A backward control approach for aerial load transportation using a multi-agent system

Design and verification of a distributed backward control approach which solves task assignment problem of an under-actuated nonlinear multi-agent system is investigated in this paper. This under-actuated nonlinear multi-agent system includes several quadrotors work together to transport a load aerially. All quadrotors are connected to the load by cables. In this paper, these cables are modelled as several series of masses, springs and dampers to consider their masses and curvatures. There is no real control on the load and cable masses. Therefore, a backward control approach is presented which is based on some virtual controls considered for the load and masses of the cables. By using this control approach, path tracking of the load is performed by controlling formation of the quadrotors during transportation. Solving consensus, formation control and task assignment problems in the case study in less than respectively one, six and five seconds, is the result of using the proposed approach. An Integral BackStepping-Sliding Mode controller is used for formation tracking of a multi-quadrotor system in the presence of external disturbances. Two theorems are presented to guarantee the stability and convergence of the proposed control systems. In addition, simulation example is used to illustrate the effectiveness of the presented control approach.