| dc.description.abstract | Moiré optical measurement is non-contact, non-destructive, low cost,
etc. At the same time, the method of using Moiré fringes to calculate and
analyze the surface vibration or subtle changes in object size is faster and
more efficient than traditional digital image processing methods.
At this stage, digital Moiré uses projectors to project gratings. There
are two important factors that affect the measurement quality. (1) Because
the sampling frequency of the camera does not match the projection
frequency of the projector, the recorded image will be affected by the
projector slide. Light flicker causes noise, which cause the result to have
image bias during the final data analysis. (2) The angle between the projector
and the camera does not reach a suitable angle, so that the Moiré contour line
phenomenon cannot be generated in the recording image, diminishing the
image feature value emphasis effect.
The optimization of this study is based on the experiments according
to the above shortcomings. (1) The frame rate of the camera is changed from
30fps to 60fps, which is the same as the projector’s fps. (2) The installation
position adopts the grating side projection, and the camera shoots from the
front. (3) The focal length of the grating is 0~5cm in front of the object.
The results show that the hardware position adjustment has been improved.
In the past, the digital Moiré did not have the shortcomings of contour lines.
In addition, the speaker output fixed frequency to verify the accuracy of the
system. At 7Hz vibration frequency, the data measured by the contour image
iv
can effectively emphasize the waiting period. For the characteristic value of
the measured object, the intensity of the data before optimization is only 7.5
at 7 Hz, and there is a relative value error of 0.6 Hz and 8 Hz. While the
optimized data shows that there is a clear peak at 7 Hz, and the intensity
increased to 17 Hz, which is quite More than twice the size of the previous
system. The noise is reduced and the overall signal strength is significantly
increased from less than 2 to more than 4, which truly achieves the effect of
Moiré′s enhanced image and becomes one of the reliable tools for measuring
vibration. | en_US |