Structure Design and Mechanical Modeling of a Variable Stiffness Joint

Compared with traditional rigid robot joints, elastic joints with a certain flexibility in operation have higher safety and environmental adaptability. Since the requirements for joint stiffness of robots vary with different usage scenarios, it is necessary to design variable stiffness joints so that the robot has the ability to adapt to the working scene and change the joint stiffness in real-time. This paper discusses the importance of designing variable stiffness joints for robots and how to achieve real-time stiffness adjustment to adapt to different usage scenarios. The paper proposes a stiffness adjustment structure based on the principles of a cam disc - cam follower - nonlinear spring mechanism and derives the mathematical model of the variable stiffness joint. The paper also created a simple prototype and conducted experiments to test the output performance of the variable stiffness joint. Finally, the paper successfully designed and manufactured a joint with variable stiffness characteristics, the maximum and minimum instantaneous output stiffness in the elastic range is 39.56 Nm/rad and 3.33 Nm/rad, respectively.