a b s t r a c tIn this study, we present an algorithm for the dynamic modeling of an excavator equipped with bucket wheels, which is used for surface mining activities. To develop a dynamic model of the excavator while working, we used data from the design theme, which described the mass distribution and elasticity of the technological system. During technological tests, the signals for vibrations and mechanical stresses were recorded in critical areas of the excavator structure. These records contained some modal information, which was also used to develop a simplified dynamic model. We also measured the elasticity of the thrust ball bearing, which is an oscillatory bearing and one of the most heavily loaded components in the excavator's structure. Finally, using the dynamic model, we calculated the natural frequencies for the principal subassemblies of excavator, where the modal frequencies obtained by the sensors while the excavator was running confirmed the good approximation of the model.

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Paper presents results of experimental research for the electricaldischarge processing machines efficiency improvement, machines which are using as electrode a wire, abbreviated W-EDM. These machines were equipped with special devices for the ultrasonic activation of the wire electrode. It was noticed that the introduced ultrasound influenced the erosive capacity of the machining process. The paper presents in graphical and tabular forms, the variation of erosive capacity due to the way how the ultrasonical activation of the wire electrode is produced: into the fixed or mobile arm (two subassemblies of the W-EDM machine), after a direction parallel or perpendicular to the direction of the working advance.

The paper presents the vibration control for two air compressors used in tandem to an oxygen generating station. The compressors are identical in terms of constructive and functional properties, and are both located on similar foundations. Each compressor is supported on a foundation made from one massive block of concrete, provided with some elastic and damping parts. This anti vibrating structure insulates the machines compared to other station equipment. During operation, were observed dangerous levels of vibration at one of the machines, which forced some unwanted stoppages for the station. Two hypotheses have been promoted. One of them referred to a pronounced wear of one compressor, although this was relatively new. The second hypothesis has taken in consideration the appearance of some cracks in the foundation massive concrete block. Experimental research conducted on the spot led to the identification of some errors done at foundation fabrication. The experimental results and some theoretical investigations are presented in this paper.