JP5253208B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that heats a recording material carrying a toner image by being sandwiched and conveyed by a pair of rollers, and more particularly to control that suppresses the occurrence of wrinkling of a recording material during continuous image formation.

  In an image forming apparatus that transfers a toner image onto a recording material and heat-fixes the image forming apparatus, an image heating apparatus that rotates a pair of rollers by pressing them in a heated state is mounted. In addition to a fixing device that heats and presses the transferred toner image to fix it on the recording material, the image heating device heats and presses the recording material carrying the semi-fixed or fixed toner image to adjust the surface glossiness of the image. Includes heat finishing equipment.

  In the image heating apparatus, when the fixing roller and the pressure roller expand and the outer diameter changes, the conveyance speed of the recording material changes. The temperature of the pressure roller is easier to dissipate in the longitudinal direction of the pressure roller than the center, so the temperature at the center is higher than that at the end and the center expands more thermally. The outer diameter of the roller is a so-called crown shape that is larger at the center.

  When the recording material is transported in such a state, the recording material feed speed is faster in the central portion, so that the end portion of the recording material is pulled to the center of the recording material and the recording material may be wrinkled. The wrinkles of the recording material are more conspicuous as the recording material is thinner.

  Patent Document 1 discloses a fixing device that forms a fixing nip of a recording material carrying a toner image by pressing a pressure roller against a fixing belt in contact with an image surface of the recording material. Here, it has been shown that it is effective to cool the center of the pressure roller using a blower or a cooling roller in order to suppress the occurrence of wrinkling of the recording material. By cooling the center of the pressure roller and slightly shrinking the diameter from the end, the recording material passes through the fixing nip while being pulled outward, so the recording material is pulled to the center. This is because wrinkles are not formed.

Japanese Patent Laid-Open No. 11-54242

  In recent years, in order to increase the number of images formed per minute of the image forming apparatus, the image forming process speed has been increased, and accordingly, the recording material passing through the fixing device has been increased in speed, and the recording material passing through the fixing device has been increased. The number of sheets is increasing every minute.

  For this reason, even if it does not install the air blower and the cooling roller shown in Patent Document 1, the pressure roller is removed by the recording material that passes one after another, and the central region of the pressure roller is cooled. Recording material wrinkles are less likely to occur.

  However, it is found that the recording material up to about 10 sheets after the start of continuous image formation is fixed in a state where the central area of the pressure roller is not sufficiently cooled, so that the above-mentioned recording material wrinkles are generated. did.

  Therefore, it has been studied to manufacture a pressure roller having a narrow central portion from the beginning so that the central portion of the pressure roller has a smaller diameter than the end portion without cooling. However, in this case, as continuous image formation proceeds, the central portion of the pressure roller that is cooled by the recording material becomes too small in diameter than the end portion, and there is a force that pulls the recording material to the end portion in the fixing nip. It has been found that the image becomes too large and the image is disturbed.

The present invention provides an image forming apparatus in which a heat treatment with uniform tension conditions to the outside of a recording material is performed from the beginning to the end of continuous image formation, and the recording material is less likely to cause wrinkles and image disturbance at the edges. The purpose is that.

An image forming apparatus of the present invention includes a heating roller for heating an image on a recording material, a pressure roller for forming a nip portion that sandwiches and conveys the recording material between the heating roller, and a recording material. Conveying means for conveying toward the nip portion; contacting / separating means for contacting and separating the heating roller and the pressure roller; temperature adjusting means for adjusting a temperature distribution in the longitudinal direction of the pressure roller; and the conveying means And a conveyance control means for controlling the conveyance timing of the recording material . Then, with the heating roller and the pressure roller separated by the contact / separation means, the temperature adjustment means adjusts the temperature of the longitudinal end of the pressure roller to be equal to or higher than the temperature of the longitudinal center. When the image heating process is continuously performed on a plurality of recording materials having a start-up mode that is smaller than a predetermined basis weight, the temperature of the end portion in the longitudinal direction of the pressure roller passes through the start-up mode in the longitudinal direction. The conveyance control means controls the conveyance timing of the recording material so that the first recording material reaches the nip portion when the temperature becomes higher than the central portion, and the image heating process at the nip portion is started. It is configured as follows .

  According to the present invention, even immediately after the start of the continuous heat treatment, the difference in conveyance speed between the central portion and both end portions of the recording material in the nip portion is reduced. Therefore, from the beginning to the end of continuous image formation, heat treatment is performed with the same tensioning condition to the outside of the recording material, and the recording material is not easily wrinkled.

It is explanatory drawing of a structure of the image forming apparatus of this invention. FIG. 3 is an explanatory diagram of a configuration of a fixing device. It is explanatory drawing of the heater of a fixing roller and a pressure roller. It is a perspective view of a fixing device. It is explanatory drawing of starting mode. It is explanatory drawing of a thin paper mode and a standard mode. It is explanatory drawing of the thick paper 1 mode and the thick paper 2 mode. 2 is a block diagram of a control system of the image forming apparatus. FIG. It is a flowchart of control in start-up mode. It is a flowchart of control of a thin paper mode / standard mode. It is a flowchart of control of thick paper 1 mode / thick paper 2 mode. FIG. 6 is an explanatory diagram of a configuration of a fixing device according to a second embodiment. FIG. 10 is an explanatory diagram of a configuration of a fixing device according to a third exemplary embodiment. FIG. 10 is an explanatory diagram of a configuration of a fixing device according to a fourth exemplary embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As long as the cooling state of the rotating body is changed before and after the start of continuous image formation, the present invention can be applied to another embodiment in which part or all of the configuration of the embodiment is replaced with the alternative configuration. Can be implemented.

  The fixing device according to the embodiment can be used not only as a toner image fixing device but also as an image heating device for heating and pressurizing a recording material on which a toner image has been fixed once to finish it to a predetermined surface glossiness. The fixing device according to the embodiment can be mounted not only in the full-color image forming apparatus of FIG. 1 but also in a monochrome image forming apparatus, and can be implemented not only in the intermediate transfer method but also in the direct transfer method.

  Further, the rotating body that is in contact with the image surface to be heat-treated is not limited to the first rotating body but may be the second rotating body. At least one of the first rotating body and the second rotating body may be a belt member whose inner surface is supported by a supporting rotating body instead of a roller member.

  In addition, about the general matter regarding the image forming apparatus and the fixing device disclosed in Patent Document 1, illustration is omitted and redundant description is omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus of the present invention.

  As shown in FIG. 1, the image forming apparatus 100 is a full-color printer in which yellow, magenta, cyan, and black image forming units 200 </ b> Y, 200 </ b> M, 200 </ b> C, and 200 </ b> K are arranged along an intermediate transfer belt 125.

