Abstract:
A door position sensing system includes a door claw having first and second magnets mounted thereon, and a Hall sensor mounted so as to sense the magnetic fields of the first and second magnets. The first magnet is mounted in a door half-latch position, and the second magnet is mounted in a door full-latch position. A processor is responsive to the Hall sensor to provide outputs indicating the half-latch and full-latch positions of a door. The processor may also be arranged to indicate a door open position when neither magnet is near the sensor.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to a multiple output magnetic sensor that can be used to sense multiple positions of an object. Such a sensor can be used, for example, to indicate the half-latch and full-latch positions of an automobile door. 
   BACKGROUND OF THE INVENTION 
   It is desirable and sometimes necessary to sense the positions of various devices that can assume multiple positions. One such device is the door of an automobile. The latches of such doors typically have half-latch and full-latch positions. When the door is in the full-latch position, the latch is fully engaged and the door in its fully closed position. When the door is in the half-latch position, the door in not in its fully closed position but the latch is sufficiently engaged to prevent the door from opening without further intervention by an operator. When the door is in neither the full-latch position nor the half-latch position, the door is open. 
   There are several reasons to sense these door latch positions. For example, the driver of an automobile can be notified when a door is in the full-latch position, or is in the half-latch position, or is open. Alternatively, power assist doors are being contemplated in which a motor or actuator is used to pull the door tightly closed to, for example, better shut out exterior noise. In this case, it is desirable to sense the half-latch position of the door in order to energize the motor so that it pulls the door to the full-latch position, and to then sense the full-latch position in order to prevent further pulling by the motor. 
   Hall sensors have been used to sense the position of objects by detecting the presence or absence of a magnetic field. Thus, a small magnet may be attached to an object whose position is be sensed, and the magnetic field of the magnet is detected by the Hall sensor in order to determine the position of the object. If the circuit that processes the signal from the Hall sensor is configured for uni-polar operation and has a digital output, the sensor will turn on when the magnetic field from the magnet exceeds a pre-defined threshold and will be off the rest of the time (ignoring the effects of hysteresis). Therefore, the circuit will only be able to detect when the object is in a certain discrete position. 
   In applications requiring the detection of multiple positions, such as the automobile door application discussed above, an encoded signal is frequently utilized. However, if only one Hall sensor is to be used to detect multiple positions, a complex time based extrapolation algorithm is required to determine the multiple positions. 
   To avoid the use of such an algorithm, a separate discrete Hall sensor can be used to detect each of the various positions of the object. However, the use of multiple Hall sensors increases the cost of the position detection system. In high volume industries such as the automobile industry, the cost can become significant. 
   The present invention relates to a multiple position sensor that overcomes one or more of these or other problems. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, a door position sensing system comprises a door claw, a receiver, and a processor. The door claw has first and second transmitters mounted thereon. The receiver is mounted so as to receive signals transmitted by the first and second transmitters. The processor is responsive to the receiver to provide outputs indicating first and second positions of a door corresponding to the first and second transmitters. 
   According to another aspect of the present invention, a system comprises a mounting structure having a periphery, a first magnet, a second magnet, and a magnetic field sensor. The first magnet has a first North pole and a first South pole, and the first magnet is mounted on the mounting structure at the periphery such that the first North pole faces the periphery and the first South pole faces away from the periphery. The second magnet has a second North pole and a second South pole, and the second magnet is mounted on the mounting structure at the periphery such that the second South pole faces the periphery and the second North pole faces away from the periphery. The magnetic field sensor senses the first and second magnets upon relative movement between the magnetic sensor and the mounting structure. 
   According to still another aspect of the present invention, a door latch claw comprises a door claw plate having a periphery, a first transmitter mounted on the door claw plate at the periphery to transmit a signal indicative of a half-latch position of the door claw plate, and a second transmitter mounted on the door claw plate at the periphery to transmit a signal indicative of a full-latch position of the door claw plate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages will become more apparent from a detailed consideration of the invention when taken in conjunction with the drawings in which: 
       FIG. 1  illustrates an automobile providing an exemplary application for the present invention; 
       FIG. 2  illustrates a partial door assembly for the automobile of  FIG. 1 ; 
       FIG. 3  illustrates the position of a door claw that is part of a door latch for the door of  FIG. 2  and that is shown in a door open position; 
       FIG. 4  illustrates the position of the door claw of  FIG. 3  when the door claw is in a door half-latch position; 
       FIG. 5  illustrates the position of the door claw of  FIG. 3  when the door claw is in a door full-latch position; 
       FIG. 6  illustrates an exemplary processing circuit that processes signals emitted by transmitters mounted on the door claw of  FIG. 3 ; and, 
       FIG. 7  shows a relative arrangement of transmitters and signals produced by the door claw and processing circuit shown in  FIGS. 3–6 . 
   

   DETAILED DESCRIPTION 
   As illustrated in  FIG. 1 , an automobile  10  has a door  12  which can be latched in half-latch and full-latch positions by a door latch  14 . As shown in  FIG. 2 , the door latch  14  includes a door claw  16  mounted to the door  12  and a striker  18  mounted to a post  20  of the frame of the automobile  10 . 
