JP2003057971A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent white spot point from occurring in an image forming device of both front and back surfaces of paper simultaneous transfer method using toner polarity conversion. SOLUTION: In the image forming device, the electrified polarity of a first surface toner image that is formed on a photoreceptor 1 and transferred to an intermediate transfer belt 10 is changed over to a reverse polarity by an electrifying means 17. Then, along with a second toner image formed on the photoreceptor 1, the images are transferred simultaneously to the front and the back surfaces of the paper by a transfer means 21. Resistance value of the belt 10 is detected when power source of the device is turned on and the output of the electrifying means 17 is controlled depending on the belt resistance value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of forming images on both sides of a recording medium.

[0002]

2. Description of the Related Art Some image forming apparatuses such as copiers, printers and facsimiles are constructed so that images can be formed on both sides of a recording medium (hereinafter referred to as paper).
In a conventional image forming apparatus capable of recording on both sides, an image (visual image) on one side formed on an image carrier is transferred onto a sheet of paper and fixed, and the sheet is inverted by an inversion path or the like and fed again. A two-pass system in which an image on the other side (visual image) is transferred and fixed on the back side of the sheet is generally used.

In the case of double-sided recording by this method, there are many problems in securing the reliability of paper transportation due to switching of paper transportation direction and paper curling due to fixing of one-sided image.
In addition, there is also a problem that an image defect occurs due to defective transfer onto a curled sheet. Therefore, as a method for solving these problems, a one-pass method has been proposed in which a toner image is transferred to both sides of a sheet and then fixing is performed once.

As a method of transferring a toner image to both sides of a sheet, there are a method of a plurality of transfer steps and a method of one-time transfer, that is, a method of simultaneous transfer on both front and back sides of a sheet using toner polarity conversion.

Regarding the toner polarity conversion, for example, Japanese Patent Laid-Open Nos. 8-212664 and 10-1 are available.
There are those disclosed in JP-A-04963 and JP-A-10-171264.

Further, Japanese Patent No. 2906538 (JP-A-3
No. 253881), a first image formed on a photoconductor is transferred onto a transfer belt by a first transfer means, and then a polarity of a second image formed on the photoconductor is transferred onto the photoconductor before the transfer step. It is disclosed that the first image and the second image are simultaneously transferred onto both sides of the sheet by one transfer means by reversing the first image and the second image with different polarities.

[0007]

However, in the conventional simultaneous double-sided paper transfer method utilizing toner polarity conversion, the first (previously formed) toner image for toner polarity conversion is transferred onto the paper. When doing so, there is a problem that a white spot-like abnormal image is generated.

The present invention solves the above-mentioned problems in the conventional image forming apparatus of the both-side front and back side simultaneous transfer system utilizing the toner polarity conversion, and it is possible to prevent the occurrence of white spots and always obtain a good image. An object is to provide a forming apparatus.

[0009]

According to the present invention, the above object is to transfer a first toner image formed on an image bearing member to an intermediate transfer member, and further to transfer a second toner image onto the image bearing member. Which is capable of forming an image on both sides of a recording medium by transferring and fixing the first and second toner images to both sides of the recording medium, the first and second toner images being formed on the image carrier. Toner image of the first toner image on the intermediate transfer member, the charging polarity of the first toner image on the intermediate transfer member is switched to the opposite polarity by a non-contact charging unit, and the first toner image and the second toner image are transferred. In the image forming apparatus for simultaneously transferring the image on both sides of the recording medium, the resistance value of the intermediate transfer member is detected, and the output of the charging unit is controlled according to the detected resistance value.

In order to solve the above-mentioned problems, the present invention detects the output of a transfer means for simultaneously transferring the first toner image and the second toner image to both sides of a recording medium. We propose to control according to the resistance value.

In order to solve the above problems, the present invention reduces the output of the charging means when the resistance value of the intermediate transfer member falls below a predetermined reference value, and
It is proposed to increase the output of the transfer means.

In order to solve the above-mentioned problems, the present invention sets the amount of toner adhered to the image carrier when the second toner image is formed on the image carrier to the detected resistance value. Propose to control accordingly.

Further, in order to solve the above-mentioned problems, the present invention controls the developing condition of a developing means for applying toner to the image carrier to develop the amount of toner adhered to the image carrier. Propose to control.

In order to solve the above-mentioned problems, the present invention proposes to control the charging condition of a charging means for charging the image carrier to control the amount of toner adhered to the image carrier. .

In order to solve the above-mentioned problems, the present invention controls the exposure condition of the exposing means for forming an electrostatic latent image on the image carrier to control the amount of toner adhered to the image carrier. Suggest to do.

In order to solve the above-mentioned problems, the present invention reduces the output of the charging means and reduces the output of the transfer means when the resistance value of the intermediate transfer body falls below a predetermined reference value. It is proposed that the amount of toner adhered to the image carrier be reduced while increasing the amount.

Further, in order to solve the above-mentioned problems, in the present invention, the initial value of the resistance value of the intermediate transfer member is 10 ⁷ to 10 ^9.
It is proposed to be Ω · cm. In order to solve the above-mentioned problems, the present invention proposes to display a warning when the detected resistance value of the intermediate transfer member is 10 ⁷ Ω · cm or less.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional configuration diagram of a printer that is an example of an image forming apparatus to which the present invention is applied.

In the printer shown in this drawing, a photosensitive drum 1 which is a first image carrier is arranged in the approximate center of the apparatus. Around the photosensitive drum 1, a cleaning device 2,
A charge eliminating device 3, a charging device 4, and a developing device 5 are provided. An exposure device 7 is provided above the photoconductor drum 1, and the laser light L emitted from the exposure device 7 is applied to the photoconductor 1 at a writing position between the charging device 4 and the developing device 5.

A belt unit 20 is provided below the photosensitive drum 1. The belt unit 20 is centered on the intermediate transfer belt 10 as the second image carrier,
The photosensitive member 1 is provided so that a part thereof contacts the intermediate transfer belt 10. The intermediate transfer belt 10 includes a roller 11,
It is stretched around 12 and 13 and is supported so as to be able to travel counterclockwise in the figure. The intermediate transfer belt 10 has heat resistance and has a resistance value that allows toner to be transferred.

Inside the loop of the intermediate transfer belt 10,
Backing rollers 14, 15, cooling means 16, 16, fixing roller 18, transfer means 21, etc. are provided. The fixing roller 18 has a built-in heat source such as a heater, and fixes the toner image transferred onto the sheet in cooperation with a fixing roller 19 described later. The transfer unit 21 uses the belt 10
It is provided at a position facing the photoconductor 1 with the photoconductor 1 interposed therebetween.
The toner image formed on the intermediate transfer belt 10 is transferred onto the paper from the intermediate transfer belt 10 or the intermediate transfer belt 10, and the toner image formed on the photoconductor 1 is directly transferred onto the paper.

A fixing device 30, a belt cleaning device 25, and a charging means 17 are provided on the outer peripheral portion of the intermediate transfer belt 10.
Has been deployed. The charging means 17 is the intermediate transfer belt 1.
This is for reversing the polarity of the toner transferred to 0.

The fixing device 30 has a fixing roller 19 containing a heat source such as a heater, and is rotatably supported around a fulcrum 30a. Then, the belt 10 (and the paper) is rotated by a mechanism (not shown) as indicated by an arrow G.
The fixing roller 18 can be pressed against and separated from the fixing roller 18 by sandwiching.

The cleaning device 25 for the intermediate transfer belt 10 has a cleaning roller 25a and a blade 2 inside.
5b, toner conveying means 25c, etc., and has a function of wiping off unnecessary toner remaining on the surface of the intermediate transfer belt 10. The toner accumulated in the cleaning device 25 is
The toner is conveyed to a collecting container (not shown) by the toner conveying means 25c. This cleaning device 25 has a rotation fulcrum 25d.
It is configured so as to be rotatable around the center as indicated by an arrow H.
The cleaning roller 25 a can be brought into contact with and separated from the intermediate transfer belt 10 by rotating the entire cleaning device 25 by a mechanism (not shown).

In this embodiment, the photosensitive drum (first image bearing member) 1, the cleaning device 2, the static eliminator 3, the charging device 4, the developing device 5 and the like are integrated into a unit,
The process cartridge is configured so that it can be replaced at the end of its life.

A paper feed cassette 26 is provided below the main body of the apparatus. The paper feed cassette 26 is constructed so that it can be pulled out rightward in the drawing. A transfer paper P as a recording material is stored in the cassette 26. Cassette 2
A sheet feeding roller 27 is provided at an upper position on the front end side (right side in the drawing) of sheet feeding direction 6. A registration roller pair 28 is provided on the right side of the photosensitive drum 1. The guide member 29 on the right side is a member that guides the sheet to be sent to the registration roller 28. Above the cassette 26, the electrical component E1 and the control device E2 are arranged. Further, a manual paper feeding device 35 is provided on the right side surface of the device, and a paper feeding roller 36 for delivering the paper P set on the paper setting table 37 is provided.

In FIG. 1, a switching claw 42 is provided on the left side of the belt unit 20. This switching claw 4
2 is configured to be swingable around a fulcrum 43, and switches the conveying direction of the paper sent from the belt unit 20 to a paper discharge stack section 40 provided on the upper surface of the apparatus main body or a paper discharge tray 44 on the side surface of the apparatus. . When the switching claw 42 is at the position shown in the figure, the paper is sent to the paper discharge stack section 40,
When the switching claw 42 is switched in the direction of arrow J, the paper is sent to the paper discharge tray 44.

A pair of transport rollers 33 for transporting a sheet is arranged above the switching claw 42. Further, a paper discharge roller pair 34 for discharging the paper to the paper discharge stack section 40 is arranged further above. Conveyor roller pair 33
The space between the sheet discharge roller pair 34 and the sheet discharge roller pair 34 is guided by the guide members 31a and 31b. On the other hand, on the left side of the switching claw 42, a paper discharge roller pair 32 for discharging the paper to the paper discharge tray 44 is arranged.

An image forming operation in the printer configured as described above will be described. First, the operation when images are obtained on both sides of the paper will be described. When images are to be obtained on both sides of the sheet, the image formed first is called the first side image, the image formed later is called the second side image, and the side of the sheet to which the first side image is transferred is the first side of the sheet. The surface of the paper on which the second surface image is transferred will be referred to as the second surface of the paper.

The image forming apparatus of this embodiment is a so-called printer, and a signal for writing is sent from a host machine (not shown) such as a computer. The exposure device 7 is driven based on the received image signal, and the light from the laser light source (not shown) of the exposure device is scanned by the polygon mirror 7a which is rotationally driven by the motor.
After passing through the mirror 7b, the fθ lens 7c, etc., the photosensitive drum 1 uniformly charged by the charging device 4 is irradiated with the latent image, and a latent image corresponding to the writing information is formed on the photosensitive drum 1.

The electrostatic latent image on the photosensitive member 1 is developed by the developing device 5, and a visible image with toner is formed and held on the surface of the photosensitive member. The toner image on the photoconductor 1 is transferred onto the surface of the intermediate transfer belt 10 that runs in synchronization with the photoconductor 1 by the transfer unit 21 on the back side of the intermediate transfer belt 10 that is the second image carrier.

After the image is transferred, the surface of the photosensitive member 1 is cleaned of residual toner by the cleaning device 2 and discharged by the discharging device 3 to prepare for the next image forming cycle. The intermediate transfer belt 10 carries the toner image transferred on the surface (the image transferred on the first surface of the paper) and travels counterclockwise in the drawing. At this time, the fixing device 3 is arranged so that the toner image is not disturbed.
0 and the cleaning device 25 are controlled to maintain a non-operating state (electrical input interruption or separation from the intermediate transfer belt 10).

When the intermediate transfer belt 10 travels to a predetermined position, a toner image to be transferred to the other surface (second surface) of the paper is started to be formed on the photosensitive member 1 by the above-mentioned process and is selected. Paper feeding is started from the sheet feeding device (cassette 26 or manual feed tray 35). When the paper feed roller 27 or 36 rotates in the direction of the arrow, the paper P in the paper feed cassette 26 or at the top of the paper feed tray 37 is pulled out and conveyed to the pair of registration rollers 28.

The intermediate transfer belt 10 travels in synchronism with the photoconductor 1, and the toner image (first surface image) previously transferred onto the intermediate transfer belt 10 is rotated once to rotate the belt 10 and the photoconductor 1.
Are conveyed toward the position where they touch. At this time, the polarity of the toner image carried on the belt 10 is reversed by the action of the charging means 17 provided in front of the roller 12.

By the registration roller pair 28, the positions of the toner image (second surface image) on the paper and the photosensitive member 1 and the toner image (first surface image) on the belt 10 are made normal.
The registration roller pair 28 delivers the paper at a timed timing. The paper is sent to a transfer position where the photoconductor 1 and the belt 10 are in contact with each other, and the transfer unit 21 transfers the toner images (first surface image and second surface image) to both surfaces of the paper at once.

The paper on which the toner images are transferred on both sides is sent to the fixing area by the running of the belt 10. Here, the fixing device 30 is rotated so that the fixing roller 19 is pressed against the fixing roller 18 with the belt 10 interposed therebetween.
And the fixing roller 18 work together to form a toner image on the paper (both sides)
Is fixed at once. After the toner image is transferred, the paper is fixed in a state where the paper and the intermediate transfer belt 10 are overlapped without being separated from the intermediate transfer belt 10, so that the toner image is not disturbed and the occurrence of image blur is prevented.

The sheet after fixing is curvature-separated from the intermediate transfer belt 10 by the roller 11 section, and the conveying direction is switched by the branching claw 42, and is transferred to the sheet discharge stack section 40 on the upper side of the apparatus or the sheet discharge tray 44 on the side of the apparatus. Is discharged.

When the paper is discharged to the paper discharge stack 40 on the upper surface of the apparatus, the second surface of the double-sided image, that is, the surface directly transferred from the photoconductor to the paper becomes the lower surface, and the paper discharge stack 40 is formed. In order to align the pages, the image of the second page is created first, the toner image is held on the intermediate transfer belt 10, and the image of the first page is created later. The surface of the body 1 may be directly transferred to the paper. Therefore, when the sheets are discharged to the discharge stack unit 40 in page order, the first-side image is the second-page image and the second-side image is the first-page image. The same applies to the images on the third and subsequent pages. When there are images on several pages, the images on the several pages are formed first and transferred / held on the intermediate transfer belt 10.
An odd page, which is one before this number of pages, is created later and transferred directly from the surface of the photoconductor 1 to a sheet.

On the other hand, when the sheet is discharged to the sheet discharge tray 44 on the side of the apparatus, the second surface of the double-sided image, that is, the surface directly transferred from the photoconductor to the sheet becomes the upper surface and is discharged to the sheet discharge tray 44. Placed. Therefore, in this case, they are not stacked in page order. The user can specify whether the paper is discharged to the paper discharge stack unit 40 or the paper discharge tray 44.

It is also possible to stack the sheets in the sheet discharge tray 44 in page order. In that case, conversely to the above, the first side image is the image of the first page and the second side image is the image. This is the second page image. The same applies to the images on the third and subsequent pages. If there is an image on an odd page, the image on the odd page is first formed, transferred and held on the intermediate transfer belt 10, and the even page next to the odd page is formed. Should be created later.

By the way, normally, when a reverse image (mirror image) is formed on the photoconductor 1 and directly transferred to the paper, a normal image is obtained. However, the image transferred on the intermediate transfer belt 10 is transferred to the paper. When the image is transferred onto the sheet, when it is formed as a mirror image on the photoconductor 1, the image becomes a mirror image when the sheet is transferred. Therefore, in the present embodiment, the image (first surface image) transferred from the intermediate transfer belt 10 onto the sheet is formed as a normal image on the surface of the photoconductor 1,
The toner image (second surface image) directly transferred from the photoconductor 1 onto the sheet is exposed so as to be a mirror image on the surface of the photoconductor.

The image forming order for page alignment as described above can be realized by a known technique for storing image data in a memory, and the exposure for switching between normal and reverse images can be realized by a known image processing technique.

The cleaning device 25 separated from the intermediate transfer belt 10 is provided with the cleaning roller 2 after the image is transferred from the photoconductor 1 and the intermediate transfer belt 10 onto the sheet.
Cleaning device 25 so that 5a contacts belt 10
Is rotated, and the residual toner after being transferred to the sheet is transferred to the surface of the cleaning roller 25a and scraped by the blade 25b. The toner scraped off is collected in a storage unit (not shown) by the toner conveying unit 25c.

The intermediate transfer belt 10 having passed through the cleaning area is cooled by the operation of the cooling means 16, 16. As the cooling means 16, various heat dissipation methods can be adopted. In the method of circulating air, it is convenient to circulate the air after transferring it to a recording medium (paper) so as not to disturb the toner image held on the surface of the intermediate transfer belt 10. A cooling means using a heat pipe, which takes heat by directly contacting the inner surface of the loop of the intermediate transfer belt 10, can be adopted.

Next, the operation for obtaining an image on one side of a sheet will be described. If you want to obtain an image on one side of the paper,
The step of transferring the toner to the intermediate transfer belt 10 can be omitted, and the toner image formed on the surface of the photoconductor 1 is directly transferred to the paper. In the case of a one-sided image, the toner image on the photoconductor 1 is a mirror image, and becomes a normal image when transferred onto a sheet.

In FIG. 1, the paper P is sent between the photoconductor 1 and the intermediate transfer belt 10 in synchronism with the toner image formed on the photoconductor 1, and the transfer means 2 is used.
1 causes toner to be transferred from the photoconductor 1 onto the sheet.

The sheet on which the toner image is transferred moves together with the intermediate transfer belt 10 and the toner is fixed. afterwards,
The sheet is separated from the intermediate transfer belt 10 and placed on the sheet discharge stack section 40 or the sheet discharge tray 44 depending on the direction of the switching claw. When the sheets are discharged to the discharge stack unit 40, even if the originals over several pages are processed in order from one page, the printed matter is in the page order when taken out from the discharge stack unit 40.

In order to arrange the papers in the paper discharge tray 44 in page order, the toner image formed on the photoconductor 1 is transferred to the intermediate transfer belt 10 even in the one-sided printing, and the intermediate transfer belt 10 transfers the toner image to the lower surface of the paper. It is also possible to transfer the toner image. In this case, the toner image on the photoconductor 1 is a normal image, and becomes a normal image when the paper is transferred.

In the example of FIG. 1, the fixing device 30 located outside the loop of the intermediate transfer belt 10 has a structure in which the fixing roller 19 can be pressed into contact with and separated from the fixing roller 18 with the belt 10 (and the paper) sandwiched therebetween. As shown in FIG. 2, the fixing device outside the loop of the intermediate transfer belt 10 can be a non-contact type. The fixing device 30B of FIG. 2 is of a type that does not come into contact with the conveyed paper, and fixes the toner image by the emission of light from an infrared lamp or a xenon lamp. Since it is a non-contact type, the fixing device 30B does not need to be rotatable, and is fixedly provided.

In FIGS. 1 and 2, after the toner image is transferred, the paper and the intermediate transfer belt 10 are fixed without being separated from the intermediate transfer belt 10. As in the fixing device 30C shown in the figure, a method of fixing the toner image on the sheet after separating from the intermediate transfer belt 10 can also be adopted.

Next, the image forming process during double-sided recording in this embodiment will be described with reference to FIG. However, here
The fixing device having the structure shown in FIG. 2 will be described. Also,
In the space of the drawing, the intermediate transfer belt 10 is illustrated in a state of being vertically arranged.

In FIG. 4, the image forming process during double-sided recording is (a) development and primary transfer (transfer to the belt 10), (a)
The four steps of secondary development (second surface development), (c) secondary transfer (double-sided transfer to paper), (d) fixing, and belt cleaning are shown separately. Note that, for convenience, in FIG. 4, the photoconductor 1 and the intermediate transfer belt 10 are illustrated as being separated from each other, but the photoconductor 1 and the intermediate transfer belt 10 are provided in contact with each other.

In FIG. 4A, the photosensitive member 1 is charged (-) by the charging means 4, and the developing device 5 (-) charges the electrostatic latent image formed by the writing light L from the exposure device.
It is shown that charged toner (indicated by a black circle in the figure) is applied and the toner is primarily transferred to the intermediate transfer belt 10 by the action of the transfer unit 21 (+ voltage is applied).

In FIG. 4A, a toner image (negative charge) on the second surface is formed on the photosensitive member 1, and the toner image (first surface image) carried on the intermediate transfer belt 10 is conveyed. During the conveyance, the polarity of the toner image carried on the belt 10 is reversed to the positive polarity by the charging of the charging means 17. Further, the paper P is set on the registration roller 28 at a timing so that the positions of these toner images become normal.
Is shown.

In FIG. 4C, the action of the transfer means 21 (+
By applying a voltage, both sides of the paper (first side, second side)
It is shown that the toner image is transferred at one time (second surface) to the surface). The toner (+ charge) on the intermediate transfer belt 10 is electrostatically repulsed by the transfer roller 21 to which a + voltage is applied and is transferred to the sheet, and the toner (-charge) is electrostatically transferred from the photoconductor 1 to the sheet. By being transferred by suction to
Toner is simultaneously transferred to both sides of the paper.

FIG. 4D shows a state in which the sheet is adsorbed by the intermediate transfer belt 10 and is conveyed to the fixing area to fix the toner images on both sides of the sheet. Further, the belt cleaning device 25 is pressed against the belt 10 to remove the residual toner on the belt 10.

As described above, on the second image carrier (intermediate transfer belt 10), the polarity of the toner carried (primarily transferred) on the second image carrier is non-contact charging means (charging charger 17). Since the polarity is switched by means of one transfer means (21), the toner images can be simultaneously transferred (secondary transfer) on both sides of the paper, and the applied voltage of the transfer means can be used for the primary transfer and the secondary transfer. Since it is not necessary to change the polarity of the transfer means and the configuration for switching the applied voltage polarity of the transfer means is unnecessary, the cost is excellent. Further, since the charge is not applied from the open surface of the sheet on which the toner is transferred, the disturbance of the toner image transferred on the upper surface of the sheet, the electrostatic offset at the time of fixing due to the charge-up of the transfer sheet, and the like are prevented.

When an image is obtained on only one side of the paper,
The toner image formed on the photoconductor 1 may be directly transferred to the paper, and the toner (-charge) on the photoconductor 1 is suction-transferred by the transfer roller 21 to which the + voltage is applied.

Further, the charging polarity of the photoconductor in the above description,
The toner charging polarity is an example, and the polarity may be opposite to that of the present embodiment. By the way, as a problem of the prior art, there is a case where a white spot occurs when a toner image for which the charging polarity is converted is transferred from the transfer belt to the transfer paper. The output of the charging unit for converting the toner polarity and the resistance value of the transfer belt have an influence on the occurrence of the white spots.

If the output of the charging means for converting the toner polarity is increased, the image quality becomes poor (there are many white spots).
It was found by experiments that the image quality was improved when the output was reduced, and that the image quality was poor when the belt resistance value was low. The relationship between the output of the charging means or the belt resistance value for the toner polarity conversion and the white spot is shown in the graph of FIG.

In the graph of FIG. 5, the vertical axis represents the image quality (rank of white spots), the area above the horizontal horizontal dotted line is the area where the state of white spots is within the allowable range, and The lower area is an area where white spots are outside the allowable range.
Further, the horizontal axis represents the output of the charging unit for converting the toner polarity. The charging means for converting the toner polarity is shown in FIG.
In FIG.

In FIG. 5, the broken line (thick dotted line) shows the resistance value of the transfer belt (intermediate transfer belt) at the time of machine installation (factory shipment), and the belt resistance value has decreased since the machine was installed. Is shown by a solid line. These thick dotted lines and solid lines show the fluctuations in the rank of white spots when the output of the charging means for toner polarity conversion is changed for each belt resistance value.

Here, the transfer belt (intermediate transfer belt)
Indicates that the resistance value fluctuates due to environmental conditions or aging. As shown in FIG. 5, it is assumed that the output C of the charging means for toner polarity conversion is set to C (A) when the machine is installed. Although the image quality (1) was in the white spot OK area when the machine was installed, the image quality becomes (2) when the belt resistance changes in the direction of decrease, and the image quality enters the white spot NG area.

Therefore, when the belt resistance value decreases as shown by the solid line after the machine is installed, the output of the charging means for converting the toner polarity: C is lowered from C (A) to C (B) to obtain the image quality. Becomes (3) and enters the area of the white spot OK. In the present embodiment, the resistance value of the intermediate transfer belt 17 is detected, and the output of the charging unit 17 for toner polarity conversion is controlled according to the belt resistance value, so that the white spot state falls within the allowable range. In this way, the occurrence of abnormal images is prevented.

Further, the charging means 1 for converting the toner polarity is used.
Although it is possible to prevent the generation of the white spot image by adjusting the output of No. 7, if the output of the charging unit 17 is made small, the polarity conversion may not be sufficiently performed for the first surface image, and the first surface image may not be sufficiently converted. May not be reliably transferred.
An experiment on transferability was carried out. As a result, even when the output of the charging unit 17 was reduced, by increasing the output of the transfer unit 21 that simultaneously transfers the first surface image and the second surface image to the front and back of the transfer paper, It was found that the repulsive force between the transfer belt 10 and the toner whose polarity was converted was increased, and the transfer efficiency was increased. Therefore, the output of the charging unit 17 can be reduced to prevent the occurrence of white spots, and the output of the transfer unit 21 can be increased to ensure a stable transfer efficiency of the first surface image.

Further, by adjusting the output of the charging means 17 and the output of the transfer means 21, the white spots can be prevented and the transfer efficiency of the image on the first surface can be secured. However, when the output of the transfer means 21 is increased, This will change the transfer efficiency of the surface image. Therefore, by controlling the toner adhesion amount of the second surface image on the photosensitive drum 1 by the amount of changing the output of the transfer unit 21, the final second surface image can be made appropriate. In this case, the amount of toner attached to the photoconductor can be adjusted by adjusting the developing conditions, the photoconductor charging potential, and the exposure conditions.

Further, although a good image in which the generation of the white spot image is prevented can be obtained by the control as described above, when the belt resistance value changes too much, the generation of the white spot cannot be prevented. is there. Alternatively, the transfer efficiency may not be secured in some cases. Therefore, the resistance value of the intermediate transfer member to which the present invention is applied falls within a predetermined range (initial value of 10 ⁷ to 1).
By defining the 0 ⁹ Ω · cm), to ensure a secure prevention and transfer efficiency of white spots by the above control, it is possible to provide a good image.

The specific control in this embodiment will be described below. In the present embodiment, the transfer current R1 (when applied to the transfer roller 21) when transferring the toner image on the first surface from the photosensitive drum 1 to the intermediate transfer belt 10 is 10 μ.
A, the toner images on the first and second sides are transferred onto the intermediate transfer belt 10
Transfer current (applied to the transfer roller 21) for simultaneous transfer from both sides of the transfer paper to both front and back surfaces: R2 to 10 μA
When the charging polarity of the surface image is switched to the opposite polarity on the intermediate transfer belt 10, the output current C of the charging means 17 is 200 μ.
It is set to A. Output current of this charging means 17: C =
200 μA is an initial value. Further, when the electrostatic latent image on the photosensitive drum 1 is developed, the developing bias: VB is 50
Set to 0V.

At the time of warming up when the power is turned on to the apparatus, the transfer roller 20 is contacted and rotated with the photosensitive drum 1 and the intermediate transfer belt 10.
Is applied to detect the current flowing through the photosensitive drum 1, and the belt resistance is obtained. The current flowing through the photoconductor drum 1 is detected by a detection circuit provided in a power supply unit (not shown). Then, the output current: C of the charging means 17 is controlled according to the detected belt resistance value.

In this embodiment, when the detected resistance value of the intermediate transfer belt 10 is 1 × 10 ⁸ Ωcm or more, the above parameters R1, R2, C and VB are left as they are. Further, the detected belt resistance value is 1 × 10 ⁷ to 10
^In the case of ⁸ Ωcm, the output current: C of the charging means 17 is 2
Change from 00μA to 100μA and set transfer current: R2 to 1
Change from 0 μA to 20 μA, and change the developing bias: VB ′ when developing the second side image during double-sided printing from 500 V to 450 V (Developing bias when developing the first side image: VB remains at 500 V) Is). The transfer current R1 remains unchanged. Further, when the detected belt resistance value is less than 1 × 10 ⁷ Ωcm, a serviceman call is displayed.

The above control is shown in the flow chart of FIG. That is, after the device power is turned on (S1), the resistance value R of the intermediate transfer belt 10 is detected (S2), and R is 1 × 10.
^It is determined whether it is ⁸ Ωcm or more (S3). Next, it is determined whether R is 1 × 10 ⁷ Ωcm or less (S4). If R is 1 × 10 ⁷ Ωcm or less, the process proceeds to S6 to display a serviceman call. On the other hand, in S4, R is 1 × 10 ⁷ Ω
cm, that is, the resistance value of the belt 10: R is 1 ×
When it is in the range of 10 ⁷ to 10 ⁸ Ωcm, C = 10
It is set to 0 μA, R2 = 20 μA and VB ′ = 450 V (S5).

This completes the setting when the power of the device is turned on.
Image formation is performed with the set parameters until the power is turned off. Normally, a print job for one day is performed under the conditions set when the power was turned on in the morning,
When the power is turned on the next day, the same control is performed again,
Each parameter is corrected.

In the above control, when the detected resistance value of the intermediate transfer belt 10 is 1 × 10 ⁸ Ωcm or more, white spots are not generated, and the respective parameters are set to their initial values.

The detected belt resistance value is 1 × 10 ⁷ to 10
^In the case of ⁸ Ωcm, the output current C of the charging means 17 is 20
By changing from 0 μA to 100 μA, it is possible to prevent the occurrence of white spots due to the decrease in the belt resistance value. By lowering the output current C of the charging means 17, the transfer efficiency of the image on the first side is slightly lowered. Therefore, when the toner image is transferred from the intermediate transfer belt 10 to the transfer paper, the transfer current R2 is changed from 10 μA to 20 μA. By raising it, the transfer efficiency to the transfer paper is secured.

At this time, R2 is changed from 10 μA to 20 μ
Although the transfer efficiency to the transfer paper is ensured by increasing it to A, the transfer efficiency of the second surface image (when the second surface image is transferred from the photoconductor to the transfer paper) is increased.
Therefore, by adjusting the developing bias to adjust the toner adhesion amount on the photoconductor, a stable image can be obtained for the second surface image. The amount of toner adhered to the photoconductor may be adjusted by controlling the charging potential of the photoconductor drum 1 to be low or the amount of exposure light to be low, in addition to the developing bias.

Further, the detected belt resistance value is 1 × 10.
When it is less than ⁷ Ωcm, the output current of the charging means 17 is C.
The white spot image cannot be prevented unless the value is set to less than 10 μA, but the transfer efficiency cannot be secured even if R2 is increased to 20 μA with the output of the charging unit 17, so in this case a serviceman call is displayed. There is.

Although the present invention has been described above with reference to the illustrated embodiment, the present invention is not limited to this, and various modifications can be made. For example, the initial values of the parameters R1, R2, C, VB and the like in the above embodiment and the values changed from the initial values are merely examples, and appropriate values can be set. Further, the reference value for judging the parameter change is also an example, and an appropriate value can be set. Further, the timing and detection method for detecting the resistance value of the intermediate transfer belt 10 are also arbitrary.

In the above embodiment, the transfer means 21
Is configured as a transfer roller, but contact-type transfer means other than the roller or non-contact-type transfer means such as a transfer charger may be used. As for each of the other devices, devices of any system can be adopted as long as the present invention can be implemented. For example, although the first image carrier is the photosensitive drum in the above embodiment, it may be a belt type image carrier.

Further, the exposure apparatus 7 in the above embodiment.
Is a laser method, but an LED exposure method may be used. Alternatively, the present invention can be implemented in analog exposure (analog copying machine). When a normal image is obtained on the photoconductor by analog exposure, it is possible to use a mirror.

Needless to say, the image forming apparatus is not limited to the printer but may be a copying machine or a facsimile.

[0081]

As described above, according to the image forming apparatus of the present invention, the charging means for detecting the resistance value of the intermediate transfer member and switching the charging polarity of the first toner image according to the resistance value. Since the output is controlled, it is possible to prevent the occurrence of white spots in the toner image whose charging polarity is switched.

According to the second aspect of the present invention, it is possible to prevent the generation of white spots and ensure stable transfer efficiency.

According to the structure of claim 3, white spots can be prevented by reducing the output of the charging means for switching the charging polarity of the first toner image when the resistance value of the intermediate transfer member decreases. By reducing the output of the charging unit, the polarity of the first toner image may not be sufficiently converted, and transfer failure may occur. However, the output of the transfer unit for simultaneously transferring the toner image to both surfaces of the recording medium. By increasing, the transfer efficiency can be increased and transfer failure can be prevented. Therefore, it is possible to prevent white spots and ensure transfer efficiency.

According to the structure of claim 4, it is possible to compensate for the influence on the transfer efficiency of the second toner image when the output of the transfer means for simultaneously transferring the toner image on both surfaces of the recording medium is changed. Become.

According to the fifth aspect of the invention, by controlling the developing conditions, the amount of toner adhering to the image carrier is controlled to compensate for the influence on the transfer efficiency of the second toner image due to the output change of the transfer means. You can

According to the sixth aspect of the present invention, the amount of toner adhered to the image carrier is controlled by controlling the charging condition of the charging unit that charges the image carrier, and the second method is accompanied by the change in the output of the transfer unit.
The effect on the transfer efficiency of the toner image can be compensated.

According to the seventh aspect of the present invention, by controlling the exposure condition, the amount of toner adhering to the image carrier is controlled to compensate for the influence of the output change of the transfer means on the transfer efficiency of the second toner image. You can

According to the structure of claim 8, when the resistance value of the intermediate transfer member is lowered, the output of the charging means for switching the charging polarity of the first toner image is made small to prevent the occurrence of white spots and prevent the transfer means of the transfer means. Although the transfer efficiency of the first toner image can be increased by increasing the output, the transfer efficiency of the second toner image is affected by increasing the output of the transfer unit. However, by reducing the amount of toner adhered to the image carrier, it is possible to prevent the influence on the image on the second surface and to make the image quality proper on both the front and back sides.

Since the initial value of the resistance value of the intermediate transfer member is 10 ⁷ to 10 ⁹ Ω · cm, the charging means for switching the toner image charging polarity according to the detected resistance value of the intermediate transfer member is constituted. The output control can effectively prevent the occurrence of white spots and ensure the transfer efficiency.

With the structure according to the tenth aspect, it is possible to prevent the occurrence of an abnormal image that cannot be prevented by the control of the present invention by displaying a warning.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional configuration diagram of a printer that is an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a partial cross-sectional view showing another example in which the configuration of the fixing device is different.

FIG. 3 is a partial cross-sectional view showing still another example in which the configuration of the fixing device is different.

FIG. 4 is a schematic diagram conceptually showing an image forming process during double-sided recording in the present embodiment.

FIG. 5 is a graph showing a relationship between an output of a charging unit or a belt resistance value for toner polarity conversion and a white spot.

FIG. 6 is a flowchart of control in this embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoconductor drum (image carrier) 4 Charging device (photoconductor charging means) 5 Developing device 7 Exposure device 10 Intermediate transfer belt (intermediate transfer member) 17 Charger (toner polarity conversion charging device) 20 Belt unit 21 Transfer roller (Transfer unit) 25 Belt cleaning device 30 Fixing device

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 507 G03G 21/00 372 21/14 15/08 507Z F term (reference) 2H027 DA01 EA01 EA02 EA03 EA05 EC06 EC09 EC10 ED03 ED08 ED09 ED16 ED24 ED28 FA13 FD08 2H028 BA06 BA16 BB04 BB06 BD03 2H077 AD02 AD06 AD35 DA01 DB08 DB12 DB13 DB14 DB15 DB16 DB22 2H200 FA18 GA23 GA34 GA44 GA56 GB12 GB22 HA03 HA29 HB12 HB48 JA02 JA18 JA19 JA28 JA29 JA30 JB06 JB48 JB49 JB50 JC03 JC12 JC17 JC18 JC19 JC20 LA38 MC18 NA02 NA08 PA03 PA04 PA19 PA23 PA30 PB05 PB08 PB16

Claims (10)

[Claims] 1. A first toner image formed on an image carrier is transferred to an intermediate transfer member, and a second toner image is formed on the image carrier, and the first and second toner images are formed. Is an apparatus capable of forming an image on both sides of a recording medium by transferring and fixing the toner onto both sides of the recording medium, and after transferring the first toner image formed on the image carrier to an intermediate transfer body, In an image forming apparatus for switching the charging polarity of a first toner image on a transfer member to a reverse polarity by a non-contact charging unit, and simultaneously transferring the first toner image and the second toner image to both surfaces of a recording medium. An image forming apparatus, which detects a resistance value of the intermediate transfer member and controls an output of the charging unit according to the detected resistance value. 2. The output of a transfer unit for simultaneously transferring the first toner image and the second toner image to both surfaces of a recording medium is controlled according to the detected resistance value. The image forming apparatus according to claim 1. 3. The output of the charging unit is decreased and the output of the transfer unit is increased when the resistance value of the intermediate transfer member is lower than a predetermined reference value. The image forming apparatus according to item 1. 4. The amount of toner adhered to the image carrier when the second toner image is formed on the image carrier is controlled according to the detected resistance value. Two
The image forming apparatus according to item 1. 5. The amount of toner adhering to the image carrier is controlled by controlling the developing condition of a developing unit that applies toner to the image carrier to perform development. The image forming apparatus described. 6. The image forming apparatus according to claim 4, wherein a charging condition of a charging unit that charges the image carrier is controlled to control an amount of toner adhered to the image carrier. 7. The method according to claim 4, wherein an exposure condition of an exposing unit that forms an electrostatic latent image on the image carrier is controlled to control an amount of toner adhered to the image carrier. Image forming device. 8. When the resistance value of the intermediate transfer member falls below a predetermined reference value, the output of the charging means is reduced,
The image forming apparatus according to claim 4, wherein the output of the transfer unit is increased and the amount of toner adhered to the image carrier is reduced. 9. The initial value of the resistance value of the intermediate transfer member is 10 ⁷
10. It is characterized by being 10 < ⁹ > ohm * cm.
9. The image forming apparatus according to any one of items 8 to 8. 10. The resistance value of the detected intermediate transfer member is 1
The image forming apparatus according to any one of claims 1 to 9, wherein a warning display is displayed when the resistance is 0 ⁷ Ω · cm or less.