Fabric touch sensor
A planar (two-dimensional, XY location) touch sensor may include a knitted structure and supplementary method of sensing detects human touch on a fabric surface. This sensor may be fully knitted and detect the continuous planar location and contact force of human touch along the surface of the structure. The fabric may conform to any arbitrary surface and may be a rectangle for touch pad applications. This sensor may be used for applications that include robotics and human-machine interaction, smart garments and wearables, as well as medical textiles and flexible embedded sensors. This touch sensor may require as few as only two electrode connections from the fabric to sense both planar touch and pressure, which allows it to work in areas with limited space that allow for limited complexity for wiring.
1. A touch sensor structure comprising:
a conductive sensing element layer comprising a conductive yarn and having two exit outputs, wherein the conductive yarn comprises a multi-strand twisted monofilament carbon fiber yarn;
a nonconductive layer that provides a backing for the conductive sensing element layer and prevents unwanted electrical contact with the sensing element layer; and
a spacer fabric layer that resists longitudinal deformation of the conductive sensing element layer;
wherein upon a capacitive touch on the sensing layer, the touch sensor structure can determine a position of the touch;
wherein the conductive sensing element layer comprises the two exit outputs;
wherein the two exit outputs comprise a first exit output and a second exit output, wherein the first exit output is connected to a first input and a second exit output is connected to a second input;
wherein a microcontroller generates a wave input with a 50% duty cycle to each of the first input and second input, wherein the wave input pulses are timed to charge and discharge synchronously;
wherein a first current limiting resistor is located between and directly connected to the first input and the first exit output, and the first exit output is located between and directly connected to the first current limiting resistor and the sensing element layer; and
a second current limiting resistor is located between and directly connected to the second input and the second exit output, and the second exit output is located between and directly connected to the second current limiting resistor and the conductive sensing element layer.
2. The touch sensor structure of claim 1 , wherein the nonconductive layer and the sensing element layer enclose the spacer fabric layer.
3. The touch sensor structure of claim 1 , wherein the conductive sensing element layer comprises a continuous strip that traverses a face of the touch sensor structure.
4. The sensor structure of claim 3 , wherein the continuous strip shape includes parallel rows of the sensing element layer.
5. The sensor structure of claim 4 , wherein the rows are in a weft direction within the touch sensor structure.
6. The touch sensor structure of claim 1 , wherein the twisting of the microfilament fiber yard occurs in two directions.
7. The touch sensor structure of claim 1 , further comprising a heat melt yarn at a top seam of the touch sensor structure that is steam-sealed to prevent the touch sensor structure from unraveling.
8. The touch sensor structure of claim 1 , wherein the exit outputs are snaps.
9. The touch sensor structure of claim 1 , wherein the exit outputs attach to electrodes.
10. The touch sensor structure of claim 1 wherein the wave input is a 500 Hz square wave input.
11. The touch sensor structure of claim 1 , wherein the capacitance of the capacitive touch is measured by comparing the voltage change between first and second current limiting resistors and the sensing element layer.
12. The touch sensor structure of claim 11 , wherein the capacitive touch is introduced into the sensing element layer through the electrical potential of the human body introduced to the sensing element layer through a touch of the human body.
13. The touch sensor structure of claim 12 , wherein a distance from output A to the touch of the human body on the sensing element layer is given by the formula
x
=
(
R
^
B
+
R
^
C
)
t
r
A
-
R
^
A
t
r
B
R
^
C
(
t
r
B
+
t
r
A
)
where x is the distance, RA, RB, and RC are the resistances of the first resistor, second resistor, and sensing element layer resistance respectively, and trA and trB are the rise times from the first and second inputs respectively.
14. The touch sensor structure of claim 1 , wherein the sensing element layer further comprises buttons.
15. The touch sensor structure of claim 1 , wherein the sensing element layer also measures the force applied.
16. The touch sensor of claim 15 , wherein the force applied is measured by measuring the capacitance of the capacitive touch.
17. The touch sensor of claim 1 , wherein the first output and the second output are connected to electrodes.