JP2017102156A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that detects a variation in nip position due to change over time and adjusts the amount of pressing force at both ends in the axial direction of a pressure member.SOLUTION: There is provided a fixing device comprising: a fixing member; a heat source that heats the fixing member; and a pressure roller that faces the fixing member to form a nip, the fixing device conveying a recording medium carrying an unfixed image to the nip and fixing the unfixed image to the recording medium, and including pressing mechanisms that each independently press both ends of the pressure roller to the fixing member, and pressure amount detection means in the longitudinal direction of the pressure roller, in which the pressure amount is an amount of the pressure roller pressed into the fixing member by the pressing mechanisms, and is uniform in the longitudinal direction of the pressure roller.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system.

  2. Description of the Related Art In recent years, in electrophotographic image forming apparatuses such as copying machines, printers, and fax machines, there is a demand for a fixing apparatus that has little influence on image quality regardless of long-term use as the life of the apparatus increases.

  Various types of fixing devices have been proposed. The fixing device includes a fixing roller as a fixing member maintained at a predetermined temperature, and a pressure roller as a pressure member in pressure contact with the fixing roller. A roller fixing method is known in which a recording medium carrying an unfixed toner image is heated while being nipped and conveyed by a nip portion (fixing nip portion) formed by pressure contact between the roller and the fixing roller, and is fixed.

  Further, the pressure roller and the fixing belt are provided with a fixing roller disposed opposite to the pressure roller, and an endless fixing belt (fixing sleeve) as a fixing member stretched between the fixing roller and the heating roller. There is known a belt fixing method in which heat of a heating roller is applied to a recording medium through a fixing belt at a nip portion formed by pressure contact with the recording medium to pressurize and fix an unfixed toner image on the recording medium. . A fixing method such as an electromagnetic induction heating method is also known.

  The surface layer of the pressure roller has a release layer for improving the separation property of the recording medium. On the other hand, it is difficult to select a highly durable material while ensuring sufficient release properties, and the higher the rotation speed of the pressure roller, the greater the burden on the release layer. Further, due to the variation with time, deviation occurs in the drive control in the longitudinal direction of the pressure roller and the balance of the gear train, and the abrasion speed of the release layer is different in the traveling speed at both ends. If the burden on the release layer continues, there arises a problem that the print quality cannot be maintained over time.

  In order to press the nip with a predetermined pressure, a method is disclosed in which the pressing mechanism of the pressure roller against the fixing roller is configured differently at the left and right ends of the pressure roller based on the correction amount corresponding to the accumulated print value (patent) Reference 1). However, there is a problem that versatility is low because it is necessary to individually adjust according to the characteristics of the device. Further, Patent Document 2 discloses a method for changing the nip position by detecting the paper conveyance state or the fixing belt shift, but does not detect the deviation of the nip position, and solves the burden on the release layer. It is not possible.

  The problem to be solved by the present invention is a decrease in print quality due to the fact that the pressing amount in the longitudinal direction of the pressure roller cannot be made constant over time.

  Specifically, in the fixing device that includes a fixing member and a pressure member that faces the fixing member and forms a nip, and fixes an unfixed image on a recording medium conveyed to the nip, the pressure member Detecting means for detecting a pressing amount that is an amount by which the pressing member is pressed into the fixing member by the pressing mechanism. And a fixing device that controls the pressing mechanism based on a detection result of the detection unit.

  The fixing device according to the present invention can change the amount of pressing between nips, and can maintain the print quality over time.

1 is a cross-sectional view showing an embodiment of an image forming apparatus according to the present invention. 1 is a cross-sectional view illustrating a basic configuration of a belt fixing type fixing device. It is a side view which shows the structure of a pressure roller. It is sectional drawing which shows the structure of a pressure roller. It is a perspective view which shows the control mechanism of a pressure roller. It is a front view which shows the control mechanism of a pressure roller. It is a perspective view which shows a detection means and a nip position. It is sectional drawing (A-A 'of FIG. 6) of a fixing roller and a pressure roller, and explanatory drawing of a nip position. It is explanatory drawing of a surface sensor. It is a figure which shows the bending | flexion which generate | occur | produces on a sheet passing size and a pressure roller surface. It is a figure which shows that the thickness of a release layer differs in the axial direction of a pressure roller. It is a figure which shows a crown-shaped pressure roller. It is a perspective view of a cooling mechanism and a pressure roller. It is a front view of a cooling mechanism and a pressure roller. It is a figure showing the other example of belt fixing.

