Tuned vibration absorbers have become common for passive vibration reduction in many industrial applications. Lightly damped absorbers (also called neutralizers) can be used to suppress narrowband disturbances by tuning them to the excitation frequency. If the resonance is adapted in-operation, the performance of those devices can be significantly enhanced, or inertial mass can be decreased. However, the integration of actuators, sensors and control electronics into the system raises new design challenges. In this work, the development of adaptive-passive systems for vibration reduction at an industrial scale is presented. As an example, vibration reduction of a ship engine was studied in a full scale test. Simulations were used to study the feasibility and evaluate the system concept at an early stage. Several ways to adjust the resonance of the neutralizer were evaluated, including piezoelectric actuation and common mechatronic drives. Prototypes were implemented and tested. Since vibration absorbers suffer from high dynamic loads, reliability tests were used to assess the long-term behavior under operational conditions and to improve the components. It was proved that the adaptive systems are capable to withstand the mechanical loads in an industrial application. Also a control strategy had to be implemented in order to track the excitation frequency. The most mature concepts were integrated into the full scale test. An imbalance exciter was used to simulate the engine vibrations at a realistic level experimentally. The neutralizers were tested at varying excitation frequencies to evaluate the tracking capabilities of the control system. It was proved that a significant vibration reduction is possible.
In many applications, kinematic structures are used to enable and disable degrees of freedom. The relative movement between a wheel and the body of a car or a landing gear and an aircraft fuselage are examples for a defined movement. In most cases, a spring-damper system determines the kinetic properties of the movement. However, unexpected high load peaks may lead to maximum displacements and maybe to locking. Thus, a hard clash between two rigid components may occur, causing acceleration peaks. This may have harmful effects for the whole system. For example a hard landing of an aircraft can result in locking the landing gear and thus damage the entire aircraft. In this paper, the potential of adaptive auxiliary kinematic guidance elements in a spring-damper system to prevent locking is investigated numerically. The aim is to provide additional forces in the auxiliary kinematic guidance elements in case of overloading the spring-damper system and thus to absorb some of the impact energy. To estimate the potential of the load redistribution in the spring-damper system, a numerical model of a two-mass oscillator is used, similar to a quarter-car-model. In numerical calculations, the reduction of the acceleration peaks of the masses with the adaptive approach is compared to the Acceleration peaks without the approach, or, respectively, when locking is not prevented. In addition, the required force of the adaptive auxiliary kinematic guidance elements is calculated as a function of the masses of the system and the drop height, or, respectively, the impact energy.
One of the main technical challenges in the development of dielectric elastomer (DE) stack actuators is
the design and realization of suitable electrodes. They must be compliant and be able to undergo large
strains without adding too much stiffness. Metal electrodes are therefore normally out of question due to
their high stiffness, though their electrical properties are excellent. In this work a new design approach is
presented which comprises rigid metal electrodes. Its functionality is proven by means of numerical simulations
and experimental tests. It allows the customized tailoring of transducer elements due to the designable
electrode structure. A functional demonstrator is built and tested concerning its electrical, mechanical and
electromechanical behavior. For this new actuator type a full electromechanical model is developed. It contains
all transfer characterisitcs in a nonlinear description and accounts for various physical effects arising from the
special actuator design. Due to its standardized interface configuration it can well be used in combination
with existing models for mechanical structures and electrical amplifiers to completely model active systems.
It is applicable for the realistic simulation necessary in the development of active solutions with EAP devices.
A first longterm test with 108 load cycles was performed in order to show the durability of the actuator.
Dielectric elastomers (DE) have proved to have high potential for smart actuator applications in many laboratory
setups and also in first commercially available components. Because of their large deformation capability
and the inherent fast response to external stimulation they proffer themselves to applications in the field of
active vibration control, especially for lightweight structures. These structures typically tend to vibrate with
large amplitudes even at low excitation forces. Here, DE actuators seem to be ideal components for setting up
control loops to suppress unwanted vibrations. Due to the underlying physical effect DE actuators are generally
non-linear elements with an approximately quadratic relationship between in- and output. Consequently,
they automatically produce higher-order frequencies. This can cause harmful effects for vibration control on
structures with high modal density. Therefore, a linearization technique is required to minimize parasitic
effects. This paper shows and quantifies the nonlinearity of a commercial DE actuator and demonstrates the
negative effects it can have in technical applications. For this purpose, two linearization methods are developed.
Subsequently, the actuator is used to implement active vibration control for two different mechanical
systems. In the first case a concentrated mass is driven with the controlled actuator resulting in a tunable
oscillator. In the second case a more complex mechanical structure with multiple resonances is used. Different
control approaches are applied likewise and their impact on the whole system is demonstrated. Thus, the
potential of DE actuators for vibration control applications is highlighted.
The focus of this paper is on the modeling of dielectric elastomer actuators and generators. One of the effects
that is rarely considered in modeling of these systems is the influence of the materials' specific resistance on the
performance. The non-ideal electrical properties of both elastomer and electrode material will cause undesired
parasitic effects. Although for most laboratory scale prototypes these effects are hardly recognizable, they
may however play an important role for larger structures and especially for dynamic applications. Therefore,
an analytical model is developed and presented in this paper which can give helpful instructions for the design
and fabrication process of EAP-systems. It is proven to be valid by means of the finite element method and
subsequently extended for more complex systems.
The mission of the Fraunhofer Gesellschaft, one of the biggest research facilities in Germany, is to identify technologies with a high impact potential for commercial applications and to take all necessary steps to successfully promote them by performing cooperative industrial research activities. One of these technologies is called smart structures, also known as adaptive structures. Most recently, Fraunhofer decided to strategically extend its portfolio to include this technology and summarize its R&D activities in the FIT (Fraunhofer Innovation Topics) ADAPTRONIK. To improve Fraunhofer's competencies in adaptronics, especially with respect to system design and implementation, the Fraunhofer internal project MAVO FASPAS was launched in 2003. Now, after 3 years of work, the project comes to a close. This article discusses some major project results.
The Fraunhofer Gesellschaft is the largest organization for applied research in Europe, having a staff of some 12,700, predominantly qualified scientists and engineers, with an annual research budget of over one billion euros. One of its current internal Market-oriented strategic preliminary research (MaVo) projects is FASPAS (Function Consolidated Adaptive Structures Combining Piezo and Software Technologies for Autonomous Systems) which aims to promote adaptive structure technology for commercial exploitation within the current main research fields of the participating FhIs, namely automotive and machine tools engineering. Under the project management of the Fraunhofer-Institute Structural Durability and System Reliability LBF the six Fraunhofer Institutes LBF, IWU, IKTS, ISC, AiS and IIS bring together their competences ranging from material sciences to system reliability, in order to clarify unanswered questions. The predominant goal is to develop and validate methods and tools to establish a closed, modular development chain for the design and realization of such active structures which shall be useful in its width and depth, i.e. for specific R&D achievements such as the actuator development (depth) as well as the complete system design and realization (width). FASPAS focuses on the development of systems and on the following scientific topics: 1) on design and manufacturing technology for piezo components as integrable actuator/sensor semi-finished modules, 2) on development and transducer module integration of miniaturized electronics for charge generating sensor systems, 3) on the development of methods to analyze system reliability of active structures, 4) on the development of autonomous software structures for flexible, low cost electronics hardware for bulk production and 5) on the construction and validation of the complete, cost-effective development chain of function consolidated structures through application oriented demonstration structures. The research work will be oriented towards active vibration control for existing components on the basis of highly integrated, both, more or less established and highly innovative piezoelectric actuator and sensor systems in compact, cost-effective and robust design combined with advanced controllers. Within the presentation the project work will be shown using the example of one demonstration structure which is a robust interface, here for being integrated within an automotive spring strut system. The interface is designed as a modular, scalable subsystem. Being such, it can be used for similar scenarios in different technology areas e.g. for active mounting of vibration-inducing aggregates. The interface design allows for controlling uniaxial vibrations (z-direction) as well as tilting (normal to the uniaxial effect) and wobbling (rotating around the z-axis).