Attitude-Constrained Time-Optimal Trajectory Planning for Rotorcrafts: Theory and Application to Visual Servoing

In this article, a novel real-time time-optimal trajectory planning (TOTP) approach is proposed for rotorcrafts under velocity constraints and complex nonconvex thrust, attitude input constraints. Different from existing works, the proposed method is the first real-time TOTP solution for rotorcrafts subject to velocity constraints and these nonconvex input constraints. The key insight is to transform the thrust and attitude constraints into the inequality constraints on the quadratic nonlinear function of the path parameter acceleration and the squared velocity, by exploiting the differential flatness characteristic of the rotorcraft. As a result, the constraints can be formulated as the problem of jointly solving analytical quadratic inequalities. On this basis, a path acceleration calculation algorithm is proposed to obtain the backward and forward acceleration profiles. In addition, by formulating the well-known field of view (FOV) constraints into the attitude constraints, the proposed framework can further guarantee the FOV constraint for visual servoing of rotorcrafts. Comparative experimental results are presented to show the superior performance of the proposed approach when compared with the second-order cone programming approach. In addition, some visual servoing experiments are conducted to demonstrate the capability of the proposed method to guarantee the FOV constraint.