Coordinate metrology is used by designers, engineers, and manufacturers to accurately gauge the characteristics of mechanical components. Coordinate measuring machines (CMMs) can make comparisons of components along a manufacturing line or even forecast whether a proposed system is fit for purpose by modeling coordinates onto a specified workpiece.
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The provenance of coordinate metrology can be associated with the research of individual French scholars such as Pierre de Fermat (1601–1665) and Rene Descartes (1596–1650), who came up with the concept of utilizing the coordinate system to describe components and 3D geometrical objects with a reference system. The very first coordinate measuring machines (CMMs) were created by the Scottish Ferranti in 1956 and the American Moore Tool Company in 1957, with valuable contributions from Franco Sartorio.
Is Coordinate Metrology Multi-Disciplinary?
Coordinate metrology also includes imaging techniques that use optical tools and computerized tomography for imaging substrates and entire parts. Manufacturing and production sciences, such as rapid prototyping, reverse engineering, structural engineering, and bioengineering systems techniques, are currently inconceivable without a coordinate measuring technique.
Furthermore, this technique is widely used in the inventory of artworks and the preservation of monuments, structures, and the development of infrastructure design. Electronics, dynamics, embedded systems, optoelectronics, and computer engineering developments are extensively implemented here. The advancements could not be implemented without research advancements in the field of coordinate metrology, which makes it a multidisciplinary field.
Introduction to Coordinate Measuring Machines (CMM)
The groundwork for CMM is provided by coordinate metrology. A coordinate measuring machine measures a sequence of distinct points from the configuration of a solid product using an extremely sensitive electronic probe. These assessments are used to verify that the component meets predetermined standards and specifications.
The device, measuring probe, and a computer with evaluation software are the constituents of a CMM. CMMs use a variety of probes, such as tactile, photonic, infrared, and white light probes.
The Working of CMMs
CMMs use a responsive sensor to locate a workpiece component at a synchronized spot, similar to a fingertip tracking a map for a milestone. The machines are controlled by three axes: X, Y, and Z. The X-axis is used to trace the objects horizontally sidewise, the Y-axis maps forward and backward, and the Z-axis is used for vertical mapping as the machine is observed.
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CMMs assign a specific destination to a component by taking an interpretation on these three axes. This location is critical because it is comparable to the reference as well as to all other places on the workpiece. To make judgments and estimations about the workpiece being measured, all CMMs integrate information from two data systems. This data is a hybrid of machine coordinate systems and part coordinate systems. Machine coordinate systems refer to the CMM's X, Y, and Z grids. The forms of the workpiece to be evaluated are introduced by part coordinate systems.
To thoroughly evaluate a workpiece, a CMM performs a procedure known as alignment, which is a core principle of coordinate metrology. Alignment, as a method, is older than the digitization and modernization of CMMs and coordinate metrology. This technique is extensively time-consuming, and complications arise when dealing with conical, rounded, or chamfered edges. To obtain precise measurements, such contours necessitate realignment and modifications.
The term datum has a unique and practical significance in coordinate metrology. A datum, or bit of data, is a coordinate on a workpiece for a CMM and its user. It also assists in drawing attention to the features in that coordinate. A datum on a component might be a notch, extension, or paneling.
Translation is required to identify the correlation between workpiece datums. Translation is fundamentally the transition from placing a datum in terms of a grid to finding it in relation to other datums. Rotation is the process of turning datum knowledge such that it aligns with some other datum. A CMM may use rotation to look at measurements and interrelationships, as well as assess the characteristics of different datums.
Applications of the CMM and Coordinate Metrology
Coordinate measuring machines that use coordinate metrology find use in the motor vehicles industry, manufacturing processes, electronic parts, aerospace, and many other large corporations. These machines are ideal for testing and inspecting testing equipment and devices. CMMs are used to perform complete inspections on airframes to determine the surface finish of the constituents. It could also be used for classifying functions to ensure optimum constituent linking within the specified tolerance level.
Advantages and Disadvantages
The CM machines function effectively and with excellent precision. Identifying the coordinates and distance between the two points of reference is all that is required to obtain an accurate measurement. The operator's expertise has been reduced due to the digitalization of CMMs. Furthermore, these are beneficial because they reduce preparation time, inspection fixturing and infrastructure expenses, and recording time.
However, there exist certain disadvantages including costly machines, alignment issues of the workpiece and the probe, calibration errors, as well as the breakdown of measuring software.
ISO Standards for CMM
ISO/TC 213/WG 10 is a standards body responsible for developing ISO benchmarks for CMM. Three sequences of ISO standards have been established by the working group. These industry-oriented standards are as follows:
- ISO 10360 Geometrical Product Specifications (GPS) - Acceptance and reverification tests for CMM
- ISO 15530 Geometrical Product Specifications (GPS) - Techniques for determining the uncertainty of CMM measurements
- ISO 23165 Geometrical Product Specifications (GPS) - Guidelines for the evaluation of CMM test uncertainty
The ISO 10360 standard provides the framework for acceptance test assessment techniques for CMM, and ISO 23165 incorporates these unpredictability assessment methods into the ISO 10360 acceptance test. The ISO 15530 standards specify procedures for evaluating measurement uncertainty using CMM.
Researchers from UK and Italy have published an article in the journal Precision Engineering proposing a system for investigating measurement uncertainty in coordinate metrology. Quantitative point cloud frameworks based on Gaussian random domains were used to fit high-density point clouds gained via repeated measurements.
The outcomes demonstrated the feasibility of using fitted fields and Monte Carlo simulations to evaluate the probability distribution function for shape attributes. Using the proposed statistical analysis method, it is possible to achieve thorough information regarding random estimation errors (under repeatability or reproducibility conditions), as well as bias, if a novel set of more precise measurements or a distinct forecast model is available. This method offers a novel framework for exploring how measurement error is spatially plotted.
In short, overcoming present problems will lead to the rapid commercialization of coordinate metrology and future research should be focused on developing smart and rapid processing CMM machines.
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References and Further Reading
Senin, N., et al. 2021. Statistical point cloud model to investigate measurement uncertainty in coordinate metrology. Precision Engineering 70. 44-62. Available at: https://doi.org/10.1016/j.precisioneng.2021.01.008
BrainKart, 2022. Applications Advantages, Disadvantages of Co-ordinate measuring machines. [Online]
Available at: https://www.brainkart.com/article/Applications-Advantages,-Disadvantages-of-Co-ordinate-measuring-machines_5842/
ELEY METROLOGY, 2022. What is Coordinate Metrology?. [Online]
Available at: https://eleymet.com/2020/09/14/what-is-coordinate-metrology/
Hexagon, 2022. Intro to Coordinate Metrology. [Online]
Available at: https://www.hexagonmi.com/en-US/solutions/technical-resources/metrology-101/intro-to-coordinate-metrology
Huang, L., 2022. What Is CMM Machine: Components, Uses, and Benefits. [Online]
Available at: https://www.rapiddirect.com/blog/what-is-cmm-machine/
Sładek, Jerzy A. 2016. "Coordinate metrology." Accuracy of Systems and Measurements.
Leach, Richard. 2014. Fundamental principles of engineering nanometrology. Elsevier. 263-288.