JP2010079002A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation in image quality due to foreign matter adhering to a photoreceptor drum and also to prevent the life times of a contact member and photoreceptor drum from shortening. <P>SOLUTION: The photosensitive drum 31 is a member that bears an electrostatic latent image on its surface. A blade member 371 is disposed in contact with the surface of the photoreceptor drum 31 and scrapes matter adhering to the surface of the photoreceptor drum 31. An AC bias application device 10 is a mechanism that increases force with which matter adhering to the photoreceptor drum 31 is removed from the blade member 371. A timing determination section 111 is a means for determining the timing of increasing the removing force of the blade member 371 using the AC bias application device 10. A bias application control section 112 is a means for increasing the removal force of the blade member 371 at the timing determined by the timing determination section 111. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In general, an electrophotographic image forming apparatus includes a photosensitive drum capable of carrying an electrostatic latent image on a surface, a charging device for charging the surface of the photosensitive drum, and an exposure device capable of exposing the surface of the photosensitive drum. A developing device capable of supplying a developer to the photosensitive drum, a cleaning blade for cleaning the surface of the photosensitive drum, a transfer unit for transferring an image on the photosensitive drum to paper, and an image formed on the surface A sheet conveying unit configured to convey a possible sheet and a fixing unit configured to fix an image on the sheet.

  In this image forming apparatus, the surface of the photosensitive drum is uniformly charged by the charging device, and is exposed based on the image information by the exposure device. By this exposure, an electrostatic latent image is formed on the photosensitive drum, and a developer is supplied from the developing device to the electrostatic latent image on the photosensitive drum. Then, the image on the photosensitive drum is transferred to the sheet conveyed by the sheet conveying unit in the transfer unit. Thereafter, the developer remaining on the photosensitive drum without being developed is cleaned with a cleaning blade. The sheet on which the image is transferred is conveyed to the fixing unit, and the image is fixed on the sheet. The sheet on which the image is fixed is discharged out of the apparatus by the discharge unit.

  Here, after the operation of charging the surface of the photosensitive drum is repeated, if the state where the photosensitive drum is not driven continues due to the power being cut off or the like, a discharge product or the like is generated on the surface of the photosensitive drum over time. Of foreign matter may adhere. When foreign matter such as a discharge product adheres to the photosensitive drum, image flow may occur. When image flow occurs, the image quality of the formed image deteriorates.

In order to solve such a problem, an image forming apparatus in which the pressing force of the cleaning blade to the photosensitive drum is increased is considered. However, when the pressing force of the cleaning blade to the photosensitive drum is increased, the wear amount of the photosensitive drum and the cleaning blade increases. For this reason, the lifetime of the photosensitive drum and the cleaning blade is shortened.
In order to solve the above problem, there is an apparatus in which an AC bias is applied to a contact member that contacts a photosensitive drum such as a roller or a blade (see Patent Document 1). Here, the AC bias refers to an AC voltage superimposed on a DC voltage.

  In the apparatus in which the AC bias is applied, the AC bias is applied to the contact member. Due to the AC bias applied to the contact member, a force in a direction away from the photosensitive drum acts on the foreign matter on the photosensitive drum, and the contact member vibrates with respect to the photosensitive drum. At this time, the foreign matter adhering to the photosensitive drum is easily separated from the photosensitive drum due to the influence of the AC bias, and the contact member scrapes the foreign matter from the photosensitive drum as the photosensitive drum rotates.

JP 2002-6707

  In the apparatus described in Patent Document 1, an AC bias is applied to the contact member even when the discharge product is not attached to the photosensitive drum. For this reason, the surfaces of the contact member and the photosensitive drum are worn more than necessary, and the life of the contact member and the photosensitive drum is shortened.

  SUMMARY OF THE INVENTION An object of the present invention is to prevent the image quality from being deteriorated by a foreign matter adhering to the photosensitive drum and to prevent the life of the contact member and the photosensitive drum from being shortened.

  An image forming apparatus according to a first aspect of the present invention is an image forming apparatus capable of forming an image based on image information, and includes an image carrier, a contact member, an increase mechanism, a timing determination unit, and an increase mechanism control unit. I have. The image carrier is a member capable of carrying an electrostatic latent image on the surface. The contact member is a member that can come into contact with the surface of the image carrier and scrape off deposits attached to the surface of the image carrier. The increase mechanism is a mechanism that increases the removal force for removing the deposits attached to the image carrier of the contact member. The timing determining means is means for determining the timing for increasing the contact member removal force by the increasing mechanism. The increase mechanism control means is means for increasing the removal force of the contact member at the timing determined by the timing determination means.

  In this image forming apparatus, after the image carried on the image carrier is transferred onto a sheet or the like, the developer remaining on the surface of the image carrier is scraped off by the contact member as the image carrier is rotated. The surface of the image carrier is cleaned by the contact member to prepare for the next image forming operation. Here, for example, when a discharge product adheres to the surface of the image carrier, there is a case where a substance that is difficult to be scraped off simply by driving the image carrier while contacting the contact member may adhere to the image carrier. is there. The removal force of the contact member is increased at a predetermined timing by the timing determining means. Then, foreign substances such as discharge products attached to the surface of the image carrier are removed by the contact member having an increased removal force.

  Here, since the removing force of the contact member is increased at the timing determined by the timing determining means, the foreign matter adhering to the image carrier can be removed, and the image flow caused by the foreign matter can be prevented. Further, since the removal force is increased only at the timing determined by the timing determining means, the contact member and the image carrier are not easily worn. For this reason, it is possible to prevent the life of the image carrier from being shortened. For example, by determining the timing at which foreign matter adheres to the surface of the image carrier as the timing at which the removal force of the contact member is increased, the removal force is not increased when no foreign matter is attached to the image carrier, and the contact member and It is possible to prevent the life of the image carrier from being shortened.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, further comprising image flow detecting means for detecting the image flow of the electrostatic latent image formed on the surface of the image carrier. The timing determination unit determines the timing based on the detection result of the image flow detection unit.

  Here, since the timing is determined based on the detection result of the image flow detection means, the removal force of the contact member is increased when the image flow is detected. For this reason, it is possible to prevent the image flow caused by the deposits attached to the surface of the image carrier.

  An image forming apparatus according to a third aspect is the image forming apparatus according to the second aspect, wherein the image flow detection means includes a foreign matter detection mechanism for detecting foreign matter attached to the surface of the image carrier. The image flow is detected based on the detection result.

  Here, the image flow can be detected based on the foreign matter adhering to the image carrier.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to the third aspect, wherein the foreign matter detection mechanism detects whether or not foreign matter is attached to the surface of the image carrier from a change in torque of the image carrier.

  Here, the torque change of the image carrier means a change in torque necessary for driving the image carrier.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the first aspect of the present invention, wherein a storage unit that stores time information about a time necessary for a foreign object to adhere to an undriven image carrier, and an image The apparatus further comprises stop time calculating means for calculating a stop time from the time when the driving of the carrier is completed to the next time when the image carrier is driven. The timing determination unit determines the timing based on the time information stored in the storage unit and the stop time calculated by the stop time calculation unit.

  In this image forming apparatus, the time required for foreign matter to adhere to the image carrier is stored in advance in the storage unit. Here, foreign matter such as discharge products differs depending on how long the image carrier is left to stand depending on the state of the image carrier, for example, the number of times the image carrier has been rotated from the time of manufacture. For this reason, it is not possible to determine in general the time during which foreign substances such as discharge products adhere. Therefore, in the present invention, the relationship (time information) between the time of manufacture and the time required for the discharge product to adhere is experimentally measured in advance, and this time information is stored in the storage unit in advance. Then, the time (timing) at which foreign matter adheres to the image carrier is estimated by comparing the total number of rotations and the leaving time from the time of manufacture of the image carrier with the time information stored in the storage unit. Then, the removal force of the contact member is increased at the estimated time. Here, the time information includes information on how the time required for the discharge product to change varies depending on, for example, the total number of rotations from the time of manufacture of the image carrier and the standing time. ing.

  Here, the removal force of the contact member is increased at the timing when it is estimated that the foreign substance adheres to the image carrier, so that the image flow due to the foreign substance can be prevented. In addition, since the removal force is increased at the timing when the foreign object is estimated to be attached, the contact member and the image carrier can be prevented from being worn more than necessary, and the life of the contact member and the image carrier can be prevented from being shortened. it can.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the fifth aspect of the present invention, further comprising humidity detecting means for detecting the humidity around the image carrier. The timing determination means determines the application timing based on the detection result of the humidity detection means.

  Here, the adhesion of foreign matter to the image carrier is also affected by humidity.

  Here, since the timing is determined in consideration of humidity, the foreign matter adhering to the image carrier can be removed more efficiently.

  An image forming apparatus according to a seventh aspect is the image forming apparatus according to the fifth or sixth aspect, wherein the application timing determining means determines the timing based on input / cut-off of a power source capable of supplying power for driving each functional unit. decide.

  Here, it is difficult to detect a period between the time when the power of the apparatus is shut off and the next time when the power is turned on to the apparatus, and the apparatus is likely to be left for a long time. During this period, since the image carrier is not driven, foreign matter is likely to adhere to the image carrier.

  Here, the foreign matter is removed based on the input / interruption of the power source, so that the image flow can be efficiently prevented. In particular, the foreign matter adhering to the image carrier is removed as the power is turned on. For this reason, image flow can be prevented more efficiently.

  An image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus according to any one of the first to seventh aspects, wherein the increasing mechanism has an AC bias applying device capable of applying an AC bias to the contact member. The increase mechanism control means controls the increase mechanism so that an AC bias is applied to the contact member at the timing determined by the timing determination means.

  Here, the removal force of the contact member can be increased by applying an AC bias. For this reason, it is not necessary to arrange a mechanism for increasing the removal force of the contact member, and the size can be reduced.

  An image forming apparatus according to a ninth aspect is the image forming apparatus according to any one of the first to eighth aspects, wherein the contact member is a member for cleaning the surface of the image carrier.

  Here, by using a member for cleaning the image carrier as the contact member, it is not necessary to provide a member other than the member for cleaning the surface of the image carrier as the contact member, and it is possible to prevent an increase in size and cost.

  An image forming apparatus according to a tenth aspect is the image forming apparatus according to any one of the first to ninth aspects, wherein the image carrier is a roller-like member, and the contact member extends in the axial direction of the image carrier. Shaped member.

  Here, since the contact member extends in the same direction as the direction in which the image carrier extends, the area of the contact member that scrapes the surface of the image carrier can be increased. For this reason, it becomes easier to prevent the image flow due to the foreign matter adhering to the surface of the image carrier.

  According to the present invention, it is possible to prevent the image quality from being deteriorated by the discharge product adhering to the photosensitive drum and to shorten the life of the contact member.

<First Embodiment>
[overall structure]
An MFP 1 as an image forming apparatus according to the present invention will be described below with reference to FIG. Here, FIG. 1 shows an overall outline of the multifunction machine 1 according to the present invention. This multifunction device 1 is connected to an external computer or the like. The multifunction device 1 is an apparatus that forms an image on a sheet based on image information read from a document or image information sent from a computer.

  The multifunction device 1 has various functions such as a function of copying a document and a function of transmitting image information of the document. As shown in FIG. 1, the multifunction device 1 includes a document reading unit 2, an image forming unit 3, a transfer unit 4, a sheet storage unit 5, a sheet transport unit 6, a fixing unit 7, and a discharge unit 8. , An image flow detection mechanism 9 (see FIG. 4), an AC bias application device 10 (increase mechanism) (see FIGS. 2 and 4), and a bias application control device 11 (see FIG. 4). The configuration of each functional unit will be described below. The image flow detection mechanism 9, the AC bias application device 10, and the bias application control device 11 will be described in detail later.

{Original reading unit}
The document reading unit 2 is a part for reading image information of a document. The document reading unit 2 is disposed at the top of the multifunction device 1.

{Image forming part}
The image forming unit 3 is a part for forming an image on a sheet based on image information. The image forming unit 3 is disposed between the paper storage unit 5 and the document reading unit 2. The image forming unit 3 includes four image forming units 30.

  The four image forming units 30 are arranged in a line. Each image forming unit 30 includes a photosensitive drum 31, a charging device 32, a laser unit 33, a developing device 34, a toner storage unit 35, a charge eliminating device 36, and a drum cleaning device 37. . The four image forming units 30 can form yellow, magenta, cyan, and black toner images in order from the left side of FIG. The image forming units 30 have the same configuration. The yellow image forming unit 30 will be described below.

  The photosensitive drum 31 is a member capable of carrying an electrostatic latent image on the surface. The photosensitive drum 31 has a rotation shaft extending perpendicularly to the paper surface of FIG. The photosensitive drum 31 can rotate around the rotation axis. The photosensitive drum 31 is disposed so as to contact a transfer belt 41 described later.

  The charging device 32 is a device for uniformly charging the surface of the photosensitive drum 31. The charging device 32 is disposed below the photosensitive drum 31.

  The laser unit 33 is a device for irradiating the surface of the photosensitive drum 31 with laser light based on image information. The laser unit 33 is disposed below the photosensitive drum 31.

  The developing device 34 is a device capable of supplying a developer to the electrostatic latent image carried on the photosensitive drum 31. The developing device 34 is disposed on the upper side of the laser unit 33. Further, the developing device 34 includes a developing container 341 that can store a developer of a color corresponding to each photosensitive drum 31 and a developing roller 342 attached to the developing container 341. The developing roller 342 is disposed so as to face the photosensitive drum 31.

  The toner storage portion 35 is a portion for storing toner that can be supplied to the developing device 34. The toner storage unit 35 includes a toner container 351 that can store toner corresponding to the color of each developing device 34. The toner container 351 is connected to the developing device 34 by a supply path (not shown).

  The static eliminator 36 is a device for removing charges on the surface of the photosensitive drum 31. The static eliminator 36 is disposed below the photosensitive drum 31.

  The drum cleaning device 37 is a device for cleaning the developer remaining on the photosensitive drum 31 without being used for the developing operation. As shown in FIG. 2, the drum cleaning device 37 includes a blade member 371 that contacts the surface of the photosensitive drum 31, and a waste developer storage container 372 that can store toner scraped by the blade member 371. Yes. The blade member 371 is a plate-like member. The blade member 371 extends in a direction extending along the axial direction of the photosensitive drum 31. One end of the blade member 371 in a direction orthogonal to the longitudinal direction is supported by the waste developer storage container 372. Further, the blade member 371 is made of a conductive material.

{Transcription part}
The transfer unit 4 includes a transfer belt 41, four primary transfer rollers 42, a secondary transfer roller 43, and a belt cleaning device 44.

  The transfer belt 41 is a member for transferring an image formed by the image forming unit 3 to a sheet. The transfer belt 41 is a member to which an image is primarily transferred from the photosensitive drum 31. Further, the transfer belt 41 is disposed on the upper side of the photosensitive drum 31.

  The primary transfer roller 42 is a member for transferring the image on the photosensitive drum 31 onto the transfer belt 41. The primary transfer roller 42 is disposed so as to face the photosensitive drum 31 with the transfer belt 41 interposed therebetween. Further, each primary transfer roller 42 is connected to a voltage application device (not shown). Each primary transfer roller 42 is arranged in parallel with the direction in which the photosensitive drums 31 are arranged.

  The secondary transfer roller 43 is a member for transferring the image primarily transferred from the photosensitive drum 31 to the transfer belt 41 onto a sheet. The secondary transfer roller 43 is disposed so as to face the transfer belt 41 with the paper transport path of the paper transport unit 6 interposed therebetween.

  The belt cleaning device 44 is a device for cleaning toner, paper dust, dust, and discharge products on the transfer belt 41. The belt cleaning device 44 is disposed on the left side of the transfer belt member 41 in FIG.

{Paper storage}
The paper storage unit 5 is a part for storing paper. The paper storage unit 5 is disposed at the lower part of the multifunction machine 1. Further, the paper storage unit 5 has a plurality of paper feed cassettes 51. Each paper cassette 51 stores different types (sizes, etc.) of paper. A plurality of paper feed cassettes 51 are stacked.

{Paper transport section}
The paper transport unit 6 is a part for transporting paper to each functional unit. The paper transport unit 6 has a paper transport path for transporting paper in the order of the paper storage unit 5, the image forming unit 4, the fixing unit 7, and the discharge unit 8. The paper transport unit 6 includes a paper transport guide pair 61 and a plurality of paper transport roller pairs 62.

  The paper transport guide pair 61 is a member for guiding the paper transport direction. The paper transport guide pair 61 has plate-like members arranged so as to face each other. A sheet can pass between these plate-like members.

  The paper transport roller pair 62 is a member for transporting paper in the paper transport direction. The pair of paper transport rollers 62 has two rollers arranged to face each other. The sheet can pass between the two rollers.

{Fixing part}
The fixing unit 7 is a part for fixing an image on a sheet. The fixing unit 7 is disposed on the downstream side of the transfer unit 4 in the paper transport direction. The fixing unit 7 includes a heating roller 71 that heats the image, and a pressure roller 72 that is disposed to face the heating roller 71 and presses the paper between the heating roller 71.

{Discharge unit}
The discharge unit 8 is a part for discharging the sheet to the outside of the multifunction device 1. As shown in FIG. 1, the discharge unit 8 is disposed downstream of the fixing unit 7 in the sheet conveyance direction. The discharge unit 8 has a discharge roller 81. The discharge unit 8 is disposed below the document reading unit 2. The discharge unit 8 further includes a recess 82 that is recessed rightward from the left side surface of the multifunction device 1 in FIG. Then, the sheet is discharged into the recess 82.

[Image flow detection mechanism]
The image flow detection mechanism 9 is a mechanism for detecting the image flow on the photosensitive drum 31. The image flow detection mechanism 9 has a foreign matter detection mechanism 91. The image flow detection mechanism 9 detects image flow based on the foreign matter detected by the foreign matter detection mechanism 91. That is, it is presumed that an image flow has occurred due to foreign matter adhering to the photosensitive drum 31.

  The foreign matter detection mechanism 91 is a mechanism for detecting the presence or absence of a foreign matter such as a discharge product, paper dust, and dust adhered to the photosensitive drum 31. Further, as shown in FIG. 4, the foreign object detection mechanism 91 includes a blade member 371 and a torque measurement device 911. The torque measuring device 911 is a device for detecting torque necessary for rotating the photosensitive drum 31. As shown in FIG. 3, the torque measuring device 911 is attached to one end of the rotating shaft of the photosensitive drum 31.

  The foreign matter detection mechanism 91 detects foreign matter as follows. When foreign matter adheres to the surface of the photosensitive drum 31, the foreign matter comes into contact with the blade member 371 as the photosensitive drum 31 rotates. At this time, the foreign matter hinders driving of the photosensitive drum 31 of the blade member 371. That is, the torque acting on the shaft of the photosensitive drum 31 is increased. For this reason, the foreign matter can be detected by detecting that the torque acting on the shaft of the photosensitive drum 31 is increased.

[AC bias application device]
The AC bias applying device 10 is a device for increasing the force with which the foreign material on the photosensitive drum 31 of the blade member 371 is removed. Specifically, the AC bias application device 10 applies an AC bias to the blade member 371. When an AC bias is applied to the blade member 371, foreign matter is peeled off from the photosensitive drum 31 by the AC bias applied to the blade member 371, and the blade member 371 is vibrated. For this reason, the removal force of the foreign material of the blade member 371 increases. Further, as shown in FIG. 2, the AC bias applying device 10 is connected to a blade member 371. As shown in FIG. 4, the AC bias application device 10 is connected to a bias application control device 11.

[Bias application controller]
The bias application control device 11 is a device for controlling the AC bias applied to the blade member 371. The bias application control device 11 functions as a timing determination unit 111 (timing determination unit) and a bias application control unit 112 (increase mechanism control unit) by executing a program. FIG. 4 shows a block diagram of the bias application control device 11. The bias application control device 11 will be described with reference to FIG.

  The timing determination unit 111 is a part for determining a timing at which an AC bias is applied from the AC bias applying device 10 to the blade member 371. The timing determination unit 111 is connected to the foreign object detection mechanism 91. The timing determination unit 111 determines the timing at which an AC bias is applied to the blade member 371 when a foreign object is detected by the foreign object detection mechanism 91. More specifically, the timing determination unit 111 determines the timing so that an AC bias is applied to the blade member 371 immediately before the image forming operation associated with the print command immediately after the foreign matter is detected.

  The bias application control unit 112 is a part that controls the AC bias application device 10 so that an AC bias is applied to the blade member 371 at the timing determined by the timing determination unit 111.

[Operation]
Next, the operation of the multifunction device 1 will be described.

  When image information of an original is read by the original reading unit 2 or image information is sent from a computer connected to the outside of the multifunction machine 1, an electrostatic latent image is formed on the photosensitive drum 31 based on the image information. . Specifically, the surface of the photosensitive drum 31 is charged by the charging device 32, and laser light is irradiated from the laser unit 33 to the photosensitive drum 31 based on the image information. When the electrostatic latent image is formed on the photosensitive drum 31 in this way, the developer is supplied from the developing roller 342 of the developing device 34 to the electrostatic latent image. When the developer is supplied from the developing device 34, a toner image is formed on the photosensitive drum 31.

  Then, the toner image on each photosensitive drum 31 is transferred to the transfer belt 41 (primary transfer). Then, the toner image on the transfer belt 41 is transferred to a sheet (secondary transfer). The sheet on which the toner image is transferred is conveyed to the fixing unit 7 by the sheet conveying unit 6. After the toner image is fixed on the paper by the fixing unit 7, it is conveyed to the discharge unit 8. The sheet conveyed to the discharge unit 8 is discharged out of the multifunction machine 1.

[Foreign matter detection and removal]
When the photosensitive drum 31 rotates with foreign matter attached on the photosensitive drum 31, the foreign matter comes into contact with the blade member 371 of the drum cleaning device 37. At this time, the foreign matter is scraped off by the blade member 371, but the foreign matter may not be removed from the photosensitive drum 31 if the foreign matter has a strong adhesion to the photosensitive drum 31. In this case, as the photosensitive drum 31 rotates, the blade member 371 comes into contact with the foreign matter, and the torque acting on the photosensitive drum 31 increases. The torque acting on the rotating shaft of the photosensitive drum 31 is detected by the torque measuring device 911. By detecting that the torque acting on the rotating shaft of the photosensitive drum 31 is increased, the surface of the photosensitive drum 31 is detected. Detect that foreign matter is attached to the.

  When the foreign matter detection mechanism 91 detects that a foreign matter has adhered to the photosensitive drum 31, a foreign matter removal operation is performed immediately before the image forming operation when the next print command is issued. That is, when the torque acting on the rotating shaft of the photosensitive drum 31 is increased, an AC bias is applied to the blade member 371 by the AC bias applying device 10. Then, the photosensitive drum 31 is rotated in a state where an AC bias is applied to the blade member 371, and the foreign matter adhering to the photosensitive drum 31 is scraped off by the blade member 371. In this case, the time during which the AC bias is applied to the blade member 371 is 10 to 30 seconds, but may be set according to the apparatus and the environment.

  An experiment was conducted to prevent image flow when an AC bias was applied to the blade member 371. FIG. 5 is a graph showing the results of the experiment. With reference to the graph of FIG. 5, an experiment and an experiment result in which an AC bias is applied to the blade member 371 to remove foreign matter on the photosensitive drum 31 will be described.

  The experiment was performed for a predetermined time in order to confirm the degree of recovery of image flow, that is, the degree of scraping of foreign matter, in a state where an AC bias having a frequency of 2 kHz and an execution current value of 4 mA was applied to the blade member 371. From the graph of FIG. 5, the rotation of the photosensitive drum 31 with the AC bias applied to the blade member 371 is half that of the case where the photosensitive drum 31 is rotated without applying the AC bias to the blade member 371. It can be seen that it is possible to prevent a state in which image flow occurs in the time of.

  Here, the horizontal axis in FIG. 5 indicates the time for which the photosensitive drum 31 is rotated, and the vertical axis in FIG. 5 indicates the image flow rank. As for the image flow rank, rank 1 is the most remarkable image flow, and the image flow improves as the rank increases. Specifically, rank 1 of the image flow rank indicates a state where the image flow can be detected as a white stripe when a solid image is formed. Rank 2 of the image flow rank indicates a state in which characters cannot be seen due to white stripes in the image flow. Rank 3 of the image flow rank indicates a state that can be confirmed as a white streak even in a portion filled with a light density in the image. Rank 4 shows a state in which image flow occurs but is lighter than rank 3. Rank 5 indicates a state in which no image flow occurs.

[effect]
Here, since the foreign matter on the photosensitive drum 31 can be efficiently removed, it is possible to prevent the occurrence of image flow. For this reason, it is possible to prevent deterioration in image quality due to image flow. In addition, since an AC bias is applied to the blade member 371 only when foreign matter adheres to the photosensitive drum 31, the photosensitive drum 31 and the blade member 371 are worn compared to a case where an AC bias is always applied to the blade member 371. The amount can be reduced.

<Second Embodiment>
[overall structure]
A multifunction device 100 according to a second embodiment of the present invention will be described. As shown in FIG. 6, the multifunction device 100 includes a document reading unit 101, an image forming unit 102, a fixing unit 103, a transfer unit 104, a sheet storage unit 105, a sheet transport unit 106, and a discharge unit 107. The AC bias application device 108 and the bias application control device 150 are provided. Note that the MFP 100 includes a document reading unit 101, an image forming unit 102, a fixing unit 103, a transfer unit 104, a sheet storage unit 105, a sheet transport unit 106, a discharge unit 107, and an alternating current. Since the bias applying device 108 has the same configuration as that of the first embodiment, description thereof is omitted. Further, members similar to those in the first embodiment, such as a photosensitive drum, will be described with reference to the first embodiment.

[Bias application controller]
The bias application control device 150 is a device for controlling the AC bias applied to the blade member 371 from the AC bias application device 108. In addition, the bias application control device 150 includes a storage unit 151, a timing determination unit 152 (timing determination unit), a humidity detection unit 153, and a time calculation unit 154 (stop time calculation unit).

  The storage unit 151 is a part that stores, as a threshold value, time information necessary for foreign matter to adhere to the photosensitive drum 31 that is not driven.

  Here, the adherence of the discharge product, which is a foreign substance, to the photosensitive drum 31 varies depending on the number of times the photosensitive drum 31 has been used up to the present time (total number of rotations of the photosensitive drum 31). It is influenced by the state of the photosensitive drum 31, the time that has passed in a state where the photosensitive drum 31 is stopped after discharging, and the environment (mainly humidity).

  For example, when the photosensitive drum 31 is rotated at 250,000 to 350,000 revolutions and left for 10 hours in a state where the (relative) humidity is 75% or more, image flow occurs. In the state where the photosensitive drum 31 is rotated 250,000 to 350,000, image flow does not occur when the photosensitive drum 31 is left for 10 hours in a state where the (relative) humidity is 70% or less.

  Further, when the photosensitive drum 31 is rotated at 350,000 to 400,000 rotations and left for 10 hours in a state where the (relative) humidity is 70% or more, an image flow occurs. In the state where the photosensitive drum 31 is rotated at 350,000 to 400,000 rotation, no image flow occurs when the photosensitive drum 31 is left for 10 hours with the (relative) humidity being 70% to 65%.

  As described above, when the number of rotations of the photosensitive drum 31 is 250,000 to 350,000 and the humidity is 70% or more, the foreign matter removing operation is performed when the leaving time is 10 hours or more. When the humidity is 65% or more in the state where the number of rotations of the photosensitive drum 31 is 350,000 to 400,000, the foreign matter removing operation is performed when the leaving time is 10 hours or more. In this way, a threshold value corresponding to the humidity and the total number of revolutions of the photosensitive drum 31 is experimentally detected, and this threshold value is stored in the storage unit 151 in advance.

  The timing determination unit 152 is a part for determining the timing at which the AC bias is applied to the blade member 371 by the AC bias applying device 108. The timing determination unit 152 determines whether or not the time calculated by the time calculation unit 154 exceeds a threshold determined by the humidity and the total number of revolutions, and the image forming operation of the next print command when the time exceeds the threshold An AC bias is applied immediately before.

  The humidity detector 153 is a part for detecting the humidity around the photosensitive drum 31. The humidity detector 153 has a hygrometer 153 a disposed in the vicinity of the photosensitive drum 31.

  The time calculation unit 154 is a part that calculates the time from when the photosensitive drum 31 is driven during the image forming operation to when the photosensitive drum 31 is driven next.

[Foreign substance removal operation]
The operation will be described with reference to the flowchart of the operation for removing foreign matter shown in FIG.

  First, the total number of rotations from the time when the photosensitive drum 31 is manufactured to the present is calculated. Then, the humidity near the photosensitive drum 31 is detected. A threshold relating to the stop time is determined based on the calculated total number of revolutions and humidity (S1). Then, it is determined whether a new print command has been received (S2). If a new print command has not been received (NO in S2), the process waits until a new print command is received. On the other hand, when a new print command is received (YES in S2), the stop time (left time) of the photosensitive drum 31 is detected (S3). Thereafter, it is determined whether the detected stop time exceeds a threshold value (S4). If the detected stop time does not exceed the threshold (NO in S4), an image forming operation (S7) is performed. On the other hand, when the detected stop time exceeds the threshold (YES in S4), an AC bias is applied to the blade member 371 (S5). Then, the photosensitive drum 31 is rotated for 30 seconds to 1 minute with an AC bias applied to the blade member 371 (S6). In this way, after the photosensitive drum 31 is cleaned, an image forming operation is performed (S7).

[effect]
Here, since the foreign matter on the photosensitive drum 31 can be efficiently removed, it is possible to prevent the occurrence of image flow. For this reason, it is possible to prevent deterioration in image quality due to image flow. Further, since the AC bias is applied to the blade member 371 only when foreign matter adheres to the photosensitive drum 31, the photosensitive drum 31 and the blade member 371 are worn compared to the case where the AC bias is always applied to the blade member 371. The amount can be reduced [another embodiment]
(A) In the above embodiment, the presence or absence of foreign matter is detected from the change in torque acting on the photosensitive drum 31 and the image flow is estimated from the foreign matter. However, the present invention is not limited to this. The method is fine. For example, the image flow may be detected by detecting the toner density of a solid image and detecting a portion where the toner density is low. Further, a light emitting unit and a light receiving unit are provided in the vicinity of the photosensitive drum 31, and light is irradiated to the photosensitive drum 31 from the light emitting unit. Then, the light reflected by the photosensitive drum 31 is received by the light receiving unit, and the saturation and luminance are detected. The image flow may be detected by detecting that the foreign matter is attached by detecting a portion where the saturation and luminance are different from the other portions.

  (B) In the above embodiment, the foreign matter removing operation is performed immediately before the next image forming operation at the time when the foreign matter is detected. However, the present invention is not limited to this, and the timing determining unit 111 is not limited to this. The timing may be determined so that the foreign matter removing operation is performed when the power is turned on. This is because a long time may elapse between the time when the power is shut off and the time when the power is next turned on, and the discharge product may adhere to the photosensitive drum 31 during this period. is there. For this reason, by performing the foreign matter removing operation when the power is turned on, the foreign matter adhered during the power shut-off period can be efficiently removed, and the image flow can be prevented.

  (C) Furthermore, in the above embodiment, the threshold value is calculated from the total number of revolutions of the photosensitive drum 31 and the humidity. However, the present invention is not limited to this, and the threshold value is calculated only from the total number of revolutions of the photosensitive drum 31. May be.

  (D) In the above embodiment, the multifunction peripheral has been described. However, the present invention is not limited to this, and may be a copying machine, a color printer, or the like.

  (E) In the above embodiment, the AC bias is applied to the blade member 371 to increase the foreign matter removal force. However, the present invention is not limited to this, for example, as shown in FIG. The cam 400 that contacts the 371 may be disposed in the waste developer storage container 372, and the cam 400 may be rotated in accordance with the timing of removing the foreign matter to increase the foreign matter removing force.

  (F) In the above embodiment, the blade member 371 is used as a contact member. However, the present invention is not limited to this, and another member that contacts the photosensitive drum 31 may be used. These members may be provided.

1 is an overall schematic cross-sectional view of a multifunction machine according to an embodiment of the present invention. FIG. 3 is an enlarged schematic view around the photosensitive drum. The figure which shows a torque measuring device. The block diagram of the bias application control apparatus of 1st Embodiment. The graph which shows the result of an experiment example. The block diagram of the bias application control apparatus of 2nd Embodiment. The figure which shows the flowchart which shows the foreign material removal operation | movement of 2nd Embodiment. The figure which shows the increase mechanism of other embodiment.

Explanation of symbols

1 MFP (image forming device)
9 Image Flow Detection Mechanism 10 AC Bias Application Device (Increase Mechanism)
31 Photosensitive drum (image carrier)
91 Foreign matter detection mechanism 111 Timing determination unit (timing determination means)
112 Bias application control unit (increasing mechanism control means)
150 Bias Application Control Device 151 Storage Unit 152 Timing Determination Unit (Timing Determination Unit)
153 Humidity detection unit (humidity detection means)
154 Time calculation unit (time calculation means)
371 Blade member (contact member)

Claims (10)

An image forming apparatus capable of forming an image based on image information,
An image carrier capable of carrying an electrostatic latent image on the surface;
A contact member that comes into contact with the surface of the image carrier and can scrape off deposits attached to the surface of the image carrier;
An increasing mechanism for increasing the removal force for removing the adhering matter adhering to the image carrier of the contact member;
Timing determining means for determining timing for increasing the removal force of the contact member by the increasing mechanism;
An increase mechanism control means for increasing the removal force of the contact member at the timing determined by the timing determination means;
An image forming apparatus. Further comprising image flow detection means for detecting the image flow of the electrostatic latent image formed on the surface of the image carrier,
The timing determination means determines the timing based on a detection result of the image flow detection means;
The image forming apparatus according to claim 1. The image flow detection means has a foreign matter detection mechanism for detecting foreign matter attached to the surface of the image carrier, and detects image flow based on a detection result of the foreign matter detection mechanism.
The image forming apparatus according to claim 2. The foreign matter detection mechanism detects whether or not foreign matter is attached to the surface of the image carrier from the torque change of the image carrier.
The image forming apparatus according to claim 3. A storage unit that stores time information about a time required for foreign matter to adhere to the image carrier that is not driven;
A stop time calculating means for calculating a stop time from the time when the driving of the image carrier is completed to the next time when the image carrier is driven;
The timing determining means determines the timing based on the time information stored in the storage unit and the stop time calculated by the stop time calculating means;
The image forming apparatus according to claim 1. Further comprising humidity detecting means for detecting the humidity around the image carrier,
The timing determination means determines the timing based on a detection result of the humidity detection means;
The image forming apparatus according to claim 5. The timing determination means determines the timing based on input / cut-off of a power source capable of supplying power for driving each functional unit,
The image forming apparatus according to claim 5. The increasing mechanism has an AC bias application device capable of applying an AC bias to the contact member,
The increasing mechanism control means controls the increasing mechanism to apply an AC bias to the contact member at a timing determined by the timing determining means;
The image forming apparatus according to claim 1. The contact member is a member for cleaning the surface of the image carrier.
The image forming apparatus according to claim 1. The image carrier is a roller-shaped member,
The contact member is a plate-like member extending in the axial direction of the image carrier.
The image forming apparatus according to claim 1.

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