JPH0519202A - Optical beam scanning optical device - Google Patents

Abstract

(57) [Summary] [Objective] To correct the focus shift due to temperature change while using a plastic lens for the second imaging optical system, and at the same time to simplify the configuration of the collimator lens. A first imaging optical system 2 for linearly focusing light from a light source on a reflecting surface of a deflecting device, a deflecting device 6, and a light beam deflected by the deflecting device to be scanned. And a second imaging optical system 7 that converges on the surface.
Has an anamorphic plastic lens, and the first imaging optical system 2 is a light composed of a positive power glass spherical lens 3, a negative power aspherical plastic lens 4, and a glass cylindrical lens 5. Beam scanning optical device. [Effect] At the same time as temperature compensation, the number of collimator lenses is halved (two glass spherical lenses and plastic aspherical lenses), and a high-resolution optical beam using a plastic lens with an extremely simple structure is used for the entire device. A scanning optical device can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device for scanning with an optical beam and a recording device using the same.

[0002]

2. Description of the Related Art In a scanning device using an optical beam, when a deflecting device for deflecting the optical beam such as a rotary polygon mirror whose deflecting surface can be tilted with respect to rotation is used, the tilting of this surface (generally, " The optical beam shifts in the direction perpendicular to the scanning direction due to "face misalignment"), which causes unevenness of the scanning line pitch. To correct this, a method of using an imaging optical system in which a deflecting surface and a surface to be scanned (for example, a photosensitive drum surface) have a conjugate relationship in a surface perpendicular to the scanning direction is disclosed in, for example, Japanese Patent Publication No.
-28666 is known.

Further, the optical system of the above-mentioned scanning device is provided with a characteristic (generally referred to as "fθ characteristic") for the optical beam to scan the surface to be scanned at a constant speed in the plane in the scanning direction. The performance of correcting the field curvature is also required so that the size of the spot diameter of the light beam on the surface to be scanned is always uniform with respect to the position in the scanning direction.

As described above, the characteristics in the plane in the scanning direction (hereinafter referred to as "main scanning direction" or "section in the main scanning direction") and the plane perpendicular thereto (hereinafter "sub scanning direction" or "sub scanning direction"). In order to simultaneously realize the characteristics in "cross section"), optical systems having different powers in both planes are required, and a cylinder surface, a toroidal surface or the like is used.

FIG. 11 is a block diagram showing an example of a conventional scanning optical device. In this structure, the light emitted from the light source 1 comes from a collimator lens 92 that shapes the light into substantially parallel beams and a cylinder lens 93 that linearly forms an image of the light beam from the collimator lens. An image is formed on the reflecting surface 11 of the deflecting device 6 by the first image forming optical system 91.

The optical beam reflected by the reflecting surface 11 is the second beam.
The image forming optical system 94 of FIG. At this time, the optical beam sequentially changes its direction in accordance with the rotation of the deflecting device 6 and is reflected, so that the surface to be scanned 10 is scanned. The surface to be scanned 10 corresponds to, for example, a photosensitive drum in a laser printer, and the signal exposed by the optical beam is passed to the next process as an electrostatic image.

In such a device, the collimator lens 92 has a very high power and a large NA, and
Since the wavefront aberration is required to be corrected to be extremely small, it is usually composed of about five glass lenses. As described above, the second imaging optical system 94 makes the deflection reflection surface 11 and the surface to be scanned 10 conjugate with each other in the cross section perpendicular to the scanning direction, and corrects the fθ characteristic and the field curvature. In order to meet this requirement, the second image forming optical system 94 includes the cylindrical surface 94a and the toroidal surface 9a.
4b.

However, it is very difficult to manufacture a large number of glass lenses having a special shape such as a toroidal surface by polishing with high precision. On the other hand, a plastic lens can be mass-produced by injection molding, even if the lens has a special shape as described above. Therefore, an optical system using a plastic lens has been devised.

As such an optical system, there is, for example, JP-A-61-243422. This is a system in which the second imaging optical system is replaced with a plastic lens,
It makes it possible to manufacture lenses with complex shapes.

[0010]

When the conventional optical system as described above is applied to a scanning optical device having a higher resolution (a small scanning spot diameter is required), the plastic lens is affected by a change in environmental temperature. The optical characteristics change significantly, resulting in an unacceptable focus shift.
Since the collimator lens (92) is required to have a larger aperture, it has a complicated structure in which a larger number of lenses are combined, and the effect of simplifying the structure of the second imaging optical system is offset.
There was a problem such as. Hereinafter, these problems will be described.

First, the characteristic change of the plastic lens due to the temperature change will be described. The plastic lens has a large rate of change in refractive index and a large coefficient of expansion with respect to changes in temperature,
Therefore, it is well known that when the environmental temperature changes, a focus shift easily occurs (hereinafter simply referred to as "temperature shift"). Due to this focus shift, the scanning spot increases and the resolution deteriorates. The magnitude of the characteristic change of the plastic lens with respect to temperature is, for example, PMM.
In A, the power changes about 0.9% due to the rate of change in the refractive index and expansion even when the temperature changes by about 30 degrees.

From this, for example, the focal length of the second image forming optical system is about 300 mm in the case of a laser scanning optical system corresponding to A3 paper, and this is a plastic lens made of PMMA. In this case, the magnitude of the temperature shift is about 2.7 mm. The change amount of the spot diameter with respect to the temperature shift of 2.7 mm is such that the scanning spot diameter is 10
When it is 0 μm (when the resolution is relatively low as in the conventional case), it is about 1 μm, but when the scanning spot diameter is 60 μm, it becomes about 20 μm, which means that the resolution deteriorates by 30% or more, which is unacceptable. Become.

Next, the problem of the collimator lens will be described. The collimator lens is required to have a very large NA value and extremely small wavefront aberration as compared with other elements in the scanning optical device, and is usually composed of about 5 lenses. In order to make the scanning optical device compatible with high resolution and reduce the scanning spot diameter, it is necessary to increase the beam diameter in the main scanning direction which is incident on the deflecting device. Therefore, as a collimator lens, a larger NA is required. A large-diameter, large-diameter lens is required. This makes the structure of the collimator lens more and more complicated and significantly impedes the simplification of the entire optical device.

Collimation with an aspherical plastic lens
A method of simplifying the lens is that the power change of the plastic lens due to the temperature change is extremely large (focal length 5 to 10 mm).
This method cannot be applied easily because a large amount of focus shift occurs on the surface to be scanned.

An object of the present invention is to solve the above-mentioned problems and to correct a focus shift due to a temperature change while using a plastic lens for the second image forming optical system 6 and at the same time, to construct a collimator lens. And to provide a high-resolution optical beam scanning optical device having an extremely simple structure as a whole.

[0016]

In order to achieve the above object, the present invention provides a light source 1 that diverges light and a first imaging optical system 2 that linearly images the light from the light source 1. A deflecting device 6 having a deflecting / reflecting surface at an image forming position of the first image forming optical system 2; and a second beam converging optical beam deflected by the deflecting device 6 on the surface 10 to be scanned. Imaging optical system 7 and scanning surface 1
0, an optical beam scanning optical device comprising:
The image forming optical system 7 is constructed by using an anamorphic plastic lens, and the first image forming optical system 2 has one glass spherical lens 3 having a positive power and a negative power.
It is composed of an aspherical plastic lens 4 having the above and a glass cylindrical lens 5.

By using the aspherical plastic lens 4 having negative power in the first image forming optical system 2 as described above, the temperature shift caused by the plastic lens forming the second image forming optical system 7 is prevented. It has been found that, at the same time as the correction, the wavefront aberration of the glass spherical lens can be corrected to greatly simplify the configuration of the collimator lens.

Further, in the second image forming optical system 7, an anamorphic plastic lens having a strong power in the sub-scanning direction is arranged at a position satisfying the condition shown by the following equation to shift the temperature in the sub-scanning direction cross section. Can be within an acceptable value. L ₁ / L ₀ <L ₀ / (1 / C + L ₀ ) [where C = 0.0003 · ΔT] where ΔT is the temperature change range and L ₀ is the reflecting surface 11 of the deflecting device 6 and the scanning target. The distance L _{1 from the} surface 10 indicates the distance from the reflecting surface 11 of the deflecting device 6 to the anamorphic plastic lens.

Alternatively, a temperature shift in the sub-scanning direction is corrected by holding a cylindrical lens having a negative power in the sub-scanning direction in the first optical system and setting the power optimally.

Alternatively, one surface of the aspherical plastic lens having the negative power is made a cylindrical surface having the negative power, and the power in the sub-scanning direction is optimally set, whereby the sub-scanning direction is set. Correct the temperature shift of.

[0021]

The operation and principle of the above-mentioned elements constituting the present invention will be described. First, the light source 1 emits light and performs the same operation as a conventional light source. The glass spherical lens 3
Has the function of shaping the light from the light source into substantially parallel light beams. The plastic aspherical lens 4 corrects the aberration generated by the beam shaping effect of the glass spherical lens 3 to create a substantially parallel light beam with a small wavefront aberration, and at the same time, has a cross section in the main scanning direction. By having a negative power in, the action of compensating for the temperature shift due to the plastic lens forming the second image forming optical system 7 is performed.

The correction of the temperature shift by the plastic aspherical lens 4 (hereinafter referred to as "temperature compensation") will be described. In the cross section in the main scanning direction, if the second image forming optical system 7 is composed of a plastic lens, the magnitude of the temperature shift is almost determined by the focal length of the second image forming optical system 7. For example, as described above, when the focal length of the second imaging optical system 7 is 300 mm, the magnitude of the temperature shift is about 2.7 mm (temperature change of 30 degrees), which significantly deteriorates the resolution. In order to prevent deterioration of resolution in high resolution optical system, at least temperature shift 1
mm or less is required.

To correct this temperature shift, a plastic lens having a negative power may be used.
In order to achieve this in the second image forming optical system 7, it is necessary to maintain the focal length of the second image forming optical system 7 in order to obtain a predetermined scanning width, and it is conventionally known. You have to use glass lenses together.

Therefore, it has been found that by disposing the plastic lens having the negative power in the first optical system 2, only the temperature shift can be corrected without affecting the scanning width. Further, the power of the plastic lens can be almost completely corrected for the temperature shift by making the absolute value of the power of the plastic lens constituting the second imaging optical system 7 substantially equal to that of the plastic lens.

At this time, the plastic lens arranged in the first optical system 2 is used as an aspherical lens to have a great aberration correcting function, so that the aberration correcting action of the conventional collimator lens can be simultaneously performed. It has been found that it is possible and the collimator lens can be composed of a simple single glass spherical lens.

Next, the cylinder lens 5 has the same function as a conventional cylinder lens for linearly focusing the light beam. The second imaging optical system 7 has the function of causing the light beam spot on the surface to be scanned 10 at a constant speed (scanning f.theta. Characteristic), and the light beam spot on the surface to be scanned 10 to scan. It acts to correct the field curvature so that it becomes almost uniform regardless of the position. The anamorphic plastic lens forming the second image forming optical system 7 performs the function of keeping the reflecting surface 11 of the deflecting device and the surface to be scanned 10 in a conjugate relationship (surface tilt correction) in the cross section in the sub-scanning direction.

Here, the temperature compensation in the cross section in the sub-scanning direction will be described. In the cross section in the sub-scanning direction, as described above, the second imaging optical system 7 requires that the reflecting surface 11 of the deflecting device 6 and the surface to be scanned 10 have a conjugate relationship (surface tilt correction). , The object distance becomes very short when viewed from the second imaging optical system 7, and a surface having a large power is required only in the sub-scanning direction cross section. Therefore, in the cross section in the sub-scanning direction, the position of the principal point of the second image forming optical system is substantially determined by the lens having this large power, and the magnitude of the temperature shift is determined by this image forming relationship.

FIG. 3 is a diagram conceptually showing an image forming relationship in a cross section in the sub-scanning direction. In FIG. 3, the lens 21 represents the second image forming optical system at the principal point position of the second image forming optical system, and makes the reflecting surface 11 and the surface to be scanned 10 of the deflecting device conjugate. It indicates that

When the lens 21 is a plastic lens, when the temperature changes, the focus position of the lens 21 moves to the point A, causing a focus shift ΔF (that is, temperature shift). The magnitude of this temperature shift ΔF can be expressed by the following equation derived from the equation relating to image formation. ΔF = C · ΔT (L ₀ −L ₁ ) L ₀ / L _1- (1) Here, C is a constant relating to optical characteristics such as refractive index, and P
In the case of MMA, it is about 0.0003. Further, ΔT is a temperature change amount.

FIG. 4 shows the position L ₁ / L ₀ (L ₀ of the lens 21).
3 is a graph showing a change in temperature shift ΔF with respect to (normalized by) in Equation 1. As shown in FIG.
When the position of is close to the surface to be scanned 10, the temperature shift ΔF is sufficiently smaller than the allowable value 23, but it rapidly increases as it approaches the reflecting surface 11 of the deflecting device. This is because the imaging magnification increases as the distance from the surface to be scanned (10) increases, and the imaging position moves greatly with a slight power change.

In order to set the temperature shift ΔF to the allowable value 23 or less (that is, 1 mm or less), the position of the lens 21 must be set to a predetermined distance or less from the surface 10 to be scanned (see FIG. 4). This condition is expressed as the following formula from the condition of ΔF <1 in the formula (1). L ₁ / L ₀ <L ₀ / (1 / C + L ₀ ) --- (2) [where C = 0.0003 · ΔT]

On the other hand, the position of the lens 21, which indicates the principal point of the second imaging optical system, is almost determined by the position of the anamorphic lens having a large power in the cross section in the sub-scanning direction. Therefore, it can be said that the above expression (2) shows the condition of the position where the anamorphic plastic lens is to be arranged in order to realize the temperature compensation in the second imaging optical system 7.

Therefore, in the structure of the present invention, the second image forming optical system 7 is composed of two plastic lenses, and the anamorphic plastic lens is arranged so as to satisfy the above expression (2). The inventors have found that it is possible to perform the action of correcting the temperature shift in the cross section in the sub-scanning direction.

Alternatively, when the anamorphic plastic lens of the second imaging optical system 7 is arranged near the deflecting device 6, the first optical system 2 is a plastic having a negative power in the sub-scanning direction cross section. By adding the cylindrical lens 34, it is possible to correct the temperature shift in the cross section in the sub-scanning direction.

Alternatively, making either one of the surfaces of the aspherical plastic lens 43 of the first optical system 41 a concave cylinder surface having a negative power in the sub-scanning direction cross section,
A function of compensating for the temperature shift in the cross section in the sub-scanning direction can be performed.

[0036]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram in a main scanning direction cross section showing an embodiment according to the present invention, and FIG. 2 is a diagram showing a configuration in a sub scanning direction cross section.

In this embodiment, the light source 1 and the glass spherical lens 3 are used.
A first imaging optical system 2 including a plastic lens 4 having an aspherical surface symmetric with respect to the optical axis and a glass cylindrical lens 5, a rotary polygon mirror 6 serving as a deflecting device, and a plastic lens 8 having an aspherical surface symmetric with respect to the optical axis. It is composed of a second imaging optical system 7 including an anamorphic plastic lens 9 and a surface to be scanned 10.

Next, each operation will be described. The light source 1 is a semiconductor laser in this embodiment, and divergent light is emitted from the beam from the light source 1. In the first image forming optical system 2, the glass spherical lens 3 and the plastic lens 4 having an aspherical surface which is symmetric with respect to the optical axis collimate the divergent light from the light source 1 and are substantially parallel beams. In addition to the shaping, the position adjustment is performed so that the optical beam is converged on the surface of the surface to be scanned 10 in the cross section in the main scanning direction. The glass spherical lens 3 has a positive power, and the plastic lens 4 having an optical axis symmetric aspherical surface has a negative power. Further, the focusing may be performed only by the glass spherical lens.

The glass cylindrical lens 5 in the first imaging optical system 2 has a positive power in the sub-scanning direction cross section.
And a light beam from the plastic aspherical lens 4
The beam is converged only in the sub-scanning direction to form a line image on the reflecting surface 11 of the rotary polygon mirror 6.

The rotary polygon mirror 6 is rotated (by a motor or the like) in the direction of the arrow shown in FIG. 1, and the light beam is sequentially deflected by changing the reflection angle of the reflection surface 11. Scanning is performed once while one reflecting surface passes, and scanning is performed by the number of reflecting surfaces while the rotary polygon mirror 6 makes one rotation. In this embodiment, the maximum deflection angle of the light beam is ± 34 degrees. Also. The deflection scanning of the light beam is performed in a plane (main scanning plane) substantially perpendicular to the rotation axis of the deflecting device (that is, the rotation center of the polygon mirror 6), and the light source 1 and the first imaging optical system 2 are It is arranged so that its optical axis lies in the main scanning plane.

