JP7199821B2 - image forming device - Google Patents

Description

The present invention relates to image forming apparatuses such as copiers, printers, and facsimile machines using an electrophotographic method or an electrostatic recording method.

Conventionally, for example, in an electrophotographic image forming apparatus, an image is formed on a recording material such as paper by transferring a toner image formed on a photoreceptor as an image bearing member or an intermediate transfer belt to the recording material. be. The transfer of the toner image from the image carrier to the recording material can be performed by applying a voltage to a transfer member that forms a transfer portion in contact with the image carrier. As transfer members, elastic rollers such as rubber rollers having a rubber layer on a metal core and sponge rollers having a sponge foam layer on a metal core are widely used. This elastic roller is provided with conductivity by dispersing conductive powder such as carbon black in an elastic layer such as a rubber layer or a foam layer. By applying a constant-voltage-controlled or constant-current-controlled bias to the roller, the charged toner is transferred from the image carrier to the recording material.

In such an image forming apparatus, if the transfer current is insufficient, insufficient transfer may occur, and conversely, if the transfer current is excessive, proper transfer may occur, which is called transfer penetration. phenomenon may occur. Therefore, it is desired to supply a desired transfer current to the transfer section in order to sufficiently improve transfer efficiency and perform transfer appropriately. Generally, in the transfer section, the more toner to be transferred, the larger the optimum absolute value of the transfer bias.

In Patent Document 1, image information is divided into a plurality of regions in the process progress direction, a video count value is calculated by accumulating the output level of each pixel in each region, and the absolute value of the transfer bias is increased in a region with a larger video count value. Control is proposed to improve the transferability by increasing the size.

JP 2010-8494 A

However, just increasing the absolute value of the transfer bias in accordance with the amount of toner in the direction of progress of the process, as in the above-described conventional method, may not be able to suppress an image defect called "trailing edge scattering".

"Spraying" means that when the electric charge of the recording material charged at the transfer portion is low, the toner is not sufficiently attracted to the recording material by electric force, and as shown in FIG. This is a phenomenon in which toner scatters on the surface. This "splattering" occurs particularly at the rear end of the recording material in the conveying direction where the nip becomes unstable and the charge supply to the back surface of the recording material (the surface opposite to the surface on which the toner is transferred) is insufficient due to the transfer bias. Likely to happen. This "scattering" that occurs at the trailing edge of the recording material in the conveying direction is called "trailing edge scattering", and tends to occur when the amount of toner applied is large.

"Rear end scattering" can be suppressed by increasing the absolute value of the transfer bias. However, when the amount of toner borne on the trailing edge region is small, if the absolute value of the transfer bias applied to the trailing edge region is increased, the transfer field is too strong, resulting in the occurrence of transfer omissions. The occurrence of unevenness and a decrease in transfer efficiency may become problems.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing "rear end scattering" while suppressing the occurrence of density unevenness and a decrease in transfer efficiency on the leading end side of the recording material in the conveying direction. be.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier for carrying a toner image, a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion, and a voltage is applied to the transfer member. a power supply, a first area that is an image forming area of the recording material, and a second area that is an image forming area of the recording material located on the rear end side of the first area, each pass through the transfer unit. A first mode in which the transfer voltages applied to the transfer member are equal to each other when the first area passes through the transfer unit, regardless of the amount of toner formed in the first area. a second mode in which the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion is larger than the absolute value of the transfer voltage applied to the member; and an acquisition unit configured to acquire an index value related to the amount of toner formed in the second area, wherein the control unit acquires the index value acquired by the acquisition unit. At least the first mode or the second mode can be selectively executed based on the index value obtained, and when the index value related to the amount of toner formed in the second area is less than a predetermined threshold value and the image forming apparatus , wherein the first mode is executed, and the second mode is executed when the index value relating to the amount of toner formed in the second area is equal to or greater than the predetermined threshold value. .
According to another aspect of the present invention, an image carrier that carries a toner image, a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion, and a voltage is applied to the transfer member. The power supply to be applied, the first area that is the image forming area of the recording material, and the second area that is the image forming area of the recording material located on the trailing end side of the first area are each the transfer portion. Regardless of the first mode in which the transfer voltages applied to the transfer member when passing are equal to each other and the amount of toner formed in the first region, the first mode when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member is greater than the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion; and an acquisition unit configured to acquire an index value relating to the amount of toner formed in the second area, wherein the acquisition unit selects the second area from Acquiring an index value correlated with a toner amount of a toner image transferred to each of a plurality of small areas divided in a direction substantially orthogonal to the conveying direction of the recording material, At least the first mode or the second mode can be selectively executed based on the index value for each of the plurality of small regions, and any one of the plurality of small regions has the predetermined index value executing the first mode when the index value is less than the threshold of, and executing the second mode when the index value for at least one small region among the plurality of small regions is equal to or greater than the predetermined threshold A featured image forming apparatus is provided.
According to another aspect of the present invention, an image carrier that carries a toner image, a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion, and a voltage is applied to the transfer member. The power supply to be applied, the first area that is the image forming area of the recording material, and the second area that is the image forming area of the recording material located on the trailing end side of the first area are each the transfer portion. Regardless of the first mode in which the transfer voltages applied to the transfer member when passing are equal to each other and the amount of toner formed in the first region, the first mode when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member is greater than the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion; and an acquisition unit configured to acquire an index value relating to the amount of toner formed in the second area, wherein the acquisition unit selects the second area from Acquiring an index value correlated with a toner amount of a toner image transferred to each of a plurality of small areas divided in a direction substantially orthogonal to the conveying direction of the recording material, At least the first mode or the second mode can be selectively executed based on the index value for each of the plurality of small regions, and the index value among the plurality of small regions is equal to or greater than a predetermined threshold value. when the number of small areas is less than a predetermined number, the first mode is executed, and the number of small areas whose index value is equal to or greater than the predetermined threshold among the plurality of small areas is equal to or greater than the predetermined number An image forming apparatus characterized by executing the second mode is provided.
According to another aspect of the present invention, an image carrier that carries a toner image, a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion, and a voltage is applied to the transfer member. The power supply to be applied, the first area that is the image forming area of the recording material, and the second area that is the image forming area of the recording material located on the trailing end side of the first area are each the transfer portion. Regardless of the first mode in which the transfer voltages applied to the transfer member when passing are equal to each other and the amount of toner formed in the first region, the first mode when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member is greater than the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion; Regardless of the amount of toner formed in the first area, the transfer voltage in the second area is higher than the absolute value of the transfer voltage applied to the transfer member when the first area passes through the transfer unit. a control unit capable of selectively executing a plurality of modes including a third mode in which the absolute value of the transfer voltage applied to the transfer member when passing through the transfer member is smaller; an acquisition unit configured to acquire an index value relating to the amount of toner applied, wherein the control unit is capable of selectively executing one of the plurality of modes according to the type of recording material; , an image forming apparatus capable of selectively executing at least the first mode or the second mode based on the index value acquired by the acquisition unit.

According to the present invention, it is possible to suppress the occurrence of density unevenness and a decrease in transfer efficiency on the leading end side of the recording material in the conveying direction, and to suppress the “rear end scattering”.

