JP7246901B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus. An image forming apparatus has an image carrier, and developing means, charging means, cleaning means, etc. as process means acting on the image carrier. The image forming apparatus of the present invention is an electrophotographic image forming apparatus that forms an image on a recording medium using an electrophotographic image forming method.

Examples of electrophotographic image forming apparatuses include electrophotographic copiers, electrophotographic printers (LED printers, laser beam printers, etc.), facsimile machines, word processors, and the like.

An electrophotographic image forming apparatus forms an electrostatic latent image on an image carrier with an exposure device. The electrostatic latent image is visualized as a developer image by a developer, and the developer image is transferred to a recording medium to form an image on the recording medium (image forming operation).

The developer may remain on the surface of the image carrier after the developer image has been transferred to the recording medium. In order to remove the remaining developer, a cleaning member such as a cleaning blade is brought into contact with the image carrier. The developer removed by the cleaning member is collected in a predetermined storage container or the like.

On the other hand, when the image forming operation is completed and the image carrier stops, the developer, the wax contained in the developer, the external additive, etc. are caught in the contact portion between the cleaning member and the image carrier. It is in a state of Since the cleaning member is in contact with the image carrier with a contact pressure, if the image carrier remains stationary, an adhesion area is formed on the surface of the image carrier where these components are adhered. There is The adhesion area has a lower coefficient of friction than the rest of the surface of the image bearing member.

When the image forming operation is performed in such a state, when the adhesion area reaches the contact portion of the cleaning member, the load for rotating the image carrier is momentarily reduced, and the rotation speed of the image carrier is reduced. It can be faster than normal rotation speed. At this time, the electrostatic latent image formed on the image carrier by the exposure device is misaligned and the amount of exposure on the surface of the image carrier is reduced, resulting in horizontal streaks on the image.

As a countermeasure against this horizontal streak, after the image forming operation is completed, the image carrier is stopped and then finely moved a plurality of times to discharge the deposits (developer, etc.) on the contact portion of the cleaning member. It has been proposed (Patent Document 1, Patent Document 2).

Patent No. 4194439 Patent No. 4741853

During the image forming operation, the cleaning member is in contact with the image carrier while being deformed by the image carrier. The degree of this deformation differs depending on, for example, the print rate of the image being formed. Therefore, when the image carrier stops immediately after the image forming operation, the state of the contact portion of the cleaning member contacting the image carrier is not always constant. If the state of the abutting portion is different, the amount of the adhered matter discharged will be different when the discharging operation for discharging the adhered matter such as the developer is performed.

Further, the amount of adhered matter ejected by the ejecting operation tends to increase as the image carrier is stopped for a longer period of time. On the other hand, the degree of reduction in the coefficient of friction of the surface of the image carrier due to deposits increases as the image carrier is stopped for a longer period of time. Horizontal streaks tend to stand out when the coefficient of friction drops abruptly, so it is desirable to prevent a sudden drop in the coefficient of friction while spewing out adhering matter.

SUMMARY OF THE INVENTION It is an object of the present invention to stably discharge deposits from the contact portion between the image carrier and the cleaning member while suppressing the formation of a portion where the coefficient of friction abruptly drops on the surface of the image carrier. Another object of the present invention is to provide an image forming apparatus that performs

One of the inventions according to the present application for solving the above problems is as follows.

An image forming apparatus that performs an image forming operation for forming an image on a recording medium,
an image carrier for carrying an electrostatic latent image;
a cleaning member that contacts the image carrier and removes the developer from the image carrier;
a drive source for rotating the image carrier, the drive source rotating the image carrier in a first direction in the image forming operation;
A control unit for controlling the driving source, the control unit for performing an end operation after the image forming operation is finished and the image carrier is stopped and before the next image forming operation is started. a control unit;
has
The ending operation includes a preliminary operation and an intermittent operation performed after the preliminary operation. an operation of rotating and stopping the carrier, wherein the intermittent operation is an operation in which the stopped state of the image carrier and the rotation of the image carrier in the first direction are alternately repeated;
The waiting time is shorter than the stoppage time,
In the intermittent operation, the time of the stop state after the second time is longer than the time of the stop state immediately before that,
The image forming apparatus, wherein the intermittent operation includes the stop state for a first length and the stop state for a second length longer than the first length.

As described above, according to the present invention, deposits can be removed from the contact portion between the image carrier and the cleaning member while suppressing the formation of a portion where the coefficient of friction abruptly drops on the surface of the image carrier. It is possible to provide an image forming apparatus that stably performs the ejection operation.

Cross-sectional view of an image forming apparatus Diagram showing torque fluctuation and image when the level of exposure blur is bad Diagram showing torque fluctuation and image when exposure blur level is good Diagram explaining the outline of the discharge sequence A diagram showing the state of the cleaning blade and the photosensitive drum during intermittent operation. FIG. 4 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the first embodiment; FIG. 10 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the second embodiment; FIG. 11 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the third embodiment; FIG. 10 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the fourth embodiment;

[Example 1]
<Description of Image Forming Apparatus>
An example of an electrophotographic image forming apparatus according to the present invention is shown in FIG. FIG. 1 is a sectional view of an image forming apparatus to which the invention can be applied.

