Abstract
In order to eliminate the influence of the joint torsional vibration on the system operation accuracy, the parameter identification and the elastic torsional vibration control of a flexible-joint robot are studied. Firstly, the flexible-joint robot system is equivalent to a rotor dynamic system, in which the mass block and the torsion spring are used to simulate the system inertia link and elasticity link, for establishing the system dynamic model, and the experimental prototype is constructed. Then, based on the mechanism method, the global electromechanical-coupling dynamic model of the flexible-joint robot system is constructed to clear and define the mapping relationship between the driving voltage of the DC motor and the rotational speed of joint I and joint II. Furthermore, in view of the contradiction between the system response speed and the system overshoot in the vibration suppression effect of the conventional PID controller, a fuzzy PID controller, whose parameters are determined by the different requirements in the vibration control process, is designed to adjust the driving voltage of the DC motor for attenuating the system torsional vibration. Finally, simulation and control experiments are carried out and the results show that the designed fuzzy PID controller can effectively suppress the elastic torsional vibration of the flexible-joint robot system with synchronization optimization of control accuracy and dynamic quality.
Highlights
Industrial robots can replace human beings in industrial production to achieve more efficient and safer operation; the research and development of the industrial robot system have attracted wide attention from scholars in various countries [1,2,3]
With the increase of manipulator speed and operating load, the elastic deformation of the transmission mechanism, such as the reducer and the transmission shaft, will directly affect the positioning accuracy of the robot actuators and make the robot joints have the characteristics of flexible joints, which is manifested in the vibration of the robot manipulator when it moves
In order to further verify the harmony between stability precision and rapidity of the designed fuzzy PID controller in torsional vibration suppression effect of the flexible-joint robot system, the conventional PID controller, whose parameters are determined by the trial and error method through simulation, is used for comparison and analysis
Summary
Industrial robots can replace human beings in industrial production to achieve more efficient and safer operation; the research and development of the industrial robot system have attracted wide attention from scholars in various countries [1,2,3]. In order to ensure the control accuracy and motion stability of the joint robots, the joint flexibility introduced by the harmonic reducer and the system connecting shaft should be considered comprehensively, and the corresponding restraining measures should be designed to control the joint torsional vibration. Kim and Croft designed a practical method, with only position and velocity feedback, for suppressing the torsional vibration of the industrial robots with elastic joints and the results showed that the proposed method obtained a better performance than other well-known model-based controllers [19]. In order to effectively eliminate the influence of model parameters uncertainties on the vibration control effect and to solve the contradiction between the dynamic quality and stability accuracy of the existing torsion feedback controller for the flexible-joint robot, the flexible joint of the robot is equivalent to an elastic torsion spring for establishing the system electromechanical-coupling dynamics model in this paper.
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