JP6282566B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and can be applied to, for example, an electrophotographic image forming apparatus (for example, a copying machine, a printer, a facsimile machine, etc.).

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile, after a photosensitive member as an image carrier is charged, an image is exposed by an exposure device and optical writing is performed in accordance with an image signal. An electrostatic latent image is formed. In the conventional image forming apparatus, the electrostatic latent image is converted into a toner image by toner adhesion of the developing device, and the toner image is transferred to a recording medium such as transfer paper or film. In the conventional image forming apparatus, the transferred transfer material is conveyed to a fixing device, and the toner image is fixed on the transfer material by the fixing device to obtain an image.

  Such a conventional image forming apparatus is provided with a fan that conveys the medium while adsorbing the medium on the conveyance path for the purpose of stably conveying the medium on the conveyance path constituted by rollers, belts, and the like. (For example, refer to Patent Document 1).

Japanese Patent Application No. 2012-135717

  In a conventional image forming apparatus to be transported, auxiliary control for the control performed to mitigate tension and slack of the medium (transfer material) generated in the transport path between the fixing device and the transfer unit by changing the speed of the fixing device. Playing a role. However, conventional image forming apparatuses cannot cope with various types of media (transfer materials) that have been diversified in recent years. For example, in the conventional image forming apparatus, there is a problem that a shock line of a thick paper or a thin paper sticking due to a tension or slack of a medium (transfer material), or a rubbing of a printing surface of the transfer material occurs.

  In view of the above problems, there is a demand for an image forming apparatus that can stably convey a medium even if the type and state of the medium to be conveyed are changed.

The image forming apparatus of the present invention includes (1) an image forming unit that forms an image, (2) a transfer unit that transfers an image formed by the image forming unit to a medium, and (3) a medium conveyance of the transfer unit. A fixing unit that is arranged on the downstream side in the direction and fixes the image transferred to the medium; (4) a first suction unit disposed between the transfer unit and the fixing unit; and (5) the first A second suction unit disposed between the suction unit and the fixing unit, and (6) a control unit that controls suction in the first suction unit and suction in the second suction unit; 7) a first detection unit that detects a type of a medium to be conveyed ; (8) a second detection unit that is disposed between the transfer unit and the fixing unit and detects a slack of the conveyed medium; (9) a third detection unit that detects the conveyed medium, (10) the control unit is (10-1) the medium is thin paper When the slack is detected by the second detection unit at a certain time, when the suction force of the first suction unit and the second suction unit is thick paper, the second detection unit (10-2) Based on the detection result of the third detection unit, the control is performed so that the suction force of the first suction unit and the second suction unit when the slack is detected. The switching between the suction of the first suction part and the second suction part is controlled .

  According to the present invention, it is possible to provide an image forming apparatus capable of stably transporting a medium even if the type and state of the medium to be transported are changed.

FIG. 6 is an explanatory diagram (part 1) illustrating the behavior of the printing paper when the printing paper is conveyed downstream from the nip portion in the image forming apparatus according to the first embodiment. 1 is a schematic sectional view of an image forming apparatus according to a first embodiment. FIG. 6 is an explanatory diagram (part 2) illustrating the behavior of the printing paper when the printing paper is conveyed downstream from the nip portion in the image forming apparatus according to the first embodiment. FIG. 10 is an explanatory diagram (part 3) illustrating the behavior of the printing paper when the printing paper is conveyed downstream from the nip portion in the image forming apparatus according to the first embodiment. FIG. 10 is an explanatory diagram (part 4) illustrating the behavior of the printing paper when the printing paper is conveyed downstream from the nip portion in the image forming apparatus according to the first embodiment. FIG. 6 is an explanatory diagram (part 1) illustrating the behavior of a shutter plate when transporting printing paper downstream from the nip portion in the image forming apparatus according to the first embodiment. FIG. 8 is an explanatory diagram (part 2) illustrating the behavior of the shutter plate when the printing paper is conveyed downstream from the nip portion in the image forming apparatus according to the first embodiment. FIG. 2 is a block diagram illustrating a configuration (functional configuration) of a control system of the image forming apparatus according to the first embodiment. It is a schematic perspective view shown in the state where a transfer guide part, a shutter plate, and its operation part according to the first embodiment are removed. It is explanatory drawing (the 1) shown about the operation state of the shutter board which concerns on 1st Embodiment. It is explanatory drawing (the 2) shown about the operation state of the shutter board which concerns on 1st Embodiment. It is explanatory drawing (the 3) shown about the operation state of the shutter board which concerns on 1st Embodiment. FIG. 4 is an explanatory diagram showing parameters used in the image forming apparatus according to the first embodiment. 5 is a flowchart (part 1) illustrating an operation of the image forming apparatus according to the first embodiment. 6 is a flowchart (part 2) illustrating the operation of the image forming apparatus according to the first embodiment. 6 is a flowchart illustrating an operation of an image forming apparatus according to a second embodiment. It is explanatory drawing shown about the operation state of the shutter plate concerning the image forming apparatus which concerns on 3rd Embodiment.

(A) First Embodiment Hereinafter, a first embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

(A-1) Configuration of the First Embodiment FIG. 2 is a schematic side view of the printer of the first embodiment.

  The image forming apparatus 1 includes a paper tray 100 on which printing paper P is stacked, a paper stacking plate 102, a lift-up lever 103, a motor 104, a paper feeding unit 200, a rising detection unit 201, a pickup roller 202, a feed roller 203, A retard roller 204, a paper thickness sensor 320 as a first detection unit, an image forming unit 400, a fixing unit 500, a multi-purpose tray (MPT) 600, an intermediate transfer belt unit 700, a double-sided conveyance unit 900 as a medium processing unit, And a sagging detection unit 1300.

  The paper tray 100 has the printing paper P stacked therein and is detachably mounted on the image forming apparatus 1. Inside the paper tray 100, a paper placing plate 102 supported rotatably by a support shaft (not shown) is provided, and the printing paper P is stacked on the paper placing plate 102. A lift-up lever 103 is rotatably disposed on a support shaft (not shown) on the feeding side of the paper tray 100, and the support shaft is engaged with the motor 104 so as to be able to contact and separate.

  When the paper tray 100 is inserted into the image forming apparatus 1, the lift-up lever 103 and the motor 104 are engaged, and a control unit (not shown) drives the motor 104. As the lift-up lever 103 rotates, the tip of the lift-up lever 103 lifts the bottom of the paper stacking plate 102, and the printing paper P stacked on the paper stacking plate 102 rises.

  When the printing paper P rises to a certain height, it comes into contact with the pickup roller 202 and is detected by the rise detection unit 201, and the control unit stops the motor 104 based on the information detected by the rise detection unit 201. The pickup roller 202 forms a sheet feeding portion 200 together with a feed roller 203 and a retard roller 204 arranged in a pair in contact with each other. The pickup roller 202 and the feed roller 203 are rotationally driven in the direction of an arrow by a motor (not shown), and a one-way clutch mechanism (not shown) is incorporated therein, so that even when the rotational driving is stopped, the pickup roller 202 and the feed roller 203 can idle in the direction of the arrow. ing. The retard roller 204 generates torque in the direction of the arrow by a torque generating means (not shown). Since the pickup roller 202 and the feed roller 203 incorporate a one-way clutch mechanism (not shown) inside, the pickup roller 202 and the feed roller 203 can idle in the direction of the arrow even when the rotation drive is stopped.

  Accordingly, the pick-up roller 202 pulls out the printing paper P abutting from the paper tray 100, and the feed roller 203 and the retard roller 204 can be used one by one even when a plurality of printing papers P are pulled out simultaneously. The printing paper P is sequentially fed out to the conveyance path.

  In the conveyance direction of the printing paper P, on the downstream side of the paper feeding unit 200, a paper sensor 301, a conveyance roller pair 302 that restricts the skew feeding of the printing paper P, and a sheet for detecting the driving timing of the next conveyance roller pair 304 in order. A sensor 303, a pair of conveyance rollers 304 and 305 for feeding the printing paper P to the image forming unit 400, and a writing sensor 306 for taking a writing timing in the image forming unit 400 are provided. Power is transmitted to these conveyance roller pairs 302, 304, and 305 from a conveyance drive motor (not shown) via a drive transmission unit (not shown).

  On the right side when the image forming apparatus 1 is viewed from the direction of FIG. 2, a multi-purpose tray 600 that feeds the printing paper P stacked on the paper stacking plate 604 is disposed. The multi-purpose tray 600 includes a paper stacking plate 604 on which the printing paper P is stacked, a pick roller 602 that feeds out the printing paper P in contact with the printing paper P, a paper feeding roller 601 that feeds the fed paper to the apparatus main body, and a single sheet of feeding paper. For example, a retard roller 603 urged against and in contact with the paper feed roller 601 is provided.

  The image forming unit 400 includes four image forming units 406K, 406Y, 406M, and 406C that respectively form yellow, magenta, cyan, and black images, and these are mounted on the upper portion of the intermediate transfer belt unit 700. Has been. Since these image forming units have the same internal configuration, for example, the black image forming unit 406K will be described as an example.

  In the image forming unit 406K, a photosensitive drum 401 as an image carrier is rotatably disposed. Around the photosensitive drum 401, a charging roller 402 that supplies and charges the surface of the photosensitive drum 401 in order from the upstream side in the rotation direction, and selectively applies light to the surface of the charged photosensitive drum 401. An exposure device 850 is provided for forming an electrostatic latent image by irradiating. Further, a developing roller 404 that generates a developer image by attaching toner as a black developer to the surface of the photosensitive drum 401 on which the electrostatic latent image is formed, and toner development on the photosensitive drum 401 is transferred. A drum cleaning unit 405 is disposed to remove residual toner remaining after the transfer. The toner storage unit 406K stores toner by a supply unit (not shown) and supplies the toner to the developing roller. Note that the drums or rollers used in these devices rotate by being transmitted with power via a gear or the like from a drive reduction (not shown).

  The intermediate transfer belt unit 700 transfers the toner image formed by the image forming unit 400 to the intermediate transfer belt 701, and further transfers the toner image to the printing paper P supplied from the paper tray 100 or the multi-purpose tray 600. . The intermediate transfer belt unit 700 is opposed to a drive roller 702 driven by a drive unit (not shown), a tension roller 703 that applies tension to the intermediate transfer belt 701 by an urging means such as a coil spring, and a secondary transfer roller 707. A secondary transfer backup roller 704 for transferring the toner image onto the printing paper P, and an intermediate transfer belt 701 stretched around these rollers. Further, the intermediate transfer belt unit 700 is configured to remove a toner remaining on the intermediate transfer belt 701, a belt cleaning unit 706, and a toner image formed on the photosensitive drum 401 so as to face the above-described photosensitive drum 401. A primary transfer roller 705 and the like for applying a predetermined voltage to transfer the image on the surface are provided.

  The fixing unit 500 includes an upper roller 501 having a halogen lamp 503a serving as a heat source therein and having a surface formed of an elastic body, and a roller pair of a lower roller 502 having a halogen lamp 503b also serving as a heat source and having a surface formed of an elastic body. have. The fixing unit 500 applies heat and pressure to the toner image on the printing paper P sent out from the image forming unit 400 to melt the toner image, and fixes the image on the printing paper P. The printing paper P fixed by the fixing unit 500 is conveyed by the discharge roller pairs 504a, 504b, 504c, and 504d, and is eventually discharged to the stacker unit 505. Power is transmitted to these discharge roller pairs from a drive source (not shown) via drive transmission means (not shown). A discharge sensor 506 disposed at the output unit of the fixing unit 500 detects the drive timing of the discharge roller pairs 504a, 504b, 504c, and 504d.

  When performing duplex printing, the transport path is switched by a discharge separator 901 disposed on the downstream side of the fixing unit 500. In this case, the printing paper P is guided to the double-sided conveyance unit 900 by the discharge separator 901 switched to guide the printing paper P downward. After pulling the printing paper P into the double-sided conveyance unit 900, the reverse separator 903 that switches the printing paper P to be guided to the double-sided conveyance path 916 downstream of the discharge separator 901 in the conveyance direction B of the printing paper P A reversing roller pair 902 that reverses the driving direction and switches back and conveys the printing paper P, and a retracting portion 914 that retracts the printing paper P that has been pulled in are disposed. The reversing separator 903 is also used as a reversing sensor for taking the drive switching timing of the double-sided conveyance unit 900. Further, assuming that the direction in which the printing paper P that has been switched back and conveyed by the reverse roller pair 902 is conveyed is a conveyance direction C, the conveyance roller pair 905 is sequentially provided in the double-sided conveyance unit 900 downstream from the reverse roller pair 902. A pair of horizontal transport rollers 906, a paper re-feed sensor 915 that takes the re-feed timing of the print paper P, and a re-feed roller pair 907 for transporting the print paper P to the transport roller pair 305 and performing printing again. ing. Power is transmitted to the reversing roller pair 902, the transport roller pair 905, the horizontal transport roller pair 906, and the refeed roller pair 907 from a transport drive motor (not shown) via a drive transmission means (not shown). Power is transmitted to the discharge separator 901 from a solenoid (not shown) via an operation transmission unit.

  FIG. 1 is a cross-sectional view illustrating a secondary transfer backup roller 704, a fixing unit 500 downstream of a nip portion formed by the secondary transfer roller 707, and a duplex conveying unit 900 in the image forming apparatus 1. It is.

  As shown in FIG. 1, in the image forming apparatus 1, printing is performed downstream of the secondary transfer roller 707, a transfer guide unit 1302 for guiding the printing paper P to the fixing unit 500, and downstream of the fixing unit 500. A discharge separator 901 that switches the conveyance path of the paper P to either the discharge roller pair 504a or the reverse roller pair 902 is provided.

  Air is drawn into the transfer guide portion 1302 from the suction hole (front) 1302F and the suction hole (rear) 1302R provided in the transfer guide portion 1302, and the printing paper P conveyed on the transfer guide portion 1302 is transferred to the transfer guide portion 1302. A suction fan 910 that is attracted to the section 1302 and prevents the printing paper P from floating is disposed. The conveyance guide portion 904 forms a duct portion 1307 so that air drawn from the suction hole (front) 1302F and the suction hole (rear) 1302R by the suction fan 910 can be blown out of the apparatus. In addition, a shutter plate 1303 is provided at the lower portion of the transfer guide portion 1302 on the opposite side of the conveyance surface so as to be able to operate in parallel with the transfer guide portion 1302. The shutter plate 1303 is provided with a shutter hole (front) 1303F and a shutter hole (rear) 1303R, which are positioned so as to overlap with the suction hole (front) 1302F and the suction hole (rear) 1302R, respectively. . The transfer guide unit 1302 is located at the center position in the width direction of the printing paper P to be transported, and at the center position of the suction hole (front) 1302F and the suction hole (rear) 1302R with respect to the transport direction. And a sag detecting unit 1300 including a sag sensor 1301.

  Next, the configuration of the control system according to the image forming apparatus 1 of the first embodiment will be described with reference to FIG.

  The image forming apparatus 1 performs its control by a control unit 1400 as shown in FIG. The control unit 1400 has a main control unit 1401 serving as a control center. The main control unit 1401 may be configured using, for example, a CPU including a control unit and a calculation unit, a RAM or ROM of a program memory, a timer counter, and the like. Then, the control unit 1400 activates each device and switches control based on detection signals from the paper sensor 301, the paper sensor 303, the writing sensor 306, the discharge sensor 506, the sag sensor 1301, and the paper thickness sensor 320. To do. The main controller 1401 includes a paper feed motor controller 1403, an electromagnetic clutch controller 1404, a belt motor controller 1405, an ID motor controller 1406, a fixing motor controller 1407, a shutter motor controller 1408, and a suction fan. A control unit 1410 is connected.

  The specific configuration of the paper thickness sensor 306 is not limited. For example, a mechanical configuration (for example, a configuration in which the printing paper P is sandwiched between sensors and the thickness is measured) or an optical configuration (for example, A configuration in which the printing paper P is irradiated with inspection light to measure the degree of transmission of light may be applied. In the image forming apparatus 1 of this embodiment, it is assumed that the sheet thickness sensor 306 that detects the thickness of the traveling sheet is provided. The paper thickness sensor 306 includes, for example, a fixed stage unit (not shown) having a plane parallel to the paper traveling surface and disposed below the paper traveling surface, and an upper side of the stage unit with respect to the paper traveling surface. And a lever that can move up and down above the paper travel surface, a spring that urges the lever toward the plane of the stage, and a detector that detects the distance that the lever moves up and down You may make it comprise with. In the paper thickness sensor 306, when the traveling printing paper P enters the upper surface of the stage unit that is urged by the lever unit, the lever unit is moved upward by the thickness of the printing paper P due to the thickness of the printing paper P. . The detection unit described above detects the amount of movement of the moved lever unit, and the detection unit sends the amount of movement of the lever unit to the main control unit 1401 as the sheet thickness.

  Although the specific configuration of the sag sensor 1301 is not limited, for example, a lever portion that is rotatably disposed in contact with the printing paper P (not shown) and a photo that detects the operation of the rotated lever portion. You may make it use the contact-type sensor which has the detection part comprised with a coupler etc. In this embodiment, it is for performing stable sag control regardless of the thickness, position, type, etc. of the paper, and the transmissive paper detection sensor can handle special printing paper P such as a transparent film. However, the type of detection means such as a contact type or a transmission type is not limited by the printing paper P to be used.

  The paper feed motor control unit 1403 sends an operation signal to the paper feed motor 1420 to control the paper feed motor 1420. Thus, the electromagnetic clutch control unit 1404 sends an operation signal to the electromagnetic clutch 1421 to control the operation of the electromagnetic clutch 1421, and the belt motor control unit 1405 sends an operation signal to the belt motor 1422 to control the operation, and the ID The motor control unit 1406 sends an operation signal to the ID motor 1423 to control the operation, the fixing motor control unit 1407 sends an operation signal to the fixing motor 1424 to control the operation, and the shutter motor control unit 1408 uses the shutter motor. An operation signal is sent to 1306 to control the operation, and the suction fan control unit 1410 sends an operation signal to the suction fan 910 to control the operation. Each of these motors may be configured using, for example, a phase excitation pulse motor or a DC motor. In this case, the above-described two-phase excitation pulse motor (not shown) controls acceleration / deceleration of motor rotation by supplying a constant current to each motor and switching the phase current direction at the rising edge of the clock signal or changing the clock frequency. You may make it do. In this DC motor, the rotation speed is controlled by applying a voltage to the motor terminal, and the rotation direction of the motor is controlled by the connection direction of the polarity of the motor terminal.

  As the electromagnetic clutch 1421, for example, a dry single-plate electromagnetic clutch or the like may be used. Specifically, the electromagnetic clutch 1421 may be configured by, for example, a field rotor assembly and an armature assembly in which a field incorporating a rotor and a coil is supported by a ball bearing and integrated. In this case (when the electromagnetic clutch 1421 is configured as in the above example), the above-described field rotor assembly is attached to a rotating member such as a shaft, and the armature assembly takes a slight gap from the rotor, It is fixed to members such as pulleys and gears by mounting bolts. In this case, the armature is attracted to the rotor by the magnetic flux generated in the field rotor assembly and the armature assembly by the current flowing through the coil in the electromagnetic clutch 1421, and the electromagnetic clutch 1421 is connected. In this case, mechanical motion is applied to the external mechanism connected to the electromagnetic clutch 1421. In this case, if energization to the coil is continued, the armature keeps the state attracted to the rotor, and if the current is cut off, the magnetic flux disappears, and the armature is separated from the rotor by the leaf spring and is pulled back to the original position. . In this case, this causes the power from the drive source transmitted to the gear attached to the electromagnetic clutch 1421 to be transmitted to the drive roller.

  The image forming apparatus 1 includes an operation panel 1401. The operation panel 1401 includes, for example, an input unit configured with a switch (not shown), and a display unit configured with an LED (not shown), an LCD, and the like. The operation panel 1401 can set various conditions in the image forming apparatus 1 such as font selection and paper selection by operating an input unit (not shown). In the operation panel 1401, a condition set by an input unit (not shown) is displayed on a display unit (not shown).

  In addition, the image forming apparatus 1 includes an interface unit 1402. The interface unit 1402 includes an interface connector (not shown), an interface IC, and the like, and performs processing of transferring print data sent from a host computer (not shown) to the main control unit 1401.

(A-2) Operation of the First Embodiment Next, the operation of the image forming apparatus 1 of the first embodiment having the above configuration will be described.

  In the following, a process of printing on the printing paper P stacked on the paper tray 100 will be described. In the following, the description of the printing state of the printing paper P stacked on the multi-purpose tray 600 will be described in detail because the operation after the feeding of the paper and the control after the conveyance roller pair 305 are the same regarding the operation and control after the paper feeding. Is omitted.

  Hereinafter, a control process when the printing paper P is conveyed by the image forming apparatus 1 will be described with reference to FIGS. 1 and 3 to 7. In FIGS. 1 and 3 to 7, the flow of air generated by the suction fan 910 is also illustrated.

  1, 3, 4, and 5 show the flow of wind by the printing paper P on which the printing paper P is nipped and conveyed by the secondary transfer unit 750 and the fixing unit 500, and the suction fan, respectively.

  In the state of FIG. 1, the air around the transfer guide portion 909 is caused by the rotation of the suction fan 910 to cause a suction hole (front) 1302F, a suction hole (rear) 1302R, a shutter hole (front) 1302F, and a shutter hole (rear) 1303R. And is drawn into the duct portion 1307. In the state of FIG. 1, the air drawn into the duct portion 1307 is sent to the outside of the apparatus. Further, in the state of FIG. 1, when the printing paper P passes over the transfer guide portion 1302, the printing paper P is conveyed while being sucked onto the transfer guide portion 1302 by suction of air by the suction fan 910.

  FIG. 1 shows a state where the suction by the suction fan 910 is performed and the printing paper P is slack. FIG. 3 shows a state where the suction by the suction fan 910 is performed and the printing paper P is stretched. Furthermore, FIG. 4 shows a state in which the printing paper P is slack without any suction by the suction fan 910. Furthermore, FIG. 5 shows a state in which the printing paper P is stretched without suction by the suction fine 910.

  As shown in FIG. 1, the printing paper P sucked by the suction fan 910 is sucked onto the transfer guide unit 1302. Thereafter, when the printing paper P is in a slack state, the sag sensor 1301 is turned on. At this time, the upper roller 501 and the lower roller 502 are driven so that the printing paper P is stretched by increasing the rotational speed by a predetermined amount so that the printing paper P does not loosen too much. Also, as shown in FIG. 3, the printing paper P is conveyed by the fixing unit 500 so as to remove slackness until the position where the sag sensor 1301 is turned off. Further, when the sag sensor 1301 is turned OFF, the upper roller 501 and the lower roller 502 are driven so as to loosen the rotation speed by a predetermined amount so that the printing paper P is slack so that the printing paper P does not stretch too much. This series of drive switching operations is performed until the printing paper P is completely conveyed from the fixing unit 500 to the downstream side.

  The suction fan 910 is disposed with a certain gap from the transfer guide portion 1302. Then, air is taken in by a suction hole (front) 1302F and a suction hole (rear) 1302R provided in the paper conveyance direction of the printing paper P and to the outside of the width direction. As a result, even when the printing paper P passes through the transfer guide portion 1302 and is sucked, the air is not taken into the duct portion 1307. The same applies to the shutter hole (front) 1303F and the shutter hole (rear) 1303R.

  6 and 7 are diagrams illustrating the operation of the shutter plate 1303.

  As shown in FIG. 6, the shutter plate 1303 is operated along the transfer guide portion 1303 in parallel to the upstream side in the transport direction. In the state of FIG. 6, only the suction hole (front) 1302F and the shutter hole (front) 1303F are closed so as to overlap, and the suction hole (rear) 1302R is blocked by the shutter plate 1303. In the state of FIG. 6, the suction for the printing paper P can be strengthened in this range by limiting the suction opening only to the secondary transfer unit 750 side. When the printing paper P is transported and the trailing edge of the printing paper P is transported to a certain range, the shutter paper 1303 is operated under a specific condition, and the printing paper P is about to come out of the secondary transfer unit 750. The rear end portion of the sheet is strongly sucked so as not to stick to the intermediate transfer belt 701.

  FIG. 7 shows a state where the shutter plate 1303 is operated in parallel along the transfer guide portion 1303 toward the downstream side in the transport direction. In the state of FIG. 7, only the suction hole (rear) 1302R and the shutter hole 1303R are opened so as to overlap, and the suction hole (front) 1302F is closed by the shutter plate 1303. In the state of FIG. 7, the suction for the printing paper P can be strengthened in this range by limiting the opening for suction only to the fixing unit 500 side. Then, when the printing paper P is transported and the trailing edge of the printing paper P is transported to a certain range, the printing paper that operates the shutter plate 1303 according to specific conditions and tries to enter the entrance of the fixing unit 500 The rear end portion of P is strongly sucked so as not to splash toward the exterior portion of the fixing unit 500.

  Next, a detailed configuration of the shutter plate 1303 will be described with reference to FIGS.

  FIG. 9 is a schematic perspective view showing the transfer guide portion 1302, the shutter plate 1303, and the operating portion thereof removed. FIG. 9A is a perspective view of the transfer guide portion 1302 and the shutter plate 1303 as viewed from the top surface (upper surface in a state attached to the main body of the image forming apparatus 1). FIG. 9B is a perspective view of the transfer guide portion 1302 and the shutter plate 1303 as viewed from the bottom surface (the surface opposite to FIG. 9A). As shown in FIG. 9, a rack 1305 is formed on the shutter plate 1303, and is arranged so as to be able to transmit driving to the shutter motor 1306 via a gear 1304. By driving the shutter motor 1306, the shutter plate 1303 can be moved back and forth along the transfer guide portion 1302 with respect to the transport direction.

  FIG. 10 shows that the suction hole (front) 1302F and the suction hole (rear) 1303R overlap with the openings of the shutter hole (front) 1303F and the shutter hole (rear) 1303R, respectively, and suction can be performed from the openings on either side. It is the figure which showed the state. FIG. 10A is a plan view of the suction hole (front) 1302F and the suction hole (rear) 1303R. FIG.10 (b) is the sectional view on the AA line of Fig.10 (a).

  FIG. 11 is a diagram showing a state in which the shutter plate 1303 is operated to the upstream side in the transport direction, and only the suction hole (front) 1302F and the shutter hole (front) 1303F are overlapped. FIG. 11A is a plan view of the suction hole (front) 1302F and the suction hole (rear) 1303R. FIG.10 (b) is the BB sectional drawing of Fig.11 (a).

  FIG. 12 is a diagram illustrating a state in which the shutter plate 1303 is operated to the downstream side in the conveyance direction, and only the suction hole (rear) 1302R and the shutter hole (rear) 1303R overlap each other. FIG. 12A is a plan view of the suction hole (front) 1302F and the suction hole (rear) 1303R. FIG.12 (b) is CC sectional view taken on the line of Fig.12 (a).

  As shown in FIGS. 9 to 12, by moving (sliding) the shutter plate 1303 in the paper transport direction, holes in the first half of the transfer guide portion 909 in the paper transport direction (suction holes (front) 1302F and shutter holes ( One or both of a front hole 1303F) and a second half hole in the paper conveyance direction (a suction hole (rear) 1302R and a shutter hole (rear) 1303R) are opened. It is possible to perform the suction control. In the transfer guide unit 909, the structure (suction unit) that separates the first half portion and the second half portion in the sheet conveying direction and sucks the suction fan 910 is not limited to the above-described configuration, and various suction mechanisms. Can be used. For example, a different suction fan may be provided for each area (suction part) divided on the transfer guide part 909.

  Next, in the image forming apparatus 1 according to this embodiment, an operation when the printing paper P is continuously printed will be described in detail.

  First, each parameter (including each parameter shown in FIG. 13) used in the following description will be described.

In the following, it is assumed that “P (n)” indicates the nth printing paper P in continuous printing. In the following, “P (n + 1)” represents the (n + 1) th printing paper P in continuous printing. In the following, “L” indicates the length of the printing paper P (n) in the conveyance direction. Furthermore, in the following, “M” represents the distance from the writing sensor 306 to the tip of the transfer guide portion 1302. In the following, “N” represents the distance from the writing sensor 306 to the center of the transfer guide portion 1302. Further, hereinafter, “x” represents a predetermined length in the transport direction from the rear end of the printing paper P (n). Furthermore, in the following, it is assumed that the predetermined amount “R” is a parameter obtained by the following equation (1). In the following, it is assumed that the predetermined amount “S” is a parameter obtained by the following equation (2). In the description of this embodiment, “n” is an integer represented by “n = 1, 2, 3,... N,.
R = N + L−x (1)
S = M + L−x (2)

  In addition, the numerical values and symbols in parentheses attached to symbols such as alphabets and numerical values representing parameters defined in this embodiment are, for example, the parameter P (n) This indicates the number of sheets to be fed and conveyed during continuous printing.

  In this embodiment, when the image forming apparatus 1 performs continuous printing on two or more printing papers P, each part performs the above-described operation on each printing paper P, and each printing paper P Then, image formation is performed. At this time, the image forming apparatus 1 determines that the nth printing paper P (n) on which continuous printing is performed and the (n + 1) th printing paper P (n + 1) on the next page are spaced apart from each other by a predetermined distance. It is fed from the feeding unit 200.

  Next, in this embodiment, the operation when the image forming apparatus 1 conveys one printing paper P and forms an image will be described in detail.

  First, the printing paper P is conveyed by the conveyance mechanism of the paper feeding unit 200, the conveyance roller pair 302, the conveyance roller pair 304, and the conveyance roller pair 305 disposed on the upstream side of the intermediate transfer belt unit 700. To do.

  Next, when the printing paper P is conveyed toward the intermediate transfer belt unit 700, the printing paper P is held by the intermediate transfer belt 701, the NIP portion formed by the secondary transfer roller 707, and the like in front of the printing paper P. The rear side of the printing paper P is nipped and conveyed by a conveying roller pair 305. Each of the conveyance roller pairs 302, 304, and 305 is configured so that the driven roller is pressed evenly against the driving roller in order to generate a conveyance force sufficient to convey the printing paper P. A spring (not shown) is provided at both ends of the rotating shaft. When the printing paper P continues to be conveyed, it reaches the position of the fixing unit 500 and is nipped and conveyed by the NIP unit formed by the upper roller 501 and the lower roller 502.

  Next, the operation when the image forming apparatus 1 transports a plurality of sheets to form an image and the behavior of the printing sheet P will be described in detail.

  At this time, in the image forming apparatus 1, the first printing paper P (1) is conveyed to form an image. In this process, first, when the leading edge of the printing paper P (1) is detected by the paper sensor 301, the printing paper P (1) fed out from the paper feeding unit 200 is continuously conveyed by a predetermined amount. Abutting on the NIP portion formed by the conveying roller pair 302, the skew is corrected.

  Thereafter, the printing paper P (1) that has been abutted by a predetermined amount is conveyed by the conveying roller pair 302. The paper feeding unit 200 is stopped by a driving source (not shown) after transporting the printing paper P (1) by a predetermined amount. Thereafter, when the printing paper P (1) reaches the paper thickness sensor 320, the thickness is detected by the paper thickness sensor 320. When the printing paper P (1) is conveyed in the paper conveyance direction as it is, it enters the position of the writing sensor 306 and reaches the position of the writing sensor 306 to be detected (the writing sensor 306 is detected by the main control unit 1401). To send a sensor ON signal). Thereafter, the printing paper P (1) continues to be further conveyed and comes out of the position of the writing sensor 306, and the writing sensor 306 detects that the trailing edge of the printing paper P (1) has come out. That is, the printing paper P (1) is not present at the position of the writing sensor 306 (a state in which the writing sensor 306 sends a sensor OFF signal to the main control unit 1401). Here, the driving of the transport roller pair 305 is stopped by a driving source (not shown).

  Next, the paper feeding unit 200 feeds the second printing paper P (2) with an interval between the papers by a predetermined distance. The fed printing paper P (2) is conveyed in the same manner as the printing paper P (1). Thereafter, the printing paper P (2) continues to be transported, and the printing paper P (1) is transported with a predetermined predetermined distance between the papers after the writing sensor 306 is turned off. Thereafter, the conveyance roller pair 305 is driven by a drive source (not shown) to start conveyance of the second printing paper P (2). At this time, when a predetermined time elapses from the timing when the writing sensor 306 is turned off, it is determined that the sheet has been conveyed by a predetermined amount, and the time is counted by the timer counter 1425.

  Note that the above-described preset time is determined by the conveyance speed at the time of image formation and the paper size to be conveyed, due to slippage of paper in the conveyance mechanism, delay in connection of mechanism parts (not shown), and the like. It is determined by taking into account the generated deviation as a constant value. Here, a specific example when transporting A4 size paper is given. In this case, when the above-mentioned distance L is 210 mm, M is 100 mm, N is 140 mm, and x is 30 mm, the distance R satisfying the above expression (1) is R = 140 + 210−30 = 320 [mm], (2 The distance S satisfying the formula is S = 100 + 210−30 = 280 [mm]. Here, it is assumed that the sheet conveying speed of the conveying roller pair 305 is set to be rotationally driven so as to be 200 mm / s. In this case, the time during which the printing paper P (1) is conveyed by the distance R = 320 mm is 1.60 sec, and the time during which the distance S = 280 mm is conveyed is 1.40 sec. In the setting of the printing paper P and the conveyance speed, for example, the delay between the conveyance roller pair 305 and the paper, the transmission time until the ON signal from the writing sensor 306 is transmitted to the main control unit 1401, and the like are considered. The time is set to 0.05 seconds in advance. The timing when the printing paper P (1) is actually conveyed and the printing paper P is in the ON state of the writing sensor 306 is 1.60-0.05 = 1.55 [sec], 1.40-0. The timer counter 1425 counts that 05 = 1.35 [sec] has elapsed. Thereafter, the printing paper P (2) is transported and image processed in the same manner as the printing paper P (1), and image formation is performed.

  Next, control processing performed by the image forming apparatus 1 (mainly the main control unit 1401) will be described with reference to the flowchart of FIG.

  Note that the control by the operation of the discharge sensor 506 between step S1 and step S45 in this embodiment is used to detect paper conveyance abnormality, and the front or rear end of the paper is detected by the discharge sensor 506. If not, a paper conveyance error will occur. Therefore, description regarding the operation and control of the discharge sensor 506 between step S1 and step S45 is omitted.

  First, the main control unit 1401 reads the setting conditions such as the thickness regarding the printing paper set by the operation on the operation panel 1401 (S1). The main control unit 1401 determines the paper conveyance speed, transfer voltage setting, and the like as the read paper setting conditions.

  Next, the main control unit 1401 includes motor control units, that is, a paper feed motor control unit 1403, an electromagnetic clutch control unit 1404, a belt motor control unit 1405, an ID motor control unit 1406, a fixing motor control unit 1407, and a shutter motor control. The unit 1408 and the suction fan controller 1410 are instructed (S2).

  The main control unit 1401 drives the fixing motor 1424 to rotate the upper roller 501 and the lower roller 502 in the fixing unit 500 (S3), and drives the belt motor 1422 to rotate the drive roller 702 ( S4), the ID motor 1423 is driven to rotate the respective photosensitive drums 401 of the image forming units 406K to 406C (S5), the paper feed motor 1420 is driven (S6), and the electromagnetic clutch connected to the feed roller 203 By turning ON 1421, the feed roller 203 is rotated to feed out the printing paper P from the paper tray 100 (S7).

  The fed printing paper P (1) is conveyed to the paper sensor 301, and the paper sensor 301 detects that the leading edge of the printing paper P (1) has passed (S8).

  When the paper sensor 301 detects the passage of the print paper P (1), the print roller P (1) is further conveyed by the feed roller 203 toward the NIP portion of the conveyance roller pair 302 by a predetermined amount. As a result, the leading end portion of the printing paper P (1) is conveyed by a predetermined abutting distance set in advance after being abutted against the NIP portion (S9). By this abutting operation, a skew correction operation is performed on the paper.

  The main control unit 1401 issues an instruction to the electromagnetic clutch control unit 1404 and turns on the electromagnetic clutch 1421 connected to the conveyance roller pair 302, so that the conveyance roller pair 302 transmits driving by driving the paper feed motor 1403. And rotate (S10). The conveying roller pair 302 to which the drive is transmitted conveys the printing paper P (1) to the conveying roller pair 304 and 305 to the secondary transfer unit 750.

  The printing paper P (1) fed out from the conveying roller pair 304 is conveyed to the paper thickness sensor 320 at the leading end of the printing paper P (1), and when the printing paper P (1) passes, The paper thickness is detected (S11). In FIG. 14, in order to simplify the explanation, it is limited to only two types of thick paper and thin paper. However, the present invention is not limited to this. For example, it is divided into a plurality of cases every 10 μm or 50 μm. The present invention can also be applied to a case where the paper thickness is divided into a plurality of cases and branched at an indefinite interval.

  Thereafter, in both thick paper and thin paper, the printing paper P (1) is continuously conveyed by the conveying roller pair 304, and after reaching the conveying roller pair 305, is further conveyed by a predetermined amount (S12, S22). The printing paper P (1) is conveyed to the writing sensor 306, and the writing sensor 306 detects that the leading edge of the printing paper P (1) has passed (S13, S23). Thereafter, the printing paper P (1) is held by the NIP portion between the secondary transfer roller 707 and the intermediate transfer belt 701 in the secondary transfer portion 750 by the transport roller pair 305, and is transported by a predetermined amount (S14, S24). ), The printing paper P is conveyed to a position where the sag sensor 1301 can be detected. The paper sensors 301 and 303 and the writing sensor 306 are also for detecting a paper conveyance abnormality. When the leading or trailing edge of the paper is not detected by the paper sensors 301 and 303 and the writing sensor 306, the paper A conveyance error occurs. Thereafter, the printing paper P (1) continued to be conveyed from the secondary transfer unit 750 is nipped and conveyed by the upper roller 501 and the lower roller 502 in the fixing unit 500. Here, the sag state of the printing paper P (1) stretched between the secondary transfer unit 750 and the fixing unit 500 is detected by the sag sensor 1301 (S15, S25).

  At this time, when the sag sensor 1301 is turned on, the sheet is slack as shown in FIG. 4, and when the sag sensor 1301 is turned off, the sag as shown in FIG. The sensor 1301 can detect a state in which the sheet on which the printing sheet P (1) passes is stretched a distance farther from the guide unit 1302 than the range. Whether the paper thickness detection in step S11 described above is thick paper or thin paper, if the sag sensor 1301 detects ON, the printing paper P (1) is in a slack state, and the paper sag. In order to solve this problem, the fixing motor control unit 1407 instructs to increase the driving speed of the fixing motor 1424 (S16, S26).

  Further, when the sag sensor 1301 does not detect ON, the printing paper P (1) is stretched, and the fixing motor control unit 1407 is set so as to reduce the driving speed of the fixing motor 1424 in order to eliminate the paper stretching. (S20, S29). Furthermore, when the paper thickness detection in step S11 described above is a thick paper, the paper being transported is thick and generally thick paper is stiff, so it cannot be bent easily. If you try to control the slack or tension of the paper only by controlling the speed of the mechanism that is holding and transporting, the printing surface may rub against the guide section in the case of heavy paper due to speed fluctuations or paper slippage between the transport mechanisms. There is a possibility that a shock line may occur when the trailing edge of the sheet comes out of the transport mechanism. The suction fan 910 sucks the paper in order to improve the accuracy of the slack control more effectively, rather than eliminating the slack and tension of the print paper P (1) only by controlling the speed of the fixing motor 1424.

  When the main control unit 1401 detects a slack in thick paper, the main control unit 1401 instructs the suction fan control unit 1410 to drive the rotation speed of the suction fan 910 at half speed (S17). When the main control unit 1401 detects sheet tension, the main control unit 1401 instructs the suction fan control unit 1410 to drive the rotational speed of the suction fan 910 at full speed (S21).

  Then, the main control unit 1401 keeps the fixing motor 1424 so that the sag sensor 1301 repeats ON and OFF until the printing paper P (1) is conveyed by a predetermined amount. The drive control of the suction fan 910 is repeated (S18).

  Further, when the paper thickness detection in the above-described step S11 is thin paper, the paper being transported is thin, and generally thin paper is weak in paper and can be easily bent. easily influenced. However, if it is attempted to control the slack or tension of the paper only by controlling the speed of the mechanism that is carrying the paper, there is a possibility that the paper may be slacked upward or the printing surface may be rubbed against the paper transportation path. Also in this case, in order to improve the accuracy of the sagging control more effectively, not the sagging or stretching of the printing paper P (1) only by the speed control of the fixing motor 1424. I do.

  When the slack is detected in the thin paper, the main control unit 1401 causes the suction fan control unit 1410 to stop driving the suction fan 910 in order to stop the suction of the paper by the suction fan 910 so as not to be brought into close contact with the guide. Instruct (S27).

  When the sheet tension is detected, the main control unit 1401 causes the suction fan control unit 1401 to drive the rotation speed of the suction fan 910 at a half speed so that the print sheet P (1) does not hang upward and is not sucked too much by the guide. An instruction is issued from 1410 (S30).

  Then, the main control unit 1401 keeps the fixing motor 1424 so that the sag sensor 1301 repeats ON and OFF until the printing paper P (1) is conveyed by a predetermined amount. The drive control of the suction fan 910 is repeated (S28).

  Here, when there is no print command to be printed next (S19), the main control unit 1401 issues an instruction to the electromagnetic clutch control unit 1404, and the electromagnetic clutch control unit 1404 drives the electromagnetic clutch 1421 to be joined to the feed roller 203. Stop (S32).

  Thereafter, when the printing paper P (1) continues to be conveyed, the main control unit 1401 detects that the trailing edge of the printing paper P (1) has passed the position of the discharging sensor 506, and the sensor OFF (S33).

  Then, the main control unit 1401 issues an instruction to each motor control unit and the electromagnetic clutch control unit. Receiving the instruction, the electromagnetic clutch control unit 1404 stops the driving of the electromagnetic clutch 1421 that is joined to the conveyance roller pair 302 (S34). In response to the instruction, the paper feed motor control unit 1403 stops the paper feed motor 1420 (S35). Further, the suction fan control unit 1410 that has received the instruction stops the suction fan 910 (S36). Furthermore, the ID motor control unit 1406 that has received the instruction stops driving the ID motor 1423 (S37). In response to the instruction, the belt motor control unit 1405 stops driving the belt motor 1422 (S38). Further, upon receiving the instruction, the fixing motor control unit 1407 stops driving the fixing motor 1424 (S39), and the operation ends.

  In step S19 described above, when there is a print command to be printed next (image data of a page not subjected to print processing), the main control unit 1401 returns to the next state after the write sensor 306 returns to the OFF state. The feeding of the sheet P (2) is started (S31). Then, the main control unit 1401 returns to the above-described step S7, and performs a process of feeding out, transporting, and printing the next printing paper P (2).

  As described above, the main control unit 1401 repeats the operation and performs a process of printing a plurality of printing papers P continuously.

  In the image forming apparatus 1, when printing is performed, the speed fluctuation of the transport mechanism that is different for each section is changed every moment. For this reason, in the image forming apparatus 1, when the printing paper P (medium) to be printed is a thick paper or a highly rigid paper, the paper is extremely difficult to bend. It is easy to transmit and easily affected by speed fluctuations. As a result, the shock line increases when the paper is stretched, and the print quality deteriorates, such as rubbing due to paper bouncing if it is too slack, and sticking to or rubbing the guide when the paper is easily deformed. To do. By controlling the speed of the fixing unit 500 and switching the suction fan 910 by the above-described control, it is possible to accurately control the slack of the paper regardless of the thickness of the paper. Further, the image forming apparatus 1 performs control for sucking the sheet by the shutter plate 1303 even at the position where the sheet is conveyed.

  Next, details of the operation of the shutter plate 1303 will be described.

  6 and 7 are diagrams illustrating a case where the shutter plate 1303 is operated in the front and back direction in the transport direction. 6 shows a state in which the trailing edge of the printing paper P has reached the position of the distance M from the writing sensor 306, and FIG. 7 shows a state in which the trailing edge of the printing paper P has reached the position of the distance N from the writing sensor 306. Show.

  10, 11 and 12 are cross-sectional views showing a state in which the shutter plate 1303 is operating. As shown in FIGS. 6 and 11, when the shutter motor 1306 is driven to rotate, the gear 1304 that meshes with the shutter motor 1306 is rotated. When the gear 1304 is driven to rotate, the shutter plate 1303 is operated in parallel via a rack 1305 that meshes with the gear 1304. As shown in FIGS. 6 and 11, by this operation, the shutter plate 1303 is operated in parallel to the upstream side in the transport direction, so that the suction hole (front) 1302F and the shutter hole (front) 1303F overlap and suction is performed. The positions of the hole (rear) 1302R and the shutter hole (rear) 1303R are shifted, and the suction hole (rear) 1302R is shielded by the shutter plate 1303. In this state, air suction by the suction fan 910 is performed only on the suction hole (front) 1302F side. Similarly, in FIGS. 7 and 12, the suction plate (rear) 1302R and the shutter hole (rear) 1303R overlap each other and the suction hole (front) is moved by operating the shutter plate 1303 parallel to the downstream side in the transport direction. ) 1302F and the shutter hole (front) 1303F are out of position, and the suction hole (front) 1302F is shielded by the shutter plate 1303. In this state, air is sucked by the suction fan 910 only on the suction hole (rear) 1302R side.

  FIG. 15 is a flowchart showing only the difference from the above-described FIG. 14 in the process when the movement control of the shutter plate 1303 is added in the above-described flowchart of FIG. In the flowchart of FIG. 15 (when adding movement control of the shutter plate 1303), steps S11 to S28 of FIG. 14 are replaced with steps S11 to S30 and S40 to S45. In the flowchart of FIG. 15, the processes other than steps S11 to S30 and S40 to S45 are the same as those in FIG.

  In the flowchart of FIG. 15, when the paper thickness detection result of the printing paper P (1) in step S11 is thick paper, the main control unit 1401 performs the operation up to step S17 or step S21, and then the printing paper. It is assumed that P (1) is detected by the writing sensor 306 and has been conveyed by a predetermined amount R from S13 (S40).

  At this time, the rear end portion of the printing paper P (1) is in a state as shown in FIG. At this time, the upstream side of the portion of the printing paper P (1) held and conveyed by the fixing unit 500 is in a cantilever state held only by the fixing unit 500, and the posture of the paper is not stable. Further, the rear end of the thick paper is likely to jump due to the NIP state, and the rear end of the paper may jump and come into contact with the exterior of the fixing unit 500, and the print surface before fixing may be rubbed.

  When the printing paper P (1) is conveyed until it reaches the state of step S40 described above (a state where the printing paper P (1) has been conveyed by a predetermined amount R), the shutter motor control unit 1408 instructed by the main control unit 1401 1306 is driven to operate the shutter plate 1303 downstream in the transport direction (S41). That is, as described above, the sheet is sucked only from the suction hole (rear) 1302R side.

  Further, the suction fan control unit 1410 instructed by the main control unit 1401 drives the suction fan 910 at full speed (S42) so that the rear end of the printing paper P (1) is more stably adsorbed to the guide unit 1302. Be controlled. This control prevents the trailing edge of the printing paper P (1) from jumping up. When a predetermined amount is conveyed from this state (S18), the operation according to the flowchart of FIG. 9 described above is performed. Further, when the thin paper is detected in the paper thickness detection (S11) of the printing paper P (1), the operation up to (S27) or (S30) is performed, and then the printing paper P (1) is detected by the writing sensor 306. Then, when a predetermined amount S is conveyed from (S13) (S43), the rear end portion of the printing paper P (1) is in a state as shown in FIG. At this time, the upstream side of the portion of the printing paper P (1) held and conveyed by the fixing unit 500 is in a cantilever state held only by the fixing unit 500, and the posture of the paper is not stable. Furthermore, the trailing edge of the thin paper may be attracted to the intermediate transfer belt 701 by static electricity, and the trailing edge of the sheet may jump and come into contact with the printed surface before fixing. When the printing paper P (1) is conveyed up to step S43, the shutter motor control unit 1408 instructed by the main control unit 1401 drives the shutter motor 1306 to operate the shutter plate 1303 upstream in the conveyance direction (S44). . That is, as described above, the sheet is sucked only from the suction hole (front) 1302F side.

  Further, the suction fan control unit 1410 instructed by the main control unit 1401 drives the suction fan 910 at full speed (S45) so that the rear end of the printing paper P (1) is more stably adsorbed to the guide unit 1302. Be controlled. This control prevents the trailing edge of the printing paper P (1) from jumping up. When the printing paper P (1) is conveyed by a predetermined amount from this state (S28), the process according to the flowchart of FIG. 14 described above (the process from step S19 described above) is performed.

  The opening / closing operation of the shutter plate 1303 described above is not limited to the above-described operation, and the leading end of the printing paper P is disposed on the shutter plate 1303 in accordance with the characteristics and behavior of the paper used. It may be opened and closed when it is transported to the area to be sucked, and suction may be performed to prevent the tip from being lifted.

  In the above description, the control of the suction fan 910 has been limited to three types: stop, half speed (rotating the fan at about half the speed at full speed), and full speed (rotating the fan at full speed). As described above, if the thickness can be set in multiple stages, the delimiter for controlling the rotational speed is not limited. For example, selection of rotating at least 25% without stopping the suction fan 910 is arbitrary. Specific specifications (specifications) of the suction fan 910 are not limited. For example, the fan air volume is about “0.69 m ^ 3 / min”, and the diameter of the wings constituting the fan is “60 mm ± 1 mm. The thing which sets the rotation speed (full speed) of the wing | blade which comprises a fan to 5400 rpm may be applied.

  When there is a difference between the paper thickness data sent and the paper thickness (S1) defined in advance by the user, the main control unit 1401 determines the conveyance speed of the printing operation itself, the image transfer voltage, and the fixing temperature. And the like, the control according to the set paper thickness is performed, and the drive switching of the fixing motor 1424 and the drive switching of the suction fan 910 relating to the slack can be controlled in accordance with the data of the sent paper thickness. Is possible. That is, the operation for controlling the sag of the printing paper P may optionally be switched between automatic control on the image forming apparatus 1 side and automatic control on the user side setting. Further, as described above, in this embodiment, the paper thickness can be set by the operation panel 1401 or automatically by the paper thickness sensor 306. In other words, the main control unit 1401 detects the sheet thickness of the printing sheet P to be referred to when performing each control (in particular, control of driving switching of the fixing motor 1424 and driving switching of the suction fan 910) by the sheet sensor 301. Whether to give priority to the result or to give priority to the content set by the user may be arbitrarily applied (for example, managed by a flag that can be changed by the user's setting).

  Next, specific examples of combinations of parameter settings in the image forming apparatus 1 will be described.

  Here, as an example, the sag sensor 1301 can detect the state of the printing paper P in four stages: “sag too much”, “sag”, “tension”, and “too much tension” in order of increasing distance from the sag sensor 1301. Suppose that Also, in the following, the paper thickness sensor 320 has four stages of “thick paper” (thick paper that does not cause deflection), “normal”, “thin paper”, and “ultra thin paper” in order from the thicker side of the print paper P. It can be detected by. Furthermore, it is assumed that the conveyance speed (roller rotation speed) by the fixing unit 500 can be controlled in two stages, “fast” and “slow”. Furthermore, in the following, with respect to the suction force of the suction fan 910, from the order of strong suction power (in descending order of fan rotation speed) to “strong suction” (for example, fan rotation at the above-mentioned full speed), “suction” (for example, It is assumed that the control can be performed in two stages, that is, the fan rotation at the half speed described above. Further, as described above, in the transfer guide portion 1303, the “front half” suction hole (front) 1302F and the “second half” suction hole (rear) 1302R are opened or closed, respectively. Control to a state (state in which ventilation is impossible) is possible.

  At this time, for example, a state in which the thickness of the printing paper P is “normal” and the state of the printing paper P is “sag” (hereinafter referred to as “first state”) is assumed. In the first state, for example, the main control unit 1401 sets the conveyance speed of the fixing unit 500 to “fast” and the suction force of the fan 910 to “suction”, and the transfer guide unit 1303 has suction holes in the first half and second half. May be opened to reduce sagging of the printing paper P. As a result, even in the first state, it is possible to suppress rubbing due to splashing of the printing paper P or the like.

  Further, for example, assume a state where the thickness of the printing paper P is “normal” and the state of the printing paper P is “stretching” (hereinafter referred to as “second state”). In the second state, for example, the main control unit 1401 sets the conveyance speed of the fixing unit 500 to “slow” and the suction force of the fan 910 to “suction”, and the transfer guide unit 1303 has suction holes in the first half and second half. May be opened to reduce the tension of the printing paper P. Thereby, even in the second state, it is possible to suppress the occurrence of a shock line for the printing paper P.

  Further, for example, a state is assumed in which the thickness of the printing paper P is “normal” and the state of the printing paper P is “too slack” (hereinafter referred to as “third state”). In the third state, for example, the main control unit 1401 sets the conveyance speed of the fixing unit 500 to “fast”, closes the suction holes in the first half part and the second half part of the transfer guide part 1303, and causes the printing paper P to sag. You may make it reduce. As a result, even in the second state, it is possible to suppress rubbing due to the jumping of the printing paper P or the like.

  Furthermore, for example, a state in which the thickness of the printing paper P is “normal” and the state of the printing paper P is “too stretched” (hereinafter referred to as “fourth state”) is assumed. In the fourth state, for example, the main control unit 1401 sets the conveyance speed of the fixing unit 500 to “slow”, the suction force of the fan 910 to “strong suction”, and the transfer guide unit 1303 in the first half portion and the second half portion. The holes may be opened to reduce the tension of the printing paper P. Thereby, even in the fourth state, it is possible to suppress the occurrence of a shock line for the printing paper P.

  Further, for example, a state in which the thickness of the printing paper P is “thick paper” (thick paper that does not cause deflection) and the state of the printing paper P is “stretching” (hereinafter referred to as “fifth state”). Suppose. In the fifth state, for example, the main control unit 1401 sets the conveyance speed of the fixing unit 500 to “slow”, the suction force of the fan 910 to “strong suction”, and the transfer guide unit 1303 with respect to the first half portion and the latter half portion. May be opened to reduce the tension of the printing paper P. Thereby, even in the fifth state, it is possible to suppress the occurrence of shock lines for the printing paper P.

  Furthermore, for example, a state where the thickness of the printing paper P is “ultra thin paper” (hereinafter referred to as “sixth state”) is assumed. In the sixth state, the main control unit 1401 sets the suction force of the fan 910 to “suction” when, for example, the front end of the print easy P enters the fixing unit 500 from the NIP unit, and the transfer guide unit 1303 is in the first half. It is also possible to open the intake hole only in a portion and suck the leading edge of the printing paper P toward the transfer guide portion 1303. As a result, even in the sixth state, it is possible to prevent the leading edge of the printing paper P from sticking to the intermediate transfer belt 701 and causing rubbing. In the sixth state, the main control unit 1401 sets the suction force of the fan 910 to “suction” when the rear end of the print easy P comes out of the NIP unit, and sets the suction hole only in the first half portion of the transfer guide unit 1303. In the open state, the trailing edge of the printing paper P may be sucked toward the transfer guide portion 1303. As a result, even in the sixth state, it is possible to prevent the trailing edge of the printing paper P from bouncing and coming into contact with the intermediate transfer belt 701 to cause rubbing.

  Furthermore, for example, in the setting for the main control unit 1401 (for example, user operation or setting on print data), the thickness of the printing paper P is “thick paper” and the detection result by the paper thickness sensor 320 is “thin paper” ( Hereinafter, it is referred to as “seventh state”). In the seventh state, for example, the main control unit 1401 sets the conveyance speed of the fixing unit 500 to “slow”, the suction force of the fan 910 to “strong suction”, and the suction guide holes in the first half part and the second half part of the transfer guide part 1303. May be opened to reduce the tension of the printing paper P. Thereby, even in the seventh state, it is possible to suppress the occurrence of shock lines with respect to the printing paper P.

  Furthermore, for example, in the setting for the main control unit 1401 (for example, user operation or setting on print data), the thickness of the printing paper P is “thin paper” and the detection result by the paper thickness sensor 320 is “thick paper” ( Hereinafter, it is referred to as “eighth state”). In the eighth state, for example, when the leading edge of the easy printing P enters the fixing unit 500 from the NIP unit, the main control unit 1401 sets the suction force of the fan 910 to “suction” and the first half of the transfer guide unit 1303. Only the intake hole may be opened and the leading edge of the printing paper P may be sucked toward the transfer guide portion 1303. As a result, even in the eighth state, it is possible to prevent the leading edge of the printing paper P from sticking to the intermediate transfer belt 701 and causing rubbing. In the eighth state, the main control unit 1401 “sucks” the suction force of the fan 910 when the rear end of the print easy P comes out of the NIP unit, and opens the intake hole only in the first half of the transfer guide unit 1303. As a state, the rear end of the printing paper P may be sucked toward the transfer guide portion 1303. As a result, even in the eighth state, it is possible to prevent the trailing edge of the printing paper P from bouncing and coming into contact with the intermediate transfer belt 701 to cause rubbing.

(A-3) Effects of First Embodiment According to the first embodiment, the following effects can be achieved.

  In the image forming apparatus 1 according to the first embodiment, the thickness and the bending of the printing paper P are less likely to be stable while the running (conveyance) of the printing paper P from the nip portion (transfer portion) to the fixing portion 500 is stabilized by suction control. Now, it is possible to control the slackness of the printing paper P regardless of the type. Further, by switching the suction position and strength depending on the position of the printing paper P, it is possible to prevent the shock line of thick paper, the blur due to splashing, the sticking of thin paper, etc., and to maintain the printing quality.

  Further, in the image forming apparatus 1 of the first embodiment, speed control at the fixing unit 500, switching control of the suction fan 910, switching of control based on the paper thickness, combined use or combination of switching of control based on the paper position, and the like are performed. ing. As a result, in the first embodiment, the control of the slack that is not stable due to the speed variation generated in the case of the control of only the speed switching caused by the rise in the internal temperature of the image forming apparatus 1 or the temperature variation of the fixing unit 500 is more accurate. It can be done well.

(B) Second Embodiment Hereinafter, a second embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

(B-1) Configuration and Operation of Second Embodiment The hardware configuration and functional configuration of the image forming apparatus 1 of the second embodiment are the same as those of the first embodiment described above with reference to FIGS. It can be described with reference to the drawings.

  Hereinafter, the difference between the second embodiment and the first embodiment will be described, and the description of common parts will be omitted. In the image forming apparatus 1 according to the second embodiment, a part of the operation of transporting the printing paper P when performing double-sided printing is different, and therefore, the difference will be mainly described below.

  First, the processing (the transport procedure of the printing paper P) when performing duplex printing in the second image forming apparatus 1 will be described with reference to FIG.

  In the image forming apparatus 1, when performing duplex printing, the discharge separator 901 is operated by a solenoid (not shown) and lifted upward in order to draw the printing paper P (1) into the duplex conveying unit 900. At this time, the printing paper P (1) is sent to the transport roller pair 902, and when the transport roller pair 902 transports a predetermined amount in the direction of arrow B, the driving is switched, and the transport roller pair 902 is driven in reverse. Is done. At this time, after the printing paper P (1) passes, the reverse separator 903 is lifted upward by an urging portion such as a spring (not shown), and the conveyance path in the arrow direction C is opened. Then, the printing paper P (1) is transported to the transport roller pair 905 by the reverse roller pair 902. Thereafter, the sheet is sequentially conveyed to the horizontal conveyance roller pair 306 and the refeed roller pair 307. At this time, when the re-feed sensor 915 detects that the printing paper P (1) has entered the printing paper P (1), the printing paper P (2) transported later passes before joining the transporting roller pair 305. It waits in a predetermined position until it does. When the printing paper P (2) is transported by the transport roller pair 305 and the writing sensor 306 detects the end of the passage of the printing paper P (2) and becomes OFF, after a predetermined time, the printing paper P (1) The paper is re-fed and conveyed by the re-feed roller pair 907 and sent to the conveying roller pair 305. Thereafter, the sheet (2) is conveyed downstream as in the first embodiment.

  The specific structure of the double-sided conveyance unit 900 is not limited to the above example, and various structures can be applied.

  Next, a printing operation (control processing by the main control unit 1401) in the image forming apparatus 1 of the second embodiment will be described with reference to the flowchart of FIG. In FIG. 16, the same steps as those in FIG. 15 are given the same step numbers.

  In FIG. 17, after printing of the first side of the printing paper P (1) is executed by the same processing as in the first embodiment, the printing paper P (1) is supplied into the double-sided conveyance unit 900, and the printing paper P The operation after the time point (1) is conveyed by the horizontal conveyance roller pair 906 in the double-side conveyance unit 900 and detected by the re-feed sensor 915 will be described.

  When the printing paper P (1) is detected by the re-feed sensor 915 (S46) and the printing paper P (1) is held and conveyed to the re-feeding roller pair 907 as it is (S47), it is not shown. The duplex conveyance motor is stopped (S48), and the printing paper P (1) is temporarily stopped at a predetermined position.

  Thereafter, when it is detected that the printing paper P (1) has passed through the writing sensor 306 (S49), a double-sided conveyance motor (not shown) is driven again after a predetermined time has passed (S50), and the printing paper P (1). Is conveyed by a predetermined amount (S51), and then the printing paper P (1) is conveyed again to a position where it is detected by the writing sensor (S52).

  When the re-feeded printing paper P (1) is conveyed by a predetermined amount M from the time of step S52 (S53), the shutter motor control unit 1408 instructed by the main control unit 1401 performs the shutter motor 1306. And the shutter plate 1303 is operated so as to open only the suction hole (front) 1302F side on the upstream side in the transport direction (S54).

  Further, the main control unit 1401 instructs the suction fan control unit 1410 to drive the suction fan 910 at full speed (S55).

  After that, the main control unit 1401 performs detection by the sag sensor 1301 as in the first embodiment (S25), and performs the same control as the first side for the second side of the printing paper P (1). (Including steps S26 to S30, S43 to S45, and S28).

  The second side of the printing paper P that has been fixed once and has lost moisture, or is being curled by heating during fixing while being transported on both sides, is downstream of the secondary transfer unit 750. When transporting, the leading edge of the sheet is more likely to stick to the intermediate transfer belt 701 than when transporting the first side. By performing the above-described control, it is possible to prevent the leading edge of the sheet from sticking to the intermediate transfer belt 701 by sucking strongly when the leading edge of the sheet passes through the guide portion 1302 during conveyance of the second surface.

  Further, the control is not limited to the control after step S25 in FIG. 17, but immediately before the trailing edge of the sheet passes through the secondary transfer unit 750, or when approaching the fixing unit 500, than the driving speed of the suction fan 910 on the first surface. The rotational speed may be increased. As a result, it is possible to prevent problems such as rubbing and the like even for the second side paper that is more likely to jump up than the state of the first side due to curling or the like.

(B-3) Effects of Second Embodiment According to the second embodiment, the following effects can be obtained in addition to the effects of the first embodiment.

In this way, in addition to the effects of the first embodiment, by adding control of a fan and an opening for suction during double-sided printing, it is possible to prevent paper that has been evaporated and cured, and curled paper. (C) Third Embodiment Hereinafter, a third embodiment of the image forming apparatus according to the present invention will be described in detail with reference to the drawings.

(C-1) Configuration and Operation of Third Embodiment The hardware configuration and functional configuration of the image forming apparatus 1 according to the third embodiment are the same as those in the first embodiment described above with reference to FIGS. It can be described with reference to the drawings.

  In the following, the difference between the third embodiment and the first embodiment will be described, and description of common parts will be omitted.

  17 is an explanatory diagram showing a multi-stage operation of the shutter plate 1303. FIG.

  FIG. 17A is a plan view of the shutter plate 1303.

  17B-1, FIG. 17C-1, and FIG. 17D-1 are cross-sectional views for each operating state of the shutter plate 1303 (a cross-sectional view taken along the line DD in FIG. 17A). ). 17B-2, FIG. 17C-2, and FIG. 17D-2 are cross-sectional views for each operating state of the shutter plate 1303 (the line E-E in FIG. 17A). It is a sectional view). In FIG. 17A, the DD line is located in the outer region AS-1 in the width direction of the shutter plate 1303, and the EE line is in the region AC on the center side in the width direction of the shutter plate 1303. positioned.

  As shown in FIG. 17, in the shutter hole 1303F and the shutter hole 1303R of the shutter plate 1303, the outer regions AS-1 and AS-2 in the sheet width direction with respect to the transport direction are opened small, and the center side The area AC is greatly opened (opened larger than the outer areas AS-1 and AS-2).

  In this embodiment, as shown in FIG. 17, the shutter plate 1303 has not only the conveyance direction (front-rear direction) but also the width direction (front-rear direction) according to the movement of the shutter plate 1303 about the shutter hole 1303F and the shutter hole 1303R. Open / close control is also possible for each region in the left-right direction). Specifically, for example, as shown in FIGS. 17B-1 and 17B-2, when the shutter plate 1303 is moved to the first position, the outer regions AS-1, AS-2, and The shutter hole 1303F and the shutter hole 1303R in both areas of the central area AC are opened (both opened). Further, as shown in FIGS. 17C-1 and 17C-2, when the shutter plate 1303 is moved to the second position, the outer regions AS-1, AS-2, and the central region AC. In this state, only the shutter hole 1303F in both areas is opened (only one side is opened). Further, as shown in FIGS. 17D-1 and 17D-2, when the shutter plate 1303 is moved to the third position, only the shutter hole 1303F in the area AC on the center side is opened ( Opening only on one side and opening only the central part of the paper width).

  As described above, in the image forming apparatus 1 of the third embodiment, the suction plate (rear) 1302R is provided only on the suction hole (front) 1302F side of the guide portion 1302 by operating the shutter plate 1303 in multiple stages. In addition to the opening pattern of only the side, when a narrow sheet is selected, an opening pattern in which only the central part in the sheet width direction is opened can be selected in order to more efficiently suck the sheet.

  In other words, in the image forming apparatus 1 of the present invention, the shutter plate 1303 is configured as shown in FIG. 17 described above, so that the area of the shutter plate 1303 is divided into a plurality of parts in the paper conveyance direction and / or the paper width direction. Suction control (presence / absence of suction and strength of suction) can be controlled for each region. In this embodiment, the shutter plate 1303 is divided into two in the sheet width direction (divided into the outer areas AS-1 and AS-2 and the central area AC), and further divided into two in the sheet conveyance direction (the shutter hole 1303F and the shutter). It is assumed that the suction control for each area is possible.

(C-3) Effects of Third Embodiment According to the third embodiment, the following effects can be achieved in addition to the effects of the first embodiment.

  In the third embodiment, the area of the shutter plate 1303 is divided into a plurality of areas not only in the sheet conveyance direction but also in the sheet width direction, and suction control (whether suction is performed and suction intensity) is performed for each of the divided areas. Yes. As a result, in the third embodiment, in addition to the effects of the first embodiment, the slack can be controlled more effectively by adding an opening pattern for suction even on the printing paper P having a different width. Can be done. For example, in the image forming apparatus 1, when the printing paper P to be printed is a paper having a narrow width such as a postcard, only the shutter hole in the area AC on the center side of the shutter plate 1303 is opened, so that the efficiency is improved. The printing paper P can be sucked as intended (strongly).

(D) Other Embodiments The present invention is not limited to the above-described embodiments, and may include modified embodiments as exemplified below.

  (D-1) In each of the above embodiments, an example of an image forming apparatus employing an intermediate transfer method (a toner image transfer method using an intermediate transfer belt) has been described. However, in the image forming apparatus of the present invention, Other transfer methods (for example, a direct transfer method) may be applied.

  (D-2) The member that forms the duct portion 1307 (the member that forms the paper conveyance path) may be formed by a single member or a plurality of members. As long as the holes (suction hole (front) 1302F, suction hole (rear) 1302R) provided in the duct portion 1307 can be ventilated, the shape is not limited. Further, the position of the hole provided in the duct portion 1307 is not limited to the position shown in each of the above embodiments, and a position where correction of the state of the printing paper P (for example, correction of slack) can be performed, Any shape is acceptable.

  (D-3) In each of the embodiments described above, the image processing method using four colors K, Y, M, and C is shown as the image forming unit in the image processing unit. The image processing method, the arrangement position, and the like are not limited to this.

  In each of the above embodiments, the example in which the image forming apparatus of the present invention is applied to a printer has been described. However, the present invention can be applied to various image forming apparatuses such as a copying machine, a multifunction machine, and a FAX.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, P ... Printing paper, 100 ... Paper tray, 102 ... Paper stacking board, 103 ... Lift-up lever, 104 ... Motor 200 ... Paper feeding part, 201 ... Lift detection part, 202 ... Pick-up roller, 203 ... Feed roller 204 ... retard roller 301 ... paper sensor 302 ... conveying roller pair 303 ... paper sensor 304,305 ... conveying roller pair 306 ... writing sensor 320 ... paper thickness sensor 400 ... image forming unit 401 ... photosensitive drum, 402 ... charge roller, 406, 406K, 406Y, 406M, 406C ... image forming unit, 500 ... fixing unit, 501 ... upper roller, 502 ... lower roller, 503a ... halogen lamp, 503b ... halogen lamp, 504a, 504b , 504c, 504d ... discharge roller pair, 60 ... multipurpose tray, 601 ... feed roller, 602 ... pick roller, 603 ... retard roller, 604 ... sheet stacking plate, 700 ... intermediate transfer belt unit, 701 ... intermediate transfer belt, 702 ... drive roller, 703 ... tension roller, 704 ... secondary transfer backup roller, 705 ... primary transfer roller, 706 ... belt cleaning unit, 707 ... secondary transfer roller, 900 ... double-sided conveyance unit, 901 ... discharge separator, 902 ... reverse roller pair, 903 ... reverse separator, 904... Transport guide section 905... Transport roller pair 906. Horizontal transport roller pair 907. Refeed roller pair 909. Transfer guide section 910. Suction fan 914. Retraction section 915. 916: Double-sided conveyance path, 1300: Sag detection unit, 1301 ... Sag sensor, 1 02 ... Transfer guide portion, 1302F ... Suction hole (front), 1302R ... Suction hole (rear), 1303 ... Shutter plate, 1303F ... Shutter hole (front), 1303R ... Shutter hole (rear), 1303 ... Transfer guide portion, 1304 ... Gear, 1305 ... Rack, 1306 ... Shutter motor, 1307 ... Duct section, 1400 ... Control section, 1401 ... Main control section, 1401 ... Operation panel, 1402 ... Interface section, 1403 ... Paper feed motor control section, 1404 ... Electromagnetic clutch Control unit, 1405 ... belt motor control unit, 1406 ... ID motor control unit, 1407 ... fixing motor control unit, 1408 ... shutter motor control unit, 1410 ... suction fan control unit, 1420 ... paper feed motor, 1421 ... electromagnetic clutch, 1422 ... belt motor, 1423 ... ID motor, 1 424 ... Fixer motor, 1425 ... Timer counter.

Claims (7)

An image forming unit for image formation;
A transfer unit that transfers the image formed by the image forming unit to a medium;
A fixing unit disposed on the downstream side of the transfer unit in the medium conveying direction and fixing an image transferred to the medium; a first suction unit disposed between the transfer unit and the fixing unit;
A second suction unit disposed between the first suction unit and the fixing unit;
A control unit for controlling suction in the first suction unit and suction in the second suction unit;
A first detector for detecting the type of medium being conveyed ;
A second detection unit that is disposed between the transfer unit and the fixing unit and detects sagging of the conveyed medium;
A third detection unit for detecting the medium to be conveyed,
The controller is
When the medium is thin paper, when the slack is detected by the second detection unit, the suction force of the first suction unit and the second suction unit is And control so as to be smaller than the suction force of the first suction part and the second suction part when slack is detected by the two detection parts,
An image forming apparatus that controls switching of suction between the first suction unit and the second suction unit based on a detection result of the third detection unit . A guide unit disposed between the transfer unit and the fixing unit, the guide unit including the first suction unit and the second suction unit;
A shutter provided movably with respect to the guide portion;
The controller is
By changing the position of the shutter relative to the guide portion, the suction of the first suction portion and the second suction portion is switched.
The image forming apparatus according to claim 1. The first suction part and the second suction part are:
The medium is sucked from the side opposite to the surface of the medium on which the image is transferred by the transfer unit.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The suction force of the first suction part and the second suction part before the third detection part detects sagging is:
Less than the suction force of the first suction part and the second suction part after the third detection part detects slack
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image forming apparatus according to claim 1, wherein the control unit switches a conveyance speed of the fixing unit based on a detection result of the third detection unit . A medium processing unit that supplies the medium after the image is fixed on the first surface by the fixing unit to the transfer unit again and transfers the image to the second surface;
The fixing unit fixes the image on the second surface on the medium having the image transferred on the second surface ;
The control unit includes the first suction unit and the second unit when the fixing unit fixes the image of the first surface on the medium and when the image of the second surface is fixed on the medium. The image forming apparatus according to claim 1, wherein the control content of the suction unit is changed. The second suction portion and the first suction section, the image formation according to the width direction of the medium, any of claims 1-6, characterized in that the area for sucking the medium is different apparatus.

Images