Abstract:
A control cabinet for a tablet press including an enclosure having wall, ceiling, and bottom portions of sheet metal, a door which closes an opening of the enclosure wherein a door board attached to the enclosure by means of at least one hinge only consists of two panels of a transparent material with no surrounding border between which a netting of a conductive material is disposed, and a contacting device which electrically connects the netting to a portion of the enclosure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     This invention relates to a control cabinet for a tablet press. 
     A system of a tablet pressing device, apart from the tablet press proper and other peripheral devices, includes a control cabinet in which all components and assemblies are contained for the electric activation of the tablet press and peripheral devices. Such control cabinets, as is common, have an enclosure of sheet metal and a door through which the interior of the enclosure and, hence, the individual elements are accessible in the control cabinet. For reasons of safety, the door of the control cabinet is usually closed and may be opened by authorized personnel only. This means, however, that troubles which arise in the control cabinet or are signaled therein are not available for immediate access if the authorized person is not nearby. 
     Therefore, it is the object of the invention to provide a control cabinet for a tablet press which allows a view into the interior of the control cabinet even when its door is closed, which is shielded against electromagnetic waves, and is easy to clean. 
     BRIEF SUMMARY OF THE INVENTION 
     In the inventive control cabinet, the door board is completely of a transparent material. The door board is composed of at least three layers, i.e. two outer layers of sufficiently stable, transparent material such as acrylic glass and a netting of an electrically conductive material interposed between the acrylic glass panels. The netting is structured so as to not essentially prevent a look through the door board. Thus, an operator may readily take a glance at the inter of a control cabinet and see whether certain pilot lamps or the like are responding or signaling an alarm or an error situation. 
     As mentioned earlier, the door board is assembled from the elements described. A stabilizing border or the like is unnecessary. This has the substantial advantage that the control cabinet may have smooth surfaces continuously extending from outside, which is important for sanitary reasons. 
     Connected to the netting is a contacting device which links the netting to the enclosure. This usually consists of plate-shaped metal sheets and, hence, of conductive material. Such control cabinets have to be Faraday cages, i.e. to prevent electromagnetic waves from getting into and out of the control cabinet. This shielding action is performed by the netting in the door region with a need to conduct the netting to the enclosure in an electrically conductive manner as was mentioned above. 
     Several possible constructions are imaginable to connect the netting to the enclosure. According to the invention, one consists in that the inner panel has exposed a strip of the outer panel at its edge which includes the netting, if necessary, and that a contact element is connected to the associated portion of the enclosure which contacts the exposed portion or netting when the door is in its closing position. Preferably, the contact element is formed by a sealing strip of conductive material. It is imaginable to dispose the sealing strip around the whole door opening from inside and to cause it to engage an exposed portion of the netting each. This will only produce a contacting effect when the door is closed, but there will be no protection against electromagnetic radiation when the doors of conventional control cabinets are opened. 
     A particularly preferred solution according to the invention is that material is cut off from the side of inner panel and from the wire netting by a milling operation so as to expose the adjoining panel. The exposed strip, together with the edge of the panel from which material was milled off, is coated with a layer of a conductive material such as conductive varnish, especially a conductive silver varnish. A sealing strip of a conductive material sealingly engages the conductive layer and simultaneously makes an electric contact therewith. The conductive layer is conductively connected to the netting. Preferably, the sealing strip is formed as a box-like profile so that a wide-area contact is made with the conductive layer. Preferably, the sealing strip is in the hinge region of the door board, but may also be mounted on all of the four sides of the door opening as was explained above. 
     Alternatively, a pin of electrically conductive material extending through the door board may be provided, which is connected to the door hinge and to the netting, on its part. The pin may be a usual fixing pin which connects the hinge to the door board. For this purpose, the pin extends through a bore of the door board. In another aspect of the invention, an electrically conductive bushing may be disposed in a widened bore portion of one panel, which surrounds the pin and one front-end of which abuts upon the netting and the other end of which abuts upon the head of the pin with the length of the bushing being slightly larger than the thickness of the panel. This presses the bushing against the netting and, in turn, may provide an electric line to the enclosure via the hinge. It is understood that a similar contacting action is provided via the so-called sash fastener. What is normally understood by a sash fastener is a rotary pin having a lateral lug at its inner end, which when closed grips behind an edge of the enclosure, thereby keeping the door in a closed condition. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Embodiments will now be explained in detail with reference to the drawings. 
     FIG. 1 shows a front view of the control cabinet according to the invention. 
     FIG. 2 shows a section through the door region of the control cabinet of FIG. 1 taken along line  2 — 2 . 
     FIG. 3 shows a representation similar to FIG. 1, but in a modified way of the contacting action. 
     FIG. 4 shows a way of the contacting action modified from that of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated. 
