JPH0743465B2 - Laser printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Industrial field of application” The present invention corresponds to the above recorded information by scanning a laser beam modulated based on the recorded information onto a photosensitive drum at a constant speed through a deflector. The present invention relates to a laser printer for forming an electrostatic image on a photosensitive drum, and in particular, a plurality of reflecting mirrors are arranged on the exit side of an imaging lens system having an fθ characteristic, and the optical path of the laser beam is deflected to save space. The present invention relates to improvements in laser printers.

“Prior Art” Conventionally, a laser beam modulated according to input information is made incident on a rotary polygon mirror as parallel linear focused light through a collimating lens and a cylindrical lens, and the rotary polygon mirror rotates at a predetermined angle. Fθ while deflecting and reflecting
After being incident on an image forming lens system having characteristics and converted into a uniform bundle motion, an optical dot pattern corresponding to input information is image-formed on the photosensitive drum, and thereafter, the photosensitive drum is rotated in the sub-scanning direction. However, a laser printer that repeats this process to form a predetermined electrostatic latent image is already known.

In this type of device, since the scanning beam that has passed through the fθ lens needs to be imaged on the generatrix of the photoconductor drum, the optical path length from the imaging lens to the photoconductor drum corresponds to the focal length of the lens. Therefore, there is a problem in that the distance between the rotary polygon mirror and the photosensitive drum is inevitably increased, and the device is unnecessarily increased in size.

In order to prevent such a defect, as shown in FIG.
A plurality of reflecting mirrors 2 and 3 are arranged on the exit side of the θ lens system 1 so that the scanning beam 10 swept in the main scanning direction X by the rotary polygon mirror 4 is deflected and is incident on the photosensitive drum 5. By doing so, a technique is disclosed in which the apparent optical path length of the scanning beam 10 is shortened and the apparatus is downsized. (JP-A-57-104915) In the figure, 7 is a semiconductor laser, and 8 is a frame body that integrally incorporates these various members and constitutes an optical scanning unit.

“Problems to be Solved by the Invention” However, according to such a conventional technique, the fθ lens 1
The first reflection mirror 2 on which the scanning beam 10 from
Since the optical scanning unit is arranged at a position which extends in the horizontal direction beyond the vertical tangent line HL on the downstream side of the photoconductor drum 5, the optical scanning unit is provided over almost the entire area above the photoconductor drum 5 on the upper surface side of the apparatus. Therefore, the arrangement position of the developing unit (not shown) and other peripheral devices arranged around the photosensitive drum 5 is restricted by that much, which makes the design and assembly troublesome.

Particularly, the developing unit is arranged adjacent to the downstream side of the scanning position of the laser beam, and in the printer, it is necessary to take a large toner storage volume in order to consume a large amount of toner. In such a configuration, since the optical scanning unit is occupied up to the position beyond the vertical tangent line HL on the downstream side of the photoconductor drum 5, the toner accommodating volume of the developing unit must be made small by that much, and it is frequent. The maintenance of complicated toner will be complicated.

Further, even if the toner inlet of the developing unit is provided on the upper surface side of the apparatus, it must be provided at a position away from the peripheral surface of the photosensitive drum 5, and the dead space in the apparatus increases accordingly, resulting in a large apparatus. Lead to

In view of the above-mentioned drawbacks of the prior art, the present invention achieves space saving without restricting the arrangement position of the developing unit and other peripheral devices, enables downsizing of the device, and particularly reduces the toner volume of the developing unit. Can be increased,
It is an object to provide a laser printer.

"Means for Solving Problems" The present invention is directed to fθ as shown in FIGS. 1A and 1B, for example.
Scanning beam 10 that passes through lens 1 and other imaging lens systems
In a laser printer that deflects the light by a plurality of reflection mirrors 12a, 13a or 12b, 13b and makes it incident on the photosensitive drum 5, a second reflection mirror 13a, which is located on the most downstream side of the optical path of the scanning beam 10. The beam entering / exiting positions of the first reflecting mirrors 12a, 12b are located in the region between the pair of tangents L1, L2 of the photoconductor drum 5 in parallel with the outgoing light from 13b. According to the above, the technical problems described above are achieved.

In this case, the first reflecting mirrors 12a and 12b may be arranged either upstream or downstream of the optical path of the laser beam incident on the bus line of the photoconductor drum 5 from the second reflecting mirrors 13a and 13b.

Further, it is better to arrange the reflection mirrors 12a, 13a or 12b, 13b between a pair of tangent lines of the photosensitive drum 5 extending vertically upward, from the viewpoint of assembly or the reflection mirrors 12a, 13a, or
It is also advantageous when forming an extra space for mounting the developing unit 11 on the side of 12b, 13b.

The number of the reflection mirrors 12a, 13a or 12b, 13b is not limited to two, and three or four or more reflection mirrors can be arranged within the technical range.

[Operation] According to the technical means, for example, when the optical scanning unit is arranged above the photoconductor drum 5, all the reflection is within the area sandwiched between the pair of vertical tangents L1 and L2 of the photoconductor drum 5. Since the beam entrance / exit positions of the mirrors 12a, 13a or 12b, 13b exist, as a result, the apparent optical path length between the fθ lens 1 and the photoconductor drum 5 can be shortened, and the developing unit 11 can be moved to the photoconductor drum 5. It is possible to form a space in the apparatus adjacent to the peripheral surface, and it is possible to reduce the size of the apparatus while increasing the toner storage capacity.

Further, according to the preferred embodiment of the present invention, as shown in FIG. 1B, the scanning beam 10 deflected by the plurality of reflecting mirrors 12b and 13b is incident on the photosensitive drum 5 without crossing. Configuration, in other words, a first reflecting mirror 12 that first redirects the scanning beam 10 that has passed through the imaging lens system 1.
By disposing b on the upstream side of the entrance / exit position of the second reflecting mirror 13b, that is, on the side closer to the fθ lens system 1, the mounting space of the developing unit 11 on the downstream side of the photosensitive drum 5 is further increased. I can do things.

Further, according to a preferred embodiment of the present invention, the optical path of the laser beam incident on the first reflection mirrors 12a, 12b from the f.theta. Lens 1 or its extension and the photosensitive drum 5 mother of the second reflection mirrors 13a, 13b. The optical path distance from the intersecting position with the optical path of the laser beam incident on the line to the incident position of the first reflecting mirrors 12a and 12b is the second reflecting mirror 13 from the intersecting position.
The beam optical path guided from the first reflecting mirrors 12a, 12b to the second reflecting mirrors 13a, 13b is set so as to be larger than the optical path distance to the incident positions of a and 13b. By extending in the vertical direction, it is possible to further reduce the apparent optical path length.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be exemplarily described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but merely illustrative examples. Nothing more than.

FIG. 2 is a front sectional view showing a laser printer according to an embodiment of the present invention.
Is a photoconductor drum disposed in the substantially central portion of the apparatus, on the peripheral surface of which an optical scanning unit 20, which will be described in detail later, a developing unit 11 for visualizing the electrostatic latent image, and the visible image forming unit. A transfer device 14 for transferring an electrostatic image onto a transfer paper, a cleaning member 15 for removing the residual toner after the transfer, a charge eliminating lamp 16 for erasing the residual charge on the surface, and a surface of the photosensitive drum 5 are uniformly charged for the next exposure. A charging device 17 is provided, and one side of the transfer sheet conveying path is sequentially provided from the entrance side with a sheet feeding cassette 18, a sheet feeding roller 19, a registration roller 21, a conveyance guide 22, and a heat fixing device 23.
Are arranged, and the toner image formed on the photoconductor drum 5 is transferred onto a transfer paper by a known electrophotographic printing method to be fixed and then discharged to the outside. Also, 24
Is a drive motor for rotating the photosensitive drum 5 and other rotating members.

