Hybrid Coutour Force/Position Control Of Industrial Robot Based On Variable-Gain Iterative Learning

"Numerical control tools and robotics" as one of the ten key sectors of "Made in China 2025",it is clear that industrial robots are key development areas in the future.At the same time,with the rapid development of the economy,the energy demand is increasing and the exploitation of various traditional energy is inseparable from geological equipment.For large-scale geological equipment parts with complex spatial surfaces,it is more and more common to use industrial robots with a large workspace and dexterous movement for processing.As we all know,control algorithms are indispensable for industrial robots.The robot control algorithm is the brain of the robots,and its performance directly affects the quality of robot product processing.The control methods of industrial robots in different situations are mainly divided into three categories,including trajectory tracking control,contour control and hybrid force/position control.In this paper,to improve the machining accuracy and product quality of the industrial robot,the trajectory tracking control,contour control and hybrid contour force/position control of the industrial robot are studied.The research contents are as follows:Because of the complex characteristics such as time-varying,nonlinearity and strong coupling,it is difficult and expensive to obtain an accurate dynamic model of the industrial robot.To cope with this issue,the iterative learning control(ILC)method is studied for the trajectory tracking of industrial robots.To balance the convergence rate and the suppression of external high-frequency noise amplification,the variable-gain ILC is studied.By using the contraction mapping method,the convergence of the ILC is proved and sufficient conditions for convergence are given.Finally,simulations and experiments are conducted.The results show that the number of iterations required for convergence can be reduced by more than 40% compared with low-gain ILC.At the same time,compared with high-gain ILC,the amplification of external noise with high frequency can be greatly reduced.As the basis of contour error compensation,the accuracy of contour error estimation significantly affects the performance of contour control.To improve the accuracy of contour error estimation,a high-precision iterative method is proposed.In this method,the desired reference point is taken as a datum point to iteratively find the nearest point to the position of the end effector of the industrial robot on the desired contour.This nearest point is called the optimal backward reference point.The contour error is estimated at the optimal backward reference point rather than the desired reference point.Finally,the simulations are conducted.The simulation results show that compared with the existing methods,the proposed method can improve the contour error estimation accuracy by more than 70% for parabolic contour and more than 10%for complex butterfly curve contour.Compared with the contour error estimation method based on the Newton algorithm,the proposed method can reduce the computation time by about 50%.To solve the problem that the advance control strategy based on the model is difficult to design caused by the contour error model is difficult to establish,a variable-gain ILC method for industrial robots is proposed on the basis of the iterative contour error estimation method.In this method,the iterative contour error estimation method is applied to obtain the accuracy estimation value of contour error,and the ILC is used to cancel the requirements of the dynamic model of industrial robots.By using the contraction mapping method,the convergence of the ILC is proved and sufficient conditions for convergence are given.Finally,the improvement of contour tracking accuracy is verified by simulations and experiments.A hybrid contour force/position control of industrial robots is proposed.Firstly,the desired contour force is defined as the relationship between the desired force and the position of the contour.Different from the traditional hybrid force/position control,the aim of the proposed hybrid force/position control is to track the desired position and the desired contour force.This method can realize high force accuracy even if the position control accuracy is low.For the issue that the contour error model is difficult to be obtained,the variable-gain ILC is proposed based on the iterative contour error estimation method.Finally,simulations are conducted.The results confirm that the proposed method can improve the contour control accuracy by more than 78%compared with the traditional hybrid force/position control.