JP2006343580A - Scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanner in which the intensity distribution of a laser light is adjustable in an optical system composed of a combination of an OFS and a synthesized multibeam and the quality of a picture is improved. <P>SOLUTION: A light emitting part of the scanner comprises: a plurality of light sources; a plurality of the first optical elements which convert luminous fluxes emitted from the light sources into weakly divergent light or weakly convergent light; a synthesizing means which synthesizes the luminous fluxes emitted from the plurality of light sources and emits into substantially the same directions; and a second optical element which is provided at downstream side of the synthesizing means and transforms the luminous fluxes passing through the synthesizing means into a parallel luminous flux in a main scanning direction. The light emitting part is held movably in the main scanning direction which intersects with the parallel luminous flux substantially at right angle, and both of the plurality of the first optical elements and the second optical element are adhered and fixed from a form which is freely movable in three axis directions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

    The present invention relates to a scanning device such as a copying machine or a printer.

  In recent years, as the speed of digital copying machines, laser printers, etc. increases, the number of reflecting surfaces of the polygon mirror can be increased and an overfilled scanner (hereinafter abbreviated as OFS) optical system that can perform high-speed rotational scanning by reducing the diameter. A technique relating to a multi-beam method in which the number of light sources is increased and exposure is simultaneously performed with a plurality of light beams is known. In order to further increase the scanning speed, a configuration combining both techniques is also considered.

  By the way, as shown in FIG. 7, the OFS optical system enters the light beam emitted from the light source 701 with a width wider than the facet surface of the polygon mirror 702, and partially reflects the wide light beam while the polygon mirror 702 rotates. To form a scanning beam. Therefore, it is greatly affected by the light intensity distribution in the main scanning direction of the light beam incident on the polygon mirror 702. If there is uneven light intensity distribution in the incident light beam, it becomes the light intensity distribution of the scanning line on the scanned surface as it is. Appears as image density unevenness.

  As a factor of such light intensity distribution, a semiconductor laser as a light source always has a light intensity distribution that originally shows a Gaussian distribution, but the chip in the laser unit is inclined in the main scanning direction with respect to the optical axis. This has a greater effect.

Japanese Patent Application Laid-Open No. 2001-281586 proposes a mechanism for adjusting a laser unit composed of a single light source and a collimator lens in the main scanning direction to solve such a problem.
JP 2001-281586 A

  In recent years, a configuration combining an OFS optical system and a multi-beam has been considered in order to achieve faster image formation than ever. In this case, it is technically difficult to make a multi-beam monolithic type in which all parts of a plurality of high-power lasers necessary for OFS are integrated into one semiconductor chip. For this reason, a configuration in which a plurality of independent light sources are fixed to a laser mount to form a multi-beam is conceivable. However, if a tip tilt occurs when each light source is fixed, unevenness in the intensity distribution of the light beam incident on the polygon mirror occurs and appears as image density unevenness.

  An object of the present invention is to provide a scanning device that can adjust the intensity distribution of a laser beam and improve the quality of an image.

  In order to achieve the above object, the present invention has a light emitting portion and a plurality of reflecting surfaces that reflect the light beam emitted from the light emitting portion, and the width of the reflecting surface is larger than the width of the light beam incident on the reflecting surface. In a scanning device including a narrow rotating polygon mirror and an imaging optical system that forms an image of a light beam scanned by the rotating polygon mirror on a photoconductor, the light emitting unit emits a plurality of light sources and the light sources. A plurality of first optical elements for converting the emitted light beam into weakly diverging light or weakly convergent light, a combining means for combining the light beams emitted from the plurality of light sources and emitting them in substantially the same direction, and downstream of the combining means And a second optical element that converts the light beam that has passed through the combining means into a parallel light beam in the main scanning direction, and is held so as to be movable in the main scanning direction substantially orthogonal to the optical axis of the parallel light beam. And the plurality of first optical elements When, with the second optical element, characterized in that it is bonded and fixed from the movable form with a degree of freedom in both three-axis directions.

