JPH0362013A - Optical scanner - Google Patents

Abstract

PURPOSE:To mechanically and well correct the curvature of field of the entire part of an optical system by oscillating a linear imaging lens in synchronization with the period of optical scanning so as to negate the curvature of field. CONSTITUTION:At least the linear imaging lens 14 of the 1st imaging optical system which forms image like a main scanning line is moved to negate the direction of negating the curvature of field in synchronization with the luminous flux scanning by a rotary polyhedral mirror 18. Namely, this optical scanner is so constituted that a cylindrical lens 14 is moved in an optical axis direction via a mounting member 15 in accordance with the synchronization signal obtd. with a photodetector 22b to negate the curvature of field of the optical system. The curvature of field over the entire part of the optical system is mechanically and well corrected in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical scanning device, and particularly to an optical scanning device having a field curvature correction function.

[Conventional technology]

Generally, optical scanning devices that reproduce images by performing main scanning and sub-scanning based on original images and image signals are widely used in digital copying machines, laser printers, laser plotters, laser fax machines, laser plate making machines, etc. It is being

An example of such an optical scanning device is shown in FIG. 20.

That is, a light beam emitted from a light source 1 such as a laser diode is collimated by a collimator lens 2 forming a collimating optical system, peripheral light is cut by an aperture 3, and the light beam emitted from this aperture 3 is passed through an imaging optical system. The light is focused to form a linear image by a linear imaging lens 4 forming a system.

The light beam thus formed is deflected by a rotating polygon mirror 5 having a plurality of deflection and reflection surfaces, and linearly scanned (in the main scanning direction) on a photosensitive drum 6, which is an example of a scanned medium. The imaging surface (main scanning line) formed by the linear imaging lens 4 is subject to field curvature due to residual errors of various optical characteristics, and is deflected in an arc shape as shown by the broken line in FIG. Therefore, there is a problem in that perfect linear scanning is not performed along the photoreceptor drum 6, and the light spot line on the photoreceptor becomes distorted and its diameter becomes large.This problem was solved by mechanical means and optical means. It is proposed to do so.

An example of the above mechanical means is JP-A-57-14'8
As shown in Japanese Patent No. 20 and Japanese Patent Application Laid-Open No. 116603/1983, the light source is synchronized with the movement angle of the rotating polygon mirror, in other words, the light source is synchronized with the movement of the imaging point by the reflecting surface of the rotating polygon mirror. Some lenses move (vibrate) the position of the lens in the direction of the optical axis so that the final image plane forms an accurate straight line.

Further, as an example of mechanical means, Japanese Patent Application Laid-Open No. 58-57
As shown in Publication No. 108, the light source is fixed, and the final image forming plane is made to be in an accurate straight line by moving (vibrating) the collimator lens and the condensing lens in the optical axis direction along with the deflection scanning. There is something I am doing.

On the other hand, rotating polygon mirrors are often used to speed up main scanning, and in this case, errors generally occur in the relative positional accuracy of each of the multiple reflecting surfaces. Variations occur in the final imaging plane due to surface tilt errors. In order to correct this, JP-A-63-10
A surface tilt correction optical system as shown in Japanese Patent No. 6618 is used. That is, this surface tilt correction optical system directs the light beam deflected by the one-rotation polygon mirror to the scanned medium (for example, a photoreceptor drum).
The imaging optical system that forms an image on the surface of the object is created by forming multiple lenses with a combination of spherical surfaces and toric surfaces so that the deflection reflecting surface and the scanned medium have a geometrically conjugate relationship. Corrections are being made.

[Problem to be solved by the invention]

As described above, by moving the light source or lens in the optical axis direction, the curvature of field in the main scanning direction can be corrected, but as the light source moves, a new curvature of field in the sub-scanning direction is generated. This field curvature must also be corrected at the same time. However, since the lenses in the optical system are spherical lenses, there is an astigmatism difference, and for this reason, by moving the light source or lens in the optical axis direction, the positive and
It is extremely difficult to reduce the curvature in the sub-plane scanning direction to a negligible level.

In addition, when using a surface tilt correction optical system without moving the light source, etc., the direction of the X coordinate axis and the Y coordinate axis, in other words, the main
A lens with different power in each sub-scanning direction,
For example, since a cylindrical lens exists in the optical path,
As a result, the curvature of field in the main and sub-scanning directions differs, and it is currently impossible to completely correct these.

