Research On Joint Design And Control System Of Variable Stiffness Robot Based On HEM

Variable stiffness joints are always the topic in the field of flexible robot research.In order to ensure the processing quality and work efficiency of the traditional rigid robots,they usually have the characteristics of high rigidity and high speed,so they lack flexibility and safety.The installation of a variable stiffness module in the robot joint can not only enhance the safety of the robot and human cooperation process,but also improve the robot adaptability in the surrounding working environment.At present,the realization methods of joint variable stiffness are mainly divided into two categories: improved the mechanical structure and optimized the control methods.The former variable stiffness joint has complex structure,slow response speed of stiffness adjustment and high cost.The latter is often limited by the bandwidth of the control system,the influence of hardware conditions,etc.,and the system stability is weak.In summary,the variable stiffness robot joint still faces many problems to be solved in terms of structural innovation design,stiffness adjustment principle and the optimal control method.Aiming at the above problems,this paper proposes a variable stiffness robot joint based on HEM(Hybrid Electromagnet).Due to the advantages of no contact and friction between the magnets,the stiffness adjustment response speed is very fast,and the joint structure is very simple and compact.In addition,the designed control system ensures the accuracy of the trajectory tracking of the joints.The main work completed are:(1)The advantages and disadvantages of the existing variable stiffness joints are compared and analyzed,and the variable stiffness principle of the joint proposed in this paper is determined.Through this process,the innovation and significance of this topic are demonstrated;(2)Design and analysis of the overall structure of the variable stiffness joint.It mainly includes the determination of the shape and size of the permanent magnet and the excitation coil in the hybrid electromagnet.Three-dimensional modeling of the overall structure of the variable stiffness joint was carried out using Solidworks software.The ANSYS simulation software was used to analyze the force of the key components of the variable stiffness joint.Ansoft electromagnetic simulation software was used to establish the model of the hybrid electromagnet,determine the number of permanent magnets in the mechanism,the direction of magnetization,the relative position of the permanent magnets and the excitation coil,and verify the mechanical characteristics of the hybrid electromagnet;(3)The stiffness model of the variable stiffness robot joint is established,and the dynamic model and controller of the variable stiffness joint are built on this basis.Based on MATLABSimulink,a PD position controller is constructed to improve the accuracy of joint position control.The variable stiffness joint prototype is processed,and the experimental platform is built,and the experiment proves that the variable stiffness joint designed in this paper has the ability to adjust the stiffness quickly.The trajectory tracking error of joints decreases with the increase of joint stiffness,etc.