JP2010217806A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which has a structure in which a plurality of squeezing rollers are arranged in a rotating direction of an image carrier, the image forming apparatus preventing the occurrence of image defect by stabilizing moving speed of a surface of the image carrier at a squeezing position; and to provide an image forming method using the image forming apparatus. <P>SOLUTION: A moving direction of the surface of a first squeezing roller is the same as the moving direction of the surface of a photoreceptor drum 21 at a first squeezing position P1, and circumferential speed V25 of the first squeezing roller 251 is lower than circumferential seed V21 of the photoreceptor drum 21. At a second squeezing position P2, a moving direction of the surface of the second squeezing roller 261 is the same as the moving direction of the photoreceptor drum 21 and circumferential speed of the second squeezing roller 261 is the same or nearly the same as the circumferential speed V21 of the photoreceptor drum 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for forming an image using a liquid developer, and in particular, an image forming apparatus including a plurality of squeeze rollers for recovering fog toner and excess carrier liquid from an image carrier. The present invention relates to an image forming method.

  There has been proposed an image forming apparatus that develops and visualizes an electrostatic latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a carrier liquid. In this image forming apparatus, a squeeze roller is used to remove excess developer and fog toner including an excess carrier liquid from a toner image formed on an image carrier by development. Particularly in recent years, it has been proposed to provide a plurality of squeeze rollers in order to sufficiently remove excess carrier liquid from a toner image (for example, Patent Document 1). In the apparatus described in Patent Document 1, a first squeeze roller and a second squeeze roller are arranged along the rotation direction of the photoconductor, and each of them rotates in a predetermined direction to charge the cover and excess carrier liquid on the photoconductor. Remove.

Japanese Patent Laying-Open No. 2009-14808 (FIG. 5)

  By the way, in the apparatus described in Patent Document 1, since the first and second squeeze rollers are sequentially arranged in the rotation direction of the photoconductor, the photoconductor subjected to the squeeze process by the first squeeze roller at the second squeeze position. The squeeze process by the second squeeze roller is performed on the surface. For this reason, the frictional force at the second squeeze position is larger than the frictional force at the first squeeze position, and the moving speed of the surface of the second squeeze roller that rotates while contacting the surface of the photosensitive member is the moving speed of the photosensitive member surface. If they are different, this disturbs the moving speed of the surface of the photoreceptor. This is one of the main factors causing unevenness in the movement speed of the photoreceptor surface. However, in the past, such problems have not been sufficiently studied, and the movement speed unevenness on the surface of the photoreceptor has occurred at the second squeeze position, resulting in a reduction in image quality.

  The present invention has been made in view of the above problems, and in an image forming apparatus having a structure in which a plurality of squeeze rollers are arranged along the rotation direction of an image carrier and an image forming method using the apparatus, An object of the present invention is to stabilize the moving speed of the surface of the image carrier and prevent the occurrence of image defects.

  In order to achieve the above object, an image forming apparatus according to the present invention contacts an image carrier that rotates while carrying an image, and contacts the image carrier at a first squeeze position in the same direction as the moving direction of the image carrier. The first squeeze roller that moves and squeezes the image carrier, and the second squeeze position of the image carrier squeezed by the first squeeze roller contacts the image carrier in the same direction as the moving direction of the image carrier. And a second squeeze roller that squeezes the image carrier, and the movement speed of the first squeeze roller is slower than the movement speed of the image carrier, and the movement speed of the second squeeze roller is the movement of the image carrier. It is characterized by being the same or substantially the same as the speed.

  Further, in order to achieve the above object, the image forming method according to the present invention is configured so that the first squeeze roller is brought into contact with the image carrier that carries and rotates an image at the first squeeze position. The first squeeze step of rotating the first squeeze roller in the same direction as the movement direction of the image carrier to squeeze the image carrier, and the second squeeze position of the image carrier squeezed by the first squeeze roller The second squeeze roller is rotated in the same direction as the movement direction of the image carrier while the second squeeze roller is in contact with the image carrier, and the image carrier is squeezed. 2 squeeze process, and the moving speed of the first squeeze roller in the first squeeze process is slower than the moving speed of the image carrier. The moving speed of the second squeeze rollers squeeze process is characterized in that the same or substantially the same as the moving speed of the image carrier.

  In the invention thus configured (image forming apparatus and image forming method), since the image carrier squeezed by the first squeeze roller is squeezed by the second squeeze roller, first the first squeeze position Thus, the first squeeze roller rotates while contacting the surface of the image carrier to execute the squeeze process. At that time, if the first squeeze roller vibrates at the first squeeze position, the image quality deteriorates. Therefore, in the present invention, the moving direction of the first squeeze roller surface is the same as the moving direction of the image carrier surface at the first squeeze position, and the moving speed of the first squeeze roller surface, that is, the peripheral speed of the first squeeze roller. Is set to be slower than the moving speed of the surface of the image carrier, that is, the peripheral speed of the image carrier.

  Here, the moving speed of the second squeeze roller surface (peripheral speed of the second squeeze roller) is set similarly to the moving speed of the first squeeze roller surface, that is, lower than the moving speed of the image carrier surface. However, in this case, the moving speed of the surface of the image carrier may be disturbed at the second squeeze position as described above. In other words, at the second squeeze position, the second squeeze roller comes into contact with the surface of the image carrier subjected to the squeeze process by the first squeeze roller, and the squeeze process is executed. For this reason, the frictional force generated at the second squeeze position is larger than the frictional force at the first squeeze position. Therefore, if the moving speed of the second squeeze roller surface is different from the moving speed of the image carrier surface at the second squeeze position as in the first squeeze position, the moving speed of the image carrier surface fluctuates and the image quality is degraded. It will cause. Therefore, in the present invention, the moving direction of the second squeeze roller surface at the second squeeze position is set to the same direction as the moving direction of the image carrier surface, and the moving speed of the second squeeze roller surface at the second squeeze position is determined. Unlike the moving speed of the surface of the first squeeze roller at the first squeeze position, it is set to be the same or substantially the same as the moving speed of the surface of the image carrier. This prevents the movement speed of the surface of the image carrier from being disturbed at the second squeeze position, and a high-quality image can be formed.

  A drive unit having a drive source that generates a drive force, and a power transmission unit that is connected to the drive unit and transmits the drive force to the second squeeze roller to rotate the second squeeze roller. A power switching member having a power switching member that switches between transmission and interruption of driving force to the second squeeze roller, and when the moving speed of the second squeeze roller driven by the driving force is slower than the moving speed of the image carrier However, the transmission of the driving force to the second squeeze roller may be cut off, and the second squeeze roller may be driven to rotate following the image carrier. Thereby, the moving direction and moving speed of the second squeeze roller surface can be set easily and reliably as described above. For example, a one-way clutch can be used as the power switching member.

  The driving force may be transmitted to the first squeeze roller to rotate the first squeeze roller. That is, using the drive source of the drive unit as a common drive source for the first squeeze roller and the second squeeze roller simplifies the apparatus configuration and makes it economical.

  Furthermore, vibration of the first squeeze roller at the first squeeze position is effectively prevented by setting the movement speed of the surface of the first squeeze roller to a movement speed of 99% or more and less than 100% of the movement speed of the image carrier surface. Is done.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram illustrating a configuration of an image forming station. FIG. 3 is a configuration diagram viewed from a rear side end and a front side end of the photosensitive drum. The side view of a squeeze part. The perspective view of a squeeze part. 2 is a graph showing the operation of the image forming apparatus shown in FIG.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 1 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan), and 2K (for black) that form images of different colors. The image forming apparatus 1 includes a color mode in which four color toners of yellow (Y), magenta (M), cyan (C), and black (K) are overlapped to form a color image, and black (K). A monochrome mode in which a monochrome image is formed using only toner can be selectively executed.

  FIG. 2 is a schematic configuration diagram showing the configuration of the image forming station. FIG. 3 is a configuration diagram viewed from the rear side end and front side end of the photosensitive drum. Each of the image forming stations 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. Each photosensitive drum 21 is arranged such that its rotation shaft 21a is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 2). The rotating shaft 21a of each photosensitive drum 21 is connected to a drum driving motor M21 disposed at the front side end of the photosensitive drum 21, and the photosensitive drum 21 is at a predetermined speed in the direction of arrow D21 in FIG. Driven by rotation. In the present embodiment, the photosensitive drum 21 corresponds to the “image carrier” of the present invention.

  Around each photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential, and the surface of the photosensitive drum 21 is exposed in accordance with an image signal, thereby electrostatic latent images. An exposure unit 23 for forming the electrostatic latent image, a developing unit 24 for visualizing the electrostatic latent image as a toner image, a first squeeze unit 25, a second squeeze unit 26, and transferring the toner image to the intermediate transfer member 31 of the transfer unit 3. A transfer unit 27 for cleaning, a cleaning unit 28 for cleaning the surface of the photosensitive drum 21 after the transfer, and a cleaner blade 29 are arranged along the rotation direction D21 (clockwise in FIG. 2) of the photosensitive drum 21 in this order. It is installed.

  The charger 22 does not come into contact with the surface of the photosensitive drum 21, and a conventionally well-known and commonly used corona charger can be used as the charger 22. When a scorotron charger is used as the corona charger, a negative wire current flows through the charge wire of the scorotron charger and a direct current (DC) grid charging bias is applied to the grid. When the photosensitive drum 21 is charged by corona discharge by the charger 22, the surface potential of the photosensitive drum 21 is set to a substantially uniform potential.

  The exposure unit 23 exposes the surface of the photosensitive drum 21 with a light beam in accordance with an image signal given from an external device to form an electrostatic latent image corresponding to the image signal. The exposure unit 23 can be constituted by a light beam from a semiconductor laser scanned by a polycon mirror or a line head in which light emitting elements are arranged in the main scanning direction.

  Toner is applied from the developing unit 24 to the electrostatic latent image thus formed, and the electrostatic latent image is developed with the toner. The developing unit 24 of the image forming apparatus 1 includes a developing roller 241, a supply roller 242, a developer container 243 that stores a liquid developer in which toner is dispersed in a carrier liquid in an approximate weight ratio of about 20%, a developer The toner compression corona generator 244 that mainly charges and compresses the toner is mainly configured. Of these main components, the developing roller 241 is a cylindrical member, and is provided with an elastic layer such as polyurethane rubber, silicon rubber, NBR, or PFA tube on the outer peripheral portion of an inner core made of metal such as iron. The developing roller 241 is connected to a developing roller drive motor M241 disposed at the rear side end portion, and is rotated counterclockwise on the paper surface of FIG.

  Further, a supply roller 242 is provided to supply the liquid developer to the developing roller 241, and the liquid developer is directly supplied from the supply roller 242 to the developing roller 241. As described above, the supply roller 242 has a function of supplying the liquid developer to the developing roller 241. The supply roller 242 is a roller having a concave pattern formed by a spiral groove or the like engraved finely and uniformly on the surface so as to easily carry the liquid developer. Similar to the developing roller 241, a metal cored bar wrapped with a rubber layer such as urethane or NBR, or a PFA tube is used. Further, the supply roller 242 is connected to a supply roller drive motor M242 disposed at the front side end, and is rotated counterclockwise on the paper surface of FIG. As described above, the liquid developer is supplied from the developer storage unit 246 to the developing roller 241 with a so-called two-roller configuration. However, the present invention is not limited to this configuration. It is good also as a structure (3 roller structure) which apply | coats a liquid developer to the developing roller 241. FIG. According to such a three-roller configuration, the liquid developer passes through the nip portion a plurality of times, so that the liquid developer can be sufficiently kneaded, and a uniform liquid developer film is formed by the developing roller 241. It becomes possible.

  A regulating member 245 is in contact with the supply roller 242. As the restricting member 245, a metal or a member having elasticity formed by coating an elastic body on the surface can be used. However, the restricting member 245 according to the present embodiment is a urethane rubber that comes into contact with the surface of the supply roller 242. Etc., and a plate made of metal or the like that supports the rubber part. The regulating member 245 has a function of regulating and adjusting the film thickness and amount of the liquid developer carried and conveyed by the supply roller 242 and adjusting the amount of liquid developer supplied to the developing roller 241. . Further, the liquid developer scraped off by the regulating member 245 is returned to the developer storage unit 246.

  The liquid developer stored in the developer storage section 246 is volatile at room temperature at a low concentration (1 to 2 wt%) and low viscosity using Isopar (trademark: exon) as a carrier liquid, which is generally used conventionally. A solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a non-volatile resin having a high concentration and a high viscosity at room temperature instead of a volatile liquid developer having an organic solvent, silicon oil, mineral oil Alternatively, a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) added to a liquid solvent such as edible oil together with a dispersant and having a toner solid content concentration of about 20% is used.

  As described above, the developing roller 241 supplied with the liquid developer rotates so as to move in the direction opposite to the surface of the supply roller 242, and moves in the same direction as the surface of the photosensitive drum 21. Rotate. In order to form a toner image, the rotation direction of the developing roller 241 needs to rotate with the rotation so that the surface thereof moves in the same direction as the surface of the photosensitive drum 21, but for the supply roller 242, It may be configured to move in the opposite direction or the same direction.

  A toner compression corona generator 244 and a developing roller cleaning unit 247 are arranged along the rotation direction of the developing roller 241. More specifically, a toner compression corona generator 244 is arranged on the upstream side in the rotation direction of the developing roller with respect to the developing position where the surface of the developing roller 241 is in contact with the photosensitive drum 21 to form the developing nip portion. . The toner compression corona generator 244 is an electric field applying unit that increases the charging bias of the surface of the developing roller 241, and the toner of the liquid developer conveyed by the developing roller 241 is close to the toner compression corona generator 244. An electric field is applied at the position, and charging and compression are performed. For the toner charging and compression, a compaction roller that is charged by contact may be used instead of corona discharge by applying electrolysis.

  On the other hand, a developing roller cleaning unit 247 is disposed on the downstream side in the developing roller rotation direction with respect to the developing position, and the leading end thereof is in contact with the surface of the developing roller 241. The developing roller cleaning unit 247 is made of an elastic material such as rubber, and scrapes and removes the liquid developer remaining on the developing roller 241 without contributing to development. The liquid developer thus scraped off is dropped into the developer recovery unit 248 and recovered.

  A first squeeze portion 25 is disposed on the downstream side of the developing position in the rotation direction D <b> 21 of the photosensitive drum 21, and a second squeeze portion 26 is disposed on the downstream side of the first squeeze portion 25. These squeeze portions 25 and 26 are provided with squeeze rollers 251 and 261, respectively. Then, the squeeze roller 251 comes into contact with the surface of the photosensitive drum 21 at the first squeeze position P1 to remove excess developer in the toner image. Further, in the rotation direction D21 of the photosensitive drum 21, the squeeze roller 261 comes into contact with the surface of the photosensitive drum 21 at the second squeeze position P2 downstream of the first squeeze position P1, and excess carrier liquid and fog toner of the toner image are collected. Remove. The detailed configuration and operation of the squeeze units 25 and 26 will be described in detail later.

  The toner image that has passed the squeeze positions P 1 and P 2 is primarily transferred to the intermediate transfer member 31 by the transfer unit 27. The transfer unit 27 includes a backup roller 271, and the backup roller 271 is disposed to face the photosensitive drum 21 with the intermediate transfer member 31 sandwiched at the primary transfer position, and the toner image on the photosensitive drum 21. Is transferred to the intermediate transfer member 31. By transferring the toner image by the transfer unit 27 for each color, the toner images for each color on the photosensitive drum 21 are sequentially superimposed on the intermediate transfer member 31 to form a full-color toner image.

  In the present embodiment, in order to remove excess carrier liquid from the toner image transferred to the intermediate transfer member 31, an intermediate transfer member squeeze portion 32 is disposed downstream of the primary transfer position for each color. In the intermediate transfer body squeeze portion 32, an intermediate transfer body squeeze roller 321 is disposed on the toner image carrying surface side (lower surface side) of the intermediate transfer body 31, and the intermediate transfer body squeeze roller 321 is sandwiched between the intermediate transfer body 31. A backup roller 322 is disposed opposite to the toner image, and excess carrier liquid is removed from the toner image on the intermediate transfer member 31 by the intermediate transfer member squeeze roller 321. Further, the carrier liquid adhering to the intermediate transfer member squeeze roller 321 is scraped off by the intermediate transfer member squeeze roller cleaning unit 323.

  The toner image thus transferred to the intermediate transfer member 31 is conveyed to the secondary transfer unit 4 as shown in FIG. In the secondary transfer unit 4, a secondary transfer roller 41 is disposed to face the driving roller 33 of the transfer unit 3 with the intermediate transfer member 31 interposed therebetween. Then, at the secondary transfer position where the secondary transfer roller 41 is disposed, a single-color or multiple-color toner image formed on the intermediate transfer body 31 is conveyed on the sheet material conveyance path L, a sheet, a film, It is transferred to a recording material such as cloth. The secondary transfer unit 4 is provided with a secondary transfer roller cleaning unit 42 that removes the developer remaining on the secondary transfer roller 41, and the tip blade of the secondary transfer roller cleaning unit 42 is subjected to secondary transfer. The developer is scraped off in contact with the surface of the roller 41.

  Further, downstream of the sheet material conveyance path L, a fixing unit is provided for fixing the toner image of a single color or a plurality of colors transferred to a recording material such as paper by applying heat or pressure.

  Next, configurations and operations of the first squeeze unit 25 and the second squeeze unit 26 will be described with reference to the drawings. As shown in FIG. 2, the first squeeze portion 25 has, as its main components, a first squeeze roller 251, a first support member 252, a first rotation support shaft 253, a first pressure member 254, And a first squeeze roller cleaning unit 255. In the first squeeze portion 25, the center portion of the first support member 252 is pivotally supported by a first rotation support shaft 253 that extends substantially parallel to the rotation shaft 21 a of the photosensitive drum 21. The shaft 253 is provided so as to be rotatable about the rotation center. In this embodiment, in particular, the region where the first rotation support shaft 253 is deviated from the region R sandwiched between the first squeeze position P1 and the second squeeze position P2 to the side of the anti-photosensitive drum 21 (the left hand side in FIG. 2). Is arranged.

  In addition, the first squeeze roller 251 is rotatably attached to the end portion on the photosensitive drum 21 side (upper right side in FIG. 2) of both end portions of the first support member 252, while the anti-photosensitive drum 21 side (FIG. 2). The first pressure member 254 is connected to the end of the left hand side. The first squeeze roller 251 is a member formed by coating an elastic body on the surface of a metal core, and receives the driving force generated by the squeeze roller drive motor MSQ disposed at the front side end of the roller 251. Rotate. The configuration for rotationally driving the first squeeze roller 251 and the second squeeze roller 261 will be described in detail after the configuration of the first squeeze unit 25 and the second squeeze unit 26 is described.

  The first pressure member 254 is a member formed of an elastic body such as a spring or a spring, and applies an upward force F1 to the end of the first support member 252 on the side of the anti-photosensitive drum 21 by its elastic force. As a result, the first support member 252 rotates clockwise about the first rotation support shaft 253 in FIG. 2 as the rotation center, and the first squeeze roller 251 is moved to the surface of the photosensitive drum 21 at the first squeeze position P1. Abut. Therefore, the contact pressure of the first squeeze roller 251 against the photosensitive drum 21 can be adjusted to an appropriate value by appropriately setting the elastic force F1 generated by the first pressure member 254. In the present embodiment, the contact pressure is in the range of 0.01 to 1.0 [MPa].

  Further, the first squeeze roller 251 is rotated in the width direction with the photosensitive drum 21 by receiving a driving force from the squeeze roller driving motor MSQ as described later while being in contact with the surface of the photosensitive drum 21. That is, at the first squeeze position P1, the first squeeze roller 251 is rotationally driven so that the moving direction of the surface of the first squeeze roller 251 is the same as the moving direction of the surface of the photosensitive drum 12. With this roller rotation, excess developer such as fog toner and excess carrier liquid is collected from the toner image on the photosensitive drum 21. Since the diameter of the first squeeze roller 251 and the thickness of the coated elastic body are smaller than those of the developing roller 241, the nip width with respect to the photosensitive drum 21 is smaller than the developing nip width. Further, the moving speed of the surface of the first squeeze roller 251, that is, the circumferential speed V25 of the roller 251 is slightly lower than the moving speed of the surface of the photosensitive drum 21, that is, the circumferential speed V21 of the photosensitive drum 21. It is configured. For this reason, the vibration of the photosensitive drum 21 at the first squeeze position P1 is effectively suppressed.

  Furthermore, the tip blade of the first squeeze roller cleaning unit 255 is in contact with the surface of the first squeeze roller 251 in order to scrape off the excess developer collected as described above from the first squeeze roller 251.

  The second squeeze portion 26 is disposed on the downstream side of the first squeeze portion 25 in the rotation direction D21 of the photosensitive drum 21, and the second squeeze roller 261 properly contacts the surface of the photosensitive drum 21 at the second squeeze position P2. The basic configuration is the same as that of the first squeeze portion 25 although the contact is made by pressure. However, since the friction force acting at the second squeeze position P2 is larger than the friction force at the first squeeze position P1 due to the following factors, in this embodiment, the moving speed of the surface of the squeeze roller 261, that is, the roller 261 The peripheral speed V26 is controlled to be the same as or substantially the same as the peripheral speed V21 of the photosensitive drum 21.

  The reason why the friction force acting at the second squeeze position P2 is larger than the friction force at the first squeeze position P1 is that the second squeeze position P2 is located downstream of the first squeeze position P1 in the rotation direction D21 of the photosensitive drum 21. This is because the excess carrier liquid is removed from the toner image on the photosensitive drum 21 in the order of the first squeeze roller 251 and the second squeeze roller 261. That is, since the toner image at the second squeeze position P2 is in a state where the carrier liquid is less and the solid content is richer than the toner image at the first squeeze position P1, the toner image at the second squeeze position P2 is The acting friction force is larger than the friction force at the first squeeze position P1. Therefore, a relatively large frictional force exists between the photosensitive drum 21 and the second squeeze roller 261 at the second squeeze position P2, and the peripheral speeds V21 and V26 of the two are different from each other in this state. Then, the second squeeze roller 261 disturbs the peripheral speed V21 of the photosensitive drum 21, that is, the process speed, leading to a decrease in image quality. Therefore, in this embodiment, the moving direction and moving speed of the surfaces of the first squeeze roller 251 and the second squeeze roller 261 with respect to the photosensitive drum 21 are controlled as described below.

  Next, a configuration for rotating the first squeeze roller 251 and the second squeeze roller 261 configured as described above will be described with reference to FIGS. 4 and 5. 4 is a side view of the squeeze portion, and FIG. 5 is a perspective view of the squeeze portion. In the present embodiment, a squeeze roller drive motor MSQ is provided as a drive source for rotating both rollers 251 and 261. A drive gear 51 is attached to a rotation shaft (not shown) of the squeeze roller drive motor MSQ, and an idle gear 52 is engaged with the drive gear 51. The squeeze roller drive motor MSQ, the drive gear 51 and the idle gear 52 are integrally provided to form the drive unit 5. The drive unit 5 can be attached to the apparatus main body at the front side end portions (lower left end portion in FIG. 5) of the first squeeze portion 25 and the second squeeze portion 26.

  Further, the first power transmission mechanism 6 and the second power transmission mechanism 7 are fixedly disposed at front side end portions of the first squeeze portion 25 and the second squeeze portion 26. When the drive unit 5 is attached to the apparatus main body, the intermediate gear 61 of the first power transmission mechanism 6 is connected to the idle gear 52 and the intermediate of the second power transmission mechanism 7 to the drive gear 51. A gear 71 is connected. The intermediate gear 61 of the first power transmission mechanism 6 may be connected to the drive gear 51, and the intermediate gear 71 of the second power transmission mechanism 7 may be connected to the idle gear 52. Good.

  The first power transmission mechanism 6 is a transmission mechanism that transmits the driving force generated by the squeeze roller drive motor MSQ to the first squeeze roller 251 to rotate the first squeeze roller 251. In the first power transmission mechanism 6, an intermediate gear 61 and a drive gear 63 are rotatably attached to a gear support plate 62 disposed at the front side end of the first squeeze portion 25. Among these, the intermediate gear 61 is engaged with and connected to the idle gear 52 of the drive unit 5 mounted on the apparatus main body as described above. Further, the drive gear 63 meshes with the intermediate gear 61 in a state of being attached coaxially with the rotation shaft of the first squeeze roller 251. Therefore, the driving force generated by the squeeze roller drive motor MSQ is transmitted to the first squeeze roller 251 via the drive gear 51, the idle gear 52, the intermediate gear 61 and the drive gear 63, and the first squeeze roller 251 is shown in FIG. It rotates counterclockwise on the paper surface and rotates with respect to the photosensitive drum 21. That is, the surface of the first squeeze roller 251 moves in the same direction as the movement direction of the surface of the photosensitive drum 21 at the first squeeze position P1.

  The second power transmission mechanism 7 is a transmission mechanism that transmits the driving force generated by the squeeze roller drive motor MSQ to the second squeeze roller 261 to rotate the second squeeze roller 261. In the second power transmission mechanism 7, the intermediate gear 71, the intermediate gear 73, and the drive gear 74 are rotatably attached to the gear support plate 72 disposed at the front side end of the second squeeze portion 26. Among these, the intermediate gear 71 is engaged and connected to the drive gear 51 of the drive unit 5 mounted on the apparatus main body as described above. The drive gear 74 is mounted coaxially with the rotation shaft of the second squeeze roller 261 via the one-way clutch 76, and meshes with the intermediate gear 73 in this mounted state. Further, the intermediate gears 71 and 73 mesh with each other. Therefore, the driving force generated by the squeeze roller drive motor MSQ is transmitted to the second squeeze roller 261 via the drive gear 51, the intermediate gears 71 and 73, and the drive gear 74, and the second squeeze roller 261 rotates. However, in this embodiment, the one-way clutch 76 is provided on the transmission path of the driving force to the second squeeze roller 261, and the transmission of the driving force to the second squeeze roller 261 is cut off under the switching condition described below. To do. Thus, in the present embodiment, the second power transmission mechanism 7 corresponds to the “power transmission means” of the present invention, and the one-way clutch 76 functions as the “power switching member” of the present invention. Hereinafter, the operation of the first squeeze roller 251 and the second squeeze roller 261 will be described with reference to FIG.

  FIG. 6 is a graph showing changes in the speed of the squeeze roller. In this embodiment, when image formation is performed, a motor drive command is given to the drum drive motor M21 from a control unit (not shown) that controls the entire apparatus, and the peripheral speed of the photosensitive drum 21 takes a predetermined time. After reaching a certain value V21, image formation is performed while maintaining the peripheral speed V21. Meanwhile, the squeeze roller drive motor MSQ is also given a motor drive command from the control unit at the same time, and the squeeze roller drive motor MSQ is activated to transmit the drive force toward the first squeeze roller 251 and the second squeeze roller 261. The In this embodiment, the driving of the drum driving motor M21 and the squeeze roller driving motor MSQ is started at the same time, but the driving timing is not limited to this as long as the effects described below are achieved.

  For the first squeeze roller 251, the driving force generated by the squeeze roller drive motor MSQ is transmitted as it is through the first power transmission mechanism 6, and the first squeeze roller 251 is driven regardless of the operation state of the photosensitive drum 21. The peripheral speed is accelerated to a constant value V25 over a predetermined motor acceleration period, and then maintained at the peripheral speed V25. In this embodiment, the squeeze roller driving is performed so that the peripheral speed difference Δ (= V21−V25) of the peripheral speed V25 with respect to the peripheral speed V21 of the photosensitive drum 21 is about 0% to 1% or less of the peripheral speed V21. The rotation speed of the motor MSQ, the gear ratio of the gears constituting the first power transmission mechanism 6 and the like are set. For this reason, after the motor acceleration period has elapsed, that is, when image formation is performed, the surface of the first squeeze roller 251 rotates with respect to the photosensitive drum 21, and the peripheral speed V25 of the first squeeze roller 251 is equal to the photosensitive drum. Thus, the vibration of the photosensitive drum 21 at the first squeeze position P1 is effectively suppressed.

  On the other hand, the driving force generated by the squeeze roller drive motor MSQ is also transmitted to the second squeeze roller 261 via the second power transmission mechanism 7. The second power transmission mechanism 7 is provided with a one-way clutch 76. Therefore, transmission and interruption of the driving force to the second squeeze roller 261 are switched according to the operation state of the photosensitive drum 21. That is, while the peripheral speed of the second squeeze roller 261 is equal to or higher than the peripheral speed of the photosensitive drum 21 during the motor acceleration period, the one-way clutch 76 transmits the driving force to the second squeeze roller 261 to transmit the first squeeze roller 251. Similarly, the peripheral speed of the second squeeze roller 261 is accelerated to a constant value V25 over the motor acceleration period. Further, for example, when the peripheral speed of the photosensitive drum 21 exceeds the peripheral speed V25 at the time when the motor acceleration period has elapsed or after that, the one-way clutch 76 cuts off the transmission of the driving force. As described above, in the present embodiment, the one-way clutch 76 satisfies the switching condition that the peripheral speed of the second squeeze roller 261 driven by the driving force is slower than the peripheral speed of the photosensitive drum 21. The transmission of the driving force is cut off, and the second squeeze roller 261 is driven and rotated by the photosensitive drum 21. Accordingly, during image formation by driving the photosensitive drum 21 at the circumferential speed V21, the second squeeze roller 261 rotates at the same or substantially the same circumferential speed V26 as the circumferential speed V21 of the photosensitive drum 21. As a result, the peripheral speed of the photosensitive drum 21, that is, the process speed can be effectively prevented from being disturbed at the second squeeze position P2, and a high-quality image can be formed.

  In the present embodiment, the drive connecting portion of the first power transmission mechanism 6 with respect to the drive unit 5, that is, the meshing portion 64 in which the idle gear 52 and the intermediate gear 61 mesh with each other, is the first rotation support shaft 253. It is comprised so that it may be located on. For this reason, the driving reaction force generated when the first squeeze roller 251 is rotationally driven is invalidated, and the first squeeze roller 251 can be stably rotated. Further, with respect to the second power transmission mechanism 7, the drive connecting portion with respect to the drive unit 5, that is, the meshing portion 75 where the drive gear 51 and the intermediate gear 71 are engaged with each other is positioned on the second rotation support shaft 263. Is configured to do. For this reason, the driving reaction force generated when the second squeeze roller 261 is rotationally driven is also invalidated, and the second squeeze roller 261 can be stably rotated.

  As described above, according to the present embodiment, the movement direction of the surface of the first squeeze roller 251 is the same as the movement direction of the surface of the photosensitive drum 21 at the first squeeze position P1, and the first squeeze roller 251 By controlling the peripheral speed V25 within 99% of the peripheral speed V21 of the photosensitive drum 21, it is possible to effectively prevent the photosensitive drum 21 from vibrating at the first squeeze position P1. Further, the movement direction of the surface of the second squeeze roller 261 is made to coincide with the movement direction of the surface of the photosensitive drum 21 at the second squeeze position P2, and the peripheral speed V26 of the second squeeze roller 261 is set to the peripheral speed of the photosensitive drum 21. Since it is controlled to be the same or substantially the same as V21, it is possible to prevent the peripheral speed V21 of the photosensitive drum 21 from being disturbed at the second squeeze position P2, and as a result, a high-quality image can be formed. .

  Further, the first rotation support shaft 253 and the second rotation support shaft 263 are provided in a region that is separated from the region R sandwiched between the first squeeze roller 251 and the second squeeze roller 261 toward the anti-photosensitive drum 21 side. Therefore, the first squeeze position P1 and the second squeeze position P2 can be adjacent to each other. That is, the second squeeze roller 261 can be disposed close to the downstream side of the first squeeze roller 251 in the rotation direction D21 of the photosensitive drum 21, and the distance between the squeeze rollers 251 and 261 can be shortened.

  In addition, since the squeeze roller drive motor MSQ is used as a common drive source for rotating the first squeeze roller 251 and the second squeeze roller 261, the configuration of the apparatus can be simplified and economical. In addition, as described above, since the drive connecting portions are arranged on the first rotation support shaft 253 and the second rotation support shaft 263, the squeeze rollers 251 and 261 can be stably rotated. In order to invalidate the driving reaction force when the first squeeze roller 251 is rotated, one of the meshing portions of the driving gear 51, the idle gear 52, the intermediate gear 61, and the driving gear 63 is used for the first time. What is necessary is just to comprise so that it may be located on the dynamic support shaft 253. FIG. Further, in order to invalidate the driving reaction force when the second squeeze roller 261 is rotated, one of the meshing portions of the driving gear 51, the intermediate gears 71 and 73, and the driving gear 74 is used as the second rotational support. What is necessary is just to comprise so that it may be located on the axis | shaft 263. FIG.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the first power transmission mechanism 6 is composed of the two gears 61 and 63, and the second power transmission mechanism 7 is composed of the three gears 71, 73, and 74. The above is not limited to the above embodiment.

  In the above embodiment, the present invention is applied to the image forming apparatus provided with the two squeeze portions 25 and 26. However, the application target of the present invention is not limited to this, and three or more squeeze portions are used. By applying the present invention also to an image forming apparatus in which the portion is arranged along the rotation direction of an image carrier such as a photosensitive drum, the same effect as that of the above embodiment can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 5 ... Drive unit, 7 ... 2nd power transmission mechanism (power transmission means), 21 ... Photosensitive drum (image carrier), 21a ... (Rotating shaft of photosensitive drum), 76 ... One-way clutch (Power switching member), 251 ... first squeeze roller, 261 ... second squeeze roller, D21 ... rotation direction of (photosensitive drum), MSQ ... squeeze roller drive motor (drive source), P1 ... first squeeze position, P2 ... second squeeze position, V21 ... peripheral speed (of photosensitive drum), V25 ... peripheral speed (of first squeeze roller), V26 ... peripheral speed (of second squeeze roller)

Claims (6)

An image carrier that carries an image and rotates;
A first squeeze roller that contacts the image carrier at a first squeeze position and moves in the same direction as the movement direction of the image carrier, and squeezes the image carrier;
A second squeeze position of the image carrier squeezed by the first squeeze roller contacts the image carrier and moves in the same direction as the moving direction of the image carrier, and squeezes the image carrier. 2 squeeze rollers,
The moving speed of the first squeeze roller is slower than the moving speed of the image carrier,
The moving speed of the second squeeze roller is the same as or substantially the same as the moving speed of the image carrier. A drive unit having a drive source for generating a drive force;
A power transmission unit coupled to the drive unit to transmit the driving force to the second squeeze roller to rotate the second squeeze roller;
The power transmission unit includes a power switching member that switches between transmission and interruption of the driving force to the second squeeze roller, and the moving speed of the second squeeze roller driven by the driving force is the speed of the image carrier. 2. The image formation according to claim 1, wherein when the moving speed is slower, the power switching member interrupts transmission of the driving force to the second squeeze roller and causes the second squeeze roller to be driven to rotate by the image carrier. apparatus.   The image forming apparatus according to claim 2, wherein the power switching member is a one-way clutch.   4. The image forming apparatus according to claim 2, further comprising a second drive transmission unit configured to transmit the driving force to the first squeeze roller to rotate the first squeeze roller.   5. The image forming apparatus according to claim 1, wherein the moving speed of the first squeeze roller is a moving speed that is 99% or more and less than 100% of the moving speed of the image carrier. 6. The moving direction of the first squeeze roller is the same as the moving direction of the image carrier while the first squeeze roller is brought into contact with the image carrier that rotates while carrying an image at the first squeeze position. A first squeeze step of rotating a squeeze roller to squeeze the image carrier;
At the second squeeze position of the image carrier squeezed by the first squeeze roller, the second squeeze roller moves in the second squeeze position while the second squeeze roller is in contact with the image carrier. A second squeeze step of squeezing the image carrier by rotating the second squeeze roller in the same direction as the moving direction,
The moving speed of the first squeeze roller in the first squeeze step is slower than the moving speed of the image carrier,
The image forming method according to claim 1, wherein a moving speed of the second squeeze roller in the second squeezing step is the same or substantially the same as a moving speed of the image carrier.

Images