Soft Sensor Unit for Measurement of Large Scale Multi-axis Force

Abstract

Many robotic applications that physically interact with humans require the measurement of interaction forces to ensure accurate control as well as safety. Devices that are directly attached to the human body, such as wearable devices, must use soft and flexible materials to be comfortable and safe. Most soft sensors cannot measure large amounts of force because soft materials can easily deform and break when subjected to large forces. In this paper, we present a soft force measurement unit (sFMU) that can measure three-axis force. The proposed sFMU is made of three polyurethane air sacs radially aligned in silicone rubber. The volume of each air sac is 15 ml and the size of the cylindrical sFMU is 50 mm in diameter and 20 mm in height. Depending on the magnitude and direction of the force applied to the sFMU, the volume of each air sac changes and so does the internal pressure. The simple manufacturing process of sFMU using inexpensive materials is also introduced. Experimental validation shows that the sFMU can measure up to 160N for z-axis force with 6.51 RMSE, up to 15N for x-axis with 1.63 RMSE, and up to 15N for y-axis with 2.79 RMSE.