This paper presents two types of nonlinear controllers for an autonomous quadrotor helicopter. One type, a feedback linearization controller involves high-order derivative terms and turns out to be quite sensitive to sensor noise as well as modeling uncertainty. The second type involves a new approach to an adaptive sliding mode controller using input augmentation in order to account for the underactuated property of the helicopter, sensor noise, and uncertainty without using control inputs of large magnitude. The sliding mode controller performs very well under noisy conditions, and adaptation can effectively estimate uncertainty such as ground effects.
A guidance problem for impact time control applicable to salvo attacks is considered based on the sliding mode control. To prevent the singularity of the guidance command, a positive continuous nonlinear function of the lead angle is introduced to the guidance command, which makes the Lyapunov stability negative-semidefinite. This issue is also resolved by the additional component of the guidance command, which makes the sliding mode be the only attractor still without the singularity. The capturability analysis is presented regardless of the initial launching conditions of missiles, which can guarantee a wide range of the capture region. The proposed guidance law is easily extended to a nonmaneuvering target using the predicted interception point. Simulation results confirm the effectiveness of the proposed guidance against a nonmaneuvering target as well as a stationary target with absence and presence of measurement noise.
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