JP3721812B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an image forming apparatus such as a copying machine or a printer that scans a light beam with a light beam scanning device and draws an image on a drawing target such as a photosensitive drum, and is propagated to the light beam scanning device. The present invention relates to an improvement in technology for suppressing vibrations in the light beam scanning apparatus.
[0002]
[Prior art]
A laser beam scanning device used in an image forming apparatus such as a digital copying machine or a laser printer deflects the optical path of a laser beam modulated in accordance with image data, and performs exposure scanning on the photosensitive drum. Yes. By this exposure scanning, an electrostatic latent image is formed on the photosensitive drum, which is developed to form an image. Therefore, if the exposure scanning position by the laser beam fluctuates, the image quality is adversely affected. As a method of attaching the laser beam scanning device, there is a method of screwing and fixing to the main body frame of the image forming apparatus. According to this method, the laser beam scanning device is firmly fixed to the main body frame, and its mounting accuracy can be increased. On the other hand, mechanical vibrations generated by a driving device such as a photosensitive drum other than the laser beam scanning device. (Hereinafter, referred to as “external vibration”) is directly propagated from the main body frame to the laser beam scanning device, which causes a problem that the exposure scanning position fluctuates and adversely affects image quality.
[0003]
JP-A-7-84203 can be cited as a conventional technique for solving such a problem. In this publication, vibration generated by rotation of a polygon mirror for deflecting a laser beam is absorbed by a vibration absorber attached to the base of the laser beam scanning device, thereby reducing the vibration of the device. Are disclosed.
[0004]
[Problems to be solved by the invention]
However, the above-described method of simply attaching the vibration absorber to the pedestal cannot effectively suppress external vibration. In other words, the above method is intended to suppress only vibration generated from the polygon mirror rotating at a constant speed. Therefore, if a vibration absorber corresponding to this is attached to the pedestal, a corresponding vibration suppression effect can be obtained. it can. However, the vibrations propagated as external vibrations include many high and low vibrations, and when the vibration absorber matches its natural frequency with the frequency to be controlled. Since a large damping effect can be obtained, if all of these vibrations are to be controlled, it is necessary to provide a large number of vibration absorbers for each frequency to be controlled. This not only leads to an increase in cost, but also the laser beam scanning device itself becomes heavy, which is against the demand for weight reduction of the image forming apparatus.
[0005]
The present invention has been made in view of the above-described problems, and it is possible to effectively suppress the vibration transmitted to the laser beam scanning apparatus by using a minimum vibration absorbing means, thereby degrading the image quality of a reproduced image. An object of the present invention is to provide an image forming apparatus capable of preventing the above-described problem.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is an image forming apparatus that draws an image on a drawing target by scanning a light beam with a light beam scanning device, and is provided at a rod-shaped member and an end of the rod-shaped member. The rod-shaped member is provided with a first convex portion and a second convex portion spaced apart from each other in the longitudinal direction, and the first convex portion is the light beam scanning device. The mounting base is connected to a position corresponding to or near one of the antinodes in the secondary vibration mode in the direction toward the drawing target, and the second convex portion is connected to the other vibration mode in the secondary vibration mode. It is connected to a position corresponding to the belly or a position in the vicinity thereof, and the vibration absorber suppresses vibrations of both belly parts in the secondary vibration mode via the rod-shaped member. To do.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example in which an embodiment of an image forming apparatus according to the present invention is applied to a monochrome laser printer (hereinafter simply referred to as “printer”) will be described.
FIG. 1 is a diagram illustrating a schematic configuration of the entire printer.
This printer reproduces an image on a recording sheet based on image data input from an external device such as a personal computer. When image data is input from an external device, the control unit 1 converts this into a drive signal for the laser diode, and drives the laser diode 12 (FIG. 2) inside the printer head 10 which is a light beam scanning device. The laser beam L emitted from the laser diode 12 is deflected by the folding mirror 2 and then exposes the surface of the photosensitive drum 4 in the main scanning direction.
[0009]
Around the photosensitive drum 4, a drum cleaner 5, an eraser lamp 6, a charging charger 7, a developing device 8, and a transfer charger 9 are arranged.
The photosensitive drum 4 is uniformly charged by the charging charger 7 after the residual toner is removed by the drum cleaner 5 before being exposed by the laser beam L and irradiated by the eraser lamp 6. When the charged surface of the photosensitive drum 4 is exposed by the laser beam L, an electrostatic latent image is formed, and the electrostatic latent image is visualized as a toner image by the developing device 8.
