A METHOD AND A DEVICE FOR PROTECTION OF ELECTRONIC EQUIPMENT, AS COMPUTER MONITORS

Abstract: A method and an apparatus for electromagnetically screening electronic appliances such as computer monitors. The inside of the casing (12) surrounding the monitor is provided with an electroconductive screen (31) following the inner walls, which is formed from one metal foil blank (50) by folding or from several metal foil blanks (32, 34, 36) by joining overlapping edges. The folded parts or the edges of two blanks are joined by stapling so that a screening shell of permanently the same shape as the casing is obtained.

Description: A ms-thod and a device for protection of electronic equipment, as computer monitors The present invention relates to a method and an apparatus for screening electronic appliances such as monitors or visual display units for computers, in which method inside the casing surrounding the electronic appliance there is formed an electroconductive screen substantially following the inner walls of the casing and which apparatus thus comprises an electromagnetic electroconductive screen following the inner walls of the casing. When designing, assembling and building electric appliances, attention should be paid to the electromagnetic screening of the appliances and the assemblies and to the capacity of the appliances to be in accordance with the environment without interfering with it and vice versa. Once an appliance is completed, it is too late to wonder why interferences occur and to try to eliminate them by various temporary arrangements. It is a well known fact that computers cause electromagnetic interferences, and it is also well known that computers interfere with the reception of sound or television broadcasts. The widespread use of computers and other digital microelectronics has resulted in the fact that there are large and small sources of electronic interference everywhere. This has for instance increased the risk that many electric appliances, such as various measuring and control devices, interpret the interference signals as control commands and start to function in the wrong way. On the other hand, also atmospheric electromagnetic discharges may cause damage to television sets as well as to computers. It is also known that the electromagnetic signals emitted from the computers constitute a risk in that unauthorized persons may by means of them be able to pick up data being processed in the computer. The above mentioned problems can be solved for instance by placing the computer monitor in a metal box or cage so that no radiation is discharged from it. This of course makes the computer very heavy, difficult to move, and expensive. It has also been suggested, for instance in US patent 4,785,136 and European patent application 0200513, to provide the computer with a lining, which is made for instance of resilient, metallized fabric of syntectic fibres. Till now the casings of the computer monitors have usually been painted on the inside with paints or lacquers containing copper or nickel compounds in order to guarantee electromagnetic screening. In practice, however, handling paints containing metal compounds and painting with them is expensive and troublesome. The paints are poisonous, which fact has to be taken into account when planning the working premises and the working procedure. The painting is often done by robots. It is an additional difficulty that all the surfaces which are intended not to be painted have to be individually protected during the painting. Still another difficulty is caused by the fact that the casing is provided with several ventilation openings of different sizes and shapes, through which the paint is naturally not allowed to flow to the outside of the casing. The recycling of the casings of the monitors has proved to be problematic; the casings constitute hazardous waste. It is difficult to remove paint containing metal compounds from plastic monitor casings in order to render it possible to recycle the plastic material or to combust it. German patent application 24 15 642 suggests attaching an aluminium sheet to the back wall of a television set by gluing. The aluminium sheet is formed into the shape of the back wall. When shaping aluminium sheets, the sheet has to be folded at some points, at times manifold, in order to obtain the proper shape. The aluminium screen will thus be very thick and stiff, at least in the corner areas. Another disadvantage is that this way sheet material is unnecessarily wasted, as the desired screening effect could be achieved by a single sheet layer. Furthermore, fitting the sheet inside a casing is a difficult and time-consuming operation. The object of the present invention is to provide a method and apparatus for electromagnetically screening electronic appliances which is better and cheaper than the above described. A further object is to provide a screen which can be easily and rapidly fitted into the casing of a computer monitor. Still another object is to provide an electromagnetic screen the production of which can be