JP2001147565A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device by which the tilt of a drum driving motor shaft causing an image defect (banding) is reduced. SOLUTION: In the tandem type color image forming device, a 1st motor gear 33a is arranged between the driving transmission gears 31a and 31b of two photoreceptor drums 1a and 1b arranged on an identical axial line and on an identical axial line. Then, the gears 31a and 31b are directly meshed with the gear 33a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus such as a color copying machine or a color printer employing an electrophotographic system, and more particularly to a tandem type image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, there is a tandem type multicolor image forming apparatus in which a plurality of photosensitive drums are arranged in a line.

FIG. 7 shows a typical example of a full-color printer.

In this image forming apparatus, a sheet as a transfer material loaded on a paper cassette or the like is fed to a plurality of rollers (13, 15, 14a, 14) by a paper feed roller 18 and a registration roller pair 19.
b) conveyed toward the electrostatic transfer belt 11 stretched in
While being carried between the electrostatic transfer belt 11 and the electrostatic transfer roller 11 so as to be sandwiched between the electrostatic attraction roller 22 and the electrostatic transfer belt 11, four image carriers as an image carrier arranged along the transport path are provided. The toner images composed of yellow, magenta, cyan, and black are sequentially transferred onto the sheet by the photoreceptor drums (1a, 1b, 1c, 1d) via transfer rollers (12a, 12b, 12c, 12d), and the colors are superimposed. A color image is formed by the combination, and is fixed by a fixing device 20 including a heating roller 21a and a pressure roller 21b, and is discharged to a paper discharge unit 25 by, for example, a pair of paper discharge rollers 23 and 24. Each of the photosensitive drums (1a, 1b, 1c, 1d) has a polygon mirror (9a, 9b, 9c, 9d) and an imaging lens (10a, 10b, 10c, 10d).
) And other scanner units (3a, 3b, 3c, 3d)
), An electrostatic latent image is formed, and each electrostatic latent image is developed by a developing device of each color (not shown), and the visualized toner images of each color are transferred to a transfer material at a transfer portion.

This configuration has attracted attention in recent years because printing can be performed at high speed.

However, since each color is formed by the four photosensitive drums, even higher precision is required for the rotational drive of the photosensitive drums than in a color printer in which the colors are overlapped in four passes. I have.

That is, since the four scanners and drums are independent of each other, a difference between them causes a deterioration in image quality such as color misregistration.

Conventionally, as shown in FIGS. 5 and 6, one photosensitive drum (1a, 1b, 1c, 1d) is driven by one motor (36a, 36b, 36c, 36d) and a drum driving gear ( 35a, 35b, 35c,
35d), the rotation driving accuracy of each photosensitive drum is improved by improving the component accuracy of each drum drive gear, the rotation accuracy of each motor, and the color misregistration. Image quality such as banding was improved.

[0009]

In the above-mentioned prior art, in the in-line configuration in which the plurality of photosensitive drums are arranged in a line, one photosensitive drum is generally driven to rotate by one motor. . As shown in FIGS. 5 and 6, a drum drive gear (35a, 35b, 35) as a drive transmission gear is provided at an end of each photosensitive drum (1a, 1b, 1c, 1d).
c, 35d) is fixed, and the drum drive gear (35a,
Drive motors (36a, 36b, 36c, 36d) are arranged so that the respective motor gears mesh with 35b, 35c, 35d).

Here, the drive motors (36a, 36b, 36c, 36d)
Starts rotating, as shown in FIG. 6, a driving reaction force corresponding to the load torque of the photosensitive drum is applied to the drive motor shafts (34a, 34a).
b, 34c, 34d).

As a result, the motor shafts (34a, 34b, 34c, 34d)
Falls in the direction of the reaction force, and the motor shafts (34a, 34b, 34c, 34d)
And the respective drum drive gears (35a, 35b, 35c, 35d) fixed to the end of the photosensitive drum 1
Of the photoconductor drum (1a, 1b, 1c, 1d)
Rotation unevenness occurs. The output image in this state is image unevenness (banding) in the direction orthogonal to the paper feed direction.
Will be generated.

Further, four photosensitive drums (1a, 1b, 1c, 1d)
In ()), since the rotational drive is transmitted by the gear, there is a possibility that the rotation unevenness of one tooth component of the drive transmission gear may occur.

In the above-described full-color printer having the in-line configuration, the rotation unevenness not only causes image defects such as banding but also image defects such as color misregistration and color unevenness when the four photosensitive drums do not have rotation unevenness. It will be connected.

