JP2002023449A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease deviation in image position between each color in a device forming a color image utilizing a multiple number of photoreceptors. SOLUTION: In the device, photoreceptors 1a, 1b, 1c and 1d are driven at constant rotating angle and speed and a difference is given to surface speed of each photoreceptor 1 and carrying speed of a transfer belt 2. Alignment of the image is carried out with ease by eliminating any stretching of each color image even when there is an error in a diameter or eccentricity in each photoreceptor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for forming an image of at least two colors by using an electrophotographic technique.

[0002]

2. Description of the Related Art In an electrophotographic system such as a copying machine or a printer, an electrostatic latent image corresponding to image data is formed on a photoconductor, and toner, which is a charged particle, is formed in accordance with a potential pattern of the electrostatic latent image. The latent image is visualized as a toner image by causing the toner image to adhere to the photoreceptor, and the toner image is transferred to a recording medium such as paper to form an image on the paper. When a color image is formed by this process, for example, color toners such as yellow, magenta, and cyan are overlaid.

In a color image forming apparatus, there are various features in a method of superimposing the toner images of each color, and two types of methods have been proposed so far.
One is a repetitive developing method of repeatedly developing toner of each color on one photoconductor to form a color image. The other is a simultaneous development system (also called a tandem system) in which toner of each color is simultaneously developed by a plurality of photoconductors to form a color image.

[0004] Of these methods, the repetitive developing method has a disadvantage that it takes a long time to print four pages in order to superimpose the toner images of four colors, and is therefore slow. On the other hand, the simultaneous development method can easily obtain a printing speed equivalent to that of a conventional monochrome machine, and is considered to be a method that will be increasingly used in the future. As the simultaneous development method, JP-A-9-174919 and JP-A-8-5
No. 0385 is described.

[0005]

In the color image forming apparatus of the simultaneous development system, since the images of each color are formed independently by different photoconductors, it is very difficult to superpose the toner images of each color. Since each color image is formed on a separate photoreceptor, in order to accurately overlap the positions of the images of each color, the timing of exposing the image of each color is determined by the time required for the image to pass between the photoreceptors. It is necessary to shift the exposure. For this reason, an arrangement error of the photoreceptor and the exposure unit affects the displacement of the image, and therefore, a mechanism for adjusting the timing of starting writing of the image is generally used.

However, what makes the image registration of each color most difficult is that the surface speed cannot be accurately adjusted because each photoconductor has variations such as diameter error and eccentricity. . For example, a photoconductor having a large diameter has a high surface speed, and a photoconductor having a small diameter has a low surface speed. Further, when the photoconductor has eccentricity, the surface speed fluctuates in a cycle of one rotation of the photoconductor. When the surface speed of the photoconductor increases, the image expands, and conversely, when the surface speed decreases, the image contracts. Therefore, the image formed by each photoconductor is
Each photoconductor expands and contracts due to a diameter error and eccentricity of the photoconductor, and even if the leading ends of the images are accurately aligned, the positions of the internal images are shifted. The shift of each color image has a problem that the image quality is greatly reduced, such as a change in hue and the image appears double.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which overcomes the above-mentioned problems of the prior art, absorbs an error in the image position due to a diameter error or eccentricity of the photosensitive member, and improves the image quality. .

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides at least two or more photoreceptors and a transporting means for bringing a recording medium into contact with the respective photoreceptors and simultaneously transporting the recording medium. An image forming apparatus having a transfer medium to form a multicolor image by transferring a toner image formed on each photoconductor onto the recording medium or the transfer medium, and driving each of the photoconductors at a constant rotation angular velocity. It is characterized by doing.

By keeping the rotational angular velocity of each photoconductor constant, even if there is a diameter error or eccentricity of the photoconductor, the image arrival time on the photoconductor and the transfer time of the image to the transfer position for transferring the toner become constant. , The images can be matched exactly.

Further, if each photoconductor has a diameter error or an eccentricity, the speed at the transfer position of each photoconductor becomes inconsistent, and the conveying means of the recording medium or the transfer medium becomes slack, so that each photoconductor becomes loose. There is a possibility that the image transit time between the two may change. In order to eliminate this slack, the diameter of the photoconductor is made different so that the conveyance means of the recording medium or the transfer medium is always pulled. That is, the diameter of the photosensitive member on the upstream side when viewed from the transport direction of the recording medium or the transfer medium is smaller than the diameter of the photosensitive member on the downstream side.

As another method for preventing the transfer means or the transfer medium from becoming loose, the rotational angular velocities of the respective photoconductors are made different, and the rotational angular velocities of the photoconductors on the upstream side in the transport direction are set on the downstream side. It is slower than the rotation angular speed of a certain photoconductor.

In addition to the above method, the exposure speed at which the exposure means exposes the image on each photosensitive member is the same for each photosensitive member so that the image does not expand or contract.

As a method for preventing the recording medium conveying means or the transfer medium from becoming loose, the surface speed of the conveying means for conveying the recording medium or the transfer medium is set to be higher or lower than the surface speed of each photosensitive member. Features.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of an image forming apparatus according to a first embodiment of the present invention. This image forming apparatus has a recording density of 600 dots per inch (600 dpi) capable of printing a photographic image neatly, and is capable of printing a large number of documents in a short time.
This is a color printer capable of printing 16 sheets of paper of a size in color.

The arrangement and printing operation of each component will be described with reference to the drawings. In the central part of the housing, drum-shaped photoconductors 1a, 1b, 1c, and 1d having a diameter of 40 mm and corresponding to four color toners of yellow, magenta, cyan, and black necessary for forming a color image are arranged side by side. I have. Further, the transfer belt 2 is stretched substantially horizontally in the arrangement direction of the photoconductors 1 by belt stretching rollers 3a, 3b, 3c, and 3d so as to contact the plurality of photoconductors 1. Inside the transfer belt 2, transfer assist rollers 4 a, 4 b, 4 c, 4 d for transferring a toner image from each photoconductor 1 to a sheet 10 conveyed by the transfer belt 2 are provided.

Each photoconductor 1 has, along its rotation direction,
Chargers 5a, 5b, 5 for charging each photoconductor 1 to a specified potential
Exposure units 6a, 6b, 6c and 6d for exposing the charged surface of the photoconductor 1 to form an electrostatic latent image are arranged. Each of the exposing devices 6 uses an LED array exposing device in which 600 LEDs are arranged in an array per inch in order to correspond to a latent image exposure of 600 dpi.

Further, a developing device 7a which develops the electrostatic latent image on each photoconductor 1 with toner as charged particles and visualizes the developed image.
7b, 7c, 7d, erase lamps 8a, 8b, 8c, 8d for attenuating the potential on the surface of each photoconductor 1, a photoconductor for cleaning the toner remaining on the surface of each photoconductor 1 after transferring the toner image onto paper 10 Cleaners 9a, 9b, 9c,
9d are arranged. Photoconductors 1a, 1b, 1c, 1d
Are provided with an interval at which these process components can be arranged, and the interval between the respective photoconductors 1 in this embodiment is 120 mm.

Below the transfer belt 2, a paper cassette 11 for storing paper 10 is arranged. A pick roller 12 for pulling out the paper 10 from the paper cassette 11 along the paper transport direction from the paper cassette 11, a registration roller 13 for aligning the leading edge of the paper 10, and a paper suction mechanism for electrostatically bringing the paper 10 into close contact with the transfer belt 2. 14, a transfer belt 2, a fixing device 16 for fixing the toner image transferred on the paper 10 to the paper 10 by heat and pressure, and a paper discharge mechanism 17 for discharging the paper 10 to the upper surface of the main body.

The printing process of the image forming apparatus according to the present embodiment will be described. When a print command is input to a main body controller (not shown), each photoconductor 1 and the transfer belt 2 are rotated, and the paper 10 is pulled out of the paper cassette 11 by the pick roller 12 and carried to the registration roller 13. The leading edge of the sheet 10 is aligned by the registration roller 13 and sent to the transfer belt 2 at a specified timing. The sheet that has reached the transfer belt 2 is attracted to the surface of the transfer belt 2 by the sheet attracting mechanism 14, and the sheet 10 is transported by the transfer belt 2. The transfer belt 2 here is an example of a transport unit that transports the recording medium (paper) according to the present invention described above.

On each photoconductor 1, charging, exposure and development are performed as the paper 10 passes through the nip portion with the photoconductor to form a toner image. Photoconductors 1a, 1b, 1
c, 1d, the toner image is transferred onto the paper 10 by the voltage applied to the transfer assist rollers 4a, 4b, 4c, 4d when the paper 10 passes through the nip portion. As described above, as the sheet 10 is conveyed to the transfer belt 2, the toner images of each color are transferred from each photoconductor 1, and a color image is formed on the sheet 10. The paper 10 that has passed through the nip portions of all the photoconductors is sent to a fixing device 16, and the paper 1 is
The toner on the top is fixed and transported to the outside of the main body. The image forming apparatus is 100 mm / s, which is enough to print 16 sheets of A4 size paper having a sheet length of 297 mm per minute.
(The speed is referred to as a process speed).

In the image forming apparatus of this embodiment, the diameter is 40 m.
Although the photoconductor of m is used, the current processing technology causes a diameter error of ± 0.05 mm and a deviation of about 0.1 mm due to a deviation between the center of the photoconductor and the center of the rotation axis of the photoconductor. For this reason, the speed difference between each photoconductor is ±
0.25% and a maximum of about ± 0.75% occur. At this time, if the surface speed of the photoconductor is higher than the specified speed, the surface of the photoconductor moves quickly at the exposure position, so that the interval between dots becomes large, and the image extends in the paper transport direction. On the other hand, when the surface speed of the photoconductor is lower than the specified speed, the interval between the dots becomes smaller, and the image shrinks.
If a speed difference of ± 0.25% occurs on average, the image shift caused by the expansion and contraction of the image will be ± 0 at the rear end of the image even if the image front end position is accurately adjusted, taking the A4 size image direction as an example. .25% x 290 mm, or a maximum of 0.725 mm.

In order to improve such image displacement, in the image forming apparatus of this embodiment, the photosensitive members 1a, 1b,
A driving system in which the photoconductors 1a, 1b, 1c, and 1d are driven at a constant angular velocity by connecting the gears 1c and 1d with gears and driving them with a stepping motor is applied.

FIG. 2 shows a schematic configuration of a drive section of each photosensitive member. The photoconductors 1a, 1b, 1c, and 1d are on the rotation axis of the photoconductor,
The photoreceptor gears 100 are attached to each other, and are connected to each other by a transmission gear 101 to form a gear train, and the photoreceptors 1a, 1b, 1c, and 1d are configured to rotate integrally. The drive gear 102 is a gear for driving the gear train, and is connected to the stepping motor 103. In this example, the gear ratio of each transmission gear 101 is constant, but can be changed.

The exposing unit 6a (or 6b, 6c, 6d) exposes the photosensitive member 1a (or 1b, 1c, 1d) to the exposure point, and the photosensitive member 1a (or 1b, 1c, 1d) Since the transfer point to be transferred to the paper 10 is not easily shifted during the formation of the image, the angle between the exposure point and the transfer point viewed from the rotation center of the photoconductor 1a (or 1b, 1c, 1d). Is constant. Therefore, the photoconductor 1
When a (or 1b, 1c, 1d) is driven at a constant angular velocity, the time required for the latent image exposed at the exposure point to reach the transfer point is always constant even if the photoconductor has a diameter error or eccentricity. Can be.

As another method for driving the photosensitive members 1a, 1b, 1c, and 1d at a constant angular velocity, the photosensitive members 1a, 1b,
A method in which c and 1d are connected by a belt and driven by a stepping motor, a method in which each photoconductor 1 is driven by a separate stepping motor, and the like can be applied.

Incidentally, as described above, the photosensitive members 1a, 1a
b, 1c, and 1d are driven at a constant angular velocity.
Has a diameter error and eccentricity as described above, so that the surface speed of the photoconductor at the transfer point becomes uneven. Therefore, a state where the transfer belt 2 is pulled and a state where the transfer belt 2 bends occur between the transfer points. For example, in a state where the surface speed of the photosensitive member to which an image is exposed first is high at the transfer point and the surface speed of the photosensitive member to be exposed later is low, the transfer belt 2 is shrunk. The force acts and the transfer belt 2 bends. Conversely, if two adjacent photoconductors have a low surface speed at the transfer point of the photoconductor to which an image is first exposed and a high surface speed of the photoconductor to be exposed later, the transfer belt 2 may extend. become. Such bending or elongation of the transfer belt 2 changes the time required for an image to pass between adjacent photoconductors, and thus makes it difficult to position each color image.

In the image forming apparatus of this embodiment, first, in order to prevent the transfer belt 2 from bending, the surface speed of each photoconductor 1 at the transfer point is set lower than the speed at which the transfer belt 2 conveys the paper 10. . By making the surface speed of each photoconductor 1 slower than the speed at which the transfer belt 2 conveys the paper 10, all the photoconductors 1a, 1b, 1c, and 1d become loads, so that the transfer belt 2 is bent between the photoconductors. Can be prevented.

At this time, the photosensitive members 1a, 1b, 1c, 1d
In the contact portion between the transfer belt 2 and the transfer belt 2, slippage occurs due to the speed difference.
It is necessary that the upper paper 10 be surely brought into contact with the photoreceptor and be slid smoothly. For this reason, in this embodiment, the transfer assisting rollers 4a, 4b, 4c, and 4d are configured to be covered with sponge rubber. Transfer assist rollers 4a, 4
By using a soft material such as sponge rubber for the surfaces of b, 4c, and 4d, the transfer assist rollers 4a, 4b, 4c,
The paper 10 on the transfer belt 2 can be brought into close contact with the photoconductors 1a, 1b, 1c, and 1d even if the pressing force for pressing 4d against the photoconductors 1a, 1b, 1c, and 1d is reduced. At the same time, since the pressing force can be reduced, the frictional force generated between the photoconductors 1a, 1b, 1c, 1d and the paper 10 can be suppressed, and the photoconductors 1a, 1b, 1c,
1d and the transfer belt 2 can be smoothly slid.

In the image forming apparatus of the present embodiment, the transfer belt 2 and the photosensitive members 1a, 1a, 1d are pressed by pressing the transfer assisting rollers 4a, 4b, 4c, 4d with a force of about several hundred gf.
b, 1c, and 1d and smooth sliding could be achieved. With this configuration, the photoconductors 1a, 1b, 1c, 1d
If the surface speed difference between the transfer belt 2 and the transfer belt 2 is within 5% in our study, no image defects such as a rubbing pattern were generated, and a good image was obtained.