  Further, the present invention generally combines a plurality of light sources, a plurality of first optical elements that convert light beams emitted from the light sources into weakly divergent light or weakly convergent light, and light beams emitted from the plurality of light sources. A laser unit is formed by combining a combining unit that emits light in the same direction and a second optical element that is provided downstream of the combining unit and converts a light beam that has passed through the combining unit into a parallel beam in the main scanning direction. In addition, the plurality of first optical elements and the second optical elements are both bonded and fixed in a form that can move with a degree of freedom in three axial directions.

  According to the present invention, the intensity distribution of laser light can be adjusted, and the quality of an image can be improved.

(First embodiment)
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a laser scanning device according to an embodiment of the present invention cut in the main scanning direction.

  In FIG. 1, reference numeral 1 denotes a multi-beam laser unit. The multi-beam laser unit 1 converts the light beams emitted from the two light sources 2a and 2b each formed of a laser diode into weakly divergent light by the spherical lenses 3a and 3b, and then combines the two light beams by the combining prism 5. The light is emitted in substantially the same direction. The light sources 2 a and 2 b and the spherical lenses 3 a and 3 b are integrally held by a laser mount 4. In the holding form, the light sources 2a and 2b are fixed to the laser mount 4 by press fitting, and the spherical lenses 3a and 3b are fixed by adhesion. A method of bonding the spherical lenses 3a and 3b will be described in detail with reference to FIG.

  FIG. 5A is a perspective view showing a state before the spherical lens is bonded. As shown in the figure, the spherical lenses 3a and 3b and the cylindrical portion of the laser mount 4 are configured such that a predetermined gap is secured over the entire circumference of the spherical lens. By this gap, the spherical lens can be freely moved in the directions of the three-axis arrows in FIG. 5A (a form that can move with a degree of freedom in the three-axis directions). During actual adjustment, the optical lens and focus are monitored by a measurement system (not shown) while moving a spherical lens held by a tool (not shown) in the three-axis directions indicated by the arrows, and the spherical surface is obtained when they reach a predetermined value. The position of the lens is determined, and as shown in FIG. 5B, the gap between the spherical lens and the laser mount cylindrical portion is filled with an ultraviolet curing adhesive, and then cured and fixed by irradiating ultraviolet rays. Note that an ultraviolet curable adhesive may be filled in advance before adjustment. The type of adhesive is not limited to the ultraviolet curable type.

  The combining prism 5 of FIG. 1 includes a triangular prism 5a and a parallel prism 5b, and a multilayer film that functions as a polarizing beam splitter is formed on a joint surface (polarization surface) between the triangular prism 5a and the parallel prism 5b. The parallel prism 5b includes a half-wave plate 5c on the light incident surface. Since the half-wave plate 5c rotates the polarization direction by 90 ° only for the light beam emitted from the light source 2b, the light beams emitted from the two light sources are combined on the polarization plane in the prism and emitted in substantially the same direction.

The light beams emitted from the different light sources 2 a and 2 b are combined by the combining prism 5. Although this embodiment will be described with an example of two light sources, it can also be applied to multi-beam formation with two or more light sources. The beam pitch in the sub-scanning direction is adjusted by rotating the combining prism 5 in the illustrated direction. At this time, the light beam incident on the combining prism 5 is not a parallel light beam but weakly divergent light.

  A convex lens 6 newly provided in the present embodiment has power in the main scanning direction, and functions to convert weakly diverging light emitted from the combining prism 5 into a parallel light beam in the main scanning direction. At this time, it is necessary to determine the position of the convex lens 6 with high accuracy with respect to the optical axis. As described above, since the position can be determined while moving the spherical lens 3a in the triaxial direction upstream of the combining prism 5, the position of the optical axis incident on the convex lens 6 varies. Therefore, in this embodiment, as shown in FIG. 6, the convex lens 6 is also provided with a gap around the lens like the spherical lenses 3a and 3b, and after the position is determined in a state where it can move in the multiaxial direction, Filled with UV-curing adhesive and fixed. Of course, an ultraviolet curable adhesive may be filled in advance before adjustment, and the type of adhesive is not limited to the ultraviolet curable type.

