JP6618365B2 - Image forming apparatus - Google Patents

Description

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

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method or an electrostatic recording method, an appropriate image can be formed on a drum-shaped or belt-shaped photosensitive member (electrophotographic photosensitive member) or an image carrier that is an electrostatic recording dielectric. A toner image is formed in the process. The toner image is directly transferred to a recording material (direct transfer method), or temporarily transferred to an intermediate transfer member and then secondarily transferred to a recording material such as paper (intermediate transfer method). In the direct transfer method, the toner image formed on the image carrier may be transferred to a recording material carried on the recording material carrier and conveyed. In general, the image carrier, the intermediate transfer member, or the recording material carrier is a rotatable rotary member.

  An intermediate transfer type image forming apparatus including a photosensitive drum and an intermediate transfer belt will be further described as an example. In such an image forming apparatus, the intermediate transfer belt is in contact with the photosensitive drum to form a primary transfer nip (primary transfer portion), and the toner image is primarily transferred from the photosensitive drum at the primary transfer nip. . The toner image primarily transferred to the intermediate transfer belt is then secondarily transferred to the recording material, and the toner image secondarily transferred to the recording material is fixed to the recording material by being heated and pressed by a fixing device. Is done.

  The peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt during the image forming process can be up to several percent in order to suppress image defects such as “missing” that occurs when a part of the toner image is not transferred. Although there is a difference in peripheral speed, they are almost the same. The peripheral speeds of the rotating members of the pair of rotating members that heat and press the recording material provided in the fixing device are also substantially the same in order to make no difference in the conveying speed of the recording material between the secondary transfer unit and the fixing unit. Yes. The peripheral speed of the photosensitive drum, the intermediate transfer belt, or the rotating member pair of the fixing device is generally referred to as “process speed”.

  Here, in order to form a good image under various conditions (print settings) such as the type of recording material, a plurality of process speeds corresponding to the print settings may be prepared. Depending on the print settings, the process speed may be changed for each print processing unit (job). In addition to the types of recording materials, the print settings include, for example, recording material size, print page designation, presence / absence of double-sided printing, presence / absence of aggregate printing, finishing processing, the number of copies to be printed, and the like.

  When the image forming apparatus executes continuous jobs having different process speeds, the sequence (specific operation timing specification) is once ended after the preceding job is ended, and then the sequence for the subsequent job is started. Is possible. However, in general, in order to suppress downtime (a period during which no image can be formed), the photosensitive drum and the intermediate transfer belt are kept in contact with each other as soon as the secondary transfer of the preceding job is completed. Switching to the job process speed is done. At this time, since the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt change with different time dependencies, a peripheral speed difference occurs between the photosensitive drum and the intermediate transfer belt during the process speed switching. To do. Further, when the photosensitive drum and the intermediate transfer belt are rubbed at the primary transfer nip, the photosensitive drum and the intermediate transfer belt may be worn and deteriorated. Here, this wear is simply referred to as “rubbing wear”.

  As a method for reducing the frictional wear, Japanese Patent Laid-Open No. 2004-228561 discloses that before starting the process speed switching, the developing roller is brought into contact with the photosensitive drum to transfer the toner to the photosensitive drum, and the toner is supplied to the primary transfer nip. A method for switching the process speed is disclosed. According to this method, when continuous jobs having different process speeds are executed, the toner in the primary transfer portion remains the lubricant even if the process speed is switched while the photosensitive drum and the intermediate transfer belt are in contact with each other. As a result, frictional wear can be suppressed.

  If the image forming apparatus has a separation mechanism for separating the intermediate transfer belt from the photosensitive drum, the process transfer is started after the intermediate transfer belt is separated from the photosensitive drum, and the contact is made again after the switching is completed. By doing so, rubbing wear can be suppressed. However, in this method, since the down time becomes long, a method of supplying the toner as described above to the primary transfer nip may be employed in some cases in addition to the case where there is no separation mechanism.

JP 2013-19946 A

  However, since the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt change with different time dependencies, the peripheral speed difference between the photosensitive drum and the intermediate transfer belt changes when the process speed is switched.

  In this regard, in the method disclosed in Patent Document 1, toner is placed on the photosensitive drum from the developing roller in a uniform amount, and the toner is supplied to the primary transfer nip. For this reason, when the process speed is switched, the frictional wear may not be sufficiently suppressed at the timing when the peripheral speed difference between the photosensitive drum and the intermediate transfer belt is relatively large. Conversely, at a timing when the difference in peripheral speed between the photosensitive drum and the intermediate transfer belt is relatively small, the toner supply amount becomes excessive, and the toner is unnecessarily consumed.

  In the case where toner is supplied to the primary transfer nip during a period in which the peripheral speed difference between the photosensitive drum and the intermediate transfer belt is changed, the friction of the photosensitive drum and the intermediate transfer belt is reduced. Similar problems may occur during stop operation and startup. The same problem may occur not only in an intermediate transfer type image forming apparatus but also in a direct transfer type image forming apparatus provided with a recording material carrier.

  Accordingly, an object of the present invention is to sufficiently slide while suppressing toner consumption by supplying toner to the nip in a configuration in which the peripheral speeds of the first and second rotating bodies are changed in a state where the nip is formed. An object of the present invention is to provide an image forming apparatus capable of suppressing abrasion.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a rotatable first rotating body that carries toner, toner supply means that supplies toner to the first rotating body, and a nip formed in contact with the first rotating body. A rotatable second rotating body configured to convey the toner transferred from the first rotating body in the nip, driving means for rotating the first and second rotating bodies, and the nip. The toner is so arranged that the toner is present in the nip in at least a part of a period in which the peripheral speed difference between the first rotating body and the second rotating body is changed by the driving means in a state where the toner is formed. Control means for controlling the supply of toner by the supply means, wherein the control means has the nip during a period in which the peripheral speed difference is the first peripheral speed difference during the period in which the peripheral speed difference is changed. Per unit time supplied to The toner amount per unit time supplied to the nip is larger than the toner amount so that the toner amount per unit time supplied during the period in which the peripheral speed difference is a second peripheral speed difference larger than the first peripheral speed difference is larger. An image forming apparatus that controls toner supply by a toner supply unit.

  According to the present invention, in the configuration in which the peripheral speeds of the first and second rotating bodies are changed in a state where the nip is formed, sufficient frictional wear is achieved while suppressing toner consumption due to supplying toner to the nip. Can be suppressed.

1 is a schematic sectional view of an image forming apparatus. 3 is a schematic block diagram illustrating a control mode of a main part of the image forming apparatus. FIG. It is a schematic diagram of a sequence when jobs having different process speeds continue. It is a graph which shows the circumferential speed and circumferential speed difference in a speed switching process. FIG. 6 is a graph showing a relationship between a necessary toner supply amount and a conventional toner supply amount. It is a flowchart of the method of calculating the pattern of the electrostatic latent image of a lubricating toner image. FIG. 6 is a graph showing time dependency of a required toner supply amount during a speed switching process. FIG. 6 is a graph showing the position dependency of the toner amount of a lubricating toner image during a speed switching process. FIG. 10 is a chart illustrating an example of an operation for supplying toner to a nip during a speed switching process. It is a chart figure of other examples of operation which supplies toner to a nip at the time of a speed change process. It is a graph for demonstrating the lubricating toner at the time of a stop operation | movement. It is a graph for demonstrating the lubricating toner at the time of starting. It is a chart of an example of the operation | movement which supplies a toner to a nip at the time of starting.

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

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 of this embodiment is a laser beam printer that employs an intermediate transfer method and a tandem method (four drum system).

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (stations) SY, SM, SC, and SK as a plurality of image forming units. These image forming portions SY, SM, SC, and SK are arranged side by side along the moving direction of an intermediate transfer belt 7 described later, and are respectively yellow (Y), magenta (M), cyan (C), and black. The image of each color of (K) is formed.

  In this embodiment, the basic configuration and operation of each of the image forming units SY, SM, SC, and SK are substantially the same except that the color of toner used in the developing process described later is different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol indicating an element for any color will be omitted, and the element will be described generally. In this embodiment, the image forming unit S includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 6 and the like which will be described later.

  The image forming unit S includes a photosensitive drum 1 that is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure by a drum motor M1 (FIG. 2) as a photosensitive member driving means. The photosensitive drum 1 is an example of a rotatable first rotating body that carries toner.

  The surface of the photosensitive drum 1 is uniformly charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-type charging member as a charging unit. During the charging process, a predetermined charging bias (charging voltage) is applied to the charging roller 2 from a charging power supply (high voltage power supply circuit) E1 (FIG. 2) as a charging bias applying means. In this embodiment, a voltage of −1200 V, for example, is applied to the charging roller 2 and the surface of the photosensitive drum 1 is charged to −700 V, for example.

