JPH0365918A - Optical scanner - Google Patents

Abstract

PURPOSE:To facilitate the designing of an optical system and to obtain the high-performance and inexpensive optical scanner without requiring an intricate lens system consisting of a large number of lenses in spite of the trend toward the higher density of the scanning optical system by using a lamination type piezoelectric actuator and a displacement magnifying mechanism which expands the amplitude thereof to constitute a driving system for moving a linear imaging lens in an optical axis direction. CONSTITUTION:The linear imaging lens 14 is constituted to be so oscillated in synchronization with the period of optical scanning as to negate the curvature of field. The curvature of field over the entire part of the optical system is, therefore, mechanically corrected. The designing of lenses, such as, prescribed ftheta lens 19, collimator lens 12 and cylindrical lens 14, is facilitated in this way and the high accuracy is obtd. even if the intricate lens system consisting of a large number of lenses is used in spite of the recent trend toward the higher density of the scanning optical system. The optical scanner which has the good image grade and is inexpensive is thus obtd.

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]

In general, 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 engraving machines, etc. It is being

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

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 forms an image. The light is focused by a lens 4 forming an optical system to form an image on the main scanning line.

The light beam thus formed is deflected by a rotating polygon mirror 5 having a plurality of deflection and reflection surfaces, and is linearly scanned (in the main scanning direction) on a photosensitive drum 6, which is an example of a scanned medium. The image forming surface (main scanning line) formed by the a-shaped imaging lens 4 is curvature of field 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 the light spot cannot be scanned in a perfect straight line along the photoreceptor drum 6, and the trajectory of the light spot on the photoreceptor drum 6 is distorted and the spot diameter becomes large. It is proposed that this be done by practical means.

As an example of the above-mentioned mechanical means, Japanese Patent Application Laid-Open No. 57-1482
As shown in Publication No. 0 and Japanese Patent Application Laid-open No. 116603/1982, 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 devices correct the curvature of the main and sub-scanning image planes by moving (vibrating) the position of the image plane in the optical axis direction.

Further, as an example of the above-mentioned optical means, JP-A-58-
As shown in Japanese Patent No. 57108, the light source is fixed, and the curvature of the main and sub-scanning surfaces is similarly corrected 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.

In other words, this surface tilt correction optical system uses a geometric optical system to form an image of a light beam deflected by a rotating polygon mirror onto a scanned medium (for example, a photoreceptor drum). In order to achieve a conjugate relationship, a plurality of lenses are formed using a combination of a spherical surface and a toric surface, thereby correcting the surface tilt.

[Problem to be solved by the invention]

When the light source or lens is moved in the optical axis direction as described above, although the curvature of field in the main scanning direction can be corrected, a new curvature of field in the sub-scanning direction occurs as the light source moves. 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, so by moving the light source or lens in the optical axis direction, the curvature in both the main and sub-scanning directions can be ignored. In addition, when using an optical system for correcting surface tilt without moving the light source, it is extremely difficult to reduce
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,
It is extremely difficult to make all conditions favorable.

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. In addition, in recent years, as the density of scanning optical systems has increased, various precision requirements for f-theta lenses and the like have increased, and the number of lenses has also increased, making adjustment even more difficult and forcing an increase in costs.

Therefore, one object of the present invention is to be applicable to an optical scanning device using a surface tilt correction optical system, to facilitate the design of lens optical systems such as an fθ lens, a collimating 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, the optical scanning device according to the present invention includes a collimating optical system that collimates the light beam emitted from the light source, and a first collimating optical system that forms a linear image of the light beam emitted from the 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 that is deflected by the deflection reflection surface of the rotation polygon mirror using geometrical optics. an optical scanning system comprising: a second imaging optical system that maintains a conjugate relationship; and a surface tilt correction optical system that moves the first imaging optical system in the optical axis direction as the light beam of the rotating polygon mirror scans; The device includes a layered piezoelectric actuator and a layered piezoelectric actuator as 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 scanning in the rotating polygon mirror. The present invention is characterized in that it is constructed with a displacement magnification mechanism that magnifies the amplitude of the piezoelectric actuator.

[For production]

The optical scanning device according to the present invention includes at least a linear imaging lens of the first imaging optical system that forms an image on the main scanning line, and a multilayer piezoelectric actuator that expands the amplitude of the multilayer piezoelectric actuator. By using a drive source consisting of a displacement magnifying mechanism to move in a direction to cancel field curvature in synchronization with the beam scanning by a single-rotation polygon mirror, it is possible to improve the final reproduced image. be.

