CA1320474C - Led illuminator bar - Google Patents
Led illuminator barInfo
- Publication number
- CA1320474C CA1320474C CA000612341A CA612341A CA1320474C CA 1320474 C CA1320474 C CA 1320474C CA 000612341 A CA000612341 A CA 000612341A CA 612341 A CA612341 A CA 612341A CA 1320474 C CA1320474 C CA 1320474C
- Authority
- CA
- Canada
- Prior art keywords
- cavity
- illumination
- recited
- light
- reflective
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
- G03G15/045—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with means for charging or discharging distinct portions of the charge pattern on the recording material, e.g. for contrast enhancement or discharging non-image areas
- G03G15/047—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with means for charging or discharging distinct portions of the charge pattern on the recording material, e.g. for contrast enhancement or discharging non-image areas for discharging non-image areas
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/435—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material
- B41J2/447—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources
- B41J2/45—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources using light-emitting diode [LED] or laser arrays
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G2215/00—Apparatus for electrophotographic processes
- G03G2215/04—Arrangements for exposing and producing an image
- G03G2215/0429—Changing or enhancing the image
- G03G2215/0431—Producing a clean non-image area, i.e. avoiding show-around effects
- G03G2215/0448—Charge-erasing means for the non-image area
- G03G2215/0451—Light-emitting array or panel
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/4805—Shape
- H01L2224/4809—Loop shape
- H01L2224/48091—Arched
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S362/00—Illumination
- Y10S362/80—Light emitting diode
Abstract
LED ILLUMINATOR BAR
Abstract of the Disclosure An erase bar for a xerographic printer, copier or the like has a row of light emitting diodes for illuminating a row of pixels across the photosensitive medium of the printer. Each LED is located in the bottom of a cavity. Next to the bottom of the cavity are concave reflective walls which reflect light emitted transversely from the LED toward an open end of the cavity. Reflective walls of the cavity provide multiple bounces of some of the light. Absorptive walls nearer the open end of the cavity absorb some of the light.
These features combine to illuminate a pixel of desired shape and with approximately uniform intensity of illumination. Additional uniformity may be provided by passing the illumination through a window that is at least partly absorbing for smoothing out differences in intensity.
Abstract of the Disclosure An erase bar for a xerographic printer, copier or the like has a row of light emitting diodes for illuminating a row of pixels across the photosensitive medium of the printer. Each LED is located in the bottom of a cavity. Next to the bottom of the cavity are concave reflective walls which reflect light emitted transversely from the LED toward an open end of the cavity. Reflective walls of the cavity provide multiple bounces of some of the light. Absorptive walls nearer the open end of the cavity absorb some of the light.
These features combine to illuminate a pixel of desired shape and with approximately uniform intensity of illumination. Additional uniformity may be provided by passing the illumination through a window that is at least partly absorbing for smoothing out differences in intensity.
Description
1320~7 1 LED I~LUMINATOR BAR
Background Thi~ invention relates to an illumination or erase bar for a xerographic printer or the like, having a row of light emitting diodes for llluminating an image plane in a stripe having approximately uniform intensity along ths length of the stripe.
There ara times when it i~ desirable to illuminate a selected area on a photosensitivff surface in a xarographic device such as a prlnter, copier, scanner, fac~imile machine, or tha like. ~or example, the entire breadth o~ th- medium may be illuminated as it moves along after transferring an image to paper, for completely di wharging the medium 80 that it is in a uniform ground ~tate to b- charged for receiving a new image. The antire breadth of the medium may be bathed in light of reasonably uniform intensity ~or this total Qrasure.
Ther- are other times when it is de~irable to illuminat- a selacted area on th- mediumO ~his might be don-, for exa~ple, to block out text or, in a color prlnter, to paint in background color. It might be usad, for xample, in a color printar, to bloc~ out the area o~ a letterhead on a document so that the letterhead i5 printed in color and the text of the -2- 132~`~7~
1 letter is printed ln blacX. A more sophistlcated erase bar is needed for such selective illumination.
Such an illumination bar may illumlnate two or three millimeter long segments or pixels of a stripe a two or three millimeters wide. Each of these pixels is illuminated by a separate light emitting diode (LED).
Each of the LEDs can be separately addressed or switched for illuminating a desired area on the medium. It is still important to obtain reasonably uniform illumination within the area being illuminated;
typically, an intensity difference of about two to one between the brightest and dimmest areas is acceptable.
Sometimes tighter specifications for differences in illumination are required. This means that the illumination within each pixel must be reasonably uni~orm. It also means that there cannot be gaps between ad~acent pixelQ.
Typically, one seeks to achieve an intensity of illumination across a pixel in the direction Or the length of th- row or stripe which is approximately trapezoidal. Over the ma~or portion of the length of the pixel, the inten~ity i3 reasonably uniform. At each edg-, intensity drops off rapidly with distanco toward a dark area surrounding th- pixel. It is undesirable to hav- a halo of light surrounding the illuminated pixel.
Ad~acent pix-ls in the row are arranged so that the decrQa~ing illumination of one pixel overlaps the increasing illumination o~ the next pixel, preferably with the overlap making the two SO% intens~ty levels o~
ad~acent pixels at the same location. This avoids any gap in illumination, any significant decrease in illumination between ad~acent pixels, and any significant increase in illumination due to excessive overlap.
_3_ 1320~7 1 1 Bubble lenses and the llke have been used ~or pro~ecting the llght from an LED toward an image plane for providing individually illuminated pixels. Lens systems are, however, costly and somewhat inefficient in transmitting light from the LED to the image plane. In a typical system, only about 20% o~ the light from the LED may be usefully pro;ected on the image plane.
Defects in an LED or misalignment o~ an LED may also be projected toward the image plane, thereby degrading the uniformity of light within a pixel. For example, a chipped corner on an LED may show up in the image plane as a significant change in illumination. Another difficulty with lens systems is a limited depth of field. A belt carrying the photosensltiv- medium may "flap" somewhat, varying the di~tance between the erase bar and the medium. With a len~ system thi~ can change the shapQ and size of the illuminated pixel as the medium moves in and out of focus.
It i8, therefore, desirable to provide an individually addressable LED illuminator bar which is less costly and more efficient than a lens system. It is desirable that the system be tolerant of LED defects.
It is desirabl- that the intensity oS illu~ination be approximately uniform across each pixel and between pixels, 80 that 2 uniform intensity illumination is obt~ined across the full length of the illuminator bar, across any subset of pixels, and across each individual piXQl .
An exemplary illuminator bar and some prior technlgues for illumination are described and illustrated in U.S. Patent No. 4,759,603 by Jones. In the arrangement described therein, there is appreciable absorption of light. It would be desirable to provide an LED illuminator bar with higher efficiency.
_4_ 1 3 2 0 ~
1 ~rie~ Summary o~ the Invention There is, therefore, provided in practice of this invention according to a presently preferred embodiment an illumination bar for a xerographic printer, or the like, having a plurality of light sources in a row for approximately uniformly illuminating separate areas along the length of the row. Each of the light sources on the illumination bar is in the form of a cavity open at the end facing in the direction Or illumination and closed at the opposite end. A light emitting diode at the clo~ed end o~ the cavity emit~ radiation in directions transverse to the direction of illumination.
A concave reflective wall at the closed end of the cavity reflects a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity. Occultation means are provided near the open end of the cavity ~or defining the image shape of that pixel. In a pre~erred embodiment the means for defining the shape ~f the image comprises absorptive walls ad~acent to the open end of the cavity.
Alternatively, a fac-ted or conical re~lector may be used at the closed end Or the cavity with absorptive wall for defining the shap- of the image pro~ected ~rom the cavity.
If desired, a window may be provided over the open end o~ the cavity, which is at least partially absorbing in a patt-rn for obtaining a desired illumination intensity pattern from the cavity. In an exemplary e~bodimen~, such an illumination bar may b- assembled from a plurality of layers of dif~erent geometries and surface prop~rties.
.... ~ -.
l32n~7l 4a An illumination bar for a xerographic printer or the like comprising:
a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a concave reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and occultation means between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
An illumination array comprising:
a plurality of cavities in a row, each cavity being closed at one end and open at the other end for projecting light toward an image plane, and comprising:
a reflective closed end including a portion angled for reflecting light from the closed end toward the open end of the cavity, a cylindrical absorptive wall at the open end, and a cylindrical reflective wall between the absorptive wall and the concave closed end; and a light emitting diode mounted at the bottom of the closed end of each cavity.
An illumination bar for a xerographic printer or the like comprising:
.
.-.' ~,,'.
lx2n~.~7l 4b a printed circuit board;
a plurality of light emitting diodes mounted in a row on the printed circuit board;
a deflector plate mounted on the printed circuit board;
a row of passages through the deflector plate, each passage being around a light emitting diode on the printed circuit board and having reflective walls concave in a direction away from the printed circuit board for reflecting light from the light emitting diode away from the printed circuit board;
a aperture plate mounted on the deflector plate;
a row of apertures through the aperture plate, each aperture being aligned with a passage through the deflector plate for passing light from the light emitting diode toward an image plane beyond the aperture plate.
An illumination bar for a xerographic printer or the like comprising means for projecting a stripe of light formed of a plurality of adjacent generally rectangular pixels, each means for projecting comprising:
a cavity with a generally rectangular aperture at one end of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
An illumination array comprising:
a printed circuit board;
a row of light emitting diodes mounted on the printed circuit board;
a reflector plate on the printed circuit board including a scalloped edge with a row of indentations, each indentation encompassing a light emitting diode, each indentation having a reflective concave wall l32n ~ ~
4c portion for reflecting light from the light emitting diode away from the reflector plate; and a cover plate over the reflector plate.
An illumination array comprising:
a printed circuit board;
a row of pits in the printed circuit board, each pit having walls angled for reflecting light from the bottom of the pit away from the printed circuit board;
a metal layer on the printed circuit board including a portion adjacent to such a pit and a portion in such a pit; and a side emitting light emitting diode on the metal layer in the bottom of such a pit.
