Monitoring process and system

• US 20040149939A1
• Filed: 03/29/2004
• Published: 08/05/2004
• Est. Priority Date: 06/04/2001
• Status: Active Grant

• Current Assignee: CEOS Industrial Pty Limited
• Original Assignee: CEOS Industrial Pty Limited
• Inventors: Dickson, Adam Matthew, Phillips, Austin, Spring, Jonathan, Murtonen, Casper, Robb, Terrance
• Granted Patent: US 7,522,044 B2
• Time in Patent Office: Days
• US Class Current: 250/559.12
• CPC Class Codes: G01P 3/68 using optical means, i.e. using infrared, visible, or ultraviolet light G01P3/80 takes precedence ; by reflection of waves G01S17/58
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors

Abstract

A monitoring system includes a transmitter (102) with two transmit modules (208, 210) and a receiver (104) with two receive modules (212, 214). Each of the transmit modules (208, 210) generates an optical signal modulated at a unique frequency. The optical signals are transmitted across a roadway (112) and are detected by the receive modules (212, 214). When a vehicle (110) moves between the transmitter (102) and receiver (104), the optical signals are blocked. The receiver (104) generates timestamped make and break events corresponding to the blocking and unblocking of the signals, and these are used to determine parameters for the vehicle (110) such as velocity and vehicle classification. Because each signal is modulated at a different frequency, each receive module (212, 214) can distinguish the signals received from each of the transmit modules (208, 210), allowing the lane position of the vehicle (110) in a multi-lane roadway (112) to be determined.

Claims

1. A process for monitoring a moving object, including the steps of:

generating an optical signal modulated at a modulation frequency;

transmitting said optical signal across a path of said moving object;

detecting changes in a received signal due to movement of said object by monitoring substantially at said modulation frequency; and

determining at least one parameter of said object on the basis of said changes.

2. A process as claimed in claim 1, wherein said changes represent making and breaking the receive signal due to passage of said object.

3. A process as claimed in claim 1, wherein said changes include changes in a modulation spectrum of said received signal due to the passage of said object.

4. A process as claimed in claim 2, including determining timestamps for making and breaking events, respectively, corresponding to said making and breaking of the receive signal.

5. A process as claimed in any one of the preceding claims, wherein said generating includes generating first and second optical signals modulated substantially at said modulation frequency, and said detecting includes detecting changes in first and second received signals by monitoring substantially at said modulation frequency.

6. A process as claimed in any one of claims 1 to 4, wherein said generating includes generating a first optical signal modulated at a first modulation frequency, and a second optical signal modulated at a second modulation frequency, and said detecting includes detecting a first received signal by monitoring substantially at said first modulation frequency, and detecting a second received signal by monitoring substantially at said second modulation frequency.

7. A process as claimed in claim 6, wherein said first received signal and said second received signal are detected at respective locations mutually spaced in a moving direction of said object.

8. A process as claimed in claim 7, wherein said first modulation frequency and said second modulation frequency are sufficiently close together so that harmonics of said first modulation frequency can be distinguished from harmonics of said second modulation frequency.

9. A process as claimed in claim 6, wherein said first modulation frequency and said second modulation frequency are sufficiently low that they are not significantly affected by noise that increases with frequency in an electronic circuit used to receive said received signals.

10. A process as claimed in of claim 6, wherein said first modulation frequency and said second modulation frequency are sufficiently high that they are not significantly affected by 1/f noise in an electronic circuit used to receive one of said received signals.

11. A process as claimed in claim 6, wherein said first modulation frequency and said second modulation frequency are sufficiently high that individual cycles of said frequencies are short in duration compared to the blocking of the respective optical signal due to the passage of said object.

12. A process as claimed in claim 6, wherein said first modulation frequency and said second modulation frequency are sufficiently high that the fractional bandwidth is small to maintain good noise performance.

13. A process as claimed in claim 6, wherein said step of determining includes:

generating timestamped make and/or break events representing the making and breaking of said first and second received signals due to the passage of said moving object and at least one other object past two detection locations for said signals, said locations mutually spaced in a moving direction of said objects;

selecting at least one event for said first signal;

for each selected event;

forming pairs of said selected event with events of the same type for said second signal;

for each pair, determining a velocity value from the timestamp values of said pair;

forming at least one pair of correlated event pairs by correlating event pairs for a selected event with event pairs for another selected event having a substantially equal velocity;

for each pair of correlated event pairs, determining a length value from timestamp values of said pair of correlated event pairs;

associating with said moving object at least one pair of correlated event pairs whose length value is less than a pre-determined value; and

determining at least one parameter of said moving object from timestamp values of said associated event pairs.

38. A process as claimed in any one of claims 1 to 31, wherein said at least one object parameter includes the passage of said object.

39. A process as claimed in any one of claims 1 to 31 and 38, wherein said at least one object parameter includes a moving direction of said object.

40. A process as claimed in any one of claims 1 to 31, 38, and 29, wherein said at least one object parameter includes a speed or velocity of said object.

41. A process as claimed in any one of claims 1 to 31 and 38 to 40, wherein said at least one parameter includes a dimension of said object.

42. A process as claimed in claim 41, wherein said dimension is used to classify said object.

43. A process as claimed in any one of claims 1 to 31 and 38 to 42, wherein said at least one object parameter includes a classification of said object.

44. A process as claimed in claim 43, wherein said object includes a vehicle, and said classification is into one of a number of vehicle types.

61. A monitoring system having components for executing the steps of any one of claims 1 to 44 and 58.

62. Software having program code for executing the steps of any one of claims 1 to 44 and 58.

63. A computer readable storage medium, having stored thereon program code for executing the steps of any one of claims 1 to 44 and 58.

14. A process for determining a position of a moving object, including associating a time value with at least one make or break event for each of at least three signals due to the passage of said object between a transmitter and a receiver of each of said signals, at least one of said signals being substantially inclined with respect to another of said signals, and determining the position of said object in a direction substantially transverse to said moving direction by comparing said time values.

15. A process as claimed in claim 14, including associating respective time values with four make or break events for respective signals comprising first and second substantially parallel signals substantially transverse to said moving direction, transmitted from respective first and second transmitters mutually spaced in said moving direction and received at respective first and second receivers, and third and fourth signals respectively transmitted from said first transmitter and received at said second receiver, and transmitted from said second transmitter and received at said first receiver.

16. A process as claimed in claim 14 or 15, wherein said transmitters and said receivers are positioned to substantially delineate a rectangle.

17. A process as claimed in claim 14, wherein said comparing includes determining a ratio of differences in time values for the events.

18. A process as claimed in claim 15, wherein said step of determining includes determining a ratio of a difference in time values for one of the parallel signals and at least one of said third and fourth signals and the difference in time values for said parallel signals.

19. A process as claimed in claim 17 or 18, wherein said comparing also includes scaling said ratio by the separation between a transmitter and a corresponding receiver.

20. A process for determining at least one parameter of a moving object from timestamped make and break events representing the making and breaking of first and second signals due to the passage of at least two moving objects past two detection locations for said signals, said locations mutually spaced in a moving direction of said objects, and said at least two moving objects being mutually spaced substantially transverse to said moving direction, said process including:

selecting at least two events for said first signal;

for each selected event;

forming pairs of said selected event with events of the same type for said second signal;

for each pair, determining a velocity value from the timestamp values of said pair;

forming at least one pair of correlated event pairs by correlating event pairs for a selected event with event pairs for another selected event having a substantially equal velocity;

for each pair of correlated event pairs, determining a length value from timestamp values of said pair of correlated event pairs;

associating with said object a pair of correlated event pairs whose length value is less than a pre-determined value; and

determining at least one parameter of said object from timestamp values of said associated event pairs.

21. A process for discriminating between objects moving in a moving direction and spaced substantially transverse to said moving direction, including:

sending signals across a path of said moving objects;

detecting changes in state of said signals and recording events for said changes with respective times; and

processing said events of said signals to group events corresponding to a respective moving object on the basis of said times for said events.

22. A process as claimed in claim 21, wherein the process includes determining at least one parameter of a respective moving object on the basis of said times for said events.

23. A process as claimed in claim 21, wherein said at least one parameter includes a distance value in said transverse direction for said object.

24. A process as claimed in claim 21, wherein said object is a vehicle and said distance value identifies a lane within a multi-lane roadway.

25. A process as claimed in claim 21, wherein the events in a group include events of said signals having corresponding times, and said processing includes determining a velocity on the basis of a separation distance for said signals for events having corresponding times.

26. A process as claimed in claim 21, wherein said processing includes placing events representing a common velocity in a group.

27. A process as claimed in claim 21, wherein said processing includes further determining said groups of events on the basis of dimensions for said moving objects having the velocity of said group.

28. A process for monitoring a moving object, including receiving an optical signal modulated at a modulation frequency, converting said optical signal to an electrical signal, digitising said electrical signal, and downconverting said digitised signal to provide data representative of at least one parameter of said object.

29. A process as claimed in claim 28, wherein said downconverting is digital quadrature amplitude modulation direct downconversion.

30. A process as claimed in claim 28 or 29, wherein said data represents the making and/or breaking of said optical signal due to movement of said object.

