GB2109340A - Fork assembly provided on a load carrier for industrial trucks - Google Patents

Abstract

A fork assembly provided on a load carrier for industrial trucks comprises at least two fork arms 8, 9 which are movable in unison and adapted to be moved into- or under a load. The fork arm composite is freely transversely movably mounted on transverse tracks 5, 33. Friction-reducing bearing means for backing the load and for facilitating the transverse movement and centring means 72, 73 are provided between the fork arm composite and the transverse tracks 5, 33. The bearing means comprise at least one roller. Adjustable stops 12, 13 serve to limit the transverse displacement of the fork arm composite and to centre the latter in its central position. The fork arms 8, 9 of the fork arm composite are separably and adjustably interconnected 17, 19, 21, 61-67 and 16, 18, 20, 68-71 and may consist of telescopic fork subassemblies. <IMAGE>

Description

SPECIFICATION Fork assembly provided on a load carrier for industrial trucks This invention relates to a fork assembly provided on a load carrier for industrial trucks, which fork assembly comprises at least two fork arms, which are movable in unison and adapted to be moved into or under a load.

In accordance with Laid-open German Application 29 35 553 the fork arms of a fork assembly are mounted to be vertically movable up and down between two end positions while retaining their relative position. In one range of movement the fork arms can move to their lower end position by gravity or the weight of the fork arms can be compensated by a spring assembly. In that known design the fork arms can be properly moved under a pallet because they are in sufficiently exact alignment whereas oblique positions of pallets can be compensated and the threading should be facilitated under such circumstances.

German Utility Model 1,834,471 discloses a fork assembly which is intended to facilitate the taking up and depositing of loads. For that purpose the fork arms are pivotally movable about a vertical axis and are individually displaceable in a horizontal direction. The pivotal movement and displacement are effected by hand or by means of a hydraulic actuator.

Springs may be provided to return the fork arms to a central position. German Patent Application 891,225 discloses a stacker having fork arms which can be adjusted by a hydraulic system so that their spacing is varied in adaptation to a pallet to be engaged from underneath.

The last-mentioned known embodiments require actuating means for the lateral movements of individual fork arms. Owing to these actuating means which are required, the tracks and their actuating means are arranged in a certain spatial position between the mast and the front wheels.

Such movement to be effected by an actuator requires the attention of the operator and involves the disadvantage that a wrong control or overshooting is possible. It has also been admitted that the known design has the disadvantage that the length of the vehicle is increased by the means for effecting a displacement or pivotal movement. There is also a higher power requirement and a controllable operation is involved, which renders the normal sequence of operation more complicated.

In the known embodiment, a gripping or clamping action is intended particularly in connection with the actuator.

The known actuation of individual fork arms in the load carrier or in a fork arm composite involves a danger of accidents because the load-supporting surface of the load carrier may be changed and may not be sufficient for supporting the load in certain applications.

The invention is based on a fork assembly in industrial trucks which are operated between racks, particularly automatically, without a driver, to positions at desired racks.

Such positioning can be controlled by expensive feedback position control systems which use optical, acoustic or electromagnetic sensors to measure the desired position, and positioning actuators, such as hydraulic units or electric motors, for effecting a movement to the desired position.

These positioning circuits are very expensive too.

A problem arising in connection with industrial trucks which are to be moved and positioned between racks resides in that the mass of such industrial trucks varies from time to time in dependence on the load so that the inertial forces differ in magnitude. Besides, mechanical devices, such as brakes, which are effective in conjunction with the feedback control systems, may exert different actions as a result of wear or of environmental influences, such as moisture, temperature, etc.

It is an object of the invention to provide a fork assembly which in the operation of industrial trucks permits a simplified positioning and ensures that a load will be satisfactorily taken up even if the positioning is inaccurate to some extent.

In this connection it is pointed out that such industrial trucks have a lifting frame and a load support, which can be raised along the lifting frame and can be extended forwardly or laterally.

That object is accomplished according to the invention in that the fork arms, which are connected to each other, are mounted on transverse tracks to be freely transversely movable, at least two fork arms are provided with friction-reducing bearing means for backing a load and facilitating the transverse movement, and centring means are provided between the fork arm composite and the transverse tracks.

