Processing methods for speckle-based motion sensing

• US 20090040062A1
• Filed: 08/06/2007
• Published: 02/12/2009
• Est. Priority Date: 08/06/2007
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Bailey, Jeffry C., Xu, Yansun, Todoroff, Brian, Lang, Robert J.
• Granted Patent: US 8,263,921 B2
• Time in Patent Office: Days
• US Class Current: 340/686.100
• 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
• CPC Class Codes: G06F 3/03543 Mice or pucks G06F3/03541 takes precedence
• CPC Class Codes: G06F 3/038 Control and interface arrangements therefor, e.g. drivers or device-embedded control circuitry

Abstract

One embodiment relates to a method of tracking motion using a speckle-based motion sensor. A distance moved is determined by a first signal processing procedure, and a distance moved is determined by a second signal processing procedure. Selection between said distances is made based on whether the distance determined by the first signal processing procedure exceeds a predetermined threshold distance. According to a preferred embodiment, the first signal processing procedure makes a more accurate determination of distance for slower speeds, while the second signal processing procedure makes a more accurate determination of distance for higher speeds. Other embodiments, aspects and features are also disclosed.

Claims

1. A method of tracking motion using a speckle-based motion sensor, the method comprising:

determining a distance moved by a first signal processing procedure;

determining a distance moved by a second signal processing procedure; and

selecting between said distances based on whether the distance determined by the first signal processing procedure exceeds a predetermined threshold distance.

2. The method of claim 1, wherein one of the two said signal processing procedures makes a more accurate determination of distance for slower speeds, while the other signal processing procedure makes a more accurate determination of distance for higher speeds.

3. The method of claim 2, wherein the first signal processing procedure comprises:

averaging a first set of group signals to generate a first average group signal;

averaging a second set of group signals to generate a second average group signal; and

processing the first and second average group signals to determine a phase change between said two average group signals.

4. The method of claim 3, wherein said group signals comprise trigonometric signals.

5. The method of claim 3, wherein the phase change is determined and accumulated relative to a baseline signal, and further wherein the baseline signal is updated once an accumulated phase change exceeds a pre-determined threshold.

6. The method of claim 2, wherein the second signal processing procedure comprises a multiscale-averaging procedure.

7. The method of claim 6, wherein the multiscale-averaging procedure comprises:

calculating a first phase difference for a first time interval;

calculating a second phase difference for a second time interval which is not equal to the first time interval; and

processing the first and second phase differences to compute a phase change that can be larger than the Nyquist limit for either time interval.

8. The method of claim 1, further comprising:

determining a signal strength; and

outputting a signal indicative of no motion if the signal strength is below a predetermined threshold strength.

9. The method of claim 8, wherein the signal strength is determined by a summation of squares of trigonometric signals from multiple sensor arrays.

10. An apparatus for tracking motion based on speckle patterns, the apparatus comprising:

an array of detectors, connected in groups, each group producing a group signal;

circuitry configured to sample each group signal at a sequence of discrete times to produce a sequence of sets of sampled group signals;

signal processing circuitry configured to process the sets of sampled group signals to produce a sets of phase signals which are responsive to relative phases of the speckle patterns on the array of detectors, wherein the phase signals are quasi-periodic with distance moved; and

signal processing circuitry configured to calculate a change in phase from a first set of sampled group signals to a second set of sampled group signals so as to determine a displacement characterizing relative motion occurring between the first and second sets.

11. The apparatus of claim 10, further comprising:

signal processing circuitry configured to average the first set of group signals to produce a first average group signal;

signal processing circuitry configured to average the second set of group signals to produce a second average group signal; and

signal processing circuitry configured to calculate a phase change between the first average group signal and the second average group signal.

12. The apparatus of claim 11, further comprising:

signal processing circuitry configured to store a baseline signal;

signal processing circuitry configured to accumulate phase changes with respect to the baseline signal; and

signal processing circuitry configured to updating the baseline signal once the accumulated phase changes surpass a predetermined threshold.

13. The apparatus of claim 10, further comprising:

signal processing circuitry configured to form a velocity phase signal from two consecutive sampled group signals.

14. The apparatus of claim 13, further comprising:

multiple arrays of detectors, wherein each array produces a velocity phase signal, and further wherein a relative motion of the apparatus is determined in part by summing the velocity phase signals from the multiple arrays.

15. The apparatus of claim 13, further comprising:

signal processing circuitry configured to sum a sequence of velocity phase signals to give an average velocity phase signal that is utilized to determine a phase difference over an averaging interval.

