JP2618009B2 - Method for stabilizing surface potential of electrophotographic photoreceptor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION (a) Industrial Field of the Invention The present invention relates to an image forming apparatus for forming an image using an electrophotographic photoreceptor, and to a method for stabilizing the image quality of a formed image.

(B) Conventional technology The surface of an electrophotographic photosensitive member used in a copier, a laser printer, or the like is first charged uniformly, and then exposed to a document reflected light or the like to form an electrostatic latent image. The image is developed with toner and transferred to paper to form an image. In such an image forming process, a uniform charging potential on the photoreceptor surface has a great influence on the image quality in which the image is formed. That is, if the potential of the uniform charging is not appropriate, problems such as fogging of the formed image and a decrease in image density occur. Therefore, conventionally, a method of stabilizing a charging potential by performing a charging process after a photoreceptor is lightly fatigued to some extent by static elimination light has been widely used.

However, the photo-depletion state of the photoreceptor due to light elimination is affected by the pause time and continuous use time of the photoreceptor, and the longer the pause time, the more light must be irradiated, and the longer the continuous use time. If this is the case, light fatigue is likely to occur, so the amount of static elimination must be reduced accordingly. In view of this, the present inventors have adjusted the amount of static elimination light in Japanese Patent Application No. 62-181696 by changing the duty ratio of the static elimination lamp in accordance with the idle time and the continuous use time.

(C) Problems to be Solved by the Invention Light fatigue of the photoreceptor and its recovery change by drawing a logarithmic curve, and it is desirable that the setting of the light elimination light amount be changed logarithmically. However, the conventional setting of the pause time, the duty ratio according to the continuous use time, and the operation time at the duty ratio is such that when the state of the photoconductor reaches a substantially equilibrium state, for example, the photoconductor is paused for 2 hours (7200 seconds) or more. Since the state of the photoconductor and the state of the photoconductor do not change any more, a logarithmic curve was set based on the time to reach the equilibrium state. Therefore, when the pause time is short, control is started from the middle of the logarithmic curve, which may cause an inconvenience of overcorrection.

For example, FIG. 5 is a duty ratio table of a conventional static elimination lamp. After a rest time of 7200 seconds, a 1/10 duty ratio is 4 seconds → a 1/11 duty ratio is 4 seconds → a 1/12 duty ratio is 6 seconds. ... is performed and the charge removal light amount is set logarithmically, for example, during a pause of 300 seconds, the charge removal is performed suddenly at a 1/20 duty ratio for 65 seconds, and subsequently,
Control is performed at 1/24 duty ratio for 117 seconds. That is, this does not correspond to the logarithmic fatigue curve of the photoconductor, resulting in overexposure.

In view of such inconveniences, the present invention sets the logarithm of the charge elimination amount in response to light fatigue of the photoreceptor and its recovery, so that the surface potential of the electrophotographic photosensitive member can perform charge elimination exposure without overcorrection. It is intended to provide a stabilization method.

(D) Means for Solving the Problems The present invention relates to a method for stabilizing a charging potential by irradiating a static elimination light to the surface of a photoconductor before a charging step to stabilize a charging potential. At the same time as the pause time, the static elimination light during continuous operation is logarithmically reduced from the static elimination light set at the start of operation based on the continuous operation time from the start of operation. At the same time, the setting time is changed so that the section time from when the operation is started to the time when the static elimination light amount is reduced based on the continuous operation time is shortened and gradually increased at the beginning of the operation.

(E) Function If the method for stabilizing the surface potential of the electrophotographic photosensitive member according to the present invention is applied to an image forming apparatus, first, at the time of starting the operation, the amount of static elimination light is set according to the idle time up to that time. When the operation is started, it is set so as to logarithmically decrease from the static elimination light amount set at the start of the operation, corresponding to the continuous operation time from the start of the operation. At the same time as the light elimination light quantity gradually decreases, the operation time from the start of the operation is gradually increased without fixing the time in each section until the charge elimination light quantity decreases as shown in FIG. Like that.
As a result, regardless of the idle time, the amount of static elimination light can be controlled in response to the fatigue of the photoconductor from the start of operation, eliminating the need for over-correction, etc., and stabilizing the charging potential on the photoconductor surface. Can be kept in condition.

