Broetje-Automation from Wiefelstede near Oldenburg has been active in the international aircraft industry for over 36 years. In addition to its core business with machines and systems for riveting, joining and assembling complete aircraft structures, the Lower Saxony-based company manufactures systems for the production and processing of components made of carbon fiber reinforced plastics (CFRP), for robot applications and for process-monitoring image processing. Leading European and American aircraft manufacturers and their suppliers are currently showing great interest in the so-called MPAC (Multi Panel Assembly Cell) systems in particular: "These systems connect the fuselage components with tens of thousands of rivets," explains Dr. Christian Heyers, Head of Control Technology at Broetje-Automation. The MPAC systems can rivet almost all shells of the various sections of all common aircraft models directly from the CAD model. And with extreme precision: the highly complex end effector of an MPAC with its five positioning axes each for the lower tool and riveting head achieves an electronically controlled and sensor-monitored accuracy of ±0.1 mm when drilling, applying sealant, setting rivets and upsetting.

This linearity is achieved not only by the full-surface multi-tooth engagement, but also by the fact that there is virtually no gap between the tooth carrier and the internal toothing of the ring gear - and therefore hardly any bending length. In addition, the flat tooth contact ensures optimum load distribution across the width. Last but not least, the Galaxie kinematics are completely backlash-free because the teeth - thanks to their cylindrical guidance in the tooth carrier - automatically optimize their alignment and engagement with the internal gearing. At the same time, the hydrodynamic lubrication ensures that the round tooth bodies slide smoothly into the tooth carrier bores. The zero backlash therefore remains constant and permanent.

Overall, the Galaxie kinematics achieve up to 6.5 times more load-bearing tooth surface than helical planetary gears - as previously installed by Broetje-Automation on the process-leading A2 axis of its MPAC riveting machines. All in all, the new technology offers up to 170% more maximum torque compared to other common gearbox kinematics of a comparable size, up to three times greater overload protection and a hollow shaft diameter that is up to 70% larger.

One feature of the backlash-free Galaxie drive that should be emphasized is the very high rigidity under alternating load at zero crossing, which does not change during operation.

© Wittenstein

"The decisive factors for us were the improved torsional rigidity of the kinematics and their absolute freedom from backlash, even with alternating loads in zero passage," says Dr. Axel Peters, Executive Vice President Fastening at Broetje-Automation, referring to the specific benefits when used in the company's own MPAC riveting machines. "This allows us to achieve significantly more precise motion control, even at reversal points, as well as around 30% faster positioning of the lower tool." In other words, whereas the machine previously needed one second to move one inch between two riveting points, it now takes just 0.7 seconds. This in turn has increased the riveting cycle from 18 to 21 rivets per minute. According to Dr. Axel Peters, this is not the end of the story: "Even 0.5 seconds now seems feasible to us. This is possible because Galaxie has doubled the speed of movement of the axis, acceleration is now 140% better and the rate of change of acceleration - the jerk - has even been increased by 250%."

Installation space compatibility simplifies integration

Despite the significantly improved performance data, the new drive system is very compact due to the short individual teeth and the flat polygon bearing - comparable hollow shaft gearboxes would have to be at least two sizes larger for the same torque. Another advantage is that Broetje-Automation no longer needs a separate bearing for the A2 axis thanks to the gearbox's high-performance output bearing - which simplifies assembly and reduces costs. "Galaxie was therefore a perfect fit for the installation situation in the MPAC," concludes Dr. Christian Heyers.

Get the hang of it

Thanks to the new drive system, DMT lathes achieve significantly better performance values when milling. The detailed image shows the installation situation of the Galaxie unit.

© DMT

The Lörrach-based company DMT is a manufacturer of lathes for manual, cycle and CNC machining - also with interactive contour machining if required. The machine portfolio covers performance ranges with maximum swing diameters from 280 mm to 1100 mm, center distances between 500 mm and 6000 mm and drive powers between 11.5 kW and 46 kW. "In addition to the standard machines from the various CD series, some of which can also be upgraded with tool turrets, driven tools and power clamping devices, we also manufacture special turning machines with individual performance requirements," explains Friedrich Spohn, Managing Director at DMT.

As the machining of high-quality materials and the ever-increasing precision requirements of customers are placing new demands on the existing machine technology, the company set out to find a drive system that would enable it to meet requirements such as improved machining quality and higher productivity. The analysis of the milling processes revealed that the torsional rigidity and the backlash of the main motor-gear unit were the decisive variables, as they have a significant influence on the dynamic positioning accuracy. "This in turn affects the machining quality, tool life and cutting performance of the machines during machining operations with the C-axis, among other things," says Friedrich Spohn, explaining the correlations.