JPH10307490A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of irregularities in an image during consecutive printing, without decrease in productivity by correcting a signal value for a transfer voltage applied to a transfer member, when a constant-voltage control voltage starts to be applied and the variation of a detected output current is greater than a desired value twice or more. SOLUTION: At an interval between papers to be supplied during the consecutive printing, PTVC control 2 is executed. At such the interval, a paper interval bias VT0 is applied and a transfer current IT0 flows. Then, the value of the paper interval bias VT0 during the consecutive printing is monitored at the point of time, to detect a transfer current I0 ' at this point. When this current value is further than a transfer current I0 by a set value or more at least twice or more, an optimum transfer current value can not be secured at a transfer bias VT1 set by PTVC control 1, because of a change in the resistance of a transfer roller, so that it can be judged that a defect in the image such as the irregularities in the image and a failure in transfer occurs. In such a case, a PWM value DT1 is changed to be DTa and the value of the transfer voltage VT1 is made a transfer bias VTa .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine
The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus such as a BP (laser beam printer) or the like, and in particular, is capable of electrostatically transferring a transferable image on an image carrier to a recording material (paper or the like). The present invention relates to an image forming apparatus having a contact rotation type transfer unit.

[0002]

2. Description of the Related Art For example, an electrophotographic copying machine or LBP
An image forming apparatus such as a (laser beam printer) includes an electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) as an image carrier generally having a rotary drum type, and image forming process means for charging, image exposure, and development. To form a toner image as a transferable image corresponding to the target image information, transfer the toner image to the recording material side by the transfer means, and further introduce the recording material into the fixing means to record the toner image. The image is thermally fixed as a permanent fixed image on the material surface and output as an image formed product (copy, print). After the transfer of the toner image onto the recording material, the photosensitive drum is cleaned by removing residual contaminants such as transfer residual toner and paper dust remaining on the surface thereof, and is subjected to an image forming process repeatedly.

As a means for transferring a toner image from a photosensitive drum to a recording material, there is an advantage that the conveyance path of the recording material can be simplified and stabilized at the same time. A contact-rotation type transfer member that applies a voltage and sandwiches and conveys a recording material at a transfer portion that is a nip portion with the photosensitive drum to electrostatically transfer a toner image on the photosensitive drum side to the recording material side, a so-called contact member. In recent years, transfer means using a transfer roller has been widely used.

The transfer roller has a resistance value of 1 × 10 ⁶ to 1
The transfer roller has been adjusted to a value of about × 10 ¹⁰ (Ω). However, a transfer roller proposed in recent years is provided with an elastic layer 118 on the outer peripheral surface of a conductive metal core 117 as shown in FIG. 11
8 is made to have conductivity. Transfer roller 11
No. 6 is roughly classified into the following two types depending on the manner of imparting the conductivity. That is, a transfer roller having an electronic conductive system and a transfer roller having an ionic conductive system. The transfer roller of FIG.
The elastic layer 118 has a conductive filler dispersed therein, and examples thereof include an EPDM roller and a urethane roller in which a conductive filler such as carbon or metal oxide is dispersed.

In the transfer roller, the elastic layer 118 contains an ion conductive material. For example, a material such as urethane having conductivity may be used, or a surfactant may be added to the elastic layer 1.
18 are dispersed.

Further, it is known that the resistance of the transfer roller is liable to fluctuate in accordance with the temperature and humidity of the atmospheric environment, and the fluctuation of the resistance of the transfer roller may induce poor transfer, explosion and scattering, and paper marks. There is concern.

Therefore, in order to prevent the occurrence of transfer defects and paper marks due to the fluctuation of the resistance of the transfer roller, the resistance value of the transfer roller is measured, and the transfer voltage applied to the transfer roller is changed according to the measurement result. “Applied transfer voltage control” for appropriately controlling is adopted.

As such an applied transfer voltage control means,
There is ATVC control (Active Transfer Voltage Control) disclosed in JP-A-2-123385.

The ATVC control is a means for optimizing the voltage applied to the transfer roller at the time of transfer, and is intended to prevent transfer failure and paper marks. The transfer voltage applies a desired constant current voltage from the transfer roller to the photosensitive drum during the pre-multi-rotation process of the image forming apparatus, and detects the resistance of the transfer roller by maintaining the voltage value at that time, thereby detecting the resistance of the transfer roller. During transfer, a constant voltage corresponding to the resistance value is applied to the transfer roller as a transfer voltage.

As another applied transfer voltage control, there is a PTVC control (Programmable Transfer Voltage Control) disclosed in Japanese Patent Application Laid-Open No. 5-181373.

