United States Patent 5
`Allen
`
`Aa
`
`US005754217A
`(11) Patent Number:
`[45] Date of Patent:
`
`5,754,217
`May 19, 1998
`
`[54]
`
`PRINTING SYSTEM AND METHODUSING A
`STAGGERED ARRAYSPATIAL LIGHT
`MODULATOR HAVING MASKED MIRROR
`ELEMENTS
`
`3/1994 Takanashi ot al. ..eunscsereeen 359/72
`5,299,042
`
`347/255 XK 5/1995 Nochebuena et al.
`5,414,553
`7/1995 Nelson ............
`« BAT25S K
`5,430,524
`10/1995 Venkateswar ........cssecessees 347/255 X
`5,459,492
`FOREIGN PATENT DOCUMENTS
`
`62-35323—D/L9BT Japa o.cecssssecarseceesssesseeetenesees 359/224
`
`John B. Allen, Lucas, Tex.
`Inventor:
`[75]
`
`[73]
`
`Assignee: Texas Instruments Incorporated.
`Dallas, Tex.
`
`Primary Examiner—David F. Yockey
`Attorney, Agent, or Firm—Charles A. Brill; James C.
`Kesterson; Richard L. Donaldson
`
`[21]
`
`[22]
`
`[51]
`(52)
`[58]
`
`[56]
`
`Appl. No.: 424,917
`
`Filed:
`
`Apr. 19, 1995
`
`Int. CLS oo B41J 2/47; GO2B 26/00
`ULS. Ce cresecseorencsnesseateceees 347/239; 359/291; 359/292
`Field of Search 00.0...ccssssscseecerese 347/134, 239,
`347/255; 359/223, 224, 298, 290, 291,
`292
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`
`4,001,635
`1/1977 D'Auria etal. oo... 250/568 X
`
`a 359/224
`5,061,049 10/1991 Hombeck ....
`1/1992 Hombeck....
`wee 359/291
`5,083,857
`
`oo 355/229
`5,101,236
`3/1992 Nelson et al.
`22/1992 Nelson .....csscssscsescsstecceenesenes 355/200
`5,172,161
`
`[57]
`
`ABSTRACT
`
`A system 10 for independently illuminating a plurality of
`areas on an object 26 such as a printer drum is disclosed
`herein. The system 10 includes a light source 12 such as an
`LED or a plurality of LEDs. A spatial light modulator 14,
`which may be a movable mirror device. for receives light
`from the light source 12 andreflects selected portions of the
`light. The spatial light modulator 14 includesat least n rows
`of independently modulated pixels wherein a mask prevents
`more than I/nth of each the rows from receiving and
`reflecting light at any point in time. The light from the spatial
`light modulator 14 is imaged (e.g.. with imaging lens 24)
`onto rows and columns of the object 26 to be illuminated.
`The object 26 is illuminated in a way that each column is
`illuminated by a corresponding row of pixels.
`
`28 Claims, 6 Drawing Sheets
`
`J4——
`
`MASK WITH APERTURES
`IN IT
`—
`
`J Od Co) Lu)
`
`wo ARRAY
`
`[4
`
`VWGoA EX1058
`VWGOAv. Spero
`IPR2023-00318
`
`VWGoA EX1058
`VWGoA v. Spero
`IPR2023-00318
`
`

`

`U.S. Patent
`
`May 19, 1998
`
`Sheet 1 of 6
`
`5,754,217
`
`
`
`
`Fig. 1b
`
`LIGHT SOURCEoth12
`
`

`

`U.S. Patent
`
`May19, 1998
`
`Sheet 2 of 6
`
`5,754,217
`
`28 30
`
`
`
`
`
`Fig. 2a
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`Fig. 2b
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`

`

`U.S. Patent
`
`May19, 1998
`
`Sheet 3 of 6
`
`5,754,217
`
`
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`12345 6
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`a
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`
`

`

`U.S. Patent
`
`May19, 1998
`
`Sheet 4 of 6
`
`5,754,217
`
`IMAGE PLANE
`
`J12 . \ ‘4
`
`ILLUMINATION
`
`MASK
`
`LENS
`
`DMD
`
`Fig. 5
`
`38
`
`34
`
`OBJECT PLANE
`12
`
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`
`|
`/
`iLLUMINATION
`
`14
`
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`Fig. 7a
`
`Fig. 6
`
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`34 ey IN IT
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`Fig. 7b
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`
`Fig. 8b
`
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`
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`
`
`
`
`

`

`U.S. Patent
`
`May 19, 1998
`
`Sheet 5 of 6
`
`5,754,217
`
`28
`
`DMD
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`LONG SINGLE LED ELEMENT
`
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`a 12
`
`Fig. 14
`
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`
`
`
`
`
`
`
`
`
`

`

`U.S. Patent
`
`May19, 1998
`
`Sheet 6 of 6
`
`5,754,217
`
`19
`16
`DMD
`fy. 14
`
`27
`
`24
`
`26
`
`Fig. 15
`
`

`

`5,754,217
`
`1
`PRINTING SYSTEM AND METHOD USING A
`STAGGERED ARRAYSPATIAL LIGHT
`MODULATOR HAVING MASKED MIRROR
`ELEMENTS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`The following patents and/or commonly assigned patent
`applications are hereby incorporated herein by reference:
`
` Patent No. File Date Issue Date TI Case No.
`
`
`
`5,061,049
`09/13/90
`10/29/91
`TI-13173B
`5,083,857
`06/29/90
`01/28/62
`TI-14568
`5,101,236
`12/21/89
`03/3 1/92
`TL-14585
`5,172,161
`12/31/90
`12/15/92
`TI- 15602
`
`03/28/94 07/04/055,430,524 TE-i5602AC
`
`
`
`1. Field of the Invention
`This invention generally relates to display and printer
`systems and specifically to a printing system which uses a
`staggered array spatial light modulator.
`2. Background of the Invention
`The requirement for hardcopy output is an ubiquitous
`element of the information revolution. In particular, elec-
`trophotography has become one of the most widely used
`systems and the dry toner process, has become the most
`popular for creating copies and prints of documents in a host
`of environments. The basics of electrophotography are well
`know to those skilled in the art. The fundamental elements
`of a electrophotographic printer or copier using the dry toner
`process include a photo sensitive medium,
`typically an
`organic photoreceptor (OPC), which is charged electrostati-
`cally to a predetermined voltage and polarity. Upon expo-
`sure to an optical image, generated by reflection or a light
`modulating system, portionsof the originally uniform elec-
`trostatic charge on the OPC are erased where illuminated.
`Thus, an electrostatic latent image of the original (or the
`electronic) documentis created on the OPC. In most modern
`systems,
`this image is passed by a source of developer
`materials which consists of electrostatically charged toner
`particles held to ferromagnetic carrier beads. The carriers are
`used to facilitate the transport of the materials into contact
`with the above mentioned latent image through the action of
`magnetic fields and rotating magnets within sleeved
`cylinders,
`typically called developer rollers. Through a
`designed interplay of electrostatic charges, the toner par-
`ticles that are typically in the 10 micron diameter range, are
`separated from the carrier beads, typically 50 micron diam-
`eter particles, and retained in-place on the appropriate por-
`tions of the latent image resident on the OPC surface. The
`magnetic forces associated with the developerrollers carry
`the depleted ferromagnetic carrier beads back to the position
`where they are re-mixed with additional toner for develop-
`ment of subsequent images.
`As is well known,
`the toner materials are normally
`plastics with flow promoting agents, charge control agents,
`and color pigments which melt at a predetermined tempera-
`ture. The OPC surface then carries a developedlatent image
`after exiting the proximity of the developing roller.
`Subsequently, the photoreceptor surface carrying the devel-
`oped image is brought into contact with an image receptor,
`which in most common applications of electrophotography
`is a sheet of paper, but may be an intermediate material
`suitable for the build-up of multiple pigmented images as
`required for color printing. Electrostatic charging systems
`
`2
`are typically used to transfer the toner from the OPC tothe
`image receptor.
