Alternative to laser vibrometers: a non-contact vibration measurement based on enhanced laser speckle pattern and stroboscopic sampling

This research introduces a novel technique for non-contact vibration measurement: the laser speckle stroboscope. Non-contact vibration measurement always yields superior results compared to contact methods as it does not impose any sensor load on the system, making it crucial for sensitive systems. Non-contact measurement techniques are also employed to assess vibrations in extreme temperatures and chemical environments where conventional sensors are prone to damage. This system, built with a laser, lenses, and a photodiode, offers significant improvements in precision compared to traditional stroboscopes. Conventional stroboscopes struggle to accurately measure linear vibrations, while high-precision alternatives like Laser Doppler Vibrometers (LDVs), are expensive. This study attempts to address the limitations associated with laser vibrometers. The laser speckle stroboscope addresses these limitations with a compact and cost-effective design. The system works by creating a laser-generated speckle pattern on the vibrating surface. The pattern is then sampled using a stroboscopic method in which the sampling period is synchronized with the vibration frequency. Rigorous testing confirmed the system’s effectiveness. The focused laser beam precisely captured the rotational movements. For linear vibrations, the system detected deviations as low as 3 Hz for specific frequencies. The rotational measurements showed a maximum deviation of 2 Hz for two out of four tested speeds. These results were validated using an external laser vibrometer, proving the system’s reliability.