Robust Control Study For Robot System Based On Control Constraints

Input saturation widely exists in practical systems, there is also this phenomenon in the actuators of the robot system owing to the physical limit. However, so far, most controllers have been designed based on arbitrary large torque of the actuator so that in the practical application, good performances of the resulting closed-loop system can not be guaranteed and even sometimes it results in control failure. Therefore, the controller should be designed on the base of considering the control input saturation and based on the control constraint the design technique and method are proposed. To this end, some research is addressed for robust and adaptive control of robot systems with control constraints in this paper. The following main results are given.First, under the consideration of the control constraint, a new kind of composite function is developed based on hyperbolic tangent function in order to designing the bounded controller for the practical control system. The proposed function is different from the standard saturation function, which has a good character of derivative continuity besides finite values. Therefore, it is a useful mathematical tool for the composite function to design the bounded controller.Second, adaptive control problem is researched. Taken the control constraints into consideration, the set-point problem is addressed for robot system with unknown parameters and external disturbance. Based on Lyapunov stability theory, an adaptive control law is given by combining the composite function and an integral algorithm. The proposed control algorithm satisfies the control performance of the closed-loop system.Last, robust control problem is studied. A further study is done for the un-modeling dynamics compensation since the adaptive control is fit for parameter uncertainty. Under the same methodology above-mentioned, a newrobust bounded control algorithm is given by exploiting the composite function. This algorithm guarantees robust stability of the closed-loop system and attenuates the external disturbance effectively.