JPH10186886A - Transferring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply obtain a stable transfer-separating performance irrespective of a humidity condition by correcting a specific current quantity based on comparing result of comparing potential on charge applying area when differential current becomes the specific current quantity between a present state of a transfer material in a transferring position and the absent state. SOLUTION: This device controls a transfer power source 75 by a controlling device 78 prior to the transfer paper entering in a transferring nip part N, so that the differential current 11 becomes to the target value, and detects the applying voltage V1 at this time and gets storing means to store. In timing when a leading end of the transfer paper reaches an outlet part N1 of the transferring nip N, the applying voltage V2 by the transfer power source 75 is detected. Then, V1 and V2 are compared by the controlling part as comparing means. At this time, in the case becoming to V1>=V2, the target value of the differential current is corrected so as to become to large, by the controlling part provided with function as correcting means too.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device used in an image forming apparatus such as a copying machine, a facsimile, a printer, etc., and more particularly, to a transfer device in which a transfer material is brought into contact with the surface of an image carrier on which an image to be transferred is formed. The present invention relates to a transfer device provided with a belt.

[0002]

2. Description of the Related Art Conventionally, in an apparatus using a transfer belt of this type, a surface of a photoreceptor serving as a latent image carrier, a transfer paper, and a transfer belt are brought into close contact with each other, and the transfer belt is placed in the transfer belt. The toner image on the photoreceptor is transferred to a transfer sheet by injecting electric charges into the back surface of the belt to form an electric field. However, in a high-humidity environment, since the resistance of the belt decreases, charges are excessively injected into the belt, which causes problems such as poor separation.

As a technique for solving the above problem, for example, in Japanese Patent Application Laid-Open No. 3-231274, a transfer electrode or a corona charger as a charge supply means to which a predetermined voltage is applied is connected to an image carrier side of a transfer belt. Supplies the transfer charge to the opposite surface, detects the amount of current flowing into at least one of the plurality of support rollers on which the transfer belt is stretched, and according to the detected amount of current, the transfer electrode and the corona charging. A transfer device that controls the amount of current flowing to a container is disclosed. Thus, constant current control is performed to keep the current flowing to the photoconductor constant.

[0004]

However, in a high-humidity environment, the resistance of not only the belt but also the transfer paper is often reduced. For this reason, Japanese Unexamined Patent Publication No. Hei.
By controlling the amount of current flowing through the transfer electrode or the corona charger in accordance with the amount of current flowing into at least one of the above-described support rollers as disclosed in Japanese Patent Application Laid-Open No. 4 (1994) -208, the current flowing toward the photoconductor is maintained constant. In a transfer device that performs constant current control, not only the current flowing from the transfer belt to the photoconductor,
The amount of current flowing into the transfer paper having a reduced resistance and flowing into the housing via a portion other than the photoconductor, for example, a registration roller, is also included in the current amount. Therefore, the total sum of the current flowing from the transfer belt to the photoconductor and the current flowing to a portion other than the photoconductor via the transfer paper having reduced resistance is made constant. For this reason, the current flowing into the photoreceptor is reduced, and the transfer electric field is reduced, and the reduction in the electric field causes problems such as transfer failure and separation failure.

As a technique for solving the above problem, for example, the resistance of a transfer belt and a transfer paper disclosed in Japanese Patent Application Laid-Open No. Hei 3-223779 is measured, and a current amount of a means for supplying a charge to the transfer belt is measured. There is a technology to control.
However, there is a problem in that a measuring means for measuring the resistance is required, so that the apparatus is complicated and the cost is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a simple transfer apparatus capable of obtaining stable transfer separation performance regardless of humidity conditions.

[0007]

To achieve the above object, according to the present invention, there is provided a transfer belt for bringing a transfer material into contact with a surface of an image carrier on which an image to be transferred is formed, and a transfer belt for supporting the transfer belt. A belt support, a charge supply unit for supplying charge for transfer to the transfer belt, and a difference current between the amount of output current from the charge supply unit and the amount of current flowing from the transfer belt to the belt support is predetermined. And a constant current control means for controlling the charge supply means so that the amount of current becomes equal to the electric current amount of the electric charge supplied to the charge supply area of the transfer belt. Detecting means for detecting the potential of the charge supply region when the difference current reaches the predetermined current amount in a state where there is no transfer material at the transfer position by the potential detecting means; Ah Comparing means for comparing the potential of the charge supply region when the difference current reaches the predetermined current amount with the result detected by the potential detecting means in the state, and the predetermined value based on the comparison result by the comparing means. And a correcting means for correcting the amount of current.

In this transfer device, the potential detecting means detects the potential of the charge supply area of the transfer belt to which the charge is supplied by the charge supply means, and the comparing means has no transfer material at the transfer position. In the state, the result of detecting the potential of the charge supply region when the differential current reaches the predetermined current amount by the potential detecting means, and the differential current is determined by the predetermined current amount in a state where the transfer material is present at the transfer position. Then, the potential of the charge supply region is compared with the result of detection by the potential detection means. Then, the predetermined amount of current is corrected by the correcting means based on the result of comparison by the comparing means. Specifically, when the transfer current is not present at the transfer position and the difference current reaches the predetermined current amount, the potential of the charge application region is equal to the transfer current at the transfer position. If the potential is equal to or higher than the potential of the charge application area when the predetermined current amount is reached, it is considered that the current is flowing to a portion other than the image bearing member via the transfer material. To increase. Thereby, the transfer electric field can be stably maintained.

According to a second aspect of the present invention, there is provided a transfer belt for bringing a transfer material into contact with a surface of an image carrier on which an image to be transferred is formed, a belt support for supporting the transfer belt, and a voltage for transferring to the transfer belt. And a voltage applying means for applying a voltage so that the difference current between the amount of output current from the voltage applying means to the transfer belt and the amount of current flowing from the transfer belt to the belt support becomes a predetermined amount of current. And a constant current control unit for controlling the transfer position, wherein the transfer voltage is applied to the transfer position by applying the voltage applied by the voltage applying unit such that the differential current becomes the predetermined current amount in a state where there is no transfer material at the transfer position. Comparing means for comparing the applied voltage by the voltage applying means such that the differential current becomes the predetermined current amount in a state where the transfer material is present; and the predetermined current amount based on the comparison result by the comparing means. In which it characterized in that a positive correcting means.

In this transfer device, the comparing means transfers the voltage applied by the voltage applying means such that the difference current becomes the predetermined current amount when there is no transfer material at the transfer position, and transfers the voltage to the transfer position. In a state where the material is present, the applied voltage is compared with the applied voltage by the voltage applying means such that the differential current becomes the predetermined current amount. Then, the predetermined amount of current is corrected by the correcting means based on the result of comparison by the comparing means. Specifically, the voltage applied by the voltage applying means such that the difference current becomes the predetermined current amount in a state where the transfer material is not present at the transfer position is equal to the difference current when the transfer material is present in the transfer position. If the voltage is equal to or higher than the voltage applied by the voltage applying unit so that the predetermined current amount is obtained, it is considered that the current is flowing to a portion other than the image carrier via the transfer material. Increase the current. Thereby, the transfer electric field can be stably maintained.

According to a third aspect of the present invention, in the transfer device of the first or second aspect, a transfer material size detecting means for detecting a size of the transfer material in the belt width direction is provided, and a detection result by the transfer material size detecting means is provided. Wherein the correction means is configured to correct the predetermined current amount based on the following.

In this transfer device, the size of the transfer material is detected by the transfer material size detection means, and the predetermined current amount is corrected based on the detection result. Specifically, the larger the transfer material is, the larger the current flowing through the transfer material other than the image carrier through the transfer material becomes, so the predetermined current amount is increased. Thereby, the transfer electric field can be held more stably.

According to a fourth aspect of the present invention, there is provided a transfer belt for bringing a transfer material into contact with a surface of an image carrier on which an image to be transferred is formed, a belt support for supporting the transfer belt, and a voltage for transferring to the transfer belt. Voltage applying means for applying a voltage, a voltage varying means for changing an applied voltage by the voltage applying means, and an output current amount from the voltage applying means to the transfer belt and a current amount flowing from the transfer belt to the belt support. A differential current amount detecting means for detecting a differential current amount, wherein the voltage is adjusted so that a detection result by the differential current amount detecting means becomes a predetermined current amount in a state where there is no transfer material at the transfer position. When the voltage applied by the voltage applying means is changed by the variable means, the difference between the applied voltage and the result of detection by the difference current amount detecting means in the state where the transfer material is at the transfer position is the predetermined current amount. Comparing means for comparing the applied voltage when the applied voltage by the voltage applying means is changed by the voltage varying means, and applying the applied voltage by the voltage applying means based on the comparison result by the comparing means. Control means for setting.

In this transfer device, the voltage applying means applies the voltage by the voltage varying means so that the comparison result by the difference current amount detecting means becomes a predetermined current amount in a state where there is no transfer material at the transfer position. The applied voltage when the applied voltage is changed by the means and the voltage by the voltage varying means so that the detection result by the differential current amount detecting means becomes the predetermined current amount in a state where the transfer material is present at the transfer position. The applied voltage when the voltage applied by the applying means is changed is compared with the applied voltage. Then, an applied voltage by the voltage applying means is set based on a comparison result by the comparing means. Specifically, the voltage applied by the voltage applying means such that the difference current becomes the predetermined current amount in a state where the transfer material is not present at the transfer position is equal to the difference current when the transfer material is present in the transfer position. If the voltage is equal to or higher than the voltage applied by the voltage applying means so that the predetermined current amount is obtained, it is considered that the current flows to a portion other than the image carrier via the transfer material, and thus the difference current The applied voltage is set so as to increase the amount. In other cases, the applied voltage is set so that the difference current amount maintains the predetermined current amount. Thereby, the transfer electric field can be stably maintained.

According to a fifth aspect of the present invention, in the transfer device of the fourth aspect, a transfer material size detecting means for detecting the size of the transfer material in the belt width direction is provided, and based on a detection result by the transfer material size detecting means. The control means is configured to set the applied voltage.

In this transfer device, the size of the transfer material is detected by the transfer material size detecting means, and the control unit sets the applied voltage based on the detection result. Specifically, the larger the transfer material, the larger the current flowing through the transfer material other than the image carrier through the transfer material, so that the applied voltage is set so that the amount of the differential current increases. I do. Thereby, the transfer electric field can be held more stably.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a transfer device of an image forming apparatus will be described below. FIG. 2 is a schematic configuration diagram of a copying machine as an image forming apparatus including the transfer device according to the present embodiment. In FIG. 2, a drum-shaped photosensitive member 1 as an image carrier, which is uniformly charged by a charging charger 2 as a uniform charging means, rotates in the direction of an arrow, and an electrostatic latent image is formed by laser exposure 3 corresponding to image information. It is formed. Then, the electrostatic latent image on the photoconductor 1 is visualized by the developing device 4 to become a toner image. The toner image formed on the photoconductor 1 is transferred to a transfer belt 71 of a transfer device 7.
Is transferred to the transfer paper 6 as a transfer material conveyed in the direction of the arrow by the registration roller 5 at the transfer nip N in contact with the photoreceptor 1 and is conveyed to a fixing device (not shown). Be established. The residual toner is removed from the surface of the photoreceptor 1 after the transfer of the toner image by the cleaning blade 8 a of the cleaning device 8.
Removes the residual charges, and prepares for the next image formation.

FIG. 1 is a schematic configuration diagram of the transfer device 7. The transfer device includes a transfer belt 71 for bringing a transfer sheet as a transfer material into contact with the surface of the photoreceptor 1 as an image carrier on which an image to be transferred is formed, and a bias roller 74 as an electrode member contacting the transfer belt. The bias roller 7
4, a voltage applying means for applying a voltage for transfer to the transfer belt via the transfer belt 4, support rollers 72 and 73 as belt supports for supporting the transfer belt, and a transfer flow to the transfer belt via the bias roller 74. Output current IT and the current Ir flowing from the transfer belt to the support rollers 72 and 73
1 and a constant current control means for controlling the voltage applying means so that the difference current from Ir2 becomes a predetermined current amount. Specifically, the constant current control means includes a current detection device 77 serving as a difference current amount detection means for detecting the difference current amount (IT-Ir1-Ir2);
And a control device 78 as differential current control means for controlling the voltage applied by the voltage applying means so that the differential current amount becomes a predetermined current amount based on the detection result by the control unit 7. As the transfer belt 71, a belt formed by coating a resin layer on a medium-resistance rubber belt can be used. The transfer belt 71 includes support rollers 72, 7
3 and a bias roller 74. Of these two support rollers, the downstream support roller 72 in the transfer paper transport direction is a drive roller, and the upstream support roller 73 is a driven roller. The support rollers 72 and 73 are each grounded.

A transfer power supply 75 for applying a transfer bias voltage and outputting an output current IT for transfer is connected to the bias roller 74, and the roller 74 and the transfer power supply 75 are connected.
Constitutes the voltage applying means. A part of the electric charge supplied from the bias roller 74 to the transfer belt 71 by the application of the transfer bias voltage by the voltage applying means flows into the grounded driving roller 72 and the driven roller 73, and returns to the node N1 as feedback currents Ir1 and Ir2, respectively.
Is returned to the transfer power supply 75.

The current detecting device 77 detects a difference current I1 = IT-Ir1-Ir2 obtained by subtracting the feedback currents Ir1 and Ir2 from the transfer output current IT. The difference current I1 can be considered to be that the current I2 flowing through the photoconductor from the transfer nip portion N of the transfer output current IT has returned via the ground (I1 = I
2). Then, the transfer power supply 75 is controlled by the control device based on the detection result by the current detection device 77 so that the difference current amount becomes a predetermined target value, so that the transfer nip N passes through the photosensitive member. The flowing current I2 is kept substantially constant. Since the current is maintained at a predetermined current amount, even if the transfer belt has uneven resistance in the circumferential direction, the charge injected to the belt at the transfer nip is kept constant, and the transfer at the transfer nip is performed. It is possible to keep the electric field.

The transfer device includes a transfer paper size detecting device (not shown), and corrects the predetermined target value according to the detection result by the transfer paper size detecting device. Specifically, the transfer paper size detection device detects the width of the transfer paper 6 in the photoconductor axis direction, that is, the width direction of the transfer paper belt, and corrects the target value so that the target value increases as the width of the transfer paper 6 decreases. I do. For example, in the illustrated transfer apparatus, 50 μA is initially set as a target value. When the width of the transfer paper 6 in the transfer belt width direction is equal to or less than A4 width (210 mm), the target value is corrected to 70 μA. . As a result, even when the amount of current flowing directly from the transfer belt to the photoreceptor when the width of the transfer paper 6 is small, the electric charge accumulated on the back surface of the paper is sufficiently maintained, and the transfer electric field is substantially constant regardless of the transfer paper size. Can be held. (Hereinafter, margin)

In the transfer apparatus according to the present embodiment, when the transfer material is not present at the transfer position, the applied voltage V1 and the applied voltage V1 by the voltage applying means are set so that the difference current amount I1 becomes the predetermined current amount. Comparing means for comparing an applied voltage V2 by the voltage applying means such that the difference current amount I1 becomes a predetermined current amount when a transfer material is present at the transfer position; and the predetermined means based on a comparison result by the comparing means. And a correction means for correcting the amount of current. Hereinafter, this configuration operation will be described with reference to FIG. FIG. 3 is a flowchart illustrating a control example of the transfer device 7 during the copying operation of the copying machine. When the copying operation of the copying machine starts, the width of the transfer paper in the width direction of the transfer belt is detected by the transfer paper size detecting means (step 1). Thereafter, the image forming operation on the transfer paper 6 starts (step 2), and the target value of the difference current I1 is determined based on the detection result by the transfer paper size detecting means (step 3). Then, the transfer paper 6 is transferred to the transfer nip N
Before entering the differential current I1
The transfer power supply 75 is controlled so that the target voltage is equal to the target value, and the applied voltage value V1 at this time is detected (step 4) and stored in a storage unit (not shown). Then, while controlling the control device 78 so that the difference current I1 becomes the target value, a predetermined time has elapsed from the start of the image forming operation and the leading end of the transfer paper 6 is moved to the exit of the transfer nip portion N. At the timing of reaching the portion N1, the applied voltage value V2 from the transfer power supply 75 is detected (step 5). Then, V1 and V2 are compared by a control unit (not shown) as the comparing means (step 6). At this time, V1 ≧ V2
(Y in step 6), the difference current I1
It is considered that the current flowing through the transfer member 6 other than the photoreceptor 1 due to the decrease in the resistance of the transfer sheet 6 causes the current I2 flowing through the photoreceptor 1 to decrease and the transfer electric field to decrease. . Therefore, the control unit, which also has a function as the correction unit, corrects the difference current so that the target value becomes large (step 7). And the difference current I
The transfer operation is performed while controlling the transfer power supply 75 so that 1 becomes the corrected target value, and then the image forming operation ends (step 8). On the other hand, if V1 ≧ V2 is not satisfied (N in step 6), the current flowing through the transfer current 6 to portions other than the photoconductor 1 due to the decrease in the resistance of the transfer paper 6 among the difference current I1 is negligible. Considered small. Therefore, the difference current I can be obtained without correcting the target value.
The transfer operation is performed while controlling the transfer power supply 75 so that 1 becomes the target value determined in step 3, and then the image forming operation ends (step 9). Then, it is detected whether or not the repeat copy is completed (step 9). If not completed (N in step 9), the next image forming operation is started. When the transfer is completed (Y in step 9), the control of the transfer device is completed.

As described above, the transfer paper 6 under a high temperature and high humidity environment
Even if a leakage current flows through the transfer paper 6 to a portion other than the photoconductor 1 due to a decrease in resistance due to moisture absorption, the target value of the difference current I1 is increased to increase the difference current I1 from the transfer belt 71 via the photoconductor 1. The flowing current I2 can be prevented from lowering. Therefore, the transfer electric field in the transfer nip portion is kept substantially constant regardless of the humidity condition, and stable transfer separation performance can be obtained. Further, unlike the case where a measuring unit for measuring the resistance of the transfer belt or the transfer paper is provided, the apparatus configuration is simple.

Further, in the present embodiment, the size of the transfer paper in the transfer belt width direction is large so that the increment of the target value due to the correction of the difference current target value differs depending on the detection result of the transfer paper size. The above correction is performed so that the larger the increment becomes, the larger the increment becomes. For example, Step 3
When the difference current target value determined in the step is set to 50 μA when the width of the transfer paper in the transfer belt width direction is larger than the A4 width, and 70 μA when the width is smaller than the A4 width, the difference current target value after the correction in step 7 is performed. Is 70 μA, A4
The size is 80 μA for a size smaller than the width. As the size of the transfer paper 6 increases, the current flowing through the transfer nip portion to a portion other than the photoreceptor via the transfer paper 6 increases, so that the current I2 flowing to the photoreceptor decreases. The current I2 flowing through the photoreceptor can be ensured regardless of the size of the transfer sheet by correcting the difference current I1 so as to increase as the size of the transfer paper increases. Therefore, the transfer electric field can be stably maintained regardless of the size of the transfer paper, and good transfer separation performance can be obtained, so that the selection range of the size of the transfer paper is expanded.

In the control example of FIG. 3, the comparison of the applied voltage and the correction of the difference current are performed every time an image is formed on one transfer sheet 6, so that the humidity control of the transfer sheet is adjusted. Good transfer separation performance can be obtained even when it differs depending on the paper.

In the above embodiment, only the example in which the transfer voltage is applied to the transfer belt by using the voltage applying means to supply the transfer charge is described. The charge may be supplied to the transfer belt 71 using a unit. In this case, a potential detecting means for detecting a potential of a charge supply area of the transfer belt to which the charge is supplied by the charge supplying means is provided, and the potential detecting means detects V1 and V2. If the configuration is such that the target value is corrected by using, the same effect as in the above embodiment can be obtained.

Next, a control example of a transfer device according to another embodiment will be described. FIG. 4 is a flowchart showing the control example. The basic configuration operation of this transfer device is the same as that of the transfer device according to the above embodiment. The transfer device is configured such that the voltage applied by the voltage applying means such that the differential current becomes the predetermined current amount when the transfer material is not present at the transfer position and the differential current is generated when the transfer material is present at the transfer position. Comparison means for comparing the voltage applied by the voltage application means with the predetermined current amount, and control means for setting the applied voltage by the voltage application means based on the comparison result by the comparison means are provided. Things. Then, similarly to the case of the transfer device according to the embodiment, in a state where the transfer material is not present at the transfer position, the applied voltage V1 by the voltage applying unit and the transfer position are set so that the differential current becomes the predetermined current amount. In a state where the transfer material is present, a comparison is made with the applied voltage V2 by the voltage applying means such that the difference current becomes the predetermined current amount. Unlike the transfer device of the embodiment, the comparison is performed based on the comparison result. The control means sets the voltage applied by the voltage applying means.
Specifically, switching means for switching between constant current control by the differential current control means and constant voltage control for applying a predetermined applied voltage to the electrode member is provided, and the switching means controls the constant current by the differential current control means. The voltage applied by the voltage applying means is set by switching between control and constant voltage control for applying a predetermined applied voltage to the electrode member. More specifically, the voltage applied by the voltage applying means such that the differential current becomes the predetermined current amount in a state where there is no transfer material at the transfer position is equal to the differential current when the transfer material is present at the transfer position. When the voltage is equal to or higher than the voltage applied by the voltage applying means so that the predetermined current amount is obtained, the constant voltage control that applies the predetermined application voltage set so that the differential current amount increases to the electrode member is performed. Switch. Hereinafter, this will be described in detail with reference to FIG.

In the example of FIG. 4, the operation up to step 6 is the same as that of the example of FIG. 3, so the description up to step 5 is omitted, and the operation after step 6 will be described. In the example of FIG. 4, in step 6, the control unit (not shown) as the comparing means compares V1 and V2. If V1 ≧ V2 (Y in step 6), the transfer of the difference current I1 is performed. It is considered that a decrease in the resistance of the paper 6 causes a current to flow through the transfer paper 6 to a portion other than the photoreceptor 1, and the current I2 flowing to the photoreceptor 1 is reduced to lower the transfer electric field. At this time, the control section switches from the constant difference current control for keeping the difference current I1 constant to the constant voltage control for keeping the voltage V applied to the transfer belt 71 by the transfer power supply 75 constant (step 11). And, by the control unit as the control means,
The applied voltage V is set (step 12). Specifically, the applied voltage V is set to a value equal to or higher than V1 such that the difference current I1 becomes larger than the predetermined target value. Then, the transfer operation is performed while applying the applied voltage V by the transfer power supply 75, and then the image forming operation is completed (step 13). On the other hand, when V1 ≧ V2 is not satisfied (N in step 6), the current flowing through the transfer paper 6 to a portion other than the photoconductor 1 due to a decrease in the resistance of the transfer paper 6 is negligible. Considered small. Therefore, the difference current I can be obtained without switching to the constant voltage control.
The transfer operation is performed while controlling the transfer power supply 75 so that 1 becomes the target value determined in step 3, and then the image forming operation ends (step 13). After that, the control section changes the constant current control to keep the applied voltage V to the transfer belt 71 from the transfer power supply 75 to the difference current I
The control is switched to the constant difference current control in which 1 is kept constant (step 14). Then, it is detected whether or not the repeat copy has been completed (step 15). If it has not been completed (N in step 15), the next image forming operation starts. When the transfer is completed (Y in step 15), the control of the transfer device is completed.

As described above, the transfer paper 6 under a high temperature and high humidity environment
Of the photosensitive member 1 through the transfer paper 6 due to the decrease in resistance due to moisture absorption
When the leakage current flowing to the other part occurs, the difference current I1 is larger than the predetermined target value.
By setting the applied voltage V by the voltage applying means large, it is possible to prevent the current I2 flowing from the transfer belt 71 via the photoconductor 1 from decreasing. Therefore, the transfer electric field in the transfer nip portion is kept substantially constant regardless of the humidity condition, and stable transfer separation performance can be obtained. Further, unlike the case where a measuring unit for measuring the resistance of the transfer belt or the transfer paper is provided, the apparatus configuration is simple.

When setting the applied voltage V in the step 12 in FIG. 4, the applied voltage V
It is desirable that the value be larger than one. This is because when the transfer paper 6 is located between the transfer belt 71 and the photosensitive member, a resistance component in the thickness direction of the transfer paper 6 is added in series, so that the voltage applied to the resistance component is higher than V1. This is because the transfer electric field can be sufficiently secured even when the transfer paper 6 is located between the transfer belt 71 and the photoconductor 1 by increasing the transfer paper 6. Furthermore, as the size of the transfer paper 6 increases, the area where the current flows to the photoconductor via the transfer paper 6 in the transfer nip becomes wider, and the area where the current flows directly to the photoconductor becomes narrower. Therefore, the area affected by the resistance component is widened, and the voltage required to secure the transfer electric field is increased. In this embodiment, the increment α = V−V1 of the applied voltage V with respect to V1 differs depending on the result of detection of the transfer sheet size. Specifically, the larger the size of the transfer sheet in the transfer belt width direction is, the larger the increase is. Is set so as to increase the applied voltage.
For example, when the difference current target value determined in step 3 is set to 50 μA for a size of the transfer paper in the transfer belt width direction larger than the A4 width and 70 μA for a size smaller than the A4 width, the applied voltage set in step 12 is set. V is defined as V which is larger than the width of A4 paper in the width direction of the transfer paper.
1 + 1kV, V1 + 0.5kV for A4 width or less
And Therefore, the transfer electric field can be stably maintained regardless of the size of the transfer paper, and good transfer separation performance can be obtained, so that the selection range of the size of the transfer paper is expanded.

In the control example of FIG. 4, as in the case of the control example of FIG. 3, the comparison of the applied voltages and the setting of the applied voltages are performed every time an image is formed on one transfer sheet 6. Therefore, good transfer separation performance can be obtained even when the degree of humidity control of the transfer paper differs depending on the paper.

[0032]

According to the present invention, the potential of the charge supply region and the transfer position when the difference current reaches the predetermined current amount in a state where there is no transfer material at the transfer position. The transfer electric field is stabilized by correcting the predetermined amount of current based on a comparison result obtained by comparing the potential of the charge supply region when the difference current reaches the predetermined amount of current with the transfer material present. Therefore, there is an excellent effect that stable transfer separation performance can be obtained regardless of humidity conditions. Further, since there is no need for a measuring means for measuring the resistance, there is an excellent effect that the device configuration is simple.

According to the second and third aspects of the present invention, the voltage applied by the voltage applying means and the transfer position are set such that the difference current becomes the predetermined current amount when there is no transfer material at the transfer position. The transfer electric field is stabilized by correcting the predetermined amount of current based on the result of comparing the applied voltage by the voltage applying means such that the difference current becomes the predetermined amount of current in a state where the transfer material is present. Therefore, there is an excellent effect that stable transfer separation performance can be obtained regardless of humidity conditions. Also,
Since a measuring means for measuring the resistance is not required, there is an excellent effect that the device configuration is simple.

In particular, according to the third aspect of the present invention, the size of the transfer material is detected by the transfer material size detecting means,
By correcting the predetermined current amount based on the detection result, there is an excellent effect that the transfer electric field can be further stably maintained, and stable transfer separation performance can be obtained regardless of the size of the transfer material.

According to the invention of claims 4 and 5, the voltage applied by the voltage applying means and the transfer position so that the differential current becomes the predetermined current amount in a state where there is no transfer material at the transfer position. The voltage applied by the voltage applying means is set based on a result of comparison between the voltage applied by the voltage applying means such that the differential current becomes the predetermined current amount in a state where the transfer material is present. Then, the voltage applied by the voltage applying means is such that the difference current becomes the predetermined current amount in a state where the transfer material is not present at the transfer position. When the voltage is equal to or higher than the voltage applied by the voltage applying means, the difference current amount is increased, and in other cases, the difference current amount is equal to the predetermined current. By setting the applied voltage so as to maintain the amount, the transfer electric field can be stably maintained. Therefore, there is an excellent effect that stable transfer separation performance can be obtained regardless of humidity conditions. Further, since there is no need for a measuring means for measuring the resistance, there is an excellent effect that the device configuration is simple.

In particular, according to the invention of claim 5, the size of the transfer material is detected by the transfer material size detecting means,
By setting the applied voltage based on the detection result, there is an excellent effect that the transfer electric field can be held more stably and stable transfer separation performance can be obtained regardless of the size of the transfer material.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a transfer device according to an embodiment.

FIG. 2 is a front view showing a schematic configuration of a copying machine provided with the transfer device.

FIG. 3 is a flowchart showing a control example of the transfer device 7 during the copying operation of the copying machine.

FIG. 4 is a flowchart illustrating a control example of a transfer device 7 according to another embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 7 transfer device 71 transfer belt 72 drive roller 73 driven roller 74 bias roller 75 transfer power supply 77 current detection device 78 control device

Claims (5)

[Claims] A transfer belt for bringing a transfer material into contact with a surface of an image carrier on which an image to be transferred is formed; a belt support for supporting the transfer belt; and a charge supply for supplying a transfer charge to the transfer belt. Means, and constant current control means for controlling the charge supply means such that a difference current between the amount of output current from the charge supply means and the amount of current flowing from the transfer belt to the belt support becomes a predetermined current amount. And a potential detecting means for detecting a potential of a charge supply area of the transfer belt to which the charge is supplied by the charge supply means, and the difference current is determined when the transfer material is not present at the transfer position. The result of detecting the potential of the charge supply region when the predetermined current amount is reached by the potential detection means and the charge supply when the difference current reaches the predetermined current amount with the transfer material at the transfer position. A transfer means for comparing the potential of the area with a result of detection by the potential detection means, and a correction means for correcting the predetermined current amount based on the comparison result by the comparison means. . 2. A transfer belt for bringing a transfer material into contact with a surface of an image carrier on which an image to be transferred is formed, a belt support for supporting the transfer belt, and a voltage application for applying a transfer voltage to the transfer belt. A constant current for controlling the voltage applying means so that a difference current between an output current amount from the voltage applying means to the transfer belt and a current amount flowing from the transfer belt to the belt support becomes a predetermined current amount. A transfer device provided with control means, wherein a state in which there is no transfer material at the transfer position and a voltage applied by the voltage applying means such that the differential current becomes the predetermined current amount, and a state in which the transfer material is at the transfer position A comparing means for comparing the applied voltage by the voltage applying means such that the difference current becomes the predetermined current amount, and a correcting means for correcting the predetermined current amount based on a comparison result by the comparing means. A transfer device comprising: 3. The transfer device according to claim 1, further comprising a transfer material size detecting means for detecting a size of the transfer material in the belt width direction, wherein the predetermined size is determined based on a detection result by the transfer material size detecting means. Wherein the correction means is configured to correct the amount of current. 4. A transfer belt for bringing a transfer material into contact with a surface of an image carrier on which an image to be transferred is formed, a belt support for supporting the transfer belt, and a voltage application for applying a transfer voltage to the transfer belt. Means for changing a voltage applied by the voltage applying means, and detecting a difference current amount between an output current amount from the voltage applying means to the transfer belt and a current amount flowing from the transfer belt to the belt support. And a difference current amount detecting means, wherein the voltage variable means adjusts the voltage so that the detection result by the difference current amount detecting means becomes a predetermined current amount in a state where the transfer material is not present at the transfer position. When the applied voltage when the applied voltage is changed and the transfer material is present at the transfer position and the transfer current is detected by the differential current amount detecting means, the voltage is adjusted so that the predetermined current amount is obtained. Comparing means for comparing the applied voltage when the voltage applied by the voltage applying means is changed by the pressure varying means, and control means for setting the applied voltage by the voltage applying means based on the comparison result by the comparing means And a transfer device. 5. The transfer apparatus according to claim 4, further comprising a transfer material size detecting means for detecting a size of the transfer material in the belt width direction, and applying the applied voltage based on a detection result by the transfer material size detecting means. Wherein the control means is configured to perform the following settings: