Design of Highly Sensitive Joint Torque Sensor for Collision Detection in Robotic Manipulators

Joint torque sensors (JTS) are widely used in robots for collision detection (CD) and continuous monitoring of the joint torque during path planning, manipulation, and tool operation. There is a strong demand for such sensors that ensure efficient CD and safe operation by virtue of their responsive sensitivity, overload capacity, and avoidance of resonance. This research investigated a highly sensitive strain gauge-based JTS design, with a novel pear-shaped hole on its spoke structure. A safety factor of 4 was assumed during the design phase to secure the high overload capacity of the sensor structure. The proffered sensor was designed for robotic applications involving high-frequency vibrations, with minimal risk of achieving mechanical resonance. Finite element method (FEM) optimization was carried out to maximize the sensitivity, precluding resonance. An instrumentation amplifier-based sensor-mountable data acquisition unit was also designed and fabricated to acquire the amplified strain gauge data. The experimental results showed that the proposed sensor has 38 mV/Nm sensitivity and 0.04 Nm resolution in the measurement range of +/- 25 Nm torque. The sensor resolution and sensitivity were shown to be 60% and 26.78% better than extant sensors, respectively. The reduction in strain over the sensing area along the length of the spoke structure was constrained to 5.42%, which secured uniform strain distribution under strain gauges, for enhanced sensitivity. The proposed methodology can very well be applied to design sensors with maximum sensitivity for the prescribed vibration constraints.