The Study Of Variable Structure Control Based On Sliding Mode And Its Application To Robot

The variable structure control based on sliding mode that is brought in 50's is attention-getting because of its ideal robustness. The sliding mode movement of variable structure system holds the invariance for the change of system parameters, outside disturbance, uncertain mode and model uncertainty of the system. Its flaw is that after the system state getting to the sliding plane, it will produce high frequency chattering around the sliding plane and the control variable of the system will also produce high frequency chattering. For this point, many advanced control theories, such as adaptive control, fuzzy control and neural network, have been applied to sliding mode variable structure system to reduce the chattering. The main works of this paper are as follows:Firstly, on the basis of many foreign and civil references, this paper introduces the basic theories and items, summaries the history, actuality and foreground of sliding mode variable structure control.Secondly,This paper designs a controller for a class of nth order dynamic system in order to avoid the chattering phenomenon that is inherent to sliding mode control. The fuzzy sliding mode control is obtained by combining the fuzzy control and the conventional sliding mode control. And on the basis of sliding mode control, the paper introduces adaptive fuzzy sliding controller, and control rules dynamically on line, which reduces the human limitation in the design of the controller. Through the result of the simulation and the comparison between several control methods, we can see the strong robustness and the advantage of fuzzy sliding mode control.Thirdly, adaptive sliding mode control approach is proposed for a class of unknown SISO affine nonlinear system based on neural network. In this approach, the neural network is used to learning the nonlinear function of the system. The network weights are derived using Lyapunov-based design and are adapted on-line. Due to the existence of neural network approximation error and external disturbance, the sliding mode control which is insensitive to disturbance and parameter is used to achieve robust tracking for the system.Fourthly, sliding mode control holds the invariance for change of system parameters and outside disturbance of the system. Its algorithm is very simple. So sliding mode control is fitting for the robot. Firstly, a global fast terminal sliding mode control is designed for robot in the paper. Combining the advantages of terminal sliding mode and traditional linear sliding mode, this controller can drive systems to reach the equilibrium point in finite time with reduced steady state error. Secondly, a fuzzy sliding mode control based on filter is proposed in the paper. We make use of the filter to restrain the high frequency chattering of the sliding mode control torque, and use fuzzy control and global sliding mode control theory to restrain the chattering in the sliding mode phase. The result of the simulation shows the effective of the approach.