Abstract:
Provided is a magnetic absolute rotary encoder, comprising a rotation shaft, multiple rotating wheels that can rotate along the rotation shaft, multiple encoding units that correspond to the multiple rotating wheels one-to-one, and one or more permanent magnet assemblies that provide the magnetic bias to the multiple encoding units. Each encoding unit comprises a magnetically permeable encoder disc, the structure thereof enabling the magnetic permeability thereof to be different according to the different positions of the rotation shaft, and comprises multiple sensor units that comprise multiple magnetic sensors. The sensor units are used to sense the magnetic permeability of the magnetically permeable encoder disc and to output the sensor signals that characterize the relative position of the magnetically permeable encoder disc. According to the sensor signals of the sensor units, each encoding unit outputs the value that characterizes the selected rotation position of the corresponding rotation wheel, thereby enabling an absolute magnetic rotating encoder that is simple and low in cost and has more precise magnetic encoder discs.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a rotary encoder. More particularly, the present invention relates to an improved absolute magnetic rotary encoder. 
       BACKGROUND OF THE INVENTION 
       [0002]    Existing encoders may be used in automatic utility meter reading or any application where total flow must be monitored at remote locations over long time periods. They can be included in any device that utilizes rotating wheels to measure cumulative flow of gas or liquid. In these meters, the total number of rotations of the wheels is indicative of the total flow through the meter. Common encoders involving optical, electrical contacts, or inductive mechanisms may be used. Absolute rotary encoders are a subset of rotary encoders, which provide information about the rotational position of each reel at any time, without the need to monitor and count pulses caused by the movement of the wheel. These encoders typically include a rotating wheel and provide an appropriate output of the wheel position. Although there are many possible ways of counting, each wheel&#39;s rotation typically represents 10 digits, for example, the encoder wheel can be numbered from 0 to 9. In addition to electronic output, these encoders also may provide visual readings. A common encoder is configured with at least one wheel, if the recording time is long such that several decades of counting is needed, more wheels are necessary. In these multi-wheel arrangements, the first wheel of a pair turns one full rotation, causing the second wheel to turn 0.1 rotations, although a different ratio may be used. Within a multi-wheel meter, generally except for the first wheel, one full rotation of the preceding wheel N will cause the successive N+1 wheel to rotate 0.1 turns. This multi-wheel assembly configured as such can therefore record readings over several decades. 
         [0003]    Other encoder technologies are known in the art such as: optical transmission, optical reflectance, electrical contact. Optical methods suffer from problems from dirt and light pollution, and high expense due to needed electronic components for both light source and light detector. Electrical contact encoders suffer from low reliability as they wear out over time. Other magnetic encoder technologies are known in the art such as magnetic targets with alternating magnetizations, and inductive detectors. Magnetic targets are more expensive; their physical precision is limited by the ability to impress a permanent magnetization on the material. 
         [0004]    To overcome these shortcomings an improved invention with lower cost, simpler design, and magnetic disks with greater precision will be useful to the flow metering industry. 
       SUMMARY OF THE INVENTION 
       [0005]    The purpose of the present invention is to overcome the above problems of the prior art, to provide an improved electronic absolute magnetic rotary encoder technology. Specific technical improvements include the following: 1) the use of a magnetically permeable “soft” magnetic material with specific geometry instead of permanent magnet encoder wheels, 2) addition of magnetic switch circuitry that reduces output noise near magnetic transitions, 3) inclusion of an optional ferromagnetic flux closure device that reduces magnetic “cross talk” between neighboring wheels, 4) optimization of the encoder disk geometry design according to modeled and measured magnetic field values present near the disk in the plane of the sensing axis, and 5) 4 and 5 sensor designs for decoding 10 distinct rotary positions. 
         [0006]    To achieve the above technical objectives, the present invention is realized by the following technical scheme: 
         [0007]    A magnetic rotary encoder comprising 
         [0008]    A rotation shaft; 
         [0009]    A plurality of wheels on the rotation shaft; 
         [0010]    A plurality of encoding units one for each of the plurality of wheels; and 
         [0011]    For each encoding unit one or more permanent magnets to provide magnetic field bias. 
         [0012]    Each encoding unit further comprises: 
         [0013]    a permeable magnetic disk structure, wherein the permeability of the disk varies with rotation angle of the disk about the rotation shaft; and 
         [0014]    multiple magnetic sensor units disposed in the same plane for sensing the magnetic permeability of the encoder disk, thereby outputting a signal characterizing the position of the encoder disk, where the axis of the rotation shaft is perpendicular to the plane of the sensors, 
         [0015]    Either the permeable magnetic encoder disk or the sensor unit rotates with the wheel, while the other remains stationary. 
         [0016]    The output signals of each sensing unit characterize the rotational position of each corresponding wheel. 
         [0017]    Preferably, one or more permanent magnet assemblies and the magnetic encoder disk have directions of magnetization respectively aligned parallel to the rotation axis, and the sensing axis of each of the magnetic sensors is substantially parallel to a direction that is radial directed from the rotation axis. 
         [0018]    Preferably each sensor unit comprises 4 or 5 magnetoresistive sensors, to detect 10 rotational positions of each wheel. 
         [0019]    Preferably, the magnetic rotary encoder includes a plurality of permanent magnet assemblies, with one permanent magnet assembly for each encoding unit. 
         [0020]    Preferably, the magnetic rotary encoder provides a separate permanent magnet for each encoder unit to provide magnetic biasing. 
         [0021]    Preferably the permanent magnet assembly includes at least one ring shaped permanent magnet or a plurality of permanent magnets arranged in a circle. 
