JP7706951B2 - Image forming device - Google Patents

Description

The present invention relates to image forming devices that use electrophotographic recording methods, such as laser printers, copiers, and facsimiles.

In electrophotographic image forming devices, a photosensitive drum serving as an image carrier is uniformly charged, and then exposed to light according to an image pattern to form an electrostatic latent image on the photosensitive drum. The electrostatic latent image on the photosensitive drum is then developed with toner to become visible, and transferred to a recording material such as paper. Residual toner remaining on the photosensitive drum is then removed and collected from the photosensitive drum. There are several cleaning methods for removing residual toner, but a configuration using a brush is widely known as one of the most effective methods.

Patent document 1 discloses a configuration in which a brush for cleaning toner on a photosensitive drum is disposed upstream of a charging means in the direction of movement of the photosensitive drum and downstream of a transfer means in the direction of movement of the photosensitive drum. According to this document, for example, when image formation is interrupted due to a paper jam or the like, the brush is charged to a predetermined polarity to prevent untransferred toner on the photosensitive drum from accumulating on the brush, thereby maintaining cleaning performance.

JP 2007-65580 A

However, Patent Document 1 has the following problems. In an image forming apparatus in which a brush as disclosed in Patent Document 1 is disposed, when a recording material is passed through the apparatus, water vapor inside the apparatus adheres to the brush. The water vapor accumulated on the brush condenses on the surface of the photosensitive drum as the stop time passes, and exists as a lump of water droplets. In this state, when the next image forming operation is performed, the lump of water droplets adhering to the brush may transfer onto the photosensitive drum, changing the condition of the surface of the photosensitive drum and causing image defects. For example, at the development contact portion, which is the contact portion between the photosensitive drum and the developing member, the lump of water droplets adhering to the photosensitive drum may attract toner, causing toner contamination.

The present invention was made to solve the above technical problems, and aims to suppress image defects caused by toner stains caused by water droplets adhering to the brush.

In view of the above, the present invention provides a developing device comprising: a rotatable photosensitive drum; a charging member which charges the surface of the photosensitive drum in a charging section; a developing member which supplies toner onto the surface of the photosensitive drum charged by the charging member to form a toner image; a transfer member which contacts the photosensitive drum to form a transfer section and transfers the toner image formed on the photosensitive drum to a transfer recipient in the transfer section; a brush member which is downstream of the transfer section and contacts the surface of the photosensitive drum upstream of the charging section in the rotation direction of the photosensitive drum; a drive section which rotates the photosensitive drum; a storage section which stores information regarding the usage history of the photosensitive drum; and a control section which controls the drive section, In this image forming apparatus, the toner transferred to the developing member is recovered, and the image forming apparatus is capable of performing a first image forming operation for forming an image on a transfer medium , a second image forming operation performed following the first image forming operation , and a rotation operation for rotating the photosensitive drum before the second image forming operation is performed , the control unit controls the number of rotations of the photosensitive drum in the rotation operation based on the information and a stop time from the end of the first image forming operation to the start of the rotation operation, and is characterized in that when the number of transfer mediums that have passed between the transfer unit and the developing unit in the first image forming operation is a first number, the control unit controls the number of rotations of the photosensitive drum in the rotation operation to be smaller than when the number is a second number that is greater than the first number .

As described above, the present invention can suppress image defects caused by toner stains caused by water droplets adhering to the brush.

FIG. 1 is an explanatory diagram of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic diagram of a brush member according to the first embodiment. FIG. 2 is a control block diagram according to the first embodiment. FIG. 4 is a diagram showing water vapor adhering to a brush member in Example 1. 5A and 5B are diagrams illustrating a state around the photosensitive drum during an image output operation in the first embodiment. FIG. 13 is a diagram showing an extension time of the pre-rotation process in the first embodiment. FIG. 4 is a graph showing the results of toner contamination in Example 1. FIG. 4 is a timing chart of a pre-rotation process in the first embodiment. FIG. 4 is a diagram showing toner and water vapor on a brush member in Example 1. FIG. 13 is a diagram showing an extension time of the pre-rotation process in the second embodiment.

The following describes in detail the embodiments of the present invention with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments should be changed as appropriate depending on the configuration and various conditions of the device to which the invention is applied. In other words, it is not intended to limit the scope of the present invention to the embodiments described below.

1. Image Forming Apparatus Fig. 1 is a schematic diagram of an image forming apparatus 100 according to a first embodiment of the present invention.

The image forming apparatus 100 of this embodiment is a monochrome laser beam printer that employs a cleanerless system and a contact charging system. The image forming apparatus 100 has a photosensitive drum 1, which is a drum-type (cylindrical) electrophotographic photosensitive member that serves as a rotatable image carrier. When an image output operation is started, the photosensitive drum 1 is driven to rotate in the direction of arrow R1 in the figure by a drive motor (drive unit) (Figure 3) serving as a drive means 110. The outer diameter of the photosensitive drum 1 is 24 mm, and the peripheral speed (surface speed) is 140 mm/sec.

The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of normal polarity (negative polarity in this embodiment) by the charging roller 2, which is a roller-type charging member serving as a charging means, in the vicinity of the charging portion a where the photosensitive drum 1 and the charging roller 2 contact each other. More specifically, the charging roller 2 charges the surface of the photosensitive drum 1 by discharging generated in at least one of the small gaps between the charging roller 2 and the photosensitive drum 1 formed on the upstream side and downstream side of the contact portion with the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1. However, here, the contact portion between the charging roller 2 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is assumed to be the charging portion. The charging roller 2 is an elastic roller having a conductive elastic layer provided around a core metal, and is arranged in contact with the photosensitive drum 1 and is rotated in the direction of the arrow R2 in the figure by a driving motor (not shown). In this embodiment, the charging roller 2 is driven to rotate, but it may be configured to rotate following the rotation of the photosensitive drum 1. A predetermined charging voltage, which is a negative DC voltage, is applied to the charging roller 2 from a charging power source E1 (FIG. 3) serving as a charging voltage application means. In this embodiment, a negative DC voltage is applied as the charging voltage to the charging roller 2 during charging. As an example, the charging voltage in this embodiment is set to -1200V. As a result, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark potential Vd of -600V.

