Raster output scanner fraction-of-scan polygon rephasing and algorithm

A controller for calculating image registration in a process direction by minimizing a required phase shift of a rotating polygon in a raster output scanner, said controller performing the steps of:

• determining a requested phase shift in clock cycles of said rotating polygon to align a beam reflected from a first facet of said rotating polygon to a location on a photoconductive surface;
• if said requested phase shift in clock cycles is greater than a number of clock cycles equal to one-half of a period between said first facet and a neighboring, subsequent second facet, subtract a number of clock cycles equal to a period between said first facet and said second facet from said requested phase shift in clock cycles to determine a required phase shift and decrement a line counter by one;
• if said requested phase shift in clock cycles is less than a negative number of clock cycles equal to one-half of a period between said first facet and said second facet, add a number of clock cycles equal to a period between said first facet and said second facet from said requested phase shift in clock cycles to determine said required phase shift and increment said line counter by one;
• and
• if said requested phase shift in clock cycles is greater than or equal to a negative number of clock cycles equal to one-half of a period between said first facet and said second facet and is less than or equal to a number of clock cycles equal to one-half of a period between said first facet and said second facet, equate said required phase shift to said requested phase shift;
• wherein said line counter represents a number of pixel lines before a start of image registration on said photoconductive surface.

A raster output scanner imaging apparatus, comprising:

• a photoconductive surface adapted to move in a process direction relative to a frame;
• a first rotating polygon rotatably mounted to said frame and having a plurality of facets adapted to reflect a beam onto said photoconductive surface in the form of first scanlines oriented transverse to said process direction;
• a first sensor corresponding to said first rotating polygon and mounted to said frame and near said photoconductive surface to enable positional information of said photoconductive surface to be detected;
• a second rotating polygon rotatably mounted to said frame and having a plurality of facets adapted to reflect a beam onto said photoconductive surface in the form of second scanlines oriented transverse to said process direction;
• a second sensor corresponding to said second rotating polygon and mounted to said frame and near said photoconductive surface to enable positional information of said photoconductive surface to be detected;
• a controller in communication with said first rotating polygon, said first sensor, said second rotating polygon and said second sensor for synchronizing said first rotating polygon and said second polygon to position said first scanlines and said second scanlines at a common location on said photoconductive surface by the use of clock cycle counts;
• wherein said controller is adapted to adjust a rotational position of at least one of said first rotating polygon and said second rotating polygon based at least on a difference in a first distance between said first rotating polygon and said first sensor and a second distance between said second rotating polygon and said second sensor.

A raster output scanner imaging apparatus, comprising:

• a photoconductive surface adapted to move in a process direction relative to a frame;
• a rotating polygon rotatably mounted to said frame and having a plurality of facets adapted to reflect a beam onto said photoconductive surface in the form of scanlines oriented transverse to said process direction;
• a sensor corresponding to said rotating polygon and mounted to said frame and near said photoconductive surface to enable positional information of said photoconductive surface to be detected;
• a controller in communication with said rotating polygon and said sensor for adjusting a rotational position of said rotating polygon to position said scanlines at a desired location on said photoconductive surface by the use of clock cycle counts based at least on a distance between said rotating polygon and said sensor.

An imaging system for forming multiple superimposed image exposure frames on a photoconductive surface moving in a process direction, comprising:

• a raster output scanner forming a plurality of scanlines in a transverse direction across the width of said member by reflecting modulated beams from a plurality of facets of a rotating polygon;
• a photoconductive surface indicator for registering images on the photoconductive surface;
• means for detecting the beginning of a scanline and providing a start of scan (SOS) signal representing the detection;
• means to detect the relative phase between the lead edge of the start of scan signals and the detection of said indicator including a fast clock timer to provide a phase shift digital count;
• means to detect the rephase adjust required to correct for a distance between said raster output scanner and a sensor corresponding to said raster output scanner;
• and
• means to change the speed of the rotating polygon to synchronize the phase of said indicator with the lead edge of said SOS signals and incorporate said rephase adjust.

In an imaging system for forming multiple superimposed image exposure frames on a photoconductive surface moving in a process direction, a method of providing scanning speed and phase shift control comprising the steps of:

• forming a plurality of scanlines in a transverse direction across the width of said member by reflecting modulated beams from a plurality of facets of a rotating polygon;
• sensing scanning speed;
• providing a signal representing image exposure frame registration;
• detecting the beginning of a scanline and providing a start of scan (SOS) signal representing the detection;
• detecting the rephase adjust required to correct for a distance between said rotating polygon and a sensor corresponding to said rotating polygon;
• determining the relative phase between the start of scan signal and the signal representing image exposure frame registration;
• converting scanning speed and relative phase into digital signals;
• and
• summing the digital signals and subtracting the rephase adjust and inverting the polarity in order to change the speed of the rotating polygon to synchronize the signal representing image exposure frame registration with the SOS signal.