Abstract:
The present invention is an seat sensor calibration system used to calibrate the output of a pressure sensor embedded in a vehicle seat. The embedded pressure sensor is used in a vehicle to determine the force which air bags should deploy during a collision. The seat sensor calibration system has an assembly for dropping a body weight form on a vehicle seat from a fixed height. The calibration system also has data acquisition electronics for controlling the positional of the body weight form over the seat and for measuring the output of the pressure system. The seat sensor calibration system acquires the output of the pressure sensor upon impact and then immediately after lifting the weight form from the vehicle seat.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a method and apparatus for calibrating a seat sensor, and more particularly to calibrating a seat sensor in an automobile air bag system.  
         BACKGROUND OF THE INVENTION  
         [0002]    Government regulation require that air bags be installed in all newly manufactured vehicles. Some air bag systems are capable of sensing the weight of the seat occupants. Typically, such air bag utilize a pressure or weight sensor in order to accomplish this determination. Accordingly, there is a need that such pressure sensors be calibrated in order to function properly.  
         SUMMARY OF THE INVENTION  
         [0003]    It is an object of the present invention to provide a system and method for calibrating a vehicle air bag sensor system.  
           [0004]    It is another object of the present invention to provide an air bag calibration system and method in which a weight is dropped on a vehicle seat in a near free-fall manner.  
           [0005]    It is another object of the present invention to provide an air bag calibration system that can be operated under computer control.  
           [0006]    The seat sensor calibration system (SSCS) of the present invention is used to calibrate the output of a pressure sensor associated with a vehicle seat. This pressure sensor in used in a vehicle air bag system to determine the weight of an occupant seated in a vehicle such that the air bags can deploy with the desired level of force depending upon the weight of the occupant. For instance, the air bag will deploy with a relatively lower amount of force when it is determined that a relatively lighter occupant is seated in the seat. The SSCS has an assembly for dropping a body weight form on a vehicle seat from a fixed height. The pressure sensor outputs a signal that is functionally related to the weight of the object that is dropped on the vehicle seat. The output signal upon impact is measured with a measuring device such as a computer, voltage meter, or a data acquisition system. (The output signal from the pressure transducer is first measured prior to impact.) The body weight form is dropped at approximately the same location on each vehicle seat to be calibrated. The body weight form is inhibited from moving to adjacent positions on the vehicle seat by guiding the body weight form during near-free-fall when the body weight form is dropped. This near-free-fall only deviates from a true free-fall by the small amount of friction induced in the guiding mechanism. After impact and acquisition of the pressure output, the body weight form is lifted off the seat and the output of the pressure sensor is measured. The measurements of the pressure sensor output upon impact and immediately after impact when the weight form is lifted provide the necessary information needed to calibrate a vehicles air bag sensor system so that the air bags deploy with a reduced force when a smaller vehicle occupant is seated on a vehicle seat. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic of an embodiment of the seat sensor calibration system that uses a pivoting mechanism for positioning a body weight form over a vehicle seat.  
         [0008]    [0008]FIG. 2 is a schematic of the free fall assembly used with the present invention;  
         [0009]    [0009]FIG. 3 is an enlarged view of parts shown in FIG. 2;  
         [0010]    [0010]FIG. 4 is a view similar to FIG. 1 showing parts in a different position;  
         [0011]    [0011]FIG. 5 is a schematic of an embodiment of the present invention in which the free-fall assembly is mounted on an overhead beam;  
         [0012]    [0012]FIG. 6 is an exploded view of the mounting system used to secure the free-fall assembly shown in FIG. 5;  
         [0013]    [0013]FIG. 7 is a perspective view of an embodiment of the present invention that utilizing a translationally movable table for positioning the free fall assembly; and  
         [0014]    [0014]FIG. 8 is an exploded view of the mounting system used to secure the free-fall assembly shown in FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Reference will now be made in detail to presently preferred embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventor.  
         [0016]    With reference to FIGS. 1, 2, and  3  a schematic of an embodiment of air bag sensor calibration system  2  is provided. Free-fall assembly  4  comprising body weight form  6  is attached to pedestal  8 , which is preferably angular. The combination of body weight form  6  and pedestal  8  simulate the distribution of weight that an occupant exerts on a seat. Pedestal  8  is attached to guide bars  10 ,  12 ,  14 ,  16 . Guide bars  10 ,  12 ,  14 ,  16  are attached to guide plate  18  which in turn is attached to cable  20 . Cable  20  is secured to pin  22  which protrudes from cable arm  24 . Cable arm  24  has a hole  26  on one end. The distance between pin  22  and the center of hole  26  determines the height from which body form  6  is dropped on vehicle seat  28 . Preferably the distance between pin  22  and the center of hole  26  is between 1 and 5 inches. Drive shaft  30  feeds through hole  26 . Cable arm  24  is not pinned to drive shaft  30  in any manner. Instead, cable arm  24  is free to rotate relative to drive shaft  30 . Drive arm  32  has hole  34  through which drive shaft  30  is also positioned. However, drive arm  32  is pinned to drive shaft  30  such that drive arm  32  moves is a similar fashion to the hands of a clock when drive shaft  30  is rotated. Drive arm  32  is capable of being moved in a clockwise or counter clockwise direction. Drive pin  36  protrudes from drive arm  32  at a distance of approximately 1.5 inches. Drive pin  36  contacts cable arm  24  during rotation of drive arm  32  and drive shaft  30 . This contact causes cable arm  24  to move in unison with drive arm  32  during the upward swing from the 6 o&#39;clock to the 12 o&#39;clock position. Drive shaft  30  is attached to motor shaft  38  with coupler  40 . Motor shaft  38  emerges from electric motor  44 .  
         [0017]    During operation of the SSCS, cable arm  24  is stopped at the apex of rotation which is approximately the 12 o&#39;clock position. At this position, body weight form  6  is suspended at a fixed height over vehicle seat  28  which has imbedded within it pressure sensor  43 . A preferred pressure sensor embedded within vehicle seat  28  is the PODS-B air bladder available from Delphi-Delco Electronic Systems. The output of pressure sensor  43  is measured prior to impact by computer  46  which is equipped with an analog-to-digital converter through interface cable  48 . A measurement during impact is commenced by operating electric motor  44 . When drive arm  32  rotates slightly past the 12 o&#39;clock position, gravity causes cable arm  24  to disengage from drive arm  32  and swing downward towards the 6 o&#39;clock position. Accordingly, body weight form  6  falls towards and impacts vehicle seat  28 . Upon impact the output of pressure sensor  43  embedded in vehicle seat  28  is measured via computer  46 . Drive arm  32  continues rotating until a position slightly before the 6 o&#39;clock position, at which point a limit switch causes drive arm  32  and motor  44  to stop. Computer  46  via interface cable  50  causes electric motor  44  and drive arm  32  to start rotating in the upward swing after the impact measurement is made. Drive arm  44  makes contact with cable arm  24  at approximately the 6 o&#39;clock position. The upward rotation of drive arm  32  once again moves cable arm  24  towards the 12 o&#39;clock position. Drive arm  32  is then stopped at approximately the 12 o&#39;clock position. A limit switch is used to automatically stop drive arm  32  at this position. Once body weight form  6  is lifted from vehicle seat  28  a third measurement is made of the output of the pressure sensor. The measurements of the output of pressure sensor  43  output upon impact and immediately after impact when body weight form  6  is lifted provide the necessary information needed to calibrate a vehicles air bag sensor system so that the air bags deploy with a reduced force when a smaller vehicle occupant is seated on a vehicle seat.  
         [0018]    With reference to FIG. 2, guiding mechanism  56  is described. During free-fall, body weight form  6  is directed by guides  58 ,  60 ,  62 ,  64  and the same type of guides on the opposite face of grid frame  66 . Bearing are inserted within guides  58 ,  60 ,  62 ,  64  and the guides on the opposite face so that friction with guide bars  10 ,  12 ,  14 ,  16  is reduced. Guide bars  10 ,  12 ,  14 ,  16  are inserted through guides  58 ,  60 ,  62 ,  64 . Guides  58 ,  60 ,  62 ,  64  and its guides on its opposite face are attached to guide frame  66 .  
         [0019]    The present invention includes several variations for mounting guide frame  66  and electric motor  44 . With reference to FIGS.  1 - 4 , a particular embodiment of the present invention is provided. The SSCS is mounted to frame  68  which pivots towards and away from vehicle seat  28  when calibration measurements are performed. Electric motor  44  is mounted to arm  70  by plate  72  and by shaft plate  74 . Guide frame  66  is mounted of the front face of arm  76 . Arms  70  and  76  extends from post  82 . Post  82  is attached to base frame  84  such that post  82  is able to pivot relative to base frame  84 . Drive  86  attaches to post  82  via rod  88  on one end and mount  90  on the opposite end such that post  82  pivots away from vehicle seat  28  when rod  88  is retract by drive  86 . Drive  86  can either be a pneumatic cylinder or an electromechanical linear actuator. The motion of actuator  86  is controlled by computer  46  via interface cable  90 . Accordingly, frame  68  pivots away from vehicle seat  28  in direction d 1  when vehicle seat  28  is to be removed and another seat moved into position to be calibrated. FIG. 4 illustrates frame  68  in the away position.  
         [0020]    With reference to FIGS. 5 and 6 another embodiment of the present invention is provided. Free-fall assembly  4  is mounted to overhead beam  92 . Translation assembly  94  moves free-fall assembly  4  over vehicle seat  28  when a measurement is to be commenced and away from vehicle seat  28  when vehicle seat  28  is to be removed and another seat positioned for measurement. Guide frame  66  attaches to support arm  96  and electric motor  44  attaches to support arm  98 . Brackets  100 ,  101 ,  102 , and  103  hold support arms  96 ,  98  in place. Actuator  106  contacts support brackets  102  and  103  such that free-fall assembly  4  is move along direction d 2  towards and away from a vehicle seat as desired. Actuator  106  mounts on support frame  110  which is mounted on overhead beam  92 . The motion of actuator  106  is controlled by computer  46  via interface cable  112 . Actuator  106  is preferably an electromechanical linear actuator.  
         [0021]    With reference to FIG. 7 and  8 , another embodiment of the present invention is provided. The free-fall assembly  4  is mounted to frame  114 . Frame  114  is attached to translation table  116 . Translation table  116  moves is a linear fashion relative to base frame  118 . A motor connected to base frame  118  allows translation table  116  to move relative to base frame  118 . During operation translation table  116  carries frame  114  and free-fall assembly  4  along direction d 3  to a position such that body weight form  6  is positioned over the seat to be calibrated. When the measurement is complete, translation table  116  carries free-fall assembly  4  away from the vehicle seat. Actuator  120  which is mount within base frame  118  is in communication with translation table  116  via connector  122 . Operation of actuator  120  causes movement of translation table  116  in the d 3  direction. The motion of actuator  120  is controlled by computer  46  via interface cable  124 . Actuator  120  is preferably an electromechanical linear actuator.  
         [0022]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.