Robotic Aircraft Finishing System

During my second year at Lockheed Martin Aeronautics I worked on the Robotic Aircraft Finishing System (RAFS) for the F-35 Joint Strike Fighter.

RAFS test spray
A dry-run test spray on RAFS to test interference zone logic

System Description

RAFS applies the “low observable” coatings to the F-35. These coatings must be applied to tight tolerances; too thin and stealth is compromised, too thick and flight performance is compromised by added weight. In addition, coatings must applied in confined areas like the inlet ducts, and target thickness varies widely by area. Robots are used to apply coatings far more precisely and repeatably than is possible manually.

RAFS comprises three 6-axis Fanuc robots mounted on 2 and 3-axis rail systems. In addition to the rails, long end-effectors are required to reach the entire workspace. Coatings are sprayed through a nozzle on each end-effector. NC programmers use special software integrated with CAD models to generate spray trajectories. Regulating coating delivery through the nozzles is just as critical to performance as controlling robot motion. Each robot requires a Coating Delivery System (CDS) consisting of agitators, pumps, flowmeters, and pneumatics to regulate coating flow and shape the plume.

When used in production, RAFS operates fully autonomously while operators watch from an adjacent room. A human-machine interface allows them to select spray routines and monitor for faults.

RAFS human-machine interface
The RAFS human-machine interface. The coating delivery system cabinet is visible through the window.

My Contribution

I joined the project during the installation phase. Following installation I helped to thoroughly validate hardware and software functionality. One example is the testing of “interference zone logic” which prevents collisions between robots. I also oversaw modifications, like the addition of tachometers on the agitators. I redesigned end-effector components to increase backside clearance when spraying in the inlet ducts. I tuned CDS parameters to achieve the desired flowrate and plume shape.

Most of my time was spent conducting test sprays on a fiberglass mockup of the F-35 to check that coating thicknesses were within tolerance. NC programmers could tweak robot speeds to adjust thickness, but needed thickness measurements at trajectory waypoints to do so. To facilitate this I designed and fabricated a pneumatic marking device that mounted to the nozzle. I wrote code to automatically step through spray trajectories and actuate the device at each waypoint, marking measurement locations. To help the NC programmers utilize the data, I also wrote code that displays thickness measurements at their proper locations on the CAD model, for which I was awarded a Certificate of Achievement.

RAFS measurement location marking with teach pendant
Stepping through a spray program by teach pendant, marking thickness measurement locations

Relevant Publications

Neal Seegmiller, Jonathan Bailiff, and Ron Franks, Precision Robotic Coating Application and Thickness Control Optimization for F-35 Final Finishes, SAE International Journal of Aerospace, Vol. 2, No. 1, March, 2010, pp. 284-290. Paper# 2009-01-3280. |pub|pdf|

Acknowledgements

Jonathan Bailiff and Ron Franks oversaw my work on RAFS at Lockheed Martin. Pratt & Whitney Automation was contracted to install RAFS and program the human-machine interface.

Copyright © 2014 Neal Seegmiller