Parameters Identification Of LuGre Friction Model Of Revolute Joints In A2-degree-of-freedom Robot

The revolute joint is the fundamental component of a robot and its performanceinfluences the robot directly.Friction exits in all the joints, so the positioning, tracking error, limit cycleoscillation, etc. caused by friction have become the main obstacles to improve robotperformance. Therefore, how to resolve the non-linear friction is one of the mostdifficult problems in the field of robotics.The analysis on this problem has direct impact on the robot control. The frictionis so complicated that there has been nearly no exact and sole mathematical model ontheoretical level. Among the available models, LuGre friction model can betterexplain static and dynamic characteristics. However, it is really hard to identify itsparameters.Without loss of generality, the problem about parameters identification of LuGrefriction model of revolute joints in a2-degree-of-freedom robot has been investigatedin the thesis, as follows:Firstly, on the basis of the dynamic equations of a2-degree-of-freedom(DOF)robot and combining with the LuGre friction model, the LuGre friction models of2revolute joints in the2-DOF robot have been built.Secondly, after the theoretical analysis of the LuGre friction models of therevolute joints in the2-DOF robot, the minimum objective functions are obtained foridentifying the static and dynamic parameters respectively. Meanwhile, it has beenpointed out that the friction parameter identification can be implemented on the basisof developing the experiment of joint torque control. Then on the basis of detailedanalysis of the key techniques such as particle swarm optimization structure,parameter settings and algorithm improvement, the programs for identifying the staticand dynamic parameters of LuGre friction models are written in the environment ofMatlab.Moreover, the test prototype of the2-DOF robot is built based on AC servo motors in order to get the joint torque control. Also the parameter settings anddebugging of the test prototype are finished and the programs based on joint torquecontrol for obtaining the data of the motions of the motors are written.Finally,2groups of experiments for identifying the friction parameters on thetest prototype are given, in which the2motors are controlled separately as well asthey are controlled at the same time. The experimental results are comparatively idealwhich have indicated that the experimental methods for parameter identification arefeasible, however the precision of identification results need improving further.