Intelligent vehicle highway system sensor and method

• US 5,546,188 A
• Filed: 01/10/1994
• Issued: 08/13/1996
• Est. Priority Date: 11/23/1992
• Status: Expired due to Term

• Current Assignee: OSI Defense Systems LLC (OSI Systems Incorporated)
• Original Assignee: Schwartz Electro-Optics Incorporated
• Inventors: Gustavson, Robert L., Wangler, Richard J., McConnell, Robert E. II, Fowler, Keith L.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/179,568
• Time in Patent Office: 946 Days
• Field of Search: 356/376, 356/398
• US Class Current: 356/5.01
• CPC Class Codes: A01M 7/0089 Regulating or controlling systems the delivery being related to the movement of a vehicle B05B9/06
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• 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 17/14 wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/50 Systems of measurement based on relative movement of target
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/486 Receivers
• 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
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors

Abstract

An object sensor and method using pulsed laser range imaging technology is adapted for determining the velocity and three dimensional profile of a vehicle passing the sensor for classifying the type of vehicle for use in Intelligent Vehicle Highway Systems. A pair of scanned laser beams are provided by splitting a continuously pulsed laser beam from a transmitter and an optical receiver determines the presence of a vehicle in a predetermined zone such as a highway weigh station or toll booth. Range, angle and time data are collected and stored for use in determining the speed of the vehicle passing the sensor and its three dimensional profile. Forward and backward scanned beams are provided using alternate embodiments of a rotating mirror and using two transmitters/receivers in another embodiment. The pulsed energy is sent into the two divergent beams, which are received as reflective energy in a receiver. The receiver accepts reflections from the beams and provides inputs for purposes of determining time of flight, and for measuring the time interval between interceptions of the two divergent beams for a given vehicle. An encoder tracks the position of the mirror for providing angle data with associated range measurements. The vehicle speed is calculated for range data collected when the vehicle passes through the forward and backward scanned beams. Three dimensional profiles are compared with preselected vehicle profiles for classifying the vehicle.

Claims

1. A laser sensor useful in determining the shape of a vehicle, the sensor comprising:

laser means for determining a range from the sensor to points on a vehicle when the vehicle travels within a sensing zone of the sensor and for providing range data outputs corresponding to sensor angles for ranges from the sensor to the points on the vehicle;

means for scanning the laser means within a plane across the vehicle for determining the range for the points on two dimensions of the vehicle, the scanning means having a scanning direction generally orthogonal to a direction of travel for the vehicle the scanning means providing means for determining the range and a corresponding sensor angle for each point within the scanning plane;

means for determining a vehicle speed; and

means for processing the ranges, angles and vehicle speed for providing a multiplicity of two dimensional cross-sectional profiles of the vehicle, the processing means positioning the profiles based on the vehicle speed for providing a three dimensional image representative of the vehicle, the image useful in classifying the vehicle.

2. The sensor as recited in claim 1, wherein the speed determining means comprises:

means for providing a forward beam and a backward beam emitted by the laser means, the forward and backward beams diverging at a predetermined angle, the beams directed toward the sensing zone through which zone the vehicle travels, the beams separated by a predetermined distance;

a first time signal provided by the laser means representative of an interception of a point on the vehicle with the forward beam; and

a second time signal provided by the laser means representative of the interception of the point by the backward beam to travel between the beams, the first and second times providing the travel time for the predetermined distance between the beams, the time signals determined from time-of-flight data provided by the range processing means.

3. A sensor as recited in claim 1, wherein the scanning means comprises:

a mirror intercepting the emitted beam and reflecting the beam into a plane, a reflected beam directed back toward the mirror being similarly directed into corresponding apertures of a receiver;

means for rotating the mirror about an axis for scanning the beam, the rotating mirror reflecting the scanning beam within the plane; and

an encoder communicating with the mirror for providing the beam orientation and corresponding sensor angle.

