Component Tolerances Research Articles

Illumination-related errors in limited-angle optical diffraction tomography.

In the paper, the design and tolerances of optical systems and scanning components used in limited-angle optical diffraction tomography are analyzed in order to improve the performance of the measurement systems and to encourage the application of tomography as a standard method for quantitative analysis of 3D refractive index distribution in biological microstructures. The first part of the presented analysis consists of component selection for the scanning device and optical system in the illumination part of the setup and the influence of the illumination wavefront on reconstruction quality. In the second part, the sensitivity of the tomographic reconstruction quality to three representative measurement-related errors based on synthetic data is demonstrated. Finally, a configuration of the system, selected to minimize reconstruction errors, is proposed and alignment tolerances simulated using the Monte Carlo method are provided.

Parametric fault detection of analog circuits based on Bhattacharyya measure

This paper presents a fault detection algorithm to detect parametric fault in linear and weakly non-linear analog circuits by Bhattacharyya measure, a statistical metric. Linear feedback shift register (LFSR) generated pseudo-random bit sequences are fed to digital-to-analog converter (DAC) to obtain random analog input stimuli for the circuit under test (CUT). Bhattacharyya coefficient is measured from the probability density function (PDF) of the output. The non-Gaussian auto-regressive model is used to estimate the PDF. Component tolerance is mapped into statistical space by Monte Carlo simulation. The proposed methodology is validated through three benchmark circuits: continuous-time low pass state variable filter circuit, fourth order low pass Chebyshev filter circuit and cascade amplifier. All the circuits are simulated with CADENCE Virtuoso using UMC-180nm technology. Defect screening is also measured with linear regression analysis. Detectability of the proposed method for parametric fault is reasonably large in comparison to functional test method.

A Novel Tolerance Design Approach to Manufacturing and Quality Loss Cost Optimization in Mechanical Assemblies

Tolerance design has a profound impact on the manufacturability, ease of assembly, performance, quality and cost of mechanical components. However, assigning appropriate tolerances is still far from being a trivial engineering task. The optimization of dimensional and geometric tolerances for components that control functional dimensions in mechanical assemblies is receiving continuous attention from researchers. In this paper a novel tolerance design approach is introduced. The basic concept of the proposed approach is the transformation of an unconstrained optimization problem of multiple decision variables to a constrained optimization problem of a single variable in order to improve the convexity of the set of feasible solutions. Through the development of a Quasi-Newton algorithm, our objective is the optimization of both the manufacturing cost of each component and the quality loss cost of the mechanical assembly. A step-by-step mathematical formulation of the approach is presented by using the widely referenced example of the overrunning clutch assembly. The experimental results obtained for this application example are directly compared with alternative tolerance synthesis techniques that are found in technical literature, illustrating that the proposed approach is reasonable and effective.

Adaptive Tuning of Large-Signal Resonant Circuits Using Phase-Switched Fractional Capacitance

Inductively coupled systems used in applications such as RFID and wireless power often require high ${Q}$ factor resonant transmitters to maximize the magnetic field and achieve high overall efficiency. However, these are sensitive to environmental detuning as well as component tolerances. Existing methods for accurate tuning require search algorithms, usually requiring the suspension of normal operation in order to calibrate the resonant inductor–capacitor circuit, thus reducing power throughput and increasing system complexity. We describe here how zero-voltage switched fractional capacitance techniques may be used to achieve continuous and real-time adaptive tuning of large-signal resonant inductor–capacitor circuits. Minimal additional circuitry is required and tuning is maintained without disrupting normal operation. Many variants are possible for the implementation of the system, and some tradeoffs relating to the available tuning range and operating voltages are analyzed for two alternative topologies. Experimental results are presented for a 125-kHz demonstration system.

An Electronic Implementation of Lorenz Chaotic Oscillator Synchronization for Bistatic Radar Applications

The authors report the simulation and actual implementation of chaotic oscillator synchronization for a pair of three-state variable Lorenz systems. The first oscillator performs as a driver (transmitter), while the second system is made to respond the received waveform. Specifically, one of the state variables of the driver circuit is judiciously selected to generate an RF waveform. This waveform is transmitted through a noisy channel and is used to drive the response system until both the systems of all three state variables achieve complete replacement synchronization. It is known that this synchronization is sensitive to changes in received power. To overcome this, a technique hereon called generalized projective synchronization is employed to accept an attenuated version of the transmitted waveform. A sensitivity analysis reveals that generalized projective synchronization is robust with respect to deviations in the control parameter values of the response system due to tolerances of electronic components. The potential of the generalized projective synchronization is illustrated for a bistatic radar system case, where synchronization is necessary to obtain the range-Doppler information of a moving target. In this instance, the cross correlation, short-time cross-correlogram and cross ambiguity surface of the transmitted and synchronized waveforms are of high quality as indicated by their entropy measures.

RETRACTED ARTICLE: A novel hybrid approach based on principal component analysis and tolerance rough similarity for face identification

Face identification plays one of the most important roles in biometrics to recognize a person. However, face identification is very difficult because of variations in size, orientations, different illuminations, and face expressions. In this paper, a hybrid approach is proposed based on principal component analysis (PCA) and tolerance rough similarity (TRS) for face identification. This paper comprises of three steps. First, PCA has been used to extract the feature vector from face images (eigenvectors). Second, the tolerance rough set-based similarity is applied for face matching and finally, the test image is compared with lower and upper approximation of similarity values that were found using TRS. The proposed hybrid approach gives a better recognition rate compared to other standard techniques like Euclidean distance and cosine similarity. The proposed work is evaluated on three face databases namely OUR databases and ORL databases and Yale databases. The experimental result of the proposed PCA-TRS approach is compared with other standard classification techniques like support vector machine (SVM), multilayer perceptron (MLP), back propagation network (BPN) and simple decision tree (CART) to conclude that proposed approach is better for face identification because of high accuracy and minimum error rate.

Reducing Risk by Segmentation

The paper provides analysis of the various mechanisms through which the segmentation improves reliability and reduces technical risk and presents a classification of risk-reduction techniques based on segmentation. On the basis of theoretical arguments and examples, it is demonstrated that segmentation increases the tolerance of components to flaws causing local damage, reduces the rate of damage accumulation and damage escalation and reduces the hazard potential. The paper also demonstrates that segmentation essentially replaces a sudden failure on a macro-level with gradual deterioration of the system on a micro-level through non-critical failures. It is demonstrated that segmentation can even reduce the likelihood of a loss from opportunity bets and the likelihood of erroneous conclusion from imperfect tests. Finally, a comprehensive classification of methods and techniques for reducing risk, based on segmentation, has been proposed.

The Effects of Component Tolerances on the Thermo-Mechanical Reliability of SOFC Stacks

The reliability of solid oxide fuel cell (SOFC) systems is nowadays close to meet the requirements for market implementation. However, mechanical failures remain salient issues, which often limit the practical lifetime of SOFC stacks and directly impact the costs. To our knowledge, the capability for in-operando monitoring of the risks of their occurrence has not yet been demonstrated. Mechanical issues are typically identified indirectly once a critical failure already occurred, e.g. from cell open-voltage measurements. Therefore, numerical thermo-mechanical investigations are of high interest to understand and predict potential failure modes in SOFC stacks. Finite-element (FE) stack models commonly consider idealized components, i.e. computational domains imported from computer-aided design. In reality, the dimensions and geometry of the produced stack components have statistical variations, because of the imperfections of manufacturing processes and of the costs associated with component quality. In this study, production data shows that the interconnect is a component that is subject to such manufacturing tolerances. The resulting variability in shape, e.g. flatness and/or thickness, is expected to have an impact on the distribution of the contact pressure over the active area. Therefore, a dedicated measurement and simulation workflow has been developed to simulate the effects of component initial deformation. One repeating unit of an SOFC stack is meshed and implemented in the thermo-mechanical model here presented, to maintain the computational time at a few days on a workstation. Modified periodic boundary conditions are imposed on the upper and lower parts of the meshed domain to model the conditions at the middle of a large stack. The mechanical interaction between the components is modelled by softened contact or constrained node displacement, depending upon the interface. Further adjustments of the interface properties are performed during the analysis to account in a simplified manner for the stack conditioning steps, such as sintering of the contact pastes and crystallisation of the glass sealant. The material constitutive laws implemented in the model include (i) rate-independent elasto-plasticity and (ii) combined primary-secondary creep for the interconnect alloy and the anode cermet. Only secondary creep is considered for the materials of the other SRU parts. The elastic properties of the gas-diffusion layer (GDL) materials are estimated by computational homogenization. This allows the modelling of the GDLs as simplified continuum geometries to reduce the stack simulation runtime. The workflow for thermo-mechanical analysis developed in this study starts with the measurement of the deformation profile of several real interconnects, followed by implementation in the stack model, before the simulation of the stack assembly. Then, the stack conditioning procedure is simulated to account for the effects of the stack manufacturing on the stress-state just before operation. After this initialization step, the simulation of stack operation consists in importing temperature profiles from thermo-electrochemical simulations into the FE thermo-mechanical model. The simulated scenarios are either thermal cycling without operation or long-term operation in co-flow configuration at nominal conditions (0.4 A cm-2), interrupted by thermal cycles. For the considered design and for a given amplitude of initial interconnect deformations, the simulation results show that the distribution of the contact pressure over the active area can be already altered at the end of the stack qualification. In such cases, the GDLs cannot fully accommodate for the interconnect initial deformation, resulting in zones subjected to either higher or lower contact pressure, compared to the case of idealized initial components. This may lead to hot spots and locally pronounced irreversible deformations of the GDLs, among others, with potentially severe loss of contact pressure upon thermal-cycling or long-term operation. The stress in the sealant after thermal cycling increases after prolonged operation. In this situation, the regions of the sealants exposed to higher temperatures during long-term operation are subjected to larger stress at room temperature.

Highly precise acoustic calibration method of ring-shaped ultrasound transducer array for plane-wave-based ultrasound tomography

Ultrasound computed tomography (USCT) is promising for a non-invasive, painless, operator-independent and quantitative system for breast-cancer screening. Assembly error, production tolerance, and aging-degradation variations of the hardwire components, particularly of plane-wave-based USCT systems, may hamper cost effectiveness, precise imaging, and robust operation. The plane wave is transmitted from a ring-shaped transducer array for receiving the signal at a high signal-to-noise-ratio and fast aperture synthesis. There are four signal-delay components: response delays in the transmitters and receivers and propagation delays depending on the positions of the transducer elements and their directivity. We developed a highly precise calibration method for calibrating these delay components and evaluated it with our prototype plane-wave-based USCT system. Our calibration method was found to be effective in reducing delay errors. Gaps and curves were eliminated from the plane wave, and echo images of wires were sharpened in the entire imaging area.

Multiple harmonic elimination‐based feedback controller for Shunt Hybrid Active Power Filter

This study presents a multiple harmonic elimination-based feedback controller for shunt hybrid active power filter (SHAPF) to perform an effective harmonic compensation performance in a wide harmonic frequency band. The conventional control methods presented for SHAPF cannot perform an adequate performance, because of the disturbances such as phase delays caused by controller methods and measurement circuitries, tolerances of passive filter components and supply voltage harmonics. In the proposed controller, the conventional feedback controller is improved by using supply side individual current harmonics which are extracted by the synchronous reference frame method. To prevent the performance degradation effects of disturbances, proportional–integral controllers are applied to each d and q components of individual current harmonics. The compensation performance of the proposed method is compared with conventional methods both theoretically and experimentally. The experimental results verify the advanced harmonic compensation performance of the proposed control method.

The Effects of Component Tolerances on the Thermo-Mechanical Reliability of SOFC Stacks

The reliability of solid oxide fuel cell (SOFC) systems is closing the gap to meet the requirements for market implementation. Finite-element (FE) stack models, typically used for stack reliability analyses, commonly consider idealized components. In reality, dimensions and geometry of the produced stack components have statistical variations. The resulting variability in shape is expected to have an impact on the distribution of the contact pressure over the cell active area. In this study, the initial deformation of the metallic interconnect (MIC) is implemented in the stack model. The simulation starts with the simulation of the stack production and qualification. The results of this first calculation are used to simulate either thermal cycling or prolonged continuous operation. The distribution of the simulated contact pressure on the active area is found to evolve differently during thermal cycling and operation, if the initial deformation of the MIC is included in the stack model.

Laser beam welding of atmosphere aluminum die cast material using high frequency beam oscillation and brilliant beam sources

In the serial production of components for automotive applications such as cooling and air-conditioning systems, aluminum die-cast materials are frequently used due to their excellent castability. The aim of providing light weight components can be approached with thin walled cross sections even for complex structural parts. However, cast components are usually connected to semifinished products such as profiles or tubes. The connections have to be mostly pressure tight. The joining technique for these applications has to be highly productive to obtain high component outcome and cost-efficient. Laser beam welding techniques are especially suitable for these tasks. Die-cast components have limited or no weldability due to their manufacturing process. This is due to entrapped gases within pores or cavities under high pressure conditions. Furthermore, the mold release agents for the die-cast process are inappropriate for obtaining homogeneous and sound weld seams. Consequently, this results in a larger number of pores in the weld seam and stochastic melt pool blow-outs, which prohibit mostly the use of the component. To solve these issues, a new welding technique, remoweld®T, has been developed at Fraunhofer IWS. This unique method has been extensively tested and used for serial-production. The decisive step was to use laser sources with brilliant beam quality in combination with a high frequency beam oscillation within the melt pool. In this paper, the technological approach will be presented. With the remoweld®T method, it was possible to obtain homogeneous weld seams with low porosity and a strongly reduced distortion for the first time. Minor component tolerances and a reproducible joining technique with a high output for serial production can be achieved.

A measurement‐based approach with accuracy evaluation and its applications to circuit analysis and synthesis

SummaryIn this paper, we evaluate a useful general model for linear direct current (DC) networks, containing design parameters, multiple inputs and outputs. The outputs are rational multivariate functions of the parameters and linear functions of the inputs. For an unknown linear system, the unknown coefficients of these functions can be determined by taking a suitable number of measurements and solving a set of linear equations constructed from selected measurement data. The rational functions are useful to support the design such that outputs can be constrained to a desired interval. An interesting result was the particular case where the parameter varied is located at the output terminal. This is an alternative way to estimate the Thévenin equivalent of a circuit. Real data are in general noisy with accuracy dependent on the tolerance of components and on the measurement device used. We present a detailed analysis of the application of the measurement‐based approach under real experiments. Initially, a resistive DC circuit case is presented, and the results are verified by simulation and experimental laboratory data. Finally, practical circuits, such as a conditioning signal stage with an operational amplifier, and a boost DC–DC converter are considered. Copyright © 2017 John Wiley & Sons, Ltd.

Sensitivity of effective relative permeability for gapped magnetic cores with fringing effect

Magnetic component tolerances are caused by variations in air-gap and core relative permeability. This study presents the derivation for sensitivity of effective relative permeability to variations in the relative core permeability and relative gap length for magnetic cores with and without fringing effect. The expressions for the fringing factor and effective relative permeability for the magnetic cores have been derived. The effect of air-gap on the core properties, which includes core power loss density, magnetic flux density, and magnetic field intensity is addressed for cores used in low-frequency and high-frequency applications. An example core is selected to support the theoretical predictions. The expressions to determine the inductor tolerances are presented.

Measuring Nanoscale Thermostability of Cell Membranes with Single Gold–Diamond Nanohybrids

AbstractMuch of the current understanding of thermal effects in biological systems is based on macroscopic measurements. There is little knowledge about the local thermostability or heat tolerance of subcellular components at the nanoscale. Herein, we show that gold nanorod–fluorescent nanodiamond (GNR‐FND) hybrids are useful as a combined nanoheater/nanothermometer in living cells. With the use of a 594 nm laser for both heating and probing, we measure the temperature changes by recording the spectral shifts of the zero‐phonon lines of negatively charged nitrogen‐vacancy centers in FNDs. The technique allows us to determine the rupture temperatures of individual membrane nanotubes in human embryonic kidney cells, as well as to generate high temperature gradients on the cell membrane for photoporation and optically controlled hyperthermia. Our results demonstrate a new paradigm for hyperthermia research and application.

Measuring Nanoscale Thermostability of Cell Membranes with Single Gold-Diamond Nanohybrids.

Much of the current understanding of thermal effects in biological systems is based on macroscopic measurements. There is little knowledge about the local thermostability or heat tolerance of subcellular components at the nanoscale. Herein, we show that gold nanorod-fluorescent nanodiamond (GNR-FND) hybrids are useful as a combined nanoheater/nanothermometer in living cells. With the use of a 594 nm laser for both heating and probing, we measure the temperature changes by recording the spectral shifts of the zero-phonon lines of negatively charged nitrogen-vacancy centers in FNDs. The technique allows us to determine the rupture temperatures of individual membrane nanotubes in human embryonic kidney cells, as well as to generate high temperature gradients on the cell membrane for photoporation and optically controlled hyperthermia. Our results demonstrate a new paradigm for hyperthermia research and application.

Penerapan Metode Monte-Carlo untuk Analisis Toleransi Perubahan Nilai Komponen Terhadap Kinerja Osilator Frekuensi 2,3 GHz

In telecommunications equipment, an oscillator has a function to generate a carrier signal. As the carrier signal, a high stability performance is required. The frequency shift caused by component tolerances. In this research, a Monte-Carlo method was used to analyze a component tolerance on the performance of the oscillator at a frequency 2.3 GHz. A simulation was performed by software Advance Design System (ADS). In this research, the iterations were carried out as many as 212 times with tolerance component values by 10%. The analyzed performance consists of a fundamental frequency shift, a phase noise, the value of power fundamental, and a harmonic power. Meanwhile, the oscillator has a structure of bias BJT common base-bias BFR183 with Vcc = 20 V, Vce = 8.2 V and Ic = 15 mA and a dielectric resonator as a resonator. The oscillator has a fundamental frequency 2.3 GHz, phase noise -135.6 dBc / Hz, power fundamental 10.8 dBm, and harmonic power -11.2 dBm. The simulation results showed that the oscillator has a good performance with a high degree of stability on a fundamental frequency by 73%, stability phase noise 100%, stability power fundamental 64%, and stability harmonic power 61%. This simulation has a confidence level of 95.4%, an error ± 3%, and the estimation accuracy 95%.

Blind source computer device identification from recorded VoIP calls for forensic investigation

The VoIP services provide fertile ground for criminal activity, thus identifying the transmitting computer devices from recorded VoIP call may help the forensic investigator to reveal useful information. It also proves the authenticity of the call recording submitted to the court as evidence. This paper extended the previous study on the use of recorded VoIP call for blind source computer device identification. Although initial results were promising but theoretical reasoning for this is yet to be found. The study suggested computing entropy of mel-frequency cepstrum coefficients (entropy-MFCC) from near-silent segments as an intrinsic feature set that captures the device response function due to the tolerances in the electronic components of individual computer devices. By applying the supervised learning techniques of naïve Bayesian, linear logistic regression, neural networks and support vector machines to the entropy-MFCC features, state-of-the-art identification accuracy of near 99.9% has been achieved on different sets of computer devices for both call recording and microphone recording scenarios. Furthermore, unsupervised learning techniques, including simple k-means, expectation-maximization and density-based spatial clustering of applications with noise (DBSCAN) provided promising results for call recording dataset by assigning the majority of instances to their correct clusters.

Robust Output Synchronization of Arrays of Chaotic Sprott Circuits

This article presents a technique for synchronizing arrays of a class of chaotic systems known as Sprott circuits. This technique can be applied to different topologies and is robust to parametric uncertainties caused by tolerances in the electronic components. The design of coupling signals is based on the definition of a set of functionals which depend on the errors between the outputs of the nodes and the errors between the output of a reference system and the outputs of the nodes. When there are no parametric uncertainties, we establish a criterion to design the coupling signals using only one state variable of each system. When the parametric uncertainties are present, we add a robust observer and a low pass filter to estimate the perturbation terms, which are subsequently compensated through the coupling signals, resulting in a robust closed loop system. The performance of the synchronization technique is illustrated by real-time simulations.

Mahalanobis Distance Based Approach for Anomaly Detection of Analog Filters Using Frequency Features and Parzen Window Density Estimation

Analog filters play a very important role in insuring the availability of electronic systems. Early detection of anomalies of analog filters can prevent the impending failures and enhance reliability. The complex architecture and the tolerances of multiple components make it very difficult to detect anomalies in analog filters. To address this concern, A Mahalanobis distance (MD) based anomaly detection method for analog filters is proposed in this paper. The conventional frequency features and the moment of frequency response are selected as the feature vector. Mahalanobis distance is used to transform the frequency feature vector to one dimensional MD data. The anomaly detection threshold is obtained based on probability density of the health MD data sets which is estimated by Parzen window density estimation method. The efficiency of the proposed method has been verified by two case studies. In the case studies, a comprehensive indicator constructed by miss alarm and false alarm is used to obtain an optimal anomaly detection threshold. One class SVM (OCSVM) based anomaly detection method is used as a comparison with our approach. The results illustrate that: (1) the proposed frequency features can effectively clarify the degradation of analog filters; (2) the proposed MD based approach can detect anomalies in analog filters effectively at an early time stage. (3) the proposed MD based approach can detect anomalies in analog filters more accurately than OCSVM based method.