JPH11149033A - Write-in unit for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image having excellent image quality by enhancing supporting rigidity, reducing the resonance frequency of an oscillation frequency band area to be evaded and reducing the vibration of a reflection mirror without causing a remarkable change in a conventional fixed structure. SOLUTION: As for a write-in unit provided with an optical unit 2 having a laser light source part 4 and a polygon motor 5, the reflection mirror reflecting a laser beam 7 radiated by the optical unit 2 to a photoreceptive drum 8 and a frame 1 to hold the optical unit, at least one guide 9 out of a pair of the guides 9 holding both ends of the reflection mirror 3 is installed by having an angle to a direction orthogonal with the longitudinal direction of the reflection surface of the reflection mirror 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writing unit suitable for an image forming apparatus such as an electrophotographic laser printer, a copying machine, and a facsimile, and more particularly to an improvement in a fixing structure of a folding mirror.

[0002]

2. Description of the Related Art The basic structure of a writing unit used in an image forming apparatus using laser light is as follows: an optical unit having a laser light source, a polygon motor and an Fθ lens;
The laser light emitted from the optical unit is reflected on the photoreceptor by a folding mirror. The laser light emitted from the laser light source is scanned by a polygon mirror that is rotated by a polygon motor and passed through an Fθ lens to be folded. Reach the mirror. The laser light that has reached the turning mirror is reflected downward and reflected on the photosensitive drum, and the rotation of the photosensitive drum forms a dot image for one page as an electrostatic latent image on the photosensitive drum. In the above, the vibration from the drive system due to the polygon motor and the peripheral gears is transmitted to the folding mirror and the frame, and these resonate, so that the laser light irradiated on the photoconductor fluctuates due to the vibration, and the writing is performed. Is disturbed and the image quality is degraded. That is, one of the factors that hinder the improvement of the image quality of electrophotography is a phenomenon called jitter or banding. Note that jitter and banding are synonymous, and are a phenomenon in which, when optical writing is performed at a constant pitch in any given direction, a black and white stripe is formed in a written image due to a shift. . In particular, when the improvement of image quality is promoted by the introduction of digital technology, the positional accuracy of each line of writing by laser is strictly required. In addition, for a color image, several colors of toner are superimposed on the same position a plurality of times to express a desired color. Therefore, in a situation where such jitter or banding occurs, color misregistration or image blur is caused. Occurs. Therefore, reduction of the blurring of the laser beam is an important technology in developing a product for obtaining a high-quality image. In this regard, for example, in the invention described in Japanese Patent Application Laid-Open No. 8-2000, the propagation of vibration is prevented by arranging the polygon motor and the folding mirror in separate frames. Further, in the invention described in Japanese Patent Application Laid-Open No. Hei 2-253274, a flexural vibration of the mirror is attenuated by arranging a buffer member on the side of the folded mirror that is orthogonal to the semi-paper or plane. Further, JP-A-60-24
In the invention described in Japanese Patent No. 491, the bending vibration of the mirror is attenuated by attaching a buffer member and a metal member to the non-reflective surface of the folding mirror.

[0003]

