JP2007206153A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which peeling of a form is performed by discharge of compressed air, formation of turbulence of the discharge air is suppressed, retention of the discharge air near a heating member is prevented, and to provide an image forming apparatus equipped with the fixing device. <P>SOLUTION: The fixing device of the image forming apparatus fixes a toner image onto a form, by conveying the form carrying the unfixed toner image subjecting it to heating and pressurizing, in a nip area formed by a first rotor having a heating means and a second rotor arranged to face the first rotor. The fixing device has a peeling means for peeling the form from the first rotor or the second rotor by discharging the compressed gas. The peeling means is equipped with a compressed gas discharge member for discharging the compressed gas, in such a manner that the compressed gas heads toward both ends along the circumference of the first rotor and the second rotor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine using electrophotographic technology, and a fixing device used for these image forming apparatuses.

  In an image forming apparatus based on electrophotography, a sheet carrying an unfixed toner image is nipped by a nip formed by a rotating member such as an opposing roller or a belt, and conveyed while being heated under pressure. A fixing device that fixes an image on a sheet is widely used.

  Such a fixing device is wound around a roller or a plurality of rollers by a roller-shaped heating member having a heater as a heating means inside or a belt-shaped heating member wound around the roller-shaped heating member. A belt-like pressure member is arranged to face each other, and a sheet carrying a toner image is sandwiched between these two rotating members, and conveyed while being heated under pressure to perform a fixing process.

  In such a type of fixing device, since the unfixed toner image formed on the paper is in direct contact with the peripheral surface of the heating member, the paper sticks to the heating member due to the viscosity of the molten toner, and the paper There is a possibility of causing a so-called winding phenomenon that does not peel from the heating member. In order to avoid such a problem, a paper sheet wrapped around the heating member is provided by providing a peeling claw made of metal or heat-resistant resin and placing the tip of the peeling claw in contact with the peripheral surface of the heating member. A method called a peeling claw method that peels the tip of the tape from the peripheral surface has come to be widely adopted.

  However, in the peeling claw method, a small pressing force is applied to the peeling claw so that the peeling claw is always brought into contact with the peripheral surface of the heating member. For this reason, the tip of the peeling claw and the peripheral surface of the heating member are worn, and sometimes, deposits on the peripheral surface of the heating member accumulate on the tip of the peeling claw and cause damage to the peripheral surface of the heating member. May be generated.

  Further, the peeled paper front end portion advances while the image surface immediately after fixing is brought into contact with the peeling claw, so that image quality such as scratches may be deteriorated.

  In order to reduce the scratches generated on the peripheral surface of the heating member, many methods using a release sheet instead of the release claw have been adopted. However, in this method, the release sheet and the conveyance guide member that regulates the conveyance direction of the paper after peeling come into contact with the image surface immediately after the fixing of the paper, so often image quality such as image distortion and gloss unevenness is obtained. Bring about a decline.

  In order to cope with the above-mentioned disadvantages, an air pump, an air opening / closing device is not provided without providing a member that directly contacts the paper or the heating member such as a peeling claw or a peeling sheet for peeling the paper from the peripheral surface of the heating member. There is also a fixing device that is equipped with a compressed air discharge device consisting of a valve, a compressed air discharge member, etc., and blows air to the leading edge of the paper that sticks to the heating member and advances at a preset timing. (For example, refer to Patent Document 1).

However, while the above-described peeling of the paper by the discharge of compressed air has the strength that the image surface of the paper does not contact the peeling member, the discharge of the compressed air can be performed even after the leading edge of the paper is peeled off from the heating member. Since the sheet continues for a while, the turbulent flow created by the discharged air may disturb the paper advance. In particular, a thin sheet having low rigidity and low basis weight is easily affected by such turbulent flow, and causes troubles such as jams during conveyance. Further, since the high temperature air that touches the peripheral surface of the heating member is appropriately diffused into the image forming apparatus, the temperature of the developer may be increased and the photosensitive member may be poorly cleaned.
Japanese Patent Laying-Open No. 2005-49647 (second page)

  The present invention has been made in view of the above-described situation, and an object of the present invention is a fixing device that separates a sheet by discharging compressed air, which suppresses the turbulence of discharged air, An object of the present invention is to provide a fixing device that prevents staying in the vicinity of a heating member and an image forming apparatus that includes the fixing device.

The object is achieved by the invention described below.
1. A sheet carrying an unfixed toner image is heated and pressurized at a nip formed by a first rotating body having a heating means and a second rotating body arranged opposite to the first rotating body. A fixing device of an image forming apparatus that conveys the toner image on a sheet while conveying the toner image,
Peeling means for peeling the paper from the first rotating body or the second rotating body by discharging compressed gas;
The fixing device includes a compressed gas discharge member that discharges the compressed gas toward both ends along the peripheral surfaces of the first rotating body and the second rotating body.
2. 2. The fixing device according to claim 1, further comprising exhaust means provided with gas suction ports in the vicinity of both end portions of the first rotating body or the second rotating body.
3. 3. The fixing device according to claim 1, further comprising discharge angle changing means for changing a gas discharge angle of the compressed gas discharge member.
4). An image forming apparatus for forming a toner image on paper,
An image forming apparatus comprising the fixing device according to claim 1.
An image forming apparatus provided with the fixing device described in Section 5.3,
An input operation means for inputting paper information;
Control means for controlling the discharge angle changing means based on the inputted paper information;
An image forming apparatus comprising:

  The turbulent flow of the discharge air is suppressed by directing the direction of the compressed air to be discharged from the center of the paper to both ends, and the stay of the discharge air in the vicinity of the heating member is prevented. The conveyance of the sheet peeled off from the sheet is stabilized, and the temperature rise in the image forming apparatus is prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a digital image forming apparatus G called a multifunction machine having functions of a copying machine, a facsimile, and a printer.

  The image forming apparatus G has an automatic document feeder ADF at the top of the main body. The main body includes an image reading unit 1, an image writing unit 2, an image forming unit 3, an input operation unit 4, a paper feeding unit 5, a paper discharge re-feeding unit. The sheet feeding unit 6, the fixing device 7, the control unit C, and the like are included.

  The automatic document feeder ADF feeds the documents placed on the document table 11 to the document conveying means 13 one by one by the document separating means 12, and the document conveying means 13 conveys the sent documents to the document discharging means 14. Then, the document discharge means 14 discharges the sent document to the document discharge table 15. The document image is read by a slit 21 provided in the document conveyance path, which is a document image reading position of the image reading unit 1.

  When reading images on both sides of the document, the document which has been read on the first surface is reversed by the document reversing means 16 having a pair of rollers, and is sent again to the document conveying means 13 to re-feed the second surface. Reading is done. The document that has been read is discharged to the document discharge table 15.

  The image reading means 1 is a means for reading a document image to obtain image data. The document image irradiated with light by the lamp 231 at the position of the slit 21 is a first mirror unit 23 and a second mirror unit 24. And an imaging lens 25 to form an image on the image sensor 26 which is a linear CCD. The signal output from the image sensor 26 is A / D converted by the image processing unit of the control means C, subjected to processing such as shading correction and image compression, and is stored in the memory M as image data.

  The image writing means 2 is an image carrier 31 that is rotated by being uniformly charged by a charging means 32 by a laser beam and a polygon mirror based on image data that has been called from the memory M and subjected to predetermined image processing. The electrostatic latent image corresponding to the original image is formed on the surface of the image carrier 31 by scanning the surface.

  The electrostatic latent image is reversely developed by the developing unit 34 of the image forming unit 3, and a toner image is formed on the image carrier 31.

  Corresponding to the timing of toner image formation, the paper P is fed from the manual paper feeding means 55 or the paper feeding means 5 having a cassette or tray for storing the paper P, and is conveyed by the conveying roller 56. The roller 39 synchronizes for alignment with the toner image formed on the image carrier and sends it to the transfer area.

  In the transfer area, the toner image formed on the surface of the image carrier 31 is transferred to the paper P charged to the opposite polarity by the transfer means 35.

  The sheet P carrying the toner image is separated from the surface of the image carrier 31 by the action of the separation / elimination means 36 and sent to the fixing device 7.

  In the fixing device 7, the paper P carrying a toner image is conveyed while being heated and pressurized by a heating roller 71 as a first rotating body and a pressure roller 72 as a second rotating body. Is fixed to the paper P and discharged by a discharge roller 63 to a discharge tray 64 outside the apparatus.

  When the paper P is turned upside down and discharged onto the paper discharge tray 64, the paper P is guided to the paper discharge refeed means 6 by the switching guide 62, and the paper P is switched back and sent to the discharge roller 63. .

  Further, when forming an image on both sides of the paper P, the paper P that has been fixed on the first side is guided to the paper discharge refeed means 6 by the switching guide 62 and reversed by the reversing unit 65. Then, the sheet is fed to a conveyance path 66 for paper feeding and used for image formation on the second surface.

  On the other hand, the surface of the image carrier 31 after the transfer of the toner image onto the paper P is prepared for the next image formation after the residual toner is removed by the cleaning means 37.

  FIG. 2 is a block diagram illustrating a control relationship of the image forming apparatus G.

  The control means C is a computer system including a CPU, a memory M, an arithmetic unit, an I / O port, a communication interface, a drive circuit, etc. (not shown). They are connected by corresponding I / O ports, communication interfaces, and drive circuits.

  Control by the control means C is performed by executing a predetermined program stored in the memory M.

  The automatic document feeder ADF is also smaller in scale than the control means C, but is provided with similar control means centered on the CPU, and is connected to the control means C by communication means R. .

  In the drawing, the description of blocks not directly related to the description of the present invention is omitted.

  FIG. 3 is a conceptual diagram of the fixing device 7 having the peeling means 750 by discharging compressed air.

  The heating roller 71 (first rotating body) includes a heater H that is a heating unit inside, and has an elastic body 701 having high thermal conductivity in the periphery.

  The pressure roller 72 (second rotating body) is a roller provided with an elastic body 702 in the periphery or not provided with an elastic body.

  The nozzle 75 of the peeling means 750 is a compressed gas discharge member that discharges compressed gas in a predetermined direction, and a plurality of nozzles are arranged at predetermined intervals in the depth direction of the drawing. The number of nozzles 75 is determined in advance according to the size of the paper P allowed by the image forming apparatus G. Moreover, although air is used as the compressed gas that is usually used, other gases such as nitrogen can also be used.

  The leading edge of the paper P carrying the toner image traveling along the arrow a is detected by the paper detection sensor S, and the detection signal is sent to the control means C. Further, the leading end portion of the paper P that has advanced is pressurized and heated at the nip portion NP, and is sent out in the tangential direction e away from the peripheral surface of the pressure roller 72 at the outlet of the nip portion NP. As described above, it is desirable that the leading edge of the paper P is always peeled off from the peripheral surface of the heating roller 71 due to the rigidity of the paper P. The image surface may travel as indicated by an arrow f while being in close contact with the heating roller 71.

  In order to peel the paper P in such a state from the peripheral surface of the heating roller 71, when the leading end portion of the paper P comes out of the nip portion, air is discharged from the nozzle 75 toward the leading end portion for a predetermined time. The peeled paper P is guided to the guide members 77 and 78 and proceeds as indicated by the dotted arrow b.

  The nozzle 75 is attached at a position where the nozzle mouth is 10-20 mm away from the exit of the nip portion NP and as close as possible within a range where the nozzle 75 does not contact the peripheral surface of the heating roller 71. The angle α formed by the nozzle 75 and the horizontal plane is determined by experiment.

  The force required to peel the leading edge of the paper P from the heating roller 71 depends on the toner amount of the image at the leading edge of the paper P and the rigidity of the paper. Therefore, the paper P having the lowest rigidity among the papers P to be used and having the toner image with the largest amount of toner adhering to the leading end, that is, the paper that is most difficult to peel off after fixing is surely provided. The strength and time for discharging the air blown onto the leading end of the paper P are determined so that the P is peeled off.

  The discharged air hits the leading edge of the paper P before peeling, the image surface of the paper P after peeling, the peripheral surfaces of the heating roller 71 and the pressure roller 72, and the guide members 77 and 78, and becomes turbulent. Accordingly, the leading edge of the peeled paper P vibrates violently due to this turbulent flow, and in some cases, a paper conveyance failure may occur in which the leading edge does not advance along the guide member.

  FIG. 4 is a diagram illustrating an example of such a paper conveyance failure.

  The paper P that has progressed as indicated by the arrow a is peeled off from the peripheral surface of the heating roller 71 by the compressed air discharged from the nozzle 75 after exiting the nip portion NP, and then the leading end portions are guided to the guide members 77 and 78. In some cases, the tip does not travel in the direction of the arrow b, and the leading end is wound around the peripheral surfaces of the heating roller 71 and the pressure roller 72 as indicated by the arrow h or arrow i due to the turbulent flow as described above. These paper conveyance failures often occur on low rigidity paper such as thin coated paper.

  Further, the air in contact with the heating roller 71 at a high temperature diffuses into the image forming apparatus G through the peripheral surfaces of the heating roller 71 and the pressure roller 72, the guide members 77 and 78, and the opening of the exterior of the fixing device 7. And increase the temperature inside the aircraft. Such a temperature rise in the machine causes a temperature rise of the developer and a cleaning failure, and should be suppressed as much as possible.

  The present invention prevents the air discharged from the nozzle from becoming turbulent, reduces the time during which the discharged air stays on the peripheral surface of the heating roller 71 having a high temperature, and is heated early. The temperature inside the machine is prevented from rising by exhausting the air outside the machine.

  FIG. 5 is a top view for explaining the arrangement relationship between the heating roller 71 and the nozzle 75.

  The sheet P is heated under pressure at a nip portion formed by the heating roller 71 and the pressure roller 72, and the leading end portion is heated by the compressed air discharged from the plurality of nozzles 75 when the leading end portion exits the nip portion. It moves away from the peripheral surface of 71 and proceeds in the direction of arrow x.

  The plurality of nozzles 75 are attached so as to have a predetermined angle β with respect to the traveling direction x of the paper P as shown in the figure, and the discharged air is heated by the heating roller as shown by the dotted arrows in the figure. It advances toward both ends of the paper P along the peripheral surfaces of 71 and the pressure roller 72. By making the flow of the discharged air in this way, the air discharged from the nozzle 75 as in the conventional case is greatly compared to the case where the air is opposed to the traveling direction x of the paper P (β = 180 degrees). In addition, the magnitude of the turbulent flow is suppressed, and the retention of air on the peripheral surface of the heating roller 71 is reduced.

  Further, a gas suction duct 76 that is a suction port of the exhaust unit 760 is provided in the vicinity of both ends of the heating roller 71 or the pressure roller 72, for example, at a position 2 to 10 mm apart. The high-temperature air that has flowed to both ends of the roller 72 is discharged out of the machine by the exhaust means 760, and is prevented from diffusing into the machine.

  FIG. 6 is a conceptual diagram of the discharge angle changing means 780 that makes the nozzle angle β variable.

  The nozzle 75 is rotatably held at a fulcrum 781 in the vicinity of the discharge port, and a rack 783 combined with a rotary screw 782 is attached to the rear end, and moves from a solid line position to a dotted line position by the rotation of the rotary screw 782. . The rotation screw 782 and the rack 783 are formed so that the screw thread directions are symmetrical at a position substantially intersecting with the center line of the paper P traveling, and as shown in the figure, the nozzle 75 is sandwiched between the center lines l. Are configured to move symmetrically.

  The nozzle 75 to which the rack 773 is not attached is connected to the nozzle 75 to which the rack 783 is attached by a connecting member 784 comprising a rotating attachment fulcrum and a lever, and moves together.

  The rotating screw 782 is driven by a stepping motor 785, and the number of steps is controlled by the control means C so that the stepping motor 785 rotates by a predetermined angle from the reference position detected by the position sensor HP. That is, the control means C can control the nozzle angle β by controlling the number of steps of the stepping motor 785. By such control of the control means C, the discharge direction of the compressed air discharged from the nozzle 75 can be changed.

  FIG. 7 is a block diagram showing the configuration of the compressed air discharge means 770 of the peeling means 750 for peeling the paper P from the heating roller 71 by the discharge of compressed air from the nozzle 75.

  The compressed air discharge means 770 is constituted by a known technique.

  The air tank 776 is a tank filled with air, and the internal pressure is maintained at a predetermined pressure by controlling the air pump 777 by the control means C based on the signal of the pressure sensor PS. The air compressed to a predetermined pressure advances through the air duct 779 when the electromagnetic valve 778 is opened, and is discharged from the nozzle 75. Note that the timing of opening and closing the electromagnetic valve 778 is controlled by causing the control means C to execute a predetermined program based on a signal from the paper detection sensor S.

  FIG. 8 is a conceptual diagram illustrating the exhaust means 760.

  The air discharged from the nozzle 75 and traveling along the peripheral surfaces of the heating member 71 and the pressure member 75 passes through the gas suction ports of the exhaust means 760 provided in the vicinity of both ends of the heating member 71 and the pressure member 75. It is drawn into a certain gas suction duct 76 and is discharged out of the machine indicated by a solid arrow by an exhaust fan 761.

  FIG. 9 shows a flow of control of the discharge angle changing unit that acquires the sheet information of the sheet used for image formation and changes the gas discharge angle by changing the angle β of the nozzle 75 of the peeling unit 750. It is a flowchart.

  Changing the direction of the nozzles depending on the paper P is an effective method for setting an optimum peeling condition corresponding to the type of paper.

  Information relating to the paper of the paper P loaded in the tray or cassette of the paper feeding means 5 input from the input operation means 4 of the image forming apparatus G, such as paper type, basis weight, and size information Information is stored in a predetermined area of the memory of the control means C.

  When the start button of the image forming apparatus G is pressed (step S1: Y), the paper information is read (step S2), and a nozzle angle setting table in which the relationship between the preset paper information and the nozzle angle is set. Is referred to (step S3), and the angle to be set is determined. Next, the angle of the currently stopped nozzle is read out from a predetermined storage area, collated with the set angle, and the moving angle, that is, the direction and the number of steps necessary for the movement are calculated (step). S5). Based on the calculation result, the stepping motor 785 is driven by a predetermined number of steps (step S6), and a new stop angle is stored in a predetermined storage area (step S7).

  As described above, in the fixing device or the image forming apparatus according to the present invention, the turbulent flow of the discharge air is suppressed by directing the direction of the compressed air to be discharged from the central portion of the paper to the both ends. By preventing the discharge air from staying in the vicinity of the heating member, the conveyance of the paper peeled from the heating member is stabilized.

  The description of the present embodiment is based on an example in which compressed air is discharged using a plurality of nozzles 75 as a compressed gas discharge member, but an air duct as shown in FIG. 10 is used instead of the plurality of nozzles. It may be provided. Further, the gas suction port of the exhaust means 760 and the duct may be integrated. In this case, the gas suction port is disposed outside the maximum width of the paper size.

1 is a schematic configuration diagram of an image forming apparatus. 2 is a block diagram illustrating a control relationship of the image forming apparatus. FIG. It is a conceptual diagram of a fixing device having a peeling means. FIG. 6 is a diagram illustrating an example of paper conveyance failure. It is a top view which shows the arrangement | positioning relationship between a nozzle and a heating roller. It is a conceptual diagram of a discharge angle change means. It is a block diagram which shows the structure of the compressed air discharge part of a peeling means. It is a conceptual diagram explaining an exhaust means. It is a flowchart which shows the flow of control of a discharge angle change means. It is a figure which shows the example of an air duct.

Explanation of symbols

4 Input operation means 7 Fixing device 71 Heating roller (first rotating body)
72 Pressure roller (second rotating body)
75 nozzle (compressed gas discharge member)
750 peeling means 760 exhaust means 770 compressed air discharge means 780 discharge angle changing means C control means G image forming apparatus M memory S paper detection sensor

Claims (5)

A sheet carrying an unfixed toner image is heated and pressurized at a nip formed by a first rotating body having a heating means and a second rotating body arranged opposite to the first rotating body. A fixing device of an image forming apparatus that conveys the toner image on a sheet while conveying the toner image,
Peeling means for peeling the paper from the first rotating body or the second rotating body by discharging compressed gas;
The fixing device includes a compressed gas discharge member that discharges the compressed gas toward both ends along the peripheral surfaces of the first rotating body and the second rotating body. The fixing device according to claim 1, further comprising an exhaust unit provided with a gas suction port in the vicinity of both end portions of the first rotating body or the second rotating body. The fixing device according to claim 1, further comprising a discharge angle changing unit that changes a gas discharge angle of the compressed gas discharge member. An image forming apparatus for forming a toner image on paper,
An image forming apparatus comprising the fixing device according to claim 1. An image forming apparatus comprising the fixing device according to claim 3,
An input operation means for inputting paper information;
Control means for controlling the discharge angle changing means based on the inputted paper information;
An image forming apparatus comprising:

Images