Abstract:
A switch useful for, inter alia, a touch type keyboard or keypad which may be used for a personal computer or the like in a substantially waterproof form while being relatively inexpensive to manufacture.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 10/596,714 filed Dec. 6, 2004, which is a National Stage Application filed under 371 from International Application No. PCT/IB2004/004020 filed Dec. 6, 2004, which claims priority to GB 0329985.6 filed Dec. 24, 2003, all of which are hereby incorporated by reference. 
    
    
     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     This invention relates to keyboards, keypads, and the like, and more particularly, to a switch for a touchtype keyboard or keypad, for use with, for example, a personal computer or the like. 
     In essence, a keyboard for a computer comprises a series of switches connected to a microprocessor that monitors the state of each switch and initiates a specific response to a change in that state. 
     In a typical keyboard, a key matrix is provided which comprises a grid of circuits underneath the keys, whereby each circuit is broken at the point below a specific key. Pressing the key bridges the gap in the circuit, allowing a tiny amount of current to flow through. The processor monitors the key matrix for signs of continuity at any point on the grid. When it finds a circuit that is closed, it compares the location of that circuit on the key matrix to a character map in its ROM. The character map is basically a comparison chart for the processor that tells it what the key at x, y coordinates in the key matrix represents. 
     Keyboards rely on switches that cause a change in the current flowing through the circuits in the keyboard. When the key presses the keyswitch against the circuit, there is usually a small amount of vibration between the surfaces, known as bounce. The processor in the keyboard recognizes that this very rapid switching on an off is not caused by repeated pressing of the same key, and filters such tiny fluctuations out of the signal and treats it as a single key press. 
     Keyboards use a variety of switch technologies, although it is interesting to note that a user tends to like to have some audible and tactile response when typing on the keyboard. Such different technologies include: rubber dome mechanical, capacitive non-mechanical, metal contact mechanical, membrane mechanical and foam element mechanical. 
     Probably the most popular switch technology in use today is rubber dome. In such keyboards, each key sits over a small, flexible rubber dome with a hard carbon centre. 
     When the key is pressed, a plunger in the bottom of the key pushes down against the dome. This causes the carbon centre to push down also, until it presses against the hard flat surface beneath the key matrix. As long as the key is held, the carbon centre completes the circuit for that portion of the matrix. When the key is released, the rubber dome springs back to its original shape, forcing the key back up to its rest position. 
     Rubber dome switch keyboards are inexpensive, have relatively good tactile response and are fairly resistant to spills and corrosion because of the rubber layer covering the key matrix. Membrane switches are very similar in operation to rubber dome keyboards. A membrane keyboard does not, however, have separate keys. Instead, it has a single rubber sheet with bulges for each key, and are often used in devices designed for heavy industrial use or extreme conditions. However, because they offer little or no tactile response and can be somewhat difficult to manipulate, these keyboards are seldom found on normal computer systems. Furthermore, the membrane cannot be used if even one of the bulges is defective, and each pad molding is specific to a particular keyboard design. 
     Waterproofing a keypad suitable for machine controls by clamping the periphery of the elastomeric pad between the top and bottom shells of the keypad has been proposed in the past. However, such keypads do not have, nor are they intended to have, a touch type feel, and there has been no disclosure or suggestion as to how such proposals could be practically applied to much larger, high volume, touch type keyboards. 
     Although, as stated above, rubber dome switch keyboards are relatively fairly resistant to spills and corrosion because of the rubber layer covering the key matrix, they are not waterproof, and a keyboard will, therefore malfunction due to a short circuit if liquid enters the keyboard. Nevertheless, the rubber dome keyboards remain one of the most popular types of keyboard because of their relatively good tactile response. 
     In an attempt to provide a waterproof dome switch keyboard, some arrangements have been proposed. However, such arrangements tend to a have a complex structure, are costly to manufacture and, in any event, are still not completely waterproof, such that liquid can still enter and cause a short circuit. 
     For example, in the arrangement disclosed in U.S. Pat. No. 4,705,925 use is made of individual domes. Each dome is secured in a keycap housing to facilitate handling and assembly. The base of each dome in an assembly is pressed against the membrane to exclude dust, but by doing so affects the feel of the keys because of air pressure inside the dome. Such sealing does not, in any event, waterproof the keyboard. U.S. Pat. No. 4,021,630 describes a switch for a surgical knife in which a dome is clamped between a housing and the membrane to effect a waterproof seal, but it is not intended to have a touch type feel, and would not be practically suitable for use in a computer keyboard or the like. 
