Image forming apparatus

Abstract

The purpose of the present invention is to suppress the generation of stripes in an image forming apparatus capable of color printing and monochrome printing. The image forming apparatus (1) includes first to third developing rollers bearing a color developer, a fourth developing roller bearing a black developer, first to fourth photosensitive drums corresponding to the first to fourth developing rollers, and a processing motor driving the first to fourth developing rollers and the first to fourth photosensitive drums. And a first output gear (781), a first gear train (791), and a second gear train (792) that are disposed coaxially with the processing motor and that output driving force from the processing motor. The first gear train (791) includes a first intermediate gear (79A) that meshes with the first output gear (781), and transmits the driving force of the processing motor to the first to fourth developing rollers. A second gear train (792) is provided with a second intermediate gear that meshes with the first output gear, and transmits the driving force of the processing motor to the first to fourth photosensitive drums.

Description

[0001] This application is a divisional application of the following application:

[0002] Original application filing date: March 30, 2021

[0003] Original application number: 202110339100.7

[0004] Original application title: Image forming apparatus TECHNICAL FIELD

[0005] The present application relates to an image forming apparatus. BACKGROUND

[0006] As an image forming apparatus of an electrophotographic system, there is known, for example, a tandem printer provided with a plurality of developing units corresponding to yellow, magenta, cyan, and black colors. As such a tandem printer, in order to correspond to color printing and monochrome printing, a structure is proposed in which the developing units of yellow, magenta, and cyan colors and the developing unit of black color are driven by respective motors (for example, refer to Patent Literature 1).

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: Japanese Patent Application Publication No. 2015-87585

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] In the structure of Patent Literature 1, the motor that drives the developing unit of black color also drives a fixing section or the like. Specifically, a gear train is provided that branches at a midpoint of the gear train from the motor to the fixing section and transmits driving force to the developing unit of black color. However, since high load is applied in driving of the fixing section, rotation unevenness that occurs in the fixing section can be transmitted to the developing unit of black color, thereby generating banding. SUMMARY OF THE INVENTION

[0012] An object of the present application is to, in an image forming apparatus capable of color printing and monochrome printing, drive all developing rollers and photosensitive drums by the same motor, and branch a gear train that drives the developing rollers and a gear train that drives the photosensitive drums directly from the motor, thereby suppressing generation of banding.

[0013] MEANS OF SOLVING THE PROBLEMS

[0014] The image forming apparatus of the present application has a first developing roller, a second developing roller, and a third developing roller that carry color developing agents, a fourth developing roller that carries a black developing agent, a first photosensitive drum corresponding to the first developing roller, a second photosensitive drum corresponding to the second developing roller, a third photosensitive drum corresponding to the third developing roller, and a fourth photosensitive drum corresponding to the fourth developing roller. In addition, the image forming apparatus has a motor that drives the first developing roller, the second developing roller, the third developing roller, and the fourth developing roller, and the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum, and a first output gear that is coaxially arranged with the motor and outputs driving force from the motor. In addition, the image forming apparatus has a first gear train that has a first intermediate gear that meshes with the first output gear and transmits the driving force of the motor to the first developing roller, the second developing roller, the third developing roller, and the fourth developing roller. In addition, the image forming apparatus has a second gear train that has a second intermediate gear that meshes with the first output gear and transmits the driving force of the motor to the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum.

[0015] According to the above-described structure, all of the developing rollers and the photosensitive drums are driven by the same motor, and the first gear train that drives each developing roller and the second gear train that drives each photosensitive drum are branched directly from the first output gear of the motor, whereby uneven rotation of each is less likely to be transmitted to the other gear train, and the generation of a band can be suppressed.

[0016] In the above-described image forming apparatus, the first gear train can have a third gear train that transmits driving force to the first developing roller, the second developing roller, and the third developing roller, and a fourth gear train that transmits driving force to the fourth developing roller. The third gear train has a pendulum gear that is arranged upstream of the first developing roller, the second developing roller, and the third developing roller and can swing to a first position at which driving force is transmitted and a second position at which driving force is cut off. The fourth gear train has an electromagnetic clutch that is arranged upstream of the fourth developing roller and can be displaced to a first state at which driving force is transmitted and a second state at which driving force is cut off.

[0017] According to the above-described structure, cost reduction is achieved by using a pendulum gear, and space saving is achieved by using an electromagnetic clutch.

[0018] In the above-described image forming apparatus, the third gear train can include the first intermediate gear, and the fourth gear train can be branched from upstream of the pendulum gear of the third gear train.

[0019] In the image forming apparatus described above, the third gear train can include a third intermediate gear engaged with the first intermediate gear, and the fourth gear train can branch from the third intermediate gear.

[0020] According to the above-described configuration, the rotation unevenness of one of the third gear train and the fourth gear train is difficult to be transmitted to the other gear train by branching the gears as close as possible to the first output gear of the motor, and each gear is stably driven. In addition, the fourth gear train can be made shorter than a configuration directly branching from the first output gear.

[0021] In the image forming apparatus described above, a part of the gears of the third gear train can be arranged coaxially with a part of the gears of the fourth gear train.

[0022] According to the above-described configuration, the first gear train can be downsized.