`Whether the final image bearing memberis ultimately
`paperor an other material, it can be successively operated on
`by multiple photoreceptors, a single photoreceptor. or an
`image bearing intermediate member to build up the full
`color image. It exits the printing process through a station
`referred to as the fuser. where the appropriate heat and/or
`pressure is applied to the image receptor and thereby fixes
`the image permanently.
`One technology which has been found to be useful in
`printing and display applications utilizes a movable mirror
`device such as the Digital Micromirror Device (also referred
`to as Deformable Mirror Device or simply a DMD) manu-
`factured by Texas Instruments, Inc. The movable mirror
`device is composed of many small mirrors called micromir-
`rors which rotate about a fixed axis. The movable mirror
`device is illuminated with a beam of light. The rotation of
`the micromirror causes the light illuminating the micromir-
`ror to be deflected under the control of the rotation. Thus,
`each micromirror of a movable mirror device can be selec-
`tively rotated thereby patterning light reflected from the
`array. Specific details of movable mirror devices are pro-
`vided in U.S. Pat. Nos. 5.061.049 and 5.083.857, each of
`which is incorporated herein by reference.
`Whenusing a movable mirrordevice in print applications.
`a long and narrow movable mirror device will typically be
`used. As an example, a movable mirror device array with
`about 100 rows and 7,000 columns may be utilized. To
`produce a device of this size, the chip may typically be 5.0
`inches long. A chip. a chip which is shorter in length. and
`accordingly has less columns, is desired.
`
`SUMMARYOF THE INVENTION
`
`Other objects and advantages will be obvious, and will in
`part appear hereinafter and will be accomplished by the
`present invention which provides a printing system and
`method which utilizes a staggered array spatial light modu-
`lator.
`
`A system for independently illuminating a plurality of
`areas on an object such as a printer drum is disclosed herein.
`The system includes a light source such as a single light
`emitting diode (LED) or a plurality of LEDs. A spatial light
`modulator, which may be a movable mirror device such as
`the Digital Micromirror Device (DMD) manufactured by
`Texas Instruments, Inc., receives light from the light source
`and reflects selected portions of the light. In some embodi-
`ments the mirror device is illuminated in a scanning mode,
`ie., each row of mirror elements is illuminated individually
`and sequentially by scanning a beam oflight over all of the
`micromirrors. In other embodiments, the mirror device is
`illuminated in a staring mode. i.e., the all the mirror elements
`of the entire array are iuminated simultaneously. The light
`from the spatial light modulator is imaged onto the object to
`be illuminated whichis partitioned in rows of pixels (picture
`elements). The objectis illuminated in a way that each pixel
`is, over time, illuminated by light from a corresponding
`column of micromirrors.
`
`it reduces the
`An advantage of the invention is that
`number of columns of micromirrors required by the movable
`mirror device. This reduction may be importantin printing
`applications where the number of columns is very high
`resulting in physically large integrated circuit chips which
`are difficult to illuminate. The reduction in the size of the
`chip will reduce the cost to manufacture the chip as well as
`the cost of the optical subsystem to illuminate the chip
`
`10
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`15
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`5,754,217
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`3
`thereby reducing the cost of the system which the chip
`subsequently is installed.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The above features of the present invention will be more
`dearly understood from consideration of the following
`descriptions in connection with accompanying drawings in
`which:
`
`FIG. 1A is a block diagram of a first scanning mode
`embodiment printing system;
`FIG. 1B is a block diagram of a second scanning mode
`embodimentprinting system;
`FIG.1C is a block diagram of a staring mode embodiment
`printing system:
`FIG. 1D is a block diagram of a second staring mode
`embodimentprinting system;
`FIG. 2A is a block diagram of a movable mirror device
`array illustrating the portion of each micro-mirror element
`which is illuminated;
`FIG. 2B illustrates a representation of the line which will
`eventually be printed;
`FIGS.3A and 3C illustrate objects (such as an OPC) to be
`illuminated FIGS. 3B and 3D illustrates movable mirror
`devices to provide the illumination to illuminate the objects
`in FIGS. 3A and 3C, respectively;
`FIGS. 4A and 4B illustrate alternative movable mirror
`device arrays;
`FIG. 5 illustrates an image plane application for illumi-
`nating the movable misror device;
`FIG.6 illustrates a mask which is utilized to control the
`illumination of the movable mirror device;
`FIG. 7A and 7Billustrates an object plane implementation
`of illuminating the movable mirror device array;
`FIGS. 8A, 9A, and 10A are block diagrams of alternative
`embodiments of movable mirror device arrays;
`FIGS. 8B, 9B. 9C, and 10B are representations of the line
`which will be written by the array of the corresponding
`FIGS. 8A, 9A, or 10A.
