Pose-Following with Dual Quaternions

This work focuses on pose-following, a variant of path-following in which the goal is to steer the system's position and attitude along a path with a moving frame attached to it. Full body motion control, while accounting for the additional freedom to self-regulate the progress along the path, is an appealing trade-off. Towards this end, we extend the well-established dual quaternion-based pose-tracking method into a pose-following control law. Specifically, we derive the equations of motion for the full pose error between the geometric reference and the rigid body in the form of a dual quaternion and dual twist. Subsequently, we formulate an almost globally asymptotically stable control law. The global attractivity of the presented approach is validated in a spatial example, while its benefits over pose-tracking are showcased through a planar case-study.Comment: This paper has been accepted for publication at the IEEE Conference on Decision and Control (CDC), 2023. Copyright @ IEE

Real-Time Neural MPC: Deep Learning Model Predictive Control for Quadrotors and Agile Robotic Platforms

Model Predictive Control (MPC) has become a popular framework in embedded control for high-performance autonomous systems. However, to achieve good control performance using MPC, an accurate dynamics model is key. To maintain real-time operation, the dynamics models used on embedded systems have been limited to simple first-principle models, which substantially limits their representative power. In contrast to such simple models, machine learning approaches, specifically neural networks, have been shown to accurately model even complex dynamic effects, but their large computational complexity hindered combination with fast real-time iteration loops. With this work, we present Real-time Neural MPC , a framework to efficiently integrate large, complex neural network architectures as dynamics models within a model-predictive control pipeline. Our experiments, performed in simulation and the real world onboard a highly agile quadrotor platform, demonstrate the capabilities of the described system to run learned models with, previously infeasible, large modeling capacity using gradient-based online optimization MPC. Compared to prior implementations of neural networks in online optimization MPC we can leverage models of over 4000 times larger parametric capacity in a 50 Hz real-time window on an embedded platform. Further, we show the feasibility of our framework on real-world problems by reducing the positional tracking error by up to 82% when compared to state-of-the-art MPC approaches without neural network dynamics

An Open-Source Hardware/Software Architecture for Quadrotor UAVs

International audienceIn this paper, we illustrate an open-source ready-to-use hardware/software archi- tecture for a quadrotor UAV. The presented platform is price effective, highly customizable, and easily exploitable by other researchers involved in high-level UAV control tasks and for educational purposes as well. The use of object-oriented programming and full support of Robot Operating System (ROS) and Matlab Simulink allows for an efficient customization, code reuse, functionality expansion and rapid prototyping of new algorithms. We provide an extensive illustration of the various UAV components and a thorough description of the main basic algorithms and calibration procedures. Finally, we present some experimental case studies aimed at showing the effectiveness of the proposed architecture

Infections after kidney transplantation: A comparison of mTOR‐Is and CNIs as basic immunosuppressants. A systematic review and meta‐analysis

Background Side effects of the immunosuppressive therapy after solid organ transplantation are well known. Recently, significant benefits were shown for mTOR‐Is with respect to certain viral infections in comparison with CNIs. However, reported total incidences of infections under mTOR‐Is vs CNIs are usually not different. This raises the question to additional differences between these immunosuppressants regarding development and incidence of infections. Methods The current literature was searched for prospective randomized controlled trials in renal transplantation. There were 954 trials screened of which 19 could be included (9861 pts.). The 1‐year incidence of infections, patient and graft survival were assessed in meta‐analyses. Results Meta‐analysis on 1‐year incidence of infections showed a significant benefit of an mTOR‐I based therapy when combined with a CNI vs CNI‐based therapy alone (OR 0.76). There was no difference between mTOR‐I w/o CNI and CNI therapy (OR 0.97). For pneumonia, a significant disadvantage was seen only for mTOR‐I monotherapy compared to CNI's (OR 2.09). The incidence of CMV infections was significantly reduced under mTOR‐I therapy (combination with CNI: OR 0.30; mTOR w/o CNI: OR: 0.46). There was no significant difference between mTOR‐I and CNI therapy with respect to patient survival (mTOR‐I w/o CNI vs CNI: OR 1.22; mTOR‐I with CNI vs CNI: OR 0.86). Graft survival was negatively affected by mTOR‐I monotherapy (OR 1.52) but not when combined with a CNI (OR 0.97). Conclusion Following renal transplantation the incidence of infections is lower when mTOR‐Is are combined with a CNI compared to a standard CNI therapy. Pneumonia occurs more often under mTOR‐I w/o CNI

Proceedings of the Association for Research in Vision and Ophthalmology and Champalimaud Foundation Ocular Oncogenesis and Oncology Conference

