The present invention concerns a device for the contactless clamping of an object, in particular a work piece that is to be processed, for example by means of milling, drilling, grinding or the like.

By "contactless clamping" is meant here, as is known, that the object concerned is fixed in such a manner that it is held with only one side against a clamping surface, but that this object is free from any clamping elements from all other approach angles and thus can be easily processed over a maximum surface.

A device for the contactless clamping of an object is already known, which device is provided with a magnetic table. Examples of such magnetic tables are described for example in KR 100708013, GB 2,350,933 and international patent application No. 2009/034425.

Usually, such a magnetic table comprises one or several electromagnets or electro-permanent magnets which are put under a clamping plate and which can be switched on and off by switching means provided to that end which activate or deactivate the power supply of the electromagnets, or transmit an electrical pulse to the electro-permanent magnets, as a result of which they change polarity, with magnetization or demagnetization as a result.

By switching on the electromagnets or reversing the polarity of the electro-permanent magnets, a magnetic field is generated which attracts an object made of a magnetic material or a magnetisable material, such as a ferromagnetic material, against the aforesaid clamping plate, such that this object is clamped so to say and can thus be processed, for example by means of milling.

A disadvantage of such magnetic tables is that they do not allow for any clamping of non-magnetic or non-magnetisable materials, such as stainless steel, plastics (PVC, PET, PP, etc.) or organic materials (wood, porcelain, etc.) and the like.

Another disadvantage of such magnetic tables is that, especially when dealing with thin ferromagnetic materials, chips will come off as a result of the material processing and may adhere to the object, which is disadvantage to the processing accuracy and which may lead to damage of the surface of the clamped object, for example when such chips end up between a milling head and the object concerned. Vacuum clamping tables are also known, for example as described in DE 202009007827, which consist for example of a plate in which a number of grooves are provided, and whereby a bore is provided in said groove opening into a terminal in the vacuum clamping table for a vacuum pump or other means which may create an underpressure, such as a venturi or the like.

By providing a flexible sealing cord in the known manner in said grooves according to any required pattern, depending on the shape of the object to be clamped, a part of the plate is isolated as it were in such a manner that, between the object to be clamped, the plate and the sealing cord, a space is created in which, by switching on the vacuum pump or the like, an underpressure can be created in relation to the ambient pressure, such that the object can be held against the plate. An advantage of such vacuum clamping tables in relation to said magnetic tables is that they allow for the clamping of non-ferromagnetic materials and the clamping of thin ferromagnetic materials without any chips adhering to the material .

However, a disadvantage of vacuum clamping tables is that they do not allow for any clamping of large or thick ferromagnetic materials for "heavy processing" or, in other words, for any processing requiring large forces being exerted on the object such as for example milling, since the vacuum force and consequently also the frictional resistance between the object and the vacuum clamping table is restricted, as a result of which a positional fixation cannot be guaranteed in such cases.

Another disadvantage of the known vacuum clamping tables is that they are often provided with numerous inside ducts in order to connect them to all types of vacuum pumps or the like, as a result of which such vacuum clamping tables are expensive.

When ferromagnetic as well as non-ferromagnetic objects are to be clamped, use must be made of a separate vacuum clamping table and a separate magnetic table to that end, which is expensive to purchase and to maintain and which occupies a lot of space. Additionally, the use of a vacuum clamping table on the one hand and a separate magnetic table on the other hand requires considerable changeover times of for example an hour .

In DE 3.525.584 is described a combined device for the contactless clamping of an object, which device is equipped with a magnetic table on the one hand and a vacuum clamping table to be provided on the latter on the other hand which can be clamped against said magnetic table, and whereby the vacuum clamping table is provided with a connection for attaching a vacuum pump or the like.

However, such an embodiment is disadvantageous in that the vacuum clamping table is complex and expensive in this case, and has a large height and/or inside ducts.

The present invention aims to provide a remedy to one or several of the above-mentioned and/or other disadvantages.

