Robot CT Investigates Large Assembly Defects January 18, 2021

Fraunhofer EZRT has been researching and developing in the field of industrial X-ray technology for over 20 years and has extensive know-how in software and hardware components for X-ray and computed tomography systems, especially for demanding special applications. With its components and know-how, the Fraunhofer EZRT partners with plant manufacturers and system integrators in the implementation of innovative X-ray and computed tomography projects.

Advanced Hardware Components and Versatile Software

One of the most important components of an X-ray system is the X-ray detector used, as it largely determines the image quality. The radiation-stable X-ray cameras from the EZRT XEye series are suitable for a wide variety of purposes: The newest and largest detector, the XEye5640, has a significantly larger recording area than other detectors and at the same time has a very high radiation resistance for up to 450 keV X-ray energy. The pixel size from 50 micrometers enables a more flexible and at the same time more efficient handling of test objects. Large objects with thick walls, required several measurement runs previously, can now be fully displayed or checked with just one measurement due to the detector area of ​​40 cm x 56 cm. Application examples can be found in the inline CT of clutch housings or the radiography of engine blocks within the production line inside the production cycle. With the high-speed X-ray cameras XEye-HS of the XEye series, fast, dynamic processes of hidden processes can be recorded. The image area, pixel size and maximum frame rate can be specifically adapted to the respective issue such as the observation of material deformations or turbulent flows.

On the software side, the Fraunhofer EZRT presents has developed the firefly software library which contains various modules: For example, an extension for the calibration of CT systems is available, which enables good CT results to be achieved despite an imprecise or unknown positioning of the X-ray components. The software is delivered together with a specially developed calibration body. In addition, the possibilities for fast measurements with few projections for the optimization of the quality of measurements of components with strongly differently absorbing materials such as plastic and copper and for the correction of scattered radiation artifacts are available. In addition, algorithms for improving and accelerating CT measurements are available.

Dozens of Special Systems in Use

Numerous special systems have already been developed and put into operation together with partners. The robot-assisted computed tomography system ‘RoboCT’ developed for the BMW Group non-destructively analyzes the quality of complete vehicles in automobile production in the early development phase, thereby shortening development cycles. Compared to conventional CT systems, there is the significant advantage of being able to reach test positions on objects of complex shape, such as a vehicle body or in a particularly large work area.

“The automobile manufacturers often only need the CT of a very specific vehicle part,” explains Wolfgang Holub. “The RoboCT is ideally suited for these questions.” The idea for this came up at the EZRT back in 2005. In order to record CTs of aircraft wings, the X-ray source and detector were to be rotated around the object with the help of robotic arms. An ambitious project that succeeded in 2015 in cooperation with an aviation supplier on the outer wing of a business jet.

What sounds simple is difficult to implement in practice. With RoboCT, the X-ray source and the detector must always be exactly opposite each other while they rotate around the object. “The best industrial robots are only accurate to within a millimeter,” explains Holub. For a CT, however, an accuracy of at least ten micrometers is required. In order to still get sharp images, Wolfgang Holub’s team uses geometry calibration. The robots pick up a calibration object from different directions. This data can be used to calculate the inaccuracy of the system and thus compensate for the error in the correct measurement.

BMW is already so convinced of RoboCT that two systems are now in operation. One in the research and innovation center in Munich, where the RoboCT examines the hand-made prototypes of the future models in the pilot plant. The other system is in the Eching test center, where BMW’s Erlkönige have to prove themselves under the most adverse conditions. Not only the glued and welded connections are examined, but also corrosion, the seat of seals or the position of wiring harnesses in the headliner. “Since the CT findings are available much faster than the results of a classic dismantling, automobile manufacturers can use RoboCT to significantly reduce their development times,” emphasizes Holub.

At the moment, the systems still have to be controlled by specially trained experts. The RoboCT team is already working intensively on a simplified operation – with the help of a digital twin of the systems in which the CAD data of the car to be checked can be entered. Then nothing stands in the way of widespread use in production and the chisels for dismantling the body are obsolete.