Abstract:
A magnetically-based position sensor. The sensor includes a magnet, a first collector, a second collector, and a magnetic sensing element. The magnet has at least two poles, and moves along a path. The first collector has a first end and a second end and is configured to collect a magnetic flux. In addition, the first collector is positioned at an angle relative to an axis running parallel to the path and perpendicular to the magnet. The second collector is configured to collect a magnetic flux, and is positioned at an angle relative to the axis running parallel to the path and perpendicular to the magnet, and parallel to the first collector. The magnetic sensing element is coupled to the first and second collectors. A magnetic flux is collected by the first and second collectors, and varies as the magnet moves along the path such that the magnetic flux collected by the first and second collectors indicates a position of the magnet along the path.

Description:
BACKGROUND 
       [0001]    The present invention relates to position measurement using a magnetic sensor. More particularly, embodiments of the invention relate to repeatable position measurements by sensing a magnet&#39;s position relative to a set of angled flux collectors. 
         [0002]    There are many known types of position sensors, including a number of magnetic position sensors. In a typical magnetic sensor, a magnet is connected or otherwise coupled to an element that moves. When the element moves, the magnet moves. Broadly speaking, changes in the magnetic field caused by movement of the magnet can be correlated to position. Magnetic sensing has many advantages over other technologies, including immunity to a “dirty” environment and relative simplicity when using commercially available sensing integrated circuits (ICs) (e.g., Hall-based and magnetoresistive sensors). 
       SUMMARY 
       [0003]    One challenge or deficiency of current magnetic sensors relates to their inability to measure a long range while using a magnet whose largest linear dimension is a small fraction of the measurement range (e.g., have a repeatable measurement over a 50 mm range using a cylindrical magnet that is only 6 mm long). 
         [0004]    In one embodiment, the invention provides a magnetically-based position sensor. The sensor includes a magnet, a first collector, a second collector, and a magnetic sensing element. The magnet has at least two poles, and moves along a path. The first collector has a first end and a second end and is configured to collect a magnetic flux. In addition, the first collector is positioned at an angle relative to an axis running parallel to the path and perpendicular to the magnet. The second collector is configured to collect a magnetic flux, and is positioned at an angle relative to the axis running parallel to the path and perpendicular to the magnet, and parallel to the first collector. The magnetic sensing element is coupled to the first and second collectors. A magnetic flux is collected by the first and second collectors, and varies as the magnet moves along the path such that the magnetic flux collected by the first and second collectors indicates a position of the magnet along the path. 
         [0005]    In another embodiment, the invention provides magnetically-based position sensor including a magnet, at least one magnetic sensing element, a first collector, a second collector, and a common collector. The at least one magnetic sensing element magnetically is coupled to a first pole of the magnet. The first collector is coupled to one of the at least one magnetic sensing elements, and is fixed in position. The second collector is coupled to one of the at least one magnetic sensing elements, and is fixed in position. The common collector is configured to travel along a path, and has a first end magnetically coupled to a second pole of the magnet, and a second end angled such that when the common collector is positioned at a first end of the path, the second end of the common collector is positioned over the first collector only, and when the common collector is positioned at a second end of the path, opposite the first end of the path, the common collector is positioned over the second collector only. 
         [0006]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic representation of a position measuring system with angled collectors. 
           [0008]      FIG. 2  is a schematic representation of the position measuring system of  FIG. 1  showing travel of the magnet. 
           [0009]      FIG. 3  is a schematic representation of the position measuring system of  FIG. 1  showing travel of the magnet. 
           [0010]      FIG. 4  is a schematic representation of the position measuring system of  FIG. 1  showing travel of the magnet. 
           [0011]      FIG. 5  is a graph of the output of the position measuring system of  FIG. 1 . 
           [0012]      FIG. 6  is a schematic representation of an alternative position measuring system. 
           [0013]      FIG. 7A  is a schematic representation of the position measuring system of  FIG. 6  showing travel of the magnet. 
           [0014]      FIG. 7B  is a schematic side view of the position measuring system shown in  FIG. 7A . 
           [0015]      FIG. 8A  is a schematic representation of the position measuring system of  FIG. 6  showing travel of the magnet. 
           [0016]      FIG. 8B  is a schematic side view of the position measuring system shown in  FIG. 8A . 