An apparatus main body M of the image forming apparatus is provided with a process cartridge P that can be attached to and detached from the apparatus main body M. As shown in FIG.

The process cartridge P includes an image carrier (photosensitive drum) 1 that carries an electrostatic latent image as a member to be charged, and a charging roller 4 as a charging member. The process cartridge P includes a cleaning member (cleaning blade) 2 that contacts the photosensitive drum 1 and removes developer (toner) 3 from the photosensitive drum 1 . A contact portion (tip portion of the cleaning blade 2) where the cleaning blade 2 contacts the photosensitive drum 1 is formed of an elastic member such as rubber. The photosensitive drum 1 is a conductive drum with an OPC (organic photo-semiconductor) photosensitive layer formed on the outer peripheral surface thereof, and is rotationally driven by a driving force transmitted from a main body at a predetermined process speed. The surface of the photosensitive drum 1 is charged to a predetermined polarity and potential by a charging roller 4 to which a charging bias (voltage) is applied. After being charged, the surface of the photosensitive drum 1 is scanned and exposed by a scanner 6 as an exposure device. As a result, an electrostatic latent image corresponding to the desired image information is formed on the surface of the photosensitive drum 1 .

The process cartridge P includes a developing roller 7 as a developer carrier that carries toner 3 for developing an electrostatic latent image. Further, the process cartridge P includes a magnet roller (not shown) arranged inside the developing roller 7 of the developing container 9 and a regulating member (developing blade) 8 that contacts the developing roller 7 . The toner 3 accommodated in the developing container 9 is conveyed toward the developing roller 7 and carried on the developing roller 7 by the magnetic force of the magnet roller. The thickness of the layer of toner 3 carried on the developing roller 7 is regulated by the developing blade 8 . A predetermined developing voltage is applied to the developing roller 7 . Toner 3 is supplied from the developing roller 7 to the photosensitive drum 1, and the electrostatic latent image is developed (visualized) as a toner image.

In this embodiment, a magnetic developer (preferably a magnetic one-component developer) is used as the toner 3, but the present invention uses a non-magnetic developer (preferably a non-magnetic one-component developer). can be applied even if

On the other hand, the apparatus main body M includes a paper feed cassette 102 containing a recording medium 10 such as paper, a transfer roller 11 as a transfer member, and a fixing device 12 as a fixing device. A recording medium 10 is fed by a feeding roller and conveyed between the photosensitive drum 1 and the transfer roller 11 . A toner image is transferred to the surface of the recording medium 10 by a transfer bias between the photosensitive drum 1 and the transfer roller 11 . The recording medium 10 to which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and conveyed to a fixing device 12, where it is heated and pressurized to fix the toner image.

On the other hand, on the surface of the photosensitive drum 1 after the toner image has been transferred, there is residual toner that has not been transferred onto the recording medium 10 . Toner remaining on the photosensitive drum 1 is removed by the cleaning blade 2 . The removed developer is stored in the removed toner storage chamber of the cleaning container 5 . Part of the toner intervenes between the contact portion of the cleaning blade 2 and the photosensitive drum 1 and is scattered on the surface of the photosensitive drum 1 to reduce the frictional resistance of the photosensitive drum 1 . As a result, the cleaning blade 2 is prevented from being turned over, and a good image forming process can be continued.

After being cleaned by the cleaning blade 2, the surface of the photosensitive drum 1 is charged again, and thereafter, the flow of exposure, development, and transfer is repeated to complete a series of image forming cycles. As described above, the operation for forming an image (toner image) on the recording medium 10 is called an image forming operation in this embodiment.

In the image forming apparatus according to this embodiment, the process equipment including the photosensitive drum 1, the charging roller 4, the developing container 9, and the cleaning container 5 are integrally incorporated in a cartridge container, which can be attached to and removed from the main body M of the image forming apparatus. constitutes the process cartridge P. A device corresponding to the process cartridge P may be fixed to the main body M of the device.

The apparatus main body M is provided with a driving motor 101 as a driving source for rotating the photosensitive drum 1 . In this embodiment, the drive motor 101 of the image forming apparatus transmits a driving force to the photosensitive drum 1 via a drive gear, and the photosensitive drum 1 is driven to rotate. Here, the rotating direction of the photosensitive drum 1 in the image forming operation is called a normal rotating direction (first direction). Rotation in the normal rotation direction is called forward rotation or normal rotation.

The apparatus main body M includes a control section (CPU and controller) 100 for controlling a driving motor 101 . A control unit 100 controls a driving motor 101 to perform an image forming operation. Further, the control unit 100 controls the driving motor 101, and after the image forming operation is finished and the photosensitive drum 1 is stopped, before the next image forming operation is started, a discharge sequence as a finishing operation to be described later is executed. .

