Protective screen for a visual display device

Abstract: A protective screen (15) for a visual display unit -VDU- (16) comprises a filter layer which is operative to protect the operator from electrostatic and electromagnetic fields and from residual radiation of a cathode ray tube -CRT- (18) of the VDU. The VDU comprises a body structure (20) for the CRT and the screen comprises a support frame (21) for the filter layer, an intermediate support (22) between the frame (21) and the body structure (20) of the VDU and a pair of fixing plates (37) which are adjustable both front to back and angularly, for fixing the intermediate support (22) to the upper portion of the body structure (20) independently of the specific form of the body structure. The frame (21) of the screen is also pivoted (26) to the intermediate support (22) to permit the filter layer to be disposed in front of the display surface of the CRT (18) or be swung up to expose the CRT screen.

Description: The present invention relates to a protective screen for a visual display unit with a cathode ray tube having a display surface and a body structure for the cathode ray tube. The screen compromises a filter layer which is operative for protection purposes, a support frame for the filter layer, fixing means for fixing the screen to the body structure and an intermediate member linking the fixing means and the support frame and enabling a pivot movement of the frame between a position covering the VDU display surface and a position out of the vicinity of the display surface. Cathode ray tubes of more modern display units have levels of electrostatic and electromagnetic fields and of other radiations which are generally considered not to be harmful. In order to lower the levels of the above-mentioned fields and residual radiations, it may be appropriate or it may be required by some health regulations to dispose in front of the display screen a protective screen which performs a filter function in regard to the electrostatic and electromagnetic fields and the residual radiation emitted by the cathode ray tube. In addition, when VDU displays are viewed in daylight or particular other light conditions they may present reflections and glare which can be tiring for the operator. It may thus be appropriate or it may be required by some health regulations to dispose in front of the display screen an anti-reflection screen. GB-A-2 067 380, on which the preamble of claim 1 of this application is based, relates to an anti-reflection screen of this latter type, comprising a fine mesh of nylon supported by a flat framework. The screen may be attached to the structure of the cathode ray tube by means of a fastener carrying self-adhesive tape. The screen itself is linked to the fastener by two bendable metal strips which allow the screen to pivot upwards, away from and out of the vicinity of the VDU display. This screen has the disadvantage that it cannot be fastened to body structures of different shape. Moreover it is not suitable for multi-layer screens of heavy weight such as the protective screen necessary for optimizing filtering of electromagnetic fields and reflections. US-A-4,468,702 relates to a protective screen for a cathode ray tube (CRT) formed by a fabric mesh of conducting and non-conducting fibers affixed to a frame. The mesh is electrically connected to a grounding wire by means of a conductive glue. The screen is positioned adjacent to and touching the display surface of the CRT, although no method for so mounting the screen is described. US-A-3,952,152 describes a protective screen for a CRT which is permanently mounted between the body structure and the display surface of a CRT. This construction is expensive since it adds the cost of the screen to the cost of the display unit, even when the screen is not strictly necessary. In addition this construction does not permit the protective screen to be removed from the display screen for cleaning the screen or to provide a better view of the images on the cathode ray tube. US 4712870 describes a Fresnel lens and filter supported in front of a VDU screen by means of an adjustable screw-clamp. The screw-clamp is fastened to the upper surface of the VDU housing and a bar extending from the combined Fresnel lens and filter is slidably mounted in the clamp. This mounting arrangement uses a rather long mounting bar and so allows the lens to be supported at some distance from the VDU screen and positioned in the line-of-sight of the VDU operator so as to magnify the image on the screen. The lens may need to be mounted rather above the height of the VDU screen to achieve this, which is enabled by pivoting the screw-clamp. The mounting arrangement is thus flexible but complicated, the screw-clamp alone comprising four separate components. The invention provides a protective screen for a VDU as defined in the appendant independent claim. Preferred features of the invention are defined in dependent subclaims. Advantageously, a protective screen according to the invention can be easily fixed to VDU body structures of different shapes and can be moved away from the VDU display to permit direct viewing of the VDU display. The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of the screen according to the invention in the position of use, Figure 2 is a side view of part of the screen shown in Figures 1, Figure 3 shows some sectioned details of the screen shown in Figure 2, on an enlarged scale, Figure 4 is a plan view of part of some details of the screen shown in Figure 1, on an enlarged scale, Figure 5 shows details from Figure 4 in section taken along line V-V and on an enlarged scale, Figure 6 shows the details illustrated in Figure 5, in a second working position, Figure 7 shows other details from Figure 1 in section taken along line VII-VII and on an enlarged scale, Figure 8 shows further details from the screen illustrated in Figure 1, in section taken along line VIII-VIII in Figure 4, Figure 9 shows other details from Figure 1, in section taken along line IX-IX and on an enlarged scale, and Figure 10 is a front view of part of the structure shown in Figure 9. Referring to Figures 1, 2 and 3, a protective screen 15 for a display unit (VDU) 16 comprises a filter layer 17 which is operative to provide the protection effect. The display unit 16 of known type is indicated in dash-dotted lines in the drawings and comprises cathode ray tube 18 having a display surface 19 and a body structure 20 for the cathode ray tube 18. In accordance with the invention, the screen 15 comprises a support frame 21 for the filter layer 17, an intermediate support 22, adjustable fixing means 24 for fixing the intermediate support 22 to the upper portion of the body structure 20 and pivot means 26 between the frame 21 and the intermediate support 22 for pivoting the filter layer 17 with respect to the display surface 19 of the cathode ray tube 18 when the support 22 is fixed to the body structure 20. The frame 21 comprises two half shell portions 28 and 29 (see Figures 3 and 7) of plastics material which are provided with complementary coupling elements 31 and 32 respectively for interengagingly locking the shell portions 28 and 29 together, and ribs 30 on the shell portion 28 for correct positioning of the filter layer 17 between the two shell portions 28 and 29. The complementary elements 31 and 32 are introduced and locked relative to each other by means of a simple pressure. The two shell portions 28 and 29 are each of a C-shaped section. The outside edges of the shell portions 28 and 29 are in mutual contact and their inside edges are resiliently urged against the filter layer 17 in such a way as to compensate for any dimensional differences in the filter layer 17. In use the intermediate support 22 (see Figures 1, 3 and 4) is substantially centered with respect to the screen 15 and the body structure 20 of the VDU 16 and extends over a fraction, for example half, of the maximum width of the screen 15. The intermediate support 22 has an axis of symmetry 34 and a first adjustable fixing means 24 comprising a guide 36 extending front to back. On the lower portion of the support 22, parallel to the axis 34, is a rectangular plate member 37 which is capable of being fixed to the body structure 20 of the VDU 16, for example by means of a double-sided adhesive pad 38. The plate member 37 is provided with a rib 39 (see Figure 5) extending front to back and carrying a cylindrical body 54 which can both slide in the guide 36, with freedom of front-to-back translatory movement with respect to the support 22, and freedom to turn about the axis of the cylinder (compare Figs. 5 and 6) in this way the screen 15 is capable of being disposed at the optimum distance from the surface 19 of the CRT 18, at a position corresponding to an optimised position for fixing of the plate member 37 to the body structure 20. The plate member 37 is disposed to the left side of the axis of symmetry 34 of the support 22. The fixing means 24 are completed by a second plate member 42 which is identical to the plate member 37 and which is disposed symmetrically to the plate member 37, with respect to the transverse axis of symmetry 34 of the support 22, and can also be fixed to the body structure 20 by means of a double-sided adhesive pad 38. The plate member 42 also comprises a rib 39 and a cylindrical body 54 by means of which it is slidable in a guide 43 on the support 22, which is identical to the guide 36 and which is disposed symmetrically to the guide 36 with respect to the axis 34. The cylindrical bodies 54 of the plate members 37 and 42, together with the guides 36 and 43, form cylindrical coupling joints as indicated at 46 and 47 (see Figure 5) which allow the plate members 37 and 42 rotational freedom with respect to the intermediate support 22. That makes it possible to adjust the angular positions of the plate members