In this paper, we propose a new concept of robot which is hybrid, including aerial and crawling subsystems and an arm, and also modular with interchangeable crawling subsystems for different pipe configurations, since it has been designed to cover most industrial oil & gas end-users' requirements. The robot has the same ability than aerial robots to reach otherwise inaccessible locations, but makes the inspection more efficient, increasing operation time since crawling requires less energy than flying, and achieving better accuracy in the inspection. It also integrates safety-related characteristics for operating in the potentially explosive atmosphere of a refinery, being able to immediately interrupt the inspection if a hazardous situation is detected and carry the sensible parts such as batteries and electronic devices away as soon as possible. The paper presents the design of this platform in detail and shows the feasibility of the whole system performing indoor experiments.

The paper presents a multiple task-priority inverse kinematics algorithm for a dual-arm aerial manipulator. Both tasks defined as equality constraints and inequality constraints are handled by means of a singularity robust method based on the Null-Space based Behavioral control. The proposed schema is constituted by the inverse kinematics control, that receives the desired behavior of the system and outputs the reference values for the motion variables, i.e. the UAV pose and the arm joints position, and a motion control, that computes the vehicle thrusts and the joint torques. The method has been experimentally validated on a system composed by an underactuated aerial hexarotor vehicle equipped with two lightweight 4-DOF manipulators, involved in operations requiring the coordination of the two arms and the vehicle.

Winged aerial robots represent an evolution of aerial manipulation robots, replacing the multirotor vehicles by fixed or flapping wing platforms. The development of this morphology is motivated in terms of efficiency, endurance and safety in some inspection operations where multirotor platforms may not be suitable. This paper presents a first prototype of compliant dual arm as preliminary step towards the realization of a winged aerial robot capable of perching and manipulating with the wings folded. The dual arm provides 6 DOF (degrees of freedom) for end effector positioning in a human-like kinematic configuration, with a reach of 25 cm (half-scale w.r.t. the human arm), and 0.2 kg weight. The prototype is built with micro metal gear motors, measuring the joint angles and the deflection with small potentiometers. The paper covers the design, electronics, modeling and control of the arms. Experimental results in test-bench validate the developed prototype and its functionalities, including joint position and torque control, bimanual grasping, the dynamic equilibrium with the tail, and the generation of 3D maps with laser sensors attached at the arms.

The proximity between the multirotor blades and the environmental obstacles restricts the application of aerial manipulators in inspection tasks due to the risk of impacts, the limitation in the reach of the arm, and the physical interactions. This paper presents a long reach aerial manipulator consisting of a hexarotor platform equipped with a 2-DOF compliant joint arm attached at the tip of a one-meter-length link in passive pendulum configuration. The arm integrates magnetic encoders for force/torque estimation-control based on joint deflection, a range sensor in the forearm link for measuring the distance to the contact point, and a camera for visual inspection. A 2-DOF wearable exoskeleton interface has been developed, allowing the teleoperation of the arm with visual feedback in a more intuitive way. The paper also covers the kinematics and dynamics of the aerial manipulator, including the dynamics of the flexible long reach link. The developed system has been evaluated in test-bench and in outdoor flight tests.

This paper presents a low weight (1.3 kg), human size dual arm system with compliant joints designed for aerial manipulation with a multirotor platform. Each arm provides four degrees of freedom (DOF) for end effector positioning in a kinematic configuration close to the human arm: shoulder pitch, roll and yaw, and elbow pitch. The aluminum frame structure of the arms has been designed with a double purpose: protecting the servo actuators against direct impacts and overloads, and allowing the integration of a compliant transmission mechanism with deflection measurement between the servo shaft and the output link Mechanical joint compliance increases safety in the physical interactions with the environment, removing also joint overloads typical in closed kinematic chain configurations. The dual arm system has been integrated in a hexarotor platform with a visual servoing system for object grasping, evaluating its performance first in a fixed base test bench and later in outdoor flight tests.

This paper presents the design and experimental validation of a Fault Detection, Identification and Recovery (FDIR) system intended for multi-UAV applications. The system exploits the information provided by internal position, attitude and visual sensors onboard the UAVs of the fleet for detecting faults in the measurements of the position and attitude sensors of any of the member vehicles. Considering the observations provided by two or more UAVs in a cooperative way, it is possible to identify the source of the fault, but also implement a Cooperative Virtual Sensor (CVS) which provides a redundant position and velocity estimation of the faulty UAV that can be used for replacing its internal sensor. The vision-based FDIR system has been validated experimentally with quadrotors in an indoor testbed. In particular, fault detection and identification has been evaluated injecting a fault pattern offline on the position measurements, while the CVS has been applied in real time for the recovery phase.

This paper presents the design and experimental validation of a compliant and lightweight 3-DOF robotic arm - shoulder yaw, shoulder pitch and elbow pitch joints - equipped with a compliant finger module intended for aerial inspection and manipulation in contact with the environment. A simple transmission mechanism consisting in a pair of compression springs and a flange bearing is integrated in the shoulder pitch and elbow pitch joints between the servo shaft and the output frame. Joint deflection measurement with potentiometer allows joint torque but also contact force estimation and control. The low stiffness of the compliant finger has been exploited for soft collision detection and obstacle localization, in such a way that the contact forces do not significantly disturb the UAV. Fixed-base experiments have been performed with the arm, including the characterization of the compliant joints and the control of the contact force at wrist point.

This paper proposes a method called Segmentation-adaptive Pseudospectral collocation to address the problem of safe trajectory generation in missions with cooperating multiple aerial vehicles. Pseudospectral collocation can generate optimized collision-free trajectories, but for multiple aerial vehicles it cannot guarantee that the safety separation distance is maintained in the whole trajectories, since the constraints are only enforced in discrete points in the trajectory (collocation points). Hp-adaptive pseudospectral collocation increases iteratively the number of collocation points and the degree of the approximating polynomial, but this may lead to an exponential increase of the computational load. The proposed method solves the problem by selectively adding new collocation points where they are needed, only in the segments with conflicts in each iteration, thus effectively reducing the number of collocation points and the computation time with respect to other pseudospectral collocation formulations. The proposed method allows both changes of speed and changes of heading for each aerial vehicle to guarantee the safety distance between them. Its computational load and scalability are studied in randomly generated scenarios. Moreover, a comparison with other method is presented. Several experiments to test the validity of the approach have been also carried out in the multivehicle aerial testbed of the Center for Advanced Aerospace Technologies.

This paper presents an aerial manipulator consisting of a multirotor equipped with a robotic multi-link arm attached to the top of the multirotor body. This setup has strong potentialities for inspection of structures, since the arm is able to safely touching the structure surface with a sensor while flying, taking measurements from the underside for example in bridges. The paper presents the dynamic model of the system and the derivation of a nonlinear controller, which is tested in simulation. First flight experiments with prototype of the system are also presented.

This paper presents the design and experimental validation of a low weight compliant arm for aerial manipulation, which uses a linear actuator to move the elbow joint. The proposed arm design allows for estimating payload mass, as well as detecting collisions against obstacles in the forearm. The compliant arm design is intended to be applied in aerial manipulation and transportation, being mounted on the base of an Unmanned Aerial Vehicle (UAV) like a multirotor or a small autonomous helicopter. The payload mass estimation can be useful in the adaptation and stabilization of UAV altitude and attitude controllers when objects of unknown weight are grasped by the arm, while compliance reduces the effect of physical interaction when lifting an object on UAV stability. The paper addresses the mechanical design and construction of a three DoF arm prototype (elbow, wrist roll and pitch), deriving the equations for estimating the payload mass. A set of experiments for payload mass estimation and collision detection and reaction have been performed to test the validity of the approach.

