Development and construction of optical systems for checking defects in composite panels

Ready-made calibration body for 71 system setup i3mainz, CC BY SA 4.0

Sandwich components are panels made of composite materials that are required to build house and hall walls or cold rooms. In the production process, small errors that are not immediately recognizable can occur, which lead to visual defects or difficulties in the later design process. This results in rework obligations and correspondingly high costs for the producer. Thyssen is therefore interested in developing a measurement method that identifies defects during production.


A typical deficiency can B. a longitudinal waviness on the plates with an amplitude between 1 and 3 mm over a length of several meters. This should be recognized with an accuracy of 1 mm.

In addition, defects in the form of dents are to be detected with an accuracy of 0.1 mm. The panels are connected using a groove and joint system. The groove and the joint (between 4 cm and 22 cm wide) must fit together exactly so that, for example, temperature insulation is guaranteed. When checking the grooves and joints, an accuracy of 1 mm is required.


After the research and selection of the hardware and software components was carried out in 2011, the focus in 2012 was on the conception of the necessary evaluation and analysis tools, especially for the problem of longitudinal ripple.

The concept for the system structure for recording longitudinal waviness, which was completed last year, provides for two high-resolution measurement cameras with a high recording frequency and a line laser. The line laser is aimed at the board at right angles to the running direction, while the two cameras monitor the laser and record the deformations. Two cameras are required to capture the 1 m wide panel with sufficient resolution.

This system with two cameras requires an orientation and calibration concept in order to put the observations of both cameras into a common context. The shared context ensures that the actual profile is captured across the board. This is the only way to draw a qualitative and quantitative comparison to a target from a CAD template.

The orientation and calibration concept was developed, implemented and tested on the i3mainz. A calibration body was designed from the calibration concept, which was then manufactured by the project partner. With this calibration body, it should then be possible for the project partner to set up and check the system himself.

In 2013, the focus was on evaluating the test data and developing software tools for analysis and the first partial solutions.

Last year’s test setup generated 10GB of test data with 13,000 images. In order to simplify the evaluation of the test data, the development of analysis tools was preferred. The evaluation of last year’s test setup confirmed that the desired resolution and accuracy can be achieved with the system design.

The evaluation showed that some assumptions about the admission conditions were incomplete. Local variations in the measurement situation can be better compensated for in the future. Compared to the target from the CAD planning, the beginning of the profiling varies. There are also deformations on the surface due to mechanical effects from rolling and cutting in the production process. These phenomena cover up the errors to be actually detected by at least ten times. Therefore, in the forthcoming development phase, a deformed target is used or algorithmic compensation is integrated.


The further development and adaptation of the analysis tools for the surface inspection were included as new work for the next phase of the project. Basically, the feasibility and usability of the system was demonstrated. A critical milestone was reached with the results of the activities in 2013, with which the continuation of the project was secured in a further project phase.