JPH04317022A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To provide the small-sized, highly accurate and low-cost light beam scanning device which makes a flat light beam incident on a deflecting means so that an incidence optical path and a reflection optical path contain a certain angle when viewed sideward. CONSTITUTION:The light beam scanning device is equipped with an incidence optical system 51 which makes the flat light beam 5 incident on the deflecting means 12 in a specific direction wherein the incidence optical path to the deflecting means 2 and the reflection optical path from the deflecting means are put one over the other at the certain angle when viewed sideward. Then this device is equipped with a light source 6 which is arranged by the incidence optical path and a reflecting means 22 which reflects the light beam from the light source 6 onto the incidence optical path in the specific direction and makes the light beam incident on the deflecting means 2, and the incidence optical system 51 is installed at such an attitude that the same plane R of the reflecting means 22 that the incidence optical path and reflection optical path pass is along the incidence optical path to the deflecting means 2.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a light beam scanning device used in image forming apparatuses such as copying machines, facsimile machines, and laser beam printers that form images using an electrophotographic method. A light source that emits a light beam, a deflection means that reflects and deflects the light beam for scanning, an optical path for the light beam from the light source to enter the deflection means, and an optical path for reflection from the deflection means, as seen from the side. The present invention relates to a light beam scanning device including an incident optical system that causes light to enter a deflection means in directions that overlap each other at an angle.

0002

2. Description of the Related Art A light beam scanning device of this type is disclosed, for example, in Japanese Patent Application Laid-open No. 30214/1983. Since the light beam is incident from a predetermined direction so that the incident optical path to the polygon mirror, which is the deflection means, and the reflected optical path from the polygon mirror overlap at a certain angle when viewed from the side, the incident side to the polygon mirror The optical systems can be arranged so as not to interfere with the optical path or optical system on the reflective side so as not to interfere with each other.

[0003] Therefore, this is advantageous when it is desired to suppress the planar expansion of the optical system. In addition, in a scanning optical system that does not use an fθ lens, in order to simplify the inconsistency in the optical system as much as possible, the light beam is transferred to a flat polygon mirror without interference between the incident side optical system and the reflective side optical system. It is also possible to perform scanning by making the light incident from the center front of the scanning area as viewed from the plane.

[0004] Incidentally, an input optical system for making a light beam incident on the deflecting means is usually an arrangement of a light source and various lenses. If this was simply installed in the direction of the incident optical path of the light beam to the polygon mirror, the entire optical system would become bulky due to the inclination of the incident optical path.

Therefore, in the known method, the optical system on the incident side is installed almost horizontally to suppress the overall bulk of the optical system, and the incident light beam to the polygon mirror in the inclined optical path is This is achieved by refraction.

[0006]

However, in order to satisfy the above-mentioned incident condition by refracting a light beam by a lens, the light beam must pass through the outer diameter portion of a lens having a large aperture. For this reason, if a lens with the required aperture is used as is, the device will become larger and heavier. To avoid this, lenses are cut out to leave only the necessary parts. Therefore, processing of the lens requires a great deal of effort and is therefore expensive.

Furthermore, the change in the direction of the optical path by the lens in the input optical system depends solely on the processing accuracy of the lens. For this reason, the optical path cannot be changed as designed, and the imaging characteristics tend to deteriorate.

Furthermore, since the refractive index of the lens changes due to changes in temperature, etc., the optical path changes accordingly, sometimes making it impossible to obtain the required accuracy.

Accordingly, the present invention solves the above-mentioned conventional problems by reflecting a light beam using a reflecting means that is easy to process and maintain accuracy, and thereby obtaining the necessary angle of incidence without adding bulk to the optical system. The object of the present invention is to provide a scanning optical system that can perform the following steps.

0010

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the present invention includes a light source that emits a flat light beam, a deflection means that reflects and deflects the light beam for scanning,
A light beam comprising an incident optical system that causes the light beam from a light source to enter the deflection means in a direction such that the incident optical path to the deflection means and the reflected optical path from the deflection means overlap at a certain angle when viewed from the side. In the scanning device, the incident optical system includes a light source disposed on the side of the incident optical path, and a reflecting means for reflecting the light beam from the light source onto the incident optical path in the predetermined direction and making it incident on the deflecting means. The incident optical system is characterized in that the incident optical system is installed in such a manner that the same plane through which the incident optical path in the reflecting means and the reflected optical path pass is along the incident optical path to the deflecting means.

[0011]

[Operation] According to the above structure of the present invention, the incident optical system reflects the light beam from the light source arranged laterally with respect to the incident optical path to the deflecting means by the reflecting means, and directs the light beam toward the deflecting means in a predetermined direction. The incident optical path of the light beam and the reflected optical path at the reflecting means are on the same plane, and this same plane is on the optical axis of the incident optical system or approximately along this. and is oriented along the incident optical path from the reflecting means to the deflecting means by the inclination about the axis,
A flat light beam from the light source can be made incident on the deflection means in a predetermined direction.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light beam scanning device as an embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the overall configuration of the light beam scanning device, and FIGS. 2 and 3 show its optical system. As shown in Figure 1, there is a polygon mirror 2 at the center of the rear of the casing 1.
is provided and supported by a rotating shaft 4 perpendicular to the bottom plate 3 of the casing 1.

A laser oscillator 6 is provided on one side between the front and rear portions of the casing 1 to emit a light beam 5 inward to irradiate the polygon mirror 2. As shown in FIG. 2, the laser oscillator 6 includes a semiconductor laser 11, a collimator lens 12, a plano-convex lens 13, and a cross-sectional shape of the emitted light beam 5, as in the conventional one. It has an aperture 14 that regulates the minor axis to be about 16:1. In this embodiment, two prisms 15 and 16 are further provided in the middle to flatten the light beam 5 from the semiconductor laser 11 into an extremely flat ellipse.

These two prisms 15 and 16 can efficiently flatten the cross-sectional shape of the light beam 5 by refracting the light beam 5 emitted from the semiconductor laser 11 in two steps. It can be shaped to a shape close to the regulated cross section. Therefore, the vignetting of the light beam 5 at the aperture 14 is reduced, and the output efficiency of the light beam 5 is improved.

Furthermore, as a result of refracting the light beam 5 in two stages by the two prisms 15 and 16, the prisms 15 and
The incident optical path and the outgoing optical path of the light beam 5 at 16 can be made parallel with a slight difference in level, which suppresses the expansion of the optical path and is advantageous for subsequent optical path design.

The light beam 5 emitted from the laser oscillator 6 passes through a cylindrical lens 21 and is then reflected by a mirror 22 . By this reflection, the direction of the light beam 5 is rotated by an angle α=90° (FIG. 3) when viewed from the plane, so that it is directed toward the polygon mirror 2. The light beam 5 is incident from the mirror 22 to the polygon mirror 2 from the center of the front as seen from the plane in the deflection range ρ of the light beam 5 reflected and deflected by the polygon mirror 2, as shown in FIG. , and is reflected and deflected toward the deflection area ρ.

In order to make such an incident optical path and a deflection zone optical path overlap vertically without interfering with each other, the incident light beam 5 from the mirror 22 to the polygon mirror 2 is tilted upward from a slightly downward angle. .beta. (FIG. 6), and the light beam 5 reflected by the polygon mirror 2 is reflected toward a slightly upward deflection region .rho. having the same inclination angle .beta..

The light beam 5 reflected and deflected by the polygon mirror 2 passes through mirrors 31 and 32 disposed at the front of the casing 1 and a long lens 33, and then passes through the lower surface of the front of the casing 1. The light is incident on the photosensitive drum 41 located in the recess 34 and formed into an image, and is main scanned in the axial direction of the photosensitive drum 41. Image exposure is performed on the photosensitive drum 41 using the rotation of the photosensitive drum 41 as a sub-scanning, and the image signal is converted into an image signal. thus forming an electrostatic latent image.

Note that this electrostatic latent image is developed with toner by a developing device (not shown) to become a developed image.

This developed image is transferred to a transfer sheet and then fixed to complete printing.

As shown in FIGS. 1 to 3, the mirror 31
Another beam detection mirror 42 is provided next to the beam detection mirror 42. When the light beam 5 reflected and deflected by the polygon mirror 2 rotating in the direction of the arrow reaches a predetermined position near the scanning area ρ, the light beam 5 is reflected by the beam detection mirror 42 and the polygon mirror The beam is made incident on a beam detector 44 provided on the side of 2 through a cylindrical lens 43.

As a result, it is detected that the light beam 5 deflected by the polygon mirror 2 has reached a predetermined position set slightly before the scanning area ρ, and from this detection signal, the image in the deflection area ρ is detected. The timing of writing is determined.

By the way, the reflective surface 2a of the polygon mirror 2
The upper reflection point changes to mirror 2 due to the rotation of polygon mirror 2.
Moves back and forth relative to 2. Further, since the light beam 5 is incident on the reflective surface 2a at an angle β, the reflection point on the reflective surface 2a also moves up and down as the reflection point moves up and down due to the rotation of the polygon mirror 2. These causes curves in the scanning lines on the scanning surface of the photosensitive drum 41.

Therefore, it is desirable that the finite angle β be small. However, if the angle β is made small, the incident optical system needs to be far away from the polygon mirror 2 so as not to interfere with the optical path reflected from the polygon mirror 2, and the optical system is simply arranged in the direction of incidence of the light beam 5 on the polygon mirror 2. In the case of such an incident optical system, the size of the apparatus would be significantly increased.

In this embodiment, as described above, the light beam 5 is emitted from the side of the scanning area ρ, rotated by the angle α by the mirror 22, and made incident on the polygon mirror 2. This prevents it from becoming larger.

[0027] In addition, in order for the image to be formed using an appropriate beam spot that has undergone modulation control (accompanied by modulation for main scanning uniformity) of the light beam 5 in accordance with the image signal, it is necessary to The major axis direction in the cross section of the light beam 5 incident on the reflective surface 2a of the polygon mirror 2 from the polygon mirror 2 needs to coincide with the main scanning direction.

In order to satisfy this requirement, in this embodiment, the incident optical system 51 for making the light beam 5 incident on the reflective surface 2a of the polygon mirror 2 has the same plane R through which the incident optical path and the reflected optical path at the mirror 22 pass. (FIG. 6) is provided in a posture along the incident optical path to the reflective surface 2a of the polygon mirror 2.

For this purpose, as shown in FIGS. 4 and 5, the bottom plate 3 of the casing 1 is provided with a seating surface 51 on which the laser oscillator 6 is installed, a seating surface 52 on which the cylindrical lens 21 is installed, and a mirror 22. A seat surface 53 to be installed is formed so as to be inclined with respect to the bottom plate 3 by a predetermined angle γ in a direction perpendicular to the optical path of the light beam 5.

In this embodiment, since the angle α between the incident optical path and the reflected optical path of the light beam 5 at the mirror 22 is 90°, γ=β, and the incident optical system 51 rotates around its own optical axis. It will be tilted by a predetermined angle γ. Such an inclination does not cause bulkiness due to the arrangement of the input optical system 51.

However, if the angle α between the incident optical path and the reflected optical path deviates from 90° as shown in FIG. 7 due to the arrangement of the optical system, γ≠β.

[0032] Various studies on the relationship between α, β, and γ have revealed that tanγ=tanβ·tan (α/2), and in the case of β, γ 1, γ=β·tan (α/2).

This will be explained in detail below. A band-shaped light beam 5 having a width L emitted from a laser oscillator 6 is incident on a mirror 22 having the same inclination while being inclined by a finite angle γ around its optical axis.

Here, the light rays on both sides of the light beam 5 that are incident on the mirror 22 are denoted by a and b, respectively. Incident light a, b
are reflected at points a0 and b0 on the mirror 22, respectively. The reflected light beams a' and b' are reflected by the polygon mirror 2.
The light is rotated by an angle α on the plane XY perpendicular to the rotation axis 4, and is incident on the reflecting surface 2a at an angle of a finite angle β.

As a result, the reflected lights a' and b' are reflected by the reflective surface 2a of the polygon mirror 2 as outgoing lights a'' and b'', and are deflected and scanned by the rotation of the polygon mirror 2.

The reflected lights a' and b' enter the elongated lens 33 and are imaged onto the scanning surface of the photosensitive drum 41 to have a desired beam diameter.

