RJVS: A novel, compact and integrated rotating joint with variable stiffness

Abstract

A variable stiffness joint is a key element for structural deformation, which is widely used in morphing mechanisms including mechanical arms, folding wings, etc. By adjusting the stiffness of the joint according to the external environment and/or system instruction, the motion response of the mechanical system can be controlled and its security and stability can be guaranteed. However, to develop a variable stiffness joint with small size and large bearing capacity is still challenging. Also, an accurate mathematical model and control method to describe the variable stiffness joint is very important. In this paper, a novel, compact and integrated rotating joint with variable stiffness is developed, whose rotational stiffness and motion can be real-time controlled. A new configuration of a stiffness-adjusting module with superior mechanical properties is proposed by changing the arm length of cantilever leaf springs. Then a universal mechanical model of stiffness which adapts to a wide range of deformation is proposed. The status of the stiffness-adjusting module is changed by rope driven in order to minize the structure. Angular displacement sensors and torque sensors are integrated to observe the static and dynamic performance of the joint. According to the established rotational stiffness model, the stiffness of the joint is adjusted by reverse calculation of the motor’s rotating angle. A nonlinear Proportion-Integral-Derivative method based on a Genetic Algorithm is proposed for motion control. The experimental results show that the proposed joint, with large bearing capacity and a wide range of stiffness adjustment, has integration functions of driving and sensing, and can achieve a good motion control performance.