Maximilian Laiacker

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

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.

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

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.

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

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.

Remote water sampling using flying robots

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.

On the Cooperation between Mobile Robots and Wireless Sensor Networks

Employing cooperative heterogeneous systems can enrich application scenarios and achieve higher application performance. The combination of mobile robots and Wireless Sensor Networks (WSNs) is a good example of such cooperation, and many recent research results have highlighted the benefits of the marriage of these two technologies. The main objectives of this chapter include: (1) providing a survey on a variety of applications with cooperating mobile robots and WSNs based on the roles they play for interaction, and (2) elaborating different cooperative interactions of robots and WSNs in our ongoing project, PLAtform for the deployment and operation of heterogeneous NETworked cooperating objects (PLANET), which is an integrated framework of heterogeneous cooperative objects for network deployment and operations.

Modular scalable system for operation and testing of UAVs

In this paper we present a system for operation and testing of different UAVs. The system allows easy development and modification of control and mission software. The system is composed of hard- and software modules with a standardized interface. We have been using the system with rotary and fixed wing UAVs with a take-off mass between 10 and 100 kg. For larger platforms the system can be used in a redundant setup. The software modules are integrated in a special real-time framework, which supports execution, scheduling, communication and system monitoring. A modular simulation and control infrastructure allows for flexible, integrated design and analysis of control laws. The code for the computational part of the modules can be generated from Matlab/Simulink-models or from Modelica-models. The system supports debugging, soft- and hardware in the loop simulations, operator training as well as real flight experiments. The main design concepts are explained at hand of our solar powered high altitude platform ELHASPA and the 10 years experience in development and operation will be summarized.

Helicopter UAV systems for in situ measurements and sensor placement

The use of unmanned aerial systems (UAS) is growing in research and civil applications. Advancing technology offers huge potential which is just starting being used. We present a method to have a helicopter UAS interacting with the environment physically. This basic technology, which includes high precision control and a vision system can be adapted for different in situ measurement tasks. Applications cover a wide range from placement of sensors or direct measurements to sampling. While UAS systems get more complex, we describe a way of interacting with a them by means of an interactive control framework, which can also include other systems and sensors.

Landing of a fixed-wing UAV on a mobile ground vehicle

The development of solar-powered high-altitude UAV has gained increasing attention in the recent years. Several aircraft have had successful flights in the stratosphere, but despite advances in lightweight design they can only carry small payloads compared to the total takeoff mass. This paper suggests to eliminate the need for a landing gear by landing on a mobile ground vehicle. This would not only increase the payload capacity, but also simplify landings in crosswind conditions and thus increase the operational availability. A system with a small UAV and a car-mounted landing platform is prepared as a technology demonstrator. Different aspects of the landing problem are studied in simulations and real experiments and algorithms for the cooperative control of both vehicles are proposed. Simulations as well as experiments with the real car and a simulated UAV show the feasibility of such landings.

Automatic aerial retrieval of a mobile robot using optical target tracking and localization

In this paper we present a system for automatic deployment and retrieval of a mobile ground robot using a helicopter UAV. Our system allows using a mobile outdoor robot in areas that cannot be reached other than from the air and aerial measurements alone are not sufficient. For example a ground robot can perform in situ measurements and even take samples that can later be analyzed when the robot is returned by the aerial system. We use a helicopter UAV with a rotor diameter of 1.8m and a takeoff mass of 11kg as a proof-of-concept platform. The UAV is equipped with our modular autopilot system. The real time control and navigation is done by the flight control computer. The target detection is done by the image processing computer connected to a downward looking camera. In addition to the autopilot payload the helicopter can carry an extra mass of around 2kg. The ground robot we used had a mass of 1.1kg and is equipped with a GPS sensor and a communication system that is used to send its current position estimate to the UAV. The aerial system is using a high precision hover position controller and a multi-sensor fusion module which is used for detection and precise localization of the mobile robot. It combines GPS-based localization for obtaining an initial estimation of the ground robot location and a vision-system for its accurate localization. We use a known optical marker on the ground robot for its precise localization relative to the aerial system. All control and sensor processing and fusion are performed on board of the UAV. The docking system we developed is very similar to the probe-and-drogue aerial refueling system. It is used to compensate position disturbances of the UAV during the docking maneuver. Results from multiple successful outdoor flight experiments will be presented.

Analysis and development of a reliable fixed wing UAV control system for mission profiles with restricted GPS availability

This paper is motivated by the actual need for safer and more reliable flight control systems for fixed wing UAVs. In certain mission scenarios, it is necessary to fly close to big structures at low altitudes where the availability of GPS sensor data cannot be guaranteed. Two different control strategies have been analyzed, with the main difference consisting in the utilization of GPS data for flight control. An extended system allowing those two control strategies to complement one to another has been developed. Its performance has been analyzed through simulation and in flight experiments. The result is a more reliable flight control system for flying in areas with restricted GPS signal.