JP2001265073A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device forming an image of high definition with high reproducibility of a line width. SOLUTION: When a dark part potential is deemed to be VD, a light part potential is deemed to be VL, quantity of exposure required for the light part potential is deemed to be E0, exposure and potential curve of a photoreceptor 2 is deemed to be EV, a straight line that is passed through the dark part potential VD at the quantity of exposure '0' where EV is passed and the light part potential VL at the quantity of exposure '0' where EV is passed is deemed to be EV', an area surrounded by the curve EV and the straight line EV' is deemed to be ΔS and ratio η=ΔS÷ (VD-VL)×E0} is obtained. An image of high definition with the high reproducibility of the line width can be formed by being provided with a characteristics fulfilling ratio η<=0.1 of the photoreceptor drum 2.

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 which a developer mainly adheres to an image bearing member such as an electrophotographic photosensitive member at a dark portion potential of an unexposed portion other than an exposed bright portion potential. Yes, for example, applied to a digital image forming apparatus of background area exposure.

[0002]

2. Description of the Related Art A digital image forming apparatus of an image area exposure system in which a dark portion potential and a bright portion potential are formed on an electrophotographic photosensitive member as an image carrier, and a toner as a developer is mainly attached to a bright portion potential portion. Has been widely known.

On the other hand, a digital image forming apparatus of a background area exposure system in which a dark portion potential and a bright portion potential are formed on an electrophotographic photoreceptor and toner is mainly attached to a dark portion potential portion also exists.

A digital image forming apparatus of a background area exposure system has a digital exposure means because it can directly use elemental technologies such as charging and development cultivated in an image forming apparatus having an analog exposure means. There is a merit that it can be easily applied to an image forming apparatus.

[0005]

However, the digital image forming apparatus of the background area exposure system, in which toner adheres to the dark area potential, is inferior in the line reproducibility to the digital image forming apparatus of the image area exposure system, and has a poor line width. The biggest disadvantage is that it is thin.

[0006] If the line width is small, it may be difficult to read a character or the like, resulting in a poor impression, or the thin line may be interrupted and image information may be lost.

To solve this problem, if the toner is applied to the electrophotographic photosensitive member as much as possible, the line width surely increases, but at the same time, the fogging phenomenon that the toner adheres to the white background increases. It is not a fundamental measure.

Therefore, under the same latent image condition and developing condition,
It has been found that the image area exposure method has better line reproducibility. For this reason, an image forming apparatus using a general digital exposure employs an image area exposure method.

However, the digital image forming apparatus of the image area exposure method has a difficulty in utilizing the technology cultivated in the image forming apparatus having the analog exposure means. Disadvantageous.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an image forming apparatus for forming a high-quality image with high line width reproducibility. It is in.

[0011]

According to the present invention, there is provided an image bearing member, a charging device for uniformly charging the image bearing member to a dark portion potential, and Exposure means for exposing the charged image carrier in such a manner as to form a light portion potential on the image carrier, and developing means for applying a developer on a dark portion potential other than the light portion potential of the image carrier. ,
Wherein the dark portion potential is VD,
The light-portion potential is VL, the exposure amount for obtaining the light-portion potential is E0, the exposure / potential curve of the image carrier is EV, and the dark-portion potential VD at the exposure amount 0 passing through the EV passes through the EV. A straight line passing through the bright portion potential VL at the exposure amount E0 and EV ′
When the ratio η = ΔS {(VD−VL) × E0} as the area ΔS surrounded by the curve EV and the straight line EV ′, the image carrier satisfies the ratio η ≦ 0.1. It is characterized by having characteristics.

Therefore, a high-quality image with high line width reproducibility can be formed, and the line width can be reproduced at the same level as that of the image area exposure method.

It is preferable that the image carrier is adjusted so as to satisfy the characteristic of the ratio η ≦ 0.1 by changing the dark portion potential VD, the light portion potential VL, or the exposure amount E0.

As a result, the material of the image carrier itself has the ratio η.
Even if the characteristics of ≦ 0.1 are not satisfied, the characteristics can be satisfied by adjusting the dark portion potential VD, the light portion potential VL, or the exposure amount E0, and the line width reproducibility can be improved.

