Evaluation of short-time fourier-transformation spectrograms derived from the vibration measurement of internal-combustion engines

The main contribution of the paper is that multiple vibration components are available to be tracked on the image using a self-developed component-tracking method. The results can be transformed backwards into frequency-domain to describe the operating status of the engine after the manufacturing process. Vibration data recorded at the end of the production line by laser-vibrometer pointed on the cylinder block of an internal-combustion engine (ICE) were treated using spectrograms created by Short-Time Fourier-transformation (STFT). The resulted spectrograms can be transformed into grayscale image where image processing methods are used to extract information about the vibration components reducing the required computational resource. The preparation of the image was necessary in order to improve those areas which contain important information in case of the vibration components. This can be executed with Brightness-Contrast-Gamma correction and with many technique e.g. morphological filtering.