JPH1130917A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a photoreceptor belt from being biased due to the difference in parallelism between a photoreceptor and an intermediate transfer body by providing one pulley having a specific coefficient of friction with a photoreceptor, in the vicinity of the contact part, of the photoreceptor with the intermediate transfer body or the contact part. SOLUTION: The photoreceptor 15 is wound on a driving pulley 10, between C- and D-points and the driving pulley 10 is rotated in the direction of the arrow, to carry the photoreceptor 15. A tension pulley 14 imparts uniform tensile force to the photoreceptor 15 by springs 20 arranged in bearings at both ends. Driven pulleys 12 and 13 are arranged in the vicinity of the contact part N of the intermediate transfer body 40 with the photoreceptor 15. In such a case, it is constituted so that when the coefficient of friction and contact angle of the driven pulley 12 with the photoreceptor belt 15 are defined as μ and ϕrespectively, the angle of the shaft of the pulley 12 with an intermediate transfer drum shaft is defined as θ, the tensile force of the belt 15 is defined as T and the carrying force of the intermediate transfer drum 40 by the photoreceptor 15 is defined as P, these values satisfy μ>Pe.sinθ/(2.T.sin(ϕ/2)).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, and more particularly to an apparatus using a belt-shaped photoreceptor or an intermediate transfer member, wherein the photoreceptor is arranged in partial contact with the photoreceptor. The present invention relates to an electrophotographic apparatus having an intermediate transfer member, and configured to obtain a color image by superimposing and forming toner images of different colors on the intermediate transfer member.

[0002]

2. Description of the Related Art An electrophotographic apparatus such as a laser printer for forming a color image by using an electrophotographic technique uniformly charges the surface of a photosensitive member such as a drum or a belt and exposes the photosensitive member by exposing a laser beam. The toner image formed by developing the electrostatic latent image formed on the body surface is temporarily transferred to an intermediate transfer member such as a drum or a belt and transferred, and this process is repeated for each different color toner image. A color image is formed thereon, and then the toner image is collectively transferred to a transfer material such as paper and fixed by a fixing device to form a color image.

In an apparatus using a belt stretched over a plurality of pulleys as a photoreceptor or an intermediate transfer member, the belt tends to be shifted due to a parallelism error between the pulleys. In a color image in which images are superimposed a plurality of times, the transfer position of the toner from the photosensitive member to the intermediate transfer member differs for each color, and thus there is a problem that the image appears as a color shift.

[0004] The superimposition accuracy of each color required for a color electrophotographic apparatus is generally 0.1 mm or less. In order to realize this, parallelism error between pulleys that pass over a belt,
In particular, it is necessary to reduce the parallelism error between rollers with a large belt winding to 0.1 mm or less. However, no matter how small the parallelism error between the pulleys is, if the belt unit is attached to the main body of the apparatus, the parallelism between the pulleys will increase because the main body of the apparatus is also distorted. A degree error occurs, and it is difficult to maintain required accuracy.

[0005] As means for preventing the belt from shifting,
A sensor for detecting the position of the belt is provided on the end surface of the belt, and one of the pulleys for bridging the belt is movable, and the pulley is displaced in accordance with the belt position via an actuator or the like, thereby sequentially detecting the parallelism error between the pulleys. A correction method is disclosed in JP-A-7-36314.

Means for controlling the degree of parallelism by adjusting the position of a portion supporting the belt is also well known.

However, the above prior art requires a sensor for detecting the belt position and an actuator for displacing the pulley, so that the apparatus becomes large, the number of parts increases, and the cost becomes high when the photosensitive member is made into a cartridge. In addition, there is a problem that productivity due to adjustment is reduced, and it is difficult to reduce the size and cost of the electrophotographic apparatus.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional apparatus, and an object of the present invention is to reduce the distortion of the apparatus body and the belt without increasing the size of the apparatus. It is an object of the present invention to provide an electrophotographic apparatus capable of preventing the belt from being shifted even if the parallelism error between the contacting drum shaft and the belt unit is large, and capable of obtaining a good image at a small size and at low cost. .

