JPH06308816A - Image forming device - Google Patents

Abstract

PURPOSE:To make the retaining amount of developer constant over the length direction of a gap, to prevent the developer from spilling, and to-restrain uneven electrostatic charge caused on the surface of a photosensitive drum. CONSTITUTION:The developing gap g2 between a developing roller 16 and the photosensitive drum 30 in the center in the length direction is larger than the developing gap g2 at both ends in the length direction. Therefore, the developer 26 leaks more in the center of the gap g2, and the retaining amount of the developer 26 becomes nearly constant over the length direction of the gap g2. Then, charge is uniformly injected in the drum 30 from the roller 16 through the developer 26. Since a doctor blade 28 is shorter than the roller 16, the developer 26 is prevented from spilling from both ends of the gap g2.

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,
In particular, for example, the present invention relates to an image forming apparatus that charges a photoconductor drum by applying a bias to a developing roller and injecting a charge into the photoconductor drum through a developer.

[0002]

2. Description of the Related Art In the conventional image forming apparatus 1 shown in FIG.
A developing roller 3 provided with a gap g ′ from the photosensitive drum 2 is biased. Then, a thin layer is formed by the doctor blade 4 and thereafter the charge is injected into the photoconductor drum 2 through the developer 5 retained in the gap g ′, whereby the photoconductor drum 2 is charged.

[0003]

However, the gap g '
Is constant over the lengthwise direction of the photosensitive drum 2, and since the doctor blade 4 has the same length as the photosensitive drum 2 and the developing roller 3, due to the fluidity of the developer 5, There was a problem that it overflowed from both ends in the length direction.

In order to solve this problem, there is an image forming apparatus 1 in which the doctor blade 4 is designed to be shorter than the developing roller 3 as shown in FIG. 11, but when the doctor blade 4 is shortened in this way, a gap g ' The amount of the developer 5 staying at both ends in the lengthwise direction of the photosensitive drum 2 becomes small, so that both ends of the photosensitive drum 2 are not sufficiently charged, and as shown in FIG. It was lower than in the center.

Therefore, a main object of the present invention is to provide an image forming apparatus in which the developer does not overflow and uneven charging occurs on the surface of the photosensitive drum.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an image forming apparatus for charging a photosensitive drum by applying a bias to the developing roller and injecting a charge into the photosensitive drum through a developer. The image forming apparatus is characterized in that the gap width at the center in the length direction is made larger than the gap width at both ends in the length direction.

[0007]

Since the gap at the center is larger than the gaps at both ends, the amount of developer leaked from the center is larger than at both ends. Therefore, the retention amount of the developer becomes substantially constant over the length direction.

[0008]

According to the present invention, since the amount of developer retained in the gap is constant over the length of the gap, it is possible to suppress uneven charging occurring on the surface of the photosensitive drum without the developer overflowing. You can The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an image forming apparatus 1 of this embodiment.
0 includes a developing device 12. A toner box 14 is provided in the developing device 12, and a developing roller 16 is arranged in the opening at the lower end of the toner box 14. The developing roller 16 is provided with a magnetic roller 18 having S poles and N poles alternately formed on its peripheral surface, and a developing sleeve 20 is rotatably covered on the outer periphery of the magnetic roller 18. This developing sleeve 2
0 rotates counterclockwise. The developing roller 16 has
A bias voltage of, for example, -20V is applied by the bias power source 22. An agitating roller 24 is arranged slightly above the right side surface of the developing roller 16 inside the toner box 14 to prevent the developer 26 stored in the toner box 14 from solidifying. In addition, the developer 26
Is a two-component toner, it is mixed well.

Toner box 1 above the developing roller 28
A doctor blade 28 is mounted on the surface 4, and a thin layer of the developer 26 is formed on the surface of the developing sleeve 20 by the gap (doctor gap) g ₁ between the doctor blade 28 and the developing roller 16. The photoconductor drum 30 is disposed on the left side surface of the developing roller 16, and the developing roller 1
Rotate clockwise at a speed of 1/6 to 1/8 of 6.
Therefore, the developing roller 16 and the photosensitive drum 30 developing gap g ₂ in balance with the gap amount of the developer 26 supplied from the amount and the doctor gap g ₁ of the developer 26 dropped from (development gap) g ₂ and The developer 26 stays.