An object of the invention according to the present invention has been made in view of the above circumstances, and provides an image forming apparatus in which the inclination of a drum drive motor shaft which causes image defects (banding) is reduced. It is.

As another object, image defects (color shift, color unevenness) due to differences in rotation unevenness of a plurality of photosensitive drums.
An object of the present invention is to provide an image forming apparatus which does not cause the problem.

[0016]

According to a first aspect of the present invention, there are provided a plurality of rotating image carriers which are arranged along a transfer material conveying direction and arranged on the same straight line, and a plurality of rotating image carriers. A driving device that drives the plurality of image carriers by transmitting a driving force to each of the drive transmission gears fixed to the shaft ends, wherein the driving device includes:
A pair of adjacent drive transmission gears is provided as a set, and a drive source is provided in each set. A drive source gear having an even number of teeth attached to the drive source is provided between the two drive transmission gears and a drive source gear having an even number of teeth. It is characterized in that it is arranged on a straight line connecting the central axes of the image carriers and directly meshes with both of the drive transmission gears.

In the first invention, the plurality of image carriers are arranged at equal intervals, and the interval L is a value obtained by dividing the length of one circumference of the image carrier by the number of teeth of the drive transmission gear. It is characterized in that it is approximately an integral multiple.

A third aspect of the present invention is characterized in that the four image carriers are arranged, and the developed images of different colors are respectively transferred so as to be superimposed on the transfer material.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, an embodiment of a multicolor image forming apparatus according to the present invention will be described in detail with reference to the drawings.

[Overall Configuration of Color Image Forming Apparatus] First, the overall configuration of a color image forming apparatus will be outlined with reference to FIG. FIG. 4 is a longitudinal sectional view showing the entire configuration of a full-color laser beam printer 100 which is one mode of the color image forming apparatus.

The color image forming apparatus 100 shown in FIG.
Photoconductor drums 1a, 1b, 1c, and 1d as four image carriers that are arranged in a horizontal direction are provided. The photosensitive drum 1 is driven to rotate clockwise in FIG. 1 by a driving unit (not shown). A charging roller 2 (2a, 2b, 2c, 2d) that uniformly charges the surface of the photosensitive drum 1 in order according to the rotation direction around the photosensitive drum 1, and irradiates a laser beam based on image information to the photosensitive roller 1 Drum 1
The scanner unit 3 (3a, 3a) for forming an electrostatic latent image on
b, 3c, 3d), a developing roller 4 (4a, 4b, 4c,
4d), an electrostatic transfer device 5 for transferring the toner image on the photosensitive drum 1 to the transfer material S, and a cleaning device 6 (6) for removing the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer.
a, 6b, 6c, 6d) and the like.

Here, the photosensitive drum 1 and the charging roller 2,
The developing roller 4 and the cleaning device 6 are integrally formed as a cartridge to form a process cartridge 7.

Hereinafter, the photosensitive drum 1 will be described in detail.

The photosensitive drum 1 is formed, for example, by applying an organic photoconductor layer (OPC photosensitive member) to an outer peripheral surface of an aluminum cylinder having a diameter of 30 mm. Photoconductor drum 1
Are rotatably supported at both ends by support members (not shown), and drive transmission gears 31a, 31b, 31c, and 31d are fixed to one end as shown in FIG. Although details will be described later, a drive motor is arranged so as to mesh with the drive transmission gear, and the photoreceptor drum 1 is driven to rotate clockwise by rotation of the drive motor and transmission of the driving force.

As the charging roller 2, a contact charging type one can be used. The charging roller is a conductive roller formed in a roller shape. The roller is brought into contact with the surface of the photosensitive drum 1, and a charging bias voltage is applied to the roller 2 to thereby charge the photosensitive drum 1.
Is charged uniformly.

The scanner unit 3 is arranged in a substantially vertical direction of the photosensitive drum 1 and has a laser diode (not shown).
The image light corresponding to the image signal is rotated at high speed by a scanner motor (not shown).
(9a, 9b, 9c, 9d). The image light reflected by the polygon mirror 9 is transmitted to the imaging lens 10 (10a,
10b, 10c, 10d), the surface of the charged photosensitive drum 1 is selectively exposed to form an electrostatic latent image.

Each of the developing rollers 4a, 4b, 4c, and 4d is composed of a developing unit that stores a toner of each color of yellow, magenta, cyan, and black.

Further, all the photosensitive drums 1a, 1b,
An electrostatic transfer belt 11 that circulates and moves so as to face and contact with 1c and 1d is provided. The electrostatic transfer belt 11 is 10
Approximately 1 with a volume resistivity of ¹¹ to 10 ¹⁴ Ω · cm
It is composed of a 50 μm film-shaped member. The electrostatic transfer belt 11 is supported by rollers on four axes in the horizontal direction, and circulates so that the transfer material S is electrostatically attracted to the outer peripheral surface on the upper side in the drawing and the transfer material S comes into contact with the photosensitive drum 1. I do. As a result, the transfer material S is transported to the transfer position by the electrostatic transfer belt 11, and the toner image on the photosensitive drum 1 is transferred.

The inner surface of the electrostatic transfer belt 11 abuts,
The transfer rollers 12 (12a, 12b, 12c, 12c) are located at positions facing the four photosensitive drums 1a, 1b, 1c, 1d.
d) is juxtaposed. A positive charge is applied from the transfer roller 12 to the transfer material S via the electrostatic transfer belt 11, and an electric field generated by the charge causes the transfer material S in contact with the photosensitive drum 1 to be transferred to the transfer material S on the photosensitive drum 1. A negative toner image is transferred.

The electrostatic transfer belt 11 has a circumference of about 700 mm,
It is a belt having a thickness of 150 μm. The belt is wound around four rollers of a driving roller 13, driven rollers 14a and 14b, and a tension roller 15, and rotates in the direction of the arrow in the figure. Thus, the toner image is transferred while the transfer material S is conveyed from the driven roller 14a side to the drive roller 13 side by the circulating movement of the electrostatic transfer belt 11 described above.

The paper feed unit 16 feeds and conveys the transfer material S to the image forming unit. A plurality of transfer materials S are stored in a paper feed cassette 17. Feed roller 1 during image formation
8 (half-moon roller), the registration roller pair 19 is driven and rotated in accordance with the image forming operation, and the transfer material S in the sheet cassette 17 is rotated.
Are separated and fed one by one, and the leading end of the transfer material S abuts against the pair of registration rollers 19 and temporarily stops. After forming a loop, the rotation of the electrostatic transfer belt 11 and the image writing position are synchronized, and the pair of registration rollers S 19 feeds the paper to the electrostatic transfer belt 11.

The fixing unit 20 fixes the toner images of a plurality of colors transferred to the transfer material S, and presses the rotating heating roller 21a against the transfer roller S to apply heat and pressure to the transfer material S. And a roller 21b.

That is, the transfer material S onto which the toner image on the photosensitive drum 1 has been transferred is conveyed by the fixing roller pair 21 when passing through the fixing unit 20, and is given heat and pressure by the fixing roller pair 21. Thereby, the toner images of a plurality of colors are fixed on the surface of the transfer material S.

In the image forming operation, the process cartridges 7a, 7b, 7c, 7d are sequentially driven in accordance with the printing timing, and the photosensitive drum 1 is driven in accordance with the driving.
a, 1b, 1c, and 1d are driven to rotate clockwise. Then, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven. By this driving, the charging roller 2 applies a uniform electric charge around the photosensitive drum 1 and the scanner unit 3 causes the photosensitive drum 1
The peripheral surface is exposed according to the image signal to form an electrostatic latent image on the peripheral surface of the photosensitive drum 1. The developing roller in the developing roller 4 transfers toner to a low potential portion of the electrostatic latent image to form (develop) a toner image on the peripheral surface of the photosensitive drum 1.

When the leading end of the toner image on the peripheral surface of the photosensitive drum 1 at the uppermost stream is rotated and conveyed to a point opposed to the electrostatic transfer belt 11, the printing start position of the transfer material S is set at the opposed point. The registration roller pair 19 starts rotating and feeds the transfer material S to the electrostatic transfer belt 11 so as to match.

The transfer material S is pressed against the outer periphery of the electrostatic transfer belt 11 so as to be sandwiched between the electrostatic attraction roller 22 and the electrostatic transfer belt 11, and between the electrostatic transfer belt 11 and the electrostatic attraction roller 22. By applying a voltage to the transfer material S, a charge is induced in the transfer material S, which is a dielectric, and the dielectric layer of the electrostatic transfer belt 11, and the transfer material is electrostatically attracted to the outer periphery of the electrostatic transfer belt 11. ing. Thereby, the transfer material S
Is stably attracted to the electrostatic transfer belt 11 and is conveyed to the most downstream transfer section.

While being conveyed as described above, the toner image on each photosensitive drum 1 is sequentially transferred onto the transfer material S by the electric field formed between each photosensitive drum 1 and the transfer roller 12.

The transfer material S to which the four color toner images have been transferred is
The electrostatic transfer belt 11 is controlled by the curvature of the belt drive roller 13.
And is carried into the fixing unit 20. Transfer material S
After the toner image is heat-fixed by the fixing unit 20, the toner image is discharged from the main body by the discharge roller pair 23 and 24 from the discharge unit 25 with the image surface down.

Next, the photosensitive drum driving structure, which is a feature of the present invention, will be described in detail with reference to FIGS.

As shown in FIGS. 1 and 2, each photosensitive drum 1
Four (1a, 1b, 1c, 1d) are arranged at equal intervals on one straight line in the horizontal direction. A drive transmission gear 31 (31a, 31b, 31b) is provided at the shaft end of the photosensitive drum shaft of the photosensitive drum 1.
31c, 31d) are press-fitted and fixed, and serve as rotation direction restricting means for restricting rotation of each drive transmission gear 31 with respect to the photosensitive drum shaft along an axial direction in a shaft hole of the drive transmission gear. A groove (not shown) is formed, and a parallel pin attached to a photosensitive drum shaft is fitted so as to engage with the groove, so that each photosensitive drum and each drive transmission gear do not rotate separately. Has been fixed.

As shown in FIGS. 1 and 2, the first motor gear 33a is located on a straight line L1 connecting the central axes of the yellow photosensitive drum 1a and the magenta photosensitive drum 1b, and at the midpoint thereof. are doing. First motor gear 33a
Are press-fitted and fixed to the rotating shaft of the first stepping motor 32a, and mesh with the drive transmission gears 31a and 31b press-fitted and fixed to the shaft ends of the photosensitive drum 1a and the photosensitive drum 1b, respectively. I have.

Similarly, a second motor gear 33b is disposed on a straight line L1 connecting the central axes of the cyan photosensitive drum 1c and the black photosensitive drum 1d, and at the center thereof. The second motor gear 33b is press-fitted and fixed to the rotating shaft of the second stepping motor 32b, and is connected to the drive transmission gears 31c and 31d respectively press-fitted and fixed to the respective shaft ends of the photosensitive drum 1c and the photosensitive drum 1d. Are engaged.

In the present embodiment, the first motor gear 33a and the second motor gear 33b have an even number of eight teeth, and each of the drive transmission gears 31a, 31b, 31
The number of teeth of c and 31d is formed by 30 teeth, and both gears are set by the module 0.5.

In the present embodiment, two photosensitive drums are driven to rotate by one stepping motor, which is different from the conventional structure in which one photosensitive drum is driven by one motor. The photoconductor can be driven at low cost.

FIG. 3 is a partial view showing the operation of driving the photosensitive member. FIG. 3 shows the first stepping motor 32a.
The motor gear 33a press-fitted and fixed to a (not shown) motor shaft 34a (not shown) rotates counterclockwise, and the drive transmission gears 31a and 31 mesh with the first motor gear 33a.
b. By the rotation of the drive transmission gear 31,
The photosensitive drums 1a and 1b rotate clockwise.

When transmitting the driving force, the motor drive shaft 34a responds to the magnitude of the load torque of the photosensitive drum 1a according to the magnitude of the load torque.
A drive reaction force Fa is received from the drive transmission gear 31a. At the same time, it receives a driving reaction force Fb from the driving transmission gear 31b of the photosensitive drum 1b.

The driving reaction force F is applied to the motor driving shaft 34.
a is tilted. As a result, the first motor gear 33
The meshing between a and the drive transmission gear 31 is deteriorated, and the rotation of the photosensitive drum 1 becomes uneven, which leads to an image defect such as banding. The rotation unevenness includes a relatively high frequency of one gear cycle and a low frequency of one rotation of the motor drive shaft.

In the present embodiment, the drive transmission gears 31a,
The arrangement of the first motor gear 33a and the first motor gear 33a is devised (the same applies to the second motor gear 33b and the drive transmission gears 31c and 31d), and the number of teeth of the first motor gear 32a is set to an even number, whereby the drive transmission gear is set. The drive reaction force Fa to the drive transmission gear 31b is always balanced with the drive reaction force Fa to the drive transmission gear 31b, thereby enabling a configuration in which no external force is applied to the motor drive shaft 34a. By setting the number of teeth of the first motor gear 32a (the second motor gear 32b) to an even number, the drive transmission gears 31 meshing with the first motor gear 32a, respectively.
a and the drive transmission gear 31b are completely engaged with each other, and the vibration of the first motor 32a due to the external force of the motor drive shaft 34a is also reduced.

The axial distance L between the photosensitive drum 1a and the photosensitive drum 1b shown in FIG. 3 satisfies the following relationship.

L ≒ K × (peripheral length of photosensitive drum / number of teeth of drive transmission gear 31) Here, the distance L is set so that K is an integer value.

In this embodiment, the photosensitive drum diameter is 30,
Since the length of one circumference of the photosensitive drum is set to 30π, the number of teeth of the drive transmission gear is set to 30, and K = 25, L = (25 ×
π) ≒ 78.5 mm.

By adopting the configuration of the present embodiment, when the rotation unevenness due to one tooth component of the drive transmission gear 31 occurs,
The influence of the rotation unevenness of the photosensitive drums 1a and 1b and the photosensitive drums 1c and 1d on the image becomes the same, and image defects such as color shift and color unevenness between the two photosensitive drums can be prevented.

That is, since the number of teeth of the motor gear is even, the engagement of the gears when the yellow toner image is transferred to the transfer material S and the transfer of the magenta toner image to the same position on the transfer material S Gears are in exactly the same state. As a result, when minute banding of one tooth component of the gear of the photosensitive drum 1 occurs, the images overlap, and an image in which color misregistration and color unevenness are not conspicuous is obtained.

Of course, in order to match the phase of the rotation unevenness of one tooth component of all the photosensitive drums, the positions of the first motor gear 33a and the second motor gear 33b are monitored and controlled by an external sensor. Thus, the rotation phases of the first stepping motor 34a and the second stepping motor 34b can be matched.

[0055]

As described above, according to the present invention,
A drive source gear of a drive source such as a motor is arranged on a straight line connecting the centers of two adjacent image carriers and at a midpoint thereof, and the number of teeth of the gear is set to an even number so that the motor shafts are opposed by 180 degrees. Since the drive reaction force is received from the two drive transmission gears arranged at the positions, the drive reaction forces cancel each other, and the force received by the motor shaft is minimized. As a result, the amount of tilt of the shaft can be reduced, the deterioration of the meshing caused by the tilt of the motor shaft can be prevented, and the image quality can be improved.

The distances between adjacent image carriers are all equal, and the distance between them is approximately an integer of a value obtained by dividing the length of one circumference of the image carrier by the number of teeth of a drive transmission gear fixed to the end of the image carrier. Because of the double configuration, rotation unevenness due to one tooth component caused by gear drive transmission occurs in the same phase on all image carriers, so image defects such as color misregistration and color unevenness when colors are superimposed are anticipated. Have successfully prevented it.

[Brief description of the drawings]

FIG. 1 is a perspective view of a photosensitive drum driving mechanism according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the drive mechanism of FIG.

FIG. 3 is a partial sectional view showing the operation of the embodiment of the present invention.

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

FIG. 5 is a perspective view of a conventional photosensitive drum driving mechanism.

FIG. 6 is a partial cross-sectional view of the photosensitive drum driving mechanism of FIG.

FIG. 7 is a cross-sectional view of an image forming apparatus including the photoconductor driving mechanism of FIG.

[Explanation of symbols]

 1 (1a, 1b, 1c, 1d): photosensitive drum 3 (3a, 3b, 3c, 3d): scanner unit 11: electrostatic transfer belt device 31 (31a, 31b, 31c, 31d): drive transmission gear 32a First stepping motor 32b Second stepping motor 33a First motor gear 33b Second motor gear 34 Drive shaft

Claims (3)

[Claims] 1. A plurality of rotating image carriers arranged in the same straight line and arranged along the transfer direction of a transfer material, and respective drive transmissions fixed to ends of rotation axes of the plurality of image carriers, respectively. A driving device that drives the plurality of image carriers by transmitting a driving force to a gear, wherein the driving device includes two adjacent driving transmission gears.
As a set, a drive source is provided for each set, and a drive source gear having an even number of teeth attached to the drive source is provided between the two drive transmission gears and on a straight line connecting the central axes of the two image carriers. Wherein the first and second drive transmission gears are directly engaged with each other. 2. The plurality of image carriers are arranged at equal intervals, and the interval L is substantially an integral multiple of a value obtained by dividing the length of one circumference of the image carrier by the number of teeth of the drive transmission gear. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the four image carriers are arranged, and transfer the developed images of different colors to the transfer material so as to be sequentially superimposed.