         [0022]    Preferably, each of the encoding unit further comprises a flux closure means made of a soft ferromagnetic material. 
         [0023]    Preferably, the permeable magnetic encoder disk structure includes at least one slot. 
         [0024]    Preferably, the permeable magnetic encoder disk structure includes at least one bump and/or one tab. 
         [0025]    Preferably, the permanent magnet assembly made of a material selected from the group of ferrite, barium ferrite, cobalt ferrite, or NdFeB. 
         [0026]    Preferably, the permeable magnetic encoder disk made of a material selected from a nickel-iron, soft iron, high permeability magnetic alloys, soft steel, or a soft ferrite. 
         [0027]    Preferably, in each encoding unit, a gap of 0.1-4 mm exists between the permeable magnetic encoder disk and the magnetic sensor unit. 
         [0028]    According to the present invention, a magnetic rotary encoder with lower cost, simpler operation, and higher accuracy can be obtained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIGS. 1A-1D  show the front and end view schematic of multi-wheel rotary encoder assembly, magnets for each wheel. 
           [0030]      FIGS. 2A-2E  show the front and end view schematic of a second alternative for magnet placement multi-wheel rotary encoder assembly, with shared magnets. 
           [0031]      FIGS. 3A-3B  show a schematic diagram of the encoding unit of a third implementation of a magnetic rotary encoder assembly. 
           [0032]      FIGS. 4  A - 4 B show a schematic diagram of the encoding unit of a fourth implementation of a magnetic rotary encoder assembly. 
           [0033]      FIGS. 5A-5B  show a schematic diagram of the encoding unit of a fifth implementation of a magnetic rotary encoder assembly. 
           [0034]      FIGS. 6A-6B  show a schematic diagram of the encoding unit of a seventh implementation of a magnetic rotary encoder assembly. 
           [0035]      FIGS. 7A-7C  show the implementation of the encoding unit of a seventh implementation of a magnetic rotary encoder assembly. 
           [0036]      FIGS. 8A-8B  show the response curve of the seventh implementation of a magnetic rotary encoder assembly. 
           [0037]      FIGS. 9A-9B  show a schematic diagram of the encoding unit of an eighth implementation of a magnetic rotary encoder assembly. 
           [0038]      FIGS. 10A-10C  show the implementation of the encoding unit of an eight implementation of a magnetic rotary encoder assembly. 
           [0039]      FIGS. 11A-11B  show the response curve of the eighth implementation of a magnetic rotary encoder assembly. 
           [0040]      FIG. 12  shows a permeable magnetic disk with holes, tabs, and raised regions. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    The invention is described below in detail with reference to the appended drawings and preferred implementation examples. In the drawings, the same or similar reference numerals identify the same or similar components. 
         [0042]      FIGS. 1A-1D  show the construction of a multi-turn encoder of the present invention, showing different perspective views of the five wheels.  FIG. 1  rotary encoder includes an axis of rotation  107 ,  5  rotatable wheels on the axis of rotation  107  denoted  101 ,  102 , . . . ,  105 , with one wheel per encoding unit, and one or more permanent magnets  114  to provide magnetic bias per coding unit. The rotary encoder comprises a rotating portion and the fixed portion, where the rotating portion can support the encoder disk, under effect of an external torque it rotates with the wheel on the axis of rotation; the rigidly fixed portion does not rotate about the rotation axis, but is supported by a mounting bracket. Each encoding unit includes a magnetically permeable encoder disk  110  and sensor assembly  117 . Magnetically permeable encoder disk  117  has a specific geometry and it is assembled such that it can rotate with respect to the sensing surface of the sensor assembly  117 . In order to provide a magnetic bias to the encoder disk  110 , an appropriate permanent magnet  114  is chosen such that it will not saturate the magnetic sensors. Hysteretic magnetic switches are placed on a printed circuit board (PCB)  112 , the output signal of the switches exhibits two stable states, such that the transition regions of the rotating magnetic field do not produce noise in the electronic output. The magnetically permeable structure  110  on the encoder disk is designed such that its permeability varies as a function of rotational position around the axis of rotation  107 . The encoder disk  110  within the wheel is set up with multiple positions corresponding to selected locations about the rotation axis. The permeability encoder disk  110  in each of these positions corresponding to an angle of rotation, has a geometry which provides a unique set of magnetic field configurations onto the plurality of magnetic field sensors in the sensing unit. Sensing unit  117  includes multiple magnetic field sensors  116  set in the same plane, which is perpendicular to the axis of rotation  107 . When the permeable encoder disk rotates relative to the sensor assembly  117 , the permeability of the encoder disk induces different magnetic fields on the sensor assembly, such that the output signal of the sensors characterizes the position of the encoder disk. The encoder disk and angular positioning of the sensor components can be used to generate a digital code, the magnetic sensor output code thereby representing the angular position of the wheel. The measured signal of each encoding unit output provides a measure of the angular position of the corresponding wheel. 
         [0043]    The entire assembly provides a visual and electronic recording of the total number of rotations taken by the right-most wheel  101 . The visual recording is taken from the top-most number on each wheel. Thus, the current reading is 00,019 turns. This means the rightmost wheel  101  has already done one complete turn and is almost done with its second turn. We will give it the name “10 0 ” because that is the order of magnitude it represents in a base-10 number. The second wheel from the right,  102 , is named “10 1 ”. The third wheel from the right,  103 , is named “10 2 ”. The fourth wheel from the right,  104 , is named “10 3 ”. The fifth wheel from the right,  105 , is named “10 4 ”. 
         [0044]    The motion of the 102 wheel  102  is coupled to the motion of the 101 wheel with the ratio of 10:1. This means 10 0  wheel  101  makes ten revolutions for every 1 revolution of 10 1  wheel  102 . In the same way, 10 1  wheel  102  makes ten revolutions for every 1 revolution of 10 2  wheel  103 . More generally, the 10 n  wheel makes ten revolutions for every 1 revolution of 10 n+1 . While this drawing shows a five-wheel encoder, the same description could easily apply to one with any number of wheels. 
       Example 1 
       [0045]    A first example of a preferred embodiment of the present invention, has one permanent magnet for each coding unit. 
         [0046]    As shown in  FIG. 1 , each rotor has a permanent magnet count corresponding thereto, i.e. each encoding unit corresponds to the permanent magnet.  FIG. 1A  shows an end-on view of the five wheels illustrated on the right side as  FIG. 1B  which shows a side view of the rotary encoder device  100 . In order to more easily see the two parts of the wheel, the wheel is broken into two parts illustrated in  FIGS. 1C and 1D . In this embodiment, the piece shown in  FIG. 1C  is a the fixed portion, and that shown in  FIG. 1D  is a rotating portion. All of the wheels  101 ,  102 , . . . ,  105  rotate on shaft  106  whose axis is co-axial with the axis of rotation  107 . Magnetically permeable disk  110  is mounted on wheel  101  so that the permeable disk  110  and wheel  101  rotate together about axis  107 . Magnet  114  is mounted in a way that is does not rotate, but rather is fixed to an external support. Printed circuit board (PCB)  112  is also fixed. Five magnetic sensors,  116 . 1 ,  116 . 2 ,  116 . 3 ,  116 . 4 ,  116 . 5 , are physically attached to PCB  112  which also provides electrical interconnections for sensors  116 . The combination of PCB  112  and sensors  116  is called the sensor unit  117 . The sensor unit  117 , together with fixed magnet  114  forms  122 , the fixed assembly. 
         [0047]    Disk  110  has structural variation  113 . This structural variation is a geometrically distinct pattern formed in magnetically soft permeable disk  110 . The purpose of this variation is to cause a change in the magnetic field measured by the nearby sensors as the disk rotates about axis  107 . The variation must be distinct and precise for the invention to function properly. It must be formed in a way that provides a unique set of magnetic fields to the 5 sensors at each of the 10 positions of angular rotation. Further details of the magnetic encoding design will be discussed in later diagrams. The disk  110  and wheel  101  together form the rotating assembly  121 . This assembly rotates about the axis  107  in the angular direction indicated by arrow  118 , wheel rotation. 
       Example 2 
       [0048]    Magnetic rotary encoder preferred implementation example 2 provides a permanent magnet that is shared by two wheels. 
         [0049]    A different arrangement of fixed magnets  114  is shown in  FIG. 2 . The upper left part of  FIG. 2  shows an end on view of the 5-wheel assembly whose side view is in the upper right. The end-on view is broken into three parts in the lower half of  FIG. 2  in order to more easily see the parts of the wheel clearly. The lower left and lower right of  FIG. 2  have the two portions of the wheel that are fixed, and the lower center has the portion that rotates. Here, the fields from one of magnets  114  are detected by two sensor assemblies  117 . This saves space and cost in a multi-wheel assembly. In this arrangement, magnet  114  is the only component of a separate fixed assembly  123 . Rotating assembly  121  is constructed the same as in  FIG. 1 . The sensor assemblies  117  form fixed assembly  122 ′. 
         [0050]    In a multi-wheel magnetic rotary encoder, the arrangement used in this embodiment saves space and cost. 
         [0051]    The arrangement used in this embodiment may be used in conjunction with other embodiments. 
       Example 3 
       [0052]    Magnetic rotary encoder preferred implementation example 3 provides a magnet is located on the wheel, and the encoder disk can be rotated together with the rotor about a rotation axis, and the sensor unit comprises five sensors, as shown in  FIG. 3 . 
         [0053]      FIG. 3A  is a right side view of a coding unit, and  FIG. 3B  is a cross-sectional view taken along the direction A in  FIG. 3A . PCB  112  is drawn in outline only at left in order to enable a clearer view of the other components. In this arrangement, magnet  114  is placed on wheel  101  in very close proximity to, or touching, disk  110 ; these components rotate together about the axis  107 . PCB  112  is shown as a rectangular form in  FIG. 3 . If designed with a mechanical connection means, PCB  112  can serve the purpose of structural support for the wheel assembly in addition to providing electrical connections for sensors  116 . 1 - 116 . 5 . 
         [0054]    The active elements in sensors  116  are present near the surface furthest away from the PCB  112 . They are sensitive in a direction perpendicular to the axis of rotation. The plane that passes through the sensing elements and is parallel to the sensing axis of each sensor is called the sensing plane,  124 , The sensing axis of each sensor is designed to be parallel to the radial direction in this figure, which corresponds to the short direction of each sensor. This convention will be used throughout the remainder of this technical description. 
         [0055]    The magnet  114  in this embodiment is similar in shape to the ring magnets shown in  FIGS. 1 and 2 . The orientation of the magnetization vector  184  of magnet  114  is substantially parallel to the rotation axis  107 , and nominally uniform within the body of the magnet  114 . The stray fields from magnet  114  are also substantially parallel to the rotation axis  107 . The permeable magnetic encoder disk  110  rotates such that its face is in a disk plane  125 , which is parallel to sensing plane  124 . These two planes are set apart mechanically at a designed distance from one another. This space between planes  124  and  125  is called the Gap, and has the designed distance shown as G,  126 . With this single large ring magnet design, the magnetic field effect from the magnet at each of the 5 sensors is identical regardless of the angular position; this fact can be understood by observing the angular symmetry of ring magnet  114  with respect to sensors  116 . Any variation in magnetic field at a sensor as disk  110  rotates is due only to variation  113 . 
         [0056]    Some possible materials for permanent magnet  114  include barium ferrite, cobalt ferrite, neodymium iron boron, ferrite, and any other common permanent magnet material that retains significant magnetization after a saturating magnetizing field is removed, and require a relatively large magnetic field to saturate its magnetization. Some possible materials for the permeable magnetic encoder disk  110  are: permalloy, soft iron, mu metal, soft steel, soft ferrite. Here, “magnetically soft” means that the residual net magnetization is very small compared to its saturation magnetization; and a relatively small magnetic field will saturate the magnetization. 
       Example 4 
       [0057]    A fourth implementation including 5 small permanent magnets and 5 sensors on fixed assembly is shown in  FIG. 4 .  FIG. 4A  is a right side view showing the fourth embodiment of the encoding unit, and  FIG. 4B  is a cross-sectional view along the direction A in  FIG. 4A . Mechanical support  131  is drawn in outline only at left in order to enable a clearer view of the other components. Also drawn in outline only are 5 small permanent magnets  114 . 1 ,  114 . 2 ,  114 . 3 ,  114 . 4 ,  114 . 5 , and PCB  112 . In this arrangement, small disk magnets  114 . 1 - 114 . 5  are placed on mechanical support  131  and located such that their axis of symmetry is parallel to the rotation axis  107  and passes through one of corresponding sensors  116 . 1 - 116 . 5 . Both magnets  114  and sensors  116  are on the mechanically fixed assembly. PCB  112  is shown as a circular form in this figure. It provides electrical connections for sensors  116 . 1 - 116 . 5 ; it is structurally attached to and supported by mechanical support  131 . 
         [0058]    The sensing assembly design in the present example is the same as for the previous example 3. The active elements in sensors  116 . 1 - 116 . 5  are present near the surface furthest away from the PCB  112 . They are sensitive in the plane parallel to the PCB. The plane that passes through the sensing elements and is substantially parallel to the sensing axis of each sensor is called the sensing plane,  124 . The sensing axis of each sensor is designed to be parallel to the radial direction in this figure, which corresponds to the short direction of each sensor. The disk face nearest the sensor is in disk plane  125 . The spacing between planes  124  and  125  is called the Gap, and has the designed distance shown as G  126 . 
         [0059]    The permanent magnet biasing design in this example has several differences from the ring magnets shown in  FIGS. 1 and 2 . The orientation of magnetization vectors  184 . 1 ,  184 . 2 ,  184 . 3 ,  184 . 4 ,  184 . 5  of magnets  114 . 1 ,  114 . 2 ,  114 . 3 ,  114 . 4 ,  114 . 5 , respectively, are parallel to the rotation axis  107 , and nominally uniform within the body of the magnets  114 . 1 - 114 . 5 . The stray fields from magnets  114 . 1 - 114 . 5  are also largely parallel to the rotation axis  107 , though some bending of magnetic field lines is unavoidable. The permeable magnetic encoder disk  110  rotates such that its face is in a disk plane  125 , that is parallel to sensing plane  124 . These two planes are set apart mechanically at a designed distance G,  126 , from one another. With this 5-small magnet biasing design, the magnetic field effect from the permanent magnets at each of the 5 sensors is identical regardless of the angular position because the magnets  114 . 1 - 114 . 5  are mounted rigidly to the fixed sensor assembly  117 . Any variation in magnetic field at a sensor as disk  110  rotates is due only to variation  113 . 
         [0060]    This magnetic bias design has the biasing magnets  114 . 1 - 114 . 5  outside Gap  126 , but biasing magnets  114 . 1 - 114 . 5  are behind sensors  116 . 1 - 116 . 5  rather than behind disk  110  as in example 3. 
         [0061]    The selection choices of magnet and disk materials for the present example 4 are the same as for example 3. In the present embodiment, there is one small permanent magnet for each sensor, that is, 5 permanent magnets and t5 sensors. In principle, this situation applies to any number of sensors and permanent magnets, one embodiment that will be described later uses 4 permanent magnets and 4 sensors. 
       Example 5 
       [0062]    A fifth implementation is shown in  FIG. 5 , including fours sensors on a fixture and large ring magnet on the rotating wheel.  FIG. 5A  is a right side view of the embodiment of the encoding unit  5 , and  FIG. 5B  is a cross-sectional view taken along the direction A in  FIG. 5A . The distinctive features in this example are an optional flux closure plate  133 , the use of only 4 sensors  116 . 6 - 116 . 9 , and moving ring magnet away from disk  110  compared to example 3. PCB  112  is shown as a circular form in this diagram. It provides electrical connections for sensors  116 . 6 - 116 . 9 . 
         [0063]    The sensing assembly design in the present example is the similar to that in the previous example 4 with the obvious difference of having 4 sensors rather than 5. The active elements in sensors  116 . 6 - 116 . 9  are present near the surface furthest away from the PCB  112 . They are sensitive in the plane parallel to the PCB. The plane that passes through the sensing elements and is parallel to the sensing axis of each sensor is called the sensing plane,  124 . The sensing axis of each sensor is designed to be parallel to the radial direction in this figure, which corresponds to the short direction of each sensor. The disk face nearest the sensor plane is in disk plane  125 . The space between planes  124  and  125  is called the Gap, and has the designed distance shown as G  126 . 
         [0064]    The magnet  114  in this design is similar in shape to the ring magnets shown in  FIGS. 1 and 2 . The magnetic biasing design is similar to Example 3. The orientation of the magnetization vector  184  of magnet  114  is parallel to the rotation axis  107 , and nominally uniform within the body of the magnet  114 . The stray fields from magnet  114  are also largely parallel to the rotation axis  107 , though some bending of magnetic field lines is unavoidable. The permeable magnetic encoder disk  110  rotates such that its face is in a disk plane  125 , which is parallel to sensing plane  124 . These two planes are set apart mechanically at a designed distance from one another. With this single large ring magnet design, the magnetic field effect from the magnet at each of the 4 sensors  116 . 6 - 116 . 9  is identical regardless of the angular position; this fact can be understood by observing the angular symmetry of ring magnet  114  with respect to sensors  116 . 6 - 116 . 9 . Any variation in magnetic field at a sensor as disk  110  rotates is due only to variation  113 . 
         [0065]    An added feature in this example is magnetic flux closure plate  133 . The plate is made from soft magnetic materials, similar to those used for disk  110  though not necessarily identical. But the purpose of plate  133  is to reduce the magnetic reluctance path for magnetic flux coming from the back side of bias magnet  114 . The back side is furthest away from Gap  126 . This flux closure performs a few functions including: reducing stray magnetic fields present at other wheels in the assembly ( 102  and beyond), reducing magnetic interference from other sources including outside magnetic fields, increasing the efficiency of delivery of magnetic flux from magnet  114  to the desired region. 
         [0066]    The selection choices of magnet and disk materials for the present Example 5 are the same as for Example 3. The selection material choices for flux closure plate  133  are similar to that of soft permeable disk  110 . 
         [0067]    The features of this specific embodiment may be used in conjunction with other embodiments. 
       Example 6 
       [0068]    In this Example 6, the fixed device has four sensors and four small permanent magnets. This embodiment does not use a drawing because it combines the implementations shown in  FIGS. 4 and 5  into a single design. It uses the same sensor positions shown in  FIG. 5A , that is 116.6-116.9, having the same angular positions about the axis of rotation  107 . The 4 small permanent magnets are positioned analogously to those in  FIGS. 4A and 4B . As can be seen from  FIG. 4 , a small permanent magnet  114 . 1 - 114 . 5  is installed on the rear of bracket  131  each centered with respect to the corresponding center of the sensors  116 . 1 - 116 . 5 . In order to make such a design suitable for the present embodiment, the position of the center of each of the 4 small permanent magnets should be the same as the center of each of the corresponding 4 sensors  116 . 6 - 116 . 9 . To summarize, in this embodiment, there is no large ring magnet  114 . 
         [0069]    The following two examples,  7  and  8 , show the magnetic biasing design and the magnetic encoding design in more detail. Example 7 shows a 5-sensor design in  FIGS. 6 ,  7 , and  8 , Example 8 shows a 4-sensor design in  FIGS. 9 ,  10 , and  11 . 
       Example 7 
       [0070]      FIGS. 6A and 6B  show an right-side and cross section view of disk  110 , magnet  114 , and sensors  116 . 1 - 116 . 5 . The purpose is to explain the magnetic biasing design and the magnetic encoding design, and how the location and orientation of magnetic sensors is related to these designs. Cross section D, shown in the  FIG. 6B , is taken from  FIG. 6A . The horizontal axis below, labeled R, is taken from the line passing though θ=0° and θ=180° in the upper diagram. The vertical Z axis in  FIG. 6B  is the out-of-plane direction in the upper diagram taken along rotation axis  107  of  FIG. 6A . 
         [0071]    Several important values for radii are given in  FIG. 6A . The disk  110  has an inner radius labeled  166  R DI , and outer radius labeled  167  R DO . Ring magnet  114  has an inner radius labeled  164  R MI , and an outer radius labeled  165  R MO . Variations  113 . 1  and  113 . 2  have an inner radius labeled  162 R VI , and an outer radius labeled  163  R VO . A dashed circle called  190  Track, has a radius labeled  161  R Track . Track  190  is a non-physical marking showing the circle of radial symmetry of ring magnet  114  and disk  110 . R Track    161  is exactly halfway between  166  R DI  and  167  R DO , and halfway between  162  R VI  and  163  R VO . This symmetry is not required for the design to work, but it does simplify the description and understanding of the magnetic fields in the vicinity of these objects. 
         [0072]    The magnetic biasing design is shown in  FIG. 6B . Magnet  114  is a permanent magnet having a magnetization orientation  184  that is parallel to the Z axis, and rotation axis  107 . This orientation is indicated by the solid arrow in the body of magnet  114 . Magnetic disk  110  is a “soft magnetic material” meaning it only has significant internal magnetization if an external field is applied. The internal magnetization of disk  110  is called disk magnetization  182  and is indicated by the white hollow arrows in its body. Referring to the top diagram again, one can see that at θ=0° there is a sensor  116 . 1  and variation  113 . 1  in disk  110 . One can see that at θ=180°, there is no sensor, and no variation either. These differences are shown in the bottom figure. 
         [0073]    The behavior of magnetically soft ferromagnetic plate in the presence of a large amplitude magnetic field from a nearby parallel plate is well known in the literature. The magnetization  182  of disk  110  is parallel to the magnetization  184  of magnet  114 . The magnetic fields  181 ′ between two such magnetized parallel plates is also parallel to the magnetization  184 . This is true to the extent that the plates are close together compared to the radial dimensions of the plates. As one get closer to the edges of magnet  114 , fields  181 ′ are non-uniform and are “spreading” away from the magnet. At radius R Track  at the magnet  114  is a uniform magnetic field. This behavior of fields  181 ′ is shown on the right half of  FIG. 6B . 
         [0074]    In contrast, on the left half of  FIG. 6B , magnetic fields  181  are not uniform between the magnet  114  and disk  110 . This is due to the presence of variation  113 . 1 . The variation  113 . 1  causes there not to be a parallel plate arrangement like on the right side. Instead, the magnetic flux lines tend to follow the path of lowest magnetic reluctance (that is, through the path with material having the greatest magnetic permeability). This path looks something like the field lines  181  shown on the left half of the bottom figure. Note that there are magnetic field lines, not shown here for clarity, coming into the bottom of magnet  114  and going out of the top of disk  110 . These omitted magnetic field lines complete the magnetic flux loops generated by permanent magnet  114 . 
         [0075]    The sensors  116 . 1 - 116 . 5  are placed in order to have their axis of sensitivity be parallel to the radial direction R at the particular angle they are located. They have no sensitivity in the Z direction and θ direction.  FIG. 6A  shows the angles at which each sensor is placed, thus their direction of sensitivity. They are [sensor:angle of sensitivity (degrees)]: [ 116 . 1 , 0], [ 116 . 2 , 72], [ 116 . 3 , 144], [ 116 . 4 , 216], [ 116 . 5 , 288]. They are placed at a radius slightly larger than  161  R track . Referring to  FIG. 6B , one can see that the magnetic fields just outside of R Track  are bending outward to greater R on the left half (θ=0°) and not bending at all on the right half (θ=180°). The bending of the field in the positive radial direction means there is a small component of the total field that is parallel to the positive radial direction for θ=0°. Magnetic modeling results for this radial component B Radial  at the sensor location, are plotted as curve  191  in  FIG. 8  below. The sensor  116 . 1  is sensitive to B Radial  but not B z  by design. If a sensor was placed at a radius just greater than R Track  on the RIGHT half of the lower diagram (θ=180°), it would not detect any field because B Radial  is 0 at θ=180°. In summary, as the disk  110  rotates with respect to the fixed sensors  116 . 1 - 116 . 5 , the magnitude of magnetic field detected by the sensors is small but greater than zero when a particular sensor is near a variation, and much closer to zero when that sensor is not near a variation. 
         [0076]    Therefore, magnetic sensors can detect the presence and absence of variations in soft magnetic permeable disks as they those disks rotate with respect to the sensors. This effect is used to design magnetic encoders. Each of the sensors, arrayed at specific angular locations, provide an electronic signal that differs from one disk position to the next. Electronic circuitry can convert the analog signals from the magnetic sensors to digital 1/0 to signal “variation” or “no variation”. Further, one can make a set of variations  113 . 1  and  113 . 2  such that the set of signals from sensors  116 . 1 - 116 . 5  are different for each of the 10 positions of the encoder wheel  101  as it and disk  110  rotate with respect to the fixed sensors. 
         [0077]    A summary diagram of such an encoding scheme is shown in  FIG. 7 .  FIG. 7A  shows 10 different angular positions of disk  110  with respect to sensors  116 . 1 - 116 . 5 . The table in  FIG. 7B  has a column for “Digit” which corresponds to the number showing on the wheel for each of these 10 positions. The “Degrees” column is the amount of rotation  8  that has occurred from the θ=0° position. The “sensor number” column shows the number of sensors on the fixed circuit board for a given angular location. The sensor output value columns show what signal is output from each of the 5 sensors. These 5 values together make a “code” of “1&#39;s and “0”s at each Degree. These five-digit codes are placed in the labels above each of the circles in  FIG. 7A . For example for digit 4 (upper row, far right) starting at θ=0° and going clockwise from sensor sensors  116 . 1  and  116 . 4  see no structural variation, sensors  116 . 2 ,  116 . 3 , and  116 . 5  correspond to regions with structural change. This occurs at angular rotation value θ=144° and results in an output code of 10010. 
         [0078]      FIG. 8  shows the relationship between the magnetic field and the output of the 5-sensor sensing units. When the disk rotates through an entire rotation from θ=0° to θ=360°. The rotation angle of disk  110  is on the bottom axis of the plot. On the left axis is the resulting B Radial  from a magnetic field model. Magnetic field (Gauss) vs. Angle (Degrees) is plotted in the heavy solid line with diamond data labels, curve  191 . The right axis is the sensor voltage output of a magnetic switch sensor which has been described in the art. Sensor output voltage (volts) vs. Angle (degrees) is plotted as the fine curve  192 . 
         [0079]      FIG. 8B  shows a plot containing a representative response from a commercial digital magnetic switch to an applied magnetic field. This switch converts an analog value of magnetic field to a digital (two-state) electronic output. The horizontal axis is magnetic field (gauss), the vertical axis is Switch Sensor Output (Volts). The output voltage of a digital magnet switch vs. applied magnetic field is plotted here as curve  193 . Note that there is hysteresis in the curve. When the applied magnetic field is negative, the output is low at value V L . As the field increases, becomes positive, and increases beyond the defined field Operate Point B OP , the sensor output switches from low to high, V H . Then, as the magnetic field decreases from a large positive value, the output switches back to V L  at a field value of B Reset Point or B RP . The two magnetic field switching threshold values B OP  and B RP , are plotted as dashed lines  194  and  195  on the upper plot. So, when sensor external field curve  191  crosses the B OP  and B RP  dashed lines, the sensor output behaves accordingly as shown in curve  193 . 
         [0080]    There are many ways to use this invention that involve modifications of the underlying concept shown in this example. For instance, one could invert the “1”s and “0”s for a different digital code. The rotation could be done counter-clockwise rather than clock-wise. The sensors could rotate on the wheel while the disk remains fixed. All of these kinds of devices, though not explicitly described in detail here, would still be within the spirit and scope of the present invention. 
       Example 8 
       [0081]    Example 8 has two differences compared to Example 7: It uses 4 sensors rather than 5, and it has an encoder disk design with 3 variations. These concepts are described in  FIGS. 9 ,  10 , and  11 . 
         [0082]      FIGS. 9A and 9B  show a right-side and cross sectional view of disk  110 ′, magnet  114 , and sensors  116 . 6 - 116 . 9 . The purpose is to explain the magnetic biasing design and the magnetic encoding design, and how the location and orientation of magnetic sensors is related to these designs. Cross section E in  FIG. 9B  comes from  FIG. 9A . The horizontal axis below, labeled R, is taken from the line passing though θ=0° and θ=180° in  FIG. 9A . The vertical Z axis in  FIG. 9B  is the out-of-plane direction in  FIG. 9A  taken along rotation axis  107 . 
         [0083]      FIG. 9A  illustrates several radius values. The disk  110 ′ has an inner radius labeled  166 , R DI , and outer radius labeled  167  R DO . Ring magnet  114  has an inner radius labeled  164  R MI , and an outer radius labeled  165  R MO . Variations  113 . 5 ,  113 . 6  and  113 . 7  have an inner  162  R VI , and outer radius labeled  163  R VO . A dashed circle called  190  Track, has a radius labeled  161  R Track . Track  190  is a non-physical marking showing the circle of radial symmetry of ring magnet  114  and disk  110 ′. R Track    161  is exactly halfway between  166  R DI  and  167  R DO , and halfway between  162  R VI  and  163  R VO . This symmetry is not required for the design to work, but it does simplify the description and understanding of the magnetic fields in the vicinity of these objects. 
         [0084]    The magnetic biasing design is shown in  FIG. 9B . Magnet  114  is a permanent magnet having a magnetization orientation  184  that is parallel to the Z axis, and rotation axis  107 . This orientation is indicated by the solid arrow in the body of magnet  114 . Magnetic disk  110 ′ is a “soft magnetic material” meaning it only has significant internal magnetization if an external field is applied. The internal magnetization of disk  110 ′ is called disk magnetization  182 ′ and is indicated by the white hollow arrows in its body. Referring to  FIG. 9A  again, one can see that at θ=0°, there is a sensor  116 . 6  and variation  113 . 5  in disk  110 ′. One can see that at θ=180°, there is a sensor  116 . 8 , and no variation. These differences are shown in the bottom figure. 
         [0085]    The behavior of magnetic soft magnetic plate in the presence of a large amplitude magnetic field from a nearby parallel plate is well known in the literature. The magnetization  182 ′ of disk  110 ′ is parallel to the magnetization  184  of magnet  114 . The magnetic fields  181 ′ between two such magnetized parallel plates is also parallel to the magnetization  184 . This is true to the extent that the plates are close together compared to the radial dimensions of the plates. As one get closer to the edges of magnet  114 , fields  181 ′ are non-uniform and are “spreading” away from the magnet. This behavior of fields  181 ′ is shown on the right side of  FIG. 9B . 
         [0086]    In contrast, on the left side of  FIG. 9B , magnetic fields  181  are not uniform at disk radius R Track  between the magnet  114  and disk  110 ′. This is due to the presence of variation  113 . 5 . The variation  113 . 5  causes there not to be a parallel plate arrangement like on the right side. Instead, the magnetic flux lines tend to follow the path of lowest magnetic reluctance (that is, through the path with material having the greatest magnetic permeability). This path looks something like the field lines  181  shown on the left half of the bottom figure. Note that there are magnetic field lines, not shown here for clarity, coming into the bottom of magnet  114  and going out of the top of disk  110 ′. These un-shown magnetic field lines complete the magnetic flux loops generated by permanent magnet  114 . 
         [0087]    The sensors  116 . 6 - 116 . 9  are placed in order to have their axis of sensitivity be parallel to the radial direction R at the particular angle they are located. They have zero sensitivity in the Z direction and θ direction.  FIG. 9A  shows the angles at which each sensor is placed, thus their direction of sensitivity. They are [sensor:angle of sensitivity (degrees)]: [ 116 . 6 , 0], [ 116 . 7 , 72], [ 116 . 8 , 180], [ 116 . 9 , 288]. They are placed at a radius slightly larger than  161  R track . Referring to  FIG. 9B , one can see that the magnetic fields just outside of R Track  are bending outward to greater R on the left half (θ=0°) and not bending at all on the right half (θ=180°). The bending of the field in the positive radial direction means there is a small component of the total field that is parallel to the positive radial direction for θ=0°. Magnetic modeling results for this radial component B Radial  at the sensor location, are plotted as curve  191 ′ in  FIG. 11  below. The sensors  116 . 6  and  116 . 8  are sensitive to B Radial  but not B z  by design. Sensor  116 . 8  is placed at a radius just greater than R Track  in  FIG. 9B  (θ=180°), it does not detect any field because B Radial  is 0 at θ=180°. In summary, as the disk  110 ′ rotates with respect to the fixed sensors  116 . 6 - 116 . 9 , the magnitude of magnetic field detected by the sensors is small but greater than zero when a particular sensor is near a variation, and much closer to zero when that sensor is not near a variation. 
         [0088]    Therefore, magnetic sensors can detect the presence and absence of variations in soft magnetic permeable disks as they those disks rotate with respect to the sensors. This effect is used to design magnetic encoders. Each of the sensors, arrayed at specific angular locations, provide an electronic signal that differs from one disk position to the next. Electronic circuitry can convert the analog signals from the magnetic sensors to digital 1/0 to signal “variation” or “no variation”. Further, one can make a set of variations  113 . 5 ,  113 . 6 , and  113 . 7  such that the set of signals from sensors  116 . 6 - 116 . 9  are different for each of the 10 positions of the encoder wheel  101  as it and disk  110 ′ rotate with respect to the fixed sensors. 
         [0089]    A summary diagram of such an encoding scheme is shown in  FIG. 10 . The upper half of  FIG. 10  shows 10 different angular positions of disk  110 ′ with respect to fixed sensors  116 . 6 - 116 . 9 . The table in the lower left has a column for “Digit” which corresponds to the number showing on the wheel for each of these 10 positions. The “Degrees” column is the amount of rotation θ that has occurred from the θ=0° position. The “sensor number” column shows the number of sensors is on the fixed circuit board for a given angular location. The sensor output value columns show what signal is output from each of the 4 sensors. These 4 values together make a “code” of “1&#39;s and “0”s at each Degree. These four-digit codes are placed in the labels above each of the circles in the upper half of  FIG. 10 . For example for digit 4 (upper row, far right) starting at θ=0° and going clockwise: sensors  116 . 6  and  116 . 7  are in a regions with no variation, whereas sensors  116 . 8  and  116 . 9  are in a regions with variation. This occurs at angular rotation value θ=144° and results in an output code of 0011. 
         [0090]      FIG. 11  shows a curve illustrating the relationship between the magnetic field and the output of the 4-sensor sensing units. When the magnetic field expected to be present and detected by sensor  116 . 6  situated at θ=0° while disk rotates through an entire rotation from θ=0° to θ=360° as shown in  FIG. 11A . The rotation angle of disk  110 ′ is on the bottom axis of the plot. On the left axis is the resulting B Radial  from a magnetic field model. Magnetic field (Gauss) vs. Angle (Degrees) is plotted in the heavy solid line with diamond data labels, curve  191 ′. The right axis is the sensor voltage output of a magnetic switch sensor which has been described in the art. Sensor output voltage (volts) vs. Angle (degrees) is plotted as the fine curve  192 ′. 
         [0091]      FIG. 11B  shows a plot containing representative data from a commercial digital magnetic switch. This switch converts an analog value of magnetic field to a digital (two-state) electronic output. The horizontal axis is magnetic field (gauss), the vertical axis is Switch Sensor Output (Volts). The output voltage of a digital magnet switch vs. applied magnetic field is plotted here as curve  193 . Note that there is hysteresis in the curve. When the applied magnetic field is negative, the output is low at value V L . As the field increases, becomes positive, and increases beyond the defined field Operate Point B OP , the sensor output switches from low to high, V H . Then, as the magnetic field decreases from a large positive value, the output switches back to V L  at a field value of B Reset Point or B RP . The two magnetic field switching threshold values B OP  and B RP , are plotted as dashed lines  194  and  195  on the upper plot. So, when sensor external field curve  191  crosses the B OP  and B RP  dashed lines, the sensor output behaves accordingly as shown in curve  193 . 
         [0092]      FIG. 12  shows alternative methods for bending the magnetic flux from the permanent magnet in order to create the signals necessary for the magnetic encoder. The drawing in the top row is the same as the concept shown in  FIG. 9 , using slotted disks. The drawing in the center row shows another possible modification in which the permeable disk is bent at the outer edge in order to form tabs that distort the magnetic flux in the vicinity of the sensor when the tab passes near the sensor. The drawing in the bottom row shows another possible modification in which the permeable disk is stamped in order to form raised regions that distort the magnetic flux in the vicinity of the sensor when the raised regions pass near the sensor. 
         [0093]    There are many ways to use this invention that involve modifications of the underlying concept shown in this example. For example, the number of sensors could be any number, not only 4- and 5-sensor examples shown here. Also, the number and shape of the variations in magnetically permeable disk could be different. All of these kinds of devices, though not explicitly described in detail here, would still be within the spirit and scope of the present invention. 
         [0094]    The invention described here has been explained using the simplest coordinate axes and geometrical symmetry possible. This makes the explanation of magnetic field biasing and magnetic sensing easier to understand. However, the degree of symmetry and orthogonality described here should not be taken to limit in any way the scope of the invention. In particular, design elements such as magnetization  182  of disk  110 , magnetization  184  of magnet  114 , sensing plane  124 , encoder disk plane  125 , and Gap  126  need not be exactly parallel or perpendicular to their specified geometry. In practical sensing systems, many mechanical and magnetic imperfections are accounted for with calibration routines and software. Generally, then, the description of present invention should be understood to include designs such that items are “substantially parallel” or “substantially perpendicular”, where this allows an alignment tolerance of +/−30 degrees. Similarly, the dimension of gap  126  can allow variations up to +/−30% of its specified distance. 
         [0095]    The above described preferred embodiments of the present invention do not limit the possible variations of the invention, and those skilled in the art can make various modifications and changes that do not exceed the scope of the invention. Any modification made within the spirit and principle of the present invention by replacement with equivalent or improved features falls within the scope of the present invention.