JP3347361B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer (LBP).

[0002]

2. Description of the Related Art When an image is formed on a photosensitive drum (electrophotographic photosensitive member) as an image carrier, a latent image is formed on the photosensitive drum by exposure means, and the latent image is developed by developing means to form a toner image. It is necessary to transfer the toner image onto a transfer material by a transfer unit after visualizing the toner image.

Incidentally, since the above-described series of image forming operations is performed while the photosensitive drum is being rotated, the photosensitive drum needs to be rotationally driven at a uniform constant speed. For example, if the rotation speed of the photosensitive drum during one rotation is uneven, the latent image on the photosensitive drum expands and contracts during exposure, and the image on the transfer material expands and contracts during transfer, and these expansions and contractions are integrated. Since image unevenness is caused, image quality is degraded.

Accordingly, when the photosensitive drum is driven to rotate by the drive motor, the rotation center axis of the photosensitive drum and the drive motor shaft are directly connected without interposing a gear or a belt between the two, and the gear or belt or the like is used. 2. Description of the Related Art There has been proposed an image forming apparatus which prevents the speed unevenness of the photosensitive drum from occurring.

[0005]

In the case of an image forming apparatus in which the rotation center axis of the photosensitive drum and the drive motor axis are directly connected, the rotation speed of the photosensitive drum fluctuates due to an eccentric component caused by an axis shift occurring between these two axes. Occurs. When the rotation speed of the photosensitive drum fluctuates as described above, the image expands and contracts, and when a multi-color image such as a full-color image is formed, an image defect such as a color shift occurs. Hereinafter, this will be described in detail.

As shown in FIG. 5 , a drum shaft 251a which is a rotation center axis of the photosensitive drum 251 is connected to a rigid coupling 2
53 is connected to the motor shaft 252a of the drive motor 252. The drive motor 252 is stopped at one point by a stopper 252b. In this state, if the motor shaft 252a is rotated at a predetermined constant angular speed ω ₀ in the direction of the arrow X in the figure, the drum shaft 251a also rotates at a constant angular speed ω ₀ in the same direction.

However, in the configuration in which the drum shaft 251a and the motor shaft 252a are connected by the rigid coupling 253, the positional accuracy of the shaft hole of the rigid coupling 253, the bending of the motor shaft 252a due to the weight of the drive motor 252, and the stopper 252b Even if the motor shaft 252a is rotating at a constant angular velocity ω ₀ , an axis shift e occurs between the drum shaft 251a and the motor shaft 252a due to friction, a fall when the drive motor 252 is mounted, and the like. The angular velocity ω of the shaft 251a fluctuates during one rotation cycle. That is, the angular velocity ω of the drum shaft 251a is expressed by the following equation.

[0008]

Where ω = ω ₀ (1 + A · sin θ) where A: a constant determined by the axis deviation e θ: the rotation angle of the photosensitive drum 251 The peripheral speed v of the photosensitive drum 251 at this time is:

[0009]

V = R · ω = R · ω ₀ (1 + A · sin θ) (1) where R is the radius of the photosensitive drum 251, and the photosensitive drum 251 is accelerated and decelerated during one rotation cycle. Are repeated to generate rotation unevenness (see FIG. 6 ).

Here, considering only the variation Δv of the peripheral speed v of the photosensitive drum 251 when ω ₀ = 1,

[0011]

Δv = R · A · sin θ (2)

The variation l ₁ of the length exposed in a unit time (time t = 1) in an exposure device (not shown) due to the variation Δv of the peripheral speed v of the photosensitive drum 251 is:

[0013]

Δl ₁ = Δv · t = R · A · sin θ (∵t = 1) (3)

Further, the variation Δl ₂ of the length transferred to the transfer material per unit time at the transfer position (not shown) is:

[0015]

Δl ₂ = −Δv · t = −R · A · sin (θ−π) (∵t = 1) (4)

Here, from the relationship of sin (θ−π) = − sin θ, the expression (4) is expressed as follows.

[0017]

Δl ₁ = R · A · sin θ (5) That is, if the variation Δv represented by the above equation (2) exists in the peripheral speed v of the photosensitive drum 251, Δl ₁ =
The length of each image fluctuates by R · A · sin θ and Δl ₂ = R · A · sin θ at the transfer position, and the image expands and contracts.

Therefore, when the respective variations Δl ₁ and Δl ₂ at the exposure position and the transfer position are added, the expansion and contraction Δl of the image on the transfer material becomes

[0019]

Δl = Δl ₁ + Δl ₂ = 2R · A · sin θ (6), and the image expands / contracts which does not occur if the photosensitive drum 251 rotates at a constant angular velocity ω ₀ . This state is shown in FIG. This image expansion and contraction Δl
Is caused, the image quality is deteriorated, and when a multi-color image is formed, a color shift or the like also occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is to form a high-quality image by preventing expansion and contraction of an image caused by a deviation between a photosensitive member and a driving means thereof. To provide an image forming apparatus capable of performing the above.

[0021]

In order to achieve the above object, the present invention provides a photosensitive member in the form of a drum and an image light on the photosensitive member.
Exposure means for irradiating the electrostatic latent image formed on the photoconductor
Developing means for developing and transferring the developed visible image to a transfer material
And a driving unit for driving the photoreceptor, a rotation drive shaft of the driving unit,
The center axis of rotation of the photoconductor is connected by a universal joint.
Exposure position on the photoreceptor about the rotation axis of the photoreceptor
And the transfer position is 180 ° .

[0022]

[Action] When that connects a rotation center axis of the rotary drive shaft and the photosensitive member drive means in the universal joint, the rotation unevenness occurs 2 cycles per rotation of the photosensitive member, about the rotation axis of the photoconductor
Set the angle between the exposure position and the transfer position on the photoreceptor to 180 °
That when, for image stretch and the image stretch on the transfer material is offset in the image stretch the transfer position at the exposure position is theoretically 0, the expansion and contraction of the image due to axial misalignment of the photosensitive member and the driving means Thus, a high-quality image is formed.

[0023]

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

FIG. 4 shows a cross section of an image forming apparatus capable of forming a full-color image using magenta, cyan, yellow and black toners. In an apparatus main body 15 of the image forming apparatus, four image stations 7 each including a photosensitive drum 1, a charger 2, an exposure unit 3, a developing unit 4, a transfer charger 5 and a cleaning unit 6 are provided. In the first image station 7A indicated by the subscript A, a yellow image is formed by the yellow toner,
, A magenta image is formed by magenta toner, a third image station 7C indicated by suffix C forms a cyan image by cyan toner, and a fourth image station 7D indicated by suffix D outputs black. Black images are respectively formed by the toner.

The above four image forming stations 7A, 7
B, 7C, 7D, drive rollers 8a, 8b,
A transfer material transfer device 8 including a transfer roller 8c, a transfer belt 8d, and the like is provided. A paper feed cassette 9 for holding the transfer material P, a paper feed roller 10 for taking out the transfer material P from the paper feed cassette 9, and a transfer material for the transfer material P A registration roller 11 and a guide plate 12 for setting a transfer timing to the apparatus 8 are provided. A fixing device 13 and a paper discharge tray 14 are provided on the paper discharge side of the transfer material transport device 8. The details of the configuration of the image station 7 are shown in FIG.

Next, an image forming operation of the image forming apparatus having the above configuration will be described.

In the first image station 7A, when the photosensitive drum 1A uniformly charged by the charger 2A is exposed to image light based on the yellow image information from the exposure means 3A, the electrostatic latent image is placed on the photosensitive drum 1A. An image is formed, and this electrostatic latent image is developed by a developing device 4A using yellow toner, and is visualized as a toner image. here,
The transfer material P is transported by the transport belt 8d of the transfer material transport device 8, but the photosensitive drum 1A is transferred onto the transfer material P transported at an appropriate timing by the registration roller 11.
The above toner image is transferred by the action of the transfer charger 5A. The photosensitive drum 1A after the transfer is cleaned by removing the residual toner by the cleaning device 6A, and is prepared for the next image formation.

Thereafter, magenta, cyan, and black toner images are transferred onto the transfer material P in the same manner in the second, third, and fourth image stations 7B, 7C, and 7D.

On the other hand, the transfer material P taken out one by one from the paper feed cassette 9 by the paper feed roller 10 passes through the guide plate 12 and the registration roller 11 and is transferred by the transfer roller 8c to the transfer belt 8d of the transfer material transfer device 8 by the transfer roller 8c. It is positioned and held on top.

