Shape Visual Servoing of a Cable Suspended Between Two Drones

In this letter, we propose a shape visual servoing approach for manipulating a suspended cable attached between two quadrotor drones. A leader-follower control strategy is presented, where a human operator controls the rigid motion of the cable by teleoperating one drone (the leader), while the second drone (the follower) performs a shape visual servoing task to autonomously apply a desired deformation to the cable. The proposed shape visual servoing approach uses an RGB-D camera embedded on the follower drone and has the advantage to rely on a simple geometrical model of the cable that only requires the knowledge of its length. In the same time, our control strategy maintains the best visibility of the cable in the camera field of view. A robust image processing pipeline allows detecting and tracking in real-time the cable shape from the data provided by the onboard RGB-D camera. Experimental results demonstrate the effectiveness of the proposed visual control approach to shape a flexible cable into a desired shape. In addition, we demonstrate experimentally that such system can be used to perform an aerial transport task by grasping with the cable an object fitted with a hook, then moving and releasing it at another location.