JP6685718B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device that fixes a toner image on a recording medium (medium).

  To fix an image formed on a recording medium by toner in the image forming apparatus such as a copying machine using an electrophotographic method, a printer, a facsimile, and a multifunction machine having a plurality of these functions. A fixing device is used for. As the fixing device, a fixing device using a roller that is a heating rotator or a belt-shaped fixing member and a roller that is a pressure rotator or a belt-shaped pressing member is generally used.

  Due to recent diversification of compatible recording media, it is necessary to perform optimum fixing processing on various types of paper such as plain paper and special paper such as envelopes. Therefore, conventionally, a technique has been proposed in which various fixing conditions such as a temperature and a pressing force (fixing nip pressure) are changed to cope with various recording media. Among them, in particular, for a cylindrical recording medium such as an envelope, many techniques have been proposed for setting an optimum pressure for exclusive use of the envelope to suppress wrinkles during conveyance of the fixing nip.

  Focusing on the paper width of plain paper and envelopes as a determination means for changing the pressing force, a technique has been proposed in which the pressing force is changed to the dedicated pressing force for envelopes when it is determined that the envelope is a standard envelope depending on the width of the paper. (Patent Document 1).

JP, 2007-271681, A

  Envelopes are made by laminating a part of what is folded back into a tubular shape, and there are various types even with only standard sizes. Even with the same size, there are various ways to fold it. For example, in a rectangular or oblong envelope, there are “center attachment” which has a bonding portion at the center of the envelope and “side attachment” which has a bonding portion at one end of the envelope. Further, in the case of a Western-style envelope, there are “flame sticking” which has a sticking part on both end portions, and “diamond sticking” which has a triangular flap and a sticking part having an oblique shape.

  In addition, there are various base papers and basis weights used for envelopes, and there are various types of base papers such as kraft, Kent, high-quality paper, and cotton paper. There is.

  Conventionally, when the fixing process is performed on the various types of envelopes by using the fixing nip pressure with the envelope-dedicated pressure, the fixing nip pressure is set to be lighter than that of plain paper to set the envelope wrinkle. In that case, although the envelope wrinkle can be reduced, the pressure applied to the bonded portion may be insufficient due to the shape and basis weight of the envelope, and fixing failure (peeling) may occur.

  In addition, since the printing surface of an envelope with a large grammage and the printing surface of a small envelope overlap each other with two or more sheets of paper, the actual pressure applied to the printing surface differs greatly even with the same pressing force due to the difference in thickness. There is a difference in image quality such as color tone.

  In that case, the user needs to finely adjust the pressure force according to the type of envelope to find the pressure force that achieves envelope wrinkle, fixing property, and image quality, and it takes time to adjust and wastefully use the envelope. Will be done.

  The present invention has been proposed in view of the above. It is an object of the present invention to provide a fixing device that can reduce the load of the user's adjustment work on various types of envelopes and can perform good fixing processing.

A fixing device according to the present invention includes a first rotating body and a second rotating body that form a nip portion for fixing a toner image on a recording medium, the first rotating body, and the second rotating body. A contacting / separating unit that can change the pressure at the nip portion by contacting and separating with a heating unit that heats the first rotating body so that the first rotating body has a set target temperature; A control unit capable of controlling the target temperature to be heated by the heating unit and the pressure in the nip unit changed by the contacting / separating unit according to the type of the medium; When the fixing process is performed on the envelope, the pressure at the nip portion is set to a first pressure, and when the fixing process is performed on the second envelope having a basic weight larger than that of the first envelope, the nip portion is set. The fixing process can be performed by setting the pressure at the second pressure lower than the first pressure. When the fixing process is performed on the third envelope having the same basic weight and the narrow width as the first envelope, the pressure at the nip portion is set to the third envelope lower than the first pressure. and sets the pressure, the a first of said target temperature and the same when performing a fixing process on the envelope can perform a fixing process is set to the target temperature, characterized in that.

  According to the present invention, it is possible to reduce the load of the user's adjustment work on various types of envelopes and to perform the fixing process satisfactorily.

Flowchart and block diagram explaining the nip forming operation Schematic diagram of an example of an image forming apparatus FIG. 3 is a perspective view of the fixing device according to the embodiment. Left side view of the device (illustration of belt tension mechanism) Cross-sectional view of the device (when the nip is formed) Cross-sectional view of the device (when the nip is released) Diagram showing the types and sizes of typical envelopes and the shape of the envelopes A diagram showing the relationship between the details of the overlapping part of the side-attached envelope and the fixability The figure which showed the fixing pressure applied to the width direction of the oblong 3 side sticking envelope of 120 gsm basis weight. The figure which showed the fixing pressure applied to the width direction of the oblong 3 side sticking envelope with a basis weight of 70 gsm. The figure which showed the set value of the envelope pressure force of the Example.

[Example 1]
In the following description, regarding a recording medium (recording material, medium), an envelope is a bag-shaped recording medium in which a plurality of sheets of paper are overlapped with each other and folds are formed. Says that enclose pictures and photos. The recording medium other than the envelope is a single-sheet recording medium including transparency paper, and is hereinafter referred to as plain paper (material is not limited to paper). In addition, these recording media are collectively referred to as paper.

(1) Image Forming Section The overall structure of an example of the image forming apparatus will be described with reference to FIG. The image forming apparatus 1 in this embodiment is a color laser printer that employs an electrophotographic method. Reference numeral 10 denotes a control unit (hereinafter, referred to as CPU), which inputs various information such as image information from an external device 23 such as a personal computer (PC) via an interface 22. An operation unit 24 exchanges various kinds of information with the CPU 10.

  The printer 1 includes an image forming unit U (UY, UM, UC, UK) that forms toner images of Y (yellow), M (magenta), C (cyan), and K (black). In each image forming unit U, the photosensitive drum 2 is charged in advance by the charging roller (roll) 3. After that, a latent image is formed on the photosensitive drum 2 by the laser scanner 4. The latent image becomes a toner image by the developing device 5.

  The toner image on the photosensitive drum 2 in each image forming unit U is sequentially superimposed and transferred onto the intermediate transfer belt 8 of the intermediate transfer unit 7 by the primary transfer roller 6. As a result, an unfixed color toner image is synthetically formed on the intermediate transfer unit 7. The intermediate transfer belt 8 is suspended around the rollers 11, 12, and 13 and is circulated.

  On the other hand, the paper (plain paper or envelope) S contained in the first or second paper feed cassette (paper feed tray) 15 or 16 is separated and fed one by one by the operation of the paper feed mechanism, and is conveyed. It is sent to the registration roller pair 18 through the path 17 in the V direction. The registration roller pair 18 temporarily receives the sheet S, and if the sheet is skewed, straightens it. Then, the registration roller pair 18 conveys the sheet S between the intermediate transfer belt 8 and the secondary transfer roller 14 in synchronization with the toner image on the intermediate transfer belt 8.

  The toner image on the intermediate transfer belt 8 is transferred onto the sheet S by the secondary transfer roller 14. The sheet S to which the toner image has been transferred is introduced into the fixing device (fixing device) 100, which is an image heating device, through the transport path 19 and is heated and pressed to fix the unfixed toner image. Then, the paper S that has left the fixing device 100 is conveyed and discharged as a product (image-formed product) to the discharge tray 21 by the discharge roller pair 20.

(2) Fixing device (2-1) Basic configuration FIG. 3 is a perspective view of the fixing device 100, FIG. 4 is a left side view of the same device (a diagram for explaining the belt tension mechanism), and FIG. 5 is a cross-sectional view of the same device. FIG. 6 is a cross-sectional view of the apparatus (when the nip is formed) (when the nip is released). The fixing device 100 is a belt nip type and an electromagnetic induction type (IH type) image heating device.

  Reference numeral 303 denotes a base frame of the fixing device 100, and an upper frame 305 is fixedly supported on the base frame 303. Below the upper frame 305, the lower frame 306 rotates about a hinge shaft 304. Supported as possible. The upper frame 305 is provided with an upper belt unit A, an IH heater (heater) 170, a roughening roller 400, and the like. A lower belt unit B is arranged on the lower frame 306.

  In the upper belt unit A, 105 is an endless fixing belt (endless belt) as a heating rotator (first rotator) that heats the toner image t on the sheet (recording material), and the toner on the sheet S The toner image is heated in contact with the image bearing surface. The fixing belt 105 is wound around two supporting rollers, that is, a driving roller 131 and a tension roller 132 having a function of applying a belt tension, so as to be rotatably rotatable.

  The fixing belt 105 may be appropriately selected as long as it can be heated by the IH heater 170 and has heat resistance. For example, a magnetic metal layer such as a nickel metal layer or a stainless steel layer having a thickness of 75 μm, a width of 380 mm, and a perimeter length of 200 mm is coated with a silicone rubber having a thickness of 300 μm, for example, and a PFA tube is coated on the surface layer.

  The drive roller 131 is, for example, a roller formed by integrally molding a heat-resistant silicone rubber elastic layer on a core metal surface layer having an outer diameter of φ18 made of solid stainless steel. The drive roller 131 is disposed on the paper exit side of the nip portion (fixing nip) N formed by the fixing belt 105 and the pressure belt 120 on the lower belt unit B side, and presses on the lower belt unit B side. The elastic layer is elastically distorted by a predetermined amount by the pressure contact of the roller 121.

  A pad stay 137 made of, for example, stainless steel (SUS material) is arranged on the upstream side of the drive roller 131 in the sheet conveying direction V so as to contact the inside of the fixing belt 105.

  The tension roller 132 is a hollow roller formed of, for example, stainless with an outer diameter of φ20 and an inner diameter of approximately φ18. The tension roller 132 functions as a steering roller that adjusts meandering in the width direction orthogonal to the moving direction of the fixing belt 105, and a belt tension roller. Also works as. Both ends 132a of the tension roller 132 are supported by bearings 153, and a tension spring 156 applies a tension of 200 N to the fixing belt 105 via the bearings 153.

  Although not shown in the figure, the IH heater 170 includes an exciting coil that heats the fixing belt 105 by electromagnetic induction heating, a magnetic core, and a holder that holds them, and is provided near the upper surface layer of the fixing belt 105. . The exciting coil generates an alternating magnetic flux by an alternating current from an exciting circuit (not shown), and the alternating magnetic flux is guided to the magnetic core to generate an eddy current in the fixing belt 105 which is an induction heating element. The eddy current generates Joule heat due to the specific resistance of the induction heating element.

  The surface temperature of the fixing belt 105 is detected by the thermistor 220, and the detected temperature information is input to the CPU 10. Based on the detected temperature information, the CPU 10 moves from the exciting circuit to the coil so that the surface temperature of the fixing belt 105 is raised to and maintained at a predetermined image heating temperature (a temperature at which the image heating process is performed: for example, about 150 ° C.). Control the power supply.

  The roughening roller 400 is a rubbing rotator that rubs the surface of the fixing belt 105. The roughening roller 400 has abrasive grains densely adhered to the surface of a φ12 mm stainless steel core through an adhesive layer. It is preferable to use abrasive grains having a count (grain size) of # 1000 to # 4000 according to the target glossiness of the image. Reference numeral 415 is a cleaning roller as a cleaning rotary member that cleans the roughening roller 400.

  In the lower belt unit B, 120 is an endless pressure belt (endless belt) as a pressure rotating body (second rotating body) that forms a nip portion N for nipping and conveying the sheet S together with the fixing belt 105. . The pressure belt 120 is rotatably circulated around two supporting rollers, that is, the pressure roller 121 and a tension roller 122 having a function of applying a belt tension, and is stretched with a predetermined tension (for example, 200 N).

  In this embodiment, the pressure belt 120 may be properly selected as long as it has heat resistance. For example, a nickel metal layer having a thickness of 50 μm, a width of 380 mm, and a peripheral length of 200 mm is coated with a silicone rubber having a thickness of 300 μm, for example, and a PFA tube is coated on the surface layer.

  The pressure roller 121 is a roller that suspends the pressure belt 120 having an outer diameter of φ20 made of, for example, solid stainless steel, and is disposed on the paper exit side of the nip portion N formed by the pressure belt 120 and the fixing belt 105. It is set up. A pressure pad 125 made of, for example, silicone rubber is arranged on the upstream side of the pressure roller 121 in the paper conveyance direction so as to contact the inside of the pressure belt 120.

  The tension roller 122 is a hollow roller made of, for example, stainless with an outer diameter of φ20 and an inner diameter of φ18, and functions as a belt tension roller. Both ends 122a of the tension roller 122 are supported by bearings 158, and a tension spring 127 applies a tension of 200 N to the pressure belt 120 via the bearings 158.

  A pressure cam shaft 307 is attached to the base frame 303, and pressure cams 308 are provided at both ends thereof. A pressure gear 309 (FIG. 3) is fixed on the pressure cam shaft 307 to transmit the driving force of the pressure motor 302 controlled by the CPU 10. By rotating the pressure cam 308 by a predetermined amount by this drive system, the lower frame 306 rotates about the hinge shaft 304 and is displaced between the pressure position C shown in FIG. 5 and the separated position D shown in FIG. To do.

  The lower frame 306 is provided with a pressure spring 311 for pressing the pressure frame 312 at the pressure position C. When the lower frame 306 moves to the pressing position C, the pressing spring 311 causes the lower belt unit B to press the upper belt unit A (for example, 400 N).

  In this pressure state, the driving roller 131 and the pressure roller 121 are in pressure contact with the fixing belt 105 and the pressure belt 120 sandwiched therebetween. Further, the pad stay 137 and the pressure pad 125 are in pressure contact with each other with the fixing belt 105 and the pressure belt 120 interposed therebetween. As a result, a wide nip portion (fixing nip portion) N is formed between the fixing belt 105 and the pressure belt 120 in the sheet conveying direction V.

  A drive motor 301 is controlled by the CPU 10, and is arranged outside the base frame 303 of the fixing device 100. Drive is input to the drive input gear 310 fixed on the shaft 131a of the drive roller 131 to rotate the fixing belt 105.

  At the separated position D of the lower frame 306 shown in FIG. 6, the lower belt unit B is lifted from the upper belt unit A, the pressure belt 120 is separated from the fixing belt 105, and the nip is released.

  In the present embodiment, the motor 302, the lower frame 306, the cam shaft 307, the cam 308, the gear 309, the spring 311, the frame 312, etc. are the fixing belt 105 and the pressure belt 120 as the first and second rotating bodies. Is a press-contact mechanism (pressurizing mechanism) that presses each other.

(2-2) Fixing Operation As shown in FIG. 5, the driving roll 131 is rotationally driven in a state where the lower frame 306 is rotated to the pressing position C and the lower belt unit B is pressed against the upper belt unit A. As a result, the fixing belt 105 circulates and rotates in the clockwise direction indicated by the arrow in FIG. The pressure belt 120 on the lower belt unit B side is also rotated by the frictional force of the fixing belt 105 in the nip portion N and is rotated in the counterclockwise direction indicated by the arrow following the rotation of the fixing belt 105. The fixing belt 105 is heated by the IH heater 170, raised to a predetermined fixing temperature, and temperature-controlled.

  In this state, the sheet S carrying the unfixed toner image t is introduced from the entrance side to the fixing device 100, guided by a guide member (not shown), enters the nip portion N, and is nipped and conveyed. As a result, the toner image t is thermally and pressure-fixed on the sheet S as a fixed image. The sheet S exits the nip portion N and is discharged from the exit side of the fixing device 100.

(2-3) Nip Forming Operation FIG. 1 is a flow chart and a block diagram illustrating the nip forming operation for each type of paper (media) used.

  First, the user selects the type and basis weight of the paper to be used from the input unit (operation unit 24 or external device 23) <S6-1>. Based on the selection, the CPU 10 determines whether the used paper S is an envelope or another paper <S6-2>.

  When the user selects paper other than envelopes (coated paper or plain paper), the CPU 10 uses a media table (not shown) stored in the memory 25 in advance to fix the fixing conditions according to the selected paper type, surface property, and size. (S6-6> referring to the applied pressure (nip pressure) and the controlled temperature. Then, the start of the print job (JOB) under the fixing condition is permitted <S6-7>.

  When the user selects an envelope, the CPU 10 determines whether the envelope selected by the user is a standard envelope (square No. 2 or long No. 3) or an irregular envelope <S6-3>.

  In the case of a fixed-size envelope, the CPU 10 uses an envelope table (FIG. 11), which will be described later, stored in the memory 25 in advance, based on the fixed-size width information and the basis weight information selected by the user. <S6-5> referring to the temperature control temperature). That is, the pressure is set to be lower than the pressure applied to paper other than envelopes (coated paper or plain paper). Then, the start of the print job (JOB) under the fixing condition is permitted <S6-7>.

  Further, in the case of an irregular envelope, the envelope width information is acquired from the setting width (setting regulation width) of the side regulation plate (not shown) in the paper feeding cassette (paper feeding tray) 15 or 16 accommodating the envelope. <S6-4>. Then, similar to the standard envelope, the CPU 10 refers to the fixing condition (pressurizing force (nip pressure), temperature controlled temperature) from the envelope table (FIG. 11) based on the width information and the basis weight information <S6-5>. Then, the start of the print job (JOB) under the fixing condition is permitted <S6-7>.

  When the print job is started <S6-8>, a pressure command is issued from the CPU 10 <S6-9>. Then, the pressure motor 302 is rotated N times in the CW direction by the motor driver 126 <S6-12> based on the set value of the media table or the envelope table described above <S6-11>.

  As a result, the pressure cam 308 rotates by a predetermined amount and the lower frame 306 is moved up to the pressure position C (FIG. 5) (the pressure roller 121 and the pressure pad 125 move to the pressure position). Due to this ascending movement, the lower belt unit B supported by the lower frame 306 is pressed by the biasing force of the pressure spring 311 to form the nip portion N between the fixing belt 105 and the pressure belt 120 <S6. -14>.

  When the CPU 10 issues a separation command <S6-10>, the pressure motor 302 rotates R in the CCW direction <S6-15>. As a result, the pressure cam 308 rotates by a predetermined amount and the lower frame 306 is moved down to the separated position D (FIG. 6) (the pressure roller 121 and the pressure pad 125 move to the separated position) <S6-16>. By this downward movement, the lower belt unit B is lifted from the upper belt unit A, the pressure belt 120 is separated from the fixing belt 105, and the nip is released <S6-17>.

(2-4) Envelope Type and Shape Next, the envelope type and shape will be described. FIG. 7 is a diagram showing the types and sizes of typical envelopes, and the bonding shape of the envelopes, and FIG. 8 is a diagram showing the details of the bonding portion of the side-bonded envelopes and the fixing property.

  As described above, the envelope is formed by laminating a part of the folded back tubular shape, and there are various types even with only the standard size. The typical envelope width is shown in FIG. 7 (a), but when typical envelopes from Japan and overseas are arranged, they are widely present from 98 mm to 240 mm in width. Although not shown in FIG. 7A, there is an envelope having a width of 13 inches.

  In addition, even if it is the same type, there are various ways to fold it. For example, in the case of a rectangular or oblong envelope, “Center pasting” (FIG. 7 (b)) having a pasting part in the center of the envelope or pasting to one end of the envelope There is a “side attachment” (FIG. (C)) having a part. Furthermore, in the case of Western-style envelopes, there is a "glue sticking" with sticking parts on both sides (Fig. (D)), and a "diamond sticking" with a triangular flap and a slanting sticking part (Fig. (E)). Exists.

  In addition, there are various base papers and basis weights used for envelopes, and there are various types of base papers such as kraft, Kent, high-quality paper, and cotton paper. There is.

  When the fixing process is performed on these various types of envelopes, a technique for suppressing envelope wrinkles is often adopted by using an envelope-dedicated pressure lighter than plain paper. However, according to a study made by the present inventors, a lighter pressure can reduce the wrinkles of the envelope, but depending on the shape and the basis weight of the envelope, the pressure applied to the bonding portion is insufficient and the fixing is defective (peeling). Is known to occur.

  Specifically, as shown in FIG. 8, three envelopes each having an attachment portion at an end in a direction (width direction) orthogonal to the conveying direction of the envelope, for example, an envelope like a side-attached elongated No. 3 sheet. It has been known that fixing failure is likely to occur at the boundary between the overlapping and the overlapping of two sheets. One of the factors is that there is a step for one sheet of paper at this boundary portion, the fixing belt 105 cannot follow this portion, and the pressure is partially insufficient to lower the fixing property. .

  Another factor is that the pressure roller 121 has a crown shape in order to form a fixing nip having a uniform length. Due to the crown shape, when the pressure is lowered, the pressure at the center does not decrease so much, but tends to decrease from the pressure at the end. For this reason, the end pressure is further insufficient, so that fixing failure is likely to occur at the boundary portion.

  In this way, the following verification was performed paying attention to the pressure at the end portion in the envelope width direction of the side sticking or the bark sticking in which the fixing property becomes the most severe in each envelope width. FIG. 9 is a diagram showing the fixing pressure applied in the width direction of a long No. 3 side-adhesive envelope having a basis weight of 120 gsm, and FIG. 10 is a view showing the fixing pressure applied in the width direction of an elongated No. 3 side-attached envelope having a basis weight of 70 gsm. FIG. 11 and FIG. 11 are diagrams showing the set value of the envelope pressing force.

  First, the fixing pressure applied in the width direction of the elongated No. 3 side sticking envelope having a basis weight of 120 gsm will be described with reference to FIG. The horizontal axis of the graph represents the longitudinal width of the fixing belt 105, and the vertical axis represents the pressure applied to the fixing belt (envelope). In the longitudinal width, the portion where the envelope is sandwiched is the envelope width, and the pressure distribution portion depending on the shape of the envelope is shown in the figure. P1 is the pressure applied to the address surface, P2 is the pressure applied to the pressure release portion, P3 is the pressure applied to the bonding portion, and P4 is the pressure required for fixing.

  As shown in the graph, when an envelope having a grammage of 120 gsm is sandwiched, the larger the grammage, the thicker the paper thickness, and the larger the pressure applied to the bonding portion. On the other hand, since the pressure drop portion P2 at the boundary of the bonding portion has a large difference in paper thickness, the pressure drop becomes large. The pressure P1 applied to the address surface, which is the printing surface, is larger than the pressure P2 because the basis weight is large. Due to such a pressure distribution, pressure loss occurs at P2 at the boundary of the bonded portion, as described above, and causes a defective fixing. In order to deal with this, in an envelope having a high basis weight, the fixing pressure is set such that a predetermined pressure is applied to the pressure P2 applied to the pressure release portion, so that an appropriate fixing process is performed.

  Further, for an envelope having a large basis weight, a means for setting a larger fixing pressure may be considered in order to satisfy the pressure applied to P2. However, if the pressure of the bonding portion P1 becomes too large, the pressure on the fixing belt 105 is too high and the surface layer of the belt is likely to be damaged and scratched. Therefore, in consideration of damage to the surface layer of the belt, the setting that applies the minimum necessary pressure to P2 is adopted as the pressing force.

  Next, the fixing pressure applied in the width direction of the elongated No. 3 side sticking envelope having a basis weight of 70 gsm will be described with reference to FIG. In the case of an envelope having a small basis weight, for example, as shown by a broken line in the figure, when the fixing process is performed with the same pressing force as that of an envelope having a large basis weight, the pressing force as a whole tends to decrease because the paper thickness is thin. . In addition, as a feature of the envelope having a small basis weight, the pressure P3 applied to the bonding portion tends to be small and the pressure P2 applied to the pressure releasing portion tends to be large due to the influence of the thin paper thickness.

  As described above, even with envelopes having the same width, when the basis weight is small, the pressure P1 applied to the addressing surface is less than the pressure P2 applied to the bonded portion. Therefore, when compared with an envelope with a large basis weight, not only in terms of fixability but also in image quality such as color tone and gloss deteriorates, so the fixing pressure is increased to ensure the same image quality as an envelope with a large basis weight. There is a need.

  Further, as described above, the end pressure tends to decrease as the envelope width increases, such as the corner 2 and ISO-C5. Therefore, the fixing pressure needs to be set higher as the envelope width increases. Even in that case, the tendency depending on the basis weight does not change, and therefore it is possible to perform the same verification and set the optimum pressing force.

  Based on the above results, the set value (envelope table) of the envelope pressure in this embodiment is shown in FIG. In this embodiment, the envelope types (sizes) are classified into three types in the direction (width direction) orthogonal to the conveying direction of the envelopes. Specifically, the length is 130 mm or less (L1) of the elongated type No. 3 or COM10, 131 to 220 mm (L2) including ISO-C5, and 221 mm or more (L3) including corner 2. The basis weight of envelopes is also classified into three types. Specifically, it is 50 to 75 gsm (W1), 75.5 to 110 (W2), and 110.5 to 150 (W3).

  For these setting values, the fixing pressure should be small basis weight (large pressing force) → large basis weight (small pressing force), small envelope width (small pressing force) → large envelope width (large pressing force) The number of rotation pulses of the pressure motor 309 that determines the fixing pressure is set. The larger the number of rotation pulses of the pressure motor 309, the larger the fixing pressure.

  By determining this set value in <S6-2> of FIG. 1 and setting it in the pressure command <S6-3> by the CPU 10, it becomes possible to perform an appropriate fixing process for each envelope.

  Further, as the fixing basis weight increases, the amount of heat required for the fixing process also increases. Therefore, the setting value of the present embodiment is set so that the temperature (the temperature at which the image heating process is performed) also increases according to the basis weight.

  In this way, the CPU 10 changes the pressure contact force of the pressure contact mechanisms 302, 306 to 309, 311 and 312 based on the type of recording material. When the recording medium on which the fixing process is performed is an envelope, the CPU 10 can set a plurality of pressure contact forces according to the width of the envelope and the basis weight of the base paper by using a preset table. Then, the pressure contact force is set so that the pressure applied to the overlapping step portion of the envelope becomes a predetermined pressure or more, and the pressure contact force is set lower as the basis weight of the base paper increases. The larger the width of the envelope, the higher the pressure contact force.

  The CPU 10 changes the pressure contact force based on at least three pieces of envelope width information and envelope basis weight information. Further, the temperature at which the image heating process is performed is changed along with the change in the pressure contact force. The CPU 10 can substantially release the pressure at the nip portion N.

  When this embodiment is used, the optimum fixing condition can be automatically selected for each envelope and the optimum fixing process can be performed. As a result, it becomes possible to reduce the load of the user's adjustment work. As a means for achieving this, it was realized by providing a table for setting appropriate pressing force and temperature based on envelope width information and basis weight information according to the standard size of the envelope.

  The configuration of the fixing device according to the present invention described above is summarized as follows. It has a first rotating body 105 and a second rotating body 120 that form a nip portion N for fixing the toner image t on the recording medium S. It has control units 302, 306 to 309, 311, 312, 10 that control fixing conditions according to the type of the recording medium S. Then, the control unit sets the pressure at the nip portion N to the first pressure when the fixing process is performed on the first envelope. When the fixing process is performed on the second envelope having the grammage larger than that of the first envelope, the pressure at the nip portion N is set to the second pressure lower than the first pressure (FIG. 11).

  The controller sets the target fixing temperature to the first temperature when the fixing process is performed on the first envelope, and sets the target fixing temperature to be higher than the first temperature when the fixing process is performed on the second envelope. Set to a higher second temperature (FIG. 11). The control unit controls the pressure at the nip portion N to be lower than the first pressure when the fixing process is performed on the third envelope having the same basic weight and the narrow width as the first envelope. (Fig. 11). The control unit sets a common fixing target temperature when the fixing process is performed on the first envelope and when the fixing process is performed on the third envelope (FIG. 11).

[Other matters]
(1) The first and second rotating bodies 105 and 120 forming the nip portion N are not limited to the case where both are endless belts as in the apparatus 100 of the embodiment. It is also possible to adopt an apparatus configuration in which one is an endless belt and the other is a roller. It is also possible to adopt a device configuration in which both are rollers.

  (2) The fixing device is not limited to use as a device for fixing an unfixed toner image formed on a recording medium as a fixed image. It is also effective as a device for adjusting the surface texture of an image such as improving the glossiness of the image by re-heating and pressing the toner image once fixed or assumedly attached to the recording medium. Device called).

  (3) The image forming apparatus is not limited to the image forming apparatus that forms a full-color image as in the embodiment, but may be an image forming apparatus that forms a monochrome image. Further, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multi-functional machine having a plurality of these functions, in addition to necessary equipment, equipment, and housing structure.

  100..Fusing device, 105..First rotating body (fixing belt), 120..Second rotating body (pressurizing belt), N..nip portion, S..recording medium, t..toner image , 302, 306 to 309, 311, 312, 10 ... Control unit

Claims (4)

A first rotating body and a second rotating body that form a nip portion for fixing the toner image on the recording medium;
A contacting / separating means capable of contacting / separating the first rotating body and the second rotating body to change the pressure at the nip portion;
Heating means for heating the first rotating body so that the first rotating body reaches a set target temperature;
A control unit capable of controlling the target temperature heated by the heating unit and the pressure at the nip unit changed by the contacting / separating unit according to the type of the recording medium;
When performing the fixing process on the first envelope, the control unit sets the pressure at the nip portion to the first pressure, and performs the fixing process on the second envelope having a larger basis weight than the first envelope. In the case of applying the fixing process, the fixing process can be performed by setting the pressure in the nip portion to the second pressure lower than the first pressure, and the basis weight is substantially the same as that of the first envelope. When the fixing process is performed on the third envelope having a narrow width, the pressure at the nip portion is set to a third pressure lower than the first pressure and the fixing process is performed on the first envelope. possible is executing the fixing process is set to the target temperature and the same the target temperature when,
A fixing device characterized by the above. Wherein the control unit is configured in the case of performing the fixing process in the first envelope and set the target temperature to a first temperature, said pre-Symbol targets temperature when subjected to fixing process in the second envelope Set to a second temperature higher than the first temperature,
The fixing device according to claim 1, wherein: Both the first rotating body and the second rotating body are endless belts or rollers, or one is an endless belt and the other is a roller.
The fixing device according to any one of claims 1 or 2, characterized in that. The heating means includes an exciting coil that is heated by electromagnetic induction heating,
The fixing device according to any one of claims 1 to 3, characterized in that.