JP2008233133A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for a fixing device, the apparatus being designed so as to fix a recording medium, which has nonuniform thickness as in an envelope, without causing so-called envelope noise. <P>SOLUTION: A pressing member disposed inside a pressure belt 92 and used to press the pressure belt toward a heat roller 26 includes a soft pad 94 and a hard pad 96 disposed in the middle area and downstream area respectively in the direction of paper passage. The fixing device 22 has a press switching mechanism that switches between a standard mode and a special mode. When a uniform recording medium, which has uniform thickness, is fixed, both the soft and hard pads are pressed against the heat roller at all pressure. When a nonuniform recording medium, which has nonuniform thickness, is fixed, all the pressure is decreased by moving both the soft and hard pads in the direction reverse to the direction in which the heat roller is pressed, and after that only the soft pad is pressed against the heat roller. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device used in an electrophotographic copying machine, an image forming apparatus such as a printer or a facsimile.

  In an image forming apparatus such as an electrophotographic copying machine, a printer, or a facsimile, a latent image is formed by uniformly charging the surface of a member to be charged (photoconductor) using a charging device and exposing the image on the surface. Is formed. The formed image latent image is developed with toner to form a toner image, which is transferred to a sheet of paper, or transferred to an intermediate transfer member, for example, an intermediate transfer belt, and further transferred to a recording medium. An image is formed by heat-fixing the image with a fixing device.

  As a fixing device used in such an image forming apparatus, a fixing device in which a nip region is formed by pressing a heating roller and a pressure belt is used (see, for example, Patent Documents 1 and 2). ) In this type of fixing device, a wide soft pad made of a soft elastic member is provided inside the pressure belt, and a hard hard pad is provided adjacent to the soft pad to heat the soft pad and the hard pad. A nip region is formed by pressing toward the roller.

  By the way, in order to prevent the paper that has passed through the nip area from sticking to the heating roller due to the adhesive force of the molten toner, the hard pad provided in the terminal area of the nip area is pressed against the heating roller with a predetermined pressure contact force. Thus, the paper is separated from the heating roller by locally deforming the elastic layer of the heating roller.

  However, if the pressing member is urged toward the heating roller with a large force in order to exert such a separating action, the thickness of the sheet having different thicknesses such as an envelope is different when the fixing process is performed. There is a problem of so-called envelope noise in which wrinkles are generated at the edge and the flaps of the envelope are displaced.

In order to solve such a problem, in the prior art, when fixing a sheet having a portion having a different thickness such as an envelope, the total pressure of the pressure member is reduced. In the fixing device in which the thickness of the elastic layer of the heating roller is increased, the so-called envelope noise can be suppressed to some extent by reducing the total pressure, but simply reducing the total pressure only reduces the pressure of the soft pad. The pressure of the hard pad does not drop so much, and the peak pressure generated in the paper conveyance direction in the nip area does not drop below a certain value. The presence of such peak pressure causes the above-described envelope noise problem.
JP-A-9-222814. JP-A-9-258596.

  Therefore, a technical problem to be solved by the present invention is to provide a fixing device of an image forming apparatus capable of fixing a recording medium having a different thickness such as an envelope without so-called envelope noise. .

Means and actions / effects for solving the problem

In order to solve the above technical problem, according to the present invention,
Image formation in which an unfixed image formed on a recording medium is heated and fixed by passing through a nip region formed between the heating roller and an endless pressure belt pressed against the heating roller. A fixing device for the device,
The pressure member provided inside the pressure belt and pressing the pressure belt toward the heating roller includes a soft elastic soft pad provided in an intermediate portion in the paper passing direction and a hard member provided in a downstream portion in the paper passing direction. Hard pads, and
The fixing device includes:
When fixing a uniform thickness recording medium having a uniform thickness, a standard mode in which a soft pad and a hard pad are pressed against the heating roller with full pressure;
When fixing a non-uniform thickness recording medium having different thicknesses in the recording medium, after reducing the total pressure by moving the soft pad and hard pad in the anti-heat roller pressing direction, only the soft pad There is provided a fixing device for an image forming apparatus, comprising a pressing switching mechanism for switching to a special mode for pressing the toner toward the heating roller.

  According to the above configuration, when the standard mode is selected by the press switching mechanism, the hard pad and the soft pad press the heating roller with the full pressure, so that the uniform thickness recording medium with uniform thickness can be fixed as before. Processing can be performed. If the special mode is selected with the pressure switching mechanism, the peak pressure is reduced due to the withdrawal of the hard pad, and only the soft pad forms the nip region. It is possible to reduce a difference in pressure contact force caused by a fold level difference or a flap level difference in a non-thickness recording medium having a wrinkle, and it is possible to prevent wrinkles or flaps from being caused by a shift in conveyance speed due to the pressure difference.

