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Abstract

The present invention provides an ink-jet ejection device which is capable of ejection or ink (including hot melt ink) jet frequencies greater than 50,000 Hz. A cantilevered beam of selected shape is mounted at its base to a piezoelectric element which oscillates the base. The beam is shaped so that its moment of inertia is reduced toward its free end. The element is activated by an oscillating electrical signal the frequency of which is equal to or close to a natural frequency of oscillation of the beam. In the preferred embodiment herein a third or higher modal frequency is utilized. Because of the structural configuration of the cantilevered beam and the selected frequency of oscillation thereof, the tip of the beam oscillates over an amplitude which is significantly greater than the oscillation amplitude of the base. The beam is highly damped and made of low density material so that the tip amplitude is extremely responsive to variations in the base amplitude. The tip of the beam is provided with an aperture which is preferably tapered in cross-section. One opening of the tapered aperture is in fluid communication with a reservoir of ink and the other opening of the aperture is positioned at an appropriate distance from a recording medium such as paper towards which individual droplets of ink from the reservoir are to be propelled. When the tip amplitude is above a predetermined threshold the solid-fluid interaction between the tapered aperture and the ink causes a drop of ink to accelerate through the aperture and be ejected upon each excursion of the tip of the beam toward the printing media.

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First Claim