JP6577391B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and is suitable for application to, for example, an electrophotographic image forming apparatus (so-called printer).

  Conventionally, as an image forming apparatus, for example, a toner image is generated in an image forming unit and transferred to an intermediate transfer belt, and a sheet as a medium is conveyed by a conveyance unit, and a toner image is transferred from the intermediate transfer belt to the sheet in a secondary transfer unit. Has been proposed in which an image is printed by transferring the image and fixing the sheet by applying heat or pressure (for example, see Patent Document 1).

Japanese Patent Laying-Open No. 2006-12020 (FIG. 1)

  However, in the image forming apparatus having such a configuration, particularly when the paper is relatively thick, the periphery and the print density are within a narrow band-like range along the width direction at a position away from the end of the printed paper by a predetermined distance. There is a problem in that different areas are formed, and print quality may deteriorate.

  The present invention has been made in consideration of the above points, and intends to propose an image forming apparatus capable of improving the quality of an image formed on a thick medium.

In order to solve such a problem, the image forming apparatus of the present invention has a sandwiching body that sandwiches a sheet-shaped medium that has been cut in advance from both sides at a sandwiching location, and drives the sandwiching body to obtain a predetermined medium. A transport unit that transports along the transport path, a speed control unit that controls the driving speed of the clamping body in the transport unit, a detection unit that is provided on the transport path and detects the medium, and a thickness that detects the thickness of the medium The detection unit, the image forming unit that forms an image with the image carrier , and the downstream side of the sandwiching body on the conveyance path , and provided at a position where no other sandwiching body is provided between the sandwiching body , A transfer unit that transfers the image of the image carrier to the medium conveyed by the conveyance unit, and the speed control unit has a thickness of the medium detected by the thickness detection unit equal to or greater than a predetermined thickness threshold value. If the detection result of the medium by the detection unit Based, then controlled to increase the driving speed of the holding member when passing through the clamping portions in all end range is a range in which the hardness is increased pressure is applied during cutting of the ends of the medium, the thickness the thickness of the medium of When it is less than the threshold value, the driving speed of the sandwiching body is controlled to be constant .

The present invention increases the drive speed of the sandwiching body when the thickness of the medium is equal to or greater than the thickness threshold and the entire end range of the medium is the sandwiching position, and immediately before the medium is unwound from the sandwiching body. It can avoid that a conveyance speed falls and can convey at a substantially constant speed. Accordingly, it is possible to suppress or eliminate the deterioration of the image quality without expanding or contracting the image transferred to the medium by the transfer unit on the downstream side of the sandwiching body.

  According to the present invention, an image forming apparatus capable of improving the quality of an image formed on a thick medium can be realized.

1 is a schematic diagram illustrating a configuration of an image forming apparatus. It is a basic diagram which shows the structure of a middle conveyance part. It is a basic diagram which shows the structure of an image forming unit. 1 is a schematic block diagram illustrating a circuit configuration of an image forming apparatus. It is a basic diagram which shows conveyance of the paper by a conveyance roller pair. It is a basic diagram which shows the speed change when a shock line generate | occur | produces. It is a basic diagram which shows generation | occurrence | production of the shock line in the image on paper. It is a basic diagram which shows the speed change at the time of suppressing generation | occurrence | production of a shock line. It is a basic diagram which shows the relationship between the increase rate of the thickness and speed of a paper, and a shock line. 6 is a flowchart illustrating a sheet conveyance processing procedure. It is a basic diagram which shows the structure of the conveyance roller pair by other embodiment. It is a basic diagram which shows conveyance of the paper by other embodiment.

  Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[1. Configuration of image forming apparatus]
As shown in the left side view of FIG. 1, the image forming apparatus 1 is a color electrophotographic printer, and prints a desired color image on a paper P. In the image forming apparatus 1, various components are arranged inside a housing 2 formed in a substantially box shape. In the following, the right end portion in FIG. 1 is defined as the front surface of the image forming apparatus 1, and the vertical direction, the horizontal direction, and the front-back direction when viewed from the front surface are defined and described.

  The image forming apparatus 1 is configured to perform overall control by a control unit 3 provided in the housing 2. At the bottom of the housing 2, a paper feed cassette 4 that stores paper P that is a paper-like medium is provided. The paper feed cassette 4 is formed in a hollow rectangular parallelepiped shape, for example, and the upper surface is open. Incidentally, the paper P is a so-called cut paper cut into, for example, A4 size.

  A paper feeding unit 5 is provided at the front upper side of the paper feed cassette 4. The paper feeding unit 5 includes a plurality of rollers such as a pickup roller 5A, a feed roller 5B, and a retard roller 5C, a paper feed motor described later, and the like. The paper feeding unit 5 appropriately rotates each roller to separate only the uppermost one of the papers P stored in the paper feed cassette 4 from the other papers P, and feeds it obliquely upward to the front.

  A lower transport unit 6 that transports the paper P is provided on the front side or the upper side of the paper feed unit 5. The lower transport unit 6 forms a transport path W that causes the paper P delivered from the paper feeding unit 5 to advance forward and upward by a transport guide that guides the paper P, and then returns to the rear. The lower conveyance unit 6 is provided with a conveyance roller pair 7 composed of two conveyance rollers facing each other across the conveyance path W. The transport roller pair 7 feeds the paper P by rotating each transport roller by a driving force supplied from a transport motor described later and transporting the paper P upward along the transport path W. Delivered to the middle conveyance unit 13 located above the cassette 4. A paper sensor 8 for detecting the paper P is provided on the upstream side of the transport roller pair 7, that is, on the side near the paper feed cassette 4 on the transport path W.

  A multipurpose tray 11 is provided at a position protruding forward from the front side surface of the housing 2. The multipurpose tray 11 is formed in a thin plate shape in the vertical direction, and sheets P are stacked on the upper surface thereof. In the vicinity of the rear end of the multipurpose tray 11, a multipurpose paper feeding unit 12 is provided. The multipurpose sheet feeding unit 12 is configured in the same manner as the sheet feeding unit 5, and separates and feeds the sheets P stacked on the multipurpose tray 11 one by one and delivers them to the rear middle conveyance unit 13. Yes. The multi-purpose tray 11 is used, for example, when feeding a sheet P of a size or type that is not frequently used, or a sheet P that is not so bent as much as possible because of its relatively large thickness.

  As shown in the enlarged view of FIG. 2, the middle conveyance unit 13 forms a conveyance path W in a straight line along the front-rear direction by a conveyance guide 41 that guides the paper P. The middle conveyance unit 13 is provided with a conveyance roller pair 42 at a position on the rear side of the conveyance roller pair 7 and on the rear side of the multipurpose sheet feeding unit 12, and is separated from the conveyance roller pair 42 rearward by a predetermined interval. The conveyance roller pair 43 is provided at the location.