The control unit 100 of the image forming main body can control not only ON/OFF of the driving of the photosensitive drum 1, but also the timing of driving and stopping the photosensitive drum 1, and minute driving of less than one rotation of the drum. In particular, micro-driving can be executed using the rise before the driving motor 101 reaches steady rotation, due to the correlation between the driving signal (input time) to the driving motor 101 and the actual motor rotation operation. In that case, electric power is not required until the drive motor 101 reaches steady rotation, and micro-driving with very small electric power becomes possible.

Further, the apparatus main body M can detect the time from the stop of the photosensitive drum 1 to the next drive. Elapsed time from is detectable as stop time.

Further, the detection unit 103 of the apparatus main body M can also detect the contents of the previous job (printing rate, environment, number of sheets passed, printing mode such as continuous or intermittent operation). Based on these detection results, the control unit 100 performs minute driving and stopping of the photosensitive drum 1 as a discharge sequence between after image formation and before the next image formation, thereby discharging the developer from the contact portion. It is possible to

<Decrease in Friction Coefficient of Photosensitive Drum Surface and Effect on Images>
A decrease in the coefficient of friction of the surface of the photosensitive drum 1 and its influence on images will be described.

When the image forming operation is finished and the photosensitive drum 1 stops, the developer, wax contained in the developer, and It is in a state where an external additive or the like is sandwiched. Since the cleaning blade 2 is in contact with the photosensitive drum 1 with a contact pressure, if the photosensitive drum 1 continues to be in a stopped state, an adhesion area is formed on the surface of the photosensitive drum 1 where these components are adhered. Sometimes. This adhesion area is an area where the coefficient of friction is lower than that of the other surface of the photosensitive drum 1 .

When the image forming operation is performed again in such a state, the load for rotating the photosensitive drum 1 is momentarily reduced when the adhesion area reaches the contact portion of the cleaning blade 2 . As a result, deformation of a member (for example, drive gear) for driving the photosensitive drum 1 is released, so that the rotational speed of the photosensitive drum 1 becomes faster than the normal rotational speed. As the rotation speed of the photosensitive drum 1 increases, the surface of the photosensitive drum 1 passes through the portion exposed by the scanner 6 faster. At this time, the position of the electrostatic latent image formed on the photosensitive drum 1 by the scanner 6 shifts from its original position. Also, the amount of exposure on the surface of the photosensitive drum 1 is reduced compared to the portion exposed at the normal speed. Due to this effect, horizontal streaks (low density portions) occur due to the increased rotation speed of the photosensitive drum 1 .

After the adhesion area passes through the abutting portion of the cleaning blade 2, the rotational speed of the photosensitive drum 1 is maintained at the normal rotational speed until the photosensitive drum 1 returns to the normal rotational speed (until the drive gear or the like follows). lower than When the rotation speed of the photosensitive drum 1 slows down, the surface of the photosensitive drum 1 passes slowly through the portion exposed by the scanner 6 . At this time, the position of the electrostatic latent image formed on the photosensitive drum 1 by the scanner 6 shifts from its original position. In addition, the amount of exposure on the surface of the photosensitive drum 1 also increases compared to the portion exposed at the normal speed. Due to this effect, horizontal streaks (high-density portions) are generated due to the slower rotation speed of the photosensitive drum 1 .

These horizontal streaks occur in pairs. Hereinafter, this phenomenon is called exposure blur. This exposure blur is conspicuous in a so-called halftone image or an image in which horizontal lines parallel to the rotation axis of the photosensitive drum 1 are arranged at regular intervals in the rotation direction of the photosensitive drum 1 . In addition, horizontal streaks (portions of low density) caused by the increased rotational speed of the photosensitive drum 1 are more likely to occur than horizontal streaks (portions of high density) caused by the decreased rotational speed of the photosensitive drum 1. is more noticeable.

Focusing on the rotation torque of the photosensitive drum 1 when exposure blur occurs, the relationship between the rotation torque of the photosensitive drum 1 and the image level when the exposure blur is bad and when the exposure blur is good will be described with reference to FIGS. 2 and 3. FIG. do. FIG. 2 is a diagram showing torque fluctuations and an image when the level of exposure blurring is bad (relatively conspicuous on the image). FIG. 2(a) shows the rotational torque at that time. FIG. 2(b) shows an image at that time. FIG. 3 is a diagram showing torque fluctuations and an image when the level of exposure blur is good (relatively inconspicuous on the image). FIG. 3(a) shows the rotational torque at that time. FIG. 3(b) shows an image at that time. In the images of FIGS. 2B and 3B, horizontal lines extending in the main scanning direction (same as the scanning direction of the scanner 6) are arranged at regular intervals in the sub-scanning direction (same as the conveying direction of the recording medium 10). This is an image. The upper side of each figure is the downstream side in the conveying direction of the recording medium 10 . The sub-scanning direction is orthogonal to the main scanning direction. The main scanning direction is parallel to the direction of the rotational axis of the photosensitive drum 1 . The sub-scanning direction corresponds to the rotating direction of the photosensitive drum 1 .

