JP2001221969A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning optical device not having the position deviation of a scanning line formed on a photoreceptor drum by a laser beam passing an fθ lens before and after occurrence of the thermal expansion of the fθ lens suppressed from one side and made of plastics. SOLUTION: The scanning optical device 1 is equipped with a scanning optical system 100 which forms the scanning line on a photoreceptor drum 150 through an image-formation optical system 130 by performing the deflection scanning of the laser beam emitted from a light source part 110 by a polygon mirror 120. A third lens 133 to compose the fθ lens 130 is the plastic lens long- sized in the main scanning direction which has the power making the laser beam to converge in mainly the sub-scanning direction, and is fixed in a lens frame 20 by being pressed down by leaf springs 29 and 29 from one side of the sub-scanning direction to abutting surfaces 28 and 28 of the opposite side. Connecting members 31 and 32 connecting alternately the lens frame 20 and a casing 10 equipped with the scanning optical system 100 along the sub-scanning direction, depress the lens frame 20 by the amount of displacement of the optical of the third lens 133 by the thermal expansion, and compensates the deviation of the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a scanning optical device for scanning a spot light on a photosensitive drum surface by mechanically deflecting and scanning modulated light emitted from a laser with a rotary polygon mirror.

[0002]

2. Description of the Related Art Conventionally, an image forming device for writing provided in an image forming apparatus such as a copying machine, a printer, a facsimile printer or the like converts an electric signal of image information into modulated light using a laser or an LED element. By scanning the modulated light on a photoconductor using a scanning optical system, image information is recorded. Among these, as an imaging device using a semiconductor laser, an electrophotographic image forming apparatus including a scanning optical system including a semiconductor laser unit, a collimating lens, a cylindrical lens, a rotating polygon mirror, and an fθ lens, and a photosensitive drum is used. is there.

A scanning optical system using a semiconductor laser as a light source is used for a scanning optical device for monochrome printing, or a so-called tandem scanning optical system having a plurality of the above-described scanning optical systems and photosensitive drums for each color component. Used in optical devices. In a tandem scanning optical apparatus that performs color printing by forming a beam light on each photosensitive drum for each color component, the photosensitive drum for each color component overlaps each color on one scanning line on printing paper. By printing, a color image is formed. At this time, by making the positions of the scanning lines in the sub-scanning direction relatively constant with respect to the plurality of photosensitive drums, it is possible to obtain a printing result without color shift.

In such a scanning optical system, a divergent laser beam emitted by a semiconductor laser is converted into a parallel light beam by a collimator lens, and is once converged only in a sub-scanning direction near a reflecting surface of a polygon mirror by a cylindrical lens, and has a uniform angular velocity. Is mechanically deflected and scanned by a polygon mirror rotating at high speed. The laser light that has been deflected and scanned is converged in the main scanning direction and the sub-scanning direction by the fθ lens, and is imaged as a spot light on the photosensitive drum. On the surface of the photosensitive drum, a scanning line is formed by the locus of the spot light, and exposure according to image information is performed.

In the above-described scanning optical system, a part of the lens constituting the fθ lens may be formed as a plastic lens due to cost and workability. Conventionally, a configuration has been adopted in which the plastic lens constituting the fθ lens is fixed to the housing by pressing the plastic lens from one side in the sub-scanning direction onto a contact surface of the housing with a leaf spring or the like.

[0006]

However, if the lens having the power to converge the laser beam in the sub-scanning direction among the lenses constituting the fθ lens is made of plastic, it is built in an image forming apparatus such as a copying machine or a color printer. This plastic lens thermally expands because heat is radiated from a number of devices such as a fixing device to be used or a device such as a drive motor of a polygon mirror built in the scanning optical device. Then, the plastic lens expands from one side in the sub-scanning direction in a direction to push back the leaf spring or the like pressed, and the optical axis of the plastic lens shifts away from the contact surface. Therefore, the position of the scanning line formed on the photosensitive drum by the laser beam transmitted through the plastic lens is shifted in the sub-scanning direction. Further, when there are two or more lenses having power in the sub-scanning direction, aberration occurs due to optical axis shift between these lenses.

Further, in an image forming apparatus for color printing provided with a plurality of such scanning optical devices and corresponding to each of a plurality of photosensitive drums, the above-described shift occurs in a scanning line, so that a photosensitive drum for each color component is formed. However, the position of each scanning line in the sub-scanning direction cannot be made uniform, and there is a problem that a color shift exceeding an allowable range (several tens of μm) occurs in a printing result.

[0008] In order to prevent the above-described optical axis shift, at both ends of the plastic lens in the main scanning direction,
It is conceivable to keep the plastic lens neutral in the sub-scanning direction by clamping the plastic lens in the sub-scanning direction, but in this case, since the side surface of the plastic lens must be separated from the housing, the thermal expansion as described above occurs. Therefore, the entire plastic lens may be distorted. With such distortion, the scanning line formed on the photosensitive drum by the laser light transmitted through the plastic lens is curved (bowed) or distorted.

Accordingly, an object of the present invention is to solve the problem that a plastic lens having a power for converging laser light in the sub-scanning direction among the lenses constituting the fθ lens is opposed from one side in the sub-scanning direction by a leaf spring or the like. The scanning line formed on the photosensitive drum by the laser light is curved even if the laser light is transmitted through the thermally expanded plastic lens, even though the laser light is transmitted through the thermally expanded plastic lens. An object of the present invention is to provide a scanning optical device that does not move or shift its position.

[0010]

In order to achieve the above object, the present invention provides a method for converging a laser beam emitted from a light source and deflected and scanned by a deflector, wherein the scanning laser beam is deflected by the deflector. A scanning optical system including a plastic lens having a plane side surface substantially parallel to the scanning surface to be formed and having a power for converging laser light in at least a sub-scanning direction orthogonal to the scanning surface. In the scanning optical device, while holding a scanning optical system other than the plastic lens, a housing formed with an emission edge through which laser light emitted from the scanning optical system passes, and a scanning surface of the housing in the scanning surface A connecting member fixed to a portion located on one side and formed of a member having a higher expansion coefficient than the housing, and the housing in the connecting member; The scanning surface is fixed to a position offset from the fixing point with respect to the scanning surface, and the scanning member is disposed on the side opposite to the fixing point with the housing in the connecting member with the scanning surface interposed therebetween, on the emission side relative to the emission edge. A lens frame having a contact surface formed in parallel with the scanning surface for holding the plastic lens, and having spring means for pressing the plastic lens against the contact surface.

With this configuration, when the scanning optical device is heated, the plastic lens having power in the sub-scanning direction expands in a direction to push back the spring means, and the optical axis of the plastic lens is applied. Displaces away from the surface. On the other hand, the connecting member thermally expands in the direction opposite to the direction in which the optical axis of the plastic lens is displaced with respect to the contact surface.

Therefore, in the scanning optical device according to the present invention, even if the plastic lens expands due to heat and its optical axis is displaced to one side in the sub-scanning direction, the plastic lens is applied by the thermal expansion of the connecting member. The optical axis of the plastic lens is maintained at a fixed position by pulling the attached contact surface back to the other side in the sub-scanning direction. Therefore, even if the laser light is transmitted through the plastic lens, the scanning line formed on the photosensitive drum by the laser light does not curve or shift in position even if the plastic lens is thermally expanded.

Thus, for example, at least two scanning optical devices each having the above-described configuration are combined.
In the case where scanning lines of each color are printed on the same line of printing paper by the respective photosensitive drums corresponding to the color components of the color or more, the scanning optical device that forms each scanning line may be heated. However, since the optical axis of the plastic lens having the power to converge the laser beam in the sub-scanning direction does not shift in the sub-scanning direction, the scanning lines formed on all the photosensitive drums are at the same position on the printing paper. Are printed respectively.

Similarly, even when the scanning lines are formed side by side on the same photosensitive drum by a plurality of scanning optical devices having the above configuration, the positions of the scanning lines can be aligned.

In the scanning optical device according to the present invention, the fixing point of the connecting member to the housing and the fixing point to the lens frame are at different positions in the sub-scanning direction. The attachment surface can be displaced with respect to the housing.

In the scanning optical device according to the present invention, the housing and the connecting member may be in close contact with each other via a joining surface perpendicular to the scanning surface along the main scanning direction, or the expansion of the connecting member with respect to the housing may be performed. May be brought into close contact with each other via a parallel moving means for guiding the direction in the sub-scanning direction. As the parallel moving means, a groove and a rail along the sub-scanning direction are formed between each other, these grooves and the rail are fitted together, and when the connecting member thermally expands, the groove and the rail are along the sub-scanning direction. For example, a method of contacting them so that they can expand in parallel to each other is conceivable.

Further, in the scanning optical device according to the present invention, the housing and the connecting member, or the connecting member and the lens frame may be fixed by screwing, or may be fixed by an adhesive or the like. The spring means may be a leaf spring or a coil spring.

The scanning optical device according to the present invention may be provided for each photosensitive drum corresponding to four color components. In this case, the four color components may be used for color printing as black, cyan, magenta, and yellow. Alternatively, a scanning optical device may be provided for each photosensitive drum corresponding to three color components of cyan, magenta, and yellow.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a scanning optical device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a scanning optical device 1 according to an embodiment of the present invention. FIG. 2 is a side view of the scanning optical device 1 of the present embodiment, FIG. 3 is a front view of the scanning optical device 1, and FIG. 4 is a longitudinal section of the scanning optical device 1 taken along line AA shown in FIG. FIG.

As shown in FIG. 1, a scanning optical device 1 according to this embodiment includes a housing 10 and a connecting member 3 connected to the housing 10.
The scanning optical system 100 is assembled in a housing including the lens frame 20 held via the first and second lenses 32.

The scanning optical system 100 includes a light source unit 110 that emits a parallel laser beam, a polygon mirror 120 that is a deflector that deflects and scans the laser beam emitted by the light source unit 110 in the main scanning direction, and a polygon mirror 120. Fθ lens 130, which is an imaging optical system that forms a scanning line by forming an image on the photosensitive drum 150 with the laser beam deflected by the scanning.

The light source section 110 includes a semiconductor laser and a collimating lens for converting divergent light emitted from the semiconductor laser into parallel light. Light source unit 110 and polygon mirror 1
A cylindrical lens 115 having a power for converging the laser light only in the sub-scanning direction is provided between the cylindrical lens 115 and the lens 20.

The fθ lens 130 includes a first lens 131 and a second lens 132 fixed in the housing 10, and a third lens 133 fixed in the lens frame 20. The first lens 131 is a plastic lens that bears a function of correcting aberration (for example, curvature of field in the main scanning direction, fθ characteristic error, and the like), and the second lens 13
Reference numeral 2 denotes a glass lens having a power for converging laser light mainly in the main scanning direction, and a third lens 133 is an anamorphic plastic lens having a power for converging laser light mainly in the sub-scanning direction.

The laser light emitted from the light source section 110 as parallel light is reflected by the polygon mirror 120 as parallel light in the main scanning direction, and forms an image on the photosensitive drum 150 by the convergence power of the fθ lens 130. In the sub-scanning direction, the light is once converged by the cylindrical lens 115 in the vicinity of the polygon mirror 120, enters the fθ lens 130 as diffused light, and as shown in FIG. Image on top.

At this time, in the sub-scanning direction, due to the conjugate effect of the fθ lens 130, the deviation of the scanning position due to the inclination of the reflecting surface of the polygon mirror 120 (so-called “surface tilt”) is corrected, and the laser light is Regardless of the reflection surface of any one of the reflecting surfaces 120, the imaging point coincides.

The laser light that is deflected and scanned in accordance with the rotation of the polygon mirror 120 at a constant angular velocity is f
through the θ lens 130, the photosensitive drum 15
It is scanned at a constant speed on zero.

Between the second lens 132 and the third lens 133 of the fθ lens 130, a light beam outside the effective scanning range on the photosensitive drum 150 is used as monitor light as the light receiving sensor 14
A folding mirror 140 that folds back toward 2 is disposed, and the monitor light reflected by the folding mirror 140 is condensed on the light receiving sensor 142 via the condensing lens 141 for monitor light.

The condensing lens 141 for the monitor light has an f
In order to collect the monitor light separated without passing through the third lens 133 having the main converging power in the sub scanning direction in the θ lens 130 on the light receiving sensor 142, the θ lens 130 is configured as a cylindrical lens having the converging power in the sub scanning direction. Have been.

From the light receiving sensor 142, the light source 11
Every time the reflection surface of the polygon mirror 120 on which the laser light from 0 enters is switched, a synchronization signal that determines the timing of the writing start position in the main scanning direction is output.

Next, the housing 10 by the connecting members 31 and 32
The connection structure between the lens frame 20 and the lens frame 20 and the holding structure of the third lens 133 of the fθ lens 130 by the lens frame 20 will be described.

FIG. 5 is a perspective view of the upper surfaces of the housing 10, the connecting members 31, 32 and the lens frame 20 as viewed obliquely from the front. FIG. 6 is a perspective view of the lower surfaces of the connection members 31 and 32 and the lens frame 20 as viewed obliquely from the front, and FIG. 7 is an enlarged side view of the connection member 32 and the lens frame 20.

In the scanning optical device 1, the third lens 133 of the fθ lens 130 in the above-described scanning optical system 100
Only the scanning optical system 100 is fixed to the housing 10 while only the lens frame 20 is fixed. The housing 10 and the lens frame 20 are formed of the same material such as a BMC resin bulk molding compound or aluminum, and the housing 10 and the lens frame 20 are made of a material having a higher coefficient of thermal expansion (for example, Polymethyl methacrylate (PMMA), polycarbonate (P
C) and the like.

The housing 10 is formed in a thin, generally box-like shape by having side walls surrounding four sides on the upper surface of a flat bottom plate 15. However, in this case 10, one of the side walls surrounding the four sides is cut off along the up-down direction, and the end surface thereof has a U-shape (in fact, it seems that the “U” is rotated by 90 degrees. , Concave shape), and only the bottom plate 15 is extended on this concave end surface while leaving the vicinity of both side ends (hereinafter, referred to as “joining surfaces 11a, 12a”, respectively). It is formed in a protruding shape. Hereinafter, a direction perpendicular to the up-down direction within this end face is referred to as a “left-right direction”, a direction perpendicular to the end face is referred to as an “optical axis direction”, and a direction facing the end face is referred to as a “rear”.

In the case 10, the left and right side walls on the upper surface of the bottom plate 15 are the side walls 11 and 12, respectively. As shown in FIG. 5, the rear end portions of the side walls 11 and 12 are bent in a direction away from each other to form a flat surface perpendicular to the front-rear direction. And a part of the joint surfaces 11a and 12a described above.

In the vicinity of the center of the front side wall on the upper surface of the bottom plate 15 of the housing 10, the polygon mirror 120 of the above-described scanning optical system 100 is disposed with its rotation axis directed perpendicular to the bottom plate 15. I have. Then, the light source unit 110
When the polygon mirror 120 deflects and scans the laser light supplied from the polygon mirror 120, the scanning surface crossed by the reflected laser light is substantially parallel to the bottom plate 15. Hereinafter, the bottom plate 15
A plane parallel to is referred to as a “horizontal plane”.

On the upper surface of the bottom plate 15 of the housing 10, the polygon mirror 120 is located closer to the polygon mirror 120 between the plane including the joint surfaces 11 a and 12 a (ie, the above-described concave end surface) and the polygon mirror 120. , Fθ lens 130 and a second lens 132.

The first and second lenses 131 and 132
Is arranged so as to coincide with the optical path of the light beam passing through the center in the effective scanning range when the polygon mirror 120 deflects and scans the parallel laser light, and the two joint surfaces 1
It is arranged in a direction orthogonal to a plane including 1a and 12a. Therefore, the horizontal direction in the housing 10 corresponds to the main scanning direction in laser scanning, and the vertical direction generally corresponds to the sub-scanning direction.

The left and right joining surfaces 11a, 12 of the casing 10
In the vicinity of the upper end of a, screw holes 11b, 1 parallel to the optical axis direction are provided.
2b are respectively formed. These two screw holes 11b,
12b is formed at the same height in the vertical direction, and connecting members 31 and 32 for connecting the housing 10 and the lens frame 20 are connected to the respective connecting surfaces 11a and 12a.

The connecting members 31 and 32 are formed in a substantially rectangular parallelepiped shape having the same height as the vertical height of both joint surfaces 11a and 12a of the housing 10. Those connecting members 31 and 3
2 has the same size as the projecting amount of the portion of the bottom plate 15 of the housing 10 projecting rearward from the left and right joint surfaces 11a, 12a, and the connecting members 31, 3
2 has the same size as the length from the left and right side edges of the protruding portion to the left and right ends of the joint surfaces 11a and 12a. Hereinafter, these connecting members 31, 3
2 are referred to as first joint surfaces 31a, 32a and second joint surfaces 31b, 32b.

Further, the connecting members 31 and 32 are not complete rectangular parallelepipeds, and the same rectangular parallelepiped projections 31c and 32c are provided at the lower ends of the second bonding surfaces 31b and 32b, respectively. , 32b. The width in the up-down direction of these protrusions 31c, 32c is formed smaller than the thickness of the bottom plate 15 of the housing 10.

Further, each of these second bonding surfaces 31b, 32
b, immediately above the centers of the protrusions 31c and 32c (second
In the vicinity of the upper ends of the joint surfaces 31b and 32b), through holes 31d and 32d parallel to the optical axis direction are formed at the same height in the vertical direction.

The through holes 31d and 32d are formed when the first joint surfaces 31a and 32a of the connecting members 31 and 32 and the joint surfaces 11a and 12a of the casing 10 are brought into close contact with the upper and lower ends and the right and left ends thereof. They are formed at positions coaxial with the screw holes 11b and 12b formed in the surfaces 11a and 12a, respectively.

Each of the connecting members 31 and 32 is
1 and 52 are inserted into the through holes 31d and 32d, respectively, and screwed into the screw holes 11b and 12b, whereby the housing 10
On the joint surfaces 11a and 12a.

When the connecting members 31 and 32 are fixed to the housing 10, respectively, the rear end surface of the portion of the bottom plate 15 of the housing 10 protruding rearward from the bonding surfaces 11a and 12a and the second bonding surface. 31b and 32b are arranged so as to be included in the same plane perpendicular to the optical axis direction. At this time, that is, when the connecting members 31 and 32 are fixed to the housing 10, the entire rear ends of the connecting members 31 and 32
Assuming that c and 32c are not formed, they are formed on a concave flat surface.

The connecting members 31 and 32 fixed to the housing 10 in this manner further have screw holes 3 parallel to the optical axis direction.
1e and 32e are formed inward from the second joint surfaces 31b and 32b.

Each of these screw holes 31e and 32e is
At the joining surfaces 31b, 32b, the protrusions 31c, 32c
Are located at the same height between the through holes 31d, 32d formed near the upper ends of the second joint surfaces 31b, 32b and the protruding portions 31c, 32c, respectively. I have. And these screw holes 31
The lens frame 20 is joined to the second joining surfaces 31b and 32b where the e and 32e are formed.

FIG. 8 is a cross-sectional perspective view of the rear surfaces of the casing 10 and the lens frame 20 viewed from obliquely above along the line AA shown in FIG. FIG. 9 is an enlarged vertical sectional view of the housing 10 and the lens frame 20 along the line AA. FIG.
FIG. 11 is a partially enlarged rear view of the lens frame 20. FIG.

As shown in FIGS. 8 and 9, the above-described lens frame 20 is a housing that is formed in a substantially box shape that is long in the left-right direction (main scanning direction), and the inside thereof is f.
The lens storage section 25 stores the third lens 133 of the θ lens 130. Therefore, the lens housing 25 has a width slightly larger than the width of the third lens 133 of the fθ lens 130 in the left-right direction and the up-down direction.
Is formed.

The opening end of the lens housing portion 25 is formed on the front surface (the surface on the side of each of the connecting members 31 and 32) 20a of the lens frame 20, and has a rectangular flat flat surface.
5 is formed in a shape provided with a rectangular opening.

The opening end of the lens housing portion 25 on the front surface 20a of the lens frame 20 is formed in a stepped shape with its outer peripheral edge cut slightly along the optical axis direction. Hereinafter, the vicinity of the left and right ends of the front surface 20a of the lens frame 20 will be referred to as joint surfaces 21b and 22b, and these joint surfaces 21b and 22b
A surface facing forward at the outer peripheral edge of the opening end of the lens housing portion 25 is defined as a leaf spring mounting surface 25a.

Then, by bringing the second joint surfaces 31b, 32b of the connecting members 31, 32 into close contact with these joint surfaces 21b, 22b, the lens frame 20 is connected to the connecting members 31, 32.
To the housing 10 via the

The length of the lens frame 20 in the up-down direction is slightly shorter than the length in the up-down direction of the joining surfaces 11a and 12a of the housing 10, and the length in the left-right direction of the housing 10 is It is formed to have the same length as the interval between the left end of the joining surface 11a and the right end of the joining surface 12a.

The lens frame 20 thus formed in a substantially box shape has through holes 21d, 2d parallel to the optical axis direction.
2d are formed. These through holes 21d, 22d
Are arranged near the left and right ends and near the lower end of the lens frame 20, respectively.
b, 22b.

The two through-holes 21d and 22d are provided with a counterbore (having the same central axis as the through-holes 21d and 22d and having an inner diameter larger than the inner diameter thereof).
Counterbore formed stepwise with respect to 22d) 21a,
22a is formed from the rear. However, as shown in FIGS. 6 and 7, since the inner diameters of the counterbore 21 a and 22 a are formed to be large, the left and right sides of the lower end face of the lens frame 20 and the lower sides of the left and right end faces are respectively formed. Some have been cut out.

The through holes 21d and 22d are formed rearward from the joint surfaces 21b and 22b so as to have the same length as the projecting portions 31c and 32c of the connecting members 31 and 32. As shown in the figure, portions behind the rear ends of both through holes 21d and 22d are cut off by deep spot facings 21a and 22a. In the following, for the sake of explanation, this counterbore 21
a, 22a is not formed, and the part protruding downward is
As shown in FIGS. 5 to 7, the projections 21c and 22c are used.

Further, each of the projections 21c, 22c is
The protruding portions 31c and 32c of the connecting members 31 and 32 are cut into lower portions by the length in the vertical direction,
Is formed.

Therefore, the left and right side surfaces of the lens frame 20 and the connecting members 31 and 32 fixed to the housing 10 are flush with each other, and the second joint surfaces 31b and 32b and the joint surfaces 21b and 22b are Are joined to each other,
The connecting members 31 and 32 fixed to the
Can be joined.

At this time, the convex portions 21c, 2 of the lens frame 20
Projecting portions 31c, 3 of connecting members 31, 32 are provided on the lower end surface of 2c.
2c so that the upper end surfaces thereof are almost in contact with each other.
By sandwiching the portion of the lens frame 20 from which the bottom plate 15 protrudes between the lenses 32c, the lens frame 20 can be easily positioned with respect to the housing 10 without significantly shifting left, right, up, or down.

When the lens frame 20 is fitted between the two connecting members 31 and 32 fixed to the housing 10, the screw holes 31e and 32e of the connecting members 31 and 32 and the through holes of the lens frame 20 are inserted. Since the lens frames 21d and 22d are formed at coaxial positions, the lens frame 20 is
2 is inserted into these through holes 21d and 22d, respectively, and screwed into the screw holes 31e and 32e, thereby being fixed to the housing 10 via the connecting members 31 and 32 without causing displacement.

As described above, since the counterbore 21a and 22a are formed in the lens frame 20, the operator can
By guiding the tip of a driver or the like along the space formed by these deep spot facings 21a and 22a, the vicinity of the tip does not interfere with any of the lens frames 20.
Through-holes 21d, 2 formed in projections 21c, 22c
The screws 61 and 62 inserted into 2d can be turned. By removing the screws 61 and 62, the lens frame 20 can be easily removed from the housing 10.

As described above, the lens frame 20 that can be attached to and detached from the housing 10 has a holding mechanism for holding the third lens 133 of the fθ lens 130 in the lens storage section 25.

Third lens 1 fixed in lens frame 20
Reference numeral 33 has a substantially rectangular parallelepiped shape that is long in the left-right direction (main scanning direction) as shown in a two-dot chain line in FIG. 1 and a cross-sectional shape in FIG. The rear surface is depressed into the shape of the lens surface, whereby the inside is formed as a toric lens surface 133a.

A slit 80 penetrating along the optical axis direction to the back of the lens frame 20 is formed in the lens housing 25 for housing the third lens 133. As shown in FIG. 8, the slit 80 is formed to be long in the left-right direction (main scanning direction), and passes the laser light deflected and scanned in the left-right direction by the polygon mirror 120.

Behind the slit 80, a window 90 made of a sheet glass elongated in the left-right direction is fixed to the lens frame 20 by a leaf spring, and the laser beam passing through the slit 80 passes through the window 90. I do. The window 90 is arranged slightly inclined from a position perpendicular to the optical axis direction.

The slit 8 in the lens housing 25
As shown in FIG. 8 and FIG. 9, the lens seat 2 formed in a flat plate shape is provided at the four corners of the inner surface where 0 is formed.
6 are provided respectively. Lens seats 26 at these four corners
Are arranged such that their front surfaces (hereinafter, the respective front surfaces of the lens seats 26 are referred to as “applying surfaces 26a”) are included in the same plane parallel to the horizontal plane. Four corners on the back surface of the third lens 133 are respectively applied.

As shown in FIG. 10, the third lens 133 is located near the left and right ends of the upper and lower sides of the leaf spring mounting surface 25a formed on the outer peripheral edge of the opening end of the lens housing portion 25.
Four leaf springs 27 for pressing the four corners on the front of
Each is attached.

Each of the four leaf springs 27 has an overall shape formed into a substantially L-shaped flat plate by joining one side of a rectangular flat plate to the longer side of a rectangular flat plate having a longer side than the one side. ,
A through-hole is formed at the center of the rectangular flat plate, and a pad for preventing the third lens 133 from being damaged is provided on a surface of the rectangular flat plate that contacts the third lens 133.

Since these four leaf springs 27 are fixed on the leaf spring mounting surface 25a by set screws, the amount of step between the joint surfaces 21b and 22b and the leaf spring mounting surface 25a is reduced by the amount of the four steps. When the two leaf springs 27 are screwed to the leaf spring mounting surface 25a with set screws, the leaf springs 27 and the set screws are secured so as not to protrude forward from the joint surfaces 21b and 22b.

Further, these four leaf springs 27 are formed so as to have a symmetrical shape on the left and right sides with respect to a plane that bisects the lens housing section 25 in the left-right direction. Thus, the left and right ends of the third lens 133 are attached to the contact surfaces 26 of the lens seats 26 at the four corners from the front surface.
a toward the third lens 133.
Is fixed in the optical axis direction in the lens housing portion 25 of the lens frame 20.

At the left and right ends of the inner surface (hereinafter referred to as the floor surface) of the inner surface of the lens housing portion 25 which faces upward, lens receiving seats 28, 28 formed in a rectangular plate shape are provided. I have. These lens seats 28, 28 are arranged such that their upper surfaces are included in the same plane parallel to the horizontal plane, and the upper surfaces thereof (hereinafter, the upper surfaces of the lens seats 28, 28 are referred to as contact surfaces 28a, 28a). ) Includes the third lens 1
The right and left ends of the lower surface of 33 are respectively applied.

A through hole 23 is formed in the center of the floor surface of the lens housing 25 in the left-right direction to penetrate to the lower surface of the lens frame 20, and the cross-sectional shape thereof is shown in FIGS. Thus, it is formed in a rectangular shape. The through-hole 23 has a third lens 133 to be described later.
The positioning boss 133b is inserted.

Further, near the left and right ends above the leaf spring mounting surface 25a formed on the outer peripheral edge of the opening end of the lens housing portion 25, the upper surface of the third lens 133 is placed on the left and right lens seats 28, 28. Leaf spring 29 for pressing against
29 are attached.

The two leaf springs 29, 29 are formed by bending a strip-shaped flat plate at substantially right angles along the short side direction, and form one of two end pieces at substantially right angles to each other. The length from the fold line to the tip is formed longer than that of the other end piece. A through hole for inserting a set screw is formed in the end piece having a shorter length from the fold line to the tip. Hereinafter, the end piece whose length from the fold line to the tip is long is referred to as a pressing side piece.

As shown in FIGS. 9 and 10, these leaf springs 29, 29 are fixed on the leaf spring mounting surface 25a by set screws, and their pressing side pieces are Upper surface (the inner surface facing downward from the inner surface)
Substantially along the rear side in the optical axis direction.
The respective leaf springs 29, 29 are connected to the third lens 13
By pressing the left and right ends of the upper surface of 3 toward the contact surfaces 28, 28 from above, respectively, the third lens 133
The lens frame 20 is fixed in the vertical direction (sub-scanning direction) in the lens storage section 25.

Incidentally, reference numeral 133c in FIG. 9 denotes fθ
This shows so-called burrs that are solidified at an injection port (lens gate) when a plastic material is injected into a mold for manufacturing the third lens 133 of the lens 130 and solidified.

Reference numeral 133b denotes a third lens 133.
The positioning boss 133b protrudes downward from the center in the left-right direction of the lower surface of the positioning boss 133b.
Are integrally formed with the third lens 133. The positioning boss 133b is formed in a rectangular parallelepiped shape, and is inserted into a through hole 23 penetrating through the floor surface of the lens housing portion 25 of the lens frame 20. At this time, the third lens 133
Are fixed in the left-right direction (main scanning direction).

The third lens 1 inserted into the through hole 23
The width of the positioning boss 133b in the left-right direction is equal to the width of the through hole 25 in the left-right direction, so that the center of the third lens 133 in the left-right direction is the center of the lens frame 20 in the left-right direction. Can be easily adapted to

When the third lens 133 is placed on the contact surfaces 28a of the lens seats 28, 28,
A minus screwdriver or the like is inserted into the through hole 23 from the lower surface of the lens frame 20, and the positioning boss 13 of the third lens 133 is inserted.
By pushing back 3b, the four corners on the back surface of the third lens 133 can be applied to the contact surfaces 26a of the four lens seats 26.

Further, since the upper and lower surfaces of the third lens 133 are formed with drafts for removing the third lens 133 from the mold, the upper and lower surfaces are parallel to the optical axis direction. It is not formed to be flat. Therefore, the left and right ends of the lower surface of the third lens 133 are arranged as shown in FIG.
As shown in FIG. 11 to FIG. 11, when the lower surface of the third lens 133 is applied to the contact surfaces 28a of the upper surfaces of the lens seats 28, 28, the optical axis of the third lens 133 is parallel to the optical axis direction. So that the wedge-shaped abutment seats 133d, 133d
Are formed respectively. This abutment seat 133d, 133
d is provided only on the left and right ends of the lower surface of the third lens 133,
The left and right widths are substantially the same as the contact surfaces 28a, 28a, respectively, and are integrally formed with the third lens 133.

As described above, the optical axis of the third lens 133 of the fθ lens 130 fixed in the lens frame 20 is adjusted when the lens frame 20 is fixed to the housing 10.
The first and second lenses 131 and 132 of the fθ lens 130 fixed to the upper surface of the bottom plate 15 are disposed coaxially with the optical axes.

The laser light deflected in the left-right direction by the rotation of the polygon mirror 120 provided in the housing 10 is transmitted to the first to third lenses 1 of the fθ lens 130.
After sequentially transmitting the light beams 31 to 133, scanning lines are formed on the surface of the photosensitive drum 150.

As described above, in the scanning optical device 1,
The lens frame 20 that fixes the third lens 133 of the fθ lens 130 inside is fixed to the housing 10 that holds another configuration of the scanning optical system 100 via the connecting members 31 and 32. .

However, when heat is applied to such a scanning optical device 1, the third lens 133 of the fθ lens 130 is made of plastic having a larger coefficient of thermal expansion than that of the glass lens, so that the third optical lens 133 has its own optical axis. Causes thermal expansion so as to shift. At this time, the third lens 133 thermally expands only upward (one side in the sub-scanning direction) while pushing back the leaf springs 29, 29 pressing against the contact surfaces 28a, 28a from the upper surface of the third lens 133. The optical axis of the third lens 133 is displaced upward.

On the other hand, since the connecting members 31 and 32 have a higher coefficient of thermal expansion than the housing 10 and the lens frame 20,
When heat is applied to the entire scanning optical device 1, the screws 41, 4
2, connecting members 31, 3 fixed to the housing 10
With the vicinity of the upper end of the base 2 as a base point, the connecting members 31 and 32 thermally expand relatively downward. At this time, the connecting members 31, 32
First joint surfaces 31a, 32a and second joint surfaces 31b, 32
b are arranged so as to be perpendicular to the optical axis direction, so that the lens frame 20 moves downward in the vertical direction (sub-scanning direction) with respect to the housing 10 while moving substantially in parallel. Will be reduced.

However, these connecting members 31 and 32 are provided at the centers of the screws 51 and 52 for fixing the connecting members 31 and 32 to the housing 10 when the scanning optical device 1 is heated from a cold state to a certain temperature. Screw 6 for fixing the wire and lens frame 20
The third lens 133 is formed of a material having a coefficient of thermal expansion such that the amount of increase in the distance between the center lines of the lenses 1 and 62 and the amount of displacement of the optical axis of the third lens 133 with respect to the contact surfaces 28a and 28a become equal. ing.

Therefore, when the scanning optical device 1 is heated or cooled, the width of the optical axis of the third lens 133 with respect to the contact surfaces 28 a of the lens frame 20 is fixed to the housing 10. Abutment surface 2 of lens frame 20 with respect to the optical axes of first and second lenses 131 and 132 of fθ lens 130
The third lens 133 and the connecting members 31 and 32 expand at a constant rate such that the width of the upper and lower portions 8a and 28a is always equal.

Therefore, the first and second lenses 131 and 13
The optical axes of the second lens 133 and the third lens 133 are kept coaxial without deviation due to heating or cooling of the scanning optical device 1.

As a result, even if heat is applied to the scanning optical device 1, the optical axis of the third lens 133 does not deviate from the optical axis of the scanning optical system 100. The scanning line formed on the photosensitive drum 150 by passing through the fθ lens 130 is formed at a fixed position on the photosensitive drum 150 without shifting in the sub-scanning direction.

Also, since the optical axis of the third lens 133 does not deviate from the optical axis of the scanning optical system 100, aberration occurs due to the deviation of the optical axis from another lens having power in the sub-scanning direction. Nothing to do.

The scanning optical apparatus 1 of the present embodiment described above is used by being incorporated in an image forming apparatus for monochrome printing, or as a single optical unit provided with a set of scanning optical systems 100 as a copying machine. And a plurality of image forming apparatuses such as color printers and the like. Hereinafter, an example of an image forming apparatus including the scanning optical device of the present example on each of a plurality of photosensitive drums will be described.

FIG. 12 is a schematic configuration diagram of an image forming apparatus 200 incorporating the scanning optical devices 1a to 1d according to the embodiment of the present invention. The image forming apparatus 200 shown in FIG.
Each of the photosensitive drums 150a to 150d independent of each color component of black, cyan, magenta, and yellow is provided with a scanning optical device 1a to 1d, and forms a color image by multiplex printing on one print sheet 300. .

Each of the scanning optical devices 1a to 1d has the same configuration as the scanning optical device 1 shown in FIG. 1, and includes a scanning optical system including a light source unit, a polygon mirror, and an fθ lens each including a housing and a lens frame. Provided in the housing. Laser light corresponding to the color components of the photosensitive drums 150a to 150d is emitted from the light source units provided in these scanning optical devices 1a to 1d, and each laser light is deflected by each polygon mirror, and An image is formed by a lens.

The method of providing a plurality of combinations of the scanning optical system and the photosensitive drums 150a to 150d for each color component as in this example is called a tandem system, and the scanning optical system for each color component is independently provided. A scanning line of each color component is formed on each of the photosensitive drums 150a to 150d by deflecting and scanning the laser beam.

The scanning optical devices 1a to 1d of the present embodiment are similar to those shown in FIG.
As shown in the figure, four of the four are arranged in parallel inside the image forming apparatus 200. The laser light emitted from each of the scanning optical devices 1a to 1d to the right side in FIG. 12 is reflected by the folding mirrors 160a to 160d so that the photosensitive drums 15 of the respective color components arranged in parallel in the sheet supply / discharge direction.
0a to 150d, respectively. Thus, a scanning line is formed on each of the photosensitive drums 150a to 150d by each laser beam, and image information for each color component is exposed.

The printing paper 300 conveyed by the paper feed roller 180 is sequentially transferred to each of the photosensitive drums 150a to 150a.
0d pass through each lower end. Each photosensitive drum 150a-
The toner of each color adhered (developed) in accordance with the pixel information (electrostatic latent image) on the surface of the photosensitive drum 150d
Transfer charger 170 arranged opposite to the lower surface of 150d
The charge wires 175a to 175d of a to 170d are successively transferred and superimposed on the printing paper 300 by corona discharge.

The printing paper 3 on which the toner of each color is transferred
00 is sent to the fixing device 190. The fixing device 190 fixes the unfixed toner of each color to the printing paper 300 by heating and pressing the printing paper 300 by the heat roller 191 having the halogen lamp 192 and the press roller 193. At the same time, the printing paper 300 on which the toners of the respective colors have been fixed is applied to the rollers 191 and 19 of the fixing device 190.
The paper is discharged out of the image forming apparatus 200 by the rotation of the third rotation.

At this time, since the scanning lines of each color component to be multiplexed on one scanning line on the printing paper 300 are drawn at the adjusted positions on the respective photosensitive drums 150a to 150d, each scanning line is drawn. The lines are printed on the same scanning line of the printing paper 300 without any color shift. Around these photosensitive drums 150a to 150d, in addition to an exposure process unit by the scanning optical devices 1a to 1d, a main charger, a developing unit, a cleaning unit, and a main unit for executing respective processes of charging, developing, cleaning, and discharging. Although device units such as a static eliminator are arranged, they are not shown here.

In a typical image forming apparatus, since a large amount of heat is generated from various devices such as the fixing device 190, the amount of heat received by each of the scanning optical devices 1a to 1d depends on the positional relationship with respect to the device serving as a heat source. Each will be mixed. Then, fθ built in each scanning optical device
Since the influence of heat on the third lens 133 of the lens 130 also differs for each device, the amount of displacement when the optical axis shifts due to thermal expansion of the third lens 133 also varies.

For this reason, if the scanning lines of the respective color components to be multiplexed on one scanning line are slightly misaligned and are printed in a non-uniform manner, the image formed on the printing paper will have uneven color. As a result, it is not possible to obtain a regular color image.

However, even if each scanning optical device 1
Even if the amounts of thermal expansion of the third lenses 133 a to 1 d are different, the connecting members 31 and 32 expand by a considerable amount, so that the position of each scanning line with respect to the plurality of photosensitive drums 150 a to 150 d is determined. Can be aligned relatively constant,
A printing result without color shift can be obtained.

[0102]

As described above, according to the scanning optical apparatus of the present invention, the plastic lens having the power to converge the laser beam in the sub-scanning direction among the lenses constituting the fθ lens is used in the sub-scanning direction. Even when the lens is fixed to the lens frame by being applied from one side to an abutting surface by a leaf spring or the like, since the optical axis position does not shift, the laser light transmits through the thermally expanded plastic lens. However, the scanning line formed on the photosensitive drum by the laser light does not curve or shift in the sub-scanning direction.

[Brief description of the drawings]

FIG. 1 is a plan view of a scanning optical device according to an embodiment of the present invention.

FIG. 2 is a side view of the scanning optical device according to the embodiment of the present invention.

FIG. 3 is a front view of the scanning optical device according to the embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of the scanning optical device taken along line AA shown in FIG. 1;

FIG. 5 is a perspective view of the upper surface of the housing, the connecting member, and the lens frame of the present example as viewed obliquely from the front.

FIG. 6 is a perspective view of the lower surface of the connecting member and the lens frame of the present example viewed obliquely from the front.

FIG. 7 is an enlarged side view of the connecting member and the lens frame of the present example.

FIG. 8 is a cross-sectional perspective view of the rear surface of the housing and the lens frame seen from obliquely above along the line AA shown in FIG. 1;

FIG. 9 is an enlarged vertical sectional view of the housing and the lens frame along the line AA shown in FIG. 1;

FIG. 10 is a rear sectional view of the lens frame of the present example.

FIG. 11 is a partially enlarged view of a rear cross section of the lens frame of the present example.

FIG. 12 is a schematic configuration diagram of an image forming apparatus incorporating a scanning optical device according to an embodiment of the present invention.

[Explanation of symbols]

 1 to 1d Scanning optical device 10 Housing 11, 12 Side wall 11a, 12a Joint surface 20 Lens frame 21b, 22b Joint surface 25 Lens storage section 26, 28 Lens seat 26a, 28a Abutment surface 27, 29 Leaf spring 31, 32 Connecting member 31a, 32a First joint surface 31b, 32b Second joint surface 51, 52 Screw 61, 62 Screw 100 Scanning optical system 110 Light source unit 120 Polygon mirror 130 fθ lens 131 First lens 132 Second lens 133 Third lens 140 Folding mirror 150-150d Photosensitive drum

Claims (7)

[Claims] A deflector for converging a laser beam emitted from a light source and deflected and scanned by a deflector, having a flat side surface substantially parallel to a scanning surface on which the scanning laser beam is deflected by the deflector; And a scanning optical device including a scanning optical system including a plastic lens having a power to converge laser light in at least a sub-scanning direction orthogonal to the scanning surface, wherein the scanning optical system other than the plastic lens is held. A housing formed with an emission edge through which laser light emitted from the scanning optical system passes; and a portion fixed to one side of the scanning surface in the housing, and A connecting member formed of a member having a high coefficient of expansion, and a position of the connecting member offset to the scanning plane side from a fixing point of the connecting member to the housing. Affixed and formed on the opposite side of the connecting member to the case with the housing with the scanning surface interposed therebetween, and formed in parallel with the scanning surface to hold the plastic lens on the emission side from the emission edge. A lens frame having a contact surface and a spring means for pressing the plastic lens against the contact surface. 2. The connecting member is provided on both sides in the main scanning direction orthogonal to the optical axis of the plastic lens and the sub-scanning direction, in a symmetrical shape with respect to the optical axis of the plastic lens. The scanning optical device according to claim 1, wherein: 3. The scanning optical apparatus according to claim 2, wherein the connecting members are provided near both ends of the emission edge. 4. The housing and the connecting members are in close contact with each other via a joining surface orthogonal to the scanning surface along the main scanning direction, and the connecting members are attached to the housing. 4. The scanning optical device according to claim 2, wherein the scanning optical device is fixed by an axis parallel to an optical axis of the plastic lens. 5. The connecting member and the lens frame are in close contact with each other via a joining surface orthogonal to the scanning surface along the main scanning direction, and the lens frame is attached to each of the connecting members. 5. The scanning optical device according to claim 2, wherein the scanning optical device is fixed by an axis parallel to an optical axis of the plastic lens. 6. The housing according to claim 1, wherein said connecting member is provided between said contact surface of said lens frame and an optical axis of said plastic lens in a sub-scanning direction due to a thermal expansion of said plastic lens. The scanning optics according to claim 1, wherein the scanning optics expands so that an amount of displacement in a sub-scanning direction between a fixing point of the connection member and the contact surface of the lens frame becomes equal. apparatus. 7. The scanning optical device according to claim 1, wherein said spring means is a leaf spring.