Video/optical requirements for a highlight color laser scanner

The desire to print high quality, highlight color documents at production rates has generated the need for a single-pass highlight color laser scanner. We examine a pulsed-imaging, pulse-width-modulated polygon laser scanner that enables multilevel exposure and subsequent development of black and highlight color toner. As currently used in the Xerox 4850 and 4890 digital printers, this laser scanner writes three different exposure levels; zero-level exposure, mid-level exposure and high exposure for black, white, and highlight color, respectively. In this paper we review the functioning of a pulsed-imaging laser scanner and then examine how it is used in a pulse-width-modulated trilevel mode. A first-order linear-systems model is used to examine the specialized video required for achieving uniform line appearance for both black and highlight color. This model further describes how resolution enhancement may be enabled. A complete laser/xerographic model is used to generate simulated output. The electronics that provide the pulse width and position modulated video signals are described, and photomicrographs of sample prints from the Xerox 4850 are shown. ©