JP3804471B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, and more specifically, while simplifying a cleaning mechanism for residual toner adhering to an image carrier such as a photosensitive drum or an intermediate transfer member, The present invention relates to an improvement for forming a high-quality recorded image.
[0002]
[Prior art]
In general, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a toner image is formed on the surface of a photosensitive drum in accordance with image data, and then the toner image is transferred to a recording sheet. A recorded image is obtained by heat-fixing the image on a recording sheet. In recent full-color copying machines and full-color laser beam printers, the toner image formed on the photosensitive drum is primarily transferred to an intermediate transfer member, and four colors of yellow, cyan, magenta, and black are transferred onto the intermediate transfer member. It is also known to form a full-color recording image by superimposing toner images and collectively transferring these synthesized toner images onto a recording sheet.
[0003]
The transfer efficiency of the toner image is affected by fluctuations in the resistance value of the recording sheet and the intermediate transfer member due to changes in the surface condition of the photosensitive drum and intermediate transfer member, and temperature / humidity. It is difficult, and the toner remains on the surface of the photosensitive drum or the intermediate transfer member from which the toner image is transferred even after the toner image is transferred. For this reason, conventionally, for image carriers such as photosensitive drums and intermediate transfer members, a cleaning device is provided on the downstream side of the transfer portion of the toner image to remove residual toner prior to the next toner image formation. Has been done.
[0004]
As this type of cleaning device, as disclosed in Japanese Patent Laid-Open No. 4-29283, a brush roll planted with countless rubbing hairs is brought into contact with an image carrier such as a photosensitive drum, A configuration is known in which a potential difference corresponding to the charging polarity of the toner is applied between the image carrier and the residual toner is electrostatically adsorbed from the image carrier to the brush roll. There is also known a cleaning device configured such that a soft roll made of a soft elastic body instead of a brush roll is brought into contact with the image carrier, and residual toner is electrostatically adsorbed from the image carrier to the surface of the soft roll. .
[0005]
In any configuration, there is a limit to the amount of toner that can be held by the brush roll or soft roll, and if a large amount of toner is held in contact with the image carrier, the cleaning capability itself will be reduced. For this reason, a so-called detoning mechanism for separating and collecting toner from these brush rolls and soft rolls is required. For example, a protrusion called a flicker bar is provided in the rotation range of the rubbing bristles for the brush roll, and the toner is forcibly tapped off from the brush roll by hitting the rubbing bristles against the flicker bar. Is collected in the collection box using a transporting means such as an auger.
[0006]
However, when such a detoning mechanism is provided, the cleaning device becomes large. In particular, in a so-called tandem type color image forming apparatus provided with a photosensitive drum for each of four colors of yellow, magenta, cyan and black, it is necessary to provide a cleaning device for each photosensitive drum. In an image forming apparatus that transfers a toner image to a recording sheet via an intermediate transfer member, it is necessary to provide a cleaning device for the intermediate transfer member. For this reason, in miniaturization of a color copying machine, a color laser beam printer, etc., it is extremely important to downsize and simplify the cleaning device as follows.
[0007]
From this point of view, the color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-074448 is provided with a brush roll for removing residual toner for each of the plurality of intermediate transfer members. On the other hand, no detoning mechanism is provided, and the toner adhering to each brush roll is collected and collected in one place between image forming jobs. Specifically, the brush roll provided on each intermediate transfer member works to clean and hold the residual toner during the image forming job so as not to interfere with the formation and transfer of the toner image. In the meantime, the toner held by these brush rolls is discharged onto the intermediate transfer member and transferred to the downstream roll in the same manner as the transfer of the toner image, and provided for the final roll. It collects with the collect | recovery apparatus collected collectively.
[0008]
In this way, when the toner held by each brush roll is collected in one place and collected at once, the cleaning device itself for cleaning each image carrier becomes very simple and must be cleaned. In a color image forming apparatus having a large number of image carriers that must be reduced, the size can be reduced extremely advantageously.
[0009]
[Problems to be solved by the invention]
However, a so-called collection job for discharging the toner held by each brush roll must be periodically performed. The amount of toner that the brush roll removes from the image carrier during the image forming job and the brush roll during the collection job. When the amount of toner discharged is compared, if the former amount is not large, the toner contains enough toner that the brush roll can only hold, and the image quality of the recorded image deteriorates due to poor cleaning of the image carrier. . In addition, the amount of toner held by the brush roll during an image forming job varies depending on the contents of the image forming job, such as the number of recording sheet passing sheets, the image area ratio, and the toner image transfer efficiency. If only the job is performed, the toner may overflow from the brush roll, and a high-quality recorded image cannot be stably obtained over a long period of time.
[0010]
The present invention has been made in view of such problems, and an object of the present invention is to be able to easily configure a cleaning mechanism for an image carrier and to achieve downsizing of the apparatus even in colorization. In addition, it is an object of the present invention to provide an image forming apparatus capable of stably forming a high-quality recorded image without causing defective cleaning even in long-term use.
[0011]
[Means for Solving the Problems]
That is, the present invention is an image forming apparatus for forming a recorded image by transferring a toner image corresponding to image information from an image carrier to a recording sheet, and removing unnecessary toner adhering to the surface of the image carrier. A temporary collection toner holding member is provided, and a collection job for discharging unnecessary toner held on the temporary toner holding member onto the image carrier is periodically executed to collect the unnecessary toner in a final collection unit. The temporary toner holding member discharges all unnecessary toner collected during the image forming job to the surface of the image carrier, even though the recovery job is applied to the image forming apparatus configured as described above. In this case, it is possible to prevent the toner from being accumulated in the toner temporary holding member.
[0012]
For this reason, in the present invention, the length of the execution time of the collection job is made variable according to the amount of unnecessary toner accumulated in the image forming job. In other words, if the amount of unnecessary toner held by the temporary toner holding member is large, it takes a long time to discharge such unnecessary toner onto the image carrier. The length of the execution time of the collection job is changed according to the amount of unnecessary toner collected from the surface of the image carrier. In this way, the temporary toner holding member can sufficiently discharge the collected unnecessary toner during the collection job, and the amount of unnecessary toner held on the temporary toner holding member is cumulatively increased. It is possible to prevent unnecessary toner from overflowing from the temporary toner holding member during the forming job.
[0013]
As a guideline for knowing the amount of unnecessary toner collected from the surface of the image carrier by the temporary toner holding member, the number of recording sheets passed in the image forming job and the cumulative amount of the image area ratio in the image forming job can be used. . The large number of recording sheets passed through means that a large amount of toner images are formed on the image carrier, and the amount of residual toner (unnecessary toner) that remains on the image carrier without being transferred. Will also increase that much. Further, as the cumulative amount of the image area ratio increases, the physical amount of toner transferred from the image carrier to the recording sheet itself increases, so that it is not transferred by that amount on the image carrier. The amount of residual toner that remains is also increased. That is, in these cases, the toner temporary holding member collects a lot of unnecessary toner from the image carrier in the image forming job.
[0014]
Accordingly, the collection job is started after the end of the image forming job, and unnecessary toner is discharged from the temporary toner holding member to the surface of the image carrier, and the length of the collection job is determined according to the number of sheets to be passed in the image forming job. If variable, all unnecessary toner collected in the immediately preceding image forming job can be discharged from the temporary toner holding member to the image carrier, and unnecessary toner is accumulated in the temporary toner holding member. Can be prevented.
[0015]
In the image forming apparatus of the present invention, when a single image forming job for forming an image on a plurality of recording sheets is executed, the amount of unnecessary toner held by the temporary toner holding member is limited during the job. If it is determined that the image forming job is reached, it is necessary to interrupt the image forming job and execute the collection job. At this time, when the image forming job is interrupted can be determined from the number of recording sheets passed in the image forming job. If a predetermined number of recording sheets are passed, the image forming job is interrupted. The collection job can be started immediately without waiting for the end of the forming job. Further, the determination may be made using the cumulative value of the additional area ratio instead of the number of recording sheets to be passed.
[0016]
However, the amount of unnecessary toner on the image carrier cannot be determined only from the number of recording sheets, and is affected by various factors. For example, in a low temperature and low humidity environment, the transfer efficiency of the toner image deteriorates, and a large amount of transfer residual toner is generated on the surface of the photosensitive drum or intermediate transfer member. In addition, when a high-resistance recording sheet such as an OHP sheet or a second recording sheet during double-sided printing is passed, the toner image transfer efficiency tends to decrease and a large amount of residual toner tends to be generated. . Further, since the electrical performance of the temporary toner holding member deteriorates with time, the cleaning performance of the image carrier is lowered, and the amount of unnecessary toner that can be held tends to decrease with time.
[0017]
Therefore, from these viewpoints, even when the collection job is started according to the cumulative number of sheets and the image area ratio of recording sheets in the image forming job, the recording that causes the collection job to start. The cumulative number of sheets to be passed and the image area ratio are preferably changed according to the ambient temperature and humidity, the type of recording sheet, the cumulative number of sheets to be passed through the image carrier, and the like.
