JP5762066B2 - Image heating apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image heating device such as a fixing device that heats a toner image formed on a recording material, and an image of a printer, a copier, a facsimile, or a composite machine including these image heating devices. The present invention relates to a forming apparatus.

An image heating device such as a fixing device having a heating rotator such as a fixing roller or a fixing belt and a nip forming member such as a pressure roller or a pressure belt is known. In this image heating apparatus, a nip forming member is pressed against a heating rotator to form a nip portion, and the toner image on the recording material is melted by passing the recording material on which the toner image is formed in the nip portion. Then, it is crushed and fixed as an image on the surface of the recording material.

  In the case of such an image heating apparatus, if the heating amount for the toner image on the recording material is too large, the toner is easily offset to the surface of the heating rotator. When the toner is offset to the heating rotator, a hot offset is generated in which the toner adheres to the recording material sent to the image heating apparatus and then becomes dirty. On the other hand, if the heating amount for the recording material is too large, paper wrinkles and a phenomenon such as so-called blistering called a paper blister are likely to occur with respect to the coated paper. On the other hand, if the heating amount for the toner image is too small, the toner image is not sufficiently melted and fixing failure tends to occur.

  Recently, an image forming apparatus capable of executing a series of image forming jobs while using different types of recording materials has been put into practical use. According to this type of image forming apparatus, for example, thick paper can be used for the front cover and the back cover, and thin paper can be used for the main body portion sandwiched between the covers. It is also possible to scan a plurality of document groups at once with a scanner, copy the first scanned document group with thin paper, and then scan the scanned document group with thick paper. Similarly to this, it is also possible to easily realize printing by changing the type of recording material for each of a plurality of image data supplied from a client device such as a personal computer.

  When continuous image formation is performed on different types of recording materials in this way, if the heating rotator is set to an appropriate heating amount for thick paper and the thin paper is sent to the nip, the amount of heating will be too high and hot offset will occur. And paper wrinkles may occur. Conversely, if thick paper is sent to the heating nip with the heating rotator set to an appropriate heating amount for thin paper, the heating amount may be too small and fixing failure may occur.

  In view of these points, a technique has been proposed in which the amount of heating by the image heating device is adjusted according to whether the recording material is thick paper or thin paper (see Patent Document 1). In addition, a technique has been proposed in which the paper thickness of the recording material is detected to switch the pressing force (see Patent Document 2).

JP 2001-154533 A JP-A-4-73785

  In the case of the configuration in which the heating amount is adjusted according to the type of the recording material as in the invention described in Patent Document 1, since the setting temperature of the heat source provided in the heating rotator is simply switched, until the setting temperature is reached. It takes time. For this reason, when switching the type of recording material, it is inevitable that the waiting time becomes long. When a series of image forming jobs are executed while using different types of recording materials, productivity is significantly reduced. End up.

Further, as in the invention described in Patent Document 2, in the case of a configuration in which the paper thickness of the recording material is detected and the applied pressure is changed, the heating rotating body or the nip forming member that is elastically deformed greatly according to the applied pressure. If it is not a structure having, sufficient effects cannot be obtained. This is because the amount of heating to the recording material is adjusted by changing the applied pressure to change the nip width formed by the heating rotator and the nip forming member . Therefore, in the case of the invention described in Patent Document 2, the heating rotating body or the nip forming member is limited to a configuration having an elastic layer that can be largely elastically deformed.

In view of such circumstances, the present invention is not limited to the configuration of the heating rotator or the nip forming member , and it is desirable to realize a structure that can reduce the decrease in productivity even if the heating conditions are changed according to the recording material. Invented.

The present invention switches between a first set temperature set for the first recording material and a second set temperature set for a second recording material different from the first recording material and different from the first set temperature. The first recording material or the second recording material is sandwiched between the heating rotator and the heating rotator that rotates and heats the toner image on the first recording material or the second recording material. A nip forming member for forming a nip portion, a third set temperature set for the second recording material, and a fourth set temperature that is set during standby and different from the third set temperature. and an auxiliary member to the heating rotating body contact assisting the switching of the temperature, and moving means for contacting and separating the auxiliary member against the heating rotator, each set temperature of the auxiliary member and the heating rotating body Switching and controlling the contacting / separating means And a control unit, wherein the control means, in succession after the first job for the heating to the first recording medium, when executing the second job for heating to the second recording medium In addition, before the start of the first job, the set temperature of the heating rotator is set to the first set temperature, the set temperature of the auxiliary member is set to the fourth set temperature, and the execution of the first job is performed. The auxiliary member is switched to the third set temperature while the auxiliary member is separated from the heating rotator, and the set temperature is set to the third set temperature after completion of the first job. The auxiliary heating member is brought into contact with the heating rotator and the set temperature of the heating rotator is switched to the second set temperature .

According to the present invention, even if the heating conditions are changed according to the recording material, the reduction in productivity can be reduced. Therefore, it is possible to provide an image heating apparatus that can maintain high productivity when a series of image forming jobs are executed while using different types of recording materials. Further, since it is not necessary to change the nip width between the heating rotator and the nip forming member in order to change the heating condition, the configuration of the heating rotator or the nip forming member is not limited.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram of a fixing device according to a first embodiment. The schematic block diagram which shows one example of an approach / separation means. 6 is a flowchart when printing is started with thin paper in the temperature control of the first embodiment. Similarly, a flowchart when printing is started with thick paper. FIG. 5 is a schematic configuration diagram of a fixing heater of a fixing roller according to a second embodiment of the present invention. FIG. 9 is a schematic configuration diagram of a fixing device according to a third embodiment of the present invention. 10 is a flowchart for starting printing with thin paper in the temperature control of the third embodiment. Similarly, a flowchart when printing is started with thick paper.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a fixing device that fixes an unfixed toner image on a recording material will be described. However, the present invention is configured to heat and press a recording material carrying a fixed image or a semi-fixed image to change the surface properties of the image. It can implement also as the heat processing apparatus to adjust.

[Image forming apparatus]
First, the image forming apparatus of this embodiment will be described with reference to FIG. The image forming apparatus 100 is a tandem type full-color laser printer in which yellow, magenta, cyan, and black image forming portions Y, C, M, and K are disposed along the intermediate transfer belt 6.

  The image forming portions Y, C, M, and K are arranged so as to transfer the toner images to the intermediate transfer belt 6 in order from the bottom to the top of the drawing, and each is a photosensitive drum 1 on which a toner image is formed using an electrophotographic process. It has. Around each photosensitive drum 1, a charging device 2, a developing device 3, a primary transfer roller 9, and a cleaning device 4 are arranged along the rotation direction of the photosensitive drum 1. The exposure device 5 is arranged so that the photosensitive drums 1 of the image forming units Y, C, M, and K are commonly exposed using a laser scanning exposure optical system.

  In the image forming units Y, C, M, and K, the exposure device 5 performs scanning exposure based on the image data on the photosensitive drum 1 uniformly charged by the charging device 2 and scans the surface of the photosensitive drum 1. An electrostatic image corresponding to the exposure image is formed.