The interconnected fork arms constitute a so-called fork arm composite. Whereas the composite consists of two fork arms in the preferred embodiments, the composite may comprise more than two fork arms, such as three or four fork arms. The fork arms of the composite may be separable and adjustable relative to each other, as will be discussed hereinafter, but during operation the composite ensures the presence of a defined loadsupporting surface, which can be adjusted.

To permit a compensation of a possibly inaccurate positioning of the vehicle, the interconnected fork arms can be transversely moved and means are provided which facilitate such a transverse movement for an adaptation during the movement of the fork arms into or under a load. The centering means ensure that a proper relation to the vehicle will be obtained for a compensation of weight in the central position when the load has been taken up and also in an unloaded state.

Because the interconnected fork arms are freely transversely movable within the limits defined by the dimensions of the load carrier which comprises the fork assembly, an automatic elignment and introduction are ensured as the fork arms can align themselves at the receiving passages or blocks provided on the pallets. The friction-reducing bearing means facilitate the adjustment but under the pressure applied when the load has been taken up ensure that the fork arms will then be held in position. Specially designed bearings may be used to facilitate the movement in the transverse direction.

It is known to provide the forks at their tips at least at their outer edges with a taper toward the end of the fork arm so that a wedge-shaped engaging surface is obtained.

This feature is included as a means for effecting an automatic adjustment of the fork arm composite.

In a particularly preferred embodiment the friction-reducing bearing means comprise a load-backing roller, which is mounted on an axle and during a lateral displacement rolls on a bearing surface and takes up the load oftthe fork arm. The load-backing roller or rollers facilitate the transverse movement. When the load has been taken up, the transverse movement may be resisted by a higher friction so that the stability of the arrangement will be improved. It should be borne in mind that centring means are provided.

The centring means advantageously comprise springs urging the fork arm composite towards its central position. This action will overcome the friction and will always ensure the proper adjustment of the load carrier relative to the vehicle.

The centering means preferably comprise two springs or spring arrangements disposed on respective sides of the fork arm composite.

The expression "spring arrangements" covers also a plurality of parallel springs which are distributed over the height of the load carrier.

Centring will then be ensured by the fact that the springs are provided on the sides, specifically the outer sides, of the fork arm composite and act toward each other. Alternatively, a spring arrangement may be disposed centrally between outer fork arms; such a spring arrangement is secured at the center of the fork arrangement.

A preferred embodiment of the invention comprises springs for returning the fork arms to a central position as well as adjustable stops for limiting the lateral excursion of the fork arm composite and for centring the latter in its central position. In that case the lateral excursion will be restricted but centring will be permitted because the stops are adjustable.

In a special embodiment the lateral stops consist of cylinder-piston devices, which are adapted to be connected in parallel to a common pressure fluid so that equal forces can be exerted on both sides to effect a centring and will be assisted by the forces of the spring so that centring will be permitted.

The resulting arrangement can be used satisfactorily under various conditions.

In a preferred arrangement the joint between the at least two fork arms of the fork arm composite is separable and adjustable and the distance between the at least two fork arms is adjustable. It must be borne in mind that a truck may have to be operated in different warehouse sections or warehouse buildings in which pallets or loads or different types are to be taken up so that an adaptation to the various conditions is required. For this purpose, transverse connecting elements are suitably provided, which consist of bars which are firmly connected to the fork arms or to fork holders extending at right angles to the fork arms and are detachably connected by an overlapping strap. In a preferred embodiment an adjustment is permitted by the provision of a screw-slot joint between the bars and the strap.It may also be advantageous to provide remotely controllable, solenoid-operable bolts between the bars and the strap. In that case the separation of the joint can be controlled from the driver's seat and a separate adaptation of the individual fork arms will be permitted if these fork arms are guided by springs of the centring means.

In a preferred embodiment the fork arrangement comprises fork arms, which consist of portions which are engageable with the load, and fork holders extending at right angles to such portions. To facilitate the transverse adjustment, transverse guiding means are provided, which are suitably mounted at the top ends of the fork holders and are transversely movable along a pivot pin and friction-reducing bearing means are provided in the lower region of the fork holders and engage a frame of the load carrier. That design is desirable because the fork arms can be tilted upwardly and because the backing of the load by the bearing means results in a relief during the transverse movement of the fork arm composite.

