Abstract:
The invention relates to a form of a tilt switch that solves the problem of poor electrical contact, excessive/unpredictable hysteresis, high contact resistance, short life and/or electrical bounce. The tilt switch uses conventional ball-in-tube construction and adds a graphite powder film to all electrically conductive surfaces in the switch. This non-mercury tilt switch provides additional features such as enhanced electrical contact, reduced or eliminated hysteresis, lowered contact resistance, increased contact life and eliminates electrical bounce.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/401,162 entitled “DEVICE TO REDUCE THE INCIDENCE OF ASPIRATION” filed Apr. 10, 2006, which claims the benefit of priority to U.S. provisional patent application No. 60/670,842 entitled “HOSPITAL BED INCLINATION SENSOR AND ALARM” filed Apr. 13, 2005. This application also claims the benefit of priority of U.S. provisional patent application No. 61/067,000 entitled “TILT SWITCH EMPLOYING GRAPHITE” filed Feb. 25, 2008. 
     
    
     FIELD 
       [0002]    This invention relates generally to tilt switches in particular those that eliminate or minimize actuation electrical power, reduce operating hysteresis, provide positive electrical function, eliminate the need for switches containing mercury or other toxic liquid metals and reduce manufacturing costs. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Various methods have been devised to provide tilt switches in prior art. These switches may be classified as electrically actuated and self actuated. 
         [0004]    The first class, electrically actuated, utilizes some form of electrically powered sensor or inertial stabilized element to sense the angle between the local gravity vertical and the reference plane of the switch (i.e. the “tilt angle”). Examples of such devices are servo pendulum accelerometers (U.S. Pat. No. 3,111,036, Kistler, and U.S. Pat. No. 5,006,487, Stokes), vibratory accelerometers (U.S. Pat. No. 2,928,668, Blasingame and U.S. Pat. No. 4,306,456, Maerfeld), convective accelerometers (U.S. Pat. No. 2,455,394, Webber and U.S. Pat. No. 6,182,509, Leung), and gyroscopic stabilized platforms (U.S. Pat. No. 1,563,934, Sperry) to name a few. These instruments generally have very low “operating hysteresis” (i.e. the angular difference between actuation during increasing tilt angle and deactivation during decreasing tilt angle or vice versa). The cited instruments suffer since they require electrical power to maintain any angle measuring capability either before or after the desired tilt angle is achieved. This generally prevents the extended duration use of such electrical switches in portable, battery powered devices. 
         [0005]    The second class, self actuated, utilizes some form of gravity powered sensor or gravity stabilized element to sense the tilt angle. Examples of such devices are pendulum switches (U.S. Pat. No. 778,444, Carstarphen, Jr., U.S. Pat. No. 1,055,153, Ferguson, U.S. Pat. No. 3,962,693, Schamblin), rolling ball switches (U.S. Pat. No. 306,050, Bartlett, U.S. Pat. No. 1,414,932, Chisman and U.S. Pat. No. 1,241,888, Safford), mercury switches (U.S. Pat. No. 1,079,380, Thomas and U.S. Pat. No. 1,391,782, McDannold), and electrolytic switches (U.S. Pat. No. 2,852,645) to name a few. 
         [0006]    These instruments have an advantage over powered sensors since they require no power to maintain angle measuring capability either before or after the desired tilt angles are achieved. All of these instruments suffer from the fact that they generally have very large operating hysteresis or require heavy masses (e.g. heavy pendulum bob) or large dimensions (e.g. long pendulum) to reduce operating hysteresis. The liquid electrical switches suffer from the use of toxic metals (e.g. mercury switches) or decomposable electrolytes (e.g. electrolytic switches). Rolling ball electrical switches generally suffer from poor electrical contact, excessive/unpredictable hysteresis, high contact resistance, short life and/or electrical bounce. 
