Premium Aerotec - Nordenham
Premium Aerotec - Nordenham

Laser Tracker corrects the exact position of robots in aircraft construction

With A350, it‘s a different story. Each aircraft fuselage is provided with profiles, so-called stringers, for reinforcement. Up until now, they have mainly been made of aluminium.

In general, they are manually positioned over holes created by a milling machine. With the A350, which is primarily comprised of carbon fibre-reinforced plastics (CFP), this doesn‘t work. The material hardens in an autoclave, a pressurised oven, so it can‘t be drilled.

As an aerostructure supplier, the aircraft manufacturer supplies large parts for the new generation of Airbus’ long-haul aircraft, the maiden voyage of which is scheduled for the middle of this year. This includes the entire front fuselage. “The stringers have to be attached precisely to avoid subsequent drops in quality.

Manual positioning is uneconomical here, as ultimately up to 13 aircraft of this type are to be built per month in the future. Our goal is to automate aircraft assembly with robots as well. The requirement, however, is that the robot works as precisely as a milling machine.”

Put more specifically: to not jeopardise subsequent production and assembly processes, stringers for the A350
XWB (which can be up to 18 m long) must be set in place in the circumferential direction with a tolerance of +/- 0.3 mm and in the longitudinal direction with a tolerance of +/- 1 mm. After initial experiments, disillusionment spread in Nordenham. The first robot was supposed to move 3,000 mm, but stopped after 2,997 mm. The second always moved 1.5 mm too far. “A difference of 0.1 percent seems marginal at first, but with a stringer length of 18 m, it adds up. This was unacceptable to us,” said Lewerenz.

Robot manufacturer Fanuc wasn’t at fault, though, as the values were within the robots’ specifications. This means that robots work less precisely than milling machines, as they respond to changes in weight and force, which leads to deviations. The automotive industry gets around this by “teaching” the robots, but Lewerenz dismissed this possibility: “The system technology is designed for 800 aircraft in all. Sample components for teaching are thus not economically feasible. This is why we at Premium Aerotec have to assume that the machines are programmed fully offline so that everything is right during production.”

So the aerospace industry supplier began searching for an option to move robots to the correct position without teaching them, that is, after taking corrective measures. A system was needed which could be placed on the robot head. With the Leica Absolute Tracker, a camera (the so called Leica T-Cam) and a Leica T-Mac the 3D coordinates of a point and its orientation in space (i, j, k or roll, pitch and yaw) can be captured simultaneously. This is important because 6D monitoring of the robot is required (it has six degrees of freedom). This means not only the position of the robot head can be monitored, but also its orientation.

If the three spatial orientations (roll, pitch and yaw) are required as in the application at hand, they are determined using the Leica T-Cam for the LED arrangement of a Leica T-Mac. The vario zoom enables nearly distance independent precision of these photogrammetrically determined measurement values within the volume of work. . . . .

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