Holger Hanselka

Development and design of an active work piece holder driven by piezo actuators

The use of piezo actuators in machine tools is a current topic. There are many research works which show the advantages of this kind of actuators in various fields around machining. In this paper an active work piece holder is presented, which is designed for reducing the dynamic displacement between the tool and the work piece relatively. The paper shows the design process for the fixture, the finite element analysis of the mechanical parts and the actuators. Also a specially designed power amplifier is presented which fits best to the needs of voltage and frequency range of the active work piece holder. First experimental results are shown.

Development and design of flexible Fowler flaps for an adaptive wing

Civil transport airplanes fly with fixed geometry wings optimized only for one design point described by altitude, Mach number and airplane weight. These parameters vary continuously during flight, to which means the wing geometry seldom is optimal. According to aerodynamic investigations a chordwide variation of the wing camber leads to improvements in operational flexibility, buffet boundaries and performance resulting in reduction of fuel consumption. A spanwise differential camber variation allows to gain control over spanwise lift distributions reducing wing root bending moments. This paper describes the design of flexible Fowler flaps for an adaptive wing to be used in civil transport aircraft that allows both a chordwise as well as spanwise differential camber variation during flight. Since both lower and upper skins are flexed by active ribs, the camber variation is achieved with a smooth contour and without any additional gaps.

Transient simulation of adaptive structures

This paper examines an approach used to design adaptive systems by means of Rapid-Prototyping on the basis of a simulation. The vibration behavior of mechanical systems including actuators, sensors, and an adaptive controller in the time domain will be modeled. This approach includes the calculation of the dynamic behavior of the mechanical structure with the help of the Finite Element Method (FEM). The FE model of the mechanical structure is transformed into modal space, then reduced and embedded as a state-space model in the MATLAB/Simulink environment. Thereby, a simple mechanical problem is solved analytically with the FEM as well as with the reduced MATLAB model. The comparison of the results shows a good agreement. Actuators and sensors are attached to the mechanical structure. Based on the resulting dynamical behavior of the mechanical structure, an adaptive control algorithm for the reduction of structural vibration is developed. Experimental tests are performed to verify and update the simulations. The hardware-in-the-loop simulations are carried out with a dSpace system. Some differences (with respect to speed-up, precision) between this simulation and other methods are presented later in the paper. This procedure allows the development and the evaluation of more complex adaptive mechanical structures.

> Elektromobilität — Elemente, Herausforderungen, Potenziale

Begrenzte Ressourcen, die CO2-Debatte und der Schutz unserer Umwelt sind beherrschende Themen in der offentlichen Diskussion. Es ist mittlerweile Konsens, dass der effiziente Umgang mit Energie eine der vordringlichsten Herausforderungen der Zukunft darstellt.

Uncertainty in loading and control of an active column critical to buckling

Buckling of load-carrying column structures is an important design constraint in light-weight structures as it may result in the collapse of an entire structure. When a column is loaded by an axial compressive load equal to its individual critical buckling load, a critically stable equilibrium occurs. When loaded above its critical buckling load, the passive column may buckle. If the actual loading during usage is not fully known, stability becomes highly uncertain. This paper presents an approach to control uncertainty in a slender flat column structure critical to buckling by actively sta- bilising the structure. The active stabilisation is based on controlling the first buckling mode by controlled counteracting lateral forces. This results in a bearable axial compressive load which can be theoretically almost three times higher than the actual critical buckling load of the considered system. Finally, the sensitivity of the presented system will be discussed for the design of an appropriate controller for stabilising the active column.

Automated Structural Integrity Monitoring Based on Broadband Lamb Wave Excitation and Matched Filtering

This paper discusses a structural health monitoring procedure for locating damage in plate-like structures. The concept is based on the propagation of Lamb waves which are excited and received by surfacemounted piezoelectric transducers. In an initial approach, narrowband burst signals can be used to excite the Lamb waves. This methodology is very widespread in the literature and has been adapted in most papers. However, noise, dispersion, and multiple reflections caused by damage make signal analysis very complex in this case. A new excitation and signal processing method is proposed here. This method is based on broadband excitation in conjunction with matched filtering, a method which is very common in radar technology. It can be used to enhance the signalto-noise ratio and makes the test method more stable and reliable. After a short description of the basic idea of this method experimental results are described that confirm this approach.

Festigkeitskonzepte für schwingbelastete geschweißte Bauteile

Kurzfassung Für die schwingfeste Bemessung von Schweißverbindungen an Stahl- oder Aluminiumstrukturen behauptet sich in jüngster Zeit das Kerbspannungskonzept zunehmend gegenüber den traditionell angewendeten Nenn- und Strukturspannungskonzepten. Insbesondere bei der Anwendung des Kerbspannungskonzeptes auf Schweißverbindungen von dünnen Blechen mit dem Referenzradius rref = 0,05 mm zeigen sich vielfältige Einflussfaktoren auf die Bemessungswöhlerlinie, welche durch Größeneinflüsse erklärt werden können.

Approach for a Consistent Description of Uncertainty in Process Chains of Load Carrying Mechanical Systems

Uncertainty in load carrying systems e.g. may result from geometric and material deviations in production and assembly of its parts. In usage, this uncertainty may lead to not completely known loads and strength which may lead to severe failure of parts or the entire system. Therefore, an analysis of uncertainty is recommended. In this paper, uncertainty is assumed to occur in processes and an approach is presented to describe uncertainty consistently within processes and process chains. This description is then applied to an example which considers uncertainty in the production and assembly processes of a simple tripod system and its effect on the resulting load distribution in its legs. The consistent description allows the detection of uncertainties and, furthermore, to display uncertainty propagation in process chains for load carrying systems.

Adaptronics as a Key Technology for Intelligent Lightweight Structures

Adaptronics is a new and highly innovative technology in mechanical engineering. The main objectives are active noise and vibration control, active form and positioning control, and health monitoring. This concept starts from the development of adaptive systems which, due to their self-regulating mechanisms, are able to self-adapt to different external conditions. This requires a system-optimized linking of sensors and actuators on the basis of new functional materials, such as piezoceramic fibers and patches with adaptive controllers. Adaptronic structures fulfill both load-bearing and actuator] sensor functions and, hence, are multifunctional. Therefore, adaptronics will become an essential prerequisite for further development of ultralight structures.

THE 'PROMISE' OF SMART MATERIALS FOR SMALL SATELLITES

Abstract In this paper the potential use of ‘smart’ materials to improve the performance and cost efficiency of small satellites is introduced. The basic operating performance of the structural smart materials are reviewed as are some of the foreseen application areas. The state of the art in applying smart materials for use in space is then discussed with a focus on areas where information is lacking. A series of actions to alleviate these shortcomings are proposed and some current activities of the DLR-Institute of Structural Mechanics to answer these calls for action are highlighted.