Image forming device

Abstract

To provide an image formation device which can constantly keep a distance between sheets without stopping the sheets in a re-conveyance path.SOLUTION: A control unit can perform a normal control in which the conveying speed of a second re-conveying roller is set to a first speed, and a deceleration control in which the conveying speed of the second re-conveying roller is set to a second speed lower than the first speed during double-sided printing in which an image formation unit forms images on the front and back surfaces of a preceding sheet and on the front and back surfaces of a succeeding sheet fed from a sheet cassette after the preceding sheet. As shown in steps S18 to S25, the control unit performs the deceleration control when the preceding sheet is positioned in a re-conveyance path during the normal control and the succeeding sheet is supplied to a feeding path so that the sheet-to-sheet distance between the leading edge of the preceding sheet conveyed by the second re-conveying roller and the trailing edge of the succeeding sheet is a predetermined distance.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, image forming apparatuses capable of double-sided printing on sheets have used 21 transport control, 2413 transport control, 2416 transport control, 2461 transport control, etc., as sheet transport control. For example, in 2461 transport control, printing is performed in the order of the back side of the first sheet (page 2), the back side of the second sheet (page 4), the back side of the third sheet (page 6), and the front side of the first sheet (page 1) (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-140114 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the configuration of Patent Document 1, when a sheet is supplied from a sheet cassette while a preceding sheet is passing through the re-conveyance path, the preceding sheet is stopped on the re-conveyance path, and the conveyance of the stopped sheet is resumed after the sheet has been supplied from the sheet cassette. This keeps a constant distance between the trailing edge of the sheet supplied from the sheet cassette and the leading edge of the sheet passing through the re-conveyance path.

[0005] However, when the re-conveying rollers are stopped to stop the sheet on the re-conveying path, the sheet does not stop immediately but slips between the re-conveying rollers and the sheet, which may leave a slip mark on the sheet due to the re-conveying rollers.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can maintain a constant inter-sheet distance without stopping the sheets on the re-conveyance path. [Means for solving the problem]

[0007] The image forming apparatus of the present invention includes an apparatus main body having an image forming unit that forms an image on a sheet, a sheet tray that supports sheets to be supplied to the image forming unit, and a control unit. The apparatus main body includes a feed path for feeding sheets from the sheet tray to the image forming unit, a re-conveyance path for re-conveying sheets with an image formed on one side by the image forming unit to the feed path, and re-conveyance rollers arranged on the re-conveyance path. The control unit is capable of performing normal control, in which the conveyance speed of the re-conveyance roller is set to a first speed, and deceleration control, in which the conveyance speed of the re-conveyance roller is set to a second speed slower than the first speed, during double-sided printing, in which the image forming unit forms images on the front and back sides of a preceding sheet and the front and back sides of a succeeding sheet fed from the sheet tray after the preceding sheet. During the normal control, when the preceding sheet is positioned on the re-conveyance path and the succeeding sheet is fed to the feed path, the control unit performs the deceleration control so that the sheet-to-sheet distance between the leading edge of the preceding sheet conveyed by the re-conveyance roller and the trailing edge of the succeeding sheet becomes a predetermined distance.

[0008] According to the above configuration, by slowing down the conveying speed of the re-conveying roller, the sheet inter-sheet distance can be kept constant without stopping the sheet on the re-conveying path, which can prevent slip marks of the re-conveying roller from being left on the sheet.

[0009] In the above-mentioned image forming apparatus, the device main body may have a first sensor that detects a sheet upstream of the re-conveying roller in the sheet conveying direction on the re-conveying path, and the control unit may perform the deceleration control a predetermined time after the first sensor detects the preceding sheet.

[0010] According to the above configuration, by disposing the first sensor immediately before the re-conveyance roller, it is possible to detect the position of the sheet on the re-conveyance path with high accuracy.

[0011] In the above-mentioned image forming apparatus, the device main body may have a second sensor that detects a sheet being fed from the sheet tray to the feeding path, and the control unit may be configured to delay the timing of ending the deceleration control the longer the time from the start of the deceleration control until the second sensor detects the trailing end of the subsequent sheet.

[0012] According to the above configuration, by arranging the second sensor in the feeding path, it is possible to control the timing of ending the deceleration control with high precision.

[0013] In the image forming apparatus described above, if the timing to end the deceleration control is Tm, the theoretical timing to end the deceleration control is Tt, the timing to start the deceleration control is T1, the timing when the second sensor detects the trailing edge of the subsequent sheet is T2, the theoretical time from the start of the deceleration control until the second sensor detects the trailing edge of the subsequent sheet is Tb, the first speed is V1, and the second speed is V2, then: It can be calculated as Tm=Tt+{(T2-T1)-Tb}×V2 / (V1-V2).

[0014] According to the above configuration, the timing Tm at which the deceleration control is to be ended can be calculated from the calculation formula.

[0015] In the above-mentioned image forming apparatus, the apparatus main body may have a drive motor and a drive force transmission unit that transmits the drive force of the drive motor to the re-conveying roller, and the drive force transmission unit may have a first transmission mechanism that drives the re-conveying roller at the first speed and a second transmission mechanism that drives the re-conveying roller at the second speed.

[0016] According to the above configuration, the first transmission mechanism is used during normal control, and the second transmission mechanism is used during deceleration control, so there is no need to change the rotation speed of the drive motor.

[0017] In the image forming apparatus, the driving force transmission section may have an electromagnetic clutch that switches between the first transmission mechanism and the second transmission mechanism.

[0018] According to the above configuration, the use of an electromagnetic clutch allows the driving force transmission section to be made smaller.

[0019] In the image forming apparatus, the apparatus main body may include a transport roller that is disposed upstream of the re-transport roller in the re-transport path in the sheet transport direction and that is driven at the same speed as the re-transport roller.

[0020] According to the above configuration, even short sheets can be transported.

[0021] In the above-described image forming device, the control unit may form images in the image forming unit in the double-sided printing in the order of the back side of the first sheet, the back side of the second sheet, the back side of the third sheet, the front side of the first sheet, and the back side of the fourth sheet, and the preceding sheet may be the second sheet and the succeeding sheet may be the fourth sheet.

[0022] The above configuration can be applied to the transport control 2461.

[0023] In the above-mentioned image forming apparatus, the control unit may be configured to perform the deceleration control so that when the first sheet is positioned on the re-conveying path and the third sheet is supplied to the feeding path during the normal control, the sheet-to-sheet distance between the leading end of the first sheet and the trailing end of the third sheet conveyed by the re-conveying roller becomes the predetermined distance.

[0024] According to the above configuration, the deceleration control can also be used to keep the inter-seat distance between the first seat and the third seat constant. [Effects of the Invention]

[0025] According to the present invention, during double-sided printing in an image forming apparatus, the distance between sheets can be kept constant without stopping the sheets on the re-conveyance path. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a central cross-sectional view showing an image forming apparatus to which a discharge unit according to an embodiment is attached; [Figure 2] 1 is a central cross-sectional view showing an image forming apparatus with a cover attached thereto according to an embodiment; [Figure 3] FIG. 2 is a block diagram illustrating a conveying unit of the image forming apparatus according to the embodiment. [Figure 4] 10 is a flowchart of transport control. [Figure 5] 1 is a central cross-sectional view showing the image forming apparatus in a state where the leading edge of the first sheet is at a position before reaching the flapper and the second sheet is being fed. FIG. [Figure 6] FIG. 6 is a diagram showing a transport state following FIG. 5. [Figure 7] FIG. 7 is a diagram showing a transport state following FIG. [Figure 8] FIG. 8 is a diagram showing a transport state following FIG. 7. [Figure 9] FIG. 9 is a diagram showing a transport state following FIG. 8. [Figure 10] FIG. 10 is a diagram showing a transport state following FIG. 9. [Figure 11] FIG. 11 is a diagram showing a transport state following FIG. [Figure 12] FIG. 12 is a diagram showing a transport state following FIG. [Figure 13] FIG. 13 is a diagram showing a transport state following FIG. [Figure 14] FIG. 14 is a diagram showing a transport state following FIG. [Figure 15] FIG. 15 is a diagram showing a transport state following FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 are defined as the front and rear sides, respectively, of the image forming apparatus 1, and the front and rear sides of the paper are defined as the right and left sides, respectively, of the image forming apparatus 1. Also, the top and bottom sides of FIG. 1 are defined as the top and bottom sides, respectively, of the image forming apparatus 1.

[0028] [Overall configuration of image forming device] 1 is a central cross-sectional view of an image forming apparatus equipped with a discharge unit according to one embodiment. The image forming apparatus 1 is a color laser printer that uses electrophotography to form an image on a sheet S, such as paper or an OHP sheet, by superimposing developer images of multiple colors. However, the image forming apparatus 1 can also be configured as a monochrome laser printer that forms an image on a sheet using a single-color developer image. The image forming apparatus 1 can also be configured as an inkjet printer.

[0029] The image forming apparatus 1 includes an apparatus main body 2, a feeding section 3 that supplies sheets S, an image forming section 5 that forms an image on the conveyed sheets S, and a conveying section 7 that conveys the sheets S conveyed from the image forming section 5. The apparatus main body 2 is a box formed in a substantially rectangular parallelepiped shape, and houses the feeding section 3, the image forming section 5, and the conveying section 7. An ejection tray 23a that is recessed and slopes downward from the front to the rear is formed on an upper surface 23 of the apparatus main body 2. The image forming section 5 is included in the apparatus main body 2.

[0030] The feeding section 3 includes a sheet cassette 31, a first feeding roller 32, a pair of first conveying rollers 34, and a pair of registration rollers 35. A feeding path P0 for feeding the sheet S from the sheet cassette 31 to the image forming section 5 is formed within the apparatus main body 2.

[0031] The sheet cassette 31 supports a plurality of sheets S in a stacked state. The sheet cassette 31 is an example of a sheet tray that supports sheets to be fed to the image forming unit 5. The sheets S supported by the sheet cassette 31 are sent out one by one to a feeding path P0 by a first feeding roller 32. The sheets S sent out to the feeding path P0 are conveyed towards the image forming unit 5 by a first conveying roller 34 and a registration roller 35.

[0032] The device body 2 also has an opening 2A that opens to the front, and a front cover 29 that can open and close the opening 2A. The opening 2A is open when the front cover 29 is open, and is closed when the front cover 29 is closed.

[0033] The feeding unit 3 includes a second feeding roller 38. When the front cover 29 is open, the sheet S placed on the front cover 29 is sent to a feeding path P0 by the second feeding roller 38. The sheet S sent to the feeding path P0 is transported toward the image forming unit 5 by registration rollers 35. When the front cover 29 is open, it is an example of a sheet tray that supports the sheet to be fed to the image forming unit 5.

