Abstract:
An impact absorbing system for a flat switch panel has an impact spacer. The impact spacer, a rigid layer that is fixed to an energy-absorbing layer, attaches to the top surface of a flat switch panel just under the overlay. During a condition of switch abuse, the impact absorbing system disperses the energy from a high impact actuation force over a large area of the rigid layer, which in turn causes a large volume of energy-absorbing layer material to be deformed, directing the otherwise damaging impact away from a raised part of the switch that normally accepts a user provided actuation force. Preferably there is an embossed area in the rigid layer and a pip on the raised part of the switch, both improving the function and tactile feedback of the switch. The most preferred embodiment includes a polycarbonate backer on the bottom of the flat switch panel to additionally protect switch components from being damaged by a high impact actuation force.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Numerous devices are operated when a user presses a pushbutton located on a flat switch panel. Increasingly, such devices are set up at locations that are not monitored, such as ATM machines and gas pumps. If a single switch on a device fails, the entire device must be shut down until the failed switch can be repaired or replaced. As designed, pushbutton switches on a flat panel are intended to be operated by a fingertip and, preferably, give a tactile feedback to the user. Unfortunately, careless and impatient users cause most flat switch panel failures. Gas pump pushbutton switches, for example, are frequently operated by the tip of a gas nozzle that is struck against the flat switch panel for the purpose of actuating a particular switch. It is desirable to have a sealed switch for devices that are exposed to the elements and to harmful contaminants. A magnetically-coupled pushbutton switch is one type of flat panel switch that may be sealed and offers good tactile feedback to a user, but a magnetically-coupled pushbutton switch includes a sheet metal armature that is relatively thin compared to a gas nozzle.  
           [0002]    Magnetically-coupled switches have a metal armature that is normally held spaced from switch contacts by a sheet magnet. A user-provided actuating force applied to the armature causes it to snap free of the sheet magnet and close the switch contacts by electrically connecting them. Release of the actuating force allows the magnet to attract the armature back to a normal position, in coupled engagement with the magnet so the armature is spaced from the switch contacts, to reopen the switch. A magnetically-coupled switch typically has the switch contacts formed on a non-conductive substrate. A non-conductive spacer layer is fixed to the substrate, with an opening in the spacer layer exposing the switch contacts. The sheet magnet overlies the spacer layer. The armature is magnetically-coupled to the bottom of the sheet magnet so that the armature is housed within the opening in the spacer layer. Preferably, the armature has a crown that protrudes through an aperture in the magnet layer. Most often, a polyester membrane layer with suitable graphics overlies the magnet layer to direct a user of the switch as to location and function of the switch. The benefits of magnetically-coupled pushbutton switches have been demonstrated in U.S. Pat. Nos. 5,523,730, 5,666,096, 5,990,772 and 6,069,552, incorporated herein by reference.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention concerns an impact spacer that protects a pushbutton armature from being damaged during high impact actuation. The impact spacer is installed under a switch overlay, the overlay usually being a thin polyester sheet that has graphics printed thereon to show a user where various switches are located on a flat switch panel. The impact spacer is preferably a thick sheet of polycarbonate plastic adhesively fixed to a thick sheet of silicone rubber. When a high impact force is directed at a flat switch panel, the crown of an armature is susceptible to being crushed. The impact spacer protects the armature and crown by spreading the energy of a high impact force throughout a large volume of the impact spacer materials. The polycarbonate plastic layer is rigid, so it spreads a localized impact laterally across a large area of the flat switch panel. The underlying sheet of silicone rubber dissipates the energy that has been spread out over a large area of the impact spacer by deforming and compressing to absorb the excess force delivered to the flat switch panel. Under a normal actuation force, there is very little deformation of the silicone rubber layer so that the tactile feedback delivered by the armature is crisply transferred to a user.  
           [0004]    Preferably, the polycarbonate plastic layer of the impact spacer has an embossed area above each pushbutton switch. The embossed area prevents excessive preloading of switches so that thicker impact spacers may be used. Additional features of the switch of the present invention include a pip on the crown of an armature to preserve good tactile feedback, and a backer that is fixed to the bottom of the flat switch panel to protect a circuit layer of the switch against bending and cracking. Electrical leads connect the circuit layer of the switch to electronics that are external to the switch. Electrical conductors on the circuit layer are arranged within the switch so that the pushbutton armature of the switch is movable into and out of shorting relationship with the electrical conductors to change the circuit logic for a circuit incorporating the switch. As used herein, the term “top” refers to that surface of any part in a cross sectional figure of the drawings that faces the top edge of the page, while “bottom” refers to that surface of any part in a cross sectional figure of the drawings that faces the bottom edge of the page. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a cross-section of an impact absorbing system according to the present invention incorporated for use with a magnetically-coupled pushbutton switch.  
         [0006]    [0006]FIG. 2 is a cross-section similar to FIG. 1, but with a second type of impact spacer.  
         [0007]    [0007]FIG. 3 is an exploded perspective view of the switch and impact absorbing system of FIG. 1.  
         [0008]    [0008]FIG. 4 is an exploded perspective view of the impact spacer of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    As shown in FIGS. 1 through 4, the impact absorbing system of the present invention always includes an impact spacer  2  that has a rigid layer  4  and an energy-absorbing layer  6 , but there are several additional features shown and described in the foregoing description that, though preferred, are not necessary and may be excluded from the impact absorbing system where cost or preference dictates otherwise. FIGS. 1 and 3 show the ideal impact absorbing system as it would appear on a magnetically-coupled pushbutton switch  8 , or other flat panel switch that would benefit from the impact absorbing system of the present invention. An impact absorbing system that is capable of providing good tactile feedback and a very high level of protection for a flat switch panel will preferably include the following features: an embossed area  10  on the rigid layer  4 ; a selective adhesive layer, not shown, between the impact spacer  2  and the magnetically-coupled pushbutton switch  8 ; a reinforcement backer  12 ; and a pip  14  on the switch armature  16 . Preferred materials and methods of attachment will be discussed, but these preferences are not intended to exclude other suitable or functionally equivalent materials or methods of attachment.  
         [0010]    [0010]FIG. 1 shows a magnetically-coupled pushbutton switch  8 , similar to the ones shown and described in the aforementioned U.S. Patents, that has been modified to incorporate the impact absorbing system of the present invention. A magnetically-coupled pushbutton switch  8  typically includes, from the top down, a magnet coupler layer  22 , an aperture  24  through the magnet coupler layer, a metal armature  16  having a crown  26  that protrudes through the aperture, a spacer layer  28  that defines a switch cavity  30 , and a substrate  32  that has electrical conductors formed thereon. The impact spacer  2  of the present invention is fixed to the top of the magnet coupler layer  22  such that the energy-absorbing layer  6  is on or adjacent the crown  26  of the armature  16 . A thin polyester overlay  18  covers the impact spacer  2 .  
         [0011]    As already mentioned, the impact absorbing system of the present invention always includes an impact spacer. The impact spacer  2  is preferably made from two different sheets of material that are adhesively bonded to each other by an elastomeric adhesive. General adhesive, such as acrylic adhesive, will suffice, but the elastomeric adhesive is preferred because of its superior ability to permanently bond the layers of the impact spacer together. The top sheet of the impact spacer  2  is the rigid layer  4 , while the bottom sheet of the impact spacer is the energy-absorbing layer  6 . During an impact, the rigid layer  4  spreads a localized impact over a larger area of the energy-absorbing layer  6 . The energy-absorbing layer  6  compresses and changes shape to disperse the energy of the impact throughout a large volume of the energy-absorbing layer material. Some of the force from the localized impact is transferred through the energy-absorbing layer  6  to depress the pushbutton armature  16  and actuate the switch, but the armature is protected from being crushed or bent because of the impact spacer  2 .  
