Roberto Naldi

Robust full degree-of-freedom tracking control of a helicopter

We consider the problem of controlling the vertical, lateral, longitudinal and yaw attitude motion of a helicopter along desired arbitrary trajectories with only restrictions on the time derivatives imposed by the functional controllability of the system. To this purpose we design a nonlinear controller, obtained by suitably combining feedforward control actions and high-gain and nested saturation feedback laws, which succeeds in enforcing the desired trajectories robustly with respect to uncertainties characterizing the physical and aerodynamical parameters of the helicopter. Experimental results are also given to show the effectiveness of the method to accomplish aggressive maneuvers.

Modeling and control of a flying robot for contact inspection

This paper focuses on the modeling and control of a flying robot. The complete system, composed of a quadrotor unmanned aerial vehicle and a custom-made manipulator, has been designed for remote inspection by contact of industrial plants. The goal of this paper is to show the dynamical characteristics of the flying robot during tasks that require physical interaction, and to determine a control strategy that allows to safely interact with unknown environments. The methodology has been implemented on a real prototype and tested in an indoor area. Experimental results validate the proposed controller and show its effectiveness.

Developing an aerial manipulator prototype: physical interaction with the environment

This article focuses on the design, modeling, and control of an aerial manipulator prototype, i.e., an innovative configuration consisting of a miniature quadrotor helicopter endowed with a robotic manipulator. The overall system is designed to accomplish operations that require physical interaction with the surrounding environment while remaining airborne. To investigate the dynamical model of the aerial manipulator, a simple planar benchmark is used to analyze the interactions between the quadrotor, the robotic manipulator, and the environment. A control strategy for the planar system is designed to guarantee robustness in the presence or absence of contacts. Experiments on a real setup validate the control in the two different scenarios in which the aerial manipulator is either freely flying or physically interacting with the environment.

Control of Aerial Robots: Hybrid Force and Position Feedback for a Ducted Fan

This article has dealt with the modeling and control of a class of aerial robots capable of interacting with the environment to accomplish robotic operations midair rather than being constrained to the ground. Discussed in detail are the design of hybrid force and position control laws for a ducted fan aeriaI vehicle. Particular attention has been placed on keeping track of how the stability properties of the systems zero dynamics are affected by the position of the vehicles center of gravity, which can be mechanically designed to infer desired stability properties. The described control laws are state feedback and rely upon partial feedback linearizing techniques. In this respect, future extensions concern the development of output feedback control strategies, whereby the nonminimum-phase behavior of the system imposes fundamental limitations to the achievable tracking performance regardless of the kind of control strategy adopted. The present article fits in a broader research context in which aerial vehicles are considered to he a support to human beings in all those activities that require the ability to interact safely with airborne environments. In this context, future research attempts are directed to develop teleoperation algorithms, according to which x human operator can remotely supervise the motion of the CAV by means of haptic devices. Experimental activities in the above interaction scenarios are also planned in the near future.

Impedance control of an aerial manipulator

This work focuses on the modeling and control of an innovative configuration of aerial robot arising from the combination of a vertical take-off and landing aircraft and a robotic arm. The overall system, denoted as aerial manipulator, is able to accomplish operations requiring the physical interaction with the surrounding environment while remaining airborne. After introducing a detailed dynamical model, a control law, based on the impedance control paradigm, able to govern all the degrees of freedom of the system is proposed. The effectiveness of the proposed control algorithm are investigated also considering the case in which contacts with the surrounding environment are achieved.

Aerial service robotics: The AIRobots perspective

This paper presents the main vision and research activities of the ongoing European project AIRobots (Innovative Aerial Service Robot for Remote Inspection by Contact, www.airobots.eu). The goal of AIRobots is to develop a new generation of aerial service robots capable of supporting human beings in all those activities that require the ability to interact actively and safely with environments not constrained on ground but, indeed, airborne. Besides presenting the main ideas and the research activities within the three-year project, the paper shows the first technological outcomes obtained during the first year and a half of activity.

Robust Take-Off for a Quadrotor Vehicle

This paper addresses the problem of robust take-off of a quadrotor unmanned aerial vehicle (UAV) in critical scenarios, such as in the presence of sloped terrains and surrounding obstacles. Throughout the maneuver, the vehicle is modeled as a hybrid automaton whose states reflect the different dynamic behaviors exhibited by the UAV. The original take-off problem is then addressed as the problem of tracking suitable reference signals in order to achieve the desired transitions between different hybrid states of the automaton. Reference trajectories and feedback control laws are derived to explicitly account for uncertainties in both the environment and the vehicle dynamics. Simulation results demonstrate the effectiveness of the proposed solution and highlight the advantages with respect to more standard open-loop strategies, especially for cases in which the slope of the terrain renders the take-off maneuver more critical to achieve.

Optimal transition maneuvers for a class of V/STOL aircraft

This paper focuses on the problem of computing optimal transition maneuvers for a particular class of tail-sitter aircraft able to switch their flight configuration from hover to level flight and vice versa. Both minimum-time and minimum-energy optimal transition problems are formulated and solved numerically in order to compute reference maneuvers to be employed by the onboard flight control system to change the current flight condition. In order to guide the numerical computation and to validate its results, in a first stage approximated solutions are obtained as a combination of a finite number of motion primitives corresponding to analytical trajectories of approximated dynamic models. The approximated solution is then employed to generate an initial guess for the numerical computation applied to a more accurate dynamic model. Numerical trajectories computed for a small scale prototype of tail-sitter aircraft are finally presented, showing the effectiveness of the proposed methodology to deal with the complex dynamics governing this kind of systems.

Taut Cable Control of a Tethered UAV

This paper focuses on the design of a stabilizing control law for an aerial vehicle which is physically connected to a ground station by means of a tether cable. When the cable is taut, the resulting dynamic model is shown to be characterized by a new set of equilibria which untethered aircraft are unable to maintain in steady state. The control objective is to steer the UAV to a desired set-point while maintaining the cable taut at all times. This leads to a nonlinear control problem subject to constraints. A cascade control scheme is proposed and proven to asymptotically stabilize the overall system by means of ISS arguments. Constraint satisfaction is guaranteed using a modified thrust vector control coupled with a reference governor strategy. The effectiveness of the proposed control strategy is shown via numerical simulations.

Modeling and control of VTOL UAVs interacting with the environment

In this paper we focus on the problem of modeling and controlling a certain configuration of UAV (Unmanned Aerial Vehicle) considering explicitly the interaction with the environment. This innovative problem is particularly interesting in order to employ unmanned aircrafts in tasks and operations which may require explicitly or implicitly contacts between the UAV itself and the environment such as manipulation of remote objects or indoor flight. For a class of VTOL (Vertical Take-Off and Landing) aircrafts we start studying the problem of safe take-off from hostile terrains and the control of the vehicle when in contact with vertical fixed surfaces.