JPH11149220A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus capable of preventing occurrence of transfer failure in both low humidity and high humidity environments. [Structure] A photosensitive drum (image carrier) on which a visible image is formed
3, a transfer charger (transfer unit) 24 for transferring the visible image of the photosensitive drum 3 to the recording material P, and a transfer belt (recording material carrier) 130 that carries and transports the recording material P
A recording material P provided near the transfer portion on the downstream side in the recording material conveyance direction at the transfer portion in non-contact with the transfer belt 130;
Static elimination needle (static elimination means) for eliminating static electricity from the transfer belt 130
0, the current value flowing into the static elimination needle 70 is controlled by continuously moving the static elimination needle 70 between the first position and the second position.

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 such as a copying machine, a facsimile, and a printer for obtaining a hard copy by forming an image on a recording material using an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, a color image is formed by forming a plurality of image forming units, forming toner images of different colors in each image forming unit, and transferring the toner images sequentially overlaid on the same recording material. Various image forming apparatuses have been proposed. Under such circumstances, a multicolor electrophotographic color copying machine using an endless recording material carrying member is used for high-speed recording.

Here, an example of a color electrophotographic recording apparatus will be outlined with reference to FIG.

FIG. 1 is a sectional view of a color electrophotographic recording apparatus. First, second, third and fourth image forming sections Pa, Pb, Pc and Pd are provided in a main body of the color electrophotographic recording apparatus.
Are formed in parallel, and toner images of different colors are formed in each of the image forming portions Pa to Pd through a latent image, a development process, and a transfer process.

[0005] Each of the image forming units Pa to Pd is provided with an electrophotographic photosensitive drum 3a, 3
b, 3c, and 3d, and a toner image of each color is formed on each of the photosensitive drums 3a to 3d.

A transfer belt 130 as a recording material carrier is provided adjacent to each of the photosensitive drums 3a to 3d.
The toner images of the respective colors formed on the photosensitive drums 3a to 3d are transferred onto the recording material P carried and conveyed on the transfer belt 130. The recording material P to which the toner images of the respective colors have been transferred is heated and pressed by the fixing device 9 to fix the toner image, and then is discharged out of the device as a recorded image.

Incidentally, exposure lamps 111a, 111b, 111c, and 111 are provided on the outer periphery of the photosensitive drums 3a to 3d.
d, drum chargers 2a, 2b, 2c, 2d, potential sensors 113a, 113b, 113c, 113d, developing device 1
a, 1b, 1c, 1a, transfer chargers 24a, 24b, 2
4c, 24d and cleaners 4a, 4b, 4c, 4d are provided, respectively, and a light source device and a polygon mirror 117 (not shown) are installed above the device.

The polygon mirror 117 is rotated to scan the laser light emitted from the light source device, and the light beam of the scanned light is deflected by the reflection mirror, and is deflected by the fθ lens on the generatrix of each of the photosensitive drums 3a to 3d. The latent image is formed on each of the photosensitive drums 3a to 3d according to the image signal.

By the way, each of the developing units 1a to 1d has:
A predetermined amount of toner of cyan, magenta, yellow, and black is filled by a supply device (not shown) as a developer. The developing devices 1a to 1d develop the latent images on the photosensitive drums 3a to 3d, respectively, and visualize the latent images as a cyan toner image, a magenta toner image, a yellow toner image, and a black toner image.

On the other hand, the recording material P is accommodated in a recording material cassette 10 and is supplied from there to a transfer belt 130 via a plurality of conveyance rollers and registration rollers 12, and is conveyed by the transfer belt 130 to each of the photosensitive drums 3a to 3d. The sheets are sequentially sent to the opposite transfer unit.

The transfer belt 130 is made of a dielectric resin sheet such as a polyethylene terephthalate resin (PET resin) sheet, a polyvinylidene fluoride resin sheet, a polyurethane resin sheet, and the both ends thereof are overlapped and joined. Then, it is formed into an endless shape or a seamless (seamless) belt shape.

When the transfer belt 130 is rotated by the driving roller 13 and it is confirmed that the recording material P is at a predetermined position, the recording material P is moved to the registration roller 12.
Is transferred to the transfer belt 130, and the recording material P is conveyed toward the transfer unit of the first image forming unit Pa. At the same time, the image writing signal is turned ON, and an image is formed on the photosensitive drum 3a of the first image forming unit Pa at a predetermined timing based on the signal.

The transfer charger 24a applies an electric field or electric charge at the lower transfer portion of the photosensitive drum 3a, so that the first color toner image formed on the photosensitive drum 3a is transferred onto the recording material P. Is done. By this transfer, the recording material P is securely held on the transfer belt 130 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter.

The transfer chargers 24a to 24d include:
A non-contact charger such as a corona discharger or a contact charger using a transfer charging member such as a blade, a roller, or a brush is used. The non-contact charger generates ozone and is charged via air, so that it is vulnerable to changes in the temperature and humidity environment of the atmosphere, and has a problem that an image cannot be stably formed. On the other hand, the contact charger has advantages such as being ozone-less, resistant to environmental changes in temperature and humidity, and capable of obtaining high image quality.

The second to fourth image forming units Pb to Pd
Is performed in the same manner as in the first image forming unit Pa.

The recording material P to which the four color toner images have been transferred is neutralized by the separation charger 32 at the downstream portion of the transfer belt 130 in the transport direction, and the electrostatic attraction force is attenuated.
The transfer belt 130 is separated from the end. The drive roller 13 is normally grounded for stable separation. Since the separation charger 32 charges the recording material P in a state where the toner image is not fixed, a non-contact charger is used for this.

The recording material P detached from the transfer belt 130
Is transported to the fixing device 9 by the transport unit 62.

The fixing device 9 includes a fixing roller 51 and a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning the respective rollers, and roller heaters 56 and 57 installed in the rollers 51 and 52. An application roller 50 for applying a release agent oil such as dimethyl silicone oil to the fixing roller 51; an oil reservoir 53; and a thermistor 58 for detecting the temperature of the surface of the pressure roller 52 and controlling the fixing temperature. ing.

In the recording material P on which the four color toner images have been transferred, the toner images are mixed and fixed by fixing.
The sheet is discharged to the sheet discharge tray 63 as a full-color copy.

Incidentally, the photosensitive drums 3a to 3d after the transfer are completed.
Are removed and cleaned by the cleaners 4a to 4d to prepare for the formation of the next latent image. Further, the toner and other foreign matters remaining on the transfer belt 130 are wiped off by bringing the cleaning web (nonwoven fabric) 19 into contact with the surface of the transfer belt 130.

As described above, the transfer belt 130 used in the image forming apparatus having the above configuration
It is composed of a dielectric sheet such as an ET sheet, a polyvinylidene fluoride sheet, and a polyurethane sheet, and its volume resistance is generally 10 ¹³ to 10 ¹⁸ Ωcm.

In the transfer chargers 24a to 24d, it is known that an image is stabilized when the current contributing at the time of transfer is fixed at an appropriate current.

Therefore, when the volume reduction efficiency of the transfer belt 130 changes depending on the type (thickness, material, etc.) of the recording material, moisture absorption conditions, and the like, it is common to perform constant current control so as to obtain a constant current. In this case, several kV to several tens kV are applied as the transfer voltage.

In an image forming apparatus that performs multiple transfer, a higher voltage is required at each transfer stage than at the time of the previous transfer, and particularly at the last transfer, the transfer voltage is considerably higher than at the time of the first transfer. The recording material having received the transfer of the toner image at such a high pressure in the transfer unit is separated from the image carrier, and is conveyed downstream while maintaining the charged state by the transfer.

However, during transport of the recording material, electric charges on the recording material and the metal near the transfer nip and near the image carrier leak, or the toner scatters due to the potential difference between the toner and the metal, and the degree is severe. There has been a problem that an image defect of a polka dot pattern sometimes occurs.

The above-mentioned image defects may be caused by a recording material having a high resistance due to being left in a particularly low humidity environment (for example, a temperature of 23 ° C. and a humidity of 5% RH), or a recording material after the transfer process is completed once, such as a double-sided mode. This occurs remarkably at the time of transfer to the second surface or the like after the resistance is increased by thermal drying after passing through the heat fixing device once or immediately after the transfer.

Therefore, in order to suppress the occurrence of the above-described image defects, as shown in FIG. 1, a conductive member (hereinafter, referred to as a ground) is provided downstream of each transfer portion below the transfer belt 130.
Excess charges on the recording material P and the transfer belt 130 are eliminated by providing the static elimination needles 70a, 70b, 70c, and 70d to prevent the recording material P and the transfer belt 130 from being excessively charged.

[0028]

However, although the static elimination needles 70a to 70d exhibit their effects in a low humidity environment,
The following problems are caused in a high humidity environment.

For example, when forming an image on a recording material P whose resistance has been reduced by leaving it in a high humidity environment, the static elimination needles 70a to 70a
0d, transfer chargers 24a to 24d, and photosensitive drums 3a to 3d
When the transfer belt 130 and the recording material P close to d are at the positions shown in FIG. 2, if the resistance of the recording material P is reduced due to various conditions, a remarkable transfer failure as described below occurs.

That is, the toner image developed on the photosensitive drums 3a to 3d is not well transferred to the recording material P (phenomenon 1), or the toner image once transferred to the recording material P is Problems such as transfer to the drums (3b to 3d) again (phenomenon 2) occur. Generally, the low volume efficiency of the recording material P is about 2 × 1 depending on the type of the recording material P and the moisture absorption conditions.
0 ⁷ changes to ~4 × 10 ¹⁴ Ωcm.

The above phenomenon will be described with reference to FIGS.

During formation of an image on the recording material P with reduced resistance, when the recording material P is at the position shown in FIG. 2, the entire system is replaced with an electric circuit (equivalent circuit) as shown in FIG. You can think. At this time, static elimination needles 70a-7
When the electric field between 0d and the back surface of the transfer belt 130 reaches the dielectric breakdown voltage, the charge pairs accumulated on the transfer belt 130 are released. The positive charge on the back surface of the transfer belt 130 is
The recording material P moves to the ground through a to 70d, and the negative charge on the surface of the recording material P moves to the transfer portion. At this time, the current Ia indicates a case where the negative charge on the surface of the recording material P becomes a part of the transfer current, and causes the phenomenon 1. The current Ib is a case where the negative charges on the surface of the recording material P flow to the ground through the photosensitive drums 3a to 3d, and cause the phenomenon 2. When the transfer is performed on the recording material P via the transfer belt 130, the transfer voltage becomes a high voltage of several kV to several tens of kV due to the resistance of the transfer belt 130 itself, so that the above phenomena 1 and 2 also appear remarkably.

As described above, when an image is formed on a low-resistance recording material, the above-described transfer failure occurs due to the presence of the static elimination needle.

The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of preventing occurrence of transfer failure in both low and high humidity environments. .

[0035]

According to a first aspect of the present invention, there is provided an image bearing member on which a visible image is formed, and a method for transferring the visible image of the image bearing member onto a recording material. Transfer means, a recording material carrier for carrying and transporting the recording material, and a recording unit provided near the transfer unit on the downstream side in the recording material transport direction in the transfer unit without contacting the recording material carrier. In an image forming apparatus including a material and a static eliminator for eliminating a recording material carrier, a current value flowing into the static eliminator is controlled.

According to a second aspect of the present invention, in the first aspect of the present invention, the static eliminator is configured to move continuously between a first position and a second position.

According to a third aspect of the present invention, in the first aspect of the present invention, the static elimination means is grounded via a variable resistor.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the static elimination means is grounded via a power supply.

[0039]

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

<Embodiment 1> FIG. 1 is a sectional view of an image forming apparatus (color electrophotographic recording apparatus) according to the present invention.
In the following description, the same members as those described above are denoted by the same reference numerals.

As a dielectric sheet material for the transfer belt 130, PET, polyacetal, polyamide, polyvinyl alcohol, polyether ketone, polystyrene,
Polybutylene terephthalate, polymethylpentene, polypropylene, polyethylene, polyphenylene sulfide, polyurethane, silicone resin, polyamide imide,
Polycarbonate, polyphenylene oxide, polyether sulfone, polysulfone, aromatic polyester,
Engineered plastic film-shaped sheets such as polyetherimide and aromatic polyimide are generally used. This embodiment is made of polyimide resin in view of mechanical properties, electrical properties, flame retardancy, etc., and has a volume resistance of 10 ¹⁶ Ωc.
m, a seamless type having a thickness of 100 μm was used.

The process speed is 100 mm / s.

The transfer charger 24 (24a to 24d) is formed of a rectangular plate-like conductive rubber extending in a direction (thrust direction) orthogonal to the recording material conveyance direction. The plate-like conductive rubber is transferred to the photosensitive drum 3 via the transfer belt 130.
a, 3b, 3c, and 3d. By the transfer charger 24 (24a to 24d), the recording material P conveyed to the transfer portion is charged from the rear surface side with the opposite polarity (positive in the present embodiment) to the toner, so that the surfaces of the photosensitive drums 3a to 3d are charged. Side toner image is recording material P
Is electrostatically transferred to the surface of the substrate. In this embodiment, constant current control is performed, and the transfer current is set to 10 μA.

The separation charging unit 32 is disposed at the uppermost downstream of the transfer belt 130 (ie, above the drive roller 13 of the transfer belt 130), and has a discharge wire. The discharge wire is stretched in the thrust direction, and a predetermined tension is applied to the discharge wire by providing a spring at one end of the discharge wire. The power supply to the discharge wire is performed from a main body side connector via a power supply terminal, a power supply pin, and a spring (not shown). The drive roller 13 is connected to the main body ground, and also functions as a corresponding electrode of the discharge wire. In this embodiment, the distance between the transfer charger 24d and the separation charging unit 32 is 50 mm, and an AC voltage of 10 kVpp is applied to the separation charging unit 32.

By the way, the static elimination needle 7 in the present embodiment
0a to 70d are FIGS. 4 (a) and 4 (b) ((a) is a side view,
As shown in (b) is a front view), it is made of saw-toothed stainless steel metal and is grounded to the main body. The static elimination needle 70
Details of the installation state of a to 70d are shown in FIG.

Under this condition, the discharge starting voltage is determined according to the Paschen rule depending on the distance between the transfer belt 130 and the charge eliminating needles 70a to 70d. That is, if the distance between the transfer belt 130 and the static elimination needles 70a to 70d is short, the static elimination needles 70a to 70d
The current flowing to 70d increases, and vice versa.
For example, a high temperature and high humidity environment (temperature 30 ° C., humidity 80% RH,
At an absolute water content of 21.6 g / kg), the basis weight is 64 g.
/ M ² , when the image is formed on the recording material P, when the distance a between the transfer belt 130 and the tip of the charge eliminating needle 70 (70a to 70d) shown in FIG. 5 is 5 mm, the current flowing through each of the charge eliminating needles 70a to 70d is: Although the transfer current is 90% or more, the distance a is 1
If it exceeds 5 mm, it will be 5% or less.

On the other hand, the recording material P conditioned in a low-humidity environment and the recording material P conditioned in a high-humidity environment change in volume and efficiency by about seven digits at the maximum. In the equivalent circuit diagram shown in FIG. 3, the value of Rp changes. Therefore, the resistance of the recording material P changes depending on the installation environment of the image forming apparatus, the storage environment of the recording material P, and the like.
The current Ia flowing through 70d also changes accordingly.

Further, the recording material P used in the image forming apparatus generally covers a wide variety of paper, such as plain paper and OHT, and the volume reduction efficiency also changes greatly in accordance with the variety. Therefore, the current Ia flowing into the static elimination needles 70a to 70d also changes according to the type of the recording material P for the above reason. For example, in a high-temperature and high-humidity environment (temperature 30 ° C., humidity 80% RH, absolute water content 21.6 g / k)
g), the transfer belt 130 and the static elimination needle 7 shown in FIG.
0 (70a to 70d) When the distance a from the leading end is 10 mm, when an image is formed on a recording material P having a basis weight of 64 g / m ² , the current Ia flowing through each of the static elimination needles 70a to 70d is 5% or less of the transfer current. However, if the recording material P is made to be OHT under the same conditions, the volume low efficiency of OHT is as high as about the 16th power, so that the HV output shown in FIG. And accordingly the static elimination needle 70
The inflow current Ia to a to 70a is 30% or more of the transfer current.

The basis weight of plain paper is about 50 g / m ² -20
The recording material is as wide as 0 g / m ^2, and generally the thicker the recording material having a larger basis weight. Therefore, when an image is formed on a recording material P having a large basis weight, the actual resistance in the direction perpendicular to the paper surface becomes large, so that the HV output shown in FIG. 3 increases to perform constant current control. Since the resistance of the recording material P in the vicinity of the needles 70a to 70d, that is, Rp shown in FIG. 3, becomes small, the current Ia flowing into the static elimination needles 70a to 70d increases, and a transfer failure occurs.

Therefore, in the present embodiment, the static elimination needle 70a
To 70d are measured at any time, and the positions of the static elimination needles 70a to 70d are moved from the first position to the second positions in accordance with the information.
The above object has been achieved by continuously changing the current to the position shown in FIG. 3 and controlling the current Ia flowing into the static elimination needles 70a to 70d. The current Ia flowing into the static elimination needles 70a to 70d is 1% of the transfer current.
It is desirable to control it to at least 10%. Further, the static elimination needle moving device according to the present embodiment always operates from the start to the end of the image forming operation.

FIG. 6 shows a static elimination needle moving device according to this embodiment.

The static elimination needle moving device according to the present embodiment includes a forward / reverse rotation motor 71a such as a pulse motor, a pinion gear 71b provided on the shaft thereof, and static elimination needles 70 (70a to 70a).
The pinion gear 71b and the gear 71c are meshed with each other, including a vertical gear 71c provided on the 0d) side. The forward / reverse rotation motor 71 is controlled by the motor control circuit 71d.
When the rotation angle of a is controlled in the normal / reverse direction, the static elimination needle 70 (70a to 70d) moves up and down and moves up and down.

In this embodiment, the static elimination needle 70 (70a
To 70d) as a signal S1 to the CPU 90, which is the main control circuit, and the static elimination needle 70 (70a to 70d).
Motor control circuit 71d based on signal S1 so that the amount of current flowing into d) is 1% or more and less than 10% of the transfer current.
Is controlled. FIGS. 6 and 7 show how the neutralization needle 70 (70a to 70d) takes the first position (FIG. 6) and the second position (FIG. 7) by the forward / reverse rotation motor 71a. Note that the measured discharge needle inflow current is negative or already 1% to 10% of the transfer current.
If it is less than the position, the position of the static elimination needle 70 (70a to 70d) is stored as it is.

The signal S1 is not limited to the needle removal current input current.
It is an absolute water content of the environment in which the image forming apparatus is installed or the storage environment of the recording material P obtained from the temperature and humidity sensor, or an electrical characteristic signal of the recording material P measured before the recording material P enters the transfer section. Even in such a case, the CPU 90 determines that the motor control circuit 71d based on the signal S1 so that the amount of current flowing into the charge eliminating needle 70 (70a to 70d) is 1% or more and less than 10% of the transfer current. Controlled.

The installation environment of the image forming apparatus is determined from the absolute moisture content of the installation environment obtained by the temperature and humidity detecting means, and the electrical characteristics of the recording material P are determined before the recording material P enters the transfer section. Can be obtained by measuring the volume low efficiency and thickness.

An example of controlling the position of the static elimination needle based on the absolute water content in the environment in which the image forming apparatus is installed or the environment in which the recording material is stored will be described below.

Normal temperature and low humidity environment (temperature 23 ° C., humidity 5% R
(H, absolute water content 0.5 g / kg), in this embodiment, the distance a is set to 10 mm and this position is set as the first position so that the excess charge of the transfer belt 130 can be removed.

High temperature and high humidity environment (temperature 30 ° C., humidity 80% R
H, an absolute water content of 21.6 g / kg), the current flowing into the static elimination needle increases, so in the present embodiment, the distance a = 15 m
m, and this position is a second position. In the present embodiment, a static elimination needle 70 (70a) is provided between the first position and the second position.
70d) can be controlled by a forward / reverse rotation motor 71a such as a pulse motor under the conditions shown in Table 1.

[0059] Note that the area between the first position and the second position may be divided into any number of steps as long as the number of steps is two or more. In detecting the atmospheric temperature and humidity, the operator or service person may input the temperature and humidity from the operation unit or the like.

The type of the recording material P may be automatically determined by using a mechanical sensor or an optical sensor, and an appropriate volume reduction efficiency and thickness according to the type may be used as the input signal S1.
The type of the recording material P may be determined by the operator, and the operator may specify the type from the operation unit or the like.

In the present embodiment, the discharging needle inflow current is defined as a range for obtaining a stable transfer image from 1% to less than 10% of the transfer current. However, if a stable transfer image is obtained, the discharging needle inflow current may be set. Is not limited to this range, and
The amount of current flowing into the static elimination needle may be set to an appropriate value as the limit value.

As the transfer chargers 24a to 24d, a corona charger, a conductive elastic roller, a brush, or the like may be used as the transfer charging member, and the same effect as described above was obtained. Also, transfer belt 1
Not only the transfer drum 30 but also a transfer drum may be used. Not only the transfer to the recording material P, but also the transfer from the photosensitive drums 3a to 3d to the intermediate transfer member or the transfer from the intermediate transfer member to the recording material P There may be.

The possible first and second positions of the charge eliminating needles 70 (70a to 70d) do not have to be aligned in a direction perpendicular to the recording material conveyance direction. Even when the static elimination needle 70 (70a to 70d) continuously moves between the positions, the static elimination needle 70 (70a to 70d) does not need to move in a straight line connecting the first position and the second position. .

The image bearing member as a member to be charged is not limited to the electrophotographic photosensitive member, but may be a dielectric in electrostatic recording.

As a method of developing an electrostatic latent image on an image carrier, generally, a non-magnetic toner is coated on a sleeve with a blade or the like, and a magnetic toner is coated by a magnetic force and conveyed. A one-component non-contact developing method for developing in a non-contact state with a body, a one-component contact developing method for developing in a state in contact with an image carrier, and developing a mixture of toner particles and a magnetic carrier. Two-component contact developer method in which a developer is transported by magnetic force using the developer and developed in a state of contact with an image carrier, and two-component non-contact development in which the two-component developer is developed in a non-contact state The methods are roughly divided into four types. In the present invention, any of these developing methods may be used. The two-component contact developing method is often used from the viewpoints of high image quality and high stability.

<Second Embodiment> Next, a second embodiment of the present invention will be described.

As described above, the current flowing into the static elimination needle greatly changes depending on the installation environment of the image forming apparatus, the storage environment of the recording material, the electrical characteristics of the recording material, and the like. In the first embodiment, the position of the static elimination needle 70 (70a to 70d) is controlled to control the inflow current of the static elimination needle 70. However, in the present embodiment, the static elimination needle 70 (70a to 70d) is connected to the variable resistor 100.
, And the resistance value is changed according to the situation to control the current flowing into the static elimination needle.

FIG. 8 shows the configuration of the present embodiment.

The current flowing into the static elimination needle is measured at any time by current measuring means 80 such as a current probe, and the information is transferred to a CPU 90 as a control device. The CPU 90 determines that the measured discharge needle inflow current is a percentage of the transfer current (10 μA).
It is determined whether the current flowing into the static elimination needle is 1% or more of the transfer current.
The variable resistance value is controlled by the variable resistor 100 until the value becomes less than%. As a result, the current flowing into the static elimination needle is always stable,
A good transfer image can be obtained. Note that the variable resistance value is kept as it is until the measured discharge needle inflow current is negative or has already become 1% or more and less than 10% of the transfer current.

Third Embodiment Next, a third embodiment of the present invention will be described.

As described above, the current flowing into the static elimination needle greatly changes depending on the installation environment of the image forming apparatus, the storage environment of the recording material, the electrical characteristics of the recording material, and the like. In the first embodiment, by controlling the position of the static elimination needle 70 (70a to 70d), in the second embodiment, the static elimination needle 70 (70a to 70d) is controlled.
70d) is grounded via the variable resistor 100 to control the inflow current of the static elimination needle, respectively, but in the present embodiment, the static elimination needle 70 (70a to 70d) is grounded via the power supply 110 to thereby eliminate the static elimination needle. The inflow current is controlled.

FIG. 9 shows the configuration of the present embodiment.

The current flowing into the static elimination needle is measured at any time by current measuring means 80 such as a current probe, and the information is transferred to the CPU 90 as a control device. The CPU 90 determines what percentage of the measured discharging needle inflow current is the transfer current (10 μA), and determines whether the discharging needle inflow current is 1% to 10% of the transfer current.
The output of the power supply 110 is controlled until it becomes less than. As a result, the discharging needle inflow current is always stable, and a good transfer image can be obtained. It should be noted that the power supply 11 is used until the measured discharge needle inflow current is negative or has already become 1% or more and less than 10% of the transfer current.
The output value of 0 is stored as it is.

[0074]

As is apparent from the above description, according to the present invention, an image bearing member on which a visible image is formed, and a transfer means for transferring the visible image of the image bearing member onto a recording material. A recording material carrier that carries and conveys the recording material, and a recording material and a recording material that are provided near the transfer portion on the downstream side in the recording material conveyance direction at the transfer portion without contact with the recording material carrier. In the image forming apparatus provided with a static elimination unit for static elimination of the carrier, since the current value flowing into the static elimination unit is controlled,
The effect is obtained that the occurrence of transfer failure can be prevented in both low-humidity and high-humidity environments.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an image forming apparatus (color electrophotographic recording apparatus) according to the present invention.

FIG. 2 is a cross-sectional view of an image forming unit of the image forming apparatus.

FIG. 3 is an equivalent circuit diagram of a transfer unit during image formation.

FIG. 4 is a configuration diagram of a static elimination needle.

FIG. 5 is a cross-sectional view of the image forming unit showing a state where the static elimination needle is placed at the first position in the image forming apparatus according to Embodiment 1 of the present invention;

FIG. 6 is a cross-sectional view of the image forming unit showing a state where the static elimination needle is placed at a first position in the image forming apparatus according to Embodiment 1 of the present invention;

FIG. 7 is a cross-sectional view of the image forming unit showing a state where the static elimination needle is placed at the second position in the image forming apparatus according to Embodiment 1 of the present invention;

FIG. 8 is a sectional view of an image forming unit of the image forming apparatus according to Embodiment 2 of the present invention.

FIG. 9 is a sectional view of an image forming unit of the image forming apparatus according to Embodiment 3 of the present invention.

[Explanation of symbols]

 3a-3d Photosensitive drum (image carrier) 24a-24d Transfer charger (transfer means) 70a-70d Static elimination needle (static elimination means) 71a Forward / reverse rotation motor (static elimination needle moving device) 71b Pinion gear (static elimination needle moving device) 71c Gear ( 71d Motor control circuit (static elimination needle moving device) 80 Current measuring means 90 CPU 100 Variable resistor 110 Power supply 130 Transfer belt (recording material carrier) P recording material

Claims (4)

[Claims] An image carrier on which a visible image is formed; a transfer unit for transferring the visible image of the image carrier to a recording material;
A recording material carrier for supporting the recording material and transporting the recording material, and a recording material and a recording material carrier provided near the transfer portion on the downstream side in the recording material transport direction in the transfer portion without contacting the recording material carrier. An image forming apparatus comprising: a static eliminator for removing electricity from a body, wherein the value of a current flowing into the static eliminator is controlled. 2. The image forming apparatus according to claim 1, wherein said static eliminator is configured to move continuously between a first position and a second position. 3. An image forming apparatus according to claim 1, wherein said static eliminator is grounded via a variable resistor. 4. The image forming apparatus according to claim 1, wherein said static eliminator is grounded via a power supply.