With the increasing intelligence of industrial robots, human-robot collaboration based on force sensing has also become a hot research topic. Among them, robot traction teaching for human-robot collaboration is revolutionary for the future development of robot teaching technology due to its interactive and friendly characteristics. However, if there is a load at the end of the robot during traction teaching, it is not possible to decouple the teaching traction force and the contact force at the end of the robot, so the robot traction teaching cannot be widely used in industry. In order to solve this problem, a traction-type six-dimensional force sensor is designed in this paper.

The six-dimensional force sensor is able to decouple the traction force and the robot end contact force from the structure when the robot is directly taught by traction. In this way, the direct teaching of human traction force can be achieved even when the robot has a working load. The main design work of the traction-type six-dimensional force sensor is as follows.

(1) The traction force sensor system for industrial robots is designed, including the industrial robot platform, six-dimensional force elastomer, strain gauge group bridge circuit, data acquisition card hardware, data acquisition software, and data processing algorithms. The division of labor and roles of each component of the sensor system are also introduced.

(2) Based on the advantages and disadvantages of different sensor elastomer structures and the characteristics of manual traction-type six-dimensional force, the monolithic full-shear six-dimensional force thin-walled cylinder sensor is designed as the structure of the traction-type six-dimensional force sensor. Further, important dimensional parameters of the monolithic thin-walled cylindrical six-dimensional force elastomer were assumed. A mechanical stress analysis of the elastomer structure was performed under six-dimensional forces. The important dimensional parameters of the elastomer were obtained using the sensitivity requirements of the elastomer and the permissible stresses as boundary conditions. The innovative design idea greatly reduces the pre-dimensional design problems of the sensor and presents a proven method and guideline for the design of thin-walled cylindrical elastomers.

(3) The finite element model of the elastomeric sensitive body is established. The main static characteristics of the sensor (sensitivity, inter-dimensional coupling and linearity) are analyzed according to the stress-strain of the finite element model of the elastic sensitive body under six-dimensional forces. It provides the basis for the subsequent design of the patch and group bridge circuit.

(4) The strain gauge set for measuring six signals and its mounting orientation were designed to ensure the maximum sensitivity of the strain gauge set to the measured force or torque. The bridge circuit for the six-signal strain gauge set was designed to ensure that the coupling effect of the other five dimensions of force or moment on the measured signal is theoretically zero.(5) The sensor calibration experiments were designed to analyze the actual static characteristics of the sensor to meet the design requirements. Finally, the decoupling matrix is calculated according to the least squares method of measuring multiple sets of data to achieve the decoupling of the six-dimensional sensor.

A compact wireless six-dimensional force sensor based on the resistance-strain principle is designed to address the problems of large size, cumbersome operation and complex application scenarios of the current six-dimensional force sensors. Firstly, the elastomer of the sensor is designed based on the cross-beam structure, and the optimal structural dimensions of the sensor are determined by the structural static analysis with ANSYS software; secondly, the internal hardware circuit of the sensor is designed based on the design requirements of miniaturization and wireless transmission, including a four-arm full-bridge circuit, a two-stage amplifier circuit, and a data acquisition and transmission circuit, which effectively reduces the size of the sensor and enhances the flexibility; finally, the sensor is designed based on the principle of resistance-strain. Finally, the static calibration method and static decoupling algorithm were designed and optimized to reduce the inter-dimensional coupling interference of the sensor and improve the measurement accuracy. The experimental results show that the indoor wireless transmission distance of the sensor reaches 8 m, the transmission rate can meet the low and medium frequency force signal measurement, and the Class I and Class II errors can meet the use in high precision requirements.