The transfer material P is transferred to the first, second, third and fourth image stations 7 by the movement of the transfer belt 8d.
A, 7B, 7C, 7D photosensitive drums 1A, 1B, 1C,
In the process of passing between 1D and the transfer chargers 5A, 5B, 5C, 5D, toner images of four colors are transferred. Then, the transfer material P to which the toner image has been transferred is conveyed to the fixing device 13 by the transfer material conveying device 8, and the toner image is melted and mixed by the fixing device 13 and fixed on the transfer material P, so that the toner image is fixed. The transferred transfer material P is discharged out of the apparatus and stacked on the discharge tray 14.

As shown in FIG. 3, the exposure position S on the photosensitive drum 1 by the exposure means 3 is provided on the side opposite to the transfer position Q on the photosensitive drum 1 by the transfer charger 5 by 180 °.

The photosensitive drum 1 is driven to rotate in the direction of arrow X by a drive motor 16 (see FIG. 1) as a driving means at the time of image formation. FIG. 1 shows the coupling relationship between the photosensitive drum 1 and the drive motor 16. This will be described below.

As shown in FIG. 1, a drum shaft 1 a which is a rotation center axis of the photosensitive drum 1 and a motor shaft 16 a which is a rotation drive shaft of a drive motor 16 are connected by a universal joint 17.

The universal joint 17 includes a boss 17a fitted to the drum shaft 1a and a boss 1 fitted to the motor shaft 16a.
7d is connected by pins 17d and 17e via a top 17c. Here, the boss 17a and the top 17c are rotatable around the pin 17e.

Accordingly, it is possible to transmit the rotational force of the drive motor 16 from the motor shaft 16a to the drum shaft 1a of the photosensitive drum 1 while the drum shaft 1a and the motor shaft 16a maintain a constant declination α.

The drive motor 16 is fixed to the apparatus main body by a plurality of screws 18, and the deflection of the motor shaft 16 a due to the weight of the drive motor 16 and the detent friction of the drive motor 16 may affect the universal joint 17. Absent.

Further, the eccentricity and the inclination of the motor shaft 16a and the drum shaft 1a when the drive motor 16 is mounted are absorbed by the declination α of both when the drive motor 16 is mounted, so that the motor shaft 16a and the drum shaft 1a are connected. It is easily connected. Therefore, it is possible to prevent expansion and contraction of an image caused by a positional error between the motor shaft 16a and the drum shaft 1a.

Next, the mechanical characteristics of the universal joint 17 will be described.

Assuming that the angular velocity of the motor shaft 16a is ω ₀ (= constant), the angular velocity of the drum shaft 1a is ω, the mounting deviation angle of the motor shaft 16a and the drum shaft 1a is α, and the rotation angle of the motor shaft 16a is θ.

[0040]

It is well known that the following relationship holds: ω = {cos α / (1−sin ² θ · sin ² α)} ω ₀ (7)

Equation (7) indicates that even if the motor shaft 16a is rotating at a constant angular velocity ω ₀ , 1 /
This means that rotation unevenness occurs in two rotation cycles. This is applied to the above equations (3) to (6).

Here, the angular velocity ω ₀ of the motor shaft 16a is set to 1
(Ω ₀ = 1), the variation Δω of the angular velocity ω of the drum shaft 1a becomes

[0043]

Δω = cos α / (1−sin ² θ · sin ² α)

Since the variation Δv of the peripheral speed v of the photosensitive drum 1 is obtained by multiplying the radius R of the photosensitive drum 1 by the variation Δω of the angular velocity ω of the drum shaft 1a, the unit time at the exposure position S (t = 1) The variation ΔL ₁ of the length exposed to

[0045]

ΔL ₁ = Δv · t = R · Δω = R {cos α / (1−sin ² θ · sin ² α)} (8)

Similarly, the variation ΔL of the length transferred to the transfer material P per unit time (t = 1) at the transfer position Q
₂ is

[0047]

ΔL ₂ = −Δv · t = −R · Δω = −R {cos α / (1−sin ² (θ−π) · sin ² α)} (9)

Here, since the exposure position S is located at a position (π = 180 °) on the opposite side of the transfer position Q with respect to the drum shaft 1a, the term of {sin ² θ} in the above equation (8). Is {sin ² (θ−π)} in equation (9).

