A Compliant Three-Axis Force Sensor With Solid–Liquid Hybrid Cover for Prosthetic Fingertip

To realize compliant contact, current three-axis force sensors for prosthetic or robotic hands always contain flexible, sensitive materials or elastic cover layer, which inevitably increases hysteresis and decreases measurement accuracy of the sensors due to the viscoelasticity of materials. To overcome this problem, this article proposes a compliant three-axis force sensor with a friendly solid-liquid hybrid cover. The tactile sensor consists of four parts: an elastic cavity layer, a dielectric liquid layer, four silicon-based pressure dies, and a flexible printed circuit board (FPCB). When a three-axis contact force is applied to the sensor, the elastic cavity layer deforms, and then the fluid in the cavity is compressed, which leads to different resistance changes on the four silicon-based pressure dies. By combining the resistance changes, the normal and shear components of the three-axis force can be calculated. A sensor prototype is fabricated, and a series of performance tests are implemented. Results show that the sensor has good sensitivities with 1.36, 1.39, and 0.47 V/N were 0–1.1, 0–1.1, and 0–6 N, respectively. In addition, the sensor showed low hysteresis and high repeatability, with a hysteresis error of 2.23% and a repeatability error of 1.02%. Meanwhile, daily life grabbing and texture recognition tests were performed, and results showed that the grip force and texture could be accurately detected.