JPH09127443A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which increases the image forming speed without increasing the rotating speed of an optical deflector. SOLUTION: This device has faces to be scanned on bath sides of a single optical deflector 2 and scans these faces while making modulated beams SL and SR incident on deflecting faces of the optical deflector 2 facing the faces to be scanned. An intersection T of virtual extensions of incident beams SL and SR is off a center line (y) of the optical deflector 2 parallel with faces to be scanned and to one side of this line.

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, and more particularly to a deflecting surface of an optical deflector which has a surface to be scanned on both sides of a single optical deflector and which faces the surface to be scanned. The present invention relates to an optical scanning device that performs optical scanning while causing a modulated beam to enter.

[0002]

2. Description of the Related Art Conventionally, a surface to be scanned is arranged on both sides of a single optical deflector, and a modulated beam is incident on a deflecting surface of the optical deflector facing the surface to be scanned. Optical scanning devices that perform scanning are well known. In order to form an image forming apparatus using such an optical scanning device and form a color image, three colors of yellow, magenta, and cyan, or four colors obtained by adding black to these are exposed on the photoconductor. It takes time to form an image because it needs to be developed.
It is desired to reduce the image forming time.

[0003]

However, in order to increase the speed of image formation, it is necessary to increase the scanning speed of the optical deflector that optically scans the photoconductor, and the rotational speed of the optical deflector is mechanically increased. Although it has been attempted to increase the cost, there is a problem that noise, vibration, power consumption increase and cost increase. It is also possible to increase the number of faces of the polygon mirror without increasing the speed to substantially increase the speed of scanning, but in this case, the reflecting surface becomes narrower, and the light beam of the required thickness becomes the edge of the reflecting surface. However, there is a problem that everything cannot be reflected.

In order to solve such a problem, it is conceivable to make the reflecting surface large by enlarging the polygon mirror. However, the optical system becomes large and the rotating motor itself requires a large motor, resulting in an increase in cost. There is a problem. Therefore, there is a demand for an optical scanning device that increases the image forming speed without increasing the rotation speed of the optical deflector.

In view of the above circumstances, an object of the present invention is to provide an optical scanning device which increases the image forming speed without increasing the rotational speed of the optical deflector. Another object of the present invention is to provide an optical scanning device which is downsized and whose manufacturing cost is reduced.

[0006]

The optical scanning device according to the present invention is characterized in that the surface to be scanned is arranged on both sides of a single optical deflector, and the light is opposed to the surface to be scanned. In an optical scanning device that performs optical scanning while making a modulated beam incident on the deflecting surface of a deflector, an intersection point that intersects a virtual extension line of the incident beam must intersect on a center line parallel to a scanned surface of the optical deflector. Instead, it was configured to be located on that side.

Further, it is preferable that the respective incident beams are configured so as to enter the respective incident surfaces at different incident angles. Further, it is preferable that the optical deflector is configured by a polygon mirror, and the virtual extension lines intersect each other on the downstream side in the rotation direction from the center line of the optical deflector.

As shown in FIG. 2, the angle formed by the laser beam SL and the center line K connecting the widthwise centers of the recording media on the left and right sides is defined as the incident angle θL,
The angle formed by the center line K and the laser beam SR is the incident angle θR.
And θL> θR, the laser beam beam and the virtual extension lines SL ′ and SR ′ of SR intersect at the point T on the left side of the center line y.

As shown in FIG. 4, θL (62 °)> θR
When set to (49 °), the laser beam to the polygon mirror 2 takes the incident light path and the reflected light path shown in FIG. Then, the laser incident beam SL is reflected by a BD (beam detector) sensor that starts scanning from one end of the recording medium on the left side shown in FIG. The distance ε2L between the intersection M1 of the reflecting surfaces 2f1 and 2a1 and the axis of the incident light SL, which is indicated by a dotted line when reflected as the light SL1, and the reflected light SL3 in which the laser incident beam SL is directed to the other end of the recording medium. The distance ε1L between the intersection M6 of the reflecting surfaces 2f3 and 2e3 indicated by the chain double-dashed line and the axis of the incident light SL can be set to be equal.

