A Design and Modeling of the Bionic Variable Stiffness Unit Based on the Elbow Joint

Due to problems of slow response speed and complex mechanisms, the application of variable stiffness joints is limited. The variable stiffness element can be divided into the part with variable stiffness and the part with adjustable external force point. The variable stiffness part adopts the lever principle and changes the stiffness of the joint by changing the length of the lever arm. The external force adjustment part adopts the two-stage four-bar mechanism, which transforms the gravity of the object into the horizontal movement of the slider on the guide rail. The response speed of the unit is greatly improved by the use of the pure mechanism. It is ensured that the stiffness of the variable stiffness unit can be adjusted at the same time with smaller size and a wide range of stiffness adjustment. Based on the elbow joint, a bionic variable stiffness unit is proposed. It can automatically change the stiffness according to the different grasping of a weight, which is same as the human arm. On the basic of/According to the derivation of the Variable Stiffness Unit mathematical model, the three-dimensional model of the Variable Stiffness unit is drawn.