Automated guided vehicle

• US 4,996,468 A
• Filed: 03/13/1989
• Issued: 02/26/1991
• Est. Priority Date: 09/28/1987
• Status: Expired due to Fees

• Current Assignee: Tennant Company
• Original Assignee: Tennant Company
• Inventors: Field, Bruce F., Kasper, Joseph G.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/322,103
• Time in Patent Office: 715 Days
• Field of Search: 318/575, 318/576, 318/577, 318/587, 15/319, 15/320, 180/167, 180/168, 180/169, 364/424.01, 364/424.02, 901/1, 901/46, 901/47
• US Class Current: 318/587
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4972 Alignment of sensor
• 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 retroreflective 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. A guided vehicle comprising drive means, steering means, a plurality of targets mounted along a desired path of the vehicle, manual control means connected to the vehicle and manipulable by an operator for controlling the drive and steering means, fault detection means for sensing conditions which preclude continued safe operation of the vehicle and controlling the drive and steering means in response thereto, computer control means for controlling the drive and steering means so as to cause the vehicle to traverse a programmed path and sighting means on the vehicle for successively sensing one of the targets and controlling the drive and steering means to maintain a specified relationship between the vehicle and the targets, the manual control means, fault detection means, computer control means and sighting means defining command types which are connected in a command hierarchy, in that order, wherein each command type can automatically take control away from any type following it.

2. A guidance system for controlling an automated guided vehicle such that the vehicle travels along a desired path, comprising a plurality of targets mounted in the path, sighting means on the vehicle for successively sensing each one of the targets one at a time and the direction of the one target being sensed at a given time relative to the sighting means, and control means including a set of pre-programmed instructions, said control means steering the vehicle either in response to the sighting means such that the vehicle maintains a specified relationship to the targets, or in response to a programmed instruction to turn the vehicle a specified number of degrees, with the programmed instruction taking precedence over the sighting means and further comprising means for measuring the distance traveled, said distance measuring means being mounted on each side of the vehicle so that the control means can use measurements of distance traveled by the outer side of the vehicle during a turn to determine when a programmed turn has been completed.

3. The guidance system of claim 2 wherein the means for measuring distance comprises two microwave Doppler motion sensors.

4. A guidance system for controlling an automated guided vehicle such that the vehicle travels along a desired path, comprising a plurality of targets mounted in the path, sighting means on the vehicle for successively sensing each one of the targets and its direction relative to the sighting means, a pair of motion sensors, one mounted on each side of the vehicle, and control means including a set of pre-programmed instructions, said control means steering the vehicle in accordance with inputs from the sighting means and the instructions, with the motion sensors determining the completion of a turn ordered by an instruction and wherein the motion sensors measure the distance traveled, so that the control means can use the measurements of distance traveled by the outer side of the vehicle during a turn to determine when a programmed turn has been completed.

5. The guidance system of claim 4 wherein the motion sensors comprise two microwave Doppler motion sensors.

6. A method of automatically guiding a vehicle to cause it to traverse a predetermined path, comprising the steps of placing a plurality of targets along the 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 the target-in-view signal substantially continuously as the vehicle moves, detecting the direction from which reflected light is received, defining a reference line, comparing the detected light direction to the reference line to determine an heading error angle, steering the vehicle, when a target-in-view signal is present, so as to reduce the heading error angle to zero, and steering the vehicle in a straight line when no target-in-view signal is present, regardless of the heading error angle.

7. A guidance system for controlling an automated guided vehicle such that the vehicle travels along a desired path, comprising a plurality of targets mounted along the path in at least two parallel rows, the targets in each row having markings thereon defining a code, with the code of each row being distinct from the code in the other row, sighting means on the vehicle for successively sensing each one of the targets, its code and its direction relative to the sighting means, the sighting means being capable of sensing more than one row of the targets at once, and control means including a set of preprogrammed instructions, said control means steering the vehicle in response to the sighting means such that the vehicle maintains a specified relationship to the targets, with the programmed instructions indicating to the control means which row of coded targets is currently effective and which row of coded targets to ignore for the time being.

8. An automated guided vehicle having a frame, first and second drive wheels mounted on the frame, first and second motors for driving the wheels, a guidance system for guiding the vehicle along a predetermined path, the guidance system comprising a plurality of targets mounted along the path, sighting means on the vehicle for successively sensing at least one of the targets and its direction relative to the sighting means, and control means for steering the vehicle in response to the sighting means such that the vehicle maintains a specified relationship to the targets, the control means including first and second ramp circuits associated with the first and second motors, respectively, each ramp circuit having a plurality of selectable ramps for altering the motor speed at different rates depending on vehicle speed to provide two-wheel differential steering which makes prompt steering corrections without hunting.

9. The vehicle of claim 8 wherein the ramp circuits are resistance-capacitance circuits.