Printing system exposure module optic structure and method of operation

• US 5,142,303 A
• Filed: 09/20/1991
• Issued: 08/25/1992
• Est. Priority Date: 12/21/1989
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Nelson, William E.
• Primary Examiner(s): Reinhart, Mark J.
• Application Number:
  US07/763,472
• Time in Patent Office: 340 Days
• Field of Search: 346/108, 346/107 R, 346/76 C, 346/160, 355/202, 359/315, 359/316, 359/317, 359/318, 359/291, 358/296
• US Class Current: 347/239
• CPC Class Codes: G06K 15/12 by photographic printing , e.g. by laser printers
• CPC Class Codes: G06K 15/1252 using an array of light modulators, e.g. a linear array
• CPC Class Codes: H04N 1/1275 using a solid-state deflector, e.g. an acousto-optic deflector or a semiconductor waveguide device
• CPC Class Codes: H04N 1/195 the array comprising a two-dimensional array or a combination of two-dimensional arrays

Abstract

There is disclosed a deformable mirror device (DMD) exposure unit and method of operation for use in a xerographic printing system. The exposure unit is constructed with an integral unmodulated light source condensing light onto a substrate containing, in one embodiment, a multi-row set of deflectable mirrors. The deflection of each mirror is controlled by electronic circuitry established on the same monolithic integrated substrate. The substrate is arranged with mirror elements which can be adjusted easily during assembly to eliminate time consuming construction or maintenance routines. An optic structure, using integral light baffles and deflection edges, assures the proper contrast and light energy level at the image. In the case of multiple rows of pixels, the on-chip circuitry acts to reregister the spatially separated images through a suitable time delay. The formation of printed images of suitable uniformity and quality is achieved by the incorporation of an overlap factor relative to the multiple rows of pixels as defined on the integrated substrate.

Claims

1. A printing system exposure unit, said exposure unit comprising

a) a source of light separately positioned with respect to

b) a spatial light modulator device such that unmodulated light from said source falls upon said device, said device comprising;

i) a substrate;

ii) at least one linear array of pixel elements positioned over said substrate, such that an air gap exists between said array of pixel elements and said substrate, each said pixel being electrostatically deflectable;

iii) addressing circuitry arranged in said substrate beneath said pixels, said addressing circuitry operable upon receipt of a serial data signal to select ones of said array so as to electrostatically deflect and latch said selected ones such that light from said selected ones is directed to said focusing apparatus, said addressing circuitry being arranged only on areas of said substrate physically removed both above and below said linear array of deformable mirror elements, thus separating the spatial light modulator superstructure from lying directly above the substrate structure;

c) a focusing lens for accepting light from said selected ones of said array;

d) mounting supports integrated into a removable housing containing all elements of said exposure unit in proper optical alignment, to removably attach to said exposure unit to said printing system while maintaining a proper alignment, such that said exposure unit is entirely contained within the confinements of said housing.

2. The spatial light modulator exposure unit set forth in claim 1 wherein said exposure unit is required to provide a row length of r pixels for said printing system, selected from pixels of said spatial light modulator device which contains m pixels, where m is greater than r, wherein the desired dot-line of information consisting of r pixels can be electronically shifted left or right within said m pixels, by said addressing circuitry, to permit alignment of the printed image to the print media.

3. The spatial light modulator exposure unit set forth in claim 1 wherein said linear array of pixels are arranged into two substantially parallel rows, separated by exactly twice the row height, and interdigitated with the even pixels in the first of said rows and the odd pixels in the second of said rows, wherein said pixels are slightly larger than the effective pitch of the combined rows thereby establishing some overlap of the edges of the respective pixels in the two rows.

4. The spatial light modulator exposure unit set forth in claim 2 where in said addressing circuitry comprises first and second substantially parallel arrays of delay buffers preceding a mirror driver element on said first row, so that serial line data introduced to the deformable mirror device is split into two sets of bits, one set of bits going to said first row only after an intervening electronic delay of approximately two dot-lines, thereby spatially reinterlacing the pixels of the first row with the corresponding second row pixels at a photoreceptor approximately two dot-lines later.

5. The printing system set forth in claim 1 wherein said exposure unit further comprises a lens housing having a central flat surface for aligning said focusing lens to said deformable mirror spatial light modulator, said housing having a first end for holding said light source also in alignment to said deformable mirror spatial light modulator.

6. The deformable mirror device spatial light modulator exposure unit set forth in claim 5 wherein said spatial light modulator is an elongated rectangular structure supportable by its sides in a plane substantially perpendicular to said flat surface of said exposure unit, further including locating features for attachment of said spatial light modulator, such that said features permit a degree of translation and rotation of said modulator device with respect to the optical axis of said exposure module.

8. The deformable mirror device spatial light modulator exposure unit set forth in claim 6 wherein said exposure unit further includes a channel in said flat surface, said channel arranged to receive light rays from selected pixels to be reimaged onto a printer photoreceptor by said focusing lens.

7. 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.

9. A printing system exposure unit comprising at least two spatial light modulator devices, said exposure unit including a feature for adjustably mounting said devices with respect to the other devices, offset from said other devices such that respective images of all said spatial light modulator devices can be independently aligned so as to operate in concert to produce a continuous exposed light image in a printing system.

10. 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.

11. The method set forth in claim 10 wherein said exposure unit has a base, and wherein said substrate is positioned on one side of said base and said surface is positioned on the other side of said base, and wherein said focusing of said image on said surface includes the step of:

transmitting said image to at least one mirror positioned to reflect said image to said surface via a slot in said exposure unit base.

12. The method set forth in claim 10 wherein when the velocity of said surface rotations fluctuate, a banding of the final printing image occurs and wherein said substrate includes at least two rows of selectively addressable mirrors, said method further including the step of:

coordinating the selective timing of said rotation of mirrors in alternate rows to coincide with variations in rotation of velocity of said surface so as to electronically compensate for said banding.

13. 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.

14. The method set forth in claim 13 wherein said focusing apparatus is operative to communicate images to a drum in a xerographic printing process.

15. 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.

16. The system set forth in claim 15 wherein said common first axis passes through the center of an imaging lens lying concentrically within said energy baffle, and wherein said first axis is perpendicular to said energy modulating device.

17. The system set forth in claim 16 wherein said dead-band is wide enough to maintain separation of said images at common plane of focus.

18. The system set forth in claim 16 wherein said common first axis plane of focus is approximately the aperture plane of said imaging lens.

19. The system set forth in claim 16 wherein said intervening optical lens elements form reflected images at said aperture plane of suitable magnification to create within said dead-band no image energy of said source;

and wherein

said dead-band lies midway between respective images of said source formed along said common first axis and said common second axis.

20. The system set forth in claim 16 wherein the angle between said reflected images of said energy source is determined by the deflection angle of said deflectable elements of said modulation device.

21. The system set forth in claim 16 wherein said source is arrayed at an angle with respect to said modulator device to position images of said source along said first and second common axes to permit maximum energy transfer to said imager lens of said reflected energy image.