Constructing a waveform from multiple threshold samples

• US 20040070746A1
• Filed: 04/15/2003
• Published: 04/15/2004
• Est. Priority Date: 04/15/2002
• Status: Active Grant

• Current Assignee: Robert Bosch LLC (Robert Bosch GmbH)
• Original Assignee: Robotoolz Incorporated (Robert Bosch GmbH)
• Inventors: Lewis, Robert, Varian, George, Thompson, Chad
• Granted Patent: US 6,950,177 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

Technology is disclosed for measuring distances. A measurement device emits a beam that reflects on the surface of an object. The measurement device determines the distance to the object, based on the time of flight of the beam from transmission to capture by the measurement device. The measurement device derives feedback reference pulses from pulses in the emitted beam and injects them into the device'"'"'s receive path—creating a receive waveform that includes one or more feedback reference pulses and corresponding pulses in the return beam. The device uses the pulses in the waveform to measure time of flight. The measurement device can attenuate the feedback reference pulses to intensities similar or equal to the intensities of the return pulses. The measurement device can include a histogram processor that collects waveform samples at varying comparison thresholds. The device employs the most accurate information at each threshold to create a digitized composite waveform that corresponds to the analog waveform received by the measurement device. In some instances the measurement device can process the digitized waveform—removing noise, scaling reference pulses, and removing distortions caused by pulse trailing edges running into subsequent pulses.

Claims

1. A method for generating a waveform, said method including the steps of:

(a) generating a plurality of waveform histograms for a set of waveforms; and

(b) constructing a composite waveform, based on said plurality of waveform histograms.

2. A method according to claim 1, wherein said method includes the step of:

(c) setting at least one acquisition parameter for each waveform histogram in said plurality of histograms.

3. A method according to claim 2, wherein said at least one acquisition parameter includes a threshold voltage for waveform sampling.

4. A method according to claim 2, wherein said step (c) is performed prior to generating each waveform histogram in said plurality of waveform histograms.

5. A method according to claim 4, wherein said at least one acquisition parameter includes a number of waveforms to sample for a waveform histogram in said plurality of waveform histograms, and spacing between histogram intervals.

6. A method according to claim 1, wherein said step (a) includes the step of:

(1) determining an amplitude for an interval, wherein said interval is included in multiple waveform histograms in said plurality of waveform histograms.

7. A method according to claim 6, wherein said step (a)(1) includes the steps of:

(i) determining an amplitude component for said interval, based on a waveform histogram in said multiple waveform histograms; and

(ii) weighting said amplitude component to obtain a weighted amplitude component.

8. A method according to claim 7, wherein said step (a)(1)(i) and said step (a)(1)(ii) are performed for each waveform histogram in said multiple waveform histograms.

9. A method according to claim 8, wherein said step (a)(1) includes the step of:

(iii) accumulating all of said weighted amplitude components determined for said interval to obtain an accumulated weighted amplitude component.

10. A method according to claim 9, wherein said step (a)(i) includes the step of:

(iv) dividing said accumulated weighted amplitude component by an accumulated weighting factor.

11. A method according to claim 7, wherein said step (a)(1)(i) includes the step of:

determining an additional amplitude.

12. A method according to claim 11, wherein said step (a)(1)(i) includes the step of:

adding said additional amplitude to a waveform sampling threshold associated with said waveform histogram.

13. A method according to claim 11, wherein:

said step (a)(1) includes the step of;

(v) determining an adjusted threshold for said waveform histogram; and

said step (a)(1)(i) includes the step of;

adding said additional amplitude to said adjusted threshold.

14. A method according to claim 11, wherein:

said step (a)(1) includes the step of;

(v) determining an adjusted threshold for said waveform histogram; and

said step (a)(1)(i) includes the steps of;

adding said additional amplitude to said adjusted threshold to obtain a sum; and

applying a re-sampling function to said sum.

15. A method according to claim 14, wherein said re-sampling function corrects for shift in at least one sampling clock.

16. A method according to claim 11, wherein said step of determining an additional amplitude includes the steps of:

determining a sample ratio for said interval in said waveform histogram; and

identifying a value in an inverse error function that corresponds to said additional amplitude.

