JP2020027143A - Image forming apparatus - Google Patents

Abstract

To prevent dirt on the back side of a recording material caused by a toner on a developing member in which the electric charge is reduced during a standby time, while preventing extension of FPOT.SOLUTION: In an image forming apparatus 100, control means 50 operates contact/separation means 11 such that a second time at which an image carrier 1 and a transfer member 7 are brought into contact at the start-up comes after a first time at which a surface of the image carrier 1 facing a surface of a developing member 42 that is at a regulation position C when the rotation of the developing member 42 is started reaches a transfer position D.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic method.

  In an image forming apparatus using an electrophotographic method, the surface of an image carrier such as a rotatable photosensitive drum is charged by a charging unit at a charging position, and the surface of the image carrier after the charging process is developed at a developing position. The toner is supplied by the member to form a toner image. As the charging unit, a charging roller or the like, which is a rotatable charging member disposed in contact with the image carrier, is used. During the charging step, a charging bias (charging voltage) is applied to the charging member. Further, as the developing member, a rotatable developing roller or the like disposed in contact with or close to the image carrier is used. During the developing process, a developing bias (developing voltage) is applied to the developing roller. In addition, the regulating member is disposed in contact with the developing member, and regulates the toner carried on the developing roller, and also frictionally charges the toner.

  Then, the toner image formed on the surface of the image carrier is transferred to the transfer target at the transfer position. In a direct transfer type image forming apparatus, a toner image formed on an image carrier is directly transferred to a recording material such as paper at a transfer position. During the transfer step, a transfer bias (transfer voltage) is applied to a direct transfer member such as a transfer roller arranged in contact with the image carrier. Note that a transfer bias is applied to a direct transfer member disposed opposite to the image carrier through the recording material carrier that carries the recording material, and a toner image is formed on the recording material on the recording material carrier from the image carrier. Some configurations are transferred. In an intermediate transfer type image forming apparatus, a toner image formed on an image carrier is primarily transferred to an intermediate transfer member such as an intermediate transfer belt that can rotate at a primary transfer position. Further, the toner image primarily transferred to the intermediate transfer body is secondarily transferred to a recording material such as paper at a secondary transfer position. In the primary transfer step, a primary transfer bias (primary transfer voltage) is applied to a primary transfer member such as a primary transfer roller arranged in contact with the inner peripheral surface of the intermediate transfer body. In the secondary transfer step, a secondary transfer bias (secondary transfer voltage) is applied to a secondary transfer member such as a secondary transfer roller arranged in contact with the outer peripheral surface of the intermediate transfer member. The direct transfer member, the recording material carrier, the intermediate transfer member, the primary transfer member, the secondary transfer member, and the like are collectively referred to as a “transfer member” for transferring the toner image formed on the image carrier to the recording material. Say.

  Here, it is desirable that the application of the developing bias to the developing member is started after the surface of the image carrier at the charging position when the application of the charging bias is started reaches the developing position. If the timing is shifted, unnecessary toner moves from the developing member to the image carrier, and a belt-shaped toner image (here, also referred to as a “toner band”) extending in a direction substantially perpendicular to the moving direction of the surface of the image carrier. ) Is formed. Then, the toner band may move to the transfer member, and the transfer member may be stained with the toner, and the back stain of the recording material may occur. For example, in the case of a direct transfer type image forming apparatus, this toner band moves to a direct transfer member or a recording material carrier. In the case of an intermediate transfer type image forming apparatus, the toner band moves to the intermediate transfer member and further moves to the secondary transfer member.

  In Patent Documents 1 and 2, a transfer member is provided so as to be able to come into contact with and separate from the image carrier, and the toner band passes through the transfer position. It is proposed to maintain the separated state until the contact is made, and then to make contact after passing. Patent Document 3 proposes that the amount of toner moving from the developing member to the image carrier at the start of image formation is reduced by applying a bias having a polarity opposite to that during image formation to the developing member. I have.

JP 2005-258243 A JP-A-2000-75670 JP 2013-117591 A

  However, not only the toner band due to the above-described bias application timing shift but also a toner band due to a decrease in the charge of the toner on the developing member is generated, and as a result, the same back contamination of the recording material as described above occurs. I found that there was. The back stain on the recording material is likely to occur when the time from the last image formation to the first image formation is long.

  More specifically, of the toner on the developing member, the toner is applied to a region between a regulating position where the developing member and the regulating member are in contact with each other and a developing position where the developing member and the image carrier are opposed to each other. During standby, the toner is naturally discharged because no charge is supplied. Since the toner in the above-mentioned area on the developing member has already passed through the regulating member, it is sent to the developing position without being charged at the start of the next image formation. It is difficult to electrostatically control the toner (here, also referred to as “zero toner”) whose charge has been reduced due to charge removal. Therefore, a toner band may be formed on the image carrier even with the zero toner. Then, the toner band due to the zero toner may move to the transfer member, and the transfer member may be stained with the toner, and the back stain of the recording material may occur. For example, in the case of an image forming apparatus of a direct transfer type, a toner band of zero toner moves to a direct transfer member or a recording material carrier. In the case of an intermediate transfer type image forming apparatus, the toner band of zero toner moves to the intermediate transfer member and further moves to the secondary transfer member.

  The back contamination of the recording material due to the toner band due to the zero toner moved to the transfer member can be suppressed by forming an image after performing the transfer member cleaning step. However, since this cleaning process takes time, the first print output time (here, simply “FPOT”), which is the time from when the start of a print job is instructed to when the ejection of the first recording material is completed, is also referred to. ) Becomes longer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing back contamination of a recording material caused by toner on a developing member having a reduced charge during standby while suppressing FPOT from becoming long. It is.

  The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a rotatable image carrier, charging means for applying a charging voltage to charge the surface of the image carrier at a charging position, and applying a voltage to the charging means. An application unit for supporting the toner on the surface, applying a developing voltage, and attaching the toner to the surface of the image carrier at a developing position downstream of the charging position with respect to the rotation direction of the image carrier, rotatable; A developing member, a second applying unit for applying a voltage to the developing member, and a regulating position upstream of the developing position with respect to a rotation direction of the developing member, regulating the toner carried on the surface of the developing member. A regulating member for frictionally charging the toner and a transfer member rotatable with the image carrier at a transfer position downstream of the developing position with respect to the rotation direction of the image carrier; Body and front The image forming apparatus includes: a contacting / separating unit configured to contact / separate from a transfer member; and a control unit, and supplies toner from the rotating developing member to a surface of the rotating image carrier that has been charged by the charging unit. Forming a toner image on the surface of the image carrier, and transferring the toner image formed on the image carrier to a recording material by using the transfer member rotating while being in contact with the image carrier. In the image forming apparatus that performs image formation, the control unit may be configured to stop rotation of the image carrier, the developing member, and the transfer member, and to separate the image carrier from the transfer member. At the time of start-up from the state to the state where image formation is possible, the surface of the developing member that was in the regulation position when the rotation of the developing member was started and the image carrier first facing the developing position at the developing position. The surface first reaches the transfer position When the time is a first time and the time at which the image carrier and the transfer member are in contact with each other is a second time, the contact / separation unit is configured such that the second time is later than the first time. Is an image forming apparatus.

  According to the present invention, it is possible to suppress the back contamination of the recording material due to the toner on the developing member, the charge of which has decreased during standby, while suppressing the FPOT from becoming long.

FIG. 2 is a schematic sectional view of the image forming apparatus. FIG. 2 is a schematic sectional view of an image forming unit. FIG. 2 is a schematic block diagram illustrating a control mode of a main part of the image forming apparatus. FIG. 4 is a timing chart illustrating a sequence at the time of startup in the first embodiment. It is a flowchart figure which shows the outline of selection control of contact timing. FIG. 14 is a timing chart illustrating a sequence at the time of startup in the second embodiment. FIG. 14 is a timing chart illustrating a sequence at the time of startup in the third embodiment.

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

[Example 1]
1. FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 of the present embodiment is a tandem-type printer that employs an intermediate transfer method and can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes, as a plurality of image forming units, four image forming units Sy, Sm, Sc, which form yellow (y), magenta (m), cyan (c), and black (k) images, respectively. Sk. Elements having the same or corresponding functions or configurations in each of the image forming units Sy, Sm, Sc, and Sk are omitted from the suffixes y, m, c, and k indicating that they are elements for any color. Then, there are times when it is explained comprehensively. In this embodiment, the image forming unit S includes a photosensitive drum 1, a charging roller 2, an exposing device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 6, and the like, which will be described later. FIG. 2 is a schematic sectional view showing one image forming unit S as a representative.

  The image forming section S has a photosensitive drum 1 that is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image carrier. The photosensitive drum 1 is driven to rotate in an arrow R1 direction in the figure. The surface of the rotating photosensitive drum 1 is charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging roller 2 which is a roller-shaped charging member as charging means. The charging roller 2 is arranged in contact with the surface of the photosensitive drum 1, and rotates following the rotation of the photosensitive drum 1. During the charging process, a predetermined charging bias (charging voltage) is applied to the charging roller 2 by the charging power source E1. In this embodiment, the predetermined charging bias during image formation is a DC voltage of -1000V. In the present embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark potential (charge potential) of -500 V by applying the predetermined charging bias to the charging roller 2. The charging roller 2 charges the surface of the photosensitive drum 1 at a charging position (charging portion) A in the rotation direction (the moving direction of the surface) of the photosensitive drum 1. The charging roller 2 has a small gap between the charging roller 2 and the photosensitive drum 1 formed on the upstream and downstream sides of the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. The surface of the photosensitive drum 1 is charged by the action of discharge in at least one of the above. However, for the purpose of understanding the present invention, the contact portion between the charging roller 2 and the photosensitive drum 1 may be simulated as the charging position A.

  The surface of the charged photosensitive drum 1 is scanned and exposed according to image information by an exposure device (laser scanner) 3 as an exposure unit, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. . The exposure device 3 irradiates the surface of the photosensitive drum 1 with light at an exposure position (exposure unit) F in the rotation direction of the photosensitive drum 1. The exposure device 3 may be configured as one unit that exposes the photosensitive drum 1 for each color.

  The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying a toner as a developer by a developing device 4 as a developing unit, and a toner image is formed on the photosensitive drum 1. The developing device 4 includes a developing container 41 containing toner, a developing roller 42 as a rotatable developing member (developer carrying member) supported by the developing container 41, and a regulating member as a regulating member supported by the developing container 41. A developing blade 43. The developing roller 42 is driven to rotate in the direction of arrow R2 in the figure. The developing roller 42 supplies toner to the surface of the photosensitive drum 1 at a developing position (developing unit) B in the rotation direction of the photosensitive drum 1. In this embodiment, the developing roller 42 is arranged in contact with the surface of the photosensitive drum 1. In this embodiment, the contact position between the photosensitive drum 1 and the developing roller 42 in the rotating direction of the photosensitive drum 1 (or the contact position between the developing roller 42 and the photosensitive drum 1 in the rotating direction of the developing roller 42) is the developing position. B. Further, the developing blade 43 regulates the toner carried on the surface of the developing roller 42 (forms a thin layer of toner) at a regulating position (regulating portion) C in the rotation direction (the direction of movement of the surface) of the developing roller 42. At the same time, the toner is frictionally charged. In this embodiment, the developing blade 43 is arranged in contact with the surface of the developing roller 42. In this embodiment, the contact position between the developing roller 42 and the developing blade 43 in the rotation direction of the developing roller 42 is the regulation position (friction charging position) C. Note that a predetermined bias may be applied to the developing blade 43. The toner contained in the developing container 41 is carried on the surface of the developing roller 42. The toner carried on the surface of the developing roller 42 is sent to the regulation position C as the developing roller 42 rotates. The toner sent to the regulation position C is frictionally charged by the developing blade 43 and is applied to the surface of the developing roller 42 as a toner layer having a uniform thickness. The toner layer formed on the developing roller 42 at the regulation position C is sent to the developing position B as the developing roller 42 rotates. Then, at the developing position B, toner is supplied from above the developing roller 42 onto the photosensitive drum 1 according to the electrostatic image on the photosensitive drum 1. In this embodiment, the developing device 4 uses a non-magnetic one-component developer (non-magnetic toner) as a developer. However, the developing device 4 may be a device using a magnetic one-component developer (magnetic toner) or a two-component developer including a non-magnetic toner and a magnetic carrier. Further, in the present embodiment, the charged portion of the photosensitive drum 1 is charged to the exposed portion (image portion) on the photosensitive drum 1 where the absolute value of the potential is reduced by being exposed according to the image information after being uniformly charged. A toner charged to the same polarity as the polarity (negative in this embodiment) adheres. In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during the developing process, is negative. During the developing process, a predetermined developing bias (developing voltage) is applied to the developing roller 42 by the developing power source E2. In this embodiment, the predetermined developing bias during image formation is a DC voltage of -300V. Note that an AC voltage may be superimposed on the developing bias.

  An intermediate transfer belt 7 composed of an endless belt as an intermediate transfer member is arranged to face each photosensitive drum 1. The intermediate transfer belt 7 is an example of a transfer member capable of abutting on the image carrier for transferring a toner image formed on the image carrier onto a recording material. The intermediate transfer belt 7 is stretched over a plurality of stretching rollers (supporting rollers) and stretched with a predetermined tension. The intermediate transfer belt 7 is driven to rotate in a direction indicated by an arrow R3 in the figure by a driving roller that is one of a plurality of stretching rollers. On the inner peripheral surface side of the intermediate transfer belt 7, a primary transfer roller 5, which is a roller-shaped primary transfer member as a primary transfer unit, is arranged corresponding to each photosensitive drum 1. The primary transfer roller 5 is configured to be pressed toward the photosensitive drum 1 via the intermediate transfer belt 7 so that the photosensitive drum 1 can be brought into contact with the intermediate transfer belt 7. As described above, the toner image formed on the photosensitive drum 1 is rotated at a primary transfer position (primary transfer portion) D in the rotation direction of the photosensitive drum 1 while being in contact with the surface of the photosensitive drum 1. The primary transfer is performed on the transfer belt 7. At this time, the intermediate transfer belt 7 is pressed from the inner peripheral side by the primary transfer roller 5 and is pressed against the surface of the photosensitive drum 1. In this embodiment, the position at which the photosensitive drum 1 and the intermediate transfer belt 7 can come into contact with each other in the rotation direction of the photosensitive drum 1 is the primary transfer position D. At the time of the primary transfer step, a primary transfer bias (primary transfer voltage), which is a DC voltage having a polarity opposite to the normal charge polarity of the toner (positive in this embodiment), is applied to the primary transfer roller 5 by the primary transfer power supply E3. Applied. For example, when a full-color image is formed, the toner images of each color of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially primary-transferred so as to be superimposed on the intermediate transfer belt 7. Toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 7 in the primary transfer process (primary transfer residual toner) is removed from the photosensitive drum 1 and recovered by the drum cleaning device 6 as a photosensitive member cleaning unit. You. The drum cleaning device 6 uses the cleaning blade 61 to scrape off the primary transfer residual toner from the surface of the rotating photosensitive drum 1, and stores it in the cleaning container 62. 1 and 2 show a state in which the intermediate transfer belt 7 is in contact with the photosensitive drum 1. However, as described later, in this embodiment, the intermediate transfer belt 7 can be separated from each photosensitive drum 1.

  On the outer peripheral surface side of the intermediate transfer belt 7, a roller-shaped secondary transfer member as a secondary transfer means is provided at a position facing a secondary transfer opposing roller which is one of a plurality of stretching rollers. The next transfer roller 8 is provided. The secondary transfer roller 8 is pressed toward the secondary transfer opposing roller via the intermediate transfer belt 7, and a secondary transfer position (secondary transfer portion) G where the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact with each other. To form At the secondary transfer position G, the toner image formed on the intermediate transfer belt 7 as described above is a recording material such as paper (paper) that is conveyed while being sandwiched between the intermediate transfer belt 7 and the secondary transfer roller 8. The secondary transfer is performed on P. During the secondary transfer step, the secondary transfer roller 8 is supplied with a secondary transfer power supply E4 to apply a secondary transfer bias (secondary transfer voltage) having a polarity opposite to the normal charge polarity of the toner (positive in this embodiment). Is applied. The recording material P is conveyed on a conveyance path by a feeding device at a timing synchronized with the toner image on the intermediate transfer belt 7 and supplied to the secondary transfer position G. Toner remaining on the intermediate transfer belt 7 without being transferred to the recording material P in the secondary transfer process (secondary transfer residual toner) is removed from the intermediate transfer belt 7 by a belt cleaning device 9 as an intermediate transfer body cleaning unit. Collected. The belt cleaning device 9 uses the cleaning blade 91 to scrape off the secondary transfer residual toner from the surface of the rotating intermediate transfer belt 7 and store it in the cleaning container 92.

  The recording material P to which the toner image has been transferred is conveyed to a fixing device 10 as a fixing unit. The fixing device 10 heats and pressurizes the recording material P carrying the unfixed toner image to fix (melt and fix) the toner image on the recording material P. The recording material P on which the toner image is fixed is discharged (output) outside the apparatus main body of the image forming apparatus 100.

  The image forming apparatus 100 according to the present exemplary embodiment has a contact / separation mechanism 11 as a contact / separation unit for bringing each photosensitive drum 1 and the intermediate transfer belt 7 into and out of contact. In the present embodiment, the contact / separation mechanism 11 is provided independently for each image forming unit S. The contact / separation mechanism 11 switches between a state in which the primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 7 and a state in which the primary transfer roller 5 is separated from the photosensitive drum 1. Thereby, the contact / separation mechanism 11 switches the state of the intermediate transfer belt 7 between the state in which the intermediate transfer belt 7 contacts (contacts) the photosensitive drum 1 and the state in which the intermediate transfer belt 7 is separated from the photosensitive drum 1. The contact / separation mechanism 11 has a support member 11A that rotatably supports the primary transfer roller 5 and movably supports the primary transfer roller 5 in a direction toward and away from the photosensitive drum 1. Further, the contact / separation mechanism 11 has a pressure spring 11B as an urging member as an urging means for urging the primary transfer roller 5 toward the photosensitive drum 1 via the support member 11A. Further, the contact / separation mechanism 11 has a cam 11C as a switching member as switching means for engaging with the support member 11A. The contact / separation mechanism 11 moves the primary transfer roller 5 in a direction away from the photosensitive drum 1 by rotating the cam 11C and moving the support member 11A against the urging force of the pressure spring 11B, thereby moving the intermediate transfer belt. 7 is separated from the photosensitive drum 1. The contact / separation mechanism 11 allows the primary transfer roller 5 to move toward the photosensitive drum 1 by allowing the cam 11C to rotate and the support member 11A to move by the urging force of the pressure spring 11B. The transfer belt 7 is brought into contact with the photosensitive drum 1.

  In the present embodiment, the image forming apparatus 100 is in a state in which all the photosensitive drums 1 and the intermediate transfer belt 7 are separated during standby (a state in which the start of a print job is instructed). Is done. When the start of the print job is instructed, when the image forming apparatus 100 is started, the intermediate transfer belt 7 is brought into contact with the photosensitive drum 1 as described later in detail.

  In this embodiment, the outer diameter of the photosensitive drum 1 is 24 mm, and the outer diameter of the developing roller 42 is 12 mm. In a cross section substantially orthogonal to the rotation axis direction of the photosensitive drum 1, the angle formed by the charging position A and the developing position B in the rotation direction of the photosensitive drum 1 with respect to the rotation center of the photosensitive drum 1 is 60 °. In the definition of this angle, the charging position A and the developing position B are each represented by the center in the rotation direction of the photosensitive drum 1. Further, in a cross section substantially orthogonal to the rotation axis direction of the photosensitive drum 1, the angle formed by the developing position B and the primary transfer position D with respect to the rotation center of the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is 120 °. In the definition of this angle, the developing position B and the primary transfer position D are each represented by the center in the rotation direction of the photosensitive drum 1. Further, in a cross section substantially orthogonal to the rotation axis direction of the photosensitive drum 1, the angle formed by the developing position B and the regulating position C in the rotation direction of the developing roller 42 with respect to the rotation center of the developing roller 42 is 215 °. In the definition of this angle, the developing position B and the regulating position C are each represented by the center in the rotation direction of the developing roller 42.

  In this embodiment, the moving speed (peripheral speed) of the surface of the photosensitive drum 1, the developing roller 42, and the intermediate transfer belt 7 is 100 mm / sec. In this embodiment, the photosensitive drum 1, the developing roller 42, and the intermediate transfer belt 7 are rotationally driven by transmitting a driving force from a driving motor 12 as a common driving unit. In the present embodiment, the rotation of the photosensitive drum 1, the developing roller 42, and the intermediate transfer belt 7 is started in synchronization, and the rotation is stopped in synchronization. Further, in this embodiment, at the time of activation, the drive motor 12 is driven for 200 msec from the start of driving until the drive speed is stabilized at a predetermined drive speed during image formation (until it converges to a predetermined rotation speed). is necessary.

  Further, in this embodiment, it takes 40 msec from the state where the charging bias is OFF to the time when the charging bias rises to a predetermined charging bias during image formation (-1000 V in this embodiment). In the present embodiment, it takes 40 msec from the state where the developing bias is OFF to the time when the developing bias rises to a predetermined developing bias during image formation (−300 V in the present embodiment).

  In this embodiment, the time required for the contact / separation mechanism 11 to switch from a state in which the photosensitive drum 1 and the intermediate transfer belt 7 are separated to a state in which the photosensitive drum 1 is in contact (contact state) is 200 msec.

2. Control Mode FIG. 3 is a schematic block diagram illustrating a control mode of a main part of the image forming apparatus 100 according to the present embodiment. The control unit 50 as a control unit includes a CPU 51 as an arithmetic control unit, which is a central element for performing arithmetic processing, and a memory (storage medium) 52 such as a RAM and a ROM as storage units. The RAM, which is a rewritable memory, stores information input to the control unit 50, detected information, calculation results, and the like, and the ROM stores a control program, a previously obtained data table, and the like. The CPU 51 and the memory 52 can transfer and read data from each other.