[0018]
On the other hand, if an image forming job is interrupted and a collecting job is performed, a toner image cannot be formed according to the image information during the collecting job, and therefore it takes a long time to complete the image forming job. turn into. Therefore, from the viewpoint of minimizing the amount of unnecessary toner accumulated in the temporary toner holding member, the so-called interface between the recording sheets fed continuously, that is, between the toner images moving back and forth on the image carrier. It is preferable to execute the collection job also in the image area. Since such an inter-image area is extremely short, it is impossible to discharge all unnecessary toner held on the temporary toner holding member. However, even in a very small amount, the inter-image area repeatedly visits between successive recording sheets. If unnecessary toner is discharged, it is possible to prevent unnecessary toner from being accumulated in the temporary toner holding member. This eliminates the need to interrupt the image forming job and perform a collecting job even for an image forming job with a large number of recording sheets to be passed, and shorten the time for the collecting job after the image forming job is completed. Can be realized.
[0019]
Also, from the viewpoint of reducing the amount of unnecessary toner accumulated in the temporary toner holding member as much as possible, when the image forming job cannot be started immediately, the collection job is actively performed. It is preferable to carry out. For example, when a long time has passed without the image forming job being performed and the temperature of the fixing device for fixing the toner image to the recording sheet is lowered, or immediately after the main power of the image forming apparatus is turned on. . In this case, if it is determined that the fixing device needs to be warmed up before the start of the image forming job, the collection job may be executed within the warm-up time.
[0020]
Further, when a long time has passed without an image forming job being performed, the charge amount of the unnecessary toner held by the temporary toner holding member naturally decreases, and then the image carrier When the toner starts to move, the held unnecessary toner tends to be discharged onto the image carrier. Accordingly, from the viewpoint of preventing such a problem, if the waiting time until the next image forming job exceeds a predetermined time after the end of the collection job, it is determined whether or not the fixing device needs to be warmed up. First, it is preferable to execute the collection job before the start of the image forming job.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image forming apparatus of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a schematic configuration of a full-color laser beam printer to which the present invention is applied. In addition, the arrow in FIG. 1 has shown the rotation direction of each rotation member.
[0022]
As shown in FIG. 1, this full-color printer includes photosensitive drums 11, 12, 13, and 14 for yellow (Y), magenta (M), cyan (C), and black (K), and these photosensitive drums. 11 to 14, primary charging roller 21, 22, 23, 24 and yellow (Y), magenta (M), cyan (C), and black (K) laser beams 31, 32, 33. , 34 irradiating a laser optical unit (not shown), developing devices 41, 42, 43, 44, and a first primary contacting the two photosensitive drums 11, 12 of the four photosensitive drums 11-14. A second primary intermediate transfer drum 52 that contacts the intermediate transfer drum 51 and the other two photosensitive drums 13 and 14, and a secondary intermediate transfer drum that contacts the first and second primary intermediate transfer drums 51 and 52. 5 When, in a final transfer roll 60 in contact with the secondary intermediate transfer drum 53, a main part is configured.
[0023]
Among these configurations, each of the photosensitive drums 11 to 14, the charging rolls 21 to 24, the developing devices 41 to 44, the first and second primary intermediate transfer drums 51 and 52, and the secondary intermediate transfer drum 53 are single. The image forming unit 1 is integrated. For example, when the image quality is deteriorated due to deterioration of the photosensitive drum or the like, the image forming unit 1 is replaced as it is.
[0024]
The photosensitive drums 11, 12, 13, and 14 are arranged at a predetermined interval so as to have a common tangential plane M. Further, the first primary intermediate transfer drum 51 and the second primary intermediate transfer drum 52 have a surface target relationship in which each rotation axis is parallel to the photosensitive drums 11 to 14 and a predetermined target surface is a boundary. Arranged to be. Further, the secondary intermediate transfer drum 53 is arranged so that the rotation axis is parallel to the photosensitive drums 11 to 14.
[0025]
When forming a full-color image, a signal corresponding to image information for each color is rasterized by an image processing unit (not shown) and input to a laser optical unit (not shown). In this laser optical unit, yellow (Y), magenta (M), cyan (C), and black (K) laser beams 31 to 34 are modulated and irradiated to the corresponding photosensitive drums 11 to 14. The
[0026]
An image forming process for each color is performed around each of the photosensitive drums 11 to 14 by a known electrophotographic method. First, as the photoconductor drums 11 to 14, photoconductor drums using OPC photoconductors are used, and the surfaces of these photoconductor drums 11 to 14 are charged rolls 12, 22, and a DC roll to which a DC voltage of about -800V is applied. For example, the voltage is uniformly charged to about −300 V by 32 and 42. In this embodiment, only the DC component is applied to the charging roll, but the AC component may be superposed on the DC component.
[0027]
The laser beams 31 to 34 modulated in accordance with the input image information for each color are irradiated from the laser optical unit onto the surfaces of the photosensitive drums 11 to 14 having a uniform surface potential in this way. An electrostatic latent image corresponding to the color image information is formed at a predetermined timing. When the electrostatic latent image is written by the laser optical unit, the surface potential of the image exposure portion on the photosensitive drums 11 to 14 is discharged to about −60V or less.
[0028]
The electrostatic latent image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) formed on the surface of the photosensitive drums 11 to 14 is developed with the corresponding color. The images are developed by the devices 41 to 44 and visualized on the photosensitive drums 11 to 14 as toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Each of the developing devices 41 to 44 is filled with a developer including yellow (Y), magenta (M), cyan (C), and black (K) toners and carriers of different colors.
[0029]
Next, the yellow (Y), magenta (M), cyan (C), and black (K) toner images formed on the respective photosensitive drums 11 to 14 are converted into the first primary intermediate transfer drum 51. And electrostatically primary-transferred onto the second primary intermediate transfer drum 52. The yellow (Y) and magenta (M) color toner images formed on the photoconductive drums 11 and 12 are formed on the first primary intermediate transfer drum 51 and cyan (on the photoconductive drums 13 and 14). The toner images of C) and black (K) are transferred onto the second primary intermediate transfer drum 52, respectively. By shifting the electrostatic latent image writing start timing on the photosensitive drums 11, 12, 13, and 14 for each color, yellow (Y) and magenta (M) primarily transferred on the first primary intermediate transfer drum 51. A double-color image in which the toner images of the cyan (C) and black (K) are appropriately superimposed on the second primary intermediate transfer drum 52 is formed. A color image is formed.
[0030]
The surface potential necessary for electrostatically transferring the toner images from the photosensitive drums 11 to 14 onto the first and second primary intermediate transfer drums 51 and 52 is about +250 to 500V. The optimum surface potential varies depending on the charged state of the toner, the ambient temperature, and the humidity. However, if the charged amount of the toner is in the range of -20 to -35 μC / g and is in a normal temperature and humidity environment, The surface potential of the second primary intermediate transfer drums 51 and 52 is preferably about + 380V.
[0031]
Thereafter, the double-color toner images formed on the first and second primary intermediate transfer drums 51 and 52 are electrostatically secondary-transferred onto the secondary intermediate transfer drum 53. Therefore, a final toner image in which four colors of yellow (Y), magenta (M), cyan (C), and black (K) are overlapped is formed on the secondary intermediate transfer drum 53.
[0032]
The surface potential necessary for electrostatically transferring the toner image from the first and second primary intermediate transfer drums 51 and 52 onto the secondary intermediate transfer drum 53 is about +600 to 1200V. The optimum surface potential varies depending on the charged state of the toner, the ambient temperature, and the humidity as in the case of primary transfer. Further, since what is necessary for the transfer is a potential difference between the first and second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53, the first and second primary intermediate transfer drums 51 and 52 have different potentials. It is necessary to set the value according to the surface potential. As described above, the toner charge amount is in the range of −20 to −35 μC / g, and the surface potential of the first and second primary intermediate transfer drums 51 and 52 is +380 V in a normal temperature and humidity environment. The surface potential of the secondary intermediate transfer drum 53 is about + 880V, that is, the potential difference between the first and second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53 is about + 500V. It is desirable to set to.
[0033]
Finally, the quadruple toner image formed on the secondary intermediate transfer drum 53 is tertiary-transferred onto the paper passing through the paper transport path P by the final transfer roll 60. The paper passes through a paper transporting roll 90 through a paper feeding process (not shown), and is fed into the nip portion between the secondary intermediate transfer drum 53 and the final transfer roll 60. After this final transfer step, the final toner image formed on the paper is fixed by the fixing device 70, and a series of image forming processes is completed.
[0034]
In the laser beam printer of this embodiment configured as described above, a temporary toner holding member is arranged for each of the photosensitive drums 11 to 14 and the primary intermediate transfer drums 51 and 52.
