BACKGROUND OF THE INVENTION In machines intended for cutting metal bar, metal sections and metal wire, there is generally a feed arrangement which feeds material to the cutting arrangement. Such feed arrangements exist in a number of different variants but can be divided into two types: roller feeders and gripper feeders. In a roller feeder, the material is conveyed at in principle constant speed by means of wheels or rolls (rollers) which propel the wire (the material to be cut is referred to below as the wire, although it can just as well consist of bar, tube or section) forwards. In a gripper feeder, the feed takes place stepwise. A gripper feeder consists of a propulsion arrangement and at least one gripping device.

The gripping device can consist of an actuator, a set of clamping jaws with a groove which is adapted in order appropriately to grip the item fed and a housing which accommodates these parts. The gripping device is in turn fixed to a propulsion arrange- ment. The propulsion arrangement moves the gripping device with a reciprocating movement, and the gripping device alternates between gripping the wire and releasing it. When the gripping device moves forwards, the gripping device grips the wire, and when it goes backwards, it releases the wire. The wire will thus be fed forwards stepwise. In most cases, the gripping device is supplemented by a stationary gripping device which holds the wire when the movable gripping device releases the wire and moves backwards. There are two reasons for this: on the one hand to ensure that the wire does not move backwards on account of friction or external interference, and on the other hand to fix the wire during the cutting operation itself. In what are known as double feeders, which are a type of gripper feeder, the stationary gripping device is exchanged for another movable gripping device. This second gripping device also moves to and fro, synchronously with the first gripping device, but always in the opposite direction compared with it. The second gripping device releases the wire when the first gripping device grips the wire and vice versa. In a double feeder, double the

feed rate is obtained for the same movement rate of the gripping devices, which is a major advantage in the production of large volumes of cut items. In some double feeders, the stationary gripping device is retained for fixing the wire (three gripping devices altogether), while in other cases the two movable gripping devices are both made to grip the wire at the same time while the actual cutting operation takes place, which also ensures that the wire does not move unpredictably. The trend towards faster machines of necessity increases the requirement for high rates in gripper feeders. This increases the requirement for short times throughout the arrangement, not least in the gripping devices. It is becoming increasingly important for the time it takes the gripping devices to grip the wire and release it to be as short as possible. Another important characteristic of the movable gripping devices is their mass. The lighter the gripping devices are, the smaller the force required to accelerate them when they are to move to and fro. These forces become greater when the rate increases and can decrease only by reducing the mass. Great forces of inertia set increased requirements for size and stability in the propulsion arrangement and increase the power consumption of the feed arrangement as a whole. Moreover, the difficulty of achieving the desired accuracy in the feed and the risk of wear increase. The relatively great force needed to grip the wire without risk of slipping means that an obvious solution is to use hydraulic cylinders. In a typical application, the clamping force necessary may amount to 20 kN. For a hydraulic cylinder which works at 100 bar system pressure, the driving area necessary is then roughly 20 cm2. If the end surface of the hydraulic piston is used as the driving area, the diameter of the piston then has to be roughly 50 mm. In most cases, the movement of the hydraulic piston does not have to be greater than roughly one milli- metre. In this type of construction, it is necessary to have hydraulic seals and sliding bands, and if appropriate wipers as well. All these sealing components of necessity add to the length of the hydraulic piston and thus to the length of the housing. Overall, this means that the total length of the hydraulic piston, and thus its cylinder, is scarcely less than roughly 60 mm. For a movement of roughly 1 mm. Such a piston, if it is made of steel, weighs roughly 900 g. It is also relevant that the short stroke, 1 mm, is not good for the service life of seals, a well-known phenomenon in hydraulic systems.

The aim of this invention is to provide an improved gripping device. A further aim is to provide a gripping device which can produce a great clamping force even though the mass of the gripping device is small. The invention is suitable for use in a gripper feeder for metal bar, metal sections and metal wire but can also be used for gripping other objects. Further aims of the invention are to provide an improved installation for

handling and machining workpieces and also an improved method for handling workpieces.

