In the previous article I showed my successful implementation of ShArc, a novel bend/shape sensor using capacitive sensing. My video showed that the system could track the bend shape of the sensor but it was not quantitively analysed.
To take this a little further I wanted to show the relationship between the signal that the sensor generates and the radius of curvature. To begin with I 3D printed a flexible covering for the flex using TPU filament and the modified extruder I designed to enable TPU printing on my Monoprice 3D printer.
The sensor is made of two flexible circuit boards (“flexes”) stacked either side of multiple layers of polyimide material, which is the same material used for the flex substrate. Both flexes are constrained together at one end, and when the flexes are bent, they slide relative to each other. The topmost flex (TX Flex) has a series of transmit electrodes along its length, while the bottom most flex (RX Flex) has a series of corresponding receive electrodes along its length. As the two flexes slide relative to each other, the capacitance between each TX and RX electrode pair changes. By measuring this capacitance the system can infer the relative slide between the two flexes and in turn infer the bend radius.