### Contents of Journal of Mechanical Engineering 52, 1 (2001)



L. STAREK: Inverse eigenvalue problem in vibration of mechanical
systems (Review paper) (in Slovak)                                         1

B. SAMANTA, K. R. AL-BALUSHI: Use of wavelet transforms and neural
network in gear fault diagnosis                                           21

CZ. J. JERMAK, M. RUCKI: Pneumatic injector as a length measuring
sensor                                                                    32

M. WIECZOROWSKI: Optical followers -- their fidelity in surface
topography measurements                                                   39

I. BALLO: Some remarks on the sky-hook and ground-hook concepts
(Letter to the Editor) (in Slovak)                                        55



# Abstracts

### Inverse eigenvalue problem in vibration of mechanical systems

L. STAREK

This paper reviews recent literature on inverse eigenvalue problem in vibration relating to the reconstruction or estimation of the physical properties of mechanical systems from a knowledge of (some of) their spectral and/or modal data. The review takes into account exclusively linear systems (small vibration of mechanical systems). The paper deals with various types of vibrating systems: continuous and discrete, damped and undamped, the various types of data (spectral and/or modal, complete or incomplete).

### Use of wavelet transforms and neural network in gear fault diagnosis

B. SAMANTA, K. R. AL-BALUSHI

A procedure for fault diagnosis of gears by wavelet transforms and artificial neural network (ANN) is presented. The time domain acoustic emission (AE) signals of a rotating machine with normal and defective gears are processed by wavelet transform and decomposed in terms of low-frequency (approximate) and high-frequency (detailed) components. The extracted features from the wavelet transform are used as inputs to an ANN based diagnostic approach. The ANN is trained using the back-propagation algorithm with a subset of the experimental data for known machine conditions and tested using the remaining set of data. The procedure is illustrated through the experimental acoustic emission signals of a gearbox.

### Pneumatic injector as a length measuring sensor

CZ. J. JERMAK, M. RUCKI

In the article, the new construction of the pneumatic measuring gauge is described. It is based on the injection phenomenon in particular position of the nozzles. Comparing with other injectors it is simple and its static metrological properties are good. Substantial influence on the properties has distance L between nozzles and the angle \alpha between nozzle head surface and its axis. The best metrological characteristics were reached for configuration of L = 4 mm and \alpha \in (-45o, 5o). The usage of pressured air is decreased, too.

### Optical followers - their fidelity in surface topography measurements

M. WIECZOROWSKI

In the paper author presents a comparison analysis of three different probes used for surface topography measurement. Skid and skidless stylus probes were used as contact pick-ups, while an optical autofocussing pick-up was applied as a non-contact one. The analysis was performed using several different topography parameters. It showed that a skid causes some relatively small distortions as far as the surface representation is concerned. On the other hand, the optical probe proved to be a very difficult measuring tool, particularly for surfaces with steep slopes and sharp edges. Yet even for very smooth surfaces a great attention must be paid while measuring with this kind of pick-up is considered.