JP2013127514A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of appropriately cleaning the surface of a developing sleeve without providing a new member.SOLUTION: An image forming device includes: a photoreceptor 10; a developing sleeve 27 for developing a latent image into a toner image by rotating while facing the photoreceptor; and a cleaning member 40 for recovering toner on the photoreceptor at a position downstream from a transfer position. The image forming device also includes an image forming control part 45 for performing a normal mode in which a normal image formation is performed in a state in which a transfer from the photoreceptor to a material to be transferred is switched on and a sleeve soil removal mode in which a solid image within a range of 70 to 100% of image density is formed in a length equal to or greater than the length corresponding to one round of the developing sleeve on the photoreceptor in a state in which the transfer to the photoreceptor to the material to be transferred is switched off, and a peripheral velocity control part for controlling a peripheral velocity of the developing sleeve. The peripheral velocity control part makes the peripheral velocity of the developing sleeve slower as compared with the time of performing the normal mode when the sleeve soil removal mode is performed.

Description

  The present invention relates to an electrophotographic image forming apparatus. More specifically, the present invention relates to an image forming apparatus using a developing device having a magnet roller and a developing sleeve rotatably disposed on the outer periphery thereof.

  Conventionally, an image forming apparatus using a developing device having a fixed magnet roller and a rotating developing sleeve has been known. At the time of image formation, toner is supplied to the electrostatic latent image formed on the image carrier by a developing device to form a toner image. At that time, a developing bias is applied between the developing sleeve and the image carrier. In general, a voltage obtained by superimposing a DC component and an AC component is used as the developing bias. In order to increase the speed and space saving of the image forming apparatus and further improve the development efficiency, the AC component of the development bias tends to have a high Vpp and frequency.

  In a developing device using a two-component developer including toner and carrier, a slight vibration of the toner occurs between the developing sleeve and the image carrier due to the AC component of the developing bias. The slight vibration may cause the toner to leave the carrier. In some cases, the toner that has not been used for development remains attached to the developing sleeve without returning to the developing tank. As described above, it is known that when the amount of toner adhering to the developing sleeve increases, adverse effects such as density unevenness occur in a toner image formed thereafter.

  Therefore, conventionally, there has been a technique for cleaning the developing sleeve to reduce the amount of adhering toner (see, for example, Patent Document 1 and Patent Document 2). The developing device described in Patent Document 1 has a cleaning member that peels off the developer from the developing sleeve, exposes the surface of the developing sleeve, and cleans the portion. The apparatus described in Patent Document 2 rotates a sleeve at least once before developing an electrostatic latent image when humidity is low. According to Patent Document 2, when the sleeve is rotated, the developer adhering to the sleeve rubs against the developer in the developer tank, so that the dirt on the sleeve is removed.

JP-A-7-191552 JP-A-8-54787

  However, the apparatus disclosed in Patent Document 1 is provided with a dedicated cleaning member in the developing device, which requires space and costs. Furthermore, since the cleaning member deteriorates with use, there is a problem that the cleaning performance gradually decreases. In addition, the technique disclosed in Patent Document 2 cannot be said to sufficiently remove toner. Even when the humidity is not particularly low, a large amount of toner may remain on the sleeve.

  In particular, in recent image forming apparatuses, a toner having a smaller diameter is used, or a larger developing bias of Vpp is applied. For this reason, the amount of toner that leaves the carrier increases, and the amount of toner that adheres to the developing sleeve also tends to increase. In such an apparatus, it has been desired that the developing sleeve can be cleaned more satisfactorily.

  The present invention has been made to solve the above-described problems of the prior art. That is, the object is to provide an image forming apparatus capable of appropriately cleaning the surface of the developing sleeve without providing a new member.