The surface of the charged photosensitive drum 1 is scanned and exposed by a laser beam L modulated according to image data by an exposure device (laser exposure unit) 4 as an exposure means (electrostatic image forming means). The exposure device 4 repeatedly exposes the photosensitive drum 1 to the laser beam L in the main scanning direction (rotation axis direction) and also in the sub-scanning direction (surface movement direction) to form an electrostatic latent image on the photosensitive drum 1. In this embodiment, the absolute value of the dark area potential Vd of the surface of the photosensitive drum 1 formed by uniformly charging is reduced by exposure by the exposure device 4 to a light area potential Vl of -100 V. In the rotation direction of the photosensitive drum 1, the exposure position on the photosensitive drum 1 by the exposure device 4 is the image exposure section b. The exposure device 4 is not limited to a laser scanner device, and may be, for example, an LED array in which multiple LEDs are arranged along the longitudinal direction of the photosensitive drum 1.

The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by the developing device 3 as a developing means using toner as a developer. The toner used as the developer in this embodiment is a spherical non-magnetic toner with an average particle size of 6.4 μm and an average circularity of 0.98. The average circularity of the non-magnetic toner used in this embodiment is preferably high, specifically 0.96 or higher. The average circularity in this embodiment is used as a simple method of quantitatively expressing the shape of the particles, and the particle shape is measured using a flow type particle image analyzer FPIA-2100 manufactured by Toa Medical Electronics Co., Ltd., and the circularity is calculated using the following formula 1.

Furthermore, the average circularity is defined as the sum of the circularities of all measured particles divided by the total number of particles, as shown in the following formula 2.

The developing device 3 is composed of a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber 33 that stores toner, and a developing blade 34. The toner stored in the developer storage chamber 33 is stirred by a stirring member 35 and supplied to the surface of the developing roller 31 by the toner supply roller 32. The toner supplied to the surface of the developing roller 31 is uniformly thinned by passing through the contact portion between the developing roller 31 and the developing blade 34, and is charged to a negative polarity by abrasion charging. In this embodiment, a one-component non-magnetic contact development method is adopted, but this is not limited to this, and a two-component non-magnetic contact or non-contact development method may be adopted. A magnetic development method may also be adopted. In this embodiment, the normal polarity of the toner is negative, but is not limited to negative. The normal polarity may be positive, in which case the voltage relationship described later may be appropriately reversed. The developing roller 31 is rotated counterclockwise in the direction of the arrow R3 in the figure by the driving motor 110 so that the moving directions of the surface of the photosensitive drum 1 and the surface of the developing roller 31 are the same in the developing section c where the photosensitive drum 1 and the developing roller 31 are in contact with each other. The driving motor as the driving means 110 for driving the developing roller 31 may be a main motor common to the driving means 110 for the photosensitive drum 1, or separate driving motors may rotate the photosensitive drum 1 and the developing roller 31, respectively. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power source E2 (FIG. 3) as a developing voltage applying means. In this embodiment, during development, a negative DC voltage is applied to the developing roller 31 as the developing voltage, and the developing voltage is set to -300V. In this embodiment, toner charged with the same polarity (negative in this embodiment) as the charge polarity of the photosensitive drum 1 adheres to the exposed surface (image area), which is the image forming area on the photosensitive drum 1, where the absolute value of the potential has been reduced by exposure after being uniformly charged. This development method is called a reversal development method.

In addition, in this embodiment, the developing roller 31 is configured to always be in contact with the photosensitive drum 1 at the developing section c, but the developing roller 31 and the photosensitive drum 1 may be configured to be in a contact state or a separated state. In this case, a developing contact/separation mechanism may be separately provided. During the rotation operation, which is the pre-rotation process described below, the photosensitive drum 1 may be rotated with the developing roller 31 separated from the photosensitive drum 1.

The toner image formed on the photosensitive drum 1 is sent to the transfer section d, which is the contact section between the photosensitive drum 1 and the transfer roller 5, which is a roller-type transfer member serving as a transfer means. The transfer roller 5 in this embodiment is a roller made of conductive NBR (nitrile butadiene rubber)-hydrin sponge rubber with an outer diameter of 12 mm and a hardness of 30° (Asker-C, 500 gf load), and is pressed against the photosensitive drum 1 with a predetermined pressure. Meanwhile, in synchronization with the toner image on the photosensitive drum 1, the recording material P, which is the transfer target, is transported from the storage section 6 to the transfer section d by the transport roller 8 or the like. Then, the toner image on the photosensitive drum 1 is transferred to the recording material P, which has been transported while being sandwiched between the photosensitive drum 1 and the transfer roller 5, by the action of the transfer roller 5 at the transfer section d. At this time, a predetermined transfer voltage, which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner, is applied to the transfer roller 5 from the transfer power source E3 (FIG. 3). This creates an electric field between the transfer roller 5 and the photosensitive drum 1, and the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material P. In this embodiment, the transfer voltage during this transfer is +1000V, for example. The toner image is then electrostatically transferred from the photosensitive drum 1 to the recording material S by the action of the electric field created between the transfer roller 5 and the photosensitive drum 1.

The recording material P onto which the toner image has been transferred is sent to a fixing device 9, which serves as a fixing means. In the fixing device 9, heat and pressure are applied to the recording material P, and the toner image is fixed to the recording material P.

Meanwhile, the residual toner that has not been transferred to the recording material P and remains on the photosensitive drum 1 is sent to the brush member 10, which is installed downstream of the transfer roller 5 in the rotation direction of the photosensitive drum 1. The brush member 10 used in this embodiment is described below.

2. Configuration of the Brush Member Next, the paper dust removal mechanism in this embodiment will be described. As shown in Fig. 1, the image forming apparatus 100 in this embodiment has a brush member 10 (collection member) which is a contact member serving as the paper dust removal mechanism. In this embodiment, the image forming apparatus 100 has the brush member 10 which contacts the surface of the photosensitive drum 1 downstream of the transfer unit and upstream of the charging unit in the rotation direction of the photosensitive drum 1 to form a brush contact portion (brush contact position). Here, the contact portion between the brush member 10 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is considered to be the brush contact portion.

