Such loading devices comprise a loading bridge with an upward pivotable platform, a front edge of which can be carried to the same level as the loading floor of a truck. The loading device herein usually further contains an extensible lip which can protrude into the loading space of the truck and the leading edge of which can be lowered onto the loading floor. When the loading device has thus been placed in the active position a forklift truck can for instance be driven over the platform and the lip in and out of the loading space of the truck in order to place therein or remove freight therefrom.

In accordance with an important aspect of the present invention, driving of the platform and, if present, the lip takes place using air under pressure. In the usual loading devices of this type the driving takes place by hydraulic means. It has been found, however, that during adjustment of the platform, i.e. placing thereof in the active position, only small forces occur, namely only those which are caused by the weight of the platform itself and the components connected thereto. The desired movement of the platform can thus still be obtained with a comparatively small drive power which can be generated pneumatically with simple means.

At the location where a loading device of the present type is used compressed air is usually already present, so that the acquisition and installation costs of the loading device according to the invention can remain limited compared to a hydraulic embodiment.

The drive for the reciprocally movable lip on the front end of the platform can also take place pneumatically in suitable manner. In view of the small forces, use can be made in favourable manner of a drive cylinder of plastic, in particular PVC. The cost of manufacturing such a cylinder is low, which contributes toward a low cost price of the whole device.

According to a favourable further development, the drive power is provided pneumatically while with the compressed air a liquid is placed under pressure with which the drive motors, such as cylinders and/or bellows of the loading device, are activated. The great advantage hereof is that the cylinders and/or bellows are not elastically compressible as a result of the compressibility of the compressed air as in the case of purely pneumatic devices. The pneumatic/hydraulic device according to the preferred embodiment of the invention can, in appropriate manner with the usual restrictions and dampings, be given the same behaviour as typical hydraulically operated loading devices while still retaining the advantage of the comparatively low cost price.

The invention will be further elucidated with reference to the annexed figures.

Figure 1 shows a partly schematic longitudinal section of a loading device according to the invention in a rest position, wherein the pneumatic circuit is shown wholly schematically.

Figure 2 is a view substantially corresponding with figure 1 of the loading device in an intermediate position, with a drive modified to a pneumatic/hydraulic drive.

Figure 3 shows the loading device according to the invention in the position of use.

Figure 4 shows schematically a circuit as applied in the loading device according to the invention and a

preferred embodiment of a piston/cylinder unit there for.

The loading device 1 comprises a loading bridge 2, also referred to as a "dock leveller". This loading bridge 2 is built into a loading bay 3 such that a platform 5 thereof connects onto the upper surface of the bay 3.

The platform 5 is connected movably to the frame 4 of loading bridge 2 by means of a hinge 6.

Platform 5 can be moved up and downward with its forward edge 9 by moving means 7 in the form of a pneumatic bellows.

The forward edge 9 is situated on an extensible portion 8 of platform 5. By means of extending member drive means 12, which are here also formed by one or more pneumatic cylinders 12, this portion 8 can be extended to the left as seen in figure 1 and moved back again.

Loading device 1 serves to enable easy loading and unloading of a truck 11 by means of for instance a forklift truck which can travel over platform 5 into the loading space of truck 11.

In order to place loading bridge 2 and truck 11 in the situation in which the truck can be loaded or unloaded, the platform 5 is first moved upward by the bellows 7 as shown in figure 2 and the extending part 8 is pushed out. The movements are indicated in figure 2 with arrows. In this situation of loading bridge 2 the truck 11 can reverse until a chassis part 13 thereof strikes against a stop block 14.

A leading edge 9 of the extending part 8 of platform 5 is herein carried into the loading space of truck 11.

The bellows 7 is then first reactivated to pivot the leading edge 9 of platform 5 downward, wherein a protruding hook 15 is moved onto the loading floor 16.

Cylinder 12 is then activated in order to gradually retract the extensible part 8. The hook 15 herein slides

over loading floor 16 until the end of loading floor 16 is reached. The hook 15 of the coupling means on loading bridge 2 can then drop into an eyelet 17 on the truck 11.

As figures 1 and 2 show, the bellows 7 is activated using the three-position valve 26. In the position of the valve 26 moved to the right compressed air from compressed air conduit 27 can flow to bellows 7, whereby this expands and moves platform 5 upward into the position shown in figure 2. For lowering of the platform the valve 26 is placed in the position moved to the left, whereby air can escape from bellows 7.

The cylinder 12 for the extending means is activated with three-position valve 25. Here also in the position of the valve 25 moved to the right compressed air from the conduit 27 is carried behind the piston in cylinder 12, whereby the piston rod of the cylinder, and thus the extending part 8, is moved outward from the position of figure 1 to that of figure 2. In order to move the extending part 8 back, the valve 25 is placed in the position moved to the left, whereby compressed air from compressed air conduit 27 is carried in front of the piston in cylinder 12, whereby the piston rod and the extending part 8 are moved to the right.

In the embodiment of figure 2 the same valves 25, 26 are applied but a plurality of reservoirs 28 is arranged in the lines to the bellows 7 and cylinder 12.

These reservoirs are filled with a liquid, which may be hydraulic oil but may also be water provided with an antifreeze agent.

The compartment 29 of reservoir 28 is incorporated in the conduit which leads to the rear end of cylinder 12. When valve 25 is therefore placed in the position moved to the right, compressed air 27 will flow into the top of reservoir 29 and the liquid present therein will be displaced to cylinder 12. In the return movement liquid is carried out of compartment 30 to the front part of the cylinder and liquid is displaced at the rear which is fed back to compartment 29. The operation

of cylinder 12 is in fact therefore entirely hydraulic.

Restrictions can be arranged in the usual manner in the conduits between cylinder 12 and compartments 29, 30 in order to damp the movement of the piston rod relative to the cylinder so that a suitable spring action can be adjusted or such a spring action can be fully disabled.

A compartment 31 of reservoir 28 is also incorporated in the feed conduit to the bellows 7. When valve 26 is activated liquid thus flows to bellows 7 and back therefrom under the influence of compressed air from compressed air conduit 27. Damping means can herein also be arranged in suitable manner in the conduit between compartment 31 and bellows 7, whereby possible spring action of platform 5 can be adjusted to a desired value or can be eliminated.

Figure 4 further shows a suitable circuit with emergency switch-off. The cylinder 30 applied in this circuit is manufactured from plastic, in particular PVC.

Cylinder 31 is manufactured from a piece of commercially available PVC tubing. The end covers 32, 33 are manufactured from pieces of solid PVC into which are hollowed out chambers in which the ends of cylinder 31 are glued fixedly.

End cover 33 is likewise of PVC and hollowed out to fit the inner diameter of cylinder 31. In the periphery of piston 42 is hollowed out a groove into which an O-ring 34 is received. A sealing ring is likewise arranged in end cover 32.

Because use is made of non-rusting plastic material, the liquid included in the system for activating the cylinder can, in appropriate and environmentally-friendly manner, be a water-based liquid.

Cylinder 30 is activated using a valve 35 which, when pressed in, carries compressed air from compressed air conduit 41 to reservoir 36. From reservoir 36 the liquid 37 is carried to the space under the piston 42 of cylinder 30, whereby the piston with piston rod will move upward.

When the emergency stop valve 40 is activated, the compressed air pressure is placed on closing valve 39, whereby the connecting conduit between the cylinder and the reservoir is closed.

A per se known panic circuit is further incorporated in the connecting conduit.

Instead of reservoir 36 as shown, wherein a direct contact can be present between the liquid 37 and the compressed air, this reservoir 36 may also be replaced by a per se known accumulator with a separating membrane.