Apparatus and method for identifying scanned reflective anonymous targets

• US 5,367,458 A
• Filed: 08/10/1993
• Issued: 11/22/1994
• Est. Priority Date: 08/10/1993
• Status: Expired due to Term

• Current Assignee: John Bean Technologies Corporation
• Original Assignee: Caterpillar Industrial Inc (Caterpillar Incorporated)
• Inventors: Miles, Russell W., Roberts, Malcolm T.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): DAY, JULIE
• Application Number:
  US08/104,867
• Time in Patent Office: 469 Days
• Field of Search: 364/424.02, 364/449, 364/559, 364/561, 364/513, 250/563, 250/561, 180/169, 356/1, 356/375, 356/152, 901/47, 901/1
• US Class Current: 701/25
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G05D 1/0244 using reflecting strips
• CPC Class Codes: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00

Abstract

A method and apparatus for verifying the identity of an observed anonymous target 16 from a plurality of anonymous reflective targets 16 positioned at predetermined spaced apart locations within an area 14 of operation of an automatic guided vehicle 10 is provided. The anonymous targets 16 each have a predetermined width and a predetermined orientation angle. A dead reckoning system 78 and scanner 12 on the vehicle 10 each deliver signals to the onboard computer 52. The onboard computer 52 processes the signals in accordance with preprogrammed instructions and corrects the position and heading of the vehicle 10 based on the sensed position of the reflected electromagnetic radiation delivered from the spaced anonymous targets 16. The onboard computer 52 verifies the identity of the reflecting anonymous targets 16 through an incident and subtended angle analysis which considers the orientation and width of the anonymous targets 16.

Claims

1. A method for determining the identity of an observed anonymous target from a plurality of anonymous targets positioned at predetermined spaced apart locations within an area of operation of an automatic guided vehicle, said vehicle having a scanner and said scanner being adapted to deliver electromagnetic radiation, said targets having a substantially planar reflective upright surface and a predetermined width defined by spaced first and second upright edges, said targets each being oriented at a preselected angle relative to predetermined coordinates, said targets being adapted to reflect the delivered electromagnetic radiation and said scanner being adapted to receive said reflected electromagnetic radiation and deliver a signal in response to receiving said reflected electromagnetic radiation, said automatic guided vehicle having an onboard computer, said computer having memory, and said computer being adapted to process signals delivered from said scanner according to preprogrammed instructions, said predetermined location, orientation, and width of each anonymous target being stored in memory, said vehicle having dead reckoning means for sensing the position of the vehicle and delivering a responsive dead reckoning signal, said computer being adapted to receive said dead reckoning signal and process said dead reckoning signal according to preprogrammed instructions, said method comprising:

estimating the position and heading of the vehicle based on dead reckoning signals;

estimating a bearing angle of the anonymous targets relative to the vehicle based on the estimated position and heading of the vehicle and predetermined anonymous target locations and storing in memory the estimated bearing angles;

delivering electromagnetic radiation and receiving a reflection of the delivered electromagnetic radiation from a first of the plurality of anonymous targets;

measuring the bearing angle of the first anonymous target as a function of reflected electromagnetic radiation received from the first anonymous target;

comparing the measured bearing angle of the first anonymous target with the estimated bearing angle of an associated one of the plurality of anonymous targets and verifying that the measured bearing angle of the first anonymous target is within a preselected bearing angle limit of the estimated bearing angle of the one associated anonymous target;

measuring one of a subtended angle and width of the first anonymous target reflecting said electromagnetic radiation;

calculating one of a subtended angle and width of the related anonymous target selected from memory as a function of the estimated vehicle position and the predetermined target position;

comparing one of the measured width and subtended angle of the first anonymous target with a respective one of the calculated width and subtended angle of the related anonymous target and verifying that the compared one of the width and subtended angle of the first anonymous target and related anonymous target being within a predetermined relative tolerance range of each other; and

storing an identity of the first target in a plausible target list in said computer.

2. A method, as set forth in claim 1, including the steps of:

calculating an incident angle of reflection of the first anonymous target as a function of one of the measured and estimated bearing angles, the orientation of a related anonymous target stored in memory, and an estimated heading of the vehicle;

comparing the calculated incident angle with a predetermined incident angle maximum value; and

preforming said one subtended angle and width calculations and measurements in response to said calculated incident angle being less than said incident angle maximum value.

3. A method, as set forth in claim 2, wherein said incident angle maximum value is 50 degrees.

4. A method, as set forth in claim 1, wherein the estimated subtended angle of the anonymous target is determined according to the calculation:

##EQU6## where ω

=estimated subtended angle, W=width of target, i=incident angle of reflection, and r=distance from vehicle to the target.

5. A method as set forth in claim 1, including the step of:

determining a normalized squared innovation of the first anonymous target and each of a plurality of targets stored in the plausible target list in accordance with the following equation;

##EQU7## where Θ

m=measured angle, θ

=estimated angle, and S=measurement prediction variance.

6. A method as set forth in claim 5, including the steps of:

comparing the normalized squared innovation of the first anonymous target with the plurality of anonymous targets; and

delivering a signal to the guidance computer and correcting the vehicle position and heading in response to the normalized square innovation of the first anonymous target being smaller that the normalized square innovation of each of the plurality of anonymous targets stored in plausible target list.

7. A method as set forth in claim 1, wherein each of said targets having a predetermined region of reflected light and including the step of determining the position of said vehicle being within a region of reflection of the first target based on the estimated position of the vehicle and one of the measured and estimated bearings of the first target.

8. A method as set forth in claim 1, wherein the area of operation of the vehicle is divided into a plurality of discrete areas, said targets being located at preselected locations within said discrete areas, and including the step of considering only those targets located within discrete areas based on the position and heading of the vehicle.

9. A method, as set forth in claim 8, including the step of considering only those targets plausible that are located within a radius having a preselected magnitude, said radius being generated from a preselected point on the vehicle, and said plausible targets being based on the estimated position of the vehicle and the stored position of the targets in memory.

10. A method, as set forth in claim 1, wherein the estimated bearing angle of the related anonymous target is determined by the equation:

##EQU8## where θ

=estimated bearing angle, Y_t =known Y coordinate position of target, Y_v =estimated coordinate position of vehicle, X_t =known X coordinate position of target, X_v =estimated X coordinate position of vehicle, and ω

=estimated heading of vehicle.

11. A method, as set forth in claim 1, wherein the preselected bearing angle association limit is within a range of 3 to 30 degrees.

12. A method, as set forth in claim 1, wherein said scanner being rotatable to deliver said electromagnetic radiation in the form of a light beam in a direction outwardly from an axis of rotation of said scanner during rotation of said scanner at a predetermined speed about said axis, said scanner having a receiver, said receiver being adapted to receive a reflection of said beam, said scanner having a means for sensing the angle of rotation of the scanner, said method including the steps of:

receiving a reflection of said beam in response to said beam sweeping across said target between the first and second edges of said first target;

delivering a signal in response to receiving said reflection;

measuring the angle of rotation of said scanner beam; and

determining the subtended angle of the first target based on the delivered signal and the measured angle of rotation of said scanner.

13. A method, as set forth in claim 1, wherein said dead reckoning means includes sensor means for sensing the direction and distance of travel of said vehicle.

14. A method, as set forth in claim 1, wherein the identity of the first anonymous target being stored in said plausible target list only in response to one of said subtended angle and width of the first anonymous target and respective subtended angle and width of the related anonymous target being within said predetermined relative tolerance range.

15. A method for verifying the identity of an observed anonymous target from a plurality of anonymous targets positioned at predetermined spaced apart locations within an area of operation of an automatic guided vehicle having a laser scanner, dead reckoning means, and an onboard computer having a memory, comprising the steps of:

estimating the position and heading of the vehicle based on dead reckoning;

estimating a bearing angle of the anonymous targets relative to the vehicle based on the estimated position and heading of the vehicle and the predetermined anonymous target locations, and storing in memory the estimated bearing angles;

scanning the area with a laser beam delivered from said laser scanner and receiving a reflection of the laser beam from a first anonymous target of the plurality of anonymous targets;

measuring the bearing angle of the first anonymous target as a function of the laser beam reflection;

comparing the estimated bearing angles of the anonymous targets with the measured bearing angle of the first target and verifying that the measured bearing angle of the first target is within a preselected bearing angle limit of the estimated bearing angle of a related one of the anonymous targets;

calculating an incident angle of reflection of the first anonymous target as a function of one of the measured and estimated bearing angles, the orientation of the related anonymous target stored in memory, and an estimated heading of the of the vehicle;

comparing the calculated incident angle with a predetermined incident angle maximum value;

measuring one of a subtended angle and width of the first anonymous target reflecting said electromagnetic radiation;

calculating one of a subtended angle and width of the related anonymous target selected from memory as a function of the estimated vehicle position and the predetermined target position;

comparing one of the measured width and subtended angle of the first anonymous target with a respective one of the calculated width and subtended angle of the related anonymous target and verifying that the compared one of the width and subtended angle of the first anonymous target and related anonymous target being within a predetermined relative tolerance range of each other; and

storing an identity of the first target in a plausible target list in said computer.

16. A method, as set forth in claim 15, including the steps of:

estimating the position and heading of the vehicle based on dead reckoning;

estimating a bearing angle of the anonymous targets relative to the vehicle based on the estimated position and heading of the vehicle and the predetermined anonymous target locations, and storing in memory the estimated bearing angles;

scanning the area with a laser beam delivered from said laser scanner and receiving a reflection of the laser beam from a second anonymous target of the plurality of anonymous targets;

measuring the bearing angle of the second anonymous target as a function of the laser beam reflection;

comparing the estimated bearing angles of the anonymous targets with the measured bearing angle of the second anonymous target and verifying that the measured bearing angle of the second anonymous target is within a preselected bearing angle limit of the estimated bearing angle of a related one of the anonymous targets;

calculating an incident angle of reflection of the second anonymous target as a function of one of the measured and estimated bearing angles, the orientation of the related anonymous target stored in memory, and an estimated heading of the of the vehicle;

comparing the calculated incident angle with a predetermined incident angle maximum value;

measuring one of a subtended angle and width of the second anonymous target reflecting said electromagnetic radiation;

calculating one of a subtended angle and width of the related anonymous target selected from memory as a function of the estimated vehicle position and the predetermined target position;

comparing one of the measured width and subtended angle of the second anonymous target with a respective one of the calculated width and subtended angle of the related anonymous target and verifying that the compared one of the width and subtended angle of the second anonymous target and related anonymous target being within a predetermined relative tolerance range of each other; and

storing an identity of the second anonymous target in a plausible target list in said computer.

17. A method, as set forth in claim 15, wherein said identity of the first anonymous target being stored in said plausible target list only in response to one of said subtended angle and width of the first anonymous target and respective subtended angle and width of the related anonymous target being within said predetermined relative tolerance range.

18. A method, as set forth in claim 15, wherein said identity of the first anonymous target being storable in said plausible target list only in response to the calculated incident angle of reflection of the first anonymous target being less than a preselected value and one of said subtended angle and width of the first anonymous target and respective subtended angle and width of the related anonymous target being within said predetermined relative tolerance range.

19. A method for verifying the identity of an observed anonymous target from a plurality of anonymous targets positioned at predetermined spaced apart locations within an area of operation of an automatic guided vehicle, said vehicle having a scanner and said scanner being adapted to deliver electromagnetic radiation, said targets having a substantially planar reflective upright surface and a predetermined width defined by spaced first and second upright edges, said targets each being oriented at a preselected angle relative to predetermined coordinates, said targets being adapted to reflect the delivered electromagnetic radiation and said scanner being adapted to receive said reflected electromagnetic radiation and deliver a signal in response to receiving said reflected electromagnetic radiation, said scanner having means for sensing the angular position of the scanner relative to the heading of the vehicle, said automatic guided vehicle having an onboard computer, said computer having memory, and said computer being adapted to process signals delivered from said scanner according to preprogrammed instructions, said predetermined location, orientation, and width of each anonymous target being stored in memory, said vehicle having dead reckoning means for sensing the position of the vehicle and delivering a responsive dead reckoning signal, said computer being adapted to receive said dead reckoning signal and process said dead reckoning signal according to preprogrammed instructions, said method comprising:

measuring one of a subtended angle and width of the first anonymous target reflecting said electromagnetic radiation;

calculating one of a subtended angle and width of a related anonymous target selected from memory as a function of the estimated vehicle position and the predetermined target position;

comparing one of the measured width and subtended angle of the first anonymous target with a respective one of the calculated width and subtended angle of the related anonymous target and verifying that the compared one of the width and subtended angle of the first anonymous target and related anonymous target being within a predetermined relative tolerance range of each other; and

storing an identity of the first target in a plausible target list in said computer.

20. A method, as set forth in claim 19, including the steps of:

calculating an incident angle of reflection of the first anonymous target as a function of one of a measured and an estimated bearing angles of said target, the orientation of a related anonymous target stored in memory, and an estimated heading of the vehicle;

comparing the calculated incident angle with a predetermined incident angle maximum value; and

performing said one subtended angle and width calculation and measurement in response to said calculated incident angle being less than said incident angle maximum value.

21. An automatic guided vehicle, comprising:

a plurality of anonymous targets positioned at predetermined spaced apart locations within an area of operation of the automatic guided vehicle, said targets each having a substantially planar reflective upright surface and a predetermined width defined by spaced first and second upright edges, said targets each being oriented at a preselected angle relative to predetermined coordinates, said targets being adapted to reflect the delivered electromagnetic radiation;

a scanner rotatable about an upright axis, said scanner delivering electromagnetic radiation, receiving a reflection of electromagnetic radiation, and delivering a signal in response to receiving said reflected electromagnetic radiation,

encoder means for delivering an angle signal responsive to the rotated position of the scanner, said encoder means being connected to the scanner;

dead reckoning means for sensing the direction and distance of travel the vehicle and delivering a responsive dead reckoning signal;

a processor mounted onboard the vehicle and being connected to receive the signals from said scanner, encoder, and dead reckoning means, said processor having memory and being adapted to process signals delivered from the scanner, encoder, and dead reckoning means according to preprogrammed instructions, said predetermined location, orientation, and width of each anonymous target being stored in memory, said processor calculating one of a subtended angle and a width of a first anonymous target reflecting said electromagnetic radiation based on measurements of the scanner and encoder signals, calculating one of a subtended angle and width of a related anonymous target selected from memory as a function of the estimated vehicle position based on said signals from the dead reckoning means as corrected by previous laser scanner measurements, and comparing one of the measured width and subtended angle of the first anonymous target with a respective one of the calculated width and subtended angle of the related anonymous target and verifying that the compared one of the width and subtended angle of the first anonymous target and related anonymous target being within a predetermined relative tolerance range of each other, and storing an identity of the first target in a plausible target list in said memory.

22. An automatic guided vehicle, as set forth in claim 21, wherein said processor calculating an incident angle of reflection of the first anonymous target as a function of one of a measured bearing angle of the first anonymous target and an estimated bearing angle of said related anonymous target, the orientation of a related anonymous target stored in memory, and an estimated heading of the of the vehicle, comparing the calculated incident angle with a predetermined incident angle maximum value, and performing said one subtended angle and width calculation and measurement in response to said calculated incident angle being less than said incident angle maximum value.

23. A method for determining the identity of an observed anonymous target from a plurality of anonymous targets positioned at predetermined spaced apart locations within an area of operation of an automatic guided vehicle, said vehicle having a scanner and said scanner being adapted to deliver electromagnetic radiation, said targets having a substantially planar reflective upright surface and a predetermined width defined by spaced first and second upright edges, said targets each being oriented at a preselected angle relative to predetermined coordinates, said targets being adapted to reflect the delivered electromagnetic radiation and said scanner being adapted to receive said reflected electromagnetic radiation and deliver a signal in response to receiving said reflected electromagnetic radiation, said automatic guided vehicle having an onboard computer, said computer having memory, and said computer being adapted to process signals delivered from said scanner according to preprogrammed instructions, said predetermined location, orientation, and width of each anonymous target being stored in memory, said method comprising:

estimating the position and heading of the vehicle;

estimating a bearing angle of the anonymous targets relative to the vehicle based on the estimated position and heading of the vehicle and predetermined anonymous target locations;

storing in memory the estimated bearing angles;

delivering electromagnetic radiation and receiving a reflection of the delivered electromagnetic radiation from a first of the plurality of anonymous targets;

measuring a subtended angle of the first anonymous target reflecting said electromagnetic radiation;

calculating a subtended angle of the related anonymous target selected from memory as a function of the estimated vehicle position and the predetermined target position;

comparing the measured subtended angle of the first anonymous target with the subtended angle of the related anonymous target and verifying that the compared subtended angle of the first anonymous target and related anonymous target being within a predetermined relative tolerance range of each other; and

storing an identity of the first target in a plausible target list in said computer.

24. A method, as set forth in claim 23, including the steps of:

calculating an incident angle of reflection of the first anonymous target as a function of one of the measured and estimated bearing angles, the orientation of a related anonymous target stored in memory, and an estimated heading of the vehicle;

comparing the calculated incident angle with a predetermined incident angle maximum value; and

executing said subtended angle calculation and measurement in response to said calculated incident angle being less than said incident angle maximum value.