Design and Implementation of a Stiffness-Switching Joint for Versatile Assembly Systems

In this paper, we present a robotic joint with adjustable stiffness for versatile assembly systems. A typical rigid robotic arm equipped with this joint can perform multiple tasks, which contributes to the development of flexible systems. This joint consists of two main parts, the main body and suspension plate, with springs and magnets used to form the joint. The main body is directly mounted on the robot, while the suspension plate is connected to the robotic gripper. In this paper, we also discuss the requirements for selecting the springs and magnets, which serve as a reference for the fabrication of this joint. This joint features two modes (low and high stiffness) and is capable of switching between these modes by rotating a disk equipped with magnets. The switching between the low- and high-stiffness modes is very fast, with a transition time of less than 0.5 s. The joint in the low-stiffness mode has six degrees of freedom, indicating its high flexibility. The joint in the high-stiffness mode does not require additional force to maintain its stiffness. The results from the stiffness measurements show that the stiffness of the joint in the high-stiffness mode is approximately five times that of the joint in the low-stiffness mode. The theoretical stiffness of the joint is calculated and compared with values obtained from experiments, and the results are consistent with the experimental results. The effectiveness of the two stiffness modes is confirmed through peg-in-hole and coating experiments.