  The developing device 3 develops the electrostatic image formed on the surface of the photosensitive drum 1 as a toner image. The developing device 3 of the image forming unit Y is yellow toner, the developing device 3 of the image forming unit C is cyan toner, the developing device 3 of the image forming unit M is magenta toner, and the developing device 3 of the image forming unit K is black. Each toner is filled. Therefore, a yellow toner image is formed on the photosensitive drum 1 of the image forming unit Y, a cyan toner image is formed on the photosensitive drum 1 of the image forming unit C, and a magenta toner image is formed on the photosensitive drum 1 of the image forming unit M. A black toner image is formed on each of the K photosensitive drums 1.

  The single color toner images of the respective colors developed on the respective photosensitive drums 1 of the image forming portions Y, C, M, and K are placed at predetermined positions on the intermediate transfer belt 6 that rotates at a constant speed in synchronization with the rotation of the photosensitive drum 1. The primary transfer is performed so that the images are sequentially superimposed in the aligned state. As a result, an unfixed full-color toner image is synthesized and formed on the intermediate transfer belt 6.

  In the present embodiment, an endless intermediate transfer belt 6 is used. The intermediate transfer belt 6 is stretched around a drive roller 7, a secondary transfer counter roller 14, and a tension roller 8, and is rotationally driven by the drive roller 7. Is done.

  The primary transfer rollers 9 of each of the image forming units Y, C, M, and K urge the intermediate transfer belt 6 toward the photosensitive drum 1 so that the toner image is transferred between the photosensitive drum 1 and the intermediate transfer belt 6. A primary transfer portion is formed.

  A bias power source (not shown) applies a primary transfer bias having a reverse polarity to the toner image to the primary transfer roller 9. As a result, the toner images of the respective colors are primarily transferred from the photosensitive drums 1 of the image forming units Y, C, M, and K to the intermediate transfer belt 6.

  After the toner image is primarily transferred from the photosensitive drum 1 to the intermediate transfer belt 6 in the image forming units Y, C, M, and K, the transfer residual toner remaining on the photosensitive drum 1 is removed by the cleaning device 4.

  By performing such steps in the yellow, cyan, magenta, and black image forming portions Y, C, M, and K in synchronism with the rotation of the intermediate transfer belt 6, toner images of each color are formed on the intermediate transfer belt 6. Sequentially superimposing and primary transfer. It should be noted that the above process is performed only for the target color image forming section (for example, the black image forming section K) during single-color image formation (single color mode).

  On the other hand, the recording material S set in the recording material cassette 10 is separated and fed by the feeding roller 11, and stops through the conveyance path 10 a with the leading end in contact with the registration roller 12. The recording material S is conveyed with a central reference. The registration roller 12 is activated at a predetermined control timing and feeds the recording material S to a secondary transfer portion that is a nip portion between the intermediate transfer belt 6 and the secondary transfer roller 13.

  The secondary transfer roller 13 is in contact with the intermediate transfer belt 6 supported from the inner side by the secondary transfer counter roller 14 connected to the ground potential to form a secondary transfer portion of the toner image on the recording material S. The toner image that has been primarily transferred and superimposed on the intermediate transfer belt 6 is subjected to batch secondary transfer onto the recording material S by a bias power source (not shown) applying a bias having a polarity opposite to that of the toner to the secondary transfer roller 13. Is done. The secondary transfer residual toner remaining on the intermediate transfer belt 6 that has passed through the secondary transfer portion is removed by the belt cleaning device 15.

  The recording material S on which the toner image has been secondarily transferred is separated in curvature from the intermediate transfer belt 6 and is introduced into a fixing device F, which is an image heating device, through a conveyance path 10b. The fixing device F melts and crushes the toner image and fixes the full-color image on the recording material in the process of nipping and conveying the recording material on which the toner image has been secondarily transferred while being heated and pressurized.

  The recording material S sent out from the fixing device F is discharged to the discharge tray 16 as a full-color print or a mono-color print through the conveyance path 10c.

[Fixing device]
The fixing device F of this embodiment will be described with reference to FIGS. The fixing device F includes a fixing roller 17 that is a heating rotator, a pressure roller 21 that is a nip forming member , an auxiliary roller 29 that is an auxiliary member , a cam mechanism 40 that is a contact / separation unit, and a control that is a control unit. Device 20.

  The fixing roller 17 is heated from the inner surface side and the surface side comes into contact with the recording material, and is rotatably supported by a fixed portion of the apparatus. The fixing roller 17 has a core metal 17a made of a metal such as aluminum or iron as a base layer, and a heat-resistant elastic layer 17b such as silicone rubber or fluororubber is coated on the surface thereof. Furthermore, the surface layer of the elastic layer 17b is covered with a release layer 17c composed of a heat-resistant fluorine tube. The fixing roller 17 is rotationally driven by a driving device (not shown) and the rotational speed is controlled.

A fixing heater 18 as a heating source is disposed in the fixing roller 17. The fixing heater 18 is a heat generating element such as a halogen heater disposed at the center of the fixing roller 17 and heats the inner surface of the cored bar 17 a of the fixing roller 17 by infrared rays. The fixing heater 18 can adjust the surface temperature of the fixing roller 17 to a plurality of set temperatures as will be described later. This temperature adjustment is performed based on detection of a contact type thermistor 19 which is a temperature detection means. The thermistor 19 contacts the surface (outer peripheral surface) of the fixing roller 17 and detects the surface temperature. The temperature detecting means for detecting the surface temperature of the fixing roller 17 may be, for example, an infrared detection type non-contact thermistor.

  The pressure roller 21 is rotatably supported by a fixed portion of the apparatus, and is arranged so that the rotation axis thereof is parallel to the rotation axis of the fixing roller 17. Further, both ends of the rotating shaft supported by the fixed portion are urged toward the rotating shaft of the fixing roller 17 by a spring member (not shown). As a result, the pressure roller 21 is pressed against the fixing roller 17 to form the fixing nip portion N. Similar to the fixing roller 17, the pressure roller 21 is formed by covering the surface layer of the core metal 21a with the elastic layer 21b and covering the outer side with the release layer 21c.

The pressure roller 21 may or may not have a heating source inside the cored bar 21a. However, in the present embodiment, the heating roller is not provided for simplification. Something is used. In this embodiment, a roller type is used as the heating rotator. However, a belt-type heating rotator may be adopted as long as it can form a fixing nip by pressing against the pressure roller 21. The same applies to the nip forming member .

  Such a fixing roller 17 has a metal core 17a and a relatively thick elastic layer 17b, and therefore has a large heat capacity, and the heat conductivity of the elastic layer 17b is low. For this reason, even if the amount of heat of the fixing heater 18 is increased in order to rapidly increase the fixing roller surface temperature, it is difficult to rapidly increase the fixing roller surface temperature. On the other hand, even if the amount of heat of the fixing heater 18 is reduced in order to rapidly reduce the fixing roller surface temperature, it is difficult to rapidly decrease the fixing roller surface temperature.

For this reason, in the present embodiment, when it is desired to rapidly change the fixing roller surface temperature, an auxiliary roller 29 that is an auxiliary member that changes the fixing roller surface temperature by contacting the fixing roller 17 is provided. .