DESCRIPTION OF THE INVENTION The invention relates to a gripping device for gripping objects. The gripping device according to the invention comprises a wall element and a flexible diaphragm arranged adjacent to the wall element so that the wall element and the diaphragm define a chamber between them. The chamber is intended to be pressurized, the diaphragm being arranged to bulge when the pressure in the chamber changes. The gripping device also comprises a first clamping jaw functionally connected to the diaphragm so that bulging of the diaphragm brings about movement of the clamping jaw and a second clamping jaw arranged to interact with the first clamping jaw so that an object can be gripped between the clamping jaws when bulging of the diaphragm brings about movement of the first clamping jaw towards the second clamping jaw. The diaphragm is preferably arranged to cause the clamping jaw to move when the pressure in the chamber is increased. In one embodiment of the invention, the diaphragm and the first clamping jaw can be functionally interconnected via a clamping piston which, at its one end, is in direct contact with the diaphragm and, at its other end, is arranged to act against the first clamping jaw. A return element can be arranged to act against the clamping piston so that the return element guides the clamping piston back towards its starting position when it is no longer acted on by the flexible diaphragm.

Furthermore, the gripping device can also comprise a block with a through-hole, through which hole the clamping piston is arranged to be movable in order to act against the clamping jaw. In one embodiment of the invention, the return element is an elastic element arranged to be compressed by the clamping piston or an element movable together with the clamping piston when the clamping piston moves through the through-hole of the block in order to act against the first clamping jaw.

The clamping jaws are preferably provided with elongate grooves in order to receive and grip objects in the form of metal wire or bars.

In one embodiment of the invention, the through-hole in the block has at least a first part with a first dimension which corresponds to an external dimension of the clamping piston and a second part with a second dimension which is greater than the first dimension. The second part is arranged adjacent to the first part so that the first part and the second part are separated by a step, and the elastic return element is arranged in the

second part so that one end of the elastic return element bears against the step which separates the first part from the second part of the through-hole of the block. The elastic return element can also have a through-hole, through which hole the clamping piston is arranged to move towards the first clamping jaw so that at least part of the clamping piston is surrounded by the elastic return element. The through-hole of the block can also have a third part with a third dimension which exceeds the dimension of the second part. The third part is suitably arranged adjacent to the second part so that the second part and the third part of the through-hole of the block are separated by a further step.

The movement of the clamping piston towards the first clamping jaw can then be limited by virtue of the clamping piston or an element movable with the clamping piston being arranged to be stopped in its movement towards the first clamping jaw by the further step so that the further step forms a mechanical end position. The clamping piston can be designed with a first collar arranged to act against the elastic element when the clamping piston moves towards the first clamping jaw so that movement of the clamping piston towards the first clamping jaw brings about compression of the elastic element, on the clamping piston. The clamping piston can also have a second collar, the external dimension of which exceeds the external dimension of the first collar. The second collar is then arranged to meet the further step when the clamping piston has moved a certain distance in the direction towards the first clamping jaw.

In one embodiment, the first and the second clamping jaws are separated by elastic spacing means such as springs. The elastic spacing means then tend to press the clamping jaws apart.

Each of the clamping jaws suitably comprises a cradle with a recess and a gripping part arranged in the recess of the cradle, and the gripping part is preferably mounted firmly in the cradle by, for example, soldering. The gripping part is preferably provided with an elongate groove in order to receive and grip objects in the form of metal wire or bars.

The gripping device can also comprise a housing with a fixed end wall and a detachable end wall. The clamping jaws can then be arranged in the housing between the detachable end wall and the fixed end wall, at least one resilient element being arranged to press the clamping jaws towards the fixed end wall in the direction of the elongate grooves of the clamping jaws.

In one embodiment, the gripping device comprises a block on which the wall element is mounted, and the diaphragm is mounted loosely between the wall element and the block so that the diaphragm can creep radially when it bulges axially.

In another possible embodiment, the gripping device comprises a block on which the wall element is mounted, and the diaphragm is fixed to the wall element and provided with a bend which functions as an extension zone and takes up the extension present in the diaphragm when it bulges.

The invention also relates to an installation for handling and machining elongate work- pieces, which installation comprises a gripping device which is arranged movably from a first position to a second position and a cutting arrangement arranged adjacent to or in proximity to the second position of the gripping device so that a workpiece guided to the second position by the movable gripping means can be cut.

Furthermore, the invention also relates to a method for handling a workpiece, which method comprises provision of a gripping device, which gripping device comprises a flexible diaphragm arranged to act on a clamping jaw arranged in the gripping device.

In the method according to the invention, a workpiece is provided, which is gripped by the gripping device. The gripping device is then moved from a first position to a second position in which a machining operation-for example a cutting operation-can be performed on the workpiece.

The invention also relates more generally to use of a flexible diaphragm in order to transmit force in a gripping device which constitutes part of a gripper feeder in a machine intended for cutting metal bar, metal sections or metal wire.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows the gripping device according to the invention seen from the rear.

Figure 2 shows the gripping device according to the invention seen from the front.

Figure 3 shows the gripping device according to the invention seen from above.

Figure 4 shows a cross section along A-A in Figure 3.

Figure 5 shows a cross section along B-B in Figure 3.

Figure 6 shows an exploded view of the gripping device according to the invention.

Figure 7 shows diagrammatically an installation which comprises the gripping device according to the invention.

Figure 8 shows a conceivable embodiment of the diaphragm.

Figure 9 shows an enlarged view of some of the components shown in Figure 6.

Figure 10 shows an enlarged view of some more of the components shown in Figure 6.

DETAILED DESCRIPTION OF THE INVENTION Figure 1, Figure 5 and Figure 6 show a gripping device 1 for gripping objects 2. The gripping device 1 comprises a wall element 3 and a flexible diaphragm 4 arranged adjacent to the wall element 3 so that the wall element 3 and the diaphragm 4 define a chamber 5 between them. The chamber 5 is intended to be pressurized, and the diaphragm 4 is arranged to bulge when the pressure in the chamber 5 changes. The diaphragm 4 is made of an elastic material. A suitable material for the diaphragm 4 can be spring steel. In one possible embodiment of the invention, the diaphragm 4 consists of a steel plate with a thickness of around 0.6 mm. The steel plate can be a circular plate with a diameter of around 90 mm. If the diaphragm 4 is a steel plate, a suitable thick- ness can lie in the range 0.5 mm-1. 0 mm. Within the scope of the invention, use can be made of steel plate with another thickness, but the range indicated can be regarded as advantageous. If the plate is thicker than 1 mm, it becomes more rigid than can be considered advantageous. The diaphragm 4 can also be made of another elastic material, for example rubber. A first clamping jaw 6 is functionally connected to the diaphragm 4 so that bulging of the diaphragm 4 brings about movement of the clamping jaw 6. A second clamping jaw 7 is arranged to interact with the first clamping jaw 6 so that an object can be gripped between the clamping jaws 6,7 when bulging of the diaphragm 4 brings about movement of the first clamping jaw 6 towards the second clamping jaw 7.

The clamping jaws 6,7 are preferably provided with elongate grooves 12 in order to receive and grip objects in the form of metal wire or bars. Pressurized fluid, for example oil, can be supplied to the chamber 5 through a line 50 in the wall element 3. With a 0.6 mm thick steel plate as the diaphragm 4 and clamping forces in the order of 20 kN, the pressure in the chamber 5 can be in the order of 100 bar. It is to be understood that the chamber 5 can be very thin. In the unloaded state, the thickness of the chamber 5 can to all intents and purposes be equal to zero.

The diaphragm 4 is preferably arranged to cause the clamping jaw 6 to move when the pressure in the chamber 5 is increased. In principle, it is possible to envisage having a pressure reduction in the chamber 5 bring about the bulging of the diaphragm, in which case the diaphragm 4 can be fixed to the clamping piston 9. In a preferred embodiment, however, use is made of a pressure increase in the chamber 5 in order to make the diaphragm 4 bulge and in this way act on the clamping jaw or clamping jaws.

Figure 4 and Figure 5 show how the diaphragm 4 and the first clamping jaw 6 can be functionally interconnected via a clamping piston 9 which, at its one end, is in direct contact with the diaphragm 4 and, at its other end, is arranged to act against the first clamping jaw 6.