Generally speaking, in a surface tilt correction optical system that does not have a mechanism for mechanically correcting field curvature, the main and sub-scanning field curvature, f
Theta characteristics (magnification error, linearity), spherical aberration, and sine conditions are the design conditions for fθ lenses, but since these various conditions have a relationship where they influence each other, all conditions must be made good. is extremely difficult.

Therefore, if the field curvature among these various conditions can be corrected satisfactorily, the degree of design freedom for improving the other conditions will increase, and the design will become easier. Furthermore, as the density of scanning optical systems has increased in recent years, various precision requirements for f-theta lenses and the like have become higher, and the number of lenses has also increased, making adjustment difficult and resulting in increased costs.

Therefore, an object of the present invention is to be applicable to an optical scanning device using a one-sided tilt correction optical system, to facilitate the design of lens optical systems such as an fθ lens, a collimator lens, and a cylindrical lens, and to improve the design of a scanning optical system. It is an object of the present invention to provide a high-performance, inexpensive optical scanning device that can sufficiently cope with increased density without using a complicated lens system with a large number of lenses.

[Means to solve the problem]

In order to achieve the above-mentioned object, an optical scanning device according to the present invention includes a collimating optical system that converts a light beam emitted from a light source into a parallel light beam, and a first collimating optical system that forms a linear image of the light beam emitted from this collimating optical system. an imaging optical system, a rotating polygon mirror having a deflecting reflection surface that deflects and scans the light beam emitted from the first imaging optical system, a scanned medium that is scanned by the light beam deflected by the rotating polygon mirror; The deflection-reflection surface and the scanned medium are arranged between the scanning medium and the rotating polygon mirror in a plane perpendicular to the deflection plane of the light beam deflected by the rotation polygon mirror's deflection-reflection surface. a second imaging optical system that maintains a conjugate relationship with the rotary polygon mirror; and a surface tilt correction optical system that moves the light flux of the first imaging optical system in the optical axis direction as the light flux is scanned by the rotating polygon mirror. In the scanning device,
a drive source for moving at least the linear imaging lens of the first imaging optical system in the optical axis direction in synchronization with the linear scanning by the rotating polygon mirror; , a cone-shaped amplitude magnifier having a large diameter tip and a small diameter tip, the base end of which is fixed to the vibration surface of the vibrator, and the tip of which supports the linear imaging lens. It is characterized by this.

[For production]

The optical scanning device according to the present invention provides a first optical scanning device that forms an image in the form of a main scanning line.
At least a linear imaging lens of the imaging optical system is moved in a direction to cancel field curvature using a drive source consisting of a vibrator and an amplitude magnifier in synchronization with light beam scanning by a rotating polygon mirror. This makes it possible to improve the quality of the reproduced image that is finally obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic top view of a field curvature correction optical system in an optical scanning device according to an embodiment of the present invention. A collimator lens 12 forms a parallel beam of light, and an aperture 13 disposed behind the collimator lens 12 cuts off unnecessary peripheral parts to form a linear beam of light. This linear light beam is imaged onto a surface of a photoreceptor drum 21, which will be described later, by a cylindrical lens 14, which is an example of a linear imaging lens forming a first imaging optical system. The light beam passing through the cylindrical lens 14 is deflected and scanned by a polygon mirror 18, which is an example of a rotating polygon mirror having a deflection reflecting surface. Then, the deflected and scanned light beam is
A spot image is formed on the circumferential surface of the photoreceptor drum 21 via the fθ lens 19 and the cylindrical lens 20 sequentially.

The fθ lens 19 maintains a geometrically optically conjugate relationship between the mirror surface of the polygon mirror 18 and the photoreceptor drum 21 in a plane perpendicular to the plane of deflection of the light beam deflected by the mirror surface of the polygon mirror 18. be.

Further, the light beam at the end of scanning is guided by a mirror 22a to a photodetector 22b, and this photodetector 22b is used as a reference for data writing synchronization.

Then, the cylindrical lens 14 is moved in the optical axis direction via the mounting member 15 by a drive source, which will be described later, based on a synchronization signal obtained by the photodetector 22b, thereby canceling the field curvature of the optical system. ing.

FIG. 2(A) is a conceptual optical path diagram developed on the deflection scanning surface (main scanning surface) side of the optical system of the optical scanning device shown in FIG. 1, and FIG. 2(B) is , is a conceptual optical path diagram developed perpendicular to the deflection scanning plane, that is, on the sub-scanning plane.

In this optical system, the fθ lens 19 is an anamorphic optical system, and the surface tilt correction is performed by arranging the mirror surface of the polygon mirror 18 and the image surface in a geometrically conjugate relationship in the sub-scanning direction. .

As one configuration of the optical system for correcting surface tilt, which is a feature of the present invention, the curvature of field is corrected by moving the cylindrical lens 14 in the optical axis direction as shown in FIG. Details of the moving state of the lens 14 will be explained using FIG. 3.

In the figure, the state of the cylindrical lens 14 before movement is shown by a solid line, and the state after movement is shown by a broken line.

Therefore, when the amount of movement of the cylindrical lens 14 is Δcy, the amount of movement of the imaging position is ΔcmS, and the imaging position of the cylindrical lens 14 before movement and the fθ lens 19
Let S be the distance from the front principal point H.

If the image distance of the fθ lens 19 is S', and the focal length of the fθ lens 19 is f, then s=s' ・f/ (S' - f) S+Δcy=(S' -Δzs) f/(S' -Δ1s
-f), therefore, Δcy=Δ 5-f2/(S'-Δ s −f)(S
'-f).

Here, if Δcy 5 ((S'-f), Δcy'': Δ1
s-f''/(S' f)2=ΔWork S/Durance However, m=S'/S.

From the above explanation, when the amount of field curvature is Δxs, the sub-scanning field curvature can be corrected by moving the cylindrical lens 14 by Δcy=Δ■S/rrI'.

At this time, regarding the main scanning, as shown in FIG. 2(A), there is no power of the cylindrical lens 14, so there is no change in the curvature of field.

Further, as a specific example of the occurrence of field curvature before correction, for example, the solid line is the field curvature in the sub-scanning direction, and the broken line is the field curvature in the main scanning direction. represents curvature. What is the field curvature before correction?

Since it is designed to be small in the main scanning direction and no consideration is given to reducing the curvature of field in the sub-scanning direction, the curvature of field is arcuate or parabolic. The amount of field curvature ΔS in this embodiment is approximately 10 ww+ at a position of ±30° in terms of the scanning half angle of the polygon mirror 18 (±15° in terms of the rotation angle of the polygon mirror 18).

Such a curve of field curvature can be approximated by a portion of a sine wave or a cosine wave, and when the amount of correction and the amount of curvature of field are plotted, the result is as shown in FIG. That is, if the amount of field curvature of ±30" in FIG. However, θ is the rotation angle of the polygon mirror 18, and when θ=O, the image height ratio becomes 0.

In this example, since the number of mirror surfaces of the polygon mirror 18 is six, the polygon rotation angle θ on one mirror surface is ±
30 @ roar.

Therefore, between this ±30', the cylindrical lens 14
If it moves by n periods (n is an integer greater than or equal to 1), the mirror surface and the polygon mirror 19 can be synchronized. In other words, when the number of mirror surfaces of the polygon mirror 18 is N, the polygon mirror rotation angle θ is ±180'/N, and n
The cylindrical lens 14 moves by the period. In this way, the curvature of field in the secondary scanning direction can be corrected as shown in FIG. 4(B).

Next, one of the field curvature correction optical systems that is a feature of the present invention.
As shown in FIG. 6(A) and FIG. 6(B), a cylindrical lens 23 is additionally provided, and by moving this cylindrical lens 23 in the optical axis direction, the field curvature in the sub-scanning direction is reduced. This is to correct the 6th
As shown in FIG. 6(A) is an optical path diagram showing the surface on the deflection scanning surface (main scanning surface) side, and FIG. Collimator lens 12
A cylindrical lens 23 having power in the main scanning direction is disposed between the polygon mirror 18 and the cylindrical lens 18, and similarly to the cylindrical lens 14 described above, it moves in the optical axis direction to correct field curvature in the main scanning direction.

In the main scanning plane, if the distance between the rear principal point of the cylindrical lens 23 and the front principal point of the fθ lens 9 is d, and the focal lengths of the cylindrical lens 23 and the fθ lens 19 are fcy f5θ, then the fθ lens 19
The distance S' between the rear principal point and the overall focal position of the cylindrical lens 23 and fO lens 19 is S' = ffθ (fay' - d)/(fcy' + f
fθ−d).

