JP2012022045A - Fixing device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption by suppressing the surface temperature of a fixing rotating body from being increased unnecessarily, without deteriorating the fixability of a toner image to paper.SOLUTION: The energization of halogen heaters H1 and H2 is independently controlled based on the detected temperatures of temperature sensors 2a and 2b arranged in the central portion and end portion of a fixing roller 11 in its rotational axial direction and the surface temperatures of the central portion and both end portions of the fixing roller 11 in its rotational axial direction are kept at predetermined set temperatures. The initial set temperatures of the central portion and end portion of the fixing roller 11 in its rotational axial direction are made T1. When the surface temperature of a pressure roller 12 reaches TA1, the set temperature of the end portion of the fixing roller 11 in its rotational axial direction is decreased to "T1-t".

Description

  In the present invention, an unfixed toner image on a transfer member is heated and applied by passing the transfer member through a nip portion formed by press contact between a fixing rotator heated by a heat source and a pressure rotator. The present invention relates to a fixing device that melts and fixes to a member to be transferred and an image forming apparatus including the same.

  As a fixing device used in an image forming apparatus such as a facsimile, a printer, and a copying machine, a fixing device in which a fixing roller heated by a heat source such as a halogen heater and a pressure roller is pressed is widely used. . In such a fixing device, the temperature of the fixing roller is detected by a temperature sensor, and energization to the heat source is controlled so that the fixing roller maintains a predetermined temperature.

  In addition, when a small-sized sheet passes, there is a difference in the surface temperature of the fixing roller between the area where the sheet passes and the area where the sheet does not pass. The area is divided and the surface temperature of the fixing roller is made uniform in the direction of the rotation axis.

  Further, in Patent Document 1, when a temperature sensor is provided in a non-sheet-passing area, the surface temperature of the sheet-passing area cannot be detected with high accuracy and the surface temperature of the sheet-passing area is excessively reduced. A technique has been proposed in which the fixing roller is set at a higher temperature as the formation time is longer.

Japanese Patent Laid-Open No. 2002-148999

  However, in the proposed technique, when the paper is thin or the temperature inside the apparatus is high, the surface temperature of the fixing roller may become higher than necessary.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to suppress an unnecessarily increase in the surface temperature of the fixing roller without deteriorating the fixing property of the toner image onto the paper. An object of the present invention is to provide a fixing device that can reduce power consumption.

  The present inventor has made extensive studies to achieve the above object. Normally, the nip width between the fixing roller and the pressure roller is longer at both ends than at the central portion in the rotation axis direction. If the temperature is uniform in the direction of the rotation axis, the knowledge that the fixing property of the toner image to the paper is higher at both ends than at the center in the direction of the rotation axis has been obtained, and the present invention has been made. That is, a fixing device according to the present invention includes a fixing rotator, a pressure rotator that presses against the fixing rotator to form a nip portion, a central portion in the rotational axis direction of the fixing rotator, and both end portions in the rotational axis direction. A first heat source and a second heat source, a first temperature detecting means and a second temperature detecting means for detecting a surface temperature of a central portion and an end portion in the rotation axis direction of the fixing rotating body, a first temperature detecting means, A fixing device including control means for controlling energization to the first heat source and the second heat source based on the temperature detected by the second temperature detecting means and maintaining the surface of the fixing rotating body at a predetermined set temperature; And a third temperature detecting means for detecting a surface temperature of the pressurizing rotating body, wherein the set temperature of the end of the fixing rotating body is changed based on the temperature detected by the third temperature detecting means. To do.

  Here, when the detected temperature of the third temperature detecting means rises and reaches a preset temperature, it is preferable to lower the set temperature at the end of the fixing rotator from the initial set temperature.

  Moreover, it is preferable that a 3rd temperature detection means detects the surface temperature of the axial direction center part of the said pressurization rotary body.

  Further, according to the present invention, the fixing rotator, the pressure rotator that presses against the fixing rotator to form a nip portion, and the center and both ends of the fixing rotator in the rotation axis direction are heated. A heat source, a second heat source, a first temperature detecting means and a second temperature detecting means for detecting a surface temperature of a central portion and an end of the fixing rotating body in a rotation axis direction; a first temperature detecting means and a second temperature detecting means; And a controller that controls the energization of the first heat source and the second heat source based on the detected temperature of the first heat source and maintains the surface of the fixing rotator at a predetermined set temperature. 4th temperature detection means and 5th temperature detection means which detect the surface temperature of the rotation-axis direction center part of a body, and an edge part are further provided, Based on the detected temperature difference of a 4th temperature detection means and a 5th temperature detection means And changing the set temperature at the end of the fixing rotator. A fixing device is provided to.

  Here, when the detected temperature difference between the fourth temperature detecting means and the fifth temperature detecting means becomes large and becomes a preset temperature difference, the set temperature of the end portion of the fixing rotator is lowered from the initial set temperature. Is preferred.

  Furthermore, according to the present invention, there is provided an image forming apparatus comprising any one of the fixing devices described above.

  According to the fixing device and the image forming apparatus of the present invention, it is possible to suppress an unnecessarily increase in the surface temperature of the fixing roller without deteriorating the fixability of the toner image to the paper, thereby reducing power consumption. it can.

1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 2 is a side sectional view of a fixing device used in the image forming apparatus of FIG. 1. FIG. 2 is a schematic front view of a fixing device used in the image forming apparatus of FIG. 1. It is a figure which shows the temperature control example of the conventional fixing device. FIG. 6 is a diagram illustrating a change with time in fixing strength in a conventional fixing device. It is a figure which shows the temperature control example of the fixing device which concerns on 1st invention. It is a figure which shows the other temperature control example of the fixing device which concerns on 1st invention. 6 is a flowchart illustrating an example of temperature control at an end of a fixing roller in a rotation axis direction. FIG. 6 is a schematic front view of a fixing device according to a second invention. It is a figure which shows the temperature control example of the fixing device which concerns on 2nd invention. FIG. 6 is a schematic view showing another embodiment of the fixing device according to the present invention.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus and a fixing device of the present invention. The image forming apparatus D in FIG. 1 is a so-called tandem color printer. Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. Further, the image forming method is not limited to the tandem method, and other methods, for example, four developing devices are arranged around the rotation shaft, and these are sequentially opposed to the electrostatic latent image carrier to be full color. A so-called four-cycle method of creating an image or a monochrome method of creating a monochrome image with one developing device may be used.

  The image forming apparatus D includes an endless intermediate transfer belt 40. The intermediate transfer belt 40 is hung by three rollers 41, 42, and 43 and rotates counterclockwise. A secondary transfer roller 44 is in pressure contact with the outside of the belt portion supported by the roller 41. The toner image formed on the intermediate transfer belt 40 at the nip portion (secondary transfer region) between the secondary transfer roller 44 and the intermediate transfer belt 40 is transferred to the conveyed paper P.

  A cleaning member 45 for cleaning the surface of the intermediate transfer belt 40 is provided outside the belt portion supported by the roller 43. The cleaning member 45 is in pressure contact with the roller 43 via the intermediate transfer belt 40 and collects untransferred toner at the contact portion.

  Below the intermediate transfer belt 40, four image forming units 3K, 3Y, black (K), yellow (Y), magenta (M), cyan (C) are sequentially formed from the upstream side in the rotation direction of the intermediate transfer belt 40. 3M and 3C (hereinafter may be collectively referred to as “image forming unit 3”) are arranged. In these image forming units 3, corresponding color toner images are created using the respective color developers.

  The image forming unit 3 includes a cylindrical photoreceptor 30 as an electrostatic latent image carrier. Around the photoconductor 30, a charger 31, an exposure device 32, a developing device 33, a primary transfer roller 34, and a photoconductor cleaning member 35 are arranged in this order along the rotation direction (clockwise direction). Yes. The primary transfer roller 34 is in pressure contact with the photoconductor 30 with the intermediate transfer belt 40 interposed therebetween to form a nip portion (primary transfer region). A control device 61 that controls the entire image forming apparatus D is disposed below the cleaning member 45. An exposure control device 62 is disposed below the image forming unit 3. An image signal is sent from the control device 61 to the exposure control device 62, and the exposure control device 62 controls each exposure device 32 to form an electrostatic latent image corresponding to each color on the photoreceptor 30.

  In the embodiment shown in this figure, a corona discharge charging charger is used as the charger 31, but the type of the charger 31 is not particularly limited, and a roller charging member, a blade-shaped charging member, Of course, a brush-like charging member or the like may be used. In this embodiment, a plate-like blade is used as the photosensitive member cleaning member 35, and one end thereof is brought into contact with the outer peripheral surface of the photosensitive member 30 to collect and remove the toner remaining on the surface of the photosensitive member 30. The photosensitive member cleaning member 35 is not limited to a plate blade, and for example, a fixed brush, a rotating brush, a roller, and a combination of these members can also be used. Note that the photoconductor cleaning member 35 is not necessarily provided, and a cleanerless system in which the untransferred toner on the photoconductor 30 is collected by the developing device 33 may be employed.

  A sheet feeding cassette 50 as a sheet feeding device is detachably attached to the apparatus main body below the exposure control device 62. The sheets (transferred members) P stacked and accommodated in the sheet feed cassette 50 are sent out one by one to the transport path in order from the top sheet by the rotation of the sheet feed roller 51 disposed on the upper side of the sheet feed cassette 50. . The paper P sent out from the paper feed cassette 50 is conveyed to the registration roller pair 52 and is sent out to the secondary transfer area at a predetermined timing.

  The image forming apparatus D can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners. .

  An image forming operation example in the color mode will be briefly described. First, in each image forming unit 3, the outer peripheral surface of the photoreceptor 30 that is rotationally driven at a predetermined peripheral speed is charged by the charger 31. Next, light corresponding to image information is projected from the exposure device 32 onto the charged surface of the photoconductor 30, and an electrostatic latent image is formed on the surface of the photoconductor 30. Subsequently, the electrostatic latent image is made visible by toner as a developer supplied from the developing device 33. When the toner images of the respective colors formed on the surface of the photoreceptor 30 in this manner reach the primary transfer region by the rotation of the photoreceptor 30, the toner image is transferred from the photoreceptor 30 to the intermediate transfer belt in the order of black, yellow, magenta, and cyan. 40 is transferred (primary transfer) and superimposed.

  Untransferred toner remaining on the photoreceptor 30 without being transferred to the intermediate transfer belt 40 is scraped off by the photoreceptor cleaning member 35 and removed from the outer peripheral surface of the photoreceptor 30.

  The superimposed four color toner images are conveyed to the secondary transfer region by the intermediate transfer belt 40. On the other hand, the paper P is conveyed from the registration roller pair 52 to the secondary transfer area in accordance with the timing. Then, the four color toner images are transferred (secondary transfer) from the intermediate transfer belt 40 to the paper P in the secondary transfer region. The paper P on which the four color toner images are transferred is conveyed to the fixing device 1. In the fixing device 1, the paper P passes through a nip portion N (shown in FIG. 2) between the fixing roller 11 and the pressure roller 12. During this time, the paper P is heated and pressurized, and the toner image on the paper P is melted and fixed on the paper P. A specific configuration of the fixing device 1 will be described later. The paper P on which the toner image is fixed is discharged to the paper discharge tray 53.

  On the other hand, the intermediate transfer belt 40 that has passed through the secondary transfer region is cleaned by a cleaning member 45, and is transported to a waste toner container (not shown) by a transport screw (not shown) and collected. Thereafter, the rotational drive of each photoconductor 30 and the intermediate transfer belt 40 is stopped.

  FIG. 2 is a side view showing a schematic configuration of the fixing device 1 mounted on the image forming apparatus of FIG. The fixing device 1 includes a fixing roller 11 and a pressure roller 12. The pressure roller 12 is pressed toward the fixing roller 11 by a pressing member (not shown) such as a spring, and a nip portion N is formed between the fixing roller 11 and the pressure roller 12. The fixing roller 11 is rotated counterclockwise in the figure by a rotation driving unit (not shown), and thereby the pressure roller 12 is driven to rotate clockwise.