31. A process as claimed in claim 30, wherein the process includes determining timestamps for said making and/or breaking events.

32. A system for monitoring a moving object, including a receiver for receiving an optical signal modulated at a modulation frequency, said receiver including an input module for converting said optical signal to an electrical signal, an analog-to-digital (ADC) converter for digitising said electrical signal, and a digital signal processor (DSP) for demodulating said digitised signal and providing output data representative of at least one parameter of said object.

33. A system as claimed in claim 32, wherein said output data includes I and Q quadrature data.

34. A system as claimed in claim 33, including means to lock a frequency of at least one oscillator to said modulation frequency on the basis of said quadrature data.

35. A system as claimed in any one of claims 32 to 34, wherein said system includes two receivers mutually spaced in a moving direction of said object.

36. A system as claimed in any one of claims 32 to 35, wherein a speed of said object is determined by a time difference between respective signal making or breaking data of said two receivers.

37. A system as claimed in any one of claims 32 to 36, including at least one switch-mode power supply synchronised to half of the ADC sampling frequency, and wherein said DSP is adapted to reduce digital signal artifacts from said power supply.

45. A receive module for receiving a signal modulated at a modulation frequency, said receive module including a sensor coupled to an input circuit having at least one variable resonant circuit, and feedback circuitry for matching the resonant frequency of said resonant circuit to said modulation frequency to maximise the input impedance of the input circuit at said modulation frequency.

46. A receive module as claimed in claim 45, wherein said at least one variable resonant circuit includes a varactor and an inductor in parallel.

47. A receive module as claimed in claims 45 or 46, wherein the impedance of said variable resonant circuit at said modulation frequency is at least several Mega-ohms.

48. A receive module as claimed in any one of claims 45 to 47, wherein said signal is an optical signal, and said sensor is an optical sensor.

49. A receive module as claimed in claim 48, wherein one of said variable resonant circuits includes an inductor used for biasing said optical sensor.

50. A receive module as claimed in any one of claims 45 to 49, wherein said input circuit includes an input electrode sensitive to capacitance of said sensor and said input circuit, at least one guard electrode, and a bootstrap circuit for matching the potential of said at least one guard electrode to the potential of said input electrode.

51. A receive module as claimed in claim 50, wherein said bootstrap circuit includes an amplifier and a variable resonant circuit for reducing noise coupled into said input electrode from said amplifier.

52. A receive module as claimed in claim 51, wherein said variable resonant network of said bootstrap circuit includes a varactor and an inductor in parallel.

53. A receive module as claimed in any one of claims 50 to 52, wherein said bootstrap circuit has substantially unity gain and substantially zero phase shift at said modulation frequency.

54. A receive module as claimed in any one of claims 50 to 53, wherein said bootstrap circuit can be selectively disabled by grounding said at least one guard electrode.

55. A receive module as claimed in any one of claims 45 to 54, wherein said input circuit includes a signal amplifier with variable feedback.

56. A receive module as claimed in claim 55, wherein said variable feedback and said at least one variable resonant circuit are varied under control of a microprocessor of said receiver to maintain stability of said input circuit.

57. A receive module as claimed in any one of claims 55 and 56, wherein said signal amplifier and at least one associated feedback component are components of a transimpedance amplifier.

58. A process for tuning the bias varactor of the bias circuit and the bootstrap varactor of the bootstrap circuit claimed in any one of claims 50 to 57, including the steps of,

(i) setting said bootstrap varactor to a nominal value;

(ii) enabling the bootstrap circuit;

(iii)maximising loop gain of a signal amplifier of said bootstrap circuit at said modulation frequency by tuning said bias varactor;

(iv) disabling said bootstrap circuit;

(v) maximising the loop gain of said signal amplifier at said modulation frequency by tuning said bootstrap varactor; and

(vi)repeating steps (ii) to (v) until the tuning voltages applied to each varactor converge.

59. A receiver including at least two receive modules, said receive modules being mutually spaced in a moving direction of an object, and each receive module being adapted to receive an optical signal modulated at a unique frequency.

60. A system for monitoring a moving object, including at least two transmitter modules for transmitting respective optical signals, each of said optical signals being modulated at a unique frequency.

64. A monitoring system for vehicles, including:

transmit modules for transmitting separated optical signals at respective modulation frequencies across a carriageway for said vehicles;

receive modules for detecting optical signals substantially at said modulation frequencies, respectively;

means for generating make and break event data corresponding to unblocking and blocking of said signals by at least one of said vehicles; and

means for determining at least one parameter for the vehicle on the basis of said event data, which includes time values corresponding to said unblocking and blocking.