         [0007]    Other examples of metal-to-metal electrical switches are ball contact magnetic relays where a ferromagnetic ball is attracted (or repelled) by a solenoid or magnet to make or break an electrical circuit using the ferromagnetic ball as an electrical bridge between two electrical contacts. These devices generally suffer from poor electrical contact characteristics due to the nature of the metal ball surface electrical properties. As such, a large magnetic force is required to hold the metal ball in place between the contacts ensuring a good electrical connection between the contact terminals of the switch. 
         [0008]    Prior art methods of increasing the electrical conductive properties of the ball have been attempted. For example, U.S. Pat. No. 6,180,873, Bitko, utilizes the discovery that certain liquids have varying dielectric properties depending upon the thickness of the liquid layer. These liquids are called mesoscopically conductive liquids or mesoscopic conductors or mesoscopic liquids. Thick layers of these mesoscopic liquids are insulators; whereas thin layers are conductors. One embodiment of the Bitko device involves a use of mesoscopic conductors in a current carrying device wherein a conductor moves relative to a conducting surface, which it engages. The Bitko device has the disadvantage of requiring containment of a (sometimes toxic) liquid substance which increases production costs and adds leakage risk. 
         [0009]    German Patents DE9007264 and DE4021055, Gillert, utilize a cylindrical housing of electrically conductive material that encloses a space having a downwardly tapered conical portion in which a ball rides in a partial filling of conductive powder or granular material, preferably graphite or metallic dust. In the rest position the ball is seated in the taper making no contact between the switch terminals. At a predetermined angle of tilt, the ball rolling is damped by the bed of powder. Thus, the switch contact is substantially free from bounce even when the apparatus is jolted due to the dampening effect of the graphite powder. The Gillert device uses a large amount of graphite powder to dampen the motion of the ball and is at a serious disadvantage since the pile of graphite can also short between the contacts thus increasing the hysteresis of the tilt switch. 
       SUMMARY 
       [0010]    The present invention is directed to tilt switches and other devices exploiting conductive graphite films. Graphite films operate as an insulator and as a conductor as a function of the thickness of a layer of the graphite film. 
         [0011]    In one embodiment, the graphite film is applied to a charge carrying device as an interface between electrodes. In long distances across a film surface, the graphite film has high resistivity, acting as an insulator and thereby preventing or substantially eliminating charge transfer between electrodes. The graphite film conductor separating the electrodes transfers charge or current when the current carrying members touch each other. In such an embodiment, the electrodes might be movable into and out of engagement or be permanently engageable. The relative movement of electrodes might involve rolling, rotating, sliding, or the like, or any combination thereof. 
     
    
     
       DRAWINGS 
         [0012]    The objects and advantages of embodiments of the present invention are apparent from the following detailed descriptions of preferred embodiments in connection with the accompanying drawings in which like numerals designate like elements, and in which: 
           [0013]      FIG. 1  is a longitudinal sectional view of a first embodiment of the invention with the longitudinal axis oriented at an angle to the horizontal, utilizing a spherical ball as a shorting element; 
           [0014]      FIG. 2  is an end view of  FIG. 1 , showing the proximity of the ball to the case; 
           [0015]      FIG. 3  depicts another embodiment similar to  FIG. 1  but using a cylinder as the shorting element; 
           [0016]      FIGS. 4   a  and  4   b  are fragmentary views depicting an interface between the roller and the case and an interface between the roller and the insulated electrode; 
           [0017]      FIGS. 5   a  and  5   b  depict yet another embodiment of the invention; 
           [0018]      FIGS. 6   a - 6   c  depicts another embodiment wherein the electrodes are in permanent, relatively rollable engagement; 
           [0019]      FIG. 7  depicts an additional embodiment wherein the electrodes are in permanent, relatively rollable and/or slidable engagement; 
           [0020]      FIG. 8  is a side view of still another embodiment of the invention where the electrodes are in permanent relatively slidable engagement; 
           [0021]      FIG. 9   a  is a cross-sectional view of another embodiment of the present invention wherein a tilt switch is in a normally open state; 
           [0022]      FIG. 9   b  is a view of the switch according to  FIG. 9   a  after being tilted to a closed state; 
           [0023]      FIG. 10   a  is a cross-sectional view of another embodiment of the invention wherein a tilt switch is in a normally closed state; 
           [0024]      FIG. 10   b  is a view of the switch according to  FIG. 10   a  after being titled to an open state; 
           [0025]      FIG. 11   a  is a view of another embodiment of the present invention wherein a tilt switch is in a dual angle measuring mode, center position normally closed; and 
           [0026]      FIG. 11   b  is a view of the switch according to  FIG. 11   a  after being titled to an open state. 
