JP6201181B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms a transfer area by pressing a rotating body against a transfer body carrying a toner image, and transfers the toner image onto a sheet in the transfer area.

  Conventionally, as this type of image forming apparatus, for example, there is an apparatus described in Patent Document 1. In this image forming apparatus, after toner images of corresponding colors are formed on the peripheral surface of the photosensitive drum, the toner images of the respective colors are sequentially transferred to the same area on the intermediate transfer belt. An image is formed. The intermediate transfer belt rotates in a predetermined direction and conveys the composite toner image to the transfer area. Thereafter, the composite toner image on the intermediate transfer belt is transferred to a sheet (typically, paper) in the transfer region. Further, a cleaning device that collects toner remaining on the surface of the intermediate transfer belt is provided on the downstream side in the rotation direction of the intermediate transfer belt with respect to the transfer region and on the upstream side of the photosensitive drum. .

  In Patent Document 1, a toner pattern having a length WD in the main scanning direction may be formed on the intermediate transfer belt. Further, the cleaning device includes a cleaning blade (hereinafter simply referred to as a blade) having a length in the main scanning direction of WBC in order to scrape off the toner on the surface of the intermediate transfer belt. Further, assuming that the maximum length in the main scanning direction of the maximum sheet that can be printed by the image forming apparatus is WS, the WD, WBC, and WS are configured to satisfy the relationship of WD> WBC> WS.

JP 2004-272118 A

  However, depending on the density and / or formation position of the toner pattern, if the toner pattern is too long in the sub-scanning direction, the toner pattern may slip through the blade. Furthermore, even the stationary layer that should be formed immediately before the contact portion between the blade tip and the intermediate transfer belt may slip through the blade tip. Due to slipping of the toner pattern (including the static layer), the frictional force at the blade tip may be increased, and the contact portion at the blade tip may be pulled up in the rotational direction of the intermediate transfer belt. In order to suppress the turning-up, it is necessary to appropriately adjust the density of the toner pattern.

  By the way, in the printing process, when a jam occurs, the sheet is not sent to the transfer area, and as a result, the composite toner image on the intermediate transfer belt may remain on the intermediate transfer belt. In this case, since a high-density synthetic toner image is supplied to the blade, there is a problem that the possibility that the blade is turned up is increased.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that can further prevent the blade from turning up.

In order to achieve the above object, an aspect of the present invention is an image forming apparatus, comprising: a transfer body that carries a toner image that is charged with a predetermined polarity and transports it to a predetermined transfer area; and the transfer area. A rotating body that presses against the transfer body, a cleaning device that removes toner remaining on the transfer body on the downstream side of the transfer area along the rotation direction of the transfer body, and a downstream side of the transfer area The first determination unit for determining whether or not the toner image remains on the transfer body, the second determination unit for determining the position and density of the toner image on the transfer body, and the first determination unit When it is determined that an image remains, a power supply circuit that applies a secondary transfer voltage including a voltage having a polarity opposite to the predetermined polarity to the rotating body based on the position and / or density determined by the second determination unit; equipped with a, you to the transfer body The toner image carrying region is divided into a plurality of unit regions arranged in the main scanning direction and the sub-scanning direction, and the unit regions arranged in the main scanning direction each constitute a unit region row, and the second region The determination unit determines whether the evaluation value of the toner density exceeds a predetermined reference value for each unit region row, and the power supply circuit determines that the toner image remains by the first determination unit. As the secondary transfer voltage, when the evaluation value of the toner density exceeds a predetermined reference value, while the unit area row determined by the second determination unit passes through the transfer area, the polarity is opposite to the predetermined polarity. Is applied to the rotating body, and while the unit region row determined by the second determination unit that the evaluation value of the toner density is equal to or less than a predetermined reference value passes through the transfer region, the predetermined polarity The same polarity voltage is applied to the rotating body. Give.

  According to the above aspect, it is possible to provide an image forming apparatus that can further prevent the blade from turning up.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged perspective view showing an intermediate transfer belt shown in FIG. FIG. 2 is a control block diagram illustrating a main part of the image forming apparatus in FIG. 1. FIG. 4 is a schematic diagram illustrating a unit area obtained by dividing a support area on an intermediate transfer belt. 6 is a timing chart showing control of a secondary transfer voltage at normal time (when no jam occurs). 4 is a timing chart showing control of a known secondary transfer voltage when a jam occurs. 6 is a timing chart showing control of a well-known secondary transfer voltage when returning from jam processing. It is a flowchart which shows control of the secondary transfer voltage at the time of jam generation in this embodiment. It is a figure which shows the specific example of a synthetic | combination coverage and an average value. 6 is a timing chart showing control of a secondary transfer voltage when a jam occurs in the present embodiment. It is a flowchart which shows control of the secondary transfer voltage at the time of jam generation in a 1st modification. It is a schematic diagram which shows the calculation method of the coverage in a 2nd modification. FIG. 6 is a schematic diagram showing a toner image carried on a carrying region in the upper stage, and a graph showing a time change in torque when the toner image is scraped off by a cleaning blade. It is a schematic diagram which shows the setting method of the reference value in a 3rd modification. 6 is a graph showing a variation in torque of the cleaning blade with respect to the life of the intermediate transfer belt. 6 is a graph showing a change in the frictional force of the cleaning blade with respect to the surface temperature of the intermediate transfer belt. It is a schematic diagram which shows the change of the duty ratio with respect to the supply distance of a secondary transfer voltage.

<Embodiment>
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. First, in the figure or in the following description, the lowercase letters a, b, c, and d described after the reference numerals mean yellow (Y), magenta (M), cyan (C), and black (Bk). Is a subscript. For example, the photosensitive drum 51a means the yellow photosensitive drum 51.

<< Configuration and operation of image forming apparatus >>
First, refer to FIG. The image forming apparatus 1 is, for example, a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions. (Film). The image forming apparatus 1 generally includes a supply unit 2, a registration roller unit 3, a registration sensor Se 1, an image forming unit 4, a fixing device 6, a discharge tray 7, and a control circuit 8. And a power supply circuit 9.

  The supply unit 2 generally includes a supply tray and a supply roller. The supply tray is configured so that unprinted sheets Sh can be stacked. The supply roller is configured to be rotatable under the control of the control circuit 8, and picks up the sheet Sh from the supply tray one by one and sends it out to the conveyance path FP indicated by the broken line in FIG. This sheet Sh is conveyed toward the registration roller unit 3 on the conveyance path FP.

  The roller unit 3 includes, for example, a pair of two rollers. The roller pairs are in contact with each other to form a registration nip, and are configured to be rotatable under the control of the control circuit 8. While the roller pair is stopped, the sheet Sh from the supply unit 2 hits the registration nip and stops temporarily. Thereafter, the roller pair starts to rotate for secondary transfer, and sends the sheet Sh to the secondary transfer area (details will be described later).

  The sensor Se1 is, for example, an optical sensor or an image sensor, and is provided at a position immediately upstream of the registration nip (that is, immediately before) in the transport path FP. The sensor Se1 outputs, to the control circuit 8, a signal indicating the passage state of the sheet Sh immediately before the roller unit 3 in binary (Hi or Lo) during the printing process. In the present embodiment, Hi indicates that the sheet Sh exists in the registration nip, and Lo indicates that the sheet Sh does not exist in the registration nip.

  The image forming unit 4 includes image forming units 41a to 41d, an exposure device (sometimes referred to as a print head unit) 42, an intermediate transfer belt 43, a driving roller 44, a driven roller 45, and primary transfer rollers 46a to 46d. A secondary transfer roller 47, a cleaning device 48, and a toner density sensor Se2. The sensor Se2 is not a configuration used in the present embodiment, but a configuration used in the first modification.

  Further, the image forming units 41 a to 41 d are arranged so as to be linearly arranged from left to right on a frame (not shown) of the image forming apparatus 1. The image forming unit 41a includes a photosensitive drum 51a of a corresponding color. Around the photosensitive drum 51a, a charger 52a, a developing device 53a, an eraser 54a, and a cleaner 55a are arranged from the upstream side to the downstream side in the rotation direction (that is, the sub-scanning direction indicated by the arrow α). Are provided in this order. Similarly, the image forming units 41b to 41d also include photosensitive drums 51b to 51d, chargers 52b to 52d, developing devices 53b to 53d, erasers 54b to 54d, and cleaners 55b to 55d.

  In the image forming unit 4, the chargers 52a to 52d are typically chargers using corona discharge (corotron or scorotron) or chargers using proximity discharge (charging roller or charging brush). These chargers 52a to 52d uniformly charge the peripheral surfaces of the rotating photosensitive drums 51a to 51d (charging process). The exposure device 42 can typically use a so-called laser scanning method or an LED array method. When the exposure device 42 receives image data of each color from the control circuit 8 described later, the exposure device 42 generates light beams Ba to Bd modulated with the image data for each color. Then, the exposure device 42 sequentially scans the peripheral surfaces of the photosensitive drums 51a to 51d charged by the chargers 52a to 52d for each line in the main scanning direction for each line (exposure process). By the above charging / exposure process, electrostatic latent images of corresponding colors are formed on the peripheral surfaces of the photosensitive drums 51a to 51d.

  Further, in the image forming unit 4, the developing devices 53a to 53d supply corresponding color toners to the electrostatic latent images formed on the photosensitive drums 51a to 51d (development process). Here, it is assumed that the toner of each color is negatively charged. By this development process, Y, M, C, and Bk toner images are formed on the peripheral surfaces of the photosensitive drums 51a to 51d. Here, in the following description, the process from the charging process to the development process may be referred to as an image forming process.

  The erasers 54a to 54d are provided between the primary transfer region (described later in detail) of the corresponding color and the chargers 52a to 52d, and remove charges remaining on the photosensitive drums 51a to 51d. The cleaners 55a to 55d are also provided between the primary transfer areas of the corresponding colors and the chargers 52a to 52d, and remove and collect the toner remaining on the photosensitive drums 51a to 51d.

  Here, FIG. 2 is also referred to in addition to FIG. The intermediate transfer belt 43 is an endless belt stretched between the driving roller 44 and the driven roller 45 so that the outer peripheral surface thereof is in contact with the upper end portions of the photosensitive drums 51a to 51d. It is configured to rotate in the direction shown.

  The primary transfer rollers 46a to 46d are arranged so as to press the inner peripheral surface of the intermediate transfer belt 43 and push the outer peripheral surface of the intermediate transfer belt 43 into the photosensitive drums 51a to 51d by a certain amount. Hereinafter, a position where the intermediate transfer belt 43 and the photosensitive drums 51a to 51d are in contact with each other is referred to as a primary transfer region. Further, a primary transfer voltage having a polarity opposite to that of the toner is applied to each of the primary transfer rollers 46a to 46d by a power supply circuit (not shown). As a result, the toner images on the photosensitive drums 51 a to 51 d are transferred onto the intermediate transfer belt 43. This process is hereinafter referred to as a primary transfer process. Here, the toner images of the respective colors are sequentially transferred to the same area on the outer peripheral surface of the intermediate transfer belt 43 by appropriately adjusting the rotational speed and arrangement of the intermediate transfer belt 43 and the photosensitive drums 51a to 51d. As a result, a full-color composite toner image is formed on the intermediate transfer belt 43. Such a composite toner image is conveyed to a predetermined secondary transfer region (details will be described later) while being held on the intermediate transfer belt 43 by the rotation of the intermediate transfer belt 43.

  As described above, the intermediate transfer belt 43 is stretched and supported by the drive roller 44 and the like. The secondary transfer roller 47 is disposed so as to face the drive roller 44 from the lateral direction with the intermediate transfer belt 43 interposed therebetween, and is disposed so as to be pushed into the intermediate transfer belt 43 on the transport path FP. As a result, the intermediate transfer belt 43 and the secondary transfer roller 47 form a secondary transfer nip. The sheet Sh is fed from the roller unit 3 to the secondary transfer nip. In addition, a secondary transfer voltage is applied to the secondary transfer roller 47 by the power supply circuit 9 in various aspects including a secondary transfer process described later. As a result, the composite toner image on the intermediate transfer belt 43 is transferred onto the sheet Sh sent to the secondary transfer nip. This process is hereinafter referred to as a secondary transfer process. The secondary transfer nip is a secondary transfer area. The sheet Sh is sent out from the secondary transfer nip toward the fixing device 6. The toner remaining on the intermediate transfer belt 43 is scraped off and collected by the cleaning blade provided in the cleaning device 48 by the rotation of the intermediate transfer belt 43.

  Here, only FIG. 1 will be referred to again. The toner concentration sensor Se2 is, for example, a magnetic permeability sensor, and is provided so as to face the outer peripheral surface of the intermediate transfer belt 43 immediately before the secondary transfer region. The sensor Se2 outputs a signal indicating, for example, a binary (Hi or Lo) passing state of the composite toner image carried by the intermediate transfer belt 43 immediately before the secondary transfer region to the control circuit 8 during the printing process. In this embodiment, Hi indicates that a synthetic toner image exists, and Lo indicates that no synthetic toner image exists.

  The fixing device 6 typically includes two rotating bodies that are in contact with each other to form a fixing nip, and can use a heat belt method or a heat roller method. The fed sheet Sh is heated by one rotating body and pressurized by the other rotating body. By this fixing process, the synthetic toner image on the sheet Sh is fixed. The sheet Sh is discharged as a printed matter Sh to a discharge tray 7 provided on the downstream side of the conveyance path FP with respect to the fixing device 6.

  As shown in FIG. 3, the control circuit 8 includes an engine unit and a controller unit.

  The engine unit includes a CPU 81, a nonvolatile memory (for example, EEPROM) 82, and a main memory (for example, SDRAM) 83. The CPU 81 controls the printing process by operating according to a program stored in the nonvolatile memory 82 while using the main memory 83 as a work area.

  A computer and / or a scanner is connected to the image forming apparatus 1, and image data representing an image to be printed by the image forming apparatus 1 is sent from the computer or the like. In the control circuit 8, the controller unit converts the received image data into image data of each color of Y, M, C, and Bk, and transmits the image data to the exposure device 42. The exposure device 42 generates light beams Ba to Bd based on such received image data, and irradiates the peripheral surfaces of the photosensitive drums 51a to 51d.