  The auxiliary roller 29 can be brought into (pressing) contact with and separated from the fixing roller 17 by a cam mechanism 40 as contact / separation means shown in FIG. Such an auxiliary roller 29 has a core metal 29a formed of a metal such as aluminum or iron as a base layer, and a surface of which is coated with a release layer 29c of fluorine coating. Further, an auxiliary heater 30 as a heating source is disposed in the auxiliary roller 29.

The auxiliary heater 30 is a heat generating element such as a halogen heater disposed at the center of the auxiliary roller 29, and heats the inner surface of the core metal 29 a of the auxiliary roller 29 by infrared rays. The auxiliary heater 30 can adjust the surface temperature of the auxiliary roller 29 to a plurality of set temperatures as will be described later. This temperature adjustment is performed based on detection of a contact type thermistor 31 which is a temperature detection means. The thermistor 31 contacts the surface (outer peripheral surface) of the auxiliary roller 29 and detects the surface temperature. The temperature detection means for detecting the surface temperature of the auxiliary roller 29 may be, for example, an infrared detection type non-contact thermistor.

  As shown in FIG. 3, the cam mechanism 40 includes a swing member 41, a spring 42 that is a biasing means, a cam 43, and a motor 44. The oscillating member 41 has a base end portion rotatably supported by a fixed portion of the apparatus and a tip end portion rotatably supporting an auxiliary roller 29. The spring 42 is disposed between the swinging member 41 and the fixed portion of the apparatus, and biases the auxiliary roller 29 supported by the swinging member 41 in the direction of moving toward the fixing roller 17. The cam 43 and the swing member 41 are disposed so as to come into contact with each other, and are rotated by a motor 44. When the cam 43 rotates, the swing member 41 swings, and the auxiliary roller 29 is brought into contact with and separated from the fixing roller 17. In addition, as a contact / separation means, you may employ | adopt other structures other than such a cam mechanism.

The control device 20 switches the set temperatures of the fixing heater 18 of the fixing roller 17 and the auxiliary heater 30 of the auxiliary roller 29 and controls the motor 44 of the cam mechanism 40. That is, the control device 20 controls the output of the fixing heater 18 based on the detection result of the thermistor 19, and keeps the surface temperature of the fixing roller 17 detected by the thermistor 19 within a certain set temperature range. I am doing so. Further, the control device 20 controls the output of the auxiliary heater 30 based on the detection result of the thermistor 31 so that the surface temperature of the auxiliary roller 29 detected by the thermistor 31 falls within a certain set temperature range. I am doing so. Further, the control device 20 controls the amount and angle of rotation of the motor 44 so that the auxiliary roller 29 contacts or separates from the fixing roller 17. Note that the amount of rotation of the motor 44 is detected by an encoder or the like.

  Further, the control device 20 determines whether it is necessary to change the surface temperature of the fixing roller 17, that is, whether to change the heating condition. Such a determination can be made, for example, by executing a series of image forming jobs while using different types of recording materials, or by changing the type of recording materials for each of a plurality of image data supplied from a client device such as a personal computer. Use this when printing.

In particular, in the present embodiment, the control device 20 performs the following control. That is, before the recording material that requires switching of the setting temperature of the fixing heater 18 passes through the fixing nip N, the setting temperature of the auxiliary heater 30 is switched in a state where the auxiliary roller 29 is separated from the fixing roller 17. . The set temperature of the fixing heater 18 is switched according to, for example, at least one of the thickness of the recording material, the size of the recording material, and whether or not the surface of the recording material is coated. That is, the fixing heater 18 has a first set temperature set for the first recording material and a second set temperature set for a second recording material different from the first recording material and different from the first set temperature. Switching is possible. The auxiliary heater 30 can be switched between a third set temperature set for the second recording material and a fourth set temperature that is set during standby and different from the third set temperature.

Further, when the set temperature of the fixing heater 18 is switched from a high temperature to a low temperature, the set temperature of the auxiliary heater 30 is set to a temperature lower than the set temperature of the low-temperature fixing heater 18 . On the other hand, when the set temperature of the fixing heater 18 is switched from the low temperature to the high temperature, the set temperature of the auxiliary heater 30 is set to a temperature higher than the set temperature of the high temperature fixing heater 18 . When the surface temperature of the fixing roller 17 is switched from the first set temperature to the second set temperature , the auxiliary roller 29 adjusted to the third set temperature after switching the surface temperature is brought into contact with the fixing roller 17.

[Temperature control]
The above control will be described more specifically with reference to FIGS. 4 and 5. 4 and 5 are flowcharts showing the temperature control in the present embodiment, respectively. In this embodiment, in order to prevent fixing failure on thick paper (thick recording material), hot offset and paper wrinkle on thin paper (thin recording material), the surface temperature of the fixing roller 17 is the case of thick paper and thin paper. It is changing. Specifically, the surface of the fixing roller 17 is fixed to 200 ± 3 ° C. when fixing the toner image on the thick paper (when using thick paper) and 180 ± 3 ° C. when fixing the toner image on the thin paper (when using thin paper). Adjust the temperature.

  Here, the thick paper is paper that is thicker than, for example, plain paper used for the cover of a booklet, and the thin paper is paper such as plain paper. However, regarding the relationship between the thick paper and the thin paper, a paper having a thickness approximately equal to that of the plain paper may be a thick paper, and a paper thinner than this may be a thin paper. The temperature setting in this case is determined by design. In short, in this embodiment, when a toner image is fixed on a recording material of a different type, the surface temperature of the fixing roller 17 is adjusted (switched) to a temperature corresponding to the recording material.

The surface temperature of the auxiliary roller 29 has three set temperatures depending on the situation. That is, the standby temperature is 190 ° C. (fourth preset temperature) , the switching temperature from thin paper to thick paper is 220 ° C. (third preset temperature) , and the switching temperature from thick paper to thin paper is 150 ° C. (third The surface temperature of the auxiliary roller 29 is adjusted to ( set temperature) .

[Switch from thin paper to thick paper]
Regarding the temperature control in the present embodiment, when the first print job starts from thin paper, that is, continuously to the thick paper (second recording material) after the first job for heating the thin paper (first recording material). The case of executing the second job for heating the image will be described with reference to FIG. First, in order to pass thin paper (first recording material) before the start of the first job, the surface temperature of the fixing roller 17 is adjusted to 180 ° C. (first set temperature) for thin paper (S101). Further, the surface temperature of the auxiliary roller 29 is adjusted to the standby temperature of 190 ° C. (fourth set temperature) until it is found that the recording material type is changed (S102). At this time, the auxiliary roller 29 is separated from the fixing roller 17. When the surface temperature of the fixing roller 17 is adjusted to 180 ° C., printing (first job) is started (S103).

When printing is started, the control device 20 determines whether there is a change in the recording material (that is, a change in the set temperature of the fixing roller 17) (S104). For example, first, it is confirmed whether there is a setting for using a different recording material during a series of image forming jobs. Among these, it is determined whether or not the temperature of the fixing roller 17 needs to be changed by confirming whether or not there is a change from thin paper (first job) to thick paper (second job) . Also, with respect to a plurality of image data supplied from a client device such as a personal computer, it is determined whether it is necessary to change the temperature of the fixing roller 17 by confirming the setting of the recording material set in the image data. .