`FIG, 11 is a schematic of a second embodimentprinting
`system;
`FIG.12 illustrates a gray level algorithm for an alternative
`system which using isomorphic optics;
`FIG. 13 illustrates an LED array which may be utilized
`the systems of the present invention.
`FIG. 14 illustrates an LED array which maybeutilized
`the system of the present invention; and
`FIG. 15 is a schematic of a system utilizing an LED array.
`DETAILED DESCRIPTION OF ILLUSTRATIVE
`EMBODIMENTS
`
`The making and use of various embodiments are dis-
`cussed below in detail. However, it should be appreciated
`that the present invention provides many applicable inven-
`tive concepts which can be embodied in a wide variety of
`specific contexts. The specific embodiments discussed are
`merely illustrative of specific ways to make and use the
`invention. and do not delimit the scope of the invention.
`A first embodimentof the staggered array printing system
`10 is of the scan mode variety and is depicted in FIG. 1A.
`A light source 12. such as a light laser diode illuminates a
`spatial light modulator 14. The spatial light modulator 14
`may comprise a movable mirror device such as the Digital
`Micromirror Device (DMD) manufactured by Texas Instru-
`
`4
`ments and described in U.S. Pat. Nos. 5.061.049 and 5,083,
`857, incorporated herein by reference. For the sake of the
`simplicity, the details of the movable mirror device will not
`be repeated herein.
`In the system of FIG. 1A,the light from the light source
`12 is scanned over the movable mirror device by means of
`light scanning optics 13. The light illuminating the movable
`mirror device from source 12 forms a long and narrow beam
`on the movable mirror device. The length of the beam is
`equal to the length of the movable mirror device 14 array
`and the width of the beam is equal to the width of the
`illuminated portion of micromirrors.
`In the preferred
`embodiment, each row of micromirrors of the movable
`mirror device array is sequentially illuminated.
`In the
`scanned mode, the beam is scanned rapidly enough that all
`of the mirror elementsare illuminated during a timeinterval
`short enough that the drums turns only a small fraction of a
`pixel.
`Modulated light is reflected from spatial light modulator
`14 into projection lens 24 which images the light onto drum
`26. Lens 24 may be an anamorphiclens if it is desired to
`have a printing beam which is not the same shape as the
`micromirror. The rotating drum 26 may then transfer toner
`to a sheet of paper 27.
`In the embodiment illustrated in FIG. 1B, the light scan-
`ning optics 13 comprises a first lens 18, a scanner 20, and
`third lens 22. The scanner 20 scansthe light beam down the
`array within spatial light modulator 14 in the vertical direc-
`tion successively illuminating the movable mirror device
`mirror elements in each row.
`FIG. 1C depicts a staring mode embodiment of the
`staggered array printing system 10. A light source 12, such
`as a light emitting diode (LED). illuminates a spatial light
`modulator 14. As in the embodiments of FIGS. 1A and 1B,
`spatial light modulator 14 may comprise a movable mirror
`device such as the Digital Micromirror Device (DMD)
`manufactured by Texas Instruments and described in U.S.
`Pat. Nos. 5.061.049 and 5.083.857.