           [0027]      FIG. 12   a  is a view of another embodiment of the present invention wherein a tilt switch is in a dual angle measuring mode, center position normally open; and 
           [0028]      FIG. 12   b  is a view of the switch according to  FIG. 12   a  after being titled to a closed state. 
           [0029]      FIG. 13   a  is a view of another embodiment of the present invention as an omnidirectional tilt switch, center position normally closed; and 
           [0030]      FIG. 13   b  is a view of the switch according to  FIG. 11   a  after being titled to an open state. 
           [0031]      FIG. 14   a  is a view of another embodiment of the present invention including a visual tilt indicator; and 
           [0032]      FIG. 14   b  is a view of the switch according to  FIG. 14   a  after being titled to an alternate state. 
       
    
    
     DRAWINGS-Reference Numerals 
       [0000]    
       
           10  Tilt Switch 
           12  Case 
           14  Shorting Member 
           16  Inner Surface 
           17  Cylindrical Portion 
           18  Chamber 
           20  Circular Portion 
           22  Extended Flange 
           24  Extended Flange 
           26  Conductive Shell 
           28  Tab 
           30  Electrically Conductive Terminal 
           32  Insulator 
           50  Electrically Conductive Interface 
           51  Terminal Face 
           52  Electrically Conductive Interface 
           60  Semi-circular Segments 
           62  Semi-circular Segments 
           70  Semi-circular Electrode Segments 
           72  Semi-circular Electrode Segments 
           80  Rotatable Cylindrical Surfaces 
           82  Rotatable Cylindrical Surfaces 
           90  Surface 
           92  Moveable Member 
           100  Electrically Conductive Ball 
           112  Conductive Casing 
           114  Terminal 
           120  Electrically Conductive Ball 
           122  Terminal Head 
           124  Terminal 
           126  Edge 
           128  Casing 
           130  Recess 
       
     
       DETAILED DESCRIPTION 
       [0066]    The present invention involves the use of graphite film conductors in devices wherein current is conducted, and particularly wherein the current is to be modified, e.g., insulated, reduced, amplified, or otherwise regulated. For example, the invention includes the use of graphite film conductors in devices wherein a current carrying element is insulated under certain circumstances but permitted to conduct under other predetermined circumstances, e.g., a switch. 
         [0067]    Graphite film conductors are characterized by their ability to adhere to metal surfaces. This property produces a highly conductive, non-corroding surface on the metal surface. The natural self adhering graphite layer can be used on any conductive metal surface to enhance the electrical conductivity between two metal surfaces. This is particularly useful to enhance a point contact (e.g. a bearing resting on a flat surface) or a line contact (e.g. a cylinder resting on a flat surface) electrical connection as typically found in tilt switches. 
         [0068]    A graphite film conductor can be applied in any manner for use in the invention. For example, dusting, wiping, brush application, rolling, solvent application, spraying, etc. can all be used in the invention. This disclosure contemplates that there will always be at least a minimal continuous layer (i.e., at least one molecule thick) of graphite film conductor between electrodes. A significant characteristic of graphite film conductors is that these films possess high resistivity in the transverse (i.e. parallel to the largest area dimension) direction across thin films but low resistivity in the normal direction through the graphite thin film. 
         [0069]    The unique and advantageous properties of graphite film conductors ensure that such conductors will prove to be useful in a wide variety of applications. For example, graphite film conductors will be useful in the fabrication of various types of switches, magnetically operated relays, thermocouples, thermostats, pressure sensors, accelerometers, adjustable capacitors (i.e., electronically adjustable), and other such devices that will readily suggest themselves to the skilled worker in this art in view of the present disclosure. 
