JP2007034051A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is capable of suppressing waste of toner and the increase of waste toner by reducing a discharge amount of toner other than highly charged toner which may bring about poor charging, out of toner in a developing device by a refresh means. <P>SOLUTION: In the image forming apparatus having a refresh process of discharging residual toner in a developing device 11 out of the developing device 11, the refresh process is executed after fresh toner is replenished into the developing device 11. Otherwise the refresh process is executed without replenishing fresh toner into the developing device 11, under a prescribed condition, and the refresh process is executed after replenishing fresh toner into the developing device 11, under a specific condition other than the prescribed condition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using a two-component developer.

  In an image forming apparatus using a two-component developer, if toner that does not contribute to development due to deterioration is accumulated in the developing device, a charging failure may occur, leading to image formation defects such as fogging. In particular, when the printing rate of the formed image is low, the amount of toner flying from the developing device to the image carrier (for example, a photosensitive drum) is small, and the toner is repeatedly charged in the developing device. As a result, problems such as the generation and accumulation of deteriorated toner and the occurrence of charging failure associated with it become prominent.

In order to solve the above problems, Patent Document 1 provides an image forming apparatus provided with a refresh process that periodically discharges deteriorated toner in the developing device to the outside of the developing device during non-image formation. Has been.
JP 2003-195607 A

However, in the above image forming apparatus, when the refresh process is executed, not only the deteriorated toner in the developing device but also the toner that has not deteriorated is discharged to the outside of the developing device. Therefore, there is a possibility that another problem such as waste of toner and increase of waste toner may occur.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus in which the amount of toner discharged other than deteriorated toner is reduced and the waste of toner and the increase in waste toner are suppressed when the refresh process is executed. .

In order to achieve the above object, the present invention provides:
(1) A developer carrying member that transports toner to a developing region and an electrostatic latent image carrying member arranged to face the developer carrying member, and on the developer carrying member during non-image formation In the image forming apparatus capable of executing a refreshing process for transporting toner to the electrostatic latent image carrier and refreshing the surface of the developer carrier, the refreshing process is performed by supplying unused toner in the developing unit. An image forming apparatus, which is executed later;
(2) a developer carrying member that transports toner to the development area; and an electrostatic latent image carrying member arranged to face the developer carrying member, and on the developer carrying member during non-image formation In an image forming apparatus capable of executing a refresh process for transporting toner to the electrostatic latent image carrier and refreshing the surface of the developer carrier, the refresh process is not performed in the developer under a predetermined condition. An image forming apparatus that is executed without being replenished with used toner, and that is executed after replenishing unused toner in the developing unit under a specific condition different from the predetermined condition. ,
(3) A blank image forming process is executed after the refresh step, and the refresh step is executed again when the image density of the obtained blank image does not satisfy a preset condition. The image forming apparatus according to (1) or (2),
Is to provide.

  Since the unused toner has a higher charging ability than that of the deteriorated toner and has a large electrostatic adhesion force to the carrier, the unused toner is replenished in the developing device before the refreshing process of the surface of the developer carrying member. Thus, most of the surface of the carrier can be coated with unused toner. In addition, as a result, the deteriorated toner has less electrostatic action with the carrier and is less likely to be restrained by the carrier, so that the deteriorated toner is easily transferred from the developing device to the image carrier.

Therefore, according to the image forming apparatus of the present invention, it is possible to efficiently discharge the deteriorated toner in the developing device in the refreshing process of the surface of the developer carrying member. While being suppressed, it is possible to suppress the occurrence of charging defects accompanying the repetition of the image forming process.
Furthermore, by performing the operation of replenishing unused toner into the developing device only under specific conditions before executing the refreshing process on the surface of the developer carrying member, the discharge efficiency of deteriorated toner and the amount of unused toner can be reduced. It is possible to balance the efficiency of the image forming process accompanying the replenishment operation.