  The charged surface of the photosensitive drum 1 is scanned and exposed in accordance with image information by an exposure device (scanner unit) 3 as exposure means (electrostatic image forming means). The exposure apparatus 3 includes a reflection mirror and a laser diode (light emitting element), and irradiates the photosensitive drum 1 with laser light modulated according to image information. In the present embodiment, the potential of the portion irradiated with the laser beam on the surface of the photosensitive drum 1 is, for example, −100V. Thereby, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 using toner as a developer. The developing device 4 includes a developing roller 41 as a developer carrying member that carries toner and conveys the toner to a portion (developing portion) facing the photosensitive drum 1. During the developing process, a predetermined developing bias (developing voltage) is applied to the developing roller 41 from a developing power supply (high voltage power supply circuit) E2 (FIG. 2) as a developing bias applying means. In this embodiment, a voltage of −350 V, for example, is applied to the developing sleeve 41. In this embodiment, the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) is applied to the exposed portion on the photosensitive drum 1 where the absolute value of the potential has been lowered by being exposed after being uniformly charged. ) Is charged with charged toner (reverse development). In this embodiment, the regular charging polarity, which is the charging polarity of the toner during development, is negative. In this embodiment, the developing roller 41 is brought into contact with the photosensitive drum 1 during the development process, and is appropriately separated from the photosensitive drum 1 when development is not performed.

  An intermediate transfer belt 7 composed of an endless belt as an intermediate transfer member is disposed facing the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units SY, SM, SC, and SK. The intermediate transfer belt 7 is wound around a driving roller 71, a tension roller 72, and an auxiliary roller 73 as a plurality of support members (stretching rollers), and is stretched with a predetermined tension. The intermediate transfer belt 7 is rotated (circularly moved) in the direction of the arrow R2 in the drawing by the driving roller 71 being rotationally driven by a belt motor M2 (FIG. 2) as an intermediate transfer body driving means, so that the driving force is transmitted. To do. On the inner peripheral surface side of the intermediate transfer belt 7, primary transfer rollers 5Y, 5M, which are roller-type primary transfer members serving as primary transfer means, corresponding to the photosensitive drums 1Y, 1M, 1C, 1K, 5C and 5K are arranged. The primary transfer roller 5 is urged (pressed) toward the photosensitive drum 1 via the intermediate transfer belt 7, and a primary transfer nip (primary transfer nip) that is a contact portion between the photosensitive drum 1 and the intermediate transfer belt 7. Part) N1 is formed. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8 that is a roller-type secondary transfer member as a secondary transfer unit is disposed at a position facing the driving roller 71. The secondary transfer roller 8 is urged (pressed) toward the driving roller 71 via the intermediate transfer belt 7, and a secondary transfer nip (2) that is a contact portion between the intermediate transfer belt 7 and the secondary transfer roller 8. Next transfer portion) N2 is formed. The intermediate transfer belt 7 is an example of a second rotator that contacts the first rotator to form a nip and transports toner transferred from the first rotator at the nip.

  The toner image formed on the photosensitive drum 1 as described above is transferred (primary transfer) onto the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer portion N1. At the time of the primary transfer process, the primary transfer roller 5 has a polarity opposite to the normal charging polarity of toner from a primary transfer power supply (high voltage power supply circuit) E3 (FIG. 2) as a primary transfer bias applying means. A next transfer bias (primary transfer voltage) is applied. In this embodiment, a primary transfer bias having a positive polarity of +1000 V, for example, is applied to the primary transfer roller 5. For example, during the formation of a full-color image, the primary transfer is sequentially performed so that the toner images of yellow, magenta, cyan, and black formed on the photosensitive drums 1Y, 1M, 1C, and 1K are superimposed on the intermediate transfer belt 7. Is done.

  The toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 and collected by a drum cleaning device 6 as a photosensitive member cleaning unit. The drum cleaning device 6 scrapes and collects the primary transfer residual toner from the surface of the rotating photosensitive drum 1 by a cleaning blade as a cleaning member disposed in contact with the photosensitive drum 1.

  The toner image formed on the intermediate transfer belt 7 is, for example, paper that is nipped and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 by the action of the secondary transfer roller 8 in the secondary transfer portion N2. Transfer (secondary transfer) is performed on the recording material P. During the secondary transfer process, the secondary transfer roller 8 has a secondary transfer power supply (high voltage power supply circuit) E4 (FIG. 2) serving as a secondary transfer bias applying means, which has a polarity opposite to the normal charging polarity of the toner. A next transfer bias (secondary transfer voltage) is applied. The recording material P is fed from the recording material storage unit 9 by the pickup roller, and after the leading end position is detected by the registration sensor 11, the recording material P is transported once at a position where the leading end slightly passes through the pair of conveying rollers 12 (12a, 12b). Stopped. Then, the conveyance of the recording material P is resumed so that the timing coincides with the toner image at the secondary transfer portion N2 sandwiched between the intermediate transfer belt 7 and the secondary transfer roller 8.

  The recording material P onto which the toner image has been transferred is conveyed to a fixing device 13 as a fixing unit, and is heated and pressed by a pair of fixing rollers 13a and 13b of the fixing device 13 so that the toner image is fixed (fixed) thereon. After being discharged, it is discharged (output) out of the machine.

  In this embodiment, toner remaining on the surface of the intermediate transfer belt 7 after the secondary transfer process (secondary transfer residual toner) is removed from the surface of the intermediate transfer belt 7 by electrostatic cleaning and collected. On the outer peripheral surface side of the intermediate transfer belt 7, a charging brush 74 as a toner charging unit is disposed downstream of the secondary transfer portion N2 and upstream of the most upstream primary transfer portion N1Y in the moving direction of the intermediate transfer belt 7. Yes. The charging brush 74 forms a charging nip (charging portion) CL that is a contact portion with the intermediate transfer belt 7. The charging brush 74 is connected to a cleaning power source (high voltage power circuit) E5 (FIG. 2) as a cleaning bias applying unit. When the secondary transfer residual toner enters the charging nip CL, a predetermined cleaning bias (cleaning voltage) is applied to the charging brush 74 from the cleaning power source E5. As a result, the secondary transfer residual toner is charged to a desired polarity (in this embodiment, positive polarity that is opposite to the normal charging polarity), and the primary transfer portion (for example, the most upstream primary transfer portion N1Y). In FIG. The secondary transfer residual toner transferred to the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the drum cleaning device 6 and collected. In this embodiment, the charging brush 74 is made of conductive nylon and has a width of 4 mm and a bristle length of 4 mm in the circumferential direction of the intermediate transfer belt 7. The charging brush 74 is brought into contact with the intermediate transfer belt 7 with an intrusion amount of 1 mm with the driving roller 71 as an opposing member.

2. Control Mode FIG. 2 is a schematic block diagram showing a control mode of the main part of the image forming apparatus 100 of the present embodiment. In this embodiment, the operation of each unit of the image forming apparatus 100 is controlled by a control unit 50 as a control unit provided in the apparatus main body of the image forming apparatus 100. The control unit 50 includes an arithmetic control unit (CPU), a storage unit (ROM, RAM), and the like, and the arithmetic control unit controls the operation of each unit of the image forming apparatus 100 according to programs and data stored in the storage unit. To control. In relation to the present embodiment, the control unit 50 controls various power sources E1, E2, E3, E4, E5, the exposure apparatus 3, the drum motor M1, the belt motor M2, and the like to execute a sequence described later.

  In this embodiment, the primary transfer power source E3, the secondary transfer power source E4, and the cleaning power source E5 can apply positive and negative voltages to the primary transfer roller 5, the secondary transfer roller 8, and the charging brush 74, respectively. ing. The primary transfer power supply E3, the secondary transfer power supply E4, and the cleaning power supply E5 can change the applied voltage ON / OFF and the polarity and value of the applied voltage at predetermined timings according to instructions from the control unit 50. In this embodiment, a primary transfer power source E3 is independently connected to each primary transfer roller 5 of each image forming unit S so that the applied voltage can be controlled independently.

3. The sequence (here, in particular the image forming sequence) is a specification of the operation timing of each part in order to stably execute the above-described image forming process in consideration of the characteristics of each part of the image forming apparatus 100 and the like. It is. The sequence is roughly divided into three steps: a pre-rotation step, an image forming step, and a post-rotation step. Each of these steps is performed in this order.

  The pre-rotation process is a period in which a preparatory operation is performed before the laser beam irradiation by the exposure device 3 for the image forming process. Each motor, each bias, the temperature control of the fixing device 13 is started up, and the developing roller 41 is brought into contact with the photosensitive drum 1, and control of each bias is performed.

  The image forming process is a period in which the above-described image forming process is performed. When images are continuously formed on a plurality of recording materials P, the above-described image forming process is continuously performed at a predetermined throughput. Here, in the image forming process, images are formed on a plurality of recording materials P in addition to a period in which electrostatic latent image formation, toner image development, toner image primary transfer, and secondary transfer are actually performed. In this case, a corresponding period is included between the recording material P and the recording material P.

  The post-rotation process is a period in which the organizing operation (preparation operation) is performed after the image formation on the last page (including the case where only one page is formed) is completed. In the post-rotation process, the temperature control of each motor, each bias, and the fixing device 13 is lowered, and the developing roller 41 is separated from the photosensitive drum 1.

  Here, a processing unit (print processing unit) for forming and outputting an image on a single or a plurality of recording materials P according to one start instruction is referred to as a “job”. A sequence for executing a job generally includes a pre-rotation process, an image formation process, and a post-rotation process, as described above. However, as described later, when a plurality of jobs are input to the image forming apparatus 100, at least a part of the post-rotation process of the preceding job and the pre-rotation process of the subsequent job is omitted.

  The above-described image forming process is executed in the same manner even when conditions such as the type of the recording material P, the size of the recording material P, and the environment (at least one of the temperature or humidity inside or outside the apparatus main body) are different. . However, a plurality of operation settings (print settings) with different process speeds and bias conditions are prepared so that a high-quality image can be obtained regardless of these conditions. The control unit 50 uses a plurality of operation settings in accordance with at least one of the above conditions. That is, when receiving a job request, the control unit 50 refers to the condition such as the type of the recording material P included in the job request and the environmental condition detected by the environment detection unit (not shown), The print setting suitable for is selected, and a sequence corresponding to the selected print setting is executed.

  In this embodiment, during the image forming process, the photosensitive drum 1 and the intermediate transfer belt 7 are rotationally driven at substantially the same peripheral speed so that the moving direction at the contact portion is the same direction. Here, the peripheral speed of the photosensitive drum 1 during the image forming process is referred to as “process speed”. Usually, the process speed is constant from the start to the end of the sequence.

  In addition, in order to suppress image defects such as “missing” that occurs when part of the toner image is not transferred between the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt during the image forming process. For example, a peripheral speed difference of about several percent may be provided. However, in this case as well, the peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 is generally substantially constant from the start to the end of the sequence.

4). Switching of Process Speeds FIG. 3 is a schematic diagram showing two sequences that can be mainly taken when the image forming apparatus 100 receives requests for continuous jobs having different process speeds.

  As shown in FIG. 3A, the first method is a method of once ending the sequence while executing continuous jobs having different process speeds. That is, in the sequence of the process speed of the preceding job, when the image forming process is completed, the post-rotation process is executed, and the sequence is completed once. Then, the process speed sequence of the subsequent job is started from the pre-rotation process.

  As shown in FIG. 3B, the other method is a method in which a sequence is executed without being interrupted while a continuous job having a different process speed is executed. That is, in the sequence of the process speed of the preceding job, when the image forming process is completed, a speed switching process for changing to the process speed of the subsequent job is executed. When the process speed is switched, the image forming process for the subsequent job is started.

  In the former method, the downtime is generally longer than in the latter method due to the execution of the post-rotation process of the preceding job and the pre-rotation process of the subsequent job. Therefore, it is preferable to adopt the latter method for suppressing downtime. In this embodiment, the latter method is adopted.

  In the speed switching process, in order to shorten the downtime, the operation that can be omitted when the image forming process is executed continuously among the operations performed in the post-rotation process and the pre-rotation process is not performed. It is preferable to switch the peripheral speeds of the intermediate transfer belt 7. Therefore, in the speed switching step, the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 are switched while the primary transfer nip N1 is formed by bringing the photosensitive drum 1 and the intermediate transfer belt 7 into contact with each other. Is called.

5). Next, rubbing wear that occurs when the photosensitive drum 1 and the intermediate transfer belt 7 directly rub at the primary transfer nip N1 in the speed switching step will be described. Here, one image forming unit S will be described, but the same applies to any image forming unit S.

  FIG. 4 shows the time dependency Vd (t) of the peripheral speed of the photosensitive drum 1, the time dependency Vb (t) of the peripheral speed of the intermediate transfer belt 7, and the time of the peripheral speed difference therebetween in the speed switching step. It is a graph which shows dependence Vdif (t). Vchb and Vcha in FIG. 4 indicate the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 before and after the speed switching step, respectively.

  In the speed switching step, the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 are both switched from Vchb to Vcha, but the time dependency Vd (t) of the peripheral speed of the photosensitive drum 1 and the time of the peripheral speed of the intermediate transfer belt 7. It is different from the dependency Vb (t). Therefore, in the speed switching step, a time dependency Vdif (t) of the peripheral speed difference occurs between the photosensitive drum 1 and the intermediate transfer belt 7. Vdif (t) is always generated except when Vd (t) and Vb (t) match.

  As described above, the speed switching step is performed in a state where the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other to form the primary transfer nip N1. Therefore, in a time zone (period) in which there is a peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 (herein, also referred to as “peripheral speed difference generation time zone”), the photosensitive drum 1 and the intermediate transfer belt. There is a possibility that wear (rubbing wear) and deterioration may occur due to rubbing with 7.

  In this embodiment, in the image forming process, the peripheral speed of the photosensitive drum 1 and the peripheral speed of the intermediate transfer belt 7 are substantially equal, and the peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 is substantially equal. 0 mm / s. In this embodiment, the circumferential speed difference occurrence time zone is a time zone in which a circumferential speed difference greater than 0 mm / s occurs between the photosensitive drum 1 and the intermediate transfer belt 7. In the image forming process, when a peripheral speed difference is provided between the photosensitive drum 1 and the intermediate transfer belt 7, the peripheral speed difference occurrence time zone is set between the photosensitive drum 1 and the intermediate transfer belt 7. It may be a time zone in which a peripheral speed difference different from that in the process occurs. Further, regardless of the presence or absence of the peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 during the image forming process, a frictional wear exceeding an allowable amount is generated between the photosensitive drum 1 and the intermediate transfer belt 7. A time zone in which a circumferential speed difference equal to or greater than the obtained circumferential speed difference occurs may be set as a circumferential speed difference occurrence time zone.

6). In this embodiment, in order to prevent the photosensitive drum 1 and the intermediate transfer belt 7 from rubbing directly at the primary transfer nip (also simply referred to as “nip”) N1, the speed is reduced. The toner is placed in the nip N1 during the peripheral speed difference occurrence time zone in the switching process. In this embodiment, toner can be supplied to the nip N1 from the photosensitive drum 1 or the intermediate transfer belt 7. Here, a case where toner is supplied from the intermediate transfer belt 7 to the nip N1 will be described as an example.

  First, the amount of toner supplied to the nip N1 per unit time necessary to prevent the photosensitive drum 1 and the intermediate transfer belt 7 from rubbing directly at the nip N1 (here, simply referred to as “necessary toner supply amount”). The time-dependent TN (t)) will be described.

  As the peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 (herein simply referred to as “peripheral speed difference”) increases, the photosensitive drum 1 and the intermediate transfer belt 7 rub against each other per unit time. The distance becomes longer and the toner supplied to the nip N1 is likely to be exhausted. Therefore, it is necessary to supply more toner to the nip N1 as the peripheral speed difference is larger. Therefore, in this embodiment, the time dependency TN (t) of the required toner supply amount is proportional to the peripheral speed difference. The proportionality constant of this proportional relationship can be obtained by the following method.

Table 1 shows the results of evaluating frictional wear by changing the amount of toner supplied to the nip N1. The test was conducted as follows. The photosensitive drum 1 and the intermediate transfer belt 7 were normally rotated with the peripheral speed of the photosensitive drum 1 being 100 mm / s, the peripheral speed of the intermediate transfer belt 7 being 200 mm / s, and the difference in peripheral speed being 100 mm / s. 0.01 mg / cm ² , 0.05 mg / cm ² , and toner are uniformly distributed over the entire area of the intermediate transfer belt 7 in the width direction (direction substantially perpendicular to the movement direction) and the circumferential direction (direction substantially parallel to the movement direction). It mounted with the loading amount of 0.1 mg / cm < ² >, 0.2 mg / cm < ² >, respectively. Note that the whole area in the width direction of the intermediate transfer belt 7 is the whole area where image formation is possible in which a toner image can be formed (hereinafter, the same applies to the whole area in the longitudinal direction of the photosensitive drum 1). . Then, the degree of wear on the surfaces of the photosensitive drum 1 and the intermediate transfer belt 7 was evaluated. The evaluation results are shown as “NG” when rubbing wear that may cause a problem with respect to the life required for each of the photosensitive drum 1 and the intermediate transfer belt 7 is indicated as “NG”, and when not generated as “OK”.

From Table 1, when the peripheral speed difference is 100 mm / s, it is sufficient to place a toner image having a density of 0.05 mg / cm ² or more on the intermediate transfer belt 7 that is rotationally driven at a peripheral speed of 200 mm / s. It can be seen that rubbing wear can be suppressed. Therefore, the proportionality constant can be calculated by the following equation.
(0.05 mg / cm ² ) × (200 mm / s) / (100 mm / s) = 0.1 mg / cm ²

As described above, the necessary toner supply amount TN (t) can be set to a value obtained by multiplying the time dependency Vdif (t) of the peripheral speed difference by the proportional constant 0.1 mg / cm ² as in the following equation.
TN (t) = 0.1 mg / cm ² × Vdif (t) (mg · mm / s · cm ² )

  If the value of the proportional constant is not the optimum value for other peripheral speed differences, the proportional constant is determined and applied in the same manner as described above for each arbitrary peripheral speed difference (or peripheral speed difference range). can do.

Next, the conventional problem will be further described. According to the conventional method, a toner image having a uniform density (mounting amount) is formed on the intermediate transfer belt 7 and supplied to the nip N1. FIG. 5 shows the time dependency TN (t) of the required toner supply amount in accordance with the conventional method, and the time dependency TDa (t), TDb () of the toner supply amount to the nip N1 per unit time. It is a graph which shows the relationship with t). TN (t) in FIG. 5 is for executing the speed switching step shown in FIG. Further, TDa (t) and TDb (t) in FIG. 5 are obtained when toner images having uniform densities Da and Db (Da <Db) are placed on the intermediate transfer belt 7, respectively. TDa (t) and TDb (t) are respectively expressed as toner amounts Da and Db per unit distance in the circumferential direction of the intermediate transfer belt 7 in the toner image on the intermediate transfer belt 7 as shown in the following equations. It can be calculated by multiplying the time dependence Vb1 (t) of the peripheral speed.
TDa (t) = Da × Vb1 (t)
TDb (t) = Db × Vb1 (t)

  When a toner image having a uniform density Da on the intermediate transfer belt 7 is supplied to the nip N1, TDa (t) is greater than the required toner supply amount TN (t) in the time zone from Ta to Tb in FIG. Less. Therefore, rubbing wear cannot be sufficiently suppressed, and the photosensitive drum 1 and the intermediate transfer belt 7 may be deteriorated. On the other hand, when a toner image having a uniform density Db on the intermediate transfer belt 7 is supplied to the nip N1, the required toner supply amount TN (t) is TDb (t) especially in a time zone where the peripheral speed difference is relatively small. Becomes excessive. As a result, toner is unnecessarily consumed.

  The case where a toner image is formed on the intermediate transfer belt 7 and the toner is supplied from the intermediate transfer belt 7 to the nip N1 has been described above as an example. The same problem occurs when a toner image is formed on the photosensitive drum 1 and toner is supplied from the photosensitive drum 1 to the nip N1. That is, when a toner image having a uniform density is formed on the photosensitive drum 1 or the intermediate transfer belt 7, the toner supplied to the nip N1 is excessive or insufficient to suppress frictional wear.

  Therefore, in this embodiment, as will be described in detail below, the amount of toner supplied to the nip N1 is an amount that does not become excessive by supplying the amount of toner that takes into account the change in the peripheral speed to the nip N1. The amount should be sufficient to suppress frictional wear.

7). In the present embodiment, the amount of toner supplied to the nip N1 per unit time in the peripheral speed difference occurrence time zone of the speed switching process increases as the peripheral speed difference increases. A toner image is formed on the intermediate transfer belt 7. Then, the toner of the toner image is supplied from the intermediate transfer belt 7 to the nip N1 during the peripheral speed difference occurrence time zone of the speed switching step. Here, the toner image supplied to the nip N1 in the peripheral speed difference occurrence time zone is also referred to as a “lubricated toner image”.

  With reference to FIG. 6, a method for obtaining a pattern of an electrostatic latent image necessary for forming a lubricating toner image will be described. FIG. 6 is a schematic flowchart showing a flow of processing for obtaining the pattern of the electrostatic latent image of the lubricating toner image. In the present embodiment, this process is executed by the control unit 50.

  First, in (1) to (3) of FIG. 6, the time dependency TN1 (t) of the necessary toner supply amount in the speed switching process of this embodiment is calculated. TN1 (t) is obtained in advance in the same manner as that generally described as TN (t) and the time dependency Vdif1 (t) of the peripheral speed difference in the speed switching process of the present embodiment, as described above. It is possible to calculate from the obtained proportionality constant. Further, Vdif1 (t) can be calculated from the time dependencies Vd1 (1) and Vb1 (t) of the respective peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 in the speed switching step of this embodiment.

Next, in FIG. 6 (4), the time dependency TNL1 (t) of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 is calculated. The time dependency TNL1 (t) of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 is the time dependency TN1 (t) of the necessary toner supply amount as shown in the following equation. It can be calculated by dividing by the time dependence Vb1 (t) of the peripheral speed. FIG. 7 is a graph showing Vb1 (t), TN1 (t), and TNL1 (t) during the speed switching process of the present embodiment.
TNL1 (t) = TN1 (t) / Vb1 (t)

  Next, in FIG. 6 (5), the position dependency TNL1 (x) of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 is calculated. FIG. 8 is a graph showing the calculation result of TNL1 (x). The position-dependent TNL1 (x) is obtained by converting the horizontal axis of the time-dependent TNL1 (t) into a position on the intermediate transfer belt 7. The relationship between the time used for this conversion and the position on the intermediate transfer belt 7 is calculated by integrating the time dependency Vb1 (t) of the peripheral speed of the intermediate transfer belt 7 in (1) of FIG.

  Next, in (6) of FIG. 6, the pattern of the electrostatic latent image necessary for forming the lubricating toner image is calculated. The lubricating toner image is assumed to have a toner amount distribution (density distribution) of TNL1 (x) on the intermediate transfer belt 7 in the circumferential direction of the intermediate transfer belt 7. Further, it is preferable that the toner has a uniform toner amount in the width direction of the intermediate transfer belt 7 so that the frictional wear can be suppressed throughout the width direction of the intermediate transfer belt 7. In this embodiment, the lubricating toner image is formed in the entire area of the intermediate transfer belt 7 in the width direction (longitudinal direction of the photosensitive drum 1). The pattern of the electrostatic latent image of the lubricating toner image is assumed to obtain a toner image having such a density. In this embodiment, the toner amount of the lubricating toner image is controlled by controlling the exposure by the exposure device 3 in the image forming process described above.

  As described above, the pattern of the electrostatic latent image necessary for forming the lubricating toner image can be obtained.

  Next, a lubricating toner image forming process and a process of supplying the formed lubricating toner image to the nip N1 will be described with reference to FIG. FIG. 9 is a timing chart showing the operation of each part in the formation process of the lubricating toner image and the supply process to the nip N1 when the toner of the lubricating toner image is supplied from the intermediate transfer belt 7 to the nip N1. This operation is executed under the control of the control unit 50.

  In FIG. 9, TB1 indicates a peripheral speed difference occurrence time zone. CH1 indicates the timing for starting the formation of the electrostatic latent image of the lubricating toner image. EX1 represents an electrostatic latent image of the lubricating toner image. Further, the state in which the position on the photosensitive drum 1 or the intermediate transfer belt 7 corresponding to the lubricating toner image sequentially passes through each bias applying unit is indicated by arrows sequentially from EX1.

  The controller 50 finishes the image forming process of the job at the process speed (preceding job) before the speed switching process and before the timing CH1 at which the formation of the lubricating toner image is started, as described above. The pattern of the electrostatic latent image is calculated. Then, the control unit 50 continues driving the photosensitive drum 1 and the intermediate transfer belt 7 at the timing CH1 and continues applying the developing bias and the primary transfer bias to the electrostatic latent image EX1 of the lubricating toner image. Start formation. In this embodiment, at the timing CH1, the secondary transfer process of the preceding job has not been completed yet, and the application of the secondary transfer bias and the cleaning bias is continued. The application of the developing bias is temporarily stopped after the lubricating toner image developing process is completed. The application of the secondary transfer bias and the cleaning bias is temporarily stopped after the secondary transfer process of the preceding job and the charging process of the secondary transfer residual toner are completed.

  Subsequently, the electrostatic latent image of the lubricating toner image formed on the photosensitive drum 1 is developed. Further, the lubricating toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 7, passes through the secondary transfer nip N2, and then passes through the charging nip CL. When the lubricating toner image passes through the secondary transfer nip N2 and the charging nip CL, each of the secondary transfer roller 8 and the charging brush 74 has a polarity opposite to that during the image forming process (same as the normal charging polarity of the toner). Polarity) bias is applied. Thereby, the toner of the lubricating toner image is suppressed from adhering to the secondary transfer roller 8 and the charging brush 74 due to electrostatic repulsion.

  Thereafter, the lubricating toner image on the intermediate transfer belt 7 enters the nip N1 substantially simultaneously with the start of the peripheral speed difference occurrence time zone TB1. Thus, by supplying the amount of toner corresponding to the peripheral speed difference to the nip N1 during the peripheral speed difference occurrence time zone, it is possible to sufficiently suppress the frictional wear while suppressing toner consumption. When the lubricating toner image passes through the nip N1, a bias having a polarity opposite to that in the image forming process (same polarity as the normal charging polarity of the toner) is applied to the primary transfer roller 5. As a result, the toner of the lubricating toner image is transferred to the photosensitive drum 1 and is collected by the drum cleaning device 6.

  The method for supplying the toner of the lubricating toner image from the intermediate transfer belt 7 to the nip N1 has been described above. However, the toner of the lubricating toner image can be supplied from the photosensitive drum 1 to the nip N1. That is, in this case, the lubricating toner image formed on the photosensitive drum 1 is directly supplied to the nip N1. FIG. 10 is a timing chart showing the operation of each part in the formation process of the lubricating toner image and the supply process to the nip N1 in that case. TB2, CH2, and EX2 in FIG. 10 are the same as TB1, CH1, and EX1 in FIG.

  Also in this case, the control unit 50 continues to drive the photosensitive drum 1 and the intermediate transfer belt 7 at the timing CH2 and continues to apply the developing bias and the primary transfer bias. The formation of EX2 is started. Thereafter, the electrostatic latent image of the lubricating toner image formed on the photosensitive drum 1 is developed. The lubricating toner image formed on the photosensitive drum 1 enters the nip N1 substantially simultaneously with the start of the peripheral speed difference occurrence time zone TB2. Thus, by supplying the amount of toner corresponding to the peripheral speed difference to the nip N1 during the peripheral speed difference occurrence time zone, it is possible to sufficiently suppress the frictional wear while suppressing toner consumption. When the lubricating toner image passes through the nip N1, a bias having a polarity opposite to that in the image forming process (same polarity as the normal charging polarity of the toner) is applied to the primary transfer roller 5. As a result, the toner of the lubricating toner image passes through the nip N1 and is collected by the drum cleaning device 6.

  As described above, in this embodiment, the control unit 50 determines the information on the time dependency of the peripheral speed of the photosensitive drum 1 in the speed switching process, the intermediate transfer belt 7 prior to the peripheral speed difference occurrence time zone in the speed switching process. The information on the time dependency of the peripheral speed and the information on the necessary toner supply amount for each peripheral speed difference are acquired. In the present embodiment, these pieces of information are obtained in advance and stored in the storage unit of the control unit 50. Further, prior to the peripheral speed difference occurrence time zone, the controller 50 uses the above information to determine the position and toner amount (density) of the lubricating toner image formed on the intermediate transfer belt 7 in the circumferential direction of the intermediate transfer belt 7. (Density distribution) and the electrostatic latent image pattern of the lubricating toner image. Then, the control unit 50 starts forming the electrostatic latent image of the lubricating toner image after the image forming process of the preceding job and before the speed switching process. Thereafter, the control unit 50 transfers the lubricating toner image onto the intermediate transfer belt 7 and switches the speed so that the peripheral speed difference generation time zone starts at the timing when the lubricating toner image on the intermediate transfer belt 7 enters the nip N1. Start the process. Alternatively, the control unit 50 uses the above information prior to the circumferential speed difference occurrence time zone to determine the position and toner amount (density) of the lubricating toner image formed on the photosensitive drum 1 in the circumferential direction of the photosensitive drum 1. The relationship (density distribution) and the electrostatic latent image pattern of the lubricating toner image are obtained. Then, the control unit 50 starts forming the electrostatic latent image of the lubricating toner image after the image forming process of the preceding job and before the speed switching process. Thereafter, the control unit 50 starts the speed switching process so that the peripheral speed difference generation time zone starts at the timing when the lubricating toner image formed on the photosensitive drum 1 enters the nip N1. Which side of the intermediate transfer belt 7 and the photosensitive drum 1 the toner is supplied to the nip N1 can be selected depending on the situation.

  Although one image forming unit S has been described above, in the present embodiment, formation of lubricating toner and supply to the nip N1 are performed in all four image forming units S. Typically, the patterns of the lubricating toner images formed by the four image forming units S may be substantially the same. Typically, the formation of the electrostatic latent images of the lubricating toner images in the four image forming units S may be started substantially simultaneously. In this case, when the toner of the lubricating toner image is supplied from the intermediate transfer belt 7 to the nip N1, the lubricating toner image formed in one image forming unit S generates a difference in peripheral speed in the nip N1 of another image forming unit S. You will pass before the time zone. Therefore, in this case, in the image forming portion S in which the lubricating toner image passes through the nip N1 before the peripheral speed difference occurrence time zone, the primary transfer roller 5 has the same polarity as that in the image forming step during the passage. A bias (typically the same bias as in the image forming process) may be applied.

  As described above, in this embodiment, the image forming apparatus 100 includes the control unit 50 that controls the supply of toner by the toner supply unit that supplies toner to the first rotating body 1. In the present exemplary embodiment, the toner supply unit includes the charging roller 2, the exposure device 3, and the developing device 4. This control means 50 is used in at least a part of a period during which the peripheral speed difference between the first rotating body 1 and the second rotating body 7 is changed by the driving means M1 and M2 with the nip N1 formed. Control is performed so that toner is present in the nip N1. Then, the control means 50 has a first amount higher than the toner amount per unit time supplied to the nip N1 during the period in which the peripheral speed difference is the first peripheral speed difference. Control is performed so that the period of the second circumferential speed difference that is larger than the circumferential speed difference is larger.

  In particular, in the present embodiment, the period in which the peripheral speed difference is changed is the first and second rotating bodies 1 between consecutive jobs having different peripheral speeds of the first and second rotating bodies 1 and 7. , 7 is a period in which the peripheral speed is changed. In this case, the toner supplied by the toner supply unit may be supplied to the nip N1 from the first rotating body. Alternatively, the toner supplied by the toner supply unit may be transferred from the first rotating body 1 to the second rotating body 7 and then supplied to the nip N1 from the second rotating body. When the toner is supplied from above the first rotating body, the toner distribution in the circumferential direction of the first rotating body 1 of the toner to be placed on the first rotating body 1 is obtained by the control means 50. Further, when the toner is supplied from the second rotating body 7, the toner amount distribution in the circumferential direction of the second rotating body 7 of the toner to be placed on the second rotating body 7 is obtained by the control means 50. Then, the control unit 50 controls the toner supply unit so as to supply the toner having the toner amount distribution.

  Therefore, according to the present embodiment, it is possible to sufficiently suppress the frictional wear in the peripheral speed difference occurrence time zone while suppressing toner consumption during the speed switching step.

[Example 2]
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 first embodiment. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions and configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

1. Outline of the present embodiment In the first embodiment, an example in which frictional wear during a period in which the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 are changed between consecutive jobs having different process speeds has been described. In this embodiment, the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 when the photosensitive drum 1 and the intermediate transfer belt 7 are stopped from the rotating state or when the photosensitive drum 1 and the intermediate transfer belt 7 are started from the stopped state are set. An example will be described in which the sliding wear during each changed period is suppressed.

  That is, similar to the speed switching step, the peripheral speed and the intermediate transfer of the photosensitive drum 1 are also performed at the time of stopping the rotation of the photosensitive drum 1 and the intermediate transfer belt 7 and at the time of starting (that is, at the end and start of the sequence). It changes with a time dependency different from the peripheral speed of the belt 7. Therefore, a peripheral speed difference is generated between the photosensitive drum 1 and the intermediate transfer belt 7. Accordingly, if the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other and the primary transfer nip N1 is formed to stop and start the rotation of the photosensitive drum 1 and the intermediate transfer belt 7, the process speed is changed. As with the case, frictional wear may occur. Similarly to the speed switching step, the peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 also changes when the photosensitive drum 1 and the intermediate transfer belt 7 are stopped and started.

  Therefore, in this embodiment, in order to prevent the photosensitive drum 1 and the intermediate transfer belt 7 from directly rubbing at the nip N1, the rotation of the photosensitive drum 1 and the intermediate transfer belt 7 is stopped and the rotation at the time of startup is performed. The toner is placed in the nip N1 during the speed difference generation time zone. In the same manner as in the first embodiment, the amount of toner supplied to the nip N1 is an amount that does not become excessive and an amount that can sufficiently suppress frictional wear.

  In this embodiment, during the operation of stopping the rotation of the photosensitive drum 1 and the intermediate transfer belt 7 (herein, also simply referred to as “stop operation”), the stop operation of the photosensitive drum 1 and the intermediate transfer belt 7 is completed. The toner is supplied to the nip N1 from the later timing. In this embodiment, when the rotation of the photosensitive drum 1 and the intermediate transfer belt 7 is started (herein simply referred to as “start-up”), the activation of the photosensitive drum 1 and the intermediate transfer belt 7 is started. The toner is supplied to the nip N1 from the earlier timing. The toner supplied to the nip N1 at the time of activation is placed on the photosensitive drum 1 or the intermediate transfer belt 7 in advance when the rotation of the photosensitive drum 1 and the intermediate transfer belt 7 is stopped before the activation.

  The calculation method of the time dependency of the required toner supply amount, the time dependency and position dependency of the toner amount to be placed per unit distance in the circumferential direction, and the electrostatic latent image pattern of the lubricating toner image is the same as that of the first embodiment. It is the same.

2. 2. Supply of toner to the nip at the time of stop operation and startup 2-1. During the Stop Operation First, a method for supplying the toner of the lubricating toner image to the nip N1 during the stop operation will be described. Here, one image forming unit S will be described, but in the present example, as in the first embodiment, the formation of the lubricating toner image and the supply to the nip N1 are performed in all four image forming units S.

  During the stop operation, the toner of the lubricating toner image is supplied to the nip N1 from the later of the photosensitive drum 1 and the intermediate transfer belt 7 when the stop operation is completed. This is because toner is supplied to the nip N1 over the entire circumferential speed difference occurrence time zone from the photosensitive drum 1 and the intermediate transfer belt 7 from the side where the stop operation is completed in the middle of the circumferential speed difference occurrence time zone. It is because it is not possible. In other words, this corresponds to preventing the denominator (Vb1 (t)) of TNL1 (t) = TN1 (t) / Vb1 (1) in (4) of FIG. Also during the stop operation, the electrostatic latent image pattern of the lubricating toner image is calculated according to the flow of FIG. 6 described in the first embodiment.

  FIG. 11A shows the time dependency Vd2 (t) of the peripheral speed of the photosensitive drum 1 and the time dependency Vb2 (t) of the peripheral speed of the intermediate transfer belt 7 during the stop operation of this embodiment. It is a graph which shows the time dependence Vdif2 (t) of the peripheral speed difference between. Vchb2 in FIG. 11A indicates the peripheral speed of the photosensitive drum 1 and the intermediate transfer belt 7 before the stop operation is started. In this embodiment, at the time of the stop operation, the photosensitive drum 1 and the intermediate transfer belt 7 start the stop operation almost simultaneously, and the intermediate transfer belt 7 of the photosensitive drum 1 and the intermediate transfer belt 7 completes the stop operation. Will be later. Therefore, in this embodiment, the toner of the lubricating toner image is supplied from the intermediate transfer belt 7 to the nip N1 during the stop operation.

  11B shows Vb2 (t), the time dependency TN2 (t) of the necessary toner supply amount, and the toner to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 during the stop operation of this embodiment. It is a graph which shows quantity time-dependent TNL2 (t). FIG. 11C is a graph showing the position dependency TNL2 (x) of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7.

  The timing of calculation of the electrostatic latent image pattern of the lubricating toner image during the stop operation, formation of the electrostatic latent image, and subsequent processes are the same as those shown in FIG. 9 described in the first embodiment. However, during the stop operation, the stop operation of the photosensitive drum 1 and the intermediate transfer belt 7 is executed instead of the speed switching step in FIG.

  That is, in the present embodiment, the control unit 50 acquires the following information prior to the peripheral speed difference occurrence time zone during the stop operation during the stop operation. Information on the time dependency of the peripheral speed of the photosensitive drum 1, information on the time dependency of the peripheral speed of the intermediate transfer belt 7 during the stop operation, and the stop operation completion timing of either the photosensitive drum 1 or the intermediate transfer belt 7. This is information on whether it is later and information on the required toner supply amount for each peripheral speed difference. In the present embodiment, these pieces of information are obtained in advance and stored in the storage unit of the control unit 50. Further, prior to the circumferential speed difference occurrence time zone, the control unit 50 uses the above information to determine the position of the lubricating toner image and the toner amount (density) in the circumferential direction with the later stop operation completion timing. The relationship (density distribution) and the electrostatic latent image pattern of the lubricating toner image are obtained. Then, the control unit 50 starts forming an electrostatic latent image of the lubricating toner image after the image forming process of the job before the stop operation and before the stop operation. Thereafter, the control unit 50 causes the photosensitive drum 1 and the photosensitive drum 1 and the photosensitive drum 1 so that the peripheral speed difference generation time period starts at a timing when the lubricant toner image formed on the later stop operation completion timing enters the nip N1. The stop operation of the intermediate transfer belt 7 is started.

2-2. Next, a method for supplying the toner of the lubricating toner image to the nip N1 at the time of startup will be described. Here, one image forming unit S will be described, but in the present example, as in the first embodiment, the formation of the lubricating toner image and the supply to the nip N1 are performed in all four image forming units S.

  At the time of start-up, the toner of the lubricating toner image is supplied to the nip N1 from the photosensitive drum 1 and the intermediate transfer belt 7 whose start is started first. This is because, from the photosensitive drum 1 and the intermediate transfer belt 7 that starts in the middle of the peripheral speed difference occurrence time zone, toner can be supplied to the nip N1 over the entire peripheral speed difference occurrence time zone. It is not possible. The calculation of the electrostatic latent image pattern of the lubricating toner image is also performed according to the flow of FIG.

  Further, since the lubricating toner image supplied to the nip N1 at the time of activation cannot be formed after the activation, it is formed before the photosensitive drum 1 and the intermediate transfer belt 7 are stopped when the preceding sequence is finished. However, since the type of sequence to be executed next at startup is usually indefinite, the time dependency of the peripheral speed difference between the photosensitive drum 1 and the intermediate transfer belt 7 at startup is dependent on the speed switching process and the stop operation. It cannot be specified like time. Therefore, in this embodiment, a lubricating toner image is formed so that the frictional wear can be sufficiently suppressed regardless of which of a plurality of possible sequences is executed after activation.

  FIG. 12A shows the time dependency Vd3 (t) of the peripheral speed of the photosensitive drum 1, the time dependency Vb3 (t) of the peripheral speed of the intermediate transfer belt 7 at the time of starting the present embodiment, and the interval between them. It is a graph which shows the time dependence Vdif3 (t) of the peripheral speed difference of. Vchb3 in FIG. 12A indicates the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 after the start-up is completed. In this embodiment, at the time of start-up, the timing at which the intermediate transfer belt 7 starts to start is earlier than the photosensitive drum 1 and the intermediate transfer belt 7, and the photosensitive drum 1 and the intermediate transfer belt 7 are started substantially simultaneously. Completion (peripheral speed is stabilized at a predetermined value). Therefore, in this embodiment, the toner of the lubricating toner image is supplied from the intermediate transfer belt 7 to the nip N1 at the time of activation.

FIG. 12B shows Vb3 (t), the time dependency TN3 (t) of the required toner supply amount, and the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 at the time of starting the present embodiment. It is a graph which shows time-dependent TNL3 (t). Here, FIG. 12B shows an example in which the sequence executed after activation is an image forming sequence of a job having a predetermined process speed. FIG. 12C is a graph showing the position dependency TNL31 (x), TNL32 (x), and TNL3m (x) of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 as follows. FIG. TNL 31 (x) is the case where the time dependence of the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 is Vd3 (t) and Vb3 (t) shown in FIG. On the other hand, TNL 32 (x) is a case where the time dependency of the peripheral speeds of the photosensitive drum 1 and the intermediate transfer belt 7 is different from Vd 3 (t) and Vb 3 (t) shown in FIG. . TNL3m (x) takes the larger value (maximum value) of TNL31 (x) and TNL32 (x) at all the circumferential positions of the intermediate transfer belt 7 as in the following equation. is there.
TNL3m (x) = max (TNL31 (x), TNL32 (x))

  As described above, the formation of the lubricating toner image supplied to the nip N1 at the time of start-up is performed when the preceding sequence is completed. Usually, the sequence to be executed next when the lubricating toner image is formed is indefinite. Depending on the sequence executed after activation, the position dependency of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 may be different as TNL31 (x) and TNL32 (x). In this case, as described above, a lubricating toner image having TNL3m (x) having a maximum value in the position dependency of the toner amount at any position is formed at the end of the preceding sequence. As a result, even when any sequence is executed after activation, it is possible to sufficiently suppress frictional wear while suppressing toner consumption. For example, after starting, whether the job with the fastest process speed or a job with half the process speed is executed, the frictional wear is sufficiently suppressed while suppressing toner consumption at the time of starting. be able to.

  It should be noted that even when there are three or more cases where the position dependency of the toner amount to be placed per unit distance in the circumferential direction of the intermediate transfer belt 7 is different, the same method can be used. That is, here, the case where there are two types of TNL 31 (x) and TNL 32 (x) has been described, but even in the case where more cases are assumed depending on the type of sequence executed after startup, the same as above. TNL3m (x) can be calculated.

  Next, with reference to FIG. 13, the formation process of the lubricating toner image supplied to the nip N1 at the start-up and the supply process of the formed lubricating toner image to the nip N1 will be described. FIG. 13 is a timing chart showing the operation of each part at the start-up and in the sequence preceding it when supplying the toner of the lubricating toner image from above the intermediate transfer belt 7 to the nip N1. This operation is executed under the control of the control unit 50. TB3, CH3, and EX3 in FIG. 13 are the same as TB1, CH1, and EX1 in FIG.

  The controller 50 calculates the electrostatic latent image pattern of the lubricating toner image as described above by the time CH3 when the image forming process in the preceding sequence is completed and the formation of the lubricating toner image is started. . Then, the control unit 50 continues driving the photosensitive drum 1 and the intermediate transfer belt 7 at the timing CH3, and continues to apply the developing bias and the primary transfer bias to the electrostatic latent image EX3 of the lubricating toner image. Start formation. In this embodiment, at the timing CH3, the secondary transfer process of the job has not been completed yet, and the application of the secondary transfer bias and the cleaning bias is continued. The application of the developing bias is stopped after the lubricating toner image developing process is completed. The application of the secondary transfer bias and the cleaning bias is temporarily stopped after the secondary transfer process of the job and the charging process of the secondary transfer residual toner are finished.

  Subsequently, the electrostatic latent image of the lubricating toner image formed on the photosensitive drum 1 is developed. The lubricating toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 7, passes through the secondary transfer nip N2, and then passes through the charging nip CL. Note that when the lubricating toner image passes through the secondary transfer nip N2 and the charging nip CL, as in the first embodiment, the secondary transfer roller 8 and the charging brush 74 each have a polarity (toner opposite to that in the image forming process). (A normal charging polarity of the same polarity) is applied.

  Thereafter, the control unit 50 starts the stop operation of the intermediate transfer belt 7 so that the stop operation of the intermediate transfer belt 7 is completed immediately before the lubricating toner image on the intermediate transfer belt 7 enters the nip N1. As a result, an amount of toner corresponding to the peripheral speed difference can be supplied to the nip N1 during the peripheral speed difference occurrence time zone at the start of the next sequence, and sufficient frictional wear can be achieved while suppressing toner consumption. Can be suppressed. Here, the fact that the lubricating toner image is immediately before entering the nip N1 is close to the nip N1 so that the sliding abrasion at the start can be sufficiently suppressed by starting the conveyance of the lubricating toner image at the start. Or the case where it exists in the position which contacts is included. In addition, when the lubricating toner image passes through the nip N1 at the time of activation, a bias having a reverse polarity (same polarity as the normal charging polarity of the toner) can be applied to the primary transfer roller 5 during the image forming process. As a result, the toner of the lubricating toner image is transferred to the photosensitive drum 1 and is collected by the drum cleaning device 6. Alternatively, the lubricating toner image may be collected once in the same manner as the secondary transfer residual toner after being conveyed to the cleaning nip CL.

  Thus, in the present embodiment, the control unit 50 acquires the following information prior to the end of the preceding sequence at the time of activation. Information on the time dependency of the peripheral speed of the photosensitive drum 1 and information on the time dependency of the peripheral speed of the intermediate transfer belt 7 at the time of starting the next sequence, either the photosensitive drum 1 or the intermediate transfer belt 7 starts to start. This is information on whether the timing is first and information on the necessary toner supply amount for each peripheral speed difference. In the present embodiment, these pieces of information are obtained in advance and stored in the storage unit of the control unit 50. Further, prior to the end of the preceding sequence, the control unit 50 uses the above information to determine the relationship between the position of the lubricating toner image and the toner amount (concentration) in the circumferential direction with the earlier start timing. Density distribution) and the electrostatic latent image pattern of the lubricating toner image. Then, when the preceding sequence ends, the control unit 50 starts forming an electrostatic latent image of the lubricating toner image. Thereafter, the control unit 50 stops the photosensitive drum 1 and the intermediate transfer belt 7 so that the stop operation is completed immediately before the lubricating toner image formed on the one having the start timing earlier enters the nip N1. Start operation.

  As described above, during the period in which the peripheral speed difference is changed, the first and second rotating bodies 1 and 7 when the first and second rotating bodies 1 and 7 are stopped from the rotating state are used. It may be a period in which the peripheral speed is changed. When the timing of completing the stop operation is later in the second rotating body 7 than in the first rotating body 1, the controller 50 supplies the toner to the nip N1 from the second rotating body. In this manner, the toner supply by the toner supply unit is controlled. On the other hand, when the timing for completing the stop operation is later in the first rotating body 1 than in the second rotating body 7, the control means 50 causes the toner to reach the nip N1 from above the first rotating body. The toner supply by the toner supply means is controlled so that the toner is supplied. The period during which the peripheral speed difference is changed is the peripheral speed of the first and second rotating bodies 1 and 7 when the first and second rotating bodies 1 and 7 are started from a stopped state. It may be a period in which each is changed. When the start timing of the second rotary body 7 is earlier than that of the first rotary body 1, the control unit 50 supplies the toner to the nip N1 from the second rotary body. In this manner, the toner supply by the toner supply unit is controlled. At this time, typically, when the stopping operation of the second rotating body 7 is completed, the toner supplied by the toner supplying means is present immediately before the nip N1 in the toner transport direction by the second rotating body 7. Control is performed. On the other hand, when the start timing of the first rotating body 1 is earlier than that of the second rotating body 7, the control unit 50 causes the toner to be placed on the nip N1 from above the first rotating body. The toner supply by the toner supply means is controlled so that the toner is supplied. At this time, typically, when the stop operation of the first rotating body 1 is completed, the toner supplied by the toner supplying means immediately before the nip N1 in the toner transport direction by the first rotating body 1 is present. Control is performed.

  Therefore, according to the present embodiment, the frictional wear during the peripheral speed difference occurrence time period is sufficiently suppressed while suppressing the toner consumption even during the stop operation and the start-up of the rotation of the photosensitive drum 1 and the intermediate transfer belt 7. Can be suppressed.

  Further, there may be a plurality of relationships between the position and density of the lubricating toner image to be supplied to the nip N1 at the time of startup due to a difference in the sequence after the startup. In this case, the control unit 50 obtains the relationship between the position and the density of the lubricating toner image so that the maximum density of the plurality of relationships is obtained at all the positions of the lubricating toner image, and the static toner satisfying the relationship is obtained. Find the pattern of the electrostatic latent image. As a result, in any of the plurality of relationships, it is possible to sufficiently suppress the frictional wear in the peripheral speed difference occurrence time zone at the start-up while suppressing toner consumption.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiments, the electrostatic latent image pattern of the lubricating toner image is calculated in the image forming apparatus prior to the formation of the lubricating toner. However, the present invention is not limited to this. For all or some cases where formation of the lubricating toner image is expected, the electrostatic latent image pattern of the lubricating toner image and its formation start based on each information in the same manner as described in the above embodiments Timing and the like may be obtained in advance and stored in a control unit or the like.

  Further, in the above-described embodiment, the image forming sequence including the image forming process is particularly described as an example of the sequence executed in the image forming apparatus. In many cases, the present invention is applied when the sequence is an image forming sequence as in the above-described embodiment, and works well. However, the present invention is not limited to this. For example, it is assumed that, for example, an adjustment operation including a rotation operation of the photosensitive drum and the intermediate transfer belt is periodically performed regardless of job input to the image forming apparatus. In this case, the peripheral speed difference occurrence time zone is set during the speed switching process during the sequence including the adjustment operation (adjustment sequence), during the stop operation when ending the adjustment sequence, or during startup when starting the adjustment sequence. It is assumed that it will occur. Even when one before and after the speed switching step is an image forming sequence and the other is an adjustment sequence, it is assumed that a peripheral speed difference occurrence time zone occurs during the speed switching step. The present invention can be applied to any of these cases, and the same effects as those of the above-described embodiments can be obtained.

  In the above-described embodiment, the formation of the lubricant toner image and the supply to the nip are performed in all the four image forming units, but the present invention is not limited to this. For example, the image forming apparatus may have a plurality of modes in which the number of image forming units used for image formation is different, such as a full color mode and a monochrome mode. In an image forming unit that is not used for image formation, the intermediate transfer belt may be separated from the photosensitive drum. In such an image forming apparatus, for example, a case where jobs in monochrome mode having different process speeds are continuously input to the image forming apparatus can be considered. In this case, it is conceivable that the photosensitive drum and the intermediate transfer belt are in contact with each other only in the black image forming unit, and the process speed is changed in a state where these are separated from each other. In this case, the lubricating toner image may be formed and supplied to the nip only in the black image forming unit among the plurality of image forming units included in the image forming apparatus. Similarly, the number of image forming units that form the lubricating toner image and supply it to the nip is arbitrary among the image forming units of the image forming apparatus. The present invention can be applied regardless of whether or not the image forming apparatus has a separation mechanism. However, according to the present invention, it is possible to reduce the necessity of providing a separation mechanism in the image forming apparatus, which is advantageous for simplification and miniaturization of the image forming apparatus.

  Further, even when a lubricating toner image is supplied to the nips of a plurality of image forming units, it is not limited to forming a lubricating toner image that each image forming unit supplies to its own nip. When supplying the toner of the lubricating toner image from the intermediate transfer belt to the nip, the lubricating toner image supplied to the nip of the other image forming unit is at least one of the plurality of image forming units included in the image forming apparatus. Can be formed. For example, a lubricating toner image supplied to all nips of four image forming units may be formed by one image forming unit.

  In the second embodiment, the timing at which the stop operation is completed is different between the photosensitive drum and the intermediate transfer belt during the stop operation. However, the present invention can be applied, for example, when the timing for starting the stop operation is different and the timing for completing the stop operation is substantially the same. In this case, the toner of the lubricating toner image may be supplied to the nip from either the photosensitive drum or the intermediate transfer belt during the stop operation. Further, in Example 2, the timing for starting activation differs between the photosensitive drum and the intermediate transfer belt at the time of activation. However, the present invention can also be applied to the case where, for example, the start timing is substantially the same, and the start completion timing is different. In this case, the toner of the lubricating toner image may be supplied to the nip from either the photosensitive drum or the intermediate transfer belt at the time of activation.

  Further, in the above-described embodiment, the toner is present in the nip in all the peripheral speed difference occurrence time zones. However, if allowed from the viewpoint of suppressing the frictional wear, the peripheral speed difference occurrence time zones can be set as desired. In some cases, there can be toner in the nip. That is, the toner having a toner amount distribution corresponding to the peripheral speed difference may be in the nip in at least a part of the peripheral speed difference occurrence time zone.

  In the above description, the case where the present invention is applied to an intermediate transfer type image forming apparatus has been described as an example. However, the present invention can also be applied to a direct transfer type image forming apparatus. As is well known to those skilled in the art, the direct transfer type image forming apparatus has a recording material carrier constituted by an endless belt or the like, instead of the intermediate transfer member in the above-described embodiment. In this case, the recording material carrier is an example of the second rotation. The toner image formed on the photosensitive member is transferred to the recording material carried on the recording material carrier. Even in such an image forming apparatus, the speed switching process, the stop operation, or the activation may be performed in a state where the photosensitive member and the recording material carrier are in contact with each other to form a nip. Therefore, by applying the present invention to such an image forming apparatus, the same effect as in the above-described embodiment can be obtained. Further, the first rotating body is not limited to the drum type, and may be an endless belt. The second rotating body is not limited to an endless belt, and may be a drum type. Further, the image carrier is not limited to a photoconductor, but may be an electrostatic recording dielectric.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure apparatus 4 Developing apparatus 5 Primary transfer roller 6 Drum cleaning apparatus 7 Intermediate transfer belt 8 Secondary transfer roller 50 Control part M1 Drum motor M2 Belt motor

Claims (15)

A rotatable first rotating body carrying toner;
Toner supply means for supplying toner to the first rotating body;
A rotatable second rotating body that contacts the first rotating body to form a nip, and transports toner transferred from the first rotating body in the nip;
Drive means for rotating and driving the first and second rotating bodies, respectively.
In a state where the nip is formed, toner is present in the nip during at least a part of a period during which the peripheral speed difference between the first rotating body and the second rotating body is changed by the driving unit. Control means for controlling the supply of toner by the toner supply means;
Have
In the period when the peripheral speed difference is changed, the control means is configured to make the difference in peripheral speed more than the amount of toner per unit time supplied to the nip during the period in which the peripheral speed difference is the first peripheral speed difference. Control of toner supply by the toner supply means so that the amount of toner per unit time supplied to the nip is larger during a period in which the second peripheral speed difference is greater than the first peripheral speed difference. An image forming apparatus.   The toner supply unit includes: an electrostatic image forming unit that forms an electrostatic image on the first rotating body; and a developing unit that develops the electrostatic image with toner. The control unit includes the first rotating unit. The image forming apparatus according to claim 1, wherein the toner amount per unit time supplied to the nip is controlled by controlling an electrostatic image formed on the rotating body.   The period in which the peripheral speed difference is changed is a period in which the peripheral speeds of the first and second rotating bodies are changed between consecutive jobs in which the peripheral speeds of the first and second rotating bodies are different. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The control means supplies the toner supplied by the toner supply means to the nip from the first rotating body, or supplies the toner supplied by the toner supplying means from the first rotating body to the nip. 4. The image according to claim 3, wherein the toner supply unit controls toner supply so that the toner is supplied to the nip from the second rotating body after being transferred to the second rotating body. 5. Forming equipment.   During the period in which the peripheral speed difference is changed, the peripheral speeds of the first and second rotating bodies when the first and second rotating bodies are stopped from the rotating state are respectively changed. The image forming apparatus according to claim 1, wherein the period is a period. When the first and second rotating bodies are stopped, the timing of completing the stopping operation is later in the second rotating body than in the first rotating body,
The control unit is configured to supply the toner supplied from the toner supply unit to the nip from the second rotating body after the toner is transferred from the first rotating body to the second rotating body. The image forming apparatus according to claim 5, wherein toner supply by the toner supply unit is controlled. When the first and second rotating bodies are stopped, the timing of completing the stopping operation is later in the first rotating body than in the second rotating body,
The control means controls toner supply by the toner supply means so that the toner supplied by the toner supply means is supplied to the nip from the first rotating body. The image forming apparatus according to 5.   During the period in which the peripheral speed difference is changed, the peripheral speeds of the first and second rotating bodies when the first and second rotating bodies are started from a stopped state are respectively changed. The image forming apparatus according to claim 1, wherein the period is a period. When the first and second rotating bodies are activated, the timing at which activation is started is before the second rotating body than the first rotating body,
The control unit is configured to supply the toner supplied from the toner supply unit to the nip from the second rotating body after the toner is transferred from the first rotating body to the second rotating body. The image forming apparatus according to claim 8, wherein toner supply by the toner supply unit is controlled.   The controller is configured to stop the first and second rotating bodies immediately before the nip in the toner conveyance direction by the second rotating body when the stopping operation of the second rotating body is completed. The image forming apparatus according to claim 9, wherein toner supply by the toner supply unit is controlled so that there is toner supplied by the toner supply unit. When the first and second rotating bodies are activated, the timing at which activation is started is before the first rotating body than the second rotating body,
The control means controls toner supply by the toner supply means so that the toner supplied by the toner supply means is supplied to the nip from the first rotating body. The image forming apparatus according to 8.   When the first and second rotating bodies are stopped, the control means immediately before the nip in the toner transport direction by the first rotating body when the stopping operation of the first rotating body is completed. 12. The image forming apparatus according to claim 11, wherein toner supply by the toner supply unit is controlled so that there is toner supplied by the toner supply unit.   During the image forming step, the first rotating body and the second rotating body are driven to rotate at substantially the same peripheral speed, or are driven to rotate so that the difference in peripheral speed is substantially constant. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The second rotating body is an intermediate transfer body that carries and transports the toner image primarily transferred from the first rotating body for secondary transfer to a recording material, or toner from the first rotating body. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording material carrier that carries and conveys a recording material to which an image is transferred.   The image forming apparatus according to claim 1, wherein the second rotating body is an endless belt.

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