Abstract:
Individual switch actuators are formed by etching offset grooves in opposite sides of a thin metal plate. The groove on one side of the plate falls just within the groove on the other side of the plate. A web is formed between the adjacent groove walls which provides significant localized flexibility. A discrete contact pad is defined on the inside that is in the plane of the metal plate.

Description:
This application is a continuation, of application Ser. No. 502,925, filed June 10, 1983, now abandoned. 
    
    
     FIELD OF INVENTION 
     This invention relates to a control panel, plate or keyboard which is in the form of a thin metal sheet, different regions of which may be depressed, as by digital pressure, to cause a conductive element to bridge circuit strips of a circuit board. 
     BACKGROUND OF THE INVENTION 
     Known switch control panels are generally of two types, perforate and imperforate. One type has holes through which movable button actuators project. Foreign particles can enter the interior via the through clearance spaces between the holes and the buttons. Such a panel is difficult to clean. The imperforate type utilizes a thin plate that provides an environmental seal with the case. Such a plate is easily cleaned. The thin plate has suitable legends and actuator regions printed or etched on its surface. Digital pressure at the actuator regions causes flexure which, in turn, causes switch members beneath the plate to engage. Since flexure at the point of application of digital pressure produces proportionate flexure at adjacent regions, some means must be provided for discrete mechanical movement to prevent unintended closure of adjacent switches. One method is shown and described in U.S. Pat. No. 4,249,054 issued Feb. 3, 1981 to Sharp Kabushiki Kaisha as assignee. 
     In the Sharp structure, a broad area of a stainless steel cover plate is uniformly etched to provide a flexible membrane. A rubber support sheet is laminated to the membrane. A spacer sheet of electrical insulation material is interposed between the membrane laminate and a circuit board. The circuit board has pairs of contact areas or segments arrayed about the board surface. The spacer sheet has access openings about the pairs of contact segments. A conductive rubber pad carried by the membrane laminate is located at each spacer sheet opening. The spacer sheet is just slightly thicker than the pads. If one actuator area of the stainless steel plate is engaged, only its companion conductive pad protrudes beyond the plane of the spacer sheet to engage the contact segments of the circuit board. Adjacent pads remain slightly recessed within the plane of the insulator sheet. 
     A structure of this type, while entirely operational, requires an extremely thin localized switch actuator for flexibility such as about 0.03 millimeters or 0.012 inches. Metal this thin is easily punctured, and is subject to fatigue failure. 
     In a structure shown and described in U.S. Pat. No. 4,293,754 issued Oct. 6, 1981 to Sharp Kabushiki Kaisha as assignee, discrete motion is accomplished through removal of the material around all but a portion of the pad. This provides discrete motion but has the disadvantage in that openings are formed around the pad that allow liquid and contaminants to enter the switching system. 
     The primary object of the present invention is to provide a simple system utilizing a relatively thick imperforate cover plate in which the material of the cover plate itself serves as the bridging contact element. 
     SUMMARY OF THE INVENTION 
     In order to accomplish the foregoing objective, independent switch actuators are formed by etching a perimetric groove on the outside of the cover plate to define each actuator, and by etching a registering, but just slightly inwardly offset, perimetric groove on the inside of the cover plate. A thin web is thus formed between the adjacent recess walls which provides localized flexibility, all without undue reduction in wall thickness. A contact pad is formed on the inside of the cover plate that is in the plane of the cover plate itself. A simple spacer sheet is interposed between the cover plate and the circuit board on which contact segment pairs are formed. The spacer sheet has holes to expose the contact pad to the corresponding pair of contact segments. No supplemental conductive pads or the like are required to build up a contactor. The resulting structure is simple and effective. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of the invention will be made with reference to the accompanying drawings wherein like numerals designate corresponding parts in the several figures. 
     FIGS. 1 and 2 are top and bottom plan views of a typical metal cover plate incorporating the present invention. 
     FIG. 3 is a bottom plan view of the spacer sheet. 
