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Terrestrial Scanning: A Game Changer

Joel Martin
By Joel Martin Director of Product Sales Management, North America, Hexagon AB’s Manufacturing Intelligence Division

In many manufacturing industries today, 100% inspection is commonplace. This market-changing trend obviously drives OEMs to design inspection devices that collect data much faster than in the past. The data-capture issue becomes more formidable with larger, complex components, particularly in the aerospace manufacturing industry where tolerances continue to get tighter and assemblies continue to get bigger.

A good example is a company that produces a small component that requires inspection of all surfaces with 100% coverage.

The part is about the size of a coffee cup and inspection tolerances are somewhere around a thousandth of an inch. In this particular case, the company would have several viable measurement technologies to choose from, such as an automated structured light system with a turn table or an articulated arm integrated with a scanner.

On the other hand, what would that same company do if their 100% surface coverage requirement was to encompass an entire wide-body commercial jet airliner?

What if the company needed to scan the entire aircraft with submillimeter inspection accuracies?

The major concern here is twofold starting with the sheer size of the object. The second matter is the required measurement uncertainty. There are metrology solutions used to measure objects of this size, and the first tool that comes to mind is terrestrial laser scanners.

Several large aerospace manufacturers have tried to apply the technology with varying results as the terrestrial laser scanners have improved in accuracy. The usage limitation usually comes down to either the achievable accuracy or the required workflow.

The problem with accuracy is the difference between how the manufacturing industry specifies what is required to measure a part, and what is typically used in the geomatics world. In geomatics, it is standard practice to specify a product with a 1 sigma uncertainty value (≈68%), where metrology devices are usually specified with a maximum permissible error or MPE specification (≈100%). It is common for manufacturers to require a 4:1 or even a 10:1 ratio for their inspection equipment, meaning that if a part has a 1mm tolerance, the inspection device must have an MPE measurement uncertainty of 250um or less.

In light of these technical issues and the quest for 100% surface coverage for aerospace structures, the metrology industry has pushed forward with exciting advancements.

In recent years, users of laser scanners can capture data into a single coordinate system within volumes up to 197 ft. when tracked with a laser tracker.

This breakthrough not only decreases the global uncertainty of the survey, but also solves the “scan everything” workflow. These scanners can have as much as a three-foot standoff (distance from the scanner to the part) and a two-foot-wide scan line to allow large complex parts to be scanned in situ from a single laser tracker station.

As large-volume hand scanners have started to bridge the gap between terrestrial laser scanners and metrology grade solutions, another leap in technology continues this trend. A non-contact scanning Absolute Distance Meter (ADM) was introduced into the Leica Absolute Tracker family, creating a completely new field of terrestrial laser trackers that can register sub millimeter non-contact surface scans with metrology grade SMR (spherically mounted retro-reflector) laser tracker measurements.

The data capture results are dense, precise and stunning in a visual way. Users can take these portable, single battery powered IP54 sensor systems to the factory floor or transport them to remote outdoor locations for data acquisition operations on the tarmac.

The aerospace industry is always out front of the innovation curve demanding the same from its technology partners. Their pioneering role can take 3D terrestrial scanning for industrial applications into a new era of large-scale 100% inspection.

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