17. A method according to claim 7, wherein said step (a)(1)(i) employs a weighting factor, wherein said step (a)(1) includes the step of:

(vi) determining said weighting factor, wherein said weighting factor reflects a level of reliability for said amplitude component.

18. A method according to claim 17, wherein said step (a)(1)(vi) includes the steps of:

determining a sample ratio for said interval in said waveform histogram; and

selecting a value in a Gaussian distribution that corresponds to said sample ratio.

19. A method according to claim 6, wherein said step (a)(1) is performed for multiple intervals in said multiple waveform histograms.

20. At least one processor readable storage device having processor readable code embodied on said at least one processor readable storage device, said processor readable code for programming one or more processors to perform a method comprising the steps of:

(a) generating a plurality of waveform histograms for a set of waveforms; and

(b) constructing a composite waveform, based on said plurality of waveform histograms.

21. At least one processor readable storage device according to claim 20, wherein said method includes the step of:

(c) setting at least one acquisition parameter for each waveform histogram in said plurality of histograms.

22. At least one processor readable storage device according to claim 21, wherein said at least one acquisition parameter includes a threshold voltage for waveform sampling.

23. At least one processor readable storage device according to claim 21, wherein said step (c) is performed prior to generating each waveform histogram in said plurality of waveform histograms.

24. At least one processor readable storage device according to claim 23, wherein said at least one acquisition parameter includes a number of waveforms to sample for a waveform histogram in said plurality of waveform histograms, and spacing between histogram intervals.

25. At least one processor readable storage device according to claim 20, wherein said step (a) includes the step of:

(1) determining an amplitude for an interval, wherein said interval is included in multiple waveform histograms in said plurality of waveform histograms.

26. At least one processor readable storage device according to claim 25, wherein said step (a)(1) includes the steps of:

(i) determining an amplitude component for said interval, based on a waveform histogram in said multiple waveform histograms; and

(ii) weighting said amplitude component to obtain a weighted amplitude component.

27. At least one processor readable storage device according to claim 26, wherein said step (a)(1)(i) and said step (a)(1)(ii) are performed for each waveform histogram in said multiple waveform histograms.

28. At least one processor readable storage device according to claim 27, wherein said step (a)(1) includes the step of:

(iii) accumulating all of said weighted amplitude components determined for said interval to obtain an accumulated weighted amplitude component.

29. At least one processor readable storage device according to claim 28, wherein said step (a)(i) includes the step of:

(iv) dividing said accumulated weighted amplitude component by an accumulated weighting factor.

30. At least one processor readable storage device according to claim 26, wherein said step (a)(1)(i) includes the step of:

determining an additional amplitude.

31. At least one processor readable storage device according to claim 30, wherein said step (a)(1)(i) includes the step of:

adding said additional amplitude to a waveform sampling threshold associated with said waveform histogram.

32. At least one processor readable storage device according to claim 30, wherein:

said step (a)(1) includes the step of;

(v) determining an adjusted threshold for said waveform histogram; and

said step (a)(1)(i) includes the step of;

adding said additional amplitude to said adjusted threshold.

33. At least one processor readable storage device according to claim 30, wherein:

said step (a)(1) includes the step of;

(v) determining an adjusted threshold for said waveform histogram; and

said step (a)(1)(i) includes the steps of;

adding said additional amplitude to said adjusted threshold to obtain a sum; and

applying a re-sampling function to said sum.

34. At least one processor readable storage device according to claim 33, wherein said re-sampling function corrects for shift in at least one sampling clock.

35. At least one processor readable storage device according to claim 30, wherein said step of determining an additional amplitude includes the steps of:

determining a sample ratio for said interval in said waveform histogram; and

identifying a value in an inverse error function that corresponds to said additional amplitude.

36. At least one processor readable storage device according to claim 26, wherein said step (a)(1)(i) employs a weighting factor, wherein said step (a)(1) includes the step of:

(vi) determining said weighting factor, wherein said weighting factor reflects a level of reliability for said amplitude component.

37. At least one processor readable storage device according to claim 36, wherein said step (a)(1)(vi) includes the steps of:

determining a sample ratio for said interval in said waveform histogram; and

selecting a value in a Gaussian distribution that corresponds to said sample ratio.

38. At least one processor readable storage device according to claim 25, wherein said step (a)(1) is performed for multiple intervals in said multiple waveform histograms.

39. An apparatus, comprising:

at least one storage device; and

at least one processor in communication with said at least one storage device, said at least one processor performs a method comprising the steps of;

(a) generating a plurality of waveform histograms for a set of waveforms; and

(b) constructing a composite waveform, based on said plurality of waveform histograms.

40. An apparatus according to claim 39, wherein said method includes the step of:

(c) setting at least one acquisition parameter for each waveform histogram in said plurality of histograms.

41. An apparatus according to claim 40, wherein said at least one acquisition parameter includes a threshold voltage for waveform sampling.

42. An apparatus according to claim 40, wherein said step (c) is performed prior to generating each waveform histogram in said plurality of waveform histograms.

43. An apparatus according to claim 42, wherein said at least one acquisition parameter includes a number of waveforms to sample for a waveform histogram in said plurality of waveform histograms, and spacing between histogram intervals.

44. An apparatus according to claim 39, wherein said step (a) includes the step of:

(1) determining an amplitude for an interval, wherein said interval is included in multiple waveform histograms in said plurality of waveform histograms.

45. An apparatus according to claim 44, wherein said step (a)(1) includes the steps of:

(i) determining an amplitude component for said interval, based on a waveform histogram in said multiple waveform histograms; and

(ii) weighting said amplitude component to obtain a weighted amplitude component.

46. An apparatus according to claim 45, wherein said step (a)(1)(i) and said step (a)(1)(ii) are performed for each waveform histogram in said multiple waveform histograms.

47. An apparatus according to claim 46, wherein said step (a)(1) includes the step of:

(iii) accumulating all of said weighted amplitude components determined for said interval to obtain an accumulated weighted amplitude component.

48. An apparatus according to claim 47, wherein said step (a)(i) includes the step of:

(iv) dividing said accumulated weighted amplitude component by an accumulated weighting factor.

49. An apparatus according to claim 45, wherein said step (a)(1)(i) includes the step of:

determining an additional amplitude.

50. An apparatus according to claim 49, wherein said step (a)(1)(i) includes the step of:

adding said additional amplitude to a waveform sampling threshold associated with said waveform histogram.

51. An apparatus according to claim 49, wherein:

said step (a)(1) includes the step of;

(v) determining an adjusted threshold for said waveform histogram; and

said step (a)(1)(i) includes the step of;

adding said additional amplitude to said adjusted threshold.

52. An apparatus according to claim 49, wherein:

said step (a)(1) includes the step of;

(v) determining an adjusted threshold for said waveform histogram; and

said step (a)(1)(i) includes the steps of;

adding said additional amplitude to said adjusted threshold to obtain a sum; and

applying a re-sampling function to said sum.

53. An apparatus according to claim 52, wherein said re-sampling function corrects for shift in at least one sampling clock.

54. An apparatus according to claim 49, wherein said step of determining an additional amplitude includes the steps of:

determining a sample ratio for said interval in said waveform histogram; and

identifying a value in an inverse error function that corresponds to said additional amplitude.

55. An apparatus according to claim 45, wherein said step (a)(1)(i) employs a weighting factor, wherein said step (a)(1) includes the step of:

(vi) determining said weighting factor, wherein said weighting factor reflects a level of reliability for said amplitude component.

56. An apparatus according to claim 55, wherein said step (a)(1)(vi) includes the steps of:

determining a sample ratio for said interval in said waveform histogram; and

selecting a value in a Gaussian distribution that corresponds to said sample ratio.

57. An apparatus according to claim 44, wherein said step (a)(1) is performed for multiple intervals in said multiple waveform histograms.

58. An apparatus according to claim 39, wherein said apparatus is a distance measurement device.