CA1107105A - Optical scanner and system for laser beam exposure of photo surfaces - Google Patents
Optical scanner and system for laser beam exposure of photo surfacesInfo
- Publication number
- CA1107105A CA1107105A CA304,782A CA304782A CA1107105A CA 1107105 A CA1107105 A CA 1107105A CA 304782 A CA304782 A CA 304782A CA 1107105 A CA1107105 A CA 1107105A
- Authority
- CA
- Canada
- Prior art keywords
- mirror
- axis
- plane
- wheel
- scanning
- 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
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
- G02B26/10—Scanning systems
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Mechanical Optical Scanning Systems (AREA)
- Facsimile Scanning Arrangements (AREA)
- Preparing Plates And Mask In Photomechanical Process (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Optical scanning apparatus including a rotating pyramidal mirror scanning wheel with reflector segments for deflecting a laser beam into and away from a doublet mirror roof reflector associated with said scanning wheel. The scanning wheel introduces components of vertical and horizontal angular deviation into the beam, the vertical deviation component being cancelled by inversion through the roof reflector while the horizontal angular component is doubled upon the second reflection from the scanning wheel so that the output beam is vertically wobble-free and stable while the beam is scanned through the sum of the horizontal angular components intro-duced by the wheel. The scanner is employed to create a flying spot scan from a laser beam in photosensitive plate exposure apparatus, one form of which employs superimposed laser read and expose (write) beams of different frequencies which are simultaneously scanned without chromatic aberration, and subsequently separated to read copy and to expose a photosensitive plate surface as in the production of printing plates.
Optical scanning apparatus including a rotating pyramidal mirror scanning wheel with reflector segments for deflecting a laser beam into and away from a doublet mirror roof reflector associated with said scanning wheel. The scanning wheel introduces components of vertical and horizontal angular deviation into the beam, the vertical deviation component being cancelled by inversion through the roof reflector while the horizontal angular component is doubled upon the second reflection from the scanning wheel so that the output beam is vertically wobble-free and stable while the beam is scanned through the sum of the horizontal angular components intro-duced by the wheel. The scanner is employed to create a flying spot scan from a laser beam in photosensitive plate exposure apparatus, one form of which employs superimposed laser read and expose (write) beams of different frequencies which are simultaneously scanned without chromatic aberration, and subsequently separated to read copy and to expose a photosensitive plate surface as in the production of printing plates.
Description
~7~
Background of the Invention This invention relates generally to optical scanners and more particularly to an optical scanner for creating a flying spot linear trace of a beam of laser light. The inven-tion finds particular use in t~ i~1d of laser beam scanners as are used for r~ading info.rmation from a copy boand and directly transferr mg the rea~ information for the exposure of photosensitive surfaces as in the pr.oduction of printing plates.
In Canc~dian application Serial No. 243,825 fi.led Janua~y 20, 1976, Richard E. Amtcwer, there is show.n an apparatus for producin~ an exposed photo plate rom a copy board paste-up~ A l.aser scanning system having a read laser beam is focused to a spot scanned across the copy board in a predeterm med pattern, such as a raster-like scan, the reflection from the copy board being sensed, read and used to control the intensity of a second laser beam via a mcdulator~ The second laser beclm impinges upon and scans a photosensi~ive sur~ace~ The read lase bec~m and the write laser beam are cc~bined and passed through deflection optics, and the tw~ beams are subsequ~ntly separated to impinge ~on and be fo~used at the copy board and photo-sensit:ive surface, respectively. Tn -this way there is a resultc~nt exposure of the photosensitive surface in accord-ance with the copy. As shown in Serial NoO 243,825, the scannin~ optics employed u-tilizes a moving mirror galvano~
meter, with both the rec~d and write laser bec~ms being aligned cl~l superimposed upon each other through suitable beam comb ~ optics ~or being:passed th~ough the galvanometer simul neously ~nd subssquently separated by suitable beam ~30 : deflecticn optics~to the respective planes. Ano~her optical system shown:ther2in employs a polygonal scanning wheel . -`
hav~ng a plurality Oe surlsces psrsllel to ths aris of ~ ~ ~
rotation of the wheel, ~ith the surfaces serving to scan the read and write beams through an angle, thereby creating a flying spot scan.
In United States Patent 4,081,842 March 28, 197B, Steven K.
Harbaugh et al there is disclosed a variation o~ laser read~write apparatus in which a facsimile system is developed. As disclosed therein, a duplica-tion of read and write equipment at separate locations can ke coordinated to form a facsimile transmlssion system. At the read st~tion an optical scc~nner scans the input copy ~ith the scanning spot and the reflected light produces a video read da~a signal, a portion of which is directed through a spatial mask to pr~vide a transmitter video reference which gates a video read data before transmission. In the receiver, a second optical scanner ~f similar construction is controlled by a video writ~ data signal. The -~ video write data si~nal gates a scanning spot of exposure laser keam light on and off to expose the output photosensitive copy surface at the receiver.
Additianally, the scanning light is debected through a further spatial mask to provide a receiver video reference signal utilized to form a video write signal. The spatial masks in the transmitter and receiver have a kncwn relationship, e.g., so that the scannLng of the output copy in the receiver can be spatially synchronized with the scannm g of the inpu~ copy in the 2Q transmitter. As therein disclosed, each of the scanning op~ics includes a~galvanom~ter-operated mirror for scanning the incident laser keam kac~ and forth,through a horizontal angl~.
l~e foregoing instruments as disclosed in the cross-reEerenced ~pplication employ a field-flatteniny lens for causing the beam provided from the sca~ming device to be focused at the pl~le oE the copy boarl and photosensitive surface res~ tively, and are known thereEore as flat bed sc~nners. The scc~ning optics, hcwever, are subject to a number oE errors which de~rade the perform3n~ of the system. In a polygonal drum scc~nLng ~ design, ~ery close~tolerano~s are requii0d during the manufacturing processes ~ so as to o~trol ~acet-to tacet tilt~ A~y error Ln facet ~Eacet orienta-`~ tion, together ., .
.
:: - : .
~ 7~
with bearing run-out errors and the lik~, contribute to produce an angular or positional error component normal to the scan line. This error has come to be known as "wobble" or vertical errox. In addition, the scan ef-ficiency of a polygonal drum ~canning system is limited to about 50 percent. Accordingly, the polygonal design is expensive to produce due to ~he tolerances required, and the facet-to-facet error h~s to be removed by ~ome suitable means, termed a "dewobbler".
In a resonant or oscillating galvanom2ter scan-ner, the mirror pivots in a sinusoidal manner, and only the center portion of the scan is linear enough to be utilized. This results in a scan efficiency of approxi-mately 50~ with a 25% deviation in exposure or scan vel-ocity. However, it is necessary to scan back and orth in opposing directions in order to maintain this effici-ency level. Such scanning requires lag compensation which is accomplished by deviating the read beam from its normal course as a function of system time delays and scan velocity. Such compensation adds to the cost and complexity of the system and in many instances is only partially e~fective. In addition, if multiple ma-chines are to communicate in a facsimile system, a great deal of calibration of each machine is required to norm~
alize ~he amount of 12g produced in each machine. Lag errors and other errors in the facsimile process when scanning in both directions, result in left writing and right writing images that are no longer superimposed, re-sult.ing in severe image deyradatioll for even small errors.
Furthex, at the higher speeds particularly associated with facsimile systems, the scanner requirements exceed the capabilities of a galvanometer mirror system because of the high torque to which the mirror and its support struc-ture are subject~d.
Other existing systems utili~e cylindrically curved fields but are also limited in scan efficiency.
For example, in one ~uch system using a spinner-type scanner in a cylindrical configuration, one scan is ac-complished for each rotation of the scanning device.
: -4-7~
With the exposure times commonly associated with a standard printing format, extremely high rotational speeds are required, and synchronization of facsimile versions is difficult~ Furthermore, ~uch curved field systems xequire that the exposure surface be adaptable to a curved conformation which is often incompa~ible with printing plate production.
Ideally, a 6canning system should provide a high scan efficiency, a scanning operation in a single direction 50 as to eliminate the problem of lag, and a constant scanning velocity so as to reduce the cost ~f the associated electronics. In addition, the system should be ree of vertical error or wobble and should be entirely reflective so as to above ab~rra~ion errors caused by the read and write beam frequencies being at different portions of the spectrum. Additionally, such a scanning system should be compatible with flat field optics so that the resulting flying spot scan can read copy and expose plates lying on plane surfaces.
Objects and Summary of the Invention In general it is an object of the invention to provide a laser beam optical scanning apparatus which will overcom~ the above limitations and disadvantages and supply error-free scanning within the foregoing guide-lines.
It is a further object of the invention to pro-vide an optical scanning apparatus o the above character which utilizes a rotating element and provides a resultant scan which is free of vertical error or ~obble, which is compatible with ~lat fie~d scanning, and which simultan-eously has a substantially uniform scan velocity and high scan efficiency while operatiny in a single dixection of scan.
It is a further object of the invention to pro-vide a laser beam optical scanning apparatus of the above chaxacter which is inherently adaptable to extremely high scanning ~peeds.
~5--~7~
Ano~her object of the invention is to provide a~ optical scanner of the.abo~e character which is read-ily adapted to synchronous ~acsimile ~peration.
A urthex object of the invention is to provide a scanner of the above character which is designed for multiple-beam read/write operation utilizing beams of dif~
ferent frequencies without introducing chromatic ~berra-tion.
The.se and other objects are achieved in accord-ance with the invention by providing a pyramidal mirror having a plurality of reflective surfaces inclined at an acute angle relative to a plane perpendicular to the axis of the mirror. The mirror is rotated about its axis to move the reflective surfaces successively through the path of a beam to provide a varying deflection of the beam from each successive surf~ce of the ~irror as that surface moves through the path and presents a varying an-gle of incidence to the beam, and optical means such as a roof mirror doublet receives the deflected beam from each successive ~urface and returns an inverted image of the beam to the æame surface for further reflection by that surface along an output path. As ea~h segment ro-tates through the beam path, its varying angular orienta-tion introduces horizontal and vertical components of an-gular de~iation into the beam, with the horizontal angular component being doubled upon the second (output) reflec-tion from the rotating segment while the vertical compon-ent i~ cancelled by the inversion provided by the roof mirror.
In a system for scanning reading and writing suraces wi~h laser beams, the beams are combined and the combined beam .is deflected by the pyramidal mirror and the roof mirror doublet to produce the desired scanning action, following which the beams are separated and dir-ected to the~respective readlng and writing surfaces.
~:
~ ~ , :;; : ;:
.:: :
`
:
.- .: - . ~. . . . .
Q~j;
In accordance with ~he inv~ntion there is provided in a scanning apparatus for causing a laser beam ~o scan a line at an output plane in space:
first mirror means forming a first planar reflective surface having a surface vector lying in a plane common to said beam, second mirror means forming a second planar reflective surface having its surface vector lying in the common plane, said irst and second mirror means being disposed relative to each other to form a reflective doublet about a line perpendicular to said common plane, a pyramidal mirror having a plurality of reflective segments inclined ; at an acute angle relative to a plane perpendicular to the axis of the mirror, and means Eor rotating said mirror about its axis to move said segments suc-cessively through the path of the beam so that the beam is reflected from the segment in the path to the doublet and back to the same segment or further reflection by that segment along an output path with a varying component of angular deviation perpendicular to the common plane and substantially no com-ponent of angular deviation parallel to the common plane.
: In accordance with another aspect of the invention there is provided in scanning apparatus: a pyramidal mirror having a plurality of reflective surfaces inclined at an acute angle relative to a plane perpendicular to the axis of the mirror, means for rotating the mirror about its axis to move the : 20 re1ective surfaces successively through the path Gf a beam to provide a vary- `
~; ing deflection of the beam from each successive surface of the mirror as that surface moves through the path and presents a vary:ing angle of inc.idcnce to the beam, said deflection having components along first and second axes per-~ pendicular to the mirror axis and to each other, and optical means for re-ceiving the deflect;d beam from each successive surface and returning an image of the beam inverted about the first axis to the same surface for further re flection by that surface along an output path with a varying component of angular deviation a.long the first axis and substantially no component of angu-:. lar deviation ai~ong the second axis.
~ .
:
: :
~ - 6a -,f ~
; .
Brief Descri~tion of_the Drawin~
Figure 1 is a diagrammatic perspective view of one embodiment of laser beam optical sc~nniny apparatus constructed .in accordance with the inven~ion for reading a copy and exposing a photosensitive plate.
Figure 2 is an elevational view, partly in cross-section, of the scanner assembly of the apparatus of Fig-ure 1, taken generally along the line 2-2 thereof.
Figure 3 is a top plan view taken along the line 3-3 of Fiyure 2.
Figure 4 is a front face view of ~he scanning wheel of the apparatus of Figure 1, taken along the line 4 4 of Figure 3.
Figure 5 is a ~op view of a roof doublet mirror assembly of the scanner of Figure 1, taken along the line 5-5 of Figure 2.
Figure 6 is a cro~s-sPctional view of the upper mirror of the doublet mirror asse~bly, taken along the line 6-6 of Figure 5.
Figure 7 is a cross sectional view taken along the line 6 6 of Figure 5.
Figure 8 is a front, or input, view of the doub-let mirror assembly taken along the line 8-8 of Figure 5.
: Figure g is a diagrammatic view illustrating the principle by whi~h vertical angular deviation is removed . from the beam as it passes through the roof mirror double~
assembly~
:~ Figure 10 is a perspective diagrammatic view il ~ lustrating the scanner portion of the invention and show-; ing a ray trace of the principal beam path therethrough at an intermediate angle of orientat:ion of the scanner whePl.
E'igura llA is a front view of the scanner wheel of Figure 1 lllustratirlg a beam impinging on one segment of ~he wheel when that segment is at the mid-position of its travel through the input beam path.
Figure llB shows a beam trace in a ver~ical plane taken along the line llB-llB of Figure llA.
.
:
. .. ; . , - . . .. . ., . ,, ~ .. , . . . .. . ~ . . . .
7~
Figure llC shows a ~op plan r or horizon~al plane, ray trace of the beam of Figure llA taken along the line llC llC thereof.
Figure 12A is a front view of the scanner wheel of Figure l illuætrating a beam impinging ~n one segment of the wheel when that segment is at an interm diate posi-tion in its travel through the input beam path~
~ Figure 12B shows a beam trace in a vertical plane taken along the line 12B 12B o~ Figure 12A.
Figure 12C shows a top plan, or hori20ntal plane, ray trace of the beam of Figure 12A taken along the line 12C-l~C thereof.
Figure 13A i5 a front view of the scanner wheel of Figure 1 illustxa~ing a beam impinging on one segment of the wheel when that segment is near the end of its trav-el through ~he input beam path.
Figure 13B shows a beam trace in-a vertical plane taken along the line 13B-13B of ~igure 13A.
Figure 13C shows a top plan, or horizontal plane, ray trace of the beam of Figure 13A taken along the line 13C-13C thereof~
Detailed Description of the Prefexred Embodiment _ _ ,~ Referring now to Figures 1 and 2 there is shown a laser read/write system constructed in accordance with the invention which includes a~station 20 definin~ a sup-port ~or an exposure or write platen 22 and another sta-tion 24 defining a support for a read platen 26. The ex-posure platen receives a pho~osensitive plate at 22 which will be scanned by the apparatus to be described and there-by exposed for ~ubsequent development into a printing plate.
The copy to b~ read i~ positioned on the read platen 26. A
laser beam station 30 is provided, the output of which is directed through a scanning system 32 and redirected there-by~to~cause~wrlte beam 34 and read beam 36 to ~can across the respective platens. The scanning system 32 includes a table 38 supported on a linear transport mechanism includ ing~parallel guides 40 engaged in a prede~ermined direction, ~; ~ as indica~e~ at 48. The table is driven by a lead screw 44 and~ro~ary motor drive 46 which may conveniently be disposed ~ -8-on a suitable apparatus framework (not shownj so that the laser beam station and platens remain subskantially fixed in space while the acanni~g ~able moves along the direction indicated at 48.
The table carrîes a horizontal sc~nning sub-system 50 (Figure 2) constructed in accordance with the invention which shifts the beam fxom side to side ~hori-zontally) as the table is carried forward to thereby develop raster scans 52,54 of the laser beams across both the read and exposure platens.
Means i~ provided or generating the read laser beam 36 and consists of a helium-neon ~He/Ne) laser 58 having an output at 6,328 angstroms i~ the red portion of the visible spectrum which is then passed through a beam expander and collimator 60 and turning mirror 62 for developing the same into a collimated beam along a predetermined path 66 passing through a dichroic beam co~biner 64 having surfaces selectively transmissive to 6,328 angstroms.
Means is provided for providing an exposure laser beam which is actinic to the photosensitive sur-face of the exposure plate carried at platen 22. One typical system utilizes an argon ion laser 68 having an output beam 34 at 4,880 angstroms in ~he blue portion of the spectr~m at a power output of about 10 milliwatts.
This output beam is passed through an aoousto-optical modulator 74 which controls the intensity of the beam transmitted therethrough. Beam 34 i5 routed by a turn-ing mirror 76 through a beam expander and collimator 78 to the dichroic beam combiner 67. The beam combiner re-flects beam 34 along path 66 and thereby combines it with read beam 36. The combined beams pass along the common path to a turning mirror 80 cArried on the scan table and then to the scanning apparatus 50. As indicated in Fig-ure 1, the scanning apparatus serves to deflect the com-bined beams through a horizontal angle to ultimately scan the beams across the respective surfaces of read platen 26 and write platen 22. A flat field lens 82 serves to : focus the scanning beams at the æurfaces of the respec-tive platen~. After passing through lens 82, the combined .;, _g_ ~ ` .
.
S
beams pass to a dichroic beam splitter 84 which reflects the blue actinic write beam 34 upwardly ~o a turning mir-ror 86 and thence downwardly through an aperture 88 in the table to exposure platen 22. The dichroic beam split-ter 84 (similar to combiner 64) passes the red read beam 36 to a folding mirror 90 which directa the beam downward-ly through a second aperture 93 in the scanning table to impinge upon copy at read pla`ten 26.
An optical reader 94 is carried by ~he scanning table for receiving read beam energy reflect~d by the copy on platen 2~. ~rhe reader comprises a fiber optic bundle 96 which includes fibers arranged in elongated linear ar~
ray extending across the width of the copy to be scanned.
The output of the fiber ~ptic rea~er i5 directed to a pho-tomultiplier tube (not shown) and converted to an electrical signal which controls the intensity of the output of modu-lator 74.
