JPH11218703A - Optical writing device - Google Patents

Abstract

(57) [Problem] To provide an optical writing device in which the influence of a plane mirror is very small and can be ignored. SOLUTION: A deflector 4 for deflecting a laser beam emitted from a light source, fθ lenses 5a and 5b for passing a laser beam 14 deflected from the deflector, and a laser beam on the emission side of the fθ lenses 5a and 5b In the writing apparatus 2 provided with the plane mirror 6 for reflecting the light 14 on the recording medium 1, the cross-sectional shape of the plane mirror 6 taken along a plane perpendicular to the scanning direction is substantially rectangular. The side 22 is configured as a reflection surface, and the long side 23 is configured as a holding surface. At this time, the ratio of the length of the long side 23 to the length of the short side 22 is preferably set to 2.5 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing apparatus for writing an image by scanning a light beam, such as a laser beam printer and a laser facsimile.

[0002]

2. Description of the Related Art Optical writing is performed by a writing device such as a laser beam printer for forming an image on a photosensitive member by scanning a light (laser) beam modulated according to an image signal. In this optical writing device, a polygon mirror is used as an optical deflector, and a light beam scanned by the polygon mirror at a constant angular velocity is converted to a constant velocity deflection by using an fθ lens group or an fθ mirror group to expose the light. It scans over the body and writes.

FIG. 4 is an explanatory diagram showing a basic configuration of a general fθ lens system writing device, and FIG. 5 is an explanatory diagram showing a general configuration of a reflection type writing device using an fθ mirror.
In the following description, the same or substantially the same portions are denoted by the same reference numerals, and overlapping description will be omitted.

First, the basic configuration of a general fθ lens system writing device will be described with reference to FIG. A laser beam emitted from a laser light generator (not shown) modulated by an image signal is deflected and scanned by a deflector (polygon mirror) 4 of a writing device 2. This deflector 4
Is rotated by the motor 3. The beam light from the deflector 4 is converted from constant angular velocity deflection to constant velocity deflection by fθ lenses 5a and 5b, which are imaging lenses, reflected by the plane mirror 6, and is reflected on the recording medium 1 such as a photosensitive drum. It is imaged. A dustproof glass 7 is provided between the plane mirror 6 and the recording medium 1 to shield the writing device 2 from the outside.

On the other hand, as shown in FIG. 5, in the reflection type writing device 8, the laser beam deflected by the deflector 4 is reflected by the fθ mirror 9, further reflected by the first plane mirror 11, and reflected by the lens 10. It is collected.
During this time, the laser beam converted from the constant angular velocity deflection to the constant velocity deflection is further reflected by the second plane mirror 12 and irradiated onto the recording medium 1.

Here, the support state of the plane mirrors 6, 11 and 12 in the two writing devices will be described with reference to FIG. 6 taking the plane mirror 6 as an example. FIG. 6 is an explanatory diagram showing a holding state of a plane mirror in a conventional writing device.

The plane mirror 6 has the same surface as the reflection surface of the laser beam 14 from the deflector 4 as a holding surface of the plane mirror itself. In other words, both ends in the longitudinal direction of the long side 15 in the substantially rectangular cross-sectional shape (which is not strictly rectangular because there are chamfers and the like) in which the plane mirror 6 is substantially perpendicular to the laser beam scanning direction are defined as reflecting surfaces. Abuts on the mirror support 16 also serving as a position regulating function. An elastic member 17 abuts on the back surface opposite to the abutted surface, and elastically presses and fixes the flat mirror 6 in the direction of the mirror support 16. Further, a through hole 19 for irradiating the photoconductor 1 with the laser beam 14 reflected from the plane mirror 6 is formed in the bottom plate of the writing device 2.

[0008]

By the way, image forming apparatuses such as laser beam printers are required to have high image quality and high resolution, and there is an increasing demand for higher precision writing apparatuses. As a result, as a writing apparatus, countermeasures against vibration of the flat mirror 21 are particularly important. That is, as described above, since the long side 15 side is used as the reflecting surface and the mounting surface, as shown in FIG. The vibration is in the direction perpendicular to the direction, that is, the arrow 18. As a result, the reflection surface oscillates, causing a change in the optical path length or a change in the angle. This change appears as a change in the emission position of the laser beam 14. Further, since the support surface of the mirror support 16 is the same as the reflection surface of the plane mirror 6, it must be positioned outside the scanning range of the laser beam 14, so that both ends of the plane mirror 6 serve as nodes. (The amplitude is also large) is assumed.

The present invention has been made in view of such a situation of the prior art, and has as its object to provide an optical writing device which can minimize the influence of vibration of a plane mirror and can even ignore it. It is in.