The second image-forming optical system 7 finally has a function of converging the light beam to one point on the surface to be scanned 10, and also has a reflecting surface 11 of the rotary polygon mirror in a cross section in the sub-scanning direction. By making the scanning surface 10 and the scanning surface 10 conjugate with each other, the positional deviation of the scanning line in the sub-scanning direction due to the inclination error (surface tilt) of the reflecting surface 11 of the rotary polygon mirror with respect to the rotation axis is prevented.

The second image forming optical system 7 also has a constant velocity scanning (f.theta. Characteristic) of the light spot on the surface to be scanned 10 described above by optimally correcting the aberration, and the spot size. Achieving uniformity. The plastic aspherical lens (8) constituting the second image forming optical system 7 has an aspherical surface that is biaxially symmetric on both sides, and mainly performs the aberration correction action of f · θ characteristic and field curvature.

The surface of the anamorphic plastic lens 9 forming the second image forming optical system 7 on the side of the deflecting device 6 is a toric surface, and the surface on the side of the surface to be scanned 10 is an aspheric surface which is symmetrical about the optical axis. Thus, the reflecting surface 11 of the rotary polygon mirror and the surface to be scanned 10 are made to have a conjugate relationship mainly in the cross section in the sub-scanning direction. The surface to be scanned 10 corresponds to, for example, a photosensitive drum in a laser printer or the like, a signal is recorded by exposure with an optical beam, and the signal is passed to the next process.

Next, the temperature compensation method of this embodiment will be described. FIG. 5 is a diagram for explaining temperature compensation in the main scanning direction of this embodiment. FIG. 5 shows the light source 1 to the surface to be scanned 10 of this embodiment arranged along the optical path. Figure 5
In, the solid line 24 with an arrow and the broken line 25 schematically represent the state of the light beam after the temperature change.

A broken line 25 shows a case where a temperature shift is caused by the plastic lenses 8 and 9. In order to compensate for this, a plastic lens having a negative power may be used as described above, but if it is simply arranged in the second image forming optical system 7, the second image forming optical system 7 may be used. Power of system
Since it becomes impossible to obtain a predetermined scanning width, it becomes necessary to introduce a glass lens, and the optical system becomes very complicated. Therefore, it has been found that by disposing the plastic lens having the negative power in the first optical system (2), only the temperature shift can be corrected without affecting the scanning width.

Further, at this time, the surface of the plastic lens arranged in the first optical system (2) is made an aspherical surface to simultaneously perform a strong aberration correcting action, thereby collimating the conventional collimator lens. It becomes possible to perform the action with one simple glass spherical lens,
The inventors have found that the conventional collimator lens can be realized with an extremely simple structure. The power of the plastic lens 4 is substantially equal in absolute value to the power (usually positive power) of the plastic lens forming the second image forming optical system 7 and has an opposite sign (that is, negative power). By setting-), the temperature shift can be corrected almost completely.

In FIG. 5, a solid line 25 with an arrow shows the ray after being compensated in this way. In this way, it was clarified that an optical device having an extremely simple structure can be realized as the entire system including the first imaging optical system 2.

The temperature compensation in the sub-scanning direction is realized by arranging the anamorphic plastic lens 9 having a large power in the sub-scanning direction near the surface to be scanned 10 according to the above-mentioned FIG.

In this embodiment, the reflecting surface 1 of the deflecting device 6 is used.
The distance from 1 to the scanned surface 10 is 370 mm, and the distance between the anamorphic plastic lens 9 and the scanned surface 10 is 80 mm. The magnitude of the temperature shift in this embodiment is 0.1 m in the main scanning direction with respect to a temperature change of 30 ° C.
m, 0.8 mm in the sub-scanning direction, both of which satisfy the target performance for a high-resolution optical system. The scanning spot size on the surface 7 to be scanned of the optical device of this embodiment is 60 μm.
(1 / e ² spot diameter).

FIG. 6A shows the field curvature performance of this embodiment. The solid line 26 is the main scanning direction and the broken line (27) is the sub scanning direction.

FIG. 6B shows the performance of the amount of deviation from the f.theta. Characteristic (hereinafter referred to as linearity).

In FIGS. 6A and 6B, the vertical axis represents the scanning position as a relative value, and zero represents the center of scanning.

Further, in the above anamorphic plastic lens 9 of the present embodiment, the toric surface may be set on the surface to be scanned 10 opposite to that of the present embodiment, or on both surfaces of the anamorphic plastic lens 9 of the present invention. It does not impair the effect.

FIG. 7 is a block diagram in the main scanning direction cross section showing a second embodiment according to the present invention, and FIG. 8 is a block diagram in the sub scanning direction cross section. The present embodiment differs from the first embodiment in that the anamorphic plastic lens 38 of the second imaging optical system 36 is arranged near the deflecting device 6. With the above arrangement, the temperature shift in the sub-scan section becomes large as described in FIG. 4, but it is compensated by adding a plastic cylindrical lens 34 having a negative power in the sub-scan direction to the first imaging optical system 31. is doing. The plastic cylindrical lens 34 having the negative power has a function of moving the image forming position of the first image forming optical system 31 in the sub-scan section when the temperature changes, and thereby the second image forming optical system. System 36
It is possible to correct the temperature shift due to the plastic lens.

With the above construction, the number of lenses of the first image forming optical system 31 is increased as compared with the first embodiment, but the effect of the present invention, which can greatly simplify the conventional collimator lens, is impaired. is not. As a result, the size of the anamorphic plastic lens 38 of the second imaging optical system 36 can be made smaller than that of the first embodiment.

FIG. 9 is a block diagram in the main scanning direction cross section showing the third embodiment according to the present invention, and FIG. 10 is a block diagram in the sub scanning direction cross section. In this embodiment, the second
In contrast to the above embodiment, the second imaging optical system is composed of one anamorphic plastic lens 45, and the first imaging optical system 41 has the functions of the plastic cylindrical lens and the plastic aspherical lens. It is realized by a plastic lens 43 having two negative powers, and is composed of three lenses including a glass spherical lens 42 and a glass cylindrical lens 44.

In the plastic lens 43, the surface 43a on the light source 1 side is an aspheric surface which is symmetric about the optical axis, and the surface 4 on the side opposite to the light source 1 is formed.
3b is composed of a cylinder surface having a negative power in the sub-scanning direction. The surface 43a corrects the wavefront aberration by the glass spherical lens 42, and also corrects the temperature shift in the main scanning direction by the plastic lens 45 of the second imaging optical system.

The surface 43b corrects the temperature shift in the sub-scanning direction due to the anamorphic plastic lens 45 of the second image forming optical system. The surface 45a of the anamorphic plastic lens 45 on the deflecting device 6 side is a toroidal surface having negative power, and the surface 45b on the scanned surface 10 side has the same shape as the meridional section of the axisymmetric aspherical surface in the main scanning section and the sub scanning section. In (1), the toroidal surface has a large positive power and corrects all the aberrations required for the second imaging optical system.

In the present embodiment, even if the surface 45a is a toroidal surface having the same shape as the meridional section of the axisymmetric aspherical surface in the main scanning section, the effect of the present invention is not impaired. Further, the same effect can be obtained by using a toroidal surface having the same shape as the meridional section of the axisymmetric aspherical surface in the main scanning section for the plastic lens 43 having the negative power in the same manner as the surface 45b.

Needless to say, the above-described optical beam scanning optical device according to the present invention can be used not only in laser printers but also in recording devices such as copy devices and facsimile output devices. It can also be applied to a device for directly recording a signal on a device such as a computer.

[0061]

As described above, according to the present invention, it is possible to facilitate the production of a lens having a special shape by using a plastic lens in spite of a scanning optical device having a minute scanning spot size corresponding to high resolution. In addition, the focus shift with respect to the temperature change is sufficiently corrected so that the resolution is not deteriorated, and further, the collimator lens, which is conventionally composed of 3 to 5 lenses, is replaced with two glass spherical lenses and plastic aspherical lenses. The number of lenses can be reduced to less than half, and the optical beam scanning optical device can be realized with an extremely simple structure as a whole.

[Brief description of drawings]

FIG. 1 is a configuration diagram in a main scanning section showing an embodiment of the present invention.

FIG. 2 is a configuration diagram in a sub-scan section showing an embodiment of the present invention.

FIG. 3 is a conceptual diagram showing an image formation relationship in a cross section in the sub-scanning direction.

FIG. 4 is a graph showing changes in temperature shift amount in a cross section in the sub-scanning direction.

FIG. 5 is an explanatory diagram showing a temperature shift in a cross section in the main scanning direction.

FIG. 6 is an aberration diagram showing optical performance of an example according to the present invention.

FIG. 7 is a configuration diagram in a main scanning section showing a second embodiment of the present invention.

FIG. 8 is a configuration diagram in a sub-scan section showing a second embodiment of the present invention.

FIG. 9 is a configuration diagram in a main scanning cross section showing a third embodiment of the present invention.

FIG. 10 is a configuration diagram in a sub-scan section showing a third embodiment of the present invention.

FIG. 11 is a configuration diagram showing an example of a conventional scanning optical device.

[Explanation of symbols]

1 light source 2 First imaging optical system 3 glass spherical lens 4 Plastic aspherical lens 5 glass cylindrical lens 6 Deflection device 7 Second imaging optical system 8 plastic aspherical lens 9 plastic toroidal lens 10 Scanned surface 11 Reflective surface of deflection device

Claims (9)

[Claims] 1. A light source 1 for diverging light and a first imaging optical system 2 for linearly imaging the light from the light source 1.
A deflecting device 6 having a deflecting / reflecting surface at an image forming position of the first image forming optical system 2; and a second beam converging optical beam deflected by the deflecting device 6 on a surface 10 to be scanned. Imaging optical system 7 of
The second imaging optical system 7 includes at least one anamorphic plastic lens, and the first imaging optical system 2 is a glass having a positive power. An optical beam scanning optical device comprising a spherical lens 3, a plastic lens 4 having a negative power, and a glass cylindrical lens 5. 2. The plastic lens 4 having the negative power has substantially the same size as the power of the plastic lens of the second image forming optical system 7 in the cross section in the scanning direction, but has the opposite sign. 2. The optical beam scanning optical device according to claim 1, further comprising: a focus error which is caused by a change in temperature caused by the plastic lens of the second image forming optical system 7. 3. The optical beam scanning optical device according to claim 2, wherein the plastic lens 4 having the negative power has an asymmetrical aspherical surface. 4. The optical beam scanning optical device according to claim 3, wherein the anamorphic plastic lens 9 in the second image forming optical system 7 is arranged at a position represented by the following equation. L ₁ / L ₀ <L ₀ / (1 / C + L ₀ ) [where C = 0.0003 · ΔT] where ΔT is the temperature change range and L ₀ is the reflecting surface 11 of the deflecting device 6 and the scanning target. The distance L _{1 from the} surface 10 indicates the distance from the reflecting surface 11 of the deflecting device 6 to the anamorphic plastic lens. 5. A light source 1 for diverging light and a first imaging optical system 3 for linearly imaging the light from the light source 1.
1, a deflecting device 6 having a deflecting / reflecting surface at an image forming position of the first image forming optical system 31, and a light beam deflected by the deflecting device 6.
Second imaging optical system 36 for converging the beam on the surface to be scanned 10
And the surface to be scanned 10, the second imaging optical system 36 has at least one anamorphic plastic lens, and the first imaging optical system 31 has a positive power. The glass spherical lens 32 having the same, the plastic lens 33 having negative power, and the plastic cylindrical lens 34 having negative power in a cross section perpendicular to the scanning direction.
And an optical beam scanning optical device comprising a glass cylindrical lens (35) having a positive power in a cross section perpendicular to the scanning direction. 6. The plastic lens 33 having the negative power has substantially the same size as the power of the plastic lens of the second imaging optical system 36 in a cross section in the scanning direction, but has a power of the opposite sign. 6. The optical beam scanning optical device according to claim 5, wherein the optical beam scanning optical device according to claim 5, further comprising: for correcting a focus shift with respect to a temperature change caused by the plastic lens of the second imaging optical system. 7. The optical beam scanning optical device according to claim 6, wherein the plastic lens 33 having the negative power has an aspherical surface which is symmetric with respect to the axis. 8. The plastic lens 4 having the negative power has an anamorphic aspherical surface, and has substantially the same size as the power of the plastic lens of the second image forming optical system 7 in the cross section in the scanning direction. An optical beam scanning optical device according to claim 3, wherein the optical beam scanning optical device has powers of opposite signs. 9. The plastic lens 4 having the negative power has one surface formed by an axisymmetric aspherical surface and the other surface formed by a cylindrical surface, and has a second connecting surface in a cross section in the scanning direction. 4. The optical beam scanning optical device according to claim 3, wherein the optical beam scanning optical device has a power having substantially the same size as the power of the plastic lens of the image optical system 7 and an opposite sign.