No abstract

No abstract

To facilitate accurate tracking in unknown/uncertain environments, this paper proposes a simple learning (SL) strategy for feedback linearization control (FLC) of aerial robots subject to uncertainties. The SL strategy minimizes a cost function defined based on the closed-loop error dynamics of the nominal system via the gradient descent technique to find the adaptation rules for feedback controller gains and disturbance estimate in the feedback control law. In addition to the derivation of the SL adaptation rules, the closedloop stability for a second-order uncertain nonlinear system is proven in this paper. Moreover, it is shown that the SL strategy can find the global optimum point, while the controller gains and disturbance estimate converge to a finite value which implies a bounded control action in the steady-state. Furthermore, utilizing a simulation study, it is shown that the simple learning-based FLC (SL-FLC) framework can ensure desired closed-loop error dynamics in the presence of disturbances and modeling uncertainties. Finally, to validate the SL-FLC framework in real-time, the trajectory tracking problem of a tilt-rotor tricopter unmanned aerial vehicle under uncertain conditions is studied via three case scenarios, wherein the disturbances in the form of mass variation, ground effect, and wind gust, are induced. The real-time results illustrate that the SL-FLC framework facilitates a better tracking performance than that of the traditional FLC method while maintaining the nominal control performance in the absence of modeling uncertainties and external disturbances, and exhibiting robust control performance in the presence of modeling uncertainties and external disturbances. INDEX TERMS Feedback linearization control, nonlinear system, uncertain systems, learning control, unmanned aerial vehicle.

Aerial cinematography is revolutionizing industries that require live and dynamic camera viewpoints such as entertainment, sports, and security. However, safely piloting a drone while filming a moving target in the presence of obstacles is immensely taxing, often requiring multiple expert human operators. Hence, there is a demand for an autonomous cinematographer that can reason about both geometry and scene context in real-time. Existing approaches do not address all aspects of this problem; they either require high-precision motion-capture systems or global positioning system tags to localize targets, rely on prior maps of the environment, plan for short time horizons, or only follow fixed artistic guidelines specified before the flight. In this study, we address the problem in its entirety and propose a complete system for real-time aerial cinematography that for the first time combines: (a) vision-based target estimation; (b) 3D signed-distance mapping for occlusion estimation; (c) efficient trajectory optimization for long time-horizon camera motion; and (d) learning-based artistic shot selection.We extensively evaluate our system both in simulation and in field experiments by filming dynamic targets moving through unstructured environments. Our results indicate that our system can operate reliably in the real world without restrictive assumptions. We also provide in-depth analysis and discussions for each module, with the hope that our design tradeoffs can generalize to other related applications. Videos of the complete system can be found at https://youtu.be/ookhHnqmlaU. K E Y W O R D S aerial robotics, cinematography, computer vision, learning, mapping, motion planning Within the filming context, this cost function measures jerkiness of motion, safety, environmental occlusion of the actor, and shot quality (artistic quality of viewpoints). This cost function depends on the environment and , and on the actor forecast ξ a , all of which are sensed on-the-fly. The changing nature of the environment and ξ a demands replanning at a high frequency. Here we briefly touch upon the four components of the cost function J(ξ q ) (refer to Section 7 for details and mathematical expressions): Smoothness J smooth (ξ q ): Penalizes jerky motions that may lead to camera blur and unstable flight; Safety J obs (ξ q , ): Penalizes proximity to obstacles that are unsafe for the UAV; Occlusion J occ (ξ q , ξ a , ): Penalizes occlusion of the actor by obstacles in the environment; Shot quality J shot (ξ q , ξ a , Ω art ): Penalizes poor viewpoint angles and scales that deviate from the desired artistic guidelines, given by the set of parameters Ω art . In its simplest form, we can express J(ξ q ) as a linear composition of each individual cost, weighted by scalars λ i . The objective is to * = ( ) ()={ } J J J J J J xyz J J J J J J x y z J occ + J obs 99.4 ± 2.2 94.2 ± 7.3 86.9 ± 9.3 J obs 98.8 ± 3.0 87.1 ± 8.5 75.3 ± 11.8 Avg. dist. to ξ shot (m) J occ + J obs 0.4 ± 0.4 6.2 ± 11.2 10.7 ± 13.2 J obs 0.05 ± 0.1 0.3 ± 0.2 0.5 ± 0...

No abstract