Defect Diagnosis for Rolling Element Bearings Using Acoustic Emission

Rolling element bearings are very common components in rotating machinery. Hence, condition monitoring and the detection of defects are very important for the normal and safe running of these machines. Vibration based techniques are well established for the condition monitoring of rolling element bearings, although they are not so effective in detecting incipient defects in the bearing. Acoustic emission (AE) is receiving increasing attention as a complementary method for condition monitoring of bearings as AE is very sensitive to incipient defects. This paper presents an experimental study to investigate the AE characteristics of bearing defect and validates the relationship between various AE parameters and the operational condition of rolling element bearings. To analyze the characteristic vibration frequency of the bearing using the AE signal, short-time rms and autocorrelation functions are integrated to extract the actual characteristic frequency. The AE signal is then analyzed using standard parameters of the signals to explore the source characteristics and sensitivity of typical rolling element bearing faults. The results demonstrate that the proposed method is very effective to extract the actual characteristic frequency of the bearing by AE signal. Furthermore the AE parameters are always sensitive to the running and fault conditions, which have a strong influence on the strain and deformation within the bearing material.

“Etymologia Est Origo Vocabulorum…”

Summary The study wants to contribute to the explication of Isidore of Sevilla’s conception of etymology starting with the definition “Etymologia est origo vocabulorum, cum vis verbi vel nominis per interpretationem colligitur” (Etym. I, xxix, 1). At first sight the problem of interpretation results from the contradiction between the static character of the principal clause (est origo)and the dynamic character of the subordinate clause (colligitur). This contradiction is resolved in favour of the dynamic aspect by changing origo into originatio on the basis of a teleological and historical interpretation. In a second step, an attempt has been made to arrive at a comprehensive assessment of the definition by interpreting the constituents of the subordinate clause and by defining its relation with the principal clause. The first question concerns the function of the conjunction cum (the hypothesis of a conditional nexus is rejected from the first); in the course of the examination of this problem the constituents of the subordinate clause are analyzed (in particular interpretatio and vis). As to interpretatio it is shown that it corresponds to the justification of the origo (“Stellae dictae a stando, quia fixae stant in caelo nec cadunt”); vis is then described as a relational notion that is defined by the relation between the semantic contents of the origo and an actual characteristic property of the thing. Finally an examination of Isidore’s actual proceeding demonstrates that the knowledge of vis results immediately from the knowledge of the origo (originatio) and the interpretatio. Consequently, the conjunction cum can be defined as cum coincidens.