automated to a very large extent. In order to achieve the above objects, the method according to the invention for electromagnetically screening electronic appliances is characterized by - forming from one or several metal foil blanks an inner screening shell of substantially the same shape as the casing surrounding the electronic appliance by folding a metal foil blank into a screening shell of the same shape as the casing or by disposing several suitably shaped metal foil blanks with the edges overlapping so that a screening shell of the same shape as the casing is obtained; - joining, by stapling or in some other suitable way, the folded parts of the metal foil blank or the overlapping edges of the metal foil blanks to each other so that a screening shell permanently of the same shape as the casing is obtained, and by - lining the casing of the electronic appliance with the inner screening shell formed in this way so as to form an electromagnetic screen. The electromagnetic screen or lining can thus be formed even from a single aluminium foil blank, which is bent and folded into the proper shape and in which the folds are secured to each other tightly by stapling. In this way it is guaranteed that the shape of the lining is preserved and that the lining takes as little room as possible. If too much material gathers at the folding points, it is of course possible to remove the excess by cutting it away. However, the screening shell is preferably made so that substantially straight-sided blanks, for instance of a rectangular or oblique-angled shape, are cut, punched, or formed in some other similar manner, from an aluminium web, and joined by stapling into a screening shell. Straight-sided blanks can easily be cut from an aluminium web so that nearly the whole web is utilized and the waste pieces are very small. The oblique-angled blanks can be cut so that the oblique side of one piece matches that of another. According to the invention, a lining of suitable size for a casing can thus be "tailor-made" from blanks. In order to save foil material the blanks should be formed from parts which are as straight-sided as possible so that the wastage of material is kept to the minimum. Thus the screening shell according to the invention to be installed in the casing of a computer monitor is formed, the shape of- the casing allowing it, for instance from one substantially straight-sided elongated blank which forms, for instance, the vertical walls of the screening shell or the roof, back wall and bottom of the screening shell, plus from other smaller, possibly oblique-angled blanks that might be necessary. The elongated blank is bent into the desired shape and the smaller blanks are attached to it to form a screening shell of the desired shape. In computer monitors in which the bottom is detachable, the screening shell for the bottom is made of separate blanks. The electric contact between the bottom and the screening shells of the other parts of the casing can be achieved in the same way as between the casing and the mask, which will be described later. It is obvious that the larger the number of the blanks from which the screening shell is made, the better conformity of the screening shell to the shape of the casing can be achieved. On the other hand, it is also obvious that the larger the number of blanks from which the screening shell is made, the larger the number of joints which have to be made in it. It is therefore advantageous to make the screening shell according to the principal shape of the casing, without considering all the small details of the shape. When manufacturing the screening shell, these small details are provided for by making the shell large enough to make it possible to shape it in desired detail when it is being installed. The screening shell can thus advantageously be made from relatively thin, 0.05 to 0.15 mm, aluminium foil, which can easily be formed to follow the inner wall of the casing. When forming the aluminium foil in conformity with the inner wall of the casing, small wrinkles might appear, which however, for instance when the surfaces are large, only have a supporting effect on the screening shell and are not harmful. At the places where there are openings in the casing, for instance inlet openings for cables and ventilation holes, corresponding necessary openings are made in the screening shell. The screening shell can, if desired, be attached to the inner wall of the casing by gluing, welding or by means of fastening members. At the outer edge of the screening shell, protrusions or tabs can be made in the foil when it is being cut, which can be bent over the edge of the casing for fastening the shell to the casing. If desired, the edge of the screening shell can be bent along its whole length over the edge of the casing. The adjacent edges of the blank of the screening shell are advantageously joined to each other using automatic stapling machines. In this case, the blanks cut to measure are placed in the stapling machine onto a counter core having the same shape as the screening