1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus; FIG. FIG. 2 is a schematic block diagram showing a control mode of main parts of the image forming apparatus; FIG. 10 is a schematic diagram showing an example of how a divided video count is obtained; 5 is a graph diagram for explaining secondary transfer bias control; FIG. FIG. 4 is a flow chart of control in Example 1; FIG. 10 is a schematic diagram showing another example of how a divided video count is obtained; FIG. 10 is a flow chart of control in Example 2; FIG. 10 is a schematic cross-sectional view for explaining transfer omission at the trailing edge; FIG. 10 is a flowchart of control in Example 3; It is a schematic diagram for demonstrating trailing edge splashing.

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

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem-type printer that employs an intermediate transfer method and is capable of forming a full-color image using an electrophotographic method.

The image forming apparatus 100 has first to fourth image forming units UY, UM, UC and UK for forming yellow (Y), magenta (M), cyan (C) and black (K) images, respectively. Elements having the same or corresponding functions or configurations in each of the image forming units UY, UM, UC, and UK omit Y, M, C, and K at the end of the code indicating that they are elements for one of the colors. may be described in a comprehensive manner. The image forming unit U includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a primary transfer power source D1, a cleaning device 6, and the like, which will be described later.

The image forming unit U has a photosensitive drum 1 which is a rotatable drum-type photosensitive member (electrophotographic photosensitive member) as a first image carrier that carries a toner image. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed in the direction of an arrow R1 (clockwise) in the figure. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-type charging member as charging means. The charged surface of the photosensitive drum 1 is scanned and exposed according to image data (image information signal) by an exposure device (laser scanner) 3 as exposure means, and an electrostatic charge is formed on the photosensitive drum 1 according to the image data. An image (an electrostatic latent image) is formed. The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by a developing device 4 as developing means, and a toner image (visualized) is formed on the photosensitive drum 1 according to image data. A developer image) is formed. In this embodiment, the exposure portion (image portion) on the photosensitive drum 1, which has been uniformly charged and then exposed to light, the absolute value of the potential of which has decreased is charged to the same polarity as the charging polarity of the photosensitive drum 1. Toner adheres.

An intermediate transfer belt 7, which is a rotatable endless belt serving as a second image bearing member for carrying a toner image, is arranged so as to face the four photosensitive drums 1. there is The intermediate transfer belt 7 is stretched over a driving roller 71 , a tension roller 72 , idler rollers 73 and 74 , and a secondary transfer counter roller 75 as a plurality of tension rollers (support rollers). The intermediate transfer belt 7 is, for example, a film-like material made of a resin such as polyimide or polyamide or various rubbers containing and dispersed an appropriate amount of a conductive filler such as carbon or an ionic conductive material. endless belt. The intermediate transfer belt 7 is formed to have an initial surface resistivity of 5×10 ¹⁰ to 1×10 ¹² Ω/□. Further, the intermediate transfer belt 7 has a thickness of, for example, about 40 to 60 μm. The drive roller 71 is driven by a motor with excellent constant speed to circulate (rotate) the intermediate transfer belt 7 . A tension roller 72 applies constant tension to the intermediate transfer belt 7 . The idler rollers 73 and 74 support the intermediate transfer belt 7 extending along the arrangement direction of the photosensitive drums 1Y, 1M, 1C and 1K. The secondary transfer counter roller 75 functions as a member (counter electrode) facing the secondary transfer roller 8, which will be described later. The intermediate transfer belt 7 is driven to circulate (rotate) by a driving roller 71 in the direction indicated by an arrow R2 (counterclockwise) at a predetermined peripheral speed. In this embodiment, the intermediate transfer belt 7 is rotationally driven at a peripheral speed of 200 mm/s. The tension of the intermediate transfer belt 7 with respect to the tension roller 72 is about 5 kgf. On the inner circumferential surface side of the intermediate transfer belt 7, primary transfer rollers 5, which are roller-type primary transfer members as primary transfer means, are arranged corresponding to the respective photosensitive drums 1. As shown in FIG. In this embodiment, the primary transfer roller 5 is composed of a metal roller. The primary transfer roller 5 is urged toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) T1 where the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other.

The toner image formed on the photosensitive drum 1 as described above is primarily transferred onto the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 at the primary transfer portion T1. During the primary transfer process, the primary transfer roller 5 is supplied with a direct current having a polarity opposite to the normal charging polarity of the toner (the charging polarity of the toner during development) (positive polarity in this embodiment) by the primary transfer power source D1. A primary transfer voltage (primary transfer bias) is applied. For example, when forming a full-color image, the Y, M, C, and K toner images formed on the photosensitive drums 1 are superimposed on the intermediate transfer belt 7 at the primary transfer portions T1. primary transfer sequentially.

A secondary transfer roller 8 , which is a roller-type secondary transfer member as a secondary transfer means, is arranged at a position facing the secondary transfer facing roller 75 on the outer peripheral surface side of the intermediate transfer belt 7 . The secondary transfer roller 8 is urged toward the secondary transfer opposing roller 75 via the intermediate transfer belt 7, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 7 and the secondary transfer roller 8 are in contact is formed. ) to form T2. The toner image formed on the intermediate transfer belt 7 as described above is nipped and conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 by the action of the secondary transfer roller 8 at the secondary transfer portion T2. is secondarily transferred onto a recording material (recording medium, sheet) P such as paper. During the secondary transfer process, the secondary transfer roller 8 is supplied with a secondary transfer voltage (secondary transfer bias), which is a DC voltage having a polarity opposite to the normal charging polarity of the toner, from a secondary transfer power source D2 (FIG. 2). is applied. In this embodiment, the secondary transfer roller 8 is configured by forming a rubber layer made of NBR rubber, EPDM rubber, or the like as an elastic layer around a metal core (base material).

The recording material P is supplied to the secondary transfer portion T2 by a recording material supply device 10 as a recording material supply unit. The recording material feeding device 10 includes a recording material containing portion (cassette, tray, etc.) 11 for containing the recording material P, a pickup roller 12 for feeding out the recording material P one by one at a predetermined timing from the recording material containing portion 11, and a It has a conveying roller pair 13 for conveying the recording material P and the like. The recording material P conveyed by the conveying roller pair 13 is synchronized with the toner image on the intermediate transfer belt 7 by the registration roller pair 50 as a registration correction unit, and conveyed to the secondary transfer portion T2. .

The recording material P onto which the toner image has been transferred is conveyed to a fixing device 9 as fixing means. The fixing device 9 fixes (melts, adheres) the toner image to the recording material P by heating and pressurizing the recording material P bearing the unfixed toner image. The recording material P on which the toner image is fixed is discharged (output) to the outside of the main body of the image forming apparatus 100 by a discharge roller pair 30 as a discharge unit.

