Ink jet printers operate by using ink ejectors that eject small droplets of liquid ink onto print media according to a predetermined pattern. In some implementations, the ink is ejected directly on a final print media, such as paper. In some implementations, the ink is ejected on an intermediate print media, e.g. a print drum, and is then transferred from the intermediate print media to the final print media. Some ink jet printers use cartridges of liquid ink to supply the ink jets. In some implementations, the solid ink is melted in a page-width print head which jets the molten ink in a page-width pattern onto an intermediate drum. The pattern on the intermediate drum is transferred onto paper through a pressure nip.
The ink jet ejectors of ink jet printers may become blocked by particles or bubbles in the ink or may have other conditions that result in weak, missing or intermittent jetting. These conditions can cause undesirable printing defects.