Design of a Ring-Type Bearingless Torque Sensor With Low Crosstalk Error

Cooperative robots usually use joint torque sensors to achieve compliant human–machine interaction. In practical applications, nontorque loads on robot joints will cause crosstalk in joint torque sensors. In most robot joints equipped with joint torque sensors, a cross roller bearing (CRB) is usually used to support the torque sensor, reducing crosstalk error. Nevertheless, CRBs will increase the cost and weight of joints, especially in robot joints with speed reducers other than harmonic drive. This study proposes a ring-type bearingless torque sensor (RBL-TS) structure design and data fusion method. It adopts a ring structure with equally spaced support and strain beams, effectively reducing crosstalk error and increasing flexural stiffness. Its structure is simple, and it is convenient to be integrated into modular robot joints with various speed reducers. The proposed data fusion method can fuse output data of two Wheatstone full-bridges to obtain the actual output of RBL-TS to reduce the crosstalk error further and avoid crosstalk anisotropy of the flexural moments. The FEM analysis and experiments verified that the proposed structure design and data fusion method can effectively reduce the crosstalk error of RBL-TS to 1.14%, which is one-fourth of the crosstalk error of other existing torque sensors without CRBs and close to that of the torque sensors with CRBs. The results showed that RBL-TS can be used in robot joints without CRBs.