Papers by Keyword: Repeatability

Abstract: Gauge repeatability and reproducibility are becoming a versatile tool for determining the effectiveness or adequacy of manual and automatic measuring systems. The knowledge of variation is essential as variation is inherent in every measurement process and is sometimes unpredictable. Understanding and controlling variation in measurement systems is critical to reducing variability. This paper presents a design of an experiment to analyze gauge capability and uses the same designed experiment to test and compare the variation for two automatic measurement systems. Three factors were determined as a starting point and were compared at two levels. The test results were analyzed using the expanded ANOVA method in Minitab. Significant conclusions were drawn out and a recommendation for further work is suggested.

Abstract: Chemical etching is an integral part of metallographic sample preparation. Maintaining precise etch times can be difficult and therefore repeatability is limited. The aim of this work is to improve the repeatability of sample preparation using robotization. Prior to etching, metallographic samples of S355J2 (1.0577) structural steel were finely mechanically polished. For verification, 15 specimens were prepared using an in-house designed automated etching machine with a built-in 5-axis robotic arm and 15 specimens prepared manually by an expert metallographer. The samples were etched with Kourbatoff no. 4 reagent for 8 seconds in a beaker placed in an ultrasonic cleaner at 80 kHz. The samples were then cleaned in 7 beakers of cleaning fluid also placed in the ultrasonic cleaner. The robotic etching and cleaning process was optimized and the quality of the resulting surface is at least as good as that of the samples prepared by an expert metallographer. The surfaces were compared using a light optical microscope (LOM) and a confocal laser scanning microscope (CLSM). The repeatability of the preparation process is a key aspect for obtaining a large dataset of steel microphotographs for training a deep neural network that will be used in future research.

Abstract: The straightness movement error of the machine tools axis contributes significantly to the straightness of the workpiece machining feature. This paper focuses on the assessment study of CNC machine tools’ straightness geometric error for obtaining recommendation information to improve machine geometric accuracy. A research method by determining measurement parameters according to ISO 230 procedure, no-load measurement of straightness vertical-horizontal geometric error using a laser interferometer, collecting data, data analysis. Data analysis calculates positional straightness deviation, mean positional deviation, systematic positional deviation, repeatability, and accuracy of straightness movement for each machine axis, and generating error compensation values for improving machine geometric error. The travelled distance of the X, Y, and Z-axis CNC milling machine tested is about 1100 mm, 560 mm, and 520 mm. The assessment result shows mean deviation straightness horizontal of X, Y, and Z-axis is 4.14 μm, 3.41μm, and 0.95 μm. The mean deviation straightness vertical of X, Y, and Z-axis is 3.75 μm, 2.63 μm, and 2.30 μm. Finally, the assessment outcome is generating error compensation values of each axis. It could be recommendation information for setting back error compensation parameter on CNC controller, hence the mean deviation of straightness geometric error machine tools to be less than 1 μm.

Abstract: N-type 4H-SiC homo-epitaxial films were grown on 150 mm diameter wafers by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratio on short-term and long-term repeatability of the SiC films was investigated. By tuning of growth condition, high uniform SiC film with in-wafer thickness uniformity of ±2.8 % (1.6 % σ/mean) and carrier concentration uniformity of ±3.1 % (1.9 % σ/mean) was successfully grown at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio higher than 1.0 on the whole wafer. This result was comparable to the film grown at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio lower than 1.0 on the whole wafer. On the other hand, the films on 13 wafers successively grown at higher introduced C/Si ratio indicated low fluctuation from 1.85 to 3.09 % (σ/mean), and the short-term repeatability of the in-wafer carrier concentration uniformity of the films grown at higher introduced C/Si ratio was improved compared with the films grown at lower introduced C/Si ratio. Additionally, in-wafer carrier concentration uniformity of the films on 171 wafers grown at higher introduced C/Si ratio showed 75 % quartile of 4.26 % (σ/mean), and this result was greatly superior to that of 8.21 % (σ/mean) for the films on 130 wafers grown at lower introduced C/Si ratio.

Abstract: N-type 4H-SiC homo-epitaxial films were grown by high speed wafer rotation vertical CVD tool, and both short term repeatability and long term repeatability of epitaxial growth were investigated. In the short term repeatability investigated by 6 epitaxial wafers chosen from successively grown 12 epitaxial wafers using same recipe, it was found that total variation of thickness and carrier concentration for all measurement points of 6 wafers is 1.44 and 4.64 % respectively, which indicates excellent repeatability as well as high uniform thickness and carrier concentration. In the long term repeatability investigated by a very large number of growth experiments, probability achieving target uniformity of thickness and carrier concentration of the SiC films was increased up to 1.32 times by optimizing gas nozzle structure in gas inlet compared with in the case of conventional gas nozzles. Moreover, adjustment range of C/Si ratio necessary to achieve target uniformity of thickness and carrier concentration of the films was considerably reduced to 22 % by optimized gas nozzles.

Abstract: Shear stress-shear strain rate and shear stress-shear time curves of epoxy resin samples with the number average molecular weight of 283 g/mol were measured at 50 °C under the modes of steady test and transient test, respectively. Effects of dealy time (t₁) and measurement time (t₂) on the shear stress-shear responses of the epoxy resin oligomer material were studied. It was found that the repeatability of the test results at small shear rates was significantly influenced by the delay time and the measurement time. The values of t₁ and t₂ parameters to be used for the steady test of epoxy resin oligomer material could be optimized based upon the transient test. The measurement repeatablity at shear rates smaller than 7 s^-1 was apparently improved by setting the delay time and the measurement time longer than 20 s seperately (t₁ ³ 20 s, t₂ ³ 20 s) with the total delay time and the measurement time shorter than 80 s (t₁ + t₂ £ 80s).

Abstract: In recent years, the static modulus of elasticity is one of the most discussed property of hardened concrete. The aim of this article is to show results of 6 performed experiments focused on test results precision. The measurements were made according to the standards ISO 6784 and ISO 1920-10. More than 20 participants (laboratories) from Europe took part in these experiments. Test results were compared using the statistical methods for interlaboratory comparison. Repeatability and reproducibility, which provide more detailed information about range of expected values of elastic modulus, are the most discussed characteristics in the article.

Abstract: The aim of this paper is to summarize the results of 11 experiments which focused on assessing the precision of results of fresh concrete testing. The observed characteristics are slump test, flow table test, density and air content. More than twenty participants (testing laboratories) took part in these experiments. The test results were evaluated with statistical methods used for evaluations of interlaboratory comparisons. The article deals especially with the values of repeatability and reproducibility, which provide further understanding of the interval within which it is possible to expect with the given probability the test results measured in one or more laboratories.

Abstract: A dynamic calibration method based on elliptical standard was put forward to further improve the calibration repeatability of measurement system of form measuring instruments. In this method, the radius difference of the major axis to the minor axis of elliptic contour acts as the standard value to calibrate the measuring system, and a low pass filter is used to filter the roughness, electrical noise and high frequency vibration signal which mixed into measurement data, the elliptic contour feature can be obtained accurately based on the low order harmonic properties. Compared with the traditional calibration method of flick standard, the proposed method ensure the calibration state is well consistent with the normal measuring state of the measuring system. Experimental results indicate that the calibration repeatability with 10nm can be achieved by measuring an elliptical standard. This method has been used in the calibration of measurement system of self-made ultra-precision cylindricity measuring instrument.

Abstract: Quasi-static absolute calibration is using force with semi-sinusoidal pulse to calibrate pressure measuring system. The pulse width must be wide enough in order to guarantee the effective bandwidth of frequency spectrum be in the flat section of amplitude-frequency characteristics of the tested system. In this way, the result is similar to that from static calibration. The working characteristic parameters for measuring system which is gained from quasi-static calibration is different form static calibration in species, physical meanings and attainment methods. Therefore, the research is of great significance in forming quasi-static calibration system and improving measurement accuracy. The pilot scheme will be introduced in this essay. What is more, the calculation of working characteristic parameters for measuring system will be discussed by taking the force with specific pulse as example, including sensitivity when force transfer to pressure, linearity and repeatability which are used to evaluate the uncertainty of measurement.