Further, the laser incident beam S is applied to the sensor for detecting the scanning start of the scanning line, which starts scanning from one end to the other end of the recording medium on the right side shown in FIG. 3B.
A reflecting surface 2 indicated by a dotted line in which R reflects as reflected light SR1
A distance ε2R between the intersection M3 of b1 and 2c1 and the axis of the incident light SR, and a reflecting surface 2a3 indicated by a chain double-dashed line that reflects the laser incident beam SR as reflected light SR3 traveling toward the other end of the recording medium. The interval ε1R between the intersection M2 of 2c3 and the axis of the incident light SR can be set to be equal.

Therefore, if the interval ε2L and the interval ε1L corresponding to the recording medium on the left side are set to be equal and the half of the laser beam is designed to fit within the interval ε, the reflecting surface of the polygon mirror can be used efficiently. be able to. In addition, the interval ε2R and the interval ε corresponding to the recording medium on the right side
If 1R is set to be equal and the design is such that half of the laser beam is within the interval ε, the reflecting surface of the polygon mirror can be used efficiently.

Therefore, by setting the incident angle of the laser beam in the above condition, the laser beam is not chipped at the end of the recording medium, the reflecting surface area of the polygon mirror can be efficiently set, and the outer diameter can be set. The number of reflective surfaces can be increased without increasing the size.
The image forming time can be shortened.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.

FIG. 1 is an external view of an image forming apparatus to which the present invention is applied, FIG. 2 is a view showing an embodiment of an optical scanning device according to the present invention, and FIG. 3 is a diagram for explaining the operation of the present invention. Figure, Figure 4
Is a graph showing the relationship between the incident angle ε and the incident position ε, FIG. 5 is an explanatory diagram for deriving the incident position ε, and FIG. 6 is
7A and 7B are diagrams for explaining the problem, and FIG. 7 is a diagram for explaining the problem.

An image forming apparatus applied to the present invention is shown in FIG.
As shown in FIG. 3, the light beams from the laser beams 5A and 5B are passed through the mirrors 4, 6, 7 and 8 by the optical scanning system 1 including the polygon mirror 2, the lens systems 3A and 3B, and the like, and the photosensitive drum 9A. And 9B form an electrostatic latent image. These photosensitive drums 9A and 9B are provided with chargers 23A and 23B for charging the photosensitive drums and cleaning mechanisms 24A and 24B for removing residual toner on the photosensitive drums.

The surfaces of the photosensitive drums 9A and 9B are in contact with the intermediate transfer sheet 26. The intermediate transfer sheet 26 is a resistor having a volume resistivity of 10 ¹⁰ to 10 ¹⁴ Ωcm in a medium resistance region and a thickness of 150 μm. It is molded with a certain amount of polycarbonate, polyimide, polyether ether ketone, or the like.

The photosensitive drum 9A is further provided with a developing device 10A for black toner and a developing device 10B for magenta toner, which are developing devices on the upstream side.
B is provided with a developing device 10C for yellow toner and a developing device 10D for cyan toner, which are developing devices on the subsequent stage side. These developing devices include shafts 22A, 22B, 22C,
22D, the cam shafts 25A, 25 are rotatable by 22D, are urged clockwise by means (not shown), and are rotatable forward and backward by a cam shaft drive mechanism (not shown).
The positions are regulated by B, 25C, and 25D, respectively.

A cam shaft 25A for regulating the position of the developing device 10A
Provides a cam surface by cutting a cylinder into a half-moon shape in cross section. When the circumferential surface of the cam shaft 25A and the contact surface of the developing device 10A are in contact with each other, the developing roller and the photosensitive drum 9A are separated from each other. The developing roller and the photosensitive drum 9A are configured to come close to each other when they are separated by the maximum distance and the abraded surface of the cam shaft 25A and the abutting surface of the developing device 10A face each other to a developable state.

Similarly to 25A, the cam shaft 25B for regulating the position of the developing device 10B has a circular surface and a cut surface formed by cutting a cylinder in a semicircular cross section, and the circumferential surface of the cam shaft 25B. And the contact surface of the developing device 10B are in contact with each other, the developing roller and the photosensitive drum 9A are separated by the maximum distance, and the cam shaft 25
When the cut surface of B and the contact surface of the developing device 10B face each other, the developing roller and the photosensitive drum 9A are configured to come close to each other to a developable state.

Incidentally, the cam shafts 25C and 25D for the second-stage developing device
The abutting surface of the developing device at the rear stage comes into contact with the cam shaft 25 in the same manner as the abutting surface of the developing device at the preceding stage.
With C and 25D, the same operation as the former developing device is performed.

