JP2009014829A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve fixability at a fixation nip part according to recording medium. <P>SOLUTION: The fixing device 6 is configured to make a recording medium P on which an unfixed toner image is transferred pass through the fixation nip part N6 formed between a thermal fixing member 6a and a pressure member 6b coming into press contact with the thermal fixing member 6a, and thermally fix the unfixed toner image. The fixing device 6 includes: a pressure member position changing means 660 for changing the position of the pressure member to the thermal fixing member according to the type of the recording medium passing through the fixation nip part; and a surface temperature detecting means 612 for detecting the surface temperature of the thermal fixing member 6a, also, configured to attach/detach to/from the thermal fixing member in conjunction with the position change of the pressure member. When the recording medium passing through the fixation nip part has a thickness of a prescribed value or more, the pressure member position changing means moves the pressure member in a direction separate from the thermal fixing member, and the surface temperature detecting means moves in a direction separate from the thermal fixing member in conjunction with the movement of the pressure member. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device, and more particularly, to a mechanism for adjusting a nip width and a pressure in a fixing nip portion serving as a pressure contact region between a heating roller and a pressure roller provided in the fixing device.

  In the image forming apparatus, a fixing device serving as a fixing mechanism that melts and fixes unfixed transfer toner transferred by a transfer mechanism onto a transport sheet is disposed. As the fixing device, the part where the unfixed toner is melted and fixed is heated at the fixing nip portion where the heating roller and the pressure roller are in contact with each other, and the transfer toner on the transport paper is heated. A heat fixing roller type apparatus for fixing the toner is widely used. Such a fixing device is normally configured such that the surfaces of both rollers are heated by a heater serving as a heat generation source included in the heating and pressure rollers.

  The transported paper is melted at the fixing nip portion and fixed on the paper. Normally, the types of paper conveyed to the fixing device are classified into thin paper, plain paper, and thick paper. In the fixing nip portion, as described above, the unfixed toner is applied by the pressure of the heating / pressure roller and the temperature of the heating roller surface. Then, the sheet is fixed to the sheet, and the conveying sheet is warmed by the surface temperature of the pressure roller, so that the smooth process of the vapor fixing process is assisted.

  However, among the transport papers, some of the thick papers are extremely thick because they are extremely thick, such as postcards, and many thin papers are stacked like envelopes. Some paper types include an air layer between them. When such a plurality of paper types are fixed with a fixed fixing nip width and fixing nip pressure, some paper may cause a fixing failure in which unfixed toner does not melt, or wrinkles may occur on the transport paper. .

In order to solve such a defect such as fixing failure, in Patent Document 1, a pressure that changes the internal pressure of the elastic layer of the heating / pressurizing roller having an elastic layer according to the type of transport paper as a transfer material. An image forming apparatus including a fixing mechanism that stabilizes the fixing performance by adjusting the nip width and pressure of the fixing nip portion by providing an adjusting mechanism is disclosed.
JP 09-311574 A

  However, in the technique disclosed in Patent Document 1 described above, it has been proposed to stabilize the fixing performance by changing the internal pressure of the elastic layer of the heating / pressurizing roller. It has been found that it is not only the fixing nip width and fixing nip pressure that are determined. In other words, the fixing performance is that the paper passing between the fixing nip widths receives heat from the surface of the heating roller, warms the paper, melts and fixes unfixed toner on the paper, and the pressure roller surface temperature. Is determined by warming the conveyance sheet from the fixing back surface and assisting the fixing process. For this reason, in the fixing mechanism of the image forming apparatus described in Patent Document 1, only the fixing nip width is discussed, and no response is made to the surface temperature of the heating roller, etc., so that the fixing performance can be sufficiently stabilized. It did not come. In particular, when the transport paper is a thick recording medium such as cardboard, postcard, envelope, etc., the surface temperature of the heating / pressurizing roller takes a large amount of heat away from the transport paper. "Inferior" was sometimes invited. In addition, the envelope that passes through the fixing nip width set by the fixing device includes an air layer in the envelope in addition to the size of the thickness. “Phenomenon” occurs, and a printed matter with “wrinkles” may be provided. In other words, when the transport paper is thicker than a predetermined thickness, such as thick paper or envelopes, problems such as wrinkling of the transport paper and unfixed / overfixed toner transferred onto the recording medium may be observed. It was.

  Accordingly, the present invention has been made in view of the above problems of a fixing device (fixing mechanism) provided in a conventional image forming apparatus, and an object of the present invention is to fix the fixing nip portion according to the type of recording medium. It is an object of the present invention to provide a new and improved fixing device capable of further improving the fixing performance and an image forming apparatus including the fixing device.

  In order to solve the above problems, according to an embodiment of the present invention, an unfixed toner image is transferred to a fixing nip formed between a heat fixing member and a pressure member pressed against the heat fixing member. A fixing device that heats and fixes the recorded recording medium, and changes the position of the pressing member relative to the heat fixing member according to the type of the recording medium that passes through the fixing nip portion; and There is provided a fixing device comprising: a surface temperature detecting unit that detects a surface temperature of the heat fixing member and contacts and separates from the heat fixing member in conjunction with a position change of the pressure member.

  With such a configuration, a suitable pressure, nip width, and fixing temperature in the fixing nip portion are set according to the type of the recording medium to be conveyed. Unfixed / overfixing of the transferred toner is prevented in advance, and the fixing performance of the transferred toner onto the recording medium in the fixing nip portion of the fixing device is improved.

  At this time, in the above embodiment, the pressure member position changing means moves the pressure member in a direction away from the heat fixing member when the recording medium passing through the fixing nip portion has a predetermined thickness or more. It is also possible to make it.

  In this way, when the recording medium to be transported paper is a predetermined thickness or more such as thick paper, postcard, envelope, etc., the pressure roller to be a pressure member is set more than when the recording medium is thin paper such as plain paper. By moving in a direction away from the heating roller serving as the heat fixing member, the pressure applied by the pressure roller serving as the pressure member can be reduced and the nip width can be reduced. For this reason, in particular, when a recording medium having a predetermined thickness or more such as thick paper, postcard, envelope, or the like, on which transfer toner is likely to be poorly fixed, is used as the conveyance paper, wrinkling of the conveyance paper due to the pressure of the fixing nip portion is generated. Will be prevented.

  At this time, in the above embodiment, the surface temperature detecting means may move in a direction away from the heat fixing member when the recording medium passing through the fixing nip portion has a predetermined thickness or more.

  In this way, when the recording medium to be transported paper is a predetermined thickness or more such as thick paper, postcard, envelope, etc., by separating the thermistor serving as the surface temperature detecting means that is pressed against the heating roller from the heating roller. Since an air layer is formed between the thermistor and the surface of the heating roller, the temperature of the surface of the heating roller can be naturally increased. For this reason, the surface temperature of the heating roller is raised from that of plain paper, so the amount of heat taken away from the surface temperature of the heating / pressurizing roller is large, and unfixed toner is insufficiently melted. It is possible to improve the fixing performance of unfixed toner in a recording medium having a predetermined thickness or more, such as thick paper, which is frequently called. In addition, the fixing nip temperature (fixing set temperature) caused by the surface temperature of the heating roller can be adjusted more easily than the fixing temperature setting by the conventional control means.

  At this time, in the above embodiment, the surface temperature detecting means is within a range in which the temperature rise of the heat fixing member due to the separation of the surface temperature detecting means from the surface of the heat fixing member does not exceed the heat resistance characteristic temperature of the heat fixing member. The heat fixing member may be separated from the heat fixing member, or may be separated from the heat fixing member within a range where the unfixed toner transferred to the recording medium passing through the fixing nip portion does not become overfixed.

  As described above, since there is an air layer between the surface of the heating roller serving as the heat fixing member and the thermistor serving as the surface temperature detecting means, when the thermistor detects the fixing set temperature, the heating roller is the original fixing setting. It has risen above the temperature. For this reason, the fall of the heating function of a heating roller is suppressed by separating a thermistor from a heating roller in the range which does not exceed the heat resistance characteristic temperature of a normal heating roller. Further, by separating the thermistor from the heating roller so that the surface temperature of the heating roller separated from the thermistor rises by about +10 to + 20 ° C. compared to the normal fixing setting temperature, the toner is excessively heated from the heating roller. It is possible to avoid the “high temperature offset” that is affected and becomes overmelted and adheres to the heating roller.

