Vacuum plate

Field of the Invention

The present invention provides a vacuum plate for releasably fastening work pieces.

Background of the Invention

In the art of machining work pieces it is well known to fasten the material piece to be worked on to the machine. For example when desiring to drill, mill or grind objects these are usually by means of clamps, bolts or the like fastened to the machine Thereafter the working process may be carried out and afterwards the work piece may be released from the machine.

As an alternative to mechanical fastening means as clamps, bolts and the like, magnets and vacuum plates are used.

As magnets only work when the work piece to be machined is made from a magnetic material this invariably limits its use for other materials, such as for example certain light metals, carbon or polymer materials.

The prior art vacuum plate, see for example a vacuum plate disclosed in GB2403680 which comprises a number of suction apertures which are connected to a source of vacuum. This arrangement besides being very expensive due to the cost of a suitable source of vacuum, having the necessary power to be able to fix the work pieces, also has a number of drawbacks. The suction action is directed to the suction apertures in the vacuum plate. When the work piece is smaller than the plate, some of the suction apertures are not covered. This, in addition to create noise, also makes it possible for material, such as shavings, dust or other pollution may enter the suction channels/ducts, which connect the suction aperture to the source of vacuum.

Object of the Invention

It is consequently an object of the present invention to alleviate the disadvantages with the prior art devices and at the same time provide an apparatus which will not be pol-

luted and thereby clog up and be the cause of down time and costly cleaning processes and which is easy and cheap to use.

The invention addresses this by providing a vacuum plate for releasably fastening item to be worked on to a surface of said plate, wherein said plate comprises a box structure having a bottom plate, four sides and a top plate, where the top plate is provided with at least one aperture, and where the volume enclosed by the box structure comprises for each aperture a separate air duct passing under the aperture, and where all air ducts are connected to a source of pressurised air, such that an airflow may be created past the aperture, and that upstream in relation to the aperture in each air duct a venturi is arranged, and down stream from said aperture an air outlet is provided, and further that the aperture is in communication with the air duct, between the venture and the outlet.

Instead of connecting the vacuum plate to a source of vacuum the present invention connects to a source of pressurised air which is a much cheaper device than a vacuum device and at the same time for most work shops a source of pressurised air is available at most work stations. Therefore, in order to implement the present invention at a number of work stations it is not necessary to change the constructions surrounding the work stations, but simply by adding a side pipe connection to the existing source of pressurised air it becomes possible to drive the vacuum plate according to the invention. By arranging an air duct under the aperture and communicating with an aperture in the top side of the top plate, i.e. on the surface on which the pieces to be worked on are meant to be releasably fastened, it becomes possible to create an underpressure immediately adjacent the aperture just below the surface of the top plate. This is done by creating an increased air speed by means of a venturi right before the aperture's communication with the air duct and allowing this pressurised air through the venturi to propagate outside the vacuum plate. In this manner even if polluting items such as shaves, chips or the like enter the aperture and thereby the air duct, the pressurised air and the air flow created by the pressurised air will blow the pollutants out through the opposite end of the vacuum plate as there need not be any restrictions to the air flow once the air flow has passed the venturi and thereby created the underpressure adjacent the aperture in the top plate.

In a further advantageous embodiment of the invention a silencer is provided in the air duct downstream of the aperture and upstream of the outlet.

Pressurised air may when the air flow is altered create a relatively loud noise, but this noise may be contained by guiding the air flow into a silencer, for example an enlarged section inside the vacuum plate where the energy is dissipated from the pressurised air and thereby the noise is contained inside the vacuum plate.

In a still further advantageous embodiment of the invention one common silencer is provided down stream of the apertures and connected to all air ducts, and where one common outlet is connected to the silencer. This may be advantageous in that a relatively large silencer room may be provided in each vacuum plate. In addition to creating a cheaper construction due to less machining of the vacuum plate, this also provides for a lighter construction which will be easier to handle and more work-friendly.

hi a still further advantageous embodiment the air pressure of the source of pressurised air is in the range of 4 bars to 12 bars, more preferred 6 bars to 8 bars, and where 20 to 80 litres air per minute are supplied, more preferred 30 to 60 litres per minute, and most preferred 40 to 50 litres per minute. The relatively low pressures in combination with the relatively low amount of air being used per minute create a relatively strong vacuum due to the sign of the venruri and at the same time makes it possible to utilize commonly available sources or pressurised air such that in order to implement the present invention it is not necessary to purchase expensive equipment in order to create the necessary pressurised air flow.

hi order to foresee different working situations the vacuum plate may in a further advantageous embodiment have a size and construction where the air ducts are integral with the bottom or top plate, and the vacuum plate is 500 mm by 1000 mm, more preferred 600 mm by 400 mm and between 20 mm to 60 mm thick. These sizes of vacuum plates make it possible that the plates are handled by a single worker in that the weight of such a device is relatively low, i.e. from about 10-20 kilos and therefore may easily be handled by a worker without any lifting aids.

