Autonomous diagnostics and prognostics in machining processes through competitive learning-driven HMM-based clustering

A prerequisite to widespread deployment of condition-based maintenance (CBM) systems in industry is autonomous yet effective diagnostics and prognostics algorithms. The concept of ‘autonomy’ in the context of diagnostics and prognostics is usually based on unsupervised clustering techniques. This paper employs an unsupervised competitive learning algorithm to perform hidden Markov model (HMM) based clustering of multivariate temporal observation sequences derived from sensor signal(s). This method improves autonomy of the diagnostic engine over the more traditional classifier based diagnostics models. Classifier models, such as the model presented by Baruah and Chinnam [Baruah, P. and Chinnam, R.B., 2005. HMM for diagnostics and prognostics in machining processes. International Journal of Production Research, 43 (6), 1275–1293] employ ‘labelled’ feature vectors for supervised model building and subsequent health-state classification during condition monitoring. Improving the autonomy of the diagnostics model also improves the autonomy of the prognostics module that often builds upon information extracted through the diagnostics module. We have validated the proposed methods on a physical test-bed that involved monitoring drill-bits on a CNC machine outfitted with thrust-force and torque sensors. Experimental results demonstrate the ability of this method to estimate on-line the remaining-useful-life of a drill-bit with significant accuracy.     

A specialized isotope mass spectrometer for noninvasive diagnostics of Helicobacter pylori infection in human beings

A specialized isotope mass spectrometer for noninvasive diagnostics of Helicobacter pylori infection in human beings based on the carbon-13 isotope breath test has been designed and constructed. Important stages of the work included (i) calculating a low-aberration mass analyzer, (ii) manufacturing and testing special gas inlet system, and (iii) creating a small-size collector of ions. The proposed instrument ensures ¹³C/¹²C isotopic ratio measurement to within 1.7‰ (pro mille) accuracy, which corresponds to requirements for a diagnostic tool. Preliminary medical testing showed that the mass spectrometer is applicable to practical diagnostics. The instrument is also capable of measuring isotopic ratios of other light elements, including N, O, B (for BF₂+ ions), Ar, Cl, and S.     

Using a failure modes, effects and diagnostic analysis (FMEDA) to measure diagnostic coverage in programmable electronic systems

One of the key issues in the quantitative evaluation of programmable electronic systems is the diagnostic capability of the equipment. This is measured by a parameter called the Coverage Factor, C. This factor can vary widely. The range of possible values is often the subject of great debate. Within limits, the diagnostic coverage factor can be calculated by knowing which component failure modes are detected by diagnostics. An extension of the Failure Modes and Effects Analysis (FMEA) can be used to show this information. This extension, called a Failure Modes, Effects and Diagnostic Analysis can serve as a useful design verification tool as well as a means to provide more precise input to reliability and safety modeling.     

Elastic moduli of boron oxyfluoride glasses: experimental determinations and application of Makishima and Mackenzie's theory

Oxyfluoride glass system based on 60B₂O₃–(40 – x)PbO–xPbF₂, where x = 0, 5, 10, 15, 20 and 25 mol% was prepared. The density of each glass was measured and the molar volume was calculated. The velocities for both the longitudinal and the transverse ultrasonic waves were measured by using the pulse-echo technique. The longitudinal, shear, Young's and bulk moduli were calculated from the measured velocity and density values. Makishima and Mackenzie's theory was applied to calculate the elastic moduli of the present glasses. The calculated values are consistent with the measured ones. The measured and the calculated moduli were correlated for the composition of the glasses as a function of PbF₂ content and they are increased with increasing PbF₂. This is due to some structural changes which occur upon replacing PbF₂ instead of PbO content in the glass matrix.     

Beam-plasma discharge dynamics in an adiabatic magnetic trap

The rate of plasma expansion in the direction perpendicular to the magnetic field lines was determined and the turbulent plasma diffusion coefficient was calculated using data obtained by methods of X-ray diagnostics. A correlation between the plasma diffusion coefficient and the amplitude of the RF oscillations in the system was established. This correlation leads to an increase in the electron temperature and the expansion of plasma in the radial direction. The transfer processes in the plasma are markedly influenced by the magnetic field: for example, the relationship D_t ~ \frac1B² D_\tau \sim \frac{1}{{B^2 }} was observed in the range of magnetic field strengths B<2 kG.     

