JP2557938B2 - Light beam scanning device with tilt correction function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light beam scanning device used in, for example, a laser beam printer, and more specifically, a tilt correction function (a light beam deflecting / reflecting surface is used). It has a function of automatically correcting the path of the light beam so that the scanning beam reflected from the reflecting surface scans at a correct predetermined scanning position even if it is tilted slightly inclined from the predetermined posture. The present invention relates to a light beam scanning device.

[Conventional technology]

In a scanning device that scans a light beam, a rotary polygon mirror is widely used as a deflector of the light beam. that time,
If there is an inclination error (this inclination is called tilt or surface tilt) with respect to the center axis of rotation of each reflecting surface (deflecting surface) of the rotary polygon mirror, the scanning position varies for each surface, resulting in uneven scanning pitch. In order to correct this so that the same position on the scanned surface can be scanned regardless of the inclination of the reflecting surface, the positional relationship between the polygonal mirror surface (deflection surface) and the scanned surface is optically conjugate. A method of arranging an image forming optical system having a relationship (relationship between object point and image point) between the polygonal mirror surface and the surface to be scanned is known, for example, from Japanese Patent Publication No. 52-2866. .

Further, the deflection scanning optical system of such a light beam scanning device is provided with a constant velocity scanning characteristic (generally referred to as fθ characteristic) that enables a light beam to scan a surface to be scanned at a constant velocity. It is also required to have a function of correcting the field curvature so that the spot diameter of the light beam on the surface to be scanned is always uniform at each position in the scanning direction.

In this way, in order to simultaneously realize the characteristics in the plane in the scanning direction and the characteristics in the plane perpendicular to this, an optical system having different powers in both planes is required, and the rotary polygon mirror (deflector) is required.
The cylindrical surface and the toroidal surface are used by arranging the cylindrical lens and the toroidal lens in the front and rear optical paths.

Further, in order to focus the light beam on the surface to be scanned both in the scanning direction and in the direction perpendicular to the scanning direction, only between the light beam generation source and the deflector (rotary polygon mirror) in the direction perpendicular to the scanning direction. A first optical system for focusing the light beam and forming a horizontally long line image in the scanning direction on the deflection surface (reflection surface) is arranged (in contrast, an optical system having the above-mentioned fθ characteristic is scanned thereafter). Optical system).

In such a light beam scanning device, the cylinder surface and the toroidal surface are much more difficult to process than the conventional lens spherical surface, and there is a problem that the manufacturing accuracy is poor.
In particular, in the cross section perpendicular to the scanning direction, in order to focus the light beam diverging from the deflecting surface of the deflector on the surface to be scanned, it is necessary to increase the lens power as compared with the cross section in the scanning direction.
It is easily affected by the deterioration of accuracy and causes a large focus shift.

This causes a phenomenon (such as a so-called astigmatic difference) in which the focusing position of the light beam in the cross section in the scanning direction is deviated from the focusing position in the cross section perpendicular to the scanning direction.

As a method of correcting this, for example, Japanese Patent Laid-Open No. 144517/1982.
As disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, there is known a method of moving and adjusting the first optical system in the optical axis direction according to the shape error of the scanning optical system. According to this method, only the focusing position in the cross section perpendicular to the scanning direction can be independently moved, and the astigmatic difference can be corrected.

[Problems to be Solved by the Invention]

In the conventional light beam scanning device as described above, when the focus position of the light beam is deviated due to the shape error of the scanning optical system, the first optical system is moved in the optical axis direction for adjustment. A conceptual diagram of this adjustment is shown in FIG.

FIG. 13 (a) conceptually shows a cross section perpendicular to the scanning direction along the optical axis. The light beam 106 diverging from the light emitting source 105 and collimated by the collimator lens 104 is
It is focused on the deflecting surface 100 by the first optical system 103, and is again focused on the scanned surface 102 by the scanning optical system (deflecting optical system) 101. Here, if the shape of the scanning optical system 101 changes as indicated by the broken line due to an error, the focus position of the light beam is changed to a point 107.
From to point 108. FIG. 13 (b) shows the first optical system 1
It shows the state where 03 is moved to correct this.

As can be seen from this figure, in the conventional light beam scanning device, it is possible to correct the focus position of the light beam so as to come to the point 107 on the surface to be scanned. However, since the conjugate point of the point 107 comes to the point 109 distant from the deflecting surface 100, the tilt correction condition of the deflecting surface (the positional relationship between the deflecting surface and the scanned surface is in a conjugate relationship) is broken, and the deflection There is a problem that the unevenness of the scanning pitch of the light beam due to the tilt of the surface cannot be sufficiently corrected.

In particular, when a toroidal surface is used in the scanning optical system 101, the toroidal surface has a sensitivity of deviation of the light beam focusing point with respect to a shape error that is 10 times or more larger than other surfaces. , The focal point may be off by 6 mm or more.

If this is corrected by the movement of the first optical system 103,
The tilting tolerance of the deflection surface is about 10 seconds, which is extremely severe.

In the following, the surface formed by scanning the light beam is the main scanning surface, the scanning direction parallel to the main scanning surface is the main scanning direction, the plane perpendicular to the main scanning surface is the sub scanning surface, and the sub scanning surface is parallel to the above. The direction perpendicular to the main scanning plane is called the sub-scanning direction.

The object of the present invention is to solve the above problems and to independently correct the focal point shift in the sub-scanning direction while maintaining the surface tilt correction condition, which is sufficient even for the shape error of the scanning optical system. An object of the present invention is to provide a light beam scanning device capable of coping with the surface tilt correction function maintained.

[Means for solving the problem]

The object is to configure the scanning optical system with at least two lenses, and one of them (the first lens) has a negative power stronger than that of any other negative power surface in the sub-scanning surface. The other lens (second lens) has a surface having a positive power stronger than any positive power surface of the other lens in the sub-scanning surface (the first lens and the second lens). The lenses must always be separate lenses, and the same lens cannot be used as well), and this is achieved by making the first lens or the second lens movable and adjustable in the optical axis direction.

Further, the surface of the first lens having negative power in the sub-scanning surface is a surface in which the power in the sub-scanning surface is stronger than the power in the main scanning surface, and the second lens is The surface having a positive power in the sub-scanning plane is achieved by configuring the surface in the sub-scanning surface to have a stronger power than in the main scanning surface.

[Action]

In order to solve the above-mentioned problems of the prior art, the focusing position shift in the sub-scanning direction due to the shape error of the scanning optical system is adjusted by the lens of the scanning optical system (the first lens or the second lens). Good. It can be said that the present invention provides a configuration for realizing this.

First, the effect of adjusting with the lens of the scanning optical system
It will be conceptually described with reference to FIG. Figure 14 (a) shows the light source.
This is a view showing the path from 115 to the surface 112 to be scanned as seen along the sub-scanning direction.

The scanning optical system has a configuration of two lenses as an example. The light beam 116 collimated by the collimator 114 is focused on the deflecting surface 111 by the first optical system 113, and is again focused on the scanned surface 112 by the lenses 117 and 118 forming the scanning optical system.

If the shape of the lens 118 of the scanning optical system changes as indicated by the broken line due to an error, the focus position of the light beam moves from the point 119 to the point 120.

FIG. 14B shows a state in which the lens 118 itself of the scanning optical system is moved and corrected.

As shown in FIG. 14B, after the correction by the movement of the lens 118, the light beam focusing position returns to the original point 119 on the surface 112 to be scanned, and the conjugate point of the light beam focusing position 119 also remains. It is on the deflection surface 111, and the condition for correction of surface tilt is strictly maintained.

However, if the shape error of the scanning optical system is simply corrected by moving the lens of the scanning optical system as described above, performance deterioration such as distortion often occurs.

Here, focusing on the shape of the lens of the scanning optical system, in an optical system that uses a toroidal surface (including a cylindrical surface) of positive power in the sub-scanning direction, this toroidal surface causes a large negative image in the sub-scanning direction. Causes surface curvature. To correct this, a toroidal surface (or a cylindrical surface) having negative power in the sub-scanning direction was used.

When viewed in the sub-scanning plane, there are a plane having a positive power and a plane having a negative power, and the power of these planes is assumed to be relatively stronger than the power of the entire system.

According to the present invention, if either of these two surfaces is independently moved in the optical axis direction, it has high sensitivity to the focus position and can move the focus position largely with a small amount of movement, so that performance is not deteriorated. Can be corrected.

