Abstract:
A position sensor system including a magnet, a magnetic flux sensor positioned a distance away from the magnet, the magnetic flux sensor and the magnet defining a flux path therebetween, and a flux guide positioned in the flux path to guide magnetic flux to the magnetic flux sensor.

Description:
BACKGROUND 
     The present application relates to position sensor systems and, more particularly, to position sensor systems including at least one magnetically anisotropic flux guide. 
     Position sensor systems have been used to monitor the position of rotating motor shafts. A traditional position sensor system, generally designated  10  in  FIG. 1A , typically includes a motor shaft  12 , permanent magnets  14 ,  16  and an array of Hall effect sensors  18 ,  20 ,  22 . The magnets  14 ,  16  are secured to the motor shaft  12  such that the magnets  14 ,  16  have alternating polarities. For example, magnet  14  may have a north polarity and magnet  16  may have an opposite, south polarity. 
     The array of Hall effect sensors  18 ,  20 ,  22  is positioned in close proximity to the magnets  14 ,  16  to maximize the magnetic flux density at the sensors  18 ,  20 ,  22 . As shown in  FIG. 1A , the sensors  18 ,  20 ,  22  are positioned about 1.2 mm from the magnets  14 ,  16 , thereby providing the flux density versus lateral sensor position profile shown in  FIG. 1B . 
     Thus, as the motor shaft  12  rotates about its axis, the sensors  18 ,  20 ,  22  provide binary output signals depending upon the polarity of the magnetic field they are facing. For example, a north polarity may generate a first logical output (e.g., logic hi) and a south polarity may generate a second logical output (e.g., logic low). 
     Oftentimes it is desirable to space the sensors  18 ′,  20 ′,  22 ′ a greater distance away from the magnets  14 ′,  16 ′, as shown by the system  10 ′ illustrated in  FIG. 2A . For example, a user may wish to increase the spacing between the sensors  18 ′,  20 ′,  22 ′ and the magnets  14 ′,  16 ′ to avoid damage to the sensors by heat generated by the motor or to use various packaging and mounting schemes, such as surface-mounted Hall elements or to sense through walls. 
     However, the magnetic flux density decreases rapidly as the sensors  18 ′,  20 ′,  22 ′ move away from the magnets  14 ′,  16 ′. For example, sensors  18 ′,  20 ′,  22 ′ are positioned about 6.0 mm from the magnets  14 ′,  16 ′, thereby providing the flux density versus lateral sensor position profile shown in  FIG. 2B . However, this shown flux density profile may not have a sufficiently high magnitude, therefore failing to trigger the Hall effect devices in a manner that is suitable for generating the desired hi-lo binary output of the Hall sensor. 
     Accordingly, there is a need for a position sensor system capable of achieving greater magnetic flux densities at increased sensor-magnet spacings. 
     SUMMARY 
     In one aspect, the disclosed position sensor system includes a magnet, a magnetic flux sensor positioned a distance away from the magnet, the magnetic flux sensor and the magnet defining a flux path therebetween, and a flux guide positioned in the flux path to guide magnetic flux to the magnetic flux sensor 
     In another aspect, the disclosed position sensor system includes a magnet, a Hall effect sensor positioned a distance away from the magnet and a flux guide positioned at least partially between the magnet and the Hall effect sensor. 
     In another aspect, the disclosed position sensor system includes a shaft defining a rotation axis, a plurality of magnets connected to the shaft and coaxially arranged about the rotation axis, each of the plurality of magnets having an opposite polarity than adjacent ones of the plurality of magnets, at least one Hall effect sensor positioned a distance away from the plurality of magnets and a flux guide positioned in a flux path between the plurality of magnets and the Hall effect sensor, wherein the flux guide includes at least three alternating layers of a ferro-magnetic material and a non-magnetic material. 
     Other aspects of the disclosed position sensor system will become apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic illustration of a prior art position sensor system including magnetic flux lines; 
         FIG. 1B  is a graphical illustration of flux density versus lateral sensor position of the system of  FIG. 1A ; 
         FIG. 2A  is a schematic illustration of the prior art position sensor system of  FIG. 1A , wherein the spacing between the sensors and magnets was increased; 
         FIG. 2B  is a graphical illustration of flux density versus lateral sensor position of the system of  FIG. 2A ; 
         FIG. 3  is a front elevational view, partially in section, of one aspect of the disclosed position sensor system including a magnetically anisotropic flux guide; 
         FIG. 4  is a side elevational view, partially in section, of the position sensor system of  FIG. 3 ; 
         FIG. 5  is a front perspective view of a second aspect of the disclosed position sensor system; 
         FIG. 6A  is a schematic illustration of the position sensor system of  FIG. 5  including magnetic flux lines; and 
         FIG. 6B  is a graphical illustration of flux density versus lateral sensor position of the system of  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 3 and 4 , one aspect of the disclosed position sensor system, generally designated  100 , may include a shaft  102 , magnets  104 A,  104 B, a flux guide  106  and a magnetic flux sensor  108 , such as a Hall effect sensor. The sensor  108  may be a surface-mounted Hall effect sensor and may be mounted to a circuit board  110  or other surface or mounting assembly (not shown), or may otherwise be spaced from the magnets  104 A,  104 B. Signals from the sensor  108  may be communicated to a control unit or other processor by way of communication lines  112 A,  112 B. 