`In the system of FIG. 1C.the light from the light source
`12 is directed toward the movable mirror device by means
`of light directing optics 16. Thelight beam illuminates all of
`the micromirrors of the moving mirror device simulta-
`neously. Modulated light
`is reflected from spatial
`light
`modulator 14 into projection lens 24 which imagesthelight
`onto drum 26.
`In the preferred embodiment, the light source 12 is pulsed
`(rapidly turned on and then off) at a period equal to that
`required by the drum 26 to rotate through one pixel. The
`light pulse will preferably have a 10% duty cycle so that a
`sharp image of the mirror element is formed on the drum
`(i.e., the mirror element image is not “smeared” by the
`rotation of the drum). Lens 24 may be an anamorphic lens
`if it is desired to have a printing beam whichis not the same
`shape as the micromirror. The rotating drum 26 may then
`transfer toner to a sheet of paper 27.
`In FIG. 1D,the light source 12 is a linear array of LED
`emitters and the light directing optics 16 is a toroidal lens
`which magnifies the LED emitters so that the image of each
`emitter fills the DMD.
`A first embodiment spatial light modulator 14.2 for the
`embodiments of FIG.1 is illustrated in the simplified version
`in FIG. 2A. The spatial light modulator 14.2 preferably
`comprises a movable mirror device such as the Digital
`Micromirror Device (DMD) manufactured by Texas
`Instruments, Inc. This movable mirror device 14.2 is con-
`figured in a plurality of rows and columnsasillustrated in
`
`10
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`15
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`25
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`30
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`35
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`5,754,217
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`5
`6
`FIG. 2A. Each of the rows comprises a plurality of mirror
`Similarly, at a third time t, the first, fourth, seventh. etc.
`elements (sometimes called micromirrors) 28.
`In the
`columnsC,, ofline 3 of the object can be illuminated by the
`embodimentillustrated here, each row of mirror elements 28
`light reflected from mirror elements 28 in the first row R, of
`is displaced in the horizontal direction by ‘4 of a mirror
`movable mirror device 14.3b. Once again. the first and
`dimension. Each of the three rows will illuminate | of the
`second lines are not illuminated since they are now aligned
`object to be illuminated, e.g., drum 26 as shown in FIG.1.
`with the upper non-illuminated portion of the second row Ry
`While illustrated herein with three rows each shifted a 4 of
`and the lower non-illuminated portion ofthe first row R, of
`a mirror dimension, it should be noted that any number of
`mirror elements 28, respectively.
`rowslarger than one may be used. In general, if n-rows are
`At a fourth time t, both line 1 and line 4 are simulta-
`used each mirrorwill be displaced in the horizontal direction
`neously printedas illustrated by the pixels labeled t, in FIG.
`by 1/nth of a mirror dimension.
`3A.Thefirst, fourth, seventh, etc. (columns C,)ofline 4 are
`In the embodimentillustrated in FIG. 2A only the center
`illuminated bylight reflected from mirror elements 28 from
`30 of each mirror element28is illuminated. In this case, the
`the first row R, of movable mirror device 14. At the same
`area of each mirror element28 illuminatedis a square whose
`time, line 1 is now aligned with light from the second row
`dimension on each edgeis '4 of the length of the movable
`mirror device mirror element 28. Ofcourse. if the number of
`R, of mirror elements 28. Accordingly. the second, fifth.
`rows in a set of rows is different
`than three,
`then the
`eight, etc. (columns C,)ofthis line can be illuminated. Note
`dimension of the illuminated portion will be different.
`that during the fourth time t,, the second and third lines are
`Thefirst row will print the pixels labeled 1 in FIG. 2B, the
`not illuminated since they are now aligned with the upper
`second row will print the pixels labeled 2 in FIG. 2B and the
`non-illuminated portion of the second row R, and the lower
`third row will print the pixels labeled 3 in FIG. 2B. Since
`non-illuminated portion of the first row R, of mirror ele-
`three rows of movable mirror device 14.2 are used to print
`ments 28, respectively.
