Line laser utilization in passenger tire testing.

Optical measurements are said to be an interesting tool for the analysis of different material properties, as well as the products themselves. They play an important role in the rubber industry, where they are frequently used in product testing.

A relatively simple optical technique for registration of displacement history is presented in (ref. 1). Optical techniques determine the evolution of actuating forces. This is based on the relative displacement of two grids. The method can be used for measuring velocities of up to 200 m/s.

In the study (ref. 2), the measuring system, which is based on a trigonometric technique, is suggested. The analyzer consists of two CCD cameras and a line laser. This system is able to measure a profile of spatial objects in conjunction with approximate profile.

An interesting subject for industry is the measuring of surface deformation of tested objects, which are under the influence of higher temperature, pressure and humidity (ref. 3). The non-contact measurement uses two CCD cameras for the determination of the object's image before and after deformation. A combination of optical techniques with electronic interferometry is suggested. This method is simple and applied in industry institutions.

The results of sidewall deformation in the dynamic regime were studied and compared in (ref. 4). A local deformation was determined by a profilometer. The second introduced a commercial system using two CCD cameras, and the deformation of the sidewall in the dynamic regime was determined. The results are full color images that can be compared with FEM results.

In work (ref. 5), the authors present the characteristic features of systems working in the dynamic regime, evaluation of such data and condition of testing. Testing of rubber samples in the dynamic regime is described in (ref. 6).

In this article, we introduce a non-contact optical system with one CCD camera, which registers the distortion of a laser wave-front caused by the measured deformed object, and present the possibilities of using this system in the rubber industry.

Experimental arrangement and discussion

The presented system is used for the determination of the profile changes and tire width by laser line module. The shape of line laser copies the profile of an object. The length of a laser trace defines a width of the object.

The measuring apparatus consists of laser, CCD camera, computer and competent software. Figure 1 presents a principle measurement by line laser method. The line laser trace is in the normal incidence of the measured object, and the CCD camera is focused directly on the laser trace. Measurement of the deformation of an object is based on detection of a laser's front wave shape changes.

[FIGURE 1 OMITTED]

Calibration of the system is necessary before the measurement. The camera has to be perpendicular to the measured object. This way, it determines the width and thickness of the object. This system offers three possibilities of calibration of a test object. Baseline checking gives way to measure the displacement on dependence of laser line, which is created by the connection of two end points.

In the first step, we tested the precision of the apparatus in the static regime. The results are in figure 2. The straight line represents values measured by the presented method, and blue squares values are measured by hand measurements with measuring equipment of the precision 0.01 mm. The repetition ability of measurements was also tested, and the obtained results are in figures 3 and 4. The tested object was a glass fabric laminate plate. The results presented in figure 3 were obtained after the complete decomposition of the apparatus and successive measurements of the object for ten times. The obtained precision of measurements was 170.13 [+ or -] 0.03 ram. The results presented in figure 4 show the repetition ability of the apparatus at given settings of the measured sample for ten times. Obtained precision in this case was similar and equal to the value 170.10 [+ or -] 0.02 mm.

[FIGURES 2-4 OMITTED]

After this initial information about precision of the apparatus, we present the application of this method in static measurements of tires in the next section.

The simplest utilization of the presented method is non-contact evaluation of the tire dimensions. After the positioning of the test tire in the holder by laser level, the setting of the camera and line laser, and the calibration of the whole apparatus, we obtain an electronic picture of the tire in digitalized form, and the software is able to measure it point by point (figures 5 and 6).

[FIGURES 5&6 OMITTED]

Figure 8 shows the electronic picture of the real tire from figure 7. It is possible to test tread wear using the same method.

[FIGURES 7&8 OMITTED]

Then we tested the static properties of the tires. For these measurements, we used the hydraulic stand shown in figure 5. The tire was illuminated near the contact area of the tire. Deformation of the tire after applying the static loading is shown in figure 9.

[FIGURE 9 OMITTED]

In the next step, we tested the relaxation of the tire after immediately stopping it from a velocity of 100 km/h. The results can be seen in figure 10. The measurement has been realized on the testing machine described in figure 6.

[FIGURE 10 OMITTED]

Afterwards, we started with dynamic measurements of the tire. In the first step, we tested the creation of the equilibrium state of the tire dimensions at a constant velocity of 100 km/h. The results of this experiment are shown in figure 11. It is possible to see that after approximately 10 minutes of rolling, the tire reaches the equilibrium dimension.

[FIGURE 11 OMITTED]

The deformation of the tire tread at different velocities in steady state conditions is shown in figure 12. The realization of the experiment was according to figure 6. The tire was illuminated against the contact area and the testing machine.

[FIGURE 12 OMITTED]

Conclusions

The presented method gives the possibility to measure mean values of the dimension of a sidewall, as well as a tread at a defined position given by a laser trace. The apparatus has a very good sensitivity on the level [+ or -] 0.03 mm. It is possible to realize the measurements in the static or dynamic regime. All of the obtained results are digitized and prepared for use in FEM analysis. In comparison with a commercial system (Aramis), it is not necessary to lay the patterns on the surface of the tested sample. On the other hand, a disadvantage of our system is the local measurement (given by position of laser trace) of the mean value of a displacement at quasi-equilibrium conditions. The presented method is quick, low in price, with easy matching and very good repeatability.

References

(1.) J. Degrieck and P. Verleysen, Experimental Mechanics', 42, 298 (2002).

(2.) T.H. Tsai, K.C. Fan and J.J. Mou, Measurement Science & Technologies, 13, 190 (2002).

(3.) J.F. Roman and V. Moreno, Journal of Modern Optics, 46, 653 (1999).

(4.) P. Kostial, M. Mokrysova, L Kopal, M. Klabnik and P. Ziacik, Proceedings of the International Conference on Machine Dynamic Problems, Poland (2004).

(5.) P. Kostial, M. Mokrysova, I. Kopal, M. Klabnik and P. Ziacik, Of Third Youth Symposium on Experimental Solid Mechanics, Italy (2004).

(6.) R Kostial, M. Mokrysova, I. Kopal, M. Klabnik and P. Ziacik, Kautsch. Gummi und Kunsts., 7-8, 371 (2002).