JP2003029183A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize compact size, reduction in cost and simplification of the assembling work of an optical scanner by reducing the number of parts in providing two optical means, which are to be arranged in between a rotary polygon mirror and a surface to be scanned. SOLUTION: An fθ lens 122 for changing a beam 105 emitted from parallel beams to contraction light for forming an image to a specified size on the surface of a photoreceptor drum 200, in the scanning surface direction and changing constant angular velocity motion to constant speed motion in the scanning surface direction on the surface of the drum 200, and a toroidal lens 126 correcting the plane tilt of the beam 105 and also forming the image in the specified size on the surface of the drum 200 from diffused light, in a direction orthogonal to the scanning surface direction, are provided in the optical path of the emitted beam leading to the drum 200 from a polygon mirror 120. The fθ lens is constituted of a single cylindrical lens, and by eliminating a concave lens, number of parts is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device which is used in an image forming apparatus for forming an image by an electrophotographic method and which scans a surface to be scanned with a light beam emitted from a light beam irradiating means.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine for performing electrophotographic image formation, an image modulated by image data from an optical scanning device is applied to a surface of a photoconductor to which a single-polarity charge is uniformly applied. Light (light beam) is irradiated to form an electrostatic latent image on the surface of the photoconductor (scanned surface) by photoconductive action.
The optical scanning device drives a light beam irradiating means including a light source such as a semiconductor laser based on image data to form an image of the image light radiated from the light beam irradiating means on the surface of the photoconductor. Are scanned in the main scanning direction. For this reason, the optical scanning device is provided with a rotary polygonal mirror whose peripheral surface is composed of a plurality of reflecting surfaces, and an fθ lens which converts a constant angular velocity motion of light into a constant velocity motion. While rotating, the image light emitted from the light beam irradiating means is distributed to each reflecting surface of the rotating polygon mirror that moves at a constant angular velocity, and the image light reflected on each reflecting surface of the rotating polygon mirror is converted into a uniform velocity motion. It is converted and irradiated on the surface of the photoconductor.

As such an optical scanning device, there is a so-called overfill type optical scanning device in which an incident beam emitted from a light beam irradiating means is simultaneously incident on a plurality of reflecting surfaces of a rotary polygon mirror. For example, in Japanese Unexamined Patent Application Publication No. 11-218702, as shown in FIG. 7, a light beam emitted from a light beam irradiating means 61 is passed through a lower side of a central portion of an fθ lens 62 in a scanning direction to form a rotary polygon mirror. 63 is distributed to the reflecting surface 63a of the rotary polygon mirror 63, and the reflected light of the light beam on the reflecting surface 63a of the rotary polygon mirror 63 is passed from the upper side of the central portion of the fθ lens 62 in the scanning direction to the scanned surface 64 via the cylindrical mirror 66. A configuration for distributing light is disclosed.

The overfill type optical scanning device has a higher transmission light rate of the optical system than the underfill type optical scanning device in which the incident beam is incident on only a part of a single reflecting surface of the rotating polygon mirror. In order to compensate for the lowness and to reflect a part of the incident beam to the surface to be scanned, a higher-power light beam irradiating means is required. Although there is a drawback that the amount of light tends to be non-uniform, it is possible to reduce the area of the reflecting surface required to form a beam spot of a certain size on the surface to be scanned, and to use the rotating polygon mirror of the same diameter to reflect more light. Since the surface can be formed and the rotational speed of the rotary polygon mirror can be made relatively low, there is an advantage that the motor for generating the rotational force of the rotary polygon mirror can be downsized.

