There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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.

/pdf/aerial-manipulation-a-literature-review-2gq2uh3t8a.pdf

Aerial Manipulation: A Literature Review

The art installation Flight Assembled Architecture [1] is one of the first structures built by flying vehicles. Culminating in a 6-m-tall tower composed of 1500 foam modules (see Figures 1 and 2), the installation was assembled by four quadrocopters in 18 hours during a four-day-long live exhibition at the Fonds R?gional d'Art Contemporain (Regional Contemporary Art Fund) du Centre in Orl?ans, France. This article documents the design and development of specific elements of the autonomous system behind this one-of-a-kind installation and describes the process and challenges of bringing such a complex system out of the laboratory and into the public realm, where live demonstration and human-in-the-loop interaction demand high levels of robustness, dependability, and safety. The installation is a 1:100 scale model of what was originally conceived of as a 600 m-high vertical village (see "The Vertical Village" for details) and is an exploration of aerial construction in architecture. Architects have been exploring the use of digital technologies for the design and assembly of structures for some time now, and many facilities for investigating nonstandard architectural design and fabrication using industrial robots have sprung up in the past decade [2]-[4]. However, robot arms and computer numerical control (CNC) machines are limited by predefined working areas that constrain the size of the workpiece they can act upon and are thus also limited in their scale of action to a small portion or component of the overall structure, or to model-sized fabrication [5]. In contrast, flying machines are not constrained by such tight boundaries. The space that flying machines can act upon is substantially larger than the size of the machines themselves, making it feasible for the machines to work on the structure as a whole at a 1:1 scale, thus offering architects a new framework for realizing their designs.

The Flight Assembled Architecture installation: Cooperative construction with flying machines

In this paper we present the design and control of a novel six degrees-of-freedom aerial vehicle. Based on a static force and torque analysis for generic actuator configurations, we derive an eight-rotor configuration that maximizes the vehicle's agility in any direction. The proposed vehicle design possesses full force and torque authority in all three dimensions. A control strategy that allows for exploiting the vehicle's decoupled translational and rotational dynamics is introduced. A prototype of the proposed vehicle design is built using reversible motor-propeller actuators and capable of flying at any orientation. Preliminary experimental results demonstrate the feasibility of the novel design and the capabilities of the vehicle.

Design, modeling and control of an omni-directional aerial vehicle

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

In this paper we describe a system for aerial manipulation composed of a helicopter platform and a fully actuated seven Degree of Freedom (DoF) redundant industrial robotic arm. We present the first analysis of such kind of systems and show that the dynamic coupling between helicopter and arm can generate diverging oscillations with very slow frequency which we called phase circles. Based on the presented analysis, we propose a control approach for the whole system. The partial decoupling between helicopter and arm - which eliminates the phase circles - is achieved by means of special movement of robotic arm utilizing its redundant DoF. For the underlying arm control a specially designed impedance controller was proposed. In different flight experiments we showcase that the proposed kind of system type might be used in the future for practically relevant tasks. In an integrated experiment we demonstrate a basic manipulation task - impedance based grasping of an object from the environment underlaying a visual object tracking control loop.

/pdf/first-analysis-and-experiments-in-aerial-manipulation-using-43wwpmpb9k.pdf

First analysis and experiments in aerial manipulation using fully actuated redundant robot arm

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

Aerial manipulation robot composed of an autonomous helicopter and a 7 degrees of freedom industrial manipulator

This paper is devoted to the control of aerial robots interacting physically with objects in the environment and with other aerial robots. The paper presents a controller for the particular case of a small- scaled autonomous helicopter equipped with a robotic arm for aerial manipulation. Two types of influences are imposed on the helicopter from a manipulator: coherent and non-coherent influence. In the former case, the forces and torques imposed on the helicopter by the manipulator change with frequencies close to those of the helicopter movement. The paper shows that even small interaction forces imposed on the fuselage periodically in proper phase could yield to low frequency instabilities and oscillations, so-called phase circles.

/pdf/closed-loop-behavior-of-an-autonomous-helicopter-equipped-5br7pdsw58.pdf

Closed-Loop Behavior of an Autonomous Helicopter Equipped with a Robotic Arm for Aerial Manipulation Tasks:

In this paper, we present a multi-sensor system for automatic landing of fixed wing UAVs. The system is composed of a high precision aircraft controller and a vision module which is currently used for detection and tracking of runways. Designing the system we paid special attention to its robustness. The runway detection algorithm uses a maximum amount of information in images and works with high level geometrical models. It allows detecting a runway under different weather conditions even if only a small part is visible in the image. In order to increase landing reliability under sub-optimal wind conditions, an additional loop was introduced into the altitude controller. All control and image processing is performed onboard. The system has been successfully tested in flight experiments with two different fixed wing platforms at various weather conditions, in summer, fall and winter.

/pdf/vision-aided-automatic-landing-system-for-fixed-wing-uav-45c3k65egv.pdf

Vision aided automatic landing system for fixed wing UAV

Sampling of water for laboratory measurements is important in various circumstances. We present reasoning why it is of great importance for sensible ecosystems like natural parks which include wetlands. Since many places are hard or impossible to reach by other means, a system for sampling of water using an unmanned helicopter is proposed. The technical difficulties in handling the sample and controlling the system are described as well as appropriate solutions. The system was also integrated into a control framework allowing easy access and control by scientists, in our case biologists. Several trials have been performed, including flights in the final application fields. Water samples could be acquired reliably.

Marc Schwarzbach

Papers

First analysis and experiments in aerial manipulation using fully actuated redundant robot arm

Aerial manipulation robot composed of an autonomous helicopter and a 7 degrees of freedom industrial manipulator

Closed-Loop Behavior of an Autonomous Helicopter Equipped with a Robotic Arm for Aerial Manipulation Tasks:

Vision aided automatic landing system for fixed wing UAV

Remote water sampling using flying robots