JPH11142757A - Method for adjusting optical scanner, optical scanner and multi-colored image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct scanning magnification and curvature of field through simple adjustments. SOLUTION: To correct the tilt or scan magnification of an image plane, a 2nd lens G2 constituting an fθ lens 50 is set as a correcting lens; and the curvature of field is compensated by rotating the 2nd lens G2 on a reference point $1 on the optical axis LD and linearlity (fθ characteristic) is corrected by rotating the 2nd lens G2 on a reference point $2 on the optical axis LD. Therefore, the best image plane can be matched with a scanned surface without varying the linearlity and a beam diameter which is uniform over the entire scanned area is obtained to obtain a print of high resolution and good picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting an optical scanning device, an optical scanning device, and a multicolor image forming apparatus. The present invention relates to a method of adjusting an optical scanning device that includes a scanning imaging optical system having a plurality of lenses for imaging and scans a light beam in a predetermined direction, an optical scanning device, and a multicolor image forming apparatus.

[0002]

2. Description of the Related Art In recent years, there has been a demand for higher image quality of image forming apparatuses such as laser beam printers and digital copiers, and it has been desired for optical scanning apparatuses to reduce the beam diameter of light beams, that is, to increase the density. . Further, in order to increase the productivity of the color image forming apparatus, a multicolor image forming apparatus using a plurality of optical scanning devices so as to form each of a plurality of colors independently has been put to practical use.

In an image forming apparatus or a multicolor image forming apparatus, a range in which a target value of a beam diameter can be obtained is defined as a DOF (Depth).
However, when a light beam having a small diameter is used in accordance with the above-described high density, the range becomes narrow, and a target beam diameter can be obtained even if the best image plane position changes due to a temperature change or the like. Is designed to eliminate field curvature.

However, even in the optical scanning device, even if the field curvature and the linearity in design are corrected well, the best image is produced due to a manufacturing error such as a processing error of a scanning lens or a mirror or an assembly error to the device. The slanted surface makes the beam diameter non-uniform, which is a factor that hinders high performance.

In the same manner as described above, a scanning magnification error may occur due to a manufacturing error, resulting in asymmetric left and right, resulting in image distortion. Further, when a plurality of scanning devices are used, distortion of the image between the colors causes color misregistration, and a good image cannot be obtained. In particular, it is known that color misregistration is easily perceived by human eyes, and even a color misregistration of several tens of μm may be perceived. For this reason, the demand for the color misregistration becomes very fierce, and it is necessary to correct the linearity difference of each optical scanning device.

In order to solve the above problem, a technique of decentering a part of an image forming lens for forming an image of a deflected light beam with respect to an optical axis in order to correct field curvature (Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. Hei 4-3413) and a technique for correcting field curvature in the main scanning direction or the sub-scanning direction by displacing one of the scanning imaging lenses in the main scanning direction.
No. 2222) has been proposed.

Also, in order to correct the scanning magnification, it is described that a color shift due to a magnification error is corrected by moving one of the imaging lenses (Japanese Patent Laid-Open No. 2-3).
08213).

[0008]

In the prior art, however, a part of the imaging lens is decentered in order to correct the field curvature and to correct the color shift due to the difference in scanning magnification left and right. When the adjustment is performed by moving the image lens, both the field curvature and the scanning magnification left / right difference change. As described above, when both the field curvature and the scanning magnification left / right difference change, when correcting the field curvature, the scanning magnification left / right difference changes, and in some cases, unacceptable image distortion or color misregistration occurs. On the other hand, when correcting color misregistration, the curvature of field fluctuates and the beam diameter becomes non-uniform, so that a good image may not be obtained.

More specifically, as shown in FIG. 23A, in the optical scanning device, the scanning image forming lens L is moved in a direction intersecting the optical axis (the direction indicated by the arrow A in FIG. 23) within the deflection surface to form an image. Surface curvature and the like were determined. FIG. 24 shows the result, where (1) shows the field curvature in the main scanning direction, and (2) shows f.
It shows the linearity as the θ characteristic, and (3) shows the change in the local error.

Further, as shown in FIG. 23 (2), in the optical scanning device, the scanning image forming lens L is rotated counterclockwise (in the direction of arrow B in FIG. 23) about the lens L so that the field curvature is obtained. And so on. FIG. 25 shows the result, in which (1) shows the curvature of field in the main scanning direction, (2) shows the linearity, and (3) shows the change of the local error.

In the drawing, the performance in design is shown by a solid line.
The performance after the movement is indicated by a dotted line. As is clear from these figures, the best image plane is tilted, the field curvature changes, and the linearity also changes, resulting in a left-right difference in scanning magnification. This means that the image plane is tilted due to manufacturing errors,
Even if it is attempted to correct the error caused by the difference in scanning magnification by moving the adjusting lens, both the field curvature and the linearity are corrected unless the error is almost the same as the ratio between the field curvature change amount and the linearity change amount accompanying the movement of the adjustment lens. This indicates that it cannot be corrected to a good state.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of adjusting an optical scanning device, an optical scanning device, and a multicolor image forming apparatus capable of correcting a scanning magnification and a field curvature by a simple adjustment in consideration of the above fact. .

[0013]

As described above, a part of the imaging lens is adjusted by eccentricity or movement in order to correct the field curvature and the color shift due to the difference in scanning magnification left and right. However, since both the field curvature and the scanning magnification left / right difference change, image distortion and color misregistration occur, and a good image cannot be obtained.

The inventor of the present invention has moved at least some of the lenses of a scanning imaging optical system having a plurality of lenses in a deflection plane in order to form a light beam on an object to be irradiated,
Paying attention to the fact that the amount of change in the image plane tilt and the amount of change in the scanning magnification left / right difference when the lens is rotated are different, and by rotating some of the lenses around a position separated from the lens by a predetermined distance, the image plane is rotated. The present inventors have found that it is possible to independently correct only the inclination or only the difference in scanning magnification, leading to the present invention.

Specifically, in order to achieve the above object, the invention according to claim 1 comprises a scanning image forming optical system having a plurality of lenses for forming a light beam on an object to be irradiated, An adjustment method for an optical scanning device that scans a light beam in a predetermined direction, the method being based on a predetermined position on the optical axis of the scanning imaging optical system at a position separated by a predetermined distance from the scanning imaging optical system. In order to correct the inclination of the image plane or the scanning magnification, a part of the lens constituting the scanning image forming optical system is defined around the reference point, and the effective range of the lens defines the scanning range. It is characterized in that adjustment is performed by rotating within an adjustment range that includes all of them.

According to the first aspect of the present invention, a predetermined position on the optical axis of the scanning image forming optical system at a predetermined distance from the scanning image forming optical system is defined as a reference point. A part of the lens constituting the scanning image forming optical system is adjusted by rotating around the reference point. This rotation is performed so that the effective range such as the effective diameter defined by the diameter of the entrance pupil of the lens and the lens outer shape includes the adjustment range including the entire scanning range. Therefore, the inclination of the image plane or the scanning magnification can be corrected by rotating a part of the lens constituting the scanning image forming optical system around the reference point.

It is preferable that the correction of the inclination of the image plane and the correction of the scanning magnification are performed simultaneously. In view of the above, the invention according to claim 2 includes a scanning image forming optical system having a plurality of lenses for imaging a light beam on an irradiation target, and adjusting an optical scanning device that scans the light beam in a predetermined direction. A method, wherein two different predetermined positions at a position separated by a predetermined distance from the scanning imaging optical system and on the optical axis of the scanning imaging optical system are defined as a first reference point and a second reference point. In order to correct the inclination of the image plane, a part of the lens forming the scanning image forming optical system around the first reference point is set within an adjustment range where the effective range of the lens includes the entire scanning range. Rotate with
In order to correct the scanning magnification, a part of the lens is adjusted by rotating a part of the lens within the adjustment range around the second reference point.

