Fabrication and characterization of bending and pressure sensors for a soft prosthetic hand

Abstract

We demonstrate fabrication, characterization, and implementation of 'soft-matter' pressure and bending sensors for a soft robotic hand. The elastomer-based sensors are embedded in a robot finger composed of a 3D printed endoskeleton and covered by an elastomeric skin. Two types of sensors are evaluated, resistive pressure sensors and capacitive pressure sensors. The sensor is fabricated entirely out of insulating and conductive rubber, the latter composed of polydimethylsiloxane (PDMS) elastomer embedded with a percolating network of structured carbon black (CB). The sensor-integrated fingers have a simple materials architecture, can be fabricated with standard rapid prototyping methods, and are inexpensive to produce. When incorporated into a robotic hand, the CB-PDMS sensors and PDMS carrier medium function as an 'artificial skin' for touch and bend detection. Results show improved response with a capacitive sensor architecture, which, unlike a resistive sensor, is robust to electromechanical hysteresis, creep, and drift in the CB-PDMS composite. The sensorized fingers are integrated in an anthropomorphic hand and results for a variety of grasping tasks are presented.

Toward a Smart Compliant Robotic Gripper Equipped with 3D‐Designed Cellular Fingers

“…For each test trial, the structural gripper grasped the object firmly when the motor is supplied with 12 V to actuate to its maximum capacity; then, the capacitance was recorded before and after grasping the object. The capacitance and applied pressure stress ( σ ) are related by using Hooke's law where E is the Young's modulus of the auxetic structure (0.33 MPa) between the plates for our case . The grasping test is repeated for ten consecutive cycles and the average of maximum force is calculated.…”

High Resolution Soft and Stretchable Circuits with PVA/Liquid‐Metal Mediated Printing

“…Stretchable electronics have a wide range of applications in flexible displays, [ 1 ] sensors, [ 2–6 ] health monitoring devices, [ 7–10 ] structural electronics, [ 11,12 ] wearable motion sensing, [ 13 ] and e‐textiles; [ 14–17 ] reviews of these applications exist in the literature. [ 18 ] Such circuits should ideally remain functional under bending, folding, twisting, and tensile strain.…”

Capacitive Bio-Inspired Flow Sensing Cupula

“…For this work, resistive and capacitive sensing are particularly attractive due to their prevalence in soft robotics. Soft resistive sensors typically consist of rubber embedded with conductive particles and have been developed with applications in medical monitoring [31], motion tracking [31], bio-inspired unmanned air vehicles [32], and prosthetics [33]. Following Ohm’s law, deformation results in either increased or decreased conductance due to changes in micro and macro geometry.…”

“…In contrast to traditional, non-hyperelastic strain gauges whose material (i.e., constantan alloy foil) can generally be assumed to maintain constant conductivity, the separation and contact of the filler material within conductive elastomers invalidates this assumption and often results in greater sensitivity. These conductive rubbers, however, are vulnerable to hysteresis, viscoelastic responses, and drift under environmental influences, such as humidity or temperature [31,32,33]. (Note that temperature sensitivity for our device is discussed in Appendix A.)…”

“…This value can be measured accurately even when the electrodes and interconnects have low and/or inconsistent conductivities. As a result, the resistive hysteresis and drifting behavior of conductive rubbers that make some piezoresistive sensing applications infeasible are not a major limitation for measuring capacitance, allowing the use of such materials in capacitive sensors [31,33]. Regardless, liquid metals have been applied to comb capacitor stretch sensors [37] and grid-based capacitive skins [38,39,40], particularly where viscoelasticity, total loss of conductivity, or spotty performance is a concern (e.g., during hyperelastic stretch).…”