Highly dynamic compensation kinematics for aircraft construction

Engineer Live News Desk
ADMAS system at IFAM in Stade: An articulated robot from MABI Robotic with a hexapod from Physik Instrumente processing a CFK part. Photo via Fraunhofer IFAM.

At the International Aerospace Exhibition ILA Berlin in June, Physik Instrumente (PI) presented itself as a partner in the LuFo VI-1: ADMAS (Advanced Machining and Sealing) research project.

Under the leadership of Airbus, PI has contributed its more than thirty years of expertise in hexapod development to the research project. The project, which was publicly funded by the German Federal Ministry for Economic Affairs and Climate Protection and supervised by the DLR Project Management Agency for Aviation Research, was successfully completed at the end of April 2024.

As part of the joint project, PI developed the high-performance hexapod H-900K101 for highly dynamic compensation kinematics in aircraft construction. The aim was to increase the processing and sealing precision for CFK components in RTM (resin transfer molding) manufacturing processes and to reduce manufacturing times and process costs. Thanks to its low weight and high stiffness, the fibre composite material CFK makes a decisive contribution to greater energy efficiency and CO2 savings in aircraft.

Dynamic Compensation of Process Forces

The focus of the compensation kinematics is the contour machining of the single-aisle wing shells of the Wing of Tomorrow made of CFK by means of milling and deburring, as well as their subsequent sealing and drilling. Combined with an articulated robot for rough positioning, PI's hexapod is used for the fine positioning of the machining and sealing tools.

“With the new H-900K101 hexapod, we have implemented a highly dynamic system that can accelerate a payload of up to 40 kg in the XY plane at up to 12,000 mm/s²," said Dr Christian Sander, Head of Technology Development Parallel Kinematics at PI in Karlsruhe, Germany "The system is able to dynamically compensate for high-frequency path deviations under the influence of process forces during milling."

The newly developed hexapod system was designed for the specific boundary and environmental conditions of the application and is therefore optimised in particular for the time-critical manufacturing processes with the specified tolerances of the aerospace industry.

Fine Positioning of Tools

In addition to this high dynamic performance, the hexapod system offers fibre optic data transmission between the hexapod controller and the driver electronics, a very low latency time when using the EtherCAT interface and IP54-sealed components. Fibre optic data transmission allows the hexapod controller to be conveniently located in the control cabinet outside the processing cell without compromising the variety of interfaces while controlling the driver electronics over a distance of up to 100m. For the EtherCAT interface, a deep integration of the EtherCAT functionality into PI's controller and driver architecture has been realised. As a result, PI's positioning system contributes only a minimal amount of dead time to the complex control loop for path error compensation between the edge-detection sensor system, the articulated robot, and the hexapod. The response time in the EtherCAT control loop between the hexapod's position request and position response is 1.5m/s.

Recently, the ADMAS LuFo project investigated the use of acceleration sensors for wear detection on individual hexapod struts in the context of condition monitoring. The frequency spectrum of vibrations within a single strut can be mapped to characteristic eigenfrequencies of drive components, providing an indicator of system changes.

Modular Systems

Hexapods offer six degrees of freedom in the smallest space. For industrial applications, combinations of absolute position sensors, software, and motion controllers are available to control complex motion profiles. All drive technologies are customisable. PI's precision hexapods are available in standard configurations for loads from 1-250kg and repeatability to ±0.06μm. Customised precision hexapods can support loads in excess of 2,000kg.

With travel ranges from a few millimeters to several hundred millimeters, the machines enable precision down to the nanometer range and velocities from 0.1mm/s to 500mm/s. PI hexapods are used worldwide in silicon photonics, automation, medical technology, astronomy, and research. Depending on requirements, they can be specified for environments such as IP54, laboratory, cleanroom, high vacuum, and ultrahigh vacuum.

www.pi.de

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