In the embodiment just described the friction-reducing bearing means preferably comprise rollers which have vertical axes extending parallel to the fork holders. That feature will facilitate the horizontal adjustment particularly if the rollers consist suitably of backing rollers provided on the fork holders in the lower portion thereof. The means for mounting a fork arm on a transversely extending pivot pin preferably consist of a combination of slide bushings, which surround the pivot pin, and a linear ball bearing, which is preferably yieldably supported on a rubber or rubber-like element. This arrangement will ensure that the forkarm composite will be guided and held in position during transverse and tilting movements and that it can easily be displaced under no load.

In another advantageous embodiment, telescopic forks are provided, the telescopic fork assemblies which are provided instead of the fork arms discussed hereinbefore are mounted to be movable on transverse rails and in addition to the friction-reducing bearing means for backing a load the transverse tracks comprise rails which constitute a track surface that extends at right angles to the direction in which the telescopic forks can be extended. In such an arrangement, even telescopic forks provided in a fork arm composite can be adjusted.

In that embodiment the friction-reducing bearing means desirably consist of load-packing rollers, which are mounted on axles that are parallel to the direction in which the telescopic forks can be extended, and said rollers move in a channel-shaped portion of the rail. In that arrangement the rails comprise upper and lower bearing surfaces for engagement by these load-backing rollers.

These rails consist suitably of I-section rails and the fork arm subassemblies are provided with braking projections having top and bottom brake liners, which extend into a recess of said rails so that under load the brake liner engages a flange of the rails. This will ensure in a desirable manner that the forks will be held in position.

In that embodiment too the spring arrangements and the outer stops consist suitably of cyclinder-piston devices. For centring, the stops may be displaced against the action of the centrally disposed compression spring.

This concept is also applicable to the other embodiment.

The springs or compression springs preferably consist of mechanical springs although gas compression springs and the like may also be used.

The invention will now be explained with reference to illustrative embodiments shown on the drawings, in which Figure 1 is a perspective view showing an embodiment of a load carrier, Figure 2 is a fragmentary vertical sectional view taken on line ll-ll in Fig. 1, Figure 3 is a vertical sectional view showing how a fork arm is mounted on a pivot pin, Figure 4 is a fragmentary perspective view showing a load carrier provided with telescopic forks, Figure 5 is a fragmentary vertical longitudinal sectional view showing a telescopic fork subassembly, Figure 6 is a view which corresponds to Fig. 5 but is taken on a section line which is spaced from and parallel to the section line on which Fig. 5 is taken, and Figure 7 is a schematic elevation showing a detail of Fig. 1.

Figure 1 shows a load carrier generally designated 2 and comprising a slide plate 1.

At its forward end, the slide plate 1 is provided with a transversely extending pivot pin 5, which is mounted in bearing lugs 3, 4.

Transverse guiding elements 6, 7 consisting of bearings connected to fork arms 8, 9 are transversely movably guided on said pivot pin.

These fork arms extend from the lower ends of fork holders 10, 11, which extend at right angles to the fork arms 8. 9 and carry the transverse guiding elements 6, 7, which will be described more in detail with reference to Figs. 2 and 3.

In the present case the fork holders 10, 11 are provide with transverse connecting elements, which are disposed, e.g., on different levels and consist of bars 16, 17, 18, 19, which are separably and adjustably connected by an overlapping strap 20, 21. As has been shown for the bars 17, 19, the bars 16 to 19 have slots 60 to 63, and screws 64 to 67 extending through the slots 60 to 63 are screwed in tapped holes of the strap 20, 21.

This arrangement permits an adjustment of the fork arms 8, 9 in the fork arm composite in adaptation to the conditions of operation.

As has been shown in connection with the bar 1 8 and the strap 20, a remotely controllable, solenoid-operable bolt 71 may be provided which has an armature that extends through an opening of the strut 20 and can be selectively inserted into various holes 68 to 70 of the bar 1 8. The use of a solenoidoperable bolt affords the advantage that the parts of the fork arm composite can be separated even during operation when an adjustment is required for a special positioning function.

If this is possible, a compression spring extending along the line 22 will be provided between the fork arms 8, 9, particularly between the fork holders 10, 11.

A compression spring 72 or 73 is provided between the outside of each transverse guiding element 6 or 7 of the fork arms and the adjacent bearing lug 3 or 4. These compression springsare of equal strength and surround the pivot pin 5 and centre the fork arm composite. Any compression spring provided at 22 has desirably the same spring force as both compression springs 72, 73.

