Source: http://www.google.com/patents/US6717704?dq=7565338
Timestamp: 2014-11-28 07:12:53
Document Index: 170008957

Matched Legal Cases: ['art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52', 'art 52']

Patent US6717704 - Optical scanning system - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn optical scanning system for scanning a plurality of light beams on scanned surfaces, such as photosensitive drums, includes a light source, a front optical system, a deflector (e.g., a rotating polygon mirror) that scans the light beams in a main scanning direction, and a rear optical system for directing...http://www.google.com/patents/US6717704?utm_source=gb-gplus-sharePatent US6717704 - Optical scanning systemAdvanced Patent SearchPublication numberUS6717704 B2Publication typeGrantApplication numberUS 10/397,301Publication dateApr 6, 2004Filing dateMar 27, 2003Priority dateApr 8, 2002Fee statusPaidAlso published asUS20030189743Publication number10397301, 397301, US 6717704 B2, US 6717704B2, US-B2-6717704, US6717704 B2, US6717704B2InventorsYoko NakaiOriginal AssigneeFuji Photo Optical Co., LtdExport CitationBiBTeX, EndNote, RefManPatent Citations (5), Referenced by (6), Classifications (13), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetOptical scanning systemUS 6717704 B2Abstract An optical scanning system for scanning a plurality of light beams on scanned surfaces, such as photosensitive drums, includes a light source, a front optical system, a deflector (e.g., a rotating polygon mirror) that scans the light beams in a main scanning direction, and a rear optical system for directing the light beams toward the scanned surfaces so that separations of the light beams in a sub-scanning direction that is orthogonal to the main scanning direction increase due to the light beams entering the rear optical system at diverging angles. The front optical system includes a lens group that is adjacent to the deflector and is of negative refractive power at least in the second direction. The rear optical system includes cylindrical lens parts that are oppositely inclined relative to the optical axis in a plane that includes the sub-scanning direction in order to correct curvatures of the scanning lines.
BACKGROUND OF THE INVENTION Optical scanning systems are conventionally used to form images in laser beam printers and similar devices. The optical scanning system emits a light beam, conventionally a laser beam, that scans as a light spot along a scanned surface where photosensitive material is present. More precisely, the optical scanning system includes a collimator lens to collimate a light beam emitted from a light source, such as a semiconductor laser device, and then uses an optical deflector, such as a high-speed rotating polygon mirror, to deflect the collimated light beam onto a scanned surface, such as a photosensitive drum surface.
BRIEF SUMMARY OF THE INVENTION The present invention relates to an optical scanning system in which plural light beams are spaced to be separable on the image side of an optical deflector and the optical deflector has a small thickness in the sub-scanning direction so that high speed printing can be realized in optical scanning devices, such as laser printers.
FIG. 4 shows the light beams of FIG. 1 as seen in enlarged cross-sectional views along the lines IVA�IVA, IVB�IVB, and IVC�IVC of FIGS. 3A-3B;
DETAILED DESCRIPTION The present invention will now be described in terms of preferred embodiments of the invention with reference to the attached drawings. First, a preferred embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 shows a plan view of the basic components of the optical scanning system of a preferred embodiment of the invention in the plane that includes the main scanning direction. FIG. 2 shows a cross-sectional view along line II�II of FIG. 1, which is a plane that includes the sub-scanning direction. The splitting mirror 8 and folding mirrors 9A to 9D (that will be described later) in FIG. 2 are omitted in FIG. 1 and the folded optical paths are shown as straightened in FIG. 1.
The optical scanning system includes a light source 1 that emits plural light beams, a front optical system PRE provided in the optical path of the light beams L1 to L4 from the light source 1, a polygon mirror 4 which is used as an optical deflector that is positioned at the rear of the front optical system and shared by the light beams L1 to L4, and a rear optical system PST provided between the polygon mirror 4 and the scanned surface 7. In the description which follows, �front� refers to the light source 1 side of the polygon mirror 4 and �rear� refers to the side after reflection from the polygon mirror 4.
FIG. 4 shows the light beams of FIG. 1 in enlarged cross-sectional views along the lines IVA�IVA (left column), IVB�IVB (middle column), and IVC�IVC (right column) of FIGS. 3A and 3B. The cross-sectional views are in the direction orthogonal to the directions of travel of the light beams L1 to L4 while they pass through the second optical system 3. The left column of FIG. 4 shows the cross-sectional view of the light beams L1 to L4 at the line IVA�IVA in FIGS. 3A-3B between the first cylindrical lens 31A and the spherical lens 31B. The first cylindrical lens 31A has refractive power only in the first direction. Therefore, the cross-sections of the light beams L1 to L4 shown in the left column of FIG. 4 are extended in the first direction, the main scanning or x-axis direction, but not in the second direction, the sub-scanning y-axis direction, as they approach the spherical lens 31B.
The center column of FIG. 4 shows the cross-sectional views of the light beams L1 to L4 at the line IVB�IVB in FIGS. 3A-3B that is immediately before the second cylindrical lens 32. After passing through the spherical lens 31B, the cross-sections of the light beams L1 to L4 shown in the center column of FIG. 4 are reduced in the y-axis direction and the separations of the light beams L1 to L4 become smaller as they approach the second cylindrical lens 32. Comparing the left column versus the center column of FIG. 4, the expansion in the x-axis direction and the reduction in the y-axis direction of the cross-sections of light beams L1 to L4 is evident.
The right column of FIG. 4 shows a cross-sectional view of the light beams L1 to L4 at the line IVC�IVC in FIGS. 3A-3B that is immediately before the reflecting surface 41 of the polygon mirror 4. After passing through the second cylindrical lens 32, the light beams L1 to L4 are individually converged in the second direction so as to have a linear cross-section. At the same time, the light beams L1 to L4 have larger separations in the second (y-axis) direction. After being reflected by the reflecting surface 41, the light beams L1 to L4 proceed with their separations progressively increasing to an extent that they are separable by the splitting mirror 8.
FIGS. 15A-15C show simplified enlarged cross-sectional views of the light incident surface of the fourth cylindrical lens 52 of FIG. 13 but with the cylindrical lens 52 inclined at different angles. FIGS. 16A-16C show simplified enlarged cross-sectional views of the light incident surface of the cylindrical lens of FIG. 13 but with the cylindrical lens inclined at angles different from those of FIGS. 15A-15C. FIGS. 15A-15C and FIGS. 16A-16C also show variations in curvature of the scanning lines on the imaginary surface 57 immediately after the first lens part 52A in accordance with inclinations of the first lens part 52A, including incident surface 53A, of the fourth cylindrical lens 52. For a simplified explanation, the original incident angles α1 and α2 of FIG. 10A are assumed to be �3 a� and �a� in FIGS. 15A-15C and FIGS. 16A-16C.
FIG. 15A shows the case in which the inclination angle θ of the first lens part 52A is �a.� In this case, the incident angle β1 of the light beam L1 at the incident surface 53A of the first lens part 52A is �2 a� and the incident angle β2 of the light beam L2 is zero. The light beam L2 enters at a right angle in the plane including the second direction. The scanning line K2 is subject to the curvature that occurs when the light beam L2 passes through the third cylindrical lens 51 obliquely. The third cylindrical lens 51 has a negative refractive power in the first direction. Therefore, the scanning line K2 has an opposite direction of curvature to the scanning line K1, as indicated in FIG. 15A.
FIG. 16A shows a case in which the inclination angle θ of the first lens part 52A is �b� which is slightly smaller than �a.� As shown in FIG. 16A, with the inclination angle being �b,� the third cylindrical lens 51 and the fourth cylindrical lens 52 produce the scanning line curvatures equal in magnitude but opposite in direction so that the curvatures cancel each other, preventing curvature in the scanning line K2. This eliminates the need of a cover glass for the light beam L2, which otherwise may be used for correcting the curvature, as described later. Here, the light beam L1 still produces a curved scanning line K1. Its curvature is smaller than the case in which the first lens part 52A is not inclined (as shown in FIG. 6A). As shown in FIGS. 16A-16C, as the inclination angle θ increases from θ equals b to θ equals 3 b, the curvature of K1 decreases. Thus, inclining the fourth cylindrical lens moderates the correction factor for curvature required of a cover glass, as will be described later.
