Method and apparatus for process magnification adjustment

A raster output scanner (ROS) for generating a latent image on a portion of a photoreceptor traveling along a closed path past the ROS, comprising:

• a light source operative to generate light according to image data;
• a scanning mechanism that directs light from the light source toward a photoreceptor according to a selected clock input;
• a fixed frequency ROS master clock input signal;
• an adjustable frequency ROS master clock input signal;
• and
• a clock select component that selectively connects one of the input signals to the selected clock input according to a select input, wherein the photoreceptor includes a plurality of image panel zones in which the ROS generate latent image, with successive panel zones separated by inter panel zones, wherein the controller provides the ROSs with a control parameter indicatinq whether a latent image to be generated on an upcoming panel zone is to be fixed to a first side or a second side of the substrate, and wherein the ROSs individually select one of the output signals for use in generating a latent image on the upcoming panel zone based on the control parameter.

A duplex printing method comprising:

• receiving image data for print job pages;
• selectively generating latent images on panel zone portions of a photoreceptor that continuously moves along a closed path using a plurality of raster output scanners (ROSs) positioned along the path, the latent image being generated by a given one of the ROSs by selectively operating the given ROS according to a fixed frequency ROS master clock signal if the latent image being generated by the given ROS is to be fixed to a first side of a substrate or according to an adjustable frequency ROS master clock signal if the latent image being generated by the given ROS is to be fixed to a second side of the substrate;
• developing toner of a given color on the latent images on the photoreceptor using a plurality of developers individually located downstream of a corresponding one of the ROSs;
• transferring the developed toner to a substrate traveling along a first substrate path using a transfer station;
• fixing the transferred toner to the substrate using a fusing station;
• for two-sided printing, selectively directing the substrate along a second path using a duplex router;
• and
• for two-sided printing, selectively inverting the substrate using a media inverter located along the second path and returning the inverted substrate to the first path upstream of the transfer station.

In a document processing system having a fixed frequency clock source providing a fixed frequency output signal to a plurality of raster output scanners (ROSs) and a numerically controlled oscillator (NCO)-based adjustable frequency clock source providing an adjustable frequency output signal to the ROSs, a magnification adjustment method comprising:

• (a) using a controller to determine a frequency setting for a phase increment control input signal to the NCO-based adjustable frequency clock source;
• (b) starting the document processing system;
• (c) using the controller to set a phase accumulator control input to the frequency setting determined in step (a) above;
• (d) sending a message to a ROS control module (RIM) in the document processing system prior to imaging, wherein the message the correct clock source to use for the next image, the correct clock source being either the fixed frequency clock source or the NCO-based adjustable frequency clock source;
• and
• (e) applying the correct clock source synchronously to the beginning of an inter image panel zone.