JP2010164895A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of wrinkles and crease and further printing disturbance by changing setting in a fixing device by the kind of recording paper. <P>SOLUTION: The CPU of an image forming apparatus executes a program including a step (S102) of detecting the kind of the recording paper, when copying is started (YES in S100), a step (S104) of determining whether the recording paper is an envelope or not, a step (S106) of determining whether the envelope is thick or not, when the recording paper is the envelope, and steps (S108, S110, S120, S122, S130, and S132) of setting press-contact release motor rotation time and fixing motor speed correction, based on the determination that the recording paper is the envelope which is thick, the envelope which is not thick or just the recording paper. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes toner as a developer in an electrophotographic image forming apparatus (such as a printer), and in particular, the setting in the fixing device is changed depending on the type of recording paper, and wrinkles or creases are formed. The present invention relates to a fixing device that can suppress the occurrence and suppress printing disturbance. The present invention also relates to an image forming apparatus provided with such a fixing device.

  In an image forming apparatus using an electrophotographic method such as a laser beam printer, a digital copying machine, or a laser facsimile, a thermal fixing device is used as a fixing device for fixing an unfixed image (toner image) transferred to a recording sheet onto the recording sheet. Is widely used.

  This heat fixing device includes a heat roller provided with a halogen lamp heater or the like as a heat source therein, and a pressure roller pressed against the heat roller (this pressure roller may also include a heat source). The recording paper conveyed between the heat roller and the pressure roller is heated and pressurized while being conveyed, thereby melting the toner on the recording paper and fixing the toner image on the recording paper.

  In an image forming apparatus provided with such a thermal fixing device, an envelope may be used as recording paper. Since the envelope is thicker than plain paper because a plurality of sheets overlap, wrinkles or creases may occur when the envelope is fixed.

  For this reason, Japanese Patent Laid-Open No. 2007-212526 (Patent Document 1) discloses that a recording sheet is passed between nips formed by pressing a pressure member against a fixing member, and toner is applied to an envelope by heat and pressure. A fixing device for fixing an image, wherein a pressing force of a pressure member with respect to a fixing member can be changed, and a pressing force at the time of envelope feeding is set to 45 to 60% at the time of passing ordinary paper, and an envelope is passed through Disclosed is a fixing device that raises the fixing temperature at the time of paper more than that at the time of passing plain paper.

  This fixing device prevents the envelope from wrinkling by lowering the pressurizing force when feeding the envelope, and also prevents the fixing failure by reducing the pressurizing force by raising the fixing temperature, ensuring the fixability. can do.

  Further, Japanese Patent Laid-Open No. 2002-023546 (Patent Document 2) discloses an image forming apparatus that changes the fixing pressure in the double-sided printing mode. In this image forming apparatus, the developer image formed on the surface of the electrostatic latent image carrier is transferred to a recording sheet by a transfer unit, and the developer image transferred onto the recording sheet is heated by a fixing unit. And pressure are fixed on the recording paper. This image forming apparatus has a plurality of process modes having different process speeds, which are peripheral speeds of the electrostatic latent image carrier, and is configured to be able to switch process speeds according to the selected process mode. The image forming apparatus includes a fixing pressure variable unit that switches a fixing pressure that is a pressure of the fixing unit, and a control that drives the fixing pressure variable unit to control the fixing pressure according to the process speed of the selected process mode. And the temperature of the fixing unit is controlled to a predetermined constant value regardless of the process speed. In particular, this image forming apparatus has a double-sided printing mode for forming images on both the front and back sides of the recording paper. When the double-sided printing mode is selected, the control unit is more than forming an image on only one side of the recording paper. Also, the fixing pressure is controlled so that the fixing pressure becomes small.

  According to this image forming apparatus, in the double-sided printing mode, the moisture content of the recording paper is reduced by passing through the fixing portion at the time of front side printing. Although there is a problem that the performance is not constant, when the double-sided printing mode is selected, the pressure of the fixing unit is controlled so that the fixing pressure is smaller than that during single-sided printing. For this reason, it is possible to suppress a decrease in the moisture content of the recording paper during front side printing, and there is no need to change the transfer voltage or the fixing temperature between front side printing and back side printing. The front and back transfer performance in the duplex printing mode can be matched with the temperature.

JP 2007-212526 A JP 2002-023546 A

  However, in the fixing device disclosed in Patent Document 1, when the envelope is passed, the fixing pressure is lowered and the fixing temperature is increased compared to the case where plain paper is passed. It is only a thing which secures fixability while preventing the above. It is not possible to prevent printing disturbance at the trailing edge of the envelope due to a decrease in conveying force caused by weakening the fixing pressure contact force. In particular, when the conveyance direction of the recording sheet to the fixing device provided in the image forming apparatus is vertically upward, the envelope is conveyed against gravity, and therefore, when the conveyance force decreases, the envelope moves toward the rear end of the envelope. As the amount of conveyance increases, the print quality decreases.

  In the image forming apparatus disclosed in Patent Document 2, there is no mention or suggestion of an envelope, and in the double-sided printing mode, the fixing pressure is made smaller than in the single-sided printing mode, and the moisture content of the recording paper is reduced. It merely prevents the discrepancy in image quality due to the deterioration of transfer efficiency between the front and back surfaces due to the influence. For this reason, as described above, it is impossible to prevent printing disturbance at the rear end of the envelope due to a decrease in the conveyance force caused by weakening the fixing pressure contact force.

  Further, in the image forming apparatus disclosed in Patent Document 2, the fixing pressure in the process mode having a slow process speed (which is a peripheral speed of the electrostatic latent image carrier and also related to a passing speed of the fixing unit) is low. The control pressure is controlled to be smaller than the fixing pressure in the process mode having a high process speed. That is, the slower the passage speed at the fixing unit, the smaller the fixing pressure. Even if this can be applied when passing through envelopes, it is possible that wrinkles or creases can be prevented by reducing the fixing pressure as disclosed in Patent Document 1, but the passing speed at the fixing unit Is delayed, the deviation of the conveyance amount at the rear end of the envelope is further increased.

  Accordingly, an object of the present invention is to change the setting in the fixing device depending on the type of recording paper, to suppress the occurrence of wrinkles or creases, and to fix a printing disturbance and an image provided with the fixing device. A forming apparatus is provided.

  A fixing device according to an aspect of the present invention is a fixing device that includes a pair of fixing rollers and fixes a toner image on a recording sheet. The fixing unit adjusts the pressing force for sandwiching the recording sheet by the pair of fixing rollers. A force adjusting means, a speed adjusting means for adjusting the conveyance speed of the recording paper by the pair of fixing rollers, a judging means for judging the type of the recording paper, and a pressure contact force based on the judged type of the recording paper And a control means for controlling the pressure contact force adjusting means and the speed adjusting means so as to adjust the conveyance speed.

  In the case where the determined recording paper type is a recording paper of a type in which wrinkles or creases are generated due to a high pressure contact force, the control means reduces the pressure contact force and conveys speed. Can be configured to include a means for controlling. Further, the control means can be configured to include a means for controlling so that the higher the degree of decreasing the pressure contact force, the greater the conveyance speed. Note that the recording paper is either an envelope or a cardboard.

  Further, the pressure contact force adjusting means can be configured to include means for adjusting the pressure contact force by changing the nip amount of the pair of fixing rollers as the rotating member rotates. In this case, the control means can be configured to include means for controlling the rotation time of the rotating member.

  An image forming apparatus according to another aspect of the present invention is an image forming apparatus including any of the fixing devices described above.

  According to the fixing device and the image forming apparatus including the fixing device according to the present invention, when the recording paper is thick like an envelope or the like, a wrinkle or a crease is generated if the pressure contact force of the fixing roller remains high. Therefore, the pressure contact force is reduced. Even if a decrease in the conveyance force due to a decrease in the pressure contact force occurs, if the conveyance speed (fixing speed) in the fixing device is increased in accordance with the decrease in the pressure contact force, a deviation in the conveyance amount also toward the rear end of the envelope It is possible to suppress a decrease in print quality by suppressing the increase in the print quality. As described above, the setting (pressing force and fixing speed) in the fixing unit is changed depending on the type of recording paper, so that the generation of wrinkles or creases can be suppressed and the disturbance of printing can be suppressed.

1 is a cross-sectional view illustrating an internal structure of an image forming apparatus including a fixing unit according to a first embodiment of the present invention. FIG. 2 is a side view showing an outline of a pressure contact force adjusting mechanism in the fixing unit in FIG. 1. FIG. 2 is a functional block diagram illustrating a hardware configuration of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the speed change table memorize | stored in ROM in FIG. It is a flowchart which shows the control structure of the program performed with CPU in FIG. 6 is a flowchart illustrating a control structure of a program executed by a CPU in an image forming apparatus according to a second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same parts are denoted by the same reference numerals. Their functions and names are also the same. The same step number is assigned to the same process. These processes are also the same. Therefore, detailed description thereof will not be repeated. In the following description, the image forming apparatus according to the embodiment of the present invention is described as a tandem full color type, but may be a full color type of another format (for example, four cycles) or a monochrome type. .

<First Embodiment>
[Entire configuration of image forming apparatus]
FIG. 1 is a cross-sectional view showing an internal structure of an image forming apparatus 100 including a fixing unit (fixing device) 7 according to the first embodiment of the present invention.

  The image forming apparatus 100 forms a multicolor image or a single color image on a predetermined recording sheet (sheet) according to image data transmitted from the outside. 100 main body units 110 and an automatic document processing apparatus 120. The main body 110 includes an optical scanning device 1, a developing device 2, a photosensitive drum 3, a cleaner unit 4, a charger 5, an intermediate transfer belt unit 6, a fixing unit 7, a paper feed cassette 81, a paper discharge tray 91, and the like. Configured.

  A document placing table 92 made of transparent glass on which a document is placed is provided on the upper part of the main body 110, and an automatic document processing device 120 is attached to the upper side of the document placing table 92. The automatic document processing device 120 automatically conveys the document on the document placing table 92. Further, the automatic document processing device 120 is configured to be rotatable in the direction of arrow M, and the document can be placed manually by opening the document table 92.

  Image data handled in the image forming apparatus 100 is data corresponding to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, four developing devices 2, photosensitive drums 3, chargers 5, and cleaner units 4 are provided so as to form four types of latent images corresponding to the respective colors, and four of black, cyan, magenta, and yellow are provided. One image station is configured.

  The charger 5 functions to uniformly charge the surface of the photosensitive drum 3 to a predetermined potential. The optical scanning device 1 is configured as a unit including a laser emitting unit and a reflection mirror. The optical scanning device 1 includes a polygon mirror that scans a laser beam, and optical elements such as a lens and a mirror for guiding the laser beam reflected by the polygon mirror to the photosensitive drum 3.

  The optical scanning device 1 has a function of forming an electrostatic latent image corresponding to the image data on the surface thereof by exposing the charged photosensitive drum 3 according to the input image data. The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners of four colors (Y, M, C, K). The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 6 disposed above the photosensitive drum 3 includes an intermediate transfer belt 61, an intermediate transfer belt driving roller 62, an intermediate transfer belt driven roller 63, an intermediate transfer roller 64, and an intermediate transfer belt cleaning unit 65. I have. Four intermediate transfer rollers 64 are provided corresponding to the respective colors Y, M, C, and K. The intermediate transfer belt driving roller 62, the intermediate transfer belt driven roller 63, and the intermediate transfer roller 64 are driven to rotate while the intermediate transfer belt 61 is stretched. The intermediate transfer roller 64 provides a transfer bias for transferring the toner image on the photosensitive drum 3 onto the intermediate transfer belt 61.

