System Identification and Parameter Space Control Design for a Small Unmanned Aircraft

Initial tests in cooperative control for autonomous landings of an Unmanned Aerial Vehicle (UAV) on a moving car have presented promising results. However, the identification of a high-fidelity simulation model is a step of great importance towards the development of more effective model predictive control strategies, which rely on precise models to allow cooperative control of High Altitude, Long Endurance (HALE) UAVs with autonomous ground vehicles. In this context, this work aims to develop a reliable model for the Penguin BE aircraft used in cooperative landing tests at the German Aerospace Center (DLR), and to design a high-performance pitch attitude controller applying the parameter space approach. The system identification procedure has been carried out by applying both, the Output Error and the Two Step methods, and a linear longitudinal model of the aircraft has been developed. Parameter Space Control has been applied to the identified model in order to suggest a set of alternative gains to the ones that are currently in use, which have been fine-tuned in flight, using the Ziegler-Nichols method, which will not be viable in the scope of stratospheric missions

High-Fidelity Modeling and Control Design for a Cooperative High Altitude Long Endurance Aircraft Landing System

High Altitude Long Endurance (HALE) aircraft can take flight to altitudes as high as 20 km and can stay there for long periods of time. In this article, the viability of landing such an aircraft on a mobile platform using a cooperative control strategy for motion synchronization is examined. Time domain system identification is applied to create a model of the Elektra 2 Solar HALE aircraft, which was found to be high fidelity by the Federal Aviation Administration (FAA) standards. An analysis is made to evaluate the feasibility of autonomously landing the HALE Unmanned Aerial Vehicle (UAV) on top of a ground vehicle with a roof-mounted landing platform. Controller synthesis is done for the individual vehicles as well as the cooperative landing control, leading to an examination of the overall system stability and performance, using both deterministic and stochastic methods

Hierarchical Control of Redundant Aerial Manipulators with Enhanced Field of View

Providing the operator with a good view of the remote site is of paramount importance in aerial telemanipulation. In light of that, this paper proposes the application of a hierarchical control framework in order to tackle the problem of adjusting the field of view of an on-board camera as a secondary task. The proposed approach ensures that the flying base, and consequently the camera, can be steered in order to provide a distant operator with a desired field of view without disturbing the end-effector pose. The approach is focused on aerial manipulators with torque-controlled arms, like the DLR Suspended Aerial Manipulator (SAM), while allowing the base to be directly torque-controlled or, alternatively, through an inner-loop velocity controller. Quantitative, qualitative, and real-scenario experimental validation is carried out using the SAM and confirms the need for such an approach and its efficacy in achieving decoupled field-of-view control

Whole-Body Teleoperation and Shared Control of Redundant Robots with Applications to Aerial Manipulation

This paper introduces a passivity-based control framework for multi-task time-delayed bilateral teleoperation and shared control of kinematically-redundant robots. The proposed method can be seen as extension of state-of-the art hierarchical whole-body control as it allows for some of the tasks to be commanded by a remotely-located human operator through a haptic device while the others are autonomously performed. The operator is able to switch among tasks at any time without compromising the stability of the system. To enforce the passivity of the communication channel as well as to dissipate the energy generated by the null-space projectors used to enforce the hierarchy among the tasks, the Time-Domain Passivity Approach (TDPA) is applied. The efficacy of the approach is demonstrated through its application to the DLR Suspended Aerial Manipulator (SAM) in a real telemanipulation scenario with variable time delay, jitter, and package loss

Energy-Based Cooperative Control for Landing Fixed-Wing UAVs on Mobile Platforms Under Communication Delays

The landing of a fixed-wing UAV on top of a mobile landing platform requires a cooperative control strategy, which is based on relative motion estimates. These estimates typically suffer from communication or processing time delays, which can render an otherwise stable control system unstable. Such effects must therefore be considered during the design process of the cooperative landing controller. In this paper the application of a model-free passivity-based stabilizing controller is proposed, which is based on the monitoring of energy flows in the system, and actively dissipating any given active energy by means of adaptive damping elements. In doing so, overall system passivity and consequently stability is enforced in a straightforward and easy to implement way. The proposed control system is validated in numerical simulations for round trip delays of up to 4 seconds