circuit according to claim 10, wherein the means for computing velocity predictors for the said first direction using average velocity values comprises means for computing average phase angle changes along the said first direction using K sets of phase angle changes from the preceding successive K frames.

12. A circuit according to claim 10, wherein the means for computing wrapped phase angle changes comprises means for computing changes in phase angles between two successive sample frames, calculated from an inverse tangent function using at least one set of quasi-sinusoidal signals responsive to motion.

13. A circuit according to claim 9, wherein the means for generating at least one set of quasi-sinusoidal signals comprises means for generating at least two sets of quasi-sinusoidal signals, the first set related to motion in the first direction and a second set related to motion in a second direction.

14. A circuit according to claim 13, wherein the means for determining a value of distance moved comprises means for determining a value of distance moved in two-dimensions.

15. A method for detecting movement of a surface relative to an optical sensor having an array of photosensitive elements, the method comprising steps of:

generating at least two sets of quasi-sinusoidal signals responsive to motion of light received on the array, the first set of quasi-sinusoidal signals related to motion in a first direction and the second set of quasi-sinusoidal signals related to motion in a second direction;

at a first time combining said first set of quasi-sinusoidal signals to generate a wrapped phase angle value for said first direction at the first time, and combining said second set of quasi-sinusoidal signals to generate a wrapped phase angle value for said second direction at the first time;

at a second time combining said first set of quasi-sinusoidal signals to generate a wrapped phase angle value for said first direction at the second time, and combining said second set of quasi-sinusoidal signals to generate a wrapped phase angle value for said second direction at the second time;

computing wrapped phase angle changes between the first time and the second time for said first and second directions;

computing the unwrapped phase angle changes for said first and second directions using velocity predictors computed for said first and second directions; and

determining a value of distance moved in the first and the second directions.

16. A method according to claim 15, wherein the step of computing the unwrapped phase angle changes for said first and second directions comprises the step of computing velocity predictors for said first and second directions using average velocity values from a number, K, of preceding successive frames, where K is a whole number greater than or equal to two.

17. A method according to claim 16, wherein the step of computing velocity predictors for said first and second directions using average velocity values comprises the step of computing average phase angle changes along said first and second directions using K sets of phase angle changes from the preceding successive K frames.

18. A method according to claim 16, wherein the step of computing wrapped phase angle changes comprises the step of computing changes in phase angles between two successive sample frames, calculated from an inverse tangent function using at least two sets of quasi-sinusoidal signals responsive to motion in the said first and second directions.

19. A method according to claim 15, further comprising the step of computing radius values in addition to phase angle values at each sample frame as an indication of the quality of the at least two sets of quasi-sinusoidal signals related to motion in the first direction and in the second direction.

20. A method according to claim 19, wherein the computed radius values are used as weighting factors in computing velocity predictors for the first direction and the second direction using unwrapped average phase angle changes from a number, K, of preceding successive frames.