Printing system exposure module optic structure and method of operation

A system for modulating light energy, said system comprising:

• a) a source of light energy;
• b) a spatial light modulator device, said modulator device including:
• i) an array of deflectable pixel elements deflectable into at least two orientations with respect to said energy source;
• ii) addressing circuitry arranged so as to follow each element of said array to be independently operable for modulating a reflected image of the source of said light energy along a common first axis under control of a modulating signal input to said circuitry and for modulating said reflected image of said source along a common second axis when said modulating signal input to said circuitry is of opposite binary sense, said images of said source separated when reimaged in the aperture plane of imaging lens by a dead-band, defined as containing no appreciable light energy from either the modulated or unmodulated image of the light source;
• c) a lens element for directing light from said source to said modulating device;
• d) an imaging lens displaced from said set of pixel elements and arranged along said first axis.

The method of establishing an exposure unit for a xerographic printing system where images are created on a photoconductive surface for transfer to a printed surface, said method comprising the steps of:

• establishing a source of light rays at a first location within said unit;
• positioning a substrate at a second location within said unit, said substrate containing at least one row of spaced apart individually selectable and rotatable mirrors;
• directing said light rays onto a desired active area of said substrate by positioning lens elements constrained by said exposure unit to collect, direct, and suitably aperture light rays from said source onto said substrate to form an image of said source rays magnified so as to fall at, and substantially fill, the aperture of a subsequent imager lens;
• constructing a light ray baffle between said first and second location, said baffle being a series of saw-tooth steps with walls of said steps perpendicular to the optic path of light rays reflected by said mirrors;
• mounting a reflected light ray imaging lens in conjunction with said baffle such that said light rays controllably reflected from said mirrors to said imaging lens will be focused via said lens onto said surface;
• and
• adjusting said substrate so that light rays from said source which impinge on said substrate are reflected away from said imaging lens by said wells of said light gathering baffle when said mirrors have not been selected for rotation and such that upon the selective rotation of any mirror light rays from that selected mirror will pass through said baffle without impacting said baffle walls and thence into an aperture of said imaging lens.

A method of operating an electrophotographic printing system to avoid undesirable banding of the final printing image due to a fluctuations in the rotation of a photoreceptor drum, said system using an exposure unit containing a and deformable mirror spatial light modulator device array, and a source of light separately positioned with respect to said spatial light modulation devices such that unmodulated light from said source illuminates the entire array of said device and a focusing lens for accepting light selectively reflected from certain pixels of said device, and wherein said pixels of said substrate include at least two rows of selectively deflectable mirrors, said method comprising the steps of:

• electrostatically deflecting selected ones of a plurality of pixel elements within each line formed in a substrate, said deflecting controlled by addressing circuitry also formed in said substrate in response to input signals;
• receiving data representative of the rotational velocity of said photoreceptor drum;
• processing said received data to determine the variation of the surface velocity about a desired nominal value, and calculating a correction value to be added to or subtracted from the deformable mirror deflection time;
• and
• instantaneously applying the correction value to the selective timing of said deflection of mirrors in alternate pixel rows to coincide with variations in rotation an velocity of said drum so as to electronically reduce said mechanically introduced banding in the printed image.

A system for modulating energy, said system comprising:

• an energy modulating device;
• a source of energy arrayed at an angle to said energy modulating device, and directed onto said device by intervening optical lens elements;
• said device operable for modulating said energy to provide an array of independent energy modulated spots, and said device comprising a set of deflectable elements which can be displaced into at least two orientations with respect to said energy source, each said element independently operable for focusing a reflected image of said energy source along a common first axis under control of a modulating signal and for focusing said reflected image along a common second axis when said modulating signal is not present, said images separated by a dead-band;
• and
• an energy baffle at least partially surrounding and disposed along both said axes, said baffle arranged to pass said first axis reflected images while attenuating said second axis reflected images.