  The image forming apparatus according to the present invention, which has been made for the purpose of solving this problem, has a photosensitive member that rotates to receive a toner image formed on the surface and transfers the toner image to a transfer target, and rotates while facing the photosensitive member. A developing sleeve for converting the latent image of the photosensitive member into a toner image by supplying toner to the photosensitive member, and a cleaning member for collecting the toner on the photosensitive member at a position downstream of the transfer position to the transfer target. An image forming apparatus, in which normal image formation is performed with the transfer from the photoconductor to the transfer target turned on, and image transfer with the transfer from the photoconductor to the transfer target turned off. An image forming control unit for performing a sleeve dirt removal mode for forming a solid image within a range of 70 to 100% on the photosensitive member over a length corresponding to one turn of the developing sleeve, and a peripheral speed of the developing sleeve. Peripheral speed to be controlled And a control unit, peripheral speed controller, at the time the sleeve soil removal mode executed, is to slow down the circumferential speed of the developing sleeve as compared to the normal mode execution.

  According to the image forming apparatus of the present invention, the normal mode and the sleeve dirt removal mode are executed by the image forming control unit. The normal mode is a mode for performing normal image formation. The sleeve dirt removal mode is a mode for collecting toner remaining on the developing sleeve by forming a high-density toner image corresponding to one or more rounds of the developing sleeve on the photosensitive member. In the present invention, since the peripheral speed of the developing sleeve is slowed when the sleeve dirt removal mode is executed, it is possible to avoid a large amount of toner from concentrating on the cleaning member. Accordingly, it is possible to suppress wiping residue on the cleaning member. Thus, the image forming apparatus can appropriately clean the surface of the developing sleeve without providing a new member.

Further, in the present invention, it is desirable that the peripheral speed control unit is configured so that the peripheral speed of the developing sleeve is 5/9 or less when the normal mode is executed when the sleeve dirt removal mode is executed.
With this level, the cleaning member can appropriately recover the toner on the photosensitive member by executing the sleeve dirt removal mode.

Further, according to the present invention, the image forming control unit is configured to perform a predetermined time after completion of image formation or a predetermined number of images after the previous execution of the sleeve dirt removal mode, and before that time. It is desirable to execute the sleeve dirt removal mode only when a solid image within the range of image density of 70 to 100% has never been printed during a predetermined period.
When a solid image having an image density in the range of 70 to 100% is printed, there is an effect of removing the sleeve dirt as in the execution of the sleeve dirt removal mode. Thus, in this way, it is possible to avoid the waste of executing the sleeve dirt removal mode even though the dirt is removed.

Further, according to the present invention, the image formation control unit executes the sleeve dirt removal mode if there is at least one portion where the solid image is not formed for each portion where the axial direction of the developing sleeve is divided into a plurality of portions. It is desirable that
The effect of removing the stain on the sleeve by the solid image appears at each position in the axial direction of the developing sleeve. If the stain remains even at one location, the image quality of the formed image may be adversely affected. In other words, when it is considered that all the spots in the axial direction of the developing sleeve have been removed, the sleeve dirt removal mode need not be executed.

  According to the image forming apparatus of the present invention, the surface of the developing sleeve can be appropriately cleaned without providing a new member.

1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to an embodiment. It is a perspective view which shows a developing sleeve. FIG. 6 is a potential waveform diagram of a developing bias. It is explanatory drawing which shows the difference in the generation | occurrence | production situation of the image density nonuniformity by a printing rate. It is explanatory drawing which shows the example of a test pattern. FIG. 6 is an explanatory diagram showing a toner adhesion amount to a developing sleeve. It is explanatory drawing which shows the relationship between the surface potential of a photoreceptor, and a sleeve dirt removal rate. It is explanatory drawing which shows the example of the implementation timing of a sleeve dirt removal mode. It is explanatory drawing which shows the example of a memory confirmation pattern.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an electrophotographic monochrome image forming apparatus.

  As shown in FIG. 1, the main part of the image forming apparatus 1 according to the present embodiment includes a photoreceptor 10, a developing device 20, a transfer member 30, and a cleaning member 40. Although not shown in the drawing, various members for forming an electrostatic latent image on the photoconductor 10 are further provided around the photoconductor 10. The image forming apparatus 1 includes, for example, a charging member that charges the photoreceptor 10, an exposure member that exposes the charged photoreceptor 10, and the like. Any of these non-illustrated members may be known.

