An adaptive precision ball screw drive concept is presented in which a self-sufficient actuator is able to adjust the axial preload during the operation. The adjustment is effected by thermal shape memory alloy pucks, which either expand or contract according to the surrounding temperature field of the process. For this purpose, no external energy is needed and so the system is self-supported (energy harvesting). In this case, the extrinsic two-way shape memory effect occurs and the reversible full cycle of shape change is accomplished by a bias force of a flexure. Basing on temperature and force measurements on a double nut ball screw, a thermo-mechanical model is developed. Using the investigated principles adaptive mechanisms, a shape memory-based actuator is designed. Initial tests reveal an unwanted reduction of the preload of up to 800 N with rising temperature. Due to the shape memory actuation device, experiments results show an increase in axial load in approximated 70 % of the reduction.
The production of car body panels are defective in succession of process fluctuations. Thus the produced car body panel
can be precise or damaged. To reduce the error rate, an intelligent deep drawing tool was developed at the Fraunhofer
Institute for Machine Tools and Forming Technology IWU in cooperation with Audi and Volkswagen. Mechatronic
components in a closed-loop control is the main differentiating factor between an intelligent and a conventional deep
drawing tool. In correlation with sensors for process monitoring, the intelligent tool consists of piezoelectric actuators to
actuate the deep drawing process. By enabling the usage of sensors and actuators at the die, the forming tool transform to
a smart structure. The interface between sensors and actuators will be realized with a closed-loop control.
The content of this research will present the experimental results with the piezoelectric actuator. For the analysis a
production-oriented forming tool with all automotive requirements were used. The disposed actuators are monolithic
multilayer actuators of the piezo injector system. In order to achieve required force, the actuators are combined in a
cluster. The cluster is redundant and economical. In addition to the detailed assembly structures, this research will
highlight intensive analysis with the intelligent deep drawing tool.
In machine tools several time and position varying heat sources causes complex temperature distributions. The resulting
problems are varying thermal deformations which cause a loss of accuracy as well as non optimal drive conditions. An
option to deal with that issue is to use structure integrated SM-actuators which use the thermal energy accumulated by
machining processes to yield an actuator displacement. That creates a structure inherent control loop. There the shape-memory-
elements work as sensing element as well as actuation element. The plant is defined by the thermal and
mechanical behaviour of the surrounding structure. Because of the closed loop operation mode, the mechanical design
has to deal with questions of stability and parameter adjustment in a control sense. In contrast to common control
arrangements this issues can only be influenced by designing the actuator and the structure.
To investigate this approach a test bench has been designed. The heat is yielded by a clutch and directed through the
structure to the shape memory element. The force and displacement of the actuator are therefore driven directly by
process heat. This paper presents a broad mechanical design approach of the test bench as well as the design of the SM-actuator.
To investigate the thermo-mechanical behaviour of the structure-integrated actuator, a model of the test bench
has been developed. The model covers the thermal behaviour of the test bench as well as the thermo-mechanical
couplings of the shape memory actuator. The model has been validated by comprehensive measurements.
Machine tools for small work pieces are characterized by an extensive disproportion between workspace and cross
section. This is mainly caused by limitations in the miniaturization of drives and guidance elements. Due to their high
specific workloads and relatively small spatial requirements, Shape-Memory-Alloys (SMA) possess an outstanding
potential to serve as miniaturized positioning devices in small machines. However, a disadvantage of known actuator
configurations, such as SMA wire working against a mechanical spring, is that energy is steadily consumed to hold
defined positions. In this paper we present a novel SMA actuator design, which, due to an antagonistic arrangement of
two SMA elements does only require a minimum amount of energy whilst holding position. The SMA actuators were
designed regarding material, geometrical parameters, applied load, and control aspects. Furthermore, closed loop control
concepts for positioning applications are implemented. These not only cover approaches using sensors, but also sensorless
concepts which utilize the distinctive length - resistance - correlation of SMAs for position controlling. Furthermore,
an actuator demonstrator has been used to demonstrate the designs capabilities to serve as miniaturized positioning
device in small machines. In addition the novel design concept of the SMA actuator will be compared with commonly
Proc. SPIE. 7644, Behavior and Mechanics of Multifunctional Materials and Composites 2010
KEYWORDS: Homogenization, Metals, Composites, Structured optical fibers, Computer simulations, Capacitance, Finite element methods, Computed tomography, Microsoft Foundation Class Library, Chemical elements
The behavior of piezo-metal-compounds made of laminar piezo-modules and sheet metal which are formed by
various forming processes is simulated. To evaluate the formability of the piezo-modules strains and stresses
have to be known. Otherwise finite element models with a discretization in the dimension of the piezomaterial
are not suitable for forming simulation concerning the size of the model. The simulation method of unit cells is
used to homogenize the material parameters. In order to achieve the real strains and stresses of the piezomaterial
the strains/stresses obtained with the homogenous material parameters are superimposed with the phase
concentrations from the unit load cases.
As known, the electrical induced strain of conventional piezoceramic materials is limited by 0.12 % (2 kV/mm), which
often requires strain transformation designs, like levers, in order to meet application needs. High fabrication accuracy
and low tolerances are crucial points in mechanical manufacturing causing high device costs.
Therefore, we developed a piezoelectric composite actuator with inherent stress - strain transformation. Basically,
piezoceramic sheets are laminated with spring steel of a certain curvature, which can be realised by a comparatively
simple fabrication technique. The working diagram of these composite bow actuators showed a high level of
performance adaptable to a wide range of applications. The authors established the value chain covering the
piezoceramic formulation, the processing technology and the design in view of optimum system performance.
The paper presents an overview of the design principles, simulation and various aspect of fabrication technology
including lamination, sintering and polarization. The new devices are useable in different sectors, for example in
automotive industry as solid state transducer or as the active part in injectors. Moreover, the composite bow actuators
may find application in microsystems technology, micro optics and micro fluidics as well as vibration dampers. The
composite bow actuators can be used as single component transducer, as well as multi-bow actuator in series or parallel
combination on demand.
This paper reports a study about the possibilities for direct integration of piezo-fibers in sheet metal. In the
Transregional Collaborative Research Centre 39 PT-PIESA "Production Technologies for light metal and fiber
reinforced composite based components with integrated PIEzoceramic Sensorand and Actuators", set up with the
promotion of the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG), effective technologies for
the production of adaptronic components are investigated. One idea is the direct integration of piezo-fibers in sheet
metal like for instance aluminum sheets. A detailed finite-element-model was developed to design a functional part in
the sheet metal by means of directly integrated fibers or micro-structured composite elements. Several versions of
design were investigated. So the geometry of the microstructure, the material parameter and the geometry of the
isolation layer, the piezo-elements and the piezo-mode (d31- or d33-effect) and also the field direction was varied. Two
different designs are promising. The first design is characterized by the usage of the d33-effect across the fiber. The
second promising design is characterized by the use of slotted piezo-fiber-composites.
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).
This paper reports a numerical and experimental study on a new multi mode vibration reduction concept for struts of machine tools or shafts of automotives. The example described in detail validates this new concept for high dynamic parallel kinematic struts. The structural advantages of parallel kinematic mechanisms are undisputed. However statical and dynamical bending and torsional loads must be considered during the design process of the structure and thus effect the shape of the strut geometry. The here described new actuator concept for multi mode vibration reduction is to influence these bending and torsional loads. It uses piezopatches based on the MFC technology licensed by NASA. Initial simulation and experimental tests were done at an one side clamped aluminium beam with applicated 45°-MFC's on both sides. Simulation results show, that driving the piezos in opposite direction leads to a bending deflection of the beam, driving them in the same phase leads to a torsional deflection of the aluminium beam. Experimental measurements confirm the simulation results. The benefit we get is a decreased number of actuators for multimode vibration reduction. Likewise these actuators allow the separation or selective combination of bending and torsion. This new actuation concept is not limited on beams. Further simulations for cylindrical struts result in a design of a MFC-ring with eight segments with changing fiber orientation for separation of bending and torsion on struts and shafts. The selective controlled activation of each of the segments leads to bending in x-direction, bending in y-direction or torsion.
The structural advantages of parallel kinematic mechanisms for highly dynamic motions are undisputed. The mass values to be moved are essentially determined by the structure of the end effector platform. The accuracy of machines with parallel kinematic drive concepts is decisively defined by the joint and feed unit assemblies. Statical (except in hexapods) and dynamical bending and torsional loads limit the shape of the strut geometry. As a rule, an increase in volume to enhance stiffness at the same times results in an increase in weight and thus worse dynamic characteristics. Active compensation and damping elements provide an alternative to passively increasing stiffness by geometries fitted to load. An active compensation of torsion is aimed at achieving a high "virtual" torsional stiffness of the whole drive unit by means of a compensation drive which is based on piezoelectric actuators. The compensation drive works autonomously and measures and corrects the appearing torsional deformation in a self-controlled manner, independent of the end effector platform' s position in the working space adjusting feed units.