Here, on the coordinates of the XY plane perpendicular to the rotation axis 4 of the polygon mirror 2, the coordinates of the reflection points a0 and b0 are a0 = (x, y, z), b0 = (0,
0,0). Also, let the height of point P be z'.

If z' is not equal to z, there will be a difference in the height of the reflective surface 2a of the polygon mirror 2, and the output light a,
b is tilted. Therefore, the desired beam diameter cannot be obtained for the light beam 5 that is imaged onto the photosensitive drum 41 by the lens 33.

Therefore, in order to make z and z' equal, as shown in FIG. 8, the incident lights a and b of the light beam 5 having a width L are rotated in advance in the optical axis direction by an angle γ, and the height is adjusted with respect to the XY plane. H
It is necessary to make a difference between

[0040] Also, the difference in height between reflection points a0 and b0 is z
Therefore, z=H=Lsinγ.

By the way, as is clear from FIG. 9, the line a0 b0 which is the beam reflection area on the mirror 22 is x2
+y2 =Lcosγ/sin(π/2-α/2)∴x
2 +y2 = Lcosγ/cos(α/2). As a result, x=ycos[(π/2)-(α/2)]=ysin(
α/2) ∴x=tan(α/2)・Lcosγ. And, z=xtanβ z=tan(α/2)・tanβ・Lcosγ, and Lsinγ=tan(α/2)・tanβ・Lcosγ
is obtained. Therefore, tanγ=tanβ·tan(α/2). If β and γ are 1, then γ=β·tan(α/2).

[0042]

According to the present invention, the incident optical system reflects the light beam from the light source arranged laterally with respect to the incident optical path to the deflecting means by the reflecting means, and directs the light beam to the deflecting means in a predetermined direction. The light beam is incident on the deflecting means toward the incident optical path, and the incident optical path and the reflected optical path of the light beam in the reflecting means are on the same plane, and this same plane is the optical axis of the incident optical system or approximately along this. By tilting around the axis, the light beam is aligned along the incident optical path from the reflecting means to the deflecting means, and the flat light beam from the light source can be incident on the deflecting means in a predetermined direction, facilitating processing. Since a reflective means is used that is large in size and is not easily affected by temperature or the like in terms of accuracy, it is cheaper than using a lens, and high accuracy can be obtained, and this can be guaranteed for a long period of time. Furthermore, since the input optical system can be tilted around its own optical axis or an axis close to this, the bulkiness of the optical system can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the overall structure of a light beam scanning device to which the present invention is applied.

FIG. 2 is a perspective view showing the optical system of the device in FIG. 1;

FIG. 3 is a plan view of the optical system in FIG. 2 with a part removed.

FIG. 4 is a perspective view of the casing of the device in FIG. 1 with the optical system removed.

FIG. 5 is an enlarged view showing the mounting portion of the entrance optical system of the casing in FIG. 4;

FIG. 6 is a schematic diagram showing a state in which a light beam emitted from a laser oscillator reaches a polygon mirror via a mirror and is reflected.

7 is a schematic diagram showing a case where the reflection angle of a light beam by a mirror is different from the case of FIG. 6; FIG.

8 is an explanatory diagram of the state shown in FIG. 6 viewed from above; FIG.

FIG. 9 is an explanatory diagram showing an enlarged view of a part of FIG. 8;

[Explanation of symbols]

2 Polygon mirror 2a Reflective surface 5 Light beam 6 Laser oscillator 22 Mirror 51 Incidence optical system R Same plane

Claims (1)

[Claims] 1. A light source that emits a flat light beam, a deflection means for reflecting and deflecting the light beam for scanning, and an incident optical path of the light beam from the light source to the deflection means and a reflected optical path from the deflection means. In the light beam scanning device, the light beam scanning device includes an incident optical system that causes the light to be incident on the deflecting means in a predetermined direction such that the light beams overlap at a certain angle when viewed from the side, the incident optical system being disposed on the side of the incident optical path. and a reflecting means for reflecting the light beam from the light source onto an incident optical path in the predetermined direction and making it incident on the deflecting means, and an incident optical system that includes an incident optical path and a reflected optical path in the reflecting means. A light beam scanning device characterized in that the light beam scanning device is installed in such a manner that the same plane through which the light beams pass along an incident optical path to the deflection means.