JPH04283718A - Exposure device - Google Patents

Abstract

PURPOSE:To offer the exposure device which has no variance in beam diameter on a photosensitive body even if there is variance in the divergence angle of a semiconductor laser and forms a sharp image as to an exposure device used for an image formation device such as a printer, facsimile equipment, a copying machine, etc., employing an electrophotography system. CONSTITUTION:This device is equipped with a light source 10 which emits divergent scanning light from a fixed position and a rotary elliptic surface mirror 11 which is arranged having an aperture surface within a range of the minimum divergence angle thetamin of the scanning light emitted by the light source 10 and can rotate or swing around the focus or an axis passing its specific nearby range in a main scanning direction. The scanning light from the light source 10 is made incident on the rotary elliptic surface mirror 11 and a photosensitive body 12 is scanned with latent image formation light deflected by the rotation or swinging.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus used in image forming apparatuses such as printers, facsimile machines, and copying machines that employ electrophotography.

[0002] In recent years, image forming apparatuses such as printers, facsimile machines, and copying machines that employ electrophotography to obtain high-quality images have been developed and put into practical use. Such image forming apparatuses use an exposure device that scans the photoreceptor by irradiating the photoreceptor with light, such as a laser beam, in order to form a latent image corresponding to the image to be printed on the photoreceptor. .

[0003] Such an exposure apparatus uses an optical system composed of a large number of optical elements such as lenses and mirrors for convergence and deflection of light. Therefore, the structure of the exposure apparatus itself has become complicated and large, and it has also become expensive. Therefore, there is a need for an exposure apparatus that has a simple structure, can be miniaturized, and is inexpensive.

0004

2. Description of the Related Art In conventional image forming apparatuses, an exposure device is used to form a latent image on a photoreceptor as an image carrier.

Such an exposure apparatus includes, for example, a semiconductor laser to generate light according to information to be recorded, a collimating lens that narrows down the beam diameter of a diverging beam emitted from the semiconductor laser and converts it into parallel light, and A cylindrical lens for correcting aberrations of a laser beam whose beam diameter is narrowed down by a collimating lens and converted into parallel light, and a rotating polygon mirror or swinging for deflecting the laser beam corrected by the cylindrical lens. It is composed of a one-sided mirror, an f-theta lens or an arc-sin theta lens for correcting the scanning speed of the laser beam deflected by these mirrors and forming an image on the photoreceptor.

[0006] In such an exposure apparatus, recorded information corresponding to an image to be printed, which is sent from, for example, a host device, is subjected to a predetermined modulation and then supplied to a semiconductor laser. As a result, the semiconductor laser blinks, that is, emits light, in accordance with the recorded information.

The laser beam emitted from this semiconductor laser is generally a diverging beam. This diverging beam is converted into parallel light by a collimating lens. Further, this collimating lens focuses the light beam to a predetermined beam diameter.

The diameter of the laser beam that has passed through this collimating lens is elliptical, but by passing through the cylindrical lens, its aberrations are corrected and the beam is converted into a nearly perfect circle, which is then incident on a rotating polygon mirror or a single mirror. Ru. At this time, the rotating polygon mirror rotates at a constant speed, and the one-sided mirror swings at a constant speed. Therefore, the laser beam reflected by these rotating polygon mirrors or single mirrors is deflected at a constant angular velocity. Therefore, in this state, uniform speed scanning will not be performed on the photoreceptor, but low speed scanning will be performed near the center of the photoreceptor, and high speed scanning will be performed near both ends.

Therefore, the laser beam reflected by the rotating polygonal mirror or the single-sided mirror is converted to scan at a constant velocity on the photoreceptor by passing through an fθ lens or an arcsinθ lens, and an image is formed on the photoreceptor. be done. Then, the photoreceptor is scanned at a constant speed by a flashing laser beam, and the uniformly charged surface of the photoreceptor is neutralized according to the recorded information.
A latent image is formed.

0010

SUMMARY OF THE INVENTION As described above, such a conventional exposure apparatus requires a large number of optical elements, which hinders miniaturization and cost reduction of the apparatus.

[0011] Therefore, in an exposure apparatus that employs a galvano system, a curved mirror is used in the mirror section and the mirror has a function of condensing light, etc., thereby eliminating the need for a correction lens such as a cylindrical lens. A mirror scanner is contemplated by the inventors. An exposure apparatus to which this curved galvanomirror scanner is applied has the advantage that the apparatus can be made smaller by the amount of optical elements such as lenses that are removed, and the cost can be significantly reduced.

However, the above-mentioned curved galvanometer mirror
In a scanner, when trying to reflect divergent laser light from a semiconductor laser on the curved mirror to form an image on the photoreceptor, if the divergence angle of the semiconductor laser varies,
The problem remained that the beam diameter on the photoreceptor also varied, and that a clear latent image could not be formed.

The present invention has been made in view of the above circumstances, and provides an exposure device that can form a clear latent image without varying the beam diameter on the photoreceptor even if the divergence angle of the semiconductor laser varies. The purpose is to

[0014]

[Means for Solving the Problems] As shown in principle in FIG. 1, the exposure apparatus of the present invention includes a light source 10 that generates divergent scanning light from a fixed position, and a light source 10 that generates divergent scanning light from a fixed position. an ellipsoidal mirror 11 arranged to have an aperture within the range of the minimum divergence angle θ min and rotated or oscillated in the main scanning direction about an axis passing through the focal point or a predetermined range in the vicinity thereof; The spheroidal ellipsoidal mirror 11 is characterized by receiving the scanning light generated from the light source 10 and scanning the photoreceptor 12 with latent image forming light that is deflected by its rotation or swinging.

[0015]

[Operation] In the present invention, the aperture surface of the spheroidal mirror 11 that receives the scanning light from the light source 10 having a diverging property such as a semiconductor laser has a minimum divergence angle θmin of the light source 10.
The spheroidal mirror 11 rotates or oscillates in the main scanning direction about an axis that passes through the focal point or a predetermined range near the focal point to deflect the scanning light. The light deflected by the spheroidal mirror 11 is scanned over the photoreceptor 12 as latent image forming light.

As described above, since the aperture surface of the spheroidal mirror 11 is positioned within the range of the minimum divergence angle θmin of the light source 10, the entire surface of the aperture surface is always exposed to the light source 10.
The scanning light is received and reflected as latent image forming light. Therefore, even if the divergence angle of the light source 10 varies, the beam diameter on the photoreceptor 12 does not vary, making it possible to form a clear latent image.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a diagram showing, in a simplified manner, the configuration of essential parts of an embodiment of the exposure apparatus of the present invention.

In the figure, reference numeral 10 denotes a semiconductor laser as a light source, which generates a laser beam (scanning beam) that blinks in accordance with the image to be formed. This semiconductor laser 1
Generally, the light generated by 0 has a divergent property, and the angle of spread differs depending on the direction of the divergence.

Reference numeral 12 denotes a photosensitive drum as a photosensitive member. The photosensitive drum 12 carries an electrostatic latent image formed while being rotated, for example, in the direction of arrow A in the figure (hereinafter referred to as the "sub-scanning direction"). That is, the surface of the photoreceptor drum 12, which is uniformly charged by a charger (not shown) and moves in the sub-scanning direction, is moved in the direction of the arrow BC (hereinafter referred to as "main") by the latent image forming light that blinks in accordance with the image to be generated. The image is scanned in the scanning direction (referred to as "scanning direction"), and the portion irradiated with light is charged and an electrostatic latent image is formed.

The electrostatic latent image formed on the photosensitive drum 12 is developed by adhering toner to form a toner image, and the toner image is transferred to paper and fixed. , an image will be formed on the paper.

Reference numeral 11 is an ellipsoidal mirror of revolution. The spheroidal mirror 11 rotates an ellipse formed by two focal points.
It is constructed by cutting out a part of the spheroidal surface that is formed when the object is rotated around an axis that passes through two focal points.

The spheroidal mirror 11 is molded of resin, glass, or the like, and is fabricated by vapor-depositing a metal material or the like having a high reflectance on a concave surface that serves as a reflective surface.

The spheroidal mirror 11 thus produced has the semiconductor laser 10 as the light source located at the first focal point of the spheroidal mirror 11, and the photosensitive drum 12 located at the second focal point. It is arranged so that the imaging point on the surface is located.

13 is a drive motor. The spheroidal mirror 11 is fixed to the shaft 14 of the drive motor 13. The drive motor 13 is controlled so as to be rotated only in one direction of arrows D and E in the figure, or to rotate (swing) alternately at a predetermined angle in the directions of arrows D and E in the figure.

FIG. 3 shows the spheroidal mirror 1 in FIG.
FIG. 3 is a cross-sectional view taken along a plane (indicated by S in FIG. 2) passing through two focal points of FIG. The semiconductor laser 10 as a light source has a first
The light emitted from this light emitting point is reflected by the spheroidal mirror 11, and the light is emitted from the photoreceptor drum 1.
The image is focused on a second focal point (imaging point) 15 on the surface of the lens. Note that 16 is the rotation axis of the spheroidal mirror 11.

The elliptical shape of this spheroidal mirror 11 is as follows:
It can be expressed by the following formula.

Here, a is the major axis of the ellipse, and b is the minor axis of the ellipse. The exposure apparatus configured as described above operates as follows.

That is, when a signal corresponding to the image to be formed is supplied to the semiconductor laser 10, the semiconductor laser 10
It emits light in response to the signal. The light beam generated from the semiconductor laser 10 placed at the first focal point is irradiated onto the spheroidal mirror 11 as scanning light. The light beam reflected by the spheroidal mirror 11 reaches the second focal point as latent image forming light due to the nature of the ellipsoidal mirror.

Here, since the light emitted from the semiconductor laser 10 is a diverging beam, all the light rays emitted from the first focal point pass through the second focal point, so they are converged at the second focal point. . As a result, an image is formed on the photoreceptor drum 12 with a preset focused beam diameter, and the corresponding portion on the photoreceptor drum 12 is neutralized.

This operation is performed by the spheroidal mirror 11 which is rotated or oscillated by the drive of the drive motor 13.
This is repeatedly executed while moving the image forming position on the photosensitive drum 12 in the main scanning direction. When the main scanning for one line is completed, the same operation as described above is performed on the photosensitive drum 12, which has been moved in the sub-scanning direction by one scanning line pitch due to rotation. Such an operation is repeated for one page, for example, to obtain one page of electrostatic latent images on the surface of the photoreceptor drum 12.

The exposure apparatus having such a structure has the advantage that an optical system or the like for converting the divergent beam generated by the semiconductor laser 10 into parallel light is unnecessary, and the structure of the exposure apparatus becomes simple.

Next, the size and location of the spheroidal mirror 11 will be explained.

In this embodiment, as shown in FIG. 4, the spheroidal mirror 11 is disposed at a position completely within the range of the divergence angle θ of the semiconductor laser 10.

Here, the size of the aperture (the incident beam diameter) di that the spheroidal mirror 11 should have and the photosensitive drum 12
The relationship with the above focused beam diameter do is based on the following formula.

[0036] dm i =(k・f・λ)/dm o...
(4) Formula ds i = (k・f・λ)/ds o...
(5) Formula where each parameter is as follows,
It is defined as shown in FIG. That is, Figure (a) is a side view, Figure (b) is a vertical projection of the aperture plane from top to bottom in the figure, and Figure (c) is the shape of the focused beam. FIG. 2 is a further enlarged view when viewed from the beam irradiation direction.

dm i : Incident beam diameter in the main scanning direction (value of 1/e2) dm o : Condensed beam diameter in the main scanning direction (value of 1/e2
value) ds i: Incident beam diameter in the sub-scanning direction (1/
e2 value) ds o: Condensed beam diameter in the sub-scanning direction (
1/e2 value) f: imaging distance λ: wavelength k: coefficient However, k = (4/π) ~ 2.5, usually 1.6 ~
It is about 1.8. If there is no aberration, it is 4/π, and increases to about 2.5 depending on the aberration.

Note that the above equations (4) and (5) are based on the relationship between the ellipsoidal mirror 1 of rotation and the light emission direction of the semiconductor laser 10.
1 is arranged vertically, and when the spheroidal mirror 11 is used at an angle, the incident beam diameter di
is calculated by converting it into a dimension corresponding to an appropriate angle of incidence.

Further, the distance fc between the light source (semiconductor laser 11) and the spheroidal mirror 11 is determined within the range of the following formula.

Minimum value fc m of distance fc in the main scanning direction
min is fc m min = dm i /{2sin
(θm max /2)}...(6) The maximum value fc m max of the distance fc in the main scanning direction is fc
m max =dm i /{2sin(θm min
/2)}...(7) The minimum value fc s min of the distance fc in the sub-scanning direction is fc s min =
ds i /{2sin(θs max /2)}…(
8) Formula Maximum value fc s of distance fc in the sub-scanning direction
max is fc s max = ds i
/{2sin(θs min /2)} (9) where each parameter is as follows and defined as shown in FIG. The figure (a) is in the main scanning direction, the figure (b)
indicates the spread angle in the sub-scanning direction.

dm i , dm o , ds i , d
s o is the same as above θm max: Maximum value of the spread angle in the main scanning direction (value of 1/e2) θm
min: Minimum value of the spread angle in the main scanning direction (1/e2
value) θs max: Maximum value of the spread angle in the sub-scanning direction (value of 1/e2)
θs min: Minimum value of the spread angle in the sub-scanning direction (1/
e2 value) Among the above parameters, dm o , ds
o, k, f, and λ are uniquely determined based on the specifications of the device.

