Abstract:
A position sensor ( 5 ) including a moveable agent ( 14 ) and a magnetic sensor ( 15 ) for detecting the change in magnetic induction caused by displacement of the magnet. The magnet is oriented relative to the path of displacement such that the magnet moves angularly relative to the magnetic sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims priority to U.S. provisional application serial No. 60/237,346, the teachings of which are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to linear position sensors.  
         BACKGROUND OF THE INVENTION  
         [0003]    In a wide variety of applications it is necessary and advantageous to sense the linear position of a translating element. For example, in automotive seat applications the seat translates fore and aft on associated track assemblies, either manually or automatically via electro-mechanical means. It is advantageous in automotive application to sense the linear position of the seat on the rack For example, the linear position may be used in a mechanism for controlling deployment of an air bag. Also, the sensed position maybe used for controlling the electro-mechanical actuator that causes translation of the seat, e.g. to provide a seat position memory feature. To date, however, there remains a need for a linear position sensor that is efficient, accurate, and cost-effective. Accordingly, there is a need in the art for a linear position sensor that obviates the deficiencies of the prior art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    Exemplary embodiments of the invention are set forth in the following description and shown in the drawings.  
         [0005]    [0005]FIGS. 1 through 4 are top, isometric, side and end views, respectively, of an exemplary linear position sensor consistent with the invention;  
         [0006]    [0006]FIGS. 5 through 8 are top, isometric, side, and end views, respectively, of another exemplary linear position sensor consistent with the invention;  
         [0007]    [0007]FIG. 9 is a plot of magnet position vs. sensed field strength, for three exemplary configurations consistent with the invention;  
         [0008]    [0008]FIG. 10 is an isometric view of another exemplary linear position sensor consistent with the invention, in a cylindrical configuration;  
         [0009]    [0009]FIG. 11 is an isometric view of another exemplary linear position sensor consistent with the invention, in a rotary configuration;  
         [0010]    [0010]FIG. 12 and  13  is a side view of a variation on the exemplary linear position sensor shown in FIG. 11;  
         [0011]    [0011]FIG. 14 and  15  illustrate top view of two exemplary linear position sensors suitable for application to a rotating disk; and  
         [0012]    [0012]FIG. 16 is an end view of another exemplary linear position sensor consistent with the invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]    Referring to FIGS. 1 through 4, an exemplary linear position sensor consistent with the invention will be described in connection with a Hall effect sensor. Those skilled in the art will recognize, however, that a variety of sensing means may be used. For example, optical, magneto-resistive, fluxgate sensors, etc. may be useful in connection with a sensor consistent with the invention.  
         [0014]    In FIGS. 1 through 4, there is shown an exemplary linear position sensor  5  consistent with the invention. As shown, the position sensor  5  includes two stators  10  delimiting an air gap  11  within which a Hall effect sensor  15  is disposed. A yoke  12  is disposed beneath the stators  10 , as shown, so as to define an air gap  13  therebetween, within which a magnet  14  may travel. The magnet  14  is oriented such that, along the x- and y-axes, none of its edges are parallel or perpendicular to the stators  10  or the yoke  12 . The magnet  14  is disposed within the air gap  13  such that the linear travel path of the magnet  14  is parallel to the length of the principal air gap  11  and the sensor  15 , along the y-axis. Thus, as the magnet  14  travels on its linear path along the y-axis, the sensor  15  detects the change in magnetic induction caused by the linear displacement of the magnet  14  along the x-axis. When the magnet is secured to a moving part e.g. an automotive seat track, the position of the seat track, and hence the seat, is directly proportional to the output of the sensor.  
         [0015]    [0015]FIGS. 5 through 8 illustrate another exemplary linear position sensor consistent with the invention. In this embodiment, the operation and configuration of the linear position sensor is similar to that shown in FIGS. 1 through 4 and described above, with the exception that the yoke  22  and the magnet  24  move in tandem, instead of the yoke  22  being fixed with respect to the stators  20 . Also, the forward end of the magnet is positioned at an angle relative to the remainder of the magnet, as shown for example in FIG. 5.  
