Technical field This invention relates to apparatuses for carrying out operations on a mechanical workpiece e. g. tools or machines for pressing, riveting, clinching, cutting, welding etc. The tools and machines could be of stationary or hand-held type. The power source could be of any type, hydraulic, pneumatic, electric etc.

Background art One type of tool belonging to the category defined above is previously known from the International patent application W089/07020.

According to the principle of the tool described in said patent application a pair of overlaying metal sheet members are joined together by lancing and forming a part of one member through an unblanked part of the other member. Thereafter a staking procedure is carried out on the lanced and formed part of the one member to an adjacent surface of the other member to secure the members together in overlaying relation.

Typically this type of tools or machines provide very high forces during the joining procedure, the opening, or gap, for introducing the workpieces is

relatively narrow and the strokes carried out by the active machine elements are short and fast.

On one hand a narrow gap and short stroke could be chosen in order to give the tool a fast operation which of course gives a more efficient tool with more joints per unit time. On the other hand the same parameters are of course limiting the form and dimensions of the workpiece which could be operated on by the tool.

If, on the other hand a wider gap and longer stroke are chosen, without any compromise on the time for making a joint, the tool will require a more powerful drive unit. The implementation of this idea thus implies costs at two levels : investment costs for a larger high-power drive installation and higher energy costs for the operation of the tool.

Brief description of the invention One object of the present invention is to provide a machine for pressing, riveting, clinching, cutting, welding etc. which is fast and efficient and possible to use on work-pieces with different geometries and much larger dimensions than heretofore.

The inventive idea takes into consideration the fact that when making one of the above mentioned operations, pressing, clinching, riveting, inserting, cutting etc. the total active force is only needed for a short part of the stroke of the tool. The rest of the stroke is needed for approaching the active parts of the tool to the point of operation.

Another object of the invention is to provide a so called work head with a pivoting part for which the locking mechanism has been arranged outside and away from the working zone. This makes it possible to use the work head in very

restricted areas. The pivoting part will in this way also be much lighter and the process correspondingly faster.

The present invention, which provides a solution to the said technical problems, 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 schematically shows an apparatus according to the present invention in open position, Figure 2 shows the same tool in closed position ready for the active part of the stroke, Figure 3 shows the apparatus according to figures 1 and 2 along two different sections B-B'and A-A', Figure 4 shows a second embodiment of the apparatus according to the invention, Figure 5 shows a third embodiment of the apparatus according to the invention, Detailed description of the invention

Figure 1 schematically shows an apparatus according to the present invention in open position, The apparatus generally comprises a C-frame 1 having an upper jaw 2 and a lower jaw 3. Co-operating tool 4,5 are fixed on these jaws. This assembly is called a work head. Such a work head can be used with any process like clinching, riveting, welding, etc. carried out on a workpiece 6,7, here illustrated as two superimposed profiled pieces of sheet metal 6,7.

The lower (or upper) jaw is according to the invention provided with a moving part 8 pivoting around a pivot axis 9. By means of this arrangement an approaching part of the stroke can be achieved during which the tools are brought into a working position shown in figure 2. The C-frame could alternatively be equipped with two articulations and thus two pivoting jaws.

For achieving the second high force second part of the stroke a force unit or process actuator 10 is arranged on one of the jaws, here illustrated as the upper jaw 2. It could of course alternatively be fixed to the lower jaw. Two actuators could also be envisaged.

It should be noted that the moving jaw 8 is not pivoting around a point close to the centre of gravity for this part. In order to achieve the pivoting movement of the part 8 an actuator 11 is arranged between the fixed part of the C-frame and the moving part 8 creating a rotation around the pivoting point 9 when activated.

This actuator could be of hydraulic, electric or any other suitable type.

A pushing rod 13 is arranged fixed to the moving part 8 by means of a rod axis 12. This pushing rod is offering the advantage of moving the locking pin 14 and the associated mechanism away from the working zone around the tools 4,5 without making the moving jaw e. g. more heavy. In addition it can be designed in such a way that the deformation of the C-frame, which is always detrimental to

the quality of the joints, can be counteracted by the fact that the pushing rod works like a leg of a parallelogram (similar to the design of a racing car suspension). By designing the work head taking into account the stiffness of the lower jaw, the distances between the axis 9 and 12 and the distance between the axis through the tool and the axis 9 the movement of the lower tool can be made parallel to axis through the tools.

Figure 3 shows in the section B-B'one embodiment of the arrangement of the locking mechanism. The pushing rod 13 is provided with a guiding slot 15 in which the locking pin 14 is sliding. At the end of stroke, i. e. when the C-frame has been completely closed, the locking pin is positioned in front of a through hole 16 in the pushing rod. In this case the locking pin has the form of a piston rod of a hydraulic actuator 17. If this actuator is now actuated the pin will enter the hole and lock the pushing rod and thereby the moving part 8. Other mechanisms as e. g. pneumatic or electric could of course be used.

Details, such as sensors and valves etc. are not shown as they form part of general knowledge in the field.

Thus, the logic sequence is as follows. Introduce the work piece 6,7, close the pivoting jaw 8 with the closing actuator 11 until end-of-stroke, then actuate the locking actuator 17, until the locking pin 14 is fully engaged. Then operate the process actuator 10. A series of operations can be made on the work piece if desired. Then retract the locking pin 14 and re-open the pivoting jaw 8, allowing to remove the work piece.

Sensors or detectors can be installed for checking each of the moving elements and giving the appropriate signals to controlling the sequence which is current know-how in automation.

Figures 4 and 5, show variants with hydraulic locking and active compensation of the displacement due to the flexibility of the C-frame.

In figure 4 the function of the actuator 11 and the pushing rod 13 have been taken over by a single hydraulic cylinder-piston assembly 41. This cylinder has an internal end-of-stroke which defines the end position of the moving part 8.

The compensation of the deformation of the C-frame will obviously take place in this embodiment too. The actuator could alternatively be of the electric or any other suitable type.

In the embodiment according to figure 5 the end of stroke is arranged on the jaw. More precisely contact surfaces 53,54 on the fixed and moving parts of the C-frame will in contact define the end of stroke in this case.

This arrangement will creates a bending moment on the jaw 3, in such a way that it could compensate the bending moment due to the force applied by the tooling. By calculating the hydraulic cylinder 41 section, the oil pressure, and the distance between the two pin axis 8,42 of the pivoting part, it is possible to compensate the bending moment produced by the tool. The deviation of the C- frame becomes parallel (or approximately parallel) to the motion of the tooling, thus improving the quality of the process.