Also, since the parallel light flux from the collimator lens 12 enters the cylindrical lens 23 via the cylindrical lens 14, the amount of field curvature at this time is set as Δprocess M, and the corresponding correction movement amount of the cylindrical lens 23 is Δcy.
' Then, in the same way as in the case of Δcy described above, Δcy' = ΔM - ffθ/(S' - ΔIN - f f
θ)(S'-ffθ).

Therefore, by moving the cylindrical lens 23 independently of the cylindrical lens 14 described above, it is possible to correct the field curvature in both the main scanning direction and the sub-scanning direction.

Specific examples of corrections made in this way include:
For example, as shown in Japanese Unexamined Patent Publication No. 172317/1982, in an optical system having the spherical aberration/sine conditions, field curvature, field curvature, and fθ characteristics shown in FIG. 7(A), a cylindrical lens 14 The movement of ΔIs(θ)=−Δ1s−cos(18θ)+Δworks′
Then, correction is made so that the cylindrical lens 23 is moved by ΔIM(θ)=ΔIM−sin(6θ).

Here, the values of N and n mentioned above are N=6, n=3 in the sub-scanning direction, and n=1 in the main-scanning direction.

On the other hand, as shown in FIG. 9(A) showing a surface in the main scanning direction and FIG. 9(B) showing a surface in the sub-scanning direction, an elongated cylindrical lens 24 in which an fθ lens 19 is arranged in the main scanning direction
It goes without saying that even in an optical scanning device that includes a surface tilt correction optical system including the above, the curvature of field can be corrected by moving the cylindrical lens 14 in the optical axis direction in the same manner as described above.

Further, the present invention can also be applied to the optical system shown in FIG. 10(A).

That is, the emitted light beam from the laser light source 25 is collimated by the collimator lens 26, reflected by the mirror 27, and then emitted onto the reflective surface of the polygon mirror 28. This mirror 27 is designed to shorten the longitudinal dimension of the optical system by folding the mirror 27 in order to go against the demand for more compact equipment since arranging the entire optical path in a straight line would lengthen the overall dimension of the optical system. It was established with the intention of

The light beam deflected by the polygon mirror 28 is converted into a linear light beam corresponding to main scanning by a linear imaging lens 29, and the light beam deflected by the polygon mirror 28 is turned into a linear beam corresponding to main scanning. A geometrically conjugate relationship is maintained between the mirror surface of the polygon mirror 28 and the scanned medium (photosensitive drum 31) in a plane perpendicular to the plane of deflection of the light beam deflected by the polygon mirror 28.

Further, in the optical system shown in FIG. 10(A), the waist position in the main scanning direction is shown by a solid line and the position in the sub-scanning direction is shown by a broken line as shown in FIG. 10(B). There is.

Furthermore, as for the field curvature, as shown in FIG. 10(C), the curvature in the main scanning direction is shown by a solid line, and the curvature in the sub-scanning direction is shown by a broken line.

In this case, the curvature of field in the sub-scanning direction is practically negligible, and in order to correct the curvature of field in the main-scanning direction, the linear imaging lens 29 must be synchronized with the deflection angle of the polygon mirror 28. This vibration is performed at a frequency F and an amplitude Δ.

Then, the characteristic obtained by superimposing the curve representing the state of this field curvature and the curve representing the vibration of the linear imaging lens 29 is obtained as the eleventh characteristic.
As shown in the figure.

That is, the curvature of field is shown by a dashed line, and the vibration is shown by a solid line. This is the position coordinate of the body drum 31 in the main scanning direction, and in the case of vibration, it is the time axis. In addition, the vertical axis is the amount of field curvature in the case of field curvature,
In the case of vibration, it is the amount of vibration (amplitude).

Therefore, by applying vibration in synchronization with the change period of the field curvature, the field curvature can be reduced to a practically negligible extent. The frequency F of the vibration in this example is 1, for example 4.25 KI (z), and the amplitude Δ is 235 μm.

Next, a specific example of a drive source for vibrating the linear imaging lens on each side will be described.

The drive source in the present invention uses a piezoelectric, electrostrictive, or magnetostrictive vibrator to which a cone-shaped amplitude expander is fixed. When a conical shape is used as the amplitude expander, its shape is mainly shown in FIGS. 12(A) to 12.
There is something shown in each of Figure (D).

