Automated guided vehicle

• US 4,790,402 A
• Filed: 09/28/1987
• Issued: 12/13/1988
• Est. Priority Date: 09/28/1987
• Status: Expired due to Fees

• Current Assignee: Tennant Company 701 N Lilac Drive Minneapolis
• Original Assignee: Tennant Company
• Inventors: Field, Bruce F., Kasper, Joseph G.
• Primary Examiner(s): Love, John J.
• Assistant Examiner(s): MAR, MICHAEL Y
• Application Number:
  US07/101,508
• Time in Patent Office: 442 Days
• Field of Search: 180/167, 180/168, 180/169, 364/424, 356/141, 358/103, 358/93, 358/229, 318/587
• US Class Current: 180/169
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G05D 1/0238 using obstacle or wall sensors G05D1/0246 and G05D1/0289 take precedence; lidar systems designed for anti-collision purposes G01S17/93
• CPC Class Codes: G05D 1/0244 using reflecting strips

Abstract

An unmanned, self-propelled vehicle in the nature of a mobile robot has an on-board computer that stores path and machine function instructions and activates the drive and steering systems so as to cause the machine to follow a desired path. A plurality of retroreflectve targets are mounted along the desired path. They do not have to be mounted at a specific height or distance apart, nor need they be square to the path. An improved guidance system for keeping the vehicle on the prescribed path includes a laterally scanning laser transmitter-receiver mounted on the vehicle. An electromechanical tracking device controls the angle of elevation of the laser beam so as to keep it aimed at each target successively as the vehicle moves. The laser produces signals which steer the vehicle such that the laser transmitter and targets are kept aligned in a vertical plane. A positioning device can move the laser transmitter transversely on the vehicle so that the vehicle centerline may travel in the vertical plane of the laser or may travel in an offset line parallel to the vertical laser plane. Certain ones of the targets are bar coded and a target counter senses and counts them as the machine moves past them to keep track of where the vehicle is located along its desired path. A motion sensing system using reflective microwave sensors provides speed and distance information.

Claims

1. In an automated guided vehicle having a frame, drive means mounted on the frame for propelling the vehicle, and steering means associated with the frame for controlling the vehicle'"'"'s direction of travel, an improved guidance system for controlling the drive means and steering means so as to guide the vehicle along a desired predetermined path, the guidance system comprising:

a plurality of spaced retroreflective targets mounted in a sequential manner along the desired path;

sighting means mounted on the vehicle including transmitting means for emitting a light beam and receiving means for detecting said emitted light beam reflected from one of said targets and defining a target-in-view signal when such light is detected;

tracking means on the vehicle for controlling the angle of elevation of the transmitted light beam, with reference to a horizontal plane, so as to maintain a target-in-view signal substantially continuously as the vehicle moves by automatically tracking said targets in a sequential manner; and

control means responsive to the sighting means for activating the drive means or steering means so as to keep the vehicle on the desired path.

2. The vehicle of claim 1 wherein the receiving means detects the direction from which reflected light is received and the sighting means defines a reference line, compares the detected light direction to the reference line to determine a heading error angle, and sends signals to the control means which activates the drive or steering means so as to reduce the heading error angle to zero.

3. The vehicle of claim 2 wherein the sighting means is mounted on the vehicle frame such that the reference line is parallel to the vehicle'"'"'s longitudinal center line.

4. The vehicle of claim 1 wherein the targets are mounted at non-specific elevations along the desired path.

5. The vehicle of claim 1 wherein the transmitting means further comprises a beam sweeping means for moving the transmitted light beam in a scanning plane.

6. The vehicle of claim 5 wherein the beam sweeping means moves the transmitted light beam through a scanning angle less than 180 degrees.

7. The vehicle of claim 6 wherein the receiving means detects the direction from which reflected light is received and the sighting means defines a reference line as the bisector of the scanning angle, compares the detected light direction to the reference line to determine a heading error angle, and signals the control means which activates the drive or steering means so as to reduce the heading error angle to zero.

