This paper reports on ways to better predict droplet ejection velocity of push-mode piezo inkjet technology by upgrading the conventional equivalent circuit model. Calculation results from the traditional model imply that the driving pulse width conditions without ink ejection only periodically exist in the pull-push piezo driving mode. However, ink ejection is actually observed under any pulse width condition. The displacement of the diaphragm with respect to the piezo element input voltage waveform was measured with a highly accurate capacitive displacement gauge to correct for the difference between the actual measurements and calculations. The equivalent circuit model was then modified so that the measured diaphragm residual oscillations could be expressed. We presumed that an actual inkjet printhead contains an effective spring oscillation component, effective actuator mass, and damping component larger than that used in conventional equivalent circuit model calculations. We demonstrated that the difference between the calculated results and actual measurements could be reduced. Modifications to equivalent circuit model are based on the addition of an effective mechanical spring oscillation component having the same function as the ink chamber compliance, an increase in actuator inertance corresponding to the mass of the actuator, and an effective resistance element expressing a damped oscillation.
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