JPH01315718A - Scanning optical system - Google Patents

Abstract

PURPOSE:To excellently form the image of the light of a light source by compensating the variation of the light condensing position of the light caused by temperature variation by means of the plastic lenses of 1st and 2nd image forming optical systems. CONSTITUTION:The 1st image forming optical system 5 has a glass-made cylindrical lens having a positive refracting power and a plastic lens having a negative refracting power and toric surface and the 2nd image forming optical system has at least one plastic lens having a positive refracting power. Both of the 1st and 2nd image forming optical systems have positive refracting powers. Therefore, when the focal length of one of the 1st and 2nd image forming optical systems becomes longer, that of the other becomes shorter. Thus the variation of the condensing positions of light beams in a half surface containing the paths of the light beams can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a scanning optical system suitably implemented in printing devices such as laser printers and facsimiles, and reading devices such as facsimiles, image scanners, and barcode readers.

In conventional laser printers, the surface of a charged right cylindrical photoreceptor is selectively irradiated with a light beam while scanning parallel to the axial direction of the photoreceptor to remove static electricity. A latent image is formed. The static latent image is developed into a toner image by a developing device, and this toner image is transferred onto recording paper for printing.

The scanning optical system for scanning the surface of the photoreceptor with a light beam includes a light source such as a semiconductor laser device, a cylindrical lens that focuses the light beam from the light source, and forms a linear image.
A deflector that has a deflection reflecting surface near the linear image formed by the linear image formation and changes the traveling direction of the light beam over time in order to scan the surface of the photoreceptor; It is composed of an fθ lens designed to form an image as a spot on the surface of the photoreceptor and to maintain a constant scanning speed of the surface of the photoreceptor by the light beam. The deflector is, for example, a regular hexagonal prism having a regular hexagonal cross section perpendicular to the axis and uniform in the axial direction, the side surface of which serves as a reflecting mirror, and is driven to rotate around the axis. The deflector is arranged such that its axis is perpendicular to a plane including the optical axis of the cylindrical lens and the optical axis of the fθ lens.

The light beam generated from the light source is formed into a linear image near the deflection reflection surface of the deflector by the cylindrical lens, and the direction of the IH force is changed over time by the deflector. The light beam reflected on the deflection reflecting surface is imaged as a spot on the surface of the photoreceptor through an fθ lens, and the spot moves in a direction parallel to the axis of the photoreceptor as the direction of travel of the light beam changes. do. As a result, main scanning of the surface of the photoreceptor is performed, and sub-scanning is performed by rotating the photoreceptor. In this way, an electrostatic latent image is formed on the surface of the photoreceptor.

In recent years, plastic has been used as a material for fθ lenses instead of glass due to the complexity of their shape, cost, mass production, and other requirements.

Problems to be solved by the invention However, plastics are susceptible to changes in the environment, especially temperature and
It has the property that its shape, refractive index, etc. change easily due to changes in humidity. Therefore, when an f-theta lens is configured to include a plastic lens, its shape and refractive index change with changes in the environment, which causes the focal length to change. If the value changes, the light beam will not be imaged as a spot on the surface of the photoreceptor, and the image will therefore become unclear, resulting in poor print quality, for example in a laser printer.

Also, plastic has a lower refractive index than glass,
When a lens is formed, its refractive power is small and the degree of freedom in design is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning optical system that uses a plastic lens and enables good imaging of source light to a desired position regardless of changes in the environment.

Means for Solving the Problems The present invention includes a light source, a first imaging optical system, a KJ direction device,
a second imaging optical system, the light source light that passes through the first imaging optical system forms a line image near the deflector, and the deflector changes its traveling direction in the main scanning direction over time. , in a scanning optical system that scans a medium to be scanned by a point beam source on the medium to be scanned moving in the sub-scanning direction via a second imaging optical system, the first optical system has a positive refractive power. The first imaging optical system has a glass cylindrical lens having a negative refractive power in the sub-scanning direction and a toric surface, and this first imaging optical system has a positive refractive power as a whole. the second imaging optical system has at least one plastic lens having positive refractive power; the second imaging optical system has positive refractive power as a whole; Scanning characterized in that a plastic lens of the imaging optical system and a plastic lens of the second imaging optical system are used to compensate so that the convergence position of the light source light does not change depending on temperature. It is an optical system.

The present invention also provides a light source, a first imaging optical system, a deflector,
a second imaging optical system, the light source light that passes through the first imaging optical system forms a line image near the deflector, and the deflector changes its traveling direction in the main scanning direction over time. , a scanning optical system that scans a scanning medium by forming a point image on the scanning medium moving in the sub-scanning direction via a second imaging optical system, the first imaging optical system has a positive refraction system. It has a glass cylindrical lens with a strong refractive power and a positive refractive power in the main scanning direction.
The first imaging optical system has a positive refractive power as a whole, and the second imaging optical system has a positive refractive power. the second imaging optical system has a positive refractive power as a whole, and the plastic lens of the first imaging optical system and the second imaging optical system This scanning optical system is characterized in that a lens made of plastic is used to compensate for the condensing position of the light source light in the sub-scanning direction from changing depending on temperature.

In the present invention, the first imaging optical system includes a glass cylindrical lens having positive refractive power and a plastic lens having negative refractive power and a toric surface. The imaging optical system includes at least one plastic lens having positive refractive power, and both the first and second imaging optical systems have positive refractive power. As a result, when the focal length of either the first imaging optical system or the second imaging optical system becomes longer, the focal length of the other becomes shorter.

Moreover, since the first condensation optical system includes a plastic lens having a toric surface, the convergence position of the light beam within the deflection plane created by the light beam deflected by the deflector, and the convergence position of the light beam within the deflection plane Any variation in the focusing position of the light beam within a vertical plane that includes the optical path of the light beam can be suppressed. That is, fluctuations in scanning linearity on the photoreceptor surface are suppressed.

Further, in the present invention, the first imaging optical system includes a glass cylindrical lens having a positive refractive power, a positive refractive power in the main scanning direction, and a negative refractive power in the sub-scanning direction. and a plastic lens having a toric surface.

EXAMPLE It is known that the refractive index of plastics has greater temperature dependence than that of glass. For example, for polymethyl methacrylate (PMMA), between the temperature t('C) and the refractive index n+s at the sodium D line: no=1.4933 1.1xlO-'t 2. lX
It has been announced that there is the following relationship (Industrial Materials, 35, [5], (36
-40), "87). Also, the refractive power ψ of the lens, the focal length f, the refractive index n, and the radius of curvature r of the surface on the upstream side in the direction of light propagation.
l, the radius of curvature r2 of the downstream surface satisfies the following relationship, however, the radius of curvature is positive when the center of curvature of the corresponding surface is on the downstream side in the direction of light travel with respect to that surface, and when it is on the upstream side considered negative.

From the above equations 1 and 2, it can be seen that when the temperature rises, the focal pressure Mf increases in a lens with a positive refractive power ψ, and the focal length f decreases in a lens with a negative refractive power ψ. Recognize. In addition, with respect to changes in humidity, a lens with a positive refractive power T and a lens with a negative refractive power ψ are both different when the focal pressure if of one lens increases, and the focal length of the other lens increases. is known to decrease.

Therefore, by appropriately combining a lens with a positive refractive power T and a lens with a negative refractive power T, it is possible to construct a lens system in which the focal length f fluctuates less in response to changes in the environment.

