JP2000039782A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of transfer property by reducing the effect of a current leaked between a contact transfer member and a discharge needle in the case that voltage Vto applied to a contact transfer member by an ATVC system is detected when a constant current is applied as for a contact transfer system image forming device, an ATVC system image forming device and a record medium discharge system image forming device by the discharge needle. SOLUTION: The constant current control of a transfer bias applying means is executed so that the current flowing to the contact transfer member of a transfer means becomes a previously set constant current value at timing that a transfer part is a non-image area and the voltage level of discharge bias applied to the discharge needle of a discharge means is low. Based on the voltage applied at this time, transfer bias with respect to the contact transfer member of the transfer means is decided. Then, a transfer feasible image is transferred on a record medium from an image carrier by applying the above mentioned decided transfer bias to the contact transfer member from the transfer bias applying means by a constant voltage control action when the transfer part is an image area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transfer means for transferring a transferable image formed and carried on an image carrier to a recording medium,
The present invention relates to a transfer type image forming apparatus, comprising: a recording medium discharging unit for separating a recording medium from the image carrier.

[0002]

2. Description of the Related Art A transferable image of image information, which is generally a toner image, is formed and carried on a surface of an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric by an appropriate image forming process. Transferable image forming apparatuses that transfer the transferable image to a recording medium such as paper, fix the image, output the image as a formed image (copy, print), and repeatedly use the image carrier for image formation have been widely used. Practical.

As a transfer means for transferring a toner image as a transferable image formed on an image carrier such as an electrophotographic photosensitive member to a recording medium such as paper, a contact means using a contact transfer member represented by a transfer roller is used. The transfer method of the system is widespread, and compared with the non-contact transfer method using a corona charger, there are advantages such as a smaller power supply capacity and a smaller amount of discharge products represented by ozone. is there.

A transfer roller as a contact transfer member is composed of, for example, a metal core and a medium-resistance elastic layer formed around the metal core, and has a predetermined resistance to the image carrier against the elasticity of the elastic layer. The transfer portion (transfer nip portion) is formed by pressing with the pressing force of the image bearing member, and rotates at a peripheral speed substantially equal to the rotational peripheral speed of the image carrier in the forward direction of the rotation of the image carrier.

[0005] The recording medium fed to the transfer site is conveyed while nipping the transfer site with its surface in close contact with the image carrier.
Further, during the period from when the leading end of the recording medium arrives at the transfer site to when the trailing end of the recording medium comes out of the transfer site, a transfer bias applying means (transfer output power supply device, transfer voltage generating power source, external A predetermined transfer bias (transfer voltage) is applied from a power supply.

[0006] In the process of nipping and transporting the recording medium between the transfer portions, the toner image on the image carrier is sequentially transferred to the recording medium by the action of the transfer electric field formed by the transfer roller and the pressing force at the transfer portion. It is transcribed.

The recording medium that has passed through the transfer portion is electrostatically attracted to the surface of the image carrier. Therefore, a static elimination needle as a recording medium static elimination means is disposed adjacent to the transfer roller on the recording medium exit side of the transfer part, and the static elimination needle electrostatically adsorbs to the surface of the image carrier through the transfer part. The recording medium is discharged and separated from the surface of the image bearing member, and is introduced into the next fixing unit. The static elimination needle is grounded, or a voltage having the same polarity as the charging polarity of the toner image (a polarity opposite to the transfer bias to the transfer roller) is applied.

In the contact transfer method, a transfer roller as a contact transfer member undergoes characteristic changes due to environmental changes and the like. Therefore, a general measure is to appropriately control the transfer voltage applied to the transfer roller in accordance with the characteristic change of the transfer roller. Can be

As one of the applied transfer voltage control methods, A
There is a TVC method (Auto Transfer Voltage Control).

The ATVC controls the transfer bias applying means so that the current flowing to the transfer roller becomes a preset constant current value Io at the timing when the transfer portion is in the non-image area (at the time of non-sheet passing). In the current mode, the applied voltage Vto at this time is detected.

The transfer voltage Vt is determined based on the detected voltage Vto.
To determine. For example, the transfer voltage Vt is calculated and determined by using a calculation formula of Vt = a × Vto + b [kV].

When the transfer area is in the image area (when the paper is passed)
In step (2), the transfer voltage Vt determined above is applied to the transfer roller under constant voltage control to transfer the toner image from the image carrier to the recording medium (constant voltage mode).