`a single line, the movable mirror device 14.2 can be built
`At timet, thefirst line is aligned with the third row R, of
`with only 4 of the total columns. This decrease in the
`mirror elements 28 so that portions of three lines (e.g.. lines
`number of columns provides a significant manufacturability
`1, 4, and 7 at timet,) are being simultaneously illuminated.
`advantage over the prior art.
`This shifting will continue until each of the lines of object
`The operation of a staring system embodiment(e.g., as
`32 have been selectively Mluminated.
`illustrated in FIGS. 1C and 1D) will now be described with
`FIGS. 3C and 3D can be utilized to demonstrate a scanned
`reference to FIGS. 3A and 3B. FIG. 3B illustrates a simple
`system as illustrated in FIG. 1A or 1B. In the scanned
`movable mirror device array 14.35 which includes 3 rows
`system, each row R,. Rp. or R, is illuminated at a different
`(labeled R,. R, and R,.) by 4 columnsof mirror elements 28.
`time by a beam which is as long as the movable mirror
`FIG. 3A represents the object 32 to be illuminated where
`each of the boxes 38 is one pixel. In printing applications,
`device and whose height is equal to that of the illuminated
`this object 32 may bearotating printer drum (e.g.. element
`portion of the mirror element on the movable mirror device.
`26 in FIG. 1A) which will transfer toner to a sheet of paper
`Accordingly, at time t, line 1 is illuminated. During times t,
`(element 27 in FIG. 1A). Thefirst row R, of movable mirror
`and t,. no part of object 32 is illuminated since nopart is
`device 14.3 will print the pixels under the columns labeled
`aligned with the array 14.3d. Note that at time t,,. line 1 of
`C, (e.. columns 1, 4, 7, etc.) in FIG. 3A, while the second
`the object 32 is aligned with the second row Ra of spatial
`tow Rgwill print the pixels under the columns labeled C,
`light modulator 14.3b. This sequence will continue until
`andthe third row R, will print the pixels under the columns
`each pixel 38 is imaged.
`labeled C,. The resulting line of imagery correspondsto that
`It is, of course, noted that in the scanning mode the light
`illustrated in FIG. 2B.
`illuminates the apertures for only one third of the timethat
`the beam is scanned over the movable mizror device. This
`To understand how the pixels are printed, imagine the box
`of FIG. 3A being slid down the page over the movable
`inefficiency. however,
`is made up for because the light
`mirror device array of FIG. 3B. In the known electrographic
`source can be turned on only when the scanneris pointed to
`(Le., xerographic} printing process, this movement occurs
`the aperture over each mirror element 28. Hence. the light
`when the drum 26 (FIG. 1A) rotates such that different
`source can be turned on only when the scanneris pointed to
`portions of the drum 26 are in the light path of the beam
`the aperture over the mirror elementIn addition, during the
`reflected from movable mirror device 14.3b. To print, toner
`scanned mode one third of the light transmitted will reach
`{not shown)is applied to the drum 26 surface and adheres to
`the movable mirror device (as illustrated by the fact that the
`the spots where the modulated light impacts the drum. This
`illuminated portion 30 extends one third of each mirror
`toner, in turn, is transferred to a piece of paper (27 in FIG.
`element). In the staring mode in which the entire movable
`1A) which is moved adjacent to the drum 26. For a more
`mirror device is illuminated. only one-ninth of the light
`detailed description of a light energy management system
`reaches the movable mirror device since the area occupied
`which can be used with a xcrographic reproduction system,
`by the apertures over the mirror elements account for only
`reference should be made to U.S. Pat. No. 5,101,236,
`one ninth of the area of the movable mirror device.
`incorporated herein by reference.
`FIGS. 4A and 4Billustrate two alternate embodiments of
`Returning to FIGS. 3A and 3B,ata first time t, the first,
`movable mirror device arrays 14.4a and 14.46. These
`fourth, seventh, etc. columns C, ofline 1 of object 32 will
`embodimentsare similar to those previously discussed with
`be selectively illuminated by light from the illuminated
`respect to FIGS. 2A (and 3B and 3D). In the embodimentin
`portions 30 of the first row R, of mirror elements 28. The
`FIG. 4A, the mirror elements 28 are disposed in aligned
`areas on object 32 which may be illuminated are labeled t,.
`columns.In this case, the illuminated portionsare staggered
`Ata second time t,, the box will have shifted down such that
`such that the illuminated portion 3@A in row 1 is aligned to
`line 2 of the object is illuminated by light from the first row
`the left edge of mirror element 28A while the illuminated
`R, of mirror elements 28.
`portion 30B is centered in mirror element 28B and illumi-
`At time t,, nothing can be written to line 1 since this line
`nated area 30C is aligned to the right edge of mirror element
`will now be aligned to the lower non-illuminated portion of
`28C. Using this technique, the sameresults as illustrated by
`first row R, of mirror elements 28.
`FIGS.3A and 3B (or 3C and 3D) maybe achieved. It is also
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`noted that the illuminated portions 30 do not need to be
`centered in the staggered array (FIG. 2A).
`FIG. 4B has been included to illustrate the fact that the
`illuminated portions 30d are not required to be square. In
`this example, the illuminated portions comprise rectangular
`areas 30d on each mirror element 28. The resulting pixel
`elements which will be printed will be rectangular in this
`case. While square pixel elements are typically preferred.it
`is noted that other shaped elements such as rectangles,
`circles, triangles and other polygons may also be used. Of
`course. if anamorphic optics are used, the rectangular por-
`tion of the mirror element can be used to create a square
`image.
`The controlled illumination can be obtained by object
`plane or image plane illumination as depicted in FIGS. 5
`through 7. In image plane illumination, a mask 34 (shownin
`FIG. 6 as well) containing apertures is illuminated by
`illumination source 12 and imaged by a lens 36 onto the
`movable mirror device 14 as shown in FIG. 5. The apertures
`38 may comprise square apertures as well as other shaped
`apertures.
`Alternatively. as illustrated in FIG. 7A. in object plane
`illumination the mask 34 is placed very dose to the movable
`mirror device 14. Effectively, the movable mirror device 14
`is in the object plane of the mask 34. Object plane illumi-
`nation maytypically be preferred since there is no interven-
`ing lens 34 to introduce distortions. Also, the resulting
`system is smaller. The smaller structure is easier to make
`rigid. As illustrated in FIG. 7B, the mask 34 should be dose
`to the movable mirror device 14 so that the beam falling on
`the movable mirror device mirror element 28 (FIG. 2A)is
`about the same size as the mask aperture 38 (FIG. 6).
`Calculations indicate that the distance of less than about 10
`microns, for example about 3 to 6 microns, should suffice.
`If the beam defracts so much that the entire mirror element
`28 is illuminated. a large fraction of the light reflected back
`from the mirror 28 will not exit the aperture and pass
`through the remainder of the optics.
`The movable mirror device 14 is imaged onto the drum as
`illustrated in FIG. 1. Since the drumis rotating, the exposure
`should be short in time so the charge generated on the drum
`is not “smeared” resulting in the loss of image in the
`direction of motion of the drum. The short exposure can be
`obtained bydriving the light source with a pulsed waveform.
`Typical waveforms have a pulsed duration of 33 microsec-
`onds with a 10% duty cycle. A 10% duty cycle is maybe
`inefficient in terms of light output since the source is off 90%
`of the time. An efficient approachis to leave the light source
`12 on continuously and scan the beam over the mask 38 at
`such a speed that the aperture is illuminated for only a short
`time, for example 33 microseconds. Since the apertures are
`spaced at a different distance apart equal to three times their
`dimension,the light source 12 can be operated at a 33% duty
`cycle without loss andefficiency. The source can be pulsed
`as described so long as the scanned beam illuminates only a
`single row of mirrors at a given instant.
`In other movable mirror device applications, the use of
`coherent illumination of the movable mirror device has
`resulted in spurious and offensive diffraction patterns from
`the movable mirror device hinges and mirror elements.
`There should be not such scattering problems here since the
`location of the mask 34 controls the portion of the movable
`mirror device 14 which is illuminated. The mask can be
`positioned so that only the desired portion 30 of the mirror
`element 30 is illuminated.
`The concept of a mask offers an alternative means of
`manufacturing movable mirror devices. The movable mirror
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`device 14 need not be designed so that the mirror element 28
`is of optical quality throughout all portions of the mirror
`element. This design tolerance is possible since the portions
`of the mirror 28 which are not of optical quality can be
`covered with the mask 34. The mask 34 also allowsthe size
`of the mirror elements 28 to be effectively changed without
`actually changingthe physical dimension of the elements. A
`standard movable mirror device can be built with a single
`mirror size and effective size of the mirror set by thesize of
`the mask aperture.
`An alternate embodimentspatial light modulator array 14
`is illustrated in FIG. 8A. In this embodiment, a smaller
`mirror element 42 is included. The smaller mirror element
`42 covers only a portion of the area of the larger mirror
`elements (as in FIG. 2A). In the example illustrated in FIG.
`8A, the mirror element 42 has a length and width whichis
`one half of the full coverage mirrors (as in FIG. 2A).
`Accordingly, two rows R, and Rgare utilized to image each
`line of text. A representation of the text line is illustrated in
`FIG. SB.
`The micromirrors 42 shown in FIG. 8A are shaded and
`cross-hatched. This pattern is repeated along the movable
`mirror device in the process dimension. As an example, the
`micromirrors 42 may be on about 17 micron centers and may
`be about 8 micronsonthe side. As before. the pixels may be
`square and, for example, about 42 micronson the side. The
`shaded micromirrors 42 (in FIG. 8A) expose the shaded
`pixels (in FIG, 8B) andthe cross-hatch micromirrors expose
`the cross-hatch pixels. In one possible embodiment,
`the
`array 14 is 2.4 inches long and 2.18 mm high and may be
`magnified by a factor of 5 on the drum. This version has 600
`dpi (dots per inch) performance. In a second embodiment.
`the array is 4.8 inches by 2.18 mm and is magnified by a
`factor of 2.5 to the movable mirror device. This embodiment
`has 1200 dpi performance.
`The operation of the embodiment of 8A is analogous to
`the operation of the previously described systems. This
`embodiment provides the advantage of eliminating the
`necessity of mask 34 of FIGS. 5-7. As with the other
`embodiments, the spatial light modulator array 14 can be
`used in either a scanned system (FIGS. 1A and 1B) or a
`staring system (FIGS. 1C and 1D).
`An alternate architecture of the movable mirror device
`14.9a is shown in FIG. 9A. The mirror elements 44 are
`diamond shaped. In this context. diamond shaped mirror
`elements 44 include any mirror elements which are rotated
`such that non-parallel edges of adjacent mirror elements are
`next to each other. In the illustrated example, the mirror
`elements 44 are square but other shapes may also be utilized.
`For example, the mirror elements 44 may be 11.3 microns
`long on the side and spaced on 17 micron centers. This
`architecture, if used directly, will produce pixels as shown in
`FIG. 9B. Note that the imaged pixels are non-contiguous.
`The non-exposed region is not the shape of the micromirrors
`and cannot be exposed by them for contiguous coverage as
`was possible with the system of FIG. 1.
`However. if the array 14.92 of FIG. 9A isutilized with a
`scanned system as illustrated in FIGS. 1A and 1B,the
`discontinuities of coverage cam be eliminated. In this
`embodiment,the first row R, of mirror elements will image
`the pixels labeled C, in FIG. 9C. The object 32 will then
`shift (e.g. the drum 26 will rotate) and the second row R, of
`mirror elements will
`image the pixels labeled Cy. The
`scanned modewill continue alternating between the first row
`R, until the entire page has been written to.
`Another embodiment architecture for the movable mirror
`device 14 is shown in FIG. 10A. The upper portion of FIG.
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