As shown in FIG. 2(a), when the exposure blur is bad, the torque fluctuation is confirmed such that the rotational torque drops sharply at the moment when the adhesion area passes the cleaning blade 2, and then returns. Moreover, the image at that time becomes like FIG.2(b). As shown in FIG. 2B, when the photosensitive drum 1 rotates rapidly, the interval between the horizontal lines widens and then narrows, resulting in shading on the image. When the torque fluctuation occurs suddenly, it is not good as an exposure blur, and a sharp and conspicuous blurred image is obtained.

On the other hand, as shown in FIG. 3(a), when the exposure blur is good, a torque fluctuation was confirmed in which the torque gradually decreased from the moment the adhesion area passed the cleaning blade and then returned. Moreover, the image at that time becomes like FIG.3(b). As shown in FIG. 3B, when the photosensitive drum 1 rotates quickly, the interval between the horizontal lines widens and then narrows, which is the same as in FIG. In other words, it can be seen that there is a correlation between torque fluctuations in the adhesion area and exposure blurring, and exposure blurring can be suppressed by reducing sudden torque fluctuations.

<Summary of discharge sequence>
Next, a discharge sequence as a termination operation will be described with reference to FIG. FIG. 4 is a diagram for explaining an outline of the ejection sequence.

The ejection sequence is performed by controlling the drive motor 101 by the control unit 100 . The discharge sequence includes a reset operation as a preliminary operation, which will be described later, and an intermittent operation performed after the reset operation.

The ejection sequence is performed after the image forming operation on the recording medium 10 is completed and the photosensitive drum 1 is stopped and before the next image forming operation is started.

The reset operation is an operation of rotating and stopping the photosensitive drum 1 after the waiting time has elapsed after the image forming operation is finished and the photosensitive drum 1 is stopped. As shown in FIG. 4, the photosensitive drum 1 rotating during the image forming operation stops after rotating for a predetermined period of time (completion of the image forming operation). The photosensitive drum 1 rotates (D0) after a standby time T0 has passed since this stop. and stop.

The intermittent operation is an operation in which the photosensitive drum 1 is oriented in the normal rotation direction and intermittently minutely driven (a plurality of times of minutely driven). In other words, the intermittent operation is an operation in which the photosensitive drum 1 is alternately stopped and slightly rotated in the normal rotation direction. Hereinafter, a minute rotating motion of the photosensitive drum 1 in the normal rotating direction in the intermittent motion is simply referred to as a "rotating motion". As shown in FIG. 4, after the reset operation is finished (after the photosensitive drum 1 is stopped), the rotation operation (D1) of the photosensitive drum 1 is performed after a stop state (length of stop state) T1. After that, the stopped state of length T2, the rotating motion D2, the stopped state of length T3, the rotating motion D3, the stopped state of length T4, and the rotating motion D4 are repeated.

<Reset operation>
During the image forming operation, the tip (contact portion) of the cleaning blade 2 is deformed following the rotation of the photosensitive drum 1 . Immediately after the photosensitive drum 1 stops after the image forming operation, the cleaning blade 2 remains deformed, which is different from the state of the contact portion when the photosensitive drum 1 stops during intermittent operation. It should be noted that the contact portion when the photosensitive drum 1 stops after the image forming operation is deformed more than the contact portion when the photosensitive drum 1 stops during the intermittent operation.

The degree of deformation varies depending on, for example, the print rate of the image being formed. That is, when the photosensitive drum 1 stops immediately after the image forming operation, the state of the contact portion of the cleaning blade 2 contacting the photosensitive drum 1 is not always constant. If the state of the abutment portion differs, the abutment pressure on the photosensitive drum 1 and the like will fluctuate, and the amount of deposits that are ejected by the intermittent operation will differ. Therefore, the effect of the intermittent operation for suppressing exposure blurring may vary.

Therefore, in this embodiment, in order to reset the state of the contact portion of the cleaning blade 2 immediately after image formation (reduce deformation), the cleaning blade 2 is driven once (rotated forward or backward) immediately after stopping immediately after image formation. After that, it was decided to perform intermittent operation.

In the reset operation in this embodiment, the photosensitive drum 1 is driven in the normal rotation direction (corresponding to D0 in FIG. 4) after a waiting time of 1 second (corresponding to T0 in FIG. 4) after the image forming operation. Even when the photosensitive drum 1 is driven in the normal rotational direction, the effect of reducing the deformation of the contact portion of the photosensitive drum 1 can be obtained by performing the operation after temporarily stopping. Even if the photosensitive drum 1 is driven in a direction (second direction) opposite to the normal rotation direction, the effect of reducing the deformation of the contact portion of the photosensitive drum 1 can be obtained.

Here, the waiting time T0 described above is shorter than the stopped state time (T1 to T4) in the intermittent operation described later. In other words, the waiting time T0 is shorter than the shortest of the stoppage times (T1 to T4). In other words, the stopped state time (T1 to T4) in the intermittent operation described later is longer than the standby time T0. This is because during the standby time T0, the contact portion of the cleaning blade 2 is in the state before the deformation is reset, and it is desirable to suppress the adherence of deposits in that state. . On the other hand, during T1 to T4, it is desirable that the attached matter adheres to the photosensitive drum 1 to some extent because the attached matter is ejected by the rotation operation after the stop state.

