Autonomous landing control of quadrotor UAVs

Autonomous landing, also called auto-landing, is one of the most specific features for miniature quadrotor UAVs (unmanned aerial vehicles). In this paper, an auto-landing control scheme is presented. It can be regarded as one-step-further development for our quadrotor UAV systems which are capable of auto altitude holding, auto position holding and point-to-point auto-navigation in outdoor environments. Using the state measurements from 9 DOF IMU (inertial measurement unit), sonar/barometer, accelerometer and GPS, a set of linear P+D+DD controller for attitude control and translation control have been implemented in a control system configuration including an outer positioning loop and an inner attitude loop. Based on the reliable position hold control, the auto-landing is realized by descending the target altitude gradually using the altitude, vertical velocity and vertical acceleration feedback. Given the control strategy, the effectiveness of the landing control algorithm is validated by successful experimental outcomes.