Precision In Situ Volume Measurement Of Micro Droplets

This research presents an in situ droplet volume measurement system which is applied to the one drop fill (ODF) process of liquid crystal display (LCD) manufacture. The system developed utilizes a stroboscopic technique to synchronize the triggering of a strobe light and a CCD camera. A steady image of the droplet flying in free space can be captured in situ by the CCD camera. The method of precise volume estimation is based on a rotationally symmetric model of the droplet's shape. Polynomial fitting is used to reconstruct the droplet profile. The image resolution can thus be enhanced by a subpixel technique. Compared to a precision electronic balance, the total weight measured by this system has an error within +/- 0.3%, and the computation time for each droplet is about 0.4 s. This satisfies the actual ODF requirements.