Force-sensitive occupancy sensing technology
View Patent ↗A force-sensitive capacitive sensor that includes a first conductive plate, a second conductive plate that is spaced apart from the first conductive plate, and a compressible dielectric insulator positioned between the first conductive plate and the second conductive plate. The sensor also includes 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 sensor may also include electromagnetic shielding. The circuit is configured to 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 sensor or a support surface positioned above the sensor, and transmit output based on the sensed change in capacitance.
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 configured to:
automatically, without user intervention, calibrate the force-sensitive capacitive sensor;
calculate capacitance between the first conductive plate and the second conductive plate;
determine an occupancy state based on the automatic calibration and the calculated capacitance between the first conductive plate and the second conductive plate;
determine at least one force-sensitive measurement based on the automatic calibration and the calculated capacitance between the first conductive plate and the second conductive plate; and
transmit output based on the determined occupancy state and the determined at least one force-sensitive measurement.
2. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to determine the occupancy state based on a sensed change in capacitance between the first conductive plate and the second conductive plate.
3. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to determine the occupancy state by detecting occupancy based on measuring a force greater than a threshold and detecting a lack of occupancy based on measuring a force less than the threshold.
4. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to calculate capacitance between the first conductive plate and the second conductive plate by:
utilizing a Schmitt-trigger along with a resistor to oscillate between digital logic levels at a frequency directly related to capacitance and an RC time constant created with the resistor;
using an oscillating signal of the digital logic levels to serve as a clock source for a counter;
measuring a difference in counter value over a known period of time; and
calculating capacitance between the first conductive plate and the second conductive plate based on a number in the counter.
5. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to calculate capacitance between the first conductive plate and the second conductive plate by introducing a transient input in voltage or current and measuring a response to the transient input with respect to time, and calculating capacitance based on the measured response and time.
6. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to determine at least one force-sensitive measurement by translating the calculated capacitance to force applied to the force-sensitive capacitive sensor.
7. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to determine at least one force-sensitive measurement by using a force-capacitance equivalence function represented as an interpolation of known loads and measured capacitances.
8. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to determine at least one force-sensitive measurement by estimating force using a capacitance to force lookup table.
9. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to automatically, without user intervention, calibrate the force-sensitive capacitive sensor by statistically profiling capacitance values.
10. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to automatically, without user intervention, calibrate the force-sensitive capacitive sensor by performing unsupervised machine learning processes.
11. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to determine at least one force-sensitive measurement by determining different force measurements at different locations across the force-sensitive capacitive sensor.
12. The force-sensitive capacitive sensor of claim 11 , wherein the circuit is configured to localize force measurements to specific regions of a sensor surface of the force-sensitive capacitive sensor.
13. The force-sensitive capacitive sensor of claim 12 , comprising multiple sensing outputs provided for each of the first conductive plate and the second conductive plate,
wherein each of the multiple sensing outputs is associated with a specific region of the sensor surface, and
wherein the circuit is configured to analyze the multiple sensing outputs to provide force measurements for specific regions.
14. The force-sensitive capacitive sensor of claim 12 , wherein the first conductive plate and the second conductive plate each comprise multiple, separate plates across the sensor surface, and the circuit is configured to take a force measurement for each pair of separate plates.
15. The force-sensitive capacitive sensor of claim 11 , wherein the circuit is configured to determine a distribution of force across the force-sensitive capacitive sensor based on different force measurements at different locations across the force-sensitive capacitive sensor.
16. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to transmit data to indicate a particular occupancy state that lasts more than a threshold period of time.
17. The force-sensitive capacitive sensor of claim 1 , wherein the circuit is configured to delay transmission until storage on the circuit is within a threshold storage amount of being full and transmit all stored data when storage on the circuit is within a threshold storage amount of being full.
18. The force-sensitive capacitive sensor of claim 1 , wherein the circuit comprises a wireless radio configured to transmit output wirelessly to a remote location.
19. The force-sensitive capacitive sensor of claim 1 , wherein the first conductive plate, the second conductive plate, the compressible dielectric insulator, the first protective insulator, and the second protective insulator are all flexible such that the force-sensitive capacitive sensor is flexible.
20. The force-sensitive capacitive sensor of claim 1 , wherein the first conductive plate and the second conductive plate are constructed of metalized foil.