JP5794477B2 - Transfer device and image forming apparatus - Google Patents

Description

  The present invention relates to a transfer device for transferring an image, and an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine including the transfer device.

  Indirect transfer system that, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a composite machine of these, once images on a plurality of photosensitive members are once transferred to an intermediate transfer member, and then the transferred images are transferred to transfer paper It has been known. In this indirect transfer method, an intermediate transfer belt as an intermediate transfer member is brought into contact with a photosensitive member to form a transfer nip. As a method for forming the transfer nip, there are a direct pressure transfer method and an offset transfer method.

  In the direct pressure transfer method, as shown in FIG. 9, a transfer roller 11 having a surface formed of an elastic body is pressed against the intermediate transfer belt 8 at a position immediately below the photosensitive member 2, so that a transfer nip is formed at the contact point. In this method, N1 and N2 are formed (see Patent Document 1). On the other hand, in the offset transfer method, as shown in FIG. 10, the transfer roller 11 is brought into contact with the intermediate transfer belt 8 at a position shifted from directly below the photoreceptor 2, so that the intermediate transfer belt 8 is brought into contact with the photoreceptor 2. In this method, the transfer nips N1 and N2 are formed by winding (see Patent Document 2).

  In the case of the direct pressure transfer system shown in FIG. 9, the widths of the transfer nips N1 and N2 (widths in the belt running direction indicated by arrows in the figure) W1 and W2 are determined by the hardness of the transfer roller 11 and the pressing force. If rollers of hardness and pressing force are used, the transfer nip widths W1 and W2 can be formed to the same width. On the other hand, in the case of the offset transfer system shown in FIG. 10, the widths of the transfer nips N1 and N2 (widths in the belt running direction indicated by arrows in the drawing) W1 and W2 are the belts entering the photoreceptors 2 in the horizontal direction. It is determined by the angles θ1 and θ2. Therefore, if the belt entrance angles θ1 and θ2 to the respective photoreceptors 2 are set to the same angle, the transfer nip widths W1 and W2 can be formed to have the same width.

  However, as shown in FIG. 10, depending on the arrangement of the stretching roller 9 that stretches the intermediate transfer belt 8, the belt approach angle θ1 to the most upstream photoconductor 2 in the belt traveling direction may be downstream. In some cases, the angle of entrance θ2 of the belt to the photosensitive member 2 is smaller. As a result, the widths W1 and W2 of the transfer nips N1 and N2 vary, and there is a problem that an image having a uniform density cannot be transferred for each color.

  Therefore, in order to eliminate variations in the transfer nip width in the offset transfer system, there is a type in which a backup roller 30 is provided between the most upstream transfer roller 11 and the stretching roller 9 as shown in FIG. By pushing up the intermediate transfer belt 8 by the backup roller 30, the belt approach angle θ <b> 1 to the most upstream photoreceptor 2 can be set to the same angle as the belt entrance angle θ <b> 2 to the downstream photoreceptor 2. As a result, the width becomes the same as the transfer nip widths W1 and W2, and uniform image transfer can be realized.

  By the way, in an image forming apparatus including an intermediate transfer belt, in order to prevent a permanent deformation of the belt due to the same portion of the intermediate transfer belt being in contact with the photoconductor for a long time, Some are configured to separate the intermediate transfer belt from the photoreceptor. In addition, for the purpose of suppressing wear and deterioration of the color image photosensitive member and developing device during monochrome image formation, the intermediate transfer belt is separated from the color image photosensitive member, and only the black image photosensitive member is used. Some are configured to contact the intermediate transfer belt.

  There are two methods for separating the intermediate transfer belt and the photoconductor: a method of moving the photoconductor and a method of moving the transfer roller. When the primary transfer roller is moved in the configuration including the backup roller, the following method is used. Such a problem arises.

  As shown in FIG. 12, in the configuration using the backup roller 30, the intermediate transfer belt 8 can be separated from the photoreceptor 2 by moving the primary transfer roller 11 downward. However, in this case, due to the presence of the backup roller 30, a sufficient separation distance between the most upstream photoreceptor 2 and the intermediate transfer belt 8 cannot be secured. For this reason, as shown in FIG. 12, if the intermediate transfer belt 8 has irregularities Z such as curl wrinkles, there is a risk that the intermediate transfer belt 8 and the photoreceptor 2 will rub against each other.

  As a method of avoiding this, it is conceivable that the backup roller 30 is disposed in advance below the position shown in FIG. 12 and a sufficient separation distance between the uppermost photosensitive member 2 and the intermediate transfer belt 8 is secured. However, if the backup roller 30 is disposed in advance downward, the transfer nip widths θ1 and θ2 will vary, causing a problem that the image density of each color cannot be maintained uniformly.

  In view of such circumstances, the present invention can ensure a sufficient separation distance when the transfer belt is separated from the image carrier, and can form a transfer nip width to a desired width. And an image forming apparatus provided with the transfer device.

  In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an image carrier that carries an image on its surface, an endless shape that is supported so as to form a transfer nip in contact with the image carrier and to be able to run around. A transfer belt and a transfer member that contacts an inner peripheral surface of the transfer belt, and a center point of a contact nip between the transfer member and the transfer belt is a center of the transfer nip between the image carrier and the transfer belt In the transfer device offset to the downstream side in the belt running direction, the transfer nip contacts the inner peripheral surface of the transfer belt upstream of the transfer nip in the belt running direction in order to form the transfer nip with a desired width. A backup member that rotates, and a backup holding member that rotates to hold the backup member movably in a direction opposite to the direction in which the backup member is pressed against the transfer belt. A transfer holding member that holds the transfer member movably in a direction opposite to the direction in which the transfer member is pressed against the transfer belt, a connecting member that interlocks and connects the transfer holding member and the backup holding member, and the transfer holding Driving means for rotating the transfer holding member and the backup holding member by applying a driving force to any one of the member, the backup holding member, and the connecting member, and in a direction of pressing the transfer member and the backup member against the transfer belt The transfer belt is brought into contact with the image carrier by moving, and the transfer belt is moved away from the image carrier by moving the transfer member and the backup member in the direction opposite to the direction of pressing the transfer belt against the transfer belt. It is characterized by that.

  According to the first aspect of the present invention, since the transfer nip can be formed with a desired width by the backup member, good transferability can be ensured. Further, when the transfer belt is separated from the image carrier, the backup member is moved in a direction opposite to the direction in which the backup member is pressed against the transfer belt, so that the separation between the image carrier and the transfer belt is smaller than when the backup member is not moved. A sufficient distance can be secured. This increases the certainty of avoiding contact between the transfer belt and the image carrier when the belt is separated.

  Further, since the transfer holding member and the backup holding member are interlocked and connected via a connecting member, the transfer member and the backup member are moved together by applying a driving force to any of these members. Can be made. That is, since the driving means for driving the transfer member and the driving means for driving the backup member can be shared, the number of parts can be reduced, and the cost and the size can be reduced.

  Further, the pressing force of the transfer member against the transfer belt can be adjusted by changing the length from the rotation axis of the transfer holding member to the position where the transfer member is held. Similarly, the pressing force of the backup member against the transfer belt can be adjusted by changing the length from the rotation axis of the backup holding member to the location where the backup member is held.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of an overall configuration of a transfer device included in the image forming apparatus. It is a figure which shows the other example of offset arrangement | positioning. It is a figure which shows the moving mechanism of the primary transfer roller for yellow images arrange | positioned in the most upstream, and a backup roller. It is a figure for demonstrating the arrangement | positioning position of a backup roller. FIG. 4 is a diagram illustrating a state in which an intermediate transfer belt is separated from each color image photoreceptor. It is an enlarged view of a belt cleaning device. It is a figure which shows the structure which arrange | positioned the press roller. It is a figure which shows the structure of the transfer apparatus of a direct pressure transfer system. It is a figure which shows the structure of the transfer apparatus of an offset transfer system. It is a figure which shows the structure of the conventional transfer apparatus provided with the backup roller. It is a figure for demonstrating the subject of the conventional transfer apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in each drawing for explaining the embodiment of the present invention, components such as members and components having the same function or shape are once described by giving the same reference numerals as much as possible. The description is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, in the image forming apparatus of the present embodiment, four process units 1Y, 1M, 1C, and 1Bk as image forming units are detachably attached to the image forming apparatus main body 100.

  The process units 1Y, 1M, 1C, and 1Bk have the same configuration except that they contain toners of different colors of yellow, magenta, cyan, and black corresponding to the color separation components of the color image. Specifically, the process units 1Y, 1M, 1C, and 1Bk are charged as charging means for charging the photoreceptors 2Y, 2M, 2C, and 2Bk as image carriers and the surfaces of the photoreceptors 2Y, 2M, 2C, and 2Bk. Developing devices 4Y, 4M, 4C, 4Bk as developing means for supplying toner (developer) to the surfaces of the rollers 3Y, 3M, 3C, 3Bk, the photoreceptors 2Y, 2M, 2C, 2Bk, and the photoreceptors 2Y, 2M , 2C, 2Bk, and cleaning blades 5Y, 5M, 5C, 5Bk as cleaning means.

  Here, the letters Y, M, C, and Bk indicate yellow, magenta, cyan, and black. However, the process unit, the photosensitive member, the charging roller, the developing device, the cleaning blade, and the other described below. Unless otherwise specifically indicated, the characters indicating the identification of these colors are omitted for the symbols indicating the members.

