Painting of surfaces having numerous facets and/or curved surfaces is a time-consuming process that requires the application of several coats (layers) of paint. Such surfaces are often found on vehicles that have complex surface combinations that include facets, curves, and compound curves. While the primary function of paint is often corrosion control, paint also may be applied as a top coat for utilitarian, branding, aesthetic, and/or marketing purposes.

The large-scale robotic system inkjet-prints intricate graphics on aircraft and other complicated surfaces. (Southwest Research Institute)

Creating these graphics requires significant time and labor expenditures. This is particularly true of the initial masking step that obliges workers to manually fix a stencil on the vehicle to prevent overspray into non-decorated areas. Because of the difficulty in accurately laying down the masking material on large, complex surfaces, this process is prone to error. In addition, masking operations and the multiple paint/cure cycles limit throughput in paint hangars, which further increases operational costs.

Inkjet technology has the potential to eliminate masking requirements by directly printing graphics on complex surfaces. This capability is analogous to inkjet printing on paper, and uses many of the same technologies. Current inkjet printing techniques have demonstrated great versatility with respect to scale and printing substrate; however, current inkjet printing technologies can only reliably and accurately print on flat or nearly flat surfaces. To fully leverage the advantages of inkjet printing on complex surfaces, one must be able to print on all (or most) surfaces, including those with complex physical geometries such as compound curves.

A large-scale robotic inkjet printing system was developed that can print multiple graphic swaths of color onto complex surfaces, creating a continuous graphic image. For the aviation industry, the system can replace traditional, labor-intensive painting techniques to apply large graphics to aircraft fuselages, wings, tail fins, and engine nacelles. Each pass of color, or graphic swath, can be aligned over curved surfaces without spaces, gaps, or discontinuities.

A vision sensor detects an encoded pattern to ensure accurate application of graphic images. The encoded pattern is deposited on the surface in a known location with respect to the most recently deposited graphic swath. The printing system includes high-bandwidth servo actuators to locate the print head with respect to the encoder pattern to permit precise positioning for the next swath.

The new technique is based on earlier work on a laser coating removal (LCR) system. That system combines a mobile robotic platform, laser scanning technology, and high-powered lasers for safe and efficient removal of paint and other coatings. The new inkjet system addressed and overcame obstacles associated with the large, complex surfaces to be painted, as well as the need to adjust for inaccuracies in robot positioning and vibration of robot structures.

For more information, contact Deb Schmid at 210-522-2254.


Tech Briefs Magazine

This article first appeared in the January, 2019 issue of Tech Briefs Magazine.

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