Event-Based Vibration Frequency Measurement with Laser-Assisted Illumination Based on Mixture Gaussian Distribution

Vibration measurement is an important part of monitoring the movement of objects and the working state of equipment. Noncontact vibration measurement can be achieved without installing a measuring device on the object to be measured; thus, it has stronger applicability. However, traditional noncontact measurement methods, such as frame-based visual measurement, are prone to motion blur and difficult data processing. Event cameras encode the relative change of light intensity rather than the absolute value of the intensity recorded by conventional cameras, and this unique imaging mechanism makes them stand out with no motion blur, high temporal resolution, and low power consumption. The displacement produced by the vibration of the object causes changes in light intensity, which are naturally captured by the event camera. Therefore, the use of event camera for vibration frequency measurement has inherent advantages. However, the existing event-based methods cannot work under unstable lighting conditions, because changes in ambient light trigger events and interfere with the generation of events triggered by changes in light intensity produced by vibrations. Moreover, the existing event-based computational methods do not model the mapping relationship between events and vibrations, the results of which are, thus, inaccurate. This article presents a method that utilizes laser-assisted illumination to help measure vibration frequencies. At the same time, a mixture Gaussian distribution is proposed to fit the frequency distribution. The experimental results show that the proposed method achieves accurate noncontact vibration frequency measurement of the object fixed on a vibrating table in the measurement range from 20 to 300 Hz, with a relative error of 6.23 parts per thousand, 4.03 parts per thousand, and 5.45 parts per thousand under the ambient lighting of 0.01, 55, and 3800 lux, respectively. Furthermore, the measurement results of the vibration frequency of the loudspeaker show that the proposed method can measure the vibration in multiple directions.