That is, the amplitude expander 32A shown in FIG. 2(A) is formed into a cylindrical shape with a large diameter on the base end side (the side where the vibrator is fixed) and on the distal side (the side where the cylindrical lens 14 is fixed). side) is formed into a small-diameter columnar shape, and the space between the two is continuous with a smooth arc-shaped curve.

Further, the amplitude expander 32B shown in FIG. 12(B) is formed continuously with a catenoidal curve between the base end side and the distal end side, and the amplitude expander 32C shown in FIG. 12(C) is It is formed by an exponential curve, and is shaped like a truncated cone as shown in FIG. 12(D).

Amplitude expanders 32A~ formed in various shapes in this way
32D (hereinafter collectively referred to as "amplitude magnifier 32") is made of mild steel, nickel-chromium steel, etc. In this example, the conical amplitude magnifier 32D (Fig. 12 ( (see D)).

The various quantities necessary for designing each part of this amplitude expander 32A are shown below.

SL: Cross-sectional area of large-diameter end (-) S2: Cross-sectional area of small-diameter end (aj) D: Diameter of large-diameter end (all) D2: Diameter of small-diameter end (■) ρ: Density of material (g/ad) C: Speed of sound in material (■/5ec) ω: Resonance angular frequency 2 if (1/see) m Mass of Nijilintorical lens 14 (g) mt Equivalent mass of Nijilintorical lens 14 (g) Party; Length (range) of half-wavelength resonance A: Mass coefficient ω・m t / S z・ρ・CCt
Speed of sound in the nijilintorical lens 14 (B/5e
e) Qt: Length (L5) of the cylindrical lens 14 whose cross section is approximately -like αt: Coefficient (,1/Ct (1/an) Now,
If the diameters D□, D2 of the large and small diameter ends of the amplitude expander 32 are set to D:D = 7:1, it is obvious that the ratio of the cross-sectional areas S, S2 of the large and small diameter ends, that is, Sl
:52=7'' :1, so 1 77 go π=7.

Further, as shown in FIG. 13, the shape of the cylindrical lens 14 is such that each of the height Ll, depth L2, and width is la.
n, and if the material of the cylindrical lens 14 is BK7, the density ρ is 2.54 (g/a+?), so its approximate mass is Ll XL2 XL, x ρ = 2.54 (g ).

Here, the mass m of the cylindrical lens 14 including the mass of the attachment member for fixing the cylindrical lens 14 to the tip of the amplitude expander 32 is assumed to be 20 (g).

Also, the coefficient αt is ω/Ct, so αt=2πX4
．． 25 X↓Q315.2 XIO'=0.051
4, and if the length of the cylindrical lens 14 including the mounting housing is Qt = 4 (an), αt - Qt = 0.0514x4 = 0.2056,'', t
anαt-12t=0.2085 On the other hand, the equivalent mass mt of the cylindrical lens 14 is mt=m-tan(αt)・Qt/αt-Qt, so mt=20.28 (g) Also, the mass coefficient A is A=ω+mt/S2+ρ・C=2π×・20.28/(πX (1/2) ”X7.
8 x 5.2 x 10') = 4. OX 10-'
is obtained.

Also, V1]-71chi-=7 and A=4,0X1o-'
=o, the value of αt-n is 3.93 from the graph shown in FIG.

Therefore, the length of the amplitude expander 32 is 12=3.93/αt=3.9310.05 ], 4
=76.46 (cm).

On the other hand, the conical (truncated cone-shaped) amplitude expander 32D is
As shown in FIG. 15, a vibrator 33 is often directly soldered or silver brazed to the base end thereof, and a cylindrical lens 14 is fixed to the tip of the amplitude expander 32 via a mounting member 15.

In this case, it is necessary to fix the amplitude expander 32 to an immovable member such as an external base via a suitable support member 34, and this fixed support position may be the cylindrical surface of vibration (so-called nodal point). desirable.

That is, the distance to the vibration nodal surface (the distance from the end surface of the amplitude expander 32 to the cylindrical surface) in the characteristics of the amplitude distribution as shown in FIG. 16 caused by the vibration of the vibrator 33 is expressed as
Then, XN / Q = tan-1 [α・Q・x 2
/(fGoNeg7717possible-1)]/α・α is established, so by substituting the above-mentioned quantities into the above formula, XN
=26.4 ((1)) is obtained.

Therefore, with XN=26.4 (ai) as the support point,
The amplitude of the vibrator 33 can be most effectively transmitted to the cylindrical lens 14 when it is fixedly supported by the support member 34, and for example, an exponential type amplitude expander 32' is interposed at the tip of the amplitude expander 32. By doing so, a larger amplitude expansion can be achieved.

The amplitude magnification factor of such a conical horn is, for example, as shown in FIG. 17, when the area ratio tz is 7, the magnification factor M is 7, which is necessary for field curvature correction in an optical scanning device. It is sufficient to use a vibrator 33 having an amplitude that is 1/7 of 235 (μm) of the amplitude, that is, 235/7=33.6 (μm).

It goes without saying that the vibrator 33 may be of a piezoelectric type, an electrostrictive type, a magnetostrictive type, or the like.

Now, when a linear imaging lens such as the cylindrical lens 14 is vibrated, this vibration is transmitted to the entire scanning optical device and causes other optical elements to vibrate as well. Vibration of optical elements other than the linear imaging lens adversely affects the shape of the scanning beam, and ultimately the beam does not have a predetermined diameter on the surface of the scanned medium.

It is also conceivable that the vibration of the linear imaging lens causes resonance with the entire device including the scanning optical system, causing the entire device to vibrate slightly. If the entire device vibrates, it will also have an adverse effect on the image creation process, significantly reducing the quality of the final image.

Therefore, it is necessary to mechanically insulate the linear imaging lens and its vibration source from at least the scanning optical system.

As one specific example, as shown in FIG. 18, an amplitude expander 32 has a vibrator 33 fixed to a large diameter end face, and a cylindrical lens element 4 fixed to a small diameter end face via a mounting member 14'. A support member 34 supporting the scanning optical system is mounted on a base 35 that is mechanically insulated from a base 36 to which each member constituting the scanning optical system is mounted.

By doing this, the energy generated when the vibrator 33 is vibrated for field curvature correction is transferred to the base 33.
6 and reduce the image quality, or conversely,
The energy of vibration generated in an image forming member such as a printer provided on the base 36 is transmitted to the cylindrical lens 14.
This prevents the signal from being transmitted directly to the field curvature correction operation and thereby hindering the normal field curvature correction operation.

Further, as shown in FIG. 19, a vibration isolating rubber 37 is installed between a support member 34 that supports the amplitude expander 32 to which the vibrator 33 is fixed in the same manner as described above, and a base 36 to which this support member 34 is to be attached. By interposing it, the vibration of the vibrator 33 and the vibration of the image forming member attached to the base 36 can be insulated.

Therefore, it is possible to prevent both vibrations from adversely affecting each other and degrading the image quality.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the linear imaging lens is vibrated in synchronization with the period of light scanning so as to cancel the curvature of field, so that the entire optical system is The field curvature of the image plane can be well corrected mechanically, making it easier to design other optical components such as fθ lenses, collimator lenses, and cylindrical lenses. Accordingly, it is possible to provide an optical scanning device that can achieve high accuracy without using a lens system with a large number of lenses, has good image quality, and is inexpensive.

Furthermore, since this vibration is applied by magnifying the vibration of the vibrator using an amplitude magnifier, the amplitude required by the vibrator may be small, and the shape can be made smaller.

