Today‘s cars are increasingly custom-built. One customer might want electric windows and heated door mirrors, while another is satisfied with the minimum basic equipment. The situation with aircraft is no different: each airline is looking for different interior finishes. Yet the customer‘s freedom is the manufacturer‘s challenge. Since individual parts and mountings have to be installed in different locations along the fuselage, automated assembly is often not an economical alternative. For many assembly steps, manufacturers have to rely on manual labor instead.
But if errors creep in – if, for instance, a bracket is mounted backwards or in the wrong place – correcting them can get expensive later on. The fuselage has to be reworked at great expense. Today, employees use design drawings to determine whether the individual parts have been attached properly, or manufacturers use rigid and inflexible testing systems to check the part against comparison photos. This calls for an identical part for the template photo – and that can be difficult where one-off parts are concerned.
Researchers at the Fraunhofer Institute for Factory Operation and Automation IFF in Magdeburg, Germany, have come up with a testing technology that is reliable and economic even for one-off production runs. The automated visual testing system generates a digital template and uses it to compare with the assembled components, reliably identifying any errors.
First, an automated camera system takes hundreds of photos of individually assembled holders, load-bearing elements, and parts on the inside of the fuselage shell. For every picture taken, the system determines the exact position of the camera relative to the fuselage shell. At the same time, the software generates the same shots again – but this time using a “virtual“ camera. So essentially, it creates “photos“ using the data of the digital design model. The system compares the photos of real parts with the “virtual“ images. If the system detects any deviations – if, say, a bracket is backwards – it issues a warning. Parts that have not been installed properly are highlighted on the monitor screen. The interesting thing is these steps are completely automatic.
In addition to a two-dimensional check using the photos, the system can also check a completed aircraft fuselage in three dimensions: as in the case of the photos, it uses design data to generate 3D data that it then compares with measurements on the real assembly. Here, conventional 3D measurement methods are used to digitize the components. The system also automatically draws up the testing plan: first, it identifies the best measuring position for every part to be tested. The system forwards the results to the robot, which in turn travels to the position identified, where it shoots the two or three-dimensional images. The result is a continuous process, from design to the finished and assembled part.
The main challenge to researchers was to set up the virtual camera that uses design models to “photograph“ the as-yet non-existent component. Another crunch point was to quickly and automatically locate the interesting areas from among the many millions of points in the 3D images – to hunt down, in the mass of points, the tiny components such as brackets and holders, and to check to see whether they are properly fitted. The fields of application for this testing technology are diverse: the technology can be used wherever flexibility is required and individual parts frequently change. The only condition: design data must be available.