Patent Publication Number: US-2004055360-A1

Title: Device for reducing wear of ink strips in a position sensor

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to linear and rotary position sensors, and more particularly, to a slider assembly having a slider housing which includes standoffs for providing a predetermined contact pressure between spring fingers and an ink strip.  
       BACKGROUND OF THE INVENTION  
       [0002] Several devices utilized in motor vehicles include components that wear after repeated use. A device having such components is a contact position sensor that detects the position of an object such as an armature. Referring to FIG. 1, portions of a linear position sensor  10  having a slider assembly  12  is shown. The slider assembly  12  is positioned adjacent a board  32  having first  28  and second  30  ink strips which may be resistive inks used in forming a sensing circuit for detecting position. In another configuration, one of the ink strips may be conductive and the other resistive.  
       [0003] The slider assembly  12  includes a base  14  and a plunger  16  that is adapted to be received by an armature. The base  14  includes a center member  18  located between first  20  and second  22  arms which extend outwardly from the base  14  to form a substantially U-shaped configuration. The first  20  and second  22  arms include first  24  and second  26  finger elements which are adapted to contact the first  28  and second  30  ink strips, respectively, so as to form electrical contact. In use, the first  24  and second  26  finger elements move across the first  28  and second  30  ink strips in accordance with corresponding armature movement. This provides an output, such as a voltage output, which is proportional to the relative position of the first  24  and second  26  finger elements with respect to the first  28  and second  30  ink strips.  
       [0004] The first  20  and second  22  arms and first  24  and second  26  finger elements are fabricated from a resilient material having spring properties. The slider assembly  12  is positioned relative to the board  32  such that the first  24  and second  26  finger elements exert a spring force for biasing the first  24  and second  26  finger elements against the first  28  and second  30  ink strips. This provides a predetermined contact pressure suitable for minimizing wear of the first  28  and second  30  ink strips.  
       [0005] During typical motor vehicle operation the slider assembly  12  is frequently subjected to vibrations which are of sufficient magnitude to overcome the spring force exerted by the first  24  and second  26  finger elements. This substantially increases the frequency with which the first  24  and second  30  spring elements move across portions of the first  28  and second  30  ink strips, thus increasing relative motion therebetween and causing accelerated wear of the first  28  and second  30  ink strips. A method for reducing the relative motion is to increase the spring force exerted by the first  24  and second  26  finger elements on the first  28  and second  30  ink strips. However, this results in an increased ink wear rate due to increased finger element contact pressure. Another method is to use more stringent mechanical clearances when fabricating the sensor. A disadvantage with this approach is that manufacturing costs are increased. In addition, further control of relative motion is desired in order to reduce the ink wear rate and ultimately increase the reliability of such sensors.  
       SUMMARY OF THE INVENTION  
       [0006] A slider assembly for use in a position sensor having a board that includes at least one ink strip. The slider assembly includes a housing for attachment to an object whose position is being detected. The housing includes standoffs for contacting portions of the board which are adjacent the ink strip. An arm extends the housing, wherein the arm includes finger elements which contact the ink strip. The assembly further includes a spring for biasing the standoffs against the board to then bias the finger elements against the ink strip so as to provide a predetermined contact pressure.  
       [0007] The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, may be best understood by reference to the following description taken in conjunction with the accompanying figures. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 is a perspective view of portions of a linear position sensor.  
     [0009]FIG. 2 is a side view of slider assembly in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0010] While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of FIGS.  1 - 2 .  
     [0011] Referring to FIG. 2, a side view of a slider assembly  34  for use in a position sensor in accordance with the present invention is shown. The slider assembly  34  includes a slider housing  36  that is adapted to be connected to an object whose position is to be detected, such as an armature, which moves as depicted by arrow  38 . The slider assembly  36  includes at least one contactor  40  that extends toward the board  32 . The contactor  40  includes a spring arm  42  and spring fingers  44  which are formed on an end of the spring arm  42 . The spring fingers  44  contact an associated ink strip  46  so as to form electrical contact as part of a position sensing circuit. The spring arm  42  and spring fingers  44  are fabricated from a resilient material to enable biasing of the spring fingers  44  against the ink strip  46 . In use, the spring fingers  44  move across the ink strip  46  in accordance with corresponding armature movement. This provides an output, such as a voltage output, which is proportional to the relative motion of the spring fingers  44  with respect to the ink strip  46 .  
     [0012] The slider housing  36  includes legs or standoffs  48  which are adapted to contact portions of the board  32  adjacent to the ink strip  46 . The standoffs  48  are sized such that the spring fingers  44  are biased against the ink strip  46  to provide a predetermined contact pressure. A spring  50  is located between a back surface  52  of the slider housing  36  and a surface of a sensor housing  54 . The spring  50  is adapted to move in conjunction with the slider assembly  34 , and may be located in a channel formed in the sensor housing  54 , for example. The spring  50  is configured to exert a force against the slider housing  36  to bias the standoffs  48  against the board  32  to thus bias the spring fingers  44  against the ink strip  46  so as to provide the predetermined contact pressure. The spring  50  enables the slider assembly  34  to be free floating, thus substantially isolating the spring fingers  44  from vibrations which occur during typical motor vehicle operation. In addition, this arrangement substantially reduces the need for highly precise alignment of the slider assembly  34 , thus enabling the use of less stringent mechanical tolerances when fabricating the sensor.  
     [0013] While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the foregoing description. It is noted that the present invention may be used in either linear or rotary position sensors, although it may be more adaptable to rotary arrangements. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.