[0005]

However, in the overfill type optical scanning device, it is necessary to increase the number of reflecting surfaces of the rotary polygon mirror to increase the scanning angle in order to improve the scanning efficiency. To obtain proper optical characteristics,
Between the rotary polygon mirror and the surface to be scanned, three optical means, that is, two fθ lenses consisting of a concave lens and a cylindrical lens and one cylindrical mirror are arranged, and the cost increases due to an increase in the number of parts. In addition, there is a problem that the adjustment work during assembly becomes complicated. Further, since the outgoing beam passes through the three optical means, it is difficult to resinize the fθ lens in order to prevent a significant decrease in the amount of light. Even if the fθ lens can be resinized, a special coat is required and a sufficient cost reduction is realized. I can't.

The object of the present invention is to provide two optical means to be arranged between the rotary polygon mirror and the surface to be scanned,
It is an object of the present invention to provide an overfill type optical scanning device which can realize downsizing of the device by reducing the number of parts, cost reduction and simplification of assembly work.

[0007]

The present invention has the following structure as means for solving the above problems.

(1) Optical scanning in which an incident beam emitted from a light beam irradiating means is simultaneously incident on a plurality of reflecting surfaces of a rotary polygon mirror, and a surface to be scanned is scanned by an outgoing beam reflected by the reflecting surface of the rotary polygon mirror. In the device, in the optical path of the outgoing beam between the rotating polygon mirror and the surface to be scanned, a cylindrical shape that forms the outgoing beam into an image on the surface to be scanned in the scanning plane direction and converts the uniform angular velocity motion of the outgoing beam into a uniform velocity motion. It is characterized in that a lens and a toroidal lens for forming an image of an outgoing beam on a surface to be scanned in a direction orthogonal to the scanning surface are arranged.

In this structure, the outgoing beam reflected on the reflecting surface of the rotary polygon mirror is scanned by the two optical means, the cylindrical lens and the toroidal lens, which are arranged between the rotary polygon mirror and the surface to be scanned. The image is formed on the surface to be scanned in the direction orthogonal to the scanning direction and the direction of the scanning surface, and moves at the same speed in the scanning direction. Therefore, it is not necessary to provide a concave lens between the rotary polygon mirror and the surface to be scanned in order to scan the surface to be scanned at a constant speed by the emitted beam, and the number of parts is reduced.

(2) Part of the cylindrical lens is located in the optical path of the incident beam between the light beam irradiation means and the rotary polygon mirror.

In this structure, the incident beam emitted from the light beam emitting means passes through a part of the cylindrical lens and is distributed to the rotary polygon mirror. Therefore, the incident beam of diffused light emitted from the light beam emitting means is
The emitted beam is collimated in the scanning plane direction by using a part of a cylindrical lens that forms an image on the surface to be scanned and is distributed to the rotary polygon mirror.

(3) The cylindrical lens is characterized by having a refractive index of 1.7 to 1.923.

In this structure, the refractive index of the cylindrical lens is 1.7, which is a physical limit of 1.923.
To be done. Therefore, the outgoing beam of parallel light reflected by the reflecting surface of the rotary polygon mirror in the scanning surface direction is reliably imaged on the surface to be scanned without causing an excessive curvature of field due to the cylindrical lens.

[0014]

1 is a diagram showing a configuration of a main part of an image forming apparatus to which a laser scanning unit which is an optical scanning device according to an embodiment of the present invention is applied. The image forming apparatus 1 rotatably supports a cylindrical photosensitive drum 200, and a charger 201, a developing unit 202, a transfer unit 203, and a cleaner 204 are provided around the photosensitive drum 200 so as to surround the photosensitive drum 200. Are arranged in this order along the direction of rotation. The surface of the photoconductor drum 200 is the surface to be scanned according to the present invention, and is located from the position facing the charger 201 in the rotation direction of the photoconductor drum 200 to the developing unit 2.
The laser beam emitted from the laser scanning unit 22 is exposed up to the position facing the laser beam 02. The image forming apparatus 1 includes a sheet feeding cassette 210 to a sheet feeding roller 211.
A transport path for the sheets P fed one by one is configured by the fixing device 23 that heats and pressurizes the paper P on the downstream side of the transport path between the photoconductor drum 200 and the transfer unit 203. Are arranged.