  The photoconductor 2 is a cylindrical photoconductor drum of φ24, and is rotated at a peripheral speed of 100 to 200 mm / s in the clockwise direction in the drawing by a driving device (not shown). The charging roller 3 is in contact with the surface of the photoreceptor 2, and the charging roller 3 is driven to rotate by the rotation of the photoreceptor 2. Further, the charging roller 3 is configured to be applied with a DC or a bias in which AC is superimposed on DC by a high voltage power source (not shown). The developing device 4 is a one-component contact type developing device in which one-component toner as a developer is stored. The developing device 4 is configured to be supplied with a predetermined developing bias from a high voltage power source (not shown).

  In FIG. 1, an exposure device 6 that exposes the surface of the photoreceptor 2 to form an electrostatic latent image is disposed above each process unit 1Y, 1M, 1C, 1Bk. The exposure device 6 has a laser beam scanner or LED using a laser diode, and irradiates the surface of each photoconductor 2 with laser light based on image data.

  A transfer device 7 is disposed below each process unit 1Y, 1M, 1C, 1Bk. The transfer device 7 has an intermediate transfer belt 8 as a transfer body. As the intermediate transfer belt 8, a conductive material such as PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer) or the like is used. A resin film-like endless belt in which a conductive material is dispersed is used. In the present embodiment, a belt having a thickness of 90 to 160 μm and a width of 230 mm that has a tensile modulus of 1000 to 3000 MPa is used.

  The intermediate transfer belt 8 is stretched around a driving roller 9 and a tension roller 10 as support members. When the driving roller 9 rotates counterclockwise in the figure, the intermediate transfer belt 8 is in a direction indicated by an arrow in the figure. It is comprised so that it may run around (rotate). Further, the intermediate transfer belt 8 is given a predetermined tension by pressurization of springs (not shown) provided at both ends of the tension roller 10. Further, both ends of the driving roller 9 and the tension roller 10 are supported by side plates (not shown) of the transfer device 7.

  Four primary transfer rollers 11Y, 11M, 11C, and 11Bk as primary transfer members are disposed at positions facing the four photoconductors 2. Each primary transfer roller 11 presses the inner peripheral surface of the intermediate transfer belt 8 at each position, whereby the primary transfer nip is located at a position where the pressed portion of the intermediate transfer belt 8 and each photoconductor 2 are in contact with each other. Is formed. In the present embodiment, a metal roller of φ8 to φ12 is used as the primary transfer roller 11. Each primary transfer roller 11 is connected to a power source (not shown), and a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to the primary transfer roller 11. A conductive blade, a conductive sponge roller, or the like can be used as the primary transfer member.

  Further, a secondary transfer roller 12 as a secondary transfer member is disposed at a position facing the drive roller 9. The secondary transfer roller 12 presses the outer peripheral surface of the intermediate transfer belt 8, whereby a secondary transfer nip is formed at a location where the secondary transfer roller 12 and the intermediate transfer belt 8 are in contact with each other. The secondary transfer roller 12 is configured by covering a metal cored bar with a conductive elastic body. As the secondary transfer roller 12, for example, a conductive roller, an electronic conductive type roller (EPDM), or the like can be applied. In the present embodiment, a roller having an Asker C hardness of 35 to 55 ° is used. The resistance value of the secondary transfer roller 12 is measured by installing the secondary transfer roller 12 on a conductive metal plate and measuring 100 to 1 kV between the metal plate and the core metal of the secondary transfer roller 12. It calculated from the electric current value which flows when a voltage is applied. Similar to the primary transfer roller 11, the secondary transfer roller 12 is connected to a power source (not shown), and a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to the secondary transfer roller 12. It is like that.

  A belt cleaning device 13 for cleaning the surface of the intermediate transfer belt 8 and a toner mark sensor (TM sensor) 14 are disposed around the intermediate transfer belt 8. Further, a waste toner transfer hose (not shown) is attached from the belt cleaning device 13, and the tip of the toner transfer hose is connected to the entrance of a waste toner container 17 disposed below the transfer device 7. .

  The belt cleaning device 13 includes a cleaning blade (belt cleaning member) 15 that is in contact with the outer peripheral surface of the intermediate transfer belt 8 and a cleaning counter roller that is in contact with the inner peripheral surface of the intermediate transfer belt 8 at a position facing the cleaning blade 15. Cleaning opposing member) 16. As a material for the cleaning blade 15, urethane rubber having a thickness of 1.5 to 3 mm and a rubber hardness of 65 to 80 ° is used. Further, the cleaning blade 15 is disposed so as to come into contact with the traveling direction of the intermediate transfer belt 8 in the counter direction. Further, when the belt cleaning device 13 is assembled, it is possible to prevent the cleaning blade 15 from rolling up by applying a lubricant to at least one of the contact portions of the intermediate transfer belt 8 and the cleaning blade 15. Further, by applying the lubricant, a dam layer of the lubricant can be formed in the cleaning nip portion where the cleaning blade 15 abuts, and the cleaning property can be improved.

  The toner mark sensor 14 is a combination of a light emitting element and a light receiving element for measuring the toner image density and each color position on the intermediate transfer belt 8 using a regular reflection type or diffusion type sensor, and adjusting the image density and color matching. is there.

  At the bottom of the image forming apparatus main body 100, a paper feed tray 18 that stores a recording medium P such as paper or an OHP sheet, and a paper feed roller 19 that feeds the recording medium P from the paper feed tray 18 are disposed. Has been. A pair of registration rollers 20 as a conveying unit for conveying the recording medium P to the secondary transfer nip is disposed in the middle of the conveying path for conveying the recording medium P from the paper feed tray 18 to the secondary transfer nip. Further, a fixing device 21 for fixing the image on the recording medium P is disposed in the middle of the conveyance path for conveying the recording medium P from the secondary transfer nip upward in the drawing and discharging it to the outside of the apparatus.

  The fixing device 21 includes a fixing roller 22 having a heating element such as a halogen heater therein, and a pressure roller 23 that is pressed against the fixing roller 22 to form a fixing nip. In this embodiment, the process speed at the time of fixing is changed depending on the type of the recording medium P. For example, when a recording medium P having a large basis weight is used, the recording medium P is allowed to pass through the fixing nip over 1.5 to 2.5 times the normal time by lowering the process speed. Thereby, even in the recording medium P having a large basis weight, sufficient heat can be applied, and the fixing property of the image can be ensured.

Next, the basic operation of the image forming apparatus will be described with reference to FIG.
When the image forming operation is started, the photoconductors 2 of the process units 1Y, 1M, 1C, and 1Bk are rotationally driven clockwise in the drawing, and the surface of each photoconductor 2 is made uniform to a predetermined polarity by the charging roller 3. Is charged. Based on the image information of the document read by a reading device (not shown), the exposure device 6 irradiates the charged surface of each photoconductor 2 with laser light, and an electrostatic latent image is formed on the surface of each photoconductor 2. . At this time, the image information to be exposed on each photoconductor 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. As the electrostatic latent image formed on the photosensitive member 2 is supplied with toner by each developing device 4, the electrostatic latent image is visualized (visualized) as a toner image.

  A driving roller 9 that stretches the intermediate transfer belt 8 is rotationally driven to rotate the intermediate transfer belt 8 in the direction of the arrow in the figure. Further, when a predetermined transfer bias (+300 to +1000 V) is applied to each primary transfer roller 11 from a power source (not shown), a transfer electric field is generated in the primary transfer nip between each primary transfer roller 11 and each photoreceptor 2. It is formed. Then, the toner images of the respective colors on the respective photoconductors 2 are sequentially superimposed and transferred onto the intermediate transfer belt 8 by the transfer electric field formed in the primary transfer nip. Thus, the intermediate transfer belt 8 carries a full-color toner image on its surface. On the other hand, the toner on each photoreceptor 2 that could not be transferred to the intermediate transfer belt 8 is removed by the cleaning blade 5.

  When the image forming operation is started, the paper feed roller 19 rotates and the recording medium P is fed from the paper feed tray 18. The fed recording medium P is timed by the registration roller 20 and sent to the secondary transfer nip between the secondary transfer roller 12 and the intermediate transfer belt 8. At this time, a predetermined transfer bias is applied to the secondary transfer roller 12 by a power source (not shown), thereby forming a transfer electric field in the secondary transfer nip. Then, the toner image on the intermediate transfer belt 8 is collectively transferred onto the recording medium P by the transfer electric field formed in the secondary transfer nip. Further, the toner remaining on the intermediate transfer belt 8 is removed by the belt cleaning device 13, and the removed toner is conveyed to the waste toner container 17 and collected. Thereafter, the recording medium P is sent to the fixing device 21 and the toner image is fixed on the recording medium P. The recording medium P is discharged out of the apparatus by a pair of discharge rollers (not shown).

  The above description is an image forming operation when a full-color image is formed on a recording medium. A single color image is formed using any one of the four process units 1Y, 1M, 1C, and 1Bk, and 2 Two or three process units can be used to form a two or three color image.

Next, the configuration of the transfer device 7 will be described in detail.
FIG. 2 is a schematic diagram of the overall configuration of the transfer apparatus.
As shown in FIG. 2, each primary transfer roller 11 has an intermediate transfer belt on the downstream side in the belt running direction of the intermediate transfer belt 8 from a position (primary transfer nip) where the photosensitive member 2 contacts the intermediate transfer belt 8. 8 is arranged so as to contact 8. The “belt running direction” here refers to the position where the image of each color is transferred onto the intermediate transfer belt 8 (primary transfer nip), and the image is transferred last from the position where the image is transferred first. It is the direction toward the position. Therefore, in the case of the present embodiment, the yellow image photoreceptor 2Y becomes the most upstream photoreceptor, and the magenta image photoreceptor 2M, cyan image photoreceptor 2C, and black image in that order from the downstream. The photosensitive member 2Bk for use is disposed.

As shown in FIG. 3, the primary transfer roller 11 may be disposed so as to come into contact with the photoreceptor 2 via the intermediate transfer belt 8. That is, the primary transfer roller 11 has a center point Oq of the contact nip Q between the primary transfer roller 11 and the intermediate transfer belt 8 with respect to a center point On of the primary transfer nip N between the photoreceptor 2 and the intermediate transfer belt 8. What is necessary is just to be arrange | positioned so that it may be offset to the belt running direction downstream. In particular, in FIG. 3, when the diameter of the photoreceptor 2 is E [mm], the diameter of the primary transfer roller 11 is F [mm], and the thickness of the intermediate transfer belt 8 is G [mm] (not shown), the primary transfer is performed. It is preferable to dispose the primary transfer roller 11 so that the distance L between the axis of the roller 11 and the axis of the photosensitive member 2 satisfies the relationship represented by the following formula (1).
L> (E / 2) + (F / 2) + G Expression (1)

  In FIG. 2, among the primary transfer rollers 11Y, 11M, and 11Bk, the color image rollers 11Y, 11M, and 11C other than the black image primary transfer roller 11Bk are respectively pressed against the intermediate transfer belt 8 and the direction thereof. It is configured to be movable in the opposite direction. That is, these primary transfer rollers 11Y, 11M, and 11C are movable in a direction crossing the intermediate transfer belt 8.

  Further, a backup roller 30 as a backup member that contacts the inner peripheral surface of the intermediate transfer belt 8 is disposed further upstream of the primary transfer roller 11Y on the most upstream side in the belt traveling direction and downstream of the cleaning counter roller 16. It is installed. In particular, the backup roller 30 is provided to form a primary transfer nip having a desired width in the most upstream photoconductor 2Y in the belt traveling direction. In this embodiment, in the state where the backup roller 30 and each primary transfer roller 11 are disposed at the positions indicated by the solid lines in FIG. 2, the widths of the primary transfer nips (widths in the belt running direction) of the respective photoreceptors 2 are all the same. The width is set. Similarly to the primary transfer rollers 11Y, 11M, and 11C for color images, the backup roller 30 is movable in the direction pressed against the intermediate transfer belt 8 and in the opposite direction, that is, in the direction crossing the intermediate transfer belt 8. It is configured.

  A backup member other than the roller shape (backup roller 30) can be used. However, the backup member is formed in a roller shape as in the present embodiment, so that the inner member of the intermediate transfer belt 8 can be formed. The backup member can be brought into contact with the intermediate transfer belt 8 stably without damaging the peripheral surface. Further, when the backup roller 30 and the primary transfer rollers 11Y, 11M, 11C, and 11Bk have the same roller shape, a common member can be used, so that the component cost can be reduced and the manufacturing can be performed at low cost. It becomes possible.

Hereinafter, a specific configuration for moving the primary transfer rollers 11Y, 11M, and 11C for color images and the backup roller 30 in a direction intersecting the intermediate transfer belt 8 will be described.
FIG. 4 is a view showing a moving mechanism between the primary transfer roller for yellow image and the backup roller arranged on the most upstream side.
As shown in FIG. 4, the primary transfer roller 11Y is held by a transfer holding member 31, and the transfer holding member 31 is configured to be rotatable about a rotation shaft 31a in the direction of arrow A in the figure. By rotating the transfer holding member 31 around the rotation shaft 31a, the primary transfer roller 11Y can move in a direction opposite to the direction pressed against the intermediate transfer belt 8.

  The backup roller 30 is held by a backup holding member 32, and the backup holding member 32 is configured to be rotatable in the direction of an arrow B in the figure around a rotation shaft 32a. By rotating the backup holding member 32 around the rotation shaft 32a, the backup roller 30 can move in a direction opposite to the direction in which the backup roller 30 is pressed against the intermediate transfer belt 8.

  Further, the transfer holding member 31 and the backup holding member 32 are interlocked and connected by a connecting member 33. The connecting member 33 is configured to be movable in the direction of the arrow D in the figure, and the connecting member 33 moves in the direction along with the rotation operation of the transfer holding member 31 and the backup holding member 32. In the present embodiment, as a driving means for driving them, a tension spring 34 as an urging means attached to the transfer holding member 31, and a transfer holding member against the urging force (tensile force) of the tension spring 34. 31, a backup holding member 32, and a driving mechanism (not shown) that applies a driving force to any one of the connecting members 33. In addition, as a material of the connection member 33, in order to reduce drive torque and to reduce power consumption, it is desirable to use a member having slidability such as polyacetal.

  Usually, the transfer holding member 31 is applied with a force in a direction of rotating clockwise in the drawing by the tensile force of the tension spring 34, so that the primary transfer roller 11 </ b> Y is pressed against the intermediate transfer belt 8. It is energized. Further, since the rotational force is applied to the transfer holding member 31 in this way, the connecting member 33 is urged to the left side in the drawing, and thereby the backup holding member 32 rotates in the clockwise direction in the drawing. Power is given. For this reason, the backup roller 30 is also urged in the direction in which it is pressed against the intermediate transfer belt 8 in the same manner as the primary transfer roller 11Y. Note that the transfer holding member 31 may be urged in the same direction by using a compression spring instead of the tension spring 34 as in the present embodiment. In addition to the transfer holding member 31, a backup holding member 32 or a connecting member may be used. 33 may be provided with a biasing means such as a spring.

  In the present embodiment, a positioning unit 35 is provided in a photoconductor case (not shown) that holds the photoconductor 2. The transfer holding member 31 that receives the clockwise force of the drawing by the tension spring 34 rotates against the urging force of the tension spring 34 when the end portion (contact portion 31 b) contacts the positioning portion 35. Is regulated, and the primary transfer roller 11Y is positioned. Further, since the rotation of the transfer holding member 31 is restricted, the rotation of the backup holding member 32 connected to the transfer holding member 31 is also restricted, and the backup roller 30 is also positioned. The positioning portion 35 may be disposed at a position where it comes into contact with the backup holding member 32 or the connecting member 33.

  Further, when a driving force is applied to any one of the transfer holding member 31, the backup holding member 32, and the connecting member 33 against the tensile force of the tension spring 34 by a driving mechanism (not shown), the transfer holding member 31 and the backup holding member 31. The member 32 rotates counterclockwise in the figure. As a result, the primary transfer roller 11Y and the backup roller 30 move in a direction opposite to the direction in which the primary transfer roller 11Y and the backup roller 30 are pressed against the intermediate transfer belt 8, and are disposed at positions indicated by two-dot chain lines in the drawing.

  The moving mechanism between the primary transfer roller 11Y for yellow image and the backup roller 30 has been described with reference to FIG. 4. However, the moving mechanism for the other primary transfer rollers 11M and 11C is the primary transfer roller for yellow image. The same thing as 11Y is applied. That is, the moving mechanism of the primary transfer rollers 11M and 11C for magenta image and cyan image includes a transfer transfer member 31 that is rotatable as described above, and an urging means such as a tension spring 34 that urges this. The positioning unit 35 includes a driving mechanism that applies a driving force to the transfer holding member 31 against the urging force of the urging means.

FIG. 5 is a diagram for explaining the arrangement position of the backup roller.
In the offset transfer method as in this embodiment, unlike the direct pressure transfer method, it is not necessary to use an elastic roller as a primary transfer roller, and a metal roller can be used. Further, by using the same metal roller as the backup roller 30, it is possible to provide an inexpensive transfer device. As described above, when the backup roller 30 is formed of a conductive member such as a metal roller, the back surface of the intermediate transfer belt 8 can be stably discharged by grounding the backup roller 30. It becomes like this. As a result, it is possible to prevent the toner image from being disturbed due to charging on the back side of the intermediate transfer belt 8 and subsequent discharge.

  However, if the grounded backup roller 30 is disposed at a position close to the photoreceptor 2Y, the transfer bias applied to the primary transfer roller 11Y flows into the backup roller 30 along the back surface of the intermediate transfer belt 8. There is a possibility that a sufficient electric field for transferring the toner image cannot be formed. Therefore, it is desirable that the backup roller 30 is disposed at a position farther from the photoreceptor 2Y than the primary transfer roller 11Y. Specifically, in FIG. 5, the primary transfer nip where the photoreceptor 2Y and the intermediate transfer belt 8 are in contact is N1, the contact nip where the primary transfer roller 11Y and the intermediate transfer belt 8 are in contact is Q1, and the backup roller 30 If the contact nip where the intermediate transfer belt 8 contacts is R, the distance Y from the primary transfer nip N1 to the contact nip R of the backup roller 30 is the distance from the primary transfer nip N1 to the contact nip Q1 of the primary transfer roller 11Y. It is desirable to set X or more. By setting in this way, the transfer bias can be prevented from flowing into the backup roller 30, and a sufficient transfer electric field can be formed.

Hereinafter, an operation when a monochrome image is formed in the image forming apparatus of the present embodiment will be described with reference to FIG.
As shown in FIG. 6, when forming a monochrome image, the color image rollers 11Y, 11M, 11C and the backup roller 30 except the primary transfer roller 11Bk for the black image are connected to the intermediate transfer belt 8. Move in the direction opposite to the direction of pressing. As a result, the intermediate transfer belt 8 is moved from the position indicated by the two-dot chain line in the drawing to the position indicated by the solid line, and the intermediate transfer belt 8 is separated from the respective photoreceptors 2Y, 2M, 2C other than the photoreceptor 2Bk for black image. It becomes a state. When the image forming operation is started, an image is formed only on the black image photoreceptor 2Bk, and the image is transferred to the recording medium P via the intermediate transfer belt 8 in the same manner as in the above-described full-color image formation. After that, the image is fixed by the fixing device 21 and discharged outside the apparatus. As described above, in this embodiment, when a monochrome image is formed, the color image photosensitive members 2Y, 2M, and 2C are separated from the intermediate transfer belt 8, so that the color toner is consumed and deteriorated. Thus, the wear and the like of the photosensitive members 2Y, 2M, and 2C for use are suppressed.

  In the present embodiment, the color image primary transfer rollers 11Y, 11M, and 11C and the backup roller 30 are separated from the intermediate transfer belt 8, and only the black image photoreceptor 2Bk is connected to the intermediate transfer belt 8. The black image photoreceptor 2Bk is disposed about 1 to 8 mm below the other photoreceptors 2Y, 2M, and 2C so that they can come into contact with each other.

  Further, when forming a full color image after forming a monochrome image, the primary transfer rollers 11Y, 11M, and 11C for color image formation and the backup roller 30 are moved in a direction in which they are pressed against the intermediate transfer belt 8. Return to position. In this way, by returning the primary transfer rollers 11Y, 11M, and 11C for color image formation and the backup roller 30 to their original positions, the intermediate transfer belt 8 comes into contact with all the photoreceptors 2Y, 2M, 2C, and 2Bk again. It will be in the state.

FIG. 7 is an enlarged view of the belt cleaning device.
As described above, since the backup roller 30 is configured to be movable in the present embodiment, as the backup roller 30 moves, the intermediate transfer belt 8 is wound around the cleaning counter roller 16 as shown in FIG. The applied amount (width of the contact nip) changes between U1 and U2, and this may cause a cleaning failure.

  Therefore, as shown in FIG. 8, the pressing roller 36 as a pressing member that presses the outer peripheral surface of the intermediate transfer belt 8 is disposed between the backup roller 30 and the cleaning blade 15, so that the backup roller 30 moves. However, the belt winding amount (contact nip width) of the cleaning counter roller 16 can be kept constant. As a result, stable cleaning performance can be exhibited, and occurrence of cleaning failure can be prevented.

  It is possible to adopt a member other than the roller shape (pressing roller 36) as the pressing member. The pressing member can be brought into contact with the intermediate transfer belt 8 stably without damaging the surface.

  As described above, according to the embodiment of the present invention, by providing the backup roller 30, the width of the primary transfer nip in all the photoconductors 2Y, 2M, 2C, and 2Bk can be reduced during full color image formation. Can be the same. Thereby, the image density of each color can be made uniform and good image formation can be performed.

  Further, when forming a monochrome image, the backup roller 30 is moved in a direction opposite to the direction in which the backup roller 30 is pressed against the intermediate transfer belt 8, so that the yellow image is used as compared with the case where the backup roller 30 is not moved (see FIG. 12). A sufficient separation distance between the photosensitive member 2Y and the intermediate transfer belt 8 can be secured. Accordingly, even when the intermediate transfer belt 8 has irregularities such as curl wrinkles, it is possible to avoid the possibility that the irregularities will contact the photoreceptor 2Y for yellow image.

  As described above, according to the embodiment of the present invention, it is possible to realize good image formation during full-color image formation and to reliably avoid contact between the intermediate transfer belt and the most upstream photoconductor during monochrome image formation. Can raise the sex.

  In the present embodiment, as described with reference to FIG. 4, the transfer holding member 31 and the backup holding member 32 are interlocked and connected via the connecting member 33. By applying a biasing force and a driving force to the member, it is possible to move both the primary transfer roller 11Y and the backup roller 30 together. That is, since the driving means for driving the primary transfer roller 11Y and the driving means for driving the backup roller 30 can be shared, the number of parts can be reduced, and the cost and the size can be reduced.

  Further, it is only necessary to provide one positioning portion 35 for positioning the primary transfer roller 11Y and the backup roller 30. In particular, the transfer holding member 31 can be positioned by contacting the photosensitive member case or the like, but it is effective in the case where it is difficult to secure a plurality of positioning portions, such as when there is no place where the backup holding member 32 contacts. is there.

  Further, the pressing force of the primary transfer roller 11Y against the intermediate transfer belt 8 can be adjusted by changing the length from the rotation shaft 31a of the transfer holding member 31 to the location where the primary transfer roller 11Y is held. Similarly, the pressing force of the backup roller 30 against the intermediate transfer belt 8 can be adjusted by changing the length from the rotation shaft 32a of the backup holding member 32 to the location where the backup roller 30 is held. .

  Further, as in the present embodiment shown in FIG. 4, a tension spring 34 (or a compression spring) that urges the transfer holding member 31 and the like is disposed in the horizontal direction, so that the transfer device 7 as a whole is arranged in the height direction. The size can be reduced and the size can be reduced.

  In addition, this invention is not limited to the above-mentioned embodiment, Of course, a various change can be added in the range which does not deviate from the summary of this invention. For example, in the configuration of the above-described embodiment, when the density of the transfer image from the photoconductor for the yellow image is lower than the density of the transfer image from the other photoconductor, the backup roller is positioned higher than the uppermost position in the embodiment. It may be possible to move further upward. As a result, the width of the primary transfer nip for a yellow image having a low density can be secured larger than the width of the other primary transfer nip, so that the density of each image can be adjusted uniformly. That is, in order to make the image density of each color uniform, the width of some primary transfer nips may be adjusted to be different from the width of other primary transfer nips (to a desired width) by a backup roller.

  In the above-described embodiment, the configuration of the present invention is applied to a transfer device that can contact and separate the intermediate transfer belt with respect to each color image photosensitive member except the black image photosensitive member. The configuration of the present invention can also be applied to a transfer device that can contact and separate the intermediate transfer belt with respect to all the photoconductors including the image photoconductor. The configuration of the present invention can also be applied to a transfer apparatus having only one photoconductor. The image forming apparatus of the above-described embodiment is an intermediate transfer system using an intermediate transfer belt, but a direct transfer system that directly transfers an image on a photoconductor onto a recording medium carried on an endless transfer belt. The configuration of the present invention can also be applied to this apparatus.

2 Photoconductor (image carrier)
7 Transfer device 8 Intermediate transfer belt (transfer belt)
11 Primary transfer roller (transfer member)
15 Cleaning blade (belt cleaning member)
16 Cleaning counter roller (cleaning counter member)
30 Backup roller (backup member)
31 Transfer holding member 31a Rotating shaft 32 Backup holding member 32a Rotating shaft 33 Connecting member 34 Tension spring (biasing means)
35 Positioning part 36 Pressing roller (pressing member)

JP 2007-3769 A JP 2007-286270 A

Claims (10)

An image carrier that carries an image on the surface, an endless transfer belt that is in contact with the image carrier to form a transfer nip and is supported so as to be able to run around, and a transfer that contacts the inner peripheral surface of the transfer belt With members,
In the transfer device in which the center point of the contact nip between the transfer member and the transfer belt is offset to the downstream side in the belt running direction with respect to the center point of the transfer nip between the image carrier and the transfer belt,
In order to form the transfer nip to a desired width, a backup member that contacts the inner peripheral surface of the transfer belt on the upstream side of the transfer nip in the belt traveling direction;
A backup holding member that holds the backup member movably in a direction opposite to the direction in which the backup member is pressed against the transfer belt by rotating;
A transfer holding member that holds the transfer member movably in a direction opposite to the direction in which the transfer member is pressed against the transfer belt by rotating;
A connecting member for interlockingly connecting the transfer holding member and the backup holding member;
Drive means for rotating the transfer holding member and the backup holding member by applying a driving force to any of the transfer holding member, the backup holding member, and the connecting member;
By moving the transfer member and the backup member in the direction of pressing the transfer belt, the transfer belt is brought into contact with the image carrier, and by moving the transfer member and the backup member in the direction opposite to the direction of pressing the transfer belt, A transfer device configured to separate a transfer belt from an image carrier.   The driving means biasing the transfer holding member, the backup holding member, or the connecting member so as to press the transfer member and the backup member against the transfer belt; A direction in which a driving force is applied to any one of the transfer holding member, the backup holding member, and the connecting member against the biasing force of the biasing unit to press the transfer member and the backup member against the transfer belt, respectively. The transfer device according to claim 1, further comprising: a drive mechanism that moves in a direction opposite to that of the transfer device.   Positioning portions that abut against any one of the transfer holding member, the backup holding member, and the connecting member and position the transfer member and the backup member at predetermined positions against the urging force of the urging means. The transfer device according to claim 2 provided. A transfer device in which a plurality of the image carrier and the transfer member are arranged in parallel in a belt traveling direction,
The backup member is disposed upstream of the most upstream transfer member in the belt traveling direction among the plurality of transfer members, and the backup member and the most upstream transfer member are connected to the connecting member. 4. The transfer device according to claim 1, wherein the transfer device is held by the backup holding member and the transfer holding member that are interlockedly connected via each other. 5.   The transfer device according to claim 1, wherein the backup member is made of a conductive member and is grounded.   The backup member is disposed such that the distance from the transfer nip to the contact nip between the backup member and the transfer belt is equal to or greater than the distance from the transfer nip to the contact nip between the transfer member and the transfer belt. The transfer device according to claim 5. A transfer provided with a belt cleaning member that contacts the outer peripheral surface of the transfer belt upstream of the backup member in the belt running direction, and a cleaning counter member that contacts the inner peripheral surface of the transfer belt at a position facing the belt cleaning member. A device,
A pressing member that presses an outer peripheral surface of the transfer belt between the belt cleaning member and the backup member in order to maintain a constant width of a contact nip between the cleaning facing member and the transfer belt. The transfer device according to any one of 1 to 6.   The transfer device according to claim 1, wherein the backup member is configured in a roller shape.   The transfer device according to claim 1, wherein the connecting member is configured by a member having slidability.   An image forming apparatus comprising the transfer device according to claim 1.

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