         [0070]    The present invention provides, among other things, a current carrying device including a pair of electrodes and a mobile or variably positioned conductive or charge carrying element (or shorting element or member) surrounded by, or separated from an electrode by, a layer of graphite film. In one embodiment, the mobile shorting element is perpetually in electrically conductive proximity (or graphite film proximity) to at least one electrode. As such, the mobile shorting element functions as a variably positioned extension of at least one electrode. Alternatively, the current carrying device comprises a pair of electrodes coated with a graphite film, the coated electrodes separated by a layer of graphite film coated on a suitable shorting element. 
         [0071]    Known tilt switches may experience dramatic electrical hysteresis in operation. For a typical tilt switch wherein the circuit closes at 42° the circuit may only leave contact at 30°. The application of a graphite film reduces this electrical hysteresis to 1° or less, a reduction of approximately 90%. 
         [0072]    In one embodiment the electrodes and mobile current carrying element are configured so that at least one electrode and the mobile current carrying element are substantially in perpetual graphite film proximity; under specified conditions, the mobile current carrying element moves into graphite film proximity, and thus electrically connects, the remaining electrode. The action of the mobile current carrying element is such that the electrodes are functionally isolated from each other only by the orientation of the mobile current carrying element and the graphite film. When the distance between the mobile current carrying element and the remaining electrode is great, i.e., a super-graphite film distance, there is no electrical connection; when the distance is small, i.e., a sub-graphite film distance or within graphite film proximity, an electrical connection is effected. 
         [0073]    The present invention provides a method for regulating or controlling current flow through a current carrying device including separating electrodes by a layer of graphite film, and regulating the current flow between the electrodes by varying the current carrying distance of the graphite film conductor separating the electrodes. In such a method, the current flow is either facilitated or prevented as a function of the contact with the graphite film separating the electrodes. 
         [0074]    Such a device will be recognized by one of ordinary skill in the art as a useful substitute for a tilt switch, particularly a mercury switch. 
         [0075]    More particularly, an embodiment of tilt switch  10  is depicted in  FIGS. 1 and 2 . This embodiment comprises case  12  and ball-shaped, i.e., spherical, shorting member  14  displaceably mounted within chamber  18  formed by the casing. Inner surface  16  of the casing, which includes cylindrical portion  17  and circular portion  20 , is symmetrically configured about longitudinal axis B of the chamber, and is formed of an electrically conductive material such as a metal. The diameter of the cylindrical portion is larger than the diameter D of shorting member  14 . 
         [0076]    At an end of the casing opposite circular surface portion  20 , electrically conductive terminal  30  is sealed by insulator  32  within conductive shell  26 , which shell has extended flange  24  welded to extended flange  22  of case  12 . Conductive shell  26  has tab  28  which provides for electrical termination of the case. An end of terminal  30  projects into chamber  18  and includes terminal face  51  desirably, but not necessarily, shaped as a spherical segment of the same radius as sphere  14 , i.e., one half diameter D. Other surface shapes could be used as well. 
         [0077]    Terminal  30  extends along axis A, which axis A is offset relative to axis B so that when shorting member  14  rolls into contact with terminal  30 , the axis A will pass through the geometrical center of shorting member  14  for alignment of that member in terminal face  51 . The mutually contacting faces of terminal  30  and sphere  14  define electrically conductive interface  52  (see  FIG. 4   a ) which is desirably, but not necessarily, shaped to maximize the contact area between terminal  30  and shorting member  14 . In similar manner, the diameter of shorting member  14  is preferably selected to maximize the contact area with inner surface  17  of the casing at interface  50  established therebetween (see  FIG. 4   b ). The contacting faces can be formed of any suitably conductive material such as steel, iron, copper, silver, gold, etc. Inner surface  16  and ball shaped shorting member  14  are coated with a film of graphite to provide the previously cited benefits of this invention. 
