Abstract:
A contactless potentiometer is described wherein the conductive and resistive traces of the potentiometer are contained within a sealed channel formed of non-conductive material. The electrical gap between the conductive and resistive traces is bridged by a magnetically reactive contactless tap. A magnetic force is applied to the tap through the surface of the channel holding the conductive and resistive traces. This provides a drawing magnetic force to the tap which pulls the tap against the traces and allows for changing the resistance of the potentiometer by laterally moving the tap along the traces as the tap moves to follow the motion of the external force.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to patent application number 20 2005 010 424.8 filed in the German Patent and Trademark Office on Jun. 29, 2005. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a tap for potentiometers, and more particularly to a contactless tap for resistive surfaces by means of magnets. 
         [0004]    2. Background and Related Art 
         [0005]    Film potentiometers on the market operate with an actuating pressure on the tapping pressure pin. Over time, the actuating pressure on the tapping pressure pin strips the upper plastic film on the resistive path, causing the film to wear out. As the plastic film on the resistive path wears out, the resistive path may become increasingly pre-formed and as a result the top layer can pre-actuate electrically, or the contact wiper can physically tear the top layer. This decreases the life of the film potentiometers and can result in locations of lost contact. 
         [0006]    Existing film potentiometers also require a parallel guidance of the tapping pressure pin. This increases manufacturing costs as relatively large additional structure must be provided to support and provide the guidance of the tapping pressure pin. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    A potentiometer is described wherein the conductive and resistive traces of the potentiometer are contained within a sealed channel formed of non-conductive material. The gap between the conductive and resistive traces is bridged by a tap formed from a conductive permanent magnet or by a conductive ferromagnetic material. A magnetic force may be applied to the tap through the surface of the sealed channel by means of a magnet located outside the sealed channel. This pulls the tap against the traces to make electrical contact between the traces. This allows for changing the resistance of the potentiometer by moving the tap along the traces within the sealed channel, as the tap moves according to the magnetic force exerted from without the sealed channel. The force exerted on the tap may be modified by changing the characteristics of the external magnetic force. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0008]    The objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0009]      FIG. 1  shows a perspective view of one embodiment of the invention that comprises a backing and paths; 
           [0010]      FIG. 2  shows a perspective view of the embodiment of  FIG. 1  with a spacer added; 
           [0011]      FIG. 3  shows a perspective view of a tap for use with the embodiment of  FIGS. 1 and 2 ; 
           [0012]      FIG. 4  shows a perspective view of the embodiment of  FIGS. 1-3  with a cover added. 
           [0013]      FIG. 5  shows an inverted perspective view of the embodiment of  FIG. 4  with an external control element added. 
           [0014]      FIG. 6  shows a cross-sectional view of the embodiment of  FIG. 5 . 
           [0015]      FIG. 7  shows a view of an embodiment having a non-linear shape. 
           [0016]      FIG. 8  shows a view of an embodiment having an arc-like shape. 
           [0017]      FIG. 9   a  shows a view of an embodiment having a semi-circular shape. 
           [0018]      FIG. 9   b  shows a view of an embodiment having a circular shape. 
           [0019]      FIG. 10   a  shows a view of an embodiment having a non-linear shape. 
           [0020]      FIG. 10   b  shows a view of an embodiment having a non-linear shape. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring now to the figures, a description of some embodiments of the present invention will be given. It is expected that the present invention may take many other forms and shapes, hence the following disclosure is intended to be illustrative and not limiting, and the scope of the invention should be determined by reference to the appended claims. 
         [0022]    In some embodiments, the invention comprises a sealed channel containing conductive and resistive traces; a tap comprised of one or more materials that are measurably subject to magnetic forces; and an external control element that is measurably subject to magnetic forces. In some embodiments, a permanent magnet or an electromagnet is used as either the tap or the external control element. In some embodiments, because the channel is sealed, there is no physical contact between the tap and the external control element during operation of the invention. 
         [0023]      FIGS. 1 through 4  illustrate the components of one embodiment of the invention comprising a linear slide potentiometer having three connection terminals  30 , as is well-known in the art of potentiometers. The terminals  30  facilitate making connections with the potentiometer for electrical circuits, as is known in the art. Each of the terminals  30  may be physically and electrically connected to one of three paths on a non-conductive backing  32 . The backing  32  may be relatively thin and non-conductive, and may be made of a non-magnetic heat-resistive material such as epoxy or various types of plastic. The overall length of the potentiometer shown in  FIGS. 1 through 4  as well as the lengths of the exemplary paths may be varied to suit the needs of the specific application in which the potentiometer will be used. 
         [0024]    In  FIG. 1 , the topmost terminal  30  is connected to a conductive path  34  that may be a conductive film path made from any number of conductive materials. As non-limiting examples, the conductive path  34  may be made of silver, gold, copper, or aluminum. The conductive path  34  is attached to the backing  32  by any means known in the art, or it may be originally deposited on the backing  32  during manufacture of the backing  32 . In  FIG. 1 , the lower two terminals  30  are connected in an electronic loop that passes through a resistive path  36  and a conductive path  38  in series. The conductive path  38  may be of a different width or thickness than conductive path  34 . All of the paths  34 ,  36 , and  38  may be placed on the top surface of the backing  32  so as to be electrically insulated from the bottom surface of the backing  32 , and available to electrical contact from above the backing  32 . In some configurations, one or more of the paths may be configured to lie in different planes from one another, according to manufacturing or design requirements. 
         [0025]    Although  FIG. 1  shows each of the terminals  30  exiting from one side of the potentiometer, the layout shown in  FIG. 1  may be varied to place the location of the terminals  30  at different positions than shown. For example, the topmost or bottommost terminals  30  might optionally be placed on the right and connected to the conductive paths  34  and  38  respectively. Because the conductive paths  34  and  38  are conductive, this change in terminal location would have no electrical effect. These types of variations are known in the art to facilitate connection of the potentiometer in whatever way is most useful for the particular application, and are embraced by the invention. The various paths  34 ,  36 ,  38  may be routed around mounting hole  40  or any variety of other shape configurations of backing  32  in order to allow the potentiometer to be fixedly mounted within an electrical application. 
         [0026]    The resistive path  36  may be formed by any number of materials and processes known in the art of forming such resistive paths. The resistive path  36  may be of a thickness similar to conductive path  34  to facilitate contact between the resistive path  36  and the connecting tap (not shown in  FIG. 1 ) and between the conductive path  34  and the connecting tap (not shown in  FIG. 1 ). In one embodiment, the resistive path  36  may be made of a special conductive resistor that is laid down on the backing  32 , as is commonly used for slide or linear potentiometers. 
         [0027]      FIG. 2  shows the same embodiment as  FIG. 1  but with the addition of a non-conductive spacer  42  that has been placed on top of the backing  32  and attached to the backing  32 . The spacer  42  may be constructed of any material that does not provide an electrical connection between terminals  30  and paths  34 ,  36 , and  38 . Non-limiting examples of such materials include ceramics and many types of plastics. Further, the method of attaching spacer  42  to backing  32  may be done by any method that does not provide any electrical connections between the terminals  30  and paths  34 ,  36 ,  38 . Non-limiting methods that may be used to attach spacer  42  to backing  32  include gluing and laminating. 
         [0028]    The spacer  42  may comprise a cut-out or window  44  that leaves the conductive path  34  and the resistive path  36  uncovered or exposed over at least a portion of their length, while at the same time sealing the perimeter of the part to the entry of foreign particles or environmental contaminants. In this manner, the spacer  42  forms a trough or channel in which the tap (not shown in  FIG. 2 ) for the potentiometer may move to provide an electrical contact between the conductive path  34  and the resistive path  36 . Then, as is known in the art, the resistance between the topmost terminal  30  and either of the two lower terminals  30  may be varied by moving the tap (not shown) laterally within the channel formed by the window  44 . 
         [0029]      FIG. 3  shows a perspective view of one embodiment of a tap  46  for use with the embodiment of the potentiometer shown in  FIGS. 1 and 2 . In this embodiment, the tap  46  may be contactless, in that movement of the tap is controlled or caused by an element that is not in physical contact with the tap. The tap  46  may be formed out of either an electrically-conductive permanent magnet or an electrically-conductive ferromagnetic material that will react to an externally-applied magnetic force. In one embodiment, tap  46  comprises a neodymium-iron-boron NdFeB or other “rare-earth” magnet. The diameter  48  of the tap  46  may be chosen so as to be small enough that the tap  46  fits within the channel formed by the window  44  of the spacer  42  but also so as to be large enough to contact both the conductive path  34  and the resistive path  36  even when the tap  46  is contacting any side of the window  44  while in the channel. The thickness  50  of the tap is chosen so as to be thinner than the thickness of the spacer  42  so as to allow free non-frictionally-impaired movement of the tap within the channel after a non-conductive cover is placed over the channel, as described hereinafter. 
         [0030]    In use, the tap  46  is placed within the channel or trough formed by the window  44 . If the orientation of the externally-applied magnetic field to control the tap  46  will be important and if the tap  46  is a permanent magnet, the orientation of the tap  46  is chosen so as to properly interact with the externally-applied magnetic field, as will be appreciated by one skilled in the art from the following description of use of the tap  46  in the potentiometer. After the tap  46  is placed in the channel, a non-conductive cover  52  is placed over the window  44  and attached to the spacer  46  in a fashion similar to the attachment of the spacer  46  to the backing  32 . (See  FIG. 4 .) The cover  52  may be made of any non-conductive material, and may be formed of a material similar to the material used for the backing  32  or the material used for spacer  46 . In this embodiment, the cover  52  seals the window  44 , preventing the intrusion of dirt or other environmental contaminants on to paths  34  and  36 , and thus increasing the useful life of the potentiometer. 
         [0031]    In the embodiment shown in  FIGS. 1-4 , the body of the potentiometer is thus formed by backing  32 , spacer  46 , and cover  52 , which together comprise a sealed channel in which tap  46  is contained.  FIG. 6  shows a cut-away view of backing  32 , spacer  42 , and cover  52 , with tap  46  and traces  34  and  36  visible (in addition to other elements of one embodiment to be discussed below). 
         [0032]    In other embodiments, a sealed channel may be formed from a unitary piece of material into which traces and a tap are added, or from a smaller or larger number of individual components formed to create a sealed channel containing traces and a tap. In some embodiments, the materials used to create a sealed channel comprise transparent or semi-transparent materials that permit viewing of the tap; in some embodiments, the materials used to create a sealed channel are substantially opaque. Different portions of the sealed channel or the components thereof may have varying opacity as required by a specific application. The sealed channel may further comprise flexible materials or materials that resist flexure. The heat-resistant properties and durability of the materials comprising the sealed channel may be selected based on the requirements of a specific application by one skilled in the art. 
         [0033]    In some embodiments, the bottom surface of the backing  32  is in contact with the external control element during use of the potentiometer, such that the external control element biases the tap against the paths  34  and  36  to create an electrical connection. In such an embodiment, the cover  52  may become the surface of the potentiometer that may be attached to the device with which the potentiometer is to be used.  FIG. 5  shows such an inverted potentiometer with the bottom surface of the backing  32  exposed, and the window  44  shown in outline form. Paths  34  and  36  are not shown in  FIG. 5 . An external control element  54  is shown in  FIG. 5 , positioned so as to affect the position of the tap  46  within the sealed channel. In  FIG. 5 , tap  46  is positioned directly under external control element  54 , into the page in this view. The external control element  54  magnetically interacts with the tap  46  and, via the magnetic force existing between the external control element  54  and the tap  46 , pulls the tap  46  against the conductive path  34  and the resistive path  36  so as to electrically connect the conductive path  34  and the resistive path  36  at the location of the external control element  54 . In this embodiment, this magnetic interaction simultaneously secures the external control element  54  to the potentiometer, obviating the need for an external structure to guide the path of the external control element  54 . In some embodiments, the external control element  54  does not physically contact the sealed channel, but moves within an external structure that permits magnetic interaction with the tap  46 . In this manner, the forces exerted on the paths  34  and  36  and on the materials comprising the sealed channel are minimized. 
         [0034]    Because the only contact between the external control element  54  and the tap  46  is magnetic, the force applied to the conductive path  34  and the resistive path  36  is constant and unaffected by most external forces applied to the external control element  54 . For example, if the user of the potentiometer applies a downward force (into the plane of  FIG. 5 ) to the external control element  54 , that force has no effect on the force between the tap  46  and the conductive path  34  and the resistive path  36 . This prevents externally-applied forces from causing damage to the thin films or traces forming the various paths  34 ,  36 . If an external force causes the external control element  54  to move laterally so as to be outside the area defined by the window  44 , the magnetic interaction between the external control element  54  and the tap  46  may simply fade. In some embodiments, the external control element  54  can thus be removed, and if the removal was accidental, the external control element  54  may simply be placed along the backing  32  so as to be over the window  44  and then moved about until it interacts with the tap  46  again. If desired, an external structure corresponding to the window  44  may be provided so as to prevent accidental movements of the external control element  54  beyond the area defined by the window  44 . 
         [0035]    The present invention not only provides for a constant force between the tap  46  and the conductive path  34  and the resistive path  36 , but also provides a means for precision control of the force applied to those paths  34  and  36  by the tap  46 . This may be appreciated by reference to  FIG. 6 .  FIG. 6  is a cross-sectional view of the body of the potentiometer and one embodiment of the external control element  54 . This cross-sectional view clearly shows the interaction of the various members of the body of the potentiometer: the backing  32 , the spacer  42 , and the cover  52 .  FIG. 6  also shows how the conductive path  38  is sandwiched between the spacer  42  and the backing  32 , and hence the exact dimensions of the conductive path  38  are of lesser importance than the dimensions of the conductive path  34  and the resistive path  36 . 
         [0036]      FIG. 6  also illustrates the interaction of the tap  46  with the external control element  54 . In one embodiment, the external control element  54  includes one or more permanent magnets  56 . The permanent magnet or magnets  56  are positioned and oriented so as to attractively interact with the tap  46 . This draws the tap  46  against the conductive path  34  and the resistive path  36  so as to form an electrically-conductive bridge between those paths  34 ,  36 . As the external magnets  56  of the external control element  54  are moved laterally (in and out of the plane of  FIG. 6 ), they draw the tap  46  along the paths  34  and  36  so as to vary the resistance of the potentiometer and provide the potentiometer&#39;s functions. The force that the tap  46  applies to the conductive path  34  and the resistive path  36  may be varied by varying the number of permanent magnets  56  in the external control element  54 . In  FIG. 6 , four permanent magnets  56  are shown as being used. 
         [0037]    In some embodiments, the tap  46  may comprise a magnet and the external control element may comprise a ferromagnetic material; in some embodiments, the external control element may comprise an electromagnet. 
         [0038]    The movement of the external control element  54  may be facilitated by providing an optional housing  58  (shown in outline form in  FIG. 6 ) that contains the external control element (permanent magnet(s)  56  in this embodiment) and thus provides a larger surface or structure to facilitate movement. The housing  58  may also be configured to interact with an external structure that keeps the housing  58  in contact with the body of the potentiometer and keeps the housing  58  aligned with the window  44 . The housing  58  may also provide an additional method for controlling the magnetic force applied to the tap  46 . The housing  58  may be provided with a mechanism to vary the distance of the external control element  54  from the backing  32  and thus the body of the potentiometer. Because magnetic force decreases with distance, the force is varied and controlled by varying the distance of the permanent magnet(s)  56 . In one embodiment, this may be accomplished by attaching the magnet(s)  56  to a screw or nut mechanism, the mechanism screwing in and out of the housing  58 . Alternatively, several housings may be provided that hold the magnet(s)  56  different distances from the body of the potentiometer. 
         [0039]    If the tap  46  is a permanent magnet, the permanent magnet(s)  56  may be oriented so as to provide an attractive force on the tap  46 . If the tap  46  is a ferromagnetic material, the orientation of the permanent magnets  56  does not matter. Alternatively, if the tap  46  is a magnet, the permanent magnets  56  may be replaced with a ferromagnetic material. The magnetic force is then provided primarily by the tap  46 . 
         [0040]    The present invention may assume many other forms. For example, while the illustrated potentiometer is linear, many other shapes could be used as desired.  FIGS. 7 ,  8 ,  9 , and  10  illustrate some of the many possible shapes of embodiments of the present invention. The illustrations in  FIGS. 7-10  are not intended to illustrate any scale relative to one another or to limit the possible sizes or configurations of the invention, as the dimensions and characteristics of an embodiment may be modified, as described herein, according to a particular application as is known in the art. 
         [0041]    Further, the resistive characteristics of the resistive path within the sealed channel may be varied as is known in the art to create a variable resistance profile that suits a particular application. For example, the potentiometer may have a linear or logarithmic resistance profile. 
         [0042]    In some embodiments, the sealed channel in which the tap is contained is configured to move or be moved by a user or by a device with which the potentiometer is intended to operate, while the contactless tap within the sealed channel remains substantially stationary. 
         [0043]    In some embodiments, a discrete external control element is not used. Instead, in some embodiments, the tap within the sealed channel responds to a magnetic force originating with one or more devices with which the potentiometer is intended to interact, such as an electric motor or similar electric device; a speaker; or another electric or electronic device generating or having a magnetic field or magnetic force capable of interacting with the tap of an embodiment of the present invention. 
         [0044]    Various embodiments of the present invention may be used in a multitude of applications, including both applications where potentiometers are currently used and could benefit from the advantages of the present invention, and also applications where potentiometers are not presently used but where a potentiometer having the characteristics of the present invention may make such use feasible or desirable. Non-limiting examples of applications of embodiments of the present invention include a liquid level sensor; a sensor of linear, non-linear, or rotary motion; or a traditional adjustable switch. Such applications may be found in industrial applications where environmental contaminants make the use of traditional potentiometers problematic, such as use as a sensor in food or chemical processing operations; in consumer goods such as appliances, including washing machines and refrigerators; in automotive products; and in many others. 
         [0045]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.