Abstract:
A magnetically actuated pushbutton switch has individual switch modules preassembled as standalone subassemblies. Each subassembly has a platform with a cavity on its underside. A portion of the platform is magnetized. A metallic armature is held in the cavity by the magnetic attraction of the platform. The switch subassemblies are mounted on a substrate that has switch contacts thereon. The armature is movable into and out of shorting relation with the contacts. A major spacer on the substrate has openings aligned with the switch contacts for receiving the subassemblies. An overlay film covers the subassemblies and major spacer. The armature may have a lens therein for transmitting backlighting. The platform can be magnetized at the time of installation on the substrate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Magnetically actuated pushbutton switches have a metal armature normally held spaced from switch contacts by a magnet. Pushing on the armature causes it to snap free of the magnet and close the switch contacts by shorting them. Release of the actuating pressure allows the magnetic force to withdraw the armature from the contacts to reopen the switch. The switches typically are made in panels having a non-conductive substrate with electrical contacts formed thereon. A non-conductive spacer layer lies on the substrate with openings therein exposing the contacts. A sheet magnet overlies the spacer with the armatures underneath the magnet layer in the spacer openings. The armatures preferably have actuating buttons that protrude through apertures in the magnet layer. Most often the magnet layer itself is covered by a membrane or the like, the upper surface of which carries suitable graphics. The benefits of magnetically-actuated pushbutton switches have been demonstrated in U.S. Pat. Nos. 5,523,730, 5,666,096, 5,867,082 and U.S. patent application Ser. No. 09/160,645, filed Sep. 25, 1998, the disclosures of which are incorporated herein by reference.  
           [0002]    Although the pushbutton switch as shown and described in the foregoing patents is very robust and easy to manufacture, relative to its counterparts, certain improvements in the manufacturing process are addressed by the present invention. The most difficult and expensive process in the manufacture of the described pushbutton switches is assembling all of the individual layers consistently. This can be a problem around the individual switch areas where the alignment with the armature is critical. Using pins to align the individual layers relative to each other is adequate to assemble a magnetically actuated pushbutton switch, although it is most advantageously done with special assembly apparatus. Tolerances are always a problem, however. As the overall size of the switch panel increases, the tolerances become difficult to control. The present invention teaches an alternative method of construction to eliminate the problems with assembly and to significantly reduce the overall product cost.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention concerns a magnetically actuated pushbutton switch wherein each switch includes a pre-assembled, free-standing actuator subassembly. Because each subassembly is separate from the others on a switch panel, they are sometimes referred to herein as island modules. The subassembly is made up of a platform which defines a cavity on its underside. The platform can be either stratified or monolithic. At least a portion of the platform is magnetized. A metallic armature fits into the cavity and is held therein by the magnetic attraction of the magnetized portion of the platform. The stratified platform may comprise a local spacer having a local opening therein, and a coupler which is a magnet. The coupler may have an aperture that allows an actuating button formed on the armature to protrude and receive the actuating force. An upper spacer may surround the protruding button to provide a top surface for supporting a membrane or overlay. The alternate, monolithic platform is formed as a single, integral component. Magnetization of the monolithic platform can take place immediately prior to installation of the subassembly.  
           [0004]    The actuator subassemblies are mounted on a substrate. The substrate carries electrodes which include at least one set of switch contacts. In some applications it may be desirable to place a major spacer over the substrate with openings in the major spacer aligned with the switch contacts. The actuator subassemblies are then placed into these openings to complete the switch. The armature may be provided with a lens to disperse backlighting. Tactile domes may be added to the actuator subassemblies. The subassemblies may have multiple armatures.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is an exploded perspective view of a full switch panel according to the present invention.  
         [0006]    [0006]FIG. 2 is an exploded perspective view of an actuator subassembly.  
         [0007]    [0007]FIG. 3 is a section through the completed subassembly of FIG. 2.  
         [0008]    [0008]FIG. 4 is a top plan view of the subassembly.  
         [0009]    [0009]FIG. 5 is a section through an alternate embodiment of a switch panel having a monolithic island module.  
         [0010]    [0010]FIG. 6 is an exploded perspective view of the bottom of the monolithic island module.  
         [0011]    [0011]FIG. 7 is an exploded perspective view of the top of the monolithic island module.  
         [0012]    [0012]FIG. 8 is a perspective view of a further alternate embodiment of a switch panel having a substrate, major spacer and top film with an integrated rotary switch.  
         [0013]    [0013]FIG. 9 is a perspective view of the switch panel of FIG. 8 with the top film removed to reveal the major spacer and the multiple armature island module.  
         [0014]    [0014]FIG. 10 is a perspective view of the switch panel of FIG. 8 with both the top film and major spacer removed to reveal the substrate.  
         [0015]    [0015]FIG. 11 is a top plan view of a tactile dome.  
         [0016]    [0016]FIG. 12 is a section taken along line  12 - 12  of FIG. 11.  
         [0017]    [0017]FIG. 13 is a section through a further alternate embodiment of a switch panel having a lens in the armature for transmitting light through the actuator subassembly.  
         [0018]    [0018]FIG. 14 is a view similar to FIG. 13 showing a further variation.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 illustrates a switch panel  10  according to the present invention. The panel includes a substrate  12  which is formed of either rigid or flexible non-conductive material. For example, the substrate can be made of printed circuit board material or plastic film such as polyester. At least one surface of the substrate has electrodes formed thereon by a suitable process such as etching or screen printing. Electrodes can be arranged in any suitable manner and will typically include leads  14  which extend to an appropriate connector portion at an edge of the substrate. The electrodes will also include sets of spaced switch contacts such as the pads shown at  16 A,  16 B and  18 A,  18 B. As can be seen, the switch contacts  16 ,  18  are suitably connected to various ones of the leads  14  and the contacts themselves are spaced apart. It will be understood that the electrodes and contacts can be arranged in any configuration needed. For example, instead of the simple pads shown at  16  and  18 , a more complex arrangement of spaced, interleaved fingers could be used.  
         [0020]    A major spacer  20  is mounted on the substrate  12 . The spacer is made of a thick film or rigid material, preferably with adhesive located on the top and bottom surfaces. A typical material used in this application would be closed cell adhesive foam such as one manufactured by 3M Corporation and sold under their trademark VHB Series. This material is supplied with a high bond adhesive on both the top and bottom surfaces. Release liners cover the adhesive layers prior to assembly. One advantage of using closed cell foam as a spacer is that the flexibility of the material allows the adhesive to bond readily with the substrate, even if it has a rough surface. Typical imperfections on the surface would be conductive traces such as the screened silver or etched copper leads  14 . The closed cell foam material protects the switch from liquids and gases and allows the assembly to be sealed. While the use of adhesive is the preferred method of joining the major spacer and substrate, mechanical means could be used, either alone or in combination with adhesive.  
         [0021]    The major spacer  20  has openings  22  formed therein and located so as to expose the sets of contacts on the substrate. Thus, opening  22 A is aligned with the switch contacts  16  while opening  22 B is aligned with and exposes contacts  18 . Individual island modules or actuator subassemblies  24  fit into the openings  22 . Details of the subassemblies  24  will be described below. Miscellaneous components can also be pre-assembled on to the substrate  12 . When such components are included, holes similar to openings  22  are cut into the major spacer to accommodate these components. This is shown in more detail in FIGS. 9 and 10.  
         [0022]    After insertion of the switch subassemblies  24  into openings  22 , release liners, if present, are removed from the top surfaces of the major spacer  20  and the subassemblies  24 . A top film layer or membrane  26  is placed over the major spacer and actuator subassemblies  24 . The film layer  26  is made of flexible plastic or elastomeric material. It can have suitable graphics printed thereon to instruct a user as to the location of a switch subassembly. The film layer adheres to the major spacer  20  and, optionally, to the top of the subassemblies  24 . As mentioned above, mechanical methods may also be used to secure the film layer  26 .  
         [0023]    Looking now at FIGS.  2 - 4 , details of the actuator subassembly or island module  24  will be described. Each subassembly has two major components, a platform and an armature. The platform defines a cavity for receiving the armature. The embodiment of FIGS.  2 - 4  shows a stratified platform which includes a local spacer  28 , a coupler  30  and an upper spacer  32 . The local spacer  28  is made of non-conductive material such as polyester. It has a local opening  34 , an upper surface  36  and a lower surface  37 . The local opening  34  extends all the way through the thickness of the local spacer. The coupler  30  also has an aperture  38  all the way through its thickness. The coupler is a sheet magnet. Together the coupler  30  and the local spacer  28  define a cavity in the area of the local opening  34 . The upper spacer  32  has three legs  40  forming three sides of a rectangle and defining an open area which surrounds the coupler aperture  38 . The parts of the stratified platform may be held together by adhesive (not shown). Thus, adhesive may be deposited on the top and bottom sides of the upper spacer  32  and on the top surface  36  and the lower surface  37  of the local spacer  28 . Release liners may cover any of these adhesive layers until such time as joining with adjacent members is desired. For example, the lower surface  37  of the local spacer would have a release liner that would remain in place until it is time for the subassembly  24  to be mounted on the substrate  12 . If adhesive is used on the top of the upper spacer, a release liner thereon would be removed just prior to installation of the film layer  26 .  
         [0024]    The second major component of the actuator subassembly  24  is an armature  42 . It is made of electrically conductive, magnetic material, i.e., material that is affected by a magnet. Typically the armature is soft steel. The armature shown has a disc-like configuration with an upstanding or protruding actuating button  44  formed on one side of the disc. The actuating button protrudes through the aperture  38  in the coupler  30 . The actuating button extends above the top surface of the coupler to the same extent as the thickness of the upper spacer  32 . Thus, the top of the button  44  and top of the upper spacer  32  terminate in the same plane. This provides a smooth, level surface for the top film layer  26 . Alternately, the button  44  could extend above the upper spacer  32  and cause a slight bulge in the film layer to provide a visual and tactile indication of the button&#39;s location.  
         [0025]    The subassembly  24  is placed on the substrate  12  by removing the release liner from the bottom surface  37  of the local spacer  28  and pressing the subassembly into the appropriate opening  22  in the major spacer  20 . Once that is done the armature  42  will reside above the switch contacts  16  or  18 . It will be noted in FIG. 4 that one corner of the subassembly may be beveled as at  45 . The major spacer opening  22  is similarly shaped. This affords a non-symmetrical configuration that prevents putting the subassembly in backwards.  
         [0026]    When a user presses on the actuating button  44  it causes the left side (as viewed in FIG. 3) of the armature to break away from the coupler  30  until the left side of the armature bottoms on the switch contact pad, e.g.  16 A. Continued actuating pressure then causes the right side of the armature to break away and engage the other contact pad  16 B. This shorts the contact pads and closes the switch. Removal of the actuating pressure allows the magnetic force of the coupler  30  to pull the armature  42  back up off of the contacts and into the position shown in FIG. 3 wherein the armature is spaced from the contact pads.  
         [0027]    An alternate embodiment of the actuator subassembly is shown in FIGS.  5 - 7 . In this embodiment, which may be referred to as a monolithic island module, the platform  46  is made as a single, integral part. It includes a coupler layer  48  having an aperture  50  therethrough. The underside of the coupler  48  has a rim  52  around its perimeter. The rim defines a depression or cavity  54  in which the armature  42  sits. The top side of the coupler  48  has an upper spacer  56  around three side edges. The armature  42  resides in the cavity  54  with its actuating button  44  extending through the aperture  50 . It can be seen that the monolithic platform has just one part compared to the three part stratified platform.  
         [0028]    This construction offers a number of advantages in addition to ease of manufacture. For example, the sheet magnet material used in other switches is magnetized in a series of parallel poles of opposite polarity. This makes it difficult to specifically magnetize a particular area to a certain polarity or to increase its magnetic force. The unitary design of the monolithic island module platform allows for the magnetic poles to be placed at very specific points, thus allowing for high magnetic forces to be placed in the position where they will allow for increased and optimum switch actuation force and travel characteristics. Additionally, state of the art sheet magnet materials are limited to relatively low force ferrite magnet materials. The molded construction of this teaching allows the magnets to be fabricated from high magnetic force rare earth materials such as neodymium iron boron and samarium cobalt. In addition, thicker magnets can be fabricated that have greater magnetic induction strengths. Much smaller switches thus can be fabricated since the monolithic platform does not suffer the limitations of prior art products which, at least to some extent, are limited by the overall area of the switch armature and the thickness of the magnet material. Another advantage of the monolithic platform is it can be molded but not magnetized until it is ready for assembly. The platform is magnetized at the time of installation of the substrate, i.e., either just prior to or immediately after installation on a substrate. This timing makes it much easier to keep the platform clean after its fabrication but prior to installation. Also, the unassembled, unmagnetized platforms are easier to handle in containers such as bags or boxes because they don&#39;t stick together as much as magnetized components do. Greater control of the magnetic field strength is also possible. The platform could be magnetized with multiple parallel poles or with just two poles.  
         [0029]    FIGS.  8  -  10  illustrate a further variation on the island switch. This switch panel  58  comprises a substrate  60 , a major spacer  62  and a top film layer  64 . These may be made of materials similar to those of the FIG. 1 embodiment. The top film layer may have a tail  66  that extends to a connector  68  for attachment to an associated electronics unit (not shown). The top film has conductors on its underside as needed to create a rotary switch. The switch rotor is shown at  70 . Further details of the rotary switch are shown in U.S. Pat. No. 5,867,082. FIG. 9 illustrates the major spacer  62  and a large opening  72  therein which accommodates a multiple-armature island switch module. This module has a platform  74  that has three cavities underneath it for receiving three separate armatures  76 A,  76 B and  76 C. The platform  74  fits within opening  72 . The major spacer  62  also has a plurality of smaller openings  78 . These accommodate surface mounted components such as those illustrated diagrammatically at  80  in FIG. 10. These components are mounted on the printed circuit board that forms the substrate  60 . FIG. 10 also shows how the platform  74  rests on the top surface of the substrate  60 . It will be understood that the top of the substrate would also have electrodes (not shown) formed thereon to connect to switch contact pads underneath the armatures  76 .  
         [0030]    The island switch modules of FIGS. 2 and 5 are also applicable to a dome switch. For years, the membrane switch industry, and indeed most tactile pushbutton switch manufacturers, have utilized metal or plastic domes to provide tactile feel for their switches. The major problem associated with the tactile dome membrane switches has been repeatability from one switch to another within a switch panel. These inconsistencies are due primarily to inconsistencies in alignment and assembly of the layers. In the present invention, assembly of the dome switches can be automated and the domes can be placed as individual islands, thus eliminating the prior art inconsistencies for all intents and purposes. One example of how such an island would look is shown in FIGS. 11 and 12. A tactile dome  82  is held in place on top of the actuator subassembly by a dome retainer  84 . The retainer may be adhesively fixed to the magnet layer  30 . The dome may fit within the legs  40  of the upper spacer  32 .  
         [0031]    Looking now at FIGS. 13 and 14, another aspect of the present invention is shown and described. In many switch applications, backlighting of the individual switch positions or modules is required. There are a number of alternative techniques available at the present time for providing lighting. Among these are edge lighting, light pipes and electroluminesence. Each of these various techniques has different degrees of difficulty, cost and limitations. This disclosure offers a unique method of lighting magnetically actuated pushbutton switches. The basic construction is similar to that of the switch panel  10  in FIG. 1 and the actuator subassembly  24  in FIGS. 2 and 3. Common elements are given common reference numbers and their description will not be repeated. The island module shown generally at  86  includes a back light source  88  shown schematically in this example as an LED. It will be understood that the LED is electrically connected to a suitable power source and physically mounted in a suitable housing underneath the substrate  12 . The armature  90  has a lens or crystal  92  insert molded as part of the armature. Alternately, the lens  92  can be snapped in place in an opening in the armature. As shown in FIG. 13, the light is piped up from underneath the armature and through either an opening or transparent portion of the substrate  12 . Light is scattered at the top surface of the lens  92  through the overlay film  26 . This allows the center of the individual switch module to be lighted.  
         [0032]    The shape of the lens is important in that the light has to be scattered to provide uniformity across the face of the switch. A faceted design is shown in the figure on the top and bottom surfaces. It is important to note that since the actual switch contacts are not in the center of the lens  92 , the switch contact integrity is not compromised, as is often the case with domed or standard membrane switches.  
         [0033]    The light scattering can be enhanced by providing a diffraction grating as shown in FIG. 14 at  94 . This grating is placed between the overlay film  26  and the upper spacer  32 . Alternatively, the diffraction grating could be placed just on top of the lens  92 . A diffraction grating is a series of diffracting lines either etched or molded into the surface and extending as concentric rings around the center of the light source. Providing a fluorescing layer on the bottom surface of the top film can enhance the light scattering. This layer is loaded with fluorescing dye and can either be screened on the bottom surface of the overlay or inserted as a separate film.  
         [0034]    While a preferred form of the invention has been shown and described, it will be realized that alterations and modifications may be made thereto without departing from the scope of the following claims. For example, while at least a portion of the platform is described as being magnetized and the armature is made of magnetic material, this could be reversed so the armature is a magnet and the platform is magnetic material. Also, while the island switch modules have been described as joined to the substrate by adhesive which is covered by a release liner prior to installation, the modules could be retained by other means not requiring adhesive or release liners.