JPH09244434A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent soiling of an image due to, for examples, toner scatter around a toner image, which is caused by an insufficiency of transfer bias, and a transfer failure by varying the transfer bias according to the number of consecutively-passed both-sided sheets at the time of image formation. SOLUTION: A printer control part 28 consecutively forms images on the first sides of transfer sheets via a high voltage control part 17. Also, when the number of consecutively-passed both-sided sheets, with images formed consecutively on the second sides of the same transfer sheets, exceeds a specific number, the control part 28 detects increases of the temperature and resistance of a transfer roller 5 which is in contact with a photoreceptor drum 1, and it exerts constant-current control over the transfer roller 5 each time the number of sheets exceeds the specific number. A transfer bias in which a specific voltage is added to the voltage applied at this time is determined by the printer control part 28, and this transfer bias is applied to the transfer roller 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus which is connected to a host device such as a personal computer, an office computer or a mini computer and which continuously feeds paper on both sides according to image information from the host device. .

[0002]

2. Description of the Related Art A conventional image forming apparatus has a structure in which a toner image electrostatically formed on the surface of an image carrier is further electrostatically transferred to a transfer material such as transfer paper.

That is, the surface of a drum-shaped electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") as a cylindrical image bearing member that rotates in one direction is made uniform by the charging bias applied to the charging roller. Be charged.

An electrostatic latent image is formed on the photosensitive drum by irradiating the charged surface thereof with an image signal such as an image-modulated laser beam. When the electrostatic latent image reaches the developing portion where the photosensitive drum and the developing device face each other as the photosensitive drum rotates, toner is supplied from the developing device and adheres to the electrostatic latent image to form a toner image. To be done.

Further, when the toner image on the photosensitive drum reaches a transfer portion, which is a nip portion where the photosensitive drum and the transfer roller are in contact with each other, and the transfer paper is supplied to the transfer portion in accordance with this, the transfer roller is transferred to the transfer roller. A transfer bias is applied, and the toner image on the surface of the photosensitive drum is transferred to the transfer paper by the action of the electric field formed at the transfer site.

In such an image forming apparatus, transfer bias control includes transfer failure due to insufficient transfer current in a low humidity environment, transfer failure due to excessive transfer current in a high humidity environment,
Furthermore, in order to prevent transfer defects and the like that occur during transfer of small size paper such as postcards and envelopes, JP-A-2-123
ATVC control disclosed in Japanese Patent No. 385 (AutomaticTra
nsfer Voltage Control) is used. That is, in the transfer bias control described above, the resistance value of the transfer roller is detected by performing constant current control when the transfer sheet does not pass through the transfer portion, and the voltage at that time or a voltage calculated based on this voltage is detected. In this control, constant voltage control is performed when the transfer paper passes through the transfer site. By using this control, problems such as transfer failure due to insufficient transfer current in low humidity environment, transfer failure due to excessive transfer current in high humidity environment, and transfer failure occurring during transfer of small size paper can be solved. Can achieve a certain effect.

In the above-mentioned transfer bias control, even if the number of continuous double-sided sheets, in which the image is continuously formed on the first surface of the transfer material and the image is continuously formed on the second surface of the same transfer material, The transfer bias voltage is the same. That is, for example, when 1000 sheets are automatically passed on both sides, the transfer bias voltage is the same for both the first sheet and the 1000th sheet. Immediately after that, when the second surface is continuously fed, the temperature of the transfer roller rises by about 25 ° C. and the resistance of the transfer roller also rises from 1.2 × 10 ⁸ Ω to 6.7 × 10 ⁸ Ω. FIG. 5 shows the relationship between the transfer roller temperature and the transfer roller resistance.

[0008]

However, in the transfer bias control of the conventional example, the continuous feeding of the first side is completed,
Since the transfer bias voltage applied to the transfer roller is not changed immediately before continuously passing the second surface, the transfer roller may be changed according to the resistance value change due to the environment (particularly humidity) of the transfer roller before automatic double-sided continuous paper passing. Even if the transfer bias voltage applied to the sheet is improved by the ATVC control method, the resistance value of the transfer roller increases by about half an order when the automatic double-sided continuous paper feed exceeds a predetermined number. A large amount of image stains due to a phenomenon in which toner is scattered around characters due to insufficient bias (hereinafter referred to as “explosion”), and similarly, image stains due to defective transfer caused by insufficient transfer bias are output.

The present invention has been made to solve the above-mentioned problems, and the transfer bias is varied according to the number of continuous double-sided sheets at the time of image formation, and image stains caused by explosion or transfer failure are caused. An object of the present invention is to provide an image forming apparatus that prevents the above.

[0010]

In order to achieve the above object, according to the image forming apparatus of claim 1 of the present invention,
When a transfer material is present at a transfer portion, which is a nip portion between the image carrier and the transfer means, the transfer means is in contact with the image carrier, and a constant current control is performed on the transfer means to control the voltage at this time. And a constant voltage control is performed on the transfer means by the held voltage when the transfer material is present at the transfer portion, and image formation is continuously performed on the first surface of the transfer material. When the number of continuous double-sided sheets continuously image-formed on the second side of the same transfer material exceeds a predetermined number, a transfer bias for changing the transfer bias applied to the transfer means in accordance with the number exceeding the predetermined number A control means is provided.

According to the second aspect of the present invention, the transfer bias control means performs constant current control on the transfer means every time the number of continuous double-sided sheets exceeds a predetermined number every time the predetermined number is exceeded. A transfer bias obtained by adding a predetermined voltage to the voltage at this time is applied to the transfer means.

According to the third aspect of the present invention, there is provided a transfer unit that comes into contact with the image carrier, and the transfer unit is provided when a transfer material is not present at a transfer site which is a nip portion between the image carrier and the transfer unit. Constant voltage control is performed to hold the voltage at this time, and when the transfer material is present at the transfer site, the transfer means is subjected to constant voltage control with the held voltage. Depending on the number of double-sided sheets passed within a predetermined time when the number of continuous double-sided sheets that have been continuously image-formed on the first side of the material and the second side of the same transfer material has exceeded a predetermined number And a transfer bias control means for changing the transfer bias of the transfer means.

According to the fourth aspect of the present invention, the transfer bias control means performs constant current control on the transfer means each time the number of continuous double-sided sheets exceeds the predetermined number, every time the predetermined number is exceeded. A transfer bias obtained by adding a predetermined voltage to the voltage at this time is applied to the transfer means.

According to a fifth aspect of the present invention, there is provided a transfer unit that comes into contact with the image carrier, and when the transfer material is not present at a transfer site which is a nip portion between the image carrier and the transfer unit, the transfer unit is provided. In contrast, a constant current control is performed to hold the voltage at this time, and when the transfer material is present at the transfer site, the transfer means is controlled to the constant voltage by the held voltage. When the number of continuous double-sided sheets that have been continuously image-formed on the first side of the material and continuously formed on the second side of the same transfer material exceeds a predetermined number, the paper is passed after the number of sheets exceeds the predetermined number. A transfer bias control unit is provided for changing the transfer bias according to a change in the resistance value of the transfer unit due to the interruption.

According to the sixth aspect of the present invention, the transfer bias control means performs constant current control on the transfer means each time the number of continuous double-sided sheets exceeds a predetermined number every time the predetermined number is exceeded. A transfer bias obtained by adding a predetermined voltage to the voltage at this time is applied to the transfer means.

[Operation] Based on the above construction, the number of continuous double-sided sheets in which the image is continuously formed on the first surface of the transfer material and the image is continuously formed on the second surface of the same transfer material exceeds the predetermined number. In this case, the transfer bias is changed as the temperature and the resistance of the transfer unit contacting the image carrier rise.

In this case, when the number of continuous double-sided sheets is exceeded, the temperature and resistance of the transfer means contacting the image carrier are detected to rise, and the transfer means is transferred to the transfer means every time the number of sheets exceeds the predetermined number. Then, constant current control is performed to determine a transfer bias obtained by adding a predetermined voltage to the voltage at this time by the transfer bias control means, and the transfer bias is applied to the transfer means. Further, the transfer bias is changed in accordance with the change in the resistance value of the transfer means due to the interruption of the paper passage after the passage of a predetermined number of sheets.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. <First Embodiment> FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention.

In FIG. 1, reference numeral 1 is a drum-shaped electrophotographic photosensitive member (hereinafter simply referred to as "photosensitive drum") as an image bearing member which rotates in the direction of arrow R1, and the photosensitive drum 1 is in contact with this. The surface is uniformly charged by the charging bias applied from the high voltage power source 12 to the charging roller 2.

The charged surface of the photosensitive drum 1 is irradiated with an image signal 3 such as an image-modulated laser beam to form an electrostatic latent image. When the electrostatic latent image formed on the photosensitive drum 1 reaches the developing portion 11 where the photosensitive drum 1 and the developing device 4 face each other as the electrostatic latent image rotates, toner is supplied from the developing device 4 and the electrostatic latent image is generated. A toner image is formed by adhering to the latent image.

Further, the toner image on the photosensitive drum 1 reaches a transfer portion 6 which is a nip portion where the photosensitive drum 1 and the transfer roller 5 contact each other, and in accordance with this, a transfer guide 7 transfers a transfer sheet as a transfer material. When P is supplied to the transcription site 6,
A transfer bias is applied to the transfer roller 5, and the toner image on the surface of the photosensitive drum 1 is transferred to the transfer paper P by the action of the electric field formed at the transfer portion 6.

After that, the transfer paper P on which the toner image is transferred
Is separated from the photosensitive drum 1, the charge is removed by the charge elimination needle 9, and is conveyed to a fixing device (not shown) via the conveyance guide 10 to fix the toner image on the surface by the fixing device. Further, the residual toner on the surface of the photosensitive drum 1 after the transfer is removed by the cleaner 8.

Transfer bias control in such an image forming apparatus occurs in transfer failure due to insufficient transfer current in a low humidity environment, transfer failure due to excessive transfer current in a high humidity environment, and further during transfer of small size paper. ATVC control (Automatic Transfer Voltage Con
trol) is used. That is, in the transfer bias control, constant resistance control is performed to control the resistance value of the transfer roller 5 by performing a constant current control during a sheet interval in which the transfer sheet P does not pass through the transfer portion 6 and during non-sheet passing such as when the photosensitive drum 1 is rotating forward and rotating. The voltage at that time is detected and calculated and stored, and constant voltage control is performed when the transfer paper P passes through the transfer portion 6 with this voltage or a voltage obtained by calculation based on this voltage. Control.

An embodiment of the present invention will be described with reference to FIGS. 2 and 3 using a copying machine (printer) which is an electrophotographic image forming apparatus as described above.

First, the user of the printer 21 selects a print mode on the host device 22 and displays the control panel 13 shown in FIG. When the print environment information such as the size of the paper, the number of prints, and the distinction between the 1st and 2nd prints is set on the control panel 13, the signals of the print environment information and the image data are transferred to the printer 21. These signals are sent to the printer 21 via the path 23 of the block diagram shown in FIG.
It reaches the internal interface unit 26. Then, the interface unit 26 converts the image data into an image expansion unit 27.
The printer environment information is divided and transmitted to the printer control unit 28 as a transfer bias control unit.

The printer control section 28 issues a command to the motor control section 18 to drive the main motor 31 and the scanner motor 32 as appropriate. Further, the printer controller 28 drives the high voltage controller 17 to apply a voltage to the charging roller 2 to uniformly charge the photosensitive drum 1. Further, the printer control unit 28 uses the image expansion unit 27.
The exposure controller 16 is controlled based on the image data from the semiconductor laser 29 to irradiate a laser beam from the semiconductor laser 29 to form an electrostatic latent image on the photosensitive drum 1. The printer control unit 2
Reference numeral 8 applies a voltage to a developing roller (not shown) of the developing device 4 to visualize the electrostatic latent image formed on the photosensitive drum 1 (to form a toner image). The printer control unit 28 also feeds the transfer sheet to the transfer unit 6 in synchronization with the visible image on the photosensitive drum 1 when the visible image on the photosensitive drum 1 reaches the transfer unit 6. Control 34. Then
The printer control unit 28 selects an optimum transfer bias (voltage) and drives the high voltage control unit 17 to control the transfer roller 5 at a constant voltage. The printer control unit 28 controls the fixing heater 33 via the fixing control unit 19 so as to fix the unfixed toner image on the transfer paper.

By the way, the above-mentioned optimum transfer voltage is determined as follows.

At the time of pre-rotation immediately before printing, the transfer roller 5
In order to detect the resistance value of the transfer roller 5, the transfer roller 5 is subjected to constant current control with respect to the charged surface of the photosensitive drum 1 which is normally charged when the paper is not passed, and the resistance value of the transfer roller 5 is calculated from the generated voltage V _{0 at} that time. ATVC control for detecting AT in this case
In VC control, constant current control is performed at 1.5 μA, and the generated voltage V ₀ is detected. The current value of 1.5 μA when performing the constant current control is a value that prevents the plus memory (in the present invention, the reversal development method using negative toner) from remaining on the photosensitive drum 1. After that, at the time of printing (at the time of passing the sheet), constant voltage control is performed with a transfer voltage Vt (= V ₀ + Vp) obtained by adding a predetermined voltage (addition voltage) Vp to the generated voltage V ₀ .

In this embodiment, the transfer roller 5 having the sponge layer made of EPDM foam is used. However, the image is continuously formed on the first surface of the transfer paper and the second surface of the same transfer paper is continuously formed. Image-formed continuous paper is, for example, 1
When the automatic double-sided continuous paper feeding is performed after the predetermined number of sheets of 000 sheets, the temperature of the transfer roller 5 remarkably rises due to the temperature rise inside the machine due to the residual heat from the fixing heater 33. Then, since the resistance value of the transfer roller 5 increases as the temperature rises,
The resistance value of the transfer roller 5 also increases by performing the automatic double-sided continuous paper feeding. FIG. 4 shows changes in the temperature of the transfer roller 5 depending on the number of sheets automatically passed on both sides. FIG. 5 is a diagram showing a change in resistance value with respect to a change in temperature of the transfer roller, FIG.
FIG. 6 is a diagram showing changes in the resistance value of the transfer roller 5 with respect to the number of sheets automatically passed on both sides.

Therefore, as shown in FIG. 6, when the resistance value of the transfer roller 5 changes and the number of continuously fed double-sided sheets exceeds a predetermined number, image deterioration due to transfer cannot be ignored. Therefore, it is necessary to change the transfer bias when the number of continuously passed double-sided sheets exceeds a predetermined number.

In the present embodiment, as a method of changing the transfer bias, the printer control unit 28 stores the transfer bias for the first transfer roller 5 of the first side when automatic double-sided continuous sheet passing is performed. The transfer roller 5 for the first sheet of the first side for every 100 sheets of automatic double-sided continuous paper feeding
A command for changing the transfer bias according to the value of is sent from the printer control unit 28 to the high voltage control unit 17.

FIG. 7 is a diagram showing the value of the transfer bias that changes every 100 automatic continuous double-sided sheets.

The value of the added voltage Vp on the first side is 1 to 100 when the number of sheets automatically passed on both sides is 1 to 50 (the number of used sheets is 50).
For double-sided printing up to one sheet), the proper transfer bias for the first side is +2500 V when printing on plain paper. The value of the added voltage Vp on the second side is + 400V, and when the number of sheets automatically passed on both sides is from 1 to 100, the transfer bias on the second side is + 2900V. The value of the added voltage Vp in the case where the number of automatically continuous double-sided sheets passed is 1 to 100 is set as a default value, and when the number of automatically double-sided continuous sheets passed exceeds 100, the added voltage Vp is used as a reference.
The value of is + 2800V for the transfer bias on the first side from 101 to 200 sheets (a value obtained by adding + 300V to the transfer bias on the first side for 1 to 100 sheets), and the transfer bias for the first side from 201 to 300 sheets is + 3050V (101 The transfer bias of the first side from + to 200 sheets is + 250V), the transfer bias of the first side from 301 to 400 is + 3250V (the value of + 200V is added to the transfer bias of the first side from 201 to 300), and 401 to 500 The transfer bias of the first side up to the first sheet is + 3400V (value obtained by adding + 150V to the transfer bias of the first side from 301 to 400 sheets), and the transfer bias of the first side from 501 to 600 sheets is + 3500V (the first side from 401 to 500 sheets). + 100V to the transfer bias), 601 to 700
The transfer bias of the first side up to the number of sheets is + 3550V (501
From +701 to 600 sheets, the transfer bias of the first side from 701 to 800 sheets is + 3580V (the value of + 30V to the transfer bias of the first sheet from 601 to 700 sheets), 801 to 900 The transfer bias of the first side up to the first sheet is + 3600V (value obtained by adding + 20V to the transfer bias of the first side from 701 to 800 sheets), and the transfer bias of the first side from 901 to 1000 sheets is + 3610V (the first side from 801 to 900 sheets). When the number of automatic double-sided continuous paper feeds exceeds 1000, the resistance value of the transfer roller 5 becomes stable as shown in FIG.
The transfer bias of the first side from 01 sheets is 901 to 10
It is the same as the transfer bias of the first side up to 00 sheets. Similarly, the transfer bias of the second surface is a value obtained by adding + 400V to the transfer bias of the first surface.

Table 1 and FIG. 7 show experimental examples of the transfer bias on the first side and the second side depending on the number of sheets automatically continuously passed on both sides.

[0035]

[Table 1] In the comparative example in which the transfer bias was not changed in accordance with the number of continuously passed double-sided sheets, explosion occurred from the 100th sheet onward and transfer failure of the solid black image on the 200th sheet onward. On the other hand, when the transfer bias is changed according to the number of continuous double-sided sheets, as in the present embodiment, the automatic double-sided continuous sheet feeding is reduced to one.
Even when the number of sheets exceeds 100, stable transferability can always be obtained, and a good image can be obtained without deterioration due to transfer such as explosion and transfer failure of a solid black image on one surface. <Second Embodiment> The electrophotographic printer used in this embodiment is the same as that in the first embodiment.

First, the user of the printer 21 selects a print mode on the host device 22 and displays the control panel 13 shown in FIG. When the print environment information such as the size of the paper, the number of prints, and the distinction between the 1st and 2nd prints is set on the control panel 13, the signals of the print environment information and the image data are transferred to the printer 21. These signals are sent to the printer 21 via the path 23 of the block diagram shown in FIG.
It reaches the internal interface unit 26. Then, the interface unit 26 converts the image data into an image expansion unit 27.
The printer environment information is divided and transmitted to the printer control unit 28.

The printer control unit 28 selects the optimum transfer voltage and drives the high voltage control unit 17.

At this time, as shown in FIG. 6, when the number of sheets automatically passed on both sides exceeds a predetermined number, the resistance value of the transfer roller 5 changes remarkably, and image deterioration cannot be ignored.

Therefore, in the case of performing automatic double-sided continuous paper feeding exceeding a predetermined number, when the number of automatic double-sided continuous paper feeding reaches a predetermined number, one round of the transfer roller 5 is performed before the next printing is performed. The space between the sheets is opened, and the ATVC control for detecting the resistance value of the transfer roller 5 is performed. Then, the optimum transfer bias (voltage) Vt is determined, and the determined transfer bias V
The next automatic double-sided continuous paper feeding is performed depending on t. And AT
When the number of automatically continuous double-sided sheets has reached the predetermined number after performing the VC control, the paper is separated by one or more rounds before the next printing, and the resistance value of the transfer roller 5 is increased, as before. The automatic transfer voltage Vt is detected to determine the optimum transfer voltage Vt, continuous automatic double-sided sheet passing is continued by the transfer bias Vt thus determined, and the operation is repeated to prevent image deterioration due to transfer. However, ATV
There is no problem even if the automatic double-sided continuous paper feeding is once stopped to perform C control.

FIG. 8 is a flow chart showing the second embodiment of the present invention.

In the comparative example in which the transfer bias is not changed in accordance with the number of sheets continuously fed on both sides, an explosion occurs from the 100th sheet onward.
From the 200th sheet onward, a transfer failure of a solid black image on one surface occurred. On the other hand, as in the present embodiment, before the next printing for every 100 sheets, the paper gap for one round of the transfer roller 5 is opened, and the AT
If automatic double-sided continuous paper feeding is performed after performing VC control, stable transferability can be obtained at all times even when automatic double-sided continuous paper feeding is performed over 100 sheets, and an explosion or a solid black image on one surface can be obtained. No deterioration due to transfer such as transfer failure of
Good images can be obtained. <Third Embodiment> The electrophotographic printer used in this embodiment is the same as that in the first embodiment.

First, the user of the printer 21 selects the print mode on the host device 22 and displays the control panel 13 shown in FIG. When the print environment information such as the size of the paper, the number of prints, and the distinction between the 1st and 2nd prints is set on the control panel 13, the signals of the print environment information and the image data are transferred to the printer 21. These signals are sent to the printer 21 via the path 23 of the block diagram shown in FIG.
It reaches the internal interface unit 26. Then, the interface unit 26 converts the image data into an image expansion unit 27.
The printer environment information is divided and transmitted to the printer control unit 28.

The printer control unit 28 selects the optimum transfer voltage and drives the high voltage control unit 17.

At this time, as shown in FIG. 6, when the number of sheets automatically passed on both sides exceeds a predetermined number, the resistance value of the transfer roller 5 changes remarkably and the image deterioration cannot be ignored.
However, if the time until the next automatic double-sided continuous paper feed starts after the image formation by the automatic double-sided continuous paper feed is completed, that is, the amount of data for the next image formation is large and the number of automatic double-sided continuous paper feeds is the predetermined In the case where it exceeds the limit, if it takes time to develop the image with the formatter when reading the original and outputting the image information with the laser beam, the temperature of the transfer roller 5 does not rise so much even with automatic double-sided continuous paper feeding.
It was found that the resistance value of the transfer roller 5 did not increase so much either.

FIG. 9 is a diagram showing the positional relationship between the paper discharge sensor and the TOP sensor mounted on the image forming apparatus according to the embodiment of the present invention. In FIG. 9, the same or equivalent components as in FIG. Are denoted by the same reference numerals and redundant description will be omitted.

In the image forming apparatus shown in FIG.
a and 14b are a pair of registration rollers, 20 is a TOP sensor,
15a is a fixing film, 15b is a pressure roller, 24 is a paper discharge sensor, and 25 is a re-feed position.

The image forming apparatus of this embodiment has a process speed of 50 mm / sec.

The image forming apparatus is adapted to detect the image development time of the next print.

In the conventional example, an explosion occurs after 100 sheets of automatic double-sided continuous paper feeding, and a transfer failure of solid black on one side occurs after 200 sheets. Therefore, such transfer is also performed in the third embodiment of the present invention. Avoid defects. That is, when two or more two-sided copies of two or more originals are to be copied, for example, the image development time of the first side and the image development time of the second side are detected by the first 100 sheets, and from 1 in automatic double-sided continuous paper feeding Up to 100, 101 to 20
0 to 201 to 300, 301 to 400
For example, up to 100 sheets, the average value of the image development time of the next print for every 100 sheets is measured, and the optimum transfer bias of the next print is determined according to the average value of the image development time.

Table 2 shows the temperature and resistance of the transfer roller according to the image development time of the next print after the automatic double-sided continuous paper feeding.

[0051]

[Table 2] Therefore, as can be seen from Table 2, when the number of sheets automatically continuously passed on both sides exceeds a predetermined number, the temperature of the transfer roller 5 rises, and the resistance of the transfer roller 5 also rises. Transfer roller 5 when printing the first side
Therefore, the resistance of the transfer roller 5 does not increase so much.

Table 3 shows the optimum transfer bias depending on the image development time of the next print.

[0053]

[Table 3] Therefore, when automatic double-sided continuous paper feeding of a predetermined number or more is performed, the image development time of the next print on the first and second sides is detected for the first 100 sheets, and the transfer bias is determined from the image development time of the next print. By making the determination, it is possible to prevent image contamination such as explosion and solid black transfer failure on one surface.

[0054]

As described above, according to the present invention,
Change in resistance of the transfer roller during continuous double-sided paper passing when continuous image formation on the first side of the transfer material and continuous continuous double-sided image formation on the second surface of the same transfer material exceed a predetermined number. The optimum transfer conditions are set according to the above, so stable transfer performance can be obtained at all times even with continuous paper feeding on high-speed machines and double-sided machines, and the transfer bias is insufficient, and the toner around the toner image It is possible to obtain a good image free from the image scattering phenomenon and image stain due to poor transfer.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a control panel of a printer displayed on a host device according to the present invention.

FIG. 3 is a control block diagram of a printer operation according to the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the number of sheets automatically passed on both sides of the present invention and the temperature change of the transfer roller.

FIG. 5 is a characteristic diagram showing the relationship between temperature change and resistance change of the transfer roller of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between the number of sheets automatically passed on both sides of the present invention and a resistance change of a transfer roller.

FIG. 7 is a characteristic diagram showing a relationship between the number of automatic double-sided continuous paper feeds and a transfer bias to be changed according to the first embodiment of the present invention.

FIG. 8 is a flowchart according to a second embodiment of the present invention.

FIG. 9 is a schematic configuration diagram showing an image forming apparatus according to a third embodiment of the invention.

[Explanation of symbols]

 1 image carrier (photosensitive drum) 5 transfer means (transfer roller) 6 transfer site P transfer material (transfer paper) 28 transfer bias control means (printer control section)

Claims (6)

[Claims] 1. A transfer means for contacting an image carrier is provided, and constant current control is performed on the transfer means when a transfer material does not exist at a transfer site between the image carrier and the transfer means. In an image forming apparatus that holds a voltage and controls the transfer unit with a constant voltage by the held voltage when the transfer material is present at the transfer portion, an image is continuously formed on the first surface of the transfer material. With
When the number of continuous double-sided sheets, on which images are continuously formed on the second side of the same transfer material, exceeds a predetermined number, the transfer bias control for changing the transfer bias applied to the transfer means in accordance with the number exceeding the predetermined number. An image forming apparatus comprising means. 2. The transfer bias control means, when the number of continuous double-sided sheets exceeds a predetermined number, performs a constant current control on the transfer means every time the predetermined number is exceeded, and a predetermined voltage is set at this time. The image forming apparatus according to claim 1, wherein a transfer bias obtained by adding the voltage is applied to the transfer unit. 3. A transfer means for contacting an image carrier is provided, and constant current control is performed on the transfer means when a transfer material does not exist at a transfer site between the image carrier and the transfer means. In an image forming apparatus that holds a voltage and controls the transfer unit with a constant voltage by the held voltage when a transfer material is present at the transfer site, while continuously forming an image on the first surface of the transfer material. ,
Transfer bias control for changing the transfer bias of the transfer means according to the number of double-sided sheets passed within a predetermined time when the number of double-sided sheets continuously image-formed on the second side of the same transfer material exceeds a predetermined number. An image forming apparatus comprising means. 4. The transfer bias control means, when the number of continuous double-sided sheets exceeds a predetermined number, performs constant current control on the transfer means every time the predetermined number of sheets is exceeded, and a predetermined voltage is set at this time. The image forming apparatus according to claim 3, wherein a transfer bias obtained by adding the voltage is applied to the transfer unit. 5. A constant current control is performed on the transfer means when a transfer material is provided at a transfer portion between the image support and the transfer means, the transfer means being in contact with the image support. In the image forming apparatus, the voltage of the transfer material is held, and when the transfer material is present at the transfer portion, the transfer means is controlled to a constant voltage by the held voltage. Along with
When the number of continuous double-sided sheets, on which images are continuously formed on the second side of the same transfer material, exceeds a predetermined number, depending on a change in the resistance value of the transfer means due to interruption of the sheet passing after passing the predetermined number of sheets. An image forming apparatus comprising: a transfer bias control unit that changes a transfer bias. 6. The transfer bias control means, when the number of continuous double-sided sheets exceeds a predetermined number, performs a constant current control on the transfer means every time the predetermined number of sheets is exceeded, and a predetermined voltage is set at this time. The image forming apparatus according to claim 5, wherein a transfer bias obtained by adding the voltage is applied to the transfer unit.