JPH07225521A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device capable of excellently holding a sheet on an endless transfer body without turning up the sheet by making the electrostatic charge quantity of a region corresponding to the edge part of the sheet in its transferring direction large than that of the other region, in the endless transfer body. CONSTITUTION:In the image forming device provided with the endless transfer body 21 electrostatically attracting the sheet on which an image is formed and simultaneously transferring the sheet in a prescribed direction, the endless transfer body 21 is provided with a carrying means carrying the sheet to the endless transfer body 21, an electrifying means 31 electrifying the endless transfer body 21 and an electrostatic charge quantity control means making the electrostatic charge quantity of the region corresponding to the edge part of the sheet larger than that of the other region in the endless transfer body 21. The body 21 whose electrostatic charge quantity is controlled by the electrostatic charge control means holds the edge part of the sheet in its transferring direction with electrostatic attracting force larger than that in the other region. Thus, even if the sheet passes through the curved parts of rollers 22 and 23, the leading edge of the sheet is never peeled and tuned up from the endless transfer body 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image on a sheet. For more details,
The present invention relates to an image forming apparatus including an endless transfer member.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus, an endless transfer member such as an endless transfer belt or a cylindrical transfer drum is provided, and the transfer member holding a sheet on its outer peripheral surface is rotated by the number of colors to be transferred. It is known that a multicolor image is formed by superposing different color toners on a sheet for each rotation. As a method of holding a sheet on this endless transfer member, a method of charging the surface of the endless transfer member and holding the sheet on the surface of the endless transfer member by electrostatic attraction is known.

[0003]

However, the endless transfer member has a thick paper or a sheet for an overhead projector (hereinafter,
It is referred to as an OHP sheet. ), Etc., if the endless transfer member has a large curvature, the leading end or the rear end of the sheet will be peeled off from the endless transfer member and turned up, and the sheet cannot be held well. There is a problem.

If an endless transfer member having a large diameter (small curvature) is used, even a strong sheet can be satisfactorily held, but the space for installing the endless transfer member becomes large, and thus the apparatus itself. It becomes large.

[0005]

It is therefore an object of the present invention to provide an image forming apparatus in which an endless transfer member can satisfactorily hold a sheet without causing the sheet to be turned up.

[0006]

In order to solve the above-mentioned problems, an image forming apparatus according to a first aspect of the present invention comprises a conveying means for conveying a sheet to an endless transfer body, and a charging means for charging the endless transfer body. An image forming apparatus including: a charge amount control unit that makes a charge amount of an area of the endless transfer member corresponding to a sheet end portion in a sheet transport direction larger than a charge amount of other areas.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the charge amount control means includes a changing means for changing a potential supplied to the charging means.

An image forming apparatus according to a third aspect is the image forming apparatus according to the first aspect, wherein the charge amount control means includes an insulating film adhered onto the endless transfer member.

An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the first aspect, wherein the endless transfer member is an endless belt wound around a plurality of rollers.

[0010]

According to the image forming apparatus of the first aspect, the endless transfer member whose charge amount is controlled by the charge amount control means is
The end portion of the sheet in the sheet transfer direction is held by an electrostatic attraction force larger than other areas.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a schematic structure of a multicolor copying machine, and FIG. 2 is a perspective view showing a structure of a transfer belt 21. The photoconductor 1 is an endless belt having a photosensitive layer on the outer peripheral surface thereof, and a rotation detection sensor 2 including a pulse encoder
It is wound around the roller 3 and the rollers 4 and 5, and is configured to move in the arrow a direction based on the rotation of the roller 3. A charger 6, a developing device 7, a cleaning device 8 and an eraser lamp 9 are arranged around the photoconductor 1. The developing device 7 includes four developing devices 7.
1, 72, 73, and 74, and the developing devices 71, 72, 73, and 74 contain developer of yellow, magenta, cyan, and black colors, respectively, and are in a developing state and a non-developing state. It can be switched.

The image reading device 10 has an opening / closing cover 11 on the upper side.
It is placed below the platen glass 12 covered with
A document illumination lamp 13 is configured to move in the direction of arrow b while illuminating a document (not shown) placed on the platen glass 12. Further, the reflected light from the document is read by the line sensor 16 via the mirror system 14 and the lens system 15 as color signals of the three primary colors, and the signals of the respective colors are output to the image processing circuit 17.

The image exposure device 18 is provided with a laser emitting device 19, emits a laser beam 20 based on the output from the image processing circuit 17, and emits the laser beam 20 between the charger 6 and the developing device 7. To expose the outer peripheral surface of the photoreceptor 1.