(F) Embodiment <1> Principle as Premise of Configuration of Embodiment Hereinafter, a copying machine using a method for stabilizing the surface potential of an electrophotographic photosensitive member according to an embodiment of the present invention will be described with reference to the drawings.

In this embodiment, the charge remaining characteristic on the photoreceptor surface is such that the amount of charge remaining at a deep energy level is smaller than the amount of charge remaining at a shallow energy level, and the amount decreases logarithmically.

Charges remain in order from a shallow energy level.

The remaining charge is released in order from the shallow energy level.

Due to these characteristics, the fatigue caused by the use of the photoreceptor progresses along a logarithmic change curve, and the recovery due to pause also progresses along a logarithmic change curve. Here, the logarithmic change refers to a change in which the degree is initially fast and gradually and gradually becomes gentle. Also, if the photoreceptor is completely fatigued once and is used again without completely recovering from this fatigue, the charge remaining at the deepest energy level is not released, and the charge remains again from the shallow energy level . As a result, the charge may remain separately at shallow energy and deep energy, and there may be a gap between which the charge does not remain. In the photoreceptor thus fatigued, the recovery curve when the charge of the shallow energy level is released and the recovery curve when the charge of the deep energy level is released become discontinuous.

Therefore, in this embodiment, during continuous operation, light fatigue on the surface of the photoreceptor gradually increases with the operation, so that the amount of charge removal before the uniform charging step is gradually reduced. The reduction is performed so as to change logarithmically. This is to correct the photo-fatigue characteristic of the photoreceptor surface, make the fatigue state at the time of charging the same, and stabilize the charging potential. Further, when the next operation is started after the suspension, the amount of charge removal is set to be larger than that at the end of the previous operation, according to the length of the suspension time. At this time, it is set so that the amount of static electricity removed at the start of the previous operation increases in response to the short pause time, and thereafter increases gradually (corresponding to the long pause time). What is necessary is just to set each increase curve of the light elimination light quantity to become a logarithmic curve. This control is performed in accordance with the release characteristics of the charge remaining at the shallow energy level and the charge remaining at the deep energy level.

By performing these controls, it is possible to maintain exactly the same photoconductor surface potential even during continuous operation and after a long pause.

<2> Description of Embodiment Configuration FIG. 3 is a schematic block diagram of a control unit of a copying machine in which a method for stabilizing the surface potential of an electrophotographic photosensitive member according to an embodiment of the present invention is used. The microcomputer 20 for controlling the charge elimination lamp 27 of the photoconductor drum has a ROM 21 in which a control program and a duty ratio table to be described later are stored, counters A to C, flags and a timer in which RA is set.
M22 is connected. Also this microcomputer 2
To 0, a signal input device 25 and a driver array 26 are connected via interfaces 23 and 24. Signal input device
Reference numeral 25 denotes a main control unit which controls the operation of the entire image forming apparatus, and outputs a command to start or stop the operation of the charge removing 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 pulse width control.

FIG. 2 shows an example of a duty ratio table set in the ROM 21. The horizontal axis of this table represents the division during continuous operation, and the vertical axis is assigned a pause time. The lighting duty ratio of the static elimination lamp 27 corresponding to the continuous operation time after each pause time is stored in the table. The pause time is divided into 10 stages, and the time of each of the divided stages is made to increase exponentially. The operation time during the continuous operation is set to increase exponentially in accordance with the pause time. As a result, the lighting duty ratio (light elimination light amount) due to the elapse of the operation time and the pause time
Will change logarithmically. This is due to photoreceptor fatigue
This is in accordance with the recovery characteristics. Further, the lighting duty ratio of the charge removing lamp 27 is set to decrease exponentially as the operation time elapses (that is, the denominator of the duty ratio increases exponentially). This is also adapted to the fatigue / recovery characteristics of the photoreceptor.

<3> Description of the operation of the embodiment Next, the static elimination lamp 27 based on this duty ratio table
Will be described.