The role of f-states in the electronic and optical properties of rare-earth trifluorides (RF3, R = Ce and Gd): a full potential study

A theoretical investigation of the role of f-states on electronic and optical properties of CeF₃ and GdF₃ is presented. Our calculations are based on density functional theory using the full potential linearized augmented plane wave method with the inclusion of spin–orbit coupling. We employed the Coulomb-corrected local spin density approximation (LSDA + U), known for treating the highly correlated 4f electrons properly. The LSDA + U calculations shift the f-states away from Fermi energy (E _F) yielding an insulating ground in agreement with experiment. We find that electronic structure is greatly influenced by the occupancy of f electron. Our calculated reflectivity spectra are compared with the experimental data. The value of calculated reflectivity for both CeF₃ and GdF₃ compounds stays low till ~7 eV which is consistent with their large energy gaps. The results are analyzed in the light of band to band transitions. We have also presented the frequency-dependent dielectric constant and corresponding spectrum of the refractive index for these compounds.     

On improved crack tip plastic zone estimates based on T‐stress and on complete stress fields

Cracked ductile structures yield locally to form a plastic zone (pz) around their crack tips, which size and shape controls their structural behaviour. Classical pz estimates are based solely on stress intensity factors (SIF), but their precision is limited to very low σ_n/S_Y nominal stress to yield strength ratios. T‐stresses are frequently used to correct SIF‐based pz estimates, but both SIF and SIF plus T‐stress pz estimates are based on truncated linear elastic (LE) stress fields that do not satisfy boundary conditions. Using Griffith's plate complete LE stress field to avoid such truncated pz estimates, the influence of its Williams’ series terms on pz estimation is evaluated, showing that T‐stress improvements are limited to medium σ_n/S_Y values. Then, corrections are proposed to introduce equilibrium requirements into LE pz estimates. Finally, these improved estimates are compared with pz calculated numerically by an elastic–plastic finite element analysis.     

Some Comments on Spectral Analysis of Time Series

The Average Run Length of a Cusum chart for controlling a normal mean is calculated by solving the systems of linear equations which approximate the integral equations for the required quantities. The accuracy of approximation by this method is numerically evaluated and the results are compared with those obtained by other approximate methods. The construction and use of a new nomogram based on the contours of Average Run Lengths L_a . and L_r drawn in the h√n/σ—|μ – k|√n/σ plane is discussed. Numerical examples are given to illustrate the flexibility and convenience provided by this nomogram in the design of Cusum charts.     

The formation and characterization of freon 22 cluster beams

Freon 22 (CF₂HCl) clusters have been found upon gasdynamic cooling of these molecules in a pulsed supersonic beam. A method for diagnostics of the cluster beams of freon 22 has been developed based on the phenomenon of UV multiphoton ionization in combination with the time-of-flight mass spectrometry and the IR photodissociation of clusters. The velocities of directed motion and the longitudinal and transverse velocity components of the thermal motion of (CF₂HCl)_n clusters in a beam of freon 22 were measured for various stagnation pressures P ₀. The degree of beam clusterization was estimated.     

The three-parameter corresponding states principle

A multiproperty approach for the evaluation of the existing three-parameter corresponding states principles (CSP) and calculation of the corresponding states parameter is presented. This technique is based on the assumption that contribution of the third parameter to the thermophysical properties is much smaller than the contributions of the first two parameters. The first two parameters are, generally, the molecular energy and length parameters, /k and (or critical temperature and volume, T _c and V _c ). Based on the present multiproperty technique, several existing three-parameter CSPs are evaluated. It is demonstrated that the three-parameter CSP, which is based on the two- and three-body intermolecular potential parameters, effectively satisfies the requirements of this technique. The corresponding states parameters of several compounds, including normal alkane hydrocarbons (CH₄ to C₂₀H₄₂), for which proper thermophysical data are available, are calculated through the present technique, and they are reported here.     