However, the structure disclosed in Japanese Patent Application Laid-Open No. 8-2000 has a drawback that the frame is separated, so that the apparatus becomes large, and it is difficult to reduce the size and cost. Also, JP-A-2-253274,
Although the device disclosed in Japanese Patent Application Laid-Open No. 60-24491 has a vibration damping effect, it does not cover all vibration frequency bands because a resonance point is generated by its natural vibration frequency. By the way, the relationship between the visual sensitivity of an image and the space or frequency depends on the characteristics of the human visual system.
A density change in the range of 2 to 4 lines / mm (= 5 mm to 0.25 mm pitch) is most noticeable and is easily recognized as jitter or banding. That is, it is necessary to avoid vibration at least in the range from the minimum value of the visual sensitivity of the linear velocity / pitch to the maximum value of the visible sensitivity of the linear velocity / pitch. If this is applied to the case where the linear velocity is 200 mm / s, the minimum frequency to be avoided is 40 to 800 Hz. Jitter,
The relationship between the banding image unevenness (pitch), the laser vibration frequency, and the linear velocity (rotation speed × drum radius) of the photoconductor surface can be expressed by pitch = linear velocity / vibration frequency. For example, when the linear velocity is 200 mm / s and the vibration frequency is 200 Hz, the pitch of the image unevenness is 1 mm, and the linear velocity is 250 mm.
In the case of / s and the vibration frequency of 500 Hz, the pitch of the image unevenness is 0.5 mm. Taking these into consideration, it is required to avoid laser blurring in a certain frequency range. As means for avoiding this blur, the present inventor has focused on increasing the support rigidity of the folding mirror. However, the length of the mirror is set to the width of the paper, and there are restrictions on the reflection area, etc., so the basic support structure and material cannot be changed. Without changing to the above, it was examined to increase the support rigidity as much as possible within the range. The present invention has been made based on the above, and an object of the present invention is to improve the support rigidity without significantly changing the conventional fixed structure by devising the support structure of the folding mirror, and to improve the vibration to be avoided. An object of the present invention is to provide a writing unit of an image forming apparatus in which a resonance frequency in a frequency band is reduced and vibration of a folding mirror is reduced, thereby achieving high image quality.

[0004]

According to a first aspect of the present invention, there is provided an optical unit having a laser light source unit and a polygon motor, and a laser beam emitted from the optical unit is applied to a photosensitive member. In a writing unit including a reflecting mirror for reflecting and a frame for holding the optical unit, a guide line in which at least one of the pair of guiding means for holding both ends of the reflecting mirror supports the reflecting mirror surface is provided. The folding mirror is installed at an angle with respect to a width direction orthogonal to the longitudinal direction of the reflection surface of the folding mirror. Therefore, according to the first aspect of the present invention, it is possible to increase the support rigidity of the folding mirror and increase the resonance frequency with a simple structure, and to obtain an image forming apparatus with less jitter and banding. According to a second aspect of the present invention, the guide line for supporting the folding mirror surface by the pair of guide means for holding the folding mirror is linear, and each guide line is in a width direction perpendicular to the longitudinal direction of the reflecting surface of the folding mirror. Since they are installed at an angle with respect to each other and are installed so as to be non-parallel to each other, a sufficient support length at both ends can be ensured, and higher image quality can be obtained. According to a third aspect of the present invention, the guide line for supporting the folding mirror surface by the pair of guide means for holding the folding mirror is linear, and the angle is set to the width direction orthogonal to the longitudinal direction of the reflecting surface of the folding mirror. It is characterized by being held and held in parallel with each other, so that a sufficient supporting length can be secured. The invention according to claim 4 is characterized in that the pair of guide means for holding the folding mirror is shaped like a letter guide for supporting the surface of the folding mirror, so that the supporting length on both sides can be further secured. The invention according to claim 5 is characterized in that each of the U-shaped guide lines for holding the folding mirror is installed symmetrically, so that the support length at both ends can be sufficiently increased without interfering with the reflection area. Can be secured. The invention according to claim 6 is
When H is the height dimension of the reflection surface of the folding mirror and T is the dimension in the thickness direction, H ≦ T is satisfied. In addition to the above effects, the mirror itself can be formed in a vibration mode with less resonance. According to a seventh aspect of the present invention, there is provided an image forming apparatus including a writing unit including the guide unit having the configuration described in any one of the first to sixth aspects.

[0005]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG.
1 schematically shows a writing unit in an image forming apparatus to which the present invention is applied. The writing unit in the figure has an optical unit 2 and a folding mirror 3 mounted on a frame 1. The optical unit 2 includes a laser light source 4, a polygon motor 5, and an Fθ lens 6. Laser light 7 emitted from the laser light source 4 is scanned by the polygon mirror 5 and transmitted through the Fθ lens 6. The laser beam 7 transmitted through this portion is reflected by the turning mirror 3 and irradiates the surface of the photosensitive drum 8 to form an electrostatic latent image. In addition,
The photoreceptor drum 8 works with a toner cartridge (not shown), a paper feed system driving mechanism, and the like, and transfers the toner adhered to the electrostatic latent image onto paper. The paper to which the toner has been transferred is sent to a fixing device and fixed by heat. In the above configuration, the frame 1 of the writing unit is usually placed in a state where external vibration (disturbance vibration) from a motor or a driving body existing inside and outside the unit is transmitted. When the natural frequency of the component in the unit is similar, the component resonates and exhibits a unique dynamic deformation (vibration mode) according to the resonance frequency. On the other hand, since the folding mirror 3 needs to reflect the scanning light as its function, as shown in FIG. In order to reach the space, a space A (see FIG. 1) for transmitting light is required below the fixed portion of the folding mirror 3.
Therefore, the support area of the folding mirror 3 is limited to a portion surrounded by hatching in the drawing, avoiding the reflection area 11, and as shown in FIG. In general, a structure in which both ends are pressed and fixed at two points. On the other hand, the length of the folding mirror 3 needs at least an image width, in other words, a printing paper width.
mm to about 440 mm. When the mirror 3 having such a length is supported at both ends, a plurality of resonance frequencies of the folding mirror 3 are generated in the above-described region of the oscillation frequency to be avoided, which causes the above-described jitter and banding.
These resonance frequencies depend on the dimensions, shape, fixed form, and material of the mirror. For example, the dimensions of the folding mirror 3 are length L = 266 mm, height H = 14 mm, thickness t = 5 mm,
FIG. 4 shows the resonance modes of the conventional mirror at the respective resonance frequencies when the fixed position R = 8 mm from both ends and the material = glass.

In FIG. 4, (a), (c), (d)
Are vibrations in the direction perpendicular to the reflection surface of the turning mirror 3, and these vibrations directly cause blurring of the laser beam 7, and are resonances to be dealt with as much as possible. The vibration is a vibration in a direction horizontal to the reflection surface of the mirror 3, and these vibrations do not directly cause blur in the laser light, but when the vibration frequency received from the outside is different from the resonance frequency, the reflection surface This is a resonance that is desirably handled because it is slightly deformed even in a direction perpendicular to the direction. Table 1 below shows the relationship between the image uneven pitch and the resonance frequency.

[0007]

[Table 1] In any case, it is necessary to reduce the resonance frequency in the vibration frequency band to be avoided, in other words, to increase each resonance frequency. As described above, the human visual characteristic has a spatial frequency of 0.2 to 4 line / mm (= 5 mm to 0.
The density change in the range of (25 mm pitch) is most noticeable, and has a peak especially at 0.5 line / mm. Therefore,
Even if resonance is unavoidably left in the frequency band to be avoided, raising the frequency a little makes it less noticeable to humans, so that the image can be improved. For this reason, in the present invention, the shape of the guide for fixing the both ends of the mirror has the structure described in claims 1 to 4, so that the resonance frequency is increased. In addition to the above measures, the resonance frequency can be further increased by making the height of the cross section in the longitudinal direction of the mirror equal to the thickness or increasing the thickness to increase the rigidity of the mirror itself. .

[0008]

Next, based on the above-mentioned viewpoints, as a folding mirror, a length L = 266 mm, a height H = 14 mm, and a thickness t = 5.
mm, fixed position R = 8 mm from both ends, material = glass, linear velocity 220 mm / s, the difference between the conventional example and the present invention will be described. FIG. 5 shows a conventional example. As shown by a bold line in FIG. 5, a folding mirror 3 is provided on a line (hereinafter referred to as a guide line) GL parallel to the height direction of the mirror reflecting surface. The guide 10 is supported by a spring 10 (see FIG. 3), and the position of the guide line GL is
Is 8 mm wide from its end on both sides. In this case, the vibration frequency band to be avoided is 40 to 880 Hz,
Three resonances occurred in this band. Guideline G
L indicates a line where the guide 9 and / or the leaf spring 10 shown in FIG. 3 respectively support the folding mirror, in other words, a line in contact with (or along) the mirror surface, and the guide 9 and the leaf spring 10 Include the case where they both touch (along) the illustrated guideline GL and the case where only one of them touches (along). Therefore, it means that the guide 9 or the leaf spring 10 is configured so that the shape of the surface (surface along) that comes into contact with the turning mirror is in accordance with the guideline GL. Therefore,
In the claims, the guide 9 and / or the leaf spring 10 are collectively referred to as guide means. This point is similarly applied to the description of the embodiment below.

In contrast to the above-mentioned conventional supporting structure, the supporting structure of the present invention has a guideline GL as shown in FIGS.
The shape of the guide is set so that at least one of them has an angle with respect to a direction perpendicular to the longitudinal direction of the reflecting surface of the turning mirror. The folding mirror 3 has a reflection area in the center and a space below the reflection area, so that the area that can be used for fixing is limited. Therefore, in the following description of the embodiment, a case will be described as an example in which a fixed region exists in a region 12 mm inward from both ends in the longitudinal direction of the mirror. A basic feature common to each embodiment is that at least one of the pair of guide lines GL is not parallel to the width direction (width direction along the plane) orthogonal to the longitudinal direction of the folding mirror, but has a certain angle. It is configured to have. In the conventional supporting method, the distribution (stress) of the force for bending the mirror is in a direction horizontal to the height direction of the mirror, so that the mirror is easily bent by a small force. In this embodiment, however, the stress distribution has an angle with respect to the height direction of the mirror, and as a result, the stress is dispersed. For this reason, in the present embodiment, the force required to cause substantially the same bending increases,
This means that the resonance frequency increases. Furthermore, for example, when applying a certain bending force with both ends of a rectangular parallelepiped object made of the same length, height, and material, bending the thicker one causes more force. It is the same theory that a thicker one has a higher resonance frequency. In any of the embodiments described below, the resonance frequency in the target frequency band of 40 to 880 Hz can be higher than that of the conventional example, or the number of resonances can be reduced. First, the folding mirror 3 shown in FIG.
Are set in such a manner that the guide lines GL on both sides are not parallel to the direction (width direction) orthogonal to the longitudinal direction of the reflecting surface of the folding mirror 3, but are set at a predetermined angle with respect to the width direction, and are in a C-shape with each other. (Including the inverted letter C) The dimensions from both ends are as shown.

Next, in the folding mirror 3 shown in FIG. 7, the guide lines GL on both sides of the folding mirror 3 are not parallel to the direction (width direction) orthogonal to the longitudinal direction of the reflecting surface of the folding mirror 3, but intersect at a predetermined angle with respect to the width direction. And placed in parallel with each other. When the guide line is composed of one straight line, the parallel guide line can maximize the resonance frequency. This is because the stresses spreading from the guidelines are parallel to each other and do not intersect.
This is apparent from the example of the embodiment shown in FIGS. 6 and 8 having the guideline composed of one straight line and the example of the resonance frequency corresponding to the embodiment shown in FIG. 7 (Table 2). Next, in the folding mirror 3 shown in FIG. 8, one of the guide lines GL on both sides is orthogonal to the longitudinal direction of the reflecting surface of the folding mirror (parallel to the width direction), and the other is inclined. When bending the mirror with the guide line as a fulcrum, the stress basically proceeds in a direction orthogonal to the guide line while being affected by the shape of the mirror. That is, when the two guidelines have an angle with each other, the stresses spreading from the left and right support ends are not in the same direction, and the stresses are dispersed. That is,
The resonance frequency will be higher.

