Image forming apparatus

Abstract

To provide an image forming apparatus capable of improving the stability of the rotational speed of a photoreceptor drum.SOLUTION: An image forming apparatus includes a drive source configured to supply a drive force, a photosensitive drum configured to be rotated by the drive force and to have a surface on which a toner image is formed, an intermediate transfer body configured to be rotated by the drive force and to have the toner image transferred from the photosensitive drum, a first drive transmission mechanism connected to the drive source and configured to transmit the drive force from the drive source to the photosensitive drum, and a second drive transmission mechanism connected to the drive member and configured to transmit the drive force received from the drive member to the intermediate transfer body.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus for forming an image on a recording material. [Background technology]

[0002] Patent Document 1 describes stabilizing the transmission of rotational driving force by increasing the rigidity of a coupling that transmits the rotational driving force of a drive motor to an intermediate transfer belt or a photosensitive drum. Patent Document 2 describes damping the rotational vibration of a photosensitive drum by using a flywheel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-132988 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-134138 Summary of the Invention [Problem to be solved by the invention]

[0004] When the rotation direction of the photosensitive drum during image formation is the forward direction, the photosensitive drum is rotated in the forward direction by the driving force of the drive source while receiving a load torque in the opposite direction to the forward direction. However, there are cases where a forward torque acts on the photosensitive drum due to a cause other than the driving force of the drive source, and this forward torque exceeds the load torque. In this case, the photosensitive drum rotates in a state where the gears and other components constituting the drive transmission mechanism from the drive source to the photosensitive drum are disengaged, causing the rotation speed of the photosensitive drum to become unstable. Fluctuations in the rotation speed of the photosensitive drum during image formation can result in a deterioration of image quality.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus capable of improving the stability of the rotation speed of a photosensitive drum. [Means for solving the problem]

[0006] One aspect of the present invention is an image forming device comprising: a drive source that supplies a drive force; a photosensitive drum that is rotated by the drive force and forms a toner image on its surface; an intermediate transfer body that is rotated by the drive force and onto which the toner image is transferred from the photosensitive drum; a first drive transmission mechanism connected to the drive source and transmitting the drive force from the drive source to the photosensitive drum, the first drive transmission mechanism having a drive member that is arranged coaxially with the photosensitive drum and rotates together with the photosensitive drum; and a second drive transmission mechanism connected to the drive member and transmitting the drive force received from the drive member to the intermediate transfer body. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an image forming apparatus capable of improving the stability of the rotation speed of the photosensitive drum. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] An enlarged view of a portion of Figure 1. [Figure 3] Enlarged view of the meshing area between the drum gear and idler gear (a, b). [Figure 4] FIG. 2 is a diagram showing a driving configuration of a photosensitive drum and an intermediate transfer belt according to the first embodiment. [Figure 5] FIG. 2 is a diagram showing a driving configuration of a photosensitive drum and an intermediate transfer belt according to the first embodiment. [Figure 6] FIG. 10 is a diagram showing a driving configuration of a photosensitive drum and an intermediate transfer belt according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing a driving configuration of a photosensitive drum and an intermediate transfer belt according to a third embodiment. [Figure 8] FIG. 4 is a diagram showing a driving configuration of a photosensitive drum according to a reference example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] (Image forming device) An overview of the overall configuration and image forming operation of an image forming apparatus 1 according to one embodiment will be described below. The configuration of the image forming apparatus 1 described below is common to Examples 1 to 3 described below.

[0011] 1 is a schematic diagram showing the cross-sectional configuration of an image forming apparatus 1 according to this embodiment. The image forming apparatus 1 is a color image forming apparatus that uses an electrophotographic system. The image forming apparatus 1 includes an image forming unit 1B, which is an electrophotographic engine of an intermediate transfer system, and an apparatus main body 1A that houses the image forming unit 1B.

[0012] The image forming apparatus 1 can form an image on a recording material P based on image information received from an external computer and output it as a finished product. A variety of sheet materials of different sizes and materials can be used as the recording material P (recording medium), including paper such as plain paper and cardboard, surface-treated sheet materials such as coated paper, specially shaped sheet materials such as envelopes and index paper, plastic film, cloth, and the like.

[0013] The image forming section 1B includes four process units Sa, Sb, Sc, and Sd, an exposure device 7, and a transfer unit 1C including an intermediate transfer belt 9 as an intermediate transfer member. The process units Sa, Sb, Sc, and Sd form images of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. The four process units Sa, Sb, Sc, and Sd are arranged in a line along the intermediate transfer belt 9 at regular intervals. The process units Sa to Sd may be cartridges that are detachable from the apparatus main body 1A.

[0014] In this embodiment, the four process units Sa, Sb, Sc, and Sd have substantially the same configuration except for the different colors of toner used to form images. Therefore, with regard to some of the components of the process units Sa to Sd, only the black process unit Sd is shown with a reference numeral.

[0015] Each of the process units Sa to Sd has a photosensitive drum 3 as an image carrier, a charging roller 21 as a charging member, a developing unit 22 as a developing means, and a cleaning unit 24 as a cleaning means.

[0016] The photosensitive drum 3 is a photosensitive member formed in a drum shape (cylindrical shape). The developing unit 22 has a developer container that contains toner as a developer, and a developing roller 23 (developer carrier) that carries the toner and supplies it to the photosensitive drum 3. In addition, an exposure section I that is irradiated with light from an exposure device 7 is provided downstream of the charging roller 21 and upstream of the developing roller 23 in the rotation direction R1 of the photosensitive drum 3 during image formation. The exposure device 7 in this embodiment is a laser scanner unit that irradiates laser light, but the exposure device 7 may also be an LED exposure device that uses an LED as a light source.

[0017] The developing roller 23 comes into contact with the photosensitive drum 3, and receives a driving force from a driving source mounted in the apparatus main body 1A to rotate in a rotation direction R4 (with direction) along the rotation direction R1 of the photosensitive drum 3. The rotation direction R4 is a direction in which the movement direction of the circumferential surface of the photosensitive drum 3 and the movement direction of the circumferential surface of the developing roller 23 are substantially the same in an opposing region (developing section) where the developing roller 23 and the photosensitive drum 3 face each other.

[0018] The cleaning unit 24 has a cleaning blade 25 as a cleaning member that contacts the photosensitive drum 3. The tip of the cleaning blade 25 is pressed against the surface of the photosensitive drum 3 with a predetermined contact pressure. The cleaning blade 25 rubs against the surface of the photosensitive drum 3 as the photosensitive drum 3 rotates, and scrapes off foreign matter such as residual toner from the photosensitive drum 3.

[0019] The transfer unit 1C includes an intermediate transfer belt 9, a drive roller 62, a driven roller 61, a tension roller 63, four primary transfer rollers 4, a secondary transfer roller 10, and a belt cleaner 20. The intermediate transfer belt 9 is stretched across the drive roller 62, the driven roller 61, and the tension roller 63. The intermediate transfer belt 9 rotates in a rotation direction R3 (with direction) that is aligned with the rotation direction R1 of each photosensitive drum 3 by rotation of the drive roller 62 connected to a drive source mounted in the apparatus main body 1A. The intermediate transfer belt 9 is endless in the rotation direction R3. The rotation direction R3 is a direction in which the movement direction of the circumferential surface of the primary transfer roller 4 and the movement direction of the circumferential surface of the intermediate transfer belt 9 are substantially the same at a facing portion (primary transfer portion N1) where the primary transfer roller 4 and the intermediate transfer belt 9 face each other.

[0020] The four primary transfer rollers 4 are disposed on the inner circumferential side of the intermediate transfer belt 9 and are in pressure contact with the photosensitive drums 3, with the intermediate transfer belt 9 sandwiched therebetween. A primary transfer portion N1 is formed as a nip portion where the intermediate transfer belt 9 and each photosensitive drum 3 come into contact. Furthermore, a secondary transfer roller 10 is disposed on the outer circumferential side of the intermediate transfer belt 9 and is in pressure contact with a drive roller 62, with the intermediate transfer belt 9 sandwiched therebetween. A secondary transfer portion N2 is formed as a nip portion where the intermediate transfer belt 9 and secondary transfer roller 10 come into contact with each other.

[0021] The belt cleaner 20 is disposed upstream of the most upstream photosensitive drum 3 and downstream of the secondary transfer portion N2 in the rotation direction R3 of the intermediate transfer belt 9. The belt cleaner 20 has a cleaning blade 20a that contacts the outer peripheral surface of the intermediate transfer belt 9, and removes foreign matter such as residual toner from the intermediate transfer belt 9 as the intermediate transfer belt 9 rotates.

[0022] The image forming apparatus 1 further includes a feed cassette 2, a feed roller 30, conveyance rollers 31 and 32, a fixing device 33, a discharge roller 34, and a discharge tray 35. The feed cassette 2 stores recording material P and is attached to the apparatus main body 1A so that it can be pulled out. The feed roller 30 is a feeding member that feeds the recording material P toward the image forming unit 1B. The fixing device 33 is a thermal fixing type that includes a pair of rotating bodies that sandwich and convey the recording material P and a heat source that heats the image on the recording material P. The discharge roller 34 is a discharge member that discharges the recording material P with an image formed thereon to the outside of the apparatus main body 1A. The discharge tray 35 is a stacking section on which the recording material P discharged after image formation is stacked.

[0023] The following describes the flow of the image forming operation, which is a series of operations in which the image forming apparatus 1 forms an image while conveying the recording material P. The control unit of the image forming apparatus 1 starts the image forming operation when, for example, it receives a print execution instruction together with image information (print data) from an external computer.

[0024] When the image formation operation begins, the photosensitive drums 3 and intermediate transfer belt 9 of each process unit Sa to Sd are rotated in the predetermined rotation directions R1 and R3, respectively. The charging rollers 21 uniformly charge the surfaces of the photosensitive drums 3. The exposure devices 7 are driven based on data obtained by separating image information into the respective color components of yellow, magenta, cyan, and black, and irradiate the photosensitive drums 3 with light to expose the surfaces of the photosensitive drums 3. As a result, electrostatic latent images are formed on the surfaces of the photosensitive drums 3. Each development unit 22 supplies developer (toner) to the photosensitive drums 3 via the development rollers 23, developing the electrostatic latent images into toner images. This toner image is primarily transferred to the intermediate transfer belt 9 at the primary transfer section N1 by applying a voltage to the primary transfer roller 4.

[0025] The formation of toner images in the four process units Sa to Sd proceeds in parallel, and primary transfer is performed so that the toner images of each color are superimposed on the intermediate transfer belt 9. As a result, a full-color image is formed on the intermediate transfer belt 9. This image is carried on the intermediate transfer belt 9 and transported to the secondary transfer unit N2.

[0026] In parallel with the above process, a feed roller 30 feeds recording material P one sheet at a time from a feed cassette 2. The fed recording material P is transported to a secondary transfer portion N2 by transport rollers 31 and 32. At the secondary transfer portion N2, an image is secondarily transferred from the intermediate transfer belt 9 to the recording material P by applying a voltage to a secondary transfer roller 10. After passing through the secondary transfer portion N2, the recording material P is sent to a fixing device 33. The fixing device 33 fixes the image on the recording material P by applying heat and pressure to the recording material P while nipping and transporting the recording material P at a nip portion (fixing nip) of a pair of rotating bodies. After passing through the fixing device 33, the recording material P is discharged by a discharge roller 34 and stacked on a discharge tray 35.

[0027] (Rotation state of the photosensitive drum during image formation) Next, the rotating state of the photosensitive drum 3 during image formation will be described. Figure 2 is an enlarged view of a part of Figure 1.