     The shaft  102  may be a motor shaft extending from a motor (not shown), such as a brushless motor or the like, or may be any rotating shaft. The magnets  104 A,  104 B may extend coaxially about the periphery of the shaft  102  and may have alternating polarities. Those skilled in the art will appreciate that various numbers and arrangements of magnets  104 A,  104 B on the shaft  102  may be used according to the disclosed position sensor system  100 . 
     Referring to  FIG. 3 , the flux guide  106  may be a layered structure formed by alternating layers of a ferro-magnetic material  114  and a non-magnetic separator  116 . The ferro-magnetic material  114  may be formed from or may include steel (e.g., steel strips), iron or any other ferro-magnetic material or combinations thereof. The non-magnetic separator  116  may be formed from or may include air or any other non-magnetic material or combinations thereof. 
     The thickness of each layer  114 ,  116  of the flux guide  106  may be selected to facilitate guiding magnetic flux to the sensor  108 . Those skilled in the art will appreciate that each layer  114 ,  116  may have a uniform thickness or, alternatively, a different thickness. In one aspect, the thickness T fm  of the ferro-magnetic layers  114  may be about 0.1 mm to about 0.5 mm and the thickness of the T nm  of the non-magnetic layers  116  may be about 0.1 mm to about 0.5 mm. In another aspect, the thickness T fm  of the ferro-magnetic layers  114  may be about 0.5 mm to about 2.0 mm and the thickness of the T nm  of the non-magnetic layers  116  may be about 0.5 mm to about 2.0 mm. 
     For example, a flux guide  106  may be formed by alternating layers of steel strips and polystyrene foam strips, wherein the steel and polystyrene foam strips may be about 10.0 mm wide by about 20.0 mm long and may have a thickness of about 0.5 mm. Alternatively, a flux guide  106  may be formed by assembling a layered structure, wherein steel strips are separated by non-magnetic spacers such that ambient air forms the non-magnetic layers  116 . 
     Referring to  FIG. 4 , the flux guide  106  may be positioned in the flux path F between the magnets  104 A,  104 B and the sensor  108  such that the layers  114 ,  116  of the flux guide  106  are generally parallel with and generally radially aligned with the rotational axis A of the shaft  102 . A radial gap G may be provided between the flux guide  106  and the magnets  104 A,  104 B, wherein the gap G may, for example, have a length of about 0.5 mm to about 1.0 mm. 
     Thus, the flux guide  106  may guide the magnetic flux F of the magnets  104 A,  104 B to the sensor  108 , thereby increasing the density of the magnetic flux at the sensor. 
     Referring to  FIGS. 5 and 6A , one alternative aspect of the disclosed position sensor system, generally designated  100 ′, may include a shaft  102 ′, magnets  104 A′,  104 B′,  104 C′,  104 D′,  104 E′,  104 F′,  104 G′,  104 H′, flux guides  106 A′,  106 B′,  106 C′ and an array of magnetic flux sensors  108 A′,  108 B′,  108 C′ (e.g., Hall effect sensors). The flux guides  106 A′,  106 B′,  106 C′ may be positioned in the flux paths ( FIG. 6A ) between the magnets  104 A′,  104 B′,  104 C′,  104 D′,  104 E′,  104 F′,  104 G′,  104 H′ and the sensors  108 A′,  108 B′,  108 C′, which may be vertically displaced by about 6.0 mm, thereby providing the flux density versus lateral sensor position profile shown in  FIG. 6B . 
     Upon comparing  FIG. 6B  with  FIG. 2B , both of which represent a 6.0 mm sensor-magnet spacing, one skilled in the art will appreciate the improved magnetic flux density achieved by using flux guides  106 A′,  106 B′,  106 C′ according to an aspect of the disclosed position sensor system. 
     Accordingly, those skilled in the art will appreciate that the disclosed position sensor system may facilitate mounting Hall effect sensors at various locations spaced away from the magnets without the traditional deterioration in position signal performance. Therefore, the disclosed position sensor system may reduce assembly and manufacturing costs by eliminating the need for mounting sensors in very close proximity to the magnets. 
     Although various aspects of the disclosed position sensor system have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.