Background art A machine according to the above typically makes one or several"strokes" (tool elements are approaching each other from opposite sides of the workpiece) towards the workpiece in order to achieve the expected effect. The opening between the active machine elements, for introducing the workpieces can be decreased in a first part of the stroke, the approach stroke, before the second active part of the stroke takes place. At the end of the active stroke very high forces are typically applied (squeezing).

An apparatus or machine of this type could be exemplified by an apparatus for joining sheet formed members together by means of a technique usually called clinching, thereby producing leakproof or non-leakproof joints between the sheet formed members.

A joint of this type could be made by means of drawing said sheet formed members into a cup-shaped or protruding portion having a cylindrical or slightly conical side wall and a bottom wall and subsequently compressing said bottom wall creating a lateral extrusion of the same thereby forming a laterally enlarged shape which mechanically interlocks the sheet formed members.

Typically the machines used for clinching provide very high forces especially at the end of the joining procedure during the lateral extrusion of the material when the workpiece is squeezed between a punch and a co-operating anvil. The counter forces are taken up by a C-frame which could have considerable dimensions due to the fact that the pressure between the two co-operating tools could be in the range of several tons.

On one hand, in order to make the machine safe, fast and stable it is an advantage to make the gap for introducing the workpieces between the co- operating tools, a punch and a die, narrow. On the other hand this is of course limiting the form and dimensions of the workpiece which could be operated on by the tool.

There has been proposed solutions to this problem providing a C-frame comprising two parts arranged pivoting relative to each other. When entering the workpiece the C-frame is first opened in order to enlarge the gap between the tool parts. In this way it will be possible to use work-pieces with different geometries and larger dimensions. The C-frame is then closed which means that the active tool parts are brought closer to each other in an approach stroke which only needs a low force but should be relatively fast. The work stroke is then following which is carried out with much higher force.

In view of the high forces produced in the machine it is for safety reasons extremely important that the active stroke is not started before the machine as such is ready, the workpiece in correct position and the operator has safely

removed his fingers or other parts of his body from the working area. One way of achieving this, known in the art, works in the following way. As parameter indicating that the machine is in the correct position for safely carrying out the work stroke the mutual position of the toolheads is used. As the distance between the toolheads in the position for carrying out the work stroke is only slightly larger than the thickness of the workpiece it is assumed that the operator in this position has safely removed his fingers from the working area. This position can be measured in different ways, e. g. by means of optical or electronic equipment. The result of the measurement is controlling e. g. an electric switch or a pneumatic or hydraulic valve which in its turn controls the enabling of the actuator for the work stroke. Thus, the work stroke can not be triggered before the machine is in the correct position.

There is of course the risk with this type of more or less sophisticated arrangements that e. g. the sensor fails. In such a case an accident could occur.

Brief description of the invention One object of the present invention is to provide a safety arrangement for an apparatus for carrying out a squeezing type of operation on a mechanical workpiece which arrangement is completely mechanical and thus more robust and safer than arrangements according to the prior art.

Another object of the present invention is to provide a safety arrangement which can be used on machines having articulated C-frames as well as on machines with fixed C-frame.

The above and further objects are realised by means of the present invention which is characterised according to the appended claims.

Brief description of the figures Other objects, uses and advantages of this invention will be apparent from the reading of this description which proceeds with reference to the accompanying drawings forming part thereof and wherein: Figure 1 shows in a schematic view, partly in section a hand held machine for squeezing type of operation on a mechanical workpiece.

Figures 2a-c show in a schematic view, a detail of the machine according to figure 1.

Figure 3 shows in a schematic view, the detail according to figures 2a-c from above.

Figures 4a-d show in a schematic view, a second embodiment of the detail according to figures 2a-c.

Figure 3 shows in a schematic view, an implementation of the inventive idea on a machine having a fixed C-frame.

Figure 6 shows in a schematic view, a detail of the machine according to figure 5.

Detailed description of the invention

Figure 1 shows in a schematic view, partly in section a hand held machine, generally designated 1, for squeezing type of operation on a mechanical workpiece (not shown).

The C-frame in this example is articulated and comprises two parts or jaws 2 and 3 arranged pivoting in relation to each other around the pivoting point 4.

Suitable toolheads (not shown) are fixed on the left end-portions 5 and 6 of the jaws 2 and 3, respectively. The workpiece is to be entered between these end- portions 5 and 6.

The rear end-portions 7 and 8 of the pivoting parts 2 and 3, respectively, are provided in this example with rollers 9-11, cf. below. The lower part 3 is in this example fixed to the rest of the machine. The right hand part of the machine comprises the actuator 12 for the active part of the stroke (the power stroke). In figure 1 this actuator comprises a pneumatic cylinder-piston assembly 13,14 but other types of motors could be envisaged like electrical or hydraulic motors etc..

The piston is provided with a piston rod 16 and a return spring 17. The chamber 18 has in-and outlets for the air (not shown). The machine is of course connected to a power and control system of some common type, not shown.

The end portion of the piston rod 16 opposite the piston 14 is provided with an actuator head 19 having a surface 21 parallel to the axis of the piston rod and an inclined surface 20. The middle portion of the machine forms the grip which suitably is provided with a trigger for the power stroke.

A typical machine of this type has a weight of a few kilos. To make it easier for the operator the machine is therefore usually suspended in a ring 22 arranged on a ballbearing on the outside of the house of the machine close to a plane through the center of gravity for the assembly.

In the starting position the piston 14 is positioned to the right in the figure. This means that the upper jaw 2 is freely movable around the pivoting point 4 and the workpiece can be entered in the gap between the toolheads at 5 and 6 in the figure. The toolheads are now approached towards each other by pivoting the jaw 2. This movement can be carried out manually as in the present case or be assisted or fully achieved by means of some suitable motor.

