Patent Application
20130336670
1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
An image forming apparatus such as a laser beam printer includes a photosensitive drum as an image bearing member, a transfer roller as a transfer unit, and a cleaning blade as a cleaning unit. At the time of performing an image forming operation, a predetermined transfer voltage is applied to the transfer roller in order to transfer a toner as a developer on the photosensitive drum to a recording medium such as paper.
There is known such a configuration that, when the image forming operation is stopped halfway due to a generation of a paper jam or the like, a recovery operation is performed before resuming the image forming operation, to thereby remove the toner remaining on the photosensitive drum without being transferred to the recording medium. The removal of the toner remaining without being transferred is performed by conveying the toner adhered on the photosensitive drum to the cleaning blade along with rotation of the photosensitive drum. At this time, if a voltage having the same polarity as that of the voltage applied in the image forming operation is applied to the transfer roller, the toner on the photosensitive drum is transferred to the transfer roller, and contaminates the transfer roller. Thus, an image defect may occur in the next image formation.
To cope with this problem, Japanese Patent Application Laid-Open No. H04-163560 discloses a configuration for suppressing contamination of the transfer roller due to transfer of the toner on the photosensitive drum to the transfer roller by applying, in the recovery operation, a voltage having a polarity opposite to that of the voltage applied in the image forming operation to the transfer roller.
However, with the method disclosed in Japanese Patent Application Laid-Open No. H04-163560, when the recovery operation is performed in response to the stop of the image forming operation occurring in a state in which a large amount of toner is adhered to the photosensitive drum, a large amount of toner is conveyed to the cleaning blade, and hence the toner may not be completely removed by the cleaning blade. In such a case, the toner that cannot be completely removed and slips through the cleaning blade is adhered to the charging roller, causing a charging failure, which may generate a defective image such as a streaky image. In addition, the toner that has slipped through the cleaning blade may be printed in the next image formation after the recovery operation, causing an image defect such as a streak on an image.
The present invention has been made to suppress an image defect due to a failure in removing a developer by a cleaning unit.
According to an exemplary embodiment of the present invention, there is provided an image forming apparatus, including: an image bearing member provided in a rotatable manner; a developing unit configured to supply a developer onto the image bearing member; a transfer unit provided downstream of the developing unit in a rotation direction of the image bearing member, and configured to transfer the developer on the image bearing member to a recording medium by a transfer voltage applied to the transfer unit; a voltage applying unit configured to apply the transfer voltage to the transfer unit; and a cleaning unit configured to remove the developer on the image bearing member, wherein when the image forming apparatus stops an image forming operation halfway, the image forming apparatus executes a recovery operation of rotating the image bearing member to cause the cleaning unit to remove the developer remaining on the image bearing member without being transferred to the recording medium, and when the image forming apparatus executes the recovery operation, the voltage applying unit applies a voltage to the transfer unit so that a part of the developer remaining on the image bearing member without being transferred to the recording medium is once transferred from the image bearing member to the transfer unit, transferred again from the transfer unit to the image bearing member, and then removed by the cleaning unit.
According to another exemplary embodiment of the present invention, there is provided an image forming apparatus, including: an image bearing member provided in a rotatable manner; a developing unit configured to supply a developer onto the image bearing member; a transfer unit configured to transfer the developer by a transfer voltage applied to the transfer unit; a voltage applying unit configured to apply the transfer voltage to the transfer unit; and a cleaning unit configured to remove the developer on the image bearing member, wherein when the image forming apparatus stops an image forming operation halfway, the image forming apparatus executes a recovery operation of rotating the image bearing member to cause the cleaning unit to remove the developer remaining on the image bearing member without being transferred to a recording medium, and when the image forming apparatus executes the recovery operation, the voltage applying unit applies a voltage to the transfer unit so that a part of the developer remaining on the image bearing member without being transferred to the recording medium is once transferred from the image bearing member to a collecting unit, and a part of the developer transferred to the collecting unit is transferred to the image bearing member and then removed by the cleaning unit.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An overall configuration of an image forming apparatus according to an exemplary embodiment of the present invention will be described with reference to
The photosensitive drum 1 is rotatably provided to receive a driving force at the time of performing an image forming operation and to rotate in a direction indicated by an arrow R1 in
The charging roller 2 is provided so as to abut against the photosensitive drum 1 and uniformly charges a surface of the photosensitive drum 1. The charging roller is arranged upstream of the developing device 4 in a rotation direction of the photosensitive drum 1. The exposing device 3 emits a laser beam L to expose the surface of the photosensitive drum 1 via a reflection mirror 3a.
