Capacitive sensing and method
AssigneeTK Holdings Inc.
InventorsJudson Grant McDonnell, Phillip Maguire, Shawn Tracy
Life of this patent
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Abstract
A capacitive vehicle sensor includes a sensing electrode configured to generate an electric field, a shield electrode configured to reduce the electromagnetic influence of electric fields generated by objects outside of the electric field, a circuit coupled to the sensing electrode and shield electrode that allows a plurality of impedances to be coupled between the sensing electrode and the shield electrode, and a control system. The control system configures the impedances between the sensing electrode and the shield electrode, is configured to measure current to the sensing electrode in each configuration, and is configured to calculate a measure related to the impedance from the sensing electrode to ground.
Claims21
An occupant sensing system for a seat, comprising:
- a sensing electrode configured to generate an electric field when power is supplied to the electrode;
- a shield electrode configured to form a layer parallel to the sensing electrode, the shield layer configured to reduce the electromagnetic influence of electric fields generated by objects located outside of the electric field;
- and
- a circuit coupled to the sensing electrode and configured to sense a change in the electric field caused by an occupancy state of the seat, the circuit further configured to ground the shield layer for measuring a first impedance at the sensing electrode, to ground the sensing electrode for measuring a second impedance at the shield layer, to electrically couple the sensing electrode and shield electrode together for measuring a third impedance at the sensing electrode and shield electrode, and to determine the impedance from the sensing electrode to ground based on the first, second, and third impedances,
- wherein the determined impedance from the sensing electrode to ground does not include an impedance from the sensing electrode to the shield layer.
A method for measuring a change in capacitance at a vehicle sensor based on an impedance from the sensor to ground, comprising the steps of:
- generating an electric field at a capacitive sensing electrode, the electromagnetic influence of electric fields generated by objects located outside of the electric field being reduced by a shield layer parallel to the sensing electrode;
- grounding the shield layer and measuring a first impedance at the sensing electrode;
- grounding the sensing electrode and measuring a second impedance at the shield electrode;
- electrically coupling the sensing electrode and shield electrode together and measuring a third impedance at the sensing electrode/shield electrode;
- and
- determining the impedance from the sensing electrode to ground based on the first, second, and third impedances,
- wherein the determined impedance from the sensing electrode to ground does not include an impedance from the sensing electrode to the shield layer.
A capacitive vehicle sensor, comprising:
- a sensing electrode configured to generate an electric field;
- a shield electrode configured to reduce the electromagnetic influence of electric fields generated by objects outside of the electric field;
- a circuit coupled to the sensing electrode and shield electrode that allows a plurality of impedances to be coupled between the sensing electrode and the shield electrode;
- and
- a control system that configures the impedances between the sensing electrode and the shield electrode, is configured to measure current to the sensing electrode in each configuration, and is configured to calculate a measure related to the impedance from the sensing electrode to ground.
An occupant sensing system for a seat, comprising:
- a sensing electrode configured to generate an electric field when a signal is supplied to the electrode;
- a shield electrode configured to form a layer parallel to the sensing electrode;
- a circuit coupled to the sensing electrode and configured to sense a change in the electric field caused by an occupancy state of the seat, the circuit further configured to allow a plurality of coupling impedances between the sensor and shield;
- wherein the system calculates a measure related to the impedance from the sensing electrode to ground using the results of separate measurements taken while the coupling impedances are in different configurations.
A method for measuring a change in capacitance at a vehicle sensor based on an impedance from the sensor to ground, comprising the steps of:
- generating an electric field at a capacitive sensing electrode;
- driving the shield layer with a signal substantially equal to the sensing signal and measuring the current sent to the sensing electrode;
- driving the shield layer with a signal marginally different than the sensing signal and measuring the current sent to the sensing electrode;
- driving the shield layer with a signal substantially equal to the sensing signal while electrically coupling the sensing electrode and shield electrode together and measuring the current sent to the sensing electrode;
- driving the shield layer with a signal marginally different than the sensing signal while electrically coupling the sensing electrode and shield electrode together and measuring the current sent to the sensing electrode;
- and
- determining the impedance from the sensing electrode to ground based on the four measurements,
- wherein the determined impedance from the sensing electrode to ground does not include an impedance from the sensing electrode to the shield layer.
Dependencies are inferred from the claim text.