We observed the generation of ink droplets expelled from Kyzer type pulse on demand ink jet head of multi-nozzle with a high speed motion picture camera, which was made in our laboratory. This camera is able to approach some phenomena which cannot be observed by a synchronous lighting method, i.e., varying time delay from the start of droplet generation to the turning on of the light source. The camera takes pictures of ink jets by moving a roll of film and flashing a light source. The camera has the maximum flaming rate of 15000 frames per second, and can record 141 frames at a time. The frame are 2mm wide and 24mm long. Their resolution is about 30 micro-meter. This camera system is very easy to operate and requires a little time for setting up. It takes only half a minute to get one motion picture. Furthermore, the sequential frames makes measuring jet velocity easy and observation of droplet generation clear. This paper shows four kinds of motion pictures: ejected distilled water, jets of ink expelled by four different drive pulse-voltagies applied on piezoelectric crystals, jets of ink expelled by varying time interval between burst droplet generation and ink expelled by five different piezo crystal drive frequencies. Those photographs indicate that two factors are important to generate stable droplets: the standing wave frequency of ink flow in the pressure chamber of the print head and thixiotropic effect of ink.
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