  The conveyance roller pair 42 includes a drive roller 42A disposed on the lower side of the conveyance path W and a driven roller 42B disposed on the upper side of the conveyance path W. Incidentally, in the middle conveyance unit 13, a plurality of conveyance roller pairs 42 are respectively arranged at positions separated in the left-right direction.

  The drive roller 42A is formed in a flat columnar or cylindrical shape having a central axis along the left-right direction and relatively short in the left-right direction, and is made of a material (for example, rubber) having a high friction coefficient on the outer peripheral portion thereof. A high friction member is attached. The driving roller 42A rotates in the direction of arrow R2 when a driving force is supplied from the transport motor 44 via the electromagnetic clutch 42C.

  Similarly to the drive roller 42A, the driven roller 42B is formed in a flat columnar or cylindrical shape having a central axis along the left-right direction and relatively short in the left-right direction. The driven roller 42B can be freely rotated by a support member (not shown) and can be freely displaced in the vertical direction, and is further urged downward by a urging member (not shown).

  As a result, the driven roller 42B is in contact with the peripheral side surface of the drive roller 42A in the vicinity of the lower end of the peripheral side surface on the conveyance path W. When the paper P is transported along the transport path W, the driven roller 42B is lifted upward according to the thickness of the paper P, and the paper P is sandwiched between the driving roller 42A. It becomes a state. The conveying roller pair 42 can transmit the driving force from the driving roller 42A to the paper P by rotating the driving roller 42A in such a state, and can convey the paper P forward. For convenience of description, the driving roller 42A and the driven roller 42B are also referred to as a sandwiching body below.

  Incidentally, the transport roller pair 7 of the lower transport unit 6 described above is composed of a drive roller 7A and a driven roller 7B, like the transport roller pair 42, and is driven from the transport motor 44 to the drive roller 7A via the electromagnetic clutch 7C. When the force is supplied, each roller is rotated and the paper P is conveyed.

  The transport roller pair 43 is configured in substantially the same manner as the transport roller pair 42, and includes a drive roller 43A and a driven roller 43B corresponding to the drive roller 42A and the driven roller 42B, respectively. However, the driving roller 43A is partially different from the driving roller 42A and does not incorporate an electromagnetic clutch, and the driving force from the transport motor 44 is directly transmitted.

  Further, the middle conveyance unit 13 includes paper sensors 45 and 46 that detect the presence or absence of the paper P in the conveyance path W on the slightly upstream side of the conveyance roller pair 42 and the conveyance roller pair 43, that is, on the front side where the paper P is conveyed. Is provided. Further, the middle conveyance unit 13 is provided with a paper thickness sensor 47 that detects the thickness of the paper P slightly downstream (that is, the rear side) of the conveyance roller pair 42.

  With this configuration, the middle transport unit 13 sequentially transmits the driving force by the transport roller pairs 42 and 43 to the paper P transported from the lower transport unit 6 or the multipurpose tray 11 (FIG. 1). Can be advanced backward along the conveyance path W. For convenience of explanation, hereinafter, the rear direction in which the sheet P is conveyed by the middle conveyance unit 13 is also referred to as a conveyance direction.

  A secondary transfer unit 14 is provided on the rear side of the middle conveyance unit 13. The secondary transfer unit 14 is arranged so that the conveyance path W is sandwiched from above and below by the lower secondary transfer roller 14A and the upper secondary transfer backup roller 14B, similarly to the conveyance roller pairs 42 and 43. .

  On the other hand, a belt traveling unit 20 is provided above the middle conveyance unit 13 and the secondary transfer unit 14. In the belt running unit 20, an intermediate transfer belt 23, which is a wide endless belt, is stretched around the tension roller 21, the drive roller 22, and the secondary transfer backup roller 14B. The intermediate transfer belt 23 is sandwiched between the secondary transfer roller 14 </ b> A and the secondary transfer backup roller 14 </ b> B of the secondary transfer unit 14 at the lower portion thereof, and is in contact with the conveyance path W of the paper P. . The drive roller 22 rotates when a driving force is supplied from the belt motor 24, and accordingly, the intermediate transfer belt 23 travels in the arrow B1 direction.

  An image forming unit 25 is provided above the belt running unit 20. The image forming unit 25 mainly includes four image forming units 26 (26Y, 26M, 26C, and 26K) that form images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). It is structured around. Above each image forming unit 26, toner cartridges 27 (27Y, 27M, 27C, and 27K) that store toner as an image carrier are disposed. In each image forming unit 26, an LED (Light Emitting Diode) head 28 (28Y, 28M, 28C and 28K) is provided.

  As shown in FIG. 3 in which a part of FIG. 1 is enlarged, the image forming unit 26 includes therein a toner container 31, a supply roller 32, a developing roller 33, a developing blade 34, a photosensitive drum 35, a charging roller 36, and a charging roller 36. A cleaning blade 37 and the like are provided. The supply roller 32, the developing roller 33, the photosensitive drum 35, and the charging roller 36 are all supplied with driving force from a drum motor 38.

  The toner storage unit 31 is located on the upper rear side of the image forming unit 26 and stores the toner supplied from the toner cartridge 27. Each of the supply roller 32, the developing roller 33, and the charging roller 36 is formed in a cylindrical shape with the central axis extending in the left-right direction, and rotates in the direction of the arrow R1, which is the clockwise direction in the drawing, around each central axis. Each peripheral side surface can be charged. The supply roller 32 is in contact with the developing roller 33 at its peripheral side surface.

  The developing blade 34 is made of a plate-like metal material that is long in the left-right direction, and its long side is brought into contact with the peripheral side surface of the developing roller 33 using elastic deformation. The photosensitive drum 35 is disposed directly under the LED head 28, and is formed in a cylindrical shape with the central axis extending in the left-right direction, like the supply roller 32, and rotates around the central axis. A photosensitive material is applied to the peripheral side surface of the photosensitive drum 35.

  The photosensitive drum 35 is in contact with the developing roller 33 and the charging roller 36 at the peripheral side surface. A primary transfer roller 29 is disposed adjacent to the lower side of the photosensitive drum 35. That is, the photosensitive drum 35 is in a state where the intermediate transfer belt 23 is sandwiched between the photosensitive drum 35 and the primary transfer roller 29. The primary transfer roller 29 can charge the peripheral side surface, and rotates in the arrow R1 direction.

  In the LED head 28, a plurality of LED elements are aligned in the left-right direction, and each LED element emits light with a light emission pattern based on the control of the control unit 3. Further, the mounting position of the LED head 28 is adjusted so that the light emitted from each LED element is focused on the surface of the photosensitive drum 35.

  When forming a toner image, the image forming unit 26 first rotates the photosensitive drum 35 in the direction of the arrow R2 by the driving force supplied from the drum motor 38 based on the control of the control unit 3 (FIG. 1). The supply roller 32, the developing roller 33, and the charging roller 36 are rotated in the direction of the arrow R1. The intermediate transfer belt 23 travels in the direction of the arrow B1 as the drive roller 22 is rotated by the driving force supplied from the belt motor 24 (FIG. 1).

  Further, the image forming unit 26 charges the supply roller 32, the developing roller 33, the developing blade 34, and the charging roller 36 by applying predetermined bias voltages, respectively. The supply roller 32 adheres the toner in the toner containing portion 31 to the peripheral side surface by this charging, and causes the toner to adhere to the peripheral side surface of the developing roller 33 by rotation. The rotating developing roller 33 removes excess toner from the peripheral side surface by the developing blade 34 so that the toner adheres in a uniform thin film having a predetermined layer thickness, and then the peripheral side surface is attached to the photosensitive drum. It is made to contact | abut to the surrounding side surface of 35.

  On the other hand, the charging roller 36 is in contact with the photosensitive drum 35 in a charged state, thereby uniformly charging the contact portion on the peripheral side surface of the photosensitive drum 35. The LED head 28 exposes the peripheral side surface of the photosensitive drum 35 by emitting light with a light emission pattern based on the image data supplied from the control unit 3 (FIG. 1). Thereby, an electrostatic latent image based on the image data is formed on the photosensitive drum 35 in the vicinity of the upper end on the peripheral side surface.

  Subsequently, as the photosensitive drum 35 rotates in the direction of the arrow R2, the portion where the electrostatic latent image is formed is sequentially brought into contact with the developing roller 33. As a result, the photosensitive drum 35 is transferred with toner from the peripheral side surface of the developing roller 33, and develops a toner image based on the electrostatic latent image on the peripheral side surface. Further, the photosensitive drum 35 rotates in the direction of the arrow R2 to advance the developed toner image to the lower end, that is, to a position where the intermediate transfer belt 23 contacts the primary transfer roller 29, and the primary transfer roller The toner image is transferred from the peripheral side surface to the intermediate transfer belt 23 by the charge of 29.

  As described above, the image forming unit 26 forms a toner image on the peripheral side surface of the photosensitive drum 35 based on the exposure pattern by the LED head 28, and transfers the toner image to the intermediate transfer belt 23. Incidentally, the length of the toner image along the running direction on the intermediate transfer belt 23 is equal to the length along the transport direction in a state where the toner image is transferred to the paper P later.

  The belt running unit 20 (FIG. 1) runs the intermediate transfer belt 23 to transfer the toner images of the respective colors formed by the respective image forming units 26 so as to be sequentially superimposed on the intermediate transfer belt 23, and this transfer is performed. The toner image is advanced to the secondary transfer unit 14. The secondary transfer unit 14 rotates the secondary transfer roller 14A in an appropriately charged state, thereby transferring the image data on the intermediate transfer belt 23 onto the paper P, and a fixing unit positioned behind the paper P. Proceed to 15.

  In the fixing unit 15, an upper roller 15 </ b> U and a lower roller 15 </ b> L, each having a central axis directed in the left-right direction and a built-in heater, are disposed so as to be in contact with each other above and below the conveyance path W. The fixing unit 15 fixes the toner image on the paper P by applying heat and pressure to the conveyed paper P while rotating the upper roller 15U in the direction of arrow R1 and rotating the lower roller 15L in the direction of arrow R2. The paper P is further advanced backward. As a result, an image based on the image data is formed on the paper P.

  A switcher 16 is disposed behind the fixing unit 15 so that the transport destination of the paper P is switched to the lower duplex printing unit 17 or the rear upper transport unit 18. The duplex printing unit 17 includes a combination of a plurality of conveyance guides that form a conveyance path for the paper P, a pair of conveyance rollers that convey the paper P, and a switch that switches the conveyance destination of the paper P. The duplex printing unit 17 switches the front and back by switching back the paper P received from the switch 16 and reversing the direction of travel, and again immediately before the pair of transport rollers 43 (FIG. 2) in the middle transport unit 13. At this point, the ink is joined to the transport path W.

  Similar to the lower conveyance unit 6 and the middle conveyance unit 13, the upper conveyance unit 18 includes a conveyance guide that guides the paper P and a plurality of conveyance roller pairs. The upper transport unit 18 forms a transport path W so that the sheet P delivered from the front fixing unit 15 at the lower end advances upward, and is sent forward in the vicinity of the upper end. Incidentally, a discharge sensor 18 </ b> S for detecting the presence or absence of the paper P is provided behind the switcher 16 in the upper transport unit 18.

  Further, on the front side of the upper end of the upper transport unit 18 and on the upper surface of the housing 2, a stacker unit 19 for stacking (stacking) the sheets P on which images are formed is provided. The upper transport unit 18 transports the paper P delivered from the fixing unit 15 upward along the transport path W and discharges the paper P forward, thereby accumulating the paper P in the stacker unit 19.

  In this way, the image forming apparatus 1 transports the paper P along the transport path W by the intermediate transport unit 13 and the like, and the toner image formed on the intermediate transfer belt 23 by the image forming unit 25 is transferred to the secondary transfer unit 14. An image is formed on the paper P by transferring it to the paper P and further fixing it.

  Next, the circuit configuration of the image forming apparatus 1 will be described with reference to the block diagram of FIG. As described above, the image forming apparatus 1 is configured to perform overall control by the control unit 3. The control unit 3 is configured around a main control unit 51. The main control unit 51 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a flash memory, and the like (not shown). The CPU of the main control unit 51 executes various processes related to image printing by reading various programs from the ROM or flash memory, developing them in the RAM, and executing them. The main control unit 51 includes a timer counter 51T that measures time.

  An operation panel 61 and an interface unit 62 are connected to the main control unit 51. The operation panel 61 is constituted by a touch panel in which a liquid crystal panel for displaying information and a touch sensor for receiving a touch operation are integrated, a physical button, and the like, and presents various information to the user. Various operations by the user are accepted.

  The interface unit 62 conforms to a standard such as a wired LAN (Local Area Network) conforming to a standard such as IEEE (Institute of Electrical and Electronics Engineers) 802.3u / ab or IEEE 802.11a / b / g / n / ac. The wireless LAN performs communication processing, and receives image data, a print instruction, and the like from a host device (not shown).

  Further, the control unit 3 includes a conveyance motor control unit 52, a paper feed motor control unit 53, an electromagnetic clutch control unit 54, a belt motor control unit 55, a drum motor control unit 56, and a fixing motor control unit 57. The carry motor control unit 52 is connected to the carry motor 44.

  The carry motor 44 is, for example, a two-phase excitation pulse motor. When a rectangular wave current is supplied from the carry motor control unit 52 to the windings of a plurality of phases with a phase shift, the transfer motor 44 according to the order of shifting the phases. When the rotation direction is switched and the period of the rectangular wave (that is, the clock frequency) is changed, the rotation speed is changed. The output of the conveying motor 44 is transmitted to the driving roller 43A (FIG. 2) of the conveying roller pair 43 via a gear (not shown), and the driving roller 42A via the electromagnetic clutches 42C and 7C of the conveying roller pair 42 and 7. And 7A (FIG. 2), respectively.

  That is, the transport motor controller 52 controls the transport motor 44 to adjust the rotational speed of the drive roller 43A and the like (hereinafter also referred to as drive speed), that is, the transport speed of the paper P in the middle transport section 13. Can be adjusted.

  The paper feed motor control unit 53 controls the paper feed motor 5M. The paper feed motor 5M is configured in the same manner as the transport motor 44, and transmits driving force to the pickup roller 5A, the feed roller 5B, and the retard roller 5C of the paper feeding unit 5 (FIG. 1) via an electromagnetic clutch (not shown). And rotate.

  The belt motor control unit 55 controls the belt motor 24 of the belt running unit 20 to run or stop the intermediate transfer belt 23 and adjust its running speed. The drum motor control unit 56 controls the drum motor 38 to rotate or stop the photosensitive drum 35 and the like of the image forming unit 26. The fixing motor control unit 57 controls the fixing motor 15M of the fixing unit 15 to rotate or stop the upper roller 15U and the lower roller 15L, respectively.

  In this way, the control unit 3 controls the conveyance motor 44 by the conveyance motor control unit 52 provided therein, thereby conveying the conveyance roller pairs 42 and 43 of the middle conveyance unit 13 (FIG. 2) and the conveyance of the lower conveyance unit 6. The paper P is conveyed by the roller pair 7 and its speed can be adjusted.

[2. Conveying paper by the middle conveyance unit]
Next, when the sheet P is relatively thick, for example, when the thickness is 0.2 [mm] or more, the conveyance of the sheet P by the middle conveyance unit 13 and the transfer of the toner image in the secondary transfer unit 14 will be described. To do.

[2-1. Generation of shock line]
First, it is assumed that the conveyance motor control unit 52 (FIG. 4) of the control unit 3 controls the conveyance motor 44 (FIG. 2) to rotate at a constant speed. In this case, it is expected that the driving roller 43A of the conveying roller pair 43 to which the driving force is transmitted from the conveying motor 44 rotates at a constant rotational speed, and the paper P is conveyed at a constant conveying speed.

  As described above, the conveyance roller pair 43 (FIG. 2) of the middle conveyance unit 13 is driven by the conveyance motor 44 with the sheet P sandwiched between the lower drive roller 43A and the upper driven roller 43B. Is transmitted to the driving roller 43A and rotated, thereby conveying the sheet P along the conveying path W to the secondary transfer portion 14 on the rear side.

  By the way, in the image forming apparatus 1, if the traveling speed of the intermediate transfer belt 23 and the transport speed of the paper P are different, the image transferred to the paper P in the secondary transfer portion 14 expands and contracts in the front-rear direction, and the image quality is increased. May deteriorate. Therefore, in the image forming apparatus 1, it is necessary to control the traveling speed of the intermediate transfer belt 23 and the conveyance speed of the paper P with high accuracy.

  Therefore, it is desired that the middle conveying unit 13 rotates the driving roller 43A in the conveying roller pair 43 at a desired rotational speed and reliably transmits the driving force of the driving roller 43A without slipping on the paper P. Therefore, in the conveying roller pair 43, the driven roller 43B is urged with a relatively strong force with respect to the driving roller 43A.

  Accordingly, as shown in FIG. 5A in which a part of FIG. 2 is enlarged, the conveyance roller pair 43 is driven by the driving roller 43A and the upper driven roller 43B of the paper P when the paper P is relatively thick. The sandwiched portion is deformed so as to be slightly crushed.

  This is because the paper P is an aggregate of fibrous members and is formed as a sheet of paper with a gap between the fibers, and when an external force is applied, each fiber deforms to narrow the gap. It is presumed that the cause is to do. Incidentally, this deformation is elastic deformation, and the amount of deformation is extremely small. For this reason, the distance between the driving roller 43A and the upper driven roller 43B is slightly narrower than the thickness of the sheet P in a state where no pressure is applied, that is, the original thickness of the sheet P.

  For convenience of explanation, in the following, a virtual line along the vertical direction connecting the rotation center points of the driving roller 43A and the upper driven roller 43B is referred to as a sandwiching line 43L, and the lowermost side of the driven roller 43B. That is, the portion that intersects the sandwiching line 43L is referred to as a sandwiching location 43BH.

  When the location where the sheet P is held by the conveyance roller pair 43 moves to the end side as it is conveyed backward, the sheet P is deformed so that the newly held location is crushed and is no longer held. The part returns to its original shape by an elastic action or the like. In other words, it can be considered that the sheet P is slightly thinner than the original thickness at the portion sandwiched between the conveyance roller pair 43.

  Here, since the sheet P is a cut sheet as described above, each edge is cut at the time of manufacture. When the paper P is cut, pressure is applied to the periphery of the edge. As a result, the paper P is changed to a state in which the gap between the fibers is slightly clogged in the vicinity of the edge, and the hardness is increased and “hard” compared to other portions.

  For this reason, as shown in FIG. 5B, the conveying roller pair 43 sandwiches the vicinity of the end of the paper P, that is, a range of about 5 to 10 mm from the end (hereinafter referred to as the end range EA). In this case, the sheet cannot be elastically deformed until just before that, and the distance between the driving roller 43A and the upper driven roller 43B needs to be increased to the original thickness of the sheet P. In other words, the driven roller 43B needs to run over the end range EA in which the thickness of the paper P is slightly larger than that of the other portions.

  Here, in the middle conveyance unit 13, as shown in a schematic waveform diagram in FIG. 6A, a speed (hereinafter referred to as a conveyance control speed) instructed from the conveyance motor control unit 52 to the conveyance motor 44 is constant. The speed is V1. In spite of this, in the intermediate conveyance unit 13, the driven roller 43B is “ridden” after the time point T1 when the end range EA of the paper P reaches the clamping portion 43BH of the driven roller 43B, that is, the clamping line 43L. The rotational speed of 43B and the drive roller 43A will fall. As a result, the conveyance speed of the paper P is lowered to a speed V2 lower than the speed V1, as shown in FIG. 6B corresponding to FIG.

  At this time, in the secondary transfer portion 14 (FIG. 2), the intermediate transfer belt 23 on which the toner image is transferred travels at the speed V1, which is the original travel speed, while the transport speed of the paper P temporarily changes to the speed V2. It will decline. Accordingly, as schematically shown in FIG. 7, the secondary transfer unit 14 transfers the toner image onto the paper P so as to be compressed in the transport direction (that is, the front-rear direction), and the density is originally increased. As a result, a high concentration region AH is also formed.

  Further, in the conveying roller pair 43, the sheet P is conveyed by the action of the urging force acting on the driven roller 43B at the time T2 when the pinching portion 43BH of the driven roller 43B, that is, the holding line 43L passes through the end PE of the sheet P. It is flipped backwards that is the direction. Here, since the paper P is relatively thick, it acts like a rigid body, and is ejected rearward as a unit including the portion sandwiched by the secondary transfer unit 14 without causing bending. At the same time, in the secondary transfer unit 14, a force is applied to the sheet P from the secondary transfer roller 14 </ b> A to return the lowered transport speed to the original speed V <b> 1.

  For this reason, as shown in FIG. 6 (B), in the middle transport unit 13, the transport speed of the paper P is set higher than the original speed V1 in a short period of time T3 when a slight time has elapsed from the time T2. The speed is increased to a higher speed V3, that is, higher than the traveling speed of the intermediate transfer belt 23. As a result, as shown in FIG. 7, the secondary transfer unit 14 transfers the toner image onto the paper P as if it was extended in the transport direction (that is, the front-rear direction), and the density thereof was lowered below the original level. The low concentration area AL is formed.

  Thereafter, the secondary transfer unit 14 expands and contracts the toner image in the front-rear direction from the intermediate transfer belt 23 to the paper P while transporting the paper P at the speed V1, which is the original transport speed, by the secondary transfer roller 14A and the like. And transfer at the correct ratio.

  As described above, in the intermediate transport unit 13 and the secondary transfer unit 14, when the end range EA of the relatively thick paper P is sandwiched by the transport roller pair 43, the transport motor 44 is driven at a constant rotational speed corresponding to the constant speed V 1. In spite of being controlled to rotate at, the conveyance speed of the paper P may be temporarily changed. Such a change in the speed of the sheet P can be regarded as if a force like “stickiness” is generated between the conveying roller pair 43 and the sheet P. At this time, on the paper P, a high density area AH and a low density area AL may be formed in the transferred toner image. For convenience of explanation, hereinafter, the high concentration region AH and the low concentration region AL are collectively referred to as a shock line SL.

  Incidentally, when the thickness of the sheet P is relatively thin, the deformation degree of the sheet P becomes relatively small in the intermediate conveyance unit 13 at the holding line 43L by the conveyance roller pair 43 (FIG. 5A). As a result, in the intermediate conveyance unit 13, it is not necessary for the driven roller 43 </ b> B to run on the end range EA, and the shock line SL hardly occurs in the transferred image.

[2-2. Eliminate shock line]
Therefore, in the image forming apparatus 1, when an image is printed on a relatively thick paper P, the shock line SL (FIG. 7) is eliminated by appropriately controlling the transport speed of the paper P in the middle transport unit 13. It was supposed to be.

  That is, the control unit 3 of the image forming apparatus 1 controls the conveyance motor 44 from the conveyance motor control unit 52 as shown in FIG. 8A corresponding to FIG. At time T1 when the line 43L reaches the end range EA of the paper P, the conveyance control speed is changed from the speed V1 to the higher speed V5.

  Incidentally, the control unit 3 stores in advance a distance LS (FIG. 5A) from the detection position of the paper P in the paper sensor 46 to the holding line 43L in the transport roller pair 43. For this reason, the control unit 3 holds the paper P by the calculation using the speed V1 of the paper P, the elapsed time from the time when the leading edge PS of the paper P is detected by the paper sensor 46, and the distance LS. The distance from the tip PS in the portion passing through the line 43L can be accurately grasped.

  Here, in order to find an appropriate value of the speed V5, different paper P is used with thicknesses ranging from 0.2 [mm] to 0.65 [mm] in increments of 0.05 [mm], and the conveyance control speed is set to speed. An evaluation test for evaluating the appearance state of the shock line SL (FIG. 7) was performed for each case of increasing in increments of 1 [%] from 1 [%] to 5 [%] with respect to V1.

  In this evaluation test, the appearance state of the shock line SL was visually evaluated. The evaluation of the shock line SL was made in three stages: whether the shock line SL could be suppressed satisfactorily, whether the shock line SL could be suppressed to some extent, or whether the shock line SL appeared. Here, when the shock line SL in the paper P can be satisfactorily suppressed, this means that the transport speed of the paper P can be substantially maintained at a constant speed V1 as shown in FIG. 8B.

  As a result of this evaluation test, the evaluation results summarized in the table format in FIG. 9 were obtained. From FIG. 9, it is understood that at least the shock line SL can be suppressed to some extent when the conveyance control speed is increased from the speed V1 in the range of 1 to 3%. Further, from FIG. 9, when the conveyance control speed is increased from the speed V <b> 1 in the range of 2 to 3 [%] especially for the paper P having a thickness of 0.35 [mm] to 0.65 [mm]. In addition, it can be seen that the shock line SL can be satisfactorily suppressed.

  Incidentally, in the image forming apparatus 1, in order to normally print the next sheet P, as shown in FIG. 8A, it is necessary to reduce the conveyance control speed to the original speed V1 at time T4. . This time T4 is a time when a sufficient time has passed for the end PE of the paper P to pass through the pinching line 43L of the conveying roller pair 43 after the time T1, and more than when the next paper P is transported. It is set to be before.

  In the image forming apparatus 1, the thickness of the paper P can be detected by the paper thickness sensor 47 (FIG. 2) provided in the middle conveyance unit 13. For this reason, the control unit 3 acquires the detection result from the paper thickness sensor 47, thereby recognizing the thickness of the paper P being conveyed by the middle conveyance unit 13, and executing processing corresponding to the thickness. Can do.

  Therefore, when printing on the paper P having a thickness of 0.2 [mm] or more, the control unit 3 of the image forming apparatus 1 controls the transport motor 44 so that the pinching line 43L of the transport roller pair 43 becomes the paper P. At the time point T1 (FIG. 8A) reaching the terminal range EA, the conveyance control speed is increased by 2 [%] from the speed V1. In addition, the control unit 3 decreases the transport control speed to the original speed V1 at a time T4 when a predetermined time has elapsed from the time T1. Thus, the image forming apparatus 1 can maintain the conveyance speed of the paper P at a constant speed V1 as shown in FIG. 8B, and can suppress the shock line SL (FIG. 7).

[2-3. Transport processing procedure]
Next, a specific sheet conveyance processing procedure when an image is printed on the sheet P in the image forming apparatus 1 will be described with reference to a flowchart of FIG. Here, settings relating to the paper P (hereinafter referred to as paper settings) such as the size and type of the paper P set by the user in the paper feed cassette 4 or the multipurpose tray 11 are registered in advance, and the main control unit in the control unit 3 is registered. It is assumed that the data is stored in the flash memory 51.

  When the control unit 3 (FIG. 4) of the image forming apparatus 1 acquires image data and a print instruction thereof from a host device (not shown) such as a personal computer via the interface unit 62, the main control unit 51 uses a flash memory or the like. The paper transport program is read out and executed, thereby starting the paper transport processing procedure RT1 (FIG. 10), and proceeds to step SP1.

  Incidentally, the control unit 3 executes a predetermined image forming program in parallel with the sheet conveyance processing procedure RT1, and appropriately controls the image forming unit 25, the belt running unit 20 (FIG. 1), and the like, thereby the intermediate transfer belt 23. A toner image based on the image data is formed on the top, and the toner image reaches the secondary transfer unit 14.

  In step SP1, the control unit 3 reads the paper setting from the flash memory in the main control unit 51, and proceeds to the next step SP2. In step SP2, the control unit 3 starts driving each motor such as the conveyance motor 44 by the conveyance motor control unit 52 and the like, and proceeds to the next step SP3.

  In step SP3, the control unit 3 feeds and transports the paper P by the paper feeding method designated by the host device in accordance with the print instruction, and the leading end thereof is detected by the transport roller pair 42 (FIG. 2), that is, by the paper sensor 45. To the next step SP4. At this time, when the paper feed cassette 4 is designated as the paper feed source of the paper P, the control unit 3 feeds the uppermost sheet P from the paper feed cassette 4 by the paper feed unit 5 and transports it downward. The section 6 is transported along the transport path W, and the leading end thereof reaches the transport roller pair 42. Further, when the multipurpose tray 11 is designated as the paper P feeding source, the control unit 3 feeds the uppermost sheet P from the multipurpose tray 11 by the multipurpose paper feeding unit 12 and sends it to the rear. Then, the front end is made to reach the conveying roller pair 42.

  In step SP4, the control unit 3 detects the thickness of the paper P by the paper thickness sensor 47 (FIG. 2) while continuing to transport the paper P along the transport path W by the transport roller pair 42, and next step SP5. Move on. In step SP5, the control unit 3 determines whether the detected paper P is a thick paper, specifically, whether the thickness is 0.2 [mm] or more. If a positive result is obtained here, this means that a shock line SL (FIG. 7) may be generated when the paper P is printed, and this needs to be suppressed. At this time, the control unit 3 moves to the next step SP6.

  In step SP6, the control unit 3 continuously rotates the transport motor 44 at a constant speed, thereby rotating each roller of the transport roller pair 42 to transport the paper P at the speed V1 (FIG. 8). Control goes to step SP7. In step SP7, the control unit 3 determines whether or not the leading end PS of the paper P is detected by the paper sensor 46 (FIG. 2). If a negative result is obtained here, the control unit 3 returns to step SP6 again, and waits for the leading edge PS of the paper P to reach the position of the paper sensor 46, that is, immediately before the conveying roller pair 43.

  On the other hand, if an affirmative result is obtained in step SP7, this means that the leading edge PS of the paper P has reached the detection position of the paper sensor 46, that is, immediately before the transport roller pair 43. This indicates that the transport amount (that is, the transported length) of the paper P can be grasped. At this time, the control unit 3 moves to the next step SP8.

  In step SP8, the control unit 3 rotates each roller of the pair of transport rollers 43 for a predetermined transport time TC1 to transport the paper P at the speed V1 (FIG. 8), so that the end range EA of the paper P, ie, The portion immediately before the terminal PE is made to reach the holding line 43L (FIG. 5) of the pair of conveying rollers 43, and the process proceeds to the next step SP9.

  The time point when the conveyance time TC1 elapses after the leading edge PS of the paper P is detected by the paper sensor 46 and the process proceeds to step SP9 corresponds to the time point T1 in FIG. Incidentally, the control unit 3 acquires the length along the transport direction based on the size of the paper P set by the user, calculates the distance from the leading end PS to the end range EA, and stores it in advance. An appropriate transport time TC1 is calculated based on the distance LS (FIG. 5A) and the speed V1.

  In step SP9, the control unit 3 controls the transport motor 44 by the transport motor control unit 52, thereby increasing the transport control speed by 2 [%] from the speed V1 to the speed V5 (FIG. 8A). Control goes to step SP10. Thus, the control unit 3 can maintain the sheet speed of the sheet P at the speed V1 when the end range EA of the sheet P is sandwiched between the conveyance roller pair 43 (FIG. 5B) (FIG. 8). (B)).

  In step SP10, the control unit 3 rotates the conveyance roller pair 43 as it is for a predetermined time until the time T4 (FIG. 8A) with the conveyance control speed being the speed V5. After the PE is advanced further forward than the holding line 43L of the transport roller pair 43, the process proceeds to the next step SP11. This indicates that the paper P has been fed backward from the conveyance roller pair 43.

  In step SP11, the control unit 3 controls the transport motor 44 by the transport motor control unit 52, thereby reducing the transport control speed from the speed V5 and returning it to the original speed V1 (FIG. 8A). Move to SP12. Thereby, the conveyance roller pair 43 can convey the sheet P at an appropriate speed V1 when the next sheet P is conveyed.

  In step SP12, the control unit 3 continuously rotates the respective motors such as the transport motor 44 for a predetermined time, thereby appropriately rotating the secondary transfer roller 14A and the transport roller pairs of the respective units to feed the paper P to the transport path W. Then, the process proceeds to the next step SP16. Incidentally, after the toner image is fixed on the paper P by the fixing unit 15, the control unit 3 transports the paper P along the transport path W by the upper transport unit 18 (FIG. 1), and further stacker unit 19 (FIG. 1). ).

  On the other hand, if a negative result is obtained in step SP5, this indicates that the paper P is relatively thin and there is no possibility of the shock line SL occurring. At this time, the control unit 3 performs the same processing as the above-described steps SP6 and SP7 in the next step SP13 and the next step SP14, respectively, so that the leading edge of the paper P is positioned at the position of the paper sensor 46, that is, the transport roller pair. After reaching the position just before 43, the process proceeds to step SP15.

  In step SP15, the control unit 3 rotates each roller of the transport roller pair 43 over a predetermined transport time TC2 to transport the paper P at the speed V1, thereby feeding the paper P backward from the transport roller pair 43. Then, the process proceeds to the next step SP16. Incidentally, the control unit 3 is based on the length along the transport direction of the paper P obtained based on the size of the paper P preset by the user, the distance LS stored in advance, and the speed V1. An appropriate transport time TC2 is calculated.

  In step SP <b> 16, the control unit 3 determines whether or not to print on the next paper P by referring to the print instruction acquired from the host device. If an affirmative result is obtained here, the control unit 3 moves to the next step SP17, and similarly to step SP3, feeds and conveys the next sheet P by the sheet feeding method designated by the upper apparatus by the print instruction, The leading end is made to reach the conveyance roller pair 42 (FIG. 2), the process returns to step SP4 again, and a series of processes is repeated.

  On the other hand, if a negative result is obtained in step SP16, the control unit 3 moves to step SP18, and controls and stops each motor such as the conveyance motor 44 by the conveyance motor control unit 52 and the like, thereby causing each conveyance roller pair to be stopped. After stopping, the process proceeds to the next step SP19, and the paper transport processing procedure RT1 is completed.

[3. Effect]
In the above configuration, when the sheet P is a thick sheet, the control unit 3 of the image forming apparatus 1 controls the conveyance motor 44 from the conveyance motor control unit 52 (FIG. 4), thereby conveying the conveyance roller pair 43 (FIG. 5). Thus, the conveyance control speed is increased by 2 [%] at the time point T1 (FIG. 8) at which the end range EA of the paper P, that is, the portion immediately before the end PE is sandwiched (FIG. 8A).

  For this reason, the image forming apparatus 1 temporarily decreases in speed when the end range EA of the paper P passes through the holding line 43L of the pair of transport rollers 43, which may occur when the transport control speed is maintained at a constant speed V1. 6 (B)) can be appropriately canceled and the sheet can be conveyed at a substantially constant speed V1 (FIG. 8 (B)). As a result, the image forming apparatus 1 can satisfactorily suppress or eliminate the occurrence of the shock line SL (FIG. 7) that may have occurred due to a temporary change in the speed of the paper P.

  In particular, the image forming apparatus 1 evaluates the occurrence state of the shock line SL when the thickness of the paper P and the increase width of the conveyance control speed are variously changed (FIG. 9), and then the paper P is 0.2. When it is [mm] or more, the increase width of the conveyance control speed is set to 2 [%]. Thereby, the image forming apparatus 1 can suppress the shock line SL to some extent if the thickness of the paper P is 0.2 to 0.3 [mm], and further the thickness of the paper P is 0.35 to 0.6 [mm]. mm], the shock line SL can be satisfactorily suppressed.

  Further, the image forming apparatus 1 detects the thickness of the paper P by the paper thickness sensor 47, and when the thickness is 0.2 [mm] or more, that is, when the paper P is a thick paper, the image forming apparatus 1 is transported. While the control speed is temporarily increased, if the thickness of the paper P is less than 0.2 [mm], that is, if it is thin paper, the transport control speed is kept constant. (FIG. 10). As a result, the image forming apparatus 1 can appropriately avoid deterioration in image quality caused by changing the conveyance control speed even in the case of thin paper that does not inherently generate a shock line SL.

  By the way, in the image forming apparatus 1, the distance LS (FIG. 5) from the paper sensor 46 to the holding line 43L of the conveying roller pair 43 is relatively short. In addition, in the paper P, the length along the front-rear direction of the end range EA is inherently extremely short, such as 5 to 10 [mm]. Therefore, in the image forming apparatus 1, the time difference between the time point when the paper sensor 46 detects the end PE of the paper P and the time point when the end range EA reaches the pinching line 43L is extremely short. That is, if the control unit 3 uses the time point when the paper sensor 46 detects the end PE of the paper P as a reference, the control unit 3 may not be in time for the calculation process at the time when the end range EA reaches the holding line 43L, There is also a possibility that the range EA has reached the holding line 43L.

  Therefore, the image forming apparatus 1 sets the end range EA to the holding line 43L of the conveyance roller pair 43 based on the time point when the leading end PS of the paper P is detected, not when the paper sensor 46 detects the end PE of the paper P. The arrival time point T1 is calculated, and the conveyance control speed is changed in accordance with this (FIG. 10, step SP8). As a result, the image forming apparatus 1 can accurately calculate the time T1 at which the end range EA reaches the holding line 43L at a time sufficiently earlier than the end range EA actually reaches the holding line 43L. The conveyance control speed can be increased at an appropriate timing without causing occurrence.

  According to the above configuration, when the paper P is a thick paper, the control unit 3 of the image forming apparatus 1 holds the end range EA of the paper P by the conveyance roller pair 43 (FIG. 5) (T1 (FIG. 8)). In addition, the conveyance control speed is increased by 2 [%] (FIG. 8A). As a result, the image forming apparatus 1 appropriately cancels the temporary speed reduction (FIG. 6B) when the end range EA of the paper P passes through the holding line 43L of the pair of conveying rollers 43, and the substantially constant speed V1. (FIG. 8B). As a result, the image forming apparatus 1 can satisfactorily suppress or eliminate the occurrence of the shock line SL (FIG. 7).

[4. Other Embodiments]
In the above-described embodiment, the case where the increase rate of the conveyance control speed at the time T1 (FIG. 8A) is set to 2 [%] when the paper P is a thick paper has been described. However, the present invention is not limited to this, and other values such as 3 [%] may be used. The point is that the value is within a range in which the shock line SL can be satisfactorily suppressed as shown in FIG.

  In the above-described embodiment, the case has been described in which the threshold for determining whether the paper P is a thick paper or a thin paper in the paper thickness sensor 47 is 0.2 [mm]. However, the present invention is not limited to this, and other values such as 1.5 [mm] and 2.5 [mm] may be used. In short, the lower limit value at which the shock line SL appears when the conveyance control speed is kept constant may be set as the threshold value. Furthermore, for example, when the increase rate of the appropriate conveyance control speed differs according to the paper thickness, a plurality of threshold values are set to divide the paper thickness into a plurality of stages, and the conveyance control speed is increased for each divided paper thickness. The increase rate may be changed. Alternatively, for example, when a decrease in image quality is not recognized even when the conveyance control speed is increased for a relatively thin paper P, the paper thickness sensor 47 is omitted, and the conveyance control is performed at time T1 regardless of the thickness of the paper P. The speed may be increased.

  Further, in the above-described embodiment, the end range EA of the paper P is set to a range of 5 to 10 [mm] from the end PE (FIG. 5B), and the end range EA defines the holding line 43L of the conveying roller pair 43. The case where the conveyance control speed is increased with time T1 (FIG. 8) as the time of passing has been described (FIG. 8). However, the present invention is not limited to this. For example, a virtual front end line 43LF (FIG. 5B) extending in the vertical direction passing through the front end 43AF located on the most front side (that is, the upstream side) of the drive roller 43A is assumed. In this case, the time point T1 may be the time when the end PE of the paper P reaches the rear side of the front end portion 43AF. In this case, the conveyance control speed may be increased while the terminal PE of the paper P passes through at least the range from the front end line 43LF to the pinching line 43L.

  Further, in the above-described embodiment, the case where the transport control speed is decreased and returned to the original speed V1 at the time T4 when a predetermined time has elapsed from the time T1 has been described (FIG. 8A). However, the present invention is not limited to this. For example, when the end PE of the paper P passes through the pinching line 43L of the conveyance roller pair 43, the original speed V1 may be restored. As a result, even if the interval until the next sheet P is transported due to a transport accuracy problem or the like in the upstream lower transport unit 6 or the like becomes relatively short, the next sheet P is moved to the original speed. It can be conveyed by V1. In short, it is only necessary to return to the original speed V1 after the end PE of the paper P passes through the pinching line 43L of the conveyance roller pair 43 and before the next paper P arrives.

  Alternatively, for example, like the conveying roller pair 143 shown in FIG. 11, the high friction member 143AR provided on the outer peripheral portion of the driving roller 143A is relatively soft and crushes the portion that contacts the paper P biased by the driven roller 43B. You may make it deform | transform. In this case, the time T1 may be the time when the end PE of the paper P passes through the most upstream (ie, front) portion 143ARF of the portion of the high friction member that deforms and contacts the paper P. The conveyance control speed may be increased while the terminal PE is in contact with the high friction member.

  Further, in the above-described embodiment, the case where the paper P is sandwiched and conveyed by the rotating drive roller 43A and the driven roller 43B has been described (FIG. 5A). However, the present invention is not limited to this, and the sheet P may be nipped and conveyed by the rotating roller 243 and the belt 251 of the conveying belt unit 250 as in the middle conveying unit 213 shown in FIG. In this case, for example, a roller 253 may be disposed at a position facing the roller 243 in the transport belt unit 250 so that a sufficient force is applied to the paper P so as to be held.

  Furthermore, in the above-described embodiment, the case where the transport motor 44 (FIG. 2) is a two-phase excitation pulse motor has been described. However, the present invention is not limited to this, and may be a DC (Direct Current) motor, for example. The DC motor can adjust the rotation speed by changing the voltage applied to the electrodes, and can switch the rotation direction by changing the polarity (that is, positive or negative) of the voltage applied to each electrode. In short, any motor may be used as long as it can adjust the rotation speed and direction by appropriately changing the voltage, polarity, period, phase, and other characteristics of the electric signal to be supplied.

  Further, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus 1 configured as a so-called printer has been described. However, the present invention is not limited to this, and various types of printing are performed by transferring and fixing a toner image onto a sheet as a medium by an electrophotographic method, such as a facsimile machine, a copying machine, or a multifunction machine combining these functions. You may apply to an electronic device.

  Further, the present invention is not limited to the above-described embodiment and other embodiments. That is, the scope of the present invention extends to embodiments in which some or all of the above-described embodiments and other embodiments described above are arbitrarily combined, and embodiments in which some are extracted. is there.

  Further, in the above-described embodiment, the middle conveyance unit 13 as the conveyance unit, the conveyance motor control unit 52 as the speed control unit, the paper sensor 46 as the detection unit, and the image formation unit 25 as the image formation unit. The case where the image forming apparatus 1 as the image forming apparatus is configured by the secondary transfer section 14 as the transfer section has been described. However, the present invention is not limited to this, and an image forming apparatus may be configured by a conveyance unit, a speed control unit, a detection unit, an image forming unit, and a transfer unit having various other configurations.

  The present invention can be used in a printer that prints an image on paper by, for example, an electrophotographic system.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3 ... Control part, 6 ... Lower conveyance part, 13 ... Middle conveyance part, 14 ... Secondary transfer part, 14A ... Secondary transfer roller, 14B ... Secondary transfer backup Roller, 15... Fixing section, 20... Belt running section, 23... Intermediate transfer belt, 25... Image forming section, 26 ... image forming unit, 41 ... transport guide, 42, 43, 7. Roller pair, 42A, 43A ... Driving roller, 42B, 43B ... Driving roller, 43AF ... Front end, 43BH ... Holding location, 43L ... Holding wire, 43LF ... Front end wire, 44 ... Conveyance motor, 45, 46 ... Paper sensor, 47 ... Paper thickness sensor, 51 ... Main control unit, 52 ... Conveyance motor control unit, P ... Paper, PE ... End, PS ... End, EA ... End range , SL …… Shock line, T1, T2, T3, T ...... point in time, V1, V2, V3, V5 ...... speed, W ...... conveying path.

Claims (7)

A conveyance unit that has a nipping body that nipping a sheet-shaped medium that has been cut in advance from both sides at a nipping location, and that conveys the medium along a predetermined conveyance path by driving the nipping body;
A speed control unit for controlling the driving speed of the clamping body in the transport unit;
A detection unit provided on the conveyance path for detecting the medium;
A thickness detector for detecting the thickness of the medium;
An image forming unit that forms an image with an image carrier;
An image carrier for the medium transported by the transport unit provided at a position downstream of the sandwich body on the transport path and where no other sandwich body is provided between the sandwich body and the transport body. And a transfer section for transferring images of
When the thickness of the medium detected by the thickness detection unit is equal to or greater than a predetermined thickness threshold , the speed control unit determines the end of the medium based on the detection result of the medium by the detection unit . Control is performed so as to increase the driving speed of the clamping body when passing through the clamping portion in all the end ranges, which are ranges in which pressure is applied during cutting and the hardness is increased, and the thickness of the medium is less than the thickness threshold value If there is, the image forming apparatus is controlled so that the driving speed of the holding body is constant . The clamping body rotates and conveys the medium by advancing the outer peripheral portion along the conveyance path,
When the thickness of the medium detected by the thickness detection unit is equal to or greater than a predetermined thickness threshold , the speed control unit follows the conveyance path based on the detection result of the medium by the detection unit. direction in respect, all during the end pass of the medium ranges across the clamping position from the upstream side end portion in the holding member, the claims and the control unit controls so as to increase the rotational speed of the holding member The image forming apparatus according to 1. The clamping body rotates and advances the outer peripheral portion along the conveyance path to convey the medium, and deforms the vicinity of the clamping portion in the outer peripheral portion to contact the medium,
The speed control unit determines the most upstream portion of the deformed portion in the vicinity of the clamping portion of the outer peripheral portion of the clamping body based on the detection result of the medium by the detection unit. There between all the ends of the medium is contacting the moiety the deformation from the time that has passed, the image forming apparatus of claim 1, wherein the controller controls so as to increase the rotational speed of the holding member . Said speed control section, an image forming apparatus according to claim 1, characterized in that in the range of 5 to 10 [mm] the end range of the end of the medium. When the speed of the medium detected by the thickness detector is equal to or greater than a predetermined thickness threshold and the driving speed of the sandwiching body is increased, the speed control unit is configured such that the end of the medium defines the sandwiched portion. The image forming apparatus according to claim 1 , wherein the control is performed so that the driving speed is restored after passing. The image forming apparatus according to claim 1 , wherein the thickness threshold is 0.2 [mm]. When the speed control unit increases the driving speed of the clamping body, the amount of increase in the driving speed is set to 1 [%] to 3 [%].
The image forming apparatus according to claim 1.

Images