Data Analytics for Noise Reduction in Optical Metrology of Reflective Planar Surfaces

On-line data collection from the manufactured parts is an essential element in Industry 4.0 to monitor the production’s health, which required strong data analytics. The optical metrology-based inspection of highly reflective parts in a production line, such as parts with metallic surfaces, is a difficult challenge. As many on-line inspection paradigms require the use of optical sensors, this reflectivity can lead to large amounts of noise, rendering the scan inaccurate. This paper discusses a method for noise reduction and removal in datapoints resulting from scanning the reflective planar surfaces. Utilizing a global statistic-based iterative approach, noise is gradually removed from the dataset at increasing percentages. The change in the standard deviation of point-plane distances is examined, and an optimal amount of noisy data is removed to reduce uncertainty in representing the workpiece. The developed algorithm provides a fast and efficient method for noise reduction in optical coordinate metrology and scanning.

Recent developments on an interferometric multilateration measurement system for large volume coordinate metrology

A mobile multilateration measurement system developed at the Physikalisch-Technische Bundesanstalt (PTB) around 2010 has been thoroughly investigated and refined to gain better performance with smaller uncertainties even when applied to the calibration of large complex workpieces. The mathematical background of multilateration and the propagation of uncertainties for the algorithms involved is explained in detail. Using the example of simple 1D and 2D measuring tasks, the influence of certain parameters characterizing the setup of the measurement system on the overall uncertainty is quantified. A strategy is developed to incorporate multi-stylus measurements which are often inevitable when workpieces feature complex shapes. The findings are verified on a large involute gear which is 2 m in diameter. All measurements are performed on PTB's large coordinate measuring machine with a working range of 5 m x 4 m x 2 m.

Reference Measurement of Roundwood by Fringe Projection

The metrological verification of log scanners requires logs with accurately known dimensions as test objects. The measurement of the lengths and diameters must be traceable back to the SI (International System of Units) unit of length. The results have to be reported with the corresponding measurement uncertainties. The uncertainties are required to be 5 to 10 times lower than the corresponding maximum permissible errors allowed for the log scanner under test. This article presents a procedure for the reference measurement of logs using an off-the-shelf fringe projection system along with uncertainty budgets for the measured dimensions. The length and diameters are determined from the highly resolved mesh obtained by fringe projection using techniques from computational geometry and coordinate metrology. Corrections are applied to the length and diameter values to remove the systematic effect caused by scattering of projected light below the partially transparent log surface. The influence of the fringe projection system on the measured dimensions is determined by measurements of calibrated artifacts, which also provide the traceability back to the SI unit of length. The measurement is illustrated by the example of a log with a length of 2 m and a diameter of 280 mm. The corresponding uncertainty budgets, confirmed by repeat measurements, result in expanded uncertainties (confidence interval 95%) of 6 mm and 0.13 mm for length and diameter, respectively. These low values qualify the fringe projection measurement along with accompanying evaluation procedure to provide logs as reference objects for the verification of log scanners.

The dependence of coordinate measurements error of the geometric elements shape characteristics of products on the control points number

The issues of estimating the error of coordinate measurements of the shape characteristics of geometric elements of products depending on the number of control points, taking into account a given confidence probability, are considered. Analytical models are proposed for estimating the error based on a priori data, similar to estimating uncertainty by type B. The correspondence of model and experimental results is verified by the Monte Carlo method using a specially developed program in VBA and the library functions of the Statistical Analysis package of the Microsoft Excel program. Such a characteristic of the shape of the part as roundness is investigated. The influence of the parameters of regular structures associated with the features of the technological processes of manufacturing the part on the parameters of the distribution function of the coordinates of the control points is revealed. Fourier analysis is used to identify and quantify regular structures on the surface of the part. The sources of error that have a significant impact on the results of measurements of the shape characteristics of geometric elements of products are given. Based on the results of statistical calculations, the dependence of the measurement error of the shape characteristics on the number of control points is analyzed, the scope of application of analytical formulas for estimating the error of single measurements for a given confidence probability is determined. The article is intended for specialists in the field of practical coordinate metrology and related fields.

Computer support for the shape formation of helical surfaces with a disk tool

An analytical description of the process of making helical surfaces with a disk tool with a substantiated definition of the objective function is proposed. By analogy with coordinate metrology, it is proposed to adopt a minimum tolerance zone as an objective function. This allows to specify the required solution error and eliminates the need to use normal lines or tangents to the profiles. An example of calculating the profile of a helical groove of a twotoothed end mill, performed with an error of 0.05 mm is presented. Keywords: helical surface, disk tool, computer support, optimization, minimum tolerance. [email protected]