According to a second aspect of the present invention, two different predetermined positions on the optical axis of the scanning image forming optical system which are located at a predetermined distance from the scanning image forming optical system are defined as the first reference point and the second reference point. Determined as a point. This is because it is possible to individually adjust the image plane tilt and the scanning magnification left / right difference by rotating the same lens about two different positions. Therefore, by rotating the lens about each of the first reference point and the second reference point, the image plane tilt and the scanning magnification difference can be corrected independently and simultaneously.

The above method can be realized by the following apparatus. According to a third aspect of the present invention, there is provided an optical scanning apparatus comprising a scanning image forming optical system having a plurality of lenses for imaging a light beam on an irradiation target, and scanning the light beam in a predetermined direction. In order to correct the inclination of the image plane or the scanning magnification at a position separated by a predetermined distance from the imaging optical system and about a predetermined reference point at a predetermined position on the optical axis of the scanning image forming optical system. And an adjusting means for rotating a part of the lens constituting the scanning image forming optical system within an adjustment range in which the effective range of the lens includes the entire scanning range.

According to a third aspect of the present invention, there is provided an adjusting means for adjusting the inclination of the image plane or the scanning magnification at a position which is separated by a predetermined distance from the scanning image forming optical system. With a predetermined reference point at a predetermined position on the optical axis of the scanning image forming optical system as a center, a part of the lens constituting the scanning image forming optical system, the effective range of this part of the lens covers the entire scanning range Rotate within the adjustment range including. By rotating in this manner, the inclination of the image plane or the scanning magnification can be corrected.

The above-described optical scanning device is for scanning a light beam in a predetermined direction. Generally, a deflection means such as a polygon mirror is used. Since the deflecting means is often rotated at a constant rotational speed, it is necessary to correct the deflected light beam so that the scanning speed is substantially constant. For this reason, it is preferable that the scanning image forming optical system further has a function of an fθ lens for correcting a scanning speed when scanning the light beam in a predetermined direction. By rotating a part of the lens of the scanning imaging optical system further having the function of the fθ lens as described above, the scanning image forming optical system can adjust the inclination of the image plane and the scanning of the light beam whose scanning speed has been corrected. The magnification can be corrected.

In the scanning image forming optical system further having such a function of the fθ lens, the invention according to claim 5 is characterized in that the reference point is a predetermined predetermined value at which the scanning speed correction characteristic of the fθ lens does not change. It is preferable to set it within the range.
That is, although the scanning speed of the light beam is corrected in the scanning image forming optical system, the reference point is set within a predetermined range where the correction characteristic of the scanning speed does not change, so that the system of the scanning image forming optical system is corrected. As a whole, the inclination of the image plane and the scanning magnification can be corrected without deteriorating the characteristics.

Further, the image plane is tilted by rotating the lens. Generally, the tilt of the image plane has an allowable range at the beginning of design. Therefore, as described in claim 6,
The reference point is set within a predetermined allowable range where the best image plane position of the scanning image forming optical system does not substantially change. By doing so, the best image plane position of the scanning image forming optical system does not substantially change, and the correction can be performed while suppressing the change in the inclination of the image plane.

As described above, since it is preferable that the correction of the tilt of the image plane and the correction of the scanning magnification are simultaneously performed, a plurality of light beams are formed on the object to be illuminated. A scanning image forming optical system having a lens, and scanning the light beam in a predetermined direction, wherein the light of the scanning image forming optical system is located at a predetermined distance from the scanning image forming optical system. In order to correct the inclination of the image plane around two different predetermined first reference points and second reference points on the axis, a part of the lens constituting the scanning image forming optical system is replaced with a part of the lens. In order to rotate within an adjustment range where the effective range includes the entire scanning range, and to correct the scanning magnification, one of the lenses around the second reference point is used as a center.
An adjusting unit that adjusts the unit by rotating the unit within the adjustment range.

As described above, the adjusting means can rotate the lens about each of the first reference point and the second reference point, and can independently and simultaneously correct the image plane tilt and the scanning magnification difference.

Here, a multi-color image forming apparatus which has been put to practical use in order to increase the productivity of the color image forming apparatus is provided with a plurality of optical scanning devices for forming each of a plurality of colors independently. The resulting image may cause different image distortion.

According to an eighth aspect of the present invention, there is provided a scanning device having a plurality of lenses for performing main scanning of a photoconductor and a light beam in a predetermined direction and forming the light beam into an image of the light beam on the photoconductor. A plurality of color image forming apparatuses including an optical scanning device having an image forming optical system and a developing device, and a sub-scanning device for performing sub-scanning in a direction intersecting with the main scanning direction; Performing a two-dimensional multi-color image formation on the same recording material by performing at least one of the optical scanning devices at a predetermined distance from the scanning imaging optical system. The scanning imaging optical system is configured to correct a tilt of an image plane and a scanning magnification around a predetermined at least one reference point at a predetermined position on the optical axis of the scanning imaging optical system. Part of the lens to be Wherein the scope is equipped with adjusting means for rotating within the adjustment range including all the range of the scanning.

As described above, for at least one of the plurality of optical scanning devices, the adjusting device is provided by adjusting a part of the lens by rotating the lens within the adjustment range. The optical scanning device provided can correct the inclination of the image plane and the scanning magnification, and eliminates the color shift caused by the color of the optical scanning device provided with the adjusting means, for example, by substantially matching with other colors. be able to.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, laser scanning for emitting a laser beam as a light beam of a color image forming apparatus having an image forming unit for each color of black (K), yellow (Y), magenta (M), and cyan (C) The present invention is applied to a device.

FIG. 1 shows a color image forming apparatus 10 according to an embodiment of the present invention. The color image forming apparatus 10 includes a control unit 16 including a CPU, a ROM in which a program for controlling the entire color image forming apparatus 10 is stored, a RAM as an input / output buffer and a work area, an operation panel, and the like. An image reading apparatus 1 that separates the optical signal obtained by scanning the image into signals of each color by a filter and photoelectrically converts these signals to form image signals of each color
4, two pairs of transport rollers 30, 32, and transport roller 3
And an endless transfer belt 24 that is wound around 0 and 32 and can transmit light.

Above the transfer belt 24, an image forming section 12A for forming a black (K) image, a yellow (Y)
An image forming section 12B for forming an image, an image forming section 12C for forming a magenta (M) image, and an image forming section 12D for forming a cyan (C) image are arranged at substantially equal intervals in the transport direction (the direction of arrow A). ing.

The image forming units 12A to 12D have the same configuration, and each of the image forming units 12A to 12D
The photosensitive drums 20 are arranged such that the axial direction is orthogonal to the transport direction (the direction of arrow A).
A charger 34 for charging the photosensitive drum 20, a laser scanning device (ROS) 18 for forming a latent image on the charged photosensitive drum 20, and for attaching toner of each color to the latent image Developing device 22 and photosensitive drum 20
A cleaner 36 for removing the remaining toner is disposed.

In the color image forming apparatus 10, the R, G, and B image signals read by the image reading device 14 are converted into image data C, M, Y, and K, and
Output to The control unit 16 outputs a laser drive signal (modulation signal) for driving the laser light source of each color to the image forming units 12A to 12D. Image forming unit 12A for each color
In 12D, the photosensitive drum 20 is exposed by driving the laser light source according to the input signal.

