JP2002156842A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which obtains a satisfactory transfer ability for a transfer material of any size in any circumstance and obtains a satisfactory image free from a transfer defect such as explosive or scattering independently of the supply paper width. SOLUTION: The image forming device has a transfer roll 2 of a contact type electrifying means, and a transfer bias is applied from a power source 4 to the transfer roll 2 to transfer a toner image on a photosensitive drum 1 to a transfer material P supplied to a transfer part. The power source 4 is a constant current and constant voltage power source controlled by a CPU 9, and the transfer bias is controlled to a constant current of 3.5 μA in the case of (the length in the lengthwise direction of the transfer roll (312 mm)-(the width of the transfer material)<=40 mm and is controlled to a constant voltage (ATVC control) in the other case that the length in the lengthwise direction of the transfer roll (312 mm)-(the width of the transfer material)>40 mm in accordance with the supply paper width in the direction orthogonal to the supply direction of the transfer material P, which is detected by a width detection means 10.

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 or a printer using an electrophotographic system, and more particularly to a transfer control thereof.

[0002]

2. Description of the Related Art An image bearing member and a transfer means (transfer member) pressed against the image carrier are provided. A transfer material is passed through a transfer portion formed between the two, and a transfer bias is applied to the transfer member. An image forming apparatus for transferring a toner image formed on an image carrier to a transfer material is known and has been put to practical use. FIG. 5 is a sectional view showing a typical example of such an image forming apparatus.

As shown in FIG. 5, an image forming apparatus includes a drum-shaped photosensitive member having an axis perpendicular to the paper surface as an image carrier,
That is, the photosensitive drum 1 includes a photosensitive drum 1 having a diameter of, for example, 30 mm.
It is rotationally driven at a peripheral speed (process speed) of / sec.
In the rotation process, the surface of the photosensitive drum 1 is uniformly set to a potential VD = -700 by a charging roller 3 having an outer diameter of 12 mm to which a primary charging bias is applied from a charging / transfer power supply (high-voltage power supply) 8.
After being charged to V, the exposure device 5 performs image exposure using a laser beam modulated with image information, and the exposed portion on the surface of the photosensitive drum 1 is attenuated to a potential VL = −150 V, so that the surface has image information. A corresponding electrostatic latent image is formed.

Then, toner is adhered to the latent image on the photosensitive drum 1 by a developing device 6, and the latent image is developed as a toner image. The toner image formed on the photosensitive drum 1 has a diameter of 18.1 which is a transfer member as the photosensitive drum 1 rotates.
The 0 mm transfer roller 2 is moved to the transfer site where it abuts,
At the same time, the transfer material P is supplied to the transfer portion via the transport path 7, and a transfer bias is applied to the transfer roller 2 from the power supply 8, so that a charge of the opposite polarity to the toner is applied to the back surface of the transfer material P. Thereby, the toner image on the photosensitive drum 1 is transferred onto the transfer material P.

After the transfer of the toner image, the photosensitive drum 1 is used for the next image formation by removing the transfer residual toner remaining on the surface by a cleaning device (not shown). The transfer material P onto which the toner image has been transferred is conveyed to a fixing device (not shown), where the toner image is fixed to the transfer material by heat and pressure, and is discharged outside the image forming apparatus as a print image.

An OPC (organic optical semiconductor) photosensitive member is used for the photosensitive drum 1. The charging roller 3 is installed in pressure contact with the surface of the photosensitive drum 1, and rotates following the rotation of the photosensitive drum 1. The transfer roller 2 is a semiconductive type that applies a positive charge to the back surface of the transfer material, and is also placed in pressure contact with the surface of the photosensitive drum 1. The image exposure is an image exposure, and the formed latent image is reversely developed using a negative toner by applying VDC = −450 V to the developer carrier of the developing device 6.

In such an image forming apparatus, a constant current control or a constant voltage control is performed for the transfer bias control, or a constant current control is performed when the transfer material is not present at the transfer portion when the paper is not fed. ATVC control or the like is used in which a voltage is detected and stored, and constant voltage control is performed using a voltage stored during paper passing or a voltage calculated based on the voltage.

[0008]

In an image forming apparatus employing the above-described contact charging method, in order to transfer a toner image formed on a photosensitive drum to a transfer material in a satisfactory manner, a constant value is required in accordance with the process speed. It is necessary to apply a transfer charge of an amount or more to the back surface of the transfer material. The amount of transfer charge on the back surface of the transfer material is determined by the amount of current flowing between the transfer roller 2 and the photosensitive drum 1. An example is shown in FIG.

As shown in FIG. 6, considering that the process speed and the amount of current flowing to the transfer portion have a linear relationship of one to one, it is reasonable to control the transfer bias by constant current control. However, when the transfer bias is controlled at a constant current, the following problem occurs.

In general, in this type of apparatus, a small-sized transfer material can be used within a range not larger than the maximum usable transfer material size. When used, the portion where the photosensitive drum and the transfer roller are in direct contact increases. In this state, if constant current control is performed at 3.5 μA, for example, most of the current flows into the non-sheet passing portion that directly contacts, almost no current flows into the sheet passing portion, and the back surface charge of the transfer material becomes insufficient.
Image defects such as explosion and scattering occur.

As shown in FIG. 7, the explosion splatters the charge C2 on the back surface of the non-image area where the toner image of the transfer material P does not exist, compared with the charge C1 on the back surface of the transfer material P where the toner image T exists. This is a phenomenon in which an electric field E that attracts the toner constituting the toner image T to the non-image portion side is generated, and the toner scatters sharply to the non-image side.

Instead of the constant current control, the constant current control is performed when the transfer material is not present at the transfer portion when the sheet is not passed, and the voltage at that time is stored, and the voltage at that time or the voltage calculated based on this voltage is used. In ATVC control or the like that performs constant voltage control during paper feeding, by setting an appropriate voltage, it is possible to compensate for the decrease in the current flowing through the paper passing portion when a small-size transfer material is used. It is inevitable that the back surface charge per unit area is reduced as compared with the case of using.

Of course, in the constant voltage control, the transfer current changes due to the change in the resistance value of the transfer member caused by the change in temperature and humidity, so that good transfer is difficult.

That is, in this type of apparatus, it is difficult to obtain good transferability to transfer materials of all sizes in all environments by any method of constant voltage control, constant current control, and ATVC control. It was the current situation.

Accordingly, it is an object of the present invention to provide a good image transferability to a transfer material of any size in any environment, and to provide a good image free from transfer failure such as explosion scattering regardless of the paper passing width. To provide an image forming apparatus capable of obtaining the following.

[0016]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
Transferring a visible image formed on the image carrier to a transfer material passed through a transfer portion of the image carrier, a transfer unit in contact with the image carrier, and a transfer unit perpendicular to a paper passing direction of the transfer material. In an image forming apparatus provided with a width detecting unit for detecting a sheet passing width, A is a longitudinal direction width of the transfer unit, B is a sheet passing width of the transfer material, and C is a predetermined constant. When the transfer means is controlled at a constant current, when AB> C,
An image forming apparatus, wherein the transfer unit is controlled at a constant voltage.

According to the present invention, the constant C is changed according to the resistance value of the transfer means. When performing the constant voltage control, first, when the transfer material is not present in the transfer portion, the transfer device is controlled with a constant current, and the voltage value generated in the transfer device at this time is detected, and the transfer material is transferred to the transfer portion. When it exists,
The transfer unit is controlled at a constant voltage with a voltage value calculated from the detected voltage value.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention.

The present invention is characterized in that the transfer bias is controlled in accordance with the size of the transfer material in order to obtain good transferability with respect to transfer materials of all sizes in all environments. .

Other configurations of the present invention are basically the same as those of the conventional image forming apparatus shown in FIG.

The image forming apparatus includes a photosensitive drum (drum-shaped photosensitive member) 1 as an image carrier.
Is formed on an OPC photosensitive member having a diameter of 30 mm, and is driven to rotate at a peripheral speed (process speed) of 75 mm / sec in a direction indicated by an arrow X in FIG. The photosensitive drum 1 is charged and charged during the rotation process.
After the surface is uniformly charged to a negative polarity by the charging roller 3 to which a primary charging bias is applied from a transfer power supply (high-voltage power supply) 4, image exposure is performed by a laser beam modulated by image information by an exposure device 5. Then, the exposed portion on the surface of the photosensitive drum 1 is attenuated, and an electrostatic latent image corresponding to the image information is formed on the surface. By attaching a negative (negative) toner to the potential attenuating portion of the latent image on the photosensitive drum 1 by the developing device 6, the latent image is reversely developed as a toner image.

As a transfer means (transfer member), the photosensitive drum 1 is located downstream of the developing device 6 when viewed in the rotation direction of the photosensitive drum 1.
A semiconductive (for example, 10 ⁶ to 10 ¹⁰ Ω) transfer roller 2 pressed against the transfer roller 2 is disposed, and a pressing nip portion between the two forms a transfer portion. The width of the transfer roller 2 in the longitudinal direction (axial direction) is 312 mm.

The toner image formed on the photosensitive drum 1 is
With the rotation of the photosensitive drum 1, the transfer roller 2 is moved to the transfer site where the transfer roller 2 is in contact, and at the same time, the transfer material P is supplied to the transfer site via the transport path 7. A toner image on the photosensitive drum 1 is transferred onto the transfer material P by applying a positive transfer bias to apply a charge having a polarity opposite to that of the toner to the back surface of the transfer material P.

The photosensitive drum 1 after the transfer of the toner image is used for the next image formation by removing the transfer residual toner remaining on the surface by a cleaning device (not shown). The transfer material P onto which the toner image has been transferred is conveyed to a fixing device (not shown), where the toner image is fixed to the transfer material by heat and pressure, and is discharged outside the image forming apparatus as a print image.

Experiments have confirmed that, in the present image forming apparatus, the transfer bias applied to the transfer roller 2 at the time of the transfer requires a transfer current of about 3 μA in order to prevent explosion and scattering. ing.

According to the present embodiment, the charging / transfer power supply 4 is a constant current / constant voltage power supply, and is capable of constant voltage control and constant current control. At this point, a predetermined current and voltage are applied. The power supply 4 detects the paper passing width (length in a direction perpendicular to the paper passing direction) of the transfer material P passed through the transfer portion by the width detecting means 10, and according to the detected paper passing width, the CPU 4
9 is controlled as described later.

In the present invention, the width A of the transfer roller 2 in the longitudinal direction, the width B of the transfer material, and the predetermined constant C are defined as follows.
(A) When the transfer roller longitudinal direction width A-transfer material sheet width B ≦ C, the transfer roller is controlled with a constant current. (B) When the transfer roller longitudinal direction width A-transfer material sheet width B> C, the transfer roller is controlled. Is controlled at a constant voltage.

The constant C is a numerical value that changes according to the resistance value of the transfer roller 2. In this embodiment, the width A of the transfer roller in the longitudinal direction is 312 mm, and the constant C is set to 40 mm.

Therefore, in the present embodiment, (A) width in the longitudinal direction of the transfer roller (312 mm) -transfer material passing width ≦ 40 m
m, the transfer bias is controlled by a constant current of 3.5 μA,
(B) When the width of the transfer roller in the longitudinal direction (312 mm) -the width of the transfer material passing> 40 mm, the transfer bias is controlled at a constant voltage.

In the present invention, the above constant voltage control is performed by the ATVC
Performed by control. At the time of the ATVC control, during pre-rotation before printing, that is, when the transfer material does not exist at the transfer portion, the transfer bias is applied to the transfer roller 2 by controlling the transfer bias at a constant current of 3 μA by the power supply 4, and the voltage value VO generated at that time is applied. Detect and store. Then, the constant current control is stopped, and when paper is passed, that is, when a transfer material is present at the transfer portion, a transfer voltage VT is calculated by the following equation (1) using the stored voltage value VO, and VT ( V) = VO + 1250 (1) The transfer bias is applied to the transfer roller 2 with constant voltage control at VT.

In this apparatus, a case where a transfer material having a small paper passing width, for example, an A4 size transfer material is passed vertically (paper passing width 210 mm) will be described.

In this case, the width of the transfer roller in the longitudinal direction−the width of the transfer material passing paper = 312 mm−210 mm = 102 mm> 40
mm, the transfer bias is ATVC controlled.
For example, in an L / L (low temperature / low humidity) environment, when the transfer material does not exist at the transfer portion (when paper is not passed), the transfer bias is set to 3
When applied to the transfer roller 2 with constant current control at μA, the voltage VO generated at that time indicates the relationship between the applied voltage to the transfer roller in the L / L environment and the transfer current flowing at that time (transfer VI characteristic). From FIG. 2 shown, about 1750 V is detected.

Therefore, from equation (1), VT = 175
0 + 1250 = 3000 V is calculated, and at the time of paper passing, the transfer bias is set to 3000 V and the transfer roller 2 is controlled at a constant voltage.
Is applied.

FIG. 2 shows that when the transfer bias is controlled at a constant voltage of 3000 V, the transfer current for transferring a solid black image in the L / L environment is about 3.75 μA. Therefore,
Even for a transfer material having a small paper passing width, such as when the A4 size paper is passed in the vertical direction, a sufficient current for preventing explosion and scattering can be secured, and good transferability can be obtained.

Next, a case will be described in which a paper passing width equal to the width of the transfer roller in the longitudinal direction, for example, A3 size transfer material is passed in the vertical direction (paper passing width of 297 mm). Material passing width = 312mm-29
Since 7 mm = 15 mm <40 mm, the transfer bias is controlled at a constant current of 3.5 μA.

In other words, when a transfer material having a width equal to the width of the transfer roller in the longitudinal direction is passed, a constant transfer current can flow regardless of the type and thickness of the transfer material, and good transfer properties can be obtained. It can be obtained, and image defects such as explosion and scattering do not occur.

As described above, according to this embodiment,
Good transferability can be obtained for transfer materials of all sizes in all environments, and a good image free from transfer failure such as explosion scattering can be obtained regardless of the paper passing width.

Embodiment 2 The transfer bias is controlled by constant current control or constant voltage control (ATV
It is preferable that the boundary of the C control) is changed by the resistance of the transfer roller 2. This is because the higher the resistance value of the transfer roller 2, the smaller the current flowing in the non-sheet passing portion.

In this embodiment, the transfer bias was set as shown in Table 1 in the image forming apparatus of the first embodiment.

[0041]

[Table 1]

The reason set as above will be described below. FIG. 3 shows the width of the transfer roller in the longitudinal direction (31 in this embodiment).
2 mm) to the ratio of the transfer material passing width to (transfer material passing width /
(Transfer roller longitudinal direction width), the ratio of the transfer bias current flowing through the paper passing portion is equal to (transfer material sheet width / transfer roller longitudinal direction width) × 85% of the transfer material passage. The paper width is displayed with respect to the resistance value of the transfer roller 2 (when 2 kV is applied). The above-mentioned 85% means that when the constant current control is performed, according to an experiment by the present inventor, if the ratio of the current flowing through the paper passing portion falls below 85% of (transfer material paper passing width / transfer roller longitudinal direction width). This value is determined from the occurrence of explosion and scattering.

On the other hand, FIG. 4 shows the voltage value generated at the transfer roller 2 when the constant current control is performed at 3 μA with respect to the resistance value of the transfer roller 2 (when 2 kV is applied).

Table 1 can be created based on FIG. 3 and FIG.
From the output voltage value during TVC constant current control, constant current control and A
The boundaries of TVC control (constant voltage control) can be determined.

As an example, a case where the output voltage at the time of the ATVC constant current control is 1400 V will be described. When the voltage of the ATVC constant current control is 1400 V, when a transfer material having a paper passing width of 240 mm or more is used, the constant current control is performed according to Table 1.
When a transfer material of less than 240 mm is used, ATVC control may be used.

That is, in this embodiment, the boundary between whether to perform the constant current control or the ATVC control at the time of paper passing is made variable in accordance with the voltage at the time of the constant current control in the ATVC control. For the transfer material having the size of, the transferability even better than that of Example 1 can be obtained, and the transfer failure such as the explosion splattering can be further prevented irrespective of the paper passing width, and a good image without the transfer failure can be obtained. Obtainable.

[0047]

As described above, according to the present invention,
When a transfer material having a wider paper width is used at a predetermined paper width, a transfer bias control is set to a constant current control, and when a transfer material having a narrower paper width is used, Since the transfer bias is controlled by constant voltage control such as ATVC control, it is possible to prevent transfer failure such as explosion scattering and obtain a good image regardless of the environment and the sheet passing width. In addition, the boundary between transfer current control and constant voltage control of the transfer bias is made variable according to the resistance of the contact type transfer means, so that it is possible to further improve the prevention of transfer failure such as explosion splattering, and further improve the image quality. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram showing VI characteristics in an L / L environment of a transfer roller used in control in the embodiment of FIG.

FIG. 3 shows a transfer material passing width used in the control in another embodiment of the present invention, in which the ratio of the current flowing in the paper passing portion of the transfer portion is 85% of (transfer material passing width / transfer roller longitudinal width). FIG. 3 is a diagram illustrating a relationship between the transfer roller resistance and the resistance of the transfer roller.

FIG. 4 shows an AT used in control in another embodiment of the present invention.
FIG. 6 is a diagram illustrating a relationship between a voltage and a resistance of a transfer roller during VC constant current control.

FIG. 5 is a schematic sectional view showing a conventional image forming apparatus.

FIG. 6 is a diagram illustrating a relationship between a process speed and a required transfer current in the image forming apparatus of FIG. 5;

FIG. 7 is a schematic diagram illustrating a state of explosion and scattering of an image which has conventionally occurred.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Transfer roller 4 Constant current / constant voltage power supply 6 Developing device 9 CPU 10 Width detection means P Transfer material

Claims (3)

[Claims] 1. A transfer means for transferring a visible image formed on an image carrier to a transfer material passed through a transfer portion of the image carrier, the transfer means being in contact with the image carrier, and a paper passing of the transfer material. An image forming apparatus provided with a width detecting unit for detecting a paper passing width in a direction perpendicular to the direction, wherein the longitudinal width of the transfer unit is A, the paper passing width of the transfer material is B,
When a predetermined constant is C and AB ≦ C, the transfer unit is controlled with a constant current,
When B> C, the image forming apparatus controls the transfer unit at a constant voltage. 2. The image forming apparatus according to claim 1, wherein the constant C is changed according to a resistance value of the transfer unit. 3. When performing the constant voltage control, first, when there is no transfer material at a transfer portion, the transfer means is controlled with a constant current, and a voltage value generated in the transfer means at this time is detected. An image forming apparatus, wherein when a transfer material is present at a site, the transfer unit is controlled at a constant voltage with a voltage value calculated from the detected voltage value.