Flexible touch sensing system and method with deformable material
A single volume soft sensor capable of sensing real-time continuous contact and stretching. An electrical impedance tomography (EIT) technique with support vector machine (SVM) learning is employed to estimate changes of resistance distribution on the sensor caused by fingertip contact even during sensor deformation events. A deformation switch is incorporated to maintain the localization during deformation events.
1. A sensing system, comprising:
a stretchable base material having a resistance distribution that changes in response to being mechanically deformed as a result of a human body contact, the base material having a rebound elasticity such that it remains mechanically deformed for a period after the human body contact has ended;
a plurality of electrodes attached to a perimeter of the base material;
a capacitive sensing channel attached to the base material; and
a controller operatively connected to the plurality of electrodes and the capacitive sensing channel, the controller configured to:
measure instantaneous voltage measurements from the plurality of electrodes;
determine whether the base material is mechanically deformed based on the instantaneous voltage measurements using a support vector machine classifier;
while the base material is not mechanically deformed, (i) determine voltage differences between the instantaneous voltage measurements and a homogenous baseline voltage and (ii) determine a location of the human body contact using electrical impedance tomography (EIT); and
while the base material is mechanically deformed, determine the location of the human body contact based on the voltage differences determined most recently before being mechanically deformed.
2. The sensing system of claim 1 , the controller being further configured to:
begin adaptively updating a baseline EIT measurement when the human body contact with the base material begins; and
stop updating the baseline EIT measurement when the human body contact with the base material ends.
3. The sensing system of claim 2 , the controller further configured to:
measure capacitance measurements from the capacitive sensing channel; and
determine a beginning and ending of the human body contact based on the capacitance measurements.
4. The sensing system of claim 1 , wherein the base material comprises a carbon filled elastomer.
5. The sensing system of claim 1 , wherein the controller utilizes a neighboring method to measure the instantaneous voltage measurements from the plurality of electrodes, said neighboring method comprising:
a) measuring a first voltage differential between a first adjacent pair of electrodes in the plurality of electrodes;
b) measuring a second voltage differential between a second adjacent pair of electrodes in the plurality of electrodes, the first and second adjacent pairs of electrodes having a common electrode; and
c) continuing to measure voltage differentials between successive neighboring pairs of the electrodes until all adjacent pairs of the electrodes have been evaluated for their voltage differential.
6. The sensing system of claim 1 , the controller being further configured to:
determine the homogenous baseline voltage based on instantaneous voltage measurements from the plurality of electrodes while the base material is not mechanically deformed.
7. The sensing system of claim 1 , the controller being further configured to:
determine an image reconstruction of the location and shape of the human body contact using electrical impedance tomography; and
apply a color filter to the image reconstruction to localize a contact coordinate of the location of the human body contact.
8. The sensing system of claim 1 , wherein the base material is imprinted with graphics to indicate control buttons of a device user control interface.
9. The sensing system of claim 1 , wherein the plurality of electrodes are evenly spaced along the perimeter of the base material.
10. The sensing system of claim 1 , further comprising:
a current source connected between the controller and the plurality of electrodes.
11. The sensing system of claim 1 , further comprising:
an amplifier connected in a return path from the plurality of electrodes to the controller.
12. The sensing system of claim 1 , the controller being further configured to:
while the base material is mechanically deformed, determine a deformation level using a support vector machine regression.