JP4031920B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus capable of forming an image on both sides of a recording medium.
[0002]
[Prior art]
2. Description of the Related Art Some image forming apparatuses such as copying machines, printers, and facsimiles are configured to form images on both sides of a recording medium (hereinafter referred to as paper). In a conventional image forming apparatus capable of double-sided recording, an image on one side (developed image) formed on an image carrier is transferred and fixed on a sheet, the sheet is reversed by a reversing path, and fed again. In general, a two-pass method is used in which an image on the other side (a visible image) is transferred and fixed on the back side of the paper.
[0003]
In the case of double-sided recording by this method, there are many problems in ensuring the reliability of paper conveyance by switching the paper conveyance direction or by curling paper by fixing a single-sided image. There is also a problem of image failure due to transfer failure to curled paper. 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 fixed once.
[0004]
As a method for transferring a toner image onto both sides of a sheet, there are a method using a plurality of transfer steps and a method using one transfer, that is, a method using simultaneous transfer of both sides of a sheet using toner polarity conversion.
[0005]
Examples of toner polarity conversion include those disclosed in Japanese Patent Application Laid-Open Nos. 8-21664, 10-104963, and 10-171264.
[0006]
In Japanese Patent No. 2906538 (Japanese Patent Laid-Open No. 3-253881), a first image formed on a photoconductor is transferred to a transfer belt by a first transfer unit, and then a second image formed on the photoconductor. The first image and the second image are simultaneously transferred to both sides of the sheet by one transfer means by reversing the polarity of the first image and the second image on the photosensitive member before the transfer step, and making the first image and the second image have different polarities. Is disclosed.
[0007]
[Problems to be solved by the invention]
However, in the conventional simultaneous transfer method on both the front and back sides of the paper using toner polarity conversion, the first (previously formed) toner image for toner polarity conversion is a white spot-like abnormal image when transferred onto the paper. There is a problem that occurs.
[0008]
The present invention provides an image forming apparatus that solves the above-described problems in the conventional image forming apparatus of the paper front and back both-side simultaneous transfer method using toner polarity conversion, and can always obtain a good image by preventing the occurrence of white spots. The issue is to provide.
[0009]
[Means for Solving the Problems]
According to the present invention, the first toner image formed on the image carrier is transferred to the intermediate transfer member, and the second toner image is formed on the image carrier. 2 is a device capable of forming an image on both sides of a recording medium by transferring and fixing the toner image on both sides of the recording medium, and transferring the first toner image formed on the image carrier to an intermediate transfer body. Thereafter, the charging polarity of the first toner image is switched to the opposite polarity by the non-contact charging means on the intermediate transfer member, and the first toner image and the second toner image are simultaneously transferred to both surfaces of the recording medium. In the image forming apparatus, 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 addition, the output of the transfer means for simultaneously transferring the first toner image and the second toner image to both surfaces of the recording medium is controlled according to the detected resistance value, and the resistance value of the intermediate transfer body Is reduced below a predetermined reference value, the output of the charging unit is reduced and the output of the transfer unit is increased. Is solved.
[0012]
In order to solve the above problems, the present invention controls the amount of toner adhering to the image carrier when the second toner image is formed on the image carrier according to the detected resistance value. Suggest to do.
[0013]
In order to solve the above-described problems, the present invention controls the amount of toner attached to the image carrier by controlling the development conditions of a developing unit that applies toner to the image carrier and performs development. Propose.
[0014]
In order to solve the above problems, the present invention proposes to control the amount of toner adhering to the image carrier by controlling the charging conditions of the charging means for charging the image carrier.
[0015]
In order to solve the above-mentioned problem, the present invention controls the amount of toner attached to the image carrier by controlling the exposure conditions of an exposure means for forming an electrostatic latent image on the image carrier. suggest.
[0016]
In order to solve the above problems, the present invention reduces the output of the charging unit and increases the output of the transfer unit when the resistance value of the intermediate transfer member is lower than a predetermined reference value. It is proposed to reduce the amount of toner attached to the image carrier.
[0017]
In order to solve the above problems, the present invention provides an initial value of the intermediate transfer member resistance value of 10 ⁷ -10 ⁹ Propose that it is Ω · cm.
In order to solve the above-described problem, the present invention provides that the detected resistance value of the intermediate transfer member is 10. ⁷ It is proposed to display a warning when Ω · cm or less.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram showing an outline of a printer as an example of an image forming apparatus to which the present invention is applied.
[0019]
In the printer shown in this figure, a photosensitive drum 1 serving as a first image carrier is disposed at substantially the center in the apparatus. Around the photosensitive drum 1, a cleaning device 2, a static elimination device 3, a charging device 4, and a developing device 5 are disposed. An exposure device 7 is provided above the photosensitive drum 1, and a laser beam L emitted from the exposure device 7 is irradiated to the photosensitive member 1 at a writing position between the charging device 4 and the developing device 5.
[0020]
A belt unit 20 is provided below the photosensitive drum 1. The belt unit 20 is centered on an intermediate transfer belt 10 as a second image carrier, and the photosensitive member 1 is provided so that a part thereof is in contact with the intermediate transfer belt 10. The intermediate transfer belt 10 is stretched around rollers 11, 12, and 13 and supported so as to be able to run counterclockwise in the drawing. The intermediate transfer belt 10 has heat resistance and has a resistance value that enables transfer of toner.
[0021]
Inside the loop of the intermediate transfer belt 10, backing rollers 14 and 15, cooling means 16 and 16, a fixing roller 18, a transfer means 21 and the like are arranged. The fixing roller 18 incorporates a heat source such as a heater and fixes the toner image transferred onto the paper in cooperation with a fixing roller 19 described later. The transfer means 21 is provided at a position facing the photoconductor 1 with the belt 10 interposed therebetween, and transfers the toner image formed on the photoconductor 1 from the intermediate transfer belt 10 or the intermediate transfer belt 10 onto a sheet. The toner image formed on the body 1 is directly transferred onto the paper.
[0022]
A fixing device 30, a belt cleaning device 25, and a charging unit 17 are disposed on the outer peripheral portion of the intermediate transfer belt 10. The charging unit 17 is for reversing the polarity of the toner transferred to the intermediate transfer belt 10.
[0023]
The fixing device 30 includes a fixing roller 19 incorporating a heat source such as a heater, and is supported so as to be rotatable about a fulcrum 30a. Then, it is rotated as shown by an arrow G by a mechanism (not shown) so that the belt 10 (and paper) can be pressed against and separated from the fixing roller 18.
[0024]
The cleaning device 25 for the intermediate transfer belt 10 includes a cleaning roller 25a, a blade 25b, a toner conveying unit 25c, and the like, 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 transported to a collection container (not shown) by the toner transport means 25c. The cleaning device 25 is configured to be rotatable as indicated by an arrow H about a rotation fulcrum 25d. The cleaning roller 25 a can be moved toward and away from the intermediate transfer belt 10 by rotating the entire cleaning device 25 by a mechanism (not shown).
[0025]
In this embodiment, the photosensitive drum (first image carrier) 1, the cleaning device 2, the charge eliminating device 3, the charging device 4, the developing device 5 and the like are integrated into a unit and can be replaced as a process cartridge at the end of its service life. It is configured.
[0026]
A paper feed cassette 26 is provided at the lower part of the apparatus main body. The paper feed cassette 26 is configured to be drawn rightward in the drawing. A transfer paper P as a recording material is stored in the cassette 26. A paper feed roller 27 is provided at an upper position of the cassette 26 in the paper feed direction front end side (right side in the figure). 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 fed to the registration roller 28. Above the cassette 26, an electrical component E1 and a control device E2 are arranged. Further, a manual paper feeder 35 is provided on the right side of the apparatus, and a paper feed roller 36 for feeding the paper P set on the paper set stand 37 is provided.
[0027]
In FIG. 1, a switching claw 42 is provided on the left side of the belt unit 20. The switching claw 42 is configured to be swingable around a fulcrum 43, and the direction in which the sheet fed from the belt unit 20 is conveyed is set to the discharge stack unit 40 provided on the upper surface of the apparatus main body or the discharge tray on the side of the apparatus. Switch to 44. When the switching claw 42 is in the position shown in the figure, the paper is sent to the paper discharge stack unit 40. When the switching claw 42 is switched in the direction of arrow J, the paper is sent to the paper discharge tray 44.
[0028]
A conveying roller pair 33 for conveying the paper is disposed above the switching claw 42. Further, a pair of paper discharge rollers 34 for discharging the paper to the paper discharge stack unit 40 is disposed further upward. The conveyance roller pair 33 and the discharge roller pair 34 are guided by 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 disposed.
[0029]
An image forming operation in the printer configured as described above will be described.
First, the operation for obtaining images on both sides of a sheet will be described. When obtaining images on both sides of the paper, the image formed first is called the first side image, the image formed later is called the second side image, the paper side on which the first side image is transferred is the first side of the paper, The sheet surface on which the second surface image is transferred will be referred to as a sheet second surface.
[0030]
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 light from a laser light source (not shown) of the exposure device is scanned by a polygon mirror 7a that is rotationally driven by a motor, and passes through a mirror 7b, an fθ lens 7c, and the like. Then, the photosensitive drum 1 uniformly charged by the charging device 4 is irradiated, and a latent image corresponding to the writing information is formed on the photosensitive member 1.
[0031]
The electrostatic latent image on the photoreceptor 1 is developed by the developing device 5, and a visible image by toner is formed and held on the surface of the photoreceptor. The toner image on the photosensitive member 1 is transferred to the surface of the intermediate transfer belt 10 that runs in synchronization with the photosensitive member 1 by the transfer means 21 on the back side of the intermediate transfer belt 10 that is the second image carrier.
[0032]
The remaining toner on the surface of the photoconductor 1 after the image transfer is cleaned by the cleaning device 2, and the charge is removed by the charge removal device 3 to prepare for the next image forming cycle.
The intermediate transfer belt 10 carries a toner image transferred to the surface (image transferred to the first surface of the paper) and travels counterclockwise in the drawing. At this time, the fixing device 30 and the cleaning device 25 are controlled so as to maintain an inoperative state (electrical input interruption or separation from the intermediate transfer belt 10) so that the toner image is not disturbed.
[0033]
When the intermediate transfer belt 10 travels to a predetermined position, a toner image to be transferred to another surface (second surface) of the sheet starts to be formed on the photosensitive member 1 in the above-described process, and the selected paper feed is performed. Paper feeding is started from the apparatus (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 drawn out and conveyed to the registration roller pair 28.
[0034]
The intermediate transfer belt 10 travels in synchronism with the photoreceptor 1, and the toner image (first surface image) previously transferred onto the intermediate transfer belt 10 rotates once and the belt 10 and the photoreceptor 1 come into contact with each other. It is conveyed toward. 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.
[0035]
By the registration roller pair 28, the registration roller pair 28 performs timing so that the position of the toner image (second surface image) on the sheet and the photoreceptor 1 and the toner image (first surface image) on the belt 10 become normal. Is taken out and the paper is sent out. The sheet is fed to a transfer position where the photosensitive member 1 and the belt 10 are in contact with each other, and toner images (first surface image and second surface image) are transferred onto both surfaces of the sheet at once by the transfer unit 21.
[0036]
The sheet on which the toner images are transferred on both sides is sent to the fixing area as the belt 10 travels. 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 toner image (both sides) on the paper is formed by the cooperation of the fixing roller 19 and the fixing roller 18. Established at once. After the toner image is transferred, fixing is performed with the sheet and the intermediate transfer belt 10 overlapped without separating the sheet from the intermediate transfer belt 10, so that the toner image is not disturbed and image blurring is prevented.
[0037]
The sheet after fixing is separated in curvature from the intermediate transfer belt 10 by the roller 11 part, the transport direction is switched by the branching claw 42, and discharged to the paper discharge stack part 40 on the upper surface of the apparatus or the paper discharge tray 44 on the side surface of the apparatus. .
[0038]
When paper is discharged to the paper discharge stack unit 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 is placed on the paper discharge stack unit 40. Therefore, 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 image may be transferred directly from the paper to the paper. Therefore, when the sheets are discharged to the discharge stack unit 40 in the order of pages, the first side image is the second page image, and the second side image is the first page image. The same applies to images after the third page. When there is an image on the divisor page, the image of the divisor page is first formed, transferred and held on the intermediate transfer belt 10, and 1 of the divisor page. An odd page before the next is created and transferred directly from the surface of the photoreceptor 1 to a sheet.
[0039]
On the other hand, when paper is discharged to the paper 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 paper is the top surface and is placed on the paper discharge tray 44. The 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.
[0040]
It is also possible to stack the sheets in the paper discharge tray 44 in the order of pages. In this case, contrary to the above, the first side image is the first page image and the second side image is the second page. Image. The same applies to the third and subsequent images. When there is an image on an odd page, the odd page image is first formed, transferred and held on the intermediate transfer belt 10, and the next even page after the odd page. Can be created later.
[0041]
Normally, a reverse image (mirror image) is formed on the photosensitive member 1 and directly transferred onto a sheet to obtain a normal image. However, the image transferred onto the intermediate transfer belt 10 is transferred onto the sheet. In this case, when a mirror image is formed on the photosensitive member 1, it becomes a mirror image when the paper is transferred. Therefore, in this embodiment, an image (first surface image) transferred from the intermediate transfer belt 10 to a sheet is formed as a normal image on the surface of the photoreceptor 1 and a toner image (first image) directly transferred from the photoreceptor 1 to the sheet. The two-sided image is exposed so as to be a mirror image on the surface of the photoreceptor.
[0042]
The order of image formation for page alignment as described above is a known technique for storing image data in a memory, and exposure for switching between normal and reverse images can also be realized by a known image processing technique.
[0043]
The cleaning device 25 that has been separated from the intermediate transfer belt 10 rotates the cleaning device 25 so that the cleaning roller 25a contacts the belt 10 after the image is transferred from the photoreceptor 1 and the intermediate transfer belt 10 to the paper. The residual toner after being transferred to is transferred to the surface of the cleaning roller 25a and scraped off by the blade 25b. The toner scraped off is collected in a storage unit (not shown) by the toner conveying means 25c.
[0044]
The intermediate transfer belt 10 that has passed through the cleaning area is cooled by the operation of the cooling means 16. As the cooling means 16, various heat dissipation methods can be adopted. In the system in which air is circulated, it is advantageous that air is circulated after being transferred to a recording medium (paper) so as not to disturb the toner image held on the surface of the intermediate transfer belt 10. Cooling means using a heat pipe that directly contacts the inner surface of the loop of the intermediate transfer belt 10 to remove heat can also be employed.
[0045]
Next, an operation for obtaining an image on one side of a sheet will be described.
In the case of obtaining 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 photoreceptor 1 is directly transferred to the paper. In the case of a single-sided image, the toner image on the photoconductor 1 is a mirror image and becomes a normal image when transferred to paper.
[0046]
In FIG. 1, in synchronization with the toner image formed on the photosensitive member 1, the paper P is fed between the photosensitive member 1 and the intermediate transfer belt 10, and is transferred onto the paper by the transfer unit 21. Is transferred from the photoreceptor 1.
[0047]
The sheet on which the toner image is transferred moves together with the intermediate transfer belt 10 and the toner is fixed. Thereafter, the sheet is separated from the intermediate transfer belt 10 and placed on the sheet discharge stack unit 40 or the sheet discharge tray 44 according to the direction of the switching claw. When the sheets are discharged to the paper discharge stack unit 40, even if documents of several pages are processed in order from the first page, when the paper is taken out from the paper discharge stack unit 40, the printed matter is in page order.
[0048]
In order to align the sheets in the sheet order on the discharge tray 44, the toner image formed on the photoreceptor 1 is transferred to the intermediate transfer belt 10 even during single-sided printing, and the toner image is transferred from the intermediate transfer belt 10 to the lower surface of the sheet. It is also possible to transfer. In this case, the toner image on the photosensitive member 1 is a normal image, and becomes a normal image when the paper is transferred.
[0049]
In the example of FIG. 1, the fixing device 30 outside the loop of the intermediate transfer belt 10 has a configuration in which the fixing roller 19 can be pressed and separated from the fixing roller 18 with the belt 10 (and paper) interposed therebetween. As shown, the fixing device outside the loop of the intermediate transfer belt 10 can be a non-contact type. The fixing device 30B in FIG. 2 is a type that does not contact the conveyed paper, and fixes the toner image by light emission from an infrared lamp, a xenon lamp, or the like. Since it is a non-contact type, the fixing device 30B does not need to be configured to be rotatable, and is provided fixedly.
[0050]
1 and 2 fix the sheet in a state where the sheet and the intermediate transfer belt 10 are overlapped without separating the sheet from the intermediate transfer belt 10 after the toner image is transferred. The fixing device shown in FIG. A method of fixing the toner image on the paper after separation from the intermediate transfer belt 10 as in 30C can also be adopted.
[0051]
Next, an image forming process at the time of double-sided recording in the present embodiment will be described with reference to FIG. Here, the fixing device will be described with the configuration shown in FIG. Further, the intermediate transfer belt 10 is illustrated in a vertical direction in the drawing space.
[0052]
In FIG. 4, the image forming process during double-sided recording includes (a) development and primary transfer (transfer to belt 10), (b) secondary development (second side development), and (c) secondary transfer (to paper). These are divided into four steps: double-sided transfer), (d) fixing, and belt cleaning. For convenience, FIG. 4 shows the photosensitive member 1 and the intermediate transfer belt 10 as being separated from each other, but the photosensitive member 1 and the intermediate transfer belt 10 are provided in contact with each other.
[0053]
In FIG. 4A, the photosensitive member 1 is charged (-) by the charging means 4, and (-) charged toner (-) is charged from the developing device 5 to the electrostatic latent image formed by the writing light L from the exposure device. Further, a state in which the toner is primarily transferred to the intermediate transfer belt 10 by the action of the transfer unit 21 (+ voltage is applied) is shown.
[0054]
In FIG. 4A, a toner image (-charged) on the second surface is formed on the photosensitive member 1, and a toner image (first surface image) carried on the intermediate transfer belt 10 is transported. On the way, 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, a state is shown in which the paper P is sent out by the registration roller 28 at a timing so that the positions of these toner images are normal.
[0055]
FIG. 4C shows a state in which the toner image is transferred (secondary transfer) at a time onto the front and back surfaces (first surface, second surface) of the sheet by the action of the transfer means 21 (+ voltage is applied). Has been. The toner (+ charge) on the intermediate transfer belt 10 is electrostatically repelled by the transfer roller 21 to which a + voltage is applied and transferred to the sheet, and the toner (−charge) is electrostatically transferred from the photoreceptor 1 to the sheet. The toner is simultaneously transferred onto both sides of the paper by being sucked and transferred to the paper.
[0056]
FIG. 4D shows a state where the sheet is attracted to the intermediate transfer belt 10 and conveyed to the fixing region, and the toner images are fixed on both sides of the sheet. Further, the belt cleaning device 25 is pressed against the belt 10 to remove residual toner on the belt 10.
[0057]
Thus, on the second image carrier (intermediate transfer belt 10), the polarity of the toner carried (primarily transferred) on the second image carrier is switched by the non-contact charging means (charge charger 17). Therefore, it is possible to simultaneously transfer (secondary transfer) toner images onto both sides of the paper with one transfer means (21), and the polarity of the voltage applied to the transfer means can be changed between primary transfer and secondary transfer. There is no need to change, and the configuration of switching the applied voltage polarity of the transfer means is unnecessary, so that the cost is excellent. Further, since no charge is applied from the open surface of the paper on which the toner is transferred, disturbance of the toner image transferred to the upper surface of the paper, electrostatic offset at the time of fixing due to charging up of the transfer paper, and the like are prevented.
[0058]
When an image is obtained only on one side of the sheet, the toner image formed on the photoreceptor 1 may be directly transferred to the sheet, and the toner (-charge) on the photoreceptor 1 is sucked by the transfer roller 21 to which a + voltage is applied. Transcript.
[0059]
Further, the photosensitive member charging polarity and the toner charging polarity in the above description are merely examples, and can be reversed to those of the present embodiment.
By the way, as a problem of the prior art, white spots may occur when a toner image to be subjected to charge polarity conversion is transferred from a transfer belt to a transfer paper. The factors affecting the occurrence of white spots include the output of the charging means for toner polarity conversion and the resistance value of the transfer belt.
[0060]
When the output of the charging means for toner polarity conversion is increased, the image quality is deteriorated (there are many white spots), and when the output is decreased, the image quality is improved, and when the belt resistance is low, the image quality is poor. However, it became clear by experiment. The relationship between the charging means output or belt resistance value and white spots for toner polarity conversion is shown in the graph of FIG.
[0061]
In the graph of FIG. 5, the vertical axis indicates the image quality (rank of white spots), the area above the horizontal line of the fine dotted line is the area where the state of the white spot is within the allowable range, and the area below the thin dotted line Is a region where the state of vitiligo is outside the allowable range. The horizontal axis represents the output of the charging means for toner polarity conversion. The charging means for toner polarity conversion is a charging charger 17 in FIG.
[0062]
In FIG. 5, the resistance value of the transfer belt (intermediate transfer belt) at the time of machine installation (factory shipment) is indicated by a broken line (thick dotted line), and the belt resistance value decreased from the time of machine installation by a solid line. It is shown. These thick dotted lines and solid lines indicate the variation in the rank of white spots when the output of the charging means for toner polarity conversion is changed with the respective belt resistance values.
[0063]
Here, the resistance value of the transfer belt (intermediate transfer belt) fluctuates depending on environmental conditions or time, and as shown in FIG. If (A) is set, the image quality (1) in the region of white spots OK when the machine is installed changes to the direction in which the belt resistance decreases, but the image quality becomes (2). Enter the NG area.
[0064]
Therefore, when the belt resistance value decreases as shown by the solid line since the installation of the machine, the image quality is (3) by lowering the output of the charging means for changing the toner polarity: C from C (A) to C (B). ) To enter the region of white spots OK. In this 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 state of white spots falls within an allowable range. In this way, the occurrence of abnormal images is prevented.
[0065]
Further, the occurrence of a white spot image can be prevented by adjusting the output of the charging unit 17 for toner polarity conversion. However, if the output of the charging unit 17 is reduced, the polarity conversion for the first surface image is sufficiently performed. There is a possibility that the first surface image is not reliably transferred. As a result of conducting an experiment on transferability, even when the output of the charging unit 17 is lowered, by increasing the output of the transfer unit 21 that simultaneously transfers the first side image and the second side image to the front and back of the transfer paper, It was found that the repulsive force between the transfer belt 10 and the polarity-converted toner is increased, and the transfer efficiency is increased. Therefore, generation of white spots can be prevented by reducing the output of the charging unit 17, and stable output efficiency of the first surface image can be ensured by increasing the output of the transfer unit 21.
[0066]
Further, by adjusting the output of the charging unit 17 and the output of the transfer unit 21, white spots can be prevented and the transfer efficiency of the first surface image can be ensured. However, when the output of the transfer unit 21 is increased, This will change the transfer efficiency. Therefore, the final second surface image can be made appropriate by controlling the toner adhesion amount of the second surface image on the photosensitive drum 1 by the amount of change of the output of the transfer means 21. In this case, the amount of toner adhering to the photoconductor can be adjusted by adjusting the development conditions, adjusting the photoconductor charging potential, and adjusting the exposure conditions.
[0067]
In addition, a good image in which the occurrence of a white spot image is prevented by the control as described above can be obtained. However, when the belt resistance value fluctuates too much, the occurrence of white spots may not be prevented. Alternatively, the transfer efficiency may not be ensured. Therefore, the resistance value of the intermediate transfer member to which the present invention is applied is within a predetermined range (initial value is 10). ⁷ -10 ⁹ (Ω · cm) makes it possible to reliably prevent the occurrence of white spots and ensure transfer efficiency by the above-described control, and provide a good image.
[0068]
Hereinafter, specific control in the present embodiment will be described.
In the present embodiment, the first surface and second surface toner images are transferred at a transfer current: R1 of 10 μA when the first surface toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 10 (applied to the transfer roller 21). Is transferred simultaneously from the intermediate transfer belt 10 to the front and back surfaces of the transfer paper (applied to the transfer roller 21): R2 is set to 10 μA, and the charging polarity of the first surface image is set to the opposite polarity on the intermediate transfer belt 10 The output current C of the charging means 17 when switching is set to 200 μA. The output current of the charging means 17: C = 200 μA is an initial value. Further, the developing bias (VB) when developing the electrostatic latent image on the photosensitive drum 1 is set to 500V.
[0069]
Then, at the time of warm-up performed when the power is supplied to the apparatus, a voltage of 2 kV is applied from the transfer roller 20 while the photosensitive drum 1 and the intermediate transfer belt 10 are in contact with each other and rotated, thereby the photosensitive drum 1. The belt resistance is obtained by detecting the current flowing through the belt. The current flowing through the photosensitive 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.
[0070]
In the present embodiment, the detected resistance value of the intermediate transfer belt 10 is 1 × 10. ⁸ If it is Ωcm or more, the above parameters R1, R2, C, VB are left as they are. The detected belt resistance value is 1 × 10 ⁷ -10 ⁸ In the case of Ωcm, the output current C of the charging unit 17 is changed from 200 μA to 100 μA, the transfer current R2 is changed from 10 μA to 20 μA, and the development bias when developing the second side image during double-sided printing: VB ′ is changed from 500V to 450V (development bias when developing the first side image: VB remains at 500V). The transfer current: R1 remains as it is. Furthermore, the detected belt resistance value is 1 × 10 ⁷ If it is less than Ωcm, a serviceman call is displayed.
[0071]
The above control is shown in a flowchart in FIG. That is, after the apparatus power is turned on (S1), the resistance value R of the intermediate transfer belt 10 is detected (S2), and R is 1 × 10. ⁸ It is determined whether it is Ωcm or more (S3). Next, R is 1 × 10 ⁷ Judge whether it is Ωcm or less (S4), R is 1 × 10 ⁷ If Ωcm or less, the process proceeds to S6 to display a service man call. On the other hand, R is 1 × 10 in S4 ⁷ More than Ωcm, that is, the resistance value of the belt 10: R is 1 × 10 ⁷ -10 ⁸ If it is in the range of Ωcm, C = 100 μA, R2 = 20 μA, and VB ′ = 450 V are set (S5).
[0072]
This completes the setting when the apparatus power is turned on, and 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 is turned on in the morning, and when the power is turned on the next day, the same control is performed again to correct each parameter.
[0073]
In the above control, the detected resistance value of the intermediate transfer belt 10 is 1 × 10. ⁸ When it is Ωcm or more, white spots are not generated, and each parameter remains at the initial value setting.
[0074]
The detected belt resistance is 1 × 10 ⁷ -10 ⁸ In the case of Ωcm, by changing the output current C of the charging means 17 from 200 μA to 100 μA, it is possible to prevent the occurrence of white spots due to a decrease in the belt resistance value. Since the transfer efficiency of the first surface image is slightly reduced by lowering the output current C of the charging unit 17, the transfer current R2 when transferring the toner image from the intermediate transfer belt 10 to the transfer paper is changed from 10 μA to 20 μA. As a result, the transfer efficiency to the transfer paper is secured.
[0075]
At this time, the transfer efficiency to the transfer paper is ensured by increasing R2 from 10 μA to 20 μA. However, the second surface image (when the second surface image is transferred from the photosensitive member to the transfer paper is secured. ) Since the transfer efficiency is increased, a stable image can be obtained for the second surface image by adjusting the developing bias and adjusting the toner adhesion amount on the photoconductor. The toner adhesion amount on the photosensitive member may be adjusted by control such as lowering the charging potential of the photosensitive drum 1 or reducing the exposure light amount in addition to the developing bias.
[0076]
Furthermore, the detected belt resistance value is 1 × 10 ⁷ If it is less than Ωcm, the white spot image cannot be prevented unless the output current C of the charging unit 17 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. Therefore, in this case, the service man call is displayed.
[0077]
As mentioned above, although this invention was demonstrated by embodiment of illustration, this invention is not limited to this, A various deformation | transformation is possible.
For example, the initial values of the parameters R1, R2, C, VB, etc. and the values changed from the initial values are only examples, and appropriate values can be set. The reference value for determining parameter change is also an example, and an appropriate value can be set. Furthermore, the timing and detection method for detecting the resistance value of the intermediate transfer belt 10 are also arbitrary.
[0078]
In the above-described embodiment, the transfer unit 21 is configured as a transfer roller. However, a contact-type transfer unit other than the roller or a non-contact type transfer unit such as a transfer charger may be used. Any other apparatus can be employed as long as the present invention can be implemented. For example, in the above-described embodiment, the first image carrier is a photosensitive drum, but a belt-type image carrier can also be used.
[0079]
Furthermore, although the exposure apparatus 7 in the above embodiment is a laser system, it may be an LED exposure system. Alternatively, the present invention can be implemented in analog exposure (analog copying machine). When a normal image is obtained on the photoreceptor by analog exposure, it is possible to use a mirror.
[0080]
Needless to say, the image forming apparatus is not limited to a printer, and may be a copying machine or a facsimile.
[0081]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the resistance value of the intermediate transfer member is detected, and the output of the charging unit that switches the charging polarity of the first toner image is controlled according to the resistance value. Further, it is possible to prevent the occurrence of white spots in the toner image whose charge polarity is switched.
[0082]
Also In addition, it is possible to prevent the occurrence of white spots and ensure stable transfer efficiency.
[0083]
Also When the resistance value of the intermediate transfer member is reduced, the output of the charging means for switching the charging polarity of the first toner image can be reduced to prevent the occurrence of white spots, but the output of the charging means is reduced. As a result, the polarity conversion of the first toner image is not sufficiently performed, and transfer failure may occur. Transfer failure can be prevented. Therefore, prevention of white spots and securing of transfer efficiency can be realized.
[0084]
Claim 2 With this configuration, 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 to both surfaces of the recording medium is changed.
[0085]
Claim 3 With this configuration, it is possible to control the amount of toner adhering to the image carrier by controlling the development conditions, and to compensate for the influence on the transfer efficiency of the second toner image accompanying the change in the output of the transfer means.
[0086]
Claim 4 By controlling the charging condition of the charging means for charging the image bearing member, the amount of toner attached to the image bearing member is controlled, and the influence on the transfer efficiency of the second toner image accompanying the change in the output of the transferring means. Can be supplemented.
[0087]
Claim 5 With this configuration, the amount of toner adhering to the image carrier can be controlled by controlling the exposure conditions, and the influence on the transfer efficiency of the second toner image accompanying the change in the output of the transfer means can be compensated.
[0088]
Claim 6 With this configuration, when the resistance value of the intermediate transfer member decreases, the output of the charging unit that switches the charging polarity of the first toner image is reduced to prevent the occurrence of white spots, and the output of the transfer unit is increased. Although the transfer efficiency of the first toner image can be increased, the transfer efficiency of the second toner image is affected by increasing the output of the transfer means. However, by reducing the amount of toner attached to the image carrier, the influence on the second surface image can be prevented, and the image quality on both the front and back surfaces can be made appropriate.
[0089]
Claim 7 With this configuration, the initial resistance value of the intermediate transfer member is 10 ⁷ -10 ⁹ Since it is Ω · cm, it is possible to effectively prevent the occurrence of white spots and ensure transfer efficiency by controlling the output of the charging means for switching the toner image charging polarity according to the detected resistance value of the intermediate transfer member.
[0090]
Claim 8 With this configuration, 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 the drawings]
FIG. 1 is a cross-sectional configuration diagram showing an outline of a printer as an example of an image forming apparatus to which the present invention is applied.
FIG. 2 is a partial cross-sectional view illustrating 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 at the time of double-sided recording in the present embodiment.
FIG. 5 is a graph showing the relationship between charging means output or belt resistance value and white spots for toner polarity conversion.
FIG. 6 is a flowchart of control in the present embodiment.
[Explanation of symbols]
1 Photosensitive drum (image carrier)
4 Charging device (photoconductor charging means)
5 Development device
7 Exposure equipment
10 Intermediate transfer belt (intermediate transfer member)
17 Charger (charging means for toner polarity conversion)
20 Belt unit
21 Transfer roller (transfer means)
25 Belt cleaning device
30 Fixing device

Claims (8)

A first toner image formed on the image carrier is transferred to an intermediate transfer member, a second toner image is formed on the image carrier, and the first and second toner images are formed on both sides of the recording medium. The apparatus is capable of forming an image on both sides of a recording medium by transferring and fixing the toner image on the recording medium. After the first toner image formed on the image carrier is transferred to the intermediate transfer member, the first toner image is formed on the intermediate transfer member. In the image forming apparatus, the charging polarity of one toner image is switched to a reverse polarity by a non-contact charging means, and the first toner image and the second toner image are simultaneously transferred to both surfaces of a recording medium.
Detecting the resistance value of the intermediate transfer member, and controlling the output of the charging means according to the detected resistance value ;
Controlling the output of the transfer means for simultaneously transferring the first toner image and the second toner image to both surfaces of the recording medium in accordance with the detected resistance value;
An image forming apparatus , wherein when the resistance value of the intermediate transfer member is lower than a predetermined reference value, the output of the charging unit is reduced and the output of the transfer unit is increased . Wherein the second toner adhesion amount of the toner image to the image bearing member when formed on the image bearing member, and controlling in accordance with the resistance value the detection, images according to claim 1 Forming equipment. The image forming apparatus according to claim 2 , wherein the amount of toner attached to the image carrier is controlled by controlling a developing condition of a developing unit that applies toner to the image carrier and performs development. . The image forming apparatus according to claim 2 , wherein a toner adhesion amount to the image carrier is controlled by controlling a charging condition of a charging unit that charges the image carrier. The image forming apparatus according to claim 2 , wherein an exposure condition of an exposure unit that forms an electrostatic latent image on the image carrier is controlled to control an amount of toner attached to the image carrier. When the resistance value of the intermediate transfer member is lower than a predetermined reference value, the output of the charging unit is decreased, the output of the transfer unit is increased, and the amount of toner attached to the image carrier is decreased. The image forming apparatus according to claim 2 , wherein: Characterized in that said initial value of the intermediate transfer member resistance is 10 ⁷ ~10 ⁹ Ω · cm, the image forming apparatus according to any one of claims 1-6. Wherein the resistance value of the detected intermediate transfer member, characterized in that a warning display when: 10 ⁷ Ω · cm, the image forming apparatus according to any one of claims 1-7.

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