New measuring head from Pixargus to monitor the quality of laser-assisted tape winding in FRP pressure vessel manufacturing

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New measuring head from Pixargus to monitor the quality of laser-assisted tape winding in FRP pressure vessel manufacturing - JEC

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In a collaborative project with the Fraunhofer Institute for Production Technology (IPT) and industrial partner Taniq, a new measuring head from Pixargus has proved highly successful in monitoring the quality of laser-assisted tape winding in FRP pressure vessel manufacturing. Measuring technology specialist Pixargus plans to take the successful prototype from this project to series maturity.

Whether as mobile tanks for gas or hydrogen, or as stationary storage tanks: Great expectations are associated with pressure vessels made of fibre-reinforced plastic (FRP) and their role for key technologies in the field of light-weight engineering. Tanks for higher pressures are reinforced with thermoplastic carbon tapes to increase their pressure resistance strength. As part of the joint R&D project DaQoTa between the Fraunhofer Institute for Production Technology (IPT) from Aachen, Germany, and the Rotterdam-based manufacturer of robotized winding systems, Taniq, Pixargus has recently developed an inline inspection system that takes digital quality control of safety-critical pressure vessels to an entire new level in terms of reliability, security and efficiency.

In the project plant set up at the Fraunhofer IPT, the carbon tape paid off from a dispensing coil runs through the new Pixargus prototype measuring head. The measuring system is a weight- and size-reduced further development of the Pixargus ProfilControl technology. The optical sensor is so compact and light that it can be mounted directly on the robotic arm of the winding system. Thus, the tape can even be thoroughly checked while under dynamic loading and directly where the laser process is taking place. The robotic laser arm that joins the carbon tape in thin layers with the pressure vessel surface uses the quality data continuously generated by the measuring system in real time to optimize the winding process.

The production scenario: Production of pressure vessels that have to comply with particularly exacting pressure strength requirements. The new inspection technology: While the systems currently available on the market can only inspect either the surface or the dimension, the new two-in-one prototype from Pixargus can do both. In just one measurement, the optical sensor detects surface defects and the thickness and width of the tape.

The highly elaborate surface inspection process of the new system uses light reflection and light transmission techniques. While defects such as inclusions, loose threads and other flaws in the tape are reliably detected by direct incident light, gaps and ruptures are detected by means of penetrating light. All this has been made possible through a camera and lighting element arrangement perfectly adapted to the specific tape properties. The optical sensor captures up to 50 million pixels per second at a resolution of about 25 µm, detecting even the smallest defects down to 0.3 mm in size – and that with the project plant at a maximum production speed of 18 m/min.

In the experimental setup, the tape thickness and width are measured by laser triangulation. “Both measurements are a challenge,” says Stephan Hennicken. Because of the dark colour of the carbon filament, the tape surface is highly light absorbing. For optical laser triangulation measurements, this is definitely a challenging task. “The width measurement is by no means a trivial undertaking – as we have realized during the project. The tape arches as it is being drawn through the inspection system. In order to be able to measure a “curved length”, highly complex mathematical methods have to be applied,” explains the Pixargus Product Manager.

The measuring technology experts from Würselen have successfully solved this task in the project by conceiving a perfect concept of sophisticated lighting, size-optimized design and evaluation algorithms specifically adapted to this demanding inspection task.

Measuring Technology Engineer Hennicken summarizes the second groundbreaking success of the project as follows: “We are now not only able to detect the quality-relevant properties of the FRP tape during the tank winding process, but we can also correlate the quality data of the tape with any position of the tank after winding.” To this purpose, the measuring system features equipment such as an incremental encoder to obtain the relevant path and position information. “In connection with the other data from the tape winding process, we can thus generate a digital twin of the complete pressure tank.” The digital twin makes it possible to document the pressure strength of every tank and the existence of weak points if any. This results in a tremendous boost in safety in the production of high-performance pressure vessels. The layout of the project system would also make it possible to transmit the quality data to downstream components in real time and help optimize processes in subsequent production stages.

After completion of the project, the measuring system expert from Pixargus gives a positive summary. “This system of extremely small and light-weight design has achieved very good inspection performance with – or because of – a system-independent software solution. Even at this small scale, we use the same HMI and the same high networking capability as our full-scale systems,” Hennicken puts it in a nutshell. Within the framework of an adequate customer order, Pixargus would take the next step and develop this prototype into a series-ready system. Apart from this, the measuring experts from Würselen will use the new knowhow acquired during the R&D project for other purposes. “Customers often turn to us with the request for smaller, more compact measuring heads,” says Pixargus Sales Manager Michael Frohn. “This is a topic we will definitely go about.”

The project »DaQoTa« (Digitized and Quality-controlled Production of Composite Pressure Tanks) was carried out within the European funding program »Eurostars«. The German partners received funding from resources of the German Federal ministry of Education and Research (BMBF). Grant no. 01QE1931C

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New measuring head from Pixargus to monitor the quality of laser-assisted tape winding in FRP pressure vessel manufacturing - JEC