GB2133176A

GB2133176A - Vehicle guidance system

Info

Publication number: GB2133176A
Application number: GB08125320A
Authority: GB
Inventors: Royston Hugh Tilbury; Alison Baker
Original assignee: Cableform Ltd
Current assignee: Cableform Ltd
Priority date: 1981-08-19
Filing date: 1981-08-19
Publication date: 1984-07-18

Abstract

The invention provides a wire vehicle guidance system in which the vehicle can make limited movements off the wire. The vehicle carries a control system comprising a position monitor which indicates the position of the vehicle relative to the path network, a route memory for storing data indicative of a route to be followed by the vehicle through the network, a steering control memory for storing data indicative of the course to be steered by the vehicle away from the wire track when turning from one path onto an intersecting path, means for determining from the position monitor when a point is reached along a vehicle's route at which the vehicle must start a turn onto an intersecting path, and means for enabling the wire following means to steer the vehicle after a turning point is reached in accordance with data derived from the steering control memory and to detect and follow the wire track of the said intersecting path after a turn has been completed.

Description

SPECIFICATION Wire guidance system for vehicles The present invention relates to a wire guidance system for vehicles.

It is known to guide a vehicle along a wire track by transmitting a signal of predetermined amplitude over the unscreened wire, detecting signals radiated by the wire track, and steering the vehicle in dependence upon the amplitude of the detected signals. It is also known to control the vehicle to for example start or stop by transmitting a separate control signal over the same or a separate wire, detecting the control signal radiated by the wire, and controlling the vehicle accordingly.

The vehicle mounted guidance signal detector is generally in the form of two spaced apart identical pick-ups such as coils mounted transversely with respect to the intended direction of travel of the vehicle. A transverse position signal is obtained by subtracting the output of one coil from that of the other so that the magnitude 0 the resulting difference signal represents the distance between the wire and a reference point half way between the two coils.

Currently available vehicle guidance systems are capable of following straight or curving tracks.

The tightest curve that can be followed is a function of the steering geometry of the vehicle in question. All the known systems are designed such that the vehicle always closely follows the wire track.

If a warehouse is to make maximum use of available space, the racking must be arranged in straight rows to define a grid of passageways therebetween, the grid being made up of perpendicular passageways. The end of each rack extends as near as possible to each passageway junction. If wire guided vehicles are to operate in a warehouse however and they cannot make sharp turns the corner of the racking adjacent junctions must be pulled back, wasting space. In addition the radius of curvature of the track laid in the warehouse floor must be carefully controlled to prevent too tight a turn being demanded of a vehicle. This increases installation costs.

In the known system if a vehicle is to be able to turn left, go straight on, or turn right at a junction between two passagewa'ys, it is necessary to lay a leftwards curving track, a straight on track, and a rightwards curving track. As the vehicle approaches the junction, only one of the three tracks must be energised so that the vehicle is not confused as to where it should go. Thus the track must be switchable from a central control unit.

This greatly increases the complexity and cost of the track. Furthermore the system is very inflexible, making it essential to define the system in minute detail prior to installation and making subsequent adjustments to the layout of the system difficult.

It is an object of the present invention to provide an improved wire guidance system for vehicles.

According to the present invention there is provided a vehicle guidance system ccomprising a wire track laid along paths which it is desired to cause vehicles to follow, the wire track defining a network of paths at least two of which intersect and each of which is straight or curved to allow a vehicle to follow it accurately, and wire following means mounted on a vehicle to be guided for detecting radiation emitted by the wire track and steering the vehicle in dependence upon the detected radiation, characterised in that at the or each point of intersection between the paths the wire track of one path intersects the wire track of the other path at an angle which requires the vehicle when turning from one path to the other to follow a course not defined by the wire track of either of the intersecting paths, all the wiretrack is energised continuously, and the vehicle carries a control system comprising a position monitor which indicates the position of the vehicle relative to the path network, a route memory for storing data indicative of a route to be followed by the vehicle through the network, a steering control memory for storing data indicative of the course to be steered by the vehicle away from the wire track when turning from one path onto an intersecting path, means for determining from the position monitor when a point is reached along a vehicle's route at which the vehicle must start a turn onto an intersecting path, and means for enabling the wire following means to steer the vehicle after a turning point is reached in accordance with data derived from the steering control memory and to detect and follow the wire track of the said intersecting path after a turn has been completed.

Thus a simple grid of orthogonally intersecting wire tracks can be laid down and vehicles can be caused to turn onto intersecting tracks without having to provide curved branch tracks at points of intersection. Effectively the steering control memory defines imaginary track elements which enable the vehicle to turn between intersecting parts of the real track.

All of the wired track may carry the same guidance signal, or alternatively two guidance signals may be supplied to the track such that at each point at which two lengths of track intersect one of the intersecting tracks carries one of the guidance signals and the other tracks carries the other guidance signal.

Preferably each vehicle carries a dead reckoning position monitor which monitors position by reference to movement over the ground, for example by monitoring wheel rotation or by monitoring speed of movement over the ground using doppler shift techniques. Beacons will be located at appropriate points in the system to enable undating of the dead-reckoning system at intervals as no dead reckoning system can be relied upon to maintain perfect accuracy.

Each vehicle steering control memory may contain steering control information in respect of left and right turns. Ideally this will enable the vehicle to make a very tight turn, as if steered by a human operator, to minimise waste of space at junctions. This requires a fairly complicated sequence of steering adjustments. Alternatively the steering control information may simply be in the form of "turn the wheels through x degrees, disable wire track sensor, travel y metres with the wheels turned through x degrees, turn on the wire track sensor, and then resume the normal track following routine".This would mean that a vehicle could turn a corner in a way which passed it through a point equidistant from two wire tracks carrying the same guidance signal without the vehicle being confused as the wire track sensor would be disabled for periods in which the signals received from the tracks was of much the same amplitude.

If the intersecting wire tracks carry different guidance signals the track sensor could monitor the signals for the two tracks continuously and therefore would not be steering 'blind' at any time.

Alternatively, if the coils could be made directionally selective, and the selectivity could be controlled, the same effect could be obtained using a single guidance signal.

It will be appreciated that the present invention is based on the concept of limited "off-wire" operation, the operation off-wire being controlled by stored information of a simple nature that can be made specific to the particuiar steering geometry of the vehicles in question. Thus although the basic freedom of movement of the vehicles is determined by a physical track, movements requiring transfer from one element of track to another are defined by information carried by the vehicles.

Claims

1. A vehicle guidance system comprising a wire track laid along paths which it is desired to cause vehicles to follow, the wire track defining a network of paths at least two of which intersect and each of which is straight or curved to allow a vehicle to follow it accurately, and wire following means mounted on a vehicle to be guided for detecting radiation emitted by the wire track and steering the vehicle in dependence upon the detected radiation, characterised in that at the or each point of intersection between the paths the wire track of one path intersects the wire track of the other path at an angle which requires the vehicle when turning from one path to the other to follow a course not defined by the wire track of either of the intersecting paths, all the wiretrack is energised continuously, and the vehicle carries a control system comprising a position monitor which indicates the position of the vehicle relative to the path network, a route memory for storing data indicative of a route to be followed by the vehicle through the network, a steering control memory for storing data indicative of the course to be steered by the vehicle away from the wire track when turning from one path onto an intersecting path, means for determining from the position monitor when a point is reached along a vehicle's route at which the vehicle must start a turn onto an intersecting path, and means for enabling the wire following means to steer the vehicle after a turning point is reached in accordance with data derived from the steering control memory and to detect and follow the wire track of the said intersecting path after a turn has been completed.

2. A vehicle guidance system according to claim 1, wherein all of the wired track carries the same guidance signal.

3. A vehicle guidance system according to claim 1 , wherein at least two guidance signals are supplied to the track such that at each point at which twq lengths of track intersect one of the intersecting tracks carries one of the guidance signals and the other track carries the other or another guidance signal.

4. A vehicle guidance system according to any preceding claim, wherein each vehicle carries a dead reckoning position monitor which monitors position by reference to movement over the ground.

5. A vehicle guidance system according to claim 4, wherein beacons are located at appropriate points in the system to enable undating of the dead-reckoning system at intervals.

6. A vehicle guidance system according to any preceding claim, wherein each vehicle steering control memory contain steering control information in respect of left and right turns.

7. A vehicle guidance system substantially as hereinbefore described.