JP2001265133A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device, capable of satisfactorily transferring by supplying an appropriate current in between an image carrier and a transfer means according to a transfer material and an ambient environment. SOLUTION: A constant current source 87 is connected to a transfer power source 88 for supplying a current to a transfer roller 176, and a resistance r31 and a constant voltage source 152 are connected in parallel to the source 87. In the case of transferring a toner image to the transfer material 5, the current i1 related with the toner image transfer flows via a low resistance component r1 and a current i2 leaking via the transfer material 5 flows through the resistance component r2. Usually in the case the resistance values of the resistance components r1 and r2 are high, the current supplied from the constant voltage source 152 to the resistance components r1 and r2 are a few, and the transfer process is not affected, but under an environment where the temperature and humidity are high, the shortage of the transfer current to the resistance component r1 becomes conspicuous. By this invention, the current is supplied to the resistance component r1 and the resistance component r2 by the constant voltage source 152, the current is sufficiently supplied to the transfer part, the quantity of the supplied current i1 related with the transfer is not reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printing apparatus, and an electrophotographic image forming apparatus such as a facsimile for transferring and fixing a visualized image to a transfer material such as a recording paper or an OHP sheet. More specifically, the present invention relates to an image forming apparatus that performs transfer to a transfer material by supplying an appropriate current according to the type and size of the transfer material.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, an image visualized by a developer such as a toner carried on a photosensitive drum serving as an image carrier is transferred to a transfer material such as recording paper. A corona charger is used as a transfer means for performing the transfer. When a corona discharge is performed by the corona charger to perform transfer to a transfer material, ozone (O ₃ ) is generated as a by-product. This ozone has a peculiar odor and, at high concentrations, irritates the human respiratory tract. Therefore, an image forming apparatus that does not generate ozone has been demanded.

Therefore, an image forming apparatus using a transfer roller has been developed as a configuration that does not generate ozone when a toner image is transferred to a transfer material, and the number of used image forming apparatuses is increasing. The transfer roller is disposed in contact with or close to the photosensitive drum, and presses the transfer material against the photosensitive drum to transfer the toner image carried on the photosensitive drum. Further, a transfer power supply for supplying a predetermined current to the transfer roller is connected to the transfer roller, whereby the toner image can be more reliably transferred to the transfer material.

FIG. 7A shows an example of the configuration of a conventional transfer section of an image forming apparatus using a transfer roller 176.
In the conventional transfer unit, one end of a transfer power source 87 which is a constant current source is directly connected to the transfer roller 176, and the other end of the transfer power source 87 is grounded. Further, between the transfer roller 176 and the photosensitive drum 178, as shown in the equivalent circuit diagram of FIG. 7B, a current i1 related to the transfer of the toner image flows through the resistance component r1 and the transfer material 5 The current i2 leaking through the resistor component flows through the resistance component r2. In addition, the leakage current i2 generally leaks to the static elimination needle, the paper feed roller and the registration roller disposed behind the fixing / separation area via the transfer material 5, and under high temperature and high humidity, the transfer current 5 This is a current that leaks due to moisture on the surface of the conveyance path or the surface of the paper guide.

As described above, in the configuration using the transfer roller 176, when a toner image is transferred to plain paper, the output current supplied from the transfer power supply 87 is applied to another member, such as a fixing unit or a resist, via the recording paper. The problem of leaking to the means occurs. In order to compensate for the leakage current of the transfer current, a transfer power source having a large capacity is required.

On the other hand, when a toner image is transferred to a high-resistance sheet such as a thick paper or an OHP sheet, almost no current leaks to a fixing means or a registration means, so that the current is less than that of plain paper. Is too large or the applied voltage is too high. Therefore, image deterioration such as scattering of toner and reverse transfer may occur.

The transfer roller 176 and the photosensitive drum 1
In the minute gap with 78, a discharge is generated, which not only easily causes image deterioration, but also causes pinholes in the photosensitive drum 178 and deterioration (enlargement) of the existing pinholes. This has been a factor in reducing the life of the body drum 178. Therefore, when a thick paper or an OHP sheet is used as the transfer material 5, it is necessary to provide a configuration for variably controlling the transfer voltage.

For example, when plain paper is used as the transfer material 5, the combined resistance value of the resistance component r1 and the resistance component r2 calculated from the circuit current at the time of transfer and the applied potential at that time is about 200 MΩ. When an OHP sheet is used as the transfer material 5, the combined resistance value of the resistance component r1 and the resistance component r2 is approximately 500 MΩ. Therefore, O
When the HP sheet is used, the output voltage of the transfer power supply 87 becomes 2.5 times that of when the plain paper is used. Furthermore, when the resistance component r1 and the resistance component r2 of the OHP sheet are compared, the resistance component r1 is usually smaller than the resistance component r2 under a normal temperature and normal humidity environment. Therefore, the applied voltage is almost applied to the transfer area. Therefore, when the OHP sheet is used, the above-described problem due to an overcurrent occurs.

Therefore, even if the transfer is performed well when plain paper is used as the transfer material 5, if the OHP sheet is used as the transfer material 5, the resistance component r2 becomes very large, and the current is reduced. Overcurrent is concentrated on the component r1, and image deterioration such as toner scattering and reverse transfer easily occurs.

In a high-temperature and high-humidity environment, when the plain paper used as the transfer material 5 absorbs moisture and its resistance value decreases,
The leakage of the transfer current easily occurs. In this case, for example, in FIG. 7, the resistance component r1 is 100 MΩ, whereas the resistance component r2 is extremely reduced to 50 MΩ.
About. Then, the current flows intensively at r2. As a result, the current flowing through the resistance component r1 decreases, and the current contributing to the transfer becomes insufficient, so that desired transfer cannot be performed and transfer failure occurs.

In order to solve these problems, if a high-level insulating treatment is applied to a portion such as a fixing unit or a resisting unit, current leakage does not occur, and the above-described problem is avoided. However, other inconveniences such as a fixing offset and an image being disturbed by friction caused by the insulating means have occurred.

Japanese Patent Application Laid-Open No. 9-179413 discloses a control in which a high resistance is arranged in parallel with the impedance of a transfer area so that a necessary transfer current is not reduced even if the transfer current leaks. A technique regarding an image forming apparatus is disclosed. In this configuration, even if the resistance between the transfer roller and the ground is reduced due to the paper whose resistance has been extremely reduced due to moisture absorption at high temperature and high humidity, for example, the transfer current may be leaked, With the effect of the high resistance arranged in parallel to the above, the current supplied from the power supply does not concentrate on the transfer portion and the transfer current does not run short, and image deterioration is prevented.

Japanese Patent Application Laid-Open No. 9-138595 discloses a transfer belt device, which includes a transfer bias roller that contacts a belt and transfers electrification to the belt at a position where the belt is sandwiched between the belt and a photosensitive drum. A control resistor inserted between the contact position with the belt transfer bias roller and the constant voltage power supply, and a resistance circuit parallel to the current path from the transfer bias roller to the photosensitive drum via the belt are formed on the surface of the belt. And a setting roller that is in contact with the belt so as to be formed along the belt.

In this configuration, when the electric resistance of the sheet-like member changes due to environmental fluctuations, the electric resistance of the resistance circuit parallel to the current path from the terminal member to the photosensitive drum via the sheet-like member becomes equal. As a result, the value of the current flowing in the current path from the terminal member to the photosensitive drum via the sheet-shaped member is kept substantially constant. Therefore, a desired amount of electric charge can be supplied to the sheet-shaped member or the paper regardless of the fluctuation of the temperature, the humidity, and the like, and problems such as transfer failure and background fog can be prevented.

[0015]

Problems to be Solved by the Invention
Patent Document 3 discloses an image forming apparatus and Japanese Patent Application Laid-Open No. 9-1.
The transfer device disclosed in Japanese Patent No. 38595 exhibits a certain level of printing performance when using ordinary recording paper. However, for example, when narrow paper is used at high temperature and high humidity, a transfer current necessary for good transfer is not supplied to the transfer unit, which causes image deterioration. In other words, when a narrow sheet such as a postcard is used in a high-temperature and high-humidity environment, when a toner image is transferred, there are many portions where the photoconductor and the transfer roller are in direct contact with each other. For this reason, there is a problem that the transfer current concentrates on the portion, the current does not flow in the transfer portion, and sufficient transfer cannot be obtained.

Further, when a delicate current value in the transfer section affects a transferred image, an appropriate transfer current value differs depending on characteristics of a transfer material to be used. However, there is a problem that a good image cannot be obtained.

To solve this problem, Japanese Unexamined Patent Publication No. 9-17941
Japanese Patent Application Laid-open No. 3 (1993) -313 discloses a configuration in which another resistance element for adjustment is connected via a switch in parallel with the resistance element in the static elimination circuit. However, since the adjustment resistor is a fixed resistor, the resistance value is fixed. Therefore, the resistance value cannot be delicately changed according to the surrounding environment or the material and size of the transfer material.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to suppress damage to an image carrier and a transfer means, and to provide an image carrier according to a transfer material and a surrounding environment. An object of the present invention is to provide an image forming apparatus capable of supplying an appropriate current to a transfer unit and performing good transfer to obtain good image quality over a long period of time.

[0019]

The present invention has the following arrangement as means for solving the above-mentioned problems.

(1) A potential difference is applied from a power supply unit between an image carrier for carrying a visualized image and a transfer unit for transferring the image to a recording medium in contact with the image carrier, and the image is provided. In an image forming apparatus for forming, a resistance unit and a second power supply unit capable of compensating an amount of current supplied to the transfer unit are disposed in parallel with the transfer unit with respect to the power supply unit. It is characterized by comprising a compensating means connected in series.

In this configuration, a potential difference is applied between a transfer means for transferring an image to a recording medium in contact with an image carrier for carrying a visualized image and the image carrier to form an image. And a compensating means arranged in parallel with the transfer means with respect to the power supply means for performing the operation. The compensating means comprises a resistance means and a second power supply capable of compensating the amount of current supplied to the transfer means. Means. Therefore, since the image forming apparatus has the compensating means including the resistor connected in parallel to the power supply means and the second power supply means,
The current supplied to the transfer unit can be increased or decreased in accordance with the increase or decrease in the electric load between the transfer unit and the image carrier, for example, the resistance of the transfer material used is extremely reduced, such as in a high-temperature and high-humidity environment. However, even if a sufficient current cannot be supplied to the transfer section, the second
The necessary current is supplied by the power supply, and transfer failure can be avoided. In addition, a large-capacity power supply capable of outputting a required current value is not required, and cost can be reduced.

(2) The second power supply means is a constant voltage power supply means.

In this configuration, the second power supply means capable of compensating the amount of current supplied to the transfer means is a constant voltage power supply means. Therefore, for example, when the resistance of the transfer material is extremely high such as in a low-temperature and low-humidity environment, the transfer is not affected, and a necessary current can be supplied only when necessary, such as in a high-temperature and high-humidity environment.

(3) The output of the second power supply means is variable.

In this configuration, the output of the second power supply is variable. Therefore, since the output value of the second power supply unit can be variably controlled, optimal transfer conditions can be realized according to the characteristics of the transfer material used and the use environment.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A schematic configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 can be used as an output device of a computer. In addition, the image forming apparatus 1 can be used as a word processor, a facsimile printing unit, and a digital copier printing unit. The image forming apparatus 1 includes an image forming unit 3 that forms an image, and a sheet feeding device 10 that supplies a transfer material 5 that is a transfer material to the image forming unit 3.

The image forming unit 3 applies a uniform charge to the surface of the photosensitive drum 178 around the photosensitive drum 178 which is an image carrier having a photosensitive layer disposed on an aluminum tube, and around the photosensitive drum 178. A charging roller 179 serving as a charging unit, a charging power supply 86 for supplying a potential to the charging roller 179, and a laser scanning unit (hereinafter, referred to as an exposure unit) serving as an exposure unit for irradiating the surface of the charged photosensitive drum 178 with laser light in accordance with image data. LSU) 180. A developing unit 183 for supplying a toner 21 as a developer to the electrostatic latent image as a charge pattern formed by exposure to form a toner image as a visualized image; The transfer roller 17 is a transfer unit that presses the toner image 5 on the photosensitive drum 178 to transfer the toner image formed on the photosensitive drum 178 to the transfer material 5 such as plain paper.
6, a cleaning device 185 for collecting the toner remaining on the surface of the photosensitive drum 178, and a charge removing lamp 177 for removing the residual charge after the transfer of the toner image on the photosensitive drum 178.

The developing means 183 has the toner 21 inside,
After the toner 21 has a predetermined characteristic (for example, negative polarity), a sleeve (developing roller) 22 for rotating the toner 21 is provided;
At least.

A transfer power supply 88 is connected to the transfer roller 176. The transfer power supply 88 includes a constant current source 87 that outputs a current of, for example, 20 μA when transferring the toner image, and a constant voltage source 152 that is a constant voltage power supply that outputs a voltage of 700 V.
And a configuration including:

The paper feeding device 10 includes a cassette 4 for accommodating the transfer material 5, a pickup roller 6 for feeding out the transfer material 5 from the cassette 4, a paper feed guide 7 for guiding the supplied transfer material 5, and a fed transfer. A pair of registration rollers 125 for transporting the material 5 at a predetermined speed are provided. The paper supply device 10 also includes a paper supply sensor (not shown) that detects that the transfer material 5 has been supplied, and a fixing device that fixes the toner image formed on the transfer material 5 to the transfer material 5 by heating and pressing. Part 11
It has.

The fixing unit 11 includes a heating roller 12, a heater 1
3, a pressure roller 14, a temperature sensor 15, and a temperature control circuit 80. The heating roller 12 has a thickness of 2 mm, for example.
Aluminum tube. The heater 13 includes, for example, a halogen lamp, and is built in the heating roller 12. The pressure roller 14 is made of, for example, a silicone resin. The heating rollers 12 provided opposite to each other
In addition, a load of, for example, 2 kg is applied to both ends of each shaft by a spring or the like (not shown) so that the pressure roller 14 can press against the paper. Temperature sensor 15 measures the surface temperature of heating roller 12. The temperature control circuit 80 is controlled by the main control unit of the image forming apparatus 1, and controls ON / OFF of the heater 13 based on the measurement result of the temperature sensor 15, and adjusts the temperature of the surface of the heating roller 12 to, for example, 150 ° C. To hold.

The fixing unit 11 has a paper ejection sensor (not shown) for detecting that the paper has been ejected. The materials of the heating roller 12, the heater 13, the pressure roller 14, and the like are as follows.
There is no particular limitation. Further, the surface temperature of the heating roller 12 is not particularly limited.

The rollers such as the pickup roller 6 and the photosensitive drum 178 provided in the sheet feeding device 10 are driven to rotate by a driving device (not shown). The rotation drive of each roller and the photosensitive drum 178 is appropriately controlled at a predetermined timing by a process control unit (not shown).

On the paper output side of the image forming apparatus 1, a pair of paper discharge rollers 175 for discharging the transfer material 5 out of the apparatus and a paper discharge tray 8 for holding the discharged transfer material 5 are provided. Is provided.

The charging roller 179 is made of, for example, solid rubber whose base material is urethane and has a resistance value of 1e5 Ω · cm. The charging power supply 86 causes the charging roller 179 to
A voltage is applied to the grounded photoconductor drum 178 such that the surface potential of the photoconductor drum 178 becomes −600 V. Further, the transfer roller 176 is formed of a foam rubber layer of JIS-A 30 ° also made of urethane as a base material.

The charge removing lamp 177 is composed of LEDs of a certain number, and is used for irradiating light to the surface of the photosensitive drum 178 to neutralize the charge remaining on the surface of the photosensitive drum 178 to remove the charge. .

Next, the image forming operation of the image forming apparatus 1 shown in FIG. 1 will be described. Upon receiving a print command from a host computer (not shown), image forming apparatus 1 starts a printing operation. That is, first, one transfer material 5 is taken out of the cassette 4 by the pickup roller 6 and sent to the position of the registration roller 125. The registration roller 125 sends out the transfer material 5 to a region (transfer portion) where the photosensitive drum 178 and the transfer roller 176 face each other at a predetermined speed.

In synchronization with this operation, a potential of, for example, about −1200 V is supplied to the charging roller 179 from the charging power supply 86, and the potential of the charging roller 179 is uniformly applied to the surface of the photosensitive drum 178 by about −600.
Charge is supplied so as to exhibit a surface potential of V. When the photosensitive drum 178 rotates, this charged area is
, The LSU 180 irradiates the charged area of the photosensitive drum 178 with laser light corresponding to desired image data. Photosensitive drum 17 irradiated with laser light
8, a charge image (hereinafter, referred to as an electrostatic latent image) 182 due to electrostatic charge is formed. The electrostatic latent image 182 moves to a region facing the developing unit 183 by rotation of the photosensitive drum 178.

The electrostatic latent image 182 is supplied with the toner 21 by the developing means 183 to become a toner image 182a (not shown). The toner image 182a further moves with the rotation of the photosensitive drum 178, and reaches a region facing the transfer roller 176. Then, the toner image 182 a formed on the photosensitive drum 178 comes into contact with the transfer material 5 also conveyed to the facing area, and is transferred to the transfer material 5. Thereafter, the transfer material 5 moves to the fixing unit 11 and is fixed,
The sheet is fed to the position of the discharge roller 175, and is further discharged to the discharge tray 8 by the discharge roller 175.

The photosensitive drum 178 and the transfer roller 1
The cleaning device 185 removes the toner remaining on the surface of the electrostatic latent image 182 that has passed through the facing region 76. Then, the electrostatic latent image 182 is
7, the discharge lamp 177 irradiates the entire surface of the region opposite the photosensitive drum 178 and the discharge lamp 177 with discharge light, and the unnecessary charge of the electrostatic latent image 182 is neutralized.

Although the image forming apparatus 1 shown in FIG. 1 uses the LSU 180 using a laser as an exposure means for forming the electrostatic latent image 182, the present invention is not limited to this. For example, an LED head using a plurality of LEDs instead of a laser may be used. Further, the exposure means may be a means for exposing the photosensitive drum 178 by irradiating an image signal sent from a computer or an image signal sent from an image processing unit of a digital copying machine, for example. In addition, for example, an exposure apparatus of an analog image forming apparatus that exposes a photosensitive drum with reflected light of light applied to a document placed on a document table may be used.

Next, a method of applying a transfer potential in the image forming apparatus according to the embodiment of the present invention will be described. FIG.
FIG. 1A is a diagram schematically illustrating a configuration of a transfer unit of an image forming apparatus according to an embodiment of the present disclosure. FIG.
FIG. 3 is an equivalent circuit diagram of the configuration shown in FIG.

As shown in FIG. 2A, one end of a transfer power supply 88a is connected to the transfer roller 176, which is a transfer means, and the other end is grounded. The transfer power supply 88a includes a constant current source 87 as a power supply. Further, a fixed resistor r31 of 100 MΩ, which is a resistance unit, and a constant voltage source 152 for applying a voltage of 700 V, which is a second power supply unit, are connected in series to constitute a compensation unit. Are connected in parallel.

When the toner image is transferred to the transfer material 5 by the transfer roller 176, the current i1 relating to the transfer of the toner image flows through the resistance component r1 as described above. Further, through the transfer material 5, a static elimination needle, a paper feed roller and a registration roller disposed behind the fixing / separation area, and under high temperature and high humidity, remove moisture on the surface of the transfer path of the transfer material 5 and the surface of the paper guide. The leaked current i2 flows through the resistance component r2. Further, a current i31 flows through the fixed resistor r31. In addition, the resistance component r1 and the resistance component r2 are
And a fixed resistor r31 and a constant voltage source 15 connected in series.
2 are connected in parallel with each other.

Normally, when the resistance values of the resistance components r1 and r2 are large, the current supplied from the constant voltage source to the resistance components r1 and r2 is very small and has little effect on the transfer. On the other hand, in a high temperature and high humidity environment, the resistance component r
1, and the difference between the resistance component r2 and the leakage current is further increased, so that a shortage of current to the resistance component r1 for transfer becomes significant.

However, in the present invention, since the constant voltage source 152 is provided as described above, the current is supplied to the resistance component r1 and the resistance component r2 by the constant voltage source 152, so that the current is sufficiently supplied to the transfer unit. Current i1 involved in transcription
Does not decrease.

When an OHP sheet is used as the transfer material 5, the resistance components r1 and r2 rise extremely in the conventional configuration, and the constant current source 87 generates a very high voltage. In No. 2, almost no current is supplied from the constant voltage source to the resistance components r1 and r2, and a predetermined current i31 flows through the fixed resistor r31. Therefore, the current i1 between the transfer roller 176 and the photosensitive drum 178 does not increase extremely, the voltage applied to the transfer area does not increase, and image deterioration due to toner scattering and reverse transfer does not occur. Further, since a discharge at the transfer portion is avoided, a good toner image is transferred.

As described above, conventionally, as the load on the transfer area increases, the applied voltage also increases.
In the present invention, the fixed resistor r31 and the constant voltage source 152
The current is compensated by this. Therefore, good transfer can be achieved without applying an unnecessary high voltage, and good transfer can be maintained without excessively decreasing the current value. Further, since a large-capacity constant current source capable of outputting a required current value is unnecessary, cost can be reduced.

In the embodiment shown in FIG. 2, the constant voltage source 15
2, the same effect can be achieved with a constant current source. However, with the constant current source as described above, for example, when the resistance value of the transfer section increases in a low-temperature and low-humidity environment, desired characteristics cannot be obtained, which is not desirable. On the other hand, when the resistance value of the transfer unit increases in a low-temperature and low-humidity environment, the current of the transfer unit decreases with the constant voltage source, and the transfer of the current does not affect the constant voltage source serving as the second power supply unit. Therefore, FIG.
A configuration using a constant voltage source like this is more desirable.

In the configuration of FIG. 2, for example, OHP
When a transfer sheet is used, good conditions for the transfer voltage and current easily vary depending on the type of the OHP sheet to be used, and more strict conditions need to be set particularly at low temperature and low humidity. In such a state, it is difficult to set conditions for performing good transfer on all of various OHP sheets.

Therefore, in the present invention, the constant voltage source 15
It is desirable that the output value of No. 2 can be finely adjusted as appropriate so that a good image can be obtained. Thereby, good image formation can be achieved even when various transfer materials are used by adjusting the transfer current supplied to the transfer unit. Further, in the embodiment shown in FIG. 2, the fixed resistor r31 is connected in series to the constant voltage source 152, but this can be a variable resistor.

FIG. 3A is a diagram schematically showing the configuration of a transfer section having a variable resistor. FIG. 3 (B) is FIG. 3 (A)
3 is an equivalent circuit diagram of the configuration shown in FIG.

As shown in FIG. 3A, one end of a transfer power supply 88b is connected to the transfer roller 176, which is a transfer means, and the other end is grounded. The transfer power supply 88b includes a constant current source 87 as a power supply. Further, a variable resistor r32 of 100 to 300 MΩ as a resistance means, and a constant voltage source 15 for applying a voltage of 700 V as a second power supply means.
2 are connected in series to form compensating means, and are connected in parallel to both ends of the constant current source 87.

In the configuration shown in FIG. 3, the user of the image forming apparatus 1 changes the resistance value of the variable resistor r32 so that the current i3
2 can be adjusted. Thus, the value of the current flowing through the resistance component r1 can be finely adjusted, and the image quality can be finely adjusted.

Further, in a high-temperature and high-humidity environment, when the transfer material 5 absorbs moisture and its resistance value decreases, leakage of transfer current easily occurs. However, although a leakage current occurs, the resistance component r2 extremely decreases, the current i2 increases, and the current supplied to the resistance component r1 tends to decrease. However, the resistance value of the variable resistor r32 is changed to the resistance component r1. And the resistance r2 is set to be much larger than the combined resistance. In the present invention, as described above, the constant voltage source 152
, The current is supplied by the constant voltage source 152 to compensate the current. Thus, the resistance component r
1 can be avoided, and the current contributing to the transfer flows sufficiently, and the desired transfer can be performed, so that a good image can be formed.

As described above, the electrical characteristics of the conventional transfer unit in the image forming apparatus are as follows: the case where ordinary paper is used as the transfer material 5 and the case where thick paper or OHP sheet is used and the apparent resistance value is When the voltage is doubled, the applied voltage is also doubled. On the other hand, in the configuration as shown in FIG. 3, the user appropriately sets the resistance value of the variable resistor r32 and supplies the current from the constant voltage source 152, so that the total resistance value of the transfer area is doubled. Can also be controlled so that the applied voltage is twice or less.

As described above, conventionally, as the load on the transfer area increases, the applied voltage also increases.
In the present invention, the variable resistor r32 prevents the current value more than necessary from flowing into the transfer area. Therefore, good transfer can be achieved without applying an unnecessary high voltage, and good transfer can be maintained without excessively decreasing the current value.

The above embodiment is effective even when the transfer material 5 having a narrow paper width is used. That is, in the case of the transfer material 5 having a narrow paper width, the current concentrates on the contact portion between the transfer roller 176 and the photosensitive drum 178. Therefore, in the conventional configuration, the desired current does not flow through the transfer material 5 and the transfer failure occurs. Is easy to occur. This will be described with reference to FIG.

FIG. 4A is a diagram schematically showing a cross section of a transfer portion when a transfer material 5 having a small paper width is used. FIG. 4B is an equivalent circuit diagram of the configuration shown in FIG. As shown in FIG. 4A, for example, when a transfer material 5 having a paper width of about half the length of the transfer unit in the main scanning direction is used, the transfer material 5 is sandwiched between the transfer roller 176 and the photosensitive drum 178. Instead, the area S1 where the two directly contact each other is generated over a length of about half of the main scanning direction. In the region S1, the resistance between the transfer roller 176 and the photosensitive drum 178 is lower than that in the region where the transfer material 5 is sandwiched because the transfer material 5 is not interposed, and current concentrates in this region S1.

Since the state described above is obtained, the state shown in FIG.
In the equivalent circuit diagram shown in FIG. 7, the resistance component r1 through which the current i1 relating to the transfer of the toner image at the transfer portion flows is determined by the transfer material 5
And the resistance component r12 in the region S1 can be displayed as shown in the equivalent circuit diagram of FIG. 4B. The resistance value of the resistance component r12 in the region S1 is extremely low as described above, and current flows intensively.

Therefore, in the conventional configuration, the resistance component r11
Is not supplied with sufficient current. Therefore, it was necessary to supply a larger current to the transfer section. However, since the constant current source 87 is used as a power supply, it is impossible to supply a current of a predetermined value or more. Therefore, the transfer material 5
Did not supply sufficient current, and good transfer was not obtained.

On the other hand, in the configuration shown in FIG. 4, when the width of the transfer material 5 is reduced, the resistance value of the resistance component r12 between the transfer roller 176 and the photosensitive drum 178 is reduced. A current is supplied from the constant voltage source 152 by appropriately setting the resistance value of the variable resistor r32. As a result, the current i11 increases, and a situation in which the necessary transfer current is insufficient is avoided.

Further, according to the present invention, good transfer is possible even when a part of the transfer material 5 is a solid image. This will be described with reference to FIG. FIG. 5 is a diagram schematically illustrating a cross section of the transfer unit when the transfer material 5 having the solid image 21 is used. Note that a circuit diagram is the same as that in FIG.

As shown in FIG. 5, there is a case where a part (left half in FIG. 5) of the toner image is a solid image area 21a and another part is an area S2 where no toner 21 exists. In this case, when the region S2 exists between the transfer roller 176 and the photosensitive drum 178, current concentrates on a contact portion between the transfer material 5 and the photosensitive drum 178. Therefore, FIG.
In the conventional configuration shown in (1), a current necessary for transferring the solid image area 21a is not supplied, and transfer failure is likely to occur. Further, a portion other than the solid image area 21a, that is, a portion without the toner 21a, and the transfer material 5 and the photosensitive drum 17
If the region S2 where the substrate 8 is in direct contact is formed in a very wide range, since the toner does not intervene in the region S2, the resistance is lower than that of the solid image region where the toner exists, and the current concentrates in this region S2. I do.

Therefore, in the conventional configuration, the transfer roller 17
Although the resistance between the photosensitive drum 6 and the photosensitive drum 178 becomes small, the current cannot exceed a predetermined value because the constant current source 87 is used as the power supply, and the current is sufficiently supplied to the image area 21a. Since it is not supplied, good transfer cannot be obtained.

On the other hand, in the configuration of FIG. 5, a solid image area 21a exists partially, and this state is the same as the case where the paper width is narrow as shown in FIG. Therefore, the supplied current is concentrated in the area S2, but the value of the current supplied from the constant voltage source 152 to the solid image area 21a is increased by adjusting the variable resistor r32 so that the transfer current required in the solid image area 21a is increased. Is avoided, and good transfer can be achieved.

Further, in a high-temperature, high-humidity environment, a small-size and high-resistance transfer material such as a PET (polyethylene terephthalate) label sheet or a price tag (hereinafter, referred to as special paper).
Is used, for example, the current concentration in the region S1 in FIG. Therefore, the current to the transfer material 5 for transferring the toner image is insufficient, and image deterioration and transfer failure occur. However, in the present invention, when the transfer current in the image area is insufficient, the current can be supplied from the constant voltage source 152. For example, when special paper is used in a high-temperature and high-humidity environment, the resistance value of the variable resistor r32 is reduced to increase the supply of current to the transfer unit, and the current value flowing through the transfer material 5 is increased. Is possible. Conversely, in printing in a low-temperature and low-humidity environment, the resistance value of the variable resistor r32 can be increased so that adjustment can be made so that an overcurrent is not applied to the transfer portion.

FIG. 6 is a schematic perspective view of the image forming apparatus according to the embodiment of the present invention. The variable control means of the variable resistor and the variable control means of the second power supply use, for example, an operation panel 190 as an input means arranged above the entrance 16 of the cassette 4 as shown in FIG. It is also possible to control it. As the control means, for example, a volume is preferable. In addition, the image forming apparatus 1
It is desirable to appropriately adjust as a configuration that can be adjusted by another device connected to the device, for example, a host computer (not shown).

In the above embodiment, the monochrome (black) image forming apparatus 1 is illustrated, but the present invention is not limited to this. For example, a color image forming apparatus using yellow, magenta, cyan, and black toners The present invention can also be applied to

At this time, depending on the characteristics of the toner used,
The transfer current required for good transfer is different. Therefore, it is preferable that the current supplied be different depending on the characteristics of the toner of each color. Further, it is preferable that the voltage value of the variable resistor r32, the voltage of the constant voltage source, the adjustable voltage width, and the like are appropriately determined according to the characteristics of each toner.

Further, the number of parts to be used can be reduced by using both a variable resistor and a power source for the toner having the same current characteristics at the time of transfer.

In the above embodiment, the transfer roller used is an example of a transfer roller. However, the present invention can be applied to various transfer units such as a brush, a blade, and a belt. Good transfer can be achieved.

In particular, for contact transfer means such as transfer rollers, brushes, and belts, a large proportion of the current supplied to the fixing means and the like via the transfer material 5 leaks. Occurs more prominently. However, by using the present invention, the above-mentioned problems can be avoided.

[0074]

According to the present invention, the following effects can be obtained.

(1) To form an image by applying a potential difference between a transfer means for transferring an image to a recording medium in contact with an image carrier for carrying a visualized image and an image carrier. Compensating means arranged in parallel with the transfer means with respect to the power supply means, the compensating means includes a resistance means, and a second power supply means capable of compensating the amount of current supplied to the transfer means. Since the image forming apparatus has a compensating means including a resistor connected in parallel with the power supply means and the second power supply means, an electric load between the transfer means and the image carrier is provided. The current supplied to the transfer unit can be increased or decreased in accordance with the increase or decrease of the transfer member. When the necessary current is supplied from the second power supply, Good can be avoided. In addition, a large-capacity power supply capable of outputting a required current value is not required, and cost can be reduced.

(2) By using a constant-voltage power supply as the second power supply capable of compensating the amount of current supplied to the transfer means, the resistance of the transfer material can be reduced, for example, in a low-temperature and low-humidity environment. When the temperature is very high, the transfer is not affected, and the necessary current can be supplied only when necessary, such as in a high temperature and high humidity environment.

(3) Since the output of the second power supply means is variable, the output value of the second power supply means can be variably controlled, so that the optimum transfer conditions can be adjusted according to the characteristics of the transfer material used and the use environment. Can be realized.

[Brief description of the drawings]

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

FIG. 2A is a diagram schematically illustrating a configuration of a transfer unit;
(B) is an equivalent circuit diagram of the configuration shown in (A).

3A is a diagram schematically illustrating a configuration of a transfer unit including a variable resistor, and FIG. 3B is an equivalent circuit diagram of the configuration illustrated in FIG.

4A is a diagram schematically showing a cross section of a transfer unit when a transfer material 5 having a small paper width is used, and FIG. 4B is an equivalent circuit diagram of the configuration shown in FIG.

FIG. 5 is a diagram schematically showing a cross section of a transfer portion when a transfer material 5 having a solid image 21 is used.

FIG. 6 is a schematic perspective view of an image forming apparatus according to an embodiment of the present invention.

7A is a diagram schematically showing a conventional transfer device of an image forming apparatus using a transfer roller, and FIG. 7B is an equivalent circuit diagram of the configuration shown in FIG.

[Explanation of symbols]

 5-transfer material 88-transfer power supply 87-constant current source 152-constant voltage source 176-transfer roller 178-photosensitive drum i1, i2, i31, i32-current r1, r2-resistance component r31-resistance (fixed resistance)

Continuing from the front page (72) Inventor Kohei Kamei 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Hideki Onishi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Sharp (72) Inventor Hiroshi Doshoda 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 2H032 AA05 BA12 BA13 BA23 CA02 CA12

Claims (3)

[Claims] 1. An image forming apparatus according to claim 1, further comprising: applying a potential difference from a power supply between an image carrier for carrying a visualized image and a transfer unit for transferring the image to a recording medium in contact with the image carrier. In the image forming apparatus, a resistance unit and a second power supply unit capable of compensating an amount of current supplied to the transfer unit are arranged in series with the power supply unit together with the transfer unit. An image forming apparatus comprising a compensating means connected to the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the second power supply is a constant voltage power supply. 3. The image forming apparatus according to claim 2, wherein an output of said second power supply unit is variable.