  There is no problem even if the laser unit is moved in the main scanning direction in the case of parallel light such as a light beam emitted from a laser unit comprising a single light source and a collimator lens. However, when divergent light or convergent light is emitted from the multi-beam laser unit 1, if the positional relationship with the diverging lens 7 is changed by moving the multi-beam laser unit 1 in the main scanning direction, the photosensitive member is a photosensitive member. There arises a problem that the image surface tilt occurs in the drum 15 and the focus surfaces are shifted at both ends of the photosensitive drum 15. Therefore, a convex lens 6 is provided in the multi-beam laser unit 1 so that the light beam emitted from the multi-beam laser unit 1 becomes parallel light.

  By fixing the spherical lenses 3a and 3b and the convex lens 6 in this way, the multi-beam laser unit 1 as a whole can adjust the optical axis with high accuracy. In this embodiment, the light beam that has passed through the spherical lens is weakly divergent light, but this may be a convergent light beam.

  The light beam emitted from the multi-beam laser unit 1 sequentially passes through the diverging lens 7, the diaphragm 8, and the cylindrical lens 9 having power in the sub-scanning direction, and is bent by the incident mirror 10. 12, and enters the polygon mirror 13.

  The light beam incident on the polygon mirror 13 having a plurality of reflection surfaces becomes a parallel light beam (the width of this light beam is wider than the width of each reflection surface of the polygon mirror 13) when passing through the fθ lenses 11 and 12. Is irradiated over the adjacent surface to form an OFS configuration.

  The deflected light beam reflected by the polygon mirror 13 passes through the fθ lenses 11 and 12 again, and further passes through the long lens 14 and forms an image in a spot shape on the photosensitive drum 15 that is the surface to be scanned.

  The long lens 14 has power in the sub-scanning direction, forms a light beam in the sub-scanning direction, and corrects the tilt of the polygon mirror 13 by making the deflection point of the polygon mirror 13 and the drum surface 15 substantially conjugate. ing. The fθ lenses 11 and 12 and the long lens 14 are referred to as an imaging optical system.

  Next, laser beam intensity distribution adjustment will be described with reference to FIGS. 2 and 3 are explanatory diagrams for adjusting the intensity distribution of the laser beam in the laser scanning device according to the embodiment of the present invention. In each figure, the cross section of the incident system in the main scanning direction is schematically shown. And shows the intensity distribution of the incident light beam.

Here, FIG. 2A shows an ideal state where the light sources 2a and 2b, which are two semiconductor lasers, have no chip tilt and the two light intensity distributions are aligned at the center of the optical axis. In such a state, since the light beams emitted from the light sources 2a and 2b have the same optical axis and intensity distribution,
The light intensity decreases in a well-balanced manner from the center of the image toward both ends, and the light intensity unevenness is minimized.

  On the other hand, FIG. 2B shows a state in which the tip tilt α occurs in one light source 2b, and the two light intensity distributions are asymmetric with respect to the optical axis. Due to this asymmetry of the light intensity distribution, the difference (ΔE) in the light intensity distribution becomes larger than that in (a), which directly becomes exposure unevenness in the main scanning direction of the photosensitive drum surface, and the density is different at both ends of the image. This causes image degradation.

  In such a case, in the present embodiment, the multi-beam laser unit 1 is shifted in parallel in the direction of the arrow in the main scanning plane perpendicular to the optical axis from the state shown in FIG. By doing so, the center of the light intensity distribution of the laser can be made substantially coincident with the optical axis so as to change from FIG. 3 (a) to FIG. 3 (b). The state can be changed to substantially the same state as in FIG.

  At this time, as described above, the light beam after passing through the prism by the convex lens 6 is a parallel light beam in the main scanning direction. Therefore, even if the multi-beam laser unit 1 is shifted in the main scanning direction, Image plane tilt does not occur.