By determining the transfer voltage by such a method, the transfer voltage applied to the transfer roller can be appropriately controlled in accordance with the change in the characteristics of the contact transfer member regardless of the change in the characteristics of the transfer roller due to environmental changes or the like. As a result, good transferability can always be obtained.

Here, the timing when the transfer portion is in the non-image area is one timing after the drive of the image forming apparatus in the standby state is started based on the print start signal.
The timing of the image carrier non-image area (= non-sheet passing) at the transfer site during the so-called “pre-rotation” of the image forming apparatus until the leading end of the recording medium reaches the transfer site, or continuous feeding. In the paper print mode, in the non-image area of the image carrier at the transfer portion at the so-called "paper interval", which is the interval between the trailing edge of the recording medium and the leading edge of the next recording medium (= non-paper passing) Timing.

[0015]

As described above, the transfer means for transferring the transferable image on the image carrier to the recording medium, and the recording medium discharging means for separating the recording medium from the image carrier, as described above. Wherein the transfer means includes a contact transfer member that presses against the image carrier to form a transfer portion, and allows the recording medium to be introduced into and passed through the transfer portion, and from the transfer bias applying means to the contact transfer member. This is a contact transfer method in which a transfer bias is applied to transfer a transferable image formed on the image carrier to the recording medium side.The recording medium static elimination means includes a static elimination needle, and applies a static elimination bias to the static elimination needle from the static elimination bias applying means. In an image forming apparatus of a type that applies a voltage to a recording medium by applying a voltage, voltages having polarities different from each other are applied to the contact transfer member and the charge removing needle. Further, the contact transfer member and the static elimination needle are arranged close to each other.

As a result, a current leak occurs between the contact transfer member and the static elimination needle, and the
In the system, there is a problem that the applied voltage Vto when a constant current is applied to the contact transfer member fluctuates. If the applied voltage Vto in the ATVC system fluctuates due to current leakage, the transfer voltage Vt determined based on the voltage Vto also changes, causing a problem that transferability deteriorates.

Therefore, the present invention relates to a contact transfer method, ATVC
When the applied voltage Vto at the time of applying a constant current to the contact transfer member in the ATVC method is detected in the image forming apparatus of the recording medium charge elimination method using the charge elimination needle, the influence of the current leak between the contact transfer member and the charge elimination needle is considered. An object is to reduce the transferability by reducing the size.

[0018]

According to the present invention, there is provided an image forming apparatus having the following constitution.

(1) An image forming apparatus comprising: a transfer unit for transferring a transferable image on an image carrier to a recording medium; and a recording medium discharging unit for separating the recording medium from the image carrier. The transfer unit includes a contact transfer member that presses against the image carrier to form a transfer site, and guides the recording medium through the transfer site, applies a transfer bias to the contact transfer member from the transfer bias application unit, and applies a transfer bias to the image carrier. A transfer transfer image formed on the recording medium side, wherein the recording medium discharging unit includes a discharging needle, and applies a discharging bias to the discharging needle from the discharging bias applying unit to discharge the recording medium. The transfer bias of the transfer unit with respect to the contact transfer member is such that the transfer site is a non-image area, and the voltage level of the charge removal bias applied to the charge removal needle of the charge removal unit is The transfer bias applying means is controlled with a constant current so that the current flowing through the contact transfer member becomes a preset constant current value at the timing, and is determined based on the applied voltage at this time. An image forming apparatus, wherein a transferable image is transferred from an image bearing member side to a recording medium side by applying a determined transfer bias to a contact transfer member under constant voltage control from a transfer bias applying unit.

(2) The image forming apparatus according to (1), wherein the charge removing bias for the charge removing needle is a potential having a polarity opposite to that of the transfer bias for the contact transfer member.

(3) The image forming apparatus according to (1) or (2), wherein the level of the charge removing bias for the charge removing needle is controlled in two stages.

(4) The image forming apparatus according to (1) or (2), wherein the level of the charge removing bias for the charge removing needle is controlled in three stages.

(5) Charging means for uniformly charging the image carrier, image information writing means for forming an electrostatic latent image of image information on the charged image carrier, and static electricity formed on the image carrier. The image forming apparatus according to any one of (1) to (4), further including a developing unit configured to convert the latent image into a visible image, wherein a transferable image is formed on the image carrier.

(6) The image forming apparatus according to (5), wherein the electrostatic latent image is visualized by reversal development.

(7) The transferable image formed and carried on the image carrier is a toner image (1) to (6).
Any one of the image forming apparatuses.