[0023] In the image forming apparatus described above, the third developing roller can be arranged adjacent to the fourth developing roller, and the part of the gears of the third gear train can be a second output gear arranged coaxially with the third developing roller and outputting a driving force to the third developing roller.

[0024] In the image forming apparatus described above, the fourth gear train can include a clutch input gear inputting a driving force to the electromagnetic clutch, and a clutch output gear having a different number of teeth from the clutch input gear and outputting a driving force from the electromagnetic clutch.

[0025] According to the above-described configuration, the rotation of the clutch output gear is stabilized by deceleration or acceleration of the electromagnetic clutch, and the image quality is improved.

[0026] In the image forming apparatus described above, the fourth gear train can include a third output gear arranged coaxially with the fourth developing roller and outputting a driving force to the fourth developing roller, and the clutch output gear can be engaged with the third output gear.

[0027] In the image forming apparatus described above, a sheet metal member having a positioning hole and supporting the fourth gear train, a first cover having a first engaging portion, fixed to one side of the sheet metal member and supporting the electromagnetic clutch, and a second cover having a second engaging portion engaged with the positioning hole and the first engaging portion, fixed to the other side of the sheet metal member and supporting one end of the clutch output gear can be provided.

[0028] According to the above structure, the second cover is positioned on the sheet metal component, and the first cover is positioned on the second cover, thereby enabling precise positioning of the electromagnetic clutch and the clutch output gear.

[0029] The image forming apparatus described above may also include: a belt conveyor that conveys a sheet relative to the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum; and a fifth gear train that branches off from the second gear train at the second intermediate gear and transmits driving force to the belt conveyor.

[0030] According to the above structure, by branching the fifth gear train from the second intermediate gear at the uppermost end of the second gear train, it is possible to suppress the transmission of uneven rotation between the fifth gear train and the second gear train.

[0031] In the image forming apparatus described above, the second gear train and the fifth gear train may also have a reverse rotation prevention mechanism to prevent the gears from rotating in reverse when the motor rotates in reverse. The reverse rotation prevention mechanism includes: a protrusion, which is present on one of two coaxially arranged gears; and a first abutment and a second abutment, which are present on the other of the two coaxially arranged gears, and which the protrusion can abut against. Furthermore, when the motor rotates forward, the protrusion abuts against the first abutment and the two gears rotate; when the motor switches from forward to reverse rotation, the two gears idle between the protrusion and the first abutment and between the protrusion and the second abutment.

[0032] Based on the above structure, abnormal noise generated from the pendulum gear is suppressed when the pendulum gear is separated. Therefore, in the case of temporarily reversing the motor, the photosensitive drum and belt conveyor can be prevented from reversing.

[0033] Invention Effects

[0034] According to the present invention, in an image forming apparatus capable of performing color printing and monochrome printing, all developing rollers and photosensitive drums are driven by the same motor, and the first gear train driving the developing rollers and the second gear train driving the photosensitive drums are directly branched from the motor, thereby suppressing the generation of stripes. Attached Figure Description

[0035] Figure 1 This is a central cross-sectional view of an image forming apparatus according to one embodiment.

[0036] Figure 2 This is a left-side view of the drive unit.

[0037] Figure 3 This is a right-side view of the drive unit.

[0038] Figure 4 Is Figure 3 The diagram has removed the states of the main motor and the cover type.

[0039] Figure 5 Is Figure 4 The diagram shows the state of the sheet metal parts and each photosensitive drum after they have been removed.

[0040] Figure 6 This is the front view of the second intermediate gear.

[0041] Figure 7 yes Figure 6 BB cross-sectional view.

[0042] Figure 8 yes Figure 2 AA sectional view.

[0043] Symbol Explanation

[0044] 1 Image forming apparatus

[0045] 42 Belt Conveyor Section

[0046] 56A First developing roller

[0047] 56B Second Developing Roller

[0048] 56C Third Developing Roller

[0049] 56D Fourth Developing Roller

[0050] 55A First Photosensitive Drum

[0051] 55B Second Photosensitive Drum

[0052] 55C Third Photosensitive Drum

[0053] 55D Fourth Photosensitive Drum

[0054] 70A Second Intermediate Gear

[0055] 73 First Cover

[0056] 74 Second Cover

[0057] 75 sheet metal parts

[0058] 78 Handling motors (electric motors)

[0059] 79A First Intermediate Gear

[0060] 79B Third Intermediate Gear

[0061] 79D Pendulum Gear

[0062] 79J Second Output Gear

[0063] 79T clutch input gear

[0064] 79U Electromagnetic Clutch

[0065] 79V clutch output gear

[0066] 79W Third Output Gear

[0067] 91 First landing section

[0068] 92 Second landing section

[0069] 93. Protrusion

[0070] 731 First Card Unit

[0071] 741 Second Card Section

[0072] 781 First Output Gear

[0073] 791 First Gear System

[0074] 792 Second Gear System

[0075] 793 Third Gear System

[0076] 794 Fourth Gear System

[0077] 795 Fifth Gear System

[0078] S-sheet material. Detailed Implementation

[0079] In the following explanation, Figure 1 The left and right sides are defined as the front and rear sides of the image forming apparatus 1, respectively. Figure 1 The front side and the inner side of the paper are defined as the right and left sides of the image forming apparatus 1, respectively. Additionally, Figure 1 The upper and lower sides are defined as the upper and lower sides of the image forming apparatus 1, respectively.

[0080] [Overall structure of the image forming apparatus]

[0081] Figure 1 This is a central cross-sectional view of an image forming apparatus 1 according to one embodiment. The image forming apparatus 1 is formed by an apparatus body 2, which is a generally rectangular box-shaped shell. The apparatus body 2 has a main frame (not shown) that supports the various components and a main cover 21 that forms the appearance of the main frame. The main frame has a left frame 20 disposed on the left side (see reference). Figure 2 The main body cover 21 has a discharge tray 211 on its upper surface.

[0082] Image forming apparatus 1 is a color laser printer that forms multi-color images on sheets S such as paper and OHP sheets using an electrophotographic method. Sheet tray 3, transport section 4, image forming section 5, re-transport section 6, drive section 7, and MP tray 8 are housed within apparatus body 2. Inside apparatus body 2, image forming section 5 is positioned approximately at the top and center; transport section 4 is positioned below and behind image forming section 5; re-transport section 6 is positioned throughout the front and rear of apparatus body 2 and below transport section 4; sheet tray 3 is positioned below re-transport section 6; drive section 7 is positioned to the left of sheet tray 3 and re-transport section 6; and MP tray 8 is positioned in front of image forming section 5.

[0083] An opening 22, serving as an insertion port for a sheet tray 3, is formed on the lower front surface of the device body 2. The sheet tray 3 has a box-shaped sheet storage section 31 with an open top and a pressure plate 32 that supports the sheet S and allows it to be raised and lowered. By moving the sheet tray 3 through the opening 22 in the front-back direction, the sheet tray 3 can be inserted into or removed from the device body 2.

[0084] An opening 23, serving as a receiving opening for the MP tray 8, is formed above the opening 22 on the front surface of the main body 2. The MP tray 8 includes a tray 81 that can be opened and closed with the lower end of the opening 23 as a fulcrum, and a pressure plate 82 that supports the sheet S for lifting. The MP tray 8 can be in a closed position covering the opening 23. Figure 1 The position indicated by the double-dotted line) and the opening position that makes the opening 23 open ( Figure 1 The MP tray 8 can swing between positions indicated by solid lines. When in the open position, the MP tray 8 can support multiple overlapping sheets S.

[0085] The conveying unit 4 is composed of various components arranged along the conveying path P1, and conveys the sheet S along the conveying path P1. The conveying path P1 is the path through which the sheet tray 3 or MP tray 8 is connected to the discharge tray 211 via the image forming unit 5. The conveying unit 4 is composed of a supply unit 41, a belt conveying unit 42, and a discharge unit 43 in sequence from the upstream side of the conveying direction of the conveying path P1.

[0086] The supply unit 41 includes: a supply mechanism 41A for separating and conveying sheets S stored in sheet tray 3 one by one; a supply mechanism 41B for separating and conveying sheets S accumulated in MP tray 8 one by one; and a pair of alignment rollers 415. The supply mechanism 41A includes a supply roller 411, a separation roller 412, a separation pad 413, and a pair of conveying rollers 414.

[0087] Sheets S, contained in sheet tray 3, are fed one by one onto conveyor path P1 via feed roller 411, separation roller 412, and separation pad 413. Sheets S fed onto conveyor path P1 are conveyed toward image forming unit 5 via conveyor roller pair 414 and registration roller pair 415.

[0088] The supply mechanism 41B includes a supply roller 416, a separation roller 417, and a separation pad 418. Sheets S, housed in the sheet tray 3, are fed one by one onto the transport path P1 via the supply roller 416, the separation roller 417, and the separation pad 418. The sheets S fed onto the transport path P1 are transported toward the image forming unit 5 via the registration roller pair 415.

[0089] The conveyor unit 42 includes: a drive roller 421 that rotates in conjunction with the image forming unit 5; a driven roller 422 that is configured to rotate in a position separate from the drive roller 421; and a conveyor belt 423 wound between the drive roller 421 and the driven roller 422. Then, the conveyor belt 423 rotates with the sheet S loaded, thereby conveying the sheet S along the conveyor path P1 opposite to the underside of each photosensitive drum 55A to 55D of the image forming unit 5, and then to the fixing unit 53.

[0090] The discharge section 43 includes an intermediate discharge roller pair 431 and a discharge roller pair 432 disposed between the branch P11 of the conveying path P1 and the discharge tray 211. The intermediate discharge roller pair 431 and the discharge roller pair 432 are configured as reversing rollers capable of switching between forward and reverse rotation. The intermediate discharge roller pair 431 and the discharge roller pair 432 rotate forward when discharging the sheet S conveyed from the fixing section 53 onto the discharge tray 211, and rotate reverse when reversing the sheet S and conveying it to the re-conveying path P2.

[0091] The image forming unit 5 is a direct-connect structure capable of both color and monochrome printing, comprising a first drum unit 51A, a second drum unit 51B, a third drum unit 51C, and a fourth drum unit 51D arranged sequentially in the front-to-back direction. In other words, the first drum unit 51A is positioned at the foremost position in the front-to-back direction, and the fourth drum unit 51D is positioned at the rearmost position. The image forming unit 5 also includes a first exposure LED head 52A, a second exposure LED head 52B, a third exposure LED head 52C, and a fourth exposure LED head 52D arranged sequentially in the front-to-back direction. Furthermore, the image forming unit 5 includes a fixing unit 53 and a cleaning device 54.

[0092] The first drum unit 51A corresponds to yellow, the second drum unit 51B to magenta, the third drum unit 51C to cyan, and the fourth drum unit 51D to black toner (developer), respectively. The first drum unit 51A includes a first photosensitive drum 55A, a first developing roller 56A, and a first transfer roller 57A that is opposite the first photosensitive drum 55A across the conveyor belt 423.

[0093] Similarly, the second drum unit 51B includes a second photosensitive drum 55B, a second developing roller 56B, and a second transfer roller 57B opposite to the second photosensitive drum 55B across the conveyor belt 423. The third drum unit 51C includes a third photosensitive drum 55C, a third developing roller 56C, and a third transfer roller 57C opposite to the third photosensitive drum 55C across the conveyor belt 423. The fourth drum unit 51D includes a fourth photosensitive drum 55D, a fourth developing roller 56D, and a fourth transfer roller 57D opposite to the fourth photosensitive drum 55D across the conveyor belt 423.

[0094] In this image forming unit 5, each photosensitive drum 55A-55D, which is uniformly charged by a charger, is selectively exposed by each exposure LED head 52A-52D. Through this exposure, the charge is selectively removed from the surface of each photosensitive drum 55A-55D, and an electrostatic latent image is formed on the surface of each photosensitive drum 55A-55D.

[0095] A developing bias voltage is applied to each developing roller 56A-56D. When the electrostatic latent image formed on each photosensitive drum 55A-55D is opposite to each developing roller 56A-56D, toner is supplied from each developing roller 56A-56D to the electrostatic latent image through the potential difference between the electrostatic latent image and each developing roller 56A-56D. As a result, a toner image is formed on the surface of each photosensitive drum 55A-55D.

[0096] The sheet S, which is being conveyed toward the image forming unit 5, is being transported by the conveyor belt 423 and passes between the conveyor belt 423 and each photosensitive drum 55A to 55D in sequence. Then, when the toner image on the surface of each photosensitive drum 55A to 55D is facing the sheet S, it is transferred to the sheet S by the transfer bias applied to each transfer roller 57A to 57D.

[0097] The fixing unit 53 is disposed downstream of the fourth photosensitive drum 55D in the transport path P1. The fixing unit 53 includes a heating roller 531 and a pressure roller 532 that presses against the heating roller 531. The heating roller 531 is disposed on the image forming surface side of the sheet S and is driven to rotate synchronously with the conveyor belt 423 to heat the toner and impart a transport force to the sheet S.

[0098] On the other hand, the pressure roller 532 is positioned on the opposite side of the heating roller 531, with the sheet S in between, and presses the sheet S toward the heating roller 531. As a result, the pressure roller 532 is driven to rotate by the rotational force from the heating roller 531 through the sheet S in contact with the heating roller 531.

[0099] In addition, the fixing unit 53 has a fixing discharge roller pair 533 arranged downstream of the sheet S in the conveying direction compared to the heating roller 531 and the pressure roller 532.

[0100] In the image forming unit 5, the toner image transferred onto the sheet S is heat-fixed as it passes between the heating roller 531 and the pressure roller 532. After the toner image is heat-fixed, the sheet S is held by the fixing discharge roller pair 533 and conveyed to the intermediate discharge roller pair 431.

[0101] The cleaning device 54 is disposed between the belt conveyor section 42 and the re-transport section 6 and is a component used to recover waste toner from the conveyor belt 423.

[0102] The cleaning device 54 includes a support roller 541, a cleaning roller 542, a recovery roller 543, a scraper 544, a recovery chamber 545, and a waste ink cartridge 546.

[0103] The support roller 541 is disposed inside the conveyor belt 423 and contacts the conveyor belt 423 from above. The cleaning roller 542 is disposed opposite to the support roller 541 across the conveyor belt 423 and contacts the conveyor belt 423 from below.

[0104] In the cleaning device 54, the waste toner attached to the conveyor belt 423 is recovered by the cleaning roller 542, the recovery roller 543, the scraper 544 and the recovery chamber 545, and the recovered waste toner is collected in the waste ink cartridge 546.

[0105] The cleaning operation begins after image formation in the image forming unit 5 has finished. During the cleaning operation, waste toner adhering to the surface of the conveyor belt 423 is electrostatically held on the surface of the cleaning roller 542 by a bias voltage applied to it, and then electrostatically transferred to the recovery roller 543. The waste toner transferred to the recovery roller 543 is scraped off by the scraper 544 and falls into the recovery chamber 545. The waste toner falling into the recovery chamber 545 is conveyed rearward by a conveying device (not shown) and collected in the waste ink cartridge 546.

[0106] The re-transport unit 6 is composed of components arranged along the re-transport path P2, which transports the sheet S. The re-transport path P2 branches off from the branch point P11 between the fixing unit 53 and the intermediate discharge roller pair 431 in the transport path P1, passes above the sheet tray 3, and merges at the confluence point P12 between the sheet tray 3 and the image forming unit 5. With this structure, the re-transport path P2 can be shortened compared to a structure in which the re-transport path P2 is arranged below the sheet tray 3.

[0107] The re-transfer unit 6 is located above the sheet tray 3 and below the image forming unit 5, and is equipped with a removable re-transfer unit 61. The re-transfer unit 61 includes a pair of inclined feed rollers 611 and a re-transfer roller 612 for guiding the sheet S along the re-transfer path P2. A driven roller 613 is disposed on the device body 2 above the re-transfer roller 612, and the driven roller 613 forms a rolling gap with the re-transfer roller 612.

[0108] An opening 24, serving as an insertion port for the re-transfer unit 61, is formed on the rear surface of the device body 2. By moving the re-transfer unit 61 through the opening 24 in the front-back direction, the re-transfer unit 61 can be inserted into or removed from the device body 2. Furthermore, the arrangement of the re-transfer unit 61 is not particularly limited; for example, it can be arranged below the sheet tray 3.

[0109] The re-transport unit 6 conveys the sheet S, on one side of which an image has been formed, from the intermediate discharge roller pair 431 to the confluence unit P12. The sheet S, re-transported from the confluence unit P12 to the image forming unit 5, is then discharged from the discharge unit 43 to the discharge tray 211 after an image is formed on the other side by the image forming unit 5. In the event of a blockage in the re-transport unit 6, the blockage can be cleared by pulling out the re-transport unit 61.

[0110] Thus, double-sided printing can be performed in the image forming apparatus 1, that is, the sheet S on which the image forming unit 5 forms an image on one side is transported back to the image forming unit 5 via the retransmission path P2, and an image is formed on the other side of the sheet S.

[0111] The drive unit 7 consists of an electric motor and a gear system located on the left side of the left frame 20, which drives the sheet tray 3, the conveying unit 4, the image forming unit 5, the re-conveying unit 6, and the MP tray 8. The drive unit 7 will be described in detail below, along with the structure for suppressing strip formation.

[0112] [Drive Section]

[0113] Figure 2 This is a left-side view of drive unit 7. Figure 3 This is a right-side view of drive unit 7. Figure 4 Is Figure 3 The diagrams showing the states of the main motor 76 and the cover type have been removed.Figure 5 Is Figure 4 The diagram shows the state of the sheet metal component 75 and each photosensitive drum 55A-55D, excluding those components. (See diagram below.) Figure 2 to Figure 5 As shown, the drive unit 7 includes a first drive unit 71, a second drive unit 72, a first cover 73, a second cover 74, and a sheet metal component 75.

[0114] <First Drive Unit>

[0115] The first drive unit 71 is a unit that drives the pressure plate 32 of the sheet tray 3, the pressure plate 82 of the MP tray 8, the supply unit 41, the fixing unit 53, the discharge unit 43, and the re-transport unit 6. The first drive unit 71 includes a main motor 76 (see reference). Figure 3 ) and the first drive transmission mechanism 77 connected to the main motor 76 (see reference) Figure 4 and Figure 5 The first drive transmission mechanism 77 has multiple gear systems 771 to 773 that transmit driving force to the aforementioned parts.

[0116] <Second Drive Unit>

[0117] The second drive unit 72 drives the belt conveyor 42, each drum unit 51A-51D, and the cleaning device 54. The second drive unit 72 is separate from the first drive unit 71, which drives components such as the fixing unit 53 that are subjected to high loads, and drives components such as the drum units 51A-51D that directly affect image quality. Therefore, uneven rotation of the first drive unit 71 is not transmitted to the second drive unit 72, and striping can be suppressed.

[0118] like Figure 4 and Figure 5 As shown, the second drive unit 72 includes a processing motor 78 (an example of a motor), a first output gear 781, and a second drive transmission mechanism 79. The first output gear 781 is a gear coaxially disposed with the processing motor 78 and outputs driving force from the processing motor 78. In this embodiment, the first output gear 781 is a gear fixed to the rotating shaft of the processing motor 78. The second drive transmission mechanism 79 includes a first gear train 791, a second gear train 792, and a fifth gear train 795 that transmit driving force to the aforementioned components.

[0119] (First gear train)

[0120] The first gear train 791 is a gear train that transmits the driving force of the processing motor 78 to the first developing roller 56A, the second developing roller 56B, the third developing roller 56C, and the fourth developing roller 56D. The first gear train 791 is composed of a third gear train 793 that transmits driving force to the first developing roller 56A, the second developing roller 56B, and the third developing roller 56C, and a fourth gear train 794 that transmits driving force to the fourth developing roller 56D.

[0121] (Third gear train)

[0122] The third gear train 793 includes a first intermediate gear 79A that meshes with the first output gear 781, a third intermediate gear 79B that meshes with the first intermediate gear 79A, a gear 79C that meshes with the third intermediate gear 79B, and a pendulum gear 79D that meshes with gear 79C. Additionally, the third gear train 793 includes a gear 79E that meshes with the pendulum gear 79D, a gear 79F that meshes with the gear 79E, a gear 79G that meshes with the gear 79E, a gear 79H that meshes with the gear 79G, and a second output gear 79J that meshes with the gear 79H.

[0123] The first intermediate gear 79A is a secondary gear integrally formed with the right-side input gear 79K, which meshes with the first output gear 781, and the left-side output gear 79L, which meshes with the third intermediate gear 79B. Alternatively, the first intermediate gear 79A can also be a primary gear meshing with both the first output gear 781 and the third intermediate gear 79B. Furthermore, the first intermediate gear 79A also outputs driving force to the cleaning device 54.

[0124] Gear 79F is coaxially configured with the first developing roller 56A and outputs driving force to the first developing roller 56A. Gear 79G is coaxially configured with the second developing roller 56B and outputs driving force to the second developing roller 56B. Second output gear 79J is coaxially configured with the third developing roller 56C and outputs driving force to the third developing roller 56C.

[0125] Gear 79E is a secondary gear integrally formed with the input gear 79M on the left side, which meshes with the pendulum gear 79D, and the output gear 79N on the right side, which meshes with gears 79F and 79G. Alternatively, gear 79E can also be a primary gear that meshes with the pendulum gear 79D, gear 79F, and gear 79G.

[0126] The pendulum gear 79D is a gear positioned upstream of the first developing roller 56A, the second developing roller 56B, and the third developing roller 56C, and outputs driving force to these rollers. The pendulum gear 79D can swing to a first position where it meshes with the input gear 79M to transmit driving force. Figure 4 and Figure 5 The position indicated by the solid line in the middle) and the second position where the driving force is disconnected from the input gear 79M and cut off. Figure 4 and Figure 5 (The position is indicated by a double-dotted line).

[0127] Therefore, color printing is possible when the pendulum gear 79D is in the first position, and monochrome printing is possible when the pendulum gear 79D is in the second position. By using the pendulum gear 79D as a device for transmitting and cutting off driving force, cost reduction is achieved.

[0128] (Fourth gear train)

[0129] The fourth gear train 794 includes a gear 79P meshing with the third intermediate gear 79B, a gear 79Q meshing with the gear 79P, a gear 79R meshing with the gear 79Q, a gear 79S meshing with the gear 79R, and an electromagnetic clutch 79U. Additionally, the fourth gear train 794 includes a clutch input gear 79T meshing with the gear 79S to input driving force to the electromagnetic clutch 79U, a clutch output gear 79V outputting driving force from the electromagnetic clutch 79U, and a third output gear 79W meshing with the clutch output gear 79V.

[0130] Gear 79S is coaxially arranged with the second output gear 79J on the left side. Gear 79S and the second output gear 79J are separate and rotate independently. Furthermore, the coaxially arranged gears are not limited to these two gears; any gear from the third gear train 793 or the fourth gear train 794 can be used. Thus, by coaxially arranging a portion of the gears in the third gear train 793 and a portion of the gears in the fourth gear train 794, the first gear train 791 can be miniaturized.

[0131] The third output gear 79W is configured coaxially with the fourth developing roller 56D and outputs driving force to the fourth developing roller 56D.

[0132] The electromagnetic clutch 79U is a component disposed upstream of the fourth developing roller 56D and outputs driving force to the fourth developing roller 56D. The electromagnetic clutch 79U can be displaced to a first state of transmitting driving force and a second state of cutting off driving force. Therefore, when the electromagnetic clutch 79U is in the first position, monochrome or color printing can be performed. By using the electromagnetic clutch 79U as a device for transmitting and cutting off driving force, space can be saved.

[0133] The clutch input gear 79T is disposed to the left of the electromagnetic clutch 79U, and the clutch output gear 79V is disposed coaxially with the clutch input gear 79T to the left of the clutch input gear 79T. Preferably, the number of teeth of the clutch output gear 79V is different from the number of teeth of the clutch input gear 79T. In this embodiment, the clutch output gear 79V is a gear with fewer teeth than the clutch input gear 79T.

[0134] Alternatively, the clutch output gear 79V can also be a gear with more teeth than the clutch input gear 79T. In this way, by making the number of teeth of the clutch input gear 79T different from the number of teeth of the clutch output gear 79V, the speed is reduced or increased when the electromagnetic clutch 79U is in motion. As a result, the rotation of the clutch output gear 79V is stabilized, and the image quality in the fourth drum unit 51D is improved.

[0135] The fourth gear train 794 meshes with the third intermediate gear 79B via gear 79P, thus branching off from the third gear train 793 at the third intermediate gear 79B. This ensures that the fourth gear train 794 branches off at the third intermediate gear 79B, which is as close as possible to the first output gear 781 fixed to the rotating shaft of the processing motor 78. Consequently, uneven rotation between the third gear train 793 and the fourth gear train 794 is less likely to be transmitted to the other gear train, thus ensuring stable drive of each gear. Furthermore, the fourth gear train 794 can be made shorter than a structure that branches directly from the first output gear 781.

[0136] Alternatively, the fourth gear train 794 can simply branch from the upstream of the pendulum gear of the third gear train, for example, it can also branch from the first output gear 781 or gear 79C.

[0137] (Second gear train)

[0138] The second gear train 792 is a gear train that transmits the driving force of the processing motor 78 to the first photosensitive drum 55A, the second photosensitive drum 55B, the third photosensitive drum 55C, and the fourth photosensitive drum 55D. The second gear train 792 includes a second intermediate gear 70A meshing with the first output gear 781, a gear 70B meshing with the second intermediate gear 70A, a gear 70C meshing with the gear 70B, and a gear 70D meshing with the gear 70C. Additionally, the second gear train 792 includes a gear 70E meshing with the second intermediate gear 70A, a gear 70F meshing with the gear 70E, and a gear 70G meshing with the gear 70F.

[0139] The second intermediate gear 70A is a secondary gear that is assembled and rotates as a single unit with the left input gear 70H, which meshes with the first output gear 781, and the right output gear 70J, which meshes with gears 70B and 70E.

[0140] Gear 70D is coaxially configured with the first photosensitive drum 55A and outputs driving force to the first photosensitive drum 55A. Gear 70B is coaxially configured with the second photosensitive drum 55B and outputs driving force to the second photosensitive drum 55B. Gear 70E is coaxially configured with the third photosensitive drum 55C and outputs driving force to the third photosensitive drum 55C. Gear 70G is coaxially configured with the fourth photosensitive drum 55D and outputs driving force to the fourth photosensitive drum 55D.

[0141] According to the first gear train 791 and the second gear train 792 described above, the first intermediate gear 79A of the first gear train 791 and the second intermediate gear 70A of the second gear train 792 directly mesh with the first output gear 781 fixed to the rotating shaft of the processing motor 78. In this way, the first gear train 791 that drives each developing roller 56A to 56D and the second gear train 792 that drives each photosensitive drum 55A to 55D branch directly from the processing motor 78, thereby making it difficult for uneven rotation of each to propagate to the other gear train, thus suppressing the generation of stripes.

[0142] (Fifth Gear System)

[0143] The fifth gear train 795 is a gear train that transmits the driving force of the processing motor 78 to the belt conveyor 42. The fifth gear train 795 has a gear 70K that meshes with the input gear 70H of the second intermediate gear 70A, a gear 70L that meshes with the gear 70K, and a gear 70M that meshes with the gear 70L.

[0144] Gear 70L is a two-stage gear that integrates the input gear 70N on the left, which meshes with gear 70K, and the output gear 70P on the right, which meshes with gear 70M, into a single rotating unit.

[0145] Gear 70M is a gear that outputs driving force to the drive roller 421 of the belt conveyor 42. Gear 70M is a secondary gear integrally formed with the input gear 70Q on the left side, which meshes with the output gear 70P of gear 70L, and the output gear 70R on the right side, which meshes with the gear (not shown) of the drive roller 421. Alternatively, gear 70M may also be a primary gear that meshes with both the output gear 70P and the gear of the drive roller 421.

[0146] The fifth gear train 795 meshes with the second intermediate gear 70A via gear 70K, thereby branching off from the second gear train 792 via the second intermediate gear 70A. In this way, by branching off from the second intermediate gear 70A, the upstream second gear train 792, the transmission of uneven rotation between the fifth gear train 795 and the second gear train 792 can be suppressed.

[0147] (Reverse rotation prevention mechanism)

[0148] The second intermediate gear 70A and gear 70L have a reverse rotation prevention mechanism 9. The reverse rotation prevention mechanism 9 is a mechanism that prevents the output gear 70J of the second intermediate gear 70A and the output gear 70P of the gear 70L from rotating in reverse when the motor 78 is being processed.

[0149] Figure 6 This is the front view of the second intermediate gear 70A. Figure 7 yes Figure 6BB sectional view. The input gear 70H has a cylindrical portion 701 protruding to the right about the rotation axis. The cylindrical portion 701 has a cut extending along the rotation axis direction, one end face of the cut forming a first abutment portion 91, and the other end face of the cut forming a second abutment portion 92.

[0150] The output gear 70J has a rotating shaft portion 702 that is inserted into the cylindrical portion 701 and supported for rotation, and a protrusion 93 that protrudes radially from the rotating shaft portion 702 in the space portion inside the teeth. The protrusion 93 has a third abutting portion 931 that can abut against the first abutting portion 91 and a fourth abutting portion 932 that can abut against the second abutting portion 92.

[0151] The reverse rotation prevention mechanism 9 is composed of the first abutment portion 91, the second abutment portion 92, and the protrusion 93 described above. When the motor 78 is rotating in the forward direction, the third abutment portion 931 of the protrusion 93 abuts against the first abutment portion 91. Figure 7 (The state is represented by a solid line in the middle), the input gear 70H and the output gear 70J rotate as a whole.

[0152] Furthermore, when the motor 78 switches from forward rotation to reverse rotation, the third abutment portion 931 of the protrusion 93 separates from the first abutment portion 91, and the fourth abutment portion 932 abuts against the second abutment portion 92. Figure 7 (The state is indicated by a double-dotted line). At this time, during the period from the separation of the protrusion 93 from the first abutment 91 to the abutment of the protrusion 93 with the second abutment 92, the input gear 70H idles while the output gear 70J does not rotate. Therefore, reverse rotation of the output gear 70J is prevented during the idling of the input gear 70H.

[0153] The reverse rotation prevention mechanism of gear 70L has the same structure as the above-described structure, so its detailed description is omitted.

[0154] By employing this reverse rotation prevention mechanism 9, abnormal noise generated from the pendulum gear 79D is suppressed when the pendulum gear 79D is disengaged. Therefore, even when the processing motor 78 is temporarily reverse-rotated, reverse rotation of each photosensitive drum 55A-55D and the belt conveyor 42 can be prevented. Furthermore, the reverse rotation of the processing motor 78 is achieved by one or two teeth of the gear.

[0155] Alternatively, the structure can be reversed, with the first abutment portion 91 and the second abutment portion 92 provided on the output gear 70J, and the protrusion portion 93 provided on the input gear 70H. That is, the reverse rotation prevention mechanism 9 can be constructed simply by having the protrusion portion 93 of one of the two coaxially arranged gears and the first abutment portion 91 and the second abutment portion 92 of the other gear.

[0156] In addition, the reverse rotation prevention mechanism 9 can be provided on gears other than the second intermediate gear 70A and gear 70L, as long as it is in the second gear train 792 and the fifth gear train 795.

[0157] <First Cover>

[0158] like Figure 2 As shown, the first cover 73 is a resin cover, fixed to one side of the sheet metal component 75 and supporting the electromagnetic clutch 79U. In this embodiment, the first cover 73 is threaded to the left surface of the sheet metal component 75. Figure 8 yes Figure 2 AA sectional view. For example... Figure 8 As shown, the first cover 73 has a first engaging portion 731 that engages with the second engaging portion 741 of the second cover 74 and a third engaging portion 732 that engages with the elongated hole 752 of the sheet metal component 75. The first engaging portion 731 and the third engaging portion 732 are cylindrical bosses protruding toward the sheet metal component 75.

[0159] <Second Cover>

[0160] like Figure 3 As shown, the second cover 74 is a resin cover, fixed to the other side of the sheet metal component 75 and supporting one end of the clutch output gear 79V. In this embodiment, the second cover 74 is threaded to the right surface of the sheet metal component 75. Figure 8 As shown, the second cover 74 has a first engaging portion 731 of the first cover 73 and a second engaging portion 741 that engages with the positioning hole 751 of the sheet metal component 75. The second engaging portion 741 is a cylindrical boss protruding toward the sheet metal component 75.

[0161] 〈Sheet metal parts〉

[0162] Sheet metal component 75 is a sheet metal piece that supports the gear trains 791-795, the first cover 73, and the second cover 74. For example... Figure 8 As shown, the sheet metal component 75 has a circular positioning hole 751 that engages with the second engaging portion 741 of the first cover 73.

[0163] Based on the first cover 73, the second cover 74, and the sheet metal component 75, the outer peripheral surface of the second engaging portion 741 engages with the positioning hole 751 of the sheet metal component 75, and the inner peripheral surface of the second engaging portion 741 engages with the outer peripheral surface of the first engaging portion 731. Thus, the second cover 74 is positioned on the sheet metal component 75, and the first cover 73 is positioned on the second cover 74. Therefore, the electromagnetic clutch 79U supported on the first cover 73 and the clutch output gear 79V supported on the second cover 74 can be positioned with good precision.

[0164] like Figure 2 and Figure 4As shown, the sheet metal component 75 has an elongated hole 752 that engages with the third engaging portion 732 of the first cover 73. By engaging the third engaging portion 732 with the elongated hole 752, during assembly operations, when assembling the first cover 73 onto the sheet metal component 75 with the second cover 74 assembled thereon, rotation of the first cover 73 around the first engaging portion 731 as a fulcrum can be prevented. Therefore, operability is improved.

Claims

1. An image forming apparatus, characterized in that, have: A first developing roller, a second developing roller, and a third developing roller that carry color developer; The fourth developing roller carrying the black developer; The first photosensitive drum corresponding to the first developing roller; The second photosensitive drum corresponding to the second developing roller; The third photosensitive drum corresponding to the third developing roller; The fourth photosensitive drum corresponding to the fourth developing roller; An electric motor that drives the fourth developing roller and the fourth photosensitive drum; An output gear, which is coaxially configured with the motor and outputs driving force from the motor; A gear train having an intermediate gear that meshes with the output gear and transmits the driving force of the motor to the fourth photosensitive drum; The belt is opposite to the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum; as well as A belt gear train, wherein the intermediate gear branches off from the gear train and transmits driving force to the belt.

2. The image forming apparatus according to claim 1, characterized in that, The intermediate gear is a two-stage gear with a first gear and a second gear. The first gear drives the transmission to the fourth photosensitive drum, and the second gear drives the transmission to the belt.

3. The image forming apparatus according to claim 2, characterized in that, The first gear has a smaller diameter than the second gear.

4. The image forming apparatus according to claim 1, characterized in that, It also features a belt cleaning device that recovers toner from the belt. The motor drives the cleaning device.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that, It also has sheet metal that supports the gear train. The motor is located on one side of the sheet metal. The output gear and the gear train are located on the other side of the sheet metal.

6. The image forming apparatus according to claim 5, characterized in that, The gear train is located on the other side of the sheet metal.

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