GB2284907A

GB2284907A - Navigation system for automatically guided vehicle

Info

Publication number: GB2284907A
Application number: GB9325933A
Authority: GB
Inventors: Andrew Mckaig
Original assignee: Central Systems & Automation L
Current assignee: Central Systems & Automation L
Priority date: 1993-12-18
Filing date: 1993-12-18
Publication date: 1995-06-21
Anticipated expiration: 2013-12-18
Also published as: GB9325933D0; GB2284907B

Abstract

A navigation system for an automatically guided vehicle 1 comprises a target 3a positioned in line with the direction of travel of the vehicle 1 and a camera 2 mounted on the vehicle 1. The target 3a has a pattern 4, 5 formed on it. The camera 2 forms an image of the target 3a and control means determine the position of the pattern in the image of the target 3a and steer the vehicle 1 towards a position in which the position of the pattern is indicative of the vehicle 1 being in its desired position. The distance from the vehicle 1 to the target 3a may be determined from the pattern 4, 5 so that the vehicle can be made to turn at the correct place BCDE. <IMAGE>

Description

Title - Navigation System for Automatically Guided Vehicle This invention relates to a navigation system for an automatically guided vehicle (AGV).

AGVs are generally unmanned vehicles which are used in many different types of manufacturing plants and warehouses. They are used, for example, to retrieve goods from warehouses.

AGVs are frequently quite large in size, typically being of the order of 2m in length and being capable of carrying loads of up to one ton or more. AGVs move at speeds of the order of 1.0-1.5 m/s.

The environments, such as warehouses, in which AGVs frequently operate are commonly very restricted. Since it is important that the greatest possible use is made of the available space the aisles are relatively narrow. AGVs passing along the aisles must therefore be guided with great accuracy, deviations from the desired line of travel being no more than a few millimetres.

Various different navigation systems for AGVs have been proposed. Some of these involve the vehicle following a track laid or buried in the floor of the building in which the vehicle operates. The track may, for example, be a wire which is laid in a loop and through which an electrical guidance signal is passed. The vehicle is fitted with one or more appropriate sensors which detect the guidance signal, and control the vehicle's drive system in such as way that deviations from the path defined by the wire loop are compensated. Another known system involves optical scanning of a track mounted above the path of the vehicle.

Guidance systems of the type described above suffer from the disadvantage that they are relatively inflexible. The track to be followed by the vehicle must be positioned very accurately, and alteration of the path to be followed involves relaying the track. This may necessitate digging up of buried wires, which is clearly undesirable and time-consuming.

Other optical guidance systems are known. Some involve a vehicle being automatically steered towards a light-emitting target. Other known systems involve a rotating laser mounted on the vehicle which scans reflective targets positioned at various pre-determined points along the vehicle's path. The targets incorporate identification bar-codes and the position of the vehicle is calculated by triangulation. Systems of this kind are relatively complex and are reliant on the accurate positioning of numerous targets.

There has now been devised a navigation system for an automatically guided vehicle which overcomes or substantially mitigates the disadvantages of known such systems.

According to the invention, there is provided a navigation system for an automatically guided vehicle, the system comprising a target positioned in line with the direction of travel of the vehicle, the target having a pattern printed or otherwise formed thereon, a forwardly-directed camera mounted on the vehicle such that, in use, the camera forms an image of the target, and control means including means for determining the position of the pattern in the image of the target and for steering the vehicle towards a position in which the position of the pattern is indicative of the vehicle being in its desired position.

The navigation system according to the invention is advantageous primarily in that it is relatively simple. The targets in particular are simple and can very readily be positioned and repositioned. The system also does not rely on any tracks or wires fixed or buried in the surface over which the vehicle moves.

The pattern is preferably printed on the target and preferably includes at least one vertical line or band. Most preferably, the pattern comprises one or more vertical bands printed in a contrasting colour to the background of the target. It is particularly preferred that the pattern should comprise one or more dark bands on a light background.

The pattern may include characteristic elements which enable identity of the target to be established. In addition, the pattern may include elements which enable the distance of the vehicle from the target to be calculated.

It may be necessary for the camera to be fitted with a zoom lens. In such a case, the image formed by the camera will be constant, independent of the distance of the vehicle from the target. The zoom lens may be provided with an autofocus mechanism, or may be motor-driven in accordance with a preprogrammed operating sequence. Where the image viewed by the camera is independent of the distance of the vehicle from the target, then control of the distance travelled by the vehicle along each section of its path must be by some other means.

For instance, the length of each section of the path may be preprogrammed and the vehicle may be fitted with one or more encoders which are reset at specific points in the vehicle's path, eg at the points at which the vehicle executes a turn.

When the encoder is reset the distance to be travelled to the next turning point is retrieved from memory, as is the distance to the target, the zoom lens being adjusted accordingly.