<Operation> That is, according to the present invention, in an image forming apparatus of a contact transfer system, an ATVC system, and a recording medium neutralization system using a static elimination needle, an applied voltage Vto at the time of applying a constant current to a contact transfer member in the ATVC system. Since the detection timing is a timing at which the voltage level of the static elimination bias applied to the static elimination needle is low (including a timing when no voltage is applied to the static elimination needle), the applied voltage Vto when the constant current is applied to the contact transfer member is set. At the time of detection, it is possible to reduce the influence of current leak between the contact transfer member and the static elimination needle. That is, it is possible to reduce the fluctuation of the transfer voltage Vt caused by the current leak from the contact transfer member to the charge eliminating needle, and it is possible to suppress the deterioration of the transferability.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (FIGS. 1 to 3) FIG. 1 is a schematic structural diagram of an image forming apparatus according to this embodiment. The image forming apparatus of this embodiment is an apparatus of an electrophotographic process, a contact transfer method, an ATVC method, and a recording medium discharging method using a discharging needle.

(1) Overall Schematic Configuration of Image Forming Apparatus Reference numeral 101 denotes an electrophotographic photosensitive member as an image carrier, which is a rotating drum type having a photosensitive layer on its surface (hereinafter referred to as a photosensitive drum). The photosensitive drum 101 is driven to rotate in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed), and an image forming process is applied to the rotating photosensitive drum.

A. Charge: photosensitive drum 1 that is driven to rotate
01 has a predetermined polarity by the charging device 102
It is uniformly charged to a potential.

B. Exposure: Next, image exposure 103 is performed on the charged surface by image exposure means (not shown) such as a scanning exposure apparatus for image-modulated laser beam and a projection exposure apparatus for original images as image information writing means. Then, the charged potential of the light-exposed portion is attenuated, and an electrostatic latent image corresponding to the exposed image information is formed on the surface of the photosensitive drum.

C. Present image: The electrostatic latent image is
4 sequentially forms visible images as transferable toner images (developed images).

D. Transfer: The toner image is transferred to a recording sheet (transfer material) P as a recording medium by a transfer unit at a transfer portion T. The transfer unit in this example is a contact transfer type transfer unit using a roller-shaped contact transfer member 105 (hereinafter, referred to as a transfer roller).

The transfer roller 105 includes a metal core 105
a, and a conductive elastic layer formed in a roller shape around the cored bar. The photosensitive drum 101 is brought into pressure contact with a predetermined pressing force against the elasticity of the elastic layer to transfer the transfer portion T.
(A transfer nip portion, a pressure contact nip portion between the photosensitive drum and the transfer roller) is formed, and the photosensitive drum 101 rotates in the forward direction at substantially the same peripheral speed as the rotational speed of the photosensitive drum 101.

The recording paper P is fed from a feeding unit (not shown), passes through a registration roller / transfer guide (not shown) disposed in front of the transfer site T, and is transferred to the transfer site T at a predetermined control timing. Will be fed. The registration roller operates such that when the leading end of the toner image formed on the surface of the rotating photosensitive drum 101 reaches the transfer site T, the recording paper P is moved so that the leading end of the recording paper P just arrives at the transfer site T. To the transfer site T.

The recording paper P fed to the transfer site T is conveyed while nipping the transfer site T with its surface in close contact with the rotating photosensitive drum 101. Further, during a period from when the leading end of the recording paper P arrives at the transfer site T to when the trailing end of the recording paper P comes out of the transfer site T, the transfer roller 105 has a transfer power source 107 ( Transfer bias applying means)
A predetermined transfer voltage (potential having a polarity opposite to the charge polarity of the toner image) by the ATVC is applied to the recording paper P from the transfer portion T.
In the process of nipping and conveying, the rotating photosensitive drum 1
The toner image on the 01 side is sequentially transferred to the recording paper P by the action of the transfer electric field formed by the transfer roller 105 and the pressing force at the transfer portion T.

E. Separation: Recording paper P passing through transfer site T
Are electrostatically attracted to the surface of the photosensitive drum 101. Therefore,
A discharging needle 109 as a recording medium discharging unit is disposed adjacent to the transfer roller 105 on the recording paper exit side of the transfer portion T,
By removing the recording paper P electrostatically attracted to the surface of the photosensitive drum 101 through the transfer portion T by the discharging needle 109, separation of the recording paper P from the photosensitive drum 101 is promoted.

The top of the static elimination needle 109 is disposed slightly below the center of the transfer nip, and a predetermined static elimination needle voltage (a potential having a polarity opposite to the transfer voltage to the transfer roller 105) is applied to the static elimination needle 109. The static elimination needle voltage is
The voltage is supplied from a static elimination needle voltage power supply 108 (static elimination bias applying means).