Ideal-Gas Heat Capacity Values and Equations for Hydrofluorocarbon (HFC) Refrigerants Based on Speed-of-Sound Measurements

Final values of ideal-gas heat capacity c ⁰ _p derived from speed-of-sound measurements using an acoustic spherical resonator and equations of c ⁰ _p as a simple function of temperature are provided from an overall assessment of speed-of-sound measurements for five hydrofluorocarbon (HFC) refrigerants, difluoromethane (R32), pentafluoroethane (R125), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), and 1,1-difluoroethane (R152a). Some of the experimental results had systematic errors in comparison with theoretical calculations based on spectroscopic data, which seem to result from the impurity of the sample fluids. The agreement of the experimentally determined and theoretically calculated c ⁰ _p values was confirmed for HFC refrigerants. The uncertainty of c ⁰ _p values calculated from the proposed equations is estimated to be 0.1 or 0.2% corresponding to an ISO uncertainty with a coverage factor of k=1. An erratum for Table I in a previous report by Yokozeki et al. in 1999 is provided as an appendix.     

Algebraic model of turbulent boundary layer on a convex curvilinear surface

A simple algebraic model of turbulent boundary layer on convex curvilinear surfaces is suggested that is based on the generalization of the two-layer one-parameter algebraic model for a flat plate [ 1 ]. The model is tested in a wide range of variation of the curvature parameter (0.01 ≤ δ₀/R _w ≤ 0.09, where δ₀ is the thickness of the boundary layer at the initial cross section of the curvilinear region andR _w is the curvature radius of the surface), the results of which are indicative of a good agreement between the experimental and calculated data on the integral characteristics of the boundary layer, namely, the friction coefficientC _f , the displacement thickness δ^* and momentum thickness δ^**, and the form parameterH = δ^*/δ^**. Based on the comparison between the calculated and experimental data on the distribution of tangential turbulent stresses, a conclusion is made that the model predicts a much lower effect of the curvature on the suppression of turbulence in the outer region of boundary layers at a mild curvature of the surface (δ ₀ /R _w = 0.01) than in experiments. However, this difference has a tendency to decrease as the surface curvature increases. An analysis of the calculated and experimental velocity profiles plotted in the variables of the wall law leads to a conclusion that the generalized Townsend wall law is partially realized on a curvilinear surface.     

Monitoring manufacturing quality for multiple Li-BPIC processes based on capability index C pmk

The multi-process performance analysis chart (MPPAC) based on process capability indices has been developed to analyse the manufacturing performance for multiple processes, which conveys critical information regarding the departure of the process mean from the target value, process variability, capability levels, which provides a guideline of directions for capability improvement. Existing MPPAC researches have plotted the sample estimates of the process indices on the chart. Conclusions were then made on whether processes meet the capability requirement and directions need to be taken for further quality improvement. Such an approach is highly unreliable since the sample point estimate is a random variable with no assessment of the sampling errors. Further, existing MPPAC researches only considered one single sample. Current quality control practice is to estimate process capability using multiple groups of control chart samples rather than one single sample. In this paper, we propose the C _pmk MPPAC combining the accuracy index C _a to access the performance of multiple manufacturing processes. Distributions of the estimated C _pmk and C _a are derived based on multiple control chart samples, and accurate lower confidence bounds are calculated. The lower confidence bounds of the estimated C _pmk and C _a are then employed to the MPPAC to provide reliable capability grouping for those multiple processes. A real-world example is presented to illustrate the applicability of the proposed MPPAC.     

Structural stabilities, electronic structures and lithium deintercalation in LixMSiO4 (M = Mn, Fe, Co, Ni): A GGA and GGA + U study

Dilithium-orthosilicate oxides Li₂MSiO₄ (M denotes transition metals) have been one of the focuses in the field of new cathode materials for Li-ion batteries recently, due to their possible high capacities and probabilities achieving by experiment. Using the density functional theory within both the generalized gradient approximation (GGA) and GGA + U frameworks, the structural stabilities, electronic structures and delithiation process for the dilithium-orthosilicate oxides Li₂MSiO₄ (M = Mn, Fe, Co, Ni) are systematically investigated. Within the GGA + U approach, LiMSiO₄ is shown to be a stable non-stoichiometric structure, while the compound Li_1.5MSiO₄ are unstable relative to a two-phase form containing Li₂MSiO₄ and LiMSiO₄, which is consistent with the experimental voltage profiles. For Li_0.5MSiO₄, though the formation energies are negative for Mn-system and Ni-system, the absolute values are so small that they would be likely to also undergo phase separation at room temperature. The average deintercalation voltages calculated by the GGA + U scheme are in good agreement with the available experimental data. Furthermore, the possibility of the exchange of two electrons per M in Li₂MSiO₄ is also discussed based on the calculated results.     

Nonequilibrium distributions in superconductors

The nonequilibrium distribution functions of quasiparticles and phonons in superconductors are calculated for various cases. The conditions at which the nonequilibrium distributions exist are found. The dependences of the temperature and concentration of excitations on the pumping intensity, the sample thickness, and other parameters of the superconductor are calculated. In the current state the dependences of these quantities on the superfluid velocity and the current are investigated, and it is found that the dependenceT(v _s ) has a minimum, and the current for v_s>v _so ⁽¹⁾ becomes negative. It is also shown that in the nonequiibrium superconductor the state withv _s ^* 0 andJ(v _s ^* )=0 may exist. We have determined the nonequilibrium distribution function for a tunnel junction and investigated theV-A characteristic at some conditions for which an absolute negative resistance may exist.     

Molecular dynamics simulation on diffusion of 13 kinds of small molecules in polyethylene terephthalate

Understanding the diffusion of migrants in polyethylene terephthalate (PET) and calculating the diffusion coefficients are very important for migration research. In this study, the diffusion coefficients of 13 kinds of small molecules with molecular weights ranging from 32 to 339 g/mol in amorphous PET are calculated based on molecular dynamics (MD) simulation. By comparison of diffusion coefficients simulated by MD simulation techniques, predicted by the Piringer model and by experiments, the accuracy of the Piringer model and MD simulation techniques for the estimation of diffusion coefficients of migrants in PET is evaluated. The MD simulation shows that D_simu is very close to D_exp, within one order of magnitude of the experimental diffusion coefficients except for a few samples. The possible reasons for the differences among D_simu, D_pred and D_exp are analysed from the molecular weight and temperature. The results show that the Piringer‐model‐predicted values at high temperatures overestimate significantly higher than that at lower temperatures. The activation energy is calculated by the Arrhenius equation, which shows the relationship between diffusion coefficient and temperature. It is shown that the MD simulation yields acceptable activation energy. The study suggests that MD simulation may be a useful approach to calculate the diffusion coefficients of small molecules in PET. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of the electroluminescence features of silicon metal-insulator-semiconductor structures as a tool for diagnostics of the injection properties of a dielectric layer

A technique for diagnostics of the injection properties of thin dielectric layers based on analysis of the data on silicon electroluminescence in a metal-insulator-semiconductor structure is proposed. The possibility of applying this technique to control the electron injection energy (in particular, when the barrier parameters are poorly known) is demonstrated by the example of samples with CaF₂ and HfO₂/SiO₂. The results obtained are important for application of the insulators under study in microelectronic devices.     

The influence of interaction between Rydberg atoms and slow electrons on distribution function in the ultracold plasma

Expressions for the cross sections and rate constants of transitions during collisions of Rydberg atoms with electrons whose energy E is lower than the transition energy E _if are proposed. The populations of Rydberg states were calculated using the numerical solution of the set of kinetic balance equations as functions of time in an ultracold plasma based on the obtained transition rate constants. The calculation results are in good agreement with the experiment.     

Saturated Liquid Densities for 33 Binary Refrigerant Mixtures Based on the ISM Equation of State

In this work, the ISM equation of state based on statistical-mechanical perturbation theory has been extended to liquid refrigerant mixtures by using correlations of Boushehri and Mason. Three temperature-dependent parameters are needed to use the equation of state: the second virial coefficient, B₂(T), an effective van der Waals covolume, b(T), and a scaling factor, α (T). The second virial coefficients are calculated from a correlation based on the heat of vaporization, ΔH_vap, and the liquid density at the normal boiling point, ρ_nb. α(T) and b(T) can also be calculated from second virial coefficients by a scaling rule. The theory has considerable predictive power, since it permits the construction of the PVT surface from the heat of vaporization and the liquid density at the normal boiling point. The equation of state was tested on 33 liquid mixtures from 12 refrigerants. The results indicate that the liquid densities can be predicted to at most 2.8% over a wide range of temperatures, 170–369 K.