Now, above the photoconductor drum 5, a vertical wall part 251 passing near the vertical tangent line on the downstream side of the photoconductor drum 5, a vertical wall part 254 provided on the paper discharge side, and an opening window part 253 having an inclined step are provided. A partition wall 25 including a horizontal wall portion 252 extending in the direction of the heat fixing device 23 is provided, and the optical scanning unit 20 is brought into contact with the position regulating surface formed by the horizontal wall portion 252 and the vertical wall portion 251 to position and fix it. Then, the optical scanning unit 20 is arranged in a closed space formed by these walls 251, 252, 254 and the upper surface of the apparatus.

By providing the partition for regulating the position of the optical scanning unit 20 in the apparatus as described above, the distance between the optical scanning unit 20 and the photoconductor drum 5 bus line is made constant, and the toroidal lens assembled in the optical scanning unit 20 is provided. Scanning beam emitted from 30
Alignment (coincidence) between the optical axis 10 and the vertical line of the bus line passing through the axis of the photosensitive drum 5 can be easily and accurately taken.

Further, the beam entrance / exit points of the first and second reflecting mirrors 12 and 13 assembled in the optical scanning unit 20 are sandwiched between a pair of vertical tangents of the photosensitive drum 5 (drum diameter width) as will be described later. ), The reflecting mirrors 12, 13
Naturally, the side plate 43 supporting the side plate 43 and the vertical wall portion 251 abutting on the outer surface of the side plate 43 are naturally located in the vicinity of the vertical tangent line of the photosensitive drum 5, and as a result, the vertical wall portion 251 and the drive motor 24 It is possible to secure a large spare space for disposing the developing unit 11 in the apparatus in between.

Therefore, in the present embodiment, the toner containing portion 111 of the developing unit 11 is formed so as to extend to the vicinity of the opening / closing cover 112 on the upper surface of the apparatus to enable free maintenance.

The partition wall 25 is provided with a slit opening 255 at a position directly above the bus line of the photoconductor drum 5 of the horizontal wall part 252 so that the scanning beam 10 can be incident on the photo bus line of the photoconductor drum. 252 A sponge-like water droplet absorbing material 26 is attached to the lower surface, and when water vapor generated from a transfer paper or the like is condensed on the partition wall 25, it is absorbed by the water droplet absorbing material 26, resulting in a problem caused by the attachment and drop of water droplets. Is being prevented. Then, the water absorbed by the water droplet absorbing material 26 is sequentially evaporated by heating the heat fixing device 23.

On the other hand, an ozone filter 27 is provided on the closed space side of the opening window portion 253, and a pair of blowers is provided on both sides (see FIG. 3) of the optical scanning unit 20 inside the vertical wall portion 254 located on the paper discharge side of the apparatus.
28 and 29 are arranged respectively.

As a result, due to the rotation of the blowers 28 and 29 during the recording operation, the internal air around the photosensitive drum 5 is changed to the open window portion.
Since it is sucked from 253 into the closed space through the ozone filter 27 and is discharged to the outside of the device while passing around the synchronous motor 31 sandwiched between the optical scanning unit 20 and the horizontal wall portion 252, the corona of the charging device 17 or the like is used. Ozone generated in the vicinity of the photoconductor drum 5 due to the electric discharge is easily adsorbed by the ozone filter 27 attached to the opening window portion 253, so that ozone harmful to the human body can be prevented from being discharged to the outside.

Further, the ventilation by the blowers 28 and 29 serves as an air curtain that cools the synchronous motor 31 and shuts off between the optical scanning unit 20 and the thermal fixing device 23.
It prevents the heat generated from 23 from propagating to the optical scanning unit 20.
As a result, it is possible to ensure the steady rotation of the synchronous motor 31 and prevent errors due to temperature fluctuations of the semiconductor laser 7 arranged in the optical scanning unit 20.

Next, the configuration of the optical scanning unit 20 will be described in detail with reference to FIGS. 2 and 3.