In one embodiment of the invention which can be seen best from Figures 4 and 5, a return element 8 is arranged to act against the clamping piston 9 so that the return element guides clamping piston 9 back towards its starting position when it is no longer acted on by the flexible diaphragm 4. The gripping device 1 can also comprise a block 10 with a through-hole 11, through which hole 11 the clamping piston 9 is arranged to be movable in order to act against the first clamping jaw 6. The return element 8 is preferably an elastic element 8 arranged to be compressed by the clamping piston 9 or an element movable together with the clamping piston 9 when the clamping piston 9 moves through the through-hole 11 of the block 10 in order to act against the first clamping jaw 6. The elastic return element 8 can consist of, for example, a rubber body.

The return element 8 could also consist of a steel spring or another elastic body. In an advantageous embodiment of the invention, the through-hole 11 in the block 10 has at least a first part 13 with a first dimension which corresponds to an external dimension of the clamping piston 9 and a second part 14 with a second dimension which is greater than the first dimension. The second part 14 is arranged adjacent to the first part 13 so that the first part 13 and the second part 14 are separated by a step 15. The elastic return element 8 is then arranged in the second part 14 so that one end of the elastic return element 8 bears against the step 15 which separates the first part 13 from the second part 14 of the through-hole 11 of the block 10. The elastic return element 8 also has a through-hole 16, through which hole 16 the clamping piston is arranged to move towards the first clamping jaw so that at least part of the clamping piston 9 is surrounded by the elastic return element 8. The through-hole 11 of the block 10 can also have a third part 25 with a dimension which exceeds the dimension of the second part 14, which third part 25 is arranged adjacent to the second part 14 so that the second part 14 and the third part 25 of the through-hole of the block 10 are separated by a further step 26. The movement of the clamping piston 9 towards the first clamping jaw 6 is then limited by virtue of the clamping piston or an element movable with the clamping piston 9 being arranged to be stopped in its movement towards the first clamping jaw 6 by the further step 26 so that the further step 26 forms a mechanical end position 26.

The clamping piston can be made in the following way. On the clamping piston 9, there is a first collar 28 arranged to act against the elastic element 8 when the clamping piston 9 moves towards the first clamping jaw 6 so that movement of the clamping piston 9

towards the first clamping jaw 6 brings about compression of the elastic return element 8. The clamping piston 9 can also have a second collar 29, the external dimension of which exceeds the external dimension of the first collar 28. The second collar 29 is arranged to meet the further step 26 when the clamping piston 9 has moved a certain distance in the direction towards the first clamping jaw 6. The second collar 29 then acts against the mechanical end position 26. The second collar 29 is preferably arranged directly adjacent to the first collar 28. The clamping piston 9 then has a first portion 40 with a certain length in the movement direction of the clamping piston 9, and a second portion in the form of the first collar 28, which also has a certain length in the move- ment direction of the clamping piston 9. The length of the first portion 40 of the clamping piston 9 and the first collar 28 suitably exceeds the combined length of the first and second parts 13,14 of the through-hole 11. The difference in length can then constitute the stroke of the clamping piston 9. The stroke of the clamping piston 9 is suitably 0.5 mm-2 mm. The stroke of the clamping piston 9 is preferably approxi- mately 1 mm.

Reference is now made to Figure 9. In one embodiment of the invention, the first clamping jaw 6 and the second clamping jaw 7 are separated by one or more elastic spacing element (s) 17 such as springs. The elastic spacing elements 17 tend to press the clamping jaws 6,7 apart.

Each of the clamping jaws 6,7 can suitably comprise a cradle 18 with a recess 19 and a gripping part 20 arranged in the recess 19 of the cradle 18. The gripping part 20 is preferably provided with an elongate groove 12 in order to receive and grip objects 2 in the form of metal wire 2 or bars 2.

In an advantageous embodiment, the gripping device comprises a housing 21 with a fixed end wall 22 and a detachable end wall 23. The clamping jaws 6,7 are then arranged in the housing between the detachable end wall 23 and the fixed end wall 22, and at least one resilient element 24 is arranged to press the clamping jaws 6,7 towards the fixed end wall 22 in the direction of the elongate grooves 12 of the clamping jaws 6, 7. The resilient elements 24 can advantageously consist of screws 24 which are provided with spring-loaded balls at their ends. Such elements are standard elements available on the market. In an advantageous embodiment of the invention, the resilient elements 24 are located in holes in the detachable end wall 23 so that the spring-loaded balls are directed towards the clamping jaws 6,7 which are shown in inter alia Figure 6.

The spring-loaded balls in the detachable end wall 23 will press the clamping jaws 6,7

towards the fixed end wall 22 above all during the retardation of a backward movement, when the inertial forces also help to ensure that the clamping jaws 6,7 lie pressed firmly against the fixed end wall 22. This is advantageous for maintaining precision in the feed length. The detachable end wall 23 is held in place by holders 61 which can be seen best from Figure 2.

In an advantageous embodiment of the invention, the wall element 3 is mounted on the block 10 of the gripping device, and the diaphragm 4 is mounted loosely between the wall element 3 and the block 10 so that the diaphragm 4 can creep radially when it bulges axially.

In another possible embodiment which can be seen in Figure 8, the wall element 3 is mounted on the block 10 while the diaphragm 4 is fixed to the wall element 3 and provided with a bend 27 which functions as an extension zone and takes up the extension present in the diaphragm 4 when it bulges. In the embodiment shown in Figure 8, the clamping piston 9 has only one collar 28.

Reference is now made to Figure 7. The invention also relates to an installation for handling and machining elongate workpieces 2, which installation comprises a gripping device 1 which is arranged movably from a first position to a second position. The gripping device 1 comprises a wall element 3 and a flexible diaphragm 4 arranged adjacent to the wall element 3 so that the wall element 3 and the diaphragm 4 define a chamber 5 between them. The chamber 5 is intended to be pressurized, the diaphragm 4 being arranged to bulge when the pressure in the chamber 5 changes. A first clamping jaw 6 has a mechanical connection to the diaphragm 4, and a second clamping jaw 7 is arranged to interact with the first clamping jaw 6 so that an elongate workpiece can be gripped between the clamping jaws 6,7 when bulging of the diaphragm 4 brings about movement of the first clamping jaw 6 towards the second clamping jaw 7. The installation also comprises a cutting arrangement 31 arranged adjacent to or in proximity to the second position of the gripping device 1 so that a workpiece 2 guided to the second position by the movable gripping means 1 can be cut. The cutting arrangement 31, which is shown only diagrammatically here, can be, for example, an arrangement such as is indicated in Swedish patent application no. 0201064-3 which is owned by the applicant for the present application. Swedish patent application 0201064- 3 indicates an arrangement comprising a striking unit, a tool housing, a damper unit, a movable cutting tool and a fixed cutting tool, the tool housing having two curved support surfaces for the movable cutting tool, which support surfaces have the same radius, and a recess for a striking piston forming part of the striking unit being arranged

between the support surfaces. It is possible, however, to use types of cutting arrangement other than that indicated in Swedish patent application no. 0201064-3 referred to above.

The invention also relates to a method for handling a workpiece 2, which method comprises the following steps: a) provision of a gripping device 1, which gripping device 1 comprises a wall element 3, a flexible diaphragm 4 arranged adjacent to the wall element 3 so that the wall element 3 and the diaphragm 4 define a chamber 5 between them, which chamber 5 is intended to be pressurized, and the diaphragm 4 being arranged to bulge when the pressure in the chamber 5 changes, a first clamping jaw 6 with a mechanical connection to the diaphragm 4, a second clamping jaw 7 arranged to interact with the first clamping jaw 6 so that an object can be gripped between the clamping jaws 6,7 when bulging of the diaphragm 4 brings about movement of the first clamping jaw 6 towards the second clamping jaw 7, _ b) provision of a workpiece 2, c) movement of at least one of the workpiece 2 and the gripping device 1 to a position in which the clamping jaws 6,7 of the gripping device 1 surround at least part of the workpiece 2, d) supply of pressurized fluid to the chamber of the gripping device 1 so that the flexible diaphragm 4 bulges and in this way causes the first clamping jaw 6 to move towards the second clamping jaw 7 so that the workpiece 2 located between the clamping jaws 6,7 is gripped firmly between the clamping jaws 6,7.

In an advantageous embodiment of the method, the gripping device 1 comprises at least one elastic spacing element 17 which tends to separate the clamping jaws 6,7. After the clamping jaws 6,7 have gripped the workpiece 2, the gripping device 1 is, together with the workpiece 2, moved from a first position to a second position, after which the pressure in the chamber of the gripping device 1 is lowered so that the clamping jaws 6, 7 are separated by the elastic spacing element 17. The gripping device 1 is then returned to the first position so that a new work cycle can be initiated.

It is also possible to perform a machining operation on the workpiece 2 when the gripping device 1 is located in the second position and holds the workpiece 2 between the clamping jaws 6,7.

Although the'invention has been described as a gripping device, an installation, a use and a method, it is to be understood that these categories represent only different aspects of the same invention. The gripping device according to the invention can therefore be used in the installation according to the invention and in the method according to the invention. It is also to be understood that the method according to the invention can comprise such steps and actions as are a natural consequence of use being made of the gripping device according to the invention or the installation according to the invention, irrespective of whether or not such steps or actions have been expressly indicated.

By using a flexible diaphragm in order to transmit pressure and force, inter alia the advantage is achieved that the weight of the gripping device is lower than if a hydraulic cylinder were used. As a consequence of the relatively low weight, the advantages that power consumption can be kept lower and that the reaction time for clamping and release is shorter are also achieved. A further advantage of the use of a diaphragm is that the number of components can be reduced, which makes possible a lower manufacturing cost.

By virtue of the use of a return element, the advantage that the clamping piston can be returned to its starting position is achieved. By virtue of the use of an elastic return element, the advantage is achieved that it is not necessary to use an active medium such as, for example, hydraulic oil for return of the clamping piston 9. This also contributes to a reduced risk of oil leakage.

By virtue of the fact that the flexible diaphragm acts against the first clamping jaw via a clamping piston, inter alia the advantage that the clamping piston can distribute the clamping force uniformly over the clamping jaw is achieved. Moreover, the advantage is achieved that the clamping piston can interact with a mechanical end position and an elastic return element.

By virtue of the fact that the through-hole of the block is provided with parts with different dimensions which are separated by steps, the advantage is achieved that the elastic return element can be positioned in a part of the through-hole of the block in

such a way that it is compressed when the clamping piston moves. Moreover, the advantage that one of the steps can constitute a mechanical end position for the clamping piston is achieved. By virtue of the fact that the clamping piston is provided with collars, the advantage is achieved that the clamping piston itself can compress the elastic return element and that the clamping piston itself can act against the mechanical end position.

By virtue of the fact that the clamping jaws are separated by one or more elastic spacing element (s), the advantage is achieved that the clamping jaws move away from one another when the clamping piston no longer acts against the clamping jaws. The work- piece gripped between the clamping jaws is then released. It is possible, however, to envisage embodiments of the invention in which such spacing elements between the jaws are not used.

If the diaphragm is mounted loosely in between the wall element and the block, inter alia the advantage that the diaphragm can creep radially when it bulges axially is achieved. This results in inter alia the risk of the diaphragm being damaged during bulging being reduced. Another advantage is that greater bulging is possible.

If the diaphragm is fixed to the wall element 3 and provided with a bend, the advantage that the bend functions as an extension zone during bulging is achieved. This results in inter alia the risk of the diaphragm being damaged during bulging being reduced.

Another advantage is that greater bulging is possible.

If the clamping jaws are provided with elongate grooves, inter alia the advantage is achieved that the clamping jaws can more easily receive and grip objects in the form of metal wire or bars.

If the gripping device has a housing with a fixed end wall and a detachable end wall with clamping jaws arranged in the housing between the detachable end wall and the fixed end wall, this results in the advantage that the end walls can prevent the clamping jaws moving in the longitudinal direction of the workpiece (for example of the wire).

When the gripping device according to the invention forms part of an installation with a machining station, inter alia the advantage is achieved that the gripping device can move more rapidly on account of its relatively low weight, as a result of which the whole installation can work more rapidly.