  The image forming unit 200 </ b> Y forms a yellow toner image on the photosensitive drum 120 </ b> Y and performs primary transfer onto the intermediate transfer belt 125. The image forming unit 200M forms a magenta toner image on the photosensitive drum 120M and superimposes the yellow toner image on the intermediate transfer belt 125 for primary transfer. The image forming units 200C and 200K form a cyan toner image and a black toner image, respectively, and primarily transfer them to the intermediate transfer belt 125.

  The full color toner image formed by superimposing the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image is conveyed to the secondary transfer unit 126 along with the rotation of the intermediate transfer belt 125 and is secondary to the recording material P. Transcribed.

  The recording materials stored in the recording material cassette 110 are separated one by one by the separation roller 111 and fed to the registration rollers 112. The registration roller 112 waits for the recording material P and sends the recording material P to the secondary transfer unit 124 in synchronization with the full-color toner image on the intermediate transfer belt 125.

  The recording material on which the full-color toner image is secondarily transferred by the secondary transfer unit 126 is nipped and conveyed by the fixing nip portion N by the fixing device 1 to fix the full-color toner image on the surface.

  In the single-sided printing mode, the recording material on which the full-color toner image is fixed proceeds to the paper discharge path 130 and is discharged onto the discharge tray 150 by the discharge roller 131 and stacked.

  In the double-sided printing mode, the recording material having the full-color toner image fixed on one side proceeds to the reverse path 140 and is switched back to be sent to the double-sided conveyance path 141 and waits at the registration roller 112. Thereafter, the recording material P is sent to the secondary transfer unit 126 by the registration roller 112, the full color toner image is secondarily transferred to the back surface, and the full color toner image is fixed by the fixing device 1.

  The image forming units 200Y, 200M, 200C, and 200K are configured in substantially the same manner except that the colors of toner used in the attached developing devices 123Y, 123M, 123C, and 123K are different. In the following, the image forming unit 200Y will be described, and the other image forming units 200M, 200C, and 200K will be described by replacing Y at the end of the reference code with M, C, and K.

  A charging device 121Y, an exposure device 122Y, a developing device 123Y, a primary transfer device 124Y, and a cleaning device are disposed around the photosensitive drum 120Y.

  The charging device 121Y contacts a charging roller to which an oscillating voltage obtained by superimposing an AC voltage on a DC voltage is applied to charge the surface of the photosensitive drum 120Y to a uniform negative potential.

  The exposure device 122Y scans a laser beam that is ON-OFF modulated in accordance with an image signal obtained by developing the image data, and writes an electrostatic image of the image on the surface of the photosensitive drum 120Y.

  The developing device 123Y stirs the two-component developer to charge the non-magnetic toner to the negative polarity and the magnetic carrier to the positive polarity, and supports the developer sleeve in a thin layer state and supplies it to the electrostatic image on the photosensitive drum 120Y. To do. By applying an oscillating voltage in which an AC voltage is superimposed on a DC voltage to the developing sleeve, the toner is transferred to the exposed portion of the photosensitive drum 120Y having a relatively positive polarity, and the electrostatic image is reversed and developed.

  The primary transfer device 124Y presses the inner surface of the intermediate transfer belt 125 with a primary transfer roller to form a primary transfer portion between the photosensitive drum 120Y and the intermediate transfer belt 125. By applying a positive DC voltage to the primary transfer roller, the toner image carried on the photosensitive drum 120Y passing through the primary transfer portion is primarily transferred to the intermediate transfer belt 125.

  The cleaning device rubs the photosensitive drum with a cleaning blade to remove residual toner remaining on the surface of the photosensitive drum 120Y that has passed through the primary transfer portion.

Example 1
<Image heating device>
FIG. 2 is an explanatory diagram of the configuration of the fixing device, FIG. 3 is an explanatory diagram of a heater for the fixing roller and the pressure roller, and FIG. 4 is a perspective view of the fixing device.

  As shown in FIG. 2, the fixing device 1 sandwiches and conveys the recording material P onto which the full-color toner image T has been secondarily transferred by the fixing nip portion N, and heats and melts the full-color toner image T on the recording material. To fix the surface of the recording material P.

  A conveyance roller pair 52 is disposed downstream of the fixing nip portion N in the conveyance direction of the recording material P. The conveyance roller pair 52 guides the recording material P after fixing by the sheet conveyance upper guide 50 and the sheet conveyance lower guide 51 to the discharge tray (150: FIG. 1) or the duplex conveyance path (141: FIG. 1). Transport.

A fixing nip portion N is formed between a fixing roller 2 as an example of a heating roller and a pressure roller 3 as an example of a pressure roller, and the recording material is nipped and conveyed.

  The fixing roller 2 covers the outer surface of a metal pipe 2a such as aluminum or iron with an elastic layer 2b having elasticity such as silicon rubber or fluorine rubber. The outer surface of the elastic layer 2b is further covered with a release layer 2c such as PFA or PTFE.

  The fixing roller 2 is equipped with a fixing center portion heater 6 and a fixing end portion heater 7 as heat sources so that the fixing roller 2 is heated by heat generated from the inside.

  As shown in FIG. 3A, the fixing center heater 6 and the fixing end heater 7 are formed such that the heater linear density in the longitudinal direction is shifted toward the center and the end, respectively.

  As shown in FIG. 3B, the fixing central portion heater 6 is a halogen lamp heater having a total wattage of 600 W with a light distribution (heat generation amount) characteristic of 100% at the center and 30% at the end.

  As shown in FIG. 3C, the fixing end heater 7 is a halogen lamp heater with a total wattage of 700 W, with a light distribution (heat generation amount) characteristic of 30% at the center and 100% at the end.

The temperature adjustment circuit 61 controls the fixing center portion heater 6 and the fixing end portion heater 7 in accordance with the outputs of the fixing center portion temperature sensor 17 and the fixing end portion temperature sensor 18 to bring the fixing roller 2 to an appropriate temperature. Control the temperature to maintain. As shown in FIG. 4, the fixing central portion temperature sensor 17 is a non-contact type that detects the surface temperature of the central portion in the longitudinal direction of the fixing roller 2 in a non-contact manner. Fixing end temperature sensor 18 is a contact type for detecting the surface temperature by rubbing in the longitudinal direction end portion of the fixing roller 2 to rotation.

  The pressure roller 3 covers the outer surface of a metal pipe 3a such as aluminum or iron with an elastic layer 3b having elasticity such as silicon rubber or fluorine rubber. The outer surface of the elastic layer 3b is further covered with a release layer 3c such as PFA or PTFE of a fluororesin material.

  The pressure roller 3 is equipped with a pressure center heater 9 and a pressure end heater 10 as heat sources so that the pressure roller 3 is heated by heat generated from the inside.

  As shown in FIG. 3 (a), the pressurization center heater 9 and the pressurization end heater 10 which are examples of the heating device have heater linear densities in the longitudinal direction at the center and the end, respectively. It is formed by offsetting.

  As shown in FIG. 3B, the pressure central portion heater 9, which is an example of a first heating element in which the calorific value at the central portion in the longitudinal direction of the roller is larger than the calorific value at the end portion, has a light distribution characteristic. Is a halogen lamp heater with a total wattage of 400 W, with 100% at the center and 30% at the ends.

  As shown in FIG. 3C, the pressure end portion heater 10 which is an example of the second heating element in which the heat generation amount at the end portion in the longitudinal direction of the roller is larger than the heat generation amount at the center portion has a light distribution characteristic. Is a halogen lamp heater with a total wattage of 400 W, with 30% at the center and 100% at the ends.

  The temperature adjustment circuit 61 controls the pressure center heater 9 and the pressure end heater 10 according to the outputs of the pressure center temperature sensor 19 and the pressure end temperature sensor 20, and the pressure roller 3. The temperature is controlled so as to maintain a proper temperature.

As shown in FIG. 4, the pressure center portion temperature sensor 19 is an example of a temperature detecting means for detecting the temperature of the longitudinal center portion of the roller is a non-contact surface temperature of the central portion in the longitudinal direction of the pressure roller 3 Non-contact type that detects the

  A pressure end temperature sensor 20, which is an example of temperature detecting means for detecting the temperature of the end of the roller in the longitudinal direction, is a contact that rubs against the end of the rotating pressure roller 3 in the longitudinal direction and detects the surface temperature. Type.

  As shown in FIG. 4, the fixing roller 2 is rotatably supported at both ends by a bearing 5 fixed to the upper unit 4 of the fixing device 1. The fixing roller 2 is rotationally driven by a drive motor (not shown).

As shown in FIG. 2, the pressure roller 3 is pivotally supported at both ends by a bearing 11 fixed to the pressure mechanism 8 a of the fixing device 1. The pressure mechanism 8 a supports the pressure roller 3 so as to be able to contact and separate from the fixing roller 2 and can change the pressure contact force of the pressure roller 3 to the fixing roller 2 in a plurality of stages.

  The pressure roller 3 is connected to the drive gear train of the fixing roller 2 via a one-way clutch (not shown). When the pressure roller 3 is in pressure contact with the fixing roller 2 by the pressure mechanism 8a, the one-way clutch is idled to fix the fixing roller. 2 Followed rotation. On the other hand, in the state separated from the fixing roller 2 by the pressurizing mechanism 8a, it is driven to rotate at a peripheral speed slower than that of the fixing roller 2 through the one-way clutch.

<Contact / separation mechanism>
FIG. 5 is an explanatory diagram of the start-up mode, FIG. 6 is an explanatory diagram of the thin paper mode and the standard mode, and FIG. 7 is an explanatory diagram of the thick paper 1 mode and the thick paper 2 mode.

  As shown in FIG. 5, the control unit (60: FIG. 2) has the pressure roller 3 lower than the fixing roller 2 in a state where the pressure roller 3 is separated from the fixing roller 2 before the continuous heating process. Allow the temperature to adjust. Then, immediately before the recording material P is fed, the pressure roller 3 is brought into pressure contact with the fixing roller 2 to form a fixing nip portion N. Accordingly, a sufficiently high temperature can be applied to the image surface of the recording material P through the fixing roller 2 while avoiding excessive heating of the entire thickness of the recording material P. Further, by keeping the surface temperature of the pressure roller 3 in contact with the back surface of the recording material P lower than that of the fixing roller 2, the fixed image on the back surface is not melted when the double-sided image is formed.

  As shown in FIG. 2, a pressure mechanism 8 a that is an example of a contact / separation mechanism moves the pressure roller 3 from the fixing roller 2. The lower unit 8 of the fixing device 1 is provided with a pressure mechanism 8a composed of the following members in order to raise and lower the pressure roller 3 and switch the pressure.

  The pressurizing mechanism 8 a has a press spring 13 interposed between a pressurizing arm 12 and a pressurizing lever 14 that are rotatably supported by a support shaft 16. The pressure lever 14 moves the pressure roller 3 up and down and switches the applied pressure by moving the rotation end up and down according to the rotation angle of the pressing cam 15.

  The pressure arm 12 is fixed to a bearing 11 that rotatably supports the shaft end of the pressure roller 3, and the pressing spring 13 has an upper end locked to the pressure arm 12 and a lower end locked to the pressure lever 14. Has been. The pressure spring 13 urges the pressure arm 12 in a direction in which the pressure roller 3 is pressed against the fixing roller 2 and presses the pressure roller 3, and the pressure roller 3 is pressed upward by the urging force of the pressure spring 13. Press contact with the fixing roller 2.

  The pressure lever 14 is pivotally supported by the lower unit 8 so as to be rotatable around the support shaft 16, and presses the pressure roller 3 against the fixing roller 1 in a state where the pressure spring 13 is compressed.

  The pressing cam 15 is provided in contact with the lower portion of the pressure lever 14. When the control unit 60 operates the drive motor 15a, the pressure lever 14 is rotated by the pressing force generated by the cam rotation of the pressing cam 15, and the lower end of the pressing spring 13 is moved up and down in a plurality of stages.

  That is, when the pressing cam 15 rotates counterclockwise, the pressure lever 14 rotates clockwise about the support shaft 16 and the pressing spring 13 is compressed. By applying a compressive force of the compressed pressure spring 13 to the pressure arm 12, an urging force that presses the pressure roller 3 against the fixing roller 2 is generated, and the fixing is performed between the fixing roller 2 and the pressure roller 3. A nip portion N is formed.

  As shown in FIG. 6, in the thin paper mode and the standard mode, a low fixing pressure is generated by setting the rotation angle of the pressing cam 15 in the counterclockwise direction to 45 degrees.

  As shown in FIG. 7, in the thick paper 1 mode and the thick paper 2 mode, a high fixing pressure is generated by setting the counterclockwise rotation angle of the pressing cam 15 to 80 degrees.

  As shown in FIG. 5, when the continuous image forming job is completed, the pressing cam 15 rotates clockwise and the pressure lever 14 rotates counterclockwise, and the urging force of the pressing spring 13 is eliminated. Thus, the pressure roller 3 is separated from the fixing roller 2.

<Cooling means>
As shown in FIG. 4, the lower unit 8 of the fixing device 1 is provided with a cooling fan unit 30 as an example of cooling means for cooling the central portion of the recording material contact area of the pressure roller 3. However, the cooling means is not limited to the fan. For example, the central portion of the fixing roller 2 can be cooled by bringing a pipe-shaped cooling roller into contact with the central portion of the fixing roller 2.

  The cooling fan unit 30 takes in air outside the main body of the image forming apparatus (100: FIG. 1) through a fan duct 35 provided below the cooling fan unit 30.

  The central cooling fans 31 and 32 can cool the central part of the recording material contact area of the pressure roller 3 by blowing the air taken in through the fan duct 35 to the central part in the longitudinal direction of the pressure roller 3. The end cooling fans 33 and 34 can cool the end portion of the pressure roller 3 that has been overheated by sending air to the end portion in the longitudinal direction of the pressure roller 3.

The central cooling fans 31 and 32 used had a diameter of 60 mm, 4.8 W, and an air volume of 0.5 m ³ / min.

  In the fixing device 1 as shown in FIG. 2, when the fixing roller 2 and the pressure roller 3 expand after the start of the heating operation and the outer diameter changes, the conveyance speed of the recording material P changes.

  As for the temperature of the pressure roller 3, the end portion in the longitudinal direction of the pressure roller 3 is more likely to dissipate heat than the center portion, so that the temperature at the center portion becomes higher than the end portion after the heating operation is started. For this reason, the central part tends to thermally expand from the end part, and the outer diameter of the pressure roller 3 has a crown shape that is larger in the central part.

  When the recording material is conveyed in such a state, since the conveyance speed is higher in the central portion, the end portion of the recording material approaches the center, and the recording material is likely to be wrinkled at the rear end thereof. The wrinkle of the recording material is more conspicuous as the recording material has a lower rigidity.

  Since the fixing device 1 is a heat roller system in which the heat capacity of the fixing roller 2 and the pressure roller 3 is large, even if the pressure roller 3 is cooled by the cooling fans 31 and 32, the end portion of the pressure roller 3 is immediately Temperature does not rise above the temperature in the center. For this reason, if the cooling fans 31 and 32 are operated simultaneously with the start of continuous image formation, the recording material wrinkles may occur on the first to tenth sheets. In particular, immediately after the fixing device 1 is started up, the temperature difference between the central portion and the end portion of the pressure roller 3 is large, so that the recording material is likely to be wrinkled.

  Therefore, in the fixing device 1, after the heating operation of the roller (3) is started, the temperature of the end portion in the longitudinal direction of the roller (3) is equal to the temperature of the central portion or higher than a predetermined temperature. The conveyance timing of the conveyance means (112) is controlled so that the recording material is conveyed to N). By optimizing the temperature difference between the central portion and the end portion of the pressure roller 3 with the pressure roller 3 separated from the fixing roller 2, printing is started and the first heat treatment is performed. Prevents wrinkles, fixing defects, image misalignment, and the like.

  Specifically: In a state where the pressure roller 3 is separated from the fixing roller 2, the temperature difference between the central portion and the end portion of the pressure roller 3 is reduced, or the temperature of the end portion is set higher than the temperature of the central portion, and the pressure roller 3 is straightened. Alternatively, after forming the reverse crown shape, the first heat treatment of the continuous heat treatment is performed. As a result, the pressure roller 3 is corrected to have the same temperature distribution and diameter distribution in the longitudinal direction as in the continuous heat treatment, and passes through the fixing nip portion N formed by pressing the pressure roller 3 against the fixing roller 2. The occurrence of wrinkling of the recording material P is prevented.

  In addition, the central cooling fans 31 and 32 that cool the central portion of the pressure roller 3 reduce the temperature of the central portion of the pressure roller 3 and at the same time heat the end portion of the pressure roller 3. The temperature of the end of the pressure roller 3 is raised by the heater 10. In this way, by optimizing the temperature difference between the central portion and the end portion of the pressure roller 3 and starting printing, the time until the temperature difference is optimized is shortened and the waiting time until the printing starts is reduced. Can be shortened.

  Further, the central cooling fans 31 and 32 that cool the central portion of the pressure roller 3 are stopped after the start of printing, thereby preventing the temperature of the fixing roller 2 and the pressure roller 3 from decreasing immediately after the start of continuous image formation. Prevents fixing failure.

  Further, while the temperature difference between the central portion and the end portion of the pressure roller 3 is optimized, the pressure roller 3 is separated from the fixing roller 2, so that the fixing roller 2 changes the temperature of the pressure roller 3. It is difficult to receive and the temperature of the end of the fixing roller 2 does not become too high. Therefore, it is possible to prevent image misalignment at the end of the recording material in the fixing nip N after the start of continuous image formation.

  In addition, depending on the printing medium, there is provided a mode for waiting for the printing to start until the temperature difference between the center and end of the pressure roller 3 reaches the set temperature, and a mode for starting printing before the temperature difference reaches the set temperature. ing. Thereby, in the case of thick paper or the like in which the recording material has a large rigidity and the recording material is less likely to wrinkle, the waiting time until the start of printing can be shortened.

  Further, by increasing the target temperature of the pressure roller 3 for a predetermined time after completion of the warm-up of the fixing device 1 after the predetermined time has elapsed, the end of the pressure roller 3 is not easily affected by the temperature change. It will be in the state.

  Note that changing the temperature distribution of the fixing roller 2 that is in direct contact with the toner image to be fixed may affect the image quality (glossiness) of the fixed image. For this reason, in the fixing device 1, the temperature distribution in the axial direction of the pressure roller 3 that is in contact with the opposite side surface of the toner image to be fixed and does not affect the fixed image is changed to optimize the recording material wrinkles. ing. However, even if the cooling fan unit is disposed so as to cool the central portion of the fixing roller 2, or the cooling fan unit is disposed so as to cool both central portions of the fixing roller 2 and the pressure roller 3, It is effective at least for suppressing wrinkles of the recording material.

<Control unit>
FIG. 8 is a block diagram of a control system of the image forming apparatus. In FIG. 8, blocks not directly related to the present invention are omitted.

  As shown in FIG. 8, the control unit 60 includes an arithmetic processing unit including a CPU, a memory and the like, and a circuit for exchanging data with the outside such as an I / O port and a communication interface. The control unit 60 controls the operation of the image forming apparatus (100: FIG. 1) by sequentially executing a plurality of programs stored in the memory according to the situation.

  When the user inputs information about the recording material from the operation unit 62 or the like, the control unit 60 sets the operating conditions of the fixing device 1 according to the type and basis weight of the recording material on which an image is formed. Waiting for the rise of the fixing device 1, the writing start timing of the exposure devices 122Y to 122K shown in FIG. Thereby, conveyance control of the recording material is performed.

  As shown in FIG. 2, the controller 60 performs temperature control of the fixing roller 2, temperature control of the pressure roller 3, pressure control of the pressure mechanism 8 a, air supply control of the cooling fan unit 30, and print standby control. .