  The controller unit further includes dot counters (hereinafter simply referred to as counters) 84a to 84d. The counter 84a counts the number of dots by the irradiation light beam Ba to the photosensitive drum 51a. More specifically, Y, M, C, and Bk toner images are synthesized and carried in the same area of the intermediate transfer belt 43. Hereinafter, this region is referred to as a carrying region A. As shown in FIG. 4, the carrying area A has x rows in the sub-scanning direction (in other words, the rotation direction of the intermediate transfer belt 43) and in the main scanning direction (in other words, the width direction of the intermediate transfer belt 43). It is divided into y columns, and thereby divided into x × y rectangular unit regions. In the present embodiment, the carrier region A is, for example, twenty-four unit regions A1 to A24 having the same area, and is divided into six rows in the sub-scanning direction and four rows in the main scanning direction.

  The counter 84a counts the Y dot numbers D1a to D24a in the unit areas A1 to A24, and then obtains Y coverages C1a to C24a in the unit areas A1 to A24 and transmits them to the CPU 81. In the present embodiment, coverage is a value indicating the amount of toner used in a unit area. For example, when the entire unit area A1 is filled with Y toner, the coverage C1a is 100%.

  Similarly, the counters 84b, 84c, and 84d indicate the number of dots D1b to D24b, D1c to D24c, and D1d to D24d by the irradiation light beams Bb, Bc, and Bd to the photosensitive drums 51b, 51c, and 51d, and unit regions A1 to A24. Count every time. Thereafter, the counters 84b, 84c, and 84d obtain coverages C1b to C24b, C1c to C24c, and C1c to C24c for the unit areas A1 to A24 and transmit them to the CPU 81.

  The CPU 81 controls the secondary transfer voltage to be applied to the secondary transfer roller 47 based on the output signals of the sensors Se1 and Se2 and the count values of the counters 84a to 84d. The control of the secondary transfer voltage will be described in detail later.

<Control of normal secondary transfer voltage>
Next, control of the secondary transfer voltage of the image forming apparatus 1 will be described. First, a case where a jam (that is, jamming of the sheet Sh on the transport path FP) does not occur will be described with reference to the timing chart of FIG. In FIG. 5, when the TOD (Top Of Data) of the image data arrives at time t0, the CPU 81 starts the image forming process and connects the clutch for the supply unit 2 at a predetermined time t1. Accordingly, the supply unit 2 picks up one sheet Sh and sends it out to the transport path FP. Further, the CPU 81 uses the main memory 83 to periodically manage the current position on the transport path FP for each of the fed sheets Sh. Specifically, the transport distance of the sheet Sh on the transport path FP from the system speed of the image forming apparatus 1 (that is, the transport speed of the sheet Sh) and the elapsed time since the sheet Sh is sent out from the supply unit 2. This transport distance is used as the current position. In addition, the current position is corrected based on the detection results of sensors provided at important points on the transport path FP.

  The sheet Sh goes to the registration roller unit 3. In the process, when the top of the sheet Sh passes the installation position of the sensor Se1, the CPU 81 receives an output signal of Hi from the sensor Se1 at a predetermined time t2. Immediately after receiving the signal, the sheet Sh hits the stopped roller unit 3 and stops temporarily. At the time of this stop (that is, time t3), the CPU 81 once disengages the supply roller clutch. Further, for example, a negatively charged composite toner image is formed on the intermediate transfer belt 43 from time t0 to time t3. The CPU 81 connects the clutch of the supply roller and the clutch of the registration roller unit 3 at a timing (that is, time t4) at which the top of the printing area on the sheet Sh coincides with the top of the carrying area A. As a result, the sheet Sh is sent out toward the secondary transfer region. Thereafter, under the control of the CPU 81, the power supply circuit 9 performs a secondary operation of about +1000 V (that is, positive polarity) for a predetermined time from the time t5 (that is, until the carrying region A passes through the secondary transfer region). A transfer voltage is applied to the secondary transfer roller 47. Thus, the negatively charged composite toner image is transferred from the intermediate transfer belt 43 to the sheet Sh.

<< Explanation of Reference Example >>
Here, as a reference example, well-known secondary transfer voltage control when a jam occurs in a conventional image forming apparatus will be described with reference to a timing chart of FIG. In FIG. 6, the image forming process is started on the basis of the arrival time of TOD (time t0), and one sheet is sent out to the conveyance path at the same time t1. This sheet is directed to the registration roller portion. However, if the registration sensor signal is Lo even after the time t2 when the registration sensor signal should be Hi, the image forming apparatus determines that a jam has occurred. Thereafter, at least until the composite toner image on the intermediate transfer belt passes through the secondary transfer area, a secondary transfer voltage of about −500 V (that is, negative polarity) is applied to the secondary transfer roller. This prevents the negatively charged composite toner image from moving from the intermediate transfer belt to the secondary transfer roller, and prevents the secondary transfer roller from being stained with toner.

  As a reference example, well-known secondary transfer voltage control at the time of return from jam processing in a conventional image forming apparatus will be described with reference to the timing chart of FIG. In FIG. 7, a voltage of about −500 V is applied to the secondary transfer roller for a time corresponding to one rotation, thereby cleaning the negatively charged toner adhering to the secondary transfer roller. Thereafter, a voltage of +500 V is applied to the secondary transfer roller for a time corresponding to one rotation, thereby cleaning the positively charged toner that may adhere to the secondary transfer roller. This series of operations is repeated a predetermined number of times, thereby preventing the sheet Sh from being soiled in the printing process.