[0028] In this embodiment, the photosensitive drum 3 is in contact with each of the developing roller 23, the intermediate transfer belt 9, the charging roller 21, and the cleaning blade 25. The photosensitive drum 3, the developing roller 23, and the intermediate transfer belt 9 are each driven to rotate in predetermined rotation directions R1, R3, and R4 by driving forces from a driving source. The rotation directions R3 and R4 of the developing roller 23 and the intermediate transfer belt 9 are parallel to the rotation direction R1 of the photosensitive drum 3. Meanwhile, the charging roller 21 rotates counterclockwise in the figure, following the photosensitive drum 3, due to frictional force received from the photosensitive drum 3. The cleaning blade 25 is pressed against the photosensitive drum 3 with a predetermined pressure, and rubs against the surface of the photosensitive drum 3 as the photosensitive drum 3 rotates.

[0029] Here, if the peripheral speed (process speed) of the photosensitive drum 3 during image formation is 100%, the peripheral speed of the developing roller 23 during image formation is set to 110%, and the peripheral speed of the intermediate transfer belt 9 during image formation is set to 103%. This setting is merely an example, and can be changed as appropriate depending on the specific configuration of the image forming apparatus 1.

[0030] By providing a speed difference between the peripheral speed of the image carrier and the peripheral speed of the transferee at the transfer section, shear forces act on the toner, reducing the effects of toner cohesion, resulting in advantages such as improved transfer efficiency and reduced voids. In other words, in this embodiment, by setting the peripheral speed of the intermediate transfer belt 9 during image formation faster than the peripheral speed of the photosensitive drum 3, it is possible to improve transfer efficiency and reduce voids in the primary transfer process. Furthermore, as is known as the slip transfer method, when relative slippage is allowed between the surfaces of the photosensitive drum 3 and the intermediate transfer belt 9, the effects of eccentricity of the photosensitive drum 3 are reversed between the exposure section I and the primary transfer section N1, which can be used to reduce color misregistration.

[0031] Furthermore, by making the peripheral speed of the developing roller 23 faster than the peripheral speed of the photosensitive drum 3 during image formation, the latent image on the photosensitive drum 3 has more opportunities to come into contact with the toner on the developing roller 23, thereby preventing insufficient image density.

[0032] As described above, in this embodiment, the peripheral speed of the developing roller 23 during image formation is faster than the peripheral speed of the photosensitive drum 3. Also, the peripheral speed of the intermediate transfer belt 9 during image formation is faster than the peripheral speed of the photosensitive drum 3. Therefore, the photosensitive drum 3 receives torque in the rotation direction R1 from the developing roller 23 as it rubs against the intermediate transfer belt 9. Also, the photosensitive drum 3 receives torque in the rotation direction R1 from the intermediate transfer belt 9 as it rubs against the intermediate transfer belt 9.

[0033] Hereinafter, the torque that attempts to rotate the photosensitive drum 3 in the same direction (forward direction) as the rotation direction R1 during image formation due to an external force (a force other than the driving force of the driving source) applied to the photosensitive drum 3 is referred to as forward torque T1. Note that in this embodiment, the causes of the forward torque T1 have been described as the developing roller 23 and the intermediate transfer belt 9, but the image forming apparatus 1 may have other causes that generate the forward torque T1. For example, when the charging roller 21 is driven to rotate at a circumferential speed faster than that of the photosensitive drum 3, the forward torque T1 acts from the charging roller 21 to the photosensitive drum 3.

[0034] On the other hand, the photosensitive drum 3 receives a load torque T2 in a direction R2 opposite to the rotation direction R1 during image formation. The load torque T2 includes the frictional force that the photosensitive drum 3 receives from the cleaning blade 25, the frictional resistance of a bearing portion that rotatably supports the photosensitive drum 3, and the load that the photosensitive drum 3 receives when the charging roller 21 rotates following the photosensitive drum 3.

[0035] Normally, the forward torque T1 is smaller than the load torque T2. During image formation, it is preferable that the photosensitive drum 3 be rotationally driven at a constant peripheral speed (process speed) in a state where the sum of the forward torque T1 and the forward torque (driving torque) acting on the photosensitive drum 3 due to the driving force of the drive source is balanced with the load torque T2.

[0036] However, there are cases where the forward torque T1 exceeds the load torque T2 for some reason. In this case, as will be explained below, the photosensitive drum 3 rotates in a state where the gears and other components that constitute the drive transmission mechanism from the drive source to the photosensitive drum 3 are disengaged, causing instability in the rotation speed of the photosensitive drum 3. Fluctuations in the rotation speed of the photosensitive drum 3 during image formation may result in a deterioration in image quality.

[0037] This will be described in detail using the reference example in Fig. 8. Fig. 8 is a diagram showing the drive configuration of the photosensitive drum 3 in the reference example. The photosensitive drum 3 is connected to a motor 41 as a drive source via a drive transmission mechanism consisting of a coupling 47, a drum gear 44, an idler gear 43, and a pinion gear 42. The idler gear 43 meshes with the pinion gear 42 attached to the output shaft of the motor 41 and the drum gear 44. The drum gear 44 is disposed coaxially with the photosensitive drum 3 and rotates integrally with the coupling 47 and the photosensitive drum 3. That is, during image formation, the drum gear 44 rotates in the same rotation direction R1 as the photosensitive drum 3, and the idler gear 43 rotates in a rotation direction R5 along the drum gear 44 rotating in the rotation direction R1.

[0038] 3(a), the idler gear 43 and the drum gear 44 are usually in contact with each other at meshing surfaces 432, 442 for transmitting the driving force of the motor 41 to the photosensitive drum 3. The meshing surface 432 of the idler gear 43 is a side surface on the downstream side in the rotation direction R5 of the teeth 431 of the idler gear 43. The meshing surface 442 of the drum gear 44 is a side surface on the upstream side in the rotation direction R1 of the teeth 441 of the drum gear 44.

[0039] 8, when the forward torque T1 exceeds the load torque T2 during image formation, the meshing surfaces 432, 442 of the idler gear 43 and the drum gear 44 separate as shown in FIG. 3(b). In other words, when the forward torque T1 exceeds the load torque T2, the photosensitive drum 3 rotates at a speed faster than the normal rotation speed (process speed). The normal rotation speed is determined by the rotation speed of the motor 41 and the reduction ratio of the drive transmission mechanism from the motor 41 to the photosensitive drum 3.

[0040] Then, as the drum gear 44 rotates together with the photosensitive drum 3 at a speed faster than the normal rotation speed, the meshing surface 442 of the drum gear 44 separates from the meshing surface 432 of the idler gear 43. In other words, the drum gear 44, which is a driving member arranged coaxially with the photosensitive drum 3, and the idler gear 43, which is a drive transmission element upstream of the drum gear 44, are disengaged.

[0041] When the meshing surfaces 432, 442 are separated (when the engagement between the drum gear 44 and the idler gear 43 is released), the driving force of the motor 41 is not transmitted to the drum gear 44. This state can be said to be a state in which the connection between the drum gear 44 and the motor 41 is cut off (hereinafter referred to as a disconnected state). When the drum gear 44 is in the disconnected state, the photosensitive drum 3 is also in a state in which the connection between the photosensitive drum 3 and the motor 41 is cut off.

[0042] Even when the drum gear 44 is in the disconnected state, the photosensitive drum 3 can rotate in the rotation direction R1 by receiving a forward torque T1 from the developing roller 23 and the intermediate transfer belt 9. However, in the disconnected state, the rotation speed of the photosensitive drum 3 becomes unstable compared to a state in which the meshing surfaces 432, 442 are in contact and the drum gear 44 is connected to the motor 41 (connected state). This is because, in the connected state, the rotation speeds of the photosensitive drum 3 and the drum gear 44 are constrained by the rotation speed of the motor 41, whereas in the disconnected state, the rotation speeds of the photosensitive drum 3 and the drum gear 44 are not constrained by the rotation speed of the motor 41 and are therefore susceptible to external disturbances.

[0043] Specifically, the developing roller 23 is driven while being affected by fluctuations in the toner flow load, and therefore the rotation speed of the developing roller 23 is not stable. Fluctuations in the toner flow load refer to, for example, the movement of toner in the developing container due to the rotation of an agitator in the developing container, which causes irregular changes in the ease of toner flow around the developing roller 23 and fluctuations in the resistance that the developing roller 23 receives from the toner. In addition, the frictional force between the developing roller 23 or intermediate transfer belt 9 and the photosensitive drum 3 can also fluctuate due to changes in the amount of toner present at the contact point between the developing roller 23 and the photosensitive drum 3 or at the primary transfer unit N1, etc.

[0044] For the reasons described above, the magnitude of the forward torque T1 that the photosensitive drum 3 receives from the developing roller 23 and the intermediate transfer belt 9 during image formation steadily fluctuates slightly. Therefore, in the reference example, when the drum gear 44 enters a disconnected state, the rotation speeds of the photosensitive drum 3 and the drum gear 44 become unstable. The instability of the rotation speed of the photosensitive drum 3 causes degradation of image quality, such as uneven density of the image in the sub-scanning direction (banding) and non-uniformity in the scale of the image in the sub-scanning direction.

[0045] In the above explanation, attention has been focused on the meshing surfaces 432, 442 of the drum gear 44 and the idler gear 43, but if the state in which the forward torque T1 exceeds the load torque T2 continues, the meshing (engagement) between the gears will also be released upstream of the idler gear 43. In other words, the drum gear 44 pushes the idler gear 43, causing the idler gear 43 to rotate at a speed faster than the normal rotation speed, which may result in the meshing (engagement) between the idler gear 43 and the pinion gear 42 being released. In this way, in a configuration in which the drum gear 44 is connected to the motor 41 via multiple gears, there is a possibility that the rotational speed of the photosensitive drum 3 may fluctuate greatly due to the influence of backlash at each of the multiple meshing portions between the gears.

[0046] Furthermore, although the above description has been made on the case where the forward torque T1 fluctuates steadily and minutely, there are cases where an external force is applied to the photosensitive drum 3 at a predetermined timing during the conveyance process of the recording material P.

[0047] Specifically, as shown in FIG. 2, an impact is applied to the intermediate transfer belt 9 at the timing when the leading edge of the recording material P enters the secondary transfer portion N2 and the timing when the trailing edge of the recording material P leaves the secondary transfer portion N2, which can cause fluctuations in the rotational speed of the intermediate transfer belt 9. If this causes relative slippage between the intermediate transfer belt 9 and the photosensitive drum 3 at the primary transfer portion N1, this can cause distortion of the image transferred to the intermediate transfer belt 9 at the primary transfer portion N1 (transfer blur). Furthermore, if the impact is transmitted to the photosensitive drum 3 via the intermediate transfer belt 9, causing fluctuations in the rotational speed of the photosensitive drum 3, this can cause distortion of the electrostatic latent image written on the photosensitive drum 3 at the exposure portion I (latent image blur). Both transfer blur and latent image blur lead to degradation of image quality.

[0048] Therefore, in this embodiment, a configuration capable of improving the stability of the rotation speed of the photosensitive drum 3 is proposed, as will be described in the following Examples 1 to 3.

[0049] Example 1 The configuration of the image forming apparatus 1 according to Example 1 will be described. Fig. 4 is a perspective view showing the drive configuration of the photosensitive drum 3 and intermediate transfer belt 9 according to Example 1. Fig. 5 is a view showing the drive configuration of the photosensitive drum 3 and intermediate transfer belt 9 according to Example 1 as viewed in the direction of the rotation axis of the photosensitive drum 3. Hereinafter, the photosensitive drum 3 in this example is the photosensitive drum 3 closest to the drive roller 62 in Fig. 1 (the photosensitive drum 3 of the black process unit Sd).

[0050] As shown in FIGS. 4 and 5, the image forming apparatus 1 has a motor 41 as a drive source, a first drive transmission mechanism D1 (first drive train), and a second drive transmission mechanism D2 (second drive train).

[0051] The first drive transmission mechanism D1 is connected to the motor 41 and transmits the drive force of the motor 41 to the photosensitive drum 3. The first drive transmission mechanism D1 includes a pinion gear 42 attached to the output shaft of the motor 41, an idler gear 43 meshing with the pinion gear 42, a drum gear 44 meshing with the idler gear 43, and a coupling 47 engaging with the photosensitive drum 3. The configuration of the first drive transmission mechanism D1 in this embodiment is basically the same as the drive transmission mechanism shown in the reference example (FIG. 8). The first drive transmission mechanism D1 is a speed reduction mechanism that reduces the rotation of the output shaft of the motor 41 and transmits it to the photosensitive drum 3.

[0052] The drum gear 44 is an example of a driving member arranged coaxially with the photosensitive drum 3. The drum gear 44 is connected to the photosensitive drum 3 via a coupling 47. The drum gear 44 rotates together with the photosensitive drum 3 around the rotation axis of the photosensitive drum 3. When the process units Sa to Sd are attached to or detached from the apparatus main body 1A, the coupling 47 engages with and disengages from the photosensitive drum 3. Note that the coupling 47 may be omitted, and the drum gear 44 may be formed integrally with the photosensitive drum 3.

[0053] The second drive transmission mechanism D2 is connected to the drum gear 44 of the first drive transmission mechanism D1, and rotates the drive roller 62 by the drive force of the motor 41 received from the drum gear 44. As described above, the drive roller 62 is a roller that rotates the intermediate transfer belt 9. The second drive transmission mechanism D2 is connected to the drum gear 44 (drive member) that is arranged coaxially with the photosensitive drum 3, and is configured to transmit the drive force received from the drum gear 44 to the intermediate transfer belt 9 (intermediate transfer body).

[0054] The second drive transmission mechanism D2 includes a first idler gear 46a that meshes with the drum gear 44, a second idler gear 46b that meshes with the first idler gear 46a, and a drive roller gear 45 that meshes with the second idler gear 46b. The drive roller gear 45 is disposed coaxially with the drive roller 62 and rotates integrally with the drive roller 62.

[0055] As described above, in this embodiment, the second drive transmission mechanism D2 for transmitting the drive force to the intermediate transfer belt 9 is connected downstream of the drum gear 44 in the drive transmission direction. In other words, the drive force of the motor 41 is distributed from the drum gear 44 (drive member) arranged coaxially with the photosensitive drum 3 to the second drive transmission mechanism D2.

[0056] Therefore, the drum gear 44 receives not only the load torque T2 caused by the rotational resistance of the photosensitive drum 3, but also a load torque T3 caused mainly by the rotational resistance of the intermediate transfer belt 9 (FIG. 5). The load torque T3 is a torque in the direction R2 opposite to the rotational direction R1 of the photosensitive drum 3 during image formation. The load torque T3 is caused by the rotational resistance of the intermediate transfer belt 9, which is the frictional force that the intermediate transfer belt 9 receives from the cleaning blade 20a (FIG. 1) and the frictional resistance of the bearing portions of the rollers that stretch the intermediate transfer belt 9. The load torque T3 may also include the frictional resistance of the bearing portions of the gears that make up the second drive transmission mechanism D2.

[0057] In this embodiment, the torque in the reverse direction R2 acting on the drum gear 44 during image formation is the sum of a load torque T2 caused by the rotational resistance of the photosensitive drum 3 and a load torque T3 caused mainly by the rotational resistance of the intermediate transfer belt 9. Therefore, unless the forward torque T1 exceeds the sum of the load torques T2 and T3, the meshing surface 442 of the drum gear 44 does not separate from the meshing surface 432 of the idler gear 43 (see FIG. 3(b)). In other words, the state in which the meshing surface 442 of the tooth 441 (first tooth) of the drum gear 44 is pressed against the meshing surface 432 of the tooth (second tooth) of the idler gear 43 is maintained.

[0058] That is, according to this embodiment, the drum gear 44 is less likely to enter a disconnected state during image formation than in the reference example. In other words, the drum gear 44 of this embodiment receives not only the load torque T2 caused by the rotational resistance of the photosensitive drum 3, but also an additional load torque T3 from the second drive transmission mechanism D2. Therefore, the engagement between the drum gear 44 (drive member) arranged coaxially with the photosensitive drum 3 and the drive transmission element (idler gear 43) upstream of the drum gear 44 is less likely to be released. As a result, even if the magnitude of the forward torque T1 that the photosensitive drum 3 receives from the developing roller 23 and the intermediate transfer belt 9 during image formation fluctuates, the rotation speed of the photosensitive drum 3 is less likely to fluctuate.

[0059] That is, according to this embodiment, it is possible to improve the stability of the rotation speed of the photosensitive drum 3. Furthermore, it is possible to reduce the degradation of image quality caused by fluctuations in the rotation speed of the photosensitive drum 3.

[0060] In recent years, in order to extend the life of the photosensitive drum 3, a hard, highly slidable material has been used on the surface of the photosensitive drum 3, and as a result, the load torque T2 that the photosensitive drum 3 receives from the cleaning blade 25 and the like tends to become smaller. According to this embodiment, even under conditions in which the load torque T2 is small, the stability of the rotation speed of the photosensitive drum 3 can be improved.

[0061] Furthermore, according to this embodiment, the photosensitive drum 3 and the intermediate transfer belt 9 are connected via the drum gear 44 and the second drive transmission mechanism D2, and rotate in conjunction with each other. Therefore, even if the rotation speed of the intermediate transfer belt 9 fluctuates at the timing when the leading edge of the recording material P enters the secondary transfer portion N2 and the timing when the trailing edge of the recording material P leaves the secondary transfer portion N2, relative slippage between the intermediate transfer belt 9 and the photosensitive drum 3 can be suppressed.

[0062] For example, suppose that the leading edge of the recording material P enters the secondary transfer portion N2 as shown in Figure 2, causing an impact to be applied to the intermediate transfer belt 9 in a direction along the rotation direction R3 during image formation. In this case, an instantaneous torque is applied to the drive roller 62 and the drive roller gear 45 in a rotation direction R6 (see also Figure 5) along the rotation direction R3 of the intermediate transfer belt 9. Furthermore, as shown in Figure 5, this torque is transmitted upstream through the second drive transmission mechanism D2 to the drum gear 44, and then from the drum gear 44 to the photosensitive drum 3.

[0063] In this way, the impact when the recording material P enters is transmitted to both the intermediate transfer belt 9 and the photosensitive drum 3, making it difficult for relative slippage to occur between the intermediate transfer belt 9 and the photosensitive drum 3 at the primary transfer portion N1. As a result, it is possible to suppress the occurrence of transfer blurring and the resulting deterioration in image quality.

[0064] Example 2 An image forming apparatus 1 according to Example 2 will be described. Fig. 6 is a perspective view showing the drive configuration of the photosensitive drum 3 and intermediate transfer belt 9 according to Example 2. Hereinafter, elements with the same reference symbols as those in Example 1 will have basically the same configurations and functions as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0065] In the following description of this embodiment, the four photosensitive drums 3 are designated by different reference numerals as photosensitive drums 3a, 3b, 3c, and 3d to be distinguished from one another. The photosensitive drums 3a, 3b, 3c, and 3d belong to process units Sa, Sb, Sc, and Sd, respectively.

[0066] As shown in FIG. 6, the image forming apparatus 1 has a motor 41 as a drive source, a first drive transmission mechanism D1 (first drive train), and a second drive transmission mechanism D2 (second drive train).

[0067] The first drive transmission mechanism D1 has a pinion gear 42, an idler gear 43, drum gears 44a, 44b, 44c, and 44d, and idler gears 143a, 143b, and 143c. The drum gear 44a is disposed coaxially with the yellow photosensitive drum 3a and rotates together with the photosensitive drum 3a. The drum gear 44b is disposed coaxially with the magenta photosensitive drum 3b and rotates together with the photosensitive drum 3b. The drum gear 44c is disposed coaxially with the cyan photosensitive drum 3c and rotates together with the photosensitive drum 3c. The drum gear 44d is disposed coaxially with the black photosensitive drum 3d and rotates together with the photosensitive drum 3d. The idler gear 143a meshes with both the drum gears 44a and 44b. The idler gear 143b meshes with both the drum gears 44b and 44c. The idler gear 143c is in mesh with both the drum gears 44c and 44d.

[0068] The first drive transmission mechanism D1 of this embodiment transmits the drive force of the motor 41 to each of the four photosensitive drums 3a to 3d. Furthermore, the drum gears 44a to 44c other than the black drum gear 44d are connected to the second drive transmission mechanism D2 via the black drum gear 44d.

[0069] The second drive transmission mechanism D2 is connected to the black drum gear 44d, and rotates the drive roller 62 by the drive force of the motor 41 received from the drum gear 44d. That is, the second drive transmission mechanism D2 is connected to the drum gear 44d (drive member) coaxial with the first photosensitive drum, and transmits the drive force received from the drum gear 44d to the intermediate transfer belt 9. The configuration of the second drive transmission mechanism D2 may be the same as that of the second drive transmission mechanism D2 in the first embodiment.

[0070] In this embodiment as well, a second drive transmission mechanism D2 for transmitting a drive force to the intermediate transfer belt 9 is connected downstream of the drum gear 44d in the drive transmission direction. That is, the drive force of the motor 41 is distributed from the drum gear 44d (drive member) arranged coaxially with the photosensitive drum 3d to the second drive transmission mechanism D2.

[0071] Therefore, the load torque T3 for rotating the intermediate transfer belt 9 acts on the drum gear 44d (driving member) arranged coaxially with the photosensitive drum 3d. Therefore, similar to the first embodiment, the stability of the rotation speed of the photosensitive drum 3d can be improved.

[0072] In this embodiment, the drum gears 44a to 44c other than the black drum gear 44d are connected to the second drive transmission mechanism D2 via the black drum gear 44d. In other words, the first drive transmission mechanism D1 in this embodiment has a second drive member that is arranged coaxially with the second photosensitive drum and rotates together with the second photosensitive drum. The second drive member constitutes a drive transmission path from the drive source to the first drive member and is connected to the second drive transmission mechanism D2 via the first drive member. If the black photosensitive drum 3d is defined as the first photosensitive drum and the drum gear 44d is defined as the first drive member, any one of the other photosensitive drums 3a to 3c is an example of the second photosensitive drum, and one of the corresponding drum gears 44a, 44b, and 44d is an example of the second drive member.

[0073] Therefore, each of the drum gears 44a to 44c other than the black drum gears receives the load torque T3 caused by the rotational resistance of the intermediate transfer belt 9 via the second drive transmission mechanism D2 and the black drum gear 44d. Therefore, it is possible to prevent each of the multiple drum gears 44a to 44d from entering a disconnected state in which connection with the motor 41 is cut off during image formation, and it is possible to improve the stability of the rotation speed of each of the multiple photosensitive drums 3a to 3d.

[0074] Example 3 An image forming apparatus 1 according to Example 3 will be described. Fig. 7 is a perspective view showing the drive configuration of the photosensitive drum 3 and intermediate transfer belt 9 according to Example 3. Hereinafter, elements with the same reference symbols as those in Example 1 will have basically the same configurations and functions as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0075] As shown in Fig. 7, a flywheel 252 serving as an inertial body is attached to the first idler gear 46a in this embodiment. The flywheel 252 is made of a metal (e.g., steel plate) with a higher specific gravity than POM (polyacetal), which is the material of the gears of the first drive transmission mechanism D1 and the second drive transmission mechanism D2, and has a large outer diameter, so it has a large moment of inertia. The moment of inertia of the flywheel 252 (inertial body) is greater than the moment of inertia of the photosensitive drum 3. In other words, the moment of inertia of the flywheel 252 with respect to the rotation axis of the first idler gear 46a is greater than the moment of inertia of the photosensitive drum 3 with respect to the rotation axis of the photosensitive drum 3.

[0076] Here, it is preferable that the flywheel 252 (inertial body) is attached to a rotating member that rotates at a higher rotation speed during image formation than the drum gear 44 or the drive roller 46. This makes it possible to prevent the flywheel 252 itself from becoming larger and heavier, while enhancing the stabilization of the rotational speed.

[0077] In this embodiment, the rotation speed (rpm) of the first idler gear 46a during image formation is 3.6 times the rotation speed of the drum gear 44 and 1.6 times the rotation speed of the drive roller gear 45. Generally, when the rotation of the first rotating shaft is accelerated by a gear train or the like and transmitted to the second rotating shaft, the magnitude of the moment of inertia acting on the first rotating shaft by the inertial body on the second rotating shaft is a value obtained by multiplying the moment of inertia of the inertial body itself by the square of the ratio of the rotation speeds of the first rotating shaft and the second rotating shaft. Therefore, in this embodiment, the rotation speed is approximately 13 times (=3.6) times faster than when the flywheel 252 is arranged coaxially with the drum gear 44. 2) moment of inertia acts on the drum gear 44. In addition, the moment of inertia is about 2.6 times (=1.6 2 ) acts on the drive roller gear 45.

[0078] As described above, also in this embodiment, the second drive transmission mechanism D2 for transmitting the drive force to the intermediate transfer belt 9 is connected downstream of the drum gear 44 in the drive transmission direction. In other words, the drive force of the motor 41 is distributed from the drum gear 44 (drive member) arranged coaxially with the photosensitive drum 3 to the second drive transmission mechanism D2.

[0079] Therefore, the load torque T3 for rotating the intermediate transfer belt 9 acts on the drum gear 44d (driving member) arranged coaxially with the photosensitive drum 3d. Therefore, similar to the first embodiment, the stability of the rotation speed of the photosensitive drum 3 can be improved.

[0080] Furthermore, according to this embodiment, fluctuations in the rotational speed of the drum gear 44 and the drive roller gear 45 are suppressed by the action of the moment of inertia of the flywheel 252, thereby further improving the stability of the rotational speed of the photosensitive drum 3 and the intermediate transfer belt 9.

[0081] In particular, by providing the flywheel 252, in addition to suppressing relative slippage between the intermediate transfer belt 9 and the photosensitive drum 3 at the primary transfer portion N1 as described in the first embodiment, it is possible to suppress latent image blurring caused by fluctuations in the rotational speed of the photosensitive drum 3. That is, the action of the flywheel 252 reduces fluctuations in the rotational speed of the intermediate transfer belt 9 when an impact is received when the leading or trailing edge of the recording material P passes through the secondary transfer portion N2, thereby reducing the impact transmitted to the photosensitive drum 3 via the intermediate transfer belt 9. Furthermore, even if the photosensitive drum 3 receives an impact via the intermediate transfer belt 9, the action of the flywheel 252 suppresses fluctuations in the rotational speed of the photosensitive drum 3. In this way, the flywheel 252 acts in multiple stages, making it possible to suppress fluctuations in the rotational speed of the photosensitive drum 3 that cause latent image blurring.

[0082] Other Examples In Examples 1 to 3, examples have been described in which the first drive transmission mechanism D1 and the second drive transmission mechanism D2 are each configured with a gear train. A part or all of the first drive transmission mechanism D1 may be a belt drive mechanism configured with a belt and a pulley. Also, a part or all of the second drive transmission mechanism D2 may be a belt drive mechanism. The belt of the belt drive mechanism may be a toothed belt (timing belt) that meshes with the teeth of a pulley. Also, the "drive member" arranged coaxially with the photosensitive drum 3 may be a pulley. Note that even when a part or all of the first drive transmission mechanism D1 is a belt drive mechanism, if the forward torque T1 acting on the photosensitive drum 3 exceeds the load torque T2, a problem similar to that in the above-described embodiment may occur due to backlash between the belt and the pulley.

[0083] Furthermore, in the first to third embodiments, the drum gear 44 and the photosensitive drum 3 are detachably connected via the coupling 47, but the drum gear 44 may be fixed to the photosensitive drum 3.

[0084] In addition, in Example 2, a configuration example was described in which all four drum gears 44a to 44d are connected in series, but some of the drum gears 44a to 44d may be connected in parallel to the motor 41, and the number of photosensitive drums 3a to 3d and drum gears 44a to 44d is not limited to four.

[0085] Furthermore, in the first to third embodiments, the image forming apparatus 1 has been described as including the charging roller 21, the developing roller 23, the cleaning blade 25, and the intermediate transfer belt 9 as members that come into contact with the photosensitive drum 3. However, the present invention is not limited to this, and for example, the process units Sa to Sd may be configured without a cleaning member that comes into contact with the photosensitive drum 3. The process units Sa to Sd may be of a simultaneous development and cleaning type (cleanerless type) in which the developing roller 23 collects the residual toner after transfer into the developing unit 22, for example.

[0086] Furthermore, the "intermediate transfer body" is not limited to the intermediate transfer belt 9, which is an endless member stretched over a plurality of rollers, but may be a cylindrical or cylindrical rotating body.

[0087] Furthermore, the positional relationship between the photosensitive drum 3 and the intermediate transfer belt 9 shown in FIG. 1 is merely an example, and the photosensitive drum 3 may be disposed above the intermediate transfer belt 9, for example.

[0088] Summary of the Disclosure The present disclosure includes at least the following configurations or methods. (Configuration 1) a driving source that supplies driving force; a photosensitive drum that is rotated by the driving force and that forms a toner image on its surface; an intermediate transfer member that is rotated by the driving force and onto which the toner image is transferred from the photosensitive drum; a first drive transmission mechanism connected to the drive source and configured to transmit the drive force from the drive source to the photosensitive drum, the first drive transmission mechanism including a drive member disposed coaxially with the photosensitive drum and rotating together with the photosensitive drum; a second drive transmission mechanism connected to the drive member and configured to transmit the drive force received from the drive member to the intermediate transfer body; An image forming apparatus comprising: (Configuration 2) a peripheral speed of the intermediate transfer body during image formation is faster than a peripheral speed of the photosensitive drum during image formation; 2. The image forming apparatus according to claim 1, (Configuration 3) a developing roller that is in contact with the photosensitive drum and supplies toner to the photosensitive drum; a peripheral speed of the developing roller during image formation is faster than a peripheral speed of the photosensitive drum during image formation; 3. The image forming apparatus according to claim 1, wherein: (Configuration 4) a cleaning blade that rubs and cleans the surface of the intermediate transfer body; a load torque caused by a frictional force that the intermediate transfer member receives from the cleaning blade acts on the driving member via the second drive transmission mechanism; 4. The image forming apparatus according to any one of configurations 1 to 3. (Configuration 5) the drive member has a first tooth; the first drive transmission mechanism includes a gear having second teeth that mesh with the first teeth and that transmits the drive force to the drive member; 5. The image forming apparatus according to any one of configurations 1 to 4. (Configuration 6) The driving member is connected to the driving source via a plurality of gears. 6. The image forming apparatus according to any one of configurations 1 to 5. (Configuration 7) When the photosensitive drum is a first photosensitive drum and the driving member is a first driving member, a second photosensitive drum that is rotated by the driving force and that forms a toner image on its surface; the first drive transmission mechanism has a second drive member that is arranged coaxially with the second photosensitive drum and rotates together with the second photosensitive drum, The second driving member constitutes a driving force transmission path from the driving source to the first driving member, and is connected to the second driving force transmission mechanism via the first driving member. 7. The image forming apparatus according to any one of configurations 1 to 6. (Configuration 8) the second drive transmission mechanism includes an inertial body having a moment of inertia greater than that of the photosensitive drum; 8. The image forming apparatus according to any one of configurations 1 to 7. (Configuration 9) the intermediate transfer body is endless in the rotation direction, a drive roller around which the intermediate transfer body is stretched and which rotates by receiving the drive force from the second drive transmission mechanism; the second drive transmission mechanism has a rotating member, and the rotation speed of the rotating member during image formation is greater than the rotation speed of the photosensitive drum and the rotation speed of the drive roller; The inertial body is attached to the rotating member. 9. The image forming apparatus according to any one of configurations 1 to 8. [Explanation of symbols]

[0089] 3...photosensitive drum / 9...intermediate transfer body (intermediate transfer belt) / 41...driving source (motor) / 44...driving member (drum gear) / D1...first driving transmission mechanism / D2...second driving transmission mechanism

Claims

1. a driving source that supplies driving force; a photosensitive drum that is rotated by the driving force and that forms a toner image on its surface; an intermediate transfer member that is rotated by the driving force and onto which the toner image is transferred from the photosensitive drum; a first drive transmission mechanism connected to the drive source and configured to transmit the drive force from the drive source to the photosensitive drum, the first drive transmission mechanism including a drive member disposed coaxially with the photosensitive drum and rotating together with the photosensitive drum; a second drive transmission mechanism connected to the drive member and configured to transmit the drive force received from the drive member to the intermediate transfer body; An image forming apparatus comprising:

2. a peripheral speed of the intermediate transfer body during image formation is faster than a peripheral speed of the photosensitive drum during image formation; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. a developing roller that is in contact with the photosensitive drum and supplies toner to the photosensitive drum; a peripheral speed of the developing roller during image formation is faster than a peripheral speed of the photosensitive drum during image formation; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. a cleaning blade that rubs and cleans the surface of the intermediate transfer body; a load torque caused by a frictional force that the intermediate transfer member receives from the cleaning blade acts on the driving member via the second drive transmission mechanism; 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. The drive member has a first tooth; the first drive transmission mechanism includes a gear having second teeth that mesh with the first teeth and that transmits the drive force to the drive member; 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The driving member is connected to the driving source via a plurality of gears.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. When the photosensitive drum is a first photosensitive drum and the driving member is a first driving member, a second photosensitive drum that is rotated by the driving force and that forms a toner image on its surface; the first drive transmission mechanism has a second drive member that is disposed coaxially with the second photosensitive drum and rotates together with the second photosensitive drum; the second driving member constitutes a driving force transmission path from the driving source to the first driving member, and is connected to the second driving force transmission mechanism via the first driving member; 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. the second drive transmission mechanism includes an inertial body having a moment of inertia greater than that of the photosensitive drum; 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. the intermediate transfer body is endless in the rotation direction, a drive roller around which the intermediate transfer body is stretched and which rotates by receiving the drive force from the second drive transmission mechanism; the second drive transmission mechanism has a rotating member, and the rotation speed of the rotating member during image formation is greater than the rotation speed of the photosensitive drum and the rotation speed of the drive roller; The inertial body is attached to the rotating member.

9. The image forming apparatus according to claim 8,

Images