Spatial light modulator exposure unit and method of operation

• US 5,072,239 A
• Filed: 12/21/1989
• Issued: 12/10/1991
• Est. Priority Date: 12/21/1989
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Nelson, William E., Mitcham, Larry D.
• Primary Examiner(s): Reinhart, Mark J.
• Application Number:
  US07/454,566
• Time in Patent Office: 719 Days
• Field of Search: 346/108, 346/107 R, 346/1.1, 346/160, 350/353, 350/355, 350/360
• US Class Current: 347/255
• 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: G06K 15/1257 on more than one main scanning line
• CPC Class Codes: G06K 15/1295 using a particular photoreceptive medium

Abstract

There is disclosed an exposure unit and method of operation having advantage of deformable mirror device (DMD) technology. The exposure unit is used to provide front end image processing for a xerographic process printing system. The unit, in one embodiment, is constructed as a unitary member having a lamp socket, a support for holding a flat DMD substrate, a set of light focusing lenses, an image focusing lens, a light baffle and an extra light trap chamber. The unit is separated from the xerographic drum by a solid base which contains a slot positioned so that the image from the image lens passes therethrough for supplying the image to the drum. The light bundle is directed to the xerographic drum location along an optical path formed by a system of fold mirrors in the lower body of the unitary member.

Claims

1. An optical exposure unit for use in a xerographic printing system having both and exposure portion and a contact reproductive portion, said contact reproductive portion operative in response to presentation of exposure unit optical dot patterns said dot patterns representing final images on a print transfer medium residing in said reproductive portion which subsequently transfers said represented image to a final printed surface, said exposure unit comprising;

a light source at one position thereof;

a support disposed opposite said light source for holding an array of spatial light modulator elements, said elements individually controllable for modulating light to form said dot patterns;

at least one condensing lens mountable in said unit between said light source and said support;

an image projection lens mountable in said unit between said light modular array and said contact reproduction portion;

an optical, light-absorbing baffle interposed between said array and said imager lens for eliminating light reflected from inactive portions of said spatial light modulator array, thereby spatially separating said light rays from actively modulated light directed towards the image lens, said light baffle including a plurality of concentric, tapering, stepped light baffles; and

an exit aperture in the base of said unit for presenting said dot patterns accepted by said image lens to said contact reproductive process.

2. The exposure unit set forth in claim 1 further comprising a light baffle interposed between said array and said image lens for directing away from said image lens off-state light reflected from said array portions not a part of the dot pattern process or from nonselected ones of said modulator elements.

3. The exposure unit set forth in claim 2 wherein said light baffle includes a plurality of concentric, tapering, stepped light baffles.

4. The exposure unit set forth in claim 3 wherein each said light baffle includes first and second concentric surfaces, said first surface for intercepting said off-state light and reflecting said intercepted light back against said second surface where it is reflected for the second time toward a cover of said exposure unit.

5. The exposure unit set forth in claim 4 wherein said second surface is undercut with respect to said first surface.

6. The exposure unit set forth in claim 5 wherein said reflected light from said first surface impacts said second surface at approximately an angle of 37 degrees.

7. The exposure unit set forth in claim 2 wherein said imager lens is mounted concentrically within said baffle around the optic axis of light dot patterns of selected modulator elements.

8. An exposure unit for use in a printing system, said printing system having a reproductive unit for accepting light images from said exposure unit, said images comprising a plurality of individual bits each controlled by an off/on data signal, said exposure unit having first and second ends and a base and comprising:

a housing adjacent said first end for accepting a light bulb;

a support adjacent said second end for accepting a spatial light modulator array positioned away from and facing said light source such that unmodulated illumination from said source will fall on pixels of said array, said array being substantially flat, and when in said supports project upward from said base to hold the edges of said array, said array being positioned slightly from the perpendicular to said base so as to create an optical axis for light reflected by said array pixels slightly downward with respect to said base;

a focusing element support for accepting a focusing element adopted for controlling the image formed by light reflected by modulated ones of said pixels; and

a sloping indention in said base in the shape of a bee thorax and extending along said optical axis, said indention positioned between said focusing element support and said array support, the tapering end of said thorax facing said array, said thorax adapted to include said focusing element support for accepting light selectively reflected from modulated pixels and for communicating said reflected light to said reproductive unit while rejecting all light reflected from unmodulated pixels or from inactive areas of a said array mounted in said support.