  The fixing roller 11 includes a cored bar 111 formed in a cylindrical shape. And in the axial direction of the center part of the metal core 111, two halogen heaters H1 and H2 are provided as heat sources. The material of the metal core 111 is preferably a metal material such as aluminum or iron. The thickness is preferably in the range of 0.1 to 5 mm, and more preferably in the range of 0.2 to 1.5 mm in view of weight reduction and shortening of the warm-up time. Further, in order to improve the surface releasability, a tube made of a fluorine material such as PFA, PTFE, ETFE or the like is attached to the surface of the core metal 111, or a coating layer is formed with the fluorine material. It is good also as a surface layer. The thickness of the surface layer is preferably in the range of 5 to 100 μm. Further, the contact angle with water is preferably 90 degrees or more, more preferably 110 degrees. Furthermore, the surface roughness Ra is preferably in the range of 0.01 to 50 μm. Commercially available “PFA350-J”, “451HP-J”, and “951HP Plus” (all manufactured by Mitsui / DuPont Chemical) can be suitably used as the fluorine-based tube. In order to increase the width of the nip portion N, an elastic layer may be further provided between the core metal 111 and the surface layer. The material of the elastic layer is preferably a material having elasticity and heat resistance, and examples thereof include silicone rubber and fluorine rubber. Although there is no limitation in particular in the thickness of an elastic layer, Usually, the range of 0.05-2 mm is preferable.

  The pressure roller 12 is formed by forming an elastic layer 122 made of silicone rubber on the surface of a cylindrical cored bar 121 and attaching a PFA tube 123 as a surface layer to the surface. Note that suitable modes of the cored bar 121, the elastic layer 122, and the surface layer 123 are the same as those of the fixing roller 11.

  FIG. 3 is a front view showing a schematic configuration of the fixing device 1. A halogen heater H1 (first heat source) and a halogen heater H2 (second heat source) are disposed at the central portion and both ends of the central portion of the fixing roller in the rotational axis direction. The both ends of the fixing roller in the rotation axis direction are heated by the halogen heater H2. A temperature sensor (first temperature detection means) 2a and a temperature sensor (second temperature detection means) 2b are spaced apart from the surface of the fixing roller at a central portion and an outer peripheral portion of the end portion in the rotation axis direction of the fixing roller. It is arranged. A temperature sensor (third temperature detecting means) 2c is also disposed on the outer peripheral portion of the central portion in the rotation axis direction of the pressure roller 12 with a minute gap from the surface of the pressure roller.

  The control device 61 (shown in FIG. 1) independently energizes the halogen heaters H1 and H2 based on the detected temperatures of the temperature sensors 2a and 2b arranged at the center and the end of the fixing roller 11 in the rotation axis direction. Thus, the surface temperatures of the central portion and both ends of the fixing roller 11 in the rotation axis direction are respectively held at predetermined set temperatures. As shown in FIG. 2, the conveyed paper P has a nip portion N between the fixing roller 11 and the pressure roller 12 so that the surface on which the unfixed toner image t is placed is on the fixing roller 11 side. Pass through. While passing through the nip portion N, the toner image t is heated and pressurized, and the toner image t is melted and fixed on the paper P. Then, the paper P on which the toner image t is fixed is separated from the fixing roller 11 and discharged to a paper discharge tray 53 (shown in FIG. 1).

  The temperature sensors 2a, 2b, 2c used in the present invention may be the same or different. As the temperature sensors 2a, 2b, and 2c, a thermistor, a thermocouple, a platinum resistance temperature detector, an IC temperature sensor, a surf mobile, an NC sensor, or the like can be used.

  In the fixing device 1 having such a configuration, conventionally, the set temperatures of the central portion and the end portion in the rotation axis direction of the fixing roller are the same. FIG. 4 shows changes over time in the detected temperatures of the temperature sensors 2a, 2b, and 2c. When the temperature detected by the temperature sensors 2a and 2b reaches a predetermined temperature (fixing temperature), paper feeding is started and the fixing process is started. When the fixing process is started, the surface temperature of the pressure roller is temporarily decreased due to heat taken by the paper, but thereafter gradually increases due to heat transfer from the fixing roller. When the pressure roller reaches a specific temperature or higher, the fixing strength at the end portion in the rotation axis direction becomes higher than that at the central portion.