An illumination array comprising means for illuminating a plurality of adjacent pixels, each means for illuminating comprising a light source having a transparent window, and characterized by each window including a photochromic material for selectively darkening in response to differences in illumination.
A xerographic printer or the like comprising:
a movable photosensitive medium; and a plurality of means for projecting a plurality of separately addressable images directly on the photosensitive medium without a lens, each means for projecting comprising:
a cavity with a generally rectangular aperture at one end of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
An illumination bar for a xerographic printer or the like comprising:
132()~7~
4d a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and at least partly absorbing walls between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
An illumination bar for a xerographic printer or the like comprising means for projecting a stripe of light formed of a plurality of adjacent generally rectangular pixels, each means for projecting comprising:
a cavity with a generally rectangular absorptive walls forming an aperture at one end of the cavity;
a reflective closed end at the other end of the cavity having a portion angled for reflecting a major part of the light striking the reflective angled portion toward the open end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the angled reflective portion of the cavity.
_5_ 1 3 2 0 ~
1 Drawinqs These and other features and advantages will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a fragmentary top view of three pieces used to assemble an illumination bar, offset laterally from each other so that the relation o~ the parts, as assembled, can be seen:
FIG. 2 ls a side view of the parts in FIG.
exploded from each other;
FIG. 3 is a transverse cross-section of the assembled illumination bar adjacent to a photosensitive medium;
FIG. 4 is a fragmentary longitud~nal cross-section o~ the deflector plate from the middle o~ the a~sembly illustrated in FIGS. 1 to 3;
FIG. 5 i~ a back or botto~ view of a fragm-nt of ths deflector plate;
FIG. 6 i8 a top view of a fragment of the aperture plate of FIGS. 1 to 3 also indicating a fragment of the underlying deflector plat-;
FIG. 7 i5 a fragmentary top view of a pr$nted circuit board from the embodiment of FIGS. 1 to 3;
FIG. 8 is an isometric view of an exemplary window which may be u~ed on an illumination bar;
FIG. 9 i~ a transverse cross-section of a deflector plate Or anothQr embodiment of illumination bar;
FIG. 10 i8 a fragmentary ~ront face view of the lllumination bar of FIG. 9:
FIG. 11 i~ another view of the front ~ace of the illumination bar of Fig. 9, showing additional detail;
Fig. 12 i5 a perspective cut-away view of another embodim~nt of illumination bar;
,,,.
1'.~20'~7 1 1 FIG. 13 is a transverse cross-section of the illumination bar of FIG. 12: and FIG. 14 is a longitudinal cross section of another shape of cavity.
~ 3 2 ~ :1 s ~
1 Descri~tion An exemplary illumlnation bar is conveniently assembled as a sandwich of three strips or elongated plates as illustrated in FIGS. 1 to 3. The top or front s strip is an aperture plate 10 which, in this embodiment, is made of an absorptive black polycarbonate plastic.
The middle layer of the sandwich is a deflector plate 11 which, in this embodiment, is preferably mads of a re~lective white polycarbonate plastic. Colors are imparted to the plastic by pigments such as carbon or Tio2. Preferably, the aperture plate and de~lector plate are made of the same thermoplastic material, so that they can be ultrasonically welded together.
It is convenient to form the deflector plate in a series of strips shorter the aperture plate, which are then assembled in controlled locations on the back side of ths apsrture plate.
Th~ third layer in the ~andwich forming the illumination bar is a printed circuit board 12, which forms the back of the sandw~ch. After assembling the de~lector plate or plates on the back of the aperture plate, the printed circuit board i8 fastened to the aperture plate. A pair of posts 13 on the back of the aperture plate extend through holes 14 through the printed circuit board, thereby aiding alignment of the aperture plate and printed circuit board.
It will be recognized that only one end of the parts making up an illumination bar are illustrated in FIGS. 1 and 2. Such a bar has an overall length sufficient for illuminating the medium to be used in a printer or the like. Thus, for example, the length of the active region of the erase bar could be a little over 216 millimeters for a printer handling standard 8-1/2 inch wide or smaller paper. The erase ~ar may be made longer a~ desired for handling wider paper.
-8- 1 3 2 0~17~
1 The sandwich is assembled from two subassemblies.
one of these is the printed circuit board with a row of light emitting diodes (LEDs) 16 mounted thereon. The other subassembly comprises the aperture plate 10 with one or more deflector plates 11 bonded thereto. Since careful alignment is important to obtain good optical quality, a plurality o~ short studs 17 on the back of the aperture plate (hidden in Fig. 2) fit into shallow pits 18 on the front of the deflector plate or plates.
Small triangular ridges (not shown) may be left on one o~ the facing surfaces for ultrasonically welding the deflector plates to the aperture plate.
When these two subass-mblies have passed inspection, they are a~sembled with the posts 13 extending through the holes 14. In addition, pins 19 on the back Or the deflector plate extend through holes 21 through the printed circuit board. The protruding ends Or the pins 19 are heat staked to ~asten the sandwich asszmbly together. A clear polycarbonate protective window 22 extends along the front face of the aperture plate. The window can be added berore or after the sandwich is assQmbled.
A row of LEDs 16 i8 assembled in the center of each of a row of m~tallized pads 23 on the front face o~ the printed circuit board (FIG. 7). The pad serves as one electrical contact for the light emitting diode. The second electrical connection (not shown) is made by wire-bonding ~rom the top of the LED to an ad~acent rectangular contact pad 24.
Th~ LEDs are conventional, a~ are their connection In an exemplary embodiment, such an LD
may be 0.25 millimeter square and hav~ a thicXness of 0.2 millimeter. The electrical connection to the top of such an LED may be a 25 micrometer wire bonded to a 75 micrometer spot on the LED. Pre~erably, the LED~ are '- `
-9- 1~
1 transparent side emitting LEDs; that i5, part o~ the light i~ emitted from the top face of the LED and a ma~or portion of the light is emitted laterally. Thus, for example, in an exemplary embodiment, a green emitting LED may be used, which emits light from the top as well as the ~ides. Such side-emitting diodes are desirable since they are more efficient than top-emitting diodes.
The aperture plate has a row of apertures 26 extending along its active length. In the illustrated embodiment, each aperture is substantially rectangular with somewhat rounded corners. The walls of the aperturQ form a rectangular cylinder. In an exemplary erase bar, the apertures are on 2.5 millimeter centers and have an opening 1.8 by 2.0 millimeters.
A row of passages 27 extend through the deflector plate 11. The sandwich is aligned so that each passage is aligned with a respective aperture through the aperture plate as seen in Fig. 6 which is a face view of a fragment of the aperture plate overlying the deflector plate. Similarly, each LED on the printed circuit board is centered in a respective passage through the deflector pl~te. Collectively, such a passage and aperture form a cavity which is closed at its bottom end by the printed circuit board and i8 open (for emission of light) at the window end of the aperture. There is an LED at the closed end of each such cavity. Each such cavity serves as a light source illuminating a separate area along the langth of an assembled erase bar: that is, each cavity illuminates one pixel in an imags plane in front of the window.
$ypically, th- photosensitive medium 25 (Fig. 3) moving past the cav~ty is about a millimeter away from the ap-rture end of the cavity. By ad~usting the dimensions and concave surface~ in the cavity, there may --Io-- 1 3 2 (~
1 be digtances o~ up to five millimeters between the end o~ the cavity and the photosensitive medium. Within such distances, the image shape projected from the aperture at the end oS the cavity directly onto the photosensitive surface retains a shape similar to the shape of the aperture without USQ 0~ any lenses. This direct projection from the cavity has a better depth of ~ield than when lenses are used for focussing the light;
hence, less preci~ion i9 needed in spacing the medium and light source. Further, there is no need for careful al~gnment o~ lenses.
The passage through the d-~lector plate has a ~ront portion extending about halr o~ the thickness of the plate in the form of a right circular cylinder 28. In one embodiment the passage has a diameter o~ 2.1 millimeters. At the opposite end of the passage: that is, at the closed end o~ the cavity ad~acent the printed circuit board, there is a surSace 29 in the form of a relatively shallower cone. Between the conical surface 29 and the right circular cylindrical walls 28, there is a second somQwhat steeper conical sur~ace 31. The two conical surface Sorm a concave reflective wall which r~lects light from the LED toward the open end o~ the cavity.
In an exemplary embodiment, the shallower cone near the closed end of the cavity ha~ a total included angle B oS 82-. The somewhat ~teeper cone 31 has a total included angl- A of 60-. The total depth o~ the passage i8 1- 6 mlllimeters. It will be recognized that these exemplary dimensions are for a speci~ic embodiment to obtain an acceptable light distribution and intensity ~or illuminating a pixel o~ desired dimensions. The specifics oS a cavity are determined by the properties desired in the produc* and are aSfected by other equipment parameters such as the properties oS the - .
Background Thi~ invention relates to an illumination or erase bar for a xerographic printer or the like, having a row of light emitting diodes for llluminating an image plane in a stripe having approximately uniform intensity along ths length of the stripe.
There ara times when it i~ desirable to illuminate a selected area on a photosensitivff surface in a xarographic device such as a prlnter, copier, scanner, fac~imile machine, or tha like. ~or example, the entire breadth o~ th- medium may be illuminated as it moves along after transferring an image to paper, for completely di wharging the medium 80 that it is in a uniform ground ~tate to b- charged for receiving a new image. The antire breadth of the medium may be bathed in light of reasonably uniform intensity ~or this total Qrasure.
Ther- are other times when it is de~irable to illuminat- a selacted area on th- mediumO ~his might be don-, for exa~ple, to block out text or, in a color prlnter, to paint in background color. It might be usad, for xample, in a color printar, to bloc~ out the area o~ a letterhead on a document so that the letterhead i5 printed in color and the text of the -2- 132~`~7~
1 letter is printed ln blacX. A more sophistlcated erase bar is needed for such selective illumination.
Such an illumination bar may illumlnate two or three millimeter long segments or pixels of a stripe a two or three millimeters wide. Each of these pixels is illuminated by a separate light emitting diode (LED).
Each of the LEDs can be separately addressed or switched for illuminating a desired area on the medium. It is still important to obtain reasonably uniform illumination within the area being illuminated;
typically, an intensity difference of about two to one between the brightest and dimmest areas is acceptable.
Sometimes tighter specifications for differences in illumination are required. This means that the illumination within each pixel must be reasonably uni~orm. It also means that there cannot be gaps between ad~acent pixelQ.
Typically, one seeks to achieve an intensity of illumination across a pixel in the direction Or the length of th- row or stripe which is approximately trapezoidal. Over the ma~or portion of the length of the pixel, the inten~ity i3 reasonably uniform. At each edg-, intensity drops off rapidly with distanco toward a dark area surrounding th- pixel. It is undesirable to hav- a halo of light surrounding the illuminated pixel.
Ad~acent pix-ls in the row are arranged so that the decrQa~ing illumination of one pixel overlaps the increasing illumination o~ the next pixel, preferably with the overlap making the two SO% intens~ty levels o~
ad~acent pixels at the same location. This avoids any gap in illumination, any significant decrease in illumination between ad~acent pixels, and any significant increase in illumination due to excessive overlap.
_3_ 1320~7 1 1 Bubble lenses and the llke have been used ~or pro~ecting the llght from an LED toward an image plane for providing individually illuminated pixels. Lens systems are, however, costly and somewhat inefficient in transmitting light from the LED to the image plane. In a typical system, only about 20% o~ the light from the LED may be usefully pro;ected on the image plane.
Defects in an LED or misalignment o~ an LED may also be projected toward the image plane, thereby degrading the uniformity of light within a pixel. For example, a chipped corner on an LED may show up in the image plane as a significant change in illumination. Another difficulty with lens systems is a limited depth of field. A belt carrying the photosensltiv- medium may "flap" somewhat, varying the di~tance between the erase bar and the medium. With a len~ system thi~ can change the shapQ and size of the illuminated pixel as the medium moves in and out of focus.
It i8, therefore, desirable to provide an individually addressable LED illuminator bar which is less costly and more efficient than a lens system. It is desirable that the system be tolerant of LED defects.
It is desirabl- that the intensity oS illu~ination be approximately uniform across each pixel and between pixels, 80 that 2 uniform intensity illumination is obt~ined across the full length of the illuminator bar, across any subset of pixels, and across each individual piXQl .
An exemplary illuminator bar and some prior technlgues for illumination are described and illustrated in U.S. Patent No. 4,759,603 by Jones. In the arrangement described therein, there is appreciable absorption of light. It would be desirable to provide an LED illuminator bar with higher efficiency.
_4_ 1 3 2 0 ~
1 ~rie~ Summary o~ the Invention There is, therefore, provided in practice of this invention according to a presently preferred embodiment an illumination bar for a xerographic printer, or the like, having a plurality of light sources in a row for approximately uniformly illuminating separate areas along the length of the row. Each of the light sources on the illumination bar is in the form of a cavity open at the end facing in the direction Or illumination and closed at the opposite end. A light emitting diode at the clo~ed end o~ the cavity emit~ radiation in directions transverse to the direction of illumination.
A concave reflective wall at the closed end of the cavity reflects a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity. Occultation means are provided near the open end of the cavity ~or defining the image shape of that pixel. In a pre~erred embodiment the means for defining the shape ~f the image comprises absorptive walls ad~acent to the open end of the cavity.
Alternatively, a fac-ted or conical re~lector may be used at the closed end Or the cavity with absorptive wall for defining the shap- of the image pro~ected ~rom the cavity.
If desired, a window may be provided over the open end o~ the cavity, which is at least partially absorbing in a patt-rn for obtaining a desired illumination intensity pattern from the cavity. In an exemplary e~bodimen~, such an illumination bar may b- assembled from a plurality of layers of dif~erent geometries and surface prop~rties.
.... ~ -.
l32n~7l 4a An illumination bar for a xerographic printer or the like comprising:
a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a concave reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and occultation means between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
An illumination array comprising:
a plurality of cavities in a row, each cavity being closed at one end and open at the other end for projecting light toward an image plane, and comprising:
a reflective closed end including a portion angled for reflecting light from the closed end toward the open end of the cavity, a cylindrical absorptive wall at the open end, and a cylindrical reflective wall between the absorptive wall and the concave closed end; and a light emitting diode mounted at the bottom of the closed end of each cavity.
An illumination bar for a xerographic printer or the like comprising:
.
.-.' ~,,'.
lx2n~.~7l 4b a printed circuit board;
a plurality of light emitting diodes mounted in a row on the printed circuit board;
a deflector plate mounted on the printed circuit board;
a row of passages through the deflector plate, each passage being around a light emitting diode on the printed circuit board and having reflective walls concave in a direction away from the printed circuit board for reflecting light from the light emitting diode away from the printed circuit board;
a aperture plate mounted on the deflector plate;
a row of apertures through the aperture plate, each aperture being aligned with a passage through the deflector plate for passing light from the light emitting diode toward an image plane beyond the aperture plate.
An illumination bar for a xerographic printer or the like comprising means for projecting a stripe of light formed of a plurality of adjacent generally rectangular pixels, each means for projecting comprising:
a cavity with a generally rectangular aperture at one end of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
An illumination array comprising:
a printed circuit board;
a row of light emitting diodes mounted on the printed circuit board;
a reflector plate on the printed circuit board including a scalloped edge with a row of indentations, each indentation encompassing a light emitting diode, each indentation having a reflective concave wall l32n ~ ~
4c portion for reflecting light from the light emitting diode away from the reflector plate; and a cover plate over the reflector plate.
An illumination array comprising:
a printed circuit board;
a row of pits in the printed circuit board, each pit having walls angled for reflecting light from the bottom of the pit away from the printed circuit board;
a metal layer on the printed circuit board including a portion adjacent to such a pit and a portion in such a pit; and a side emitting light emitting diode on the metal layer in the bottom of such a pit.
An illumination array comprising means for illuminating a plurality of adjacent pixels, each means for illuminating comprising a light source having a transparent window, and characterized by each window including a photochromic material for selectively darkening in response to differences in illumination.
A xerographic printer or the like comprising:
a movable photosensitive medium; and a plurality of means for projecting a plurality of separately addressable images directly on the photosensitive medium without a lens, each means for projecting comprising:
a cavity with a generally rectangular aperture at one end of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
An illumination bar for a xerographic printer or the like comprising:
132()~7~
4d a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and at least partly absorbing walls between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
An illumination bar for a xerographic printer or the like comprising means for projecting a stripe of light formed of a plurality of adjacent generally rectangular pixels, each means for projecting comprising:
a cavity with a generally rectangular absorptive walls forming an aperture at one end of the cavity;
a reflective closed end at the other end of the cavity having a portion angled for reflecting a major part of the light striking the reflective angled portion toward the open end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the angled reflective portion of the cavity.
_5_ 1 3 2 0 ~
1 Drawinqs These and other features and advantages will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a fragmentary top view of three pieces used to assemble an illumination bar, offset laterally from each other so that the relation o~ the parts, as assembled, can be seen:
FIG. 2 ls a side view of the parts in FIG.
exploded from each other;
FIG. 3 is a transverse cross-section of the assembled illumination bar adjacent to a photosensitive medium;
FIG. 4 is a fragmentary longitud~nal cross-section o~ the deflector plate from the middle o~ the a~sembly illustrated in FIGS. 1 to 3;
FIG. 5 i~ a back or botto~ view of a fragm-nt of ths deflector plate;
FIG. 6 i8 a top view of a fragment of the aperture plate of FIGS. 1 to 3 also indicating a fragment of the underlying deflector plat-;
FIG. 7 i5 a fragmentary top view of a pr$nted circuit board from the embodiment of FIGS. 1 to 3;
FIG. 8 is an isometric view of an exemplary window which may be u~ed on an illumination bar;
FIG. 9 i~ a transverse cross-section of a deflector plate Or anothQr embodiment of illumination bar;
FIG. 10 i8 a fragmentary ~ront face view of the lllumination bar of FIG. 9:
FIG. 11 i~ another view of the front ~ace of the illumination bar of Fig. 9, showing additional detail;
Fig. 12 i5 a perspective cut-away view of another embodim~nt of illumination bar;
,,,.
1'.~20'~7 1 1 FIG. 13 is a transverse cross-section of the illumination bar of FIG. 12: and FIG. 14 is a longitudinal cross section of another shape of cavity.
~ 3 2 ~ :1 s ~
1 Descri~tion An exemplary illumlnation bar is conveniently assembled as a sandwich of three strips or elongated plates as illustrated in FIGS. 1 to 3. The top or front s strip is an aperture plate 10 which, in this embodiment, is made of an absorptive black polycarbonate plastic.
The middle layer of the sandwich is a deflector plate 11 which, in this embodiment, is preferably mads of a re~lective white polycarbonate plastic. Colors are imparted to the plastic by pigments such as carbon or Tio2. Preferably, the aperture plate and de~lector plate are made of the same thermoplastic material, so that they can be ultrasonically welded together.
It is convenient to form the deflector plate in a series of strips shorter the aperture plate, which are then assembled in controlled locations on the back side of ths apsrture plate.
Th~ third layer in the ~andwich forming the illumination bar is a printed circuit board 12, which forms the back of the sandw~ch. After assembling the de~lector plate or plates on the back of the aperture plate, the printed circuit board i8 fastened to the aperture plate. A pair of posts 13 on the back of the aperture plate extend through holes 14 through the printed circuit board, thereby aiding alignment of the aperture plate and printed circuit board.
It will be recognized that only one end of the parts making up an illumination bar are illustrated in FIGS. 1 and 2. Such a bar has an overall length sufficient for illuminating the medium to be used in a printer or the like. Thus, for example, the length of the active region of the erase bar could be a little over 216 millimeters for a printer handling standard 8-1/2 inch wide or smaller paper. The erase ~ar may be made longer a~ desired for handling wider paper.
-8- 1 3 2 0~17~
1 The sandwich is assembled from two subassemblies.
one of these is the printed circuit board with a row of light emitting diodes (LEDs) 16 mounted thereon. The other subassembly comprises the aperture plate 10 with one or more deflector plates 11 bonded thereto. Since careful alignment is important to obtain good optical quality, a plurality o~ short studs 17 on the back of the aperture plate (hidden in Fig. 2) fit into shallow pits 18 on the front of the deflector plate or plates.
Small triangular ridges (not shown) may be left on one o~ the facing surfaces for ultrasonically welding the deflector plates to the aperture plate.
When these two subass-mblies have passed inspection, they are a~sembled with the posts 13 extending through the holes 14. In addition, pins 19 on the back Or the deflector plate extend through holes 21 through the printed circuit board. The protruding ends Or the pins 19 are heat staked to ~asten the sandwich asszmbly together. A clear polycarbonate protective window 22 extends along the front face of the aperture plate. The window can be added berore or after the sandwich is assQmbled.
A row of LEDs 16 i8 assembled in the center of each of a row of m~tallized pads 23 on the front face o~ the printed circuit board (FIG. 7). The pad serves as one electrical contact for the light emitting diode. The second electrical connection (not shown) is made by wire-bonding ~rom the top of the LED to an ad~acent rectangular contact pad 24.
Th~ LEDs are conventional, a~ are their connection In an exemplary embodiment, such an LD
may be 0.25 millimeter square and hav~ a thicXness of 0.2 millimeter. The electrical connection to the top of such an LED may be a 25 micrometer wire bonded to a 75 micrometer spot on the LED. Pre~erably, the LED~ are '- `
-9- 1~
1 transparent side emitting LEDs; that i5, part o~ the light i~ emitted from the top face of the LED and a ma~or portion of the light is emitted laterally. Thus, for example, in an exemplary embodiment, a green emitting LED may be used, which emits light from the top as well as the ~ides. Such side-emitting diodes are desirable since they are more efficient than top-emitting diodes.
The aperture plate has a row of apertures 26 extending along its active length. In the illustrated embodiment, each aperture is substantially rectangular with somewhat rounded corners. The walls of the aperturQ form a rectangular cylinder. In an exemplary erase bar, the apertures are on 2.5 millimeter centers and have an opening 1.8 by 2.0 millimeters.
A row of passages 27 extend through the deflector plate 11. The sandwich is aligned so that each passage is aligned with a respective aperture through the aperture plate as seen in Fig. 6 which is a face view of a fragment of the aperture plate overlying the deflector plate. Similarly, each LED on the printed circuit board is centered in a respective passage through the deflector pl~te. Collectively, such a passage and aperture form a cavity which is closed at its bottom end by the printed circuit board and i8 open (for emission of light) at the window end of the aperture. There is an LED at the closed end of each such cavity. Each such cavity serves as a light source illuminating a separate area along the langth of an assembled erase bar: that is, each cavity illuminates one pixel in an imags plane in front of the window.
$ypically, th- photosensitive medium 25 (Fig. 3) moving past the cav~ty is about a millimeter away from the ap-rture end of the cavity. By ad~usting the dimensions and concave surface~ in the cavity, there may --Io-- 1 3 2 (~
1 be digtances o~ up to five millimeters between the end o~ the cavity and the photosensitive medium. Within such distances, the image shape projected from the aperture at the end oS the cavity directly onto the photosensitive surface retains a shape similar to the shape of the aperture without USQ 0~ any lenses. This direct projection from the cavity has a better depth of ~ield than when lenses are used for focussing the light;
hence, less preci~ion i9 needed in spacing the medium and light source. Further, there is no need for careful al~gnment o~ lenses.
The passage through the d-~lector plate has a ~ront portion extending about halr o~ the thickness of the plate in the form of a right circular cylinder 28. In one embodiment the passage has a diameter o~ 2.1 millimeters. At the opposite end of the passage: that is, at the closed end o~ the cavity ad~acent the printed circuit board, there is a surSace 29 in the form of a relatively shallower cone. Between the conical surface 29 and the right circular cylindrical walls 28, there is a second somQwhat steeper conical sur~ace 31. The two conical surface Sorm a concave reflective wall which r~lects light from the LED toward the open end o~ the cavity.
In an exemplary embodiment, the shallower cone near the closed end of the cavity ha~ a total included angle B oS 82-. The somewhat ~teeper cone 31 has a total included angl- A of 60-. The total depth o~ the passage i8 1- 6 mlllimeters. It will be recognized that these exemplary dimensions are for a speci~ic embodiment to obtain an acceptable light distribution and intensity ~or illuminating a pixel o~ desired dimensions. The specifics oS a cavity are determined by the properties desired in the produc* and are aSfected by other equipment parameters such as the properties oS the - .
3 ~
1 photosensitive medium, the pixel area, the speed of the medium moving past the erase bar, the distance between the cavity and the medium, and the like.
The die for injection molding the deflector plate is highly polished so that the conical surfaces 29 and 31 and the cylindrical surface 28 are also polished.
The smooth, white plastic surface provides excellent reflection of the light emitted laterally from the light emitting diode toward the image plane beyond the open end of the cavity. Reflectivity may be enhanced, if desired, by met~llizing such surfaces. However, good efficiency of utilization o~ llght i~ obtained without need for metallizing. Efficiency can easily be twice the efficiency of an illumination system using a lens.
The concave reflector formed by the two conical surfaces in combination with the metallized pad on the printed circuit board proves quite effective in directing light from the LED approximately uniformly across the pixel illuminated by the cavity. Other concave reflective wall~ might be used, but it has not proved important to ~ake parabolic or elliptical reflectors ~or collimating light from the cavity. That may not even ~e feasible sinc- the LED is a rather large area light source, rather than a point source.
In this context, "concave" is used in the sense of having concavity in a longitudinal cross section through the cavity, such as seen in Figs. 3 and 4. A single conical surface in the closed end of the cavity could be considered concave ln a transverse cross section.
Further, thia arrange~ent o~ reflective surfaces tends to throw light throughout the area of the open end of the cavity and is guite insen-itive to defects in the LED or moderate misalignment or mispositioning o~ the LED. Ray traces show one or two bounces of the light off the reflective walls. There is some light going 1 directly from the LED toward the open end of the cavity with no bounces and a very minor part with three bounces. Most of the scrambling of the light comes from a single bounce of the light off the concave walls of s the cavity. Since the angles of the walls vary by reason of the concavity, there is a tendency to promote substantial uniformity of light intensity across the pixel illuminated by the cavity.
A shallow counterborQ 32 is providsd on the back face of the deflector plate to provide clearance for the wire bond connection between the rectangular pad 24 on the PC board and the top of the LED. Although the counterbore interrupts a portion of the circumference of the shallower cone 29 near the bottom of the cavity, there is ample scrambling Or the light by reflections off the concave walls that the illumination is approximately uniform across ths pixel and the shadowed area i~ not significant.
Further, the shadow of the contact wire and the pad to which it i8 bonded do not appear to affect the uni~ormity of illum$nation. This may be contra~ted with ~ lens system where such artifacts could slgnificantly degrade the uniformity of illumination acros~ the pixel.
Further, since a ma~or portion of the light from the LED
is directed toward the open end of the cavity by the concavo re~lective walls in the closed end of the cavity, high efficiency is o.btained. It appears that the efficisncy of illumination for a given power to the LED~ for a system as provided in practice of this inventlon is at least twice as high as the efficiency of a system employing lenses for illuminating the pixsls.
The black walls of the substantialiy rectangular aperture through the aperture plate tend to absorb a ma~or part of the radiation striking the walls at high angles of incidence. Light striking at low angles of .
-13- ~ 3 2 0 ~ ~ i 1 inc~dence 1~ retained ln the cavity and helps provide uniformity Or illumination. By absorbing light that is not directed out of the cavity at a low angle from its axis, the absorbent walls minimize any halo of light around the illuminated pixel.
By making the aperture at the open end of the cavity rectangular, it serves as an occultation mask for defining a generally rectangular image shape. By clipping or rounding the corners of the rectangle, the drop-off of light intensity at the edge of the pixel along the length of the stripe can be controlled so that the average light intenslty where pixel edge~ overlap can be maintained with approxlmate uni~ormity. The aspect ratio of the rectangular opening of tho cavity may be varied as desired to obtain a desired image shape. The pro~ected image may be square, or rather elongated either transverse to or along the photosensitive medium. The rounding or clipping of the corner~ for shaping the pro~-cted image can be varied through a considerable range.
If desired, the ab~orption ~y the walls of the aperture may bo enhanced by roughoning. This could also dif~us- re~lected light and onhance uniformity of -illumination. No special ef~ort w 9 made to roughen the walls and, although they app-ar somewhat shiny, they have proved effoctive as ab~orbers. Rather than being a rectangular cylinder, the ab~orbing wall~ couid also be in tho form of a prism converging slightly toward the open end of the cavity.
Reflective walls may also be used for occulting part o~ the light from the cavlty and shaping the pro~octod imag-. White re~lective walls ara not as effective as black ab~orptive walls ln defining a sharp edge on the imago. Metallizing the walls to maXo them highly reflective may be used for enhancing image ... , ~ ~ . .
. , ~
-14- 1 3C~
1 sharpnQss. When re~leCt~VQ walls are used it may also be de~lrable to taper the walls so they converge slightly toward an aperture at the open end o~ the cavity having a shape similar to the shape o~ the image it is desired to project.
Because of the high efficiency obtained with the reflective concave cavity, an additional technique may be employed, i~ desired, ~or assuring uniformity of illumination. A pattern may be provided on the transparent window at the open end o~ the cavity for selectively absorbing light, as well a~ shaping the image. FIG. 8 illustrates such an mbodiment.
In such an embodiment, a gen-rally r-ctangular area 36 of the window over a cavity is surrounded by an opaque area 37. The perimeter or the transparent area may serve as a shadow mask helping to de~ine the edges o~ the pixel. Further, i~ need be, an area 38, indicated by a stippling in the drawing, where llght intensity would otherwise be too high, can be made partially absorbing for reducing light intensity.
The partially absorbing ar~a may be produced by any o~ a variety Or conventional techniques. For example, a pattern of ~ine dots of varying BiZ- or density may be -used in the manner Or a half-tone ~creen to occult more or less area as desired. A photographic emulsion may also be selectively darkened to be partially absorbent.
Alternatively, opaqua bands or other patterns o~ partly or totally absorbing areas may be used to cast somewhat darkened shadows on the image plane and make the resultant illumination more uniform. For example, an opa~ue band may be placed across the center o~ the apertur- ir th- central illumination i~ too bright. The scrambling Or the light within the pixel illuminates the area behind the band with an intensity near the average intensity throughout the pixel.
5 ~ 3 ~
1 Alternatlvely, a partially abgorbing area may be madQ on an ad hoc basis by incorporating a photochromic material in the window. In such an embodiment the window selectively darkens in response to di~ferent intensities of illumination. In areas with higher light intensity, the window gets darker or more absorbent than in areas with les~ illumination. As a consequence, the l$ght transmitted through the window is made more uniform.
FIGS. 9 to 11 illustrats part of another embodiment o~ illuminating cavity constructed according to principles oS this invention. In these drawlngs, the concave reflectivQ walls at the closed end of such a cavity are illustrated. It will be understand that additional reSlective and/or absorbing walls are employed for completing the cavity ~rom which light is pro~ected.
In this embodiment, it is as iS the concave reflective walls o~ th~ deflector plate are combined with th- flat reSlective surSace on the Sront Sace of the printed circuit board. Thus, the printed circuit board 41 has a row Or concave pits 42 in the ~ront face.
The bottom oS each pit ha~ a Slat central area 43 which has around it four egually spac-d arcuate lobes 44. The lobes are not ln the same plane a~ the flat bottom of the pit. They are tilted away from the flat bottom at an angle C, which may be in a range oS from 25 to 30 degrees.
The concave walls 45 of each pit are, in cross-section, two circular arcs, the centars oS which are onopposite sides o~ th- center line Or the pit. These continuous complex curved walls tend to reflect light ~rom a light emitting diod- 46 in the bottom oS the pit (FIG. 11) toward the open end oS a cavity for illuminating a pixel. Additional rerlecti~e and/or '., ' ' . ' -16- 1 ~ 20`~71 1 absorptive walls (not shown) provide additional reflections for obtaining approximate uniformity of illumination and absorption for defining a desired shape and size of pixel.
The four lobes at the bottom of the pit cut into the curved walls to a small extent, thereby diminishing the concave area from which light is re~lected. Light is reflected, however, from the portion of the curved walls between the lobes. The result is a pattern of light di~tribution, which tends to fill in the corners of the illuminated pixel, ther~by a~suring uniform light distribution. Th~ angled floors of the lobes also reflect light toward the open end o~ the cavity to combine with light reflected from the curved concave walls and provide uniform illumination.
The substrate having the reflective pits also serves a~ a printed circuit board for making connections to tho light-emitting diode~. The walls and bottoms of the pit~ are motallizQd. The motal layer 47 from each pit extends onto the front Jur~ace of the board and laterally in on- dlrection to a plated-through hole 48 for making connection to printed circuits (not shown) on the back o~ the bo~rd. A tab 49 on each metallized area provlde-~ a means for making a wiro bonded connection to the top of the ~D in the next pit along the row. These connection~ may be used when connecting ~he LEDs in series ~or illuminating an entire photosens$tive medium.
A metallized stripe 51 extends along the opposite edgo o~ the board. When it i~ desired to make separate electrical connoctions ror each LED ~or illuminating only selectod area~ of the photo~ensitive medium, an electrical connection can be wire bonded between a tab 52 on this stripe and an ad~acent LED. This provides mean~ for making electrical contact with each LED along the illumination bar ~or individually energizing each s 1 LED separately from the other LEDs. It will be noticed that with this pattern o~ printed circuits on the board, this is a "generic" board which can be used for either parallel or series connection of LEDs as may be desired.
The metallized areas may be made by a conventional technique such as electroless deposition of copper, masking and etching, and electroplating with soft gold, for example. All that is needed is that the plating throws adequately into the pits to assure good electrical contact. Such gold metallized concave walls in the pits are highly re~lective and provide efficient sources of illumination.
FIGS. 12 and 13 illustrate a fragment o~ another embodiment of illumination bar or erase bar for use in a xerographic printer or the like. This embodiment is particularly useful in a location where Qpace is at a premium. A very narrow ~tripe can be made, where each pixel extends a substantially greater distanco along the length o~ the stripe than the width of the pixel across the stripe. In thls embodiment, a row o~ ~ide-emitting LEDs 56 are mounted on onQ face of a printed circuit board 57. Conventional electrical conductors are printed on the board for making lectrical contacts with the ~EDs. These are omitted from the drawing for clarity of illustration.
~ reflector plate 58 is mounted on the front face of the PC board and this, in turn, is covered by a cover plate 59. Thls three-layer sandwich is held tqgether by fasteners 61. Ir desirod, cut-outs 62 can be made in the re~lector plate ~o that additional components can be mounted on the printed circuit board. The reflector plate may be made of reflective white plastic, or the re~lecting surfaces may be metallized to enhance re~lection.
-18- ~320~
1 The rrOnt edge Or the re~lector plate is scalloped by a row o~ concave indentations Each LED is positioned in one o~ the indentations Between each ad~acent indentation, there is a converging wall 63 Each indentation is in ths ~orm of a pair of curved walls, which may, for example, be approximately parabolic or elliptical and have centers offset from the center of the indentation ~hus, where the two curved walls intQrsect in the center o~ the indentation, there is a small cusp 64 behind the LED
~ ight ~rom the sid--emitting LED is re~lected ~rom the concave reflective wall~ o~ the reflector plate and directed toward the open end Or the cavity formed by the indentations and the parallel walls o~ the printed circuit board and the cover plate, as indicated by a few arrows ln Fig 12 Since the walls are roughly parabolic, they approximat-ly colllmat- the light pro~ected from the cavity It ia desirable, however, that th-ro b- some multlple bounc-s o~ light o~ o~ the walls ~or scrambling th- light and providing a reason~bly unifor~ inten~ity o~ illumination along the length o~ th- assembly The rac-s o~ the printed circuit board and cover plate bounding two sides of the cavity are largely non-reflective, ther-by assuring a narrow stripe of illumination A transparent window 66 along the fron' edge o~ th- a~s-mbly protects the LEDs and ren ectlve sur~aces within th- cavities I~ desirQd, the window may be mad- ~lightly convex ~or broadening the image pro~ected ~rom th- cavity I~ de~Ired, a portion o~ the walls 63 between ad~acent cavltles can be made non-re~lective They may also be extend-d beyond the location illustrated in FIGS 12 and 13 ~or ~urther minimizing cross-talk between ad~acent pixels and enhancing uni~ormity o~ the 132(1 ~
1 illumlnation Toward that same end, partially absorbing areas may be provided on the window 66 Fig 14 illustrates in longitudinal cross section another embodiment of cavity constructed according to principles of this invention In this embodiment an LED
71 is mounted on a printed circuit board 72 This is surrounded by a passage 73 through a derlector plate 74 The passage is in the ~orm Or a pyramid with four ~lat reflective walls at an angle from the plane o~ the printed circuit board $n the order o~ 45 Over the deflector plate is an aperture plato 7S which has a generally square aperture 76 ali7ned with the base of the pyramidal passage 73 The walls of the aperture are absorptive Light from the LED 71 reflect~ Orr the flat facets or walls of th- passage and toward the open end of the cavity The ab30rptiv- walls of the aperture derlne the shape of the image pro~ect-d from the cavity Alter-n~tively, there could be reflQctive walls from the base o~ the pyramidal passage part way to the open end of the cavity, as indicated by a phantom line ~7, with the balance Or the distance to the open end o~ the cavity being absorptive walls ~or defining the image shape A rather similar embodiment, which would appear in longitudinal cros~ section similar to Fig 14, has a conical reflectiv- passag- through the derlector plate for rerlecting light from th- LED toward th- open end of the c vlty A conical refl-ctive wall may fill the corner~ of ~ gen-rally rectangular aperture with more uniform int-n-ity of illumination than a paQsage with four ~lat r-~lective walls Alternat$vely, four rlat fac-t~ may be provided in the corners Or an otherwise pyramidal passage for enhancing reflection Or light toward the corners Or a rectangular absorptive aperture The corners of such an aparture can, Or course, be . . ~ 7,. .'-~, ' ` ~1.
1 32~ ~7 1 1 rounded or clipped as mentioned above. In each of such embodiments the reflective walls at the closed end of the cavity are straight in a longitudinal cross section instead of concave. The straight reflective walls are at an angle to the longitudinal axis of the cavity for reflecting light toward the open end of the cavity.
Although limited embodiments of illumination or Qrase bar have been described and illustrated herein, many modifications and variatlons will be apparent to one skilled in the art. Thu~, although specific materials, LEDs and the like have been mentioned, it will be apparent that these are merely exemplary. The particular shapes of the cavities may be the product of balancing variations in length, w~dth, and other parameters of the cavitles and LEDs to achieve a desired illumination efficiency and illumination distribution.
Conical and complex curv-d walls ~that is, curving in more than two dimensions) have been specifically mentioned, however, it will be apparent that other concave surfaces may be employed. A plurality Or facets would be an example. It is, therefore, to be understood that, within the scope of thQ appended claims, the invention may b~ practiced otherwise than as speci~ically described.
- .... .
1 photosensitive medium, the pixel area, the speed of the medium moving past the erase bar, the distance between the cavity and the medium, and the like.
The die for injection molding the deflector plate is highly polished so that the conical surfaces 29 and 31 and the cylindrical surface 28 are also polished.
The smooth, white plastic surface provides excellent reflection of the light emitted laterally from the light emitting diode toward the image plane beyond the open end of the cavity. Reflectivity may be enhanced, if desired, by met~llizing such surfaces. However, good efficiency of utilization o~ llght i~ obtained without need for metallizing. Efficiency can easily be twice the efficiency of an illumination system using a lens.
The concave reflector formed by the two conical surfaces in combination with the metallized pad on the printed circuit board proves quite effective in directing light from the LED approximately uniformly across the pixel illuminated by the cavity. Other concave reflective wall~ might be used, but it has not proved important to ~ake parabolic or elliptical reflectors ~or collimating light from the cavity. That may not even ~e feasible sinc- the LED is a rather large area light source, rather than a point source.
In this context, "concave" is used in the sense of having concavity in a longitudinal cross section through the cavity, such as seen in Figs. 3 and 4. A single conical surface in the closed end of the cavity could be considered concave ln a transverse cross section.
Further, thia arrange~ent o~ reflective surfaces tends to throw light throughout the area of the open end of the cavity and is guite insen-itive to defects in the LED or moderate misalignment or mispositioning o~ the LED. Ray traces show one or two bounces of the light off the reflective walls. There is some light going 1 directly from the LED toward the open end of the cavity with no bounces and a very minor part with three bounces. Most of the scrambling of the light comes from a single bounce of the light off the concave walls of s the cavity. Since the angles of the walls vary by reason of the concavity, there is a tendency to promote substantial uniformity of light intensity across the pixel illuminated by the cavity.
A shallow counterborQ 32 is providsd on the back face of the deflector plate to provide clearance for the wire bond connection between the rectangular pad 24 on the PC board and the top of the LED. Although the counterbore interrupts a portion of the circumference of the shallower cone 29 near the bottom of the cavity, there is ample scrambling Or the light by reflections off the concave walls that the illumination is approximately uniform across ths pixel and the shadowed area i~ not significant.
Further, the shadow of the contact wire and the pad to which it i8 bonded do not appear to affect the uni~ormity of illum$nation. This may be contra~ted with ~ lens system where such artifacts could slgnificantly degrade the uniformity of illumination acros~ the pixel.
Further, since a ma~or portion of the light from the LED
is directed toward the open end of the cavity by the concavo re~lective walls in the closed end of the cavity, high efficiency is o.btained. It appears that the efficisncy of illumination for a given power to the LED~ for a system as provided in practice of this inventlon is at least twice as high as the efficiency of a system employing lenses for illuminating the pixsls.
The black walls of the substantialiy rectangular aperture through the aperture plate tend to absorb a ma~or part of the radiation striking the walls at high angles of incidence. Light striking at low angles of .
-13- ~ 3 2 0 ~ ~ i 1 inc~dence 1~ retained ln the cavity and helps provide uniformity Or illumination. By absorbing light that is not directed out of the cavity at a low angle from its axis, the absorbent walls minimize any halo of light around the illuminated pixel.
By making the aperture at the open end of the cavity rectangular, it serves as an occultation mask for defining a generally rectangular image shape. By clipping or rounding the corners of the rectangle, the drop-off of light intensity at the edge of the pixel along the length of the stripe can be controlled so that the average light intenslty where pixel edge~ overlap can be maintained with approxlmate uni~ormity. The aspect ratio of the rectangular opening of tho cavity may be varied as desired to obtain a desired image shape. The pro~ected image may be square, or rather elongated either transverse to or along the photosensitive medium. The rounding or clipping of the corner~ for shaping the pro~-cted image can be varied through a considerable range.
If desired, the ab~orption ~y the walls of the aperture may bo enhanced by roughoning. This could also dif~us- re~lected light and onhance uniformity of -illumination. No special ef~ort w 9 made to roughen the walls and, although they app-ar somewhat shiny, they have proved effoctive as ab~orbers. Rather than being a rectangular cylinder, the ab~orbing wall~ couid also be in tho form of a prism converging slightly toward the open end of the cavity.
Reflective walls may also be used for occulting part o~ the light from the cavlty and shaping the pro~octod imag-. White re~lective walls ara not as effective as black ab~orptive walls ln defining a sharp edge on the imago. Metallizing the walls to maXo them highly reflective may be used for enhancing image ... , ~ ~ . .
. , ~
-14- 1 3C~
1 sharpnQss. When re~leCt~VQ walls are used it may also be de~lrable to taper the walls so they converge slightly toward an aperture at the open end o~ the cavity having a shape similar to the shape o~ the image it is desired to project.
Because of the high efficiency obtained with the reflective concave cavity, an additional technique may be employed, i~ desired, ~or assuring uniformity of illumination. A pattern may be provided on the transparent window at the open end o~ the cavity for selectively absorbing light, as well a~ shaping the image. FIG. 8 illustrates such an mbodiment.
In such an embodiment, a gen-rally r-ctangular area 36 of the window over a cavity is surrounded by an opaque area 37. The perimeter or the transparent area may serve as a shadow mask helping to de~ine the edges o~ the pixel. Further, i~ need be, an area 38, indicated by a stippling in the drawing, where llght intensity would otherwise be too high, can be made partially absorbing for reducing light intensity.
The partially absorbing ar~a may be produced by any o~ a variety Or conventional techniques. For example, a pattern of ~ine dots of varying BiZ- or density may be -used in the manner Or a half-tone ~creen to occult more or less area as desired. A photographic emulsion may also be selectively darkened to be partially absorbent.
Alternatively, opaqua bands or other patterns o~ partly or totally absorbing areas may be used to cast somewhat darkened shadows on the image plane and make the resultant illumination more uniform. For example, an opa~ue band may be placed across the center o~ the apertur- ir th- central illumination i~ too bright. The scrambling Or the light within the pixel illuminates the area behind the band with an intensity near the average intensity throughout the pixel.
5 ~ 3 ~
1 Alternatlvely, a partially abgorbing area may be madQ on an ad hoc basis by incorporating a photochromic material in the window. In such an embodiment the window selectively darkens in response to di~ferent intensities of illumination. In areas with higher light intensity, the window gets darker or more absorbent than in areas with les~ illumination. As a consequence, the l$ght transmitted through the window is made more uniform.
FIGS. 9 to 11 illustrats part of another embodiment o~ illuminating cavity constructed according to principles oS this invention. In these drawlngs, the concave reflectivQ walls at the closed end of such a cavity are illustrated. It will be understand that additional reSlective and/or absorbing walls are employed for completing the cavity ~rom which light is pro~ected.
In this embodiment, it is as iS the concave reflective walls o~ th~ deflector plate are combined with th- flat reSlective surSace on the Sront Sace of the printed circuit board. Thus, the printed circuit board 41 has a row Or concave pits 42 in the ~ront face.
The bottom oS each pit ha~ a Slat central area 43 which has around it four egually spac-d arcuate lobes 44. The lobes are not ln the same plane a~ the flat bottom of the pit. They are tilted away from the flat bottom at an angle C, which may be in a range oS from 25 to 30 degrees.
The concave walls 45 of each pit are, in cross-section, two circular arcs, the centars oS which are onopposite sides o~ th- center line Or the pit. These continuous complex curved walls tend to reflect light ~rom a light emitting diod- 46 in the bottom oS the pit (FIG. 11) toward the open end oS a cavity for illuminating a pixel. Additional rerlecti~e and/or '., ' ' . ' -16- 1 ~ 20`~71 1 absorptive walls (not shown) provide additional reflections for obtaining approximate uniformity of illumination and absorption for defining a desired shape and size of pixel.
The four lobes at the bottom of the pit cut into the curved walls to a small extent, thereby diminishing the concave area from which light is re~lected. Light is reflected, however, from the portion of the curved walls between the lobes. The result is a pattern of light di~tribution, which tends to fill in the corners of the illuminated pixel, ther~by a~suring uniform light distribution. Th~ angled floors of the lobes also reflect light toward the open end o~ the cavity to combine with light reflected from the curved concave walls and provide uniform illumination.
The substrate having the reflective pits also serves a~ a printed circuit board for making connections to tho light-emitting diode~. The walls and bottoms of the pit~ are motallizQd. The motal layer 47 from each pit extends onto the front Jur~ace of the board and laterally in on- dlrection to a plated-through hole 48 for making connection to printed circuits (not shown) on the back o~ the bo~rd. A tab 49 on each metallized area provlde-~ a means for making a wiro bonded connection to the top of the ~D in the next pit along the row. These connection~ may be used when connecting ~he LEDs in series ~or illuminating an entire photosens$tive medium.
A metallized stripe 51 extends along the opposite edgo o~ the board. When it i~ desired to make separate electrical connoctions ror each LED ~or illuminating only selectod area~ of the photo~ensitive medium, an electrical connection can be wire bonded between a tab 52 on this stripe and an ad~acent LED. This provides mean~ for making electrical contact with each LED along the illumination bar ~or individually energizing each s 1 LED separately from the other LEDs. It will be noticed that with this pattern o~ printed circuits on the board, this is a "generic" board which can be used for either parallel or series connection of LEDs as may be desired.
The metallized areas may be made by a conventional technique such as electroless deposition of copper, masking and etching, and electroplating with soft gold, for example. All that is needed is that the plating throws adequately into the pits to assure good electrical contact. Such gold metallized concave walls in the pits are highly re~lective and provide efficient sources of illumination.
FIGS. 12 and 13 illustrate a fragment o~ another embodiment of illumination bar or erase bar for use in a xerographic printer or the like. This embodiment is particularly useful in a location where Qpace is at a premium. A very narrow ~tripe can be made, where each pixel extends a substantially greater distanco along the length o~ the stripe than the width of the pixel across the stripe. In thls embodiment, a row o~ ~ide-emitting LEDs 56 are mounted on onQ face of a printed circuit board 57. Conventional electrical conductors are printed on the board for making lectrical contacts with the ~EDs. These are omitted from the drawing for clarity of illustration.
~ reflector plate 58 is mounted on the front face of the PC board and this, in turn, is covered by a cover plate 59. Thls three-layer sandwich is held tqgether by fasteners 61. Ir desirod, cut-outs 62 can be made in the re~lector plate ~o that additional components can be mounted on the printed circuit board. The reflector plate may be made of reflective white plastic, or the re~lecting surfaces may be metallized to enhance re~lection.