FIG. 15 (a) shows this sensitivity.
FIG. 6B shows the amount of deterioration of typical performance due to movement. The horizontal axis of FIG. 15 (a) is the amount of movement of each lens, and the vertical axis is the amount of movement of the focusing position. When the positive power surface is moved, the beam focusing position changes as shown in the graph 121 in the figure, and when the negative power surface is moved, it changes like 122 and the entire system moves. Then, the beam focusing position changes like 123. As can be seen, the graphs of 121 and 122 are about 10 times more sensitive than the case of 123. In the case of 123, the effects of 121 and 122 cancel each other out.

On the other hand, the amount of performance deterioration depends on the shape in the main scanning direction, is almost the same in all cases, and changes like 124 in FIG. 15 (b). In FIG. 15 (b), the horizontal axis represents the amount of movement, the vertical axis represents the amount of inferior deterioration, and the performance shows an example of distortion as a relative value.
The same applies to the case of field curvature.

From Fig. 15 (b), if the allowable value of inferiority deterioration is represented by 1252, a lens movement of about 0.5 mm is possible within that range,
As a result, it is possible to correct the focusing position movement up to about 7 mm by the graph of FIG. 15 (a). This is a considerably large amount of focus position shift due to a shape error.

As described above, in order to independently move the surface of strong positive power or the surface of strong negative power in the sub-scanning direction, both may be arranged in separate lenses. Further, the surface of strong negative power is 60% or more of the sum of the powers of all surfaces having negative power in the sub-scanning direction, and the surface of strong positive power is in the sub-scanning direction. The above effect can be achieved by having a power of 60% or more of the sum of the powers of all the surfaces having a positive power.

As described above, with the above configuration, it is possible to independently correct only the focusing position in the sub-scanning direction without breaking the condition for correcting the surface tilt.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples. First
The figure is a block diagram of an embodiment of the present invention. FIG. 2 is a sectional view in the sub-scanning direction of this embodiment.

In the present embodiment, a light beam deflector including a light source 1 which is a light beam generation source, a collimator lens 2, a cylinder lens (cylindrical lens) 3, a rotating polygon mirror 4 and a motor 5 for rotating the same, and a scanning optical system. The first lens 6 (consisting of the cylinder surface 6a and the spherical surface 6b) and the second lens
Lens 7 (comprising a cylinder surface 7a and a toroidal surface 7b), a surface 8 to be scanned, a movable base 12 mounted to move the second lens 7 in the optical axis direction, and an adjustment for moving the movable base 12. Base for fixing the positions of screws 13 and adjusting screws 13.
It is composed of 14.

Next, the operation of this embodiment will be described. The light source 1 is a semiconductor laser light source, and a divergent laser beam is emitted as a light beam. The collimator lens 2 collimates this and shapes the light beam into a substantially parallel beam. The cylinder lens 3 has power only in the sub-scanning plane, focuses the light beam from the collimator lens 2 in the sub-scanning direction, and forms a line image parallel to the main scanning direction on the reflecting surface 15 of the rotary polygon mirror 4. Form.

The rotary polygon mirror 4 deflects the light beam from the cylinder lens 3 in a predetermined direction by the reflecting surface 15 thereof and is rotated by the motor 5 to change the deflection angle of the light beam with time. For example, the beams 11a and 11b. , 11c causes the light beam to scan the surface 8 to be scanned.

A scanning optical system is configured by the first lens 6 and the second lens 7 so that the light beam is focused on the scanned surface 8 at one point, and the light beam scans the scanned surface 8 at a constant speed. Act on.

It is needless to say that the main scanning optical system also operates so that the reflecting surface 15 of the rotary polygon mirror 4 and the surface to be scanned 8 are in an optically conjugate relationship within the sub-scanning surface.

By maintaining this conjugate relationship, even if the reflecting surface 15 of the rotary polygon mirror 4 tilts with respect to its rotation axis 9, the light beam on the scanned surface 8 scans the same position without causing uneven scanning position. Possible (compensation correction).

The allowable value of the scanning position unevenness of the light beam on the surface to be scanned 8 is extremely severe. For example, when the present optical system is used in a laser beam printer, it is said that the printing density is 4 μm or less at 600 dpi.

In the present optical system, when the surface tilt correction is not performed at all, the tilt angle of the reflecting surface 15 of the rotary polygon mirror 4 is set to 2. In order to make the uneven scanning position of the light beam 4 μm or less.
It is necessary to set the time to 5 seconds or less, and it becomes technically extremely difficult to manufacture the rotary polygon mirror with high precision, and the cost becomes expensive.

In the present embodiment, the allowable value of the tilt angle of the reflecting surface 15 of the rotary polygon mirror 4 is relaxed to 10 minutes by the surface tilt correction (design value).

The reason why the permissible value does not become infinite is that the position where the light beam is reflected is slightly displaced as the polygon mirror 4 rotates, and thus the strict conjugate relation does not occur at the scanning end. By the way, the width of the deflection angle of the light beam of this embodiment is
The scanning width on the surface 8 to be scanned is 60 mm, and the number of reflecting surfaces of the rotary polygon mirror is 8.

Next, the first lens 6 and the second lens 6 which constitute the scanning optical system.
The operation of each part of the lens 7 will be described.

The surface 6a on the rotary polygon mirror side of the first lens 6 forming the scanning optical system is a cylinder surface having negative power only in the sub-scanning direction, and corrects the field curvature in the sub-scanning direction.

Here, the field curvature in the sub-scanning direction refers to a phenomenon in which the focusing position of the light beam as seen in the sub-scanning surface departs from the surface to be scanned 8 toward the end of scanning on the surface to be scanned 8 and is apart from this. The amount is called the size of the field curvature in the sub-scanning direction. A similar phenomenon seen in the main scanning plane is called field curvature in the main scanning direction. Further, the scanning speed of the light beam is not constant and the surface to be scanned 8
The magnitude that varies depending on the upper scanning position will be called distortion.

In other words, the surface 6b of the first lens 6 in the scanning optical system on the side of the surface to be scanned 8 is a spherical surface and serves to correct the field curvature and the distortion in the main scanning direction.

While the first lens 6 in the scanning optical system mainly corrects each aberration, the second lens 7 mainly focuses the light beam on the scanned surface 8 at one point. Are doing.

The surface 7a on the rotary polygon mirror side of the second lens 7 is a cylinder surface having a negative power in the sub-scanning plane, and the residual amount of the field curvature in the sub-scanning direction corrected by the first lens 6 is corrected. are doing.

The surface 7b of the second lens 7 on the scanned surface 8 side is a toroidal surface having a positive power in the main scanning surface and a positive power stronger than this in the sub-scanning surface. The light beam is focused on the surface 8 to be scanned in both directions.

The light beam is reflected by the reflecting surface 15 of the rotary polygon mirror 4 in the sub-scanning plane.
Since it is in a state of being diverged from an object point extremely close to that in the main scanning plane, the shape of the surface 7b on the scanned surface 8 side of the second lens 7 has a power in the sub-scanning plane. , Which is stronger than the power in the main scanning plane.

If the light beam scanning device is applied to a laser beam printer, for example, the surface to be scanned 8 is a photosensitive drum, and the photosensitive drum is composed of a cylindrical object whose rotation axis is arranged in the main scanning direction. While rotating around the axis of the cylinder, the signal of the light beam is sequentially charged and recorded.

The movable table 12 has a function of mounting the second lens 7 of the scanning optical system on the movable table 12 so as to be movable in the optical axis direction. The head of the adjusting screw 13 is fixed to a base 14 which is a mounting base for each component of the optical system, and its rotation drives the movable table 12 in the optical axis direction. FIG. 3 shows this adjusting mechanism in an enlarged manner.

When the focusing position of the light beam in the sub-scanning direction is deviated due to the shape error of the lens or the like, the second lens 7 can be moved and adjusted in the optical axis direction by the rotation of the adjusting screw 13.

 This adjustment method will be described later.

Numerical examples of the lens shape and arrangement of the scanning optical system in the above-described embodiment of the present invention are shown below.

