JPH06324547A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent periodic color misregistration in a color image formed by multilayer printing using an image forming device having a plurality of printing stations continuously arranged on an image transfer belt. CONSTITUTION:When the gear ratio of each worm 42 to a worm wheel 39 is eta, the interval at which photoreceptor drums 26 are arranged is P, the length of the outer periphery of each photoreceptor drum 26 is L, an integer variable is (n), and the internal angle between each worm 42 and the next worm 42 in an eccentric direction is theta, the following relation is met: theta deg.=etaXkP/LX360 deg.-(n)X360 deg. so that the plurality of photoreceptor drums 26 are equal to one another in the fluctuation period of their speeds of rotation relative to printing paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In recent years, electrophotography has been developed as one of electrostatic image forming methods. In this method, an electrostatic latent image is formed on a charged photoconductor by optical scanning or the like, and the electrostatic latent image is developed with charged toner and transferred to a recording medium.
Various types of printers using this electrophotographic method are known, but at present, a printer capable of performing color printing is desired. For example, as an image forming apparatus using an electrophotographic method, a printing station is provided, which is sequentially opposed to the outer peripheral surface of a photosensitive drum that rotatably supports at least a drum charging device, an exposing device, and a developing device. Has been proposed in which a plurality of printing stations for printing a monochromatic image are continuously arranged on a rollable image transfer belt such as a paper transfer belt or a transfer belt.

As a conventional example of such an image forming apparatus, a color printer disclosed in Japanese Patent Laid-Open No. 62-145262 will be described here with reference to FIGS. First, as shown in FIG. 7, the color printer 1, which is the image forming apparatus, has four printing stations 3 _{1 at} positions facing the paper transport belt 2, which is an endless image transfer belt stretched substantially horizontally. It has a structure in which ~ 3 ₄ are connected in series.

Here, these printing stations 3 ₁ ...
3 _4, the toner cleaner 4, the drum discharger 5, the drum charger 6, a laser scanner 7 which is an exposure device, a developing device 8 ₁ to
The photosensitive drum 9 in which 8 _{4 and the} like are arranged facing each other on the outer peripheral surface in order is positioned on the paper conveying belt 2, and the transfer device 10 is arranged opposite to the photosensitive drum 9 via the paper conveying belt 2. There is. Further, the four developing devices 8 ₁ to
8 ₄ are each yellow, magenta, cyan, and accommodates a black color toner (not shown) of the developing roller 11 mounted rotatably in its lower part the photosensitive drum 9
Is in contact with the outer peripheral surface of. The paper transport belt 2
At both front and rear ends, a paper feed tray 13 for storing the printing paper 12 and a fixing device 14 which also serves as a paper discharge device are arranged opposite to each other.

In the color printer 1 having such a configuration, the printing paper 12 supplied from the paper feed tray 13 is used.
Is electrostatically adsorbed to the sheet conveyance belt 2 and conveyed. Therefore,
In each of the printing stations 3 _{1 to} 3 ₄ that operate in synchronization with the movement of the printing paper 12, the outer peripheral surface of the photosensitive drum 9 charged by the corona discharge of the drum charger 6 is selectively discharged by the optical scanning of the laser scanner 7. Then, an electrostatic latent image is formed, and this electrostatic latent image is developed with charged toner supplied from the developing device 8 to form a single color image for transfer. In this way, the printing paper 12 on the surface of which a monochromatic image is sequentially formed forms a color image such that the monochromatic images of the respective colors are superposed on each of the printing stations 3 _{1 to} 3 ₄ . Therefore, the printing paper 12 on which the color image has been formed is pressurized and heated by the fixing device 14 and discharged to the outside of the device, whereby the color printer 1 completes the print formation of the color image.

Here, the above publication proposes several kinds of means for driving the photosensitive drums 9 of the _four printing stations 3 _{1 to} 3 ₄ of the color printer 1 at the same speed. . In one of the means, as illustrated in FIG. 8, a sprocket is provided on a passive shaft 15 and a drive shaft 17 of a drive motor 16 such as a stepping motor, which are directly connected to the photosensitive drums 9 of the _four printing stations 3 ₁ to 34. 1
8 and 19 are mounted, and these sprockets 18 and 19 are connected by a chain 20.

