scholarly journals Robust Estimation of Optimal Sample Size for CMM Measurements with Statistical Tolerance Limits

2018 ◽  
Vol 220 ◽  
pp. 04001 ◽  
Author(s):  
Petr Chelishchev ◽  
Aleksandr Popov ◽  
Knut Sørby
Keyword(s):  
Sample Size ◽  
Cross Sections ◽  
Coordinate Measuring Machine ◽  
Cylindrical Part ◽  
Tolerance Limits ◽  
Optimal Sample ◽  
Free Model ◽  
Measuring Machine ◽  
Statistical Tolerance ◽  
Selection Of

The paper proposes the kernel probability density function approach to estimate the distribution of measurements on a part which is measured in a coordinate measuring machine (CMM). The study is based on the experimental data derived from internal cylinder measurements. The distribution free model suggested by Wilks was used as a reference for the selection of the sample size. Three cross sections of a cylinder were measured regarding to this reference. The work defines the minimum required sample size for obtaining at least 0.95 proportion of radius variation for particular studied cylindrical part with 95% confidence level.

scholarly journals Influence of measuring force on CMM accuracy

2018 ◽  
Vol 208 ◽  
pp. 03004
Author(s):  
Bin Wang
Keyword(s):  
Cross Sections ◽  
Measurement Accuracy ◽  
Coordinate Measuring Machine ◽  
Point Of View ◽  
Signal Acquisition ◽  
Force Model ◽  
Thin Part ◽  
Measuring Machine ◽  
The Relationship ◽  
Measuring Force

The measuring accuracy of CMM (Coordinate Measuring Machine) is influenced by many factors, such as temperature, humidity, measuring force and method of signal acquisition. For thin parts, the influence of measuring force is especially obvious. In this paper, the relationship between measuring force and measurement accuracy is studied for a thin part with a U-shaped cross-section. By analyzing the structure of the probe and establishing the force model, the influencing factors of the accuracy of CMM are obtained, and the influence of the contact deformation and the bending deformation on the measurement accuracy is analyzed from the point of view of material mechanics. At the same time, the measurement accuracy of different measuring cross-sections is analyzed. Through the research of this paper, the relationship between measuring force and CMM is established, and an effective method to improve the accuracy of CMM is also found.

Best Fit Uncertainty Analysis for Computing Geometric Tolerances

1997 ◽  
Author(s):  
Hong-Tzong Yau
Keyword(s):  
Sample Size ◽  
Measurement Data ◽  
Coordinate Measuring Machine ◽  
Point Location ◽  
Geometric Tolerances ◽  
Surface Deviation ◽  
Measuring Machine ◽  
Point Data ◽  
Geometric Variables ◽  
Best Fit

Abstract In computing geometric tolerances using point data from a coordinate measuring machine (CMM), a best fit process needs to be carried out to bring the measurement data to the coordinate system of the substitute geometry. The measurement data does not precisely conform to the substitute geometry. It involves errors from machining as well as measurement itself. With this error-carrying measurement data, the best fit result contains uncertainties which in turn reduce the accuracy of the evaluated tolerances. In this paper, a model is proposed to estimate the best fit uncertainties caused by surface deviation, point location, and CMM sample size. The model was verified by simulation and experiment. To explore factors that affect the uncertainty variations, geometric variables that influence the uncertainties were first studied. Then, to understand the effect of point location on the uncertainty, optimization using the conjugate gradient method was developed to find the best measurement locations by minimizing the total uncertainties. In addition, simulations showed that the uncertainty is inversely proportional to the squared root of the number of points. This result can be used to predict the CMM sample size that will control the best fit uncertainty under certain tolerances.

Application of the sampling strategies in the inspection process

2017 ◽  
Vol 231 (4) ◽  
pp. 565-575 ◽  
Author(s):  
Syed Hammad Mian ◽  
Abdulrahman M Al-Ahmari
Keyword(s):  
Sample Size ◽  
Adaptive Sampling ◽  
Sampling Methods ◽  
Fundamental Problem ◽  
Coordinate Measuring Machine ◽  
Sampling Strategy ◽  
Point Distribution ◽  
Coordinate Metrology ◽  
Inspection Process ◽  
Measuring Machine

The selection of appropriate sample size and point distribution on the measuring surface has been a fundamental problem in the contemporary coordinate metrology. It is usually resolved by the users depending on their instinct or prior experience. As a result, inspection results have to be compromised between accuracy and measurement time. However, to deliver quality products in minimum time, effort, and cost, a reliable and an efficient sampling plan is mandatory. Although there have been a remarkable progress due to the development of various procedures for computing the sample size and selecting the appropriate point distribution, still users are inconversant with the characteristics and applications of the available sampling methods due to the absence of a proper review. Accordingly, a systematic review, giving insight into the various strategies available for the sample size and the point distribution, is presented. In this article, different algorithms and their application in the estimation of sample size and point distribution have been reviewed comprehensively. The classification of sampling methods and the importance of adaptive sampling have also been described. It has been concluded that the effectiveness of inspection process or the performance of coordinate measuring machine can be escalated through the application of a suitable sampling strategy. Therefore, the metrologists should either develop an effective method for defining sampling strategy or select the most suitable method from the available resources before carrying out the inspection process.

scholarly journals An investigation of Outlier Detection Procedures for CMM Measurement Data

2018 ◽  
Vol 220 ◽  
pp. 04002 ◽  
Author(s):  
Petr Chelishchev ◽  
Aleksandr Popov ◽  
Knut Sørby
Keyword(s):  
Outlier Detection ◽  
Cross Sections ◽  
Experimental Verification ◽  
Measurement Data ◽  
Coordinate Measuring Machine ◽  
Data Sets ◽  
Dimensional Measurement ◽  
Measuring Machine ◽  
Simulation Results

The paper analyses methods for outlier detection in dimensional measurement. The cross sections of an internal cylinder were inspected by CMM (coordinate measuring machine), and received data sets were employed for further investigation. The efficiency of Rosner’s and Grubbs’ methods for excluding outliers from the measuring data had been estimated. The method of Rosner had been defined as the most effective for this case study. The simulation results were confirmed by experimental verification.

Evaluation of CMM Accuracy by Using Capability Indexes

2013 ◽  
Vol 281 ◽  
pp. 282-286
Author(s):  
Adel Elhadi M. Yahya ◽  
Martin Halaj
Keyword(s):  
Control Charts ◽  
Design Principle ◽  
Coordinate Measuring Machine ◽  
Good Method ◽  
High Accuracy ◽  
Measuring Instruments ◽  
Time Interval ◽  
Tolerance Limits ◽  
Measuring Machine ◽  
Intended Use

Capability indexes of several types belong to the most common tools used for evaluation of the measuring instruments performance over a certain period of time. The indices differ by calculation method, properties as well as by intended use. But their design principle is approximately the same. The ratio of prescribed (required) accuracy and really achieved process accuracy is always observed. However, this evaluation represents only a part of the overall measurements management system. The suitability of capability indexes for the evaluation of CMMs accuracy over a time. After analyzing the results we had found machine capability indexes good method for evaluation of Coordinate Measuring Machines (CMM) accuracy over a certain time interval. CMM are high accuracy and capable to perform the measurement of lengths, machine capability indexes helps to determine the ability for coordinate measuring machine between tolerance limits and engineering specifications, but the use of x-control charts to get and keep processes under control.

scholarly journals Selection of the Best Model of Distribution of Measurement Points in Contact Coordinate Measurements of Free-Form Surfaces of Products

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5346 ◽  
Author(s):  
Marek Magdziak
Keyword(s):  
Coordinate Measuring Machine ◽  
New Method ◽  
Free Form ◽  
Experimental Investigations ◽  
Accuracy Of Measurements ◽  
Measuring Machine ◽  
Coordinate Measurements ◽  
Free Form Surface ◽  
Free Form Surfaces ◽  
Selection Of

The article presents a new method for determining the distribution of measurement points, which can be used in the case of contact coordinate measurements of curvilinear surfaces of products. The developed method is based on multi-criteria decision analysis. In the case of the new method, the selection of the distribution of measurement points on free-form surfaces is carried out based on the analysis of five different criteria. The selection of the best model of the distribution of measurement points results from the accuracy of coordinate measurements, the time needed to complete measurement tasks, the number of measurement points, the accuracy of the substitute surface representing the measured free-form surface and the area where measurement points are located. The purpose of using the developed method of the distribution of measurement points is to increase the performance of coordinate measurements primarily by increasing the automation of strategy planning of measurements of curvilinear surfaces and improving the accuracy of measurements of free-form surfaces of products. The new method takes into account various aspects of coordinate measurements to determine the final model of the distribution of measurement points on measured surfaces of products, thereby increasing the probability of the proper determination (i.e., identifying the highest deviations of a product) of the location of measurement points on the surfaces of a measured object. The paper presents an example of the application of the created method, which concerns the selection of the best model of the distribution of measurement points on a selected free-form surface. This example is based on, among others, the results of experimental investigations, which were carried out by using the ACCURA II coordinate measuring machine equipped with the VAST XXT measuring probe and the Calypso measurement software. The results of investigations indicate a significant reduction in time of coordinate measurements of products when using the new method for determining the distribution of measurement points. However, shortening the time of coordinate measurements does not reduce their accuracy.

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