Bladder system for force sensitive resistors (FSR) sensors
A force sensing resistor (FSR) sensor with bladder system provides for ingress protection for FSR sensors by using sealed bladder areas, which act as air reservoirs. A sealed bladder area is attached to an air vent of a sensor area. The sensor area includes two conductive layers forming an open circuit in the static state, the two conductive layers separated by an air cavity. When a force is applied to the sensing area, the two conductive layers are forced toward each other to form a short circuit and the air in the air cavity is forced out the air vent into the bladder area. When the applied force is removed, the air in the bladder area returns into the air cavity separating the two conductive layers to form the open circuit. The bladder area provides a sealed environment within the FSR sensor, ensuring more reliable and consistent measurements.
1. A force sensing resistor sensor comprising:
a. a first layer comprising a first flexible substrate and a first conductive layer coupled to the first flexible substrate;
b. a second layer comprising a second flexible substrate and a second conductive layer coupled to the second flexible substrate, wherein the first conductive layer and the second conductive layer form part of an electric circuit; and
c. a middle layer comprising a middle substrate, a first opening through the middle substrate, and a second opening through the middle substrate, the first opening is interconnected to the second opening, wherein the first layer is stacked on the middle layer such that at least a portion of the first conductive layer is aligned over the first opening, further wherein the middle layer is stacked on the second layer such that at least a portion of the second conductive layer is aligned over the first opening, wherein the first layer covers the first opening and the second opening in the middle layer and the second flexible substrate covers the first opening and the second opening such that the first opening forms an air cavity and the second opening forms a bladder area interconnected to the air cavity, the air cavity and bladder area are a sealed environment.
2. The force sensing resistor sensor of claim 1 wherein the first layer is stacked on the middle layer such that the first conductive layer is facing the middle layer, and the middle layer is stacked on the second layer such that the second conductive layer is facing the middle layer.
3. The force sensing resistor sensor of claim 1 wherein the middle substrate further comprises an air channel, and the first opening is interconnected to the second opening through the air channel.
4. The force sensing resistor sensor of claim 1 wherein the portion of the first conductive layer aligned over the first opening, the first opening, and the portion of the second conductive layer aligned over the first opening form a sensor area.
5. The force sensing resistor sensor of claim 4 wherein the force sensing resistor sensor is configurable between a static state and an active state, wherein in the static state the portion of the first conductive layer in the sensor area is separated from the portion of the second conductive layer in the sensor area by air in the air cavity, further wherein in the active state at least one of the portion of the first conductive layer or the portion of the second conductive layer is forced into contact with the other of the first conductive layer or the portion of the second conductive layer.
6. The force sensing resistor sensor of claim 5 wherein forcing the portion of the first conductive layer and the portion of the second conductive layer into contact with each other forces air from the air cavity into the bladder area.
7. The force sensing resistor sensor of claim 6 wherein the force sensing resistor sensor is further configurable to return from the active state to the static state by removing the force applied to at least one of the portion of the first conductive layer or the portion of the second conductive layer, which separates the portion of the first conductive layer and the portion of the second conductive layer.
8. The force sensing resistor sensor of claim 7 wherein removing the force generates a vacuum in the air cavity that forces air from the bladder area back into the air cavity.
9. The force sensing resistor sensor of claim 5 wherein in the static state the bladder area is filled with air.
10. The force sensing resistor sensor of claim 5 wherein in the static state the bladder is pre-collapsed.
11. The force sensing resistor sensor of claim 5 wherein in the static state the electric circuit is open circuited, and in the active state the electric circuit is closed circuited.
12. The force sensing resistor sensor of claim 1 wherein the first conductive layer and the second conductive layer are configured according to a shunt mode configuration.
13. The force sensing resistor sensor of claim 1 wherein the first conductive layer and the second conductive layer are configured according to a thru mode configuration.
14. A method of making a force sensing resistor sensor, the method comprising:
a. forming a first layer that includes forming a first conductive layer on a first substrate;
b. forming a second layer that includes forming a second conductive layer on a second substrate;
c. forming a middle layer that includes forming an air cavity and a bladder area within a third substrate, wherein the air cavity is coupled to the bladder area; and
d. stacking the first layer, the middle layer, and the second layer with at least a portion of the first conductive layer facing the middle layer and aligned with the air cavity, and at least a portion of the second conductive layer facing the middle layer and aligned with the air cavity, wherein the portion of the first conductive layer, the portion of the second conductive layer, and the air cavity form a sensing area, further wherein the air cavity and the bladder area form a sealed environment within the force sensing resistor sensor.
15. The method of claim 14 wherein forming the middle layer further comprises forming an air channel in the third substrate, wherein the air channel connects the air cavity to the bladder area.
16. The method of claim 14 wherein the portion of the first conductive layer aligned over the first opening, the first opening, and the portion of the second conductive layer aligned over the first opening form a sensor area.
17. The method of claim 14 wherein the force sensing resistor sensor is configurable between a static state and an active state, wherein in the static state the portion of the first conductive layer in the sensor area is separated from the portion of the second conductive layer in the sensor area by air in the air cavity, further wherein in the active state at least one of the portion of the first conductive layer or the portion of the second conductive layer is forced into contact with the other of the first conductive layer or the portion of the second conductive layer.
18. The method of claim 17 wherein forcing the portion of the first conductive layer and the portion of the second conductive layer into contact with each other forces air from the air cavity into the bladder area.
19. The method of claim 18 wherein the force sensing resistor sensor is further configurable to return from the active state to the static state by removing the force applied to at least one of the portion of the first conductive layer or the portion of the second conductive layer which separates the portion of the first conductive layer and the portion of the second conductive layer.
20. The method of claim 19 wherein removing the force generates a vacuum in the air cavity that forces air from the bladder area back into the air cavity.
21. The method of claim 17 wherein in the static state the bladder area is filled with air.
22. The method of claim 17 wherein in the static state the bladder is pre-collapsed.
23. The method of claim 17 wherein in the static state the electric circuit is open circuited, and in the active state the electric circuit is closed circuited.
24. The method of claim 14 wherein the first conductive layer and the second conductive layer are formed according to a shunt mode configuration.
25. The method of claim 14 wherein the first conductive layer and the second conductive layer are formed according to a thru mode configuration.