<Intermittent operation>
Intermittent operation in the exhalation sequence will be described. In the following description, the first stop time after the end of the reset operation is defined as the first stop time, and the subsequent rotation operation is defined as the first rotation operation.

In order to moderate the torque fluctuation in the adhesion area and suppress the blurring of exposure, it is preferable to control the initial stop time and the developer adhesion state on the photosensitive drum 1 associated therewith.

An outline of the stop time and the developer adhesion state on the photosensitive drum 1 will be described with reference to FIG. FIG. 5 is a diagram showing the state of the cleaning blade 2 and the photosensitive drum 1 after the intermittent operation of this embodiment. The upper diagram in FIG. 5 is a cross-sectional diagram perpendicular to the rotation axis of the photosensitive drum 1 . The bottom view of FIG. 5 is a view of the photosensitive drum 1 viewed from above (in the direction of the cleaning blade 2).

After the above-described reset operation is completed, the area S1 of the photosensitive drum 1 is in a state (initial state) in which the cleaning blade 2 is brought into contact with the region S1 and stopped. After that, the photosensitive drum 1 is intermittently moved in the normal rotation direction, so that the areas S2, S3, and S4 come into contact with each other in order, resulting in the state shown in FIG.

That is, the area S1 on the photosensitive drum 1 represents the adhesion area corresponding to the first stop time (corresponding to T1 in FIG. 4) after the reset operation. Region S2, region S3, and region S4 represent adhesion regions corresponding to the second, third, and fourth stop times. With respect to the normal rotation direction of the photosensitive drum 1, the area S1 is located on the most downstream side, and the area S4 is located on the most upstream side.

Here, with respect to the normal rotation direction of the photosensitive drum 1, no adhesion area is formed on the downstream side of the area S1. Therefore, if the coefficient of friction is greatly reduced in the region S1, the difference in load from the portion downstream thereof becomes large, which tends to cause horizontal streaks.

On the other hand, the amount of deposits ejected by the intermittent operation tends to increase as the time during which the photosensitive drum 1 is stopped increases. On the other hand, the degree of decrease in the coefficient of friction of the surface of the photosensitive drum 1 due to the deposits increases as the time period during which the photosensitive drum 1 is stopped increases. Horizontal streaks tend to stand out when the coefficient of friction drops abruptly, so it is desirable to prevent a sudden drop in the coefficient of friction while spewing out adhering matter.

Therefore, the stop time of the photosensitive drum 1 in the intermittent operation is shortened at the start of the intermittent operation and lengthened just before the end of the intermittent operation. As a result, the difference in coefficient of friction between the upstream portion and the downstream portion of the photosensitive drum 1 in the normal rotation direction is suppressed from increasing. In addition, even if the discharge of adhering matter is restricted on the downstream side in the normal rotational direction, the discharge of adhering matter can be compensated for by the portion on the upstream side.

Specifically, in the intermittent operation, when the stop state times of the photosensitive drum 1 are compared in the regions S1 to S4, the stop state time after the second time is longer than or equal to the immediately preceding stop state time. Further, in intermittent operation, at least one stop time is increased. In other words, the intermittent motion includes a first length of stop and a second length of stop that is greater than the first length. That is, the rotating motion is performed after the first length of stop state, and then the rotating motion is performed after the second length of the stop state longer than the first length.

The stop time of the photosensitive drum 1 in the intermittent operation can also be expressed as follows. That is, in the intermittent operation, the first stop state time (corresponding to stop time T1 in region S1) is the shortest, and the last stop state time (corresponding to stop time T4 in region S4) is the longest. Also, the duration of the stopped state is longer than or equal to the duration of the immediately preceding stopped state. In addition, during intermittent operation, the idle time is increased at least once.

The rotation operation of the photosensitive drum 1 in the intermittent operation is minute driving such that the driving motor 101 does not reach a steady rotation as described above. The total rotation length of the photosensitive drum 1 in the intermittent operation is less than one rotation of the photosensitive drum 1 . In this embodiment, the total rotation length of the photosensitive drum 1 in the intermittent operation is less than one-eighth of the circumference of the photosensitive drum 1 . It should be noted that the rotation of the photosensitive drum 1 in the reset operation was similarly finely driven.

Although the attachment regions are formed continuously in this embodiment, the present invention is not limited to this. That is, it may be intermittent (for example, a small gap is formed between the area S1 and the area S2). However, if the gap between the regions becomes too large, the torque suddenly increases at that portion. Therefore, it is preferable to keep the gap so that the next region comes before the torque increases to worsen the exposure blur.

<Specific stop time>
A specific intermittent operation in this embodiment will be described with reference to FIG. FIG. 6 is a diagram for explaining the intermittent operation according to this embodiment.

The horizontal axis in FIG. 6 represents the timing at which the photosensitive drum 1 rotates in the intermittent operation. The vertical axis indicates the length of time during which the photosensitive drum 1 is stopped immediately before each photosensitive drum 1 rotates. The stop time corresponding to the first rotation operation represents the elapsed time after the end of the reset operation. The stop time corresponding to the second and subsequent rotations represents the elapsed time after the photosensitive drum 1 was finely driven and stopped in the previous rotation.

In this embodiment, the stop times of the regions S1 to S4 (corresponding to T1 to T4 in FIG. 4) are 5, 10, 15 and 20 seconds, respectively. That is, during the intermittent operation, the duration of each stop state from the second time onwards is longer than the duration of the immediately preceding stop state. Furthermore, the difference between the time of each stop state from the second time onwards and the time of the stop state immediately before that was made constant. The total intermittent operation time is 50 seconds.

In order to form the adhesion areas at equal intervals, it is preferable that the length of the rotation of the photosensitive drum 1 is constant. In this embodiment, the photosensitive drum 1 is driven for a substantially constant time during each rotation. More specifically, the length of each rotating motion (time during which each rotating motion is performed) is set constant within the range of 50% to 150% of the average length of the rotating motion during the intermittent motion. . It is more preferable that the length of each rotation is constant within the range of 75% of the average value to 125% of the average value. In this example, the length of the rotation motion was 4 milliseconds. Further, the rotation of the photosensitive drum 1 in the reset operation is also set within the above range, specifically 4 milliseconds.

Area S1 has a short stop time. Therefore, when the developer on the contact portion of the cleaning blade adheres to the photosensitive drum 1, the developer intervening between them adheres weakly to the surface of the photosensitive drum 1 because the contact time between the two members is short. is. In this state, the torque (the load for rotating the photosensitive drum 1) gradually decreases, and no sudden torque fluctuation occurs. As described above, there is a correlation between stop time and torque reduction. This can then be used to create optimal adhesion areas.

On the other hand, only in the region S1, the developer still remains in the contact portion. Therefore, it is necessary to form an adhesion area in the succeeding area S2 and the like, and further discharge the developer. At this time, if the time of region S2 is shortened, the torque fluctuation is small, but a large amount of developer cannot be discharged due to the short stop time. Conversely, if the stop time is too long, a sudden torque fluctuation will occur, as in the case where the stop time is lengthened in region S1. Therefore, the region S2 is stopped slightly longer than the region S1 so that the torque fluctuation is kept within a predetermined range (the range in which the exposure blur is not noticeable).

After that, the stopping time of the area S3 and the area S4 is similarly increased little by little to form a plurality of adhesion areas, so that the discharge amount can be increased toward the downstream side. For example, the vehicle stops for a long time in region S4, but also stops to some extent in region S3 immediately before that, so the difference in load fluctuation (friction coefficient) between the two is not so large.

As described above, by gradually increasing the stop time during the intermittent operation, sudden torque fluctuations can be prevented even if more developer is discharged in the latter half. Further, since a large amount of developer is discharged in the latter half, the required amount of developer can be discharged in a short time, and exposure blurring can be improved in a short time.

A sequence in which a fixed amount is gradually increased as shown in FIG. The advantages of this sequence are as follows.

The sequence of this embodiment can gradually change the adhesion state of the developer from the weak adhesion state to the strong adhesion state at a constant rate. Become. Therefore, the change in the amount of exposure with which the surface of the photosensitive drum 1 is exposed becomes gentle as a whole, and the exposure blur can be made inconspicuous on the image.

On the other hand, as a comparative example, exposure blur was observed in an operation in which the time of each stop state was constant. Specifically, after the reset operation, the operation of stopping the photosensitive drum 1 for 12.5 seconds and then rotating it was performed four times. The total duration of this operation was 50 seconds, which was the same as the intermittent operation in this example. At this time, the exposure blur in the comparative example was more conspicuous on the image than the exposure blur in the present example.

<Reflection of developer adhesion state>
The adhesion area is affected by the developer interposed between the contact portion between the cleaning blade 2 and the photosensitive drum 1 . Therefore, the amount of developer in the contact portion varies depending on the contents of the previous job (print rate, environment, print mode such as continuous or intermittent, number of sheets passed). Therefore, it is preferable to discharge the developer in consideration of the developer amount. That is, it is preferable to optimally adjust the stop time of the ejection sequence and the number of times of driving. For this reason, it is preferable to calculate the amount of developer required for ejection and the total amount of stop time required for ejection using a correction table that combines the contents of the immediately preceding job in a complex manner, and to reflect this in the ejection sequence.

In this example, the discharge sequence was performed by multiplying each coefficient shown in Table 1 by the stop time (T1 to T4) of the intermittent operation. That is, the control unit 100 executes the ejection sequence according to the detection result of the detection unit 103 and the like. Specifically, the stop time (T1 to T4) is changed according to the printing rate, print mode, environment when the ejection sequence is performed, and the number of printed sheets in the image forming operation immediately before the ejection sequence is performed. .

As for the print rate, the stop time is shortened when the print rate is high. As for the print mode, the stop time is lengthened during continuous printing. As for the environment, low temperature and low humidity make the stop time short, and high temperature and high humidity make the stop time long. Regarding the number of printed sheets, the larger the number of printed sheets (for example, the end of the life of the process cartridge), the longer the stop time.