Reference numeral 40 denotes a frame body for assembling various members of the optical scanning system at a predetermined position, which is formed of a plastic resin that can be precisely molded, and which conceals the frame body 41 with a side wall 411 provided upright on the periphery. It is composed of an upper cover 42 and a side plate 43 arranged on the mounting side of the reflection mirrors 12 and 13.

The frame body 41 has a circular opening 413 for mounting the synchronous motor 31 connected to the rotary polygon mirror 4, a slit hole 412 for emitting the scanning beam 10 on the photoconductor drum 5 bus line, and various positioning holes. Has a bottom surface portion 41A in which the bottom surface portion 4A
A partition wall 414, which is deflected inward by a predetermined angle in parallel with the side wall 411a, is formed on the side of the mounting position of the rotary polygon mirror 4 of 1A.
A mounting passage 415 for the semiconductor laser 7 and the like is formed between the side wall 411a and the side wall 411a.

Further, the output side of the rotary polygonal mirror 4 of the bottom surface portion 41A is bulged in a flat rectangular shape, and the position immediately above the slit hole 412 between the falling portion of the bulging portion 416 and the side wall 411 is formed in a concave portion 417, Recess
Stepped surfaces 418 and 419 for fixing the toroidal lens 30 and the filter 32 in place are formed on 417.

In the upper cover 42, the mounting sides of the reflecting mirrors 12 and 13 are bulged upward in a rectangular shape, and the bulging portion 421 is provided with a mounting surface on which the second reflecting mirror 13 can be mounted at a predetermined angular position. Form an extra space 42A above the side upper cover 42,
The control board 33, the controller and the like are formed so as to be accommodated.
(See FIG. 6) Next, the arrangement relationship of various members assembled to the frame body will be described.

In the mounting passage 415 located on the side of the rotary polygon mirror 4, the semiconductor laser 7 and the cylindrical lens 34 are sequentially arranged from the opening end side.
Is positioned and fixed, and after the modulated beam 10 'emitted from the semiconductor laser 7 is focused as a linear spot light parallel to the scanning direction, the deflecting mirror 35 disposed on the exit side of the mounting passage 415. Through the rotary polygon mirror 4 at a predetermined angle
It is incident on the deflecting surface of-and is imaged.

A synchronous motor 31 is connected to the rotary polygon mirror 4 via a mounting plate 401 for fixing the rotary polygon mirror 4 to the frame bottom surface portion 41A,
The rotary polygon mirror 4 is rotated by the synchronous motor 31 in synchronism with the photosensitive drum 5, and the modulated beam 10 'incident on the deflecting surface 4a is swept in the main scanning direction as a scanning beam 10 having a fan-like uniform angular velocity motion. , Fθ arranged on the exit side of the rotary polygon mirror 4
It is incident on the lens system 1.

The rotary polygon mirror 4 widens the deflection angle of the scanning beam 10 by appropriately selecting the number of deflection surfaces 4a (for example, a hexahedron) and the reflection width, and the image of the scanning beam 10 after passing through the fθ lens system 1 is selected. The angle is set to about 45 degrees.

The fθ lens system 1 includes a concave lens 1a and a convex lens as described later.
The scanning beam 10 emitted from the fθ lens system 1 is formed by a combination of two lenses 1b and is imaged on the generatrix of the photoconductor drum 5 while being deflected by the first and second reflecting mirrors 12 and 13. In other words, the focal length of the fθ lens system 1 and the optical path length from the fθ lens system 1 to the photoconductor drum 5 generatrix are the same.

As a result, the scanning beam 10 transmitted through the fθ lens system 1 can be converted from a uniform angular velocity motion to a constant velocity motion and imaged on the generatrix of the photoconductor drum 5, but the scanning beam 10 is formed by the rotary polygon mirror 4. The deflection angle is 80 degrees or more, preferably about
Astigmatism may occur because it is expanded to around 90 degrees.

However, since this astigmatism is corrected by the toroidal lens 30 described later, the pitch shape of the optical dot pattern formed on the generatrix of the photoconductor drum 5 does not become nonuniform.

The first reflection mirror 12 is attached to the side plate 43 facing the fθ lens system 1.

