Snake Aerial Manipulators: A Review <s>  <s> In this work we consider the modelling of a modular aerial robot obtained by rigidly interconnecting a certain number of ducted-fan aircraft. It is shown how different geometric configurations lead to different dynamical properties of the overall system which can be exploited to improve the achievable closed-loop performances in certain scenarios. Suitable constrained control allocation problems are formulated to show how the modular system performs in presence of possible extra payload and of force and torque disturbances that may derive from the physical interaction with the surrounding environment. <s> BIB001 </s> Snake Aerial Manipulators: A Review <s>  <s> Given significant mobility advantages, UAVs have access to many locations that would be impossible for an unmanned ground vehicle to reach, but UAV research has historically focused on avoiding interactions with the environment. Recent advances in UAV size to payload and manipulator weight to payload ratios suggest the possibility of integration in the near future, opening the door to UAVs that can interact with their environment by manipulating objects. Therefore, we seek to investigate and develop the tools that will be necessary to perform manipulation tasks when this becomes a reality. We present our progress and results toward a design and physical system to emulate mobile manipulation by an unmanned aerial vehicle with dexterous arms and end effectors. To emulate the UAV, we utilize a six degree-of-freedom miniature gantry crane that provides the complete range of motion of a rotorcraft as well as ground truth information without the risk associated with free flight. Two four degree-of-freedom manipulators attached to the gantry system perform grasping tasks. Computer vision techniques and force feedback servoing provide target object and manipulator position feedback to the control hardware. To test and simulate our system, we leverage the OpenRAVE virtual environment and ROS software architecture. Because rotorcraft are inherently unstable, introduce ground effects, and experience changing flight dynamics under external loads, we seek to address the difficult task of maintaining a stable UAV platform while interacting with objects using multiple, dexterous arms. As a first step toward that goal, this paper describes the design of a system to emulate a flying, dexterous mobile manipulator. <s> BIB002 </s> Snake Aerial Manipulators: A Review <s>  <s> In the past few decades, unmanned aerial vehicles (UAVs) have become promising mobile platforms capable of navigating semiautonomously or autonomously in uncertain environments. The level of autonomy and the flexible technology of these flying robots have rapidly evolved, making it possible to coordinate teams of UAVs in a wide spectrum of tasks. These applications include search and rescue missions; disaster relief operations, such as forest fires [1]; and environmental monitoring and surveillance. In some of these tasks, UAVs work in coordination with other robots, as in robot-assisted inspection at sea [2]. Recently, radio-controlled UAVs carrying radiation sensors and video cameras were used to monitor, diagnose, and evaluate the situation at Japans Fukushima Daiichi nuclear plant facility [3]. <s> BIB003 </s> Snake Aerial Manipulators: A Review <s>  <s> Robustness and flexibility constitute the main advantages of multiple-robot systems with respect to single-robot ones as per the recent literature. The use of multiple unmanned aerial vehicles (UAVs) combines these benefits with the agility and pervasiveness of aerial platforms [1], [2]. The degree of autonomy of the multi-UAV system should be tuned according to the specificities of the situation under consideration. For regular missions, fully autonomous UAV systems are often appropriate, but, in general, the use of semiautonomous groups of UAVs, supervised or partially controlled by one or more human operators, is the only viable solution to deal with the complexity and unpredictability of real-world scenarios as in, e.g., the case of search and rescue missions or exploration of large/cluttered environments [3]. In addition, the human presence is also mandatory for taking the responsibility of critical decisions in high-risk situations [4]. <s> BIB004 </s> Snake Aerial Manipulators: A Review <s>  <s> In this paper a novel hierarchical motion control scheme for quadrotor aerial vehicles equipped with a manipulator is proposed. The controller is organized into two layers: in the top layer, an inverse kinematics algorithm computes the motion references for the actuated variables; in the bottom layer, a motion control algorithm is in charge of tracking the motion references computed by the top layer. A simulation case study is developed to demonstrate the effectiveness of the approach in the presence of disturbances and unmodeled dynamics. <s> BIB005 </s> Snake Aerial Manipulators: A Review <s>  <s> The paper presents results on the modeling and control of a multi-body air vehicle concept that incorporates a robotic arm to a miniatute rotorcraft robot. One of our goals was to obtain a detailed model in order to identify and qualify inherent constraints provided by the interaction of both mechanical subsystems.To do this, we used the Euler-Lagrange formulation. The knowledge of the model of the interactive aerial robot allowed us to propose a hierarchical control scheme, where a nonlinear Sliding Mode Controller (SMC) handle the translational motion while the rotational motion is addressed by a H∞-based controller. Numerical simulations were carried out to validate the overal control approach. <s> BIB006 </s> Snake Aerial Manipulators: A Review <s>  <s> Compared to autonomous ground vehicles, UAVs (unmanned aerial vehicles) have significant mobility advantages and the potential to operate in otherwise unreachable locations. Micro UAVs still suffer from one major drawback: they do not have the necessary payload capabilities to support high performance arms. This paper, however, investigates the key challenges in controlling a mobile manipulating UAV using a commercially available aircraft and a light-weight prototype 3-arm manipulator. Because of the overall instability of rotorcraft, we use a motion capture system to build an efficient autopilot. Our results indicate that we can accurately model and control our prototype system given significant disturbances when both moving the manipulators and interacting with the ground. <s> BIB007 </s> Snake Aerial Manipulators: A Review <s>  <s> Micro Unmanned Aerial Vehicles (MAVs) have been used in a wide range of applications [1, 2, 3]. However, there are few papers addressing high-speed grasping and transportation of pay-loads using MAVs. Drawing inspiration from aerial hunting by birds of prey, we design and equip a quadrotor MAV with an actuated appendage enabling grasping and object retrieval at high speeds. We develop a nonlinear dynamic model of the system, demonstrate that the system is differentially flat, plan dynamic trajectories using the flatness property, and present experimental results with pick-up velocities at 2 m/s (6 body lengths / second) and 3 m/s (9 body lengths / second). Finally, the experimental results are compared with observations derived from video footage of a bald eagle swooping down and snatching a fish out of water.Copyright © 2013 by ASME <s> BIB008 </s> Snake Aerial Manipulators: A Review <s>  <s> In this paper, a multiple UAVs control scheme is developed considering the full nonlinear position/orientation model of a j-Quadrotor system. A novel second order sliding mode controller is presented which guarantees exponential and robust tracking of admissible time-varying pose. The harmful chattering is not involved and no dynamic model is required to implement the controller to yield fast and precise tracking. Additionally, well-posed terminal and controlled time convergence allows an enforced contact at given pre-defined stable contact points at the same time. A stiffness control is proposed for grasping objects considering virtual linkages approach. Our approach yields high performance from the control system, in contrast to other simple controllers proposed for load carrying. In this sense, our advanced nonlinear control solves the apparent limitations imposed by the available technology from the viewpoint of the precise tracking control, and control of the inherent unstable underactuated dynamics, for frictionless contact points (neither rolling nor sliding are considered). A numerical simulation study, under various conditions, shows the numerical feasibility of the proposed approach. <s> BIB009 </s> Snake Aerial Manipulators: A Review <s>  <s> This paper introduces a method for carrying a flexible payload with multiple attached flying vehicles. A model for a particular class of flexible structures is presented, and an estimator is derived that observes the pose of the structure in space as well as the magnitude of some characteristic deformation modes. A control strategy that controls the flexible payload to a desired pose while also controlling the deformations to zero is introduced. The presented methods are validated in the ETH Zurich Flying Machine Arena by flying with a thin, flexible ring that is carried by six quadrocopters. <s> BIB010 </s> Snake Aerial Manipulators: A Review <s>  <s> We address the problem of cooperative transportation of a cable-suspended payload by multiple quadrotors. In previous work, quasi-static models have been used to study this problem. However, these approaches are severely limited because they ignore the payload dynamics, and do not explicitly model the underactuation in the control problem. Thus, there are no guarantees on the payload trajectory or the cable tensions, which must be non