JP2012042803A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus with a high-quality printout having a well-cleaned image carrier surface with no attached matter thereon and thereby causing no dots on an image.SOLUTION: An image carrier is rotated at least once or more during the non-image formation period in a state where a transfer bias is controlled so that an image carrier surface potential in a rotational direction upstream of cleaning means has a reverse polarity to a developer.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system such as a copying machine or a printer.

  Conventionally, many methods are known as electrophotographic methods. In general, an electrostatic latent image is formed on an image carrier by using various methods for utilizing a photoconductive substance. Next, the electrostatic latent image is converted into a toner image by a developing device, and if necessary, the toner image is transferred to a transfer material such as paper, and then the toner image is fixed on the transfer material by heat or pressure to obtain a copy. It is. The toner image remaining on the image carrier is collected by a cleaning member.

  For this cleaning member, conventional blade cleaning, fur brush cleaning or roller cleaning has been widely used. However, in any of the cleaning methods, the transfer residual toner is mechanically scraped or damped and collected in a waste toner container.

  In such a mechanical cleaning method, external additives released from the toner surface may penetrate into the contact nip between the cleaning member and the image carrier due to torque fluctuations during rotation of the image carrier. It adheres to the surface of the image carrier by the pressure of the cleaning member against the external additive that has entered the nip. Once deposits are generated on the surface of the image carrier, they cannot be scraped off by the cleaning member, but pass up by pushing up the cleaning member. When the cleaning member is pushed up, the cleaning ability decreases, and a problem (cleaning failure) occurs in which the collected transfer residual toner is pulled through.

  In response to these problems, Patent Document 1 proposes to use a cleaning blade that exhibits a value of 200 kgf / cm 2 or more or breaks in a tensile stress test at 300% elongation as a cleaning member. By using such a cleaning blade, there has been proposed a technique that suppresses poor cleaning and adhesion of toner and external additives onto the image carrier.

  Further, in Patent Document 2, a discharge device is provided upstream of the cleaning device in the rotation direction of the photosensitive member, and the surface potential of the image carrier is changed to 0 ± 200 V to clean the transfer residual toner and silica as an external additive. We are proposing technologies that improve

JP 2000-147970 A JP 2004-069814 A

  However, due to the recent increase in speed and life of printers and copiers, and various usage environments, there is a tendency for the chance of abrasion of the image carrier by the cleaning member to increase. There was a problem that fine irregularities were generated on the surface of the image carrier due to the friction with the image carrier by the cleaning member, and the cleaning performance deteriorated due to the irregularities. In particular, the external additive released from the toner surface is difficult to clean because it has a smaller particle size than the toner. For this reason, if the surface of the image carrier has irregularities, the external additive slips through the cleaning member and exists as a deposit on the surface of the image carrier.

  In the area where the deposit is present, the contact between the cleaning member and the image carrier is deteriorated, which causes a problem of poor cleaning such that the toner slips through the area. When a cleaning failure occurs, an image failure occurs in which toner that has slipped out during the next image formation appears in the image. In addition, when the contact development method is adopted, the toner on the developing roller may adhere to the deposit at the development position even in the non-image region, which may be output as a black defective image defect. For this reason, although the technique of Patent Document 1 is effective for a flat image carrier by improving the cleaning performance by the cleaning blade, there is a possibility that the unevenness due to abrasion scratches on the surface of the image carrier cannot be completely cleaned. It was.

  In the technique disclosed in Patent Document 2, the surface potential of the image carrier is changed to 0 ± 200 V to improve the cleaning performance. However, Patent Document 2 aims to increase the cleaning efficiency of silica, and does not consider the cleaning of deposits other than silica.

  Accordingly, an object of the present invention is to provide a high-quality print output free from poor cleaning due to deposits on the surface of the image carrier and no black spots.

  The above object is achieved by the image forming apparatus according to the present invention.

  That is, a rotatable image carrier for carrying a latent image, a developing means for developing the latent image into a toner image with toner containing an external additive, and transferring the toner image to a transfer target. A transfer unit for performing cleaning, a cleaning unit for cleaning toner on the image carrier after the transfer, and a position upstream of the cleaning unit at the time of image formation in the rotation direction of the image carrier. The charged polarity of the image carrier is set to a predetermined polarity, and when the non-image is formed, the image carrier is charged to a polarity opposite to the predetermined polarity, and the surface of the image carrier charged to the reverse polarity is And a control unit that executes a cleaning mode in which the image carrier is rotated one or more times so as to pass through the unit.

  Without a special additional mechanism, it is possible to provide a high-quality print output free from poor cleaning due to deposits on the surface of the image carrier and no black spots.

It is a schematic sectional drawing based on 1st Embodiment which can apply this invention. FIG. 6 is a diagram illustrating a relationship between a primary transfer bias and a pre-cleaning potential according to the present embodiment. It is a schematic sectional drawing at the time of the cleaning mode based on this embodiment. FIG. 6 is a diagram illustrating a relationship between a primary transfer bias and a pre-cleaning potential in a use environment according to the present embodiment. It is a schematic sectional drawing based on 1st Embodiment which can apply this invention. It is a schematic sectional drawing based on 2nd Embodiment which can apply this invention. It is a schematic sectional drawing based on 3rd, 4th embodiment which can apply this invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

<Embodiment 1>
An image forming apparatus 100 according to a first embodiment of the present invention will be described with reference to FIG. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the invention is applied and various conditions. However, the present invention is not intended to be limited to the following embodiments.

  The configuration of the image forming apparatus of this embodiment is shown in FIG. In the figure, reference numeral 1 denotes a photosensitive drum as an image carrier. The photosensitive drum 1 is rotatably provided and rotates in the arrow R1 direction. Reference numeral 2 denotes a charging roller. The laser beam transmitted from the exposure device 3 is arranged so as to reach the exposure position A on the photosensitive drum 1.

  The developing device 6 includes a developing roller 10 that contains negative toner and is a developer carrying member. Development is performed at a development position C where the developing roller 10 faces and contacts the photosensitive drum 1.

  Under the photosensitive drum 1, a transfer belt 16 as an intermediate transfer member (transferred member) is stretched around a plurality of rollers and arranged to rotate in the R2 direction of FIG. A primary transfer unit 9 is disposed in the transfer belt 16 at a primary transfer position B where the photosensitive drum 1 and the transfer belt 16 are pressed and contacted. A secondary transfer roller 18 is disposed on one of the rollers 16b around which the transfer belt 16 is stretched so as to sandwich the transfer belt 16 therebetween. At the secondary transfer position D, the image is transferred onto the transferred transfer material 13. The transferred transfer material 13 is sent to a fixing device 17.

  A photosensitive member cleaning device 11 is installed downstream of the primary transfer position B in the moving direction of the photosensitive drum 1, and an attached blade 5 is disposed so as to scrape off the toner on the photosensitive drum 1. After the cleaning, the photosensitive drum 1 is charged again by the second charging roller.

  An operation during image formation of the image forming apparatus will be described. The term “image formation” as used herein refers to the time when operations such as charging, exposure, development, and transfer are performed in order to form an image on a recording sheet. The surface of the photosensitive drum 1 rotating at 100 mm / sec in the direction of the arrow R1 is uniformly charged by the charging roller 2 to a predetermined potential having the same polarity (negative polarity) as that of the toner. At the exposure position A, an electrostatic latent image is formed on the photosensitive drum 1 by a laser beam transmitted according to the image signal by the exposure device 3. The formed electrostatic latent image is developed by the developing device 6 at the developing position C to form a toner image. The toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 16 at the primary transfer position B.

  Specifically, a voltage of −1100 V is applied to the charging roller 2 to charge the photosensitive drum 1 to −530 V. The exposure device 3 exposes the photosensitive drum 1 in accordance with the image signal to form an electrostatic latent image on the photosensitive drum 1. The developing device 6 causes negative toner to adhere to the exposed portion and reversely develops the electrostatic latent image into a toner image. A voltage of +450 V is applied to the transfer device 9 to transfer the toner image to the intermediate transfer belt 16. The potential of the photosensitive drum 1 after the transfer is about −210 V due to the influence of the voltage by the transfer unit 9.

  An external additive is added to the toner used in this embodiment. The external additive specifically includes silica for the purpose of imparting fluidity to the toner, and specifically titanium oxide for the purpose of making the charge amount of the toner uniform.

  The cleaning device 11 in this embodiment is a blade-type device using an elastic cleaning blade 5 composed of a urethane rubber tip blade and a sheet metal as a cleaning member. The blade 5 is disposed in contact with the photosensitive drum 1 with its tip portion facing the counter with respect to the rotation direction of the drum 1 (image carrier rotation direction). The transfer residual toner on the drum surface is scraped off by the blade 5 and stored in the waste toner chamber 14 (waste toner container).

  Also in the present embodiment, as described above, because the long life, high speed, and various usage environments are supported, the surface of the image carrier is subject to fine uneven scratches due to abrasion of the blade 5 to the photosensitive drum 1. It grows in the direction of rotation. The unevenness may reduce the cleaning performance and cause deposits. It was found that this deposit could not be scraped well even if it was scraped off with the blade 5 during image formation.

  As a result of investigations by the inventors, it has been found that the cleaning property of the deposit is related to the potential of the photosensitive drum 1 immediately before the blade. This will be described below.

  FIG. 2 shows the surface potential of the photosensitive drum 1 on the upstream side of the blade 5 in the rotation direction of the photosensitive drum 1 when the transfer bias from the primary transfer power source 109 is changed in a charging bias application state equivalent to that at the time of image formation. The relationship of the potential before cleaning) is shown. Accordingly, when the absolute value of the transfer bias is increased from 0 V with the reverse polarity (positive polarity) to the toner, the polarity of the potential before cleaning is reversed from the same polarity as the toner to the reverse polarity.

  Next, the photosensitive drums 1 having almost the same number of deposits were prepared, and the potential before cleaning was changed by changing the potential before cleaning.

  Image formation is repeated a predetermined number of times to generate deposits on the photosensitive drum 1. In a state where the number of deposits deposited on the photosensitive drum 1 is substantially equal, the potential before cleaning is set to an arbitrary value by changing the primary transfer bias under the same conditions as in FIG. Table 1 shows the result of confirming the adhesion level of the photosensitive drum 1 after rotating the rotational speed of the photosensitive drum 1 to 10 and 30 in this state. The case where there is no change in the adhesion level is indicated as x, and the case where the adhesion level is reduced and the adhesion level is improved is indicated as ◯. At this time, the developing device 6 and the photosensitive drum 1 are in a non-contact state. From this result, it was found that when the pre-cleaning potential is the same polarity (negative polarity) as that of the toner, the adhesion level of the deposit is not changed and is not collected by the blade 5. On the other hand, in the case of the polarity opposite to the toner (positive polarity), the adhered matter was collected by the blade 5 and decreased from the photosensitive drum 1.

  Consider this result.

  It is considered that the external additive added to the toner has a charge polarity that is the same as that of the toner (negative polarity) and a charge polarity that is opposite to that of the toner (positive polarity).

  At the time of image formation, the potential before cleaning has the same polarity as the toner (negative polarity). When the pre-cleaning potential is the same polarity (negative polarity) as that of the toner, external additives such as silica charged to the same polarity (negative polarity) as the toner exert a repulsive force between the photosensitive drum 1. Therefore, even if unevenness occurs on the surface of the photosensitive drum 1, it is easily cleaned by the cleaning member. However, the external additive charged with a polarity (positive polarity) opposite to that of the toner is difficult to be cleaned because an attractive force acts between the external additive and the photosensitive drum 1. Further, such an external additive easily enters the contact nip between the cleaning member and the photosensitive drum 1. The external additive that has entered the nip adheres to the photosensitive drum 1 by the pressure of the cleaning member inside the nip. For this reason, by repeating the image formation, an external additive (attachment) charged to the surface opposite to the toner is generated on the surface of the photosensitive drum 1.

  As a result of experiments, when the potential before cleaning of the photosensitive drum 1 was set to the same polarity (negative polarity) as that of the toner, deposits on the photosensitive drum 1 were not removed. On the other hand, when the potential before cleaning of the photosensitive drum 1 is set to a polarity opposite to that of the toner (positive polarity), the deposits on the photosensitive drum 1 are removed and the number of deposits tends to decrease.

  This is presumably because the positively charged deposit has a reduced adhesion due to the polarity of the surface potential of the photosensitive drum 1 and can be easily cleaned. The decrease in adhered matter also varies depending on the potential before cleaning and the number of rotations that rotate the photosensitive drum 1. If the pre-cleaning potential has a polarity opposite to that of the toner and has a large absolute value, the amount of deposits is reduced even at a low rotational speed. If the potential before cleaning is a polarity opposite to that of the toner and has a small absolute value, the amount of deposits does not decrease unless the rotational speed is increased.

  In this embodiment, when the potential before cleaning is increased to a polarity opposite to that of the toner and becomes greater than 550 V, the remaining power is left as a plus memory on the photosensitive drum 1, and density unevenness occurs in the image when the next image formation is performed. did. Therefore, the potential before cleaning is preferably 550 V or less.

  Using the above result, the present embodiment is characterized in that the cleaning mode is executed at a predetermined timing during non-image formation. In the cleaning mode, when the polarity of the potential before cleaning at the time of image formation is set to a predetermined polarity, the photosensitive drum 1 is charged to a polarity opposite to the predetermined polarity. Then, the photosensitive drum 1 is rotated at least one turn so that the region charged to the opposite polarity passes through the blade 5. By doing so, the blade 5 passes through the entire circumference of the photosensitive drum 1 while being charged with a reverse polarity. Accordingly, the positively charged deposit is scraped off by the blade 5 over the entire circumference of the photosensitive drum 1.

  The execution timing of the cleaning mode is performed at the time of non-image formation after the rotation time of the photosensitive drum 1 from the previous execution of the cleaning mode reaches a predetermined value. The rotation time of the photosensitive drum 1 is stored in a storage unit included in the image forming apparatus and is used as a criterion for executing the cleaning mode.

  The cleaning mode is controlled by the CPU 60 which is a control means. The CPU 60 compares the rotation time of the photosensitive drum 1 stored in the storage unit with the threshold value for executing the cleaning mode stored in advance, and executes the cleaning mode when the rotation time exceeds the threshold value. The CPU 60 controls the rotation of the photosensitive drum 1, controls the application of a bias to the charging roller 2 and the primary transfer unit 9, and executes the cleaning mode.

  As shown in FIG. 3, the cleaning mode in this embodiment is such that the developing device 6 and the photosensitive drum 1 are in a non-contact state, the laser beam is not irradiated from the exposure device 3, the primary transfer unit 9 is in a contact state, and the photosensitive drum 1 is rotated 30 times in the direction of arrow R1.

  Here, the number of rotations of the photosensitive drum 1 is set to 30. However, the larger the number of rotations, the higher the deposit removal effect. However, if the rotational speed is large, more cleaning mode time is required, which may hinder the next print job. Therefore, the rotational speed of the photosensitive drum 1 in the cleaning mode may be changed depending on the apparatus configuration to which the invention is applied and various conditions. The photosensitive drum 1 may be rotated at least once, and a necessary number of rotations may be set according to the amount of deposits.

  Table 2 shows the bias applied during image formation and the cleaning mode in this embodiment, and the surface potential of the photosensitive drum 1 at that time. As shown in Table 2, the charging bias is the same as that at the time of image formation, and the primary transfer bias is changed so that the potential before cleaning becomes positive.

  Here, the potential before cleaning is controlled to be positive only in the cleaning mode. In the image forming apparatus that charges the photosensitive drum 1 with a negative polarity, if the surface potential of the photosensitive drum 1 is charged with a positive polarity for a long time, the photosensitive drum 1 is left as a plus memory to be used for the next image forming image. There is a possibility of being output as density unevenness. Therefore, the surface potential of the photosensitive drum 1 is preferably negative or 0, and the potential before cleaning at the time of image formation is negative and is set to be positive only in the cleaning mode.

  In this embodiment, specific applied bias values are shown in Table 2. However, as shown in FIG. 4, the conditions under which the potential before cleaning becomes positive depend on the temperature and humidity environment used. FIG. 4 is a diagram showing the relationship between the primary transfer bias and the pre-cleaning potential in the usage environment. This is because the resistance of the intermediate transfer belt 16 and the primary transfer sheet member 9a varies depending on the use environment. Thus, in the present embodiment, the condition that the potential before cleaning is positive is stored in the storage unit of the image forming apparatus depending on the environment used in advance, and is controlled according to the condition.

  By periodically performing the cleaning mode in this manner, the deposits on the photosensitive drum 1 can be effectively removed, resulting in poor cleaning due to deposits and high-quality print output without black spots. Can be provided.

  In this embodiment, an example in which a transfer sheet and an intermediate transfer belt are used as the primary transfer unit has been described. However, as illustrated in FIG. 5, transfer is performed while the transfer material 13 is moved directly between the toner image and the transfer roller. A configuration may be used.

  In the first embodiment, an example in which the potential before cleaning at the time of image formation is negative has been described. However, the present invention is applicable even when the potential before cleaning at the time of image formation is positive. is there. In that case, in the cleaning mode, the potential before cleaning is set to be negative.

<Embodiment 2>
With reference to FIG. 6, an image forming apparatus 100 according to the first exemplary embodiment of the present invention will be described. Since the basic configuration is the same as that of the first embodiment, only the features of this embodiment will be described.

  In the first embodiment, the cleaning mode is periodically performed. However, the more frequently the cleaning mode is performed, the higher the effect of suppressing the generation of deposits. Further, as described in the first embodiment, the effect of improving deposits is higher as the number of rotations of the photosensitive drum 1 during execution of the cleaning mode is larger.

  However, both the execution frequency and the number of rotations of the photosensitive drum 1 increase the possibility of hindering the next print job.

  Therefore, if a situation where deposits are likely to occur is predicted, the frequency of execution of the cleaning mode and the number of rotations of the photosensitive drum 1 may be changed depending on the situation.

  As described above, if the surface potential of the photosensitive drum 1 is charged for a long time with a positive polarity opposite to the charging polarity at the time of image formation, the remaining charge is left on the photosensitive drum 1 as a plus memory, and the next image formation is performed. There is a possibility that the image is output as density unevenness. By adopting a configuration in which the cleaning mode is executed only when necessary, as in the present embodiment, the risk that the photosensitive drum 1 generates a plus memory and causes image defects can be reduced.

  In this embodiment, the execution frequency of the cleaning mode is changed according to the environment in which it is used. In the case of a high temperature and high humidity environment, liberation of external additives from the toner surface increases. Therefore, deposits on the photosensitive drum 1 tend to be generated more easily in a high temperature and high humidity environment. Therefore, the implementation frequency is higher in a high temperature and high humidity environment, and the implementation frequency is lowered because the risk of deposits is lower in a low temperature and low humidity environment.

  The execution timing of the cleaning mode is performed at the time of non-image formation after the rotation time of the photosensitive drum 1 from the previous execution of the cleaning mode reaches a predetermined value. The rotation time of the photosensitive drum 1 is stored in a storage unit included in the image forming apparatus and is used as a criterion for executing the cleaning mode.

  In this embodiment, as shown in FIG. 6, the image forming apparatus includes a temperature detection unit 70 (environment detection unit). As shown in Table 3, according to the detection result of the temperature detection means 70, whether or not to execute the cleaning mode, the execution threshold value is stored in the storage means.

  When it is the environmental temperature at which the cleaning mode is executed, it is executed by the CPU 60 as the control means. The CPU 60 compares the rotation time of the photosensitive drum 1 stored in the storage unit with the execution threshold stored in advance, and executes the cleaning mode when the rotation time exceeds the threshold. The CPU 60 controls the rotation of the photosensitive drum 1, controls the application of a bias to the charging roller 2 and the primary transfer unit 9, and executes the cleaning mode.

  In this embodiment, the temperature is taken into consideration. However, both the temperature and the humidity may be taken into consideration, or only the humidity may be taken into consideration. For example, the implementation frequency may be higher in a high humidity environment and the implementation frequency may be lower in a low humidity environment.

  In the present embodiment, the execution threshold value is changed according to the environmental temperature. However, the rotation speed of the drum may be changed. For example, the control may be performed as shown in Table 4.

  As described above, it is determined whether the environment is a low temperature (low humidity) environment (first environment) or a higher temperature (high humidity) environment (second environment) than the first environment, and the execution frequency of the cleaning mode is changed. Or in cleaning mode.

That is, control is performed so that the frequency of executing the cleaning mode is higher in the high temperature (high humidity) environment than in the low temperature (low humidity) environment.
That is, control is performed so that the number of rotations of the photosensitive drum rotated in the cleaning mode is higher in the high temperature (high humidity) environment than in the low temperature (low humidity) environment.
Further, the execution frequency and the control of the number of rotations of the photosensitive drum may be combined and executed.

<Embodiment 3>
With reference to FIG. 7, an image forming apparatus 100 according to the first exemplary embodiment of the present invention will be described.
In the second embodiment, the frequency of deposit generation varies depending on the use environment, and therefore, the mode in which the cleaning mode is performed in accordance with the use environment is shown. The present embodiment relates to an image forming apparatus that employs a configuration in which a developing device 6 is detachably provided from a main body of the image forming apparatus. Note that the image forming apparatus main body refers to a portion other than the developing device 6 in the image forming apparatus 100.

  When the replaceable developing device 6 is employed, if the developing device 6 is replaced with a new one while the surface of the photosensitive drum 1 is uneven due to wear scratches, the new toner has more free external additives. During the initial operation (for example, toner stirring operation), deposits are likely to occur. Therefore, the cleaning mode is executed at the timing after the initial operation and before the start of image formation.

  As described above, if the surface potential of the photosensitive drum 1 is charged for a long time with a positive polarity opposite to the charging polarity at the time of image formation, the remaining charge is left on the photosensitive drum 1 as a plus memory, and the next image formation is performed. There is a possibility that the image is output as density unevenness. By adopting a configuration in which the cleaning mode is executed only when necessary as in the present embodiment, it is possible to reduce the risk that the photosensitive drum 1 generates a plus memory and causes an image defect.

  Basically, the cleaning mode is performed at a regular timing for each rotation time of the photosensitive drum 1. Therefore, when the developing device usage status detecting means 80 detects that the new developing device 6 has been inserted, the cleaning mode is immediately executed regardless of the periodic timing. That is, the cleaning mode is executed before starting image formation. As a result, even if a deposit due to an external additive is generated during a new initial operation, it can be effectively removed.

<Embodiment 4>
With reference to FIG. 7, an image forming apparatus 100 according to the first exemplary embodiment of the present invention will be described.
In the third embodiment, an example is shown in which the new developing device 6 is replaced and the cleaning mode is executed before starting image formation. However, since the new developing device has more free external additives, it corresponds to the amount of use of the developing device. Thus, the frequency of performing the cleaning mode and the number of rotations of the photosensitive drum 1 may be varied.

  In the present embodiment, when the usage amount of the developing device 6 from a new state is small, there is a high possibility that a free external additive is present in the developing device 6. The frequency of execution and the number of rotations of the photosensitive drum 1 are increased.

  As described above, if the surface potential of the photosensitive drum 1 is charged for a long time with a positive polarity opposite to the charging polarity at the time of image formation, the remaining charge is left on the photosensitive drum 1 as a plus memory, and the next image formation is performed. There is a possibility that the image is output as density unevenness. By adopting a configuration in which the cleaning mode is executed only when necessary as in the present embodiment, it is possible to reduce the risk that the photosensitive drum 1 generates a plus memory and causes an image defect.

  In the present embodiment, as shown in FIG. 7, the image forming apparatus 100 includes a developing device usage status detection unit 80. The image forming time is used as the usage amount of the developing device. For example, the image forming time after the developing device is replaced with a new one is stored in a storage means (memory tag) provided in the developing device. Then, the cleaning mode is controlled based on the image formation time stored in the memory tag.

  As shown in Table 5, the cleaning mode execution threshold is stored in the storage unit according to the image forming time detected by the developing device usage status detection unit 80.

  The cleaning mode is executed by the CPU 60 which is a control unit. The CPU 60 compares the rotation time of the photosensitive drum 1 since the previous cleaning mode was executed with an execution threshold stored in advance, and executes the cleaning mode when the rotation time exceeds the threshold. The CPU 60 controls the rotation of the photosensitive drum 1, controls the application of a bias to the charging roller 2 and the primary transfer unit 9, and executes the cleaning mode.

  In the present embodiment, the execution threshold value is changed according to the environmental temperature. However, the rotation speed of the drum may be changed. For example, the control is performed as shown in Table 4.

  As described above, it is determined whether the developing device usage amount is small (first usage amount) or the developing device usage amount is larger than the first usage amount (second usage amount). Is changed, or the rotation speed of the photosensitive drum rotated in the cleaning mode is changed.

That is, the control is performed so that the frequency of executing the cleaning mode is lower when the usage amount of the developing device is larger than when the usage amount of the developing device is small.
That is, control is performed so that the number of rotations of the photosensitive drum rotated in the cleaning mode is reduced when the usage amount of the developing device is larger than when the usage amount of the developing device is small.
Further, the execution frequency and the control of the number of rotations of the photosensitive drum may be combined and executed.

[Others]
In the first to fourth embodiments, the primary transfer unit 9 is used as a member for forming a pre-cleaning potential in the cleaning mode, but the present invention is not limited to this. For example, the pre-cleaning potential in the cleaning mode may be controlled by changing the bias applied to the charging roller 2. In addition, the potential of the photosensitive drum 1 may be controlled by a member other than the charging roller 2 and the transfer unit 9.

  In the first to fourth embodiments, the reversal development image forming apparatus has been described. However, the present invention is not limited to this. For example, the present invention can also be applied to an apparatus for regular development in which the charging polarity of the photosensitive drum and the charging polarity of the toner at the time of image formation are reversed.

In the first to fourth embodiments, the description has been given of the monochrome image forming apparatus. The present invention can also be applied to a full-color image forming apparatus.
Moreover, you may make it perform cleaning mode combining the control of Embodiment 2-4.

1 Photosensitive drum 2 Charging roller (charging means)
3 Exposure means 5 Cleaning member 6 Developing device 9 Primary transfer member 10 Developing roller 11 Cleaning device 14 Waste toner chamber 16 Intermediate transfer belt 17 Fixing member 18 Secondary transfer member 60 CPU
70 Environment Detection Unit 80 Developing Device Usage Status Detection Unit 100 Image Forming Device 102 Charging Bias Power Supply Device 109 Primary Transfer Bias Power Supply Device

Claims (7)

A rotatable image carrier for carrying a latent image;
Developing means for developing the latent image into a toner image with toner containing an external additive;
Transfer means for transferring the toner image to a transfer medium;
Cleaning means for cleaning toner on the image carrier after transfer;
The charging polarity of the image carrier at a position upstream in the rotational direction of the image carrier relative to the cleaning unit during image formation is set to a predetermined polarity.
At the time of non-image formation, the image carrier is charged with a polarity opposite to a predetermined polarity, and the image carrier is set to 1 so that the surface of the image carrier charged with the reverse polarity passes through the cleaning means. An image forming apparatus comprising: a control unit that executes a cleaning mode that rotates more than once.   The image forming apparatus according to claim 1, wherein in the cleaning mode, the transfer unit charges the image carrier with a polarity opposite to a predetermined polarity. Equipped with environmental detection means for detecting temperature or humidity;
The first environment and an environment of higher temperature or higher humidity than the first environment as the second environment,
Depending on whether the environment detected by the environment detection means is the first environment or the second environment,
3. The image formation according to claim 1, wherein the control unit performs control so that the frequency of executing the cleaning mode is higher in the second environment than in the first environment. 4. apparatus. Equipped with environmental detection means for detecting temperature or humidity;
The first environment and an environment of higher temperature or higher humidity than the first environment as the second environment,
Depending on whether the environment detected by the environment detection means is the first environment or the second environment,
2. The control unit according to claim 1, wherein the second environment controls the number of rotations for rotating the image carrier in the cleaning mode to be higher than that in the first environment. The image forming apparatus according to claim 3. The developing means is detachably provided from the image forming apparatus main body,
Determining means for determining whether or not the developing means is new,
5. The image forming apparatus according to claim 1, wherein when the developing unit determines that the developing unit is new, the cleaning mode is executed before starting image formation. . A judging means for judging the amount of the developing means used;
As the usage amount of the developing means, when the first usage amount and the second usage amount having a larger usage amount of the developing means than the first usage amount,
Depending on whether the usage amount of the developing means determined by the determination means is the first usage amount or the second usage amount,
6. The control unit according to claim 1, wherein the second usage amount is controlled to be executed less frequently than the first usage amount. 7. The image forming apparatus described in 1. A judging means for judging the amount of the developing means used;
As the usage amount of the developing means, when the first usage amount and the second usage amount having a larger usage amount of the developing means than the first usage amount,
Depending on whether the usage amount of the developing means determined by the determination means is the first usage amount or the second usage amount,
2. The control unit according to claim 1, wherein the second usage amount is controlled so that the number of rotations for rotating the image carrier in the cleaning mode is smaller than the first usage amount. The image forming apparatus according to any one of 1 to 6.

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