This paper proposes the application of an hp-adaptive pseudospectral for trajectory generation in scenarios with multiple aerial vehicles in order to avoid collisions. This method computes an optimal solution numerically. The method assigns a speed profile to each aerial vehicle in real time such that the separation between them is greater than a minimum safety value and the total deviation from the initial trajectories is minimized. The Estimated Time of Arrival (ETA) of each aerial vehicle is also taken into account to solve the conflicts. Its computational load and scalability depending on the main parameters of the method are studied. Many simulations have been performed to analyze the best parameters of the method. Experiments have been also carried out in the multivehicle aerial testbed of the Center for Advanced Aerospace Technologies (CATEC).

This paper presents the design and control of a multirotor-based aerial manipulator developed for outdoor operation. The multi-rotor has eight rotors and large payload to integrate a 7-degrees of freedom arm and to carry sensors and processing hardware needed for outdoor positioning. The arm can also carry an end-effector and sensors to perform different missions. The paper focuses on the control design and implementation aspects. A stable backstepping-based controller for the multirotor that uses the coupled full dynamic model is proposed, and an admittance controller for the manipulator arm is outlined. Several experimental tests with the aerial manipulator are also presented. In one of the experiments, the performance of the pitch attitude controller is compared to a PID controller. Other experiments of the arm controller following an object with the camera are also presented.

This paper addresses the problem of extending the flight duration of cooperative missions with multiple gliding fixed-wing UAVs by using the energy that comes from static soaring. We consider exploration missions where UAVs should pass through a set of Point of Interest (PoI) with the presence of thermals in the space. These thermals can be exploited to provide energy in terms of altitude for each gliding UAV. The objective of the mission is to extend the flight duration of each UAV to explore the environment without landing and decreasing the time to perform the mission. An algorithm named Bounded Recursive Heuristic Search (BRHS), based on Depth-First search techniques, is applied to the PoIs and to the UAVs. The main advantage is the real time application because of the low computational load. The paper presents a set of simulations and experiments have carried out in the airfield of La Cartuja (Seville, Spain).

This paper deals with aerial manipulators consisting of an unmanned aerial vehicle equipped with a robotic multi-link arm. The paper presents methods for the control of the aerial platform taking into account the motion of the arm. It shows how a Variable Parameter Integral Backstepping controller outperforms the results obtained by using PID controllers. The paper presents a quadrotor with a new arm designed for assembly tasks and the implementation of the proposed control methods. Simulations and outdoor experiments confirm the validity of the proposed approach.

This paper presents a cooperative system architecture that extends the flight duration of multiple gliding fixed-wing Unmanned Aerial Vehicles (UAVs) for long endurance missions. The missions are defined by a set of Points of Interest (PoI) and UAVs should pass through them. A module to detect and identify thermals is implemented to exploit their energy and extend the flight duration, known as static soaring. A collision-free trajectory planner based on the RRT∗ (Optimal Rapidly-exploring Random Trees) planning algorithm is implemented. The proposed system allows applications in real time because of its low computational needs. Simulations and experiments carried out in the airfield of La Cartuja (Seville, Spain) show the performance and advantages of the proposed system.

This paper presents a sensor fault detection and diagnosis system for autonomous helicopters. The system has been tested with the MARVIN autonomous helicopter. Fault detection is accomplished by evaluating any significant change in the behaviour of the vehicle with respect to the fault-free behaviour, which is estimated by using an observer. The effectiveness of the proposed approach is demonstrated by means of MARVIN experimental results.

This paper presents a new approach that analyzes the stability of a general class of path tracking algorithms taking into account the pure delay in the control loop. The analysis has been done for straight paths and paths of constant curvature. This has sufficient generality since most usual paths can be decomposed in pieces of constant curvature. The method has been applied to the pure pursuit path tracking algorithm, one of the most widely used algorithms. The experiments performed with a computer controlled high mobility multi-purpose wheeled vehicle show good agreement with the theoretical predictions of the proposed method.