4. The sensor as recited in claim 2, wherein the forward and backward beam providing means comprises:

the mirror having a polygon shape; and

first and second reflective facets affixed to the mirror, the first and second facets inclined from each other by a predetermined facet angle, the facets forming the sides of the polygon, wherein the rotating means alternately positions the first and second facets for receiving the emitted laser beam and reflecting the beam into the forward beam when reflected from the first facet and into the backward beam when reflected from the second facet.

5. The sensor as recited in claim 2, wherein the forward and backward beam providing means comprises:

the mirror having a polygon shape wherein equally dimensioned reflective facets form the sides of the polygon;

a nodding mirror positioned to reflect the emitted beam onto the rotating mirror facets; and

means for alternately positioning the nodding mirror into a first position wherein the emitted beam is reflected onto a first portion of the rotating mirror facet for forming the forward beam, and the second nodding mirror position reflects the emitted beam onto a second portion of the rotating mirror facet for forming the backward beam.

6. The sensor as recited in claim 1, wherein the laser range determining means comprises:

a transmitter for emitting a laser beam;

means for directing the beam; and

a receiver for converting a reflected laser beam to a signal, the signal representative of a range between the receiver and a point on the vehicle.

7. A sensor as recited in claim 6, wherein the scanning means comprises:

a mirror intercepting the beam emitted from the transmitter and reflecting the beam into a scanning plane, the plane at a predetermined angle from a perpendicular to a roadway, the reflected beam directed back toward the mirror being similarly directed into 1corresponding apertures of the receiver;

a motor having a rotatable shaft affixed to the mirror for continuously rotating the mirror about the axis; and

an encoder affixed to the motor shaft so as to identify an angular position of the mirror relative to a reference angle.

8. A sensor as recited in claim 2, wherein the scanning means comprises:

a first transmitter and receiver having similarly directed apertures, the first transmitter positioned for emitting a first beam onto a first portion of a rotating reflective surface and reflecting the beam into the forward scanning beam;

a second transmitter and receiver having similarly directed apertures, the second transmitter positioned for emitting a second beam onto a second portion of a rotating reflective surface and reflecting the second emitted beam into the backward scanning beam;

an optically reflective surface for intercepting the beams and reflecting the beams at predetermined angles from a perpendicular to a roadway, the beams reflected off of the vehicle being directed back toward the mirror into corresponding apertures of the receivers;

means for rotating the reflective surface across a reflective angle sufficient for reflecting the beams across a transverse portion of the vehicle, the reflective surface positioned to receive the first beam onto a first portion of the surface and receiving the second beam onto a second portion of the surface; and

an encoder affixed to the rotating means for identifying an angular position of the mirror relative to a reference angle and providing a signal representative of the sensor angle of the scanning beams, the angle signals delivered to the processing means for providing range data at corresponding angles, the range and angle data in combination useful in providing a transverse profile of the vehicle.

9. The sensor as recited in claim 1, wherein the processing means comprises a microprocessor programmed to receive respective range and sensor angle data for storing and processing the data for a scanned cycle associated with a vehicle speed, whereby such processed data results in a shape profile suitable for use in classifying the vehicle.

10. The sensor as recited in claim 9, further comprising an algorithm for comparing the vehicle profile with a multiplicity of predetermined vehicle shapes for classifying the vehicle.

11. A sensor for detecting the presence of an object within an area, the sensor comprising:

means for emitting a first output of pulsed, coherent radiation in a forward plane toward a first fixed area a known distance from the emitting means;

means for scanning the first output radiation across the first fixed area;

means for receiving a portion of the returning first pulsed energy reflected from the first area;

means for determining a time of flight change for pulses between the first emitting and first receiving means caused by the presence of an object in the first area;

means for emitting a second output of pulsed, coherent radiation in a backward plane toward a second fixed area a known distance from the emitting means;

means for scanning the second output radiation across the second fixed area;

means for receiving a portion of the returning second pulsed energy reflected from the second area;

means for diverting the pulsed energy output of the emitting means into two diverging directional beams;

means for determining a time of flight change for pulses between the second emitting and second receiving means caused by the presence of an object in the second area; and

means for receiving input from the time of flight determining means and for providing range, angle and speed output for indicating whether the object meets one of a plurality of classification criteria.

