Aerial Robotic Manipulation by Anibal Ollero & Bruno Siciliano

Author:Anibal Ollero & Bruno Siciliano
Language: eng
Format: epub
ISBN: 9783030129453
Publisher: Springer International Publishing

4.2 Real AROMA Experiments

To address the dynamical effects of the overall system our cascaded architecture considers two different control loops at very high frequency (1 KHz), one for the arm and one for the attitude of the UAV; and a hierarchical task controller running at much lower frequency (camera frame rate), hence avoiding dynamic coupling between them. Moreover, we impose bounds on the maximum velocities and accelerations for the arm joints that in practice result also in small torques in the arm base, which the task controller is able to adequately compensate. Furthermore, instead of developing a robust 3D feature detector and tracker, we use a planar detector of a target with a known geometry to retrieve the target frame, to which we add virtual features and then compute their location with respect to the target frame, as well as their basis, i.e., the control points. At each iteration, the marker is detected in the scene and the projection of the control points is computed. Those 2D–3D feature relationships represent the input to our visual servoing algorithm.

We conducted a series of experiments with missions consisting on autonomously taking off and flying to a location in which the target appears in the field of view of the camera, turning on then the hierarchical task controller to servo the system towards a desired camera pose, and finally autonomously landing the system. The real experiments were conducted with our robot Kinton (Fig. 2), based on an Asctec Pelican quadrotor, and equipped with an onboard embedded PC (1.6 GHz CPU) and a variety of sensors including an IMU and a barometer. All our algorithms are running onboard in real time with a camera frame rate at 20 Hz.

Fig. 4Camera pose error during visual servoing. Comparison of using or not the hierarchical task priority control law with all the subtasks proposed

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