Design Characteristics of Continuum Robots Based on TSA Variable Stiffness Method

Aiming at continuum robots with high flexibility but poor stiffness, which limits its application in certain high-precision and high-load occasions, and the traditional method of changing stiffness has the problems of complicated structure, small range and slow response, etc., and this paper proposes a stiffness adjustment method based on Twisted Multi-String Actuators (hereinafter referred to as TSA) for bionic spine-like continuum robots. Firstly, a bionic spine-like configuration design is proposed to accommodate the variable stiffness method of the force-locking. Secondly, the proposed TSA variable stiffness method is theoretically analysed in terms of geometrical relationship and stiffness to provide a basis for constructing other mathematical models such as its string-twisted. Finally, an experimental prototype was constructed for flexibility testing, and then the experiments of the TSA variable stiffness method under the conditions of two/three/four-strand string were carried out to investigate the retraction and stiffness characteristics under different numbers of torsion turns and different loads, respectively. The results demonstrate that the stiffness of the robot increases with the TSA method, and the increase in the number of string strands improves the failure point of the robot, and the characteristic curves show that the design and model in this paper are more effective than the traditional force-locking design with single string. The design is simple, responsive and has a large adjustment range, which provides a reference value for the study of the stiffness of continuum robots.