Toner remaining on the photosensitive drum 1 without being transferred onto the intermediate transfer belt 7 during the primary transfer process (primary transfer residual toner) is removed from the photosensitive drum 1 by a drum cleaning device 6 as a photosensitive member cleaning means. removed and recovered. A belt cleaning device 76 as intermediate transfer member cleaning means is arranged at a position facing the drive roller 71 on the outer peripheral surface side of the intermediate transfer belt 7 . Toner (secondary transfer residual toner) and paper dust remaining on the intermediate transfer belt 7 without being transferred to the recording material P during the secondary transfer process are removed from the intermediate transfer belt 7 by a belt cleaning device 76 and collected. be.

2. Control Mode FIG. 2 is a schematic block diagram showing a control mode of the main part of the image forming apparatus 100 of this embodiment. A control unit (controller) 150 includes a CPU 151 as control means, which is a central element for arithmetic processing, and a memory (storage medium) 152 such as a ROM 152a and a RAM 152b as storage means. The RAM 152b, which is a rewritable memory, stores information input to the control unit 150, detected information, calculation results, etc., and the ROM 152a stores control programs, pre-determined data tables, and the like. The CPU 151 and the memory 152 such as the ROM 152a and the RAM 152b can transfer and read data to each other.

The control unit 150 comprehensively controls each unit of the image forming apparatus 100 to perform a sequence operation. The control unit 150 receives image forming signals (image data, control commands) and the like from an image input unit 203, which is an external host device (not shown) such as an image reading device (not shown) or a personal computer. . Then, the control unit 150 controls each unit of the image forming apparatus 100 according to this image forming signal to execute the image forming operation.

An operation unit (operation panel) 201 is connected to the control unit 150 . The operation unit 201 can display a selection screen of the recording material P to allow an operator such as a user or a service person to select the type of the recording material P to be used for image formation. Job information is input to the image forming apparatus 100 from an external host apparatus (not shown) such as a personal computer communicably connected to the image forming apparatus 100 . The job information includes not only image data (image information signal) but also data designating the type of recording material P used for image formation. Information about the type of recording material P used for image formation is input to the control unit 150 . A job (print job) refers to a series of operations for forming and outputting an image on a single or a plurality of recording materials, which is started by one start instruction. Also, the type of recording material P means the attributes based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, coated paper, manufacturer, brand, product number, basis weight, thickness, size, etc. It encompasses any distinguishable information. An operator such as a user or a service person can execute a job by operating the operation unit 201 , and the control unit 150 receives a signal from the operation unit 201 and converts the image information obtained from the image input unit 203 into image information. Based on this, various devices of the image forming apparatus 100 are operated.

An environment sensor 202 is also connected to the control unit 150 . The environment sensor 202 detects the temperature and humidity inside the housing of the image forming apparatus 100 . Information on the temperature and humidity detected by the environment sensor 202 is input to the control unit 150 . The environment sensor 202 is an example of an environment detection unit that detects at least one of temperature and humidity inside or outside the image forming apparatus 100 .

Here, the control section 150 is connected to a bias control section 60 that controls the bias applied to the secondary transfer roller 8 by the secondary transfer power source D2 under the control of the control section 150 . In this embodiment, the secondary transfer power source D2 includes a constant current circuit and a constant voltage circuit. That is, the secondary transfer power source D2 includes a current detection circuit 62 as current detection means for detecting the current flowing through the secondary transfer roller 8 while the secondary transfer power source D2 is applying a bias to the secondary transfer roller 8. is provided. The bias control circuit 60 controls the voltage output from the secondary transfer power source D2 so that the current value detected by the current detection circuit 62 becomes a predetermined current value. The bias applied to the transfer roller 8 can be controlled by constant current. In other words, the secondary transfer power source D2 can apply a bias to the secondary transfer roller 8 so that a current of a predetermined current value instructed by the bias control circuit 60 flows through the secondary transfer roller 8 . Further, the bias control unit 60 is provided with a voltage detection circuit 61 as voltage detection means for detecting a voltage value output when the secondary transfer power supply D2 applies a bias to the secondary transfer roller 8. there is The bias control circuit 60 controls the voltage output from the secondary transfer power source D2 so that the voltage value detected by the voltage detection circuit becomes a predetermined voltage value. The bias applied to the roller 8 can be controlled by constant voltage. In other words, the secondary transfer power supply D 2 can apply a bias of a predetermined voltage value instructed by the bias control circuit 60 to the secondary transfer roller 8 . In this embodiment, the secondary transfer bias is controlled by ATVC control (Active Transfer Voltage Control). ATVC control will be described later.

3. Division Video Count In this embodiment, the image forming area is divided into a plurality of predetermined length units in each of the main scanning direction and the sub-scanning direction, and the divided areas (here, also referred to as "divided areas"). ) to get the integrated value of the video count. In particular, in this embodiment, the integrated value of the output level (density level) of the image data for each pixel is obtained by video counting, and the information about the amount of applied toner for each divided area is obtained. The "main scanning direction" is a direction substantially perpendicular to the moving direction of the surfaces of the photosensitive drums 1 and the intermediate transfer belt 7 (conveying direction of the recording material P). Further, the "sub-scanning direction" is a direction substantially orthogonal to the main scanning direction (a direction substantially parallel to the conveying direction of the recording material P). Further, the "image forming area" refers to the photosensitive drum 1, the intermediate transfer belt 7, or the image formed on one sheet of recording material P, which is set according to the size of the recording material P used for image formation. This is an area on the recording material P where an image can be formed.

A processing flow of image data input from the image input unit 203 to the control unit 150 will be described. Image data input from the image input unit 203 is converted from luminance values (RGB in this embodiment) to density values (CMYK in this embodiment) by the control unit 150 . In image data converted into CMYK data, which are density values, multi-valued data for each pixel and each color component are integrated. That is, the CPU 151 of the control unit 150 integrates multi-valued data in which each color component data per pixel of the image data is represented by a plurality of bits for each color component of each pixel in a predetermined unit. In each color component having a gradation of 8 bits (0 to 255), when the Y data of the first pixel has a value of "100" and the Y data of the second pixel has a value of "50", The integrated value of the second pixel is "150". In the case of image data of A4 size and 600 dpi, color component data for a total of 34808430 pixels of 7015 pixels (main scanning direction)×4962 pixels (sub-scanning direction) are integrated per page. In this embodiment, the video count value when all pixel components in the area are 255 is expressed as 100%. Some colors are expressed by mixing YMCK colors, and the maximum value of the video count is 200%.

3A and 3B are schematic diagrams showing how the divided video count information of the image forming area is acquired when the image is formed on the recording material P of A4 size in this embodiment. In particular, in this embodiment, the image forming area for one page is divided into a first area (leading edge side area) A1 on the leading edge side in the conveying direction (process advancing direction) of the recording material P and a second area (leading edge side area) A1 on the trailing edge side ( The video count value of each area is acquired by dividing into the trailing edge area A2 and A2. As shown in FIG. 3, the leading end side region A1 is a region ranging from the leading end of the image to a position 10 mm from the trailing end of the image to the leading end side. The trailing edge area A2 is an area ranging from a position 10 mm from the trailing edge of the image to the trailing edge of the image. The maximum video count value for the tip side area A1 is 200% (100% in the case of monochrome), and the video count value of the tip side area A1 indicates its ratio (image ratio). The maximum video count value for the trailing edge area A2 is also 200% (100% for monochrome), and the video count value for the trailing edge area A2 indicates a ratio (image ratio) to that. The video count value of each of these areas correlates with the amount of applied toner in each area. Note that the trailing edge area A2 may be an area on the leading edge side of the actual trailing edge of the recording material P (in the case of marginal printing, etc.), or may be an area including the actual trailing edge of the recording material P. (such as for borderless prints). Further, in the conveying direction of the recording material P, the trailing edge area A2 is sufficiently smaller than the leading edge side area A1. The trailing edge area A2 is approximately 3 mm or more and 20 mm or less leading edge side from the trailing edge of the image forming area (or the actual trailing edge of the recording material P), typically about 5 mm or more and 15 mm or less leading edge side. is. Also, the leading edge area A1 does not necessarily have to start from the leading edge of the image forming area, and may be located at the leading edge side (downstream side) relative to the conveying direction of the recording material relative to the trailing edge area A2.

