Image forming apparatus

Abstract

The objective is to prevent jams from occurring due to the rotation of the intermediate paper discharge roller, even when the rear end of the sheet is at the position of the intermediate paper discharge roller while the sheet transport is stopped at the cutter position. [Solution] In the printer 1, a main motor 66 is provided for rotationally driving the pickup roller 50, registration roller 54, and intermediate paper discharge roller 56, and an electromagnetic clutch 72 is provided between the main motor 66 and the intermediate paper discharge roller 56 to switch the transmission of driving force. As a result, when cutting a sheet with the cutter 28 and stopping the paper discharge motor 68, the driving force generated by the main motor can be de-transmitted to the intermediate paper discharge roller by the electromagnetic clutch. Therefore, with the driving of the intermediate paper discharge roller stopped, subsequent sheets can be transported toward the image forming unit 24 and the fixing unit 26 using the transport roller 52 etc. located upstream of the intermediate paper discharge roller in the transport path 34.

Description

Technical Field

[0001] This application relates to an image forming apparatus that cuts an image-formed sheet with a cutter.

Background Art

[0002] Conventionally, an image forming apparatus for cutting sheets of standard sizes is known. Patent Document 1 describes an image forming apparatus having an image forming unit, a fixing unit, and a cutting device, which conveys a sheet heat-fixed by the fixing unit to a cutting position and stops it, and the cutting device cuts the sheet in the stopped state with a cutting blade. In the image forming apparatus of Patent Document 1, a pair of rollers for conveying the sheet from the fixing unit toward the cutting device is arranged between the fixing unit and the cutting device on the conveyance path for conveying the sheet.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an image forming apparatus that cuts a sheet using a cutter (corresponding to the cutting blade in Patent Document 1), such as the image forming apparatus in Patent Document 1, there is an image forming apparatus that has an intermediate paper discharge roller (corresponding to the roller pair in Patent Document 1) positioned between the cutter and the fixing unit on the transport path. When the image forming apparatus stops the transport of the sheet at the cutter position in order to cut the sheet using the cutter, if the roller pair of the intermediate paper discharge rollers nip the sheet, a jam will occur due to the rotation of the intermediate paper discharge roller. Therefore, it was necessary to stop the rotation of the rollers on the upstream side of the transport path, including the intermediate paper discharge roller, until the cutting of the sheet was completed. As a result, when the transport of the sheet is stopped in order to cut the sheet, there was a problem that subsequent sheets could not be transported toward the image forming unit and fixing unit by the rollers upstream of the intermediate paper discharge roller on the transport path.

[0005] The present invention was made to solve the problems of the conventional invention, and aims to provide an image forming apparatus that can prevent jams from occurring due to the rotation of the intermediate paper discharge rollers, even if the roller pair of the intermediate paper discharge rollers nip the sheet when the sheet transport is stopped at the cutter position for cutting the sheet with the cutter. [Means for solving the problem]

[0006] To achieve the above objective, the image forming apparatus of the present invention comprises: an image forming unit for forming an image on a sheet; a fixing unit for fixing the image formed on the sheet by the image forming unit to the sheet; a device body having a sheet transport path; a cutter positioned downstream of the fixing unit in the sheet transport direction in the transport path for cutting the sheet; a transport roller for transporting the sheet toward the image forming unit; a paper discharge roller for discharging the sheet cut by the cutter to the outside of the device body; an intermediate paper discharge roller located between the paper discharge roller and the fixing unit in the transport path; and the transport roller. The device comprises a first motor for rotationally driving the intermediate paper discharge roller, a paper discharge motor for rotationally driving the paper discharge roller, a clutch for switching whether or not to transmit the driving force from the first motor to the intermediate paper discharge roller, and a control unit, wherein the intermediate paper discharge roller is positioned where the rear end of the sheet is located when the sheet transport is stopped at the cutter position, and the control unit, when cutting the sheet using the cutter, rotates the first motor with the driving force not transmitted by the clutch and stops the rotational drive of the paper discharge motor.

[0007] According to the configuration of the present invention, when cutting a sheet using a cutter and stopping the paper discharge motor, the clutch prevents the driving force generated by the first motor from being transmitted to the intermediate paper discharge roller. Therefore, with the intermediate paper discharge roller stopped, subsequent sheets can be transported toward the image forming unit and fixing unit using the transport roller located upstream of the intermediate paper discharge roller in the transport path.

[0008] To achieve the above objective, the present invention provides an image forming apparatus comprising: an image forming unit for forming an image on a sheet; a fixing unit for fixing the image formed on the sheet by the image forming unit to the sheet; a main body of the apparatus having a sheet transport path; a cutter positioned at a cutter position downstream of the fixing unit in the sheet transport direction in the transport path for cutting the sheet; a transport roller for transporting the sheet toward the image forming unit; a paper discharge roller for discharging the sheet cut by the cutter to the outside of the main body of the apparatus; an intermediate paper discharge roller positioned between the paper discharge roller and the fixing unit; a first motor for rotationally driving the transport roller; a paper discharge motor for rotationally driving the paper discharge roller and the intermediate paper discharge roller; and a control unit, wherein the intermediate paper discharge roller is positioned at a location where the rear end of the sheet exists when the sheet transport is stopped at the cutter position; and the control unit rotates the first motor and stops the rotational driving of the paper discharge motor when cutting the sheet using the cutter.

[0009] According to the configuration of the present invention, when cutting a sheet using a cutter, if the paper discharge motor is stopped, the paper discharge motor can stop the rotation of not only the paper discharge roller but also the intermediate paper discharge roller, and the transport roller can be rotated by driving the first motor. Therefore, with the drive of the intermediate paper discharge roller stopped, subsequent sheets can be transported toward the image forming unit and the fixing unit using the transport roller located upstream of the intermediate paper discharge roller in the transport path.

[0010] Furthermore, the device body has a re-transport path which transports the sheet that has passed through the fixing section in the opposite direction to the sheet transport direction and transports it again toward the image forming section, and the intermediate paper discharge roller is a roller that guides the sheet that has passed through the fixing section toward the re-transport path by rotating in reverse.

[0011] According to this, while the first motor is running, the rotation of the intermediate paper discharge roller, which guides the paper to the re-transport path, can be stopped, thus shortening the gap between the sheet being transported while it is stopped for cutting and the subsequent sheet.

[0012] Furthermore, the image forming unit has a photoreceptor drum, and the sheet is conveyed in the conveying direction by the rotation of the photoreceptor drum; the fixing unit has a heating rotating body and a pressurizing rotating body that forms a nip between itself and the heating rotating body, and the sheet is conveyed in the conveying direction by the rotation of either the heating rotating body or the pressurizing rotating body; and the first motor is a motor for rotationally driving the photoreceptor drum, the rotating body and the conveying roller.

[0013] According to this, in an image forming apparatus, while the rotation of the paper discharge roller is stopped for sheet cutting, the rotation of the photoreceptor drum, the rotating body of the fuser unit, and the transport roller can be continued by the first motor. Therefore, while transport is stopped for cutting, subsequent sheets can be transported by the photoreceptor drum, the rotating body of the fuser unit, and the transport roller, thus shortening the gap between the sheet being transported for cutting and the subsequent sheet, and allowing image formation of the subsequent sheet to be performed by the image forming unit and the fuser unit.

[0014] Furthermore, the image forming unit has a plurality of photoreceptor drums, and the sheet is conveyed in the conveying direction by the rotation of the plurality of photoreceptor drums, and the fixing unit has a heating rotating body and a pressurizing rotating body that forms a nip between itself and the heating rotating body, and the sheet is conveyed in the conveying direction by the rotation of either the heating rotating body or the pressurizing rotating body, and further comprises a process motor for rotating the plurality of photoreceptor drums, and the first motor is a motor for rotating the rotating body and the conveying roller.

[0015] According to this, in an image forming apparatus, while the rotation of the paper discharge roller is stopped for sheet cutting, multiple photoreceptor drums can be rotated by process motors, and the rotating body and transport roller of the fixing unit can be rotated by a first motor. As a result, subsequent sheets can be transported by multiple photoreceptor drums, the gap between the sheet being transported stopped for cutting and the subsequent sheet can be shortened, and image formation of the subsequent sheet can be performed by the image forming unit and the fixing unit.

[0016] Furthermore, the image forming unit has a plurality of photoreceptor drums and a plurality of developing rollers that form toner images on the surfaces of the plurality of photoreceptor drums, and the sheet is conveyed in the conveying direction by the rotation of the plurality of photoreceptor drums, and the fixing unit has a heating rotating body and a pressurizing rotating body that forms a nip between itself and the heating rotating body, and the sheet is conveyed in the conveying direction by the rotation of either the heating rotating body or the pressurizing rotating body, and further comprises a process motor for rotating the plurality of photoreceptor drums, a developing motor for rotating the plurality of developing rollers, and a fixing motor for rotating the rotating bodies.

