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(2022): Grosse Hoffnungen ins neue Fachhochschulzentrum. In: Wissensplatz, S. 30-31. Online verfügbar unter https://www.fhgr.ch/fh-graubuenden/medien-und-oeffentlichkeit/publikationen/wissensplatz/september-2022/, zuletzt geprüft am 23.09.2022
Abstract: Mit dem Start der Studienrichtung Mobile Robotics (MR) im September 2020 hat auch der Aufbau des Mobile Robotics Lab an der Fachhochschule Graubünden begonnen. Nach wie vor verfolgen wir das Ziel, einen physischen Ort an der Fachhochschule zu schaffen, an dem gleichzeitig gelehrt, geforscht und diskutiert werden kann. Ich möchte hier kurz berichten, was wir diesbezüglich bereits erreicht haben und welche Chancen das Fachhochschulzentrum hierfür bieten kann.
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(2011): Design of the autonomous micro helicopter muFly. In: Mechatronics 21, S. 765-775. Online verfügbar unter https://doi.org/10.1016/j.mechatronics.2010.12.004, zuletzt geprüft am 31.03.2023
Abstract: In this paper, the design of two prototypes of the autonomous micro helicopter muFly is introduced. These prototypes have been built and flown in untethered test flights. The rotor configuration and steering principle selection of the prototypes are discussed according to the specifications, and the selection of a coaxial configuration with a swash plate steering of the lower rotor is justified based on dynamic simulation results. The two prototype designs are shown and discussed with special attention paid to their respective system integration issues, which are solved. Finally, the prototypes are compared and conclusions for future designs of autonomous micro helicopters are drawn.
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(2011): Towards Palm-Size Autonomous Helicopters. In: Journal of Intelligent and Robotic Systems 61, S. 445-471. DOI: 10.1007/s10846-010-9483-y
Abstract: muFly EU project started in 2006 with the idea to build an autonomous micro helicopter, comparable in size and weight to a small bird. Several scientific and technological objectives were identified. This spanned from system-level integration, high efficiency micro-actuation, highly integrated micro vision sensors and IMUs and also low processing power navigation algorithms. This paper shows how most of these objectives were reached, describing the approach and the role of each partner during the whole project. The paper describes also the technological developments achieved like the 80 g, 17 cm micro robotic-helicopter, the 8 g omnidirectional and steady-state laser scanner, the uIMU, the highly efficient micro motors, the high power-density fuel-cell and the successful graph-based navigation algorithms.
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(2010): Design and dynamic modeling of autonomous coaxial micro helicopters. Doctoral Thesis. ETH Zürich. Online verfügbar unter https://doi.org/10.3929/ETHZ-A-006020824, zuletzt geprüft am 31.03.2023
Abstract: This thesis deals with the design, the dynamic modeling and the simulation of autonomous coaxial micro helicopters. The helicopter prototypes and mod- eling results that are presented are part of the project muFly, a European framework research project aiming at the design of an autonomous micro helicopter that is comparable to a small bird in size and mass. The first goal of this work is to introduce two prototype designs for the mu- Fly helicopter. The first prototype is designed in a modular way, to allow for fast sensor and actuator exchange and easy testing in different configurations. This modularity, however, has to be paid by quite high a total mass, which prevents from integration of the full set of sensors required for autonomous flight. The second prototype is designed in a highly integrated fashion to reduce the total mass and integrate the complete sensor set for autonomous flight, including the x-y-position sensor consisting of laser diodes and an om- nidirectional camera. The key to achieve the reduced mass is the dual use of electronics as structure, which leads to a mass saving of approximately 17 %, while the sensor payload is increased. The second goal of this work is to lay a more theoretical foundation for fu- ture coaxial micro helicopter designs, in particular focus are their ability to stabilize passively in roll and pitch, and their steering principles. There- fore, a modular dynamic model is developed, which incorporates the active and passive flapping characteristics of a hingeless rotor system, two optional steering principles, which are swash plate steering and steering by displacing the center of mass of the helicopter, and a stabilizer bar simulation module, which is also validated experimentally. Simulation results show the advan- tages of the coaxial rotor system in terms of a stronger disturbance rejection and a lower degree of total cross coupling. Moreover, swash plate steering is identified as the better steering option for coaxial micro helicopters, both in terms of output amplitude and energy consumption. Also the limitations of the stabilizer bar in terms of passive roll and pitch stabilization are shown. Finally, the dynamic model is used for a design parameter study of the most relevant system design parameters. It aims at passive roll and pitch stabiliza- tion of the helicopter without a stabilizer bar. Simulation results show that passive stabilization can be achieved, and that the key parameter to passive stabilization is the rotor blade hinge offset, while blade flapping inertia and the distance between the rotors and the center of mass of the helicopter play a less important role.