         [0012]    The rigid layer  4  of the impact spacer  2  is preferably a sheet of polycarbonate material, such as Lexan®, having a thickness of between ten and thirty thousandths of an inch. Other materials that could be used as the rigid layer include polyester, nylon, vinyl, carbon fiber materials, or other similar materials that offer some flexibility, but are substantially impervious to compression and fracturing. The thickness of the rigid layer is often dependent upon the material selected for use as the rigid layer. There must be enough flexibility in the rigid layer so that finger pressure will cause the rigid layer to adequately flex during switch actuation. The finger pressure, or user provided actuation force, is typically in the range of five to fifteen ounces, but for some applications is fifty ounces or higher. If the desired material to be used as the rigid layer  4  is well suited for use as the overlay  18 , appropriate graphics may be printed on the rigid layer  4  so that the rigid layer takes the place of the overlay that normally covers and protects a flat switch panel. If there is concern that the graphics will wear off, the rigid layer may be transparent with the graphics printed on the bottom surface of the rigid layer. FIGS. 1 through 4 show a separate overlay  18  that would typically be adhesively fix to the top of the rigid layer  4 .  
         [0013]    Where the rigid layer covers pushbuttons on a flat switch panel that are in close proximity to each other, it may be necessary to isolate actuation forces so that a user provided actuation force applied to one pushbutton switch does not spread out over the rigid layer and cause a nearby pushbutton switch to also be actuated. Additionally, the stiffness of some rigid layer materials may cause the armature  16  to be excessively preloaded so that the switch does not fully return to an un-actuated position, or the stiffness may negatively affect the tactile feedback of a pushbutton switch making it difficult for a user to recognize whether an actuation force was adequate. An isolation structure that prevents accidental actuation of a pushbutton adjacent the pushbutton intended to receive a user provided actuation force is recommended. The preferred isolation structure is an embossed area on the rigid layer that is around each area that will be above a switch. FIGS. 1 and 3 show an embossed area  10  in the rigid layer  4 . Note that the embossing causes the area of the rigid layer  4  above each switch to bulge away from the switch. For most purposes, the size of each embossed area  10  is approximately the size of an average fingertip, or roughly one third of a square inch. The embossed area  10  improves flexibility of the rigid layer  4  just above the pushbutton, but the increase flexibility does not significantly affect the ability of the rigid layer to disperse the energy of a high impact force over a large area of the rigid layer.  
         [0014]    [0014]FIGS. 2 and 4 show a second type of isolation structure that utilizes a supplemental rigid layer  5  that is adhesively fixed to the bottom of the rigid layer  4 . Preferably, the rigid layer  4  in FIGS. 2 and 4 is polyester and the supplemental rigid layer  5  is polycarbonate, but the layers may be any of the materials previously listed for use as the rigid layer. The supplemental rigid layer  5  has cutouts  11  that align with an area above each pushbutton, that area being about the size of a fingertip. As can be seen in FIG. 4, the cutouts  11  in the supplemental rigid layer  5  may include passages that allow for pressure changes within the cutouts to be vented, thereby keeping the tactile feedback more uniform. The supplemental rigid layer  5  additionally spaces the rigid layer  4  from each switch armature  16  so that preloading is better controlled. The rigid layer  4  of FIGS. 2 and 4 is typically thinner than the embossed rigid layer of FIGS. 1 and 3 because the thickness of the supplemental rigid layer  5  contributes to the ability of the impact spacer to spread the energy of a high impact actuation over a large area of the energy-absorbing layer  6 . The supplemental rigid layer  5  does not cover a pushbutton, making it easier for a user to actuate the switch because less force is required to flex just the rigid layer  4 . The main benefit of using an isolation structure is to allow the impact spacer to be thicker than would otherwise be possible. Without an isolation structure, the thickness of the rigid layer  4  is significantly limited because of problems with excessive preloading and loss of tactile feedback.  