           [0017]      FIG. 9A  is a schematic representation of the position measuring system of  FIG. 6  showing travel of the magnet. 
           [0018]      FIG. 9B  is a schematic side view of the position measuring system shown in  FIG. 9A . 
           [0019]      FIG. 10  is a graph of the output of the position measuring system of  FIG. 1 . 
           [0020]      FIG. 11A  is a schematic representation of another position measuring system. 
           [0021]      FIG. 11B  is a top view of the position measuring system of  FIG. 11A . 
           [0022]      FIGS. 12A and 12B  show the movement of a common collector of the position measuring system of  FIGS. 11A and 11B . 
           [0023]      FIG. 13  is a graph of the ratio of the outputs of the position measuring system of  FIGS. 11A ,  11 B,  12 A, and  12 B. 
           [0024]      FIG. 14A  is a schematic representation of an alternative embodiment of the position measuring system of  FIG. 11A . 
           [0025]      FIG. 14B  is a top view of the position measuring system of  FIG. 14A . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. In addition, no single element or feature should be deemed indispensable or essential merely because it is described as part of a particular embodiment or example explained or set forth herein. 
         [0027]      FIG. 1  shows an embodiment of the invention in the form of a position measuring system  100 . The system  100  includes a magnetic sensing element (e.g., a Hall Effect sensor)  105 , a top collector  110 , a bottom collector  115 , and a magnet  120 . Arrow  122  indicates a path of travel of the magnet  120 . Arrow  122  also represents an axis relative to the magnet  120 . The top and bottom collectors  110  and  115  are positioned parallel to one another and angled relative to the axis  122 . While the figures show the collectors  110  and  115  being exactly parallel to one another, it is not necessary for them to be exactly parallel. Thus, the use of the term “parallel” in the specification and claims is meant to describe a general relationship and is not meant to infer that the collectors  110  and  115  are exactly parallel to one another. In addition, while the figures show the path of travel and axis  122  as perpendicular to the magnet  130 , it is not necessary for the path of travel or the axis  122  to be perpendicular to the magnet  130  (e.g., the magnet  130  can be tilted). The area between the collectors  110  and  115  (i.e., the gap) depicted in the figures represents a boundary between the collectors  110  and  115  which the poles of the magnet  130  pass over as the magnet  130  moves along the path. It is conceivable that the collectors  110  and  115  are positioned in offset planes and actually overlap when viewed from the magnet  130 . In this circumstance, the boundary would be blurred, but a boundary would still exist for the poles of the magnet  130  to pass over. 
         [0028]    The collectors  110  and  115  are positioned such that a significant percentage of the magnet&#39;s flux flows through magnetic circuit elements  125  and  126 , and the magnetic sensing elements  105 . The collectors  110  and  115  and the magnetic circuit elements  125  and  126  are made from a material with a relatively high magnetic permeability. In the embodiment shown, the magnet  120  is a permanent magnet having a north pole in its center and south poles in an upper end  130  and a lower end  135 . The magnet  120  travels along a path perpendicular to the length of the magnet  120 , and parallel to and a fixed distance from the plane of the collectors  110  and  115 . Arrows  140  indicate the directions of travel of the magnet  120 . As shown in  FIG. 2 , when the magnet  120  is approximately in the center of its range of travel, there is little or no flux at the magnetic sensing element  105 . As the magnet travels in a first direction from the center, the north pole moves over the top collector  110  and the lower south pole  135  moves over the bottom collector  115  (see  FIG. 3 ). As the magnet  120  moves in this direction, flux flows from the top collector  110  to the bottom collector  115  in increasing amounts and the output of the magnetic sensing element  105  goes more positive. Conversely, as the magnet travels in a second direction from the center, the north pole moves over the bottom collector  115  and the upper south pole  135  moves over the top collector  110  (see  FIG. 4 ). As the magnet  120  moves in this direction, flux flows from the bottom collector  115  to the top collector  110  in increasing amounts and the output of the magnetic sensing element  105  goes more negative.  FIG. 5  shows a graph of possible outputs of the magnetic sensing element  105  based on the position of the magnet  120 . 