While the ATVC control detects the resistance of the transfer roller by constant current control, the PTVC control performs only constant voltage control, so that the circuit is simplified and the detection accuracy is improved.

More specifically, there is provided a means for applying a constant voltage at the time of detecting the resistance of the transfer roller and detecting an output current value flowing to the photosensitive drum at this time. This is performed through software so that the constant voltage is changed and output to obtain a set value.

FIG. 8 shows a configuration diagram of the PTVC control. In the figure, first, a PWM signal (DA) having a pulse width corresponding to a desired transfer output voltage is supplied from the OUT terminal of the CPU 101.
Value). Actually, a transfer output voltage table (not shown) corresponding to the pulse width is stored in the CPU 101. This PWM signal is converted to DC by the low-pass filter 102, amplified by the amplifier 103, and transferred to the transfer voltage V.
It becomes T. Next, voltage-current conversion is performed, and a signal corresponding to the current IT flowing at this time is converted into an IN signal of the CPU 101 after DA conversion.
The signal is input to the terminal and detected in the CPU 101.

As described above, the constant voltage control is performed in advance by the CPU 1
Judging from the correspondence table between the PWM value and the transfer output voltage set in 01, a PWM signal having a pulse width corresponding to a desired voltage value is output.

As described above, the means corresponding to the constant current of the ATVC control gradually increases the PWM signal from the CPU 101, and the signal entering the IN terminal of the CPU 101 corresponds to a desired current value (constant current value). After the detection, the voltage value is held and used for the subsequent transfer process.

In order to accurately detect the transfer roller resistance by the above-mentioned ATVC control and PTVC control, and to determine the optimum applied transfer voltage, the resistance value for one round of the transfer roller is monitored and its average value is obtained. At the same time, since the transfer roller resistance has voltage dependency, it is necessary to set a constant current value such that a value close to the voltage applied at the time of transfer occurs. Therefore, the PTVC control or the like is generally performed during the pre-rotation, which has enough time in the image forming process.

[0017]

By the way, an electron whose resistance unevenness in the rotation direction of the transfer roller (hereinafter referred to as "circumferential unevenness") is good in measurement (circular unevenness 1.5 or less, longitudinal unevenness 2.0 or less). The above-described P
Images were output using the TVC control means.

At this time, even if the resistance unevenness is good in the measurement, the discharge of the transfer bias occurs in the minute area of the roller surface, and the applied constant current flows intensively, so that a paper mark, sand, etc. are generated. Where a transfer current does not flow, a transfer failure or the like occurs, so that a good image cannot be provided.

On the other hand, it is known that the ion-conductive transfer roller does not generate a discharge in a small area from the electric conductivity of the ion-conductive material. The image was printed using. The roller material is a solid roller made of NBR rubber, and the NBR rubber has resistance. The roller unevenness is 1.15 and the surface roughness is Ra
= 3.5 (μm). The transfer roller resistance is N / N
(24 ° C., 65% RH) measurement.
× 10 ⁸ (Ω) was used.

However, when an image was output by an image forming apparatus using the above-described ion conductive transfer roller, the following phenomenon occurred.

(1) Occurrence of Image Irregularity in Continuous Printing During continuous printing, even if a constant voltage is applied in the transfer process, the roller resistance is reduced due to the effect of temperature rise in the apparatus and the like. When a large current flows through the roller, image unevenness occurs. The optimum transfer voltage of the transfer roller differs depending on the roller resistance.
Although the TVC control was performed during the pre-rotation, there was no means for optimally correcting the transfer voltage even when the resistance of the transfer roller fluctuated during continuous printing. For this reason, image unevenness due to sandy ground in a halftone image or the like or roller unevenness occurs.

Further, in the case where double-sided printing or multiplex printing is continuously performed, the recording material comes out of the fixing unit, and printing is performed again with heat, the transfer roller is heated by the heat, and the resistance is further increased. And the above phenomenon becomes significant.

Further, as the image processing capability of a computer has been improved in recent years, the demand for printing a large number of halftone images has also increased. When such images are continuously printed, the above-mentioned image unevenness is likely to occur. In addition, there is an increasing demand for various types of printing from thin paper to thick paper as recording materials, and some types of recording materials are sensitive to changes in the resistance of the transfer roller. The need to perform transfer voltage control has arisen.

Therefore, in the conventional ATVC control method, the printing interval between recording materials during continuous printing is increased,
The same problem can be solved by performing the same control during the pre-rotation, but the throughput during continuous printing has been remarkably reduced, which is not practical.

(2) Generation of transfer memory at the rear end of paper During continuous printing, a transfer voltage applied in the transfer step is applied directly to the photosensitive drum at the rear end of the printing surface of the recording material to generate a transfer memory. This results in a memory image.

In general, as shown in FIG. 9, the transfer voltage in the transfer step is first multi-rotation, a cleaning bias having the same polarity as that of the toner is applied, then PTVC control is performed in the pre-rotation, and the resistance of the transfer roller is changed. After detecting the value, a transfer voltage optimal for a transfer roller resistance value for transferring the toner image on the photosensitive drum to the recording material is applied. Then, after the recording material passes through the nip between the photosensitive drum and the transfer roller, the transfer voltage is turned off, and a voltage having the same polarity as that of the toner (hereinafter referred to as a "sheet-to-sheet bias") is applied in the sheet-to-sheet process in order to prevent the reverse fogging on the photosensitive drum. Then, during continuous printing, a transfer voltage is subsequently applied. Finally, in the post-rotation step, a cleaning bias is applied to clean the transfer roller, and the printing step ends.

During continuous printing, in order to accurately transfer the toner image to the printing surface at the rear end of the recording material, the transfer voltage is applied to the very end of the rear end of the recording material, then turned off, and then the sheet gap is applied. Therefore, when switching from the transfer voltage to the inter-sheet bias, even if the recording material passes through the nip with the photosensitive drum, the transfer voltage is directly applied to the photosensitive drum and becomes a memory image in the remaining next image forming process as a transfer memory. Therefore, in order to prevent this, it is conceivable to turn off the transfer voltage earlier than the rear end of the recording material, but conversely, a transfer failure occurs at the rear end of the recording material.

Accordingly, a main object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of image unevenness during continuous printing without lowering productivity.

Another object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of a paper trailing edge transfer memory during continuous printing.

[0030]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A transferable image is formed and carried on an image carrier, and is brought into contact with the image carrier, and a contact-rotation type transfer member applying a bias,
In an image forming apparatus for electrostatically transferring the transferable image to a recording material nipped and conveyed at a transfer portion of a nip portion with the image carrier, the transfer member is a roller having ion conductivity. During the rotation process, the resistance of the transfer member is detected, the applied transfer voltage is determined, and further, when the voltage of the constant voltage control applied to the transfer member between sheets in the image forming process rises to a desired value, output is performed. An image characterized by performing current detection a plurality of times and correcting a signal value of a transfer voltage applied to the transfer member when a change amount from a desired value of the output current is larger than a desired value at least twice or more. It is a forming device.

Preferably, the roller is a solid roller having a resistance value distribution of 1.5 or less in the direction of rotation and a surface roughness Ra of 5.0 (μm) or less. When the amount of change from the desired value of the output current is at least twice or more than the desired value, control is performed to extend the sheet interval in the image forming process and determine the same transfer applied voltage as during the previous rotation. It is preferable to start over.

In the control for determining the applied transfer voltage, when the detected resistance of the transfer member is lower than a desired value,
It is preferable that a constant voltage is applied regardless of the resistance of the transfer member, and that the signal value of the transfer voltage is not corrected. In the control for determining the applied transfer voltage, it is preferable that an output signal of the transfer voltage is switched stepwise at a rear end of the recording material, and a rate of change of the output signal is 10 to 40%.
It is preferable that the amount of change of the output signal varies depending on the print mode, and the change rate is 10 to 50%. The print mode is preferably a single-sided print mode, a double-sided print mode, or a multiple print mode.

[0033]

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.

First Embodiment FIG. 1 shows an image forming apparatus according to a first embodiment. The image forming apparatus according to the present embodiment is a laser beam printer capable of performing double-sided and multiple printing using an electrophotographic process. The image forming apparatus of this embodiment has a transfer roller 9 as a transfer unit, and the transfer roller 9 is made of ion conductive solid rubber (NBR).
Rubber) elastic roller 9a and core metal 9b, peripheral unevenness 1.5 or less, roller surface roughness Ra = 5.0 (μm) or less, resistance value N / N (24 ° C., 65% RH) measurement, 2k
At the application of V, three rollers shown in Table 1 below were used.

[0035]

[Table 1]

As the transfer roller voltage control, PTVC
Controls were used. First, an image forming process for one-sided printing will be described with reference to FIG.

(1) Image Forming Process The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow. The peripheral surface of the photosensitive drum 1 is charged to a predetermined polarity and potential by a charging unit 2 as a contact charging member (primary charging). The laser beam scanner 3 as an image exposure unit outputs a laser beam L on / off-modulated according to image information input from an external device such as an image scanner (not shown) or a computer.
The charged surface on the photosensitive drum 1 is scanned and exposed. By this scanning exposure, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1.

In the developing device 4, a developer (toner) is developed on the surface of the photosensitive drum 1 from the developing sleeve 4a, and the electrostatic latent image is visualized as a toner image. In the case of LBP, a reversal development method in which toner is adhered to an exposed portion of a general electrostatic latent image and developed is used.

A recording material (hereinafter referred to as “paper”)
), And the paper feed roller 6 is driven based on the paper feed start signal, and the paper P in the paper feed cassette 5 is stored.
Are fed one by one, and are introduced at a predetermined timing through a registration roller 7 and a paper path 8a into a transfer portion T, which is a contact nip portion between the photosensitive drum 1 and the transfer roller 9. That is, the conveyance of the paper P is controlled by the registration roller 7 so as to synchronize with the timing when the leading end of the toner image on the photosensitive drum 1 reaches the transfer portion T.

The paper P introduced into the transfer site T is
At this time, a constant current bias (transfer bias) which is controlled in a predetermined manner from a transfer bias applying power source (not shown) is applied to the transfer roller 9. The transfer roller 9 and the transfer bias control will be described in the next section (2).
By applying a transfer bias having a polarity opposite to that of the toner to the transfer roller 9, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred to the surface of the paper P at the transfer portion T.

The paper P, on which the toner image has been transferred at the transfer site T, is separated and conveyed from the photosensitive drum 1 and conveyed to the fixing device 11 through the paper path 8b, and undergoes a heating and pressing fixing process of the toner image.

On the other hand, the surface of the photosensitive drum 1 after the transfer and separation is cleaned by the cleaning device 10 to remove residual toner and paper dust, and is repeatedly subjected to an image forming process.

When the "single-sided printing mode" is selected, the paper P that has passed through the fixing device 11 is guided to the paper path 8c by the first flapper 12 that has been switched to the first position, and is discharged. The paper is discharged from the opening 13 onto the paper discharge tray 14.

(2) Transfer Roller 9 and Transfer Bias Control The transfer roller 9 as a contact-rotation type transfer member is an ion conductive solid roller as described above, and has a solid rubber layer 9a on a cored bar 9b. Then, the NBR rubber is reacted with a surfactant or the like, and the circumferential unevenness is 1.5 or less, and the surface roughness Ra =
The rollers shown in Table 1 having a thickness of 5.0 (μm) were used.

FIG. 2 is a schematic diagram of a resistance measuring device of the transfer roller 9. 1. The transfer roller 9 is pressed against the rotationally driven aluminum drum 1A with a contact pressure of 1.5 kg and is driven to rotate.
The resistance was calculated by applying 0 kV and measuring the current flowing through the aluminum drum 1A with the ammeter A. Further, in the above measurement, a current value when the transfer roller 9 was rotated once or more was sampled, and a roller resistance was calculated from an average value of the sampled values.

Assuming that the maximum value and the minimum value of the sampling current value are I _MAX and I _MIN , as in the conventional example, I _MAX / I _MAX
The transfer roller 9 that _{satisfies MIN} ≦ 1.5, that is, the transfer roller 9 whose resistance unevenness (circumferential unevenness) in the rotation direction is 1.5 or less was used. In addition, the surface roughness of the transfer roller 9 is Ra
= 5.0 (μm) or less. Hereinafter, the transfer bias control will be described.

In the transfer step, PTVC control is employed. FIG. 3 shows a timing chart in the PTVC control of this embodiment.

First, during the pre-rotation, PTVC control 1 is performed to detect the transfer current I ₀ for roller resistance detection and the voltage value V ₀ at that time, as in the conventional example, and set the PWM value at this time to D ₀ .

When a print signal is received, the PTV
A transfer bias _VT1 is applied according to the C control 1, and the toner image on the photosensitive drum 1 is transferred onto the paper P. At this time, the PWM value when the transfer bias V _{T1 is} applied is defined as D _T1 .

Next, during the continuous printing, P
The TVC control 2 is performed. In the sheet interval, the sheet interval bias V _T0 is applied, and the transfer current I _T0 flows. However, the value of the sheet interval bias V _T0 during continuous printing is monitored at points and the transfer current I ₀ ′ at this time is detected. . If this current value is at least 2
If the transfer current I ₀ is separated from the transfer current I ₀ by a set value or more
Due to the change in the resistance of the transfer roller, an optimum transfer current value cannot be secured with the transfer bias V _T1 determined by the PTVC control 1,
It can be determined that image defects such as image unevenness and transfer defects occur. Therefore, the value of the transfer voltage V _T1 is set to D _Ta by changing the PWM value D _T1 , and the transfer bias is set to V _Ta .

In the subsequent continuous printing, if the value of the transfer current value I ₀ ′ between the papers is similarly larger than the set value, the correction of the transfer bias V _Ta is repeated. Thereby, the current value at the time of transfer is optimized, and image unevenness and transfer failure can be prevented.

The interval between the normal sheets is set at a short interval in order to increase the printing speed. Here, the monitor of the sheet interval bias V _T0, when even the rise time of the sheet interval bias has risen the bias consideration can not detect the exact transfer current I ₀ 'Without monitor. In addition, short sheet interval, in a state of standing up the sheet interval bias V _T0, it is difficult to measure the value of the transfer roller one turn,
It is desirable to measure at points.

[0053] However, in the pre-multi rotation, etc., perform an accurate measurement of one rotation of the roller, the voltage value V _0, and the determination of the transfer bias V _T, in addition, the circumferential unevenness roller ion conductive Since 1.5 or less is used, sufficiently accurate measurement can be performed by the point measurement between sheets, and the detection accuracy is improved by repeating this measurement.

[Experiment 1] Image forming apparatus shown in FIG. 1 (process speed: 70 mm / sec, 12 ppm, 600 d)
pi) and the transfer roller (No. 1) shown in Table 1
Was used for continuous printing. In the PTVC control 1, the transfer current I ₀ was set to be 3.5 μA, and the transfer bias was set to V _T1 = V ₀ +0.9 (kV). The inter-sheet bias current value I _T0 is measured at two points by PTVC control 2, and this value is continuously measured at least 3.5 times from 3.5 μA to 1.0 μA.
When away more, with respect to the value of V _T1 when more 1.0μA larger as the correction of the transfer bias V _T1 -0.12
To the value of time (kV) 1.0 .mu.A or less V _T1 +0.12
(KV) so that the PWM value for PTVC control is changed,
The next transfer voltage _VTa was applied. After the transfer bias V _{T1 is} corrected, the PTV is calculated based on the value of the sheet current I ₀ ′ at the time of correction.
C control 2 is performed, and the same correction is repeated when the distance is 1.0 μA or more as described above.

With the above configuration, during continuous printing, a good image could be printed with no transfer unevenness and transfer failure in a halftone image (horizontal line of one dot and two spaces).

At this time, the sheet-to-sheet current I depends on the presence or absence of the PTVC control 2.
₀ , the transfer voltage V _T , and the transfer current I _T were measured for every 100 sheets, and the results are shown in FIG. 4 (roller No. 1).

As shown in FIG. 4, when PTVC control 2 is performed, the transfer voltage is corrected at 200, 400, 600, and 900 (sheets). Transfer roller No.
Similar effects could be confirmed in 2, 3.

As described above, in the image forming apparatus that performs the PTVC control using the ion conductive solid roller, the transfer roller resistance detection of the PTVC control is performed in the pre-rotation, and the transfer current of the sheet gap bias is performed during the continuous printing. If the amount of change from the initial value is larger than the set amount multiple times, the transfer bias can be corrected to optimize the transfer current value during continuous printing, resulting in good image quality. Can be provided.

Although the description has been given of the case of single-sided printing, it goes without saying that similar effects can be obtained in image forming apparatuses having different print modes (double-sided printing, multiple printing).

Next, the image forming process in the double-sided and multiple print modes in the image forming apparatus shown in FIG. 1 will be described.

In FIG. 1, when the “double-sided printing mode” is selected, the paper P on which one-side printing has been performed after passing through the fixing device 11 is transferred by the first flapper 12 switched to the second posture. The path is guided to the path 8d side and further guided to the paper path 8e by the second flapper 15 which is switched to the first position, and the paper path (switchback section) is driven by the normally driven switchback roller pair 8f. )
Before the rear end of the paper P carried into 8g passes through the second flapper 15 and passes through the switchback roller pair 8f, the switchback roller pair 8f is turned to the reverse rotation drive, and the second flapper 15 is moved The paper P in the paper path 8g is pulled out and conveyed by switching to the two positions, and the paper path 8h
Is introduced into the paper path 8i in a reversed state.

Then, the second side of the sheet P is re-input to the transfer portion T in the path of the paper path 8k, the registration roller 7, and the paper path 8a, and the toner image is transferred to the second side of the paper P. The first flapper 12 which has been subjected to the fixing process on the second side and has been switched to the first position, is guided to the paper path 8c side, and
Is discharged onto the discharge tray 14 as a double-sided printed product (double-sided print).

When the “multiple printing” mode is selected, the paper P on which one-side printing has been performed after passing through the fixing device 11 is moved toward the paper path 8 d by the first flapper 12 switched to the second posture. The path is guided to the paper path 8j by the second flapper 15, which is further switched to the third position, and is introduced into the paper path 8i without being reversed. Upon receiving the retransfer of the image, the multi-print image is discharged in the same manner as the above-described steps.

As in the case of single-sided printing, the inter-sheet PTVC control 2 for double-sided and multiple printing detects the sheet-to-sheet current at a point and corrects the transfer voltage based on the magnitude of the change from the initial current value. .

This makes it possible to optimize the transfer current during double-sided, multiple continuous printing, and to output a good image free from image unevenness, transfer failure, and the like.

Embodiment 2 Next, Embodiment 2 of the present invention will be described.

In the configuration of the first embodiment, after a long pause,
For example, immediately after the start of work, the apparatus is turned on at the start of printing, and the temperature of the fixing unit is controlled by the previous multiple rotations, and the apparatus is in a weight state and warms. As a result, the temperature inside the machine, which has been cold, rises, and the dew may be partially formed. Therefore, there is a possibility that the condensed water droplets adhere to the transfer roller via paper or the like at the start of printing.

As a result, the roller resistance fluctuates greatly instantaneously due to the influence of water droplets, and an optimum transfer current cannot be obtained with the transfer voltage determined by the previous rotation, etc., and the inter-sheet transfer current also becomes excessive immediately after the start of printing. It can be inferred that

For example, when the image forming apparatus main body is operated immediately after the start of work and continuous double-sided printing is performed, even if the transfer voltage is corrected between the sheets, transfer unevenness may occur after about 10 sheets. .

Therefore, in the present embodiment, the following control is performed. That is, as in the first embodiment, at the time of continuous printing, the PVTC control 2 is performed at points between papers, and the transfer current is detected. Here, when the amount of change in the current from I ₀ is larger than the value of B for two or more consecutive times, the PTVC control 1 is performed by extending the sheet interval. The value of B, unlike the first embodiment, when the change amount of I ₀ is particularly large, eg I ₀ is a value indicating the amount of change, such as when they are two to three times. At this time, the resistance of the roller is different from that at the time of detecting the PTVC control at the start of printing.
That is a big change. Therefore, only the inter-sheet I _0, when performing correction of the transfer voltage can not be accurately corrected. Therefore, by optimizing the transfer voltage with the transfer roller resistance once again for the primary portion, transfer unevenness and transfer failure during continuous printing can be prevented.

Third Embodiment Next, a third embodiment of the present invention will be described. Example 1,
In No. 2, transfer unevenness during continuous printing was prevented by detecting the transfer current between sheets using an ion-conductive transfer roller using PTVC control and correcting the transfer voltage according to the value.

However, usually, the roller resistance is remarkably reduced in a high-temperature, high-humidity environment, and PTVC control may not be performed in such a state. This is because the transfer high-voltage transformer is required to output from a low output to a high output because the transfer voltage output is in accordance with the resistance of the transfer roller. This is because the response decreases and it is not possible to output according to the PWM signal value.

More specifically, the low resistance mode is set when the roller is used in a high-temperature and high-humidity environment. The low resistance of the paper to which the toner is transferred is low, and the applied transfer voltage is low. There is no transfer current concentration. Therefore, even if the transfer bias is not corrected by the PTVC control 2 between the sheets, transfer unevenness and transfer failure do not occur during continuous printing.

In the low resistance mode detection by the PTVC control 1, when a PWM signal at the time of normal detection is input, the transfer current I _T0 is read when the resistance of the transfer roller is low.
The value of the DA value input to the CPU becomes a large value. This value is a value not shown if it is a normal resistance value, and it can be determined that the transfer roller has low resistance.

Accordingly, at the start of printing, if it is determined that the transfer roller resistance is low in the process of PTVC control 1 as described above, a constant voltage may be applied to both the transfer bias and the sheet gap. That is, when it is determined that the transfer roller has a low resistance, the correction of the transfer voltage-PWM signal value is omitted, and a fixed transfer voltage and a sheet-to-sheet voltage are applied, so that transfer failure due to insufficient current and excessive current may occur. The occurrence of transfer unevenness and paper marks can be prevented.

Embodiment 4 Next, Embodiment 4 of the present invention will be described with reference to FIG. The present embodiment particularly relates to a configuration for preventing occurrence of a paper rear end transfer memory during continuous printing.

The switching of the transfer voltage and the paper interval bias in the transfer step in the continuous printing are set as shown in FIG. In the figure, the print process transfer voltage V _T is applied corresponding to the PWM value D _A of PTVC control circuit. Then D _A smaller D _B the PWM value in the paper rear end X,
D _C is switched step by step, and D _{D of} smaller value is
Enter

As a result, the transfer voltage at the rear end of the paper is gradually reduced. Therefore, the transfer current at the rear end of the paper is also small, and no excessive current flows to the photosensitive drum even if the rear end of the paper passes through the transfer nip, and no transfer memory is generated at the rear end of the paper. The occurrence of transfer memory can be prevented.

Regarding the PWM value switching timing in this embodiment, if the speed is too fast, a transfer failure may occur at the trailing edge of the paper. Normal printing is guaranteed up to 5 mm inside the paper. It is desirable to start near. Further, it is desirable that the PWM value at the rear end X of the paper is switched about once or twice from the viewpoint of the process speed and the time between the papers being short and the response of the high voltage transformer.

[Experiment 2] Continuous printing was performed using the image forming apparatus (transfer roller No. 1) used in Experiment 1. At this time, the transfer voltage was switched twice at the rear end of the paper with the above configuration, and an image was output. The setting of the voltage is as follows.
_T0 = 0.2 kV The transfer voltage is V at a duty of 22.0% of the PWM value.
_T = 1.1 kV The paper rear end transfer voltage is V at a PWM value duty of 18.0%.
_T = 0.9 kV The switching start position was a position 5 mm from the rear end of the paper.

As a result, the transfer current at the rear end of the paper was reduced as compared with the first embodiment, and no transfer memory was generated at the rear end of the paper.
When the transfer current at the rear end of the paper was measured, 3.8 μA was obtained for “with switching” and 4.7 μA for “without switching”.
A, and it was confirmed that the transfer current was reduced. In addition, switching at the above timing did not cause the transfer failure of the paper rear end.

As a result of further study, it was found that the change amount of the transfer voltage at the rear end of the paper was 10 to 10%.
It was found that 40% was effective.

Embodiment 5 Next, Embodiment 5 of the present invention will be described. When double-sided printing was performed using the configuration of Example 4, paper trailing edge memory was generated on the single-sided printing surface during continuous printing. Therefore, the present embodiment relates to a configuration for preventing the occurrence of a back-end transfer memory on the one-side printing surface during continuous printing on both sides.

In FIG. 6, PT is used in the two-side printing process.
A transfer voltage V _T2 corresponding to the PWM value D _E of the VC control circuit is applied, and then the PWM value is set to a value smaller than D _E at the rear end Y of the paper.
_F, D _G stepwise switching inputs D _D of smaller values in the sheet interval. Then, the one side print step, as in Example 4, the transfer voltage V _T1 corresponding to the PWM value D _A is applied, D _A smaller D _B the PWM value in the paper rear end Z,
D _C is switched step by step, and D _{D of} smaller value is
Enter

Further, in the present embodiment, as in the fourth embodiment, the transfer voltage is switched in the area of the trailing edge of the paper 2 → 1 plane: Y area and in the area of 1 → 2 plane: Z area. Is set to be larger than the change Z2 in the Z region. This switching can be performed by changing the PWM signal value and inputting the changed value, whereby the transfer voltage is output according to the value. As a result, it is possible to prevent the occurrence of the memory at the trailing end of the paper during single-sided printing during continuous double-sided printing.

Considering the reason below, the transfer voltage is set to be higher than one surface because of the high paper resistance during two-surface printing. Therefore, the transfer electric field at the rear end of the paper is larger than that at the rear end of one surface, and the transfer current increases. Therefore, the transfer memory at the rear end of the paper is deteriorated with the same transfer voltage switching amount as that of one surface. That is, it is necessary to increase the amount of change in the switching to such an extent that the same transfer current flows on one surface.

[Experiment 3] Double-sided continuous printing was performed using the image forming apparatus (transfer roller No. 1) used in Experiment 1.
At this time, an image was output by switching the transfer voltage at the rear end of the paper once with the above configuration. The voltage setting is as follows: the paper _interval bias is V _T0 at a duty of 10.0% of the PWM value.
= 0.2 kV One-sided transfer voltage is V _T1 at a PWM value duty of 22.0%.
= 1.1 kV Two-sided transfer voltage is V _T2 at a duty of 32.0% of the PWM value.
= 1.6 kV Double-sided paper rear end (Y) Transfer voltage is PWM value duty 1
At 8.0%, V _T1 = 0.9 kV One-side paper rear end (Z) transfer voltage is PWM value duty 1
At 8.0%, V _T2 = 0.9 kV The switching start position was set to a position 5 mm from the trailing edge of the paper.

As described above, by increasing the amount of decrease in the transfer current at the rear end of the two surfaces, it is possible to prevent the memory at the rear end of the paper at the time of printing on one surface. That is, the rear end of the two-sided paper 3.8 μA The rear end of the one-sided paper 3.8 μA The rear end of the two-sided paper (Example 4) is 5.3 μA, and the transfer current at the rear end of the two-sided paper is the same as the rear end of the one-sided paper. It was confirmed that it was.

As a result of further study, the change amount of the transfer voltage at the rear end of the paper is 10 to 40% of the change rate of the PWM value at the rear end of the first sheet of paper. It was found that setting the content in the range of% was effective in preventing the memory at the trailing edge of the paper.

[0090]

As is apparent from the above description, according to the present invention, the transfer member is a roller having ion conductivity, and the resistance of the transfer member is detected during the pre-rotation step.
Determine the applied transfer voltage, and further, when the voltage of the constant voltage control applied to the transfer member rises to a desired value between sheets in the image forming process, perform output current detection a plurality of times, and obtain a desired value of the output current. By correcting the signal value of the transfer voltage applied to the transfer member when the amount of change from the value is at least twice or more than the desired value, it is possible to prevent the occurrence of image unevenness during continuous printing, and to achieve high quality. Images can be obtained.

In the control for determining the applied transfer voltage, the output signal of the transfer voltage is switched stepwise at the rear end of the recording material and the rate of change of the output signal is 10 to 40%.
Accordingly, it is possible to prevent the occurrence of a paper trailing edge transfer memory during continuous printing, and to obtain a good image.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic view showing a transfer roller resistance measuring device.

FIG. 3 is a timing chart illustrating a sheet interval PTVC control according to the first exemplary embodiment.

FIG. 4 is a graph showing a change in transfer current in PTVC control 2 in Example 1.

FIG. 5 is a timing chart for switching the application of the paper trailing edge transfer voltage in Example 4.

FIG. 6 is a timing chart of switching of the application of a paper rear end transfer voltage in a fifth embodiment.

FIG. 7 is a perspective view illustrating an example of a conventional transfer roller.

FIG. 8 is a configuration diagram of conventional PTVC control.

FIG. 9 is a process diagram showing a conventional transfer voltage application process.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 9 transfer roller (transfer member)

Claims (7)

[Claims] 1. A transferable image is formed and carried on an image carrier, and a contact-rotation type transfer member which is brought into contact with the image carrier and to which a bias is applied, and a transfer portion of a nip portion between the image carrier and the transfer member. In the image forming apparatus for electrostatically transferring the transferable image onto a recording material nipped and conveyed, the transfer member is a roller having ion conductivity, and the resistance of the transfer member is detected during a pre-rotation process. Determining the applied transfer voltage, and further, when the voltage of the constant voltage control applied to the transfer member rises to a desired value between the paper sheets in the image forming process, performs output current detection a plurality of times to determine the desired output current. An image forming apparatus that corrects a signal value of a transfer voltage applied to the transfer member when a change amount from the value is larger than a desired value at least twice or more. 2. The roller according to claim 1, wherein said roller is a solid roller, and has a resistance value distribution of 1.5 or less in a rotating direction and a surface roughness Ra of 5.0 (μm) or less. 1 image forming apparatus. 3. When the amount of change of the output current from a desired value is at least two times or more than the desired value, the paper interval in the image forming step is extended, and the same applied transfer as during the pre-rotation step is performed. 2. The image forming apparatus according to claim 1, wherein control for determining the voltage is performed again. 4. In the control for determining the applied transfer voltage, when the detected resistance of the transfer member is lower than a desired value, a constant voltage is applied regardless of the resistance of the transfer member, and the transfer voltage is controlled. 2. The image forming apparatus according to claim 1, wherein the signal value is not corrected. 5. The control for determining the applied transfer voltage, wherein the signal value of the transfer voltage is switched stepwise at the rear end of the recording material, and the rate of change of the signal value is 10 to 40%. The image forming apparatus according to claim 1, wherein: 6. The image forming apparatus according to claim 5, wherein a change amount of the signal value differs depending on a print mode, and the change rate is 10 to 50%. 7. The image forming apparatus according to claim 6, wherein the print modes are a single-sided print mode, a double-sided print mode, and a multiple print mode.