JP2002132069A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-quality image at low cost by using a contact type transfer member for transfer, even if processing speed is high. SOLUTION: In this image forming device, an ion conduction type transfer roller is used, and a transfer bias control system is provided with three constant- current sources, whose constant current values are I0, I1 and I2 and one constant-voltage power source. When controlling the transfer bias in an ATVC system, ambient humidity is detected, and the constant-current power sources are selected in accordance with an environmental value E. By applying the constant current value I0 in the case of E=0 (ordinary environment), the constant current value I1 in the case of E=1 (low-humidity environment) and the constant current value I2 in the case of E=2 (high humidity environment), generated voltage at such a time Vt0, Vt01 or Vt02 is monitored. According to a function Vt0=F1(Vt01) and F2(Vt02), Vt0 in the case of E=1, 2 is calculated. In the above-mentioned way, Vt0 is found as amount obtained by measuring the resistance of a transfer roller in all the cases of E=0, 1, 2. The constant voltage bias VT is decided in accordance with a function VT=F3(Vt0), and VT is applied to the transfer roller so as to perform transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus such as a copying machine or a laser beam printer, and more particularly, to transferring a visible image on an image carrier to a recording material such as paper. More particularly, the present invention relates to an image forming apparatus using a contact-type transfer member.

[0002]

2. Description of the Related Art For example, an image forming apparatus such as an electrophotographic laser beam printer is an electrophotographic photosensitive member which is generally a rotary drum type as an image bearing member, that is, a photosensitive drum, and which is used for primary charging, image exposure, and development. An image forming process means forms a toner image as a visible image corresponding to target image information on the surface of the photosensitive drum, transfers the toner image to a recording material such as paper by a transfer means, and further fixes the recording material to a fixing means. And heat-fixes the toner image to a recording material as a permanent fixed image, and outputs the image as a formed image (copy, print).

The photosensitive drum on which the transfer of the toner image has been completed is
Adhered contaminants such as transfer residual toner and paper powder remaining on the surface are removed by cleaning, and are repeatedly used in an image forming process.

[0004] The above-mentioned transfer means has an advantage that the conveyance path of the recording material can be simplified and can be stabilized. Therefore, a contact-rotation type transfer member, a so-called transfer roller, has been frequently used in recent years. . The transfer roller abuts on the photosensitive drum to form a nip portion that forms a transfer portion, and the recording material is nipped and conveyed at the transfer portion, and the toner image on the photosensitive drum is transferred by a transfer voltage applied to the transfer roller. Is electrostatically transferred to a recording material.

The transfer roller is adjusted to a resistance value of about 10 × ⁶ to 10 × ¹⁰ Ω. A transfer roller proposed in recent years is provided with a rubber elastic layer on the outer peripheral surface of a conductive cored bar. The layers are made to have ionic conductivity. The resistance of the ion-conductive transfer roller tends to fluctuate under the influence of the temperature and humidity of the environment atmosphere, and the fluctuation of the resistance of the transfer roller induces poor image transfer, explosion and scattering, and paper marks.

Therefore, in order to prevent transfer failure or paper marks due to a change in resistance of the transfer roller, the resistance value of the transfer roller is measured, and a transfer voltage (transfer bias) applied to the transfer roller is determined according to the measurement result. An applied transfer voltage control method for appropriately controlling is adopted. An example of such an applied transfer voltage control means is an ATVC (Active Tranafer Voltage Cont.) Disclosed in Japanese Patent Application Laid-Open No. 2-123385.
trol) is known.

The ATVC control is a means for optimizing a transfer voltage applied to a transfer roller at the time of transfer, and can prevent occurrence of transfer failure, paper marks, and the like. In the ATVC control, a desired constant current is applied from the transfer roller to the photosensitive drum during the pre-rotation process of the image forming apparatus, and the voltage value generated at that time is measured to detect the resistance of the transfer roller, thereby detecting the resistance of the transfer roller. During transfer, a voltage corresponding to the resistance value is applied as a transfer voltage to the transfer roller by constant voltage control.

[0008] As another applied transfer voltage control method, a PTVC (Pro) disclosed in JP-A-5-181373 is disclosed.
gramable Transfer Voltage Control). The PTVC control applies a constant voltage for resistance detection to the transfer roller during the pre-rotation process, detects a current flowing through the photosensitive drum at this time, and when the current value is apart from a set value, the detection constant voltage. The constant voltage value at which the current set value can be obtained by repeatedly detecting the current while changing the current value.

While the ATVC control detects the resistance of the transfer roller by a constant current control, the PTVC control is performed only by a constant voltage control. Therefore, there is an advantage that the power supply circuit is simplified and the detection accuracy is improved.

In order to accurately detect the transfer roller resistance and determine the optimum applied transfer voltage by the above-mentioned ATVC control and PTVC control, the resistance value for one round of the transfer roller is monitored and the average value is taken. In addition, since the transfer roller resistance has a voltage dependency, it is important to set a constant current value such that a value close to the voltage applied during transfer occurs. Therefore, as described above, usually P
The TVC control and the like are performed during the pre-rotation, which has a time margin in the image forming process.

[0011]

By the way, with the speeding up of the laser beam printer, usages similar to those of copying machines, such as printing a plurality of identical documents by the printer, have been expanding. For this reason, there is a demand for further high-speed printers, and at the same time, high image quality and low cost as in the past, and high functions as in a copying machine.

However, in order to use the transfer roller by the conventional transfer voltage control, a high-output high-voltage power supply is required, which increases the cost and causes a problem of leakage.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image at a low cost by using a contact-type transfer member even when a process speed is increased. To provide.

[0014]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A transfer member to which a visible bias on the image carrier is transferred in contact with the back surface of the recording material, a transfer bias is applied, and a transfer bias applying unit that applies a transfer bias to the transfer member,
Control means for detecting the resistance of the transfer member during non-image formation and controlling a transfer bias applied to the transfer member;
An image forming apparatus having an environment detecting means for detecting an environment, wherein the transfer bias applying means has a constant voltage power supply and a plurality of constant current power supplies, and the constant current power supply is provided in accordance with an environment detected by the environment detecting means. And determining the output voltage of the constant voltage power supply during image formation by detecting the resistance of the transfer member using the selected constant current power supply.

According to the present invention, the environment detecting means detects the humidity of the environment. Alternatively, both the humidity and the temperature of the environment are detected by the environment detecting means. The transfer member is an ion conductive transfer roller.

The present invention is also directed to a transfer member to which a transfer bias is applied for transferring a visible image on an image carrier in contact with the back surface of a recording material, and a transfer bias applying means for applying a transfer bias to the transfer member. And control means for controlling the transfer bias applied to the transfer member by detecting the resistance of the transfer member during non-image formation, and environment detecting means for detecting the environment. A constant voltage power supply that can control the output voltage of the constant voltage power supply at the time of constant voltage output, detects the output current of the transfer bias applying unit, and when the output current reaches a desired value. In the image forming apparatus which determines the output voltage of the constant voltage power supply at the time of image formation by detecting the resistance of the transfer member by the voltage of the transfer member, the resistance of the transfer member is determined according to the environment detected by the environment detecting means. By performing the resistance-detection of the transfer member to switch the desired value of the output current, an image forming apparatus and determines the output of the constant voltage power supply at the time of image formation.

The present invention further provides a transfer member to which a transfer bias is applied for transferring a visible image on an image carrier to a back surface of a recording material, and a transfer bias applying means for applying a transfer bias to the transfer member. And a control means for detecting a resistance of the transfer member during non-image formation and controlling a transfer bias applied to the transfer member, wherein the transfer bias applying means includes a constant voltage power supply and a plurality of constant voltage power supplies. Having a current power supply, detecting an environment by the detected resistance of the transfer member, selecting the constant current power supply in accordance with the detected environment, and using the selected constant current power supply, the transfer member Wherein the output of the constant voltage power supply at the time of image formation is determined by detecting the resistance of the image forming apparatus.

[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 shows an embodiment of the image forming apparatus of the present invention. This image forming apparatus is a laser beam printer (LBP) capable of forming a double-sided image using an electrophotographic process.

A feature of the present invention is that the resistance of the rubber roller of the ion conductive type used for the transfer means is detected with high accuracy, and highly accurate transfer bias control is enabled. First, a schematic configuration of the image forming apparatus will be described.

In this image forming apparatus, as shown in FIG. 1, a photosensitive drum (rotating drum type electrophotographic photosensitive member) 1 as an image carrier, a charging roller 2 as a contact rotary type charging member, and an image exposure means Laser scanner 3, developing device 4,
It includes a transfer roller 9 as a contact-rotation type transfer member, a cleaning device 10, a fixing device 11, a paper feed cassette 5, and the like, and further has an environment sensor 16 for measuring an environmental atmosphere.

The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed (process speed) in the clockwise direction of the arrow, and in the course of this rotation, the outer peripheral surface is charged to a predetermined polarity and potential by the charging roller 2 (primary charging). ). Next, the laser scanner 3 outputs a laser beam L on / off-modulated in accordance with image information input from an external device such as an image scanner or a computer (not shown) to scan and expose the surface of the photosensitive drum 1. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1.

The electrostatic latent image on the photosensitive drum 1 is developed by a developing device 4 using a developer (toner or toner + carrier), and is visualized as a toner image. The developer is carried on a rotating developing sleeve 4 a of the developing device 4 and is conveyed to a developing unit facing the photosensitive drum 1, where toner adheres to the latent image on the photosensitive drum 1 to form the latent image. develop. In the case of a laser beam printer, a reversal development method is generally used in which toner is adhered to an exposed portion of a laser beam to develop a latent image.

The paper feed cassette 5 is installed below the image forming apparatus, and stores paper (paper) P as a recording material.
The paper P in the cassette 5 is fed one by one by a paper feed roller 6 or the like driven based on a paper feed start signal, and passes through a registration roller 7 and a paper path 8a, where the photosensitive drum 1 and the transfer roller 9 Is supplied to the transfer portion T, which is a contact nip portion of the transfer member. At this time, after the paper P is once stopped by the registration roller 7, the paper P is transferred from the registration roller 7 so that the leading end of the toner image on the photosensitive drum 1 reaches the transfer portion at the same timing as the transfer portion T reaches. Will be sent out.

The paper P supplied to the transfer site T is nipped and conveyed by the photosensitive drum 1 and the transfer roller 9, and at the same time, a transfer bias (not shown) is applied to the transfer roller 9 from a transfer bias application power source (not shown). Transfer voltage) is applied under constant voltage control. By applying the transfer bias, the toner image formed on the photosensitive drum 1 at the transfer portion T is electrostatically transferred to the surface of the paper P. The transfer roller 9 and the transfer bias control will be described later.

The paper P on which the toner image has been transferred at the transfer site T
Is transported separately from the photosensitive drum 1 and introduced into the fixing device 11 through the paper path 8b, where the toner image is fixed by heating and pressing, and then guided by the first flapper 12 to the ascending paper path 8c side. Then, the paper is discharged from the paper discharge port 13 onto a paper discharge tray 14 on the upper surface of the apparatus. On the other hand, the photosensitive drum 1 on which the transfer of the toner image has been completed is
Then, the transfer residual toner and paper dust on the surface are cleaned and removed, and are repeatedly used for image formation.

The above is the process in the single-sided print mode for forming an image on one side of the sheet P. When the double-sided print mode for forming an image on the other side (second side) in addition to one side (first side) of the paper P is selected,
By switching the first flapper 12, the paper P that has passed through the fixing device 11 is sent through the second flapper 19 to the descending paper path 8d. Next, the second flapper 19 is switched, the sheet P is fed to the double-sided paper path 8e with the rear end thereof leading, and is supplied to the transfer portion T via the registration roller 7 and the paper path 8a. As a result, the paper P is supplied with the second side facing the photosensitive drum 1 at the transfer portion, and thereafter, the image is transferred and fixed as in the case of single-sided printing, and a fixed image is obtained on the second side of the paper P. Thereby, the double-sided image formation ends.

According to this embodiment, the transfer member of the contact rotary type, that is, the transfer roller 9 is an ionic conductive solid roller, and a solid rubber obtained by reacting NBR rubber with a surfactant or the like on the core 9b. The layer 9a is formed. Unevenness of circumferential resistance value of transfer roller 9 (circular unevenness)
Is 1.5 or less as in the conventional case, and the surface roughness is R
a = 5.0 μm.

The resistance (set resistance) and the resistance unevenness (circumferential unevenness) of the transfer roller 9 were measured using the resistance measuring device shown in FIG.

The measuring apparatus has an aluminum drum 100 which is driven to rotate. The transfer roller 9 is pressed against the drum 100 with a contact pressure of 1.5 kgf (14.7 N), and the transfer roller is driven to rotate. When 2.0 kV is applied from the bias power supply 20 between the roller core 9b and the ground and the current flowing through the drum 100 at that time is measured by the ammeter A, the resistance of the transfer roller is measured. At this time, the above current measurement is performed for one or more rounds of the transfer roller 9, a plurality of current values at that time are sampled, and a roller resistance is obtained by using an average value of the plurality of current values. The resistance unevenness is obtained as a ratio Imax / Imin, where Imax is the maximum value of the sampled current value and Imin is the minimum value. In this embodiment, as described above, the resistance unevenness is 1.5
Hereinafter, that is, Imax / Imin ≦ 1.5.

In this embodiment, the transfer bias is controlled by the transfer bias control system shown in FIG. 3 and applied to the transfer roller. The transfer bias control system includes an environment sensor 16, a high-voltage power supply (transfer bias application power supply) 25, and a power supply driving circuit 2.
6, memory 28, I / O port 29, and CPU (control unit) 27 for transmitting and receiving signals to and from these via bus 30
Is provided.

The environmental sensor 16 is provided with a sensor section in a portion where the atmosphere of the image forming apparatus is most easily measured. In this embodiment, the environment sensor 16 can detect relative humidity (RH), and its linear measurable area is 20% RH to 7%.
Those having a performance of 0% RH were used. The main body of the sensor 16 is provided with a circuit that outputs the detected humidity (relative humidity) as an electric signal, and the CPU 27 A / D converts the voltage signal and recognizes it as humidity.

The recognized humidity is determined at a plurality of environmental levels based on a predetermined threshold value. In the present embodiment, two thresholds of the environmental level E are set to 30% RH and 70% RH. In a low humidity environment where the humidity is less than 30% RH, E = 1,
E = 2 was determined for a high humidity environment greater than 70% RH, and E = 0 for a normal humidity environment (normal environment) where the humidity was 30% RH or more and 70% RH or less.

A high voltage power supply 25 for applying a transfer bias is a constant current power supply 2 for outputting constant currents of current values I0, I1, and I2.
1, 22, 23 and one constant voltage power supply 24. C
The PU (control unit) 27 can perform selection of these constant current power supplies 21 to 23, monitoring of a voltage when a constant current is applied, and control of turning on / off each power supply via a power supply drive circuit 26.

Next, detection of the resistance of the transfer roller 9 will be described. The resistance of the transfer roller is detected as a voltage value generated when a constant current is applied to the transfer roller. According to the present invention, the resistance detection of the transfer roller is performed as follows according to the value of the environment value E recognized by the CPU 27.

(1) When Environment Value E = 0 (Normal Environment) A constant current power source 21 applies a constant current bias having a constant current value I0 to the transfer roller 9, and a voltage Vt0 generated at that time is measured. The constant current value I0 to be applied is A at room temperature and normal humidity.
A current value suitable for the TVC system is selected, and an appropriate value of the current value is determined by a process speed, a transfer roller length, and the like.

(2) When Environment Value E = 1 (Low Humidity Environment) A constant current bias of constant current value I1 is applied to the transfer roller 9 by the constant current power supply 22, and the voltage Vt01 generated at that time is measured. As the constant current value I1 to be applied, a value smaller than the constant current value I0 is selected.

(3) When Environment Value E = 2 (High Humidity Environment) A constant current bias of constant current value I2 is applied to the transfer roller 9 by the constant current power supply 23, and the voltage Vt02 generated at that time is measured. As the constant current value I2 to be applied, a value smaller than the constant current value I1 is selected.

The voltages Vt0, Vt0 detected by the above method
1. Since Vt02 has a different constant current value, it is necessary to correct Vt01 and Vt02 in order to use it as a detected amount of the resistance of the transfer roller. When E = 0, no correction is made, and the measured voltage Vt0 is used as it is.

When E = 1, 2, F1 (x), F2
Assuming that (x) is a function of x, the correction is made according to the following equation when E = 1: Vt0 = F1 (Vt01), and when E = 2: Vt0 = F2 (Vt02).

The functions F1 (x) and F2 (x) are set as follows: F1 (x) = x × a F2 (x) = x ÷ b The constants a and b are defined as follows: a = I0 / I1 = 1.5 b = I2 / I0 = 3 for the sake of simplicity.

Further, a transfer bias VT calculated by VT = F3 (Vt0) is applied at the time of image formation by using the function F3 (x) of x, using Vt0 corrected by the above method. F3 (x) will be described later.

In this embodiment, the process speed is 145 m
The transfer bias was controlled by detecting the resistance of the transfer roller using a laser beam printer having a maximum paper size of A3 at m / sec. The constant current value I0 of the constant current power supply 21 is 8 μA
This is an optimum current value for use of a printer of this specification at normal temperature and normal humidity. Also, the constant current value I of the constant current power supplies 22 and 23
1 and I2 were 5.3 μA and 24 μA, respectively. The constant voltage power supply 24 is controlled by an input from the CPU 27, and has a maximum output of 6 kV.

The method for detecting the transfer roller resistance and controlling the transfer bias in this embodiment will be described with reference to the flowchart of FIG.

First, the output of the environment sensor is detected (step S1). Next, a constant current power supply used for performing the ATVC control is selected according to the value of the environment value E (step S).
2, S3). If the environment value E = 0, the power source 21 is selected, if E = 1, the power source 22 is selected, and if E = 2, the power source 23 is selected, and the flow is branched.

When E = 0 (normal environment), a current having a constant current value I0 is applied from the constant current power supply 21, and the voltage Vt0 at that time is monitored (step S3). Otherwise, that is, when E = 1 (low humidity environment), a current having a constant current value I1 is applied by the constant current power supply 22 and the voltage Vt01 at that time is monitored. When E = 2 (high humidity environment), A current having a constant current value I2 is applied by the constant current power supply 23, and the voltage Vt02 at that time is monitored (Step S).
5).

Next, the functions F1 (Vt01) and F2 (Vt0)
According to 2), Vt0 in the case of E = 1, 2 is calculated (step S6). As described above, in all cases of E = 0, 1, and 2, the measured resistance of the transfer roller is Vt0
Can be calculated.

At the time of image formation, a function VT as shown in FIG.
= F3 (Vt0), the constant voltage bias VT is determined (step S7), and VT is applied to the transfer roller to perform transfer. The function VT = F3 (Vt0) is obtained by
We select the one that does not cause paper marks, transfer failure, etc.

When the transfer by the transfer roller is performed and the process speed of the image forming apparatus is high, a very large amount of current is required. However, when the transfer roller 9 of the ion conductive type is used as in the present invention. In addition, since the resistance fluctuation due to the environment is large, a problem such as leakage occurs, so that the transfer bias applying power source has an upper limit in the maximum output. In the case of the present embodiment, the maximum voltage output of the constant voltage power supply 24 is 6 kV. However, even if the transfer output is set to 6 kV or more, a voltage drop due to leakage occurs and transfer failure occurs. Therefore, the current resistance is increased by lowering the set resistance of the transfer roller 9.

Similarly, when the resistance of the ion-conductive transfer roller is detected by the ATVC control, there has been a disadvantage that the resistance cannot be detected with high accuracy in the past because the resistance fluctuates due to the environment. According to the embodiment, the following favorable effects were obtained.

In a high-humidity environment, that is, in an environment where the transfer roller has a low resistance, the voltage Vt0 generated by detecting the transfer roller resistance becomes very small in the conventional method, and the measurement accuracy of the transfer roller resistance cannot be obtained. However, in this embodiment, a voltage three times as high as Vt0 obtained with an ATVC constant current value of 8 μA in a normal environment can be obtained.
Specifically, while Vt0 is a value of 0 to 1 kV in the conventional method, it is a value of about 0 to 4 kV in the present embodiment, so that the measurement accuracy of the transfer roller resistance is significantly improved.

On the other hand, in a low-humidity environment, that is, in an environment in which the transfer roller has a high resistance, Vt0 becomes extremely large in the conventional method, and exceeds the output range of the constant current power supply or is used near the upper limit. As a result, control accuracy cannot be obtained. In this embodiment, the ATVC in a normal environment
Two thirds compared to Vt0 obtained with a constant current value of 8 μA
Double voltage can be obtained. More specifically, Vt0 has a value of 4 to 7 kV in the conventional method, but has a value of about 2 to 5 kV in the present embodiment. Therefore, the maximum output of the power supply can be reduced, and the leakage is reduced. And other problems can be avoided.

The image forming apparatus shown in FIG. 1 is capable of both-side printing and multiple printing. In the case of such printing, since the resistance of the sheet after fixing increases, it is better to apply a constant voltage bias larger than the above-described F3 (Vt0) as the transfer constant voltage bias during image formation.

Embodiment 2 In this embodiment, a temperature and humidity sensor capable of detecting temperature and humidity was used as the environment detecting means. The configurations of the image forming apparatus and the transfer roller are basically the same as those in the first embodiment.

The temperature and humidity sensor has a humidity of 20 to 70% RH,
Those capable of linear detection at a temperature of 10 to 40 ° C were used. In the first embodiment, only the influence of humidity is taken into consideration. However, by taking into account the influence of temperature, finer control becomes possible.

The CPU determines an environment value based on a table as shown in FIG.
Is stored. Environment value E = 1 is a low temperature environment, E = 2 is a normal humidity to high humidity and high temperature or high humidity and normal temperature environment, and E = 0 is a low humidity and high temperature or low humidity to normal humidity and normal temperature environment excluding them. .

According to the environment value E detected in this way,
In the same manner as in the first embodiment, Vt0 was calculated as the measured amount of the transfer roller resistance, and the constant voltage bias VT was determined to perform transfer and image formation was performed. On the side, it was confirmed that high image quality could be obtained and transfer bias control with high accuracy could be performed.

Embodiment 3 In this embodiment, the voltage monitored at the time of applying a constant current is used instead of detecting the environment by the environment sensor in the first embodiment, and the environmental value E is changed according to the magnitude of the voltage. The value is determined, and the constant current power supply is switched to detect the resistance of the transfer roller.

The resistance detection and the transfer bias control in this embodiment will be described with reference to the flowchart of FIG. 7. First, a constant current value I0 is applied to the transfer roller by the constant current power supply 21 to detect the transfer roller resistance. The voltage Vt0 is monitored (step S1). Next monitored voltage V
From the value of t0, the environment value E is determined using 1.0 kV and 5.0 kV as thresholds (step S2). After that, according to the first embodiment shown in FIG. 4, the constant current power supplies 22 and 23 are selected according to the value of the environment value E (steps S3 and S4).
= 1, a current having a constant current value I1 is applied from the constant current power supply 22, and the voltage Vt01 at that time is monitored.
When = 2, the current of the constant current value I2 is applied from the constant current power supply 23, and the voltage Vt02 at that time is monitored (step S5).

Next, the functions F1 (Vt01) and F2 (Vt0)
According to 2), Vt0V is calculated when E = 1 and 2 (step S6). As described above, Vt0 is calculated in all cases of E = 0, 1, and 2, and at the time of image formation, the constant voltage bias VT is determined according to the function VT = V3 (Vt0) as shown in FIG. (Step S7) Transfer is performed by applying VT.

In this embodiment, Vt0 and VT are obtained and image formation is performed in the same manner as in Embodiment 1 in accordance with the environmental value E detected as described above. With respect to the above, it was confirmed that high image quality could be obtained and that the transfer bypass control with high precision was performed.

In the present embodiment, the rotation time of the device for detecting the resistance becomes longer, and the first print time may be longer than in the first and second embodiments. Need not be newly provided, and the cost can be reduced.

Embodiment 4 In this embodiment, the transfer bias was controlled by detecting the resistance of the transfer roller by the PTVC control method.

In this embodiment, the transfer bias application power source is
It is assumed that a constant voltage power supply capable of controlling the voltage according to the input from the CPU is provided. As the environment detecting means, the environment sensor 16 capable of detecting the humidity shown in the first embodiment is used, and the CPU determines three values of the environmental values E = 0, 1, and 2 according to the detection result, as in the first embodiment. Take.

The resistance of the transfer roller is detected by the PTVC method. As shown in the flowchart of FIG. 8, three types of current values I0, I1, and I2 are set as target current values flowing when a constant voltage is applied to the transfer roller. The target current values I0, I1, and I2 are switched according to the detection result of the environment sensor (steps S1, S2, S3), and the resistance of the transfer roller is detected by the PTVC method (steps S4, S5).

Thereafter, as in the first embodiment, the function F1 (V
t01), according to F2 (Vt02), Vt0 is calculated for E = 1, 2 (step S6), and Vt0 for all cases of E = 0, 1, 2 is obtained. The constant voltage bias VT is determined according to the function VT = V3 (Vt0) (step S7), and transfer is performed by applying VT.

In this embodiment, as described above, when Vt0 and VT are obtained by PTVC control according to the environmental value E to form an image, the transfer roller has a high resistance side and a low resistance side depending on the environment. It was confirmed that image quality was obtained and high-precision control was performed.

[0068]

As described above, according to the present invention,
The transfer bias can be set by detecting the resistance of the ion conductive rubber roller used as the transfer member of the transfer unit with high accuracy in all environments regardless of the high humidity environment or low humidity environment. High image quality can be obtained, and even in a high-speed image forming apparatus with a large process speed,
High image quality can be obtained.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view schematically showing an apparatus for detecting a resistance (set resistance) of a transfer roller of the image forming apparatus of FIG.

FIG. 3 is a schematic diagram illustrating a transfer bias control system of the image forming apparatus of FIG. 1;

FIG. 4 is a flowchart showing transfer roller resistance detection and transfer bias control by the ATVC method in consideration of the environment in the embodiment of FIG. 1;

FIG. 5 is a graph showing a table used for determining a transfer bias under the control of FIG. 4;

FIG. 6 is an explanatory diagram showing a table used for determining an environment value in another embodiment of the present invention.

FIG. 7 is a flowchart illustrating transfer roller resistance detection and transfer bias control by an ATVC method in consideration of the environment according to still another embodiment of the present invention.

FIG. 8 is a flowchart illustrating a transfer roller resistance detection and a transfer bias control by a PTVC method in consideration of an environment according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 9 transfer roller 16 environment sensor 21-23 constant current power supply 24 constant voltage power supply 25 transfer bias application power supply 27 CPU

Claims (6)

[Claims] A transfer member for applying a transfer bias to transfer a visible image on an image carrier to a back surface of a recording material; a transfer bias application unit for applying a transfer bias to the transfer member; An image forming apparatus comprising: a control unit configured to control a transfer bias applied to the transfer member by detecting a resistance of the transfer member during image formation; and an environment detection unit configured to detect an environment. A voltage power supply and a plurality of constant current power supplies, wherein the constant current power supply is selected according to the environment detected by the environment detection means, and the resistance of the transfer member is detected using the selected constant current power supply. The image forming apparatus determines the output voltage of the constant voltage power supply at the time of image formation. 2. A transfer member to which a transfer bias is applied to transfer a visible image on an image carrier to a back surface of a recording material, a transfer bias application unit for applying a transfer bias to the transfer member, The image forming apparatus includes a control unit that detects a resistance of the transfer member during image formation and controls a transfer bias applied to the transfer member, and an environment detection unit that detects an environment. The transfer bias application unit can control a voltage. A constant voltage power supply, changing the output voltage at the time of constant voltage output of the constant voltage power supply,
The output voltage of the constant voltage power supply at the time of image formation is determined by detecting the output current of the transfer bias applying unit and detecting the resistance of the transfer member based on the voltage when the output current reaches a desired value. In the image forming apparatus, the output of the constant voltage power supply at the time of image formation is determined by performing a resistance detection of the transfer member by switching a desired value of the output current in accordance with the environment detected by the environment detection unit. An image forming apparatus. 3. An image forming apparatus according to claim 1, wherein said environment detecting means detects environmental humidity. 4. An image forming apparatus according to claim 1, wherein said environment detecting means detects both humidity and temperature of the environment. 5. A transfer member to which a transfer bias is applied for transferring a visible image on an image carrier to a back surface of a recording material, a transfer bias application unit for applying a transfer bias to the transfer member, In an image forming apparatus having a control unit for detecting a resistance of the transfer member during image formation and controlling a transfer bias applied to the transfer member, the transfer bias application unit includes a constant voltage power supply and a plurality of constant current power supplies. Has an environment detected by the detected resistance of the transfer member, selects the constant current power supply according to the detected environment, and detects the resistance of the transfer member using the selected constant current power supply. The output of the constant voltage power supply at the time of image formation. 6. The image forming apparatus according to claim 1, wherein the transfer member is an ion conductive transfer roller.