Piezoelectric and Other Drop Ejection Technologies for Drop-On-Demand Inkjet

Abstract

Drop-on-demand (DOD), or impulse, inkjet has been in practical use as a printing and deposition technology for over thirty years. The popularity and growth of this technology can be attributed to evolutionary improvements in the physics of operation, materials, and ink or fluid chemistry. In addition to traditional desktop printing, DOD inkjet is finding acceptance in the areas of industrial printing and digital fabrication. In general, most applications of DOD inkjet technology have centered on thermal and piezoelectric technology as actuators for drop ejection. However, other types of actuators such as thermal membrane, electrostatic membrane and electrostatic inkjet may provide advantages in a more specific range of applications. Although this paper will focus on piezoelectric actuators, a review of the history, physical principles, and current state of each type of inkjet actuator is presented. Thermal inkjet made DOD technology and color graphics available to millions of users on the desktop as well as many other printing applications. Low cost piezoelectric technology entered the marketplace just prior to the rising wave of digital fabrication and materials deposition applications. The wider materials compatibility has led to broader use of piezoelectric inkjet in industrial applications. The physics of the piezoelectric inkjet drivers and the efficacy of the technology for printing applications are also reviewed. Links are drawn between the deformation modes and the varieties of actuation chamber design. Simple one dimensional acoustic theory can be used to model the propagation of pressure waves induced by piezoelectric actuation. The use of multi-pulse waveforms for the control of drop formation is discussed. Free boundary fluid models describe the interaction of pressure wave energy and surface tension that leads to an ejection of a small volume of fluid. Two-phase fluid models describe the dynamics of drop flight, including the formation of satellites and the consequences of drop size modulation techniques. A model of drop placement accuracy is presented. The techniques and tools of piezoelectric inkjet characterization are reviewed, including advances in imaging techniques and the emerging use of modeling and simulation as a primary tool in an iterative design-simulate-prototype-test printhead development process. These explicit models have allowed the successful development of miniaturized piezoelectric designs fabricated with MEMS techniques, which represent the state-of-the-art and future of piezoelectric inkjet. Lastly, the paper will view these significant milestones and technological advances in light of how inkjet technology might influence the future.