A Study on Robot Motion Recognition and Regeneration

Abstract

Robot motion control is an attractive field because of its applications in industrial area. A lot of knowledge and experiments are demanded to accomplish robot motion control. This study proposes a method for robot motion recognition and regeneration used in painting and welding industries. In the first part of this research, various control algorithms are reviewed and summarized. The main difficulties in robot motion control are: • Modeling or mathematical model identification of the robot system. • The nonlinear characteristics of robot system. • The parameter variation of robot system during operation due to change in payload and friction, etc. • High-speed hardware and complication in programming due to high order of control system. • Requiring reprogramming due to change of the work pattern in short period. These difficulties motivate us to propose a robot motion control approach by using robust control theory. Model is essential for control system design, since most of controller system design are accomplished based on the model of robot. In this research, the joint models of robot are identified individually. To identify the transfer function of each joint, the step responses obtained from experiments are used. In this study, two models representing for the dynamics of robot system are described and used to design controllers to achieve good performance. In the first case, from the experiment, step responses at several set points of a joint are obtained, and one of them is chosen as a representative one for the dynamic motion of this joint. Then the nominal model is identified from the representative step response. And the controller is designed based on the control framework to cope with the discrepancy between the real plant with the model due to unmodelled system dynamics, nonlinear characteristic, reducing of system orders and changing in parameters during operation, etc. In the second case, the experimental step responses of a joint are implemented in the operating range and the models is calculated from these responses. Then a nominal model is chosen and the variation range of uncertain parameters in model is defined. Where, the robust control strategy is also introduced. In this case, the stability and performance of system are guaranteed in spite of parameter variation in the defined range. In this study, to obtain the target route, the operator moves the end effector of robot to the desired positions and orientations. Then the joint motions are recorded in the memory. And the data are used to calculate the reference signals. To evaluate the validity of the proposed designing methods, experiments are tried for the three degree of freedom (3DOF) robot. Proportional Integral Derivative (PID) control is used for the same system to compare robustness to uncertain parameters, disturbance inputs and control performance with the proposed method. And in the experiments, the results show that the proposed control strategy gives better properties than the traditional method.