Ophthalmic researc

Neue Ansätze zur Regelung überaktuierter, unbemannter Luftfahrzeuge

Standard quadrotor UAVs are inherently underactuated as they posses only four independent control inputs - their four propeller spinning velocities. Therefore they only possess a limited mobility in space for the six dofs parameterizing the quadrotor position/orientation. This implies that for standard quadrotors it is impossible to follow an arbitrarily designed trajectory. A standard quadrotor for example cannot translate position while remaining horizontal. The common use of UAVs and quadrotors in particular is changing from common observer tasks to more applied flying service robot tasks including interaction with the environment. Here the loss of mobility on the basis of the inherent underactuation can constitute a limiting factor. In this thesis we will present a novel quadrotor UAV design that surmounts these limitations by additional four control inputs actuating the four propeller tilting angles. First, we will show that our novel quadrotor UAV with tilting propellers offers behavior as a fully-actuated flying vehicle with full actuation of the quadrotor position and orientation in space. Second, a comprehensive modeling and control framework for the proposed quadrotor is presented, and the hardware/software specifications of an experimental prototype will be introduced. Finally, the results of several simulations and real experiments are reported to illustrate the capabilities of the proposed novel UAV design.Unbemannte Quadrocopter und ähnliche Luftfahrzeuge (z.B. Hubschrauber) haben eine eingeschränkte Manövrierbarkeit aufgrund ihres konzeptuell unteraktuierten Systems. Das heißt diese Luftfahrzeuge besitzen weniger Steuereingänge (im Falle von Quadrocoptern die vier Rotationsgeschwindigkeiten der Rotoren) als die sechs translatorischen und rotatorischen Freiheitsgrade eines Körpers im Raum. Daraus folgt das diese Luftfahrzeuge einer beliebigen Trajektorie im Raum nicht notwendigerweise folgen können. Beispielsweiße ist eine horizontale Translation ohne Rotation nicht möglich. Da unbemannte Luftfahrzeuge mehr und mehr als fliegende Serviceroboter, die auf ihre Umgebung einwirken, verwendet werden, ist dieser Mangel an Mobilität ein grundsätzlich limitierender Faktor. In dieser Doktorarbeit wird ein konstruktiv neuartiger Entwurf eines Luftfahrzeuges vorgestellt - der Holocopter. Beim Holocopter ist zusätzlich die Orientierung der Rotoren regelbar, hier durch ist die beschriebene Unteraktuierung nicht mehr gegeben. Das System ist nun überaktuiert, da den nun acht Steuereingängen sechs Freiheitsgrade gegenüberstehen. Die vier zusätzlichen Steuereingänge ermöglichen eine vollständige Steuerbarkeit der Position und Orientierung des Holocopters im Raum. Daher lässt sich der Holocopter als vollständig steuerbarer, fliegender Roboter verwenden. In dieser Arbeit wurde zunächst ausführlich das kinematische Modell des Holocopters hergeleitet und ein passender Regler basierend auf dynamischer, linearisierter Zustandsrückführung entworfen. Anschließend wurde ein Prototyp entworfen und gebaut und das nötige Software-Framework entwickelt. Zentraler Bestandteil der Arbeit sind ausführliche Simulationen und tatsächliche Tests mit den Prototypen. Abschließend bietet die Arbeit einen Ausblick auf Interaktionsszenarios des Holocopters mit der Umgebung

Fundamental Actuation Properties of Multi-rotors: Force-Moment Decoupling and Fail-safe Robustness

International audienceIn this paper we shed light on two fundamental actuation capabilities of multi-rotors. The first is the amount of coupling between the total force and total moment applied by the propellers to the whole body. The second is the ability to robustly fly completely still in place after the loss of one or more propellers, when the used propellers can only spin in one direction. These two actuation properties are formalized through the definition of some algebraic conditions on the control allocation matrices. The theory is valid for any multi-rotor, with arbitrary number, position and orientation of the propellers, including the more classic ones. As a show case for the general theory we show and explain why standard star-shaped hexarotors with collinear propellers are not able to robustly fly completely still at a constant spot using only five of their six propellers. To deeply understand this counterintuitive result, it is enough to apply our theory, which clarifies the role of the tilt angles and locations of the propellers in the vehicle. The theory is also able to explain why, on the contrary, both the tilted star-shaped hexarotor and the Y-shaped hexarotor can fly with only five out of six propellers. The analysis is validated with both simulations and experimental results testing the control of multi-rotor vehicles subject to rotor loss

Modeling and Control of FAST-Hex: a Fully-Actuated by Synchronized-Tilting Hexarotor

Accepted for the 2016 IEEE/RSJ International Conference on Intelligent Robots and Systems, Daejeon, South Korea, Oct. 2016International audienceWe present FAST-Hex, a novel UAV concept which is able to smoothly change its configuration from underactuated to fully actuated by using only one additional motor that tilts all propellers at the same time. FAST-Hex can adapt to the task at hand by finely tuning its configuration from the efficient (but underactuated) flight (typical of coplanar multi– rotor platforms) to the full-pose-tracking (but less efficient) flight, which is attainable by non-coplanar multi-rotors. We also introduce a novel full-pose geometric controller for generic multi-rotors (not only the FAST-Hex) that outperforms classical inverse dynamics approaches. The controller receives as input any reference pose in R 3 ×SO(3) (3D position + 3D orientation). Exact tracking is achieved if the reference pose is feasible with respect to the propeller spinning rate saturations. In case of unfeasibility a new feasible desired trajectory is generated online giving priority to the positional part. The new controller is tested with the FAST-Hex but can be used for many other multi-rotor platforms: underactuated, slightly fully-actuated and completely fully-actuated

Control of Statically Hoverable Multi-Rotor Aerial Vehicles and Application to Rotor-Failure Robustness for Hexarotors

International audienceStandard hexarotors are often mistakenly considered 'by definition' fail-safe multi-rotor platforms because of the two additional propellers when compared to quadrotors. However this is not true, in fact, a standard hexarotor cannot statically hover with 'only' five propellers. In this paper we provide a set of new general algebraic conditions to ensure static hover for any multi-rotor platform with any number of generically oriented rotors. These are elegantly formulated as the full-rankness of the control moment input matrix, and the non-orthogonality between its null-space and the row space of the control force input matrix. Input saturations and safety margins are also taken into account with an additional condition on the null-space of control moment input matrix. A deep analysis on the hoverability properties is then carried out focusing on the propeller loss in a hexarotor platform. Leveraging our general results we explain why a standard hexarotor is not robust and how it can be made robust thanks to a particular tilt of the rotors. We finally propose a novel cascaded controller based on a preferential direction in the null-space of the control moment input matrix for the large class of statically hoverable multi-rotors, which goes far beyond standard platforms, and we apply this controller to the case of failed tilted hexarotor