FIG. 1 is a system diagram showing the basic configuration of a scanning optical system 1 which is an embodiment of the present invention. A signal corresponding to information to be written on a scanned medium 4 such as a photoreceptor is given from a processing circuit 3 to a light source 2 realized by a semiconductor laser device or the like, and thereby the light source 2 receives the given signal. A light beam is generated in response to the The light beam is
Via the first imaging optical system 5, the deflection reflection surface 6b of the deflector 6
Focuses in a line in the vicinity. The light beam deflected by the deflection reflection surface 6b is shaped by the fθ lens 7 constituting the second imaging optical system so that its cross section on the scanned medium 4 is approximately circular, and Focus to form a spot on the surface.

The fθ lens 7 is designed to keep the scanning speed of the surface of the scanned medium 4 by the light beam constant and to shape the light beam to form a good spot on the scanned medium 4 .

The medium 4 to be scanned has, for example, a right cylindrical shape, and its axis and the optical axis 7a of the fθ lens 7 are perpendicular to each other.

The light beam basically follows the optical axis 5a of the first imaging optical system 5.
The direction of movement changes only within a plane that includes the optical axis 7a of the fθ lens 7. The deflector 6 is, for example, a regular hexagonal prism whose axis-perpendicular cross section is a regular hexagon and is uniform in the direction of the axis 6a, and each side is a reflecting mirror (configuring an intraoral reflecting surface 6b).

The deflector 6 has an axis t! perpendicular to a plane containing the axis of the scanned medium 4 and the optical axis 7a of the fθ lens 7. It is rotated around it 6 a in the direction of arrow 11.

The first imaging optical system 5 includes a cylindrical lens 51 made of glass and a toric lens 52 made of plastic having a toric surface.

The fθ lens 7 is composed of a first fθ lens portion 71 and a second fθ lens portion 72.

When the deflector 6 rotates around its axis 6a, the angle formed between the normal line of the deflection reflection surface 6b and the light beam incident on the deflection reflection surface 6b, that is, the angle of incidence of the light beam on the deflection reflection surface 6b is: As the angle of reflection changes over time, the position of the spot formed by the light beam focused on the medium 4 to be scanned moves in the direction of arrow 12 parallel to the axis of the medium 4 to be scanned. do. In this way, the light beam performs main scanning on the surface of the scanned medium 4, and sub-scanning is performed by rotating the scanned medium 4 about its axis.

FIG. 2 shows the deflection reflection of the deflector 6, which is perpendicular to a plane containing the optical axis 5a of the first quadrant optical system 5 and the optical axis 7a of the fθ lens 7, and includes the two optical axes. FIG. 6 is a cross-sectional view taken along a plane folded back at surface 6b. The first imaging optical system 5 includes a glass cylindrical lens 51 having a positive refractive power within the cut plane shown in FIG. 2, and a plastic toric lens 52 having a negative refractive power within the cut plane.
It consists of The cylindrical lens 51 and the toric lens 52 have curvatures of R1, R2:R3°R4 on the upstream and downstream sides in the traveling direction of the light beam, respectively, so that the first imaging optical system 5 has positive refractive power. is selected appropriately. As a result, the light beam is formed into a linear image near the deflection reflection surface 6b of the IH deflector 6. The fθ lens 7 is
The first and second fθ lens portions 71 and 72 are made of plastic so as to satisfy the above-mentioned characteristics, and the entire lens has a positive refractive power. In this embodiment, as will be described later, the surface R5 on the upstream side in the traveling direction of the light beam of the first fθ lens portion 71 is a spherical surface, the surface R6 on the downstream side is an aspherical surface, and the surface R6 on the downstream side is an aspherical surface. The surface R7 on the upstream side in the beam traveling direction is a toric surface, and the surface R8 on the downstream side is a spherical surface. The light beam incident on the fθ lens 7 is focused to form a spot on the scanned medium 4. Note that the fθ lens does not need to be composed of two lenses as long as it satisfies the above characteristics.

FIG. 3 is a diagram for explaining the detailed shape of the first imaging optical system 5. As shown in FIG. FIG. 3 (1) shows the first imaging optical system 5
3(2) is a cross-sectional view taken along a plane perpendicular to a plane including the optical axis 5a of the first imaging optical system 5 and the optical axis 7a of the fθ lens 7, and including the optical axis 5a of the first imaging optical system 5. is a sectional view taken along a plane including optical axis 5a and optical axis 7a. For example, the surface R2 of the cylindrical lens 51 is a plane, and the radius of curvature r12 thereof is, for example, 1. The center of curvature of the circular arc portion is located on the downstream side in the traveling direction of the light beam, and therefore is a surface having a positive radius of curvature rll.

Surfaces R3 and R4 of the toric lens 52 are toric surfaces, and have a negative radius of curvature r13v and a positive radius of curvature r14v, respectively, within the cut plane of FIG. 3(1). ) within the cutting plane, each with a negative radius of curvature r13g
, has a negative radius of curvature r14M. Said surface R3, R
The center of curvature corresponding to each radius of curvature of 4 is the optical axis 5.
Exists on a. Further, the cylindrical lens 51 has a thickness on its optical axis (hereinafter referred to as axial thickness) d12, and a distance f/i d23 between the surfaces R2 and R3 on the optical axis 5a.
The toric lenses 52 have an axial thickness d.
It has 34.

FIG. 4 shows the optical axis 5a of the first imaging optical system 5 and the fθ lens 7.
FIG. 3 is a cross-sectional view of the fθ lens 7 in a plane including the optical axis 7a of FIG. The first fθ lens portion 71 has an axial thickness dSS, and the second fθ lens portion 72 has an axial thickness d2. The surface R6 of the first f.theta. lens portion 71 and the surface R7 of the second f.theta. lens portion 72 are disposed apart from each other by a distance mast on the optical axis.

FIG. 5 is a diagram for explaining a more detailed shape of the first fθ lens portion 71, and the first surface R5, which is a cross-sectional view taken along the cut plane of FIG. 4, is a spherical surface, and its center of curvature is
One surface R6, which is located on the optical axis 7a on the downstream side in the traveling direction of the light beam and therefore has a positive radius of curvature r15, shapes the light beam so that a good spot is obtained on the scanned medium 4. It is an aspherical surface, has a paraxial radius of curvature r16, and its center of curvature is located above the optical axis 7a. The 1st f
The θ lens portion 71 has the axial thickness aSS as described above.

FIG. 6 is a diagram for explaining the detailed shape of the second fθ lens portion 72. FIG. 6(1) is a sectional view taken along the cutting plane of FIG. 4, and FIG. 6(2) is a sectional view taken along the cutting plane line Vl--Vl shown in FIG. 6(1). Figure 6 (1
), in a plane including the axis of the scanned medium 11 and the optical axis 7a of the fθ lens 7, the surface R7 has a negative radius of curvature r 17 N, and the center of curvature is on the optical axis 7a. One existing surface R8 is a spherical surface with a negative radius of curvature r18
The center of curvature is located on the optical axis 7a. Further, the second fθ lens portion 72 has the axial thickness ate as described above.

Referring to FIG. 6(2), in a plane that includes the optical axis 7a of the fθ lens 7 and is perpendicular to the plane, the surface R7 has a positive radius of curvature r 17 v, and the center of curvature is on the optical axis. Exists on 7a. In this way, surface R7 becomes a toric surface. Furthermore, since the surface R8 is a spherical surface as described above, it also has a radius of curvature r18 within the plane.

The fθ lens 7 configured as described above has an I of the deflector 6.
It is arranged so that the positional relationship between the N-direction reflecting surface b and the scanning position of the scanned medium 4 is optically conjugate, and the radius of curvature and refractive index of the first fθ lens portion 71 and the second fθ lens portion 72 are is selected such that it does not satisfy the above conditions. By doing this, the axis 6a of the deflector 6 is aligned with the first
Even if the optical axis 5a of the imaging optical system 5 and the optical axis 7a of the f.theta. The position where the spot is formed on the scanned medium 4 does not change in the direction perpendicular to the plane containing the axis of the scanned medium 4 and the optical axis 7a of the fθ lens 7.

In an fθ lens, when a light beam forming an angle θ1 with the optical axis is incident, the distance between the spot formed on a plane perpendicular to the optical axis and the intersection of the plane and the optical axis, that is, the image height 11 is h = f・θ1...(3
) (where f is the focal length of the fθ lens). Therefore, the characteristics of the fθ lens (hereinafter referred to as fθ characteristics) can be evaluated as 1+(θ1), where the actual image height is expressed as a function of the angle θ1.

In the case of plastic lenses, scanning linearity, or fθ characteristics, change due to changes in temperature and humidity.6 However,
In the present invention, the toric lens 5 of the first imaging optical system 5
2 and the fθ lens 7 have a compensation function for both the main scanning direction and the sub-scanning direction of the scanned medium 4, and compensation is also performed for scanning linearity.

The inventor of the present invention conducted experiments under the following conditions. That is, polymethyl methacrylate (refractive index rl=1,48>) is used as the plastic, and the first imaging optical system 5
) r12=-■ ...(
6) r13e-820...(7) r13v=-19,703...(8) r14. =-8
20・-<9) r14v=19.703
=110)cL□=3.0
...(11)d2ko21,0

... (12) (134=2.0
...(13), where surfaces R3 and R4 are toric surfaces. Also,
The fθ lens 7 has r15=459.763...(1
4) r16=-105,7438...(15) r17
I+=-150,35-(+6>r17V=47.81
7-(17)r18=-144,
521...(18)ds&=17.20
...(19) ds7=0.50
...(20)(1,,=3.5
0...(21). However, the surface R6 is an aspheric surface, and the surface R7 is a toric surface.

Further, the distance 1ao (see FIG. 1) between the deflection reflection surface 6b of the deflector 6 and the point R5 of the first fθ lens portion 71 is d n = 57, 85
...(22) 6 However, the units of numerical values related to the above lengths are all millimeters (m
m>.

In the scanning optical system 1 configured as described above,
It has been confirmed through the above-mentioned experiment that the spot shape and scanning linearity are kept substantially uniform on the surface of the scanned medium 4 regardless of changes in temperature and humidity.

As described above, in this embodiment, the first imaging optical system 5 includes a plastic toric lens having a negative refractive power and a toric surface, and the fθ lens 7
is made of a plastic lens having positive refractive power. Therefore, compensation for fluctuations in the condensing position of the light beam and fluctuations in scanning linearity on the scanned medium due to changes in temperature and humidity can be achieved by adjusting the optical axis 5a of the first imaging optical system 5 and the This will be carried out in a plane containing the axis 7a and in a plane perpendicular to said plane and containing the optical path of the light beam.

As a result, the shape and position of the spot imaged on the surface of the scanned medium 4 can be maintained even with changes in temperature and humidity.
It is kept in a similar state. Therefore, when the scanning optical system 1 is applied to a laser printer, for example, a high quality image can be obtained.

In addition to the above-mentioned embodiment, the first imaging optical system 5 includes a glass cylindrical lens 51 having a positive refractive power in the cross section shown in FIG. , and a plastic toric lens 52 having a negative refractive power in the sub-scanning direction.The cylindrical lens 51 and the toric lens 52 are configured such that the first imaging optical system 5 has a positive refractive power. Upstream and downstream surfaces R1, R2; R3, r(4
The curvature of is chosen appropriately. As a result, the light beam is formed into a linear image near the deflection reflecting surface 6b of the deflector 6. f
The θ lens 7 is composed of first and second fθ lens portions 71 and 72 made of plastic so as to satisfy the above-mentioned characteristics, and has a positive refractive power as a whole. As shown in FIG.
The surface R7 on the upstream side in the traveling direction of the light beam is a toric surface, and the surface R8 on the downstream side is an aspherical surface. The light beam incident on the fθ lens 7 is focused to form a spot on the scanned medium 4. Note that the fθ lens does not need to be composed of two lenses as long as it satisfies the above characteristics.

FIG. 7 is a diagram for explaining the detailed shape of the first imaging optical system 5. Note that in FIG. 7 and subsequent figures, the same parts as in the previous embodiment are given the same reference numerals.

FIG. 7(1) is perpendicular to a plane including the optical axis 5a of the first imaging optical system 5 and the optical axis 7a of the fθ lens 7, and includes the optical axis 5a of the first imaging optical system 5. This is a sectional view taken along a plane, and FIG. 7(2) is a sectional view taken along a plane including the optical axis 5a and the optical axis 7a.

For example, the surface R2 of the cylindrical lens 51 is a flat surface, and therefore its radius of curvature r12 is, for example, 1. R1 is a surface forming an arc portion in a cross section perpendicular to the longitudinal direction of the cylindrical lens 51, and the center of curvature of the arc portion is on the downstream side in the traveling direction of the light beam, and therefore has a positive radius of curvature rll. It is a aspect of having.

Surfaces R3 and R4 of the toric lens 52 are toric surfaces and have a negative radius of curvature r13v and a positive radius of curvature r14v, respectively, within the cut plane of FIG. 7(1). ) have a positive radius of curvature r15 and a negative radius of curvature r14□, respectively. Said surface R3, R
The center of curvature corresponding to each radius of curvature of 4 is the optical axis 5.
Exists on a. Further, the cylindrical lens 51 has a thickness on its optical axis (hereinafter referred to as axial thickness) d, 2, and surfaces R2 and R3 are disposed apart from each other by a distance d23 on the optical axis 5a, and the toric lens 52 has an axial thickness d.

FIG. 8 shows the optical axis 5a of the first imaging optical system 5 and the fθ lens 7.
FIG. 3 is a cross-sectional view of the fθ lens 7 in a plane including the optical axis 7a of FIG. The first fθ lens portion 71 has an axial thickness d5g, and the second fθ lens portion 72 has an axial thickness d1. The surface R6 of the first f.theta. lens portion 71 and the surface R7 of the second f.theta. lens portion 72 are arranged at a distance dat on the optical axis.

FIG. 9 is a diagram for explaining a more detailed shape of the first fθ lens portion 71, and the 0-plane R5, which is a cross-sectional view taken along the cut plane of FIG. 8, is a spherical surface, and its center of curvature is
It is located on the optical axis 7a on the downstream side in the traveling direction of the light beam, and therefore has a positive radius of curvature r15. In order to shape the light beam so as to obtain a good spot on the scanned medium 4, the surface R6 is made an aspherical surface, has a paraxial radius of curvature r16, and its center of curvature is located above the optical axis 7a. exist. The 1st f
The θ lens portion 71 has the axial thickness dSS as described above.

FIG. 10 is a diagram for explaining the detailed shape of the second fθ lens portion 72. Figure 10 (1) is a sectional view taken along the cut plane of Figure 4, and Figure 10 (2) is a cross-sectional view of Figure 10 (1).
) is a sectional view taken along the illustrated section line xx; 10th
Referring to FIG. 1, in a plane including the axis of the scanned medium 4 and the optical axis 7a of the fθ lens 7, the surface R7 has a negative radius of curvature r17, and the center of curvature is the optical axis 7a. exists above. Surface R8 is an aspherical surface, and has a center curvature of r
19, the center of curvature of which is located on the optical axis 7a. Further, the second rθ lens portion 72 has the axial thickness ate as described above.

With reference to the 1121st (2>), the optical axis 7a of the fθ lens 7
In a plane perpendicular to the plane, the surface R7 has a positive radius of curvature r 17 v, and its center of curvature is along the optical axis 7
Exists on a. In this way, surface R7 becomes a toric surface.

The fθ lens 7 configured as described above is disposed so that the positional relationship between the deflection reflection surface 6b of the deflector 6 and the scanning position of the scanned medium 4 is optically conjugate, and the first fθ lens portion The radii of curvature and refractive index of the lens portion 71 and the second fθ lens portion 72 are selected so as to satisfy the above-mentioned conditions. By doing so, even if the axis 6a of the deflector 6 is slightly inclined with respect to the normal to the plane including the optical axis 5a of the first imaging optical system 5 and the optical axis 7a of the fθ lens 7, Furthermore, even if the deflection reflection surface 6b is not parallel to the axis 6a, the position where the spot is formed on the scanned medium 4 is a plane that includes the axis of the scanned medium 4 and the optical axis 7a of the fθ lens 7. It will no longer change in the direction perpendicular to .

In an fθ lens, when a light beam making an angle θ1 with the optical axis is incident, the distance between the spot formed on a plane perpendicular to the optical axis and the intersection of the plane and the optical axis, that is, the f High 11 is h=f θ1...value 2
3) (However, ideally, f should be equal to the focal pressure of the fθ lens. Therefore, the characteristics of the fθ lens (hereinafter referred to as fθ characteristics) are h as the actual image height as a function of the angle θ1.
It can be expressed as (θ1) and evaluated as (fθ characteristic) (%)=E(SuAnie141x100(%)...ri24)f·θ1.

In the case of plastic lenses, scanning linearity, that is, fθ characteristics, change due to changes in temperature and humidity. but,
In the present invention, the toric lens 5 of the first imaging optical system 5
2 and the fθ lens 7 have a compensation function for the sub-scanning direction of the scanned medium 4, and compensation is also performed for scanning linearity.

In this example, the present inventor conducted an experiment under the following conditions. That is, polymethyl methacrylate (refractive index n=1°48) was used as the plastic, and the first
The imaging optical system 5 has rll=21.200...
(25) r12=-ω...(
26) r131I=645.642'
,,,(27)r13v=-36,312...(
28) r14□=645.642
...(29) r14v=36.312
...(30) a, t=3.0
...(31) dzt= ],, O...
ku3Z) d 31 = 2, 0
...(33). However, R3, R4
is a toric surface. Moreover, the fθ lens 7 has r15-316.278...
(34) r 17M=-178.274
-(35)r17v=32.613
...(36) d, s= 13
, 1 ・
...(37) (lay=14, 2
...(38) d,,=g,
7...
(39), where surfaces R6 and R8 are aspherical surfaces, and R7 is a toric surface.

The aspherical shapes of the surfaces R6 and R8 are determined by the following equation.

...(40) The aspheric data of R6 is f10= 170.46022...
・(41) K=-13,94716516... Ku4
2) A, = 1.636066xl(l'
...(43) A! =-1,003659X10-”
...(44) The aspherical surface data of R8 is R,=-160,61118...(45)K=3.
47020421
... (46) A, = -2,045441x
1.0-'...〈47)Aa"3.3
20088X10-"...(
48) Furthermore, the distance Mdo (see FIG. 1) between the one-way reflecting surface 6b of the deflector 6 and the surface R5 of the first fθ lens portion 71 is d,=56.1−(49). However, the unit of the above-mentioned numerical values regarding length is millimeter (ro m ).

As described above, in the present invention, the refractive power of the second imaging optical system 7 can be supplemented by making the refractive power of the plastic lens 52 of the first imaging optical system 5 positive in the main scanning direction. That is, by supplementing the refractive power of the second imaging optical system 7, the distance from the polarizer 6 to the scanned medium 4 can be shortened, and the entire scanning optical system can be made compact.

In the scanning optical system 1 configured as described above,
It has been confirmed through the above-mentioned experiment that the spot shape and scanning linearity are kept substantially uniform on the surface of the scanned medium 4 regardless of changes in temperature and humidity.

In this embodiment, the first optical system 5 has a negative refractive power in the sub-scanning direction and includes a plastic toric lens having a toric surface, and the fθ lens 7 has a sub-scanning direction. The lens is made of plastic and has a positive refractive power in the scanning direction.

Effects of the Invention As described above, according to the present invention, it is possible to form a good image of the light source light at a desired position using a plastic lens, regardless of changes in the environment. That is, the cross-sectional shape of the light source light formed as a point image on the scanned medium is kept uniform regardless of changes in the environment.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the basic configuration of a scanning optical system 1 which is an embodiment of the present invention, and FIG.
It is cut by a plane that is perpendicular to a plane that includes the optical axis 5a of the imaging optical system 5 and the optical axis of the fθ lens 7, and that is folded at the deflection reflection surface 6b of the deflector 6 so as to include the two optical axes. A sectional view, FIG. 3 is a diagram for explaining the detailed shape of the first imaging optical system 5, and FIG. 4 shows the optical axis 5a of the first imaging optical system 5 of the fθ lens 7 and the optical axis of the fθ lens 7. 7a, FIG. 5 is a diagram for explaining the shape of the first fθ lens portion 71, and FIG. 6 is a cross-sectional view of the second fθ lens portion 7.
FIG. 7 is a diagram for explaining the shape of the first imaging optical system 5 in another embodiment, and FIG. 8 is a diagram for explaining the shape of the first imaging optical system 5 in another embodiment.
FIG. 9 is a cross-sectional view of the fθ lens 7 in a plane including the optical axis 7a and the optical axis 7a, and FIG.
FIG. 0 is an explanatory diagram of the shape of the second fθ lens portion 72. ]...Scanning optical system, 2...Light source, 4...Scanned medium, 5...First imaging optical system, 6...Deflector, 7...
・fθ lens, 51...Cylindrical lens, 52
... Toric lens, 71... 1st f-theta lens part, 72... 2nd f-theta lens part Agent Patent attorney Saikyo Keibu 4th Ward Figure 5 Figure 6 Figure S 7 380 Figure 9/7 10 prisoners

Claims (2)

[Claims] (1) It includes a light source, a first imaging optical system, a deflector, and a second imaging optical system, and the light source light via the first imaging optical system forms a line image in the vicinity of the deflector, The traveling direction of the medium is changed over time in the main scanning direction by a deflector, and a point image is formed on the scanned medium moving in the sub-scanning direction via the second imaging optical system. In the scanning optical system that scans on the scanning medium, the first imaging optical system includes a glass cylindrical lens having positive refractive power and negative refractive power in the sub-scanning direction,
and a plastic lens having a toric surface, the first imaging optical system having positive refractive power as a whole, and the second imaging optical system having at least one plastic lens having positive refractive power. The second imaging optical system has a positive refractive power as a whole, and the plastic lens of the first imaging optical system and the plastic lens of the second imaging optical system have Accordingly, there is provided a scanning optical system that compensates for the condensing position of the light source light to not fluctuate depending on the temperature. (2) including a light source, a first imaging optical system, a deflector, and a second imaging optical system, the light source light passing through the first imaging optical system forms a line image in the vicinity of the deflector; The traveling direction of the medium is changed over time in the main scanning direction by a deflector, and a point image is formed on the scanned medium moving in the sub-scanning direction via the second imaging optical system. In the scanning optical system that scans on the scanning medium, the first imaging optical system includes a glass cylindrical lens having positive refractive power, and having positive refractive power in the main scanning direction,
The first imaging optical system has a positive refractive power as a whole, and the second imaging optical system has a positive refractive power. the second imaging optical system has a positive refractive power as a whole, and the plastic lens of the first imaging optical system and the second imaging optical system What is claimed is: 1. A scanning optical system comprising: a plastic lens to compensate for temperature-dependent convergence position of light source light in the sub-scanning direction;