  The temperature control of the fixing roller 2 is performed so that the temperature detected by the fixing center temperature sensor 17 becomes a temperature set according to the type and basis weight of the recording material and the fixing end heater 6 and the fixing end. The heater 7 is OFF / ON controlled.

  The temperature control of the pressure roller 3 is performed with the pressure center heater 9 so that the temperature detected by the pressure center temperature sensor 19 becomes a temperature set according to the type and basis weight of the recording material. OFF / ON control of the pressure end heater 10 is performed.

  In the pressure control of the pressurizing mechanism 8a, the pressure cam 15 is rotated to a rotation angle set according to the type and basis weight of the recording material, and the length of the fixing nip portion N in the recording material conveyance direction is set to the recording material. Optimized according to the type and basis weight.

  In the air blowing control of the cooling fan unit 30, the central portion is set so that the temperature difference between the detected temperatures of the pressurizing central portion temperature sensor 19 and the pressurizing end portion temperature sensor 20 becomes a set value corresponding to the type and basis weight of the recording material. The cooling operation is controlled by controlling the cooling fans 31 and 32 OFF / ON.

  Further, during continuous image formation, in order to avoid the end portion of the fixing nip portion N not in contact with the recording material P from being overheated, the end of the fixing end portion temperature sensor 18 is set to a predetermined temperature. The part cooling fans 33 and 34 are OFF / ON controlled.

  The print standby control waits until the temperature difference between the detected temperatures of the pressurization center temperature sensor 19 and the pressurization end temperature sensor 20 reaches a set value corresponding to the type and basis weight of the recording material, and continuous image formation. To start. The central cooling fans 31 and 32 are operated to cool the central portion of the pressure roller 3, and continuous image formation proceeds with the temperature difference between the detected temperatures of the pressure central temperature sensor 19 and the pressure end temperature sensor 20. Continuous image formation is started after approaching the state.

  As shown in FIG. 1, the control unit 60, which is an example of a conveyance control unit, commands the start timing of image formation using the photosensitive drums 120 </ b> Y, 120 </ b> M, 120 </ b> C, and 120 </ b> K. Thereby, the conveyance timing of the recording material P by the registration roller 112 which is an example of the conveyance unit, that is, the start timing of the continuous heating process by the fixing device 1 is controlled.

  As shown in FIG. 5, the start-up mode controls the start-up operation of the fixing device 1 from the power-on of the image forming apparatus 100 to the REDY state (a state in which the print mode can be shifted to each print mode immediately). .

  In the print standby control, the temperature difference that permits the start of printing is set according to the type and basis weight of the recording material. In the thin paper mode and the standard mode in which wrinkling of the recording material is likely to occur, “detection temperature by the pressure center temperature sensor 19 ≦ temperature detected by the pressure end temperature sensor 20” is set. Set to unrelated to.

  After starting up the fixing device 1 by executing the start-up mode, the control unit 60, as shown in Table 1, according to the type and basis weight of the recording material, the thin paper mode, the standard mode, the thick paper 1 mode, or Set the thick paper 2 mode.

Thin paper mode is applied controlled basis weight 40~79g / ^{m 2} plain paper and a basis weight of 60 to 90 g / ^{m 2} of coated paper. Further, the standard mode is applied controlled basis weight 80~105g / ^{m 2} plain paper and a basis weight 91~120g / ^{m 2} of coated paper.

  As shown in FIG. 6, in the thin paper mode and the standard mode, the compression amount of the pressure spring 13 is small, the force with which the pressure roller 3 is pressed against the fixing roller 2 is small, and the length of the fixing nip portion N is 10 mm. Set to

  In the thin paper mode, the temperature setting of the fixing roller 2 is set to 200 ° C., and the temperature setting of the fixing roller 2 is set to 210 ° C. in the standard mode in which heat is removed from the fixing nip portion N than in the thin paper mode.

Heavyweight mode is applied controlled basis weight 106~180g / ^{m 2} plain paper and a basis weight 121~150g / ^{m 2} of coated paper. Thick paper 2 mode is applied controlled basis weight 181~300g / ^{m 2} plain paper and a basis weight 151~250g / ^{m 2} of coated paper.

  As shown in FIG. 7, in the thick paper 1 mode and the thick paper 2 mode, the compression amount of the pressure spring 13 is large, and the force with which the pressure roller 3 is pressed against the fixing roller 2 is large, and the length of the fixing nip portion N is increased. Is set to 15 mm.

  In the thick paper 1 mode, the temperature setting of the fixing roller 2 is set to 210 ° C., and in the thick paper 2 mode that removes heat from the fixing nip N more than in the thick paper 1 mode, the temperature setting of the fixing roller 2 is set to 220 ° C.

<Start-up mode>
FIG. 9 is a flowchart of start-up mode control.

  As shown in FIG. 9 with reference to FIG. 5, when the power switch of the image forming apparatus (100: FIG. 1) is turned on, the fixing device 1 has the pressing cam 15 of the pressing mechanism 8a in the A state. The pressure roller 3 is separated from the fixing roller 2.

  The controller 60 turns on the fixing center heater 6 and the fixing end heater 7 to heat the fixing roller 2 (S201).

  When the temperature detected by the fixing center temperature sensor 17 of the fixing roller 2 reaches 180 ° C. (S202), the controller 60 rotates the pressing cam 15 counterclockwise and stops it in the state B shown in FIG. . As a result, the pressure roller 3 is in contact with the fixing roller 2 and is driven to rotate (S203), and is heated through the surface of the fixing roller 2.

  When the temperature detected by the fixing center temperature sensor 17 reaches 200 ° C. (S204), the controller 60 rotates the pressing cam 15 clockwise to move the pressure roller 3 from the fixing roller 2 as shown in FIG. Separate (S205).

  Since the end of the pressure roller 3 in the longitudinal direction is easier to dissipate heat than the center, the controller 60 turns on the pressure end heater 10 (S206), and the longitudinal end of the pressure roller 3 So that the temperature does not drop.

  Even if only the pressure end heater 10 is turned on, the controller 60 heats the metal pipe 3a and raises the temperature of the central portion of the pressure roller 3. The power is turned on (S207), and the central portion of the pressure roller 3 is cooled.

  When the temperature detected by the pressurization center temperature sensor 19 becomes equal to or lower than the temperature detected by the pressurization end temperature sensor 20 (S208), the control unit 60 stops the center cooling fans 31 and 32 (S209) and starts up. Exit mode.

  As shown in FIG. 5, the temperature of the fixing roller 2 is controlled to 210 ° C. in the longitudinal direction with the pressure roller 3 being separated from the fixing roller 2. The pressure roller 3 is temperature-controlled so that the longitudinal center temperature is 150 ° C. and the longitudinal center temperature ≦ longitudinal end temperature.

