Appl. Sci. 2023 , 13 , 1389
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analysis of their series of images [20,21]. Thanks to advances in electronics, it is now possible to record sequences of images of processes occurring during strength tests of various materials in real-time. The series of images obtained in this way can be reviewed in any way, focusing on the significant phenomena occurring during the experiment, and can also be subjected to automatic analysis, the purpose of which is a quantitative description of a given process. An example of such a solution is the Lenso vision system for recording the surface of materials subjected to mechanical testing. Thanks to the use of Digital Image Correlation [22,23] in the square areas of successive images in the sequence, they allow for precise estimation of local deformations of the observed surfaces. Vision systems are also used in papermaking and printing to detect defects and assess the quality of produced paper or print [24]. This is possible thanks to the use of advanced algorithms for detecting defects visible in subsequent images of the recorded sequence, and often also algorithms for automatic recognition of the type of defect. Implementation of these operations in real time requires the use of computers with high computing power. This allows to control the production line based on the information received and improve the parameters of the production process or reject a defective product. Observing the shape of paper samples during the crushing resistance test allows for associating changes in the shape of the sample with the magnitude of the force acting on it during the test. To make this possible, it is necessary to record images of the sample being tested and synchronize the resulting series of images with data from the machine.
2. Materials and Methods 2.1. Measuring Setup
The use of digital image analysis methods in measuring the crushing resistance of pa- per required solving the problem of synchronization of measurement in a universal testing machine with the recording of images of the tested samples. In order to simultaneously record the displacement of the moving handle of the testing machine and the force acting on the compressed sample and the images of the sample to be tested, the measuring setup shown in Figure 1a was prepared.
( a ) ( b ) Figure 1. Viewof ( a ) the measuring station, ( b ) the handles of the testing machine with sticked checkerboard patterns and the paper sample to be tested. The stand consists of a testing machine (1) Zwick Roell Z 010, an SCT test holder (2), a camera placed on a tripod (3)—a Canon EOS 6D Mark II full-frame DSLR with a Canon MP-E 65 mm f/2.8 1–5 × Macro lens (4) and an illuminator providing constant illumination with the possibility of adjusting its direction (not visible in the photo). This
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