8. The vehicle of claim 7 wherein the scanning angle is 90 degrees.

9. The vehicle of claim 1 further comprising positioning means for moving the sighting means laterally of the vehicle'"'"'s longitudinal center line.

10. The vehicle of claim 9 wherein the transmitting means is pivotally mounted on the positioning means about a horizontal axis perpendicular to the vehicle'"'"'s longitudinal center line, and the tracking means comprises an actuator connected between the positioning means and transmitting means, responsive to the receiving means to pivot the transmitting means as required to maintain a target-in-view signal as the vehicle moves.

11. The vehicle of claim 1 wherein the transmitting means is pivotally connected to the frame about a horizontal axis perpendicular to the vehicle'"'"'s longitudinal center line, and the tracking means comprises an actuator connected between the frame and transmitting means, responsive to the receiving means to pivot the transmitting means as required to maintain a target-in-view signal as the vehicle moves.

12. The vehicle of claim 11 wherein the actuator is operable at two different speeds.

13. The vehicle of claim 11 wherein the actuator includes an electronic dynamic brake.

14. The vehicle of claim 11 wherein the tracking means further comprises means defining upper and lower limits for the angle of elevation.

15. The vehicle of claim 14 wherein the means for defining the upper and lower limits are proximity switches.

16. In an automated guided vehicle having a frame, drive means mounted on the frame for propelling the vehicle, and steering means associated with the frame for controlling the vehicle'"'"'s direction of travel, an improved method of controlling the drive means and steering means so as to guide the vehicle along a desired predetermined path, the method comprising the steps of:

placing a plurality of spaced retroreflective targets in a sequential manner along the desired path;

transmitting a light beam from the vehicle;

detecting at the vehicle transmitted light reflected from one of said targets and defining a target-in-view signal when such light is detected;

controlling the angle of elevation of the transmitted light beam, with reference to a horizontal plane, so as to maintain a target-in-view signal substantially continuously as the vehicle moves by automatically tracking said targets in a sequential manner; and

activating the drive means or steering means in response to detected light signals so as to keep the vehicle on the desired path.

17. The method of claim 16 further comprising the steps of detecting the direction from which reflected light is received, defining a reference line, comparing the detected light direction to the reference line to determine a heading error angle, and activating the drive or steering means so as to reduce the heading error angle to zero.

18. The method of claim 16 further comprising the step of sweeping the transmitted light beam in a scanning plane.

19. The method of claim 18 wherein the scanning angle is less than 180 degrees.

20. The method of claim 19 further comprising the steps of detecting the direction from which reflected light is received, defining a reference line through the optical center of the transmitter and parallel to the longitudinal axis of the vehicle, comparing the detected light direction to the reference line, determining a heading error angle, and activating the drive or steering means so as to reduce the heading error angle to zero.

21. The method of claim 20 wherein the scanning angle is 90 degrees.

22. The method of claim 20 further comprising the step of laterally moving the location on the venicle from which the light beam is transmitted and detected.

23. The method of claim 16 further characterized in that the targets are placed at non-specific elevations along the desired path.

24. The method of claim 16 wherein the step of controlling the angle of elevation is further characterized in that when the target-in-view signal is lost the angle of elevation is corrected so as to regain the target-in-view signal by increasing the angle if the vehicle is moving forwardly at the time the signal loss occurs and by decreasing the angle of elevation if the vehicle is moving backwardly at the time of the signal loss.

25. The method of claim 24 further including the steps of defining upper and lower limits for the angle of elevation, releasing tracking of a first target when one of the limits is exceeded and searching for a second target by changing the angle of elevation in the sense opposite the angle correction which produced the overreaching of the limit.

26. The method of claim 24 further comprising the steps of defining upper and lower limits for the angle of elevation, releasing tracking of a first target when one of the limits is exceeded and searching for a second target by changing the angle of elevation at a rate higher than that used when changing the angle of elevation under a lost target-in-view condition.