However, in order to drive the _four printing stations 3 _{1 to} 3 ₄ by the combination of the chain 20 and the sprockets 18 and 19 as described above, the backlash between the chain 20 and the sprockets 18 and 19 causes the photosensitive drums to travel. The rotation of 9 tends to fluctuate, and further, cumulative error occurs in the driving force transmitted to the printing stations 3 _{1 to} 3 ₄ separated from the driving motor 16 due to the extension of the chain 20. In this case, four printing stations 3 ₁ to
Since the rotational speed of the photosensitive drum 9 is not synchronized between the 3 _4, and the like deviate the four-color monochromatic images to overprint printing quality is lowered.

Therefore, in another means for solving the above problems, as illustrated in FIG. 9, the passive shaft 1 directly connected to the photosensitive drums 9 of the _four printing stations 3 _{1 to} 3 ₄ is used.
5, a worm wheel 22 is mounted via a reduction gear 21, and one drive shaft 1 directly connected to the drive motor 16
Four worms 23 are mounted on the worm wheel 7, and the worm gear 24 is formed by connecting the four worms 23 and the worm wheel 22.

[0009]

[SUMMARY OF THE INVENTION In the color printer 1 described above, for example, by a single drive motor 16 by utilizing the worm gear 24 four printing stations 3 ₁ -
The 3 ₄ photosensitive drums 9 are each driven at the same speed.

However, in the device for driving the _four printing stations 3 _{1 to} 3 ₄ by the worm gear 24 as described above,
Worm wheel 22 and worm 2 due to manufacturing error etc.
3, the eccentricity inevitably occurs. Therefore, as illustrated in FIG.
A large-amplitude, low-frequency fluctuation having one rotation of two cycles and a small-amplitude, high-frequency fluctuation of one rotation of the worm 23 will occur.

Here, the speed fluctuation of the photosensitive drum 9 due to the eccentricity of the large diameter worm wheel 22 is large, but the eccentricity of the worm wheel 22 which is such a large component can be improved by a simple means. The applicant has also proposed various means, as will be described later in the examples. On the other hand, the speed fluctuation of the photosensitive drum 9 due to the eccentricity of the small-diameter worm 23 is small, but this is not preferable because it causes color misregistration in the color image overprinted on the printing paper 12 by the _four printing stations 3 _{1 to} 3 _4. .

That is, when the rotation speed of the photosensitive drum 9 is changed as described above, for example, when only one monochrome image is printed by one printing station 3, the monochrome image is periodically minute in the sub-scanning direction. Since it only expands and contracts, the deterioration of print quality is not significant. However, in the case of forming a color image by overlappingly printing a single-color image that is cyclically expanded and contracted in the sub-scanning direction in this way, the cyclic expansion and contraction of a plurality of overprinted single-color images do not match. As a result, the print quality is extremely deteriorated.

The present invention is to obtain an image forming apparatus having good print quality.

[0014]

The invention according to claim 1 is
A worm wheel is connected to a passive shaft protruding laterally from a rotatable photosensitive drum, and at least a drum charger, an exposing device, and a developing device are arranged to face each other on the outer peripheral surface of the photosensitive drum to form a printing station. A single drive shaft in which the photosensitive drums of the printing stations are continuously arranged on an endless image transfer belt stretched rotatably, and are arranged in parallel to the direction in which the image transfer belt is stretched, and to which a drive motor is connected. In an image forming apparatus having a plurality of worms individually engaged with the worm wheel, the gear ratio between the worm and the worm wheel is η, the arrangement pitch of the photosensitive drums is P, and the outer peripheral length of the photosensitive drums is Is L, a variable consisting of an integer is n, and an internal angle in the eccentric direction between each worm and the next worm is θ °, θ ° = η × P / L × 360 ° −n × 360 ° Satisfy the relationship.

According to a second aspect of the present invention, a worm wheel is connected to a passive shaft protruding laterally of a rotatable photosensitive drum, and at least a drum charger, an exposure device and a developing device are provided on the outer peripheral surface of the photosensitive drum. The printing stations are arranged facing each other, and the plurality of photosensitive drums of the printing stations are continuously arranged on an endless image transfer belt which is rotatably stretched, and arranged parallel to the stretching direction of the image transfer belt. In an image forming apparatus in which a plurality of worms individually engaged with the worm wheel are mounted on one drive shaft connected with a drive motor, an eccentric fixing mechanism for fixing the worm to the drive shaft in an eccentric state is provided. The eccentric fixing mechanism is arranged at a position 180 ° from the eccentric direction of the worm.

[0016]

According to the first aspect of the present invention, since the fluctuation cycles of the rotational speeds of the plurality of photosensitive drums with respect to the printing paper can be matched, for example, periodical color misregistration of color images due to overprinting can be prevented. Therefore, it is possible to obtain an image forming apparatus having good printing quality.

According to the second aspect of the present invention, the eccentricity of the worm caused by a manufacturing error or the like can be offset by the eccentricity of the eccentric fixing mechanism to reduce the speed fluctuation of the photosensitive drum. Obtainable.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus of the present invention will be described with reference to FIGS. First, in the color printer 25 which is the image forming apparatus, as illustrated in FIG. 2, the drum cleaner 27, the drum charger 28, and the laser which is the exposure device are provided on the outer peripheral surface of the photosensitive drum 26 which is rotatably supported. Scanner 29, developing roller 31 of developing device 30, drum static eliminator 32
The printing station 33 is formed by sequentially arranging the same and so on. Therefore, in this color printer 25,
Four printing stations of the above-mentioned structure 33 _1-3
3 ₄ of the photosensitive drums 26, a pair of support rollers 34,
Rollably continuously disposed on the surface of the sheet conveying belt 36 of endless was stretched at 35, transfer roller in a position facing the photosensitive drum 26 of the printing station 33 _to 333 ₄ via the sheet conveying belt 36 37 is rotatably supported.

In the color printer 25, as illustrated in FIGS. 1 and 3, the worm wheel 39 ₁ is attached to the passive shafts 38 directly connected to the photosensitive drums 26 of the _four printing stations 33 _{1 to} 334, respectively. to 39 ₄ is mounted, fitted with a plurality of worm 42 _{1-42 4} to one single drive shaft 41 coupled to drive motor 40 stretched direction parallel to to the sheet conveying belt 36, these worm 42 _{1 to} 42 ₄ and the worm wheel 39 _{1 to} 39 ₄
And are individually engaged to form worm gears 43 ₁ to 43 ₄ .

Here, these worms 42 _{1 to} 42 ₄
As shown in FIGS. 3 and 4, a screw 45 is formed at the center of a cylindrical body through which the shaft hole 44 penetrates, and a holding portion 46 formed at each of both ends is provided with the shaft hole 44 from the outer peripheral surface.
A screw hole 47 that penetrates up to is formed. Therefore, in the color printer 25, the worms 42 _{1 to} 42 _{4 are used.}
By pressing the drive shaft 41 inserted through the shaft hole 44 with the set screw 48 fastened to each of the screw holes 47,
The worms 42 _{1 to} 42 ₄ are attached to the drive shaft 4 by an eccentric fixing mechanism 49 including the set screw 48 and the screw hole 47.
1 is fixed in an eccentric state.

In the color printer 25, the worms 42 _{1 to} 42 ₄ and the worm wheel 39 are used.
_{1-39 4} a gear ratio of eta, the P array pitch of the photosensitive drum 26, the outer peripheral length of the photosensitive drum 26 L, a variable of integers n, each said worm 42 _{1-42 3} and following the The internal angle in the eccentric direction with the worms 42 _{2 to} 42 ₄ is θ °
Then, as illustrated in FIG. 3, the relationship of θ ° = η × P / L × 360 ° −n × 360 ° is satisfied.

Further, in the color printer 25, the worms 42 _{1 to} 42 ₄ are eccentric with the outer peripheral surface of the screw 45 and the shaft hole 44 due to a manufacturing error, but as shown in FIG. The eccentric fixing mechanism 49 including the set screw 48 and the screw hole 47 is arranged at a position 180 ° from the eccentric direction.

Further, in this color printer 25, as shown in FIG.
As illustrated in FIG. 3, the sheet feeding device 50 is disposed in proximity to the conveyance start position at one end of the paper conveyance belt 36 in the stretching direction, and the rotatable paper holding member is held on the surface of the paper conveyance belt 36 at the conveyance start position. The roller 51 and the transfer charger 52 are sequentially arranged. Further, a fixing device 53, which also serves as a paper discharge mechanism, is disposed opposite to a conveyance end position at one end in the stretching direction of the paper conveyance belt 36 on the side opposite to the paper feeding device 50 and the like.
A belt static eliminator 54 and a belt cleaner 55 are provided at a position facing the lower surface of the paper transport belt 36 stretched substantially horizontally.
And are facing each other.

The paper transport belt 36 has a structure in which a conductive layer (both not shown) is formed under the insulating layer located on the surface, and two support rollers 34, which are in contact with the conductive layer, Ground line (not shown) on one side of 35
Are connected. Then, in the color printer 25, the developing unit 30 of the printing station 33 _to 333 ₄ in the direction of movement of the order of the surface of the sheet conveying belt 36
One-component non-magnetic toners of yellow, magenta, cyan, and black are individually stored in.

[0025] In this structure, if in this color printer 25 to print the color image, in the respective printing station 33 _to 333 _4, the photosensitive drum is rotated 26
The outer peripheral surface of the photosensitive drum 26 is electrically charged by corona discharge of the drum charger 28 and then selectively discharged by optical scanning of the laser scanner 29 to form an electrostatic latent image. Is developed into a single-color image with the toners of the respective colors supplied from the developing device 30, and then the drum static eliminator 32 eliminates static electricity.

On the other hand, in the color printer 25, and feeds the print paper 56 from the paper feeding device 50 onto the sheet conveying belt 36 in synchronism with the operation of the printing station 33 _to 333 ₄ as described above, the printing paper 56 is a paper holding roller 51
The transfer charger 52 applies an electric charge while being pressed and held on the paper transport belt 36. Then, since the printing paper 56 is charged together with the paper transport belt 36, the transfer voltage can be applied to the printing paper 56 electrostatically attracted to the paper transport belt 36.

[0027] Then, in the color printer 25, the printing station 33 at a position of the transfer roller 37 to the printing paper 56 conveyed by the sheet conveying belt 36 that rolls _to 333
_By pressing the _four photosensitive drums 26, the monochrome images of yellow, magenta, cyan, and black are sequentially superimposed and printed on the printing paper 12 from the photosensitive drums 26. Further, the printing paper 56 on which the color image is transferred in this manner is conveyed by the paper conveyance belt 36, and the printing paper 56 separated from the paper conveyance belt 36 is heated and pressed by the fixing device 53 and then discharged to the outside of the apparatus. By doing so, the printing of the color image is completed.

In the color printer 25, the paper transport belt 36 after the printing paper 56 is peeled off as described above is continuously rolled for a predetermined time, and the surface thereof is subjected to corona discharge of the belt static eliminator 54. After the charge is removed, dust such as toner and paper dust attached to the surface is removed by rubbing the belt cleaner 55. Similarly, printing paper 56
Each printing station 33 ₁ after the transfer of the monochrome images to
33 ₄ of the photosensitive drum 26 is also continuously driven to rotate by a predetermined time, the drum cleaner 27 of the toner remaining on the surface
The color printer 25 waits for the next printing operation by scraping and removing with.

[0029] Here, the color printer 25, the photosensitive drum single drive motor 40 to one of the long drive shaft 41 and four of the worm gear 43 _{1-43 4} and with four printing stations 33 _to 333 ₄ Since they are connected to the passive shaft 38 of 26, these photosensitive drums 26 are adapted to rotate at the same speed. At this time, the four printing stations 33 ₁ are connected by the worm gears 43 ₁ to 43 ₄ in this way.
To 33 ₄ in the apparatus for driving a is the worm wheel 39 ₁ for such manufacturing errors to 39 ₄ and the worm 42 _{1-42 4}
Since eccentricity inevitably occurs in, as shown in FIG.
The rotation speed of the photosensitive drum 26 depends on the worm wheel 39
And low frequency variation in large amplitude to _{1-39 4} one revolution of one cycle, and the high-frequency fluctuations will occur a small amplitude to one period of one rotation of the worm 42 _{1-42 4.} In this case, due to the speed variation of the photosensitive drum 26 due to the eccentricity of the small-diameter worms 42 _{1 to} 42 ₄ , the monochrome image transferred to the printing paper 56 by the photosensitive drum 26 is minutely expanded and contracted in the sub-scanning direction periodically.

However, in the color printer 25, the worms 42 _{1 to} 42 ₄ and the worm wheels 39 _{1 to} 39 are used.
The gear ratio with ₄ is η, the arrangement pitch of the photosensitive drums 26 is P,
The outer peripheral length of the photosensitive drum 26 is L, the variable consisting of an integer is n,
Each worm 42 _{1 to} 42 ₃ and the next worm 42 _{2 to} 42
_When the internal angle in the eccentric direction with respect to ₄ is θ °, as shown in FIG. 3, by satisfying the relationship of θ ° = η × P / L × 360 ° −n × 360 °, the example shown in FIG. As described above, the fluctuation periods of the rotation speeds of the four photosensitive drums 26 match the printing paper 56. In this way, in the color printer 25, four photosensitive drums 26 of the printing station 33 _to 333 ₄ printing paper 56
Since the expansion / contraction cycle in the sub-scanning direction of the single-color image transferred to the printer is the same, it prevents the occurrence of periodic color misregistration in the overprinted single-color image and contributes to the improvement of the print quality of the color image. ing. Although FIG. 5 illustrates the speed fluctuation of the photosensitive drums 26 of the two printing stations 33 for simplification of the drawing, the other two photosensitive drums 26 are illustrated.
The same applies to the speed fluctuations.

Further, in the color printer 25 that the applicant of the present invention actually made a trial, the gear ratio η = 90 between the worms 42 _{1 to} 42 ₄ and the worm wheels 39 _{1 to} 39 ₄ and the photosensitive drum 2 were used.
Since the arrangement pitch P of 6 is 88.9 (mm) and the outer peripheral length L of the photosensitive drum 26 is 30.042 (mm), each worm 42 _{1 to} 42 ₃
Angle between the worm and the next worm 42 _{2 to} 42 ₄ in the eccentric direction θ °
Is θ ° = 90 × 88.9 / 30.042π × 360 ° −n × 360 ° ≈ 30518.84 ° −n × 360 °. Therefore, in order to satisfy 0 ° ≦ θ ° <360 °, substituting “84” as an appropriate integer for n, θ ° = 278.84 °.

Further, the color printer 25 is shown in FIG.
In the worms 42 _{1 to} 42 _{4 as} described above, the outer peripheral surface of the screw 45 and the shaft hole 44 are eccentric due to a manufacturing error.
_Since the eccentric fixing mechanism 49 that fixes _{1 to} 42 ₄ to the drive shaft 41 in an eccentric state is arranged at a position of 180 ° from the eccentric direction, the eccentricity due to the manufacturing error of the worms 42 _{1 to} 42 ₄ can be prevented from occurring in the eccentric fixing mechanism 49. It is designed to offset by eccentricity. By doing so, the color printer 25 can eliminate the eccentricity of the outer peripheral surfaces of the worms 42 _{1 to} 42 ₄ mounted on the drive shaft 41, so that the speed fluctuation of the photosensitive drum 26 can be reduced and the print quality can be reduced. To contribute to the improvement of.

As described above, the worms 42 ₁ ...
42 to eliminate the speed variation of the photosensitive drum 26 by ₄ of the eccentric, the photosensitive due to the eccentricity of the worm wheel 39 relative to driven shaft 38 in order to further improve the print quality drum 2
It is necessary to eliminate both the speed fluctuation 6 and the speed fluctuation due to the eccentricity of the photosensitive drum 26 itself. Therefore, in this color printer 25, as shown in FIG. 6, a passive shaft 38 made of stainless steel, a worm wheel 39 made of polyacetal, and a photosensitive drum 26 made of aluminum are connected to a split mold 57,
By forming it integrally with 58 and then by precision cutting,
The eccentricity between the worm wheel 39 and the photosensitive drum 26 with respect to the passive shaft 38 is almost completely eliminated.

[0034]

According to the present invention, the gear ratio between the worm and the worm wheel is η, the arrangement pitch of the photosensitive drums is P, the outer peripheral length of the photosensitive drums is L, a variable consisting of an integer is n, and each worm is The inner angle in the eccentric direction with the next worm is θ
When θ, θθ = η × P / L × 360 ° −n × 360 ° is satisfied, so that the fluctuation periods of the rotational speeds of the plurality of photosensitive drums with respect to the printing paper can be matched. For example, it is possible to prevent periodic color misregistration of color images due to overprinting, and to obtain an image forming apparatus with good print quality.

According to the second aspect of the present invention, an eccentric fixing mechanism for fixing the worm to the passive shaft in an eccentric state is provided, and the eccentric fixing mechanism is arranged at a position 180 ° from the eccentric direction of the worm. Since the eccentricity of the worm due to the eccentricity can be canceled by the eccentricity of the eccentric fixing mechanism, the speed fluctuation of the photosensitive drum can be reduced, so that an image forming apparatus having good print quality can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing a main part of a color printer which is an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a vertical sectional side view showing the entire color printer.

FIG. 3 is a front view showing a positional relationship in the eccentric direction of worms of a plurality of worm gears.

FIG. 4 is a front view showing a positional relationship between a worm and a drive shaft.

FIG. 5 is a characteristic diagram showing speed fluctuations of a photosensitive drum.

6A is a vertical sectional front view showing a state in which a worm wheel is integrally formed on a passive shaft by a split mold, and FIG. 6B is a state in which a photosensitive drum is integrally formed by a split mold on a passive shaft. FIG.

FIG. 7 is a vertical sectional side view showing an entire color printer which is a conventional example of an image forming apparatus.

FIG. 8 is a side view showing one row of a drive mechanism of the photosensitive drum.

FIG. 9 is a side view showing another example of the drive mechanism of the photosensitive drum.

FIG. 10 is a characteristic diagram showing speed fluctuations of the photosensitive drum.

[Explanation of symbols]

 25 image forming apparatus 28 drum charger 29 exposure device 30 developing device 26 photosensitive drum 33 printing station 36 image transfer belt 38 passive shaft 39 worm wheel 40 drive motor 41 drive shaft 42 worm 49 eccentric fixing mechanism

Claims (2)

[Claims] 1. A printing station in which a worm wheel is connected to a passive shaft protruding laterally of a rotatable photosensitive drum, and at least a drum charger, an exposure device, and a developing device are arranged to face each other on an outer peripheral surface of the photosensitive drum. And a plurality of photosensitive drums of the printing station are continuously arranged on an endless image transfer belt which is rotatably stretched, and the driving motors are connected in parallel with the stretching direction of the image transfer belt. In an image forming apparatus in which a plurality of worms that are individually engaged with the worm wheel are mounted on one drive shaft, the gear ratio between the worm and the worm wheel is η, the arrangement pitch of the photosensitive drums is P, and When the outer peripheral length of the photosensitive drum is L, a variable consisting of an integer is n, and an internal angle in the eccentric direction between each worm and the next worm is θ °, θ ° = η × P / L × 360 An image forming apparatus characterized by satisfying a relationship of ° -nx360 °. 2. A printing station in which a worm wheel is connected to a passive shaft protruding laterally of a rotatable photosensitive drum, and at least a drum charger, an exposure device and a developing device are arranged opposite to each other on the outer peripheral surface of the photosensitive drum. And a plurality of photosensitive drums of the printing station are continuously arranged on an endless image transfer belt which is rotatably stretched, and the driving motors are connected in parallel with the stretching direction of the image transfer belt. In an image forming apparatus in which a plurality of worms that are individually engaged with the worm wheel are mounted on one of the drive shafts, an eccentric fixing mechanism that fixes the worms to the drive shaft in an eccentric state is provided. An image forming apparatus, which is arranged at a position of 180 ° from the eccentric direction of the worm.