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Ball segway, a ballbot-type personal carrier robot, is an actual under-actuated system with second-order nonholonomic velocity constraints and input coupling case. The two-dimensional ball segway system has two outputs consisting of ball position and body tilt angle, which needs to be controlled but has only one torque driving the ball. Actuators directly drive the ball and the body has no direct control. The main objective of this study is to design a robust controller for the ball segway so that the ball is transferred in a point-to-point motion while the body is maintained in the vertical position. The proposed controller is designed on the basis of hierarchical sliding mode control technique. Both simulations and experiments were conducted to verify the quality and stability of the control system.

Unmanned aerial vehicles, especially quadcopters, play key roles in many real-world applications and the related quadcopter autonomous control algorithms have attracted a great deal of attention. In this paper, we address the vision-based autonomous landing problem of a quadcopter on a ground moving target. Firstly, we propose a disturbance observer-based control algorithm, consisting of a nonlinear disturbance observer and robust altitude and attitude controllers. This algorithm is based on the quadcopter dynamics model, and its stability is strictly proved using Lyapunov's theory. Secondly, we develop an autonomous landing planner which we test for various landing scenarios to deliver improved reliability and accuracy of the landing mission. These theoretical studies are complemented by a numerical feasibility study, before demonstrating the effectiveness of our approach under actual flight conditions with an experimental quadcopter platform.INDEX TERMS autonomous vehicle, quadcopter, unmanned aerial vehicle, precision landing, moving target, disturbance observer, robust control, mission planing.

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