The image forming apparatus of the present invention includes a developer carrying member that conveys toner to a developing region, and an electrostatic latent image carrying member that is disposed to face the developer carrying member. A refreshing step can be performed in which the toner on the developer carrier is transported to the electrostatic latent image carrier to refresh the surface of the developer carrier.
In the image forming apparatus of the present invention, the refreshing step is executed after the unused toner is replenished in the developing unit, or the unused toner is put in the developing unit under a predetermined condition. The refresh process is performed without replenishment, and under a specific condition different from the predetermined condition, the refresh process is performed after the unused toner is replenished in the developer.

Hereinafter, an image forming apparatus of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
An image forming apparatus 10 shown in FIG. 1 includes a developing unit 11, a developing roller (developer carrying member) 12 that is disposed in the developing unit 11 and carries a developer on the surface thereof, and is not installed in the developing unit 11. Toner replenishing means 13 for replenishing used toner, a stirring roller 14 for stirring the developer in the developing device 11, and a photosensitive drum (electrostatic latent image) on which an electrostatic latent image and a toner image are carried. An image carrier 15, a charging roller 16 for applying a voltage to the surface of the photosensitive drum 15, an exposure device 17 for exposing the surface of the photosensitive drum 15 in accordance with a formed image, and the photosensitive drum 15. A transfer roller 18 for transferring the toner image formed on the transfer body 19, a control unit 20 for executing a refreshing process, a reading unit 21 for reading a document of a formed image, and a photoconductor Formed on drum 15 A concentration sensor 22 for measuring the concentration of toner image, is provided.

The control unit 20 includes a number counter 23 that counts the number of printed sheets and a timer 24 that counts the driving time of the developing roller 12.
The reading unit 21 is provided with a printing rate measuring means 25 for measuring the printing rate (printing density) of the formed image.
The control unit 20
(A) An average calculated based on the number n of prints counted by the number counter 23 reaches a preset threshold, and the print rate P measured by the print rate measuring means 25. When the printing rate <P> falls below a preset value P ₀ , unused toner is supplied from the toner hopper 13 into the developing device 11, and the developer in the developing device 11 is stirred by the stirring roller 14. While the toner on the developing roller 12 is conveyed to the photosensitive drum 15 to refresh the surface of the developing roller 12;
(B) When the number n of printed sheets reaches the preset threshold value and the average print rate <P> is lower than the preset value P ₀ , and the average print rate <P> is continuously set to the preset value. P ₀ and less than the number N, and the when reaching a preset threshold, the (a) and similarly, the unused toner replenishment, agitation of the developer, and the refresh operation of the developing roller 12 surface, On the other hand, when the number N of times does not reach the preset threshold value, the process of refreshing the surface of the developing roller 12 by omitting the replenishment of unused toner, and
(C) After the refresh operation of the developing roller 12, the blank image is output, the image density of the blank image is measured, and when the occurrence of fog is detected, the process of refreshing the surface of the developing roller 12 again.
Is to execute.

When unused toner is replenished in the developing device 11, an aging operation of the developer is performed, and a refresh operation of the surface of the developing roller 12 described later is performed. The aging operation of the developer means that the developer in the developing device 11 and the replenished unused toner are stirred by the stirring roller 14 for a predetermined time.
The aging time until the refresh operation is performed is not particularly limited, and may be set as appropriate according to the amount of developer stored in the developing unit 11, the cumulative value of the number of printed sheets n, the history of the average printing rate <P>, and the like. Although not limited to this, in general, the aging operation may be performed for about 30 seconds.

  Since the unused toner replenished in the developing device 11 has a higher charging ability than the deteriorated toner remaining in the developing device 11, the developer in the developing device 11 is agitated after the unused toner is replenished. The surface of the carrier is occupied with unused toner. In addition, as a result, the unused toner is strongly restrained by the carrier, while the deteriorated toner can reduce the restraining force from the carrier, that is, can be in a semi-floating state. Therefore, it is possible to selectively transfer (discharge) the deteriorated toner to the surface of the photosensitive drum by a refresh operation on the surface of the developing roller described later.

  During the replenishment of unused toner and the aging operation, the developer is conveyed onto the developing roller 12 in order to prevent the toner from being transferred onto the photosensitive drum 15 and the accompanying toner waste. It is controlled not to be done. Specific means for preventing the developer from being conveyed onto the developing roller 12 include, for example, adjusting a developing bias applied to the developing roller 12.

Further, in order to prevent the toner from transferring onto the photosensitive drum 15 during the replenishment and aging operation of unused toner, instead of the above-described means, for example, between the developing roller 12 and the photosensitive drum 15 Means such as adjusting the potential difference as appropriate can also be taken.
In the refresh process in the developing roller 12, a predetermined bias voltage is applied to the developing roller 12 and the photosensitive drum 15 in a state where no electrostatic latent image is formed on the photosensitive drum 15 (during non-image formation). This is accomplished by transferring (discharging) the deteriorated toner in the developing unit 11 to the surface of the photosensitive drum.

The bias voltage applied to the developing roller 12 and the photosensitive drum 15 and the driving time of the refresh process during the refresh operation are not limited to this. For example, the history of the average printing rate <P>, the number of printed sheets n What is necessary is just to set suitably according to a cumulative value. Thereby, the discharge amount of the deteriorated toner can be set appropriately.
The absolute value of the bias voltage applied to the developing roller 12 is set smaller than the absolute value of the bias voltage applied during normal image forming processing. In addition, these bias voltages are graphs (so-called development sensitivity curves) showing the relationship of the amount of toner transferred from the developing roller 12 to the photosensitive drum 15 with respect to the potential difference between the developing roller 12 and the photosensitive drum 15. It is set in a range where there is a significant difference between the transfer amount of deteriorated toner and the transfer amount of unused toner.

Further, during the refresh process, in order to prevent the deteriorated toner discharged on the photosensitive drum 15 from adhering to the transfer roller 18, a high voltage having the same polarity as the toner charging polarity is applied to the transfer roller 18. A bias is applied.
The print rate P of the formed image is measured by measuring the image data as the number of dots by a central processing unit (CPU; not shown) in the control unit 20 and the like, and measuring the document print rate an on the image. A print image based on a method for obtaining an average print rate <P> based on the document print rates a1, a2, a3,..., An for each surface of the medium, or on image information of a document image read by the reading unit 21. It can be obtained from the ratio of the image forming portion occupying the print surface, or by measuring the formed image using the printing rate measuring means 25.

  As a method for obtaining the printing rate P from the formed image, for example, the density sensor 22 measures the image density of the toner image formed on the surface of the photosensitive drum 15 or the formed image transferred onto the transfer target 19. By doing so, it can also be measured. In these cases, the printing rate measuring means 25 may be appropriately disposed, for example, in the vicinity of the photosensitive drum 15 or the transfer target 19.

FIG. 2 is a flowchart illustrating an example of a control procedure for executing the refresh process.
In the image forming apparatus 10 shown in FIG. 1, as shown in FIG. 2, when the image forming process is started, the number counter 21 is reset (step S1), and the number counter 23 starts counting the number of printed sheets n. Then, the printing rate P of the formed image is measured by the printing rate measuring means 25 (step S3).

Based on the counted number of printed sheets n, it is selected whether to return to step S2 or move to the next step (step S4). That is, when the number of printed sheets n has not reached the predetermined number (preset threshold value) n ₀ (NO in step S4), the process returns to step S1 and a series of procedures is repeated. On the other hand, when the printing number n has reached the preset threshold value n ₀ (YES in step S4), and the number of printed sheets n, on the basis of the measurement result of the printing rate P, the average printing ratio <P> (%) is calculated (Step S5).

Next, based on the calculation result of the average printing rate <P>, it is selected whether to return to step S1 or to move to the next step (step S6). That is, the average printing ratio <P> is when a predetermined value (preset value) P ₀ or more (NO in step S6), and returns to step S1, a series of steps is repeated. On the other hand, (YES at step S6) when the average printing ratio <P> is below the preset value P _0, by referring to the selection history in the step S6, preset average printing ratio <P> is continuously the number of times N is counted in the case of less than the value _{P 0} (step S7).

Next, based on the counted number N, it is selected whether to proceed to step S9 or omit steps S9 and S10 and proceed to step S11 (step S8). That is, when the number N has reached the predetermined number (preset threshold) N ₀ (YES in step S8), unused toner is replenished in the developing device 11 (step S9), and an aging process is executed. In step S10, a refreshing process for conveying the toner on the developing roller to the photosensitive drum is executed (step S11). On the other hand, when the number N does not reach the preset threshold value N ₀ (NO at step S8), and not the unused supply and aging of the toner to the step S9 and S10 is omitted (the developing device 11 is executed Ii) A refresh process is executed (step S11).

After execution of the refresh process, the blank image is developed (step S12), and the image density C of the blank image is measured by the density sensor 22 (step S13). Further, based on the measurement result of the image density C of the blank paper image, it is determined whether or not fogging has occurred, and whether to return to step S1 or to return to step S11 is selected (step S14). That is, when the image density C of the blank paper image is 0 or close to 0 and therefore no occurrence of fog is detected (NO in step S14), the process returns to step S1 and the series of procedures is repeated. On the other hand, when the image density C of the blank image reaches a preset density (preset threshold value) C ₀ and it is determined that fogging has occurred (YES in step S14), the process returns to step S11. The refresh process is executed again.

The control procedure from steps S1 to S11 shows an example of the control procedure when the process shown in (b) above is executed using the image forming apparatus described in (2) above.
The “predetermined condition” in the image forming apparatus described in (2) above is a condition in which NO is selected in step S8 in the case of the above control procedure. Specifically, the number N of times reaches the predetermined number. That is not. The “specific condition” in the image forming apparatus described in (2) above is a condition in which YES is selected in step S8 in the case of the above control procedure. Specifically, the number N is a predetermined number. It is to have reached.

  In the control procedure shown in FIG. 2, when setting the predetermined condition and the specific condition, two factors of the number n of printed sheets and the average print rate <P> of the formed image are used. In the present invention, the factors for setting the predetermined condition and the specific condition are not limited to the above two factors. For example, the driving time t of the developing device 11, the number n of prints, and the print rate of the formed image One or two or more factors may be arbitrarily used from factors such as P and average printing rate <P>.

Specifically, for example, the same control as that shown in FIG. 2 can be executed by using two factors of the driving time t and the average printing rate <P>. In this case, a process (step S1 ′) for resetting the timer 24 for measuring the driving time of the developing device 11 is executed together with step S1 (simultaneously with or immediately before or after step S1), and thereafter with step S2. Then, the timer 24 measures the drive time t (step S2 ′), and instead of step S4, the following step S4 ′ is executed. 'In, the drive time t is whether reached a predetermined time (preset threshold) t ₀ is determined, when the above-mentioned driving time t has not reached the preset threshold value t ₀ (step S4' step S4 is NO ), Steps S1, S1 ′, S2, S2 ′ and S3 are executed again. On the other hand, when the drive time t has reached the preset threshold value _{t 0} (YES at step S4 '), the procedure moves to step S5. The control after step S5 is the same as the control procedure shown in FIG.

Even when the two factors of the driving time t and the average printing rate <P> are used, the “predetermined condition” and the “specific condition” in the image forming apparatus described in (2) are as described above. Same as the case.
Among the above factors, for the printing rate, the value P for each formed image can be used instead of the value <P> averaged by the number n of printed sheets. However, even when the print rate P of the formed image is small, the apparent print rate taking into account the history of the formed image increases by repeatedly executing the image forming process. Therefore, in order to efficiently execute the refresh process, it is preferable to use the average printing rate <P> averaged by the number of printed sheets n rather than using the printing rate P of the formed image as the factor.

In the control procedure shown in FIG. 2, steps S7 and S8 can be omitted. When steps S7 and S8 are omitted, it is not determined whether or not it is necessary to replenish unused toner when the refresh process is executed. Therefore, before the refresh process is executed, the unused toner to the developing device 11 is always used. The replenishment and the aging process are executed.
That is, among the steps S1 to S11, the control procedure executed by omitting steps S7 and S8 performed the process shown in (a) above using the image forming apparatus described in (1) above. An example of the control procedure in this case is shown.

Even in the control procedure in which steps S7 and S8 are omitted, it is necessary to determine whether or not to replenish unused toner when executing the refresh process, that is, to select whether or not to execute steps S9 and S10. it can. Specifically, for example, when the average printing ratio at step S6 <P> below the preset value P _0, under normal conditions, supply of fresh toner (step S9) and aging treatment (Step S10) Are skipped and the process proceeds to a refresh process (step S11). Under conditions different from normal conditions, replenishment of unused toner (step S9) and aging processing (step S10) are executed. You may control to transfer to a refresh process (step S11). Here, as conditions different from the normal conditions, for example, when the image forming process in a state in which the printing rate P is lower than the preset value P ₀ is repeated more than a predetermined number of printed sheets n ₀ , without performing the replenishment time it was driven developing device 11 t is, when it reaches the preset threshold value t _0, and the like.

In the above-described control procedure, the refresh process is controlled based on the printing rate and the number of printed sheets. Unlike this, for example, development is performed using a timer 22 provided in the control unit 19. The driving time t of the device 11 may be measured, and the refresh process may be controlled to be executed when the cumulative value of the driving time reaches a predetermined time (preset threshold).
In the control procedure shown in FIG. 2, steps S12 to S14 can be omitted. When steps S12 to S14 are omitted, after executing the refresh process (step S11), the process returns to step S1 and a series of procedures is repeated.

On the other hand, when the processing is executed without omitting steps S12 to S14, the presence or absence of fogging is detected. Therefore, it is determined whether or not the deteriorated toner has been sufficiently discharged by executing the refreshing step (step S11). be able to.
The control means from step S12 to step S14 shows an example of a control procedure when the process shown in (c) above is executed using the image forming apparatus described in (3) above.

When the occurrence of fog is detected in step S14 (YES in step S14) and the refresh process (step S11) is executed again, steps S13 and S14 following step S11 may be omitted and the process may return to step S1.
When the occurrence of fogging is detected in step S14 (YES in step S14), the process returns to step S9 to execute replenishment of unused toner and aging processing (steps S9 and S10), and then the refresh process (step S14). S11) may be executed again. However, if unused toner is replenished, the deteriorated toner may float again, and as a result, the operation time of the refresh process may become too long. By suppressing the discharge of the deteriorated toner to such an extent that the image is not adversely affected, the waste of the toner is prevented, and the time required for the image forming process (particularly, the waiting time of the image forming process caused by the execution of the refresh process) It is preferable from the viewpoint of shortening.

  In the above control procedure, the presence / absence of fogging is determined by measuring the image density on the photosensitive drum 15 by the density sensor 22, but instead of this, for example, the image density on the transfer object 19 is measured. Or by measuring the image density on the intermediate transfer member when an intermediate transfer member is disposed between the photosensitive drum 15 and the transfer member 19. it can.

The refresh process in the developing device 10 is not only periodically and automatically executed according to the above-described control procedure, but may be arbitrarily executed based on, for example, a user's judgment.
The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

1 is a block diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a flowchart which shows an example of the control procedure of a series of operation including a refresh process.

Explanation of symbols

10 Image forming apparatus 11 Developer

Claims (3)

A developer carrying body for transporting toner to the development area; and an electrostatic latent image carrying body arranged to face the developer carrying body,
In an image forming apparatus capable of executing a refreshing step of refreshing the surface of the developer carrying body by transporting the toner on the developer carrying body to the electrostatic latent image carrier side during non-image formation,
2. The image forming apparatus according to claim 1, wherein the refreshing step is executed after unused toner is replenished in the developing unit. A developer carrying body for transporting toner to the development area; and an electrostatic latent image carrying body arranged to face the developer carrying body,
In an image forming apparatus capable of executing a refreshing step of refreshing the surface of the developer carrying body by transporting the toner on the developer carrying body to the electrostatic latent image carrier side during non-image formation,
The refresh process includes
Under a predetermined condition, the developing device is executed without replenishing unused toner, and
The image forming apparatus is executed under a specific condition different from the predetermined condition after the unused toner is replenished in the developing device.   2. The blank image forming process is executed after the refresh step, and the refresh step is executed again when the image density of the obtained blank image does not satisfy a preset condition. Or the image forming apparatus according to 2;

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