Therefore, dm i and ds i are determined from equations (4) and (5). That is, the aperture size of the spheroidal mirror 11 is determined.

Further, the distance fc between the light source (semiconductor laser 11) and the mirror (spheroidal mirror 11) is θm m
ax , θm min , θs max , θs mi
Since n is uniquely determined by the characteristics of the semiconductor laser 10, by determining the above dmi and ds i,
Calculated using equations (6) to (9).

Therefore, when the entire surface of the spheroidal mirror 11 is used as an aperture, if the mirror size in the main scanning direction is Mm and the mirror size in the sub-scanning direction is Ms, then
It is best to define them within the range of formulas (1) and (2) below, respectively.

2fc m min · sin (θm min /2
) ≦Mm ≦2fc m max・sin(θm
max /2) ...(1) Formula 2fc s min
・sin(θs min /2) ≦Ms ≦2fc
s max ・sin(θs max /2)...
(2) Formula In this case, Mm = dmi, Ms = d
When s i , the light generated by the semiconductor laser 10 can be received most efficiently.

The embodiment shown in FIG. 4 shows the case where the scanning section of the exposure apparatus is constructed using the spheroidal mirror 11 having the size calculated in this way, and FIG. FIG. 2B is a projection view of the semiconductor laser 10 seen from above.

With this configuration, even if the spread angle of the light generated by the semiconductor laser 10 varies, the spheroidal mirror 11 always exists within the range of the spread angle, so that the light on the photoreceptor drum 12 The beam diameter does not vary, and a condensed beam with a constant diameter can be obtained at the imaging position. As a result, the latent image forming characteristics become constant and a clear latent image can be obtained.

Further, the divergence angle characteristics of the semiconductor laser 10 may be significantly different between the main scanning direction and the sub-scanning direction. In this case, as shown in FIG. 7, the size of the spheroidal mirror 11 can be changed depending on the characteristics of the divergence angle.

In the embodiment described above, the spheroidal mirror 1
All of the aperture surfaces of the semiconductor laser 10 exist within the spread angle of the light generated by the semiconductor laser 10. Therefore, the spheroidal mirror 1
If there is a chip or sag in the peripheral area of 1, the direction of reflection and the amount of reflected light will not be constant, and the diameter of the condensed beam will vary at the imaging position, and the amount of light will be uneven, so it is difficult to obtain a clear image. The disadvantage is that it cannot be done.

Therefore, in order to solve this problem, as shown in FIG.
and the spheroidal mirror 11. The arrangement is such that all the light passing through the hole 21 is received by the spheroidal mirror 11. As a result, the periphery of the spheroidal mirror 11 is not irradiated with light, and the diameter of the incident beam received by the spheroidal mirror 11 is always constant. Therefore, the diameter of the condensed beam at the imaging position is also always constant and does not vary. As a result, a clear image can be formed on the photoreceptor drum 12, and the drawbacks of the above embodiments are eliminated.

To specifically illustrate the mounting position of the mask 20, as shown in FIG.
It is possible to attach it directly to the

Further, as shown in FIG. 10, it may be configured to be attached to the semiconductor laser 10. This configuration has the effect that the addition of the drive motor 13 can be reduced compared to the example shown in FIG.

[0053] Furthermore, the mask 20 is used for the semiconductor laser 10.
Alternatively, instead of being attached to the spheroidal mirror 11, as shown in FIG. 11, it may be configured to be movable independently of these. With this configuration, the amount of light passing through the hole 21 can be adjusted, and there is an effect that the device can be used for more general purposes.

[0054]

As described in detail above, the present invention provides an exposure apparatus that can form a clear latent image without varying the beam diameter on the photoreceptor even if the divergence angle of the semiconductor laser varies. be able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is a diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a diagram for explaining the arrangement position of the spheroidal mirror according to the embodiment of the present invention.

FIG. 4 is a diagram for explaining the positional relationship between the spread angle of the diverging light of the semiconductor laser and the spheroidal mirror according to the embodiment of the present invention.

FIG. 5 is a diagram for explaining the relationship between the incident beam diameter and the condensed beam diameter in the embodiment of the present invention.

FIG. 6 is a diagram for explaining the relationship between the divergence angle θ and the light source-mirror distance fc in the embodiment of the present invention.

FIG. 7 is a diagram for explaining the shape and arrangement position of the spheroidal mirror when the divergence angle in the main scanning direction is large according to the embodiment of the present invention.

FIG. 8 is a diagram showing the configuration of another embodiment of the present invention.

FIG. 9 is a diagram showing an example in which the mask is attached to the spheroidal mirror in FIG. 8;

FIG. 10 is a diagram showing an example in which a mask is attached to a semiconductor laser in FIG. 8;

FIG. 11 is a diagram showing an example in which the mask is independently movably attached in FIG. 8;

[Explanation of symbols]

10 Light source (semiconductor laser) 11　Spheroidal mirror 12 Photoreceptor (photoreceptor drum) 20 Mask means (mask) 21 Hole

Claims (10)

[Claims] 1. A light source (10) that generates divergent scanning light from a fixed position; and a light source (10) disposed so as to have an aperture within the range of the minimum divergence angle θmin of the scanning light generated by the light source (10), an ellipsoidal mirror (11) that is rotated or oscillated in the main scanning direction about an axis that passes through the focal point or a predetermined range in the vicinity thereof, and the ellipsoidal mirror (11) is connected to the light source (10). The latent image forming light that is deflected by the rotation or oscillation of the scanning light reflected from the photoreceptor (
12) An exposure apparatus characterized by performing upper scanning. 2. The exposure apparatus according to claim 1, wherein the light source (10) is a semiconductor laser. 3. The aperture size of the spheroidal mirror (11) in the main scanning direction and the sub-scanning direction perpendicular to the main scanning direction is determined according to the spread angle of the light source (10). The exposure apparatus according to claim 1, characterized in that: 4. An aperture size Mm in the main scanning direction and an aperture size Ms in the sub-scanning direction of the spheroidal mirror (11).
3. The exposure apparatus according to claim 1, wherein: is within the range of the following expressions (1) and (2). 2fc m min ・sin (θm min /2
) ≦Mm ≦2fc m max・sin(θm
max /2) ...(1) Formula 2fc s min
・sin(θs min /2) ≦Ms ≦2fc
s max ・sin(θs max /2)...
(2) where θm min is the minimum value of the spread angle in the main scanning direction, θm max is the maximum value of the spread angle in the main scanning direction, θs min is the minimum value of the spread angle in the sub-scanning direction, and θs max is the minimum value of the spread angle in the sub-scanning direction. The maximum value of the spread angle in the scanning direction, fc m min is the distance between the light source (10) and the spheroidal mirror (11) when the spread angle is θm max ,
fc m max is the distance between the light source (10) and the spheroidal mirror (11) when the divergence angle is θm min, f
c s min is the distance between the light source (10) and the spheroidal mirror (11) when the divergence angle is θs max, fc
s max is the distance between the light source (10) and the spheroidal mirror (11) when the divergence angle is θs min . 5. The aperture size Mm of the spheroidal mirror (11) in the main scanning direction is the incident beam diameter d in the main scanning direction.
3. The exposure apparatus according to claim 1, wherein the aperture size Ms in the sub-scanning direction is the incident beam diameter dsi in the sub-scanning direction. 6. A light source (10) that generates a diverging scanning light from a fixed position, and a passage hole for the scanning light (
21), and an aperture surface is arranged so as to receive all the scanning light that has passed through the hole (21) of the mask means (20), and the aperture surface is arranged so as to receive all the scanning light that has passed through the hole (21) of the mask means (20), an ellipsoidal mirror (11) rotated or oscillated in the main scanning direction about an axis passing through the range, the ellipsoidal mirror (11) is emitted from the light source (10), and the ellipsoidal mirror (11) is emitted from the light source (10) and An exposure apparatus characterized in that scanning light that has passed through a hole (21) in a means (20) is incident, and a photoreceptor (12) is scanned with latent image forming light that is deflected by the rotation or swinging of the scanning light. 7. The exposure apparatus according to claim 6, wherein the mask means (20) is fixed to the spheroidal mirror (11). 8. The exposure apparatus according to claim 6, wherein the mask means (20) is fixed to the light source (10). 9. The exposure method according to claim 6, wherein the mask means (20) is arranged to be movable independently of the light source (10) or the spheroidal mirror (11). Device. 10. The spheroidal mirror (11) includes:
10. The exposure apparatus according to claim 1, wherein the exposure apparatus is manufactured by molding.