Since the variation in the surface speed due to the diameter error and the eccentricity of each photoconductor 1 is about 0.75%, the difference in the surface speed between the photoconductors 1a, 1b, 1c, 1d and the transfer belt 2 is obtained. It is desirable that the speed is larger than the surface speed variation of the photoconductors 1a, 1b, 1c, and 1d, and smaller than the speed at which the image deteriorates. Therefore, in this embodiment, the photosensitive member 1 is transported at a transport speed of 100 mm / s for transporting the paper 10.
a, 1b, 1c, 1d 2% slower at 98 mm /
The photoconductors 1a, 1b, 1c, and 1d are rotated so as to reach s.

Specifically, in order to rotate a photosensitive member having a diameter of 40 mm at a constant angular speed, the photosensitive members 1a, 1b, 1c, and 1d are rotated.
Is rotated at a rotational speed of 47.75 revolutions / minute at a process speed of 100 mm / s and an angular speed of 46.79 revolutions / minute against 286.5 degrees / second, and at a speed of 280.7 degrees / second. ing.

Next, in the image forming apparatus of the present embodiment, in order to suppress the elongation of the transfer belt 2 which causes the image position shift, the elongation of the belt caused by the tension generated in the transfer belt 2 adjusts the image alignment. The transfer belt 2 is made of a material and a thickness that does not cause any problem.

In the above configuration, since the speed of the transfer belt 2 is higher than the surface speed of the photosensitive member, the photosensitive members 1a, 1b, 1c,
1d is a load on the transfer belt 2. This load is generated by friction between the photoconductor 1 and the paper on the transfer belt. The frictional force between the photoreceptor and the transfer belt is obtained by multiplying the force by which the transfer belt presses the photoreceptor, that is, the pressing force of the transfer assist roller, by the coefficient of friction between the photoreceptor and the paper on the transfer belt. The pressing force of the transfer assisting rollers 4a, 4b, 4c, and 4d is several hundred gf, and the photosensitive member 1a (or 1b, 1c,
1d) and the friction coefficient of the paper 10 on the transfer belt 2 vary depending on the type of the paper 10 to be used, but in our study, it is about 0.2 to 1.0.

The photosensitive member 1a for transporting the transfer belt 2
The loads 1b, 1c, and 1d are respectively about several tens to several hundreds gf. When the load on the transfer belt 2 is examined in the order of arrangement of the photoconductors 1a, 1b, 1c, and 1d, the frictional force of one photoconductor between the photoconductor 1a and the photoconductor 1b is several tens to several hundreds g.
f, twice as much load is applied to the transfer belt 2 between the photoreceptor 1b and the photoreceptor 1c and three times as much between the photoreceptor 1c and the photoreceptor 1d.

Therefore, the transfer belt 2 has at least several k
It will be pulled with a force of about gf. Transfer belt 2
The maximum amount of elongation is about half of one dot at the maximum. In the image forming apparatus of this embodiment, the dot density per inch is 600, and the size of one dot is about 42 μm, and the elongation of the transfer belt is 20 μm.
m. For this reason, in the present embodiment, even when the maximum load of several kgf is applied, the elongation of the belt is 1
The Young's modulus is 20,000 which is suppressed to about half of the dot.
A resin belt of kgf / square cm and a thickness of 0.15 mm is used.

Next, a method of driving the transfer belt will be described. In this embodiment, the transfer belt 2 is stretched by belt stretching rollers 3a, 3b, 3c, and 3d, and the transfer belt 2 is driven by driving the belt stretching roller 3d. In this image forming apparatus, all the photoconductors 1a, 1b, 1
Since c and 1d are loads, the portion between the photosensitive member 1d and the belt stretching roller 3d has the highest tension. For this reason, tension is applied to the transfer belt 2 stably, and slippage is less likely to occur between the transfer belt 2 and the belt stretching roller 3d, and the transfer belt 2 can be driven stably.

Further, since the transfer belt 2 is stretched long in the arrangement direction of the photosensitive members 1, the photosensitive members 1a, 1b, 1c,
The belt stretching roller 3d that stretches the transfer belt 2 at the end in the arrangement direction of 1d can increase the winding angle of the transfer belt 2 and can drive the transfer belt 2 more stably. .

Further, a belt stretching roller 3 as a drive shaft
To prevent the eccentricity of d from affecting the alignment of the image,
The belt stretching roller 3d is driven by a stepping motor that can be driven at a constant rotation angular velocity, and the outer peripheral length of the belt stretching roller 3d is made equal to the interval between the photoconductors 120mm. That is, the outer peripheral length of the belt stretching roller 3d is 120 mm.
The diameter is set to 38.2 mm so that

By setting the rotational speed of the belt tension roller 3d to be constant, the time required for the belt tension roller 3d to make one revolution is constant even if the belt tension roller has eccentricity. When the length is equal to the distance between the transfer points, the time for the image to move between the transfer points of the photoconductors 1a, 1b, 1c, and 1d is always constant, and the belt tension roller 3
The image position shift due to the eccentricity of d can be further reduced.