  An external device 200 such as a personal computer is connected to the control unit 50. An operation unit (operation panel) 80 provided in the image forming apparatus 100 is connected to the control unit 50. The operation unit 30 includes a display unit that displays various information to an operator such as a user or a service person under the control of the control unit 50, and an input unit that allows the operator to input various settings related to image formation to the control unit 50. And is configured. The control unit 50 is connected to a charging power source E1, an exposure device 3, a developing power source E2, a primary transfer power source E3, a secondary transfer power source E4, a contact / separation mechanism 11, a drive motor 12, and the like. The control unit 50 controls each unit of the image forming apparatus 100 based on an image forming signal (image data, control command) from the external device 200 to execute an image forming operation.

  Here, the image forming apparatus 100 executes a print job (print operation), which is a series of operations for forming and outputting an image on one or a plurality of recording materials P, started by one start instruction. A print job generally has an image forming step, a pre-rotation step, a sheet interval step for forming images on a plurality of recording materials P, and a post-rotation step. The image forming process is a period during which an electrostatic image of an image actually formed and output on the recording material P, a toner image, primary transfer, secondary transfer, and fixing of the toner image are performed. The term “image forming period” refers to this period. More specifically, the timing of image formation differs at the positions where the respective steps of forming an electrostatic image, forming a toner image, performing primary transfer, secondary transfer, and fixing of a toner image are performed. The pre-rotation step is a period during which a preparatory operation before the image forming step is performed from the input of the start instruction to the start of actual image formation. The inter-sheet process is a period corresponding to the interval between the recording materials P when performing image formation on a plurality of recording materials P continuously (continuous image formation). The post-rotation step is a period during which the sorting operation (preparation operation) after the image forming step is performed. The non-image forming period (non-image forming period) is a period other than the image forming period, and includes the above-described pre-rotation step, sheet interval step, post-rotation step, and further from the time of turning on the power of the image forming apparatus 100 or the sleep state. And a pre-multi-rotation step, which is a preparatory operation at the time of return of the operation.

3. Overview of Contact Timing of Intermediate Transfer Belt in the Present Embodiment Next, a description will be given of a timing of bringing the photosensitive drum 1 into contact with the intermediate transfer belt 7 when the image forming apparatus 100 is started in the present embodiment.

  Here, the activation of the image forming apparatus 100 means that the rotation of the photosensitive drum 1, the developing roller 42, and the intermediate transfer belt is stopped, and the image is transferred from a state in which the photosensitive drum 1 and the intermediate transfer belt 7 are separated from each other. It means starting up to a state where formation is possible. Also, here, the timing at which the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other at the time of activation will be described focusing on one image forming unit S as a representative. Timing may be used. The times at which the photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other among the plurality of image forming units S may be different. For example, the photosensitive drum 1 of each image forming unit S and the intermediate transfer belt 7 are sequentially contacted from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 7 in accordance with the image forming operation in each image forming unit S. It may be going to go. Further, for example, in a configuration in which an image can be formed in a mode in which an image is formed by all of the plurality of image forming units S and a mode in which an image is formed by only a part of the image forming units S, only the image forming unit S to be used is used. The photosensitive drum 1 and the intermediate transfer belt 7 may be brought into contact with each other.

  In the present embodiment, at the time of start-up, the intermediate transfer belt 7 is applied to the photosensitive drum 1 at the timing when the toner band of zero toner passes through the primary transfer position (here, also simply referred to as “transfer position”) D. Make contact.

4. Operation Timing of Each Unit FIG. 4 is a timing chart showing the operation timing of each unit of the image forming apparatus 100 at the time of startup in this embodiment (only the parts necessary for the description of this embodiment are shown. ). In this embodiment, the control unit 50 causes each unit of the image forming apparatus 100 to perform a sequence operation according to the timing chart.

  When the control unit 50 receives the print job and starts the print job and the temperature of the fixing device 10 reaches a predetermined temperature, the drive of the drive motor 12 is started and the application of the charging bias is started (t1). . The charging bias rises to a predetermined charging bias during image formation after 40 msec. Due to the rotation of the photosensitive drum 1, the surface of the photosensitive drum 1 at the charging position A when the rotation of the photosensitive drum 1 is started reaches the developing position B after 225 msec (t2). At time t2, application of the developing bias is started. In this embodiment, similarly to the charging bias, the developing bias rises to a predetermined developing bias during image formation after 40 msec. Therefore, in the present embodiment, both the charging bias and the developing bias are applied to the surface of the photosensitive drum 1 that was at the charging position A when the rotation of the photosensitive drum 1 was started. The surface of the photosensitive drum 1 at the charging position A when the rotation of the photosensitive drum 1 is started reaches the transfer position D 251 msec after the time t2 (t3). The surface of the photosensitive drum 1 at the charging position A when the predetermined charging bias (charging bias rising to the predetermined potential) during the image formation starts to reach the transfer position D after 40 msec from the time t3. (T4). Similarly, the surface of the photosensitive drum 1 that was at the developing position B when the predetermined developing bias (the developing bias that has risen to the predetermined potential) during the image formation began to be moved to the transfer position D 40 msec after the time t3. Is reached (t4).

  On the other hand, when the rotation of the photosensitive drum 1 is started (that is, when the rotation of the developing roller 42 is started), the surface of the developing roller 42 at the regulation position C (more specifically, the toner thereon) is The rotation of the developing roller 42 reaches the developing position B after 325 msec (t5). In addition, the photosensitive drum 1 facing (in this embodiment, in contact with) the surface of the developing roller 42 (more specifically, the toner thereon) at the regulation position C when the rotation of the photosensitive drum 1 is started at the developing position B Reaches the transfer position D after 251 msec from the time t5 (t6).

  Therefore, the period during which the zero toner may move to the area from the developing position B to the transfer position D on the photosensitive drum 1 is the period (t1 to t6) indicated as “zero toner band occurrence” in FIG. When the intermediate transfer belt 7 is brought into contact with the photosensitive drum 1 in a state where there is a toner band of zero toner on the surface of the photosensitive drum 1, the zero toner moves to the intermediate transfer belt 7 and further moves to the secondary transfer roller 8. Therefore, there is a possibility that the back stain of the recording material P occurs.

  Therefore, in the present embodiment, the timing for bringing the intermediate transfer belt 7 into contact with the photosensitive drum 1 at the time of startup is set as follows. Here, when the rotation of the photosensitive drum 1 is started, the surface of the developing roller 42 at the regulation position C and the surface of the photosensitive drum 1 that first faces the developing position B at the developing position B first reach the transfer position D. 1 (time t6 in FIG. 4). The time at which the photosensitive drum 1 contacts the intermediate transfer belt 7 is referred to as a second time (time t7 in FIG. 4). At this time, in the present embodiment, the contact / separation mechanism 11 is operated such that the second time t7 is after the first time t6. Specifically, the primary transfer roller by the contact / separation mechanism 11 is moved back from the second time t7 at which the photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other by 200 msec, which is the time required for switching the contact / separation state. The contact operation of No. 5 with the photosensitive drum 1 is started (t8). Typically, the contact / separation mechanism 11 is operated such that the second time t7 is substantially the same as the first time t6. However, the second time t7 is a sufficiently short time after the first time t6, for example, a time after the first time t6 that is less than or equal to a time required for the photosensitive drum 1 to make one rotation, preferably, The time may be set to be about 50 msec or less from the first time t6.

  The image forming apparatus 100 according to the present embodiment is configured such that the time t2 is before the time t5. Time t2 is a time at which the surface of the photosensitive drum 1 at the charging position A when the rotation of the photosensitive drum 1 is started first reaches the developing position B. At time t5, the time when the surface of the developing roller 42 at the regulation position C first reaches the developing position B when the rotation of the photosensitive drum 1 is started (that is, when the rotation of the developing roller 42 is started). It is. This configuration in which the time relationship is reversed is not desirable because the toner moves to the surface of the photosensitive drum 1 where the potential is not determined without passing through the charging process.

  As described above, the image forming apparatus 100 of the present embodiment includes the charging unit 2 that applies a charging voltage to charge the surface of the image carrier 1 at the charging position A. Further, the image forming apparatus 100 carries the toner on the surface, and when a developing voltage is applied, the toner is applied to the surface of the image carrier 1 at a developing position B downstream of the charging position A in the rotation direction of the image carrier 1. It has a rotatable developing member 42 to attach. Further, the image forming apparatus 100 regulates the regulating member 43 that regulates the toner carried on the surface of the developing member 42 and frictionally charges the toner at the regulating position C upstream of the developing position B in the rotation direction of the developing member 42. Have. Further, the image forming apparatus 100 includes a transfer member 7 that can be brought into contact with the image carrier 1 at a transfer position D downstream of the developing position B in the rotation direction of the image carrier 1 and is rotatable. Further, the image forming apparatus 100 has a contact / separation unit 11 for bringing the image carrier 1 and the transfer member 7 into and out of contact with each other. Further, the image forming apparatus 100 includes a control unit 50. The image forming apparatus 100 forms an image as follows. That is, toner is supplied from the rotating developing member 42 to the surface of the rotating image carrier 2 that has been charged by the charging means 2 and a toner image is formed on the surface of the image carrier 1. Further, the toner image formed on the image carrier 1 is transferred onto the recording material P by using the rotating transfer member 7 in a state of being in contact with the image carrier 1.

  In this embodiment, the control unit 50 controls the state in which the rotation of the image carrier 1, the developing member 42, and the transfer member 7 is stopped, and the image carrier 1 and the transfer member 7 are separated from each other. At the time of activation to a state where image formation is possible, the contact / separation unit 11 is operated as follows. Here, at the time of activation, the surface of the image carrier 1 that first faces the surface of the developing member 42 that was at the regulation position C when the rotation of the developing member 42 was started at the developing position B is first transferred to the transfer position D. Is the first time. At the time of activation, the time at which the image carrier 1 and the transfer member 7 contact each other is defined as a second time. At this time, the control unit 50 operates the contact / separation unit 11 so that the second time is after the first time. In the present embodiment, when the image forming apparatus 100 is activated, the surface of the image carrier 1 that was at the charging position A when a predetermined charging voltage during image formation started to be applied to the charging unit 2 is initially activated. Then, after reaching the developing position B, a predetermined developing voltage during image formation is started to be applied to the developing member 42. In this embodiment, the first time is equal to the time when the surface of the image carrier 1 at the developing position B first reaches the transfer position D when the predetermined developing voltage is applied to the developing member 42. Is also later. In the present embodiment, the transfer member 7 is an intermediate transfer member that conveys the toner image transferred from the image carrier 1 to the recording material P for transfer.

5. Effect Conventionally, the intermediate transfer belt 7 is moved to the photosensitive drum 1 at a timing (time t4 in FIG. 4) at which the surface of the photosensitive drum 1 to which a predetermined charging bias and a developing bias are applied during image formation reaches the transfer position D. Had been abutted. However, if time has elapsed since the previous image forming operation was completed and the stopped state (standby state) of the image forming apparatus 100 has been continued for a long time, the image forming apparatus 100 moves from the developing position B to the transfer position D on the photosensitive drum 1. A toner band due to zero toner may be generated in the area. In the case of the conventional contact timing described above, before the toner band due to the zero toner passes through the transfer position D (the period from time t4 to t6 in FIG. 4), the toner band moves to the intermediate transfer belt 7, and The recording material P may move to the secondary transfer roller 8 and stain the back side of the recording material P.

  On the other hand, in the present embodiment, the intermediate transfer belt 7 is brought into contact with the photosensitive drum 1 after the toner band of zero toner has passed the transfer position D (typically almost simultaneously). Therefore, even when a toner band due to zero toner is generated, it is possible to suppress the toner band from moving to the intermediate transfer belt 7 and suppress the back contamination of the recording material P due to the toner band. Further, since the toner band due to the zero toner is prevented from moving to the intermediate transfer belt 7 and further moving to the secondary transfer roller 8, the cleaning process of the intermediate transfer belt 7 and the secondary transfer roller 8 before image formation is performed. There is no need to provide Therefore, it is possible to suppress the FPOT from becoming longer due to this cleaning step.

  As described above, according to the present embodiment, it is possible to suppress the back dirt of the recording material P due to the toner on the developing roller 42 whose charge has decreased during standby while suppressing the FPOT from becoming long. .

6. Modification In the present embodiment, the second time is set to be after the first time regardless of the length of the stop time (standby time) of the image forming apparatus 100, and the toner band of zero toner is transferred to the intermediate transfer belt 7. And the movement is suppressed. On the other hand, the contact timing between the photosensitive drum 1 and the intermediate transfer belt 7 at the time of startup may be varied according to the length of the stop time (standby time) of the image forming apparatus 100. For example, as shown in FIG. 3, the image forming apparatus 100 has an acquisition unit that acquires information on a time period from when the rotation of the developing roller 42 is last stopped to when the rotation of the developing roller 42 is first started. A timer 70 is provided. Then, based on the information acquired by the timer 70, the control unit 50 operates the contact / separation 11 so that the second time is after the first time, or sets the second time to the first time. It is possible to select whether to operate the contact / separation 11 so that it is earlier than that. In this case, for example, as shown in FIG. 5, when receiving the print job, the control unit 50 determines whether the time indicated by the information acquired by the timer 70 is greater than a predetermined threshold (S1). If the value is equal to or greater than the threshold, the control unit 50 determines to operate the contact / separation mechanism 11 such that the second time is equal to or later than the first time (S2). If the time indicated by the information acquired by the timer 70 is smaller than the threshold, the control unit 50 operates the contact / separation mechanism 11 so that the second time is earlier than the first time. It is decided to make it (S3). After that, the control unit 50 activates the image forming apparatus 100 in accordance with the determined contact timing to execute image formation. When operating the contact / separation mechanism 11 so that the second time is earlier than the first time, typically, the following operation may be performed. That is, the intermediate transfer belt 7 is brought into contact with the photosensitive drum 1 at a timing (time t4 in FIG. 4) when the surface of the photosensitive drum 1 to which the predetermined charging bias and the developing bias are applied during image formation reaches the transfer position D. It should be done. By performing such an operation, the waiting time can be reduced for a user who repeats printing in a short span.

  Further, in order to advance the second time, the drive speed of the drive motor 12 may be temporarily increased at the time of startup. In the present embodiment, the photosensitive drum 1 and the developing roller 42 are driven by a common drive motor 12, but when driven by independent drive motors, the drive speed of at least one drive motor is reduced at the time of startup. Can be temporarily faster. As a result, the time required for moving at least one surface of the photosensitive drum 1 or the developing roller 42 is shortened, so that the waiting time for the toner band by the zero toner to reach the transfer position D is shortened, and the FPOT is shortened. Can be. That is, from an arbitrary point in time during image formation to a point in time when the surface of the photosensitive drum 1 that first faces the surface of the developing roller 42 at the regulating position C and the developing position B at the time reaches the transfer position D first. This time is defined as a first time. The time from the start of the rotation of the developing roller 42 at the time of activation to the first time is defined as a second time. At this time, the control unit 50 controls the rotation speed of at least one of the photosensitive drum 1 and the developing roller 42 during a part of the startup so that the second time is shorter than the first time. The rotation speed can be higher than the rotation speed during image formation. That is, the control unit 50 can operate the driving unit of at least one of the photosensitive drum 1 and the developing roller 42 as described above.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus according to the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description is omitted. I do.

1. Overview of the First Embodiment When the image forming apparatus 100 is started, toner other than zero toner may move to the photosensitive drum 1 as a toner band. Even if a small amount of toner including zero toner moves to the photosensitive drum 1 at the time of startup, if this movement is repeated, a considerable amount of toner may be wasted. Therefore, in the present embodiment, it is an object to suppress waste of toner while achieving the same object as in the first embodiment.

  Here, in this embodiment, it takes 25 msec from the state where the charging bias is OFF to the time when the voltage rises to -500 V which is half the potential of the predetermined charging bias during image formation.

  In this embodiment, the bias is applied to the charging roller 2 and the developing roller 42 before the driving of the driving motor 12 starts, so that the toner other than the zero toner that moves from the developing roller 42 to the photosensitive drum 1 at the time of starting is started. Reduce the amount.

2. Operation Timing of Each Unit FIG. 6 is a timing chart showing the operation timing of each unit of the image forming apparatus 100 at the time of startup in this embodiment (only the parts necessary for the description of this embodiment are shown. ). In this embodiment, the control unit 50 causes each unit of the image forming apparatus 100 to perform a sequence operation according to the timing chart.

  When the control unit 50 receives the print job, the print job is started, and the temperature of the fixing device 10 reaches a predetermined temperature, the reverse of the driving to the developing roller 42 is performed prior to the time (t1) at which the driving of the drive motor 12 is started. The application of the bias is started (t9). Prior to the time t1, application of a weak bias to the charging roller 2 is started (t10). In the present embodiment, at time t9, which is 40 msec before time t1, the application of a reverse bias of +200 V, which is a reverse bias to the predetermined developing bias during image formation, to the developing roller 42 is started. Further, in the present embodiment, at time t10, which is 25 msec before time t1, a bias having the same polarity as the predetermined charging bias during image formation and having a smaller absolute value than the charging bias during image formation is -500V. The application of the bias to the charging roller 2 is started. Thereafter, at the same time as the drive of the drive motor 12 is started, the rise to a predetermined charging bias during image formation is started (t1).

  By applying a reverse bias to the developing roller 42 before the driving of the drive motor 12 is started, it is possible to electrostatically attract toner other than zero toner to the developing roller 42 and prevent the toner from moving to the photosensitive drum 1. Further, before the driving of the drive motor 12 is started, a weak bias having a potential difference equal to or smaller than the discharge threshold value with respect to the photosensitive drum 1 is applied to the charging roller 2, and at the same time as the driving of the drive motor 12 starts, a predetermined charging bias during image formation is applied. Start launching. As a result, it is possible to suppress the occurrence of discharge marks on the photosensitive drum 1 due to the discharge while the photosensitive drum 1 is stopped, and to raise the charging bias to a predetermined charging bias during image formation in a shorter time.

  Also, when the rotation of the photosensitive drum 1 starts rising to a predetermined charging bias during image formation (that is, when the rotation of the photosensitive drum 1 is started), the photosensitive drum 1 that was at the charging position A was started. Reaches the developing position B after 225 msec (t2). Prior to time t2, the rise of the bias applied to the developing roller 42 from a reverse bias to a predetermined developing bias during image formation is started (t11). In the present embodiment, at time t11, which is 40 msec before time t2, the rise to a predetermined developing bias during image formation is started. Thereafter, the application of the predetermined developing bias during the image formation starts after the surface of the photosensitive drum 1 to which the predetermined charging bias has been applied during the image formation reaches the developing position B. As a result, the surface of the photosensitive drum 1 to which a predetermined developing bias is applied during image formation is uniformly charged by the predetermined charging bias during image formation, so that toner is wastefully moved to the photosensitive drum 1. Is suppressed.

  The subsequent operation timings of the respective units are the same as in the first embodiment. The operations at times t1 to t8 in FIG. 6 are the same as the operations at times t1 to t8 in FIG. 4 described in the first embodiment, respectively.

  That is, the surface of the photosensitive drum 1 at the charging position A when the rise to the predetermined charging bias during image formation is started (that is, when the rotation of the photosensitive drum 1 is started) is at the time t2. 251 msec later, the transfer position D is reached (t3). The surface of the photosensitive drum 1 at the charging position A when the predetermined charging bias (charging bias rising to the predetermined potential) during the image formation starts to reach the transfer position D after 40 msec from the time t3. (T4).

  On the other hand, when the rotation of the photosensitive drum 1 is started (that is, when the rotation of the developing roller 42 is started), the surface of the developing roller 42 at the regulation position C (more specifically, the toner thereon) is The rotation of the developing roller 42 reaches the developing position B after 325 msec (t5). In addition, the surface of the photosensitive drum 1 facing the surface of the developing roller 42 at the regulation position C when the rotation of the photosensitive drum 1 is started (contact in the present embodiment) at the developing position B is 251 msec after the time t5. The transfer position D is reached (t6).

  Then, in the same manner as in the first embodiment, the surface of the photosensitive drum 1 that first opposes the surface of the developing roller 42 at the regulation position C when the rotation of the photosensitive drum 1 is started at the developing position B is the transfer position D first. Is a first time (time t6 in FIG. 4). The time at which the photosensitive drum 1 contacts the intermediate transfer belt 7 is referred to as a second time (time t7 in FIG. 4). At this time, in the present embodiment, as in the first embodiment, the contact / separation mechanism 11 is operated such that the second time t7 is equal to or later than the first time t6. Specifically, the primary transfer roller by the contact / separation mechanism 11 is moved back from the second time t7 at which the photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other by 200 msec, which is the time required for switching the contact / separation state. The contact operation of No. 5 with the photosensitive drum 1 is started (t8).

  As described above, in the present embodiment, the control unit 50 operates the charging power source E1 as described below at the time of startup. That is, before the rotation of the photosensitive drum 1 is started, a bias having the same polarity as the predetermined charging bias during image formation and having a smaller absolute value than the predetermined charging bias is applied to the charging roller 2. The control unit 50 starts to apply the predetermined charging bias to the charging roller 2 after the rotation of the photosensitive drum 1 is started. Further, in the present embodiment, the control unit 50 operates the developing power source E2 at the time of startup as follows. That is, before the rotation of the photosensitive drum 1 is started, a voltage having a polarity different from a predetermined developing voltage during image formation is applied to the developing roller 42. Further, after the surface of the photosensitive drum 1 at the charging position A first reaches the developing position B when the predetermined charging bias during image formation is started to be applied to the charging roller 2, the predetermined roller is applied to the developing roller 42. The development voltage starts to be applied.

3. Effects In the present embodiment, a reverse bias is applied to the developing roller 42 while the zero toner is in the region from the regulation position C to the developing position B on the developing roller 42. As a result, the toner whose charge has not become substantially zero can be electrostatically attracted to the developing roller 42. Therefore, it is possible to reduce the amount of toner that moves to the photosensitive drum 1 unnecessarily.

  Unlike the present embodiment, when the application of the predetermined charging bias and the predetermined developing bias is started at the same time as the rotation of the photosensitive drum 1 is started, the period until the rise to the predetermined potential is completed is However, the effect of retaining the toner on the developing roller 42 by the bias cannot be obtained. Therefore, the toner may be moved to the photosensitive drum 1 unnecessarily.

  As described above, in this embodiment, the application of the reverse bias to the developing roller 42 and the application of the weak bias to the charging roller 2 are performed before the rotation of the photosensitive drum 1 is started. This makes it possible to suppress waste of toner while obtaining the same effects as in the first embodiment.

[Example 3]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus according to the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description is omitted. I do.

1. Overview of the Present Embodiment Depending on the rotation speed of the photosensitive drum 1 (conveying speed of the recording material P) and the rising speed of the drive motor 12, it takes time for the photosensitive drum 1 and the intermediate transfer belt 7 to rise to a predetermined rotation speed. Sometimes. If the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other before the rotation speed converges to a predetermined rotation speed, the rotation speed during the rising is unstable. There is a possibility that the photosensitive drum 1 is scratched by being rubbed by the belt 7. Thus, in the present embodiment, an object is to suppress the occurrence of scratches on the photosensitive drum 1 while achieving the same object as in the first embodiment.

  In this embodiment, the moving speed (peripheral speed) of the surfaces of the photosensitive drum 1, the developing roller 42, and the intermediate transfer belt 7 is 250 mm / sec. Further, in the present embodiment, at the time of startup, the drive motor 12 is driven for 500 msec from the start of drive until the drive speed is stabilized at a predetermined drive speed during image formation (until it converges to a predetermined rotation speed). is necessary.

  In the present embodiment, the third time at which the drive speed of the drive motor 12 converges to the predetermined speed is later than the first time described in the first embodiment. In this embodiment, the timing at which the intermediate transfer belt 7 is brought into contact with the photosensitive drum 1 is adjusted to the later third time. Thus, the occurrence of scratches on the photosensitive drum 1 due to the photosensitive drum 1 being rubbed against the intermediate transfer belt 7 is suppressed.

2. Operation Timing of Each Unit FIG. 7 is a timing chart showing the operation timing of each unit of the image forming apparatus 100 at the time of startup in this embodiment (only the parts necessary for the description of this embodiment are described. ). In this embodiment, the control unit 50 causes each unit of the image forming apparatus 100 to perform a sequence operation according to the timing chart. The operations at times t1 to t8 in FIG. 7 are the same as the operations at times t1 to t8 in FIG. 4 described in the first embodiment, respectively.

  In the present embodiment, the maximum speed of the drive motor 12 is faster than in the first embodiment, but it takes time for the drive speed of the drive motor 12 to converge. Therefore, in this embodiment, the surface of the photosensitive drum 1 at the charging position A when the rotation of the photosensitive drum 1 is started passes through the developing position B (t2), and reaches the transfer position D (t3). ), 388 msec (476 msec in the first embodiment). Further, in this embodiment, when the rotation of the photosensitive drum 1 is started, the surface of the photosensitive drum 1 that is opposed to the surface of the developing roller 42 at the regulation position C at the developing position B reaches the transfer position D (see FIG. (t6: first time) 436 msec is sufficient (576 msec in the first embodiment). In this embodiment, since the time required for the drive motor 12 to turn off to converge to the predetermined drive speed is 500 msec, the third time t12 at which the drive speed of the drive motor 12 converges is It will arrive after the first time t6. Therefore, in the present embodiment, the contact / separation mechanism 11 is operated such that the second time t7, which is the time when the photosensitive drum 1 and the intermediate transfer belt 7 contact each other, becomes the third time t12 or later. Specifically, the primary transfer roller by the contact / separation mechanism 11 is moved back from the second time t7 at which the photosensitive drum 1 and the intermediate transfer belt 7 come into contact with each other by 200 msec, which is the time required for switching the contact / separation state. The contact operation of No. 5 with the photosensitive drum 1 is started (t8). Typically, the contact / separation mechanism 11 is operated such that the second time t7 is substantially the same as the third time t12. However, the second time t7 is a sufficiently short time after the third time t12, for example, a time after the third time t12 to about the time required for the photosensitive drum 1 to make one rotation or less, preferably The time may be set to be about 50 msec or less from the third time t12.

  The time at which the rotational speeds of the photosensitive drum 1 and the intermediate transfer belt 7 reach the predetermined steady speed is defined as a third time. At this time, the control unit 50 operates the contact / separation mechanism 11 so that the second time t7 is equal to or later than the first time t6 and the third time t12 after the first time t6. Can be done.

3. Effects In the present embodiment, the time when the drive speed of the drive motor 12 converges to the predetermined drive speed comes later than the time when the toner band of zero toner passes through the transfer position D. Therefore, in the present embodiment, the contact of the intermediate transfer belt 7 with the photosensitive drum 1 is adjusted to the timing at which the drive speed of the drive motor 12 converges, thereby suppressing back contamination of the recording material P due to the toner band due to zero toner. In addition, the occurrence of scratches on the photosensitive drum 1 can be suppressed.

  Unlike the present embodiment, if the intermediate transfer belt 7 is brought into contact with the photosensitive drum 1 before the drive speed of the drive motor 12 converges, the photosensitive drum 1 and the transfer belt 7 are in the process of starting up. The contact occurs when the speed difference is unstable. For this reason, there is a possibility that the peripheral speed difference is unintentionally large and the photosensitive drum 1 is damaged.

  As described above, in this embodiment, the photosensitive drum 1 and the intermediate transfer belt 7 are moved in synchronization with the timing at which the drive speed of the drive motor 12 converges, which is later than the timing at which the toner band of zero toner passes through the transfer position D. Abut. This makes it possible to suppress damage to the photosensitive drum 1 caused by the photosensitive drum 1 being rubbed by the intermediate transfer belt 7 while obtaining the same effect as in the first embodiment.

4. Modification In the case of a configuration in which the photosensitive drum 1 and the intermediate transfer belt 7 are driven by independent drive motors, there is a difference in the time required for the drive speeds of the respective drive motors to converge due to different performances of the respective drive motors. May appear. In this case, the time when the drive speed of the slower drive motor converges is set as the third time, and the timing at which the photosensitive drum 1 and the intermediate transfer belt 7 are brought into contact with each other may be determined.

  In the case of image forming apparatuses having the same main cross section, the higher the drive speed and the longer the time required for startup, the later the time at which the drive speed of the drive motor 12 converges tends to be later. In other words, when there are a plurality of operation settings in which the drive speed of the drive motor 12 is different, the drive speed of the drive motor 12 is shorter than the time when the zero toner arrives at the transfer position D in the predetermined operation setting in which the drive speed is fast and the rise takes time. The time at which the speed converges may come later. Therefore, in the case of the image forming apparatus 100 operable with such a plurality of operation settings, the following configuration may be adopted. That is, according to the operation setting, the timing of bringing the photosensitive drum 1 into contact with the intermediate transfer belt 7 is adjusted to the time when the toner band of zero toner passes the transfer position D, and the time when the drive speed of the drive motor 12 converges. And the two cases are mixed. That is, the image forming apparatus 100 has a first mode in which the first time arrives after the third time at the time of activation, and a third time which is greater than the first time at the time of activation. It may also be possible to perform image formation in the second mode that comes later. Typically, the steady speed in the second mode is higher than a predetermined steady speed of the rotation speed of the photosensitive drum 1 and the intermediate transfer belt 7 in the first mode. The operation at the time of startup in the first mode corresponds to the operation shown in FIG. 4 described in the first embodiment, and the operation at the time of startup in the second mode is shown in FIG. 6 described in the present embodiment. This corresponds to the operation shown. The switching between the first mode and the second mode can be performed by the control unit 50 according to an instruction from the operation unit 80 or the external device 200, for example. The control unit 50 determines the first type according to the type of recording material P used for image formation (such as plain paper or cardboard), which is instructed from the operation unit 80 or the external device 200 or detected by a media sensor. The mode and the second mode may be automatically switched.

[Others]
As described above, the present invention has been described with reference to the specific embodiments, but the present invention is not limited to the above embodiments.

  In the above embodiment, the image forming apparatus of the intermediate transfer system has been described as an example. However, the present invention is also applicable to an image forming apparatus of the direct transfer system. For example, in a monochrome image forming apparatus, the timing at which an image carrier is brought into contact with a transfer roller or the like as a transfer member is the same as the timing at which an intermediate transfer body as an image transfer member is brought into contact with the image carrier in the above-described embodiment. Should be set to. Further, in the color image forming apparatus provided with the recording material carrier, the timing at which the recording material carrier as the transfer member and the image carrier are brought into contact with each other is determined by the intermediate transfer member as the transfer member and the image carrier in the above-described embodiment. What is necessary is just to set similarly to the timing which contacts a body. As the recording material carrier, a recording material carrying belt composed of an endless belt similar to the intermediate transfer member in the above-described embodiment is often used. In addition, a direct transfer member such as a transfer roller having the same function as the primary transfer member in the above-described embodiment is often provided on the inner peripheral surface side of the recording material carrying belt. In this case, the recording material carrying belt can be brought into and out of contact with the image carrier by directly bringing the transfer member into and out of contact with the image carrier in the same manner as the primary transfer member in the above-described embodiment.

Reference Signs List 1 photosensitive drum 2 charging roller 3 exposure device 4 developing device 5 primary transfer roller 6 drum cleaning device 7 intermediate transfer belt 11 contact / separation mechanism 12 drive motor 42 developing roller 43 developing blade A charging position B developing position C regulating position D transfer position

Claims (11)

A rotatable image carrier,
Charging means for charging the surface of the image carrier at a charging position to which a charging voltage is applied;
First applying means for applying a voltage to the charging means;
A rotatable developing member that carries toner on the surface, a developing voltage is applied, and adheres the toner to the surface of the image carrier at a developing position downstream of the charging position with respect to the rotation direction of the image carrier; ,
Second applying means for applying a voltage to the developing member;
A regulating member that regulates toner carried on the surface of the developing member and frictionally charges the toner at a regulating position upstream of the developing position with respect to the rotation direction of the developing member;
A transfer member rotatable with respect to the image carrier at a transfer position downstream of the developing position with respect to the rotation direction of the image carrier,
Contact / separation means for contacting / separating the image carrier and the transfer member;
Control means;
Has,
The toner is supplied from the rotating developing member to the surface of the rotating image carrier that has been subjected to the charging process by the charging unit to form a toner image on the surface of the image carrier. An image forming apparatus for forming an image in which the formed toner image is transferred to a recording material using the transfer member that is rotating while being in contact with the image carrier,
The control unit is configured to stop the rotation of the image carrier, the developing member, and the transfer member, and change a state in which the image carrier and the transfer member are separated from each other to a state in which image formation is possible. During the start-up, the surface of the image bearing member that first faces the developing member at the regulation position when the rotation of the developing member is started reaches the transfer position first. When the time at which the image carrier is brought into contact with the transfer member is a second time, the contact time and the separation time are set such that the second time is after the first time. An image forming apparatus characterized by operating means.   At the time of the start, after the surface of the image carrier at the charging position first reaches the developing position when a predetermined charging voltage during image formation is started to be applied to the charging unit, A predetermined developing voltage during image formation is started to be applied to the developing member, and the first time is at the developing position when the predetermined developing voltage is started to be applied to the developing member. The image forming apparatus according to claim 1, wherein the image forming apparatus is located after the surface of the image carrier first reaches the transfer position.   At the time of the start, the time when the surface of the image carrier, which was at the charging position when the rotation of the image carrier was started, first reaches the developing position, the rotation of the developing member was started. 3. The image forming apparatus according to claim 1, wherein the surface of the developing member that has been at the regulation position is before a time when the surface of the developing member first reaches the developing position. 4.   The control unit has the same polarity as the predetermined charging voltage during image formation on the charging unit and has an absolute value smaller than the predetermined charging voltage before the rotation of the image carrier is started at the time of the startup. The method according to claim 1, wherein the first application unit is operated so that the predetermined charging voltage starts to be applied to the charging unit after a voltage is applied and rotation of the image carrier is started. The image forming apparatus according to any one of claims 1 to 3.   The control unit applies a voltage having a polarity different from a predetermined developing voltage during image formation to the developing member before the rotation of the image carrier is started at the time of the start, and an image is applied to the charging unit. The application of the predetermined developing voltage to the developing member starts after the surface of the image carrier at the charging position first reaches the developing position when the predetermined charging voltage during formation starts to be applied. The image forming apparatus according to claim 1, wherein the second application unit is operated as described above.   The control unit is configured such that, at the time of the start, when a time at which the rotation speeds of the image carrier and the transfer member reach a predetermined steady speed is a third time, the second time is the first time. The image forming apparatus according to any one of claims 1 to 5, wherein the contact / separation unit is operated so as to be at or after a later time between the time and the third time.   A first mode in which the first time arrives later than the third time at the time of the activation, and a third mode in which the third time is later than the first time at the time of the activation. An image formation can be performed in an incoming second mode, and the steady speed in the second mode is faster than the steady speed in the first mode. 7. The image forming apparatus according to 6.   The control unit may be configured such that, from an arbitrary time during image formation, the surface of the image bearing member that first faces the developing member at the regulation position at the time at the time is the transfer position. Part of the time of the start-up such that the time taken from the start of rotation of the developing member at the start-up to the first time is shorter than the time taken to reach the start-up. Operating a driving unit of at least one of the image carrier and the developing member so that a rotation speed of at least one of the image carrier and the developing member is higher than a rotation speed during image formation. The image forming apparatus according to claim 1, wherein: Acquisition means for acquiring information about the time from the last stop of the rotation of the developing member to the first start of the rotation of the developing member,
The control unit operates the contact / separation unit based on the information acquired by the acquisition unit so that the second time is after the first time, or the second time is The image forming apparatus according to any one of claims 1 to 8, wherein it is possible to select whether to operate the contact / separation unit so as to be earlier than the first time.   The control means, when the time indicated by the information acquired by the acquisition means is larger than a predetermined threshold, the second time is operated such that the second time is after the first time, When the time indicated by the information acquired by the acquisition means is smaller than the threshold, the contact / separation means is operated such that the second time is earlier than the first time. The image forming apparatus according to claim 9.   The image forming apparatus according to claim 1, wherein the transfer member is an intermediate transfer body that conveys the toner image transferred from the image carrier to transfer the toner image to a recording material. apparatus.

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