     Referring to FIG. 1, a control cabinet  10  is outlined, which has an enclosure  12  of plate-like sheet metal. The cuboid-shaped cabinet  10  has a front opening  14  that can be closed by a door  16 . The door is linked to the enclosure  12  by two hinges on the left-hand side where the fixing pins  18 ,  20  for fixing the door  16  to the hinges are outlined. A so-called sash fastener is disposed at  22 , which can be rotated and has its inner end fitted with a transverse lug which grips behind an edge of the enclosure  12  to lock the door  16 . 
     Referring to FIG. 2, it can be seen that the door  16  consists of two superposed panels  24 ,  26  which are formed from a transparent material such as acrylic glass. Located between the panels  24 ,  26  is a netting  28  of a conductive material which, however, does not obstruct a view through the door  16 . 
     It can be seen in FIG. 2 that the pin  20  has a flange-like head  30  and a threaded shank  32  which extends through a bore of the panels  24 ,  26 . The shank  32  also extends through a portion  34  of a box-like profile  36  which has a bearing eyelet  38  close to the opening  14 , which is placed on a bearing pin  40  attached to the corresponding wall of the enclosure  12  by means of a plate portion  42 . The hinged profile  36  is conformed to the inner contour of the enclosure  12  which, however, is not of particular significance for the present case. A nut  44  secures the portion  34 , which extends in parallel with the inside of the panel  24 , to the panel  24  so that the door  16  is suspended and may be pivoted from the closing position to the opening position, and vice versa. Only one hinge is illustrated in FIG. 2 while the control cabinet  10  of FIG. 1 has two hinges. The structure of the second one is identical to that of FIG.  2 . 
     Attached to the inwardly-bent portion  46 , to which the portion  42  is also fixed, e.g. by welding, is a sealing strip  48  which sealingly interacts with the inside of the inner panel  24 . The sealing strip  48  of an elastic material may extend across the whole opening  14  of the cabinet  10 . It prevents moisture and dust from entering the interior of the cabinet. 
     As can be further seen from FIG. 2 a bushing  50  of an electrically conductive material is seated in an widened bore portion of panel  26 . The length of the bushing is slightly larger than the thickness of the panel  26  so that it is pressed by the head  30  against the netting  28 . The shank  32  is surrounded by a sleeve-shaped sealing  52  which, at its ends, abuts upon flat sealings  54  and  58 , respectively, of a conductive material. This connects the netting  28  in an electrically efficient way to the hinge profile  36  which, in turn, is electrically connected to the enclosure  12  which is structured from electrically conductive metal sheets. 
     In the embodiment of FIG. 3, the parts which are identical to those of FIG. 2 are indicated by the same reference numbers. 
     Referring to FIG. 3, the inner panel  24   a  is of smaller dimensions so that a strip of the panel  26  and the netting  28  is exposed. Such a strip may extend around the whole door leaf. A sealing  48   a  which is attached in a way similar to the sealing  48  of FIG. 2, is larger in height and consists of an electrically conductive material. It electrically contacts the netting  28  when the door is in the closing position as is shown in FIG.  3 . Thus, a contact of the netting  28  is established with the enclosure  12  over a large length which may extend around the whole circumferential surface of the door  16   a.    
     In the embodiment of FIG. 4, a door board  16  can be seen which comprises an inner panel  24   b,  a middle panel  25 , and an outer panel  26   b.  A netting  28  is disposed between the panels  24   b  and  25 . Extending through all panels is a bore  52 , which can be passed through by a pin which forms part of a hinge as is shown in FIG.  3  and is described earlier. No further reference should be made thereto. The hinge is appropriately connected to the enclosure  12 , which is only slightly outlined in FIG.  4 . This is fitted, in the region of the door opening as outlined at  27 , with an inwardly-bent border  60  to which a sealing strip  62  box-shaped in cross-section of a conductive material is attached, e.g. by pasting. 
     As can be further seen from FIG. 4 a recess  64  has been formed by milling off material from the panel  24   b  and the conductive netting  28 , which recess is coated with a conductive layer, e.g. a conductive varnish  66 . At this point, the left-hand edge of the panel  24   b  will be coated, too, so as to connect the layer  66  to the netting  28  in an electrically conductive way. The recess  64 , along with the sealing strip  62 , is formed such that the sealing strip engages the recess  64  when the door board  16   b  is closed and comes to lie against the conductive layer  66  on the panel  25  and, simultaneously, against the lateral edge of the panel  24   b  including the appertaining conductive netting  28 . Thus, an efficient electric connection is obtained between the netting  28  and the conductive enclosure  12 . The expenditure involved is relatively low. The panels  24   b,    25 , and  26   b  are efficiently interconnected with no need for a border or frame. Merely one extra machining operation is required because a strip-shaped portion is milled off from the panel  24   b  and the netting  28 . 
     The above Examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.