Mechanism Theory And Control On Actuator With Variable Stiffness For Bionic Wrist Based On SMA

By the development of robotics,traditional rigid robots have been unable to meet the practical work requirement because of the more and more complex work environment.For solving this problem,bionic robots have been valued by more and more scholars.Bionic robots have remarkable robustness for unstructured work environment,so they can adapt to complicated and changeful work environment.The most significant reason for these advantages is that bionic robots can easily have variable stiffness characteristic.According to these development conditions,it implies that it is important for the research of variable stiffness drive mechanism and control stratagem for bionic robots joints.The start work of this project is to design a bionic wrist driven by antagonistic according to the requirement of performance index and print an experiment prototype using 3D printer.Then,the theory of variable stiffness drive mechanism and control of trajectory tracking for bionic wrist is researched by the combination of theoretical modeling and experiment test.In order to analyze the theory of variable stiffness drive mechanism of bionic wrist,the relationship among rotation angle,driving torque and current of bionic wrist is modeled based on kinetic model.The characteristic of antagonistic variable stiffness driving is validated by simulation and experiment adjusting couple of input current of bionic wrist.Numerical recipes software Matlab is used to validate the variable stiffness characteristic of bionic wrist: during austenite phase transformation of SMA,when the couple of input currents of bionic wrist are adjusted from(0,0)A to(0.30,0.30)A,the joint stiffness of bionic wrist increases from 0.0242 Nm/rad to 0.0484 Nm/rad with 100% improvement.So,it is concluded that the two degree of freedom bionic wrist driven by antagonistic stiffness designed by this project has a remarkable adaptive capacity to environment.It can not only work steadily at a hostile environment,but also work with people without hurting people.In research of trajectory tracking control of bionic wrist,in order to improve control performance and dynamic response ability of bionic wrist,the analysis of three proposed controllers is executed in theory and test by experiment.It is also concluded from experiment result that the NPID and PID-P3 controllers have better effort than traditional PID controller against the severe hysteresis of SMA actuated manipulator no matter static trajectory tracking or dynamic trajectory tracking.Furthermore,the frequency of dynamic trajectory tracking is improved to 1/20 HZ with the error smaller than 1° by using the NPID controller.