To this end, the invention concerns a device for the contactless clamping of an object, which device is provided with a magnetic table with a clamping plate and means for generating a magnetic field for clamping a magnetic or magnetisable object against said clamping plate, whereby said device comprises an at least partly magnetic or magnetisable vacuum clamping table which can be clamped against said clamping plate of the magnetic table by the aforesaid magnetic field, whereby said magnetic table is provided with a connection for means for creating an underpressure . An advantage of the device according to the invention is that it allows for the contactless clamping of ferromagnetic materials as well as non-ferromagnetic materials as it can be very easily converted from a magnetic clamping system into a vacuum clamping system and vice versa, with a considerable reduction of the changeover time .

This also eliminates the necessity to provide two different machines, as a result of which costs can be saved, not only as far as the purchase of the machine is concerned, but also regarding maintenance and the required factory space.

Another advantage of such a device according to the invention is that objects made of a thin material which is only magnetisable to a limited extent and onto which chips adhere due to the strong magnetic field can be clamped significantly better thanks to the vacuum than if a magnetic table were used.

The device according to the invention is also advantageous in that it is now possible to use an extremely simple vacuum clamping table without any inside ducts and possibly of a very low height.

According to a preferred characteristic of the invention, said magnetic table is provided with a connection for means to create an underpressure such as for example a venturi system.

Preferably, the vacuum clamping table is moreover free of conduits forming a connection with such means for creating an underpressure while in use. An advantage thereof is that the vacuum clamping table can remain free of numerous and complex inside ducts, such that it can be made considerably cheaper than known vacuum clamping tables.

Moreover, the vacuum clamping table can be built in a particularly simple manner. According to a very simple variant of the embodiment, the vacuum clamping table mainly consists of a plate, at least partly made of a magnetic or magnetisable material. Such a plate may be relatively thin, for example with a thickness between 1 and 2 cm, or having a thickness of only 8 mm, since the general stiffness of the device is already offered by the magnetic table.

The invention also concerns a method for the contactless clamping of an object by means of a device comprising a magnetic table with a clamping plate and means for generating a magnetic field, whereby this method comprises the step of magnetically clamping a vacuum clamping plate against said clamping plate.

Such a method according to the invention offers the same advantages as the device described above, in particular eliminating the need to provide two separate machines, which offers considerable cost savings and additionally, as explained above, significantly reduces the changeover time. The invention also concerns the use of a device for the contactless clamping of an object, which device comprises a magnetic table with a clamping plate and means for generating a magnetic field, characterised in that said magnetic table is used for the contactless clamping of a vacuum clamping table which is at least partly magnetic or magnetisable . In order to better explain the characteristics of the invention, the following preferred embodiments of a device according to the invention for the contactless clamping of an object are described by way of example only without being limitative in any way, with reference to the accompanying drawings, in which: figure 1 represents a magnetic table as part of a device according to the invention;

figure 2 represents a vacuum clamping table which is part of a device according to the invention;

figure 3 is an exploded front view of a device according to the invention;

figure 4 represents a variant of a vacuum clamping table that can be used in a device according to the invention.

Figure 1 shows a magnetic table 1 which is part of a device according to the invention for the contactless clamping of an object.

The aforesaid magnetic table 1 is built in a manner practically known as such and comprises a clamping plate 2 with a number of poles (N and Z) and means for generating a magnetic field which are not represented in the figure, for example in the shape of one or several electro-permanent magnets, which can be switched on and off, for example by means of a switch provided to that end but which is not represented in the figure either. In order to feed the electric part of the magnetic table 1, this magnetic table 1 is equipped with an electric terminal 3 providing a connection with a power supply source. Said electric terminal 3 can for example have the shape of an electric plug, but it may also form a fixed connection for a power supply cable, for example.

In this case, but not necessarily, a number of blind holes 4 are provided in the top of the clamping table 2 in which, as is known, possible pole extensions can be fixed, for example by means of a threaded connection.

According to a preferred characteristic of the invention, the magnetic table 1 is further provided with a connection 5 for means for creating an underpressure, such as a vacuum pump, a venturi or the like, which connection 5 in this case comprises two almost perpendicularly connecting bores in a massive part of the magnetic table 1. A first bore extends in this case as of a side of the magnetic table 1 and forms a single through duct with the second bore extending as of the top of the magnetic table 1.

In the figure as represented, said connection 5 is provided with the magnetic table 1 on the right side, but it goes without saying that this connection 5 can also be provided elsewhere, for example on the left side or centrally. This connection is preferably provided in a massive part of the magnetic table 1, in particular in a part of the magnetic table 1 which is free of magnets and/or electric coils.

Figure 2 represents a vacuum clamping table 6 of a device according to the invention. In the top surface of the vacuum clamping table 6 are in this case provided a number of longitudinal and transversal grooves 7 which are in this case provided at equal mutual distances, thus forming a regular pattern or grid.

According to the invention, the vacuum clamping table 6 is at least partly magnetic or magnetisable. The vacuum clamping table 6 is further also provided with an opening 8 extending over the entire height of the vacuum clamping table 6 in this case and thus forming a passage with a minimal length, namely as of the bottom of an aforesaid groove 7 up to the lower side of the vacuum clamping table 6.

The use and working of the device according to the invention is very simple and will be discussed hereafter with reference to figure 3.

Figure 3 represents an exploded front view of a device according to the invention, whereby the vacuum clamping table 6 is shown at the top whereby a part is cut at the opening 8, whereas the magnetic table 1 is shown at the bottom.

In order to clamp a magnetic or magnetisable object by means of a device according to the invention, this object must be simply placed on the magnetic table 1, after which the electromagnets or electro-permanent magnets are activated and the object concerned is drawn against the clamping plate 2 by means of the created magnetic field. Next, this object can be processed in the known manner by means of milling, grinding, boring or the like.

Once the processing is finished, the electromagnets or electro-permanent magnets are deactivated, as a result of which the magnetic field is neutralized and the object concerned can be simply removed from the clamping plate 2.

In order to clamp a non-magnetic and non-magnetisable object, for example made of plastic, the vacuum clamping table 6 is placed on the magnetic table 1.

Possibly, but not necessarily, the magnetic table 1 may be provided with positioning means to position the vacuum clamping table 6 on the clamping plate 2, which positioning means may be stops for example, not represented in the figures, which are fixed to the side of the magnetic table, for example by means of screws. Alternatively, the vacuum clamping table 6 may be provided with positioning means to position the vacuum clamping table 6 on the clamping plate 2. These means may consist for example of tapped holes in which may be provided a stop .

If such a stop particularly consists of a threaded rod with an eccentrically provided stud on it, the latter can be used to position the vacuum clamping table 6 on the clamping plate 2, in particular when the stud is directed downward, as well as to position the object to be processed on the vacuum clamping table 6, in particular after the eccentrically provided stud has been rotated, such that it reaches above the surface of the vacuum clamping table 6. According to the invention it is also possible to provide only one stop, but preferably at least two such stops are provided, according to a preferred characteristic at the connection 5. Said stops may also serve, other than for the positioning of the vacuum clamping table 6, for the positioning of the object to be clamped.

Next, the electromagnets or electro-permanent magnets are activated, as a result of which the vacuum clamping table 6 is clamped against the clamping plate 2, since this vacuum clamping table 6 is at least partly magnetic or magnetisable . According to a special preferred characteristic of the invention, the opening 8 in the vacuum clamping table 6, when the vacuum clamping table 6 is clamped on the clamping plate 2, is connected to said connection 5 for means for creating an underpressure. In particular, said opening 8, when the vacuum clamping table is in a clamped condition, is connected directly to the duct of the connection 5.

As shown, the device 1 preferably comprises a seal 9 which, while in use, is provided between the vacuum clamping table 6 and the clamping plate 2 of the magnetic table 1 round said opening 8 and round the opposite far end of the duct of the connection 5.

A recess may possibly be provided in the bottom wall of the vacuum clamping table 6 and/or in the upper surface of the magnetic table 1, concentrically or almost concentrically round said opening 8 and/or round the aforesaid far end of the duct of the connection 5, in which recess said seal 9 can be placed, although this is not strictly necessary according to the invention.

After the vacuum clamping table 6 has been clamped, a sealing cord is provided in the known manner in said grooves 7 according to a specific pattern, depending on the shape and dimensions of the object to be clamped, after which the object to be clamped is placed on the vacuum clamping table 6.

Then, the means for creating an underpressure are activated, which means create an underpressure in the sealed space between the object to be clamped, the vacuum clamping table 6 and the sealing cord, via the opening 8, which of course must at all times be situated within the perimeter confined by the sealing cord. Thus, the object is clamped against the vacuum clamping table in order to be processed. In order to remove the object after the required processing, one only has to eliminate the underpressure by deactivating said means and by connecting said confined space to the atmosphere.

As the connection 5 for means for creating an underpressure is provided on the magnetic table, the vacuum clamping table 6 is very easy to realise and must not be provided with complex inside ducts; while in use, it will always be free of conduits forming a connection with the means for creating an underpressure. From what precedes it is clear that the device according to the invention can be very easily and quickly transformed from a vacuum clamping system into a magnetic clamping system and vice versa. Consequently, there is no need for two separate installations, as a result of which considerable costs can be saved.

Figure 4 represents another embodiment of a vacuum clamping table 6 which can be used in a device according to the invention .

In this case, the vacuum clamping table 6 is not provided with a large number of grooves as in the embodiment from figure 2, and it is provided in particular with an upward directed surface which is mainly flat when in use.

In this example, the vacuum clamping table 6 is used in combination with a mat 10 provided with a number of circular ribs 11 on top which each comprise a disc-shaped mat part in which is provided an opening 12.

On the bottom side, said mat 10 is provided with a number of slots which are such that they form a duct system as of a common point, which duct system is such that every aforesaid opening 12 is connected to this point via said slots .

The use of a device according to the invention which is provided with a vacuum clamping table 6 according to figure 4 is practically analogous to that of the above-described embodiment of figures 1 to 3, as here also the vacuum clamping table 6 is first magnetically clamped on the clamping table 2.

Next, the means for creating an underpressure are activated, as a result of which a vacuum is created via the connection 5 and the opening 5 in every space which is surrounded by an aforesaid rib 11, so that a series of suction cups are formed by the mat 10 as it were.

Naturally, it is important that the aforesaid point which is connected to the openings 12 via the slots in the mat 10, while the device is in use, is connected to said connection 5 in order to be able to create said underpressure in all suction cups. A specific advantage of the use of this variant consists in that it is possible to entirely drill through the clamped object without the vacuum being lost, such that the object remains clamped against the vacuum clamping table. Indeed, when the vacuum in one of the suction cups is lost as the sealed space is connected to the atmospheric pressure, the underpressure will be preserved in the other suction cups. Naturally, apart from that, such a variant still offers the same advantages as those mentioned above with respect to the preceding embodiment, namely the considerable cost saving and the simple and quick transformation from a magnetic clamping system into a vacuum system and vice versa.

It is clear that this vacuum clamping table 6 as used in the last described application in combination with the mat 10, whereby the surface of this vacuum clamping table 6 is not provided with the many grooves as in the embodiment from figure 2, and the vacuum clamping table 6 as represented in figure 2 and the accompanying applications may concern one and the same element. Indeed, the two main faces of a vacuum clamping table 6 may be realised in such a way that they can be used for both applications by simply turning them, at least if one of the main faces is provided with grooves 7 as discussed, whereas the opposite face is mainly flat.

A major advantage which is thus obtained, apart from the cost saving as two functions are combined in a single element, consists in that when such a vacuum clamping table 6 is used in combination with the mat 10, certain zones can be deliberately excluded from the vacuum circuit by simply providing one or several O-rings in the grooves 7. In this application, this grooved side is provided at the bottom, i.e. in contact with the clamping table 2.

According to the invention it is possible to provide positioning holes in the vacuum clamping table which make it possible to correctly position an object to be clamped and/or an above-mentioned mat 10 on the vacuum clamping table .

If such positioning holes are provided on the side of the vacuum clamping table 6 which is provided with grooves 7, either or not in the shape of a grid, they may be provided with internal thread to fix clamping means and/or stops.

If such positioning holes are provided on the side of the vacuum clamping table 6 which is mainly flat, they can be made without internal thread or as chambers. The latter positioning holes or chambers can for example be used to anchor protruding parts, for example bumps, on the bottom side of the mat 10, such that one can easily obtain that the central point which is connected to the respective suction caps via the slots always connects to the opening 8 in the vacuum clamping table 6.

The present invention is by no means restricted to the embodiments described by way of example and represented in the accompanying drawings; on the contrary, such a device according to the invention for the contactless clamping of an object can be made in all sorts of shapes and dimensions while still remaining within the scope of the invention.