negative. In this paper, we develop a complete dynamic model for the case when payload is a point load and for the case when the payload is a rigid body. We show in both cases the resulting system is differentially flat when the cable tensions are strictly positive. We also consider the case where the tensions are non negative (including the case with zero tensions) and establish that these systems are differentially flat hybrid systems by considering the switching dynamics induced by the unilateral tension constraints. We use the differential flatness property to find dynamically feasible trajectories for the payload+quadrotors system. We show using numerical and experimental methods that these trajectories are superior to those obtained by quasi-static models. <s> BIB011 </s> Snake Aerial Manipulators: A Review <s>  <s> This paper is devoted to a system for aerial ::: manipulation, composed of a helicopter and an industrial manipulator. The usage of an industrial manipulator is motivated by practical applications which were identified in different cooperation projects with the industry. We address the coupling between manipulator and helicopter and show that even in case when we have an ideal controller for manipulator and a highperformance controller for helicopter, an unbounded energy flow can be generated by internal forces between helicopter and manipulator if both controllers are used independently. To solve this problem we propose a new kinematical coupling for control by introducing an additional manipulation DoF realized by helicopter rotation around its yaw axis. The new experimental setup and required modifications in the manipulator controller for this purpose are described. Further, we propose dynamical coupling which is implemented by modification of the helicopter controller feeding the interaction force/torque, measured between ::: manipulator base and fuselage, directly to the actuators ::: of the rotor blades. At the end, we present experimental results for aerial manipulation and their analysis <s> BIB012 </s> Snake Aerial Manipulators: A Review <s>  <s> We address the problem of cooperative transportation of a cable-suspended rigid-body payload by multiple quadrotors. We develop a coordinate-free dynamical model of the system by developing equations of motions directly on the unit sphere and the special orthogonal group. This model is used to design a geometric feedback control to track a reference trajectory for the load's pose (position and orientation), as well as the yaw angle of each quadrotor, and the orientation of each cable. Simulation results and formal proofs of the controller are presented to demonstrate the stability properties of the controller. <s> BIB013 </s> Snake Aerial Manipulators: A Review <s>  <s> In this paper, an impedance control scheme for cooperative quadrotors with robotic arms is proposed in order to limit both the contact forces, due to the object/environment interaction, and the internal forces, due to the manipulators/ object interaction. To this aim, two impedance filters are used to determine the reference trajectories for manipulator end effectors: the first is aimed at conferring a compliant behavior at the object level (external impedance), while the second filter, is aimed at avoiding large internal loading of the object (internal impedance). Such trajectories are fed to a motion controller including an inverse kinematics algorithm and a PD controller with gravity compensation. The effectiveness of the proposed approach is then verified in simulation. <s> BIB014 </s> Snake Aerial Manipulators: A Review <s>  <s> We propose an hierarchical control framework for multiple cooperative quadrotor-manipulator systems, which allows us to endow the common grasped object with a user-specified desired behavior (e.g., trajectory tracking, compliant interaction, etc.). To achieve this, our control framework consists of the following hierarchical layers: 1) object desired behavior design; 2) optimal cooperative force distribution; and 3) individual quadrotor-manipulator control based on object stiffness model, which can also take into account different dynamics characteristics of the (slower/coarse) quadrotor-platform and the (faster/fine) manipulator. Simulations of object transport and compliant interaction with three quadrotor-manipulator systems are performed to illustrate the theory. <s> BIB015 </s> Snake Aerial Manipulators: A Review <s>  <s> The design, modeling, and control of a new class of modular aerial robots, obtained by rigidly interconnecting a number of ducted-fan aircraft, are presented in this paper. A remarkable feature of the proposed class of vehicles is the fact that different dynamical behaviors, ranging from underactuated to fully actuated, can be obtained by adopting a suitable interconnection topology. To exploit this variety of actuation scenarios, a combination of control allocation and feedback control algorithms is proposed. The control allocation module exploits actuator redundancy by identifying the directions in the input space that affect the vehicle dynamics, whereas the feedback controller provides stabilization of the actuated degrees of freedom over desired attitude and position trajectories. A physical prototype, realized by interconnecting two ducted-fan vehicles, is employed to experimentally demonstrate the effectiveness of the proposed methodology. <s> BIB016 </s> Snake Aerial Manipulators: A Review <s>  <s> This paper presents the full dynamics and control of arbitrary number of quadrotor unmanned aerial vehicles (UAV) transporting a rigid body. The rigid body is connected to the quadrotors via flexible cables where each flexible cable is modeled as a system of arbitrary number of serially connected links. It is shown that a coordinate-free form of equations of motion can be derived for the complete model without any simplicity assumptions that commonly appear in other literature, according to Lagrangian mechanics on a manifold. A geometric nonlinear controller is presented to transport the rigid body to a fixed desired position while aligning all of the links along the vertical direction. A rigorous mathematical stability proof is given and the desirable features of the proposed controller are illustrated by numerical examples and experimental results. <s> BIB017 </s> Snake Aerial Manipulators: A Review <s>  <s> This paper presents a framework for human-in-the-loop control of multi-agent systems (MASs), comprised of different unmanned aerial vehicles (UAVs), with realistic communication channels that give rise to intermittent, corrupted and delayed information. We propose a novel design of a human-machine interface (HMI) that allows a human to become a supervisor, when necessary, instead of a single unit operator. The proposed framework allows the supervisor to interact with its surroundings by deploying a dexterous aerial robot within MASs. Experimental results, presented at the end of the paper, verify functionality of the proposed framework by bringing together a heterogeneous team of aerial robots, each with its particular capabilities, and a human operator in order to close a valve in a disaster stricken industrial environment. <s> BIB018 </s> Snake Aerial Manipulators: A Review <s>  <s> In this paper we introduce a particularly relevant class of aerial manipulators that we name protocentric. These robots are formed by an underactuated aerial vehicle, a planar-Vertical Take-Off and Landing (PVTOL), equipped with any number of different parallel manipulator arms with the only property that all the first joints are attached at the Center of Mass (CoM) of the PVTOL, while the center of actuation of the PVTOL can be anywhere. We prove that protocentric aerial manipulators (PAMs) are differentially flat systems regardless the number of joints of each arm and their kinematic and dynamic parameters. The set of flat outputs is constituted by the CoM of the PVTOL and the absolute orientation angles of all the links. The relative degree of each output is equal to four. More amazingly, we prove that PAMs are differentially flat even in the case that any number of the joints are elastic, no matter the internal distribution between elastic and rigid joints. The set of flat outputs is the same but in this case the total relative degree grows quadratically with the number of elastic joints. We validate the theory by simulating object grasping and transportation tasks with unknown mass and parameters and using a controller based on dynamic feedback linearization. <s> BIB019 </s> Snake Aerial Manipulators: A Review <s>  <s> In this paper, an impedance control scheme for aerial robotic manipulators is proposed, with the aim of reducing the end-effector interaction forces with the environment. The proposed control has a multi-level architecture, in detail the outer loop is composed by a trajectory generator and an impedance filter that modifies the trajectory to achieve a complaint behaviour in the end-effector space; a middle loop is used to generate the joint space variables through an inverse kinematic algorithm; finally the inner loop is aimed at ensuring the motion tracking. The proposed control architecture has been experimentally tested. <s> BIB020 </s> Snake Aerial Manipulators: A Review <s>  <s> We present a control methodology for underactuated aerial manipulators that is both easy to implement on real systems and able to achieve highly dynamic behaviors. The method is composed by two parts: i) a nominal input/state trajectory generator that takes into account the full-body dynamics of the system exploiting its differential flatness property; ii) a decentralized feedback controller acting on the actuated degrees of freedom that confers the needed robustness to the closed-loop system. We demonstrate that the proposed controller is able to precisely track dynamic trajectories when implemented on a standard hardware. Comparative experiments clearly show the benefit of using the nominal input/state generator. <s> BIB021 </s> Snake Aerial Manipulators: A Review <s>  <s> This contribution presents a modeling technique for an aerial manipulator based on a quad-rotor vehicle provided with a robotic arm. Dual quaternions, which are a little explored but powerful mathematical tool, are proposed as an alternative to the classical Euler angles approach for the kinematic and dynamic modeling. A feedback control law based on dual quaternions is used to validate the proposed model, taking into account the external effects of the robotic limb. Numerical simulations and experiments validate the proposal, opening a path for future research. <s> BIB022 </s> Snake Aerial Manipulators: A Review <s>  <s> This paper presents the planning and control synthesis of cooperative aerial manipulators to carry an unknown object together. The online parameter estimation algorithm is designed to estimate the unknown physical parameters of the common payload such as mass and moment of inertia, without the need of multiaxis force/torque sensors. Based on the augmented adaptive sliding mode controller with the estimated physical parameters, the desired trajectory of each aerial manipulator is generated to track the desired trajectory of corresponding end effector. In order to carry an unknown object safely considering the actuation limit of the hexacopter, we use the task priority to satisfy the unilateral constraints determined by the allowable flight envelope. To validate our approach, the experimental result on a successful transportation by using multiple custom-made aerial manipulators is shown. This result suggests that the proposed approach can be utilized for safe cooperative aerial transportation. <s> BIB023 </s> Snake Aerial Manipulators: A Review <s>  <s> Micro aerial vehicles have the potential to assist humans in tasks such as manipulation and transportation for construction and humanitarian missions, beyond simply acquiring data and building maps. In this letter, we address the state estimation, control, and trajectory planning in cooperative transportation of structures, which are either too heavy or too big to be carried by small microvehicles. Specifically, we consider small quadrotors, each equipped only with a single camera and inertial measurement unit as a sensor. The key contributions are 1) a new approach to coordinated control, which allows independent control of each vehicle while guaranteeing the system's stability and 2) a new cooperative localization scheme that allows each vehicle to benefit from measurements acquired by other vehicles. The latter relies on the vehicles exploiting the inherent rigid structure information to infer additional constraints between the vehicles' poses allowing us to formulate the pose estimation problem as an optimization problem on the Lie group SE(3). The proposed approach is validated through experimental results with multiple quadrotors grasping and transporting a rigid structure. <s> BIB024 </s> Snake Aerial Manipulators: A Review <s>  <s> In this letter, we introduce a novel transformable aerial robot called DRAGON, which is a dual-rotor-embedded multilink robot with the ability of multi-degree-of-freedom (DoF) aerial transformation. The new aerial robot can control the full pose in $\mathsf {SE}(3)$ regarding the center of gravity (CoG) of multilinks and can render the multi-DoF aerial transformation, which is accomplished by the original two-DoF force vectoring mechanism on each link called the dual-rotor gimbal module. The dynamics is derived on the basis of the special definition of CoG orientation, followed by a control method decoupled into thrust force control and rotor gimbal control. In the thrust force control, the minimum force norm is considered to avoid force saturation, and the rotor gimbal control method is developed to enhance both translational and rotational stabilities during hovering and large-scale aerial transformation. The prototype composed of four links is constructed, and associated preliminary experiments are performed. The feasibility of the novel mechanical design and the proposed control method for the aerial transformation is demonstrated. <s> BIB025 </s> Snake Aerial Manipulators: A Review <s>  <s> In this paper, we introduce the concept of a multilink unmanned aerial system (ML-UAS) designed for multi-cargo transportation tasks. Such system features three links who are actuated by four flying robots. We present in detail the dynamics modeling based on the Euler-Lagrange formulation. A preliminary control scheme based on robust Adaptive Integral Sliding Mode Control (AISMC) is applied considering the ML-UAS model uncertainties and external disturbances. The control objective is to follow/track avian-inspired acquiring patterns