JP2000075694A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the transfer defect of a transfer member such as the drum ghost of constant voltage printing or a black spot from occurring by detecting the resistance of the transfer member plural times in the midst of a pre-rotation process and deciding different transfer constant voltage bias in every resistance detection process when the detected resistance of the transfer member is lower than a desired value. SOLUTION: After pre-rotation is started (S2), ATVC I is executed first (S3). Then, it is judged whether the resistance of a transfer roller is the low resistance I or not. In the case of NO as the result, the transfer bias is set to be the constant voltage Vt1 (S3'). In the case of YES, ATVC II is executed (S4). Then, it is judged whether the resistance of the transfer roller is the low resistance II or not. In the case of YES as the result, the transfer bias is set to be the constant voltage Vt2 (S4'). In the case of NO, the constant voltage Vt3 of the transfer bias corresponding to the resistance of the roller is decided (S5) after the resistance of the transfer roller is normally detected. Thus, the optimum transfer bias corresponding to the resistance of the roller can be applied even in a constant voltage applying mode when the resistance of the transfer roller is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type image forming apparatus.

[0002]

2. Description of the Related Art For example, an image forming apparatus such as an LBP (laser beam printer) or a copying machine utilizing a transfer type electrophotographic process is an electrophotographic photosensitive member (hereinafter, referred to as a rotary drum type) as an image carrier. A toner image as a transferable image corresponding to the target image information is formed on the surface of the photosensitive drum by image forming process means such as charging, image exposure, and development, and the toner image is transferred by the transfer means. The image is transferred to the surface of the recording material, and the recording material is introduced into a fixing unit to thermally fix the toner image as a permanent fixed image 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 adhered contaminants such as transfer residual toner and paper powder on the surface thereof, and the photosensitive drum is subjected to an image forming process repeatedly. Is done.

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, to which a voltage is applied and a recording material is nipped and conveyed at a transfer portion which is a nip portion with the photosensitive drum to electrostatically transfer the toner image on the photosensitive drum side to the recording material side, a so-called contact-type transfer 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 -1.
The transfer roller is adjusted to a value of about × 10 ¹⁰ (Ω), but the transfer roller proposed in recent years is provided with an elastic layer on the outer peripheral surface of a conductive cored bar so that the elastic layer has conductivity. . The transfer roller is roughly classified into the following two types depending on how to impart the conductivity.

That is,. Transfer roller with electronic conduction system. This is a transfer roller having an ion conductive system.

The transfer roller having an electronic conductive system is obtained by dispersing a conductive filler in an elastic layer. Examples thereof include an EPDM roller and a urethane in which a conductive filler such as carbon or metal oxide is dispersed. Rollers can be mentioned.

The transfer roller having an ion conductive system of
The elastic layer contains an ion conductive material, for example,
Examples thereof include materials in which a material such as urethane itself has conductivity, and materials in which a surfactant is dispersed in an elastic layer.

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

Therefore, in order to prevent the occurrence of transfer failures and paper marks due to fluctuations in 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 adjusted according to the measurement result. "Applied transfer voltage control" (transfer roller bias 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 prevents transfer failure and occurrence of 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 is performed only by constant voltage control. Therefore, the circuit is simplified and the detection accuracy is improved. More specifically, a constant voltage is applied when the resistance of the transfer roller is detected, and a means for detecting an output current value flowing through the photosensitive drum at this time is provided. This is performed through software so that the output is changed and the set value is obtained.

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 0UT terminal of the CPU 101.
Value, pulse width modulation signal (Pulse Width Modulation). 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 becomes a transfer voltage VT.

Next, a voltage-to-current conversion is performed, and a signal corresponding to the current IT flowing at this time is converted into an I / O signal of the CPU 101 after the DA conversion.
The signal is input to the N terminal and detected in the CPU 101.

As described above, the constant voltage control is performed in advance by the CPU
Judging from the correspondence table between the PWM value set in Ol and the transfer output voltage, 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 and determine the optimum applied transfer voltage by the above-described ATVC control and PTVC control, 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.

After detecting the resistance by the above-described ATVC and PTVC controls, a transfer bias suitable for the roller resistance is applied. When the roller resistance is low, a constant voltage is generally applied regardless of the detection resistance. . The reason is that, after the control, the transfer bias is performed from the high-voltage transformer, but the output characteristics of the transformer do not change linearly. That is, when high output is guaranteed by the high voltage transformer, the characteristics on the low output side (low load) are reduced, and the input / output characteristics of the transformer are reduced as shown in FIG.
It becomes as shown in. For this reason, since the output of the roller resistance on the low load side is not stable, it is difficult to output with the bias varied depending on the roller resistance. Therefore, the transfer bias on the low resistance side becomes a constant voltage.

Here, FIG. 10 shows a process diagram of a printing (printing) process.

A. Pre-multi-rotation step: a start (start) operation period (warming period) of the image forming apparatus. When the main power switch is turned on, the main motor of the apparatus is driven to rotate the photosensitive drum, and the preparation operation of the required process equipment is executed.

B. Pre-rotation step: a period during which a pre-print operation is performed. This pre-rotation step is executed subsequent to the pre-multi-rotation step when a print signal is input during the pre-multi-rotation step. When the print signal is not input, the drive of the main motor is temporarily stopped after the completion of the previous multi-rotation step, the rotation drive of the photosensitive drum is stopped, and the apparatus is maintained in a standby state until a print signal is input. . When a print signal is input, a pre-rotation step is performed.

C. Printing process (image forming process): When a predetermined pre-rotation process is completed, an image forming process is subsequently performed on the rotating photosensitive drum, and a toner image formed on the rotating photosensitive drum surface is transferred to a recording material and fixed. The fixing process of the toner image is performed, and the image formed matter is printed out.

In the case of the continuous printing (continuous printing) mode, the above printing process is repeatedly executed for a predetermined set number of prints n.

D. In the continuous printing mode, after the trailing edge of one recording material passes through the transfer nip portion and before the leading edge of the next recording material reaches the transfer nip portion, This is a non-sheet passing state period of the recording material.

E. Post-rotation step This is a period in which the main motor continues to be driven for a while to rotate the photosensitive drum to perform a predetermined post-operation even after the last n-th printing step is completed.

F. Standby When the predetermined post-rotation process is completed, the drive of the main motor is stopped, the rotation drive of the photosensitive drum is stopped, and the apparatus is kept in the standby state until the next print start signal is input.

In the case of printing only one sheet, after the printing is completed, the apparatus enters a standby state through a post-rotation process.

When a print start signal is input in the standby state, the apparatus shifts to a pre-rotation step.

A multi-rotation step before a and e. In the post-rotation step, a cleaning bias having the same polarity as the charged polarity of the toner is applied to the transfer roller, so that the toner adhered as dirt on the transfer roller is transferred to the photosensitive drum surface side to clean the transfer roller. Is executed.

In the paper interval step d, a paper interval bias different from the transfer voltage in the printing step c is applied to the transfer roller.

[0032]

By the way, using the applied transfer voltage control (transfer roller bias control) described above,
When an image was printed by applying a constant voltage Vt1 using the transfer roller T1 having a low resistance, no image failure occurred in an N / N environment (normal environment: 23 ° C., 60% RH). / H environment (high temperature and high humidity environment: 32.5 ° C, 80%
In (RH), a drum ghost due to an excessive transfer current and a sandy black spot image were observed.

Next, when the constant voltage value was set to Vt2 (<Vt1) using the same low-resistance transfer roller T1, no image failure was found in the H / H environment, and transfer failure of explosion splattering was found in the N / N environment. Occurred.

The above phenomenon is caused by the difference in the optimum transfer voltage value of the low resistance roller T1 between the N / N environment and the H / H environment. That is, in the H / H environment, the optimum transfer voltage at which no drum ghost, black spots, and transfer failures occur is Vt2, whereas in the N / N environment, the above-described phenomenon and the optimum transfer voltage at which no explosion scattering occurs are Vt1. It becomes.

As described in the conventional example, the transfer roller resistance is detected, and the ATVC and PTVC controls are performed so that a transfer voltage suitable for the roller resistance can be applied. This is generally performed during rotation, and when it is determined in this resistance detection step that the roller resistance is lower than a desired value, a constant voltage is applied to the uniform roller. Since there is only one value of the constant voltage, a transfer failure image occurs when the margin for the transfer voltage image failure is not sufficient.

Also, this phenomenon is caused by the electron conductive EPDM.
This is more remarkable in the ion conductive NBR roller than in the roller. That is, as shown in FIG. 11, the transfer roller resistance is
N / N environment, H / H environment, L / L environment (low temperature and low humidity environment:
The resistance change in the three environments (15 ° C., 10% RH)
This is because the roller is of the order of 0.7 while the NBR roller of the ion conductive type is as large as 2.0.

That is, in the ion conductive NBR roller, 1.0 × 10 ⁸ (Ω) in the N / N environment became 1.0 × 10 ⁷ (Ω) in the H / H environment, and the application was performed in the N / N environment. At a constant voltage Vt3, an abnormal image such as a drum ghost occurs due to a transfer current of about 10 times flowing in an H / H environment.

On the other hand, the EPDM roller has a resistance change of 0.4.
The above phenomenon is slight even when used at a constant voltage because of the small order.

To eliminate the abnormal image, the resistance range of the transfer roller may be reduced so as not to enter the constant voltage mode. However, considering the resistance variation at the time of manufacturing the roller, the cost is increased.

In addition, the low-resistance transfer roller T1 described above
A similar transfer failure occurred in continuous printing on both sides in an N / N environment. One side of the double-sided print is conveyed to a fixing device (fixing device) and is heated and fixed. After contacting the transfer roller at the time of two-side transfer, the transfer roller is heated by the heat of one side of the paper, and the resistance is reduced. This is because the transfer current flows excessively. This phenomenon is also relied on with an ionic conductive roller having a large resistance change at a greenhouse temperature.

Accordingly, a first object of the present invention is to provide an image forming apparatus having a contact transfer member resistance detecting means, in which a transfer failure such as a drum ghost, a black spot, and an explosion splatter when a constant voltage is applied to the transfer member. Is to prevent.

A second object of the present invention is to provide an image forming apparatus having a plurality of print modes such as double-sided printing and multiple printing modes, such as drum boost, black spots, and explosion scattering when a constant voltage is applied to the contact transfer member during continuous printing. The purpose is to prevent the occurrence of transfer failure.

[0043]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) A contact-rotation type transfer member for forming a transfer nip portion in contact with the image carrier is provided. A recording material is introduced into the transfer nip portion to be nipped and conveyed, and a bias is applied to the transfer member. In an image forming apparatus for electrostatically transferring a transferable image formed and carried on the image carrier by application to the recording material, the transfer member is a member having ionic conductivity, and a pre-rotation step of the device is performed. During the resistance detection of the transfer member by the resistance detection means a plurality of times, if the detected resistance of the transfer member is lower than a desired value, the transfer voltage control means for determining a different transfer constant voltage bias for each resistance detection step An image forming apparatus comprising:

(2) The resistance detecting means is an ATVC control, wherein a plurality of ATVC controls have different constant current bias values, and the ATVC control is performed from a smaller constant current bias value. The image forming apparatus according to (1).

(3) The transfer voltage control means has a transfer bias application chart, and determines a transfer voltage from the transfer bias application chart according to the resistance detecting step for each print mode and number of printed sheets. The image forming apparatus according to (1).

(4) The image forming apparatus according to (3), wherein the printing modes are a double-sided printing mode and a multiple printing mode.

<Operation> i) In order to achieve the first object, according to the present invention, in an image forming apparatus having a transfer member resistance detecting means using an ion conductive transfer member, the transfer member resistance detecting means is used. The resistance detection of the transfer member is performed a plurality of times.

More specifically, at the time of resistance detection of the ATVC control, it is determined whether the resistance can be detected by the applied voltage at this time by starting from a case where the constant current value is small. The bias constant voltage v1 is determined. If it can be detected, then the same control is performed by increasing the constant current value. Similarly, if it is determined that the resistance r2 is low, the transfer bias constant voltage v2 is determined. If it can be detected, a transfer bias suitable for the transfer member resistance is applied.

As a function, even when the resistance of the transfer member cannot be detected and the resistance is low, it is possible to have a plurality of transfer bias constant voltage values, to apply the optimum voltage according to the transfer member, In addition, it is possible to prevent the occurrence of drum ghosts, black spots, explosion scattering and the like, and to provide a good transfer image.

Ii) In order to achieve the second object, according to the present invention, in an image forming apparatus having a continuous printing process such as double-sided printing, multiplexing, etc. At the time of application, the applied constant voltage value is switched according to the print mode and the number of sheets. As the switching means, the CPU is provided with a transfer bias application chart corresponding to the print mode, and thereby the applied voltage value is switched.

As a function, even when the transfer roller resistance changes in double-sided printing or the like, it is possible to correct the transfer bias by the transfer bias application chart and to apply a proper transfer voltage, thereby preventing drum ghosts, black spots and the like. Can provide images.

[0053]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (1) Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus in the present embodiment. The image forming apparatus of the present embodiment is a laser beam printer (LBP) capable of performing double-sided, multiple printing.

The photosensitive drum 1 as an image carrier is driven to rotate at a predetermined peripheral speed (process speed) in the direction of the arrow. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller 2 as a contact charging member.

The laser beam scanner 3 as an image exposure means is turned on / off in accordance with image information input from an external device such as an image scanner or a computer (not shown).
The off-modulated laser light L is output and the rotating photosensitive drum 1
Is subjected to scanning exposure. This scanning exposure forms an electrostatic latent image on the surface of the photosensitive drum 1 according to the image information.

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

A recording material (hereinafter, referred to as paper) P is stored in the paper feed cassette 5, and a paper feed roller 6 is driven based on a paper feed start signal, and the paper P in the paper feed cassette 5 is removed. Sheets are fed one by one, and are introduced at 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 that the timing at which the leading end of the toner image on the photosensitive drum 1 reaches the transfer portion T and the timing at which the leading end of the paper P reaches the transfer portion T are synchronized. You.

The paper P introduced into the transfer site T is
At this time, a predetermined transfer bias is applied to the transfer roller 9 from a transfer bias application power source (not shown). 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 copied on the surface of the paper P at the transfer portion T. The transfer roller 9 and the transfer bias control will be described in the next section (2).

The paper P to 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 the heating and pressing fixing process of the toner image.

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

When the "single-sided printing mode" is selected, the paper P on which single-sided printing has passed through the fixing device 11 is guided to the paper path 8c side by the first flapper 12 in the first posture state and discharged. The paper is discharged from the paper slot 13 onto the paper discharge tray 14.

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 moved by the first flapper 12 switched to the second posture to the recirculating paper path mechanism. The path is guided to the paper path 8d side, guided by the second flapper 15 in the first posture state to the switchback roller pair 8f further driven in the forward direction, and introduced into the switchback path 8g. Then, the rear end of the paper P passes through the second flapper 15, and the switchback roller pair 8f
Just before passing through, the switchback roller pair 8f
Is turned to the reverse drive, and the second flapper 15 is
The posture is changed to the posture, the paper P in the paper path 8g is pulled out and conveyed, and is introduced from the paper path 8h to the paper path 8i in a reversed state. Further, the second side is re-fed to the transfer portion T face up along the path of the paper path 8k, the registration roller 7, and the paper path 8a,
The toner image is transferred to the second side of the paper P.

Thereafter, in the same manner as in the single-sided printing mode, the paper path 8b → the fixing device 11 → the first flapper 12 in the first posture state → the paper path 8c → the paper discharge port 13 passes onto the paper discharge tray 14 Is discharged.

When the “multiple printing mode” is selected, the paper P on which the first printing has been performed after passing through the fixing device 11 is
The path is guided to the paper path 8d of the recirculating paper path mechanism by the first flapper 12 switched to the second posture, and further guided to the paper path 8i by the second flapper 15 switched to the third posture. The paper is then fed into the paper path 8i without being fed, and is again fed to the registration roller 7 through the paper path 8k. Then, the sheet is re-fed to the transfer portion T from the registration roller 7 and the paper path 8a at a predetermined control timing, so that a second toner image transfer is performed on the surface of the paper P on which the first printing has been performed.

Thereafter, similarly to the case of the single-sided printing mode, the paper path 8b → the fixing device 11 → the first flapper 12 in the first posture state → the paper path 8c → the paper discharge port 13 passes through the paper discharge tray 13 onto the paper discharge tray 14. Is discharged.

(2) Transfer Roller 9 and Transfer Bias Control The transfer roller 9 as a contact transfer member is composed of an elastic layer 9a of ion conductive solid rubber (NBR rubber) and a core 9b, and has a resistance value of N / N. (24 ° C., 65% RH) measurement, 2 kv applied, and three rollers R shown in Table 1 below
1, R2, R3 were used. ATVC control was used as transfer roller voltage control.

Table 1 No. Resistance (Ω) R1 1.0E + 08 (1 × 10 ⁸ ) R2 8.0E + 07 (8 × 10 ⁷ ) R3 5.0E + 07 (5 × 10 ⁷ ) 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 rotatably driven aluminum drum 1A at a contact pressure of 1.5 kg and is driven to rotate. The resistance was calculated by applying Okv 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 is rotated one or more times is sampled,
The roller resistance was calculated from the average value of the sampling values.

In the transfer step, ATVC control is employed. FIG. 3 shows an ATVC control timing chart in this embodiment.

In FIG. 3, the ATVC control during the pre-rotation is performed in two stages of I and II. At this time, the constant current value for ATVC detection is made different in i1 and i2 (i1> i2) to be in two stages. Thus, each of I and II can have a constant voltage bias value at the time of low resistance.

Therefore, even in the constant voltage application mode when the transfer roller has a low resistance, it is possible to apply the optimum transfer bias according to the roller resistance, and the occurrence of a drum ghost, a black spot, an explosion and the like irrespective of the environment. It is possible to output good images.

More specifically, FIG. 4 shows a flowchart at the time of the ATVC control of this embodiment.

In FIG. 4, after the start of the pre-rotation (Step 2), ATVCI (Step 3) is first performed to determine whether or not the resistance of the transfer roller is low I. Here, NO.
If so, the transfer bias is set to Vt1 constant voltage (step 3 '). YES. If it is, ATVC II (step 4) is performed to determine whether the resistance is low II. At this time, YES. If so, the transfer bias is set to Vt2 constant voltage (step 4 '). Then, after the normal transfer roller resistance detection, the transfer bias Vt3 constant voltage corresponding to the roller resistance is determined (step 5).

(3) Experiment 1 The image forming apparatus shown in FIG. 1 (process speed: 24 mm)
/ Sec), and using the ion-conductive transfer roller shown in Table 1 above, the following experiment was performed in the image forming process of single-sided printing.

Using the transfer roller shown in Table 1, the ATVC
The constant current value for detection was set to 2.0 (μA) for ATVCI and 4.0 (μA) for ATVCII, and the results of printing images in N / N environment and H / H environment are shown in Table 2. , And Table 3.

As shown in Table 2, when the constant voltage value is set to one in the N / N environment and Vt1 = 550 V, the explosion and scattering occurred at the roller R2. By setting Vt1 = 550 V and Vt2 = 750 V, a good transferred image could be output.

Similarly, as shown in Table 3, the roller resistance is 1
Even at low H / H environment, two constant voltage values are provided.
Drum ghost can be prevented by applying a voltage lower than the N / N environment.

As described above, in the ATVC control, two constant current values for resistance detection are provided, and the ATVC control is performed from the smaller constant current value, and a low resistance is detected in each control, and the constant voltage is simultaneously detected. By providing two applied constant voltage values, even when the roller resistance is low, the area for applying the optimum transfer voltage is widened, and it is possible to prevent drum ghosts, black spots, and explosion scattering and to output a good transfer image. .

In addition, it goes without saying that by further increasing the value of the constant current for ATVC control detection, the accuracy of low resistance detection is improved. However, if it is increased too much, it takes time during pre-rotation and the first print time becomes longer. It is not preferable.

In the first embodiment, the case where the ATVC control is performed has been described. However, in the case of the PTVC control, it goes without saying that the same effect can be obtained by reducing the applied voltage for detection.

[0080]

[Table 1] <Example 2> (1) Double-sided printing In the image forming apparatus of Example 1, when 200 images of double-sided printing (double-sided printing) were continuously performed using the transfer roller R2, drum ghosts and black spots were generated from 150 images. . At this time, the transfer voltage is 750v per side, 1300v per side,
It has become.

When the transfer roller resistance was measured for 200 sheets, it was 4.0 × 10 ⁷ (Ω). From the result of Experiment 1, it can be seen that the transfer voltage was not optimal.

This is because the transfer roller resistance is reduced in double-sided printing. To prevent drum ghost, it is necessary to perform another resistance detection such as ATVC control. is there.

The present embodiment has improved this. FIG.
FIG. 11 shows a control flowchart for duplex printing in the second embodiment. In the figure, after ATVC control, it is determined whether or not the transfer roller resistance is single-sided printing (step 4).
S. Then, the ATVC control shown in the first embodiment is performed, and the transfer bias Va is obtained (step 4 '). NO. If this is the case, the ATVC control is performed in the same manner, and the one-side and two-side transfer biases Vb and Vc after the resistance detection are obtained (step 5).

The above transfer bias may be a constant voltage at the time of low resistance or a constant voltage according to the roller resistance.

Next, from the transfer bias chart according to the print mode and the number of prints written in the CPU,
Surface: Vb ', Surface 2: Vc' (Step 6).

As described above, the applied transfer bias is determined (step 7), and the transfer bias is applied (step 9).

As described above, even when the transfer roller is heated by the temperature rise and the resistance is lowered after the two-sided printing, the applied transfer bias can be corrected, and the optimum transfer bias that does not generate drum ghosts, black spots, etc. is always applied. Becomes possible.

Also in the multiple continuous printing, if the transfer bias is similarly corrected, it is possible to always apply the optimum transfer voltage, and it goes without saying that a good image can be printed.

(2) Experiment 2 Here, in the image forming apparatus used in Experiment 1, the resistance of the roller Rl (1.0 × 10 ⁸ (Ω)) was measured during continuous double-sided printing, as shown in FIG. become,
In 150 images, a resistance drop of the order of 0.35 was observed.

The roller R2 shows a similar tendency.
When a transfer bias chart as shown in Table 4 was prepared and an image was printed, no drum ghost or black spots occurred in 1000 images of continuous printing on both sides.
FIG. 7 shows a change in the transfer roller bias in Experiment 2.

As described above, in an image forming apparatus using an ion conductive transfer roller and having a plurality of print modes such as double-sided and multiple, a transfer bias control CPU is provided with a transfer bias chart, and after the transfer roller resistance is detected,
By correcting the transfer bias at the time of continuous printing according to the chart, a good image can always be output.

[0092]

[Table 2] <Others> 1) The image carrier 1 is not limited to the electrophotographic photosensitive member, but may be an electrostatic recording dielectric or the like, and the principle and process of forming a transferable image on the image carrier are arbitrary. Further, it is not limited to the drum type, but may be a belt type, a web type, a sheet type, or the like.

2) The contact transfer member 9 is not limited to the roller type,
A belt type, a combination of a belt and an electrode blade, and the like are optional.

3) The recording material may be an intermediate transfer member such as an intermediate transfer drum or an intermediate transfer belt. The image carrier 1 may be an intermediate transfer member.

[0095]

As described above, in an image forming apparatus having a transfer bias control with an ion conductive contact transfer member, the detection of the transfer bias-constant voltage application is performed a plurality of times, so that the constant voltage value is detected for each detection. Can be set.
Therefore, even when a low-resistance transfer member is used, a constant voltage that matches the resistance of the transfer member can be applied, and a good image free of drum ghosts, black dots, etc. can be output regardless of the environment.

Further, the transfer bias chart is controlled by CP
By providing U, the transfer bias can be corrected even when the transfer member resistance changes in double-sided continuous printing or the like, and a good image can always be provided regardless of the transfer member resistance.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of a transfer roller resistance measuring device.

FIG. 3 is an ATVC control timing chart according to the first embodiment.

FIG. 4 is an ATVC control flowchart according to the first embodiment.

FIG. 5 is an ATVC control flowchart according to the second embodiment.

FIG. 6 is a diagram illustrating a change in transfer roller resistance during double-sided printing.

FIG. 7 is a diagram showing a change in transfer roller bias.

FIG. 8 is a diagram showing PTVC control of a conventional example.

FIG. 9 is a diagram showing input / output characteristics of a high-voltage transformer.

FIG. 10 is an operation process diagram of the image forming apparatus.

FIG. 11 is a diagram showing a change in environmental resistance of a transfer roller.

[Explanation of symbols]

1. photosensitive drum, 2. charging means, 3. scanner, 4. developing device, 5. paper cassette, 6. paper feeding roller, 7. registration roller, 8 (ak) • paper path, 9 • transfer roller, 10 • cleaning device, 1
1 ··· Fixing device, 12, 15 ·· Flapper, 13 ···
Paper output port, 14 ... Paper output tray

Claims (4)

[Claims] An image forming apparatus includes a transfer member of a contact rotary type that forms a transfer nip portion by contacting an image carrier. A recording material is introduced into the transfer nip portion to be nipped and conveyed, and a bias is applied to the transfer member. An image forming apparatus for electrostatically transferring a transferable image formed and carried on the image carrier to the recording material, wherein the transfer member is a member having ionic conductivity, and And a transfer voltage control means for determining a transfer constant voltage bias different for each resistance detection step when the resistance of the transfer member is lower than a desired value by causing the resistance detection means to perform resistance detection of the transfer member a plurality of times. An image forming apparatus comprising: 2. The resistance detection means is ATVC control,
2. The image forming apparatus according to claim 1, wherein a constant current bias value in a plurality of ATVC controls is different, and the ATVC control is performed from a smaller constant current bias value. 3. The transfer voltage control means has a transfer bias application chart, and determines a transfer voltage from the transfer bias application chart according to the resistance detecting step for each print mode and number of printed sheets. The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 3, wherein said print modes are a double-sided print mode and a multiple print mode.