to the particular shape of that part of the body structure of the VDU 16 to which the plate members are to be fixed, as can be seen in Figures 5 and 6. In Figures 5 and 6, the body structures 20 have different curvatures. The guides 36 and 43 each comprise a central rib 48 which is parallel to the axis 34 and which projects from the lower portion of the support 22 and pairs of side flanges 51 and 52 which are parallel to the rib 48 and which, together with the terminal portion of the rib 48, define a corresponding cylindrical seat 53. Each coupling joint 46 and 47 comprises the cylindrical seat 53 of the support 22 and the cylindrical body 54 of the respective plate members 37 and 42. Each cylindrical body 54 is thus capable of sliding and rotating between the corresponding limbs 51 and 52 with freedom for translatory and rotational movement with respect to the intermediate support 22. The side flanges 51 and 52 are each provided with a projection 56 which defines a constriction 57 for the cylindrical body 54. The flanges 51 and 52 are also capable of resiliently yielding to permit each cylindrical body 54 to be snapped into position and removed therefrom by way of the constriction 57 of the flanges 51 and 52. The two ribs 48 are each toothed (58) along their length. A corresponding tooth 59 on each cylindrical body 54 is capable of co-operating with the teeth 58 with an interference fit, for the purposes of locking the plate members 37 and 42 in the desired position. Manual movement of the support 22 in a transverse direction will cause the teeth 58 to be ridden over, resulting in positioning in incremental steps of the support 22. On the other hand, the interengagement of the teeth 59 with the teeth 58 does not impede the rotary movement of the plate members 37 and 42 with respect to the support 22 and the dimensions of the teeth 59 are such as to guarantee coupling to the teeth 58 in all possible angular positions of the two plate members. The frame 21 (see Figure 1) is defined by four sides, to give a rectangular shape, in which the upper side and the lower side are longer than the other two sides when the screen 15 is mounted on the VDU 16. The upper side of the frame 21 comprises two lugs 61 and 62 which are provided on the outside shell portion 28. The two lugs 61 and 62 project upwardly from the upper side and with respect to the upper side of the inner shell portion 29 and define a rectangular space 63 in which the intermediate support 22 is housed. The support 22 (see Figure 3) comprises a plate of substantially parallelepipedic shape and which is downwardly hollow and which is defined by an upper plate 66, a pair of side walls 67 and a pair of front and rear walls 68. The pivot means 26 comprise two pairs of pivot seats 69 and corresponding pins 70 which are interposed between the side walls 67 of the support 22 and the projecting lugs 61 and 62 of the frame 21. A friction ring 71 (see Figure 8) of resiliently yielding material, for example rubber, is forced between each wall 67 of the support 22 and the projecting lug 61,62 of the frame 21 to permit the filter layer 17 to rotate with respect to the display surface of the CRT 18 in a damped fashion (see Figure 2). In addition the frame 21 can assume a stable position affording total access to the surface 19 by virtue of a rotary movement of more than 180°, in which an upper edge 72 of the shell portion 28 of the frame 21, in the space 63, is arrested against the upper plate 66 of the support 22 in the position shown in dotted lines. In use the filter screen 17 remains, under the force of gravity, in a substantially vertical position, with an upper edge 73 (see Figure 3) of the shell portion 29 arrested against a vertically downwardly projecting limb 74 of the upper plate 66 of the support 22. Finally a damping block 75 (see Figure 2), for example of rubber, is disposed on the lower edge of the shell portion 29 and prevents damage to the screen 15 and the VDU 16 in the event that the filter layer 17 is moved violently towards the surface 19. The filter layer 17 which is known per se is transparent and has two metallised and transparent surface layers. The frame 21 is of insulating material and comprises a mounting 76 for a socket 77 (see Figure 9) of conductive material, provided with two resilient limbs 78 in electrical contact with the layer or the metallised layers of the filter layer 17. The socket 77 comprises a cylindrical opening 79 which is coaxial with an opening 81 of the mounting 76 to permit the introduction of a plug 82 into the opening 79, and in turn is capable of permitting an earthing connection for the filter layer 17 by means of a cable 83. The above-described protective screen is capable of being easily fixed to the body structure 20 of the VDU 16 and ensures that the filter layer 17 can be easily removed by rotary movement of the frame 21 about the pins 70 to the stable position shown in dotted lines in Figure 2.

Claims: A protective screen for a visual display unit (16) comprising a cathode ray tube (18) having a display surface (19) and a body structure (20), said screen comprising; a filter layer (17) which is operative for protection purposes; a support frame (21) for the filter layer; fixing means (37,42,38) for being fixed to the body structure; and an intermediate member (22) linking the fixing means and the support frame and enabling a pivot movement of said frame away from and out of the vicinity of the display surface (19); characterised by; adjustment means (46,47) for adjusting the position of the screen relative to the fixing means, comprising two coupling bodies (54) on said fixing means slidingly engaged with two corresponding guide members (36,43) on said intermediate member (22), the coupling bodies being slidable within the guide members for a back and forth adjustment of the position of the intermediate member (22) and the protective screen with respect to the display surface (19) when in use, a first of the two guide members being parallel to and laterally spaced from the second of said two guide members. A protective screen according to claim 1, characterised in that said intermediate member (22) is symmetrical about an axis of symmetry (34) and said first and second guide members (36,42) are disposed parallel to and on opposite sides of said axis of symmetry. A protective screen according to claim 1 or 2, characterised in that said fixing means (37,42,38) comprises two plate members (37,42) which can be individually fixed to the body structure (20) and in that said coupling bodies (54,54) can pivot within the guide members (36,43) in a plane parallel to the filter layer to accommodate the angular positions of the plate members (37,42) required for fixing to the body structure (20). A protective screen according to claim 3, characterised in that said coupling bodies project outwardly from said plates. A protective screen according to any of claims 1 to 4, characterised in that each guide member comprises a pair of flanges (51,52) and in that each corresponding coupling body (54) has a cylindrical portion capable of sliding and pivoting within said pair of flanges to permit translatory and rotational movement respectively. A protective screen according to claim 5, characterised in that said flanges (51,52) are resilient to permit snap insertion and removal of the cylindrical portions of each coupling body (54). A protective screen according to any preceding claim, characterised by resilient toothed positioning elements (58,59) between at least one coupling body (54) and the corresponding guide (36,43) for movement in incremental steps as between the intermediate member (22) and the fixing means (37,42,38). A protective screen according to any preceding claim, characterised in that at least one guide member and the corresponding coupling body carry mutually interengable means comprising resilient teeth (58,59) for releasably retaining the coupling body within the guide member in selected translational positions. A protective screen according to claim 5, characterised in that at least one guide member comprises a row of teeth along an edge of a rib extending parallel to said flanges, and the corresponding coupling body comprises a tooth on said cylindrical portion, the tooth extending circumferentially around the cylindrical portion sufficiently far to maintain engagement with said teeth of said guide member in all possible angular positions of the coupling body within the guide member. A protective screen according to any preceding claim, characterised in that said intermediate member (22) is of substantially parallelepipedal shape having an upper portion (66) and side portions (67,67). A protective screen according to claim 10, characterised in that the support frame (21) can pivot on the intermediate member (22) through pivot means (26) comprising two lugs (61,62) projecting from an upper portion of the support frame and spaced apart from each other, engaged with first and second pivotal couplings on the side portions (67,67) of said intermediate member. A protective screen according to claim 10 or 11, characterised in that said upper portion (66) and said side portions (67,67) define a downwardly hollow portion and wherein said first and second guide members (36,43) are located in said hollow portion. A protective screen according to claim 10 or 11, characterised in that said support frame is of rectangular shape with four sides of which one upper side of greater length comprises said two lugs and in which the first and second pivotal couplings are spaced apart a distance substantially equal to about a half of the length of said one upper side of greater length. A protective screen according to any preceding claim, characterised in that said filter layer (17) has at least one conductive surface and said support frame (21) is of insulating material and comprises a housing (81) in which there is provided a socket (77) of conductive material, which socket is in electrical contact with said conductive surface of the filter layer and is housed in said housing to permit a ground connection for said filter layer.

Inventors: SOLERO GIORGIO, SOLERO,GIORGIO
Applicants: BALTEA SPA, BALTEA S.P.A.
Application year: 1989
Main classification: H04N5
IPC codes: H01J29, G06F1, H04N5, G09F9