for acquiring operations. The effectiveness of the proposed strategy is validated by numerical simulations. <s> BIB026 </s> Snake Aerial Manipulators: A Review <s>  <s> The recent advances in state estimation, perception, and navigation algorithms have significantly contributed to the ubiquitous use of quadrotors for inspection, mapping, and aerial imaging. To further increase the versatility of quadrotors, recent works investigated the use of an adaptive morphology, which consists of modifying the shape of the vehicle during flight to suit a specific task or environment. However, these works either increase the complexity of the platform or decrease its controllability. In this letter, we propose a novel, simpler, yet effective morphing design for quadrotors consisting of a frame with four independently rotating arms that fold around the main frame. To guarantee stable flight at all times, we exploit an optimal control strategy that adapts on the fly to the drone morphology. We demonstrate the versatility of the proposed adaptive morphology in different tasks, such as negotiation of narrow gaps, close inspection of vertical surfaces, and object grasping and transportation. The experiments are performed on an actual, fully autonomous quadrotor relying solely on onboard visual-inertial sensors and compute. No external motion tracking systems and computers are used. This is the first work showing stable flight without requiring any symmetry of the morphology. <s> BIB027 </s> Snake Aerial Manipulators: A Review <s>  <s> This paper presents the design concept, modeling and motion planning solution for the aerial robotic chain. This design represents a configurable robotic system of systems, consisting of multi-linked micro aerial vehicles that simultaneously presents the ability to cross narrow sections, morph its shape, ferry significant payloads, offer the potential of distributed sensing and processing, and allow system extendability. We contribute an approach to address the motion planning problem of such a connected robotic system of systems, making full use of its reconfigurable nature, to find collision free paths in a fast manner despite the increased number of degrees of freedom. The presented approach exploits a library of aerial robotic chain configurations, optimized either for cross-section size or sensor coverage, alongside a probabilistic strategy to sample random shape configurations that may be needed to facilitate continued collision-free navigation. Evaluation studies in simulation involve traversal of constrained and obstacle-laden environments, having narrow corridors and cross sections. <s> BIB028
Since the beginning of the decade of 2010, the MM-UAV (Mobile Manipulating Unmanned Aerial Vehicle) is an area of gradual growth. Until 2012 the concept was limited to aerial vehicles with robotic manipulator arms attached to their structures. In this way, and according to the requirements of  , these are systems of decoupling tasks, that is to say, systems in which the dynamics and kinematics between the manipulator and the aircraft can be controlled with certain degree of independence or decoupling  , BIB012 BIB018  BIB019 BIB021 BIB020 BIB005 BIB006 BIB007 BIB008 BIB022 BIB002 Fig. 3 . Thus, this scheme is restricted to the use of multiple coordinated MM-UAVs each one equipped with a robotic arm coupled in a rigid way or by means of cables (e.g. AEROARMS and ARCAS projects). BIB014 BIB015 BIB009 BIB010 . The associate editor coordinating the review of this manuscript and approving it for publication was Yangmin Li . On the other hand, since 2011 approximately, the essential notions of coupled task aerial manipulation theory were developed  BIB016 BIB024 BIB001 BIB017 BIB026 BIB011 BIB013  BIB003   BIB023  . Although their approaches covered exclusively the cargo-lifting and coordinated transport of objects rigidly attached to the body of each member of an aircraft team, also suitable by means of deformable and elastic cables. Such publications are the basis for understanding the coupled task aerial manipulator concept, that where manipulation and transport tasks cannot be separated because the aircraft-team or the array of propellers, are by themselves the engine elements and also the channel of dexterity and manipulation. Fig. 1,2,4 They are a kind of coupled task aerial manipulator with bidimensional or three-dimensional robotic handling skills through the interaction of multicopters or propellers that constitute two or more bifurcated kinematic chains called arms, with dexterity and transitional capacity between open and closed kinematic structures. This bifurcation starts from a common point of reference and analysis, which can be, the geometric center, the gravity center, the mass center, the flotation center, or any other point of particular interest. Such structures can be reconfigurable and shape morphing  BIB027 BIB025 BIB004 BIB028 .