Results_and_Discussion
3.2.1.3 Results and Discussion
In Fig. 3–23 we can see analyses of holographic interferograms showing oscillations of the saw blade fixed in the flange of the massive fixture, excited by the electromagnetic exciter.
The detail of the saw blade radius is displayed in Fig. 3–23 b, where the highlighted line is the one from which the Bessel function values were calculated (Fig. 3–23 c). There are also displayed the positions of the interference fringes measured and calculated by the RGB function presented in Fig. 3–23 d, which records the intensities of both the minimum and maximum of interference fringes (the value of pixels of 0 is displayed in black and the value of 255 is displayed in white, while the other values are displayed in shades of grey). From the formula (3.47) the deviation of the oscillating saw blade is calculated and graphed on the highlighted line.
(A – analysed part)
Fig. 3–23 Analysis of resonance frequencies of the saw blade
In the cases of resonant oscillations it is useful to know the distribution and the value of the amplitudes, as they show us which parts of the saw blade are the most deformed and where it is suitable to intervene in order to change the rigidity if we want to retune the system of the saw blade points. The shapes of the saw blade vibrations depend on its dimensions as well as on the excititation frequency, and are expressed by Chladni patterns obtained through holographic recording.
Fig. 3–24 and Fig. 3–26 such possibilities of saw blade modification are illustrated, where the intervention in order to reduce the deviation amplitudes in axial direction can be realised. These modifications are also executable by cutting out apertures (Kvasna et al, 2004) or by local mechanical prestress. By these modifications the saw blade resonance surface is disturbed to lower its amplitudes, which can reduce axial deviations occuring at operating speed.
a)b)
Fig. 3–24 Possibilities of saw blade modifications by cutting out grooves
a) for number of nodal diameters k =2 and at f = 1 700 Hz
b) for number of nodal diameters k = 3 and at f = 2 400 Hz
(cross-hatched round area)
As it was mentioned above in the theoretical analysis of harmonically oscillating movement of the object, from the reconstructed hologram it is possible to determine the value of deviation defined by two neighbouring interference fringes. From the course of the fringes we can determine the oscillation shape and from the number of the fringes we can determine the oscillation amplitude.
The aim of this experiment was to judge the possibility of holographic interferometry application for the study of resonance shapes of saw blades (Mikleš, Tuharský, 1999). In any case, many experiments are to be carried out aimed at the behaviour of saw blades at lateral thrusts, operating speeds (Svoreň, Javorek, 1993), and operating temperature adaptation to the state of discs.
