Frequency Scanning Interferometry For High Accuracy

Frequency scanning interferometry uses a tunable laser to provide highly accurate distance measurements. It was first developed by researchers at the University of Oxford who were working on the Large Hadron Collider at CERN. The system they have developed enables a single measurement device to simultaneously direct multiple laser beams to many targets, measuring each with extreme accuracy.


Photo of Frequency Scanning Interferometry Lab

Frequency Scanning Interferometry Lab at NPL

If you are still reading this article then I guess you are inquisitive, or perhaps you are bored. In either case, I am by no means claiming to understand the mathematical physics (one of my advisors forced me to take that course – another world) of how frequency scanning interferometry works, but according to the article in the key is the use of a tunable laser.

The UK’s National Physical Laboratory (NPL) has taken this state of the art, obscure technology and developed it into a much more practical and versatile measurement system, addressing the needs of large-scale manufacturing of aircraft and wind turbines, for instance.

Photo of Frequency Scanning Interferometry Target

Frequency Scanning Interferometry Target

In particular, the aerospace industry requires a more accurate and faster way to measure coordinates at large scales. Reducing the fuel burn of aircraft means improving their aerodynamic efficiency, with manufacturers aiming for natural laminar flow wings in the next generation of civil aircraft.

This will require measurements which are approximately an order of magnitude more accurate than what is achievable with a laser tracker. Increasing production rate and reducing manufacturing cost will require a much faster assembly process. Achieving part-to-part interchangeable assembly will also require a step change in large scale measurement accuracy.

NPL’s solution to this challenge is divergent beam FSI. It has the potential to track multiple targets at a frequency of 30Hz and accuracy of tens of micrometers. It is cost-effective because a single laser, detector and controller can be used to measure multiple distances. The laser is split and fiber-channeled to multiple measurement devices, each of which directs beams to all of the targets. The returned light follows the same path back to the detector, housed with the laser. Each distance is then uniquely determined from the returned light using Fourier transform analysis.

For the full article in click here.

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