[0010]
On the other hand, a recording sheet is fed from the sheet feeding cassette 20 by a pickup roller 21 and a timing roller 22. This recording sheet is conveyed by the transfer belt 23 to a transfer position directly below the photosensitive drum 4. At the transfer position, the toner image on the photosensitive drum 4 is transferred onto the recording sheet by the action of the transfer charger 9. The recording sheet to which the toner image has been transferred is further conveyed by the transfer belt 23 and the conveyance belt 24, and after the toner is fixed by the fixing device 25, the recording sheet is discharged to the discharge tray 28.
[0011]
FIG. 2 is a schematic configuration diagram of the inside of the printer head 10 as viewed from above.
The printer head 10 is configured by housing a laser diode 12, a collimator lens 13, a cylindrical lens 14, a polygon mirror 15, a toroidal lens 16 and an fθ lens 17 in a casing 11.
In such a configuration, the laser beam L emitted from the laser diode 12 is converted into parallel light by the collimator lens 13, condensed in the sub-scanning direction by the cylindrical lens 14, and rotated at a constant speed by a polygon motor (not shown). Is deflected by the polygon mirror 15. Thereafter, it passes through the toroidal lens 16 and the fθ lens 17 and reaches the folding mirror 2 as described above.
[0012]
FIG. 3 is a perspective view showing a state in which the laser beam L emitted from the printer head 10 performs exposure scanning on the photosensitive drum 4, and here, from the printer head 10 to the photosensitive drum 4 is illustrated. The members are omitted. The printer head 10 is mounted on a mounting base 30 fixed to the front frame 26 and the rear frame 27 of the printer main body with two screws S, respectively. Further, as shown in the figure, the mounting base 30 is a plate-like body and has a structure in which the four sides are bent to increase the rigidity. In this way, if the mounting base 30 is screwed and fixed, the mounting accuracy of the printer head 10 itself can be increased. However, as described above, external vibration is propagated and the printer head 10 vibrates. The problem that it ends up also arises.
[0013]
Therefore, in the printer according to the present embodiment, the vibration absorber 50 is located on the back surface of the mounting base 30 to which the printer head 10 is attached, at a position corresponding to the antinode when the mounting base 30 vibrates in the secondary vibration mode. Is attached so as to effectively suppress the transmitted vibration and prevent deterioration of the reproduced image.
A plate-like body such as the mounting base 30 generally has a plurality of natural frequencies F1, F2,. . It is known that when a vibration having substantially the same frequency as this natural frequency is propagated, it vibrates (resonates) in a specific shape (vibration mode) according to the natural frequency. Further, as is well known, when the frequency of the transmitted vibration is deviated from the natural frequency, the amplitude is smaller than that in the case of resonance. This natural frequency is a natural frequency obtained from the mass of the mounting base 30 and the spring constant.
[0014]
As this vibration mode, there are ones as shown in FIGS. Both figures show the mounting base 30 when viewed from the direction of arrow X in FIG. 3 (direction parallel to the main scanning direction on the photosensitive drum 4), and in the direction of arrow Y in FIG. 3 (photosensitive drum). 4 shows a state in which the mounting base 30 vibrates in a vibration mode in which the traveling direction is 4). Here, the vibration mode when the mounting base 30 vibrates as shown in FIG. 4A due to the propagated external vibration is called a primary vibration mode, and the vibration when the mounting base 30 vibrates as shown in FIG. 4B. The mode is called secondary vibration mode. In addition, both figures are exaggerated to clarify the shape when the mounting base 30 vibrates in each mode, and is practically invisible.
[0015]
As shown in FIG. 4A, when the mounting base 30 vibrates in the primary vibration mode, both end portions become nodes, and the position having the largest amplitude (center portion) becomes an antinode. The node portion has an amplitude of zero or minimum, and the antinode portion moves up and down with the position indicated by the broken line as a reference position. When the mounting base 30 vibrates in this way, the laser beam L emitted from the printer head 10 mounted on the mounting base 30 translates in the vertical direction. Since this movement amount is very small, it hardly affects the reproduced image.
[0016]
On the other hand, as shown in FIG. 4B, when the mounting base 30 vibrates in the secondary vibration mode, both end portions and the central portion become nodes, and the positions having the largest amplitude (the left end portion, the central portion, and the right end portion) Two places (intermediate middle portions) become stomachs. As in the first-order mode, the node portion has zero or minimum amplitude regardless of vibration. The abdomen portions are alternately moved so that when the position indicated by the broken line is the reference position, when one abdomen is located above, the other abdomen is located below. That is, the mounting base 30 swings in the vertical direction with the node at the center as a fulcrum, and the laser beam L emitted from the printer head 10 also swings in the vertical direction. In this case, the exposure scanning position on the photosensitive drum 4 by the laser beam L is enlarged in the sub-scanning direction as compared with the case of simply moving in the vertical direction as in the case of vibrating in the primary vibration mode. It will fluctuate, and the density of the scanning pitch becomes remarkable.
[0017]
Actually, other vibration modes also occur, but the degree of influence of the secondary vibration mode on the quality of the reproduced image becomes larger. If the vibration in the secondary vibration mode is suppressed, the image quality deterioration can be minimized. Therefore, in this printer, the vibration absorber 50 is attached only to the portion corresponding to the antinode where the amplitude is the largest.
[0018]
5 is a cross-sectional view taken along line AA in FIG. The vibration absorber 50 in this printer is a position substantially corresponding to the left antinode shown in FIG. 4B, and is approximately D / L from the left end when the length of the mounting base 30 in the arrow Y direction in FIG. It is attached at a position of 4 lengths. The position of the antinode is obtained by analyzing (simulating) the printer itself by representing the vibration system model with finite degrees of freedom. The position of the belly is the position when the mounting base 30 which is a plate-like body is screwed and fixed to the front frame 26 and the rear frame 27. For example, the shape of the mounting base 30 and the fixing method to the printer body frame, etc. If the conditions are different, it will vary accordingly. Therefore, it is necessary to obtain the exact position of the antinode by performing the above simulation or an experiment (vibration experiment) for forcibly applying vibrations of various frequencies to the mounting base 30. Such simulations and vibration experiments can be performed relatively easily, whereby the position of the antinode of the secondary vibration mode can be specified.
[0019]
FIG. 6 is a schematic external view of the vibration absorber 50. The vibration absorber 50 is a well-known one composed of a viscous damping part 51 and an auxiliary mass part 52 made of a spring and a damping member. Since the vibration absorber 50 is provided to suppress the vibration of the mounting base 30 in the secondary vibration mode, the mass, the spring constant, and the like are determined so as to exhibit the vibration damping effect in the secondary vibration mode. The Specifically, if the natural frequency of the vibration absorber 50 is adjusted to be substantially the same as the frequency of the secondary vibration mode of the mounting base 30, the auxiliary mass unit 52 vibrates most in the secondary vibration mode. Thus, the vibration of the belly portion of the mounting base 30 is suppressed, and the greatest vibration damping effect can be obtained. The frequency of the secondary vibration mode can also be obtained by the simulation. Further, the vibration absorber 50 is bonded to the back surface of the mounting base 30 so as not to come off due to vibration.
[0020]
Thereby, it is possible to efficiently absorb the vibration that affects the image with the minimum vibration absorber 50.
FIG. 7A shows a case where the vibration absorber 50 is not attached to the mounting base 30, and the relationship between the frequency of vibration propagated to the mounting base 30 and the maximum amplitude when the mounting base 30 vibrates. FIG. 7B is a schematic diagram showing the relationship between the frequency of the vibration and the amount of positional deviation of the exposure scanning position in the sub-scanning direction on the photosensitive drum 4. It was obtained by simulation.
[0021]
From FIG. 7 (a), the amplitude of the antinode portion when vibrating in the primary vibration mode is larger than that in the secondary vibration mode. The positional deviation amount of the scanning position is larger in the secondary vibration mode and exceeds the target level of the positional deviation amount in the sub-scanning direction which is acceptable as a range that does not affect the image quality of the reproduced image. Yes. As described above, in the vibration in the primary vibration mode, the laser beam L only moves in the vertical direction, but in the secondary vibration mode, the laser beam L swings up and down. This is because the amount of misalignment of the exposure scanning position increases.
[0022]
On the other hand, FIG. 7C shows a case where the vibration absorber 50 (the natural frequency matched to the frequency of the secondary vibration mode) is attached to the mounting base 30 and the vibration transmitted to the mounting base 30. FIG. 7D is a schematic diagram showing the relationship between the frequency and the maximum amplitude when the mounting base 30 vibrates. FIG. 7D shows the frequency of the vibration and the exposure scanning position in the sub-scanning direction on the photosensitive drum 4. It is a schematic diagram which shows the relationship with positional offset amount, These were calculated | required by simulation of the same method as Fig.7 (a) (b).
[0023]
FIG. 7 (c) shows that the amplitude in the primary vibration mode is almost the same as that in FIG. 7 (a), but the amplitude in the secondary vibration mode is kept small. As a result, as shown in FIG. 7D, even if the mounting base 30 vibrates in the primary vibration mode or the secondary vibration mode, the positional deviation amount of the exposure scanning position by the laser beam L is targeted. It can be seen that it can be reduced to below the level.
[0024]
In this way, if the vibration absorber 50 is attached at a position corresponding to the antinode of the secondary vibration mode, the number of vibration absorbers can be compared with a method of attaching a large number of vibration absorbers at arbitrary positions as in the prior art. It is possible to reliably suppress vibrations that adversely affect image quality while reducing image quality.
Up to now, the mounting pedestal 30 has been described in the form of vibration in the secondary vibration mode in which the direction of arrow Y shown in FIG. 3 is the traveling direction. However, in the plate-like body like the mounting pedestal 30, Not only in such a form, but when the vibration of a frequency different from the frequency of the primary and secondary vibration modes is propagated, the mounting base 30 sets the direction of arrow X in FIG. 3 as the traveling direction. There may be a form that vibrates in the secondary vibration mode. However, even if such a situation occurs, the scanning line on the photosensitive drum 4 is approximately the same amount as the amount that the printer head 10 swings about the axis about the line AA in FIG. Only a slight rocking is required, and the influence on the image is small. From this, it can be said that the case where the mounting base 30 vibrates in the secondary vibration mode in the arrow X direction need not be considered here.
[0025]
Further, it goes without saying that the present invention is not limited to the above embodiment, and the following modifications can be considered.
(1) In the above embodiment, the vibration absorber 50 is attached to a position corresponding to one antinode of the secondary vibration mode. However, as shown in FIG. 8, it corresponds to both antinodes of the secondary vibration mode. The vibration absorber 50 may be attached to a position to be placed (positions approximately D / 4 and 3D / 4 in length from the left end of the mounting base 30). In this case, two vibration absorbers 50 are required. However, the vibration damping effect is higher than that in the case of one, and the displacement amount of the exposure scanning position can be further reduced, and the image quality can be improved.
[0026]
Further, as shown in FIG. 9, the vibration damping effect can be obtained by using the vibration absorbing means 60 provided with the vibration absorber 62 at the end of the rod-shaped member 61. FIG. 10 is a cross-sectional view taken along line BB in FIG. 9 and 10, the rod-shaped member 61 is provided with convex portions 611 and 612 for connecting to the mounting base 30 at positions corresponding to both antinodes in the secondary vibration mode of the mounting base 30. Yes. With this configuration, when the mounting base 30 tries to vibrate in the secondary vibration mode, the vibration absorber 62 provided at the end of the mounting base 30 suppresses vibration of the abdominal portion via the rod-shaped member 61. Thus, the amplitude of the abdominal part can be reduced. Although this method requires the rod-shaped member 61 separately, there is an advantage that vibrations of both bellies can be absorbed by one vibration absorber 62.
[0027]
(2) In the above embodiment, when the length of the mounting base 30 in the direction of arrow Y in FIG. 3 is D, the vibration absorber 50 is positioned at a position approximately D / 4 from the left end of the mounting base 30. Is attached to suppress the vibration of the antinode portion of the amplitude, but this damping effect does not disappear if the attachment position of the vibration absorber 50 is slightly deviated from the antinode position.
[0028]
As can be seen from the secondary vibration mode in FIG. 4B, the peak of the amplitude is at the antinode, but the amplitude is almost the same as the peak value even in the vicinity thereof. If the vibration absorber 50 is attached to a place with a large amplitude, a vibration absorption effect corresponding to the vibration absorber 50 can be obtained. Therefore, even if the vibration absorber 50 is attached to a place with a large amplitude near the belly, substantially the same effect can be obtained.
[0029]
(3) In the above embodiment, the printer head 10 and the mounting base 30 are separate members. However, the casing 11 of the printer head 10 is supported by the front frame 26 and the rear frame 27 without using the mounting base 30. Also good. In this case, if the casing 11 itself becomes the mounting base 30 and the vibration absorber 50 is attached at a position corresponding to the antinode when vibrating in the secondary vibration mode, the same vibration damping effect can be obtained.
