Research On Passive No-power-source Stiffness Self-adjusting Unit For Elbow Joint

Robot is no longer confined to the structured environment to complete the traditional industrial production,but gradually liberates from the enclosed work space,enters into the unstructured environment and works together with people.Traditional industrial robots with high stiffness joints have excellent precise positioning and anti-jamming capabilities,but they lack the capabilities of cushioning and energy storage.If directly used in unstructured environments,it is easy collide with objects and people surrounding them,which could cause the destruction of the robot body by a strong shock,and even cause fatal injuries to people around them.In order to solve the security problem in the process of man-machine cooperation in unstructured environment,it is an effective way to make the robot joint flexible.Therefore,it is of great practical value and significance to carry out related research on variable stiffness joints.Compared with active variable stiffness joint,passive variable stiffness joint has unique advantages and attracts wide attention.The core variable stiffness element of passive variable stiffness joint mainly has two forms:1)equipped with special stiffness adjusting motor(or two equivalent parameters of the motor,coupling to achieve joint drive and stiffness control)and special sensors,this way increases the complexity of the joint,the overall size is relatively large;2)not equipped with special stiffness adjusting motor,degree regulation motor,but equipped with special sensors to provide information feedback,with the joint drive motor to achieve stiffness adjustment,this way of control is difficult.At present,both of these methods depend on sensors and special control algorithms,resulting in the joint response speed constrained by bandwidth constraints.In this paper,a new passive stiffness adjusting unit for robot elbow joint is proposed.It is not necessary to equip special stiffness adjusting motor and any sensor.It can adjust the stiffness in a wide range by pure mechanical way.It does not need any sensor and control algorithm,and the response speed is effectively guaranteed.The main contents of this paper are as follows:(1)Research on the principle of stiffness self-adjusting unit.Based on the research status of variable stiffness joints at home and abroad and the mechanism of bionic elbow joints,a novel passive stiffness self-adjusting element mechanism for robot arm elbow joints was synthesized.(2)Theoretical basic research.Mathematical models of kinematics,statics and stiffness of passive variable stiffness elements are established.Parameters optimization was carried out and the variation trend of joint stiffness under different conditions was obtained.(3)Model design and prototype development.On the basis of principle research and parameter determination,a three-dimensional virtual prototype model of passive stiffness self-adjusting unit was established,and simulation analysis and optimization design were carried out.(4)Experimental research.The experimental platform was built,and the experimental results were analyzed and discussed.The validity of the new mechanism and the correctness of the theoretical research were verified.