In a still further advantageous embodiment between 2 and 10 apertures, more preferred 4 and 8 apertures are provided in the top plate. The apertures are the points where the vacuum is created in the top plate and therefore also the points where the piece to be worked on are attached to the vacuum plate, and according to the size of the vacuum plate and the size of the work piece to be machined any number of apertures may be implemented in the top plate with corresponding air ducts provided underneath inside the box structure, but for many purposes between 2 and 10 apertures will provide a vacuum plate which is able to address most purposes.

Description of the Drawing

The invention will now be explained with reference to the accompanying figures, wherein

Fig. 1 illustrates a vacuum plate according to the invention arranged in a machine tool holder;

Fig. 2 illustrates a cross section through a vacuum plate Fig. 3 illustrates a perspective view of a corner of a work plate

Detailed Description of the Invention

The invention uses pressurised air as the source for creating the necessary underpressure which will be referred to as vacuum. It is acknowledged that the scientific term vacuum is not corresponding to the term within this patent, but within this context vacuum is designated to mean sufficient underpressure in order to releasably fasten a workpiece to the apparatus according to the invention.

This is achieved by arranging a venturi in the air flow channel inside the device. A venture is a partial constriction of the airflow channel, whereby the so-called venture- effect occurs.

The Venturi effect is a special case of Bernoulli's principle, in the case of fluid or air flow through a tube or pipe with a constriction in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli effect. It is named after Giovanni Battista Venturi, (1746-1822), an Italian physicist.

The vacuum created by the venturi is used in order to create the desired holding of the workpiece on the vacuum plate.

In figure 1 is illustrated a vacuum plate 1 arranged in a tool holder 2 in a grinding machine. The fact that it is a grinding machine is not important relating to the vacuum plate in that any type of machine where it is desirable to fixate objects in order to work on these objects are suitable to be used with the vacuum plate according to the invention.

The vacuum plate 1 comprises a top plate 3 which in this embodiment is provided with a pattern (relief) such that the debris, shavings and the like will be lodged in the lower part of the relief pattern whereby the work piece to be worked on touches the uppermost parts of the relief pattern in order to achieve a stable support. The work piece may be positioned anywhere on the vacuum plate 1. In this example however the workpiece may be positioned overlapping the white line representing a silicon seal 4. The work piece will in this illustration be placed substantially central on the top plate 3 of the vacuum plate 1. The silicon seal delimits an area and will abut against the underside of the work piece to be worked on as will be evident from figure 3 and will thereby limit a space formed by the top plate 3, the silicon seal 4 and the underside of the work piece (not illustrated). Centrally in this limited area is an aperture 5 which aperture when a source of pressurised air is attached to the vacuum plate will create a vacuum as will be explained below, hi the illustrated embodiment a plurality of apertures 5' is illustrated and any number according to the purpose may be provided.

A source of pressurised air 6 is connected for example by a rapid coupling device 7 to the vacuum plate. Rapid coupling devices are in widespread use is workshops and do not require any special skills of the operator, so that it is easy for any user to attach the source of pressurised air 6 by means of a rapid coupling device 7 to the vacuum plate 1 according to the invention.

Turning to figure 2 a cross section through the vacuum plate 1 is illustrated. The pressurised air will be supplied through the coupling 7 in the direction of the arrow 10. Inside the vacuum plate 1 is provided an air duct 8 which air duct is partly constricted upstream from the aperture 5 being connected to the air duct. The constriction creates the venturi effect (see above). The venturi 9 will as explained above create a partial

vacuum downstream from the constriction such that due to the connection to the aperture 5 a vacuum will be present between the work piece 11 and the top plate 3 of the vacuum plate according to the invention.

hi this embodiment a silencer 12 is provided downstream of the aperture 5 in order to dissipate the energy in the air supplied by the source of pressurised air and thereby taking the noise out of the air which after passing the silencer may be dissipated to the surroundings through the outlet 13.

Turning to figure 3 the top plate is illustrated in a plane view where an arbitrary number of apertures 5' are illustrated. The coupling for allowing the source of pressurised air 6 to be connected to the vacuum plate is also illustrated. In the vacuum plate air ducts are connecting the coupling 7 with each aperture 5' either in a way such that each aperture 5' is connected by a separate air duct connecting the coupling 7 to that particular aperture or that a limited number of air ducts connects one or more apertures.

As is evident from the explanation above there are many variations possible for a vacuum plate according to the invention, but preferably vacuum plates having a size fitting into the tool holders 2 of common machines where these types of vacuum plates are applicable are most desired.

The air ducts 8, the Venturis 9, the silencers 12 and the outlets 13 may be machined into the bottom plate 15 of the vacuum plate 1.

Turning to figure 2 the bottom plate 15 is separated from the top plate by a dashed line 16 in this example such that the top plate is very thin and the bottom plate 15 is relatively thick, but other divisions may also be feasible. Alternatively, the top plate 3 may be provided with a bottom plate and an intermediate plate corresponding to the plate 15 wherein the air ducts are integrated. A further alternative may include a construction where the air ducts are in the shape of pipes such that the top plate and the bottom plate create a box shape together with a side member .