Abstract:
An assembly for rotably supporting a magnet, the assembly has an outer ring member with a bearing member rotably mounted within the outer ring member and the bearing member has an inner opening for receiving and engaging a magnet. The magnet has an inner opening and a shaft at one end engaged within the inner opening of the magnet and the other end of the shaft is coupled to a mechanism for providing a rotational force to the shaft. A Hall effect sensor is mounted to the outer ring member and the Hall effect sensor is receptive to the angular position of the magnet.

Description:
TECHNICAL FIELD 
     The present invention relates to Hall effect sensors. In particular, an apparatus for mounting a movable magnet for use in a Hall effect sensor is disclosed. 
     BACKGROUND OF THE INVENTION 
     Hall sensors pick up and convert the magnetic field intensity of a magnet into a useful electrical signal. For example, known quantities such as position, speed, orientation and temperature etc. of an object can be determined by the intensity of the magnetic field sensed by the Hall sensor. 
     As expected, numerous applications utilizing a Hall effect position sensor have been employed. One such application is a Hall angular position sensor which determines the angular position of an object. Here, a magnet is mounted for rotation about an axis and according to the rotational position of the magnet&#39;s North Pole with respect to the axis, indicates that position of an object. 
     However, a major problem encountered with Hall angular position sensors is accurately controlling the distance between the magnet and the Hall sensor during rotation. For example, as a change in distance between magnet and the Hall sensor occurs, the intensity of the magnetic field surrounding the sensor is changed. This results in the Hall sensor interpreting the change in the magnetic field intensity being measured as a change in the angular position of the magnet which, of course, relates to the angular position of an object. Accordingly, unwanted change in the positioning of the magnet with respect to the Hall sensor will result in undesired false readings. 
     Accordingly, there is a need for an improved means for mounting and controlling the position of a magnet in a Hall effect sensor. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment, a plastic bearing is inserted into a steel ring and a magnet is fixedly secured within an inner opening of the bearing. The bearing and its mounting allows the magnet to rotate about an axis without any unwanted movement. 
     The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of an apparatus for rotatably supporting a magnet for use in a Hall effect sensor system; 
     FIG. 2 is a view along the lines  2 — 2  of the FIG. 1 embodiment; and 
     FIG. 3 is a cross-section of the view of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1-3, an assembly  10  for rotably supporting a magnet  12  is illustrated. Magnet  12  is received within an opening  14  of a bearing  16 . The outer diameter of magnet  12  is slightly larger than the inside diameter of opening  14  in bearing  16 . Accordingly, magnet  12  is press fitted within opening  14 , and the press fitting of magnet  12  within opening  14  provides a rigid securement of magnet  12 . Bearing  16  is received within a ring member  18 . In an exemplary embodiment, bearing  16  is molded out of plastic. This allows bearing  16  to be magnetically transparent so as not to interfere with the magnetic field of magnet  12 . In addition, and since bearing  16  is manufactured out of plastic, it is easily molded and relatively inexpensive to manufacture. 
     Bearing  16  has an inner ring member  20  and an outer ring member  22 . A plurality of ball bearings  24  are located in between inner ring member  20  and outer ring member  22 . Ball bearings  24  allow magnet  12  to rotate with respect to outer ring member  18  as well as outer ring member  22  of bearing  16 . In an exemplary embodiment, bearings  24  are plastic. As an alternative, bearings  24  are stainless-steel. In either case, bearings  24  do not interfere with the intensity of the magnetic field generated by magnet  12 . Inner ring member  20  is configured about its periphery to define a channel  25  to receive and retain the plurality of ball bearings positioned in between inner ring member  20  and outer ring member  22 . In addition, the inner surface of outer ring member  22  is also configured to define a channel  27  to receive and retain the plurality of ball bearings. This configuration allows inner ring member  20  to rotate with respect to outer ring member  22 . 
     The outer diameter of bearing  16  or outer ring member  22  is slightly larger than the inner diameter of outer ring member  18 . Accordingly, bearing  16  is press fitted into outer ring member  18 . This provides a snug fit of bearing  16  within outer ring member  18 . 
     Bearing  16  is also configured to have a pair of notches  26  along the periphery of bearing  16 . Notches  26  are located approximately 90 degrees from each other. Notches  26  are sufficiently large enough to accommodate a Hall sensor  28 . In an exemplary embodiment, there are two notches and two Hall sensors. Of course, it is contemplated that apparatus  10  may employ a plurality of notches and sensors. 