4. Secondary Transfer Bias Control In this embodiment, the secondary transfer bias is determined by ATVC control performed at the pre-rotation timing of each job. The electrical resistance value of the secondary transfer roller 8 varies greatly depending on environmental factors such as temperature and humidity, and the duration of energization. By performing ATVC control, it is possible to apply an optimum secondary transfer bias even when the electrical resistance value of the secondary transfer roller 8 changes.

The ATVC control in this embodiment will be further explained. FIG. 4 is a schematic diagram showing the relationship (voltage-current characteristics) between the applied voltage value and the detected current value measured in ATVC control. The secondary transfer bias value (Vout) is calculated as follows. First, in a pre-rotation period during which no toner image (recording material P) passes through the secondary transfer portion T2, a plurality of levels of voltage values Vα and Vβ having different potentials are applied to the secondary transfer roller 5. The flowing current values Iα and Iβ are detected. Then, from the voltage-current characteristics, a voltage value corresponding to the target current (Itarget) required for secondary transfer is interpolated to obtain a transfer voltage (Vtarget) corresponding to the target current (Itarget). This transfer voltage (Vtarget) corresponds to the secondary transfer member shared voltage. Further, the obtained transfer voltage (Vtarget) is added with a recording material allotted voltage (Va) corresponding to the electrical resistance value of the recording material P, which is preset according to the type of recording material P and the environment. It is set as the next transfer bias (Vout). That is, the control section 150 performs constant voltage control so that the secondary transfer bias becomes Vout when the leading edge side area A1 passes through the secondary transfer section T2. Note that the control unit 50 refers to the table data stored in the memory 152 based on the information indicating the type of the recording material P included in the job information and the detection result of the environment sensor 202, and performs recording. A material sharing voltage (Va) can be obtained.

In this embodiment, as an example, it is assumed that the target current for secondary transfer of plain paper having a basis weight of 75 gsm is set to 40 μA and the recording material shared voltage is set to 500 V in an environment of 23° C. temperature and 50% humidity. The optimum values of the target current and the recording material apportionment voltage change depending on the charge amount of the toner to be used, the assumed electric resistance of the recording material P, and the like.

5. Relationship Between Divided Video Count Value and Transfer Bias Next, the control of the secondary transfer bias for suppressing the "rear end scattering" in this embodiment will be described. The image forming apparatus 100 of the present embodiment uses the divided video count value of the trailing edge area A2 to correct the secondary transfer bias and corrects the secondary transfer bias when determining that the risk of "trailing edge scattering" is higher than a certain level. Suppress "rear end scattering". In other words, “rear end scattering” is likely to occur when there is an image with a certain amount or more of toner borne-on in a certain range at the rear end of the recording material P in the conveying direction. "Rear end scattering" can be suppressed by increasing the absolute value of the secondary transfer bias. However, if the absolute value of the secondary transfer bias is uniformly increased over the entire area in the conveying direction of the recording material P, the transfer electric field will be too strong in the portion other than the trailing edge, especially in the case of a halftone image. Due to this, transfer omission (strong omission) may occur. Therefore, in this embodiment, based on the divided video count value of the trailing edge area A2, if there is an image with a toner amount greater than a certain amount in the trailing edge area A2, the divided video count value of the leading edge area A1 is the same. Even in this case, the absolute value of the secondary transfer bias for the trailing edge area A2 is increased. A more detailed description will be given below.

In this embodiment, the secondary transfer bias determined by the ATVC control is multiplied by different correction coefficients for the leading end region A1 and the trailing end region A2, respectively, to obtain a difference between the leading end region A1 and the trailing end region A2. A different secondary transfer bias is applied to each of them when secondary transfer of the toner image is performed. Table 1 shows correction coefficients (correction values) applied to the set voltage (Vout) of the secondary transfer bias determined by ATVC control in this embodiment. 1.2 times in the table means that the secondary transfer bias (Vout) determined by ATVC control is multiplied by 1.2 as a correction coefficient. In the case of no correction in the table, the secondary transfer bias determined by ATVC control may not be corrected itself, or 1 may be applied as a correction coefficient.

As shown in Table 1, in this embodiment, the secondary transfer bias applied to the leading end side area A1 is controlled by a constant voltage with the secondary transfer bias Vout determined by ATVC control. On the other hand, the secondary transfer bias applied to the trailing edge area A2 is changed according to the video count value of the image formed in the trailing edge area A2. That is, when the video count value of the trailing edge area A2 is equal to or greater than a predetermined value, the secondary transfer bias applied to the trailing edge area A2 is larger than the absolute value of the secondary transfer bias applied to the leading edge area A1. Increase the absolute value (second mode: right side of Table 1). Further, when the video count value in the trailing edge area A2 is less than the predetermined value, the secondary transfer bias applied to the leading edge side area A1 and the secondary transfer bias applied to the trailing edge area A2 are made equal. (first mode: left side of Table 1).

In other words, in this embodiment, the following control is performed according to the video count value formed in the rear end area A2. That is, when the video count value is the same in the leading end region A1 and the trailing end region A2, the absolute value of the secondary transfer bias applied to the trailing end region A2 is higher than the absolute value of the secondary transfer bias applied to the leading end region A1. Increase the absolute value of the transfer bias.

This is for the following reasons. In other words, in the trailing end region A2 on the trailing end side of the conveying direction of the recording material P, the nip of the secondary transfer portion T2 becomes unstable, and the back surface of the recording material P (the side opposite to the surface on which the toner image is transferred) becomes unstable. The charge supply to the surface) tends to be insufficient. Therefore, the absolute value of the secondary transfer bias is made larger for the rear end region A2 than for the front end region A1, thereby suppressing the occurrence of "rear end scattering" due to insufficient charge supply. On the other hand, if the absolute value of the secondary transfer bias is increased for the leading end region A1 as well as the trailing end region A2, transfer omission occurs due to the excessively strong electric field, resulting in density unevenness and transfer. Loss of efficiency can be a problem.

6. Control Flow Next, the procedure for controlling the secondary transfer bias in this embodiment will be described. FIG. 5 is a flow chart showing an outline of the secondary transfer bias control procedure in this embodiment.

When a job is started by an operator operating the operation unit 201, the control unit 150 executes ATVC control (S101). Next, the control unit 150 acquires divided video count information for each of the leading end region A1 and the trailing end region A2 based on the image information captured by the image input unit 203 (S102). Next, the control unit 150 determines whether or not the divided video count value of the rear end area A2 is 80% or more (S103). If the controller 150 determines in S103 that it is 80% or more, the secondary transfer bias for the trailing edge region A2 is increased by 1.2 times the secondary transfer bias determined by ATVC control based on Table 1. A corrected secondary transfer bias (second mode) is determined (S104). On the other hand, if the controller 150 determines in S103 that it is not 80% or more (less than 80%), it does not correct the secondary transfer bias for the trailing edge area A2 (first mode). Then, the control unit 150 applies the secondary transfer bias determined by the ATVC control to each of the front end region A1 and the rear end region A2 to form an image (S105). Next, the control unit 150 determines whether or not all image formation of the job has been completed (S106). If the control unit 150 determines in S106 that the process has not ended, the process returns to S102 and repeats the acquisition of divided video count information, the setting of the secondary transfer bias, and the image formation regarding the next image formation. . Further, when the control unit 150 determines that the operation is finished in S106, the operation of the image forming apparatus 100 is finished.

In this embodiment, when the divided video count value of the trailing edge area A2 is less than a predetermined threshold value, the secondary transfer bias is not corrected for the trailing edge area A2. The absolute value of the secondary transfer bias is uniformly increased. On the other hand, the absolute value of the secondary transfer bias may be increased as the risk of "trailing edge scattering" increases, that is, as the divided video count value of the trailing edge area A2 increases. That is, a plurality of threshold values may be set for the divided video count value of the trailing edge area A2, and the absolute value of the secondary transfer bias for the trailing edge area A2 may be changed in multiple steps. Table 2 shows an example of correction coefficients applied to the set voltage (Vout) of the secondary transfer bias determined by ATVC control in this case.

As shown in Table 2, when the video count value of the trailing edge area A2 is equal to or greater than the first predetermined value, the absolute value of the secondary transfer bias applied to the trailing edge area A2 is set to A first value larger than the absolute value of the secondary transfer bias to be applied (second mode: right end of Table 2). If the video count value of the trailing edge area A2 is equal to or greater than the second predetermined value, which is smaller than the first predetermined value, and less than the first predetermined value, the following is performed. That is, the absolute value of the secondary transfer bias applied to the trailing edge area A2 is larger than the absolute value of the secondary transfer bias applied to the leading edge area A1 and smaller than the first value. A value of 2 (second mode: middle of Table 2). Further, when the video count value in the trailing edge area A2 is less than the second predetermined value, the secondary transfer bias applied to the leading edge side area A1 and the secondary transfer bias applied to the trailing edge area A2 are are equal (first mode: leftmost in Table 2). That is, the first mode and the second mode are selectively executed based on the video count value of the trailing end area.

Thus, in this embodiment, the image forming apparatus 100 has the control section 150 capable of selectively executing a plurality of modes including the following first mode and second mode. In the first mode, the first area A1, which is the image forming area of the recording material P, and the second area A2, which is the image forming area of the recording material P located on the rear end side of the first area A1, are respectively transferred. In this mode, the transfer voltages applied to the transfer member 8 when passing through the portion T2 are equal to each other. In the second mode, the absolute value of the transfer voltage applied to the transfer member 8 when the second area A2 passes the transfer portion T2 is higher than the absolute value of the transfer voltage applied to the transfer member 8 when the first region A1 passes the transfer portion T2. In this mode, the absolute value of the applied transfer voltage is larger. The image forming apparatus 100 also has an acquisition unit that acquires an index value relating to the amount of toner formed in the second area A2. In this embodiment, the CPU 151 has the function of an acquisition unit. Then, the control unit 150 can selectively execute at least the first mode or the second mode based on the index value acquired by the acquisition unit 151 . In particular, in this embodiment, the control unit 150 executes the first mode when the index value regarding the amount of toner formed in the second area A2 is less than the predetermined threshold. On the other hand, the control unit 150 executes the second mode when the index value regarding the amount of toner formed in the second area A2 is equal to or greater than a predetermined threshold value. In this embodiment, in the conveying direction of the recording material P, the first area A1 is an area extending from the leading edge of the image forming area to a position a predetermined distance from the trailing edge of the image forming area to the leading edge side. In this embodiment, the second area A2 is an area extending from the position at the predetermined distance from the rear end of the image forming area to the rear end of the image forming area. Further, in the present embodiment, the image forming apparatus 100 divides the image forming area into a plurality of areas in each of the conveying direction of the recording material P and the direction substantially perpendicular to the conveying direction. It has a divided video count unit that counts the count value. In this embodiment, the CPU 151 of the control section 150 has the function of the divided video count section. Then, in this embodiment, the acquiring unit 151 acquires the index value based on the count result of the divided video counting unit.

As described above, according to this embodiment, by correcting the secondary transfer bias for the trailing edge area A2 based on the divided video count value of the trailing edge area A2, it is possible to suppress the "trailing edge scattering". can.

[Example 2]
Another embodiment of the present invention will now be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Accordingly, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted. do.

In this embodiment, the trailing edge area A2 is also divided in the direction (main scanning direction) substantially perpendicular to the conveying direction of the recording material P, and the divided video count value of each area is used to determine whether the toner density is locally high. To suppress the occurrence of "rear end scattering" even in cases.

FIG. 6 is a schematic diagram showing how the divided video count information of the image forming area is acquired when the image is formed on the recording material P of A4 size in this embodiment. In the present embodiment, as in the first embodiment, the image forming area for one page is divided into a leading end region A1 on the leading end side in the conveying direction (process advancing direction) of the recording material P and a trailing end region A2 on the trailing end side. and divide into In this embodiment, the trailing end area A2 is further divided into a plurality of small areas (in this embodiment, five areas A21 to A25) in a direction substantially orthogonal to the conveying direction of the recording material P (a direction substantially orthogonal to the process progress direction). To divide. Then, the video count value of each area of the leading end side area A1 and the five trailing end small areas A21 to A25 is obtained. As shown in FIG. 6, the leading end side region A1 is a region extending from the leading end of the image to a position 10 mm from the trailing end of the image to the leading end side. The trailing edge area A2 is an area extending from a position 10 mm from the trailing edge of the image toward the leading edge side to the trailing edge of the image. Each area is divided into five areas in a direction substantially orthogonal to . The maximum video count value for the tip side area A1 is 200% (100% in the case of monochrome), and the video count value of the tip side area A1 indicates its ratio (image ratio). In addition, the maximum video count value for each of the trailing edge small areas A21 to A25 is also 200% (100% in the case of monochrome), and the video count value of each trailing edge small area A21 to A25 is the ratio (image ratio).

Next, a procedure for controlling the secondary transfer bias in this embodiment will be described. FIG. 7 is a flow chart showing an outline of the secondary transfer bias control procedure in this embodiment. The processing of S201 to S206 in FIG. 7 is the same as the processing of S101 to S106 in FIG. 5 in the first embodiment. However, in this embodiment, in S202, the control unit 150, based on the image information captured by the image input unit 203, divides video count information for each of the leading end side area A1 and each of the trailing end small areas A21 to A25. to get Further, in this embodiment, the control unit 150 determines in S203 whether or not the divided video count value of one or more (at least one) of the rear end small regions A21 to A25 is 80% or more. to decide. Then, if the control unit 150 determines in S203 that one or more of the trailing edge small areas A21 to A25 is 80% or more, the secondary transfer bias for the trailing edge area A2 is set as follows. It decides to correct (S204). That is, the secondary transfer bias determined by the ATVC control is corrected to 1.2 times based on Table 1 (same as in Example 1) (second mode). On the other hand, if the control unit 150 determines in S203 that none of the trailing edge small areas A21 to A25 is 80% or more (less than 80%), the secondary transfer bias for the trailing edge area A2 is determined. is not corrected (first mode).

In this embodiment, the secondary transfer bias for the trailing edge area A2 is corrected when the divided video count value of any one of the plurality of trailing edge small areas A21 to A25 is equal to or greater than a predetermined threshold value. . On the other hand, if the divided video count value of a predetermined plurality or more, for example, a majority (three or more in this embodiment) of the plurality of rear end small areas A21 to A25 is a predetermined threshold or more, The secondary transfer bias may be corrected for the edge area A2. In other words, if there are many trailing edge regions with a toner amount equal to or greater than a certain amount among the plurality of trailing edge regions, the secondary transfer bias for the trailing edge region is corrected, and if it is small, the correction is not performed. can. Further, the secondary transfer bias correction amount of the trailing edge area A2 (secondary transfer bias The amount by which the absolute value of is increased) may be changed. Typically, the larger the number of trailing edge areas having a threshold value or more, the larger the correction amount of the secondary transfer bias for the trailing edge area A2.

Further, based on the divided video count information of the plurality of trailing edge small areas A21 to A25 and the position information of the plurality of trailing edge small areas A21 to A25 in the direction substantially orthogonal to the conveying direction of the recording material P, the trailing Correction of the secondary transfer bias for the edge area A2 may be controlled. For example, the secondary transfer bias can be corrected if even one divided video count value is equal to or greater than a predetermined threshold value for the rear end small area in the center. On the other hand, for example, for the trailing edge small area on the edge side, the secondary transfer bias may not be corrected even if the divided video count value is equal to or greater than the predetermined threshold value. Alternatively, for the trailing end small area on the edge side, the secondary transfer bias may be corrected when the divided video count value of a predetermined plurality of small areas or more is equal to or greater than a predetermined threshold value. The mode of presence/absence of correction at the center and at the end may be reversed, and may be determined, for example, depending on how conspicuous the "rear edge scattering" is.

Further, as described in the first embodiment, a plurality of thresholds for the divided video count value can be set, and in any of the above cases, the absolute value of the secondary transfer bias can be changed in a plurality of steps. can be done.

As described above, in this embodiment, the obtaining unit 151 obtains the toner amount of the toner image transferred to each of the plurality of small areas obtained by dividing the second area A2 in the direction substantially perpendicular to the recording material conveying direction. Get correlated metric values. Then, the control unit 150 can selectively execute one mode out of a plurality of modes based on the index value for each of the plurality of small areas. In particular, in this embodiment, the control unit 150 executes the first mode when the index value is less than the predetermined threshold value for any of the plurality of small areas. On the other hand, the control unit 150 executes the second mode when the index value for at least one small area among the plurality of small areas is equal to or greater than a predetermined threshold. Alternatively, as described above, the control unit 150 can execute the first mode when the number of small regions whose index value is equal to or greater than a predetermined threshold among the plurality of small regions is less than a predetermined number. On the other hand, the control unit 150 can execute the second mode when the number of small areas whose index value is equal to or greater than the predetermined threshold among the plurality of small areas is equal to or greater than a predetermined number.

As described above, according to this embodiment, the toner density is locally high by correcting the transfer bias for the rear end region A2 based on the divided video count values of the plurality of rear end small regions A21 to A25. It is possible to suppress "rear end scattering" even in such cases.

[Example 3]
Another embodiment of the present invention will now be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Accordingly, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted. do.

1. Overview of this Embodiment “Trailing edge scattering” can be suppressed by increasing the absolute value of the secondary transfer bias in the trailing edge region. However, when the absolute value of the secondary transfer bias in the trailing edge region is increased, especially in the recording material P having high rigidity such as thick paper, there is a possibility that the missing transfer occurs. Description will be made with reference to FIG. FIG. 8 is a schematic cross-sectional view enlarging the vicinity of the secondary transfer portion T2. When the recording material P is thick paper or the like with high rigidity, a gap is likely to occur between the intermediate transfer belt 7 and the trailing end region of the recording material P at the upstream position B of the secondary transfer portion T2. In this case, if the absolute value of the secondary transfer bias is large, discharge occurs at the position B, and the charge of the toner image on the intermediate transfer belt 7 is lost, resulting in missing transfer. A halftone image with a smaller amount of toner is more susceptible to discharge than a solid image, and transfer omission is more noticeable.

Therefore, in the present embodiment, when the risk of "rear end transfer omission" is high according to the type of recording material P, correction (third mode) is performed to reduce the absolute value of the secondary transfer bias for the rear end region. . On the other hand, depending on the type of recording material P, when the risk of "rear end scattering" is high, correction (second mode) is performed to increase the absolute value of the secondary transfer bias.

2. Secondary Transfer Table In this embodiment, a secondary transfer table is set for each type of recording material P. FIG. Table 3 shows the secondary transfer table used by the image forming apparatus 100 of this embodiment under the environment of 23° C. temperature and 50% humidity. Plain paper is paper with a basis weight of about 75 gsm, and thick paper is paper with a basis weight of about 150 gsm and relatively high rigidity. In general, the higher the basis weight (or thickness) of paper, the higher the recording material apportionment voltage is set. In this embodiment, the recording material assigned voltage is set higher for thick paper than for plain paper.

3. Relationship Between Divided Video Count Value and Transfer Bias Table 4 shows correction coefficients (correction values) applied to the set voltage (Vout) of the secondary transfer bias determined by the ATVC control in this embodiment.

As shown in Table 4, in the present embodiment, the secondary transfer bias applied to the leading end side area A1 is under constant voltage control with the secondary transfer bias Vout determined by ATVC control. On the other hand, the secondary transfer bias applied to the trailing edge area A2 is changed according to the video count value of the image formed in the trailing edge area A2.

That is, with plain paper, when the video count value of the trailing edge area A2 is equal to or greater than a predetermined value, the absolute value of the secondary transfer bias applied to the trailing edge area A1 is higher than the absolute value of the secondary transfer bias applied to the trailing edge area A2. The absolute value of the next transfer bias is increased (second mode: right side of Table 4). Further, when the video count value in the trailing edge area A2 is less than the predetermined value, the secondary transfer bias applied to the leading edge side area A1 and the secondary transfer bias applied to the trailing edge area A2 are made equal. (first mode: left side of Table 4).

In other words, with plain paper, the following control is performed according to the video count value formed in the trailing edge area A2. That is, when the video count value is the same in the leading end region A1 and the trailing end region A2, the absolute value of the secondary transfer bias applied to the trailing end region A2 is higher than the absolute value of the secondary transfer bias applied to the leading end region A1. Increase the absolute value of the transfer bias. As a result, "rear end scattering" can be suppressed. That is, for plain paper, the first mode and the second mode are selectively executed based on the video count value of the trailing edge area.

On the other hand, for thick paper, when the video count value of the trailing edge area A2 is equal to or greater than a predetermined value, the absolute value of the secondary transfer bias applied to the trailing edge area A2 is set to the secondary transfer bias applied to the leading edge area A1. A first value smaller than the absolute value of the transfer bias is set (third mode: right side of the lower table of Table 4). Further, when the video count value in the trailing edge area A2 is less than the predetermined value, the following is performed. That is, the secondary transfer bias applied to the trailing edge region A2 is set to a second value that is smaller than the secondary transfer bias that is applied to the leading edge region A1 and smaller than the first value ( 3rd mode: Left side of the bottom table of Table 4).

In other words, in the case of thick paper, when the video count value is the same between the leading end region A1 and the trailing end region A2, the absolute value of the secondary transfer bias applied to the leading end region A1 is greater than the absolute value of the secondary transfer bias applied to the trailing end region A2. The absolute value of the applied secondary transfer bias is made smaller. As a result, it is possible to suppress the "rear end transfer omission".

"Rear end scattering" is an image defect in which toner scatters and stains a non-image area, and "transfer failure" is an image defect in which toner itself is not transferred. In the case of thick paper, in order to avoid transfer defects that result in loss of image information, countermeasures against "transfer defects" are prioritized over countermeasures against "rear end scattering". "Transfer missing" is more likely to be affected as the amount of toner decreases, so the lower the video count value of the trailing edge area A2, the larger the width (change amount) for reducing the absolute value of the secondary transfer bias. Note that when the video count value of the trailing edge area A2 is equal to or greater than a predetermined value and the "missing transfer" is within the allowable range, the secondary transfer bias applied to the leading edge side area A1 and the trailing edge area The secondary transfer bias applied to A2 may be the same (first mode). That is, for thick paper, the first mode and the third mode can be selectively executed based on the video count value of the trailing edge area.

4. Control Flow Next, the procedure for controlling the secondary transfer bias in this embodiment will be described. FIG. 9 is a flow chart showing an outline of the secondary transfer bias control procedure in this embodiment.

When a job is started by an operator operating the operation unit 201 or the like, the control unit 150 executes ATVC control (S301). Next, the control unit 150 acquires information on the type of recording material P used for image formation, and determines whether the recording material P is plain paper or thick paper (S302).

When the control unit 150 determines in S302 that the recording material P is plain paper, based on the image information captured by the image input unit 203, the control unit 150 divides the leading end area A1 and the trailing end area A2 into separate videos. Count information is acquired (S303). Next, the control unit 150 determines whether or not the divided video count value of the rear end area A2 is 80% or more (S304). If the controller 150 determines in S304 that it is 80% or more, the secondary transfer bias for the trailing edge region A2 is increased by 1.2 times the secondary transfer bias determined by ATVC control based on Table 4. A corrected secondary transfer bias is determined (second mode) (S305). On the other hand, if the controller 150 determines in S304 that it is not 80% or more (less than 80%), it does not correct the secondary transfer bias for the trailing edge area A2 (first mode).

If the control unit 150 determines in S302 that the recording material P is thick paper, the control unit 150 counts the divided video of each of the leading end region A1 and the trailing end region A2 based on the image information captured by the image input unit 203. Information is acquired (S306). Next, the control unit 150 determines whether or not the divided video count value of the rear end area A2 is 80% or more (S307). If the control unit 150 determines in S307 that the secondary transfer bias is 80% or more, the secondary transfer bias for the trailing edge region A2 is increased by 0.8 times the secondary transfer bias determined by ATVC control based on Table 4. A corrected secondary transfer bias is determined (third mode) (S308). On the other hand, if the controller 150 determines in S307 that it is not 80% or more (less than 80%), it determines to correct the secondary transfer bias for the trailing edge area A2 as follows ( S309). That is, the secondary transfer bias determined by ATVC control is corrected to 0.6 times based on Table 4 (third mode).

Then, the control unit 150 executes image formation using the secondary transfer bias set for each of the front end region A1 and the rear end region A2 (S310). Next, the control unit 150 determines whether or not all image formation of the job has been completed (S311). If the control unit 150 determines in S311 that the control unit 150 has not ended, the process returns to S302 to acquire information on the type of the recording material P related to the next image formation, acquire divided video count information, and obtain the secondary transfer bias. setting and image formation processing are repeated. Further, when the control unit 150 determines that the operation has ended in S311, the operation of the image forming apparatus 100 ends.

In this embodiment, in the case of a recording material P with high rigidity such as thick paper, if the divided video count value in the trailing edge region is less than a predetermined threshold value, the secondary transfer bias is higher than if it is equal to or greater than the predetermined threshold value. reduced the absolute value of On the other hand, when the divided video count value of the trailing end region is less than a predetermined threshold and is equal to or greater than another threshold smaller than the predetermined threshold (for example, 50% or more), the value is 2 more than the case of being equal to or greater than the predetermined threshold. The absolute value of the next transfer bias may be reduced. Further, as described above, when the divided video count value of the trailing edge region is equal to or greater than the predetermined threshold value, the correction to reduce the absolute value of the secondary transfer bias may not be performed (first mode).

Further, as described in the first embodiment, a plurality of threshold values for the divided video count value can be set. The absolute value of the transfer bias can be changed in multiple stages.

Further, as in the second embodiment, correction of the secondary transfer bias is controlled based on the divided video count value of each small area obtained by dividing the trailing edge area A2 into a plurality of small areas in the direction substantially orthogonal to the conveying direction of the recording material P. may In this case, for the recording material P with high rigidity such as thick paper, the secondary transfer bias when there are only areas less than the predetermined threshold among the plurality of trailing edge small areas is greater than when there are areas above the predetermined threshold. can reduce the absolute value of

Thus, in this embodiment, the multiple modes include the third mode. In this third mode, the transfer voltage applied to the transfer member 8 when the second area A2 passes through the transfer portion T2 is higher than the absolute value of the transfer voltage applied to the transfer member 8 when the first area A1 passes through the transfer portion T2. In this mode, the absolute value of the transfer voltage applied to is smaller. In this embodiment, the control unit 150 can selectively execute one mode out of a plurality of modes according to the type of the recording material P. FIG. In this embodiment, in the case of the first recording material, the first mode or the second mode is selectively executed based on the index value correlated with the toner amount of the toner image transferred to the second area A2. do. On the other hand, in the case of the second recording material having a basis weight larger than that of the first recording material, the first mode or the third mode is selectively executed based on the index value of the second area A2. Alternatively, in the case of the first recording material, the first mode or second mode may be selected based on the index value correlated with the toner amount of the toner image transferred to the second area A2. selectively execute On the other hand, in the case of the second recording material having a basis weight larger than that of the first recording material, the third mode is executed. When executing the third mode, the absolute value of the transfer voltage when the index value of the second area A2 is less than the predetermined threshold value is higher than the absolute value of the transfer voltage when the index value of the second area A2 is less than the predetermined threshold value. The absolute value of the transfer voltage can be made smaller.

As described above, according to the present embodiment, the secondary transfer bias is corrected based on the divided video count value of the trailing edge area A2 according to the type of recording material P, thereby preventing "trailing edge scattering" and It is possible to suppress "rear end transfer omission".

[others]
Although the present invention has been described with reference to specific examples, the present invention is not limited to the above-described examples.

For example, numerical values used for explanation in the above-described embodiments are examples, and the present invention is not limited to them.

Further, in the above-described embodiments, the image forming apparatus is configured such that information on the type of recording material is input from the operation unit or the host device. It may be configured to automatically determine the type of recording material.

Further, in the above-described embodiments, the present invention is applied to a color image forming apparatus, but the present invention can also be applied to a monochrome image forming apparatus, and the same effects as those of the above-described embodiments can be obtained.

7 intermediate transfer belt 8 secondary transfer roller 150 control unit D2 secondary transfer power supply

Claims (9)

an image carrier that carries a toner image;
a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion;
a power supply that applies a voltage to the transfer member;
When each of the first area, which is the image forming area of the recording material, and the second area, which is the image forming area of the recording material located on the rear end side of the first area, passes through the transfer unit, the Regardless of the first mode in which the transfer voltages applied to the transfer member are equal to each other and the amount of toner formed in the first region, the first mode is applied to the transfer member when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion is larger than the absolute value of the transfer voltage applied to the second region. a controller capable of selectively executing
an acquisition unit that acquires an index value related to the amount of toner formed in the second area;
has
The control unit is capable of selectively executing at least the first mode or the second mode based on the index value acquired by the acquisition unit . The first mode is executed when the index value is less than a predetermined threshold, and the second mode is executed when the index value related to the amount of toner formed in the second area is equal to or greater than the predetermined threshold. An image forming apparatus characterized by: an image carrier that carries a toner image;
a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion;
a power supply that applies a voltage to the transfer member;
When each of the first area, which is the image forming area of the recording material, and the second area, which is the image forming area of the recording material located on the rear end side of the first area, passes through the transfer unit, the Regardless of the first mode in which the transfer voltages applied to the transfer member are equal to each other and the amount of toner formed in the first region, the first mode is applied to the transfer member when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion is larger than the absolute value of the transfer voltage applied to the second region. a controller capable of selectively executing
an acquisition unit that acquires an index value related to the amount of toner formed in the second area;
has
The acquiring unit acquires an index value correlated with a toner amount of a toner image transferred to each of a plurality of small areas obtained by dividing the second area in a direction substantially perpendicular to a conveying direction of the recording material,
The control unit is capable of selectively executing at least the first mode or the second mode based on the index value for each of the plurality of small regions acquired by the acquisition unit. executing the first mode when the index value for any of the regions is less than a predetermined threshold, and when the index value for at least one of the plurality of small regions is greater than or equal to the predetermined threshold; and, executing the second mode. an image carrier that carries a toner image;
a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion;
a power supply that applies a voltage to the transfer member;
When each of the first area, which is the image forming area of the recording material, and the second area, which is the image forming area of the recording material located on the rear end side of the first area, passes through the transfer unit, the Regardless of the first mode in which the transfer voltages applied to the transfer member are equal to each other and the amount of toner formed in the first region, the first mode is applied to the transfer member when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion is larger than the absolute value of the transfer voltage applied to the second region. a controller capable of selectively executing
an acquisition unit that acquires an index value related to the amount of toner formed in the second area;
has
The acquiring unit acquires an index value correlated with a toner amount of a toner image transferred to each of a plurality of small areas obtained by dividing the second area in a direction substantially perpendicular to a conveying direction of the recording material,
The control unit is capable of selectively executing at least the first mode or the second mode based on the index value for each of the plurality of small regions acquired by the acquisition unit. executing the first mode when the number of small regions whose index value is equal to or greater than a predetermined threshold among the regions is less than a predetermined number; An image forming apparatus, wherein the second mode is executed when the number of small areas is equal to or greater than the predetermined number. an image carrier that carries a toner image;
a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a recording material at a transfer portion;
a power supply that applies a voltage to the transfer member;
When each of the first area, which is the image forming area of the recording material, and the second area, which is the image forming area of the recording material located on the rear end side of the first area, passes through the transfer unit, the Regardless of the first mode in which the transfer voltages applied to the transfer member are equal to each other and the amount of toner formed in the first region, the first mode is applied to the transfer member when the first region passes the transfer portion. a second mode in which the absolute value of the transfer voltage applied to the transfer member when the second region passes through the transfer portion is larger than the absolute value of the transfer voltage applied to the first region; Regardless of the amount of toner formed, the absolute value of the transfer voltage applied to the transfer member when the first area passes the transfer section is higher than the absolute value of the transfer voltage when the second area passes the transfer section. a third mode in which the absolute value of the transfer voltage applied to the transfer member is smaller;
an acquisition unit that acquires an index value related to the amount of toner formed in the second area;
has
The control unit is capable of selectively executing one of the plurality of modes according to the type of recording material, and based on the index value acquired by the acquisition unit, at least the first 1. An image forming apparatus capable of selectively executing the first mode or the second mode . The control unit
when the recording material is the first recording material, selectively executing the first mode or the second mode based on an index value correlated with the toner amount of the toner image transferred to the second area;
When the recording material is a second recording material having a basis weight larger than that of the first recording material, the first mode or 5. The image forming apparatus according to claim 4 , wherein said third mode is selectively executed. The control unit
when the recording material is the first recording material, selectively executing the first mode or the second mode based on an index value correlated with the toner amount of the toner image transferred to the second area;
when the recording material is a second recording material having a basis weight larger than that of the first recording material, executing the third mode;
When executing the third mode, when the index value relating to the amount of toner formed in the second area is equal to or greater than a predetermined threshold value, the second area is applied to the transfer member when the second area passes through the transfer unit. When the index value related to the amount of toner formed in the second area is less than the predetermined threshold value, the second area is applied to the transfer member when the second area passes through the transfer portion than the absolute value of the transfer voltage. 5. The image forming apparatus according to claim 4 , wherein the absolute value of the applied transfer voltage is made smaller. 7. The image forming apparatus according to claim 1 , wherein the image carrier is an endless belt. In the conveying direction of the recording material, the first area is an area extending from the leading end of the image forming area to a position a predetermined distance from the rear end of the image forming area toward the leading end, and the second area is the image forming area. 8. The image forming apparatus according to any one of claims 1 to 7 , wherein the area extends from the position at the predetermined distance from the rear end to the rear end of the image forming area. a divided video count unit that counts a video count value correlated with image density for each of a plurality of regions obtained by dividing an image forming region into a plurality of regions in a recording material conveying direction and a direction substantially perpendicular to the conveying direction;
The image forming apparatus according to any one of claims 1 to 8 , wherein the acquisition unit acquires the index value based on a count result of the divided video count unit.

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