Vibro-acoustic quality control using laser vibrometers and optimized data processing techniques

Laser Doppler vibrometers are widely used for noise analysis in research and development. Recently laser vibrometer have started to emerge as an important element for inspection and quality control in manufacturing processes. In this paper we present three different applications for non-intrusive inspection of automotive components in a rough production environment. The first application is the detection of cracks. Cracks in materials usually result in a change of resonance frequencies and damping. Although the environmental noise on the production floor is very high, it is shown in this paper how to extract the relevant parameters for quality control using impulse excitation and analysis of the acoustic-related vibration response. Another application is the test of a bulb filament commonly used in headlights. By combining a suitable excitation of the bulb with vibro-acoustic signal processing and appropriate classification, bulbs could be detected and removed from the production line that would otherwise have failed prematurely. Small electric motors with gears are common components in automobiles. The vibration signals that are produced when they are activated are measured with a laser vibrometer. Statistical tools are then used to analyse and classify these parts. Motors with defects and unacceptable noise contributions can be extracted. It can be shown that the result has a very high correlation with subjective human response.