A digital image forming apparatus of a background area exposure system is preferred.

This eliminates the greatest disadvantage that the line width is narrow. The elemental technology such as charging and developing cultivated in an image forming apparatus having an analog exposure means is applied to a background area exposure using a digital exposure means. It can be applied to a digital image forming apparatus of a system.

[0017]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The materials, shapes, relative arrangements, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

(First Embodiment) A first embodiment will be described with reference to FIGS. FIG. 1 schematically shows a printer as an example of the image forming apparatus according to the present embodiment.

This printer is provided with a cylindrical photosensitive drum 2 which is an electrophotographic photosensitive member as an image carrier in the center of the main body 1 of the apparatus. The photosensitive drum 2 includes the apparatus main body 1
Is rotatably supported in the direction of arrow R1.

Around the photosensitive drum 2, a static eliminator 3 for erasing the potential on the photosensitive drum 2 and a primary charger 4 as a charging means for uniformly charging the surface of the photosensitive drum 2 are arranged along the rotation direction. An exposure means 5 for exposing the surface of the photosensitive drum 2 to form an electrostatic latent image, a potential sensor 6 for measuring a potential on the photosensitive drum 2 after exposure, and applying a toner as a developer to the electrostatic latent image. A developing device 7 as a developing means for forming a toner image; a transfer charger 8 for transferring the toner image onto the transfer material P; a separation charger 9 for separating the transfer material P from the photosensitive drum;
Cleaner 10 for removing residual toner on photosensitive drum 2
Is arranged.

A transfer material P to which a toner image is transferred is supplied from a paper feed deck 11. Below the photosensitive drum 2, that is, below the inside of the apparatus main body 1, a paper feed deck 11 for storing the transfer material P is arranged.

The transfer material P in the paper feed deck 11 is fed by a paper feed roller 12 and supplied between the photosensitive drum 2 and the transfer charger 8 via a transport roller 13 and a registration roller 15.

The toner image is transferred from the photosensitive drum 2 to the transfer material P here.
Transported to The transfer material P to which the toner image is fixed by the heat and pressure applied by the fixing device 17 is discharged onto a discharge tray 20 by a discharge roller 19 as a final copy.

In the above-mentioned printer, the exposure means 5
The laser beam emitted from the semiconductor laser 30 in accordance with the image signal is scanned by the polygon mirror 31 and guided to the photosensitive drum 2 via the imaging lens 32 and the reflection mirror 33.

FIG. 2 is a diagram schematically illustrating an electric configuration around a control board for operating the image forming apparatus main body.

In FIG. 2, a ROM in which a control program is described and a RAM which is a temporary storage element of necessary data on the program are connected to a CPU which is a central element of processing in a control board.

The interface element I / O
A / D converters and D / A converters as data conversion elements are connected to the primary charger 4 and the semiconductor laser 30 as external peripheral devices.

The voltage applied to the primary charger 4 is adjusted in accordance with a command from the CPU, so that a desired dark portion potential VD can be obtained. The exposure amount of the semiconductor laser 30 is also adjusted in accordance with the command from the CPU. It is possible to obtain the light portion potential VL.

FIG. 3 is a schematic explanatory view of the periphery of the photosensitive drum 2, and is an experimental explanatory view for the present embodiment. Around the photosensitive drum 2, a static eliminator 3, a primary charger 4, an exposure unit 5, a potential sensor 6, and a developing device 7 are arranged in this order along the rotation direction R 1. In the experiment, after removing the developing device 7, An external potential sensor 50 was attached to measure the potential on the photosensitive drum 2.

Thus, the potential on the photosensitive drum 2 when the toner adheres at the position of the developing device 7 and is visualized can be confirmed.

FIG. 4A is a correlation diagram (so-called EV curve) between the exposure amount E and the drum surface potential V of the photosensitive drum 2 (hereinafter, OPC drum) using an organic photosensitive member.

Photosensitive drum A having three types of organic photosensitive layers
B and C are prepared, the exposure is performed with the dark portion potential VD being the same, and the developing device 7 is detected by the external potential sensor 50 shown in FIG.
The potential on the drum at the position was measured.

The three types of photosensitive drums 2 showed different curves due to differences in sensitivity. Note that the notation is such that the bright portion potential VL is obtained at the exposure amount E0 by normalizing the exposure amount to obtain the bright portion potential VL. Further, the specific potential of the dark part is set to 450V, and the specific potential of the light part is set to 50V.

FIG. 4B shows an exposure amount E · of the photosensitive drum 2 having an amorphous silicon layer (hereinafter a-Si drum).
It is a correlation diagram (so-called EV curve) of the drum surface potential V.

Photosensitive drums D, E, and F having three types of amorphous silicon layers are prepared, and dark section potential VD is set as shown in FIG.
Exposure was performed with the same dark portion potential as in (a), and the potential on the drum at the position of the developing device 7 was measured by the external potential sensor 50 shown in FIG.

The three types of photosensitive drums 2 showed different curves due to the difference in sensitivity, and also showed different curves for the three types of OPC drums shown in FIG. Note that the light portion potential V
The notation is such that L is normalized by the amount of exposure to obtain, and the light portion potential VL is obtained at the amount of exposure E0. Further, a specific dark portion potential is set to 450 V and a bright portion potential is set to 50 V.

FIG. 5 is a correlation diagram of the exposure amount E and the drum surface potential V in one photosensitive drum having an arbitrary EV curve, and is a diagram for explaining the potential condition of the present invention.

In FIG. 5, the point indicating the dark portion potential VD at the exposure amount 0 is point P, and the bright portion potential VL at the exposure amount E0.
Is assumed to be a point Q, a correlation curve EV between the exposure amount E and the drum surface potential V between the two points, and a straight line EV ′ passing between the two points can be considered.

Further, as the point of interest in the present invention, the area surrounded by the curve EV and the straight line EV 'can be obtained by the following equation as ΔS.

(Equation 1)

It should be noted that the photosensitive drum 2 used in the experiment by the authors has a positive ΔS, but the present invention can be realized even if the photosensitive drum 2 has a negative value.

Next, the point indicating VL at an exposure amount of 0 is represented by R
Assuming that a point indicating the VD at the point and the exposure amount E0 is an S point,
The area of the square RPSQ is {(VD−VL) × E0}, and the ratio η of the area of ΔS to the area of the square RPSQ is

(Equation 2) Is defined as

The area ratio η is a variable found by the present inventors, and the present inventors have found that managing this ratio η is an essential condition for background exposure.

That is, it has been found that excellent image quality can be obtained when the area ratio η ≦ 0.1, and by using the photosensitive drum 2 having such characteristics, an image having high line width reproducibility can be obtained. It is possible to obtain.

Table 1 shows the relationship between the photosensitive drums A, B, C, D, EF and the six types of EV curves shown in FIG.
The area ratio η is determined, the line width is measured, and the determination result is described.

In calculating the ratio η of the area of each photosensitive drum, ΔS must be calculated. However, the calculation can be easily performed by replacing the EV curve of each photosensitive drum with a higher-order approximation auxiliary line.

The line width is obtained by outputting a line corresponding to four pixels of the apparatus as a digital image forming apparatus, measuring the line width, and calculating a ratio W of the line width of the four pixels to the output line width. is there.

In this embodiment, since the image forming apparatus has a resolution of 600 dpi in the vertical and horizontal directions, four pixels correspond to about 1 pixel.
This corresponds to a thickness of 70 μm.

The smaller the line width ratio W, the narrower the line width and the lower the reproducibility of the line width, that is, the lower the image quality. The actual judgment includes the visual impression, and when the ratio W is 90% or more and 110% or less, "reproducible"
If it is 80% or more and less than 90%, it is "normally reproduced", and if it is 70% or more and less than 80%, it is "finely reproduced".
If it is less than 70%, it is determined to be “extremely thin”.

In an image area exposure type digital image forming apparatus, it is known that the ratio W of the line width is usually from 80% or more to 110% or less, and so-called "normal reproduction" or "solid reproduction" is performed. In this state, it is an index for comparison with the present invention.

[0050]

[Table 1]

In Table 1, photosensitive drums A to C are OPC
In the case where the photosensitive drums have the same characteristics as the photosensitive drums A and B, the area ratio η of the present invention is larger than 0.1,
It can be seen that the ratio W of the line width becomes small and the reproducibility of the line width is extremely low.

In general, many OPC drums such as photosensitive drums A and B are seen, and it is considered that OPC drums are not widely used in digital image forming apparatuses using background exposure.

However, even in the case of the OPC drum, if the components of the photosensitive layer, the film forming method and the film thickness are devised, or if the photosensitive drum is selected, the area ratio η of the photosensitive drum C is equal to 0.
In this case, the line width is rarely narrowed, and "normally reproduced" is obtained.

The photosensitive drums D to F are a-Si drums. When the photosensitive drums have characteristics like those of the photosensitive drums E and F, the area ratio η is 0.1 or less and the line width ratio W is sufficient. It can be seen that the reproducibility of the line width is high.

Generally, in the a-Si drum, the photosensitive drum E
And F are often seen, which indicates that they are suitable for background exposure. However, even in the case of the a-Si drum, there is a difference in the components of the photosensitive layer and the film forming method, or when the photosensitive drum is sorted out, the photosensitive drum D has an area ratio η larger than 0.1. In some cases, the image is manufactured, and in this case, the image has a small line width and low reproducibility of the line width.

As described above, it can be seen that the area ratio η shown in the present embodiment has a dominant effect on the line width reproducibility.

Therefore, by adjusting the components of the photosensitive layer of the photosensitive drum 2 and the film forming method, or by selecting the photosensitive drum, it is possible to establish an image forming apparatus capable of maintaining image quality at a high level. Becomes

(Second Embodiment) In the present invention, EV
By managing the curve area ratio η, the image quality of the digital image forming apparatus in the background exposure can be managed.

In the first embodiment, as a method for this purpose, the components of the photosensitive layer of the photosensitive drum, the film forming method, and the photosensitive drum are selected and managed. On the other hand, in the present embodiment, the image quality is adjusted and managed by changing the dark portion potential VD and the bright portion potential VL of the photosensitive drum so that the area ratio η according to Equation 2 becomes 0.1 or less. .

Since the image forming apparatus has been described in the first embodiment, the main part of this embodiment will be described.

FIG. 6 shows the area of the EV curve when the light portion potential VL is changed using the photosensitive drum B having the OPC photosensitive layer in FIG. 4A.

In the photosensitive drum B as shown in Table 1, when VD is 450 V and VL is 50 V, the area ratio η is 0.16, which is larger than 0.1. V curve area ΔS is square RPSQ
The reason is that it is large.

Therefore, the bright portion potential VL increased to 150V
When 2 is used, the area ΔS2 of the EV curve becomes smaller, and as a result, the area becomes smaller for the square (R2) P (S2) (Q2), that is, the area ratio η decreases.

In the case of the present embodiment, the bright portion potential VL2 is set to 1
In the case of 50 V, the area ratio η was about 0.1, and the line width was satisfactory.

FIG. 7 shows the area of the EV curve when the dark portion potential VD is similarly changed using the photosensitive drum B. Here, the dark portion potential VD3 is increased to 550 V, and the area ΔS3 of the EV curve becomes large in the figure. However, since the square R (P3) (S3) (Q3) also increases, the area ratio η is consequently increased. To decrease.

In the case of the present embodiment, the dark portion potential VD3 is set to 5
In the case of 50 V, the area ratio η is about 0.1,
The line width was satisfactory.

Also in FIGS. 6 and 7, the line width surely increases from that shown for the photosensitive drum B in Table 1.

However, in FIG. 6, since the difference between VD and VL, which is called the latent image contrast, is reduced, the image itself tends to be thin.

Also in FIG. 7, the latent image contrast V
Although the line width increases because the difference between D and VL increases, it is difficult to make a large change because other phenomena occur, such as the entire image being darkened and the toner consumption increasing.

Therefore, as shown in FIG.
Is used, the dark part potential VD4 and the light part potential VL4 are both changed to equalize or substantially equalize the latent image contrast.

Here, VD4 is set to 500 V, and VL4 is set to 1
Assuming 00V, the area ΔS4 of the EV curve is deformed,
The ratio η of the area to the squares (R4) (P4) (S4) (Q4) decreases.

In this embodiment, the dark portion potential VD4 is set to 500
When V and the light portion potential VL4 are 100 V, the area ratio η is about 0.1, and the line width is satisfied.

As described above, the components of the photosensitive layer of the photosensitive drum, the film forming method, and the selection of the photosensitive drum are not performed as described in the first embodiment, and the photosensitive drum is used as shown in the present embodiment. The image quality can also be managed by changing the dark portion potential VD and the bright portion potential VL.

[0074]

As described above, according to the present invention, the ratio η
By using an image carrier that satisfies the characteristic satisfying ≦ 0.1, a high-quality image with high line width reproducibility can be formed.

Even if the material of the image carrier does not satisfy the characteristics of the ratio η ≦ 0.1, the characteristics can be satisfied by adjusting the dark portion potential VD, the bright portion potential VL, or the exposure amount E0 to reproduce the line width. It can also enhance the character.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a printer as an example of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic electrical configuration diagram showing a periphery of a control board according to the first embodiment.

FIGS. 3A and 3B are a schematic explanatory view and a schematic explanatory view showing the periphery of a photosensitive drum.

FIG. 4 is a correlation diagram showing a correlation between an exposure amount and a drum surface potential of a photosensitive drum using an organic photosensitive member and an amorphous silicon layer.

FIG. 5 is a diagram illustrating a potential condition according to the present invention.

FIG. 6 is a correlation diagram of an exposure amount and a drum surface potential when a bright portion potential according to the second embodiment is changed.

FIG. 7 is a correlation diagram of the exposure amount and the drum surface potential when the dark portion potential according to the second embodiment is changed.

FIG. 8 is a correlation diagram of an exposure amount and a drum surface potential when a dark portion potential and a bright portion potential are changed in the second embodiment.

[Explanation of symbols]

Reference Signs List 2 photosensitive drum 4 primary charger 5 exposure means 6 potential sensor 7 developing device 30 semiconductor laser 50 external potential sensor VD dark portion potential VL bright portion potential E0 Exposure amount EV for obtaining bright portion potential VL Curve showing EV EV curve EV ′ A straight line ΔS, ΔS2, ΔS3, ΔS4 connecting a point indicating VD at the exposure amount 0 and a point indicating VL at the exposure amount E0. The curve EV and the straight line EV ′
Area enclosed by η ratio

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/29 9A001 F term (Reference) 2H003 AA01 BB11 CC01 DD08 EE08 2H027 DA02 DA06 DA07 EA01 EA02 EC06 EC20 2H076 AB05 CA16 CA18 DA06 DA21 5C051 AA02 CA07 DB30 DE03 DE30 EA02 5C074 AA02 BB03 BB26 CC26 DD08 EE20 GG12 9A001 JJ35 KZ16 KZ17

Claims (3)

[Claims] An image carrier, a charging unit for uniformly charging the image carrier to a dark portion potential, and exposing the image carrier uniformly charged by the charging unit to the image carrier. An image forming apparatus, comprising: an exposure unit that forms a light portion potential; and a developing unit that attaches a developer onto a dark portion potential other than the light portion potential of the image carrier. A potential is VL, an exposure amount for obtaining the bright portion potential is E0, an exposure / potential curve of the image carrier is EV, a dark portion potential VD at an exposure amount 0 passing through the EV, and an exposure amount E0 passing at the EV. , A straight line passing through the bright portion potential VL and EV ′, an area ΔS surrounded by the curve EV and the straight line EV ′, and a ratio η = ΔS {(VD−VL) × E0}. The image bearing member has a characteristic satisfying a ratio η ≦ 0.1. Forming apparatus. 2. The image carrier according to claim 1, wherein the dark portion potential VD, the light portion potential VL, or the exposure amount E0 is changed so as to satisfy a characteristic of a ratio η ≦ 0.1. 2. The image forming apparatus according to 1. 3. A digital image forming apparatus of a background area exposure system.
An image forming apparatus according to claim 1.