Design And Performance Analysis Of Wearable Compliant Actuator Elbow Joint With Variable Stiffness

In recent years,the market demand for rehabilitation-oriented and service-oriented robots in China has seen explosive growth.This type of robot is in direct contact with the user’s body,and its performance requirements such as responsiveness,human-robot interaction safety,flexibility,and comfort are extremely critical,among which the adaptability to unstructured or unknown environments is a priority for service-oriented robots.In this case,the traditional rigid drive joints have certain safety risks and are unable to fully perform.In contrast,the traditional rigid drive joints,the variable stiffness compliant actuator have more significant advantages in the adaptation to the unstructured environment,and can also ensure the safety of the human body in the human-machine cooperative work,and more accurate understanding of the movement intention to complete complex and changing tasks.In this paper,a variable stiffness compliant actuator is proposed and the following research is conducted to address the problems of complex structure,insufficient stiffness adjustment performance and poor applicability of existing variable stiffness flexible drive joints,combining two variable stiffness principles of changing elastomer characteristics and mechanical mechanism control.At first,we propose the stiffness adjustment principle of the joint based on the transmission principle of a special four-bar linkage with a zero-length rack,and its stiffness and torque model has been established.Varying the stiffness of the joint by changing the relative coupling angle,the number of branches of the flexible unit,and the physical characteristics of the elastic element.The design analysis of the variable stiffness compliant actuator is based on the design requirements of the bionic joint,and the reconfigurability design is carried out to generate 12 mechanism configuration options,and the variable stiffness characteristics of the mechanism with different configuration options are elaborated.The proposed variable stiffness compliant actuator is integrated into the elbow joint,and the overall structure of the wearable variable stiffness compliant elbow joint is designed comprehensively.Secondly,the dynamics of the wearable variable stiffness compliant actuated elbow joint is modeled,according to its design,by utilizing Lagrange dynamics.And the frequency characteristics of the system are analyzed with its dynamics model.Dynamics simulation with Adams to analyze the joint output torque characteristics and the frequency response of the system under different initial conditions with different elastic elements,different configurations and different preload forces of the flexible unit of the mechanism.Further reveals its operating performance,while verifying the correctness of the theoretical design.Finally,in order to verify further the theoretical design and characteristics of the wearable variable stiffness compliant elbow joint,relevant components are selected and the experimental platform is built according to the experimental requirements.The experiments on joint output torque,stiffness discrimination,position step characteristics and energy storage characteristics are performed on the basis of the constructed experimental platform.The theoretical model of variable stiffness compliant elbow joint is further verified by analyzing the experimental data.The performance variation characteristics of the output torque and stiffness of the variable stiffness compliant elbow joint,as well as the position tracking and energy storage characteristics of the mechanism are revealed.