  Next, an adjustment mechanism for adjusting the light intensity distribution in the present embodiment will be described with reference to FIG. FIG. 4 is a perspective view for explaining an adjustment mechanism of the laser scanning device according to the embodiment of the present invention, and shows a part of the configurations of the multi-beam laser unit 1 and the case 16 before being attached. The multi-beam laser unit 1 and the case 16 are installed inside an image forming apparatus such as a copying machine or a printer.

  A mounting surface 16a of the multi-beam laser unit 1 provided in the case 16 is perpendicular to the optical axis, and pins 16b and 16c as fitting convex portions of the multi-beam laser unit 1 are provided in the mounting surface 16a. Is provided. The pins 16b and 16c are axes included in a main scanning plane that passes through the optical axis.

  The multi-beam laser unit 1 is provided with a long hole 1b and a long hole 1c having a center at a position facing the pins 16b and 16c on the case side. After shifting in a direction perpendicular to the optical axis in the scanning plane, the screws 17 and 18 can be used to fix the light intensity distribution of the laser described above.

  The shift mechanism of the multi-beam laser unit 1 is not limited to the configuration described here as long as it can be moved and fixed in the main scanning direction while the position in the sub-scanning direction is fixed.

  According to the present invention, in a laser scanning device that combines an OFS optical system and a combined laser unit, the light source, spherical lens, combining prism, and convex lens are integrally adjusted in the main scanning direction, and the light intensity of the laser diode is adjusted. The distribution can be adjusted and the quality of the image can be improved.

  Further, by adopting an adhesive fixing configuration in which the spherical lens and the convex lens in the multi-beam laser unit 1 are all movable in a plurality of dimensions, it is possible to perform accurate optical axis adjustment as a multi-beam laser unit.

It is a top view of a laser scanning device. It is explanatory drawing in the case of performing intensity distribution adjustment of the laser beam in a laser scanning apparatus. It is explanatory drawing in the case of performing intensity distribution adjustment of the laser beam in a laser scanning apparatus. It is a perspective view explaining the adjustment mechanism of a laser scanning device. It is the perspective view which showed the state before and behind bonding a spherical lens. It is the perspective view which showed the state which adhere | attached the convex lens on the multi-beam laser unit. It is a figure which shows an overfilled scanner optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multi-beam laser unit 2a, 2b Light source 3a, 3b Spherical lens 5 Synthetic prism 6 Convex lens 7 Diverging lens 8 Diaphragm 9 Cylindrical lens 11, 12 f (theta) lens 13 Polygon mirror 14 Long lens 15 Photosensitive drum 16 Case

Claims (3)

A light emitting unit;
A rotating polygon mirror having a plurality of reflecting surfaces for reflecting the light beam emitted from the light emitting unit, and the width of the reflecting surface being narrower than the width of the light beam incident on the reflecting surface;
An imaging optical system that forms an image on a photosensitive member with a light beam scanned by the rotary polygon mirror,
The light emitting unit is substantially identical by combining a plurality of light sources, a plurality of first optical elements that convert light beams emitted from the light sources into weakly diverging light or weakly convergent light, and light beams emitted from the plurality of light sources. And a second optical element that is provided downstream of the combining unit and converts a light beam that has passed through the combining unit into a parallel beam in the main scanning direction, and an optical axis of the parallel beam While being held so as to be movable in a substantially orthogonal main scanning direction,
The scanning apparatus, wherein the plurality of first optical elements and the second optical element are both bonded and fixed in a form in which they can move with a degree of freedom in three axial directions.   The light emitting unit is configured as one unit, and the unit can be freely positioned in a main scanning direction with respect to a laser scanning device including the rotary polygon mirror and the imaging optical system. 2. The scanning device according to 1. Combining a plurality of light sources, a plurality of first optical elements that convert light beams emitted from the light sources into weakly diverging light or weakly convergent light, and combining light beams emitted from the plurality of light sources and emitting them in substantially the same direction And a second optical element that is provided downstream of the combining unit and converts the light beam that has passed through the combining unit into a parallel beam in the main scanning direction forms a laser unit,
The scanning apparatus, wherein the plurality of first optical elements and the second optical element are both bonded and fixed in a form in which they can move with a degree of freedom in three axial directions.

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