         [0016]    [0016]FIG. 9 is a plot of magnet position vs. sensor output in Gauss, illustrating the relationship between magnetic induction and the position of the magnet with respect to the sensor, at various positions, for three exemplary configurations. In the first and second configurations, curves  91  and  92  show the magnetic induction measurements for the exemplary linear position sensor illustrated in FIGS. 1 through 4 and described above, with a 0.40 and 0.25 air gap, respectively. In the third configuration, curve  93  shows the magnetic induction measurements for the exemplary linear position sensor illustrated in FIGS. 5 through 8 and described above, wherein the magnet and the yoke move in tandem Advantageously, each curve is substantially linear, thereby allowing position sensing based on the sensor output  
         [0017]    [0017]FIG. 10 illustrates another exemplary linear position sensor consistent with the invention, in a cylindrical configuration As shown, a pair of arcuate stators  30  define an air gap  31  therebetween, within which a Hall effect sensor  35  is disposed. The yoke  32  is cylindrical and is disposed so as to permit its linear travel parallel to the length of the air gap  31 , and so as to define an air gap  33  between the yoke  32  and the stators  30 . The magnet  34  is attached to the yoke  32  such that the magnet  34  and the yoke  32  move in tandem. The magnet  34  is oriented such that none of the edges of the magnet  34  are parallel or perpendicular to the direction of travel of the cylindrical yoke  32 , or to the stators  30 . Thus, as the magnet  34  travels on its linear path in tandem with the yoke  32 , the sensor  35  detects the change in magnetic induction caused by the displacement of the magnet  14  along an arc defined by the arcuate edges of the stators  30 .  
         [0018]    [0018]FIG. 11 illustrates another exemplary linear position sensor consistent with the invention, in a rotary configuration. As shown, a pair of arcuate stators  40  define an air gap  41  therebetween, within which a Hall effect sensor.  45  is disposed. The yoke  42  is cylindrical and is disposed so as to permit its rotation about its axis. Another air gap is defined by the area between the cylindrical yoke  42  and the stators  40 . An elongate spiral magnet is disposed around the cylindrical yoke  42  such that the magnet  44  and the yoke  42  move in tandem. Thus, as the yoke  42  rotates in tandem with the magnet  44 , the  4 . sensor  45  detects the change in magnetic induction caused by the linear displacement of the magnet  44  in a direction parallel to the axis of rotation of the yoke  42 .  
         [0019]    [0019]FIGS. 12 and 13 depict a variation on the exemplary linear position sensor shown in FIG. 11. As shown in FIGS. 12 and 13, a pair of arcuate stators  50  define an air gap  52  having a Hall effect sensor  54  disposed therein. Also similar to the embodiment illustrated in FIG. 11, a cylindrical yoke  56 , capable of rotating about its axis, is spaced apart from the stators  50  defining another air gap  58  therebetween. Disposed about the circumference of the yoke  56  is an elongated magnet  60  capable of moving in tandem with the yoke  56 . However, in contrast to the embodiment illustrated in FIG. 11, the magnet  60  of the present embodiment is discontinuous, such that there exists a circumferential space  62  between the first end  64  and the second end  66  of the magnet  60 . As with the previous embodiment, as the yoke  56  rotates in tandem with the magnet  60 , the Hall effect sensor  54  detects the change in magnetic induction caused by the linear displacement of the magnet  60  in a direction parallel to the axis of rotation of the yoke  56 . Consistent with this embodiment, a linear output can be obtained for rotational angles of up to about 300 degrees. As with the embodiment illustrated in FIG. 11, the instant embodiment consistent with the present invention may be configured such that the magnet, stators, and Hall effect sensor are disposed within the interior of a tubular yoke.  
         [0020]    Referring to FIGS. 14 and 15 there is shown two exemplary linear positions sensors consistent with the present invention. Referring first to FIG. 14, the position sensor includes two spaced apart stators  70  having and air gap  72  therebetween. Disposed within the air gap  72  is a Hall effect sensor  74 . The two stators  70  and the Hall effect sensor  74  are disposed above a surface of a disk shaped yoke  76  separated by an air gap. Disposed upon the surface of the yoke  76  is an elongated magnet  78  configured in the shape of a spiral. Accordingly, when the yoke  76  and magnet rotate in tandem about the axis of the yoke the Hall effect sensor  74  detects the change in magnetic induction caused by the linear displacement of the magnet  78  in a direction radial to the axis of rotation of the yoke  76 .  
