Design and Optimization of High-Stiffness Joint Torque Sensor with Taper Lock Spokes

For compliance and safety in environments involving interaction with humans, the joint torque of collaborative robots should be accurately measured for sensitive force control and collision detection. Accordingly, many collaborative robots have joint torque sensors (JTSs) installed in each joint. However, these sensors not only cause reduced joint stiffness, leading to degraded robot performance, but also suffer from crosstalk error because of the dynamic nature of robots. In previous studies, these drawbacks have been overcome by using an expensive cross-roller bearing (CRB). In this study, we propose a taper lock spoke-type JTS (TS-JTS) that provides high torsional stiffness and effective crosstalk cancellation without the use of a CRB. The JTS comprises four thin plate-shaped sensing spokes, each equipped with a double-shear-type strain gauge (SG). The spokes are firmly fixed to the sensor frame via compatible tapered surfaces. The design parameters for the JTS were optimized through finite-element method analysis, and the performance of a designed sensor was assessed through the experimental analysis. The designed JTS had a high stiffness of 617.5 kN·m/rad and 0.74% crosstalk error, with a ±150-N·m capacity and a 0.07-N·m resolution. Thus, the loss of robot rigidity as a result of the JTS's installation was considerably reduced. Eliminating the use of a CRB allows the JTS and robot joint to be designed independently, allowing easy application of the JTS on robot joints while maintaining low crosstalk error.