The developing device 4 includes a developing roller 4a as a developing unit, which is rotatably provided. The developing roller 4a carries a toner as a developer on its surface, and supplies the toner to the photosensitive drum 1. In this embodiment, a magnetic one-component toner having a negative charging property is used as the toner.
The transfer roller 5 abuts against the photosensitive drum 1 so as to be rotatable in a direction indicated by an arrow R2 in
The cleaning device 6 includes a cleaning blade 6a as a cleaning unit in contact with the photosensitive drum 1. At the time of performing an image forming operation, the cleaning blade 6a scrapes the toner remaining on the photosensitive drum 1 after the toner is transferred to the recording medium P by the transfer roller 5 to remove the toner from the photosensitive drum 1. The cleaning blade 6a is arranged downstream of the transfer roller 5 in the rotation direction of the photosensitive drum 1.
An overall image forming operation of the image forming apparatus will be described below with reference to
Detection of a stop of the image forming operation will be described below with reference to
The image forming apparatus illustrated in
The registration sensor 8a is a sensor which is configured to match the timing at which the recording medium P is conveyed to the transfer position TR and the timing at which the toner image formed on the photosensitive drum 1 is conveyed to the transfer position TR. The sheet discharge sensor 8b is a sensor which is configured to confirm whether or not the recording medium P is discharged to the outside of the image forming apparatus.
When the sheet discharge sensor 8b does not detect the recording medium P until a predetermined time is elapsed after the registration sensor 8a detects the recording medium P, it is detected that the image forming operation is stopped because there is a paper jam between the registration sensor 8a and the sheet discharge sensor 8b. Further, when the sheet discharge sensor 8b is not turned OFF until a predetermined time is elapsed after the sheet discharge sensor 8b detects the recording medium P (i.e., the recording medium P is continuously detected), it is detected that the image forming operation is stopped because there is a paper jam in the fixing device 7. In both the cases of detection, information of the sensor is processed in a controller unit 100 (see
A flow up to transition to a standby state by performing a recovery operation after the image forming operation is stopped will be described below with reference to
A sequence after detecting a paper jam will be described below with reference to
The image forming apparatus according to this embodiment is configured to convey the toner, which remains on the photosensitive drum 1 without being transferred, to the cleaning blade 6a multiple times when executing the recovery operation. When a large amount of toner is conveyed at a time to the cleaning blade 6a, the cleaning blade 6a may not completely remove the toner. That is, the image forming apparatus according to this embodiment is configured to suppress incomplete removal of the toner by the cleaning blade 6a and consequent slip-through of the toner. The sequence according to this embodiment is useful when the toner exists on the photosensitive drum 1 at the time when the paper jam is detected.
As illustrated in
Timings for applying the voltages to the transfer roller 5 and the charging roller 2 according to this embodiment will be described below with reference to
As illustrated in
“V0” in
“T0” in
“T4” indicates a timing for ending the application of a voltage −V4 to the charging roller 2 to adjust the potential on the photosensitive drum 1 during a discharge process to transfer the toner transferred to the transfer roller 5 again to the photosensitive drum 1. “T5” indicates a timing for ending the discharge process to transfer the toner transferred to the transfer roller 5 again to the photosensitive drum 1. That is, the timing T5 indicates a timing for ending the process of Step SS3 illustrated in
As illustrated in
A period from T2 to T3 is a period during which the drive is in an ON state to recover from the emergency stop so that a voltage +V1 of a positive polarity is applied to the transfer roller 5, and a voltage −V4 is applied to the charging roller 2. A period from T3 to T4 is a period during which a voltage −V2 of a negative polarity is applied to the transfer roller 5, and the voltage −V4 is continued to be applied to the charging roller 2. A period from T4 to T5 is a period during which the voltage −V2 is continued to be applied to the transfer roller 5. On the other hand, the adjustment of the surface potential on the photosensitive drum 1 to transfer the toner from the transfer roller 5 to the photosensitive drum 1 is ended, and hence the application of the voltage to the charging roller 2 is turned OFF. The timing T5 is the timing at which the discharge of the toner from the transfer roller 5 to the photosensitive drum 1 is ended, and hence the application of the voltage to the transfer roller 5 at T5 is turned OFF.
As described above, at the time of executing the recovery operation, during a period in which a portion of the surface of the photosensitive drum 1, to which the developer is supplied by the developing roller when the image forming operation is stopped, is rotated to move away from the developing unit and then first arrives at a position at which the portion comes into contact with the transfer roller 5, the developer is transferred to the transfer roller 5. After that, the developer is transferred from the transfer roller 5 to the photosensitive drum 1, enabling the cleaning to be performed efficiently. Further, at the time when the image forming operation is stopped, a portion of the photosensitive drum 1 located in the region B is configured to transfer a part of the developer to the transfer roller 5 when the portion first arrives at a position at which the portion comes into contact with the transfer roller 5. As a result, the time required until the recovery is completed can be shortened. That is, when the image forming operation is brought to an emergency stop due to a paper jam or the like, a part of the untransferred toner existing in the region B is transferred to the transfer roller 5 immediately after the recovery operation is started, and hence the above-mentioned effect can be achieved.
In
In a case where “circumferential length C>distance A+distance B” is satisfied, it is not necessary to consider whether the timing T3 is the timing at which the region B passes through the abutment position between the photosensitive drum 1 and the transfer roller 5 or the timing at which the region A passes through the abutment position as described above. It is because, in the case where “circumferential length C>distance A+distance B” is satisfied, when the toner transferred to the transfer roller 5 is conveyed again to the abutment position through the rotation of the transfer roller 5, the region A always passes through the abutment position by then.
Experimental results on an amount of the toner on the photosensitive drum 1 and slip of the toner through the cleaning blade 6a will be described below. In this experiment, the charging roller 2, the developing roller 4a, and the transfer roller 5 were arranged around the photosensitive drum 1 so that the distance A illustrated in
Firstly, in this experiment, a relationship between the amount of the toner on the photosensitive drum conveyed to the cleaning blade 6a and the slip of the toner through the cleaning blade 6a was confirmed. The results of the slip-through obtained at each voltage while changing the voltage applied to the transfer roller 5 from +300 V to +1,500 V are shown in Table 1. In Table 1, a case where the slip-through occurred and caused a risk of an image defect is indicated by “×”, a case where slight slip-through was confirmed but did not cause a risk of an image defect is indicated by “Δ”, and a case where there was no slip-through is indicated by “∘”.
As can be seen from Table 1, when 75% of the toner remained on the photosensitive drum 1 (i.e., 25% of the toner was transferred to the transfer roller 5), the slip-through of the toner occurred. Although the slip-through was not such a high level that an image defect was confirmed, because it is preferred that no slip-through occurs, it can be said that more than 25% of the toner (developer) remaining on the photosensitive drum 1 is preferred to be transferred to the transfer roller 5, where it is assumed that the amount of the toner (developer) remaining on the photosensitive drum 1 is 100%. When 50% of the toner remained on the photosensitive drum 1 (i.e., when 50% of the toner was transferred to the transfer roller 5), there was no slip-through of the toner. That is, in order to prevent the slip-through of the toner, it is preferred that the amount of the toner (developer) remaining on the photosensitive drum 1 and conveyed to the cleaning blade 6a be 50% or less. In other words, it is preferred that the amount of the toner of 50% or more be transferred to the transfer roller 5.
Further, a relationship between the slip-through of the toner and the voltage applied to the transfer roller 5 was confirmed. Experiments 1 to 5 are shown in Table 2 in this order from the left. As can be seen from Table 1, it is preferred that the amount of the toner conveyed to the cleaning blade 6a without being transferred to the transfer roller 5 be 50% or less, and hence the voltage V1 applied to the transfer roller 5 was set to +1,500 V in Experiments 1 to 4 and +600 V in Experiment 5. In each of the experiments, the surface potential of the photosensitive drum 1 was set to −100 V.
Experiment 1 will be described first. In the process of Step SS2 illustrated in
In Experiment 2, the voltage V1 in the process of Step SS2 illustrated in
In Experiments 3 and 4, the voltage V1 in the process of Step SS2 illustrated in
In Experiment 5, the voltage V1 in the process of Step SS2 illustrated in
From the above-mentioned experimental results, it has been found that the slip-through of the toner at the cleaning blade 6a can be prevented from occurring by controlling the voltage applied to the transfer roller 5 to be the values in Experiments 3 to 5. In Experiment 3, the number of revolutions of the transfer roller 5 was two. Thus, all the toner once transferred to the transfer roller 5 was transferred again to the photosensitive drum 1. In Experiments 4 and 5, the numbers of revolutions of the transfer roller 5 were four and one, respectively. Thus, all the toner once transferred to the transfer roller 5 was transferred again to the photosensitive drum 1. That is, it can be said that the image forming apparatus can be recovered from the stopped state most efficiently by performing the control of Experiment 5 in which the photosensitive drum 1 travels the shortest distance. In other words, although it is ideal that all the toner transferred to the transfer roller 5 is conveyed to the cleaning blade 6a through one revolution of the rotation of the transfer roller 5, two revolutions or more are still acceptable. For example, when a flexible material is used for the cleaning blade 6a, the amount of the toner that can be conveyed at a time is small, and hence it can be considered to suppress the amount of the toner conveyed by rotating the transfer roller 5 through two revolutions or more. In addition, if the control of Experiment 5 is used and if the circumferential length C of the transfer roller 5 and the distance B are equal to each other, the image forming apparatus can be recovered from the stopped state even more efficiently. It is because the collection of the toner at the transfer roller 5 can be performed through just one revolution of the transfer roller 5, and immediately after that, the toner can be discharged to the photosensitive drum 1.
Control of the voltage applied to the transfer roller 5 in the sequence of the recovery operation will be described with reference to
The image forming apparatus according to this embodiment is configured to intermittently convey the toner, which tightly remains on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1, to the cleaning blade 6a at the time of executing the recovery operation after an emergency stop of the image forming operation. This configuration will be described in detail below.
“t1” in
It goes without saying that simply switching the voltages in an alternate manner can achieve the effect instead of switching the voltages cyclically at equal intervals in an alternate manner because it suffices that the residual toner not be conveyed to the cleaning blade 6a at a time. Further, the voltage is switched at the transfer voltage V0, but the voltage V1, which is lower than the transfer voltage V0, or the like can be used instead. In this case, the voltage V1 and the voltage −V1 may be applied in an alternate manner, and the voltage V1 and the voltage −V0 may be applied in an alternate manner.
In the case where the transfer voltage V0 is applied, the toner on the photosensitive drum 1 is transferred to the transfer roller 5 at the transfer position TR illustrated in
In this manner, the toner tightly remaining on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 at the time of the emergency stop is divided into a portion where the toner remains on the photosensitive drum 1 and a portion where the toner does not remain on the photosensitive drum 1, and is intermittently conveyed to the cleaning blade 6a. In the portion where the toner remains on the photosensitive drum 1, a pressure is applied to the cleaning blade 6a by the toner, while no pressure is applied to the cleaning blade 6a by the toner in the portion where the toner does not remain on the photosensitive drum 1.
That is, the pressure by the toner is intermittently applied to the cleaning blade 6a. In this manner, in a configuration in which the pressures by the toner is intermittently applied to the cleaning blade 6a, a tip of the cleaning blade 6a is released from the pressure by the toner before the tip of the cleaning blade 6a is caught in the rotation direction of the photosensitive drum 1. As a result, the slip-through of the toner can be reduced.
“t2” in
When the voltage −V0 having a polarity opposite to that of the transfer voltage V0 is continuously applied to the transfer roller 5, all the toner transferred to the transfer roller 5 is transferred again to the photosensitive drum 1 at the transfer position TR during a period from t1 to t2. The voltage V0 and the voltage −V0 are applied in an alternate manner during the period from t1 to t2, and hence the toner transferred to the transfer roller 5 also exists intermittently on the transfer roller 5. As a result, the toner transferred again to the photosensitive drum 1 exists intermittently on the photosensitive drum 1.
Therefore, in the same manner as in the period from t1 to t2, even after the timing t2 at which the voltage −V0 is continuously applied, the toner is intermittently conveyed to the cleaning blade 6a. Accordingly, the toner can be removed without causing slip-through of the toner at the cleaning position CL.
“t3” in
Experimental results on a relationship between a switching cycle of the voltage applied to the transfer roller 5 by the bias applying unit 5d and the slip-through of the toner will be described with reference to Table 3. This experiment was conducted as follows. Firstly, during printing of an image of a considerably high coverage rate (solid black), the image forming operation was intentionally brought to an emergency stop in the image forming operation. At this time, the toner tightly and continuously remained in the circumferential direction of the photosensitive drum 1 between the developing position DE and the transfer position TR on the surface of the photosensitive drum 1. In this state, the transfer voltage V0 and the voltage −V0 were applied to the transfer roller 5 in an alternate manner at frequencies shown in Table 3. The circumferential length between the developing position DE and the transfer position TR on the surface of the photosensitive drum 1 used in this experiment was 20 mm. For each frequency, a case where the slip-through of the toner occurred and caused a risk of an image defect is indicated by “×”, a case where slight slip-through of the toner occurred but did not cause a risk of an image defect is indicated by “Δ”, and a case where there was no slip-through of the toner is indicated by “∘”.
When the voltage −V0 is continuously applied to the transfer roller 5 (i.e., the frequency is 0 Hz), all the toner remaining on the photosensitive drum 1 was conveyed to the cleaning blade 6a without being collected by the transfer roller 5. That is, the toner of the length of 20 mm continuously existing on the photosensitive drum 1 in the circumferential direction was conveyed to the cleaning blade 6a. In this case, the pressure by the toner was continuously applied on the cleaning blade 6a with no interruption, and hence the tip of the cleaning blade 6a was caught in the rotation direction of the photosensitive drum 1. As a result, it was confirmed that the slip-through of the toner occurred.
When the frequency was set to 10 Hz, the length of the toner remaining and continuously existing on the photosensitive drum 1 in the circumferential direction of the photosensitive drum 1 was 5 mm. That is, the toner of the length of 5 mm in the circumferential direction was continuously conveyed to the cleaning blade 6a, and with an interval of 5 mm, the next toner of the length of 5 mm was conveyed. In this case, the length of the toner continuously conveyed in the circumferential direction of the photosensitive drum 1 was still long, and hence the tip of the cleaning blade 6a was caught due to the pressure of the toner continuously applied on the cleaning blade 6a. As a result, it was confirmed that the slip-through of the toner slightly occurred.
When the frequency was set to 25 Hz, the length of the toner remaining and continuously existing on the photosensitive drum 1 in the circumferential direction of the photosensitive drum 1 was 2 mm. That is, the toner of the length of 2 mm in the circumferential direction was continuously conveyed to the cleaning blade 6a, and with an interval of 2 mm, the next toner of the length of 2 mm was conveyed. In this case, there was no slip-through of the toner. This is because a portion of the surface of the photosensitive drum 1 on which no toner exists arrived at the cleaning blade 6a before the tip of the cleaning blade 6a was caught in the rotation direction of the photosensitive drum 1 due to the pressure by the toner so that the cleaning blade 6a was released from the pressure by the toner. In the same manner, when the frequency was set to 50 Hz, there was no slip-through of the toner. From these facts, it has been found that the frequency suitable for reducing the slip-through of the toner is 25 Hz or higher. Further, it is preferred that the frequency be 25 Hz or higher and 50 Hz or lower.
As described above, in this embodiment, when performing the recovery operation after the image forming operation is stopped, the toner remaining on the photosensitive drum 1 is intermittently conveyed to the cleaning blade 6a. Therefore, the tip of the cleaning blade 6a is released from the pressure of the toner before the tip of the cleaning blade 6a is caught in the rotation direction of the photosensitive drum 1. Accordingly, the slip-through of the toner can be reduced and the defective cleaning can be reduced. As a result, an image defect due to a defective charging caused by an adherence of the toner to the charging roller 2 can be reduced.
So far, as illustrated in
A configuration of the image forming apparatus will be described first with reference to
An intermediate transfer belt (intermediate transfer member) 64 as a transfer material formed of an endless belt is arranged in the image forming apparatus. As illustrated in
On the inner circumferential surface of the intermediate transfer belt 64, primary transfer rollers 5y to 5b as a transfer unit are arranged to face the photosensitive drums 1y to 1b, respectively. The primary transfer rollers 5y to 5b presses against the intermediate transfer belt 64 so that the intermediate transfer belt 64 abuts against the photosensitive drums 1y to 1b. Positions on respective surfaces of the photosensitive drums 1y to 1b, which are pressed against the respective primary transfer rollers 5y to 5b, are defined as primary transfer positions TRy to TRb, respectively.
On the other hand, a secondary transfer opposed roller 68 is arranged at a position facing the secondary transfer roller 65 across the intermediate transfer belt 64. By the secondary transfer roller 65 and the secondary transfer opposed roller 68 nipping and conveying the recording medium P, a toner image formed on the intermediate transfer belt 64 (intermediate transfer member) is secondarily transferred to the recording medium P. A position on the intermediate transfer belt 64 where the secondary transfer is performed is defined as a secondary transfer position F.
The image forming apparatus further includes a registration sensor 8a and a sheet discharge sensor 8b as a stop detecting unit 8. As illustrated in
An overall image forming operation of the image forming apparatus will be described with reference to
Further, the recording medium P is conveyed to the secondary transfer roller 65 in synchronization with the circulating movement of the intermediate transfer belt 64, and the toner images of the respective colors that are formed on the intermediate transfer belt 64 in a superimposing manner are secondarily transferred to the recording medium P in a collective manner by an operation of the secondary transfer roller 65. The toner images transferred to the recording medium P are pressurized and heated by the fixing device 7 and fixed on the recording medium P. After that, the recording medium P on which the toner images are fixed is conveyed to the outside of the image forming apparatus, and hence a sequence of the image forming operation is completed.
After a stop of the image forming operation is detected, the control illustrated in the flowchart of
The sequence of the recovery operation in a case where the image forming operation is brought to an emergency stop so that the toner continuously exists on the intermediate transfer belt 64 in this embodiment will be described with reference to
As illustrated in
As a result, a toner 10ya, which is a part of the toner 10y on the photosensitive drum 1y, is transferred to the intermediate transfer belt 64, which is a collecting unit, at the primary transfer position TRy. Therefore, a toner 10yb remaining on the photosensitive drum 1y intermittently exists on the photosensitive drum 1y, and is intermittently conveyed to a cleaning blade 6ay as a cleaning unit. Therefore, the tip of the cleaning blade 6ay is released from the pressure by the toner before the tip of the cleaning blade 6ay is caught in the rotation direction of the photosensitive drum 1y due to the pressure by the toner. Accordingly, there is no slip-through of the toner at the cleaning blade 6ay.
On the other hand, by the circulating movement of the intermediate transfer belt 64 as the collecting unit, a toner 10ym remaining on the intermediate transfer belt 64 between the primary transfer position TRy and the primary transfer position TRm and the toner 10ya are conveyed to the primary transfer position TRm. The transfer voltage V0 and the voltage −V0 are applied to the transfer roller 5m in an alternate manner, and hence a toner 10ma, which is a part of the toner 10m on the photosensitive drum 1m, is transferred to the intermediate transfer belt 64 at the primary transfer position TRm, and the rest of toner, that is, a toner 10mb remains on the photosensitive drum 1m. At the same time, a toner 10ymb, which is a part of the toner 10ym on the intermediate transfer belt 64, is transferred to the photosensitive drum 1m at the primary transfer position TRm.
That is, the amount of the toner existing on the photosensitive drum 1m is a sum of the toner 10mb, which is a part of the toner 10m remaining on the photosensitive drum 1m, and the toner 10ymb transferred to the photosensitive drum 1m from the toner 10ym remaining on the intermediate transfer belt 64 as the collecting unit. In this manner, the amount of the toner existing on the photosensitive drum 1m and conveyed to a cleaning blade 6am is large. However, the toner exists on the photosensitive drum 1m intermittently, and hence the toner is intermittently conveyed to the cleaning blade 6am as the cleaning unit. Therefore, the tip of the cleaning blade 6am is released from the pressure of the toner before the tip of the cleaning blade 6am is caught in the rotation direction of the photosensitive drum 1m. Accordingly, there is no slip-through of the toner at the cleaning blade 6am.
The timing of ending the application of the voltages having different polarities from each other to the transfer rollers 5 in an alternate manner will be described below. In the same manner as the first embodiment, a timing at which a portion of the surface of the photosensitive drum 1y which is located at a developing position DEy at the time when the image forming operation is brought to the emergency stop arrives at the primary transfer position TRy is defined as t2. Further, a timing at which a portion of the surface of the intermediate transfer belt 64 which is located at the primary transfer position TRy at the time when the image forming operation is brought to the emergency stop arrives at the primary transfer position TRm located immediately downstream of the primary transfer position TRy in the circulating movement direction of the intermediate transfer belt 64 is defined as t4.
When t2>t4 is satisfied, at the timing t2, it is preferred to end the control of applying the transfer voltage V0 and the voltage −V0 in an alternate manner and perform control of applying the voltage −V0 to each transfer roller 5 in a continuous manner. The reason is as follows.
At the timing t2, all the toner 10ym remaining on the intermediate transfer belt 64 between the primary transfer position TRy and the primary transfer position TRm at the time of the emergency stop of the image forming operation passes through the primary transfer position TRm. That is, at the timing t2, a part of the toner 10ym (toner 10ymb) exists intermittently on the photosensitive drum 1m, and the other toner (toner 10yma) exists intermittently on the intermediate transfer belt 64.
Therefore, at the timing t2, by ending the control of applying the transfer voltage V0 and the voltage −V0 in an alternate manner and performing the control of applying the voltage −V0 to each transfer roller 5 in a continuous manner, all the toner on the intermediate transfer belt 64 can be transferred to the photosensitive drum 1. At this time, all the toner exists intermittently on the intermediate transfer belt 64 as described above, and hence all the toner transferred from the intermediate transfer belt 64 to the photosensitive drum 1 also exists intermittently.
When t2<t4 is satisfied, at the timing t4, it is preferred to end the control of applying the transfer voltage V0 and the voltage −V0 in an alternate manner and perform control of applying the voltage −V0 to each transfer roller 5 in a continuous manner. The reason is as follows.
When t2<t4 is satisfied, at the timing t2, all the toner 10ym remaining on the intermediate transfer belt between the primary transfer position TRy and the primary transfer position TRm at the time when the image forming operation was brought to the emergency stop does not pass through the primary transfer position TRm. That is, as illustrated in
Therefore, at the timing t4, by ending the control of applying the transfer voltage V0 and the voltage −V0 in an alternate manner and performing the control of applying the voltage −V0 to each transfer roller 5 in a continuous manner, all the toner on the intermediate transfer belt 64 can be transferred to the photosensitive drum 1. At this time, all the toner exists intermittently on the intermediate transfer belt 64 as described above, and hence all the toner transferred from the intermediate transfer belt 64 to the photosensitive drum 1 also exists intermittently.
As described above, at the time of performing the recovery operation after the stop of the image forming operation, the toners remaining on the photosensitive drum 1 and the intermediate transfer belt 64 are intermittently conveyed to the cleaning blade 6a. Therefore, the tip of the cleaning blade 6a is released from the pressure by the toner before the tip of the cleaning blade 6a is caught in the rotation direction of the photosensitive drum 1. Accordingly, the slip-through of the toner can be reduced and the defective cleaning can be reduced. As a result, an image defect due to a defective charging caused by an adherence of the toner to the charging roller 2 can be reduced.
Although an inline-type full-color image forming apparatus is described above, the same effect can also be obtained by using a rotary-type full-color image forming apparatus. Further, although the intermediate transfer belt is used as the collecting unit, the transfer roller as the transfer unit or a belt (ETB) configured to attract and convey a sheet of paper by using an electrostatic attraction force can also be used as the collecting unit.
As described above, in this embodiment, the toner remaining on the photosensitive drum 1 can be removed by conveying the toner to the cleaning blade 6a with a time delay. Therefore, a large amount of the toner is never conveyed to the cleaning blade 6a at a time, and hence the slip-through of the toner can be suppressed. As a result, a defective charging caused by an adherence of the toner to the charging roller 2 due to the slip-through of the toner can be suppressed, and hence an image defect caused by the defective charging can be suppressed.
Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application Nos. 2012-133721, filed Jun. 13, 2012, 2012-181106, Aug. 17, 2012, and 2013-118051, filed Jun. 4, 2013, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-133721 | Jun 2012 | JP | national |
| 2012-181106 | Aug 2012 | JP | national |
| 2013-118051 | Jun 2013 | JP | national |