         [0029]      FIG. 6  shows another embodiment of the invention in the form of a position measuring system  200 . The system  200  includes a magnetic angle sensor  205 , a top collector  210 , an upper-middle collector  215 , a lower-middle collector  220 , a bottom collector  225 , and a magnet  230 . The collectors  210 ,  215 ,  220 , and  225  are positioned parallel to one another and angled relative to the magnet  230 . Again, the collectors  210 ,  215 ,  220 , and  225  and magnetic circuit elements  235  are made from a material with a relatively high permeability. In the embodiment shown, the magnet  230  is a permanent magnet having a single pole pair—a north pole  240  and a south pole  245 . The magnet  230  may be a magnet assembly, including magnets and/or pole pieces. 
         [0030]    The magnet  230  travels perpendicular to the length of the magnet  230 , parallel to and a fixed distance from the plane of the collectors  210 ,  215 ,  220 , and  225 . Arrows  250  indicate the directions of travel of the magnet  230 . As shown in  FIG. 7A , when the magnet  230  is at a first end  260  of its range of travel, the magnetic angle sensor  205  detects a first flux angle  265  (e.g., 270°). When the magnet  230  is approximately in the center  270  of its range of travel, the magnetic angle sensor  205  detects a second flux angle  275  (e.g., 225° or about 45° from the first flux angle  265 ) (see  FIG. 8A ). When the magnet  230  is at a second end  280  of its range of travel, the magnetic angle sensor  205  detects a third flux angle  285  (e.g., 180° or about 90° from the first flux angle  265 ) (see  FIG. 9A ). 
         [0031]      FIGS. 7B ,  8 B, and  9 B show a position of a u-shaped magnet  205  relative to the collectors  210 ,  215 ,  220 , and  225  at the first end  260 , the center  270 , and the second end  280 , respectively. When the magnet  230  is positioned at the first end  260  (e.g.,  FIGS. 7A and 7B ), the magnetic flux travels from the upper-middle collector  215  to the bottom collector  225 . As the magnet  230  moves from the first end  260  to the center  270 , the magnetic flux travels over multiple paths (e.g., from the top collector  210  and the upper-middle collector  215  to the lower-middle collector  220  and the bottom collector  225 ). When the magnet  230  is positioned at the second end  280  (e.g.,  FIGS. 9A and 9B ), the magnetic flux travels from the top collector  210  to the lower-middle collector  220 . The flux angle changes relatively linearly over the course of travel of the magnet  230 .  FIG. 10  shows a graph of a possible output of the magnetic angle sensor  205  based on the position of the magnet  230 . 
         [0032]    A monotonic shifting of the flux angle at the sensor  205  occurs as the magnet  230  changes position. If the gap between the magnet  230  and the collectors  210 ,  215 ,  220 , and  225  changes, the measured angle does not change significantly. The magnitude of the flux density at the sensor  205  may change, but the ratio of the flux traveling down each magnetic circuit path stays approximately the same. It is generally believed that the monotonic shifting of the angle in the measuring system  200  provides a more accurate determination of magnet position than the position measuring system  100 . 
         [0033]      FIGS. 11A and 11B  show yet another alternative embodiment of the invention—a position measuring system  400 . The system  400  includes a common collector  405 , a first collector  410 , a second collector  415 , a first magnetic sensor  420  (coupled to the first collector  410 ), a second magnetic sensor  425  (coupled to the second collector  415 ), a magnet  430 , and magnetic circuit elements  435 . The first and second collectors  410  and  415 , the magnet  430 , the sensors  420  and  425 , and the magnetic circuit elements  435  are positioned relative to each other as shown in the figures. In order to increase the magnetic flux detected, the sensors  420  and  425  are located in the vicinity (i.e., near) of the collectors  410  and  415 , respectively. The common collector  405  includes a lowered element  440  that is angled (i.e., a magnetic feature) such that at a first end  450  of the lowered element  440  shares an axis  455  with the first collector  410 , and a second end  460  of the lowered element  440  shares an axis  465  with the second collector  415 . The common collector  405  moves in the directions shown by the arrows  470 . When the common collector  405  is at a first end of its range of travel (see  FIG. 12A ), a magnetic coupling with the first collector  410  occurs. As the common collector  405  travels to a second end of its range of travel (see  FIG. 12B ), the magnetic coupling switches from the first collector  410  to the second collector  415 .  FIG. 13  shows a graph of a ratio of the possible outputs of the magnetic sensors  420  and  425  based on the position of the common collector  405 . 
         [0034]      FIGS. 14A and 14B  show another embodiment of the invention—a position measuring system  500 . The system  500  includes a common collector  505 , a first collector  510 , a second collector  515 , a magnetic angle sensor  520 , a magnet  530 , and magnetic circuit elements  535 . The first and second collectors  510  and  515 , the magnet  530 , the sensor  520 , and the magnetic circuit elements  535  are positioned relative to each other as shown. The common collector  505  includes a lowered element  550  that is angled the same as common collector  405 . As common collector  505  moves through its range of motion, a flux angle detected by the magnetic angle sensor  520  changes as discussed above with respect to previous embodiments. 
         [0035]    The common collectors  405 / 505  can be a stamped piece of material, and have a relatively high magnetic permeability and a relatively low magnetic hysteresis. 
         [0036]    In the constructions described above, the magnet can be a permanent magnet (e.g., a ferrite, an alnico, a samarium-cobalt, a neodymium-iron-boron, or other type of magnet). It is also possible for the magnet to be an active magnetic field generator, like an electro-magnet, although in most applications a permanent magnet will be selected because of the lower system cost. 
         [0037]    Also in the constructions described above, the magnets have a simple shape. However, it is also possible to use magnets of other shapes to improve performance or meet packaging constraints. As an example, the magnets could take on a “U” shape to better direct the flux lines to the collectors. In addition, the magnets could take on a shape to reduce the influence of movement in the direction orthogonal to the movement the system is trying to measure. For example the magnet poles could be wider or narrower than the collectors so that movement “up” or “down” would have a much smaller influence on the coupling between the magnet poles and the relevant collector. In addition, the magnets in this description may include pole pieces as part of a magnet assembly. 
         [0038]    For repeatable sensor performance it is important that the nonmoving components and their associated magnetic circuits stay approximately fixed relative to each other. Therefore, the collectors are held in place with mechanical constraints. For example, the components could be held in place with over-molded plastic supports or with potting. 
         [0039]    It is also important that the sensors are held in place relative to the magnetic circuit elements and the magnetic flux concentrators directing the flux to the sensor(s). 
         [0040]    In the constructions using magnetic sensing elements, the sensor itself is preferably a Hall Effect sensor or other magnetic sensor that can measure flux density. In the constructions using a magnetic angle sensor, the sensor can be a magnetoresistive sensor (e.g., AMR, GMR, and TMR) or a Hall-based angle sensor. Typically, multiple Hall sensors in a single device are used to collectively measure the angle of the magnetic flux. Other technologies that can measure flux angle can also be used. Commercially available sensors (e.g., from Allegro, Micronas, Infineon, NXP, and others) can be used in the embodiments described above. 
         [0041]    The collectors and magnetic circuit elements are depicted above as simple shapes, but they could be complex 3-dimensional shapes. For example, the collector could be relatively flat with a tab coming out of one edge (top edge, bottom edge, or side edges), perpendicular to the collector, and eventually leading to the sensor area. The magnetic circuit elements leading to the sensor(s) could be any shape and connected anywhere on the collectors. Effectively, the magnetic circuit elements are a part of the respective magnetic collectors. In other constructions, the sensor could be placed directly next to the collector such that there is no identifiable magnetic circuit element coming from the collector. Those knowledgeable in the art will recognize that this does not change the concepts within this invention. 
         [0042]    The flux collector and magnetic circuit elements are designed to be compatible with the flux densities expected within the application. The design considers the flux level at which the collector or the magnetic circuit element may saturate. Saturation causes the magnetic circuit reluctance to change and will, as a consequence, change the measurement from the expected measurement for the magnet&#39;s position. 
         [0043]    Also, the orientation of the magnet (distance between the collectors and the magnet) and the relative orientation of the magnet with respect to the collectors can also be modified. 
         [0044]    It is also possible to create collectors that follow the path of a magnet when the magnet does not travel in a straight line. For example, if a magnet travels along a curve, the collectors could be designed to fit along the inside or outside of the curve and, as long as the distance between the magnet and the collectors is approximately constant, the output signal (ratio or angle) would vary continuously with the magnet position. 
         [0045]    Various features and advantages of the invention are set forth in the following claims.