JP2014164149A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: when a contact-type main thermistor performing temperature adjustment of an external heating member is contaminated with toner or paper powder, the actual temperature of the external heating member is increased, and a contact-type sub thermistor of the external heating member arranged at a position corresponding to a non-paper feeding area detects a high-temperature error that is detection of abnormal high temperature, resulting in stoppage of an image forming apparatus.SOLUTION: When a contact-type sub thermistor of an external heating member detects a predetermined temperature that is lower than a high-temperature error detection temperature, a fixing device reduces a target temperature of the external heating member or turns off a heating source of the external heating member so as to reduce the occurrence of a high-temperature error, and thereby reducing the frequency of stoppage of an image forming apparatus.

Description

  The present invention relates to an electrophotographic fixing device capable of forming an image on a recording material such as a multifunction machine, a copying machine, a printer, and a fax machine.

  In recent years, image forming apparatuses such as copiers, printers, and multifunction machines have been required to increase speed, improve image quality, color, and save energy. Furthermore, multimedia compatibility that supports various recording materials such as thin paper, thick paper, rough paper (rough paper), uneven paper (embossed paper, etc.), coated paper (gloss coated paper, matte coated paper, etc.) In addition, high productivity (the number of images formed per unit time) is also required. In particular, in order to increase the productivity of a recording material having a large weight such as cardboard, it is necessary to improve the recording material heating performance of the fixing device.

  However, the amount of heat necessary for fixing the toner on the recording material (thick paper) having a large amount of weight is much larger than that on the recording material (thin paper) having a small amount of weighing. For this reason, if toner is fixed to a recording material with a large amount of weight under the same conditions as a recording material with a small amount of weight, the fixing member of the fixing device that heats the toner loses heat and the surface temperature decreases, resulting in poor fixing. The problem occurs.

  Therefore, in order to ensure the fixing property of the thick paper (adhesive force between the toner and the recording material), it is necessary to keep the surface temperature of the fixing member constant. For this purpose, the fixing process is performed by reducing the productivity of cardboard, for example, by increasing the interval between the recording materials conveyed to the fixing device or by reducing the rotation speed of the fixing member.

  A fixing roller as such a fixing member is formed by, for example, coating a heat-resistant elastic layer such as silicone rubber or fluororubber on a metal pipe-shaped metal core having a halogen heater heating source disposed therein. Generally, it has a structure in which a release layer such as a fluororesin is formed on the layer. In such a fixing roller, heat from the halogen heater is blocked by a metal core or an elastic layer having low thermal conductivity and is not easily transmitted to the surface of the fixing roller.

  There is also a structure in which an elastic layer is not provided as a fixing roller. In the case of this structure, since the heat from the halogen heater is easily transmitted to the surface of the fixing roller because there is no elastic layer, the surface temperature decrease is small. In the case of a fixing roller without this elastic layer, in a recording material with large irregularities, the toner in the recesses is difficult to contact the fixing roller, and the toner in the recesses becomes poorly fixed. Further, even in a normally used recording material (plain paper), particularly in a color image, since the surface of the unfixed image cannot be melted uniformly, uneven fixing, uneven gloss, and uneven color occur. Quality will deteriorate. Therefore, it is preferable to cover the fixing member with an elastic layer in view of multimedia compatibility and image quality corresponding to various recording materials.

  In any case, in order to prevent a decrease in the surface temperature of the fixing roller, a structure in which a high-power halogen heater is disposed in the fixing roller and heated rapidly can be considered. However, in the case of this structure, the core metal temperature of the fixing roller rapidly increases, and the thermal deterioration of the adhesive layer between the core metal and the elastic layer, or the thermal deterioration of the adhesive layer between the core metal and the release layer. May progress quickly, and peeling between the cored bar and the elastic layer or peeling between the cored bar and the release layer may occur. Furthermore, the elastic layer is thermally deteriorated (softening deterioration or hardening deterioration), the hardness change of the fixing roller is increased, and the width of the fixing nip portion (the roller circumferential direction) that is a pressure contact portion with the pressure roller as a pressure member There is also a possibility that the elastic layer may be destroyed due to a change in fixing property due to a change in the width of the pressure contact portion or a softening deterioration.

  Therefore, as a technique for preventing the surface temperature of the fixing roller from being lowered due to the passing of the recording material, improving the heating performance of the recording material, and improving the productivity, the fixing roller is not only from the internal heater, There has been proposed an external heating type fixing device in which an external heating member having a heating source is brought into contact with the fixing roller to heat the fixing roller from the outside.

  The external heating type fixing device prevents the surface temperature of the fixing roller from lowering, improves the fixability and productivity, and lowers the core temperature of the fixing roller to separate the core metal from the elastic layer, This has the advantage that the life of the fixing roller can be extended by preventing the peeling between the gold and the release layer or the thermal deterioration of the elastic layer.

  For example, Patent Document 1 proposes a configuration in which a core metal temperature is decreased by bringing an external heating roller as an external heating member into contact with the fixing roller and controlling the surface temperature of the fixing roller. The configuration described in Patent Document 1 includes contact / separation means that presses and separates a plurality of external heating members from the fixing roller, and adjustment means that presses the plurality of external heating members uniformly against the surface of the fixing roller. A plurality of external heating members are uniformly pressed against the fixing roller to effectively heat the surface of the fixing roller, thereby improving the productivity of cardboard.

  As a technique for improving the external heating performance, for example, Patent Document 2 proposes a configuration in which an external heating belt is brought into contact with the fixing roller. In the configuration described in Patent Document 2, an external heating belt is brought into contact with the fixing roller, and a belt-like region in the outer peripheral direction of the fixing roller is heated to supply a sufficient amount of heat to the fixing roller, thereby fixing the toner image. Is stabilized. This external heating belt system can increase the contact portion between the external heating member and the fixing roller even in a configuration in which the fixing roller does not have an elastic layer, so that sufficient heat can be supplied from the external heating member to the fixing roller. With the advantages that are possible.

  Furthermore, for example, Patent Document 3 proposes a configuration in which a plurality of heat sources included in a plurality of external heating members operate in the same manner as a technique capable of simplifying the configuration of the external heating device and reducing costs. The configuration described in Patent Document 3 includes a control unit that controls a plurality of heat sources of a plurality of external heating members to operate in the same manner according to a temperature detected by one temperature detection element (thermistor). This configuration simplifies the apparatus and enables cost reduction.

JP 2004-37555 A JP 2004-198659 A JP 2008-224903 A

  A fixing device has been proposed in which, for example, an external heating roller as an external heating member having a heating source is brought into contact with a fixing roller as a fixing member having a heating source.

  This external heating roller has a thermistor as a temperature detection element that incorporates, for example, a halogen heater as a heating source and detects the surface temperature of the external heating roller. In this thermistor, an external heating main thermistor for detecting the temperature of the central portion of the external heating roller and an external heating sub-thermistor for detecting the temperature of the end of the external heating roller are arranged.

  Then, the surface temperature of the external heating roller is maintained at the target temperature by ON / OFF control of the halogen heater of the external heating roller so that the detected temperature of the external heating main thermistor becomes the target temperature. Therefore, the external heating main thermistor is a thermistor for adjusting the temperature of the external heating roller.

On the other hand, the external heating sub-thermistor is a temperature detection thermistor used as a safety device for detecting the temperature of the end of the external heating roller or detecting an abnormally high temperature of the external heating roller.
Here, as the thermistor of the external heating roller, a contact type thermistor that contacts the external heating roller is conventionally used. This is because a non-contact thermistor with low heat resistance cannot be used because the external heating roller is at a high temperature.

  However, in such a conventional configuration, the external heating main thermistor, which is a contact thermistor of the external heating roller, is contaminated by toner or paper powder due to long-term use of the fixing device. The toner, paper dust, and the like are transferred from the recording material in the order of the fixing roller and the external heating roller, and finally adhere to the external heating main thermistor. The amount of toner, paper dust, and the like adhering to the externally heated main thermistor is very small for a single recording material, but it may become a large lump as the number of sheets passed increases. Then, when toner, paper powder or the like enters between the external heating roller and the external heating main thermistor, the external heating main thermistor floats from the external heating roller. Therefore, the external heating main thermistor cannot accurately detect the surface temperature of the external heating roller, and detects it at a temperature lower than the actual temperature of the external heating roller.

  In such a state, the external heating main thermistor controls ON / OFF of the halogen heater so as to maintain the surface temperature of the external heating roller at the target temperature. Therefore, even if the detected temperature of the external heating main thermistor is the target temperature, The actual temperature of the external heating roller is higher than the target temperature.

  Then, the external heating roller becomes high temperature, the external heating sub-thermistor detects a predetermined high temperature, turns off the halogen heater, and stops the image forming apparatus, resulting in a “high temperature error” state. There is a possibility that the problem that it becomes impossible to occur.

  Here, the external heating sub-thermistor is disposed at the position of the external heating roller corresponding to the non-sheet passing portion or the non-image portion of the fixing roller, and is hardly contaminated with toner or paper dust. Therefore, the actual temperature of the external heating roller that has become high is detected.

  In order to prevent the high temperature error detected by the external heating sub-thermistor from occurring, if the detection temperature for detecting the high temperature error is increased, the high temperature error is less likely to occur, but members around the external heating roller, for example, external heating There is a possibility that the heat resistance temperature of the heat-insulating bush or bearing supporting the sub-thermistor and the external heating roller will be exceeded, resulting in damage.

  Therefore, in view of the circumstances as described above, the present invention reduces the increase in the actual temperature of the external heating roller even when the external heating main thermistor is contaminated with toner, paper powder, or the like. And even if the high temperature error detection temperature is not set higher than necessary, the external heating sub-thermistor reduces the detection of the high temperature error detection temperature, thereby reducing the stop of the image forming apparatus.

  The present invention includes a fixing member having a heating source 1, an external heating member having a heating source 2 that contacts the outer peripheral surface of the fixing member and heats the fixing member, and a pressure member.

A temperature detecting element 1 for detecting the temperature of the sheet passing area at the center of the fixing member surface, and a contact-type temperature detecting element for detecting the temperature at the center of the surface of the external heating member (the part corresponding to the sheet passing area of the fixing member) 2 and a contact-type temperature detection element 3 that detects the temperature of a substantially end portion of the surface of the external heating member (a portion corresponding to a non-sheet passing region or a non-image region of the fixing member).
The temperature detection element 1 controls the heating source 1 of the fixing member to adjust the temperature so as to maintain the surface temperature of the fixing member at the target temperature 1, and the temperature detected by the temperature detection element 2. Thus, the heating source 2 of the external heating member is controlled to adjust the temperature so that the surface temperature of the external heating member is maintained at the target temperature 2.
In the fixing device for fixing an image on a recording material by passing a recording material carrying an unfixed image through a pressure contact portion between the fixing member and the pressure member, the temperature detecting element 2 and the temperature detecting element 3 When detecting a predetermined temperature 1 higher than the target temperature 2, it is considered that an abnormally high temperature has been detected, and image formation of the image forming apparatus is stopped, and a “high temperature error” is displayed.
And when the said temperature detection element 3 detects the predetermined temperature 2 higher than the said target temperature 2 and lower than the said predetermined temperature 1, it has a temperature control means to reduce the target temperature 2 of the said external heating member. The fixing device characterized by the above.
In addition, when the temperature detection element 3 detects a predetermined temperature 3 higher than the target temperature 2 and lower than the predetermined temperature 1, it has a heating source control means for turning off the heating source 2 of the external heating member. The fixing device is characterized in that.

  According to the present invention, the external heating main thermistor, which is a contact thermistor for adjusting the temperature of the external heating member, is contaminated with toner or paper powder, and the actual temperature of the external heating member becomes higher than the target temperature, and the external heating When the sub-thermistor detects a predetermined temperature or higher, it is possible to reduce the external heating member temperature from rising to the high temperature error temperature by lowering the target temperature of the external heating member or turning off the heating source of the external heating member. Therefore, occurrence of a high temperature error can be reduced, and the stop of the image forming apparatus can be reduced. Accordingly, since the frequency of calling a service person to repair for a user is reduced, a fixing device that can reduce downtime of the image forming apparatus and an image forming apparatus including such a fixing device are provided. can do.

1 is a schematic sectional view showing an example of an image forming apparatus according to the present invention. 1 is a schematic cross-sectional view of a fixing device according to a first embodiment. 1 is a schematic configuration diagram showing the position of a temperature detection element of a fixing device according to a first embodiment. The flowchart figure which concerns on the temperature control of the external heating member which concerns on 1st Embodiment. Schematic sectional view of a fixing device according to a second embodiment Schematic sectional view of a fixing device according to a third embodiment

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS.

<Image forming apparatus>
First, the image forming apparatus according to the present embodiment will be described with reference to FIG. The image forming apparatus shown in FIG. 1 has four image forming units Y (yellow), M (magenta), C (cyan), and Bk (black) that form toner images of four different colors. . An endless intermediate transfer belt 10 as an intermediate transfer member is disposed so as to pass through these image forming units.

  These four image forming units Y, M, C, and Bk have the same configuration. Hereinafter, the configuration of the yellow image forming unit Y will be described as a representative. For the other image forming units, members having the same configuration and function as those of the image forming unit Y are given the same numbers, and the subscripts indicating the respective units are changed.

  As an image carrier, for example, a cylindrical electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1Y whose surface layer is made of OPC (organic optical semiconductor) is driven to rotate in the direction of an arrow. 2Y is a charging roller for uniformly and uniformly charging the surface of the photosensitive drum 1Y. The charging roller 2Y to which a predetermined bias is applied rotates in contact with the photosensitive drum 1Y and charges the surface of the photosensitive drum 1Y to a predetermined potential. The charged photosensitive drum 1Y is exposed to exposure light (laser light or the like) by the exposure device 3Y, and an electrostatic latent image corresponding to the color separation image of the input document is formed. The developing device 4Y develops the electrostatic latent image using the toner charged by the developing roller, and forms a toner image corresponding to the electrostatic latent image on the surface of the photosensitive drum 1Y. The toner image on the photosensitive drum 1Y is rotated by the primary transfer roller 5Y at the primary transfer portion T1Y between the photosensitive drum 1Y and the primary transfer roller 5Y at an intermediate speed rotated at substantially the same speed as the peripheral speed of the photosensitive drum 1Y. Primary transfer is performed on the transfer belt 10.

  The primary transfer residual toner on the photosensitive drum 1Y after the primary transfer is collected by a photosensitive drum cleaning device 6Y provided with a blade or a brush. Then, the photosensitive drum 1Y from which the primary transfer residual toner has been removed is uniformly charged again by the charging roller 2Y and repeatedly used for image formation.

  The intermediate transfer belt 10 is stretched around a drive roller 11, a support roller 12, and a backup roller 13. Then, while being in contact with the photosensitive drums 1Y, 1M, 1C, and 1Bk of the four image forming units Y, M, C, and Bk, the drive roller 11 is rotationally driven by the rotation in the arrow direction.

  When the full color mode (full color image formation) is selected, the image forming operation as described above is executed by the four image forming units Y, M, C, and Bk. Then, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image respectively formed on the photosensitive drums 1Y, 1M, 1C, and 1Bk are sequentially sequentially transferred onto the intermediate transfer belt 10. Note that the color order is not limited to the above, and is arbitrary depending on the image forming apparatus.

  The four-color toner images transferred onto the intermediate transfer belt 10 are collectively transferred onto the recording material P by the secondary transfer roller 14 at the secondary transfer portion T2 between the backup roller 13 and the secondary transfer roller 14. Secondarily transferred. The recording material P is separated and fed from a sheet feeding cassette (not shown), and is aligned with the multiple transfer toner image on the intermediate transfer belt 10 on the secondary transfer portion T2 by a pair of registration rollers (not shown). Supplied at a predetermined control timing.

  In the present embodiment, the image forming unit that forms an image on the recording material is configured as described above. The image (toner image) formed on the recording material by such an image forming unit is fixed on the recording material by the fixing device 100. That is, the recording material P onto which the toner image has been transferred is introduced into the fixing device 100, and the toner image on the recording material P is pressurized and heated to fix the full color toner image on the recording material P.

  The secondary transfer residual toner on the intermediate transfer belt 10 after the secondary transfer is collected by the intermediate transfer cleaning device 15 in which a blade or a brush is disposed. The intermediate transfer belt 10 from which the secondary transfer residual toner has been removed is subjected to primary transfer for repeated image formation.

  Further, for example, in the case of a black monochromatic mode (monocolor image formation) or a 2-3 color mode, image formation on a photosensitive drum is executed in an image forming unit of a necessary color. At this time, the photosensitive drum in the unnecessary image forming unit is idly rotated. Then, the toner image is primarily transferred onto the intermediate transfer belt 10 at the primary transfer portion T1, and then secondarily transferred onto the recording material P at the secondary transfer portion T2 and introduced into the fixing device 100. Executed.

<Fixing device>
Next, the fixing device 100 will be described.

As shown in FIG. 2, the fixing device 100 includes a fixing roller 101 as a fixing member, a pressure roller 102 as a pressure member, and an external heating roller 103 as an external heating member. The fixing roller 101 is rotationally driven in a direction indicated by an arrow at a predetermined speed, for example, a peripheral speed of 300 mm / sec, by a driving source (not shown), and A4 (horizontal) is printed at 70 ppm (Page Per Minute). The pressure roller 102 and the external heating roller 103 are driven to rotate by the rotation of the fixing roller 101. Further, the upper limit of the basis weight of the recording material that can ensure the fixability of the fixing device of the present embodiment is 250 g / m ² .

  In the fixing roller 101 and the pressure roller 102, a heat-resistant elastic layer and a heat-resistant release layer are sequentially coated on a metal core on a cylinder.

  The cored bar of the fixing roller 101 is made of aluminum having an outer diameter of 74 mm, a thickness of 6 mm, and a length of 350 mm, for example. The elastic layer is made of, for example, silicone rubber having a thickness of 3 mm (for example, JIS-A hardness 20 degrees) and covers the outer peripheral surface of the cored bar. The release layer is made of, for example, a fluororesin (eg, PFA tube) having a thickness of 70 μm and covers the surface of the elastic layer in order to improve releasability with the toner.

  The metal core of the pressure roller 102 is made of stainless steel having an outer diameter of 54 mm, a thickness of 5 mm, and a length of 350 mm, for example. The elastic layer is made of, for example, silicone rubber having a thickness of 3 mm (for example, JIS-A hardness 24 degrees) and covers the outer peripheral surface of the cored bar. The release layer is made of, for example, a fluororesin (eg, PFA tube) having a thickness of 70 μm and covers the surface of the elastic layer in order to improve releasability with the toner.

  Inside the cored bar of the fixing roller 101, as shown in FIG. 2, a halogen heater 111 having a rated power of 1200 W, for example, which generates heat when energized is disposed as a heating source. Then, heating is performed from the inside so that the surface temperature of the fixing roller 101 becomes a predetermined target temperature. The surface temperature of the fixing roller 101 is detected by a thermistor 121a which is a temperature detecting means. Then, the temperature control means 130 controls the heating source control means 140 based on the temperature information detected by the thermistor 121a, and thereby controls the halogen heater 111 to be turned on / off, whereby a predetermined target temperature, for example, 180 ° C. The temperature is adjusted.

  As shown in FIG. 2, a halogen heater 112 having a rated power of 600 W, for example, which generates heat when energized is disposed as a heating source in the core of the pressure roller 102. And it heats from the inside so that the surface temperature of the pressure roller 102 may become a predetermined target temperature. The surface temperature of the pressure roller 102 is detected by a thermistor 122a that is a temperature detecting means. Then, the temperature control means 130 controls the heating source control means 140 based on the detected temperature information of the thermistor 122a, and controls the halogen heater 112 to be turned on / off, so that a predetermined target temperature, for example, 120 ° C. The temperature is adjusted.

  In this embodiment, a heat source is disposed on the pressure roller 102 in order to ensure the fixability. However, a configuration in which the pressure roller 102 does not have a heat source may be used as long as the fixability can be ensured.

  The pressure roller 102 is pressed against the fixing roller 101 with a predetermined pressure by a not-shown pressing means to form the fixing roller 101 and the fixing nip portion N1, and is rotated by the fixing roller 101 in the direction of the arrow. The Note that the circumferential width of the fixing nip portion N1 is about 10 mm, for example.

  Next, the external heating roller 103 serving as an external heating member that contacts and heats the fixing roller 101 is, for example, a mold release from toner on an aluminum core bar having an outer diameter of 30 mm, a thickness of 3 mm, and a length of 350 mm. In order to improve the properties, for example, a 15 μm fluororesin (for example, PFA coat) is coated as a heat-resistant release layer. The external heating roller 103 is pressed against the fixing roller 101 with a predetermined pressure by a pressing unit (not shown). Then, an external heating nip portion N2 is formed between the external heating roller 103 and the fixing roller 101. The external heating roller 103 is driven to rotate in the direction of the arrow with respect to the fixing roller 101. Note that the circumferential width of the external heating nip portion N2 is, for example, about 5 mm.

  Inside the external heating roller 103, as shown in FIG. 2, a halogen heater 113 having a rated power of 800 W, for example, that generates heat when energized is disposed as a heating source. And it heats from the inside so that the surface temperature of the external heating roller 103 may become a predetermined target temperature. Note that the surface temperature of the external heating roller 103 is detected by a thermistor 123a which is a temperature detecting means described later. Then, the temperature control means 130 controls the heating source control means 140 based on the detected temperature information of the thermistor 123a, and thereby controls the halogen heater 113 to be turned on / off, whereby a predetermined target temperature, for example, 220 is controlled. Temperature controlled to ° C.

  Each roller of the fixing device 100 configured as described above performs a separation or pressure-bonding operation during standby and during printing. This separation / crimping operation will be described.

  During standby, in order to prevent deformation or distortion of the elastic layer of the fixing roller 101 and the elastic layer of the pressure roller 102, the pressure roller 102 and the external heating roller 103 are separated from the fixing roller 101 by a separation unit (not shown). The

  On the other hand, during printing, that is, during the fixing (heating) operation of the image on the recording material, the pressure roller 102 and the external heating roller 103 are pressed against the fixing roller 101 by a pressure unit (not shown).

  Note that when the rollers remain pressed without being separated during standby, deformation or distortion of the elastic layer at the fixing nip portion N1 and the external heating nip portion N2 remains during printing, and the horizontal streaks are formed on the image. And gloss streaks (gloss unevenness) occur and the image quality deteriorates. Therefore, it is preferable to separate the rollers during standby as in this embodiment.

  Further, as described above, the fixing device 100 fixes the toner image formed on the recording material P in the image forming unit to the recording material P. That is, as shown in FIG. 2, the recording material P carrying the toner K is conveyed in the direction of the arrow and introduced into the fixing nip portion N1. The recording material P is heated and pressurized by passing through the fixing nip portion N1, and the toner K is fixed to the recording material P. At this time, the portions where the recording material P is deprived of heat at the fixing nip portion N1 on the surface of the fixing roller 101 and the pressure roller 102 are the amount of heat from the halogen heaters 111 and 112 and the external heat roller 103 to the outside. It is heated by the heating nip portion N2 and rises to a predetermined temperature. Thereafter, the fixing operation is performed by repeatedly applying heat to the recording material P at the fixing nip portion N1.

  On the other hand, the portion of the external heating roller 103 where the heat is taken by the fixing roller 101 at the external heating nip portion N2 is heated by the amount of heat from the halogen heater 113 and rises to a predetermined temperature. Thereafter, the fixing operation is performed by repeatedly applying heat to the fixing roller 101 at the external heating nip portion N2.

  Next, a thermistor as temperature detecting means for detecting the surface temperatures of the fixing roller 101, the pressure roller 102, and the external heating roller 103 will be described.

  The image forming apparatus of the present embodiment is a center reference sheet.

  As shown in FIG. 3, the thermistors 121a, 122a, 123a that detect the surface temperature of each roller are arranged at least in the paper passing area of the minimum size paper of each roller, or in the corresponding part of the paper passing area. Each of the thermistors is disposed at a substantially central portion in the width direction of each roller. However, the thermistor may be separated from the substantially central portion in the width direction as long as it is within the range of the minimum size paper width or the range corresponding to the minimum size paper width. It may be arranged at a different position. Since the minimum size paper in this embodiment is A5 length (width 148.5 mm), the thermistors 121a, 122a, 123a are arranged within the width of 74.25 mm on both the left and right sides from the center.

  The thermistors 121a, 122a, 123a detect the surface temperature of each roller in the paper passing area and the paper passing area corresponding portion, and the temperature control means 130 sets each roller to a predetermined target temperature based on these temperature information. The temperature control thermistor controls the halogen heaters 111, 112, and 113 to be turned on and off by controlling the heating source control unit 140 so as to be maintained.

  The thermistor 121a preferably detects the temperature immediately before the fixing nip portion N1 of the fixing roller 101 in order to keep the fixing property constant. In the present embodiment, the thermistor 121a is referred to as a fixing main thermistor 121a.

  Similarly, the thermistor 122a preferably detects the temperature immediately before the fixing nip portion N1 of the pressure roller 102 in order to keep the fixing property constant. In the present embodiment, the thermistor 122a is referred to as a pressurized main thermistor 122a. In the present embodiment, the thermistor 123a is referred to as an external heating main thermistor 123a.

  As shown in FIG. 3, the thermistors 121b, 122b, and 123b that detect the surface temperature of each roller are arranged at least in the non-image area of the maximum size paper of each roller, or in a corresponding portion of the non-image area. More preferably, each roller is disposed in a non-sheet passing area of the maximum size sheet or a portion corresponding to the non-sheet passing area. The maximum size paper of this embodiment is 13 × 19 inch paper (width 330 mm), and the maximum image area is width 320 mm. Therefore, in each roller, at least from the center to the left and right sides of 160 mm, more preferably at the center. Thermistors 121b, 122b, 123b are arranged outside 165 mm on both the left and right sides. In the present embodiment, the thermistors 121b, 122b, and 123b are arranged outside 165 mm on both the left and right sides from the center so that toner and paper dust do not adhere.

  The thermistors 121b, 122b, and 123b are temperature detection thermistors that detect the temperature of the non-sheet-passing area of each roller or the non-sheet-passing area corresponding portion, or detect the temperature of each roller as a safety device.

  The thermistor 121b has a sub role with respect to the fixing main thermistor 121a for temperature adjustment. Therefore, in the present embodiment, the thermistor 121b is referred to as a fixing sub-thermistor 121b.

  Similarly, the thermistor 122b is referred to as a pressure sub-thermistor 122a in this embodiment because of its subordinate role with respect to the temperature-adjusting pressure main thermistor 122a.

  Similarly, the thermistor 123b is referred to as an external heating sub-thermistor 123b in the present embodiment because of the sub role of the temperature adjustment external heating main thermistor 123a.

  The fixing main thermistor 121a and the pressure main thermistor 122a employ a non-contact type thermistor so that the fixing roller 101 and the pressure roller 102 are scratched, and streaks and gloss unevenness do not occur in the image. Is more preferred.

  Since the fixing sub-thermistor 121b and the pressure sub-thermistor 122b are at least non-image areas of the fixing roller 101 and the pressure roller 102, either a non-contact type or a contact type thermistor may be employed.

  Since the external heating main thermistor 123a and the external heating sub-thermistor 123b have a very high target temperature of the external heating roller 103 and cannot use a non-contact type thermistor having low heat resistance, a contact type thermistor is used. Is common.

<Temperature control of external heating member>
Next, temperature control of the external heating member will be described using the flowchart of FIG.

  In this embodiment, in the temperature control of the external heating roller 103, the temperature is adjusted to the target temperature by the main thermistor 123a, and the detected temperature of the sub-thermistor 123b is higher than the target temperature and lower than the high temperature error temperature and detects a predetermined temperature or higher. In this case, the target temperature of the main thermistor 123a is reduced or the heater 113 is turned off to reduce the occurrence of a high temperature error.

  FIG. 4 shows an example of temperature control of the external heating roller 103 as an external heating member.

  As shown in FIG. 4, when the power of the image forming apparatus is turned on (S1), temperature control of the external heating roller 103 is started (S2).

  When the power of the image forming apparatus is turned on, it is in a state of startup (warm-up), standby, printing, etc., and the target temperature of the external heating roller 103 is set in each state. In this embodiment, for example, the target temperature of the external heating roller 103 is set to 220 ° C., the detected temperature of the main thermistor 123 a is input to the temperature control unit 130, and the heater 113 is controlled to be turned on / off by the heating source control unit 140. Then, the surface temperature of the external heating roller 103 is maintained at 220 ° C. (S3).

  The sub-thermistor 123 b always detects the end temperature of the external heating roller 103 and inputs it to the temperature control means 130. Therefore, the temperature control means 130 always monitors the detected temperature of the sub-thermistor 123b with respect to the threshold value: 230 ° C. (S4). Normally, when toner or paper dust is not attached to the main thermistor 123a, the detection temperature of the sub-thermistor 123b is less than 230 ° C. (NO in S4), and when the temperature control of the external heating roller 103 is continued ( NO in S5), the temperature is adjusted by the main thermistor 123a, and the target temperature of the external heating roller 103 is maintained at 220 ° C.

  Here, when the recording material P is passed through the fixing nip N between the fixing roller 101 and the pressure roller 102, the recording material P is deprived of heat in the non-sheet passing area between the fixing roller 101 and the pressure roller 102. As a result, the temperature rises. As the temperature of the non-sheet passing area of the fixing roller 101 rises, the temperature of the non-sheet passing area corresponding portion of the external heating roller 103 also rises slightly, but even if it rises, it is about 225 ° C., and the detected temperature of the sub-thermistor 123a is 230. It is less than ℃.

  When the temperature control of the external heating roller 103 is finished (YES in S5), for example, when the power of the image forming apparatus is turned off or when the standby state of the image forming apparatus has exceeded a predetermined time, the heater 113 Is OFF, and the image forming apparatus shifts to the sleeve state (S13).

  On the other hand, when the durability of the image forming apparatus advances and toner or paper dust adheres to the main thermistor 123a, the actual temperature of the external heating roller 103 rises to a target temperature of 220 ° C. or higher, and the sub-thermistor 123b becomes 230. When it is detected that the temperature is higher than or equal to ° C. (YES in S4), the temperature control means 130 changes the target temperature of the external heating roller 103 to 215 ° C. so as to be, for example, “target temperature −5 ° C.” The heater 113 is ON / OFF controlled so that the detected temperature becomes 215 ° C. (S6).

  Next, the temperature control unit 130 monitors the detected temperature of the sub-thermistor 123b with respect to the threshold value: 235 ° C. (S7). When the detected temperature of the sub-thermistor 123b is lower than 235 ° C. (NO in S7) and when the temperature control of the external heating roller 103 is continued (NO in S8), the detected temperature of the sub-thermistor 123b with respect to the threshold value: 230 ° C. Is also monitored (S4).

  Then, the target temperature of the external heating roller 103 is changed from 220 ° C. to 215 ° C. (S6), and the actual temperature of the external heating roller 103 decreases, so that the detected temperature of the sub-thermistor 123b becomes less than 230 ° C. again. In the case (NO in S4), the target temperature of the external heating roller 103 is returned to the original 220 ° C. (S3).

  On the other hand, even if the target temperature of the external heating roller 103 is changed from 220 ° C. to 215 ° C. (S6) and the actual temperature of the external heating roller 103 is decreased, the main thermistor 123a is greatly contaminated with toner and paper dust. When the detected temperature of the thermistor 123b is 230 ° C. or higher, the target temperature of the external heating roller 103 is maintained at 215 ° C. (S6).

  When the detected temperature of the sub-thermistor 123b is detected to be 230 ° C. or higher and again becomes lower than 230 ° C., the actual temperature of the external heating roller 103 is reduced by lowering the target temperature of the external heating roller 103 by the above temperature control. For example, or when the actual temperature of the external heating roller 103 decreases due to, for example, toner or paper dust adhering to the main thermistor 123a being accidentally peeled off and removed from the main thermistor 123a. Etc.

  When the durability of the image forming apparatus further advances and toner or paper dust adheres to the main thermistor 123a, the actual temperature of the external heating roller 103 further increases, and the sub-thermistor 123b exceeds 235 ° C. If detected (YES in S7), the temperature control unit 130 controls the heating source control unit 140 to turn off the heater 113 (S9).

  Next, the temperature control unit 130 monitors the detected temperature of the sub-thermistor 123b with respect to the threshold value: 240 ° C. (S10). When the detected temperature of the sub-thermistor 123b is less than 240 ° C. (NO in S10) and when the temperature control of the external heating roller 103 is continued (NO in S11), the detected temperature of the sub-thermistor 123b with respect to the threshold value: 235 ° C. Is also monitored (S7).

  When the heater 113 is turned off (S9) and the detected temperature of the sub-thermistor 123b becomes lower than 235 ° C. again due to a decrease in the actual temperature of the external heating roller (NO in S7), the external heating roller The target temperature of 103 is returned to the original 215 ° C. (S6), and the heater 113 is ON / OFF controlled. Accordingly, the S9 control is a control aspect in which the temperature is adjusted so that the detected temperature of the sub-thermistor 123b is 235 ° C.

  Next, when the actual temperature of the external heating roller 103 rises and the sub-thermistor 123b detects 240 ° C. or higher (YES in S10), the image forming apparatus is stopped as a high temperature error (abnormally high temperature), and the image A high temperature error is displayed on the forming apparatus (S12).

  The high temperature error is detected when the main thermistor 123a and the sub thermistor 123b detect 240 ° C. or more, for example, when an abnormality such as a heater runaway occurs and the temperature of the external heating roller 103 becomes abnormally high. The image forming apparatus is stopped. The heater runaway is, for example, that the heater is turned on and the external heating roller 103 becomes abnormally high temperature even though the temperature control means 130 instructs the heating source control means 140 to turn off the heater 113. It is a phenomenon that ends up.

  The reason why the high temperature error temperature is set to 240 ° C. in this embodiment is that the heat resistance temperature of the thermistor is 250 ° C.

  The temperature control of the external heating roller 103 is basically always performed while the image forming apparatus power is on, and the temperature control of the external heating roller 103 ends when the image forming apparatus power is off. The same applies to other rollers that control the temperature of the fixing device 100.

  Conventionally, a high temperature error of the sub-thermistor 123b due to contamination of toner or paper dust of the main thermistor 123a has occurred, causing a problem that the image forming apparatus stops. According to the present embodiment, the occurrence of such a high temperature error can be reduced, and the occurrence frequency of a problem that stops the image forming apparatus can be reduced. Accordingly, the main body can be stopped by detecting a high temperature error only at the time of a true abnormality such as when the heater 113 runs away.

  In the present embodiment, the sub-thermistor 123b is disposed at the end of the external heating roller 103 corresponding to the non-sheet passing area of the fixing roller 101 and the pressure roller 102. Since there is almost no adhesion, the temperature of the external heating roller 103 can always be accurately detected even in durability. Therefore, it is preferable to use the sub-thermistor 123b for temperature control of the present embodiment by monitoring the temperature of the external heating roller 103.

  Further, the sub-thermistor 123b may be disposed at the end of the external heating roller 103 corresponding to at least the non-image area of the fixing roller 101 and the pressure roller 102. This is because toner hardly adheres to the sub-thermistor 123b, and even if paper dust adheres to the sub-thermistor 123b, there is no adhesive like toner. Is easily peeled off, so that paper dust hardly accumulates. Therefore, even in such a case, it is preferable to use the sub-thermistor 123b for temperature control of the present embodiment by monitoring the temperature of the external heating roller 103.

  In the present embodiment, the control for lowering the target temperature of the external heating roller 103 (S4 and S6) and the control for turning off the heater 113 (S7 and S9) are used at two predetermined temperatures. Even if only the control for lowering the target temperature of the roller 103 (S4 and S6) or only the heater OFF control (S7 and S9), the occurrence of a high temperature error can be reduced and the problem of stopping the image forming apparatus occurs. The frequency can be reduced.

  Further, the control for lowering the target temperature of the external heating roller 103 or the control for turning off the heater 113 is control that operates when the actual temperature of the external heating roller 103 rises above the target temperature. Since there is no change in the target temperature, the surface temperature of the fixing roller 101 during printing is maintained at the target temperature of the fixing roller 101, so that there is no adverse effect such as a decrease in fixability and hot offset due to toner overmelting. This is because, during printing, when the actual temperature of the external heating roller 103 rises and the amount of heat supplied from the external heating roller 103 to the fixing roller 101 increases, the heater 111 is less lit. The surface temperature is kept constant.

  In this embodiment, a halogen heater is used as a heating source. However, the effect of the present invention is the same regardless of whether an electromagnetic induction heating or a resistance heating element is selected or an arbitrary heating source is selected in the fixing device configuration. .

  In the present embodiment, the temperature detection element of the external heating roller is limited to a contact type thermistor. However, depending on the fixing device, a non-contact type thermistor can be used that satisfies heat resistance, and a non-contact type thermistor. Even if the thermistor of this type is configured such that toner, paper dust, wax contained in the toner adheres, the temperature cannot be detected accurately, and the actual temperature of the external heating roller rises, The effect of the present invention is the same in a contact type thermistor.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIGS.

  Although the first embodiment has one external heating member, the second embodiment will be described with respect to a case where there are a plurality of external heating members.

<Fixing device>
The fixing device 100 of this embodiment will be described.

  As shown in FIG. 5, in the fixing device 100, a fixing roller 101 as a fixing member and a pressure roller 102 as a pressure member are the same as those in FIG. 2 of the first embodiment. Unlike the first embodiment shown in FIG. 2, two external heating members, an external heating roller 103 and an external heating roller 104, are arranged.

  The configuration and temperature adjustment of the fixing roller 101, the pressure roller 102, and the external heating roller 103 shown in FIG. 5 are the same as those of the first embodiment shown in FIG.

  The two external heating rollers 103 and 104 abut on the fixing roller 101 to obtain an external heating nip width that is approximately twice that of the external heating nip portion N2 (about 5 mm) and the external heating nip portion N3 (about 5 mm). As a result, the external heating performance is improved.

  By improving the external heating performance, a decrease in the surface temperature of the fixing roller 101 during paper passing can be reduced and the surface temperature of the fixing roller 101 can be maintained at a high temperature, so that the fixability is improved.

Therefore, by improving the fixability, it is possible to increase the productivity by increasing the speed of the image forming apparatus, or it is possible to increase the basis weight of the recording material that can be fixed. For example, even if the fixing roller 101 is rotationally driven at a peripheral speed of 300 mm / sec to 350 mm / sec and A4 (horizontal) is changed from 70 ppm to 80 ppm, printing is possible. Alternatively, for example, the fixing roller 101 is rotationally driven at a peripheral speed of 300 mm / sec and A4 (horizontal) remains at 70 ppm, but the upper limit of the basis weight of the printable recording material is 250 g / m ² to 300 g / It has the advantage that it can be expanded to m ² .

  Note that the external heating roller 103 and the external heating roller 104 of the present embodiment have the same configuration and the same temperature adjustment.

  Therefore, 124a for detecting the surface temperature of the external heating roller 104 is disposed at least in the portion corresponding to the sheet passing area of the minimum size paper, and is disposed at a substantially central portion in the width direction of the external heating roller 104. As long as it is within the corresponding range, it may be arranged at a position deviating from the substantially central portion in the width direction. Since the minimum size paper in this embodiment is A5 length (width 148.5 mm), the thermistor 124a is disposed within the width of 74.25 mm on both the left and right sides from the center.

  The thermistor 124a detects the surface temperature of the portion corresponding to the sheet passing area of the external heating roller 104, and the temperature control means 130 performs heating so as to maintain the external heating roller 104 at a predetermined target temperature based on this temperature information. The temperature control thermistor controls the halogen heater 114 on / off by controlling the source control means 140.

  In the present embodiment, the thermistor 124a is referred to as an external heating main thermistor 124a.

  The thermistor 124b that detects the surface temperature of the external heating roller 104 is disposed at least in the non-image area corresponding portion of the maximum size paper. More preferably, the external heating roller 104 is disposed at the portion corresponding to the non-sheet passing area of the maximum size paper. The maximum size paper of this embodiment is 13 × 19 inch paper (width 330 mm), and the maximum image area is width 320 mm. Therefore, in each roller, at least from the center to the left and right sides of 160 mm, more preferably at the center. Thermistor 124b is disposed outside 165 mm on both right and left sides. In the present embodiment, the thermistor 124b is disposed outside the right and left sides of 165 mm from the center so that toner and paper dust do not adhere.

  The thermistor 124b is a temperature detection thermistor that detects the temperature of the part corresponding to the non-sheet passing region of the external heating roller 104, or detects the temperature of the external heating roller 104 as a safety device.

  In the present embodiment, the thermistor 124b is referred to as an external heating sub-thermistor 124b because the thermistor 124b has a sub role with respect to the external heating main thermistor 124a for temperature adjustment.

  As the external heating main thermistor 124a and the external heating sub-thermistor 124b, since the target temperature of the external heating roller 104 is very high, a non-contact type thermistor having low heat resistance cannot be used. Therefore, a contact type thermistor is used. Is common.

<Temperature control of external heating member>
Next, temperature control of the external heating member will be described.

  In the first embodiment, the temperature control of the external heating roller 103 shown in FIG. 2 has been described with reference to the flowchart of FIG.

  The temperature control of the external heating roller 103 and the temperature control of the external heating roller 104 shown in FIG. 5 of the present embodiment are the same as those in the flowchart of FIG.

  In the present embodiment, the temperature control of the external heating roller 103 and the temperature control of the external heating roller 104 are controlled independently.

  Therefore, due to the difference in the adhesion state of the toner and paper dust of the main thermistors 123a and 124a, for example, one target temperature is 220 ° C., the other target temperature is 215 ° C., and the target temperature is different. In addition, for example, a situation occurs in which one target temperature is 220 ° C. and the other heater is turned off.

  In the fixing device using a plurality of external heating members as in the present embodiment, conventionally, a high temperature error of the sub-thermistors 123b and 124b due to contamination of toner and paper dust of the main thermistors 123a and 124a has occurred. There was a problem that would stop. According to the present embodiment, the occurrence of such a high temperature error can be reduced, and the occurrence frequency of a problem that stops the image forming apparatus can be reduced. Therefore, the main body can be stopped by detecting a high temperature error only at the time of a true abnormality such as when the heater 113 and the heater 114 run away.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIGS.

  Although the first and second embodiments have been described with respect to the external heating roller as the external heating member, the third embodiment will be described with respect to the external heating belt as the external heating member.

<Fixing device>
The fixing device 100 of this embodiment will be described.

  The fixing device 100 shown in FIG. 6 has a configuration in which the external heating rollers 103 and 104 shown in FIG. 5 of the second embodiment are used as heating support rollers, and an external heating belt 105 is stretched around the heating support rollers.

  Therefore, the fixing roller 101 as the fixing member, the pressure roller 102 as the pressure member, and the heating support rollers 103 and 104 shown in FIG. 6 are the same as the fixing roller 101 and the pressure roller shown in FIG. 5 of the second embodiment. 102 and the external heating rollers 103 and 104, the description thereof will be omitted.

  As shown in FIG. 6, the external heating belt 105 as an external heating member is stretched around the heating support rollers 103 and 104 and is brought into contact with the fixing roller 101.

  When the external heating belt 105 comes into contact with the fixing roller 101, the external heating nip portion N4 becomes about 30 mm, and the external heating nip width is about three times as large as about 10 mm (about 5 mm + about 5 mm) of the external heating nip portion in FIG. Since it can be obtained, the external heating performance is improved.

By improving the external heating performance, the productivity can be increased by increasing the speed of the image forming apparatus, or the basis weight of the recording material that can be fixed can be increased. For example, printing can be performed even if the fixing roller 101 is speeded up at a peripheral rotational speed of 350 mm / sec to 400 mm / sec and A4 (horizontal) is changed from 80 ppm to 90 ppm. Alternatively, for example, the fixing roller 101 is rotationally driven at a peripheral speed of 300 mm / sec and A4 (horizontal) remains at 70 ppm, but the basis weight upper limit of the printable recording material is from 300 g / m ² to 350 g. It has the advantage that it can be expanded to / m ² .

  The external heating belt 105 is, for example, a 15 μm fluororesin (for example, PFA coat) as a heat-resistant release layer on a polyimide base layer having an inner diameter of 52 mm and a thickness of 90 μm, for example, in order to improve releasability from the toner. Is covered.

  The external heating belt 105 is stretched around the heating support rollers 103 and 104, and the heating support rollers 103 and 104 are pressed against the fixing roller 101 with a predetermined pressure by a pressing unit (not shown). Then, an external heating nip portion N4 is formed between the external heating belt 105 and the fixing roller 101. The external heating belt 105 rotates following the direction of the arrow with respect to the fixing roller 101. The circumferential width of the external heating nip portion N4 is, for example, about 30 mm.

As shown in FIG. 6, halogen heaters 113 and 114 with a rated power of 800 W, for example, that generate heat when energized are disposed as heating sources inside the heating support rollers 103 and 104. And it heats from the inside so that the surface temperature of the external heating belt 105 may become a predetermined target temperature. As shown in FIG. 6, the surface temperature of the external heating belt is detected by thermistors 123a and 124a which are temperature detecting means described later. The thermistors 123a and 124a also function as a safety device, and are arranged so as to detect the surface temperature of each part of the external heating belt that contacts the heating support rollers 103 and 104.
Then, the temperature control means 130 controls the heating source control means 140 based on the detected temperature information of the thermistors 123a and 124a, thereby controlling the halogen heaters 113 and 114 to be ON / OFF respectively. The temperature is controlled to a target temperature, for example, 220 ° C.

  The thermistors 123a and 124a for detecting the surface temperature of the external heating belt 105 are disposed at least at the corresponding portion of the minimum size paper passing area and are disposed at the substantially central portion in the width direction of the heating support rollers 103 and 104. As long as it is within the range corresponding to the size paper width, it may be arranged at a position deviating from the substantially central portion in the width direction. Since the minimum size paper in this embodiment is A5 length (width 148.5 mm), the thermistors 123a and 124a are disposed within the width of 74.25 mm on both the left and right sides from the center.

  The thermistors 123a and 124a detect the surface temperature of the portion corresponding to the sheet passing area of the external heating belt 105, and the temperature control means 130 maintains the external heating belt 105 at a predetermined target temperature based on this temperature information. The temperature control thermistor controls each of the halogen heaters 113 and 114 by controlling the heating source control means 140.

  In the present embodiment, the thermistors 123a and 124a are referred to as external heating main thermistors 123a and 124a.

  The thermistors 123b and 124b that detect the surface temperature of the external heating belt 105 are disposed at least in the non-image area corresponding portion of the maximum size paper. More preferably, the external heating belt 105 is disposed at the portion corresponding to the non-sheet passing area of the maximum size paper. The maximum size paper of this embodiment is 13 × 19 inch paper (width 330 mm), and the maximum image area is 320 mm wide, so at least in each part of the external heating belt 105 that contacts the heating support rollers 103 and 104. Thermistors 123b and 124b are arranged outside the 160 mm from the center on both the left and right sides, more preferably outside the 165 mm from the center on both the left and right sides. In the present embodiment, the thermistors 123b and 124b are arranged outside 165 mm on both the left and right sides from the center so that toner and paper dust do not adhere.

  The thermistors 123b and 124b are temperature detection thermistors that detect the temperature of the part corresponding to the non-sheet-passing region of the external heating belt 105, or detect the temperature of the external heating belt 105 as a safety device.

  The thermistors 123b and 124b have sub-functions with respect to the external heating main thermistors 123a and 124a for temperature adjustment. In the present embodiment, the thermistors 123b and 124b are referred to as external heating sub-thermistors 123b and 124b.

  Since the external heating main thermistors 123a and 124a and the external heating sub-thermistors 123b and 124b have a very high target temperature of the external heating belt 105, a non-contact type thermistor having low heat resistance cannot be adopted. Is generally adopted.

<Temperature control of external heating member>
Next, temperature control of the external heating member will be described.
In the second embodiment, the temperature control of the external heating rollers 103 and 104 shown in FIG. 5 has been described with reference to the flowchart of FIG.

  The temperature control of the external heating belt 105 shown in FIG. 6 of the present embodiment is also the same as the flowchart of FIG.

  In the present embodiment, the temperature control of the heating support roller 103 and the temperature control of the heating support roller 104 are controlled independently.

  Therefore, due to the difference in the adhesion state of the toner and paper dust of the main thermistors 123a and 124a, for example, one target temperature is 220 ° C., the other target temperature is 215 ° C., and the target temperature is different. In addition, for example, a situation occurs in which one target temperature is 220 ° C. and the other heater is turned off.

  Even in the fixing device using the external heating belt as in the present embodiment, conventionally, there has been a high temperature error in the sub-thermistors 123b and 124b due to contamination of toner and paper dust in the main thermistors 123a and 124a, and the image forming apparatus is stopped. There was a problem of doing. According to the present embodiment, the occurrence of such a high temperature error can be reduced, and the occurrence frequency of a problem that stops the image forming apparatus can be reduced. Therefore, the main body can be stopped by detecting a high temperature error only at the time of a true abnormality such as when the heater 113 and the heater 114 run away.

  Further, in the present embodiment, the description has been given using the heating support roller having both of the heating sources as the two supporting rollers of the external heating belt 105. However, for example, the heating having only one supporting roller has the heating source. Even if the present invention is applied as a support roller and the other one is a support roller without a heating source, the effect of reducing the occurrence of a high temperature error in the external heating member is the same.

The numerical values and schematic diagrams in each of the above-described embodiments are examples for simplifying the description, and can be arbitrarily determined according to the configuration and settings of the image forming apparatus and the fixing apparatus.
Further, the present invention is not limited to the fixing device described in each embodiment, and can be applied to other types of fixing devices such as any combination of the embodiments.

  In the above-described embodiment, when the external heating sub-thermistor detects a predetermined temperature, the temperature control for changing the target temperature of the external heating member and the heat source control for turning off the external heating source are combined. As described above, only one of the controls has an effect of reducing the occurrence of a high temperature error of the external heating member.

  In this embodiment, the halogen heater is used as the heating source. However, the effect of the present invention is equivalent to a fixing device using another heating source such as a resistance heating element or an electromagnetic induction heating method. .

DESCRIPTION OF SYMBOLS 100 ... Fixing device, 101 ... Fixing member (for example, fixing roller), 102 ... Pressure member (for example, pressure roller), 103 ... External heating member (for example, external heating roller, or heating support roller) ), 104... External heating member (for example, external heating roller or heating support roller), 105... External heating belt, 111/112/113/114... Halogen heater (heating source), 121/122 / 123/124 ... thermistor (temperature detection means), 130 ... temperature control means (for example, CPU), 140 ... heating source control means (for example, heater drive circuit), P ... recording material, K ... Toner, N1... Nip between fixing member and pressure member, N2 / N3 / N4... Nip between external heating member and fixing member

Claims (6)

A fixing member including the heating source 1, an external heating member including the heating source 2 and contacting the outer peripheral surface of the fixing member to heat the fixing member, and a pressure member.
A temperature detecting element 1 for detecting the temperature of the sheet passing area at the center of the fixing member surface, and a contact-type temperature detecting element for detecting the temperature at the center of the surface of the external heating member (the part corresponding to the sheet passing area of the fixing member) 2 and a contact-type temperature detection element 3 that detects the temperature of a substantially end portion of the surface of the external heating member (a portion corresponding to a non-sheet passing region or a non-image region of the fixing member),
By controlling the heating source 1 of the fixing member according to the detected temperature of the temperature detecting element 1, temperature adjustment is performed so that the surface temperature of the fixing member is maintained at the target temperature 1.
By controlling the heating source 2 of the external heating member according to the detection temperature of the temperature detection element 2, temperature adjustment is performed so as to maintain the surface temperature of the external heating member at the target temperature 2.
In a fixing device for fixing an image on a recording material by passing a recording material carrying an unfixed image through a pressure contact portion between the fixing member and the pressure member,
When the temperature detection element 2 and the temperature detection element 3 detect a predetermined temperature 1 or higher that is higher than the target temperature 2, it is considered that an abnormally high temperature has been detected, and image formation of the image forming apparatus is stopped. `` High temperature error '' is displayed,
When the temperature detection element 3 detects a predetermined temperature 2 higher than the target temperature 2 and lower than the predetermined temperature 1, it has a temperature control means for reducing the target temperature 2 of the external heating member. A fixing device. A fixing member including the heating source 1, an external heating member including the heating source 2 and contacting the outer peripheral surface of the fixing member to heat the fixing member, and a pressure member.
A temperature detecting element 1 for detecting the temperature of the sheet passing area at the center of the fixing member surface, and a contact-type temperature detecting element for detecting the temperature at the center of the surface of the external heating member (the part corresponding to the sheet passing area of the fixing member) 2 and a contact-type temperature detection element 3 that detects the temperature of a substantially end portion of the surface of the external heating member (a portion corresponding to a non-sheet passing region or a non-image region of the fixing member),
By controlling the heating source 1 of the fixing member according to the detected temperature of the temperature detecting element 1, temperature adjustment is performed so that the surface temperature of the fixing member is maintained at the target temperature 1.
By controlling the heating source 2 of the external heating member according to the detection temperature of the temperature detection element 2, temperature adjustment is performed so as to maintain the surface temperature of the external heating member at the target temperature 2.
In a fixing device for fixing an image on a recording material by passing a recording material carrying an unfixed image through a pressure contact portion between the fixing member and the pressure member,
When the temperature detection element 2 and the temperature detection element 3 detect a predetermined temperature 1 or higher that is higher than the target temperature 2, it is considered that an abnormally high temperature has been detected, and image formation of the image forming apparatus is stopped. `` High temperature error '' is displayed,
When the temperature detecting element 3 detects a predetermined temperature 3 higher than the target temperature 2 and lower than the predetermined temperature 1, it has a heating source control means for turning off the heating source 2 of the external heating member. A fixing device characterized.   After the temperature detection element 3 of the external heating member detects the predetermined temperature 2 or higher, or the predetermined temperature 3 or higher and changes the temperature control or heating source control of the external heating member, the temperature detection element 3 of the external heating member When the temperature of less than the predetermined temperature 2 or less than the predetermined temperature 3 is detected, the temperature control of the external heating member or the heating source control is returned to the original state. Fixing device.   4. The device according to claim 1, wherein when there are a plurality of external heating members, the temperature control or the heating source control is performed independently for each external heating member. 5. Fixing device.   The fixing device according to any one of claims 1 to 4, wherein the external heating member is an external heating roller or an external heating belt.   An image forming apparatus comprising the fixing device according to claim 1.