In addition, the capacity of the vibration drive power source can be made small.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram showing an example of an optical system of an optical scanning device to which the present invention can be applied, and FIG. 2(A) is a conceptual diagram of the optical system shown in FIG. 1 developed in the main scanning direction. The optical path diagram shown in
FIG. 2(B) is a conceptual optical path diagram expanded in the sub-scanning direction, FIG. 3 is an optical path diagram for explaining changes accompanying movement of the linear imaging lens, and FIG. Figure (A) is a characteristic diagram showing an example of field curvature in a light scanning optical system, and Figure 4 (
B) is a characteristic diagram when the field curvature shown in FIG. 4 (A) is corrected, FIG. 5 is a diagram showing an example of field curvature correction, and FIG. An optical path diagram showing another example of an optical system of an optical scanning device to which the present invention is applicable developed in the main scanning direction;
FIG. 6(B) is an optical path diagram similarly developed in the sub-scanning direction, and FIGS. 7(A) to 7(E) are diagrams showing states before and after correction of various aberration characteristics. Of these, Figure 7 (A
) is a characteristic diagram of spherical aberration and sine conditions, and Figure 7 (B) is
A characteristic diagram of the image capture curvature in the main scanning direction, FIG. 7(C) is a characteristic diagram of the field curvature in the sub-scanning direction, FIG. 7(D) is the fθ characteristic, and FIG. 7(E) is the correction A characteristic diagram of the curvature of field afterward, FIG. 8 is a diagram for explaining changes accompanying movement of the linear imaging lens, and FIG. 9(A) is an optical scanning device to which the present invention can be applied. FIG. 9(B) is an optical path diagram showing still another embodiment of the optical system developed in the main scanning direction. FIG. 10(A) is an optical path diagram showing the same developed in the sub-scanning direction. FIG. 10(B) is an optical path diagram showing still another embodiment of the optical system of the optical scanning device to which the invention is applicable developed in the main scanning direction.
A) is a characteristic diagram showing the waist positions in the main and sub-scanning directions superimposed on each other in the optical path diagram shown in A), and FIG. ,
FIG. 11 is a diagram for explaining changes accompanying movement of the linear imaging lens, and FIGS. 12(A) to 12(D).
) are side views showing the basic structure of the amplitude expander used in the embodiments of the present invention, FIG. 13 is a perspective view showing the dimensions of each part of the cylindrical lens, and FIG.
FIG. 15 is a side view showing an embodiment of the present invention, FIG. 16 is a diagram showing a modified embodiment of the present invention and its vibration form, and FIG. 17 is a characteristic diagram showing the correlation with t-α. ,V]]"=71
The characteristic diagram shown in FIG. 18 showing the correlation between 1- and the amplitude expansion rate is as follows.
FIG. 19 is a side view showing an example of a portion where the drive source is insulated, FIG. 19 is a perspective view showing another example, and FIG. 20 is an optical path diagram showing an example of an optical system of a conventional optical scanning device. 11.25... Laser diode (light source), 1
2.26... Collimator lens, 14.23.
29... Cylindrical lens (linear imaging lens). 4'...Support member, 8.28...Polygon mirror (rotating polygon mirror),
9.30... fθ lens (second imaging optical system),
1.31...Photosensitive drum (scanned medium), 2
．． 32A to 32D, 32'... amplitude expander, 3
... Vibrator, 4 ... Supporting member, 5.36 ... Base, 7 ... Vibration isolating rubber (mechanical insulating member). Figure 1 (A) (8) Figure 6 (A) CB) Figure (A) (B) (C) (D) (E) Figure 9 (A) (B) Figure 2 (A ) (B) (C) (D) No.] 3 Figure L 14 Figure 5 Figure 6 Figure 7 Figure f 7-1 Figure 8 Figure 1 Figure 0

Claims (2)

[Claims] (1) A collimating optical system that converts the light beam emitted from the light source into a parallel light beam; a first imaging optical system that forms a linear image of the light beam emitted from the collimating optical system; a rotating polygon mirror having a deflection reflecting surface that deflects and scans the light beam, a scanning medium scanned by the light beam deflected by the rotating polygon mirror, and a rotating polygon mirror disposed between the scanning medium and the rotating polygon mirror; a second imaging optical system that maintains a geometrically optically conjugate relationship between the deflection reflection surface and the scanned medium in a plane perpendicular to the deflection surface of the light beam deflected by the deflection reflection surface of the rotating polygon mirror; In an optical scanning device having a surface tilt correction optical system that moves the light beam by the first imaging optical system in the optical axis direction as the light beam is scanned by the rotating polygon mirror, and a driving source for moving at least the linear imaging lens of the first imaging optical system in the optical axis direction, and the driving source is connected to a vibrator, and a base end thereof is connected to a vibrating surface of the vibrator. An optical scanning device comprising a cone-shaped amplitude magnifier having a large diameter tip and a small diameter tip, which is fixed and supports the linear imaging lens at its tip. (2) An amplitude magnifier whose one end supports at least the linear imaging lens of the first imaging optical system and a vibrator fixed to the base end of the amplitude magnifier are connected together through a mechanical insulating member. 2. The optical scanning device according to claim 1, wherein the optical scanning device is fixedly supported by an immovable member.