JP2005025038A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of outputting an image with good stability without any unevenness in pitch when outputting a half toner image or a text image such as a photograph or graphics. <P>SOLUTION: The typical image forming apparatus of the present invention is provided with an image carrier to carry a toner image and a transfer roll to be brought into press-contact with the image carrier.The image carrier and the transfer roll are driven by one driving source. A driving transmission path to the image carrier is made different from that to the transfer roll. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system such as a copying machine, a laser beam printer, or a facsimile.
[0002]
BACKGROUND OF THE INVENTION
As an image forming apparatus (laser beam printer) that forms an image by a conventional electrophotographic method, the sheet material S is conveyed to the image forming means by the feeding and conveying means to transfer the toner image, and is conveyed to the fixing means to be fixed by toner. However, there is one that discharges to a discharge unit (see, for example, Patent Document 1).
[0003]
An outline of such an image forming apparatus will be described below with reference to FIGS. 8 is a configuration diagram of the image forming apparatus, FIG. 9 is a sectional view showing a drive transmission path of the image forming unit, FIG. 10 is a perspective view showing a drive transmission path of the image forming unit, and FIG. 11 is a drive transmission unit to the transfer roller. FIG.
[0004]
First, a schematic configuration of the image forming apparatus will be described along the flow of the sheet material S. As shown in FIG. 8, the sheet material S stacked and stored in the cassette 311 in the sheet material feeding unit 201 at the lower part of the apparatus is sequentially fed from the uppermost sheet by the feeding roller 312 that rotates counterclockwise. It is fed out and sent to the image forming unit 201 by a pair of conveying rollers 313 and 314. In the image forming unit 201, the laser scanner 321 irradiates laser light corresponding to the image information onto the photoconductor 322 rotating in the clockwise direction, and an electrostatic latent image is formed on the photoconductor 322. This electrostatic latent image is developed with toner by a developing unit (not shown) in the process cartridge 323 to form a toner image. The sheet material S is transferred with the toner image by the image forming unit 201, fixed with the toner image by the fixing unit 203, and discharged to the outside of the apparatus by the discharge conveyance roller pair 333. An electrical component 204 having a power supply unit of the apparatus and a control board that controls the apparatus is formed between the cassette 311 and the image forming unit 201.
[0005]
Next, front and back double-sided recording of the sheet material S will be described. When recording is performed on both sides of the sheet material S, the sheet material S that has passed through the fixing unit 203 and has an image recorded on the front side is switched back by the reverse rotation drive of the discharge conveyance roller pair 333 and the conveyance roller 331 and conveyed. The sheet is conveyed to the image forming unit 201 by the roller pair 341 and 342, image recording is performed on the back side of the sheet material S, and the sheet is discharged out of the apparatus as described above.
[0006]
Next, drive transmission and an image forming process in the image forming unit will be described in detail. As shown in FIGS. 9 and 10, the driving force generated by the motor M is transmitted to the coupling gear 303 via the motor pinion 301 and the idler gear 302. The coupling gear 303 is coupled by a coupling portion 305a of the photoconductor gear 305, and the photoconductor gear 305 is caulked to the photoconductor 322 by a gear portion 305b. The gear portion 305 b meshes with the transfer roller gear 307, and the transfer roller gear 307 is fixed on the rotation shaft of the transfer roller 324.
[0007]
The driving force transmitted to the coupling gear 303 is transmitted to the photoconductor 322 via the photoconductor gear 305, and is transmitted to the transfer roller 324 via the photoconductor gear 305 (gear portion 305 b) and the transfer roller gear 307. Both ends of the transfer roller 324 are supported by bearings 309 and pressed toward the center of the photoconductor 322 by a transfer spring (compression spring) 308, and the transfer roller 324 is urged by the photoconductor 322.
[0008]
As shown in FIG. 11A, when the process cartridge 323 is not attached, the transfer roller 324 is positioned slightly closer to the photosensitive member 322 than the predetermined position shown in FIG.
[0009]
As shown in FIG. 11B, when the process cartridge 323 is mounted, the photoconductor 322 pushes down the transfer roller 324 so that the transfer roller 324 is in a predetermined position. At this time, the gear portion 305b of the photoconductor gear 305 and the transfer roller gear 307 are engaged, and the gear portion 305b and the transfer roller gear 307 do not escape from each other.
