Soft curvature sensors for joint angle proprioception

Abstract

Abstract-We introduce a curvature sensor composed of a thin, transparent elastomer film (polydimethylsiloxane, PDMS) embedded with a microchannel of conductive liquid (eutectic Gallium Indium, eGaIn) and a sensing element. Bending the sensor exerts pressure on the embedded microchannel via the sensing element. Deformation of the cross-section of the microchannel leads to a change in electrical resistance. We demonstrate the functionality of the sensor through testing on a finger joint. The film is wrapped around a finger with the sensing element positioned on top of the knuckle. Finger bending both stretches the elastomer and exerts pressure on the sensing element, leading to an enhanced change in the electrical resistance. Because the sensor is soft (elastic modulus E ∼ 1 MPa) and stretchable (>350%), it conforms to the host bending without interfering with the natural mechanics of motion. This sensor represents the first use of liquid-embedded elastomer electronics to monitor human or robotic motion.

Cable-Driven Finger Exercise Device With Extension Return Springs for Recreating Standard Therapy Exercises

“…The actuator-spring designs developed in the current study can be implemented with future modifications of the finger exercise device, which will include reducing the size of the spooling actuation system, scaling up from a single finger device to a full hand rehabilitation device, including sensors to provide force and joint position feedback [19], and implementing safety mechanisms to protect repaired finger from excessive mechanical loading. In addition, the device should have an output display that provides information on time, joint angles, and force applied so as to allow therapists and surgeons to know the details of the CPM intervention and the corresponding results.…”

Multi-mode strain and curvature sensors for soft robotic applications

“…Additionally, the current work is able to measure curvature without knowing the geometry of, or even requiring, an underlying host. This is in contrast to previous work which used deflection of a mechanical joint to induce strain in a liquid metal sensor, and required re-calibration on a per-host basis [14,15]. Finally, the current work expands upon the previous example of multi-layer liquid metal sensors by placing strain gauges in parallel, rather than orthogonally [23].…”

“…By combining two of these strain/curvature sensors, we demonstrate a device which can differentiate between positive curvature, negative curvature and strain. Individually, each element of the devices in this paper behaves according to the theory described in [14] and [15], which we revisit in our theoretical discussion below. In previously published devices, uniaxial strain and bending produced the same sensor output, resulting in ambiguous measurements.…”

“…Elastomer-based sensors with encapsulated liquid metals such as those described in this work are well represented in the literature. Previously reported soft sensory devices based on elastomers substrates include joint angle and curvature sensors [14,15], pressure sensors [16,17] capacitance-based multi-element force sensors [18,19], liquid-metal/conductive fluid hybrid strain sensors [20,21,22], and multi-mode resistance-based devices measuring in-plane strain and out-of-plane pressure [23].…”

Extremely robust and conformable capacitive pressure sensors based on flexible polyurethane foams and stretchable metallization

“…Several groups have recently reported artificial tactile skins for applications in macroelectronics, soft robotics, prosthetics, and bio-inspired electronics. These "soft" pressure sensing technologies rely on microstructured elastomers 1,2 or composite polymers [3][4][5] integrated in resistive or capacitive devices, ferroelectric sensors, 6 liquid metal microfluidics, 7 optical waveguides 8,9 or inorganic semiconductor nanomembranes printed on elastomeric substrate. 10 In all cases, the soft polymer is implemented as the carrier or the sensitive material and is usually a homogeneous elastomer with an elastic modulus in the 10 s-1000 s kPa range.…”