[0017] According to this, while the rotation of the paper discharge roller is stopped for sheet cutting, multiple photosensitive drums can be rotated by process motors, and the rotation of the fixing unit's rotating body can be rotated by a fixing motor, and the rotation of the transport rollers can be rotated by a first motor. Multiple developing rollers can be rotated by developing motors. As a result, the gap between the sheet being transported stopped for cutting and the subsequent sheet can be shortened, and the image formation of the subsequent sheet can be performed by the image forming unit and the fixing unit.

[0018] Furthermore, the paper discharge roller is characterized by having a first paper discharge roller located upstream of the cutter position in the sheet transport direction and a second paper discharge roller located downstream of the cutter position in the sheet transport direction.

[0019] According to this, it becomes possible to convey the sheet cut by the cutter by the first paper discharge roller and the second paper discharge roller in a state of being sandwiched at the cutting position, and the sheet cut by the cutter can be appropriately conveyed.

Advantages of the Invention

[0020] According to the image forming apparatus according to the present application, when cutting a sheet using a cutter, in the case of stopping the paper discharge motor, with the driving of the intermediate paper discharge roller stopped, a subsequent sheet can be conveyed toward the image forming unit and the fixing unit using a conveying roller located upstream of the intermediate paper discharge roller in the conveying path.

Brief Description of the Drawings

[0021] [Figure 1] It is a cross-sectional view showing a schematic configuration of a printer according to a first embodiment of the present application. [Figure 2] It is a perspective view showing a schematic configuration of a cutter included in the printer of FIG. 1. [Figure 3] It is a schematic view showing the relationship between rollers and motors in the printer of FIG. 1. [Figure 4] It is a flowchart showing the procedure of sheet printing and cutting processing executed by the CPU of the printer of FIG. 1. [Figure 5] It is a flowchart showing the detailed procedure of image forming processing (first side) included in the sheet printing and cutting processing of FIG. 4. [Figure 6] It is a flowchart showing the detailed procedure of sheet inversion processing included in the sheet printing and cutting processing of FIG. 4. [Figure 7] It is a flowchart showing the detailed procedure of image forming processing (second side) included in the sheet printing and cutting processing of FIG. 4. [Figure 8] It is a flowchart showing the detailed procedure of sheet cutting processing included in the sheet printing and cutting processing of FIG. 4. [Figure 9] It is a schematic view showing the relationship between rollers and motors in a printer of a comparative example. [Figure 10]This is a schematic diagram showing the relationship between rollers and motors in a conventional printer. [Figure 11] This is a schematic diagram showing the relationship between the roller and the motor in a printer according to the second embodiment of the present application. [Figure 12] This is a cross-sectional view showing the schematic configuration of a printer according to the third embodiment of the present application. [Figure 13] Figure 12 is a schematic diagram showing the relationship between the rollers and the motor in the printer. [Figure 14] This is a schematic diagram showing the relationship between the roller and the motor in a printer according to the fourth embodiment of the present application. [Modes for carrying out the invention]

[0022] The embodiments of this application will be described in detail below with reference to the drawings.

[0023] (First Embodiment) Hereinafter, a first embodiment of the color laser printer, which is an embodiment of the image forming apparatus of the present invention, will be described with reference to Figure 1. Figure 1 is a cross-sectional view of the first embodiment of the color laser printer (hereinafter referred to as "printer") 1, showing a cross-sectional view of the printer 1 as seen from the right side. The printer 1 is an image forming apparatus capable of forming a color image on a sheet S by an electrophotographic method. In the following description, for the sake of explanation, the vertical and horizontal directions of the printer 1 will be defined as shown by the arrows in Figure 1. Also, the front side of the paper will be defined as the right, and the back side of the paper will be defined as the left.

[0024] The printer 1 comprises a reading unit 10 and a printing unit 12. The reading unit 10 reads images formed on a medium such as paper, and includes an image reading sensor such as a CCD (Charge Coupled Device) or CIS (Contact Image Sensor), and a moving mechanism for moving the image reading sensor.

[0025] The printing unit 12 comprises a main body 20, a transport unit 22, an image forming unit 24, a fixing unit 26, and a cutter 28.

[0026] The main body of the device 20 is formed in a roughly rectangular parallelepiped shape and includes a supply tray 30, a discharge tray 32, a transport path 34, and a re-transport path 36. The supply tray 30 is detachably attached to the lower part of the main body of the device 20. A sheet S is placed on the supply tray 30. The sheet S is a standard-sized sheet, such as A4 size. The sheet S is a paper medium such as plain paper or cardboard, but is not limited to this and may also be an OHP film. The discharge tray 32 is provided on the upper part of the main body of the device 20, and a sheet S with an image formed on it is placed on the discharge tray 32.

[0027] The transport path 34 is a path for transporting the sheet S placed on the supply tray 30 in the transport direction toward the discharge tray 32 via the image forming unit 24. The re-transport path 36 is a path for transporting the sheet S, on which an image has been formed on one side, in the opposite direction to the transport direction, toward the image forming unit 24 again. The re-transport path 36 starts at the branching position D on the transport path 34 and ends at the junction position J on the upstream side of the transport direction of the pre-cash register sensor SE1 on the transport path 34.

[0028] The transport unit 22 includes a pickup roller 50, a transport roller 52, a registration roller 54, an intermediate paper discharge roller 56, a first paper discharge roller 58, a second paper discharge roller 60, re-transport rollers 62 and 64, a pre-register sensor SE1, a post-register sensor SE2, an ejection sensor SE3, and a sheet sensor SE4. The various rollers, such as the pickup roller 50, are composed of roller pairs and can nip the sheet S. The pickup roller 50, conveyor roller 52, and registration roller 54 are examples of conveyor rollers.

[0029] The pickup roller 50 picks up the sheet S placed on the supply tray 30 and transports it toward the transport path 34. The transport roller 52 is located downstream of the pickup roller 50 in the transport path 34 and transports the sheet S toward the registration roller 54. The registration roller 54 is located upstream of the image forming unit 24 in the transport path 34 and, after aligning the direction of the front end of the sheet S, transports the sheet S toward the image forming unit 24. The intermediate paper discharge roller 56 transports the sheet S after it has passed through the fixing unit 26 toward the first paper discharge roller 58.

[0030] The first paper discharge roller 58 and the second paper discharge roller 60 are examples of paper discharge rollers. The first paper discharge roller 58 and the second paper discharge roller 60 are located downstream of the intermediate paper discharge roller 56 in the transport path 34. The first paper discharge roller 58 is located upstream of the cutter position where the cutter 28 is located, and the second paper discharge roller 60 is located downstream of the cutter position.

[0031] The re-transport rollers 62 and 64 are positioned on the re-transport path 36. The re-transport rollers 62 and 64 transport the sheet S that has been transported on the re-transport path 36 from the branching point D on the transport path 34 toward the merging point J upstream of the pre-cash register sensor SE1 on the transport path 34.

[0032] Furthermore, the pre-register sensor SE1 is positioned upstream of the registration roller 54 in the transport path 34 and is a sensor that detects when the sheet S passes. As the pre-register sensor SE1, a sensor with an actuator that swings when the sheet S comes into contact with it, or an optical sensor, etc., can be used. The pre-register sensor SE1 outputs an ON signal when the sheet S is passing and an OFF signal when the sheet S is not passing.

[0033] The post-register sensor SE2 is positioned downstream of the registration roller 54 in the transport path 34, specifically between the registration roller 54 and the image forming unit 24, and is a sensor that detects when the sheet S passes through. The post-register sensor SE2 has the same configuration as the pre-register sensor SE1.

[0034] The discharge sensor SE3 is positioned between the fixing unit 26 and the intermediate paper discharge roller 56 in the transport path 34 and detects when a sheet S passes through. The discharge sensor SE3 has the same configuration as the pre-cash register sensor SE1.

[0035] The sheet sensor SE4 is positioned between the first paper discharge roller 58 and the second paper discharge roller 60 and detects when the sheet S passes the cutter position. The sheet sensor SE4 has the same configuration as the pre-cash register sensor SE1.

[0036] Furthermore, the image forming unit 24 forms an image on the sheet S and is housed inside the main body of the apparatus 20. The image forming unit 24 includes a drum unit 74, a laser unit 76, and a transfer unit 78.

[0037] The drum unit 74 includes four toner cartridges 80Y, 80M, 80C, and 80B, four photoreceptor drums 82Y, 82M, 82C, and 82B, and four chargers 84.

[0038] The toner cartridges 80Y, 80M, 80C, and 80B correspond to four colors: yellow (Y), magenta (M), cyan (C), and black (B), respectively, and are arranged in this order from the front to the back of printer 1. Each toner cartridge has a corresponding developer roller 86Y, 86M, 86C, and 86B. The toner cartridges 80Y, 80M, 80C, and 80B contain toner for each of the YMCB colors, and by rotating the developer rollers 86Y, 86M, 86C, and 86B, toner is supplied to the respective color photoreceptor drums 82Y, 82M, 82C, and 82B. The developer rollers 86Y, 86M, 86C, and 86B are rotated by the rotational drive force transmitted from the process motor 98 (see Figure 3).

[0039] Note that the four toner cartridges 80Y, 80M, 80C, and 80B have different toner colors, but their other components are the same. Therefore, in the following explanation, when referring to the four toner cartridges 80Y, 80M, 80C, and 80B corresponding to each color, we will refer to them collectively as "toner cartridge 80." In addition, other components corresponding to each color (photoconductor drum 82, developer roller 86, etc.) may be described individually by adding the letters Y, M, C, or B after the designation, similar to toner cartridge 80, or they may be described collectively without a designation.

[0040] The photoreceptor drum 82 is a cylindrical member extending in the left-right direction and is held by the device body 20 so as to be rotatable around a rotation axis parallel to the left-right direction. Four chargers 84 are provided corresponding to each color. The chargers 84 are located behind the photoreceptor drum 82 and are, for example, scorotron-type chargers having charging wires or grids. The chargers 84 are connected to a high-voltage power supply, and by applying voltage from the high-voltage power supply to the charging wires, corona discharge is generated, uniformly positively charging the surface of the photoreceptor drum 82. Note that the device for charging the photoreceptor drum 82 is not limited to a scorotron-type charger; other devices such as roller-type charging rollers may also be used. Furthermore, the polarity of charging the photoreceptor drum 82 is not limited to positive charging; negative charging is also possible.

[0041] The laser unit 76 is located at the top of the main body 20 of the device and includes a light-emitting unit that emits laser light, a polygon mirror that polarizes the laser light emitted from the light-emitting unit, and the like. As shown by the dashed line in Figure 1, the laser unit 76 irradiates the photoreceptor drum 82 of the drum unit 74 with a beam polarized by the polygon mirror, exposing the photoreceptor drum 82. The laser unit 76 irradiates the photoreceptor drum 82 with a beam to form an electrostatic latent image based on image data on the surface of the photoreceptor drum 82.

[0042] The transfer unit 78 is located between the supply tray 30 and the drum unit 74 in the vertical direction and includes a drive roller 90, a driven roller 92, an endless transfer belt 94, and four transfer rollers 96. The transfer belt 94 is stretched between the drive roller 90 and the driven roller 92, with its upper surface in contact with the photoreceptor drum 82. The four transfer rollers 96 are provided corresponding to each color and are positioned inside the transfer belt 94, sandwiching the transfer belt 94 between the corresponding photoreceptor drum 82. The photoreceptor drum 82 rotates by the rotational driving force transmitted from the process motor 98 (see Figure 3), and transports the sheet S in the transport direction along the transport path 34, sandwiched between the transfer rollers 96.

[0043] In response to the printing operation, the photoreceptor drum 82 is positively charged by the charger 84, then exposed by the laser unit 76 to form an electrostatic latent image. The developing roller 86 supplies toner to the photoreceptor drum 82, developing the electrostatic latent image formed on the surface of the photoreceptor drum 82 and causing it to bear a toner image. The toner carried on the developing roller 86 moves to the electrostatic latent image on the photoreceptor drum 82 due to the potential difference between the developing roller 86 and the electrostatic latent image formed on the photoreceptor drum 82, forming a toner image. This toner image is transferred to the sheet S in the transport path 34 by applying a negative voltage to the transfer roller 96 while the photoreceptor drum 82 is in contact with the sheet S.

[0044] Furthermore, a fixing unit 26 is located downstream of the image forming unit 24 in the transport path 34, and the sheet S onto which the toner image has been transferred is transported to the fixing unit 26. The fixing unit 26 has a heating roller 100 and a pressure roller 102. The heating roller 100 is an example of a heating rotating body and heats the sheet S with a heater 104. The pressure roller 102 is an example of a pressure rotating body and pressurizes the sheet S by sandwiching it between the heating roller 100 and the pressure roller 102. The pressure roller 102 rotates to transport the sheet S in the transport direction by the driving force of the main motor 66. As a result, the fixing unit 26 heats the sheet S with the heating roller 100 and rotates the pressure roller 102, so that the sheet S is transported while being pressurized by the heating roller 100 and the pressure roller 102, thereby fixing the image formed on the sheet S in the image forming unit 24 to the sheet S.

[0045] Furthermore, a cutter 28 is positioned at the cutter location between the first paper discharge roller 58 and the second paper discharge roller 60 in the transport path 34. The printer 1 stops the rotation of the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 so that the cutting position on the sheet S reaches the cutter location. Then, with the rotation of the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 stopped, the printer 1 cuts the sheet S using the cutter 28.

[0046] Figure 2 shows a schematic configuration of the cutter 28. The cutter 28 includes a cutter frame 110, a slide rail 112, a fixed blade 113, a sheet passage section 114, a movable blade 115, a slide holder 116, and a cutter motor 118. The cutter frame 110 extends in the axial direction. The slide rail 112 is a rail formed on the cutter frame 110 that extends in the axial direction. The fixed blade 113 is a flat, plate-shaped blade that extends in the axial direction and is fixed to the cutter frame 110. The sheet passage section 114 is a space formed on the cutter frame 110 through which a sheet S passes. In this embodiment, the sheet passage section 114 is formed between the slide rail 112 and the fixed blade 113. The movable blade 115 is a disc-shaped blade that is rotatably fixed to the slide holder 116.

[0047] The slide holder 116 engages with the slide rail 112 and is mounted on the cutter frame 110 so as to be slidable along the slide rail 112. When the cutter motor 118 is driven, the slide holder 116 slides from one side to the other in the axial direction. That is, the slide holder 116 moves, for example, from the initial position shown by the solid line in Figure 2 to the completed cutting position shown by the dashed line. When the sheet S is in the cutter position and the slide holder 116 moves along the slide rail 112 to the completed cutting position, one sheet S is sandwiched between the fixed blade 113 and the movable blade 115 and cut into two sheets. After the sheet S is cut, the printer 1 rotates the intermediate paper output roller 56, the first paper output roller 58 and the second paper output roller 60 for a predetermined time to discharge the two sheets S into the output tray 32.

[0048] Figure 3 is a schematic diagram showing the relationship between the rollers and the motor in the printer shown in Figure 1. The direction from left to right in Figure 3 is the direction of sheet S transport. Figure 3 shows that the main motor 66 is a motor that outputs driving force to the pickup roller 50, registration roller 54, pressure roller 102, intermediate paper discharge roller 56, and re-transport rollers 62 and 64. Although not shown in Figure 3, the main motor 66 also outputs driving force to the re-transport rollers 62 and 64. The main motor 66 is configured so that the driving force is transmitted to the various rollers such as the pickup roller 50 by gears (not shown). The CPU 120 controls the drive of the main motor 66.

[0049] The main motor 66 is connected to the pickup roller 50 via an electromagnetic clutch 70. The electromagnetic clutch 70 is a clutch that switches whether or not the driving force from the main motor 66 is transmitted to the pickup roller 50. Turning the electromagnetic clutch 70 on enables the driving force of the main motor 66 to be transmitted to the pickup roller 50. Conversely, turning the electromagnetic clutch 70 off prevents the driving force of the main motor 66 from being transmitted to the pickup roller 50. The on / off control of the electromagnetic clutch 70 is performed based on a control signal from the CPU 120.

[0050] Furthermore, the main motor 66 is connected to the intermediate paper discharge roller 56 via an electromagnetic clutch 72. The electromagnetic clutch 72 is a clutch that switches whether or not the driving force from the main motor 66 is transmitted to the intermediate paper discharge roller 56. By turning the electromagnetic clutch 72 on, the driving force of the main motor 66 is transmitted to the intermediate paper discharge roller 56. On the other hand, by turning the electromagnetic clutch 72 off, the driving force of the main motor 66 is not transmitted to the intermediate paper discharge roller 56. Note that the electromagnetic clutch 72 is just one example of a clutch. The on / off control of the electromagnetic clutch 72 is performed based on a control signal from the CPU 120.

[0051] When the main motor 66 is driven in the forward direction, the pickup roller 50, registration roller 54, and pressure roller 102 rotate to transport the sheet S in the transport direction.

[0052] When the main motor 66 is driven in reverse, the pickup roller 50, registration roller 54, and pressure roller 102 are configured not to receive driving force from the main motor 66 via gears (not shown).

[0053] Furthermore, the re-transport rollers 62 and 64 shown in Figure 2 are configured such that when the main motor 66 is driven in the forward direction, the driving force from the main motor 66 is not transmitted by a gear (not shown), but when the main motor 66 is driven in the reverse direction, the driving force from the main motor 66 is transmitted by a gear (not shown). Therefore, when the main motor 66 is driven in the reverse direction, the re-transport rollers 62 and 64 rotate to transport the sheet S toward the junction J upstream of the register sensor SE1 in the transport path 34.

[0054] When the electromagnetic clutch 72 is turned on and the main motor 66 is driven in the forward direction, the intermediate paper discharge roller 56 rotates to transport the sheet S in the transport direction. When the electromagnetic clutch 72 is turned on and the main motor 66 is driven in the reverse direction, the intermediate paper discharge roller 56 rotates to transport the sheet S towards the re-transport path 36.

[0055] The process motor 98 is a motor that outputs driving force to multiple photoreceptor drums 82 and multiple developing rollers 86. The photoreceptor drums 82 rotate as driving force is transmitted from the process motor 98, and in the transport path 34, they transport the sheet S between the drum and the transfer rollers 96 in the transport direction. The developing rollers 86 rotate as a result of the rotation of the process motor 98. The CPU 120 controls the drive of the process motor 98.

[0056] The paper discharge motor 68 is a motor that outputs driving force to the first discharge roller 58 and the second discharge roller 60. The paper discharge motor 68 is, for example, a stepping motor. When the paper discharge motor 68 is driven forward, the first discharge roller 58 and the second discharge roller 60 rotate to discharge the sheet S toward the discharge tray 32. When the paper discharge motor 68 stops rotating, the transport of the sheet S can be stopped so that the cutter position KP coincides with a predetermined position (center) in the transport direction of the sheet S. On the other hand, when the paper discharge motor 68 is driven in reverse, the first discharge roller 58 and the second discharge roller 60 rotate to transport the sheet S toward the re-transport path 36. The CPU 120 controls the drive of the paper discharge motor 68.

[0057] The cutter motor 118 is a motor that outputs a driving force to slide the slide holder 116 as described above. The CPU 120 controls the operation of the cutter motor 118.

[0058] With the rotation of the intermediate paper output roller 56, the first paper output roller 58, and the second paper output roller 60 stopped, the printer 1 cuts the sheet S using the cutter 28. Figure 3 shows the state in which the transport of sheet S1 has stopped at cutter position KP, with sheet S1 nipped by the intermediate paper output roller 56, specifically positioned where the trailing end of sheet S1 is located, and the subsequent sheet S2 being transported by the photoreceptor drum 62, etc. When the transport of the sheet S1 is stopped at cutter position KP, the intermediate paper discharge roller 56 stops rotating by turning off the electromagnetic clutch 72 while the CPU 120 maintains the rotation command for the main motor 66. Furthermore, the paper discharge motor 68 stops rotating when the CPU 120 commands it to stop rotating. When the paper discharge motor 68 stops rotating, the transport of the sheet S1 can be stopped by the first paper discharge roller 58 and the second paper discharge roller 60 so that the predetermined position (center) of the sheet S1 in the transport direction coincides with the cutter position KP.

[0059] Even when the transport of sheet S1 is stopped at cutter position KP, the CPU 120 maintains the rotation instruction for the main motor 66 and the process motor 98, allowing the pickup roller 70 to start transporting the subsequent sheet S2, and enabling the photoreceptor drum 82 and the like to form an image on sheet S2.

[0060] The control processes performed by printer 1, configured as described above, will be explained in detail below with reference to Figures 4 to 8.

[0061] Figure 4 shows the procedure for the sheet printing and cutting process executed by the CPU 120 (see Figure 3), which is the control unit of printer 1. This sheet printing and cutting process is started when printer 1 receives a print job or print command that includes instructions to print (form an image) on both sides of sheet S and instructions to cut the printed sheet S. Hereafter, in the description of each process, steps will be denoted as "S".

[0062] In Figure 4, first the CPU 120 turns on the heater 104 (S10) and controls the heater 104 so that the heating roller 100 reaches the target temperature. Next, the CPU 120 outputs a control signal to drive the main motor 66 in the forward direction (S12) and a control signal to drive the process motor 98 (S14). The electromagnetic clutch 70 of the pickup roller 50 and the electromagnetic clutch 72 of the intermediate paper discharge roller 56 are initially turned off. Next, the CPU 120 executes a pickup command (S15). This causes the CPU 120 to turn on the electromagnetic clutch 70 of the pickup roller 50. When the electromagnetic clutch 70 is turned on, the driving force of the main motor 66 is transmitted to the pickup roller 50, so that the sheet S in the supply tray 30 is picked up and transported towards the transport path 34.

[0063] Next, the CPU 120 executes the image forming process (first surface) (S16). Figure 5 shows the detailed procedure for the image forming process (first surface) that forms an image on the first surface of the sheet S. In Figure 5, the CPU 120 first waits until the post-registration sensor SE2 switches from off to on (S52: NO). As described above, the post-registration sensor SE2 is positioned between the registration roller 54 and the image forming unit 24 in the transport path 34, and outputs an ON signal when the sheet S is passing through and an OFF signal when the sheet S is not passing through. Therefore, in S52, the CPU 120 waits until the post-registration sensor SE2 detects the front edge of the sheet S. Then, when the post-registration sensor SE2 detects the front edge of the sheet S (S52: YES), the CPU 120 starts image forming on the sheet S (S54). Note that image forming may be started by triggers other than the post-registration sensor SE2 detecting the front edge of the sheet S. Image formation should be performed such that the toner image formed by the photoreceptor drum 82 is correctly transferred to the image formation position on the sheet S.

[0064] Next, the CPU 120 waits until the discharge sensor SE3 switches from off to on (S56: NO). As described above, the discharge sensor SE3 is positioned between the fixing unit 26 and the intermediate paper discharge roller 56 in the transport path 34, and outputs an ON signal when a sheet S is passing through and an OFF signal when a sheet S is not passing through. Therefore, in S56, the CPU 120 waits until the discharge sensor SE3 detects the front end of the sheet S. When the discharge sensor SE3 detects the front end of the sheet S (S56: YES), the CPU 120 turns on the electromagnetic clutch 72 of the intermediate paper discharge roller 56 (S58). When the electromagnetic clutch 72 is turned on, the driving force of the main motor 66 is transmitted to the intermediate paper discharge roller 56, so that the sheet S in the transport path 34 is transported in the transport direction. Furthermore, the CPU 120 drives the paper discharge motor 68 in the forward direction (S60). As the paper discharge motor 68 rotates in the forward direction, the first paper discharge roller 58 and the second paper discharge roller 60 transport the sheet S in the transport path 34 in the transport direction.

[0065] The CPU 120 waits until a predetermined time has elapsed (S62: NO), and once the predetermined time has elapsed (S62: YES), the CPU 120 finishes image formation (S64) and terminates the image formation process. The "predetermined time" in S62 is, for example, the time from when the discharge sensor SE3 detects the front end of the sheet S in the transport direction until the rear end of the sheet S passes between the heating roller 100 and the pressure roller 102.

[0066] Returning to Figure 4, the CPU 120 then performs the sheet inversion process (S18). Figure 6 shows the detailed procedure for the sheet inversion process. In Figure 6, the CPU 120 first waits until the sheet S reaches the branching point D on the transport path 34 (S70:NO). The CPU 120 determines whether or not the sheet S has reached the branching point D. The CPU 120 determines whether or not the rear end of the sheet S in the transport direction has reached the branching point D by, for example, determining whether or not a predetermined time has elapsed since the discharge sensor SE3 detected the front end of the sheet S in the transport direction.

[0067] Then, when the sheet S reaches branching position D (S70:YES), the CPU 120 reverses the drive of the main motor 66 (S72). The CPU 120 also reverses the drive of the paper discharge motor 68 (S74). As the main motor 66 reverses its drive, the intermediate paper discharge roller 56 rotates in the opposite direction to the rotation that transports the sheet S in the transport direction, and as the paper discharge motor 68 reverses its drive, the first paper discharge roller 58 and the second paper discharge roller 60 rotate in the opposite direction to the rotation that transports the sheet S in the transport direction. As a result, the sheet S is transported towards the re-transport path 36. The sheet S transported to the re-transport path 36 is then transported towards the image forming unit 24 by the re-transport rollers 62 and 64.

[0068] The CPU 120 waits, as in S52 above (see Figure 5), until the post-cash sensor SE2 switches from off to on (S76: NO). Then, when the post-cash sensor SE2 detects the front end of the sheet S (S76: YES), the CPU 120 drives the main motor 66 in the forward direction (S78) and terminates the sheet inversion process.

[0069] Returning to Figure 4, the CPU 120 executes the image forming process (second surface) (S20). Figure 7 shows the detailed procedure of the image forming process (second surface) which forms an image on the second surface of the sheet S that has been transported via the re-transport path 36. The image forming process (second surface) is configured by omitting the processes S52 and S58 included in the image forming process (first surface) of Figure 5. Therefore, in the process of Figure 7, the same reference numerals are used for processes that are the same as those included in the image forming process of Figure 5, and their explanations are omitted. The reason why the image forming process (second surface) is configured by omitting the process S52 included in the image forming process (first surface) of Figure 5 is that the process of S52 has already been executed in S76 (see Figure 6), so there is no need to execute it again. Also, the reason why the image forming process (second surface) is configured by omitting the process S58 included in the image forming process (first surface) of Figure 5 is that in the process of S58, the driving force of the main motor 66 is already transmitted to the intermediate paper discharge roller 56.

[0070] Returning to Figure 4, the CPU 120 determines whether the current job has a next sheet to print (S22). If the determination is that there is a next sheet to print (S22: YES), the CPU 120 executes a pickup command, similar to S50 (see Figure 5) above (S24). As a result, the CPU 120 turns on the electromagnetic clutch 70 of the pickup roller 50, causing the sheet S in the supply tray 30 to be picked up by the pickup roller 50 and transported towards the transport path 34.

[0071] Next, the CPU 120 performs the sheet cutting process (S26). Figure 8 shows the detailed procedure for the sheet cutting process. In Figure 8, the CPU 120 first waits until the sheet S, which is being transported by the first paper discharge roller 58 and the second paper discharge roller 60, reaches the sheet stopping position (S80: NO). The sheet stopping position is, for example, the position where the center of the sheet S reaches the cutter position of the cutter 28 when the sheet S is cut in the center in the transport direction. The position where the center of the sheet S reaches the cutter position of the cutter 28 is the position where the sheet S has passed the fixing unit 26, and the rear end of the sheet S is not nipped by the fixing unit 26. The CPU 120 determines whether the sheet S has reached the sheet stopping position by, for example, detecting the front end of the sheet S based on the detection result of the sheet sensor SE4, and counting the number of steps of the paper discharge motor 68. When the sheet S reaches the sheet stopping position (S80: YES), the CPU 120 stops driving the paper discharge motor 68 (S82). As the paper discharge motor 68 stops, the transport of the sheet S by the first paper discharge roller 58 and the second paper discharge roller 60 also stops. Furthermore, when the sheet S reaches the sheet stopping position (S80: YES), the CPU 120 turns off the electromagnetic clutch 72 of the intermediate paper discharge roller 56 (S84). When the electromagnetic clutch 72 is turned off, the driving force of the main motor 66 is no longer transmitted to the intermediate paper discharge roller 56, so the transport of the sheet S by the intermediate paper discharge roller 56 also stops. In this way, the transport of the sheet S by the first paper discharge roller 58, the second paper discharge roller 60 and the intermediate paper discharge roller 56 stops, and the sheet S comes to a stop at the sheet stopping position. Then, the CPU 120 drives the cutter motor 118 to slide the slide holder 116, and the sheet S is cut by the fixed blade 113 and the movable blade 115 (S86).

[0072] Next, the CPU 120 drives the paper output motor 68 in the forward direction (S88) and turns on the electromagnetic clutch 72 of the intermediate paper output roller 56 (S90). As a result, the sheet S cut by the cutter 28 is transported toward the output tray 32 by the first paper output roller 58, the second paper output roller 60, and the intermediate paper output roller 56.

[0073] Next, the CPU 120 waits until the ejection of the cut sheet S is complete (S92: NO). Here, one possible method for determining whether the ejection of the cut sheet S is complete is to determine whether a predetermined time has elapsed after processing S88 and S90, that is, the time required for the ejection of the cut sheet S to be completed.

[0074] Once the ejection of the cut sheet S is complete (S92:YES), the CPU 120 stops the drive of the paper ejection motor 68 (S94), turns off the electromagnetic clutch 72 of the intermediate paper ejection roller 56 (S96), and then terminates the sheet cutting process.

[0075] In Figure 4, the image forming process (first surface) (S16) is performed after the sheet cutting process (S26), but the sheet cutting process (S26) and the image forming process (first surface) (S16) are performed in parallel. In other words, in the process of S24, the sheet S in the supply tray 30 is picked up by the pickup roller 50 and the processes from S16 onwards are performed on the sheet S that have been transported toward the transport path 34. Therefore, for example, while the sheet cutting process is being performed on the Nth sheet S, the image forming process (first surface) and subsequent processes are performed on the N+1th sheet S.

[0076] On the other hand, if there is no next sheet to print (S22: NO), the CPU 120 performs the sheet cutting process (S28) in the same way as in S26 (see Figure 4). In other words, it performs the sheet cutting process on the final sheet S. After the process in S28, the CPU 120 turns off the heater 104 (S30). Subsequently, the CPU 120 outputs a control signal to stop the main motor 66 (S32), and after outputting a control signal to stop the process motor 98, it terminates the sheet printing and cutting process.

[0077] In this type of sheet printing and cutting process, the sheet output motor 68 stops (S82) and the electromagnetic clutch 72 of the intermediate output roller 56 is turned off (S84) during the sheet cutting process shown in Figure 8, and the sheet S is cut (S86). In other words, the main motor 66 is driven while the sheet S is being cut, but the transport of the sheet S by the intermediate output roller 56 stops when the electromagnetic clutch 72 is turned off. Therefore, the transport roller 52, registration roller 54, and pressure roller 102 are rotating while the sheet S is being cut. Also, since the process motor 98 is driven while the sheet S is being cut, the photoreceptor drum 82 and developing roller 86 are also rotating. Therefore, the sheet S is transported by the transport roller 52, registration roller 54, pressure roller 102, photoreceptor drum 82, etc., while the sheet S is being cut. In addition, when the electromagnetic clutch 70 of the pickup roller 50 is turned on, the sheet S is supplied from the supply tray 30 to the transport path 34.

[0078] In more detail, in conventional printers, as shown in Figure 9, an electromagnetic clutch was not provided for the intermediate paper output roller 56. Therefore, when sheet S1 is cut by the cutter 28, the first paper output roller 58 and the second paper output roller 60 stop when the paper output motor 68 stops. However, when the main motor 66 is driven to transport sheet S2, the intermediate paper output roller 56 rotates, and there is a risk that sheet S1 being cut may jam due to the rotation of the intermediate paper output roller 56. Thus, in conventional printers, when sheet S1 is cut by the cutter 28, the main motor 66 stops and sheet S2 is not transported. Therefore, it was not possible to shorten the distance between sheet S1 being cut and the next sheet S2 to be transported.

[0079] On the other hand, in printer 1, as shown in Figure 3, an electromagnetic clutch 72 is provided for the intermediate paper discharge roller 56. Therefore, when sheet S1 is cut by the cutter 28, the first paper discharge roller 58 and the second paper discharge roller 60 stop when the paper discharge motor 68 stops, and the intermediate paper discharge roller 56 stops when the electromagnetic clutch 72 is turned off. Meanwhile, sheet S2, which is transported after sheet S1, is transported by the transport roller 52, registration roller 54, pressure roller 102, photoreceptor drum 82, etc. Note that the transport roller 52 is omitted in Figure 3. In this way, when sheet S1 is cut by the cutter 28, printer 1 can shorten the distance between sheet S1, which is being transported by the first paper discharge roller 58 and the second paper discharge roller 60 while the paper discharge rollers are stopped, and the next sheet S2 that is being transported, by transporting the subsequent sheet S2 when sheet S1 is cut by the cutter 28.

[0080] Furthermore, in printer 1, an electromagnetic clutch 72 is provided with respect to the intermediate paper discharge roller 56, allowing the first paper discharge roller 58 and the second paper discharge roller 60 to be positioned close to the intermediate paper discharge roller 56. Specifically, as shown in Figure 10, when an electromagnetic clutch is not provided with respect to the intermediate paper discharge roller 56, the first paper discharge roller 58 and the second paper discharge roller 60 are positioned away from the intermediate paper discharge roller 56 so that the sheet S1 being cut by the cutter 28 does not come into contact with the intermediate paper discharge roller 56. By positioning the first paper discharge roller 58 and the second paper discharge roller 60 away from the intermediate paper discharge roller 56 in this way, the main motor 66 can be driven to transport the sheet S2 when the sheet S1 is cut by the cutter 28. This shortens the distance between the sheet S1 being cut and the next sheet S2 being transported. However, because the first paper discharge roller 58 and the second paper discharge roller 60 need to be positioned away from the intermediate paper discharge roller 56, the device becomes larger.

[0081] On the other hand, in printer 1, as shown in Figure 3, an electromagnetic clutch 72 is provided with respect to the intermediate paper discharge roller 56, and when the sheet S1 is cut by the cutter 28, the intermediate paper discharge roller 56 stops as the electromagnetic clutch 72 is turned off. Therefore, by arranging the first paper discharge roller 58 and the second paper discharge roller 60 close to the intermediate paper discharge roller 56, the main motor 66 can be driven even when the sheet S1 being cut by the cutter 28 comes into contact with the intermediate paper discharge roller 56. As a result, in printer 1 with the first paper discharge roller 58 and the second paper discharge roller 60 arranged close to the intermediate paper discharge roller 56, it becomes possible to transport sheet S2 when sheet S1 is being cut, and the distance between the sheet S1 being cut and the sheet S2 being transported next can be shortened. This makes it possible to miniaturize printer 1 with the first paper discharge roller 58 and the second paper discharge roller 60 arranged close to the intermediate paper discharge roller 56.

[0082] As described above, the first embodiment provides the following effects. (1) The printer 1 of this embodiment includes an image forming unit 24 having a photoreceptor drum 82 and forming an image on a sheet S, the image forming unit 24 which transports the sheet S in the transport direction as the photoreceptor drum 82 rotates, and a fixing unit 26 having a heating roller 100 and a pressure roller 102 which forms a nip between itself and the heating roller 100, the fixing unit 26 which fixes the image formed on the sheet S by the image forming unit 24 to the sheet, the fixing unit 26 which transports the sheet in the transport direction as the rotating body of either the heating roller 100 or the pressure roller 102 rotates, and a device body 20 having a transport path 34 for the sheet S, and in the transport path 34, The device is characterized by comprising: a cutter 28 positioned at the cutter position downstream in the sheet transport direction for cutting the sheet S; a pickup roller 50 for feeding the sheet S toward the image forming unit 24; paper discharge rollers 58, 60 for discharging the sheet S cut by the cutter 28 to the outside of the device body 20; an intermediate paper discharge roller 56 positioned between the paper discharge rollers 58, 60 and the fixing unit 26; a main motor 66 for rotationally driving the pickup roller 50 and the intermediate paper discharge roller 56; a paper discharge motor 68 for rotationally driving the paper discharge rollers 58, 60; and an electromagnetic clutch 72 for switching the transmission of driving force between the main motor 66 and the intermediate paper discharge roller 56.

[0083] According to this, the main motor 66 rotates the intermediate paper discharge roller 56 via the electromagnetic clutch 72, and the rotational drive of the intermediate paper discharge roller 56 can be stopped by the electromagnetic clutch 72. Therefore, as described above, when the paper discharge motor 68 is stopped in order for the cutter 28 to cut the sheet S, the driving force of the main motor 66 is not transmitted to the intermediate paper discharge roller 56 by the electromagnetic clutch 72, and the rotational drive of the intermediate paper discharge roller 56 can be stopped. As a result, the main motor 66 can continue to rotate when cutting the sheet S, so that the pickup roller 50, the image forming unit 24, and the fixing unit 26 can transport the next sheet S2 after the sheet S1 being cut, thus shortening the gap between the sheet S1 being cut and the next sheet S2.

[0084] Furthermore, as described above, by positioning the paper output rollers 58 and 60 near the intermediate paper output roller 56, the main motor 66 can be driven even when the sheet S1 being cut by the cutter 28 comes into contact with the intermediate paper output roller 56. Therefore, in a printer 1 in which the paper output rollers 58 and 60 are positioned near the intermediate paper output roller 56, it becomes possible to transport sheet S2 while sheet S1 is being cut, and the distance between the sheet S1 being cut and the next sheet S2 being transported can be shortened. As a result, the printer 1 in which the paper output rollers 58 and 60 are positioned near the intermediate paper output roller 56 can be made more compact.

[0085] (2) The main body of the apparatus 20 has a re-transport path 36 which is a path for transporting the sheet S that has passed through the fixing unit 26 in the opposite direction to the sheet transport direction and transporting it again toward the image forming unit 24, and the intermediate paper discharge roller 56 is a roller that guides the sheet S that has passed through the fixing unit 26 toward the re-transport path 36 by rotating in the reverse direction.

[0086] This allows the rotation of the intermediate paper discharge roller 56, which guides the paper to the re-transport path 36, to be stopped while the main motor 66 is running, thereby shortening the gap between the sheet S1 being cut and the next sheet S2.

[0087] (3) The image forming unit 24 has a plurality of photoreceptor drums 82, and the printer 1 has a process motor 98 for rotating the plurality of photoreceptor drums 82.

[0088] This allows multiple photoreceptor drums 82 to be rotated by the process motor 98 when cutting sheet S1. As a result, multiple photoreceptor drums 82 can transport the next sheet S2 after the sheet S1 being cut, thus shortening the distance between the sheet S1 being cut and the next sheet S2.

[0089] (4) The main motor 66 is characterized by being a motor for rotationally driving the rotating body and the pickup roller 50.

[0090] This allows the pickup roller 50 and fixing unit 26 to transport the next sheet S2 after the sheet S1 being cut, thus shortening the gap between the sheet S1 being cut and the next sheet S2.

[0091] (5) The paper discharge rollers 58 and 60 are characterized by having a first paper discharge roller 58 located upstream of the cutter position in the sheet transport direction and a second paper discharge roller 60 located downstream of the cutter position in the sheet transport direction.

[0092] This makes it possible to transport the sheet S cut by the cutter 28 by the first paper discharge roller 58 and the second paper discharge roller 60 while it is held in place at the cutting position, thereby enabling proper transport of the sheet S cut by the cutter 28.

[0093] (6) The paper discharge rollers 58, 60 and the intermediate paper discharge roller 56 do not rotate while the sheet S is being cut by the cutter 28, but the pickup roller 50, the rotating bodies 100, 102 and the photosensitive drum 82 rotate even while the sheet S is being cut by the cutter 28.

[0094] This allows the pickup roller 50, image forming unit 24, and fixing unit 26 to transport the next sheet S2 while sheet S1 is being cut, thus shortening the distance between the sheet S1 being cut and the next sheet S2.

[0095] (Second Embodiment) Next, a second embodiment of the present invention will be described. In the printer 1 of the first embodiment described above, the intermediate paper output roller 56 is connected to the main motor 66 via an electromagnetic clutch 72.

[0096] Figure 11 is a schematic diagram showing the relationship between the roller and the motor in the printer of Figure 1, and illustrates a second embodiment. The difference between the printer 1 of the first embodiment shown in Figure 3 and the printer 1 of the second embodiment shown in Figure 11 is that an intermediate paper discharge roller 56 is connected to the paper discharge motor 68.

[0097] The paper discharge motor 68 is a motor that outputs driving force to the intermediate paper discharge roller 56, the first discharge roller 58, and the second discharge roller 60. When the paper discharge motor 68 is driven forward, the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 rotate to discharge the sheet S toward the discharge tray 32. When the paper discharge motor 68 stops rotating, the transport of the sheet S can be stopped so that the cutter position KP coincides with a predetermined position (center) in the transport direction of the sheet S. On the other hand, when the paper discharge motor 68 is driven in reverse, the first paper discharge roller 58 and the second paper discharge roller 60 rotate to transport the sheet S toward the re-transport path 36. The CPU 120 controls the drive of the paper discharge motor 68.

[0098] With the intermediate paper output roller 56, the first paper output roller 58, and the second paper output roller 60 stopped rotating, the printer 1 cuts the sheet S1 using the cutter 28. Figure 11 shows the state in which the sheet S1 is nipped by the intermediate paper output roller 56, specifically the state in which the rear end of the sheet S1 is located, when the transport of the sheet S1 is stopped at the cutter position KP. When the transport of the sheet S1 is stopped at the cutter position KP, the CPU 120 maintains the rotation command for the main motor 66, and the intermediate paper output roller 56, the first paper output roller 58, and the second paper output roller 60 stop rotating.

[0099] Even when the transport of sheet S1 is stopped at cutter position KP, the CPU 120 maintains the rotation instruction for the main motor 66 and the process motor 98, allowing the pickup roller 70 to start transporting the subsequent sheet S2, and enabling the photoreceptor drum 82 and the like to form an image on sheet S2. In the following descriptions of the second to fourth embodiments, components similar to those in the first embodiment described above will be denoted by the same reference numerals, and their descriptions will be omitted as appropriate.

[0100] As described above, the second embodiment provides the following effects. (1) The printer 150 of this embodiment includes an image forming unit 24 having a photoreceptor drum 82 and forming an image on a sheet S, the image forming unit 24 which transports the sheet S in the transport direction as the photoreceptor drum 82 rotates, and a fixing unit 26 having a heating roller 100 and a pressure roller 102 which forms a nip between itself and the heating roller 100, fixing the image formed on the sheet S by the image forming unit 24 to the sheet, the fixing unit 26 which transports the sheet in the transport direction as the rotating body of either the heating roller 100 or the pressure roller 102 rotates, and the apparatus main body having a transport path 34 for the sheet S The device is characterized by comprising a body 20, a cutter 28 positioned downstream of the fixing unit 26 in the sheet transport direction in the transport path 34 for cutting the sheet S, a pickup roller 50 for feeding the sheet S toward the image forming unit 24, paper discharge rollers 58, 60 for discharging the sheet S cut by the cutter 28 to the outside of the device body 20, an intermediate paper discharge roller 56 positioned between the paper discharge rollers 58, 60 and the fixing unit 26, a main motor 66 for rotationally driving the pickup roller 50, and a paper discharge motor 68 for rotationally driving the paper discharge rollers 58, 60 and the intermediate paper discharge roller 56.

[0101] According to this, by stopping the paper discharge motor 68 so that the cutter 28 can cut the sheet S, the rotational drive of the paper discharge rollers 58, 60 and the intermediate paper discharge roller 56 can be stopped. As a result, the main motor 66 can continue to rotate while the sheet S is being cut, so that the pickup roller 50, the image forming unit 24 and the fixing unit 26 can transport the next sheet S2 after the sheet S1 being cut, thus shortening the gap between the sheet S1 being cut and the next sheet S2.

[0102] Furthermore, similar to the first embodiment, by arranging the paper discharge rollers 58 and 60 near the intermediate paper discharge roller 56, the main motor 66 can be driven even when the sheet S1 being cut by the cutter 28 comes into contact with the intermediate paper discharge roller 56. As a result, in the printer 150 in which the paper discharge rollers 58 and 60 are arranged near the intermediate paper discharge roller 56, it becomes possible to transport sheet S2 when sheet S1 is being cut, and the distance between the sheet S1 being cut and the sheet S2 being transported next can be shortened. This makes it possible to miniaturize the printer 150 in which the paper discharge rollers 58 and 60 are arranged near the intermediate paper discharge roller 56.

[0103] (Third embodiment) Next, a third embodiment of the present invention will be described. This embodiment is constructed by modifying a part of the printer 1 described in the first embodiment above, so the description will focus on the modified parts, and descriptions of other parts will be omitted as appropriate.

[0104] Figure 12 shows a cross-sectional view of the printer 160 of the third embodiment. In the printer 1 of the first embodiment, a transport path 34 and a re-transport path 36 are formed as paths for transporting the sheet S. In the printer 160 of the third embodiment, a transport path 34, a re-transport path 36, and a branch transport path 162 are formed as paths for transporting the sheet S. The branch transport path 162 is a path for transporting the sheet S, which has an image formed on one side, in the opposite direction to the transport direction, toward the re-transport path 36. The branch transport path 162 extends diagonally upward and backward from the branch position D on the transport path 34. A reversing roller 164 is positioned in the branch transport path 162. The reversing roller 164 transports the sheet S transported in the branch transport path 162 toward the re-transport path 36. In addition, a re-transport roller 168 is positioned between the branch position D of the re-transport path 36 and the re-transport roller 62. The re-transport roller 168 transports the sheet S, which was transported from the branch transport path 162 by the reversing roller 164, towards the re-transport roller 62 in the re-transport path 36.

[0105] Furthermore, a flapper 166 is positioned at branching position D. The flapper 166 swings between a first position (position 166A, shown by a solid line in Figure 12) and a second position (position 166B, shown by a dashed line in Figure 12) by a solenoid (not shown). The first position 166A is the position that guides the sheet S conveyed from the fixing unit 26 to the conveying path 34. The second position 166B is the position that guides the sheet S conveyed from the fixing unit 26 to the branching conveying path 162.

[0106] Therefore, when the sheet S with an image formed on one side is transported from the fixing unit 26 to the image forming unit 24, the flapper 166 swings to the second position 166B, and the sheet S with an image formed on one side is guided by the flapper 166 to the branch transport path 162. At this time, the reversing roller 164 rotates to transport the sheet S in the transport direction, and the sheet S with an image formed on one side is transported by the reversing roller 164 toward the interior of the branch transport path 162. After the sheet S has been transported toward the interior of the branch transport path 162, the reversing roller 164 rotates to transport the sheet S in the opposite direction to the transport direction. As a result, the sheet S that has been transported toward the branch transport path 162 is transported toward the re-transport path 36 by the reversing roller 164. Then, the sheet S that has been transported toward the re-transport path 36 is transported toward the image forming unit 24 by the re-transport rollers 62, 64, and 168. In other words, the sheet S with an image formed on one side is transported toward the image forming unit 24 again. Then, an image is formed on the other surface in the image forming unit 24, and the sheet S with images formed on both sides is conveyed toward the fixing unit 26. At this time, the flapper 166 swings to the first position 166A, and the sheet S with images formed on both sides is guided toward the conveyance path 34 by the flapper 166. Then, the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 rotate to convey the sheet S in the conveyance direction, and the sheet S with images formed on both sides is conveyed toward the cutter position.

[0107] Figure 13 is a schematic diagram showing the relationship between the rollers and the motor in the printer shown in Figure 12. The main motor 170 outputs driving force to the pickup roller 50 and the registration roller 54. When the main motor 170 is driven in the forward direction, the pickup roller 50, the transport roller 52, and the registration roller 54 rotate to transport the sheet S in the transport direction. The re-transport rollers 62 and 64 receive driving force from the main motor 170 and operate in the same manner as in the first embodiment.

[0108] On the other hand, when the main motor 170 is driven in reverse, the driving force is not transmitted to the pickup roller 50, the transport roller 52, and the registration roller 54, but the driving force is transmitted to the re-transport rollers 62 and 64.

[0109] The main motor 170 is connected to the pickup roller 50 via an electromagnetic clutch 70. Therefore, by turning on the electromagnetic clutch 70, the driving force of the main motor 170 is transmitted to the pickup roller 50. Conversely, by turning off the electromagnetic clutch 70, the driving force of the main motor 170 is not transmitted to the pickup roller 50.

[0110] The process motor 172 outputs driving force to the four photoreceptor drums 82. When the process motor 172 is driven forward, the four photoreceptor drums 82 rotate to transport the sheet S in the transport direction. The developing motor 174 outputs driving force to the four developing rollers 86. The fixing motor 176 outputs driving force to the pressure rollers 102. When the fixing motor 176 is driven forward, the pressure rollers 102 rotate to transport the sheet S in the transport direction.

[0111] Furthermore, the paper discharge motor 68 outputs driving force to the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60. When the paper discharge motor 68 is driven forward, the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 rotate to discharge the sheet S toward the discharge tray 32. When a stop command is input to the paper discharge motor 68, the transport of the sheet S can be stopped. On the other hand, when the paper discharge motor 68 is driven in reverse, the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 rotate to transport the sheet S toward the re-transport path 36. The paper discharge motor 68 is controlled by a CPU (not shown).

[0112] Although not shown in the diagram, the DX motor outputs driving force to the reversing roller 164 and the re-transport roller 168.

[0113] In the printer 160 of the third embodiment configured in this way, as in the printer 150 of the second embodiment, the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 are connected to the paper discharge motor 68. Therefore, by stopping the paper discharge motor 68 so that the cutter 28 can cut the sheet S, the rotational drive of the intermediate paper discharge roller 56, the first paper discharge roller 58, and the second paper discharge roller 60 can be stopped. As a result, the main motor 170, the process motor 172, the developing motor 174, and the fixing motor 176 can continue to rotate while the sheet S is being cut, so that the pickup roller 50, the image forming unit 24, and the fixing unit 26 can transport the next sheet S2 after the sheet S1 being cut, thus shortening the gap between the sheet S1 being cut and the next sheet S2.

[0114] Furthermore, in a printer 160 where the first paper output roller 58 and the second paper output roller 60 are positioned near the intermediate paper output roller 56, similar to the second embodiment, it becomes possible to transport sheet S2 when cutting sheet S1, and to shorten the distance between sheet S1 being cut and the next sheet S2 to be transported. As a result, the printer 160 with the first paper output roller 58 and the second paper output roller 60 positioned near the intermediate paper output roller 56 can be made more compact.

[0115] As described above, the third embodiment provides the following effects. (1) The image forming unit 24 has a plurality of photoreceptor drums 82 and a plurality of developing rollers 86 that form toner images on the surfaces of the plurality of photoreceptor drums 82. Furthermore, the printer 160 is characterized by having a process motor 172 for rotating the plurality of photoreceptor drums 82 and a developing motor 174 for rotating the plurality of developing rollers 86.

[0116] This allows multiple photoreceptor drums 82 to be rotated by the process motor 172 and multiple developing rollers 86 to be rotated by the developing motor 174 when cutting sheet S1. As a result, multiple photoreceptor drums 82 can transport the next sheet S2 after the sheet S1 being cut, thus shortening the distance between the sheet S1 being cut and the next sheet S2.

[0117] (2) The printer 160 is characterized by having a fuser motor 176 for rotating the heating roller 100.

[0118] This allows the heating roller 100 to transport the next sheet S2 after the sheet S1 being cut, thus shortening the gap between the sheet S1 being cut and the next sheet S2.

[0119] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. The printers 1,150 and 160 of the first to third embodiments described above are color printers, but the printer of the fourth embodiment is a monochrome printer. For this reason, the printers 1,150 and 160 of the first to third embodiments described above have four photoreceptor drums 82 and four developing rollers 86, but as shown in Figure 14, the printer 180 of the fourth embodiment has one photoreceptor drum 82 and one developing roller 86.

[0120] Figure 14 is a schematic diagram showing the relationship between the rollers and the motor in the printer 180 of the fourth embodiment. The main motor 66 outputs driving force to the pickup roller 50, registration roller 54, intermediate paper discharge roller 56, photoreceptor drum 82, developer roller 86, and pressure roller 102. When the main motor 66 is driven in the forward direction, the pickup roller 50, registration roller 54, intermediate paper discharge roller 56, photoreceptor drum 82, developer roller 86, and pressure roller 102 rotate to transport the sheet S in the transport direction.

[0121] On the other hand, when the main motor 66 is driven in reverse, the driving force is not transmitted to the pickup roller 50, registration roller 54, photoreceptor drum 82, developing roller 86, and pressure roller 102, but the driving force is transmitted to the intermediate paper discharge roller 56.

[0122] The main motor 66 is connected to the pickup roller 50 via an electromagnetic clutch 70 (see Figure 3). Therefore, by turning on the electromagnetic clutch 70, the driving force of the main motor 66 is transmitted to the pickup roller 50. Conversely, by turning off the electromagnetic clutch 70, the driving force of the main motor 66 is not transmitted to the pickup roller 50.

[0123] Furthermore, the main motor 66 is connected to the intermediate paper discharge roller 56 via an electromagnetic clutch 72. Therefore, by turning on the electromagnetic clutch 72, the driving force of the main motor 66 is transmitted to the intermediate paper discharge roller 56. Conversely, by turning off the electromagnetic clutch 72, the driving force of the main motor 66 is not transmitted to the intermediate paper discharge roller 56. Note that the electromagnetic clutch 72 is an example of a clutch.

[0124] Furthermore, the paper discharge motor 68 outputs driving force to the first paper discharge roller 58 and the second paper discharge roller 60. When the paper discharge motor 68 is driven forward, the first paper discharge roller 58 and the second paper discharge roller 60 rotate to discharge the sheet S toward the discharge tray 32. When a stop command is input to the paper discharge motor 68, the transport of the sheet S can be stopped. On the other hand, when the paper discharge motor 68 is driven in reverse, the first paper discharge roller 58 and the second paper discharge roller 60 rotate to transport the sheet S toward the re-transport path 36.

[0125] As described above, the fourth embodiment provides the following effects. (1) The main motor 66 is characterized by being a motor for rotationally driving the photoreceptor drum 82, the heating roller 100, and the pickup roller 50.

[0126] This allows the photoreceptor drum 82, heating roller 100, and pickup roller 50 to be rotated by the main motor 66 when cutting sheet S1. As a result, the photoreceptor drum 82, heating roller 100, and pickup roller 50 can transport the next sheet S2 after the sheet S1 being cut, thus shortening the distance between the sheet S1 being cut and the next sheet S2.

[0127] Furthermore, since the printer 180 of the fourth embodiment has the same structure as the printer 1 of the first embodiment, except that it has one photosensitive drum 82 and one developing roller 86, it can achieve the same effects as the printer 1 of the first embodiment.

[0128] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. For example, in the printer 160 of the third embodiment, the intermediate paper output roller 56 is connected to the paper output motor 68, but the intermediate paper output roller 56 may also be connected to another motor such as the main motor 170 via an electromagnetic clutch. Furthermore, for example, in the printer 180 of the fourth embodiment, the intermediate paper output roller 56 is connected to the main motor 66 via an electromagnetic clutch 72, but the intermediate paper output roller 56 may also be connected to the paper output motor 68. Furthermore, the image forming unit of this invention is not limited to a printing unit that performs printing, but may also be an image forming unit that forms other images, such as fax data, onto a sheet. Therefore, the image forming apparatus of this invention is not limited to a printer, but may also be a fax machine. In addition, the image forming apparatus of this invention may be a multifunction device equipped with multiple functions such as printing, copying, faxing, and scanning. Therefore, the configuration of the image forming unit can be appropriately changed according to the functions provided by the image forming apparatus. Furthermore, although the printers 1,150, 160, and 180 in each of the above embodiments are configured to print on both sides, they may also be configured to print on one side only. [Explanation of Symbols]

[0129] 1: Printer (image forming apparatus) 20: Main unit 24: Image forming section 26: Fixing section 28: Cutter 34: Transport path 36: Re-transport path 50: Pickup roller (paper feed roller) 56: Intermediate paper discharge roller 58: First paper discharge roller (paper discharge roller) 60: Second paper discharge roller (paper discharge roller) 66: Main motor (first motor) 68: Paper discharge motor 72: Electromagnetic clutch (clutch) 82: Photoreceptor drum 86: Developing roller 98: Process motor 100: Heating roller (heating rotating body) 102: Pressure roller (pressure rotating body) 170: Main motor (first motor) 172: Process motor 172: Process motor 174: Developing motor 176: Fixing motor

Claims

1. An image forming unit that forms an image on a sheet, A fixing unit that fixes the image formed on the sheet by the image forming unit onto the sheet, A device body having a sheet transport path, A cutter positioned downstream of the fixing section in the sheet transport direction in the transport path is provided for cutting the sheet, A conveying roller that transports the sheet toward the image forming unit, A paper discharge roller for discharging the sheet cut by the cutter to the outside of the main body of the device, An intermediate paper discharge roller located between the paper discharge roller and the fixing unit in the transport path, A first motor for rotationally driving the transport roller and the intermediate paper discharge roller, A paper ejection motor for rotating the aforementioned paper ejection roller, A clutch that switches whether or not to transmit the driving force from the first motor to the intermediate paper discharge roller, Control unit and Equipped with, The intermediate paper discharge roller is positioned to nip the sheet when the sheet transport is stopped at the cutter position. The control unit, When cutting the sheet using the cutter, the first motor is rotated while the driving force is not transmitted by the clutch, and the rotational drive of the paper ejection motor is stopped. An image forming apparatus characterized by the following features.

2. An image forming unit that forms an image on a sheet, A fixing unit that fixes the image formed on the sheet by the image forming unit onto the sheet, A device body having a sheet transport path, A cutter positioned downstream of the fixing section in the sheet transport direction in the transport path is provided for cutting the sheet, A conveying roller that transports the sheet toward the image forming unit, A paper discharge roller for discharging the sheet cut by the cutter to the outside of the main body of the device, An intermediate paper discharge roller located between the paper discharge roller and the fixing unit, A first motor for rotationally driving the aforementioned transport roller, A paper discharge motor for rotating the aforementioned paper discharge roller and the aforementioned intermediate paper discharge roller, Control unit and Equipped with, The intermediate paper discharge roller is positioned to nip the sheet when the sheet transport is stopped at the cutter position. The control unit, When cutting the sheet using the cutter, the first motor is driven to rotate, and the rotational drive of the paper ejection motor is stopped. An image forming apparatus characterized by the following features.

3. The main body of the aforementioned device is The sheet that has passed through the fixing section is transported in the opposite direction to the sheet transport direction and is transported again toward the image forming section, and has a re-transport path. The aforementioned intermediate paper discharge roller is By rotating in the reverse direction, the roller guides the sheet that has passed through the fixing section to the re-transport path. The image forming apparatus according to feature 1 or 2.

4. The image forming unit has a photosensitive drum, and the sheet is conveyed in the conveying direction by the rotation of the photosensitive drum. The fixing unit has a heating rotating body and a pressurizing rotating body that forms a nip between itself and the heating rotating body, and the sheet is conveyed in the conveying direction by the rotation of either the heating rotating body or the pressurizing rotating body. The first motor is, This is a motor for rotating the photosensitive drum, the rotating body, and the transport roller. The image forming apparatus according to feature 1 or 2.

5. The image forming unit has a plurality of photoreceptor drums, and the sheet is conveyed in the conveying direction by the rotation of the plurality of photoreceptor drums. The fixing unit has a heating rotating body and a pressurizing rotating body that forms a nip between itself and the heating rotating body, and the sheet is conveyed in the conveying direction by the rotation of either the heating rotating body or the pressurizing rotating body. Furthermore, The process motor is used to rotate the plurality of photoreceptor drums, The first motor is, This is a motor for rotating the aforementioned rotating body and the aforementioned conveying roller. The image forming apparatus according to feature 1 or 2.

6. The image forming unit has a plurality of photoreceptor drums and a plurality of developing rollers that form toner images on the surfaces of the plurality of photoreceptor drums, and the sheet is conveyed in the conveying direction by the rotation of the plurality of photoreceptor drums. The fixing unit has a heating rotating body and a pressurizing rotating body that forms a nip between itself and the heating rotating body, and the sheet is conveyed in the conveying direction by the rotation of either the heating rotating body or the pressurizing rotating body. Furthermore, A process motor for rotating the plurality of photosensitive drums, and a developing motor for rotating the plurality of developing rollers, A fixing motor for rotating the aforementioned rotating body, Equipped with, The image forming apparatus according to feature 1 or 2.

7. The paper discharge roller comprises a first paper discharge roller located upstream of the cutter position in the sheet transport direction and a second paper discharge roller located downstream of the cutter position in the sheet transport direction. The image forming apparatus according to feature 1 or 2.

Images