Design And Experimental Research Of Variable Stiffness Joint Of Flexible Manipulator

Due to the variable stiffness joint(VSJ) with high load/weight ratio 、flexibility and good buffering capacity, which is making robots have outstanding performance in the safety、adaptability to the unknown environment and energy utilization rate areas. Therefore it’s becoming the research hotspots in the flexible robot field in recent years. The paper designs a new active variable stiffness joint from the application prospect of the VSJ, and the following investigations have been carried out.(1) We design the whole structure of the joint. Firstly, we put forward some design indexes of the joint, and describe the VSJ mechanism principle which achieves stiffness variation through a cam disk-roller-spring mechanism with the variable stiffness mechanism(VSM) and harmonic drive gear in series form; Secondly, confirm the overall transmission scheme, and design all the joint module structure which is divided into the core module 、main motor module and the stiffness adjustment module; Finally, finish the joint sensors integrated design and limited position protection design, in case of the joint exceeding the maximum deformation angle due to the undesirable impact.(2) The stiffness characteristic of the joint is analyed and some structual optimization design of the joint is carried out. The force analysis of the preliminary core module is studied which is verified through the ADAMS simulation. Several torque and stiffness characteristic curve of the joint are drawed with different stiffness preset values which provide data references for the subsequent joint control. The strength of the key components of the joint is checked thro ugh the software ANSYS, optimizing the joint partial structure including the core module. Whether the joint is moving slowly or bears sharp impact, it can always run normally, which will not easily be destroyed.(3) The dynamic and control model of the joint are established. Because the Variable Stiffness Joint has certain similarity with Series Elastic Actu ator(SEA), Therefore, Firstly, we summarize the commonly used dynamic model and control method of the SEA; Secondly, As the current SEA dynamic model is too simple, we gradually in-depth reserach the factors to be considered when modeling. Based on that, A perfect joint dynamic model is built and the dynamic performance is simulated through MATLAB/SIMULINK. The simulation results show that the joint has wide bandwidth; Finally, We set up the joint control model using PID method based on force source control idea. The open and closed loop transfer function of the system are derived, and the characteristics of the open and closed loop are analyzed by Simulink. The results show that PID control can greatly improve the output performance of the joint force. Whether it is following the expected step signal or the sinusoidal signal, the joint output force has good following characteristics, which shows fair good robustness.(4) On the basis of not changing any the structure of the core module, a simple joint prototype is built, and parts of the joint data is collected, and the main source of error is analyzed. Results show that the joint has certain characteristic s of variable stiffness, but the actual performance is not good, the running state of the core module is not good, sometimes there is stuck phenomenon, leading to the stiffness value is relatively high.