If the controller 20 determines that there is no need to change the temperature, the surface temperatures of the fixing roller 17 and the auxiliary roller 29 are maintained as they are, and printing is continued (S105). When the job is finished (S106), the printing is finished.

On the other hand, if it is determined in S104 that there is a change in the recording material, that is, the set temperature of the auxiliary roller 29 is switched during execution of the first job (S107). Since it is determined that there is a change from thin paper to thick paper this time, the set temperature of the auxiliary roller 29 is higher than the set temperature of the high-temperature fixing roller 17 (200 ° C. , second set temperature ), from thin paper to thick paper. The temperature is switched to 220 ° C. (third set temperature) . That is, the surface temperature of the auxiliary roller 29 is adjusted to 220 ° C. by increasing the heating amount by the auxiliary heater 30. This temperature switching is performed during image formation on thin paper ( during execution of the first job) , and the surface temperature of the auxiliary roller 29 is switched from thin paper to thick paper before switching from thin paper to thick paper (second job) . It is preferable that the temperature is adjusted to the third temperature (third set temperature) .

Next, when printing on thin paper is finished (S108) (after the first job is finished) , printing is temporarily interrupted (S109). Then, the auxiliary roller 29 whose surface temperature is adjusted to 220 ° C. (third set temperature) as described above is brought into contact with the fixing roller 17 (S110). That is, by driving the motor 44 and rotating the cam 43, the swing member 41 can swing in the biasing direction by the spring 42. Then, the oscillating member 41 is oscillated by the urging force of the spring 42, and the auxiliary roller 29 supported at the tip of the oscillating member 41 is pressed against the fixing roller 17 by the urging force of the spring 42.

Subsequently, adjustment of the surface temperature of the fixing roller 17 is started to 200 ° C. (second set temperature) , which is the temperature for thick paper (S111). That is, the surface temperature of the fixing roller 17 is increased by increasing the amount of heating by the fixing heater 18. The surface temperature of the fixing roller 17 is 180 ° C. (first set temperature) when the thin paper printing (first job) is completed. Even if heat is supplied from the fixing heater 18, the surface of the fixing roller 17 is immediately The temperature does not rise. However, in this embodiment, since the auxiliary roller 29 having a surface temperature of 220 ° C. is brought into contact with the fixing roller 17, heat is transferred from the auxiliary roller 29 to the surface of the fixing roller 17.

As described above, in this embodiment, when the surface temperature of the fixing roller 17 is switched to that for thick paper (second set temperature) , heat is supplied from the fixing heater 18 and the auxiliary roller 29 to the surface of the fixing roller 17. For this reason, the surface temperature of the fixing roller 17 rises in a shorter time than when only the heat supply of the fixing heater 18 is used.

  When the surface temperature of the fixing roller 17 reaches 200 ° C., the auxiliary roller 29 is separated from the surface of the fixing roller 17 (S112). That is, by driving the motor 44 and rotating the cam 43, the swing member 41 is swung against the urging force of the spring 42, and the auxiliary roller 29 supported at the tip of the swing member 41 is fixed to the fixing roller. 17 away from the surface. At this time, the temperature is adjusted by the fixing heater 18 so that the surface temperature of the fixing roller 17 is maintained at 200.degree.

Then, the printing is resumed (the second job is started) (S113), and the thick paper is passed. The auxiliary roller 29 adjusts the standby temperature to 190 ° C. (fourth set temperature) in preparation for the next change (S114). Printing is continued (S105). As soon as the job is finished (S106), printing is finished. When switching from thin paper to thick paper, the second set temperature (200 ° C.) for the second thick paper job of the fixing roller 17 is higher than the first set temperature (180 ° C.) for the first thin paper job. Further, the third set temperature (220 ° C.) for the thick paper as the second recording material of the auxiliary roller 29 is higher than the fourth set temperature (190 ° C.) for standby.

[Switch from thick paper to thin paper]
Next, when the first print job starts from thick paper, that is, after the first job for heating the thick paper (first recording material), the thin paper (second recording material) is heated. The case of executing the second job will be described with reference to FIG. First, before the start of the first job, in order to pass thick paper (first recording material) , the surface temperature of the fixing roller 17 is adjusted to 200 ° C. (first set temperature) for thick paper (S201). The surface temperature of the auxiliary roller 29 is adjusted to the standby temperature of 190 ° C. (fourth set temperature) until it is found that the recording material type is changed (S202). At this time, the auxiliary roller 29 is separated from the fixing roller 17. When the surface temperature of the fixing roller 17 is adjusted to 200 ° C., printing (first job) is started (S203).

When printing is started, the control device 20 determines whether there is a change in the recording material (that is, a change in the set temperature of the fixing roller 17) as in the case described above (S204). If the controller 20 determines that there is no need to change the temperature, the surface temperatures of the fixing roller 17 and the auxiliary roller 29 are maintained as they are, and printing is continued (S205). When the job is finished (S206), the printing is finished.

On the other hand, if it is determined in S204 that there is a change in the recording material, that is, the set temperature of the auxiliary roller 29 is switched during execution of the first job (S207). Since it is determined that there is a change from thick paper to thin paper this time, the set temperature of the auxiliary roller 29 is lower than the set temperature of the low-temperature fixing roller 17 (180 ° C. , second set temperature ), from thick paper to thin paper. The temperature is switched to 150 ° C. (third set temperature) . That is, the surface temperature of the auxiliary roller 29 is adjusted to 150 ° C. by reducing the heating amount from the auxiliary heater 30. This temperature switching is performed during image formation on the thick paper ( during execution of the first job) , and the surface temperature of the auxiliary roller 29 is switched from the thick paper to the thin paper before switching from the thick paper to the thin paper (second job) . It is preferable that the temperature is adjusted to the third temperature (third set temperature) .

Next, when printing on thick paper is finished (S208) (after the first job is finished) , printing is temporarily interrupted (S209). Then, the auxiliary roller 29 whose surface temperature is adjusted to 150 ° C. (third set temperature) as described above is brought into contact with the fixing roller 17 (S210). Subsequently, adjustment of the surface temperature of the fixing roller 17 is started to 180 ° C. (second set temperature) , which is the temperature at the time of thin paper (S211). That is, the surface temperature of the fixing roller 17 is lowered by reducing the heating amount by the fixing heater 18. The surface temperature of the fixing roller 17 is 200 ° C. (first set temperature) when the thick paper printing (first job) is completed. Even if the heat supply from the fixing heater 18 is reduced (for example, the heat supply is stopped). ) The surface temperature of the fixing roller 17 does not drop immediately. However, in this embodiment, since the auxiliary roller 29 whose surface temperature is 150 ° C. is in contact with the fixing roller 17, the heat of the surface of the fixing roller 17 is taken away by the auxiliary roller 29.

As described above, in the present embodiment, when the surface temperature of the fixing roller 17 is switched to that for thin paper (second set temperature) , the heat supply from the fixing heater 18 is reduced (for example, cut), and the fixing roller is fixed by the auxiliary roller 29. I'm taking heat away from the 17's surface. For this reason, the surface temperature of the fixing roller 17 decreases in a shorter time than the case where only the heat supply of the fixing heater 18 is reduced.

When the surface temperature of the fixing roller 17 reaches 180 ° C., the auxiliary roller 29 is separated from the surface of the fixing roller 17 (S212). At this time, the temperature is adjusted by the fixing heater 18 so that the surface temperature of the fixing roller 17 is maintained at 180 ° C. Then, printing is resumed (the second job is started) (S213), and thin paper is passed. The auxiliary roller 29 adjusts the standby temperature to 190 ° C. (fourth set temperature) in preparation for the next change (S214). Printing is continued (S205). As soon as the job is finished (S206), printing is finished. When switching from the above-described thick paper to thin paper, the second preset temperature (180 ° C.) for the second thin paper job of the fixing roller 17 is lower than the first preset temperature (200 ° C.) for the first thick paper job. Further, the third set temperature (150 ° C.) for the thin paper as the second recording material of the auxiliary roller 29 is lower than the fourth set temperature (190 ° C.) for standby.

  In the above description, the case where the recording material is changed from thin paper to thick paper and from thick paper to thin paper has been described. In this embodiment, it is also possible to change from thin paper to thick paper and then change to thin paper, and from thick paper to thin paper and then change to thick paper. Specifically, if S204 and subsequent steps in FIG. 5 are executed after S114 in FIG. 4, it is possible to change from thin paper to thick paper and then change to thin paper. Similarly, if step S104 and subsequent steps in FIG. 4 are executed after step S214 in FIG. 5, a change from thick paper to thin paper can be made and then change to thick paper can be performed.

According to the present embodiment, when the set temperature of the fixing roller 17 is switched, the auxiliary roller 29 whose set temperature has been switched is brought into contact with the fixing roller 17, so that the set temperature of the fixing roller 17 can be quickly switched. That is, even if the recording material is changed from thick paper to thin paper and from thin paper to thick paper, the surface temperature of the fixing roller 17 can be quickly matched. As a result, even if the heating conditions are changed according to the recording material, the reduction in productivity can be reduced. Therefore, it is possible to provide an image heating apparatus that can maintain high productivity when a series of image forming jobs are executed while using different types of recording materials.

  That is, when there is no auxiliary roller 29, a print job with a change in recording material changes the surface temperature of the fixing roller 17, and thus a long interruption time occurs. For this reason, productivity falls. Particularly in a print job in which the recording material is frequently changed, the productivity is remarkably reduced. However, in this embodiment, by changing the surface temperature of the fixing roller 17 according to the type of the recording material, it is possible to prevent poor fixing with thick paper, hot offset with thin paper, and paper wrinkling. Also, by providing the auxiliary roller 29 for changing the temperature of the fixing roller 17 during the job, the surface temperature of the fixing roller 17 can be changed in a short time, and the interruption time can be shortened. As a result, it is possible to improve productivity in a print job in which the recording material is changed.

  Further, in the case of the present embodiment, in order to change the heating condition by the fixing roller 17, it is not necessary to change the nip width between the fixing roller 17 and the pressure roller 21 as described in Patent Document 2 described above. good. For this reason, the configuration of the fixing roller 17 or the pressure roller 21 is not limited. For example, a structure without the thick elastic layers 17b and 21b as in the present embodiment may be employed.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIGS. 1 and 2 and FIG. In the first embodiment described above, the thick paper and thin paper jobs have been described. However, the present invention can also be applied to a case where a series of image forming jobs are executed while using different sizes of recording materials. For example, perpendicular (orthogonal) to the conveying direction of the recording material by the fixing roller 17 when continuously printed the size of the small length direction (the width direction) to the fixing device F, the non-sheet passing portion Atsushi Nobori occurs. In this case, if the recording material is passed on the basis of the center, that is, if the paper is passed so that the center in the width direction of the recording material and the center in the width direction of the fixing roller 17 are substantially coincident with each other, The temperature rises.

  Since the elastic layer 17b of the fixing roller 17 expands as the temperature rises, the expansion of the end portion of the fixing roller 17 becomes larger than the center of the fixing roller 17 when the above-described temperature rise of the non-sheet passing portion occurs. . In this state, when a recording material having a length in the width direction that is longer than the above-described small size is passed, both ends of the large size recording material pass through the non-sheet passing portion of the small size recording material. Become. As a result, the conveyance speed of the large-sized recording material becomes faster at the end with respect to the center, and the rear end may jump up, resulting in a rear end splash that disturbs the unfixed image before entering the nip.

Therefore, in the present embodiment, as shown in FIG. 6, the heating source of the auxiliary roller 29 is configured by a plurality of auxiliary heaters 30a and 30b that generate heat by energization and have different heat generation distributions, and change the temperature distribution in the width direction. I am trying to do it. In the example shown in the figure, the auxiliary heater 30a (first heater) is configured such that the heat generation amount is larger at the width direction center than at both ends in the width direction, and the auxiliary heater 30b (second heater) is formed at both ends in the width direction. The part side is configured to generate a larger amount of heat than the center part in the width direction.

In the case of this embodiment configured as described above, a job for switching from a recording material having a small size in the width direction (first recording material) to a recording material having a large size (second recording material) , that is, for the first recording material. In the case where the second job for heating the second recording material is executed continuously after the first job for heating, the recording material of a small size is being fed (during execution of the first job). ) , The temperature distribution of the auxiliary roller 29 is set high at the center. For example, in a state where the auxiliary roller 29 is separated from the fixing roller 17, the auxiliary heater 30a (first heater) is energized and the auxiliary heater 30b (second heater) is de-energized. When the recording material is switched from a small size to a large size, that is, after the first job is completed, the temperature difference of the fixing roller can be made in a very short time by contacting the auxiliary roller 29. As a result, the occurrence of edge splashes can be prevented and the recording material switching time can be shortened to improve productivity.

  In the case of continuously passing a large size recording material, when switching between thick paper and thin paper, both the auxiliary heaters 30a and 30b of the auxiliary roller 29 are energized so that the above-mentioned first Control as in the first embodiment is performed. On the other hand, when the recording material of a small size is continuously passed and when switching between thick paper and thin paper, only the auxiliary heater 30a of the auxiliary roller 29 is energized so that the first implementation described above is performed. Control like a form. Other structures and operations are the same as those in the first embodiment.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, two external heating rollers 22 and 25 that are a plurality of external heating members are disposed on the outer periphery of the fixing roller 17. Since the elastic layer 17b on the surface of the fixing roller 17 is relatively thick and has low thermal conductivity, it is an obstacle to supplementing the amount of heat taken by the recording material from the fixing heater 18 of the fixing roller 17 when fixing the toner image. Become. In order to realize a high speed fixing device F, if only the fixing heater 18 of the fixing roller 17 is relied on, it is difficult to keep the surface temperature of the fixing roller 17 constant because the thermal response is not in time.

  Therefore, the first and second external heating rollers 22 and 25 are provided so as to be able to come into contact with and separate from the fixing roller 17 so as to directly heat the surface of the fixing roller 17 whose temperature is lowered by contacting the recording material when fixing the toner image. ing. Further, first and second external heaters 23 and 26 are provided inside the first and second external heating rollers 22 and 25, respectively. Further, by applying heat also from the first and second external heating rollers 22 and 25, the amount of heat applied to the surface of the fixing roller 17 is increased, and the speed of the fixing device F is realized.

  The first external heating roller 22 is disposed on the upstream side in the rotation direction of the fixing roller 17 when viewed from the fixing nip portion N between the fixing roller 17 and the pressure roller 21. Then, it is urged by a contact / separation mechanism (not shown) such as the cam mechanism shown in FIG. The first external heating roller 22 has a core metal 22a made of a metal such as aluminum or iron as a base layer and a surface coated with a release layer 22c of fluorine coating.

  The first external heater 23 is a heat generating element such as a halogen heater included in the first external heating roller 22, and heats the inner surface of the core metal 22 a of the first external heating roller 22 by infrared rays. The contact type thermistor 24 is in contact with the surface of the first external heating roller 22 to detect the surface temperature.

  The control device 20 controls the output of the first external heater 23 based on the detection result of the thermistor 24, and sets the surface temperature of the first external heating roller 22 detected by the thermistor 24 to a certain temperature range. Fit.

The second external heating roller 25 is disposed downstream of the first external heating roller 22 when viewed from the fixing nip N between the fixing roller 17 and the pressure roller 21. In other words, it is arranged on the most downstream side in the rotation direction of the fixing roller 17 with respect to the fixing nip portion N. Then, it is urged by a contact / separation mechanism (not shown) such as the cam mechanism shown in FIG. The second external heating roller 25 and the first external heating roller 22 are configured such that they can be pressurized and separated independently. The second external heating roller 25 has a core metal 25a made of a metal such as aluminum or iron as a base layer and a surface coated with a release layer 25c of fluorine coating.

  The second external heater 26 is a heat generating element such as a halogen heater included in the second external heating roller 25, and heats the inner surface of the core metal 25 a of the second external heating roller 25 by infrared rays. The contact type thermistor 27 is in contact with the surface of the second external heating roller 25 to detect the surface temperature.

  The control device 20 controls the output of the second external heater 26 based on the detection result of the thermistor 27 so that the surface temperature of the second external heating roller 25 detected by the thermistor 27 falls within a certain temperature range. Fit.

In the present embodiment, the second external heating roller 25 also serves as an auxiliary member , that is, an auxiliary roller. The first and second external heating rollers 22 and 25 can apply more heat to the fixing roller 17 as the temperature difference from the surface of the fixing roller 17 is larger. Since the fixing roller 17 takes heat away from the recording material at the fixing nip portion N and the surface temperature is lowered, the fixing roller 17 is fixed at the contact portion with the first external heating roller 22 on the upstream side of the fixing nip portion N in the rotation direction of the fixing roller 17. The temperature difference from the surface of the roller 17 increases. On the other hand, since the contact portion between the second external heating roller 25 and the fixing roller 17 passes through the contact portion with the first external heating roller 22, the surface of the fixing roller 17 and the surface of the second external heating roller 25. The temperature difference between Therefore, when there are a plurality of external heating rollers, the amount of heat given to the fixing roller is larger on the upstream side than the downstream side in the rotation direction of the fixing roller 17 with respect to the fixing nip portion N. For this reason, when a large amount of heat is required, a plurality of external heatings are effective, but when the amount of heat below a certain level is sufficient, only the upstream with a large amount of heat applied is sufficient.

  Immediately after the start of paper feeding from standby or when trying to increase the set temperature of the fixing roller, the heating from the fixing heater 18 of the fixing roller 17 is not in time, and it is necessary to supply heat from a plurality of external heating rollers. . However, when sufficient heat is supplied from the fixing heater 18 of the fixing roller 17 while the paper is being passed, the fixing is performed only by supplying heat from the upstream first external heating roller 22 having a large amount of heat. The temperature of the roller 17 can be maintained.

In the present embodiment, when the temperature of the fixing roller 17 can be maintained only by supplying heat from the first external heating roller 22, the second external heating roller 25 is separated and functions as an auxiliary member .

[Temperature control]
8 and 9 are flowcharts showing the temperature control in the present embodiment. In the present embodiment, the surface temperature of the fixing roller 17 is changed between thick paper and thin paper in order to prevent fixing failure on thick paper, hot offset on thin paper, and paper wrinkles. Specifically, the temperature is adjusted to 200 ± 3 ° C. for thick paper and to 180 ± 3 ° C. for thin paper.

The surface temperature of the first external heating roller 22 is adjusted to 210 ° C. The surface temperature of the second external heating roller 25 has three temperatures depending on the situation. That is, the normal (standby) temperature is 210 ° C. (fourth set temperature) , the change temperature from thin paper to thick paper is 230 ° C. (third set temperature) , and the change temperature from thick paper to thin paper is 150 ° C. The surface temperature of the second external heating roller 25 is adjusted to (third set temperature) .

[Switch from thin paper to thick paper]
Regarding the temperature control in the present embodiment, when the first print job starts from thin paper, that is, continuously to the thick paper (second recording material) after the first job for heating the thin paper (first recording material). The case of executing the second job for heating the image will be described with reference to FIG. First, in order to pass thin paper (first recording material) before the start of the first job, the surface temperature of the fixing roller 17 is adjusted to 180 ° C. (first set temperature) for thin paper (S301). Further, the surface temperatures of the first and second external heating rollers 22 and 25 are adjusted to 210 ° C. which is a normal temperature until it is understood that the recording material type is changed (S302). At this time, the first and second external heating rollers 22 and 25 are in contact with the fixing roller 17. Then, when the surface temperature of the fixing roller 17 is adjusted to 180 ° C., printing (first job) is started (S303).

When printing is started, the control device 20 determines whether there is a change in the recording material (that is, a change in the set temperature of the fixing roller 17) (S304). If the controller 20 determines that there is no need to change the temperature, the surface temperatures of the fixing roller 17 and the first and second external heating rollers 22 and 25 are maintained as they are, and printing is continued (S305). At this time, the first and second external heating rollers 22 and 25 may be brought into contact with and separated from each other in accordance with the control of the surface temperature of the fixing roller 17. When the job is finished (S306), the printing is finished.

  On the other hand, if it is determined in S304 that there is a change in the recording material, it is first determined whether the surface temperature of the fixing roller 17 can be maintained only by the first external heating roller 22 (S307). This may be judged from the electric power supplied to the first external heating roller 22 and the second external heating roller 25, and the temperature of the fixing roller 17 is lowered by actually separating the second external heating roller 25. You may check. If it is determined that the temperature of the fixing roller 17 can be maintained only by the first external heating roller 22, the second external heating roller 25 is immediately separated (S308).

At the same time, that is, during execution of the first job, since it is determined that there is a change from thin paper to thick paper this time, the setting temperature of the second external heating roller 25 is set to the setting of the high-temperature fixing roller 17. The temperature is switched to 230 ° C. (third set temperature) that is higher than the temperature (200 ° C. , second set temperature ), which is a temperature for switching from thin paper to thick paper (S309). That is, the surface temperature of the external heating roller 25 is adjusted to 230 ° C. by increasing the amount of heating by the second external heater 26. This temperature switching is performed during image formation on thin paper ( during execution of the first job) , and the surface temperature of the second external heating roller 25 is changed from thin paper to thick paper before switching from thin paper to thick paper (second job) . It is preferable that the temperature is adjusted to the switching temperature (third set temperature) .

Next, when printing on thin paper is finished (S310) (after the first job is finished) , printing is temporarily interrupted (S311). Then, the second external heating roller 25 whose surface temperature is adjusted to 230 ° C. (third set temperature) as described above is brought into contact with the fixing roller 17 (S312). Subsequently, adjustment of the surface temperature of the fixing roller 17 is started to 200 ° C. (second set temperature) , which is the temperature for thick paper (S313). That is, the surface temperature of the fixing roller 17 is increased by increasing the amount of heating by the fixing heater 18. The surface temperature of the fixing roller 17 is 180 ° C. (first set temperature) when the thin paper printing (first job) is completed. Even if heat is supplied from the fixing heater 18, the surface of the fixing roller 17 is immediately The temperature does not rise. However, in this embodiment, since the second external heating roller 25 having a surface temperature of 230 ° C. is in contact with the fixing roller 17, heat is transferred from the second external heating roller 25 to the surface of the fixing roller 17. Done.

On the other hand, when it is determined in S307 that the temperature of the fixing roller 17 cannot be maintained only by the first external heating roller 22, the second external heating roller 25 is kept in contact with the fixing roller 17 (S314). As such a case, for example, a case where the temperature of the environment in which the apparatus is installed is low, the time has not passed since the power is turned on, and the temperature inside the apparatus is also low can be considered. Then, printing is continued as it is, and when printing on thin paper is completed (S315), printing is temporarily interrupted (S316). Then, the set temperature is switched to 230 ° C. while keeping the second external heating roller 25 in contact with the fixing roller 17 (S317). Subsequently, adjustment of the surface temperature of the fixing roller 17 is started to 200 ° C., which is the temperature for thick paper (S313).

As described above, in the present embodiment, when the surface temperature of the fixing roller 17 is switched to that for thick paper (second set temperature) , the fixing is performed from the second external heating roller 25 in addition to the fixing heater 18 and the first external heating roller 22. Heat is supplied to the surface of the roller 17. For this reason, the surface temperature of the fixing roller 17 rises in a shorter time than when only the heat supply of the fixing heater 18 and the first external heating roller 22 is used.

  When the surface temperature of the fixing roller 17 reaches 200 ° C., the second external heating roller 25 is separated from the surface of the fixing roller 17 (S318). At this time, the temperature is adjusted by the fixing heater 18 and the first external heating roller 22 so that the surface temperature of the fixing roller 17 is maintained at 200.degree.

Then, the printing is resumed (the second job is started) (S319), and the thick paper is passed. The second external heating roller 25 is adjusted to 210 ° C. (fourth set temperature) , which is a normal temperature, in preparation for the next change (S320). Printing is continued (S305), and as soon as the job is finished (S306), printing is finished. When switching from thin paper to thick paper, the second set temperature (200 ° C.) for the second thick paper job of the fixing roller 17 is higher than the first set temperature (180 ° C.) for the first thin paper job. Further, the third set temperature (230 ° C.) for the thick paper as the second recording material of the second external heating roller 25 is higher than the fourth set temperature (210 ° C.) for standby.

[Switch from thick paper to thin paper]
Next, when the first print job starts from thick paper, that is, after the first job for heating the thick paper (first recording material), the thin paper (second recording material) is heated. The case where the second job is executed will be described with reference to FIG. First, before the start of the first job, in order to pass thick paper (first recording material) , the surface temperature of the fixing roller 17 is adjusted to 200 ° C. (first set temperature) for thick paper (S401). Further, the surface temperatures of the first and second external heating rollers 22 and 25 are adjusted to 210 ° C. which is a normal temperature until it is understood that the recording material type is changed (S402). At this time, the first and second external heating rollers 22 and 25 are in contact with the fixing roller 17. When the surface temperature of the fixing roller 17 is adjusted to 200 ° C., printing (first job) is started (S403).

When printing is started, the control device 20 determines whether there is a change in the recording material (that is, a change in the set temperature of the fixing roller 17) (S404). If the controller 20 determines that there is no need to change the temperature, the surface temperatures of the fixing roller 17 and the first and second external heating rollers 22 and 25 are maintained as they are, and printing is continued (S405). At this time, the first and second external heating rollers 22 and 25 may be brought into contact with and separated from each other in accordance with the control of the surface temperature of the fixing roller 17. When the job is finished (S406), the printing is finished.

  On the other hand, if it is determined in S404 that there is a change in the recording material, it is first determined whether the surface temperature of the fixing roller 17 can be maintained only by the first external heating roller 22 (S407). If it is determined that the temperature of the fixing roller 17 can be maintained only by the first external heating roller 22, the second external heating roller 25 is immediately separated (S408).

At the same time, that is, during execution of the first job, since it is determined that there is a change from thick paper to thin paper this time, the setting temperature of the second external heating roller 25 is set to the setting of the low-temperature fixing roller 17. The temperature is switched to 150 ° C. (third set temperature) that is lower than the temperature (180 ° C. , second set temperature ), which is a temperature for switching from thick paper to thin paper (S409). That is, the surface temperature of the external heating roller 25 is adjusted to 150 ° C. by reducing the amount of heat from the second external heater 26. This temperature switching is performed during the image formation on the thick paper ( during the execution of the first job) , and the surface temperature of the second external heating roller 25 is changed from the thick paper to the thin paper before switching from the thick paper to the thin paper (second job) . It is preferable that the temperature is adjusted to the switching temperature (third set temperature) .

Next, when the printing on the thick paper is finished (S410) (after the first job is finished) , the printing is temporarily interrupted (S411). Then, the second external heating roller 25 whose surface temperature is adjusted to 150 ° C. (third set temperature) as described above is brought into contact with the fixing roller 17 (S412). Subsequently, adjustment of the surface temperature of the fixing roller 17 is started to 180 ° C. (second set temperature) , which is the temperature when thin paper is used (S413). That is, the surface temperature of the fixing roller 17 is lowered by reducing the heating amount by the fixing heater 18. The surface temperature of the fixing roller 17 is 200 ° C. (first set temperature) when the thick paper printing (first job) is completed. Even if the heat supply from the fixing heater 18 is reduced (for example, the heat supply is stopped). ) The surface temperature of the fixing roller 17 does not drop immediately. However, in this embodiment, since the auxiliary roller 29 whose surface temperature is 150 ° C. is in contact with the fixing roller 17, the heat of the surface of the fixing roller 17 is taken away by the auxiliary roller 29. At this time, the first external heating roller 22 may be separated from the fixing roller 17 or the first external heating heater 23 may be turned off.

On the other hand, if it is determined in S407 that the temperature of the fixing roller 17 cannot be maintained only by the first external heating roller 22, the second external heating roller 25 is kept in contact with the fixing roller 17 (S414). Then, the printing is continued as it is, and the printing is temporarily interrupted (S416) when the printing on the thick paper is finished (S415). Then, the set temperature is switched to 150 ° C. while keeping the second external heating roller 25 in contact with the fixing roller 17 (S417). Subsequently, adjustment of the surface temperature of the fixing roller 17 is started to 180 ° C., which is the temperature for thick paper (S413). At this time, the first and second external heating rollers 22 and 25 may be separated from the fixing roller 17 or the first and second external heating heaters 23 and 26 may be turned off.

As described above, in this embodiment, when the surface temperature of the fixing roller 17 is switched to that for thin paper (second set temperature) , the heat supply from the fixing heater 18 is reduced (for example, turned off), and the second external heating roller 25 is used. As a result, heat is taken from the surface of the fixing roller 17. For this reason, the surface temperature of the fixing roller 17 decreases in a shorter time than the case where only the heat supply of the fixing heater 18 is reduced.

When the surface temperature of the fixing roller 17 reaches 180 ° C., the second external heating roller 25 is separated from the surface of the fixing roller 17 (S418). At this time, the temperature is adjusted by the fixing heater 18 so that the surface temperature of the fixing roller 17 is maintained at 180 ° C. Then, printing is resumed (second job is started) (S419), and thin paper is passed. The second external heating roller 25 adjusts to the normal temperature of 210 ° C. (fourth set temperature) in preparation for the next change (S420). Continue to print (S405), the job as soon as the end (S 4 06), to end the print. When switching from the above-described thick paper to thin paper, the second preset temperature (180 ° C.) for the second thin paper job of the fixing roller 17 is lower than the first preset temperature (200 ° C.) for the first thick paper job. Further, the third set temperature (150 ° C.) for the thin paper as the second recording material of the second external heating roller 25 is lower than the fourth set temperature (210 ° C.) for the standby time.

  In the above description, the case where the recording material is changed from thin paper to thick paper and from thick paper to thin paper has been described. In this embodiment, it is also possible to change from thin paper to thick paper and then change to thin paper, and from thick paper to thin paper and then change to thick paper. Specifically, if S404 and subsequent steps in FIG. 9 are executed after S320 in FIG. 8, the change from thin paper to thick paper can be performed and then the change to thin paper can be performed. Similarly, if step S304 and subsequent steps in FIG. 8 are executed after step S420 in FIG. 9, the change from thick paper to thin paper can be performed, and then the change to thick paper can be performed.

In the case of the present embodiment, as described above, in the fixing device having a plurality of external heating rollers with high productivity for printing the same recording material, the external heating roller on the downstream side in the rotation direction of the fixing roller 17 also serves as an auxiliary member. ing. For this reason, even in printing with a change in recording material, fixing failure on thick paper, hot offset and paper wrinkle on thin paper can be prevented, and high productivity can be obtained.

In the present embodiment, only the second external heating roller 25 also serves as an auxiliary member , but the first external heating roller 22 may also serve as an auxiliary member . In short, it is sufficient that at least one of the plurality of external heating rollers also serves as an auxiliary member .

Further, the present invention is to abut against the heating rotator when the temperature switch, an auxiliary member to assist the temperature switching, when it is determined the temperature switch, prior to temperature control switch, to switch the temperature of the auxiliary member It is characterized by. Therefore, to this extent, another embodiment in which a part or all of the configuration of each of the above-described embodiments is replaced with the alternative configuration can be implemented. Furthermore, the configurations of the above-described embodiments can be combined as appropriate.

Further, in each of the above-described embodiments, the surface temperature of the fixing roller 17 is switched depending on the thickness of the recording material (thick paper and thin paper) or the size of the recording material. Switching may be performed with or without a coat. That is, when switching from coated paper to non-coated paper and from non-coated paper to coated paper, the auxiliary member is adjusted to an appropriate temperature and then brought into contact with the fixing roller 17. Also, these three conditions can be combined as appropriate. In short, the set temperature of the fixing roller 17 is switched according to at least one of the thickness of the recording material, the size of the recording material, and the presence / absence of the coating on the surface of the recording material.

DESCRIPTION OF SYMBOLS 17 ... Fixing roller (heating rotary body), 20 ... Control apparatus (control means), 21 ... Pressure roller ( nip forming member ), 22 ... 1st external heating roller (external heating member) 25 ... second external heating roller (external heating member, auxiliary member ), 29 ... auxiliary roller ( auxiliary member ), 40 ... cam mechanism (contact / separation means), 100 ... image forming apparatus, Y, M, C, K: Image forming unit, N: Fixing nip, F: Fixing device (image heating device), S: Recording material

Claims (6)

The rotation can be switched between a first set temperature set for the first recording material and a second set temperature set for a second recording material different from the first recording material and different from the first set temperature. A heating rotator for heating the toner image on the first recording material or the second recording material;
A nip forming member for forming a nip portion for sandwiching the first recording material or the second recording material with the heating rotator;
A third set temperature which is set to the second recording medium, can be switched between the set fourth set temperature different from the third set temperature during standby, the switching of the heating rotating body contact temperature An auxiliary member to assist ,
Contacting / separating means for contacting / separating the auxiliary member to / from the heating rotating body;
The switching of each of the set temperature of the heating rotating body and said auxiliary member, and, and a control means for controlling said moving means,
When the control unit executes a second job for heating the second recording material continuously after the first job for heating the first recording material,
Before the start of the first job, the set temperature of the heating rotator is set to the first set temperature and the set temperature of the auxiliary member is set to the fourth set temperature,
During execution of the first job, the auxiliary member is switched to the third preset temperature with the auxiliary member being separated from the heating rotator,
After completion of the first job, the auxiliary member whose set temperature is set to the third set temperature is brought into contact with the heating rotator and the set temperature of the heating rotator is switched to the second set temperature.
An image heating apparatus. The first recording material is thin paper;
The second recording material is cardboard,
The second set temperature is higher than the first set temperature,
The third preset temperature is higher than the fourth preset temperature;
The image heating apparatus according to claim 1, wherein: The first recording material is cardboard;
The second recording material is thin paper;
The second set temperature is lower than the first set temperature,
The third preset temperature is lower than the fourth preset temperature;
The image heating apparatus according to claim 1, wherein: A plurality of external heating members that contact the heating rotator and heat the heating rotator;
Of the plurality of external heating members, the external heating member on the most downstream side in the rotation direction of the heating rotator with respect to the nip portion also serves as the auxiliary member .
The image heating apparatus according to claim 1, wherein the image heating apparatus is any one of claims 1 to 3. A heating rotator for heating the toner image on the recording material while rotating and conveying the recording material;
A nip forming member that forms a nip portion for sandwiching the recording material with the heating rotator, and
A first heater that generates heat when energized, and has a heat generation amount that is greater in the width direction center part orthogonal to the conveyance direction of the recording material by the heating rotator than in the width direction both end parts, and the width direction both end parts are in the width direction A second heater that generates a larger amount of heat than the center side, and an auxiliary member that contacts the heating rotator,
Contacting / separating means for contacting / separating the auxiliary member to / from the heating rotating body;
Switching between the first heater and the second heater, and a control means for controlling the contact and separation means,
The control means heats the second recording material having a size larger in the width direction than the first recording material continuously after the first job for heating the first recording material. When executing a job,
During the execution of the first job, the auxiliary heater is energized to the first heater while being separated from the heating rotator, and the second heater is de-energized,
After the first job, the auxiliary member is brought into contact with the heating rotator.
An image heating apparatus. An image forming apparatus comprising: an image forming unit that forms a toner image on a recording material; and a fixing device that fixes the toner image formed on the recording material by the image forming unit to the recording material.
The fixing device is the image heating device according to any one of claims 1 to 5.
An image forming apparatus.

Images