  The image forming apparatus 1 of the present embodiment shown in FIG. 1 is of a direct transfer type that directly transfers a toner image formed on a photoreceptor 10 to a recording member P. The transfer member 30 transfers the toner image from the photoconductor 10 to the recording member P that passes between the photoconductor 10 and the transfer member 30. The cleaning member 40 removes toner remaining on the photoreceptor 10 after transfer. The cleaning member 40 of this embodiment is of a blade type, and scrapes off the toner by rubbing the surface of the photoreceptor 10.

  As shown in FIG. 1, the developing device 20 has a developing housing 21, and the inside thereof is a developer tank 22 for containing the developer. A developer carrier 23 and developer conveying screws 24 and 25 are arranged in the developer tank 22. A part of the developer carrying member 23 faces the photoconductor 10 and supplies toner to the electrostatic latent image on the photoconductor 10. The developer transport screws 24 and 25 are for transporting the developer in opposite directions in the depth direction in the drawing. The stored developer is appropriately stirred by the developer conveying screws 24 and 25. Note that the image forming apparatus 1 of the present embodiment uses a two-component developer containing a negatively charged toner.

  The developer carrying member 23 includes a developing sleeve 27 and a fixed magnet 28 disposed inside thereof. As shown in FIGS. 1 and 2, the developing sleeve 27 is a cylindrical rotatable member. At the time of image formation, the photosensitive member 10, the developing sleeve 27, and the transfer member 30 rotate as indicated by arrows in FIG. At this time, the developing sleeve 27 is rotated in the follower direction so that the moving direction in the vicinity of the photoconductor 10 is the same. Here, a developing sleeve 27 having an axial length of 330 mm and a circumferential length of 50 mm is used.

  Further, the image forming apparatus 1 has a power source 26 for applying a developing bias between the developer carrier 23 and the photosensitive member 10 as shown in FIG. The power supply 26 applies a developing bias in which a direct current component and an alternating current component are superimposed to the developer carrier 23. The photoconductor 10 is grounded.

  Furthermore, the image forming apparatus 1 of the present embodiment has a control unit 45 that controls each unit. The controller 45 controls the rotation operation of the photosensitive member 10, the operation of each unit in the developing device 20, the voltage applied by the power supply 26, and the like. The controller 45 also controls on / off of the transfer of the toner image from the photoconductor 10 to the recording member P by the transfer member 30 and controls the rotational speed of the photoconductor 10 and the developing sleeve 27.

  An example of the development bias waveform is shown in FIG. The developing bias in this example is obtained by superimposing a square wave (AC) with a frequency of 2.5 kHz at Vpp 1.6 kV on DC of −300 V. In the example shown in this figure, the average value of the potential of the developer carrier 23 is −300V, the minimum value of the potential is −1100V, and the maximum value is 500V.

  At the time of image formation, the surface potential of the photoconductor 10 is set to a positive potential from the average value of the developing bias in the colored portion, and is set to a negative potential from the average value of the developing bias in the white portion. Is done. For example, the surface potential of the photoconductor 10 at the time of image formation in the image forming apparatus 1 of the present embodiment is set to be −40V at an image density 100% and −400V at a white area. Further, at the portion of the intermediate color, the surface potential of the photoconductor 10 is set to a potential between −40V and −300V.

  Therefore, the toner (negatively charged) on the developing sleeve 27 is attracted to the photosensitive member 10 and moves at the colored portion. On the other hand, in the white portion, it is pressed against the developing sleeve 27 and does not move to the photosensitive member 10. As a result, a toner image is formed. Therefore, the toner tends to remain on the developing sleeve 27 after the white portion is formed, and the sleeve is likely to become dirty. On the contrary, the toner hardly remains on the developing sleeve 27 after the dark portion is formed. This is because the higher the image density is, the more the surface potential of the photoconductor 10 becomes farther to the positive side than the average value of the developing bias.

