Process parameters determination for precision manufacturing

Conventional process planning in manufacturing operations presents fixed process means and process tolerances for all operations and allows actual outputs to be distributed around these fixed values, as long as the final outputs fall within acceptable specifications. Some approaches attempt to maximize the process tolerances of all manufacturing operations for part production. Other approaches intend to minimize the tolerance cost or quality loss based on known functions. Most of them consider process mean and process tolerance as independent decision variables in process planning, with the condition that the resultant working dimensions are equal to the design target values of blueprint dimensions. These approaches assume that there is no process drift or deterioration. However, these conventional approaches are inappropriate for small‐volume, high‐value and precision processing, particularly of a complex part. Hence this study introduces an alternative approach to the tolerance‐balancing problem that does not provide specific objective functions, which determines process means and process tolerances simultaneously and adjusts them sequentially. Copyright © 2000 John Wiley & Sons, Ltd.     

Accuracy and precision of single-pulse one-dimensional vibrational coherent anti-Stokes Raman-scattering temperature measurements

The accuracy and precision of time-resolved one-dimensional temperature measurements using single-pulse one-dimensional N(2) vibrational coherent anti-Stokes Raman scattering along a line have been investigated in air in the temperature range from 300 to 1500 K. For this, the experimental spectra were taken in a high-temperature oven at atmospheric pressure. A planar BOXCARS phase-matching geometry was employed to generate the signal along a 6.16-mm line directed perpendicular to the beam propagation. With the used imaging optics, in this direction a spatial resolution of 86 mum was achieved. Depending on the set temperature, the agreement between the thermocouple readings and the mean values of the evalutated coherent anti-Stokes Raman-scattering temperatures is better than 40 K. The applicability of this new technique for the time-resolved measurement of temperature gradients is demonstrated along a line that crosses the flame front in a premixed laminar CH(4)-air flame.     

Method for determination of precision of analog-digital devices

A new method for estimating precision of analog-digital devices based on the entropy approach is proposed. A special feature of the method is its sensitivity to a constant error component.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 3–5, June, 1994.     

Accuracy and precision in the estimation of peak areas: The effects of apodization

Weiss, G.H., Kiefer, J.E. and Ferretti, J.A., 1988. Accuracy and precision in the estimation of peak areas: the effects of apodization. Chemometrics and Intelligent Laboratory Systems, 4: 223-229.The problem of finding optimal apodization functions for the numerical estimate of peak areas is investigated. The formalism in such studies is presented and the effects are analyzed for a set of functions of the type exp[(-t/T_f)^α], where α = 1, 2 are the most frequently used values of this parameter. A measure of generalized error that combines bias and instrumental noise effects in peak area measurements is used to compare different apodization functions. It is found that increasing the value of α always decreases the generalized error but at the cost of requiring more precise knowledge of T₂*. Effects of varying other parameters available to the experimenter are also studied.     

Accuracy of color determination from spectroscopic ellipsometry measurements

In many coating and display applications, quantitative determination of the sample color is required. Standard procedures exist for converting an experimentally measured reflectivity spectrum into color coordinates such as CIE L*a*b*. In this paper we evaluate CIE L*a*b* color coordinates using a reflectivity spectrum which is calculated from an optical model determined by a spectroscopic ellipsometry (SE) analysis of the sample. The accuracy of the SE-determined color coordinates are compared with traditional color measurements, and the advantages of using SE for color determination are discussed.     

Human posture simulation to assess cumulative spinal load due to manual lifting. Part II: accuracy and precision

For assessing a large number of variable manual lifting jobs, posture specification for using the University of Michigan Three Dimensional Static Strength Prediction Program and the revised National Institute for Occupational Safety and Health Lifting Equation may be time-consuming, tedious and subject to human errors. To expedite data analysis with desirable accuracy and precision for the two risk assessment tools, a new data analysis method based on human posture simulation was developed and evaluated. The accuracy and precision of the posture simulation method were evaluated by a repeated measures study design with six postures, three viewing angles and three trial repetitions as experimental factors. The effects of the experimental factors on the average accuracy and precision of the simulation method are reported and discussed. The study results also demonstrated pros and cons of human posture simulation as a means of posture specification for ergonomic risk assessments. The findings about the accuracy and precision of the human posture simulation method for quantifying the risk of musculoskeletal disorders due to manual materials handling may provide researchers with a new way of ergonomic assessments.     

Spectrophotometric method for precision determination of elements of the nuclear fuel cycle

Published data on precision spectorphotometric determination of U, Th, Pu, and other elements of the nuclear fuel cycle in solutions on a two-channel analyzer with the relative random uncertainty S _r = 0.1?C0.2% are summarized. The method was used for certification and fabrication of Pu and U total weight fraction standards for mass spectrometer calibration. New data on precision determination of U, Ru, Er, Gd, Sm, Re, and Tc on serial Shimadzu UV devices in the photometric mode with the relative random uncertainty S _r = 0.02?C0.04% are presented. The relative total uncertainty that can be attained with the spectrophotometric method is as low as 0.03?C0.05%, which makes this method competitive with other precision methods used.     

Accuracy of electromagnetic shower position determination by a wide-gap drift chamber

The electromagnetic shower position was measured by a wide-gap drift chamber placed behind an active converter. Different methods for the shower-position determination based on MHTDC and flash ADC were used. A spatial resolution of 1.9 mm (rms) at an energy of 3 GeV and a converter thickness of 3X₀ was achieved. The transverse charge distribution at different depths of the e.m. shower in the lead-glass was measured.     

Strategies and data precision requirements for the mass spectrometric determination of structures from combinatorial mixtures

Mass spectrometric data can be obtained for compounds in bead-bound combinatorial mixtures by several techniques. However, little specific information is available regarding (1) how well these data differentiate between candidate structures in large combinatorial pools, (2) what precision of data is required to achieve adequate specificity in these analyses, and (3) what are the best strategies for applying these data. In this work, computer modeling is used to address these questions. Strategies employing multiple filters (i.e., those that differentiate possible structures using more that one measured mass spectral parameter) are found to provide better specificity and to be more robust (that is, the specificity is less dependent on the precision of the data) than discrete filters. With moderate precision data (e.g., 50 ppm mass precision, 10% isotope ratio precision), multiple filter strategies are found to give unequivocal results for ～80% of the populations of combinatorial mixtures with most of the remaining degeneracy at the 2-fold level. A simple protocol for the application of multiple filter methods is presented.     

Mass spectrometric determination of 234U/238U ratio with improved precision

A new mass spectrometric method is proposed for measurement of 234U/238U ratio with a single Daly electron multiplier detector using the general peak jump method. The method is based on precise measurement of the 235U/238U ratio and 234U/235U ratio, which are used to calculate the 234U/238U ratio using the equation 234U/238U = 235U/238U x 234U/235U. The results show a significant improvement, i.e., more than 35 times better precision in measuring the (234)U/(238)U ratio with this method (sigma = 2.9 x 10(-8)) as compared to direct measurement of 234U/238U (sigma = 1.1 x 10(-6)). The method widens the applicability of the single collector system, and it will potentially be helpful to improve the precision in the case of the static multicollector system also.     

Accuracy of determination of the density of a gas by the multibeam-interferometry method

We estimate the accuracy of the determination of the density of a gas in rarefied streams by using the photometric method of multibeam interferometry. We give the numerical values of the relative error in the measurements for various experimental conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 1, pp. 50–52, January, 1977.     

Improvement of measurement precision of SPME-GC/MS determination of tributyltin using isotope dilution calibration

A unique approach was developed to improve the precision of quantification of tributyltin (TBT) in sedimentsby solid phase microextraction (SPME) using isotope dilution GC/MS. The precision of the analytical technique was initially evaluated using standard calibration solutions. In selective ion monitoring (SIM) mode, the relative standard deviation (RSD) obtained for TBT based on peak area response was 18% (n = 11). When an internal standard, tripropyltin (TPrT), was used, the RSD decreased to 12%. A significant improvement in the precision using SPME was noted when a 117Sn-enriched TBT spike was employed; the RSD decreased 4-fold to 3%. Detection limits of 0.2 and 20 ng(Sn) L(-1) were achieved with SPME sampling and liquid-liquid extraction, respectively. Six analyses were performed for determination of TBT in PACS-2 sediment Certified Reference Material using both standard additions and isotope dilution procedures. For the latter, a 117Sn-enriched TBT spike was used. A concentration of 0.88 +/- 0.03 microg g(-1) (RSD 3.4%) obtained using standard additions was in good agreement with the certified value of 0.98 +/- 0.13 microg g(-1) as tin. Concentrations found using isotope dilution were 0.895 +/- 0.015 microg g(-1) (RSD 1.73%) as tin and 0.874 +/- 0.014 microg g(-1) (RSD 1.66%) as tin using a liquid-liquid extraction and SPME sampling, respectively. A 2-fold improvement in the precision of TBT concentration measurement using isotope dilution was clearly achieved, demonstrating its superiority in providing more accurate and precise results as compared to the method of standard additions. The isotope dilution technique eliminated the problem of poor reproducibility, which typically plagues SPME.