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(2010): Cable‐crawler. Robot for the inspection of high‐voltage power lines that can passively roll over mast tops. In: Industrial Robot 37, S. 256-262. DOI: 10.1108/01439911011037659
Abstract: Purpose The purpose of this paper is to describe the design and prototype implementation of the “Cable Crawler”, a mobile teleoperated robot for the inspection of high‐voltage power lines which rides on the topmost ground cable. By not being limited to just moving from mast to mast, it implements an innovative mechanism that allows for crossing a set of mast tops as well as smaller obstacles autonomously. Design/methodology/approach After a brief overview of the state‐of‐the‐art for this application, the basic concept of the robot is presented – which basically consists of a chassis and six motorized rubber‐coated rollers, two in a horizontal position to take the weight and four vertical ones. The four vertical rollers are pressed onto the wire by springs, which guarantees slip‐less propulsion in difficult situations. The detailed design of the most challenging components is presented, as well as the successful tests with the prototype. Findings The feasibility of the concept is proven with a prototype implementation and successful test results. Practical implications With a mass of 58 kg and only six drives, it consequently follows the industry's wish to have a robust, easy to maintain and rather cheap solution. Regarding the fields examined by the robot, the project concentrated on the detection of trees growing into proximity of the wires. Future work will mainly stress in further reducing the robot's mass and in facilitating its transport to the mast by the workers. Originality/value The presented prototype allows for moving on the topmost ground cable of high‐voltage power‐lines and to passively roll over mast tops and smaller obstacles. With these properties, it is able to inspect long distances of cables in an autonomous way and by using a relatively low‐cost and robust robot.
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(2010) : Inspection of high voltage power lines-a new approach In: Tosun, O.; Akin, H. L.; Tokhi, Mohammad Osman; Virk, Gurvinder S. (Hg.): Mobile robotics: Solutions and challenges: Proceedings of the Twelfth International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines: International Conference on Climbing and Walking Robots: Istanbul, 9. - 11. September: 2009. International Conference on Climbing and Walking Robots: Singapore; Hackensack: World Scientific, S. 455-462
Abstract: This paper presents the "Cable Crawler", a mobile teleoperated robot to inspect high voltage power lines. Its mechanism allows riding on the topmost ground cable of high voltage power lines and crossing a set of mast tips as well as smaller obstacles autonomously and thus is not limited to just move from mast to mast. The robot consists of an aluminium chassis, six propulsion units and two spaces for cameras and other electronic components. Six electrical motors drive independently six rubber-coated rollers, two in a horizontal position to take the weight and four vertical ones. The four vertical rollers are pressed onto the wire by springs, which guarantees slipless propulsion in difficult situations. A Matlab program controls the drives independently. An optical camera is mounted on the prototype, which can rotate 360° and the image can be transmitted wireless to the user's computer monitor. With a mass of 58 kg and only six drives it consequently follows the industry's wish to have a robust, easy to maintain and rather cheap solution. Regarding the fields examined by the robot, the project concentrated on the detection of trees growing into proximity of the wires.
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(2010): Modeling, system identification and robust control of a coaxial micro helicopter. In: Control Engineering Practice 18, S. 700-711. Online verfügbar unter https://doi.org/10.1016/j.conengprac.2010.02.004, zuletzt geprüft am 31.03.2023
Abstract: In this paper the design process of robust - control for a coaxial micro helicopter is presented. The process starts with the development of a nonlinear dynamic model reflecting all the important elements of the helicopter. The corresponding system parameters are identified using measurement data from test benches and real flight, as well as a nonlinear identification tool, the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). The identified and verified model is then used for the design of - controllers for attitude and heave control, which are successfully tested in flight on the real system.
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(2010) : Modeling and System Identification of the muFly Micro Helicopter In: Valavanis, Kimon P.; Beard, Randal; Oh, Paul; Ollero, Aníbal; Piegl, Leslie A.; Shim, Hyunchui (Hg.): Selected papers from the 2nd International Symposium on UAVs, Reno, Nevada, U.S.A. June 8–10, 2009: Reno, 8. - 10. Juni: 2009: Dordrecht; Heidelberg; London; New York: Springer Science+Business Media, S. 27-47
Abstract: An accurate mathematical model is indispensable for simulation and control of a micro helicopter. The nonlinear model in this work is based on the rigid body motion where all external forces and moments as well as the dynamics of the different hardware elements are discussed and derived in detail. The important model parameters are estimated, measured or identified in an identification process. While most parameters are identified from test bench measurements, the remaining ones are identified on subsystems using the linear prediction error method on real flight data. The good results allow to use the systems for the attitude and altitude controller design.
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(2009): From the Test Benches to the First Prototype of the muFly Micro Helicopter. In: Journal of Intelligent and Robotic Systems 54, S. 245-260. DOI: 10.1007/s10846-008-9264-z
Abstract: The goal of the European project muFly is to build a fully autonomous micro helicopter, which is comparable to a small bird in size and mass. The rigorous size and mass constraints infer various problems related to energy efficiency, flight stability and overall system design. In this research, aerodynamics and flight dynamics are investigated experimentally to gather information for the design of the helicopter’s propulsion group and steering system. Several test benches are designed and built for these investigations. A coaxial rotor test bench is used to measure the thrust and drag torque of different rotor blade designs. The effects of cyclic pitching of the swash plate and the passive stabilizer bar are studied on a test bench measuring rotor forces and moments with a 6–axis force sensor. The gathered knowledge is used to design a first prototype of the muFly helicopter. The prototype is described in terms of rotor configuration, structure, actuator and sensor selection according to the project demands, and a first version of the helicopter is shown. As a safety measure for the flight tests and to analyze the helicopter dynamics, a 6DoF vehicle test bench for tethered helicopter flight is used.
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(2009): Propulsion system optimization for the mufly micro helicopter. 35th European Rotorcraft Forum. Deutsche Gesellschaft für Luft- und Raumfahrt. Hamburg, 24. September, 2009. Online verfügbar unter https://dspace-erf.nlr.nl/items/dc78b498-01b8-459e-8eb2-b8ca17d9b777, zuletzt geprüft am 30.04.2023
Abstract: An appropriate design of the propulsion system for micro helicopters is an important task since most of the power on the helicopter is used for propulsion. While it is common to optimize the rotor aerodynamics, the drive train is mostly neglected. This is not sufficient for the rotor design, since it is not guaranteed that the electro motor can drive the rotor at its optimal point. Thus it is crucial to include the drive train in the simulation. This is done by using numerical Blade Element Momentum Theory (BEMT) for aerodynamic simulation which is extended by the drive train equation for truthful simulations. The new code is then used to investigate different rotor blade parameters on the drive train on the muFly helicopter. The results show that for the given drive train a thin blade with moderate camber, strong taper and twist performs best in turns of thrust to electrical power ratio.
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(2008): Nonlinear Lamb waves for the detection of material nonlinearity. In: Mechanical Systems and Signal Processing 22, S. 638-646. Online verfügbar unter https://doi.org/10.1016/j.ymssp.2007.09.006, zuletzt geprüft am 31.03.2023
Abstract: This paper reports on a method that uses nonlinear Lamb waves to detect material nonlinearity. Lamb waves are well suited for the interrogation of thin metallic layers which act as waveguides, giving Lamb waves great potential in nondestructive evaluation applications. However, measuring nonlinear Lamb waves and extracting the information necessary for nondestructive evaluation is complicated by the inherent dispersive and multi-mode nature of Lamb waves. This paper presents a procedure that overcomes these difficulties and develops a reliable and robust measurement methodology. By using hybrid wedge generation and laser interferometric detection in combination with signal processing in the time–frequency domain, it is possible to make relative measurements of material nonlinearity parameters, which are an indicator of plasticity-driven damage.
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(2008) : New design of the steering mechanism for a mini coaxial helicopter: EE International Workshop on Intelligent Robots and Systems (IROS): International Conference on Intelligent Robots and Systems: Nice, 22. - 26. September, S. 1236-1241
Abstract: Whenever the realization of a swash plate mechanism is not feasible (e.g. due to miniaturization limitations), center of gravity steering is an interesting alternative to swash plate steering. We present an approach to describe the dynamic behavior of a coaxial micro helicopter steered by a center of gravity shifting mechanism. The mechanical design of an existing system is improved to increase mechanical robustness and steering quality. In parallel, a simulation model is developed and implemented. It is used to estimate the system response to steering inputs, and to compare center of gravity to swash plate steering. Experimental flight results show an improvement of the helicopter performance due to the mechanical redesign.
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(2008) : Design and Comparison of a Steering Mechanism for an Autonomous Coaxial Indoor Helicopter: Proceedings of The ASME International Symposium on Flexible Automation (ISFA): The ASME International Symposium on Flexible Automation (ISFA): Atlanta, 23. - 26. Juni
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(2007): Experimental characterization of material nonlinearity using Lamb waves. In: Applied Physics Letters 90. DOI: 10.1063/1.2431467
Abstract: The objective of this research is to develop an accurate and reliable procedure to measure the second order harmonic of a Lamb wave propagating in a metallic plate. There are two associated complications in measuring these nonlinear Lamb waves, namely, their inherent dispersive and multimode natures. To overcome these, this research combines a time-frequency representation with a hybrid wedge generation and laser interferometric detection system. The effectiveness of the proposed procedure is demonstrated by characterizing the inherent material nonlinearity of two different aluminum plates whose absolute nonlinearity parameters are known from longitudinal wave measurements.
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(2007) : Cumulative Second Harmonic Generation in Lamb Waves for the Detection of Material Nonlinearities In: Thompson, Donald O.; Chimenti, Dale E. (Hg.): Review of progress in quantitative nondestructive evaluation: Portland, 30. Juli - 4. August: 2006 (AIP conference proceedings), S. 177-184. Online verfügbar unter https://doi.org/10.1063/1.2717971, zuletzt geprüft am 06.05.2023
Abstract: An understanding of the generation of higher harmonics in Lamb waves is of critical importance for applications such as remaining life prediction of plate‐like structural components. The objective of this work is to use nonlinear Lamb waves to experimentally investigate inherent material nonlinearities in aluminum plates. These nonlinearities, e.g. lattice anharmonicities, precipitates or vacancies, cause higher harmonics to form in propagating Lamb waves.The amplitudes of the higher harmonics increase with increasing propagation distance due to the accumulation of nonlinearity while the Lamb wavetravels along its path. Special focus is laid on the second harmonic, and a relative nonlinearity parameter is defined as a function of the fundamental and second harmonic amplitude. The experimental setup uses an ultrasonic transducer and a wedge for the Lamb wave generation, and laser interferometryfor detection. The experimentally measured Lamb wave signals are processed with a short‐time Fourier transformation (STFT), which yields the amplitudes at different frequencies as functions of time, allowing the observation of the nonlinear behavior of the material.The increase of the relative nonlinearity parameter with propagation distance as an indicator of cumulative second harmonic generation is shown in the results for the alloy aluminum 1100‐H14.
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(2006): Generation and detection of nonlinear Lamb waves for the characterization of material nonlinearities. Thesis. Georgia Institute of Technology. Online verfügbar unter https://smartech.gatech.edu/handle/1853/13986, zuletzt geprüft am 31.03.2023
Abstract: An understanding of the generation of higher harmonics in Lamb waves is of critical importance for applications such as remaining life prediction of plate-like structural components. The objective of this work is to use nonlinear Lamb waves to experimentally investigate inherent material nonlinearities in aluminum plates. These nonlinearities, e.g. lattice anharmonicities, precipitates or vacancies, cause higher harmonics to form in propagating Lamb waves. The amplitudes of the higher harmonics increase with increasing propagation distance due to the accumulation of nonlinearity while the Lamb wave travels along its path. Special focus is laid on the second harmonic, and a relative nonlinearity parameter is defined as a function of the fundamental and second harmonic amplitude. The experimental setup uses an ultrasonic transducer and a wedge for the Lamb wave generation and laser interferometry for detection. The experimentally measured Lamb wave signals are processed with a short-time Fourier transformation (STFT) and a chirplet transformation-based algorithm, which yield the amplitudes of the frequency spectrum as functions of time, allowing the observation of the nonlinear behavior of the material. The increase of the relative nonlinearity parameter with propagation distance as an indicator of cumulative second harmonic generation is shown in the results for two different aluminum alloys. The difference in inherent nonlinearity between both alloys as determined from longitudinal wave measurements can be observed for the Lamb wave measurements, too.
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: Micro Helicopter Steering: Review and Design for the muFly Project: 2008 IEEE/ASME International Conference on Mechtronic and Embedded Systems and Applications: International Conference on Intelligent Robots and Systems: Beijing, 12. - 15. Oktober: 2008, S. 216-221