| With the rapid development of robot technology,the interaction between robot and human is gradually increasing.Therefore,security issues in human-robot interaction have attracted widespread attention.Robots often work in isolated environments.This has low requirements for human robot interaction and safety level.At the same time,in order to obtain high positional accuracy and strong torque output,robot joint design often takes high rigidity as the design criterion.However,the stronger the stiffness of the joint,the weaker the compliant of the robot,and the poorer its collision safety and ability to adapt to external environments during work.To solve the above problems,a mechanical variable stiffness joint structure is introduced in this paper.On the one hand,the variable stiffness mechanisms can enhance the compliant and energy storage capacity of joint,which is beneficial to reducing or even eliminating damage to the joint system and human body during collision.On the other hand,the structural form of variable stiffness of the joint can improve the adaptability of the system when dealing with unstructured environments.Based on the principle of gear and rack,this paper designs a simple and compact robot variable stiffness joint with flexible and adjustable stiffness,and applies this joint to the research of robot single leg motion performance.The main research contents of this paper are as follows:(1)By consulting a large number of research literature and materials on variable stiffness joints,this paper analyzes the current research status of joint structure and control at home and abroad,starting with the realization principle and joint control methods of variable stiffness joints.(2)A variable stiffness mechanism of gear rack combined with spring is designed,and the effects of gear type,rack layout,and spring coefficient on joint stiffness are analyzed to determine the final joint spatial layout state.The mathematical model of joint stiffness theory is derived,and a joint dynamics model considering factors such as motor and transmission system is established.The output characteristics of the joint are verified by designing simulation experiments in Matlab/Simulink.Subsequently,a single joint performance verification experimental prototype is built to analyze the joint variable stiffness performance.Finally,in order to miniaturize and lighten the joint,structural optimization is carried out.(3)The variable stiffness joint is introduced into the single leg of the robot.The structural design of the robot’s single leg is carried out,and the degree of freedom and motion space of the robot’s single leg are analyzed.The kinematics and dynamics models of the robot’s single leg model are constructed and analyzed,and the accuracy of the model is verified in the Simulink module in Matlab.The joint motion and stiffness control method is designed.And a stiffness matching method based on the end state under external excitation is proposed.The joint drive control programs are designed to pave the way for subsequent experiments.(4)Based on the above research,the robot leg test prototype is built.And the periodic gait experiment of the robot leg is completed in combination with the normal walking state of human beings.Analyze the angle changes of the two joints and the end state of the robot during gait walking with different stiffness.Using the variable stiffness performance of the joint,an external excitation experiment of robot legs is designed to analyze the impact of external excitation on the robot leg end mechanism,explore the research on the adaptability of joints to the environment,and achieve the practical application of variable stiffness joints in robot legs. |