  Hereinafter, the configuration according to the present application will be described in detail based on the embodiment shown in FIGS.

(Image forming device)
FIG. 1 is a schematic configuration diagram illustrating the overall configuration of a tandem type color copier that is an embodiment of an image forming apparatus according to the present invention. The outline and operation of the internal configuration of the image forming apparatus will be described with reference to FIG.

  In FIG. 1, 1 is an image forming apparatus main body, 2 is a writing unit that emits laser light based on input image information, 3 is a document conveying unit that conveys a document D to a document reading unit 4, and 4 is image information of the document D. A document reading unit to be read, 7 is a paper feed unit for storing paper P (not shown) such as transfer paper, 9 is a registration roller for adjusting the conveyance timing of the paper P, and 11Y, 11M, 11C, and 11BK are each color (yellow) , Magenta, cyan, and black) on which the toner image is formed, 12 is a charging unit that charges the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each of the photosensitive drums 11Y, 11M, and 11C. , 11, a developing unit that develops the electrostatic latent image formed on 11 BK, and a transfer unit 14 that transfers the toner images formed on the photosensitive drums 11 Y, 11 M, 11 C, and 11 BK on the paper P in an overlapping manner. Iasurora (primary transfer bias roller), 15 denotes the photosensitive drums 11Y, 11M, 11C, a cleaning unit for collecting the untransferred toner on 11BK.

  Also, 16 is an intermediate transfer belt cleaning unit for cleaning the intermediate transfer belt 17, 17 is an intermediate transfer belt on which toner images of a plurality of colors are transferred, and 18 is a color toner image on the intermediate transfer belt 17 on the paper P. A secondary transfer bias roller 20 for transferring is a fixing device for fixing the toner image on the paper P.

  Hereinafter, an operation during normal color image formation in the image forming apparatus will be described. First, the document D is transported from the document table by the transport roller of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5. Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information. Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, laser light based on the image information of each color is emitted from the writing unit 2 toward the corresponding surface of the photosensitive drums 11Y, 11M, 11C, and 11BK.

  On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated counterclockwise in FIG. First, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (charging process). Thus, a charged potential is formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.

  In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a different optical path for each color component of yellow, magenta, cyan, and black (exposure process).

  The laser beam corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side. At this time, the yellow component laser light is scanned in the longitudinal direction (main scanning direction) of the rotation axis of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated on the surface of the second photosensitive drum 11M from the left, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left to form an electrostatic latent image of the cyan component. The black component laser light is applied to the surface of the fourth photosensitive drum 11BK from the left, and an electrostatic latent image of the black component is formed.

  Thereafter, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach the positions facing the developing unit 13, respectively. Then, toner of each color is supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (developing process).

  Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK after the development process reach the opposed portions to the intermediate transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the surface of the intermediate transfer belt 17 at the position of the transfer bias roller 14 (primary transfer process). .

  The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (cleaning process).

  Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a static elimination unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

  On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the photoconductive drums 11Y, 11M, 11C, and 11BK are transferred (carried) are run in the clockwise direction in the drawing and are connected to the secondary transfer bias roller 18. Reach the opposite position. Then, the color toner image carried on the intermediate transfer belt 17 is transferred onto the paper P at a position facing the secondary transfer bias roller 18 (secondary transfer step).

  Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and a series of transfer processes in the intermediate transfer belt 17 is completed.

  Here, the sheet P conveyed between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is conveyed from the sheet feeding unit 7 via the registration roller 9 and the like. .

  Specifically, the paper P fed by the paper feed roller 8 from the paper feed unit 7 that stores the paper P passes through the transport guide and is guided to the registration roller 9. The paper P that has reached the registration roller 9 is conveyed toward the secondary transfer nip at the same timing.

  Then, the paper P on which the full color image is transferred is guided to the fixing device 20 by the transport belt. In the fixing device 20, a color image (toner) is fixed on the paper P at a nip between a fixing roller 22 as a fixing member and a pressure roller 23 as a pressure member.

  Then, the paper P after the fixing process is discharged as an output image outside the apparatus main body 1 by a paper discharge roller, and a series of image forming processes is completed.

  FIG. 2 shows a basic configuration of the belt fixing type fixing device 20, and is a schematic sectional view in the longitudinal direction of the fixing roller 22.

  The fixing device 20 presses the heating roller 21, the fixing roller 22, the heating roller 21, the fixing belt 24 stretched around the fixing roller 22, and the fixing roller 22 to form a nip portion with the fixing belt 24. A roller 23 and the like are provided. The heating roller 21 has a heater 25 inside as a heating means (heat source).

  The fixing device 20 heats and fixes a sheet P carrying an unfixed toner image through a nip N between the fixing belt 24 and the pressure roller 23 formed by pressure contact between the fixing roller 22 and the pressure roller 23. Is to do.

  The sheet P is guided to the nip portion by the entrance guide 26. The heating roller 21, the fixing roller 22, and the pressure roller 23 are rotatably supported on a side plate (not shown) of the fixing device 20, and a driving means for the roller (not shown) is fixedly held on the casing.

  The heating roller 21 is a thin cylindrical body made of, for example, a metal material, and a heater 25 as a heat source is fixed inside the cylindrical body. As the heater 25, for example, a halogen heater or a carbon heater can be used. Further, both end portions of the heater 25 are fixed to the casing of the fixing device 20. The heater 25 may be an induction heating unit that heats the heating roller 21 from the outside.

  The output of the heater 25 is controlled by a power supply unit (AC power supply) of the apparatus main body, and the heating roller 21 is heated by the radiant heat from the heater 25. Further, heat is applied to the paper P from the surface of the fixing belt 24 heated by the heating roller 21. The output control of the heater 25 is performed based on the detection result of the belt surface temperature by a temperature sensor (not shown) such as a thermopile provided at a position facing the surface of the fixing belt 24.

  The fixing belt 24 is wound around the fixing roller 22 and the heating roller 21, and is in close contact with the heating roller 21 and the fixing roller 22. The fixing nip portion is configured by pressing the pressure roller 23 against the fixing belt 24 configured as described above at a position corresponding to the fixing roller 22.

  The fixing belt 24 is, for example, an endless belt having a multilayer structure in which an elastic layer such as silicone rubber and a release layer are sequentially laminated on a base layer made of PI (polyimide) resin and having a layer thickness of 90 μm.

  The elastic layer of the fixing belt 24 has a layer thickness of about 200 μm and is formed of an elastic material such as silicone rubber, fluorine rubber, and foamable silicone rubber. The release layer of the fixing belt 24 has a layer thickness of about 20 μm and is formed of PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. ing. By providing a release layer on the surface layer of the fixing belt 24, the releasability for the toner is ensured.

  The fixing roller 22 does not have a heat source, and is formed by covering a highly rigid core material (core metal 22a) such as metal (iron or aluminum) with a thick elastic layer such as silicone rubber. It is not restricted to a roller, A pad may be sufficient.

  As shown in FIG. 3B, in the pressure roller 23, an elastic layer 23b made of fluorine rubber, silicone rubber, foamable silicone rubber or the like is formed on a metal (SUS304, etc.) metal core 23c, similarly to the fixing roller 22. It is a roller member. By providing the release layer 23a on the surface of the elastic layer, the paper separation property is improved. Moreover, it is good also as a structure which provides the heater as a heat source inside a cylindrical body. Although the fluororesin is used as the material of the release layer 23a, it may be the same member as the elastic layer as long as the paper separation property can be improved.

  Further, as shown in FIG. 4, a pressure lever 40 (40a, 40b) as a displacement means of the pressure roller 23 is in contact with the metal core 23c of the pressure roller 23, and the pressure lever 40 will be described later. By moving in the direction of the arrow in the figure by the driving means, the pressure applied to the fixing roller 22 of the pressure roller 23 varies. The nip width is adjusted by controlling the pressure applied by the displacement means of the pressure roller 23. The displacing means of the pressure roller 23 is not limited to the pressure lever 40 as long as it changes the nip width by changing the pressure applied to the fixing roller 22 by the pressure roller 23. As will be described later, the pressure levers 40 exist at both ends in the axial direction and are controlled independently. This makes it possible to make the amount of pushing at both ends in the axial direction uniform.

  Returning to FIG. 2, the tension roller 27 has a role of applying a certain tension to the fixing belt 24 stretched between the two roller members, and can increase the contact area of the fixing belt 24 to the heating roller 21. . Thereby, more heat can be transferred from the heater 25 to the fixing belt 24.

  Further, a driving unit (not shown) rotates the fixing roller 22 in the clockwise direction (D). Due to the rotation of the fixing roller 22 as a driving roller, the pressure roller 23 and the fixing belt 24 that are in pressure contact with the fixing roller 22 rotate at the same speed. Note that the pressure roller 23 may be rotationally driven as a driving roller.

  The sheet P that has passed through the nip portion is separated at the leading end by a separation plate 28 disposed on the fixing roller 22 side or a separation claw 29 disposed on the pressure roller 23 side, and is provided on the downstream side in the transport direction. It is guided to the conveyance path formed by the outlet guide 30 and the lower outlet guide 31 and discharged to the next process. Note that the separation claw 29 disposed on the pressure roller 23 side may be a separation plate, similar to the fixing roller 22 side.

  The cooling mechanism 32 has a function of cooling the pressure roller 23 when the pressure roller 23 reaches a predetermined temperature or higher. Thereby, wear on the surface of the pressure roller can be reduced. The cooling mechanism 32 will be described later.

  The detection means 33 is disposed upstream of the nip and detects nip positions at both ends in the nip axial direction.

  The fixing roller 22, the fixing belt 24, and the pressure roller 23 are configured to be able to contact and separate. The reason for having the contact / separation mechanism is that when the contact is always made, the fixing roller 22 and the pressure roller 23 are always in contact deformation, which affects the image quality and durability. . When the paper is not passed, the fixing roller 22 and the pressure roller 23 are separated from each other, so that the image quality can be improved and the life of the roller can be increased.

  When the surface layer wear of the pressure roller 23 was observed over time, it was found that the surface layer wear rate was different in the longitudinal direction as shown in FIG. 3A. The darker the color, the more worn it is. That is, one side is fast and the other side is worn but the traveling speed is slow. The reason for this is that the balance of drive control and gear arrangement may be lost. Originally, the push-in amount does not vary at both ends, but it is heated to a certain temperature or more, and the balance of drive control and gear arrangement is lost over time, resulting in a deviation in the push-in amount. Deviation also occurs. Note that the degree of wear in FIG. 3 is exaggerated for the purpose of explanation, and does not represent the actual degree of wear. Further, the deviation in the wear rate is not limited to the pressure roller 23, and the same applies to the fixing belt 24 that forms a nip facing the pressure roller 23.

  Therefore, in the present invention, a mechanism for independently pressing the fixing roller 22 at both ends of the pressure roller 23 is provided.

(First embodiment)
As shown in FIG. 4, two pressure levers 40a and 40b are connected to the shaft core portions of both shafts of the pressure roller 23, and these pressure levers 40a and 40b are independently pressure controlled. The That is, when the cams 42 a and 42 b rotate, the pressure levers 40 a and 40 b rotate independently about the rotation axis 41 and are pushed into the fixing roller 22. As described above, the pressing amount at both ends in the longitudinal direction can be changed by the mechanism in which the mechanism for pressing the bearing of the pressure roller 23 is provided independently at both ends as shown in FIG. The pressing amount is the amount of force that the pressing mechanism applies to the pressure roller 23, and the pressing amount is the amount that the pressing roller 23 is pressed into the fixing roller 22.

  The control of the pressing amount will be described. The determination of the pressing amount is performed by irradiating a laser from detection means 33 provided at both axial ends of the pressure roller 23 and detecting the nip position as shown in FIG. Specifically, the nip position is determined from the arc shape of the fixing roller 22 and the pressure roller 23, the difference in the pushing amount in the longitudinal direction is read from the nip position information, and the positions of the cams 42a and 42b are moved as necessary.

  The nip position referred to here is the vicinity of the pressure contact area formed by the pressure roller 23 and the fixing roller 22 including the end portion on the paper intrusion side as surrounded by the dotted square portion shown in FIG. The difference in the nip position is derived from the difference in the pushing amount. That is, it is not necessary to detect the contact position between the fixing roller 22 and the pressure roller 23 as a pinpoint, and it is only necessary to detect the difference in the amount of pressing at both ends in the axial direction. That is, it suffices to irradiate the laser to a range having a certain extent as shown by the range surrounded by the dotted line in FIG.

  Although it is desirable that the position of the detection means 33 be set symmetrically, it is not limited to this, and the position of the detection means 33 is not particularly limited as long as the difference in the nip position is within a detectable range. The laser irradiation for adjusting the nip position may be performed during non-passing (between passing and during passing) during continuous printing, or may be performed every specific number of sheets. If it is performed during continuous printing, the amount of push-in is monitored over time, which is more effective. Further, by installing the detection means 33 in the non-sheet passing area, the push-in amount can be adjusted even during the sheet passing.

  The detection means 33 will be described with reference to FIG. In the present embodiment, a two-dimensional laser type reflective sensor is used. The detection means 33 includes a light emitting element A that irradiates a laser and a light receiving element B that receives the reflected laser. Light A ′ from the light emitting element A is applied to the pressure roller 23 which is a measurement object, and a part of the light beam B ′ reflected and diffused from the pressure roller 23 forms a spot on the light receiving element B so as to press. The distance to the roller 23 is detected to recognize the nip position.

  In the present embodiment, a two-dimensional laser shift meter is used as the detection means 33, but the present invention is not limited to this, and any device that can confirm the nip position may be used. For example, the nip position may be detected using a camera or the like.

  In this embodiment, as shown in FIG. 6, two laser irradiation means 33a and 33b are provided as detection means 33 at both ends in the longitudinal direction, but the number is not limited thereto. When there is one detection means 33, it is preferable to use two or more because the error becomes large when the nip position in the entire width direction is detected. Further, since it is necessary to detect the difference in the pressing amount and adjust the pressing amount by the above-described pressurizing mechanism, it is preferable to provide an even number of detecting means 33. As a result, a difference in pushing amount (nip position or nip height) at both ends in the longitudinal direction can be detected and adjusted by the pressure mechanism described above, so that no difference in pushing amount can be prevented.

  In a state where the fixing roller 22 and the pressure roller 23 store heat by continuous paper passing and expand in the radial direction, fixing can be performed under a fixing condition in which the pressing amount is lower than that during non-heat storage. In particular, the release layer 23a, which is the surface layer of the pressure roller 23, becomes soft during continuous paper passing, and is more susceptible to damage than when it is at a low temperature. Therefore, as described above, the burden on the surface layer of the pressure roller 23 can be further reduced by reducing the absolute amount of the pressing amount in addition to adjusting the nip pressing amount relatively on the left and right.

(Second embodiment)
For the softening of the surface layer of the pressure roller 23 and the radial expansion of the pressure roller 23 itself during continuous paper feeding, the surface layer of the pressure roller 23 is irradiated with a laser or the like instead of or in combination with the nip position information. The state of the release layer 23a may be confirmed and the fixing conditions may be changed. The surface state of the release layer 23a can be detected by the detection means 33. In order to read the surface state of the pressure roller 23 in units of microns by irradiating the laser, a large adjustment mechanism is necessary for adjusting the focal point. In this embodiment, at least the fluctuation of the laser beam is suppressed. Anything that can be confirmed can be used. The amount of fluctuation will be described later.

  FIG. 9 is an explanatory view of wear amount detection by laser irradiation. An example in which a different paper size is passed through the unused pressure roller 23 shown on the left side in the figure and the surface layer of the pressure roller 23 has a streak d1 but is less damaged (a streak trace is present). (Shallow) and (b) show examples in which the same paper size is passed and a streak d2 is generated on the surface layer of the pressure roller 23 (a streak is deep).

  Here, when the laser is irradiated, if the surface layer of the pressure roller 23 is not damaged as shown in (a), the laser beam L is irradiated as a substantially straight line, but on the other hand, the pressure is applied as shown in (b). When a trace such as a streak is generated on the surface layer of the roller 23, the focus of the laser at the streak is deviated, and the laser light L is bent at the streak. A bent portion is indicated by Lf. Based on the detection of the fluctuation amount that is the amount of bending displacement from the center position of the laser beam L, it becomes possible to grasp the wear state of the surface layer of the pressure roller 23.

  Although the detection of the surface state of the pressure roller 23 has been described so far, the softening of the surface layer of the fixing belt 24 resulting from heat storage can be similarly detected using a detection means such as a laser. In addition to or instead of detecting the surface state of the pressure roller 23, the fixing belt 24 is irradiated with a laser to grasp the wear state of the surface layer of the fixing belt 24, thereby changing the fixing conditions. Good.

  When different paper sizes are sparsely passed, the load on the surface layer of the pressure roller 23 and the fixing belt 24 is distributed to each portion. However, in actuality, as shown in FIG. 9, the same paper size is often passed, and the load is concentrated on a specific location, so that the pressure roller 23 and the fixing belt 24 are bent.

  Specifically, changes in fixing conditions using the surface state will be described. First, the surface of the pressure roller 23 corresponding to each paper size is irradiated with a laser to detect the surface state. Then, the amount of bending derived from the surface state of the detected pressure roller 23 surface layer is measured, and the productivity is controlled so that the set temperature of the heating roller 21 is changed and the number of printed sheets per unit time is reduced by the step amount. . Also, the fixing belt 24 can measure the amount of bending of the surface in the same manner as the pressure roller 23 and can perform the same productivity control.

  As a result, it is possible to reduce the burden on the surface layer of the pressure roller 23 and the fixing belt 24. In the present embodiment, the control for increasing the sheet interval during continuous printing is performed as a productivity control, but the present invention is not limited to this, for example, by increasing the sheet passing speed while increasing the sheet passing interval, It is also possible to reduce the burden on the surface layer of the pressure roller 23 without reducing productivity.

  When continuous paper passing is often used, damage to the pressure roller 23 and the fixing belt 24 increases. In this case, in addition to the productivity control, a control is performed to reduce the productivity by adding a correction value based on the bending amount. Thereby, the lifetime of the pressure roller 23 and the fixing belt 24 can be further extended.

  Wear of the release layer 23a on the surface of the pressure roller 23 is also affected by the sheet passing history. As the release layer 23a is thicker, it is necessary to apply heat, and the required amount of heat is reduced because the release layer 23a becomes thinner due to wear. A fixing control temperature suitable for the initial state of the pressure roller 23 is set, but the pressure roller 23 deteriorates depending on the use environment. On the other hand, according to the present embodiment, the deterioration state of the pressure roller 23 can be detected and controlled to a fixing control temperature suitable for the state. can do. Therefore, by reading the surface layer step amount as the surface property of the release layer 23a and reducing the temperature by the correction value corresponding to the surface layer step amount, the control temperature can be lowered and deterioration can be suppressed.

Table 1 shows a fixing control temperature (sheet passing temperature) lowering table corresponding to the surface level difference of the pressure roller 23. In the table, def indicates a predetermined fixing control temperature. For example, when the difference in thickness of the release layer 23a is 0.15 mm, the fixing control temperature is controlled to a lower fixing control temperature by the correction value A.

(Third embodiment)
As described above, when the same paper size is continuously printed, the surface layer of the pressure roller 23 is more likely to bend at a specific location than at other locations. Therefore, increasing the film thickness of the portion where the surface layer of the pressure roller 23 is likely to be bent is also a method for maintaining the image quality. Specifically, when the thinnest part of the release layer 23a is 70 μm, it is effective to change the thickness of the position where bending is likely to occur to about 1.5 to 2 times.

  However, if the film thickness of the pressure roller 23 is increased assuming a specific size of paper, it may not be possible to deal with a case where the thickness of the paper sheet to be passed is large. In such a case, as shown in FIG. 10, the film thickness is gradually increased toward the both ends in the longitudinal direction with respect to the film thickness in the central portion in the longitudinal direction. As a result, it is possible to avoid a decrease in image quality at the boundary of the film thickness change that may occur when the film thickness is locally increased. In particular, when the pressure roller 23 has a crown shape and the crown amount in the longitudinal direction has several steps of tilt angles, it is effective to increase the film thickness of the release layer according to the tilt angle. . This is because a portion with a larger inclination angle is more burdensome. The crown shape referred to here is a shape having a difference in diameter between positions close to the center and end of the roller as shown in FIG. This time, R = 1.22 and a crown amount of 1.22 mm were used.

(Fourth embodiment)
In the first to third embodiments for preventing wear of the surface layer of the pressure roller 23 described above, it is also effective to use a method of preventing the temperature of the pressure roller 23 from rising by the cooling mechanism 32 for cooling the pressure roller 23. It is. Specifically, as shown in FIG. 12, air 95 is applied to the pressure roller 23 from the opening 125 (125a, 125b, 125c) of the cooling mechanism 32 (32a, 32b, 32c), and the temperature of the pressure roller 23 is 90 degrees or more. The effect will appear if you do not go up. FIG. 13 is a front view of the pressure roller 23 and the cooling mechanism 32. In the drawing, the wind 95 is ejected only from 125a and 125c. However, the wind 95 may be ejected also from 125b, and the wind 95 may be ejected in the entire axial direction of the pressure roller 23. When air 95 is applied from the cooling mechanism 32, it is more effective to reduce the load on the release layer 23a by reducing the sheet passing speed or stopping the sheet passing. If the surface temperature of the pressure roller 23 has risen above a predetermined temperature, it is effective to increase the sheet interval during printing and to control to reduce productivity.

  Needless to say, only the fourth embodiment may be used alone. It is also possible to combine the above-mentioned embodiments 1 to 4. In that case, the pressure roller 23 surface information, the nip position information, and the temperature information of the pressure roller 23 detected by the pressure roller temperature detection means 34 are preferentially detected, and when each item exceeds a threshold value, they are used as a trigger. Control the amount of pressing.

  By using the above means, it is possible to reduce the burden on one side of the surface layer of the pressure roller 23, and it is possible to maintain the image quality.

  In the first, second, and fourth embodiments, the non-crown-shaped pressure roller 23 has been described. However, the crown-shaped pressure roller 23 illustrated in FIG. 11 is also applicable. In particular, in the case of the crown shape, the burden on the release layer 23a is greater than in the case of the non-crown shape. Therefore, the configuration in the present invention is particularly effective. Further, the softness of the pressure roller 23 and the fixing roller 22 is not limited to this embodiment. Needless to say, the present invention can also be applied to various fixing methods other than belt fixing, for example, belt fixing as shown in FIG.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Writing part 3 Original conveyance part 4 Original reading part 5 Contact glass 7 Paper feed part 8 Paper feed roller 9 Registration roller 11Y, 11M, 11C, 11BK Photosensitive drum 12 Charging part 13 Developing part 14 Transfer bias roller ( Primary transfer bias roller)
DESCRIPTION OF SYMBOLS 15 Cleaning part 16 Intermediate transfer belt cleaning part 17 Intermediate transfer belt 18 Secondary transfer bias roller 20 Fixing device 21 Heating roller 22 Fixing roller 23 Pressure roller 23a Release layer 24 Fixing belt 25 Heater 26 Entrance guide 27 Tension roller 28 Separating plate (Fixing roller side)
29 Separation claw (pressure roller 23 side)
30 Upper outlet guide 31 Lower outlet guide 32 Cooling mechanism 33 Detection means 34 Pressure roller temperature detection means 40 Pressure lever 41 Rotating axis 42a, 42b Cam 95 Wind 125 Opening P Paper (recording medium)
A Light emitting element B Light receiving element

JP-A-10-142959 JP 2002-40865 A

Claims (6)

A fixing member;
A pressure member that faces the fixing member and forms a nip, and
In a fixing device for fixing an unfixed image on a recording medium conveyed to a nip,
A pressing mechanism that presses both ends of the rotation shaft of the pressing member independently to the fixing member;
Detecting means for detecting a pressing amount, which is an amount by which the pressing member is pressed into the fixing member by the pressing mechanism;
A fixing device that controls the pressing mechanism based on a detection result of the detection means.   The fixing device according to claim 1, wherein the detection unit is disposed to face the nip and detects the pressing amount of the pressure member every predetermined sheet passing.   The fixing device according to claim 1, wherein the detection unit is disposed to face the nip non-sheet passing portion and detects a pressing amount of the pressure member during continuous sheet passing.   4. The fixing device according to claim 1, wherein the detection unit is a sensor that irradiates the nip with laser light and detects reflection of the laser light. 5.   The fixing device according to claim 1, wherein a plurality of the detection units are provided at an end portion in the axial direction of the pressure member.   An image forming apparatus comprising the fixing device according to claim 1.