  Note that immediately after the fixing device 1 is started up, the end portion in the longitudinal direction of the pressure roller 3 tends to dissipate heat more than the center portion. For this reason, the pressure end portion heater 10 is OFF / ON controlled so that the temperature detected by the pressure end portion temperature sensor 20 of the pressure roller 3 becomes 180 ° C. for 10 minutes immediately after starting. Immediately after start-up, when 10 minutes have passed without the recording material being conveyed to the fixing nip portion N of the fixing device 1, the pressure is detected so that the temperature detected by the pressure end temperature sensor of the pressure roller 3 becomes 150 ° C. The end heater 10 is OFF / ON controlled.

  That is, after the heating of the pressure roller 3 is started and raised to a predetermined temperature setting, if a predetermined time elapses without the recording material being transported to the fixing device 1, the pressure is increased more than the predetermined time elapses. The pressure end heater 10 is controlled based on the output of the pressure end temperature sensor 20 so that the temperature at the roller end is lowered.

<Thin paper mode, standard mode>
FIG. 10 is a flowchart of control in the thin paper mode / standard mode.

  As illustrated in FIG. 8, when continuous image formation using thin paper is input through the operation unit 62 or the print job (external) 63, the control unit 60 starts continuous image formation in the thin paper mode.

  As shown in FIG. 10 with reference to FIG. 6, the control unit 60 fixes the fixing central portion heater 6 so that the detected temperatures of the fixing central portion temperature sensor 17 and the fixing end portion temperature sensor 18 are both 200 ° C. And the fixing end heater 7 are OFF / ON controlled (S211).

  When the temperature detected by the pressurization center temperature sensor 19 is equal to or lower than the temperature detected by the pressurization end temperature sensor 20 (YES in S212), the controller 60 shifts to a print start state.

  The controller 60 starts image formation (S213), and rotates the pressing cam 15 to the state B before the recording material P on which the image is formed arrives, and presses the pressure roller 3 against the fixing roller 2. (S214).

  During continuous image formation, the recording material P successively passing through the fixing nip N removes heat from the central portion of the pressure roller 3, while the heat at the end of the pressure roller 3 where the recording material P does not come in contact. It becomes difficult to be taken away. For this reason, even if the center part cooling fans 31 and 32 are kept OFF, the detected temperature of the pressurization center part temperature sensor 19 can be kept lower than the detection temperature of the pressurization end part temperature sensor 20.

  On the contrary, when the temperature at the end of the pressure roller 3 rises too much and the temperature difference from the center increases, the recording material P is moved outward at the rear end of the recording material P that contacts the end of the pressure roller 3. A strong pushing force acts to easily cause image disturbance. For example, this is a case where a large amount of images are continuously formed by vertically feeding an A4 size recording material.

  For this reason, during continuous image formation, if the temperature detected by the fixing end temperature sensor 17 exceeds 230 ° C. (YES in S215), the control unit 60 turns on the end cooling fans 33 and 34 (S216). The end of the pressure roller 3 is cooled. Thereafter, when the end of the fixing roller 2 in contact with the end of the pressure roller 3 is cooled and the detection temperature of the fixing end sensor 17 falls below 220 ° C. (YES in S217), the control unit 60 causes the end cooling. The fans 33 and 34 are turned off (S218).

  When the continuous image formation of the image forming job is completed (YES in S219), the control unit 60 moves the pressure roller 3 away from the fixing roller 2 (S220) and becomes ready to receive the next job signal. .

  On the other hand, when the detected temperature of the pressurization center temperature sensor 19 is higher than the detected temperature of the pressurization end temperature sensor 20 (NO in S212), the control unit 60 proceeds to print standby control (S231 to S235).

  In the print standby control, the control unit 60 turns on the central cooling fans 31 and 32 (S232) after turning on the pressure end heater 10 (S231). Then, image formation is not started (NO in S212) until the detected temperature of the pressurizing center temperature sensor 19 becomes equal to or lower than the detected temperature of the pressurizing end temperature sensor 20 (YES in S212). If continuous image formation is started in a state where the diameter of the central portion of the pressure roller 3 is larger than that of the end portion, there is a high possibility that the recording material will be wrinkled between about 1 to 10 sheets after the start. is there.

  The pressure end heater 10 is ON / OFF controlled so that it is turned on when the temperature of the pressure end temperature sensor becomes 150 ° C. or lower and turned off when the temperature exceeds 150 ° C. However, for 10 minutes after the start-up in the start-up mode, the pressurization end heater 10 is turned on when the temperature is 180 ° C. or lower, and is turned on / off so that it is turned off when the temperature exceeds 180 ° C.

  When the temperature detected by the pressure center temperature sensor 19 is equal to or lower than the temperature detected by the pressure end temperature sensor 20 (YES in S233), the controller 60 turns off the pressure end heater 10 (S234). The central cooling fans 31 and 32 are also turned off (S235). Then, the process proceeds to the print start state (S213 to S219).

  On the other hand, when continuous image formation using standard paper is input, the control unit 60 starts standard mode continuous image formation.

  When the standard mode is selected, the fixing center heater 6 and the fixing end heater 7 are adjusted so that the detected temperatures of the fixing center temperature sensor 17 and the fixing end temperature sensor 18 during sheet passing become 210 ° C. Is OFF / ON controlled (S211).

  The subsequent steps (S212 to S235) are controlled in the same manner as in the thin paper mode.

  In the thin paper mode / standard mode, as described above, when “the temperature detected by the pressurization center temperature sensor 19 ≦ the temperature detected by the pressurization end temperature sensor 20”, the process shifts from print standby to print start.

  However, the temperature difference for shifting from print standby to print start can be changed through the operation unit 62 shown in FIG. When the recording material wrinkle prevention mode displayed on the operation unit 62 is selected, the temperature is changed to “the detected temperature by the pressurization center temperature sensor 19 + 5 ° C. ≦ the detected temperature by the pressurization end temperature sensor 20”.

  Further, as described above, the pressure end heater 10 is set so that the temperature detected by the pressure end temperature sensor 20 of the pressure roller 3 does not exceed 180 ° C. for 10 minutes immediately after the fixing device 1 is started up. OFF / ON control. Also at this time, continuous image formation is started after waiting for “the temperature detected by the pressurization center temperature sensor 19 + 5 ° C. ≦ the temperature detected by the pressurization end temperature sensor 20”. This is because immediately after the fixing device 1 is started up, the temperature difference between the central portion and the end portion of the pressure roller 3 is large, so that the recording material is likely to be wrinkled.

  As described above, by enabling the temperature difference between the central portion and the end portion of the pressure roller 3 to be variably set, the reverse crown shape of the pressure roller 3 can be varied in accordance with the print medium and the image. Since the pressure roller 3 can increase or decrease the rubbing force from the center to both ends of the recording material, the recording material wrinkles and images generated by the strength of the rubbing force against various printing media and images Image defects such as misalignment can be prevented.

<Thick paper 1 mode / Thick paper 2 mode>
FIG. 11 is a flowchart of control in the thick paper 1 mode / thick paper 2 mode.

  As shown in FIG. 8, when continuous image formation in the thick paper 1 mode is input through the operation unit 62 or the print job (external) 63, the control unit 60 selects the thick paper 1 mode or the thick paper 2 mode depending on the thickness of the recording material. Continuous image formation is started.

  As shown in FIG. 11 with reference to FIG. 7, the control unit 60 fixes the fixing center heater 6 so that the detected temperatures of the fixing center temperature sensor 17 and the fixing end temperature sensor 18 are both 210 ° C. And the fixing end heater 7 are OFF / ON controlled (S211).

  Since the recording material P in the cardboard 1 mode has a large rigidity and no wrinkle is generated, the control unit 60 determines the temperature difference between the temperature of the pressure center temperature sensor 19 and the pressure end temperature sensor 20 of the pressure roller 3. Regardless, image formation is started immediately (S213).

  The controller 60 rotates the pressing cam 15 to the state C before the image-formed recording material P reaches the fixing nip N, and presses the pressure roller 3 against the fixing roller 2 (S214).

  As a result, the length of the fixing nip portion N2 in the conveyance direction of the recording material P is set to 15 mm, which is longer than 10 mm in the thin paper mode / standard mode, and is optimal for fixing the toner image T2 on the paper in the thick paper 1 mode. The amount of heat can be applied.

  The control unit 60 controls the following (S215 to S220) similarly to the thin paper mode.

  On the other hand, when the continuous image formation in the thick paper 2 mode is input, the control unit 60 starts the continuous image formation in the thick paper 2 mode.

  When the thick paper 2 mode is selected, the fixing center heater 6 and the fixing end heater are adjusted so that the detected temperatures of the fixing center temperature sensor 17 and the fixing end temperature sensor 18 are 220 ° C. 7 is OFF / ON controlled (S211). A temperature higher than that of the thick paper 1 mode is set in the fixing nip portion N having a length equal to that of the thick paper 1 mode, and an optimal amount of heat is applied to fix the toner image T2 on the recording material P in the thick paper 2 mode.

  The following (S213 to S220) are controlled in the same manner as in the thick paper 1 mode.

  In the first embodiment, the cooling fan unit 30, which is an example of a cooling unit, can cool the central portion of the recording material contact area of the pressure roller 3. The control unit 60, which is an example of a control unit, cools before the continuous heat treatment so that the temperature relationship between the central portion and both ends of the recording material contact area of the pressure roller 3 approaches the temperature relationship during the continuous heat treatment. The fan unit 30 is controlled. As a result, even immediately after the start of continuous image formation, a temperature distribution close to the state in which continuous image formation has progressed is formed on the pressure roller 3, so recording is performed on the 1st to 10th recording materials where recording material wrinkles are likely to occur. Wrinkles are less likely to occur.

(Example 2)
FIG. 12 is an explanatory diagram of a configuration of the fixing device 100 according to the second embodiment. A fixing nip portion N is formed between a fixing belt unit 101 including a fixing roller 102 which is an example of a pair of rollers and a pressure roller 3 which is an example of a pair of rollers, and the recording material is nipped and conveyed.

  In the fixing belt unit 101, a fixing belt 105 is stretched around a fixing roller 102, an entrance roller 103 and a steering roller 104, and a fixing pad 106 is provided between the fixing roller 102 and the entrance roller 103.

  The fixing roller 102 covers the outer surface of a metal pipe such as aluminum or iron with an elastic layer having elasticity such as silicon rubber or fluorine rubber. The fixing roller 102 is equipped with a fixing center portion heater 6 and a fixing end portion heater 7 as heat sources in the same manner as in the first embodiment so that the fixing roller 102 is heated by heat generated from the inside.

  Similarly to the first embodiment, the temperature adjusting circuit 61 controls the fixing center portion heater 6 and the fixing end portion heater 7 according to the outputs of the fixing center portion temperature sensor 117 and the fixing end portion temperature sensor 118, The temperature is controlled so that the fixing roller 102 is maintained at an appropriate temperature.

  The fixing center temperature sensor 117 is a contact type that detects the surface temperature by rubbing against the central portion in the longitudinal direction of the rotating fixing roller 102. The fixing end portion temperature sensor 118 is a contact type that detects the surface temperature by rubbing against the longitudinal end portion of the rotating fixing roller 102.

  The fixing belt 105 is made of polyimide having a thickness of 75 μm, and an elastic layer such as silicon rubber or fluororubber is provided on the outer periphery of the base layer with a thickness of 300 μm. It is provided with thickness.

  The entrance roller 103 is made of a metal such as SUS and is driven to rotate by the fixing belt 105.

  The steering roller 104 is made of a metal such as SUS, and one end thereof is movable in the direction of arrow D, and the shift of the fixing belt 105 is corrected by moving the one end.

  The fixing pad 106 is a fixing member that presses the fixing belt 105 toward the pressure roller 3 and is made of heat-resistant silicon rubber as an elastic body having a thickness of 3 mm and a width of 12 mm.

  A cover in which a glass fiber cloth is coated with a fluororesin is provided on the surface of the fixing pad 106 in order to reduce the frictional force between the fixing pad 106 and the inner surface of the fixing belt 105 that slides.

  Other configurations are substantially the same as those in the first embodiment.

(Example 3)
FIG. 13 is an explanatory diagram of the configuration of the fixing device 200 of the third embodiment. A fixing nip portion N is formed between the fixing roller 2 which is an example of a pair of rollers and a pressure belt unit 201 including a pressure roller 203 which is an example of a pair of rollers, and the recording material is nipped and conveyed.

  In the pressure belt unit 201, a pressure belt 206 is stretched around a pressure roller 203, an entrance roller 204, and a steering roller 205, and a pressure pad 207 is provided between the pressure roller 203 and the entrance roller 204.

  The pressure roller 203 is made of a metal pipe such as aluminum or iron, and in the same manner as in the first embodiment, the pressure roller 203 is heated as a heat source so as to heat the pressure roller 203 by heat generated from the inside. A pressurizing end heater 10 is attached.

  The pressure belt 206 is made of polyimide having a thickness of 75 μm, and an elastic layer such as silicon rubber or fluororubber is provided on the outer periphery of the base layer with a thickness of 300 μm. The thickness is provided.

  The entrance roller 204 is made of a metal such as SUS and is driven to rotate by a pressure belt 206.

  The steering roller 205 is made of metal such as SUS, and one end thereof is movable in the direction of arrow E, and the shift of the pressure belt 206 is corrected by moving the one end.

  The pressure pad 207 is a fixing member that presses the pressure belt 206 toward the fixing roller 2 and is made of heat-resistant silicon rubber as an elastic body having a thickness of 3 mm and a width of 12 mm.

  The surface of the pressure pad 207 is provided with a cover in which a glass fiber cloth is coated with a fluororesin in order to reduce the frictional force between the pressure pad 207 and the inner surface of the pressure belt 206 that slides.

  As shown in FIG. 13, the pressure center temperature sensor 219, which is an example of the temperature detection means for detecting the temperature of the center portion in the longitudinal direction of the roller, does not contact the surface temperature of the center portion in the longitudinal direction of the pressure belt 203. Non-contact type that detects the

  A pressure end temperature sensor 220, which is an example of temperature detecting means for detecting the temperature of the end of the roller in the longitudinal direction, is a contact that rubs against the end of the rotating pressure belt 206 in the longitudinal direction and detects the surface temperature. Type.

  Similarly to the first embodiment, the temperature adjustment circuit 61 causes the pressure center heater 9 and the pressure end heater 10 to change according to the outputs of the pressure center temperature sensor 219 and the pressure end temperature sensor 220. The temperature is controlled so that the pressure roller 203 is maintained at an appropriate temperature.

  Other configurations are substantially the same as those in the first embodiment.

Example 4
FIG. 14 is an explanatory diagram of a configuration of the fixing device 300 according to the fourth embodiment. A fixing nip portion N is formed between a fixing belt unit 301 having a fixing roller 302 as an example of a pair of rollers and a pressure belt unit 304 having a pressure roller 303 as an example of a pair of rollers. The recording material is nipped and conveyed.

  In the fixing belt unit 301, the fixing belt 105 is stretched around the fixing roller 102, the entrance roller 103, and the steering roller 104 as in the second embodiment, and the fixing pad 106 is provided between the fixing roller 102 and the entrance roller 103. .

  Further, as in the second embodiment, a fixing center temperature sensor 117 and a fixing end temperature sensor 118 are provided. Then, the fixing center portion heater 6 and the fixing end portion heater 7 are controlled in accordance with the outputs of the fixing center portion temperature sensor 117 and the fixing end portion temperature sensor 118 so as to maintain the fixing roller 102 at an appropriate temperature. Control the temperature.

  In the pressure belt unit 304, the pressure belt 206 is stretched around the pressure roller 203, the entrance roller 204 and the steering roller 205 as in the third embodiment, and the pressure pad 207 is interposed between the pressure roller 203 and the entrance roller 204. Is provided.

  Further, similarly to the third embodiment, a pressurization center part temperature sensor 219 and a pressurization end part temperature sensor 220 are provided. Then, the pressurization center part heater 9 and the pressurization end part heater 10 are controlled according to the outputs of the pressurization center part temperature sensor 219 and the pressurization end part temperature sensor 220 so that the pressurization roller 203 is controlled to an appropriate temperature. The temperature is controlled so as to be maintained.

  Other configurations are substantially the same as those in the first embodiment.

  An image forming apparatus that forms a toner image using toner, forms a nip portion with a pair of rollers, and heats an unfixed toner image, a semi-fixed toner image, or a fixed toner image.

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Fixing roller 3 Pressure roller 4 Upper unit 5 Bearing 6 Fixing center part heating heater 7 Fixing end part heating heater 8 Lower unit 9 Pressing center part heater 10 Pressure end part heater 11 Bearing 12 Pressing arm 13 Pressing spring 14 Pressing lever 15 Pressing cam 16 Support shaft 17 Fixing center temperature sensor 18 Fixing end temperature sensor 19 Pressing center temperature sensor 20 Pressing end temperature sensor 30 Cooling fan units 31 and 32 Center cooling fan 33, 34 End cooling fan 35 Fan duct 50 Transport upper guide 51 Transport lower guide 52 Transport roller pair 60 Control unit 100 Image forming apparatus

Claims (7)

A heating roller for heating the image on the recording material;
A pressure roller for forming a nip portion for nipping and conveying the recording material with the heating roller;
Conveying means for conveying the recording material toward the nip portion;
Contact / separation means for contacting and separating the heating roller and the pressure roller;
Temperature adjusting means for adjusting the temperature distribution in the longitudinal direction of the pressure roller;
An image forming apparatus comprising: a conveyance control unit that controls conveyance timing of the recording material by the conveyance unit;
In the state where the heating roller and the pressure roller are separated from each other by the contact / separation unit, the temperature adjustment unit adjusts the temperature of the end portion in the longitudinal direction of the pressure roller to be equal to or higher than the temperature of the central portion in the longitudinal direction. Up mode,
When continuously performing image heating processing on a plurality of recording materials having a basis weight smaller than a predetermined basis weight, the temperature at the longitudinal end portion of the pressure roller becomes higher than the central portion in the longitudinal direction through the start-up mode. The conveyance control means controls the conveyance timing of the recording material so that the first recording material reaches the nip portion at the time, and the image heating processing at the nip portion is started. Image forming apparatus.   When the image heating process is continuously performed on a plurality of recording materials smaller than a predetermined basis weight, the diameter of the longitudinal end portion of the pressure roller becomes larger than the central portion in the longitudinal direction through the start-up mode. 2. The image according to claim 1, wherein the conveyance control means controls the conveyance timing of the recording material so that the first recording material reaches the nip portion, and image heating processing at the nip portion is started. Forming equipment.   When continuously performing image heating processing on a plurality of recording materials larger than a predetermined basis weight, the temperature of the pressure roller is raised by the raising mode, and the longitudinal ends and the longitudinal direction of the pressure roller 3. The image forming apparatus according to claim 1, wherein an image heating process for the first recording material is started when the temperature of the heating roller reaches a predetermined temperature regardless of a temperature difference in the central portion. The temperature adjusting means heats a longitudinal end of the first heater that has a higher ability to heat the longitudinal central portion than the longitudinal end of the pressure roller and a longitudinal central portion of the pressure roller. A second heater that has a high ability to perform, and a fan that selectively cools the longitudinal central portion of the pressure roller,
In the start-up mode, the temperature adjusting means adjusts the temperature of the end portion in the longitudinal direction of the pressure roller to be equal to or higher than the temperature of the central portion in the longitudinal direction by the second heater and the fan. The image forming apparatus according to claim 1.   5. The image forming apparatus according to claim 1, further comprising an operation unit that allows an operator to specify a temperature difference between a longitudinal end portion and a longitudinal center portion of the pressure roller in the start-up mode. apparatus.   6. The image forming apparatus according to claim 1, further comprising a belt stretched by the heating roller and capable of contacting a recording material at the nip portion.   The image forming apparatus according to claim 1, further comprising a belt that is stretched by the pressure roller and that can contact the recording material at the nip.

Images