The Evolution of Print Defects in Inkjet Printers at Elevated Print Gap Height

Image uniformity is a key requirement for inkjet printers. When the gap between the print-face and media is large, one of the main causes of non-uniformity is the misplacement of droplets due to air-flow instabilities. Here, we characterise the onset of printed image non-uniformity by measuring the optical density variation of images printed with varying numbers of active nozzles. The optical density data are obtained by scanning printed images, which are corrected to remove any scanner-related effects. Several transects across the image are extracted, the peak spatial frequency is computed using Fourier transform analysis, and the results from these different transects are averaged. The amplitude of the main frequency peak in image density variation exhibits the same onset behaviour as seen in numerical simulations of the fluid flow in the printhead-media gap. Using numerical simulation, we extend the range of the study to estimate the operating envelope for the printing system.