Abstract:
A magnetic encoder apparatus comprising a housing is disclosed in the present invention. The housing includes a base portion and a cover plate portion. The housing also comprises a magnet that is contained in the base portion of the housing, a sensor chip having a major surface located adjacent to the magnet, and an alignment spacer comprising a first side and a second side. The first side of the alignment spacer having an opening through to the second side of the alignment spacer, and the second side fitting into the base portion of the housing. The opening of the alignment spacer encloses the sensor chip.

Description:
RELATED APPLICATIONS  
       [0001]     The application claims priority to provisional U.S. Application Ser. No. 60/426,296, which was filed on Nov. 14, 2002, the disclosure and content of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to magnetic encoder technology and an apparatus that translates mechanical rotary motion into electronic information for use in various applications, such as motors or gasoline pumps.  
       BACKGROUND OF THE INVENTION  
       [0003]     Magnetic encoders are used in applications such as flow control, medical, aerospace, transportation, military, heavy equipment and computers. These magnetic encoders essentially convert mechanical rotary motion into electrical signals such as digital pulse streams.  
         [0004]     The technology of magnetic encoders consists of a diametrically polarized magnet, imbedded into the end of a rotating shaft, positioned over a custom Application Specific Integrated Circuit (ASIC) sensor. When the magnet is rotated, the alternating polarities cause the multiple hall effect sensors on the integrated circuit sensor chip to output two sine waves ninety degrees out of phase with each other. This information is fed into a decoding and interpolation portion of the integrated circuit sensor chip with the resulting encoder output being either an incremental 2 bit gray code, or SSI serial output.  
         [0005]     Prior art magnetic encoder devices have limited accuracy because of the placement and alignment of the diametrically polarized magnet to the sensor chip. Misalignment of the diametrically polarized magnet to the sensor chip may cause inaccuracies in the device of up to four hundred percent. Currently, there is a need in the art for a device to ensure the accurate alignment of the sensor chip to the diametrically polarized magnet. In addition, there is a need in the art for a magnetic encoder apparatus that contains the alignment device in a single housing.  
       SUMMARY OF THE INVENTION  
       [0006]     The apparatus of the present invention satisfies one or more of the above-mentioned deficiencies in the art. A magnetic encoder apparatus comprising a housing is disclosed in one aspect of the present invention. The housing includes a base portion and a cover plate portion. The housing also comprises a magnet that is contained in the base portion of the housing, a sensor chip having a major surface located adjacent to the magnet, and an alignment spacer comprising a first side and a second side. The first side of the alignment spacer has an opening through to the second side of the alignment spacer, and the second side fits into the base portion of the housing. The opening of the alignment spacer encloses the sensor chip.  
         [0007]     In an embodiment of the invention, the alignment spacer has a diameter for use in a magnetic encoder apparatus for controlling the alignment of a magnet to a sensor chip having a major surface. The alignment spacer comprising a surface having at least one tab extending outwardly from the periphery of the surface, and a raised portion extending from the surface defining an opening for receiving the sensor chip.  
         [0008]     These and other advantages and features of the invention will become apparent upon reading and following the detailed description and referring to the accompanying drawings which like numbers refer to like parts throughout. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a diagrammatic illustration of the magnetic encoder apparatus in accordance with one embodiment of the present invention;  
         [0010]      FIG. 2  is a diagrammatic illustration of another view of the encoder apparatus in accordance with one embodiment of the present invention;  
         [0011]      FIG. 3  is a diagrammatic illustration of an alignment spacer in accordance with one embodiment of the present invention;  
         [0012]      FIG. 4  is a detailed diagrammatic illustration of the magnetic encoder apparatus in accordance with one embodiment of the present invention; and  
         [0013]      FIG. 5  is a diagrammatic illustration of a composite bearing for use in the magnetic encoder apparatus in accordance with one embodiment of the current invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     As illustrated in  FIG. 1 , a magnetic encoder apparatus  10  comprises a housing  11  having a base portion  12  and cover plate portion  14 . The cover plate portion  14  is attached to the base portion  12  using screws  16 .  
         [0015]     The magnetic encoder housing  11  may contain various components such as a printed circuit board  20  including a sensor chip  23  ( FIG. 2 ), a diametrically polarized magnet  22 , and an alignment spacer  24 . The base portion  12  of the magnetic encoder enclosure housing  11  is attached to a shaft assembly  25  that provides the rotational energy that will be converted into electrical signals. For example, in one embodiment the shaft assembly  25  is a motor shaft assembly that is attached to the magnetic encoder housing  11 . The magnetic encoder apparatus  10  may sense the speed, direction, and/or the angular position of the motor shaft.  
         [0016]     Screws  16  attaching the cover plate portion  14  to the base portion  12  may be of various sizes depending on the physical dimensions of the encoder enclosure. Screws  16  may be under sized as compared to the holes  18  that are located on the cover plate  14 , printed circuit board  20 , and base portion  12 . The under sizing of the screws  16  enables the printed circuit board  20  to float within the magnetic encoder housing  11 . One skilled in the art will realize that other ways of securing cover plate  14  to base portion  12  can be utilized to attach cover plate portion  14  to base portion  12  while still allowing printed circuit board  20  to float within the magnetic encoder housing  11 .  
         [0017]     Diametrically polarized magnet  22  is embedded in shaft assembly  25  so as to allow the diametrically polarized magnet  22  to rotate along with the shaft assembly  25 . The rotation of shaft assembly  25  and the embedded diametrically polarized magnet  22  provides alternating polarities of the diametrically polarized magnet  22 . The alternating polarities of the diametrically polarized magnet  22  may cause multiple hall effect sensors on the sensor chip  23  to output two sine waves ninety degrees out of phase with each other.  
         [0018]     Referring to  FIG. 2 , alignment spacer  24  comprises a first side  25  and a second side  27 . The alignment spacer may be manufactured from a non-conductive material such as liquid crystal polymer or thermoplastic. The alignment spacer  24  has a raised portion  29  that defines an opening  28  that extends from the first side  25  to the second side  27 . Opening  28  may enclose a sensor chip  23  that is located on printed circuit board  20 . The sensor chip  23  may comprise an angular magnetic encoder integrated circuit similar to the ones manufactured by austriamicrosystems AG of Japan or RLS merlina technika d.o.o. of Ljubljana, Slovenija.  
         [0019]     The opening  28  may pilot tightly over sensor chip  23 . The opening  28  and the diameter of the alignment spacer  24  controls movement of the sensor chip  23  in a direction parallel to a reference plane. The reference plane may be defined by a major surface of the sensor chip  23 .  
         [0020]     In one embodiment, a major surface of the sensor chip  23  may be defined as a top surface  21  of sensor chip  23 . One skilled in the art will realize that a different-sensor chip surface may be defined as a major surface that may also define a reference plane. For purposes of illustration, the top surface  21  of sensor chip  23  is defined as a major surface defining a reference plane. Movement parallel to the top surface  21  or reference plane indicates movement in the X and Y direction. For example, sensor chip  23 , which is included on printed circuit board  20 , may move relative to diametrically polarized magnet  22 . In order to provide accurate alignment of the diametrically polarized magnet  22  to the sensor chip  23 , the center of the diametrically polarized magnet  22  (the rotation axis) is aligned with the center of the top surface  21  of sensor chip  23 .  
         [0021]     Accurate alignment of sensor chip  23  to diametrically polarized magnet  22  provides for increased accuracy of the magnetic encoder apparatus. Alignment spacer  24  allows the magnet to sensor alignment to be maintained to such a degree that the linearity or accuracy of the device cannot be adversely affected by assembly methods or techniques.  
         [0022]     Movement in the X or Y-axis of the sensor chip  23  away from the center of the diametrically polarized magnet  22  (the rotation axis) can reduce the accuracy of the magnetic encoder apparatus  10 . Alignment spacer  24  allows for the accurate alignment of the sensor chip  23  to the diametrically polarized magnet  22  by controlling the alignment of sensor chip  23 , which is mounted to printed circuit board  20 .  
         [0023]     In addition, the reference plane also defines movement in the Z-axis, the direction of movement of sensor chip  23  towards or away from the diametrically polarized magnet  22 .  FIG. 2  shows the Z-axis perpendicular to the top surface  21  or reference plane. Movement perpendicular to the top surface  21  or reference plane indicates movement in the Z-axis. For example, sensor chip  23 , which is mounted on the printed circuit board  20 , may move relative to diametrically polarized magnet  22 . In order to provide accurate alignment of the diametrically polarized magnet  22  to the sensor chip  23 , the center of the diametrically polarized magnet  22  (the rotation axis) is aligned with the center of top surface  21  of the sensor chip  23 . Movement of sensor chip  23  in the Z direction may reduce the accuracy of the magnetic encoder apparatus.  
         [0024]     Referring to  FIG. 3 , the alignment spacer  24  comprises a set of tabs  32  extending. outwardly from the periphery of the alignment spacer  24 . The tabs  32  control movement in the Z-axis in a direction perpendicular to top surface  21  or reference plane.  FIG. 3  shows alignment spacer  24  with a set of three tabs  32 . One skilled in the art will realize that alignment spacer  24  may have more or less than three tabs  32  extending outwardly. The tabs  32  may fit into a tightly held bore of housing  12 . The mating tolerances may be ±0.001 (line on line to 0.002 clearance fit).  
         [0025]      FIG. 4  is a detailed illustration of the components of an embodiment of the present invention. Shaft assembly  25  is connected to the housing  12  and held in position by shaft retaining clips,  42 . The shaft assembly also comprises ball bearings  44  that enable the shaft assembly  25  to rotate and provide rotational energy to the encoder apparatus  10 .  
         [0026]      FIG. 5  illustrates an alternative embodiment of the present invention in which the ball bearing may comprise a composite bearing  52 . The composite bearing may be made of a material such as “Rulon J” which is made from specially formulated PTFE compounds and machined to close tolerances.  
         [0027]     In addition, the housing may be a precision machined housing  54  manufactured from a precision screw machine instead of a cast housing. The precision machined housing  54  may be made on a precision screw machine that allows overall tolerances to be held within 0.001. The additional accuracy may improve the performance of the encoder device by maintaining the mechanical relationships to a higher degree.  
         [0028]     The embodiments of the invention, and the invention itself, are now described in such full, clear, concise and exact terms to enable a person of ordinary skill in the art to make and use the invention. To particularly point out and distinctly claim the subject matters regarded as invention, the following claims conclude this specification. To the extent variations from the preferred embodiments fall within the limits of the claims, they are considered to be part of the invention, and claimed.