Therefore, the photosensitive drums 9A and 9B are sequentially developed one color at a time from the developing device for each rotation of the drum and transferred to the intermediate transfer sheet 26 by Coulomb force. When the transfer of one color is completed, the photosensitive drum is cleaned by the cleaning mechanisms 24A and 24B to remove the toner, and then the other color is developed on the photosensitive drum. Specifically, the black color is transferred from the photosensitive drum 9A to the intermediate transfer sheet 26,
After that, the cyan color is transferred from the photosensitive drum 9B to the intermediate transfer sheet 26 rotated to the position of the photosensitive drum 9B.

After transferring the black color to the intermediate transfer sheet 26, the photosensitive drum 9A removes the residual toner by the removing means,
The magenta color is developed, and the magenta color is transferred to the intermediate transfer sheet 2
Transfer to 6. Similarly, on the photosensitive drum 9B, after transferring the yellow color, the residual toner is removed by the removing unit, and the cyan is developed, so that the transfer is performed.

When the four color toners are transferred to the intermediate transfer sheet 26, the paper stored in the paper cassette 14 passes through the passages 16 and 17 by the roller 15 and the like, and the intermediate transfer sheet 26 and the second transfer roller 19 are passed. Toners for forming each image are transferred to the sheet, and the transferred sheet is discharged to the conveying device 20 and conveyed to a fixing unit (not shown) by the conveying belt 21.

In the image forming apparatus as described above, the polygon mirror 2 as shown in FIG. 6 is conventionally arranged,
Laser reflected beam SL on the surface of photosensitive drum 9A (FIG. 1)
Angle θ at which the laser incident beam SL that irradiates 2 is incident
L and the angle θR at which the laser incident beam SR that irradiates the laser reflected beam SR2 onto the surface of the photosensitive drum 9B (FIG. 1) are incident at the same angle.

In this state, the distance ε between the end M1 of the reflecting surface 2f1 and the axis of the incident light SL when the laser light is reflected to the sensor for detecting the scanning start of the photosensitive drum 9A in the width direction.
2L is a reflecting surface 2b1 when the laser beam is reflected to a sensor that detects the start of scanning of the photosensitive drum 9B in the width direction.
Is narrower than the distance ε2R between the end M3 of the laser beam and the axis of the incident light SR and has no margin, and the laser beam cannot be reflected sufficiently.

In order to improve this, as shown in FIG. 7, if the incident angle of the laser beam is left unchanged and the polygon mirror is moved upward in the figure, the interval ε2L 'is improved, but the interval ε2R' is reduced. It becomes narrower and cannot be completely improved. Therefore, as a result of research, the inventor found out a configuration in which the incident angles of the left and right laser beams are changed.

Next, the structure of the optical scanning device used in the image forming apparatus configured as described above will be described. In FIG. 2, the polygon mirror 2 has reflecting surfaces 2a to 2f and six reflecting surfaces, and is arranged rotatably counterclockwise in the figure.
The incident laser beam SL is on the left side of the polygon mirror 2.
A surface to be scanned 28A, which is the surface of the photosensitive drum 9A that reflects light to be optically scanned through the lens system 3A, is provided, and the right side is a photosensitive surface that reflects the incident laser beam SR and optically scans through the lens system 3B. Scanned surface 2 which is the surface of drum 9B
8B is provided. These optical scanning surfaces 28A, 28
At B, beam detect sensor sensors (BD sensors) 27A and 27B for detecting the start of scanning of the laser beam are arranged.

Then, the laser incident beam S on the left side
The incident angle θL of L is the laser incident beam SR on the right side.
Since the incident angle θR is set larger than the incident angle θR, the virtual extension line SL ′ of the laser incident beam SL and the virtual extension line SR ′ of the laser incident beam SR on the right side are located on the left side of the center line y of the polygon mirror 2. It intersects at point T.

The operation of the embodiment thus constructed will be described with reference to FIG. In the figure, the number of polygon mirror surfaces is n, the radius of the circumscribed circle of the polygon mirror is Ro, the distance between the center of the polygon mirror and the recording medium is Y (negative number), and the counterclockwise polygon mirror rotation angle is α, The polygon mirror rotation angle in the clockwise direction is defined as β (negative number), the incident angle of the laser beam is defined as θ, and the intersection of the virtual extension line of the laser beams SL and SR with the center line y of the polygon mirror 2 and the polygon mirror. Assuming that the distance between the centers of rotation is δ, the intervals ε1 (A), ε2 (B), and δ in FIG.
(C) is represented by the following formula.

[0030]

(Equation 1)

The expressions (A), (B) and (C) are derived from FIG. In the figure, the laser incident beam S
An intersection Ao between the deflecting surface 2b2 and the adjacent deflecting surface 2c2 when R goes toward the center of the recording medium as a reflected beam SR2,
Intersection B between the deflection surface 2b2 and the adjacent deflection surface 2a2
o, the deflection surface 2 adjacent to the deflection surface 2b1 when the laser incident beam SR goes to the sensor as the reflected beam SR1
The intersection Aβ with c1 and the deflecting surface 2b when the laser incident beam SR is directed to the end portion of the recording medium as a reflected beam SR3.
3 and an adjoining deflection surface 2a3 are defined as Bα, and the angles formed by the points Ao, Bo, Aβ, Bα and the x-axis of the polygon mirror 2 are θAo, θBo, θAβ, θBα, respectively.
Then, θAo = −θ / 2 + π / n (1) θBo = −θ / 2−π / n (2) θAβ = −θ / 2 + π / n + β (3 ) ΘBα = −θ / 2−π / n + α (4)

The coordinates of the points Ao, Bo, Aβ, and Bα are Ao: (RoCosθAo, RoSinθAo) (5) Bo: (RoCosθBo, RoSinθBo) (6) Aβ: (RoCosθAβ, RoSinθAβ) ) (7) Bα: (RoCos θBα, RoSin θBα) ... (8)

The equation of the straight line passing through the point (x1, y1) is the following equation (9).

[0034]

(Equation 2)

Substituting the coordinates into this equation (9) gives the following equation (10).

[0036]

(Equation 3)

The x-coordinate Xc of the intersection C between this straight line and the center axis of the recording medium is given by the following equation (11) when y = Y in the above equation (10).

[0038]

(Equation 4)

This equation (11) is transformed into the following equation (12)

[0040]

(Equation 5)

When rearranged using, the following equation (13) is obtained.

[0042]

(Equation 6)

By substituting the equation (2) into the equation (13) and rearranging, the following equation (14) is obtained.

[0044]

(Equation 7)

Therefore, δ is given by the following equation (15).

[0046]

(Equation 8)

The expression (15) is further rearranged into the following expression (16).

[0048]

(Equation 9)

On the other hand, the equation of the straight line of the incident beam is expressed by tan θ × X + y−δ = 0 ... (17). On the other hand, the distance d between the straight line represented by ax + by + c = 0 and the point (x0, y0) is calculated by the following equation (18).

[0050]

(Equation 10)

Is represented by Since the distances between the straight line represented by the above equation (17) and the intersection points Aβ and Bα are εl and ε2, respectively, using the above equation (18), εl is given by the following equation (1)
9).

[0052]

[Equation 11]

Substituting a practical numerical value, tan θ · R
Since the value of ocos θBα + Rosin θBα−δ became negative, εl was set to the following equation (20).

[0054]

(Equation 12)

This equation (20) is rearranged using the above equation (4) to obtain the following equation (21).

[0056]

(Equation 13)

Further rearranging this equation (21) gives the following equation (22).

[0058]

[Equation 14]

Similarly, ε2 is given by the following equation (23),

[0060]

(Equation 15)

Substituting a practical value, tan θ · Ro
Since the value of cos θAβ + Rosin θAβ−δ is a positive value, ε2 is represented by the following equation (24).

[0062]

(Equation 16)

When this equation (24) is rearranged by substituting the equation (3), ε2 becomes the following equation (25).

[0064]

[Equation 17]

Further rearranging this equation (25), ε2
Is given by the following equation (26).

[0066]

(Equation 18)

Equations are similarly obtained on FIG. 3 (a), and from these equations, the interval ε1 between the left and right reflecting surfaces is calculated.
FIG. 4 shows L, ε2L, ε1R, and ε2R plotted with the incident angle θ varied. As shown in FIG. 3, the fact that the intervals ε1L and ε2L are equal and ε1R and ε2R are equal corresponds to the sensors arranged near one end of the recording medium in the width direction and the other end. This is a condition for effectively using the reflective surface.

