JPH07109534B2 - Method for stabilizing surface potential of electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for stabilizing a uniform charging potential of an electrophotographic photosensitive member which forms an electrostatic latent image due to a difference in charging potential on the surface.

(B) Conventional Technology The surface of an electrophotographic photosensitive member used in a copying machine, a laser printer, etc. is uniformly charged to a potential of 600 to 800 V before an electrostatic latent image is formed, and the charged electric charge exposes the image. The light is discharged to form an electrostatic latent image. After that, the electrostatic latent image is developed with toner and transferred to a sheet to form a printed matter. In the image forming process as described above, the uniform charging potential on the surface of the photoconductor has a great influence on the formed image quality. That is, if the potential of uniform charging is not appropriate,
Problems such as background fog on the formed image and reduction in image density occur. In order to stabilize the uniform charging potential and solve the above problems, a surface potential stabilization method is used widely in the prior art in which static electricity is radiated to the surface of the photoconductor before the uniform charging process to photo-fatigue the photoconductor to some extent. Has been.

(C) Problems to be Solved by the Invention By the way, the photoconductor gradually suffers light fatigue as it is used in the image forming process, and the light fatigue is gradually reduced by not using the photoconductor. I will recover. However, the conventional method of stabilizing the surface potential by photo-electrification irradiates the same amount of light-eliminating light at any time during the image forming process. As described above, the photo-fatigue state of the surface of the photoconductor is different between after a long rest and during continuous operation, and there is a problem that the uniform charging potential cannot be kept constant by such a static elimination method.

Therefore, conventionally, a method of changing the amount of static elimination light according to a pause time is disclosed in Japanese Patent Publication No. 49-4337, Japanese Patent Publication No. 57-4337, Japanese Patent Publication No. 57-147782, Japanese Patent Publication No. 55-151652. Is proposed. However, these documents do not describe what kind of control is specifically performed according to the length of the rest time, and it is impossible to apply it to an actual device as it is.

On the other hand, a method of converting the rest time exponentially (logarithmically) to control the amount of static elimination light and the bias potential is disclosed in Japanese Patent Laid-Open No. 57-185072.
Although it is described in Japanese Patent Publication No. 59-164582,
In these methods, the control contents were the same at the beginning and after the rest time.

However, the process of releasing the residual charge of the photoconductor has a characteristic that it is released from a large charge trapped in a shallow energy level, and then released a small charge trapped in a deep energy level. However, in the above-mentioned conventional control method, since control is not performed according to this characteristic, there is a problem in that the set amount of static elimination light does not follow the degree of fatigue recovery of the photoconductor and proper control is not performed.

In view of the above problems, the present invention is an electrophotographic photosensitive member that stabilizes the potential of uniform charging by changing the amount of static elimination light according to the fatigue and recovery characteristics of the photosensitive member due to downtime and continuous operation. It is an object of the present invention to provide a method for stabilizing the surface potential of

(D) Means for Solving the Problems In the present invention, the light fatigue due to the use of the surface of the photoconductor shows a logarithmic change curve, and the recovery due to rest is moderately logarithmic change in the first half that is rather sharp in the first half. It was made with a focus on drawing a curve.

The change in the surface state of the photoconductor as described above is due to the following charge residual properties of the photoconductor. That is, the amount of charges remaining in the deep energy level is smaller than the amount of charges remaining in the shallow energy level, and the amount decreases logarithmically.

The electric charge remains in order from a shallow energy level.

Residual charges are released in order from shallow energy levels.

Due to such characteristics, fatigue due to use of the photoconductor progresses in a logarithmic change curve, and recovery by rest also progresses in a logarithmic change curve. Here, the logarithmic change refers to a change that is initially fast and gradually slows. Also, if the photoconductor is completely exhausted and is used again without this fatigue being completely recovered, the charges remaining in the deepest energy level will not be released, and the charges will remain from the shallow energy level again. . As a result, the electric charge may remain in the shallow energy and the deep energy separately, and an energy level in which the electric charge does not remain may occur between them. In the photoconductor thus fatigued, the recovery curve when the electric charge of the shallow energy level is released and the recovery curve when the electric charge of the deep energy level is released become discontinuous.