   The door claw  16  is shown in more detail in  FIGS. 3 ,  4 , and  5 . The door claw  16  comprises a door claw plate  22  that is supported by the door  12  of the automobile  10  and in turn supports first and second magnets  24  and  26 . The door claw plate  22  has a periphery  28 , and the door claw plate  22  supports the first and second magnets  24  and  26  at the periphery  28 . The door claw plate  22  also has a recess  40  that engages the striker  18  mounted on the post  20  of the frame of the automobile  10 . Thus, as the door  12  is closed, the striker  18  enters the recess  40 , engages the door claw plate  22 , and rotates the door claw plate  22  about an axis of rotation  42 . 
   Also mounted on the frame of the automobile  10  is a printed circuit board  44  supporting a Hall sensor  46  and a processing circuit  48  comprising one or more electronic and/or electrical components. The printed circuit board  44  electrically couples the Hall sensor  46  to the processing circuit  48 . The printed circuit board  44  is mounted on the automobile frame so that the Hall sensor  46  senses the magnetic fields of the first and second magnets  24  and  26  as the first and second magnets  24  and  26  move past the Hall sensor  46  during rotation of the door claw plate  22 . 
     FIG. 3  shows the position of the door claw  16  when the door  12  is fully open, i.e., not in either the half-latch position or the full-latch position. As the door  12  of the automobile  10  closes, the striker  18  mounted to the post  20  of the frame of the automobile  10  enters the recess  40  and begins rotating the door claw  16  about the axis of rotation  42 . When the door claw  16  rotates to its half-latch position, the door claw  16  is in the position shown in  FIG. 4  where the first magnet  24  is in close proximity to the Hall sensor  46 . As the door  12  of the automobile  10  continues to close, the striker  18  mounted to the post  20  of the frame of the automobile  10  continues to rotate the door claw  16  about the axis of rotation  42 . When the door claw  16  rotates to its full-latch position such that the door  12  of the automobile  10  is fully closed, the door claw  16  is in the position shown in  FIG. 5  where the second magnet  26  is in close proximity to the Hall sensor  46 . 
   The Hall sensor  46  senses the presence of the first and second magnets  24  and  26  and provides corresponding output signals to the processing circuit  48 . Based on these outputs signals from the Hall sensor  46 , the processing circuit  48  provides half-latch and full-latch outputs to indicate the half-latch and full-latch positions of the door claw  16 . 
     FIG. 6  illustrates an exemplary arrangement for the processing circuit  48 , and  FIG. 7  illustrates the relative orientation and position of the first and second magnets  24  and  26  to produce half-latch and full-latch outputs from the processing circuit  48 . As shown in  FIG. 7 , the first magnet  24  may be mounted on the door claw  16  with the North pole of the first magnet  24  at the periphery  28 . On the other hand, the second magnet  26  may be mounted on the door claw  16  with the South pole of the second magnet  26  at the periphery  28 . 
   With this orientation of the first and second magnets  24  and  26 , the Hall sensor  46  provides a positive going signal in response to the first magnet  24  and a negative going signal in response to the second magnet  26 . As shown in  FIG. 6 , the processing circuit  48  includes a non-inverting first operational amplifier  50  having its positive input coupled to the output of the Hall sensor  46 , and an inverting second operational amplifier  52  having its negative input coupled to the output of the Hall sensor  46 . 
   Accordingly, as the door claw  16  rotates from its door open position shown in  FIG. 3  to its half-latch position shown in  FIG. 4 , the first operational amplifier  50  produces an output pulse  54  indicating that the door  12  has moved into the half-latch position. Then, as the door claw  16  rotates from its half-latch position shown in  FIG. 4  to its full-latch position shown in  FIG. 5 , the second operational amplifier  52  subsequently produces an output pulse  56  indicating that the door  12  has moved into the full-latch position. 
   As can be seen, both of the output pulses  54  and  56  are shown with a positive polarity. However, both of the output pulses  54  and  56  may have the same negative polarity, or one of the output pulses  54  and  56  may have a positive polarity and the other of the output pulses  54  and  56  may have a negative polarity. 
   Moreover, the output pulses may be either voltage pulses or current pulses. Furthermore, instead of providing output pulses on separate pins (the outputs of the first and second operational amplifiers  50  and  52 ), pulses may be provided on a single pin, in which case, the pulses may be distinguished by different voltage or current levels. Accordingly, the outputs can be two voltage outputs with either different or same polarities, two current outputs with either different or same polarities, one voltage output with several voltage levels, and/or one current output with several current levels. Additionally, an interface can be provided where the information is transmitted serially (for example, using pulse width modulated signals associated with particular sensed conditions). 
   Certain modifications of the present invention have been discussed above. Other modifications of the present invention will occur to those practicing in the art of the present invention. For example, as described above, the first and second magnets  24  and  26  mounted on the door claw  16  have corresponding magnetic fields, and the Hall sensor  46  is mounted so as to sense the magnetic fields of the first and second magnets  24  and  26 . The first and second magnets  24  and  26  may be viewed as magnetic field transmitters, and the Hall sensor  46  may be viewed as a magnetic field receiver. Other types of transmitters may be mounted on the door claw  16  to transmit signals indicating the position of the door claw  16 . For example, the transmitters mounted on the door claw  16  may be electromagnetic transmitters, optical transmitters, sonic transmitters, RF transmitters, etc. The sensor such as the Hall sensor  46  must be suitably chosen to complement the particular transmitter. 
   Also, as described above, the Hall sensor  46  is stationary with respect to the first and second magnets  24  and  26 . However, in some applications, the first and second magnets  24  and  26  may be stationary with respect to the Hall sensor  46 . 
   Accordingly, the description of the present invention is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which are within the scope of the appended claims is reserved.