[0035]
First, the toner temporary holding member disposed with respect to the photosensitive drum 11 is a refresher brush 215 in which conductive sliding bristles stand around a metal rotation shaft, and prevents toner from adhering to the charging roll 21. Therefore, it is positioned upstream of the charging roll 21 with respect to the rotation direction of the photosensitive drum 11. Further, a cleaning bias is applied to the refresher brush 215, and the toner whose polarity has been reversed at each transfer portion is temporarily collected from the surface of the photosensitive drum 11 until a cleaning mode described later is started. The toner is held for a while. That is, the toner is charged to (−) polarity in the developing device 41, and in each transfer process, the toner image is transferred toward a higher potential. However, when such a toner image repeatedly passes through the transfer part of each transfer process, a part of the (−) charged toner is inverted to the opposite polarity, that is, charged to the (+) polarity by Paschen discharge or charge injection. In this case, the toner whose polarity is reversed in this way is not transferred to the next process but flows backward to the upstream side. Finally, it is transferred to the photosensitive drum 11 and eventually adhered to the charging roll 21. The refresher brush 215 is provided to catch the toner whose polarity is reversed in front of the charging roll 21 and prevent the toner from adhering to the charging roll 21. Accordingly, at the time of forming a toner image, −400 V, which is lower than the surface potential of the photosensitive drum 11 −300 V, is applied to the refresher brush 215. Further, the refresher brush 215 is not provided with any driving means, and the refresher brush 215 is driven by rotation of the photosensitive drum 11 by a frictional force acting between the sliding bristles and the photosensitive drum 11. turning.
[0036]
In the above description, the refresher brush 215 provided for the photosensitive drum 11 has been described. However, the refresher brushes 216, 217, and 218 having the same structure are provided for the other photosensitive drums 12 to 14. It has been.
[0037]
On the other hand, for the primary intermediate transfer drums 51 and 52, first brush rolls 220 and 221 are disposed as temporary toner holding members having conductive sliding bristles around the metal rotation shaft. . These first brush rolls 220 are in positions where toner remaining on the surface of the primary intermediate transfer drum 51 is blocked on the front side of the photosensitive drum 12 after the end of the secondary transfer, and the first brush roll 221 ends the secondary transfer. The toner remaining on the surface of the primary intermediate transfer drum 52 later is disposed at a value for blocking the front side of the photosensitive drum 14.
[0038]
A cleaning bias is applied to the first brush rolls 220 and 221, but the polarity is opposite to that applied to the refresher brush 215. In the primary transfer, each photosensitive drum transfers only one color toner image to the primary intermediate transfer drums 51 and 52, so that the transfer efficiency can be set to be somewhat high, and the cleaning device deliberately collects residual toner. Even if the image forming apparatus is not provided, a large support is not generated in image formation, and color mixing does not occur in each of the developing devices 41 to 44. However, in the secondary transfer, the toner images for two colors that overlap each other are transferred to the secondary intermediate transfer drum 53, so that a large amount of toner remains on the primary intermediate transfer drums 51 and 52 without being transferred. This is because if the image is not collected by the apparatus, a ghost is generated in the next transferred toner image. For this reason, the residual toner charged to the (−) polarity is transferred to the first brush rolls 220 and 221 so as to be electrostatically transferred from the primary intermediate transfer drums 51 and 52 to the first brush rolls 220 and 221. A cleaning bias (for example, +600 V) higher than the surface potential of the primary intermediate transfer drums 51 and 52 is applied. Of course, if the atmospheric environment such as temperature and humidity changes and the surface potential of the primary intermediate transfer drums 51 and 52 changes, a potential difference between the first brush rolls 20 and 221 and the primary intermediate transfer drums 51 and 52 is secured. Therefore, it is necessary to change the cleaning bias. Further, these first brush rolls 220 and 221 are not provided with any driving means, and like the refresher brush 215, the first brush rolls 220 and 221 are primarily affected by the frictional force acting between the sliding bristles and the primary intermediate transfer drums 51 and 52. The intermediate transfer drums 51 and 52 are rotated.
[0039]
Further, a second brush roll 230 as a temporary toner holding member for removing the toner remaining in the tertiary transfer is also disposed on the secondary intermediate transfer drum 53. Unlike the first brush rolls 220 and 221 and the refresher brushes 215 to 218, the second brush roll 230 is driven to rotate in a direction opposite to the rotation direction of the secondary intermediate transfer drum 53 by a motor (not shown). A cleaning bias is also applied to the second brush roll 230, but for the purpose of removing residual toner generated in the third transfer from the surface of the secondary intermediate transfer drum 53, the polarity thereof is the first brush rolls 220 and 221. Is the same as that applied to. That is, the secondary intermediate transfer drum is disposed on the second brush roll 230 so that the residual toner charged to the (−) polarity is electrostatically transferred from the secondary intermediate transfer drum 53 to the second brush roll 230. A cleaning bias (for example, +1080 V) higher than the surface potential of 53 is applied.
[0040]
FIG. 2 schematically shows the flow of toner during an image forming job, that is, while a toner image formed on a photosensitive drum is being transferred to a recording sheet. During the image forming job, the toner charged to (−) polarity is transferred from the photosensitive drum to the recording sheet 100 through the primary intermediate transfer drum 51 and the secondary intermediate transfer drum 53. However, residual toner of the secondary transfer that has not been transferred from the primary intermediate transfer drum 51 to the secondary intermediate transfer drum 53 is captured by the first brush roll 220 on the way to the photosensitive drum 11. Further, the residual toner of the tertiary transfer that has not been transferred from the secondary intermediate transfer drum 53 to the recording sheet 100 is captured by the second brush roll 230 on the way to the primary intermediate transfer drum 53. On the other hand, the toner whose reverse polarity is injected at the transfer portion and the charge polarity is reversed to (+) is exposed to the secondary intermediate transfer drum through the primary intermediate transfer drum, contrary to the (−) polarity toner. The image is transferred back to the body drum, and finally is captured by a refresher brush 215 provided for the photosensitive drum.
[0041]
As described above, the refresher brushes 215 to 218, the first brush rolls 220 and 221, and the second brush roll 230 are respectively opposed to the photosensitive drums 11 to 14, the primary intermediate transfer drums 51 and 52, and the secondary intermediate transfer drum. Although the toner is captured from 53, it does not have any mechanical structure for discharging the captured toner. Therefore, when a toner image is repeatedly formed during an image forming job, the captured toner will overflow from between the rubbing hairs of each brush roll. Therefore, in the printer of this embodiment, in order to collect the toner captured by each brush roll, after the printing operation, the following collection job is performed at a predetermined timing, such as every predetermined number of sheets at the time of continuous printing. The toner temporarily captured by the brush roll is collected by a collective collecting device 80 provided for the transfer roll 60.
[0042]
In this collection job, first, for the charging rolls 21 to 24, the refresher brushes 215 to 218, the photosensitive drums 11 to 14, the primary intermediate transfer drums 51 and 52, the secondary intermediate transfer drum 53, and the final transfer roll 60, A voltage having a potential gradient is sequentially applied so that the final transfer roll 60 has the highest negative potential, and thereby, the reverse polarity (+) collected and held by the refresher brushes 215 to 218 during the printing operation. As shown in FIG. 3, the charged toner is sequentially transferred to the final transfer roll 60 and is collected by a collective collecting device 80 provided in contact with the final transfer roll 60. In this collective collection device 80, a cleaning blade 801 made of an elastic material such as silicon rubber is in contact with the peripheral surface of the transfer roll 60, and the toner transferred to the transfer roll 60 is scraped off by the cleaning blade 801 and collected in the device. It is like that. Therefore, when such a cleaning operation is started, the (+) charged toner temporarily held by the refresher brushes 215 to 218 is discharged onto the photosensitive drums 11 to 14 and the refresher brushes 215 to 218 are discharged. Will return to a clean state.
[0043]
When the collection of the (+) charged toner is completed in this way, the same potential as that at the time of toner image formation is set to the charging rolls 21 to 24, the photosensitive drums 11 to 14, the primary intermediate transfer drums 51 and 52, and the secondary. While being applied to the intermediate transfer drum 53 and the final transfer roll 60, the first brush roll and the second brush roll are given a potential having a polarity opposite to that at the time of image formation. This time, the second brush rolls 220, 221 and the second brush roll are applied. The (−) charged toner adhering to the brush roll 230 is collected. That is, as shown in FIG. 4, the first brush rolls 220 and 221 and the second brush roll 230 are given a potential having a polarity opposite to that at the time of image formation. The toner is discharged onto the primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53, and reaches the final transfer roll 60 via the secondary intermediate transfer drum 53 in the same manner as the transfer of a normal toner image, and is collected at once. It is collected by the device 80.
[0044]
It should be noted that when this collection job is executed, a toner cloud is likely to be generated around the brush roll. Therefore, in order to prevent the toner cloud from diffusing, the fan responsible for exhaust heat of the printer fixing device 70 should be stopped. good.
[0045]
By periodically executing such a collection job, the toner captured by the first, second, and second brush rolls is collected by the collective collection device 80 in any polarity, and the brush rolls are cleaned. Will be achieved.
[0046]
This collection job is basically performed immediately after the end of the image forming job, and each brush roll is immediately returned to a clean state after the image forming job. However, if the toner held by each brush roll cannot be discharged sufficiently in such a collection job, each brush roll holds the unnecessary toner captured during the previous image forming job and continues to the next. In this image forming job, unnecessary toner is captured, and each of the brush rolls is filled with unnecessary toner captured while the image forming job is repeated. When the inside of the brush roll is filled with the trapped unnecessary toner, the cleaning performance with respect to the photosensitive drums 11 to 14 and the intermediate transfer drums 51 to 53 is deteriorated, for example, attached to the secondary intermediate transfer drum 53. It is difficult to remove the transfer residual toner with the second brush roll 230. When such a situation occurs, the image of the previous recording sheet appears as a ghost image in the recording image formed on the recording sheet, and the image quality is significantly deteriorated.
[0047]
Therefore, in the printer of this embodiment, the length of the collection job to be performed immediately after is changed according to the contents of the executed image forming job. For example, as shown in FIG. 5, it is possible to set to change the execution time of the collection job performed immediately after the number of recording sheets passed in the image forming job. In other words, a large number of sheets to be passed means that each brush roll captures a large amount of toner by that amount. Therefore, in the collection job, a large amount of time is required to discharge all the captured toner. Become. At this time, the length of time of the collection job can be set in multiple stages according to the number of recording sheets passed. Further, when the number of sheets to be passed increases, the time for collecting the (+) polarity toner and the time for collecting the (−) polarity toner may be set longer, respectively. While the collection time is short, several sets of these may be repeated so that the total collection job time is increased.
[0048]
Further, instead of simply changing the length of the collection job based on the number of sheets in the image forming job, the collection job execution time may be changed according to the cumulative value of the image area ratio. According to this method, even when the number of recording sheets passed is large, the collection job execution time is set longer, and as shown in FIG. When the image is transferred to the recording sheet, the collection job is performed for a longer time. The actual amount of unnecessary toner captured by each brush roll is proportional to the amount of toner adhering to the photosensitive drums 11 to 14 and the intermediate transfer drums 51 to 53, so this method is shown in FIG. In addition, it is possible to further optimize the discharge amount of the captured toner of each brush roll in the collection job.
[0049]
Even when a collection job having a length corresponding to the number of sheets to be passed in the image forming job is executed every time the image forming job is completed, the captured toner is slightly accumulated in each brush roll. There is a tendency to go. Accordingly, when the cumulative number of sheets passed through the image forming unit 1 is increased by 200 and the image forming job is completed, the collection job longer than usual is repeated about three sets, and the toner captured by the brush roll is removed. It is preferable to exhaust thoroughly.
[0050]
Furthermore, if there are a large number of recording sheets in a single image forming job, each brush roll may become full of captured toner during the image forming job. Thereafter, when a predetermined number of recording sheets are passed, it is necessary to immediately interrupt the image forming job and execute the collection job without waiting for the end of the image forming job.
[0051]
In this case, if the environment where the printer is placed is low temperature and low humidity, the transfer efficiency of the toner image decreases, and the amount of toner captured by each brush roll tends to increase. The timing when the toner becomes full will come earlier than at normal temperature and humidity. For this reason, the printer of this embodiment is provided with an environmental sensor for measuring the temperature and humidity of the atmospheric environment, and the number of image forming jobs to be temporarily interrupted, that is, the number of interruptions is determined according to the detection value of the environmental sensor. is doing.
[0052]
FIG. 7 is a timing chart showing how often the collection job is performed when the same number of sheet-forming image forming jobs are performed under different atmospheric environments. The upper stage (a) is at room temperature and normal humidity, and the lower stage (b) is at low temperature and low humidity. Since there is a large amount of residual toner on the intermediate transfer drums 51 to 53 in a low-temperature and low-humidity environment, the number of interrupted image forming jobs is set smaller than that in a normal-temperature and normal-humidity environment, and collection jobs are frequently performed. To be done. For this reason, the time until the entire image forming job is completed is slightly delayed, but there is no trouble that the toner captured from each brush roll overflows, and even in an environment of low temperature and low humidity. High-quality recorded images can be obtained stably.
[0053]
Even when a high-resistance recording sheet such as an OHP sheet is used, it is preferable to set a small number of interruptions for inserting a collection job in an image forming job as shown in FIG. Again, when a toner image is transferred to a high-resistance recording sheet, a large amount of residual toner is generated on the secondary intermediate transfer drum 53, and the amount of toner captured by the second brush roll 230 increases. .
[0054]
Furthermore, if the electrical characteristics of the brush roll deteriorate with time, the cleaning performance of the photosensitive drums 11 to 14 and the intermediate transfer drums 51 to 53 by the brush roll deteriorates. It is preferable that the number of interrupted image forming jobs is gradually decreased as the cumulative number of recording sheets to be passed increases. For example, the number of interruptions is 48 for the cumulative number of 5000, 32 is the interruption for the 10,000, the number of interruption is 28 for the 15000, and so on.
[0055]
On the other hand, if the image forming job is interrupted and the collection job is performed in this way, it takes a long time until the end of the image forming job, which causes the user who has given the print instruction to wait. . From the viewpoint of minimizing the interruption of the image forming job, it is preferable to perform the collection job during the time when the toner image is not formed even during the image forming job. For example, as shown in FIG. 8, since no toner image is placed on the intermediate transfer drums 51 to 53 in the inter image area corresponding to the interval between successive recording sheets, the first and second areas are not included in this area. A toner image can be discharged from the brush roll to the primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53. This inter-image area is very small and may be less than one rotation of the bra sticker. However, since there are as many inter-image areas as the number of recording sheets passed in one image forming job, By gradually discharging the capture toner from the brush roll, it is possible to suppress the brush roll cleaning performance from being deteriorated by the capture toner as much as possible. As a result, the frequency of interrupting the image forming job and performing the collection job can be reduced, and the image forming job can be completed in a short time.
[0056]
Further, from the viewpoint of not interrupting the image forming job, the toner such as the warm-up time of the fixing device, the warm-up time after opening / closing the cover of the printer housing for the jamming of the recording sheet or the replacement of the toner cartridge, etc. If there is an opportunity to rotate the photosensitive drums 11 to 14 and the intermediate transfer drums 51 to 53 even though the image is not formed, a collection job is performed at such an opportunity and the brush roll holds it. It is desirable to discharge toner.
[0057]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the length of the collection job execution time can be changed according to the amount of unnecessary toner accumulated in the temporary toner holding member during the image forming job, and the temporary toner holding can be performed. Since the unnecessary toner collected by the member can be sufficiently discharged during the collection job, the amount of unnecessary toner held on the temporary toner holding member increases cumulatively, and as a result, during the image forming job. It is possible to prevent the unnecessary toner from overflowing from the temporary toner holding member, and it is possible to stably form a high-quality recorded image without causing defective cleaning even during long-term use. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a full-color laser beam printer to which the present invention is applied.
FIG. 2 is a schematic diagram illustrating a toner flow during an image forming job.
FIG. 3 is a schematic diagram illustrating a flow of (−) polarity toner collection during a collection job.
FIG. 4 is a schematic diagram showing a flow of (+) polarity toner collection during a collection job.
FIG. 5 is a timing chart illustrating how the length of a collection job is changed according to the number of sheets of an image forming job.
FIG. 6 is a timing chart showing how the length of the collection job is changed according to the image area ratio in the image forming job.
FIG. 7 is a timing chart showing changes in the number of interruptions when a collection job is executed during an image forming job.
FIG. 8 is a diagram illustrating an inter image area in an image forming job.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11-14 ... Photosensitive drum, 51, 52 ... Primary intermediate transfer drum, 53 ... Secondary intermediate transfer drum, 215-218 ... Refresher brush, 220, 221 ... First brush roll, 230 ... Second brush roll

Claims (2)

An image forming apparatus that forms a recorded image by transferring a toner image corresponding to image information from an image carrier to a recording sheet, and removes unnecessary toner adhering to the surface of the image carrier and temporarily holds the toner An image forming apparatus including a temporary holding member and configured to periodically execute a collection job for discharging unnecessary toner held on the toner temporary holding member onto the image carrier and collect the unnecessary toner in a final collection unit. In the apparatus, the collection job is executed after the end of the image forming job in which the toner image is formed and transferred, and the execution time of the collection job is changed according to the number of recording sheets passed in the immediately preceding image forming job. If the waiting time until the next image forming job exceeds the predetermined time after the above collecting job is completed, the collecting job is started before the start of the image forming job. Image forming apparatus which comprises carrying out. An image forming apparatus that forms a recorded image by transferring a toner image corresponding to image information from an image carrier to a recording sheet, and removes unnecessary toner adhering to the surface of the image carrier and temporarily holds the toner An image forming apparatus including a temporary holding member and configured to periodically execute a collection job for discharging unnecessary toner held on the toner temporary holding member onto the image carrier and collect the unnecessary toner in a final collection unit. In the apparatus, the collection job is executed after the end of the image forming job in which the toner image is formed and transferred, and is changed based on the cumulative amount of the image area ratio in the immediately preceding image forming job. If the waiting time until the next image forming job exceeds the predetermined time after the above collecting job is completed, the collecting job is started before the start of the image forming job. Image forming apparatus which comprises carrying out.

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