     FIG. 4 is an enlarged fragmentary transverse sectional view of the switch assembly incorporating the cover plate of FIGS. 1 and 2 and the spacer sheet of FIG. 3. 
     FIG. 5 is a view illustrating a cover plate of a hand calculator and showing circular switch actuators. 
     FIGS. 6 and 7 are enlarged fragmentary sectional views of switch assemblies using, respectively, sets of three and sets of four offset grooves. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description is of the best presently contemplated mode of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for purposes of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. Structural and operational characteristics attributed to forms of the invention first described shall also be attributed to forms later described, unless such characteristics are obviously inapplicable or unless specific exception is made. 
     In FIG. 1 there is illustrated a control panel or cover plate 10 made of stainless steel having a thickness of approximately 0.100 millimeters or 0.040 inches. The panel 10, in the present instance, and by way of example only, is intended to cooperate with a digital processor for controlling the flow of water to a bath spout or other outlet. The panel 10 accordingly provides a number (seventeen in this instance) of discrete switch actuators 12. The actuators, square and rectangular, in the present instance are defined by shallow grooves or channels 14 etched or otherwise formed on the surface of the panel 10. 
     Flexibility of the individual actuators 12 is provided not by the grooves 14 alone, but also by grooves or channels 16 etched on the undersurface of the panel 10 as shown in FIGS. 2 and 4. The grooves 16 on the undersurface generally parallel the grooves 14 on the top, except that they are just inwardly offset therefrom to define a series of square and rectangular contact pads 18 as shown in FIG. 2. Each groove 14 or 16 leaves about 0.250 millimeters or 0.010 inches of metal between its bottom and the opposite surface. The depth of the grooves is thus about two-thirds or three-quarters of the thickness of the cover plate itself. 
     The individual contact pads 18 form elements of a switch assembly shown in FIG. 4. The assembly includes, in addition to the cover plate 10, a circuit board 20 and a spacer sheet 22 made of electrical insulation material. The circuit board 20 has pairs of contact segments 24 arrayed in alignment with the contact pads 18. Holes 26 in the spacer sheet 22 expose the contact segments. 
     As indicated in dotted lines, digital pressure on the actuator 12 causes flexure of the cover plate 10 so that the pad 18 engages and bridges the contact segments 24. 
     The cover plate 10 is significantly flexible at each of the actuators 12 without causing proportionate flexure at the adjacent actuators. Thus, the web 28 between the offset shallow grooves 14 and 16 provides a relatively isolated region of flexure. 
     The cover plate 10 preferably is a unitary structure. However, it may be made as a laminate, or it may be made by plating a conductive layer on the inner side in order to provide the requisite electrical bridging function for the contact segments. Each of the holes 26 in the spacer sheet 22, as shown in FIG. 3, laterally joins an adjacent hole 26 as by a small slot or cut 30. This provides a bleed space to prevent any significant transient buildup of air pressure upon depression of the actuator. The shift of air also assists in isolating the region of cover plate flexure, further ensuring against spurious bridging of adjacent contact segments. 
     DESCRIPTION OF ALTERNATIVE EMBODIMENTS 
     The configuration of individual actuators and the array of actuators is unrestricted. For example, in FIG. 6 there is illustrated a panel 40 for a hand held calculator. In the present instance, the individual actuators are circular and formed by circular grooves 42 on the top and a pair of offset circular grooves 44 and 46 at the bottom. The grooves on the top, in the present instance, are non-contiguous, contrary to the arrangement of the grooves in the form of FIGS. 1 to 5. One of the grooves 46 on the surface opposed to the circuit board (not shown) is inwardly offset in order to obtain the desired flexibility and movement. Greater flexibility is achieved by adding the outwardly offset grooves 44. 
     In FIG. 7, four offset grooves 50, 52, 54 and 56 are provided to define each actuator, two on the top and two on the bottom. By increasing the number of offset grooves, the material of the cover plate can be made thicker, while achieving the same net flexibility. 
     Intending to claim all novel, useful and unobvious features shown or described, we make the following claims: