TECHNICAL FIELD

The present invention relates to a hydraulically controlled carrying and gripping device of the kind set forth in the preamble of claim 1.

BACKGROUND ART

A device of the kind referred to above is known from US Patent Specification No. 3,166,207.

When a device of this kind is placed on a fork-lift truck, it is not only possible to lift or grip and transport e.g. a packing case or box, a bale of straw or a load pallet with goods stacked thereon, situated generally symmetrically about the longitudinal plane of symmetry of the fork-lift truck, but it is also possible to shift these objects towards one side of the symmetry plane or the other in order to deposit them in locations, in which the outer dimensions of the fork-lift truck would otherwise make it impossible to deposit them.

Since a movement away from the plane of symmetry will, how¬ ever, unavoidably cause a change in the loading of the fork-lift truck, and since its wheels normally will be spring-suspended and/or be provided with pneumatic tires, the fork-lift truck will for this reason unavoidably heel over to one side or the other.

In recognition of this problem, rules have been issued cal¬ ling for a limitation of the sideways movement of the car- rying and/or gripping means of the fork-lift truck, and the device disclosed in the above-mentioned US Patent Specifica-

tion No. 3,166,207 operates in such a manner, that it con¬ forms at least in part to these rules.

In the device disclosed in the above-mentione US Patent Specification No. 3,166,207, the means for limiting the sideways movements of the plane of symmetry of the carrying or gripping means relative to the vehicle are constituted by cam-controlled valves, adapted to interrupt the supply of liquid to the translatory cylinders, when a complicated movement-dividing mechanism mechanically signals the fact that the movement has reached one of the permitted extreme positions. Since said movement-dividing mechanism must neces¬ sarily be situated close to or at least mechanically con¬ nected to the carrying or gripping means or the translatory cylinders, it is unavoidably exposed to damage, when goods are to be moved, stacked or destacked, and in addition to this, the requisite valves are rather costly and require inspection at regular intervals.

DISCLOSURE OF THE INVENTION

On this background, it is the object of the present invention to provide a carrying and gripping device of the kind re¬ ferred to initially, with which it is possible by the use of simple means to conform to the above-mentioned rules with regard to limiting the sideways movement, and this object is achieved according to the invention by means of the features set forth in the characterizing clause of claim 1. Such a volume limiter, which may e.g. consist of a cylin- der with a piston movably supported therein, may be made ex¬ tremely robust and may be placed in a protected location, where it is not exposed to impact from the objects being handled by means of the carrying and gripping device, this not least being of importance when handling large packing cases and the like.

Advantageous embodiments of the carrying and gripping device according to the invention, the effects of which will be evident from the following detailed portion of the present description, and set forth in claims 2-7.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiment of a hydraulically controlled carrying and gripping device according to the invention shown in the drawings, in which

Fig. 1 shows the device placed on a fork-lift truck,

Fig. 2 is a hydraulic circuit diagram showing the connections between those parts of the hydraulic system, with which the invention is concerned, and

Fig. 3 shows the individual components of the switching- valve unit shown in Fig. 2, as well as their mutual connec¬ tions.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The exemplary embodiment of a hydraulic-ally controlled car¬ rying and gripping device according to the invention shown in the drawing comprises in a manner known per se a left-hand fork tine 1 and a right-hand fork tine 2, by means of upper rolling means 3 and 4 and lower rolling means 5 and 6 being laterally translatably supported on a support frame 7, the latter again in a manner not shown in detail being vertically movably supported on the front side of a vehicle in the form of a motorized fork-lift truck 1. For the sake of good order, it should be noted that the expressions

"right-hand" and "left-hand" refer to the directions relative

to the normal direction of movement of the fork-lift truck 8, e.g. with the fork tines 1 and 2 pointing in a forward direction.

Each of the two fork tines 1 and 2 is connected to a hydrau¬ lic translatory cylinder Cl and C2 respectively, each of which is anchored to one of the two ends of the support frame 7. How the fork tines 1 and 2 can be moved in different ways will now be described in more detail with reference to Figures 2 and 3.

Thus, in Fig. 2 it will be possible to recognize the two cylinders Cl and C2, these being connected to a clamping control valve 10 and a shifting control valve 11 through a switching-valve unit 9, the functioning of which is illus¬ trated in more detail in Fig. 3.

By means of the control valves 10 and 11, the cylinders Cl and C2 can be made to operate simultaneously in four dif- ferent ways, viz.

- in a clamping operation, initiated by moving the movable part of the clamping valve 10 downwardly, so that the piston rods of the two cylinders and with them the fork tines 1 and 2 are made to approach each other, - in an opening operation, initiated by moving the movable part of the clamping valve 10 upwardly, so that the piston rods of the cylinders and with them the two fork tines 1 and 2 are moved away from each other,

- a leftward shifting, initiated by moving the movable part of the shifting control valve 11 upwardly, so that the piston rod in the cylinder Cl is moved outwardly and hence moves the left-hand fork tine 1 towards the left relative to the fork-lift truck 8, while at the same time the piston rod in the cylinder C2 is withdrawn and hence moves the right-hand fork tine 2 likewise towards the left, and

- a rightward shifting, initiated by moving the mo-

vable part of the valve 11 upwardly, so that the piston rod in the cylinder Cl is withdrawn and hence moves the left-hand fork tine 1 towards the right relative to the fork-lift truck 8, while at the same time the piston rod in the cylinder C2 is moved outwardly and hence moves the right-hand fork tine 2 likewise towards the right relative to the fork-lift truck 8.

It is, of course, possible to combine these movements in any manner desired by simultaneous operation of the clamping valve 10 and the shifting valve 11.

Everything having been described up to this point with re¬ ference to Figs. 1 and 2 and shown in Fig. 3 belongs the prior art, for which reason a detailed explanation is con¬ sidered to be superfluous, but for the sake of good order, the parts of the switching-valve unit 9 shown in Fig. 3 will be described in more detail, even though they, as men¬ tioned, belong to the prior art.

Thus, the switching-valve unit 9 comprises a number of con¬ necting points, viz.

- A, that is connected to that connecting point on the clamping valve 10, which in the clamping position of the latter is connected to the tank conduit T of the hydrau¬ lic system,

- Al, connected to the piston-rod side of the cylinder

Cl,

- A2, connected to the piston-rod side of the cylinder

C2,

- B, connected to that connecting point on the clam¬ ping valve 10, which in the clamping position of the latter is connected to the pump conduit P of the hydraulic system,

- Bl, connected to the end of the cylinder Cl facing away from the piston rod,

- B2, connected to the end of the cylinder C2 facing

away from the piston rod,

- SI, connected to that connecting point on the shif¬ ting valve 11, which in the leftward-movement position of the latter is connected to the pump conduit P of the hydrau- lie system, and

- S2, connected to that connecting point on the shif¬ ting valve 11, which in said leftward-movement position is connected to the tank conduit T of the hydraulic system.

(The device being shown in Fig. 2 as inserted between the connecting point SI and the shifting valve 11 will be des¬ cribed in more detail below).

In addition to the connecting points referred to above, the switching-valve unit 9 comprises three controlled check valves of the kind adapted to function like normal check valves, until pressure is applied through a special control conduit so as to make them open in both directions, viz.

- VA, opening as a check valve, when the pressure in the connecting point A is higher than in the connecting points Al and A2, and opening in both directions, when the pressure in the connecting point B exceeds a predetermined threshold value,

- VB1, opening as a check valve, when the pressure in the connecting point B is higher than in the connecting points Bl and SI, and opening in both directions, when the pressure in the connecting point 1 exceeds a predetermined threshold value, and

- VB2, opening as a check valve, when the pressure in the connecting point B is higher than in the connecting points B2 and S2, and opening in both directions, when the pressure in the connecting point A exceeds a predetermined threshold value.

By looking at Fig. 2 in conjunction with Fig. 3, persons skilled in the art of hydraulic control will easily be able

to see how the movements of the cylinders Cl and C2 and hence of the fork tines 1 and 2 can be controlled by suitable manoeuvring of the clamping valve 10 and/or the shifting valve 11.

During a lateral-shifting operation, the quantity of liquid passing through the shifting valve 11 and the connecting points SI and S2 on the switching-valve unit 9 will be in exact proportion to the movement performed by the cylinders Cl and C2 and hence by the fork tines 1 and 2, and converse¬ ly, a limiting of this liquid flow will cause a limiting of the movement of the cylinders and hence of the fork tines. On the basis of this interdependence having been recognized, the invention calls for placing a volume limiter in that flow path, in which the flow corresponds to the movement in the same direction of the two cylinders, i.e. a late¬ ral-shifting movement. In the example shown, the volume limiter is constituted by a slave cylinder 12, in which the movements of its piston rod 13 follow the movements of the cylinders Cl and C2 or rather the latter's piston rods, and hence the movements of the fork tines 1 and 2 according to Fig. 1.

The quantities of liquid on both sides of the piston in the slave cylinder 12 are attuned to the quantities of liquid on both sides of the pistons in the cylinders Cl and C2 in such a manner, that when the two fork tines 1 and 2 are at the same distance from and on either side of the vertical fore-and-aft symmetry plane of the fork-lift truck 8, the piston rod 13 will take up a central position. Corresponding¬ ly, the piston rod 13 will be in a position on one side of the central position or the other, as soon as the two fork tines 1 and 2 do not lie symmetrically relative to said plane of symmetry, i.e. that the point mid-way between them has been shifted to one side or the other relative to the plane of symmetry of the fork-lift truck 8.

If the lateral shifting movement of the two fork tines 1 and 2 continues, the movement in the quantity of liquid corresponding thereto will cause the piston rod 13 to be moved to one of its two extreme positions, and since its piston fits in a liquid-tight manner in the cylinder 12, any further flow of liquid will be prevented, and it will no longer be possible to move the fork tines 1 and 2 in the direction concerned. A movement in the opposite direction is, however, possible, until the piston rod 13 reaches its opposite extreme position, in which the flow of liquid is again blocked, thus preventing further movement of the fork tines 1 and 2. At this point, it should be noted that this blockage solely prevents the movements performed by the fork tines 1 and 2 in the same direction under the control of the shifting control valve 11, but not the clamping or opening movements performed under the control of the clamping valve 10.

In Fig. 2, the slave cylinder 12 is shown in the form of a cylinder with a through-going piston rod 13. When constructed in this manner, the slave cylinder 12 may be placed in a position, in which it can be seen by the driver of the fork-lift truck 8, so that the driver can see how far the fork tines 1 and 2 are away from the position of symmetry, such as by observing the position of the piston rod 13 re¬ lative to the slave cylinder or - preferably - relative to a scale. It is, however, also possible to construct the slave cylinder 12 or a corresponding volume limiter in the form of a remote-signalling unit, that can be placed in the location being most advantageous with regard to the placing of conduits, being adapted to send signals to e.g. a pointer instrument or a display screen placed in or near the instru¬ ment panel of the fork-lift truck 8. Alternatively or addi¬ tionally, the device can comprise signalling lamps, e.g. red signalling lamps adapted to light up, when the fork tines 1 and 2 approach their extreme positions, and a green lamp

adapted to light up, when the fork tines are in their posi¬ tion of symmetry. Instead of or in addition to these lamps, the equipement may also comprise audible alarm means, espe¬ cially to give an alarm immediately before and in the extreme positions. Further, the slave cylinder 12 or a corresponding volume limiter may be equipped with adjustable stop means for limiting the movements of the piston rod 13 or a cor¬ responding member, making it possible to adjust the extreme positions, e.g. when adapting the equipment for use with different vehicles.

The adjustable stop means may be adapted to be influenced by the pressure in the lifting cylinder 14 of the fork-lift truck 8, this pressure being an expression of the weight of the goods resting on the fork tines 1 and 2, so that the extreme positions for the lateral shifting movements of the fork tines are moved inwardly, when the goods concerned are heavy, and vice versa.

LIST OF PARTS

A Connecting point

Al Connecting point A2 Connecting point

B Connecting point

Bl Connecting point

B2 Connecting point

Cl Hydraulic translatory cylinder C2 Hydraulic translatory cylinder

P Pump conduit

51 Connecting point

52 Connecting point T Tank conduit VA Controlled check valve

VB1 Controlled check valve

VB2 Controlled check valve

1 Left-hand fork tine

2 Right-hand fork tine 3 Upper rolling means

4 Upper rolling means

5 Lower rolling means

6 Lower rolling means

7 Support frame 8 Fork-lift truck

9 Switching-valve unit

10 Clamping (control) valve

11 Shifting (control) valve

12 Slave cylinder 13 Piston rod

14 Lifting cylinder