Markus Ax

UAV Based Laser Measurement for Vegetation Control at High-Voltage Transmission Lines

Trees which are growing beneath high-voltage transmission lines have to be cut down if the distance to the conductor rope gets too close. It is very hard to find those if only single trees are affected. Chopping simply all trees under a transmission line, which was done in former times, is not a desirable solution for environmental and economic reasons. In this paper a solution is shown which uses an unmanned aerial vehicle and a laser scanner to generate a 3d point-cloud representing the trees and the conductor ropes. Using this point-cloud the decision for cutting down a specific tree can easily be made.

Realization of an autonomous team of unmanned ground and aerial vehicles

The paper presents work that has been done by three different research institutions. The aim was to realize an autonomous team of heterogeneous unmanned ground and aerial vehicles performing certain reconnaissance and surveillance tasks, where the tasks were set by an operator at a team level instead of controlling each vehicle seperately. To overcome the lack of a common middleware, the interfaces between vehicles and graphical user interface have been defined using Robot Operating System (ROS) and Battle Management Language (BML). We present approaches for autonomous control of the vehicles, focussing on the unmanned ground vehicle. Moreover, we conducted some large field experiments and present the results.

Absolute High-Precision Localisation of an Unmanned Ground Vehicle by Using Real-Time Aerial Video Imagery for Geo-referenced Orthophoto Registration

This paper describes an absolute localisation method for an unmanned ground vehicle (UGV) if GPS is unavailable for the vehicle. The basic idea is to combine an unmanned aerial vehicle (UAV) to the ground vehicle and use it as an external sensor platform to achieve an absolute localisation of the robotic team. Beside the discussion of the rather naive method directly using the GPS position of the aerial robot to deduce the ground robot’s position the main focus of this paper lies on the indirect usage of the telemetry data of the aerial robot combined with live video images of an onboard camera to realise a registration of local video images with apriori registered orthophotos. This yields to a precise driftless absolute localisation of the unmanned ground vehicle. Experiments with our robotic team (AMOR and PSYCHE) successfully verify this approach.

Development of a High Speed 3D Laser Measurement System for Outdoor Robotics

This paper describes the development of a 3D laser measurement system for application in outdoor robotics. Over the last few years several approaches have been examined concerning this issue. In the majority of cases, a 2D laser scanner, including its whole weight, is used by a rotating motion to obtain a three dimensional model of the near and far environment. To prevent the disadvantages, like particularly the loss of velocity during the scanning process due to the high mass to be accelerated, a novel approach is illustrated within this paper. By mounting a light weight mirror directly in front of the 2D laser scanner, a higher velocity can be achieved while capturing the environment. In addition, further improvements in the minimization of power consumption and also in the reduction considering the complexity of hardware can be reached. The achievement of a 6 Hz frame rate represents the result of this research.

Control Strategies for Heterogeneous, Autonomous Robot Swarms

Having robots as reliable and robust mobile sensor platforms in unknown environments is getting more and more attractive. The control of each robot as a single machine is often complicated enough. But if there are more than one robots in a given scenario, the task get’s even harder. The operators then do not only have to care about steering their robot, but they also have to cooperate with each other. In this paper we describe the results of a research project regarding control strategies for a group of heterogeneous, autonomous robots. The swarm receives orders from a central control station, that uses a Battle Management Language, which is abstract, but human readable. An abstract language postulates a certain degree of intelligence within each robot of the cooperation, because the orders are mostly more complex than simple moves from A to B. There is a command hierarchy within the swarm, but every robot implements its own control strategies, to fulfill the overall goal of the orders. The technical as well as the operational realizations are described and discussed mostly with the focus on the unmanned aerial robots.

Cooperation in heterogeneous groups of autonomous robots

By increasing complexity of tasks, autonomous outdoor robots emerge from single beings into cooperating groups. This paper first introduces the robots developed at the University of Siegen and then discusses the architecture and communication structure that is able to glue these into a group working on a common task while exploiting their different abilities. The paper describes a new software system that universally connects quite different robots into one group. Based on VSAL middle ware and ROS the CAPTAIN architecture implements complex missions via hierarchic state machines and an appropriate control scheme. This system is verified experimentally by using it in several different groups of robots.