[0009]

In order to achieve the above object, according to the present invention, at least one pulley among a plurality of pulleys over a belt-like photosensitive member or an intermediate transfer member is connected to a drum-like intermediate transfer member. Alternatively, while being arranged on the side in contact with the photoconductor, the friction coefficient μ between the pulley and the photoconductor belt, the winding angle φ between the pulley and the photoconductor belt,
When the angle θ between the shaft of the pulley and the shaft of the intermediate transfer drum, the tension T of the photoreceptor belt, and the conveying force P of the intermediate transfer drum by the photoreceptor belt, the values satisfy the following equations.

Μ> Pe · sin θ / (2 · T · sin (φ / 2))

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a color laser printer 1 according to the present embodiment.

The driving pulley 10, the driven pulleys 11, 12,
13, a belt-shaped photoconductor 15 that is wound around a tension pulley 14 and rotates at a constant speed in the direction of arrow A;
Transfer member 4 of a drum strip arranged in partial contact with the
0, a charger 18 for uniformly charging the surface of the photoconductor 15
And an exposure device 2 for exposing the surface of the uniformly charged photoconductor 15 to form an electrostatic latent image on the surface, and four developing devices 50 for developing the electrostatic latent image to form a toner image , 51,
52, 53, a transfer roller 60 for transferring the toner image to a transfer material such as paper, a fixing device 70 for fixing the toner image transferred to the paper, and a toner remaining on the surface of the photoconductor 15 after the transfer of the toner image. The image forming apparatus includes a blade 17 for removing, an erase lamp 19 for removing charges remaining on the surface of the photoconductor 15 after transferring the toner image, and a cleaner 41 for removing toner remaining on the surface of the transfer drum.

The exposure device 2 irradiates the photoconductor 15 with a laser beam in accordance with video data corresponding to a toner image sent from an information processing device (not shown).

A developing device 50 uses a black toner as a developer, a developing device 51 uses a yellow toner as a developer, and a developing device 5.
A developing device 2 uses magenta toner as a developer, and a developing device 53 uses cyan toner as a developer. Each developing device is provided with a developing function by controlling a bias voltage. Or they are going to disappear.

First, an electrostatic latent image corresponding to a black toner image is formed on the photoreceptor 15 by the exposure device 2, and the toner image developed by the black developing device 50 is contacted with the intermediate transfer member 40. It is transferred to the surface and held.

On the other hand, after the toner remaining on the photoreceptor 15 without being transferred is removed by the blade 17, the electric charge remaining on the surface of the photoreceptor 15 is removed by an erase lamp 19, and the process proceeds to the next developing step.

Next, a yellow toner image is formed in the same manner, and the yellow toner image is superimposed and transferred on the black toner image on the surface of the intermediate transfer member 40 and held on the intermediate transfer member 40.

In order to transfer the toner image formed on the surface of the intermediate transfer body 40 onto the paper 80, the paper feed roller 81 is rotated to separate the papers 80 stored in the cassette one by one. After the sheet is conveyed to the registration roller 82 to correct the skew of the sheet, the sheet is stopped. Next, the registration roller 82 starts rotating so that the sheet 80 comes into contact with the intermediate transfer member 40 at a timing such that the registration roller 82 is aligned with the toner image held on the intermediate transfer member 40.

At the timing when the leading edge of the conveyed paper comes into contact with the intermediate transfer body 40, the transfer roller 60 presses the back surface of the paper, and electrostatically transfers the toner image on the surface of the intermediate transfer body 40 onto the paper. The sheet on which the toner image has been transferred passes between the heating roller and the pressure roller of the fixing device 70, so that the toner image on the sheet is fixed, and the sheet is discharged to the outside by the sheet discharging roller 90.

Here, the photosensitive member 15 and each pulley constitute a photosensitive member cartridge 150 integrally with a cover 151 having a handle for attachment and detachment, and are detachable in the direction of arrow B.

Next, a mechanism for preventing the photosensitive belt from shifting according to the present invention will be described with reference to FIGS.

FIG. 2 is a sectional view of the photosensitive member 15 and the intermediate transfer member 40 when the photosensitive member 15 is mounted on the apparatus main body. The drive pulley 10 is wound around the photoconductor 15 between the points C and D, and rotates in the direction of the arrow to convey the photoconductor 15. The tension pulley 14 applies uniform tension to the photoreceptor 15 by a spring 20 disposed on the left and right bearings. The driven pulleys 12 and 13 are disposed near a contact portion N between the intermediate transfer body 40 and the photoconductor 15.

Also, the photoconductor 1
In order to prevent a parallelism error between the respective pulleys caused by inserting the pulley 5 into the main body device, only both shaft ends of the drive pulley 10 and one shaft end of the driven pulley 11 engage with the frame of the main body device, The other pulleys 12, 13, and 14 are supported by the side plates of the photoreceptor cartridge 150, and do not engage with the main unit frame.

Here, although the reason will be described later, in order to stably transport the photosensitive member 15 without deviation, the intermediate transfer member 40 is required.
Coefficient of friction between the driven pulley 12 and the photoreceptor 15 close to
Are the winding angle φ of the photosensitive body 15 of the driven pulley 12, the belt tension T of the photosensitive body 15, the electrostatic attraction Pe between the photosensitive body 15 and the intermediate transfer body 40, the shaft of the intermediate transfer body 40 and the driven pulley 1
Since it is necessary to make the friction coefficient larger than the critical friction coefficient μc defined from the angle θ (see FIG. 4) with the 2 axis, μ / μc> 1 (1) μc = Pe · sin θ / (2T · sin (φ / 2 )) (2)

In this embodiment, the wrapping angle φ = 20 °, the belt tension T = 2.5 kgf / 245 mm, and the angle θ is 0.
5 °, and the electrostatic attraction Pe between the photoconductor 15 and the intermediate transfer body 40 is such that the surface potential of the photoconductor 15 is −600 V,
Calculated from the surface roughness Ra = 6 μm and the contact area S = 245 × 25 mm ² , Pe = 55 kgf.

Therefore, when the condition of the friction coefficient μ of the driven roller is determined from the equations (1) and (2), μ> 0.55 because μc = 0.55. However, the friction coefficient of the driven pulley 12 is preferably 1.2 to 2 times the critical friction coefficient μc because the surface condition varies due to the environment and contact with the photoconductor 15. The material is a polyester film, and the driven pulley 12 and the driven pulley 1
3, and the surface of the tension roller 14 was coated with an ethylene propylene rubber having a thickness of 2 mm and a hardness Hs of 30 °, so that the coefficient of friction with the photoconductor 15 was 0.9.

In addition, in addition to the above, hardness Hs is 30 ° to 50 °.
May be used. Further, a metal roller whose surface is knurled may be used. Further, in the present embodiment, the driven pulleys 12 and 13 are arranged near the contact portion N between the intermediate transfer body 40 and the photoconductor 15, but their positions may be located inside the contact portion N.

Next, conditions for stably transporting the photosensitive member 15 without deviation will be described.

FIG. 3 shows a cross section of the photosensitive member 15 and the driving pulley 10 in the longitudinal direction. In order to prevent the photoconductor 15 from shifting, the inner peripheral surfaces at both ends of the photoconductor 15 have a thickness of 0.7 m.
A rib 152 made of silicone rubber having an m, a width of 4 mm and a hardness Hs of 30 ° is adhered. Both ends of the driving pulley 10 are tapered at a taper angle of 60 ° and a width of 4 mm.

Due to the parallelism error between each pulley, the photosensitive member 1
5 is offset in the direction of the arrow, the rib 152 goes up the tapered portion, and an angle α is generated between the photoconductor 15 and the driving pulley 10. As a result, the same effect as when the drive roller 10 is inclined by the angle α with respect to the photoconductor 15 is obtained, and the photoconductor 15 at points C and D (see FIG. 2) where the drive pulley 10 contacts the photoconductor 15 is obtained. Is changed so that the photosensitive member 15 is returned in the direction opposite to the arrow. That is, the space between the CDs on the drive pulley 10 is
Is configured to correct the deviation of the photoconductor 15 by passing through.

However, when the photosensitive member 15 is inserted into the main body device and the printing process is started, the surface of the photosensitive member 15 is charged, and as shown in FIG. A considerably large conveying force P acts on the body 40 due to the electrostatic attraction force Pe. Therefore, the contact portion N
When a shift occurs in the conveyance direction of the intermediate transfer body 40 and the photoconductor 15 at, a biasing force acts on the photoconductor 15.

Therefore, the photosensitive member 15 generated at the contact portion N
Is corrected between the CDs on the drive pulley 10,
If the frictional force between the driven pulley 12 and the photoconductor 15 is small,
The bias of the contact portion N causes the photosensitive belt 15 to slide on the driven pulley 12, and the correction amount between CDs is canceled before the photosensitive member 15 enters the contact portion N,
As a result, the photosensitive belt 15 is shifted in one direction.

That is, in order to prevent the photoconductor 15 from being shifted, the frictional force between at least one driven pulley 12 and the photoconductor 15 that are close to the intermediate transfer body 40 is improved, and the photoconductor 15 is prevented from slipping. There is a need to.

In FIG. 2, assuming that the friction coefficient μs between the surface of the photosensitive member 15 and the intermediate transfer member 40 is Ps, the transport force P due to the electrostatic attraction Pe between the photosensitive member 15 and the intermediate transfer member 40 is P = μs · Assuming that the belt tension T of the photoconductor 15 and the winding angle φ between the driven pulley 12 and the photoconductor 15 are Pe (3), the normal force F acting on the driven pulley 12 is F = 2 · T · sin (φ / 2) (4)

In FIG. 4, if the angle .theta. Between the axis of the intermediate transfer member 40 and the axis of the driven pulley 12 and the friction coefficient between the photosensitive member 15 and the driven pulley 12 are .mu. Friction force (μ · F) between the photosensitive member 15 and the driven pulley 12 rather than the biasing force (P · sin θ) due to the conveyance force P of
Is larger, the photoconductor 15 does not shift, and the condition for preventing the shift is as follows: μ · F> P · sin θ (5)

Therefore, from equations (3), (4) and (5), μ> μs · Pe · sin θ / (2 · T · sin (φ / 2)) (6) is derived.

In the above equation, the friction coefficient μ due to electrostatic adsorption
Assuming that s is 1, μ> Pe · sin θ / (2 · T · sin (φ / 2)) (7) is obtained.

Here, if the right side is defined as the critical friction coefficient of the driven pulley 12, the above equations (1) and (2) are derived.

In this embodiment, the driven pulleys 12 and 13
FIG. 5 shows the results of evaluating the deviation of the photoconductor 15 when the friction coefficient μ of the tension roller 14 was changed.
Shown in

The horizontal axis represents time [minutes], the vertical axis represents the position of the end surface of the photoconductor 15 from the side plate of the photoconductor cartridge 150,
That is, the distance between the photosensitive member cartridge 150 and the end surface of the photosensitive member 15 is shown. The smaller the value of this position is, the more the photoconductor 15 is shifted.
5 comes into contact with the photoconductor cartridge 150. The pulleys used in the evaluation were an aluminum roller, a urethane rubber roller, and an ethylene propylene rubber roller, and the coefficient of friction μ with the photoconductor 15 was 0.3, 0.
5, 0.9.

From this result, it can be seen that the smaller the value of the friction coefficient μ, the faster the photoconductor 15 shifts, and the critical friction coefficient μc =
With a pulley smaller than 0.55, the end face of the photoreceptor 15 contacted the side plate within about 30 minutes or less, so that traveling was impossible. On the other hand, it was found that the pulley coated with ethylene propylene rubber having a friction coefficient μ = 0.9 was stable at a position of 2.5 mm.

Therefore, as in the present invention, in the vicinity of or in the contact portion between the photoconductor 15 and the intermediate transfer member 40, at least one friction coefficient with the photoconductor 15 that satisfies the equations (1) and (2) is satisfied. By providing a pulley, the photoconductor 15
Of the photoreceptor belt due to a parallelism error between the photoreceptor belt and the intermediate transfer body 40 can be prevented.

The chlorinated polyethylene rubber described above may be used as the material having the friction coefficient μ = 0.9.

In this embodiment, the belt-shaped photosensitive member 15 and the drum-shaped intermediate transfer member 40 are combined. However, a combination of a drum-shaped photoconductor and a belt-shaped intermediate transfer body may be used.

When a drum-shaped photosensitive member and a belt-shaped intermediate transfer member are combined, the photosensitive member cartridge 15
0 corresponds to the intermediate transfer body cartridge, the friction coefficient μ is the friction coefficient between the driven pulley and the intermediate transfer body close to the photoreceptor, the winding angle φ is the winding angle of the intermediate transfer body of the driven pulley, the belt The tension T is the belt tension of the intermediate transfer member,
The critical friction coefficient μc is a critical friction coefficient defined by the angle between the axis of the photosensitive member and the driven pulley of the intermediate transfer member.

[0047]

As described above, according to the present invention, the photosensitive member can be stably transported without the necessity of adjusting the position of the cartridge and the intermediate transfer member. No good images can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an electrophotographic apparatus according to the present invention.

FIG. 2 is a cross-sectional view showing a contact state between a photoreceptor belt of the present invention and a transfer drum.

FIG. 3 is a cross-sectional view showing a mechanism for preventing the photosensitive belt of the present invention from shifting.

FIG. 4 is a cross-sectional view showing a mechanism for preventing the photosensitive belt of the present invention from shifting.

FIG. 5 is an experimental result of a friction coefficient between a photoreceptor belt and a pulley according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Color laser printer, 2 ... Optical apparatus, 10 ... Driving pulley, 11, 12, 13 ... Driving pulley, 14 ... Tension pulley, 15 ... Photoconductor, 17 ... Blade, 18 ... Charging device, 19 ... Erase lamp, 40 ... Intermediate transfer member, 41
... Cleaner, 50 ... Black developing device, 51 ... Yellow developing device, 52 ... Magenta developing device, 53 ... Cyan developing device, 6
0: transfer roller, 70: fixing device, 80: paper, 81: paper feed roller, 82: registration roller, 90: paper discharge roller.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Mori 502 Kandachi-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. Hitachi, Ltd.Electrical Equipment Division (72) Inventor Masafumi Suzaki 1-1-1, Higashitaga-cho, Hitachi City, Ibaraki Pref.Hitachi, Ltd.Electrical Equipment Division

Claims (6)

[Claims] 1. A belt-shaped photosensitive member, developing means for developing an electrostatic latent image formed on the photosensitive member to form a toner image on the photosensitive member, and transferring and transferring the toner image once An electrophotographic apparatus comprising: an intermediate transfer member to be transferred; transfer means for transferring the toner image on the intermediate transfer member to a transfer material; and fixing means for fixing the toner image transferred to the transfer material. A pulley is arranged inside the photoconductor near the position where the body and the intermediate transfer body are in contact with each other, the friction coefficient between the pulley and the photoconductor is μ, and the winding angle between the pulley and the photoconductor belt is φ, the angle between the axis of this pulley and the intermediate transfer drum axis is θ, the belt tension of the photoconductor is T, and the electrostatic attraction force between the photoconductor and the intermediate transfer body is Pe, these values are: Is an electrophotographic apparatus satisfying the following expression. μ> Pe · sinθ / (2 · T · sin (φ / 2)) 2. The electrophotographic apparatus according to claim 1, wherein a coefficient of friction between said pulley and said photosensitive member is 0.55 or more. 3. The electrophotographic apparatus according to claim 1, wherein the surface of the pulley is coated with ethylene propylene rubber or chlorinated polyethylene rubber. 4. A photoreceptor, developing means for developing an electrostatic latent image formed on the photoreceptor to form a toner image on the photoreceptor, and a belt-like form for temporarily transferring and transferring the toner image An electrophotographic apparatus, comprising: an intermediate transfer member, a transfer unit that transfers a toner image on the intermediate transfer member to a transfer material, and a fixing unit that fixes the toner image transferred to the transfer material. A pulley is arranged inside the intermediate transfer member near a position where the transfer member contacts the photoconductor, a coefficient of friction between the pulley and the intermediate transfer member is μ, and winding of the pulley and the intermediate transfer member is performed. The angle is φ, the angle between the axis of the pulley and the axis of the photoconductor is θ, the belt tension of the intermediate transfer body is T, and the electrostatic attraction force between the intermediate transfer body and the photoconductor is P.
An electrophotographic apparatus in which these values satisfy the following equation when e is satisfied. μ> Pe · sinθ / (2 · T · sin (φ / 2)) 5. The electrophotographic apparatus according to claim 4, wherein a coefficient of friction between said pulley and said intermediate transfer member is 0.55 or more. 6. The electrophotographic apparatus according to claim 4, wherein a surface of said pulley is coated with ethylene propylene rubber or chlorinated polyethylene rubber.