When the jaw 2 has been brought into position the actuator 12 is activated. Air enters the chamber 18 and the piston 14 moves to the left in the figure which means that the actuator head 19 enters between the two lower rollers 10,11 and the upper roller 9. The surface 21 on the lower side of the actuator head will be supported by the two rollers 10,11 in the axial movement to the left and the upper inclined surface 20 will gradually increase the pressure on the roller 9 and thereby force the upper jaw to pivot counter clockwise in the figure. The linear movement of the actuator head is in this way translated into a pivoting movement of the jaw 2 with considerable force. So far no safety arrangements have been shown or described.

It is clear that the actuator head 19 in another embodiment could be provided with a roller and the inclined surface could be arranged on the pivoting jaw 2.

Figures 2a-c show in a schematic view, a detail of the machine according to figure 1.

In figure 2a the rear end portions 7 and 8 of the jaws 2 and 3, respectively, are shown in a position in which the machine is fully open ready for positioning of the workpiece. On each side of the roller 9 on the jaw 2 are arranged a lateral blocking plate 24, e. g. fixed to the outside of jaw by means of screws 25, cf. figure 3. The rear part of these blocking plates 24 has in this embodiment a cylindrical surface 26 with the center axis coinciding with the pivoting axis through the pivoting point 4 and the radius R.

The actuator head 19 has been provided with lateral wings or sideplates 23, also shown in figure 3, arranged on the two sides of the head in a plane parallel to the pivoting axis and the piston rod 16. The front end of these wings 23 has in this embodiment the form of a flat surface 27 perpendicular to the axis of the linear movement of the head, i. e. vertical in figure 2a-c. Thus, if the actuator 12 is trigged when the jaws 2 and 3 are in the position shown in figure 2a, i. e. the machine is not yet ready for the power stroke, the head 19 will move to the left in the figure until it reaches the illustrated position. The surface 27 of the sideplates 23 will in this position contact the two blocking plates 24 without touching the roller 9, cf. figure 3, If the thickness d of the plates 23 and their arrangement on the head 19 are such that the contact line between a plate 23 (surface 27) and a blocking plate 24 (surface 26) will be situated at the level of the pivoting point 4 there will be no resulting force component on the jaw 2 trying to pivot the same. Thus, there is no risk that the jaw will close over the workpiece which of course could have been dangerous.

As described above the approach stroke is carried out with a relatively low force, e. g. manually. Figure 2b illustrates the situation in which the approach stroke has been started but has not yet been finalised. During this stroke the head 19 is not in contact with the jaw 2. Once again, if by mistake the actuator 12 is triggered the head 19 will move to the left until the position illustrated in figure 2b. As described in relation to figure 2a there will still be no resulting pivoting force transferred to the jaw 2, thus no risk for injuries or damages.

In figure 2c the approach stroke has been finalised which means that the power stroke can be safely carried out. The side plates 23 of the head 19 can now pass between the rear portions of the jaws which means that the inclined surface 20 of the head 19 will make contact with the roller 9. As the movement of the head

19 continues to the left the lower surface 21 of the head will be supported by the rollers 10 and 11 and a considerable force will be transferred to the jaw 2 by means of the roller 9 and the workpiece will be squeezed between the jaws 2 and 3. The lower part of the head has a protruding noose 29 which will ensure that the head is well supported by both rollers 10 and 11 at the end of the stroke when the forces are at their maximum.

Figures 4a-d show in a schematic view, a second embodiment of the detail according to figures 2a-c.

The only difference between this embodiment and the one shown in figures 2a-c and figure 3 refers to the design of the blocking plates 24'. The contact surface 26'has in this embodiment three different zones 30,31, 32 and two intermediate zones 33 and 34. The zone 30 has the same characteristics as the surface 26 of the previous embodiment. This means that in the situation illustrated in figure 4a there will be no resulting pivoting force on the jaw 2.

The zone 31 has in the shown example been designed so that the contact line between the surface 27 on the side plate 23 of the head 19 and the blocking plate has moved down, as illustrated by the opposing arrows in figure 4b, and is situated below the horizontal plane through the pivoting axis. This has been achieved by lowering the center of curvature for this zone. As a result there will be a net force transferred to the jaw 2 when the head is pressing against the jaw which force is trying to rotate the jaw clockwise in the figure 4b. Due to the friction this will not be possible and in any case such a movement would be blocked when the intermediate zone 33 is contacting the upper surface of the side plate 23. Thus, in this case too the safety arrangement works. There is no risk that the jaws will close around the workpiece.

Figure 4c is illustrating the same thing for the contact with zone 32 with the same effect.

Figure 4d finally is illustrating the same situation as figure 2c.

It should be noted that the zones 31 and 32 could also have the same form as the surface 26 and 26', i. e. cylindrical but with smaller radii than R. In that case the contact between the surfaces will take place at the interface between the zones 31 and 33 and 32 and 34, respectively. Under all circumstances the dangerous anti-clockwise rotation of the jaw 2 will be prevented.

Figures 5 and 6 show in different views, in schematic form, an implementation of the inventive idea on a machine having a fixed C-frame. The linear movement of the actuator head 19'is in this case not transferred to a pivoting movement of a jaw but to a perpendicular movement of a toolcarrying frame 36. The actuator 12'is of the same type as described above. It can as before, as an alternative, be constituted by an electrical or a hydraulic motor.

The head 19'is in the same way as before provided with wings 23'. The approach stroke corresponds to a linear vertical movement of the frame 36. This movement can be carried out manually or as in the embodiment according to the figures 5 and 6 be actuated by e. g. a small pneumatic cylinder-piston assembly 35. The frame 36 is provided with a window 37 which only will let the head 19' pass when the machine is positioned for the power stroke.