In the image forming apparatus of this embodiment, the photosensitive member 1
The surface speeds of a, 1b, 1c, and 1d are lower than the surface speed of the transfer belt 2. At this time, each photoconductor 1a, 1
Exposure units 6a, 6b, 6c, 6 for exposing b, 1c, 1d
The time interval between dots that d exposes in the rotation direction of the photoconductor is constant in all of the exposure units 6a, 6b, 6c, and 6d. In addition, the time between dots is defined so that a standard image density and a standard image length can be obtained on the sheet 10 conveyed to the transfer belt 2.

In this embodiment, the recording density is 600 dots per inch, and the surface speed of the transfer belt 2 is 100 mm / inch.
s, the time interval between dots exposed in the rotation direction of the photoconductor is set to about 423.3 μs, which is lower than the surface speed of the photoconductors 1a, 1b, 1c, and 1d, which is slower than the transfer belt 2. Regardless, the time interval is determined by the surface speed of the transfer belt 2. Thus, the exposure units 6a, 6b, 6
c and 6d make the time intervals between the dots exposed in the rotation direction of the photoreceptor the same, and determine the time intervals so that the reference image density can be obtained on the paper 10 on the transfer belt 2, whereby the photoreceptors 1a, Regardless of the surface speeds 1b, 1c, and 1d, images of the same length and pitch can be formed for each color.

As described above, in the image forming apparatus of the present embodiment, a good image without image expansion and contraction can be obtained between the images of the respective colors formed by the photoconductors 1a, 1b, 1c and 1d. As a result, a high quality image forming apparatus can be realized.

(Embodiment 2) The second embodiment of the present invention is the same color printer as the image forming apparatus of the first embodiment, and the arrangement and operation of the process components inside the apparatus are the same as those of the first embodiment. Is the same as The difference from the first embodiment is that the rotation speeds of the photoconductors 1a, 1b, 1c, and 1d and the transfer belt 2
Is the driving method.

In the image forming apparatus of this embodiment, each photosensitive member 1a, 1b, 1c, 1
The feature is that the surface speed at the transfer point d is higher than the speed at which the transfer belt 2 conveys the paper 10. By making the surface speed of the photoconductors 1a, 1b, 1c, and 1d faster than the speed at which the transfer belt 2 conveys the paper 10, the force of all the photoconductors 1 to pull the transfer belt 2 in the moving direction of the paper 10 Therefore, the transfer belt 2 can be prevented from bending between the photoconductors as in the first embodiment.

In the second embodiment, the photosensitive members 1a, 1b,
According to our study, if the surface speed difference between 1c and 1d and the transfer belt 2 was within 5% as in Example 1, no image defect such as a rubbing pattern occurred and the image was good.

The variation in the surface speed due to the diameter error and the eccentricity of the photosensitive members 1a, 1b, 1c and 1d is about 0.75% as in the first embodiment.
The difference between the surface speeds of the transfer belts b, 1c, 1d and the transfer belt 2 is preferably larger than the surface speed variation of the photoconductors 1a, 1b, 1c, 1d and smaller than the speed at which the image deteriorates. Therefore, the image forming apparatus according to the present embodiment is configured such that the photoconductors 1a, 1
The photoconductors 1a, 1b, 1c, and 1d are rotated so that the surface speeds of b, 1c, and 1d are increased by 2% to 102 mm / s. Specifically, the photoconductors 1a, 1
b, 1c, 1d rotation speed, process speed 100mm
/ S rotation speed 47.75 rotations / minute, angular speed 28
48.70 revolutions / minute, 292.
It is rotating at a speed of 2 degrees / second.

Next, a method of driving the transfer belt 2 will be described. In the image forming apparatus according to the present embodiment, unlike the first embodiment, the transfer belt 2 is driven by driving the belt tension roller 3a.
Is driving. In the image forming apparatus of this embodiment, all the photoconductors 1a, 1b, 1c, and 1d transfer the transfer belt 2 to the sheet 1
Since a pushing force is applied in the conveying direction of 0, the portion between the photosensitive member 1a and the belt stretching roller 3a has the highest tension.
Therefore, by driving the belt tension roller 3a, tension is applied to the transfer belt 2 stably, and slippage between the transfer belt 2 and the belt tension roller 3a hardly occurs.
Can be driven stably. Further, in the image forming apparatus of the present embodiment, the transfer belt 2 is connected to the photosensitive members 1a, 1b, 1
c, the photosensitive member 1
The belt stretching roller 3a that stretches the transfer belt 2 at one of both ends in the arrangement direction of a, 1b, 1c, and 1d can increase the winding angle of the transfer belt 2 and stabilize the transfer belt 2 more stably. It is possible to drive.

As described above, also in the image forming apparatus of the second embodiment, a good image without expansion or contraction of the image between the images of the respective colors formed by the photoconductors 1a, 1b, 1c and 1d. And a high-quality image forming apparatus can be realized.