12. The sensor recited in claim 11, wherein the means for emitting pulses of coherent energy comprises a laser diode.

13. The sensor recited in claim 11 wherein the receiving means comprises two detectors, the sensor further comprising means for alternately selecting between outputs of the two detectors for providing an input to the time of flight determining means.

14. A sensor for detecting the presence of a vehicle within close range and suitable for measuring traffic speed and vehicle classification, the sensor comprising:

means for emitting a directional output of pulsed energy toward a fixed area a known distance from the emitting means;

means for scanning the pulsed energy output in a fixed plane;

means for receiving a portion of returning pulsed energy reflected from the area;

means for determining a time-of-flight change for pulses between the emitting and receiving means caused by the presence of a vehicle in the area;

means for determining a vehicle speed as the vehicle passes through the fixed area;

means for processing signals received from the emitting, scanning, receiving and speed determining means for providing range and sensor angle data, the data useful in determining a vehicle profile; and

means for comparing the vehicle profile with predetermined profiles for classifying the vehicle.

15. The sensor as recited in claim 14, wherein the speed determining means comprises:

means for providing a forward beam and a backward beam emitted by the laser means, the forward and backward beams diverging at a predetermined angle, the beams directed toward the fixed area through which the vehicle travels, the beams separated by a predetermined distance in the area; and

a first time signal provided by the laser means representative of an interception of a point on the vehicle with the forward beam; and

a second time signal provided by the laser means representative of the interception of the point by the backward beam to travel between the beams, the first and second times providing the travel time for the predetermined distance between the beams, the time signals determined from time-of-flight data provided by range processing means.

16. The sensor recited in claim 14 further comprising means including a peak return signal level detector for determining a timing error caused by amplitude variations in returning reflected energy and providing a range correction thereto.

17. The sensor as recited in claim 16 wherein the timing error determining means comprises means for forming a logic-level output representative of the time-of-flight of each pulse.

18. The sensor recited in claim 14 wherein the emitting means comprises means for emitting pulses of coherent infrared radiation.

19. The sensor recited in claim 18 wherein the means for emitting pulses of coherent infrared radiation comprises a laser diode.

20. The sensor recited in claim 19 wherein the laser diode comprises a junction diode, further comprising means for collimating the output of the laser diode.

21. The sensor recited in claim 14 further comprising means for dividing the pulses of the emitting means into two diverging directional beams.

22. The sensor recited in claim 14 wherein the emitting and receiving means comprise respectively two transmitters and two receivers, the sensor further comprising means for selecting between outputs of the two detectors for providing inputs to the time-of-flight determining means.

23. The sensor recited in claim 14 further comprising means for providing an indication of the presence of a vehicle from one of an output from the time-of-flight determining means and an output from the peak return signal level detector.

24. A method for determining the shape of a vehicle useful in classify the vehicle, the method comprising the steps of:

providing a sensor having a laser beam transmitter and optical receiver for the beam;

determining a range from the sensor to a vehicle when the vehicle travels within a sensing zone of the sensor;

providing respective range data outputs corresponding with a sensor angle for a range to a point on the vehicle;

scanning the laser beam across the vehicle for determining the range for points on two dimensions of the vehicle;

determining the beam orientation and a corresponding sensor angle;

determining a vehicle speed; and

processing the ranges and corresponding angles for providing a multiplicity of two dimensional cross-sectional profiles of the vehicle;

positioning the profiles based on the vehicle speed; and

providing a three dimensional image representative of the vehicle, the image useful in classifying the vehicle.

25. The method as recited in claim 24, wherein the speed determining step further comprises the steps of:

providing a forward beam and a backward beam emitted by the laser means, the forward and backward beams diverging at a predetermined angle;

directing the beams toward the sensing zone through which zone the vehicle travels;

separating the beams by a predetermined distance within the zone;

providing a first time signal from the laser means representative of an interception of a point on the vehicle with the forward beam; and

providing a second time signal from the laser means representative of the interception of the point by the backward beam to travel between the beams, the first and second times providing the travel time for the predetermined distance between the beams, the time signals determined from time-of-flight data provided by the range processing means.

26. The method as recited in claim 24, wherein the scanning step comprises:

providing a mirror;

intercepting the emitted beam with the mirror and reflecting the beam into a plane, a reflected beam directed back toward the mirror being similarly directed into corresponding apertures of a receiver;

rotating the mirror about an axis for scanning the beam, the rotating mirror reflecting the scanning beam within the plane; and

providing an encoder for communicating the mirror orientation;

providing the beam orientation and corresponding sensor angle.

27. The method as recited in claim 25, wherein the forward and backward beam providing step comprises the steps of:

forming the mirror into a polygon shape;

affixing first and second reflective facets to the mirror for forming sides of the polygon shape mirror; and

inclining the first and second facets at angles from each other at a predetermined facet angle, wherein the rotating of the mirror alternately positions the first and second facets for receiving the emitted laser beam and reflecting the beam into the forward beam when reflected from the first facet and into the backward beam when reflected from the second facet.

28. The method as recited in claim 25, wherein the forward and backward beam providing step comprises the steps of:

forming the mirror into a polygon shape having equally dimensioned reflective facets forming the sides of the polygon;

positioning a nodding mirror for reflecting the emitted beam onto the rotating mirror facets; and

alternately positioning the nodding mirror into a first position wherein the emitted beam is reflected onto a first portion of the rotating mirror facet for forming the forward beam, and the second nodding mirror position for reflecting the emitted beam onto a second portion of the rotating mirror facet for forming the backward beam.

29. A method for determining the shape of a vehicle for purposes of classification of the vehicle, the method comprising the steps of:

providing a sensor having a laser beam transmitter and an optical receiver for the laser beam;

scanning the laser beam across the vehicle in a predetermined scanning zone;

measuring a range and angle for a plurality of scanned cycles as the vehicle travels through the zone;

measuring a time and distance traveled by the vehicle within the zone; and

processing the measured range, angle, travel time and distance data for determining a vehicle profile and speed.

30. The method as recited in claim 29, wherein the time and distance measuring step further comprises the steps of:

providing a second laser beam transmitter and second optical receiver;

scanning the second laser beam in a divergent plane form the laser beam, both beams scanned across the vehicle in the predetermined scanning zone;

measuring a range and angle for a plurality of scanned cycles as the vehicle travels through the beams in the zone; and

measuring a time interval between intersections of the two diverging beams by the vehicle for calculating the speed of the vehicle from the time and distance traveled by the vehicle within the zone.

31. The method as recited in claim 30, wherein the scanning step comprises the steps of:

providing a mirror;

placing the transmitter and receiver pairs side-by-side;

placing a mirror in the path of the laser beam and positioning the mirror for communicating with the transmitters and receivers;

placing the axis of one transmitter and receiver such that an emitted beam axis and reflected beam axis are parallel and form the forward scanned beam;

placing the axis of the second transmitter and receiver at an angle to the first transmitter and receiver such that an emitted beam axis and reflected beam axis are parallel and form the backward scanned beam divergent from the forward beam;

directing the divergent beams toward a predetermined zone;

providing a motor having a shaft;

affixing the shaft to the mirror for continuously rotating the mirror, the scanning beams being in planes diverging from a perpendicular to a path of travel by the vehicle; and

affixing an encoder to the shaft for associating a scanning angle with a range, the encoder providing a signal output representative of the angle for a given range.

32. The method for sensing an object as recited in claim 29, further comprising the steps of:

measuring a time-of-flight for a given laser beam pulse leaving the transmitter and detected by the receiver after being reflected from the vehicle, the time-of-flight indicating the range for a particular pulse; and

repeating time-of-flight measurements at a plurality of angles, the angles sufficient for scanning a transverse dimension of the vehicle.

33. The method as recited in claim 29, further comprising the steps of:

providing a microprocessor; and

processing range, angle, time and distance information by the microprocessor for calculating vehicle profiles and speed of travel;

providing a microcomputer for receiving the range, angle, time and distance information;

forming vehicle dimensional profiles for comparison with predetermined profiles; and

comparing the vehicle profile with predetermined profiles for classifying the vehicle.