[0010]
As shown in FIG. 11C, since the sheet material S is sandwiched between the photosensitive member 322 and the transfer roller 324 when the sheet material S is conveyed, the transfer roller 324 is more than the predetermined position shown in FIG. The sheet material S is lowered by the thickness. The transfer roller gear 307 receives the driving gear reaction force F from the photoconductor gear 305 in the meshing pressure angle α direction. The backlash between the gear portion 305b of the photoconductor gear 305 and the transfer roller gear 307 varies depending on the thickness of the sheet material S, the driving gear reaction force F, and the like when the sheet material S is conveyed. Therefore, the backlash value at a predetermined position where the sheet material S is not conveyed is set so that the drive transmission from the photoconductor gear 305 to the transfer roller gear 307 is possible even when the sheet material S is conveyed.
[0011]
Moreover, in such an image forming apparatus, with the recent increase in accuracy of image forming apparatuses and diversification of users, elimination of pitch unevenness and higher image quality when outputting halftone images such as photographs and graphic hooks and text images. The demand for is high.
[0012]
[Patent Document 1]
Japanese Patent Laid-Open No. 09-297473
[Problems to be solved by the invention]
However, in the conventional image forming apparatus, the torque of the transfer roller 324 changes depending on the image to be transferred, and the magnitude of the driving gear reaction force F changes. Further, the backlash changes due to a change in the thickness of the sheet material S and the like, and the meshing pressure angle α (direction of the driving gear reaction force F) changes.
[0014]
As described above, the photoconductor 322 is driven by the coupling gear 303 via the photoconductor gear 305 and is transmitted to the transfer roller gear 307. As a result, when the photosensitive member 322 is rotated, vibration is generated due to the engagement between the gear portion 305b of the photosensitive member gear 305 and the transfer roller gear 307, and the photosensitive member 322 also vibrates at this frequency. Further, the gear tooth surface is damaged due to the contact between the gear portion 305b and the transfer roller gear 307 when the process cartridge 323 is mounted, and the teeth are climbed up, which promotes vibration during gear engagement.
[0015]
Then, laser light is irradiated onto the vibrating photoconductor 322 by the laser scanner 321 to form an electrostatic latent image. For this reason, pitch unevenness of a certain frequency occurs in the electrostatic latent image, and pitch unevenness exists in the image on the sheet material on which the image is formed. Further, the balance in the axial direction of the contact pressure of the transfer roller 324 against the photosensitive member 322 changes due to the change in the backlash and the change in the driving gear reaction force F, which adversely affects the stability of the image.
[0016]
As a result, when a halftone image such as a photograph or a graphic hook or a text image is output, there is a problem that pitch unevenness is present on the image or the stability of the image is poor.
[0017]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can output a stable image without pitch unevenness when outputting a halftone image such as a photograph or a graphic hook or a text image.
[0018]
[Means for Solving the Problems]
In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image, and a transfer roller that presses the image carrier, and the image carrier and the image carrier. In the image forming apparatus having the same drive source for driving the transfer roller, the drive transmission path to the image carrier and the drive transmission path to the transfer roller are different paths.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
[First embodiment]
A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an image forming apparatus according to the first embodiment.
[0020]
First, a schematic configuration of the image forming apparatus will be described along the flow of the sheet material S. As shown in FIG. 1, the sheet material S stacked and stored in the cassette 111 in the sheet material feeding unit 1 at the lower part of the apparatus is sequentially fed from the uppermost sheet by a feeding roller 112 that rotates counterclockwise. The paper is fed out and sent to the image forming unit 2 by a pair of conveyance rollers 113 and 114. In the image forming unit 2, the laser scanner 121 irradiates laser light corresponding to image information onto the photoconductor 122 rotating in the clockwise direction, and an electrostatic latent image is formed on the photoconductor 122. This electrostatic latent image is developed with toner by a developing unit (not shown) in the process cartridge 123 to form a toner image. The sheet material S is transferred with the toner image by the image forming unit 2, fixed with the toner image by the fixing unit 3, and discharged to the outside of the apparatus by the discharge conveyance roller pair 133. An electrical component 4 having a power supply unit of the apparatus and a control board for controlling the apparatus is formed between the cassette 111 and the image forming unit 2.
[0021]
Next, front and back double-sided recording of the sheet material S will be described. When recording is performed on both sides of the sheet material S, the sheet material S that has passed through the fixing unit 3 and is recorded on the front side is switched back by the reverse rotation driving of the discharge conveyance roller pair 133 and the conveyance roller 131, and conveyed. The pair of rollers 141 and 142 is conveyed to the image forming unit 2 to record an image on the back side of the sheet material S, and is discharged out of the apparatus as described above.
[0022]
Next, drive transmission and an image forming process in the image forming unit will be described in detail. 2 is a schematic sectional view showing a drive transmission path of the image forming unit, FIG. 3 is a perspective view showing a drive transmission path of the image forming unit, and FIG. 4 is a detailed view of the drive transmission unit to the transfer roller.
[0023]
As shown in FIGS. 2 and 3, the configuration in the present embodiment is a configuration in which the driving force of the feeding unit, the conveyance unit, the image forming unit, the fixing unit, and the discharging unit of the apparatus is driven by a single motor M. ing. The driving force generated from the motor M is divided into a transmission path (not shown) of the fixing / discharging system from the motor pinion 101 and a transmission path of the feeding unit, the conveying unit, and the image forming unit, and the driving is transmitted to each path.
[0024]
In the transmission path of the feeding unit, the conveyance unit, and the image forming unit, an idler gear 11 is disposed at a position that meshes with the motor pinion 101 for driving transmission.
[0025]
In the drive transmission path to the photoconductor 122, the driving force generated by the motor M is transmitted to the photoconductor 122 via the motor pinion 101, the idler gear 11, and the coupling gear 103. The idler gear 11 meshes with the coupling gear 103, and the coupling gear 103 is coupled to the coupling portion 105 a of the photoconductor gear 105.
[0026]
In the drive transmission path to the transfer roller 124, the driving force generated by the motor M is transmitted through the idler gear 11, the reduction gear 12, the idler gears 13, 14, the clutch 15, the idler gear 16, the reduction gear 17, the idler gear 18, and the transfer roller gear 107. The drive is transmitted to 124. In addition to the drive transmission, the drive transmission is transmitted from the idler gear 14 to the feeding system, and the drive transmission is transmitted from the clutch 15 to the transport system.
[0027]
The transfer roller gear 107 is fixed on the rotation shaft of the transfer roller 124. Both ends of the transfer roller 124 are supported by bearings 109 and pressed toward the center of the photoconductor 122 by a transfer spring (compression spring) 108, and the transfer roller 124 is urged by the photoconductor 122.
[0028]
As shown in FIG. 2, the idler gear 18 is perpendicular to the straight line L1 connecting the center points of the photoconductor 122 and the transfer roller 124 on the cross section orthogonal to the central axes of the photoconductor 122 and the transfer roller 124. It arrange | positions on the straight line L2 which passes along the approximate center. The backlash between the idler gear 18 and the transfer roller gear 107 is set to be optimal when the transfer roller 124 is at the predetermined position shown in FIG. 4B or slightly lower than the predetermined position.
[0029]
Next, functions in the drive transmission configuration will be described. At the time of driving transmission to the photoconductor 122, the driving force generated by the motor M is transmitted from the coupling gear 103 to the photoconductor gear 105 by the coupling gear 103 and the coupling portions 103 a and 105 a of the photoconductor gear 105. On the other hand, the drive transmission to the transfer roller 124 is transmitted to the transfer roller 124 through a path (path of the reduction gear 12) different from the path to the photoconductor 122 branched from the idler 11.
[0030]
Accordingly, when the drive is transmitted to the photosensitive member 122, since the drive is not transmitted from the gear portion 305b (see FIG. 10) of the photosensitive member gear 305 to the transfer roller 124 as in the conventional image forming apparatus, the gear portion 305b. And vibration due to the meshing of the transfer roller gear 107 does not occur. Further, since the gear portion 305b and the transfer roller gear 107 do not mesh with each other, when the process cartridge 123 is mounted, the tooth portion of the gear portion 305b and the transfer roller gear 107 does not come into contact with each other. As a result, when the laser beam is applied to the photoconductor 122 by the laser scanner 121 according to the image information and an electrostatic latent image is formed, there is no pitch unevenness and a stable image can be output.
[0031]
Further, as shown in FIG. 4A, before the process cartridge 123 is inserted, the transfer roller 124 is located slightly above the predetermined position shown in FIG. 4B. As shown in FIG. 4B, when the process cartridge 123 is mounted, the photoconductor 122 pushes down the transfer roller 124, so that the transfer roller 124 is positioned at a predetermined position. As shown in FIG. 4C, when the sheet material S is conveyed, the sheet material S is held between the photosensitive member 122 and the transfer roller 124, and the transfer roller 124 is lowered by the thickness of the sheet material S.
[0032]
Here, as described above, the idler gear 18 is disposed on a straight line L2 that is perpendicular to the straight line L1 that connects the respective center points of the photosensitive member 122 and the transfer roller 124 and passes through the approximate center of the transfer roller 124. For this reason, when the sheet material S is conveyed, the positions of the transfer roller 124 and the transfer roller gear 107 change on a straight line L1 connecting the center points of the photosensitive member 122 and the transfer roller 124 depending on the thickness of the sheet material S.
[0033]
Since the idler gear 18 is on a straight line L2 perpendicular to the moving direction (L1 direction) of the transfer roller gear 107, the backlash between the idler 18 and the transfer roller gear 107 hardly changes. Regardless of the type of sheet material S, the meshing pressure angle α between the idler gear 18 and the transfer roller gear 107 is substantially the same, and the drive gear reaction force F to the transfer roller 124 is kept substantially constant. As a result, the axial balance of the contact pressure applied from the transfer roller 124 to the photosensitive member 122 is kept substantially constant, and transfer and conveyance to a stable sheet material can be performed, and the stability of the image is improved.
[0034]
[Second Embodiment]
Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. 5 is a cross-sectional view showing the drive transmission path of the image forming unit, FIG. 6 is a perspective view showing the drive transmission path of the image forming unit, and FIG. 7 is a detailed view of the drive transmission unit to the transfer roller. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
[0035]
The drive transmission and image forming process in the image forming unit will be described in detail. As shown in FIGS. 5 and 6, the configuration in the present embodiment is configured to drive the driving force of the feeding unit, the conveyance unit, and the image forming unit of the apparatus by a single motor M.
[0036]
The driving force generated from the motor M is divided into two transmission paths: a transmission path from the motor pinion 101 to the photosensitive member 122 and a transmission path to the feeding unit, the transport unit, and the transfer unit. In the transmission path to the photoreceptor 122, the motor pinion 101 meshes with the coupling gear 103, and the coupling gear 103 is coupled to the coupling portion 105 a of the photoreceptor gear 105.
[0037]
A reduction gear 21 is disposed at a position where the motor pinion 101 meshes with the transmission path to the feeding unit, the conveyance unit, and the transfer unit. From the reduction gear 21, it is transmitted to the feeding system and the conveying system via the reduction gear 22 and idler gears 23 to 28. The idler gear 28 meshes with the transport roller gear 29 and transmits the driving force to the transport roller pair 114. An idler gear 30 is disposed at the other end of the conveying roller pair 114 for transmission to the transfer roller gear 107, and is transmitted to the transfer roller 124 via the idler gears 30 to 33 and the transfer roller gear 107.
[0038]
The idler gear 33 is disposed at a position where the driving gear reaction force F applied to the transfer roller gear 107 works in a substantially vertical direction (arrow direction: see FIG. 7) to a straight line L1 connecting the centers of the photoconductor 122 and the transfer roller 124. The backlash is set so that the backlash does not disappear when the sheet material S shown in FIG.
[0039]
Next, functions in the drive transmission configuration will be described. At the time of driving transmission to the photoconductor 122, the driving force generated by the motor M is transmitted from the coupling gear 103 to the photoconductor gear 105 by the coupling gear 103 and the coupling portions 103 a and 105 a of the photoconductor gear 105. On the other hand, the drive transmission to the transfer roller 124 is transmitted to the transfer roller 124 through a path different from the path to the photoconductor 122 branched from the motor pinion 101 (the path of the reduction gear 21 to the idler gear 33).
[0040]
Accordingly, when the drive is transmitted to the photosensitive member 122, the drive is not transmitted from the photosensitive member gear 105 to the transfer roller 124 as in the conventional image forming apparatus. Therefore, the gear portion 305b (see FIG. 10) and the transfer roller gear 107 are connected. Vibration due to meshing does not occur. Further, since the gear portion 305b and the transfer roller gear 107 do not mesh with each other, when the process cartridge 123 is mounted, the tooth portion of the gear portion 305b and the transfer roller gear 107 does not come into contact with each other. As a result, when the laser beam is applied to the photoconductor 122 by the laser scanner 121 according to the image information and an electrostatic latent image is formed, there is no pitch unevenness and a stable image can be output.
[0041]
Further, as shown in FIG. 7A, before the process cartridge 123 is inserted, the transfer roller 124 is located slightly above the predetermined position shown in FIG. 7B. As shown in FIG. 7B, when the process cartridge 123 is mounted, the photoconductor 122 pushes down the transfer roller 124, so that the transfer roller 124 is positioned at a predetermined position. As shown in FIG. 7C, when the sheet material S is conveyed, the sheet material S is held between the photosensitive member 122 and the transfer roller 124, and the transfer roller 124 is lowered by the thickness of the sheet material S.
[0042]
When the sheet material S is conveyed, the torque of the transfer roller 124 changes depending on the image to be transferred, and the driving gear reaction force F changes. However, the driving gear reaction force F is applied in a direction substantially perpendicular to the direction of contact pressure applied from the transfer roller 124 to the photosensitive member 122 (direction of the straight line L1). For this reason, when the sheet material S is conveyed, the contact pressure applied from the transfer roller 124 to the photosensitive member 122 does not change due to the change in the driving gear reaction force F depending on the type of the sheet material S and the image to be transferred. The balance in the axial direction of the pressure is kept almost constant, so that stable transfer and conveyance to the sheet material S can be performed, and a stable image can be output.
[0043]
In the above-described embodiment, the laser beam printer is exemplified as the image forming apparatus. However, the configuration according to the present invention can be applied to other image forming apparatuses such as a facsimile or a copying machine having an image carrier and a transfer roller.
[0044]
【The invention's effect】
As described above, by configuring the drive transmission path to the image carrier and the drive transmission path to the transfer roller as separate paths, it is possible to output a stable image without pitch unevenness.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment.
FIG. 2 is a cross-sectional view illustrating a drive transmission path of an image forming unit.
FIG. 3 is a perspective view illustrating a drive transmission path of an image forming unit.
FIG. 4 is a detailed view of a drive transmission unit to a transfer roller.
FIG. 5 is a cross-sectional view showing a drive transmission path of an image forming unit according to a second embodiment.
FIG. 6 is a perspective view illustrating a drive transmission path of the image forming unit.
FIG. 7 is a detailed view of a drive transmission unit to a transfer roller.
FIG. 8 is a configuration diagram of a conventional image forming apparatus.
FIG. 9 is a cross-sectional view showing a drive transmission path of a conventional image forming unit.
FIG. 10 is a perspective view illustrating a drive transmission path of a conventional image forming unit.
FIG. 11 is a detailed view of a drive transmission unit to a conventional transfer roller.
[Explanation of symbols]
F: Driving gear reaction force L1, L2 ... Straight line M ... Motor S ... Sheet material 1 ... Sheet material feeding unit 2 ... Image forming unit 3 ... Fixing unit 4 ... Electrical components 11-14, 16, 18, 23-28, 30-33 ... idler gears 12, 17, 21, 22 ... reduction gear 15 ... clutch 29 ... transport roller gear 101 ... motor pinion 103 ... coupling gear 103a ... coupling part 105 ... photoconductor gear 105a ... coupling part 107 ... transfer roller gear 111 ... cassette 112 ... feeding rollers 113 and 114 ... transport roller pair 121 ... laser scanner 122 ... photoconductor 123 ... process cartridge 124 ... transfer rollers 131, 141, 142 ... transport roller pair 133 ... discharge transport roller pair

Claims (3)

In an image forming apparatus comprising: an image carrier that carries a toner image; and a transfer roller that is in pressure contact with the image carrier, and the drive source that drives the image carrier and the transfer roller is the same.
An image forming apparatus, wherein a drive transmission path to the image carrier and a drive transmission path to the transfer roller are different paths. A transfer roller gear provided on the shaft of the transfer roller and transmitting a driving force to the transfer roller;
An idler gear for transmitting a driving force to the transfer roller gear,
The idler gear is a straight line perpendicular to a straight line passing through the center point of the image carrier and the center point of the transfer roller on a cross section perpendicular to the axes of the image carrier and the transfer roller, and The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed so as to be positioned on a straight line passing through a substantially center of the transfer roller. A transfer roller gear provided on the shaft of the transfer roller and transmitting a driving force to the transfer roller;
An idler gear for transmitting a driving force to the transfer roller gear,
The idler gear is disposed so that a driving gear reaction force applied from the idler gear to the transfer roller gear acts in a substantially vertical direction with respect to a straight line connecting the center of the image carrier and the center of the transfer roller. The image forming apparatus according to 1.

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