(Embodiment 3) The third embodiment of the present invention is the same color printer as the image forming apparatus of the first embodiment, and the arrangement and operation of the process components inside the apparatus are the same as those of the first embodiment. However, the difference from the first embodiment is the relationship between the diameters of the photoconductors 1a, 1b, 1c, and 1d and the rotation speed of each photoconductor 1 and the transfer belt 2.

In this embodiment, in order to prevent the transfer belt 2 from being bent, the diameters of the photosensitive members 1a, 1b, 1c and 1d are made different from each other. The bodies 1a, 1b, 1c and 1d are arranged, and the photoconductors 1a, 1b, 1c and 1d are rotated at the same angular velocity.

FIG. 3 is a schematic diagram of this configuration. Photoconductor 1
The diameters of a, 1b, 1c, and 1d are sequentially increased along the moving direction of the transfer belt 2. For this reason, the photoconductor 1a,
A difference occurs in the surface speeds at the transfer points 1b, 1c, and 1d, and the surface speeds of the photoconductors sequentially increase along the moving direction of the transfer belt 2. Therefore, the transfer belt 2 always generates a frictional force in the moving direction of the transfer belt 2 at the transfer point of each photoconductor, and the transfer belt 2 is not always subjected to tension and does not bend.

In the photosensitive member 1 of this embodiment, the diameter error is ±
Since the eccentricity is about 0.05 mm and the eccentricity is about 0.1 mm, the difference between the diameters of adjacent photoconductors is set to 0.1 mm in order to increase the speed between the photoconductors in the moving direction of the transfer belt 2 in order. It needs to be 3 mm or more.

For this reason, in this embodiment, the photosensitive members 1a, 1
The diameters of b, 1c and 1d are 39.55 mm, 3
9.85mm, 40.15mm, 40.45mm,
The rotation speed of the photoconductors 1a, 1b, 1c, and 1d is based on the photoconductor diameter of 40 mm, and the photoconductor surface is
Rotation speed equal to the surface speed of 100 mm / s
It is set to 75 rotations / minute and the angular velocity to 286.5 degrees / second.
At this time, the surface speed at the transfer point is such that the photoconductors 1a and 1b are slower than the transfer belt 2 and the photoconductors 1c and 1d are faster than the transfer belt 2. As a result, the photoconductors 1a and 1b act as a load on the transfer belt 2, and the photoconductors 1c and 1d apply a force to move the transfer belt 2 in the reverse direction, so that the driving load of the transfer belt 2 can be reduced. it can.

As described above, in the image forming apparatus of the third embodiment as well, a good image without image expansion and contraction is formed between the images of the respective colors formed by the photoconductors 1a, 1b, 1c and 1d. And a high-quality image forming apparatus can be realized.

(Embodiment 4) The fourth embodiment of the present invention is the same color printer as the image forming apparatus of the first embodiment, and the arrangement and operation of the process components inside the apparatus are the same as those of the first embodiment. However, the difference from the first embodiment is the relationship between the driving method of the photoconductors 1a, 1b, 1c and 1d and the rotation speed of each photoconductor 1 and the transfer belt 2.

In the image forming apparatus of this embodiment, the photosensitive member 1
Separate stepping motors are provided for each of a, 1b, 1c and 1d to drive at a constant angular velocity. Further, in order not to deflect the transfer belt 2, each of the photoconductors 1a, 1b, 1c, 1
The photoconductors 1a, 1b, 1c, and 1d are driven by increasing the angular velocity of the photoconductors 1a, 1b, 1c, and 1d along the moving direction of the transfer belt 2 with a difference in the angular velocity of d.

The photosensitive member 1 is moved along the moving direction of the transfer belt 2.
Since the rotational angular velocities of a, 1b, 1c, and 1d are driven fast, a difference occurs in the surface speed at the transfer point of each photoconductor 1,
The surface speed of the photoconductor increases in order along the moving direction of the transfer belt 2. Therefore, the transfer belt 2 always generates a frictional force in the moving direction of the transfer belt 2 at the transfer point of each photoconductor, and the transfer belt 2 is not always subjected to tension and does not bend.

In the photoreceptor of this embodiment, the diameter error is ± 0.0
Since the eccentricity is about 5 mm and the eccentricity is about 0.1 mm, the speed difference between the adjacent photoconductors must be 0.75 in order to increase the speed sequentially between the photoconductors along the moving direction of the transfer belt 2.
% Or more.

In this embodiment, the photosensitive members 1a, 1b, 1c,
The surface speed at the transfer point 1d is the surface speed 1 of the transfer belt 2.
-1.125% and-
The rotation speed was set to 47.21 rotations / minute so as to be 0.375%, + 0.375%, and + 1.125%, respectively.
7.57 rotations / minute, 47.93 rotations / minute, 48.29 rotations / minute, angular velocity 283.26 degrees / second, 285.41 degrees / second, 287.55 degrees / second, 289.70 degrees / second And

At this time, the surface speed at the transfer point is lower for the photosensitive members 1a and 1b than for the transfer belt 2, and the photosensitive members 1c and 1d
Is faster than the transfer belt 2, but this causes the photoconductors 1a and 1b to act as a load on the transfer belt 2, and the photoconductors 1c and 1d apply a force to advance the transfer belt 2 in the reverse direction. The driving load of the belt 2 can be reduced.

As described above, also in the image forming apparatus of the fourth embodiment, a good image having no image expansion or contraction can be obtained between the images of the respective colors formed by the photosensitive members 1a, 1b, 1c and 1d. As a result, a high quality image forming apparatus can be realized.

(Embodiment 5) FIG. 4 is a schematic sectional view of an image forming apparatus according to a fifth embodiment of the present invention. In the center of the main body, four photoconductors 1a, 1b, 1c, and 1d corresponding to the four color toners of yellow, magenta, cyan, and black necessary for color image formation are arranged vertically, and each axis has its own axis. It is rotatable and connected by a support, and is provided as a structure of the integral photoconductor unit 19.

Further, the photosensitive members 1a, 1
b, 1c and 1d so that the intermediate transfer belt 19
Are stretched vertically in the arrangement direction of the plurality of photoconductors 1 by four belt stretching rollers 3a, 3b, 3c, and 3d,
The photoconductors 1a, 1b, 1c,
Transfer assist rollers 4a, 4b, 4c for transferring the toner image from the photoreceptor onto the belt at a position facing 1d.
4d is provided. Then, the photoconductors 1a, 1b, 1c, and 1d are provided on the side opposite to the side on which the intermediate transfer belt 19 is disposed.
Exposure units 6a and 6b for exposing the surface of
6c and 6d and developing units 7a, 7b, 7c and 7d for visualizing the electrostatic latent images with toner are alternately stacked in the vertical direction.

Further, the photosensitive members 1a, 1b, 1c, 1d
At the position where it contacts the intermediate transfer belt 19, it rotates downward from above. When the photoconductor rotates in this manner, the arrangement of other printing processes and the rotation direction of the intermediate transfer belt 19 are determined. In this case, the intermediate transfer belt 19
Rotates rotationally from above to below at the position where it contacts the photoreceptor. Here, the intermediate transfer belt 19 is an embodiment of the transfer medium of the present invention.

On the outer periphery of the intermediate transfer belt 19, the toner image on the intermediate transfer belt 19 is
Transfer device 20 for transferring paper 10 to intermediate transfer belt 19
A paper static eliminator 21 that peels off the toner from the paper and a belt cleaner 15 that cleans toner on the intermediate transfer belt 19 are provided. Further, a paper cassette 11, a pick roller 12, a registration roller 13, and a fixing device 16 are arranged on the transport path of the paper 10.

Around the photoconductors 1a, 1b, 1c, 1d, chargers 5a, 5b for charging the respective photoconductors 1 are provided.
5c, 5d, exposure units 6a, 6b, 6c, 6d, developing unit 7
a, 7b, 7c, 7d, the intermediate transfer belt 19, and erase lamps 8a, 8b, 8c, 8d for removing charges on the surface of the photoreceptor.
Photoconductor cleaner 9a, 9 for cleaning residual toner
b, 9c, 9d, transfer assisting rollers 4a for assisting the transfer of the toner images formed on the photoconductors 1a, 1b, 1c, 1d by the developing devices 7a, 7b, 7c, 7d onto the intermediate transfer belt 19. 4b, 4c and 4d are provided.

A printing operation in the image forming apparatus according to the present embodiment will be described. When a print command is input to a main body controller (not shown), each of the photoconductors 1 and the intermediate transfer belt 19 rotate, and image exposure is first performed by the photoconductor 1a arranged at the most upstream portion in the intermediate transfer belt moving direction. Start. The electrostatic latent image formed on the photoreceptor 1a is developed by a developing device 7a,
A toner image is formed on the photoconductor 1a. The toner image on the photoconductor 1a is transferred onto the intermediate transfer belt 19 by the transfer assist roller 4a. Thereafter, the other photoconductors 1b, 1c, 1d
Similarly, a toner image is formed, and the toner image formed by each of the photoconductors 1b, 1c, and 1d is transferred onto the intermediate transfer belt 19 as the intermediate transfer belt 19 moves, and a color image is formed on the intermediate transfer belt 19. To form

The image formed on the intermediate transfer belt 19 is
Using the transfer device 20, the paper is drawn from the paper cassette 11 by the pick roller 12, and is transferred onto the paper 20 transported by the registration roller 13. Intermediate transfer belt 1
The paper 10 on which the toner image has been transferred from above is peeled off from the intermediate transfer belt 19 by using a paper discharging unit 21, and the fixing unit 1
At 6, the toner on the paper 10 is fixed, and is conveyed to the outside of the main body by the paper discharge mechanism 17.

Also in the image forming apparatus of the present embodiment, there is a possibility that an image position shift occurs due to uneven speed of the photosensitive members 1a, 1b, 1c and 1d and the intermediate transfer belt 19. For this reason, in this embodiment, the method applied to the transfer belt 2 in the first embodiment is replaced with the intermediate transfer belt 19 as it is. That is, the surface speeds at the transfer points of the photoconductors 1a, 1b, 1c, and 1d are set lower than the speed of the intermediate transfer belt 19.

In the image forming apparatus of the first embodiment, the transfer belt 2
The toner image is superimposed on the upper sheet 10. On the other hand, in the image forming apparatus of the present embodiment, the photoconductors 1a, 1b,
Since the images formed on 1c and 1d are transferred and superimposed on the intermediate transfer belt 19, the friction coefficient is stable. Therefore, each photoconductor 1 and the intermediate transfer belt 19 can be smoothly slid.

In the intermediate transfer belt 19 of this embodiment, a thin film of a fluororesin is provided on the surface of the transfer belt 2 used in the first embodiment. In this way, the surface of the intermediate transfer belt 19 is covered with a material such as fluorocarbon resin to which the toner is unlikely to adhere, so that the releasability of the toner is ensured. At this time, the coefficient of friction between the photoreceptor and the surface of the intermediate transfer belt was 0.4
In this case, the variation in the frictional state could be reduced as compared with the image forming apparatus of the first embodiment in which the sheet 10 is conveyed between the photosensitive member and the transfer belt.

As described above, also in the image forming apparatus of the fifth embodiment, a good image without expansion and contraction of an image can be obtained between images of each color formed by each photosensitive member, and a high quality image forming apparatus is realized. It became possible to do.

[0074]

According to the present invention, even if there is a diameter error or eccentricity of each photoconductor, the rotation speed of the photoconductor is kept constant, so that the image of each color does not expand and contract, and a high quality image is obtained. There is an effect that a forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a drive mechanism of each photoconductor in the first embodiment.

FIG. 3 is a schematic diagram showing an arrangement of each photoconductor in a third embodiment of the present invention.

FIG. 4 is a sectional view schematically showing an image forming apparatus according to a fifth embodiment of the present invention.

[Explanation of symbols]

1a, 1b, 1c, 1d: photoconductor, 2: transfer belt, 3
a, 3b, 3c, 3d ... belt stretching rollers, 4a, 4
b, 4c, 4d: transfer assisting rollers, 5a, 5b, 5c,
5d: charger, 6a, 6b, 6c, 6d: exposure unit, 7
a, 7b, 7c, 7d: developing units, 8a, 8b, 8c, 8
d: erase lamp, 9a, 9b, 9c, 9d: photoconductor cleaner, 10: paper, 11: paper cassette, 12: pick roller, 13: registration roller, 14: paper suction mechanism, 15: belt cleaner, 16: fixing Container, 17: paper discharge mechanism, 18: photoconductor unit, 19: intermediate transfer belt,
Reference numeral 20 denotes a transfer unit, 21 denotes a paper neutralizer, 100 denotes a photoreceptor gear, 101 denotes a transmission gear, 102 denotes a drive gear, and 103 denotes a stepping motor.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaru Nakano 502 Kandachi-cho, Tsuchiura-shi, Ibaraki F-term in the Machine Research Laboratory, Hitachi, Ltd. (Reference) 2H030 AA01 AB02 AD17 BB02 BB16 BB71

Claims (7)

[Claims] 1. At least two or more photosensitive drums,
An image forming apparatus comprising: conveyance means for conveying a recording medium while contacting the photosensitive drum, and forming a multicolor image by transferring a toner image formed on each photosensitive drum onto the recording medium. An image forming apparatus, wherein the photosensitive drum is configured to rotate at a predetermined constant angular velocity. 2. The method according to claim 1, wherein a difference is made between the constant angular velocities of the photosensitive drums, and the angular velocities of the adjacent photosensitive drums on which an image is formed first are reduced. Characteristic image forming apparatus. 3. The photosensitive drum according to claim 1, wherein each of the photosensitive drums has a difference in diameter.
An image forming apparatus, wherein the diameter of a side on which an image is formed first by a photosensitive drum arranged adjacently is reduced. 4. The photosensitive drum according to claim 1, 2 or 3, wherein a surface speed of the conveying means is higher than a surface speed of all the photosensitive drums or a predetermined speed of each photosensitive drum arranged from upstream to downstream. An image forming apparatus characterized in that the surface speed is made faster or slower than the surface speed of the image forming apparatus. 5. At least two or more photosensitive drums,
An image forming apparatus includes a transfer medium that moves while being in contact with the photosensitive drum, and forms a multicolor image by transferring a toner image formed on each photosensitive drum onto a recording medium via the transfer medium. An image forming apparatus, wherein the photosensitive drum is configured to rotate at a predetermined constant angular velocity. 6. The surface velocity of the transfer medium according to claim 5, wherein the surface velocity of the transfer medium is higher than all surface velocities of the respective photosensitive drums or a predetermined surface velocity of each of the photosensitive drums arranged from upstream to downstream. An image forming apparatus characterized by being configured to be faster or slower. 7. The exposure device according to claim 1, wherein the exposure device provided for each photoconductor drum has the same exposure speed for exposing an image on the photoconductor drum in all the exposure devices. An image forming apparatus having the above-described configuration.