Tomas Marek

Over the past two decades, considerable progress has been made in both metrology and control systems, enabling more sophisticated approaches to geometric error identification. Static interferometric measurements are accurate but time-consuming. Therefore, this study compares the measurement uncertainty of static and dynamic (continuous) modes of measuring the geometric accuracy of machine tools. At the same time, the measurement noise value of dynamic measurements was quantified as a contribution to the standard uncertainty of type B. The measurements were performed in static and dynamic modes with a Renishaw XL-80 laser interferometer and using angular optics kit. The results of individual measurements were interpreted through the straightness of the linear axes of the two machine tools. The measurement was performed on a small ( X -axis length = 754 mm) and a large ( Z -axis length = 9134 mm) CNC machine tool with feed rates from 2000 mm min ⁻¹ to 8000 mm min ⁻¹ . The uncertainty budget calculation of the measured straightness consists of the official documentation of the laser interferometer manufacturer and on the other hand the uncertainty of the straightness was determined experimentally. The comparison of the straightness measured by the static and dynamic modes confirmed that the dynamic measurement represents a time-efficient approach to verifying the geometric accuracy, which is practically indispensable for large machines and significantly reduces downtime for smaller machines without significantly reducing the reliability of the results.

The possibility of using CNC machine tools as measuring systems brings several advantages. The main advantage is to increase the productivity of the production process through in-process intermittent measurement, which allows to save working time by eliminating intermittent operations. However, such measurement systems must meet the metrological requirements of the measurement task to ensure the credibility of the measured data. The assessment of the applicability of a CNC machine tool as a measurement system can be done by verifying conformity with specifications according to the ISO GPS, or by demonstrating the capability of the measurement system by methods that use specifical statistical approaches (e.g. ISO 22514–7:2021, MSA:2010, VDA 5:2011). Based on the result of the specification assessment, it is then possible to approve or reject the deployment of the relevant CNC machine in the measurement process. This paper critically analyzes the current state of the art in this field and presents a new approach to assessing the applicability and capability of CNC machine tools as length measurement systems. The analysis compares the measurement process on a three-axis vertical CNC machining center with the measurement process on a coordinate measuring machine. Based on the critical analysis, an original approach to properly understand and apply the concept of combined measurement uncertainty in assessing the applicability and capability of a CNC machine as a measurement system (MS) in the on-machine measurement process has been developed and presented in the paper.

Currently, emphasis is placed on the ever-higher accuracy and speed of measuring the geometric accuracy of CNC machine tools. Achieving the highest possible accuracy is often time-consuming, which results in higher financial costs. The purpose of this study was to verify the suitability of the dynamic measurement of the position CNC machine based on laser interferometry using angular optics concerning static measurement. In the case of both measurements, a commercially available laser interferometer XL-80 was used. First, a static measurement was performed on the horizontal X axis, then a set of dynamic measurements was performed, and the last static measurement was evaluated as a control. The test therefore assesses the accuracy of dynamic position measurement in accordance with ISO 230-2 parameters. The advantage of dynamic measurement is the provision of a more realistic and detailed view of CNC machine tool errors thanks to the high resolution of the measurement itself. At the same time, this research opens another unexplored area of mutual synchronization of data obtained from the CNC machine and data from the reference method.

In modern manufacturing, there is an increasing demand for reliable in-process measurement methods directly on large CNC machine tools, eliminating the need to transport workpieces to metrological laboratories. This study assesses the capability and applicability of an articulated arm coordinate measuring machine and a machine tool touch-trigger probe when measuring to a specified tolerance of 0.05 mm in a production environment. Experiments were conducted using the KOBA calibration standard and included measurements with and without applying the articulated arm coordinate measuring machine leapfrog method. The results were evaluated according to ISO 22514-7:2021 and ISO 14253-1:2017, which establish criteria for measurement system capability. The findings revealed that neither measurement system met the capability requirements of ISO 22514-7:2021, particularly due to unsatisfactory Q_MS and C_MS values. However, under ISO 14253-1:2017, both systems were deemed conditionally suitable for verifying conformity to the specifications, with the articulated arm coordinate measuring machine showing lower applicability when using the leapfrog method. This research supports the idea that unreasonable demands for compliance with current standards may lead to questioning of the systems that previously met older standards. The study contributes to the ongoing discussion on integrating advanced metrological tools into the manufacturing process and underscores the need for careful evaluation to ensure the capability and reliability of measurement systems in industrial practice.

The operating conditions of the production process significantly influence the resulting dimensional and form accuracy of the workpiece. The operating conditions include the position of the workpiece location, with internal and external heat sources influenced not only by the machine location but also by its operation. In addition, there are the cutting conditions and the feed rate requirements of CNC machine tools. These changes, such as workpiece position, feed rates, and machine heat load, are further reflected in the ability of the machine to run at the position required and interpolate within the given tolerances of circularity. For the accuracy and repeatability of positioning, the machine was set up according to ISO 230-2 and for the circular interpolation tests according to ISO 230-4. The obtained results show the importance of attention to the appropriate setting of the operating conditions of the production process, where the knowledge of the geometric accuracy of the CNC machine tool in its working space can systematically increase the manufacturing accuracy itself or be another tool suitable for predicting the dimensional and form accuracy of workpieces.

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We discuss two approaches to multilateration with a particular focus on numerical aspects for a given dataset. More precisely, we calculate the volumetric errors of the MCV 754 milling machine from the data measured by a LaserTRACER and provide criteria showing which numerical method is appropriate for the solution of the multilateration problem with respect to a given measurement dataset. In the first case, we consider two cost functions of the optimisation problem; in the second, we use the extremal principle method. We discuss the calculation accuracy depending on the matrix condition number. Our results are compared to the reference results produced by the Trac-Cal software, which is a standard used by most producers for error compensations.