In this embodiment, all the coefficients in Table 1 are multiplied, but correction may be made according to at least one of the above factors. Also, if correction is not necessary, it is not necessary.

When the state of the developer in the contact portion where the cleaning blade 2 contacts the photosensitive drum 1 changes, the effect of suppressing exposure blurring may be insufficient. Specifically, when the immediately preceding print rate or the like changes, the amount of developer in the contact portion increases or decreases. Therefore, an appropriate ejection sequence is required. Specifically, the stop time is changed according to the exposure blurring suppression level, and the sequence is designed to obtain the maximum suppression effect in a short period of time, taking into consideration the excessive rotation of the photosensitive drum 1 and the adverse effects associated with it. is preferably set.

Since this phenomenon (exposure blurring) is related to the contact portion between the cleaning blade 2 and the photosensitive drum 1, the immediately preceding printing rate greatly contributes. Therefore, by estimating the amount of developer transferred to the photosensitive drum 1 using a correction formula that largely reflects the contribution of the print rate among the parameters reflected in the immediately preceding job content, exposure blurring is effectively suppressed.

For example, in Table 1, the contribution of the printing rate is large, and the corrections other than the printing rate are minute corrections of ±0.1 times.

As in the comparative example, in the discharge sequence that only repeats the same stop time, when the amount of developer in the contact portion changes due to the previous printing rate, etc., the sequence may be performed more than necessary, or the discharge may not be sufficient, resulting in a sudden It sometimes caused torque fluctuations. In the ejection sequence of this embodiment, the amount of developer required for ejection is estimated, and the result is reflected in each stop time. Since the optimum sequence for discharging the developer can be performed, exposure blurring can be effectively improved. In addition, it is possible to shorten the duration of the exhalation sequence without taking unnecessary stop time.

It should be noted that even if the process cartridge P is provided with a storage section (memory or the like) in which the information regarding the discharge sequence and its correction is recorded, and the image forming apparatus communicates with the storage section to execute the discharge sequence. good.

As described above, according to the configuration of this embodiment, the tip of the cleaning blade 2 returns to its original position by the reset operation. Therefore, the state of the tip of the cleaning blade 2 can be kept constant during the intermittent operation regardless of the print rate of the immediately preceding job. At that time, by shortening the standby time before the reset operation is performed, it is possible to suppress the adherence of deposits to the surface of the photosensitive drum 1 when the state of the tip of the cleaning blade 2 is not constant. In addition, by gradually lengthening the stop time from the start of the sweeping operation to the end, the difference in coefficient of friction between the first stopped portion and the immediately preceding region can be reduced. Then, the discharge amount can be gradually increased. Therefore, the difference in coefficient of friction can be reduced. That is, it is possible to prevent the coefficient of friction from suddenly decreasing.

As a result, even if the content of the previous job changes, the torque fluctuation caused by the adhesion area can be kept within a predetermined range, and the image level can also be improved. In other words, the exposure blur can be suppressed by the optimum sequence method.

[Example 2]
Example 2 will be described with reference to FIG. FIG. 7 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the second embodiment.

In Example 1, the stop time of the expiratory sequence was monotonically increasing. This embodiment is characterized in that a sequence of increasing the stop time at least once or more is performed instead of performing a sequence of monotonically increasing the stop time, especially assuming a case where the amount of developer to be discharged becomes small. there is

In other words, in this embodiment, the duration of the stopped state after the second time is longer than the duration of the stopped state immediately before. However, at least one or more motions are included, followed by a rolling motion followed by a first length of stop followed by a rolling motion after a second length of stop that is longer than the first length. ing. As a result, torque fluctuation can be effectively suppressed.

In this embodiment, the ejection sequence of Embodiment 1 is changed to one in which the stop time is increased at least once. Since other contents are the same as those of the first embodiment, description thereof is omitted.

By adopting such a sequence, even if the contents of the previous job change, the torque fluctuation caused by the adhesion area can be kept within a predetermined range, and the sequence time can be shortened.

[Example 3]
Example 3 will be described with reference to FIG. FIG. 8 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the third embodiment.

In Example 1, in the intermittent operation, the difference between the time of the second and subsequent stop states and the time of the stop state immediately before that was constant. This embodiment especially assumes a case where the amount of discharged developer changes, and the stop time always increases, but the difference between the time of each stop state and the time of the stop state immediately before it is not constant. It is characterized by As a result, torque fluctuation can be effectively suppressed within a predetermined range. In addition, since the content other than this is the same as that of Example 1, description is abbreviate|omitted.

By adopting such a sequence, even if the content of the immediately preceding job changes, the torque fluctuation caused by the adhesion area can be kept within a predetermined range. Further, even if the adhesion state of the developer suddenly changes, the amount of increase can be freely set for each number of times while increasing the stop time. Therefore, the versatility is high, and it is easy to optimize the effect on exposure blurring.

[Example 4]
Example 4 will be described with reference to FIG. FIG. 9 is a diagram showing the relationship between the rotation operation of the photosensitive drum and the stop time according to the fourth embodiment.

In Example 1, in the intermittent operation, the difference between the time of the second and subsequent stop states and the time of the stop state immediately before that was constant. This embodiment is characterized in that the stop time increases cumulatively, especially assuming the case where the amount of developer to be discharged increases. As a result, torque fluctuation can be effectively suppressed within a predetermined range. In addition, since the content other than this is the same as that of Example 1, description is abbreviate|omitted.

Note that the cumulative increase represents a state in which the difference from the next stop time gradually increases, such as the stop time (2 seconds→5 seconds→14 seconds→29 seconds: four times in total). That is, in this embodiment, the difference between the time of each stop state and the time of the stop state immediately before that increases from the start to the end of the intermittent operation.

By adopting such a sequence, it is possible to keep the torque fluctuation caused by the adhesion area within a predetermined range even if the contents of the immediately preceding job are changed, and it is possible to discharge a large amount of developer in the latter half. With this method, it is possible to cope with the case where the developer adhesion amount decreases even if the stop time increases in the latter half of the plurality of stop times, or the case where the torque fluctuation with respect to the developer adhesion force due to the contact pressure slows down. In addition, it is possible to cope with the case where a predetermined stop time or more is required for developer adhesion. That is, since the second half stop time can be effectively and optimally controlled, the number of excessive control times can be reduced, and the amount of developer required for discharging can be effectively discharged within the control time.

The configurations and the like described in the present embodiment are examples, and can be appropriately changed within the scope of the present invention as necessary. For example, the number of rotations of the photosensitive drum 1 in the intermittent operation of each discharge sequence, the stop time of the photosensitive drum 1 in the reset operation and the intermittent operation, the drive time, etc. can be appropriately changed as necessary. For example, the number of stops during intermittent operation is not limited to four.

As described above, according to the present invention, while suppressing the formation of a portion where the coefficient of friction abruptly decreases on the surface of the photosensitive drum 1, the deposits can be stably removed from the contact between the image bearing member and the cleaning member. It is possible to provide an image forming apparatus that performs the operation of discharging from the contact portion.

M device main body 1 image carrier (photosensitive drum)
2 cleaning member (cleaning blade)
3 developer (toner)
10 recording medium 100 control unit (CPU and controller)
101 drive source (drive motor)

Claims (11)

An image forming apparatus that performs an image forming operation for forming an image on a recording medium,
an image carrier for carrying an electrostatic latent image;
a cleaning member that contacts the image carrier and removes the developer from the image carrier;
a drive source for rotating the image carrier, the drive source rotating the image carrier in a first direction in the image forming operation;
A control unit for controlling the driving source, the control unit for performing an end operation after the image forming operation is finished and the image carrier is stopped and before the next image forming operation is started. a control unit;
has
The ending operation includes a preliminary operation and an intermittent operation performed after the preliminary operation. an operation of rotating and stopping the carrier, wherein the intermittent operation is an operation in which the stopped state of the image carrier and the rotation of the image carrier in the first direction are alternately repeated;
The waiting time is shorter than the stoppage time,
In the intermittent operation, the time of the stop state after the second time is longer than the time of the stop state immediately before that,
The image forming apparatus, wherein the intermittent operation includes the stop state for a first length and the stop state for a second length longer than the first length. 2. An image forming apparatus according to claim 1, wherein said image carrier is rotated in said first direction in said preliminary operation. 2. The image forming apparatus according to claim 1, wherein in said preliminary operation, said image carrier is rotated in a second direction opposite to said first direction. 4. The image forming apparatus according to claim 1, wherein, in the intermittent operation, the time of the stop state after the second time is longer than the time of the stop state immediately before. 5. The image forming apparatus according to claim 4, wherein in the intermittent operation, the difference between the time of the stop state after the second time and the time of the stop state immediately before that time is constant. 5. In the intermittent operation, the difference between the time of the stop state after the second time and the time of the stop state immediately before increases from the start to the end of the intermittent operation. The image forming apparatus according to . 7. The method according to any one of claims 1 to 6, wherein in the intermittent motion, the time during which each of the rotating motions is performed falls within a range of 50 to 150% of the average value of each time of the rotating motion during the intermittent motion. The image forming apparatus according to any one of the items. 8. The image forming apparatus according to claim 7, wherein in the intermittent operation, the time during which each of the rotating operations is performed falls within a range of 75% to 125% of the average value. 9. The image forming apparatus according to any one of claims 1 to 8 , wherein in the intermittent operation, the total rotation length of the image carrier is less than one rotation of the image carrier. 10. The image forming apparatus according to claim 9 , wherein in the intermittent operation, the total rotation length of the image carrier is less than one-eighth of the rotation of the image carrier. The time of the stop state varies according to at least one of the print rate and print mode in the image forming operation immediately before the end operation is performed, the environment when the end operation is performed, and the number of printed sheets. The image forming apparatus according to any one of claims 1 to 10 , characterized in that:

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