The first reflecting mirror 12 has a long plate shape along the main scanning direction, and its entrance / exit point is located in a region sandwiched by a pair of vertical tangent lines of the photosensitive drum 5, and is guided by the reflecting mirror 12. The mounting angle is set so that the scanning beam 10 is guided to the second reflecting mirror 13.

Similarly, the second reflecting mirror 13 also has a long plate shape along the main scanning direction, is attached to the back surface of the upper cover 42 facing the slit hole 412, and the scanning beam 10 emitted from the reflecting mirror 13 is exposed to light. The mounting angle and the mounting position of the toroidal lens 30 are set so as to be guided to the optical axis of the toroidal lens 30 along a vertical line passing through the generatrix of the body drum 5.

The toroidal lens 30 is formed of a plastic lens having an entrance surface and an exit surface in a concentric arc shape, and a stepped surface 418 of a recess 417 formed immediately above the slit hole 412 so that its optical axis is parallel to the scanning direction. Place it on top and secure it with leaf spring 36.

In the stepped surface 418, in the sub scanning direction of the toroidal lens 30, the deflection surface 4a of the rotary polygon mirror 4 and the surface to be scanned (on the photoconductor drum 5 generatrix) with respect to the combined system of the fθ lens system 1 and the toroidal lens 30. (Position) is formed at a position where the conjugate relationship can be maintained.

As a result, the toroidal lens 30 can correct the optical axis shift in the sub-scanning direction of the scanning beam 10 due to the surface tilt of the rotary polygon mirror 4, and the incident surface and the exit surface of the lens 30 are concentrically formed. Therefore, it is possible to correct the astigmatism that occurs when the light passes through the fθ lens system 1.

Therefore, according to such an embodiment, since the deflection angle of the scanning beam 10 is expanded to 80 degrees or more, preferably about 90 degrees, the toroidal lens 30 for correcting astigmatism and surface tilt is disposed on the exit side. , The lens structure of the fθ lens system 1 can be configured with a small number of lenses such as about 2 to 3, and the focal length of the fθ lens system 1, that is, the optical path length can be shortened because the angle of view is widened. As a result, it is possible to reduce the size and weight of the optical scanning unit 20.

A filter 32 is provided on the exit side of the toroidal lens 30 to prevent dust from entering from the outside.

On the other hand, the exit side of the fθ lens system 1 and the first reflecting mirror
Between 12, the detection beam 37 on the scanning beam 10 scanning start side,
Photodiodes 38 are respectively arranged in areas outside the scanning area facing the detection mirror 37, and the scanning beam 10 emitted from the fθ lens system 1 is passed through the detection mirror 37 at every repeated scanning by the rotary polygon mirror 4. And guides it to the photodiode 38, and outputs a reference signal for regulating the modulation start timing of the scanning beam 10.

Next, the supporting device for various members of the scanning system will be described in more detail.

4A and 4B show the structure of a mirror supporting device 50 used for the deflecting mirror 35 and the detecting mirror 37. The mirror supporting device 50 is made of aluminum, resin or other elastic material and is formed into a substantially L shape. And the flat plate-shaped support 5 that is screwed to the bottom surface 41A of the frame body.
A mirror mounting portion 52 for fixing the reflection mirrors 35 and 37 is vertically arranged on the top of the unit 1.

The mirror mounting portion 52 has two upright pieces 521, which are formed by slits extending parallel to the mirror mounting surface 52a from the upper end to the vicinity of the lower end.
Divided into 522, the upright pieces 521 and 522 are upright pieces on the mirror mounting side.
521 is formed to be thinner than the back side upright piece 522, and a screw hole 523 is screwed near the upper end of the back side upright piece 522, and the rear surface side of the mirror mounting side upright piece 521 is pressed into the screw hole 523. Screw the possible adjusting screws 53.

A pivot 525 is attached to the lower surface of the flat plate support 51 corresponding to the intersection of the optical axis of the modulated beam 10 'and the surfaces of the reflection mirrors 35 and 37, and the reflection mirror 3 is attached via the support device 50.
5,37 can be rotated in the scanning direction.

Therefore, according to the supporting device 50, the optical axis shift in the main scanning direction with the pivot 525 as a fulcrum, and the adjusting screw 53
The rotation of the reflecting mirrors 35 and 37 together with the upright piece 521 on the reflection mirror mounting side can be slightly angle-shifted in the sub-scanning direction, whereby the optical axis shift in the sub-scanning direction can be adjusted.

FIG. 4C is another embodiment showing a modified example of the reflection mirror supporting device 50 '. It has a flat plate-shaped support base 55 formed in a U-shaped cross section and a reflection mirror mounting portion 56 standing upright from the central position of the support base 55. A fixing screw 57 is attached to the base side of the flat plate-like support base 55, and an adjusting screw 58 is attached to the U-shaped tip side, and the space width of the U-shaped portion is reduced or expanded by rotating the adjusting screw 58. The anti-slopes of the reflection mirrors 35 and 37 are angularly changed in the width scanning direction.

In this modified example, since the upper cover 42 can be removed and the adjusting screw 58 can be rotated from above, the optical axis shift in the width scanning direction does not occur even after the reflection mirror supporting device 50 'is assembled to the frame. Since adjustment can be performed, assembly adjustment and maintenance can be facilitated.

FIG. 5 shows a supporting device 60 of the fθ lens system 1.

As described above, the fθ lens system 1 is composed of a thin lens small diameter concave lens 1a having a low refractive index and a thick large diameter convex lens 1b having a high refractive index. The lens system 1 has its upper and lower both sides parallel to the main scanning direction. It is removed to form a flat shape and is integrally fixed by a supporting device 60.

The support device 60 includes a base 61 fixed to the bottom surface of the frame and the base 61.
A regulating plate 62 fixed to the upper surface of the lens 61 for regulating the distance between the both lenses 1a and 1b, and a pair of leaf springs arranged on both end sides facing the regulating plate 62 and rotatably supporting the concave lens 1a in the sub scanning direction. 63, a fixing plate 64 arranged to face the restriction plate 62 to fix the convex lens 1b at a predetermined position, and is erected in a gate shape on the base 61, and the lens system 1 is mounted along the side surface of the lens system. A support plate 65 surrounding a square shape, and an adjusting screw at the center of the upper surface of the support plate 65.
The correction plate 66 is mounted in a floating state via 67.

The correction plate 66 has a holding side 661 that presses and holds the upper surface of the concave lens 1a by surface contact, a floating side 662 that maintains a floating state at a predetermined distance above the support plate 65, and a J-shape from the floating side 662. Has a rotating side 663 that holds the concave lens 1a in a substantially linear contact, and the rotating side 663 is a concave lens by retracting the floating side 662 by tightening the adjusting screw 67.
1a is rotated in a direction of separating while pressing the upper surface, and as a result, the concave lens 1a is rotated (fallen) in the sub-scanning direction against the elastic force of the leaf spring 63 that supports the concave lens 1a at the lower end side. On the other hand, when the screw 67 is loosened, the concave lens 1a is restored to the original state by the elastic force of the leaf spring 63 together with the rotating side 663,
This makes it possible to easily correct the optical axis shift between the lenses 1a-1b in the sub-scanning direction with a simple configuration.

Therefore, according to the present embodiment, this occurs because the fθ lens system 1 is formed in a flat shape parallel to the scanning direction in order to reduce the size.
A tilt error in the width scanning direction at the time of assembly, especially the thin concave lens 1a can be easily adjusted, and since the adjustment can be easily performed from above by removing the upper cover 42, it is also possible from above maintenance. It is convenient.

Figure 6 shows a toroidal lens designed for easy support on the frame.
The shape of 30 is shown.

As described above, in the toroidal lens 30, both the entrance surface and the exit surface are formed with concentric radii of curvature. Therefore, in order to achieve accurate positioning and fixing, the support member is also formed along with the radii of curvature. However, it is extremely difficult to process such a supporting member, and since such a supporting member is generally supported by supporting both ends,
Deflection and deformation easily occur.

Therefore, in this embodiment, on the exit surface side of the plastic toroidal lens 30, the longitudinal direction (main scanning direction) is set on both ends in the lateral direction so that the bottom surface is flush with the virtual plane orthogonal to the top of the exit surface. ) Parallel to the pair of feet 71,72
And the emission surface 30A on which the scanning beam 10 is scanned is formed in the region sandwiched between the pair of legs 71, 72.
Further, flat surfaces parallel to the bottom surfaces of the foot portions 71 and 72 are formed on both end sides in the longitudinal direction on the incident surface side, and serve as leaf spring holding surfaces 73 and 74.

Then, the toroidal lens 30 is such that the lens legs 71 and 72 are placed on the stepped surfaces 418 formed on both sides above the slit holes 412 of the frame body 40, and then on the lens side from the raised portion 421 of the frame body 40. The lens 30 can be positioned and fixed by pressing the free end of the extending leaf spring 36 against the leaf spring holding surfaces 73, 74.

According to the toroidal lens 30, since the positioning and fixing portions 71 to 74 formed on the entrance / exit surface 30A side of the lens are parallel flat surfaces that face each other, a frame member is used without using a special fixing member. Accurate and easy positioning is achieved by simply forming the stepped surface 418 on the 40, and since it is placed on the stepped surface 418 over the entire length in the longitudinal direction, no bending or deformation occurs. . Further, since the foot portions 71, 72 and the leaf spring holding surfaces 73, 74 are formed in the areas deviating from the beam scanning area, the beam scanning will not be disturbed at all.

[Advantages of the Invention] As described above, according to the present invention, the entrance / exit positions of a plurality of reflecting mirrors that redirect the scanning beam emitted from the fθ lens are located within a region sandwiched between a pair of tangent lines of the photosensitive drum. Since the arrangement is made, the apparent optical path length can be shortened without being restricted by the arrangement position of the developing unit and other peripheral devices. As a result, the toner volume of the developing unit is increased with the downsizing of the device. It has various remarkable effects such as being able to do things.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A and FIG. 1B are principle explanatory views for explaining the principle of the present invention. FIG. 2 is a front sectional view showing a schematic configuration of a laser printer according to an embodiment of the present invention. FIG. 4A and FIG. 4B show a configuration of a mirror support device used for the deflection mirror and the detection mirror, and FIG. 4A is a perspective view.
FIG. 4B is a front sectional view. FIG. 4C is a front sectional view showing a modified example of the mirror support device. FIG. 5 is a perspective view showing a supporting device for the fθ lens system. FIG. 6 is a perspective view showing the shape of the toroidal lens. FIG. 7 is a front view according to the prior art.

Claims (4)

[Claims] 1. A laser printer configured such that a laser beam having passed through an imaging lens system having an fθ characteristic is incident on a generatrix of a photosensitive drum via a plurality of reflecting mirrors. The beam entrance / exit positions of all the reflection mirrors of the plurality of reflection mirrors are present in a region sandwiched between the tangents of the pair of photoconductor drums in parallel with the light emitted from the reflection mirror located on the most downstream side. Laser printer characterized by being configured as 2. The laser printer according to claim 1, wherein the laser beam optical paths deflected by the plurality of reflecting mirrors are configured to enter the photoconductor drum without intersecting each other. 3. The laser printer according to claim 1, wherein the beam entrance / exit positions of all the reflection mirrors are present between a pair of tangents of the photosensitive drum extending vertically upward. 4. A crossing position between a laser beam optical path incident on the first reflecting mirror from the imaging lens system or its extension and a laser beam optical path incident on the photoconductor drum generatrix of the second reflecting mirror. The laser printer according to claim 1, wherein the optical path distance to the incident position of the first reflecting mirror is longer than the optical path distance from the intersecting position to the incident position of the second reflecting mirror.