JP2002350760A - Optical scanner and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the fluctuation of a spot diameter caused by the fluctuation of temperature and the fluctuation of interval between scanning lines in the case of multibeam scanning by positively utilizing the unevenness of temperature in the housing of an optical scanner. SOLUTION: This optical scanner is provided with a 1st optical system for coupling divergent luminous flux from a light source, a 2nd optical system by which the coupled luminous flux is formed into an image as a line image long in a main scanning direction on the deflection and reflection surface of a light deflector, and a 3rd optical system by which the luminous flux deflected by the light deflector 4 is condensed as a light spot on a surface to be scanned. The 3rd optical system 6 is provided with one or more resin lenses 6a and 6b having positive power in the main scanning direction and/or a subscanning direction, and the 2nd optical system 3 has a resin lens 3a having negative power so as to reduce the fluctuation of power of the 3rd optical system caused by temperature change. The optical scanner is provided with temperature distribution forming means 1 and 4 forming temperature distribution so that the temperature change of an atmosphere in the vicinity of the 1st optical system: ΔT1, the temperature change of an atmosphere in the vicinity of the 2nd optical system: ΔT2, and the temperature change of an atmosphere in the vicinity of the 3rd optical system: ΔT3 satisfy a condition: ΔT1>ΔT3 and/or ΔT2>ΔT3 inside housing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical scanning device and an image forming device.

[0002]

2. Description of the Related Art Optical scanning apparatuses are widely known in connection with image forming apparatuses such as digital copying machines, laser printers, facsimile machines, optical plate making machines, optical plotters and the like. In recent years, recording density has been increased in digital copying machines and laser printers, and accordingly, it has become necessary to further reduce the spot diameter of light spots on photosensitive media. Further, in order to realize a low cost viewpoint and a special surface shape, a resin used for a lens used in a scanning image forming optical system (an optical system for forming an image of a deflected light beam on a photosensitive medium) is being developed.

In order to form a light spot having an appropriate spot diameter on a photosensitive medium, the image plane of the image formed by the scanning imaging optical system must be "better fitted" to the photosensitive medium. Is larger in focal length variation due to variation in radius of curvature and refractive index due to variation in environmental temperature and the like than glass lenses.

[0004] For this reason, when the environmental temperature changes, a change in the image surface occurs due to a change in the shape or refractive index of the resin lens, and the spot diameter of the light spot formed on the photosensitive medium increases, so-called “spot diameter increase”. Occurs, and the image quality of the recorded image is degraded due to, for example, a decrease in the resolution of the recorded image.

In recent years, the use of multi-beam optical scanning has been progressing. However, the above-mentioned fluctuation of the image plane causes an increase in spot diameter and instability of a scanning line pitch (scanning line pitch) simultaneously scanned by the multi-beam method.

[0006] As a method of reducing the above-mentioned "displacement of the image forming position of the scanning light beam with respect to the surface to be scanned due to a temperature change", the refractive index of each optical element between the light source and the surface to be scanned, the optical element Which optimizes the linear expansion coefficient and the like of a holding member for holding the image so as to “reduce the image position shift of the entire optical system” (Japanese Patent No. 2736984).
However, in the case of this method, since there is almost no parameter for canceling the imaging position shift due to the temperature fluctuation, the temperature correction effect is not always sufficient, especially when the diameter of the light spot is reduced,
Since the depth margin decreases in proportion to the square of the spot diameter, it is difficult to satisfactorily compensate for the change in spot diameter due to temperature fluctuation.

A second optical system for forming a light beam from the light source side as a "long linear image in the main scanning direction" in the vicinity of the deflecting and reflecting surface of the optical deflector has a "resin lens having negative power". Offsets the imaging position shift caused by the focal length variation of the third optical system that forms the deflected light beam on the surface to be scanned,
A method of reducing the fluctuation of the imaging position shift of the entire optical system has also been proposed (Japanese Patent No. 2804647), but in order to improve the correction effect by this method, the power of the “resin lens having negative power” is required. Must be set strongly, the radius of curvature of the resin lens becomes small, the wavefront aberration tends to deteriorate rather, and it becomes difficult to reduce the diameter of the light spot.

The temperature inside the housing for accommodating the optical elements and the like of the optical scanning device fluctuates due to heat generated by a driving motor of a rotary polygon mirror as an optical deflector included in the optical scanning device and a semiconductor laser as a light source. Such a temperature fluctuation does not occur uniformly in the housing, and a temperature distribution exists in the housing. The inventors have experimentally investigated that the temperature difference depending on the position in the housing is 20.
° C.

The above-mentioned conventional "method of reducing the deviation of the image-forming position of the scanning light beam from the surface to be scanned due to a temperature change" is performed on the premise that the temperature inside the housing is uniform. When there is a non-uniform temperature distribution, the spot diameter and the scanning line interval in the case of multi-beam scanning tend to deteriorate rather.

[0010]

SUMMARY OF THE INVENTION The present invention actively utilizes "non-uniformity of temperature" in a housing of an optical scanning device to change spot diameters due to temperature fluctuations and to prevent multi-beam scanning. It is an object to reduce “variation in scanning line interval”.

[0011]

According to an optical scanning device of the present invention, a light beam from a light source is deflected by an optical deflector, the deflected light beam is condensed to form a light spot on a surface to be scanned, and the light beam is scanned. It performs optical scanning of a surface, has a first optical system, a second optical system, and a third optical system between a light source and a surface to be scanned, and further has a temperature distribution generating means.