FIG. 15B shows the case in which the inclination angle θ of the first lens part 52A is �2 a.� In this case, both of the incident angles of the light beams L1 and L2 to the incident surface 53A of the first lens part 52A are �a.� Both the light beams L1 and L2 produce the curved scanning lines K1 and K2. However, their curvature is much smaller than the scanning line K1 when the incident angle β1 equals 2 a as shown in FIG. 15A.
As shown in FIG. 16B, when the inclination angle θ is �2 b,� which is double the �b� that produces zero curvature in the scanning line K2, the scanning lines K1 and K2 have curvatures opposite in direction but nearly the same in magnitude. This moderates the correction factors for curvature by the cover glasses, described later, compared with the scanning line K1 in FIG. 15A. Furthermore, the same correction factors in absolute value facilitates the correction.
FIG. 15C shows the case in which the inclination angle θ of the first lens part 52A is �3 a.� In this case, the incident angle β2 of the light beam L2 to the incident surface 53A of the first lens part 52A is �2 a� and the incident angle β1 of the light beam L1 is zero. The light beam L1 enters at a right angle in the plane including the second direction. The scanning line K1 is subject to the curvature that occurs when the light beam L1 passes through the third cylindrical lens 51 obliquely.
FIG. 16C shows the case in which the inclination angle θ of the first lens part 52A is �3 b.� As shown in FIG. 16C, with the inclination angle being �3 b�, the third cylindrical lens 51 and the fourth cylindrical lens 52 produce scanning line curvatures that are equal in magnitude but opposite in direction so that they cancel each other, thereby preventing curvature of the scanning line K1. This eliminates the need for a cover glass for the light beam L1, as will be described later. Here, the light beam L2 still produces a curved scanning line K2. Its curvature is larger than the case in which the first lens part 52A is not inclined (as shown in FIG. 6A).
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4547038Apr 26, 1983Oct 15, 1985Tokyo Shibaura Denki Kabushiki KaishaApparatus for scanning a plane with light beamsUS5208456Aug 19, 1991May 4, 1993Xerox CorporationApparatus and system for spot position control in an optical output device employing a variable wavelength light sourceUS5526166Dec 19, 1994Jun 11, 1996Xerox CorporationFor a printing apparatusUS6061162 *Sep 3, 1999May 9, 2000Kabushiki Kaisha ToshibaMulti-beam exposure unitUS6313906Oct 20, 1998Nov 6, 2001Minolta Co., Ltd.Multibeam scanning device* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS7031039 *Jul 12, 2004Apr 18, 2006Canon Kabushiki KaishaOptical scanning apparatus and image forming apparatus using the sameUS7133177Feb 27, 2006Nov 7, 2006Brother Kagyo Kabushiki KaishaOptical scanner and image forming apparatusUS7224503Nov 2, 2005May 29, 2007Canon Kabushiki KaishaOptical scanning apparatus and image forming apparatus using the sameUS7474286Apr 27, 2005Jan 6, 2009Spudnik, Inc.Laser displays using UV-excitable phosphors emitting visible colored lightUS7869112Jul 25, 2008Jan 11, 2011Prysm, Inc.Beam scanning based on two-dimensional polygon scanner for display and other applicationsUS7911667 *May 31, 2006Mar 22, 2011Kabushiki Kaisha ToshibaOptical beam scanning device, image forming apparatus, optical beam scanning method* Cited by examinerClassifications U.S. Classification359/204.1, 347/244, 359/207.1, 347/243International ClassificationG02B26/10, G02B26/12, H04N1/113, B41J2/44, H04N1/036Cooperative ClassificationG02B26/123, G02B26/125European ClassificationG02B26/12F, G02B26/12DLegal EventsDateCodeEventDescriptionSep 7, 2011FPAYFee paymentYear of fee payment: 8Sep 14, 2007FPAYFee paymentYear of fee payment: 4Oct 26, 2004CCCertificate of correctionMar 27, 2003ASAssignmentOwner name: FUJI PHOTO OPTICAL CO., LTD., JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:NAKAI, YOKO;REEL/FRAME:013916/0218Effective date: 20030327Owner name: FUJI PHOTO OPTICAL CO., LTD. 1-324 UETAKESAITAMA CRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google