The transfer belt 21, which is an endless transfer member, is wound around a drive roller 22 and a driven roller 23 disposed below the drive roller 22, and the tension of the belt can be adjusted by a tension roller 24. The transfer belt 21 includes a PVDF insulating layer (thickness: 30 μm, thickness: 150 μm, volume resistivity: 10 ⁸ Ω · cm) formed by dispersing carbon in polyvinylidene fluoride (PVDF), which is a fluororesin.
[mu] m, a volume resistivity of 10 ^{1 5} Ω · cm or more) are stacked 2
The belt has a layered structure, and the insulating layer constitutes the outer peripheral surface.

Inside the transfer belt 21, the transfer roller 2 is supported so as to move back and forth toward the drive roller 3.
5 is arranged, and the transfer belt 21 is moved toward and away from the photoconductor 1 by moving the transfer roller 25 forward and backward. Further, inside the transfer belt 21, a position detection sensor 26 and a transfer roller 25 are provided near the tension roller 24.
A sheet detection sensor 28 is provided below the sheet. Further, as is apparent from FIG. 2, the transfer belt 21 is provided with a small window 82, and the position detection sensor 26 and the sheet detection sensor 28 detect the position of the transfer belt by detecting the small window 82.

On the other hand, below the transfer roller 25, there is provided an assist roller pair 29 made of a conductive material such as metal for adhering the sheet to the outer peripheral surface of the transfer belt 21. The illustrated bias power supply is connected. Further, on the outside of the transfer belt 21, a belt cleaner 30 and a charging charger 31 facing the belt portion wound around the driven roller 23, a charge eliminating charger 32 facing the belt portion passing through the facing portion of the photoconductor 1,
Separation claws 33 are provided to contact and separate from the belt portion wound around the drive roller 22.

The paper feeding device 34 includes three paper feeding units 35, 36,
37 is provided, and the sheets accommodated in these paper feeding units 35, 36, and 37 are selectively supplied. The selection of the paper feed unit is designated by a paper feed unit selection switch (not shown) on the operation panel 103 (see FIG. 3). Paper feeder 3
The sheets supplied from Nos. 5, 36, and 37 are brought into contact with the timing roller 38 and temporarily stopped, and are synchronized with the transfer belt 21 so that the leading edge of the sheet is electrostatically attracted onto the area 81 (see FIG. 2). And is supplied to the transfer belt 21. Here, the area 81 of the transfer belt 21 is an area that generates a stronger electrostatic attraction force than the other areas.

The fixing device 39 and the discharge roller 40 are arranged above the transfer belt 21, and the sheet on which the toner image is fixed after passing through the fixing device 39 is discharged to the discharge tray 41 by the discharge roller 40. Is configured to.

The overall operation of the above multicolor copying machine will be briefly described. A document (not shown) is placed on the document table glass 12, and a document cover 11 is placed over the document. Next, when a print switch (not shown) on the operation panel 103 is turned on, in the image reading device 10, the document illumination lamp 1
3 illuminates the document while moving in the direction of arrow b, and the reflected light is incident on the line sensor 16 via the mirror system 14 and the lens system 15, and the line sensor 16 produces blue,
It is read as color signals of three primary colors of red and green. The color signals are processed by the image processing circuit 17 such that yellow, magenta, cyan,
It is converted into a black four-valued signal, and the output signal is output to the image exposure device 18.

In the image exposure device 18, the laser beam 20 corresponding to the yellow image is first emitted onto the photoconductor 1 based on the output signal, and when it is finished, the laser beam 20 corresponding to the magenta image is emitted. Then, after that, the laser beam 20 corresponding to the cyan image is emitted, and finally the laser beam 20 corresponding to the black image is emitted. The emission timing of each laser beam 20 will be described later.

The photoconductor 1 moves in the direction of arrow a based on the rotation of the roller 3, and the photoconductor layer on the outer periphery is charged with a predetermined electric potential at the facing portion of the charging charger 6 to be charged. The charged photoreceptor 1 is irradiated with the laser light 20 emitted from the image exposure device 18, and electrostatic latent images of different colors are sequentially formed on the outer peripheral surface. The electrostatic latent images of the respective colors are then visualized as toner images by the developing devices 71, 72, 73 and 74 having the developers of the corresponding colors.

