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

Abstract

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.

Design and experiment of a SMA-based continuous-stiffness-adjustment torsional elastic component for variable stiffness actuators

“…Then AwAS-II, designed by Jafari et al [17], realized the output stiffness by using the screw to change the action point of the spring, which can improve the range and reduced the stiffness adjustment time. In another study, Cheng et al [18] proposed a bionic variable stiffness unit that can mimic the elbow joint, including a variable lever arm and an external force adjustment part based on a two-stage four-bar mechanism. This bionic variable stiffness unit can achieve adaptive adjustment of stiffness for different grasping weights.…”

Research on coupling dynamics and coordinated control of a legged robot

“…Serious inaccuracy of these parameters will degrade control performance or even cause instability for a closed-loop system, and, on the contrary, a better coupling mechanism model can develop outstanding control methods and have greater fault tolerance. In actual working environment of a legged robot, it is difficult to precisely identify their dynamic parameters because of that the load to be captured or the unknown disturbance from the end of the manipulator (leg) is often uncertain (Cheng et al, 2018;Hou et al, 2017;Li et al, 2018). Therefore, in-depth study on coupling mechanism of reaction dynamics is extremely necessary, which is the base of control problems.…”