A Pulsed-Xenon Densitometer for On-Press Measurements.

The use of a reflection densitometer to measure the color of printing ink on paper as it is being printed is a technique that promises to reduce the amount of ink and paper wasted in the printing industry. An on-press densitometer can be used as a process monitor which measures printed colors and indicates when these colors are out of tolerance. On-press measurement of color bars as they are moving has been made practical with the use of a pulsed-xenon densitometer. This paper first describes this new densitometric approach, which is based on the use of a pulsed-xenon flashtube as a light source. It is then shown how the densitometer has been integrated into an on-press densitometer system for use in web-offset printing. This system is capable of continuously monitoring the density of process colors on both sides of the web, and alarming the operator whenever any density varies outside preset tolerance limits. Graphical displays quickly point out trends in density readings and pinpoint the source of any out-of-tolerance condition so that it can be immediately corrected. Since this system detects and identifies changes in color density before they otherwise would be measured or noticed, it allows the press operator to correct color problems before they reach an unacceptable level.