Patent Abstract:
A position sensor includes a variable capacitor assembly and a circuit board. The variable capacitor assembly includes a baseboard and a dielectric coupling element. The baseboard includes a baseboard body, a grounding electrode and two power electrodes. The grounding electrode is disposed nearby one side of the baseboard body. The two power electrodes are disposed separately near the other side of the baseboard body. The dielectric coupling element is spaced with the two power electrodes and the grounding electrode, and operable to be moved along a moving path. A covering condition is varied when the dielectric coupling element is operated to move along the moving path. When a power is alternatively applied to the power electrodes, a pair of capacitance values between the grounding electrode and the power electrodes is varied with the covering condition to accordingly determine a relative position of the coupling element along the moving path.

Full Description:
This application claims the benefit of Taiwan Patent Application Serial No. 105103757, filed Feb. 4, 2016, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The invention relates to a position sensor and a variable capacitor assembly of the position sensor, and more particularly to the position sensor and the variable capacitor assembly that can realize changes of the area covered by the dielectric coupling element at two more electrode plates so as further to alter the fringing capacitance thereof. 
     2. Description of the Prior Art 
     Generally speaking, a conventional potentiometer applies mainly a variable resistor to detect a displacement. However, the service life of such a resistor-type potentiometer is usually reduced by the wear at the carbon of the resistor. Hence, another technique for detecting the displacement is to apply the capacitance effect. 
     Referring to  FIG. 1 , the capacitance effect between two electrode plates in the art is schematically shown. In an ordinary circuit layout, the capacitor is usually seen as one of basic electronic components. The capacitance effect of the capacitor is induced by the potential difference between the two electrode plates PA 1  and PA 2 . When the two electrode plates PA 1  and PA 2  are parallel, a parallel capacitance field PEF would be formed between the two parallel electrode plates PA 1  and PA 2 . Meanwhile, at the back and lateral sides of the two respective electrode plates PA 1  and PA 2 , a fringing capacitance field FEF would be formed. 
     Referring to  FIG. 2 , a schematic view showing the work theory of a conventional area-varying capacitance sensor is provided. As shown, when the electrode plate PA 1  maintains stationary and the electrode plate PA 2  displaces horizontally along a parallel direction P 1  with respect to the electrode plate PA 1 , then it is obvious that the covering area of the electrode plate PA 2  upon the electrode plate PA 1  would vary as well. Namely, the overlapping area of these two electrode plates PA 1  and PA 2  is varied according to the movement in between. Based on the relative movement, equally the change of the overlapping area, the parallel capacitance field PEF and the fringing capacitance field FEF induced by these two electrode plates PA 1  and PA 2  would vary as well. 
     Referring to  FIG. 3 , changes of the capacitance value with respect to the horizontal displacement for the conventional area-varying capacitance sensor of  FIG. 2  are plotted. As shown, since an electric field would be induced by the potential difference between these two electrode plates, thus, in the art, a conductive metal such as a copper is usually applied as a material to produce the electrode plate. In considering the area-varying capacitance sensor, two copper electrode plates can be firstly at a separate state (displacement is 0%), then shift horizontally to become a state of completely overlapping (displacement is 50%), and shift horizontally further to become another separate state (displacement is 100%). The changes in the capacitance values between these two copper electrode plates are plotted in  FIG. 3 . as shown in  FIG. 3 , changes for these two conductive metal plates are not significant. 
     As described above, since relative movement between these two metallic electrode plates won&#39;t cause significant changes in the capacitance value, thus, by applying the technique of parallel capacitance effect to the displacement sensor, the sensitivity of the displacement detection via the change in capacitance is poor, and thus can&#39;t used as a tool to perform precise control. 
     SUMMARY OF THE INVENTION 
     In considering that the current capacitance sensor mainly applies the parallel capacitance effect to detect the displacement of the electrode plates, since the detection sensitivity of the area-varying capacitance sensor by applying the parallel capacitance effect is highly dependent on the capacitance and the length of the electrode plate, thus the increase upon the detection sensitivity can only be provided by increasing the length of the electrode plate. However, such a resort would change the size of the sensor as well, and thereby would affect the convenience of usage. Accordingly, to resolve the aforesaid shortcomings in the current area-varying capacitance sensor, it is the primary object of the present invention to provide a position sensor and a variable capacitor assembly that can apply a dielectric coupling element to cover or shield the electrodes. By varying the coverage rate upon the electrodes, the capacitance values can be altered, and further the displacement of the dielectric coupling element can be calculated. 