The slide plate 1 is provided on the outside with stops 12, 1 3, which consist of cylinder piston devices having pistons 14, 1 5 which under the action of a fluid under pressure can be inwardly extended under the control of means which are not shown. In this manner a positive centring of the fork arm composite can be effected in case of need and the fork arm composite can be held in its centred position, e.g., during a travel over a long distance. The extension of each piston may be limited in a position which corresponds to a central position of the fork arm composite, and control means may be provided for reversing the pistons when the distance between the fork arms is to be changed. The cylinders and pistons which constitute the stops 12, 1 3 have a length which permits said function.

In Fig. 7, parts shown also in Fig. 1 are designated by the same reference characters.

As is apparent from Fig. 7 the two cylinders of the stops 12, 1 3 are connected in parallel by a pressure fluid supply conduit 74. A controller 75 is provided for a connection to a pressure fluid source 76 or a drain 77. In that case, reversible pistons may be provided and the pistons 14, 1 5 may be provided with a return spring, which becomes effective in response to a pressure relief.

A transverse guiding element 6 is shown in Figs. 2 and 3.

That transverse guiding element 6 surrounds the pivot pin 5 and constitutes a bearing housing 25, which has an opening through which the pivot pin 5 extends and includes reduced guiding openings 26, 27, which are lined with slide bushings 28, 29. A backing tube 31 for a linear ball bearing 32 including bearing balls is disposed between the slide bushings and is backed by a cyclindrical elastic element 30, which preferably consists of rubber or a similar material. This arrangement ensures that the parts will be freely movable and guided relative to each other substantially without canting under no load and will be held in position when canted.

It is apparent from Fig. 2 that adjacent to another cross-member of the frame 1 the fork holders 10, 11 carry load-backing rollers 34, which constitute friction-reducing bearing means and are mounted on vertical axes 35 between bearing lugs 36, 37 provided on the fork holder 10. This arrangement permits also a vertical adjustment of the fork arms 8, 9 when the load-backing roller 34 has been lifted off.

During the threading into receiving pockets of a load, the transverse adjustment will be ensured by the fact that the fork arms are provided at their tips with profiled portions 38, 39 which are rounded or conical at least on the outside.

Figure 4 shows a load carrier 1 having a base frame 40 for carrying telescopic fork subassemblies 41, 42, which have substantially the same function as the previously described fork arms 8, 9 but are mounted on the load carrier 1 to be extensible towards both sides.

These telescopic fork subassemblies are transversely movable on track rails 43, 44 at right angles to the longitudinal direction of the forks. Said track rails, such as 44, consist of I-section rails, as is shown in Figs. 5 and 6.

A channellike track subassembly 45 shown as a closed structure is provided, e.g., centrally under the telescopic fork subassemblies and constitutes a transverse connecting element, which contains gears, which are nonrotably connected to and axially movable on a drive shaft and interengage with drive means provided in the telescopic fork subassemblies 41, 42 and serve to extend the extensible telescopic fork arms 46, 47 in one direction or the other. Additional transverse connecting elements diagrammatically indicated at 78, 79 and corresponding to the transverse connecting elements 16 to 19 and 20, 21 of Fig.

1 are provided between the telescopic fork subassemblies and can be used to adjust the distance between the telescopic fork subassemblies 41, 42. The resulting fork arm composite can be adjusted as in Fig. 1 between centring springs 80, 81, 82, 83, which correspond to the springs 72, 73 of Fig. 1. The springs 82, 83 bear on special abutments 84, 85 of the base frame 40 and the other springs 80, 81 bear on the slide plate 1. The springs are indicated schematically. Depending abutments for respective centring springs may be provided in the middle region of the telescopic fork subassemblies. In that case the associated centring spring extends in the plane of the base frame.

The telescope fork subassemblies are mounted on both track rails 43, 44, as is shown in Figs. 5 and 6 for the track rail 44.

The rails are provided, e.g., on the inside, with bearing surfaces 48, 49 extending at right angles to the direction in which the telescopic forks are extensible. Load-backing rollers 50 which constitute friction-reducing load-backing means extend between said bearing surfaces and have axles 51 which are parallel to the direction in which the telescopic forks are extensible. In the I-section 44, these load-backing rollers 9 are disposed in a channel-shaped portion of the rails.

On the respective other side, particularly on the outside, the telescopic fork subassemblied 41, 42 are provided with transversely guiding rollers 52, which are rotatable on vertical axles 53. These transversely guiding rollers 52 roll on the web 54 of the I-section so that they also enter on oppositely directed channelshaped portion of the rails.

Beside or between said rollers, a braking projection 56, which is rectangular in crosssection, is provided on a depending lug 55, as is shown, e.g., in Fig. 5 for the telescopic fork subassembly 42. The braking projection 56 is provided on the top and bottom with brake liners 57, 58 and enters the channelshaped portion 59 of the track rail 44. That portion opens, e.g., on the outside. When load is applied by extended telescopic fork arms 46, 47, the braking projection engages the upper or lower flange of the channelshaped portion 59 so that the respective telescopic fork subassembly will be held in opposition when a load is applied.

Claims (16)

1. A fork assembly on a load carrier for industrial trucks, which fork assembly comprises at least two fork arms, which are movable in unison and adapted to be moved into or under a load, characterized in that the fork arms, which are connected to each other, are mounted on transverse tracks to be freely transversely movable, least two fork arms are provided with friction-reducing bearing means for backing a load and facilitating the transverse movement, and centring means are provided between the fork arm composite and the transverse tracks.

2. A fork assembly according to claim 1, characterized in that the friction-reducing bearing means comprise a loading-backing roller, which is mounted on an axle and during a lateral displacement rolls on a bearing surface and takes up the load of the fork arm.

3. A fork assembly according to claim 1 or 2, characterized in that the centring means comprise springs urging the fork arm composite towards its central position.

4. A fork assembly according to claim 1 or 2, characterized in that two springs or spring arrangements are disposed on opposite sides of the fork arm composite.

5. A fork assembly according to claim 1 or 3, characterized by adjustable stops for limiting the lateral excursion of the fork arm composite and for centring the latter in its central position.

6. A fork assembly according to claim 1 or 3, characterized in that the lateral stops consist of cylinder-piston devices, which are adapted to be connected in parallel to a common pressure fluid source.

7. A fork assembly according to claim 1, characterized in that the joint between the at least two fork arms of the fork arm composite is separable and adjustable and the distance between the at least two fork arms is adjustable.

8. A fork assembly according to claim 7, characterized by transverse connecting elements, which consist of bars, which are firmly connected to the fork arms and or to fork holders extending at right angles to the fork arms and are detachably connected by an overlapping strap.

9. A fork assembly according to claim 8, chaacterized by a screw-slot joint between the bars and the strap.

1 Q. A fork assembly according to claim 8, characterized by the provision of remotely controllable, solenoid-operable bolts between the bars and the strap.

11. A fork assembly according to any of claims 1 to 10, wherein the fork arms consist of portions which are engageable with the load and of fork holders holders extending at right angles to such portions, characterized in that transverse guiding means are provided, which are mounted at the top ends of the fork holders and are transversely movable along a pivot pin and friction-reducing bearing means are provided in the lower region of the fork holders and engage a frame of the load carrier.

1 2. A fork assembly according to claim 11, characterized in that the friction-reducing bearing means comprise rollers which have vertical axes extending parallel to the fork holders.

1 3. A form assembly according to any of claims 1 to 12, characterized in that the means for mounting a fork arm on a transversely extending pivot pin consist of a combination of slide bushings, which surround the pivot pin, and a linear ball bearing, which is preferably yieldably supported on a rubberlike element.

14. A fork assembly according to any of claims 1 to 10, which comprises telescopic forks, characterized in that the fork arms constitute telescopic fork subassemblies which are mounted to be movable on transverse rails and in addition to the friction-reducing bearing means for backing a load comprise rollers in contact with rails having a bearing surface extending at right angles to the direction in which the telescopic forks can be extended.

1 5. A form assembly according to claim 14, characterized in that the friction-reducing bearing means consist of load-backing rollers, which are mounted on axles that are parallel to the direction in which the telescopic forks can be extended, and said rollers run in a channel-shaped portion of the rails.

16. A fork assembly according to claims 14 and 15, characterized in that the rails consist of I-section rails and the fork arm subassemblies are provided with braking projections having top and bottom brake liners, which extend into a recess of said rails so that under load the brake liner engages a flange of the rails.

1 7. A fork assembly according to claim 1, substantially as described and shown in any of Figs. 1 to 7 of the accompanying drawings.