Membrane keyboard blockout apparatus

Abstract: A keyboard (1) has an array of flexible keys (8, 10) in apertures (4, 6) arranged in a grid (50) forming the keyboard and a cover plate (30) dimensioned to span a flexible key member and to provide a tight fit within an aperture defining a key. The cover plate has a thickness providing a substantially inflexible configuration in response to normal operator manipulation and a plurality of corner support pedestals (32, 34, 36, 38) contacting respective corners of the flexible key when the cover plate is inserted in a key aperture. Thus, the pedestals provide a support between the cover plate and the flexible key member at the edges of the key member to preclude, in combination with the inflexible structural characteristic of the cover, an actuation of the flexible key member under the cover.

Description: BACKGROUND OF THE INVENTION The present invention relates to membrane switches. More specifically, the invention is directed to a membrane switch keyboard apparatus. DESCRIPTION OF THE PRIOR ART Membrane switch keyboards are well-known in the art as shown in U.S. Patent Nos. 3,860,771; 3,995,126 and 4,423,294. Membrane keyboard devices include an array of elastic bubble members corresponding to an array of individual switching units. The bubble members are actuated or deformed by the touch of an operator to cause the selected bubble member to be deflected whereby to provide a deflection of an associated flexible conductive member to provide a conductive path between adjacent first and second electrode members While such membrane keyboard devices have found great acceptance, particularly in the field of computer keyboards, by virtue of the feel of the keyboard during actuation which approximates that of a conventional switch by providing tactile feedback to the operator, they have also inherently exhibited a lack of security by a failure to provide a means for preventing an operation of certain ones of the bubble members by the operator. Thus, if the keyboard is to be limited in certain applications to particular functions, it would be desirable to provide a means to lock out certain ones of the bubble member keys to prevent an operator from either inadvertently or deliberately actuating incorrect keyboard switches and to simplify a keyboard for a particular application. SUMMARY OF THE INVENTION An object of the present invention is to provide an improved membrane keyboard lockout apparatus. In accomplishing this and other objects, there has been provided, in accordance with the present invention, a membrane keyboard utilizing key members accessed for operation through respective keyboard frame apertures characterised by a block-out apparatus comprising a cover means comprising a cover plate dimensioned to span a key member of the keyboard, to tightly fit within a respective one of the apertures providing access to the key member and to provide a substantially inflexible structure and a plurality of support pedestals located on a common surface of said cover plate and arranged to contact adjacent peripheral areas of a key member upon a completed insertion of said cover plate in a respective one of the apertures to prevent further axial motion of said cover plate within the aperture whereby operation of the associated key member is precluded. BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the present invention may be had when the following detailed description is read in connection with the accompanying drawings in which: Figure 1 is a cross-sectional illustration of a membrane keyboard apparatus, Figure 2 is a top view of a blockout cover for a membrane keyboard apparatus according to the present invention, Figure 3 is a cross-sectional illustration of the blockout cover shown in Figure 2 taken along lines 3-3, Figure 4 is a cross-sectional illustration of the blockout cover shown in Figures 2 and 3 in an inserted position in the keyboard apparatus shown in Figure 1 and Figure 5 is an alternate embodiment of the blockout cover of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figure 1 in more detail, there is shown an example of a keyboard apparatus 1 having a frame 2 of a high impact plastic material, e.g., polypropylene, polystyrene, etc., such plastics being well-known in the art. The frame 2 is provided with a plurality of apertures 4, 6 of which two are shown in Figure 1, forming a grid or matrix defining locations of keyboard switch elements. Within each aperture there is located a flexible semi-circular plastic bubble member having a top surface below the face of the frame 2. For example, a bubble member 8 is located in aperture 4 and a bubble member 10 is located in aperture 6. The flexible members 8, 10 may be of any suitable thermoplastic or thermosetting resilient and flexible plastic material, e.g. polypropylene, polyethelene, polyurethane, etc. The peripheral edges of each of the bubble members are captured beneath recesses in the frame 2 surrounding respective ones of the apertures. Thus, bubble member 8 has its peripheral edge extending beneath a recess or step 12 in the frame 2 surrounding the aperture 4. The following description is limited to a typical key element, e.g. bubble member 8. A flexible electrically conductive layer is located on an inner surface of each of the bubble members to provide an electrically conductive path upon an actuation of a switch element. Such flexible conductive layers are also well-known in the art. Thus, a first bubble member 8 has a flexible conductive layer 14 on an inner surface thereof arranged in contact with the bubble member 8 and movable therewith. Each bubble member is held against its respective recess by an electrically insulating ring, e.g. ring 16, arranged to contact bubble member 8. A pair of electrically conductive layers are spaced apart within the switch element and are arranged to be bridged by the flexible conductive layer upon an actuation of the bubble member. For example, a pair of electrically conductive elements 18, 20 are spaced from flexible conductive layer 14 attached to bubble member 8. The outer edges of the layers 18, 20 are arranged to contact the ring 16. A pair of electrically conductive pins 22, 24 are connected to respective ones of the conductive layers 18, 20. The conductive layers 18, 20 are supported by an electrically non-conductive bottom cover 26 through which the conductive pins 22, 24 extend. While only one of the switch elements has been described in detail, it should be noted that all of the switch elements in a keyboard have substantially the same structure. In operation, when the bubble member 8 is actuated by the fingertip of an operator pressing on the outer surface of the bubble member 8, the bubble 8 provides a snap action to bring the flexible conductive layer 14 in contact with the conductive elements 18, 20 to provide a switch operation. In Figure 2, there is shown a blockout cover according to the present invention for use with the membrane keyboard shown in Figure 1. The blockout cover includes a plate 30 of electrically insulating rigid material, e.g. the same material as the frame 2, having a plurality, e.g. four, of support legs or pedestals 32, 34, 36 and 38 arranged at the respective corners of plate 30. A plurality of projections or ribs, e.g. four, 40, 42, 44 and 46 are also arranged to extend outwardly from a peripheral surface of the plate 30 at respective corners of the plate 30. A cross-sectional illustration of the cover shown in Figure 2 taken along lines 3-3 is shown in Figure 3. The plate 30 is arranged to have a thickness which makes the plate 30 structurally stiff and substantially non-resilient under normal operating conditions effected by an operator, i.e. the plate 30 would be negligibly deflected. The thickness of the plate 30 would also preferably be effective to locate an outer surface of the plate 30 flush with an outer surface of the frame 2 when the plate 30 is inserted in an aperture in the frame 2 as described hereinafter. The width of the plate 30 is dimensioned to fit within the aperture, e.g. apertures 4, 6 of the keyboard 1 shown in Figure 1. The projections 40, 42, 44 and 46 "crush" or deform upon an insertion of the plate 30 in an aperture to provide an interference fit with the wall of the aperture to retain the plate 30 very tightly in the aperture. While the plate 30 has been illustrated in a substantially square or rectangular configuration, other configurations matching the apertures may be used. The legs, or pedestals, 32, 34, 36 and 38 are arranged to contact a peripheral edge of the bubble member, e.g. bubble member 8 in an inserted state of a blockout cover in an aperture as shown in the cross-sectional illustration in Figure 4. As may be seen from this illustration, the pedestals 32, 24, 36 and 38 contact the peripheral edge of the bubble member 8 and are supported thereby. Preferably, the pedestals 32, 34, 36 and 38 are arranged to support the plate 30 out of contact with the bubble member 8 to eliminate any possibility of affording a means for operating the respective keyboard switch. Accordingly, the pedestals 32, 24, 36 and 38 prevent further axial motion of the cover plate 30 in the aperture 4 after a completed insertion of the cover plate 30 in the aperture 4. Concurrently, the projections 40, 42, 44, 46 provide an interference fit with an inner peripheral wall of the aperture 4. The thickness of the plate 30 and the restraint produced by the pedestals 32, 34, 36 and 38 preclude an operator from normally depressing the bubble member 8 to provide a switching operation by preventing further axial motion of the cover plate 30. Thus, the plate 30 forms a blockout for selected ones of the keyboard switch elements. The projections 40, 42, 44 and 46 serve to retain the plate 30 very tightly in the aperture and to prevent an easy withdrawal of the blockout cover from the aperture. In Figure 5, there is shown an alternate embodiment of the present invention which may be used with a keyboard wherein an outer surface of the bubble member 8A extends flush with an outer surface of the frame 2A at a frame aperture 6A. Alternatively, this embodiment may also be used with a keyboard wherein the walls of the apertures are slanted, i.e. not vertical, and the plate 30 would not be properly retained in the aperture. In this embodiment, a cover grid 50 is provided with an aperture 52 for accommodating the plate 30 and is suitably attached, e.g. adhesive bonded by adhesive layer 54, to the frame 2A. The operation of the plate 30 with respect to the cover grid 50 is similar to that described above with respect to the keyboard shown in Figure 1. Accordingly, there has been provided, in accordance with the present invention, an improved membrane keyboard blockout apparatus.

Claims: A membrane keyboard (1) utilizing key members (8, 10) accessed for operation through respective keyboard frame apertures (4, 6) characterised by a blockout apparatus comprising a cover means comprising a cover plate (30) dimensioned to span a key member of the keyboard, to tightly fit within a respective one of the apertures providing access to the key member and to provide a substantially inflexible structure and a plurality of support pedestals (32, 34, 36, 38) located on a common surface of said cover plate and arranged to contact adjacent peripheral areas of a key member upon a completed insertion of said cover plate in a respective one of the apertures to prevent further axial motion of said cover plate within the aperture whereby operation of the associated key member is precluded. A keyboard according to Claim 1 characterised in that said cover means includes at least one outwardly extending projection (40) on a peripheral edge on said plate and arranged to provide an interference fit between said plate and a wall of an associated one of the apertures. A keyboard according to Claim 1 or 2 characterised in that four of said support pedestals are provided on said cover plate. A keyboard according to any one of the preceding claims characterised in that said plate is substantially rectangular and said pedestals are located on respective corners of said plate. A keyboard according to any one of Claims 2 to 4 characterised in that four of said projections are provided on said cover plate. A keyboard according to Claim 5 characterised in that said plate is substantially rectangular and said projections are located on a periphery of said plate at respective corners of said plate. A keyboard according to any one of the preceding Claims characterised in that said cover plate is made of the same material as the keyboard frame containing the apertures. A keyboard according to any one of the preceding Claims characterised in that said support pedestals are dimensioned to engage the aperture wall to support said cover plate flush with an adjacent surface of the keyboard surrounding the apertures. A keyboard according to any one of the preceding Claims characterised in that said cover means includes a grid plate (50) having a plurality of apertures therein corresponding in size and location to the apertures in the keyboard and attaching means (54) for retaining said grid plate on said keyboard with said apertures in said grid plate axially aligned with the apertures in the keyboard with each of said apertures in said grid plate being dimensioned to accept said cover plate whereby said cover plate is tightly retained in a respective one of said apertures in said grid plate and said support pedestals extend to peripherally contact the respective key member while maintaining said plate in said grid plate and spaced from a respective key member. A keyboard according to Claim 9 characterised in that said grid plate is made of the same material as said cover plate. A keyboard according to Claim 10 characterised in that said cover plate is made of the same material as the keyboard surface defining the apertures.

Inventors: SCHMITZ ROBERT, SCHMITZ, ROBERT
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1989
Main classification: H01H13
IPC codes: H01H13