Contact sensitive device

• US 20040160421A1
• Filed: 01/05/2004
• Published: 08/19/2004
• Est. Priority Date: 07/04/2001
• Status: Active Grant

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Hiwave Technologies (UK) Ltd (Alphabet Inc.)
• Inventors: Sullivan, Darius Martin
• Granted Patent: US 8,274,480 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 3/043 using propagating acoustic waves
• CPC Class Codes: G06F 3/0436 in which generating transducers and detecting transducers are attached to a single acoustic waves transmission substrate

Abstract

A contact sensitive device (10) comprising a member (12) capable of supporting bending waves, a first sensor (16) mounted on the member for measuring bending wave vibration in the member, the sensor (16) determining a first measured bending wave signal and a processor which calculates information relating to a contact on the member (12) from the measured bending wave signal, the processor applying a correction based on the dispersion relation of the material of the member (12) supporting the bending waves, characterised in that the device (10) comprises a second sensor (16) to determine a second measured bending wave signal which is measured simultaneously with the first measured bending wave signal and the processor calculates a dispersion corrected function of the two measured bending wave signals which is selected from the group consisting of a dispersion corrected correlation function, a dispersion corrected convolution function, a dispersion corrected coherence function and other phase equivalent functions to determine information relating to the contact.

Claims

1. A contact sensitive device comprising a member capable of supporting bending waves, a first sensor mounted on the member for measuring bending wave vibration in the member, the sensor determining a first measured bending wave signal and a processor which calculates information relating to a contact on the member from the measured bending wave signal, the processor applying a correction based on the dispersion relation of the material of the member supporting the bending waves, characterised in that the device comprises a second sensor to determine a second measured bending wave signal which is measured simultaneously with the first measured bending wave signal and the processor calculates a dispersion corrected function of the two measured bending wave signals which is selected from the group consisting of a dispersion corrected correlation function, a dispersion corrected convolution function, a dispersion corrected coherence function and other phase equivalent functions to determine information relating to the contact.

2. A contact sensitive device according to claim 1, wherein the first sensor acts as the second sensor whereby the calculated dispersion corrected function is an autocorrelation function.

3. A contact sensitive device according to claim 1 or claim 2, comprising a second pair of sensors to determine two additional measured bending wave signals from which a second dispersion corrected function is calculated.

4. A contact sensitive device according to claim 3, wherein the processor determines from each dispersion corrected function a first difference in path-length between the contact site and each of the first and second sensors and a second difference in path-length between the contact site and each of the second pair of sensors and determines the location of the contact from the first and second differences in path-length.

5. A contact sensitive device according to any preceding claim, comprising absorbers mounted around at least part of the periphery of the member to absorb reflected waves.

6. A contact sensitive device according to any preceding claim, wherein the processor is configured to remove the contribution of reflected waves from the measured bending wave signal.

7. A contact sensitive device according to claim 6, wherein the processor comprises a low-pass filtering operator which operates on the measured bending wave signal and which comprises an averaging window having a width which varies locally with time.

8. A contact sensitive device according to claim 6 or claim 7, wherein the processor is configured to provide an estimate for the distance between the contact site and each sensor, the estimate being substituted into a calculation to remove the reflected waves.

9. A contact sensitive device according to any preceding claim, comprising multiple sensors on the member whereby multiple dispersion corrected functions are determined.

10. A contact sensitive device according to claim 9, wherein the processor is configured to create a mapping function which maps the surface of the member for each dispersion corrected function.

11. A contact sensitive device according to any one of the preceding claims, wherein the member is an acoustic radiator and an emitting transducer is mounted to the member to excite bending wave vibration in the member to generate an acoustic output.

12. A contact sensitive device according to claim 11, comprising means ensuring that the acoustic output and measured bending wave signals are in discrete frequency bands.

13. A contact sensitive device according to claim 12, comprising an adaptive noise canceller for removing the contribution of the acoustic output from the measured bending wave signal.

14. A contact sensitive device according to any one of the preceding claims, wherein the member is transparent.

15. A contact sensitive device according to any one of the preceding claims, wherein the processor estimates a convolution correction coefficient which is applied to the dispersion corrected function thereby compensating for phase differences between the sensors.

16. A contact sensitive device according to any one of the preceding claims, wherein the member comprises a raised pattern on its surface whereby a contact drawn across the surface provides a variable force to the member to generate bending waves in the member.

17. A contact sensitive device according to claim 16, wherein the pattern is random whereby random bending wave vibration is generated in the member.

18. A contact sensitive device according to any one of the preceding claims, comprising means for recording sets of first and second measured bending wave signals from the or each sensor over time as the contact moves across the member.

19. A contact sensitive device according to claim 18, wherein the processor is adapted to analyse the measured bending wave signals as a sequence of frames of data.

20. A contact sensitive device according to claim 18, wherein the processor is adapted to extract information on the contact which has been averaged over the duration of the frame.

21. A contact sensitive device according to any one of the preceding claims, wherein the processor comprises an adaptive filter which calculates a convolution function between the set of first measured bending wave signals and the set of second measured bending wave signals.

22. A contact sensitive device according to claim 21, wherein the processor is adapted to use a dispersion corrected convolution function to calculate information about the contact.

48. A contact sensitive device according to any one of claims 1 to 22 and 40 to 48, wherein the device is a purely passive sensor with the bending wave vibration and hence the measured bending wave signals are generated by an initial impact or by frictional movement of the contact.

49. A contact sensitive device according to any one of claims 1 to 22 or 40 to 48, wherein the device is an active sensor comprising an emitting transducer.

50. A contact sensitive device according to claim 48 or claim 49, wherein the device is a dual active and passive sensor and is configured to switch between active and passive sensing modes depending on whether contact is applied to the device.

51. A contact sensitive device according to claim 50, wherein the device cycles between resting in passive sensing mode when no contact is detected, switching to active mode sensing when a contact is applied and returning to passive sensing mode once the contact is removed to wait for further contacts.

23. A method of determining information relating to a contact on a contact sensitive device comprising the steps of

providing a member capable of supporting bending waves and a first sensor mounted on the member for measuring bending wave vibration in the member,

determining, using the sensor, a first measured bending wave signal characterised by

providing a second sensor mounted on the member to determine a second measured bending wave signal,

measuring the second measured bending wave signal simultaneously with the first measured bending wave signal,

calculating a dispersion corrected function of the two measured bending wave signals which is selected from the group consisting of a dispersion corrected correlation function, a dispersion corrected convolution function, a dispersion corrected coherence function and other phase equivalent functions and

processing the measured bending wave signals to calculate information relating to the contact by applying the dispersion corrected function.

24. A method according to claim 23, wherein the dispersion corrected correlation function is calculated by the following steps:

calculate the Fourier transformation and complex conjugate Fourier transformation of the two measured bending wave signals;

calculate an intermediate function by multiplication of the Fourier transformation and complex conjugate Fourier transformation of the two bending wave signals;

combine a frequency stretching operation and subsequent inverse Fourier transformation with the intermediate function to give the dispersion corrected correlation function.

25. A method according to claim 23, wherein a phase equivalent function is calculated by the following steps:

calculate the Fourier transformation and complex conjugate Fourier transformation of the two measured bending wave signals;

calculate a first intermediate function by multiplication of the Fourier transformation and complex conjugate Fourier transformation of the two bending wave signals;

calculate a second intermediate function which is a function of the intermediate function;

combine a frequency stretching operation and subsequent inverse Fourier transform with the second intermediate function to give the phase equivalent function.

26. A method according to claim 25, wherein the second intermediate function is calculated by normalising the first intermediate function to give the dispersion corrected coherence function.

27. A method according to any one of claims 24 to 26, comprising removing the effect of reflections before calculating the or each intermediate function.

28. A method according to any one of claims 23 to 27, comprising using the dispersion corrected function to determine a difference in path-length between the contact site and each sensor and hence to determine the location of the contact.

29. A method according to any one of claims 23 to 28, comprising providing a transducer which acts as both the first and second sensor and calculating a dispersion corrected autocorrelation function.

30. A method according to any one of claims 23 to 29, comprising providing a second pair of sensors to determine two additional measured bending wave signals from which a second dispersion corrected function is calculated.

31. A method according to claim 30, comprising determining from each dispersion corrected function a first difference in path-length between the contact site and each of the first and second sensors and a second difference in path-length between the contact site and each of the second pair of sensors and determining the location of the contact from the first and second differences in path-length.

32. A method according to any one of claims 23 to 31, comprising removing the contribution of reflected waves from each measured bending wave signal by operating a low-pass filtering operation on the measured bending wave signals.

33. A method according to any one of claims 23 to 31, comprising providing multiple sensors on the member whereby multiple dispersion corrected functions are determined.

34. A method according to claim 33, comprising creating a mapping function which maps the surface of the member for each dispersion corrected function.

35. A method according to any one of claims 23 to 34, comprising calculating a convolution correction coefficient and applying the convolution correction coefficient when calculating the dispersion corrected function to compensate for any phase differences between the sensors.

36. A method according to any one of claims 23 to 35, comprising recording a set of first measured bending wave signals and a set of second measured bending wave signals from the or each sensor over time as the contact moves across the member.

37. A method according to claim 36, comprising analysing the sets as a sequence of frames of data.

38. A method according to claim 37, comprising extracting information relating to the contact from each frame which has been averaged over the duration of the frame.

39. A method according to claim 37 or claim 38, comprising correcting for a convolution function between the sets.

40. A contact sensitive device comprising a member capable of supporting bending waves, a sensor mounted on the member for measuring bending wave vibration in the member to determine a first measured bending wave signal and a processor which calculates information relating to a contact from the measured bending wave signal from the sensor, characterised in that the device comprises at least a second sensor to determine a second measured bending wave signal which is measured simultaneously with the first measured bending wave signal and the processor optimises a product of a set of corrected impulse response measurements from each sensor to determine information related to the contact.

41. A contact sensitive device according to claim 40, wherein the corrected impulse response measurement is calculated by using the following steps:

Calculate the Fourier transform of the measured bending wave signal;

Calculate an equivalent response from a notional sensor positioned at the contact site

Calculate the inverse Fourier transform of the equivalent response to provide a function to be optimised.

42. A contact sensitive device according to claim 41, wherein the optimisation process involve iterative refinement of estimates of the location of the contact and the time for which the maximum value of the product is obtained.

43. A contact sensitive device according to claim 42, wherein an initial estimate is derived from impulse response functions whose high frequency components have been suppressed.

47. A contact sensitive device according to any one of claims 40 to 46, wherein the processor is configured to determine the contact position by using knowledge of the periodicity of the pattern and the fact that the interval between impulses represents the time in which a contact has travelled to an adjacent feature of the pattern.

44. A contact sensitive device comprising a member capable of supporting bending waves, a sensor mounted on the member for measuring bending wave vibration in the member to determine a first measured bending wave signal and a processor which calculates information relating to the contact from the measured bending wave signal from the sensor, characterised in that a surface of the members comprises a raised pattern whereby a contact drawn across the surface provides a variable force to the member to generate bending waves in the member.

45. A contact sensitive device according to claim 44, wherein the pattern is periodic.

46. A contact sensitive device according to claim 45, wherein the pattern is quasi-periodic with a statistically well-defined spatial distribution of undulations.