Research On Design And Active Variable Stiffness Control Method Of Dual Drive Variable Stiffness Joint For Robots

Service robots,especially nursing robots,serve the elderly or patients directly,their safety and compliance in physical human-robot interaction(p HRI)is of vital importance.Variable stiffness joints not only provide elasticity and cushioning effect as traditional series elastic actuator,but also can actively adjust the stiffness of the joints,thereby improving the compliance and safety of robots.This makes the variable stiffness actuator(VSA)a popular research concentration in the field of nursing robots.Conventional variable stiffness joints use redundant driving method to control the joint displacement and stiffness,which not only increases the complexity of the mechanism arrangement,making the joints difficult to miniaturize and modularize,but also causes power waste of the stiffness-adjusting motor.All of these contribute to the fact that VSAs are rarely employed in multiple degree of freedom robotic systems.Therefore,the modular design and control algorithm of variable stiffness joints are very challenging tasks.In response to the problems mentioned above,this article proposed the design and control method of a novel modular VSA.The prototype of the joint is built and preliminary experiments are conducted.In response to the required parameters for nursing robotic arm joint and the problem of power waste for typical VSAs,this task proposed a novel joint based on bidirectional antagonistic variable stiffness,in which differential mechanism is employed to output torque and adjust the stiffness simultaneously.In this paper,the detailed design and concept analysis of the proposed VSA are presented,and the modular prototype joint is built up based on the result of mechanical design and simulation.The complete dynamics modeling is carried out according to the special structure of the proposed joint,simulation of the dynamic model is then introduced according to Force Based and Position Based control mode,respectively.The dynamic features including under-actuation,passive compliance,and explosive properties are verified by the simulation.Control system design including the construction of hardware and calibration of software is introduced as well.The platform consists of prototype joint and the control system is used to experimentally verify the designed characteristics like stiffness variable range,stiffness adjusting time,variable stiffness behavior,etc.Advanced function like impact detection,active stiffness adjustment and safety control are implemented using the proposed platform,thereby verify the practicality of the proposed joint.