Therefore, the variation Δω of the angular velocity ω of the drum shaft 1a in the equation (9) is

[0050]

Equation 12] Δω = cos α / (1- sin 2 (θ-π) · sin 2 α) = cos α / (1-sin 2 θ · sin 2 α) . Therefore, [Delta] L ₂ is

[0051]

ΔL ₂ = −R {cos α / (1−sin ² θ · sin ² α)} (10)

That is, when the relationship of the above equation (7) is established, the variation ΔL _{1 at the} exposure position S (see FIG. 2 (a)) and the variation ΔL _{2 at the} transfer position Q (see FIG. 2 (b)) The image expands and contracts by the amount obtained by adding.

From the above equations (8) and (10), the image expansion / contraction ΔL (see FIG. 2 (c)) is

[0054]

ΔL = ΔL ₁ + ΔL ₂ = 0 (11) Therefore, if the motor shaft 16a rotates at a constant angular velocity ω ₀ , the angular velocity ω of the drum shaft 1a becomes as shown in the above equation (7). Even if it fluctuates, the image does not expand or contract on the transfer material P (see FIG. 2C). That is, equation (8) becomes (1)
Since the sign is different from the expression (0), the two expressions are added (1).
In equation (1), ΔL = 0 also on the graph shown in FIG. 2C, and the image does not expand or contract.

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

As apparent from the above description, according to the present invention, a drum-shaped photosensitive member and image light are irradiated to the photosensitive member.
It is developed and exposing means for, an electrostatic latent image formed on the photosensitive member
A developing unit that, the rolling <br/> shooting means for transferring to a transfer material the developed visible image, in an image forming apparatus having a driving means for driving the photosensitive member, a rotary drive shaft of the drive means Above feeling
The rotation center axis of the light body is connected by a universal joint,
Exposure position and transfer on the photoreceptor around the rotation axis of the body
Since the angle between the positions is set to 180 °, there is an effect that a high-quality image can be formed by preventing expansion and contraction of the image due to misalignment between the photosensitive member and the driving means thereof. can get.

[Brief description of the drawings]

1 is a side view showing a coupling structure of the photosensitive drum driving motor of the image forming apparatus according to the present onset bright.

2 is a diagram showing an image stretch at the exposure position and the transfer position and the transfer material on the image forming apparatus according to the present onset bright.

3 is a sectional view showing a configuration of the image stations of the image forming apparatus according to the present onset bright.

4 is a cross-sectional view of an image forming apparatus according to the present onset bright.

FIG. 5 illustrates a photosensitive drum and a drive motor of a conventional image forming apparatus.
FIG. 3 is a cross-sectional view showing the coupling structure of FIG.

FIG. 6 shows an exposure position, a transfer position, and a position of a conventional image forming apparatus.
FIG. 3 is a diagram illustrating expansion and contraction of an image on a transfer material.

[Explanation of symbols]

Reference Signs List 1 photosensitive drum ( photoreceptor ) 1a drum shaft (center of rotation) 3 exposure means 4 developing device (developing device) 5 transfer charger (transfer device) 16 drive motor (drive device) 16a motor shaft (rotation drive shaft) 17 freely Joint P Transfer material Q Transfer position S Exposure position

Continuation of front page (56) References JP-A-63-41868 (JP, A) JP-A-63-182669 (JP, A) JP-A-2-238469 (JP, A) JP-A-4-116568 (JP) JP-A-63-11965 (JP, A) JP-A-63-115630 (JP, U) JP-A-2-9558 (JP, U) JP-A-56-85725 (JP, U) Compiled by Tomo Editor, "Skill Book (17) / Handbook of Machine Elements" (published first edition on May 20, 1977), Okawa Publishing Co., Ltd., pp. 50−51

Claims (1)

(57) [Claims] 1. A drum-shaped photoreceptor and image light on the photoreceptor
Exposure means for irradiating the electrostatic latent image formed on the photoconductor
Developing means for developing and transferring the developed visible image to a transfer material
And a driving unit for driving the photoconductor, wherein the rotation drive shaft of the driving unit and the rotation center axis of the photoconductor are
It is connected by a universal joint, with the rotation axis of the photoreceptor as the center.
The angle between the exposure position and the transfer position on the photosensitive member is 18
An image forming apparatus, wherein the angle is 0 ° .