[0034] The image forming unit 5 includes four drum units 51 arranged side by side in the front-to-rear direction. Each drum unit 51 corresponds to one of the colors: black, yellow, magenta, and cyan. Each drum unit 51 includes a photosensitive drum 51a and a developing roller 51b.

[0035] The image forming section 5 also includes a scanner unit 52 and a fixing unit 6. The scanner unit 52 is provided in the upper part of the apparatus main body 2, and a laser beam based on image data is irradiated onto the surface of the photosensitive drum 51a corresponding to each color by high-speed scanning through a polygon mirror, a lens, a reflecting mirror, etc. The fixing unit 6 is disposed further downstream than the photosensitive drum 51a located on the most downstream side in the conveying direction of the sheet S.

[0036] A transfer belt 40 is disposed below the drum unit 51 in the image forming section 5. The transfer belt 40 is stretched between a drive roller 41a and a driven roller 41b disposed behind the drive roller 41a. Transfer rollers 42 are disposed at positions facing each photosensitive drum 51a across the transfer belt 40.

[0037] In the image forming unit 5, the photosensitive drums 51a, which are uniformly charged by a charger (not shown), are selectively exposed to light by the scanner unit 52. This exposure selectively removes charge from the surfaces of the photosensitive drums 51a, and an electrostatic latent image is formed on the surfaces of the photosensitive drums 51a.

[0038] A developing bias is applied to the developing roller 51b, and when the electrostatic latent image formed on the photosensitive drum 51a faces the developing roller 51b, the potential difference between the electrostatic latent image and the developing roller 51b causes toner to be supplied from the developing roller 51b to the electrostatic latent image, thereby forming a toner image on the surface of the photosensitive drum 51a.

[0039] When the sheet S is conveyed toward the image forming unit 5 and is conveyed onto the transfer belt 40, it is conveyed by the transfer belt 40 and passes sequentially between the transfer belt 40 and each photosensitive drum 51a. Then, when the toner image on the surface of the photosensitive drum 51a faces the sheet S, it is transferred onto the sheet S by a transfer bias applied to the transfer roller 42.

[0040] The sheet S onto which the toner image has been transferred is transported to a fixing unit 6. The fixing unit 6 includes a heating roller 61 that heats the sheet S, and a pressure roller 62 that is disposed opposite the heating roller 61. The sheet S transported to the fixing unit 6 passes between the heating roller 61 and the pressure roller 62, which are in pressure contact with each other, thereby thermally fixing the toner image thereon.

[0041] The sheet S on which the toner image has been thermally fixed is transported downstream of the image forming unit 5 by the transport unit 7. The transport unit 7 has a transport path P1, a discharge path P2, and a re-transport path P3. The transport path P1 is a path along which the sheet S transported from the image forming unit 5 is transported. The discharge path P2 branches off from the transport path P1 and is a path along which the sheet S is transported to the discharge tray 23a. The re-transport path P3 has a first path P31 that branches off from the transport path P1 and along which the sheet S is temporarily transported, and a second path P32 that branches off from the discharge path P2 and the first path P31 and along which the sheet S is transported to the image forming unit 5.

[0042] A pair of post-fixing rollers 71 for conveying the sheet are provided downstream of the fixing unit 6 in the sheet conveying direction on the conveying path P1. A pair of discharge rollers 73 for conveying the sheet S are provided at the downstream end of the discharge path P2 in the sheet conveying direction, and a pair of intermediate discharge rollers 72 for conveying the sheet S are provided upstream of the discharge rollers 73 in the sheet conveying direction on the discharge path P2.

[0043] In the re-conveyance path P3, a pair of reversing rollers 74 that convey the sheet S is provided on the first path P31, and a pair of intermediate reversing rollers 75 that convey the sheet S is provided at an end of the second path P32 on the first path P31 side. A pair of first re-conveyance rollers 76a and a pair of second re-conveyance rollers 76b that convey the sheet S are provided downstream of the intermediate re-conveyance rollers 75 on the second path P32 in the sheet conveyance direction. The first re-conveyance roller 76a, which is an example of a conveyance roller, is arranged upstream of the second re-conveyance roller 76b, which is an example of a re-conveyance roller, in the sheet conveyance direction, and is driven at the same speed as the second re-conveyance roller 76b. By providing the first re-conveyance roller 76a, even short sheets can be conveyed.

[0044] A flapper 79 is provided at a branch point Ps between the conveying path P1 and the discharge path P2 and first path P31. The flapper 79 is configured to be switchable between a first position where the flapper 79 guides the sheet S conveyed along the conveying path P1 to the discharge path P2, and a second position where the flapper 79 guides the sheet S conveyed along the conveying path P1 to the first path P31. A solenoid 78 is provided in the device main body 2. The solenoid 78 is configured to be able to switch the flapper 79 between the first position and the second position.

[0045] The apparatus main body 2 has a first motor 81, a second motor 82, and a third motor 83, which are examples of drive motors. The first motor 81 drives the first feed roller 32, the post-fixing roller 71, the first re-conveyance roller 76a, and the second re-conveyance roller 76b.

[0046] A first electromagnetic clutch 84 is interposed between the first motor 81 and the first feed roller 32, and the first electromagnetic clutch 84 enables switching between transmission and interruption of the driving force from the first motor 81 to the first feed roller 32. A second electromagnetic clutch 85 is interposed between the first motor 81 and the first re-conveyor roller 76a and the second re-conveyor roller 76b, and the second electromagnetic clutch 85 enables switching of the transmission mechanism that transmits the driving force of the first motor 81 to the first re-conveyor roller 76a and the second re-conveyor roller 76b.

[0047] The second motor 82 drives the discharge rollers 73 and the intermediate discharge rollers 72. The discharge rollers 73 and the intermediate discharge rollers 72 are configured so that their rotation direction can be switched between a forward rotation direction and a reverse rotation direction by the second motor 82. The discharge rollers 73 and the intermediate discharge rollers 72 transport the sheet S toward the discharge tray 23a when rotating in the forward rotation direction, and can transport the sheet S toward the second path P32 when rotating in the reverse rotation direction. This allows the transport direction in the discharge path P2 to be reversed. When the sheet S is reversed in the discharge path P2, the leading edge of the sheet S temporarily protrudes above the discharge tray 23a.

[0048] The third motor 83 drives the reversing roller 74 and the intermediate reversing roller 75. The reversing roller 74 and the intermediate reversing roller 75 are configured so that their rotation directions can be switched between a forward rotation direction and a reverse rotation direction by the third motor 83. The reversing roller 74 is configured to convey the sheet S in a direction away from the conveying path P1 when rotating in the forward rotation direction, and to convey the sheet S toward the second path P32 when rotating in the reverse rotation direction.

[0049] This allows the conveying direction on the first path P31 to be reversed. The apparatus body 2 has an upper surface 23 with an upper surface opening 23b through which the sheet S conveyed on the first path P31 can pass. When the sheet S is reversed on the first path P31, the leading edge of the sheet S temporarily protrudes above the upper surface 23 through the upper surface opening 23b. The intermediate reversing rollers 75 are configured to convey the sheet S on the second path P32 toward the image forming unit 5 when rotating in the reverse rotation direction.

[0050] A first sensor 91 for detecting the sheet S is provided between the first re-conveyance roller 76a and the second re-conveyance roller 76b on the second path P32 of the re-conveyance path P3. That is, the first sensor 91 is located upstream of the second re-conveyance roller 76b in the sheet conveying direction. By arranging the first sensor 91 immediately before the second re-conveyance roller 76b, the position of the sheet S on the second path P32 can be detected with high accuracy.

[0051] A second sensor 92 is provided at the upstream end of the feeding path P0 in the sheet conveying direction, for detecting a sheet S fed from the sheet cassette 31 to the feeding path P0. A third sensor 93 is provided on the feeding path P0 between the registration roller 35 and the image forming unit 5 for detecting the sheet S. A fourth sensor 94 is provided on the second path P32 between the intermediate reversing roller 75 and the first re-conveying roller 76a for detecting the sheet S. A fifth sensor 95 is provided on the conveying path P1 between the fixing unit 6 and the post-fixing roller 71 for detecting the sheet S. The sheet cassette 31 is provided with a sixth sensor 96 for detecting the presence or absence of a sheet S supported by the sheet cassette 31.

[0052] A discharge unit 100 having multiple discharge trays (not shown) is removably attached to the top surface 23 of the apparatus main body 2. The discharge unit 100 has a discharge unit path P4 along which the sheet S is transported. The image forming apparatus 1 is configured so that the sheet S can be transported to the discharge unit path P4 via the discharge path P2. The discharge unit 100 is an optional device that is removably attached to the apparatus main body 2.

[0053] Furthermore, the sheet S transported along the first path P31 in a direction away from the transport path P1 can protrude above the upper surface 23 through the upper surface opening 23b in the upper surface 23 of the device body 2. The sheet S transported until it protrudes above the upper surface 23 has its transport direction reversed by switching the rotation of the reversing roller 74 from the forward rotation direction to the reverse rotation direction, and is then transported toward the second path P32.

[0054] On the top surface 23 of the device body 2, the discharge unit 100 is disposed between the discharge tray 23a and the top opening 23b. The discharge tray 23a is disposed in front of the discharge unit 100, and the top opening 23b is disposed behind the discharge unit 100. Therefore, the sheet S transported on the first path P31 protrudes upward from the top surface 23 of the device body 2 through the top opening 23b, behind the discharge tray 23a. In other words, the first path P31 is a path disposed on the opposite side of the discharge unit 100 from the discharge tray 23a.

[0055] In this way, the sheet S that protrudes from the first path P31 above the upper surface 23 protrudes upward behind the discharge unit 100. Therefore, the sheet S that temporarily protrudes from the first path P31 when the sheet S is reversed on the first path P31 is hidden by the discharge unit 100 and is difficult for a user on the discharge tray 23a side in front of the discharge unit 100 to see. This makes it possible to prevent the protruding sheet S from being removed by the user.

[0056] The length of the first path P31 from the branch point Ps to the downstream end P31d is longer than the length of the discharge path P2 from the branch point Ps to the downstream end P2d. The downstream end P31d is located at the downstream end in the sheet conveying direction when the reversing roller 74 of the first path P31 rotates in the forward rotation direction, and the downstream end P2d is located at the downstream end in the sheet conveying direction when the discharge roller 73 of the discharge path P2 rotates in the forward rotation direction.

[0057] Therefore, the protruding length of the sheet S protruding from the first path P31 when the sheet S is inverted on the first path P31 is shorter than the protruding length of the sheet S protruding from the discharge path P2 when the sheet S is inverted on the discharge path P2, so it is possible to prevent the sheet S protruding from the first path P31 from coming into contact with the sheet S discharged to the discharge tray 23a.

[0058] 2, in the image forming apparatus 1, when the discharge unit 100 is not attached, a cover 101 that closes the top opening 23b can be attached to the top surface 23 of the apparatus body 2. When the cover 101 is attached to the top surface 23 in this way, the first path P31 is formed continuously inside the cover 101, and the downstream end P31d of the first path P31 is located above the front end of the cover 101 and the downstream end P2d of the discharge path P2.

[0059] In other words, the first path P31 is a path that guides the sheet S transported from the conveying path P1 above the discharge tray 23a, and the sheet S that protrudes from the downstream end P31d of the first path P31 to the outside of the device main body 2 is positioned higher than the sheet S that is discharged from the discharge path P2 to the discharge tray 23a.

[0060] Therefore, when the cover 101 is attached to the top surface 23 of the device main body 2, the sheet S protruding from the downstream end P31d of the first path P31 to the outside of the device main body 2 will be positioned higher than the sheet S discharged from the downstream end P2d of the discharge path P2 to the discharge tray 23a, making it possible to prevent the sheet S protruding from the first path P31 from coming into contact with the sheet S already discharged to the discharge tray 23a.

[0061] Furthermore, even when the cover 101 is attached to the top surface 23 of the apparatus body 2, the length of the first path P31 from the branch point Ps to the downstream end P31d is longer than the length of the discharge path P2 from the branch point Ps to the downstream end P2d. This makes it possible to further prevent the sheet S protruding from the first path P31 from contacting the sheet S discharged onto the discharge tray 23a.

[0062] 3, the image forming apparatus 1 includes a control unit 9 configured with a CPU (Central Processing Unit). Connected to the control unit 9 are a solenoid 78, a first motor 81, a second motor 82, a third motor 83, a first electromagnetic clutch 84, and a second electromagnetic clutch 85. Also connected to the control unit 9 are a first sensor 91, a second sensor 92, a third sensor 93, a fourth sensor 94, a fifth sensor 95, and a sixth sensor 96.

[0063] The control unit 9 can switch the flapper 79 between a first position and a second position by controlling the solenoid 78. By switching the flapper 79 between the first position and the second position, the control unit 9 can set the flapper 79 to the first position when conveying the sheet S to the discharge path P2, and can set the flapper 79 to the second position when conveying the sheet S to the first path P31. In this way, by the control unit 9 switching the flapper 79 between the first position and the second position, it is possible to switch the conveyance destination of the sheet S between the discharge path P2 and the first path P31 at an appropriate timing.

[0064] The control unit 9 can switch between rotating and stopping the post-fixing roller 71 by controlling the first motor 81. The control unit 9 can switch between rotating and stopping the first feed roller 32 by controlling the first motor 81 and the first electromagnetic clutch 84. The control unit 9 can switch between rotating and stopping the first re-conveying roller 76a and the second re-conveying roller 76b by controlling the first motor 81 and the second electromagnetic clutch 85.

[0065] In this embodiment, a configuration for switching the conveying speeds of the first re-conveyance roller 76a and the second re-conveyance roller 76b includes a driving force transmission unit 86 that transmits the driving force of the first motor 81 to the first re-conveyance roller 76a and the second re-conveyance roller 76b. The driving force transmission unit 86 includes a second electromagnetic clutch 85, and has a first transmission mechanism 86a that is connected to the first motor 81 when the second electromagnetic clutch 85 is in an ON state, and a second transmission mechanism 86b that is connected to the first motor 81 when the second electromagnetic clutch 85 is in an OFF state.

[0066] The first transmission mechanism 86a is a gear train that transmits the driving force of the first motor 81, which is driven at a predetermined rotation speed, so that the conveying speed of the first re-conveyance roller 76a and the second re-conveyance roller 76b becomes a normal first speed V1. The second transmission mechanism 86b is a gear train that transmits the driving force of the first motor 81, which is driven at a predetermined rotation speed, so that the conveying speed of the first re-conveyance roller 76a and the second re-conveyance roller 76b becomes a second speed V2 that is slower than the first speed V1.

[0067] The control unit 9 can perform normal control in which the second electromagnetic clutch 85 is turned on, and deceleration control in which the second electromagnetic clutch 85 is turned off. In this way, by providing the driving force transmission unit 86, it is possible to switch the conveying speed of the first re-conveyance roller 76a and the second re-conveyance roller 76b without changing the rotation speed of the first motor 81. Furthermore, by using the second electromagnetic clutch 85, it is possible to reduce the size of the driving force transmission unit 86.

[0068] The configuration for switching the conveying speed of the first re-conveying roller 76a and the second re-conveying roller 76b is not limited to the driving force transmission unit 86, and for example, a separate drive motor may be provided to drive the first re-conveying roller 76a and the second re-conveying roller 76b at the second speed V2.

[0069] The control unit 9 can switch the rotation direction of the discharge roller 73 and the intermediate discharge roller 72 and switch between rotating and stopping them by controlling the second motor 82. The control unit 9 can switch the rotation direction of the reversing roller 74 and the intermediate reversing roller 75 and switch between rotating and stopping them by controlling the third motor 83.

[0070] In the image forming apparatus 1 configured as above, when performing double-sided printing in which images are formed on both sides of the sheet S, the control unit 9 executes transport control to print on the sheet S in a printing order that can shorten the interval between the conveyed sheets S, thereby improving the printing speed. For example, the control unit 9 is configured to be able to execute 2461 transport control in which printing is performed in the following order: the back side of the first sheet (page 2) of the first sheet → the back side of the second sheet (page 4) of the second sheet → the back side of the third sheet (page 6) of the third sheet → the front side of the first sheet (page 1) → the back side of the fourth sheet (page 8) of the fourth sheet.

[0071] When the control unit 9 performs 2461 transport control, in order to print on multiple sheets S as quickly as possible, high-speed transport control is performed to invert the sheet S using the discharge path P2 and transport it again to the image forming unit 5 when the image forming unit 5 has finished printing on the back side of the first sheet (page 2) and the back side of the second sheet (page 4), and to invert the sheet S using the first path P31 and transport it again to the image forming unit 5 when the image forming unit 5 has finished printing on the back side of the third sheet (page 6) and the back side of the fourth sheet (page 8).

[0072] In addition, if the feeding of the second sheet on which the back side (fourth page) is to be printed is delayed due to a feeding error or the like, and the first path P31 is empty when the second sheet on which the back side (fourth page) has been printed reaches in front of the flapper 79, the system is configured to execute conveyance switching control to convey the second sheet to the first path P31, invert it, and re-convey it to the image forming unit 5.

[0073] In addition, during normal control, when the preceding second sheet is positioned on the second path P32 and the following fourth sheet is supplied to the feeding path P0, deceleration control is performed so that the sheet-to-sheet distance between the leading end of the second sheet transported by the second re-conveying roller 76b and the trailing end of the fourth sheet becomes a predetermined distance (design value).

[0074] [Normal control and deceleration control] Next, the conveyance control of the sheet S during double-sided printing executed by the control unit 9, particularly the normal control and deceleration control when the conveyance control 2461 is performed, will be described. Fig. 4 shows a flowchart of the conveyance control.

[0075] In the following description, the first sheet with page 2 printed on the back side will be referred to as first sheet S1-2, and the first sheet with page 1 printed on the front side will be referred to as first sheet S1-1. The second sheet with page 4 printed on the back side will be referred to as second sheet S2-2, and the second sheet with page 3 printed on the front side will be referred to as second sheet S2-1. The third sheet with page 6 printed on the back side will be referred to as third sheet S3-2, and the third sheet with page 5 printed on the front side will be referred to as third sheet S3-1. The fourth sheet with page 8 printed on the back side will be referred to as fourth sheet S4-2.

[0076] Each sheet that is printed on its back side is switched to a sheet that is printed on its front side when the conveying direction is reversed. The second sheet S2-1 is an example of a preceding sheet, and the fourth sheet S4-2 is an example of a succeeding sheet.

[0077] Conveyance control is started when a print command is input to the control unit 9. When the conveyance control is started, the control unit 9 feeds the first sheet S1-2 supported by the sheet cassette 31 (S10). As shown in Fig. 5, the first sheet S1-2 is conveyed to the conveyance path P1 after an image is formed on it by the image forming unit 5.

[0078] 5, the control unit 9 feeds the second sheet S2-2 supported by the sheet cassette 31 (S11). In this case, the control unit 9 feeds the second sheet S2-2 at a timing when the sheet-to-sheet distance between the first sheet S1-1 and the second sheet S2-2 is such that the leading edge of the second sheet S2-2 is nipped by the heating roller 61 and the pressure roller 62 when the trailing edge of the first sheet S1-1 passes the flapper 79.

[0079] 6, the first sheet S1-2 is conveyed to the discharge path P2 through the branching portion Ps. When the first sheet S1-2 conveyed along the discharge path P2 reaches the reverse position, the control unit 9 controls the drive of the second motor 82 to switch the rotation of the discharge rollers 73 and the intermediate discharge rollers 72 from the forward rotation direction to the reverse rotation direction, thereby reversing the conveyance direction of the first sheet S1-2 (step S12). In this case, for example, the control unit 9 sets in advance the time from when the fifth sensor 95 turns off until the first sheet S1-2 reaches the reverse position, and reverses the conveyance direction of the first sheet S1-2 when the time has elapsed since the fifth sensor 95 turned off.

[0080] 7, the first sheet S1-1 whose conveying direction has been reversed is conveyed toward the second path P32, and when the leading edge of the first sheet S1-1 reaches the position of the intermediate reversing rollers 75, the first sheet S1-1 is conveyed along the second path P32 by the intermediate reversing rollers 75. As shown in FIG. 8, after the trailing edge of the first sheet S1-1 passes the flapper 79, the second sheet S2-2 is conveyed to the discharge path P2 through the branching portion Ps.

[0081] 8, the control unit 9 feeds the third sheet S3-2 supported by the sheet cassette 31 (S13). In this case, the control unit 9 feeds the third sheet S3-2 at a timing when the sheet-to-sheet distance between the second sheet S2-1 and the third sheet S3-2 is such that the leading edge of the third sheet S3-2 is nipped by the heating roller 61 and the pressure roller 62 when the trailing edge of the second sheet S2-1 passes the flapper 79.

[0082] 9, when the second sheet S2-2 conveyed along the discharge path P2 reaches the reversing position, the control unit 9 reverses the conveying direction of the second sheet S2-2 (step S14). As shown in FIG. 10, the second sheet S2-1 whose conveying direction has been reversed is conveyed toward the second path P32, and when the leading edge of the second sheet S2-1 reaches the position of the intermediate reversing rollers 75, the second sheet S2-1 is conveyed along the second path P32 by the intermediate reversing rollers 75.

[0083] When the first sheet S1-1 is in the position shown in FIG. 10, the control unit 9 determines whether the feeding of the third sheet S3-2 is delayed (step S15). If the sheet-to-sheet distance between the leading edge of the first sheet S1-1 and the trailing edge of the third sheet S3-2 is less than a predetermined distance, the control unit 9 determines that the feeding of the third sheet S3-2 is delayed (step S15: Y), terminates normal control, and executes deceleration control (step S16). The deceleration control decelerates the first sheet S1-1 and the second sheet S2-1. The deceleration of the second sheet S2-1 is performed by decelerating the second motor 82 and the third motor 83.

[0084] The control unit 9 switches from deceleration control to normal control when the inter-sheet distance between the leading edge of the first sheet S1-1 and the trailing edge of the third sheet S3-2 reaches a predetermined distance (step S17), and proceeds to step S18. This timing is calculated using the same method as in steps S22 and S24, which will be described later, and therefore will not be described here. In this way, by performing deceleration control when the feeding of the third sheet S3-2 is delayed, the inter-sheet distance between the first sheet S1-1 and the third sheet S3-2 can be kept constant without stopping the first sheet S1-1 on the second path P32.

[0085] On the other hand, if the sheet-to-sheet distance between the leading edge of the first sheet S1-1 and the trailing edge of the third sheet S3-2 is a predetermined distance in step S15, the control unit 9 determines that the feeding of the third sheet S3-2 is not delayed (step S15: N) and proceeds to step S18.

[0086] 11, when the leading edge of the second sheet S2-1 passes the first sensor 91, the control unit 9 determines whether a predetermined time has elapsed since the first sensor 91 detected the second sheet S2-1 (step S18). That is, the control unit 9 determines whether a predetermined time has elapsed since the first sensor 91 was turned on by the second sheet S2-1. The predetermined time is the time it takes for the second sheet S2-1 to reach a position where it is nipped by the second re-conveyance roller 76b, and is set in advance.

[0087] When a predetermined time has elapsed since the first sensor 91 detected the second sheet S2-1 (step S18: Y), the control unit 9 ends normal control and executes deceleration control (step S19). The deceleration control decelerates the second sheet S2-1. As shown in FIG. 12, while the second sheet S2-1 is decelerating, the control unit 9 feeds the fourth sheet S4-2 supported by the sheet cassette 31 between the first sheet S1-1 and the second sheet S2-1 (S20).

[0088] As shown in Fig. 12, the third sheet S3-2 is conveyed to the first path P31 through the branching portion Ps. As shown in Fig. 13, when the third sheet S3-2 conveyed along the first path P31 reaches the reverse position, the control unit 9 controls the driving of the third motor 83 to switch the rotation of the reversing roller 74 from the forward direction to the reverse direction, thereby reversing the conveying direction of the third sheet S3-2 (step S21). In this case, for example, the control unit 9 sets in advance the time from when the fifth sensor 95 turns off until the third sheet S3-2 reaches the reverse position, and reverses the conveying direction of the third sheet S3-2 when the time has elapsed since the fifth sensor 95 turned off.

[0089] 14, the third sheet S3-1, whose conveying direction has been reversed, is conveyed toward the second path P32, and when the leading edge of the third sheet S3-1 reaches the position of the intermediate reversing rollers 75, the third sheet S3-1 is conveyed along the second path P32 by the intermediate reversing rollers 75. As shown in FIG. 14, while the third sheet S3-1 is passing through the flapper 79, the first sheet S1-1 is conveyed to the discharge path P2 through the branching portion Ps.

[0090] The process proceeds from step S21 to step S22, where the control unit 9 determines whether the second sensor 92 has detected the trailing edge of the fourth sheet S4-2. As shown in Fig. 14, when the trailing edge of the fourth sheet S4-2 passes the second sensor 92, the second sensor 92 changes from on to off, and the control unit 9 determines that the second sensor 92 has detected the trailing edge of the fourth sheet S4-2 (step S22: Y). This means that the trailing edge of the fourth sheet S4-2 has been fed into the feeding path P0.

[0091] When the trailing edge of the fourth sheet S4-2 is fed to the feeding path P0, the control unit 9 calculates the timing Tm at which to end the deceleration control (step S23). Specifically, the calculation is performed using the following formula. Tm=Tt+{(T2-T1)-Tb}×V2 / (V1-V2) Tt: Theoretical (design) timing to end deceleration control T1: Timing when deceleration control starts T2: The timing when the second sensor 92 detects the rear end of the fourth sheet S4-2 Tb: Theoretical (design) time from the start of deceleration control until the second sensor 92 detects the rear end of the fourth seat S4-2 V1: 1st speed V2: 2nd speed

[0092] As expressed by the above formula, the longer the time (T2-T1) from the start of the deceleration control until the second sensor 92 detects the trailing edge of the fourth sheet S4-2, the later the timing Tm at which the deceleration control ends. By steps S18, S19, and S22 to S25, when the second sheet S2-1 is positioned on the second path P32 and the fourth sheet S4-2 is supplied to the feeding path P0 during normal control, deceleration control is executed so that the inter-sheet distance between the leading edge of the second sheet S2-1 conveyed by the second re-conveyance roller 76b and the trailing edge of the fourth sheet S4-2 becomes a predetermined distance.

[0093] Therefore, by slowing down the conveying speed of the first re-conveyance roller 76a and the second re-conveyance roller 76b, the inter-sheet distance can be kept constant without stopping the second sheet S2-1 on the second path P32. As a result, it is possible to prevent the second sheet S2-1 from leaving slip marks caused by the first re-conveyance roller 76a and the second re-conveyance roller 76b. Furthermore, by arranging the second sensor 92 on the feeding path P0, it is possible to detect the position of the trailing edge of the fourth sheet S4-2 with high accuracy, and therefore it is possible to calculate the timing Tm for ending the deceleration control with high accuracy.

[0094] The process proceeds from step S23 to step S24, where the control unit 9 determines whether it is time Tm to end the deceleration control. When it is time Tm to end the deceleration control (step S24: Y), the control unit 9 returns from the deceleration control to the normal control (step S25). After returning to the normal control, the second sheet S2-1 and the fourth sheet S4-2 are conveyed while maintaining a predetermined distance between them, as shown in FIG.

[0095] In the above embodiment, the path for reversing the sheet S is not particularly limited, and for example, the discharge path P2 and the first path P31 may be used alternately.

[0096] In the above embodiment, the transport control when performing double-sided printing on a sheet S supported in the sheet cassette 31 was described, but the transport control of the sheet S in this embodiment can also be applied to the transport control when performing double-sided printing on a sheet S supported in another sheet tray such as the front cover 29.

[0097] In the above embodiment, an example was described in which deceleration control was applied to 2461 transport control, but there are no particular limitations on the form of transport control when performing double-sided printing where there are preceding and succeeding sheets, and it can also be applied to 2416 transport control, for example. [Explanation of symbols]

[0098] 1. Image forming device 2. Device body 5 Image forming unit 31 Sheet cassette (sheet tray) 76a First re-transport roller (transport roller) 76b Second re-transport roller (re-transport roller) 81 First motor (drive motor) 85 Second electromagnetic clutch (electromagnetic clutch) 86 Driving force transmission section 86a First transmission mechanism 86b Second transmission mechanism 91 First Sensor 92 Second Sensor P0 Feeding route P3 Re-transportation route S seat

Claims

1. an apparatus main body having an image forming unit that forms an image on a sheet; a sheet tray for supporting sheets to be supplied to the image forming unit; a control unit, the apparatus body includes a feeding path for feeding a sheet from the sheet tray to the image forming unit, a re-conveying path for re-conveying a sheet having an image formed on one side thereof by the image forming unit to the feeding path, a re-conveying roller disposed on the re-conveying path, and a second sensor for detecting the sheet being fed from the sheet tray to the feeding path; The control unit, during double-sided printing in which the image forming unit forms images on the front and back surfaces of a preceding sheet and the following sheet fed from the sheet tray after the preceding sheet, normal control in which the conveying speed of the re-conveying roller is set to a first speed; a deceleration control for setting the conveying speed of the re-conveying roller to a second speed that is slower than the first speed, When the preceding sheet is positioned on the re-conveyance path during the normal control and the succeeding sheet is supplied to the feeding path, the deceleration control is executed so that an inter-sheet distance between a leading end of the preceding sheet conveyed by the re-conveyance roller and a trailing end of the succeeding sheet becomes a predetermined distance; The image forming apparatus is characterized in that the timing of ending the deceleration control is delayed as the time from the start of the deceleration control until the second sensor detects the trailing edge of the subsequent sheet becomes longer.

2. the apparatus main body has a first sensor that detects a sheet, the first sensor being located upstream of the re-conveyance roller in the re-conveyance path in the sheet conveyance direction; The image forming apparatus according to claim 1 , wherein the control unit executes the deceleration control after a predetermined time has elapsed since the first sensor detected the preceding sheet.

3. The timing to end the deceleration control is Tm. The theoretical timing for ending the deceleration control is Tt. The timing at which the deceleration control is started is T1. The timing when the second sensor detects the trailing edge of the succeeding sheet is T2. Tb is a theoretical time from the start of the deceleration control until the second sensor detects the trailing edge of the succeeding sheet, The first speed is V1, If the second speed is V2, 3. The image forming apparatus according to claim 1, wherein Tm=Tt+{(T2-T1)-Tb}*V2 / (V1-V2).

4. The device body includes: A drive motor; a driving force transmission unit that transmits the driving force of the drive motor to the re-conveying roller, The driving force transmission unit includes: a first transmission mechanism that drives the re-feed roller at the first speed; 4. The image forming apparatus according to claim 1, further comprising: a second transmission mechanism that drives the re-feed roller at the second speed.

5. 5. The image forming apparatus according to claim 4, wherein the driving force transmission unit has an electromagnetic clutch that switches between the first transmission mechanism and the second transmission mechanism.

6. 6. The image forming apparatus according to claim 1, wherein the device main body has a conveying roller arranged upstream of the re-conveying roller in the re-conveying path in the sheet conveying direction and driven at the same speed as the re-conveying roller.

7. the control unit forms images in the image forming unit in the order of the back side of the first sheet, the back side of the second sheet, the back side of the third sheet, the front side of the first sheet, and the back side of the fourth sheet in the double-sided printing; 7. The image forming apparatus according to claim 1, wherein the preceding sheet is the second sheet, and the succeeding sheet is the fourth sheet.

8. The image forming apparatus of claim 7, wherein the control unit executes the deceleration control so that when the first sheet is positioned on the re-conveying path and the third sheet is supplied to the feeding path during the normal control, the sheet-to-sheet distance between the leading end of the first sheet and the trailing end of the third sheet transported by the re-conveying roller becomes the predetermined distance.

Images