     Magnet  12  has an inner opening  30 . Accordingly, magnet  12  has a ring shape or can be referred to as a ring magnet. Inner opening  30  is configured to receive and engage a shaft  32 . A shaft  32  is secured to magnet  12  at one end and a mechanical device such as a motor at the other. The outside diameter of shaft  32  is slightly larger than the inside diameter of opening  30 . This provides for a rigid securement of shaft  32  to magnet  12 . Accordingly, and as the mechanical device provides a rotational force to shaft  32 , magnet  12  is also rotated. 
     A pair of Hall sensors  28  are located within notches  26 . Accordingly, and as magnet  12  is rotated in a first direction, the North Pole of magnet  12  approaches one of the Hall sensors until a point of minimal distance is reached and then the North Pole of magnet  12  moves away from the sensor until a point of maximum distance is reached. The resulting variations of the distance of North Pole of magnet  12  with respect to sensor  28  causes a variation in the intensity of the magnetic field of magnet  12 . This intensity is measured by sensor  28  and is converted into useful data such as the positioning of an object or the counting of a number of revolutions per minute. These applications may include, but are not limited to the following: steering the position; vehicle body height position; brake pedal position; and accelerator pedal position. Numerous other applications may be employed with such an arrangement. 
     Moreover, and since two sensors are positioned 90 degrees apart from each other, one of the Hall sensors will generate a Sine wave while the other will generate a Cosine wave as magnet  12  rotates. In an exemplary embodiment, magnet  12  has a single North and South Pole. As an alternative, and as applications may require, magnet  12  may be replaced by a plurality of magnets having the same overall configuration as magnet  12 . However, the resulting magnets will provide a plurality of North and South Poles and accordingly, a plurality of magnetic fields. 
     Referring now in particular to FIG. 2, ring member  18  is configured to have a shoulder portion  34  which depends away from an inner surface  36  of ring member  18 . Shoulder portion  34  provides a seat into which bearing  16  is received. 
     In an exemplary embodiment, inner opening  30  has a diameter of 3.0 mm. The outer diameter of magnet  12  is 11.0 mm. The outer diameter of bearing  16  is 21.0 mm and the height of bearing  16  is 4.0 mm. The outer diameter of ring member  18  is 25.0 mm and the height of ring member  18  is 5.0 mm. The thickness of shoulder portion is 0.5 mm. Of course, and as applications may require, it is contemplated that these measurements may be larger or greater than those indicated above. 
     A major problem encountered with Hall angular position sensors is accurately controlling the distance between the magnet and the Hall sensor during rotation. Any change in the distance between the magnet and the Hall sensor causes a change in the intensity of the magnetic field the Hall sensor is measuring. In this instance, this is interpreted incorrectly as a change in the angular position of the magnet. 
     There are two elements that can change the distance between the magnet and sensor. The first is an unwanted linear movement of the magnet and the second is an unwanted linear movement of the sensor. The unwanted movement of the sensor is corrected by normal good mounting practices. Yet, on the other hand, the movement of the magnet which is normally the rotating element is much more difficult to control. This is particularly true in high-volume, low cost applications. In order to prevent unwanted movement, the rotating magnet must have its axis shaft run very true or the runout and play will lead to large angular position errors. 
     The configuration of assembly  10  prevents unwanted movement of magnet  12  which may be misinterpreted by Hall sensors  28 . 
     In an exemplary embodiment, the rotating magnet is placed in the center of the ball bearing assembly and Hall sensors are attached to the outer race of the bearing. The bearing is then pressed into the steel ring which acts as a flux concentrator. The steel ring assists in making the magnetic field between ring  18  to magnet  12  more uniform. This provides assembly  10  with a more accurate performance. The bearing is made of plastic and the balls are either stainless-steel or plastic which makes the entire ball bearing magnetically transparent. Typical run out and play for inexpensive injection molded plastic bearings with stainless-steel balls is 0.05 mm with a six Sigma distribution of the 0.0 to 0.1 mm. 
     Referring now to FIG. 2, outer ring member  18  has a tab portion  38  which protrudes outwardly from assembly  10 . Tab portion  38  is received within an opening of a printed circuit board (not shown). Tab portion  38  can be secured to the circuit board by the use of an epoxy or other type of glue, or portion  38  can be soldered to the circuit board. Once assembly  10  is secured to the circuit board, the Hall effect sensors can be electrically coupled to the circuit board through soldering or other connection means. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.