Figure 2(a) is a schematic diagram of the brush member 10 in a standalone state, viewed along its longitudinal direction (substantially parallel to the direction of the rotation axis of the photosensitive drum 1). Also, Figure 2(b) is a schematic diagram of the brush member 10 in contact with the photosensitive drum 1, viewed along its longitudinal direction.

The brush member 10 is composed of a fixed conductive brush 11. As shown in FIG. 2, the brush member 10 is composed of conductive nylon 6 pile yarns 11a, which are a number of bristles that rub against the surface of the photosensitive drum 1, and a base cloth 11b that supports the pile yarns 11a. As described above, the brush member 10 is arranged so that it comes into contact with the photosensitive drum 1 downstream of the transfer section and upstream of the charging section in the movement direction (rotation direction) of the photosensitive drum 1.

The brush member 10 is arranged so that its longitudinal direction is approximately parallel to the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the fixed brush 11 is constructed by weaving conductive threads 11a made of nylon fibers mixed with a conductive material into a base fabric 11b made of synthetic fibers containing carbon as a conductive agent. Note that the conductive threads 11a may be made of materials other than nylon, such as rayon, acrylic, or polyester.

As shown in FIG. 2A, when the brush member 10 is in a single state, that is, when no external force is applied to bend the conductive thread 11a, the distance from the base cloth 11b to the tip of the conductive thread 11a exposed from the base cloth 11b is defined as L1. In this embodiment, L1 is 6.5 mm. The brush member 10 is arranged such that the base cloth 11b is fixed to a support member (not shown) installed at a predetermined position of the image forming apparatus 100 by a fixing means such as double-sided tape, and the tip of the conductive thread 11a penetrates into the photosensitive drum 1. In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. And, the shortest distance from the base cloth 11b of the brush member 10 fixed to the support member to the photosensitive drum 1 is defined as L2. In this embodiment, the difference between L2 and L1 is defined as the penetration amount of the brush member 10 into the photosensitive drum 1. In this embodiment, the penetration amount of the brush member 10 into the photosensitive drum 1 is 1 mm. In this embodiment, as shown in FIG. 2A, the length L3 of the brush member 10 in the circumferential direction (hereinafter referred to as the "short direction") of the photosensitive drum 1 is 5 mm when the brush member 10 is in a single state. In this embodiment, the length of the brush member 10 in the longitudinal direction is 216 mm. This allows the brush member 10 to contact the entire image forming area (area where a toner image can be formed) on the photosensitive drum 1 with respect to the rotation axis direction of the photosensitive drum 1. In this embodiment, the conductive thread 11a has a thickness of 2 denier and a density of 280 kF/inch ² (kF/inch ² is a unit of brush density and indicates the number of filaments per square inch). As described above, the brush member 10 is supported by a support member (not shown), is disposed at a fixed position relative to the photosensitive drum 1, and rubs against the surface of the photosensitive drum 1 as the photosensitive drum 1 moves.

The brush member 10 collects (recovers) any paper dust or other adhering matter that has been transferred from the recording material S onto the photosensitive drum 1 at the transfer section, reducing the amount of paper dust that moves to the charging section downstream of the brush member 10 in the direction of movement of the photosensitive drum 1, and to the developing section.

In this embodiment, the length of the brush member 10 in the circumferential direction of the photosensitive drum 1 (hereinafter, the short side direction) is set to L3 = 5 mm, but is not limited to this. For example, it may be changed as appropriate depending on the life of the image forming device or process cartridge. It goes without saying that the longer the length of the brush member 10 in the short side direction, the longer it will be able to collect paper dust.

In this embodiment, the longitudinal length of the brush member 10 is set to 216 mm, but is not limited to this. For example, it may be changed as appropriate depending on the maximum paper passing width of the image forming device.

In this embodiment, the fineness of the brush member 10 is 220T/96F (meaning 96 bundles of 220g threads per 10,000m), but it is desirable to determine this value taking into consideration the ability of paper dust to slip through. If the fineness of the brush member 10 is small, the force holding back the paper dust is weak and the paper dust can easily slip through, which can impede the charging of the photosensitive drum 1 by the charging roller 2 and cause image defects. Also, if the fineness of the brush member 10 is too large, it cannot collect toner or fine paper dust, which can cause uneven density due to uneven toner adhesion along the length of the charging roller 2, or image defects due to poor charging in the areas where paper dust has adhered.

The density of the brush member 10 in this embodiment is 280 kF/inch ² (kF/inch ² is a unit of brush density and indicates the number of filaments per square inch), but it is desirable to determine it taking into consideration the toner passing property and the paper dust collecting property. In other words, if the density of the brush member 10 is too high, the toner passing property is deteriorated and the toner is stacked, and the stacked toner is scattered and may cause problems such as dirt inside the machine. Also, if the density of the brush member 10 is too low, the ability to collect paper dust is weakened. Therefore, the thickness and density of the conductive thread 11a are preferably 1 to 6 denier and 150 to 350 kF/inch ² , respectively, from the viewpoint of the paper dust collecting property. Incidentally, the length of the brush member 10 in the short direction is preferably 3 mm or more from the viewpoint of long life. Also, a brush power source E4 (FIG. 3) is connected to the brush member 10 as a brush voltage applying means.

3. Image Output Operation In this embodiment, the image forming apparatus 100 executes an image output operation (job), which is a series of operations for forming an image on a single or multiple recording materials P, in response to a single start instruction from an external device (not shown) such as a personal computer. A job generally includes an image forming process (printing process), a pre-rotation process, a paper-interval process in the case of forming an image on multiple recording materials P, and a post-rotation process. The image forming process is a period during which the formation of an electrostatic image on the photosensitive drum 1, the development of the electrostatic image (the formation of a toner image), the transfer of the toner image, the fixing of the toner image, etc. are actually performed, and the image forming time refers to this period. More specifically, the timing of the image forming time differs depending on the positions at which the formation of the electrostatic image, the formation of the toner image, the transfer of the toner image, the fixing of the toner image, etc. are performed. Therefore, the image forming operation may be defined as the transfer of the toner image, or may be defined as the fixing of the toner image. Even if the image forming operation performed on the photosensitive drum 1 is completed and the operation of the photosensitive drum 1 is switched from the image forming operation to the non-image forming operation, the image already transferred to the recording material P is not affected, so the above definition may be used. The pre-rotation process is a period in which a preparatory operation is performed before the image forming process. The sheet-to-sheet process is a period corresponding to the interval between recording materials P when the image forming process is performed continuously on a plurality of recording materials P (continuous image formation). The post-rotation process is a period in which an arrangement operation (preparatory operation) is performed after the image forming process. The non-image forming time is a period other than the image forming time, and includes the pre-rotation process, the sheet-to-sheet process, the post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when the image forming apparatus 100 returns from a sleep state.