The "first optical system" is an optical system for coupling a divergent light beam from a light source. The first optical system has a “coupling lens” as an optical element. The form of the coupled light beam can be a “parallel light beam” or a “weakly divergent or weakly converging light beam”.

The "second optical system" is an optical system for forming a light beam coupled by the first optical system as a linear image long in the main scanning direction near the deflection reflecting surface of the optical deflector.
The “third optical system” converts the light beam deflected by the light deflector into
This is an optical system that converges a light spot on the surface to be scanned.
The “scanned surface” is actually a photosensitive surface of a “photosensitive medium” such as a photoconductive photoconductor.

The third optical system is “one or more resin lenses having a positive power in the main scanning direction and / or the sub-scanning direction”.
Having. The second optical system has one or more resin lenses having negative power so as to “reduce power fluctuation of the third optical system due to temperature change”.

The first to third optical systems, the light source, and the optical deflector are housed in a housing. "Temperature distribution generating means" includes a temperature change in the atmosphere near the first optical system: ΔT1, and a temperature change in the atmosphere near the second optical system:
ΔT2, temperature change of atmosphere near the third optical system: ΔT3
Is a means for generating a temperature distribution so as to satisfy the condition: ΔT1> ΔT3 and / or ΔT2> ΔT3.

In the optical scanning device according to the first aspect,
Temperature change in the atmosphere near the first optical system: Δm1, fluctuation in the main-scanning image position on the image plane due to ΔT1, Δs1, fluctuation in the sub-scanning image position, ΔT2 in the atmosphere near the second optical system: ΔT2
Δm2, fluctuation in the main scanning image position on the image plane due to the following, Δs2: fluctuation in the sub-scanning image position, Δm: temperature fluctuation in the atmosphere near the third optical system: Δm, fluctuation in the main scanning image position on the image plane due to ΔT3.
3. When the sub-scanning imaging position variation is Δs3, these Δ
T1 to ΔT3, Δm1 to Δm3, Δs1 to Δs3 are conditions: | Δm1 / ΔT1 + Δm2 / ΔT2 + Δm3 / ΔT3 | <
0.04 [mm / ° C] and | Δs1 / ΔT1 + Δs2 / ΔT2 + Δs3 / ΔT3 | <
It is preferable to satisfy 0.04 [mm / ° C] (claim 2).

The "temperature distribution generating means" in the optical scanning device according to the first or second aspect includes a "partition separating the first optical system and the second optical system from the third optical system" inside the housing; And a heat generating means for generating heat on the first and second optical systems separated by the first and second optical systems. In this case, the partition can "separate the optical deflector from the third optical system", and the optical deflector can be on the same side of the partition as the first and second optical systems.

As the heat generating means, a dedicated means can be used, but in the optical scanning device according to the fourth aspect, since the light source and the optical deflector are provided on the same side of the partition, these light sources and the optical deflector are heated. It can be a means (claim 5).

The "temperature distribution generating means" in the optical scanning device according to claim 1 or 2 may further include "a partition disposed between the first optical system, the second optical system, and the third optical system inside the housing. And a heat exchange means for reducing a change in temperature of the atmosphere near the third optical system ”(claim 6). In this case, an air cooling fan or a Peltier element can be used as the "heat exchange means" (claim 7).

In the optical scanning device according to the sixth or seventh aspect, as the heat generating means, a dedicated heat generating means can be used. In this case, however, the "light source and optical deflector" may be used as the heat generating means. (Claim 8).

In the optical scanning device according to any one of the first to eighth aspects, the light source is preferably a "semiconductor laser", and the optical deflector is preferably a rotary polygon mirror. In the case of multi-beam scanning, the semiconductor laser as a light source includes a semiconductor laser array. Further, as a light source, a light beam from a plurality of semiconductor lasers may be beam-combined by a beam combining prism or the like to provide a light source for multi-beam scanning.

In the optical scanning device according to any one of the first to ninth aspects, the coupling lens of the first optical system may be a “glass lens”.
0).

As is clear from the above description, the optical scanning device of the present invention can be implemented as a single beam type or a multi-beam type.

An image forming apparatus according to the present invention is an "image forming apparatus for forming an image by optically scanning a photosensitive medium", wherein the optical scanning according to any one of claims 1 to 10 is used for optically scanning a photosensitive medium. A scanning device is used (claim 11).

As the "photosensitive medium", various known ones can be used. For example, an image can be formed by using a chromogenic photographic paper, which develops color by heat, as a photosensitive medium, optically scanning the photographic paper, and developing a color using "heat energy" by a light spot.

Depending on the photosensitive medium, a latent image is formed on the photosensitive medium by optical scanning, and an image can be formed by visualizing the latent image.
In this case, for example, a silver salt film can be used as the photosensitive medium. The latent image formed on the silver halide film by optical scanning can be developed and fixed in accordance with the “normal silver halide photography process”. Such an image forming apparatus can be implemented as an optical plate making device or an optical drawing device.

As the photosensitive medium, a "photoconductive photosensitive member" can be used. In this case, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is "finally carried on a sheet-shaped recording medium".
3). If a known zinc oxide photosensitive paper is used as the photoconductive photoreceptor, the toner image formed on the zinc oxide photosensitive paper can be fixed as it is “using the zinc oxide photosensitive paper as a sheet-shaped recording medium”.

When a photoconductive photoreceptor that can be used repeatedly is used, the toner image formed on the photoreceptor is transferred to a sheet-like recording medium such as transfer paper or an OHP sheet (a plastic sheet for an overhead projector). Transfer directly or through an intermediate transfer medium such as an intermediate transfer belt,
By fixing, a desired image can be obtained.

These image forming apparatuses can be implemented as digital copiers, optical printers, optical plotters, facsimile machines and the like. Since image formation is performed by optical scanning, image information applied to the optical scanning device may be information obtained by reading a document, generated by a computer or the like, or may be information transmitted from outside. .

To supplement the description, the temperature change in the housing of the optical scanning device is not a "rapid change" but a "slow change in time". Therefore, it can be considered that the temperature of each optical element of the first to third optical systems is substantially the same as the temperature of the atmosphere surrounding the optical element.

As a specific example, the coupling lens of the first optical system is a glass lens, the second optical system includes a resin lens of negative power, and the third optical system includes a resin lens of positive power. Consider the case where a lens is included.

When there is a temperature change in the first optical system, the change in the focal length due to the temperature change of the coupling lens itself is small. In this case, it is the lens cell (metal) holding the coupling lens that causes a substantial focal length change.
Is a change in the distance between the light source and the coupling lens due to the thermal deformation of the light source.

At this time, when the ambient temperature in the vicinity of the first optical system rises, a change equivalent to a decrease in the focal length of the first optical system occurs in the coupling action of the first optical system. Also, in the second optical system, the power of the “negative-power resin lens” decreases, so that the temperature rise acts on the second optical system to shorten its focal length.

In the third optical system, since the resin lens has a positive power, the focal length of the third optical system becomes longer as the ambient temperature increases. That is, the direction in which the temperature rise brings about the focal length is opposite to each other in the first and second optical systems and the third optical system, so that the focal length change in the third optical system is caused by the first and second optical systems. It tends to be offset by changes in focal length.

Incidentally, each of the first to third optical systems has a positive power in the sub-scanning direction. In the sub-scanning direction, the third optical system has the largest focal length among these, and the first and second optical systems have relatively small focal lengths.

Therefore, when a resin lens is included in the third optical system, the amount of change in focal length caused by a change in temperature is large. Therefore, in order to effectively offset the focal length fluctuation in the third optical system by the focal length fluctuations in the first and second optical systems, it is necessary to increase the focal length fluctuation in the first optical system and the second optical system. For example, for a resin lens having a negative power included in the second optical system, the curvature of the lens surface must be increased.

According to the present invention (claim 1), the first and / or
Or, the ambient temperature near the second optical system: ΔT1 and / or
Alternatively, ΔT2 is changed to the ambient temperature near the third optical system: ΔT3
A larger temperature distribution is realized in the housing.

With this arrangement, in the first and / or second optical systems, a large change in focal length occurs due to a large temperature change, and a relatively small change in focal length occurs in the third optical system due to a small change in temperature. For example, without increasing the negative power of the resin lens in the second optical system so much, the first and second focal length fluctuations caused in the third optical system can be reduced.
It is possible to effectively offset the focal length fluctuation in the optical system. Therefore, it is possible to effectively reduce "deterioration of wavefront aberration" due to the remarkably small radius of curvature of the resin negative lens of the second optical system.

The conventional adjustment of the image forming position due to temperature fluctuation is as follows.
Since the temperature fluctuation amounts in the housing: ΔT1, ΔT2, and ΔT3 are the same, in the case described above, a strong lens surface curvature must be given to the negative resin lens of the second optical system, and moreover, in reality, When ΔT1, ΔT2, and ΔT3 become non-uniform, the result is that the imaging position shift is increased.

The temperature fluctuation in the housing is caused by the heat generated by the driving motor of the rotary polygon mirror, the semiconductor laser light source, and the like, and the heat generated during the development and fixing processes in the image forming apparatus. Therefore, it is desirable to compensate for high-temperature driving rather than low-temperature driving.

The coupling lens, which is the lens of the first optical system, has a rotationally symmetric shape with respect to the optical axis, and if its focal length (the distance between the light-emitting portion of the back focus light source and the coupling lens) is f1, f1 is: Coupling lens shape: R1 (parameter representing shape), refractive index:
It is determined by N1. These R1 and N1 change depending on the temperature of the first optical system (the temperature of the atmosphere into which the first optical system is transferred): T. The distance L1 between the coupling lens and the light emitting portion of the light source (semiconductor laser) in the lens cell of the coupling lens also changes depending on the ambient temperature. Further, when the light emission wavelength: λ of the light source changes due to a temperature change, this wavelength change also causes a change in the back focus: f1.

Accordingly, the temperature of the first optical system changes with temperature: Δ
When T1 occurs, the "shift of the imaging position of the entire system" according to the third optical system is approximately, formally in the main scanning ^{direction, Δm1 ≒ βm 2 × (∂f1} / ∂R1 · ∂ R1 / ∂T + ∂f1 / ∂N1 ・ ∂
N1 / ∂T + ∂f1 / ∂L1 ・ ∂L1 / ∂T + ∂f1 / ∂λ ・ ∂λ / ∂T)
· Delta] T1 and it can be written, formally the sub-scanning ^{direction, Δs1 ≒ βs 2 × (∂f1} / ∂R1 · ∂R1 / ∂T + ∂f1 / ∂N1 · ∂
N1 / ∂T + ∂f1 / ∂L1 ・ ∂L1 / ∂T + ∂f1 / ∂λ ・ ∂λ / ∂T)
ΔT1 can be written.

On the left-hand side of these equations, Δm1 is the above-mentioned “main-scanning imaging position variation” and Δs1 is “sub-scanning imaging position variation”.

In the right side of the above equation, ∂R1 / ∂T: fluctuation of lens shape due to temperature fluctuation of the first optical system ∂f1 / ∂R1: fluctuation of back focus due to fluctuation of lens shape of the first optical system ∂N1 / ∂T: Refractive index fluctuation due to temperature fluctuation of first optical system ∂f1 / ∂N1: Back focus fluctuation due to refractive index fluctuation of first optical system ∂L1 / ∂T: Coupling lens due to temperature fluctuation of first optical system Fluctuation of the distance between the light source and the coupling lens due to expansion and contraction of the lens cell ∂f1 / ∂L1: fluctuation of the back focus of the coupling lens of the first optical system due to expansion and contraction of the lens cell ∂λ / ∂T: fluctuation of the light source temperature Wavelength fluctuation ∂f1 / ∂λ: Back focus fluctuation due to wavelength fluctuation of the first optical system βm: Lateral magnification of the entire optical system in the main scanning direction βs: Lateral magnification of the entire optical system in the sub-scanning direction Then, Δm1 / ΔT1 ≒ βm ² × (∂f1 / ∂R1∂∂R1 / ∂T + ∂f1 / ∂N1∂∂N1 / ∂T + ∂f1 / ∂L1∂∂L1 / ∂T + ∂f1 / ∂λ ・∂λ / ∂T) (1) Δs1 / ΔT1 ≒ βs ² × (∂f1 / ∂R1∂∂R1 / ∂T + ∂f1 / ∂N1∂∂N1 / ∂T + ∂f1 / ∂L1∂∂L1 / ∂ T + ∂f1 / ∂λ · ∂λ / ∂T) (2) represents a main-scanning imaging position variation and a sub-scanning imaging position variation per unit temperature change of the first optical system.

The term due to the expansion and contraction of the lens cell of the coupling lens in the above equation: ∂f1 / ∂L1∂∂L1 / ∂T is the opposite sign to the other terms, and if the coupling lens is a glass lens In this case, this term is dominant in each right side of the equations (1) and (2). Therefore, the correction can be made in a direction to offset the imaging position shift due to the temperature fluctuation.

Similarly, when the temperature change of the second optical system is ΔT2, the main scanning imaging position change per unit temperature change is ΔT2.
m2 / ΔT2, sub-scanning imaging position variation: Δs2 / ΔT2
は Rm2 / ∂T: fluctuation of the lens shape in the main scanning direction due to temperature fluctuation of the second optical system ∂fm2 / ∂Rm2: fluctuation of the back focus in the main scanning direction due to fluctuation of the lens shape of the second optical system ∂Rs2 / ∂T : Lens shape variation in the sub-scanning direction due to temperature variation of the second optical system ∂fs2 / ∂Rs2: Back focus variation in the main scanning direction due to lens shape variation of the second optical system ∂N2 / ∂T: Temperature of the second optical system Refractive index fluctuation due to fluctuation ∂fm2 / ∂N2: Back focus fluctuation in the main scanning direction due to refractive index fluctuation of the second optical system ∂fs2 / ∂N2: Back focus fluctuation in the sub-scanning direction due to refractive index fluctuation of the second optical system ∂ λ / ∂T: wavelength fluctuation due to temperature fluctuation of light source ∂fm2 / ∂λ: back focus fluctuation in main scanning direction due to wavelength fluctuation of second optical system ∂fs2 / ∂λ: sub-scanning direction due to wavelength fluctuation of second optical system Back focus fluctuation fm3: focal length of the third optical system in the main scanning direction Betaesu3: using the third sub-scanning direction lateral magnification of the optical system, ^{formally, Δm2 / ΔT2 ≒ fm3 2 (} ∂fm2 / ∂Rm2 · ∂Rm2 / ∂T + ∂fm2 / ∂N2 · ∂N2 / ∂T + ∂fm2 / ∂λ ・ ∂λ / ∂T) (3) Δs2 / ΔT2 ≒ βs3 ² (∂fs2 / ∂Rs2∂Rs2 / ∂T + ∂fs2 / ∂N2∂N2 / ∂T + ∂fs2 / ∂ λ∂λ / ∂T) (4).

By using a resin lens having negative power for the second optical system, the terms in the above equations (3) and (4) are: ∂fm2 / ∂Rm22∂Rm2 / ∂T, ∂fm2 / ∂N2・ ∂N2 / ∂
T, ∂fs2 / ∂Rs2 · ∂Rs2 / ∂T, and ∂fs2 / ∂N2 · ∂N2 / ∂T can be reversed and dominantly signed with other terms. Therefore, the correction can be made in a direction to offset the imaging position shift due to the temperature fluctuation. Further, in the temperature change of the third optical system: ΔT3, the main-scanning imaging position change per unit temperature change: Δm3
/ ΔT3, variation in sub-scanning imaging position: Δs3 / ΔT3 is ∂Rm3 / ∂T: variation in lens shape in the main scanning direction due to temperature variation in the third optical system ∂fm3 / ∂Rm3: variation in lens shape in the third optical systemフ ォ ー カ ス Rs3 / ∂T: Lens shape fluctuation in the sub-scanning direction due to temperature fluctuation of the third optical system ∂fs3 / ∂Rs3: Back focus in the main scanning direction due to lens shape fluctuation of the third optical system Fluctuation ∂N3 / ∂T: Refractive index fluctuation due to temperature fluctuation of the third optical system ∂fm3 / ∂N3: Back focus fluctuation in the main scanning direction due to refractive index fluctuation of the third optical system ∂fs3 / ∂N3: Third optical system Back focus fluctuation in the sub-scanning direction due to refractive index fluctuation の λ / ∂T: Wavelength fluctuation due to temperature fluctuation of the light source ∂fm3 / ∂λ: Back focus fluctuation in the main scanning direction due to wavelength fluctuation of the third optical system ∂fs3 / ∂ λ: back focus in the sub-scanning direction due to wavelength fluctuation of the third optical system Δm3 / ΔT3 ≒ (∂fm3 / ∂Rm3∂∂Rm3 / ∂T + ∂fm3 / ∂N3∂∂N3 / ∂T + ∂fm3 / ∂λ∂∂λ / ∂T) × ΔT3 (5) Δs3 / ΔT3 ≒ (∂fs3 / ∂Rs3 · ∂Rs3 / ∂T + ∂fs3 / ∂N3 · ∂N3 / ∂T + ∂fs3 / ∂λ · ∂λ / ∂T) × ΔT3 (6) Can be approximated.

In equations (5) and (6), the terms on the right-hand side have the same sign, so that the imaging position shift due to temperature fluctuation: Δm
3. Δs3 becomes considerably large. In particular, when the third optical system is entirely made of resin, Δm3 and Δs3 become very large.

Each of the terms on the right side of the above equations (1) to (6), that is, ∂fm3 / ∂Rm3 · 3Rm3 / ∂T, ∂fm3 / ∂N3 · ∂N3 / ∂T, etc. It can be specified in. Therefore, by optimizing these, the condition: | Δm1 / ΔT1 + Δm2 / ΔT2 + Δm3 / ΔT3 | <
0.04 [mm / ° C] and | Δs1 / ΔT1 + Δs2 / ΔT2 + Δs3 / ΔT3 | <
The first to third optical systems of the optical scanning optical system can be configured to satisfy 0.04 [mm / ° C.].

First condition: | Δm1 / ΔT1 + Δm2 / ΔT2 + Δm3 / ΔT3 | <
0.04 [mm / ° C.] is a condition in which the imaging position shift in the main scanning direction is 0.04 mm or less when the first to third optical systems change the temperature “uniformly” by one degree, Second condition: | Δs1 / ΔT1 + Δs2 / ΔT2 + Δs3 / ΔT3 | <
The condition of 0.04 [mm / ° C.] is a condition under which the deviation of the imaging position in the sub-scanning direction when the temperature of the first to third optical systems changes “uniformly” by one degree is 0.04 mm or less.

Therefore, in an optical scanning device satisfying these conditions, if the allowable range of the imaging position shift in the main scanning direction and the sub-scanning direction is ± 1 mm, the temperature distribution in the housing is considered to be uniform. Therefore, ± 25 ° C. is allowed as a temperature fluctuation in the housing.

However, according to the present invention, temperature non-uniformity is positively generated in the housing so that the temperature of the third optical system is always lower than the temperature of the first and / or second optical systems. Therefore, Δm3 and Δs3 are smaller than when the temperature fluctuation in the housing is uniform, so that a wider temperature fluctuation is permitted.

[0053]

Embodiments of the present invention will be described below. FIG. 1 is a diagram for explaining one embodiment of the optical scanning device. In FIG. 1A, reference numeral H1 indicates a housing main body. The housing body H1 is a "shallow box"
The optical system of the optical scanning device is disposed inside.
That is, a semiconductor laser 1 as a light source, a coupling lens 2, a second optical system 3, a rotary polygon mirror 4 as an optical deflector, a glass window 5, a third optical system 6, and a folding mirror are provided in the housing body H1. 7, a mirror 8, a condenser lens 9, a light receiving element 10, and the like are provided.

As shown in FIG. 1B, the upper part of the housing body H1 is covered with a housing cover H2.
Thereby, the inside of the housing is closed. Rotating polygon mirror 4
The polygon mirror 4A is fixed to a shaft of a drive motor 4B fitted and fixed to the bottom of the housing body H1.

The coupling lens 2 is a glass lens and constitutes a first optical system together with a lens cell (not shown) for holding the glass lens. The lens cell includes the coupling lens 2 and the semiconductor laser 1 as a light source. Are held together. When the temperature inside the housing is the set temperature (25 ° C.), the divergent light beam emitted from the semiconductor laser 1 is coupled by the coupling lens 2 to become a parallel light beam.

The second optical system 3 focuses the parallel light beam incident from the light source side in the sub-scanning direction (in FIG. 1A, a direction perpendicular to the drawing), and closes the parallel light beam near the deflecting reflection surface of the polygon mirror 4A. The image is formed as a "long line image in the main scanning direction".

The luminous flux reflected by the deflecting / reflecting surface becomes a deflecting luminous flux which is deflected at a constant angular velocity as the polygon mirror 4A rotates at a constant speed, passes through the glass window 16, enters the third optical system 6, and enters the third optical system. When the light passes through the system 6, the light path is turned back by the turning mirror 7, and as shown in FIG. 1B, the light passes through the dustproof glass 11 provided so as to close the emission hole formed at the bottom of the housing body H <b> 1. The light is emitted from the housing and condensed on the photosensitive surface of the photosensitive medium 110 to form a light spot.

The photosensitive surface of the photosensitive medium 110 is a "scanned surface" and is optically scanned by a light spot. Note that, prior to optical scanning of the surface to be scanned, the deflected light beam is reflected by a mirror 8 as shown in FIG. 1A, and is condensed on a light receiving surface of a light receiving element 10 by a condenser lens 9. The start of optical scanning of the scanned surface by the light spot is synchronized with the light receiving signal of the light receiving element 10 as a reference.

The third optical system 6 is composed of two lenses 6a and 6b. These lenses 6a and 6b are both resin lenses and have positive power in the main and sub-scanning directions as a whole of the third optical system. The third optical system is a so-called fθ lens, and has a function of making light scanning by a light spot uniform.
In the configuration shown in FIG. 1, if a semiconductor laser array is used instead of the semiconductor laser 1, multi-beam optical scanning can be realized.

The second optical system 3 is composed of two lenses 3a and 3b. The lens 3a is a resin lens, and the lens 3b is a glass lens. The combined power of the lenses 3a and 3b is "positive in the sub-scanning direction". As described above, the parallel light beam incident from the light source side is focused in the sub-scanning direction, and the main scanning is performed near the deflecting reflection surface of the rotary polygon mirror 4. An image is formed as a long line image in the direction.

The resin lens 3a has negative power in the main and sub scanning directions so as to reduce power fluctuation in the main and sub scanning directions of the third optical system caused by temperature fluctuation. For this reason, when a parallel light beam enters from the light source side, the light beam is given divergence in both the main and sub-scanning directions by the action of the lens 3a.

The glass lens 3b is an anamorphic lens having a positive power in the main and sub scanning directions.
The divergent light beam incident from the lens 3a is returned to a parallel light beam in the main scanning direction, and is converted to a condensed light beam in the sub-scanning direction.

The first to third optical systems have the following conditions: | Δm1 / ΔT1 + Δm2 / ΔT2 + Δm3 / ΔT3 | <
0.04 [mm / ° C] | Δs1 / ΔT1 + Δs2 / ΔT2 + Δs3 / ΔT3 | <
It is configured to satisfy 0.04 [mm / ° C.].

In FIG. 1A, reference numerals 15 and 16 indicate “partition walls”.

The partitions 15 and 16 partition the inside of the housing together with the glass window 5, and separate the first optical system 2 and the second optical system 3 from the third optical system 6. That is, the glass window 5
Constitutes a part of “a partition separating the first optical system and the second optical system from the third optical system inside the housing”.

The partition walls 15 and 16 do not need to be heat insulating walls. However, since the inside of the housing is partitioned as described above, heat generated by convection between the first and second optical systems and the third optical system is generated. Transmission is prevented.

On the side where the first optical system and the second optical system are separated, a drive motor 4B for the semiconductor laser 1 and the rotary polygon mirror 4 is provided.
These elements generate heat when optical scanning is performed. Therefore, on the right side of the partition walls 15 and 16 in FIG. To rise.

Since the wall of the housing is not a heat insulating wall, heat exchange occurs inside and outside the housing via the housing wall, so that the ambient temperature does not rise without limit. On the other hand, in the housing, there is hardly any heat source on the side of the third optical system 6 partitioned by the partition, so that the ambient temperature rise is small on this side. Thus, as the optical scanning is performed, there is a difference between the changes in the ambient temperature on both sides of the partition wall, and ΔT1> ΔT3 and ΔT2>
The atmosphere state of ΔT3 is maintained, and as described above, the fluctuation of the main-scanning imaging position and the fluctuation of the sub-scanning imaging position are effectively reduced, and good optical scanning can be realized.

FIG. 2 shows another embodiment. In order to avoid complication, the same reference numerals as those in FIG. The manner in which optical scanning is performed is exactly the same as in the embodiment of FIG. In FIG. 2, reference numerals 17 and 18 denote partition walls inside the housing (the housing main body H1 and FIG. 1B).
Is closed with a housing cover as shown in FIG. However, unlike the embodiment of FIG. 1, air can flow between the partitioned parts inside the housing.

The housing main body H1 has an opening on the side wall, and an air cooling fan 19 is provided in this portion. Reference numeral 22 indicates an air filter. At the time of optical scanning, the ambient temperature inside the housing rises due to heat generated by the light source and the optical deflector. At this time, for example, when air inside the housing is exhausted outside the housing by the air-cooling fan 19, the air whose temperature has risen flows outside the housing. Inside the housing,
Atmosphere conditions of ΔT1> ΔT3 and ΔT2> ΔT3 are formed. The same applies even when cooling air is drawn into the housing from the outside by the air cooling fan 19.

In this manner, fluctuations in the main-scanning image forming position and in the sub-scanning image forming position can be effectively reduced, and good optical scanning can be realized.

The optical scanning device described above with reference to FIGS. 1 and 2 includes a first optical system 2 for coupling a divergent light beam from a light source 1 and a coupled light beam.
A second optical system 3 that forms a long linear image in the main scanning direction on the deflection reflection surface of the optical deflector 4; and a third optical system that focuses a light beam deflected by the optical deflector as a light spot on the surface to be scanned. In the optical scanning device having the optical system 6, the third optical system 6
Has one or more resin lenses 6a and 6b having a positive power in the main scanning direction and / or the sub-scanning direction, and the second optical system 3 reduces power fluctuation of the third optical system 6 due to a temperature change. In the housing having at least one resin lens having a negative power (lens 3a) and accommodating the first to third optical systems, the light source, and the optical deflector,
The temperature change of the atmosphere near the optical system: ΔT1, the temperature change of the atmosphere near the second optical system: ΔT2, and the temperature change of the atmosphere near the third optical system: ΔT3 are the conditions: ΔT1> ΔT3 and / or ΔT2> ΔT3. It has temperature distribution generating means 1 and 4B for generating a temperature distribution to satisfy the requirements (claim 1).

In these optical scanning devices, the variation in the temperature of the atmosphere near the first optical system: Δm1, the variation in the main scanning imaging position on the image plane due to ΔT1, the variation in the sub-scanning imaging position as Δs1, the second optical system Temperature change in the vicinity of the atmosphere: Δm2 for the main scan imaging position variation on the image plane due to ΔT2, Δs2 for the variation in the sub-scanning imaging position, and temperature change in the atmosphere near the third optical system: main scanning on the image plane due to ΔT3. Assuming that the imaging position variation is Δm3 and the sub-scanning imaging position variation is Δs3, these ΔT1 to ΔT3,
Conditions are Δm1 to Δm3 and Δs1 to Δs3: | Δm1 / ΔT1 + Δm2 / ΔT2 + Δm3 / ΔT3 | <
0.04 [mm / ° C] and | Δs1 / ΔT1 + Δs2 / ΔT2 + Δs3 / ΔT3 | <
0.04 [mm / ° C] is satisfied (claim 2).

The optical scanning device of the embodiment shown in FIG.
"Temperature distribution generating means" is provided inside the housing.
It has partition walls 5, 15, 16 for separating the optical system and the second optical system from the third optical system, and heat generating means 1, 4 for generating heat on the first and second optical system sides separated by the partition walls ( (Claim 3), the partition separates the optical deflector 4 from the third optical system 6 (Claim 4), and the heat generating means is the light source 1 and the optical deflector 4 (Claim 5).

In the optical scanning device shown in FIG. 2, the temperature distribution generating means includes partition walls 17, 18 provided between the first optical system, the second optical system, and the third optical system inside the housing.
And a heat exchange means 19 for reducing a temperature change of the atmosphere near the third optical system 6 (Claim 6), wherein the heat exchange means is an air cooling fan 19 (Claim 7), and the heat generation means is the light source 1 and the light source 1. The optical deflector 4.

1 and 2, the light source is a semiconductor laser, the optical deflector is a rotary polygon mirror, and the coupling lens 2 of the first optical system is a glass lens. ). In the embodiment of FIG. 2, instead of the air cooling fan 19 or together with the air cooling fan 19,
A Peltier element as a heat exchange means may be provided in the third optical system, and also in the embodiment of FIG. 1, a heat exchange means such as an air-cooling fan or a Peltier element is provided on the third optical system side of the partition (for example, 2 (similar to the embodiment of FIG. 2).

FIG. 3 shows an embodiment of the "image forming apparatus". This image forming apparatus is a “laser printer”.

The “laser printer” has a “photoconductive photosensitive member formed in a cylindrical shape” as the photosensitive medium 110. Around the photosensitive medium 110, a charging unit 111 (a corona charger is illustrated, but a contact-type charging roller may be used, of course), a developing device 113, and a transfer unit 114
(The type using corona discharge is shown, but a contact type transfer roller may be used), and a cleaning device 115 is provided.

The optical scanning device 1 using the laser beam LB
12 is provided so that “exposure by optical writing” is performed between the charging roller 111 and the developing device 113.
In FIG. 3, reference numeral 116 denotes a fixing device, and reference numeral S denotes a transfer sheet as a “sheet-shaped recording medium”.

When forming an image, the photosensitive medium 110, which is a photoconductive photosensitive member, is rotated clockwise at a constant speed, the surface thereof is uniformly charged by the charging means 111, and the surface of the laser beam LB of the optical scanning device 112 is charged. An electrostatic latent image is formed upon exposure by optical writing. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

The electrostatic latent image is reversely developed by the developing device 113 to form a toner image on the photosensitive medium 110. The transfer paper S is sent to the transfer unit at the same time as the toner image on the photosensitive medium 110 moves to the transfer position, and is superimposed on the toner image at the transfer unit.
The toner image is electrostatically transferred by the operation of the transfer unit 114.

The transfer paper S on which the toner image has been transferred is sent to the fixing device 116, where the toner image is fixed and discharged outside. The cleaning device 115 cleans the surface of the photosensitive medium 110 after the transfer of the toner image.
To remove residual toner and paper dust. The above-described OHP sheet can be used instead of the transfer paper, and the transfer of the toner image can be performed via an “intermediate transfer medium” such as an intermediate transfer belt.

By using the optical scanning device described in the above embodiment as the optical scanning device 112, good image formation can be performed.

As described above, the image forming apparatus of FIG. 3 using the optical scanning device of the present invention as the optical scanning device 12 is an image forming apparatus that optically scans the photosensitive medium 110 to form an image. An apparatus using the optical scanning device according to any one of claims 1 to 10 for scanning (claim 11)
Thus, a latent image is formed on the photosensitive medium by optical scanning of the photosensitive medium 110, and this latent image is visualized (claim 12). The photosensitive medium 110 is a photoconductive photoconductor, and the latent image is an electrostatic latent image. The toner image is formed as an image and visualized as a toner image, and the toner image is finally carried on the sheet-shaped recording medium S (claim 13).

[0085]

As described above, according to the present invention, a novel optical scanning device and a new image forming apparatus can be realized. The optical scanning device according to the present invention uses the resin optical element for the third optical system and effectively utilizes the temperature distribution in the housing, thereby forming a connection in the main scanning and sub-scanning directions caused by the ambient temperature fluctuation. Variations in image position can be effectively reduced, and a stable spot diameter and a stable scanning line interval in the case of a multi-beam system can be realized.

Therefore, the image forming apparatus using this optical scanning device can always form a good image regardless of the temperature fluctuation.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating one embodiment of an optical scanning device.

FIG. 2 is a diagram for explaining another embodiment of the optical scanning device.

FIG. 3 is a diagram for explaining an embodiment of the image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source (semiconductor laser) 2 Coupling lens 3 2nd optical system 4 Optical deflector (rotating polygon mirror) 6 3rd optical system H1 Housing main body H2 Housing cover

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 13/18 G02B 13/24 13/24 H04N 1/036 Z H04N 1/036 B41J 3/00 D 1 / 113 H04N 1/04 104A (72) Inventor Akihisa Itabashi 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Yoshinori Hayashi 1-3-6, Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Hiromichi Hiromichi 1-3-6 Nakamagome, Ota-ku, Tokyo, Japan Ricoh Co., Ltd. (72) Koji Sakai 1-3-6, Nakamagome, Ota-ku, Tokyo, Equity Company Ricoh F term (reference) 2C362 AA46 BA84 BA86 DA03 DA33 2H045 AA01 BA22 BA33 CB22 DA02 DA04 2H087 KA08 KA18 KA19 LA01 LA21 LA28 NA08 PA05 PA17 PB05 RA07 RA08 RA44 RA45 5C051 AA02 CA07 DA02 DB02 DB22 DB24 DB30 DB34 DC04 DC07 FA01 5C072 AA03 BA12 HA02 HA06 HA09 HA13 HA20 XA01 XA05

Claims (13)

[Claims] A first optical system that couples a divergent light beam from a light source; and a second optical system that forms the coupled light beam as a long linear image in the main scanning direction near a deflecting reflection surface of an optical deflector. A light beam deflected by the light deflector, and a third optical system for condensing the light beam on the surface to be scanned as a light spot, wherein the third optical system has a main scanning direction and / or A resin having one or more resin lenses having a positive power in the sub-scanning direction, wherein the second optical system has a negative power so as to reduce power fluctuation of the third optical system due to a temperature change. A temperature change of an atmosphere near the first optical system: ΔT1, an atmosphere near the second optical system inside the housing that houses the first to third optical systems, the light source, and the optical deflector having at least one lens made of Temperature change: ΔT
2. Optical scanning characterized by having a temperature distribution generating means for generating a temperature distribution such that the temperature change of the atmosphere near the third optical system: ΔT3 satisfies the conditions: ΔT1> ΔT3 and / or ΔT2> ΔT3. apparatus. 2. The optical scanning device according to claim 1, wherein a temperature change of the atmosphere near the first optical system: Δm1, a main scan image position change on the image plane due to ΔT1, a sub-scan image position change, Δs1, Temperature change of atmosphere near the second optical system: ΔT2
Δm2, fluctuation in the main scanning image position on the image plane due to the following, Δs2: fluctuation in the sub-scanning image position, Δm: temperature fluctuation in the atmosphere near the third optical system: Δm, fluctuation in the main scanning image position on the image plane due to ΔT3.
3. When the sub-scanning imaging position variation is Δs3, these Δ
T1 to ΔT3, Δm1 to Δm3, Δs1 to Δs3 are conditions: | Δm1 / ΔT1 + Δm2 / ΔT2 + Δm3 / ΔT3 | <
0.04 [mm / ° C] and | Δs1 / ΔT1 + Δs2 / ΔT2 + Δs3 / ΔT3 | <
An optical scanning device satisfying 0.04 [mm / ° C]. 3. The optical scanning device according to claim 1, wherein the temperature distribution generating means separates the first optical system and the second optical system from the third optical system inside the housing;
An optical scanning device comprising: heat generating means for generating heat on the first and second optical systems separated by the partition. 4. The optical scanning device according to claim 3, wherein the partition separates the optical deflector from the third optical system. 5. The optical scanning device according to claim 4, wherein the heat generating means is a light source and an optical deflector. 6. The optical scanning device according to claim 1, wherein the temperature distribution generating means includes a partition disposed between the first optical system, the second optical system, and the third optical system inside the housing; An optical scanning device comprising: a heat exchange unit configured to reduce a temperature change in an atmosphere near a third optical system. 7. The optical scanning device according to claim 6, wherein the heat exchange means is an air cooling fan or a Peltier element. 8. The optical scanning device according to claim 6, wherein the heat generating means is a light source and an optical deflector. 9. The optical scanning device according to claim 1, wherein the light source is a semiconductor laser, and the optical deflector is a rotating polygon mirror. 10. The optical scanning device according to claim 1, wherein the coupling lens of the first optical system is a glass lens. 11. An image forming apparatus for forming an image by optically scanning a photosensitive medium, wherein the optical scanning apparatus according to any one of claims 1 to 10 is used for optically scanning the photosensitive medium. Image forming device. 12. An image forming apparatus according to claim 11, wherein a latent image is formed on said photosensitive medium by optical scanning of said photosensitive medium, and said latent image is visualized. 13. The image forming apparatus according to claim 12, wherein the photosensitive medium is a photoconductive photoreceptor, the latent image is formed as an electrostatic latent image, visualized as a toner image, and the toner image is formed in a sheet shape. An image forming apparatus, which is finally carried on a recording medium according to (1).