(1) First lens 6 Cylinder surface radius of curvature R ₃ 10 mm Spherical surface radius of curvature R ₁ 569.32 mm Lens thickness l ₂ 15 mm Distance between reflecting surface 15 and cylinder surface l ₁ 60 mm Glass material refraction Ratio 1.6091 (2) Second lens 7 Curvature radius of cylinder surface R ₄ 500 mm Curvature radius of toroidal surface in main scanning direction R ₂ 184 mm Curvature radius of toroidal surface in sub-scanning direction R ₅ 46.216 mm Lens thickness l ₄ 23 mm Distance from the spherical surface of the first lens 6 to the cylinder surface of the second lens 7 l ₃ 47 mm Distance from the toroidal surface to the surface 8 to be scanned 300 mm FIGS. 4 and 5 relate to the present embodiment. It is a characteristic view which shows the aberration performance of an optical system. FIG. 4 shows the characteristic of field curvature,
The broken line is the characteristic of the amount of field curvature in the main scanning direction, and the solid line is the characteristic of the amount of field curvature in the sub scanning direction. The vertical axis represents the scanning position as a relative value, and the maximum scanning position 1.0 corresponds to the maximum deflection angle ± 30 degrees and the scanning width ± 150 mm.

This embodiment is compatible with resolutions up to 600 dpi, and the field curvature is kept within ± 1 mm so that the uniformity of the beam spot diameter can be obtained even if the light beam on the scanned surface 8 is focused small. , The aberration is corrected well.

FIG. 5 is a characteristic diagram showing distortion. The vertical axis is the fourth
Similar to that in the figure, the scanning position is indicated by a relative value, and the maximum scanning position 1.0 corresponds to the maximum deflection angle ± 30 degrees and the scanning width ± 150 mm.

It is said that the allowable value of the distortion aberration is ± 0.3 mm, and the performance of this embodiment is sufficiently smaller than this, and it can be seen that the aberration is well corrected.

In the optical system as described above, the present invention makes it easy to set the focusing position of the light beam in the main scanning direction and the focusing position of the light beam in the sub-scanning direction independently and while completely maintaining the face-tilt correction condition. It is possible to adjust to.

In the present embodiment, when the focusing position of the light beam deviates from the surface to be scanned 8 due to the shape error of the lens forming the scanning optical system, first, the collimator lens 2 shown in FIG. 1 is moved in the optical axis direction. , The focusing position in the main scanning direction can be adjusted.

Next, by rotating the adjusting screw 13, the second lens 7 is moved in the optical axis direction as shown in FIG. 1, and only the focusing position in the sub-scanning direction can be adjusted. At this time, as described above, the face-tilt correction condition is maintained.

As described above, FIG. 3 shows the moving means of the second lens 7 in an enlarged manner.

In FIG. 3, the movable base 12 to which the second lens 7 is attached can be moved only by the guide 20 in the optical axis direction.

The guide 20 is fixed to the base 14 which is a base for disposing other components of the optical system.

FIG. 3 shows a part of the base 14. Movable stand 12
The adjusting screw 13 is fitted in the screw hole of
The head is held by the support 16 from the base 14, and its movement in the optical axis direction is fixed. With such a mechanism, the second lens 7 can be moved in the optical axis direction by the rotation of the adjusting screw 13, and the focusing position can be adjusted.

Next, the reason why only the focusing position in the sub-scanning direction can be independently adjusted by the present invention will be described.

In order to have the surface tilt correction function by the scanning optical system, it is necessary to have different powers in the main scanning direction and the sub scanning direction as described above. Also needs to be a stronger positive power.

When such an examination optical system is configured by a toroidal surface, the toroidal surface has a shape having a stronger positive power in the sub scanning direction than in the main scanning direction.

However, such a toroidal surface causes a large negative image field curvature in the sub-scanning direction (undercorrection), and in order to correct this, a negative power stronger in the sub-scanning direction than in the main scanning direction is applied. The holding surface (such as the negative cylinder surface) is essential.

Then, in the sub-scanning surface of the scanning optical system, it is configured to include a surface having a relatively strong positive power and a surface having a relatively strong negative power.
The shape change and the position error have a particularly strong sensitivity to the focus position of the light beam in the sub-scanning plane.

It is conceivable to move either of these surfaces in the optical axis direction to correct the deviation of the focusing position in the sub-scanning surface.

However, since the sensitivity coefficients for the light beam focusing positions on both surfaces are opposite in sign, when both surfaces are formed on the same lens, the movement of the light beam focusing position is different for both surfaces when the lens is moved. The effects are offset, and the sensitivity is greatly reduced. If the sensitivity is low, the amount of movement of the lens becomes large, which causes deterioration of other performance.

Therefore, it is desirable to form the both surfaces on different lenses. Then, in the sub-scanning plane, the surface having the relatively strong negative power preferably has a power of 60% or more of the sum of the powers of all the surfaces having negative power,
Similarly, it is desirable that the surface having strong positive power has a power of 60% or more of the sum of the powers of all surfaces having positive power.

As described above, it is the curvature error of the toroidal surface that is most likely to cause the deviation of the focusing position of the light beam due to the processing accuracy.

In this embodiment, when the curvature of the toroidal surface in the sub-scanning direction has an error of about 0.3%, the second lens 7
It was calculated that the focusing position shift was corrected by moving the optical axis direction of the.

According to this, the focus position of the light beam in the sub-scanning direction is deviated by about 4 mm with respect to the change of the curvature of the toroidal surface by 0.3%. And the permissible value of trouble is also reduced to about 1 minute and 1/10.
FIG. 6 and FIG. 7 show the performance as a result of correcting this by the movement of the second lens 7. FIG. 6 shows the field curvature characteristics, where the broken line is the main scanning direction and the solid line is the sub scanning direction. The vertical axis and the horizontal axis are the same as those in FIG. FIG. 7 shows the characteristic of the curvature aberration. The vertical axis and the horizontal axis are the same as those in FIG.

As can be seen from FIGS. 6 and 7, these aberrations are still sufficiently smaller than the permissible values, and it can be seen that there is no problem. Further, the allowable value of the above-mentioned troubles has been restored to the original design value in 10 minutes, and it can be said that there is a 10 times more effect of alleviating the troubles than the case where the present invention is not used. Further, the amount of movement of the lens 7 at the time of this correction was 0.3 mm.

FIG. 8 is a cross-sectional view showing a second specific example of a mechanism for moving and adjusting the second lens 7 in FIG. 1 in the optical axis direction in a cross section in the sub-scanning direction.

In this, the claw 31 for positioning the second lens 7 is fixed to the base 36 on the surface to be scanned of the lens 7, and is applied to the end surface of the lens 7 via the spacer 32.

On the other hand, from the rotary polygon mirror 4 side of the lens 7, the lens 7 is pressed against the spacer 32 by the spring 34 via the auxiliary plate 33 to be positioned and fixed. Where the thickness of the spacer 32,
Alternatively, the position of the second lens 7 can be adjusted by changing the number.

In the embodiment shown in FIG. 1, the second lens 7 included in the scanning optical system is moved to adjust the focusing position in the light beam sub-scanning direction, while FIG. 9 shows the present invention. FIG. 13 is a configuration diagram showing yet another example, which is an example in which adjustment can be performed by the other lens 6 (having negative power) included in the scanning optical system.

FIG. 10 is a sectional view in the sub-scanning direction of the embodiment shown in FIG. The first lens 6 included in the scanning optical system is a base
It is arranged above 41, is movable in the optical axis direction along a guide 45, is pressed against a positioning claw 43 via a spacer 43, and is fixed by a spring 44. The position of the lens 6 is adjusted by adjusting the thickness or the number of spacers 43.

In the present embodiment, as in the case of FIG. 1, the curvature of the toroidal surface of the second lens 7 is changed by 0.3%, and the position of the first lens 6 is adjusted to adjust the focusing position of the light beam. The resulting performance is shown in Figs.

FIG. 11 shows the characteristic of field curvature, the broken line is the main scanning direction,
The solid line represents the field curvature characteristic in the sub-scanning direction. The vertical axis and the horizontal axis are the same as those in FIG.

FIG. 12 shows distortion aberration characteristics. The vertical axis and the horizontal axis are the same as those in FIG.

As can be seen from FIGS. 11 and 12, even in the method of this embodiment, no significant performance deterioration occurs.
The amount of movement of the lens 6 is 0.35 mm, and the allowable value of the face tilt angle after adjustment has recovered to about 7 minutes.

〔The invention's effect〕

As described above, according to the present invention, in the light beam scanning device, the deviation of the focusing position of the light beam in the sub-scanning direction is independently maintained and the surface tilt correction condition is completely maintained (the surface tilt angle is allowable). While maintaining the effect of relaxing the value 10 times or more), there is an effect that the correction can be easily performed without degrading other performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a sectional view in the sub-scanning direction of the embodiment shown in the drawing, FIG. 3 is an enlarged perspective view of a movement adjusting mechanism of the second lens 7 in FIG.
FIG. 4 is a characteristic diagram showing field curvature performance in one embodiment of the present invention, FIG. 5 is a characteristic diagram showing distortion aberration performance in the same embodiment, and FIG. 6 is one embodiment of the present invention. FIG. 7 is a characteristic view showing the field curvature performance after adjustment, FIG. 7 is a characteristic view showing the same distortion performance, and FIG. 8 is a sectional view showing another specific example of the moving mechanism of the lens 7 in FIG. FIG. 9 is a constitutional view showing another embodiment of the present invention, FIG. 10 is a sectional view in the sub-scanning direction of the same embodiment, and FIG. 11 is a light beam by moving the lens 6 in the embodiment shown in FIG. Fig. 12 is a characteristic diagram showing the field curvature performance after adjusting the focusing position shift of Fig. 12, Fig. 12 is a characteristic diagram showing the same distortion aberration performance, and Fig. 13 is a conventional focusing shift of the light beam in the sub-scanning direction. FIG. 14 is a conceptual diagram showing the principle of the adjusting method, and FIG. 14 is a view for adjusting the focusing position deviation of the light beam in the sub-scanning direction in the present invention. Conceptual diagram showing the principle of the method, No. 15
The figure is a characteristic diagram showing the relationship between the lens movement amount and the focusing position change amount and the relationship between the lens movement amount and the performance deterioration amount. Explanation of reference numerals 1 ... Light source, 2 ... Collimator lens, 3 ... Cylinder lens, 4 ... Rotating polygon mirror, 5 ... Motor, 6 ... First lens included in scanning optical system, 7 ... Scan Second lens included in the optical system, 8 ... Scanned surface, 9 ... Rotation center axis of rotating polygon mirror, 10 ... Light beam before being deflected, 11 ...
… Defocused light beam, 12 …… movable base, 13 …… adjustment screw, 14 …… base, 16 …… support base, 20 …… lens moving guide, 31 …… positioning claw, 32 …… Spacer, 33 ...
… Auxiliary plate, 34 …… Spring, 35 …… Spring fixing screw, 36 ……
Base, 41 ... Base, 42 ... Positioning claw, 43 ... Spacer, 44 ... Spring, 45 ... Guide, 100 ... Deflection surface, 1
01: scanning optical system, 102: surface to be scanned, 103: cylinder lens, 104: collimator lens, 105: light source, 111
... Deflection surface, 112 ... Scanned surface, 113 ... Cylinder lens, 114 ... Collimator lens, 115 ... Light source

Claims (3)

(57) [Claims] 1. A light beam generator (1), a first optical system (3) for linearly focusing a light beam generated from the light beam generator (1), and the first optical system. A deflector (4) having a deflecting / reflecting surface (15) near the line image formed by (3), and a scan surface (8) scanned by the light beam deflected by the deflector (4). ) And the scanning surface (8) and the deflection reflection surface (15), and the reflection surface (15)
And a second optical system (6, 7) for realizing a tilt correction function by maintaining a positional relationship between the scanned surface (8) and the surface to be scanned (8) in an optically conjugate relationship. In the beam scanning device, a lens surface having the maximum negative power among the lens surfaces having negative power of each lens forming the lens group is provided in the lens group forming the second optical system. A second lens different from the first lens, which includes a first lens and a lens surface having the largest positive power among the lens surfaces having the positive power of each lens forming the lens group. And a light beam scanning device having a tilt correction function, wherein the first lens or the second lens is provided so as to be movable along the optical axis direction. 2. A light beam scanning device having a tilt correction function according to claim 1, wherein a surface of the first lens having a negative power is perpendicular to a scanning direction rather than a power in a scanning direction cross section. The surface having a shape in which the power in the scanning direction is stronger, and the surface having the positive power in the second lens is the power in the direction perpendicular to the scanning direction than the power in the scanning direction cross section. A light beam scanning device characterized in that the surface is shaped so as to be strong. 3. The light beam scanning device having a tilt correction function according to claim 1, wherein the surface of the first lens having a negative power has a magnitude of power perpendicular to the scanning direction. Is 0.6 times or more the sum of the powers of all surfaces having negative power, and the magnitude of the power of the surface having positive power of the second lens is positive in the direction perpendicular to the scanning direction. The sum of the powers of all surfaces that have the power of 0.
A light beam scanning device characterized by 6 times or more.