BACKGROUND OF THE INVENTION: A vehicle body comprises a large number of components which are assembled on a production line. Such components include a floor pan, stress-bearing panels for supporting suspension components, a passenger cage comprising A, B and C pillars, doors, as well as internal and external body panels. To increase production rates, assembly of vehicle bodies is becoming increasingly automated. Thus, a partially completed vehicle body is supported on a vehicle skid and passed down a production line between work stations at which various components are added to the partially completed vehicle body by robots. These robots include robots which accurately position components on the partially completed vehicle body, as well as welding robots to weld the components in place. At each work station, the vehicle skid is halted and lowered such that a reference hole in the partially completed vehicle body can be lowered around a reference pin associated with that work station. In this manner, the robot or robots at that work station know that the partially completed vehicle body is correctly positioned to allow the work at that station to be performed. Once the work at that station has been performed, the skid is raised so that the reference hole is raised clear of the reference pin and the skid is transported to the next work station.

Skids are generally transported between work stations using a conveyor system comprising a number of adjoining conveyor sections. Each conveyor section typically comprises a six metre long frame structure supporting a plurality of transversely extending shafts, with each shaft carrying a pair of support rollers. As is disclosed in e. g. EP-A-0 103 672 and EP-A-0 149 694, the transversely extending shafts may be driven by a common drive shaft to thereby effect rotation of

the support rollers. Alternatively, and as disclosed for example in EP-A-0 255 620, the transversely extending shafts may be driven by a drive belt arrangement. The support rollers contact support rails on the vehicle skid and friction between the rollers and rails causes the skid to be transported along the conveyor section.

In order that the partially completed vehicle bodies are correctly positioned at each work station, it is imperative that the conveyor system is able to stop the vehicle skid at a location with an accuracy of e. g. +-3 mm. Furthermore, useful work is carried out on the production line only at the work stations. Thus, the transfer time between work stations should advantageously be kept to a minimum. Given that a typical skid weighs 120 kg before it carries any body components, however, it will be appreciated that a great deal of inertia is involved in accelerating and deccelerating the skids, something which is detrimental to the accuracy when trying to position the skid at each work station, particularly if the skids are transported between work stations at high speed.

SUMMARY OF THE INVENTION: It is therefore an object of the present invention to provide a conveyor system which allows for shorter transfer time between work stations, but which nevertheless satisfies positional accuracy requirements.

This object is achieved in accordance with the present invention by a conveyor system according to claim 1.

Thus, since the drive means of the conveyor system in accordance with the present invention comprises a drive belt having a toothed outer surface for engagement with a projection on the vehicle skid, an interlocking, rather than purely frictional, engagement between the drive means and the skid is attained, thereby allowing the skid to be subjected to greater acceleration and decceleration forces without loss of positional accuracy.

The invention further provides for a skid which is equipped with a suitable projection for engagement with the toothed outer surface of the drive belt of the conveyor system of the present invention.

Preferred embodiments of the conveyor system and the vehicle skid are detailed in the respective dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS: The invention will be described in greater detail in the following by way of example only and with reference to embodiments shown in the attached drawings, in which: Fig. 1 is a schematic elevational view of a conveyor system of the present invention making up part of a vehicle production line; Fig. 2 is a schematic end view taken along line II-II of Fig. 1, and Fig. 3 is a schematic perspective view of the conveyor system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS: In the drawings, reference numeral 10 generally denotes a conveyor system according to the present invention. As is known in the art, the conveyor system is made up of a number of adjoining conveyor sections 12. The conveyor sections 12 are arrange such that a vehicle skid 14 can be transported along the sections between work stations 16. Each skid 14 carries a partially completed vehicle body 18. When the skid 14 arrives at a work station 16, the conveyor section 12 at that work station is lowered such that a reference pin 20 (see Fig. 2) enters a not shown reference hole in the partially completed vehicle body 18. Once the conveyor section 12 is in its lowered position, a robot 22 or robots associated with that work station is/are able to perform operations on the partially completed vehicle body. Upon completion of working operations at the work station, the conveyor section 12 is raised such that the reference hole in the partially completed vehicle body is raised clear of the reference pin 20 and the skid 14 carrying the vehicle body is transported to the next work station for a subsequent operation.

With particular reference to Fig. 3, the conveyor system according to the present invention comprises a frame structure 24 making up a conveyor section 12. The frame structure 24 extends along a longitudinal axis 26. In the illustrated preferred embodiment, the frame structure 24 comprises a pair of parallel frame sections 28. The frame structure 24 carries a plurality of support

rollers 30 which are journalled for rotation about axes 32 transverse to the longitudinal axis 26.

Each support roller 30 has a peripheral support surface 34 for supporting the vehicle skid 14. To displace the skid 14 along the frame structure, the conveyor system is provided with drive means.

In accordance with the present invention, the drive means comprises at least one continuous drive belt 36 having a toothed inner surface for engagement with a drive gear 38 and a toothed outer surface for engagement with a projection 40 on the vehicle skid 14. The drive gear 38 is suitably connected to a motor 42, for example an electric motor, carried on the frame structure.

In addition to the peripheral support surface 34, each support roller 30 has a belt contact surface 44 adjacent the support surface for contact with at least one drive belt 36. Advantageously, the belt contact surface 44 may be provided with teeth for meshing with the teeth on the inner surface of the drive belt. In the embodiment shown in Fig. 3, the frame section comprises a first end support roller at a first end 46 of the frame section, a second end support roller at a second end 48 of the frame section and two intermediate support rollers located between the first end support roller and the second end support roller. Thus, the drive belt comprises a first drive belt 50 between the first end support roller and the adjacent intermediate support roller, a second drive belt 52 the second end support roller and its adjacent intermediate support roller, and third drive belts 54 betnveen adjacent intermediate support rollers. Thus, the belt contact surface of the intermediate support rollers is sufficiently wide to permit two adjacent drive belts to contact the surface.

The vehicle skid 14 which is to be used with the conveyor system of the present invention has at least one (in the shown embodiment two) substantially planar support rail 56 which is adapted to rest on the support surfaces 34 of the support rollers 30. The skid further comprises at least one projection 40 which is adapted to engage the toothed outer surface of the drive belts 36. To this end, the projection 40 has an extension transverse to the longitudinal axis 26 of the frame structure 24 of the conveyor system over substantially the entire axial extension of the belt contact surfaces 34 of the support rollers 30. The projection may suitably be affixed to a transverse frame member 58 connecting the two planar support rails of the skid 14. In the shown embodiment, the transverse frame member 58 carries two such projections, one for engagement with the belts of the one frame section and one for engagement with the belts of the other frame section.

The projection 40 or projections are arranged on the skid 14 such that when the skid is also supported by intermediate support rollers, approximately half the extension of the projection is in engagement with the toothed outer surface of the drive belt when the projection 40 is between support rollers 30. Thus, at the intermediate support rollers, approximately half the projection engages one drive belt and approximately half the projection engages an adjacent drive belt, the two drive belts both contacting the belt contact surface 44 of the support roller. In this manner the projection is smoothly transferred from one drive belt to the next.

The conveyor system 10 in accordance with the present invention operates in the following manner.

A skid 14 carrying a partially completed vehicle body 18 is supported on a first conveyor section 12 such that the projections 40 on the skid engage with respective drive belts 36 carried by support rollers 30 of the conveyor section. When it is desired to transport the skid 14 to a subsequent conveyor section, the motors 42 of the conveyor sections are activated such that the drive belts start running. As a result of engagement of the projections 40 with the drive belts and friction between the support rails 56 of the skid and the support surfaces 34 of the support rollers 30, the skid is transported along the first conveyor section to the next. When the skid 14 arrives at a conveyor section corresponding to a work station 16, the motors of the conveyor section are de- energized such that the skid is brought to a halt at a predetermined position. The fact that there is an interlocking engagement between the projections 40 on the skid and the toothed outer surface of the drive belts implies that the skid can be braked and accelerated relatively quickly without risk of the skid sliding on the support rollers.

Once the skid has reached its predetermined position on the conveyor section, the conveyor section is lowered such that the reference pin 20 enters the reference hole on the partially completed vehicle body. The robot or robots 22 are then able to perform their intended tasks.

When the robots have completed their intended tasks, the conveyor section is raised until it is aligned with the subsequent conveyor section and the skid can be transported further by activation of the respective motors 42.

It is to be understood that the invention is not restricted to the embodiments described above and shown in the drawings, but may be varied within the scope of the appended claims. For example, opposite support rollers of the parallel frame sections may be carried on a common shaft extending transverse to the longitudinal axis of the frame structure.