Focusing on these points, the present invention logarithmically reduces the charge removal light amount of the photoconductor according to the continuous operation time during the image forming operation, and starts the next operation as the pause time elapses during the pause. A method of stabilizing the surface potential of an electrophotographic photoconductor that increases the amount of static elimination light of the photoconductor during the rest time, until the amount of static elimination light reaches the amount of static elimination light at the start of the previous operation during the rest time. It is characterized in that it is increased at a ratio larger than the corresponding logarithmic ratio, and thereafter, it is logarithmically increased according to the light amount value set at that time.

(E) Action In the method of stabilizing the surface potential of the electrophotographic photosensitive member of the present invention,
During continuous operation, the light fatigue on the surface of the photoconductor gradually increases with the operation, so the amount of static elimination light before the uniform charging step is gradually decreased. The amount of reduction is logarithmically changed. This is because the photo-fatigue property of the surface of the photoconductor is corrected so that the fatigue state at the time of charging is the same and the charging potential is stabilized.

Further, when the next operation is started after the suspension, the amount of static elimination light is determined according to the following rule according to the length of the suspension time until then.

(A) Based on the amount of static elimination light immediately before stopping, (b) multiplying the maximum amount of static elimination light for the first fixed time of the pause time to increase the amount of static elimination light, and (c) for the rest time thereafter. It is logarithmically increased according to the set light intensity value.

This control is performed in accordance with the release characteristics of the electric charge remaining in the shallow energy level and the electric charge remaining in the deep energy level.

By performing these controls, it is possible to maintain the same photoreceptor surface potential during continuous operation and after a long rest.

(F) Embodiment FIG. 3 is a schematic block diagram of a control unit of a copying machine in which the method of stabilizing the surface potential of the electrophotographic photosensitive member according to the embodiment of the present invention is used. A microcomputer 20 for controlling the charge eliminating lamp 27 of the photosensitive drum is provided with a ROM 21 in which a control program and a duty ratio table described later are stored and a RAM 2 in which counters A to C, flags and timers are set.
2 is connected. Also this microcomputer 20
A signal input device 25 and a driver array 26 are connected to the interface via interfaces 23 and 24. Signal input device
Reference numeral 25 includes a main control unit that controls the operation of the entire image forming apparatus, and outputs a command to start or stop the operation of the static elimination lamp 27. The driver array 26 is a device for lighting the static elimination lamp 27, and the duty ratio of lighting can be increased or decreased by controlling the pulse width.

FIG. 2 shows an example of the duty ratio table set in the ROM 21. The horizontal axis of this table is assigned the operating time, and the vertical axis is assigned the rest time. In the table, the lighting duty ratio of the static elimination lamp 27 corresponding to the continuous operation time after each rest time is stored. Both operating time and rest time are divided into 10 stages, and the time of each divided stage is designed to increase exponentially. As a result, the lighting duty ratio changes logarithmically with the passage of the operating time and the rest time. This is in accordance with the fatigue / recovery characteristics of the photoconductor. Furthermore, the lighting duty ratio of the static elimination lamp 27 is set to decrease exponentially as the operating time elapses (that is, the denominator of the duty ratio increases exponentially). This is also adapted to the fatigue / recovery characteristics of the photoconductor.

Next, a method of controlling the static elimination lamp 27 based on this duty ratio table will be described.

(1) During the warm-up period after the main switch (power switch) of the copying machine is turned on, the static elimination lamp 27 is turned on with a full amount of light to completely exhaust the photoconductor. by this,
Stabilize the charging voltage at the start of operation.

(2) When used immediately after this, the lighting duty ratio of the static elimination lamp 27 before the uniform charging step (hereinafter referred to as "static elimination light amount") is 1/40. This is because it is not necessary to irradiate a large amount of light because the photoconductor is completely fatigued.

(3) The photosensitive body gradually recovers when the complete fatigue state is stopped. In order to match this recovery, the amount of static elimination light is set to increase according to the rest time. In this case, in the duty ratio table, the stage to be referred to is lowered every time the quiescent time of each stage on the vertical axis elapses, and the head of each stage is set as the amount of static elimination light at the start of operation.

For example, when the operation is started after a pause of 1000 seconds, the static elimination light amount control is performed based on the data of the stage (sixth stage) corresponding to the pause time of 1000 seconds on the vertical axis. The amount of static elimination light at the start of operation is 1/15 (6E: represents the coordinates of the duty ratio table. The same applies below)), and control by this static elimination light amount is 20
It lasts for a second.

(4) Thereafter, the row to be referred to is moved to the right every time the section time on the horizontal axis elapses by continuous operation to decrease the amount of static elimination light.

In the case of the above example, the static elimination light amount is 1/17 (6F) for 36 seconds after the lapse of 20 seconds, and then 1/20 (6G: 65 seconds), 1/24
(6H: 117 seconds), 1/30 (6I: 208 seconds), 1/40 (6J), the amount of static elimination light decreases in this order.

(5) A method of controlling the amount of static elimination light in the case where the operation is restarted after a short pause after use will be described. Here, the previous operation is (6
From E) to (6G), the case where the operation is restarted after a pause for 30 minutes (1800 seconds) will be described. In addition, during the pause, the amount of static elimination light when the operation is restarted at that time is set.

As described above, when the previous operation is completed at (6G), 1/24 (3H) is set first (setting is performed by storing in the counter A, but the corresponding column of the duty ratio table is It may be indicated by a pointer.). That is, the amount of static elimination light that is one step lower than the amount of static elimination light at the end of the previous operation is set. This is because the control phase of 1/20 (6G) has already been entered in the previous operation.
This is because setting 1/20 (4G) may result in over-control.

Then, as the rest time elapses (3H) → (4G) →
(5F) → (6E) → (7D) → (8C) →… The amount of static elimination light on the first line of each stage is set. By this process, the amount of static elimination light increases logarithmically. Here, up to 1/15 (6E), which is the amount of static elimination light at the start of the previous operation, the amount of static elimination light is set at the segment time corresponding to the first to third stages, regardless of the segment time originally corresponding to each stage. Will be transferred. By this processing, the amount of static elimination light increases at the maximum increase rate. That is, at (3H)
After 60 seconds has passed, it shifts to (4G), and at (4G) 114 seconds have passed (5
Move to (F), and after (5F) 120 seconds, move to (6E). This is because the electric charge released during the pause time so far is the residual electric charge accumulated in the previous operation and remains in the shallow energy level, so that the electric charge is promptly released. This control is called floating time control.

However, in the rest period after this, the recovery of the photoconductor slows down because the electric charge remaining from before the previous operation and trapped in the deep energy level is released, and the recovery is the same as when recovering from complete fatigue. Show the characteristics. Therefore, the amount of static elimination light set thereafter is adapted to shift in the section time originally corresponding to each stage. In other words, after (6E) is set and 594 seconds have passed, it moves to (7D), and in (7D) 1002 seconds has passed, it moves to (8C). This control is called fixed time control.

As a result, in the above example, 1/12 (8C) is set when the operation is restarted after a 30-minute rest.

Further, as is clear from the duty ratio table, no matter which stage the static elimination light amount is controlled on, the time for which the static elimination lamp 27 is irradiated with each static elimination light amount (duty ratio) is the same. This is because the fatigue of the photoconductor due to use is the same regardless of the fatigue state at the start of operation.

Here, the functions of the counts A to C, the flag and the timer set in the RAM 12 will be described. The counter A is a counter that stores the amount of static elimination light set based on the continuous operation time or the rest time as described above. The counter B is a counter that stores the section to which it currently belongs while performing the floating time control. The counter C is a counter that stores the amount of static elimination light at the start of the previous operation. The flag is for storing that the copying machine is in operation. Further, the timer measures the operating time and the rest time, but in the case of the present embodiment, it is a timer that subtracts a predetermined section time set in advance.

The operation of the control unit will be described based on the flow chart of FIG. 1 and the duty ratio table shown in FIG. In this flowchart, the control based on the simplified duty ratio table (FIG. 4) by dividing the operating time and the rest time into five stages will be described for ease of explanation. When the main switch is turned on and the operation starts
Initial processing is performed with n1. After that, it stands by until the rotation of the photoconductor drum starts (n2), and when the photoconductor starts to rotate for warming up, the charge eliminating lamp 27 (the charge eliminating lamp is referred to as PFL in this flowchart) is turned on at full duty. (N3). This lighting continues until the photosensitive drum stops (n4). As a result, the photoconductor is completely exhausted. After this, this device becomes operable, and the operation of n20 and below is performed until it is judged by the user that the operation has started (reception of the discharge lamp ON command) (n5).

At n20, the counter B that stores the interval of the pause time and the flag are reset. Next, it is judged whether or not the counter A, which stores the amount of static elimination light, is "4". If it is "4", the control level will not rise anymore due to the rest, so it will return to n5 and wait until the operation starts To do. If the content of the counter A is smaller than "4", the operation proceeds to n22 and below. At n22, it is determined whether or not the content of the counter C that stores the amount of static elimination light at the start of the previous operation is the same as the content of the counter A that stores the current amount of static elimination light. If they are not the same (if the content of counter A is smaller), n23 to n
If it is the same, the process proceeds to n34 and below. n23 to n3
The operation of 3 is a floating time control, and the operation of n34 to n44 is a fixed time control.

In the floating time control of n23 or less, the value of the counter B reset in n20 is determined. When the counter B is “0”, the process advances from n23 to n27, sets the counter B to “1” (that is, 1 is added), and sets the value of 174 seconds to the timer (n
27). Thereafter, at n31 and n32, the process waits until the count of this timer ends or the charge elimination lamp turns on (the copying operation starts). If the timer finishes counting, it means that one interval of the rest time has elapsed.
At n33, 1 is added to the counter A to increase the amount of static elimination light by one step, and then the process returns to n21. In n24 to n26 and n28 to n30, the same operation is performed correspondingly when the value of the counter B is 1 "1", "2" and "3", respectively. At this time, 324 seconds, 942 seconds and 2712 seconds are set in the timers. If the charge removal lamp is turned on while the timer is counting, the above operation is canceled and the process proceeds from n32 to n5.

On the other hand, in the fixed time control operation of n34 to n44, based on the contents of the counter A which stores the amount of light to be removed,
Performs the same operation as. That is, when the content of the counter A is "0", the process proceeds from n34 to n38, sets 174 seconds in the timer, and proceeds to n42 and below. At n42 and n43, as in the case of n31 and n32, the process waits until the count of the timer ends or the static elimination lamp is turned on, and when the count of the timer ends, 1 is added to the counter A to increase the static elimination light amount by one level (n4
4) Return to n34, and when the static elimination lamp is turned on, return from n43 to n5. The same operation is performed when the counter A is "1" (n35, n39), when the counter A is "2" (n36, n40), and when the counter A is "3" (n37, n41). ,
When the content of the counter A reaches "4", the control level does not rise even if the pause time continues for more than n5.
Then, it is judged whether or not the static elimination lamp is turned on (copy operation is started).

On the other hand, when the copying operation is started and the static elimination lamp is turned on, the process proceeds from n5 to n6. At n6, it is determined whether the flag is set or reset. Since resetting the flag means that this operation is performed first in the copy process operation this time,
The flag is set at n7, the contents of the taunter A (the amount of static elimination light at the start of operation) at this time are stored in the counter C, and then the process proceeds to n8. When the flag is set, this operation has already been performed in this copy process operation, so the process directly proceeds to n8. At n8, it is determined whether the copy lamp is on or off. When the copy lamp is on, the image forming operation is in progress, so if the amount of static elimination light is changed midway, the image quality will change in one image, so the process waits at n5, n6, and n8 until the copy lap is turned off. During the continuous copying operation, there is a timing when the copy lamp is turned off between the copying processes, and therefore the operation is performed at n9 to n17 at that time.

At n9 to n12, the value of the counter A is judged. When the value of the counter A is "1" to "4", the process proceeds to n14 to n17, and the corresponding static elimination light amount (duty ratio (1 / 20,1 / 13,1 / 10,1 / 8)
Is set, and the section time (182 seconds, 56 seconds, 18 seconds, 8 seconds) corresponding to the set charge removal light amount is set by subtracting 1 from the content of the counter A, and then the process proceeds to n18. At n18 and n19, the timer is finished counting or waits until the static elimination lamp is turned off. N18 to n5 when the timer finishes counting
After returning to the OFF state of the copy lamp (n8), set the next charge removal light amount between copying processes. When the charge eliminating lamp is turned off while the timer is counting, it is assumed that the copying operation is completed, and the operation proceeds to n20 and below.

It should be noted that when the copying operation is started, the static elimination lamp is turned on first and the copy lamp is turned on when the other preparatory operations are completed.Therefore, n5, n6, n7 and n8 are always passed through in the first operation. Operations of n9 and below are performed. Here, after the charge removal light amount is set based on the content of the counter A that is set at that time, the content of the counter A is decremented by 1, so that the operation ends with only one copying process and the charge removal lamp is turned off. Even if it is removed, the amount of static elimination light is 1
You will be able to move from n19 to n20 in the lowered state. That is, even if the copying process operation is completed without a continuous operation time such that a short copying operation is performed and the section time elapses, the photoreceptor is fatigued by the operation, and the fatigue of the photoreceptor is considered. If this is not done, the amount of charge removal light will be too large and the image quality will deteriorate. For this reason, the counter A at the end of the operation is set to the amount of static elimination light that is one step lower than the amount of static elimination light during operation.

In this embodiment, the continuous operation time, the rest time, and the amount of static elimination light are divided and controlled stepwise, but it is also possible to control steplessly for each image forming process. In this case, the operating time and the control level, and the pause time and the control level may be expressed as specific functions, and the control level may be calculated using the operating time and the pause time as variables.

(G) Effect of the Invention As described above, according to the present invention, since the amount of static elimination light gradually decreases with continuous operation, the fatigue of the photoconductor due to the operation is corrected and the charging potential of the photoconductor surface is constantly kept constant. Can be kept at Furthermore, if there is a pause between operations, the fatigue of the photoconductor gradually recovers due to this pause, so it is necessary to correct the degree of this recovery and set the amount of charge removal light to increase. Therefore, the potential on the surface of the photoconductor can be kept constant.

In this case, the above-mentioned correction can be performed more accurately by changing the reduction of the amount of static elimination light associated with the continuous operation and the increase of the amount of static elimination light associated with the rest time logarithmically according to the characteristics of the photoconductor. became. In particular, when the electric charge remains in the deep energy level and then the electric charge remains in the new shallow energy level, the increase of the charge removal light amount during the rest time is made into two stages. This better approximates a complex charge release system and keeps the surface potential of the photoconductor constant to maintain good image quality.

[Brief description of drawings]

FIG. 1 is a flow chart showing the operation of a control unit of a copying machine in which the method for stabilizing the surface potential of a photosensitive member according to an embodiment of the present invention is used. FIG. 2 is a duty set on the memory of the copying machine. FIG. 3 is a diagram showing a ratio table, FIG. 3 is a block diagram of a control unit of the copying machine, and FIG. 4 is a diagram showing a simplified duty ratio table for facilitating the explanation of the operation. 27 ... Static elimination lamp

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kinashi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Yuhi Yui 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Satoshi Kawabata 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture (56) References JP-A-55-151652 (JP, A) JP-A-55-101959 (JP, A) JP-A-57-185072 (JP, A) JP-A-59-164582 (JP, A) Kaisho 61-117586 (JP, A)

Claims (1)

[Claims] 1. An image forming operation logarithmically reduces the amount of static elimination light of a photosensitive member according to the continuous operation time, and during a rest,
A method of stabilizing the surface potential of an electrophotographic photoconductor that increases the amount of static elimination light of the photoconductor at the start of the next operation as the pause time elapses. Until that time, the electrophotographic photosensitive member is characterized in that it is increased at a rate larger than the logarithmic ratio according to the light amount value at that time, and thereafter it is logarithmically increased according to the light amount value set at that time. A method for stabilizing the body surface potential.