JP2007011015A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner and an image forming apparatus with which stray light is prevented from making incident on a face to be scanned and an photosensor even when the operation speed of a deflector is increased. <P>SOLUTION: A longitudinal directional rib 69 is provided in the vicinity of a polygon mirror unit 24 between a light source 85 and the polygon mirror unit 24. An incident side opening 77 having a slit shape which is narrow in the longitudinal direction is formed by cutting the longitudinal directional rib 69 from the upper edge. The width in a main scanning direction of a laser beam from the light source 85 is limited to a width corresponding to the width of the incident side opening 77 when the laser beam passes through the incident side opening 77 formed on the longitudinal directional rib 69. Thus, the stray light generated by the incident of the light from the light source 85 to the polygon mirror 92 when the surface of a photoreceptor drum 30 is not exposed is prevented from making incident on the surface of the photoreceptor drum 30 even when the rotation speed of the polygon mirror 92 is increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a laser printer and an optical scanning device provided in the image forming apparatus.

2. Description of the Related Art An image forming apparatus such as a laser printer is equipped with an optical scanning device for scanning the surface of a photoconductor with a laser beam and forming an electrostatic latent image based on image data on the photoconductor.
This optical scanning device includes, for example, a semiconductor laser, a rotating polygon mirror that is formed in a flat polygonal column shape, and each side surface is a reflecting surface that reflects a laser beam, and a condensing lens having fθ characteristics. Yes. The laser beam emitted from the semiconductor laser is deflected and scanned by a rotating polygon mirror, passes through a condenser lens, and is irradiated on the surface of the photosensitive member (see, for example, Patent Document 1).
Japanese Patent No. 3137195

  In recent years, the rotational speed of the rotary polygon mirror tends to increase in order to meet the demand for higher speed optical scanning devices. A general laser printer requires an operation for stabilizing the optical output of the semiconductor laser. Therefore, the laser output is kept constant by turning on the laser for a certain period of time other than exposing the surface to be scanned for each scan, detecting the light output by a monitor diode, and controlling the current flowing to the semiconductor laser. ing. In addition, a writing position detection sensor is provided in order to align the position where the image signal is written on the surface to be scanned, and light emission for a certain period of time is required to make light incident on the sensor. However, when the speed of the rotary polygon mirror is increased, the ratio of the time during which the laser is turned on during the time other than exposing the surface to be scanned as described above relatively increases. Then, the laser beam is reflected by the reflecting surface of the rotary polygon mirror, which causes a problem that it becomes stray light and enters the photosensitive member. In addition to the photosensitive member, if stray light is incident on an optical sensor such as a writing position detection sensor, a malfunction occurs in the operation of the printer.

  In the above-mentioned Patent Document 1, a light shielding plate that blocks both ends in the main scanning direction of a laser beam scanned by the rotating polygon mirror is disposed between the rotating polygon mirror and the photosensitive member, thereby providing a surface of the photosensitive member. It has been proposed to prevent stray light from being irradiated. However, in the technique according to this proposal, when the semiconductor laser is turned on at a time other than exposing the surface to be scanned, a part of the laser beam is reflected by a member other than an undesired reflecting surface or a rotating polygon mirror. It cannot be completely prevented, and generation of stray light due to such reflection cannot be prevented.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical scanning device and an image forming apparatus that can prevent stray light from entering a surface to be scanned or an optical sensor even when the operation speed of the deflector is increased. is there.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided an optical scanning device that scans a surface to be scanned with light, a light source, and deflection for deflecting and scanning light from the light source in a main scanning direction. Provided in the vicinity of the deflector between the light source and the deflector, and passes through the light from the light source and has a first aperture for limiting the width of the light, unnecessary. And a light-shielding rib for shielding light.

  According to such a configuration, the light-shielding rib that blocks unnecessary light reflected by the deflector is provided between the light source and the deflector in the vicinity of the deflector. Further, the light shielding rib has a first aperture, and the spot diameter of the light formed on the surface to be scanned can be defined by the first aperture. In other words, stray light traveling from the deflector toward the light source can be effectively blocked by using the aperture formed in the light-shielding rib to allow light traveling from the light source to the deflector to pass therethrough. Therefore, even if the operating speed of the deflector is increased, stray light generated when light from the light source is incident on the deflector at a time other than exposing the surface to be scanned causes the light output of the surface to be scanned and the semiconductor laser. It can be prevented from entering a monitor diode provided for stabilization, a writing position detection sensor provided for aligning a position where an image signal is written to the surface to be scanned, and the like.

The vicinity of the deflector means a position where no other member exists on the optical path between the deflector and the light shielding rib. In other words, it means a position where the light incident on the deflector finally passes through the opening just before the incident.
The invention described in claim 2 is characterized in that, in the invention described in claim 1, the first aperture limits the width of the light from the light source in the main scanning direction.

  According to such a configuration, stray light is generated so as to be scattered mainly in the main scanning direction as the light is deflected and scanned by the deflector. Therefore, the first aperture is formed in the main scanning direction of the light from the light source. By limiting the width of the light, stray light can be effectively prevented. In many cases, since the frame of the optical scanning device is integrally formed of resin, the first aperture has a shape that limits the width of light only in the main scanning direction and is open in the sub scanning direction. Thus, the mold structure can be facilitated, and the productivity can be improved.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the first aperture limits a width of light from the light source in the sub-scanning direction.
According to such a configuration, the width of the light in the main scanning direction and the sub-scanning direction can be limited by the first aperture of the light shielding rib.
According to a fourth aspect of the invention, there is provided the second aspect of the invention according to the second aspect, wherein the light source is arranged between the light source and the light shielding rib and limits a width of light from the light source in a sub-scanning direction. It is characterized by having two apertures.

According to such a configuration, the width of the light incident on the deflector in the main scanning direction can be limited by the first aperture, while the width of the light in the sub-scanning direction is limited by the second aperture. be able to. Therefore, the shape of the first aperture provided in the light shielding rib can be easily formed, and the width of the light in the sub-scanning direction can be accurately defined.
According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the second aperture is formed wider than the first aperture in the main scanning direction and passes light from the light source. Thus, the width of the light in the main scanning direction is also limited.

  According to such a configuration, before the first aperture limits the width of the light from the light source in the main scanning direction, the second aperture limits the width of the light in the main scanning direction and the sub-scanning direction. can do. Therefore, the generation of stray light due to the light from the light source hitting the light shielding ribs and becoming scattered light can be prevented. As a result, stray light can be more reliably prevented from entering the surface to be scanned.

  According to a sixth aspect of the present invention, in the first or second aspect of the present invention, the light deflected and scanned by the deflector is provided between the deflector and the surface to be scanned. An fθ lens for scanning at a constant speed on the scanning plane, and disposed between the deflector and the fθ lens, for limiting the width in the sub-scanning direction of the light deflected and scanned by the deflector. And a third aperture.

