JP2597364B2 - 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 a method for stabilizing a uniform charging potential of an electrophotographic photosensitive member that forms an electrostatic latent image due to a difference in charging potential on a surface.

(B) Conventional technology The surface of an electrophotographic photosensitive member used in a copying machine or a laser printer is uniformly charged to a potential of 600 to 800 V before forming an electrostatic latent image, and the charged charge is exposed to an image. To form an electrostatic latent image by light removal. Thereafter, the electrostatic latent image is developed with toner and transferred to paper to produce a printed matter. In the image forming process described above, the uniform charging potential on the surface of the photoreceptor has a great influence on the image quality to be formed. That is, when the potential of the uniform charging is not appropriate, problems such as fogging of the formed image and a decrease in image density occur. In order to stabilize the uniform charging potential and solve the above-mentioned problems, surface potential stabilization methods that irradiate the photoreceptor surface with static elimination light before the uniform charging process and light-fatigue the photoreceptor to some extent are now widely used Have been.

(C) Problems to be Solved by the Invention By the way, the photoreceptor gradually undergoes light fatigue as it is used in an image forming process. I will recover. However, in the conventional surface potential stabilization method by light neutralization, the same amount of neutralizing light is applied at any time during the image forming process. As described above, the photo-fatigue state of the surface of the photoreceptor differs between after a long pause and during continuous operation, and there has been a problem that the uniform charge potential cannot be kept constant by such a static elimination method.

Therefore, a method of changing the amount of static elimination light according to the idle time has been proposed (Japanese Patent Publication No. 4337/1979, Japanese Patent Laid-Open No.
No. 147782). However, none of these proposals proposes control of the amount of static elimination during continuous operation, and there is a problem that it is not possible to cope with a change in the light fatigue state due to continuous operation.

In view of the above problems, the present invention stabilizes the uniform charging potential by changing the amount of static elimination light in accordance with the fatigue characteristics of the photoreceptor due to operation. By doing in between
It is an object of the present invention to provide a method for stabilizing the surface potential of an electrophotographic photoreceptor in which the image quality is prevented from changing during one image forming process.

(D) Means for Solving the Problems The present invention relates to an electrophotographic photoreceptor which stabilizes a charged potential by irradiating a static elimination light to a photoreceptor surface before a uniform charging step performed at the beginning of an image forming process. The surface potential stabilization method, wherein the light amount of the static elimination light is reduced step by step in accordance with the continuous image forming process time, and the time of each step is set so as to gradually increase, the amount of the light amount The switching is performed during the image reading lamp off period immediately after the setting.

(E) Action By irradiating the surface of the photoconductor before the uniform charging step with the charge removing light, the surface potential is stabilized. However, the photoreceptor gradually fatigues as it is used continuously. here,
By using the method for stabilizing the surface potential of the electrophotographic photosensitive member according to the present invention, the amount of static elimination is gradually reduced along with the continuous image forming process operation to compensate for the fatigue of the photosensitive member associated with the continuous operation and keep the surface potential constant. be able to. The setting of the light elimination light amount is performed according to the operation time. However, by switching the light amount during the off period of the image reading lamp immediately after that, the 1
The adverse effect that the image quality changes in a single image can be prevented. In addition, by switching the amount of static elimination light in stages in accordance with the gradually increasing operation time,
Control that follows the fatigue characteristics of the photoreceptor, that is, charges gradually remain from a shallow energy level to a deep energy level, becomes possible.

(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 smaller than the charge amount because the charge amount remaining at the deep energy level remains at the shallow energy level, and the charge amount decreases logarithmically.

Charges remain in order from a shallow energy level.

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

By having such characteristics, the fatigue caused by the use of the photoreceptor progresses by drawing a logarithmic change curve, and the recovery due to the pause also takes into account the progression by drawing a logarithmic change curve. is there. 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 . This causes the charge to remain separate between shallow and deep energy,
During this time, an energy level where no charge remains may occur. 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 described later are stored, and 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 is assigned the operation time, and the vertical axis is assigned the pause interval. 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. Both the operation time and the pause time are divided into ten stages, and the time of each stage is exponentially increased. As a result, the lighting duty ratio due to the elapse of the operation time and the pause time changes logarithmically. This is in accordance with the fatigue / recovery characteristics of the photoconductor. 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 1000 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 1000 seconds on the vertical axis. At the start of the operation, the light elimination light amount 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.
This operation is not performed at the timing when the photoconductor is used (during the exposure operation), and is performed between each exposure operation in the case of the continuous copying operation.

In the case of the above example, for 36 seconds after the elapse of the above-mentioned 20 seconds, the light is illuminated with a discharge light amount of 1/17 (6F), and thereafter, 1/20 (6G: 65 seconds), 1/24.
(6H: 117 seconds), 1/30 (6I: 208 seconds), 1/40 (6J), decrease the amount of static electricity.

(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 pointer. ).
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. 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.

Further, as is clear from the duty ratio table, the irradiation time of the discharge lamp 27 is the same at each discharge light amount (duty ratio) regardless of which stage the discharge light amount is controlled. This is because the fatigue of the photoconductor due to the use of each neutralizing light is the same regardless of the fatigue state at the start of operation.

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 warming-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, and sets "1" to the counter B.
(Ie, 1 is added), and a value of 174 seconds is set in 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. The same operation is performed for n24 to n26 and n28 to n30 when the value of the counter B is "1", "2" and "3", respectively.
Is performed in correspondence with the case of. At this time, 324 seconds, 942 seconds and 2712 seconds are set in the timers, respectively. If the neutralization lamp is turned on while the timer is counting, the above operation is canceled halfway and n32 to n
Go to 5.

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. Similar operations are performed when the counter A is “1” (n35, n39), when the counter A is “2” (n36, 40), 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 the resetting of the flag means that this operation is performed first in the current copying process operation, the flag is set at n7, and the contents of the taunter 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, so the process proceeds to a straight line n8. In n8, it is determined whether the copy lamp is on or off. When the copy lamp is 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 wrap is turned off.
During the continuous copying operation, there is a timing at which the copy lamp is turned off between each copying process.
Perform the operation of n17.

In n9 to n12, the value of the counter A is determined. Counter A
If the value of “1” 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 / 1 /
8) is set, and the contents of the counter A are subtracted by 1 and the section time corresponding to the set static elimination light amount (182 seconds, 56 seconds, 18 seconds, 8 seconds)
After setting, go to n18. In n18 and n19, the counting by this timer is terminated or the process stands by until the static elimination lamp is turned off. After the timer count ends, return from n18 to n5 to determine whether the copy lamp is off (n
8) Set the following static elimination light amount during the copying process. As described above, the setting of the amount of static elimination light is performed by confirming that the copy lamp is off, so that it is possible to prevent the image density from changing during the image forming operation. 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 n19 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.

(G) Effects of the Invention As described above, according to the present invention, the amount of charge removal gradually decreases in accordance with the operation of the continuous image forming process. The potential can be kept constant. In addition, since this control is performed stepwise in accordance with the continuous copying process time, the control load can be reduced as compared with a method in which control is performed for each copying process, and errors due to copy size can be reduced. Can be eliminated. In addition, by setting the time of each step to be gradually longer, it is possible to perform static elimination in accordance with the fatigue characteristics of the photoconductor, and it is possible to always stabilize the surface potential. Further, since the reduction in the amount of static elimination is performed during the OFF period of the image reading lamp after the set value,
Even in the case where continuous image formation with restriction is performed, the image quality can be corrected without changing the image quality in one image forming process, and the image forming operation is not hindered. It should be noted that a correction error caused by not reducing the light elimination light amount during one image forming process is slight.

[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 photoreceptor according to an embodiment of the present invention is used, and FIG. 2 is a diagram showing a duty set on a memory of the copying machine. FIG. 3 is a block diagram showing 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. 27 …… Static lamp

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Kinashi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Yuhi Yui 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp shares In-company (72) Inventor Tadashi Kawabata 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Minao Masuda 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Toru Nakata 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-61-117586 (JP, A) JP-A-57-19969 (JP, A) JP-A 55 -101959 (JP, A) JP-A-55-151652 (JP, A) JP-A-57-185072 (JP, A) JP-A-59-164582 (JP, A) JP-A-58-122565 (JP, A ) Special JP-A-57-14859 (JP, A) JP-A-62-196692 (JP, A) JP-A-58-186753 (JP, A) JP-A-63-191167 (JP, A) JP-A-61-83568 (JP, A) , A) JP 2-55783 (JP, B2) JP 7-109533 (JP, B2) JP 7-109535 (JP, B2) JP 7-109534 (JP, B2) 4-56312 (JP, B2)

Claims (1)

(57) [Claims] 1. A method for stabilizing a surface potential of an electrophotographic photosensitive member, comprising irradiating a static elimination light to a surface of the photosensitive member before a uniform charging step performed at the beginning of an image forming process to stabilize a charging potential. The light amount of the static elimination light is set to decrease stepwise in accordance with the continuous image forming process time, and the time of each step is set to gradually increase, and the switching of the light amount is performed immediately after the image reading lamp off period. A method for stabilizing the surface potential of an electrophotographic photoreceptor.