• Journal of the Korean Society for Precision Engineering
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• v.19 no.9
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• pp.34-40
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• 2002

Machining accuracy is affected by quasi-static errors of machining center. Since machine errors have a direct influence upon both the surface finish and geometric shape of the finished workpiece, it is very important to measure the machine errors and to compensate these errors. The laser measurement method for identifying geometric errors of machine tool has the disadvantages such as high cost, long calibration time and usage of volumetric error synthesis model. Accordingly, this paper deals with analysis of the geometric errors of a machine tool using ball bar test without using complicated error synthesis model. Statistical analysis method was adopted in this paper for deriving geometric errors using hemispherical helix ball bar test. As a result of experiment, geometric errors of the vertical machining center are compensated by 88%.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.1
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• pp.1-7
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• 2015

In the case of an unmanned aerial vehicle (UAV) equipped with a GNSS sensor, a boundary line where the vehicle can actually exist can be calculated using a navigation error model, and safe navigation (e.g., precise landing and collision prevention) can be supported based on this boundary line. Therefore, for the safe operation of UAV, a model for the position error of UAV needs to be established in advance. In this study, the multipath error of a GNSS sensor installed at UAV was modeled through a flight test, and this was analyzed and compared with the error model of an existing manned aircraft. The flight test was conducted based on a scenario in which UAV performs hovering at an altitude of 40 m, and it was found that the multipath error value was well bound by the error model of an existing manned aircraft. This result indicates that the error model of an existing manned aircraft can be used in operation environments similar to the scenario for the flight test. Also, in this study, a scenario for the operation of multiple UAVs was considered, and the correlation between the multipath errors of the UAVs was analyzed. The result of the analysis showed that the correlation between the multipath errors of the UAVs was not large, indicating that the multipath errors of the UAVs cannot be canceled out.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.1033-1034
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• 2010

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.6
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• pp.1-7
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• 2001

It is very important to test circular motion accuracy of NC machine tools as it affects all other machines machined by them in industries. In this paper, it has become possible to detect errors of linear displacement of radial directions for circle tar motion accuracy test using newly assembled magnetic type of linear scale so called Magnescale ball-bar system. It has also organized computer program systems using tick pulses come out from computer for getting error motion data at colt start time interval in circular motion test on NC lathe. Error data gotten from test is expressed to plots and analysed to numerics by various statistical treatments.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.167-167
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• 2000

This study aims at the development of REC sensor causing the gauge error in the hot strip rolling process, and the improvement of the hydraulic AGC (Automatic Gauge Control) system. The gauge error outbreaks from the various reasons, however, mainly the roll eccentricity is considered to cause a such kind of error. In the study, the REC (Roll Eccentricity Control System) sensor is designed using sensor An On - line test of the system shows the comprehensive effects of controlling the gauge error of the hot strip. On - Line test shows the possibility of enhancing the accuracy for gauge.

• Proceedings of the Safety Management and Science Conference
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• 2008.04a
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• pp.295-299
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• 2008

This paper discusses tests of factor effect or contrast by the use of saturated design $k^n$ factorial design. The nine nonparametric rank measures in normality test using normal probability pot are proposed. Length's PSE(Pseduo Standard Error) test [4] which relies on the concept of effect sparsity is also introduced and extended to the margin of error(ME) and Simultaneous margin of error(SME).

• Journal of the Korean Society of Safety
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• v.39 no.2
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• pp.65-74
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• 2024

We analyzed the relationship between the normal measurement of the seismic accelerometer (SA) and the error rate of the output voltage linear ratio to propose an evaluation method to determine whether the SA in use is measuring normally. Utilizing a test bed, the regular operation of SA in use was evaluated using acceleration data measured through impact tests since there are no regulations regarding performance testing of SA in use. For the used SA, the error rate of the output voltage linear ratio, which is a major performance criterion, was evaluated. We analyzed common characteristics of the SA that satisfied the impact test and the performance criteria of the output voltage linear ratio error rate. The results indicated that we must consider the decreasing trend and convergence of the error rate as the measurement angle increases, ensuring that the average value of the output voltage linear ratio error rate is within 1%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.200-209
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• 2019

When forecasting future values, a model estimated after minimizing training errors can yield test errors higher than the training errors. This result is the over-fitting problem caused by an increase in model complexity when the model is focused only on a given dataset. Some regularization and resampling methods have been introduced to reduce test errors by alleviating this problem but have been designed for use with only a given dataset. In this paper, we propose a new optimization approach to reduce test errors by transforming a test error minimization problem into a training error minimization problem. To carry out this transformation, we needed additional data for the given dataset, termed pseudo data. To make proper use of pseudo data, we used three types of missing data imputation techniques. As an optimization tool, we chose the least squares method and combined it with an extra pseudo data instance. Furthermore, we present the numerical results supporting our proposed approach, which resulted in less test errors than the ordinary least squares method.

• Journal of the Korean Data and Information Science Society
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• v.24 no.4
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• pp.815-824
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• 2013

Traditional Pearson chi-squared test is not appropriate for the data collected by the complex sample design. When one uses the traditional Pearson chi-squared test to the complex sample categorical data, it may give wrong test results, and the error may occur not only due to the biased variance estimators but also due to the biased point estimators of cell proportions. In this study, the design based consistent Wald test statistics was derived for k-population homogeneity test, and the traditional Pearson chi-squared test statistics was partitioned into three parts according to the causes of error; the error due to the bias of variance estimator, the error due to the bias of cell proportion estimator, and the unseparated error due to the both bias of variance estimator and bias of cell proportion estimator. An analysis was conducted for empirical results of the relative size of each error component to the Pearson chi-squared test statistics. The second year data from the fourth Korean national health and nutrition examination survey (KNHANES, IV-2) was used for the analysis. The empirical results show that the relative size of error from the bias of variance estimator was relatively larger than the size of error from the bias of cell proportion estimator, but its degrees were different variable by variable.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.57-62
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• 2015

The test of comparing liquid flow calibration system (approved by KOLAS) for accuracy and structure change test was performed in the test bed in order to evaluate the typical characteristics of the electromagnetic flow meters and parshall flume that are generally used in the water discharging facilities. The results of the accuracy comparing test with liquid flow calibration system showed the error of less than 2%. Pharshall plume got error up to -8.3% (low flow) from the flow rate test, but less than 4% from the accumulated flow test because of offset error at high flow rate and low flow rate. Evaluation of structual change test was tested with only parshall flume using structure and it consisted of installation angle (parshall flume and level sensor) and position change. Installation angle, water level sensor angle and position changing test for parshall flume had errors of 3.1%~-9.2%, 0.4%~-5.6% and 0.2%~1.3% respectively. Especially, the error showed the largest increase when the water level sensor measured the point of decreased flow by the structure change. Therefore, error factors (change of straight pipe length, installation of obstacle or effect of foreign substances on water level sensor) that can often occur in the field should be derived and the research for optimized installation method should be carried out continuously.