GB2346599A

GB2346599A - Driverless transport system

Info

Publication number: GB2346599A
Application number: GB0002462A
Authority: GB
Inventors: Heiner Bocker
Original assignee: Indumat GmbH and Co KG
Current assignee: Indumat GmbH and Co KG
Priority date: 1999-02-15
Filing date: 2000-02-04
Publication date: 2000-08-16
Anticipated expiration: 2020-02-04
Also published as: ES2171106A1; GB0002462D0; ES2171106B1; IT1316357B1; DE19906189C2; ITMI20000228A0; GB2346599B; DE19906189A1; ITMI20000228A1

Abstract

A driverless transport system for transporting loads comprises a transport surface (7), an assembly line (1) movable relative to the transport surface, and at least one driverless transport vehicle (8) for transporting a load between the transport surface and the movable assembly line. The driverless transport vehicle is provided with three axles including a forward axle and a rearward axle which are rotatable about an upright axis, for example by means of castors (4). Control means is provided for controlling movement of the vehicle so that the vehicle in sequence moves partly on to the assembly line, waits, and then moves further on to the assembly line without the orientation of the vehicle changing.

Description

2346599 DRIVERLESS TRANSPORT SYSTEM The present invention relates to a

driverless transport system for transporting a load (such as a pallet, box pallet, order picking container and the like) by means of a driverless transport vehicle from a transport surface on to and off an assembly line (such as a plate conveyor, slat conveyor or the like) moving relative to the transport surface.

In plants in which parts to be assembled are brought to an assembly line by means of driverless transport vehicles, there is also frequently the need for the transport vehicles to drive on to the assembly line and to set down or pick up loads at a transfer point on the line. A driverless transport vehicle with conventional three-wheel kinematics (and therefore two axles) is not able to drive on to a moving assembly line without the chassis orientation of the vehicle changing in the. process. The vehicle then stands at an oblique angle to the desired direction of travel of the vehicle on the assembly line because the line will have carried the front axle further than the rear axle, since the rear axle moves on to the assembly line after the front axle. The misalignment of the vehicle leads to incorrect further movement or to protracted corrective measures for which the controller of the system must also first recognise that a positional error has arisen which - 2 occurred unintentionally.

Therefore, the object of the invention is to propose a driverless transport system in which the vehicles can drive on to and off assembly lines without losing orientation.

According to the present invention there is provided a driverless transport system for transporting loads comprising a transport surface, an assembly line movable relative to the transport surface, at least one driverless transport vehicle for transporting a load between the transport surface and the movable assembly line, the driverless transport vehicle being provided with three axles including a forward axle and a rearward axle which are rotatable about an upright axis, and control means for controlling movement of the vehicle, wherein the control means controls the driverless transport vehicle so that the vehicle in sequence moves partly on to the assembly line, waits, and then moves further on to the assembly line.

The vehicle may incorporate a sensor for initiating movement of the vehicle on detection of a corresponding signal from the assembly line or transport surface. The sensor may be responsive to a signal from an optical guide means or from a magnetic guide means.

I The optical guide means or magnetic guide means may be recessed into the assembly line or into the transport surface.

-The position of the vehicle on leaving the assembly line may be determined by indicating means positioned adjacent to the assembly line. The indicating means may comprise means for generating a magnetic signal.

Alternatively or additionally, the position of the vehicle on leaving the assembly line may be determined by measurement of the distance covered by the assembly line while the vehicle is on the assembly line. Thus, the distance covered by the assembly line may be communicated to the vehicle by means of a communications system such as a radio, infrared system, photoelectric cell or the like.

The forward and rearward axles may comprise swivelling castors.

The vehicle may include a middle axle which carries two spaced driving wheels.

Thus embodiments of the driverless transport vehicle according to the present invention, with its three-axle construction, especially when a middle axle has a differential speed drive, is able to drive on to the - 4 moving assembly line until the forward axle lies on the line but the driving wheels of the middle axle still do not touch the assembly line. A floor mark or the like can provide appropriate information about a stopping point. The forward axle on the assembly line then rotates in the direction of the relative movement of the assembly line to the transport surface, and continues supporting the vehicle but without transmitting any major transverse forces to the vehicle. In this way the original chassis orientation can be maintained. Thus, in the waiting phase the driverless transport vehicle stands partly on the assembly line and partly adjacent thereto. on receiving an external command, the vehicle then drives completely on to the assembly line. Since the two wheels of the middle axle engage the assembly line simultaneously, no relative rotation of the vehicle takes place. Thus, the vehicle is carried along the assembly line and can drive to its load transfer point. The original orientation in space is retained.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawing which is a diagrammatic representation of one embodiment of a driverless transport system according to the present invention.

The figure shows a transport surface 7 which may be, for I example, the floor of a production shop. An assembly line 1, incorporating a plurality of load transfer points 2, runs at substantially the same level as the transport surface 7. In the illustrated embodiment, in which an optical track guidance system is shown, guide lines (or tracks) 3 are marked on the assembly line 1 and form tracks to a respective load transfer point 2. Guide lines (or tracks) on the transport surface 7 are marked with the reference 6. Driverless transport vehicles 8 Are each provided with three axles, whereby a middle axle carries two spaced driving wheels 5 and forward and rearward axles are in the form of castors 4 which are able to pivot (or swivel) about an upright axis.

Operation of the driverless transport system according to the invention is as follows.

A driverless transport vehicle 8 standing in Position 1 will be considered first. The vehicle in Position 1 has travelled along the track 6 and onto the assembly line 1 until the front axle, with the front castor 4, of the vehicle bears on the assembly line 1. The middle axle with the driving wheels 5 remains on the transport surface 7 adjacent to the assembly line 1. A mark on the transport surface 7 provides information about the stopping point of the vehicle. The assembly line 1 now continues to move in the direction of the arrow at a speed V. When a guide track sensor (not shown) in the vehicle located at Position 1 detects an optical guiding track 3 which defines the path which the vehicle must follow, the sensor sends a signal to the vehicle to commence movement. The two driving wheels 5 simultaneously move the vehicle from the transport surface 7 on to the assembly line 1. The rearward swivelling castor 4 continues to support the vehicle 8 on the transport surface 7 and rotates about the upright axis to accommodate the relative motion (that is, is directed transversely to the vehicle 8), but without allowing transverse forces to act on the vehicle 8. The driverless transport vehicle 8 moves partly or completely on to the assembly line 1, guided by the track 3, to the location 2 at which it is to set down or pick up the load. The vehicle 8 then sets down or picks up the load and can then leave the line 1 forwards or backwards in the same way (having arrived at position 2 in the meantime). It can be seen that it is not necessary for the vehicle 8 to drive completely on to the assembly line 1, but that it is sufficient for the centre of gravity of the vehicle to rest on the assembly line 1.

If no optical track guidance system is provided, but a navigation system is provided with magnetic guide points, the vehicle 8 waits at the edge of the assembly line 1 until a guide magnet comes into the sensing range of a magnetic sensor strip provided on the vehicle. When the magnet is in the correct position under the vehicle 8, I - 7 the driverless transport vehicle 8 starts moving again, drives on to the assembly line 1 and reaches the location 2 for transfer of the load by measuring the distance travelled (odometry).

To leave the assembly line 1, the driverless transport vehicle 8 drives to the edge of the assembly line 1 and waits until a magnet is detected in the sensing range of the magnetic sensor strip. When the magnet is in the correct position under the driverless transport vehicle, for example level with Position 3 in the figure, the driverless transport vehicle 8 starts moving and leaves the assembly line 1.

During the time spent by the driverless transport vehicle 8 on the assembly line 1, the navigation system receives no information from the sensors about the relative change in position of the vehicle relative to the transport surface 7. This means that, on leaving the assembly line 1, the co-ordinates of the current location on the transport surface 7 stored in the driverless transport vehicle 8 are incorrect. To correct these co-ordinates, for example either of the following two options may be adopted:

1. Reference to indicating means, such as magnets, encountered by the vehicle 8 immediately after leaving the assembly line 1. This is effected in that the vehicle 8 receives information from the magnet(s) which indicates both the direction and the location of the specific magnet(s) on the transport surface 7. Evaluation logic provided in the vehicle 8 can then determine where the vehicle is located.

2. Determination of the correct location by measuring the distance covered by the assembly line 1. This method is based on the fact that the speed of the assembly line is known and the evaluation circuit of the driverless transport system can determine, from the time spent by the driverless transport vehicle 8 on the assembly line 1, the "movement" in relation to the point at which the vehicle drove on to the assembly line. Since, according to the invention, the orientation of the vehicle has not changed, only simple calculations are required to determine the precise location of the vehicle 8.

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Claims

9 CLAIMS

1. A driverless transport system for transporting loads comprising a transport surface, an assembly line movable relative to the transport surface, at least one driverless transport vehicle for transporting a load between the transport surface and the movable assembly line, the driverless transport vehicle being provided with three axles including a forward axle and a rearward axle which are rotatable about an upright axis, and control means for controlling movement of the vehicle, wherein the control means controls the driverless transport vehicle so that the vehicle in sequence moves partly on to the assembly line, waits, and then moves further on to the assembly line.

2. A driverless transport system as claimed in claim 1, wherein the vehicle incorporates a sensor for initiating movement of the vehicle on detection of a corresponding signal from the assembly line or transport surface.

3. A driverless transport system as claimed in claim 2, wherein the sensor is responsive to a signal from an optical guide means.

4. A driverless transport system as claimed in claim 2, wherein the sensor is responsive to a signal from a magnetic guide means.

5. A driverless transport system as claimed in any preceding claim, wherein the position of the vehicle on leaving the assembly line is determined by indicating means positioned adjacent to the assembly line.

6. A driverless transport system as claimed in claim 5, wherein the indicating means comprises means for generating a magnetic signal.

7. A driveless transport system as claimed in any preceding claim, wherein the position of the vehicle on leaving the assembly line is determined by measurement of the distance covered by the assembly line while the vehicle is on the assembly line.

8. A driverless transport system as claimed in any preceding claim, wherein the forward and rearward axles comprise swivelling castors.

9. A driverless transport system as claimed in any preceding claim, wherein the vehicle includes a middle axle which carries two spaced driving wheels.

10. A driverless transport system substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

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