The transfer belt 21 moves in the direction of arrow c based on the rotation of the driving roller 22 started by the ON signal of the print switch, and after the surface is cleaned by the belt cleaner 30, it is charged to a predetermined potential by the charging charger 31. To be done. This charge control will be described later. A predetermined voltage is supplied to the assist roller 29 from a bias power source. On the other hand, the paper feed unit 35, 36 or 37
The sheet sent from the sheet is sent to the transfer belt 21 via the timing roller 38, electrostatically adsorbed on the outer peripheral surface of the transfer belt 21, and further securely held by passing between the pair of assist rollers 29.

The sheet held on the transfer belt 21 is conveyed in the direction of arrow c as the transfer belt 21 moves,
When the small window 82 on the transfer belt 21 is detected by the sensor 28, the transfer roller 25 moves to the right side in the drawing to bring the transfer belt 21 into contact with the photoconductor 1. Then, the sheet is conveyed to a position where the transfer roller 25 and the photoconductor 1 come into contact with each other via the transfer belt 21 (hereinafter, referred to as “transfer position 42”), and a yellow toner image on the photoconductor 1 is formed on the sheet. Transcribed. The sheet onto which the yellow toner image has been transferred is repeatedly conveyed to the transfer position 42 with the magenta, cyan, and black toner images, respectively, and these toner images are superimposed.

The sheets to which the toner images of all the colors have been transferred are separated from the transfer belt 21 by the separating claws 33 after the electrostatic attraction force is weakened by the charge eliminating charger 32, and the toner images are heated and fixed by the fixing device 39. After being discharged, the sheet is discharged onto the sheet discharge tray 41 by the sheet discharge roller 40. On the other hand, the outer peripheral surface of the photoconductor 1 from which the toner image is deprived at the transfer position 42 is cleaned by the cleaning device 8, and then the residual charge is erased by the eraser lamp 9.

In the multicolor copying machine constructed and operated as described above, the operation of each part thereof is specifically controlled by the microprocessor. FIG. 3 is a block diagram showing the control circuit of the multicolor copying machine of this embodiment.

A microprocessor (hereinafter referred to as MPU) 100 is a ROM 101 in which a program is stored.
And a RAM 102 as a work area.
The input / output interface of the MPU 100 includes the image reading device 10, the image exposure device 18, and the operation panel 10.
3, other devices, various sensors are connected. Here, other devices include a motor (not shown) that drives the roller 3, developing units 71 to 74, a motor (not shown) that drives the drive roller 22, a fixing device 39, and the like. Further, the various sensors include a position detection sensor 26, a sheet detection sensor 28, a temperature sensor (not shown) of the fixing device, and the like.

The control contents executed by the MPU 100 will be described with reference to FIGS. FIG. 4 is a main routine showing the control contents of the multicolor copying machine. When the power switch and reset switch (not shown) are turned on, the MPU1
When 00 is reset, the program starts, and in step S1, the RAM is cleared and various registers are initialized. Next, in step S2, the internal timer is started. This internal timer determines the time required for one routine, and its value is previously set in step S1.
Set by default. Then, steps S3 to S5.
In step S10, each subroutine is called, and when the call is completed, the internal timer is awaited and the process returns to step S2. In the subroutine of step S3, a process of reading input signals from various switches and various sensors is performed, and in the subroutine of step S4, the operation panel 103 is used.
A process of outputting a signal or the like necessary for controlling the upper display element (not shown) is performed. Further, in the subroutine of step S5, various processes related to the copying operation are performed. Less than,
The copy operation process of step S5 will be described in detail.

FIG. 5 is a flow chart showing a subroutine of the copying operation process of step S5. First, in step S501, it is determined whether or not a print switch (not shown) has been pressed. If not, the process returns to step S10 of the main routine without performing the subsequent processing. The ON signal of the print switch is output in step S512 described later.
It is held until reset by. When the print switch is pressed, the image reading process subroutine is called in step S502. In the image reading process subroutine, a process of instructing the image reading device 10 to read the document image is performed. Here, if the reading of the original image has already started, the specific processing in the subroutine of the image reading processing is not performed, and the process proceeds to the next step S503.

Next, after waiting for the completion of reading the original image by the image reading device 10 (step S503), the transfer belt 2
It is determined whether or not the position detection sensor 26 has detected the small window 82 above 1 (step S504). When the small window 82 is detected, the color status CS is incremented. The color status CS indicates what color image forming process is currently being performed, and is set to 0 at the time of initialization. That is, the color status CS is incremented each time the transfer belt 21 makes one rotation, and as will be apparent from the following description, in the multicolor copying machine of this embodiment, the timing of image formation for each color and the sheet. The feeding timing to the transfer belt 21 is controlled based on the detection timing of the small window 82.

