JP2000143050A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of defective printing by immediately detecting the occurrence of skew of a paper sheet between an image forming part and a fixing part of an image forming device. SOLUTION: A side fringe part 312D of an upper plate 312 comes into contact with a lower face of a continuous paper 10 due to energizing force of an energizing member 320. In a condition in which skew does not occur on the continuous paper 10, all the microswitches 340 are maintained in a condition in which their operation piece 342 is at a position where it is pressed down by the continuous paper 10 and all the microswitches 340 are turned on because the continuous paper 10 is conveyed in a condition in which it is in contact with sections in all regions in the longitudinal direction of the side fringe part 312D of the upper plate 312. When skew occurs on the continuous paper 10, the operation piece of the microswitch 340 in a section where the continuous paper 10 floats from the side fringe part 312D oscillates to a protrusion position, and the microswitch 340 is turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus for forming an image on a sheet.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus includes an image forming unit that draws a latent image on a photosensitive drum, develops the latent image with toner, and transfers the developed toner image from the photosensitive drum to paper. A fixing unit that heats and pressurizes the toner image transferred to the sheet to fix the toner image on the sheet. The fixing unit includes a heat roller and a press roller that are disposed at a position downstream of the photosensitive drum in the transport direction and extend in a direction orthogonal to the paper transport direction. The press roller is configured to be pressed against the heat roller. The press roller is rotatably driven and rotatably supports the press roller. The paper on which the toner image has been transferred to the press contact portion between the heat roller and the press roller , The paper and the toner are heated and pressurized to fix the toner image on the paper. By the way, when the leading edge of the sheet enters the above-mentioned press contact portion, if the leading edge of the sheet is inclined with respect to the extending direction of the heat roller and the press roller, the sheet is inclined with respect to the transport direction and skew is caused. This causes the paper to be curved on the transport path between the image forming unit and the fixing unit. If such curving occurs, the paper may be wrinkled in the fixing unit, or a paper jam may occur on the conveyance path.
Will occur. The phenomenon that the paper is inclined with respect to the transport direction occurs even when the balance of the transport force applied to the paper by the heat roller and the press roller is biased in the width direction of the paper and the transport speed of the paper is different in the width direction. . For this reason, conventionally, a jam detection sensor comprising a microswitch or the like is disposed near the conveyance path between the image forming section and the fixing section, and the jam detection sensor detects the curvature of the sheet, and based on this detection operation, In this case, the paper conveyance is stopped and a warning indicating the occurrence of a jam is displayed.

[0003]

In the conventional image forming apparatus provided with the above-described paper jam detecting sensor, paper jam cannot be detected until the paper jam actually occurs. For this reason, even if a skew occurs in the sheet, the fixing operation by the fixing unit is continued until the jam is detected by the jam detection sensor and the sheet conveyance is stopped.
That is, there is a problem in that the toner fixing operation by the fixing unit is continued while the paper is skewed, and a large amount of paper having a printing failure due to wrinkling of the paper is discharged. This problem is remarkable in continuous paper. The present invention has been devised in view of the above circumstances, and an object of the present invention is to perform printing by immediately detecting that skew of a sheet has occurred between an image forming unit and a fixing unit of an image forming apparatus. An object of the present invention is to provide an image forming apparatus capable of suppressing occurrence of a defect.

[0004]

According to the present invention, a latent image is drawn on a photosensitive drum, the latent image is developed with toner, and the developed toner image is transferred from the photosensitive drum to a sheet. An image forming section, a fixing section for fixing the toner image transferred to the sheet, and a sheet extending in a width direction of the sheet orthogonal to a conveying direction of the sheet and supported so as to be displaceable in a thickness direction of the sheet; Biased to abut the lower surface of the paper passing through the transport path between the image forming unit and the fixing unit,
An image forming apparatus having a tension member that applies tension to the sheet in the transport path, wherein the two members are disposed at a position of the tension member that abuts on the sheet and detect that the sheet is separated from the position. Separation detecting means, and skew occurrence determining means for determining whether or not skew has occurred in the sheet based on a detecting operation of the separation detecting means, wherein the two separation detecting means are arranged in the width direction of the sheet. It is characterized by being disposed at one position and the other position with the center position therebetween. Further, according to the present invention, the skew occurrence determination means may be one of the two separation detection means.
It is characterized in that it is determined that skew has occurred when either one detects separation and the other does not detect separation. Further, in the present invention, the skew occurrence determining means includes:
Each time the sheet is conveyed a predetermined distance, the detecting operation of the separation detecting means is monitored, and it is determined that one of the two separation detecting means detects the separation and the other does not detect the separation. It is characterized in that it is determined that skew has occurred when the skew has occurred a number of times. Further, the present invention is characterized in that the separation detecting means includes a separation detecting sensor that outputs a detection signal in a different state when the sheet comes into contact with the portion of the tensioning means and when the sheet is separated. I do. Further, the present invention is characterized in that the separation detecting means includes a plurality of the separation detecting sensors, and the separation detecting sensors are arranged in the tensioning means at intervals in a width direction of the sheet. I do. Further, according to the present invention, the separation detection sensor includes a microswitch that is turned on or off by displacement of an operator, and the operator is pressed down when the sheet comes into contact with the location of the tensioning unit. And is configured to be displaced. Further, the present invention is characterized in that when the skew occurrence determining means determines that skew has occurred, the conveyance and printing of the paper are stopped. Further, in the present invention, the fixing unit includes a heat roller and a press roller extending in a width direction of the sheet, and a pressing mechanism for pressing the press roller against the heat roller, wherein the heat roller and the press roller The pressing mechanism is configured so that the force for pressing the press roller against the heat roller can be set at different values at both ends in the longitudinal direction of the press roller. It is characterized by having. Further, the present invention provides a skew direction determining means for determining a skew direction of the sheet based on a detecting operation of the two separation detecting means when the skew occurrence determining means determines that skew has occurred; According to the skew direction determined by the skew direction determining means, the pressing mechanism is controlled so that the force for pressing the press roller against the heat roller is set at different values at both ends in the longitudinal direction of the press roller. And a skew correction unit for performing the skew correction. In addition, according to the present invention, the pressing mechanism may include:
First pressing means for urging one end of the shaft of the press roller toward the heat roller with a constant urging force, and urging the other end of the shaft of the press roller toward the heat roller; A second configured such that the biasing force is adjustable
And a pressing means. Further, according to the present invention, the first pressing means includes a first rocking plate and a first biasing member, and the first rocking plate is in contact with an outer peripheral surface of one end of a shaft of the press roller. The pressing member is supported so as to swing in a plane orthogonal to the axis of the press roller, and the urging member is configured such that the first contact portion contacts the outer peripheral surface of one end of the shaft of the press roller. The first swinging plate is urged so as to press the press roller against the heat roller in the contact state. Further, according to the present invention, the second pressing means includes a second rocking plate, a second biasing member, and a rocking lever, and the second rocking plate is the other end of the shaft of the press roller. A second contact portion that contacts the outer peripheral surface of the press roller, and is supported so as to swing in a plane perpendicular to the axis of the press roller, and the swing lever contacts and separates from the second swing plate. Is supported so as to be swingable in a plane orthogonal to the axis of the press roller, and the second urging member connects the swing lever and the second swing plate to connect the swing lever to the second swing plate. The swing plates are urged in directions approaching each other, and the swing lever is configured to be displaced in the swing direction. Also,
According to the present invention, there is provided a cam rotatably supported in a state where a cam surface is in contact with the swing lever, and the swing lever is displaced in the swing direction by the rotation of the cam. It is characterized by the following. Further, according to the present invention, a displacement amount detecting means for detecting a displacement amount of the tensioning means, and adjusting a rotation speed of the heat roller or the press roller in accordance with the displacement amount detected by the displacement amount detecting means. In this case, there is provided a conveyance speed adjusting means for adjusting a tension acting on the sheet on a conveyance path between the image forming section and the fixing section within a predetermined range. Further, according to the present invention, the paper is a continuous paper having a constant width,
Feed holes are formed at regular intervals on both side edges in the width direction of the continuous paper. Further, the present invention is characterized in that the continuous paper is formed of perforations or the like at predetermined lengths, and cut lines for breaking the continuous paper to a predetermined length are formed.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a main part of the image forming apparatus according to the first embodiment, FIG. 2 is a front view showing a configuration of a fixing unit, a sheet conveyance speed detection unit, and a paper discharge unit, and FIG.
Is a plan view showing a state viewed from the direction of arrow A, FIG. 4 is a block diagram showing a configuration of a control circuit in the image forming apparatus according to the first embodiment, and FIG. 5 is a block diagram showing an image forming apparatus according to the first embodiment. 6 is a flowchart showing a skew detection operation, FIG.
9 is a flowchart illustrating a print stop operation performed based on skew detection in the image forming apparatus according to the first embodiment.

Referring to FIG. 1, the configuration of the image forming apparatus according to the first embodiment will be described. The image forming apparatus includes a tractor 1
00, an image forming unit 200, a conveying speed detecting unit 300, a fixing unit 400, a paper discharging unit 500, and the like. In this embodiment, the paper on which an image is formed is continuous paper 10 having a constant width, and feed holes are formed at regular intervals on both side edges of the continuous paper 10 in the width direction. Each time a perforated line or the like is formed to cut the continuous paper into a certain length. Tractor 100 in FIG.
Paper 10 supplied from the right side (upstream side in the transport direction)
Is configured to be discharged to the outside of the apparatus via the tractor 100, the image forming unit 200, the transport speed detecting unit 300, the fixing unit 400, and the paper discharging unit 500 in this order.

The tractor 100 includes pulleys 102 and 104 disposed below the left and right side edges in the width direction of the continuous paper 10 and are spaced from each other in the transport direction of the continuous paper 10. Belt 106 wrapped around 104
And a paper pressing plate 108 extending to the opposite side of the belt 106 with the continuous paper 10 interposed therebetween. The belt 106 has pins 106 that are fitted into feed holes formed on both side edges in the width direction of the continuous paper 10 to apply a conveying force to the continuous paper 10.
A are provided at intervals in the extending direction of the belt 106. The paper holding plate 108 has a feed hole for the continuous paper
The upper surface of the continuous paper 10 is held so as not to separate from the sheet 06A.

The image forming section 200 is disposed downstream of the tractor 100 in the transport direction, extends in a direction perpendicular to the transport direction of the continuous paper 10, and rotates so that the photosensitive surface contacts the upper surface of the continuous paper 10. , A charging unit 220, an exposure unit 230, a development unit 240, and a transfer unit 250 that are arranged in a process order at a portion surrounding a photosensitive surface formed on the outer periphery of the photosensitive drum 210. , A cleaning unit 260 and a charge removing unit 270. The charging unit 220 charges the photosensitive surface of the photosensitive drum 210, the exposure unit 230 draws a latent image on the charged photosensitive surface, and the developing unit 240 applies a toner to the latent image formed on the photosensitive surface. The transfer unit 250 transfers the toner image formed on the photosensitive surface to the continuous paper 10, and the cleaning unit 260 removes the toner remaining on the photosensitive surface. The charge removing section 270 removes the charge on the photosensitive surface. At the transfer unit 250, the continuous paper 10 is attracted to the photosensitive surface of the charged photosensitive drum 210 by the action of static electricity, so that the continuous paper 10 is rotated from the photosensitive drum 210 rotating along the transport direction of the continuous paper 10. A transfer force is applied in the transfer direction.

The conveying speed detecting unit 300 extends in the width direction orthogonal to the conveying direction of the continuous paper 10, is supported so as to be displaceable in the thickness direction of the continuous paper 10, and has the image forming unit 200 and the fixing unit 4.
And a plate 310 that is urged to abut one surface of the continuous paper 10 passing through the transport path 600 during the period 00 and applies tension to the continuous paper 10 on the transport path 600. The continuous paper 1 generated due to a difference between the transport speed of the continuous paper 10 at the location of the image forming unit 200 and the transport speed of the continuous paper 10 at the location of the fixing unit 400 based on the amount.
It is configured to detect a slack amount of zero. Details of the configuration of the transport speed detecting unit 300 will be described later.

The fixing unit 400 is provided at a position downstream of the conveying speed detecting unit 300 in the conveying direction, extends in a direction perpendicular to the conveying direction of the continuous paper 10, and fixes the upper and lower surfaces of the sheet to each other. The heat roller 410 and the press roller 420 are provided so as to be sandwiched between the rollers. Heat roller 410
Inside, a halogen lamp 412 as a heat source is provided extending in the axial direction of the heat roller 410. At both ends of the shaft of the press roller 420, the press roller 42
A pressing mechanism 430 for pressing the outer peripheral surface of the heat roller 410 to the outer peripheral surface of the heat roller 410 is provided. Pressing mechanism 430
Will be described later. Press roller 420
A guide plate 450 for guiding the continuous paper 10 to the pressure contact point 440 is provided on the upstream side in the transport direction of the pressure contact point 440 between the heat roller 410 and the heat roller 410 at a distance from the pressure contact point 440 in the transport direction and orthogonal to the transport direction of the continuous paper 10. It is arranged to extend in the direction of In addition, when the continuous paper 10 passes through the pressure contact point 440 of the press roller 420 at the position of the fixing unit 400, a conveying force is applied by the heat roller 410 that is driven to rotate.

The paper discharge unit 500 is disposed at a position downstream of the fixing unit 400 in the transport direction, extends in a direction perpendicular to the transport direction of the continuous paper 10, and is driven to rotate by a discharge roller 502.
And a discharge roller 504 rotatably supported and pressed against the discharge roller 502. The continuous paper 10 is provided with a conveying force toward the downstream side in the conveying direction by passing through the press-contact portions of the rotating discharge rollers 502 and 504, and is discharged from a discharge port (not shown).

Next, with reference to FIGS. 2 and 3, the configurations of the transport speed detecting unit 300 and the fixing unit 400 will be described in detail. The transport speed detecting unit 300 includes a plate 310 (corresponding to a tensioning unit in the claims), a biasing member 320, transmission optical sensors 330A and 330B (corresponding to a displacement detecting unit in the claims), and a microswitch 340. (Corresponding to a separation detection sensor in the claims).

The plate 310 is formed of a plate-like member extending in a direction perpendicular to the direction of transport of the continuous paper 10 and having an L-shaped cross section. The plate 310 has an upper plate 312 that is wide in the direction perpendicular to the longitudinal direction and faces the lower surface of the continuous paper 10 and a lower plate 314 that is narrow in the direction perpendicular to the longitudinal direction and is not facing the lower surface of the continuous paper 10. are doing. From both longitudinal edges of the upper plate 312, bent pieces 312A are erected downward, and bearing holes 312B are formed through these two bent pieces 312A, respectively. In these two bearing holes 312B, two support shafts fixed to a portion of the frame 1000 erected from the bottom of the image forming apparatus erected at a position sandwiching the plate 310 at both ends in its extending direction. 312C are inserted, and the plate 310 is swingably supported by the support shaft 312C.

The lower plate 314 and the support shaft 312 are located at a position near one end of the lower plate 314 in the longitudinal direction.
A detection plate 314A extending in a direction orthogonal to C is provided upright toward the downstream side in the transport direction. Below the detection plate 314A, a mounting portion 1006 fixed to the standing piece 1004 of the bottom frame 1002 of the image forming apparatus and extending in the horizontal direction is arranged at a distance from the detection plate 314A. I have. In the mounting portion 1006, transmission type optical sensors 330A and 330B for detecting the swinging position of the sensing end 314A1 extending downward from the sensing plate 314A are provided at different positions in the swinging direction of the sensing piece 314A. Installed.

A mounting piece 1006A is erected from a side edge of the mounting portion 1006 near the longitudinal center of the plate 310, and an upper portion 315A of the arm 315 is fixed to the mounting piece 1006A. And this arm 3
A biasing member 320 made of a coil spring is stretched between a lower portion 315B of the lower plate 15 and a portion 314B slightly closer to one end from the longitudinal center of the lower plate 314. Therefore, in FIG. 2, the plate 310 is urged clockwise around the support shaft 312C by the urging member 320.

On the other hand, the upper plate 312 has, on a side edge 312D opposite to the place where it is connected to the lower plate 314, an inclined surface 31 inclined downward toward the side edge.
2D1 is formed. The side edge 312D is provided with a plurality of openings 312E (four in the present embodiment) at a position near the lower plate 314 at intervals in the longitudinal direction of the plate 310. These openings 31
The same number (two in this embodiment) of 2E is provided at a location symmetrical in the longitudinal direction (left and right) across the central position in the longitudinal direction of the plate 310. Opening 312E
The plate 310 is provided such that the shape thereof is narrower in the longitudinal direction of the plate 310 and wider in a direction perpendicular to the longitudinal direction as viewed from a plane.

Each opening 3 is provided on the lower surface of the upper plate 312.
A microswitch 340 is attached to a location corresponding to 12E. That is, these microswitches 340
Similarly to the opening 312E, the same number (two in the present embodiment) is provided at a location symmetrical in the longitudinal direction (left and right) with respect to the central position in the longitudinal direction of the plate 310. Here, one micro-switch 340 disposed on one side (left side) of the plate 310 with respect to the longitudinal center position constitutes one separation detecting unit, and is disposed on the other side (right side). The two microswitches 340 constitute one separation detecting unit.

The microswitch 340 includes an actuator 342
Is swingably supported, and the actuator 342 is urged to be in a protruding position indicated by a broken line in FIG. The microswitch 340 is configured to turn off when the operator 342 is at the protruding position, and to turn on when the operator swings to the depressed position indicated by the solid line in FIG. The microswitch 340 is disposed on the lower surface of the upper plate 312 such that the actuator 342 at the projecting position projects from the upper surface of the upper plate 312 through the opening 312E and faces the continuous paper 10. I have.

The continuous paper 10 is conveyed in a state where the center position in the width direction coincides with the center position in the longitudinal direction of the plate 310. Then, even when the width of the continuous paper 10 is narrow, even if the width of the continuous paper 10 is narrow, two actuators 342 of the four microswitches 340 are covered with the continuous paper 10 when the width of the continuous paper 10 is wide. The location of the actuator 342 of each of the microswitches 340 is covered with the continuous paper 10.

According to the above-described configuration, the side edge 312D of the upper plate 312 of the plate 310 is configured to be brought into contact with the lower surface of the continuous paper 10 by the urging force of the urging member 320. Is tensioned. The transport path 60 between the image forming unit 200 and the fixing unit 400
If the continuous paper 10 is too loose on the
10 swings clockwise around the support shaft 312C, and in the detection end 314A1 of the detection plate 314A, the transmission optical sensor 330A is turned on (detection light transmission state), and the transmission optical sensor 330B is turned off (detection light transmission state). (Detection light non-transmission state). Further, the image forming unit 200 and the fixing unit 40
If the continuous paper 10 is excessively tensioned on the conveyance path 600 during the period 0, the plate 310 swings counterclockwise around the support shaft 312C, and the detection end 31 of the detection plate 314A.
4A1 moves so that the transmission optical sensor 330A is turned off (detection light non-transmission state) and the transmission optical sensor 330B is turned on (detection light transmission state). When the continuous paper 10 is properly tensioned on the conveyance path 600 between the image forming unit 200 and the fixing unit 400, the plate 310 is swung to a position intermediate between the two states, and the detection plate 314 is rotated.
A detection end 314A1 is a transmission type optical sensor 330A,
330B are held at positions where both of them are turned off (the detection light is not transmitted).

A control unit 710 shown in FIG.
By controlling the rotation speed of the heat roller 410 of the fixing unit 400 described below based on the detection operation of the transmission optical sensors 330A and 330B, the continuous paper 10 on the conveyance path 600 between the image forming unit 200 and the fixing unit 400 is controlled. Is set within a predetermined range. Details of this operation will be described later.

When no skew occurs in the continuous paper 10, the continuous paper 10 is placed on the side edge 31 of the upper plate 312.
Since the microswitch 340 is conveyed in a state where it is in contact with the entire area in the longitudinal direction of the 2D, all the microswitches 340 are maintained in the pressed position where the actuator 342 is pressed by the continuous paper 10 (see the solid line in FIG. 2). (Position shown), all the microswitches 340 are in the ON state. However, when a skew occurs in the continuous paper 10, the continuous paper 10 is in a state in which one of the two ends in the width direction is raised from the upper surface of the side edge 312 </ b> D of the upper plate 312, and the continuous paper 10 The microswitch 340 at a position raised from the side edge 312D is turned off by its actuator 342 swinging to the protruding position (the position indicated by the broken line in FIG. 2). Here, whether or not skew occurs in the continuous paper 10 is not related to the swing position of the plate 310. That is, regardless of the rocking position of the plate 310, the occurrence of skew can be detected based on the operation of the microswitch 340.

The fixing section 400 includes a heat roller 410 and a press roller 420. Press roller 420
Is configured to be pressed against the heat roller 410 by the pressing mechanism 430. Inside the heat roller 410, two halogen lamps 412 constituting a heater are provided.
A and 412B are disposed in a state of extending in the axial direction of the heat roller 410. A gear 414 is provided at an end of the heat roller 410, and the gear 414 has a frame 101 erected from the bottom frame 1002.
Gear 416 rotatably supported between 0, 1012
A and a rotary drive force from a motor (not shown) are transmitted through a gear train including 416B. Inside the press roller 420, a shaft 422 extending in the axial direction of the press roller 420 is provided so as to penetrate therethrough. The shaft 422 is supported by bearings 420 provided at both ends of the press roller 420. The press roller 420 is rotatably supported on the shaft 422.

The pressing mechanism 430 includes a swing plate 432, a biasing member 434, and a locking portion 436. Rocking plate 432
The recess 432 </ b> A is disposed opposite to a position sandwiching both ends of the press roller 420 and abuts and supports the outer peripheral surface of the shaft 422 protruding from both ends of the press roller 420.
have. A support shaft 432B extending in a direction parallel to the support shaft 422 protrudes from a frame 1008 erected on the opposite side to the press roller 420 with each swing plate 432 interposed therebetween. 432B corresponds to each rocking plate 43
Each of the rocking plates 432 is inserted into a bearing hole 432 </ b> C provided at a position near the transport speed detecting unit 300 on the upper part of the second plate 2.
Are swingably supported in a plane orthogonal to the shaft 422 of the press roller 420.

Further, a bearing hole 432 at the upper part of the rocking plate 432 is provided.
A rectangular notch is formed at a location opposite to C.
The frame 1008 includes an upper edge 43 of the rectangular cutout.
A stopper 432E is provided at a position where it comes into contact with the 2D, and regulates the swing range of the swing plate 432. Rocking plate 4
The engagement piece 432F is provided at a position below the 32 bearing holes 432C.
Extends downward.

The frame 1003 fixed to the bottom frame 1002 at a distance from the bottom frame 1002 is provided with a locking portion 436 at a distance from the locking piece 432F. The locking portion 436 includes a fixing plate 436A fixed to the frame 1003, and a screw portion 436B that is screwed to the fixing plate 436A and rotated to move in a direction of coming and coming from the locking piece 432F. ing. An urging member 434 composed of a coil spring is stretched between the locking piece 432F and the screw portion 436B of the locking portion 436. Therefore, the swinging plate 432 is provided with the urging member 434.
Thus, the pressure roller 420 is urged to swing upward around the support shaft 432B, that is, in a direction in which the press roller 420 is pressed against the heat roller 410. Then, by rotating the screw portion 436B, the screw portion 436B is rotated.
The distance between the locking member 432F and the urging member 434 is adjusted.
Is configured to be able to adjust the urging force.

Next, the configuration of the control circuit will be described with reference to the block diagram of FIG. The control circuit 700 includes the control unit 7
10, sheet conveyance detecting means 720, motor driving section 730,
A print control unit 740 is provided. The control unit 710 includes:
The CPU 71 includes a microcomputer and the like.
2. ROM that stores control programs for CPU
714, left and right skew counters 716A, 716 described later
A RAM 716 having a memory area for 16B and left and right skew flags 716C and 716D, an interface unit 718 for transmitting and receiving signals to and from each unit described later, and the like are provided. The interface unit 718 includes transmission-type optical sensors 330A and 330B, a sheet conveyance detection unit 720,
Each of the microswitches 340 (four in this embodiment) is connected to these transmission type optical sensors 330A, 330B,
The detection signal input from the sheet conveyance detection means 720 and the micro switch 340 is input.

The paper transport detecting means 720 is provided for the continuous paper 1
0 generates a detection signal every time a predetermined distance is conveyed. For example, the pulley 102 or 10 of the tractor 100
It is composed of a transmission type optical sensor for detecting passage of a slit formed in a disk provided on the axis 4.
The motor drive unit 730 includes the tractor 100, the photosensitive drum 2
10, the heat roller 410, and the continuous paper 10
Is to control the driving of a motor that gives a driving force for transporting the motor. The control unit 710 controls the motor drive unit 730 so that the tractor 100, the photosensitive drum 210,
The transport speed of the continuous paper by the heat roller 410 and the paper discharge unit 500 can be individually controlled. The print control unit 740 controls operations related to image formation by the image forming unit 200.

Next, with reference to FIG. 2, FIG. 3, and FIG. 4, a description will be given of a control operation of the continuous paper transport speed performed based on the detection operation of the transmission optical sensors 330A and 330B. The control unit 710 controls the rotation speed of the heat roller 410 of the fixing unit 400 as described below so that the tension given to the continuous paper 10 on the conveyance path 600 between the image forming unit 200 and the fixing unit 400 is reduced. It is set to be within a predetermined range. That is, when the continuous paper 10 is excessively slack and the transmission optical sensor 330A is turned on and the transmission optical sensor 330B is turned off, the control unit 710 controls the motor driving unit 730.
, The rotation speed of the heat roller 410 of the fixing unit 400 is increased, and the conveyance speed at the location of the heat roller 410 is compared with the conveyance speed at the location of the image forming unit 200 (corresponding to the rotation speed of the photosensitive drum 210). Then, the slack of the continuous paper 10 is removed to return the continuous paper 10 to an appropriate tension state. Conversely, the continuous paper 10 is too taut and the transmission optical sensor 330A is turned off, and the transmission optical sensor 3
When the switch 30B is turned on, the control unit 710 controls the motor driving unit 730 to reduce the rotation speed of the heat roller 410 of the fixing unit 400, and reduces the transport speed at the position of the heat roller 410 to the image forming unit 200. The excessive tension of the continuous paper 10 is relaxed by lowering the conveyance speed (corresponding to the rotation speed of the photosensitive drum 210) at the point (2) to return the tension to an appropriate tension state. The control unit 710 that controls the transport speed at the location of the heat roller 410 based on the on / off operation of the transmission optical sensors 330A and 330B controls the transport speed at the location of the image forming unit 200. Make up.

Next, the skew detecting operation of the continuous paper will be described with reference to the flowchart of FIG. Control unit 71
0 starts the process (subroutine) of the flowchart in FIG. 5 every time a detection signal is input from the paper transport detection means 720 while the continuous paper 10 is being transported. Then, it is determined whether or not the speed control is being performed, that is, whether or not the control operation of the transport speed of the continuous paper performed based on the detection operation of the transmission optical sensors 330A and 330B described above is being performed (S10). . If the result of this determination is negative (such as when the printing process has not been performed), the process ends and the process returns to the main process. On the other hand, if the determination result is affirmative, the detection state of each micro switch 340 is determined (S1).
2). That is, the control unit 710 includes the same number of micro switches 34 (two in this embodiment) on the left and right as viewed from the center position of the plate 310 in the longitudinal direction.
It is determined which of the following three ON / OFF states of 0 is present. Note that, in this example, it is assumed that the continuous paper 10 has a width that covers the locations of the actuators 342 of the four microswitches 340.

(A) At least one of the two microswitches 340 provided on the left side is off, and the two microswitches 34 provided on the right side are off.
0 is off. That is, the separation detecting means constituted by the two micro switches 340 disposed on the left side detects the separation of the continuous paper, and is constituted by the two micro switches 340 disposed on the right side. The state in which the separation detecting unit does not detect the separation of the continuous paper. At this time, the continuous paper 10 is skewed to the left as viewed from the transport direction, and the left portion of the continuous paper is in a state of being lifted off the plate 310.

(B) A state in which the two micro switches 340 provided on the left side are on, and at least one of the two micro switches 340 provided on the right side is off. That is, the separation detecting means constituted by the two micro switches 340 provided on the left side does not detect the separation of the continuous paper,
The state in which the separation detecting means constituted by the two micro switches 340 provided on the right side detects the separation of the continuous paper. At this time, the continuous paper 10 is the continuous paper 1
0 is skewed to the right when viewed from the transport direction, and the right side of the continuous paper is in a state of being lifted off the plate 310.

(C) The on / off state of the two microswitches 340 provided on the left side and the two microswitches 340 provided on the right side are the same on the left and right. That is, a state in which both of the separation detecting means provided on the left side and the right side have not detected the separation of the continuous paper or have detected the separation. At this time, if all the microswitches 340 at the locations where the continuous paper 10 passes are on, then all the locations on the left and right sides of the continuous paper are in contact with the plate 310, and the microswitches at the locations where the continuous paper 10 passes are 34
If all 0s are off, it means that all the positions on both the left and right sides of the continuous paper are separated from the plate 310. The former state shows a state in which the continuous paper 10 is normally conveyed, but the latter state shows a case where the cut line of the continuous paper 10 is mountain-folded in a direction away from the plate 310. May occur.

If the result of the determination in step S12 is (A), the control unit 710 sets the right skew flag 716
D is reset (S14). Next, the left skew counter 716A is incremented by 1 (S16). Then, it is determined whether or not the count value of the left skew counter 716A has reached the specified value N (S18).
16C is set (S20). That is, by recognizing the state in which the left skew flag 716C is set, it is possible to detect the occurrence of skew to the left.
Next, the left and right skew counters 716A and 716B are reset (S22), and the process returns to the main processing. On the other hand, S
If negative in 18, the process returns to the main process.

If the result of the determination in step S12 is (B), the left skew flag 716C is reset (S24). Next, the right skew counter 716A is set to +
1 is performed (S26). Then, the right skew counter 716
It is determined whether the count value of A has reached the specified value N (S2).
8) If affirmative, right skew flag 716D is set (S30). That is, the right skew flag 71
By recognizing the state in which 6D is set, it is possible to detect the occurrence of skew to the right. Next, the left and right skew counters 716A and 716B are reset (S22), and the process returns to the main processing. On the other hand, if NO in S28, the process returns to the main process.

If the result of the determination in step S12 is (C), the control unit 710 sets the left and right skew flags 7
16C and 716D are reset (S32), and the left and right skew counters 716A and 716B are reset (S2).
2) Return to the main processing.

If the result of the determination in S12 is (A) or (C) after the processing in S32 in the course of the repetition of the subroutine processing in FIG. 5, the processing in S1 is repeated.
4, the right skew flag 716 in the processing of S24
D, there is no need to reset the left skew flag 716C. However, if the right skew occurs with the left skew flag 716C set for some reason or the left skew occurs with the right skew flag 716C set, the left and right skews will increase. There is a possibility that the inconvenience that both the flags 716C and 716D are set at the same time may occur. In order to avoid such an inconvenience, the right skew flag 716D and the left skew flag 716 in the processing of S14 and S24, respectively.
C is being reset.

As described above, the occurrence of skew is not detected until the count values of the left and right skew counters 716A and 716B reach the specified value N. This is for the following reason. Even if skew occurs temporarily in the process of transporting the continuous paper 10, the skew may be resolved immediately, and such a temporary skew does not cause an obstacle such as jam of the continuous paper. For this reason, while the continuous paper 10 is being transported by the transport amount corresponding to the specified value N, it is determined that skew has occurred only when the microswitch 340 is continuously turned off. Therefore,
By increasing or decreasing the specified value N, it is possible to adjust the strictness of the criterion for determining the occurrence of skew.

Next, referring to FIG. 6, a description will be given of a process for stopping printing and conveyance in response to skew detection. First, the process is started when the power of the image forming apparatus (printer) is turned on. Then, a printer initialization process is performed, and processes necessary for a printing operation are performed (S3).
1). Next, the printer is ready for printing (REA
(DY state) is determined (S32). If the printer is ready for printing, R
The EADY signal is output. If the result of this determination is negative, S32 is repeated. If the determination result is affirmative, it is determined whether the print signal for instructing the start of the printing operation input from the outside is valid (S34). If this determination result is negative, the process returns to S32. If the determination result is affirmative, print start processing is performed (S36). That is, the print control unit 740
Control of the image forming unit 200 to start printing on the continuous paper 10.

Next, it is determined whether an emergency error such as a jam has been detected (S38). Needless to say, the detection of the jam is performed by a conventionally provided jam detection sensor or the like. If the determination result is affirmative, the READY signal output to the outside is turned off (S40), and an emergency stop process for stopping the conveyance and printing of the continuous paper is performed (S42). On the other hand, if the determination result in S38 is negative, the left and right skew flags 716C, 71C
It is determined whether skew has occurred based on whether the 6D flag is set (S44). If the result of this determination is affirmative, the conveyance and printing of the continuous paper are stopped when the printing process of the page being printed at that time is completed (S46). Even if skew occurs, there is no problem in performing printing processing for about one page. on the other hand,
If the determination result in S44 is negative, it is determined whether the print signal is valid (S48). If the determination result is positive, S36.
If not, the process returns to S32. According to the above-described operation, when skew is detected between the image forming unit and the fixing unit of the image forming apparatus, the conveyance of the continuous paper and the printing are stopped when the printing process of the page being printed is completed. Therefore, it is possible to prevent the occurrence of wrinkles and jams in continuous paper,
It is possible to suppress the occurrence of printing defects.

In the first embodiment described above, FIG.
S12, S16, S18, S20, S24, S26,
The control unit 710 that performs the operations of S28 and S30 constitutes a skew occurrence determination unit described in the claims.

In the above-described first embodiment, the conveyance and printing of the continuous paper 10 are stopped based on the skew detection.
It is possible to prevent wrinkles and jams in continuous paper beforehand, and it is possible to suppress the occurrence of printing defects.However, even if skew occurs, if the skew is corrected, continuous Without stopping the conveyance and printing of the paper 10, it is possible to prevent the occurrence of wrinkles and jams of the continuous paper, and to suppress the occurrence of printing defects. The second described below
In the second embodiment, the skew of the continuous paper is detected in the same manner as in the first embodiment, and the skew of the continuous paper is corrected by adjusting the right and left transport speeds of the continuous paper based on the detected skew. I am trying to do it.

FIG. 7 is a front view showing the structure of a fixing unit, a sheet conveying speed detecting unit, and a paper discharging unit of the image forming apparatus according to the second embodiment. FIG. 8 is a plan view seen from the direction of arrow B in FIG. FIG. 9 is a block diagram illustrating a control circuit of the image forming apparatus according to the second embodiment, and FIG. 10 is a flowchart illustrating a skew correction operation in the image forming apparatus according to the second embodiment. 7, 8, and 9, the same portions as those in FIGS. 1, 2, 3, and 4 showing the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

First, the configuration of the image forming apparatus according to the second embodiment, which is different from that of the first embodiment, will be described with reference to FIGS. The second embodiment is the first
What is different from this embodiment is the configuration of the pressure contact mechanism. Second
In the embodiment, the pressing mechanism 440 includes the first and second
It is composed of pressing means 440A and 440B. One end of the press roller 420 (the left end when viewed in the width direction of the continuous paper 10) is provided with the pressing mechanism 430 of the first embodiment.
The first pressing means 440A having the same structure as that of the first pressing means 440A is provided, but the second pressing means 440B having a different structure from the pressing mechanism 430 is provided at the other end (the right end in the width direction of the continuous paper 10). Are arranged.

The first pressing means 440A includes a rocking plate 432 (corresponding to a first rocking plate in the claims) and a biasing member 434 (claim), similarly to the pressing mechanism 430 of the first embodiment. , A biasing member 434 (corresponding to a first biasing member in the claims), and a locking portion 436. The swing plate 432 is connected to the press roller 4.
20 has a concave portion 432A (corresponding to a first contact portion in the claims) that contacts and supports the outer peripheral surface of the shaft portion 422 protruding from one end portion of the shaft portion 422.

The second pressing means 440 B is provided with a rocking plate 432.
(Corresponding to the second rocking plate in the claims), the urging member 43
4 (corresponding to a second biasing member in the claims), a swing lever 442, a cam 444, a cam motor 446, and the like. The swing plate 432 has a concave portion 432A (corresponding to a second contact portion in the claims) that contacts and supports the outer peripheral surface of the shaft portion 422 protruding from the other end of the press roller 420. ing.

The swing lever 442 has an L-shape in plan view and extends vertically, and an upper portion of one wall 442A parallel to the frame 1012 projects from the frame 1012 in a direction parallel to the support shaft 432B. The support shaft 443 is swingably supported in a plane perpendicular to the shaft 422 of the press roller 420 and holds one end of the urging member 434 at a lower portion of the other wall 442B perpendicular to the frame 1012. Screw portion 442C is screwed and attached.

The frame 1003 has two bearing pieces 444
A, and a motor mounting member 446A for fixing the cam motor 446 is provided upright. The cam shaft 444B extends in a direction parallel to the support shaft 443 by the bearing piece 444A, the motor mounting member 446A, and the frame 1012. It is rotatably supported in the state. The camshaft 444B has
At a location between the bearing piece 444A and the frame 1012,
A cam 444 having a cam surface 444C formed on the outer peripheral surface is attached. The wall portion 442B of the swing lever 442 faces the cam surface 444C by the biasing force of the biasing member 434 stretched between the screw portion 442C of the swing lever 442 and the locking piece 432F of the swing plate 432. Location is cam surface 444C
Is held in contact with The cam surface 444C is formed so that the radial distance from the cam shaft 444B increases or decreases along the circumferential direction of the cam shaft 444B. A gear 446B is attached to an end of the camshaft 444B remote from the frame 1012.
6B is a gear 4 attached to a drive shaft 446C of a cam drive motor 446 attached to the motor attachment member 446A.
46D.

According to the above configuration, when the drive shaft 446C of the cam motor 446 is rotationally driven, the rotational driving force is
6D, 446B, cam 444 via cam shaft 444B.
And the cam 444 is rotated in the circumferential direction of the cam shaft 444B. Swing lever 44 abutting on cam surface 444C
2 is swung about the support shaft 443 according to the shape of the cam surface 444C. Therefore, when the lower portion of the swing lever 442 is swung in a direction away from the camshaft 444B, the urging member 434 is extended, and acts on the other end of the shaft 422 of the press roller 420 from the swing plate 432. The force to do it increases. On the other hand, when the lower portion of the swing lever 442 is swung in a direction approaching the cam shaft 444B, the urging member 43
4 contracts, the force acting on the other end of the shaft 422 of the press roller 420 from the rocking plate 432 decreases. That is, the swinging plate 43 corresponds to the swinging displacement of the swinging lever 442.
2, the force acting on the other end of the shaft 422 of the press roller 420 increases or decreases, so that the press roller 420 is
The force of pressing against 10 is increased or decreased. At this time, on one side of the press roller 420, the force for pressing the press roller 420 against the heat roller 410 is applied by the first pressing means 440.
B keeps it constant. Therefore, the cam 4
By causing the swing lever 442 to swing by the rotation of the press roller 44, the press roller 420 is
Can be set to different values at both ends in the longitudinal direction of the press roller 420.

When the continuous paper 10 passes through the press contact point 444 between the press roller 420 and the heat roller 410, the force (press contact force) acting on the press contact point 444 can be increased if the continuous paper 10
The transport force applied to the continuous paper 10 decreases as the transport force applied to the continuous paper 10 decreases as the transport force applied to the press sheet 444 increases and the transport speed increases. It is known. Therefore, if the force for pressing the press roller 420 against the heat roller 410 by the operation of the above-described second pressing means 440B is set to have different values at both ends in the longitudinal direction of the press roller 420, the width direction of the continuous paper 10 The balance of the conveying force acting on the side edges of the left and right sides can be changed between left and right.
That is, the skew can be corrected by changing the transport speed of the side edge portion of the continuous paper 10 in the width direction from left to right. That is, if the pressing force acting on the left side from the center position in the width direction of the pressing position 444 between the press roller 420 and the heat roller 410 is made larger than the pressing force acting on the right side by the operation of the second pressing means 440B, the continuous paper 10 Since the left side is conveyed faster than the right side and the continuous paper is inclined to the right side, the left skew inclined to the left side can be corrected. On the contrary, if the pressing force acting on the left side from the center position in the width direction of the pressing position 444 between the press roller 420 and the heat roller 410 is made smaller than the pressing force acting on the right side by the operation of the second pressing means 440B, the continuous paper Since the right side of 10 is conveyed faster than the left side and the continuous paper is inclined to the left side, the right skew inclined to the right side can be corrected.

Next, the configuration of the control circuit according to the second embodiment will be described with reference to FIG. The same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 9, the only difference from the first embodiment is that a cam motor driving unit 750 for driving the cam motor 446 is provided. Cam motor drive unit 75
Numeral 0 is configured to control the rotational drive amount of the cam motor 446 in accordance with the control unit 710 to increase or decrease the pressing force applied to the press roller 420.

Next, the skew detection operation and the skew correction operation of the continuous paper will be described with reference to the flowchart of FIG. The control unit 710 executes the process (subroutine) of the flowchart of FIG. 10 every time a detection signal is input from the paper conveyance detection unit 720 while the continuous paper 10 is being conveyed.
To start. Note that the processing (S100) of the portion surrounded by the dashed line in FIG. 10 is completely the same as that of FIG. 5, and therefore, the same step numbers as those of FIG. S1
When the process of 00 is completed, it is determined whether or not the skew is set to be corrected (S50). If not, the process returns to the main process. If affirmative, the left and right skew flags 71
The state of 6C and 716D is checked (S52). If the left skew flag 716C is set ((D) in S52), the control unit 710 controls the pressure of the press roller to correct the left skew (S54). That is, the pressing force acting on the left side of the continuous paper 10 is made larger than the pressing force acting on the right side. Thereby, left skew is corrected. Next, the process returns to the main process. If the right skew flag 716D is set (S52 (E)), the controller 710 controls the pressure of the press roller to correct the right skew (S56). That is, the pressing force acting on the left side of the continuous paper 10 is made smaller than the pressing force acting on the right side. Thereby, the right skew is corrected. Next, the process returns to the main process. If the left and right skew flags 716C and 716D have been reset ((F) in S52), the control unit 710 controls the pressure of the press roller to a standard state (S5).
8). That is, the pressing force acting on the left side and the pressing force acting on the right side of the continuous paper 10 are made equal. Next, the process returns to the main process.

In the second embodiment described above, FIG.
0 of S12, S16, S18, S20, S24, S2
The control unit 710 that performs the operations of S6, S28, and S30 constitutes a skew occurrence determination unit described in the claims. The control unit 71 that performs the operation of S52 in FIG.
0 constitutes the skew direction determining means in the claims. The control unit 710 that performs the operations of S54 and S56 in FIG. 10 constitutes a skew correction unit described in the claims.

According to the above-described second embodiment, even if a skew occurs, the skew can be corrected, so that the conveyance of the continuous paper 10 and the printing are not stopped.
It is possible to prevent the occurrence of wrinkles and jams in continuous paper, and to suppress the occurrence of printing defects.

In the first and second embodiments, the micro sensor 340 is used as the separation detecting sensor. However, the present invention is not limited to this, and the paper may be moved from the plate 310 (tension means). Any device that can detect the separation can be used. Further, the separation detecting sensor constituting the separation detecting means may be provided on one side and one on the other side with the center position in the width direction of the continuous paper 10 interposed therebetween. If the detection sensors are arranged at intervals in the width direction of the continuous paper 10 to constitute the separation detecting means, it is possible to detect skew corresponding to a plurality of types of continuous paper 10 having different width-direction dimensions. There are advantages. In the first and second embodiments described above, the transport speed detection unit 3
00, the amount of displacement of the plate 310 is detected, and the rotation speed of the heat roller 410 is changed in accordance with the amount of displacement to change the continuous paper 10 between the image forming unit 200 and the fixing unit 300.
, The tension applied to the continuous paper 10 is omitted.
May be used only as a tensioning member that applies tension to the member.

[0056]

As is clear from the above description, the present invention
An image forming unit that draws a latent image on a photosensitive drum, develops the latent image with toner, and transfers the developed toner image from the photosensitive drum to a sheet, and a fixing unit that fixes the toner image transferred to the sheet. The sheet extends in the width direction of the sheet perpendicular to the sheet conveyance direction, is supported so as to be displaceable in the thickness direction of the sheet, and contacts a lower surface of the sheet passing through a conveyance path between the image forming section and the fixing section. An image forming apparatus comprising: a tension member urged to come into contact with the sheet, and tensioning the sheet in the conveyance path, wherein the sheet is disposed at a position of the tension member that comes into contact with the sheet, and the sheet is separated from the point. And two skew occurrence determining means for determining whether or not skew has occurred on the sheet based on the detection operation of the separation detecting means, wherein the two separation detecting means include: ,Previous Each was provided configurations in one position and the other positions sandwiching the center position in the width direction of the paper. Therefore, it is detected based on the detection operation of the two separation detecting means that one of the one side and the other side sandwiching the center position in the width direction of the paper is separated from the location of the tension member, and the detection is performed. The presence or absence of skew is determined by the skew occurrence determining means based on the operation. Therefore, if the printing operation and the conveying operation are stopped in response to the occurrence of the skew of the sheet between the image forming unit and the fixing unit of the image forming apparatus, it is possible to suppress the occurrence of the printing failure.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a main part of an image forming apparatus according to a first embodiment.

FIG. 2 is a front view illustrating a configuration of a fixing unit, a sheet conveying speed detecting unit, and a sheet discharging unit of the image forming apparatus according to the first embodiment.

FIG. 3 is a plan view showing a state in which FIG. 2 is viewed from an arrow A direction.

FIG. 4 is a block diagram illustrating a configuration of a control circuit of the image forming apparatus according to the first embodiment.

FIG. 5 is a flowchart illustrating a skew detection operation in the image forming apparatus according to the first embodiment.

FIG. 6 is a flowchart illustrating a print stop operation performed based on skew detection in the image forming apparatus according to the first embodiment.

FIG. 7 is a front view illustrating a configuration of a fixing unit, a sheet conveying speed detecting unit, and a sheet discharging unit of the image forming apparatus according to the second embodiment.

FIG. 8 is a plan view as seen from the direction of arrow B in FIG. 7;

FIG. 9 is a block diagram illustrating a control circuit of the image forming apparatus according to the second embodiment.

FIG. 10 is a flowchart illustrating a skew correction operation in the image forming apparatus according to the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Continuous paper (paper) 200 Image forming part 310 Plate (tensing member) 330A, 330B Transmission optical sensor (displacement detection means) 340 Microswitch (separation detection sensor, separation detection means) 342 Actuator 400 Fixing part 410 Heat roller 420 press roller 430, 440 pressing mechanism 440A first pressing means 440B second pressing means 710 control unit (skew occurrence determining means, skew direction determining means, skew correcting means, transport speed adjusting means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Kikuchi 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Gaku Kogyo Co., Ltd. (72) Minoru Suzuki 2-36-9 Maeno-cho, Itabashi-ku, Tokyo No. Asahi Gaku Kogyo Co., Ltd. F-term (reference) 2H027 DA32 DC04 DC05 DE03 DE07 DE09 EC06 ED16 ED25 ED30 EE05 EF09 EK03 HA02 ZA07 3F104 AA02 CA11 CA15 CA19 CA27 CA35 CA36 KA11

Claims (16)

[Claims] An image forming unit for drawing a latent image on a photosensitive drum, developing the latent image with toner, and transferring the developed toner image from the photosensitive drum to a sheet; A fixing unit to be fixed, and extending in a width direction of the sheet orthogonal to a sheet conveyance direction, supported so as to be displaceable in a thickness direction of the sheet, and passing through a conveyance path between the image forming unit and the fixing unit. It is urged to contact the lower surface of the paper,
An image forming apparatus comprising: a tension member that applies tension to the sheet in the transport path; wherein the tension member is disposed at a location of the tension member that abuts on the sheet, and detects that the sheet is separated from the location. Separation detecting means, and skew occurrence determining means for determining whether or not skew has occurred in the sheet based on the detecting operation of the separation detecting means, wherein the two separation detecting means are arranged in the width direction of the sheet. An image forming apparatus, wherein the image forming apparatus is disposed at one position and the other position sandwiching the center position. 2. The skew occurrence determination means determines that skew has occurred when one of the two separation detection means detects separation and the other does not detect separation. The image forming apparatus according to claim 1. 3. The skew occurrence determining means monitors the detecting operation of the separation detecting means every time the sheet is conveyed by a predetermined distance, and one of the two separation detecting means detects the separation. 2. The image forming apparatus according to claim 1, wherein the skew is determined to have occurred when the other side does not detect the separation for a predetermined number of times. 4. The apparatus according to claim 1, wherein the separation detecting unit includes a separation detecting sensor that outputs a detection signal in a different state when the sheet comes into contact with the portion of the tensioning unit and when the sheet is separated. The image forming apparatus according to claim 1, 2 or 3. 5. The apparatus according to claim 1, wherein the separation detecting means includes a plurality of separation detecting sensors, and the separation detecting sensors are arranged on the tensioning means at intervals in a width direction of the sheet. The image forming apparatus according to claim 4. 6. The separation detecting sensor comprises a microswitch that is turned on or off by displacement of an operator, and the operator is depressed when the sheet comes into contact with the portion of the tensioning unit. The image forming apparatus according to claim 4, wherein the image forming apparatus is configured to be displaced. 7. The printing apparatus according to claim 1, wherein when the skew occurrence determining unit determines that skew has occurred, the conveyance and printing of the sheet are stopped. An image forming apparatus according to any one of the preceding claims. 8. The fixing unit includes a heat roller and a press roller extending in a width direction of the sheet, and a pressing mechanism for pressing the press roller against the heat roller.
The heat roller and the press roller are configured so that the sheet passes through a press contact portion of the press roller, and the press contact mechanism has a force that presses the press roller against the heat roller at different values at both ends in a longitudinal direction of the press roller. 2. The apparatus according to claim 1, wherein the setting is made by the following.
The image forming apparatus according to any one of claims 1 to 7. 9. A skew direction determining means for determining a skew direction of the sheet based on a detecting operation of the two separation detecting means when the skew occurrence determining means determines that skew has occurred; According to the skew direction determined by the direction determining means, the pressing mechanism is controlled so that the force for pressing the press roller against the heat roller is set at different values at both ends in the longitudinal direction of the press roller. 9. The image forming apparatus according to claim 8, further comprising a skew correction unit. 10. The press-contact mechanism includes: first press-contact means for urging one end of the shaft of the press roller toward the heat roller with a constant urging force; and the other end of the shaft of the press roller to the other end. The image forming apparatus according to claim 9, further comprising: a second pressing unit configured to urge the heat roller toward the heat roller and adjust the urging force. 11. The first pressing means comprises a first rocking plate and a first pressing plate.
An urging member, wherein the first rocking plate has a first abutting portion that abuts on an outer peripheral surface of one end of the shaft of the press roller, and swings in a plane orthogonal to the axis of the press roller. And the urging member presses the press roller against the heat roller in a state where the first contact portion is in contact with the outer peripheral surface of one end of the shaft of the press roller. The image forming apparatus according to claim 10, wherein the moving plate is biased. 12. The second pressing means includes a second rocking plate,
A second urging member and a swing lever, wherein the second swing plate has a second abutting portion that abuts on the outer peripheral surface of the other end of the shaft of the press roller; And is supported so as to swing in a plane perpendicular to the second direction.
The swinging plate is swingably supported in a direction orthogonal to the axis of the press roller in a direction of coming and going with the swinging plate, and the second biasing member connects the swinging lever and the second swinging plate. The image according to claim 11, wherein the swing lever and the second swing plate are urged in directions approaching each other, and the swing lever is displaced in the swing direction. Forming equipment. 13. A cam which is rotatably supported in a state where a cam surface is in contact with the rocking lever, and the rocking lever is displaced in the rocking direction by rotating the cam. The image forming apparatus according to claim 12, wherein 14. A displacement amount detecting means for detecting a displacement amount of said tensioning means, and adjusting a rotation speed of said heat roller or said press roller in accordance with said displacement amount detected by said displacement amount detecting means. And a transport speed adjusting means for controlling a tension acting on the sheet on a transport path between the image forming section and the fixing section to be within a predetermined range. 2. The image forming apparatus according to claim 1. 15. The paper according to claim 1, wherein the paper is continuous paper having a constant width, and feed holes are formed at predetermined intervals on both side edges in the width direction of the continuous paper. 14. The image forming apparatus according to claim 14, 16. The continuous paper according to claim 15, wherein the continuous paper is formed of perforations and the like at predetermined lengths, and cut lines are formed for breaking the continuous paper to a predetermined length. The image forming apparatus as described in the above.