As shown in FIG. 2, the angle formed by the laser beam SL and the center line K connecting the widthwise centers of the recording media on the left and right sides is defined as the incident angle θL,
The angle formed by the center line K and the laser beam SR is the incident angle θR.
And θL> θR, the virtual extension lines SL ′ and SR ′ of the laser beams SL and SR intersect at the point T on the left side of the center line y.

As shown in FIG. 4, θL (62 °)> θR
When set to (49 °), the incident light path and the reflected light path of the laser beam on the polygon mirror 2 are shown in FIG. And
When the laser incident beam SL is reflected as the reflected light SL1 by a sensor that starts scanning from one end to the other end of the left side recording medium shown in FIG. The distance ε2L between the intersection M1 of the reflecting surfaces 2f1 and 2a1 shown by the dotted line and the axis of the incident light SL, and the two points when the laser incident beam SL is reflected as the reflected light SL3 toward the other end of the recording medium. Reflective surface 2 shown by chain line
The interval ε1L between the intersection M6 of f3 and 2e3 and the axis of the incident light SL can be set to be equal.

Further, the laser incident beam S is applied to the sensor for detecting the scanning start of the scanning line, which starts scanning from one end of the recording medium on the right side shown in FIG. 3B to the other end.
A reflecting surface 2 indicated by a dotted line in which R reflects as reflected light SR1
A distance ε2R between the intersection M3 of b1 and 2c1 and the axis of the incident light SR, and a reflecting surface 2a3 indicated by a chain double-dashed line that reflects the laser incident beam SR as reflected light SR3 traveling toward the other end of the recording medium. The interval ε1R between the intersection M2 of 2c3 and the axis of the incident light SR can be set to be equal.

Therefore, if the design is such that half (radius) of the laser beam falls within the value of the interval ε of the intersection W of the interval ε2L and the interval ε1L corresponding to the recording medium on the left side shown in FIG. The reflective surface can be used efficiently. Also, if the design is made so that half (radius) of the laser beam falls within the value of the interval ε of the intersection V of the interval ε2R and the interval ε1R corresponding to the recording medium on the right side, the reflecting surface of the polygon mirror can be used efficiently. can do.

Therefore, the incident angle of the laser beam is set to the above-mentioned condition, and the half of the laser beam is set within the interval ε so that the laser beam is not chipped at the end of the recording medium and the polygon is prevented. The area of the reflecting surface of the mirror can be efficiently set, the number of reflecting surfaces can be increased without increasing the outer diameter, and the image forming time can be shortened.

[0073]

As described above in detail, according to the present invention, the image forming speed can be increased without increasing the rotation speed of the optical deflector, the apparatus can be downsized, and the manufacturing cost can be reduced. Can be provided.

[Brief description of the drawings]

FIG. 1 is an external view of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram showing an embodiment of an optical scanning device according to the present invention.

FIG. 3 is a diagram illustrating the operation of the present invention.

FIG. 4 is a graph showing the relationship between the incident angle of a light beam and the incident position ε from the tip of the incident surface.

FIG. 5 is an explanatory diagram for deriving an incident position ε.

FIG. 6 is a diagram (1) illustrating a problem.

FIG. 7 is a diagram (2) illustrating a problem.

[Explanation of symbols]

1 Optical Scanning System 2 Optical Deflector (Polygon Mirror) 3 Lens System (3A, 3B) 5 Laser Light Source (5A, 5B) 9 Photosensitive Drum (9A, 9B) 10A Developer 1 10C Developer 2 10B Developer 3 10D Develop Device 4 11 Intermediate transfer drum 13 Cleaner unit 19 Second transfer roller 20 Conveying device 23 Charger (23A, 2A
3B) 24 cleaner (24A, 24
B) 26 intermediate transfer sheet 27 BD sensor (27A, 27
B) 28 Scanned surface (28A, 28
B)

Claims (3)

[Claims] 1. Optical scanning is performed while scanning surfaces are arranged on both sides of a single optical deflector, and a modulated beam is incident on the deflecting surface of the optical deflector facing the scanning surface. In the optical scanning device, the intersection point intersecting with the virtual extension line of the incident beam is located on one side of the optical deflector without intersecting on the center line parallel to the surface to be scanned. Optical scanning device. 2. The optical scanning device according to claim 1, wherein the respective incident beams are configured so as to enter the respective incident surfaces at different incident angles. 3. The optical deflector is composed of a polygon mirror, and the virtual extension lines intersect each other on the downstream side in the rotation direction from the center line of the optical deflector. Optical scanning device.