〔Example〕

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

FIG. 1 is an optical path diagram schematically showing an example of an optical system in an optical scanning device to which the present invention can be applied.
A collimator lens 12 forming a collimating optical system converts the light into a parallel light beam, and an aperture 13 placed behind the collimator lens 12 cuts unnecessary peripheral parts to form a linear light beam. This linear luminous flux is.

A first cylindrical lens 14, which is an example of a linear imaging lens forming the first imaging optical system, forms an image on the surface of a photoreceptor drum 21, which will be described later.

The first cylindrical lens 14 can be driven in the optical axis direction by energizing a laminated piezoelectric actuator, which will be described in detail later.

The light flux passing through this first cylindrical lens 14 is
Deflection scanning is performed by a polygon mirror 18, which is an example of a rotating polygon mirror having a deflection reflection surface.

Then, the deflected and scanned light flux passes through the fθ lens 19 and the third
sequentially through the cylindrical lens 20 of
imaged (scanned).

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

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

The laminated piezoelectric actuator is driven by a synchronization signal obtained from the photodetector 22b, and the first cylindrical lens 14 is moved in the optical axis direction to cancel the field curvature of the optical system. There is.

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. .

The curvature of field is corrected by moving the first cylindrical lens 14 of the surface tilt correction optical system in the optical axis direction as shown in FIG. The details of the state will be explained using FIG. 3.

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

Therefore, the amount of movement of the first cylindrical lens 14 is set to Δ
When cy is the amount of movement of the imaging position, ΔworkS is the imaging position of the first cylindrical lens 14 before movement and f
If the distance from the front principal point H of the θ lens 19 is S, 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'-ΔIS)・f/(S'-
Δ1s-f), therefore Δcy=Δ1s-f”/(S'-Δl5-f)(S'
-f).

Here, if Δxs((S'-f), Δcy4Δx
s·f"/(S'-f)"=Δxs/rrr (where m=s'/S).

From the above explanation, when the amount of field curvature is Δls, the first cylindrical lens 14 is set to Δcy=Δls/rr.
By moving by r, the sub-scanning field curvature can be corrected.

At this time, regarding the main scanning, as shown in FIG. 2(A), since the first cylindrical lens 14 has no power, 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. It represents curvature. The curvature of field before correction is designed to be small in the main scanning direction, and no consideration has been taken to reduce the curvature of field in the sub-scanning direction, so the curvature of field becomes arcuate or parabolic. ing. The amount of field curvature Δ□S in this embodiment is ±30° in the scanning half angle of the polygon mirror 18.
(±15° in terms of the rotation angle of the polygon mirror 18) is about 10rrta.

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, the amount of field curvature of ±30' in FIG. 4(A) is
S, the correction amount Δworks at this time is Δzs(0
)=Δls (-cos(6B)+1), where θ is the rotation angle of the polygon mirror 18, and θ
=O, the image height ratio becomes 0.

In this example, since the number of mirror surfaces of the polygon mirror 18 is 6, the polygon mirror rotation angle θ on l mirror surfaces is
is ±30'.

Therefore, if the first cylindrical lens 14 moves by n periods (n is an integer of 1 or more) during this period of ±306, synchronization with the mirror surface of the polygon mirror 19 can be achieved. In other words, when the number of mirror surfaces of the polygon mirror 18 is N, the first cylindrical lens 14 moves by n periods with the polygon mirror rotation angle θ being ±180''/N. As shown in Figure (B), the curvature of field in the sub-scanning direction can be corrected.

Next, the configuration of a second embodiment of the present invention will be described with reference to FIGS. 6(A) and 6(B). In this embodiment, a second cylindrical lens 23 is additionally provided, and by moving this second cylindrical lens 23 in the optical axis direction, the curvature of field in the main scanning direction is corrected. 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. A second cylindrical lens 23 having power in the main scanning direction is arranged between the upper collimator lens 2 and the polygon mirror 18, and is moved in the optical axis direction in the same way as the first cylindrical lens 14 described above. This corrects field curvature.

In the main scanning plane, the second cylindrical lens 23
The distance between the rear principal point and the front principal point of the fθ lens 19 is d, and the second cylindrical lens 23 and the fθ lens 19
Let fcy′ and ffθ be the focal lengths of fθ
The distance S' between the rear principal point of the lens 19 and the overall focal position of the second cylindrical lens 23 and fθ lens 19 is S' = ffθ (fay' - d)/(fCy' +
ffθ−d).

