In this paper, a high-order disturbance observer for a class of underactuated robotic systems with mismatched uncertainties is proposed. In order to improve its estimation performance, a choice method of optimal gain matrices of the high-order disturbance observer is obtained as the solution of an optimization problem. A high-order disturbance observer based sliding mode control method is also designed for this class of underactuated robotic system with mismatched disturbance. The stabilities of both the disturbance observer and the controlled closed-loop system are proved by the Lyapunov theorem. Simulations on a benchmark Acrobot system demonstrate the efficiency of proposed approaches.

This study addresses the cooperative control problem of multi‐missile systems. It proposed a two‐stage control strategy, aiming at simultaneous attack from a group of missiles at a static target. The first stage adopts a special distributed consensus protocol in order for all missiles to asymptotically achieve a consensus of states. During the second stage, the local sightline control law allows the missiles to independently reach the target. The dynamic equation of the missile agent is normalised to a quasi‐double‐integrator model which is convenient for designing the consensus protocol. The proposed strategy is suitable for missiles of different speeds that have been self‐organised without air operations centres. Two convincing simulation results are given to illustrate the efficiency of the proposed method.

To hit stationary ground targets in specified direction, a nonlinear impact angle control guidance law based on Lyapunov stability theory is proposed. The proposed law ensures the convergence of the heading angle and the miss distance to guarantee a successful engagement. The impact angle can be adjusted by varying a single parameter. And the maximum value of acceleration has been analyzed to get the proper range for control parameter. Considering the achievable impact angle set is limited, an additional phase is added to form a two-phase control strategy. The first phase is to establish a proper initial condition for the second phase, and the second phase is to hit the target with a certain impact angle. An analysis of the proper selection of control parameters to expand the achievable impact angle set is presented. The performance of the proposed guidance law is illustrated with simulations. (C) 2018 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.This is an open access article under the CC-BY-NC-ND license.