JP2009122511A - Image forming apparatus and adjustment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output an image with high quality by always optimizing a fixing nip pressure even if it is changed with time due to deterioration of a member or the like. <P>SOLUTION: A fixing device includes endless pressure belt 120 and heating belt 130, and optimizes a pressurizing force by a fixing nip part between both belts. An adjustment mode is entered upon detection of a change in fixing nip pressure. A pressure sensitive sheet which shows a coloring reaction according to the pressurizing force is fed, and pressure information is read therefrom by an image reading means to obtain "density information ". A control means arithmetically compares a density reference value with a density measurement value obtained in the pressure sensitive sheet P, and transmits an operation signal according to the difference between both values to an adjustment means, whereby the adjustment means is operated to rotate a pressurizing cam 170 to a suitable phase angle position. The pressure contact force of a lever member 171 with the pressurizing roller 121 is changed by the rotation of the pressurizing cam 170 to readjust the fixing nip pressure with the heating belt 130 side to a set optimum pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic method or an electrostatic recording method, and is applied to a sheet such as a recording material in a pressure contact portion of an image heating device as a fixing device provided in the image forming device. The present invention relates to an adjustment method for adjusting pressure.

  A fixing device that transfers a visible image formed on an image carrier of an image forming apparatus to a sheet and heats and pressurizes the visible image on the sheet to fix the image is generally a heating having an elastic layer such as rubber on the surface. It is composed of a roller and a pressure roller pair. In that case, the fixing nip portion is formed by pressing the pressure roller against the heating roller to elastically deform the surface. A sheet on which the toner image is transferred as a visible image is fed to the fixing nip portion, and the toner image is heated and pressurized to be permanently fixed, thereby recording and forming an image on the sheet.

  By the way, in the fixing nip portion, it is necessary to set so that the pressure applied to the sheet is always an appropriate pressure. If the applied pressure is excessive or insufficient and is not an appropriate pressure, stress is applied to the sheet and the toner image on the sheet, causing image defects. For example, if the applied pressure is too large, wrinkles are generated on the sheet, resulting in lack of quality. On the other hand, when the pressure is insufficient, the nip width of the fixing nip portion is narrowed, and the amount of heat for heating the necessary area of the sheet becomes insufficient. As a result, since the toner cannot be sufficiently softened, the adhesiveness is lowered and the gloss is lowered. If the applied pressure is insufficient, a slip occurs between the sheet and the heating roller to reduce the conveying force. As described above, when the pressing force is not appropriate, a high-quality image with high glossiness cannot be obtained, and the image forming efficiency is lowered, leading to a reduction in productivity.

  On the other hand, in recent years, image forming speeds have been increasingly increased in image forming apparatuses, and a larger pressing force tends to be set accordingly. As a result, the durability and long life of the image forming apparatus are also required. Therefore, it is required to stabilize the fixing nip pressure in the fixing device throughout the life cycle of the image forming apparatus with extended durability.

  In order to improve the productivity by outputting a high-quality image with high glossiness with a stable fixing nip pressure in the fixing device, the present applicant has replaced the previous roller pair structure with a fixing roller and an endless shape. A belt fixing device using a fixing belt has been proposed (for example, see Patent Document 1). A fixing device composed of a fixing belt and a pressure belt has also been proposed (see, for example, Patent Document 2).

  Usually, when a belt is used in a fixing device, a pressure roller and a spring member are often provided inside the belt in order to widen the nip width. However, in this case, a nip is formed between the belt and the heating roller, and a nip is also formed between the belt and the pressure roller, so that the shape of the fixing nip portion is complicated. In addition, if the characteristics of the spring member for pressure deteriorate due to use over time, or if the rubber elastic layer on the surface of the fixing roller or pressure roller deteriorates between the belt and the belt, the setting of the pressing force in the fixing nip portion will be lost. . In addition, when the metal part or resin part used for the member reaches creep, which is the stress limit, the surface layer of the belt is scraped away due to rotational friction with the roller side, and the pressure applied to the fixing nip part Will change.

  In consideration of such deterioration of members due to use over time, the present applicant has proposed an image forming apparatus in which the driving torque of the fixing device is constantly monitored and monitored so that the applied pressure can always be maintained at an optimum value (for example, And Patent Document 3). Further, a nip pressure adjustment method for adjusting the applied pressure by detecting a nip width and obtaining a measured value has been proposed (see, for example, Patent Document 4).

JP 2005-292713 A JP 2004-341346 A JP 2005-326719 A Japanese Patent Application Laid-Open No. 11-202661

  However, in the above-described belt-type fixing device, the pressure spring member is slidably contacted with the inner surface of the endless belt, so that there is a concern that the torque on the inner surface of the belt increases due to wear powder or the like. Therefore, in an image forming apparatus that is shipped as a product and being used by a user, it is easy to overlook the optimum adjustment timing as a real problem even if the image forming apparatus has a function of monitoring and adjusting the pressure applied to the fixing nip portion.