[0010]

In order to achieve the above object, a first means is to provide at least one mirror between an optical deflector and a surface of a photoreceptor and a light beam scanned at a constant angular velocity by the optical deflector. Conversion means for converting a beam into uniform-speed deflection, wherein the light deflector scans the surface of the photoconductor with the light deflector to perform light writing, and at least one of the mirrors One is
It is characterized in that the light beam is held by a holding means between two surfaces sandwiching a reflection surface for reflecting the light beam.

The second means is the first means, wherein the holding means supports a surface on one side of the mirror;
An elastic member for pressing the mirror supported by the support portion from the surface on the other side to the support portion side is provided.

[0013] A third means is the second means, wherein the mirror abuts on a regulating member for regulating the position at both ends of the reflecting surface outside the effective reflection range, and contacts the support portion within the effective reflection range. It is characterized by being in contact.

A fourth means is that in any one of the first to third means, the mirror has a substantially rectangular cross section perpendicular to the light scanning direction and a substantially rectangular cross section. Are set on the surface on the short side of

According to a fifth aspect, in the fourth aspect, a ratio of a long side to a short side of the rectangular section is set to about 2.0 or more, preferably 2.5 or more.

According to a sixth aspect, in the second aspect, the elastic member is provided in a pair, and is disposed at an asymmetric position with respect to the center of the mirror.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
An embodiment of the present invention will be described. FIG. 1 is an explanatory view showing a holding state of a plane mirror of an optical writing device according to an embodiment of the present invention, FIG. 2 is a plan view for explaining a holding state of a plane mirror, and FIG. It is a figure for explaining a moment.

As shown in FIG. 1, the plane mirror 21 of the present embodiment has a substantially rectangular cross section taken perpendicular to the scanning direction of the laser beam 14, and has two short sides perpendicular to the cross section. The long side 2
The surface corresponding to the third side is a holding surface. Then, as shown in FIG. 2, both ends of the short side 22 in the longitudinal direction are brought into contact with the position restricting portion 25 of the support, and the long side 23 is connected to the mirror support 2 of the support.
6 on. Therefore, the position regulating section 25 corresponds to the regulating member, and the mirror supporting section 26 corresponds to the supporting section. The other end of the elastic member 27, one end of which is fixed to the mirror support 26, is in contact with the surface of the flat mirror 21 on the side opposite to the mirror support 26 (the surface on the side of the long side 24). Is elastically pressed toward the mirror support 26. When held in this manner, the vibration of the plane mirror 21 is
The direction of the elastic pressure of the elastic member 27, that is, the direction of the arrow 28. Therefore, the reflecting surface (short side 22) moves in parallel on the same surface, the optical path length and angle do not change due to mirror deflection, and the emission position of the laser beam 14 hardly changes.

As shown in detail in FIG.
Position restricting portions 25a, 2 that are located outside the scanning range of the laser beam 14 and that support the plane mirror 21 from the laser beam irradiation side are provided at both ends in the longitudinal direction of the short side 22 corresponding to the reflecting surface of the laser beam.
5b is in contact. The two long sides 23 of the plane mirror 21 are provided on the two elastic members 2 arranged at intervals on mirror support portions 26a and 26b (not shown in FIG. 2) of the support.
7a and 27b press and fix the mirror supporting portions 26a and 26b. Although not described in detail, the mirror support portions 26a and 26b are, of course, two elastic members 27.
a, 27b, two elastic members 27a, 2
7b is a scanning range 2 of the laser beam 14 of the plane mirror 21.
9 are located at different distances c and d with respect to the center line 30 and inside the scanning range 29 of the laser beam 14. As described above, the mirror support portions 26a and 26b can be freely set inside the scanning range 29 of the laser beam 14,
By setting the position asymmetric with respect to the plane mirror 21,
It is possible to select a position where the vibration is the least or the amplitude is the smallest, so that the influence of the vibration is minimized.

When the plane mirror 21 is supported as described above, there is no problem with respect to vibration perpendicular to the long side 23 of the cross section of the plane mirror 21, but the plane mirror 21 may be twisted. Short side 22 to suppress torsional vibration
It is necessary to minimize the vibration in the direction perpendicular to the long side 23 and the long side 23 as much as possible. Since the magnitude of the vibration in the direction perpendicular to the short side 22 and the long side 23 is proportional to the second moment of area, the second moment of area in the direction perpendicular to the short side 22 is set to be at least 6 times as large as the other. I have. The second moment of area of the plane mirror 21 will be described in more detail with reference to FIG. Strength against vibration (amplitude)
Is proportional to the second moment of area. Here, assuming that the length of the short side 22 is a and the length of the long side 23 is b as a cross section of the plane mirror 21, the length of the long side 23 is n times (b = na) the short side 22. The moment of inertia at the time is expressed as follows.

Here, the second moment of area in the direction perpendicular to the short side 22 is Ix (second moment of area with respect to the X axis in FIG. 2), and the second moment of area in the direction perpendicular to the long side 23 is Iy (FIG. 2). When the second moment) with respect to Y-axis ^{in, Ix = ab 3/12,} Iy = a 3 b / 12 next, when this is substituted for ^{b = na, Ix = n 3} a 4/12, Iy = na 4 / 12. Accordingly, the ratio of the second moment is, Ix / Iy = n ² becomes proportional to the square of n.

Since the vibration in the direction perpendicular to the short side is clearly different from the vibration in the direction perpendicular to the long side, the ratio of the second moment of area is six times or more as described above. Then, Ix / Iy = n ² > 6, and the ratio n becomes n> 2.45. Therefore, the predetermined strength can be achieved by making the long side 23 approximately 2.5 times or more the short side 22, and by setting the long side 23 at least 2.0 times the short side 22, the torsional vibration is reduced. It can be suppressed effectively.

When such a mirror support structure is applied to the optical writing apparatus using the fθ mirror 9 described with reference to FIG. 5, the fθ mirror 9 and the plane mirrors 11 and 12 are used.
Since the optical path length can be ensured between the optical writing apparatus and the optical writing apparatus using the fθ lenses 5a and 5b shown in FIG.

[0023]

As is clear from the above description, according to the first and second aspects of the present invention, the change in the angle of the reflection surface of the flat mirror is affected by the vibration which is a general vibration and is perpendicular to the mounting surface. An optical writing device can be provided that is not or is very small and negligible.

According to the third aspect of the present invention, since the reflecting portion and the mounting surface of the flat mirror are separated, the mounting portion can be freely set with respect to the effective incident range of the laser beam, and the vibration of the flat mirror is reduced. It becomes higher order and the vibration amplitude can be reduced.

According to the fourth aspect of the present invention, it is possible to provide a low-cost plane mirror which suppresses torsional vibration with respect to the plane mirror, exhibits ease of holding during polishing, and has low cost.

According to the fifth aspect of the present invention, the ratio of the long side to the short side of the rectangular cross section is set to at least 2.0 or more. Can be made smaller.

According to the sixth aspect of the present invention, the vibration amplitude can be further reduced since the plane mirror is asymmetric with respect to the plane mirror, that is, the lengths of the front and rear mounting portions and the front and rear free ends are asymmetric.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a holding state of a plane mirror according to an embodiment of the present invention.

FIG. 2 is a plan view for explaining a holding state of a plane mirror.

FIG. 3 is a diagram for explaining a second moment of area of the plane mirror.

FIG. 4 is a diagram illustrating a basic configuration of a general optical writing device of an fθ lens system.

FIG. 5 is a diagram illustrating a general configuration of a reflection type optical writing device using an fθ mirror.

FIG. 6 is a diagram illustrating a holding state of a plane mirror in a conventional optical writing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording medium 2, 8 Writing device 4 Deflector 14 Laser beam 21 Flat mirror 21a Reflection surface 22 Short side 23, 24 Long side 25a, 25b Position control part 26 Mirror support part 27a, 27b Elastic member

Claims (6)

[Claims] An optical deflector includes at least one mirror between the light deflector and the surface of the photoreceptor, and a conversion means for converting a light beam scanned at a constant angular velocity by the light deflector into a constant velocity deflection. In an optical writing device that performs optical writing by scanning the surface of the photosensitive member with the emitted light beam using the optical deflector, at least one of the mirrors is held between two surfaces sandwiching a reflection surface that reflects the light beam. An optical writing device characterized by being held by means. 2. The image forming apparatus according to claim 1, wherein the holding unit includes a support portion that supports one surface of the mirror and an elastic member that presses the mirror supported by the support portion from the other surface toward the support portion. 2. The optical writing device according to claim 1, wherein: 3. The mirror according to claim 1, wherein the mirror is in contact with a regulating member for regulating a position at both ends of the reflecting surface outside the effective reflection range, and is in contact with the support portion within the effective reflection range. Item 3. The optical writing device according to Item 2. 4. The mirror according to claim 1, wherein a surface of the mirror cross-section perpendicular to the light scanning direction is formed in a substantially rectangular shape, and the reflection surface is set to a surface on a short side of the substantially rectangular cross-section. Item 4. The optical writing device according to any one of Items 1 to 3. 5. A ratio of a long side to a short side of the rectangular cross section is set to about 2.0 or more.
An optical writing device according to claim 1. 6. The optical writing device according to claim 2, wherein a pair of said elastic members are provided, and are disposed at positions asymmetric with respect to a center of said mirror.