Analysis of Ghosting in Electrophotography

A common print quality problem in electrophotographic (EP) printing is ghosting. Ghosting refers to a vestigial image repeated at regular intervals down the length of a page and appearing as light or dark areas (negative or positive ghosting, respectively) relative to the surrounding field. There are many sources of ghosting, including most EP printer subsystems and many of their components. Subsystems from charging, development, photoreceptor, to fusing can all produce ghosting. The ghosts can be both positive and negative (darker and lighter). Having multiple ghosting sources can make the sources of ghosting difficult to determine, pointing to the need for reliable diagnostic tools. This paper demonstrates how a commercially-available image analysis system is used to quantify ghosting and diagnose its causes. The system utilizes test targets specifically designed to reveal ghosting problems and are optimized for automated inspection. The analysis method uses frequency domain techniques that make it possible to isolate ghosting from other print quality problems. The method can also correlate observed ghosting to the printer component or components causing it. In addition to its role in R&D, the method is suitable for production environments as a quantitative tool for setting acceptance limits and performing quality control prior to shipping the product.