JPH05289458A - After image preventing device for photosensitive body - Google Patents

Abstract

PURPOSE:To prevent time loss at the time of starting the rotation of a photosensitive body and to prevent a cleaner blade and developer from deteriorated unnecessarily and to prevent the after image of a photosensitive body by changing a setting value related to image density at every one revolution of the photosensitive body at the time of starting the rotation of the photosensitive body. CONSTITUTION:As information related to the after image of the photosensitive body 1, there are the film thickness information of the photosensitive body, stand-by time information in the state that image formation is not performed, the temperature information of the photosensitive body 1, the kind information of the material of the photosensitive body 1 and the manufacture lot information of the photosensitive body 1. A CPU 16 fetches temperature in a device detected by a thermistor 13 and the charcteristic information of the photosensitive body 1 inputted by operating a switch. A timer provided in a RAM 18 counts a stand-by time. The CPU 16 controls the voltage of the grid power source of a charger 3, the voltage of the development bias source of a developing device 5 or the duty ratio of a destaticizing lamp 2 at every one revolution of the photsensitive body 1 at the time of starting the rotation of the photosensitive body 1 when the image formation process is started according to these information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an afterimage preventing device for a photoconductor in an electrophotographic image forming apparatus for preventing an afterimage from occurring in an image at the beginning of an image forming process.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, an image is formed using a photoconductor having photoconductivity. The photoconductor is charged by a charger such as a scorotron charger at the beginning of the image forming process, and discharged by a charge eliminator such as a charge eliminating lamp at the end of the image forming process. However, static elimination by the above static eliminator is not perfect. This is because the photo carriers are trapped in the impurity level in the photosensitive layer during the charging process, and the trapped carriers cannot be erased by the static eliminator. In this way, the photocarriers trapped in the photosensitive layer have a residual potential, which increases the surface potential at the next image forming process. In the drum-shaped photoreceptor,
When the image forming process is started from the state where the photoconductor has no residual potential, the number of photocarrier traps increases every time the photoconductor rotates once. The trap of photocarriers naturally increases logarithmically, and the residual potential also naturally increases logarithmically. Therefore, for example, in the case of a drum-shaped photoconductor, the change in surface potential is the largest between the first rotation and the second rotation of the photoconductor drum,
It becomes a little smaller between the 2nd and 3rd rotations, and the amount of change becomes smaller thereafter. When the charging and discharging processes are repeated, the residual potential eventually reaches the saturation value and the surface potential of the photoconductor becomes stable.

As described above, the residual potential changes significantly at the beginning of the image forming process. If the residual potential, that is, the surface potential changes significantly in this way, an afterimage may occur in the formed image. The afterimage phenomenon occurs with the same tendency as the change of the surface potential, is largest in the first and second rotations, becomes slightly smaller in the second and third rotations, and the difference becomes smaller thereafter. Go on. Usually, the photoconductor is formed in an endless shape, that is, a drum shape or a belt shape, and is used endlessly. Therefore, 1
It is possible that the first and second rotations of the photoreceptor will be used in one copy of the image. In such a case, light and shade of image density occurs due to an afterimage phenomenon in one copy image, which makes the image very unsightly.

[0004]

The afterimage phenomenon described above occurs until the residual potential reaches a saturation value. Normally, the residual potential reaches a saturation value while rotating 2-3 times when the number of photoreceptors is small and about 10 times when it is large. Therefore, in order to alleviate the afterimage phenomenon, it is conceivable that the several rotations at the beginning of the rotation at the start of the image forming process are not used for the image forming process, and the idling is performed. However, this method has a drawback that the first image forming processing time becomes very long,
Important specifications for image forming equipment (process time reduction)
Will be reduced. Further, since the rotation distance of the photosensitive member and the stirring time of the developer required to obtain one image become long, there arises a problem that the physical stress received by these increases and the life is shortened. For example, when the rotation distance of the photoconductor drum per image is increased, the friction between the photoconductor and the cleaner blade causes the film thickness of the photoconductive layer to be rapidly decreased, the charge density on the photoconductor surface is increased, and the real-time sensitivity is lowered. Will cause. Further, even for the cleaner blade, the edge portion is abraded at an early stage due to friction with the photosensitive drum, resulting in image defects such as cleaning failure. That is, there is a problem that the photoconductor drum and the cleaner blade have a short life.
The same applies to the developer, and the friction between the developer and the stirring roller or doctor blade in the developer causes the carrier coating material to peel off and the spent toner to increase on the carrier.
This causes the toner to have a smaller particle size, which deteriorates the development characteristics and the image quality. These problems become more serious as the probability of forming a single image is higher, or when a small number of images are formed even when forming a plurality of images.

An object of the present invention is to provide a photoconductor residual image preventive device which can prevent the above-mentioned time loss and the problem of excessive deterioration of the cleaner blade, the developer and the like, and can prevent the residual image of the photoconductor. To provide.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an electrophotographic image forming apparatus for forming an image using an endless photoconductive photosensitive member, when the photosensitive member is initially rotated when an image forming process is started, It is characterized in that a means for changing the set value relating to the image density of the formed image is provided based on the information relating to the residual potential of the photoreceptor, each time the photoreceptor rotates once.