The photosensitive drums 20 of the respective colors are arranged at predetermined intervals, and paper 26 supplied from a supply tray (not shown) is fed onto the upper surface of the transfer belt 24 and is moved in a predetermined direction (the direction of arrow A in FIG. 1). While being conveyed, they pass under each photosensitive drum 20 in order, and each color (C, M,
(Y, K) toner images are transferred at a predetermined timing.
The paper 26 onto which the toner images of the respective colors have been transferred is peeled off from the surface of the transfer belt 24 and discharged after being fixed by a fixing device.

As shown in FIG. 2, the laser scanning devices 18 provided in the image forming units 12A to 12D of the respective colors include a laser light source unit 44 having a laser light source arranged in the sub-scanning direction, and a laser light source unit 44. A collimator lens 46 for converting the laser beam emitted from the unit 44 into a parallel beam, a rotating polygon mirror (polygon mirror) 48 rotated at substantially constant angular velocity and deflecting the parallel beam, and a scanning lens for correcting a scanning speed and forming an image. Fθ lens 50 as an image lens
And a start position detection (SOS) sensor 52 for detecting an image signal writing start signal on the photosensitive drum 20 in the main scanning direction. In the drawing, LD indicates an optical axis.

Incidentally, the laser scanning device 18 actually uses a scanning image forming lens (fθ lens 50) with a cylindrical reflecting mirror (cylindrical mirror) or the like in order to correct the inclination of the deflecting surface (reflection surface of the polygon mirror). Although provided later, since the cylindrical mirror and the like hardly change the field curvature in the sub-scanning direction as correction according to the present embodiment, description thereof is omitted in the present embodiment.

[First Embodiment] In the first embodiment, a combination lens combining two negative and positive single lenses is used.
The present invention is applied to a case where an fθ lens 50 that is a scanning imaging lens is configured.

As shown in FIG. 3, the fθ lens 50 includes a first lens G1 having a negative power (a so-called concave lens) and a second lens G2 having a positive power (a so-called convex lens).

Hereinafter, optical data of the fθ lens 50 of the present embodiment will be shown. Note that the following numerical values are obtained when the focal length f =
This is normalized as 1 (mm). The curved surface of the single lens has a first surface on the object point side (polygon mirror side) and a second surface on the image point side (photosensitive drum side), and the radius of curvature r is such that the center of curvature is closer to the image point side than the curved surface. Is indicated by a positive sign, when the center of curvature is on the object point side of the curved surface is indicated by a negative sign, and when it is substantially flat, it is indicated by “∞”.

(Optical Data) First lens G1: radius of curvature r of first surface R1 = −0.60698 radius of curvature r of second surface R2 = −6.886283 Distance d = 0.027429 (near optical axis LD) (Distance from first surface R1 to second surface R2) Refractive index N = 1.712004 Second lens G2: radius of curvature r of first surface R3 = ∞ radius of curvature r of second surface R4 = −0.39721 distance d = 0.0411144 (distance from the first surface R3 to the second surface R4 near the optical axis LD) Refractive index N = 1.712004 Distance between the first lens G1 and the second lens G2 = 0.10286 (near the optical axis LD (Distance from the second surface R2 of the first lens G1 to the first surface R3 of the second lens G2) The space between the first lens G1 and the second lens G2 is filled with vacuum or air. And Further, in the following description, the combined focus of the combination of the first lens G1 and the second lens G2 is referred to as a combined focus f.

Here, the inventor of the present invention has determined the amount of change in the image plane inclination and the amount of scanning when the scanning imaging lens is moved within the deflection plane and when the scanning imaging lens is rotated on the optical axis. Focusing on the fact that the amount of change in the magnification left / right difference is different, and as a result of various studies, the amount of change in the image plane tilt and the amount of change in the scanning magnification left / right difference are independent of the movement or rotation of the scanning imaging lens. It has been found that correction is possible, that is, only rotation of the image plane or difference in scanning magnification can be corrected independently by rotating around a position separated by a predetermined distance from the scanning imaging lens.

Therefore, in the present embodiment, a correction lens for rotating the second lens G2 of the fθ lens 50 having the above configuration is set in order to correct the inclination of the image plane or the scanning magnification. That is, in the present embodiment, for each of the field curvature correction and the linearity (fθ characteristic) correction, a reference point is determined at a predetermined position on the optical axis LD, and the second lens G2 is rotated around the reference point. This provides a configuration that enables each correction.

In FIG. 3, the reference point for correcting the curvature of field is indicated by # 1, and the reference point for correcting the linearity is indicated by # 2. In the present embodiment, the reference point # 1 for correcting the curvature of field is set at a position on the optical axis LD at a distance S1 from the first surface R3 of the second lens G2. This distance S
1 is determined by + 1.18f (f: a combined focal point of a combination of the first lens G1 and the second lens G2). The sign of this distance is a positive sign from the object point side to the image point side, and the opposite sign is a negative sign. That is, “+1.
18f "indicates a position at a predetermined distance (1.18f) from the first surface R3 of the second lens G2 toward the image point. The second lens G2 is centered on the reference point # 1.
It is rotatable in a predetermined direction (direction of arrow T1 in FIG. 3) with a radius Y1 (details will be described later).

Further, a reference point リ ニ ア for linearity correction
2 is set at a position on the optical axis LD at a distance S2 from the first surface R3 of the second lens G2. This distance S2
Is defined as -0.58f. The second lens G2 has a radius Y2 in a predetermined direction (FIG. 3) around the reference point # 2.
(In the direction of arrow T2) (details will be described later).

The reference points # 1 and # 2 are obtained by performing a large number of optical calculations such as ray tracing when the second lens G2 is rotated about an arbitrary point defined on the optical axis. A position where only the field curvature or the linearity changes can be obtained.

As shown in FIG. 4, the second part of the scanning
In order to rotate the lens G2 at two radii of curvature (radius Y1 and radius Y2), the second lens G2 is mounted on the second moving body 64 on the first moving body 62 mounted on the base substrate 60. I have. The optical axis LD is provided on the base substrate 60.
An arc-shaped groove 66 having a predetermined width and a predetermined depth is provided on the inner circumference of the radius Y1 from the upper reference point # 1. Further, on the lower surface 62A of the first moving body 62, a projection having a predetermined width and a predetermined height is provided on the inner periphery of the radius Y1 so as to fit into the groove 66 of the base substrate 60. Thus, the first moving body 62 is rotatably attached to the base substrate 60 at the radius Y1.

The upper surface 62B of the first moving body 62 has an optical axis L
An arc-shaped projection 68 having a predetermined width and a predetermined height is provided on the inner circumference of the radius Y2 from the reference point # 2 on D. Also,
On the lower surface 64A of the second moving body 64, a groove having a predetermined width and a predetermined width is provided on the inner periphery of the radius Y2 so as to be applied to the projection 68 of the first moving body 62. Thus, the second moving body 64 is rotatably attached to the first moving body 62 at the radius Y2.

The second lens G is provided on the upper surface of the second moving body 64.
By attaching 2, the second lens G2 can rotate at two radii of curvature (radius Y1 and radius Y2) around different positions (reference points # 1 and # 2).

The first moving body 62 is provided with a long hole 70, and a screw 72 is screwed (fixed) through the long hole 70.
To enable this, a screw hole (not shown) is provided in the base substrate 60. The second moving body 64 is provided with a long hole 74, and a screw hole (not shown) is provided in the base substrate 60 so that the long hole 74 can be screwed (fixed) through the screw 72. .

