Anti-Swing Control for Quadrotor-Slung Load Transportation System with Underactuated State Constraints.

Quadrotors play a crucial role in the national economy. The control technology for quadrotor-slung load transportation systems has become a research hotspot. However, the underactuated load's swing poses significant challenges to the stability of the system. In this paper, we propose a Lyapunov-based control strategy, to ensure the stability of the quadrotor-slung load transportation system while satisfying the constraints of the load's swing angles. Firstly, a position controller without swing angle constraints is proposed, to ensure the stability of the system. Then, a barrier Lyapunov function based on the load's swing angle constraints is constructed, and an anti-swing controller is designed to guarantee the states' asymptotic stability. Finally, a PD controller is designed, to drive the actual angles to the virtual ones, which are extracted from the position controller. The effectiveness of the control method is verified by comparing it to the results of the LQR algorithm. The proposed control method not only guarantees the payload's swing angle constraints but also reduces energy consumption.

Adaptive control with unknown mass estimation for a quadrotor-slung-load system.

In aerial load transportation applications, knowing the mass of the load in advance is not always possible. The load dynamics depend on its mass and using a high-performance model-based controller with an inaccurate mass will introduce unmodeled disturbances to the system that will negatively affect the closed-loop performance. This paper addresses the design of a trajectory tracking controller for a quadrotor with a slung-load that has an unknown mass. The proposed solution is an adaptive controller with online estimation designed using the backstepping technique. Nonlinear control laws for thrust and angular velocity, and an adaption law for mass estimation are proposed, which guarantee the convergence of the trajectory tracking and the estimation errors to zero, and are robust to variations in load mass. Simulation and experimental results are presented to assess the validity and performance of the proposed controller.

Stability control in older adults with asymmetrical load carrying when stepping down a curb.

We investigated the effect of asymmetric load carrying using different bag types with the dominant and non-dominant hands on upper limb coordination, walking adaptations, and stability control in a curb-descend task in older adults. Fourteen participants walked on a pathway with a 16-cm curb located in the middle. They walked without a load or asymmetrically carrying a load corresponding to 7% of their body mass. The weight was placed in two different bags (with and without strap) and carried by the dominant and non-dominant hands. The upper limb coordination analysis showed that the anti-phase pattern between right and left shoulder reduced considerably due to the almost motionless shoulder of the side carrying the load. The spatial-temporal walking parameters and curb negotiation variables were unaffected by load carriage. The margin of stability (MoS) was unchanged by load transportation in the AP direction. In the ML direction, taking the bag on the same side of the foot contacting the floor increased the MoS; however, when the load was incorporated into the COM model, the MoS did not differ anymore from the control condition. The changes in interlimb coordination reflected a strategy to prevent unexpected movements of the bag that could threaten body stability. Healthy older adults were able to predict the consequences of carrying a load and kept the MoS constant. They compensated for the disturbance caused by the transport of a relatively moderate load and performed the descending curb task successfully.

Avoiding obstacles in cooperative load transportation.

This work deals with load transportation by quadrotors, when the load is attached to the vehicles through flexible cables. More specifically, two quadrotors are used to carry a single load, which is attached to both vehicles, through such kind of cables. The idea of using two quadrotors working cooperatively to carry the load is adopted to suppress any load oscillation in the direction of movement, what would happen if just one UAV were used. As a consequence of using two UAVs (or more than two) it can happen collisions between the vehicles when carrying the load, caused by the forces the load exert on the two vehicles, whose tendency is to bring the vehicles closer one to the other when they accelerate forward. The paper proposes a strategy to avoid such collisions and any collision with obstacles eventually present in the working space as well. Simulated results are shown and discussed, using two AR.Drone®2.0 quadrotor to carry the load, which validate the proposed strategy.

Asymmetrical load-carrying while stepping down a curb in young adults.

BACKGROUND: Asymmetrical load-carrying while walking requires modifications in joint forces to compensate the extra mass and ensure body stability, particularly when the environment is uneven, such as with a curb. Carrying a bag with one hand (dominant or non-dominant) may constrain the movement of the arm, altering the interlimb coordination of the upper limbs. Prior studies did not show changes in interlimb coordination when a light load was attached to the wrist, but the use of a bag to carry the load can be potentially disturbing since exaggerated movements of the bags may compromise balance. In this case, changes in interlimb coordination would be expected to minimize bag movements. However, it is not clear if these changes in interlimb coordination would be sufficient to affect the curb negotiation task. RESEARCH QUESTION: We investigated the effect of asymmetric load-carrying using different bag types with the dominant and non-dominant hands on upper limb coordination and walking adaptations in a curb negotiation task in young adults. METHODS: Seventeen young adults walked and stepped down a curb while carrying a bag with 7% of their body mass. The experimental conditions were to walk without the bag, carrying the bag (with and without strap) using the dominant and non-dominant hand. RESULTS: Carrying the bag reduced the anti-phase pattern and increased the right or left shoulder phases, depending on the side used to carry the bag. It means that the limb that carried the load almost did not move while stepping down the curb. Load transportation did not influence foot-curb negotiation variables. SIGNIFICANCE: Our study indicates that a mild load and the bag influenced the interlimb coordination of the upper limbs. Despite that, young adults compensated for the disturbance caused by the load carriage and did not compromise the curb negotiation task.

Swing-attenuation for a quadrotor transporting a cable-suspended payload.

This paper presents the problem of safe and fast transportation of packages by an Unmanned Aerial Vehicle (UAV) kind quadrotor. A mathematical model and a control strategy for a special class of underactuated mechanical systems, composed of a quadrotor transporting a cable-suspended payload, are proposed. The Euler-Lagrange formulation is used to obtain the dynamic model of the system, where the integrated dynamics of the quadrotor, cable and payload are considered. An Interconnection and Damping Assignment-Passivity Based Control (IDA-PBC) is chosen because of its inherent robustness against parametric uncertainty and unmodeled dynamics. Two cases are considered to obtain two different control laws, in the first case, the designed control law depends on the swing angle of the payload, in the second case the control law does not depend on it. The control objective is to transport the payload from point to point, with swing reduction along trajectory. Experimental results using monocular vision based navigation are shown to evaluate the proposed control law.