The information relating to the residual potential of the photoconductor includes, for example, information on the film thickness of the photoconductor, information on the standby time in a state where no image is formed, temperature information on the photoconductor, type information on the material of the photoconductor, One or a plurality of pieces of information regarding the manufacturing lot of the photoconductor are used.

As the set value relating to the image density of the formed image, for example, one or a plurality of set values of a charge amount set value, a development amount set value, and a charge removal amount set value are used.

[0009]

First, the operation of changing the set value relating to the image density will be described.

During the initial rotation of the photoconductor when the image forming process is started, the charge amount set value is changed every time the photoconductor rotates once. For example, if the charge amount setting value is increased when the residual potential of the first rotation is low, the surface potential increases,
When the residual potential of the second rotation becomes slightly high, the surface potential of the same value as that of the first rotation can be obtained by making the charge amount set value smaller than that of the first rotation. In this way, if the set value of the surface potential is changed every one rotation of the photoconductor, the surface potential can be made constant regardless of the number of rotations. Therefore, the image density becomes constant.

When the set value of the developing amount is changed as the set value relating to the image density, for example, since the surface potential is low in the first rotation, the developing amount, that is, a large amount of toner adheres to the photosensitive member. By setting the developing amount set value so that a large amount of toner can be attached even if the surface potential is low. And the number of rotations increases (the second and third rotations
.), The developing amount setting value is changed and the setting value is changed so that the toner adhesion amount becomes smaller than that in the first rotation, so that toner equivalent to that in the first rotation can be attached to the photoconductor. Like Therefore, the image density can be made constant.

Further, when the charge removal amount set value is changed as the set value relating to the image density, for example, when the first rotation and the second rotation are compared, the light removal lamp light amount is increased in the second rotation. To be done. Therefore, in the second rotation, the absolute number of photocarriers generated in the static elimination step increases, and the lifetime of these photocarriers is long and remains in the charging step. Therefore, when a large electric field is applied in the charging step, the movement starts again. As a result, the charging efficiency is lowered and the surface potential is lowered. In this way, the surface potential can be stabilized.

Next, the operation of changing the set value relating to the image density according to the information relating to the residual potential will be described.

As the photoconductor is used, the film thickness is reduced and the film thickness is reduced. Depending on the type of the photoconductor, the residual potential may decrease as the film thickness decreases, and in this case, the residual image decrease is alleviated as the photoconductor is used. However, with other types of photoconductors, the trap density may increase due to electrical deterioration of the photosensitive layer as the film thickness decreases.If this effect exceeds the effect of film loss, the trap density will increase as it is used. The potential rises, and the afterimage phenomenon due to the surface potential difference between the first rotation and the second rotation of the drum becomes more remarkable. Therefore, if the set value relating to the image density is changed based on the information on the film thickness of the photoconductor and the type of the photoconductor, the density unevenness can be reduced.

The photocarriers trapped in the photosensitive layer are gradually released when left to stand. Therefore, if the photoconductor is left for a long time (standby state) without using it, the photocarriers are opened and the residual potential gradually decreases. Since the residual potential is gradually released, if the waiting time of the photoconductor is short, the photocarriers remain and the residual potential becomes high. However, if the photoconductor is left for a long time, the residual potential is sufficiently lowered. When the image forming process is started, if the residual potential is high in advance, image density unevenness is reduced even in the first rotation. Therefore, if the set value relating to the image density is changed based on the information on the waiting time of the photoconductor, the density unevenness can be reduced.

As described above, when the photoconductor is not used (standby state), the trapped optical carrier is released. This opening speed (the speed at which the residual potential decreases) is a function of time and photoreceptor temperature. That is, if the temperature of the photoconductor is high, the probability that carriers will be released from the trap will be high and the residual potential will decrease at a high rate. Even if it does, the residual potential may not decrease. Therefore, if the set value relating to the image density is changed based on the temperature information of the photoconductor, the density unevenness can be reduced.

Raw material lot difference at the time of producing the photosensitive material,
The problem of reproducibility in prescription gives different characteristics even for the same type of photoreceptor. For example, in a function-separated type organic photoreceptor obtained by stacking a photocarrier generation layer and a photocarrier transport layer, the residual potential is determined by the film thickness of the photocarrier transport layer and the trap density. In the arsenic selenide photoconductor, the generation of the residual potential depends on the wavelength of the exposure light, but the residual potential is determined by the trap density and the depth of the trap level in the photosensitive layer as in the function-separated type organic photoconductor. To be done. In addition, differences in the amount of admixture added in the preparation of the photoconductor material and differences in stirring time caused by uneven coating of the coating film may cause differences even between photoconductors of the same type.
It also changes depending on the variations when the photoconductor is created. C
The generation efficiency of carriers in the GL layer, the trap density and the trap level in the CTL layer are different from each other, and this is one of the factors causing the afterimage phenomenon. Therefore, if the set value relating to the image density is changed based on the characteristic information of the photoconductor (information corresponding to the lot difference or the like), the density unevenness can be reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of essential parts of a general copying machine.

In this embodiment, a drum-shaped photosensitive member is used as the endless photosensitive member. A belt-shaped one may be used as the endless photoconductor. The drum-shaped photoconductor 1 has a thickness of 2 mm, a diameter of 100 mm, and a length of 340.
0.5mm μm thickness of charge generation layer on aluminum tube
Is uniformly applied, and then a charge transport layer is uniformly applied so as to have a film thickness of 34 μm. A discharge lamp 2, a charger 3, a blank lamp 4, a developing device 5, a transfer device 6, a peeling device 7, and a greener 8 are arranged around the photoconductor 1 in this order. The static elimination lamp 2 is
Driven by the driver 12, the surface of the photoconductor 1 is exposed to remove the charge on the surface of the photoconductor. The duty ratio of the discharge lamp light amount is controlled. The charger 3 includes a discharge electrode 3a made of a tungsten oxide wire having a diameter of 70 μm, a shield electrode 3c made of stainless steel surrounding the discharge electrode 3a, and a screen grid electrode made by etching a stainless material having a plate thickness of 0.1 mm. It is a scorotron charger equipped with 3b. This grid electrode 3b is
A variable output high-voltage power supply 10 is connected. The blank lamp 4 neutralizes the outside of the image forming area during copying. The developing device 5 includes a mag roller 5a, and supplies toner to the electrostatic latent image formed on the photoconductor 1 to make it visible. Magroller 5
A variable output developing bias power source 11 is connected to a. The transfer device 6 transfers the toner image formed on the photoconductor to the transfer paper 20. The peeling device 7 peels the transfer paper 20 from the photoconductor 1. After that, the toner remaining on the photoconductor 1 is removed by the cleaner 8, and the surface charge on the photoconductor 1 is removed by the discharge lamp 2.

An optical system 9 is provided above the photoconductor 1. The optical system 9 exposes the document on the document table 21 and forms an image of the reflected light on the photoconductor. A thermistor 13 is arranged near the developing device 5. The thermistor 13 detects the temperature inside the copying machine. The output of the thermistor 13 is the amplifier 1
Amplified by 4 and passed through the A / D converter 15 and then CP
Input to U16. CPU16 is ROM17, RAM
The operating unit in the copying machine is operated. The drive motor of the photoconductor 1 is provided with a rotary encoder and outputs a pulse waveform. The CPU 13 takes in this pulse and converts it into the number of rotations of the photoconductor 1. Also,
The CPU 13 takes in the temperature inside the machine detected by the thermistor 13, the characteristic information of the photoconductor input by the switch operation, and the like. The switch for inputting characteristic information of the photoconductor is provided on the side surface of the copying machine main body or the like. For example, it is configured by a DIP switch as shown in FIG. The RAM 18 is provided with a timer to measure the waiting time and the like until the image forming process is performed. The CPU 16 controls the voltage of the grid power supply 15 of the charger 2, the voltage of the developing bias power supply 16, or the duty ratio of the charge eliminating lamp 8 according to these pieces of information.

A method of preventing afterimages in the copying machine configured as described above will be described.

Comparative Example (Conventional State) FIG. 2 shows a change in the surface potential of the photosensitive member after the copy button is pressed using such a copying machine, with the drum rotation speed as the horizontal axis. The environmental conditions were standard conditions of 25 ° C. and 50%. The measurement of the electric potential was performed by installing a commercially available surface electrometer instead of the developing device 5. As can be seen from the figure, the surface potential increases with each rotation, the first rotation and the second rotation. In this state, the surface electrometer was replaced with a developing unit, and an A3 size original (uniform intermediate density 0.3
Continuous copying (multi-copy) of five sheets was performed using a halftone original document having a number of .times., And the density unevenness of the obtained copied image was measured. The result is shown in FIG. A commercially available Macbeth densitometer was used to measure the concentration.

The position of the copied image on the abscissa is set to 0 mm at the front end so that density unevenness in the circumferential direction of the photoconductor can be represented. As can be seen from this figure, a large density unevenness occurs on the first copy of the copied image, and this density unevenness decreases with the second and third copies. Although only the third sheet is shown in the figure, a uniform halftone copy with almost uniform density was obtained in the fourth image copy image. Since the positional relationship for forming an image on the photoconductor is not fixed, the density unevenness occurrence positions in each copy image are different. Also, since the diameter of the photoconductor used is 100 mm, there is a possibility that density unevenness may occur at two places at the maximum in the case of copying A3 size. Many density irregularities should occur in one copy image. The reason why the density unevenness becomes smaller as the number of sheets is increased is that the surface potential of the photoconductor reaches a stable value when the residual potential of the photoconductor reaches a certain saturation value as described above.