  FIG. 5 shows changes with time in fixing strength between the central portion and the end portion in the rotation axis direction. As can be understood from this figure, when continuous image formation is performed, heat is taken away by the paper passing through the fixing device, so that the fixing strength at the central portion and the end portion in the rotational axis direction is reduced at the initial stage of image formation. However, if the number of images formed exceeds a predetermined number, the heat supply from the halogen heaters H1 and H2 and the amount of heat taken by the paper are balanced, and the fixing strength in the central portion in the rotation axis direction is stabilized. On the other hand, the fixing strength at the end in the direction of the rotation axis is improved as the number of images formed increases. This is because, as described above, the nip width between the fixing roller and the pressure roller is longer at both end portions than at the central portion in the rotation axis direction.

  Therefore, in the present invention, power consumption is reduced by suppressing excessive fixing strength at the end portion in the rotation axis direction. Specifically, in the fixing device according to the first invention, when the temperature detected by the temperature sensor 2c, that is, the surface temperature of the pressure roller 12 rises and reaches a preset temperature, the end of the fixing roller 11 is set. Reduce power consumption by lowering the temperature from the initial set temperature. FIG. 6 shows an example of temperature control of the fixing roller 11.

  Both the initial set temperatures of the central portion and the end portion in the rotation axis direction of the fixing roller 11 are T1. Then, when the surface temperature of the fixing roller 11 reaches T1, paper feeding is started. As described above, the surface temperature of the pressure roller is temporarily lowered by the start of paper feeding, but gradually increases thereafter. When the surface temperature of the pressure roller 12 reaches TA1, the set temperature of the end portion in the rotation axis direction of the fixing roller 11 is set to “T1-t”. Thereby, an excessive increase in the fixing strength at the end of the fixing roller 11 in the rotation axis direction is suppressed.

  If the surface temperature of the pressure roller rises even after the set temperature of the end of the fixing roller 11 in the rotation axis direction is set to “T1-t”, the set temperature of the end of the fixing roller 11 in the direction of the rotation axis is stepwise. Further lowering is preferable. Table 1 shows an example of the set temperature at the end of the fixing roller 11 in the rotation axis direction according to the surface temperature of the pressure roller 12.

  In the control example in Table 1, when the surface temperature of the pressure roller reaches 75 ° C., the set temperature of the end portion in the rotation axis direction of the fixing roller 11 is lowered by 5 ° C. from the initial set temperature T1, and the surface temperature of the pressure roller thereafter increases. When the temperature rises to reach 90 ° C., the set temperature at the end of the fixing roller 11 in the rotation axis direction is lowered by 10 ° C. from the initial set temperature T1. When the surface temperature of the pressure roller continues to increase thereafter, the set temperature at the end of the fixing roller 11 in the rotational axis direction may be similarly lowered from the initial set temperature T1 when the specific temperature is reached. .

  FIG. 8 shows a flowchart of an example of temperature control of the fixing roller 11. First, when image formation is started (step S101), it is determined whether or not the surface temperature of the pressure roller is 75 ° C. or higher (step S102). If the surface temperature of the pressure roller is less than 75 ° C., the set temperature of the pressure roller is T1 (step S105). On the other hand, if the surface temperature of the pressure roller is 75 ° C. or higher (step S102), it is next determined whether or not the surface temperature of the pressure roller is 90 ° C. or higher (step S103). If the surface temperature of the pressure roller is less than 90 ° C., the set temperature of the pressure roller is T1-5 ° C. (step S106). On the other hand, if the surface temperature of the pressure roller is 90 ° C. or higher, the surface temperature of the pressure roller is set to T1-10 ° C. (step S104). Then, it is determined whether a series of image formation has been completed (step S107). If a series of image formation is not completed, the process returns to step S102 and the same control is repeated.

  FIG. 9 is a schematic view showing an embodiment of the fixing device according to the second invention. The fixing device shown in this figure is different from the fixing device according to the first invention shown in FIG. 3 in that the pressure roller 12 has a minute amount from the surface of the pressure roller at the central portion in the rotation axis direction and the outer peripheral portion of the end portion. The temperature sensor 2d (fourth temperature detection means) and the temperature sensor 2e (fifth temperature detection means) are disposed with a gap therebetween. Since other configurations are the same as those of the fixing device shown in FIG. 3, the description thereof is omitted here.