Next, in the folding mirror 3 shown in FIG. 9, the guide lines on both sides thereof are symmetrically installed at an angle angle outward toward each other with respect to a direction intersecting the longitudinal direction of the reflecting surface of the folding mirror 3. ing. The U-shape may be an obtuse angle as shown or may be an acute angle not shown. In addition, although the top of the U-shape is drawn to face outward, it may be turned to the inside. In this embodiment, the stress spreads in a direction perpendicular to the individual lines of the guide line GL bent in a V shape.
The two stresses intersect at a position slightly inside from the supporting end side where the stress is relatively small, and the stresses spread in different directions, so that the stresses are dispersed on the mirror. Therefore, an advantageous support structure can be obtained as compared with the other embodiments. This can be understood from the fact that the resonance frequency of the embodiment of FIG. 9 is highest. In addition, only one guide line may be shaped like a letter, and the other guide line may be shaped like a straight line as shown in FIGS. It is needless to say that the guide line GL in each of the above-described drawings can be arranged symmetrically in the upper, lower, left, and right directions. In this case,
In addition to providing the same effect as in the case of FIG. 9, the symmetrical shape provides an advantage that the parts can be easily manufactured.

By setting various support structures as described above, in the conventional support structure, the distribution of force (stress) used to bend the mirror is parallel to the height direction of the mirror. In contrast, in the present invention, the stress distribution tends to have an angle with respect to the height direction of the mirror, which results in the dispersion of the stress. This requires more force to produce substantially the same bending, which is equivalent to a higher resonance frequency. In other words, when making a certain bend with both ends of a rectangular parallelepiped made of the same length, height, and material, the thicker or the shorter unconstrained length has more Equivalent to a phenomenon requiring power. Table 2 below shows the resonance frequencies obtained by calculation and analysis in the case of each of the support forms shown in FIGS. FIG. 10 shows a reference example in which the guide line is set within a range of 12 mm from both ends of the mirror in the conventional support structure.

[0013]

[Table 2] As is clear from the numerical values shown in the above table, even in comparison with the conventional example and the reference example, the support structure of the present invention generally has a higher resonance frequency in each resonance mode, and the various structures of the present invention. Is advantageous. As another preferred embodiment of the present invention, when the height dimension of the reflecting surface of the folding mirror is H and the dimension in the thickness direction is T, H ≦
T can be mentioned. Normally, resonance is generated in order from the direction in which bending is easy. However, by configuring each of the above embodiments so that H ≦ T, the resonance generated first is in a direction orthogonal to the reflection direction of laser light. The resonance frequency can be further increased. In other words, the first resonance can be set to a vibration mode having little effect on the image unevenness, and further, the resonance affecting the image unevenness can be shifted to a higher frequency than the first resonance. Since all resonances can be shifted to a higher frequency, it is possible to provide a writing unit with very little jitter and banding.

[0014]

As described above, in the writing unit of the image forming apparatus according to the present invention, the resonance frequency is increased by simply changing the support structure, thereby preventing jitter and banding. High definition images can be obtained. In other words, according to the first aspect of the present invention, a guide line in which at least one of the pair of guide means holding the both ends of the folding mirror supports the folding mirror surface is perpendicular to the longitudinal direction of the reflection surface of the folding mirror. Since it is configured to have an angle with respect to the width direction, it is possible to increase the support rigidity of the folding mirror and increase the resonance frequency with a simple structure, and to obtain an image forming apparatus with less jitter and banding. . In the invention described in claim 2, the guide lines are linear, and each guide line is installed at an angle to a width direction orthogonal to the longitudinal direction of the reflecting surface of the turning mirror, and is not parallel to each other. Since it is installed, the supporting length at both ends can be sufficiently secured, and the supporting rigidity of the folding mirror can be increased by a simple structure, and the resonance frequency can be increased,
Jitter and banding can be reduced, and image quality can be improved.
According to the third aspect of the present invention, the guide line is linear, is installed at an angle to the width direction orthogonal to the longitudinal direction of the reflecting surface of the folding mirror, and is installed in parallel with each other. Thus, the resonance frequency of the folding mirror can be made higher than in the case of claim 2, jitter and banding can be reduced, and image quality can be improved. According to the fourth aspect of the present invention, since the guide line is in the shape of a letter, the supporting length can be increased without interfering with the reflection surface, and the resonance frequency of the folded mirror can be made simpler than in the case of the second and third aspects. Can be increased, jitter and banding can be reduced, and image quality can be improved. According to the fifth aspect of the present invention, since each of the U-shaped guide lines is symmetrically installed, the resonance frequency of the folding mirror can be increased with a simple structure as compared with the case of the second and third aspects. Jitter and banding can be reduced, and image quality can be improved. In addition, since a symmetrical part is manufactured, manufacturing costs can be reduced. According to the sixth aspect of the present invention, when the height dimension of the reflecting surface of the folding mirror is H and the dimension in the thickness direction is T, H ≦ T, the mirror itself can be made more resonant in addition to the above effects. It can be formed in a small vibration mode. That is, the first resonance can be set to a vibration mode having little effect on the image unevenness, and the resonance affecting the image unevenness can be shifted to a higher frequency than the first resonance. Since resonance can be shifted to a higher frequency, it is possible to provide a writing unit with very little jitter and banding. An image forming apparatus according to a seventh aspect of the present invention includes the writing unit including the guide unit having the configuration described in any one of the first to sixth aspects. Image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a writing unit of an image forming apparatus to which the present invention is applied.

FIG. 2 is an explanatory front view of a folding mirror of the unit.

FIG. 3 is an explanatory view showing a general support structure of the folding mirror.

FIGS. 4A to 4E are frame wire diagrams showing resonance modes applied to a mirror.

FIG. 5 is an explanatory view showing a conventional folding mirror support structure.

FIG. 6 is an explanatory view showing a first embodiment of a mirror support structure according to the present invention.

FIG. 7 is an explanatory view showing the second embodiment.

FIG. 8 is an explanatory view showing the third embodiment.

FIG. 9 is an explanatory view showing the fourth embodiment.

FIG. 10 is an explanatory diagram showing a reference example.

[Explanation of symbols]

 1 frame 2 optical unit 3 folding mirror 4 laser light source 5 polygon motor 7 laser beam 8 photosensitive drum 9 guide

Claims (7)

[Claims] 1. A writing unit including a laser light source unit, an optical unit having a polygon motor, a folding mirror for reflecting laser light emitted from the optical unit to a photoconductor, and a frame for holding the optical unit, Of the pair of guide means for supporting both ends of the folding mirror with respect to the frame, at least one guide means supports the folding mirror surface, and the guide line has an angle with respect to a width direction orthogonal to the longitudinal direction of the folding mirror surface. A writing unit for the image forming apparatus, wherein the writing unit is installed with the image forming apparatus. 2. A guide line in which a pair of guide means supporting the folding mirror supports the folding mirror surface is linear, and each guide line has an angle with respect to a width direction orthogonal to a longitudinal direction of the folding mirror surface. 2. The writing unit according to claim 1, wherein the writing unit is installed so as to be non-parallel to each other. 3. A guide line in which a pair of guide means for holding the folding mirror each support the folding mirror surface is linear, and is installed at an angle to a width direction orthogonal to a longitudinal direction of the folding mirror surface. 2. The writing unit of an image forming apparatus according to claim 1, wherein the writing units are installed in parallel with each other. 4. The writing unit of an image forming apparatus according to claim 1, wherein the guide means for holding each of the folding mirrors and supporting the surface of the folding mirror is shaped like a letter. 5. The writing unit of the image forming apparatus according to claim 4, wherein each of the letter-shaped guide lines for holding the folding mirror is installed symmetrically along a longitudinal direction of the folding mirror. 6. The height dimension of the reflecting surface of the folding mirror is H,
6. The writing unit of an image forming apparatus according to claim 1, wherein when a dimension in a thickness direction is T, H ≦ T is satisfied. 7. An image forming apparatus, comprising: a writing unit including the guide means having the configuration according to claim 1. Description: