Meaning
Non-contact optical measurement of surface velocity and displacement utilizes the frequency shift of reflected laser light to analyze high-frequency mechanical oscillations. Applying laser doppler vibrometry to ultrasonic welding equipment allows engineers to characterize the vibration profiles of horns and transducers without adding mass to the system. Since traditional accelerometers would alter the resonant frequency of the tool, this optical method is the standard for high-precision diagnostic work.
It is particularly useful for verifying the performance of complex, custom-molded horn profiles.
Measurement Technique
The laser beam is focused onto the active face of the vibrating horn to capture its real-time displacement during operation. Through laser doppler vibrometry, the velocity of the tool is measured, which allows the calculation of the absolute amplitude of the vibration. This test is executed across multiple points to construct a map of the amplitude distribution.
The collected data reveals if the tool is vibrating uniformly or if it contains localized dead spots.
Horn Optimization
Designers of ultrasonic tooling use the measurement data to refine the physical geometry of the horn before it is hardened. Comparing the actual amplitude profile obtained via laser doppler vibrometry against finite element analysis simulations helps in correcting non-uniformities. This step is crucial when welding large or irregular polymer parts, where even energy distribution is required to prevent local burns or cold joints.
Troubleshooting Value
The detection of micro-cracks or internal defects in older welding horns is made possible by identifying abnormal vibrational modes. High-resolution laser doppler vibrometry identifies these discrepancies long before the tool fails catastrophically or damages the molded parts.
