AUTOMATED GUIDED VEHICLE SYSTEM

Abstract: An automated guided vehicle system wherein a vehicle (3) has an on-board motive power source utilised for driving the vehicle over untracked portions of its path of movement between work stations (9) on an assembly line, the vehicles being guided over these path portions by guidance signals, and the vehicle is guided through the work stations by a track from which it derives power for driving the vehicle at higher speed and for replenishing the on-board power supply.

Description: Field of the Invention The present invention relates to an assembly line incorporating an automated guided vehicle system. It has application, for instance, in an assembly line for automobiles. Background to the Invention Assembly line systems are known in which the object being assembled (e.g. an automobile) is carried on an automated guided vehicle through a number of work stations on a shop floor, so that operations can be carried out on the article being assembled at the respective work stations. A guidance system (eg. as rails and/or buried guide wires) control the path followed by the automated guided vehicle as it moves between the work stations. In FR-A-2185567 there is disclosed an assembly line of a type incorporating an automated guided vehicle system having a vehicle for conveying an article to be assembled along a path through a plurality of work stations, and wherein the vehicle has a supply of power on-board and over a first portion of its path receives no motive power from any external source, being driven along its path by motive power obtained from its on-board supply. According to the present invention, an assembly line of the type hereinabove defined is characterised in that the vehicle is driven in two different manners into respective portions of its path, and in that the vehicle receives motive power from an external source along a second portion of its path. Summary of the Invention This externally supplied motive power may be in the form of energy, such as electricity from external contacts, or it may be in the form of a motive force applied directly to the vehicle such as from driven rollers. Typically, the vehicle will move relatively fast when it is moving under the externally supplied motive power and will move relatively slowly when it is relying on its on-board supply. It is advantageous if the on-board supply of motive power is replenished as the vehicle travels over that portion of its path in which it receives motive power from an external source. Frequently, the complete path of such an automated guided vehicle will contain a plurality of each type of path portion. Preferably, and in accordance with the invention of our copending Application No. 89113405.8, divided herefrom, over the first portion of its path the vehicle receives guidance signals but its movement is not physically constrained so that it is necessary for the vehicle to follow the path by determining its direction of travel itself. In the second portion of its path, a track is provided for the vehicle which track physically constrains the vehicle to follow the path. Typically, the vehicle will continue to receive guidance signals even along the portion of its path having the track. In the assembly line, the article to be assembled may pass through a plurality of work stations which are arranged in groups. The automated guided vehicle carrying the article to be assembled can then be driven through the work stations of one group at relatively high speed along a physically constraining track, typically under the control of a computer associated with that group of work stations. The vehicle can then move at a relatively low speed under its own power and without physically constraining tracks from one group of work stations to the next. In this manner, the area between groups of work stations can be kept free of tracks and motive power supplies for the vehicles. This can be advantageous, for instance if other types of vehicle or human personnel need to cross such areas from time to time. Description of Drawings Embodiments of the present invention, given by way of non-limiting example, will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic overview of part of a path network with a plurality of automated guided vehicles, embodying the present invention; Figure 2 is a schematic view of a vehicle according to a first embodiment of the present invention; Figure 3 is a schematic front view of the vehicle of Figure 2 with its front and rear safety buffers removed; Figure 4 is a schematic top view of the forward part of the vehicle of Figure 2; Figure 5 is a schematic detailed view of the drive system of the vehicle of Figure 2 which is used when the vehicle receives motive power from an external source; Figure 6 is a schematic view showing the pick up system for the externally supplied motive power for the vehicle of Figure 2; Figure 7 is a view equivalent to Figure 2 for a second embodiment of the present invention; Figure 8 is a view equivalent to Figure 3 for the embodiment of Figure 7; Figure 9 is a view equivalent to Figure 4 for the embodiment of Figure 7; Figure 10 is a view equivalent to Figure 5, but from a different angle, for the embodiment of Figure 7. The embodiments now to be described for convenience employ the present invention in combination with the invention subject of our above-mentioned copending divisional application. Figure 1 shows part of a path network for an automated guided vehicle in a motor car assembly line. The paths 1 in the network are defined by buried guide wires, from which the automated vehicles 3 obtain guidance for signals. The buried wires may provide these guidance signals in a passive manner, i.e. the vehicles detect the presence of the wires and follow them, without the wires providing any signal beyond their mere presence. Alternatively, the wires may provide guidance and/or control signals in an active manner, which signals could be picked up for example by electro-magnetic transducers on the vehicles. Buried wire guidance systems are known in the art. The wires 5 and the wire-detecting sensor means 7 on the vehicles 3 are best seen in Figures 3 and 8. In Figure 1, two groups 9 of work stations are shown. A vehicle 3 will carry a motor car body shell through the stations of the first group, then from the first group to the second group, and then through the stations of the second group. Along the length of each group, the vehicle 3 receives motive power from an external source, and its motion is physically constrained by a track provided at the floor along the length of the group 9 of work stations. Between the groups, the vehicles 3 move only by means of their on-board motive power supply, and are guided by the buried wires without being physically constrained by any track. The vehicles 3 have safety buffers 11 at either end. A frame 13 for carrying a motor car body shell or other article to be assembled is supported by pillars 15 on a vehicle main body 17. The main body 17 is supported on the floor of the assembly line principally by freely rotating wheels 19 mounted at either side of the body near its front and rear ends. The guide wire sensing means 7 is mounted near the front of the main body, and centrally across the width of the vehicle. A further floor contacting wheel 21 is provided near the centre of the vehicle 3. This is a drive wheel which is used to propel the vehicle 3 along those portions of the path where there is no track and no external supply of motive power. The vehicle carries electric storage batteries 23 which power an electric motor to drive the wheel 21 over these portions of the path. The preceding general description of the automated guided vehicle is common to both embodiments, and the parts described are best shown in Figures 3, 4, 8 and 9. In the embodiment of Figures 2 to 6 the physically constraining track takes the form of a guide rail 25 mounted on the floor. The externally supplied motive power is supplied in the form of electricity, from a supply board 27 (see Figures 1 and 6) mounted alongside the track. The vehicle 3 carries a power collector 29 which cooperates with the electric supply board 27 while the vehicle 3 travels over the rail 25. The electricity collected by the power collector 29 is used to power a further electric motor 31 mounted on the vehicle 3. The motor 31 drives horizontally extending (vertical axis) rollers 33 which press against either side of the floor-mounted rail 25. The reaction between the rollers 33 and the rail 25 drives the vehicle along this portion of its path. Since the vehicle 3 is receiving a supply of electric power to drive the motor 31 as it passes over the portions of its path having the physically constraining track (in the form of the rail 25), it may be convenient to provide means to recharge the batteries 23 as the vehicle passes along these portions of its path. In the embodiment of Figures 7 to 10, the externally supplied motive power is not supplied to the vehicle in the form of electricity. Instead, it is supplied in the form of a motive force applied directly to the vehicle. In this embodiment, the physically constraining track takes the form of a line of pairs of horizontally extending rollers 35 mounted just above the floor level of the assembly line. The vehicle 3 has a rail 37 which passes between them by the rollers 35 of each pair. The vehicle 3 does not carry an additional electric motor 31. Instead the rollers 35 are driven by motors 39 arranged beneath them. Because the vehicle 3 does not have a further electric motor 31 in this embodiment, it is not necessary to provide a power collector 29 on the vehicle and an electric supply board 27 alongside the track. Nevertheless, it may be convenient to provide a system for supplying the vehicle 3 with electricity as it passes along those portions of its path where it receives external supplied motive power, in order to recharge the batteries 23 carried on the vehicle. Alternatively, no provision may be made for recharging the batteries while the vehicle 3 is travelling on the path 1, and the batteries may be replaced or recharged periodically while the vehicle is being stored, serviced or otherwise not in use. As can be seen from Figure 1, there will typically be several vehicles 3 travelling in succession along the same path 1. Conveniently, while the vehicles 3 are passing a group 9 of work stations the movement of the vehicles 3 along the path 1 is controlled by a line computer associated with that group of work stations, so as to move the vehicle 3 in accordance with the needs of the work stations. Preferably the vehicles are moved between the work stations relatively quickly. This is easily provided as the external supply of motive power can be arranged to supply large amounts of motive power. In the embodiment of Figures 7 to 10, each pair of driven rollers 35 may be controlled and driven independently, or the pairs of rollers may be in groups which are driven and controlled together but independently of the rollers of other groups, rather than driving all the rollers associated with one group 9 of work stations under a common control. This division of the rollers into independently driven pairs or groups can allow the vehicles 3 to be driven past the work stations of a group 9 in a more flexible manner.

Claims: 1. An assembly line incorporating an automated guided vehicle system having a vehicle for conveying an article to be assembled along a path through a plurality of work stations, and wherein the vehicle (3) has a supply of power (23) on-board and over a first portion of its path receives no motive power from any external source, being driven along its path by motive power obtained from its on-board supply (23), characterised in that the vehicle (3) is driven in two different manners into respective portions of its path, and in that the vehicle receives motive power from an external source (27 or 35) along a second portion of its path. 2. An assembly line according to claim 1, characterised in that the externally supplied motive power (27 or 35) is in the form of electrical or mechanical energy, and the on-board supply of motive power is replenished as the vehicle travels over the second portion of its path. 3. An assembly line according to claim 1 or claim 2, characterised in that the vehicle moves relatively fast when it is moving under the externally supplied motive power and moves relatively slowly when it is relying on its on-board supply. 4. An assembly line according to claim 1 or claim 2 or claim 3, characterised in that the complete path of the automated guided vehicle contains a plurality of each type of path portions. 5. An assembly line according to any of claims 1 to 4, characterised in that, over the first portion of its path the vehicle receives guidance signals but its movement is not physically constrained so that it is necessary for the vehicle to follow the path by determining its direction of travel itself, whilst in the second portion of its path, a track (25 or 35) is provided to physically constrain the vehicle to follow the path. 6. An assembly line according to claim 5, characterised in that the vehicle (3) continues to receive guidance signals along the portion of its path having the track (25 or 35). 7. An assembly line according to claim 5 or claim 6, characterised in that the track either provides a reaction surface for driven rollers on the vehicle or provides driven rollers (35) to act on a reaction surface on the vehicle. 8. An assembly line according to any of claims 1 to 7, wherein the vehicle passes through a plurality of work stations (9) which are arranged in groups, characterised in that the automated guided vehicle (3) carrying the article to be assembled is driven through the work stations of one group at relatively high speed along a physically constraining track and the vehicle then moves at a relatively low speed under its own power and without physically constraining tracks from one group of work stations to the next.

Inventors: PIGOTT, NORMAN BRIAN
Applicants: LITTON U.K. LIMITED
Application year: 1988
Main classification: B62D65
IPC codes: B61D47, B60L13, B62D65, B62D1, B23P21