JP2006323279A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner in which a beam performance is kept with an inexpensive lens structure and color slippage is suppressed by aligning the curved direction of a bow on a face to be scanned. <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, turning back mirrors 31 to 38 for 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. The lenses 11 and 12 are symmetrical in their face shapes in a subscanning direction, the lens 13 is symmetrical in its face shape in the main scanning direction, and reversely arranged by 180° in the main scanning direction for an upper side optical path and a lower side optical path. The number of the mirrors 31 to 38 are two in the front stage of the lenses 13Y and 13M, one in the front stage of the lenses 13C and 13K, zero in the rear stage of the lenses 13Y and 13K, and one in the rear stage of the lenses 13M and 13C. <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.

  As an optical scanning device of this type of tandem image forming apparatus, A type (one optical scanning device, light source system 1, deflector 1, scanning system 1), and B type (four optical scanning devices). The light source system 1, the deflector 1, the scanning system 1) and the C type (one light scanning device, the light source system 4, the deflector 1, and the scanning systems 1 to 4).

  In the A type, since writing is possible only in one place by the optical scanning device, it is necessary to sequentially move the photosensitive member to the writing position, and it is difficult to increase the speed of image formation. Since the B type has the same number of optical scanning devices and photosensitive members, it is possible to speed up image formation. However, it is costly to provide four optical scanning devices (especially four expensive deflectors). It is disadvantageous in terms of space and space. The C type can realize high speed and low cost, and is also an object of the present invention.

  By the way, in the C type, the problem of how the beams from the four light source parts are incident on one deflector and how the beams after being deflected by the deflector are separated to obtain four photosensitive elements. The problem is whether it leads to the body. Furthermore, the C type is divided into a C1 type in which a scanning system is arranged on both sides of a deflector and a C2 type in which a scanning system is arranged only on one side.

  In the present invention, the C1 type is targeted, but it is still necessary to scan two beams on each side, and in order to guide the two beams onto the photosensitive member at different positions, an optical path separating means can be arranged in the scanning system. In addition, it is necessary to ensure the interval between two beams in the cross section in the sub-scanning direction. Patent Document 1 discloses an optical scanning device in which two beams are incident on the deflection surface at different angles in the sub-scanning direction, and a symmetric optical path is formed around the optical axis of the scanning lens system.

  However, when a pair of lens systems are used for the upper and lower optical systems, it is necessary to make the surface shape symmetrical in the sub-scanning direction. When the beam is incident on the deflector at an inclination angle in the sub-scanning direction, the surface is scanned. The curve in the sub-scanning direction (hereinafter referred to as bow) of the drawing line becomes remarkable. Such a bow results in a color-shifted image in the sub-scanning direction because the upper and lower optical systems have different bending directions. In Patent Document 1, the bow curving direction is aligned by setting the difference in the number of optical path folding mirrors between the first optical system arranged in the preceding stage and the second optical system arranged in the succeeding stage to 1.

  On the other hand, in order to improve the optical performance in the main scanning direction, the second optical system arranged after the separation mirror is made asymmetric in the main scanning direction with respect to the optical axis, or the optical performance in the sub-scanning direction such as bow In order to improve the above, it is conceivable to form an asymmetric shape also in the sub-scanning direction. In this case, the design performance is improved, but the two second optical systems arranged on the same side with respect to the rotation axis of the deflector are symmetrical with respect to a plane perpendicular to the rotation axis of the deflector. Therefore, the amount of processing error is different.

  In Patent Document 2, the amount of eccentricity in the sub-scanning direction of the second optical system is specified in order to suppress the bowing of the bow, but it is not assumed that the bow curving direction is aligned.

In a printer that synthesizes four images in a tandem system to form a color image, a deviation in the sub-scanning direction such as a bow is easily noticeable as a “color shift”, and requires higher accuracy in the sub-scanning direction than a monochrome printer.
Japanese Unexamined Patent Publication No. 64-909 JP 2003-57585 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning apparatus that can maintain beam performance even with a low-cost lens configuration, and can suppress color misregistration by aligning the bow curving direction on the scanned surface. It is in.

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 optical system, an optical path folding mirror for separating and guiding the beam transmitted through the first optical system to each scanned surface, and a second image forming each separated beam on the scanned surface In an optical scanning device comprising an optical system,
The deflector is installed in common for each light source, the lenses constituting the first optical system are arranged on the left and right sides of the deflector, and the surface shape of the lens is in the sub-scanning direction. The lenses constituting the second optical system have the same configuration with respect to all the optical paths, and the surface shape of the lens is symmetric in the main scanning direction. The upper optical path and the lower optical path are 180 in the main scanning direction. ° Inverted arrangement,
With respect to the number of optical path folding mirrors, the number of arrangement of one lower optical path is A, the number of arrangement of one upper optical path is B, the number of arrangement of the other upper optical path is C, and the number of arrangement of the other lower optical path with respect to the deflector. When the number of arranged sheets is D, the following conditions must be satisfied:
In the first stage of the second optical system,
| A−B | = 2 × i
| C−D | = 2 × j
| A−D | = 2 × m + 1
| B−C | = 2 × n + 1
However, i, j, m, and n are integers greater than or equal to 0. In the second stage of the second optical system,
| A−B | = 2 × i + 1
| C−D | = 2 × j + 1
| A−D | = 2 × m
| B-C | = 2 × n
However, i, j, m, and n 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, since the lens having a plane shape symmetrical in the sub-scanning direction is arranged in front of the folding mirror that separates the optical path, a common lens can be used in the two separated optical paths. , Become low cost. In addition, by setting the number of folding mirrors so as to satisfy the conditional expression, it is possible to align the bending direction of the bow of the drawing line on the surface to be scanned, and to effectively prevent color misregistration in the sub-scanning direction. Can be suppressed.

  Further, it is preferable that the beam emitted from each light source is incident on the deflector with a predetermined inclination angle in the sub-scanning direction plane. The beam can be separated without increasing the thickness of the deflector.

  Preferably, at least one of the optical path folding mirrors is provided with means for correcting bow on the surface to be scanned by bending the mirror in the main scanning direction. Even if a large bow remains in design, correction is possible. When the bow is corrected in this way, the conditional expression relating to the number of folding mirrors aligns the remaining amount of misalignment in the sub-scanning direction after correcting bow (secondary component of misalignment in the sub-scanning direction).

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

  The first and second lenses 11 and 12 having the same configuration 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, In addition, the surface shape 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 2 to 4).

  The third lenses 13Y, 13M, 13C, and 13K are all of the same configuration formed by the same mold, and the surface shapes of the first surface (beam incident side) and the second surface (beam output side) are mainly. Symmetric in the scanning direction Y. Further, the lenses 13Y and 13M are arranged 180 ° inverted in the main scanning direction Y. That is, in FIG. 1, the lenses 13Y and 13M are identical lenses, and are arranged in a state in which the end portions a and b are inverted 180 ° in the main scanning direction Y, respectively. This relationship is the same in the lenses 13K and 13C. The surface shape data will be described later (see Table 5).

  Regarding the number of optical path folding mirrors 31 to 38, the arrangement number of the photosensitive drums 50, that is, as shown in FIG. 3, the arrangement number of the lower left optical path (for yellow exposure) with respect to the polygon mirror 5 is A, and the upper left optical path. Assuming that the arrangement number of B (for magenta exposure) is B, the arrangement number of the upper right optical path (for cyan exposure) is C, and the arrangement number of the lower right optical path (for black exposure) is D, the second optical system (third When divided into the front and rear stages of the lens 13), they are arranged in the following number.

  In the first stage of the second optical system, A and B corresponding to the upper and lower sides on the left side are two pieces, | A−B | is an even number, and C and D corresponding to the upper and lower sides on the right side are one piece and | C− D | is an even number. In addition, A and D corresponding to the left and right on the lower side are even and odd numbers different between two and one, | A−D | is an odd number, and B and C corresponding to the left and right on the upper side are even and two and one.・ Odd numbers are different, and | B−C | is an odd number.

  In the second stage of the second optical system, A and B corresponding to the top and bottom on the left side are 0 and 1, and even and odd numbers are different, | AB | is an odd number, and C and D corresponding to the top and bottom are one on the right side. Even and odd numbers are different between 0 and 0, and | CD | is odd. In addition, A and D corresponding to the left and right on the lower side are each 0, | A−D | is an even number, B and C corresponding to the left and right on the upper side are each one, and | B−C | is an even number. .

(Bow bow direction, see Fig. 4)
FIG. 4A is a conceptual diagram relating to the bending (bows 51Y, 51M, 51C, 51K) of the scanning line in the sub-scanning direction on the second optical system (third lenses 13Y, 13M, 13C, 13K). B) is a conceptual diagram relating to the bending (bows 52Y, 52M, 52C, 52K) of the scanning line on the scanned surface (photosensitive drums 50Y, 50M, 50C, 50K) in the sub-scanning direction.

  The scanning line on the second optical system is curved to the right at the bows 51M and 51C in the upper optical path, and is curved to the left while being inverted at the bows 51Y and 51K in the lower optical path. When the beam passes through the third lenses 13M and 13C and is reflected by the folding mirrors 33 and 37, the trajectory of the beam is reversed. As a result, the bows 52M and 52C of the scanning lines on the photosensitive drums 50M and 50C are turned on. The bows 52Y and 52K in which no is arranged do not coincide with the bending direction. In this way, 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, and color misregistration of the image is effectively suppressed. be able to.

  On the second optical system, since the number of folding mirrors is the same on the side closer to the polygon mirror and the side far from the polygon mirror, the trajectory of the transmitted beam is reversed. If the same lens 13 is arranged as it is, the optical performance is deteriorated. Therefore, in this embodiment, the lens 13 whose surface shape is symmetric in the main scanning direction Y is reversely arranged in the main scanning direction Y, so that the deterioration of the optical performance is eliminated even if the beam trajectory is reversed. . However, in this state, the bow curve direction is not aligned on the surface to be scanned and the color shift is in the sub-scanning direction Z. Therefore, by arranging a folding mirror that satisfies the conditional expression at the rear stage of the lens 13, As a result, the bow bending directions on the surface to be scanned can be matched, and color misregistration in the sub-scanning direction Z can be eliminated as much as possible.

