An unmanned quadrotor presents excellent mobility to fly freely in complex environments, which makes it an ideal choice for aerial transferring tasks. During the transferring process, it is very challenging to eliminate the swing, since there is no direct control on the payload. The quadrotor transportation system presents the great challenge of the cascaded underactuated-underactuated property, which makes it extremely difficult to simultaneously implement accurate quadrotor positioning and efficient payload swing suppression. In this paper, a nonlinear hierarchical control scheme is proposed for a quadrotor transportation system, which takes full advantage of the cascade property of the system and separates the controller design for the inner loop and the outer loop, respectively, to facilitate the design procedure. More specifically, for the outer loop subsystem, based on the proposed energy storage function, a virtual control vector is designed, which introduces a saturation function to make the desired attitude free of any singularities. For the inner loop, a coordinate-free geometric attitude tracking controller is designed on the Lie group to drive the quadrotor to its desired attitude. It is shown theoretically by Lyapunov techniques and LaSalle's invariance theorem that the equilibrium point of the overall system is asymptotically stable. As illustrated by experimental results, the proposed control law presents advantages such as high control precision, effective payload swing suppression, and so on.

Cable-suspended transportation is an important way of transferring goods and materials by rotorcraft in complex and hazardous environments, where external disturbances, system uncertainties, and, especially, the underactuated characteristic bring great challenges to realize safe and smooth deliveries. In terms of the aforementioned problems, this paper presents an enhanced coupling hierarchical control scheme for both quadrotor positioning and payload swing elimination. By exploiting the cascade property of quadrotor transportation systems, we can design controllers for the inner loop and the outer one separately, provided that the growth restriction condition is well satisfied, which greatly simplifies the design procedure. As the outer loop describes the quadrotor translation and payload swing motion, our central work focuses on the controller design of this subsystem. Specifically, a generalized payload signal is introduced to increase the state coupling, based on which we construct a novel energy storage function. Consequently, an energy coupling control law is proposed, which ensures that the equilibrium point of the system is asymptotically stable by using Lyapunov techniques and LaSalle's invariance theorem. Experimental results are presented to illustrate the superior control performance, even in the presence of external disturbances and parameter uncertainties.

Aerial delivery is becoming a reality due to the development of microelectronics and communication technology. Most existing methods for cable-suspended transportation systems utilize fixed-length cable to connect the unmanned aerial vehicle quadrotor and the payload. Such aerial transportation systems present underactuated property, which is caused by the indirectly controllable payload motion and the underactuation of the quadrotor itself. In practical applications, payload hoisting and lowering motion independent of the quadrotor altitude will further expand the application scope in such areas as limited space crossing and offshore sample collection. To realize the aforementioned objectives, a flexible connection between the quadrotor and the payload is realized by mounting an actuator beneath the fuselage. Suffering from strong nonlinearity and complex dynamic coupling, the control problem becomes extremely challenging and more cumbersome, as the system’s degree of freedom (DOF) increases. To deal with these problems, in this article, a nonlinear control approach is presented by energy-based analysis, which achieves simultaneous quadrotor positioning, payload swing elimination and hoisting / lowering. Lyapunov techniques and LaSalle’s Invariance theorem are utilized to prove the asymptotic convergence of the equilibrium point. Finally, a series of hardware experiments are conducted on a self-built aerial transportation platform. As far as we know, this article provides the first mechanism and control solution for payload hoisting/lowering independent of the quadrotor altitude.

From the practical perspective, with large-scale cargoes or non-negligible hook masses, the centers of gravity of cargoes and hooks do not coincide with each other, and shipboard cranes usually exhibit complex double-pendulum effects during ship-to-ship or ship-to-harbour transportation, which dramatically increase the complexity of dynamic characteristics and make the control issue very challenging. At present, there is no reported work on control of double-pendulum shipboard cranes yet. This paper obtains the dynamic model of double-pendulum shipboard cranes and then provides an effective nonlinear anti-swing feedback controller to achieve stable cargo transportation. Specifically, new state variable signals are generated by combining the original state variables with the ship motion (induced by sea wave perturbations). By adding some elaborately designed nonlinear terms, an anti-swing feedback controller is proposed, which can achieve stable transportation with suppressed swing, and the closed-loop asymptotic stability is proven without any linearizations or approximations to the original complex nonlinear dynamics, with rigorous theoretical analysis. As far as we know, the paper provides the first solution for both controller design and stability analysis of double-pendulum shipboard cranes. Also, several groups of hardware experiments are implemented on a self-built hardware experiment platform, which verify the effectiveness of the proposed method.

Quadrotor unmanned aerial vehicles, with excellent maneuver performance and flexibility, are widely used in cargo transportation. Due to higher requirements for load capacity, dual quadrotors are expected to work cooperatively so as to transport heavy cargos. However, the aerial transportation system with dual quadrotors exhibits higher degrees of freedom, stronger nonlinearities, and more complex system couplings compared with the single quadrotor transportation system, which brings great challenges to the control of the system. This article focuses on the cooperative control of aerial transportation systems with dual quadrotors. Based on the Lagrange’s method, a redundant form of the dynamic model is constructed and presented, where the control inputs are decoupled with system dynamic. According to the cascade characteristics of the system, the inner loop subsystem on the attitude characteristics of the quadrotor, as well as the outer loop subsystem on the cargo’s swing motion and the quadrotor’s translational motion are defined. Then, a nonlinear hierarchical controller containing relative position constraints and cable tensions compensation is proposed. Specifically, by utilizing the energy-based analysis method, virtual control inputs are designed for the outer loop subsystem. Finally, LaSalle’s invariance principle is used to prove the stability of the closed-loop system. Experimental results show satisfactory control performance of the proposed controller.

Rotorcrafts, with satisfactory maneuver performance and ability under complex terrains unreachable for ground robots, are playing important roles for goods transportation. In this article, we focus on the control of the cable-suspended transportation way due to its lower costs and more agility of the rotorcraft's rotational motion. Compared with traditional crane systems and single rotorcrafts without loads, the aerial transportation system presents ``double'' underactuated property, stronger system nonlinearity, and more complex dynamic coupling, which are huge challenges for control schemes design. Meanwhile, aerial transportation usually suffers from external disturbances and uncertainties presented with aerodynamic damping coefficients and rope length. Additionally, overshoots of the rotorcraft's position are potential threats for flight safety, especially in confined and complex environments. To address these problems, a novel adaptive control scheme is designed, which ensures effective rotorcraft positioning and payload swing suppression with restricted overshoot amplitudes. Asymptotic results are obtained with rigorous theoretical derivations provided by the Lyapunov-based stability analysis and LaSalle's invariance theorem. Real-time experiments are performed to validate the effectiveness of the proposed control scheme even in the presence of external disturbances. To the best of our knowledge, this is the first method designed for aerial transportation systems which achieves simultaneous rotorcraft positioning and swing suppression, together with insurance for overshoot restriction even in the presence of parametric uncertainties.