During image formation in the image forming apparatus 1,
The photoconductor drum 200 rotates at a predetermined speed, and the charger 20
By 1, the surface of the photosensitive drum 200 is uniformly charged with a single polarity. Thereafter, an emission beam, which is image light of laser light modulated by the laser scan unit 22 based on image data, is exposed and irradiated onto the surface of the photoconductor drum 200, and the surface of the photoconductor drum 200 is photoconductively activated. An electrostatic latent image is formed. Further, the developer is supplied from the developing unit 202 to the surface of the photosensitive drum 200 on which the electrostatic latent image is formed, and the electrostatic latent image is visualized as a developer image.

Prior to the rotation of the photosensitive drum 200, one sheet P is fed from the sheet feeding cassette 210,
The photosensitive drum 20 is synchronized with the rotation of the photosensitive drum 200.
0 and the transfer unit 203. Here, the transfer device 2
The developer image carried on the surface of the photoconductor drum 200 by 03 is transferred to the surface of the paper P, and the paper P on which the developer image is transferred is heated and pressed by the fixing device 23 to form a developer image. It is melted and firmly fixed on the surface of the paper P. On the other hand, the surface of the photosensitive drum 200 that has passed the position facing the transfer unit 203 is subjected to the removal of the residual developer by the cleaner 204, and then is repeatedly subjected to the image forming process including the steps of charging, exposing, developing and transferring. used.

FIG. 2 is a perspective view showing the structure of the laser scan unit. The laser scanning unit 22 which is the optical scanning device of the present invention includes a beam unit 111 which is a light beam irradiation unit, a polygon mirror 120 which is a rotary polygon mirror, and the beam unit 111 to the polygon mirror 1.
20 and an incident optical system 101 arranged between the two, and the photosensitive drum 2 which is a surface to be scanned from the polygon mirror 120.
The output optical system 102 is arranged so as to extend to the surface of 00.

The beam unit 111 includes a semiconductor laser 112 that emits a laser beam that is an incident beam 103 that is modulated based on image data, a collimator lens 113 that converts the incident beam 103 into parallel light, and an incident beam 1.
03 is a concave lens 114 that expands in the scanning direction, and a plate-shaped aperture plate 115 in which a rectangular aperture 115 is formed. The incident optical system 101 includes a cylindrical lens 116, an incident folding mirror 117, and an fθ lens 1.
A part of 22 is arranged.

The output optical system 102 is a polygon mirror 12.
The outgoing beam 105 reflected by the reflection surface 120a of 0
Is directed to the surface of the photosensitive drum 200, and the outgoing beam 105 is imaged so that the beam spot 108 (108a to 108c) when the surface of the photosensitive drum 200 is exposed becomes a predetermined size. 105
On the surface of the photosensitive drum 200
It is moved at a constant speed in the main scanning direction (Y direction) parallel to the 0 rotation axis. Therefore, the emission optical system 102 includes the fθ lens 122, the emission folding mirror 124, the emission folding mirror 125, and the toroidal lens 126, which are the cylindrical lenses of the present invention, in the optical path of the emission beam from the polygon mirror 120 to the photosensitive drum 200. Are arranged in this order.

The fθ lens 122 is a polygon mirror 12
The output beam 105 reflected as parallel light in the scanning surface direction on each of the 0 reflection surfaces 120a is imaged in a predetermined size on the surface of the photosensitive drum 200 in the scanning surface direction, and the polygon mirror 120 that rotates at a constant speed is formed. The outgoing beam 105 that moves at a constant angular velocity in the scanning surface direction (Y direction) by being reflected by each of the plurality of reflecting surfaces 120a formed on the surface causes the outgoing beam 105 on the surface of the photosensitive drum 200 at a constant speed in the scanning surface direction. Polarize to move. Further, the toroidal lens 126 is used for the output beam 10
5, the polygon mirror 120
In each of the reflection surfaces 120a, the outgoing beam 105 reflected as diffused light in the direction orthogonal to the scanning surface direction is imaged in a predetermined size on the surface of the photosensitive drum 200 in the direction orthogonal to the scanning surface direction.

The outgoing beam 105 is emitted from the polygon mirror 12.
By the rotation of 0, the beam spot position 108a, the beam spot position 108b, and the beam spot position 108c on the surface of the photosensitive drum 200 in the scanning plane direction (Y direction).
Move in this order. While the outgoing beam 105 periodically and repeatedly moves in the main scanning beam region 107 between the image end position 107a and the image end position 107b used for image formation on the surface of the photosensitive drum 200,
The photoconductor drum 200 rotates at a predetermined speed. Therefore, the outgoing beam 105 is emitted from the photosensitive drum 20 in each cycle.
Since different positions in the circumferential direction on the surface of No. 0 are irradiated, in order to form an image accurately based on the image data, the writing start position of the main scanning beam region 107 for each cycle is the photosensitive drum. It is necessary to synchronize the output timing of the image data for each line with respect to the semiconductor laser 112 in each cycle so that they coincide with each other in the axial direction of 200.

Therefore, of the outgoing beam 105 outside the main scanning beam region 107, the main scanning beam region 1 in the scanning direction
The light emitted before 07 is synchronized with the detection beam 106.
As (106a to 106c), after passing through the fθ lens 122, the synchronous detection sensor 127 is irradiated through the synchronous folding mirror 126, and based on the light reception timing of the synchronous detection beam 106 by the synchronous detection sensor 127, line by line to the semiconductor laser 112. The output timing of the image data is determined.

In the above structure, the output folding mirrors 124 and 125 are not essential, but are arranged according to the positional relationship between the laser scan unit 22 and the photosensitive drum 200. Therefore, when the fθ lens 122, the toroidal lens 126, and the photosensitive drum 200 are arranged in a straight line in the emission direction of the emission beam 105 reflected on the reflection surface 120a of the polygon mirror 120, the emission folding mirrors 124, 1 are arranged.
25 can be omitted.

FIGS. 3A and 3B are a plan view and a side view showing states of an incident beam and an outgoing beam in the laser scan unit. Beam unit 111
In the concave lens 1 after being irradiated from the semiconductor laser 112, it is converted into parallel light by the collimator lens 113.
The incident beam 103, which has been expanded in the scanning direction by 14 and whose light amount distribution has been adjusted by the aperture plate 115, has its traveling direction changed by the incident folding mirror 117 and passes through the end of the fθ lens 122 from obliquely downward to upward. In the meantime, diffused light is converted into parallel light in the scanning plane direction, and the polygonal mirror 120 is irradiated on the central portion in the height direction of the reflecting surface 120a.

The outgoing beam 105 reflected by the reflecting surface 120a of the polygon mirror 120 is reflected by the polygon mirror 1
The light beam passes through the fθ lens 122 from obliquely downward to upward while moving in the scanning plane at an equal angular speed according to the rotation speed of 20. During this time, the emitted beam 105 is converted from parallel light in the scanning surface direction into contracted light that forms an image on the surface of the photoconductor drum 200 to a predetermined size, and at the same time, on the surface of the photoconductor drum 200 (scanning surface direction). Body drum 2
(00 axis direction: Y direction) is polarized from a uniform angular velocity motion to a constant velocity motion. After that, the outgoing beam 105 is changed in traveling direction by the outgoing folding mirrors 124 and 125 and passes through the toroidal lens 126, while the outgoing beam 105 is diffused from the diffused light to the photosensitive drum 200 in a direction orthogonal to the scanning surface direction (X direction). It is converted into contracted light that forms an image of a predetermined size on the surface and is irradiated onto the surface of the photosensitive drum 200.

As described above, in the laser scan unit 22 according to the embodiment of the present invention, the output beam 105 is converted from the parallel light in the scanning plane direction by the fθ lens 122 which is a single cylindrical lens.
00 is converted into contracted light which forms an image of a predetermined size on the surface of the photosensitive drum 200, and is polarized from the uniform angular velocity motion to the constant velocity motion in the scanning surface direction on the surface of the photosensitive drum 200. In addition, the toroidal lens 126 allows the emitted beam 105
In the direction orthogonal to the scanning plane direction is converted from diffused light into contracted light that forms an image of a predetermined size on the surface of the photosensitive drum 200.

Therefore, the optical specifications of the curvature cy in the Y direction, the curvature cx in the X direction, the spacing d, the refractive index n, and the dispersion value νd on each surface of the fθ lens 122 and the toroidal lens 126 are shown in FIG. It is set as shown in. Here, the first surface and the second surface are the flat surface 122 a of the fθ lens 122 on the polygon mirror 120 side and the photosensitive drum 200.
Side cylindrical surface 122b, the third surface and the fourth surface
The surface is the polygon mirror 120 of the toroidal lens 126.
The aspherical surface 126a on the side and the toroidal surface 126b on the side of the photosensitive drum 200. In addition, the values shown in FIG. 4 have a focal length in the main scanning direction of 360 mm and the toroidal lens 126.
In this example, the distance between the surface (fourth surface) 126b on the side of the photosensitive drum 200 and the surface of the photosensitive drum 200 is 150 mm.

Each surface 12 of the toroidal lens 126
6a and 126b are both aspherical surfaces, and are shown in FIG.
In the YZ plane shown, the curve shown in FIG.
Definition for an aspheric surface rotated by z = ch²/ [1+ {1- (k + 1) c²h²}^1/2]
+ A1h^Four+ A2h⁶+ A3h⁸+ A4h^Ten h = (x²+ Y²)^1/2 k = 0 At the aspherical surface 126a and the toroidal surface 126b.
For each, set the aspherical coefficient as shown in Figure 5.
is doing. In the above equation, c is the curvature.

In the laser scanning unit 22 of the present invention, in particular, the emitted beam 105 is converted from parallel light in the scanning plane direction into contracted light which forms an image of a predetermined size on the surface of the photoconductor drum 200, and at the same time, the photoconductor drum is converted. Since the fθ lens 122 that polarizes the uniform angular velocity motion to the constant velocity motion in the scanning surface direction on the surface of 200 is configured by only a single cylindrical lens without the conventional concave lens, the refractive index of the fθ lens 122 is a problem. Becomes That is, as shown in FIGS. 6A and 6B, when the refractive index n of the fθ lens 122 is less than 1.70, the main scanning direction (Y direction) and the sub direction of the outgoing beam 105 on the surface of the photoconductor drum 200. 3m field curvature in the scanning direction (X direction)
It becomes too large as m or more, and accurate image formation based on image data cannot be performed. On the other hand, the fθ lens 1
By setting the refractive index n of 22 to 1.70 or more, the field curvature of the outgoing beam 105 on the surface of the photoconductor drum 200 in the main scanning direction (Y direction) and the sub scanning direction (X direction) is within the allowable range. can do.

As described above, by setting the refractive index n of the single cylindrical lens forming the fθ lens 122 to 1.70 or more, the concave lens in the conventional structure can be eliminated, and the polygon mirror 120 can be used. The number of optical means to be arranged in the emission optical system 102 up to the photoconductor drum 200 can be reduced to two, and the device can be downsized and the cost can be reduced. Further, the adjustment of the initial position of each optical means is simplified, and the assembling work of the device can be facilitated.

The upper limit of the refractive index of the material constituting the lens is physically 1.923, and the lower limit is 1.70.
In consideration of the above, the refractive index n of the fθ lens 122 inevitably falls within the range of 1.7 to 1.923.

[0032]

According to the present invention, the following effects can be obtained.

(1) Two of a cylindrical lens and a toroidal lens arranged between the rotary polygon mirror and the surface to be scanned.
By the optical means of the sheet, the outgoing beam reflected by the reflecting surface of the rotary polygon mirror is imaged on the surface to be scanned in the scanning surface direction and the direction orthogonal to the scanning surface direction, and is moved at a constant speed in the scanning direction. In order to scan the surface to be scanned at a constant speed by the outgoing beam, it is not necessary to provide a concave lens between the rotary polygon mirror and the surface to be scanned, the number of parts can be reduced, the apparatus can be downsized, and the cost can be reduced. It is possible to simplify the assembly work.

(2) An incident beam of diffused light emitted from the light beam irradiating means by distributing the incident beam emitted from the light beam irradiating means to the rotary polygon mirror through a part of the cylindrical lens. Can be made parallel to the scanning surface direction using a part of the cylindrical lens that forms the outgoing beam on the surface to be scanned, and can be distributed to the rotary polygon mirror, and it is necessary to provide a dedicated cylindrical lens for the incoming beam. Therefore, the number of parts can be further reduced.

(3) By setting the refractive index of the cylindrical lens from 1.7 to the physical limit of 1.923, an outgoing beam of parallel light in the scanning plane direction reflected by the reflecting surface of the rotary polygon mirror Can be reliably imaged on the surface to be scanned in the scanning surface direction by the cylindrical lens, and the concave lens can be reliably excluded from between the rotary polygon mirror and the surface to be scanned.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of an image forming apparatus to which a laser scanning unit which is an optical scanning device according to an embodiment of the present invention is applied.

FIG. 2 is a perspective view showing a configuration of the laser scan unit.

3A and 3B are a plan view and a side view showing states of an incident beam and an outgoing beam in the laser scan unit.

FIG. 4 is a diagram showing an example of optical specifications of each surface of an fθ lens and a toroidal lens in the laser scan unit.

FIG. 5 is a diagram showing an example of other optical specification values on each surface of the toroidal lens in the laser scan unit.

FIG. 6 is a diagram showing the relationship between the refractive index of the fθ lens used in the laser scan unit and the field curvature on the surface of the photosensitive drum.

FIG. 7 is a diagram showing a configuration of a conventional optical scanning device.

[Explanation of symbols]

1-image forming apparatus 22-Laser scanning unit (optical scanning device) 103-incident beam 105-Exit Beam 111-Beam unit (light beam irradiation means) 112-semiconductor laser 120-Polygon mirror (rotating polygon mirror) 120a-reflection surface 122-fθ lens (cylindrical lens) 126-Toroidal lens 200-photosensitive drum (scanned surface)

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C362 BA04 BA84 BA86 BB03 BB22                 2H045 AA01 BA02 CA03 CA33 CA54                       CA67 CB14                 2H087 KA08 KA19 LA22 PA02 PA17                       PB02 RA07 RA08 RA42                 5C072 AA03 BA01 BA02 BA20 HA01                       HA08 HA13

Claims (3)

[Claims] 1. An optical scanning device in which an incident beam emitted from a light beam irradiating means is simultaneously incident on a plurality of reflecting surfaces of a rotary polygon mirror, and a surface to be scanned is scanned by an outgoing beam reflected by the reflecting surfaces of the rotary polygon mirror. , In the optical path of the outgoing beam between the rotating polygon mirror and the surface to be scanned,
A cylindrical lens that forms the outgoing beam on the surface to be scanned in the scanning plane direction and converts the uniform angular velocity motion of the outgoing beam into a uniform velocity motion, and a toroidal that forms the outgoing beam on the surface to be scanned in the direction orthogonal to the scanning plane. An optical scanning device characterized in that a lens is disposed. 2. The optical scanning device according to claim 1, wherein a part of the cylindrical lens is located in an optical path of an incident beam between the light beam irradiation means and the rotary polygon mirror. 3. The optical scanning device according to claim 1, wherein the cylindrical lens has a refractive index of 1.7 to 1.923.