(1) During the warm-up after the main switch (power switch) of the copying machine is turned on, the charge removing lamp 27 is turned on with a full light quantity to completely exhaust the photoconductor. This stabilizes the charging voltage at the start of the operation.

(2) When used immediately after this, the lighting duty ratio of the charge removing lamp 27 before the uniform charging step (hereinafter, referred to as “discharge 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 photoreceptor gradually recovers when it is stopped from a completely fatigued state. In order to coincide with this recovery, the amount of charge removal is set to increase according to the pause time. In this case, in the duty ratio table, the stage to be referred to is lowered each time the pause time of each stage on the vertical axis elapses, and the head of each stage is set as the static elimination light amount at the start of the operation.

For example, when the operation is started after the pause of 900 seconds, the static elimination light amount control is performed based on the data of the stage (the sixth stage) corresponding to the pause time of 900 seconds on the vertical axis. The light elimination light amount at the start of the operation is 1/15 (6E: represents the coordinates of the duty ratio table; the same applies hereinafter)).
Lasts for seconds.

(4) Thereafter, each time the section time of the horizontal axis elapses, the line to be referred to is moved to the right every time the section time on the horizontal axis elapses, and the amount of static elimination light is reduced.

In the above example, according to the process of gradually decreasing the amount of static elimination, the time of the section until the decrease is short at the beginning of the operation and gradually longer than at the beginning of the operation. For 8 seconds after the lapse of the above 4 seconds, the light is illuminated with a discharge light quantity of 1/17 (6F), and thereafter 1/20 (6G: 28 seconds), 1/24 (6H: 98).
Seconds), 1/30 (6I: 334 seconds), 1/40 (6J) in order to reduce the amount of static elimination. The section time at this time is set logarithmically for each pause time. For example, even if the duty ratio is 1/20, the pause time is 28 seconds (6G) when the pause time is 900 seconds, and 8 when the pause time is 300 seconds. Set to seconds (4G). As a result, the amount of static elimination changes logarithmically in response to the light fatigue of the photoconductor changing logarithmically.

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

When the previous operation is completed at (6G) as described above, first 1/24 (3H) is set (the setting is made by the counter A
, But the corresponding column of the duty ratio table may be indicated by a point. ).
In other words, the light elimination light amount one step lower than the light elimination light amount at the end of the previous operation is set. This is because, since the control stage of 1/20 (6G) has already been entered in the previous operation, setting 1/20 (4G) first may cause excessive control.

Then, with the elapse of the pause time, (3H) → (4G) →
(5F)->(6E)->(7D)-> (8C)---The amount of static elimination in the first row of each stage is set. Here, up to 1/15 (6E), which is the static elimination light amount at the start of the previous operation, the static elimination light amount is set in the section times corresponding to the first to third stages regardless of the section time originally corresponding to each stage. Will be transferred. That is,
(3H) shifts to 60 seconds (4G), (4G) shifts to 114 seconds (5F), and (5F) shifts to 120 seconds (6E)
Move to. This is because the electric charge released during the previous pause time is a residual electric charge accumulated in the previous operation and is left at a shallow energy level, so that the electric charge is quickly released. This control is called floating time control.

However, during the rest period after this, the photoreceptor recovers slowly to release the charges remaining before the previous operation and trapped in the deep energy level, and the same recovery as when recovering from complete fatigue Show characteristics. Therefore, the light elimination light quantity set thereafter is shifted to each stage in the section time originally corresponding to each stage. That is, (6E) is set, and after 594 seconds elapse, it moves to (7D), and (7D) becomes 1002
After a lapse of seconds (8C). This control is called fixed time control.

As a result, in the above example, 1/12 (8C) is set at the point in time when the operation is resumed after a 30-minute pause.

Here, the counts A to C set in the RAM 12 are set.
The function of the flag and the timer will be described. The counter A is a counter that stores the static elimination light amount that is set based on the continuous operation time or the pause time as described above. The counter B is a counter that stores the section to which the current time belongs while the floating time control is being performed. 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 operating. The timer measures the operating time and the pause time. In the case of the present embodiment, the timer is a timer that subtracts a predetermined section time set in advance.

The operation of the control unit will be described based on the flowchart of FIG. 1 and the duty ratio table shown in FIG.
In this flowchart, control based on a simplified duty ratio table (FIG. 4) in which the operation time and the pause time are divided into five stages for ease of description will be described. When the main switch is turned on and the operation starts, initial processing is performed at n1. Thereafter, the process waits until the rotation of the photoconductor drum starts (n2), and when the photoconductor starts rotating for warm-up, the static elimination lamp 27 (the static elimination lamp is referred to as PFL in this flowchart) is turned on at full duty (n3). ). This lighting is continued until the photosensitive drum stops (n4). This causes the photoreceptor to be completely exhausted once. Thereafter, the apparatus becomes operable, and performs the operation of n20 or less until it is determined that the user has started the operation (reception of the charge removal lamp ON command) (n5).

At n20, the counter B and the flag for storing the pause time interval are reset. Next, it is determined whether or not the counter A for storing the amount of static elimination light is "4". If the counter A is "4", the control level does not increase any more due to the pause, and the process returns to n5 and waits until the operation starts. I do. If the content of the counter A is smaller than "4", the operation proceeds to n22 or less. n22
Then, it is determined whether or not the content of the counter C storing the amount of static elimination light at the start of the previous operation is the same as the content of the counter A storing the current amount of static elimination light. If not identical (if the content of counter A is smaller) n23
To n33, and if they are the same, the operation proceeds to n34 and below. n23
The operations of .about.n33 are floating time control, and the operations of n34.about.n44 are fixed time control.

In the floating time control of n23 or less, the value of the counter B reset at n20 is determined. When the counter B is "0", the process proceeds from n23 to n27, where "1" is set to the counter B (that is, 1 is added), and a value of 174 seconds is set to the timer (n27). Thereafter, in steps n31 and n32, the process waits until the counting of this timer is completed or the neutralization lamp is turned on (copying operation starts). When the counting by the timer is completed, it means that one section time of the suspension time has elapsed, so that 1 is added to the counter A in n33 to increase the amount of static elimination by one step, and then the process returns to n21. n24 to n26 and n28 to n30 perform the same operation when the value of the counter B is "1", "2" and "3", respectively. At this time, 324 seconds, 942 seconds and 2712 seconds are set in the timers, respectively. If the neutralization lamp is turned on during the counting of the timer, the above operation is canceled on the way and the process proceeds from n32 to n5.

On the other hand, in the fixed time control operation of n34 to n44, the aforementioned n23 to n23
The same operation as the operation of 33 is performed. That is, when the content of the counter A is "0", the process proceeds from n34 to n38, the timer is set to 174 seconds, and the process proceeds to n42 or less. In steps n42 and n43, similarly to the steps n31 and n32, the process waits until the count of the timer is completed or the neutralization lamp is turned on. When the count of the timer is completed, 1 is added to the counter A to increase the neutralization 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 becomes "4", the control level does not increase even if the pause time continues any longer.
Then, it is determined whether or not the static elimination lamp is turned on (copying operation is started).

On the other hand, when the copying operation is started and the neutralization lamp is turned on, the process proceeds from n5 to n6. In n6, setting / resetting of a flag is determined. Since resetting the flag means that this operation is performed first in the current copy process operation, the flag is set at n7, and the contents of the counter A (the amount of charge removed at the start of the operation) at this time are stored in the counter C.
Proceed to n8. When the flag is set, this operation has already been performed in the current copy process operation, and the process directly proceeds to n8. In n8, it is determined whether the copy lamp is on or off. When the copy lamp is turned on, the image forming operation is being performed, and if the amount of static elimination is changed in the middle, the image quality changes in one image. Therefore, the process waits at n5, n6, and n8 until the copy lamp is turned off. During the continuous copying operation, the copy lamp is turned off between each copying process.
The operations of n9 to n12 and n50 to n70, that is, the setting of the amount of static elimination in the continuous operation are performed.

In n9 to n12, the value of the counter A is determined. Counter A
Is "0", the photo-fatigue of the photoconductor has almost reached the saturated state, and it is not necessary to further reduce the amount of charge removal (duty ratio). Therefore, the duty ratio is set to 1/40 and the timer value is infinite. Set to large and go to n71. When the value of the counter A is "1" to "4", the process proceeds to n51 to n70, the corresponding static elimination light quantity (duty ratio) is set, and the content of the counter A is decremented by one to correspond to the static elimination light quantity. After setting the section time to be performed, the process proceeds to n71.

For example, when the value of the counter A is "1" (n10), the duty ratio of the static elimination light amount is set to 1/20, and the counter A
Is subtracted by 1 (n51), and a timer value is set according to the contents of the counter B (n52 to n54) (n55 to n58). That is, the duty ratio and the section time are set logarithmically in accordance with the light fatigue of the photoconductor. Similarly, if the value of the counter A is 2, the duty ratio is set at (n11) n59 and the section time is set at n60 to n64.
If the value of is 3, the duty ratio at (n12) n65 is
The interval time is set in n66 to n68, and if the value of the counter A is 4, the duty ratio is set in n69 and the interval time is set in n70.

In steps n71 and n72, the counting by this timer is terminated or the process stands by until the static elimination lamp is turned off. When the counting of the timer is completed, the process returns from n71 to n5 to determine whether the copy lamp is off (n8), and then sets the next light elimination light amount during the copying process. If the neutralizing lamp is turned off during the counting of the timer, it is determined that the copying operation has been completed, and the operation proceeds to n20 or less.

When the copying operation is started, the discharging lamp is turned on first, and the copying lamp is turned on when other preparation operations are completed.Therefore, in the first operation, the operation always goes through n5, n6, n7 and n8. Operations below n9 are performed. Here, after the static elimination light amount is set based on the content of the counter A set at that time, the content of the counter A is decremented by one, so that the operation ends with only one copying process and the static elimination lamp is turned off. The amount of static electricity is 1
With the step lowered, the operation goes from n72 to n20. In other words, even when the copying process operation is completed without performing the continuous operation time for a short copying work and the continuous operation time elapses, the photoconductor is tired by the operation, and the fatigue of the photoconductor accompanying the operation is considered. Otherwise, the amount of static elimination is too large, resulting in lower image quality. For this reason, the counter A at the end of the operation is set to a discharge light quantity one step lower than the discharge light quantity during the operation.

In this embodiment, the continuous operation time, the pause time, and the amount of charge removal are divided and controlled stepwise, but may be controlled steplessly for each image forming process. In this case, the operation 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 operation time and the pause time as variables.

In this embodiment, the surface potential is stabilized and the image quality is improved by controlling the amount of static elimination according to the pause time and the continuous operation time. However, the exposure light amount, the charging potential, and the developing potential are controlled according to the pause time and the continuous operation time. The image quality can be improved by controlling the bias potential and the like.

(G) Effects of the Invention As described above, according to the present invention, the amount of static elimination during continuous operation is set logarithmically according to the light fatigue characteristics of the photoconductor, so that excessive control does not occur and the photoconductor is not affected. , And a good image formation can be performed.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the operation of a control unit of a copying machine in which a method for stabilizing the surface potential of a photosensitive member according to an embodiment of the present invention is used, and FIG. 2 is a duty ratio set on a memory of the copying machine. 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 description of the operation. FIG. 5 shows a conventional duty ratio table. 27 …… Static lamp

Claims (1)

(57) [Claims] 1. A method for stabilizing a charging potential by irradiating a charge erasing light to a surface of a photoreceptor before a charging step, the method comprising: In addition to setting according to the time, the static elimination light quantity during continuous operation is gradually decreased logarithmically from the static elimination light quantity set at the start of operation based on the continuous operation time from the start of operation, and at the same time, from the start of operation. A method for stabilizing the surface potential of an electrophotographic photosensitive member, wherein the section time until the amount of charge removal based on the continuous operation time is reduced is gradually shortened at the beginning of the operation.