Mobile robot machining the vertical stabiliser of an Airbus A320.
Fraunhofer IFAM
A lot of milling, drilling and assembly work is still being performed manually in aircraft construction, because the unfinished components vary both in size and design. Slight variations are unavoidable in the extremely lightweight and elastic materials, posing a challenge to automatic machining. When automated machines are used, they are generally heavy, customised gantry systems that move slowly on rails over the components. These systems are expensive, inflexible, subject to long downtimes, and are therefore not very productive.
Researchers at the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Stade, Germany, have now joined industrial partners in developing a mobile robot that can approach the components autonomously and perform all necessary work on location. The robot is versatile, and it can rapidly adapt to shape deviations and to product and type changes while fulfilling the high accuracy requirements in the aviation industry. Deviations during machining are less than half a millimetre.
Higher accuracy due to measuring systems on output-drive side
"Above all, by integrating specially developed output-side measurement systems, we managed to substantially minimize error", explains Christian Böhlmann, head of the Integrated Production Systems group. Whereas the measuring equipment is fastened to the motor in conventional industrial robots, it is located directly on the axes in the new robot. The researchers therefore know the axis positions at all times. Furthermore, the machining accuracy was enhanced by measures in the control system to compensate for frictional adherence effects in the gear units and by refined robot calibration. This calibration determines the true robot geometry by measuring it once, and takes it into account when calculating movements. As aircraft components can be up to 20 metres long, the robot was designed to be mobile: a rigid platform with three drive wheels allows it to move freely throughout the factory. It retracts its wheels and stands in a stable position as soon as it reaches its destination.