Jens Strackeljan

Feasibility of Computer-assisted Recognition of Different Dental Hard Tissues

For pattern recognition, fuzzy set theory has been proven to be highly useful. The aim of the present investigation was to combine the fuzzy set with an ultrasonic scaler, to test its suitability for automatic detection of different tooth substances. An experienced operator placed the tip of a piezoceramic ultrasonic scaler on a tooth, thereby inducing oscillations in the contact area around the ultrasonic tip. Each surface showed a characteristic oscillatory behavior in the immediate vicinity of the tip. The oscillations were then re-transmitted to the scaler tip and recorded by the measurement of variations in current and voltage. Because the ultrasonic scaler is driven by piezoceramics, it can be used as both an oscillatory excitation and a sensor system. The data were processed with Fast Fourier transformation and analyzed by means of a fuzzy pattern recognition algorithm. Re-classification of the different measurements was carried out by the experienced operators assessment. With a combination of six features (frequencies), re-classification was correct for 99% of all surfaces. The diagnostic reliability of the system was tested by the assessment of 50 teeth for which no learning data had previously been recorded. The unknown samples were correctly classified to 100%. The excellent results of these experiments suggest promising possibilities for the implementation of new diagnostic and therapeutic instruments in periodontology practice.

Fuzzy-pattern recognition for automatic detection of different teeth substances

Abstract A method for characterizing the surface of a test object on the basis of its oscillatory behaviour is presented. The basic principle of the method is the excitation of oscillations in a small surface element on the elastic solid under investigation and the appropriate measurement of the reaction to this excitation. After calculation of the Fourier transform, a total of 400 magnitude values of the oscillation are available as characteristic features for the classification of an unkown surface. For testing the measuring system experiments were conducted on various test objects and the results of measurements performed on different tooth surface are presented. The automatic classification of tooth surface is important for the detection of the cementoenamel junction in parodontological practice and the soft removal of dental calculus. Because in this application the spectra are subject to severe fluctuations by variations in the test object a fuzzy classifier with weighted distance function is employed for the automatic classification. For solving the essential problem of selecting from a total of 400 spectral features those which appear to be suited for the respective classification problem, a new feature selection algorithm is presented. The highly successful result of these experiments indicates possibilities of applying new diagnostic and therapeutic instruments in the field of periodontology.

Implicit Geometry Meshing for the simulation of Rotary Friction Welding

Abstract The simulation of Rotary Friction Welding (RFW) is a challenging task, since it states a coupled problem of phenomena like large plastic deformations, heat flux, contact and friction. In particular the mesh generation and its restoration when using a Lagrangian description of motion is of significant severity. In this regard Implicit Geometry Meshing (IGM) algorithms are promising alternatives to the more conventional explicit methods. Because of the implicit description of the geometry during remeshing, the IGM procedure turns out to be highly robust and generates spatial discretizations of high quality regardless of the complexity of the flash shape and its inclusions. A model for efficient RFW simulation is presented, which is based on a Carreau fluid law, an Augmented Lagrange approach in mapping the incompressible deformations, a penalty contact approach, a fully regularized Coulomb-/fluid friction law and a hybrid time integration strategy. The implementation of the IGM algorithm using 6-node triangular finite elements is described in detail. The techniques are demonstrated on a fairly complex friction welding problem, demonstrating the performance and the potentials of the proposed method. The techniques are general and straight-forward to implement, and offer the potential of successful adoption to a wide range of other engineering problems.

Influence of Bearing Geometry of Automotive Turbochargers on the Nonlinear Vibrations During Run-Up

This paper deals with the simulation of turbochargers run-up behaviour. To predict the main design criterions for turbocharger applications like vibrations, friction power loss, minimal gap etc. a detailed and efficient computation is needed. The rotor dynamic simulation of the turbocharger is, due to the nonlinearities resulting from the oil-film, interacting with rotor shaft bending, done within an appropriate multibody simulation. By reason of turbines high rotational speed full-floating-rings are used to reduce the oil velocity gradient in the fluid-films. The bearings are modeled based on a transient numerical solution of Reynolds’ equation at each step of time integration. The pressure distribution can be affected by geometrical modifications like annular grooves in the full-floating-rings. The effect of these changes on the run-up behaviour of an automotive turbocharger is being studied. In addition the cause of jumps between subsynchronous vibrations will be shown for an explicit turbocharger.

