Capacitive sensing apparatus for a vehicle seat
A capacitive sensing apparatus for a vehicle seat includes a deflectable dielectric mat and a flexible printed circuit that wraps around the major surfaces of the dielectric mat to define upper and lower conductor strips that overlap in a direction perpendicular to the dielectric mat. Overlapping regions of the conductor strips define an array of capacitive load cells distributed over the seating surface. A connector stub depending from the flexible printed circuit couples the conductor strips to an external circuit that measures the capacitance of the various load cells to determine occupant weight and weight distribution.
1. Capacitive apparatus for sensing occupant weight applied to a seating surface of a seat, comprising:
a deflectable dielectric mat disposed between said seating surface and a frame of said seat;
an elongate flexible circuit folded around said dielectric mat and supporting first and second sets of conductor strips in proximity to upper and lower surfaces of said dielectric mat, respectively, where said first and second sets of conductor strips periodically overlap in a direction perpendicular to the upper and lower surfaces of said dielectric mat to define a distributed array of capacitive load cells responsive to occupant weight applied to said seating surface; and
capacitance measurement circuitry coupled to said conductor strips for measuring a capacitance of a selected capacitive load cell by coupling a measurement circuit to a pair of conductor strips that define the selected capacitive load cell.
2. The apparatus of claim 1 , where the capacitance measurement circuitry applies a reference potential to conductor strips that do not define the selected capacitive load cell.
3. The apparatus of claim 1 , where said flexible circuit includes a depending connector stub for coupling said capacitance measurement circuitry to said conductor strips.
4. The apparatus of claim 1 , where said capacitance measurement circuitry sequentially measures a capacitance of each capacitive load cell.
5. The apparatus of claim 4 , where said capacitance measurement circuitry detects a cumulative change in capacitance of the capacitive load cells as a measure of deformation of said dielectric mat due to occupant weight.
6. The apparatus of claim 4 , where said capacitance measurement circuitry detects capacitance changes of said capacitive load cells to determine a distribution of the occupant weight across said seating area.