JP2952959B2 - Image forming method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an electrophotographic image forming method, and more particularly to an image forming method for forming a high-quality image by keeping a photosensitive member surface potential in a developing section constant. It is.

(Prior Art) In an electrophotographic image forming apparatus, it is important to maintain a constant surface potential on a photoreceptor in a developing unit in order to form an image with good image quality.

In general, DC corona discharge is used to charge the photoreceptor, but corona discharge is affected by atmospheric pressure, and when the atmospheric pressure decreases, the corona starting voltage decreases and discharge easily occurs. Irregular discharge caused by the attachment of foreign matter such as dust to the wire causes uneven charging, and the blade rubs against the photoreceptor. There were problems such as a decrease in potential.

Therefore, in recent years, scorotron chargers are often used to solve such a problem. In the scorotron charger, a screen grid is disposed between a photoconductor and a corona wire, and the surface potential of the photoconductor is controlled by controlling a grid voltage. That is, as the surface potential of the photoconductor increases, the current flowing in the grid increases, and when the surface potential of the photoconductor becomes equal to the grid voltage, all the current flows in the grid, so that the surface potential of the photoconductor becomes constant. It is kept.

By using a scorotron charger in this way, the above problem is almost eliminated and the surface potential immediately after charging is kept constant. However, as shown in FIG. 4, dark decay during the transition from the charging section to the developing section is performed. Therefore, there is a problem that the surface potential in the developing unit varies due to the variation in the dark decay rate because the surface potential gradually decreases.

Further, a surface voltmeter 23 is provided between a charging charger 21 composed of a scorotron charger and an exposure unit 22 as shown in FIG. 5 without using a scorotron charger. There is also known a device in which the charger 21 is feedback-controlled so as to keep the surface potential constant, thereby stabilizing the surface potential.

However, in this case as well, dark decay occurs between the surface voltmeter 23 and the developing means 24, so that the surface potential in the developing unit varies due to the variation in the dark decay rate.
The dark decay rate varies depending on various factors such as temperature, erase light quantity, number of continuous images formed, and change in the thickness of the photosensitive layer. For example, in FIG. 5, assuming that t seconds elapse from the monitor unit of the surface electrometer to the developing unit, the amount of potential decay during the t seconds changes as shown in FIG. 6 depending on the temperature.

Therefore, Japanese Patent Application Laid-Open No. 64-78268 discloses that the characteristic relationship between the temperature of the photoconductor and the dark decay rate is obtained in advance, and the amount of attenuation of the potential corresponding to the temperature detected by the temperature sensor is set to a predetermined surface potential. A method has been proposed in which the added potential is set as a target potential, and control is performed so that the potential detected by the surface voltmeter becomes equal to the target potential.

(Problems to be Solved by the Invention) However, in the method disclosed in the above publication, it is possible to correct variations in dark decay based on temperature,
In addition to temperature, the dark decay rate varies depending on factors such as temperature, the amount of erased light received up to that point, the number of continuous images formed, and the change in the thickness of the photosensitive layer. It is practically impossible to perform the correction in the dark, and it is not possible to perform the correction for the dark decay perfectly to maintain the surface potential in the developing unit with high accuracy and constant, thus stabilizing the image quality especially during color image formation. There was a problem that it was difficult to do.

In view of the above conventional problems, the present invention provides an image forming method capable of making appropriate correction for dark decay due to various factors, making the surface potential of the photoconductor in the developing unit constant, and forming a high quality image. The purpose is to provide.

(Means for Solving the Problems) The image forming method of the present invention achieves the above object,
After uniformly charging the photoconductor with a scorotron charger, the photoconductor is rotated once in the dark, and after one rotation, the photoconductor is recharged, and the dark decay rate is determined based on the grid current value at that time. The grid voltage of the scorotron charger is controlled so that a predetermined surface potential is obtained in the developing section according to the dark decay rate, and the photoconductor is uniformly charged with the scorotron charger, and then the photoconductor is exposed to form an electrostatic latent image. And developing the electrostatic latent image.

(Operation) According to the above configuration of the present invention, the dark decay during the recharging after the photoreceptor is rotated once after charging is obtained by utilizing the characteristics of the scorotron charger. Therefore, it is possible to detect the dark decay rate in which all the factors are integrated, and by using the scorotron charger to apply the surface potential corrected for the potential decrease due to this dark decay rate, the developing section stabilizes the accurate surface potential. And good image quality can be formed.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, reference numeral 1 denotes a photosensitive drum provided with a photosensitive layer for forming an electrostatic latent image on the outer peripheral surface. Reference numeral 2 denotes a scorotron charger for uniformly charging the photosensitive layer of the photosensitive drum 1, and a stabilizer 4 is provided so as to surround the corona wire 3 except for a portion facing the photosensitive drum 1. A grid 5 is arranged between the body drums 1. The corona wire 3 is connected to a charging high-voltage power supply 6 composed of a constant current transformer whose current and the like are not affected by humidity, pressure and the like. The stabilizer 4 is grounded. Means 8 is connected. From the scorotron charger 2, an exposure unit 9, a developing unit 10, a corotron shearer 11 for transfer, a cleaning unit 12, and an eraser lamp 13 are arranged in the rotation direction of the photosensitive drum 1.