According to such a configuration, the third aperture can prevent the light deflected and scanned by the deflector from deviating from the fθ lens to both sides in the sub-scanning direction, and stray light generated from the deflector and its vicinity. Can be more reliably prevented from entering the surface to be scanned.
According to a seventh aspect of the invention, there is provided a resin frame for holding the light source and the deflector according to any of the first to sixth aspects, wherein the light shielding rib is integrated with the frame. It is characterized by being formed.

  According to such a configuration, the frame and the light shielding rib can be formed simultaneously by resin molding. Therefore, the manufacturing process can be simplified. Further, since the light shielding rib is formed integrally with the frame, the frame can be reinforced in the vicinity of the deflector. Therefore, the vibration of the frame due to the vibration of the deflector can be prevented, and the generation of stray light due to such vibration can be prevented.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, a scanning optical system for forming an image of light deflected and scanned by the deflector on the surface to be scanned. The deflector is a polygon mirror that has a plurality of reflecting surfaces that reflect light from the light source and is rotated about a rotation axis passing through the center thereof, and the light source, the scanning optical system, and the polygon When one of the reflection surfaces is perpendicular to the optical path of incident light incident on the polygon mirror, the mirror reflects the incident light on the reflection surface different from the reflection surface, and the reflected light is It is characterized by being arranged so as to form an image on the surface to be scanned.

When the light source is a semiconductor laser, when the light reflected by the reflecting surface returns to the semiconductor laser, return light noise is generated and the oscillation of the semiconductor laser becomes unstable. Further, when the light reflected by the reflecting surface returns to the semiconductor laser, is disposed adjacent to the semiconductor laser, and enters the monitor diode that detects the optical output, a problem occurs in the operation for stabilizing the output of the semiconductor laser. .
When one reflecting surface of a polygon mirror is perpendicular to the optical path of incident light incident on the polygon mirror, the incident light is reflected by a reflecting surface different from the reflecting surface, so that the light reflected by the reflecting surface is reflected. It can prevent entering into a light source or a monitor diode. Therefore, it is possible to prevent the output of light from the light source from becoming unstable.

The invention according to claim 9 is the invention according to claim 8, wherein the scanning optical system scans the light deflected and scanned by the deflector at a constant speed on the surface to be scanned. an fθ lens, and the light source, the scanning optical system, and the polygon mirror,
α / 2 + W / (2 · f) -2π / N> 0
(Where α is a line formed by connecting a light reflection position on the reflection surface and a center position in the main scanning direction of a region where light is scanned on the surface to be scanned, and light incident on the reflection surface) W is half of the width in the main scanning direction of the region where light is scanned on the surface to be scanned, f is the focal length of the fθ lens, and N is the angle of the reflecting surface Number.)
It is arranged so as to satisfy the inequality.

According to such a configuration, the light source, the scanning optical system, and the polygon mirror are arranged so as to satisfy the above inequality, so that one reflecting surface of the polygon mirror is perpendicular to the optical path of incident light incident on the polygon mirror. In this case, incident light can be reflected by a reflection surface different from the reflection surface, and the reflected light can be reliably scanned on the surface to be scanned.
According to a tenth aspect of the present invention, in the image forming apparatus, the optical scanning device according to any one of the first to ninth aspects and a photosensitive device in which an electrostatic latent image is formed by scanning light with the optical scanning device. It is characterized by having a body.

  According to such a configuration, since the optical scanning device capable of preventing the generation of stray light even when the operation speed of the deflector is increased, the stray light can be generated while the speed of the device can be increased. It is possible to prevent the light from entering the photoconductor. Therefore, a high-quality electrostatic latent image can be formed on the photoconductor, and formation of a high-quality image can be achieved.

  According to the first aspect of the present invention, even if the operation speed of the deflector is increased, stray light generated by the light from the light source entering the deflector at a time other than exposing the surface to be scanned is not affected. Incident light can be prevented from entering a scanning surface, a monitor diode provided for stabilizing the optical output of the semiconductor laser, a writing position detection sensor provided for aligning the position where the image signal is written to the surface to be scanned.

According to the second aspect of the present invention, it is possible to prevent part of the light from the light source from becoming stray light scattered in the main scanning direction due to reflection of the deflector.
According to the third aspect of the invention, stray light due to reflection by the deflector can be prevented, and the width of the light from the light source in the main scanning direction and the sub-scanning direction can be limited.
According to the fourth aspect of the present invention, the shape is easy to mold and the generation of stray light from the deflector can be reliably prevented.

According to the fifth aspect of the present invention, stray light can be more reliably prevented from being irregularly reflected by the light shielding ribs and entering the surface to be scanned.
According to the sixth aspect of the present invention, it is possible to more reliably prevent stray light generated from the deflector and its vicinity from entering the surface to be scanned.
According to the seventh aspect of the present invention, it is possible to prevent the generation of stray light due to the vibration of the frame while simplifying the manufacturing process.

According to invention of Claim 8, it can prevent that the output of the light from a light source becomes unstable.
According to the ninth aspect of the present invention, the light reflected by the reflecting surface of the polygon mirror can be reliably scanned on the surface to be scanned.
According to the tenth aspect of the present invention, high-quality image formation can be achieved while the speed of the apparatus can be increased.

1. 1 is a side sectional view showing an embodiment of a laser printer as an image forming apparatus of the present invention.
The laser printer 1 includes a main body casing 2, a feeder unit 4 for feeding paper 3 in the main body casing 2, and image formation for forming an image on the paper 3 fed by the feeder unit 4. Part 5.
(1) Main Body Casing An attachment / detachment opening 6 for attaching / detaching a process cartridge 20 described later is formed on one side wall of the main body casing 2, and a front cover 7 for opening / closing the attachment / detachment opening 6 is provided. ing. The front cover 7 is rotatably supported by a cover shaft 8 inserted through a lower end portion thereof. Thus, when the front cover 7 is closed with the cover shaft 8 as a fulcrum, the attachment / detachment opening 6 is closed by the front cover 7, and when the front cover 7 is opened with the cover shaft 8 as a fulcrum, the attachment / detachment opening 6 is opened. The process cartridge 20 can be attached to and detached from the main casing 2 through the attachment / detachment port 6.

In the following description, in the laser printer 1, the side on which the front cover 7 is provided is referred to as “front side”, and the opposite side is referred to as “rear side”.
(2) Feeder unit The feeder unit 4 includes a paper feed tray 9 that is detachably attached to the bottom of the main body casing 2 along the front-rear direction, and a separation roller 10 that is provided above the front end of the paper feed tray 9. And a separation pad 11 and a paper feed roller 12 provided on the rear side of the separation roller 10 (upstream in the conveyance direction of the paper 3 with respect to the separation pad 11). In addition, the feeder unit 4 includes a paper dust removing roller 13 provided on the upper front side of the separation roller 10 (downstream in the conveyance direction of the paper 3 with respect to the separation roller 10), and a pinch disposed to face the paper dust removing roller 13. And a roller 14.

The conveyance path of the paper 3 in the feeder unit 4 is folded back in a substantially U shape from the vicinity of the paper dust removing roller 13 and extends substantially horizontally toward the process cartridge 20. And the feeder part 4 is provided with the registration roller 15 which consists of a pair of roller on the part extended in the substantially horizontal of the conveyance path | route.
Inside the paper feed tray 9, there is provided a paper pressing plate 16 on which the paper 3 can be stacked. The paper pressing plate 16 is supported at the rear end so as to be swingable, so that the front end is disposed below, the placement position along the bottom plate of the paper feed tray 9 and the front end are disposed above, It can be swung between an inclined supply position.

  A lever 17 for lifting the front end of the paper pressing plate 16 upward is provided at the front end of the paper feed tray 9. The lever 17 is supported at a position below the front end of the paper pressing plate 16 so that the rear end is swingably supported by the lever shaft 18, and the front end is inclined to the bottom plate of the paper feed tray 9. The sheet pressing plate 16 can be swung between an inclined posture to lift the paper pressing plate 16. When a driving force is input to the lever shaft 18, the lever 17 rotates with the lever shaft 18 as a fulcrum, the front end portion of the lever 17 lifts the front end portion of the paper pressing plate 16, and the paper pressing plate 16 is brought to the supply position. Move.

When the sheet pressing plate 16 is positioned at the supply position, the uppermost sheet 3 on the sheet pressing plate 16 is pressed by the sheet feeding roller 12, and the separation roller 10 and the separation pad 11 are rotated by the rotation of the sheet feeding roller 12. Feeding is started toward the separation position between the two.
When the paper feed tray 9 is detached from the main casing 2, the paper pressing plate 16 is positioned at the placement position. When the paper pressing plate 16 is positioned at the mounting position, the paper 3 can be stacked on the paper pressing plate 16.

  The sheet 3 fed toward the separation position by the sheet feeding roller 12 is rolled and fed one by one when it is sandwiched between the separation roller 10 and the separation pad 11 by the rotation of the separation roller 10. Is done. The fed paper 3 passes between the paper dust removing roller 13 and the pinch roller 14, and after the paper dust is removed there, the paper 3 is folded back along the U-shaped paper feeding side conveyance path, and the registration roller It is conveyed toward 15.

The registration roller 15 conveys the sheet 3 to the transfer position between the photosensitive drum 30 and the transfer roller 33 after the registration and to transfer the toner image on the photosensitive drum 30 to the sheet.
(3) Image Forming Unit The image forming unit 5 includes a scanner unit 19 as an optical scanning device, a process cartridge 20, and a fixing unit 21.
<Scanner part>
The scanner unit 19 is provided in the upper part of the main casing 2 and is disposed in the outer casing 22 fixed to the main casing 2, an inner casing 23 as a frame fixed to the outer casing 22, and the inner casing 23. , A light source 85 (see FIG. 2), a polygon mirror unit 24, an fθ lens 25 as a scanning optical system, a folding mirror 26 as a scanning optical system, a surface tilt correction lens 27 as a scanning optical system, and a bending mirror as a scanning optical system. 28.

  The laser beam based on the image data emitted from the light source 85 is deflected and scanned by the polygon mirror unit 24 as shown by a chain line, passes through the fθ lens 25, and then the optical path is folded by the folding mirror 26, and further tilted. After passing through the correction lens 27, the optical path is further bent downward by the bending mirror 28, so that the surface of the photosensitive drum 30 of the process cartridge 20 is irradiated.

The configuration of the scanner unit 19 will be described in detail later.
<Process cartridge>
The process cartridge 20 is provided below the scanner unit 19 in the main body casing 2 and is detachably attached to the main body casing 2 via the attachment / detachment port 6.
The process cartridge 20 includes a drum frame 29, and a photosensitive drum 30 as a photosensitive member, a scorotron charger 31, a developing cartridge 32, a transfer roller 33, and a cleaning brush 34 provided in the drum frame 29. .

  The drum frame 29 includes a drum front opening 35 for transporting the paper 3 from outside the drum frame 29 to the transfer position, and a drum rear opening 36 for transporting the paper 3 from the transfer position to the outside of the drum frame 29. Is formed. The drum front opening 35 is disposed below the developing cartridge 32 and on the front side of the transfer position, and the drum frame 29 extends along the axial direction of the transfer roller 33 (hereinafter sometimes simply referred to as “axial direction”). It is opened so as to communicate between the inside and the outside. The drum rear opening 36 is disposed on the rear side of the transfer position so as to face the drum front opening 35 across the transfer position, and communicates with the inside and outside of the drum frame 29 along the axial direction. It is open.

  The photosensitive drum 30 has a cylindrical shape, and the drum body 37 as a surface to be scanned formed by a positively chargeable photosensitive layer whose outermost layer is made of polycarbonate or the like. And a metal drum shaft 38 extending along the axial direction. The drum shaft 38 is supported by the drum frame 29, and the drum main body 37 is rotatably supported by the drum shaft 38, so that the photosensitive drum 30 is rotatable about the drum shaft 38 in the drum frame 29. Is provided. The photosensitive drum 30 is rotationally driven by the input of a driving force from a motor (not shown).

The scorotron charger 31 is supported by the drum frame 29 obliquely above the rear side of the photosensitive drum 30, and is disposed opposite to the photosensitive drum 30 so as not to contact the photosensitive drum 30. The scorotron charger 31 uniformly charges the surface of the photosensitive drum 30 to positive polarity by corona discharge.
The developing cartridge 32 is detachably attached to the drum frame 29. Therefore, the developing cartridge 32 can be attached to and detached from the main body casing 2 while being attached to the drum frame 29, and can be attached and detached alone while leaving the drum frame 29 in the main body casing 2. .

The developing cartridge 32 includes a developing case 39, a supply roller 40, a developing roller 41, and a layer thickness regulating member 42 provided in the developing case 39.
As will be described in detail later, the developing case 39 is formed in a box shape whose rear side is opened. A toner storage chamber 43 and a development chamber 44 are defined inside the development housing 39.
The toner storage chamber 43 is partitioned as an internal space on the front side of the developing housing 39. In the toner storage chamber 43, positively charged nonmagnetic one-component toner is stored as a developer. In the toner, a polymerizable monomer, for example, a styrene monomer such as styrene, an acrylic monomer such as acrylic acid, alkyl (C1 to C4) acrylate, alkyl (C1 to C4) methacrylate, A polymerized toner obtained by copolymerization by suspension polymerization or the like is used. This polymerized toner has a substantially spherical shape, has extremely good fluidity, and can achieve high-quality image formation.

Such a toner is blended with a colorant such as carbon black, wax, and the like, and an external additive such as silica is added to improve fluidity. The average particle size of the toner is about 6 to 10 μm.
An agitator 45 for agitating the toner is provided in the toner storage chamber 43. The agitator 45 includes an agitator rotating shaft 46 extending in the width direction (a direction orthogonal to the front-rear direction and the up-and-down direction, the same applies hereinafter) at the substantially center of the toner storage chamber 43, and a stirring member 47 provided on the agitator rotating shaft 46. It has. When a driving force from a motor (not shown) is input to the agitator rotating shaft 46, the agitator rotating shaft 46 is rotated, and the agitating member 47 moves in the toner containing chamber 43 in the circumferential direction around the agitator rotating shaft 46. Then, the toner in the toner storage chamber 43 is stirred by the stirring member 47 and discharged from the toner storage chamber 43 to the developing chamber 44.

The developing chamber 44 is partitioned as an internal space on the rear side of the developing housing 39.
The supply roller 40 is disposed behind the boundary portion between the developing chamber 44 and the toner storage chamber 43. The supply roller 40 includes a metal supply roller shaft 48 and a sponge roller 49 made of a conductive foam material that covers the supply roller shaft 48. The supply roller shaft 48 extends in the width direction, and both end portions thereof are rotatably supported by the developing case 39. The supply roller 40 is rotationally driven when a driving force from a motor (not shown) is input to the supply roller shaft 48.

  The developing roller 41 is disposed behind the supply roller 40 in the developing chamber 44 and is provided in contact with the supply roller 40 so as to be compressed. In addition, the developing roller 41 is disposed opposite to the photosensitive drum 30 from the upper front side in the state where the developing cartridge 32 is mounted on the drum frame 29, and is lower than the central portion in the vertical direction that protrudes most rearward. Is in contact with the photosensitive drum 30. The developing roller 41 includes a metallic developing roller shaft 50 and a rubber roller 51 made of a conductive rubber material that covers the developing roller shaft 50. The developing roller shaft 50 extends in the width direction, and both ends thereof are rotatably supported by the developing housing 39. The rubber roller 51 is made of conductive urethane rubber or silicone rubber containing carbon fine particles, and the surface thereof is coated with a urethane rubber or silicone rubber coating layer containing fluorine. The developing roller 41 is rotationally driven when a driving force from a motor (not shown) is input to the developing roller shaft 50. A developing bias is applied to the developing roller 41 during development.

The layer thickness regulating member 42 is made of a metal leaf spring material, and includes a pressing portion 52 having a semicircular cross section made of insulating silicone rubber at the free end thereof. The layer thickness regulating member 42 extends from the upper side of the developing roller 41 toward the obliquely lower front side, and the pressing portion 52 is elastically pressed onto the developing roller 41.
The toner fed into the developing chamber 44 is supplied to the developing roller 41 by the rotation of the supply roller 40, and at this time, the toner is triboelectrically charged between the supply roller 40 and the developing roller 41. The toner supplied onto the developing roller 41 enters between the pressing portion 52 of the layer thickness regulating member 42 and the developing roller 41 as the developing roller 41 rotates, and forms the developing roller 41 as a thin layer having a constant thickness. Supported on.

  The transfer roller 33 is provided below the photosensitive drum 30 in the drum frame 29, is opposed to and contacts the photosensitive drum 30 in the vertical direction, and is disposed so as to form a nip with the photosensitive drum 30. The transfer roller 33 includes a metal transfer roller shaft 53 and a rubber roller 54 made of a conductive rubber material that covers the transfer roller shaft 53. The transfer roller shaft 53 extends in the width direction and is rotatably supported by the drum frame 29. The transfer roller 33 is rotationally driven by receiving a driving force from a motor (not shown). A transfer bias is applied to the transfer roller 33 during transfer.

The cleaning brush 34 is attached to the drum frame 29, and is disposed opposite the photosensitive drum 30 on the rear side of the photosensitive drum 30. The cleaning brush 34 is disposed so as to face and come into contact with the photosensitive drum 30 and scrapes off paper dust and the like attached to the photosensitive drum 30.
The surface of the photosensitive drum 30 is first charged uniformly by the scorotron charger 31 with the rotation of the photosensitive drum 30 and then exposed by high-speed scanning of the laser beam from the scanner unit 19. An electrostatic latent image corresponding to the image to be formed on the paper 3 is formed.

  Next, when the developing roller 41 rotates, the toner carried on the developing roller 41 and charged with positive polarity is formed on the surface of the photosensitive drum 30 when it comes into contact with the photosensitive drum 30. The electrostatic latent image, that is, the surface of the photosensitive drum 30 that is uniformly positively charged, is supplied to an exposed portion where the potential is lowered by the laser beam. As a result, the electrostatic latent image on the photosensitive drum 30 is visualized, and a toner image by reversal development is carried on the surface of the photosensitive drum 30.

  Thereafter, the toner image carried on the surface of the photosensitive drum 30 is transferred from the outside of the drum frame 29 through the drum front opening 35 into the drum frame 29 as the sheet 3 conveyed by the registration roller 15, and is exposed to the photosensitive drum 30. While passing through the transfer position between the drum 30 and the transfer roller 33, the image is transferred onto the paper 3 by the transfer bias applied to the transfer roller 33. The sheet 3 onto which the toner image has been transferred is conveyed from the drum frame 29 to the outside of the drum frame 29 through the drum rear side opening 36 and is conveyed to the fixing unit 21.

The transfer residual toner remaining on the photosensitive drum 30 after the transfer is collected by the developing roller 41. Further, paper dust from the paper 3 adhering to the photosensitive drum 30 after the transfer is collected by the cleaning brush 34.
<Fixing part>
The fixing unit 21 is provided on the rear side of the process cartridge 20. The fixing unit 21 includes a fixing frame 55 and a heating roller 56 and a pressure roller 57 in the fixing frame 55.

The heating roller 56 includes a metal tube whose surface is coated with a fluororesin, and a halogen lamp for heating inserted in the metal tube. The heating roller 56 is rotationally driven by receiving a driving force from a motor (not shown).
The pressure roller 57 is disposed below the heating roller 56 so as to press the heating roller 56. The pressure roller 57 includes a metal roller shaft and a rubber roller made of a rubber material that covers the roller shaft. The pressure roller 57 is driven according to the rotational drive of the heating roller 56.