9. The exposure unit set forth in claim 8 wherein said spatial light modulator is a deformable mirror device (DMD) arranged with individual mirrors forming the pixels and arranged to change their angle upon being modulated by a data signal.

10. The exposure unit set forth in claim 8 wherein said array is contained on a substrate in conjunction with circuitry for controlling said addressing.

11. The exposure unit set forth in claim 8 wherein said array elements are deformable mirrors arranged to change their light reflective angle upon being addressed by a data signal so as to introduce light energy to said focusing element.

12. The exposure unit set forth in claim 8 wherein said exposure unit includes a slot in said base and wherein said communicated images are reflected through said slot to said reproductive unit.

13. The method of constructing an optical exposure unit for use in a reproductive system having both an exposure portion and a reproductive portion, said reproductive portion operative in response to presentation of modulated light patterns for representing said modulated patterns as image on a transfer medium, and method comprising the steps of:

positioning a light source at one end thereof;

disposing a support opposite said light source or holding an array of spatial light modulator elements, said elements individually controllable for modulating light to form said modulated patterns;

mounting at least one lens in said unit between said light source and said support;

mounting an imager lens in said unit between said light modular array and said contact reproduction portion;

interposing a light baffle system between said array and said image lens for eliminating from said imager lens off-state light reflected from said array portions not a part of said modulated pattern as well as from nonselected ones of said modulator elements; and

presenting, via an exit aperture and steering mirrors in the base of said unit, said modulated patterns accepted by said imager lens to said contact reproductive process.

14. The method set forth in claim 13 further comprising the steps of:

interposing a light baffle system between said array and said image lens for redirecting away from said image lens off-state light reflected from said array portions not a part of said modulated pattern as well as from nonselected ones of said modulator elements.

15. The method set forth in claim 14 wherein said light baffle has the shape of a bee thorax, and wherein said image lens is mounted concentrically within said thorax around the optic axis of light modulated patterns of selected modulator elements.

16. The method set forth in claim 14 wherein said exposure unit includes a light baffle having concentric saw-toothed steps and wherein said interposing step includes the steps of:

impacting said off-state light on a first surface of one of said saw-toothed steps, so that said impacted light reflects onto a second surface of said step; and

reflecting said already reflected off-state light from said second surface onto another surface of said exposure module.

17. The method of operating an exposure unit for use in a printing system, said printing system having a reproductive unit for accepting images from said exposure unit, said images comprising a plurality of individual bits each controlled by an off/on data signal, said exposure unit having first and second ends and a base and said method comprising the steps of:

positioning a light bulb in a housing adjacent said first end of said unit;

positioning a support adjacent said second end for accepting a spatial light modulator array positioned away from and facing said light source such that unmodulated illumination from said source will fall on pixels of said array, said array being substantially flat, and when in said supports project upward from said base to hold the edges of said array, said array being positioned slightly from the perpendicular to said base so as to create an optical axis for light reflected by said array pixels slightly downward with respect to said base;

accepting a focusing element adopted for controlling the image formed by light reflected by modulated ones of said pixels; and

expending a sloping indention in said base in the shape of a bee thorax along said optical axis, said indention positioned between said focusing element support and said array support, the tapering end of said thorax facing said array, said thorax adapted to include said focusing element support for accepting light selectively reflected from modulated pixels and for communicating said reflected light to said reproductive unit while rejecting all light reflected from unmodulated pixels or from inactive areas of a said array mounted in said support.

18. The method set forth in claim 17 wherein said spatial light modulator is a deformable mirror device (DMD) arranged with individual mirrors forming the pixels and arranged to change their angle upon being modulated by a data signal.

19. The method set forth in claim 17 wherein said array is contained on a substrate in conjunction with circuitry for controlling said addressing.