Dynamics analysis and time-optimal motion planning for unmanned quadrotor transportation systems

Aerial transportation is enjoying more and more popularity among disaster-oriented tasks, such as fire fighting, delivery of relief supplies, life-saving aid, and so on, which are infeasible for ground robots especially in complex terrains. However, the contradictory between transportation efficiency and payload swing suppression is an annoying problem, which badly limits the application of aerial transportation. In this paper, a time-optimal motion planning (TOMP) scheme is proposed with effective payload antiswing performance. To the best of our knowledge, it is the first minimum-time trajectory planning method designed for unmanned quadrotor transportation systems. Compared with existing methods, the proposed approach presents significant superiority in the sense that both nonlinear dynamics of the system and various constraints are taken into full consideration simultaneously. Specifically, the nonlinear system model is established using Lagrangian mechanics, based on which the augmented system is transformed into a nonlinear affine system regarding the acceleration/jerk as the control input without the need of the linearized system model. After discretization and approximation process, the time-optimal motion planning problem is converted into a standard nonlinear programming problem, wherein various practical constraints are considered, including the bounds of the payload swing, the quadrotor velocity, acceleration, and even jerk. Finally, the nonlinear programming problem is solved by the sequential quadratic programming (SQP) method. Experimental results are exhibited to illustrate the effectiveness and feasibility of the proposed approach.