Sensorization of Soft Robot Joints for accurate and durable bending measurement

In the practical implementation of soft robots, accurately tracking the deformation of links (or joints) is crucial for obtaining proper control. Therefore, there is a need for lightweight, durable, and cost-effective solutions to monitor the movement of soft segments. This study proposes sensor-equipped flexible joints capable of measuring the angle between the segments of a robotic finger, considering pure in-in-plane bending. Initially, these joints were simulated to assess their mechanical behavior and the feasibility of accommodating strain gauges to measure differential strain, which correlates with angle measurements. Based on the simulation results, three types of sensor-equipped joints with distinct mechanical properties were developed. These joints were characterized in terms of angle measurement accuracy and durability. The experimental evaluation assessed that maximum error, compared to an accurate reference angle measured using a MEMS accelerometer, was less than 1.5°. Durability tests demonstrated that joint performance remained stable over more than 3500 bending cycles, during which the joints were bent up to approximately 65°; the measured angle drift remained below 2°.