As can be seen from FIG. 2, the outer diameter of the developing roller 16 is equal from the both ends in the length direction toward the center by a constant distance, and then decreases toward the center at a constant rate. Then, in the vicinity of the center, the outer diameters are equal again. However, magnetic roller 1
The outer diameter of 8 is constant over the length direction, and the developing sleeve 20 is thin at the central portion in the length direction.
Therefore, as can be seen from FIG. 3, the developing gap g ₂ between the developing roller 16 and the photosensitive drum 28 is larger at the center in the lengthwise direction than at both ends in the lengthwise direction. Therefore, in the center of the developing gap g _2, leakage amount of the developer 26 retained more than both ends of the developing gap g _2,
The staying amount in the developing gap g ₂ is substantially constant in the length direction. Further, as can be seen from FIG. 3, since the doctor blade 28 is shorter than the developing roller 20, the developer 26 does not overflow from both ends of the developing gap g _{2 in} the length direction.

In this embodiment, the photosensitive drum 30
Has an outer diameter D ₁ of 45 mm, the outer diameter D _{2 at} both ends of the developing roller 16 in the length direction and the outer diameter D _{3 at the} center in the length direction are 18 respectively.
mm and 15 mm, the doctor gap g ₁ is 1 mm and 2 mm at both ends in the longitudinal direction and the center in the longitudinal direction, the developing gap g ₂ is 0.5 mm and 1.5 mm at both ends and the center, and one end in the longitudinal direction of the developing roller 16. To the one end of the doctor blade 28 in the lengthwise direction is set to 30 mm, and the process speed is set to 25 mm / sec.

In operation, the developer 26 contained in the toner box 14 passes through the doctor gap g ₁ and stays in the developing gap g ₂ . Therefore, the charge of the developing roller 16 passes through the accumulated developer 26 and the charge of the developing roller 16
8 and the photosensitive drum 28 is charged. And
As can be seen from FIG. 4, the surface potential of the photoconductor drum 28 is substantially constant over the lengthwise direction of the photoconductor drum 28.

Incidentally, in this embodiment, it is shown in FIG.
Although the developing roller 16 like this is used, as shown in FIG.
The diameter gradually decreases from both ends in the length direction to the center.
Developing roller 32, or from both ends as shown in FIG.
The outer diameter decreases linearly up to near the center.
Use the developing roller 34 having the same outer diameter
Needless to say, uneven charging can be prevented. Well
Also, as shown in FIG. 7, the outer diameter is 2 from the center toward both ends.
Developing roller 36 which becomes larger in the form of a second curve, as shown in FIG.
The outer diameter increases from the center to both ends in a quadratic curve.
And the developing roller 38 is equalized near both ends, or
As shown in FIG. 9, the outer diameter is equal from the center to the vicinity of both ends,
The developing roller 40 that is larger than the center only in the vicinity of both ends
Of course, even if you use
It In any case, the development gap g ₂Development in the center
The amount of leakage of the developer 26 is greater than the development gap g.₂At both ends
More than the leakage amount, and the developer 26 overflows from both ends.
Because there is nothing to do.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention.

FIG. 2 is an illustrative view showing a part of the embodiment in FIG.

FIG. 3 is an illustrative view showing another portion of the embodiment in FIG. 1;

FIG. 4 is a graph showing the surface potential of a photosensitive drum.

FIG. 5 is an illustrative view showing a modified example of a developing roller.

FIG. 6 is an illustrative view showing another modified example of the developing roller.

FIG. 7 is an illustrative view showing another modification of the developing roller.

FIG. 8 is an illustrative view showing still another modified example of the developing roller.

FIG. 9 is an illustrative view showing another modified example of the developing roller.

FIG. 10 is an illustrative view showing a conventional technique.

FIG. 11 is an illustrative view showing another conventional technique.

FIG. 12 is a graph showing the surface potential of the photosensitive drum in the conventional technique shown in FIG.

[Explanation of symbols]

 10 ... Image forming device 16, 32, 34, 36, 38, 40 ... Developing roller 20 ... Developing sleeve 26 ... Developer 28 ... Photosensitive drum

Claims (1)

[Claims] 1. An image forming apparatus for charging a photosensitive drum by applying a bias to the developing roller and injecting an electric charge into the photosensitive drum through a developer, wherein the developing roller and the photosensitive drum are centered in a longitudinal direction. The image forming apparatus is characterized in that the gap width in the is larger than the gap width at both ends in the length direction.