Experimental Example 1 First, an experiment was conducted to find out what happens when the charging condition, the developing condition, and the discharging condition are changed during the initial rotation of the photoconductor after the copying process is started.

Experimental Example 1-1 (Changing charging conditions) As shown in FIG. 4, the control program is such that the grid voltage applied to the screen grid electrode 3b of the charger becomes lower as the drum rotation speed (times) increases. It was created. On the other hand, the number of rotations of the photosensitive drum 1 is counted as the number of pulses from the rotary encoder attached to the photosensitive drum drive motor. Then, the grid voltage was controlled according to the relationship shown in FIG. 4 according to the pulse count number. Then, similarly to the comparative example, the change in the surface potential of the photoconductor after pressing the copy button was measured. FIG. 5 is a diagram showing the results, in which the vertical axis represents the change in the photosensitive member surface potential and the horizontal axis represents the drum rotation speed. By doing so, the surface potential of the photoconductor can be kept at a constant value regardless of the number of rotations of the drum. It was possible to obtain an extremely excellent image quality without density unevenness in the circumferential direction.

Experimental Example 1-2 (changing the developing conditions) As shown in FIG. 6, the control program is such that the developing bias voltage applied to the developing sleeve of the developing device becomes higher as the drum rotation speed (times) increases. It was created. Then, in the same manner as in Experimental Example 1-1, the copy button was pressed to perform the copy process, and the density of the formed copy image was measured. FIG. 7 is a diagram showing the results, where the horizontal axis represents the position of the copied image and the vertical axis represents the image density. As described above, the copied image was an excellent image in which density unevenness in the circumferential direction was extremely small.

Experimental Example 1-3 (changing the static elimination condition) As shown in FIG. 8, a control program is prepared so that the light amount of the static elimination lamp (driving duty ratio of the static elimination lamp) becomes higher as the drum rotation speed (times) increases. did. Then, in the same manner as in Experimental Example 1-1, the change in the surface potential of the photoconductor after pressing the copy button was measured. FIG. 9 is a diagram showing the results, in which the vertical axis represents changes in the surface potential of the photoconductor and the horizontal axis represents the drum rotation speed. As can be seen from this figure, the photosensitive member surface potential is in a substantially stable state regardless of the drum rotation speed. The copied image obtained by controlling in this way was an image with very little density unevenness in the circumferential direction.

Experimental Example 2 In Experimental Example 1, the charging conditions and the like were simply changed in the initial stage of the copying process. If only this control is performed, it becomes impossible to obtain stable photoconductor surface potential and copy image density when the photoconductor film is thinned. For example, the stability of the surface potential of the photoconductor was examined using a photoconductor whose initial film thickness (34.5 μm) was reduced to 25 μm by life-aging of 200,000 sheets.

First, a copying process was performed under the same charging conditions as in Experimental Example 1-1. Then, as shown in FIG. 10, the effect of the charging conditions of Experimental Example 1-1 is not sufficient in the photoconductor drum that has been subjected to life aging, and the first rotation, as compared with FIG.
The surface potential rises with every second rotation.

Further, when the copying process was carried out under the same developing conditions as in Experimental Example 1-2, and when the photoconductor drum subjected to life aging as shown in FIG. 11 was used, the image density became uneven. There is.

Similarly, in order to compare with Experimental Example 1-3, the light amount of the discharge lamp was set to be the same as in Experimental Example 1-3, and the surface potential of the photoconductor was measured. FIG. 12 is a diagram showing the result, and in the case of the photoconductor drum subjected to life aging, the surface potential gradually increases from the first rotation to the second rotation.

In order to solve the above problems, in Experimental Example 2, the charging condition, the developing condition, and the discharging condition were changed according to the film loss of the photoconductor. The total number of rotations of the photoconductor and the total number of copies can be used as a measure of the film loss of the photoconductor. In this example, the total number of copies was used. The total number of copies was further corrected by the copy size in order to count the photoconductor fatigue more accurately.
That is, A3 size is counted as 2 A4 size, and B
As for 4 sizes, A4 size was counted as 1.5 sheets.

First, the potential change at each stage of life aging was measured without correction of any of the charging condition, the developing condition and the charge eliminating condition, and the life aging dependence of the surface potential was examined. In FIG. 13, the vertical axis represents the surface potential difference between the first rotation and the second rotation of the photosensitive drum among the potential changes at each stage of life aging, and the horizontal axis represents the total number of copies (life aging stage) at that time. It is a thing. It is considered that the cause of such life dependence is that the probability that photocarriers are released from the trap order of the photosensitive layer has film thickness dependence and trap density dependence.
That is, since the film thickness of the photosensitive layer decreases as life aging is performed and the trap density increases,
It is considered that the residual potential is governed by whichever has the larger influence. This embodiment is the latter, and since the increase of the trap density has a greater effect, the residual potential increases with life aging, and the change of the surface potential of the photoconductor becomes large.

Experimental Example 2-1 FIG. 14 shows an example of a grid voltage correction coefficient for each total number of copies. A control program was created so that this correction coefficient is multiplied by the grid voltage for each drive speed shown in FIG. 4 at each total copy number (at each stage of life aging). Then, the same life aging test as the experiment shown in FIG. 13 was performed. This program is designed to increase the change of the charging condition for each rotation of the drum as the total number of copies increases in accordance with the life aging characteristics of the photoconductor of this embodiment. In this way, life aging of 200,000 sheets was performed, and when the surface potential difference between the first rotation and the second rotation during this period was examined, the surface potential of each rotation was stable at an extremely small value as in the initial case (Fig. 15). In the copied image, it was possible to obtain a uniform image quality without density unevenness over the life aging.

Experimental Example 2-2 FIG. 16 shows an example of the correction coefficient of the developing bias voltage for each total number of copies.

Then, as in the case of correcting the grid voltage, a control program was created so that this correction coefficient is multiplied by the developing bias voltage for each drum rotation speed shown in FIG. Then, a life aging test was performed on 200,000 sheets, and the density of the first copy image during this period was measured. FIG. 17 is a diagram showing the image density of the first sheet at each life aging stage, and it was possible to obtain an image having a substantially uniform density at any stage.

Experimental Example 2-3 FIG. 18 shows the correction coefficient of the duty ratio of the static elimination lamp for each total number of copies. A control program was created so as to multiply the duty ratio for each drum rotation speed shown in FIG. 8 by this correction coefficient, and a life aging test was performed on 200,000 sheets. FIG. 19 is a diagram showing the surface potential difference between the first and second sheets at each life aging stage, and could be stabilized to an extremely small value at any life aging stage. Then, it was possible to obtain a copy image of stable quality.

As described above, it was possible to obtain an image of stable quality by changing the grid voltage, the developing bias voltage, and the duty ratio of the charge eliminating lamp for each total number of copies.

Depending on the type of the photoconductor, the factor that governs the residual potential differs, and it may be difficult to correct with a unique function as in this embodiment. In such a case, it is effective to provide a correction table in the CPU. For example, as shown in FIG. 20, a table of the total number of copies and the number of rotations of the drum is provided, and the grid voltage of the charger, the developing bias voltage, the duty ratio of the discharging lamp and the like at each stage of life aging are stored. By controlling the charging device, developing device, and discharging lamp according to this table, the surface potential can be effectively corrected even in the case of a photoconductor having complicated characteristics, and a high quality copied image without afterimage can be obtained. Will be able to.

Experimental Example 3 In Experimental Example 3, the charging condition was changed according to the waiting time (standing time).
An example in which the developing condition and the charge removing condition are changed will be shown.

First, after the completion of copying, the time was measured, and the potential of five continuous multi sheets was measured at regular intervals (every 1 minute). FIG. 21 shows the surface potential difference between the first rotation and the second rotation of the photosensitive drum at this time. In the figure, the vertical axis represents the surface potential difference between the first rotation and the second rotation,
The horizontal axis represents the standing time. At the time of this measurement, neither the charging condition, the developing condition, nor the static elimination condition was corrected. The causes of such leaving time dependency are:
It is considered that the probability that the photo carriers are released from the trap level of the photosensitive layer has time dependence. That is, it is considered that when left for a long period of time, the total amount released is large, so that a low residual potential comes to be exhibited. It should be noted that if the standing time becomes longer to some extent, the residual potential also reaches a saturation value to some extent. In this example, the boundary value is about 5 minutes. Since this time depends on the trap level of the photosensitive layer and the ambient temperature, it takes different values when the type of the photosensitive material is different.

When the charging conditions and the like are not controlled as described above, the surface potential difference between the first rotation and the second rotation changes depending on the waiting time. Therefore, for example, when the grid voltage, the developing bias voltage, and the light amount of the discharge lamp are controlled with the fixed set values as shown in FIGS. 4, 6, and 8, the surface potential difference appears at the initial rotation of the photoconductor depending on the standby time. .. 22, FIG. 23, and FIG. 24 are the first rotation when the grid voltage, the developing bias voltage, and the discharge lamp light amount are controlled by the settings of FIG. 4, FIG. 6, and FIG. 8 when the standby time is 5 minutes. Surface potential difference from the second rotation, or 1-3
It is a figure showing the density of one copy image. If there is a waiting time in this way, a stable state as in Experimental Example 1 cannot be obtained. Therefore, the grid voltage, the developing bias voltage, and the light amount of the static elimination lamp are corrected according to the standby time.

FIG. 25 is an example of the correction coefficient of the grid voltage of the charger, FIG. 26 is an example of the correction coefficient of the developing bias of the developing device, and FIG.
Reference numeral 7 shows an example of a correction coefficient for the duty ratio of the charge eliminating lamp.

A program was created such that these correction factors were multiplied by the grid voltage shown in FIG. 4, the developing bias voltage shown in FIG. 6, and the duty ratio shown in FIG.

FIG. 28 is a flow chart showing a copy processing procedure performed using the program. When the drum rotation of the photoconductor is stopped (n6), the time until the counter is reset and started and the copy button is pressed is calculated (n1 → n2 → n3 → n4). Then, this leaving time is taken into the CPU, and the grid voltage or the developing bias or the duty ratio of the charge eliminating lamp is controlled based on this, and the copy processing is performed. At this time, as described above, for example, a value obtained by multiplying the grid voltage of FIG. 4 by the correction coefficient of FIG. 25 is used for the grid voltage, and the development bias voltage of FIG. The multiplied value is used.

The correction program of this experimental example is such that the change of the charging condition, the developing condition, and the discharging condition for each drum rotation speed is made larger when the standing time is long.
By doing so, it was possible to obtain a copied image with uniform image quality without density unevenness despite changes in the standing time.

For example, as shown in FIG. 29, the leaving time for each type of photoconductor, the grid voltage for each drum rotation speed,
By storing the developing bias voltage and the duty ratio of the discharging lamp, correction can be easily performed even in the case of a photoconductor having a complicated characteristic, and a high quality copy image without an afterimage can be obtained.

Experimental Example 4 Experimental Example 4 shows an example in which the charging condition, the developing condition, and the charge eliminating condition are changed according to the temperature inside the apparatus.

First, the copying machine was brought into an environmental test room, and the surface potential was measured while measuring the photosensitive material while changing the room temperature (the temperature of the copying machine). FIG. 30 shows the surface potential difference between the first rotation and the second rotation of the photosensitive drum at this time. In the figure, the vertical axis represents the surface potential difference between the first rotation and the second rotation, and the horizontal axis represents the environmental temperature. At the time of this measurement, neither the charging condition, the developing condition, nor the static elimination condition was corrected. It is considered that the cause of such temperature dependence is that the probability that the photocarriers are released from the trap level of the photosensitive layer has temperature dependence. In other words, it is considered that in a low temperature environment, the residual potential has a small opening probability, and hence a higher residual potential is exhibited.

As described above, when the charging conditions and the like are not controlled, the surface potential difference between the first rotation and the second rotation changes according to the time inside the copying machine. Therefore, for example, when the grid voltage, the developing bias voltage, and the light amount of the discharge lamp are controlled with the set values as shown in FIGS. 4, 6, and 8, the surface potential difference appears at the initial rotation of the photoconductor due to the temperature inside the machine. .. 31, 32, and 33 show the temperature inside the machine at 5
Surfaces of the first and second rotations when the grid voltage, the developing bias voltage, and the discharge lamp light amount are controlled by the settings of FIGS. 4, 6, and 8 respectively when the temperature is set to 25 ° C., 25 ° C., and 35 ° C. FIG. 6 is a diagram showing a potential difference or the densities of 1 to 5 copy images. If there is such a temperature difference in the machine, Experimental Example 1
It is not possible to get a stable state like. Therefore,
The grid voltage, development bias voltage, and the light amount of the static elimination lamp are corrected according to the temperature inside the machine.

FIG. 34 shows an example of the correction coefficient of the grid voltage of the charger, FIG. 36 shows an example of the correction coefficient of the developing bias of the developing device, and FIG.
Reference numeral 8 shows an example of a correction coefficient for the duty ratio of the static elimination lamp.

A program was created so that these correction factors may be multiplied by the grid voltage shown in FIG. 4, the developing bias voltage shown in FIG. 6, and the duty ratio of the discharge lamp shown in FIG. ..

As shown in FIG. 1, a thermistor is provided in the main body of the copying machine. The temperature inside the machine detected by the thermistor is fetched into the CPU, and the grid voltage, the developing bias voltage, and the light amount of the discharge lamp are calculated based on this temperature and the above program, and each control is performed.

The above program is designed to make the change in the charging condition, the developing condition, and the discharging condition for each drum rotation speed larger when the ambient temperature is lower than that at normal temperature. FIG. 35 and FIG. 39 show the measurement of the surface potential of the photoconductor for each rotation speed of the drum when the developing condition and the charge removing condition were controlled according to the above program, and a stable surface potential could be obtained. The environmental temperature at this time is 5 ° C. FIG. 37 shows 5 when the developing conditions are changed.
FIG. 6 is a diagram showing variations in image density under the environment of ° C, 25 ° C, and 35 ° C, and images with stable density could be obtained.

For example, as shown in FIG. 40, the temperature inside the machine for each type of photoconductor, the grid voltage for each drum rotation speed,
By storing the developing bias voltage and the duty ratio of the discharging lamp, correction can be easily performed even in the case of a photoconductor having complicated characteristics, and a high quality copied image without an afterimage can be obtained.

Experimental Example 5 Experimental Example 5 shows an example in which the charging condition, the developing condition, and the discharging condition are changed according to the characteristic information of the photoconductor.

Photosensitive drums of the same kind of photosensitive material but in different production lots were prepared, and the surface potential difference between the first rotation and the second rotation was measured for each photosensitive drum. The results are shown in Fig. 41. The vertical axis represents the surface potential difference between the first and second rotations of the drum, and the horizontal axis represents the lot number of the photoconductor. As can be seen from the figure, the value of the surface potential difference, which causes the afterimage, differs depending on the manufacturing lot of the photoconductor. Thus, the surface potential difference between the first rotation and the second rotation changes depending on the manufacturing lot. In this experimental example, each step of the surface potential difference (10
For each V), the photoconductor was divided into five classes of A to E (photoconductor characteristic class). That is, the surface potential difference is 0 to 10
The V photoconductor is A class, the 10 to 20V photoconductor is B class, and so on. The surface potential difference is 50V
The above samples are unsuitable as products because of large variations in the production of the photoconductor, and are not used as photoconductors.

A photoconductor having a different photoconductor characteristic class, for example, A
Copy processing was performed using class C, class C, and class E photoconductors. The results are shown in FIGS. 42 to 44. Figure 4
2 is the set value of the grid voltage shown in FIG.
It is a figure showing the result of having performed one copy. As can be seen from this figure, in particular, it can be seen that the density unevenness of the first copy image largely changes depending on the lot of the photoconductor, and the grid voltage setting value shown in FIG. 4 cannot cover the difference between lots. .. Similarly, FIG. 43 is a diagram showing a result of continuous multi-five-sheet copying with the setting value of the developing bias voltage shown in FIG. 6, and FIG. 44 is a continuous multi-five-sheet copying with the setting value of the discharge lamp light amount of FIG. It is the figure which showed the result. As can be seen from these figures, it is impossible to obtain an image of stable quality at the initial stage of copying even if the type of photosensitive material is the same and the manufacturing lot is different.

Therefore, the charging condition, the developing condition, and the discharging condition are corrected based on the characteristics of the photoconductor.

FIG. 45 is an example of the correction coefficient of the grid voltage of the charger, FIG. 47 is an example of the correction coefficient of the developing bias of the developing device, and FIG.
Reference numeral 9 indicates an example of the correction coefficient of the static elimination lamp. These correction factors are respectively set according to the characteristic classes (AE) of the photoconductor.
A program was created so as to be multiplied by the grid voltage shown in FIG. 4, the developing bias voltage shown in FIG. 6, and the duty ratio of the charge eliminating lamp shown in FIG. Based on this program, the copying process of continuous multi-five sheets was performed using the photoconductors of the three characteristic classes of A, C, and E. 46, 48,
FIG. 50 is a diagram showing variations in copy image density when the charging condition, the developing condition, and the discharging condition are changed based on the program. As shown in the figure, the density unevenness of the first copy image is small in any copy image formed by any photoconductor lot.

When the characteristic characteristic of the photoconductor mounted on the main body of the copying machine changes due to replacement of the photoconductor or the like, the photoconductor characteristic class (A to E) is input by the switch provided on the main body of the copying machine. FIG. 51 shows a configuration example of a switch for inputting a characteristic class. The CPU takes in information of each photoconductor characteristic class input from this switch at the time of exchanging the photoconductor, and changes the charging condition, the developing condition, the charge eliminating condition and the like based on the information.

In this embodiment shown in the above experimental example, the output change setting of the developing bias voltage is performed up to the fifth rotation of the photosensitive drum, but how many rotations of the photosensitive drum should be changed. The number of rotations is not limited to 5 depending on the information on the residual potential. However, it is sufficient to make a correction up to about 10 rotations.

[0063]

According to the present invention, it is possible to prevent the image density unevenness from occurring at the initial stage of the start of the image forming process, and it is possible to obtain an image of stable quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of a copying machine.

FIG. 2 is a comparative example showing a change in the surface potential of the photoconductor at the initial stage of image formation.

FIG. 3 is a comparative example and is a diagram showing image density unevenness at the initial stage of image formation.

FIG. 4 is a diagram showing an example of grid voltage control at the initial stage of image formation.

FIG. 5 is a diagram showing changes in the surface potential of the photoconductor when the grid voltage is controlled as in FIG.

FIG. 6 is a diagram showing an example of controlling a developing bias voltage at the initial stage of image formation.

FIG. 7 is a diagram showing copy image density unevenness when the developing bias voltage is controlled as in FIG.

FIG. 8 is a diagram showing an example of controlling the duty ratio of the charge eliminating lamp at the initial stage of image formation.

9 is a diagram showing changes in the surface potential of the photoconductor when the duty ratio of the discharging lamp is controlled as shown in FIG.

FIG. 10 is a diagram showing changes in the surface potential of the photoconductor when the control of FIG. 4 is performed when the photoconductor after life aging is used.

11 is a diagram showing changes in the surface potential of the photoconductor when the control of FIG. 6 is performed when the photoconductor after life aging is used.

FIG. 12 is a diagram showing changes in the surface potential of the photoconductor when the control of FIG. 8 is performed when the photoconductor after life aging is used.

FIG. 13 is a diagram showing the life aging dependence of the surface potential of the photoconductor.

FIG. 14: Example of correction coefficient of grid voltage for life aging

FIG. 15 is a diagram showing a photosensitive member surface potential state in life aging when grid voltage is corrected.

FIG. 16 is an example of a correction coefficient of a developing bias voltage for life aging.

FIG. 17 is a diagram showing density unevenness of pixels in life aging when the developing bias voltage is corrected.

FIG. 18 is an example of a correction coefficient of a charge eliminating lamp duty ratio for life aging.

FIG. 19 is a diagram showing a surface potential state in life aging when the duty ratio of the charge eliminating lamp is corrected.

FIG. 20 is a diagram showing a configuration example of a correction coefficient table.

FIG. 21 is a diagram showing the surface potential state when the standby time (standby time) is changed.

FIG. 22 is a diagram showing the surface potential state when the standby time is 5 minutes.

FIG. 23 is a diagram showing image density unevenness when the standby time is 5 minutes.

FIG. 24 is a diagram showing the surface potential state when the standby time is 5 minutes.

FIG. 25 is a diagram showing an example of a correction coefficient of the grid voltage of the charger.

FIG. 26 is a diagram showing an example of a correction coefficient of the developing bias of the developing device.

FIG. 27 is a diagram showing an example of a correction coefficient for the duty ratio of the static elimination lamp.

FIG. 28 is a flowchart showing a copy processing procedure.

FIG. 29 is a diagram showing a configuration example of a correction coefficient table.

FIG. 30 is a diagram showing the surface potential state when the temperature inside the machine changes.

FIG. 31 is a diagram showing a surface potential state at the initial stage of image formation when the temperature inside the apparatus is changed.

FIG. 32 is a diagram showing image density unevenness at the initial stage of image formation when the in-machine temperature is changed.

FIG. 33 is a diagram showing the surface potential state at the initial stage of image formation when the in-machine temperature is changed.

FIG. 34 is a diagram showing an example of a correction coefficient of the grid voltage of the charger.

FIG. 35 is a diagram showing a surface potential state at the time of grid voltage correction.

FIG. 36 is a diagram showing an example of a correction coefficient for the developing bias of the developing device.

FIG. 37 is a diagram showing image density unevenness during development bias voltage correction.

FIG. 38 is a diagram showing an example of a correction coefficient for the duty ratio of the static elimination lamp.

FIG. 39 is a diagram showing the surface potential state when the duty ratio of the static elimination lamp is corrected.

FIG. 40 is a diagram showing a configuration example of a correction coefficient table.

FIG. 41 is a diagram showing the surface potential state when the manufacturing lot of the photoconductor is changed.

FIG. 42 is a diagram showing the surface potential state at the initial stage of image formation when the manufacturing lot of the photoconductor is changed.

FIG. 43 is a diagram showing image density unevenness at the initial stage of image formation when the manufacturing lot of the photoconductor is changed.

FIG. 44 is a diagram showing the surface potential state at the initial stage of image formation when the manufacturing lot of the photoconductor is changed.

FIG. 45 is a diagram showing an example of a grid voltage correction coefficient of a charger.

FIG. 46 is a diagram showing the image density unevenness at the initial stage of image formation when correcting the grid voltage for each manufacturing lot.

FIG. 47 is a diagram showing an example of a developing bias voltage correction coefficient of the developing device.

FIG. 48 is a diagram showing the image density unevenness at the initial stage of image formation during development bias voltage correction, by manufacturing lot.

FIG. 49 is a diagram showing an example of a correction coefficient for the duty ratio of the static elimination lamp.

FIG. 50 is a diagram showing the image density unevenness at the initial stage of image formation when the duty ratio of the static elimination lamp is corrected, by manufacturing lot.

FIG. 51 is a diagram showing a configuration of a photoconductor characteristic input switch.

Front page continuation (72) Inventor Motoyuki Itoyama 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (3)

[Claims] 1. In an electrophotographic image forming apparatus for forming an image using an endless photoconductive photoreceptor, each time the photoreceptor rotates once during the initial rotation of the photoreceptor when the image forming process is started. A device for preventing afterimage of a photoconductor, comprising means for changing a set value relating to an image density of a formed image based on information on a residual potential of the photoconductor. 2. Information relating to the residual potential of the photoconductor, film thickness information of the photoconductor, standby time information when an image is not formed, photoconductor temperature information, and material type information of the photoconductor, An afterimage preventing device for a photoreceptor, which is at least one piece of information on the manufacturing lot of the photoreceptor. 3. The set value relating to the image density of the formed image is
An afterimage preventing device for a photoconductor, which is at least one of a charge amount setting value, a developing amount setting value, and a charge eliminating amount setting value.