         [0021]    The exemplary embodiment illustrated in FIG. 15 operates in a similar manner as the embodiment shown in FIG. 14. As illustrated, two stators  80  having an air gap  82  are disposed above a disk shaped yoke  84 . Disposed in the air gap  82  between the two stators  80  is a Hall effect sensor  86 . Disposed between the yoke  84  and the stators  80  is a magnet  88  in the shape of a ring. The magnet  88  is positioned eccentrically relative to the yoke  84 , i.e., the axis of the magnet  88  is not collinear with the axis of the yoke  84 . Accordingly, as the yoke  84  and magnet  88  rotate in tandem about the yoke&#39;s axis the Hall effect sensor  86  detects the change in magnetic induction caused by the radial displacement of the magnet  88  relative to the axis of the yoke  84 .  
         [0022]    Further to the exemplary embodiment illustrated in FIG. 15, if the magnet  88  is properly shaped and positioned relative to the axis of the yoke  84  the output from the Hall effect sensor will be a sine wave. The displacement may be calculated from the sine wave output. Alternately, the position sensor may include a second pair of stators  90  offset 90 degrees around the yoke  84  from the first pair of stators  80 . As with the first pair of stators  80 , the second pair of stators are spaced apart having an air gap  92  therebetween. Situated in the air gap  92  is a second Hall effect sensor  94 . The second pair of stators  90  will similarly produce a sine wave output resulting from the displacement of magnet  88  as it rotates in tandem with the yoke  84 . The arc tangent of the sine wave outputs of the two Hall effect sensors  86  and  94  will provide a linear output over the full 360 degree rotation of the yoke  84 .  
         [0023]    In a final illustrated exemplary embodiment shown in FIG. 16 two magnets  100  and  102  employed rendering the sensor insensitive to movement in the Y direction. The magnets  100  and  102  are angled oppositely relative to each other along the length of the magnet in the Z direction, in and out of the page as illustrated. Corresponding to each of the magnets  100  and  102  is a pair of stators  104  and  106  respectively. As with previous embodiments, each pair of stators  104  and  106  is separated by an air gap,  108  and  110  respectively. In each of the air gaps  108  and  110  is a Hall effect sensor  112  and  114 . Also, as with previous embodiments both of the two pairs of stators  104  and  106  are spaced from the magnets  100  and  102  by respective air gap  116  and  118 .  
         [0024]    As illustrated, the stator/Hall effect sensor assemblies are disposed on either side of U shaped channel  120  such that each assembly is facing the other. The magnets and accompanying stators  122  are disposed between the two stator/Hall effect sensor assemblies. Accordingly, as the magnets are translated along the Z direction each of the Hall effect sensors  104  and  106  detects the change in magnetic induction caused by the linear displacement of the respective magnets  100  and  102  in the Y direction. By averaging the outputs of the two sensors  104  and  106  the position sensor is rendered insensitive to movement in the Y direction. Additionally, while not render completely insensitive to movement in the X direction, such sensitivity is reduced.  
         [0025]    The exemplary embodiment consistent with the present invention as illustrated in FIG. 16, and described with reference thereto, may also be configured such that the two stator/Hall effect sensor assemblies are disposed adjacent to each other such that the sensing face of the two assemblies are oppositely directed. Accordingly, the two magnets  100  and  100  would be disposed on the interior of the U channel. Similarly, the two magnets  100  and  102  may be positioned side by side, therein eliminating the need for the U channel arrangement Furthermore, it should be appreciated that the principles described in conjunction to this exemplary embodiment may be applied to any of the preceding exemplary embodiments to realize the same advantages.  
         [0026]    The embodiment described herein have applicability beyond the scope of seat position sensing. These systems could apply to sensing the linear position of any translating element. The embodiments that have been described herein are, therefore, but some of the several which utilize this invention and are set forth here by way of illustration but not of limitation. It is obvious that many other embodiments, which will be readily apparent to those skilled in the art may be made without departing materially from the spirit and scope of the invention as defined in the appended claims.