In the fixing unit 21, the toner image transferred onto the paper 3 at the transfer position is thermally fixed while the paper 3 passes between the heating roller 56 and the pressure roller 57. The sheet 3 on which the toner image is fixed is conveyed toward a sheet discharge tray 58 formed on the upper surface of the main casing 2.
The paper discharge side conveyance path of the sheet 3 from the fixing unit 21 to the paper discharge tray 58 is folded back to the front side in a substantially U shape from the fixing unit 21. In the discharge side transfer path, a transfer roller 59 is provided in the middle, and a discharge roller 60 is provided at the downstream end.

The sheet 3 thermally fixed in the fixing unit 21 is transported along a transport path from the fixing unit 21 to the paper discharge tray 58 by the transport roller 59, and is discharged onto the paper discharge tray 58 by the paper discharge roller 60.
2. FIG. 2 is a plan view of the scanner unit 19, FIG. 3 is a perspective view of the scanner unit 19 as viewed from obliquely above the rear side, and FIG. 4 is a diagram of obliquely upward front side of the scanner unit 19. It is the perspective view seen from.

The outer casing 22 of the scanner unit 19 is formed by bending a sheet metal, and rises perpendicularly to the bottom plate 61 from a rectangular bottom plate 61 that is longer in the width direction than the front-rear direction and from each edge of the bottom plate 61. The side plate 62 is integrally provided.
The inner casing 23 of the scanner unit 19 is formed by resin molding, and has a container shape integrally including a substantially rectangular bottom plate 63 and a side plate 64 that rises vertically from each end edge of the bottom plate 63. There is no. The inner casing 23 is housed in the outer casing 22, and is provided with three casing fixing screws penetrating through the width direction both ends at the rear end portion of the bottom plate 63 and the width direction substantially central portion at the front end portion of the bottom plate 63. By 65, it is fixed to the bottom plate 61 of the outer casing 22 at three points. Further, the three casing fixing screws 65 are respectively provided at positions where the polygon mirror unit 24 is arranged in a region surrounded by a triangle having each casing fixing screw 65 as a vertex.

  The bottom plate 63 is formed with a beam emission hole 66 through which a laser beam emitted toward the photosensitive drum 30 (see FIG. 1) passes. The beam emission hole 66 is formed in an elongated rectangular shape extending in the width direction from the vicinity of the side plate 64 on one side in the width direction to a position exceeding the width direction center portion at a position slightly behind the center portion in the front-rear direction. ing. As shown in FIG. 1, a passage hole 67 through which the laser beam emitted from the beam emission hole 66 passes is formed in the bottom plate 61 of the outer casing 22 at a position facing the beam emission hole 66. ing.

  Further, the bottom plate 63 supports the width direction rib 68 that reinforces the inner casing 23 and the front and rear direction ribs 69 and 70 as light shielding ribs, the fθ lens support portion 71 for supporting the fθ lens 25, and the folding mirror 26. A folding mirror support 72, a lens / mirror support 73 for integrally supporting the surface tilt correction lens 27 and the bending mirror 28, and two spring supports for supporting a presser spring 83 to be described later. 74 is erected integrally with the bottom plate 63.

The width direction rib 68 rises perpendicularly from the rear edge of the beam emission hole 66 to the bottom plate 63, and extends in the width direction over the entire width of the beam emission hole 66. The front surface of the width direction rib 68 is flush with the rear end surface of the bottom plate 63 that defines the beam emitting hole 66.
The front and rear direction ribs 69 and 70 stand vertically to the bottom plate 63, extend in the front and rear direction so as to connect the middle part of the width direction rib 68 and the rear side plate 64, respectively, and are opposed to each other with a gap in the width direction. Has been. As a result, a rectangular region 75 surrounded by the rear side plate 64, the width direction rib 68 and the front and rear direction ribs 69, 70 is formed behind the beam emission hole 66. This region 75 is formed in the polygon mirror unit 24. Is a polygon placement area for placing

  Further, the width direction rib 68 and the front and rear direction ribs 69 and 70 are formed higher than the position of the upper surface of the polygon mirror 92 described later. A laser beam deflected and scanned by the polygon mirror unit 24 is formed on the width direction rib 68 by cutting out from the upper end thereof in a substantially rectangular shape at a position facing the polygon mirror unit 24 arranged in the polygon arrangement region 75. An exit side opening 76 through which the beam passes is formed. In addition, a laser beam from the light source 85 is formed on the front-rear direction rib 69 on the side close to the light source 85, which will be described later, by notching a slit shape narrower in the front-rear direction from its upper end. Is formed with an incident side opening 77 as a first aperture for entering the polygon arrangement area 75.

The fθ lens support portions 71 are provided as a pair in front of the beam emitting hole 66 so as to be able to support both ends in the width direction of the fθ lens 25, and are opposed to each other with a gap in the width direction. .
The folding mirror support portions 72 are provided in close contact with the front side plate 64, are provided as a pair so as to be able to support both ends of the folding mirror 26, and are opposed to each other with an interval in the width direction. . On the rear surface of the folding mirror support portion 72, an elastic support member 78 formed by bending a sheet metal having spring properties into a substantially C-shaped cross section is provided. The folding mirror 26 is arranged so that the upper end portion thereof is inclined toward the front plate 64 side and leans against the elastic support member 78, and is held from above by the upper end portion of the elastic support member 78. The lower end is elastically supported by contacting the front surface. Further, the folding mirror support portion 72 is integrally formed with a contact portion 79 that is in contact with the upper end portion of the folding mirror 26 from the rear side. Further, the folding mirror support portion 72 is provided with an angle adjusting screw 80 that can be screwed / unscrewed in the vertical direction, and the screw head of the angle adjusting screw 80 is located on one side in the width direction of the folding mirror 26. It is in contact with the end.

  FIG. 5 is a cross-sectional view showing the vicinity of the folding mirror support 72. The attachment angle of the folding mirror 26 (inclination angle with respect to the bottom plate 63) is adjusted by changing the height of the screw head of the angle adjusting screw 80. That is, as shown in FIG. 5A, when the angle adjusting screw 80 is turned to lower the screw head of the angle adjusting screw 80, the contact position of the screw head with the folding mirror 26 is lowered, and the folding mirror 26 is moved. The folding mirror 26 stands by the lower portion of the elastic support member 78 being pushed forward against the elastic force of the elastic support member 78. On the other hand, as shown in FIG. 5B, when the angle adjusting screw 80 is turned to raise the screw head of the angle adjusting screw 80, the contact position of the screw head with the folding mirror 26 increases, and the folding mirror 26. The lower mirror is pushed backward by the elastic force of the elastic support member 78, so that the folding mirror 26 falls down. In this way, adjustment of the mounting angle of the folding mirror 26 is achieved.

  Referring to FIGS. 2 to 4 again, the lens / mirror support part 73 is provided in a pair so as to support the surface tilt correction lens 27 and the bending mirror 28 in front of the beam emission hole 66. In the width direction, they are arranged to face each other with a gap wider than the gap between the pair of fθ lens support portions 71. The lens / mirror support portion 73 is formed at a position higher than the fθ lens support portion 71, and is formed one step higher than the lens receiving portion 81 for receiving the surface tilt correction lens 27, and behind the lens receiving portion 81, A mirror receiving portion 82 for receiving the bending mirror 28 is provided. Thereby, the surface tilt correction lens 27 is disposed at a position higher than the fθ lens 25, and the interval between the light from the polygon mirror unit 24 toward the folding mirror 26 passes between the surface tilt correction lens 27 and the bottom plate 63. Is formed. Further, the bending mirror 28 is disposed at a position higher than the surface tilt correction lens 27.

  The spring support portion 74 is formed in a substantially cylindrical shape, and is disposed opposite to the lens / mirror support portion 73 in the front-rear direction behind the width-direction rib 68. A base end portion of the presser spring 83 is fixed to the upper end portion of each spring support portion 74 by a spring fixing screw 84. The holding spring 83 is formed by bending an elongated sheet metal having spring properties into a substantially crank shape, extends forward from the upper end portion of the spring support portion 74, straddles the upper portion of the beam emission hole 66, and has a tip portion ( The free end portion) presses both ends in the width direction of the bending mirror 28 toward the mirror receiving portion 82 from above.

A light source 85 and a cylindrical lens 86 are provided on the side of the lens / mirror support portion 73 in the width direction.
The light source 85 is disposed in the vicinity of the side plate 64 at a substantially central portion in the front-rear direction. The light source 85 includes a semiconductor laser (light emitting diode) 87 and a collimator lens 88 that converts a laser beam emitted from the semiconductor laser 87 into a parallel light beam.

The cylindrical lens 86 is disposed between the lens / mirror support portion 73 and the light source 85 on the optical path of the laser beam. The laser beam emitted from the light source 85 passes through the cylindrical lens 86, is converged in the sub-scanning direction, and travels toward the polygon arrangement region 75.
In the polygon arrangement area 75, the polygon mirror unit 24 is arranged. Thereby, the inner casing 23 holds the polygon mirror unit 24 on the rear side of the beam emission hole 66, and on the front side of the beam emission hole 66, the fθ lens 25, the folding mirror 26, the surface tilt correction lens 27, The bending mirror 28, the light source 85, and the cylindrical lens 86 are held.

  The polygon mirror unit 24 includes a substantially rectangular substrate 89 whose long side is shorter than the width in the direction along the longitudinal direction of the beam emitting hole 66, a polygon motor 90 disposed on the substrate 89, and a polygon motor. And a polygon mirror 92 as a deflector supported by 90 rotating shafts 91. The polygon mirror unit 24 is arranged in the polygon arrangement region 75 and is fixed to the bottom plate 63 by three board fixing screws 93 penetrating the board 89.

The three substrate fixing screws 93 are arranged such that a straight line L passing through any two substrate fixing screws 93 intersects the longitudinal direction of the beam emission hole 66. Further, the three substrate fixing screws 93 are arranged so that the rotation shaft 91 of the polygon motor 90 is located in a region surrounded by a triangle having each substrate fixing screw 93 as a vertex.
The polygon mirror 92 is formed in a polyhedron (for example, a hexahedron) having a plurality of reflecting surfaces 94, and a rotation shaft 91 is inserted through the center of the polygon mirror 92 and supported by the rotation shaft 91. When the polygon motor 90 is driven, the polygon mirror 92 is rotated at a high speed together with the rotary shaft 91.

  The laser beam that has passed through the cylindrical lens 86 reaches the front-rear direction rib 69, passes through the incident side opening 77 formed in the front-rear direction rib 69, and enters the polygon arrangement region 75. Thus, when the laser beam passes through the incident side opening 77, the width in the main scanning direction (direction parallel to the bottom plate 63) is limited to a sufficiently small width corresponding to the width in the front-rear direction of the incident side opening 77. The excess laser beam in the main scanning direction is blocked by the front-rear direction rib 69.

  The laser beam that has passed through the incident-side opening 77 is incident on the reflecting surface 94 of the polygon mirror 92 rotating at high speed, deflected by being reflected by the reflecting surface 94, and scanned at a constant angular velocity in the main scanning direction. The laser beam thus deflected and scanned is emitted from the emission side opening 76 formed in the width direction rib 68, passes between the surface tilt correction lens 27 and the bottom plate 63, and enters the fθ lens 25.

The fθ lens 25 converts the laser beam scanned at a constant angular velocity by the polygon mirror 92 (polygon mirror unit 24) so as to be scanned at a constant velocity on the surface of the photosensitive drum 30. The laser beam that has passed through the fθ lens 25 is reflected by the folding mirror 26, its optical path is folded back obliquely upward, and enters the surface tilt correction lens 27.
The surface tilt correction lens 27 is a lens for correcting the shift of the scanning position of the laser beam caused by the surface tilt of the reflecting surface 94 of the polygon mirror 92 (inclination with respect to the rotation shaft 91 of the polygon motor 90). The light that has passed through the surface tilt correction lens 27 is reflected by the bending mirror 28, so that the optical path is bent rearward and obliquely downward, and passes through the beam exit hole 66 and the bottom plate 61 of the outer casing 22. The light passes through the holes 67 in order and is irradiated on the surface of the photosensitive drum 30.

  FIG. 6 is a diagram for explaining a more specific arrangement of the fθ lens 25, the light source 85, and the polygon mirror 92. In the scanner unit 19, the fθ lens 25, the light source 85, and the polygon mirror 92 have their reflection surfaces when one reflection surface 94 of the polygon mirror 92 is perpendicular to the optical path of the laser beam incident on the polygon mirror 92. The laser beam is reflected by a reflection surface 94 different from 94, and the reflected laser beam is imaged on the surface of the photosensitive drum 30.

  That is, the laser beam incident on the reflecting surface 94 of the polygon mirror 92 is scanned by the laser beam on the reflecting surface 94 (the incident position) and on the surface of the photosensitive drum 30 (hereinafter referred to as “effective scanning region”). The angle formed with respect to a straight line connecting the center position in the main scanning direction (hereinafter referred to as “scanning center”) is α, and the distance between the scanning center and one end of the effective scanning area in the main scanning direction ( Fθ lens when W is a half of the width of the effective scanning region in the main scanning direction, f is the focal length of the fθ lens 25, and N is the number of reflecting surfaces 94 of the polygon mirror 92. 25, the light source 85 and the polygon mirror 92 are arranged so as to satisfy the following expression (1).

α / 2 + W / (2 · f) −2π / N> 0 (1)
The distance between the position where the laser beam reflected by the reflection surface 94 of the polygon mirror 92 forms an image on the surface of the photosensitive drum 30 and the scanning center is y, and the laser beam reflected by the reflection surface 94 is scanned with the reflection position. When the angle formed with respect to the straight line connecting the center is θ, the relationship of the following equation (2) is satisfied by the characteristics of the fθ lens 25.

y = f × θ (2)
If this distance y is shorter than the distance W from the scanning center to one end of the effective scanning area in the main scanning direction, the laser beam reflected by the reflecting surface 94 of the polygon mirror 92 is irradiated onto the effective scanning area. Become. Therefore, if the following expression (3) is satisfied, when one reflecting surface 94 of the polygon mirror 92 is perpendicular to the optical path of the laser beam incident on the polygon mirror 92, the reflecting surface is different from the reflecting surface 94. The laser beam is reflected at 94, and the reflected laser beam is imaged on the surface of the photosensitive drum 30.

W> y (3)
On the other hand, when the angle formed by the laser beam incident on the reflecting surface 94 of the polygon mirror 92 with respect to the normal line of the reflecting surface 94 is β, the angle θ is
θ = 2 × β−α (4)
It is represented by Moreover, since the angle β is 2π / N, if this is substituted into the above equation (4),
θ = 2 × 2π / N−α (5)
It becomes.

Then, when the above formula (2) and the above formula (5) are substituted into the above formula (3),
W> f × θ = f × (2 × 2π / N−α)
By arranging this, the above formula (1) can be obtained. Therefore, by arranging the fθ lens 25, the light source 85, and the polygon mirror 92 so as to satisfy the above formula (1), the optical path of the laser beam in which one reflecting surface 94 of the polygon mirror 92 is incident on the polygon mirror 92. , The laser beam is reflected by a reflecting surface 94 different from the reflecting surface 94, and the reflected laser beam forms an image on the surface of the photosensitive drum 30. As a result, when one reflecting surface 94 of the polygon mirror 92 is perpendicular to the optical path of the laser beam incident on the polygon mirror 92, the laser beam is reflected by a reflecting surface 94 different from the reflecting surface 94. The laser beam reflected by the reflecting surface 94 can be prevented from returning to the light source 85.

  When the laser beam reflected by the reflecting surface 94 of the polygon mirror 92 returns to the light source 85 (semiconductor laser 87), return light noise is generated, and the oscillation of the semiconductor laser becomes unstable due to the influence of the return light noise. Accordingly, the fθ lens 25, the light source 85, and the polygon mirror 92 are arranged as described above, and the laser beam reflected by the reflecting surface 94 of the polygon mirror 92 is prevented from returning to the light source 85, whereby the light source 85 (semiconductor laser). 87), it is possible to prevent the output of the laser beam from becoming unstable.

  According to the above configuration, the front-rear ribs 69 are arranged between the light source 85 and the polygon mirror unit 24 (polygon mirror 92) in the vicinity of the polygon mirror unit 24. When the beam passes through the incident side opening 77 formed in the front-rear direction rib 69, the width in the main scanning direction is limited to a width corresponding to the width of the incident side opening 77. In this way, the incident side opening 77 formed in the front-rear direction rib 69 for passing the laser beam from the light source 85 toward the polygon mirror unit 24 is used as an aperture for limiting the width of the laser beam in the main scanning direction. As a result, stray light from the polygon mirror unit 24 toward the light source 85 can be effectively blocked. Therefore, even if the rotational speed of the polygon mirror 92 is increased, stray light generated when the laser beam from the light source 85 is incident on the polygon mirror 92 at a time other than the time when the surface of the photosensitive drum 30 is exposed, Incident on the surface, monitor diode (not shown) provided to stabilize the optical output of the semiconductor laser, write position detection sensor (not shown) provided to align the position where the image signal is written to the scanned surface Can be prevented.

  Moreover, since the front-rear ribs 69 are formed integrally with the bottom plate 63 of the inner casing 23, the inner casing 23 and the front-rear ribs 69 can be formed simultaneously by resin molding. Therefore, the manufacturing process can be simplified. Further, since the front-rear ribs 69 are formed integrally with the inner casing 23, the inner casing 23 in the vicinity of the polygon mirror unit 24 can be reinforced. Therefore, the vibration of the inner casing 23 due to the vibration of the polygon mirror unit 24 can be prevented, and the generation of stray light due to such vibration can be prevented.

  Further, stray light is generated so as to be scattered mainly in the main scanning direction along with the deflection and scanning of the laser beam by the polygon mirror 92. Therefore, the incident-side opening 77 formed in the front-rear direction rib 69 passes through the light from the light source. By limiting the width in the main scanning direction, stray light can be effectively prevented. Moreover, since the incident side opening 77 has a shape opened in the sub-scanning direction, the structure of the mold for molding the inner casing 23 can be facilitated, and the productivity can be improved.

  Furthermore, the fθ lens 25, the light source 85, and the polygon mirror 92 are different from the reflection surface 94 when one reflection surface 94 of the polygon mirror 92 is perpendicular to the optical path of the laser beam incident on the polygon mirror 92. The laser beams are arranged so as to be reflected by different reflecting surfaces 94 and the reflected laser beams are imaged on the surface of the photosensitive drum 30. As a result, when one reflecting surface 94 of the polygon mirror 92 is perpendicular to the optical path of the laser beam incident on the polygon mirror 92, the laser beam is reflected by a reflecting surface 94 different from the reflecting surface 94. The laser beam reflected by the reflecting surface 94 can be prevented from returning to the light source 85. Therefore, it is possible to prevent the output of the laser beam from the light source 85 (semiconductor laser 87) from becoming unstable.

The laser printer 1 includes the scanner unit 19 that can prevent the generation of stray light even when the rotational speed of the polygon mirror 92 is increased, so that the speed of the apparatus can be increased. It is possible to prevent stray light from entering the photosensitive drum 30. As a result, a high-quality electrostatic latent image can be formed on the photosensitive drum 30, and formation of a high-quality image can be achieved.
3. Second Embodiment of Scanner Unit FIG. 7 is a perspective view schematically showing a second embodiment of the scanner unit 19. In FIG. 7, parts corresponding to the parts shown in FIG. 2 are denoted by the same reference numerals as in FIG. Further, in the following, detailed description of the parts denoted by the same reference numerals is omitted.

  In the configuration shown in FIG. 7, an aperture 96 as a second aperture having a rectangular diaphragm hole 95 wider than the incident side opening 77 in the main scanning direction is disposed between the light source 85 and the cylindrical lens 86. Has been. The laser beam from the light source 85 passes through the aperture hole 95 of the aperture 96, passes through the cylindrical lens 86, passes through the incident side opening 77, and enters the polygon mirror 92.

According to such a configuration, when the laser beam passes through the aperture hole 95 of the aperture 96, the width of the laser beam in the main scanning direction and the sub scanning direction can be limited. Thus, before the width of the laser beam incident on the polygon mirror 92 in the main scanning direction is limited by the incident side opening 77 of the front-rear direction rib 69, the main scanning direction and the sub-scanning direction of the laser beam by the aperture 96. The width of can be limited. Therefore, the generation of stray light due to the laser beam from the light source 85 hitting the front-rear direction rib 69 and becoming scattered light can be prevented. As a result, stray light can be more reliably prevented from entering the surface of the photosensitive drum 30.
4). Third Embodiment of Scanner Unit FIG. 8 is a perspective view schematically showing a third embodiment of the scanner unit 19. 8, parts corresponding to the parts shown in FIG. 2 are denoted by the same reference numerals as in FIG. Further, in the following, detailed description of the parts denoted by the same reference numerals is omitted.

  In the configuration shown in FIG. 8, an aperture 98 as a third aperture having a rectangular diaphragm hole 97 long in the main scanning direction is disposed between the polygon mirror 92 and the fθ lens 25. Then, the laser beam deflected and scanned by the polygon mirror 92 passes through the aperture hole 97 of the aperture 98, and at this time, the width in the sub-scanning direction is limited and then enters the fθ lens 25.

According to such a configuration, the width of the laser beam incident on the polygon mirror 92 in the main scanning direction can be limited by the incident side opening 77 of the front-rear direction rib 69, and deflected by the polygon mirror 92 by the aperture 98. In addition, the width of the scanned laser beam in the sub-scanning direction can be limited. By limiting the width of the laser beam in the sub-scanning direction, stray light generated near the polygon mirror 92 and its vicinity can be more reliably prevented from entering the surface of the photosensitive drum 30.
5. Fourth Embodiment of Scanner Unit FIG. 9 is a perspective view schematically showing a third embodiment of the scanner unit 19. 8, parts corresponding to the parts shown in FIG. 2 are denoted by the same reference numerals as in FIG. Further, in the following, detailed description of the parts denoted by the same reference numerals is omitted.

In each of the above-described embodiments, the incident-side opening 77 is formed by cutting out from the upper end of the front-rear rib 69 into a narrow slit shape in the front-rear direction. However, in the configuration shown in FIG. The opening 77 is a rectangular through hole formed through the front-rear direction rib 69.
According to such a configuration, the incident-side opening 77 can limit the width of the laser beam in the main scanning direction and the sub-scanning direction.

1 is a side sectional view showing an embodiment of a laser printer as an image forming apparatus of the present invention. It is a top view of the scanner part shown in FIG. FIG. 2 is a perspective view of the scanner unit shown in FIG. FIG. 2 is a perspective view of the scanner unit shown in FIG. It is sectional drawing of the vicinity of the folding | turning mirror support part shown in FIG. FIG. 3 is a diagram for explaining a more specific arrangement of an fθ lens, a light source, and a polygon mirror shown in FIG. 2. FIG. 6 is a perspective view schematically showing a second embodiment (a mode in which an aperture is provided between a light source and a cylindrical lens) of a scanner unit. FIG. 10 is a perspective view schematically showing a third embodiment (a mode in which an aperture is provided between a polygon mirror and an fθ lens) of a scanner unit. FIG. 10 is a perspective view schematically illustrating a fourth embodiment (an aspect in which an incident side opening is a rectangular through hole formed by penetrating a front-rear direction rib) of a scanner unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser printer 19 Scanner part 23 Inner casing 25 f (theta) lens 26 Folding mirror 27 Face tilt correction lens 28 Bending mirror 30 Photosensitive drum 37 Drum main body 69 Front-back direction rib 77 Incident side opening 85 Light source 92 Polygon mirror 94 Reflecting surface 96 Aperture 98 Aperture

Claims (10)

In an optical scanning device that scans a surface to be scanned with light,
A light source;
A deflector for deflecting and scanning light from the light source in the main scanning direction;
Provided between the light source and the deflector in the vicinity of the deflector and having a first aperture for passing light from the light source and limiting the width of the light. An optical scanning device comprising: a light shielding rib for shielding.   The optical scanning device according to claim 1, wherein the first aperture limits a width of light from the light source in a main scanning direction.   3. The optical scanning device according to claim 1, wherein the first aperture limits a width in a sub-scanning direction of light from the light source. 4.   The light according to claim 2, further comprising a second aperture that is disposed between the light source and the light shielding rib and restricts a width in a sub-scanning direction of light from the light source. Scanning device.   The second aperture is formed wider than the first aperture in the main scanning direction, allows light from the light source to pass therethrough, and limits the width of the light in the main scanning direction. The optical scanning device according to claim 4. An fθ lens provided between the deflector and the surface to be scanned and configured to scan the light deflected and scanned by the deflector at a constant speed on the surface to be scanned;
A third aperture disposed between the deflector and the fθ lens and configured to limit a width in a sub-scanning direction of light deflected and scanned by the deflector; The optical scanning device according to claim 1. A resin frame that holds the light source and the deflector;
The optical scanning device according to claim 1, wherein the light shielding rib is formed integrally with the frame. A scanning optical system for imaging light deflected and scanned by the deflector on the scanned surface;
The deflector is a polygon mirror that has a plurality of reflecting surfaces that reflect light from the light source and is rotated around a rotation axis passing through the center thereof.
The light source, the scanning optical system, and the polygon mirror have incident light on the reflection surface different from the reflection surface when one of the reflection surfaces is perpendicular to an optical path of incident light incident on the polygon mirror. The optical scanning device according to claim 1, wherein the optical scanning device is arranged so that the reflected light is reflected and the reflected light is imaged on the surface to be scanned. The scanning optical system includes an fθ lens for causing the light deflected and scanned by the deflector to scan the scanned surface at a constant speed,
The light source, the scanning optical system, and the polygon mirror are:
α / 2 + W / (2 · f) -2π / N> 0
(Where α is a line formed by connecting a light reflection position on the reflection surface and a center position in the main scanning direction of a region where light is scanned on the surface to be scanned, and light incident on the reflection surface) W is half of the width in the main scanning direction of the region where light is scanned on the surface to be scanned, f is the focal length of the fθ lens, and N is the angle of the reflecting surface Number.)
The optical scanning device according to claim 8, wherein the optical scanning device is arranged so as to satisfy the inequality. An optical scanning device according to any one of claims 1 to 9,
An image forming apparatus comprising: a photosensitive member on which an electrostatic latent image is formed by scanning light with the optical scanning device.

Images