F. Attachment: The recording paper P that has exited the transfer site T and has been separated from the surface of the photosensitive drum 101 is
The toner image transferred to the fixing device 111 is guided to the fixing device 111, and the transferred toner image is subjected to a fixing process as a permanent fixed image on a recording paper surface, and is discharged as an image formed product (copy, print).

G. Cleaning: After the recording paper is separated, the surface of the photosensitive drum 101 is cleaned by a cleaning device 112 after removing contaminants such as residual toner and paper dust.
It is repeatedly used for image formation.

As an image forming method, for example, a normal developing method in which a charged photosensitive member surface is exposed corresponding to a background portion of image information (background exposure method) and a portion other than the background portion is developed, and conversely, There is a reversal development system in which exposure is performed corresponding to the image information section (image exposure system) and a non-exposed portion is developed, and these are used taking advantage of their respective characteristics.

In the image forming apparatus of the present embodiment, the polarity of the charging process by the primary charging device 102 of the photosensitive drum 101 as the image carrier is negative. Toner development of the electrostatic latent image formed on the surface of the photosensitive drum 101 by the developing device 104 is a reversal developing method using negative polarity toner (negative toner) having the same polarity as the polarity of the charging process of the photosensitive drum 101. A thin layer of toner is coated on a developing sleeve rotatably attached to the developing device 104, and a predetermined developing bias is applied to the developing sleeve from an external power supply (developing voltage application power supply) (not shown). The upper toner is selectively transferred to the photosensitive drum 101 side corresponding to the electrostatic latent image, and the electrostatic latent image is reversely developed with the toner. The transfer voltage is a positive potential, and the neutralization voltage is a negative potential.

(2) ATVC, etc. FIG. 2 shows a circuit configuration of a transfer power supply 107 as a transfer bias applying unit in this embodiment.

The transfer power supply 107 supplies a constant voltage output control signal (C
VD) and a constant current drive signal (CCD), a central processing unit (CPU) 250 in the image forming apparatus.
Is controlled by

The constant voltage output control signal (CVD) is an analog control signal for controlling an output level in a constant voltage mode for applying an arbitrary voltage to the transfer roller 105. When the signal level voltage is increased, the output of the operational amplifier 201 increases, the transistor 204 is turned on, and a current flows through the primary winding (between-) of the transformer 210. As a result, a high voltage is generated in the secondary winding (between-), and the voltage of the transfer roller 105 increases via the transfer output terminal 217.

On the other hand, the transformer 210 is provided with a voltage detection winding (between-), and a voltage proportional to the voltage generated between the secondary windings is generated in this winding. The voltage between the voltage detection windings is determined by the diode 209 and the capacitor 20.
8 and the resistor 216 rectify the
1 is input to the negative input side. With this configuration, the transfer output is stabilized at a predetermined voltage corresponding to the level of the constant voltage output control signal (CVD), and constant voltage control of the transfer output is performed.

On the other hand, a constant current drive signal (CCD)
Is a control signal for driving in a constant current mode in which a preset constant current Io is applied to the transfer roller 105.

When the constant current drive signal (CCD) goes low, the transistor 214 turns off.

Since the reference voltage Ref1 is smaller than the reference voltage Ref2, the output voltage of the operational amplifier 202 increases, and the positive input of the operational amplifier 201 via the diode 203 increases. As a result, the voltage of the transfer output terminal 217 increases as in the case of driving in the constant voltage mode described above.

On the other hand, as the transfer output voltage increases, the transfer current flowing from the transfer output also increases, and the voltage on the positive input side of the operational amplifier 202 decreases due to the occurrence of a voltage drop across the resistor 213.

With such a configuration, the transfer current It of the transfer output is stabilized at the following value, and constant current control of the transfer output is performed.

It = (Ref2-Ref1) / R3 Further, the voltage detection signal (VDETECT) is
7 is an analog signal for detecting the applied voltage.

A series of control methods of the voltage applied to the transfer roller 105 and the static elimination needle 109 when the image forming apparatus of this embodiment performs continuous printing will be described with reference to a time chart (timing chart) of FIG.

First, the first recording paper P from the start of the recording operation
In the pre-rotation until the leading end of the transfer roller 1 reaches the transfer portion T, that is, in the sections (a) and (b), the constant current Io is applied to the transfer roller 105, and the detection of the voltage Vto applied at that time is performed. Do.

Here, the applied voltage Vto is equal to the voltage detection signal (V
DETECT) is sampled and detected by the CPU 250.

Subsequently, when the leading end of the first recording paper P1 reaches the transfer site T, a constant voltage Vt is applied to the transfer roller 105 to transfer the toner image from the photosensitive drum 101 to the recording paper P1. Let The constant voltage Vt is determined using the following formula.

Vt = aXVto + b where a and b are predetermined constants, and Vto is the applied voltage in the constant current mode detected earlier.

Subsequently, when the rear end of the first recording sheet P1 reaches the transfer portion T, the mode is switched to the constant current mode again. The driving with the constant current is performed until the leading end of the second recording paper P2 reaches the transfer site T, that is, the first recording paper P1
This is performed in the "paper interval", which is the interval between the rear end of the recording paper P2 and the front end of the second recording paper P2.

On the other hand, the static elimination needle voltage (static elimination bias) is shown in FIG.
As shown in (2), control is performed so that the recording paper is turned on when the rear end thereof approaches the transfer site T, and is turned off when the recording paper passes the transfer site T.

By controlling the static elimination needle voltage in this way, the separation of the recording paper from the photosensitive drum can be promoted without disturbing the toner image on the recording paper.

The ON / OFF timing of the voltage is set in consideration of the rising / falling time of the discharging bias.

Next, a method of controlling the transfer voltage for the second recording sheet P2 will be described.

The transfer voltage Vt for the second recording sheet P2
Is calculated and determined based on the applied voltage Vto between the first recording paper P1 and the second recording paper P2.

Here, the value of the voltage detection signal (VDETECT) is applied to the CPU 25 as in the case of the previous rotation.
Sampling is performed at 0, but the sampling timing of Vto starts after the static elimination needle voltage sufficiently falls. That is, the process is performed in the β section between the sections (d) to (e).

The transfer voltage Vt for the second recording sheet P2
Is the same as that for the first recording sheet P1.

The control method for the third and subsequent sheets of recording paper P3 is the same as the series of controls for the second sheet of recording paper P2.

As described above, the sampling of the applied voltage Vto in the constant current mode between sheets is performed at the timing when the static elimination needle voltage is turned off, so that the current leak from the transfer roller 105 to the static elimination needle 109 is small. Sometimes sampling is performed, the applied voltage Vto can be detected accurately, and deterioration of transferability can be suppressed.

<Second Embodiment> (FIGS. 4 and 5) In the first embodiment, the voltage level of the static elimination needle 109 is set to two.
The present invention relates to a step, that is, a transfer control method in the case where control is performed based on whether or not voltage is applied. On the other hand, in this embodiment,
The present invention relates to a transfer control method for controlling the voltage level of the static elimination needle 109 in three steps, that is, high level / low level / 0 level.

In the image forming apparatus of this embodiment, as shown in FIG. 4, a conductive member for attracting the recording paper P to a transport guide 110 for guiding the recording paper P from the transfer device 105 to the fixing device 111 is provided. 110a. By grounding the conductive member 110a, the positively charged recording paper after the transfer is attracted to the conveyance guide 110, and the conveyance stability can be improved.

However, the charge amount of the recording paper tends to change depending on the degree of moisture absorption of the recording paper. When the potential of the recording paper fluctuates greatly, the transportability of the recording paper becomes unstable. In order to prevent this, it is effective means to control the potential of the recording paper by applying a voltage to the static elimination needle 109.

FIG. 5 is a time chart of the voltage applied to the transfer roller 105 and the discharging needle 109 in the case of continuous printing.

When a voltage is applied to the discharging needle 109, a low-level voltage: Vd1 is applied from the front end portion to just before the rear end portion of the recording paper P, and the conveyance of the recording paper by the conveyance guide 110 is stabilized. Further, a high-level voltage Vd2 is applied to the rear end of the recording paper to promote separation of the recording paper P from the photosensitive drum 101.

Next, a method of controlling the transfer voltage will be described. The application timing of the transfer voltage is the same as that of the first embodiment, but the sampling timing of the applied voltage Vto at the time of the constant current between the sheets is different from that of the first embodiment.

That is, at the time when the trailing edge of the recording paper has passed the transfer portion T, the static elimination needle voltage switches from the high level Vd2 to the low level Vd1. Sampling of the transfer voltage Vto applied at the time of the constant current is performed after the static elimination needle voltage becomes a sufficiently low level Vd1. In FIG. 5, the processing is performed in the sections (i) to (j).

As described above, the sampling of the applied voltage Vto in the constant current mode between sheets is performed at the timing when the static elimination needle voltage is at a low level, so that the current from the transfer roller 105 to the static elimination needle 109 is adjusted. Since the sampling is performed when the leak is small, the detection of the applied voltage Vto can be performed accurately in the case of the present embodiment, similarly to the case of the first embodiment, and the deterioration of the transferability can be suppressed. Can be.

<Others> 1) The image carrier 101 is not limited to an electrophotographic photosensitive member, but may be an electrostatic recording dielectric, a magnetic recording magnetic material, or the like, and forms a transferable image on the image carrier. The principle and process are arbitrary.

The present invention is not limited to the drum type, but may be any type such as a belt type, a web type, and a sheet type.

2) The contact transfer member 105 is not limited to the roller type, but may be any type such as a belt type or a combination of a belt and an electrode blade.

3) The recording medium P may be an intermediate transfer member such as an intermediate transfer drum or an intermediate transfer belt.

4) ATVC between papers at the time of continuous printing may not be performed between all papers, but may be performed with predetermined thinning.

[0080]

As described above, according to the present invention, in an image forming apparatus of a contact transfer type, an ATVC type, or a recording medium neutralization type using a static elimination needle, a constant current is applied to a contact transfer member in the ATVC type. The timing of detecting the applied voltage Vto is a timing at which the voltage level of the discharging bias applied to the discharging needle is low (including a timing at which no voltage is applied to the discharging needle). When detecting the applied voltage Vto, the effect of current leakage between the contact transfer member and the charge eliminating needle can be reduced, and the fluctuation of the transfer voltage Vt caused by the current leak from the contact transfer member to the charge eliminating needle can be reduced. It is possible to suppress deterioration of transferability.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a circuit diagram of a transfer power supply.

FIG. 3 is a time chart of transfer output and static elimination output.

FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 5 is a time chart of the transfer output and the static elimination output in the second embodiment.

[Explanation of symbols]

 Reference Signs List 101 photosensitive drum (image carrier) 102 charging device 103 image exposure light 104 developing device 105 transfer roller (contact transfer device) 106 high voltage power supply 107 transfer power supply 108 static elimination needle voltage power source 109 static elimination needle 110 transport guide 111 fixing device 112 cleaning device T Transfer site (transfer nip) P Recording paper (recording medium)

Claims (7)

[Claims] 1. An image forming apparatus comprising: transfer means for transferring a transferable image on an image carrier onto a recording medium; and recording medium discharging means for separating a recording medium from the image carrier. The means includes a contact transfer member that presses against the image carrier to form a transfer site, and introduces and passes a recording medium through the transfer site, and applies a transfer bias to the contact transfer member from the transfer bias application unit to the image carrier side. A contact transfer method for transferring a transferable image to be formed on a recording medium side, wherein the recording medium discharging unit includes a discharging needle, and a discharging bias is applied to the discharging needle from the discharging bias applying unit to discharge the recording medium. The transfer bias of the transfer unit with respect to the contact transfer member,
The transfer bias is set so that the current flowing through the contact transfer member becomes a preset constant current value at the timing when the transfer portion is a non-image area and the voltage level of the charge removing bias applied to the charge removing needle of the charge removing unit is low. The application means is controlled at a constant current and determined based on the applied voltage at this time. When the transfer portion is in the image area, the transfer bias determined above is applied from the transfer bias application means to the contact transfer member under constant voltage control. An image forming apparatus wherein transfer of a transferable image from a carrier to a recording medium is performed. 2. The image forming apparatus according to claim 1, wherein the charge removing bias for the charge removing needle has a potential having a polarity opposite to that of the transfer bias for the contact transfer member. 3. The image forming apparatus according to claim 1, wherein a level of a charge removing bias for the charge removing needle is controlled in two stages. 4. The image forming apparatus according to claim 1, wherein a level of a charge removing bias for said charge removing needle is controlled in three stages. 5. A charging unit for uniformly charging an image carrier, an image information writing unit for forming an electrostatic latent image of image information on the charged image carrier, and an electrostatic unit formed on the image carrier. The image forming apparatus according to any one of claims 1 to 4, further comprising a developing unit configured to convert the latent image into a visible image, wherein a transferable image is formed on the image carrier. 6. The image forming apparatus according to claim 5, wherein the electrostatic latent image is visualized by reversal development. 7. The image forming apparatus according to claim 1, wherein the transferable image formed and carried on the image carrier is a toner image.