16. The apparatus of claim 15, further comprising:

signal processing circuitry configured to determine a first phase difference for a first time interval T1 and a second phase difference for a second time interval T2, wherein T1 and T2 are unequal; and

signal processing circuitry configured to compute a phase change that can be larger than a Nyquist limit for either T1 or T2.

17. The apparatus of claim 15, further comprising, for each of two non-parallel axes:

signal processing circuitry configured to determine a first phase difference for a first time interval T1 and a second phase difference for a second time interval T2, wherein T1 and T2 are unequal; and

signal processing circuitry configured to compute, for a range of unwrap choices, an error based on a phase match between the first and second phase differences, and to sum the error; and

signal processing circuitry to select an unwrap choice that minimizes the sum.

18. An optical sensor apparatus for tracking motion based on a speckle pattern, the apparatus comprising:

signal processing circuitry configured to determine a distance moved by a first signal processing procedure;

signal processing circuitry configured to determine a distance moved by a second signal processing procedure; and

signal processing circuitry configured to select between said distances based on whether the distance determined by the first signal processing procedure exceeds a predetermined threshold distance.

19. The apparatus of claim 18, wherein one of the two signal processing procedures makes a more accurate determination of distance for slower speeds, while the other signal processing procedure makes a more accurate determination of distance for higher speeds.

20. A method of tracking motion using a speckle-based motion sensor, the method comprising:

determining a distance moved during three or more consecutive blocks, wherein each block comprises N frames;

determining if the distance moved during one block of the consecutive blocks differs from the distance moved during a majority of the consecutive blocks by more than a predetermined threshold difference; and

discarding data for the one block if the predetermined threshold difference is surpassed.

21. A method of tracking motion using a speckle-based motion sensor, the method comprising:

creating a speckle pattern on a surface;

detecting said speckle pattern by a plurality of optical detectors;

creating a set of electrical signals emitted from said optical detectors, such that said electrical signals vary quasi-periodically with distance moved along at least two non-parallel axes;

sampling said electrical signals at a plurality of discrete times extending over a time interval, creating a plurality of sampled electrical signals; and

processing said plurality of sampled electrical signals to determine a distance moved during said time interval.

22. The method of claim 21 wherein said processing of said plurality of sampled electrical signals includes:

dividing said time interval into subintervals and summing the values of said electrical signals within each of said subintervals.

23. The method of claim 21 wherein said processing of said plurality of sampled electrical signals includes:

multiplying the values of signals from one time interval by the values of signals from an adjacent interval to form signal products; and

adding or subtracting pairs of said signal products to form at least one b-vector.

24. The method of claim 21, wherein said processing of said plurality of sampled electrical signals includes:

representing pairs of said electrical signals as a complex phasor and computing the phase of said phasor at each of said discrete times; and

computing a distance moved from the differences in the values of said phases at two different discrete times.

25. The method of claim 23, wherein said processing of said plurality of sampled electrical signals includes:

computing a b-vector for a first subset of said optical detectors;

computing a b-vector for a second subset of said optical detectors; and

summing said two b-vectors.

26. The method of claim 23, wherein said processing of said plurality of sampled electrical signals includes the step of computing a first b-vector at a first time and computing a second b-vector at a second time and summing said two b-vectors.

27. The method of claim 23, wherein said processing of said plurality of sampled electrical signals includes:

computing a first b-vector from two sets of sampled electrical signals separated by a time interval T1; and

computing a second b-vector from two sets of sampled electrical signals separated by a time interval T2, where T1 is not equal to T2.

28. The method of claim 23, wherein said processing of said plurality of sampled electrical signals includes:

defining the signals from a first discrete time as a reference set of signals computing distance moved since said reference set of signals; and

updating said reference set when said distance moved exceeds a predefined threshold.

29. The method of claim 23, wherein said processing of said plurality of sampled electrical signals includes:

computing distance moved at a plurality of discrete times;

replacing a value of said distance moved if the difference between the computed value of said distance moved differs from the values computed for other times within said plurality by more than a specified amount.

30. The method of claim 23, wherein said processing of said plurality of sampled electrical signals includes:

reporting no motion if the magnitude of one or more or a combination of said electrical signals falls below a predefined threshold.

31. The method of claim 29, wherein said processing of said plurality of sampled electrical signals includes:

computing a plurality of b-vectors for a plurality of discrete times;

summing said b-vectors to form a resultant b-vector; and

reporting no motion if the magnitude of said resultant b-vector falls below a predefined threshold.