Control of high-resolution electrohydrodynamic jet printing

This paper discusses the development of a sensing and feedback–feedforward control system for Electrohydrodynamic jet (E-jet) printing. E-jet printing is a nano-manufacturing process that uses electric field induced fluid jet printing through nano-scale nozzles for achieving better control and resolution than traditional jet printing processes. The printing process is controlled by changing the voltage potential between the nozzle and the substrate. However, it is difficult to maintain constant operating conditions such as standoff height during a run of the printing process. The change in operating conditions results in fluctuating jet frequency and droplet diameter. For stabilizing the jetting frequency across a single run, a two degree of freedom (2 DOF) control algorithm is implemented. The feedforward voltage signal is used to compensate for repeatable changes in the operating conditions and is obtained using an Iterative Learning Control (ILC) algorithm. The feedback controller compensates for uncertainty in jetting operating conditions. The jetting frequency is determined in real time by recording electric current pulses when ink droplets are released from the nozzle. This frequency measurement is then used to control the voltage profile across a run to compensate for changing operating conditions. Experimental results are presented to validate the proposed control method.