Aerial manipulation aims at combining the versatility and the agility of some aerial platforms with the manipulation capabilities of robotic arms. This letter tries to collect the results reached by the research community so far within the field of aerial manipulation, especially from the technological and control point of view. A brief literature review of general aerial robotics and space manipulation is carried out as well.

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Aerial Manipulation: A Literature Review

The problem of formation control of a team of mobile robots based on the virtual and behavioral structures is considered in this paper. In the virtual structure, each mobile robot is modeled by an electric charge. The mobile robots move toward a circle, and due to repulsive forces between the identical charges, regular polygon formations of the mobile robots will be realized. For swarm formation, a virtual mobile robot is located at the center of the circle, and other mobile robots follow it. In the introduced approach, each mobile robot finds its position in the formation autonomously, and the formation can change automatically in the case of change in the number of the mobile robots. This paper also proposes a technique for avoiding obstacles based on the behavioral structure. In this technique, when a mobile robot gets close to an obstacle, while moving toward its target, a rotational potential field is applied to lead the mobile robot to avoid the obstacle, without locating in local minimum positions.

A Decentralized Cooperative Control Scheme With Obstacle Avoidance for a Team of Mobile Robots

This paper addresses the stability and tracking control problem of a quadrotor unmanned flying robot vehicle in the presence of modeling error and disturbance uncertainty. The input algorithms are designed for autonomous flight control with the help of an energy function. Adaptation laws are designed to learn and compensate the modeling error and external disturbance uncertainties. Lyapunov theorem shows that the proposed algorithms can guarantee asymptotic stability and tracking of the linear and angular motion of a quadrotor vehicle. Compared with the existing results, the proposed adaptive algorithm does not require an a priori known bound of the modeling errors and disturbance uncertainty. To illustrate the theoretical argument, experimental results on a commercial quadrotor vehicle are presented.

Robust Control of Four-Rotor Unmanned Aerial Vehicle With Disturbance Uncertainty

This paper describes a general passivity-based framework for the control of flexible joint robots. Recent results on torque, position, as well as impedance control of flexible joint robots are summarized, and the relations between the individual contributions are highlighted. It is shown that an inner torque feedback loop can be incorporated into a passivity-based analysis by interpreting torque feedback in terms of shaping of the motor inertia. This result, which implicitly was already included in earlier work on torque and position control, can also be used for the design of impedance controllers. For impedance control, furthermore, potential energy shaping is of special interest. It is shown how, based only on the motor angles, a potential function can be designed which simultaneously incorporates gravity compensation and a desired Cartesian stiffness relation for the link angles. All the presented controllers were experimentally evaluated on DLR lightweight robots and their performance and robustness shown with respect to uncertain model parameters. Experimental results with position controllers as well as an impact experiment are presented briefly, and an overview of several applications is given in which the controllers have been applied.

A Unified Passivity Based Control Framework for Position, Torque and Impedance Control of Flexible Joint Robots.

In this paper, we consider the problem of decentralized cohesive motion control of a formation of autonomous vehicles or robots moving in three dimensions, where the formation is required to move from its initial setting (defined by the positions of the agents in the formation) to a final desired setting and, during this motion, maintain its formation geometry defined by the initial distances between the agent pairs We propose a distributed control scheme to solve this problem utilizing the notions of graph rigidity and persistence as well as techniques of virtual target tracking and smooth switching The distributed control scheme is developed by modeling the agent kinematics as single-velocity integrator; nevertheless, extension to the cases with practical kinematic and dynamic models of fixed-wing autonomous aerial vehicles and quadrotors is discussed In this context, we examine the maintenance of geometric formation of a swarm of autonomous flight vehicles The developed coordination and control schemes are verified via a number of simulations

Distributed Cohesive Motion Control of Flight Vehicle Formations

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.

Control of a multirotor outdoor aerial manipulator

Design of a lightweight dual arm system for aerial manipulation

This paper presents the architecture of an onboard controller developed for the HERO autonomous helicopter, which is a low-cost unmanned aerial vehicle research platform. An embedded digital-signal-processor-based low-level controller is devoted to flight control, while a PC-based high-level controller is used for onboard perception tasks and interaction with other agents in a distributed system. The functional design, software architecture, and implementation of the low-level controller are analyzed in detail, focusing mainly on its runtime environment (JULIET) and its capability for flexible reconfiguration. The connectivity functions of the low-level controller with external possibly distributed agents are also addressed. Finally, the results of real autonomous flight experiments are presented, including the tracking of a smooth 3-D path described by over two hundred waypoints.

Reconfigurable Control Architecture for Distributed Systems in the HERO Autonomous Helicopter

This paper presents the design of a dual-arm aerial manipulator consisting of a multi-rotor platform with an ultra-lightweight (1.8 Kg) human-size dual arm prototype and its control system. Each arm provides three degrees of freedom (DOF) for positioning the end- effector, and two DOF for orientation. As most model-based controllers assume that joint torque feedback is available, a torque estimator for the arms is developed. Note that low cost servos used for building low weight manipulators do not provide any torque feedback or control capability. The redundant DOFs in the dual arm prototype are exploited for generating coordinated motions during contact-less phases in such a way that reaction torques can be partially canceled. Preliminary flight tests have been conducted in outdoors, evaluating the torque compensation capability in test-bench. The influence of the reaction torques exerted by the arms over the UAV controller is also analyzed in simulation.

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Lightweight and human-size dual arm aerial manipulator

This letter is devoted to benchmarks for aerial manipulation robots (drones equipped with robotic arms), which are demonstrating their potential to conduct tasks involving physical interactions with objects or the environment in high altitude workspaces, being a cost effective solution for example in inspection and maintenance operations. Thus, the letter deals with different methods and criteria to evaluate and compare the performance of aerial manipulators. This is not an easy task, taking into account the wide variety of designs, morphologies and implementations that can be found in recent works. In order to cope with this problem, this letter analyzes the capabilities and functionalities of several aerial manipulation prototypes (aerial platform + manipulator), identifying a set of relevant metrics and criteria. A number of benchmarks are defined to evaluate the performance of the aerial manipulator in terms of accuracy, execution time, manipulation capability, or impact response. Experimental results carried out with a compliant joint aerial manipulator in test-bench and in indoor-outdoor testbeds illustrate some of the benchmarks.

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Victor M. Vega

Papers

Control of a multirotor outdoor aerial manipulator

Design of a lightweight dual arm system for aerial manipulation

Reconfigurable Control Architecture for Distributed Systems in the HERO Autonomous Helicopter

Lightweight and human-size dual arm aerial manipulator

Benchmarks for Aerial Manipulation