Also, since the parallel light beam from the collimator lens 12 enters the second cylindrical lens 23 via the first cylindrical lens 14, the amount of field curvature at this time is Δ
Assuming that the corresponding corrected movement amount of the second cylindrical lens 23 as IM is ΔCy', Δcy'=Δxy・f"te/(S"-
It can be expressed as ΔIN −f fe)(S′−ffθ).

Therefore, if the second cylindrical lens 23 is moved independently of the first cylindrical lens 14 described above,
Field curvature in both the main scanning direction and the sub-scanning direction can be corrected simultaneously.

Specific examples of corrections made in this manner include (A), (B), (C), and (D) in FIG. In an optical system having spherical aberration/sine conditions, curvature of field in the main scanning direction, curvature of field in the sub-scanning direction, and fθ characteristics shown in each of the above, the movement of the first cylindrical lens 14 is expressed as Δxs(θ)=− The second cylindrical lens 23 is set to Δmm 5 acos (18θ) + Δmm S',
Correction is made so that it moves at θ) = Δt/gin(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 the surface in the main scanning direction and FIG. 9(B) showing the surface in the sub-scanning direction, the fθ lens 19 is arranged in the elongated third Even in an optical scanning device that includes a cylindrical lens 24 to form a surface tilt correction optical system, it is possible to correct field curvature by moving the first cylindrical lens 14 in the optical axis direction in the same manner as described above. Of course.

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 shortens the longitudinal dimension of the optical system by folding the mirror 27, because if the entire optical path is arranged in a straight line, the overall dimension of the optical system becomes long, which goes against the demand for compact equipment. It is designed to do this.

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.

Furthermore, the waist position of the optical system shown in FIG. 10(A) is shown in FIG. 1O CB), where the 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. .

Further, as for the curvature of field, 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 replaced by the polygon mirror 28.
It is vibrated (moved) in the optical axis direction in synchronization with the deflection angle of , and this vibration is performed at a frequency F and an amplitude Δ.

The first upper diagram shows the characteristics obtained by superimposing the curve representing the curvature of field and the curve representing the vibration of the linear imaging lens 29.

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 vibration frequency F in this example is, for example, 4.25 KHz.

The amplitude Δ is 235 μm.

Next, details of the driving sources for vibrating the linear imaging lenses on each side will be described.

The driving source in the present invention is a laminated piezoelectric actuator (hereinafter referred to as a laminated piezoelectric actuator) in which piezoelectric vibrating elements are laminated.

(abbreviated as a "laminated vibrator"), and an amplitude magnifying member as a displacement magnifying mechanism, one end of which is connected to the laminated vibrator and the other end of which is connected to the linear imaging lens, The laminated vibrator in this case is a solid-state element that uses thick film lamination technology and has a large number of internal electrode layers, and utilizes the piezoelectric longitudinal effect that extends in the direction of the electric field when a voltage is applied to piezoelectric ceramics.

This feature is small, lightweight, and takes several tens of μs.
It provides high-speed EC response, can be driven at low voltage, has high energy conversion efficiency, generates large force, has no electromagnetic noise, and has little effect on peripheral electronic circuits, and is a solid element, so it has high mechanical strength. etc.

As an example of a laminated vibrator, Figure 12 shows the correlation between applied voltage and displacement (displacement characteristics).As is clear from the figure, when the applied voltage is approximately 150 (V), the displacement is approximately 19 (μm). It will be done.

However, it is not possible to use this displacement of 19 (μm) as is to perform the field curvature correction that requires a maximum displacement of 470 (μm) as described above. In other words, in order to correct the curvature of field, the displacement of the actuator must be expanded approximately 25 times. An example of an amplitude expansion member for this purpose is shown in FIG. 13.

In the figure, two steps 33a and 33b are formed in two steps on a part of a base 33 to which various optical components constituting the light scanning optical system are attached, and a step 33b closer to the outside is formed in two steps.
The lower surface of the laminated vibrator 34 is in contact with or fixed to the surface. The laminated vibrator 34 is mounted so that its drive direction is perpendicular to the surface of the base 33.

A stationary portion 35a of the amplitude enlarging member 35 is fixed to the surface of the step 33a adjacent to the step 33b to which the laminated vibrator 34 is fixed. This amplitude enlarging member 35 utilizes the principle of a lever, and is integrally formed in this example. That is, a narrow hinge part 35c is formed continuously to the stationary part 35a, and this hinge part 35c serves as a fulcrum of a lever, and the drive part 3
5b and the driven portion 35d are formed continuously. The tip of the drive section 35b comes into contact with the upper surface of the laminated vibrator 34, and the driven object, that is, the first cylindrical lens 14, is attached to the driven section 35d.

Therefore, when a predetermined vibration voltage is applied to the laminated vibrator 34, a piezoelectric longitudinal effect occurs, causing a large number of piezoelectric elements to vibrate simultaneously, and the amplitude is doubled by the number of piezoelectric elements to press the driving portion 35b.

Then, the hinge portion 35c supported by the stationary portion 35a is bent (bent), and the driven portion 35d is accordingly bent.
is displaced (vibrated), and this displacement is equal to the magnification rate obtained by dividing the displacement in the driving part 35b by the arm length from the hinge part 35c to the driven part 35d by the arm length from the hinge part 35c to the driving part 35b. It will be multiplied, and the multilayer vibrator 3
The first cylindrical lens 14 is driven in a state in which the displacement of the first cylindrical lens 4 is greatly expanded by the amplitude enlarging member 35.

Therefore, the amplitude enlarging member 35 and the laminated vibrator 3 as described above
By combining 4, even if the laminated vibrator 34 has a small displacement, a sufficient displacement of, for example, 470 μm, which is required for field curvature correction, can be obtained.

In addition, the response characteristics of the multilayer vibrator 34 are very good as shown in FIG. 14 when the applied voltage is 100 V, for example, and the displacement is 8.7 μm. The frequency is usually about 100 KHz, which is sufficient to vibrate at 4°25 KHz as described above.

In addition, as shown in FIG. 15, the base end of the laminated vibrator 34 and the end surface of the stationary part 35a are fixed to the base, as shown in FIG.
′ may also be used.

Now, when a linear imaging lens such as the first cylindrical lens 14 is vibrated, there is a possibility that 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.

In addition, the vibration of the linear imaging lens causes resonance with the entire device including the scanning optical system, and when the entire device vibrates, it has a negative impact on the image creation process, significantly reducing the quality of the final image. descend.

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. 16, a fixing member 33' to which a laminated vibrator 34 and an amplitude enlarging member 35 are fixed is attached to a base 40 to which each member of the light scanning optical system is attached. Instead of being directly attached, it may be fixed to the base 41 via a mechanical insulating member, that is, to the base 41 on which parts such as a printer are attached.

By doing so, the energy generated when the laminated vibrator 34 is vibrated for field curvature correction is directly transmitted to the base 40, reducing image quality.
Conversely, the energy of the vibration generated in the image forming member provided on the base 40 is transmitted to the first cylindrical lens 14.
This can prevent the normal field curvature correction from being directly transmitted to the camera and causing the normal field curvature correction to deteriorate.

Further, as shown in FIG. 17, a fixing member 33' to which a laminated vibrator 34 and an amplitude enlarging member 35 are fixed is attached to a base 40 to which each member of the light scanning optical system is attached via a vibration isolating rubber 42.
By supporting the base 40, even if the laminated vibrator 34 vibrates for field curvature correction, the vibration is not transmitted to the base 40.

There is no risk of image deterioration due to vibration energy being transmitted to each member forming the optical scanning optical system, causing slight vibrations, or causing resonance.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, since the linear image lens is configured to vibrate in synchronization with the period of optical scanning so as to cancel field curvature, the image of the entire optical system is Surface curvature can be corrected mechanically and other optical components, e.g.
Lens design such as lenses, collimator lenses, cylindrical lenses, etc. becomes easier, and in response to the recent increase in the density of scanning optical systems, high precision can be obtained without using complex lens systems with a large number of lenses, improving image quality. It is possible to provide an optical scanning device with good performance and low cost.

Moreover, since a multilayer piezoelectric actuator is used as the drive source to vibrate the linear imaging lens in accordance with field curvature correction, it can be driven with low voltage, is small and lightweight, has a fast response, and has an excellent energy conversion. It has the advantages of high efficiency, no electromagnetic noise, and high mechanical strength. Furthermore, since the amplitude in the laminated piezoelectric actuator, which has such advantages, is multiplied by a displacement amplification mechanism having a simple configuration, the above-mentioned advantages become even more remarkable.

Furthermore, when the displacement magnification mechanism is of a lever type structure and its fulcrum is of a hinge type, the mechanical play of the fulcrum can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram schematically 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 an optical path diagram showing an example of the optical system shown in FIG. 2(B) is a conceptual optical path diagram developed in the sub-scanning direction, and FIG. 3 is a conceptual optical path diagram showing changes in the imaging position due to movement of the linear imaging lens. FIG. 4(A) is an optical path diagram for explaining. A characteristic diagram showing an example of the field curvature in a light scanning optical system, FIG. 4(B) is a characteristic diagram when the field curvature shown in FIG. 4(A) is corrected, and FIG. FIG. 6A is a line diagram showing an example of correction of field curvature; FIG. CB) is an optical path diagram similarly developed in the sub-scanning direction. FIGS. 7(A) to 7(E) are diagrams showing the states before and after correction of various aberration characteristics. Of these, FIG. 7(A) is a characteristic diagram of spherical aberration and sine conditions; 7(B) is a characteristic diagram of the curvature of field in the main scanning direction, FIG. 7(C) is a characteristic diagram of the curvature of field in the sub-scanning direction, and FIG. 7(D) is a characteristic diagram of the curvature of field in the main scanning direction.
Figure (E) is a characteristic diagram of field curvature after correction, Figure 8 is a line diagram for explaining changes accompanying movement of the linear imaging lens, and Figure 9 (A) is a line diagram. FIG. 9(B) is an optical path diagram showing still another example of the optical system of an optical scanning device to which the invention can be applied developed in the main scanning direction, and FIG. 10 is an optical path diagram also shown developed in the sub-scanning direction. 10(A) is an optical path diagram showing still another example of the optical system of an optical scanning device to which the present invention can be applied developed in the main scanning direction, and FIG. 10(B) is an optical path diagram shown in FIG. 10(A). Figure 10 (C) is a characteristic diagram that shows the waist positions in the main and sub-scanning directions superimposed, and Figure 11 is a characteristic diagram that also shows the curvature of field in the main and sub-scanning directions superimposed. FIG. 12 is a diagram for explaining the changes caused by the movement of the linear imaging lens; FIG. 14 is a diagram showing an example of the response characteristics of the laminated piezoelectric actuator used in the present invention, and FIG. 15 is a front view for explaining the principle of the displacement magnifying mechanism according to the present invention. FIG. 16 is a partially cutaway perspective view showing one embodiment, and FIG. 17 is a perspective view showing an example of a portion where vibrations are isolated (insulated) of the drive source according to the present invention. FIG. 18, which is also a perspective view showing the other side, 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, 14.20,
23,24.29... Cylindrical lens,
(,1liL-shaped imaging lens), 18.28...
Polygon mirror (rotating polygon 1ft). 21.31...Photosensitive drum (scanned medium). 19.30...fθ lens (second imaging optical system)
, 33.40.41...Base, 33'...
...Fixing member, 33a, 33b...Step, 34...Laminated vibrator (layered piezoelectric actuator), 35...Amplitude expansion member, 35a... ...Stationary part, 35b... Drive part, 35c...
Hinge part, 35d... Driven part, 42... Anti-vibration rubber. ” L-stroke No. 1 Fig.''-21 Fig. 2 (A) (B) To 1 Fig. 6 (A) (8) Fig. (A) CB) (C) Spherical aberration/positive arc condition field curvature image Surface curvature (Cl) (E) fθ Hunting (%) Correction Rv31M] PSn Fig. (8) Fig. 12 Fig. 3 Fig. 4 Fig. 5 Fig. 16 Fig. 3 Fig. 7 Fig. S

Claims (3)

[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 collimate optical system, and a collimating optical system that forms a linear image of the light beam emitted from the collimate 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 conjugate relationship between the deflection and reflection surface and the scanned medium in a plane perpendicular to the deflection surface of the light beam deflected by the deflection and reflection surface of the rotating polygon mirror; An optical scanning device comprising a surface tilt correction optical system that moves the first imaging optical system in the optical axis direction as the light beam of the rotating polygon mirror scans, the optical scanning device being synchronized with linear scanning by the rotating polygon mirror. The driving source for moving at least the linear imaging lens of the first imaging optical system in the optical axis direction is a layered piezoelectric actuator and a displacement magnification mechanism that expands the amplitude of the layered piezoelectric actuator. An optical scanning device characterized by comprising: (2) The laminated piezoelectric actuator for driving at least the linear imaging lens of the first imaging optical system is fixed to a stationary member via a mechanical insulating member. Optical scanning device. (3) The laminated piezoelectric actuator that drives at least the linear imaging lens of the first imaging optical system is fixed to another member that is mechanically insulated from the member to which the scanning optical system is fixed. The optical scanning device according to claim 1, characterized in that: