A Soft Sensor-Based Three-Dimensional (3-D) Finger Motion Measurement System

Abstract

In this study, a soft sensor-based three-dimensional (3-D) finger motion measurement system is proposed. The sensors, made of the soft material Ecoflex, comprise embedded microchannels filled with a conductive liquid metal (EGaln). The superior elasticity, light weight, and sensitivity of soft sensors allows them to be embedded in environments in which conventional sensors cannot. Complicated finger joints, such as the carpometacarpal (CMC) joint of the thumb are modeled to specify the location of the sensors. Algorithms to decouple the signals from soft sensors are proposed to extract the pure flexion, extension, abduction, and adduction joint angles. The performance of the proposed system and algorithms are verified by comparison with a camera-based motion capture system.

A Three-dimensional Finger Motion Measurement System of a Thumb and an Index Finger Without a Calibration Process

“…They have been developed with various mechanisms: inertia measurement units (IMU) [6], infrared-based [7,8], bending sensors [9,10], soft sensors [11], etc. Perception neuron [6] can measure whole body motion using sensing modules based on IMUs; hand motion can also be measured if the sensing modules are connected to the finger.…”

“…CyberGlove [9,10] uses bending sensors which resistance is changed according to the flexed angle. Other systems calculate the finger joint angles by measuring length change of the finger: optical linear sensors [12], potentiometers and springs [13], soft sensors [11], etc. When the finger is flexed, the wrinkles on the finger joints are smoothed out, increasing the overall length of the finger.…”

“…Soft materials have been also used for hand motion measurement. Park et al developed a soft sensor that embedded liquid metal as a micro channel in silicon material [11], which changed resistance when it was stretched, and that, properly mounted on the finger joint, allowed the computation of the joint angle.…”

Gallium‐Based Thin Films for Wearable Human Motion Sensors

“…To deploy such technology outside of the laboratory environment, manufacturing and performance need to be precisely controlled, reliable, and repeatable over fabrication cycles and use. The high surface tension of gallium prevents the formation of homogeneous films on silicone carriers and hinders the control of the electrical properties at rest and under mechanical deformation.…”

“…The gallium films can be used to produce precise, repeatable, and durable sensing devices. To date, a large variety of sensors based on liquid metal conductors have been proposed to measure finger joint movements . However, most of these demonstrations were qualitative, restricted to single or mm‐thick devices, or performed on mock‐up hand models.…”