Motion detection mechanism for laser illuminated optical mouse sensor

• US 20060226346A1
• Filed: 06/24/2005
• Published: 10/12/2006
• Est. Priority Date: 04/11/2005
• Status: Active Grant

• Current Assignee: EM Microelectronic - Marin SA (The Swatch Group AG)
• Original Assignee: EM Microelectronic - Marin SA (The Swatch Group AG)
• Inventors: Willemin, Michel, Bieber, Lawrence
• Granted Patent: US 7,876,307 B2
• Time in Patent Office: Days
• US Class Current: 250/221
• 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

There is described a method for measuring relative motion between an illuminated portion of a surface and an optical sensing device comprising a coherent light source and a photodetector array, the method comprising the steps of illuminating under a determined gradient by means of the coherent light source the surface portion at a determined flash rate; detecting by means of the photodetector array speckled light intensity pattern of the illuminated portion of the surface for a first flash; detecting a second speckled light intensity pattern of the illuminated portion of the surface for a second flash; extracting motion features of two different types from the detected first and second speckled light intensity patterns; determining a measurement of the relative motion between the optical sensing device and the illuminated surface portion based on a comparison of motion features extracted; wherein before the step of determining a measurement of the relative motion, the method further comprises the step of keeping only pairs of neighbouring motion features including one motion feature of both different types.

Claims

9. An optical motion sensing device comprising:

a coherent light source for illuminating under a determined gradient a surface portion with radiation at a determined flash rate;

a photodetector device responsive to radiation reflected from the illuminated surface portion which determines a speckled light intensity pattern for each flash;

means for extracting motion features of two different types from said speckled light intensity patterns;

processing means for determining, based on said extracted motion features, a measurement of relative motion between said sensing device and said illuminated portion of the surface;

wherein said processing means further comprise selecting means for keeping only pairs of neighbouring motion features including one motion feature of both different types.

1. A method for measuring relative motion between an illuminated portion of a surface and an optical sensing device comprising a coherent light source and a photodetector array, said method comprising the steps of:

illuminating under a determined gradient by means of said coherent light source said surface portion at a determined flash rate;

detecting by means of said photodetector array speckled light intensity pattern of said illuminated portion of the surface for a first flash;

detecting a second speckled light intensity pattern of said illuminated portion of the surface for a second flash;

extracting motion features of two different types from said detected first and second speckled light intensity patterns;

determining a measurement of the relative motion between said optical sensing device and said illuminated portion of the surface based on a comparison of motion features extracted;

wherein before the step of determining a measurement of the relative motion, said method further comprises the step of;

keeping only pairs of neighbouring motion features including one motion feature of both different types.

2. The method according to claim 1, wherein it comprises a preliminary step consisting in:

modifying/adjusting said gradient under which said surface portion is illuminated.

3. The method according to claim 2, wherein said photodetector device comprise an array of pixels and said means for extracting motion features comprise comparators, wherein the motion feature extracting step consists in:

comparing light intensity between neighbouring pixels from said detected first and second speckled light intensity patterns and extracting motion features as a result of said comparison; and

wherein the method further comprises the step of;

introducing an offset in said comparators.

4. The method according to claim 3, wherein the method comprises the step of introducing an adjustable offset in said comparators.

5. The method according to claim 2, wherein said optical sensing device comprises an optical lens to focus said radiation reflected from said illuminated surface portion on said photodetector device and wherein said method comprises a preliminary step consisting in:

adjusting the position of said coherent light source and/or moving said optical lens for obtaining an optical gradient.

6. The method according to claim 2, wherein said step for determining a measurement of relative motion comprises a sub-step consisting in:

defining an intensity threshold under which said extracting means do not extract any motion features.

7. The method according to claim 6, wherein said intensity threshold is adjustable.

8. The method according to claim 2, wherein said said step for determining a measurement of relative motion comprises sub-steps consisting in:

defining at least two intensity thresholds under which said extracting means do not extract any motion features; and

selecting one of said at least two intensity thresholds.

10. The optical motion sensing device according to claim 9, wherein it comprises filtering means for modifying/adjusting said gradient.

11. The optical motion sensing device according to claim 10, wherein said photodetector device comprise an array of pixels, wherein said means for extracting motion features comprise comparators for comparing light intensity between pixels and means for determining motion features as a result of said comparison and wherein said filtering means consist in introducing an offset in said comparators.

12. The optical motion sensing device according to claim 11, wherein said offset is an adjustable offset.

13. The optical motion sensing device according to claim 12, wherein it further comprises a feedback loop acting on said adjustable offset for adjusting the density of motion features.

14. The optical motion sensing device according to claim 13, wherein said optical motion sensing device comprises an optical lens to focus said radiation reflected from said illuminated surface portion on said photodetector device and wherein said optical gradient is obtained by adjusting the position of said coherent light source and/or moving said optical lens.

15. The optical motion sensing device according to claim 10, wherein said filtering means consist in defining an intensity threshold under which said extracting means do not extract any motion features.

16. The optical motion sensing device according to claim 15, wherein said intensity threshold is adjustable.

17. The optical motion sensing device according to claim 10, wherein said filtering means consist in defining at least two intensity thresholds under which said extracting means do not extract any motion features and wherein said sensing device further comprises selecting means for selecting one of said at least two intensity thresholds.

13-1. The optical motion sensing device according to claim 10, wherein said filtering means consist in an optical gradient.