AGV position and heading controller

• US 6,721,638 B2
• Filed: 05/07/2002
• Issued: 04/13/2004
• Est. Priority Date: 05/07/2001
• Status: Expired due to Fees

• Current Assignee: Dematic Corporation
• Original Assignee: Rapistan Systems Advertising Corporation (OSI Systems Incorporated)
• Inventors: Zeitler, David W.
• Primary Examiner(s): Louis-Jacques, Jacques H.
• Assistant Examiner(s): GIBSON, ERIC M
• Application Number:
  US10/140,484
• Publication Number:
  US 20020165648A1
• Time in Patent Office: 707 Days
• Field of Search: 701/23, 701/41, 180/408, 180/409, 180/410, 180/411, 180/445, 180/446
• US Class Current: 701/23
• CPC Class Codes: G05D 1/0236 in combination with a laser lasers per se H01S
• CPC Class Codes: G05D 1/0261 using magnetic plots
• CPC Class Codes: G05D 1/0265 using buried wires
• CPC Class Codes: G05D 1/027 comprising intertial navigation means, e.g. azimuth detector inertial navigation G01C21/16; inertial navigation combined with non-inertial navigation instruments G01C21/165
• 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 controlling the steering of an automatic guided vehicle (AGV) includes simultaneously correcting the vehicle'"'"'s heading and position errors. The vehicle may include first and second steering control loops that determine the vehicle'"'"'s position and heading errors, respectively. Separate commands are generated from these control loops to steer the vehicle in a manner that tends to reduce these errors. The vehicle may include a forward and a rearward pair of wheels. For correcting position errors, the first control loop issues the same steering command to both the forward and rearward pair of wheels. For correcting heading errors, the second control loop issues a steering command to the rearward pair of wheels that is summed together with the first control loop'"'"'s steering command prior to being applied to the rearward pair of wheels.

Claims

1. A method of controlling an automatic guided vehicle (AGV) comprising:

measuring the AGV'"'"'s heading;

measuring the AGV'"'"'s location;

determining any error between the AGV'"'"'s measured heading and a desired heading;

determining any error between the AGV'"'"'s measured location and a desired location; and

steering said AGV to simultaneously attempt to reduce said error between the AGV'"'"'s measured heading and desired heading and said error between the AGV'"'"'s measured location and a desired location, including reducing said error between the AGV'"'"'s measured heading and desired headings substantially independently of reducing said error between the AGV'"'"'s measured location and desired location.

2. The method of claim 1 further including providing at least a first steerable wheel and at least a second steerable wheel on said AGV, said first and second steerable wheels being spaced apart longitudinally on said AGV.

3. The method of claim 2 wherein said steering of said AGV includes steering, at least occasionally, both said first and said second wheels.

4. The method of claim 3 further including steering said first and said second wheels in unison whenever any position error exists but no heading error exists.

5. The method of claim 3 further including changing the steering of only one of said first and second wheels when any heading error exists but no position error exists.

6. The method of claim 1 further including providing at least two first steerable wheels and at least two second steerable wheels on said AGV, said first two wheels being spaced apart longitudinally from said second two wheels.

7. The method of claim 6 wherein said steering of said AGV includes steering, at least occasionally, both said first two wheels and said second two wheels, said first two wheels being steered in unison with each other, and said second two wheels being steered in unison with each other.

8. The method of claim 1 further comprising storing a guidepath onboard said AGV and deriving said desired position from said stared guidepath.

9. The method of claim 1 further comprising storing a guidepath onboard said AGV and deriving said desired heading from said stored guidepath.

10. A method of controlling an automatic guided vehicle (AGV) comprising:

measuring the AGV'"'"'s heading;

measuring the AGV'"'"'s location;

determining any error between the AGV'"'"'s measured heading and a desired heading;

determining any error between the AGV'"'"'s measured location and a desired location;

steering said AGV to simultaneously attempt to reduce said error between the AGV'"'"'s measured heeding and desired heading and said error between the AGV'"'"'s measured location and a desired location;

providing at least two first steerable wheels and at least two second steerable wheels on said AGV, said first two wheels being spaced apart longitudinally from said second two wheels;

generating a first steering signal adapted to reduce any difference between the AGV'"'"'s desired position and its measured position;

generating a second steering signal adapted to reduce any difference between the AGV'"'"'s desired heading and its measured heading;

applying said first steering signal to said first two steerable wheels;

adding said first and said second signals together to create an added steering signal; and

applying said added steering signal to said second two steerable wheels.

11. The method of claim 10, wherein said first two steerable wheels are leading wheels and said second two wheels are trailing wheels.

12. The method of claim 10, further including generating said first and said second steering signals multiple times per second.

13. A method of controlling an automatic guided vehicle (AGV) comprising:

measuring the AGV'"'"'s heading;

measuring the AGV'"'"'s location;

providing a first control loop that generates a first steering command based upon any difference between said measured AGV position and a desired AGV position;

providing a second control loop that generates a second steering command based upon any difference between said measured AGV heading and a desired AGV heading;

providing at least a first and a second steerable wheel on said AGV, said first and second steerable wheels being spaced apart longitudinally;

applying said first steering command to said first steerable wheel;

adding said first and second steering commands together; and

applying the added together first and second steering commands to said second steerable wheel.

14. The method of claim 13, wherein said first steerable wheel is a leading wheel on said AGV and said second steerable wheel is a trailing wheel on said AGV.

15. The method of claim 13, further including generating said first and said second steering commands multiple times per second.

16. The method of claim 15, further including storing a guidepath onboard said AGV and deriving said desired position and said desired heading from said stored guidepath.

17. A method of controlling an automatic guided vehicle (AGV) comprising:

measuring the AGV'"'"'s heading;

measuring the AGV'"'"'s location;

providing a first control loop that generates a first steering command based upon any difference between said measured AGV position and a desired AGV position;

providing a first control loop that generates a second steering command based upon any difference between said measured AGV heading and a desired AGV heading;

providing at least a first and a second steerable wheel on said AGV, said first and second steerable wheels being spaced apart longitudinally;

determining whether said first steerable wheel is a leading or trailing wheel;

determining whether said second steerable wheel is a leading or trailing wheel;

applying said first steering command to the leading wheel;

adding said first and second steering commands together; and

applying the added together first and second steering commands to the trailing wheel.

18. A method of controlling an automatic guided vehicle (AGV) comprising:

providing a guidepath;

measuring the AGV'"'"'s position;

determining a closest point on the guidepath for the AGV;

comparing the AGV'"'"'s measured position to the closest point on the guidepath for the AGV; and

generating a steering command for the AGV based upon any difference between the measured position of the AGV and the closest point on the guidepath of the AGV, said steering command causing the AGV to reduce any difference between the AGV'"'"'s measured position and the closest point on the guidepath of the AGV without substantially altering the AGV'"'"'s heading as the AGV moves.

19. The method of claim 18, further comprising:

providing a first and a second set of steerable wheels on the AGV, said first and second sets of wheels being spaced apart longitudinally; and

applying said steering command to both said first and said second sets of steerable wheels.

20. The method of claim 18, further comprising:

measuring the AGV'"'"'s heading;

determining a desired heading for the AGV;

comparing the AGV'"'"'s measured heading to the desired heading for the AGV; and

generating a second steering command for the AGV based upon any difference between the measured heading of the AGV and the desired heading of the AGV, said second steering command causing the AGV to reduce any difference between the AGV'"'"'s measured heading and the desired heading.

21. A method of controlling an automatic guided vehicle (AGV) comprising:

measuring the AGV'"'"'s position;

determining a desired position for the AGV;

comparing the AGV'"'"'s measured position to the desired position for the AGV; and

generating a steering command for the AGV based upon any difference between the measured position of the AGV and the desired position of the AGV, said steering command causing the AGV to reduce any difference between the AGV'"'"'s measured position and the AGV'"'"'s desired position without altering the AGV'"'"'s orientation as the AGV moves;

providing a first and a second set of steerable wheels on the AGV, said first and second sets of wheels being spaced apart longitudinally;

applying said steering command to both said first and said second sets of steerable wheels; and

applying said second steering command to said second set of steerable wheels.

22. The method of claim 21, further including deriving said desired heading and said desired position from a guidepath.

23. An apparatus for controlling an automatic guided vehicle (AGV) comprising:

a first controller, said first controller determining any difference between the vehicle'"'"'s measured position and a desired position, said first controller adapted to output a first command that tends to reduce any said difference;

a second controller, said second controller determining any difference between the vehicle'"'"'s measured heading, said second controller adapted to output a second command that tends to reduce any said difference between the measured and desired heading;

at least a first and second steerable wheel, said first and second steerable wheels being spaced apart longitudinally on the AGV; and

wherein said first command is applied to said first steerable wheel and said second command is not applied to said first steerable wheel.

24. The apparatus of claim 23, wherein said first and second commands are added together and applied to said second steerable wheel.

25. An apparatus for controlling an automatic guided vehicle (AGV) comprising:

a first controller, said first controller determining any difference between the vehicle'"'"'s measured position and a desired position, said first controller adapted to output a first command that tends to reduce any said difference;

a second controller, said second controller determining any difference between the vehicle'"'"'s measured heading and a desired heading, said second controller adapted to output a second command that tends to reduce an said difference between the measured and desired heading; and

a first set and a second set of steerable wheels, said first set of wheels being spaced apart longitudinally from said second set of wheels on the AGV, wherein said first command is applied to said first set of wheels and said second command is not applied to said first set of wheels.

26. The apparatus of claim 25, wherein said first and second commands are added together and applied to said second set of wheels.