  In the fixing device according to the second invention, when the detected temperature difference between the central portion and the end of the pressure roller 12 detected by the temperature sensor 2d and the temperature sensor 2e exceeds a predetermined temperature, the fixing roller 11 Reduce the power consumption by lowering the set temperature at the end from the initial set temperature. FIG. 10 shows an example of temperature control of the fixing roller 11.

  Both the initial set temperatures of the central portion and the end portion in the rotation axis direction of the fixing roller 11 are T1. Then, when the surface temperature of the fixing roller 11 reaches T1, paper feeding is started. As described above, the surface temperature of the pressure roller 12 temporarily decreases when the sheet feeding is started, but thereafter gradually increases. When the detected temperature difference between the central portion and the end portion in the rotation axis direction of the pressure roller 12 reaches ΔTA, the set temperature at the end portion in the rotation axis direction of the fixing roller 11 is set to “T1-t”. Thereby, an excessive increase in the fixing strength at the end of the fixing roller 11 in the rotation axis direction is suppressed.

  Even if the set temperature at the end of the fixing roller 11 in the rotation axis direction is set to “T1-t”, if the detected temperature difference between the central portion and the end of the pressure roller 12 in the rotation axis direction becomes large, the fixing roller 11 It is preferable to further lower the set temperature at the end in the rotation axis direction stepwise. Table 2 shows an example of the set temperature at the end portion in the rotation axis direction of the fixing roller 11 based on the detected temperature difference between the central portion and the end portion in the rotation axis direction of the pressure roller 12.

  In the control example of Table 2, when the detected temperature difference between the central portion and the end portion of the pressure roller 12 in the rotation axis direction reaches 5 ° C., the set temperature of the end portion in the rotation axis direction of the fixing roller 11 is changed from the initial set temperature T1 to T5. Decrease the temperature. When the detected temperature difference of the pressure roller 12 continues to increase and exceeds 8 ° C., the set temperature at the end of the fixing roller 11 in the rotation axis direction is lowered by 10 ° C. from the initial set temperature T1. When the detected temperature difference of the pressure roller 12 becomes large thereafter, similarly, when the detected temperature difference reaches a specific temperature, the set temperature at the end in the rotation axis direction of the fixing roller 11 is set to the initial set temperature. A predetermined temperature may be lowered from T1.

  FIG. 11 shows another embodiment of the fixing device according to the present invention. In the fixing device of FIG. 11, an endless fixing belt (fixing rotating body) 73 is suspended between the fixing roller 71 and the heating roller 72, and the pressure roller 12 is pressed against the fixing roller 71 via the fixing belt 73. Being done. The fixing roller 71 includes a cylindrical cored bar 711 and an elastic layer 712 made of silicone rubber formed on the outer periphery of the cored bar 711. In order to improve the releasability, a PFA tube may be attached to the surface of the elastic layer 712 or PFA coating may be applied. The heating roller 72 includes a cylindrical cored bar 721, and the surface of the cored bar 721 is subjected to PFA coating (not shown). Inside the metal core 721, halogen heaters H1 and H2 are disposed as heat sources. The central portion of the heating roller 72 in the rotation axis direction is heated by the halogen heater H1, and both ends of the heating roller 72 in the rotation axis direction are heated by the halogen heater H2. The temperature sensor 2a (first temperature detection means) and the temperature sensor 2b (second temperature detection) are spaced from the surface of the fixing belt 73 at the central portion of the rotation axis of the heating roller 72 and the outer peripheral portion of the end portion with a small gap. Means) is provided. A temperature sensor (third temperature detecting means) 2c is also disposed on the outer peripheral portion of the central portion in the rotation axis direction of the pressure roller 12 with a minute gap from the surface of the pressure roller.

  The fixing belt 73 is formed of an elastic layer such as silicon rubber on the outer peripheral surface of an endless base body formed of a metal material such as nickel or stainless steel or a resin material such as polyimide or polyamide, and a fluororesin or the like is formed on the surface thereof. A release layer is formed. The pressure roller 12 is the same as that of the fixing device of FIG. Thus, since both the fixing roller 71 and the pressure roller 12 include the elastic layer 712 and the elastic layer 122, the nip portion N between the fixing belt 73 and the pressure roller 12 is used in the fixing device shown in FIG. Can be increased (the length in the transport direction of the paper P). As a result, even when the image formation is performed at high speed, sufficient heating and pressurization can be performed so that the toner image t is melted and fixed on the paper P.

  The pressure roller 12 is rotated clockwise in the drawing by a driving means (not shown), for example, at a peripheral speed of 165 mm / sec, whereby the fixing belt 73 and the fixing roller 71 are driven. In addition, the heating roller 72 rotates as the fixing belt 73 rotates. Heat from the halogen heaters H 1 and H 2 is transmitted to the fixing belt 73 via the heating roller 72. The temperature control of the fixing belt 73 is performed by the temperature detected by the temperature sensors 2a and 2b arranged at the center and the end of the fixing roller 11 in the rotation axis direction. Further, the set temperature at the end portion in the rotation axis direction of the fixing belt 73 is changed based on the surface temperature of the pressure roller 12 or the surface temperature difference between the central portion and both end portions in the rotation axis direction as in the above-described embodiment. .

  In the embodiment of the fixing device described above, the sheet passing direction is the vertical direction. However, the present invention is not limited to this, and the sheet passing direction may be a horizontal direction or a predetermined angle with respect to the horizontal direction. Good.

  According to the fixing device of the present invention, an unnecessarily increase in the surface temperature of the fixing roller can be suppressed without deteriorating the fixing property of the toner image onto the paper. This is useful because it can reduce power consumption.

DESCRIPTION OF SYMBOLS 1 Fixing device 2a Temperature sensor (1st temperature detection means)
2b Temperature sensor (second temperature detection means)
2c Temperature sensor (third temperature detection means)
2d temperature sensor (fourth temperature detection means)
2e Temperature sensor (5th temperature detection means)
D Image forming apparatus H1 Halogen heater (first heat source)
H2 halogen heater (second heat source)
P paper (transferred member)
N nip portion t toner image 11 fixing roller (fixing rotating body)
12 Pressure roller (Pressure rotating body)
71 Fixing roller 72 Heating roller 73 Fixing belt (fixing rotating body)

Claims (6)

A fixing rotator, a pressure rotator that presses against the fixing rotator to form a nip portion, and a first heat source and a second heat source that heat the central portion of the fixing rotator in the rotation axis direction and both ends of the rotation shaft direction. And a first temperature detecting means and a second temperature detecting means for detecting surface temperatures of a central portion and an end portion in the rotation axis direction of the fixing rotator, and detection temperatures of the first temperature detecting means and the second temperature detecting means. Control means for controlling energization to the first heat source and the second heat source and maintaining the surface of the fixing rotator at a predetermined set temperature,
Third temperature detecting means for detecting the surface temperature of the pressure rotating body is further provided, and the set temperature of the end portion of the fixing rotating body is changed based on the temperature detected by the third temperature detecting means. Fixing device.   2. The fixing device according to claim 1, wherein when the temperature detected by the third temperature detecting means rises and reaches a preset temperature, the set temperature at the end of the fixing rotator is lowered from the initial set temperature.   3. The fixing device according to claim 1, wherein the third temperature detection unit detects a surface temperature of a central portion in the axial direction of the pressure rotating body. A fixing rotator, a pressure rotator that presses against the fixing rotator to form a nip portion, a first heat source and a second heat source that heat the central portion and both ends of the fixing rotator in the rotational axis direction; First temperature detection means and second temperature detection means for detecting the surface temperatures of the central portion and the end portion in the rotation axis direction of the fixing rotator, and the first temperature detection means based on the detected temperatures of the first temperature detection means and the second temperature detection means. A fixing device comprising: control means for controlling energization to the heat source and the second heat source and maintaining the surface of the fixing rotator at a predetermined set temperature;
The apparatus further comprises fourth temperature detection means and fifth temperature detection means for detecting the surface temperatures of the central portion and the end portion in the rotation axis direction of the pressure rotating body, and detection by the fourth temperature detection means and the fifth temperature detection means. A fixing device that changes a set temperature of an end portion of the fixing rotator based on a temperature difference.   5. The fixing according to claim 4, wherein when the detected temperature difference between the fourth temperature detecting means and the fifth temperature detecting means becomes large and reaches a preset temperature difference, the set temperature at the end of the fixing rotating body is lowered from the initial set temperature. apparatus.   An image forming apparatus comprising the fixing device according to claim 1.