The camera is preferably a video camera, the image of which is preferably digitised and fed to a microprocessor which controls the vehicle's steering and drive systems. The position of the pattern in the digitised image may readily be determined, and the direction of travel of the vehicle adjusted to compensate for any deviations. For example, where the pattern comprises a single vertical band this may, when the vehicle is precisely positioned on its path, be central in the image. If analysis of the image reveals that the band is off-centre, then corrective steering of the vehicle occurs.

The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which Figure 1 is a schematic plan view of a warehouse in which an automatically guided vehicle executes a loop-like path; and Figure 2 is a front elevational view of a target forming part of a navigation system for the AGV of Figure 1.

Referring first to Figure 1, an automatically guided vehicle (AGV) (1) operates in a warehouse and follows a path indicated by the broken line. The AGV (1) has generally conventional drive and steering systems (not shown), and generally conventional load-carrying and -manipulating means (not shown).

Mounted near the front of the AGV (1) is a forwardly-directed video camera (2). Targets (3a-e) are positioned in line with various parts of the path of the AGV (1) such that they are successively viewed by the camera (2). As shown in Figure 2, each target (3a-e) comprises a light-coloured board (4) approximately 50cm square, with two spaced apart vertical bands (5a,b) of a contrasting colour.

When the AGV (1) is in the position shown in Figure 1, the camera (2) views the target (3a). The image of the target (3a) is digitised and passed to a microprocessor (not shown) which identifies the positions of the vertical bands (5a,b). This provides a measure of the deviation of the AGV (1) from its intended path, and the microprocessor controls the steering system to rectify any deviation. The AGV (1) may, for example, be steered in such a manner that the two bands (5a,b) are equi-spaced about the centre of the image viewed by the camera (2).

In addition to the vertical bands (5a,b) providing an indication of the position of the AGV (1) relative to its intended position, the separation of the bands (5a,b) in the field of view of the camera (2) provides an indication of the proximity of the AGV (1) to the target (3a). As the AGV (1) approaches the target (3a), the bands (5a,b) become further apart in the image captured by the camera (2). When the separation of the bands (5a,b) indicates that the AGV (1) has reached the position B in Figure 1, the AGV (1) performs a 90" turn to the left, moves forward to the point C and turns through 900 to the right, in position D. This sequence of manoevres is performed entirely under software control.

Once the AGV (1) reaches position D, guidance is once more controlled by the camera (2), which views the second target (3b). Again, the AGV (1) travels towards the target (3b) until it reaches the position E, whereupon it turns 900 to the left and travels towards the next target (3c). Travel of the AGV (1) over the remaining parts of its path is controlled by reference to the remaining targets (3d,3e).

In the event that the path of the AGV (1) needs to be changed, for example if the vehicle is to be used elsewhere or in the event that the layout of the building is changed, the targets (3a-e) can easily be repositioned, together with any additional targets which may be required. The positions at which the vehicle is required to turn, and any other softwarecontrolled manoevres, are then programmed.

Claims

1. A navigation system for an automatically guided vehicle, the system comprising a target positioned in line with the direction of travel of the vehicle, the target having a pattern printed or otherwise formed thereon, a forwardly-directed camera mounted on the vehicle such that, in use, the camera forms an image of the target, and control means including means for determining the position of the pattern in the image of the target and for steering the vehicle towards a position in which the position of the pattern is indicative of the vehicle being in its desired position.

2. A navigation system as claimed in Claim 1, wherein the pattern is printed on the target.

3. A navigation system as claimed in Claim 1 or Claim 2, wherein the pattern includes at least one vertical line or band.

4. A navigation system as claimed in Claim 3, wherein the pattern comprises one or more vertical bands printed in a contrasting colour to the background of the target.

5. A navigation system as claimed in Claim 4, wherein the pattern comprises one or more dark bands on a light background.

6. A navigation system as claimed in any preceding claim, wherein the pattern includes characteristic elements which enable the identity of the target to be established.

7. A navigation system as claimed in any preceding claim, wherein the pattern includes elements which enable the distance of the vehicle from the target to be calculated.

8. A navigation system as claimed in any preceding claim, wherein the camera is fitted with a zoom lens.

9. A navigation system as claimed in Claim 8, wherein the zoom lens is provided with an autofocus mechanism.

10. A navigation system as claimed in Claim 8, wherein the zoom lens is motor-driven in accordance with a preprogrammed operating sequence.

11. A navigation system as claimed in any preceding claim, wherein the image viewed by the camera is independent of the distance of the vehicle from the target, the length of each section of the vehicle's path is preprogrammed and the vehicle is fitted with one or more encoders which are reset at specific points in the vehicle's path.

12. A navigation system as claimed in any preceding claim, wherein the camera is a video camera, the image of which is digitised and fed to a microprocessor which controls steering and drive systems provided on the vehicle.

13. A navigation system as claimed in any preceding claim, comprising a plurality of targets positioned in line with the direction of travel of the vehicle over respective sections of its path.

14. A navigation system for an automatically guided vehicle substantially as hereinbefore described and as illustrated in the accompanying figures.