The base substrate 60 is provided with a hole having substantially the same diameter as the rotating shaft so that the rotating shaft 86 of the eccentric cam 84 having the rotating shaft 86 can be rotatably mounted.
This eccentric cam 84 changes the distance from the center to the outer periphery by rotating about the rotation shaft 86,
The outer periphery is in contact with one side surface 62W of the first moving body 62. The other side surface 62 </ b> Z of the first moving body 62 has a side surface portion 9 protruding from above the base substrate 60.
0 in the direction of repulsion (first
The moving body 62 is attached so that a force directed to the eccentric cam 84 is applied. Thereby, the eccentric cam 84
By rotating, the first moving body 62 is made rotatable (adjustable), and can be fixed after the adjustment.

The other side surface 62Z of the first moving body 62
Is provided with a protruding plate portion 62R to which a spring 92 is attached, and the end of the spring 92 is applied to the second moving body 64 in a repulsive direction (so that a force toward the eccentric cam 80 is applied to the second moving body 64). To). Thereby, the eccentric cam 8
By rotating 0, the second moving body 64 is made rotatable (adjustable), and can be fixed after the adjustment.

FIG. 5 shows a change in performance when the second lens G2 is rotated about the reference point # 1 in the present embodiment. FIG. 5A shows a change in curvature of field in the main scanning direction, FIG. 5B shows a change in linearity (a change in fθ characteristic), and FIG. 5C shows a change in a local error.
In the figure, the solid line represents the design value in the present embodiment, and the broken line represents the performance when the second lens G2 is rotated.

FIG. 6 shows a change in performance when the second lens G2 is rotated around the reference point # 2. FIG. 6A shows a change in field curvature in the main scanning direction, FIG. 6B shows a linearity change, and FIG. 6C shows a local error change. In the figure, the solid line represents the design value in the present embodiment, and the broken line represents the performance when the second lens G2 is rotated.

As understood from FIG. 5, the second lens G
By rotating the second lens G2 about a reference point ＄ 1, which is a point on the optical axis + 1.28 × fmm away from the first surface R3 of FIG. 2, the linearity and the local error are substantially unchanged, and the field curvature is maintained. Can be changed (characteristics can be inclined). That is, it is possible to correct only the curvature of field without changing the linearity, and to correct the curvature of field caused by various errors.

As can be understood from FIG. 6, when the second lens G2 is rotated about the reference point ＄ 2 on the optical axis at a distance of −0.58 × fmm from the first surface, the curvature of field is reversed. Linearity and local error can be changed with almost no change. This makes it possible to correct the linearity without changing the curvature of field by adjusting the reference point # 2 as the center of rotation.

Further, in the present embodiment, the second lens G2 is rotated and moved by rotating the eccentric cam 84 to move the moving body 62 along an arc centered on the reference point # 1, and the main scanning is performed. Direction of curvature of field can be displaced. In this case, since the linearity does not change, only the field curvature is corrected. Further, by rotating the eccentric cam 80, the second lens G2 on the moving body 64 becomes
It rotates and moves along an arc centered on the reference point # 2, and only the linearity changes. In this case, since the curvature of field does not change, only the linearity is corrected without changing the curvature of field obtained by rotating the eccentric cam 84.

FIGS. 7 to 9 show experimental results (actual performance changes) of rotating the second lens G2 having an assembly error by the adjusting mechanism of the present embodiment. (1) of FIG. 7 to FIG. 9 show a change in curvature of field in the main scanning direction.
(2) shows a change in linearity, and (3) shows a change in local error.

FIG. 7 shows the performance when the scanning imaging lens 50 has an assembly error. The solid line is a design value, and the broken line is the performance when the lens on the deflection surface side, that is, the first lens G1 is moved perpendicularly to the optical axis LD within the deflection surface. It is understood that both the best image plane and the linearity are inclined with respect to the design value.

FIG. 8 shows the performance when the second lens G2 is adjusted by rotating the eccentric cam 84 about the reference point # 1. The solid line is the design value and the broken line is the performance when rotating. As understood from FIG. 8, the linearity does not change (see FIG. 8 (2)), but the field curvature is corrected so as to approximate the design value (see FIG. 8 (1)).

FIG. 9 shows the performance when only the linearity is adjusted by rotating the second lens G2 along an arc centered on the reference point # 2 by rotating the eccentric cam 80. The field curvature does not change (FIG. 9 (1)
It is understood that only the linearity changes (see FIG. 9B), and as a result, both the field curvature and the linearity are corrected to approximate the design values.

As shown in the above example, in the present embodiment, the same lens (second lens G2) is rotated about two different positions, thereby causing a component processing error and an assembly error. Any change in inclination and linearity of curvature of field can be corrected independently.

In this embodiment, the reference points {1, {
Although the above-mentioned respective reference points are determined as possible by obtaining a number 2 by performing many optical calculations such as ray tracing, the present invention is not limited to this. For example, the reference points {1,
2 is not limited to the above value, but has a predetermined tendency and an allowable range. The predetermined tendency and the allowable range will be described.

When the field curvature and linearity (fθ characteristic) are to be corrected, the degree of change varies depending on the optical data (power, arrangement, focal length, radius of curvature, etc.) of the fθ lens used, and is uniquely defined. Can not do it. Therefore, the present inventor conducted a number of experiments,
A relationship was found between the focal length of the lens used for correction (that is, the lens to be rotated) and the principal point positions (front principal point position and rear principal point position) of the fθ lens 50.

In the present embodiment, the second lens G2 (so-called positive lens) of the fθ lens 50, which is a scanning image forming lens composed of a general combination of two negative and positive lenses, is rotated. Correction lens is set.
When this positive lens is set as a correction lens and the field curvature correction is corrected, a position separated by a predetermined distance from the rear principal point position of the lens 50, regardless of the focal length and the radius of curvature,
The result is that the rotation center is a desirable position at the reference point where the rotation center is concentrated. That is, as shown in FIG. 26, the rear principal point position ＄ a, the front principal point position ＄ b, the distance Sa from the rear principal point position ＄ a, and the distance Sb from the front principal point position ＄ b, as shown in FIG. Is approximately 1.77 from the rear principal point position ＄ a.
X Distance f of f2 (f2: focal length of second lens G2)
The result obtained was that it was a desirable position at the reference point where the rotation center was concentrated at a position separated by. Therefore, it is preferable that a position separated by a distance Sa of approximately 1.77 × f2 from the rear principal point position ＄ a of the lens is set as the reference point ＄ 1.

When the second lens G2, which is a positive lens, is set as a correction lens and linearity (fθ characteristic) is corrected, regardless of the focal length and the radius of curvature, as shown in FIG. Since the center of rotation is concentrated at a position separated from the front principal point position ＄ b of the lens 50 by a distance within a range of approximately 1.1 × (−f2) to 1.3 × (−f2), a desirable position for the reference point It is. Therefore, it is preferable that a position separated from the front principal point position ＄ b by a distance within a range of about 1.1 × (−f2) to 1.3 × (−f2) be the reference point ＄ 2.

Next, the allowable range of the reference point will be described by taking the fθ lens 50 of the optical data of the present embodiment as an example.

First, the case where the second lens G2 (positive lens) is rotated and corrected (field curvature correction) when the first lens G1 (negative lens) has an off-axis error will be described. Here, as described above, the second lens G2 is rotated around the reference point ＄ 1 (S1 = + 1.18 × f) for field curvature correction.

FIG. 27 shows an experimental result (linearity (fθ characteristic)) of rotating the second lens G2.
A curve 60 shown in FIG. 27 represents an ideal fθ characteristic based on the design value of the fθ lens 50. A curve 64 represents the fθ characteristic at an off-axis error due to the first lens G1, and a curve 65 represents the characteristic of the amount of color shift.

Here, the second lens G2 is rotated about the reference point ＄ 1 so that the fθ lens 50, which is the fθ characteristic due to the error of the curve 64, has a field curvature of the designed value ± 0.1 mm. When rotated, the rotation angle was -0.115 degrees. Thus, the second lens G2 is shifted by -0.115 degrees.
Was rotated, the fθ characteristics substantially matched the curve 60 (ideal fθ characteristics according to design values).

The curve 66 in FIG. 27 shows that the focal length f of the fθ lens 50 is 290 mm, the scanning width is 297 mm, and the color from the design value when rotated about the reference point # 1 is assumed. The characteristics of the shift amount are shown. In this case, the amount of color shift from the design value is 3.3 μm at the maximum, and
When converted with an image density of 00 dpi (dot per inch),
1/13 dots.

On the other hand, the curve 62 in FIG. 27 shows the design value ± centered on the shifted reference point ＄ 1 (S1 = + 1.0 × f).
The fθ characteristics when the second lens G2 is rotated so as to have a curvature of field of 0.1 mm are shown. A curve 68 shows the characteristic of the color shift amount in this case. Therefore, the amount of color misregistration from the design value is a maximum of 23.5 μm, and is 600 dpi.
When converted by the image density of, it is approximately ｄ dot.

As is well known, this maximum color shift amount of 23.5 μm is lower than the resolution of the human eye. For this reason, the color misregistration is not perceived visually, so that the color misregistration amount of 23.5 μm can be assumed as an allowable range. Therefore, even if the distance between the reference point and the lens used for correction changes by about 20%, the color shift can be within an allowable range if the color shift is about half of the image density.

Next, the allowable range of the reference point based on the allowable amount of curvature of field when the fθ characteristic is adjusted will be described.

First, when the linearity (fθ characteristic) is corrected by rotating the second lens G2 (positive lens), the second lens G2 is rotated around the reference point ＄ 2 (S2 = −0.58 × f). Let it.

FIG. 28 shows an experimental result (characteristic of field curvature) when the second lens G2 is rotated and moved. Curve 70
Shows the ideal field curvature characteristics based on the design value of the fθ lens 50. A curve 74 represents the characteristic of the curvature of field when an error occurs in the first lens G1.

The curve 76 represents the fθ lens 50 which is the curvature of field due to the error of the curve 74 and the second lens G2
Represents the characteristic of the field curvature when is corrected by rotating about the reference point # 2. On the other hand, curve 78 in FIG.
Indicates the characteristic of the field curvature when the second lens G2 is rotated around the moved reference point ＄ 2 (S2 = −0.34 × f).

Here, the field curvature of the design value is approximately ± 0.5 m.
m, the reference point moved 移動 2 (S2 = −
At 0.34 × f), the field curvature is approximately ± 1 mm. Normally, in order to obtain good image quality, if the spot diameter is reduced to about the image density (for example, 42.3 μm) and the allowable beam diameter fluctuation is allowed to about 10%, in the present embodiment, the depth of focus ± It is about 1 mm. Therefore, even the position of the moved reference point ＄ 2 ′ (S2 ′ = − 0.34 × f) can be set as an allowable range.

[Second Embodiment] In the first embodiment,
The case where the second lens G2 of the fθ lens 50 having the above configuration is rotated to correct the tilt of the image plane or the scanning magnification has been described. However, the second embodiment has the same configuration as that of the first embodiment. In the scanning image forming lens, the first lens G1 is set as a correction lens, and the correction is performed by rotating the first lens G1. Note that, in this embodiment, since the configuration is the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description is omitted.

In this embodiment, as shown in FIG.
In order to rotate the first lens G1 of the fθ lens 50 having the above configuration, the reference point for correcting the curvature of field is set to ＄ 3, and the reference point for correcting the linearity is set to ＄ 4. The reference point # 3 for correcting the curvature of field is the optical axis L separated from the first surface R1 (a point near the optical axis LD) of the first lens G1 by a distance S3.
D. This distance S3 is +0.
26f. The first lens G1 is located at the reference point ＄
10 with a radius Y3 in a predetermined direction (arrow T in FIG. 10).
The configuration is the same as that of the above-described embodiment so as to be rotatable in three directions).

Further, a reference point リ ニ ア for linearity correction
4 is set at a position on the optical axis LD at a distance S4 from the first surface R1 of the first lens G1. This distance S4
Is defined as -0.72f. The first lens G1 has a predetermined direction (FIG. 1) with a radius Y4 about the reference point # 4.
(In the direction of arrow T4).

FIG. 11 shows the first lens G of this embodiment.
FIG. 12 shows an experimental result (actual performance change) when the sample No. 1 was rotated about the reference point # 4, and FIG. 12 shows an experimental result when the sample No. 1 was rotated about the reference point # 4. In addition,
FIGS. 11 and 12 show (1) changes in field curvature in the main scanning direction, (2) changes in linearity, and (3) changes in local error.

As understood from FIG. 11, by rotating the first lens G1 about the reference point # 3,
Only the inclination of the image plane can be changed (see FIG. 11A) without changing the linearity (see FIG. 11B). Also, as shown in FIG. 12, by rotating the first lens G1 about the reference point # 4, only the linearity is changed without changing the field curvature (see FIG. 12 (1)) (see FIG. 12 (2)). ) Is possible. Thus, even when the first lens G1 is set as a lens to be corrected, the inclination of the best image plane and the linearity can be adjusted independently.

Note that the reference points # 3 and # 4 of the present embodiment are not limited to the above, but have been described in the first embodiment, but may have a predetermined tendency or an allowable range.

In the present embodiment, the first
The lens G1 (so-called negative lens) is set as a correction lens for rotating. When this negative lens is set as a correction lens and the field curvature correction is corrected, the position separated by a predetermined distance from the rear principal point of the lens 50 is rotated regardless of the focal length and the radius of curvature. The result is that the center is a desirable position for the reference point where the center is concentrated. That is, as shown in FIG. 29, the rear principal point position ＄ a of the fθ lens 50
And the front principal point position ＄ b (the same position as in FIG. 26 of the first embodiment, but separated for convenience from the reference point ＄ 3), and from the rear principal point position ＄ a. , And the distance Sd from the front principal point position 、 b,
Approximately (−0.03) × f1 (f1: from the rear principal point position ＄ a)
The result was obtained that the center of rotation was concentrated at a position separated by a distance between the range of (focal length of the first lens G1) and 0.1 × f1, which was a desirable position for the reference point. Therefore, from the rear principal point position ＄ a of the lens, (−0.03) × f1 (f
1: a focal point of the first lens G1) to a position separated by a distance Sc in the range of 0.1 × f1 is preferably determined as the reference point # 3.

In the case of correcting the linearity (fθ characteristic), regardless of the focal length and the radius of curvature, as shown in FIG. 29, approximately 1.0 × from the front principal point position ＄ b of the fθ lens 50. This is a desirable position for the reference point because the center of rotation is concentrated at a position separated by a distance of f1. Therefore, it is preferable that a position separated by a distance of approximately 1.0 × f1 from the front principal point position ＄ b is determined as the reference point ＄ 2.

[Third Embodiment] The third embodiment has the same configuration as the first embodiment, and differs only in the following optical data.

(Optical Data) First lens G1: radius of curvature r of first surface R1 = −0.51012 radius of curvature r = ∞ of second surface R2 Distance d = 0.02694 (first surface near optical axis LD) (Distance from R1 to second surface R2) Refractive index N = 1.60911 Second lens G2: radius of curvature r of first surface R3 = ∞ radius of curvature r of second surface R4 = −0.36717 Distance d = 0. 02993 (distance from first surface R3 to second surface R4 near optical axis LD) Refractive index N = 1.712268 Distance between first lens G1 and second lens G2 = 0.07282 (first near optical axis LD) (Distance from the second surface R2 of the lens G1 to the first surface R3 of the second lens G2) The space between the first lens G1 and the second lens G2 is assumed to be filled with vacuum or air.

In this embodiment, the reference point # 1 for correcting the curvature of field is a distance S from the first surface R3 of the second lens G2.
1 (= + 1.08 × f) is set at a position on the optical axis LD, and a reference point # 2 for linearity correction is set.
Is a distance S2 (= −) from the first surface R3 of the second lens G2.
It is set at a position on the optical axis LD separated by 0.45 × f).

FIG. 13 shows a change in performance when the second lens G2 is rotated about the reference point # 1 in the present embodiment, and FIG.
The performance change when rotating around the center is shown. FIG.
14A and 14B, (1) shows a change in curvature of field in the main scanning direction, (2) shows a change in linearity, and (3) shows a change in local error. In the figure, a solid line represents a design value in the present embodiment, and a broken line represents a second lens G2.
Shows the performance when is rotated.

As can be understood from FIG. 13, the second lens G2 is rotated about a reference point ＄ 1, which is a point on the optical axis separated from the first surface R3 of the second lens G2 by + 1.08 × fmm. Thus, similarly to the first embodiment, the linearity and the local error are substantially unchanged, and only the curvature of field can be changed (the characteristic is inclined). That is, it is possible to correct only the curvature of field without changing the linearity, and to correct the curvature of field caused by various errors.

As understood from FIG. 14, the second
When the lens G2 is rotated about the reference point ＄ 2 on the optical axis at a distance of -0.45 × fmm from the first surface, the curvature of field is substantially unchanged and the linearity and the local error can be changed. This makes it possible to correct the linearity without changing the curvature of field by adjusting the reference point # 2 as the center of rotation.

[Fourth Embodiment] The fourth embodiment has a similar configuration using the optical data of the third embodiment.
In order to correct the inclination of the image plane or the scanning magnification, instead of rotating the second lens G2 of the fθ lens 50 having the above configuration, the first lens G1 is set as a correction lens, as in the second embodiment. The correction is performed by rotating the first lens G1. Note that this embodiment has substantially the same configuration as the above-described second embodiment and the third embodiment, and a detailed description thereof will be omitted.

In this embodiment, the reference point # 3 for correcting the curvature of field is a distance S from the first surface R3 of the first lens G1.
(= + 0.3 × f), and is set at a position on the optical axis LD separated from the reference point # 4 for linearity correction.
Is a distance S2 (= −) from the first surface R3 of the second lens G2.
It is set at a position on the optical axis LD separated by 0.65 × f).

FIG. 15 shows the first lens G of this embodiment.
FIG. 16 shows a performance change when the first lens G1 is rotated about the reference point # 4, and FIG. 16 shows a performance change when the first lens G1 is rotated about the reference point # 4. Note that FIG.
16 (1) shows a change in the field curvature in the main scanning direction, (2) shows a linearity change, and (3) shows a local error change.

As understood from FIG. 15, by rotating the first lens G1 about the reference point # 3,
Only the inclination of the image plane can be changed (see FIG. 15A) without changing the linearity (see FIG. 15B). Also, as shown in FIG. 16, by rotating the first lens G1 about the reference point # 4, only the linearity is changed without changing the field curvature (see FIG. 16 (1)) (see FIG. 16 (2)). ) Is possible. Thus, similarly to the second embodiment, even when the first lens G1 is set as a lens to be corrected, the inclination and the linearity of the best image plane can be independently adjusted.

[Fifth Embodiment] In a fifth embodiment, a combination lens combining two positive and positive single lenses is used.
The present invention is applied to a case where an fθ lens 50 that is a scanning imaging lens is configured.

As shown in FIG. 17, the fθ lens 50
It comprises a first lens G3 of positive power and a second lens G4 (so-called convex lens). Next, fθ of the present embodiment
4 shows optical data of the lens 50.

(Optical Data) First lens G3: radius of curvature r of first surface R5 = −0.333315 radius of curvature r of second surface R6 = −0.34291 Distance d = 0.0759 (in the vicinity of optical axis LD) (Distance from first surface R5 to second surface R6) Refractive index N = 1.51108 Second lens G4: radius of curvature r of first surface R7 = radius of curvature r of second surface R8 = -0.69584 distance d = 0.10301 (distance from the first surface R7 to the second surface R8 near the optical axis LD) Refractive index N = 1.60893 Distance between the first lens G3 and the second lens G4 = 0.06326 (near the optical axis LD) (Distance from the second surface R6 of the first lens G3 to the first surface R7 of the second lens G4) The space between the first lens G3 and the second lens G4 is filled with vacuum or air. And

In this embodiment, the reference point for correcting the curvature of field is $ 5, and the reference point for linearity correction is $ 6.
Indicated by The reference point # 5 for correcting the curvature of field is
The position is set on the optical axis LD at a distance S5 from the first surface R7 of the second lens G4. This distance S5 is +
Defined as 1.74 × f. The second lens G4 is rotatable around the reference point # 5 at a radius Y5 in a predetermined direction (the direction of the arrow T5 in FIG. 17).

Further, a reference point リ ニ ア for linearity correction
Reference numeral 6 is set at a position on the optical axis LD at a distance S6 from the first surface R7 of the second lens G4. This distance S2
Is defined as −0.03 × f. The second lens G4 is
With reference to the reference point # 6 as a center, it is rotatable in a predetermined direction (the direction of the arrow T6 in FIG. 17) with a radius Y6.

FIG. 18 shows a change in performance when the second lens G4 is rotated around the reference point # 5 in the present embodiment, and FIG. 19 shows that the second lens G4 is rotated at the reference point # 6.
The performance change when rotating around the center is shown. FIG.
19A and 19B, (1) shows a change in field curvature in the main scanning direction, (2) shows a linearity change, and (3) shows a local error change. In the figure, a solid line represents a design value in the present embodiment, and a broken line represents a second lens G4.
Shows the performance when is rotated.

As can be understood from FIG. 18, the second lens G4 is rotated about a reference point # 5, which is a point on the optical axis at + 1.74 × f mm away from the first surface R7 of the second lens G4. Thus, similarly to the first embodiment, the linearity and the local error are substantially unchanged, and only the curvature of field can be changed (the characteristic is inclined). That is, it is possible to correct only the curvature of field without changing the linearity, and to correct the curvature of field caused by various errors.

As understood from FIG. 19, the second
When the lens G4 is rotated about the reference point # 6 on the optical axis at a distance of -0.03 * fmm from the first surface R7, the curvature of field is substantially unchanged and the linearity and the local error can be changed. This makes it possible to correct the linearity without changing the curvature of field by adjusting the reference point # 6 as the center of rotation.

[Sixth Embodiment] In the fifth embodiment,
A case has been described in which the second lens G4 of the fθ lens 50, which is a scanning image forming lens, is rotated by a combination lens obtained by combining two positive and negative single lenses. The sixth embodiment is different from the second embodiment in that Similarly, the first lens G3 is set as a correction lens, and correction is performed by rotating the first lens G3. Note that, in this embodiment, since the configuration is the same as that of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description is omitted.

In the present embodiment, as shown in FIG.
In order to rotate the first lens G3 of the fθ lens 50 having the above configuration, the reference point for correcting the curvature of field is set to ＄ 7, and the reference point for correcting the linearity is set to ＄ 8. The reference point # 7 for correcting the curvature of field is the optical axis L separated from the first surface R5 of the first lens G3 (a point near the optical axis LD) by a distance S7.
D. This distance S7 is -0.0.
33f. The first lens G3 is connected to the reference point ＄
7, a predetermined direction (arrow T in FIG. 20) with a radius Y7.
(7 directions) so as to be rotatable.

The reference point ＄ for linearity correction
8 is set at a position on the optical axis LD at a distance S8 from the first surface R5 of the first lens G3. This distance S8
Is defined as -0.76f. The first lens G3 has a radius Y8 and a predetermined direction (FIG. 2) around the reference point # 8.
(In the direction of arrow T8).

FIG. 21 shows the first lens G of the present embodiment.
FIG. 22 shows a performance change when the first lens G3 is rotated about the reference point # 8, and FIG. 22 shows a performance change when the first lens G3 is rotated about the reference point # 8. Note that FIG.
(1) of FIG. 22 shows a change in curvature of field in the main scanning direction, (2) shows a change in linearity, and (3) shows a change in local error.

As understood from FIG. 21, by rotating the first lens G3 about the reference point # 7,
Only the inclination of the image plane can be changed (see FIG. 21A) without changing the linearity (see FIG. 21B). Also, as shown in FIG. 22, by rotating the first lens G3 about the reference point # 8, only the linearity is changed without changing the field curvature (see FIG. 22 (1)) (see FIG. 22 (2)). ) Is possible. Thereby, even when the first lens G3 is set as a lens to be corrected, the inclination of the best image plane and the linearity can be adjusted independently.

As described above, in each of the above-described embodiments, since a part of the lens constituting the scanning image forming optical system is configured to be rotated about a position separated by a predetermined distance as a center, the best is obtained without changing the linearity. The image surface can be made to coincide with the surface to be scanned, a uniform beam diameter can be obtained over the entire region to be scanned, and a print with high resolution and good image quality can be obtained.

In each of the above embodiments, it is not necessary to perform the field curvature correction and the linearity correction at the same time, and it is also possible to carry out only the field curvature correction or only the linearity correction in accordance with the required target of the color image forming apparatus. Included in the technical scope. For example, as another modification of FIG.
Is rotated about a position corresponding to the reference point # 1, and the second
By rotating the lens G2 about the position corresponding to the reference point # 2, the field curvature correction and the linearity correction can be independently adjusted. In this case, a plurality of correction mechanisms are required, but only a simple mechanism is required, and the adjustment work is simplified. On the other hand, the first lens G1 is set at the reference point
2 may be rotated and adjusted at a position corresponding to the reference point # 1.

In the image forming apparatus using a plurality of scanning exposure apparatuses according to the present embodiment, the lens is rotated around the position corresponding to the reference point # 2, and the linearity can be improved without changing the best image plane. By performing the correction, the fθ characteristic of another scanning exposure apparatus can be matched with the fθ characteristic of a predetermined scanning exposure apparatus, and a color print without color shift can be obtained.

In the above embodiment, the case where the present invention is applied to a multicolor image forming apparatus has been described. However, the present invention is not limited to this, and is applicable to a monochromatic apparatus such as a laser scanning apparatus. You may.

As described above, in the present embodiment, it is possible to independently correct the image distortion due to the inclination of the best image plane and the difference in scanning magnification left and right with a simple configuration. That is, from the viewpoint that the amount of change in the image plane tilt and the amount of change in the scanning magnification left / right difference when the scanning lens is moved in the deflection plane and when the scanning lens is rotated are different, a part of the scanning lens is moved from the lens to a predetermined position. By rotating around a position separated by a distance, only the image plane tilt or only the scanning magnification difference can be independently corrected. Further, by rotating the same lens about two different positions, it is possible to individually adjust the image plane tilt and the scanning magnification left / right difference.

Further, it is possible to satisfactorily correct the inclination of the best image plane mainly due to component accuracy or assembly error in the laser scanning device, and to obtain a uniform beam diameter over the front surface of the scanning area. Further, since the present invention does not cause a change in the scanning magnification difference, it is suitable for use in a color image forming apparatus using a plurality of laser scanning devices.

On the other hand, image distortion due to the difference in scanning magnification can be corrected without changing the curvature of field, so that image distortion can be maintained while maintaining a uniform beam diameter (color using a plurality of scanning devices). In the image forming apparatus, it is possible to correct color shift) and obtain a good print.

Further, it is possible to freely correct both the tilt of the image plane and the difference in scanning magnification by using a part of the scanning image forming lens, so that the adjusting mechanism can be simplified and an inexpensive adjusting mechanism can be provided.

In the above embodiment, a case where a laser beam is used as a light beam has been described, but a light beam such as an LED may be used.

[0118]

As described above, according to the adjustment method of the optical scanning device of the first aspect of the present invention, a part of the lens constituting the scanning image forming optical system is rotated about the reference point. Therefore, there is an effect that the inclination of the best image plane or the scanning magnification due to a manufacturing error mainly caused by a component accuracy or an assembly error in the optical scanning device can be favorably corrected.

In addition, since the effective range of the lens is rotated within the adjustment range including the entire scanning range, there is an effect that a uniform beam diameter can be obtained in the scanning area.

According to the second aspect of the present invention, since the lens can be rotated around each of the first reference point and the second reference point, the image plane tilt and the scanning magnification difference can be corrected independently and simultaneously. There is an effect that can be.

According to the third aspect of the present invention, the adjusting means can rotate a part of the lens constituting the scanning image forming optical system around the reference point, so that the image plane can be formed by using the part of the lens. There is an effect that both the tilt and the scanning magnification difference can be freely corrected, the adjustment mechanism can be simplified, and an inexpensive adjustment mechanism can be provided.

According to the fourth aspect of the present invention, the function of the fθ lens is provided, so that it is possible to correct the image plane tilt and the scanning magnification difference in consideration of the scanning speed. .

According to the fifth aspect of the present invention, since the reference point is set within a predetermined range where the correction characteristic of the scanning speed of the fθ lens does not change, there is no change in the scanning magnification. is there.

Further, since there is no variation in the scanning magnification difference, even when the present invention is applied to a multicolor image forming apparatus having a plurality of scanning devices having a scanning image forming optical system, color misregistration occurs. There is an effect that it is not done.

According to the sixth aspect of the present invention, since the reference point is set within a predetermined allowable range in which the best image plane position of the scanning image forming optical system does not substantially change, an image caused by a difference in scanning magnification is obtained. Can be corrected without changing the curvature of field, and the image distortion can be corrected while maintaining a uniform beam diameter.

According to the seventh aspect of the present invention, the adjusting means can rotate the lens about each of the first reference point and the second reference point, so that the image plane inclination and the scanning magnification difference can be reduced. Since the correction can be performed independently and simultaneously, it is possible to freely correct both the image plane tilt and the scanning magnification difference by using a part of the lens, thereby simplifying the adjustment mechanism and providing an inexpensive adjustment mechanism. effective.

According to the eighth aspect of the invention, at least one of the optical scanning devices is provided with the adjusting means for rotating a part of the lens about at least one reference point. The resulting image distortion can be corrected without changing the curvature of field, and the image distortion can be corrected while maintaining a uniform beam diameter to obtain a good print. Further, since the distortion of the image due to the difference in the scanning magnification can be corrected without changing the curvature of field, the color shift can be corrected while maintaining a uniform beam diameter, and a good print can be obtained. There is an effect that.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus to which the present invention can be applied.

FIG. 2 is a schematic configuration diagram of a laser scanning device included in the color image forming apparatus of FIG.

FIG. 3 is a diagram illustrating a laser scanning device according to the first embodiment;
It is a block diagram which shows the positional relationship of a (theta) lens.

FIG. 4 is a block diagram showing a configuration for rotating a second lens at two different points according to the first embodiment.

FIG. 5 is a characteristic diagram showing a performance change when the second lens G2 is rotated around a reference point # 1 according to the first embodiment.

FIG. 6 is a characteristic diagram showing a performance change when the second lens G2 is rotated around a reference point # 2 according to the first embodiment.

FIG. 7 is a characteristic diagram showing a change in performance when there is an error in the scanning imaging optical system according to the first embodiment.

FIG. 8 is a characteristic diagram showing a change in performance when the second lens is rotated around a reference point # 1 to correct the field curvature according to the first embodiment.

FIG. 9 is a characteristic diagram showing a performance change when the linearity (fθ characteristic) is corrected by rotating the second lens about the reference point ＄ 2 according to the first embodiment.

FIG. 10 is a block diagram showing a configuration for rotating a first lens at two different points according to a second embodiment.

FIG. 11 is a characteristic diagram illustrating a performance change when the first lens is rotated around a reference point # 3 according to the second embodiment.

FIG. 12 is a characteristic diagram showing a performance change when the first lens is rotated around a reference point # 4 according to the second embodiment.

FIG. 13 is a characteristic diagram showing a performance change when the second lens is rotated around a reference point # 1 according to the third embodiment.

FIG. 14 is a characteristic diagram showing a performance change when the second lens is rotated around a reference point # 2 according to the third embodiment.

FIG. 15 is a characteristic diagram showing a change in performance when the first lens is rotated around a reference point # 3 according to the fourth embodiment.

FIG. 16 is a characteristic diagram showing a performance change when the first lens is rotated around a reference point # 4 according to the fourth embodiment.

FIG. 17 is a conceptual image diagram showing a rotation and a rotation center position of a second lens G4 according to the fifth embodiment.

FIG. 18 is a characteristic diagram showing a performance change when the second lens G4 is rotated around a reference point # 5 according to the fifth embodiment.

FIG. 19 is a characteristic diagram showing a performance change when the second lens G4 is rotated around a reference point # 6 according to the fifth embodiment.

FIG. 20 is a conceptual image diagram showing a rotational movement and a rotational center position of a first lens G3 according to the sixth embodiment.

FIG. 21 is a characteristic diagram showing a performance change when the first lens G3 is rotated around a reference point # 7 according to the sixth embodiment.

FIG. 22 is a characteristic diagram showing a performance change when the first lens G3 is rotated around a reference point # 8 according to the sixth embodiment.

FIG. 23 is a conceptual image diagram showing a movement of a part of a scanning image forming lens in a conventional optical scanning device, wherein (1) shows movement in a direction perpendicular to an optical axis within a deflection surface, and (2) shows deflection. The rotation movement in a plane is shown.

FIG. 24 is a characteristic diagram showing a performance change when a lens is moved perpendicularly to an optical axis in a deflection plane in a conventional optical scanning device.

FIG. 25 is a characteristic diagram showing a performance change when a lens is rotationally moved within a deflection surface in a conventional optical scanning device.

FIG. 26 is a lens peripheral view for explaining a predetermined tendency and an allowable range of a reference point for rotating the second lens.

FIG. 27 is a diagram showing fθ characteristics when the second lens G2 is rotationally moved at reference points ＄ 1 and ＄ 1 ′.

FIG. 28 is a diagram showing characteristics of curvature of field when the second lens G2 is rotationally moved.

FIG. 29 is a lens peripheral view for explaining a predetermined tendency of a reference point for rotating the first lens.

[Explanation of symbols]

 Reference Signs List 10 color image forming device 18 laser scanning device 50 fθ lens G1, G3 first lens G2, G4 second lens

Claims (8)

[Claims] 1. A method for adjusting an optical scanning device, comprising: a scanning imaging optical system having a plurality of lenses for imaging a light beam on an irradiation target; and scanning the light beam in a predetermined direction. A predetermined position on the optical axis of the scanning image forming optical system at a position separated by a predetermined distance from the scanning image forming optical system is determined as a reference point, in order to correct the inclination of the image plane or the scanning magnification,
A part of the lens constituting the scanning image forming optical system is adjusted by rotating the lens within an adjustment range in which the effective range of the lens includes the entire scanning range around the reference point. Adjustment method for optical scanning device. 2. An adjustment method for an optical scanning device, comprising: a scanning imaging optical system having a plurality of lenses for imaging a light beam on an irradiation target; and scanning the light beam in a predetermined direction. Two different predetermined positions on the optical axis of the scanning imaging optical system at positions separated by a predetermined distance from the scanning imaging optical system are defined as a first reference point and a second reference point, and the inclination of the image plane is determined. In order to correct, a part of the lens constituting the scanning image forming optical system is rotated around the first reference point within an adjustment range where the effective range of the lens includes the entire scanning range, and the scanning is performed. A method of adjusting an optical scanning device, comprising: adjusting a part of the lens around the second reference point by rotating the lens within the adjustment range to correct a magnification. 3. An optical scanning device, comprising: a scanning imaging optical system having a plurality of lenses for imaging a light beam on an irradiation object; and scanning the light beam in a predetermined direction. To correct the inclination of the image plane or the scanning magnification with respect to a predetermined reference point at a predetermined position on the optical axis of the scanning image forming optical system at a predetermined distance from the scanning image forming optical system. An optical scanning device comprising: an adjusting unit configured to rotate a part of a lens constituting an image optical system within an adjustment range in which an effective range of the lens includes the entire scanning range. 4. The optical scanning apparatus according to claim 3, wherein the scanning image forming optical system further has a function of an fθ lens for correcting a scanning speed when scanning the light beam in a predetermined direction. apparatus. 5. The optical scanning device according to claim 4, wherein the reference point is set within a predetermined range where a correction characteristic of a scanning speed of the fθ lens does not change. 6. The optical scanning device according to claim 4, wherein the reference point is set within a predetermined allowable range where the best image plane position of the scanning image forming optical system does not substantially change. 7. An optical scanning device, comprising: a scanning imaging optical system having a plurality of lenses for imaging a light beam on an irradiation target; and scanning the light beam in a predetermined direction. To correct the inclination of the image plane around two different first reference points and second reference points at different positions on the optical axis of the scanning imaging optical system at a position separated by a predetermined distance from The second reference point for rotating a part of the lens constituting the scanning imaging optical system within an adjustment range in which the effective range of the lens includes the entire scanning range, and for correcting the scanning magnification. An optical scanning device comprising an adjusting unit that adjusts a part of the lens by rotating the lens within the adjustment range around the lens. 8. An optical scanning apparatus comprising: a photoconductor, a scanning imaging optical system having a plurality of lenses for main-scanning a light beam in a predetermined direction, and forming the light beam onto the photoconductor. A plurality of color image forming apparatuses each including a device and a developing device, and a sub-scanning device that performs sub-scanning in a direction intersecting with the main scanning direction, and performs the main scanning and sub-scanning on the same recording material A multicolor image forming apparatus for forming a two-dimensional multicolor image, wherein at least one of the optical scanning devices is located at a position separated by a predetermined distance from the scanning imaging optical system and the scanning imaging optical system In order to correct the inclination of the image plane and the scanning magnification with respect to at least one predetermined reference point at a predetermined position on the optical axis of the lens, a part of the lens forming the scanning image forming optical system is replaced with the lens The effective range of the entire scanning range Multi-color image forming apparatus characterized by comprising adjusting means for rotating within the adjustment range including.