Solid State Phenomena Vol. 144

Abstract: Haptic interfaces that represent force and tactile feeling have been utilized in the areas of telemanipulation, interaction with microscale and nanoscale phenomena, and medical training and evaluation, to mention only some applications. A multi-fingered haptic interface has greater potential for these kinds of applications than does a singlepoint haptic interface. We developed a five-fingered haptic interface robot named HIRO II, which consists of a hand with 15 dof and an arm with 6 dof. The following research issues are presented: the design method of mechanism, an interface control that takes the redundancy of the mechanism into consideration, physical simulation including frictional force and moment, a haptic rendering with a deformable object, the system architecture and two application systems--a future science encyclopedia and a VR breast palpation system.

Abstract: Well-established procedures exist to monitor and diagnose fairly severe problems with rotating machinery but little progress has been made in developing techniques to detect subtle changes in machine condition for both improved diagnostics, and to develop prognostic procedures for determining remaining service life. Of all machine faults, crack initiated problems present probably the most significant safety and loss hazard in modern turbomachinery, including aircraft engines and power generation units. Different approaches are used to model, detect, and localize crack-induced damage in rotating structures. This paper presents novel application of active magnetic bearings (AMBs) for on-line rotor crack detection. AMB-actuators provide convenient means to apply a broad spectrum of known dynamic forces and monitor responses in a rotor-bearing system, which facilitates more sensitive and precise diagnostics. The paper presents theoretical modeling and description of the experimental facility for proof-of-concept testing.

Abstract: Analysis of robustness of active magnetic bearing system is carried out in the paper. All of the most important acceptable levels of robustness are established. Rigid body model of a rotor is used for controller design, stability and analysis of robustness. Advanced tools for robust control are applied. The μ-synthesis is used to design a μ robust controller to stabilize the shaft that is supported magnetically. The influence of robust control on the sensitivity of plant with an uncertainty dynamics is shown. The influence of dynamic uncertainty on the robustness level of closed-loop system is considered. Small gain theorem and robustness theorem for an active magnetic bearing are investigated. Finally, the experimental results confirm the analytical investigations of the robust control of vibrations.

Abstract: Stabilization of a plant in case of uncertainty parameters and unmodeled dynamics are the main problems considered in this paper. A robust control of motion of a rigid shaft that is supported by magnetic bearings was used as an example. The dynamics of the active magnetic suspension system is characterized by instability and uncertainty. The uncertainty is modeled as an additive and multiplicative. Robust controller H∞ was designed for the defined plant with the uncertainty models. The robust controller assures high quality of control despite the uncertainty models. Robust control of vibrations of a rigid rotor is confirmed by experimental studies. A digital signal processor is used to execute the control algorithm in real time.

Abstract: Fluoride release from composite materials for dental fillings depending on the type of powder filler and dynamical loading is the main problem considered in the paper. The fillers used for research were fluoridated glass (based on Ba-Sr-Al-P-Na-silicate glass), ytterbium fluoride (YbF3) as a fluoride source and nanosilica. In order to estimate the influence of the usage loading value on fluoride release from analyzed samples, the wear tests were carried out by means of special tribotester in presence of phosphate buffer as a lubricant. After friction processes the fluoride release tests were performed in phosphate buffer using direct potentiometry method with fluoride selective electrode. The fluoride emission was analyzed on the basis of: 1) type and amount of fillers powder, 2) using loading. Surface roughness was also investigated. The surface of each composite was analyzed by means of SEM.

Abstract: The aim of this study was to determine the influence of powder fillers on the tribological properties of composite materials used for dental fillings. The investigated composites contain a fluoridated filler (based on Ba-Sr-Al-P-Na-silicate glass fillers) as a fluoride source as well as different powder fillers (friction modifiers) e.g. silicon nitride (Si3N4), boron nitride (BN), polyethylene (PE), polytetrafluoroethylene (PTFE). Composite disks were photo-cured and tested for wear against harder stainless-steel counterface. Wear tests were carried out by means of special tribotester in the presence of phosphate buffer as a lubricant. Influence of the load and filler contents on the friction coefficients and wear were estimated. The interaction between the filler particles and organic matrix and its influence on the tribological behavior of prepared specimens were observed. Organic powder fillers (PE, PTFE) reduced the friction coefficient and the wear of tested composite materials for dental fillings. Inorganic friction modifiers (Si3N4, BN) did not exhibit this effect.

Abstract: The paper describes a method of analytic description of impulse response (IR) signals obtained during the test of technical object. The proposed description is based on the curve fitting to obtain the values of the parameters of analytic form of auto-correlation and power spectral density function. The impulse excitation is given into thoroughly described points of object and the proper fragment of IR is selected in the order to assure the accuracy of the curve fitting over the level of 90%. This approach enables to describe changes of IR signals in the form of percentage variations in the parameters of the auto-correlation and power spectral density function (e.g. changes from the object damage).

Abstract: A focus of the paper is concerned with the issue that optimal actions of regulation, diagnostics and reliability tests of technical objects are required from the maintenance staff involved in their use and servicing, and on the other hand, that they are performed independently and autonomously in the current maintenance practice instead of being accomplished in a strictly coordinated and complex way. It was noticed that only one and common information on the object exists and provides a solid basis for coordination of the regulation, diagnostics and reliability tests. This information can be applied many times for solving various problems no matter if they concern regulation, diagnostics or reliability. Next, this paper presents an original approach of conversion of the considered information into explicit time-and-space determined “number of threshold value overshoots” of signals related to the object and its environment as well as theoretical foundations (based on various configurations of the state equation) for conversion of the considered piece of information, expressed by the aforementioned “numbers”, into the parameters of the object ability condition (i.e., its technical condition, adjustment and reliability). The theses of the presented complex method for the assessment of technical object ability were subjected to long-term verification with positive result in the study of the Allison 250 engine bearing system.