4. Control mode FIG. 3 is a schematic block diagram showing the control mode of the main part of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 150. The control unit 150 has a CPU 151 as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage element) 152 such as a ROM or RAM as a storage unit, an input/output unit (not shown) for controlling the transmission and reception of signals between various elements connected to the control unit 150, and the like. The RAM stores the detection results of the sensors and the arithmetic results, and the ROM stores a control program, a data table obtained in advance, and the like. In this embodiment, the memory 152 stores the number of rotations of the photosensitive drum 1, which is information on the use history of the photosensitive drum 1. The information on the use history of the photosensitive drum 1 is not limited to the above contents, and may be information that changes depending on the use of the photosensitive drum 1, such as the rotation time of the photosensitive drum 1, the number of sheets of recording material P printed, and film thickness information of the photosensitive drum 1. In addition, the control unit 150 has a measurement unit 153 for measuring the stop time for determining the conditions for performing the pre-rotation process described later.

The control unit 150 is a control means that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 executes a predetermined image formation sequence by controlling the transmission and reception of various electrical information signals and the timing of driving. Each part of the image forming apparatus 100 is connected to the control unit 150. For example, in relation to this embodiment, the control unit 150 is connected to the charging power source E1, the developing power source E2, the transfer power source E3, the brush power source E4, the drive motor 110, the exposure unit 4, and the like. In particular, in relation to this embodiment, the control unit 150 controls the ON/OFF and output values of the various power sources E1, E2, E3, and E4 to execute the extension operation of the pre-rotation process described later. In this embodiment, the normal pre-rotation process time is set to 2 seconds. The time of this pre-rotation process is set appropriately.

5. Extension of Pre-Rotation Process When the above-mentioned image forming apparatus 100 is used to perform a job in which recording material P is continuously passed, and then the apparatus is stopped for a predetermined time before the next job is performed, if a normal pre-rotation process is performed, toner contamination may occur. This is due to water vapor that adheres to the brush member 10 during the paper passing of the previous job. Specifically, the water vapor that adheres to the brush member 10 shown in FIG. 4(a) condenses over time immediately after the apparatus is stopped (FIG. 4(b)), and exists as a lump of water droplets on the surface of the photosensitive drum 1 (FIG. 4(c)). The size of the water droplets varies depending on the usage environment of the image forming apparatus 100 and the number of sheets passed in the previous job. For example, in a high-temperature and high-humidity environment, the recording material P contains a lot of moisture, so the larger the number of sheets passed in the previous job, the larger the size of the water droplets. In addition, after the predetermined time has passed, the water droplets evaporate over time due to the atmospheric temperature in the image forming apparatus. That is, immediately after the recording material P is passed and stopped, the water vapor condenses over time to form a lump of water droplets, which evaporates and disappears over time after a certain time has passed. When the brush member 10 of this embodiment is used, the largest water droplets exist on the surface of the photosensitive drum 1 30 seconds after the drive of the photosensitive drum 1 is stopped. The stop time varies depending on the length (L1), thickness, and density of the brush member 10. This is because the speed at which water droplets are formed, the speed at which the water droplets evaporate, the size of the formed water droplets, and so on vary depending on the length (L1), thickness, and density of the brush member 10.

Figure 5 shows the state around the photosensitive drum 1 when the next job is performed with a lump of water droplets on the surface of the photosensitive drum 1. When the job is started, the lump of water droplets shown in Figure 5 (a) moves in the direction of arrow R1 with the rotation of the photosensitive drum 1, and part of it adheres to the charging roller 2 at the charging section a. Furthermore, the water droplets that pass through the charging section a attract toner on the developing roller 31 at the developing section c (Figure 5 (b)). This phenomenon can cause image defects due to poor charging, and the toner attracted to the photosensitive drum 1 is transferred to the recording material P transported at the transfer section d, resulting in toner stains (Figure 5 (c)).

Therefore, in this embodiment, when performing a job in which recording material P is continuously fed, and then pausing for a predetermined time before performing the next job, an extension operation of the pre-rotation process is performed. In other words, the number of rotations of the photosensitive drum 1 in the pre-rotation process is controlled based on the pause time between the first image forming operation in which an image is formed on the recording material P and the second image forming operation performed following the first image forming operation.

The conditions and extension time for the pre-rotation process extension operation are explained below.

Figure 6 shows the extension time of the pre-rotation process in this embodiment. As shown in the figure, in embodiment 1, the conditions of the pre-rotation process are determined according to the number of sheets passed in the previous job, and the extension time of the pre-rotation process is longer as the number of sheets passed increases. In other words, the number of sheets passed increases as the number of sheets passed increases, so that the number of rotations of the photosensitive drum 1 increases. It can also be seen that the extension time of the pre-rotation process is longest when the stop time from the previous job is 30 seconds, and the extension time becomes shorter thereafter. The reason will be described later. The stop time and the number of sheets passed shown in Figure 6 are the cases where the stop time and the number of sheets passed are maximum values. In other words, when the stop time is described as 5 seconds, it indicates a case from 0 seconds to 5 seconds, and when it is described as 10 seconds, it indicates a case more than 5 seconds and less than 10 seconds. In addition, the value of the rotation time between the stop time and the stop time, and between the number of sheets passed and the number of sheets passed may be linearly interpolated. Although not shown, during the pre-rotation process, the fixing device 9 is subjected to the same fixing temperature control as in the image formation process. In this embodiment, the temperature control temperature during the pre-rotation and image formation process is 180°C. Furthermore, the fixing temperature during the pre-rotation process may be changed as appropriate relative to the fixing temperature during image formation.

FIG. 7 shows the results of toner staining when paper containing a large amount of moisture is passed through the above-mentioned Example 1 and the control when the pre-rotation process is not extended (comparative example). In FIG. 7, ◯ indicates that no image damage occurs due to toner adhesion to the surface of the photosensitive drum 1, △ indicates that toner adhesion occurs slightly on the surface of the photosensitive drum 1 but no image damage occurs, and × indicates that image damage occurs significantly. The recording medium used in the paper passing experiment is Xerox Vitality Multipurpose paper, Letter size, basis weight 75 g/m ² , which was left for 2 days in an environment of temperature 30° C./humidity 80% after being removed from the wrapping paper. The moisture content of the paper was 9.2% as measured by a moisture meter Moistrex MX-8000 manufactured by NDC Infrared Engineering. For comparison, the moisture content was measured immediately after opening and was 5.7%. As shown in the figure, the comparative example shows that the level of toner staining is worse as the number of sheets passed in the previous job increases. It is also seen that the level is worst when the stop time is 30 seconds, and the level improves thereafter. This is because water droplets form lumps when the stop time increases, but after a certain period of time, in this embodiment, when it is 30 seconds or more, the water droplets begin to evaporate. Therefore, the influence of water droplets decreases as the elapsed time increases. Therefore, the time period in which the level of toner staining is worst is around 30 seconds after the paper is passed. The reason why the level of toner staining does not change after the number of sheets passed is that while water vapor is generated by the paper passing, the water vapor evaporates due to the atmospheric temperature inside the image forming apparatus. In contrast, in Example 1, slight toner staining occurs when the number of sheets passed in the previous job is 50 sheets or more and the stop time is around 30 seconds, but does not occur otherwise. This is because the extension time of the pre-rotation process is set according to the number of sheets passed in the previous job and the stop time.

As described above, according to this embodiment, the pre-rotation process is extended for a necessary period of time depending on the number of sheets passed in the previous job and the downtime since the previous job. This makes it easier for water droplets on the surface of the photosensitive drum 1 to evaporate, and provides a stable image free of image defects such as toner stains.

In this embodiment, the example is described as being applied to a DC charging type image forming apparatus, but the invention can also be applied to an AC charging type image forming apparatus that uses an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed as the charging voltage.

In this embodiment, the development voltage has been described only in terms of a DC component, but the development voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.

In this embodiment, toner is used as the developer, which is a non-magnetic one-component developer, but a magnetic one-component developer may also be used.

In addition, in this embodiment, a "cleanerless system" configuration that does not have a cleaning means for the photosensitive drum 1 is used, but the present invention is not limited to this. For example, a "blade cleaning system" using a blade as a cleaning means on the downstream side of the brush member 10 and the upstream side of the charging roller 2 in the transport direction of the photosensitive drum 1 may be used.

In this embodiment, the extension time is variable based on the number of sheets of paper passed in the previous job, but this is not limited to this. For example, it may be variable based on the time or distance that the recording material P passes over the photosensitive drum 1.

From the above results, the present embodiment has the following configuration.
The image forming apparatus includes a rotatable photosensitive drum 1 and a charging roller 2 that charges the surface of the photosensitive drum 1 at a charging portion a. The image forming apparatus includes a developing roller 31 that supplies toner to the surface of the photosensitive drum 1 charged by the charging roller 2 to form a toner image. The image forming apparatus includes a transfer roller 5 that contacts the photosensitive drum 1 to form a transfer portion d and transfers the toner image formed on the photosensitive drum 1 at the transfer portion d to a recording material P. The image forming apparatus includes a brush member 10 that contacts the surface of the photosensitive drum 1 downstream of the transfer portion d and upstream of the charging portion a in the rotation direction of the photosensitive drum 1, and a drive motor 110 that rotates the photosensitive drum 1. The image forming apparatus includes a memory 152 that stores information about the use history of the photosensitive drum 1, and a control unit 150 that controls the drive motor 110. The image forming apparatus includes a measurement unit 153 that measures the stop time between a first image forming operation that forms an image on the recording material P and a second image forming operation that is performed after the first image forming operation.

After the stop time has elapsed between a first image forming operation for forming an image on a recording material P and a second image forming operation performed following the first image forming operation, a rotation operation for rotating the photosensitive drum 1 is controlled so as to be executable before the second image forming operation is performed. Based on information related to the usage history of the photosensitive drum 1 and the stop time, the number of rotations of the photosensitive drum 1 in the rotation operation performed before the second image forming operation is controlled. The object to be controlled is not limited to the number of rotations of the photosensitive drum 1, but may also be the rotation time of the photosensitive drum 1.

In addition, when the number of sheets of recording material P passing between the transfer unit d in the first image forming operation is a first number, the number of rotations of the photosensitive drum 1 in the rotation operation is controlled to be smaller than when the number of sheets of recording material P is a second number that is greater than the first number.

The stop time is the time from when the photosensitive drum 1 switches from a driven state in which it rotates to a stopped state in which the rotation of the photosensitive drum 1 stops after the first image forming operation to when the photosensitive drum 1 switches from the stopped state to a driven state to start the second image forming operation. The stop time in this embodiment is not limited to the above, so long as it is a time that correlates with the phenomenon of water droplets accumulating on the brush member 10. For example, it may be the time from immediately after the first image forming operation ends to immediately before the second image forming operation starts. Here, the stop time should include the time during which the photosensitive drum 1 is stopped.

In addition, the stop time is not limited to being measured by the measuring unit 153, but may be predicted based on the attenuation state of the surface potential of the photosensitive drum 1, the temperature transition of the image forming device 100, the temperature change of the fixing device 9, etc.

In this embodiment, as shown in FIG. 6, the extension time of the pre-rotation process is stored in the memory 152 as a table, but the value stored in the table may not be the extension time, but may be the total time including the pre-rotation process, or the extension ratio to the pre-rotation process time. Also, without preparing a table, a configuration may be used in which a coefficient according to the number of printed sheets of recording material P and the stop time is stored and the extension time is calculated each time.

Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements that have the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are given the same reference numerals as those of the image forming apparatus of the first embodiment, and detailed descriptions are omitted.

1. Features of the Second Embodiment The second embodiment is characterized in that the extension time of the pre-rotation process is variable depending on the usage environment of the image forming apparatus 100. The image forming apparatus 100 used in the second embodiment is provided with an environment sensor 300, and the extension time of the pre-rotation process described in the first embodiment is determined based on the environment information, which is the detection result of the environment sensor 300. The environment information includes information on the absolute moisture amount of the environment calculated by the CPU 151 based on the detection results of the temperature sensor 301 and the humidity sensor 302 of the environment sensor 300. In the second embodiment, the absolute moisture amount obtained by the environment sensor 300 is stored in the memory 152 in the control unit 150 in units of 0.1 g/m ^3. Then, when the image forming apparatus 100 receives a signal of an image output operation (job), the control unit 150 judges whether the absolute moisture amount is more or less than the threshold value of 10.5 g/m ^3. At this time, if the absolute moisture amount is more than the threshold value of 10.5 g/m ³ , the same extension of the pre-rotation process as in the first embodiment is executed. The extension time of the pre-rotation process is the same as that shown in FIG. 6 described in the first embodiment, and therefore the description will be omitted. Furthermore, if the absolute moisture amount is less than the threshold value of 10.5 g/ ^m3 , the extension of the pre-rotation process is not executed. This prevents the photosensitive drum 1 from being rotated unnecessarily in environments other than those with a large absolute moisture amount. Here, the absolute moisture amount for determining whether the extension time of the pre-rotation process is variable depending on the usage environment is not limited to this value, and may be changed as appropriate.

2. Effects of the Second Embodiment As described above, according to the second embodiment, the following control is performed based on the absolute moisture content obtained from the detection result of the environmental sensor 300. Only when the absolute moisture content is greater than 10.5 g/ ^m3 , the pre-rotation process is extended for a necessary time according to the number of sheets passed in the previous job and the downtime since the previous job. This makes it possible to execute an operation for effectively evaporating water droplets on the surface of the photosensitive drum 1 when necessary, without needlessly rotating the photosensitive drum 1 in environments other than those with a high absolute moisture content.

Based on the above results, Example 2 has the following configuration.

The image forming device 100 has an environment detection sensor 300 that detects the installation environment, and controls the rotation speed according to the installation environment. Here, the installation environment is the temperature or humidity detected by the environment detection sensor 300, and is the absolute moisture content. The absolute moisture content may be calculated from the results of detecting the temperature and humidity. The absolute moisture content may also be calculated by predicting the temperature or humidity.

In the second embodiment, the extension of the pre-rotation process is determined by dividing the environment into two environments, one with a large absolute moisture amount and the other, based on the absolute moisture amount obtained from the detection result of the environmental sensor 300, but this is not limited to the above. For example, the usage environment of the image forming device 100 may be divided into multiple environments, such as three environments, based on the absolute moisture amount, and the extension time of the pre-rotation process may be appropriately changed depending on the environment. In other words, multiple thresholds may be set. The extension time of the pre-rotation process may also be appropriately changed based on the absolute moisture amount. In other words, when the absolute moisture amount is detected to be the first absolute moisture amount, the rotation speed of the photosensitive drum 1 may be controlled to be increased compared to when a second absolute moisture amount smaller than the first absolute moisture amount is detected.

In addition, in the second embodiment, the environmental sensor 300 is used as a means for detecting the usage environment of the image forming apparatus 100, but this is not limited to this. For example, the usage environment may be determined based on detection of the electrical resistance value of the transfer roller 5 (result of the transfer ATVC control).

1. Brush Voltage Control This embodiment is characterized in that during the pre-rotation process, a brush voltage is applied to the brush member 10 by the brush power supply E4 shown in Fig. 3. Hereinafter, the control of the brush voltage during the pre-rotation process will be described.

In this embodiment, a predetermined brush voltage, which is a negative DC voltage, is applied to the brush member 10 from the control unit 150. Here, as the brush voltage application means E4, for example, a voltage in which a DC component and an AC component are superimposed may be applied. In this embodiment, the brush voltage during the image formation process is -300V. On the other hand, the surface potential of the photosensitive drum 1 after passing through the transfer unit d is about -50V. Therefore, among the transfer residual toner sent from the transfer unit d, the toner that is positively charged is primarily collected by the brush member 10 in the brush unit e due to the potential difference between the brush voltage and the surface potential of the photosensitive drum 1. On the other hand, the toner that is negatively charged is attracted to the photosensitive drum 1 side in the brush unit e and passes through the brush unit e. The toner that has passed through the brush unit e has the desired negative charge due to uniform discharge in the charging unit a, and is sent to the development unit c. Of the toner sent to the developing section c, the non-image area (non-exposed area) is transferred to the developing roller 31 due to the potential difference between the dark area potential (Vd) on the surface of the photosensitive drum 1 and the developing bias (Vdc), and is then collected by the developing device 3. As in the first embodiment, the dark area potential (Vd) in this embodiment is approximately -600V, and the developing bias (Vdc) is -300V. On the other hand, the image area (exposed area) is not transferred to the developing roller 31 due to the potential difference between the light area potential (Vl) on the surface of the photosensitive drum 1 and the developing bias (Vdc), and is sent as it is to the transfer section d as an image area with the rotation of the photosensitive drum 1, and is transferred to the recording material P. The light area potential (Vl) in this embodiment is approximately -100V, as in the first embodiment.

2. Pre-rotation process extension operation FIG. 8 shows a timing chart of the pre-rotation process in this embodiment. Timing A in the figure is the timing when the image forming apparatus 100 receives a signal of an image output operation (job) from an external device and starts the pre-rotation process. At this time, the control unit 150 determines the extension time of the pre-rotation process based on the number of sheets of paper passed in the previous job and the stop time from the previous job. Then, at the same timing A, the drive motor 110 starts to drive, and the output of the charging voltage and the brush voltage is turned ON. Furthermore, in the fixing device 9, output is started so that the fixing temperature control (180° C.) is the same as that in the image forming process. The ON timing of the charging voltage and the brush voltage may be appropriately changed depending on the start-up time of the power source, etc. The output timing of the fixing temperature control may also be appropriately changed depending on the responsiveness of the fixing device, etc.

The output value of the charging voltage is -1200V, the same as in the image formation process, so that the surface potential of the photosensitive drum 1 is uniformly the dark potential (-600V). With the surface potential of the photosensitive drum 1 maintained at the dark potential (-600V), the surface of the photosensitive drum 1 passes through the development section c and reaches the transfer section d. At this time, since no transfer voltage is applied to the transfer roller 5, the surface of the photosensitive drum 1 reaches the brush section e while still maintaining the dark potential (-600V). The output value of the brush voltage is -300V, the same as in the image formation process. As a result, the positive toner remaining on the brush member 10 is expelled onto the surface of the photosensitive drum 1 due to the potential difference between the brush voltage and the dark potential (-600V) of the photosensitive drum 1.

Here, in this embodiment, although a cleaning operation is performed in which the transfer residual toner that was primarily collected by the brush member 10 during the image formation process is expelled in the post-rotation process, a considerable amount of toner remains on the brush member 10. Therefore, after timing A, the positive polarity toner among the toner remaining on the brush member 10 is actively expelled. At this time, water vapor adheres to the toner, and the toner is expelled from the brush member 10 together with the surrounding water vapor. Figure 9 is a diagram showing the state of the toner and water vapor inside the brush member 10 at this time. From this figure, it can be seen that water vapor adheres to the toner on the brush member 10, and the water vapor is also expelled together with the toner expelled from the brush member 10. In this way, expelling the residual toner on the brush member 10 can promote the expulsion of water vapor adhered to the brush member 10.

In this embodiment, although no transfer voltage is applied at timing A, the brush voltage (-300V) is set to a value that does not lower the surface potential of the photosensitive drum 1, that is, a voltage value that has the same negative polarity as the surface potential of the photosensitive drum but a small absolute value.

Next, at timing B in FIG. 8, the output of the transfer voltage is turned ON. The output value of the transfer voltage at this time is +1000V. As a result, the surface potential of the photosensitive drum 1 after passing through the transfer section d becomes approximately -50V. Meanwhile, the output value of the brush voltage is still maintained at -300V, so this time the negative polarity toner remaining on the brush member 10 is expelled onto the surface of the photosensitive drum 1 due to the potential difference between the brush voltage and the surface potential (-50V) of the photosensitive drum 1. Similarly, the expulsion of water vapor adhering to the brush member 10 can be promoted. Here, timing B should be set so that there is enough time to expel the positive polarity toner from within the brush member 10, and in this embodiment, it is set to 500 ms after timing A.

In this way, by applying a brush voltage and creating a potential difference with the surface potential of the photosensitive drum 1, the positive and negative polarity residual toner in the brush member 10 is expelled, and the expulsion of water vapor is promoted.

Timing C in Figure 8 is the start timing of the image formation process if the pre-rotation process is not extended. If it is determined at timing A that the pre-rotation process should be extended, the extension starts at timing C, and the image formation process starts at timing D. In other words, the period from timing C to timing D in Figure 8 is the extended time of the pre-rotation process.

Figure 10 shows the extended time of the pre-rotation process in this embodiment. It can be seen from the figure that it is shorter than the extended time of the pre-rotation process in embodiment 1 (Figure 6). This is because in embodiment 3, the brush voltage actively expels water vapor along with the toner remaining on the brush member 10, promoting the evaporation of water droplets in the pre-rotation process.

3. Effects of this embodiment As described above, according to this embodiment, the brush voltage is used to expel residual toner from the brush member 10 at the same time as the start of the pre-rotation process, while the pre-rotation process is extended for a required time depending on the number of sheets passed in the previous job and the stop time since the previous job. This allows water vapor to be expelled together with the toner remaining on the brush member 10, thereby effectively evaporating water droplets on the surface of the photosensitive drum 1 and shortening the extension time of the pre-rotation process. As a result, it is possible to provide stable images in which the occurrence of image defects such as toner stains is suppressed, while also lengthening the life of the image forming apparatus 100.

Based on the above results, Example 3 has the following configuration.

It has a brush voltage application unit E4 that applies a brush voltage to the brush member 10. The brush member 10 is a conductive brush, and while the brush member 10 is rotating, the brush voltage application unit E4 is controlled so as to apply a brush voltage of the same polarity as the toner charged to the normal polarity to the brush member 10.

While the rotation operation is being performed, the brush voltage application unit E4 is controlled so that in the brush section e where the surface of the photosensitive drum 1 and the brush member 10 come into contact, the potential difference between the brush voltage applied to the brush member 10 and the surface potential of the photosensitive drum 1 increases stepwise.

The brush voltage application unit E4 is controlled so that the brush voltage applied to the brush member 10 and the surface potential of the photosensitive drum 1 have the same polarity, and the absolute value of the brush voltage is greater than the absolute value of the surface potential of the photosensitive drum 1. Alternatively, the brush voltage application unit E4 is controlled so that the brush voltage applied to the brush member 10 and the surface potential of the photosensitive drum 1 have the same polarity, and the absolute value of the brush voltage is less than the absolute value of the surface potential of the photosensitive drum 1.

The transfer roller 5 further includes a transfer voltage application unit E3 that applies a transfer voltage to the transfer roller 5. The transfer voltage application unit E3 is controlled so that the brush voltage applied to the brush member 10 and the surface potential of the photosensitive drum 1 at the transfer section d have the same polarity, and the surface potential of the photosensitive drum 1 at the transfer section d is smaller than the brush voltage applied to the brush member 10.

In this embodiment, the surface potential of the photosensitive drum 1 is controlled by varying the transfer voltage and brush voltage, but this is not limited to the above. For example, the transfer voltage and brush voltage may be varied with the photosensitive drum 1 grounded and the surface potential at ground (0 V). In addition, the potential relationship with the transfer roller 5 and brush member 10 may be controlled by applying a voltage directly to the photosensitive drum 1.

In addition, in this embodiment, the example is described as being applied to a DC charging type image forming apparatus, but the invention can also be applied to an AC charging type image forming apparatus that uses an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed as the charging voltage.

In addition, in this embodiment, the developing voltage has been described as being only a DC component, but the developing voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.
In this embodiment, the toner is used as the developer, which is a magnetic one-component developer, but a non-magnetic one-component developer may also be used.

In addition, in this embodiment, a "cleanerless system" configuration that does not have a cleaning means for the photosensitive drum 1 is used, but the present invention is not limited to this. For example, a "blade cleaning system" using a blade as a cleaning means on the downstream side of the brush member 10 and the upstream side of the charging roller 2 in the transport direction of the photosensitive drum 1 may be used.

In addition, in this embodiment, the extension time is variable based on the number of sheets of paper passed in the previous job, but this is not limited to this. For example, it may be variable based on the time or distance that the paper passes over the photosensitive drum.

In addition, in this embodiment, the recording material P, which is the transfer medium, is transported to the transfer section and transferred, but a transport belt that transports the recording material P to the transfer section may also be provided.

In addition, in this embodiment, a pre-exposure unit may be provided that exposes the surface of the photosensitive drum 1 downstream of the transfer section d and upstream of the charging section a in the rotation direction of the photosensitive drum 1. The pre-exposure unit may be provided upstream or downstream of the contact section e between the brush member 10 and the photosensitive drum 1. When the pre-exposure unit is provided upstream of the contact section e, the surface potential of the photosensitive drum 1 may be controlled by the pre-exposure unit.

REFERENCE SIGNS LIST 1 Photosensitive drum 2 Charging roller 5 Transfer roller 10 Brush member 31 Developing roller 110 Driving motor 150 Control unit 152 Memory

Claims (16)

A rotatable photosensitive drum;
a charging member for charging the surface of the photosensitive drum in a charging section;
a developing member for supplying toner onto the surface of the photosensitive drum charged by the charging member to form a toner image;
a transfer member that contacts the photosensitive drum to form a transfer section and transfers the toner image formed on the photosensitive drum to a transfer medium in the transfer section;
a brush member that contacts a surface of the photosensitive drum downstream of the transfer unit and upstream of the charging unit in a rotation direction of the photosensitive drum;
A drive unit that rotates the photosensitive drum;
A storage unit that stores information regarding a usage history of the photosensitive drum;
A control unit that controls the drive unit,
an image forming apparatus configured to recover, in the transfer section, toner remaining on the transfer medium that has not been transferred from the photosensitive drum to the transfer medium, into the developing member, the image forming apparatus being capable of performing a first image forming operation for forming an image on the transfer medium , a second image forming operation performed following the first image forming operation , and a rotation operation for rotating the photosensitive drum before the second image forming operation is performed,
The control unit controls the number of rotations of the photosensitive drum during the rotation operation based on the information and the stop time from the end of the first image forming operation to the start of the rotation operation , and when the number of transferred sheets that have passed between the transfer unit and the first image forming operation is a first number, the control unit controls the number of rotations of the photosensitive drum during the rotation operation to be less than when the number is a second number that is greater than the first number . The image forming apparatus according to claim 1, characterized in that the stop time is a time from when the photosensitive drum switches from a drive state in which the photosensitive drum rotates to a stop state in which the rotation of the photosensitive drum stops after the first image forming operation to when the photosensitive drum switches from the stop state to the drive state to start the second image forming operation. The image forming apparatus according to claim 1 or 2, characterized in that it has a measurement unit that measures the downtime between a first image forming operation that forms an image on a transfer medium and a second image forming operation that is performed following the first image forming operation. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit controls the number of rotations in the rotation operation performed before the second image forming operation according to the information and the stop time. an environment detection sensor that detects an installation environment of the image forming apparatus;
5. The image forming apparatus according to claim 1, wherein the control unit controls the number of rotations in accordance with the installation environment. The image forming device according to claim 5, characterized in that the installation environment is the temperature or humidity detected by the environment detection sensor. The image forming device according to claim 5, characterized in that the installation environment is the absolute moisture content detected by the environment detection sensor. The image forming device according to claim 7, characterized in that the control unit increases the rotation speed when the absolute moisture amount is detected to be a first absolute moisture amount, compared to when a second absolute moisture amount smaller than the first absolute moisture amount is detected. The image forming apparatus according to any one of claims 1 to 8, characterized in that the information is the number of transfer objects that have passed between the transfer unit and the transfer section during the first image forming operation. A brush voltage application unit that applies a brush voltage to the brush member,
The brush member is a conductive brush,
The image forming apparatus according to any one of claims 1 to 9, characterized in that the control unit controls the brush voltage application unit to apply to the conductive brush the brush voltage of the same polarity as the toner charged to the normal polarity while the rotation operation is being performed. The image forming apparatus according to claim 10, characterized in that the control unit controls the brush voltage application unit so that the potential difference between the brush voltage applied to the brush member and the surface potential of the photosensitive drum increases stepwise at the contact portion where the surface of the photosensitive drum and the brush member are in contact while the rotation operation is being performed. The image forming apparatus according to claim 10, characterized in that the control unit controls the brush voltage application unit so that the brush voltage applied to the brush member and the surface potential of the photosensitive drum have the same polarity, and the absolute value of the brush voltage is greater than the absolute value of the surface potential of the photosensitive drum. The image forming apparatus according to claim 10, characterized in that the control unit controls the brush voltage application unit so that the brush voltage applied to the brush member and the surface potential of the photosensitive drum have the same polarity, and the absolute value of the brush voltage is smaller than the absolute value of the surface potential of the photosensitive drum. A transfer voltage application unit that applies a transfer voltage to the transfer member,
14. The image forming apparatus according to claim 10, wherein the control unit controls the transfer voltage application unit so that the brush voltage applied to the brush member and the surface potential of the photosensitive drum in the transfer unit have the same polarity, and the surface potential of the photosensitive drum in the transfer unit is smaller than the brush voltage applied to the brush member. 15. The image forming apparatus according to claim 1, wherein the control unit controls a rotation time of the rotation operation in order to control a rotation speed of the photosensitive drum in the rotation operation. 16. The image forming apparatus according to claim 1, wherein the toner is a one-component developer.

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