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Published Articles


The Volume 12, No 4, December 2007




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On the Development of a Simple and Robust Active Control System for Boring Bar Vibration in Industry

Henrik Akesson, Tatiana Smirnova, Ingvar Claesson and Lars Haykansson


https://doi.org/10.20855/ijav.2007.12.4216


Vibration in internal turning is a problem in the manufacturing industry. A digital adaptive controller for the active control of boring bar vibration may not be a sufficient solution to the problem. The inherent delay in a digital adaptive controller delays control authority and may result in tool failure when the load applied by the workpiece on the tool changes abruptly, e.g. in the engagement phase of the cutting edge. A robust analog controller, based on a lead-lag compensator, with simple adjustable gain and phase, suitable for the industry application, has been developed. Also, the basic principle of an active boring bar with embedded actuator is addressed. The performance and robustness of the developed controller has been investigated and compared with an adaptive digital controller based on the feedback filtered-x algorithm. In addition, this paper takes into account those variations in boring bar dynamics which are likely to occur in industry; for example, when the boring bars is clamped in a lathe. Both the analog and the digital controller manage to reduce the boring bar vibration level by up to approximately 50 dB.


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Parametric Instability of a Pretwisted Cantilever Beam with Localised Damage

S. C. Mohanty


https://doi.org/10.20855/ijav.2007.12.4217


In the present work the effects of a localised damage on the dynamic stability of a pretwisted cantilever beam subjected to a time-dependent conservative end axial force is studied. The effects of parameters like the pretwist angle, the extent of damage, position of the damage and static load factor are studied. Three parameters are used to characterise the damaged region: location, size, and effective stiffness of the damaged region. Euler beam theory is used in the analysis. From the study it is revealed that angle of pretwist has significant effect on second and third instability zones. Increase in pretwist angle has a stabilising effect on the third instability zone and destabilising effect on the second instability zone. Variation in pretwist angle does not have significant effect on the first instability region. Extent of damage has always a destabilising effect for any pretwist angle. Localised damage has a greater destabilising effect when it is located near the fixed end than when it is towards the free end, irrespective of the pretwist angle. Increase in static load component has a destabilising effect irrespective of the value of pretwist angle.


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Experimental Analysis of Near-Field Acoustic Scattering by Rigid Spheroidal Objects

Constantine M. Tarawneh, John P. Barton


https://doi.org/10.20855/ijav.2007.12.4218


Numerous theoretical models have been developed to predict acoustic scattering by objects of various shapes, but experimental verification of these models has been scarce and limited to objects of simple geometry. Therefore, a special anechoic chamber was designed and built to study the steady-state near-field acoustic scattering by rigid spheroids. Five spheroidal objects were fabricated out of a starch powder held together by a cellulose binder (p = 1039 +- 1% kg/m3 at 20 C). The objects created are a sphere, a 2:1 prolate spheroid, a 2:1 oblate spheroid, a 5:1 prolate spheroid, and a 5:1 oblate spheroid, all having a major-axis length of about 12.9 cm. Spheroidal size parameters (h) in the range of about 10 to 20 were studied. A super-tweeter was selected as the sound source in the acoustic scattering experiments, and a 3 mm condenser microphone was used to scan the scattered sound in front and behind the five objects. The resultant experimental acoustic pressure profiles were compared to the theoretical predictions. A major contribution of this study are the experimental relative phase angle profiles which, along with the pressure profiles, offer more information about the acoustic scattering trends of rigid spheroids.Numerous theoretical models have been developed to predict acoustic scattering by objects of various shapes, but experimental verification of these models has been scarce and limited to objects of simple geometry. Therefore, a special anechoic chamber was designed and built to study the steady-state near-field acoustic scattering by rigid spheroids. Five spheroidal objects were fabricated out of a starch powder held together by a cellulose binder (p = 1039 +- 1% kg/m3 at 20 C). The objects created are a sphere, a 2:1 prolate spheroid, a 2:1 oblate spheroid, a 5:1 prolate spheroid, and a 5:1 oblate spheroid, all having a major-axis length of about 12.9 cm. Spheroidal size parameters (h) in the range of about 10 to 20 were studied. A super-tweeter was selected as the sound source in the acoustic scattering experiments, and a 3 mm condenser microphone was used to scan the scattered sound in front and behind the five objects. The resultant experimental acoustic pressure profiles were compared to the theoretical predictions. A major contribution of this study are the experimental relative phase angle profiles which, along with the pressure profiles, offer more information about the acoustic scattering trends of rigid spheroids.


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Non-singleton Fuzzy Sets for Disturbance Attenuation

Andras Simon and George T. Flowers


https://doi.org/10.20855/ijav.2007.12.4219


Active magnetic bearings provide non-contact levitation of a ferromagnetic object with controllable damping and spring constant. These nonlinear systems require active control, as the electromagnetic levitation is unstable by nature. Linear control methods have limited success in the face of such a typically nonlinear system and the presence of modelling inaccuracies often force one to consider other control strategies. Fuzzy logic control performs very well in nonlinear control situations where the plant parameters are either partially or mostly unidentified. Its effectiveness for nonlinear systems also offers advantages to magnetic bearing systems. Uncertainties originate from several sources in the fuzzy logic controller, ranging from rule definitions to shape and location of the membership functions as well as unreliable input measurements. Non-singleton fuzzy set inputs allow one to account for input measurement uncertainty due to noise and other disturbances. The current work consists of model development, controller design, simulation and experimental validation. The controller designs are implemented and tested using a bench-top rotor rig equipped with a rotor supported by a radial magnetic bearing. Some representative results are presented and discussed.


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