     It is therefore an object of the present invention to provide a switch for a keyboard, which is completely waterproof, whilst also being relatively simple in construction and inexpensive to manufacture. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a switch comprising a generally tubular housing, and a dome member having an annular rib extending from the base of said dome member, the dome member being disposed within said housing and being elastically deformable in use, said housing having an inner annular groove for receiving said annular rib of said dome member, wherein said housing is provided with a plurality of discrete tabs disposed circumferentially around an end thereof, said tabs being movable from an open configuration in which said dome member can be introduced into said housing, and a sealed configuration in which they substantially cover the base of said dome member so as to clamp said annular rib of said dome member within said annular groove and create a fluid-tight seal between said housing and said dome member. 
     In accordance with a second aspect of the present invention, there is provided a switch comprising a generally tubular housing, and a dome member having an annular rib extending from the base of said dome member, the dome member being disposed within said housing and being elastically deformable in use, said housing having an inner annular groove for receiving said annular rib of said dome member, wherein said housing is provided with clamping means which are movable from an open configuration in which said dome member can be introduced into said housing, and a sealed configuration in which they substantially cover the base of said dome member so as to clamp said annular rib of said dome member within said annular groove and create a fluid-tight seal between said housing and said dome member, at least a portion of the dome member being received within said housing with sufficient clearance such that it does not contact the inner wall of the housing when it is deformed in use. 
     In a preferred embodiment, the tabs are provided substantially all of the way around the circumference of an end of the housing, and are beneficially permanently deformable from the open configuration to the sealed configuration so as to form an annular flange covering the base of the dome member. Such deformation may be effected by means of heat and/or force. Preferably, in the sealed configuration, the tabs are substantially at right-angles to the longitudinal side wall of the housing, and substantially flush with the end thereof, such that excessive deformation of the dome portion is not required to make the desired contact. 
     In a preferred embodiment, the inside of the housing has a wider portion shaped and configured to receive the dome member and a narrower portion leading to an aperture, a key cap being slidably engaged therein and arranged to selectively deform and release the dome member, when in use. One or more apertures or slots are preferably provided in said narrower portion of the housing to allow any moisture which enters the housing beneath the keycap to escape. The annular groove is beneficially provided with a relatively sharp edge which corresponds to an intersection between said annular rib and the remainder of the dome member. 
     The present invention also extends to a keyboard including a plurality of switches as defined in accordance with the first and/or second aspects of the present invention. In this case, the keyboard preferably comprises a board member defining a plurality of such switches connected together or formed integrally with each other. 
     In accordance with a third aspect of the present invention, there is provided a dome member for use in a switch, said dome member being elastically deformable in use and having an annular rib extending from the base thereof, said annular rib being of a thickness greater than that of the side walls of said dome member, wherein generally V-shaped groove defines the intersection between said annular rib and said side walls of said dome member. 
     Preferably the edge of the annular groove of the housing is disposed within the V-shaped groove of the dome member, at the apex thereof, so as to facilitate the fluid-tight sealing between the apex thereof, so as to facilitate the fluid-tight sealing between the housing and the dome member. 
     The first aspect of the present invention further extends to a method of manufacturing a switch, comprising providing a generally tubular housing, providing a dome member having an annular rib extending from the base of said dome member within said housing, said dome member being elastically deformable in use, said housing having an inner annular groove for receiving said annular rib of said dome member, wherein said housing is provided with a plurality of discrete tabs disposed circumferentially around an end thereof, the method further comprising moving said tabs from an open configuration in which said dome member is introduced into said housing, and a sealed configuration in which they substantially cover the base of said dome member so as to clamp said annular rib of said dome member within said annular groove and create a fluid-tight seal between said housing and said dome member. 
     The second aspect of the present invention further extends to a method of manufacturing a switch, comprising providing a generally tubular housing, and providing a dome member having an annular rib extending from the base of said dome member within said housing, said dome member being elastically deformable in use, said housing having an inner annular groove for receiving said annular rib of said dome member, wherein said housing is provided with clamping means, the method further comprising moving said clamping means from an open configuration in which said dome member is introduced into said housing, and a sealed configuration in which they substantially cover the base of said dome member so as to clamp said annular rib of said dome member within said annular groove and create a fluid-tight seal between said housing and said dome member, at least a portion of the dome member being received within said housing with sufficient clearance such that it does not contact the inner wall of the housing when it is deformed in use. 
     These and other aspects of the present invention will be apparent from, and elucidated with reference to the embodiment described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
         FIG. 1  is a front view of a switch housing according to an exemplary embodiment of the present invention; 
         FIG. 2  is a plan view of the switch housing of  FIG. 1 ; 
         FIG. 3  is a plan view of a switch according to an exemplary embodiment of the present invention; 
         FIG. 4  is a schematic cross-sectional view of the switch housing of  FIG. 1 ; 
         FIG. 5  is a schematic cross-sectional view of the switch of  FIG. 3 ; 
         FIG. 6  is a schematic cross-sectional view of a dome member for use in a switch according to an exemplary embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of a switch according to an exemplary embodiment of the present invention, including a keycap; and 
         FIG. 8  is a perspective partial view of the upper surface of the upper shell of a keyboard according to an exemplary embodiment of the present invention, illustrating the aperture in the side wall of the narrower portion of the housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 ,  2  and  4  of the drawings, a switch according to an exemplary embodiment of the present invention comprises a generally tubular housing  10  of a rigid plastics material. A plurality of discrete tabs  12  (or ‘petals’) are circumferentially disposed, in side-by-side relation, around an end of the housing  10 . The housing  10  defines a channel  14 , having a wider, generally cup-shaped portion  16  for receiving an elastomeric dome member and a narrower portion  18 . An annular groove  20 , with a relatively sharp edge  22  is provided within the housing in the wider portion  16  thereof. 
     Referring to  FIGS. 3 and 5  of the drawings, during assembly, an elastomeric dome member  24  is inserted in the wider portion  16  of the recess  14  within the housing. Referring in addition to  FIG. 6  of the drawings, the dome member  24  is provided with an annular rib  26  around its base, the rib  26  having a greater thickness than that of the rest of the dome  24 . A contact member  28  is provided generally centrally on the upper, inner surface of the dome member  24 . 
     Referring back to  FIGS. 3 and 5 , when the dome member  24  is correctly inserted within the housing  10 , the annular rib  26  thereof sits within the annular groove  20  within the housing  10 , with the sharp edge  22  being located at the intersection between the rib  26  and the rest of the dome member  24 . Next, a downward force is provided on the tabs  12 , causing them to ‘fold’ down over the base of the dome member  24 , such that they are substantially at right-angles to the longitudinal sidewall of the housing  10 , and substantially flush with the edge portion  29  thereof. Optionally, heat may also be applied to the tabs  12 , causing them to at least partially soften and melt together, to form a single, substantially integral, flange completely covering the annular rib  26  at the base of the dome member  24 , so as to create a fluid-tight seal between the housing  10  and the dome member  24 . 
     The end of the housing  10  opposite to that having the tabs  12  is provided with an aperture  30  with which the stem  32  of a keycap  34  is slidably engaged, the stem  32  being communicably coupled with the upper surface of the dome member  24 . As shown in  FIG. 8 , one or more apertures  36  or slots are preferably provided in order to allow any moisture which enters the housing beneath the keycap  34  to escape. 
     In use, when a user presses the key, the stem  32  pushes the dome member  24  downwards, causing it be deformed, and causing the contact member  28  to move down wards and make complete the desired electrical circuit. When the key is released, the dome member  24  returns to its original configuration and the electrical circuit is broken. It will be appreciated that, in order to preserve the lifetime of the dome, and ensure correct operation thereof, the wider portion  16  of the channel  14  defining the recess for receiving the dome member  24  is shaped and configured so as to provide sufficient clearance such that the dome member  24  does not contact the inner wall of the housing  10  when it is deformed in use. 
     A keyboard (not shown) employing such switches comprises a single board in which a plurality of housings are integrally formed in the desired configuration. Dome members are placed in each of the housings and the respective tabs are deformed to create fluid-tight seals between each of the housings and the respective dome members. The board is then placed within top and bottom shell parts, together with a key matrix, and respective keycaps are inserted into the apertures in the housings to complete the keyboard. A fluid-tight seal is provided all around the periphery between the top and bottom shell parts. In addition, a battery compartment may be provided in the bottom shell part, which compartment is preferably also provided with a fluid-tight sealing means. 
     It should be noted that the above-mentioned embodiment illustrates rather than limits the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word “comprising” and “comprises”, and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
     Thus, although there have been described particular embodiments of the present invention of a new and useful Keyboards it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.