shell. The edges of the adjacent blanks which are to be joined are disposed so that they overlap about 5 to 20 mm, whereafter the automatic staplers preset in the machine join the edges to each other into electroconductive joints. Counter cores of different sizes and shapes can be used in the same stapling machine according to requirements. The change of the counter core and the corresponding staplers can be effected rapidly. When manufacturing the screening shells according to the invention, the staples do not have to be disposed with absolute exactness at some given place or position, i.e. the range of the set values is rather wide, which makes the stapling operation very simple and fast. The staples can be driven into the joint for instance at intervals of 20 to 50 mm. All joints can, if desired, be stapled at the same time, in which case a separate stapler is needed for each staple. If required, the stapling can of course be effected joint by joint or even staple by staple. When making the screening shell from aluminium foil, it is preferable to use staples of aluminium, i.e. so called paper staples, in order to prevent galvanic corrosion. Aluminium coated staples can also be used for this purpose. The upper length of the staples, i.e. the length of the middle portion above the joint, is preferably for instance about 10 to 20 mm, and the lower lengths of the staples, i.e. the lengths of the bent portions below the joint is about 5 to 10 mm. When the screening shell is made from several separate blanks, it is important that the blanks are joined to each other in the way that an electroconductive contact between the blanks is established. According to an advantageous embodiment, the (paper) staples are flat-pressed against the metal foil so that the straight upper part of the staple is pressed substantially along its whole length tightly against the surface of the foil on one side of the joint, while the bent lower parts of the staple on the other side are bent tightly against the foil in a direction parallel with the upper part of the staple. The staples are thus pressed substantially along their whole length tightly against the surface of the foil on both sides of the joint. When the joint is bound together by flat pressed staples, a relatively large compressed contact surface is established between the blanks and also between the blanks and the staples. In this way a good electric contact is achieved between the two blanks and also between the staples and the aluminium foil. In conventional papers staplers, the heads of the staples are usually bent in an angle towards the paper, whereby the staples do not touch the paper along their whole length. The apparatus according to the present invention for electro- magnetically screening electronic appliances, such as monitors for computers, is characterized in that the electromagnetic screen comprises an inner screening shell formed from one or several metal foil blanks, in which the blank is bent and folded or the edges of adjacent blanks are joined so that a screening shell is obtained the shape of which substantially corresponds to the shape of the casing for the electric appliances, and in which the folded parts or the overlapping edges are stapled to each other so that a screening shell permanently of the same shape as the casing is obtained. The screening shell is preferably attached to the inner surface of the casing by means of fastening members. According to an advantageous embodiment of the present invention, the edges of the lining or the screening shell made from metal foil protrude a little, for instance about 1 to 5 mm, out from the casing all around or partly. The edges are additionally bent outwards over the edges of the casing. By bending the edges outwards it is avoided that a part to be disposed inside the casing could be pushed between the foil and the wall of the casing during the assembly, thereby damaging the foil or the screening shell. At the same time, it is made sure that the foil stays in its place and is not able to slacken and hang down for instance at the upper edge of the screening shell. When, besides the back casing of the computer monitor, also the mask is provided with an electromagnetic screening, springs can be attached to the edge of the mask, which establish electric contact between the screening shells of the casing and the mask. The springs protrude partly outwards from the mask as they are meant to press tightly against the wall of the screening shell when inside the casing. During the assembly, they therefore are easily pushed between the screening shell and the wall of the casing if the screening shell is not bent sideways over the edge as described above. The screening shell does of course not have to extend over the edges of the casing along its whole length. Protrusions or tabs may of course be made only at those points where the springs attached to the mask are to be guided inside the casing. By bending the edges of the foils of the screening shells of both the back casing and the mask substantially along the whole length of the edge, the interspace between the casing and the mask can be made electroconductive even to such a degree that the above mentioned springs are not always required in order to establish electric contact between the screening shells of the casing and the mask. By the arrangement according to the invention, for instance the following advantages are achieved: - the prefabrication of the screening shell can be done as a separate stage, whereby it does not slow up the assembly of the monitor itself; - the manufacture of the screening shell can be technically automated into a very fast stage; - the stapling together of the folded parts or the edges of the blanks by a stapling machine is easily controllable, whereby the quality of the screening shells coming from the machine can be guaranteed; - the screening shell of the casing made according to the invention, the shape of which corresponds to the shape of the casing, can easily be adapted to follow the walls of the casing tightly, whereby its space requirement is small; - a carefully joined screening shell made of metal foil blanks accomplishes reliable electromagnetic screening and renders it possible to use an inexpensive plastic casing in monitors; - the metal foil can easily be detached from the plastic casing of an old monitor for recycling, and - a low-cost screening shell is obtained for the above reasons. The invention will now be described more in detail with reference to the accompanying drawings, on which FIG. 1 is a schematical axonometric view of a computer monitor; FIG. 2 is a side view of the monitor of FIG. 1; FIG. 3 schematically shows the opened back casing of the monitor of FIGS. 1 and 2, in which there is disposed an electromagnetic screen according to the invention; FIG. 4 shows a section of the casing of FIG. 3 along line AA and a corresponding sectional view of the front part or mask to be connected to the casing; FIG. 5 schematically shows the opened back casing of the monitor of FIGS. 1 and 2, in which there is disposed an electromagnetic screen according to another embodiment of the invention; FIG. 6 shows a section of the casing of FIG. 5 along line BB and a corresponding sectional view of the front part or mask to be connected to the casing; FIG. 7 is an enlarged view of the juncture of the edges of the back casing and the mask; FIG. 8 schematically shows a portion of the counter core of a stapling machine and the staplers; FIG. 9 shows two aluminium webs on which the blanks forming the screening shells 1, 2 are marked; FIG. 10 is an enlarged sectional view of the joint between the edges of two foils. FIGS. 1 and 2 show a computer monitor 10, in which there are two separate casing parts, i.e. the back casing 12 and the front part or the so called mask 14. In the mask, there is a display screen 16. In the back casing, there are several ventilation openings 18, of which only some can be seen in FIG. 2. The back casing 12 and the edge 20 surrounding the display screen of the mask is made of plastics which is permeable to radiation. FIG. 3 is a front view of the opened back casing 12 of the monitor of FIGS. 1 and 2. The back casing is formed of side walls 22, 24, a back wall 26, a roof part 28 and a bottom part 30. The bottom part 30 rises from its back part towards the back wall. The inside of the back casing is in this case lined with an aluminium foil, which forms the screening shell 31 in the casing. The screening shell is formed from one elongated, substantially straight-sided, rectangular blank 32 covering the walls, and two smaller, substantially straight-sided, oblique-angled blanks, a roof blank 34 and a bottom blank 36. The roof blank 34 is stapled to the blank 32 covering the walls, at the upper edge of it, so that an electroconductive joint 38 is formed. In the same way, the bottom blank 36 is stapled to the blank 32 covering the walls, at the lower edge of it, so that an electroconductive joint 40 is formed. FIG. 4 shows a cross section of the casing of FIG. 3 along line AA and a corresponding sectional view of the front part or mask to be connected to the casing. Fastening members 42 are disposed in the upper edge of the casing and a fastening member 44 in the lower edge, which connect the mask to the casing. The edge 20 of plastics of the mask 14 is provided with a screening shell 46 made of an aluminium foil. In the edge of the casing, there are in addition to the fastening members electrocondutive spring members 48 which, when the mask is connected to the casing, press against the aluminium foil covering the casing wall 24 as well as against the aluminium foil 46 covering the edge 20 of the mask, thereby establishing electrical contact between the aluminium foils of the casing and the wall. FIGS. 5 and 6 show the back casing 12 of the monitor, the inner screening shell of which is made from one single aluminium foil blank 50 by bending it and folding it into the shape of the casing. The folds in the corners 51, 52, 53, 54 of the screening shell are stapled tightly against each other so that the screening shell retains its casing-like shape. Openings 55, 56 are made in the blank for the cable outlets as well as a plurality of ventilation openings 18. The cup- shaped bottom part 57 which is to be connected with the support of the monitor can be completely or partially lined. As can be seen in FIG. 6, which shows a cross section of the casing of FIG. 5 along line BB, and in FIG. 7, which is an enlarged view of the edge area of the casing and the mask, the edges 60 of the aluminium foils forming the screening shell of the casing 12 are bent or turned outwards over the edge 61 of the casing. Also the edges 62 of the screening shell 46 of the mask 14 are bent or turned outwards over the edge 63 of the mask. When the mask 14 is connected with the casing 12, the edges 60 and 62 will be pressed tightly against each other, thereby forming an electroconductive contact between the layers of the screening shells of the casing and the mask. FIG. 8 shows schematically a portion of a stapling machine 66, in which a screening shell 68 for the casing is manufactured from aluminium blanks a, b and c (of which only a and b are shown) . The stapling machine comprises a counter core 70, which is of the same shape as the casing of the monitor, and stapling units 72 and 74, which consist of several individual staplers 76. The core is shown very schematically in FIG. 8. The shape of the core, which depends on the actual shape of the casing of the monitor, is thus often tapered, rounded at the corners or differs in other ways from a cube. The screening shell is manufactured by fitting the aluminium blanks a, b and c (which is not shown) , cut to measure, in a desired manner on the counter core in conformity with the shape of the screening shell. The edges of the blanks are disposed overlapping about 5 to 10 mm so as to form, inter alia, the joints 78, 80, 82 and 84. The stapling units 72 and 74, which are preset taking into account the position of the joints, are pressed against the counter core so that the stapling area coincides with the joints. The staplers drive in all the staples of the joints 78 and 80 at the same time. Also the joints 82 and 84 can, if desired, be stapled at the same time by other stapling units, which are not shown. FIG. 9 shows two aluminium webs 86 and 87, on which there are disposed templates la, lb, lc and 2a, 2b, 2c for the blanks 1 and 2 for two screening shells. The rectangular blanks la and 2a and the oblique-angled blanks lb, lc and 2b, 2c can be cut from the webs without wastage of material. The webs can of course be of different widths. FIG. 10 shows a cross section of the joint 92 formed by the edges 88 and 90 of two aluminium foils, which are stapled together by a staple 94. The middle part or the upper part 92 of the staple is pressed tightly against the edge of one foil and the lower or bent parts 98 are pressed tightly against the edge of the other foil, whereby a good electric contact is established between the staple and the foils. The invention is not limited to the embodiments described and illustrated above by way of examples, but can be varied in many ways within the scope and spirit of the invention, which is defined in the appended claims.

Claims: Claims 1. A method for electromagnetically screening electronic appliances, such as monitors for computers, in which method inside the casing (12) surrounding the electronic appliance an electroconductive screen substantially following the inner walls of the casing is formed, characterized by - forming from one or several metal foil blanks (32, 34, 36; 50) an inner screening shell of substantially the same shape as the casing surrounding the electronic appliance by folding the metal foil blank into a screening shell (31) of the same shape as the casing or by disposing several suitably shaped metal foil blanks with the edges overlapping so that a screening shell of the same shape as the casing is obtained; - joining, by stapling or in some other suitable way, the folded parts of the metal foil blank or the overlapping edges of the metal foil blanks to each other so that a screening shell permanently of the same shape as the casing is obtained, and by - lining the casing of the electronic appliance with the inner screening shell formed in this way so as to form an electromagnetic screen. 2. The method according to claim 1, characterized in that the metal foil blanks are formed from an aluminium foil web. 3. The method according to claim 1, characterized in that folded parts of an aluminium foil blank or the overlapping edges of aluminium foil blanks are joined to each other by stapling using aluminium staples in order to prevent galvanic corrosion. 4. The method according to claim 1, characterized in that the overlapping edges of the metal foil blanks are joined to each other by flat-pressed staples (94) so that a good electric contact between the metal foil parts is achieved. 5. The method according to claim 4, characterized in that the inner screening shell of the same shape as the casing is tailor-made from substantially straight-sided metal foil blanks (la, lb, lc; 2a, 2b, 2c) . 5 6. The method according to claim 1, characterized in that the inner screening shell of the same shape as the casing is formed from the metal foil blank by bending and/or folding it, in which the bends and/or folds are formed at the corners (51, 10 52, 53, 54) of the screening shell. 7. The method according to claim 1, characterized in that the metal foil blank or blanks (a, b, c) are disposed on a counter core (70) of substantially the same shape as the casing of the 15 electronic appliance, on which counter core a screening shell of the same shape as the casing is formed from the blank or blanks, and that the folded parts of the blank or the overlapping edges of the blanks are stapled together on the counter core so that a screening shell of the same shape as 20 the casing is formed. 8. The method according to claim 7, characterized in that the edges are joined using an automatic stapling machine (66) , by means of which several staples disposed one after another are 25 driven in simultaneously, and by means of which the ends of the staples are bent in the way that they are parallel with the unbent middle part of the staple, whereby a good electric contact between the staple and the aluminium foil is achieved. 30 9. The method according to claim l, characterized by - manufacturing from an aluminium foil blank a screening shell (31) which is open in the front and of the same shape as the back casing (12) of the computer monitor; - disposing the screening shell of the same shape as the 35 casing into an empty casing before mounting the separate front part or mask (14) in its place; - bending the edges (60) of the screening shell over the edges (61) of the open opening so that the edge areas of the casing are screened; - lining with an aluminium foil the sides (20) and/or the edge areas of the separate front part or mask (14) so that the aluminium foil, when the front part has been installed, establishes good electroconductive contact with the bent edges of the screening shell of the casing. 10. An apparatus for electromagnetically screening electronic appliances such as monitors for computers, which apparatus comprises an electroconductive screen (31) substantially following the inner walls (22, 24, 26, 28, 30) of the casing (12) for the electronic appliance characterized in that the electromagnetic screen comprises an inner screening shell (31) formed from one or several metal foil blanks (32, 34, 36; 50), in which the blank is bent and folded or the edges (88, 90) of adjacent blanks are joined so that a screening shell, the shape of which substantially corresponds to the shape of the casing (12) , is obtained, and in which the folded parts (51, 52, 53, 54) or the overlapping edges are stapled together so that a screening shell permanently of the same shape as the casing is obtained. 11. The apparatus according to claim 10, characterized in that the screening shell (31) is made from an aluminium foil and that the screening shell is attached to the inner surface of the casing by gluing, welding or by means of fastening members. 12. The apparatus according to claim 11, characterized in that the adjacent edges (88, 90) of the straight-sided aluminium foil blanks forming the screening shell are joined to each other by means of aluminium staples by stapling and that the aluminium staples are bent so that their bent ends (98) are substantially parallel with the unbent middle part (96) , whereby a good electric contact between the staples and the aluminium foil is established. 13. The apparatus according to claim 10, characterized in that the outer edges (60) of the open screening shell (31) disposed in the open casing (12) are bent over the edges (61) of the casing so as to screen the edge areas of the casing. 14. The apparatus according to claim 13, characterized in that in front of the casing (12) there is fitted a front part or a mask (14) , the edge areas (20) of which are covered by metal foil (46) so that an electric contact is established between the metal foil and the bent edges (60, 62) of the screening shell. 15. The apparatus according to claim 10, characterized in that in front of the casing (12) there is fitted a front part or a mask (14) , the edge areas (20) of which are covered by a metal foil (46) and that members, such as springs (48) , which bring about electric contact between the screening shell and the metal foil of the front part are disposed in the casing. 16. The apparatus according to claim 10, characterized in that the screening shell is tailor-made substantially from one straight-sided elongated metal foil blank and one or several substantially straight-sided, oblique-angled metal foil blanks. 17. The apparatus according to claim 10, characterized in that the screening shell is formed by bending and/or folding a metal foil blank and that the folds are formed at the corners of the screening shell.

Inventors: AURANEN JUHANI, AURANEN, JUHANI
Applicants: AURANEN JUHANI, SALOPLAST OY, AURANEN, JUHANI
Application year: 1995
Main classification: G12B17
IPC codes: H04N5, H05K9