  The intermediate transfer belt 61 is provided so as to be in contact with the four photosensitive drums 3, and each color toner image formed on the photosensitive drum 3 is sequentially superimposed and transferred onto the intermediate transfer belt 61. Thus, a color toner image (multicolor toner image) is formed on the intermediate transfer belt 61. The intermediate transfer belt 61 is formed in an endless shape using, for example, a film having a thickness of about 100 μm to 150 μm.

  The toner image is transferred from the photosensitive drum 3 to the intermediate transfer belt 61 by an intermediate transfer roller 64 that is in contact with the back side of the intermediate transfer belt 61. A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 64 in order to transfer the toner image. The intermediate transfer roller 64 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 mm to 10 mm and whose surface is covered with a conductive elastic material (for example, ethylene-propylene-diene rubber, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 61. In this embodiment, a roller-shaped electrode is used as the transfer electrode, but a brush-shaped electrode or the like can be used in addition to that.

  As described above, the electrostatic latent images visualized according to the respective colors on the respective photosensitive drums 3 are stacked on the intermediate transfer belt 61. Thus, the laminated image information is transferred onto the recording paper by the transfer roller 10 disposed at the contact position between the recording paper and the intermediate transfer belt 61 by the rotation of the intermediate transfer belt 61.

  At this time, the intermediate transfer belt 61 and the transfer roller 10 are pressed against each other at a predetermined nip, and a voltage for transferring the toner to the recording paper is applied to the transfer roller 10 (opposite to the toner charging polarity (−)). Polarity (+) high voltage). Further, in order to obtain the nip constantly, either the transfer roller 10 or the intermediate transfer belt driving roller 62 is made of a hard material (metal or the like), and the other is a soft material such as an elastic roller (elastic rubber roller or foaming property). A resin roller or the like is used.

  Further, as described above, the toner adhering to the intermediate transfer belt 61 by contacting the photosensitive drum 3 or the toner remaining on the intermediate transfer belt 61 without being transferred onto the recording paper by the transfer roller 10 is used in the next step. Therefore, the intermediate transfer belt cleaning unit 65 is configured to remove and collect the toner. The intermediate transfer belt cleaning unit 65 is provided with, for example, a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 61. The intermediate transfer belt 61 that comes into contact with the cleaning blade is driven by an intermediate transfer belt driven roller 63 from the back side. It is supported.

  The paper feed cassette 81 is a tray for storing sheets (recording paper) used for image formation, and is provided below the optical scanning device 1 of the main body 110. A sheet used for image formation can also be placed on the manual paper feed cassette 82. A paper discharge tray 91 provided above the main body 110 is a tray for collecting printed sheets face down.

  The main body 110 is provided with a substantially vertical sheet conveyance path S for sending the sheets of the sheet feeding cassette 81 and the manual sheet feeding cassette 82 to the sheet discharge tray 91 via the transfer roller 10 and the fixing unit 7. It has been. In the vicinity of the paper transport path S from the paper feed cassette 81 or the manual paper feed cassette 82 to the paper discharge tray 91, there are a pickup roller 11a, a pickup roller 11b, a plurality of transport rollers 12a to 12d, a registration roller 13, and a transfer roller. 10, a fixing unit 7 and the like are arranged.

  The conveyance rollers 12a to 12d are small rollers for promoting and assisting conveyance of the sheet, and a plurality of the conveyance rollers 12a to 12d are provided along the sheet conveyance path S. The pickup roller 11 a is provided near the end of the paper feed cassette 81, picks up sheets one by one from the paper feed cassette 81, and supplies them to the paper transport path S. Similarly, the pickup roller 11b is provided near the end of the manual paper feed cassette 82, picks up one sheet at a time from the manual paper feed cassette 82, and supplies it to the paper transport path S.

  The registration roller 13 temporarily holds the sheet being conveyed on the sheet conveyance path S. The sheet has a function of conveying the sheet to the transfer roller 10 at the timing when the leading edge of the toner image on the photosensitive drum 3 and the leading edge of the sheet are aligned.

  The fixing unit 7 includes a heat roller 71 and a pressure roller 72, and the heat roller 71 and the pressure roller 72 rotate with the sheet interposed therebetween. The heat roller 71 is set to have a predetermined fixing temperature by a control unit based on a signal from a temperature detector (not shown), and the pressure roller 72 and the toner are thermocompression-bonded to the sheet. The multicolor toner image transferred onto the sheet is melted, mixed and pressed, and thermally fixed to the sheet. An external heating belt 73 for heating the heat roller 71 from the outside is provided. The roller heating method may be an internal heating method (with a halogen lamp heater mounted inside the roller), or the pressure roller 72 may be heated from inside or outside.

  In this fixing unit 7, the pressure contact force by which the sheet is pressed by the heat roller 71 and the pressure roller 72 can be adjusted, and the fixing speed (conveyance of the sheet nipped by the heat roller 71 and the pressure roller 72 can be adjusted. Speed) can also be adjusted. These specific structures and their adjustment methods will be described later.

  Next, the sheet conveyance path will be described in detail. As described above, the image forming apparatus 100 is provided with the paper feed cassette 81 and the manual paper feed cassette 82 for storing sheets in advance. In order to feed sheets from these sheet feeding cassettes 81 or manual sheet feeding cassettes 82, pickup rollers 11a or pickup rollers 11b are arranged to guide the sheets one by one to the sheet conveyance path S.

  The sheet conveyed from the sheet feeding cassette 81 or the manual sheet feeding cassette 82 is conveyed to the registration roller 13 by the conveying roller 12a in the sheet conveying path S, and aligns the leading edge of the sheet with the leading edge of the image information on the intermediate transfer belt 61. It is conveyed to the transfer roller 10 at a timing, and image information is written on the sheet. Thereafter, the sheet passes through the fixing unit 7 so that the unfixed toner on the sheet is melted and fixed by heat, and is discharged onto the sheet discharge tray 91 through the conveyance roller 12b disposed thereafter. Thus, the sheet conveyance direction to the fixing unit 7 is vertically upward. In this way, since the sheet is conveyed against gravity, in a thick sheet (envelope or thick paper having a large weight per unit area), when the conveyance force decreases, the conveyance amount shifts toward the rear end of the sheet. There is a tendency for print quality to decrease.

  In the image forming apparatus 100 according to the present embodiment, when an envelope or the like is passed, the pressing force for pressing the sheet by the heat roller 71 and the pressure roller 72 is reduced, and the fixing speed (heat roller) 71 and the pressure roller 72 are controlled to increase the sheet conveyance speed). These specific control methods will be described later.

  The above-mentioned conveyance path is for a single-sided printing request for a sheet. On the other hand, when a double-sided printing request is made, the trailing edge of the sheet that has finished single-sided printing and has passed through the fixing unit 7 as described above. When the sheet is held by the final conveying roller 12b, the conveying roller 12b rotates backward to guide the sheet to the conveying rollers 12c and 12d. Thereafter, after printing is performed on the back surface of the sheet through the registration roller 13, the sheet is discharged to the discharge tray 91.

[Pressure force adjustment mechanism of fixing unit]
As described above, the pressing force for pressing the sheet by the heat roller 71 and the pressure roller 72 in the fixing unit 7 can be adjusted. For this reason, the fixing unit 7 includes a pressing force adjusting mechanism.

  FIG. 2 is a side view showing an outline of the pressure contact force adjusting mechanism. FIG. 2A shows a state in which the sheet is pressed by the press contact force adjusting mechanism, FIG. 2B shows a state in the middle of releasing the press contact force, and FIG. 2C shows the press contact force. The most released state is shown. The mechanism for adjusting the sheet pressing force in the fixing unit 7 is not limited to the mechanism shown in FIG.

  As shown in FIG. 2, the pressure contact force adjusting mechanism includes a pressure lever 74 that presses the pressure roller 72 in the direction of the heat roller 71, a pressure spring 75 for applying an elastic force to the pressure lever 74, A pressure release lever 76 that moves the pressure lever 74 against the elastic force of the pressure spring 75, a circular rotary gear 77 having a gear 77A that meshes with the gear 76A of the pressure release lever 76, and a rotary gear 77 A pressure release motor 79 that rotates forward (in the direction indicated by arrow R (1) in FIG. 2A) and reverse (in the direction indicated by arrow R (2) in FIG. 2A) and a reference point 76B of the pressure release lever 76 are provided. And a pressure release lever sensor 78 to detect.

  The pressure lever 74 is provided at, for example, at least one end portion of the pressure roller 72 and rotatably supports the pressure roller 72 and is pressed in the direction of the heat roller 71 by the pressure spring 75. The pressure spring 75 is a compression coil spring, for example. The pressure lever 74 presses the pressure roller 72 toward the heat roller 71. When the pressure release lever 76 rotates and the contact state between the pressure lever 74 and the pressure release lever 76 is changed, the position of the pressure lever 74 in the substantially horizontal direction (substantially horizontal direction in the figure) is changed. Thus, the sheet pressing force in the fixing unit 7 is adjusted. The pressure lever 74 has a contact surface 74 </ b> A that contacts the pressure release lever 76.

  The pressure release lever 76 rotates around the rotation shaft 76C. The pressure release lever 76 includes a contact portion 76 </ b> D that contacts the contact surface 74 </ b> A of the pressure lever 74. The contact portion 76D presses the contact surface 74A, and the position of the pressure lever 74 in the substantially horizontal direction is changed. From these points, it can be said that the pressure contact release lever 76 is also a rotating cam. As shown in FIG. 2A, a state where the contact portion 76D and the contact surface 74A are not in contact is a pressure state where the pressure contact force is not released. As shown in FIG. 2B, when the pressure release lever 76 rotates in the direction of the arrow X (1), the contact portion 76D contacts the contact surface 74A. When the contact portion 76D presses the contact surface 74A, the pressure lever 74 moves in the direction indicated by the arrow Y (1) against the elastic force of the pressure spring 75, and the pressure contact force is released. When the pressing force is released, the roller nip amount between the heat roller 71 and the pressure roller 72 decreases. The state shown in FIG. 2B is a state at the time when the pressure release lever sensor 78 detects the reference point 76B of the pressure release lever 76. From this state, when the pressure release lever 76 is further rotated in the direction indicated by the arrow X (1), the pressure lever 74 is further moved in the direction indicated by the arrow Y (1), and the pressure contact force is further released. As shown in C), the pressure contact force is released most.

  The pressure release lever sensor 78 includes, for example, a light projecting unit and a light receiving unit, projects light from the light projecting unit, captures the light reflected by the reference point 76B of the pressure release lever 76, and receives the reference point. 76B is detected. The type of sensor is not limited to this.

  The pressure release lever 76 rotates about the rotation shaft 76 </ b> C, and the driving force for the rotation is transmitted from the rotation gear 77. The rotation gear 77 is a circular gear that rotates about a rotation shaft 77C. A gear 77 </ b> A provided around the circular rotary gear 77 meshes with the gear 76 </ b> A of the pressure release lever 76. When the rotating gear 77 rotates in the direction indicated by the arrow R (1), the pressure contact release lever 76 rotates in the direction indicated by the arrow X (1) (pressure contact release direction). When the rotating gear 77 rotates in the direction indicated by the arrow R (2), the pressure contact release lever 76 rotates in the direction indicated by the arrow X (2) (pressure contact direction).

  Thus, in this pressure contact force adjusting mechanism, when the rotary gear 77 rotates in the direction indicated by the arrow R (1), the pressure release lever 76 rotates in the direction indicated by the arrow X (1), so that the pressure lever 74 is moved. Moving in the direction of arrow Y (1), the pressure contact force by the heat roller 71 and the pressure roller 72 is released. The rotary gear 77 is rotated by a pressure release motor 79, and the pressure release motor 79 is controlled by a pressure release motor control circuit 79C described later.

  The reference pressing force in the pressing force adjusting mechanism is generated when the pressure lever 74 is at the reference position (reference pressure position). Even if the reference position of the pressure lever 74 is the position shown in FIG. 2A, the pressure release lever sensor 78 shown in FIG. 2B detects the reference point 76B of the pressure release lever 76. It doesn't matter. A reference fixing speed is set corresponding to the reference pressing force.

  Note that the amount of movement of the pressure lever 74 in the direction of arrow Y (1) and the amount of movement in the direction of arrow Y (2) are only a small amount. The pressure contact force adjusting mechanism controls the pressure contact force that varies depending on the amount of movement by the amount of rotation of the rotary gear 77.

[Control Block Configuration of Image Forming Apparatus]
FIG. 3 is a functional block diagram illustrating a hardware configuration of the image forming apparatus 100. Referring to FIG. 3, image forming apparatus 100 includes a communication unit 312 for transmitting / receiving data to / from a personal computer or the like via a LAN (Local Area Network), and an operation capable of setting each function relating to image forming processing. Device 166, ROM (Read Only Memory) 306 for storing programs and the like, and HDD (Hard Disk Drive) which is a non-volatile storage area capable of storing programs and data even when power is cut off 302 and a RAM (Random Access Memory) 308 for providing a storage area when executing the program.

  The image forming apparatus 100 further includes a document reading unit 152, an image forming unit 154, an operation device 166, a communication unit 312, a ROM 310, an HDD 302, and a bus 310 connected to the RAM 308, and an image forming device connected to the bus 310. And a CPU (Central Processing Unit) 300 for realizing the general functions.

  The ROM 306 stores a program and data necessary for controlling the operation of the image forming apparatus 100. The CPU 300 controls the image forming apparatus 100 according to the program and data stored in the ROM 306 and executes control related to each function of the image forming apparatus 100.

  The RAM 308 provides a function as a working memory that temporarily stores the results of calculation and processing by the CPU 300 and a function as a frame memory that stores image data.

  The operation device 166 includes a plate-like operation panel 170 provided with hard keys that are numeric keys and other various operation buttons, and a display panel 172 configured from a small touch panel integrated liquid crystal display device. . The operation panel 170 and the display panel 172 are held in one housing, and the operation device 166 is configured to be integrated as a whole.

  In the operation device 166, the state of the image forming apparatus 100 and the job processing status are confirmed by the display on the display panel 172. A selection button is displayed on the display area of the liquid crystal display device of the display panel 172. When the area where the selection button is displayed is pressed with a finger, the touch panel detects the pressed position. By comparing the display position of the selection button with the position where the touch panel is pressed on the program, function setting, operation instruction, and the like of the image forming apparatus 100 are performed.

  Control of the document reading unit 152, the image forming unit 154, the plate-like operation panel 170 and the display panel 172 of the operation device 166, the communication unit 312, the ROM 306, the HDD 302, and the RAM 308 is performed by the CPU 300 executing a predetermined program. Done. In the image forming apparatus 100 according to the present embodiment, the CPU 300 executes a predetermined program, so that the sheet is fed by the heat roller 71 and the pressure roller 72 in the fixing unit 7 according to the type of the sheet to be passed. It is characterized by controlling the pressing force and the fixing speed. Hereinafter, control hardware included in the image forming unit 154 for executing this control will be described. In the control block diagram shown in FIG. 3, only the configuration related to the pressure contact force control and the fixing speed control is described as the image forming unit 154.

  The image forming unit 154 includes a pressure release lever sensor 78 that detects a reference point 76B of the pressure release lever 76, a pressure release motor control circuit 79C that controls a pressure release motor 79 that rotates the rotation gear 77 forward and backward, and a fixing motor. And a speed control circuit 7C. The pressure release lever sensor 78, the pressure release motor control circuit 79C, and the fixing motor speed control circuit 7C are connected to the CPU 300 via the bus 310, respectively.

  When the pressure release lever sensor 78 detects the reference point 76B of the pressure release lever 76, a detection signal is input from the pressure release lever sensor 78 to the CPU 300.

  The CPU 300 outputs a command signal to the pressure release motor control circuit 79C, and based on the command signal, the pressure release motor control circuit 79C is rotated by a predetermined amount (the rotation gear 77 is rotated by a predetermined amount). The pressure release motor 79 is controlled so that the pressure release lever 76 is rotated by a predetermined amount. More specifically, at the time of releasing the pressure contact, when the CPU 300 receives a signal detecting the reference point 76B from the pressure release lever sensor 78, the CPU 300 calculates the rotation time of the pressure release motor 79 after the signal is inputted. By adjusting, the pressure release motor 79 is rotated by a predetermined amount.

  The fixing motor speed control circuit 7C controls the speed of the fixing motor that drives either the heat roller 71 or the pressure roller 72 (in this case, one roller is a driven roller). For example, the CPU 300 outputs a speed command signal to the fixing motor speed control circuit 7C, and based on the speed command signal, the fixing motor speed control circuit 7C controls the fixing motor so as to reach a predetermined fixing speed. Note that the fixing motor may drive both the heat roller 71 and the pressure roller 72 via a gear train, for example.

  As described above, in the image forming apparatus 100 according to the present embodiment, the pressing force and the fixing force for pressing the sheet by the heat roller 71 and the pressure roller 72 in the fixing unit 7 according to the type of the sheet to be passed. Control the speed. In this control, when the pressure contact force is reduced, the fixing speed is increased. This relationship is stored in the ROM 306 as a speed change table. An example of the speed change table is shown in FIG. This speed change table may be stored in the HDD 302 or the RAM 308.

  As shown in FIG. 4, this speed change table shows the relationship between the rotation time of the pressure release motor 79 after the pressure release lever sensor 78 detects the reference point 76B (after the sensor is turned on) and the speed correction amount of the fixing motor. Is stipulated. For example, as shown in FIG. 4, when the rotation time of the press release motor 79 after detecting the reference point 76B is 100 msec (when the press release is defined by this time), it is the reference. When the fixing motor is increased by 0.5% from the fixing speed and the rotation time of the pressure release motor 79 is 150 msec (when the pressure release is further released), the fixing motor is increased by 1.0%. It is specified to be fast.

Software configuration
FIG. 5 is a flowchart showing a control structure of a program executed by CPU 300 of image forming apparatus 100 according to the present embodiment. In the following description, it is assumed that the image forming apparatus 100 is operated in the copy mode.

  In step (hereinafter referred to as “S”) 100, CPU 300 determines whether or not copying has been started. At this time, for example, after the user sets the operation mode of the image forming apparatus 100 to the copy mode with the operation device 166 and sets the recording paper, sets the document, etc., the (copy) start button on the operation panel 170 is performed. It is determined that copying has been started by pressing. When copying is started (YES in S100), the process proceeds to S102. Otherwise (NO in S100), this process ends.

  In S102, CPU 300 detects the type of recording paper. At this time, the CPU 300 detects the type of recording paper based on information input by the user from the operation device 166. In S104, CPU 300 determines whether or not the recording paper is an envelope. If it is determined that the recording sheet is an envelope (YES in S104), the process proceeds to S106. If not (NO in S104), the process proceeds to S130.

  In S106, CPU 300 determines whether or not the paper thickness of the envelope is thick. At this time, the CPU 300 determines that the envelope is thick when the user inputs that it is thick from the operation device 166. If it is determined that the envelope is a thick envelope (YES in S106), the process proceeds to S108. If not (NO in S106), the process proceeds to S120. Note that the determination of whether or not it is thick is not limited to this, and it may be automatically determined from the size and weight of the envelope.

  In S108, CPU 300 sets 150 msec as the pressure release motor rotation time. Thereby, after the pressure release lever sensor 78 detects the reference point 76B, the pressure release motor control circuit 79C controls the pressure release motor 79 so that the pressure release motor 79 is rotated by 150 msec. In S110, CPU 300 sets a 1.0% increase in fixing motor speed correction. As a result, the fixing motor speed control circuit 7C causes the fixing motor that drives at least one of the heat roller 71 and the pressure roller 72 to be accelerated by 1.0% from the reference fixing speed. Will be controlled.

  In S112, CPU 300 starts a sheet passing operation and forms an image on recording paper. Thereafter, this process ends.

  In S120, CPU 300 sets 100 msec as the pressure release motor rotation time. As a result, after the pressure release lever sensor 78 detects the reference point 76B, the pressure release motor control circuit 79C controls the pressure release motor 79 so that the pressure release motor 79 is rotated by 100 msec. In S122, CPU 300 sets a 0.5% increase in fixing motor speed correction. Thus, the fixing motor speed control circuit 7C controls the fixing motor so that the fixing motor is increased by 0.5% from the reference fixing speed. Thereafter, the process proceeds to S112.

  In S130, CPU 300 sets pressure release lever 76 to the reference pressure position. In S132, CPU 300 sets no fixing motor speed correction. As a result, the fixing motor speed control circuit 7C controls the fixing motor so that the fixing motor is rotated at the reference fixing speed. Thereafter, the process proceeds to S112.

[Operation]
An operation of the image forming apparatus 100 according to the present embodiment based on the above-described structure and flowchart will be described.

-Envelope with thick recording paper-
Using the operation device 166, the user sets the operation mode of the image forming apparatus 100 to the copy mode, sets the recording paper to “envelope”, and sets “thick” to set a document, etc. Then, the (copy) start button on the operation panel 170 is pressed (YES in S100).

  Since it is detected that the recording paper is an envelope (S102) and the recording paper is an envelope and thick (YES in S104, YES in S106), the pressure release motor rotation time is set to 150 msec ( In S108, a 1.0% speed increase is set for the fixing motor speed correction (S110).

  When the thick envelope is passed through the fixing unit 7 (S112), after the pressure release lever sensor 78 detects the reference point 76B, the pressure release motor 79 is rotated by 150 msec to add to the heat roller 71 in the fixing unit 7. The pressure contact force that presses the sheet with the pressure roller 72 is reduced. Further, the fixing motor is increased by 1.0% from the fixing speed as a reference.

  The thick envelope passed through the fixing unit 7 in such a state has a sufficiently low pressure contact force, so that the occurrence of wrinkles or creases can be suppressed. In this image forming apparatus 100, since the conveyance direction of the recording paper to the fixing unit 7 is vertically upward, the conveyance force decreases when the pressure contact force decreases, and the deviation of the conveyance amount increases toward the rear end of the envelope. Print quality decreases. However, since the fixing speed is sufficiently increased, the deviation of the transport amount does not increase toward the rear end of the envelope, and the deterioration of the print quality can be suppressed.

−Envelopes with thin recording paper−
The user uses the operation device 166 to set the recording paper to “envelope” and set the original without setting “thick”, and then press the (copy) start button on the operation panel 170. (YES at S100).

  It is detected that the recording paper is an envelope (S102), and since the recording paper is an envelope and not thick (YES in S104, NO in S106), the pressure release motor rotation time is set to 100 msec (S120). ), A 0.5% speed increase is set for the fixing motor speed correction (S122).

  When the thin envelope is passed through the fixing unit 7 (S112), after the pressure release lever sensor 78 detects the reference point 76B, the pressure release motor 79 is rotated by 100 msec to add to the heat roller 71 in the fixing unit 7. The pressure contact force that presses the sheet with the pressure roller 72 is reduced. Further, the fixing motor is increased by 0.5% from the reference fixing speed.

  In the thin envelope passed through the fixing unit 7 in such a state, the pressure contact force is appropriately reduced to the middle, so that generation of wrinkles or creases can be suppressed. In addition, since the fixing speed is appropriately increased halfway, the deviation of the conveyance amount does not increase toward the rear end of the envelope, and it is possible to suppress a decrease in print quality.

-Regular sheets other than envelopes-
The user presses the (copy) start button on the operation panel 170 after setting the original without setting the recording paper as “envelope” (normal sheet) using the operation device 166 (YES in S100). ).

  Since it is detected that the recording paper is not an envelope (S102) and the recording paper is not an envelope (NO in S104), the pressure release lever 76 is set to the reference pressure position (S130), and the fixing motor speed is not corrected. Is set (S132).

  When a non-envelope sheet is passed through the fixing unit 7 (S112), the pressure contact release lever 76 is in the reference pressure position, and the pressure contact force that presses the sheet with the heat roller 71 and the pressure roller 72 in the fixing unit 7 is pressed. Is the reference state. Furthermore, the fixing speed is based on the fixing motor.

  Since the sheet passed through the fixing unit 7 in such a state is a sheet even if the pressure contact force is sufficiently high, no wrinkles or creases occur. Further, even if the fixing speed is the reference speed, it is not thick, so the deviation of the transport amount does not increase toward the trailing edge of the sheet, and the print quality does not deteriorate.

  As described above, according to the fixing device and the image forming apparatus including the fixing device according to the present embodiment, when the recording paper is thick like an envelope, the pressure contact force of the fixing roller is high. If it is, wrinkles or creases are generated, so the pressure contact force is reduced. Even if a decrease in conveying force due to a decrease in pressure contact force occurs, the fixing speed is increased in accordance with the decrease in pressure contact force (the fixing speed increases as the amount of decrease in pressure contact force increases). It is possible to suppress a decrease in print quality by suppressing an increase in the deviation of the carry amount. As described above, the setting (pressing force and fixing speed) in the fixing unit is changed depending on the type of recording paper, so that the generation of wrinkles or creases can be suppressed and the disturbance of printing can be suppressed.

  In the above-described embodiment, the settings (pressure contact force and fixing speed) in the fixing unit are changed by determining whether the envelope is an envelope and whether the envelope is thick. The present invention controls the pressure contact force and the fixing speed using the absolute weight of the recording paper (whether it is thick paper or not) or the weight per unit area of the recording paper, not the envelope. It does not matter.

<Second Embodiment>
Hereinafter, a second embodiment of the present invention will be described. In the first embodiment described above, the settings (pressure contact force and fixing speed) in the fixing unit 7 are changed by determining whether or not the recording paper is an envelope, but the image according to the present embodiment. The forming apparatus changes the setting in the fixing unit 7 according to the length of the recording sheet in the transport direction. Thus, changing the setting in the fixing unit 7 can be realized by changing a part of the program structure executed by the CPU 300. The structure of the image forming apparatus according to the present embodiment differs from the first embodiment only in the program structure executed by the CPU 300. Therefore, this program structure will be described below.

Software configuration
FIG. 6 is a flowchart showing a control structure of a program executed by CPU 300 of the image forming apparatus according to the present embodiment.

  In S202, CPU 300 detects length L in the conveyance direction of the recording paper. At this time, the CPU 300 detects the recording paper conveyance direction length L based on information input from the operation device 166 by the user. Note that the CPU 300 may automatically detect the recording paper conveyance direction length L. In particular, when an arbitrary size of the recording paper can be input to the operation device 166, the CPU 300 detects the length L of the recording paper in the conveyance direction based on the input size.

  In S204, it is determined whether or not the recording sheet conveyance direction length L is equal to or greater than the first threshold value L (1). If it is determined that conveyance direction length L is greater than or equal to first threshold value L (1) (YES in S204), the process proceeds to S206. If not (NO in S204), the process proceeds to S130.

  In S206, it is determined whether or not the recording sheet conveyance direction length L is equal to or greater than the second threshold value L (2). The second threshold value L (2) is longer than the first threshold value L (1). If it is determined that conveyance direction length L is greater than or equal to second threshold value L (2) (YES in S206), the process proceeds to S108. If not (NO in S206), the process proceeds to S120.

[Operation]
An operation of the image forming apparatus 100 according to the present embodiment based on the above-described structure and flowchart will be described.

-The length L in the conveyance direction of the recording paper is L (2) or more-
After the user sets the operation mode of the image forming apparatus 100 to the copy mode using the operation device 166, sets at least the conveyance direction length L of the recording paper, and sets the document, the operation panel 170 (copy) start button is pressed (YES in S100).

  Since the recording paper transport direction length L is detected (S202), the recording paper transport direction length L is greater than or equal to the second threshold L (2) (YES in S204, YES in S206). The pressure release motor rotation time is set to 150 msec (S108), and the fixing motor speed correction is set to 1.0% speed increase (S110).

  When a recording sheet having a conveyance direction length L of L (2) or more is passed through the fixing unit 7 (S112), after the pressure release lever sensor 78 detects the reference point 76B, the pressure release motor 79 is only 150 msec. The pressure contact force by which the sheet is rotated by the heat roller 71 and the pressure roller 72 in the fixing unit 7 is reduced. Further, the fixing motor is increased by 1.0% from the fixing speed as a reference.

  In such a state, the recording paper having a length L in the conveyance direction that is passed through the fixing unit 7 has a pressure contact force sufficiently reduced, so that, for example, wrinkles along the conveyance direction occur. Can be suppressed. In this image forming apparatus 100, the recording paper conveyance direction to the fixing unit 7 is vertically upward. Therefore, when the pressure contact force decreases, the conveyance force decreases, and the deviation of the conveyance amount increases toward the rear end of the recording paper. Print quality decreases. However, since the fixing speed is sufficiently increased, the deviation in the conveyance amount does not increase toward the rear end in the conveyance direction of the recording paper, and a decrease in print quality can be suppressed.

-Length L in the conveyance direction of the recording paper is less than L (2) L (1) or more-
The user sets at least the conveyance direction length L of the recording paper by using the operation device 166, and after setting the original, presses the (copy) start button on the operation panel 170 (YES in S100).

  The recording paper conveyance direction length L is detected (S202), and the recording paper conveyance direction length L is less than the second threshold L (2) and greater than or equal to the first threshold L (1). Therefore (YES in S204, NO in S206), the pressure release motor rotation time is set to 100 msec (S120), and the fixing motor speed correction is set to 0.5% acceleration (S122).

  When a recording sheet whose conveyance direction length L is less than the second threshold value L (2) and greater than or equal to the first threshold value L (1) is passed through the fixing unit 7 (S112), the pressure release lever After the sensor 78 detects the reference point 76B, the pressure release motor 79 is rotated by 100 msec, and the pressure contact force that presses the sheet by the heat roller 71 and the pressure roller 72 in the fixing unit 7 is reduced. Further, the fixing motor is increased by 0.5% from the reference fixing speed.

  In such a state, a recording sheet having a conveyance direction length L that is passed through the fixing unit 7 is less than the second threshold value L (2) and greater than or equal to the first threshold value L (1). Is appropriately lowered halfway, so that wrinkles can be prevented from occurring. In addition, since the fixing speed is appropriately increased halfway, the deviation of the conveyance amount does not increase toward the rear end of the recording paper, and a decrease in print quality can be suppressed.

-Length L in the conveyance direction of the recording paper is less than L (1)-
The user sets at least the conveyance direction length L of the recording paper by using the operation device 166, and after setting the original, presses the (copy) start button on the operation panel 170 (YES in S100).

  Since the recording paper conveyance direction length L is detected (S202) and the recording paper conveyance direction length L is less than the first threshold value L (1) (NO in S204), the pressure release lever 76 is used. Is set as the reference pressure position (S130), and no fixing motor speed correction is set (S132).

  When a recording sheet having a conveyance direction length L less than the first threshold value L (1) is passed through the fixing unit 7 (S112), the pressure release lever 76 is at the reference pressure position and the fixing unit 7 The pressure contact force by which the sheet is pressed by the heat roller 71 and the pressure roller 72 is a reference state. Furthermore, the fixing speed is based on the fixing motor. In such a state, the recording sheet having a short conveyance direction length passed through the fixing unit 7 does not wrinkle even if the pressing force is sufficiently high. Even if the fixing speed is the reference speed, the length in the conveyance direction is short, so that the deviation of the conveyance amount does not increase toward the trailing edge of the sheet, and the print quality does not deteriorate.

  As described above, according to the fixing device and the image forming apparatus including the fixing device according to the present embodiment, when the length of the recording sheet in the transport direction is long (particularly, in the direction perpendicular to the transport direction, If the pressure contact force of the fixing roller remains high (when the length in the transport direction is long), for example, wrinkles along the transport direction may occur, so the pressure contact force is reduced. Even if a decrease in the conveyance force due to a decrease in the pressure contact force occurs, the fixing speed is increased in accordance with the decrease in the pressure contact force (the larger the amount of decrease in the pressure contact force, the faster the fixing speed is increased). It is possible to suppress a significant shift in the conveyance amount toward the rear end of the sheet, thereby suppressing a decrease in print quality. As described above, the setting (pressure contact force and fixing speed) in the fixing unit can be changed depending on the type of recording paper, so that the occurrence of wrinkles or creases can be suppressed and printing disturbance can be suppressed.

<Modification>
Note that the first embodiment and the second embodiment described above can be appropriately combined. For example, as the envelope is thicker and the length in the transport direction is longer, the amount of decrease in the pressure contact force is increased, and the fixing speed is greatly increased.

  The embodiment disclosed herein is merely an example, and the present invention is not limited to the above-described embodiment. The scope of the present invention is indicated by each claim in the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are intended. Including.

DESCRIPTION OF SYMBOLS 1 Optical operation apparatus 2 Developer 3 Photoconductor drum 4 Cleaner unit 5 Charger 6 Intermediate transfer belt unit 7 Fixing unit 71 Heat roller 72 Pressure roller 73 External pressure belt 74 Pressure lever 75 Pressure spring 76 Pressure contact release lever 77 Rotating gear 78 Intermediate transfer belt unit 79 Pressure release motor 100 Image forming device 110 Main body 120 Automatic document processing device 152 Document reading unit 154 Image forming unit 166 Operation device 170 Operation panel 172 Display panel

Claims (6)

A fixing device that includes a pair of fixing rollers and fixes a toner image on a recording sheet,
Pressure contact force adjusting means for adjusting a pressure contact force for sandwiching the recording paper by the pair of fixing rollers;
Speed adjusting means for adjusting the conveyance speed of the recording paper by the pair of fixing rollers;
Determination means for determining the type of the recording paper;
A fixing device including: a pressing force adjusting unit; and a control unit for controlling the speed adjusting unit so as to adjust the pressing force and the conveyance speed based on the determined type of the recording paper.   The control means, when the type of the determined recording paper is a recording paper of a type in which wrinkles or creases are generated by a high pressure contact force, so as to reduce the pressure contact force, and The fixing device according to claim 1, comprising means for controlling to increase the conveyance speed.   The fixing device according to claim 2, wherein the control unit includes a unit for controlling the conveyance speed so as to increase largely as the degree of decreasing the pressure contact force increases.   The fixing device according to claim 2, wherein the recording paper is one of an envelope and a thick paper. The pressure contact force adjusting means includes means for adjusting the pressure contact force by changing a nip amount of the pair of fixing rollers by rotating a rotating member,
The fixing device according to claim 1, wherein the control unit includes a unit for controlling a rotation time of the rotating member. An image forming apparatus comprising the fixing device according to claim 1.

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