  That is, the portion where the image density is printed is less likely to cause the sleeve stain, and the portion where the image density is light or the portion where the white portion is printed is likely to cause the sleeve stain. When the inventor confirmed the relationship between the printing rate and the image density unevenness by an experiment, the result shown in FIG. 4 was obtained. This figure confirms the occurrence of uneven image density on the test print image after repeatedly printing an image with a uniform printing rate on the entire surface. In this experiment, the image density of the test print was measured using a reflection densitometer manufactured by Gretag Macbeth Co., and the difference between the maximum value and the minimum value of the image density on the paper surface was defined as an image density difference (ΔID).

  The test print used in this experiment printed a gray image with a uniform density on the entire surface. Also, the horizontal axis of FIG. 4 represents the integrated rotation speed of the developing sleeve 27, and the vertical axis represents the maximum density difference in one sheet of test printing. The higher the vertical axis, the larger the density difference. Note that the printing rate is the ratio of the area where the toner image is formed to the area where an image can be formed on one sheet of paper. The image forming apparatus 1 acquires the printing rate of an image to be formed during normal image formation.

  As can be seen from the results of FIG. 4, when the images with the printing rates of 0%, 5%, and 10% were repeatedly printed, the image density unevenness exceeding the allowable range occurred. What is indicated by a one-dot chain line in the figure is the maximum allowable image density difference. Then, it was found that the image density unevenness is outside the allowable range with a smaller number of images as the printing rate is lower. Therefore, in the image forming apparatus 1 of the present embodiment, the developing sleeve is cleaned before the image density unevenness is outside the allowable range. This cleaning is an implementation of the sleeve dirt removal mode, and the image forming apparatus 1 according to the present embodiment performs the sleeve dirt removal mode at an appropriate timing.

  For example, at least an image with a printing rate of 5% or less has been printed continuously for 150 or more laps of the developing sleeve 27 since the previous cleaning, or an image with a printing rate of 10% or less for 200 laps of the developing sleeve 27. The sleeve dirt removal mode should be performed before continuous printing. However, in this experiment, in an image with a printing rate of 15% or more, image density unevenness exceeding the allowable range did not occur even when repeated printing was performed. That is, in the image forming apparatus 1, it is preferable to count the number of printed images with a printing rate of less than 15% and determine the execution timing of the sleeve dirt removal mode.

  In a general image, the printing rate varies depending on the position in the axial direction of the developing sleeve 27. For this reason, it is necessary to count the number of printed sheets described above for each position in the axial direction of the developing sleeve 27. Such a case can be grasped by, for example, an experiment for printing test patterns having different printing rates in the axial direction of the developing sleeve 27 as shown in FIG. That is, the amount of toner adhering to the developing sleeve 27 after repeatedly printing the pattern in this figure was different in the regions a, b, c, and d as shown in FIG. That is, the area a and the area d, which are areas with a low printing rate, have more sleeve dirt than the areas b and c, which are areas with a high printing rate.

  That is, the image forming apparatus 1 according to the present embodiment grasps the printing rate and the number of printed sheets for each position in the axial direction of the developing sleeve 27 in the normal mode which is a normal image forming time. Then, the image forming apparatus 1 appropriately performs the sleeve dirt removal mode and cleans the developing sleeve 27 before the image density unevenness due to the sleeve dirt falls outside the allowable range even in the region where the printing rate is the lowest. Therefore, image quality deterioration due to sleeve contamination is prevented.

  Sleeve contamination can be alleviated by forming a toner image having a high image density. Therefore, the image forming apparatus 1 according to the present embodiment performs a process of forming a toner image of a full black image over the entire width of the developing sleeve 27 over the entire length of the outer circumference of the developing sleeve 27 as the sleeve dirt removal mode. It is desirable that the toner image formed in this case is uniform over the entire printable width and corresponds to an image having a considerably high density.

  FIG. 7 shows the relationship between the image density of the toner image formed in the sleeve dirt removal mode and the sleeve dirt removal property. The horizontal axis of this figure represents the surface potential of the photoreceptor 10. As described above, the surface potential of −400 V corresponds to the white image portion, and the surface potential of −40 V corresponds to the black image having the maximum density (image density of 100%). In addition, the vertical axis in this figure represents the degree of removal of the sleeve dirt, and represents that it can be removed well. As can be seen from this figure, when the image density is in the range S of 70 to 100%, the stains on the developing sleeve 27 can be appropriately removed. Therefore, it is desirable that the image density of the toner image formed in the sleeve dirt removal mode is in the range of 70 to 100%.

  That is, the image forming apparatus 1 according to the present embodiment executes the sleeve dirt removal mode when the sleeve dirt is generated. When the sleeve contamination removal mode of the present embodiment is implemented, the image width is a solid image having a maximum width capable of forming an image in the axial direction of the developing sleeve 27 and a length of one or more circumferences of the developing sleeve 27 and an image density of 70 to 100%. An electrostatic latent image corresponding to the image is formed on the photoreceptor 10. Further, by developing the electrostatic latent image by the developing device 20, the toner remaining on the developing sleeve 27 moves to the photoconductor 10 as a part of the toner image. That is, the sleeve dirt can be removed.

  However, it is not necessary to transfer the toner image to the recording member P. Therefore, the image forming apparatus 1 causes the cleaning member 40 to collect the toner moved to the photoconductor 10 in the sleeve dirt removal mode without transferring it to the paper. However, in the process as it is, a large amount of toner is pushed toward the cleaning member 40 as compared with the normal image formation. On the other hand, there is a limit to the amount of toner that the cleaning member 40 can collect per unit time. Therefore, the cleaning member 40 cannot be properly collected when a too large amount of toner arrives.

  In that case, the cleaning member 40 passes the toner that could not be collected as it is. That is, if toner that cannot be collected is collected on the cleaning member 40, it remains as a wiping residue and remains on the photoreceptor 10. The occurrence of such unwiping of the toner is not preferable because it causes the image quality of an image to be formed later to deteriorate. Therefore, when the image forming apparatus 1 according to the present embodiment performs the stain removal mode of the developing sleeve 27, the rotation speed of the developing sleeve 27 is made slower than that in the normal mode image forming.

  That is, the control unit 45 of the image forming apparatus 1 according to the present embodiment performs a normal mode in which the transfer member 30 is turned on to perform image formation and a sleeve dirt removal mode in which the transfer member 30 is turned off to form a toner image on the photoconductor 10. Control implementation. When the sleeve dirt removal mode is executed, the rotation speed of the developing sleeve 27 is controlled to be slower than when the normal mode is executed. This prevents a large amount of toner from concentrating on the cleaning member 40 as will be described below.

  For example, in the image forming apparatus 1 of the present embodiment, the ratio of the peripheral speed of the developing sleeve 27 to the peripheral speed of the photoconductor 10 (hereinafter referred to as development θ) is 1.8 during image formation in the normal mode, and sleeve contamination removal is performed. In the mode, it is 1.0 or less. The peripheral speed is the traveling speed at each instant of one point on the outer peripheral surface of the rotating member such as the photosensitive member 10. That is, at the time of image formation, the peripheral speed of the developing sleeve 27 is 1.8 times the peripheral speed of the photoconductor 10. As a result, in the normal mode, the toner is surely placed on the electrostatic latent image on the photoconductor 10.

  On the other hand, the image forming apparatus 1 according to this embodiment controls the rotation so that the peripheral speed of the developing sleeve 27 is approximately equal to or less than the peripheral speed of the photosensitive member 10 in the sleeve dirt removal mode. However, the peripheral speed of the photoconductor 10 is the same as that during image formation in the normal mode, and is a constant speed. That is, in the sleeve dirt removal mode, the peripheral speed of the developing sleeve 27 is reduced to about 5/9 times or less that in the normal mode. In this way, in the sleeve dirt removal mode, various portions of the surface of the developing sleeve 27 can be reliably faced to the appropriately charged photoconductor 10. At the same time, the toner amount per unit area of the photoconductor 10 in the sleeve dirt removal mode is smaller than when the speed is not slowed down.

  That is, by adjusting the development θ, the toner collection amount per unit time by the cleaning member 40 is suppressed to such a level that it can be collected. Therefore, even if the same amount of toner is transferred to the photoconductor 10 as a whole, since the toner does not intensively arrive at the cleaning member 40, the occurrence of unwiping is avoided. Accordingly, the image forming apparatus 1 can reliably remove the dirt on the sleeve and can prevent the cleaning member 40 from being left unwiped.

  In the image forming apparatus 1 of the present embodiment, the timing of performing the sleeve dirt removal mode can be, for example, after image formation of a predetermined amount is performed. For example, as shown in FIG. 8, for example, it may be basically performed every time interval R of the predetermined image forming time. However, if an image having an image density of 70% to 100% is formed even once during a certain period ΔT retroactively from the scheduled execution time, it is not necessary to perform the execution at the scheduled time. This is because the stain on the developing sleeve 27 is substantially removed by forming a toner image of an image having an image density of 70 to 100%.

  In the example of FIG. 8, times T1, T2, T3, and T4 in the figure are the execution timings of the predetermined sleeve dirt removal mode. In this example, the predetermined period ΔT is half of the predetermined time interval R. That is, as shown in the figure, when an image having an image density of 70 to 100% is formed at time T, which is closer to T3 than the middle between T2 and T3, the sleeve dirt removal mode at time T3 is not performed. The fixed period ΔT is the same time as the time interval R at the maximum.

  Whether or not an image having an image density of 70 to 100% has been formed is determined for each point in the axial direction of the developing sleeve 27, and even at one place, an image having an image density of 70 to 100% is not formed. If there is, it is desirable to perform the sleeve dirt removal mode. It should be noted that this sleeve dirt removal mode may be performed immediately after the end of printing of a job or at the time immediately before the start of the next printing if it is during non-image formation. Further, as a basic timing, it may be performed every predetermined number of printed sheets.

  The inventor conducted an experiment for confirming the effect of the present invention. In this experiment, ten test patterns with a printing rate of 5% were printed, and then the sleeve dirt removal mode was performed. In the sleeve contamination removal mode in this experiment, a solid black image having a density of 100% was formed on the photosensitive member 10 with a length corresponding to two rounds of the developing sleeve 27. Further, a set of printing 10 test patterns and once in the sleeve dirt removal mode was repeated 5 times. Thereafter, the degree of contamination of the sleeve and the degree of unwiping of the photoreceptor 10 were confirmed. The present inventor conducted the same kind of experiment with four types of development θ in the sleeve dirt removal mode of 0.5, 1.0, 1.5, and 1.8.

  The degree of sleeve contamination was confirmed by forming an image of the confirmation pattern 50 shown in FIG. The confirmation pattern 50 is printed using A4 size paper in landscape orientation, and a plurality of black images 51 having a density of 100% are formed in the leading portion in the paper traveling direction with a gap (in this figure). 5). That is, in the axial direction of the photoconductor 10, a white image portion having no image data is formed between the black images 51. Further, a gray image portion 52 is formed to the full width in the axial direction at the rear of the black image 51 in the paper traveling direction. Note that when the confirmation pattern 50 is printed, the development θ is set to 1.8 which is a value at the time of image formation.

  If sleeve dirt remains on the developing sleeve 27, the effect appears in the gray image portion 52 of the confirmation pattern 50. That is, the color of the sleeve becomes slightly darker than the original color due to the influence of the sleeve dirt. However, the portion where the black image 51 is printed is removed by the black image 51 from the sleeve stain, and becomes closer to the original color. For example, as indicated by a broken line in FIG. 9, a portion that appears slightly thinner than the surroundings is generated at a location that is separated from the black image 51 by a distance corresponding to the circumferential length L of the developing sleeve 27. It looks like that because the colors other than this part are a little darker. Therefore, the formed confirmation pattern 50 was visually observed, and the presence / absence of sleeve contamination was determined based on the presence / absence of this color difference.

  In order to confirm the remaining wiping of the photoconductor 10, the apparatus is stopped after the test printing is completed, the photoconductor 10 is taken out, and the surface of the photoconductor 10 is peeled off from a location near the downstream side of the cleaning member 40 with tape or the like This was performed by visual observation. If left unwiped, toner adheres to the tape. By comparing the amount of adhesion with a predetermined reference level, it was determined whether or not the remaining amount of wiping was within the allowable range.

The results of this experiment are shown in Table 1 below. Note that the peripheral speed of the photoconductor 10 during this experiment was set to the same constant value for both the development θ and the normal mode and the sleeve dirt removal mode. The symbols indicating the results in the table have the following meanings.
○ indicates that the degree of contamination was within the allowable range.
X indicates that contamination exceeding the allowable range was observed.

  From the results of this experiment, it was confirmed that the stain on the developing sleeve 27 was eliminated by forming a toner image corresponding to an image density of 100%. It was also confirmed that the cleaning member 40 can be appropriately prevented from being wiped off by setting the development θ in the sleeve dirt removal mode to 1.0 or less.

  As described above in detail, according to the image forming apparatus 1 of the present embodiment, if it is determined that the toner adheres to the developing sleeve 27 and the sleeve dirt is generated, the sleeve dirt removal mode is set during non-image formation. To be implemented. In this sleeve contamination removal mode, the photosensitive member 10 corresponds to a solid image having an image width of 100% to 70% over the entire length in the axial direction of the developing sleeve 27 and a length equal to or greater than the circumferential length of the developing sleeve 27. An electrostatic latent image is formed. Further, the image forming apparatus 1 develops the electrostatic latent image by reducing the rotation speed of the developing sleeve 27 so that the development θ is 1.0 or less. Accordingly, the contamination of the sleeve can be removed appropriately, and image quality deterioration due to unwiping of the cleaning member 40 does not occur. Therefore, the image forming apparatus can appropriately clean the surface of the developing sleeve without providing a new member.

  In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Photoconductor 27 Developing sleeve 30 Transfer member 40 Cleaning member 45 Control part

Claims (4)

A photosensitive member that receives the formation of a toner image on the surface while rotating and transfers the toner image to a transfer member, and rotates while facing the photosensitive member to supply toner to the photosensitive member. In an image forming apparatus having a developing sleeve for converting a latent image into a toner image, and a cleaning member for recovering toner on the photosensitive member at a position downstream from a transfer position to a transfer target,
An image density of 70 to 100% is obtained in a normal mode in which normal image formation is performed with transfer from the photoconductor to the transfer target turned on, and transfer from the photoconductor to the transfer target is turned off. An image formation control unit that performs a sleeve dirt removal mode in which a solid image within a range is formed on the photosensitive member over a length corresponding to one turn of the developing sleeve;
A peripheral speed controller for controlling the peripheral speed of the developing sleeve;
The image forming apparatus according to claim 1, wherein the peripheral speed control unit is configured to slow down the peripheral speed of the developing sleeve when the sleeve dirt removal mode is executed as compared to when the normal mode is executed. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the circumferential speed control unit is configured to set the circumferential speed of the developing sleeve to 5/9 or less when the normal mode is executed when the sleeve dirt removal mode is executed. The image forming apparatus according to claim 1, wherein:
The image formation control unit
After the previous execution of the sleeve dirt removal mode, after the completion of image formation for a predetermined time or after completion of image formation for a predetermined number of images, during a predetermined period before that point, the image density 70 An image forming apparatus characterized in that the sleeve dirt removal mode is executed only when a solid image within a range of ˜100% has never been printed. The image forming apparatus according to claim 3,
The image formation control unit
The image is characterized in that the sleeve dirt removal mode is executed if there is at least one portion where the solid image is not formed for each portion obtained by dividing the axial direction of the developing sleeve into a plurality of portions. Forming equipment.

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