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Force-sensitive occupancy sensing technology

  • US 8,919,211 B1
  • Filed: 03/14/2013
  • Issued: 12/30/2014
  • Est. Priority Date: 04/17/2012
  • Status: Active Grant
First Claim
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1. A force-sensitive capacitive sensor comprising:

  • a first conductive plate;

    a second conductive plate that is spaced apart from the first conductive plate;

    a compressible dielectric insulator positioned between the first conductive plate and the second conductive plate;

    a first protective insulator;

    a second protective insulator sealed to the first protective insulator to encase the first conductive plate, the second conductive plate, and the compressible dielectric insulator; and

    a circuit attached via wires to the first conductive plate and the second conductive plate, the circuit being configured to;

    when the force-sensitive capacitive sensor is positioned below a support surface, sense a change in capacitance between the first conductive plate and the second conductive plate caused by compression of the compressible dielectric insulator resulting from a person occupying the support surface, andtransmit output based on the sensed change in capacitance between the first conductive plate and the second conductive plate,wherein the circuit is configured to detect a binary occupancy state of the support surface based on the sensed change in capacitance between the first conductive plate and the second conductive plate and transmit the detected binary occupancy state, andwherein the circuit is configured to detect the binary occupancy state of the support surface by;

    determining an average acquired signal in an unoccupied state by averaging, over a first number of samples, values of measured capacitance between the first conductive plate and the second conductive plate;

    setting an activation threshold based on the average acquired signal in the unoccupied state and a value that defines an amount of signal change required for activation;

    after setting the activation threshold, determining that a signal representative of measured capacitance between the first conductive plate and the second conductive plate has crossed the activation threshold for a pre-defined number of samples;

    based on the determination that the signal representative of measured capacitance between the first conductive plate and the second conductive plate has crossed the activation threshold, detecting occupancy of the support surface;

    determining an average acquired signal in an occupied state by averaging, over a second number of samples, values of measured capacitance between the first conductive plate and the second conductive plate;

    setting a deactivation threshold based on the average acquired signal in the occupied state and a difference between the average acquired signal in the unoccupied state and the average acquired signal in the occupied state;

    after setting the deactivation threshold, determining that the signal representative of measured capacitance between the first conductive plate and the second conductive plate has crossed the deactivation threshold for a pre-defined number of samples; and

    based on the determination that the signal representative of measured capacitance between the first conductive plate and the second conductive plate has crossed the deactivation threshold, detecting a lack of occupancy of the support surface.

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