JP2006323278A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner in which optical performance is stabilized by commonly using a focusing lens, and which can suppress color slippage in a subscanning direction, while attaining cost reduction. <P>SOLUTION: The optical scanner is provided with a plurality of light sources, a polygon mirror 5 which deflects the beams from the light sources in a main scanning direction, lenses 11 and 12 which focus the deflected beams onto faces to be scanned 50Y, 50M, 50C and 50 K, a plurality of return mirrors 31 to 38 for dividing and guiding the beams passing through the lenses to the faces to be scanned, and a lens 13 which focuses respective separated beams onto the face to be scanned. All face shapes of the lens 12 is symmetrical in a subscanning direction and the face shape of the first face of a third lens is asymmetrical in both main and subscanning directions. The number of the return mirrors 31 to 38 are three in one upper side optical path with respect to the polygon mirror, two in a lower side optical path, one in the other side optical path, and two in the other upper side optical path. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device, and more particularly to an optical scanning device that scans a plurality of beams, which are modulated based on image data, on each surface to be scanned using a single deflector.

  In recent years, in an image forming apparatus such as a full-color copying machine or printer, four photoconductors are juxtaposed corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black). The tandem method in which images of the respective colors formed on the respective photoconductors are transferred to an intermediate transfer belt and synthesized is the mainstream. In this type of tandem image forming apparatus, for example, there is an optical scanning apparatus that draws an image by simultaneously scanning four beams on each photoconductor using a single deflector (polygon mirror). It is installed.

  By the way, in this type of optical scanning device, a problem arises that the drawing line on the photoconductor is curved in the sub-scanning direction (hereinafter referred to as bow). The bow is more prominent when the beam is incident on the deflector in the sub-scanning direction with an inclination angle. If the bow is large, the scanning line becomes bowed and the image deteriorates. Further, if the bow bending direction is different on each photoconductor, the color shift in the sub-scanning direction becomes large.

  Therefore, in Patent Document 1, in order to align the bow bending direction due to the linear expansion change of the housing with temperature change, the number of folding mirrors is different evenly and oddly on the left and right of the deflector, and evenly and oddly the same number on the top and bottom. An optical scanning device constituted by the above is disclosed. However, this optical scanning device uses a non-common lens for all the optical systems, which increases the cost. Further, since the beam is not obliquely incident on the deflector in the sub-scanning direction, the deflector becomes thick, which is also a factor of high cost. Although the number of folding mirrors varies evenly and oddly on the left and right of the deflector, the upper and lower sides match even and odd numbers, so the bow bending direction due to the linear expansion of the housing can be aligned, but the design There is a problem in that it is impossible to align the curved directions of the remaining bow with four colors.

Further, in Patent Document 2, a first imaging optical system, a folding mirror, and a second imaging optical system are disposed symmetrically on the left and right sides of the deflector, and further, the second imaging optical system is provided. An optical scanning device is disclosed in which the bow is corrected by being shifted in the sub-scanning direction. However, this optical scanning device has a problem that the surface shape of the second imaging optical system is symmetric in both the main scanning direction and the sub-scanning direction, and the degree of freedom in design is small. In addition, since the combination of the number of folding mirrors between the first and second imaging optical systems is the same on the left and right sides, the second imaging optical system is eccentrically arranged in the sub-scanning direction. However, the bow can be corrected to some extent, but there is a problem that the curved direction of the bow that remains in the design cannot be aligned with four colors.
JP 2002-202472 A JP 2003-57585 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical scanning device capable of ensuring the stability of optical performance by using a common imaging lens and reducing color shift in the sub-scanning direction while realizing cost reduction. There is.

In order to achieve the above object, the present invention provides a plurality of light sources, a deflector for deflecting the beam from the light source in the main scanning direction, and forming an image of the beam deflected by the deflector on the surface to be scanned. A first imaging optical system, a plurality of optical path folding mirrors for separating and guiding the beams transmitted through the first imaging optical system to respective scanning surfaces, and scanning each separated beam In an optical scanning device including a second imaging optical system that forms an image on a surface,
The deflector is installed in common for each light source, and the lenses constituting the first imaging optical system are all symmetrical in the sub-scanning direction and are the same on the left and right sides of the deflector. The second imaging optical system has the same configuration with respect to all the optical paths and is arranged in the same direction, and has at least one lens, and the surface shape of at least one surface of the lens is the main scanning. Both the direction and the sub-scanning direction are asymmetric,
With respect to the number of optical path folding mirrors, the number of arrangement of one upper optical path is A, the number of arrangement of one lower optical path is B, the number of arrangement of the other lower optical path is C, and the arrangement of the other upper optical path. When the number of sheets is D, the following conditions are satisfied:
| A−B | = 2 × i + 1
| C−D | = 2 × j + 1
| A−D | = 2 × m + 1
However, i, j, and m are characterized by an integer of 0 or more.

  In the optical scanning device according to the present invention, the left and right sides of the deflector refer to both sides that are symmetrical about the rotation axis of the deflector. The lower optical path refers to an optical path in which the beam deflected by the deflector travels on the scanned surface side about the optical axis of the lens, and the upper optical path travels on the opposite side of the scanned surface. Say.

