Summary A cart‐pendulum system is a nonlinear underactuated mechanical system with two degrees of freedom. This paper addresses the motion trajectory design and tracking control problems for this underactuated system. First, a friction‐like control law is designed for the system. Then, the characteristics of the closed‐loop control system are analyzed. Second, a new method of constructing an optimal trajectory for the system is developed. Then, a tracking control law is designed to quickly track the constructed trajectory. It guarantees that the motion control of the cart‐pendulum system is achieved along a reference trajectory. Finally, a numerical example is presented to demonstrate the effectiveness of the theoretical results. This study constructs an optimal trajectory for the cart‐pendulum system in its whole motion space and solves the motion control objective by tracking the constructed trajectory. It has many advantages compared with other motion control methods, eg, the optimal motion control objective of the system is achieved by a single control law; and the motion process and transient characteristics (eg, the settling time) of the control system can be accurately predicted.

This paper studies the fully distributed tracking problem for high-order nonlinear multiagent systems (MASs) with directed graph. Unlike global Lipschitz condition, the nonlinear function we considered only needs to be a continuously differential one. A recursive state transformation and adaptive control technique are employed to design the tracking controllers. First, a discontinuous fully distributed tracking controller is developed for MASs. Under this controller, the follower agents track the leader agent asymptotically. Second, a continuous fully distributed tracking controller is purposely presented for MASs to avoid the chattering problem may caused by discontinuous controller. Finally, a numerical example is given to verify the effectiveness of those two fully distributed controllers. INDEX TERMS Multi-agent systems, fully distributed, tracking control, directed graph, nonlinear system.

A cart‐double pendulum system is an underactuated mechanical system that has three degrees of freedom (DOF) and has two actuators. This paper discusses the stabilizing control problem for this non‐linear mechanical system. First, an input relationship is constructed to transform the 3‐DOF cart‐double pendulum system into a 2‐DOF reduced‐order system in a fixed time. Second, a swing‐up controller is designed for the reduced‐order system to make the system infinitely approach upright equilibrium point. After that, the swing‐up controller switches to a fixed‐time balance stabilization controller, which stabilizes the cart‐double pendulum at the upright equilibrium point in a fixed time. Finally, numerical examples verify the effectiveness of this presented control strategy.

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