(Bow correction, see Fig. 5)
The bow on the scanned surface 50 can be corrected by the correcting means 25 shown in FIG. The correction means 25 moves the central portion of the folding mirror 30 in the main scanning direction by moving the screw 26 provided on the folding mirror 30 forward and backward with respect to the fixed frame 27, thereby deforming the main scanning of the mirror 30. The amount of deflection in the direction Y is adjusted. Both ends of the folding mirror 30 are held by fixing portions 39 and 39, and a leaf spring 28 is disposed on the opposite side of the screw 26.

  The bow on the scanned surface 50 can be corrected by adjusting the amount of deflection of the folding mirror 30 with the screw 26. Even if a large bow remains in design, the correction means 25 can correct the bow. When the bow is corrected in this way, the conditional expression relating to the number of folding mirrors arranged is to align the remaining positional deviation in the sub-scanning direction Z after correcting bow (secondary component of positional deviation in the sub-scanning direction).

  The correcting means 25 may be installed on any folding mirror, but it is preferable to install it on one folding mirror in each of the four color optical paths. As to which of the plurality of folding mirrors to be installed in each optical path, a mirror that is easy to install may be selected in terms of optical path design, but it is preferable to select a mirror with high correction sensitivity. In other words, the amount of change in the bow becomes larger with respect to the amount of deflection of the mirror in the mirror where the beam is incident at an obtuse angle.

(Optical element arrangement and configuration data)
Table 1 below shows the arrangement of the optical elements in the examples. Table 2 shows the free-form surface coefficient data of the first surface (the first surface of the first lens 11), Table 3 shows the free-form surface coefficient data of the second surface (the second surface of the first lens 11), and Table 4 shows the Table 4 shows the free-form surface coefficient data of four surfaces (the second surface of the second lens 12), and Table 5 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 Table 4, the fourth surface uses only even-numbered coefficients in the sub-scanning direction Z, and the first and second lenses 11 and 12 have symmetric surface shapes in the sub-scanning direction Z. Have. Thus, a common lens can be used for the upper optical path and the lower optical path, and the cost is reduced.

(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. In the said Example, it is a conceptual diagram which shows the curve direction of the bow on a 2nd optical system and a to-be-scanned surface. FIG. 3 shows a bow correcting means on the surface to be scanned, (A) is an XZ side view, and (B) is an XY plan view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser diode 5 ... Polygon mirror 11, 12 ... 1st and 2nd lens (1st optical system)
13 ... Third lens (second optical system)
25 ... Correction means 29 ... Window glass 30-38 ... Folding mirror 50 ... Photosensitive drum (scanned surface)
52Y, 52M, 52C, 52K ... Bows on the scanned surface

Claims (4)

A plurality of light sources, a deflector for deflecting a beam from the light source in the main scanning direction, a first optical system for imaging the beam deflected by the deflector on a surface to be scanned, and the first optical system In an optical scanning device comprising: an optical path folding mirror for separating and guiding the beams transmitted through the respective scanned surfaces; and a second optical system for imaging each separated beam on the scanned surface;
The deflector is installed in common for each light source,
The lenses constituting the first optical system are arranged on the left and right sides of the deflector, and the surface shape of the lens is symmetrical in the sub-scanning direction.
The lenses constituting the second optical system have the same configuration for all the optical paths, and the lens surface shape is symmetrical in the main scanning direction, and the upper optical path and the lower optical path are inverted by 180 ° in the main scanning direction. Has been
With respect to the number of optical path folding mirrors, the number of arrangement of one lower optical path is A, the number of arrangement of one upper optical path is B, the number of arrangement of the other upper optical path is C, and the other lower optical path with respect to the deflector. Satisfying the following conditions, where D is the number of sheets arranged:
In the first stage of the second optical system,
| A−B | = 2 × i
| C−D | = 2 × j
| A−D | = 2 × m + 1
| B−C | = 2 × n + 1
However, i, j, m, and n are integers greater than or equal to 0. In the second stage of the second optical system,
| A−B | = 2 × i + 1
| C−D | = 2 × j + 1
| A−D | = 2 × m
| B-C | = 2 × n
However, i, j, m, and n are optical scanning devices characterized by an integer of 0 or more.   2. The optical scanning device according to claim 1, wherein the beams emitted from the respective light sources are incident on the deflector at a predetermined inclination angle in a sub-scanning direction plane.   2. The apparatus according to claim 1, wherein at least one of the optical path folding mirrors is provided with means for correcting a curvature in the sub-scanning direction on the surface to be scanned by bending the mirror in the main scanning direction. 2. The optical scanning device according to 2.   4. The optical scanning device according to claim 3, wherein the correction means is provided for a mirror on which a beam is incident at an obtuse angle.

Images