  Such a press switching mechanism relatively retracts the hard pad by moving only the soft pad in the heating roller pressing direction in the special mode.

  The pressing switching mechanism is configured to rotate and move the pressing belt and the pressing member in the direction opposite to the heating roller pressing direction and in the direction of the soft pad.

  In the pressure switching mechanism, after the application of the total pressure is canceled by the cam, the pressure belt and the pressure member are rotated and moved by the biasing force of the spring.

  Further, the press switching mechanism is configured to slide the pressure belt and the pressing member in the direction of the hard pad while being orthogonal to the heating roller pressing direction.

  In the pressure switching mechanism, after the application of the total pressure is released, the pressure belt and the pressure member are rotated and moved by the biasing force of the spring.

  It is preferable that the soft pad has a JIS-A hardness of 5 degrees to 30 degrees so as to provide more uniform pressure in the nip region.

  The soft pad is silicone rubber or fluororubber.

  The width of the nip region in the sheet passing direction is 4 to 12 mm in the standard mode and 5 to 14 mm in the special mode.

  The fixing device 22 of the image forming apparatus 2 according to the first embodiment of the present invention will be described in detail below with reference to FIGS.

  FIG. 1 is a schematic explanatory diagram of an image forming apparatus 2 (for example, a copier, a printer, a facsimile, or a combination of them) according to an embodiment of the present invention. Currently, various types of electrophotographic image forming apparatuses have been proposed. The image forming apparatus 2 shown in FIG. 1 is a so-called tandem color image forming apparatus. The invention of the present application is not limited to this type of image forming apparatus, and other forms of image forming apparatus, for example, four developing devices are arranged around the rotation shaft, and are sequentially arranged. Can be applied to a so-called four-cycle image forming apparatus that creates a full-color image by facing each electrostatic latent image carrier, and a monochrome image forming apparatus having only one developing device.

  First, the image forming apparatus 2 will be described.

  The image forming apparatus 2 includes a paper feed cassette 44, a photosensitive member 4, an exposure device 10, a developing device 18, an intermediate transfer belt 30, a fixing device 22,

  The image forming apparatus 2 includes an endless intermediate transfer belt 30. A material having conductivity is used as the intermediate transfer belt 30. The intermediate transfer belt 30 is wound around a pair of rollers 32 and 34 disposed on the left and right in FIG. The roller 32 on the right side of FIG. 1 is connected to a motor (not shown), and the roller 32 is rotated by the rotational drive of the motor. The intermediate transfer belt 30 and the other roller 34 in contact therewith are counterclockwise in FIG. It is configured to rotate.

  A secondary transfer roller 40 is provided outside the belt portion supported by the roller 32 arranged on the right side of FIG. The secondary transfer roller 40 is in contact with the outer peripheral surface of the belt, and the contact portion (nip portion) forms a second transfer region.

  A cleaning member 42 is provided outside the belt portion supported by the roller 34 disposed on the left side of FIG. The cleaning member 42 is in pressure contact with the roller 34 via the belt 30, and the contact portion forms a collection region 62 for collecting untransferred toner.

  Under the belt portion moving from the left roller 34 to the right roller 32 in FIG. 1, yellow (Y), magenta (M), cyan (C), and black (K) are sequentially arranged from the left to the right. Four image forming units 3 (3Y, 3M, 3C, and 3K) that generate toner images of corresponding colors using a developer are arranged along the intermediate transfer belt 30.

  Each image forming unit 3 has a cylindrical photosensitive member 4 as an electrostatic latent image carrier. Around the photoreceptor 4, a charger 8, a developing device 18, a primary transfer roller 14, and a photoreceptor cleaning member 16 are arranged in that order along the rotation direction (clockwise direction in FIG. 1). . The primary transfer roller 14 is disposed inside the endless intermediate transfer belt 30. An exposure device 10 is disposed below the four photoconductors 4.

  In the image forming apparatus 2 shown in FIG. 1, a roller charging type is used as the charger 8, but the type of the charger 8 is not particularly limited, and a corona discharge type charging charger or blade. A charging member in the form of a brush or a charging member in the form of a brush can be used.

  A plate-like blade is used as the photoconductor cleaning member 16, and one end thereof is in contact with the outer peripheral surface of the photoconductor 4. However, the photosensitive member cleaning member 16 is not limited to a blade, and other cleaning members (for example, a fixed brush, a rotating brush, a roller, or a combination thereof) can be used. Furthermore, the photoconductor cleaning member 16 is not necessarily provided, and a cleanerless system in which the untransferred toner on the photoconductor 4 is collected by the developing device 18 may be employed.

  Above the intermediate transfer belt 30, a hopper 20 (20Y, 20M, 20C, 20K) for supplying toner to the developing device 18 of each color is disposed.

  A paper feed cassette 44 as a paper feed device is detachably disposed below the image forming apparatus 2. Sheets (recording media) 36 loaded and accommodated in the sheet cassette 44 are sent out one by one from the uppermost sheet 36 to the conveyance path 50 by the rotation of the sheet feed roller 52 disposed in the vicinity of the sheet cassette 44. It has become. In the vicinity of the paper feed roller 52, a pair of registration rollers 54 for feeding the paper 36 to the secondary transfer area 41 at a predetermined timing is provided.

  The conveyance path 50 extends from the paper feed cassette 44 to the paper discharge unit 58 through the nip portion of the registration roller pair 54, the secondary transfer region 41, and the fixing device 22. The configuration of the fixing device 22 will be described later.

  The image forming apparatus 2 can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners.

  Next, an example of an image forming operation in the color mode will be briefly described.

  First, in each image forming unit 3, the outer peripheral surface of the photosensitive member 4 that is rotationally driven at a predetermined peripheral speed is charged by the charger 8. Next, light corresponding to image information is projected from the exposure device 10 on the outer peripheral surface of the charged photoreceptor 4 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by the toner supplied from the developing device 18. When the toner image of each color formed on the photoconductor 4 in this way reaches the primary transfer region by the rotation of the photoconductor 4, yellow, magenta, cyan, and black are sequentially transferred from the photoconductor 4 to the intermediate transfer belt 30. Transferred (primary transfer) and superimposed.

  Untransferred toner remaining on the photoreceptor 4 without being transferred to the intermediate transfer belt 30 reaches the contact portion where the photoreceptor 4 and the cleaning member 16 come into contact with each other, and is scraped off by the cleaning member 16. It is removed from the outer peripheral surface of the photoreceptor 4.

  The superimposed four color toner images are conveyed to the secondary transfer region 41 by the intermediate transfer belt 30. On the other hand, the paper 36 accommodated in the paper feed cassette 44 is conveyed to the secondary transfer region 41 in accordance with the timing. Then, the four color toner images are transferred (secondary transfer) from the intermediate transfer belt 30 to the paper 36 in the secondary transfer region 41. The sheet 36 onto which the four color toner images have been transferred is conveyed further downstream in the conveyance path 50, and the toner image is fixed on the sheet 36 by the fixing device 22, and then sent to the paper discharge unit 58.

  The intermediate transfer belt 30 that has passed through the secondary transfer region 41 is cleaned by the cleaning blade 42. Thereafter, the rotational drive of each photoreceptor 4 and the intermediate transfer belt 30 is stopped.

  Next, the fixing device 22 according to the first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 2, the fixing device 22 includes a heating roller 26 disposed on the support frame 60, and a belt pressing body 90 disposed opposite to the heating roller 26 and disposed on the subframe 80. I have. The belt pressing body 90 includes an endless pressure belt 92 that rotates following the heating roller 26, and pressing members 94 and 96 that press the pressure belt 92 toward the heating roller 26. The sheet 36 carrying the unfixed toner image 37 is inserted into a nip region 66 formed between the pressure belt 92 and the heating roller 26. For example, the width of the nip region 66 in the sheet passing direction is 4 to 12 mm in the standard mode and 5 to 14 mm in the envelope mode.

  The heating roller 26 is formed by forming an elastic layer made of silicone rubber on a pipe-shaped cored bar made of iron, aluminum, steel or the like, and its surface is a release layer made of PFA (perfluoroalkoxy) in a tube shape or a coating form. It has a covered configuration. The heating roller 26 is rotatably attached to the support frame 60. The core metal of the heating roller 26 is rotationally driven by a drive motor (not shown). As the heating roller 26 rotates (rotates counterclockwise in FIG. 2), the pressure belt 92 is driven to rotate (rotates clockwise in FIG. 2). Further, a heater 25 such as a halogen lamp is disposed inside the pipe-shaped metal core, and heats the elastic layer on the surface to a predetermined temperature.

  The belt pressing body 90 includes a pressure belt 92, a soft pad 94 and a hard pad 96 as a pressing member, a sliding sheet, a belt support, a pad support 91, a soft pad push-up cam 116, and a spring 98. And.

  The pressure belt 92 is provided so as to slidably rotate on the outer contour sliding contact portion formed by the sliding contact surfaces of the soft pad 94 and the hard pad 96 and the peripheral sliding contact surface of the belt support. The pressure belt 92 includes an inner heat-resistant layer and an outer release layer. In addition to the two-layer structure, the pressure belt 92 may have a structure of three or more layers including at least one other layer between the heat-resistant layer and the release layer. A suitable material for the pressure belt 92 is polyimide resin. The release layer may be a material having excellent release properties, and is, for example, a fluororesin. The thickness of the heat-resistant layer is, for example, 80 μm, and the thickness of the release layer is, for example, 30 μm.

  A pad support 91 is attached inside the belt support. A hard pad 96 is fixedly attached inside the pad support 91 and a soft pad 94 is attached in a biased state by the elastic force of the spring 98. The soft pad 94 is provided in an intermediate portion in the sheet passing direction (lower portion in FIG. 2), and the hard pad 96 is provided in a downstream portion in the sheet passing direction (upper portion in FIG. 2). A spring 98 biases the bottom surface of the soft pad 94, but a soft pad push-up cam 116 is disposed so as to contact the bottom surface of the soft pad 94. By rotation of the soft pad push-up cam 116, only the soft pad 94 can protrude toward the heating roller 26 or the soft pad 94 can be retracted. In order to prevent the total pressure load on the soft pad 94, the soft pad push-up cam 116 rotates in conjunction with the operation of the mode switching cam 110 or after the mode switching cam 110 operates. It is configured.

  The soft pad 94 is made of an elastic soft material such as silicone rubber or fluorine rubber, and specifically made of silicone rubber. The soft pad 94 preferably has a JIS-A hardness of 5 degrees to 30 degrees so as to provide a more uniform pressing force in the nip region 66. The soft pad 94 provided on the inner side of the pressure belt 92 presses the inner peripheral surface of the pressure belt 92 via a sliding sheet at the intermediate portion in the sheet passing direction of the nip region 66. Accordingly, since the pressure belt 92 is pressed against the heating roller 26 by the soft pad 94 at the intermediate portion in the sheet passing direction of the nip region 66, the contact pressure between the pressure belt 92 and the heating roller 26 is made uniform. The toner image can be uniformly heated and melted.

  The hard pad 96 is made of a hard material such as a metal or a heat-resistant resin, and specifically is made of aluminum or the like. The hard pad 96 provided on the inner side of the pressure belt 92 presses the inner peripheral surface of the pressure belt 92 via a sliding sheet in the downstream portion of the nip region 66 in the sheet passing direction. Thereby, in the downstream portion in the sheet passing direction of the nip region 66, the contact portion of the pressure belt 92 pressed by the hard pad 96 passes through the nip region 66 in order to come into contact with the heating roller 26. The paper 36 is easily separated from the pressure belt 92. Therefore, it is possible to prevent the paper 36 that has passed through the nip region 66 from curling to the pressure belt 92 side, and it is possible to prevent the transportability of the paper 36 from being deteriorated.

  The sliding sheet is obtained by coating a glass cloth having heat resistance with a fluororesin, and has heat resistance, wear resistance, and slidability. Note that a lubricant such as grease or oil is applied to the surface of the sliding sheet or the inner peripheral surface of the pressure belt 92. Thereby, the friction between the sliding sheet and the soft pad 94 and the hard pad 96 is reduced, and the rotation of the pressure belt 92 by the frictional contact between the pressure belt 92 and the soft pad 94 and the hard pad 96 is achieved. Is not disturbed.

  2 and 3, a standard mode for fixing ordinary paper having a uniform thickness and an envelope mode (special mode) for fixing paper (typically envelopes) having different thickness portions in the paper. ) Will be described.

  The heating roller 26 is rotatably disposed at the center of the support frame 60, the total pressure applying mechanism 100 is disposed at the upper part of the support frame 60, and the main frame rotation shaft 62 is erected at the lower part of the support frame 60. Yes.

  The total pressure applying mechanism 100 includes a connecting body 101 having a total pressure adjusting screw 102 and a head portion 104, and a total pressure applying compression spring 108 disposed between the head portion 104 and the support guide portion 106. It is configured. The main frame 70 is connected to the support frame 60 via the total pressure applying mechanism 100 by the total pressure adjusting screw 102 being fixedly screwed into the screw hole of the link coupling portion 74 of the main frame 70. The main frame 70 that can rotate around the main frame rotation shaft 62 is urged by the total pressure applying compression spring 108 in the direction of the arrow in FIG. 2 (substantially to the left in FIG. 2). Therefore, in the case of the standard mode shown in FIG. 2, the “soft lever 94” and the hard pad 96 of the belt pressing body 90 and the pressure belt 92 are utilized by utilizing the “lever principle” with the main frame rotating shaft 62 as a fulcrum. Toward the heating roller 25 (in the direction of pressing the heating roller) with full pressure.

  A main frame 70 is disposed so as to face the support frame 60. The sub frame 80 is disposed at the center of the main frame 70 so as to be rotatable about the sub frame rotation shaft 73, the link coupling portion 74 is disposed at the upper portion of the main frame 70, and the hook portion 72 is disposed at the lower portion of the main frame 70. The second pin 78 is erected at the lower right end of the main frame 70.

  A sub frame 80 is disposed on the main frame 70 so as to overlap the main frame 70. The belt pressing body 90 is disposed at the center of the subframe 80, the third pin 84 is erected at the right end of the upper portion of the main frame 70, and the long hole 88 is disposed at the left end of the lower portion of the main frame 70. ing.

  A second pin 78 of the main frame 70 is inserted into the long hole 88 of the subframe 80. The upper end of the envelope mode tension spring 120 is locked to the third pin 84 of the subframe 80, and the lower end of the envelope mode tension spring 120 is locked to the second pin 78 of the main frame 70. It is biased in the direction of the arrow in FIG. 3 (substantially downward in FIG. 3).

  In addition, an eccentric mode switching cam 110 is disposed on the upper right side of the support frame 60. When the eccentric mode switching cam 110 rotates around the cam rotation shaft 112, it abuts on the cam abutment surface 71 of the support frame 60, and the cam abutment surface 71 rotates in the direction of the arrow in FIG. 3 (substantially to the right in FIG. 3). Is configured to move.

  In the press switching mechanism configured as described above, in the standard mode shown in FIG. 2, the eccentric mode switching cam 110 is separated from the cam contact surface 71 of the support frame 60, and the main frame rotation shaft 62 is used as a fulcrum. By utilizing the “lever principle”, the soft pad 94, the hard pad 96, and the pressure belt 92 of the belt pressing body 90 are pressed toward the heating roller 25 (in the heating roller pressing direction) with full pressure. Further, the soft pad push-up cam 116 is in a short shaft support state in which the soft pad 94 is not pushed up.

  When the mode switching cam 110 is rotated in the direction of the arrow in FIG. 2, as shown in FIG. 3, after the mode switching cam 110 contacts the cam contact surface 71 of the support frame 60, the full pressure application compression spring 108. The main frame 70 is rotated about the main frame rotation shaft 62 in the direction of the arrow in FIG. 3 (substantially rightward in FIG. 3) against the urging force. That is, the main frame 70 is rotated in the direction opposite to the direction of pressing the heating roller and in the direction of the soft pad 94. When the main frame 70 rotates clockwise around the main frame rotation shaft 62, the soft pad 94 and the hard pad 96 of the belt pressing body 90 are moved to the retracted position, and the soft pad 94 and the hard pad 96 of the belt pressing body 90 are moved. The total pressure for pressing the pad 96 and the pressure belt 92 toward the heating roller 26 is reduced.

  The sub-frame 80 that is pivotally supported by the sub-frame rotation shaft 73 with respect to the main frame 70 is operated in the direction of the arrow in FIG. Around). As a result, the hard pad 96 positioned downstream in the sheet passing direction is further away from the heating roller 26.

  In conjunction with the operation of the mode switching cam 110 or after the mode switching cam 110 operates, the soft pad push-up cam 116 rotates so as to be in a long-axis support state in which the soft pad 94 is pushed up. As a result, only the soft pad 94 located in the intermediate portion in the sheet passing direction is moved in the heating roller pressing direction, and the hard pad 96 is relatively retracted.

  Therefore, by such an operation of the press switching mechanism, the hard pad 96 positioned in the downstream portion in the sheet passing direction is further away from the heating roller 26 and only the soft pad 94 positioned in the intermediate portion in the sheet passing direction is provided. Thus, only the soft pad 94 presses the heating roller 26 via the pressure belt 92 and the sliding sheet, and the nip region 66 is formed only by the soft pad 94. It has become.

  4 and 5 show the results of measuring the pressure distribution in the nip region 66 in each of the standard mode and the envelope mode using the press switching mechanism. FIG. 4 shows a result obtained by integrating the relative pressure in the longitudinal direction of the nip region 66 (direction perpendicular to the sheet passing direction) with respect to the sheet passing direction. FIG. 5 shows an average of the relative pressure distribution in the sheet passing direction in the longitudinal direction. The result of the standard mode is indicated by a solid line, and the result of the envelope mode is indicated by a broken line.

  As apparent from FIGS. 4 and 5, in the envelope mode, the total pressure applied in the nip region 66 is lower than in the standard mode, and the peak pressure is also greatly reduced.

  As a result of applying the above-described image forming apparatus 2 including the fixing device 22 having the pressure switching mechanism to the envelope having the portions having different thicknesses, flap deviation and wrinkle of the envelope can be reduced.

  Next, the fixing device 22 according to the second embodiment of the present invention will be described with reference to FIGS. 6 and 7, but the description of the same parts as those of the first embodiment described above will be omitted, and the differences will be mainly described. explain.

  The press switching mechanism of the fixing device 22 of the first embodiment described above is a so-called rotation type in which the subframe 80 rotates with respect to the main frame 70, whereas the fixing device 22 of the second embodiment. The press switching mechanism is a so-called slide type in which the subframe 80 slides relative to the main frame 70.

  As shown in FIG. 6, the fixing device 22 includes a heating roller 26 disposed on the support frame 60, and a belt pressing body 90 disposed opposite to the heating roller 26 and disposed on the subframe 80. I have. The belt pressing body 90 includes an endless pressure belt 92 that rotates following the heating roller 26, and pressing members 94 and 96 that press the pressure belt 92 toward the heating roller 26. The sheet 36 carrying the unfixed toner image 37 is inserted into a nip region 66 formed between the pressure belt 92 and the heating roller 26. For example, the width of the nip region 66 in the sheet passing direction is 4 to 12 mm in the standard mode and 5 to 14 mm in the envelope mode.

  The belt pressing body 90 includes a pressure belt 92, a soft pad 94 and a hard pad 96 as a pressing member, a sliding sheet, a belt support, a pad support 91, a soft pad push-up cam 116, and a spring 98. And.

  A pad support 91 is attached inside the belt support. A hard pad 96 is fixedly attached inside the pad support 91 and a soft pad 94 is attached in a biased state by the elastic force of the spring 98. The soft pad 94 is provided in an intermediate portion in the sheet passing direction (lower portion in FIG. 6), and the hard pad 96 is provided in a downstream portion in the sheet passing direction (upper portion in FIG. 6). A spring 98 biases the bottom surface of the soft pad 94, but a soft pad push-up cam 116 is disposed so as to contact the bottom surface of the soft pad 94. By rotation of the soft pad push-up cam 116, only the soft pad 94 can protrude toward the heating roller 26 or the soft pad 94 can be retracted. The soft pad push-up cam 116 rotates in conjunction with the operation of the total pressure application mechanism 100 or after the total pressure application mechanism 100 operates to prevent the total pressure load on the soft pad 94. Is configured to do.

  With reference to FIGS. 6 and 7, a standard mode for fixing ordinary paper having a uniform thickness and an envelope mode for fixing paper (typically envelopes) having different thickness portions in the paper are used. A press switching mechanism that can be switched will be described.

  The heating roller 26 is rotatably disposed at the center of the support frame 60, the total pressure applying mechanism 100 is disposed at the upper part of the support frame 60, and the main frame rotation shaft 62 is erected at the lower part of the support frame 60. Yes.

  The total pressure applying mechanism 100 includes a connecting body 101 having a total pressure adjusting screw 102 and a gear head portion 105, a total pressure applying compression spring 108 disposed between the gear head portion 105 and the support guide portion 106, and a connecting body. And a drive motor 109 for driving the gear head portion 105 of the motor 101. The main frame 70 moves relative to the support frame 60 via the total pressure application mechanism 100 by the total pressure adjusting screw 102 being movably screwed into the screw hole of the link coupling portion 74 of the main frame 70. Connected as possible. The main frame 70 that can rotate around the main frame rotation shaft 62 is urged by the total pressure applying compression spring 108 in the arrow direction of FIG. 6 (substantially to the left in FIG. 6). Therefore, in the case of the standard mode shown in FIG. 6, the “soft lever 94” of the belt pressing body 90 and the pressure belt 92 of the belt pressing body 90 are utilized using the “lever principle” with the main frame rotation shaft 62 as a fulcrum. Toward the heating roller 25 (in the direction of pressing the heating roller) with full pressure. In the case of the envelope mode shown in FIG. 7, the connecting body 101 is moved by the rotation of the total pressure adjusting screw 102 (moved leftward in FIG. 6), so that the spring length of the compression spring 108 for applying total pressure is reduced. The urging force of the compression spring 108 for applying total pressure is reduced, and the pressing force with which the soft pad 94, the hard pad 96, and the pressure belt 92 of the belt pressing body 90 are pressed toward the heating roller 26 is reduced.

  A main frame 70 is disposed so as to face the support frame 60. The sub frame 80 is slidably disposed at the center of the main frame 70, the link coupling portion 74 is disposed at the upper portion of the main frame 70, and the hook portion 72 is disposed at the left end portion of the lower portion of the main frame 70. The first pin 76 is erected on the left end of the upper part of the main frame 70, and the second pin 78 is erected on the right end of the upper part of the main frame 70.

  A sub frame 80 is disposed on the main frame 70 so as to overlap the main frame 70. The belt pressing body 90 is disposed at the center of the subframe 80, the third pin 84 is erected at the right end of the lower portion of the main frame 70, and the long hole 86 is disposed at the left end of the upper portion of the main frame 70. A long hole 88 is disposed at the right end of the upper portion of the main frame 70.

  The first pin 76 of the main frame 70 is inserted through the long hole 86 of the subframe 80, and the second pin 78 of the main frame 70 is inserted through the long hole 88 of the subframe 80. The upper end of the envelope mode tension spring 120 is locked to the second pin 78 of the main frame 70, and the lower end of the envelope mode tension spring 120 is locked to the third pin 84 of the subframe 80. It is biased in the direction of the arrow in FIG. 7 (substantially upward in FIG. 7).

  Further, a substantially egg-shaped mode switching cam 110 is disposed at the upper center of the main frame 70 so as to be rotatable about the cam rotation shaft 112. In the standard mode of FIG. 6, the mode switching cam 110 is in the long axis support state in which the mode switching cam 110 is raised, and in the envelope mode in FIG. 7, the mode switching cam 110 is in the short axis support state. In any mode, the mode switching cam 110 is in contact with the cam contact surface 81 of the subframe 80. By the rotation of the mode switching cam 110, the cam contact surface 81 of the sub-frame 80 is configured to slide in the direction of the arrow in FIG. 7 (substantially upward in FIG. 7).

  In the press switching mechanism configured as described above, in the standard mode shown in FIG. 6, the “soft lever 94” and the hard pad of the belt pressing body 90 are utilized by utilizing “the lever principle” with the main frame rotating shaft 62 as a fulcrum. 96 and the pressure belt 92 are pressed against the heating roller 25 (in the pressing direction of the heating roller) with full pressure. Further, the mode switching cam 110 is in a long-axis support state in which the cam contact surface 71 of the subframe 80 is pushed down.

  When the drive motor 109 of the total pressure applying mechanism 100 is driven to move the gear head portion 105 of the coupling body 101 to the left in FIG. 6, the total pressure of the coupling body 101 screwed into the link coupling portion 74 of the main frame 70. The adjustment screw 102 moves to the left, and the spring length of the total pressure application compression spring 108 becomes longer. As a result, the biasing force of the compression spring 108 for applying total pressure is reduced, and the pressing force with which the soft pad 94, the hard pad 96, and the pressure belt 92 of the belt pressing body 90 are pressed toward the heating roller 26 is reduced. For example, the total pressure in the standard mode is about 270 N, but the total pressure is reduced to about 50 N in the envelope mode.

  When the mode switching cam 110 is rotated to bring the mode switching cam 110 into the short shaft support state, the long holes 86 and 88 of the subframe 80 slide relative to the pins 76 and 78 by the biasing force of the envelope mode tension spring 120. Then, the sub-frame 80 slides with respect to the main frame 70 in the direction of the arrow in FIG. 7 (upward in FIG. 7). That is, the sub-frame 80 slides in the direction of the hard pad 96 while being orthogonal to the heating roller pressing direction. The slide movement amount of the subframe 80 is, for example, 1 to 2 mm. As a result, the hard pad 96 positioned downstream in the sheet passing direction is further away from the heating roller 26.

  In conjunction with the operation of the mode switching cam 110 or after the mode switching cam 110 operates, the soft pad push-up cam 116 rotates so as to be in a long-axis support state in which the soft pad 94 is pushed up. As a result, only the soft pad 94 located in the intermediate portion in the sheet passing direction is moved in the pressing direction of the heating roller 26, and the hard pad 96 is relatively retracted.

  Therefore, by such an operation of the press switching mechanism, the hard pad 96 positioned in the downstream portion in the sheet passing direction is further away from the heating roller 26 and only the soft pad 94 positioned in the intermediate portion in the sheet passing direction is provided. Thus, only the soft pad 94 presses the heating roller 26 via the pressure belt 92 and the sliding sheet, and the nip region 66 is formed only by the soft pad 94. It has become.

  Accordingly, as with the fixing device of the first embodiment described above, as a result of applying the image forming apparatus 2 including the fixing device 22 according to the second embodiment to an envelope having a portion having a different thickness, flap deviation is caused. And the wrinkles of the envelope could be reduced.

1 is a schematic explanatory diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram schematically illustrating the fixing device according to the first embodiment of the present invention in a standard mode. FIG. 3 is a diagram schematically illustrating the fixing device according to the first embodiment of the present invention in an envelope mode. In the fixing device according to the first embodiment of the present invention, it is a diagram schematically showing the pressure distribution in the longitudinal direction of the nip region. In the fixing device according to the first embodiment of the present invention, it is a diagram schematically showing the pressure distribution in the sheet conveyance direction of the nip region. FIG. 10 is a diagram schematically illustrating a fixing device according to a second embodiment of the present invention in a standard mode. FIG. 10 is a diagram schematically showing a fixing device according to a second embodiment of the present invention in an envelope mode.

Explanation of symbols

2: Image forming device 22: Fixing device 25: Heating heater 26: Heating roller 36: Paper 37: Unfixed toner image 60: Support frame 62: Main frame rotating shaft 66: Nip area 70: Main frame 71: Cam contact surface 72: Hook part 73: Subframe rotation shaft 74: Link coupling part 76: First pin 78: Second pin 80: Subframe 81: Cam contact surface 84: Third pin 86: Slotted hole 88: Slotted hole 90: Belt pressing body 91: Pad support body 92: Pressure belt 94: Soft pad (pressing member)
96: Hard pad (pressing member)
98: Spring 100: Total pressure application mechanism 101: Connecting body 102: Total pressure adjusting screw 104: Head portion 105: Gear head portion 106: Support guide portion 108: Compression spring 109 for applying total pressure 109: Drive motor 110: Press switching cam 112: Cam rotating shaft 116: Soft pad push-up cam 120: Tension spring for envelope mode

Claims (10)

Image formation in which an unfixed image formed on a recording medium is heated and fixed by passing through a nip region formed between the heating roller and an endless pressure belt pressed against the heating roller. A fixing device for the device,
The pressure member provided inside the pressure belt and pressing the pressure belt toward the heating roller includes a soft elastic soft pad provided in an intermediate portion in the paper passing direction and a hard member provided in a downstream portion in the paper passing direction. Hard pads, and
The fixing device includes:
When fixing a uniform thickness recording medium having a uniform thickness, a standard mode in which a soft pad and a hard pad are pressed against the heating roller with full pressure;
When fixing a non-uniform thickness recording medium having different thicknesses in the recording medium, after reducing the total pressure by moving the soft pad and hard pad in the anti-heat roller pressing direction, only the soft pad A fixing device for an image forming apparatus, comprising a pressing switching mechanism for switching to a special mode for pressing the toner toward a heating roller.   The fixing device for an image forming apparatus according to claim 1, wherein in the special mode, the pressing switching mechanism relatively retracts the hard pad by moving only the soft pad in the pressing direction of the heating roller. .   3. The pressure switching mechanism is configured to rotate and move the pressure belt and the pressure member in a direction opposite to the heating roller pressing direction and in the direction of the soft pad. The fixing device of the image forming apparatus described above.   4. The fixing device for an image forming apparatus according to claim 3, wherein after the application of the total pressure by the cam is released, the pressure belt and the pressing member are rotationally moved by the biasing force of the spring.   The said press switching mechanism is comprised so that a pressurization belt and a press member may be slid and moved to the direction of a hard pad while orthogonally crossing with respect to the said heating-roller press direction. A fixing device of an image forming apparatus.   6. The fixing device for an image forming apparatus according to claim 5, wherein after the application of the total pressure is released, the pressure belt and the pressing member are slid by the urging force of the spring.   7. The fixing device for an image forming apparatus according to claim 1, wherein the soft pad has a JIS-A hardness of 5 degrees to 30 degrees.   8. The fixing device for an image forming apparatus according to claim 1, wherein the soft pad is made of silicone rubber or fluorine rubber.   7. The fixing of an image forming apparatus according to claim 1, wherein the width of the nip area in the sheet passing direction is 4 to 12 mm in the standard mode and 5 to 14 mm in the special mode. apparatus.   An image forming apparatus comprising the fixing device according to claim 1.

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