-18- ~320~
1 The rrOnt edge Or the re~lector plate is scalloped by a row o~ concave indentations Each LED is positioned in one o~ the indentations Between each ad~acent indentation, there is a converging wall 63 Each indentation is in ths ~orm of a pair of curved walls, which may, for example, be approximately parabolic or elliptical and have centers offset from the center of the indentation ~hus, where the two curved walls intQrsect in the center o~ the indentation, there is a small cusp 64 behind the LED
~ ight ~rom the sid--emitting LED is re~lected ~rom the concave reflective wall~ o~ the reflector plate and directed toward the open end Or the cavity formed by the indentations and the parallel walls o~ the printed circuit board and the cover plate, as indicated by a few arrows ln Fig 12 Since the walls are roughly parabolic, they approximat-ly colllmat- the light pro~ected from the cavity It ia desirable, however, that th-ro b- some multlple bounc-s o~ light o~ o~ the walls ~or scrambling th- light and providing a reason~bly unifor~ inten~ity o~ illumination along the length o~ th- assembly The rac-s o~ the printed circuit board and cover plate bounding two sides of the cavity are largely non-reflective, ther-by assuring a narrow stripe of illumination A transparent window 66 along the fron' edge o~ th- a~s-mbly protects the LEDs and ren ectlve sur~aces within th- cavities I~ desirQd, the window may be mad- ~lightly convex ~or broadening the image pro~ected ~rom th- cavity I~ de~Ired, a portion o~ the walls 63 between ad~acent cavltles can be made non-re~lective They may also be extend-d beyond the location illustrated in FIGS 12 and 13 ~or ~urther minimizing cross-talk between ad~acent pixels and enhancing uni~ormity o~ the 132(1 ~
1 illumlnation Toward that same end, partially absorbing areas may be provided on the window 66 Fig 14 illustrates in longitudinal cross section another embodiment of cavity constructed according to principles of this invention In this embodiment an LED
71 is mounted on a printed circuit board 72 This is surrounded by a passage 73 through a derlector plate 74 The passage is in the ~orm Or a pyramid with four ~lat reflective walls at an angle from the plane o~ the printed circuit board $n the order o~ 45 Over the deflector plate is an aperture plato 7S which has a generally square aperture 76 ali7ned with the base of the pyramidal passage 73 The walls of the aperture are absorptive Light from the LED 71 reflect~ Orr the flat facets or walls of th- passage and toward the open end of the cavity The ab30rptiv- walls of the aperture derlne the shape of the image pro~ect-d from the cavity Alter-n~tively, there could be reflQctive walls from the base o~ the pyramidal passage part way to the open end of the cavity, as indicated by a phantom line ~7, with the balance Or the distance to the open end o~ the cavity being absorptive walls ~or defining the image shape A rather similar embodiment, which would appear in longitudinal cros~ section similar to Fig 14, has a conical reflectiv- passag- through the derlector plate for rerlecting light from th- LED toward th- open end of the c vlty A conical refl-ctive wall may fill the corner~ of ~ gen-rally rectangular aperture with more uniform int-n-ity of illumination than a paQsage with four ~lat r-~lective walls Alternat$vely, four rlat fac-t~ may be provided in the corners Or an otherwise pyramidal passage for enhancing reflection Or light toward the corners Or a rectangular absorptive aperture The corners of such an aparture can, Or course, be . . ~ 7,. .'-~, ' ` ~1.
1 32~ ~7 1 1 rounded or clipped as mentioned above. In each of such embodiments the reflective walls at the closed end of the cavity are straight in a longitudinal cross section instead of concave. The straight reflective walls are at an angle to the longitudinal axis of the cavity for reflecting light toward the open end of the cavity.
Although limited embodiments of illumination or Qrase bar have been described and illustrated herein, many modifications and variatlons will be apparent to one skilled in the art. Thu~, although specific materials, LEDs and the like have been mentioned, it will be apparent that these are merely exemplary. The particular shapes of the cavities may be the product of balancing variations in length, w~dth, and other parameters of the cavitles and LEDs to achieve a desired illumination efficiency and illumination distribution.
Conical and complex curv-d walls ~that is, curving in more than two dimensions) have been specifically mentioned, however, it will be apparent that other concave surfaces may be employed. A plurality Or facets would be an example. It is, therefore, to be understood that, within the scope of thQ appended claims, the invention may b~ practiced otherwise than as speci~ically described.
- .... .
Claims (47)
1. An illumination bar for a xerographic printer or the like comprising:
a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a concave reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and occultation means between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a concave reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and occultation means between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
2. An illumination bar as recited in claim 1 wherein the means for defining an image shape comprises at least partly absorbing walls between the reflective walls and the open end of the cavity.
3. An illumination bar as recited in claim 1 wherein the means for defining an image shape comprises reflective walls having an aperture shape at the open end of the cavity similar to the shape of the projected image.
4. An illumination bar as recited in claim 1 wherein the concave reflective wall comprises a first relatively shallower cone nearer the closed end of the cavity and a second relatively steeper cone further from the closed end of the cavity.
5. An illumination bar as recited in claim 1 wherein the concave reflective wall comprises a continuous complex curve.
6. An illumination bar as recited in claim 1 further comprising a window over the open end of the cavity which is at least partially absorbing in a pattern for obtaining a desired illumination intensity uniformity from each cavity.
7. An illumination bar as recited in claim 1 further comprising a window over the open end of the cavity which includes a photochromic material for selectively darkening in response to differences in illumination.
8. An illumination bar as recited in claim 1 wherein at least the concave end of the cavity is metallized and the light emitting diode is a side emitting light emitting diode mounted on the metallized area.
9. An illumination bar as recited in claim 1 wherein the cavity has opposite parallel side walls and the light emitting diode is mounted on one parallel side wall of the cavity between the concave closed end and the open end.
10. An illumination array comprising:
a plurality of cavities in a row, each cavity being closed at one end and open at the other end for projecting light toward an image plane, and comprising:
a reflective closed end including a portion angled for reflecting light from the closed end toward the open end of the cavity, a cylindrical absorptive wall at the open end, and a cylindrical reflective wall between the absorptive wall and the concave closed end; and a light emitting diode mounted at the bottom of the closed end of each cavity.
a plurality of cavities in a row, each cavity being closed at one end and open at the other end for projecting light toward an image plane, and comprising:
a reflective closed end including a portion angled for reflecting light from the closed end toward the open end of the cavity, a cylindrical absorptive wall at the open end, and a cylindrical reflective wall between the absorptive wall and the concave closed end; and a light emitting diode mounted at the bottom of the closed end of each cavity.
11. An array as recited in claim 10 wherein the closed end comprises a flat bottom on the cavity, a first shallower cone adjacent the flat bottom and a second steeper cone between the first cone and the reflective cylindrical wall.
12. An array as recited in claim 10 wherein the cylindrical reflective wall is a right circular cylinder, and the cylindrical absorptive wall is a generally rectangular cylinder.
13. An array as recited in claim 10 further comprising a partially absorptive window at the open end of the cavity for absorbing a portion of the light from the cavity in selected areas of the window for obtaining a desired uniformity of illumination intensity.
14. An array as recited in claim 13 wherein each window includes a photochromic material for selectively darkening in response to differences in illumination.
15. An illumination bar as recited in claim 10 wherein the angled reflective wall is straight in a longitudinal cross section through the cavity.
16. An illumination far as recited in claim 10 wherein the angled reflective wall is concave in a longitudinal cross section through the cavity.
17. An illumination bar as recited in claim 10 further comprising means for making electrical contact with each LED along the illumination bar for individually energizing each LED separately from the other LEDs.
18. An array as recited in claim 10 wherein at least the closed end Or the cavity is metallized and the light emitting diode is a side emitting light emitting diode mounted on the metallized area.
19. An illumination bar for a xerographic printer or the like comprising:
a printed circuit board;
a plurality of light emitting diodes mounted in a row on the printed circuit board;
a deflector plate mounted on the printed circuit board;
a row of passages through the deflector plate, each passage being around a light emitting diode on the printed circuit board and having reflective walls concave in a direction away from the printed circuit board for reflecting light from the light emitting diode away from the printed circuit board;
a aperture plate mounted on the deflector plate;
a row of apertures through the aperture plate, each aperture being aligned with a passage through the deflector plate for passing light from the light emitting diode toward an image plane beyond the aperture plate.
a printed circuit board;
a plurality of light emitting diodes mounted in a row on the printed circuit board;
a deflector plate mounted on the printed circuit board;
a row of passages through the deflector plate, each passage being around a light emitting diode on the printed circuit board and having reflective walls concave in a direction away from the printed circuit board for reflecting light from the light emitting diode away from the printed circuit board;
a aperture plate mounted on the deflector plate;
a row of apertures through the aperture plate, each aperture being aligned with a passage through the deflector plate for passing light from the light emitting diode toward an image plane beyond the aperture plate.
20. An illumination bar as recited in claim 19 wherein each light emitting diode is a side emitting light emitting diode.
21. An illumination bar as recited in claim 19 wherein the walls Or the apertures are absorptive.
22. An illumination bar as recited in claim 19 wherein each passage through the deflector plate includes a cylindrical wall between the concave walls and the aperture plate.
23. An illumination bar as recited in claim 19 wherein the reflective walls in the deflector plate comprise a first relatively shallower cone nearer the printed circuit board and a second relatively steeper cone further from the printed circuit board.
24. An illumination bar as recited in claim 19 wherein the passage through the deflector plate comprises a circular opening, and the aperture through the aperture plate comprises a rectangle.
25. An illumination bar as recited in claim 19 further comprising a window over the aperture.
26. An illumination bar as recited in claim 25 wherein the window is partially absorbing in a pattern for obtaining a desired illumination intensity uniformity from each cavity.
27. An illumination bar as recited in claim 25 wherein the window includes a photochromic material for selectively darkening in response to differences in illumination.
28. An illumination bar for a xerographic printer or the like comprising means for projecting a stripe of light formed of a plurality of adjacent generally rectangular pixels, each means for projecting comprising:
a cavity with a generally rectangular aperture at one and of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
a cavity with a generally rectangular aperture at one and of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
29. An illumination bar as recited in claim 28 wherein the cavity has opposite parallel side walls and the light emitting diode is mounted on one parallel side wall of the cavity between the concave closed end and the open end.
30. An illumination bar as recited in claim 28 wherein the concave reflective end comprises a first relatively shallower cone nearer the closed end of the cavity and a second relatively steeper cone further from the closed end of the cavity.
31. An illumination bar as recited in claim 28 wherein the concave reflective end comprises a continuous complex curve.
32. An illumination bar as recited in claim 28 further comprising means for making electrical contact with each LED along the illumination bar for individually energizing each LED separately from the other LEDs.
33. An illumination array comprising:
a printed circuit board;
a row of light emitting diodes mounted on the printed circuit board;
a reflector plats on the printed circuit board including a scalloped edge with a row of indentations, each indentation encompassing a light emitting diode, each indentation having a reflective concave wall portion for reflecting light from the light emitting diode away from the reflector plate; and a cover plate over the reflector plate.
a printed circuit board;
a row of light emitting diodes mounted on the printed circuit board;
a reflector plats on the printed circuit board including a scalloped edge with a row of indentations, each indentation encompassing a light emitting diode, each indentation having a reflective concave wall portion for reflecting light from the light emitting diode away from the reflector plate; and a cover plate over the reflector plate.
34. An illumination array as recited in claim 33 wherein such a concave wall portion is in the form of two continuous curves intersecting in a cusp behind the light emitting diode.
35. An illumination array comprising:
a printed circuit board;
a row of pits in the printed circuit board, each pit having walls angled for reflecting light from the bottom of the pit away from the printed circuit board;
a metal layer on the printed circuit board including a portion adjacent to such a pit and a portion in such a pit; and a side emitting light emitting diode on the metal layer in the bottom of such a pit.
a printed circuit board;
a row of pits in the printed circuit board, each pit having walls angled for reflecting light from the bottom of the pit away from the printed circuit board;
a metal layer on the printed circuit board including a portion adjacent to such a pit and a portion in such a pit; and a side emitting light emitting diode on the metal layer in the bottom of such a pit.
36. An illumination array comprising means for illuminating a plurality of adjacent pixels, each means for illuminating comprising a light source having a transparent window, and characterized by each window including a photochromic material for selectively darkening in response to differences in illumination.
37. A xerographic printer or the like comprising:
a movable photosensitive medium; and a plurality of means for projecting a plurality of separately addressable images directly on the photo-sensitive medium without a lens, each means for projecting comprising:
a cavity with a generally rectangular aperture at one end of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
a movable photosensitive medium; and a plurality of means for projecting a plurality of separately addressable images directly on the photo-sensitive medium without a lens, each means for projecting comprising:
a cavity with a generally rectangular aperture at one end of the cavity;
a reflective concave closed end at the other end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the concave portion of the cavity.
38. A xerographic printer or the like as recited in claim 37 wherein the aperture comprises at least partly absorbing walls between the reflective closed end and the open end of the cavity.
39. A xerographic printer or the like as recited in claim 37 wherein the aperture comprises reflective walls having an aperture shape at the open end of the cavity similar to the shape of the projected image.
40. An illumination bar for a xerographic printer or the like comprising:
a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and at least partly absorbing walls between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
a plurality of light sources in a row, each light source illuminating a separate area along the length of the illumination bar, adjacent illuminated areas being located so that the illumination along the length of the illumination bar is approximately uniform; each of the light sources comprising:
a cavity open at an end facing in the direction of illumination by the illumination bar and closed at the opposite end;
a light emitting diode at the closed end of the cavity for emitting radiation in directions transverse to the direction of illumination by the illumination bar;
a reflective wall at the closed end of the cavity for reflecting a major portion of the light emitted by the light emitting diode in a direction toward the open end of the cavity; and at least partly absorbing walls between the reflective walls and the open end of the cavity for defining the shape of an image projected from the open end of the cavity.
41. An illumination bar as recited in claim 40 wherein the reflective wall is straight in a longitudinal cross section through the cavity.
42. An illumination bar as recited in claim 40 wherein the reflective wall is concave in a longitudinal cross section through the cavity.
43. An illumination bar as recited in claim 40 further comprising means for making electrical contact with each LED along the illumination bar for individually energizing each LED separately from the other LEDs.
44. An illumination bar for a xerographic printer or the like comprising means for projecting a stripe of light formed of a plurality of adjacent generally rectangular pixels, each means for projecting comprising:
a cavity with a generally rectangular absorptive walls forming an aperture at one end of the cavity;
a reflective closed end at the other end of the cavity having a portion angled for reflecting a major part of the light striking the reflective angled portion toward the open end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the angled reflective portion of the cavity.
a cavity with a generally rectangular absorptive walls forming an aperture at one end of the cavity;
a reflective closed end at the other end of the cavity having a portion angled for reflecting a major part of the light striking the reflective angled portion toward the open end of the cavity; and a light emitting diode mounted in the closed end for emitting light toward at least the angled reflective portion of the cavity.
45. An illumination bar as recited in claim 44 wherein the angled reflective wall is straight in a longitudinal cross section through the cavity.
46. An illumination bar as recited in claim 44 wherein the angled reflective wall is concave in a longitudinal cross section through the cavity.
47. An illumination bar as recited in claim 44 further comprising means for making electrical contact with each LED along the illumination bar for individually energizing each LED separately from the other LEDs.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/253,714 US4963933A (en) | 1988-10-05 | 1988-10-05 | LED illuminator bar for copier |
| US253,714 | 1994-06-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1320474C true CA1320474C (en) | 1993-07-20 |
Family
ID=22961416
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000612341A Expired - Fee Related CA1320474C (en) | 1988-10-05 | 1989-09-21 | Led illuminator bar |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4963933A (en) |
| EP (1) | EP0363132A3 (en) |
| JP (1) | JPH02156263A (en) |
| CA (1) | CA1320474C (en) |
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| US9285389B2 (en) * | 2012-04-02 | 2016-03-15 | Semiconductor Components Industries, Llc | Optical accelerometers |
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| US3970382A (en) * | 1973-06-29 | 1976-07-20 | Xerox Corporation | Spatially selective optical system |
| US4255042A (en) * | 1979-03-26 | 1981-03-10 | International Business Machines Corporation | Light pipe for accurate erasure of photoconductor charge |
| US4344691A (en) * | 1980-06-23 | 1982-08-17 | International Business Machines Corporation | Zonal concentrator for accurate erasure of photoconductor charge |
| JPS5714058A (en) * | 1980-06-28 | 1982-01-25 | Ricoh Co Ltd | Printer |
| JPS5840541A (en) * | 1981-09-03 | 1983-03-09 | Canon Inc | Lighting equipment for original |
| JPS58217962A (en) * | 1982-06-14 | 1983-12-19 | Canon Inc | Electrophotographic copying machine |
| JPS5989371U (en) * | 1982-12-03 | 1984-06-16 | シャープ株式会社 | Light irradiation device for copying machines |
| US4767172A (en) * | 1983-01-28 | 1988-08-30 | Xerox Corporation | Collector for an LED array |
| US4640601A (en) * | 1983-12-20 | 1987-02-03 | Sanyo Electric Co., Ltd. | Patent image reproducing electrophotographic machine |
| JPS60140287A (en) * | 1983-12-28 | 1985-07-25 | Mita Ind Co Ltd | Destaticizing lamp device |
| JPS6199173A (en) * | 1984-10-22 | 1986-05-17 | Canon Inc | Illuminating device and image forming device using said device |
| US4720729A (en) * | 1984-12-17 | 1988-01-19 | Kabushiki Kaisha Toshiba | Image forming apparatus with editing function |
| US4611906A (en) * | 1985-01-22 | 1986-09-16 | Sanyo Electric Co., Ltd. | Electrophotographic copying apparatus |
| US4734734A (en) * | 1985-02-01 | 1988-03-29 | Canon Kabushiki Kaisha | Image forming apparatus and erasure illumination device therefor |
| JPH0723932B2 (en) * | 1985-06-12 | 1995-03-15 | キヤノン株式会社 | Lighting equipment |
| JPS6223072A (en) * | 1985-07-24 | 1987-01-31 | Ricoh Co Ltd | Zoom erasing device |
| JPS62103670A (en) * | 1985-10-31 | 1987-05-14 | Toshiba Corp | Image forming device |
| JPS62103668A (en) * | 1985-10-31 | 1987-05-14 | Toshiba Corp | Image forming device |
| JPS62103669A (en) * | 1985-10-31 | 1987-05-14 | Toshiba Corp | Image forming device |
| JP2523481B2 (en) * | 1985-11-20 | 1996-08-07 | 株式会社リコー | Image editing equipment |
| FR2594567B1 (en) * | 1986-02-20 | 1993-10-29 | Sanyo Electric Co Ltd | ELECTROPHOTOGRAPHIC COPYING MACHINE HAVING AN EDITING FUNCTION |
| US4759603A (en) * | 1986-04-08 | 1988-07-26 | Hewlett-Packard Company | Array of limited internally reflective light guides |
| JPH0750799B2 (en) * | 1986-04-17 | 1995-05-31 | 株式会社東芝 | Light emitting device |
| US4843427A (en) * | 1987-01-05 | 1989-06-27 | Sharp Kabushiki Kaisha | Selective charge removal system for copier |
| JPS63169671A (en) * | 1987-01-08 | 1988-07-13 | Minolta Camera Co Ltd | Editing input device |
| JPS63188165A (en) * | 1987-01-31 | 1988-08-03 | Toshiba Corp | Image erasing device |
| US4928142A (en) * | 1988-10-03 | 1990-05-22 | Eastman Kodak Company | Combination erase device |
-
1988
- 1988-10-05 US US07/253,714 patent/US4963933A/en not_active Expired - Fee Related
-
1989
- 1989-09-21 CA CA000612341A patent/CA1320474C/en not_active Expired - Fee Related
- 1989-10-02 EP EP19890310071 patent/EP0363132A3/en not_active Withdrawn
- 1989-10-02 JP JP1257622A patent/JPH02156263A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02156263A (en) | 1990-06-15 |
| US4963933A (en) | 1990-10-16 |
| EP0363132A3 (en) | 1991-08-28 |
| EP0363132A2 (en) | 1990-04-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |