Compliant Force Sensors
This post provides a high-level overview of this project. For a more detailed analysis, check out this paper I wrote on the project.
Overview:
During my graduate degree, I found myself needing to measure the grip force of a prosthetic hand. I had previously seen researchers measure the grasp force by taping force-sensitive resistors to the prosthetic fingertip. Capacitive force sensors have previously been shown to perform better than commonly used force-sensitive resistors for this application. These sensors are designed to attach to a flat surface, with the force loading evenly distributed across its surface area. However, prosthetic hands undergo various loading conditions that do not represent this ideal situation. I hypothesized that encapsulating a capacitive force sensor in a compliant material would disperse the force evenly throughout the sensor, allowing for more robust measurement to various loading conditions. Both the baseline sensor and the compliant sensor are shown here.
Methods:
I calibrated the sensors under ideal conditions, with pressure evenly distributed over the sensor surface area. For all other conditions, the calibration curve was used to predict the force compared with the true force reading measured from a high accuracy load cell.
Results:
The blue line is the calibration curve for both configurations. Notice how the baseline configuration lines are all very spread out, indicating how the different loading conditions resulted in very different measured force values. The compliant configuration lines are all quite close together, showing that the compliant material helped dampen the impact of different loading conditions. Quantitatively, the baseline sensor had ten times more error when using the rounded indenter and double the error when shifting the indenter position.