Image forming device

Abstract

To provide an image forming device capable of shortening a time required for switching a rotative direction of a conveying roller.SOLUTION: An image forming device comprises a body housing, first conveying rollers 92 and 93 for conveying a sheet, a first motor M1 for supplying a driving force to the first conveying rollers 92 and 93, a second motor M2 for supplying a driving force to the first conveying rollers 92 and 93, a transmission mechanism 300 for selectively transmitting the driving force of either the first motor M1 or the second motor M2 to the first conveying rollers 92 and 93, and a control part 10. The transmission mechanism 300 can switch over between a first transmission state where the driving force of the first motor M1 is transmitted to the first conveying rollers 92 and 93 and a second transmission state where the driving force of the second motor M2 is transmitted to the first conveying rollers 92 and 93. The control part 10 switches a rotative direction of the first conveying rollers 92 and 93 by switching a transmission state of the transmission mechanism 300 in a state where the first motor M1 and the second motor M2 are respectively rotated.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus capable of switching the rotation direction of a transport roller. [Background technology]

[0002] Conventionally, there is known an image forming apparatus that includes a conveying roller that conveys a sheet and a motor that supplies a driving force to the conveying roller (see Patent Document 1). In this technology, the rotation direction of the conveying roller is switched by switching the rotation direction of the motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-248326 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with conventional technology, when switching the rotation direction of the transport rollers, the motor needs to be slowed down, stopped, and rotated in the opposite direction, which can increase the time required to switch the rotation direction of the transport rollers.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to reduce the time required to switch the rotation direction of the transport roller. [Means for solving the problem]

[0006] In order to solve the above problem, the image forming apparatus of the present invention comprises a main body housing, a first conveying roller for conveying a sheet, a first motor for supplying a driving force to the first conveying roller, a second motor for supplying a driving force to the first conveying roller, a transmission mechanism for selectively transmitting the driving force of either the first motor or the second motor to the first conveying roller, and a control unit. The transmission mechanism is switchable between a first transmission state in which the driving force of the first motor is transmitted to the first conveyor roller, and a second transmission state in which the driving force of the second motor is transmitted to the first conveyor roller. The control unit switches the rotation direction of the first conveyor roller by switching the transmission state of the transmission mechanism while rotating the first motor and the second motor.

[0007] According to this configuration, when switching the rotation direction of the first conveyor roller, there is no need to slow down, stop, or reverse the motor, so the time required to switch the rotation direction of the first conveyor roller can be reduced.

[0008] The control unit may switch the rotation direction of the first conveying roller when the first conveying roller is in contact with the sheet.

[0009] According to this configuration, the sheet conveying direction can be switched quickly.

[0010] In addition, the first conveying roller may convey the sheet toward the outside of the main body housing when the transmission mechanism is in the second transmission state, and may convey the sheet toward the inside of the main body housing when the transmission mechanism is in the first transmission state.

[0011] The image forming apparatus may further include an image forming unit including a photosensitive member and a developing unit, and the first motor may drive at least a part of the image forming unit.

[0012] According to this configuration, the rotation direction of the first conveyor roller can be switched without stopping the image forming unit.

[0013] The second motor may drive a second transport roller that rotates in one direction.

[0014] According to this configuration, the rotation direction of the first conveyor roller can be switched without stopping the second conveyor roller.

[0015] The transmission mechanism may be switchable to a disconnected state in which neither the driving force of the first motor nor the driving force of the second motor is transmitted to the first conveyor roller.

[0016] This configuration makes it possible to prevent the first conveyor roller from receiving a driving force, thereby preventing unnecessary rotation of the first conveyor roller and reducing wear. Also, for example, if a sheet becomes jammed in the first conveyor roller, the transmission mechanism can be disconnected, making it easier to remove the sheet.

[0017] The transmission mechanism may also have a first gear to which driving force is input from the first motor, a second gear to which driving force is input from the second motor, and an output gear that outputs driving force to the first conveying roller, wherein the first gear, the second gear, and the output gear are rotatable around a common axis, and the output gear is disposed between the first gear and the second gear in the axial direction, is movable in the axial direction, and is engageable with the first gear and engageable with the second gear.

[0018] According to this configuration, the transmission mechanism can be made smaller than a transmission mechanism that uses a pendulum gear, for example.

[0019] The transmission mechanism may also have a spring that urges the output gear toward one of the first gear and the second gear, and a cam that presses the output gear toward the other of the first gear and the second gear.

[0020] The output gear may have a first engaging portion that engages with the first gear in the rotational direction and a second engaging portion that engages with the second gear in the rotational direction, the first gear may have a first engaged portion that engages with the first engaging portion in the rotational direction, and the second gear may have a second engaged portion that engages with the second engaging portion in the rotational direction. [Effects of the Invention]

[0021] According to the present invention, it is possible to reduce the time required to switch the rotation direction of the transport roller. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram showing a color printer according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing a mechanism for transmitting the driving force of a motor. [Figure 3] 1A and 1B are diagrams showing the structure of the transmission mechanism, with (a) showing the disconnected state, (b) showing the first transmission state, (c) showing the second transmission state, and (d) a perspective view showing the cam. [Figure 4] 10 is a flowchart showing a printing process. [Figure 5] 10 is a flowchart illustrating a transmission mechanism switching process. [Figure 6] 10 is a flowchart showing a re-conveyance roller driving process. [Figure 7] This figure shows the operating state of each component during double-sided printing, with (a) showing the state in which the first sheet is supplied to the image forming unit and (b) showing the state in which the first sheet is transported toward the outside of the main body housing. [Figure 8] 1A is a diagram showing a state in which the first sheet is switched back, and FIG. 1B is a diagram showing a state in which the first sheet is conveyed by a re-conveyance roller. [Figure 9] 1A is a diagram showing a state in which the conveyance of the first sheet is temporarily stopped, and FIG. 1B is a diagram showing a state in which the conveyance of the first sheet is resumed. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. As shown in Figure 1, a color printer 1, which is an example of an image forming device, is configured to be able to form images on both sides of a sheet S, and includes a main body housing 2, a sheet supply unit 3, an image forming unit 4, and a conveying unit 9 arranged inside the main body housing 2.

[0024] The main body housing 2 has an upper cover 21 that opens and closes the opening at the top, an ejection tray 22 on which a sheet S with an image formed thereon is placed, and an ejection port 23 for ejecting the sheet S onto the ejection tray 22.

[0025] The sheet supply unit 3 is provided in the lower part of the main body housing 2, and includes a supply tray 31 that stores sheets S, a pressure plate 32, a supply roller 33, a separation roller 34, a roller 36, and a registration roller 37. The sheet supply unit 3 uses the pressure plate 32 to move the sheets S in the supply tray 31 toward the supply roller 33, and the supply roller 33 sends the sheets S from the supply tray 31 toward the image forming unit 4. The sheet supply unit 3 then separates the sheets S one by one using the separation roller 34, and supplies them to the image forming unit 4 using the roller 36 and the registration roller 37.

[0026] The image forming section 4 includes four LED units 5, four process units 6 as an example of an image forming section, a transfer unit 7, and a fixing unit 8.

[0027] The LED unit 5 is disposed above and facing the photosensitive drum 63, and includes a plurality of LEDs (Light Emitting Diodes) (not shown) arranged in the left-right direction at the bottom end of the LED unit 5. The LED unit 5 exposes the surface of the photosensitive drum 63 by blinking the LEDs based on image data.

[0028] The process unit 6 is disposed between the discharge tray 22 and the supply tray 31, and is detachable from the main body housing 2 when the upper cover 21 is open. Each process unit 6 is configured to include a drum cartridge 61 and a developing cartridge 62 as an example of a developing device.

[0029] Each drum cartridge 61 has a photosensitive drum 63 as an example of a photosensitive member, a charger 64, etc. The developing cartridge 62 is detachable from the drum cartridge 61. Each developing cartridge 62 has a developing roller 65, a supply roller (reference numerals omitted), a layer thickness regulating blade, a toner storage portion for storing toner, etc.

[0030] The process units 6 are designated by the symbols 6Y, 6M, 6C, and 6K, which contain toner of each color, yellow, magenta, cyan, and black, and are arranged in this order from the upstream side in the conveyance direction of the sheet S. Hereinafter, in this specification and drawings, when identifying a developing cartridge 62 or a photosensitive drum 63 corresponding to a toner color, the symbols Y, M, C, and K will be used to correspond to yellow, magenta, cyan, and black, respectively. In the following description, the "conveyance direction of the sheet S" will also be simply referred to as the "conveyance direction."

[0031] The transfer unit 7 is provided between the supply tray 31 and the process unit 6, and is configured to include a drive roller 71, a driven roller 72, an endless conveyor belt 73, and four transfer rollers 74. The conveyor belt 73 is stretched between the drive roller 71 and the driven roller 72. Inside the conveyor belt 73, a transfer roller 74 is disposed so as to sandwich the conveyor belt 73 between itself and the corresponding photosensitive drum 63.

[0032] The fixing unit 8 includes a heating roller 81 and a pressure roller 82 that is pressed against the heating roller 81 .

[0033] The image forming unit 4 charges the surface of the rotating photosensitive drum 63 with the charger 64 and exposes it with the LED unit 5, thereby forming an electrostatic latent image based on image data on the photosensitive drum 63. The image forming unit 4 also forms a toner image on the photosensitive drum 63 by supplying toner from the developer cartridge 62 to the photosensitive drum 63 with the development roller 65. The image forming unit 4 then transfers the toner image on the photosensitive drum 63 to the sheet S by supplying the sheet S between the photosensitive drum 63 and the conveyor belt 73 with the sheet supply unit 3. The image forming apparatus then transports the sheet S, on which the toner image has been transferred, between a heating roller 81 and a pressure roller 82, thereby thermally fixing the toner image to the sheet S and forming an image on the sheet S. The sheet S, on which the toner image has been thermally fixed, is conveyed from the fixing unit 8 to a conveyance path 91 by the roller 83.

[0034] The conveying unit 9 is configured to convey the sheet S discharged from the image forming unit 4 to the outside of the main body housing 2 or back toward the image forming unit 4. The conveying unit 9 includes a conveying path 91, first conveying rollers 92 and 93, a re-conveying path 94, and a plurality of re-conveying rollers 95.

[0035] The transport path 91 extends from the fixing unit 8 toward the discharge port 23. The re-transport path 94 extends from a part of the transport path 91, specifically, from the portion between the roller 83 and the first transport roller 92, passing under the supply tray 31 toward the roller 36.

[0036] The first conveying rollers 92 and 93 are configured to be rotatable in both forward and reverse directions. Specifically, the first conveying rollers 92 and 93 are configured to convey the sheet S toward the outside of the main body housing 2 when rotating forward as indicated by the solid arrows, and to convey the sheet S toward the inside of the main body housing 2 when rotating backward as indicated by the dashed arrows.

[0037] When an image is formed on only one side of the sheet S, the conveying section 9 conveys the sheet S, which has been conveyed from the image forming section 4 by the roller 83, toward the discharge outlet 23 by the first conveying rollers 92, 93 rotating in the forward direction, and discharges the sheet S onto the discharge tray 22 through the discharge outlet 23.

[0038] On the other hand, when images are to be formed on both sides of the sheet S, the conveying unit 9 conveys the sheet S, which has been discharged from the image forming unit 4 by the roller 83, toward the discharge outlet 23 by the first conveying rollers 92, 93 rotating in the forward direction, and then rotates the first conveying rollers 92, 93 in the reverse direction just before the trailing edge of the sheet S passes through the roller 83 and exits between the first conveying rollers 92. As a result, the sheet S, with an image formed on one side thereof, is conveyed to the re-conveying path 94. Thereafter, the sheet S is conveyed by the re-conveying roller 95, roller 36, and registration roller 37, and is supplied to the image forming unit 4 again.

[0039] The sheet S is again supplied to the image forming unit 4, where an image is formed on the other side thereof, and is then conveyed out of the image forming unit 4 by rollers 83. The subsequent operations are the same as when an image is formed on only one side of the sheet S, and therefore a description thereof will be omitted.

[0040] As shown in FIG. 2, the color printer 1 includes a first motor M1, a second motor M2, a transmission mechanism 300, a photosensitive member drive mechanism 110, a belt drive mechanism 120, a first development drive mechanism 130, a second development drive mechanism 210, a fixing drive mechanism 220, a sheet supply drive mechanism 230, and a re-transport drive mechanism 240.

[0041] The first motor M1 is a motor that provides driving force to the first conveyor rollers 92 and 93, the four photosensitive drums 63, the developing rollers 65Y, 65M, and 65C corresponding to yellow, magenta, and cyan, and the conveyor belt 73. When the first motor M1 is driven, the output shaft of the first motor M1 always rotates in the same direction.

[0042] The second motor M2 is a motor for supplying driving force to the first conveying rollers 92 and 93, the developing roller 65K corresponding to black, the sheet supply unit 3, the re-conveying roller 95, etc. Here, each roller of the sheet supply unit 3 (for example, the supply roller 33) and the re-conveying roller 95 correspond to the second conveying roller that rotates in one direction. When the second motor M2 is driven, the output shaft of the second motor M2 always rotates in the same direction.

[0043] The transmission mechanism 300 selectively transmits the driving force of either the first motor M1 or the second motor M2 to the first conveyor rollers 92, 93. The transmission mechanism 300 is switchable between a first transmission state, a second transmission state, and a disconnected state. When in the first transmission state, the transmission mechanism 300 transmits the driving force of the first motor M1 to the first conveyor rollers 92, 93. When in the second transmission state, the transmission mechanism 300 transmits the driving force of the second motor M2 to the first conveyor rollers 92, 93. When in the disconnected state, the transmission mechanism 300 does not transmit the driving force of either the first motor M1 or the second motor M2 to the first conveyor rollers 92, 93.

[0044] The transmission mechanism 300 includes a cam 350 for switching the state of the transmission mechanism 300. The structure of the transmission mechanism 300, including the cam 350, will be described in detail later. The driving force of the second motor M2 can be transmitted to the cam 350 via a cam clutch C1. The cam clutch C1 is, for example, an electromagnetic clutch, and can be switched between a connected state in which the driving force from the second motor M2 is transmitted to the cam 350, and a disconnected state in which the driving force from the second motor M2 is not transmitted to the cam 350.

[0045] The photosensitive member driving mechanism 110 is a mechanism for transmitting the driving force of the first motor M1 to the four photosensitive member drums 63. The photosensitive member driving mechanism 110 is made up of a plurality of gears (not shown).

[0046] The belt driving mechanism 120 is a mechanism for transmitting the driving force of the first motor M1 to the driving roller 71. The belt driving mechanism 120 is made up of a plurality of gears (not shown).

[0047] The first developing drive mechanism 130 is a mechanism for transmitting the driving force of the first motor M1 to the developing rollers 65Y, 65M, and 65C. The first developing drive mechanism 130 is made up of a plurality of gears (not shown).

[0048] The second developing drive mechanism 210 is a mechanism for transmitting the driving force of the second motor M2 to the developing roller 65K. The second developing drive mechanism 210 is composed of a developing clutch C2 and a plurality of gears (not shown). The developing clutch C2 is a clutch substantially similar to the cam clutch C1 described above, and allows or cuts off the transmission of driving force from the second motor M2 to the developing roller 65K.

[0049] The fixing drive mechanism 220 is a mechanism for transmitting the driving force of the second motor M2 to the heating roller 81. The fixing drive mechanism 220 is made up of a plurality of gears (not shown).

[0050] The sheet supply drive mechanism 230 is a mechanism for transmitting the driving force of the second motor M2 to the sheet supply unit 3, such as the supply roller 33 and the registration roller 37. The sheet supply drive mechanism 230 is composed of a supply clutch C3, a drive clutch C4, and multiple gears (not shown). The supply clutch C3 and the drive clutch C4 are clutches substantially similar to the cam clutch C1 described above. The supply clutch C3 allows or cuts off the transmission of the driving force from the second motor M2 to the drive mechanism that moves the supply roller 33 between a contact position where it contacts the sheet S and a separation position where it is separated from the sheet S. The drive clutch C4 allows or cuts off the transmission of the driving force from the second motor M2 to each roller (e.g., the supply roller 33, the roller 36, etc.) of the sheet supply unit 3.

[0051] The re-conveyance drive mechanism 240 is a mechanism for transmitting the driving force of the second motor M2 to the re-conveyance roller 95. The re-conveyance drive mechanism 240 is composed of a re-conveyance clutch C5 and a plurality of gears (not shown). The re-conveyance clutch C5 is a clutch substantially similar to the cam clutch C1 described above, and allows or cuts off the transmission of the driving force from the second motor M2 to the re-conveyance roller 95.

[0052] 3, the transmission mechanism 300 includes a first gear 310, a second gear 320, an output gear 330, a transmission gear 340, a cam 350, and a spring 360. The first gear 310, the second gear 320, and the output gear 330 are rotatable about a common axis X1. The transmission gear 340 is connected to the first conveyor rollers 92 and 93 via multiple gears (not shown).

[0053] The first gear 310 is a gear to which driving force is input from the first motor M1. The first gear 310 rotates in a first direction when the first motor M1 is driving, and stops when the first motor M1 stops.

[0054] The second gear 320 is a gear to which driving force is input from the second motor M2. When the second motor M2 is driven, the second gear 320 rotates in a second direction opposite to the first direction described above, and stops when the second motor M2 stops.

[0055] The output gear 330 is a gear that outputs driving force to the first conveyor rollers 92, 93 via a transmission gear 340 and multiple gears (not shown). The output gear 330 is disposed between the first gear 310 and the second gear 320 in the axial direction and is movable in the axial direction. The output gear 330 is engageable with the first gear 310 and the second gear 320.

[0056] Specifically, output gear 330 has a first engaging portion 331 that engages with first gear 310 in the rotational direction, and a second engaging portion 332 that engages with second gear 320 in the rotational direction. First gear 310 has a first engaged portion 311 that engages with first engaging portion 331 in the rotational direction. Second gear 320 has a second engaged portion 321 that engages with second engaging portion 332 in the rotational direction. A plurality of first engaging portions 331, second engaging portions 332, first engaged portions 311, and second engaged portions 321 are each provided at intervals in the rotational direction.

[0057] The output gear 330 is movable among an intermediate position shown in Fig. 3(a), a first position shown in Fig. 3(b), and a second position shown in Fig. 3(c). The intermediate position is a position where the output gear 330 is not engaged with either the first gear 310 or the second gear 320. The first position is a position where the output gear 330 is engaged with the first gear 310. The second position is a position where the output gear 330 is engaged with the second gear 320.

[0058] The output gear 330 meshes with the transmission gear 340 at each of the intermediate position, the first position, and the second position. Specifically, the face width of the transmission gear 340 is larger than the face width of the output gear 330. The output gear 330 is capable of moving in the axial direction while maintaining meshing with the transmission gear 340.

[0059] When the output gear 330 is in the intermediate position, the transmission mechanism 300 is in a disengaged state. When the output gear 330 is in the first position, the transmission mechanism 300 is in a first transmission state. When the output gear 330 is in the second position, the transmission mechanism 300 is in a second transmission state.

[0060] The spring 360 biases the output gear 330 from the second gear 320 toward the first gear 310. The cam 350 is capable of pressing the output gear 330 from the first gear 310 toward the second gear 320 against the biasing force of the spring 360.

[0061] 3(d), cam 350 has a first holding surface F1, a first cam surface F2, an intermediate holding surface F3, a second cam surface F4, a second holding surface F5, a guide surface F6, and gear teeth 351. The surfaces F1 to F6 are arranged in the rotation direction of cam 350 from downstream to upstream in the following order: first holding surface F1, first cam surface F2, intermediate holding surface F3, second cam surface F4, second holding surface F5, guide surface F6.

[0062] The first holding surface F1 is a surface that comes into contact with the output gear 330 and holds the output gear 330 in the first position. The intermediate holding surface F3 is a surface that comes into contact with the output gear 330 and holds the output gear 330 in the intermediate position. The second holding surface F5 is a surface that comes into contact with the output gear 330 and holds the output gear 330 in the second position.

[0063] The first holding surface F1 and the second holding surface F5 are spaced apart in the axial direction of the cam 350. The intermediate holding surface F3 is disposed between the first holding surface F1 and the second holding surface F5 in the axial direction of the cam 350, and is spaced apart from the first holding surface F1 and the second holding surface F5.

[0064] The first cam surface F2 is a surface that moves the output gear 330 from the first position to the intermediate position against the biasing force of the spring 360. The first cam surface F2 is inclined with respect to the rotation direction so as to approach the intermediate support surface F3 in the axial direction as it moves from the first support surface F1 to the upstream side in the rotation direction.

[0065] The second cam surface F4 is a surface that moves the output gear 330 from the intermediate position to the second position against the biasing force of the spring 360. The second cam surface F4 is inclined with respect to the rotation direction so as to approach the second holding surface F5 in the axial direction as it moves from the intermediate holding surface F3 to the upstream side in the rotation direction.

[0066] The guide surface F6 is a surface that guides the output gear 330 from the second holding surface F5 to the first holding surface F1. The guide surface F6 is inclined with respect to the rotation direction so as to approach the first holding surface F1 in the axial direction as it moves from the second holding surface F5 to the upstream side in the rotation direction.

[0067] The driving force of the second motor M2 can be transmitted to the gear teeth 351 via the cam clutch C1. When the cam clutch C1 is engaged and the driving force of the second motor M2 is transmitted, the cam 350 rotates in the direction shown in Figure 3(d) by an angle corresponding to the engagement time of the cam clutch C1. As the cam 350 rotates, the surfaces F1 to F6 come into contact with the output gear 330 in the following order: first retaining surface F1, first cam surface F2, intermediate retaining surface F3, second cam surface F4, second retaining surface F5, and guide surface F6. The output gear 330 contacts the guide surface F6 and then the first retaining surface F1.

[0068] As shown in FIG. 1, the color printer 1 further includes a control unit 10, a first sheet sensor 11, and a second sheet sensor 12.

[0069] The first sheet sensor 11 and the second sheet sensor 12 are sensors for detecting the sheet S being transported inside the main body housing 2, and are composed, for example, of an actuator that oscillates when the sheet S comes into contact with it, and an optical sensor that detects the oscillation of the actuator. The first sheet sensor 11 is provided between the registration roller 37 and the transport belt 73 on the transport path of the sheet S. The second sheet sensor 12 is provided between the fixing unit 8 and the roller 83 on the transport path of the sheet S.

[0070] The control unit 10 is configured with a CPU, RAM, ROM, input / output interface, etc. (not shown), and performs various calculation processes based on the detection results of the seat sensors 11, 12, etc., and preset programs, etc., to perform control.

[0071] The control unit 10 has a function of switching the rotation direction of the first conveyor rollers 92, 93 by switching the transmission state of the transmission mechanism 300 while the first motor M1 and the second motor M2 are rotating. Specifically, the control unit 10 places the transmission mechanism 300 in the second transmission state, thereby rotating the first conveyor rollers 92, 93 forward and conveying the sheet S toward the outside of the main body housing 2. Furthermore, the control unit 10 places the transmission mechanism 300 in the first transmission state, thereby rotating the first conveyor rollers 92, 93 backward and conveying the sheet S toward the inside of the main body housing 2.

[0072] The control unit 10 is configured to switch the rotation direction of the first conveying rollers 92, 93 from forward rotation to reverse rotation when the first conveying rollers 92, 93 are in contact with the sheet S. The control unit 10 also has a function of stopping the first conveying rollers 92, 93 by disconnecting the transmission mechanism 300.

[0073] The operation of the control unit 10 will be described in detail below. When the control unit 10 receives a print command, it executes the print process shown in FIG. 4, the transmission mechanism switching process shown in FIG. 5, and the re-conveyance roller driving process shown in FIG.

[0074] 4, the control unit 10 first drives the first motor M1 (S1). After step S1, the control unit 10 drives the second motor M2 and connects the developing clutch C2 to drive the photosensitive drum 63 and the developing roller 65 (S2).

[0075] After step S2, the control unit 10 determines whether the print command is a double-sided printing command (S3). If it is determined in step S3 that the print command is a double-sided printing command (Yes), the control unit 10 executes double-sided printing processing based on the print data and the double-sided printing table (S4).

[0076] The double-sided printing table is a table for determining the page order in which images are formed on sheets S by the image forming unit 4 during double-sided printing. Specifically, the page order is set in the double-sided printing table when images of even-numbered pages are formed on the front side of sheets S and images of odd-numbered pages are formed on the back side of sheets S. Specifically, for example, if the number of pages to be printed in double-sided printing is two, the page order in which images are formed is set to page 2, page 1. Also, for example, if the number of pages to be printed in double-sided printing is four, the page order in which images are formed is set to page 2, page 4, page 1, page 3. In step S4, the control unit 10 performs double-sided printing processing by supplying and exposing sheets S based on the print data and the double-sided printing table. Note that the supply of sheets S is performed by appropriately switching the states of the supply clutch C3 and the drive clutch C4 described above. Furthermore, when sheets S with images formed on the back side are transported by the sheet supply unit 3, the control unit 10 engages the drive clutch C4.

[0077] If it is determined in step S3 that the command is not for double-sided printing (No), the control unit 10 executes single-sided printing processing based on the print data (S5). Specifically, in step S5, the control unit 10 executes single-sided printing processing by supplying and exposing the sheet S based on the print data.

[0078] After printing of all pages is completed in step S4 or step S5, the control unit 10 stops the second motor M2 and disconnects the developing clutch C2 to stop the photosensitive drum 63 and the developing roller 65 (S6). After step S6, the control unit 10 stops the first motor M1 (S7) and ends the printing process.

[0079] After receiving a print command, the control unit 10 executes the transmission mechanism switching process shown in Fig. 5 and the re-conveyance roller driving process shown in Fig. 6 during the print process of step S4 or step S5. In the transmission mechanism switching process shown in Fig. 5, the control unit 10 first determines whether the sheet S has approached the first conveyance roller 92 on the upstream side in the conveyance direction (S21). Note that the determination of whether the sheet S has approached the first conveyance roller 92 may be performed, for example, by determining whether the time elapsed since the first sheet sensor 11 or the second sheet sensor 12 detected the sheet S is equal to or greater than a predetermined time. In the following description, determining whether the time elapsed since the first sheet sensor 11 or the second sheet sensor 12 detected the sheet S is equal to or greater than a threshold is also referred to as "determining based on the time elapsed since the sheet was detected."

[0080] If it is determined in step S21 that the sheet S has approached the first conveying rollers 92 (Yes), the control unit 10 switches the transmission mechanism 300 to the second transmission state to rotate the first conveying rollers 92, 93 forward (S22). After step S22, the control unit 10 determines whether the print command is a double-sided printing command (S23).

[0081] If it is determined in step S23 that the command is not for double-sided printing (No), the control unit 10 rotates the first conveyance rollers 92, 93 in the forward direction at least until the rear end of the sheet S clears the first conveyance roller 93 on the downstream side in the conveyance direction, thereby discharging the sheet S outside the main body housing 2 (S24). If it is determined in step S23 that the command is for double-sided printing (Yes), the control unit 10 determines whether the sheet S conveyed by the first conveyance rollers 92, 93 is a sheet S to be switched back based on the double-sided printing table (S25). More specifically, in step S25, the control unit 10 determines whether the sheet S conveyed by the first conveyance rollers 92, 93 is a sheet S having an image of an even-numbered page formed on its front side and an image of an odd-numbered page not formed on its back side based on the double-sided printing table, thereby determining whether the sheet S is a sheet S to be switched back.

[0082] If it is determined in step S25 that the sheet S is not a target for switchback (No), the control unit 10 proceeds to step S24, where the sheet S is discharged to the outside of the main body housing 2. If it is determined in step S25 that the sheet S is a target for switchback (Yes), the control unit 10 switches the transmission mechanism 300 to the first transmission state and reverses the first conveyance rollers 92, 93 at least at a timing before the trailing edge of the sheet S reaches the first conveyance roller 93 on the downstream side in the conveyance direction (S26). Note that the determination of whether the trailing edge of the sheet S has reached the timing before reaching the first conveyance roller 93 on the downstream side in the conveyance direction may be made based on, for example, the elapsed time since the sheet was detected.

[0083] After step S26, the control unit 10 determines whether the trailing edge of the switched-back sheet S has left the first conveying rollers 92 on the downstream side in the conveying direction (S27). Whether the trailing edge of the sheet S has left the first conveying rollers 92 may be determined based on, for example, the elapsed time since the sheet was detected.

[0084] If it is determined in step S27 that the trailing edge of the sheet S has come off the first conveying rollers 92 (Yes), or after step S24, the control unit 10 stops the first conveying rollers 92, 93 by disconnecting the transmission mechanism 300 (S28). After step S28, the control unit 10 determines whether printing has finished (S29).

[0085] If it is determined in step S29 that printing has not finished (No), the control unit 10 returns to the process of step S21. If it is determined in step S29 that printing has finished (Yes), the control unit 10 ends the transmission mechanism switching process.

[0086] 6, the control unit 10 first determines whether the print command is a double-sided printing command (S41). If it is determined in step S41 that the print command is not a double-sided printing command (No), the control unit 10 ends the re-conveyance roller drive process. If it is determined in step S41 that the print command is a double-sided printing command (Yes), the control unit 10 determines whether the sheet S has approached the re-conveyance roller 95 (S42). Whether the sheet S has approached the re-conveyance roller 95 may be determined, for example, based on the elapsed time since the sheet was detected.

[0087] If it is determined in step S42 that the sheet S has approached the re-conveyance rollers 95 (Yes), the control unit 10 connects the re-conveyance clutch C5 to rotate the re-conveyance rollers 95 (S43). After step S43, the control unit 10 determines, based on the double-sided printing table described above, whether the sheet S being conveyed by the re-conveyance rollers 95 is a sheet S for which conveyance is to be temporarily stopped (S44).

[0088] If it is determined in step S44 that the conveyance is to be temporarily stopped (Yes), the control unit 10 disengages the re-conveyance clutch C5 at a predetermined timing (S45). As a result, the re-conveyance rollers 95 stop while the sheet S is being conveyed by the re-conveyance rollers 95, and the conveyance of the sheet S is temporarily stopped. Here, whether the predetermined timing has arrived may be determined based on, for example, the elapsed time since the sheet was detected.

[0089] After step S45, the control unit 10 determines whether or not the supply of the sheet S from the supply tray 31 has been completed (S46). The determination of whether or not the supply of the sheet S from the supply tray 31 has been completed is made based on, for example, a signal from the double-sided printing table or the first sheet sensor 11.

[0090] If it is determined in step S46 that the supply of the sheet S has been completed (Yes), the control unit 10 connects the re-conveyance clutch C5 to rotate the re-conveyance rollers 95 again (S47). After step S47, or if it is determined No in step S44, the control unit 10 determines whether the trailing edge of the sheet S has come off the re-conveyance rollers 95 on the downstream side in the conveying direction (S48).

[0091] Whether the rear end of the sheet S has deviated from the re-conveyance rollers 95 on the downstream side in the conveying direction may be determined based on the elapsed time since the sheet was detected, for example, when the re-conveyance rollers 95 are not temporarily stopped (S44: No). Moreover, when the re-conveyance rollers 95 are temporarily stopped (S45), whether the rear end of the sheet S has deviated from the re-conveyance rollers 95 on the downstream side in the conveying direction may be determined by determining whether the elapsed time since the re-conveyance clutch C5 was connected is equal to or greater than a predetermined threshold.

[0092] If it is determined in step S48 that the rear end of the sheet S has deviated from the re-conveyance rollers 95 on the downstream side in the conveying direction (Yes), the control unit 10 disengages the re-conveyance clutch C5 to stop the re-conveyance rollers 95 (S49). After step S49, the control unit 10 determines whether printing has finished (S50).

[0093] If it is determined in step S50 that printing has not finished (No), the control unit 10 returns to the process of step S42. If it is determined in step S50 that printing has finished (Yes), the control unit 10 ends the re-conveyance roller driving process.

[0094] Next, an example of the operation of the control unit 10 will be described in detail. Specifically, an example will be described in which the number of pages to be printed in double-sided printing is six, and the order of pages on which images are formed is pages 2, 4, 6, 1, 3, and 5.

[0095] When the control unit 10 receives a command for double-sided printing with six print pages, it first drives the first motor M1 and the second motor M2 and connects the developing clutch C2 (S1, S2), thereby driving the image forming unit 4, which includes the photosensitive drum 63, the conveyor belt 73, the heating roller 81, etc. Then, the control unit 10 appropriately connects the supply clutch C3, etc. (S4), and as shown in FIG. 7(a), causes the sheet supply unit 3 to supply the first sheet SH1, which is the first sheet S, toward the image forming unit 4. Next, the control unit 10 causes the image forming unit 4 to form the image of the second page on the front side of the first sheet SH1 (S4).

[0096] When the first sheet SH1 approaches the first conveyor rollers 92 on the upstream side in the conveying direction, the control unit 10 switches the transmission mechanism 300 to the second transmission state (S21: Yes → S22). As a result, as shown in FIG. 7B, the driving force of the second motor M2 is transmitted to the first conveyor rollers 92, 93, and the first conveyor rollers 92, 93 rotate forward, so that the first sheet SH1 is conveyed outward from the main body housing 2 by the first conveyor rollers 92, 93.

[0097] When an image is to be formed on the front side of the sheet S, the control unit 10 determines that the sheet S is a sheet S to be switched back (S25). Thereafter, the control unit 10 switches the transmission mechanism 300 to the first transmission state (S26) just before the trailing edge of the first sheet SH1 leaves the first conveyor roller 92 on the upstream side in the conveying direction. As a result, the driving force of the first motor M1 is transmitted to the first conveyor rollers 92 and 93, causing the first conveyor rollers 92 and 93 to rotate in the reverse direction. As a result, the first sheet SH1 is conveyed into the main body housing 2 by the first conveyor rollers 92 and 93, as shown in FIG. 8(a).

[0098] After starting to supply the first sheet SH1, the control unit 10 starts to supply the second sheet SH2, which is the second sheet S, at a predetermined timing based on the double-sided printing table. The timing to start supplying the second sheet SH2 can be, for example, when the first conveying rollers 92, 93 start to rotate in the reverse direction.

[0099] Thereafter, when the trailing edge of the first sheet SH1 separates from the first conveyance roller 92 on the downstream side in the conveyance direction, the control unit 10 switches the transmission mechanism 300 to a disconnected state (S28). As a result, the first conveyance rollers 92 and 93 stop, as shown in FIG. 8(b). Furthermore, when the first sheet SH1 approaches the re-conveyance roller 95, the control unit 10 connects the re-conveyance clutch C5 (S42: Yes → S43). As a result, the first sheet SH1 is conveyed by the re-conveyance roller 95.

[0100] Thereafter, when the second sheet SH2 approaches the first conveyor rollers 92 on the upstream side in the conveying direction, the control unit 10 switches the transmission mechanism 300 to the second transmission state and then to the first transmission state, as in the case of the first sheet SH1. As a result, the first conveyor rollers 92, 93 convey the second sheet SH2 toward the outside of the main body housing 2, and then switch the conveying direction to convey the second sheet SH2 toward the inside of the main body housing 2, as shown in FIG. 9(a).

[0101] Furthermore, when the first sheet SH1 on which only the image of the second page is formed is transported by the re-conveyance rollers 95, the control unit 10 determines, based on the double-sided print data, that the transport of the first sheet SH1 being transported by the re-conveyance rollers 95 is to be temporarily stopped, and disengages the re-conveyance clutch C5 (S44: Yes → S45). As a result, as shown in Fig. 9(a), the re-conveyance rollers 95 stop and the transport of the first sheet SH1 stops, so that when the third sheet SH3, which is the third sheet S, is supplied, interference between the third sheet SH3 and the first sheet SH1 is suppressed.

[0102] After starting the supply of the second sheet SH2, the control unit 10 starts the supply of the third sheet SH3 at a predetermined timing based on the double-sided printing table. When the supply of the third sheet SH3 is completed, the control unit 10 connects the re-conveyance clutch C5 and resumes the conveyance of the first sheet SH1 (S47), as shown in FIG. 9(b). The timing at which the supply of the third sheet SH3 is completed may be any timing as long as the third sheet SH3 and the first sheet SH1 do not interfere with each other.

[0103] After forming the images of pages 2, 4, and 6 on each sheet S, the control unit 10 judges No for each sheet S in step S25, and sequentially ejects each sheet S on which the images of pages 1, 3, and 5 have been formed out of the main body housing 2.

[0104] As described above, the following effects can be obtained in this embodiment. When switching the rotation direction of the first conveyor rollers 92, 93, there is no need to slow down, stop, or reverse the rotation of the motors M1, M2, so the time required to switch the rotation direction of the first conveyor rollers 92, 93 can be shortened.

[0105] When the first conveying rollers 92, 93 are in contact with the sheet S, the rotation direction of the first conveying rollers 92, 93 is switched without slowing down, stopping, or reversing the rotation of the motors M1, M2, so that the conveying direction of the sheet S can be switched quickly.

[0106] When switching the rotation direction of the first conveyor rollers 92, 93, there is no need to stop the first motor M1 that drives part of the image forming unit, so the rotation direction of the first conveyor rollers 92, 93 can be switched without stopping the image forming unit.

[0107] When switching the rotation direction of the first conveying rollers 92, 93, there is no need to stop the second motor M2 that drives the re-conveying roller 95 as the second conveying roller, so the rotation direction of the first conveying rollers 92, 93 can be switched without stopping the re-conveying roller 95, etc.

[0108] By disengaging the transmission mechanism 300, a state can be created in which no driving force is supplied to the first conveyor rollers 92, 93, thereby suppressing unnecessary rotation of the first conveyor rollers 92, 93 and reducing wear. Also, for example, if the sheet S becomes jammed between the first conveyor rollers 92, 93, disengaging the transmission mechanism 300 can facilitate the operation of removing the sheet S. Furthermore, noise from the sheet discharge port of the main body housing 2 caused by the first conveyor rollers 92, 93 continuing to rotate unnecessarily can be suppressed.

[0109] The transmission mechanism 300 is used in which a first gear 310, a second gear 320, and an output gear 330, which are rotatable around a common axis X1, are arranged along the axial direction, so that the transmission mechanism 300 can be made smaller than, for example, a transmission mechanism that uses a pendulum gear.

[0110] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below.

[0111] In the above embodiment, the first motor M1 is configured to drive a part of the image forming unit, but the present invention is not limited to this, and the first motor may be configured to drive the entire image forming unit.

[0112] The transmission mechanism is not limited to the structure described in the above embodiment. For example, the transmission mechanism may include an electromagnetic clutch and a one-way clutch, or may include a planetary gear mechanism.

[0113] In the above embodiment, the rotation direction of the first conveyor roller is changed by switching the state of the transmission mechanism, but the rotation direction may not be changed. For example, the rotation speed of the first conveyor roller may be changed by switching the state of the transmission mechanism. Specifically, when the transmission mechanism is in a first transmission state, the first conveyor roller may rotate in a predetermined direction at a first speed, and when the transmission mechanism is in a second transmission state, the first conveyor roller may rotate in the predetermined direction at a second speed that is higher than the first speed.

[0114] The first conveying roller is not limited to a roller for switching back the sheet as in the above embodiment, but may be any roller as long as it is a roller that requires switching of the rotation direction.

[0115] In the above embodiment, the motor that rotates the first conveyor rollers 92, 93 forward is the second motor M2, and the motor that rotates the first conveyor rollers 92, 93 reverse is the first motor M1. However, the present invention is not limited to this. The motor that rotates the first conveyor rollers 92, 93 forward may be the first motor M1, and the motor that rotates the first conveyor rollers 92, 93 reverse may be the second motor M2. Furthermore, in this case, if the second sheet SH2, which is the second sheet S, is not to be supplied during the period in which the first conveyor rollers 92, 93 are rotated reversely, the first motor M1 may be stopped. Furthermore, the motor that drives the cam 350 is not limited to the second motor M2, and may be the first motor M1.

[0116] In the above embodiment, the present invention is applied to a color printer 1, but the present invention is not limited to this, and may be applied to other image forming devices, such as a copying machine or a multifunction machine.

[0117] The elements described in the above-described embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0118] 1 color printer 2 Main unit housing 10 Control Unit 92 First conveyor roller 93 First conveyor roller 300 Transmission Mechanism M1 First motor M2 Second motor S seat

Claims

1. A main body housing; an image forming unit including a photosensitive member and a developing unit; a first conveying roller for conveying the sheet that has passed through the image forming unit; a first motor that supplies a driving force to the first conveying roller; a second motor that supplies a driving force to the first conveying roller; a transmission mechanism that selectively transmits the driving force of either the first motor or the second motor to the first conveyor roller, the transmission mechanism being switchable between a first transmission state in which the driving force of the first motor is transmitted to the first conveyor roller and a second transmission state in which the driving force of the second motor is transmitted to the first conveyor roller; a control unit, The control unit In double-sided printing, where images are formed on both the front and back of a sheet, a transmission state of the transmission mechanism being set to the second transmission state while the first motor is rotated in a first rotation direction and the second motor is rotated in a second rotation direction, whereby a sheet having an image formed on its surface by the imaging unit is conveyed by the first conveying roller toward the outside of the main body housing; An image forming apparatus characterized in that, when the first conveying roller is in contact with a sheet having an image formed on its surface, the first motor is rotated in the first rotation direction and the second motor is rotated in the second rotation direction, and the transmission state of the transmission mechanism is switched from the second transmission state to the first transmission state, thereby switching the rotation direction of the first conveying roller and conveying the sheet toward the inside of the main housing by the first conveying roller.

2. The control unit In double-sided printing in which images are formed on the front and back of each of the first and second sheets, a first process of supplying the second sheet to the image forming unit when the first conveying roller contacts the first sheet having an image formed on its surface by the image forming unit and the transmission mechanism is in the first transmission state; a second process of changing the transmission state of the transmission mechanism to the second transmission state after the trailing edge of the first sheet has been released from the first conveyance roller; 2. The image forming apparatus according to claim 1, wherein the first process and the second process are performed in a state in which the first motor is rotated in the first rotation direction and the second motor is rotated in the second rotation direction.

3. An image forming apparatus as described in claim 1 or claim 2, characterized in that the first motor drives at least a part of the imaging unit.

4. 4. The image forming apparatus according to claim 1, wherein the second motor drives a second transport roller that rotates in one direction.

5. 5. The image forming apparatus according to claim 1, wherein the transmission mechanism is switchable to a disconnected state in which neither the driving force of the first motor nor the driving force of the second motor is transmitted to the first conveying roller.

6. The transmission mechanism includes: a first gear to which a driving force is input from the first motor; a second gear to which a driving force is input from the second motor; an output gear that outputs a driving force to the first conveying roller, the first gear, the second gear, and the output gear are rotatable about a common axis; 6. The image forming apparatus according to claim 1, wherein the output gear is disposed between the first gear and the second gear in the axial direction, is movable in the axial direction, and is engageable with the first gear and the second gear.

7. The transmission mechanism includes: a spring that biases the output gear toward one of the first gear and the second gear; 7. The image forming apparatus according to claim 6, further comprising: a cam that presses the output gear toward the other of the first gear and the second gear.

8. The output gear is a first engagement portion that engages with the first gear in a rotational direction; a second engagement portion that engages with the second gear in the rotational direction, the first gear has a first engaged portion that engages with the first engaging portion in the rotational direction, 8. The image forming apparatus according to claim 6, wherein the second gear has a second engaged portion that engages with the second engaging portion in the rotational direction.

Images