     In the present invention, the variable capacitor assembly is located inside a position sensor including a capacitance-detecting circuit for detecting a pair of alternative capacitance values of the variable capacitor assembly. The variable capacitor assembly includes a baseboard and a dielectric coupling element. 
     The baseboard includes a baseboard body, a grounding electrode and at least two power electrodes. The baseboard body extending in a longitudinal direction further includes an electrode layout surface. The grounding electrode for electrically coupling the capacitance-detecting circuit is located on the electrode layout surface and extends in the longitudinal direction. The at least two power electrodes are located linearly on one lateral side of the electrode layout surface by extending individually in the longitudinal direction while the grounding electrode is located on another lateral side thereof. The at least two power electrodes are alternatively connected with a power source of the capacitance-detecting circuit. The grounding electrode and each of the at least two power electrodes are spaced by a preset space in a width direction perpendicular to the longitudinal direction. 
     The dielectric coupling element has a dielectric constant and is located above the grounding electrode and the at least two power electrodes in a vertical direction perpendicular to the electrode layout surface. The dielectric coupling element is movable along a moving path parallel to the longitudinal direction. 
     In the present invention, each of the at least two power electrodes has an action surface of parallel capacitance effect facing the grounding electrode and another action surface of fringing capacitance effect facing the moving path, an area of the action surface of parallel capacitance effect is larger than that of the action surface of fringing capacitance effect, the dielectric constant is ranged between 10 and 50. While the dielectric coupling element displaces along the moving path, a position of the at least two power electrodes and the grounding electrode is covered by the dielectric coupling element. Also, the capacitance-detecting circuit detects changes of the pair of the alternative capacitance values as the covering position alters, and thus a relative position of the dielectric coupling element on the moving path is determined. 
     In one embodiment of the present invention, each of the at least two power electrodes is a rectangular plate structure. 
     In one embodiment of the present invention, the position sensor further includes a movable carrier, the movable carrier is separate from the grounding electrode and the at least two power electrodes in the vertical direction, and the movable carrier is to mount the dielectric coupling element and further has at least one control member for a user to displace the movable carrier along the moving path. The position sensor further includes a housing, and motion of the movable carrier is restrained by at least one track inside the housing. 
     In one embodiment of the present invention, the dielectric coupling element is a ceramic plate. Preferably, the ceramic plate is made of one of an Aluminum oxide, a Calcium oxide, a graphite, a superphosphate, a ferric oxide, a copper oxide, a tin oxide, a lead dioxide and a titanium oxide, a thickness of the ceramic plate is ranged between 0.5 mm and 1.2 mm, a length of the ceramic plate is ranged between 16 mm and 25 mm, a width of the ceramic plate is ranged between 10 mm and 15 mm, and a distance between the ceramic plate and a combination of the at least two power electrodes and the grounding electrode in the vertical direction is ranged between 0.1 mm and 0.5 mm. 
     In one embodiment of the present invention, the position sensor includes a variable capacitor assembly and a circuit board. The variable capacitor assembly further includes a baseboard and a dielectric coupling element. The baseboard includes a baseboard body, a grounding electrode and at least two power electrodes. The baseboard body extending in a longitudinal direction further includes an electrode layout surface. The grounding electrode for electrically coupling the capacitance-detecting circuit is located on the electrode layout surface and extends in the longitudinal direction. The at least two power electrodes are located linearly on one lateral side of the electrode layout surface by extending individually in the longitudinal direction while the grounding electrode is located on another lateral side thereof. The at least two power electrodes are alternatively connected with a power source of the capacitance-detecting circuit. The grounding electrode and each of the at least two power electrodes are spaced by a preset space in a width direction perpendicular to the longitudinal direction. 
     The dielectric coupling element has a dielectric constant and is located above the grounding electrode and the at least two power electrodes in a vertical direction perpendicular to the electrode layout surface. The dielectric coupling element is movable along a moving path parallel to the longitudinal direction. 
     The circuit board includes a capacitance-detecting circuit electrically coupling the grounding electrode and the at least two power electrodes, and is to detect a pair of alternative capacitance values of the variable capacitor assembly. 
     In the present invention, each of the at least two power electrodes has an action surface of parallel capacitance effect facing the grounding electrode and another action surface of fringing capacitance effect facing the moving path, an area of the action surface of parallel capacitance effect is larger than that of the action surface of fringing capacitance effect, the dielectric constant is ranged between 10 and 50. While the dielectric coupling element displaces along the moving path, a position of the at least two power electrodes and the grounding electrode is covered by the dielectric coupling element. Also, the capacitance-detecting circuit detects changes of the pair of the alternative capacitance values as the covering position alters, and thus a relative position of the dielectric coupling element on the moving path is determined. 
     In one embodiment of the present invention, the at least two power electrodes             a rectangular plate structure.
     In one embodiment of the present invention, the position sensor further includes a movable carrier, the movable carrier is separate from the grounding electrode and the at least two power electrodes in the vertical direction, and the movable carrier is to mount the dielectric coupling element and further has at least one control member for a user to displace the movable carrier along the moving path. The position sensor further includes a housing, and motion of the movable carrier is restrained by at least one track inside the housing. 
     In one embodiment of the present invention, the dielectric coupling element is a ceramic plate. Preferably, the ceramic plate is made of one of an Aluminum oxide, a Calcium oxide, a graphite, a superphosphate, a ferric oxide, a copper oxide, a tin oxide, a lead dioxide and a titanium oxide, a thickness of the ceramic plate is ranged between 0.5 mm and 1.2 mm, a length of the ceramic plate is ranged between 16 mm and 25 mm, a width of the ceramic plate is ranged between 10 mm and 15 mm, and a distance between the ceramic plate and a combination of the at least two power electrodes and the grounding electrode in the vertical direction is ranged between 0.1 mm and 0.5 mm. 
     In one embodiment of the present invention, the baseboard and the circuit board is integrated into a unique circuit board. 
     As described above, by comparing to the prior art that the conventional area-varying capacitance sensor mainly apply the parallel capacitance effect to derive the displacement of the electrode plate, the present invention applies the dielectric coupling element to alter the coverage rate upon the power electrodes and the grounding electrode, so as further to vary the capacitance values between each of the power electrodes and the grounding electrode, such that the position change of the dielectric coupling element can be calculated by evaluating the changes in the capacitance values. 
     All these objects are achieved by the position sensor and the variable capacitor assembly thereof described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which: 
         FIG. 1  demonstrates schematically the capacitance effect between two electrode plates in the art; 
         FIG. 2  is a schematic view showing the work theory of a conventional area-varying capacitance sensor; 
         FIG. 3  shows changes of the capacitance value with respect to the horizontal displacement for the conventional area-varying capacitance sensor of  FIG. 2 ; 
         FIG. 4  is an exploded view of a preferred embodiment of the position sensor in accordance with the present invention; 
         FIG. 5  is an exploded view of the variable capacitor assembly of  FIG. 4 ; 
         FIG. 6  is a lateral side view of  FIG. 5 ; 
         FIG. 7  shows schematically the capacitance-detecting circuit for the position sensor of  FIG. 4 ; 
         FIG. 8A  shows schematically a view of the variable capacitor assembly of  FIG. 5 , with the dielectric coupling element located at an initial position; 
         FIG. 8B  shows schematically a view of the variable capacitor assembly of  FIG. 5 , with the dielectric coupling element located at a center position; 
         FIG. 8C  shows schematically a view of the variable capacitor assembly of  FIG. 5 , with the dielectric coupling element located at a terminal position; 
         FIG. 9  shows relationship of a pair of alternative capacitance values with respect to the displacement percentage for the duration of the dielectric coupling element moving from the initial position to the terminal position along a moving path; and 
         FIG. 10  is an exploded view of another embodiment of the position sensor in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention disclosed herein is directed to a position sensor and a variable capacitor assembly of the position sensor. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention. 
     Refer now to  FIG. 4  through  FIG. 7 ; where  FIG. 4  is an exploded view of a preferred embodiment of the position sensor in accordance with the present invention;  FIG. 5  is an exploded view of the variable capacitor assembly of  FIG. 4 ;  FIG. 6  is a lateral side view of  FIG. 5 ; and,  FIG. 7  shows schematically the capacitance-detecting circuit for the position sensor of  FIG. 4 . 
     As shown, the position sensor  100  includes a variable capacitor assembly  1 , a circuit board  2 , a movable carrier  3  and a housing  4 . 
     The variable capacitor assembly  1  includes a baseboard  11  and a dielectric coupling element  12 . The baseboard  11  further includes a baseboard body  111 , a grounding electrode  112  and two power electrodes  113  and  114 . 
     The baseboard body  111  extending in a longitudinal direction L 1  has an electrode layout surface  1111 . The grounding electrode  112  located on the electrode layout surface  1111  is extended in the longitudinal direction L 1 . The two power electrodes  113  and  114  both located linearly on the same lateral side of the electrode layout surface  1111  are extended individually in the longitudinal direction L 1  by spaced a predetermined distance. The grounding electrode  112  located on another lateral side of the electrode layout surface  1111  is extended in the longitudinal direction L 1 . The grounding electrode  112  and each of the two power electrodes  113  and  114  are spaced by a preset space in a width direction W 1  perpendicular to the longitudinal direction L 1 . The two power electrodes  113  and  114  are alternatively connected with a power source (not shown in the figure). Here, the term “alternatively” indicates that connection of the power source to the two power electrodes  113  and  114  is switch-able around the power electrode  113  and the power electrode  114 . 
     The dielectric coupling element  12  with a dielectric constant K is located above, in a vertical direction D, the grounding electrode  112  and the two power electrodes  113  and  114  on the electrode layout surface  1111 . The dielectric coupling element  12  is movable along a moving path P parallel to the longitudinal direction L 1 . In this embodiment, the dielectric coupling element  12  can be a ceramic plate made of one of an Aluminum oxide, a Calcium oxide, a graphite, a superphosphate, a ferric oxide, a copper oxide, a tin oxide, a lead dioxide and a titanium oxide. In addition, the thickness of the ceramic plate is ranged between 0.5 mm and 1.2 mm, the length of the ceramic plate is ranged between 16 mm and 25 mm, and the width of the ceramic plate is ranged between 10 mm and 15 mm. The distance between the ceramic plate and each of the two power electrodes  113  and  114  and the grounding electrode  112  are ranged between 0.1 mm and 0.5 mm in the vertical direction D. 
     The circuit board  2  is located on a surface of the baseboard  11  opposing to the electrode layout surface  1111 , and includes thereon a capacitance-detecting circuit  21 . The capacitance-detecting circuit  21  is electrically connected with the grounding electrode  112  and the two power electrodes  113  and  114 , such that the aforesaid power source (Vi in the figure) can alternatively connect with the power electrodes  113  and  114  of the variable capacitor assembly  1  and thus a pair of alternative capacitance values of the variable capacitor assembly  1  can be detected. In this embodiment, the capacitance-detecting circuit  21  is consisted of a reference capacitance C, an AC/DC circuit RC, a filter circuit LC and a comparator OPA. The capacitance-detecting circuit  21  uses the reference capacitance C and a pair of the alternative capacitance values detected by the variable capacitor assembly  1  to produce two voltages V 1  and V 2  by the AC/DC circuit RC and the filter circuit LC. Further, these two voltages V 1  and V 2  are compared by the comparator OPA so as to deduce the relationship of these two capacitance values. 
     In this embodiment, the capacitance-detecting circuit  21  can be constructed at the back side of the circuit board  2 , opposing to the side thereof contacting the baseboard  11 . The capacitance-detecting circuit  21  can electrically couple the grounding electrode  112  and the two power electrodes  113  and  114  through external or internal wiring. However, since the means of electrically coupling the capacitance-detecting circuit  21 , the grounding electrode  112  and the two power electrodes  113  and  114  is ordinary in the art, and thus details thereabout would be omitted herein. In addition, in this embodiment, the baseboard  11  and the circuit board  2  can be integrated as a unique circuit board. 
     The movable carrier  3  is mounted in the vertical direction D by spacing the grounding electrode  112  and the two power electrodes  113  and  114  so as to locate the dielectric coupling element  12  in between. The movable carrier  3  further has a control member  31  for the user to move the movable carrier  3  along the moving path P and further to drive the dielectric coupling element  12  to displace along the moving path P. In this embodiment, the movable carrier  3  can further include four supports (not shown in the figure) to separate the movable carrier  3  and the baseboard  11  and to thus generate a room for mounting the dielectric coupling element  12  in between with the combination of the grounding electrode  112  and the two power electrodes  113  and  114  in the vertical direction D. 
     The housing  4  is fixed onto the baseboard  11 , so that movement of the movable carrier  3  in the longitudinal direction L 1  is restrained inside the housing  4 . In this embodiment, the movable carrier  3  can move along an internal track (not shown in the figure) of the housing  4  in the longitudinal direction L 1 , or can be restrained by the room formed between the housing  4  and the baseboard  11 . More evenly, in the housing  4 , at least one guide pillar extending in the longitudinal direction L 1  can be used to penetrate the movable carrier  3  for restraining the movable carrier  3  to displace in the longitudinal direction L 1  between the housing  4  and the baseboard  11 . 
     As shown in  FIG. 4  through  FIG. 6 , by having the power electrode  114  as a typical example, the power electrode  114  has an action surface  1141  of parallel capacitance effect facing the grounding electrode  112 , and another action surface  1142  of fringing capacitance effect facing the moving path (not shown in the figure, but located substantially at the position around the dielectric coupling element  12 ). The area of the action surface  1141  of parallel capacitance effect is greater than that of the action surface  1142  of fringing capacitance effect. The dielectric constant K of the power electrode  114  is ranged between 10 and 50. Upon alternatively coupling the power source with the power electrodes  113  and  114 , when the dielectric coupling element  12  displaces along the moving path, the covering position of the dielectric coupling element  12  over the two power electrodes  113  and  114  and the grounding electrode  112  is altered, such that the capacitance-detecting circuit  21  can detect changes of the pair of the alternative capacitance values accounted for the changes in the covering position. Upon such an arrangement, the relative position of the dielectric coupling element  12  in the moving path can be realized. 
     Refer now to  FIGS. 8A-8C  and  FIG. 9 ; where  FIG. 8A  shows schematically a view of the variable capacitor assembly of  FIG. 5 , with the dielectric coupling element located at an initial position;  FIG. 8B  shows schematically a view of the variable capacitor assembly of  FIG. 5 , with the dielectric coupling element located at a center position;  FIG. 8C  shows schematically a view of the variable capacitor assembly of  FIG. 5 , with the dielectric coupling element located at a terminal position; and,  FIG. 9  shows relationship of a pair of alternative capacitance values with respect to the displacement percentage for the duration of the dielectric coupling element moving from the initial position to the terminal position along the moving path. As shown, while the aforesaid power source connects with the power electrode  113 , the relationship between the detected capacitance value and the displacement percentage is shown by a first curve C 1  in  FIG. 9 . On the other hand, while the aforesaid power source connects with the power electrode  114 , the relationship between the detected capacitance value and the displacement percentage is shown by a second curve C 2 . As shown in  FIG. 9 , each of the displacement percentage is to read a first capacitance value on the first curve C 1  and a second capacitance value on the second curve C 2 . This pair of the alternative capacitance values is namely the first capacitance value and the second capacitance value. As described above, while the dielectric coupling element  12  is operated to displace to any position on the moving path P, a corresponding pair of the alternative capacitance values can be alternatively detected to include the first capacitance value and the second capacitance value. By analyzing the first capacitance value and the second capacitance value, the relative position of the dielectric coupling element  12  on the moving path P can be determined. 
     When the dielectric coupling element  12  is displaced from an initial position DI to a center position DC along the moving path P, the covering area of the dielectric coupling element  12  upon the power electrode  113  would decrease, while the covering area of the dielectric coupling element  12  upon the power electrode  114  would increase. As the dielectric coupling element  12  keeps moving along the moving path P to a terminal position DT, from the first curve C 1  and the second curve C 2  in  FIG. 9 , it is understood that the covering area of the dielectric coupling element  12  upon the power electrode  113  would be decreased to a minimum, evenly to a state of no coverage at all. At the same time, the covering area of the dielectric coupling element  12  upon the power electrode  114  would be increased to a maximum, evenly to a state of fully coverage. The displacement percentage in  FIG. 9  is calculated by dividing the distance ΔS (the distance measured from the initial position DI of the dielectric coupling element  12  to the instant position thereof on the moving path P) by the total distance ΔST (the distance between the initial position DI of the dielectric coupling element  12  and the terminal position DT thereof on the moving path P). The capacitance values can thus be detected by the capacitance-detecting circuit  21  through the power electrodes  113  and  114  so as to plot the curve C 1  for the power electrode  113  and the curve C 2  for the power electrode  114 . In addition, the curve CA stands for the relationship of the capacitance values for the relative moment between the aforesaid two conventional metallic electrode plates. 
     As described above, by comparing to the prior art that uses the parallel capacitance effect between the two metallic electrode plates to determine the coverage area in between, since the dielectric coupling element  12  with a dielectric constant K ranging between 10 and 50 is applied to cover the electric field generated due to the fringing capacitance effect among the grounding electrode  112  and the two power electrodes  113  and  114 , so as further to realize the corresponding capacitance values altered by the instant fringing capacitance effect among the grounding electrode  112  and the two power electrodes  113  and  114 . Thus, the displacement percentage of the dielectric coupling element  12  can be determined by judging the change in the capacitance values. 
     In addition, since the present invention applies the dielectric coupling element  12  to cover the electric field between the power electrode  113  and the grounding electrode  112  and also to cover the electric field between the power electrode  114  and the grounding electrode  112 , thus while the dielectric coupling element  12  is displaced along the moving path P above and from the power electrode  113  to the power electrode  114 , the capacitance-detecting circuit  21  can detect the changes of the curves C 1  and C 2  corresponding to the capacitance values of the respective power electrode  113  and  114 , such that the moving direction and the relative position of the dielectric coupling element  12  can be determined by judging the trends of the curves C 1  and C 2 . 
     Referring now to  FIG. 10 , an exploded view of another embodiment of the position sensor in accordance with the present invention is present. As shown, the position sensor  100 ′ includes a variable capacitor assembly  1 ′, a circuit board  2 ′, a movable carrier  3 ′ and a housing  4 ′. 
     The variable capacitor assembly  1 ′ includes a baseboard  11 ′ and a dielectric coupling element  12 ′. The baseboard  11 ′ further includes a baseboard body  111 ′, a grounding electrode  112 ′ and two power electrodes  113 ′ and  114 ′. The position sensor  100 ′ in this embodiment is similar to the aforesaid position sensor  100 . Similarly, the baseboard body  111 ′ has an electrode layout surface  1111 ′, the grounding electrode  112 ′ and the two power electrodes  113 ′ and  114 ′ are all mounted on the electrode layout surface  1111 ′, the dielectric coupling element  12 ′ is mounted to separate the movable carrier  3 ′ and the combination of the grounding electrode  112 ′ and the two power electrodes  113 ′ and  114 ′, and the housing  4 ′ is fixed above the baseboard  11 ′. The major difference between these two embodiments is that the circuit board  2 ′ of this embodiment is located at a bottom side of the baseboard  11 ′ by opposing to the electrode layout surface  1111 ′ and a capacitance-detecting circuit  21 ′ for coupling electrically the grounding electrode  112 ′ and the two power electrodes  113 ′ and  114 ′ is on the top surface of the circuit board  2 ′. 
     In summary, by comparing to the prior art that uses the parallel capacitance effect between the two metallic electrode plates to determine the coverage area in between, since the dielectric coupling element with a dielectric constant K ranging between 10 and 50 is applied to cover the electric field generated due to the fringing capacitance effect among the grounding electrode and the two power electrodes, so as further to realize the corresponding capacitance values altered by the instant fringing capacitance effect among the grounding electrode and the two power electrodes. Thus, the displacement percentage of the dielectric coupling element can be determined by judging the change in the capacitance values. Upon such an arrangement, the sensitivity in detecting the capacitance values can be enhanced, and also the non-contact detection provided by the present invention can substantially increase the service life of the position sensor. 
     While the present invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be without departing from the spirit and scope of the present invention.

Technology Classification (CPC): 6