Occupant detection system

Abstract

An occupant detection system comprises a weight sensor and an electric field sensor, each operatively coupled to a seat. The electric field sensor generates an electric field from at least one electrode in the seat bottom of the seat, provides for generating a response to an influence of the occupant thereupon, and is adapted to provide for discriminating from the response a seated infant or child seating condition from another seating condition. If a measure of weight from the weight sensor is less than a threshold, or if a seated child seating condition is detected by the electric field sensor, then a signal processor provides for disabling an associated restraint actuator. The electric field sensor may comprise a plurality of electrodes over separate first and second regions of differing proximity to a seated infant or child, or at least one electrode in cooperation with a shield or void over at least one of the regions.

1 . An electric field sensor, comprising:
 a. at least one first electrode;   b. at least one second electrode; and   c. at least one third electrode, wherein said at least one second electrode is located between said at least one first electrode and said at least one third electrode, said at least one first electrode is located proximate to a region to be sensed by said electric field sensor, and said at least one second electrode is substantially the same size as said at least one first electrode.   
     
     
         2 . An electric field sensor as recited in  claim 1 , wherein said at least one third electrode is electrically connected to a circuit ground. 
     
     
         3 . An electric field sensor as recited in  claim 1 , further comprising a sensing circuit, wherein said sensing circuit is operatively coupled to said at least one first electrode and to said at least one said second electrode. 
     
     
         4 . An electric field sensor as recited in  claim 3 , wherein said sensing circuit applies a first applied signal to said at least one first electrode and applies a second applied signal to said at least one second electrode. 
     
     
         5 . An electric field sensor as recited in  claim 4 , wherein said second applied signal is equal so said first applied signal. 
     
     
         6 . An electric field sensor as recited in  claim 3 , wherein said sensing circuit is operatively coupled to at least one said third electrode and said sensing circuit applies a third applied signal to said third electrode. 
     
     
         7 . An electric field sensor as recited in  claim 6 , wherein said third applied signal is a circuit ground potential. 
     
     
         8 . An electric field sensor, comprising:
 a. at least one electrode;   b. a first reference capacitor;   c. a second reference capacitor; and   d. a sensing circuit comprising a plurality of states, wherein in a first state said sensing circuit is operatively coupled to at least one said electrode so as to provide for generating a first signal responsive to the capacitance of said at least one said electrode, in a second state said sensing circuit is operatively coupled to said first reference capacitor so as to provide for generating a second signal responsive to the capacitance of said first reference capacitor, in a third state said sensing circuit is operatively coupled to said second reference capacitor so as to provide for generating a third signal responsive to the capacitance of said second reference capacitor, and said sensing circuit is adapted to provide for generating a measure responsive to the capacitance of said at least one said electrode responsive to said first signal, said second signal and said third signal.   
     
     
         9 . An electric field sensor as recited in  claim 8 , wherein in said third state, said sensing circuit is also operatively coupled to said first reference capacitor so that said third signal is responsive to the capacitance of a combination of said first and second reference capacitors. 
     
     
         10 . An electric field sensor as recited in  claim 8 , further comprising at least one switch operatively coupling said at least one electrode, said first reference capacitor and said second reference capacitor to said sensing circuit, wherein said first state, said second state, and said third state of said sensing circuit correspond to corresponding states of said at least one switch. 
     
     
         11 . An electric field sensor as recited in  claim 8 , further comprising at least multiplexer or demultiplexer operatively coupling said at least one electrode, said first reference capacitor and said second reference capacitor to said sensing circuit, wherein said first state, said second state, and said third state of said sensing circuit correspond to corresponding states of said at least at least one multiplexer or demultiplexer. 
     
     
         12 . An electric field sensor as recited in  claim 8 , wherein said plurality of states are repetitively sequentially cycled. 
     
     
         13 . A method of generating a response from an electric field sensor, comprising:
 a. operatively coupling an oscillatory voltage signal across a voltage divider, wherein said voltage divider comprises a first impedance operatively coupled to a switched impedance at a node;   b. switching said switched impedance in accordance with a plurality of states, wherein in a first state said switched impedance comprises at least one electrode of an electric field sensor, in a second state said switched impedance comprises a first reference capacitor, and in a third state said switched impedance comprises a second reference capacitor;   c. generating a plurality of corresponding response signals from said node corresponding to each of said first state, said second state and said third state; and   d. generating the response from the electric field sensor responsive to said plurality of corresponding response signals.   
     
     
         14 . A method of generating a response from an electric field sensor as recited in  claim 13 , wherein in said third state, said switched impedance comprises a combination of said first and second reference capacitors. 
     
     
         15 . A method of generating a response from an electric field sensor as recited in  claim 13 , wherein said plurality of states are repetitively sequentially cycled.