  At this time, in the above-described embodiment, the position change by the pressure member position changing means may be a manual movement.

  By adopting such a configuration, the user can adjust a suitable nip width and nip pressure of the fixing nip portion in advance according to the type of the conveying paper to be printed, so that the conveying paper caused by the pressure in the fixing nip portion can be obtained. This prevents the occurrence of “wrinkles” and eliminates fixing defects such as unfixed or overfixed transfer toner on the conveyance sheet.

  At this time, in the above embodiment, the position change by the pressure member position changing means may be moved in accordance with the selection of the recording medium type selected when printing on the recording medium is requested.

  With such a configuration, when a print request is made, the fixing nip portion is selected in accordance with the selected desired paper type by selecting the type of transport paper on the operation panel or the like provided in the image forming apparatus. The preferred nip width and nip pressure can be adjusted. For this reason, it is possible to avoid the occurrence of “wrinkle” of the conveyance sheet due to the pressure in the fixing nip portion, and to solve fixing defects such as unfixed / overfixing of the transfer toner on the conveyance sheet.

  At this time, in the above-described embodiment, the pressing member position changing unit presses the pressing member against the heating and fixing member, and an contacting / separating operation member for operating the pressing member with respect to the heating and fixing member. A pressure contact operation input detection unit that detects an input of the operation when the contact / separation operation member is operated, and the contact / separation operation of the surface temperature detection means with respect to the heat fixing member is performed by inputting to the pressure contact operation input detection unit. It may be determined by the presence or absence.

  By specifically configuring the pressure member position changing means for changing the position of the pressure roller in such a configuration, a suitable nip width and nip pressure of the fixing nip portion can be easily adjusted.

  In order to solve the above problems, according to another embodiment of the present invention, a latent image carrier, a transfer device for transferring a toner image formed on the latent image carrier to a recording medium, An image forming apparatus comprising: a fixing device that fixes a toner image on a recording medium; and an image forming apparatus including the fixing device according to any one of the above embodiments as a fixing device. .

  By adopting such a configuration, the pressure applied to the fixing nip portion by the pressure roller of the fixing device can be changed according to the type of the conveying paper, so that when the conveying paper passes the fixing nip portion of the fixing device. Thus, the printed matter is free from defects such as wrinkles on the transport paper, and a good print paper can be provided. In addition, it suppresses fixing defects such as unfixed and overfixing of the transfer toner on the transport paper, so that it is possible to eliminate fixing defects due to paper wrapping around the heating roller due to overfixing and insufficient melting of the toner. Can be provided.

  In particular, the surface temperature of the heating roller is raised in conjunction with reducing the pressure at the fixing nip portion when transporting a recording medium having a predetermined thickness or more, such as cardboard, postcards, and envelopes, which has conventionally been liable to cause a fixing failure. Therefore, the fixing performance of these cardboard, postcard, envelope and the like can be improved, and the same fixing performance as that when plain paper is passed can be obtained.

  As described above, according to the present invention, it is possible to set a suitable pressure, nip width, and fixing temperature in the fixing nip portion according to the type of the recording medium to be conveyed. In addition, fixing failure such as unfixing or overfixing of the transfer toner is suppressed, and the fixing performance of the transfer toner onto the recording medium in the fixing nip portion of the fixing device is improved. In particular, even when the recording medium has a predetermined thickness or more, such as thick paper, in which the recording medium is easily wrinkled or the fixing failure such as unfixed / overfixed transfer toner is likely to occur, these problems can be solved.

  Further, by improving the fixing performance of the fixing nip portion in the fixing device, the recording medium subjected to the printing process becomes a printed matter free from defects such as wrinkles and fixing defects, and it is possible to provide a good printing paper.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  First, a first embodiment of an image forming apparatus including a fixing device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing the overall configuration of an image forming apparatus including the fixing device of the present embodiment, and FIG. 2 is a partial detail view showing the configuration of the apparatus main body of the image forming apparatus.

  In the present embodiment, the image forming apparatus 1A uses a predetermined sheet-like recording sheet (hereinafter referred to as a sheet) as a recording medium by electrophotographic processing of image data read by a scanner or the like and image data transmitted from the outside. A sheet feeding tray 8 on which a plurality of sheets P can be stacked, and sheet conveyance for conveying the sheet P supplied from the sheet feeding tray 8 to the image forming unit 14. And a sheet feeding tray 8 that can automatically supply the sheet P. A document reading device 1A2 is provided above the image forming apparatus 1A so that the upper surface of the document placing table 21 can be freely opened and closed.

  As shown in FIGS. 1 and 2, the image forming apparatus 1A mainly includes an exposure unit 1, a developing device 2, a photosensitive drum 3, a charger 4, a charge eliminating device 41, a cleaner unit 5, a fixing unit 6, and a sheet conveyance. The apparatus main body 1A1 includes an apparatus 7, a paper feed tray 8, a paper discharge tray 9, a transfer mechanism 10, and the like, and an automatic document processing apparatus 1A2.

  A document placing table 21 made of transparent glass on which a document is placed is provided on the upper surface of the apparatus main body 1A1. Above the document placing table 21, the automatic document processing device 1A2 is swingably opened upward. On the other hand, a scanner unit 22 serving as a document reading unit that reads image data of a document is disposed below the document placing table 21.

  Below the scanner unit 22, an exposure unit 1, a developing device 2, a photosensitive drum 3, a charger 4, a charge eliminating device 41, a cleaner unit 5, a fixing unit 6, a paper transport device 7, a paper discharge tray 9, and a transfer mechanism. 10 is disposed, and a paper feed tray 8 in which the paper P is stored is disposed below.

  The exposure unit 1 irradiates the surface of the photosensitive drum 3 uniformly charged by the charger 4 with light according to image data (printing image data) output from an image processing unit (not shown). Thus, the electrostatic latent image corresponding to the image data is written and formed on the surface of the photosensitive drum 3.

  The exposure unit 1 is disposed immediately below the scanner unit 22 and above the photosensitive drum 3, and employs laser scanning units (LSU) 13 a and 13 b including a laser irradiation unit 11 and a reflection mirror 12. In the present embodiment, in order to perform high-speed printing processing, a technique that uses a plurality of laser beams to reduce the speed of irradiation timing is adopted, and a two-beam technique is adopted.

  In the present embodiment, the laser scanning units (LSU) 13a and 13b are used for the exposure unit 1, but light emitting elements are arranged in an array, for example, an EL or LED writing head is used. Also good.

  As shown in FIG. 2, the photosensitive drum 3 has a substantially cylindrical shape, is disposed below the exposure unit 1, and is rotated in a predetermined direction (the direction of arrow A in the figure) by a driving unit and a control unit (not shown). So that it is controlled. Along the outer peripheral surface of the photosensitive drum 3, the sheet peeling claw 31, the cleaner unit 5, and the charger 4 as an electric field generating unit are directed toward the downstream side in the rotation direction of the photosensitive drum 3 with reference to the position after the image transfer is completed. The developing device 2 and the charge eliminating device 41 are arranged in this order.

  The sheet peeling claw 31 is disposed so as to be able to contact and separate from the outer peripheral surface of the photosensitive drum 3 by a solenoid 32. When the unfixed toner image on the photosensitive drum 3 is transferred to the paper P with the paper peeling claw 31 in contact with the outer peripheral surface of the photosensitive drum 3, the paper peeling claw 31 sticks to the surface of the photosensitive drum 3. The sheet P is peeled off. Note that a driving motor or the like may be adopted as the driving means for the sheet peeling claw 31 instead of the solenoid 32, and other driving means can be selected.

  The developing device 2 visualizes the electrostatic latent image formed on the photosensitive drum 3 with black toner. The developing device 2 rotates in the rotating direction of the photosensitive drum 3 (the direction of arrow A in the figure). It is arranged substantially horizontally (right side in the figure) on the downstream side and on the side of the photosensitive drum 3. A registration roller 15 is disposed below the developing device 2 on the upstream side in the recording medium conveyance direction.

  The registration roller 15 aligns the front end of the paper P supplied from the paper feed tray 8 and the toner image on the photoconductive drum 3 and conveys it between the photoconductive drum 3 and the transfer belt 103 (not shown). The operation is controlled by the drive means and the control means.

  The charger 4 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential, and is disposed above the photosensitive drum 3 and in the vicinity of the outer peripheral surface thereof. In this embodiment, the charger type charger 4 is used. However, a contact type roller type or a brush type may be used.

  The static eliminator 41 is a pre-transfer static eliminator for reducing the surface potential of the photosensitive drum 3 in order to facilitate the transfer of the toner image formed on the surface of the photosensitive drum 3 to the paper P. It is disposed downstream of the developing device 2 in the drum rotation direction and close to the outer peripheral surface below the photosensitive drum 3. In the present embodiment, the static eliminator 41 is configured using a static elimination electrode. However, a static elimination lamp may be used instead of the static elimination electrode, or static elimination may be performed by other methods. .

  The cleaner unit 5 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer, and is located at a position substantially opposite to the developing device 2 with the photosensitive drum 3 interposed therebetween. The drum 3 is disposed substantially horizontally (left side in the drawing) on the side.

  As described above, the electrostatic image visualized on the photosensitive drum 3 is applied from the transfer mechanism 10 onto the paper P on which the electric field having the opposite polarity to the electric charge of the electrostatic image is conveyed. Transferred onto P. For example, when the electrostatic image has a charge of (−) polarity, the polarity applied to the transfer mechanism 10 is (+) polarity.

As shown in FIG. 2, the transfer mechanism 10 is bridged by a driving roller 101, a driven roller 102, and other rollers, and has a predetermined resistance value (1 × 10 ⁹ to 1 × 10 ¹³ Ω in this embodiment). A transfer belt unit having a transfer belt 103 having a range of cm) is disposed, and the surface of the transfer belt 103 is in contact with a part of the outer peripheral surface of the photosensitive drum 3 below the photosensitive drum 3. Has been placed. The transfer belt 103 conveys the paper P while pressing it against the photosensitive drum 3.

  An elastic conductive roller 105 capable of applying a transfer electric field with different conductivity from the driving roller 101 and the driven roller 102 is disposed at the contact portion 104 between the photosensitive drum 3 and the transfer belt 103. The elastic conductive roller 105 is made of a soft material such as elastic rubber or foamable resin. Since the elastic conductive roller 105 has elasticity, the photosensitive drum 3 and the transfer belt 103 are not in line contact but in surface contact having a predetermined width (referred to as a transfer nip). The transfer efficiency to P can be improved.

  Further, on the downstream side of the transfer area of the transfer belt 103 in the paper conveyance direction, a static elimination roller 106 is transferred to neutralize the electric field applied to the conveyed paper P in the transfer area and smoothly carry it to the next process. It is arranged on the back side of the belt 103.

  In addition, the transfer mechanism 10 is provided with a cleaning unit 107 that removes dirt from the residual toner on the transfer belt 103 and a plurality of charge removal mechanisms 108 that perform charge removal on the transfer belt 103. As a technique for performing static elimination used in the static elimination mechanism 108, there is a technique of grounding through an apparatus, or a technique of positively applying a polarity opposite to the polarity of the transfer electric field.

  The electrostatic image (unfixed toner) transferred onto the paper P by the transfer mechanism 10 is conveyed to the fixing unit 6 and is pressurized and heated to melt the unfixed toner and be fixed on the paper P. .

  As shown in FIG. 2, the fixing unit 6 includes a heating roller 6a and a pressure roller 6b. The heating roller 6a is rotated while the sheet P is sandwiched between the heating roller 6a and the pressure roller 6b. And a pressure roller 6b, the toner image transferred onto the paper P is melted and fixed to have a function as a fixing device. A conveyance roller 16 that conveys the paper P is provided downstream of the fixing unit 6 in the paper conveyance direction.

  The heating roller 6a has a sheet peeling claw 611, a thermistor 612 serving as a surface temperature detecting means for the heating roller 6a, and dirt adhered to the surface of the heating roller 6a at the outer periphery thereof, and at the same time, a release agent on the surface. A web cleaning unit 650 is disposed, and a heating heater 614 serving as a heat source for setting the outer peripheral surface of the heating roller 6a to a predetermined temperature (fixing set temperature: approximately 160 to 200 ° C.) is provided inside the heating roller 6a. ing.

  On the other hand, the pressure roller 6b is provided with a pressure member 621 that allows the pressure roller 6b to come into pressure contact with the heating roller 6a at a predetermined pressure amount at both ends of the roller 6b. A roller surface cleaning member 623 for cleaning dirt adhering to the outer peripheral surface of the sheet peeling claw 622 and the pressure roller 6b is disposed on the outer periphery of the paper roller in substantially the same manner as the outer periphery of the heating roller 6a. In the present embodiment, similarly to the heating roller 6a, a heater 624 serving as a heat source for heating the outer peripheral surface to a predetermined temperature is provided.

  As shown in FIG. 2, the fixing unit 6 is configured to remove unfixed toner on the conveyed paper P at a pressure contact portion 600 (called a fixing nip portion) between the heating roller 6a and the pressure roller 6b. The unfixed toner is fixed on the paper P by a throwing action on the paper P by the pressure contact force between the heating roller 6a and the pressure roller 6b. The details of the configuration of the fixing unit 6 serving as the fixing device of the present embodiment will be described later.

  The paper feed tray 8 is for accumulating a plurality of sheets (paper sheets) on which image data is output (printed). The exposure unit 1, the developing device 2, the photosensitive drum 3, the charger 4, the static elimination The image forming unit 14 is provided below the image forming unit 14 including the apparatus 41, the cleaner unit 5, the fixing unit 6, and the like. A paper pickup roller 8 a is disposed on the upper side of the paper discharge side of the paper feed tray 8.

  The sheet pickup roller 8a picks up the sheets P stacked and accommodated in the sheet feed tray 8 one by one from the uppermost layer, and moves toward the downstream side (for convenience, the flow-out side (cassette side) of the sheet P is upstream and discharged). The paper side is the downstream side.) The paper is conveyed to the registration roller 15 (also referred to as "idle roller") side on the paper conveyance path 7a constituting the paper conveyance device 7.

  In the image forming apparatus 1A according to the present embodiment, for the purpose of performing high-speed printing processing, a plurality of standard size sheets P can be stored in each tray below the image forming unit 14 in a plurality of sheets. On the other hand, a large-capacity paper feed cassette 81 capable of storing a large amount of a plurality of paper types is disposed on the side surface of the apparatus, and mainly above the large-capacity paper feed cassette 81. A manual feed tray 82 corresponding to printing of an irregular size is provided.

  The paper discharge tray 9 is disposed on the side surface of the apparatus opposite to the manual feed tray 82. Further, instead of the paper discharge tray 9, a post-processing device (device for performing stapling, punching, etc.) of paper discharge, a multi-stage paper discharge tray, and the like can be arranged as options.

  The paper transport device 7 is configured between the photosensitive drum 3 and the paper feed tray 8 described above, and receives the paper P supplied from the paper feed tray 8 via the paper transport path 7 a provided in the paper transport device 7. Each sheet is conveyed one by one to the transfer mechanism 10, in which the sheet on which the toner image is transferred from the photosensitive drum 3 is conveyed to the fixing unit 6, and after the unfixed toner image is fixed on the sheet in the fixing unit 6. The paper is transported by a paper transport path or a branching claw formed in accordance with the designated paper discharge processing mode.

  Here, a paper conveyance process corresponding to the processing mode by the paper conveyance device 7 in the image forming apparatus 1A will be described.

  As shown in FIG. 2, the paper P that matches the print request is selected from the plurality of paper feed trays 8 and is transported to the registration rollers 15 by the transport rollers in the paper transport path 7a.

  The paper P that has reached the registration roller 15 and has stopped once is conveyed to the transfer mechanism 10 when the registration roller rotates again at the timing when the leading edge of the paper P matches the image data on the photosensitive drum 3, and the paper P After an unfixed toner image (image data) is transferred from the photosensitive drum 3 to the upper side, the toner image is fixed on the paper P by the fixing unit 6 and discharged to the paper discharge tray 9.

  In the conveyance path in the sheet conveyance path 7a, the sheet discharge tray from the fixing unit 6 onward is processed by the processing mode (copier mode, printer mode, FAX mode) of the image forming apparatus 1A and the printing processing method (single-sided printing, duplex printing). The transport method up to 9 is different.

  Usually, in the copier mode, since the user performs an operation in the vicinity of the image forming apparatus 1A, a method called “face-up discharge” in which the printing surface is discharged with its upper side being used is often used.

  On the other hand, in each mode such as printer, FAX, etc., a “face-down discharge” method that aligns the page order of the discharged paper P because the user is not in the vicinity of the image forming apparatus 1A is often used.

  Accordingly, in the image forming apparatus 1A, before the sheet P that has passed through the fixing unit 6 is discharged to the sheet discharge tray 9, the sheet that meets the above-described purpose is discharged through a plurality of conveyance paths. ing.

  Here, the paper conveyance path 7a provided in the paper conveyance device 7 will be described in detail with reference to the drawings. FIG. 3 is an explanatory diagram illustrating the configuration of the sheet conveyance path of the image forming apparatus according to the present embodiment. FIG. 4 illustrates the branched sheet conveyance path that forms the sheet conveyance path and the branching claw that communicates them. It is a partial detailed view which shows a structure.

  As shown in FIGS. 3 and 4, the sheet conveyance path 7 a mainly includes the first sheet conveyance path 7 a 1 from the sheet feed tray 8 to the registration rollers 15, and the fixing unit 6 from the registration rollers 15 via the transfer mechanism 10. A second paper transport path 7a2 that passes through and reaches the downstream transport roller 16, a third paper transport path 7a3 that reaches the paper discharge roller 17 for discharging paper from the transport roller 16 to the paper discharge tray 9, and a transport roller 16 The fourth paper transport path 7a4 for reversing the paper P from the second paper, the fifth paper transport path 7a5 communicating with the fourth paper transport path 7a4, and the reverse transport roller 18 for transporting the paper P to the registration roller 15 again, the paper discharge roller A sixth paper transport path 7a6 that reverses from 17 and transports the paper P, a seventh paper transport path 7a7 that communicates with the sixth paper transport path and avoids the fifth paper transport path 7a5, and a seventh paper transport path 7a7; Communicating switchback low And an eighth sheet transport path 7a8 that reaches the track 19.

  A plurality of sheets P are arranged in the sheet transport path 7a according to the processing mode. In the present embodiment, as shown in FIG. 3, eight sheets P of (1) to (8) (indicated by encircled numbers in the figure) are arranged in the sheet transport path 7. However, the allowable number of sheets P in the sheet conveyance path can be changed by the configuration of the sheet conveyance path 7a. Further, a plurality of branching claws 20 for selecting the paper transport path 7a according to the selected processing mode and changing the transport path of the paper P are provided in the paper transport path 7a at the branch point of the paper transport path 7a. It has been.

  As shown in FIG. 4, a branch claw 20a communicating with the third paper transport path 7a3 or the fourth paper transport path 7a4 is provided in the vicinity of the downstream side of the transport roller 16 so as to be able to swing and displace. The branch claw 20a is operated by a solenoid (not shown).

  On the downstream side of the fourth paper transport path 7a4, a branch claw 20b that connects the fourth paper transport path 7a4 and the fifth paper transport path 7a5 or the fifth paper transport path 7a5 and the sixth paper transport path 7a6 swings. Displaceable. The branch claw 20b is operated by a spring member (not shown) and the elastic force of the paper P.

  On the downstream side of the sixth paper transport path 7a6, a branch claw 20c that communicates with the fifth paper transport path 7a5 or the seventh paper transport path 7a7 is provided so as to be swingable and displaceable. The branch claw 20c is operated by a solenoid (not shown).

  On the downstream side of the seventh paper transport path 7a7, a branch claw 20d that causes the seventh paper transport path 7a7 and the eighth paper transport path 7a8 or the fifth paper transport path 7a5 and the eighth paper transport path 7a8 to communicate is swung. Displaceable. The branch claw 20d is operated by a solenoid (not shown).

  On the upstream side of the fifth paper transport path 7a5, a branching claw for allowing the fourth paper transport path 7a4, the eighth paper transport path 7a8 and the fifth paper transport path 7a5 to communicate with each other and smoothly carry the paper. 20e is provided.

  According to the paper conveyance path 7a provided in the paper conveyance device 7 configured as described above, the branch claws 20a to 20d are operated according to the requested processing mode, and the conveyance path of the paper P corresponding to the processing mode can be selected. It is said.

  Next, details of the configuration of the fixing device provided in the image forming apparatus according to the present exemplary embodiment will be described with reference to the drawings. FIG. 5 is a diagram showing a schematic configuration diagram of a fixing unit serving as a fixing device of the present embodiment, FIG. 6 is a diagram showing a detailed configuration of a conventional fixing unit as a comparative example, and FIG. FIG. 3 is a front view showing a detailed configuration of a heating roller provided in the fixing device of the present embodiment in a partial cross-sectional view. 5 to 7 are examples that are simplified and described mainly with respect to main components of the fixing device of the present embodiment, and are not limited to the configuration of the fixing device of the present invention.

  In the present embodiment, as shown in FIG. 5, the fixing unit 6 is covered with an exterior portion 661 formed of a heat-resistant material and serves as a heat fixing member and a pressure applied to the heat roller 6a. A pressure roller 6b as a member is provided. In this fixing unit 6, unfixed toner having image information transferred onto the sheet by the image forming unit 14 of the image forming apparatus 1A is pressed at a pressure contact portion (fixing nip portion N6) between the heating roller 6a and the pressure roller 6b. Upon receipt of heat from the heating roller 6a and the pressure roller 6b, the toner image transferred onto the transport paper P is melted and fixed. The heating roller 6a and the pressure roller 6b are covered with a heating roller side cover 661a and a pressure roller side cover 661b, respectively.

  As described above, the sheet peeling claw 611, the web cleaning unit 650, and the thermistor 612 are provided on the outer periphery of the heating roller 6a, and the heater 614 is provided inside the heating roller 6a. On the other hand, the sheet peeling claw 622 and the roller surface cleaning member 623 are provided on the outer peripheral portion of the pressure roller 6b as described above.

  In the web cleaning unit 650, a thin web-like web sheet 651 made of a material such as an unknown cloth, paper, or cloth impregnated with silicon oil or the like is brought into contact with the surface of the heating roller 6 a via the pressing roller 652. As a result, the residual toner on the heating roller 6a is cleaned, and offset due to the residual toner on the heating roller 6a is prevented. The web cleaning unit 650 is fed from the web sheet 651 and a winding roller 653 that winds the web sheet 651 in order to send the web sheet 651 to the contact portion with the heating roller 6a. A take-up roller 654 for taking up the web sheet 651 is provided. Further, a tension roller 655 for preventing the web sheet 651 from slackening is provided between the winding roller 653 and the pressing roller 652, so that the heating roller 6a can be smoothly cleaned.

  As shown in FIG. 5, the heating roller 6a includes a heater 614 serving as a heat source in order to heat the outer peripheral surface of the heating roller 6a to a predetermined temperature. The predetermined temperature required by the outer peripheral surface (front surface) of the heating roller 6a is a temperature required to melt and fix the unfixed toner on the conveyed paper at the fixing nip portion N6. In the image forming apparatus 1A, Although there is some difference from the melting temperature of the toner used, the temperature is generally about 30-40 ° C. added to the melting temperature of the toner. For this reason, generally, the surface temperature of the heating roller 6a is controlled to 160 to 200 ° C.

  In the case of a low-speed machine with a low print processing speed, the amount of heat taken away by the paper and toner is small, so it has been the mainstream to heat the heating roller with a single heater. In the case of a high-speed machine that is high-speed, the number of passing sheets per unit time increases, and accordingly, the amount of heat taken away by the sheets and toner increases, so that a plurality of sheets (in FIG. Many have two heat sources.

  Further, since the heating roller 6a has various paper sizes used for printing and does not necessarily have to uniformly heat the entire heating roller, a plurality of heat sources are provided inside the heating roller 6a. In the present embodiment, inside the heating roller 6a, as shown in FIG. 7, a main heater 614a serving as a main heat source for heating a substantially central portion in the length direction of the heating roller 6a and the main heater 614a are heated. A sub-heater 614b is provided as a sub-heat source for heating substantially both ends of the heating roller 6a in the length direction. When the paper size to be passed is a small size paper, the main heater 614a may be energized. When large size paper is passed, the sub heater 614b is energized in addition to the main heater 614a. . In other words, a method is used in which the surface temperature of the heating roller 6a adapted to the sheet passing size is made constant. For this reason, since it is not necessary to perform extra heating in accordance with the size of the paper to be conveyed, power saving can be achieved as the image forming apparatus 1A.

  On the other hand, the pressure roller 6b pressurizes the conveying sheet P through the heating roller 6a at the fixing nip portion N6 when the conveying sheet P passes through the fixing unit 6, and conveys the molten toner on the sheet with this applied pressure. It has a function of infiltrating a fiber component such as cellulose, which is a constituent component of the paper P, and exerting a throwing action on the transport paper P when the molten toner is solidified. For this reason, depending on the arrangement of the pressure roller 6b, the pressure roller 6b may or may not have a heater 624 serving as a heat source.

  The length of the throwing action (penetration distance to the conveyance paper P) of the molten toner that exerts the throwing action on the conveyance paper P differs depending on the temperature of the conveyance paper P. The higher the paper temperature, the less the cooling of the molten toner. As a result, the permeation distance is increased, the adhesion of the toner fixed on the paper is increased, and the fixing performance can be improved. Usually, when the printing processing speed (process speed) of the image forming apparatus 1A is low, the sheet interval of continuous printing paper is long, and the surface temperature of the heating roller 6a passes through the fixing nip portion N6 and the surface of the pressure roller 6b. In order to heat, the pressure roller 6b does not need the heater 624.

  However, when the printing processing speed is increased, the interval between the transporting papers P is short, and the surface temperature of the heating roller 6a is insufficient to heat the surface of the pressure roller 6b via the fixing nip N6. A heat source is required inside or outside the building. The surface temperature of the pressure roller 6b is lower than the surface temperature of the heating roller 6a and is generally controlled to 110 to 150 ° C., and the conveyance paper P is heated at the fixing nip portion N6 via the pressure roller 6b. Thus, the throwing action is promoted.

  In this way, by including the heater 624 serving as a heat source inside the pressure roller 6b, the conveyed paper is heated, and the toner fixing performance at the fixing nip portion N6 is improved with the paper warmed. The technique is frequently used in high-speed machines in recent years. Normally, the surface temperature of the fixing nip portion N6 is 160 to 200 ° C. on the surface of the heating roller 6a, whereas the surface temperature of the transport sheet is the internal temperature of the apparatus (generally 15 to 35 ° C.). The temperature gap between the fixing nip portion N6 and the surface of the transport sheet becomes large, and the melted toner is rapidly cooled when it penetrates between cellulose in the sheet by the throwing action, and the throwing action becomes weak. In order to avoid such an adverse effect, in this embodiment, in order to increase the throwing effect, the transport sheet is heated from the opposite side to the fixing surface (one surface of the sheet holding unfixed toner). A heater 624 serving as a heat source is disposed.

  In the present embodiment, as shown in FIG. 5, in order to obtain a suitable pressure and nip width of the fixing nip portion N6 according to the type of transport paper (recording medium) passing through the fixing nip portion N6, A fixing nip adjusting mechanism 660 is provided as pressure member position changing means for changing the position by moving the pressure roller 6b toward and away from the heating roller 6a. The fixing nip adjustment mechanism 660 presses the pressure roller 6b against the heating roller 6a and the fixing nip adjustment lever 662 serving as a contact / separation operation member for operating the contact / separation operation of the pressure roller 6b with the heating roller 6a. Thus, a lever position detection sensor 663 serving as a pressure operation input detection unit that detects an input due to a change in the position of the operation when the fixing nip adjustment lever 662 is operated is provided. The fixing nip adjustment lever 662 and the lever position detection sensor 663 provided in the fixing nip adjustment mechanism 660 are provided on the pressure roller side cover 661b that covers the pressure roller 6b in the exterior portion 661 of the fixing device 6. Yes. Details of the configuration and operation of the fixing nip adjusting mechanism 660 will be described later.

  The thermistor 612 provided in the outer peripheral portion of the heating roller 6a is a temperature detection sensor having a function as a surface temperature detecting means for detecting the surface temperature of the outer peripheral surface of the heating roller 6a. For example, the electrical resistance changes by sensing the temperature. Made of ceramic semiconductor. In the present embodiment, as shown in FIG. 7, a center-side temperature detection sensor 612a is provided so as to face a substantially central portion in the length direction of the heating roller 6a, and a substantially end in the length direction of the heating roller 6a. An end side temperature detection sensor 612b is provided so as to face the part.

  Further, ON / OFF control of the heaters 614a and 614b included in the heating roller 6a is executed based on detection data from these temperature detection sensors 612a and 612b. Since the paper of all sizes passes through the substantially central portion of the fixing nip portion N6, the central temperature detection sensor 612a detects that the toner on the paper is in a molten state and adheres to the surface of the heating roller 5a. In order not to pollute the detection sensor 612a, a non-contact type temperature detection sensor is used.

  On the other hand, since the outer peripheral surface of the heating roller 6a opposed to the end side temperature detection sensor 612b is a non-sheet passing region through which all size sheets do not pass, the end side temperature detection sensor 612b is a contact type. A temperature detection sensor is used. Thus, by using a contact-type temperature detection sensor as the end side temperature detection sensor 612b, the temperature of the non-sheet passing region is detected, the end temperature of the heating roller 6a is estimated, and the sub heater 614b is detected. Energization control is performed.

  Further, in the present embodiment, the thermistor 612 is controlled so as to be in contact with and away from the heating roller 6a in conjunction with the position change of the pressure roller 6b. Specifically, the thermistor 612 is heated by an operating mechanism such as a solenoid or a cam (not shown) when the transport paper passing through the fixing nip N6 is a recording medium having a predetermined thickness or more such as thick paper or an envelope. It moves in a direction away from the roller 6a. Control of the contact / separation operation of the thermistor 612 with respect to the heating roller 6a will be described later.

  Next, a detailed configuration of the fixing nip adjusting mechanism provided in the fixing device of the present embodiment will be described with reference to the drawings. FIG. 8 is a diagram showing a detailed configuration of the fixing nip portion adjusting mechanism provided in the fixing device of the present embodiment. FIG. 8A shows a state where the fixing nip portion adjusting lever is in a closed state with respect to the lever position detection sensor. FIG. 7B is a partial cross-sectional view when the fixing nip adjusting lever is closed with respect to the lever position detection sensor. Note that FIG. 8 is an example that is simplified and described mainly with respect to main components of the fixing nip adjusting mechanism of the present embodiment, and is not limited to the configuration of the fixing device of the present invention. .

  In the present embodiment, as shown in FIG. 8, the fixing nip adjusting mechanism 660 includes a fixing nip adjusting lever 662 for operating the contacting and separating operation of the pressure roller 6b with respect to the heating roller 6a, and the fixing nip adjusting lever. A lever position detection sensor 663 is provided that detects an input due to a change in the position of the operation when the user operates the controller 662. The pressure roller 6b is supported by the fixing unit frame 6c via the pressure roller shaft portion 6b1 and the bearing 6b2. In order to move the pressure roller 6b toward and away from the fixing unit frame 6c in the direction of the fixing nip portion N6, the pressure roller shaft portion 6b1 can slide through the bearing 6b2 in the direction of contact and separation. Thus, a vertically long slit portion 6c1 is formed.

  The fixing nip adjustment lever 662 is rotatably provided through one end side of the support member 665 and a fulcrum 664, and is rotated with respect to a lever position detection sensor 663 installed on the pressure roller side cover 661b. As a result, the ON / OFF switch moves toward and away from the fixing nip N6 of the pressure roller 6b. On the other end side of the support member 665, in order to move the pressure roller 6b toward and away from the fixing nip portion N6, a pressure moving member 667 that holds the pressure roller shaft portion 6b1 is moved in this direction. For this purpose, a cam member 666 is rotatably provided via a shaft portion 666a.

  When the fixing nip adjustment lever 662 is in the ON state with respect to the lever position detection sensor 663, the cam member 666 moves the pressure roller 6b in the pressure direction as shown in FIG. When the fixing nip adjustment lever 662 is moved and is in an OFF state with respect to the lever position detection sensor 663, the fixing nip adjustment lever 662 is rotated in conjunction with the OFF operation, as shown in FIG. Then, the pressure roller 6b is moved in the opposite direction to the pressure direction, that is, in the pressure reducing direction. Thus, when the fixing nip adjustment lever 662 is rotated in the closing direction, the pressure roller shaft portion 6b1 is moved in the pressure direction in conjunction with the operation of the lever 662. The amount of movement of the pressure roller 6b is defined by the slit portion 6c1 formed in the fixing unit frame 6c.

  Further, the fixing nip adjustment lever 662 is manually operated so that the user can adjust the nip width and nip pressure suitable for the fixing nip N6 in advance according to the type of transport paper to be printed. Also, when a print request is made, the type of transport paper is selected by an operating condition setting unit 77 (see FIG. 10) such as an operation panel provided in the image forming apparatus 1A, so that the selected paper type is selected. It is also possible to adjust the nip width and pressure of the suitable fixing nip portion N6. In this embodiment, the fixing nip adjustment mechanism 660 includes a fixing nip adjustment lever 662, a lever position detection sensor 663, and a cam mechanism 666. However, a suitable fixing nip according to the type of paper to be conveyed is used. The configuration of the present embodiment is not limited as long as the nip width and pressure of the portion N6 are adjusted.

  Next, a control system of the image forming apparatus 1A including the fixing device of the present embodiment will be described with reference to the drawings. FIG. 9 is a block diagram illustrating a configuration of a control unit of the image forming apparatus according to the present embodiment.

  As shown in FIG. 9, the image forming apparatus 1 </ b> A according to the present embodiment stores image reading processing, image processing, image forming processing, paper P conveyance processing, and the like in a ROM (Read Only Memory) 55 in advance. In accordance with the program, a central processing unit (CPU) 54 serving as a control unit for each component included in the image forming apparatus 1A executes processing using a temporary storage unit such as a RAM (Random Access Memory) 56 or the like. In place of the ROM 55 and the RAM 56, a storage means such as an HDD (Hard Disk Drive) can be substituted.

  In the image forming apparatus 1A, document image data serving as image information of a document read by the scanner unit 22 or document image information transmitted from each terminal device connected to a communication network (not shown) is transmitted via the communication processing unit 58. Are input to the image processing unit 57.

  The image processing unit 57 processes the document image information stored in the storage unit such as the RAM 56 into a print image suitable for printing (image formation on paper) by the above program.

  The image information for printing is input to the image forming unit 14. The image forming unit 14, a sheet conveying unit 59 that detects and controls various types of sheets in the sheet conveying path 7 a, the paper discharge processing unit 60 that performs various types of detection and control of sheets in the fixing unit 6 and the sheet discharge roller 17, It is linked to a drive control unit 62 that controls each drive unit.

  The sheet conveyed by the sheet conveying unit 59 is subjected to a printing process for executing the image information printing process in the image forming unit 14, and then a fixing process performed by the fixing unit 6 for the printed sheet. After that, the paper is discharged to a paper discharge tray 9 serving as a paper discharge portion. As described above, the fixing unit 6 includes the temperature detection sensor (thermistor) 612 and the lever position detection sensor 663 serving as surface temperature detection means of the heating roller 6a.

  Further, the image forming apparatus 1A is provided with an operating condition setting unit 77 and a conveyance paper detection sensor 78. The operating condition setting unit 77 sets the operating conditions such as image forming or conveying conditions of the image forming apparatus 1A according to the image forming request set by the user using the operation switches or the image forming conditions such as the type of the recording medium. It is to set. The conveyance sheet detection sensor 78 is an optical sensor or the like, and detects a sheet passing through the sheet conveyance path 7a, and is provided in any part of the sheet conveyance path 7a provided in the image forming apparatus 1A.

  Further, the image forming apparatus 1 </ b> A is a document reading drive that is a driving actuator for the scanner unit 22, the sheet transport unit 59, the image forming unit 14, the fixing unit 6, the paper discharge processing unit 60, and the like according to the set operation conditions. Drive control of the synchronized operation in accordance with the operation of the CPU 54 based on the program stored in the ROM 55, that is, the operations of the unit 64, the paper conveyance drive unit 66, the print processing drive unit 68, the fixing drive unit 70, and the paper discharge drive unit 72. This is performed under the control of the unit 62.

  The document reading drive unit 64 is a drive actuator for the scanner unit 22. The paper transport drive unit 66 is a motor for driving the paper transport unit 59, specifically, the paper pickup roller 8 a and the registration roller 15 on the paper transport path 7 described above. The print processing drive unit 68 is a drive motor for the photosensitive drum 3. The fixing driving unit 70 is a driving motor for the heating roller 6 a, the pressure roller 6 b, and the web cleaning unit 650 provided in the fixing unit 6. In the present embodiment, the fixing drive unit 70 includes a thermistor contact / separation operation drive unit 70 a that is a drive source for the contact / separation operation of the thermistor 612 that is a temperature detection sensor provided in the fixing unit 6. The paper discharge drive unit 72 is a drive motor for the paper discharge roller 17 and the like. The driving motor and the moving means of each of these driving units can be appropriately configured through a power transmission mechanism using the same or different motors as driving sources.

  Further, in the image forming apparatus 1A, as an optional configuration 74, a post-processing device 81 for executing stapling, punching, and the like and an automatic document reading device (automatic document processing device 1A2, etc.) are arranged. The control unit 500 of the apparatus 1A is configured to synchronize timing adjustment with the apparatus via the communication processing unit 58 while having the control unit 74a in each optional configuration 74.

  In the present embodiment, the CPU 54 serving as a control unit for each component included in the image forming apparatus 1 </ b> A includes a fixing unit control unit 79 that controls operations of various components of the fixing unit 6. Specifically, as shown in FIG. 9, the fixing unit control means 79 includes a fixing temperature arrival determination means 79a, a conveyance paper determination means 79b, a lever position determination means 79c, and a thermistor contact / separation determination means 79d.

  The fixing unit control means 79 includes a heater 614 (614a, 614b) provided in the fixing unit 6, a thermistor 612 (612a, 612b) serving as a temperature detection sensor on the surface of the heating roller 6a, a fixing nip adjustment mechanism 660, and a thermistor 612. And a function of executing operation control of each component included in the fixing unit 6.

  The fixing temperature arrival determining unit 79a determines whether or not the fixing nip portion N6 of the fixing unit 6 has reached the fixing set temperature and is suitable for each recording medium stored in the ROM 55 of the control unit 50 of the image forming apparatus in advance. It has a function of making a judgment by collating it with the data of the fixing set temperature.

  The transport paper discriminating means 79b has a function of discriminating the type of transport paper passing through the fixing nip N6 based on the input data of the operating condition setting unit 77.

  The lever position determination unit 79c has a function of determining whether or not the lever position detection sensor 663 has detected that the position of the fixing nip adjustment lever 662 has been displaced.

  The thermistor contact / separation determining means 79d has a function of determining whether or not the thermistor 612 is separated from the heating roller 6a, and the type of transport paper passing through the fixing nip N6 determined by the transport paper determining means 79b is thick paper or the like. It has a function of determining whether or not it is necessary to perform the contact / separation operation of the thermistor 612 with respect to the heating roller 6a based on whether or not it is detected that the recording medium has a predetermined thickness or more.

  Next, an operation for changing the nip width of the fixing nip portion, the pressure, and the fixing temperature in the fixing unit serving as the fixing device of the present embodiment will be described with reference to the drawings. FIG. 10 is a flowchart showing an operation of changing the nip width, pressure, and fixing temperature of the fixing nip portion in the fixing unit of this embodiment, and FIG. 11 shows a case where the transport paper is cardboard such as cardboard or envelope. FIG. 12 is a flowchart showing an operation for changing the nip width, pressure, and fixing temperature of the fixing nip portion in FIG. 12, and FIG. It is a flowchart which shows this change operation | movement.

  As shown in FIG. 10, first, when a print request is made to the image forming apparatus 1A (step S11), the control unit 500 of the image forming apparatus 1A determines whether or not all print request contents have been inputted (step S11). Step S12). When the control unit 500 confirms that all the printing conditions have been input in step S12, it checks the type of transport paper that contributes to printing (step S13).

  Specifically, the confirmation of the type of transport paper in step S13 is executed by an operating condition setting unit (operation panel) 77 of the image forming apparatus 1A as shown in FIG. An operation display section 77a provided in the operating condition setting section (operation panel) 77 displays an overall view of the apparatus showing the usage state of the image forming apparatus 1A. The sheet feed cassette section of the overall view is attached to the sheet feed cassette. The size of the recorded paper is indicated. In the example shown in FIG. 13, the first paper cassette has a postcard, the second paper cassette has A3 size paper, the third paper cassette has B4 size paper, and the fourth paper cassette has A4R size paper is stored. Further, the operation display unit 77a is provided with a touch panel 77b. By touching a paper button in the center of the right end of the operation display unit 77a shown in FIG. Then, the paper selection screen shown in FIG. In the paper selection screen shown in FIG. 14, as an example of paper feed selection, manual feed is selected and an envelope is selected.

  In step S13, when the type of transport paper is a recording medium (hereinafter referred to as cardboard) having a predetermined thickness or more such as cardboard, postcard, or envelope, the nip width / pressure change for cardboard is changed as shown in FIG. Processing (step S14) and cardboard fixing temperature setting (step S15) are executed, and then printing processing is executed (step S16). Then, it is confirmed whether or not there is a next printing (step S17). If there is no next printing, the image forming apparatus 1A shifts to a standby state.

  On the other hand, in step S13, when the type of transport paper is a recording medium having a predetermined thickness or less (hereinafter referred to as thin paper) such as plain paper, the nip width / pressure changing process for thin paper is shown in FIG. (Step S24), the fixing temperature setting for thin papers (Step S25) is executed, and then the printing process is executed (Step S26). Then, it is confirmed whether or not there is a next printing (step S27). If there is no next printing, the image forming apparatus 1A shifts to a standby state.

  In the cardboard nip width / pressure changing process (step S14) executed subsequently when the type of transport paper is cardboard in step S13, as shown in FIG. The width (fixing nip pressure) and fixing set temperature (heating roller surface temperature) are confirmed (step S141). This step S141 is an indispensable processing step because the amount of heat taken away by the transport paper is large and wrinkles are generated on the transport paper as described above when the transport paper is thick paper.

  That is, when the nip width of the fixing nip portion is narrowed and the pressure is weakened, the melting performance of the transfer toner on the conveyance paper is lowered, and a “fixed defective” printed matter is provided. In the embodiment, in order to print cardboard, a method of increasing the fixing set temperature when the nip width is narrowed is adopted.

  When the fixing nip width (fixing nip pressure) and the fixing set temperature (heating roller surface temperature) are confirmed by a detection sensor (not shown) or the like in step S141, then it is determined whether the lever position detection sensor 663 is OFF or not. The lever position discriminating means 79c confirms the presence / absence of an input signal from the position detection sensor 663 (step S142). When the lever position detection sensor 663 is in the ON state, in order to reduce the nip width and pressure of the fixing nip portion N6, the fixing nip portion adjusting lever 662 is rotated in the opening direction so that the lever position. The detection sensor 663 is turned off (step S143).

  After confirming that the lever position detection sensor 663 is OFF in step S142, that is, the nip width and pressure of the fixing nip portion N6 are smaller than those when transporting thin paper such as plain paper, The process proceeds to step S15 for setting a fixing temperature for cardboard.

  As described above, when the nip width is narrowed in order to print cardboard, a method for increasing the fixing set temperature is adopted. However, as a method for increasing the fixing set temperature, in the present embodiment, The surface temperature of the heating roller 6a is naturally increased by separating the thermistor 612 pressed against the surface of the heating roller 6a from the heating roller 6a and providing an air layer between the thermistor 612 and the surface of the heating roller 6a. It uses the principle that makes it possible.

  For this reason, in step S15 for setting the fixing temperature for cardboard, first, the thermistor contact / separation determining means 79d determines whether or not the thermistor 612 serving as the surface temperature detection sensor of the heating roller 6a is separated from the heating roller 6a. (Step S151).

  If it is confirmed in step S151 that the thermistor 612 is separated from the heating roller 6a, then whether or not the fixing nip portion N6 has reached the fixing set temperature is checked by the fixing temperature arrival determining means 79a (step). S152) When it is confirmed that the fixing nip portion N6 has reached the fixing set temperature, the processes after the printing process (step S16) are executed as described above.

  On the other hand, if it is confirmed in step S151 that the thermistor 612 is not separated from the heating roller 6a, the thermistor contact / separation operation driving unit included in the fixing driving unit 70 is used to raise the fixing nip portion N6 to the fixing set temperature. The thermistor 612 is moved away from the heating roller 6a by driving 70a (step S153). As described above, in the present embodiment, the fixing temperature is changed by the contact / separation operation of the thermistor 612. Therefore, as in the prior art, the fixing temperature is changed by changing the set temperature of the heating roller 6a by the control unit 500. The fixing set temperature can be changed by a simpler method than executing the change control.

  As described above, since there is an air layer between the surface of the heating roller 6a and the thermistor 612, when the thermistor 612 detects the fixing set temperature, the heating roller 6a rises above the original fixing set temperature. ing. For this reason, in order to prevent deterioration of the heating function of the heating roller, it is preferable to separate the thermistor 612 from the heating roller 6a within a range not exceeding the heat resistance characteristic temperature of the normal heating roller 6a. Further, in order to avoid the “high temperature offset” in which the toner is excessively affected by the heating roller 6a and becomes overmelted and adheres to the heating roller 6a, the surface temperature of the heating roller 6a separated from the thermistor 612 is changed. The thermistor is preferably separated from the heating roller so as to increase by about +10 to + 20 ° C. compared to the normal fixing set temperature, and the separation distance is approximately 0.5 to 1.5 mm.

  Thereafter, whether or not the fixing nip portion N6 has reached the fixing set temperature is checked by the fixing temperature arrival determining means 79a (step S152). As described above, the processes after the printing process (process S16) are executed.

  On the other hand, as shown in FIG. 12, in the thin paper nip width / pressure change process (step S24), which is subsequently executed when the transport paper type is thin paper in step S13, the image forming apparatus 1A first The fixing nip width (fixing nip pressure) and the fixing setting temperature (heating roller surface temperature) are confirmed by a detection sensor (not shown) or the like (step S241).

  After step S241, whether or not the lever position detection sensor 663 is ON is confirmed by the lever position determination unit 79c based on the presence or absence of an input signal from the lever position detection sensor 663 (step S242). When the lever position detection sensor 663 is in the OFF state, in order to increase the nip width and pressure of the fixing nip portion N6, the fixing nip portion adjusting lever 662 is rotated in the direction to be in the closed state, so that the lever position is The detection sensor 663 is turned on (step S243).

  Confirm that the lever position detection sensor 663 is turned on in step S242, that is, the nip width and pressure of the fixing nip portion N6 are suitable values for transporting thin paper such as plain paper. Then, the process proceeds to step S25 for setting the fixing temperature for thin paper.

  In step S25 for setting the fixing temperature for thin paper, first, the thermistor contact / separation determining means 79d determines whether or not the thermistor 612 serving as the surface temperature detection sensor of the heating roller 6a is in pressure contact with the heating roller 6a (step). S251).

  If it is confirmed in step S251 that the thermistor 612 is in pressure contact with the heating roller 6a, whether or not the fixing nip portion N6 has reached the set fixing temperature is checked by the fixing temperature arrival determining means 79a (step). In S252), when it is confirmed that the fixing nip portion N6 has reached the fixing set temperature, the processes after the printing process (process S26) are executed as described above.

  On the other hand, if it is confirmed in step S251 that the thermistor 612 is not in pressure contact with the heating roller 6a, the thermistor contact / separation included in the fixing drive unit 70 is used to lower the fixing nip portion N6 to the fixing set temperature for thin paper. The thermistor 612 is pressed against the heating roller 6a by driving the operation driving unit 70a (step S253).

  Thereafter, whether or not the fixing nip portion N6 has reached the fixing set temperature is confirmed by the fixing temperature arrival determining means 79a (step S252). As described above, the steps after the printing process (step S26) are executed.

  As described above, in the fixing device 6 according to the present embodiment, the nip width and pressure of the fixing nip portion N6 suitable for the transport paper are set according to the type of transport paper passed through the fixing nip portion N6. In conjunction with this control, the thermistor 612 is controlled to contact and separate to set the fixing temperature suitable for the transport paper. Therefore, the generation of wrinkles on the transport paper and the undetermined transfer toner are determined. Fixing failure at the fixing nip portion N6 of the fixing device 6 is improved by preventing fixing failure such as wearing / overfixing.

  Further, the pressure applied to the fixing nip portion N6 by the pressure roller 6a of the fixing device 6 can be changed according to the type of the conveyance paper, so that the conveyance paper on the conveyance paper when the conveyance paper passes through the fixing nip portion N6. The printed matter is free from defects such as wrinkles, and good printing paper can be provided.

  Further, since fixing defects such as unfixed and overfixing of the transfer toner on the transport sheet are suppressed, fixing defects due to paper winding around the heating roller 6a due to overfixing and insufficient melting of the toner can be eliminated, and good printing is achieved. Offering of goods will be realized.

  In particular, the surface temperature of the heating roller is increased in conjunction with reducing the pressure at the fixing nip portion N6 when transporting a recording medium of a predetermined thickness or more, such as cardboard, postcards, and envelopes, which has conventionally been prone to fixing defects. Therefore, the fixing performance of these cardboard, postcard, envelope, etc. can be improved, and the same fixing performance as when plain paper is passed can be obtained.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the first embodiment, the present invention is applied to a fixing device installed in a monochrome image forming apparatus in which one toner container is installed. It is also possible to apply the fixing device of the present invention to an image forming apparatus.

1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus including a fixing device according to a first embodiment of the present invention. FIG. 2 is a partial detail view showing the configuration of the apparatus main body of the image forming apparatus in the embodiment. FIG. 4 is an explanatory diagram illustrating a configuration of a sheet conveyance path of the image forming apparatus according to the embodiment. FIG. 4 is a partial detail view illustrating a configuration of a branched paper conveyance path constituting the paper conveyance device and a structure of a branching claw for communicating them. FIG. 2 is a diagram illustrating a schematic configuration diagram of a fixing unit serving as a fixing device according to the embodiment. FIG. 7 is a diagram illustrating a detailed configuration of a conventional fixing unit as a comparative example. It is a front view showing a detailed configuration of a heating roller provided in the fixing device of the embodiment in a partial cross-sectional view, FIG. 2 is a detailed configuration diagram of a fixing nip width varying mechanism provided in the fixing device of the embodiment, and (a) is a partial cross-sectional view when a fixing nip adjustment lever is in a closed state with respect to a lever position detection sensor. (B) is a partial cross-sectional view when the fixing nip adjustment lever is in a closed state with respect to the lever position detection sensor. 3 is a block diagram illustrating a configuration of a control unit of the image forming apparatus according to the embodiment. FIG. 6 is a flowchart showing a nip width changing operation of a fixing nip portion in the fixing device of the embodiment. 5 is a flowchart showing an operation of changing the nip width, pressure, and fixing temperature of a fixing nip portion when the conveyance sheet is a thick sheet in the fixing device of the embodiment. 6 is a flowchart illustrating an operation of changing a nip width, a pressure, and a fixing temperature of a fixing nip portion when the conveyance sheet is thin paper in the fixing device of the embodiment. FIG. 3 is a diagram illustrating an example of an operation condition setting unit of an image forming apparatus including the fixing device according to the embodiment. 6 is a diagram illustrating an example of a sheet selection screen of an operation condition setting unit of an image forming apparatus including the fixing device according to the embodiment. FIG.

Explanation of symbols

1A Image forming apparatus 3 Latent image carrier (photosensitive drum)
6 Fixing device (fixing unit)
6a Heat fixing member (heating roller)
6b Pressure member (Pressure roller)
10 Transfer means (transfer mechanism)
77 Operating condition setting unit 500 Control unit 612 Surface temperature detection means (thermistor)
660 Pressure member position changing means (fixing nip adjusting mechanism)
662 Contact / separation operation member (fixing nip adjustment lever)
663 Pressure operation input detector (lever position detection sensor)
N6 pressure contact (fixing nip)
P Recording medium (paper)

Claims (9)

A fixing device that heats and fixes a recording medium having an unfixed toner image passed through a fixing nip formed between a heat fixing member and a pressure member that is in pressure contact with the heat fixing member,
Pressure member position changing means for changing the position of the pressure member with respect to the heat fixing member according to the type of the recording medium passing through the fixing nip portion;
A surface temperature detecting means for detecting a surface temperature of the heat fixing member and contacting and separating from the heat fixing member in conjunction with a position change of the pressure member;
A fixing device comprising:   The pressure member position changing means moves the pressure member in a direction away from the heat fixing member when the recording medium passing through the fixing nip portion has a predetermined thickness or more. The fixing device according to claim 1.   3. The surface temperature detecting means moves in a direction away from the heat fixing member when the recording medium passing through the fixing nip portion has a predetermined thickness or more. The fixing device according to 1.   The surface temperature detecting means is within the range where the temperature rise of the heat fixing member due to the surface temperature detecting means being separated from the surface of the heat fixing member does not exceed the heat resistance characteristic temperature of the heat fixing member. The fixing device according to claim 1, wherein the fixing device is separated from the fixing device.   The surface temperature detecting means is the unfixed toner transferred to the recording medium passing through the fixing nip portion due to the temperature increase of the heat fixing member caused by the surface temperature detecting means being separated from the surface of the heat fixing member. 5. The fixing device according to claim 1, wherein the fixing device is separated from the heat-fixing member within a range that does not cause over-fixing.   The fixing device according to claim 1, wherein the position change by the pressure member position changing unit is a manual movement.   6. The position change by the pressure member position changing means moves according to the selection of a recording medium type selected when printing on the recording medium is requested. Fixing device. The pressure member position changing means is
A contact / separation operation member for operating a contact / separation operation of the pressure member with respect to the heat fixing member;
A pressure contact operation input detection unit that detects an input of the operation when operating the contact / separation operation member so as to press the pressure member against the heat fixing member;
With
The fixing device according to claim 1, wherein the contact / separation operation of the surface temperature detection unit with respect to the heat fixing member is determined by the presence / absence of an input to the press contact operation input detection unit. An image forming apparatus comprising: a latent image carrier; a transfer device that transfers a toner image formed on the latent image carrier to a recording medium; and a fixing device that fixes the transferred toner image onto the recording medium. In
An image forming apparatus comprising the fixing device according to claim 1 as the fixing device.

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