[0030]
(4) In the above embodiment, by adjusting the natural frequency of the vibration absorber 50 to be the same as the frequency of the secondary vibration mode of the mounting base 30, the greatest vibration damping effect can be obtained. However, such a damping effect does not disappear at all when the natural frequency of the vibration absorber 50 is slightly deviated from the frequency of the secondary vibration mode. This is because the viscous damping part 51 of the vibration absorber 50 suppresses some vibrations. In the first place, the vibration absorber 50 is attached in order to reduce the positional deviation amount shown in FIG. 7D to a target level or less. Therefore, if the positional deviation amount is equal to or less than the target level, even if the vibration absorber 50 is unique. Even if the frequency is not the same as the frequency in the secondary vibration mode, the necessary damping effect is obtained.
[0031]
(5) In the above embodiment, the mono color printer has been described. However, the present invention is not limited to this, and has a light beam scanning device that scans a light beam as an image writing unit, such as a full color laser beam printer or a digital copying machine. It can be applied to general image forming apparatuses.
[0032]
【The invention's effect】
As described above, the present invention is an image forming apparatus that draws an image on an object to be drawn by scanning a light beam with a light beam scanning device. A rod-shaped member provided with two convex portions, and a vibration absorber provided at an end portion of the rod-shaped member, wherein the first convex portion is the drawing target of the mounting base of the light beam scanning device Connected to a position corresponding to one antinode in the secondary vibration mode in the direction toward the object or a position near the antinode, and the second convex portion corresponds to a position corresponding to the other antinode in the secondary vibration mode or the vicinity thereof Since the vibration absorber suppresses vibrations of both antinodes in the secondary vibration mode via the rod-shaped member, the mounting base that has the greatest influence on image formation To suppress the vibration of the secondary vibration mode It is possible to prevent the quality deterioration. This eliminates the need for providing a large number of vibration absorbers at arbitrary positions as in the prior art, and enables effective vibration suppression while reducing cost and weight.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall schematic configuration of a printer according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of the inside of the printer head of the printer as viewed from above.
FIG. 3 is a perspective view showing a state in which a laser beam emitted from the printer head performs exposure scanning on a photosensitive drum.
FIG. 4A is a diagram showing a state when the mounting base vibrates in the primary vibration mode, and FIG. 4B is a diagram showing a state in the secondary vibration mode.
5 is a cross-sectional view taken along line AA in FIG.
FIG. 6 is a schematic external view of a vibration absorber.
FIG. 7 (a) shows a relationship between the frequency of vibration propagated to the mounting base and the maximum amplitude when the mounting base vibrates when the vibration absorber is not attached to the mounting base. Schematic (b) is a schematic diagram showing the relationship between the frequency of the vibration and the amount of displacement of the exposure scanning position in the sub-scanning direction on the photosensitive drum. (C) is a schematic diagram showing the relationship between the frequency of vibration propagated to the mounting base and the maximum amplitude when the mounting base vibrates when the vibration absorber is mounted on the mounting base. (D) is a schematic diagram showing the relationship between the frequency of the vibration and the positional deviation amount of the exposure scanning position in the sub-scanning direction on the photosensitive drum.
FIG. 8 is a diagram showing a state where vibration absorbers are respectively attached to positions corresponding to both antinodes of the secondary vibration mode.
FIG. 9 is a view showing a state in which a vibration absorbing means including a rod-shaped member and a vibration absorber is attached to a mounting base.
10 is a cross-sectional view taken along line BB in FIG. 9;
[Explanation of symbols]
4 Photosensitive drum 10 Printer head 11 Casing 26 Front frame 27 Rear frame 30 Mounting base 50, 62 Vibration absorber 51 Viscoelastic part 52 Auxiliary mass part 60 Vibration absorbing means 61 Rod-shaped member L Laser beam

Claims (1)

An image forming apparatus that scans a light beam with a light beam scanning device and draws an image on a drawing target,
A rod-shaped member;
A vibration absorber provided at an end of the rod-shaped member,
The rod-shaped member is provided with a first convex portion and a second convex portion with an interval in the longitudinal direction thereof,
The first convex portion is connected to a position corresponding to one of the antinodes in the secondary vibration mode of the mounting base of the light beam scanning device in the direction toward the drawing target, or a position in the vicinity thereof. Is connected to a position corresponding to the other antinode in the secondary vibration mode or a position in the vicinity thereof,
2. The image forming apparatus according to claim 1, wherein the vibration absorber suppresses vibrations of both antinodes in the secondary vibration mode through the rod-shaped member .

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