         [0078]    Insofar as embodiments of the present invention are contemplated as substitutes for mercury tilt switches, graphite film coated conductors have the advantage of an increased temperature operating range. Thus, graphite film coated conductors will operate well outside of the typical mercury operating range of −40° C. to about 150° C. In addition, unlike most mercury tilt switches, the inventive tilt switch is made of non-frangible components (i.e. metals or plastics versus glass). 
         [0079]    Generally, inner surface  16  of the casing, shorting element  14  and face  51  are all coated by the graphite film. It will be appreciated that inner surface  16 , shorting element  14  and face  51  are not perfectly smooth, and as shown in  FIGS. 4   a  and  4   b , produce between one another, spacings of various gaps as a function of the force exerted by shorting element  14  toward face  51 . That force is a function of gravity and the roughness of the opposing materials. It is desirable for the geometry of those components to maximize the contact area which will provide the maximum number of sites where the interfacial gap is minimized. 
         [0080]    To enhance the number of such sites, it is also desirable to highly polish or smoothly finish the surfaces which define interfaces  50 ,  52 , thereby minimizing the number of large projections which, by virtue of their presence, tend to separate the surfaces in a manner creating large gaps instead of the desired small gaps. 
         [0081]    The graphite film must possess a relatively high electrical resistivity in the transverse direction (so as to avoid conducting current directly between terminal  30  and casing  12 ), and yet possess a relatively low electrical resistivity across a thin film (i.e., when disposed in interfaces  50 ,  52 ) so as to be highly electrically conductive in the direction normal to the film thickness. 
         [0082]      FIG. 3  depicts a device similar to  FIG. 1  except that the spherical shorting element has been replaced by cylindrical shorting element  14 ′ of circular cross section, and shoulders  60  have been provided on a floor of casing  12 ′ to keep the cylinder properly centered. Also, face  51 ′ of insulated terminal  30 ′ has been shaped as a segment of a cylinder to conform to the outer periphery of cylinder  14 ′. 
         [0083]    In operation, it is obvious that if the left end of insulated terminal  30  or  30 ′ is tilted so that it is above the right-hand end, shorting element  14  or  14 ′ will roll away from face  51  or  51 ′, thereby providing an open circuit. The bulk resistance of the graphite film conductor is so large that no shorting can occur between terminals  30  and  12 , or  30 ′ and  12 ′. Tilting the left end of terminal  30  to a level below the right-hand end will cause shorting element  14  or  14 ′ to contact the casing and face  51  or  51 ′ simultaneously, thereby closing the circuit. Connection to the switch is made via the external terminal portion of terminal  30 , and to the casing via shell tab  28 . The graphite film conductor contacts interfaces  50  and  52  thereby closing the circuit. Electrical resistance tests carried out in similar devices have indicated the presence of a contact resistance comparable to those found in prior art mercury switches of approximately the same size. 
         [0084]    In another embodiment, shown in  FIGS. 5   a  and  5   b , the electrodes are in the form of a pair of semi-circular segments  60 ,  62  extending through insulator  32 . The segments are horizontally spaced and include surfaces shaped complementarily to that of shorting member  14 , i.e., either spherical or cylindrical. The shorting member contacts both electrodes simultaneously during tilting of the casing to close the circuit. All internal metal surfaces and components are coated with a graphite film. 
         [0085]    In another embodiment, shown in  FIGS. 6   a - 6   c , semi-circular electrode segments  70 ,  72  are vertically spaced apart. Thus, shorting member  14  initially makes contact only with lower electrode  72  during tilting of the case (see  FIG. 6   a ). Thereafter, in response to further tilting of the casing, shorting element  14  also contacts upper electrode  70  to close the circuit (see  FIG. 6   b ). In that way, control is maintained over the extent to which the casing must tilt in order to cause the circuit to be closed. All internal metal surfaces and components are coated with a graphite film. 
         [0086]    In still another embodiment of the invention, shown in  FIG. 7 , shorting elements  14  are disposed between two relatively rotatable cylindrical surfaces  80 ,  82 . Surfaces  80 ,  82  constitute electrodes, and shorting elements  14  roll and slide while conducting current between those electrodes. All internal metal surfaces and components are coated with a graphite film. 
         [0087]    In yet another embodiment of the invention, shown in  FIG. 8 , the electrodes comprise surface  90 , and moveable member  92  variably positioned across surface  90 . All metal surfaces and components are coated with a graphite film. 
         [0088]    Depicted in  FIGS. 9   a ,  9   b  is a preferred embodiment of an omni-directional tilt switch which is normally open and is closed by being tilted in any direction by a predetermined angle. As a result of such tilting, electrically conductive ball  100  is displaced from a position seated on a spherical surface of terminal  114  ( FIG. 9   a ) to a position engaging both terminal  114  and a wall of conductive casing  112  ( FIG. 9   b ). All internal metal surfaces and components are coated with a graphite film. 
         [0089]    In  FIGS. 10   a  and  10   b  there is shown an embodiment of a tilt switch which is normally closed. That is, electrically conductive ball  120  normally engages head  122  of terminal  124  ( FIG. 10   a ) and edge  126  of casing  128 . When casing  128  is tilted beyond a predetermined angle ( FIG. 10   b ) ball  120  rolls into recess  130  of casing  128  and out of contact with terminal  124  to open the circuit. The surface of head  122  can be of any suitable shape, such as spherical to conform to the shape of ball  120 . All internal metal surfaces and components are coated with a graphite film. 
         [0090]    In  FIGS. 11   a  and  11   b , there is shown an embodiment of a dual angle tilt switch which is normally closed. That is, electrically conductive ball  120  normally contacts terminal  124  and terminal  124 ′ when the orientation of the tilt switch is less than +/− angle θ. When insulated casing  32  is tilted more than +/− angle θ ( FIG. 11   b ) ball  120  rolls into recess  130  of casing  32  and out of contact with terminal  124 ′ to open the circuit. All internal metal surfaces and components are coated with a graphite film. 
         [0091]    In  FIGS. 12   a  and  12   b , there is shown an embodiment of a dual angle tilt switch which is normally open. That is, electrically conductive ball  120  normally contacts terminals  124  when the orientation of the tilt switch is less than +/− angle θ. Since terminals  124  are in common electrical communication with each other, no circuit is completed. When insulated casing  32  is tilted more than +/− angle θ ( FIG. 12   b ) ball  120  rolls into recess  130  of casing  32  and shorts terminal  124 ′ to terminal  124  to close the circuit. All internal metal surfaces and components are coated with a graphite film. 
         [0092]    In  FIGS. 13   a  and  13   b , there is shown an embodiment of a dual angle tilt switch which is normally closed. That is, electrically conductive ball  120  normally contacts terminal  124  and terminal  124 ′ when the orientation of the tilt switch is less than +/− angle θ. When insulated casing  32  is tilted more than +/− angle θ ( FIG. 13   b ) ball  120  rolls out of hole  130  of casing  32  and out of contact with terminal  124  to open the circuit. All internal metal surfaces and components are coated with a graphite film. 
         [0093]    In all of the above embodiments of  FIGS. 1 through 13   b , a graphite film functions to significantly reduce the electrical resistivity at the terminal interfaces in the manner explained earlier herein. 
         [0094]    In  FIGS. 14   a  and  14   b , there is shown an embodiment of a dual angle tilt indicator enhancement. That is, ball  120  normally rests at the apex of internal cavity  130  when the orientation of the tilt switch is less than +/− angle θ. In this orientation ball  130  completely fills aperture  132  thus indicating state A. When casing  32  is tilted more than +/− angle θ ( FIG. 14   b ) ball  120  rolls into a recess of internal cavity  130  of casing  32  and is hidden from view in aperture  132  thus indicating state B. Of course, modifications of this indicator can be made to function as both a passive indicator and an electrical tilt switch in a common unit utilizing the advantages of the aforementioned graphite film. 
         [0095]    Although the invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.