  In particular, in the nip pressure adjusting method for measuring the nip width described in Patent Document 4, a nip is formed on a sheet such as an OHP sheet. In this case, if the gloss of the nip changes, even if the nip can be detected and measured, it is difficult to accurately read the gloss level with the document reader. Further, since the driving force is applied during operation, the dynamically measured nip width (pressure distribution) during operation differs from the nip width (pressure distribution) measured statically. Therefore, in Patent Document 4, it is difficult to set an adjustment method in consideration of the dynamic pressure distribution in which the nip width varies depending on the driving force.

  An object of the present invention is to switch to a pressure measurement mode when it is determined that the fixing nip pressure has changed due to deterioration of a member, for example, and to adjust the fixing nip pressure to an optimum pressure based on density information read from a pressure-sensitive recording material, An object of the present invention is to provide an image forming apparatus capable of outputting a high-quality image with high glossiness.

  It is another object of the present invention to provide an adjustment method for adjusting the pressure applied to a sheet at the pressure contact portion of a fixing device as an image heating device in an image forming apparatus to an optimum pressure.

  To achieve the above object, a typical image forming apparatus according to the present invention includes an image reading unit that reads image information of a document, and an image forming unit that forms a toner image on a sheet based on the image information from the image reading unit. Means, a pair of image heating members for heating the toner image formed on the sheet at the pressure contact portion, and an adjustment means for adjusting the pressure at the pressure contact portion by moving at least one of the pair of image heating members. In the image forming apparatus, the pressure information that is pressed in the pressure contact portion and recorded on the pressure-sensitive sheet is read by the image reading unit, and the adjustment unit determines the pressure information in the pressure contact portion based on the read pressure information. It is characterized by having an execution means for executing an adjustment mode for adjusting the pressure.

  The adjusting method according to the present invention includes a step of pressing a pressure-sensitive sheet at a pressure contact portion of the image heating apparatus when adjusting a pressure applied to the sheet in an image heating apparatus that heats a toner image on the sheet; A step of reading pressure information recorded on the pressure-sensitive sheet, and a step of adjusting the pressure applied to the sheet at the pressure contact portion of the image heating device based on the pressure information of the read pressure-sensitive sheet. And

  According to the image forming apparatus of the present invention, for example, when the pressure at the pressure contact portion of the image heating member changes due to deterioration of the member due to use over time, the adjustment unit that has determined that changes to the adjustment mode. The adjustment unit operates the execution unit to execute the adjustment mode, thereby adjusting the pressure of the pressure contact portion to the optimum pressure, thereby outputting a high-quality image with high glossiness to the sheet.

  Further, according to the adjustment method of the present invention, the pressure information recorded on the pressure-sensitive sheet can be read, and the pressure applied to the sheet at the pressure contact portion of the image heating apparatus can be readjusted based on the read information.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of an image forming apparatus and an adjustment method thereof according to the invention will be described in detail with reference to the drawings.

≪Image forming device main body≫
FIG. 1 shows a configuration of an apparatus main body 100 of an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine. Heat and pressure are applied to an unfixed image transferred on a sheet S such as a recording material or a transfer material. And a fixing device (image heating device) that performs permanent fixing processing. However, although a full color intermediate transfer system is shown as a specific example of the image forming apparatus, it is not particularly limited thereto.

  The apparatus main body 100 includes, for example, image carriers 20Y, 20M, which carry electrostatic latent images on the surface corresponding to four-color toner images of Y (yellow), M (magenta), C (cyan), and K (black). 20C, 20K. Hereinafter, in order to avoid complicating the description, the four image carriers are represented by the reference numeral 20, and the following charging means, exposure means, developing device, and the like are also described by the representative symbols.

  The surfaces of the four image carriers 20 are uniformly charged to a required potential by the primary charging unit 21, and then the surfaces of the image carriers 20 are exposed by the exposure unit 22, so An electrostatic latent image is formed. Then, the electrostatic latent image on the image carrier 20 is developed by the developing device 23 using a developer, and is visualized as a toner image.

  As shown in FIG. 1, in the apparatus main body 100, the image forming means 200Y, 200M, 200C, and 200K corresponding to the above four color toner image formation are arranged in series, and the process until the visible image is formed is processed in parallel for each color. The tandem method is used.

  The toner image on the image carrier 20 developed by the developing device 23 is sequentially superposed on the intermediate transfer member 25 by, for example, an endless belt by the primary transfer device 24 to be primary transferred. Then, the toner image on the intermediate transfer member 25 that has undergone primary transfer for all colors is collectively transferred onto the sheet S by the secondary transfer device 26. The sheet S is conveyed to the secondary transfer device 26 by a paper feeding unit. After the secondary transfer, the sheet S carrying an unfixed toner image is conveyed to the belt-type fixing device (image heating device) 27 according to the present embodiment, and is heated and pressed by the fixing device 27 to be determined. The fixed toner image is melted and softened and fixed, and when the fixing is completed, the toner image is discharged onto the paper discharge tray 28.

  As described above, a series of image forming processes from charging, exposure, development, transfer, and fixing are executed, and an image is recorded and formed on the sheet S. Note that only a black image forming unit exists in a monochrome image forming apparatus. The arrangement order and configuration of the image forming means for Y, M, C, and K are not limited to this.

  Note that overall system control of the apparatus main body 100 including the fixing apparatus 27 described below is performed by a control unit (not shown). The control means includes a CPU (central processing unit) that includes a control unit and a calculation unit, and a memory that can store, write, store, and read various information and data. This control means functions as an execution means for executing the “adjustment mode” as the gist of the present embodiment described below.

≪Fixing device≫
Next, the fixing device 27 provided as an image heating device in the image forming apparatus main body 100 of the present embodiment will be described in detail with reference to FIGS.

  The fixing device 27 has a pressure member made of each of the following materials shown in FIG. That is, the pressure belt 120 is formed in an endless shape that is a main part of the pressure body. The pressure belt 120 constitutes a pair of image heating members together with a heating belt 130 described later, and a fixing nip portion as a pressure contact portion is formed between the belts. In addition, the pressure belt 120 is stretched between the pressure roller 121 and the tension roller 122 and rotates. In addition, an oil application roller 123 is disposed between the tension roller 122 and the pressure pad 125, for example, so as to supply silicon oil while being urged in a direction in contact with the inner surface of the pressure belt 120. Yes. The oil application roller 123 is formed of a heat-resistant aramid felt impregnated with heat-resistant silicone oil having a viscosity of about 1000 CS and a sheet-like oil application control film made of a porous PTFE layer on the surface layer of the heat-resistant aramid felt.

  For each member of the pressure member, the pressure roller 121 is formed of, for example, a stainless steel (SUS) solid rod having an outer diameter of φ20. The pressure roller 120 includes a pressure belt 120 and a heating belt 130 described below. Located on the exit side of the nip area. The tension roller 122 is a hollow roller having an outer diameter of about 20 mm and an inner diameter of about 18 with a stainless material, for example, and functions as a roller that applies an appropriate tension to the pressure belt 120. As shown in FIG. 3, both ends of the tension roller 122 are pivotally supported by bearings 126, and are set so that an optimum tension can be constantly maintained at, for example, 100 N on the pressure belt 120 by a tension biasing spring 127. Further, a heater 128 (see FIG. 2) as a heating element is mounted inside the tension roller 122 so as to heat the pressure belt 120. Here, for example, a halogen heater is used as the heater 128, but other heaters may be used as long as they can be used as a heat source.

  Further, the pressure pad 125 corresponds to the entrance side of the fixing nip portion formed between the pressure belt 120 and the heating belt 130, that is, the upstream side of the pressure roller 121. It is provided on the inner side and is made of, for example, silicon rubber. The pressure pad 125 is pressed against the pressure belt 120 with a set pressure of 400 N, for example, and forms a nip with the pressure roller 121.

  Next, as shown in FIG. 2, in the fixing device 27, a heating body that forms a fixing nip portion as a pressure contact portion with the above-described pressure member is constituted by the following members.

  The heating body has an endless heating belt 130 as a main part, and the heating belt 130 is looped around both the driving roller 131 and the tension roller 132. The heating belt 130 can be appropriately 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 circumferential length of 200 mm coated with, for example, a 300 μm-thick silicon rubber and a surface layer coated with a PFA tube can be used. The heating belt 130 can be appropriately selected as long as it generates heat by the induction heating coil 135 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 circumferential length of 200 mm, for example, a silicon rubber with a thickness of 300 μm and a surface layer coated with a PFA tube can be used. . Therefore, when an alternating current is passed through the induction heating coil 135, magnetic lines of force are generated around the coil, and an eddy current is generated in the metal layer of the heating belt 130. This current is changed to Joule heat by the resistance of the metal layer to cause the metal layer to generate heat. Thereby, the heating belt 130 is heated.

  For each member of the heating body, the driving roller 131 is formed by integrally molding a heat-resistant silicon rubber elastic layer on a core metal surface layer having an outer diameter of stainless steel, for example, φ18. The driving roller 131 is disposed on the exit side in the fixing nip region between the heating belt 130 and the pressure belt 120, and the elastic layer of the surface rubber is elastically deformed and distorted by the pressure contact with the pressure roller 121. It can be done. The tension roller 132 applies a tension set to 120 N, for example, so as to always maintain the belt tension optimally. The tension roller 132 is a hollow roller made of, for example, a stainless material and having an outer diameter φ20 and an inner diameter φ18. Such a tension roller 132 functions as a “steering roller” for adjusting the meandering in the belt width direction orthogonal to the running direction of the heating belt 130 and also functions as a belt tension applying roller.

  Further, at the entrance side in the region of the fixing nip between the pressure belt 120 and the heating belt 130 constituting the pair of image heating members, that is, inside the heating belt 130 corresponding to the upstream side of the driving roller 131. A pad stay 137 is provided. The pad stay 137 is made of, for example, a stainless material. In addition, the pad stay 137 is pressed against the pressure pad 125 on the pressure body side described above, for example, with a set pressure 400N, and forms a nip with the drive roller 131.

  In the pressure body and the heating body configured as described above, the pressure belt 120 is maintained at 140 ° C. and the heating belt 130 is maintained at 200 ° C. during standby.

  Accordingly, the fixing device 27 operates and acts as follows.

  During normal image formation, rotational power is transmitted from the drive source to the drive roller 131, and the heating belt 130 starts to rotate in the circumferential direction. The heating belt 130 is reliably rotated by the driving roller 131 and stably conveys the sheet S such as a recording material. The pressure belt 120 is rotated by the frictional force with the heating belt 130. However, if the sheet S exists in the fixing nip portion, the pressure belt 120 may not be reliably driven. The pressure roller 121 assists such circumferential rotation of the pressure belt 120.

  In the present embodiment, the peripheral speed of the pressure roller 121 is increased by 1% with respect to the peripheral speed of the pressure belt 120 on the inner surface of the belt. The difference in speed between the rotation of the pressure belt 120 driven by the heating belt 130 and the rotation assisted by the pressure roller 121 is absorbed by the slip between the pressure belt 120 and the pressure roller 121. . In order to reduce the frictional force between the pressure belt 120 and the pressure roller 121, silicon oil is supplied from the oil application roller 123 to the inner surface of the pressure belt 120.

  During such normal operation, as shown in FIGS. 4 and 5, it is necessary to apply a corresponding force to rotate the pressure belt 120 and the heating belt 13 in the normal position without shifting during the circumferential rotation. If this force is defined as a belt holding force, when the shifting force is much higher than the belt holding force, the belt slides to one side in the belt width direction and moves to the side. The heating belt 130 is stronger and larger than the pressure belt 120 to exert a biasing force to be offset. In the present embodiment, a belt detection sensor 159 for detecting the belt end position at a position facing the end of the heating belt 130 is provided. The belt end detection signal output from the belt detection sensor 159 is sent to the control means. The control means performs control to correct the belt deviation by changing the inclination of the tension roller 132 by control based on the belt end detection signal.

≪Seat pressure adjustment mode execution≫
If such an image forming operation is repeated and used over time, the members and equipment constituting the fixing device 27 may deteriorate. In such a case, the setting of the optimum pressure changes at the fixing nip portion, which is the pressure contact portion of the sheet. The change is appropriately detected by the detecting means, and when the control means receives the detection signal, the control means sends an operation instruction signal to the adjusting means as an executing means for operation, and starts an adjustment mode for readjustment to the optimum pressure.

  However, the adjustment mode is not always started only when the optimum pressure changes due to such deterioration of the equipment. For example, when the number of copies of the sheet S passed through the fixing device 27 reaches the set limit number, a flag is set based on the number of signals, and the control means has reached a time when the fixing nip pressure needs to be readjusted by the flag signal. Judgment can be made and the adjustment mode can be started. Further, an input signal for instructing an adjustment mode is sent to the control means by pressing a selection key provided on an operation panel (operation unit) on the apparatus main body 100, or when an error signal is detected, a toner cartridge, etc. A detection signal indicating that the above has been exchanged is sent to the control means. Accordingly, the adjustment mode can be forcibly started up.

  The following is a control example in the case where the control means sets the pressure measurement mode and readjusts to an appropriate pressure with respect to a change in the fixing nip pressure due to deterioration of the member due to use over time.

  When the fixing nip pressure changes, a nip pressure detection sensor (not shown) detects it. Based on the detection signal, the control means activates the adjustment mode and outputs an instruction signal and an operation signal to that effect as a control signal. When executing the adjustment mode, the display means in the operation unit such as an operation panel displays on the display means that the shift to the adjustment mode is informed to the user.

  Further, for the reason described later, the adjustment mode is not started until the surface temperature of the heating belt 130 reaches, for example, 170 ° C. and the surface temperature of the pressure belt 120 reaches 120 ° C., and the standby time is set.

  As shown in FIG. 6 and the subsequent figures, the pressure sensitive sheet P exhibiting a color development reaction according to the applied pressure is applied to the fixing nip portion of the fixing device 27 by the start of the shift to the adjustment mode. It will be sent as “pressure paper”. The pressure-sensitive sheet P that is pressed during the sheet passing through the fixing nip develops color according to the pressure. The pressure-sensitive sheet P holding such pressure information is sent to a document reading device 160 (see FIG. 9) as image reading means, and the density is read as image information. The density information is sent to the control means. The control means compares the density measurement value based on the pressure information received from the image reading means 160 with the reference value based on the reference density stored in the memory, and operates according to the difference between the two values from the calculation result. A signal is sent to the adjusting means of the fixing device 27 to operate. That is, as shown in FIG. 12, the pressure cam 170 and the lever member 171 constituting the adjusting means are operated to readjust the pressure applied by the pressure roller 121 to the optimum pressure on the heating belt 130 side.

  Here, the pressure-sensitive sheet P is formed of a polymer, and in this embodiment, a PET resin is used as a support for a color former or a developer. It is known that PET resin softens at a high temperature of about 180 ° C. Therefore, it is unsuitable for passing through a high temperature portion such as a high temperature of 180 ° C., and therefore, as described above, the belt is kept waiting until the belt surface temperature falls below 170 ° C. to about 170 ° C. The surface temperature of the heating roller 130 as the heating body and the pressure roller 120 as the pressing body is 180 ° C. or less, depending on the feed speed when the pressure-sensitive sheet P is sandwiched and conveyed at the fixing nip portion. Execute pressure measurement mode under conditions. In the temperature management, a thermistor, a thermo switch, or the like is used as a temperature detection means disposed at a position in contact with the inner surface of the belt, and temperature detection signals from these are constantly monitored and controlled based on it.

  In the case of the present embodiment, when the temperature of the heating roller 130 constituting the heating body is maintained at around 200 ° C., and the mode is shifted to the adjustment mode triggered by a signal or display indicating an error during operation or cartridge replacement. Is convenient because the temperature of the fixing device 27 is lowered. When the belt surface temperature is lowered to 180 ° C. or lower, the control means displays an announcement informing the fact on the display section of the operation panel, and the pressure sensitive sheet P on which the pressure information is recorded is displayed on the image reading section of the image reading means. Prompt as a means to set.

  As shown in FIG. 6, an integrated fixing conveyance unit 150 such as the fixing device 27 is pulled out from the apparatus main body 100 by a display or signal notifying that the waiting time has ended. This operation can also be performed by the user.

  A pre-fixing transport belt 141 is installed on a transport path (hereinafter referred to as “pre-fixing transport path”) 140 upstream of the fixing device 27 and downstream of the secondary transfer device 26 (see FIG. 1). The pressure sensitive sheet P is placed and set on the pre-fixing conveyance belt 141.

  However, as shown in FIG. 7, the pressure sensitive sheet P is stored in the tray 142 disposed in the vicinity of the pre-fixing conveyance path 140, and the pressure sensitive sheet P is fed from the tray 142 when the adjustment mode is executed. Is possible.

  The pre-fixing conveyance path 140 has a belt conveyance structure, and air is sucked by a fan from countless holes provided in the upper part of the belt to suck and hold the pressure-sensitive sheet P being conveyed, thereby realizing stable sheet conveyance. ing. In the present embodiment, the belt conveyance structure is used, but other conveyance means in place of the belt are possible as long as the pressure-sensitive sheet P can be prevented from being colored and an unset pressure is not applied to the pressure-sensitive sheet P.

  As a specific example of the pressure sensitive sheet P, for example, a prescale (trade name of FUJIFILM Corporation) can be used. This prescale is used at an operating temperature of 25 ° C. and an operating humidity of 80% RH, and within a pressure range of 0.2 MPa to 0.6 MPa as shown in FIG. Show changing characteristics. Such a pressure-sensitive sheet P is used in a state in which an A film having a color former layer and a C film having a developer layer are overlapped. The A film is coated with microcapsules encapsulating a color former as a support, which is a PET resin, and the microcapsules are destroyed by external pressure, and the encapsulated color former reacts with the developer. This is a coloring mechanism. Because of this mechanism, the pressure applied to the microcapsules increases as the use temperature increases, so that the color development reaction becomes more prominent.

  However, the pressure-sensitive sheet P is not limited to a two-ply sheet, but may be a type that uses a pressure-sensitive sheet P that is three-ply or a plurality of ply-pulls. However, in that case, if three or more pressure-sensitive sheets P are stacked, the total thickness of the pressure-sensitive sheets P increases, which may be different from the pressure applied to the nip portion with respect to the thickness of plain paper or the like. More preferably, the total thickness of the sheet is about plain paper, and at most about 200 μm is desirable.

  Further, the size of the pressure sensitive sheet P is preferably A4 size or larger, but is arbitrary according to the size of the fixing nip portion. In the case of this embodiment, a pressure-sensitive sheet P having a recording material width dimension of 320 mm in the direction orthogonal to the conveyance direction and a recording material conveyance length dimension of 90 mm in the conveyance direction is used.

  In addition, as the pressure sensitive sheet P, the magenta density when applying pressure 0.2 MPa in an environment close to temperature 25 ° C. and humidity 80% shows a value close to 0.2, and when applying pressure 0.6 MPa. Those having a characteristic that the magenta density shows a value close to 0.9 can be used.

  Therefore, after the pressure-sensitive sheet P is placed on the pre-fixing conveyance belt 141 and set, the fixing conveyance unit 150 is inserted into the apparatus main body 100 of the image forming apparatus again and mounted.

  When the operation is turned on, the pressure-sensitive sheet P is conveyed while being sandwiched in the fixing nip portion, and then discharged to the paper discharge tray 28. The conveyance speed at that time is the same as the speed at which ordinary so-called plain paper is passed. In this embodiment, the recording material conveyance speed is set to 280 mm / sec. The pressure-sensitive sheet P sandwiched at the fixing nip portion between the pressure belt 120 and the heating belt 130 is pressurized, and the developer and the color developer react to turn red according to the pressure. The color of red is determined by the combination of the developer and the color former.

  When the pressure-sensitive sheet P is discharged to the paper discharge tray 28, an announcement is displayed on the operation panel so as to prompt the user to set the discharged and colored pressure-sensitive recording material P on the document reading device (image reading means) 160. Is done. When the pressure sensitive sheet P discharged to the paper discharge tray 28 is set on the document reading device (image reading means) 160 shown in FIG. 9, a sensor (not shown) for detecting the presence or absence of paper detects the setting of the pressure sensitive sheet P. The operation panel announces that the start button is pressed. The document can be read by using a document reading unit 161 provided as a standard on the upper surface of the copying machine, or an automatic document feeder / reader 162 (ADF), which is usually an optional specification, can be used. In the reading unit or ADF, the pressure-sensitive sheet P is set in the horizontally long feeding posture by aligning the reading direction as illustrated and the direction orthogonal to the conveyance direction of the pressure-sensitive sheet P. That is, as shown in FIG. 10, reading is performed over almost the entire width of the recording material lateral width of 320 mm with respect to the recording material conveyance longitudinal length of 90 mm.

  By pressing the start button, the control means starts reading. It is desired that the reading is performed after being set for 10 minutes after the pressure-sensitive sheet P is pressed at the fixing nip portion and exhibits a coloring reaction, after about 10 minutes. This is because the pressure-sensitive sheet P that exhibits a color reaction upon receiving pressure requires a time of about 10 minutes until the reaction is completely completed. The pressure-sensitive sheet P used in the present embodiment has a characteristic of developing 95% color in 10 minutes. However, after 10 minutes, it is optional depending on how long the concentration information stored in the information storage unit (not shown) is measured. More preferably, the concentration reading is performed after, for example, 1 hour, which is within the time when the reaction is completely completed and does not show a fading reaction.

  Therefore, the color density reading of the pressure sensitive sheet P is performed as shown in FIG. 10 by pressing the copy button on the pressure sensitive sheet P set in the document reading device 160. In the document reading unit, the density is read over the entire longitudinal direction of the image because it is read by line scanning. The density of the pressure sensitive sheet P in the transport direction can be read by moving the image reading unit in the transport direction.

  In the longitudinal direction of the pressure-sensitive sheet P, that is, in this case, the width direction of the recording material, the profile is read as the density information of the magenta (M) color component, and the read density profile signal is transmitted to the control means. The color density to be read may be arbitrary depending on the color of the color former. Among Y (yellow), M (magenta), C (cyan), and K (black), the color having the highest sensitivity to the applied pressure is selected. Should be chosen.

  The control means that has received the density profile signal executes the following control based on the density profile signal.

  As shown in FIG. 10, the density profile in the width direction of the pressure-sensitive sheet P, which is the longitudinal direction, is averaged in the recording material conveyance direction by the control means. The control means averages the density profile in the longitudinal direction of the image in the range of the effective width of 300 mm excluding 10 mm at both ends of the total width of 320 mm of the recording material width. FIG. 11 shows the concentration measured in the range of an effective width of 300 mm.

  The control means reads a reference value that is a reference density profile stored in the memory. The reference value of the density is compared with the measured value based on the density profile at the end of the recording material in the longitudinal direction obtained from the document reading device 160 and the difference is calculated by the CPU. An operation signal controlled based on the calculated value is output and transmitted to an operation actuator for operating an adjusting unit provided in the fixing device 27.

≪Fixing device adjustment means≫
Here, the configuration of the adjusting means will be described.

  As shown in FIG. 12, the adjusting means has a pressurizing cam 170, and the pressurizing cam 170 is rotated by an actuating actuator to rotate the lever member 171 with the rotation pin 171a as a fulcrum. The pressure roller 121 is pressed by the rotation of the lever member 171, and the pressure applied by the pressure roller 121, that is, the fixing nip pressure is adjusted to the optimum pressure. That is, by rotating the pressure cam 170 that applies a pressing force to the lever member 171 from the back side, the pressing force can be increased while the lever member 171 is rotationally displaced and in contact with the pressure roller 121.

  The pressing force received from the lever member 171 acts on a bearing arm that pivotally supports the end of the roller shaft of the pressure roller 121 and applies pressure to the pressure roller 121 through the bearing arm. And, it is a mechanism that applies force to the pressure belt 120 through the pressure roller 121. A pressing force is applied via a bearing arm which is a roller bearing without directly applying a pressing force to the pressure roller 121. By doing so, the pressure roller 121 is prevented from being bent and damaged by the pressing force from the lever member 171. In this case, it is desirable that the pressing force is applied to the central portion of the roller shaft of the pressure roller 121. In order to set the pressing force applied to the central portion to the target value, the outer diameter of the pressing roller 121 is set to a suitable crown shape. I have to. That is, the density of the end of the pressure sensitive sheet P is determined by the crown amount depending on the position of the phase angle of the pressure cam 170. Similarly, the density of the central portion of the pressure sensitive sheet P is determined by the crown amount according to the position of the phase angle of the pressure cam 170. Therefore, when adjusting the applied pressure transmitted to the pressure belt 120 via the pressure roller 121, the control means uses the reference value of the density determined as the reference and the measured value of the density measured at the end of the pressure-sensitive recording material. It is only necessary to compare and adjust the difference resulting from the comparison. In the concentration range shown in FIG. 11, the range that can actually be effectively used for adjusting the applied pressure is 50 mm from the end of the recording material.

  In accordance with the comparison operation between the reference value of the concentration and the measured value, the control means outputs and sends an operation signal to the variable pressure mechanism in response to it, and adjusts the adjustment means so as to obtain the optimum pressure.

  FIG. 13 is a characteristic graph showing the correlation between the phase position of the lever member 171 held by the pressure cam 170 and the applied pressure. When the pressure cam 170 is rotated to change the phase position, the applied pressure (MPa) shows a curve characteristic indicated by a solid line in the figure. As the deterioration of the member progresses in terms of durability, the rubber which is the elastic layer on the roller surface deteriorates with respect to the phase position of the pressure cam 170, as shown by the curve characteristics by the one-dot chain line in the figure. The biasing spring deteriorates due to settling or the like, and as a result, the applied pressure is small and insufficient. Then, the relationship in which the applied pressure is normally P with respect to the angle θ of the phase position of the pressure cam 170 becomes the applied pressure P ′ (P> P ′).

  In the fixing device 27 in such a state, the density of the pressure-sensitive sheet P is lower than that in a state where the applied pressure is in an appropriate range as indicated by the reference numeral A ′ in the characteristic diagram of FIG. 14. The difference between the reference concentrations A and A ′ is calculated by the calculation unit of the CPU of the control means, and the calculation unit operates on the actuating actuator so as to be the holding phase angle θ ′ of the pressure cam 170 where the applied pressure MPa becomes P. Send a signal. When the actuation actuator receives the actuation signal, the actuation actuator is rotated to an appropriate angle so that the holding phase angle of the pressure cam 170 becomes θ ′, and the applied pressure MPa is adjusted to P.

  At that time, if the pressure-variable mechanism is capable of independently developing the control in both the front and back with respect to the longitudinal direction of the pressure sensitive sheet P in this case, the direction of the width of the recording material, The pressure fluctuation when the rotational driving force is input to the pressure roller 121 can be adjusted with higher accuracy.

On the other hand, if it is a portion B in FIG. 14 that is higher than the reference concentration range, the phase angle θ ₁ of the pressure cam 170 in FIG. 13 is decreased, and the applied pressure MPa is decreased from P ₁ . In the normal concept, the pressing force decreases as the durability of the fixing device 27 decreases. Therefore, the control is performed in a direction to increase the pressing force. There is also the possibility of reducing the applied pressure.

  As is apparent from the above, the image forming apparatus according to the present embodiment provides the following operations and effects.

  (1) When the fixing nip pressure fluctuates due to deterioration due to use over time, etc., a pressure sensitive sheet P made of PET resin as a support for a color former or a developer is used as “pressure sensitive paper for a sample to be measured”. . After the surface temperatures of the heating roller 130 and the pressure roller 120 are set to 180 ° C. or less, the adjustment mode is selected and executed.

  (2) When the temperature of the fixing device 27 is lowered to 180 ° C. or less, an announcement to that effect is displayed on the operation panel, and the integrated fixing conveyance unit 150 such as the fixing device 27 is pulled out from the apparatus main body 100. It is urged to set the pressure-sensitive sheet P on the pre-fixing conveyance belt 141. The fixing conveyance unit 150 is reinserted into the apparatus main body 100 of the image forming apparatus and attached.

  (3) The pressure sensitive sheet P is sandwiched in the fixing nip portion, and is sandwiched in the fixing nip portion between the pressure belt 120 and the heating belt 130 and receives pressure. Depending on the pressure applied at that time, the pressure sensitive sheet P turns red due to the reaction between the developer and the color former.

  (4) The pressure sensitive sheet P discharged to the paper discharge tray 28 is set in the document reading device 160, and the pressure sensitive sheet P is set in a landscape feed posture. Reading is performed over almost the entire width of 320 mm.

  (5) The color density of the pressure sensitive sheet P is read by operating a push button on the pressure sensitive sheet P set in the document reading device 160. For example, the density profile of the magenta (M) color component is read, and the read density profile signal is transmitted to the control device of the apparatus main body 100. The control means of the apparatus main body 100 that has received the density profile signal executes control based on the density profile signal. That is, as shown in FIG. 10, the control means averages the density profile in the longitudinal direction of the image in the range of the effective width of 300 mm excluding 10 mm at both ends of the total width 320 mm of the width of the pressure-sensitive sheet P. To do.

  (6) In FIG. 11, the density | concentration which measured the pressure sensitive sheet P in the range of the effective width of 300 mm is shown. In practice, the range that can be effectively used for adjusting the pressure is from the end of the pressure-sensitive sheet P to 50 mm. The control means reads a reference value that is reference density profile information stored in the memory. The read reference value is compared with the measured value based on the density profile at the end of the longitudinal pressure-sensitive sheet P obtained by averaging the densities read by the document reading device 160, and the difference is calculated. An operation signal controlled based on the calculated value is sent to the operation actuator to operate the adjusting means. The pressure cam 170 of the adjusting means is rotated by an actuating actuator, and the pressure applied via the pressure roller 121, that is, the fixing nip pressure is adjusted to the optimum pressure by changing the position where the lever member 171 is held. To do.

  (7) When the pressure cam 170 is rotated to change the phase position, the applied pressure (MPs) changes. As the deterioration of the member progresses in terms of durability, the rubber that is the elastic layer on the roller surface with respect to the phase position of the pressure cam 170 deteriorates, and the urging spring for pressure deteriorates due to settling or the like. Pressure is small and short. In the fixing device 27 in such a state, the density of the pressure sensitive sheet P is lower than that in a state where the applied pressure is in an appropriate range. The difference from the reference concentration is calculated by the calculation unit of the CPU, and the applied pressure MPa is adjusted to a suitable pressure.

  (8) As described above, by adjusting and controlling the pressure applied to the sheet such as the recording material at the fixing nip portion to the optimum pressure at all times, it is impossible for the sheet and the toner image that is a visible image formed thereon. There is no stress. As a result, it is possible to print out a high quality image with high glossiness and high image quality. As a result, the image forming apparatus can be speeded up and the productivity can be improved.

  The preferred embodiments of the present invention have been described. However, the present invention is not limited to such embodiments, and other embodiments, applications, modifications, and combinations thereof are possible without departing from the technical idea of the present invention. Is possible.

  For example, in the above-described embodiment, as an example of the structure of the fixing device 27, an endless belt is used on both the pressure side and the heating side, and a fixing nip portion is formed between the two belts. It is not limited. For example, the technical idea of the present invention can be applied without problems to a fixing device using a pair of rollers including a fixing roller and a pressure roller, or a structure using a belt instead of only one of the rollers is also possible. .

1 is a diagram showing a preferred embodiment of an image forming apparatus according to the present invention. 1 is a diagram illustrating a fixing device as an image heating device provided in an image forming apparatus according to an embodiment. The figure which shows the fixing device. The figure which shows the fixing device. The figure which shows the fixing device. FIG. 3 is a diagram illustrating a fixing conveyance unit that is integrally provided with the fixing device and is attached to and detached from the image forming apparatus main body. The figure which shows the operation | movement aspect of the fixing conveyance unit. The characteristic view which shows the correlation of a magenta density | concentration and applied pressure in the same embodiment. FIG. 3 is a diagram illustrating an image reading apparatus that reads image information on a pressure-sensitive recording material in the embodiment. The figure which shows typically the aspect which reads a density | concentration as image information on a pressure-sensitive recording material in the image reading apparatus. FIG. 6 is a characteristic diagram showing a density distribution read over the recording material longitudinal direction. FIG. 3 is a diagram illustrating a configuration of an adjustment unit provided in the fixing device of the present embodiment. The characteristic view which shows the correlation with the pressurization cam and pressurization force in the adjustment means. The characteristic view which shows the correlation of the applied pressure and density | concentration in the adjustment means.

Explanation of symbols

20 Photosensitive drum (image carrier)
27 Fixing device (image heating device)
28 Paper discharge tray 100 Image forming apparatus main body 120 Pressure belt 121 Pressure roller 122 Tension roller 123 Oil application roller 124 Belt regulating flange 125 Pressure pad 126 Bearing 127 Tension spring 128 Heater 130 Heating belt 131 Heating roller 132 Tension roller 135 Induction Heating Coil 137 Pad Stay 140 Pre-fixing Conveying Path 141 Pre-Fixing Conveying Belt 142 Pressure-Sensitive Recording Material Tray 150 Fixing Conveying Unit 160 Document Reading Device (Image Reading Means)
161 Document Reading Unit 162 Document Automatic Conveyance Reading Device 170 Pressure Cam (Adjustment Unit)
171 Insulator member (adjustment means)
171a Rotating Pin for Insulator 200 Image Forming Unit S Sheet (Recording Material)
P Pressure sensitive sheet

Claims (3)

A pair of image reading means for reading the image information of the original, image forming means for forming a toner image on the sheet based on the image information from the image reading means, and heating the toner image formed on the sheet at its press contact portion An image forming apparatus comprising: an image heating member; and an adjusting unit that adjusts a pressure at the press contact portion by moving at least one of the pair of image heating members.
An adjustment mode in which pressure information that has been pressed at the pressure contact portion and recorded on the pressure sensitive sheet is read by the image reading means, and the pressure at the pressure contact portion is adjusted by the adjustment means based on the read pressure information. An image forming apparatus comprising execution means for executing the image forming apparatus.   The execution unit sets an operation unit for instructing the adjustment mode and a pressure-sensitive sheet on which pressure information is recorded when the adjustment mode is instructed in the operation unit in the image reading unit of the image reading unit. 2. The image forming apparatus according to claim 1, further comprising means for prompting to do so. In an adjustment method for adjusting a pressure applied to a sheet in an image heating apparatus for heating a toner image on the sheet,
Pressurizing the pressure sensitive sheet at the pressure contact portion of the image heating device;
Reading pressure information recorded on the pressure sensitive sheet;
Adjusting the pressure applied to the sheet at the pressure contact portion of the image heating device based on the pressure information of the read pressure-sensitive sheet;
The adjustment method characterized by having.