         [0015]    In FIGS. 1 through 4, the energy-absorbing layer  6  of the impact spacer  2  is preferably a sheet of silicone rubber material having a thickness of between thirty and eighty thousandths of an inch. There are, of course, numerous other materials that mimic the energy-absorbing property of silicone rubber such as, but not limited to, other rubber materials, gelatins and foams. The energy-absorbing layer  6  dissipates a lot of the energy of a high impact actuation force by deforming and compressing a large volume of the energy-absorbing layer material. The energy-absorbing layer  6  is usually in direct contact with the crown  26  of each pushbutton switch that is part of the flat switch panel. This direct contact causes mild preloading of each switch. Preloading normally does not result in a bulge on the top surface of the rigid layer  4  because the energy-absorbing layer  6  slightly compresses and deforms around the crown  26 . Under a normal actuation force, the energy-absorbing layer  6  is compressed above the crown  26  of a pushbutton until a breakaway force is achieved. The breakaway force causes the pushbutton to move into contact with electrical conductors of the switch. The compressed portion of the energy-absorbing layer material travels with the crown  26  during switch travel. There is a tactile feedback to the user when the pushbutton abruptly meets the substrate  32  of the switch. That tactile feedback is crisply transferred through the compressed portion of the energy-absorbing layer  6  to the rigid layer  4  and overlay  18 .  
         [0016]    An additional feature of the impact spacer  2  that is recommended is to use a selective adhesive layer, not shown, to fix the pushbutton switch  8  to the bottom of the energy-absorbing layer  6 . Adhesive layers are usually about five thousandths of an inch thick. By selective, it is meant that there are areas on the energy-absorbing layer  6  that do not receive adhesive. These areas that do not receive adhesive are above each pushbutton switch. If adhesive were left above each pushbutton switch, the energy-absorbing layer  6  could bind during actuation and prevent the switch from returning normally to an un-actuated position. Another benefit of the selective adhesive layer is that the energy-absorbing layer  6  has more freedom of movement so that it can deform more than would be possible if it were adhered to the pushbutton. Where the energy-absorbing layer  6  is silicone rubber, a silicone adhesive, such as elastomeric adhesive made by 3-M corporation, should be used so that the impact spacer  2  is permanently fixed to the switch panel.  
         [0017]    Depending on the material of the substrate  32 , there may be a need for additional support under the substrate  32 . If the substrate  32  is likely to flex so much during high impact actuation that the armature  16  may bend, or the substrate is likely to fracture, then a backer  12  should be attached to the bottom of the substrate. The backer  12  is a layer of material that provides additional support to the substrate  32  and is also capable of absorbing excess energy from a high impact actuation force. The backer  12  is preferably polycarbonate, but could also be sheet metal, wood, cork, or any of the rigid layer materials previously mentioned.  
         [0018]    For ultra high impact actuation forces, the thickness of the impact spacer should be increased. However, making a thicker impact spacer usually is at the cost of tactile feedback to the user. If it is necessary to use an impact spacer  2  that is very thick, the armature crown  26  should include a pip  14 . The pip  14  is a small raised area on the top of the crown  26 . The pip  14  is an extension of the crown  26  that allows the crown to extend farther into the energy-absorbing layer  6  so that tactile feedback can be focused and transferred through the pip  14  to the user. The pip  14  brings the top of the armature crown  26  closer to the user so that the required actuation force is lower than it would be without the pip. Because the pip  14  has very little surface area, it can poke into the energy absorbing material without contributing very much to preloading. Although the relatively small area of the pip reduces the magnitude of force directed toward the armature crown, focusing the actuation force onto the pip enhances the tactile feedback to a user.  
         [0019]    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, the impact spacer  2  could be made from a single material, such as a thermoplastic elastomer, that can function as both the rigid layer  4  and the energy-absorbing layer  6 , but the materials cost of such an alternative was not competitive at the time of invention.