<Control of secondary transfer voltage when jam occurs>
Next, with reference to FIGS. 1 to 4 and FIG. 8, the control of the secondary transfer voltage when a jam occurs according to the present embodiment will be described. The CPU 81 operates as an example of the first determination unit. When the occurrence of a jam (that is, the jam of the sheet Sh on the conveyance path FP) is detected by a method similar to the conventional method, the CPU 81 is intermediate on the downstream side of the secondary transfer region. It is assumed that the composite toner image remains on the transfer belt 43, and the processing of FIG.

  First, the CPU 81 calculates composite coverage (FIG. 8: S01). More specifically, coverages C1a to C24a, C1b to C24b, C1c to C24c, and C1d to C24d are received from the counter 84a. Thereafter, the CPU 81 obtains the average value of the corresponding coverages C1a to C1d for the unit area A1 as the combined coverage C1 of the combined toner image. In the same manner, the composite coverage C2 to C24 of the composite toner image is obtained for the remaining unit areas A2 to A24.

  Next, the CPU 81 determines the average value E of the combined coverage C for each of the unit region columns L (in this embodiment, the columns L1 to L6 as shown in FIG. 4) arranged in parallel in the main scanning direction in the carrier region A. (E1 to E6 in this embodiment) are calculated (FIG. 8: S02). For example, as shown in FIG. 4, since the unit region row L1 includes unit regions A1 to A4, the average value E1 is a simple average value of the combined coverages C1 to C4.

  Next, the CPU 81 determines whether or not the average value E calculated in S02 is greater than or equal to a predetermined first reference value R1 (FIG. 8: S03). The reference value R1 is appropriately determined in accordance with the specification of the image forming apparatus 1, but in the present embodiment, it is illustratively 50%.

  Next, if there is an average value E equal to or greater than the reference value R1, the CPU 81 sets a flag for the unit region row L (FIG. 8: S04). For example, in the example of FIG. 9, regarding the unit region row L1, the combined coverages C1 to C4 are all 50%, and their average value E1 is 50%. Therefore, a flag is set for the unit region row L1. On the other hand, regarding the unit region row L2, the combined coverages C5, C6, C7, and C8 are 10%, 50%, 0%, and 40%, and the average value E2 thereof is 25%. In this case, no flag is set for the unit region row L2.

  Next, the CPU 81 determines whether or not the average value E of the unit areas located at both ends in the main scanning direction in the unit area row L with the flag set is equal to or less than the second reference value R2 (FIG. 8: S05). The reference value R2 may also be less than the reference value R1, but in the present embodiment, it is exemplarily set to 0%.

  If there is a unit region row L whose average value E is equal to or less than the reference value R2 at both ends in the main scanning direction, the CPU 81 drops the flag for the unit region row L (FIG. 8: S06). For example, in the example of FIG. 9, the average value E3 of the unit region column L3 is 50%, but the combined coverages C9 and C12 of the unit regions A9 and A12 at both ends are 0%. Remove the flag.

  Next, the CPU 81 determines whether or not the flagged unit area row L remains (FIG. 8: S07). In S01 to S07, the CPU 81 operates as a second determination unit that determines the position and density of the toner image on the intermediate transfer belt 43. As a result of this processing, in the unit region row L where the flag is set, the toner is distributed over the entire region in the main scanning direction, so the CPU 81 considers that the cleaning blade is likely to be turned up. In this case, as shown in the timing chart of FIG. 10, the CPU 81 applies power from the power supply circuit 9 to the secondary transfer roller 47 only while the flagged unit area row L passes through the secondary transfer area. Control to supply a positive transfer secondary transfer voltage. On the other hand, while the unit area row L where the flag is not set passes through the secondary transfer area, the secondary transfer roller 47 from the power supply circuit 9 to the secondary transfer roller 47 has a secondary voltage of, for example, about −500 V (that is, minus polarity). Control is performed so as to supply a transfer voltage (FIG. 8: S08). The above S08 is also executed when it is determined NO in S05.

  On the other hand, when there is no unit area row L with a flag set (that is, when it is determined No in S03 or S07), the CPU 81 determines the power supply circuit 9 while the entire carrying area A passes through the secondary transfer nip. The secondary transfer roller 47 is controlled to supply a secondary transfer voltage of, for example, about −500 V (that is, minus polarity) (FIG. 8: S09).

<Operation and effect of secondary transfer voltage control>
As described above, the CPU 81 calculates the average values E1 to E6 for the unit region rows L1 to L6. The average values E1 to E6 are examples of toner density evaluation values in the unit region rows L1 to L6. Further, the CPU 81 sets a flag for the unit region row L in which the average values E1 to E6 are equal to or greater than the first reference value R1 and the combined coverage of the unit regions at both ends is equal to or greater than the second reference value R2. In other words, the CPU 81 specifies the unit region row L in which the toner is distributed over the entire region in the main scanning direction in the carrying region A. Only when the unit area row L passes through the secondary transfer area, the secondary transfer roller 47 has a polarity opposite to that of the toner charging polarity (minus in the present embodiment) (plus in the present embodiment). ) Secondary transfer voltage is applied. As a result, the toner moves from the unit area row L to the secondary transfer roller 47, so that the toner density of the unit area row L in the intermediate transfer belt 43 decreases. Therefore, it is possible to suppress a composite toner image including a portion having a high toner density over the entire main scanning direction from being sent to the cleaning blade. Accordingly, it is possible to prevent the end of the cleaning blade in the main scanning direction from being pulled up by being pulled in the rotation direction of the intermediate transfer belt. Here, according to the above processing, there is a high possibility that the toner adheres to the secondary transfer roller 47 and becomes dirty. However, when the secondary transfer voltage control shown in FIG. In this printing process, it is possible to prevent the sheet Sh from being stained.

<< Appendix 1 >>
In the above embodiment, it has been described that S01 to S07 in FIG. 8 are executed after the occurrence of a jam. However, the present invention is not limited to this, and S01 to S07 of FIG. 8 can be executed if image data is generated by the controller unit of the control circuit 8, and may be executed before the occurrence of a jam.

<< Appendix 2 >>
In the above embodiment, it has been described that the process of FIG. 8 is performed on the composite toner image on the intermediate transfer belt 43. However, the present invention is not limited to this, and the process shown in FIG. 8 may be performed on a toner image formed on a transfer body such as a transfer roller or a transfer drum.

<< Appendix 3 >>
In the above-described embodiment, as a preferable example, the secondary transfer voltage in S08 of FIG. 8 has a positive polarity while the flagged unit region row L passes through the secondary transfer region. Was negative polarity. However, the present invention is not limited to this, and when there is a unit area row L with a flag set, the secondary transfer voltage may have a positive polarity while all the carrying areas A pass through the secondary transfer areas. Absent.

<< Appendix 4 >>
In the above embodiment, the configuration in which the secondary transfer roller 47 presses the intermediate transfer belt 43 has been described. However, the configuration is not limited thereto, and the image forming apparatus 1 may adopt a configuration in which a rotating body such as a secondary transfer belt presses the intermediate transfer belt 43.

<< Appendix 5 >>
In the above embodiment, the toner is described as being negatively charged. However, the present invention is not limited to this, and the toner may be positively charged.

<First modification>
Here, since the sheet Sh is clogged upstream of the registration roller unit 3, it is assumed that the composite toner image on the intermediate transfer belt 43 has not passed through the secondary transfer nip at the time of jam occurrence. it can. However, as a precaution, the CPU 81 determines whether or not the trailing edge of the composite toner image carried on the intermediate transfer belt 43 has not passed through the secondary transfer nip before S01, as shown in FIG. FIG. 11: S11). Specifically, the CPU 81 periodically obtains the output signal of the sensor Se2, and if the trailing edge is detected, the trailing edge of the composite toner image has passed the secondary transfer nip. If not, it is determined that it has not passed. And when not passing, the process after S01 is performed. On the other hand, if it has passed, the CPU 81 ends the processing of FIG. 11 without starting the supply of the secondary transfer voltage from the power supply circuit 9 to the secondary transfer roller 47. Thereafter, the CPU 81 makes preparations for secondary transfer to the next sheet Sh.

《Second modification》
In the above-described embodiment, the coverages C1a to C24a, C1b to C24b, C1c to C24c, and C1d to C24d for each color of Y, M, C, and Bk have the same definition. However, Bk toner tends to absorb moisture as compared with toners of other colors (ie, Y, M, C). When such a composite toner image in which a large amount of Bk toner is used is sent to the cleaning device, the torque when the cleaning blade scrapes the composite toner image increases, so that it is easy to turn up.

  From the above background, in the second modification, the coverages C1d to C24d are multiplied by a coefficient α1 (α1 is a value exceeding 1, for example, 1.2) (see FIG. 12). As a result, for the unit region row L carrying a large amount of Bk toner, the average value E in each unit region tends to be equal to or higher than the first reference value R1. As a result, a positive polarity secondary transfer voltage is easily applied to the secondary transfer roller 47 while the unit region row L carrying a large amount of Bk toner passes through the secondary transfer region. Can be suppressed.

《Third modification》
In the image forming apparatus 1, the system speed may be adjusted according to printing conditions. Here, in the upper part of FIG. 13, an example of a toner image carried on the carrying area A is shown. Specifically, two solid patches P1 arranged in the main scanning direction are formed at the leading and trailing ends of the carrying area A, respectively. A large number of line patches P2 are formed between the leading and trailing solid patches P1. For the sake of illustration, with respect to the line patch, only one line patch is assigned the reference symbol P2. Here, the solid patch P1 is a patch having a relatively wide width in the sub-scanning direction, and the line patch P2 is a patch having a relatively narrow width in the sub-scanning direction. The lower part of FIG. 13 is a graph showing changes in torque over time when the intermediate transfer belt 43 is rotated at a high speed (for example, the system speed is full speed) and the toner image is scraped off by a cleaning blade. On the other hand, when the intermediate transfer belt 43 is rotated at a low speed (for example, the system speed is half speed) and the same toner image is scraped off by the cleaning blade, the amount of toner scraped per unit time is reduced. Therefore, the torque at the low speed (specifically, the maximum value of the torque) is approximately halved compared to that at the high speed.

  In consideration of the above, when the system speed is low, the first reference value R1 of S03 in FIG. 8 is made larger than that at high speed (see FIG. 14). In the example of FIG. 14, the reference value R1 at high speed is 50%, and the reference value R1 at low speed is 70%. Thereby, at the time of low speed, with respect to the unit region row L, the average value E in each unit region hardly becomes equal to or higher than the first reference value R1. As a result, the positive polarity secondary transfer voltage is less likely to be applied to the secondary transfer roller 47 while the unit region row L is passing through the secondary transfer region, thereby suppressing contamination of the secondary transfer roller 47. .

《Fourth modification》
Further, as illustrated in FIG. 15, the torque of the cleaning blade varies according to the total number of printed sheets (in other words, the life of the intermediate transfer belt 43) in the image forming apparatus 1. In the example of FIG. 15, the torque is relatively large at 0.10 N · m or more up to about 5000 sheets, and thereafter, it is about 0.10 N · m regardless of the surrounding environment (high temperature / high humidity environment or low temperature / low humidity environment). It becomes almost constant with a small value. The life of the intermediate transfer belt 43 is generally calculated from the total number of printed sheets or the total driving distance.

  Considering the above, when the life of the intermediate transfer belt 43 is initial (for example, when the total number of printed sheets is 5000 sheets or less), the first reference value R1 of S03 in FIG. Make it smaller. On the other hand, in the latter period (for example, when the total number of printed sheets exceeds 5000), the first reference value R1 is relatively increased, for example, 50%. Thereby, in the initial case, the average value E in each unit region of the unit region row L tends to be equal to or higher than the first reference value R1. As a result, since the secondary transfer voltage having a positive polarity is easily applied to the secondary transfer roller 47 while the unit region row L passes through the secondary transfer region, the cleaning blade can be prevented from turning up.

<< Fifth Modification >>
Further, it is known that when the surface temperature of the outer peripheral surface of the intermediate transfer belt 43 increases, the cleaning blade becomes soft and the friction coefficient increases, so that the frictional force of the cleaning blade increases as illustrated in FIG. . In the experiments of the present inventors, the cleaning blade did not turn up until the frictional force was about 3.0N.

  In consideration of the above, when the surface temperature of the outer peripheral surface of the intermediate transfer belt 43 is high (for example, 50 ° C. or more), the first reference value R1 of S03 in FIG. Make it smaller. On the other hand, when the temperature is low (for example, less than 50 ° C.), the first reference value R1 is relatively increased, for example, 50%. Thereby, in the case of high temperature, the average value E in each unit region of the unit region row L tends to be equal to or higher than the first reference value R1. As a result, since the secondary transfer voltage having a positive polarity is easily applied to the secondary transfer roller 47 while the unit region row L passes through the secondary transfer region, the cleaning blade can be prevented from turning up.

<< Sixth Modification >>
In the third to fifth modifications, an appropriate first reference value R1 is set based on the life and temperature of the intermediate transfer belt 43 and the system speed. However, the present invention is not limited to this, and the control circuit 8 may store a table as shown in Table 1 below.

  In the table, a predetermined first reference value R1 is described for each combination of the life and temperature of the intermediate transfer belt 43 and the system speed. For example, if the life of the intermediate transfer belt 43 is up to 5000 sheets and the system speed is high in a low temperature and low humidity environment, the first reference value R1 is 40%. The control circuit 8 may select the first reference value R1 corresponding to the life of the intermediate transfer belt 43, the current temperature, and the current system speed from the table.

<< Seventh Modification >>
In the above embodiment, the positive transfer secondary transfer voltage is supplied to the secondary transfer roller 47 while the unit area row L with the flag passes through the secondary transfer area (see FIG. 8: S08). Here, it is preferable that the absolute value of the secondary transfer voltage is made smaller by the value shown in Table 2 below than the absolute value of the normal secondary transfer voltage (+1000 V as shown in FIG. 5). For example, when the ambient temperature is low and the sheet Sh is plain paper, −500V is selected, so the secondary transfer voltage is + 500V. The reason why the secondary transfer voltage at the time of jam occurrence is reduced as compared with the secondary transfer voltage at normal time is that the sheet Sh does not pass through the secondary transfer area at the time of jam occurrence.

<< Eighth Modification >>
Further, since the contamination of the secondary transfer roller 47 becomes more serious as the distance or time during which the positive transfer voltage is supplied to the secondary transfer roller 47, the number of execution cycles of the secondary transfer cleaning in FIG. As shown in Table 3, it is desirable to increase the number. As a result, when returning from the jam processing, the time when the negative transfer secondary transfer voltage is applied to the secondary transfer roller 47 is applied when the toner image remains (that is, during the jam processing). Longer in relation to time. As a result, the toner adhering to the secondary transfer roller 47 can be reliably removed.

<< Ninth Modification >>
Further, in the secondary transfer cleaning, if a negative polarity cleaning voltage is applied to the secondary transfer roller 47 for a long time, a large amount of toner is transferred to the intermediate transfer belt 43, and as a result, the cleaning blade may be turned up. There is sex. Therefore, as shown in Table 4 and FIG. 17, the duty ratio in the secondary transfer cleaning of FIG. 7 is made smaller as the supply distance of the positive polarity secondary transfer voltage to the secondary transfer roller 47 becomes longer. It is desirable.

  The image forming apparatus according to the present invention can suppress the rolling-up of the cleaning blade of the transfer body represented by the intermediate transfer belt, and is suitable for a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions. .

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 43 Intermediate transfer belt 47 Secondary transfer roller 48 Cleaning device 8 Control circuit 84a-84d Dot counter 9 Power supply circuit

Claims (9)

A transfer body that carries a toner image that is charged with a predetermined polarity while transporting it to a predetermined transfer area;
A rotating body that presses against the transfer body in the transfer area;
A cleaning device that removes toner remaining on the transfer body on the downstream side of the transfer area along the conveyance direction by the transfer body;
A first determination unit for determining whether or not a toner image remains on the transfer body downstream from the transfer region;
A second determination unit for determining the position and density of the toner image on the transfer member;
When the first determination unit determines that the toner image remains, a secondary transfer voltage including a voltage having a polarity opposite to the predetermined polarity is rotated based on the position and / or density determined by the second determination unit. A power supply circuit for the body,
The toner image carrying region on the transfer body is divided into a plurality of unit regions arranged in the main scanning direction and the sub-scanning direction, and the unit regions arranged in the main scanning direction each constitute a unit region row,
The second determination unit determines, for each unit region row, whether or not a toner density evaluation value exceeds a predetermined reference value;
When the first determination unit determines that the toner image remains, the second determination unit determines that the evaluation value of the toner density exceeds a predetermined reference value as the secondary transfer voltage. while the unit region sequence is passing through the transfer region, the predetermined polarity and the opposite polarity of the voltage applied before Kikai rolling bodies, the evaluation value of the toner density to be equal to or less than a predetermined reference value the second determination unit while the determination is the unit area column passes through the transfer region by, providing said predetermined polarity voltage of the same polarity before Kikai rotating body, images forming device. The second determination unit, after multiplying the toner density by a coefficient corresponding to the color, determines the position and / or density of the toner image on the transfer body based on a multiplication value of each color for each unit region. Item 2. The image forming apparatus according to Item 1 . The image forming apparatus according to claim 1 , wherein the predetermined reference value increases as the system speed of the image forming apparatus decreases. The image forming apparatus according to claim 1 , wherein the predetermined reference value is smaller as the life of the transfer body is earlier. The image forming apparatus according to claim 1 , wherein the predetermined reference value is smaller as the ambient temperature of the transfer body is higher. The image forming apparatus according to claim 1 , wherein the predetermined reference value is a smaller value as the end unit region is in the unit region row. The power supply circuit is
When the first determination unit determines that the toner image remains, a secondary transfer voltage having a polarity opposite to the predetermined polarity and including a first voltage value is applied to the rotating body,
When the first determination unit determines that the toner image does not remain, a secondary transfer voltage having a polarity opposite to the predetermined polarity and including a second voltage value is applied to the rotating body,
The absolute value of the first voltage value is smaller than the absolute value of the second voltage value, the image forming apparatus according to claim 1. The power supply circuit is
After determining that the toner image remains by the first determination unit and applying a secondary transfer voltage including a voltage having a polarity opposite to the predetermined polarity to the rotating body,
When returning from the jam processing, a secondary transfer voltage including at least a voltage having the same polarity as the predetermined polarity is applied to the rotating body, whereby the toner attached to the rotating body is cleaned,
The jam give when returning from processing in the secondary transfer voltage to the rotator time correlates the reverse polarity voltage during the toner image remaining on the time given to the rotating body, in any one of claims 1 to 7 The image forming apparatus described. The power supply circuit is
After determining that the toner image remains by the first determination unit and applying a secondary transfer voltage including a voltage having a polarity opposite to the predetermined polarity to the rotating body,
When returning from the jam processing, a secondary transfer voltage including at least a voltage having the same polarity as the predetermined polarity is applied to the rotating body, whereby the toner attached to the rotating body is cleaned,
The jam give the same polarity of the voltage at the time of return from the processing in the rotator period, correlates the reverse polarity voltage during the toner image remaining on the time given to the rotating body, in any one of claims 1 to 7 The image forming apparatus described.

Images