In the above configuration, at the time of image formation, as shown in FIG. 3, after the residual charge is erased by the eraser lamp 13 (step # 1), the photosensitive drum 1 is uniformly charged by the scorotron charger 2 (step # 1). # 2). At this time, the current Ipc flowing to the photosensitive drum 1 side other than the current flowing to the stabilizer plate 4 side is divided into the photosensitive drum 1 and the grid 5 by controlling the grid voltage Vg. Since the upper potential is almost 0 V, a large amount of current flows on the photosensitive drum 1 side, and when it becomes almost equal to the surface potential grid voltage Vg of the photosensitive drum 1, most of the current Ipc flowing on the photosensitive drum 1 side becomes the grid. 5, the surface potential of the photosensitive drum 1 is accurately set to a constant value.
Then, the grid current Ig ₁ flowing during this time is measured (step # 3). Next, the grid voltage Vg, to calculate the charge capacity X by the following equation based on the current value Ipc and grid current Ig ₁ flowing to the photosensitive drum 1 side (step # 4).

X = (Ipc−Ig ₁ ) / Vg (μA / V) That is, the charging capability X indicates the amount of current flowing into the photosensitive drum 1 necessary to raise the surface potential of the photosensitive drum 1 by 1V. As a specific example, assuming that the total current supplied from the charging high-voltage power supply 6 to the corona wire 3 is 100 μA and 500 μA flows through the stabilizer 4, the remaining 500 μA is the current Ipc flowing to the photosensitive drum 1 side, Also the grid current Ig ₁
Is 200 μA, the current value required to charge the photosensitive drum 1 to a predetermined surface potential (Vg = 600 V) is
It is 300 μA, and the charging ability X is 0.5 μA / V. Since this charging capability X changes depending on the use conditions of the photosensitive drum 1, this value is obtained first.

Next, the photosensitive drum 1 is not exposed or erased.
The allowed around 1 charged as it once more under the same conditions (step # 5), for measuring the grid current Ig ₂ at that time (Step # 6). Here, if the dark decay is 0,
Since the surface potential is the same as the grid voltage Vg while keeping the previous surface potential, the entire current Ipc to the photosensitive drum 1 flows to the grid 5. Conversely, if the surface potential decreases greatly during one rotation of the photosensitive drum 1 due to a large dark decay, a current flows through the photosensitive drum 1 and the grid current decreases, thereby exhibiting the characteristics shown in FIG. . Therefore, the grid current Ig
By measuring ₂ , the dark decay rate can be measured. Thus, the correction amount ΔVg of the grid voltage Vg (= the surface potential of the photosensitive drum 1) is then determined according to the dark decay amount.
Is calculated by the following equation (step # 7).

ΔVg = (Ipc−Ig ₂ ) / X · (t ₁ / t ₀ ) where t ₀ : one rotation time of the photosensitive drum t ₁ : time between the charging unit and the developing unit. That is, ΔVg is from the charging unit to the developing unit. Shows the dark decay between. In the above specific example, if Ig ₂ is 400 μA, a potential corresponding to 100 μA is darkly attenuated in one rotation, and the charging ability X is 0.5 μA / V, so that 200 V dark decay occurs. And if t ₁ / t ₀ is 1/4, ΔVg is 50V
Becomes Then, in order to correct the dark decay, the grid voltage is switched to (Vg + ΔVg) (600 + 50 = 650 V) (Step # 8), and after charging is performed in this state (Step #)
9) forming an electrostatic latent image by exposing in the exposure unit 9 and developing means
An image forming process of developing at 10 and transferring to a transfer material by the transfer charger 11 is performed (step # 10). Thus,
The photosensitive drum 1 in the developing section by appropriately correcting dark decay
Can be accurately maintained at a constant potential, and a high-quality image can be stably obtained, and a high-quality image can be obtained even in a color image process.

In the present embodiment, the current Ipc supplied to the corona wire 3 is kept constant, so that the current Ipc flowing toward the photosensitive drum 1 is also kept substantially constant. As shown in FIG. 7, when the current detecting means 30 and 32 are provided, the current Ic supplied to the corona wire 3 and the stabilizing plate 4
The current Ipc flowing to the photosensitive drum 1 side can be more accurately obtained from the difference from the current Ic flowing to the photosensitive drum 1.

Here, the corona wire 3 is connected to the high voltage power supply 31 via the current detecting means 30, and the stabilizer 4 is grounded via the current detecting means 32.

(Effects of the Invention) According to the image forming method of the present invention, as is apparent from the above description, the characteristics of the scorotron charger are utilized,
Since the dark decay during that period is determined by the grid current value at the time of recharging after the photoreceptor makes one rotation after charging, the dark decay rate combining all the factors can be detected. By applying the surface potential corrected for the potential drop due to the above to the scorotron charger, an accurate surface potential can be stably obtained in the developing unit, and an effect of forming an image with good image quality can be exhibited.

[Brief description of the drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a schematic diagram of a main part, FIG. 2 is a graph showing a relationship between a dark decay rate and a grid current, and FIG. Flow chart of the operation, FIG. 4 is a graph showing the time change of the surface potential including dark decay, FIG. 5 is a schematic configuration diagram of a surface potential control method using a surface voltmeter, and FIG. FIG. 7 is a schematic diagram showing another embodiment of the present invention. 1 photoconductor drum 2 scorotron charger 5 grid 7 grid current detecting means 8 grid voltage setting means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/02 G03G 15/00 303

Claims (1)

(57) [Claims] After the photosensitive member is uniformly charged by a scorotron charger, the photosensitive member is rotated once in the dark, and after one rotation, the photosensitive member is recharged and a dark decay rate is determined based on a grid current value at that time. The grid voltage of the scorotron charger is controlled so as to have a predetermined surface potential in the developing section according to the obtained dark decay rate, and the photoconductor is uniformly charged with the scorotron charger, and then the photoconductor is exposed. Forming an electrostatic latent image by developing the electrostatic latent image, and developing the electrostatic latent image.