Next, in step S506, the setting value of the color status CS is determined. If the setting value is 1 to 4, the subroutines of steps S507 to S510 are sequentially called, and when the call is completed, this subroutine is exited. The procedure returns to step S10 of the main routine. Incidentally, step S5
In the other processes of 10, the driving of the photoconductor 1 and the transfer belt 21, the operation control of the charging charger 6, the developing device 7, the cleaning device 8 and the eraser lamp 9 are performed in response to the turning on of the print switch. Further, for example, when the color status CS is 4, the process of separating the sheet on which the transfer of the four color toner images has been completed from the transfer belt 21, the sheet separated from the transfer belt 21 is fixed by the fixing device 3
9. Processing for discharging the sheet to the sheet discharge tray 41 through the sheet discharge roller 40 is performed. On the other hand, if it is determined in step S506 that the setting value of the color status CS is not 1 to 4, a process of resetting the color status CS to 0 is performed in step S511, and an ON signal of the print switch in step S512. Is reset.

FIG. 6 is a flow chart showing a subroutine of the timing roller control of step S507.
This timing roller control subroutine is performed by the paper feeding unit 3
Sheets fed from 5, 36 and 37 and the transfer belt 21
This is a step of performing a process for synchronizing with, that is, a process required only when the color status CS is 1. Therefore, first, in step S571, the setting value of the color status CS is determined, and if the setting value is not 1, this subroutine is exited. If the color status CS is 1, the setting value of the timing status TS1 is determined in step S572, and the processing according to the setting value is performed.
The timing status TS1 is set to 1 at the time of initialization. Therefore, first, the processing of the timing status TS = 1 (steps S573-1, S573-2).
Is executed.

In the processing of the timing status TS1 = 1, the timer t11 for synchronizing the transfer belt 21 and the sheet is set, and then the timing status TS1 is incremented. The processing of the timing status TS1 = 1 is performed immediately after the color status CS is set to 1. In other words,
The timer t11 is set by the small window 8 by the position detection sensor 26.
2 in response to the detection.

In the process of timing status TS = 2 (steps S574-1 to S574-4), the timing roller 38 is turned on, the timing status TS1 is incremented, and the timer t12 is set after the timer t11 is finished. . Here, the timer t12 is for measuring the timing of stopping the timing roller 38, and is appropriately set according to the length of the sheet.

In the processing of the timing status TS1 = 3 (steps S575-1 to S575-3), the timer t1
After the end of 2, the timing roller 38 is turned off and the timing status TS1 is reset to the initial value 1.

FIG. 7 is a flow chart showing the steps of the exposure control in step S508. In the exposure control subroutine, the transfer belt 21 starts writing the latent images of yellow, magenta, cyan, and black on the photoconductor 1.
And synchronize. Therefore, in step S581, it is determined whether or not the small window 82 is detected by the position detection sensor 26, and if there is no detection, the process exits without executing the process. Here, it is assumed that the small window detection signal is held for a predetermined time (specifically, a timer t2 set time which will be described later) from the actual detection. When the small window 82 is detected, the timing status TS2 is detected in step S582.
The setting value of is determined, and the process according to the setting value is performed. This timing status TS2 is 1 at the time of initialization.
Therefore, first, the processing of timing status TS2 = 1 (steps S583-1, S583-
2) is performed.

In the processing of the timing status TS2 = 1, the timer t2 is set and the timing status TS2
An increment of 2 is performed. The timer t2 is for synchronizing the timing of writing the latent image on the photoconductor with the sheet on the transfer belt 21.

In the processing of timing status TS2 = 2 (steps S584-1 to S584-3), the timer t2
The exposure is started after waiting for the end of, and then the timing status TS2 is reset to 1. In step S584-2, if the color status CS is set to 1, exposure corresponding to the yellow data is started. Similarly, if the color status CS is 2, 3, or 4, magenta, cyan, and The exposure according to the black data is started.

FIG. 8 is a flow chart showing the contents of the transfer belt charging control in step 509.

In this subroutine, a process of charging the transfer belt 21 and holding the sheet fed through the timing roller 38 on the transfer belt 21 by electrostatic attraction is performed. That is, in this process, the color status CS is 1
This is a necessary process only when Therefore, first, in step S591, it is determined whether or not the color status CS is 1, and if it is not 1, this subroutine is terminated without performing the subsequent processing. Color status CS is 1
If it is, the setting value of the timing status TS3 is determined in step S592, and the processing according to this setting value is performed. This timing status TS3 is set to 1 at the time of initialization. Therefore, first, the processing of timing status TS3 = 1 (steps S593-1, S
593-2) is executed.

In the processing of the timing status TS3 = 1, the timer t3 for synchronizing the portion of the transfer belt 21 to be charged by the charging charger 31 and the sheet.
1 is set, and then the timing status TS3 is incremented.

In the processing of the timing status TS3 = 2 (steps S594-1 to S594-4), the timer t3
After the end of 1, the timer t32 is set, the charging with the charging potential V1 is started, and the timing status TS3 is incremented.

In the process of timing status TS3 = 3 (steps S595-1 to S595-4), the timer t3
After the end of 2, the timer t33 is set, the charging potential is switched from V1 to V2, and the timing status TS3 is incremented.

In the processing of timing status TS3 = 4 (steps S596-1 to S596-3), the timer t3
After the end of 3, the charging charger 31 is turned off and the timing status TS3 is reset.

The charging potential V1 is preferably 2600.
(V) to 4100 (V), and the corresponding area 81 of the transfer belt 21 is 2400 (V) to 380.
It is charged to 0 (V). The charging potential V2 is preferably selected from the range of 800 (V) to 2300 (V), and the corresponding area of the transfer belt 21 is 600 (V) to 200.
It is charged to 0 (V). Charging potential V in the above embodiment
1 is 3400 (V), V2 is 1800 (V), and the transfer belt 21 is 3000 due to this potential.
It is charged to (V) and 1500 (V). Further, a bias potential of −1000 (V) is applied to the assist roller 29, and the sheet supplied to the transfer belt 21 is reliably held on the transfer belt 21. However, the present invention is not limited to the above range.

As is clear from the above description, the charging char
The timers t31 to t33 are set so that the jar 31 charges the transfer belt 21 at the high charging potential V1 for a certain period (during the operation period of the timer t32) and then at the low charging potential V2 (during the operation period of the timer t33). To be done. As a result, the transfer belt 21 is charged with the charging potential V1 and a region 81 having a strong electrostatic attraction is formed. On the other hand, the area charged with the charging potential V2 generates a smaller electrostatic attraction force than the area 81. Therefore, the electrostatic attraction force at the leading edge of the sheet becomes stronger than the electrostatic attraction force at other regions. By doing so, even when the sheet passes through the curved portions of the rollers 22 and 23, that is, a portion having a large curvature, the leading edge of the sheet is not peeled off from the transfer belt and turned up. It should be noted that the attraction of the sheet with a strong electrostatic attraction force causes the deterioration of the image quality, but in the present embodiment, only the edge portion of the sheet has a large electrostatic attraction force and the image quality is deteriorated outside the edge portion. There is no particular problem because they are held by the electrostatic attraction force of the extent that they do not exist. It is more preferable to use the edge of the sheet as a margin so that an image is not formed.

In the above embodiment, the operation of holding only one sheet on the transfer belt 21 has been described, but it is also possible to hold a plurality of sheets on the transfer belt 21 at the same time. A plurality of regions 81 having a strong electrostatic attraction force may be formed.

As a means for making the electrostatic attraction force at the edge of the sheet stronger than the electrostatic attraction force at other regions, the above-mentioned charging chargter is used.
Instead of controlling the output of the charger 31, the output of the charging charger 31 may be kept constant and the bias potential of the assist roller 29 may be controlled. Specifically, a constant potential of 3400 (V) is supplied to the charging charger 31,
For the assist roller 29, -100 is applied to the area 81.
A potential of 0 (V) may be supplied, and a potential of 0 (V) may be supplied to the other regions. Further, as another means for making the electrostatic attraction force at the sheet end portion stronger than the electrostatic attraction force at other regions, it is effective to increase the thickness of the insulating layer itself of the transfer belt only at the region 81. is there. It is considered that this is because the dielectric constant of the region 81 was improved by increasing the thickness of the insulating layer. In this transfer belt, the electrostatic attraction force becomes strong in the area 81 without controlling the charging charger 31 and the assist roller 29 as described above.

The number of sheets held on the transfer belt,
Alternatively, the location of the area 81 may be switched according to the sheet size. However, in this case, the area 8 is controlled by the bias control by the above-mentioned charging charger and assist roller.
1 is formed.

Further, the charging potential may be controlled only when a strong sheet is used.

As an example, as a means for making a part on the transfer body a region having a stronger electrostatic attraction than other parts,
(1) The output of the charger 31 is kept constant for a short period of time.
It is described that (2) the bias voltage applied to the assist roller pair 29 is changed for a certain period (short period), and (3) the thickness of the insulating layer of the transfer belt is partially increased. As an insulating tape on the transfer belt, for example, polyethylene terephthalate (PET),
A tape made of polyimide or tetrafluoroethylene (both having a volume resistivity of 10 ¹⁵ Ω · cm or more) may be attached to the region 81. It is considered that this is because the same phenomenon as in the case where the insulating layer of the transfer belt 21 is thickened by applying the insulating tape is caused.

If a photosensor of the reflection type is used as the sensor 26 for detecting the position of the transfer belt 21 and the insulating tape has a light reflection characteristic different from that of the transfer belt 21, the insulating tape is used. The position of the transfer belt 21 may be detected by detecting the reflected light. In this case, it is naturally unnecessary to provide the transfer window 21 with the small window 82.

As is clear from the above description, according to the image forming apparatus of the embodiment, since the electrostatic attraction force at the leading end of the sheet is stronger than that at the rear part, even if the endless transfer member has a portion having a large curvature, the sheet is There is no curling up. Therefore,
The shape of the endless transfer member can be freely set, the space in the image forming apparatus can be effectively used, and the size of the apparatus can be reduced.

In the above-described embodiment, the example in which the area 81 corresponding to the leading end of the sheet is charged to a higher surface potential than the other areas has been described. However, the amount of charge in the area corresponding to the trailing end of the sheet is increased. By doing so, it is possible to prevent the rear end of the seat from being turned up.

[0055]

As is apparent from the above description, claim 1
According to the invention, the endless transfer member whose charge amount is controlled by the charging both control means does not cause the other end of the sheet to be turned up in the sheet transfer direction, and the endless transfer member holds the sheet well. It is possible to provide an image forming apparatus that can do this.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of a multicolor copying machine.

FIG. 2 is a perspective view showing a transfer belt 21 (endless transfer member).

FIG. 3 is a block diagram showing a control circuit of the multicolor copying machine.

FIG. 4 is a main routine showing the control contents of the multicolor copying machine.

FIG. 5 is a subroutine showing the contents of the copy operation process of step S5.

FIG. 6 is a subroutine showing the content of the timing roller control in step S507.

FIG. 7 is a subroutine showing the contents of exposure control in step S508.

FIG. 8 is a subroutine showing contents of transfer belt control in step S509.

[Explanation of symbols]

 21: transfer belt 22: drive roller 23: driven roller 26: position detection sensor 29: assist roller 31: charging charger 34: sheet feeding device 38: timing roller 81: area corresponding to sheet leading end 82: small window 100: micro Processor 101: ROM 102: RAM

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor, Hoichi Sano 2-3-13 Azuchi-cho, Chuo-ku, Osaka, Osaka International Building Minolta Co., Ltd. (72) Inventor, Masahiko Matsuura 2-chome, Azuchi-cho, Chuo-ku, Osaka No. 13 Osaka International Building Minolta Co., Ltd. (72) Hiroyuki Yamazaki Inventor Hiroyuki Yamazaki 2-33 Azuchi-cho, Chuo-ku, Osaka City Osaka International Building Minolta Co. (72) Inventor Rinsei Izumi Two Azuchi-cho, Chuo-ku, Osaka 3-13-3 Osaka International Building Minolta Co., Ltd. (72) Inventor Masami Yamada 2-33-1 Azuchi-cho, Chuo-ku, Osaka City Osaka International Building Minolta Co., Ltd.

Claims (4)

[Claims] 1. An image forming apparatus including an endless transfer member that electrostatically adsorbs a sheet on which an image is formed and transfers the sheet in a predetermined direction, and a conveying unit that conveys the sheet to the endless transfer member. A charging unit configured to charge the endless transfer member, and a charging amount control unit configured to make a charging amount of a region of the endless transfer member corresponding to a sheet end portion in a sheet transport direction larger than a charging amount of another region. An image forming apparatus characterized by the above. 2. The image forming apparatus according to claim 1, wherein the charge amount control unit includes a changing unit that changes a potential supplied to the charging unit. 3. The image forming apparatus according to claim 1, wherein the charge amount control unit includes an insulating film adhered on the endless transfer member. 4. The image forming apparatus according to claim 1, wherein the endless transfer member is an endless belt wound around a plurality of rollers.