410
5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
diminution of amplitude of the interference signal and therefore to possibility that the
signal amplitude can possess the values lower than the threshold level that will cause
signal missing, will bear systematic error into the measurement result and will cause
loss of information about the longitudinal vibration component. Laser specklometer
application for measuring USWS oscillation amplitude made it possible to overcome
this disadvantage of the laser vibrometer connected with measuring signal fading and
to produce continuous measurements, because spectral features of intensity fluctuations of dynamic speckle-field are used as informative parameters. The working face
of the microinstrument (Fig. 5.27) was illuminated with the coherent radiation from
the laser through the interface unit (IU) and illuminating light guide 3. The dynamic
speckle-field scattered by the surface of the microinstrument was registered through
the headend light guide 5 and the radiation input device (ID), and it was converted
into an electric signal with the photomultiplier tube (PMT). The signal came to the
spectrum analyzer SK4-72 through the normalization device (ND) for processing.
There were registered A 1 amplitudes of first spectral harmonic of intensity fluctuation
spectrum of radiation scattered by the surface of the working face of the microinstrument that makes harmonic oscillations. The values of the amplitude A 1 of the
first spectral harmonic were recalculated into values of vibration amplitude with a
calibration curve obtained beforehand that is shown in Fig. 5.23.
The dependence of vibration amplitude of the working facet of the USWS microinstrument on vibration frequency in the area of working frequencies of 69–71 kHz
was obtained with the laser specklometer.
Current of the ultrasonic transformer I t was registered simultaneously with
the measurement of vibration amplitude. The dependence of current on vibration
frequency is of great importance as in the ultrasonic welding unit adjustment of the
generator frequency to resonance frequency of transformer is conducted according
to the maximal value of the current of the transformer. The results of measurements
are presented in Fig. 5.25. The good coincidence of dependencies of transformer
current and vibration amplitude on the frequency in the resonance region is observed
that gives the possibility to make a conclusion about the appropriateness of the use of
transformer current for adjustment of the USWS to resonance. Resonance frequency
of vibration amplitude–frequency and transformer current is 70.2 kHz. Using the
obtained amplitude–frequency characteristic of the USWS, the quality factor Q of
the oscillation system can be determined:
Q = f p/2 f
(5.22)
where 2f is the width of the resonance curve at the level of 0.707.
It is found from Fig. 5.25 that 2f = 0.17 kHz, thus, Q = 502.
Dependence of the vibration amplitude of the working facet of the microinstrument on the transformer current is very important for designing the USWS. The
obtained dependence is presented in Fig. 5.26. It is worth mentioning that it is linear.
Vibration amplitudes were measured with the laser Doppler vibrometer [146–150].
Figure 5.26 shows dependencies of vibration amplitude on the frequency, which
were obtained with the laser specklometer and the laser vibrometer, and give the
5 Laser Specklometer, Speckle-Optical Diagnostics and Laser …
diminution of amplitude of the interference signal and therefore to possibility that the
signal amplitude can possess the values lower than the threshold level that will cause
signal missing, will bear systematic error into the measurement result and will cause
loss of information about the longitudinal vibration component. Laser specklometer
application for measuring USWS oscillation amplitude made it possible to overcome
this disadvantage of the laser vibrometer connected with measuring signal fading and
to produce continuous measurements, because spectral features of intensity fluctuations of dynamic speckle-field are used as informative parameters. The working face
of the microinstrument (Fig. 5.27) was illuminated with the coherent radiation from
the laser through the interface unit (IU) and illuminating light guide 3. The dynamic
speckle-field scattered by the surface of the microinstrument was registered through
the headend light guide 5 and the radiation input device (ID), and it was converted
into an electric signal with the photomultiplier tube (PMT). The signal came to the
spectrum analyzer SK4-72 through the normalization device (ND) for processing.
There were registered A 1 amplitudes of first spectral harmonic of intensity fluctuation
spectrum of radiation scattered by the surface of the working face of the microinstrument that makes harmonic oscillations. The values of the amplitude A 1 of the
first spectral harmonic were recalculated into values of vibration amplitude with a
calibration curve obtained beforehand that is shown in Fig. 5.23.
The dependence of vibration amplitude of the working facet of the USWS microinstrument on vibration frequency in the area of working frequencies of 69–71 kHz
was obtained with the laser specklometer.
Current of the ultrasonic transformer I t was registered simultaneously with
the measurement of vibration amplitude. The dependence of current on vibration
frequency is of great importance as in the ultrasonic welding unit adjustment of the
generator frequency to resonance frequency of transformer is conducted according
to the maximal value of the current of the transformer. The results of measurements
are presented in Fig. 5.25. The good coincidence of dependencies of transformer
current and vibration amplitude on the frequency in the resonance region is observed
that gives the possibility to make a conclusion about the appropriateness of the use of
transformer current for adjustment of the USWS to resonance. Resonance frequency
of vibration amplitude–frequency and transformer current is 70.2 kHz. Using the
obtained amplitude–frequency characteristic of the USWS, the quality factor Q of
the oscillation system can be determined:
Q = f p/2 f
(5.22)
where 2f is the width of the resonance curve at the level of 0.707.
It is found from Fig. 5.25 that 2f = 0.17 kHz, thus, Q = 502.
Dependence of the vibration amplitude of the working facet of the microinstrument on the transformer current is very important for designing the USWS. The
obtained dependence is presented in Fig. 5.26. It is worth mentioning that it is linear.
Vibration amplitudes were measured with the laser Doppler vibrometer [146–150].
Figure 5.26 shows dependencies of vibration amplitude on the frequency, which
were obtained with the laser specklometer and the laser vibrometer, and give the