3D scanning at CERN

Before you can measure particle acceleration, there are other things to measure

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Unless they've been living under a rock, anyone with a remote interest in scientific subjects has probably heard of CERN. With its large particle accelerator, and the largest particle physics laboratory in the world, CERN is present in scientific news fairly frequently. 

Naturally, most people are interested in the discoveries made with the particle accelerator. The nature of dark matter, dark energy, black holes and the expansion of the universe are all concepts that involve such advanced physics that beyond being in awe at them, I can never hope to understand them. However, for running and maintaining the largest particle physics laboratory in the world, there is a vast amount of metrology needed, to the highest achievable precision. 

Lots of different measuring solutions are needed for such advanced, precise work. X-rays, for instance are invaluable in this field, and CERN has a state-of-the-art tomograph for that purpose. Back in 2021, CERN's EN department acquired some new equipment, including a 3D scanner from Artec 3D. 

The scanner is held by a handle mounted inside a spherical shaped cage of targets. These targets are measured by a pair of cameras, mounted at a minimum of 1.5m away from the component that is being measured. CERN explains how the scanner works: "First, the cameras record the measurement volume defined by the reflective targets, as well as the position of the scanner in 3D space and its orientation, before the latter sweeps the component with blue lasers forming a grid pattern that gradually moves across the entire surface as the operator turns and moves the scanner around the object. The positions of the lasers on the surface of the component are detected and the resulting multitude of points is then used to produce a digital reconstruction of the component with a volumetric precision of between 64 and 78 microns, depending on the component's volume." 

The data is processed in a specialised program, comparing the digital reconstruction with a perfect theoretical model of the component, which allows the identification of any deviations. This is shown on a heat map for ease of identification, and also provides point-by-point data for any deviation that has been measured. This comparison then allows any necessary corrections or modifications to be made in order to make the component match as close as possible with the model. 

"This type of scanner is widely used in the automotive, aviation and aeronotics industries. Since the laboratory acquired one in January 2020, the demand for component inspection has exploded, with a wide variety of clients approaching us with all kinds of components," explains Ahmed Cherif who is in charge of the metrology laboratory. Crab cavities, magnet yokes, beam screens and even the ALICE (A Large Ion Collider Experiment, one of eight collider experiments at CERN) inner tracker have already been exposed to the scanner, which can model all kinds of material and even the most convoluted shapes (a small additional sensor can be inserted into the narrowest holes to scan their interior). The only real limitation is the size of the components to be inspected: their dimensions may not exceed 16 m3, which is the maximum volume detected by the cameras from a given position. The measurement volume can be increased by adding more stations, but the accuracy of the measurement will be somewhat affected. 

Of course there are endless other metrology applications at CERN, but it's nice to see an Artec 3D scanner being used, as it's a recognisable machine from a brand that I've written about before, and I've even had the chance to see some in real life, such as at Advanced Engineering.