Image forming apparatus

Abstract

To provide an image forming apparatus that prevents paper from being pulled between a pair of fixing rollers and a pair of paper discharge rollers.SOLUTION: A pair of paper feed rollers, a pair of fixing rollers provided downstream of the pair of paper feed rollers in a conveyance path of a sheet, a pair of paper discharge rollers provided downstream of the pair of fixing rollers in the conveyance path, a control unit configured to control conveyance speeds of the pair of paper feed rollers, the pair of fixing rollers, and the pair of paper discharge rollers, a deflection detection unit configured to detect deflection of the sheet on an upstream side of the fixing roller in the conveyance path, and a clutch unit configured to interrupt transmission of a driving force to the pair of paper discharge rollers, when the paper conveyed by the paper feed roller reaches the fixing roller, the control unit reduces a conveyance speed of the fixing roller until the deflection detection unit detects deflection of the paper, and after the paper reaches the paper discharge roller, the control unit causes the clutch unit to cut off transmission of a driving force to the paper discharge roller according to a reduction amount of the conveyance speed of the fixing roller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Inside the image forming device, a transport path is formed to send paper fed from a paper feed unit to an output tray via a pair of transport rollers, a pair of registration rollers, an image forming unit having a fixing device, and a pair of paper output rollers.

[0003] BACKGROUND ART There is known an image forming apparatus that can suppress wear of the transport mechanism, can prevent undesired force from being applied to the medium, and can reliably prevent image defects caused by contact between members (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-167094 Summary of the Invention [Problem to be solved by the invention]

[0005] In an image forming apparatus, after a toner image is thermally fixed to a sheet of paper by a fixing device, the sheet is transported from the fixing device to a pair of paper discharge rollers. At this time, if the paper is pulled by a pair of fixing rollers of the fixing device and a pair of paper discharge rollers, the paper may rub against the ribs of a guide member on the transport path, causing streaks on the paper.

[0006] An object of one aspect of the present disclosure is to provide an image forming apparatus that prevents a paper sheet from being pulled against each other between a pair of fixing rollers and a pair of paper discharge rollers. [Means for solving the problem]

[0007] An image forming apparatus according to one aspect of the present disclosure comprises a pair of paper feed rollers, a pair of fixing rollers arranged downstream of the paper feed rollers on a paper transport path, a pair of paper discharge rollers arranged downstream of the fixing rollers on the transport path, a control unit that controls the transport speeds of the paper feed rollers, the fixing rollers, and the paper discharge rollers, a deflection detection unit that detects deflection of the paper upstream of the fixing rollers on the transport path, and a clutch unit that can cut off the transmission of driving force to the paper discharge rollers, wherein the transport speeds of the paper feed rollers and the paper discharge rollers are the same, and when the paper transported by the paper feed rollers reaches the fixing rollers, the control unit reduces the transport speed of the fixing rollers until the deflection detection unit detects deflection of the paper, and after the paper reaches the paper discharge rollers, causes the clutch unit to cut off the transmission of driving force to the paper discharge rollers in accordance with the amount of reduction in the transport speed of the fixing rollers. [Effects of the Invention]

[0008] According to the image forming apparatus of the present disclosure, it is possible to prevent the paper from being pulled by the fixing roller and the paper discharge roller. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an image forming apparatus according to an embodiment. [Figure 2] 1 is a partially enlarged view of a schematic cross-sectional view showing an image forming apparatus according to an embodiment; [Figure 3] 1 is a block diagram showing a hardware configuration of an image forming apparatus according to an embodiment; [Figure 4] FIG. 4 is a timing chart of a first control method for the image forming apparatus according to the embodiment. [Figure 5] FIG. 10 is a timing chart of a second control method for the image forming apparatus according to the embodiment. [Figure 6] FIG. 10 is a timing chart of a third control method for the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0011] FIG. 1 is a schematic cross-sectional view showing an image forming apparatus according to an embodiment.

[0012] The image forming apparatus 1 is, for example, a multifunction machine having a copying function, a printer function, a scanner function, a facsimile function, and the like.

[0013] The image forming apparatus 1 includes a printing device 10, an image reading device 20, a document transport device 30, and an operation panel 40 (see FIG. 3). The image forming apparatus 1 transmits image data read by the image reading device 20 to an external device, and forms an image on paper in a single color or multiple colors based on the image data of the read document or image data received from an external device.

[0014] The printing device 10 includes a paper feed unit 110, a pair of conveying rollers 120, a pair of registration rollers (pair of paper feed rollers) 130, an image forming unit 140, a fixing unit 60, a pair of paper discharge rollers 150, a discharge tray 160, a deflection detection unit 148, a guide member 149, a main motor (drive unit) 151 (see FIG. 3), a fixing motor 152 (see FIG. 3), a paper discharge roller clutch (clutch unit) 153 (see FIG. 3), and a registration roller clutch 154 (see FIG. 3). A conveyance path R1 is formed inside the printing device 10 to send paper fed from the paper feed unit 110 to the discharge tray 160 via the pair of conveying rollers 120, the pair of registration rollers 130, the image forming unit 140, the fixing unit 60, and the pair of paper discharge rollers 150.

[0015] The paper feed unit 110 is disposed below the image forming unit 140 and includes a paper feed tray 111 that stores paper sheets, a rotating plate 112 that pushes up the stored paper sheets so that they can be fed, a pickup roller 113 provided above one end of the rotating plate 112, a paper feed roller 114 that is disposed downstream of the pickup roller 113 in the paper transport direction, and a separation roller 115 that is pressed against the paper feed roller 114. There may also be multiple paper feed units 110.

[0016] In the paper feed unit 110, a pickup roller 113 picks up paper from a rotating plate 112 and guides it to a paper feed roller 114. The paper passes between the paper feed roller 114 and a separation roller 115 to separate the paper one by one, and the paper is transported to a transport path R1 by a pair of transport rollers 120.

[0017] The pair of registration rollers 130 feeds the paper in synchronization with the timing of toner image formation. The pair of registration rollers 130 temporarily stops the paper, aligns the leading edge of the paper, and then transports (feeds) the paper in synchronization with the transfer timing of the toner image in the nip area between the intermediate transfer belt 146a and the transfer roller 147 (described later). The image forming apparatus 1 has a driving force transmission means (not shown), and a main motor 151 transmits driving force to the pair of registration rollers 130 and the pair of paper discharge rollers 150 via a driving force transmission means (not shown) composed of multiple gears. The pair of registration rollers 130 is driven by the main motor 151. A registration roller clutch 154 can switch between connecting and disconnecting the driving force of the main motor 151 to the pair of registration rollers 130. When the registration roller clutch 154 is on, the driving force of the main motor 151 is transmitted to the pair of registration rollers 130, causing the pair of registration rollers 130 to rotate and transport the paper. When the registration roller clutch 154 is off, the driving force of the main motor 151 is not transmitted to the registration roller pair 130 .

[0018] The image forming section 140 includes a photosensitive drum 141, a charger 142, an exposure unit 143, a developing unit (developing device) 144, a cleaning blade 145, an intermediate transfer belt unit 146, a transfer roller 147, and the like.

[0019] The image data handled by the image forming unit 140 corresponds to a color image of four colors: black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four photoconductor drums 141, chargers 142, developing units 144, and cleaning blades 145 are provided, each of which forms four types of latent images corresponding to the respective colors, constituting four image forming stations. Four toner cartridges are provided so as to supply toner corresponding to each image forming station. The image data handled by the image forming unit 140 may correspond to a monochrome image of black (K) only. In this case, each of the photoconductor drums 141, chargers 142, developing units 144, and cleaning blades 145 constitutes one image forming station so as to form a latent image corresponding to black (K). One toner cartridge is provided so as to supply toner corresponding to black (K).

[0020] The photosensitive drum 141 is an electrostatic latent image carrier having a photosensitive layer formed on the surface of a cylindrical conductive base. The charger 142 charges the surface of the photosensitive drum 141 to a predetermined potential. The exposure unit 143 is a laser scanning unit equipped with a laser emitter, a reflecting mirror, and the like. The exposure unit 143 exposes the charged surface of the photosensitive drum 141 to light, thereby forming an electrostatic latent image on the surface of the photosensitive drum 141 according to image data. The development unit 144 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 141 using one of four colors of toner corresponding to the development unit 144. The cleaning blade 145 removes and collects toner remaining on the surface of the photosensitive drum 141 after development and image transfer.

[0021] The intermediate transfer belt unit 146 includes an intermediate transfer belt 146a, a drive roller 146b, a driven roller 146c, and four intermediate transfer rollers 146d. The intermediate transfer belt unit 146 is disposed above the photosensitive drums 141. The intermediate transfer belt 146a is provided so as to contact each photosensitive drum 141, and each intermediate transfer roller 146d is used to transfer the toner images of each color formed on the corresponding photosensitive drum 141 onto the intermediate transfer belt 146a in a sequential, overlapping manner, thereby forming a toner image on the intermediate transfer belt 146a.

[0022] The transfer roller 147 is disposed near the drive roller 146b on the conveying path R1. When a sheet of paper passes through the nip region between the transfer roller 147 and the intermediate transfer belt 146a, the toner image formed on the intermediate transfer belt 146a is transferred onto the sheet of paper.

[0023] The deflection detection unit 148 is provided near the conveyance path between the transfer roller 147 and the pair of fixing rollers 63. That is, the deflection detection unit 148 is provided downstream of the transfer roller 147 and upstream of the pair of fixing rollers 63 on the conveyance path R1, and detects the deflection of the paper on the upstream side of the pair of fixing rollers 63 on the conveyance path R1. Details of the deflection detection unit 148 will be described later.

[0024] The fixing unit 60 thermally fixes the toner image to the paper. The fixing unit 60 is detachably provided in the printing device 10 (device main body). The fixing unit 60 is arranged above the transfer roller 147 on the conveyance path R1, in other words, on the downstream side in the conveyance direction of the paper. When the paper onto which the toner image has been transferred passes through the fixing unit 60, the toner image is heated and pressurized, and the toner image is thermally fixed to the paper. The paper onto which the toner image has been fixed is conveyed to the discharge tray 160 by the paper discharge roller pair 150. The paper discharge roller pair 150 is provided downstream of the fixing roller pair 63 on the conveyance path R1.

[0025] The pair of paper discharge rollers 150 is driven by a main motor 151. A paper discharge roller clutch 153 can cut off the driving force of the main motor 151 to the pair of paper discharge rollers 150. The paper discharge roller clutch 153 switches whether or not the driving force of the main motor 151 is transmitted to the pair of paper discharge rollers 150. When the paper discharge roller clutch 153 is on, the driving force of the main motor 151 is transmitted to the pair of paper discharge rollers 150, the pair of paper discharge rollers 150 rotates, and the paper is transported to the discharge tray 160. When the paper discharge roller clutch 153 is off, the driving force of the main motor 151 is not transmitted to the pair of paper discharge rollers 150. When the paper discharge roller clutch 153 is off, the driving force of the main motor 151 is not transmitted to the pair of paper discharge rollers 150, but the pair of paper discharge rollers 150 can be rotated by an external force.

[0026] As described above, the pair of registration rollers 130 and the pair of paper discharge rollers 150 are driven by the same main motor 151. The pair of registration rollers 130 and the pair of paper discharge rollers 150 are configured to have the same paper conveying speed. That is, in the image forming apparatus 1, the speed at which the pair of registration rollers 130 feeds paper to the transfer roller 147 and the speed at which the pair of paper discharge rollers 150 discharges paper from the discharge tray 160 are the same.

[0027] The fixing unit 60 includes a pair of fixing rollers 63, each consisting of a heating roller 61 that heats the paper and a pressure roller 62 that forms a nip with the heating roller 61 and presses the paper, a heater lamp 66 that applies heat to the heating roller, and a temperature sensor 67. The heating roller 61 may be an endless heating belt. The heater lamp 66 may heat the heating roller 61 from inside or outside the heating roller 61, and the heat source may be a heater lamp, a ceramic heater, an electric heating wire, or electromagnetic induction heating. In the fixing unit 60, the paper is transported to the nip area formed by the heating roller 61 and the pressure roller 62. The temperature sensor 67 may be a contact or non-contact type, such as a thermistor or a thermopile. The heating roller 61 is heated by the heater lamp 66 to a predetermined fixing temperature (e.g., 170°C). The pressure roller 62 is arranged to press against the heating roller 61. As the paper passes through the nip area between the pressure roller 62 and the heating roller 61, the toner image transferred to the paper is melted, mixed, and pressed against the paper, thereby thermally fixing the toner image to the paper. The fixing roller pair 63 is provided downstream of the registration roller pair 130 on the conveying path R1. The fixing motor 152 (see FIG. 3) transmits a driving force to the heating roller 61. The heating roller 61 is driven by the fixing motor 152 (see FIG. 3). At this time, the pressure roller 62 is driven by the heating roller 61. The fixing motor 152 may be configured to transmit a driving force to the pressure roller 62. At this time, the heating roller 61 is driven by the pressure roller 62.

[0028] A guide member 149 that guides the paper to the paper discharge roller pair 150 is provided between the fixing roller pair 63 and the paper discharge roller pair 150. The guide member 149 is curved to form a curved transport path, and is provided above the fixing unit 60 and below the transport path indicated by the two-dot chain line. The surface of the guide member 149 that faces the paper has multiple mountain-side ribs that are provided along the paper transport direction.

[0029] Furthermore, when an image is to be formed on the back side of the paper in addition to the front side, the paper is conveyed in the opposite direction from the discharge roller pair 150 to the reversal path R2. In the reversal path R2, the paper is guided again to the registration roller pair 130 via the reversal roller pair 170. After that, the paper, on whose back side an image has been formed in the same manner as on the front side, is conveyed to the discharge tray 160.

[0030] The image reading device 20 reads an image formed on a sheet of paper and generates image data. A transparent plate-shaped contact glass 21 for feeding and reading is provided on the left side of the top surface of the image reading device 20. A transparent plate-shaped contact glass 22 for placing and reading is provided on the top surface of the image reading device 20 to the right of the contact glass 21 for feeding and reading. A document transport device 30 is attached above the image reading device 20 via a hinge or the like so that it can be opened and closed freely. When the document transport device 30 is opened via the hinge or the like, the top surface of the image reading device 20 is exposed, and a document can be manually placed on the contact glass 22 for placing and reading. An operation panel 40 (see FIG. 3 ) is provided in front of the top surface of the image reading device 20. The operation panel 40 displays various information and accepts inputs from the user. The operation panel 40 is an example of a display operation unit and includes a display panel, a touch panel, hard keys, etc.

[0031] The image reading device 20 further includes a light source, multiple mirrors, an imaging lens, a line sensor, etc. The image reading device 20 exposes the paper surface to light from the light source, and guides the light reflected from the paper surface to the imaging lens using multiple mirrors. The imaging lens then focuses the reflected light onto the light-receiving elements of the line sensor. The line sensor detects the luminance and chromaticity of the reflected light that has focused on the light-receiving elements, and generates image data based on the image on the paper surface. A CCD, CIS, etc. is used as the line sensor.

[0032] The document transport device 30 includes a paper feed tray 31, a paper feed unit 32, a pair of transport rollers 33, a pair of paper discharge rollers 34, and a discharge tray 35. Inside the document transport device 30, a transport path R3 is formed for sending the paper fed from the paper feed unit 32 to the discharge tray 35 via the pair of transport rollers 33, the image reading device 20, and the pair of paper discharge rollers 34.

[0033] The paper feed tray 31 is a tray on which multiple sheets of paper can be placed in a stack. The paper feed tray 31 can be raised and lowered by an elevator mechanism (not shown). The discharge tray 35 is a tray on which multiple sheets of paper can be placed in a stack. The paper feed unit 32 transports the paper on the paper feed tray 31 toward the transport path R3. The transport roller pair 33 transports the paper on the transport path R3 toward the image reading device 20. The discharge roller pair 34 transports the paper on the transport path R3 toward the discharge tray 35.

[0034] Here, the detection of the sag of the paper by the sag detection unit 148 will be described.

[0035] FIG. 2 is a partially enlarged schematic cross-sectional view showing the image forming apparatus according to the embodiment.

[0036] Deflection detection unit 148 detects deflection of sheet P between transfer roller 147 and pair of fixing rollers 63. For example, deflection detection unit 148 has a lever, and when sheet P deflects as shown in FIG. 2, sheet P comes into contact with the lever and the lever is pressed down. This turns on deflection detection unit 148 and detects deflection of sheet P. Deflection detection unit 148 may also be a position sensor, a displacement sensor, a proximity sensor, or the like, and may detect deflection of sheet P by measuring the distance between sheet P and deflection detection unit 148.

[0037] The hardware configuration of the image forming apparatus 1 will be described with reference to Fig. 3. Fig. 3 is a block diagram showing the hardware configuration of the image forming apparatus 1.

[0038] The image forming apparatus 1 includes a control unit 200, a memory unit 210, a communication unit 220, a printing device 10, an image reading device 20, a document transport device 30, an operation panel 40, etc. The printing device 10 includes a main motor 151, a fixing motor 152, a paper discharge roller clutch 153, a registration roller clutch 154, etc.

[0039] The control unit 200 controls the image forming apparatus 1. The control unit 200 realizes various functions by reading and executing various programs stored in the storage unit 210. The control unit 200 is configured by, for example, one or more CPUs (Central Processing Units) or the like.

[0040] The storage unit 210 stores various programs and various data necessary for the operation of the image forming apparatus 1. The storage unit 210 is configured by, for example, one or more storage devices such as a solid state drive (SSD) or a hard disk drive (HDD), which is a semiconductor memory.

[0041] The communication unit 220 controls wireless communication of various data with an external terminal such as a computer, for example. Note that the communication unit 220 is not limited to controlling wireless communication, and may also control wired communication.

[0042] The control unit 200 is connected to a storage unit 210, a communication unit 220, the printing device 10, the image reading device 20, the document transport device 30, the operation panel 40, and the like.

[0043] The control unit 200 controls the printing device 10 to form an image on a document in single color or multiple colors based on image data read by the image reading device 20 or image data received via the communication unit 220. During image formation, the control unit 200 also controls the main motor 151, the fixing motor 152, the paper discharge roller clutch 153, and the registration roller clutch 154 to transport paper. The control unit 200 also controls the image reading device 20 and the document transport device 30 to read the image data of the document.

[0044] 4 is a timing chart of a first control method for the image forming apparatus according to the embodiment, in which control is performed when plain paper is used as the paper for image formation.

[0045] 4, the top row shows the positions of the registration roller pair 130, transfer roller 147, deflection detection unit 148, fixing roller pair 63, and paper discharge roller 150 arranged in a straight line on conveyance path R1. Below that, from top to bottom, the speed of fixing motor 152, on / off status of registration roller clutch 154, on / off status of deflection detection unit 148, and on / off status of paper discharge roller clutch 153 are listed.

[0046] Initially, the fixing motor 152 rotates at a predetermined speed, the registration roller clutch 154 is off, the deflection detection unit 148 is off, and the paper discharge roller clutch 153 is off. The predetermined speed of the fixing motor 152 is set so that the speed at which the fixing roller pair 63 conveys the paper is slower than the speed at which the registration roller pair 130 conveys the paper, in order to deflect the paper.

[0047] At time t1, the control unit 200 turns on the registration roller clutch 154. This transmits the driving force of the main motor 151 to the registration roller pair 130, causing the registration roller pair 130 to rotate and feed the paper. At this time, if the speed at which the registration roller pair 130 feeds the paper is equal to or greater than the conveying speed of the fixing roller pair 63, it is possible to prevent the paper from being pulled the moment the leading edge of the paper reaches the fixing roller pair 63.

[0048] At time t2, when the leading edge of the paper reaches the pair of fixing rollers 63, the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the pair of fixing rollers 63 by a predetermined value. As a result, the conveying speed of the pair of registration rollers 130 becomes faster than the conveying speed of the pair of fixing rollers 63. Note that the conveying speed of the paper by the pair of registration rollers 130 and the distance between the pair of registration rollers 130 and the pair of fixing rollers 63 are known in advance. Therefore, the control unit 200 can calculate the time t2 at which the paper will reach the pair of fixing rollers 63. Note that the reduction value (predetermined value) of the conveying speed of the pair of fixing rollers 63 is set in advance.

[0049] At time t3, the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the fixing roller pair 63 by a predetermined value. Note that time t3 is a predetermined time after time t2. This increases the difference between the paper conveying speed of the registration roller pair 130 and the paper conveying speed of the fixing roller pair 63. After the leading edge of the paper reaches the fixing roller pair 63, the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value every predetermined time until a slack in the paper is detected. In this way, the speed of the fixing motor 152 (that is, the conveying speed of the fixing roller pair 63) is reduced in stages until a slack in the paper is detected.

[0050] At time t4, a predetermined time has elapsed since time t3, and the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the fixing roller pair 63 by a predetermined value.

[0051] At time t5, the leading edge of the paper reaches the pair of paper discharge rollers 150, and the control unit 200 turns on the paper discharge roller clutch 153. This transmits the driving force of the main motor 151 to the pair of paper discharge rollers 150, causing the pair of paper discharge rollers 150 to rotate and start conveying the paper. The pair of paper discharge rollers 150 rotates by the driving force of the main motor 151, and its speed is the same as that of the pair of registration rollers 130. That is, at this point in time, the conveying speed of the pair of registration rollers 130 is faster than that of the pair of fixing rollers 63, and therefore the conveying speed of the pair of paper discharge rollers 150 is faster than that of the pair of fixing rollers 63. Therefore, from the moment the leading edge of the paper reaches the pair of paper discharge rollers 150, a pulling action on the paper occurs between the pair of paper discharge rollers 150 and the pair of fixing rollers 63.

[0052] At time t6, a predetermined time has elapsed since time t4, and the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the fixing roller pair 63 by a predetermined value.

[0053] At time t7, the deflection detection unit 148 is turned on. That is, the deflection detection unit 148 detects the deflection of the paper between the transfer roller 147 and the pair of fixing rollers 63. When the control unit 200 detects that the deflection detection unit 148 is turned on, it stops reducing the speed of the fixing motor 152. Therefore, after time t6, the speed of the fixing motor 152, i.e., the conveyance speed of the pair of fixing rollers 63, is maintained. Therefore, the paper continues to be pulled between the pair of paper discharge rollers 150 and the pair of fixing rollers 63. As shown in FIG. 2, because the path between the pair of paper discharge rollers 150 and the pair of fixing rollers 63 is curved, when the paper is pulled, a force acts on the paper that tries to shorten the distance between the pair of paper discharge rollers 150 and the pair of fixing rollers 63. That is, the paper is pressed against the guide member 149.

[0054] At time t8, the control unit 200 turns off the discharge roller clutch 153. That is, the control unit 200 causes the discharge roller clutch 153 to cut off the transmission of driving force from the main motor to the discharge roller pair 150. When the discharge roller clutch 153 is off, the discharge roller pair 150 can rotate. However, when plain paper conveyed from the fuser roller pair 63 hits the discharge roller pair 150, the discharge roller pair 150 does not rotate and the paper is not conveyed from the discharge roller pair 150 because plain paper is weak. In this way, when the discharge roller clutch 153 is turned off, the driving force of the main motor 151 is not transmitted to the discharge roller pair 150, and the discharge of the paper from the discharge roller pair 150 stops. At this moment, the conveying speeds of the discharge roller pair 150 and the fuser roller pair 63 are reversed, and the conveying speed of the fuser roller pair 63 becomes faster. This causes a flexure in the paper between the pair of paper discharge rollers 150 and the pair of fixing rollers 63, and the paper is displaced toward the outer periphery of the curved conveyance path and separated from the guide member 149. The control unit 200 turns off the paper discharge roller clutch 153 for a predetermined time from time t8, and this predetermined time (off time) is based on the amount of decrease in the speed of the fixing motor 152 (i.e., the conveyance speed of the pair of fixing rollers 63). This predetermined time may also be based on the difference between the conveyance speed of the pair of fixing rollers 63 and the conveyance speed of the pair of paper discharge rollers 150.

[0055] At time t9, the control unit 200 turns on the discharge roller clutch 153. This transmits the driving force of the main motor 151 to the discharge roller pair 150, causing the discharge roller pair 150 to rotate and restart the conveyance of the paper by the discharge roller pair 150. The control unit 200 varies the period between time t8 and time t9, i.e., the off-time of the discharge roller clutch 153, depending on the amount of decrease in the speed of the fixing motor 152 (i.e., the conveyance speed of the fixing roller pair 63). The control unit 200 lengthens the off-time of the discharge roller clutch 153 the greater the amount of decrease in the speed of the fixing motor 152 (i.e., the conveyance speed of the fixing roller pair 63). For example, the control unit 200 varies the off-time of the discharge roller clutch 153 depending on the number of times the speed of the fixing motor 152 is decelerated. The control unit 200 lengthens the off-time of the discharge roller clutch 153 the greater the number of times the speed of the fixing motor 152 is decelerated. 4, the speed of the fixing motor 152 is reduced at times t2, t3, t4, and t6, so the number of times the speed of the fixing motor 152 is reduced is four. Also, the control unit 200 may lengthen the off-time of the paper discharge roller clutch 153 as the difference between the conveying speed of the fixing roller pair 63 and the conveying speed of the paper discharge roller pair 150 increases.

[0056] Furthermore, when the off time (first off time) of the paper discharge roller clutch 153 based on the amount of decrease in the speed of the fixing motor 152 (i.e., the conveying speed of the fixing roller pair 63) is equal to or greater than a threshold value, the first off time may be divided into fixed time intervals, and the fixed time periods of the off time of the paper discharge roller clutch 153 and the on time of the paper discharge roller clutch 153 may be repeated. That is, the control unit 200 may repeat turning the paper discharge roller clutch 153 off and on multiple times, and the total of the repeated off times of the paper discharge roller clutch 153 may become the off time (first off time) of the paper discharge roller clutch 153 based on the amount of decrease in the speed of the fixing motor 152 (i.e., the conveying speed of the fixing roller pair 63).

[0057] At time t10, the control unit 200 turns off the registration roller clutch 154. As a result, the driving force of the main motor 151 is not transmitted to the registration roller pair 130. As a result, the sheet is not transported from the registration roller pair 130.

[0058] At time t11, the paper is discharged by the paper discharge roller pair 150, so that the paper is no longer between the transfer roller 147 and the fixing roller pair, and the deflection detection unit 148 turns off.

[0059] According to the first control method of the image forming apparatus 1 according to the embodiment, it is possible to prevent the paper from being pulled against each other by causing a deflection in the paper between the pair of fixing rollers 63 and the pair of paper discharge rollers 150. This prevents the paper from rubbing against the ribs of the guide member 149 and causing streaks on the paper.

[0060] The image forming apparatus 1 may also use the following control method.

[0061] 5 is a timing chart illustrating a second control method for the image forming apparatus according to the embodiment. In the second control method, control will be described for the case where plain paper is used as the paper during image formation, similar to the first control method.

[0062] 5, the top row shows the positions of the registration roller pair 130, transfer roller 147, deflection detection unit 148, fixing roller pair 63, and paper discharge roller 150 arranged in a straight line on the conveying path R1. Below that, from top to bottom, the speed of the fixing motor 152, the on / off state of the registration roller clutch 154, the on / off state of the deflection detection unit 148, and the on / off state of the paper discharge roller clutch 153 are listed.

[0063] Initially, the fixing motor 152 rotates at a predetermined speed, the registration roller clutch 154 is off, the deflection detection unit 148 is off, and the paper discharge roller clutch 153 is off. The predetermined speed of the fixing motor 152 is set so that the speed at which the fixing roller pair 63 conveys the paper is slower than the speed at which the registration roller pair 130 conveys the paper, in order to deflect the paper.

[0064] At time t21, the control unit 200 turns on the registration roller clutch 154. This transmits the driving force of the main motor 151 to the registration roller pair 130, causing the registration roller pair 130 to rotate and feed out the paper.

[0065] At time t22, when the leading edge of the paper reaches the pair of fixing rollers 63, the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the pair of fixing rollers 63 by a predetermined value. The conveying speed of the paper by the pair of registration rollers 130 and the distance between the pair of registration rollers 130 and the pair of fixing rollers 63 are known in advance. Therefore, the control unit 200 can calculate the time t2 at which the paper will reach the pair of fixing rollers 63. The reduction value (predetermined value) of the conveying speed of the pair of fixing rollers 63 is set in advance.

[0066] At time t23, the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the fixing roller pair 63 by a predetermined value. Note that time t23 is a predetermined time after time t22. After the leading edge of the paper reaches the fixing roller pair 63, the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value at predetermined time intervals until a slack in the paper is detected. In this way, the speed of the fixing motor 152 (that is, the conveying speed of the fixing roller pair 63) is reduced in stages until a slack in the paper is detected.

[0067] At time t24, a predetermined time has elapsed since time t23, and the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the fixing roller pair 63 by a predetermined value.

[0068] At time t25, a predetermined time has elapsed since time t24, and the control unit 200 reduces the speed of the fixing motor 152 by a predetermined value. That is, the control unit 200 reduces the conveying speed of the fixing roller pair 63 by a predetermined value.

[0069] At time t26, flexure detection unit 148 is turned on. That is, flexure detection unit 148 detects flexure of the paper between transfer roller 147 and pair of fixing rollers 63. When control unit 200 detects that flexure detection unit 148 is turned on, it stops reducing the speed of fixing motor 152. Therefore, after time t26, the speed of fixing motor 152, i.e., the conveying speed of pair of fixing rollers 63, is maintained.

[0070] At time t27, the leading edge of the paper reaches the pair of paper discharge rollers 150. The distance between the pair of fixing rollers 63 and the pair of paper discharge rollers 150 is known in advance. Therefore, the control unit 200 can calculate the time t27 at which the leading edge of the paper reaches the pair of paper discharge rollers 150.

[0071] At time t28, the control unit 200 turns on the discharge roller clutch 153. This transmits the driving force of the main motor 151 to the discharge roller pair 150, causing the discharge roller pair 150 to rotate and start conveying the paper by the discharge roller pair 150. Time t28 is a predetermined time after time t27.

[0072] The control unit 200 varies the period (resistance amount) between times t27 and t28, i.e., the time during which the leading edge of the paper hits the pair of paper discharge rollers 150 and is not conveyed, in accordance with the amount of reduction in the speed of the fixing motor 152 (i.e., the conveying speed of the pair of fixing rollers 63). The control unit 200 lengthens the time during which the leading edge of the paper hits the pair of paper discharge rollers 150 and is not conveyed, the greater the amount of reduction in the speed of the fixing motor 152 (i.e., the conveying speed of the pair of fixing rollers 63). For example, the control unit 200 varies the time during which the leading edge of the paper hits the pair of paper discharge rollers 150 and is not conveyed, in accordance with the number of times the speed of the fixing motor 152 is decelerated. The control unit 200 lengthens the time during which the leading edge of the paper hits the pair of paper discharge rollers 150 and is not conveyed, in accordance with the number of times the speed of the fixing motor 152 is decelerated. For example, in FIG. 4, the speed of the fixing motor 152 is reduced at times t2, t3, t4, and t6, so the number of times the speed of the fixing motor 152 is reduced is four. At time t27, the leading edge of the paper reaches the pair of paper discharge rollers 150, but because the paper discharge roller clutch 153 is off, paper transport at the pair of paper discharge rollers 150 stops, and paper transport from the pair of paper discharge rollers 63 continues. This causes a sag in the paper between the pair of paper discharge rollers 150 and the pair of paper discharge rollers 63. In this way, by keeping the paper discharge roller clutch 153 off for a predetermined time after the leading edge of the paper reaches the pair of paper discharge rollers 150, a sag can be generated in the paper between the pair of paper discharge rollers 150 and the pair of paper discharge rollers 63. Also, by stopping the paper against the pair of paper discharge rollers 150, the leading edge of the paper can be aligned parallel to the pair of paper discharge rollers 150, thereby correcting any skew in the paper.

[0073] At time t29, the control unit 200 turns off the registration roller clutch 154. As a result, the driving force of the main motor 151 is not transmitted to the registration roller pair 130, and the sheet is not conveyed from the registration roller pair 130.

[0074] At time t30, the paper is discharged by the pair of paper discharge rollers 150, so that the paper is no longer between the transfer roller 147 and the pair of fixing rollers, and the deflection detection unit 148 turns off.

[0075] According to the second control method of the image forming apparatus 1 according to the embodiment, it is possible to prevent the paper from being pulled against each other by causing a deflection in the paper between the pair of fixing rollers 63 and the pair of paper discharge rollers 150. This prevents the paper from rubbing against the ribs of the guide member 149 and causing streaks on the paper.

[0076] In the first and second control methods described above, the paper is plain paper. However, if the paper is cardboard, which is thicker than plain paper, the following control method may be used.

[0077] FIG. 6 is a timing chart of a third control method of the image forming apparatus according to the embodiment. In the third control method, control when thick paper is used as the paper during image formation will be described. In the image forming apparatus 1, the user can set the paper type (plain paper, thick paper, etc.). When the paper type is set to thick paper, the control unit 200 executes the following third control method.

[0078] 6, the top row shows the positions of the registration roller pair 130, transfer roller 147, deflection detection unit 148, fixing roller pair 63, and paper discharge roller 150 arranged in a straight line on the conveying path R1. Below that, from top to bottom, the speed of the fixing motor 152, the on / off state of the registration roller clutch 154, the on / off state of the deflection detection unit 148, and the on / off state of the paper discharge roller clutch 153 are listed.

[0079] Initially, the fixing motor 152 rotates at a predetermined speed, the registration roller clutch 154 is off, the deflection detection unit 148 is off, and the paper discharge roller clutch 153 is off. The predetermined speed of the fixing motor 152 is set so that the speed at which the fixing roller pair 63 conveys the paper is slower than the speed at which the registration roller pair 130 conveys the paper, in order to deflect the paper.

[0080] At time t31, the control unit 200 turns on the registration roller clutch 154. This transmits the driving force of the main motor 151 to the registration roller pair 130, causing the registration roller pair 130 to rotate and feed out the paper.

[0081] At time t32, when the leading edge of the paper reaches the pair of paper discharge rollers 150, the control unit 200 turns on the paper discharge roller clutch 153. This transmits the driving force of the main motor 151 to the pair of paper discharge rollers 150, causing the pair of paper discharge rollers 150 to rotate, and the pair of paper discharge rollers 150 begins to transport the paper.

[0082] At time t33, the deflection detection unit 148 is turned on. That is, the deflection detection unit 148 detects the deflection of the paper between the transfer roller 147 and the pair of fixing rollers 63.

[0083] At time t34, the control unit 200 turns off the discharge roller clutch 153. That is, the control unit 200 controls the discharge roller clutch 153 to cut off the transmission of the driving force from the main motor to the discharge roller pair 150. As a result, the driving force of the main motor 151 is not transmitted to the discharge roller pair 150. When the discharge roller clutch 153 is off, the discharge roller pair 150 can be rotated by an external force (here, the force of the fuser roller pair 63 to feed the paper). When the thick paper conveyed from the fuser roller pair 63 hits the discharge roller pair 150, the stiffness of the thick paper causes the discharge roller pair 150 to rotate, and the paper passes through the discharge roller pair 150 and is conveyed from the discharge roller pair 150. In this way, in the case of stiff paper such as thick paper, the paper can be conveyed by the stiffness of the paper without using the driving force of the main motor 151.

[0084] At time t35, the control unit 200 turns off the registration roller clutch 154. As a result, the driving force of the main motor 151 is not transmitted to the registration roller pair 130, the registration roller pair 130 does not rotate, and the sheet is not conveyed from the registration roller pair 130.

[0085] At time t36, the control unit 200 turns on the discharge roller clutch 153. This transmits the driving force of the main motor 151 to the pair of discharge rollers 150, causing the pair of discharge rollers 150 to rotate, and the pair of discharge rollers 150 starts conveying the paper again. The period between time t34 and time t36, i.e., the off time (clutch-off time) of the discharge roller clutch 153, may be set in advance, or the control unit 200 may vary the off time of the discharge roller clutch 153 depending on the stiffness (e.g., basis weight) of the paper. For example, in the image forming apparatus 1, the user can set cardboard as the paper type and further select a paper from multiple cardboards with different stiffness (e.g., basis weight). For example, the control unit 200 lengthens the clutch-off time when the paper is set to be stiff cardboard (high basis weight), and shortens the clutch-off time when the paper is set to be soft cardboard (low basis weight).

[0086] At time t37, the paper is discharged by the paper discharge roller pair 150, so that the paper is no longer between the transfer roller 147 and the fixing roller pair, and the deflection detection unit 148 turns off.

[0087] According to the third control method of image forming apparatus 1 according to the embodiment, the paper is transported using its own stiffness, which prevents the paper from tugging against the ribs of guide member 149. This prevents the paper from rubbing against the ribs of guide member 149 and causing streaks on the paper.

[0088] The present invention is not limited to the above-described embodiments and can be modified, and the above configurations can be replaced with substantially the same configurations, configurations that achieve the same effects, or configurations that can achieve the same purpose. [Explanation of symbols]

[0089] 1. Image forming device 10 Printing device 60 Fixing unit 63 Fixing roller pair 130 registration roller pair 150 Paper ejection roller pair 153 Paper discharge roller clutch 200 control section

Claims

1. a pair of paper feed rollers; a pair of fixing rollers provided downstream of the pair of paper feed rollers in a paper transport path; a pair of paper discharge rollers provided downstream of the pair of fixing rollers on the conveying path; a control unit for controlling the conveying speeds of the paper feed roller pair, the fixing roller pair, and the paper discharge roller pair; a deflection detection unit that detects deflection of the paper on the upstream side of the fixing roller on the conveying path; a clutch unit that can interrupt the transmission of a driving force to the paper discharge roller, The conveying speed of the paper feed roller and the conveying speed of the paper discharge roller are the same, The control unit When the paper conveyed by the paper feed roller reaches the fixing roller, the conveying speed of the fixing roller is reduced until the deflection detection unit detects the deflection of the paper; an image forming apparatus, characterized in that after the paper reaches the paper discharge roller, the clutch section cuts off transmission of driving force to the paper discharge roller in accordance with the amount of reduction in the conveying speed of the fixing roller;

2. 2. The image forming apparatus according to claim 1, wherein the control unit varies the time for which the clutch unit cuts off transmission of the driving force to the paper discharge roller in accordance with the amount of reduction in the conveying speed of the fixing roller.

3. the control unit gradually reduces the conveying speed of the fixing roller, 2. The image forming apparatus according to claim 1, wherein the time for which the clutch section cuts off the transmission of the driving force to the paper discharge roller is based on the number of times the conveying speed of the fixing roller is reduced in stages.

4. 2. The image forming apparatus according to claim 1, wherein the control unit varies the time for which the clutch unit cuts off the transmission of driving force to the pair of discharge rollers depending on the difference between the conveying speed of the pair of fixing rollers and the conveying speed of the pair of discharge rollers.

5. 2. The image forming apparatus according to claim 1, wherein the pair of paper discharge rollers and the pair of paper feed rollers receive a driving force from the same driving unit.

6. a driving force transmitting means for transmitting the driving force of the driving unit to the pair of paper discharge rollers and the pair of paper discharge rollers; 6. The image forming apparatus according to claim 5, wherein the driving force transmission means comprises a plurality of gears.

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