  According to the optical scanning device of the present invention, each of the first and second imaging optical systems can be provided with a free curved surface effectively, so that the respective lenses can be shared, and the cost can be reduced. It can be achieved and can be molded by the same lens processing apparatus, and the optical performance is stabilized. In particular, by making at least one surface of the lens of the second imaging optical system asymmetric in both the main scanning direction and the sub-scanning direction, it cannot be sufficiently corrected by designing the first imaging optical system or adjusting the deflection of the folding mirror. The bow can be corrected satisfactorily.

  Also, by setting the number of folding mirrors so as to satisfy the above conditional expression, that is, by setting the upper optical path, the lower optical path, and the left and right to be different even and odd, the mirrors were folded back. The curve direction of the bow of the drawing line on the subsequent scanning surface can be made uniform, and color shift in the sub-scanning direction can be effectively suppressed.

  In the optical scanning device according to the present invention, it is preferable that each of the lenses constituting the second imaging optical system is formed by the same mold. This greatly contributes to stabilization of optical performance and cost reduction.

  Further, it is preferable that the number of optical path folding mirrors arranged between the second imaging optical system and the surface to be scanned is the same in each optical path. It does not impair aligning the bow bending direction on the scanned surface.

  Hereinafter, embodiments of an optical scanning device according to the present invention will be described with reference to the accompanying drawings.

(See Examples, FIGS. 1-3)
FIG. 1 shows a concept of a three-dimensional arrangement, FIG. 2 shows an optical path configuration from a light source unit to a deflector, and FIG. 3 shows a sub-scan section.

  This optical scanning device is configured as an exposure scanning unit of an image forming apparatus based on tandem electrophotography, and has four photosensitive drums 50 (50Y, 50M, 50C, and 50K), as shown in FIG. A color image is formed. The four-color image (electrostatic latent image) formed on the photosensitive drum 50 is developed with toner, and then primary-transferred / combined on an intermediate transfer belt (not shown), and secondary-imaged on a recording material. Transcribed. This type of image forming process is well known and will not be described.

  In this optical scanning device, as shown in FIG. 2, the light source unit is composed of four laser diodes 1, a collimator lens 2, a cylinder lens 3, and a half mirror 4, and enters a single polygon mirror 5. That is, the beam (diffused light) emitted from each laser diode 1 is converted into parallel light by the collimator lens 2 and converted by the cylinder lens 3 into a linear shape on the deflection surface of the polygon mirror 5 in the sub-scanning direction Z. The Thereafter, the beams are combined in the main scanning direction Y by the half mirror 4 and guided to the polygon mirror 5.

  As shown in FIG. 2B, the respective light source sections are arranged at a predetermined inclination angle θ / 2 with respect to the main scanning direction axis Y ′ of the polygon mirror 5 in the sub-scanning direction Z. That is, each beam is obliquely incident on the deflection surface of the polygon mirror 5 with an inclination angle θ / 2 within the plane in the sub-scanning direction Z.

  The beam from the light source unit does not necessarily need to be incident obliquely on the polygon mirror 5, but if it is incident obliquely, the beam can be separated into the upper optical path and the lower optical path without increasing the thickness of the polygon mirror 5. Become.

  As shown in FIGS. 1 and 3, a first lens 11 constituting a first imaging optical system for imaging each beam deflected in the main scanning direction Y by the polygon mirror 5 on each photosensitive drum 50. And the second lens 12, a plurality of optical path folding mirrors 31 to 38 for guiding the beam transmitted through the lenses 11 and 12 to each photosensitive drum 50, and the separated beams are connected to each photosensitive drum 50. A third lens 13 (13Y, 13M, 13C, 13K) constituting a second imaging optical system for imaging, and dust-proof window glasses 29Y, 29M, 29C, 29K are arranged.

  The first and second lenses 11 and 12 are arranged in front of the optical path folding mirrors 31 to 38 on the left and right sides around the rotation axis 5a (see FIG. 3) of the single polygon mirror 5, and the surface shape is It is symmetric in the sub-scanning direction Z. That is, it is symmetrical in the vertical direction in FIG. The surface shape data will be described later (see Tables 3 to 5).

  The third lenses 13Y, 13M, 13C, and 13K are all of the same configuration formed by the same mold, and are arranged in the main scanning direction Y. The surface shape of the first surface (beam incident side) is the main scanning. Both the direction Y and the sub-scanning direction Z are asymmetric. The third lens 13 makes the first surface asymmetric in both the main scanning direction and the sub-scanning direction, so that a bow that cannot be corrected sufficiently by the design of the first and second lenses 11 and 12 and the deflection adjustment of the folding mirror is improved. It can be corrected. The surface shape data will be described later (see Table 6).

  Concerning the number of optical path folding mirrors 31 to 38, the number of arrangement of one upper optical path (for magenta exposure) is A, the number of arrangement of one lower optical path (for yellow exposure) is B, and the lower number of the other. When the arrangement number of the side optical path (for black exposure) is C and the arrangement number of the other upper optical path (for cyan exposure) is D, A is 3, B is 2, C is 1, D is 2 It consists of.

  That is, in FIG. 3, the number of the folding mirrors arranged is such that A and B corresponding to the upper and lower sides on the left side of the polygon mirror 5 are 3 and 2 different in even and odd numbers, and C and D corresponding to the upper and lower sides are 1 on the right side. Even number and odd number are different between two sheets. In addition, the optical paths A and D that pass through the upper side of the first and second lenses 11 and 12 are three and two, and the even and odd numbers are different, and the optical paths B and C that pass through the lower side are two and one. Even and odd are different.

(Bow bow direction, see Fig. 4)
FIG. 4 is a conceptual diagram relating to the bending (bow) of the drawing line in the sub-scanning direction on the surface to be scanned. Here, the state in which the bending directions of the bows 51a to 51f on the scanned surfaces 50a to 50f of the optical path that passes through the upper side with respect to the first and second lenses 11 and 12 change according to the number of the folding mirrors 30 arranged. Is shown. In FIG. 4, the bow of the optical path that passes through the lower side is omitted, but is curved in a direction in which the bow of the upper optical path is inverted because of vertical symmetry.

  As can be seen from FIG. 4, when the even and odd numbers are different between the left and right sides of the polygon mirror 5, the bow bending directions coincide. For example, the scanning surfaces 50a, 50c, and 50e match, and the scanning surfaces 50b, 50d, and 50f match. Thus, by setting the number of folding mirrors so as to satisfy the conditional expression described in claim 1 of the present application, the bow bending directions coincide on the surface to be scanned, that is, the positional deviation in the sub-scanning direction Z. The generation direction of the higher order components can be made uniform, and the color shift of the image can be effectively suppressed.

  In this embodiment, the number of folding mirrors arranged between the third lens 13 and the surface to be scanned 50 is zero in each optical path. However, when the folding mirrors are arranged between them, the same number in each optical path is necessary to ensure the coincidence of the bow bending directions.

(Optical element arrangement and configuration data)
Table 1 below shows the arrangement of the optical elements in the above example, and Table 2 shows eccentricity data of the seventh surface and the eighth surface. Table 3 shows free-form surface coefficient data of the first surface (first surface of the first lens 11), Table 4 shows free-form surface coefficient data of the second surface (second surface of the first lens 11), and Table 5 shows Table 4 shows the free-form surface coefficient data of the fourth surface (the second surface of the second lens 12), and Table 6 shows the free-form surface coefficient data of the fifth surface (the first surface of the third lens 13). These free-form surfaces are calculated by the free-form surface equation shown in Equation (1).

  As can be seen from Tables 3 to 5, only the even-numbered coefficient is used in the sub-scanning direction Z, and the first and second lenses 11 and 12 have surface shapes that are symmetric with respect to the sub-scanning direction Z. ing. Thus, a common lens can be used for the upper optical path and the lower optical path, and the cost is reduced. The third lens 13 has the same free-form surface data in each optical path.

(Other examples)
The optical scanning device according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

It is a three-dimensional arrangement conceptual diagram showing an example of an optical scanning device according to the present invention. The optical path structure from the light source part of the said Example to a deflector is shown, (A) is a XY top view, (B) is a XZ side view. It is a XZ side view which shows the optical path structure from the deflector of the said Example to a to-be-scanned surface. It is a conceptual diagram which shows the curve direction of the bow on a to-be-scanned surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser diode 5 ... Polygon mirror 11 ... 1st lens 12 ... 2nd lens 13 ... 3rd lens 29 ... Window glass 30-38 ... Folding mirror 50 ... Photoconductor drum (surface to be scanned)
51a-51f ... Bow

Claims (3)

A plurality of light sources, a deflector for deflecting a beam from the light source in the main scanning direction, a first imaging optical system for imaging the beam deflected by the deflector on a surface to be scanned, the first A plurality of optical path folding mirrors for separating and guiding a beam transmitted through one imaging optical system to each scanned surface, and a second imaging optical for imaging each separated beam on the scanned surface In an optical scanning device comprising a system,
The deflector is installed in common for each light source,
The lenses constituting the first imaging optical system are all symmetrical in the sub-scanning direction, and the same lens is disposed on both the left and right sides of the deflector.
The second imaging optical system has the same configuration for all optical paths and is arranged in the same direction and has at least one lens. The surface shape of at least one surface of the lens is the main scanning direction and the sub-scanning direction. Asymmetric in the scanning direction,
With respect to the number of optical path folding mirrors, the number of arrangement of one upper optical path is A, the number of arrangement of one lower optical path is B, the number of arrangement of the other lower optical path is C, and the other upper optical path with respect to the deflector. Satisfying the following conditions, where D is the number of sheets arranged:
| A−B | = 2 × i + 1
| C−D | = 2 × j + 1
| A−D | = 2 × m + 1
However, i, j, m is an optical scanning device characterized by an integer of 0 or more.   2. The optical scanning device according to claim 1, wherein each of the lenses constituting the second imaging optical system is formed by the same mold. 3. The optical scanning device according to claim 1, wherein the number of optical path folding mirrors arranged between the second imaging optical system and the scanned surface is the same in each optical path. .

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