Non-intrusive laser-based system for detecting objects moving across a planar surface

• US 6,404,506 B1
• Filed: 03/08/1999
• Issued: 06/11/2002
• Est. Priority Date: 03/09/1998
• Status: Expired due to Fees

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Shaw, Benjamin D., Katwyk, Kirk Van, Larson, Jonathan E., Cheng, Harry H., Hu, Xudong, Palen, Joe
• Primary Examiner(s): Kim, Robert H.
• Assistant Examiner(s): Nguyen, Sang H.
• Application Number:
  US09/264,828
• Time in Patent Office: 1,191 Days
• Field of Search: 356/383, 356/384, 356/385, 356/386, 356/387, 356/376, 356/285, 356/614, 356/615, 356/628, 356/634, 356/635, 356/639, 356/640, 250/559.22, 250/559.26, 250/559.24, 250/216, 250/208.2, 250/206, 348/149, 340/942, 340/934
• US Class Current: 356/634
• CPC Class Codes: G01B 11/04 specially adapted for measuring length or width of objects while moving

Abstract

In current practice, quantitative traffic data is most commonly acquired from inductive loops. In addition, video-image processing or time-of-flight laser systems can be used. These methods all have problems associated with them. Therefore, we have developed a new type of non-intrusive laser-based detection system for measurement of vehicle travel time. The system employs a fan angle laser, an image lens, a set of cylindrical optics, a linear photodetector array, and associated signal processing hardware and software. The system is positioned above the plane of detection and configured such that it can unambiguously find the object boundaries in all lighting conditions independent of the time-of-flight of the laser. Instead of depending upon the reflectance of the object being detected, or determination of the range or distance from the detector to the object being detected, the invention reflects the laser off of the pavement or other roadway surface. The lack of a reflection determines the size, shape, and “presence” of the vehicle, and the system is capable of determining the length and width of moving objects, as well as travel time, in real time with high resolution.

Claims

1. An apparatus for determining the length of an object moving along a planar surface, comprising:

(a) a laser transmitter, said laser transmitter including a line generator configured to generate a fan angle beam of light in a first plane directed toward a planar surface;

(b) a laser receiver, said laser receiver spatially offset from said laser transmitter, said laser receiver including a linear array of photodiodes configured to have a field of view for detecting light reflected from said planar surface in a second plane which is offset from said first plane; and

(c) a programmed data processor, said programmed data processor including software for carrying out the operations of processing signals received from said laser receiver and determining the length of an object passing through the field of view of the laser receiver based on absence of reflection of said beam of light from said planar surface.

2. An apparatus as recited in claim 1, further comprising an image lens positioned between said laser receiver and said planar surface.

3. An apparatus as recited in claim 2, further comprising a telescopic lens positioned between said image lens and said planar surface.

4. An apparatus as recited in claim 3, further comprising an optical filter positioned between said image lens and said telescopic lens.

5. An apparatus as recited in claim 1, wherein said photodiodes in said linear array are sampled in parallel.

6. An apparatus for determining the length of a vehicle moving along a planar roadway surface in longitudinal direction, comprising:

(a) a laser emitter;

(b) a line generator associated with said laser emitter, said laser emitter and said line generator configured to generate a fan angle beam of light laterally across said roadway surface in a first vertical plane angularly offset from a vertical plane perpendicular to said roadway surface;

(c) an optical sensor, said optical sensor having a linear array of photodiodes positioned with a field of view in a second plane substantially perpendicular to said roadway surface; and

(d) a computer, said computer including software for carrying out the operations of processing signals received from photodiodes in parallel and determining the length of said vehicle passing through the field of view of said optical sensor based on absence of reflection of said beam of light from said roadway surface.

7. An apparatus as recited in claim 6, further comprising an image lens positioned between said optical sensor and said planar surface.

8. An apparatus as recited in claim 7, further comprising a telescopic lens positioned between said image lens and said planar surface.

9. An apparatus as recited in claim 8, further comprising an optical filter positioned between said image lens and said telescopic lens.

10. An apparatus for determining the length of a vehicle moving along a planar roadway surface in a longitudinal direction, comprising:

(a) a pulsed infrared laser positioned above a plane of detection;

(b) line generating optics associated with said laser for protecting A beam on said roadway surface laterally in relation to said direction of travel of said vehicle;

(c) a photodetector positioned above said plane of detection and spatially offset from said laser, said photodetector including a plurality of linearly positioned photodiodes;

(d) imaging optics associated with said photodetector;

(e) said photodetector having a field of view laterally across said roadway surface in relation to said direction of travel of said vehicle;

(f) wherein said beam from said laser is projected in a first plane and said field of view of said photodetector is in a second plane angularly offset from said first plane in relation to said roadway surface; and

(g) a computer, said computer including software for carrying out the operations of processing signals received from photodiodes in parallel and determining the length of said vehicle passing through the field of view of said photodetector based on absence of reflection of said beam of light from said roadway surface.

11. An apparatus as recited in claim 10, wherein said imaging optics comprises:

(a) an image lens positioned between said photodetector and said planar surface; and

(b) a telescopic lens positioned between said image lens and said roadway surface.

12. An apparatus as recited in claim 11, further comprising an optical filter positioned between said image lens and said telescopic lens.

14. An apparatus as recited in claim 12, wherein each said detector unit is includes an image lens positioned between said corresponding laser receiver and said planar surface.

15. An apparatus as recited in claim 14, wherein each said detector unit includes a telescopic lens positioned between said corresponding image lens and said planar surface.

16. An apparatus as recited in claim 15, wherein each said detector unit includes an optical filter positioned between said corresponding image lens and said corresponding telescopic lens.

13. An apparatus for determining the length of an object moving along a planar surface, comprising:

(a) a first detector unit;

(b) a second detector unit spatially offset from said second detector unit;

(c) each said detector unit comprising,

(i) a laser transmitter, said laser transmitter including a line generator configured to generate a fan angle beam of light in a first plane directed toward a planar surface, and

(ii) a laser receiver, said laser receiver spatially offset from said laser transmitter, said laser receiver including a linear array of photodiodes configured to have a field of view for detecting light reflected from said planar surface in a second plane which is offset from said first plane; and

(d) a programmed data processor, said programmed data processor including software for carrying out the operations of processing signals received from said laser receiver and determining the length of an object passing through the field of view of the laser receivers based on absence of reflection of said beams of light from said planar surface.

17. An apparatus an recited in claim 13, wherein said photodiodes in each said linear array are sampled in parallel.

18. An apparatus for determining the length of a vehicle moving along a planar roadway surface in longitudinal direction, comprising:

(a) a optical first emitter/sensor pair;

(b) a optical second emitter/sensor pair;

(c) each said optical emitter/sensor pair comprising

(iii) a laser emitter,

(ii) a line generator associated with said laser emitter, said laser emitter and said line generator configured to generate a fan angle beam of light laterally across said roadway surface in a first vertical plane angularly offset from a vertical plane perpendicular to said roadway surface, and

(iii) an optical sensor, said optical sensor having a linear array of photodiodes positioned with a field of view in a second plane substantially perpendicular to said roadway surface; and

(d) a computer, said computer including software for carrying out the operations of processing signals received from photodiodes in parallel and determining the length of grid vehicle passing through the field of view of said optical sensors based on absence of reflection of said beam of light from said roadway surface.

19. An apparatus as recited in claim 18, wherein each said optical emitter/sensor pair includes an image lens positioned between said corresponding optical sensor and said and said planar surface.

20. An apparatus as recited in claim 19, wherein each said optical emitter/sensor pair includes a telescopic lens positioned between said corresponding image lens and said planar surface.

21. An apparatus as recited in claim 20, wherein each said optical emitter/sensor pair includes an optical filter positioned between said corresponding image lens and said corresponding telescopic lens.

22. An apparatus for determining the length of a vehicle moving along a planar roadway surface in a longitudinal direction, comprising:

(a) first and second laser detector units, each said laser detector unit comprising

(i) a pulsed infrared laser positioned above a plane of detection,

(ii) line generating optics associated with said laser for protecting a beam on said roadway surface laterally in relation to said direction of travel of said vehicle,

(iii) a photodetector positioned above said plane of detection and spatially offset from said laser, said photodetector including a plurality of linearly positioned photodiodes, and

(iv) imaging optics associated with said photodetector,

(v) said photodetector having a field of view laterally across said roadway surface in relation to said direction of travel of said vehicle,

(vi) wherein said beam from said laser is projected in a first plane and said field of view of said photodetector is in a second plane angularly offset from said first plane in relation to said roadway surface; and

(c) a computer, said computer including software for carrying out the operations of processing signals received from photodiodes in parallel and determining the length of said vehicle passing through the field of view of said photodetector based on absence of reflection of said beam of light from said roadway surface.

23. An apparatus as recited in claim 22, wherein said imaging optics associated with each said laser detector comprises:

(a) an image lens positioned between said corresponding photodetector and said roadway surface; and

(b) a telescopic lens positioned between said corresponding image lens and said roadway surface.

24. An apparatus as recited in claim 23, wherein said imaging optics associated with each said laser detector further comprises an optical filter positioned between said corresponding image lens and said corresponding telescopic lens.