JP2016114815A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device that ensures stable transfer properties, prevents mass consumption of toner, and lowers cost even when image formation is performed using a sheet with a small width.SOLUTION: The image formation device forms an image by transferring a toner image formed on a photoconductor drum 1 to a sheet by bias application to a transfer roller 5. The device includes: toner attachment means attaching toner on the transfer roller 5; cleaning means cleaning the toner attached on the transfer roller 5; and control means controlling the cleaning means or the toner attachment means, the control means changing a region where the toner is attached on the transfer roller 5 according to the width of a sheet to be conveyed in image formation which is perpendicular to the conveyance direction and the width of a sheet conveyed in the previous image formation.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer, an LED printer, etc.), a facsimile machine, and the like, which form an image on a recording medium using, for example, an electrophotographic image forming system.

  The image forming apparatus performs image formation by transferring a toner image formed on a photosensitive drum onto a sheet by a transfer roller. Here, when constant current control is used as a method for controlling the transfer bias applied to the transfer roller when the toner image is transferred to the sheet, the transferability may vary depending on the size of the sheet used for image formation.

  For example, as shown in FIG. 8A, when the size of the sheet used for image formation is large, an area where the sheet is not passed on the transfer roller in the sheet width direction orthogonal to the sheet conveying direction (hereinafter referred to as a non-sheet passing area). ) Is small. In this case, when a transfer current of, for example, 11 μA is flowed, the transfer current flows evenly by 2.2 μA to each region divided into, for example, 5 parts in the sheet width direction, and the charge necessary for transferring the toner image is applied to the sheet. Evenly provided. If a current of 2 μA flows in each region of the sheet, it is assumed that the charge necessary for transferring the toner image is supplied to the sheet.

  On the other hand, as shown in FIG. 8B, when the size of the sheet used for image formation is small, the width of the sheet in the direction orthogonal to the sheet conveyance direction (hereinafter referred to as the sheet width) is orthogonal to the sheet conveyance direction of the transfer roller. Since there is a large difference with the width in the direction in which the sheet is transferred, the non-sheet passing area is large on the transfer roller. When the non-sheet passing area is large as described above, when a transfer bias is applied, the current selectively flows into the non-sheet passing area on the transfer roller where the transfer roller and the photosensitive drum are in direct contact. This is because the electric resistance value of the sheet is higher than the electric resistance value of the photosensitive drum (hereinafter, simply referred to as the resistance value), so that a current easily flows in the direction of the photosensitive drum having a low resistance value. In such a case, for example, when 11 μA is passed as the transfer current, a large amount of current (for example, 4 μA) flows in the contact portion where the photosensitive drum and the transfer roller are in direct contact, and flows in each region of the sheet having a high resistance value. The current is reduced (eg 1 μA). In this case, the charge necessary for transferring the toner image is not sufficiently supplied to the sheet, the force for electrostatically holding the toner image on the sheet is reduced, and the toner image may be disturbed to cause transfer failure. .

  On the other hand, as shown in FIG. 8C, even if the non-sheet passing area on the transfer roller is large, a large amount of transfer current is passed (for example, 22 μA), so that the contact between the transfer roller and the photosensitive drum is achieved. Even if a large amount of current flows through the portion (for example, 8 μA), a current of 2 μA flows in each region of the sheet. Therefore, the charge necessary for transferring the toner image can be provided to the sheet. However, in this case, excessive charge is applied to a partial region of the photosensitive drum. For this reason, a potential difference occurs between the region where the excessive charge is applied to the photosensitive drum and the other region, and the potential difference is not eliminated immediately, and the size of the sheet used for the next image formation is large. May cause a difference in image density between these regions during image formation.

  Furthermore, when an image is formed in a high-temperature and low-humidity environment, or when an image is formed on both sides of the sheet and the back side is imaged after the sheet has passed through the fixing device and dried, the sheet resistance value is further increased. Become. Therefore, the tendency for the transfer current to selectively flow into the photosensitive drum instead of the sheet becomes stronger, and transfer defects are more likely to occur.

  Therefore, methods for preventing such transfer defects have been proposed. For example, in Patent Document 1, the sheet width of a sheet used for image formation is detected. When the sheet width is larger than a predetermined value, the transfer bias is controlled with a constant current, and when the sheet width is less than a predetermined value, the constant voltage is controlled. Thus, by controlling the constant voltage when the sheet width is less than the predetermined value, it is possible to prevent the transfer current from flowing into the photosensitive drum excessively.

  In Patent Document 2, toner as a resistor is attached to a sheet non-sheet passing region on a transfer roller, and image formation is performed with the toner remaining attached. As a result, the difference in resistance value between the paper passing area and the non-paper passing area on the transfer roller is reduced, so that the transfer current can be prevented from flowing into the photosensitive drum. In this case, the toner as the resistor on the transfer roller is cleaned by the cleaning unit after the image forming process.

Japanese Patent Laid-Open No. 11-95579 JP 9-325624 A

  However, in the invention of Patent Document 1, since it is necessary to provide both a constant voltage control power source and a constant current control power source, the cost of the apparatus increases. Further, in the invention of the above-mentioned Patent Document 2, the toner is attached to the non-sheet passing area on the transfer roller every time image formation is performed using a sheet having a sheet width of a predetermined width or less, so that a large amount of toner is consumed. Cost.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a low-cost image forming apparatus that ensures stable transferability, suppresses a large amount of toner consumption, even when an image is formed using a sheet having a small sheet width. That is.

  In order to achieve this object, the image forming apparatus according to the present invention is an image forming apparatus in which a toner image formed on an image carrier is transferred to a sheet by applying a bias to the transfer member to form an image. A toner adhering means for adhering the toner to the transfer member, a cleaning means for cleaning the toner adhering to the transfer member, and a control means for controlling the toner adhering means or the cleaning means. A region where the toner adheres to the transfer member is changed according to a sheet width in a direction orthogonal to a conveyance direction of the conveyed sheet and the sheet width of the sheet conveyed in the previous image formation. And

  According to the present invention, in consideration of the sheet width of the sheet used for image formation and the sheet width of the sheet used for previous image formation, the area of the toner adhering to the transfer roller is determined and changed. For this reason, when the toner as the resistor is attached outside the sheet conveyance area of the transfer member, the control can be performed so that the toner is attached only to an area other than the area attached at the time of the previous image formation. The amount of toner used can be reduced while ensuring transferability.

  Furthermore, since these can be performed only by constant current control, it is not necessary to provide both a power source for constant current control and a power source for constant voltage control, and the manufacturing cost of the apparatus can be suppressed.

1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram illustrating a system configuration of an image forming apparatus according to a first embodiment of the present invention. 3 is a flowchart illustrating control during image formation in the first embodiment of the present invention. It is a figure for demonstrating the characteristic in 1st Embodiment of this invention. It is a figure for demonstrating the characteristic in 1st Embodiment of this invention. It is a figure which shows the result of the experiment using the image forming apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows the result of the experiment using the image forming apparatus which concerns on 1st Embodiment of this invention. It is a figure explaining the prior art which concerns on this invention.

<Image forming apparatus>
The overall configuration of the image forming apparatus A according to the first embodiment of the present invention will be described below together with the image forming operation with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus A includes an image forming unit that transfers a toner image to a sheet, a sheet feeding unit that supplies the sheet to the image forming unit, and a fixing unit that fixes the toner image on the sheet. I have.

  The image forming unit includes a photosensitive drum 1 (image carrier), a charging roller 2 (charging member), a laser scanner unit 3 (exposure means), a developing device 4, a transfer roller 5 (transfer member), a cleaning blade 7, and the like. ing.

  In image formation, when the CPU 201 (control unit) shown in FIG. 2 issues a print signal, the sheets stacked and stored in the sheet stacking unit 10 by the feeding roller 9 and the conveying roller 8 are sent out to the image forming unit.

  On the other hand, in the image forming unit, a charging bias is applied to the charging roller 2 from a high-voltage power supply (not shown), so that the surface of the photosensitive drum 1 in contact with the charging roller 2 is charged. Then, the laser scanner unit 3 emits laser light L from a light source (not shown) provided therein, and irradiates the photosensitive drum 1 with the laser light L. As a result, the potential of the photosensitive drum 1 is partially reduced, and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 1.

  In the developing region, a developing bias is applied to the developing sleeve, whereby toner is attached to the electrostatic latent image on the photosensitive drum 1 to form a toner image. The toner image formed on the photosensitive drum 1 is sent to a transfer nip portion formed between the photosensitive drum 1 and the transfer roller 5 in contact with the photosensitive drum 1. When the toner image arrives at the transfer nip portion, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 5, and the toner image is transferred to the sheet. In this embodiment, the transfer roller 5 is described as a urethane roller having an Asker C hardness of 20 degrees to 40 degrees, but may be an ion conductive roller or an electronic conductive type roller.

  Thereafter, the sheet on which the toner image has been transferred is sent to the fixing device 11 where it is heated and pressurized to fix the toner image on the sheet. Thereafter, the sheet is conveyed by the discharge roller 12 and discharged to the discharge unit.

<Control unit>
Next, the configuration of the control unit of the image forming apparatus A according to the present embodiment will be described with reference to the drawings.

  As shown in FIG. 2, the control unit includes a CPU 201. The CPU 201 is connected to a temperature / humidity sensor 202, a sheet width detection sensor 206, a memory 203, and the like. The sheet width detection sensor 206 stores sheet size information designated by the user in the memory 203. The sheet size information is set by the user from an operation panel (not shown) before image formation, and is standard size information such as letter size, A4, and B5.

  Further, the transfer roller 5 is connected to a transfer high voltage power source 204, and a transfer bias is applied in accordance with an instruction from the CPU 201. This transfer bias is controlled at a constant current based on the temperature and humidity detected by the temperature and humidity sensor 202, and is controlled so that the current flowing in the direction of the photosensitive drum 1 becomes constant. The applied transfer bias value is detected by the transfer voltage detection circuit 205 detecting the voltage when the transfer bias is applied.

<Control during image formation>
Next, control during image formation of the image forming apparatus A according to the present embodiment will be described. The image forming apparatus A according to the present embodiment is used for the previous image formation on the transfer roller 5 when the sheet used for image formation is smaller than the sheet used for previous image formation as toner adhesion / removal control. The image forming process is performed by newly attaching toner only to the difference region between the sheet width of the sheet and the sheet width of the sheet used this time. On the other hand, when the sheet used for image formation is larger than the sheet used for image formation last time, only the toner existing in the difference area on the transfer roller 5 is removed and cleaned, and then image formation processing is performed.

  Hereinafter, first, a method of performing toner image formation on the non-sheet passing area on the transfer roller 5 as a toner adhering unit will be described. Next, a method for partially removing the toner present in the non-sheet passing area of the transfer roller 5 as a cleaning unit and performing an image forming process thereon will be described.

<Toner adhesion means>
As shown in the flowchart of FIG. 3, when an image formation instruction is given, sheet size information set by the user is detected by the sheet width detection sensor 206 and stored in the memory 203 (S1).

  Next, it is determined whether the sheet size information stored in the memory 203 is larger than a predetermined size set in advance or less than a predetermined size (S2). Here, in the present embodiment, the predetermined size refers to a so-called letter size. Therefore, in this step, it is determined whether the size of the sheet used for image formation is larger than the letter size or smaller than the letter size.

  Here, when it is determined that the size of the sheet used for image formation is larger than the letter size, all the toner adhering to the transfer roller 5 before the image formation is cleaned (S7). As a cleaning method, a cleaning bias is applied to the transfer roller 5 to move the toner on the transfer roller 5 to the photosensitive drum 1. Thereafter, the cleaning blade 7 scrapes the toner from the photosensitive drum 1 for cleaning.

  After the transfer roller 5 is cleaned, normal image formation is started (S8).

  This is because, when the size of the sheet used for image formation is larger than the letter size, even if there is a non-sheet passing area on the transfer roller 5, the area is relatively small. For this reason, even if the transfer bias is applied as it is, the charge necessary for transferring the toner image is supplied to the sheet. Therefore, in such a case, the toner consumption can be suppressed by controlling the toner not to adhere to the non-sheet passing area on the transfer roller 5.

  Further, for example, it is assumed that image formation is performed using a sheet of a letter size or less in the first image formation, and image formation is performed using a sheet larger than the letter size in the second image formation. . In this case, the toner is attached to the non-sheet passing area on the transfer roller 5 at the first image formation, and the second image formation is performed while the toner is held. When the second image formation is performed in this state, the back side of the sheet is stained. For this reason, by cleaning all the toner on the transfer roller 5 at the stage before the second image formation, it is possible to prevent the back of the sheet from being stained.

  On the other hand, if the sheet is smaller than the letter size, the next step is to calculate a difference area between the width of the sheet used for the previous image formation in the direction orthogonal to the sheet conveying direction and the width of the sheet used for the current image formation ( S3).

  Next, it is determined whether or not the size of the sheet used for the current image formation is smaller than the size of the sheet used for the previous image formation (S4).

  Here, when the size of the sheet used for the current image formation is smaller than the size of the sheet used for the previous image formation, as shown in FIG. 4A, it corresponds to the difference area calculated in the above step on the transfer roller 5. A toner as a resistor is attached to the region (S5). As a toner adhesion method, a laser beam L is irradiated from the laser scanner unit 3 to an area corresponding to the difference area on the photosensitive drum 1. As a result, the potential of the region corresponding to the difference region on the photosensitive drum 1 is partially reduced to form an electrostatic latent image. Next, a developing bias is applied to the developing sleeve, so that toner is attached to the electrostatic latent image to form a toner image. Thereafter, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 5 so that the toner image is attached to the transfer roller 5.

  As a result, the toner adheres to an area corresponding to the difference area on the transfer roller 5. In the previous image formation, toner as a resistor is attached to the non-sheet passing area on the transfer roller 5, and the toner remains as it is until the current image formation. Therefore, by attaching toner to the differential area on the transfer roller 5 this time, a state in which toner is attached to the non-sheet passing area at the time of image formation this time is formed on the transfer roller 5.

  Thereafter, as the next step, an image forming process is performed in a state where a transfer bias having a polarity opposite to that of toner is continuously applied to the transfer roller 5 (S8).

  Thus, since the sheet and the toner as the resistor exist on the transfer roller 5 when the transfer bias is applied, the difference in electrical resistance between the non-sheet passing region and the sheet passing region is reduced. Therefore, current can be prevented from flowing into the photosensitive drum 1 when the transfer bias is applied. For this reason, the charge necessary for transferring the toner image is sufficiently supplied to the sheet, and stable transferability can be secured.

  In addition, the toner as a resistor that is newly used in the current image formation is only the difference area between the sheet width of the sheet used for the previous image formation and the sheet width of the sheet used for the current image formation. Therefore, compared to control in which toner as a resistor is uniformly attached when forming an image on a small-sized sheet, the amount of toner consumption can be reduced, and the cost can be reduced.

  In addition, since the above control can be performed only by constant current control, it is not necessary to provide both a constant current control power source and a constant voltage control power source, and the manufacturing cost of the apparatus can be suppressed.

<Cleaning means>
Next, control when the sheet used for image formation is the letter size or less and the sheet size of the sheet used this time is larger than the sheet used last time will be described below.

  In such a case, the current image formation is performed in a state in which the toner as the resistor adhered to the non-sheet passing area on the transfer roller 5 remains in the previous image formation. Therefore, since toner exists in the difference area between the sheet width of the sheet used for the previous image formation and the sheet width of the sheet used this time, if the image is formed as it is, the toner in the difference area adheres to the back side of the sheet. As a result, backside dirt is generated. Therefore, in such a case, as cleaning means, control is performed to remove only the toner adhering to the difference area on the transfer roller 5 and clean it.

  First, a difference area between the sheet width of the sheet used for the previous image formation and the sheet width of the sheet used for the current image formation is calculated (S3).

  Next, cleaning is performed to remove only the toner adhering to the area corresponding to the difference area on the transfer roller 5 by a method described later (S6).

  Here, the transfer roller 5 cannot be divided into regions and the cleaning bias value cannot be changed for each region. Therefore, for example, as shown in FIG. 4B, the transfer roller 5 is divided into regions in a direction perpendicular to the sheet conveyance direction, and the cleaning bias is determined by the non-sheet passing region A of the transfer roller 5 and the difference region B from the previous time. The value of cannot be changed. For this reason, simply applying a cleaning bias to the transfer roller 5 does not control the area A to be cleaned and only the area B to be cleaned.

  Therefore, as shown in FIG. 5, the image forming apparatus A according to the present embodiment performs control so that the potentials of the regions corresponding to the region A and the region B on the surface of the photosensitive drum 1 are different from each other. Do. By this control, it is possible to remove and clean only the toner existing in the region B of the transfer roller 5 as described later.

  First, the force (F) acting on the toner existing between the transfer roller 5 and the photosensitive drum 1 is expressed as follows: when the charge amount of the toner is q and the potential difference between the transfer roller 5 and the photosensitive drum 1 is E. It is expressed by the following formula.

  F = q × E Formula (1)

  In the present embodiment, since negative polarity toner is used, the toner charge amount is expressed as -q in the above formula (1). Further, the potential on the surface of the transfer roller 5 is controlled to −800 V in both the region A and the region B. Further, the potential of the region corresponding to the region A of the photosensitive drum 1 is set to −800 V by the charging roller 2. On the other hand, in the region corresponding to the region B of the photosensitive drum 1, the laser beam L is selectively irradiated from the laser scanner unit 3 and then controlled to -100V after being charged to -800V by a charging roller as potential control means. Yes.

  When the above cleaning control is executed in this state, the force acting on the toner in the region A is 0, and the force acting on the toner in the region B is 700q. The formula is as follows.

  Force (Fa) acting on toner in area A = −q × {−800 − (− 800)} = − q × 0 = 0 Expression (2)

  Force acting on the toner in area B (Fb) = − q × {−800 − (− 100)} = − q × −700 = 700q (3)

  From the above, it can be seen that 700q electrostatic force acts on the toner in the region B in the direction of the photosensitive drum 1. Accordingly, the toner existing in the region B on the transfer roller 5 moves to the photosensitive drum 1. Thereby, the region B is cleaned. On the other hand, since the electrostatic force acting on the toner in the area A is 0, the toner existing in the area A on the transfer roller 5 remains as it is. As described above, only the toner in the region B is cleaned.

  The graph shown in FIG. 6 shows the amount of toner remaining on the transfer roller 5 after the above cleaning. In this graph, the vertical axis represents the amount of toner attached to the transfer roller 5 after the cleaning, and the horizontal axis represents the potential difference between the transfer roller 5 and the photosensitive drum 1. As shown in this graph, it can be seen that the toner of 2.00 [D] remains in the region A where the potential difference is 0V, while the toner hardly remains in the region B where the potential difference is 700V. Note that the toner amount 2.00 [D] in the region A is equal to the amount of toner adhering to the region A of the transfer roller 5 before cleaning. From this graph, it can be seen that the region A on the transfer roller 5 is not cleaned by the above control, and only the region B is cleaned.

  The image forming apparatus A performs the image forming process after performing the above cleaning (S8).

  As described above, by performing the image forming process after cleaning the toner existing in the difference area between the sheet width of the sheet used for the previous image formation and the sheet width of the sheet used for the current image formation, the image is formed on the small size sheet. Even when it is formed, stable transferability can be ensured without newly using toner as a resistor. Therefore, it is possible to reduce the toner consumption and the cost.

<Experimental result>
Next, the effect of reducing the toner consumption of the image forming apparatus A according to the present embodiment will be described in comparison with the image forming apparatus according to the comparative example with reference to the experimental result shown in FIG. The image forming apparatus according to the comparative example has a configuration in which toner is attached to a non-sheet passing region on the transfer roller every time image formation is performed, and the toner on the transfer roller is cleaned one by one after the image formation is completed.

  FIG. 7A summarizes the width in the longitudinal direction of the transfer roller 5 of the image forming apparatus A according to this experiment, the sheet width of the sheet used for image formation, the width of the non-sheet passing region in the longitudinal direction of the transfer roller 5, and the like. It is a table. As the paper size used for image formation, A5 size and letter size were used. The difference between the sheet width of the letter size sheet and the sheet width of the A5 size sheet was 68 mm.

  This experiment was performed under two conditions. As condition 1, a letter size sheet was used for the first image formation, and an A5 size sheet was used for the second image formation. On the other hand, in condition 2, the procedure was reversed from condition 1 and an A5 size sheet was used for the first image formation, and a letter size sheet was used for the second image formation.

  As a result of the experiment, as shown in FIG. 7B, when image formation is performed under condition 1, the image forming apparatus A according to the present embodiment consumes 81 g of toner, and the image forming apparatus according to the comparative example consumes 230 g of toner. was there. Therefore, the image forming apparatus A according to the present embodiment can reduce the toner consumption by 35.2% compared to the image forming apparatus according to the comparative example. Similarly, when image formation is performed under condition 2, the image forming apparatus A according to the present embodiment can reduce the toner consumption by 35.2% as compared with the image forming apparatus according to the comparative example.

  As described above, the image forming apparatus A according to the present embodiment can ensure stable transferability by constant current control and reduce toner consumption even when an image is formed on a sheet having a small sheet width. It was found that the cost can be reduced.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 2 ... Charging roller 3 ... Laser scanner unit 4 ... Developing device 5 ... Transfer roller 7 ... Cleaning roller 8 ... Conveyance roller 9 ... Feeding roller 10 ... Sheet stacking part 11 ... Fixing device 12 ... Discharge roller 201 ... CPU
DESCRIPTION OF SYMBOLS 202 ... Temperature / humidity sensor 203 ... Memory 204 ... Transfer high voltage power supply 205 ... Transfer high voltage detection circuit 206 ... Sheet width detection sensor A ... Image forming apparatus L ... Laser beam

Claims (7)

In an image forming apparatus that forms an image by transferring a toner image formed on an image carrier onto a sheet by applying a bias to a transfer member,
Toner attaching means for attaching toner to the transfer member;
Cleaning means for cleaning toner adhering to the transfer member;
Control means for controlling the toner adhesion means or the cleaning means;
With
The control unit attaches toner to the transfer member in accordance with a sheet width in a direction orthogonal to a conveyance direction of a sheet conveyed during image formation and the sheet width of the sheet conveyed during the previous image formation. An image forming apparatus characterized by changing an area. The control means includes
If the sheet width of the sheet conveyed during image formation is smaller than the sheet width of the sheet conveyed during the previous image formation, toner is applied to the transfer member in a difference area from the previous sheet width. Attach
When the sheet width of the sheet conveyed at the time of image formation is larger than the sheet width of the sheet conveyed at the previous image formation, the transfer member adheres to the difference area from the previous sheet width. The image forming apparatus according to claim 1, wherein toner adhesion and removal control for cleaning toner by the cleaning unit is performed.   The image forming apparatus according to claim 2, wherein the control unit performs the toner adhesion and removal control when the sheet width of a sheet conveyed during image formation is equal to or less than a predetermined size. Having a potential control means for controlling the potential of the surface of the image carrier;
The cleaning means moves the toner attached to the difference region out of the toner attached to the transfer member to the image carrier for cleaning by the potential difference between the surface of the image carrier and the transfer member. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The potential control means includes
A charging member for charging the image carrier;
The image forming apparatus according to claim 4, further comprising an exposure unit that selectively irradiates the image carrier charged by the charging member with light.   2. The control unit according to claim 1, wherein when the sheet width of a sheet conveyed during image formation is larger than a predetermined size, the toner adhered to the transfer member is cleaned before image formation. The image forming apparatus according to claim 5.   The image forming apparatus according to claim 1, wherein the transfer member is a transfer roller in contact with the image carrier.

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