A novel drive option for piezoelectric ultrasonic transducers

This paper concentrates on ultrasonic transducers, which are driven by piezoelectric ceramic rings that are arranged in a stack. A novel drive option, where the stack contains a new type of divided piezoelectric rings, is analyzed using the finite element method, prototyped, and tested. To gain a better sense of the vibration behavior, the studies focus initially on one ring and subsequently on the different possibilities to assemble the transducer. The investigations point out that natural bending frequencies can be excited at the transducer. Thus, multiple vibration directions of the tip can be controlled, what can be advantageous for instance in dental applications.

Validation of Simulation Models without Knowledge of Parameters Using Differential Algebra

This study deals with the external validation of simulation models using methods from differential algebra. Without any system identification or iterative numerical methods, this approach provides evidence that the equations of a model can represent measured and simulated sets of data. This is very useful to check if a model is, in general, suitable. In addition, the application of this approach to verification of the similarity between the identifiable parameters of two models with different sets of input and output measurements is demonstrated. We present a discussion on how the method can be used to find parameter deviations between any two models. The advantage of this method is its applicability to nonlinear systems as well as its algorithmic nature, which makes it easy to automate.

Experimental identification of flow properties of a S355 structural steel for hot deformation processes

A major issue in modeling the dynamics of hot deformation processes is the proper definition of the constitutive law and, therewith, the identification of material parameters. Popular approaches in relating the stress and strain rate values are equations for the power-law and the power-law breakdown regimes. The material parameters of these two models are basically described by a temperature-dependent absolute value, for example, a flow stress, and a strain rate sensitivity being often referred to as power-law exponent or ductility of the material. The current contribution addresses the experimental identification of these two parameters of a S355 structural steel by an innovative testing program on a Gleeble 3500 testing environment. This allows the identification of the hot deformation parameters for a range of temperatures by only one test with varying temperatures. Furthermore, an extrapolation technique is proposed to capture higher strain rate regimes, as occurring in hot deformation processes. A specific application of the material data on basis of a simulated friction welding process demonstrates the scope of the acquired material parameters and concludes the findings of this article.

NECESSARY CONDITIONS OF STABILITY MOVING PARTS OF ROTOR CENTRIFUGE

Design features of modern centrifuges studied. Revealed that their rotors are movable elements that revolve around horizontal axes. The dynamics of these moving parts of laboratory centrifuge considered. Using the Lagrange equation of the second kind the resulting differential equations of their motion considered. The modeling visualization of motion using the software package RecurDyn was made. The results that obtained by the research package RecurDyn and analytically showed that their motion can be unstable in the positions that are optimal in terms of the technological process. The differential equation can be not integrated in elementary functions, so direct analysis of movement is difficult. As a result of this stability conditions for motion with linear approximation investigated. Necessary conditions for stability of motion required of the design obtained.

SIMULATION UND BEWERTUNG DES DYNAMISCHEN VERHALTENS EINES PIEZOELEKTRISCHEN ULTRASCHALLWANDLERS

In diesem Beitrag wird das dynamische Verhalten eines piezoelektrisch angetriebenen Ultraschallwandlers untersucht. Speziell wird ein Langevin-Schwinger betrachtet. Dessen typische Geometrie wird mechanisch manipuliert, um die Arbeitsspitze des Systems zu Schwingungen auserhalb ihrer Langsebene anzuregen. Die Schwingungen des Systems werden mittels einer 3D-FEM Simulation berechnet und hinsichtlich einer spateren Optimierung bewertet. Das Ziel ist es, eine optimale Losung zu erarbeiten, bei der die Arbeitsspitze in moglichst vielen Raumrichtungen schwingt. This paper concentrates on the dynamic behavior of a piezoelectric driven ultrasonic transducer. The studies focus specifically on the Langevin-type transducer that is known to oscillate in one vibration direction. The typical geometry is manipulated mechanically and the vibrations of the system are simulated by means of a 3D-FEM analysis. The results are evaluated with regard to a subsequent optimization. The aim is to work out an optimal system configuration, where the application tip oscillates in multiple spatial directions.