Referring now to Figures 2 - 8, the optical scan-ner 50 will be described in greater detail. In general, the scanner consists of a roof mirror assembly 100 to which is optically coupled a generally pyramidal input/output scanning wheel 102 having mirror segments 104,106,108 there-on which progressively move through the path of the input laser beam and cause the same to be deflected, as will be described. The input turning mirror 80, which is moun~ed on the underside of the scanning table 38, is positioned to intercept the combined laser beam 66 from the laser table 30 and to deflect the same upwardly to the scanning wheel 102. The beam is then reflected by one of the mirror seg~
ments 104,106 or 108 toward a first mirror 110 of the roof mirror assembly 100, then to a æecond mirror 112 of the roof mirror assembly 100, and then back to the s~ne wheel se~ment 104,106 or 108 from which it was reflected initial-ly. After the second reflection from the wheel segment, the beam passes to an output objective lens g2. The angles of reflection of the reæpective wheel segment, roof mirrors 110~112 and turning mirror 80 define the vertical orienta-tlon of the beam as it emerges from the scanner.
:
.~
7~
Means i~ provided for mo~nting the xoof mirrors 110 and 112 in spaced relation ~o each other and includes a framework 116 and a base 114 to which the lower mirror 112 is cemented. The upper mirror 110 is carried in a support ring 118 which is adjusta~le in angulax orienta-tion by a 3-point suspension consisting of suitable dif-ferential screws 120 through an upper crosspiece 122 so as to permit accurate alignment between the mirrors. As shown, mirrors 110 and 112 are ~paced apart with a scan output opening 124 between khem from which the emerging scan beam is directed into the objective lens 82. Mirrors 1}0 and 112 are positioned with an i~cluded angle 126 of about 5508 degrees. It can be shown that the total angle through which the beam is turned is 360 degrees, including the reflection by the tl-rning mirror 80, the two reflections by the scanning wheel 102, and the reflections by the two roof mixrors 110 and 112. These angles define a fixed ang-ular relation in the vertical Airection between the input and output beams. ~he angle of tilt of the scanning wheel segment does not affect the vertical output angle but only the vertical displacement of the beam, as will be described.
The scanning wheel 102 is mounted on a spindle ox shaft 130 which is supported for rotation in bearings 132,134 mounted in a shaft housing 136. A drive motor 138 is mounted on the housing and coupled directly to the shaft.
The motor may for example be a DC motor having field wind-ings 139 and being capable of output speeds up to 10,000 rpm. An encoder wheel 140 is sonnected to the shaft and forms part of an optical ~ensor 142 for creating a chopped electrical signal indicative of the scanner wheel speed and orientation.
The scanning wheel and motor are supported by a mount 144 on table 3B, with ~he axis of rotation of the scan~ing wheel~in a plane common to the optical axis of tha output objective lens and the axis of the input beam.
Roof mirrors 110,112 are adjusted so that their surface vectors (i~eO,~ vectors perpendicular to the surfaces of the mirrors) also lie in this pl~ne.
::
r .. , . . ~.
As shown best in Figur s 2 - 4, the sca~ning wheel front reflective surfaces conform to a pyramid in shape. For convenience of manufacture the wheel is cut and machined from a circular di~c. The scanning wheel pyramid is preferably a regular triangulax pyramid having an axis of symmetry and apex (imaginary) located along the axis of rotation. As ~hown, the apex portion is flat-ted at 120a so that the wheel is technically a frustrum of a pyramid, but this trunca~ion is not material to the invention. The pyramid thus defines a plurality of at least three reflective side segments which are identical and which are di~posed symme~rically about the axi~ of rotation. Each of these segments is provided with a very accuretely formed planar reflective surface. Typically, the disc is fabricated of aluminum or beryllium and is machined to form mounting surfaces for the reflective elements. These elements are accurately formed optical flats which are secuxed to the machined surfaces of the disc by a suitable cement. It is important that each seg-ment be optically flat to a high degree of accuracy, since the input and output reflections from the segment will gen-erally not be at the same position on each reflective segment as the wheel r~tates.
Each segment defines a plane in ~pace which is tilted at a small acute angle, e.g., 6 degrees, with respect to a plane perpendicular to the axis of rotation of the wheel.
Since the segment passes throuyh the beam's path, the effect is one of passing a plane through the path with the plane varying in angle of orientatlon to the path. Since each se~-ment of a triangular mirror is limited to 120 degrees, the variation in the orientation of the plane passes from a min-imum at one side through a maximun to a minimum on the other side; that is to say, the normal vector of each segment starts by making a maximum horizontal angle of deviation ~o the sym-metry plane, passes through a null and proceeds to a maximwm angle on the other side. Thereafter, the part line 146 be-twee~ two adjacent 6egments passes through the beam path (dead time), and the process is repeated. ~he trace produced by each successive ~egment travels in ~he ~me direction from one side of the 6ystem to the other.
-~2-' ~ d~'' Thus, as illustra~ed in Fiyure 10, the beam 66 is ~eflected at lS0 by turning mirror 80 into a further series of reflections:
(a) a first reflection from ~he wheel segment 104 at 152, (b) a xeflection from the up~er mirror 110 of the roof doublet at 154, (c) a reflection from the lower mirror 112 of the roof doublet at 156, and ~d) a second reflection from the wheel segment 104 at 158, at which point the beam has been routed through vertical an-gles totaling 360 degrees and has ~een vertically displaced so as to emerge between the roof mirrors 110 a~d 112 and through the objective lens 82 in a direction parallel to the path of travel of beam 66 into turning mirror 80.
Each reflection by segment 104,106 or 108 actually introduces four possible deviations of the beam: a horizon-tal angular deviation, a vertical angular deviation, a hori-zontal di~placement, and a vertical or height displacement.
Upon consideration it will be found that in order to produce an accurate scan line tracing a straight path in the plane of focus of the objective lens 82, the only requirement of these deviations is that the vertical angular component be constant and invariable while the ~orizontal angular compo~ent progres-ses from slde to side in a repeating pattern. How this is done is best understood by reference to Figure 9.
. Figure 9 illustrates that no change in the verti-cal ang~e of a beam passing through a 90-degree roof mirror do~blet M-l,M-2 is produced by a change in the angle of tilt of a reflector R which ~exves botll as input and output to the xoof mirror. It is a known property of the roof mirror doublet itself that ~he input beam defines the angle of the output beam unambiguously. For example, with a 90-degree roof mixror doublet, the beam will be reflected out of the doublet at exactly the same angle as it enters in a plane perpendicular to the line of intersection of the roof mir-rors. This is true regardless of the angle o~ tilt of the reflector, provided the:~eflector is perfec~ly planar and serves~bo~h as~an input reflector and an output reflector to the~roof mirror system. Because of the inversion as the beam passes~:through~the roof mIrrorsl the angular component of , ~ :
~ 13-~7~
til~ of the input reflector i5 cancelled exactly, although a displacement or height error _v will oc~ur. Since the wheel segments 104,106,108 are flat, the vertical angle of the output beam in the invention remains invariable with respect to the input beam and precisely so even ~hough the input/output reflecting ~egment 104,106 or 108 introduces vertical height displacement as well as horizontal angular and position displacements. ~owever, 6ince the beam is J aligned v~r~ically with respect to the objective lens and contains no change in vertical angular component, it traces a s~raight line at each focal plane.
The oregoing i6 ~rue even under very loose tol-erances fox segment-to-segment accuracy, bearing accuracy of the spindle or haft mounting r vibration and other var-iables to which the rotating wheel is subject. The sole rigid and absolutely precise requirement is flatness of each reflective segment of the scanner wheel.
The three~dimensional charactex of the motion of the beam during scanning can be visualized by reference to the perspective view of Figure 10. The beam segments are - - labelled and charac,terized as follows:
160 stationary beam following reflection by turning mirror 80, 162 hori~ontal and vertical deviation added by first reflection from wheel, 164,166 - roof doublet reflection adding vertical ' and horizontal displacements, 168 - vextical angle removed, horizontal angle doubled, vertical and horizontal displacement increased.
Figure llA show~ the pyramidal mirror segment 104 at its mid-position, which is also the position of maximum vertical deflection. Figure llB shows the beam being routed by the roof mirrors back ~o segment 104 nearly on top of the 'input beam for its second reflection from that segment be-ore being passed between the mirrors in and out of the sys-tem. Figures 12A - 12C and 13A - 13C show the segment in progressively moved positions, first turned slightly and then progressing toward the limit of movement to one side.
`~
,:
7~
These igures also show the progression in the horizontal angular deviation, the horizontal displacement and slight vertical displacement of the beam as the mirror segment moves, while also indicating that no vertical angular de~
viation is created. These figu_es also show an intere~t-ing phenomenon in that the vertical displacement causes the second reflection from ~he ~can wheel segment to fol-low the moving reflective ~egment through its circular path of rotation, thereby avoiding the possihility of the beam walking off the reflective segment laterally.
Both the horizontal and vertical displacements of the beam are controlled by the angle of tilt of pyra-midal mirror segments 104,106 and 108. In fairly long focal length system6, as generally described herein, the horizontal sweep angle desired is about 13 degrees, and the apex angle of the pyramidal mirror is such that each surface of that mirror is inclined relative to a plane normal to the axis of rotation or axis of symmetry by an angle on the order of 6 degrees. The pyramid apex angle is the angle between the side of a xegular pyramid having an even number of sides, e.g., a square or regular pyra-mid. For pyramids having an odd number of sides, the apex angle i6 twice the angle between one of the sides and the axis of symmetry of the pyramid. Should a greater throw be desired, redesign of the component locations and an increase in this angle will provide a ~reater horizontal angular deflection. In this connection, it is also poss-ible to built the ~canning wheel with means tnot shown~ for adjusting the angle of tilt of the acets. At least for small changes, this would have the effect of varying or changing the hoxizontal scan width over a limited range, which could be very useful in certain applications. I
changes in scan width greater than a certain amount were required, the angles and positi.oning of the mirror doub-let would also be changed.
By way of example, one scanner constructed in accordance with the present invention had the following dimensional and other characteristics:
.
.. . . . .. . . .
~a) angle of introduction to segment 104 and first reflectign from segment 104 in plane of symme-try ~ 30 , (b) mirror doublet angle = 55.8 t (c) pyramidal mirror apex a~gle - 2(90 - 6~) = 168 for a segment tilt of 6 with respect to a plane normal to the axis of rotation~
(d) diameter o~ wheel 102 = B inches, (e) angle of ~otal reflection through scanning sys~
tem = 360 , (f~ rotational speed up to 10,000 rpm or 500 traces/
sec.
At high rotational speeds it is desirable to pro-vide a wind shroud 170 ~urrounding all portions of the wheel except for a small front-facing port 171 which permits the beam to enter and exit on each reflection, as illustrated in Figure 2.
It is a particular advantage of the invention that the ~can wheel can be cut from a circular disc. It is evi-dent tha~ a circular disc having an accurately machined and aligned moun~ing to the shaft of its rotational support is desirable for vibration-free operation. Achieving this re-sult in circular configuration is relatively easy, and care-ful manufacture of the wheel and rotating parts will result in a substantially symmetrical mass distribution about the axiq of rotation and permit high degxees of dymanic balance of the rotational elements.
I~ carried through its entire circle o rotation, each segment~actually txaces a sinusoidal angle of impinge-ment with respect to the axis ~ the beam as delivered to the wheel from mirror 80. Only a portion of this 360-degree cycle is utilized, namelyl a 120-degree portion which repre-sents a 6ubstantially linear change iII the angle of orienta-tion relative ~o the beam and is generally symmetrical about the maximum angle of tilt presented ^to the beam.
While operating speeds up to 7,000 rpm have been ~uggested, the inherent design o the scanner of the inven-tion permits envisioned operating speeds which may reach or even exceed 60,000 xpm. ~his would represent linear ; trace repetition time~ of up to 3,000 traces (scans) per second, which~have here~ofore been impr~ctical in apparatus o~this character. The trace times proYided by the invention ~ -16-- ~ . ~ .
e~sentially eliminate the scanning ~lement as the limiting stxucture in apparatus for the production of printing plates and the like. ~he scanning system of the invention has achieved many of the desirable advantages which are essen-tial to a good scanner. Effectively, vertical wobble has been eliminated. While scan efficiencies of at least 75%
are easy to ohtain, the scan efficiency can be increased by increasing the diameter ~f the ~canning wheel at least up to reasonable dimensional limits. The scanning is of single-direction character, and the velocity linearity for - a ~hree-se~ment wheel has been held, in the embodiment shown,well within acceptable limits. Scan times for conventional printing plates ~ith typical raster scan advance speeds and the trace speeds provided by the invention are on the order of one minutet which is a necessary objective for any system for production of printing plates at high speed. As is ev-ident, ~he cost of production of a system constructed in accordance with the invention is reasonable, since the only relatively critical tolerance is the tolerance of mirror flats. The entire system i5 reflective in character, total-ly eliminating refraction error in both single-beam and multi-beam operation. This feature enables the use of the system in multi-frequency operation where read and write beams of different frequencies are superimposed along a single beam path. In summary, by using the present inven-tion, problems associated with lag errors, back-and-forth scanning, vertical wobble, frequency dependency and other ~ disadvantages of prior systems are eliminated.
; ~ The system of the invention is also adaptable to facsimile operations such as disclosed in the co-re~er-enced application previously referred to, or in other scan-ning systems, the angular position o~ the wheel being de-termined either by the design o~ the encoder disc or by spatial masking as may be required. In addition, the fore-going scanner lends itself r~adily to incorporation into flat-~ield scanning devices as shown in the present inven-tion. The invention provides an output beam which is ver-ticall~ pr~cise and stable, and no vertical wobble compen-sation is requiredO
~ ~ -17~-:
:
To those skilled in the art to which this inven-tion pertains, many modiications and adaptations thereof will occur~ For example, while there has heen shown a three-sided frustrum of a regular triangular pyramid having a circularly cut disc-like base, changes in the pyramid apex angle, the number of sides (for example, four, fiv~
or more sides), and many design details of the scanning wheel may be made to adapt the invention to particular cir-cumstances, format sizes or ~ructur~es. Wheels having ad-justable tilt angles have alreadv been mentioned. A11 of such changes and modifications are within the scope of the invention. Additionally, while read/write laser plate pro-duction systems have been disclosed and described specific-ally and facsimil~ opera~ion has been mentioned, it should be understood that this is for brevity of explanation. The scanner of the invention is also applicable to one-, two-or even multiple-beam systems such as may be used in multi-ple-station facsimile operation. It should be understood, however, that such modifications and adaptations are to be included within the scope o the invention and by definition in the scope of the subse~uent claims, the specific embodi-ment disclosed and described herein being given for the pur-pose of illustration and not limitation on the invention.
-:, ~:
.. ..... . .....
Background of the Invention This invention relates generally to optical scanners and more particularly to an optical scanner for creating a flying spot linear trace of a beam of laser light. The inven-tion finds particular use in t~ i~1d of laser beam scanners as are used for r~ading info.rmation from a copy boand and directly transferr mg the rea~ information for the exposure of photosensitive surfaces as in the pr.oduction of printing plates.
In Canc~dian application Serial No. 243,825 fi.led Janua~y 20, 1976, Richard E. Amtcwer, there is show.n an apparatus for producin~ an exposed photo plate rom a copy board paste-up~ A l.aser scanning system having a read laser beam is focused to a spot scanned across the copy board in a predeterm med pattern, such as a raster-like scan, the reflection from the copy board being sensed, read and used to control the intensity of a second laser beam via a mcdulator~ The second laser beclm impinges upon and scans a photosensi~ive sur~ace~ The read lase bec~m and the write laser beam are cc~bined and passed through deflection optics, and the tw~ beams are subsequ~ntly separated to impinge ~on and be fo~used at the copy board and photo-sensit:ive surface, respectively. Tn -this way there is a resultc~nt exposure of the photosensitive surface in accord-ance with the copy. As shown in Serial NoO 243,825, the scannin~ optics employed u-tilizes a moving mirror galvano~
meter, with both the rec~d and write laser bec~ms being aligned cl~l superimposed upon each other through suitable beam comb ~ optics ~or being:passed th~ough the galvanometer simul neously ~nd subssquently separated by suitable beam ~30 : deflecticn optics~to the respective planes. Ano~her optical system shown:ther2in employs a polygonal scanning wheel . -`
hav~ng a plurality Oe surlsces psrsllel to ths aris of ~ ~ ~
rotation of the wheel, ~ith the surfaces serving to scan the read and write beams through an angle, thereby creating a flying spot scan.
In United States Patent 4,081,842 March 28, 197B, Steven K.
Harbaugh et al there is disclosed a variation o~ laser read~write apparatus in which a facsimile system is developed. As disclosed therein, a duplica-tion of read and write equipment at separate locations can ke coordinated to form a facsimile transmlssion system. At the read st~tion an optical scc~nner scans the input copy ~ith the scanning spot and the reflected light produces a video read da~a signal, a portion of which is directed through a spatial mask to pr~vide a transmitter video reference which gates a video read data before transmission. In the receiver, a second optical scanner ~f similar construction is controlled by a video writ~ data signal. The -~ video write data si~nal gates a scanning spot of exposure laser keam light on and off to expose the output photosensitive copy surface at the receiver.
Additianally, the scanning light is debected through a further spatial mask to provide a receiver video reference signal utilized to form a video write signal. The spatial masks in the transmitter and receiver have a kncwn relationship, e.g., so that the scannLng of the output copy in the receiver can be spatially synchronized with the scannm g of the inpu~ copy in the 2Q transmitter. As therein disclosed, each of the scanning op~ics includes a~galvanom~ter-operated mirror for scanning the incident laser keam kac~ and forth,through a horizontal angl~.
l~e foregoing instruments as disclosed in the cross-reEerenced ~pplication employ a field-flatteniny lens for causing the beam provided from the sca~ming device to be focused at the pl~le oE the copy boarl and photosensitive surface res~ tively, and are known thereEore as flat bed sc~nners. The scc~ning optics, hcwever, are subject to a number oE errors which de~rade the perform3n~ of the system. In a polygonal drum scc~nLng ~ design, ~ery close~tolerano~s are requii0d during the manufacturing processes ~ so as to o~trol ~acet-to tacet tilt~ A~y error Ln facet ~Eacet orienta-`~ tion, together ., .
.
:: - : .
~ 7~
with bearing run-out errors and the lik~, contribute to produce an angular or positional error component normal to the scan line. This error has come to be known as "wobble" or vertical errox. In addition, the scan ef-ficiency of a polygonal drum ~canning system is limited to about 50 percent. Accordingly, the polygonal design is expensive to produce due to ~he tolerances required, and the facet-to-facet error h~s to be removed by ~ome suitable means, termed a "dewobbler".
In a resonant or oscillating galvanom2ter scan-ner, the mirror pivots in a sinusoidal manner, and only the center portion of the scan is linear enough to be utilized. This results in a scan efficiency of approxi-mately 50~ with a 25% deviation in exposure or scan vel-ocity. However, it is necessary to scan back and orth in opposing directions in order to maintain this effici-ency level. Such scanning requires lag compensation which is accomplished by deviating the read beam from its normal course as a function of system time delays and scan velocity. Such compensation adds to the cost and complexity of the system and in many instances is only partially e~fective. In addition, if multiple ma-chines are to communicate in a facsimile system, a great deal of calibration of each machine is required to norm~
alize ~he amount of 12g produced in each machine. Lag errors and other errors in the facsimile process when scanning in both directions, result in left writing and right writing images that are no longer superimposed, re-sult.ing in severe image deyradatioll for even small errors.
Furthex, at the higher speeds particularly associated with facsimile systems, the scanner requirements exceed the capabilities of a galvanometer mirror system because of the high torque to which the mirror and its support struc-ture are subject~d.
Other existing systems utili~e cylindrically curved fields but are also limited in scan efficiency.
For example, in one ~uch system using a spinner-type scanner in a cylindrical configuration, one scan is ac-complished for each rotation of the scanning device.
: -4-7~
With the exposure times commonly associated with a standard printing format, extremely high rotational speeds are required, and synchronization of facsimile versions is difficult~ Furthermore, ~uch curved field systems xequire that the exposure surface be adaptable to a curved conformation which is often incompa~ible with printing plate production.
Ideally, a 6canning system should provide a high scan efficiency, a scanning operation in a single direction 50 as to eliminate the problem of lag, and a constant scanning velocity so as to reduce the cost ~f the associated electronics. In addition, the system should be ree of vertical error or wobble and should be entirely reflective so as to above ab~rra~ion errors caused by the read and write beam frequencies being at different portions of the spectrum. Additionally, such a scanning system should be compatible with flat field optics so that the resulting flying spot scan can read copy and expose plates lying on plane surfaces.
Objects and Summary of the Invention In general it is an object of the invention to provide a laser beam optical scanning apparatus which will overcom~ the above limitations and disadvantages and supply error-free scanning within the foregoing guide-lines.
It is a further object of the invention to pro-vide an optical scanning apparatus o the above character which utilizes a rotating element and provides a resultant scan which is free of vertical error or ~obble, which is compatible with ~lat fie~d scanning, and which simultan-eously has a substantially uniform scan velocity and high scan efficiency while operatiny in a single dixection of scan.
It is a further object of the invention to pro-vide a laser beam optical scanning apparatus of the above chaxacter which is inherently adaptable to extremely high scanning ~peeds.
~5--~7~
Ano~her object of the invention is to provide a~ optical scanner of the.abo~e character which is read-ily adapted to synchronous ~acsimile ~peration.
A urthex object of the invention is to provide a scanner of the above character which is designed for multiple-beam read/write operation utilizing beams of dif~
ferent frequencies without introducing chromatic ~berra-tion.
The.se and other objects are achieved in accord-ance with the invention by providing a pyramidal mirror having a plurality of reflective surfaces inclined at an acute angle relative to a plane perpendicular to the axis of the mirror. The mirror is rotated about its axis to move the reflective surfaces successively through the path of a beam to provide a varying deflection of the beam from each successive surf~ce of the ~irror as that surface moves through the path and presents a varying an-gle of incidence to the beam, and optical means such as a roof mirror doublet receives the deflected beam from each successive ~urface and returns an inverted image of the beam to the æame surface for further reflection by that surface along an output path. As ea~h segment ro-tates through the beam path, its varying angular orienta-tion introduces horizontal and vertical components of an-gular de~iation into the beam, with the horizontal angular component being doubled upon the second (output) reflec-tion from the rotating segment while the vertical compon-ent i~ cancelled by the inversion provided by the roof mirror.
In a system for scanning reading and writing suraces wi~h laser beams, the beams are combined and the combined beam .is deflected by the pyramidal mirror and the roof mirror doublet to produce the desired scanning action, following which the beams are separated and dir-ected to the~respective readlng and writing surfaces.
~:
~ ~ , :;; : ;:
.:: :
`
:
.- .: - . ~. . . . .
Q~j;
In accordance with ~he inv~ntion there is provided in a scanning apparatus for causing a laser beam ~o scan a line at an output plane in space:
first mirror means forming a first planar reflective surface having a surface vector lying in a plane common to said beam, second mirror means forming a second planar reflective surface having its surface vector lying in the common plane, said irst and second mirror means being disposed relative to each other to form a reflective doublet about a line perpendicular to said common plane, a pyramidal mirror having a plurality of reflective segments inclined ; at an acute angle relative to a plane perpendicular to the axis of the mirror, and means Eor rotating said mirror about its axis to move said segments suc-cessively through the path of the beam so that the beam is reflected from the segment in the path to the doublet and back to the same segment or further reflection by that segment along an output path with a varying component of angular deviation perpendicular to the common plane and substantially no com-ponent of angular deviation parallel to the common plane.
: In accordance with another aspect of the invention there is provided in scanning apparatus: a pyramidal mirror having a plurality of reflective surfaces inclined at an acute angle relative to a plane perpendicular to the axis of the mirror, means for rotating the mirror about its axis to move the : 20 re1ective surfaces successively through the path Gf a beam to provide a vary- `
~; ing deflection of the beam from each successive surface of the mirror as that surface moves through the path and presents a vary:ing angle of inc.idcnce to the beam, said deflection having components along first and second axes per-~ pendicular to the mirror axis and to each other, and optical means for re-ceiving the deflect;d beam from each successive surface and returning an image of the beam inverted about the first axis to the same surface for further re flection by that surface along an output path with a varying component of angular deviation a.long the first axis and substantially no component of angu-:. lar deviation ai~ong the second axis.
~ .
:
: :
~ - 6a -,f ~
; .
Brief Descri~tion of_the Drawin~
Figure 1 is a diagrammatic perspective view of one embodiment of laser beam optical sc~nniny apparatus constructed .in accordance with the inven~ion for reading a copy and exposing a photosensitive plate.
Figure 2 is an elevational view, partly in cross-section, of the scanner assembly of the apparatus of Fig-ure 1, taken generally along the line 2-2 thereof.
Figure 3 is a top plan view taken along the line 3-3 of Fiyure 2.
Figure 4 is a front face view of ~he scanning wheel of the apparatus of Figure 1, taken along the line 4 4 of Figure 3.
Figure 5 is a ~op view of a roof doublet mirror assembly of the scanner of Figure 1, taken along the line 5-5 of Figure 2.
Figure 6 is a cro~s-sPctional view of the upper mirror of the doublet mirror asse~bly, taken along the line 6-6 of Figure 5.
Figure 7 is a cross sectional view taken along the line 6 6 of Figure 5.
Figure 8 is a front, or input, view of the doub-let mirror assembly taken along the line 8-8 of Figure 5.
: Figure g is a diagrammatic view illustrating the principle by whi~h vertical angular deviation is removed . from the beam as it passes through the roof mirror double~
assembly~
:~ Figure 10 is a perspective diagrammatic view il ~ lustrating the scanner portion of the invention and show-; ing a ray trace of the principal beam path therethrough at an intermediate angle of orientat:ion of the scanner whePl.
E'igura llA is a front view of the scanner wheel of Figure 1 lllustratirlg a beam impinging on one segment of ~he wheel when that segment is at the mid-position of its travel through the input beam path.
Figure llB shows a beam trace in a ver~ical plane taken along the line llB-llB of Figure llA.
.
:
. .. ; . , - . . .. . ., . ,, ~ .. , . . . .. . ~ . . . .
7~
Figure llC shows a ~op plan r or horizon~al plane, ray trace of the beam of Figure llA taken along the line llC llC thereof.
Figure 12A is a front view of the scanner wheel of Figure l illuætrating a beam impinging ~n one segment of the wheel when that segment is at an interm diate posi-tion in its travel through the input beam path~
~ Figure 12B shows a beam trace in a vertical plane taken along the line 12B 12B o~ Figure 12A.
Figure 12C shows a top plan, or hori20ntal plane, ray trace of the beam of Figure 12A taken along the line 12C-l~C thereof.
Figure 13A i5 a front view of the scanner wheel of Figure 1 illustxa~ing a beam impinging on one segment of the wheel when that segment is near the end of its trav-el through ~he input beam path.
Figure 13B shows a beam trace in-a vertical plane taken along the line 13B-13B of ~igure 13A.
Figure 13C shows a top plan, or horizontal plane, ray trace of the beam of Figure 13A taken along the line 13C-13C thereof~
Detailed Description of the Prefexred Embodiment _ _ ,~ Referring now to Figures 1 and 2 there is shown a laser read/write system constructed in accordance with the invention which includes a~station 20 definin~ a sup-port ~or an exposure or write platen 22 and another sta-tion 24 defining a support for a read platen 26. The ex-posure platen receives a pho~osensitive plate at 22 which will be scanned by the apparatus to be described and there-by exposed for ~ubsequent development into a printing plate.
The copy to b~ read i~ positioned on the read platen 26. A
laser beam station 30 is provided, the output of which is directed through a scanning system 32 and redirected there-by~to~cause~wrlte beam 34 and read beam 36 to ~can across the respective platens. The scanning system 32 includes a table 38 supported on a linear transport mechanism includ ing~parallel guides 40 engaged in a prede~ermined direction, ~; ~ as indica~e~ at 48. The table is driven by a lead screw 44 and~ro~ary motor drive 46 which may conveniently be disposed ~ -8-on a suitable apparatus framework (not shownj so that the laser beam station and platens remain subskantially fixed in space while the acanni~g ~able moves along the direction indicated at 48.
The table carrîes a horizontal sc~nning sub-system 50 (Figure 2) constructed in accordance with the invention which shifts the beam fxom side to side ~hori-zontally) as the table is carried forward to thereby develop raster scans 52,54 of the laser beams across both the read and exposure platens.
Means i~ provided or generating the read laser beam 36 and consists of a helium-neon ~He/Ne) laser 58 having an output at 6,328 angstroms i~ the red portion of the visible spectrum which is then passed through a beam expander and collimator 60 and turning mirror 62 for developing the same into a collimated beam along a predetermined path 66 passing through a dichroic beam co~biner 64 having surfaces selectively transmissive to 6,328 angstroms.
Means is provided for providing an exposure laser beam which is actinic to the photosensitive sur-face of the exposure plate carried at platen 22. One typical system utilizes an argon ion laser 68 having an output beam 34 at 4,880 angstroms in ~he blue portion of the spectr~m at a power output of about 10 milliwatts.
This output beam is passed through an aoousto-optical modulator 74 which controls the intensity of the beam transmitted therethrough. Beam 34 i5 routed by a turn-ing mirror 76 through a beam expander and collimator 78 to the dichroic beam combiner 67. The beam combiner re-flects beam 34 along path 66 and thereby combines it with read beam 36. The combined beams pass along the common path to a turning mirror 80 cArried on the scan table and then to the scanning apparatus 50. As indicated in Fig-ure 1, the scanning apparatus serves to deflect the com-bined beams through a horizontal angle to ultimately scan the beams across the respective surfaces of read platen 26 and write platen 22. A flat field lens 82 serves to : focus the scanning beams at the æurfaces of the respec-tive platen~. After passing through lens 82, the combined .;, _g_ ~ ` .
.
S
beams pass to a dichroic beam splitter 84 which reflects the blue actinic write beam 34 upwardly ~o a turning mir-ror 86 and thence downwardly through an aperture 88 in the table to exposure platen 22. The dichroic beam split-ter 84 (similar to combiner 64) passes the red read beam 36 to a folding mirror 90 which directa the beam downward-ly through a second aperture 93 in the scanning table to impinge upon copy at read pla`ten 26.
An optical reader 94 is carried by ~he scanning table for receiving read beam energy reflect~d by the copy on platen 2~. ~rhe reader comprises a fiber optic bundle 96 which includes fibers arranged in elongated linear ar~
ray extending across the width of the copy to be scanned.
The output of the fiber ~ptic rea~er i5 directed to a pho-tomultiplier tube (not shown) and converted to an electrical signal which controls the intensity of the output of modu-lator 74.
Referring now to Figures 2 - 8, the optical scan-ner 50 will be described in greater detail. In general, the scanner consists of a roof mirror assembly 100 to which is optically coupled a generally pyramidal input/output scanning wheel 102 having mirror segments 104,106,108 there-on which progressively move through the path of the input laser beam and cause the same to be deflected, as will be described. The input turning mirror 80, which is moun~ed on the underside of the scanning table 38, is positioned to intercept the combined laser beam 66 from the laser table 30 and to deflect the same upwardly to the scanning wheel 102. The beam is then reflected by one of the mirror seg~
ments 104,106 or 108 toward a first mirror 110 of the roof mirror assembly 100, then to a æecond mirror 112 of the roof mirror assembly 100, and then back to the s~ne wheel se~ment 104,106 or 108 from which it was reflected initial-ly. After the second reflection from the wheel segment, the beam passes to an output objective lens g2. The angles of reflection of the reæpective wheel segment, roof mirrors 110~112 and turning mirror 80 define the vertical orienta-tlon of the beam as it emerges from the scanner.
:
.~
7~
Means i~ provided for mo~nting the xoof mirrors 110 and 112 in spaced relation ~o each other and includes a framework 116 and a base 114 to which the lower mirror 112 is cemented. The upper mirror 110 is carried in a support ring 118 which is adjusta~le in angulax orienta-tion by a 3-point suspension consisting of suitable dif-ferential screws 120 through an upper crosspiece 122 so as to permit accurate alignment between the mirrors. As shown, mirrors 110 and 112 are ~paced apart with a scan output opening 124 between khem from which the emerging scan beam is directed into the objective lens 82. Mirrors 1}0 and 112 are positioned with an i~cluded angle 126 of about 5508 degrees. It can be shown that the total angle through which the beam is turned is 360 degrees, including the reflection by the tl-rning mirror 80, the two reflections by the scanning wheel 102, and the reflections by the two roof mixrors 110 and 112. These angles define a fixed ang-ular relation in the vertical Airection between the input and output beams. ~he angle of tilt of the scanning wheel segment does not affect the vertical output angle but only the vertical displacement of the beam, as will be described.
The scanning wheel 102 is mounted on a spindle ox shaft 130 which is supported for rotation in bearings 132,134 mounted in a shaft housing 136. A drive motor 138 is mounted on the housing and coupled directly to the shaft.
The motor may for example be a DC motor having field wind-ings 139 and being capable of output speeds up to 10,000 rpm. An encoder wheel 140 is sonnected to the shaft and forms part of an optical ~ensor 142 for creating a chopped electrical signal indicative of the scanner wheel speed and orientation.
The scanning wheel and motor are supported by a mount 144 on table 3B, with ~he axis of rotation of the scan~ing wheel~in a plane common to the optical axis of tha output objective lens and the axis of the input beam.
Roof mirrors 110,112 are adjusted so that their surface vectors (i~eO,~ vectors perpendicular to the surfaces of the mirrors) also lie in this pl~ne.
::
r .. , . . ~.
As shown best in Figur s 2 - 4, the sca~ning wheel front reflective surfaces conform to a pyramid in shape. For convenience of manufacture the wheel is cut and machined from a circular di~c. The scanning wheel pyramid is preferably a regular triangulax pyramid having an axis of symmetry and apex (imaginary) located along the axis of rotation. As ~hown, the apex portion is flat-ted at 120a so that the wheel is technically a frustrum of a pyramid, but this trunca~ion is not material to the invention. The pyramid thus defines a plurality of at least three reflective side segments which are identical and which are di~posed symme~rically about the axi~ of rotation. Each of these segments is provided with a very accuretely formed planar reflective surface. Typically, the disc is fabricated of aluminum or beryllium and is machined to form mounting surfaces for the reflective elements. These elements are accurately formed optical flats which are secuxed to the machined surfaces of the disc by a suitable cement. It is important that each seg-ment be optically flat to a high degree of accuracy, since the input and output reflections from the segment will gen-erally not be at the same position on each reflective segment as the wheel r~tates.
Each segment defines a plane in ~pace which is tilted at a small acute angle, e.g., 6 degrees, with respect to a plane perpendicular to the axis of rotation of the wheel.
Since the segment passes throuyh the beam's path, the effect is one of passing a plane through the path with the plane varying in angle of orientatlon to the path. Since each se~-ment of a triangular mirror is limited to 120 degrees, the variation in the orientation of the plane passes from a min-imum at one side through a maximun to a minimum on the other side; that is to say, the normal vector of each segment starts by making a maximum horizontal angle of deviation ~o the sym-metry plane, passes through a null and proceeds to a maximwm angle on the other side. Thereafter, the part line 146 be-twee~ two adjacent 6egments passes through the beam path (dead time), and the process is repeated. ~he trace produced by each successive ~egment travels in ~he ~me direction from one side of the 6ystem to the other.
-~2-' ~ d~'' Thus, as illustra~ed in Fiyure 10, the beam 66 is ~eflected at lS0 by turning mirror 80 into a further series of reflections:
(a) a first reflection from ~he wheel segment 104 at 152, (b) a xeflection from the up~er mirror 110 of the roof doublet at 154, (c) a reflection from the lower mirror 112 of the roof doublet at 156, and ~d) a second reflection from the wheel segment 104 at 158, at which point the beam has been routed through vertical an-gles totaling 360 degrees and has ~een vertically displaced so as to emerge between the roof mirrors 110 a~d 112 and through the objective lens 82 in a direction parallel to the path of travel of beam 66 into turning mirror 80.
Each reflection by segment 104,106 or 108 actually introduces four possible deviations of the beam: a horizon-tal angular deviation, a vertical angular deviation, a hori-zontal di~placement, and a vertical or height displacement.
Upon consideration it will be found that in order to produce an accurate scan line tracing a straight path in the plane of focus of the objective lens 82, the only requirement of these deviations is that the vertical angular component be constant and invariable while the ~orizontal angular compo~ent progres-ses from slde to side in a repeating pattern. How this is done is best understood by reference to Figure 9.
. Figure 9 illustrates that no change in the verti-cal ang~e of a beam passing through a 90-degree roof mirror do~blet M-l,M-2 is produced by a change in the angle of tilt of a reflector R which ~exves botll as input and output to the xoof mirror. It is a known property of the roof mirror doublet itself that ~he input beam defines the angle of the output beam unambiguously. For example, with a 90-degree roof mixror doublet, the beam will be reflected out of the doublet at exactly the same angle as it enters in a plane perpendicular to the line of intersection of the roof mir-rors. This is true regardless of the angle o~ tilt of the reflector, provided the:~eflector is perfec~ly planar and serves~bo~h as~an input reflector and an output reflector to the~roof mirror system. Because of the inversion as the beam passes~:through~the roof mIrrorsl the angular component of , ~ :
~ 13-~7~
til~ of the input reflector i5 cancelled exactly, although a displacement or height error _v will oc~ur. Since the wheel segments 104,106,108 are flat, the vertical angle of the output beam in the invention remains invariable with respect to the input beam and precisely so even ~hough the input/output reflecting ~egment 104,106 or 108 introduces vertical height displacement as well as horizontal angular and position displacements. ~owever, 6ince the beam is J aligned v~r~ically with respect to the objective lens and contains no change in vertical angular component, it traces a s~raight line at each focal plane.
The oregoing i6 ~rue even under very loose tol-erances fox segment-to-segment accuracy, bearing accuracy of the spindle or haft mounting r vibration and other var-iables to which the rotating wheel is subject. The sole rigid and absolutely precise requirement is flatness of each reflective segment of the scanner wheel.
The three~dimensional charactex of the motion of the beam during scanning can be visualized by reference to the perspective view of Figure 10. The beam segments are - - labelled and charac,terized as follows:
160 stationary beam following reflection by turning mirror 80, 162 hori~ontal and vertical deviation added by first reflection from wheel, 164,166 - roof doublet reflection adding vertical ' and horizontal displacements, 168 - vextical angle removed, horizontal angle doubled, vertical and horizontal displacement increased.
Figure llA show~ the pyramidal mirror segment 104 at its mid-position, which is also the position of maximum vertical deflection. Figure llB shows the beam being routed by the roof mirrors back ~o segment 104 nearly on top of the 'input beam for its second reflection from that segment be-ore being passed between the mirrors in and out of the sys-tem. Figures 12A - 12C and 13A - 13C show the segment in progressively moved positions, first turned slightly and then progressing toward the limit of movement to one side.
`~
,:
7~
These igures also show the progression in the horizontal angular deviation, the horizontal displacement and slight vertical displacement of the beam as the mirror segment moves, while also indicating that no vertical angular de~
viation is created. These figu_es also show an intere~t-ing phenomenon in that the vertical displacement causes the second reflection from ~he ~can wheel segment to fol-low the moving reflective ~egment through its circular path of rotation, thereby avoiding the possihility of the beam walking off the reflective segment laterally.
Both the horizontal and vertical displacements of the beam are controlled by the angle of tilt of pyra-midal mirror segments 104,106 and 108. In fairly long focal length system6, as generally described herein, the horizontal sweep angle desired is about 13 degrees, and the apex angle of the pyramidal mirror is such that each surface of that mirror is inclined relative to a plane normal to the axis of rotation or axis of symmetry by an angle on the order of 6 degrees. The pyramid apex angle is the angle between the side of a xegular pyramid having an even number of sides, e.g., a square or regular pyra-mid. For pyramids having an odd number of sides, the apex angle i6 twice the angle between one of the sides and the axis of symmetry of the pyramid. Should a greater throw be desired, redesign of the component locations and an increase in this angle will provide a ~reater horizontal angular deflection. In this connection, it is also poss-ible to built the ~canning wheel with means tnot shown~ for adjusting the angle of tilt of the acets. At least for small changes, this would have the effect of varying or changing the hoxizontal scan width over a limited range, which could be very useful in certain applications. I
changes in scan width greater than a certain amount were required, the angles and positi.oning of the mirror doub-let would also be changed.
By way of example, one scanner constructed in accordance with the present invention had the following dimensional and other characteristics:
.
.. . . . .. . . .
~a) angle of introduction to segment 104 and first reflectign from segment 104 in plane of symme-try ~ 30 , (b) mirror doublet angle = 55.8 t (c) pyramidal mirror apex a~gle - 2(90 - 6~) = 168 for a segment tilt of 6 with respect to a plane normal to the axis of rotation~
(d) diameter o~ wheel 102 = B inches, (e) angle of ~otal reflection through scanning sys~
tem = 360 , (f~ rotational speed up to 10,000 rpm or 500 traces/
sec.
At high rotational speeds it is desirable to pro-vide a wind shroud 170 ~urrounding all portions of the wheel except for a small front-facing port 171 which permits the beam to enter and exit on each reflection, as illustrated in Figure 2.
It is a particular advantage of the invention that the ~can wheel can be cut from a circular disc. It is evi-dent tha~ a circular disc having an accurately machined and aligned moun~ing to the shaft of its rotational support is desirable for vibration-free operation. Achieving this re-sult in circular configuration is relatively easy, and care-ful manufacture of the wheel and rotating parts will result in a substantially symmetrical mass distribution about the axiq of rotation and permit high degxees of dymanic balance of the rotational elements.
I~ carried through its entire circle o rotation, each segment~actually txaces a sinusoidal angle of impinge-ment with respect to the axis ~ the beam as delivered to the wheel from mirror 80. Only a portion of this 360-degree cycle is utilized, namelyl a 120-degree portion which repre-sents a 6ubstantially linear change iII the angle of orienta-tion relative ~o the beam and is generally symmetrical about the maximum angle of tilt presented ^to the beam.
While operating speeds up to 7,000 rpm have been ~uggested, the inherent design o the scanner of the inven-tion permits envisioned operating speeds which may reach or even exceed 60,000 xpm. ~his would represent linear ; trace repetition time~ of up to 3,000 traces (scans) per second, which~have here~ofore been impr~ctical in apparatus o~this character. The trace times proYided by the invention ~ -16-- ~ . ~ .
e~sentially eliminate the scanning ~lement as the limiting stxucture in apparatus for the production of printing plates and the like. ~he scanning system of the invention has achieved many of the desirable advantages which are essen-tial to a good scanner. Effectively, vertical wobble has been eliminated. While scan efficiencies of at least 75%
are easy to ohtain, the scan efficiency can be increased by increasing the diameter ~f the ~canning wheel at least up to reasonable dimensional limits. The scanning is of single-direction character, and the velocity linearity for - a ~hree-se~ment wheel has been held, in the embodiment shown,well within acceptable limits. Scan times for conventional printing plates ~ith typical raster scan advance speeds and the trace speeds provided by the invention are on the order of one minutet which is a necessary objective for any system for production of printing plates at high speed. As is ev-ident, ~he cost of production of a system constructed in accordance with the invention is reasonable, since the only relatively critical tolerance is the tolerance of mirror flats. The entire system i5 reflective in character, total-ly eliminating refraction error in both single-beam and multi-beam operation. This feature enables the use of the system in multi-frequency operation where read and write beams of different frequencies are superimposed along a single beam path. In summary, by using the present inven-tion, problems associated with lag errors, back-and-forth scanning, vertical wobble, frequency dependency and other ~ disadvantages of prior systems are eliminated.
; ~ The system of the invention is also adaptable to facsimile operations such as disclosed in the co-re~er-enced application previously referred to, or in other scan-ning systems, the angular position o~ the wheel being de-termined either by the design o~ the encoder disc or by spatial masking as may be required. In addition, the fore-going scanner lends itself r~adily to incorporation into flat-~ield scanning devices as shown in the present inven-tion. The invention provides an output beam which is ver-ticall~ pr~cise and stable, and no vertical wobble compen-sation is requiredO
~ ~ -17~-:
:
To those skilled in the art to which this inven-tion pertains, many modiications and adaptations thereof will occur~ For example, while there has heen shown a three-sided frustrum of a regular triangular pyramid having a circularly cut disc-like base, changes in the pyramid apex angle, the number of sides (for example, four, fiv~
or more sides), and many design details of the scanning wheel may be made to adapt the invention to particular cir-cumstances, format sizes or ~ructur~es. Wheels having ad-justable tilt angles have alreadv been mentioned. A11 of such changes and modifications are within the scope of the invention. Additionally, while read/write laser plate pro-duction systems have been disclosed and described specific-ally and facsimil~ opera~ion has been mentioned, it should be understood that this is for brevity of explanation. The scanner of the invention is also applicable to one-, two-or even multiple-beam systems such as may be used in multi-ple-station facsimile operation. It should be understood, however, that such modifications and adaptations are to be included within the scope o the invention and by definition in the scope of the subse~uent claims, the specific embodi-ment disclosed and described herein being given for the pur-pose of illustration and not limitation on the invention.
-:, ~:
.. ..... . .....
Claims (21)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a scanning apparatus for causing a laser beam to scan a line at an output plane in space: first mirror means forming a first planar reflective surface having a surface vector lying in a plane common to said beam, sec-ond mirror means forming a second planar reflective surface having its surface vector lying in the common plane, said first and second mirror means being disposed relative to each other to form a reflective doublet about a line perpen-dicular to said common plane, a pyramidal mirror having a plurality of reflective segments inclined at an acute angle relative to a plane perpendicular to the axis of the mirror, and means for rotating said mirror about its axis to move said segments successively through the path of the beam so that the beam is reflected from the segment in the path to the doublet and back to the same segment for further reflec-tion by that segment along an output path with a varying com-ponent of angular deviation perpendicular to the common plane and substantially no component of angular deviation parallel to the common plane.
2. Apparatus as in Claim 1 in which said pyramidal mirror is formed on the axial face of a scanning wheel.
3. Apparatus as in Claim 2 in which the wheel has a generally circular base.
4. Apparatus as in Claim 2 in which said wheel is sub-stantially balanced about the axis of rotation.
5. Apparatus as in Claim 1 in which said first and sec-ond mirror means are spaced apart and the beam passes between the same in passing along the output path.
6. Apparatus as in Claim 1, further including an objec-tive lens for focusing the output beam to a small spot at the output plane.
7. Apparatus as in Claim 6 in which said lens forms a flat field at said output plane.
8. Apparatus as in Claim 1 wherein the mirror segments are disposed symetrically about the axis of the mirror.
9. Apparatus as in Claim 1 in which each of said seg-ments has a highly accurate flat reflecting surface.
10. Apparatus as in Claim 1 in which the apex angle of the pyramidal mirror is only slightly less than 180 degrees.
11. Apparatus as in Claim 1 in which the surfaces of the reflective segments are inclined at an angle on the order of 6 degrees relative to a plane perpendicular to the axis of rotation.
12. Apparatus as in Claim 1 in which the total angle of reflection of the beam by the reflective segment and the mirror doublet is on the order of 360 degrees so that the beam emerges from the apparatus in a direction generally parallel to the input path.
13. Apparatus as in Claim 6, further including a photosen-sitive surface positioned to be scanned by the beam in said output plane.
14. Apparatus as in Claim 6 further including a printing plate positioned in the output plane and having a surface to which the beam is actinic.
15. Apparatus as in Claim 7, further including a flat printing plate positioned in the output plane.
16. Apparatus as in Claim 1 in which said means for rotat-ing the pyramidal mirror comprises a motor capable of output speeds in excess of 4,000 rpm.
17. Apparatus as in Claim 1 in which said pryamidal mirror has sides conforming to a regular triangular pyramid and forming three reflective segments disposed symmetrically about the axis.
18. In scanning apparatus: a pyramidal mirror having a plurality of reflective surfaces inclined at an acute angle relative to a plane perpendicular to the axis of the mirror, means for rotating the mirror about its axis to move the reflective surfaces successively through the path of a beam to provide a varying deflection of the beam from each successive surface of the mirror as that surface moves through the path and presents a varying angle of incidence to the beam, said deflection having components along first and second axes perpendicular to the mirror axis and to each other, and optical means for receiving the deflected beam from each successive surface and returning an image of the beam inverted about the first axis to the same surface for further reflection by that surface along an output path with a varying component of angular deviation along the first axis and substantially no component of angular deviation along the second axis.
19. The apparatus of Claim 18 wherein the mirror is in the form of a triangular pyramid with three reflective surfaces disposed symmetrically about the axis of the mirror.
20. The apparatus of Claim 18 wherein the reflective surfaces are inclined at an angle on the order of 6° to the plane perpendicular to the axis.
21. The apparatus of Claim 18 wherein the optical means comprises a roof mirror doublet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80544577A | 1977-06-10 | 1977-06-10 | |
| US805,445 | 1977-06-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1107105A true CA1107105A (en) | 1981-08-18 |
Family
ID=25191590
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA304,782A Expired CA1107105A (en) | 1977-06-10 | 1978-06-05 | Optical scanner and system for laser beam exposure of photo surfaces |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5418301A (en) |
| AU (1) | AU519986B2 (en) |
| CA (1) | CA1107105A (en) |
| DE (1) | DE2825550A1 (en) |
| FR (1) | FR2394105A1 (en) |
| GB (1) | GB2000321B (en) |
| IT (1) | IT1096713B (en) |
| NL (1) | NL7806306A (en) |
| SE (1) | SE7806778L (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4304459A (en) * | 1979-07-02 | 1981-12-08 | Xerox Corporation | Reflective holographic scanning system insensitive to spinner wobble effects |
| JPS5644628A (en) * | 1979-09-20 | 1981-04-23 | Kasamatsu Kako Kenkyusho:Kk | Continuous manufacturing method and apparatus for profile tube |
| US4323307A (en) * | 1980-06-06 | 1982-04-06 | American Hoechst Corporation | Light beam scanning apparatus |
| SE439944B (en) * | 1980-12-05 | 1985-07-08 | Lars Hammarberg | ARMED BALK PROFILE AND SET FOR ITS PREPARATION |
| US4429948A (en) * | 1981-05-14 | 1984-02-07 | International Business Machines Corporation | Optical alignment compensation |
| JPS5879216A (en) * | 1981-11-06 | 1983-05-13 | Hitachi Ltd | Two beam scanning optical system |
| US4544228A (en) * | 1982-09-14 | 1985-10-01 | Spectra-Physics, Inc. | Scanning method using a rotating prism |
| US4861973A (en) * | 1987-06-18 | 1989-08-29 | Spectra-Physics, Inc. | Optical scan pattern generating arrangement for a laser scanner |
| FR2662515B1 (en) * | 1990-05-23 | 1993-10-08 | Etat Francais Delegue Armement | OPTICAL DEVICE FOR PRINTING A COLLIMATE LIGHT BEAM TRANSLATION MOVEMENT. |
| US5227910A (en) * | 1992-03-27 | 1993-07-13 | Khattak Anwar S | High resolution laser beam scanner and method for operation thereof |
| US5815329A (en) * | 1996-09-13 | 1998-09-29 | Umax Data Systems, Inc. | Tri-mirror multi-reflection optical path folding apparatus |
| DE102014108259A1 (en) * | 2014-06-12 | 2015-12-17 | Scanlab Ag | Device for laser material processing |
| EP3021153B1 (en) * | 2014-11-13 | 2018-12-12 | Canon Kabushiki Kaisha | Optical apparatus, processing apparatus, and article manufacturing method |
| WO2017029210A1 (en) | 2015-08-14 | 2017-02-23 | Laser Engineering Applications | Machining device |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3883683A (en) * | 1963-07-09 | 1975-05-13 | Us Army | High speed line scanner |
| DE2306185A1 (en) * | 1973-02-08 | 1974-08-15 | Agfa Gevaert Ag | METHOD AND DEVICE FOR COMPENSATING THE PYRAMID DEFECT OF A MIRROR WHEEL |
-
1978
- 1978-06-05 CA CA304,782A patent/CA1107105A/en not_active Expired
- 1978-06-08 AU AU36951/78A patent/AU519986B2/en not_active Expired
- 1978-06-09 NL NL7806306A patent/NL7806306A/en active Search and Examination
- 1978-06-09 IT IT24403/78A patent/IT1096713B/en active
- 1978-06-09 FR FR787817402A patent/FR2394105A1/en active Granted
- 1978-06-10 DE DE19782825550 patent/DE2825550A1/en not_active Withdrawn
- 1978-06-10 JP JP7028478A patent/JPS5418301A/en active Pending
- 1978-06-12 GB GB7826719A patent/GB2000321B/en not_active Expired
- 1978-06-12 SE SE7806778A patent/SE7806778L/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB2000321B (en) | 1982-01-27 |
| AU519986B2 (en) | 1982-01-07 |
| FR2394105B1 (en) | 1982-04-23 |
| IT1096713B (en) | 1985-08-26 |
| FR2394105A1 (en) | 1979-01-05 |
| IT7824403A0 (en) | 1978-06-09 |
| DE2825550A1 (en) | 1979-01-04 |
| GB2000321A (en) | 1979-01-04 |
| NL7806306A (en) | 1978-12-12 |
| SE7806778L (en) | 1978-12-11 |
| JPS5418301A (en) | 1979-02-10 |
| AU3695178A (en) | 1979-12-13 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1107105A (en) | Optical scanner and system for laser beam exposure of photo surfaces | |
| US4312590A (en) | Optical scanner and system for laser beam exposure of photo surfaces | |
| EP0288970B1 (en) | Optical system for flyingspot scanning system | |
| CA1159288A (en) | Light beam scanning apparatus | |
| US6445483B2 (en) | Optical scanning apparatus | |
| US5114217A (en) | Double-reflection light scanner | |
| JP3445691B2 (en) | Optical scanning device and adjustment method thereof | |
| JPS63304222A (en) | Laser light source device | |
| CA2376143C (en) | Multibeam multi-wavelength internal drum recording apparatus | |
| JP2000105347A (en) | Multibeam light source device, multibeam scanner and image forming device | |
| US4690485A (en) | Flat bed optical scanning beam deflection system | |
| EP0699308B1 (en) | Optical scanning apparatus | |
| JPH02226111A (en) | Optical deflecting device | |
| US5323259A (en) | Light deflecting device | |
| US5307198A (en) | Scanner with combined predictive and diffractive feedback control of beam position | |
| EP1352285B1 (en) | Refractive optical deflector | |
| US4934780A (en) | Constant deviation scanning apparatus | |
| CA2253623A1 (en) | Method and apparatus for illumination of light-sensitive materials | |
| US5680243A (en) | Optical scanner for finite conjugate applications | |
| US4793672A (en) | Constant deviation scanning apparatus | |
| US5381259A (en) | Raster output scanner (ROS) using an overfilled polygon design with minimized optical path length | |
| JPH01239520A (en) | Beam deflecting device and beam scanning device | |
| JPH03131817A (en) | Light beam scanning optical device | |
| JP3420643B2 (en) | Optical scanning device | |
| JPH09236764A (en) | Optical scanning device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |