JP2014153504A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of forming a temperature distribution as intended on the surface of a fixing belt.SOLUTION: A heating member 23 is formed of a plurality of heating elements 32 arranged in a width direction of a recording medium. Supply of power to the respective heating elements 32 is controlled by heating control means 26, so that when an unfixed image on paper P that passes through a nip part N has an image area and a non-image area, of the plurality of heating elements 32, a temperature of image area heating elements 32X corresponding to the image area X is increased, and a temperature of non-image area heating elements 32Y corresponding to the non-image area Y is decreased. The heating control means 26 controls the power to be supplied to the heating element 32 to be controlled according to the calorific value of the adjacent heating element.

Description

  The present invention relates to a fixing device that fixes an image on a recording medium, and an image forming apparatus including the fixing device.

  In an image forming apparatus such as an electrophotographic system, a fixing device that fixes a toner image on a sheet as a recording medium is provided. The fixing device includes a fixing rotator that is heated by a heating member, and a facing member that abuts against the fixing rotator, and the sheet passes through a nip formed by the contact between the fixing rotator and the facing member. As a result, the toner on the paper is heated and melted and fixed.

  In general, the heating member is configured to heat the fixing rotator over the entire sheet passing width, whereby the entire sheet is heated. However, when the image exists only in a partial area of the paper, heat energy is wasted in the non-image area where the image does not exist.

  Therefore, in order to reduce unnecessary heat energy consumption to the non-image area, for example, in Patent Documents 1 to 3, the heating area is changed according to the image on the recording medium, and the part necessary for fixing is heated. However, there has been proposed a fixing device configured not to heat a portion that is not necessary for fixing.

  As described above, in the configuration in which the heating area is changed according to the distribution of the image area and the non-image area in the image, the high temperature area and the low temperature area are formed on the surface of the fixing rotator. In this case, if the high temperature region and the low temperature region are adjacent to each other, thermal diffusion occurs from the high temperature region to the low temperature region, so that the high temperature region is lower than the target temperature, which may cause fixing failure. Further, when the high temperature regions are adjacent to each other, almost no thermal diffusion occurs, so that the high temperature region excessively rises in temperature and may cause image abnormality such as uneven gloss. Moreover, excessive temperature rise in a high temperature region leads to energy loss.

  In view of such circumstances, the present invention provides a fixing device capable of forming a target temperature distribution on the surface of a fixing rotator, and an image forming apparatus including the fixing device.

  In order to solve the above problems, the present invention controls a fixing rotator, a counter member that forms a nip portion between the fixing rotator, a heating member that heats the fixing rotator, and an output of the heating member. A heating control means, wherein the heating member includes a plurality of heating elements that can be supplied with power and arranged in the width direction of the recording medium, and an unfixed image of the recording medium supplied to the nip portion is an image area. And the non-image area, the heating control means causes each heating element so that, of the plurality of heating elements, the heating element corresponding to the image area becomes high temperature and the heating element corresponding to the non-image area becomes low temperature. In the fixing device in which the power supply to the heater is controlled, the heating control means controls the power supplied to the heating element to be controlled in accordance with the heat generation amount of the adjacent heating element.

  According to the present invention, the power supplied to the heating element to be controlled is controlled according to the amount of heat generated by the heating element adjacent to the heating element to be controlled. It can be determined in consideration of thermal diffusion or thermal diffusion to adjacent areas. Therefore, a desired temperature distribution can be formed on the surface of the fixing rotator, and image quality can be improved by preventing defective fixing and abnormal images while suppressing energy loss.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus to which the present invention is applicable. FIG. 2 is a cross-sectional view illustrating a basic configuration of a fixing device. FIG. 3 is a perspective view of a main part of the fixing device. It is a top view which shows an image formation pattern. FIG. 6 is a diagram illustrating a supplied power and a temperature distribution of a fixing belt in an image pattern A. FIG. 6 is a diagram illustrating a supplied power and a temperature distribution of a fixing belt in an image pattern A. FIG. 6 is a diagram illustrating a supplied power and a temperature distribution of a fixing belt in an image pattern A. It is a table | surface which shows the emitted-heat amount of each heat generating body in each image pattern. It is a principal part perspective view which shows other embodiment of a fixing device. It is a top view which shows other embodiment of a heater. FIG. 10 is a cross-sectional view of another fixing device to which the present invention is applicable. FIG. 10 is a cross-sectional view of another fixing device to which the present invention is applicable. It is a schematic block diagram of the other image forming apparatus which can apply this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus shown in FIG. 1 is a monochrome image forming apparatus, and a photoconductor 2 as an image carrier is disposed in the center of the apparatus main body 1. Around the photosensitive member 2, a charging roller 3 as a charging unit, a light source 4 and a mirror 5 constituting an exposure unit, a developing unit 7 including a developing roller 6, a transfer unit 8, and a cleaning blade 9 are provided. Means 10 and the like are arranged.

  Further, the apparatus main body 1 includes a paper feed tray 11 that stores paper P as a recording medium, a paper feed roller 12 that carries the paper P out of the paper feed tray 11, a pair of registration rollers 13 as timing rollers, A fixing device 14 that fixes an image on the paper P and a paper discharge roller 15 that discharges the paper P outside the device are provided. In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Although not shown, a manual paper feed mechanism may be provided.

Next, the basic operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the photosensitive member 2 is rotationally driven clockwise by a driving device (not shown), and the surface of the photosensitive member 2 is uniformly charged to a predetermined polarity by the charging roller 3. Next, based on image information from a reading device or a computer (not shown), the exposure light L emitted from the light source 4 is scanned through the mirror 5 and applied to the charged surface of the photoreceptor 2. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 2. By supplying toner from the developing roller 6 to the electrostatic latent image, the electrostatic latent image is visualized (visualized) as a toner image.

  When the image forming operation is started, the paper feed roller 12 starts to rotate, and the paper P is separated and sent out from the paper feed tray 11 one by one. The transport of the fed paper P is temporarily stopped by the registration roller 13, and the deviation of the posture is corrected. Thereafter, the registration roller 13 is driven to rotate in synchronization with the rotation of the photosensitive member 2, and the paper P is conveyed at a timing when the leading end of the toner image on the photosensitive member 2 coincides with a predetermined position at the leading end of the conveying direction of the paper P. Then, the toner image on the photoreceptor 2 is transferred onto the conveyed paper P by the transfer electric field formed by the transfer unit 8. The paper P on which the toner image has been transferred is conveyed to the fixing device 14, and the toner image on the paper P is fixed by the fixing device 14. Thereafter, the paper P is discharged out of the apparatus by the paper discharge roller 15.

  Residual toner remaining on the photosensitive member 2 without being transferred onto the paper P reaches the cleaning blade 9 as the photosensitive member 2 rotates, and is scraped off and removed by the cleaning blade 9. Then, the surface of the photoreceptor 2 is neutralized by a neutralizing unit (not shown) and is prepared for the next image forming process.

FIG. 2 is a cross-sectional view showing the basic configuration of the fixing device according to the present embodiment.
As shown in FIG. 2, the fixing device 14 includes a fixing belt 21 as a fixing rotator, and a pressure roller 22 as an opposing member (or an opposing rotator) that contacts the fixing belt 21 and forms a nip portion N. And a heater 23 as a heating member for heating the fixing belt.

  The fixing belt 21 is composed of an endless belt member (including a film) that is thin and flexible. Specifically, the fixing belt 21 includes a base material 21a made of SUS having an outer diameter of 40 mm and a thickness of 40 μm, an elastic layer 21b made of silicone rubber having a thickness of 100 μm covering the outer peripheral surface of the base material 21a, It comprises a release layer 21c made of a fluororesin such as PFA or PTFE having a thickness of 5 to 50 μm and covering the outer peripheral surface of the layer 21b. The base 21a of the fixing belt 21 may be made of a resin material such as polyimide.

  The pressure roller 22 includes an iron cored bar 22a having an outer diameter of 40 mm and a thickness of 2 mm, and an elastic layer 22b covering the outer peripheral surface of the cored bar 22a. The elastic layer 22b of the pressure roller 22 is made of silicone rubber and has a thickness of 5 mm. Further, in order to improve the releasability, a release layer made of a fluororesin having a thickness of about 40 μm may be disposed on the outer peripheral surface of the elastic layer 22b.

  A nip forming member 24 is disposed at a position facing the pressure roller 22 on the inner peripheral side of the fixing belt 21. The nip forming member 24 is supported by a side plate (not shown) of the fixing device 14 at both ends thereof. When the pressure roller 22 is brought into pressure contact with the nip forming member 24 by a pressure means such as a pressure lever, a nip portion N having a predetermined width is formed at the pressure contact portion between the fixing belt 21 and the pressure roller 22. ing. Note that the fixing rotator and the opposing member may be simply brought into contact with each other without applying pressure.

  The pressure roller 22 is configured to be rotationally driven in the direction of arrow B in the figure by a drive source such as a motor (not shown). When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate in the direction of arrow C in the figure. A belt support member 29 that supports the fixing belt 21 is disposed on the inner peripheral side of the fixing belt 21.

  The heater 23 is composed of a planar or plate-like heating element such as a thermal heater or a ceramic heater. A stay 31 as a support member is disposed on the inner peripheral side of the fixing belt 21, and the stay 31 causes the heater 23 to be upstream of the nip portion N in the sheet conveyance direction A, and the fixing belt 21. It is supported so as to face the inner peripheral surface. Further, a power source 25 is connected to the heater 23 so that power is supplied from the power source 25 to the heater 23. The output of the power source 25 is controlled by the heating control means 26. The heating control means 26 is composed of a microcomputer including a CPU, ROM, RAM, I / O interface and the like.

  Further, the fixing device 14 includes a first sensor 27 as a heater temperature detecting unit that detects the temperature of the heater 23, and a second sensor 28 as a belt temperature detecting unit that detects the temperature of the fixing belt 21. The first sensor 27 is disposed so as to be in direct contact with the heater 23, and the second sensor 28 is opposed to the outer peripheral surface of the fixing belt 21 on the upstream side in the belt rotation direction C with respect to the heater 23. It is arranged. The temperature information detected by the sensors 27 and 28 is input to the heating control means 26, and the heating control means 26 is configured to control the output of the power source 25 based on this input information. ing.

  A pressing roller 30 as a pressing member that presses the fixing belt 21 is disposed at a position facing the heater 23 on the outer peripheral side of the fixing belt 21. The pressing belt 30 presses the fixing belt 21 from the outer peripheral side toward the heater 23, so that the fixing belt 21 comes into contact with the heater 23. The pressing roller 30 has an outer diameter of 15 mm to 30 mm, an iron cored bar 30a having an outer diameter of 8 mm, and an elastic layer made of silicone rubber having a thickness of 3.5 mm to 11 mm covering the outer peripheral surface of the cored bar 30a. 30b. Further, in order to improve the mold release property, a mold release layer made of a fluorine-based resin having a thickness of about 40 μm may be disposed on the outer peripheral surface of the elastic layer 30b. Here, the pressing roller 30 is pressed against the fixing belt 21 by a pressing unit (not shown). However, the pressing roller 30 may be simply brought into contact without being pressed by the pressing unit.

The basic operation of the fixing device will be described with reference to FIG.
When the power switch of the image forming apparatus main body is turned on, power is supplied from the power source 25 to the heater 23, and the pressure roller 22 starts to rotate in the direction of arrow B in the figure. As a result, the fixing belt 21 is driven to rotate in the direction of arrow C in the figure by the frictional force with the pressure roller 22.

  Thereafter, when the sheet P carrying the unfixed toner image G through the image forming process is conveyed to the nip portion N between the fixing belt 21 and the pressure roller 22, the sheet P is heated and heated. The toner image G on the paper P is fixed. Then, after the sheet P is carried out from the nip portion N, it is discharged out of the apparatus.

Hereinafter, the configuration of the fixing device according to the present embodiment will be described in more detail.
As shown in FIG. 3, the heater 23 as a heating member has a plurality (seven in the figure) of heating elements 32 arranged at equal intervals in the width direction orthogonal to the transport direction of the paper P. Each heating element 32 is connected to a power source 40 so that power can be supplied to each heating element 32, and the power supplied to each heating element 32 is controlled independently by the heating control means 26.

  Specifically, the heating control means 26 controls the change of the heating range in the sheet width direction by selecting the heating element 32 to generate heat from among the plurality of heating elements 32 and the ON / OFF timing of the heating element 32. Thus, the heating range in the rotation direction can be changed, and the heating value per unit time (heating temperature) can be changed by controlling the heating value of the heating element 32. Note that the amount of heat generated (output) of the heating elements 32 is controlled by changing the power supplied to each heating element 32. This change in the supplied power is performed by changing the voltage in an analog manner or changing the lighting duty (the ratio of the ON time during a predetermined time).

  An image signal transmitted from an image reading device (not shown) of the image forming apparatus or an external device is input to the image processing means 33 shown in FIG. 2, and predetermined image processing is performed. The image information created by the image processing unit 33 is input to the heating control unit 26, and the heating control unit 26 controls the output of each heating element 32 via the power source 25 based on this image information.

  For example, as shown in FIG. 4A, in the case of the paper P on which the image area a, the non-image area b, and the image area c are formed in order from the leading end side in the paper conveyance direction A, the image area Fixing is necessary for a and c, but fixing is not necessary for the non-image area b. In such a case, based on the image information obtained from the image processing means 33, the heating control means 26 changes the temperature of the part of the fixing belt 21 corresponding to the non-image area b to the fixing belt 21 corresponding to the image areas a and c. The heater 23 is controlled so as to be lower than the temperature of the part. That is, in this case, the power supply to all the heating elements 32 is normally performed at the locations corresponding to the image areas a and c, but the power supply to all the heating elements 32 is reduced at the locations corresponding to the non-image areas b. Or stop. As described above, in the portion corresponding to the non-image region b, wasteful heat energy consumption in the non-image region b can be reduced by reducing or stopping the power supplied to the heating element 32.

  As shown in FIG. 4B, when the image area d and the non-image area e are mixed in the width direction of the paper P, it corresponds to the non-image area e among the plurality of heating elements 32. The power supply to the heating element 32 at the position (right side in the figure) is reduced or stopped. Thereby, useless heat energy consumption in the non-image area e can be reduced.

  In the example shown in FIG. 4C, the image area and the non-image area are mixed in the width direction and the conveyance direction of the paper P. In this case, the power supply to the heating element 32 is reduced or stopped in correspondence with the non-image area formed in the portion where the range of the symbol g and the range of the symbol i in the figure overlap with each other. Similarly, useless heat energy consumption in the non-image area can be reduced.

Hereinafter, the temperature control of the fixing belt will be described.
At the timing when the image areas a and c on the sheet pass through the nip portion, the power supplied to the heating element is controlled so that the temperature of the fixing belt becomes a predetermined first target temperature necessary for fixing. On the other hand, at the timing when the non-image area b passes through the nip portion, the power supply to the heating element is reduced, and control is performed so that the temperature of the fixing belt becomes a second target temperature lower than the first target temperature. Reduce wasteful heat energy consumption. Here, during the time when the image areas a and c do not pass through the nip portion, the power supply to the heating element 32 may be stopped completely. However, if the temperature is excessively lowered, the same sheet or the next sheet When the image area is supplied to the nip portion, it becomes difficult to raise the heating element to the first target temperature. Therefore, an output smaller than the output corresponding to the first target temperature is set as the output of the heating element, and when the image area is not passed, heating is performed with a small output, so that it is higher than the first target temperature Q1. It is desirable to control to maintain a second target temperature that is low but higher than room temperature. The specific second target temperature is determined according to the performance of the heater 23, the heat capacity of the fixing belt 21, and the like.

  In general, it takes a certain time for the temperature of the fixing belt to reach the target temperature after the heating of the fixing belt is started. Therefore, when the start-up with the output corresponding to the first target temperature is started when the leading edge of the image area a reaches the nip portion, the temperature rise to the first target temperature is not in time. Therefore, in consideration of the heating time of the fixing belt, it is desirable to perform preheating by output for a predetermined time from the timing before the leading ends of the image areas a and c reach the nip portion. However, from the viewpoint of energy saving, it is desirable that the preheating time is as short as possible. In addition, the temperature increase time of the fixing belt varies depending on the heat transfer coefficient of the fixing belt itself, the heat generation length in the rotation direction, and the like, and therefore it is preferable to specify the temperature beforehand by experiments.

  The fixing temperatures of the image areas a and c may be set to the same temperature (first target temperature), or the target temperatures may be varied depending on the type of image included in the image area.

  For example, when the image type of each image area is different for characters, photographs, drawings, etc., the target temperature corresponding to each image area may be varied depending on the image type. In particular, when the image is a photograph, it may be necessary to increase the glossiness of the image. Therefore, a desired glossiness can be obtained by setting a high target temperature for the image area of the photograph.

  Also, if the image pattern of each image area is different for solid images, halftone images, line images, character images, etc., or if the image pattern processing method is different for dither method, error diffusion method, etc., the image pattern and processing The target temperature corresponding to each image region may be varied depending on the method. It is known that the degree of isolation or density of toner particles differs depending on various image patterns, and the toner is more easily peeled off when it is isolated than when it is dense. Therefore, for image patterns with isolated toner, the target temperature is raised to make it difficult to peel off. On the other hand, for image patterns with dense toner, reducing the target temperature reduces energy consumption. Is possible.

  In addition, when the toner adhesion amount of each image area is different, the temperature required for fixing is different, so the toner adhesion amount is grasped based on the image information, and the target temperature is different for each image area accordingly. It may be allowed. Usually, in an image with a large amount of toner adhesion, a large amount of heat is required for melting the toner, and thus it is necessary to raise the target temperature. On the contrary, for an image with a small amount of toner, the target temperature can be lowered to reduce energy consumption.

  In a color image forming apparatus using a plurality of color toners, the amount of heat required for fixing may differ depending on the color of the toner. In this case, the target temperature may be varied depending on the color of the toner. For example, black toner often requires less heat than other color toners, such as yellow, cyan, and magenta. Therefore, in an image area where only black toner is used, the target temperature By reducing the value, energy consumption can be reduced.

[First Embodiment]
The characteristic configuration of the present invention will be described below.
The present invention is applied to the case where the image area X and the non-image area Y are mixed in the width direction of the paper P (the modes shown in FIGS. 4B and 4C) as shown in FIGS. The Hereinafter, a case where the image region X is formed in the center of the paper P in the width direction and the non-image region Y is formed on both sides thereof will be described as an example. In addition, although the number of the heat generating bodies 32 of the heater 23 is arbitrary, below, the case where the heater 23 which has arrange | positioned the five heat generating bodies 32 (h1-h5) in the width direction of the paper P is illustrated.

  FIG. 5 shows an image pattern A in which an image region X corresponding to the length of one heating element h3 is formed at the center in the width direction of the paper P, and the temperature distribution of the fixing belt 21 when fixing the image pattern A and The electric power supplied to each heating element h1-h5 is shown.

  With the start of fixing, the image information of the image pattern A is input from the image processing unit 33 to the heating control unit 26. The heating control unit 26 supplies electric power Sa to the heating element h3 corresponding to the image area X among the heating elements 32 of the heater 23, and heats the area corresponding to the image area X of the fixing belt 21 to the temperature Ta. Further, a power S1 smaller than the previous power Sa is supplied to the heating elements h1, h2, h4, h5 corresponding to the non-image area Y, and the area corresponding to the image area Y of the fixing belt 21 is lower than Ta. Heat to temperature Tbase (eg 100 ° C.).

  As shown in the figure, at the time t0 immediately after the start of heating, a rectangular wave-like temperature distribution is formed on the fixing belt 21 in which the area corresponding to the image area X is high and the non-image area Y is low. The The supply of the electric power Sa and S1 to each of the heating elements h1 to h5 is continued until the sheet escapes from the nip portion N. However, since heat spreads on both sides in the width direction on the fixing belt 21 as time elapses. After the lapse of the specified time t1 (time until the region heated by the heater 23 of the fixing belt 21 reaches the nip portion N), the temperature distribution of the fixing belt 21 has a curved shape (normal distribution curve) as shown in the figure. And the temperature of the region heated by the heating element h3 of the fixing belt 21 is lower than the initial heating temperature Ta.

  Even after the elapse of the time t1, the temperature of the fixing belt 21 heated by the heating element h3 is required to be equal to or higher than the first target temperature Ttarget (for example, 140 ° C.) that is the target temperature. The heating temperature Ta at time t0 is determined so as to satisfy this condition (for example, Ta = 160 ° C.), and the supply power Sa to the heating element h3 corresponding to the image region X is determined so as to obtain this heating temperature Ta. It is done.

  FIG. 6 shows an image pattern B in which an image region X corresponding to the length of the two heating elements h2 and h3 is formed at the center in the width direction of the paper P, and a fixing belt 21 for fixing the image pattern B. The temperature of each part and the electric power supplied to each heat generating body h1-h5 are shown.

  Also in this case, the image information of the image pattern B is input from the image processing unit 33 to the heating control unit 26 with the start of fixing. The heating control unit 26 supplies electric power Sb to the two heat generating elements h2 and h3 corresponding to the image area X among the heat generating elements 32 of the heater 23, and sets the area corresponding to the image area X of the fixing belt 21 to the temperature Tb. Until heated. The heating control unit 26 supplies power S1 to the heating elements h1, h4, h5 corresponding to the non-image area Y, and heats the area corresponding to the image area Y of the fixing belt 21 to the second target temperature Tbase. .

  At time t0 immediately after the start of heating, the fixing belt 21 has a rectangular wave-like temperature distribution in which the region corresponding to the image region X becomes high temperature and the region corresponding to the non-image region Y becomes low temperature. Also in this case, since the heat diffuses to the surroundings as time passes, the temperature distribution of the fixing belt 21 has a curved shape as shown in the figure after the time t1, and the heating element h3 is heated. The temperature of the region is lower than the initial heating temperature Tb. The heating temperature Tb at the time t0 is determined so that the temperature of the region corresponding to the image region X of the fixing belt 21 is equal to or higher than the first target temperature Ttarget that is the target temperature at the time t1 (e.g., Tb = 150 ° C.), the electric power Sb supplied to the heating element h3 corresponding to the image region X is determined so that the heating temperature Tb is obtained.

  In this case, in the region heated by the two adjacent heating elements h2 and h3 in the fixing belt 21, the high-temperature part is adjacent to each other. Therefore, the region heated by one heating element h2 and the other heating element h3. No thermal diffusion occurs across the boundary with the heated area. Therefore, the amount of temperature decrease between time t0 and time t1 is smaller than that in the case of the image pattern A shown in FIG. Therefore, in the image pattern B, the heating temperature Tb at the time t0 is set lower than the heating temperature Ta in the case of the image pattern A shown in FIG. 5 (Tb <Ta), and the heating element h2, The power Sb supplied to h3 is also made smaller than the power supply Sa in the case of FIG. 5 (Sb <Sa).

  FIG. 7 shows an image pattern C in which an image region X corresponding to the length of the three heating elements h2 to h4 is formed at the center in the width direction of the paper P, and each part of the fixing belt 21 when fixing the image pattern C. And the power supplied to each of the heating elements h1 to h5.

Also in this case, the image information of the image pattern C is input from the image processing unit 33 to the heating control unit 26 with the start of fixing. The heating control means 26 supplies electric power Sb and Sc to the three heating elements h <b> 2 to h <b> 4 corresponding to the image area X among the heating elements 32 of the heater 23, and sets the area corresponding to the image area X of the fixing belt 21. Heat to temperatures Tb and Tc. Further, the heating control unit 26 supplies power S1 to the heating elements h1 and h5 corresponding to the non-image area Y, and heats the area corresponding to the image area Y of the fixing belt 21 to the second target temperature _Tbase .

  Also in this case, at time t0 immediately after the start of heating, the fixing belt 21 has a rectangular wave-shaped temperature distribution in which the region corresponding to the image region X becomes high temperature and the region corresponding to the image region Y becomes low temperature. However, after the elapse of time t1, the temperature distribution of the fixing belt 21 has a curved shape as shown in FIG. Further, the temperature of the area corresponding to the image area X of the fixing belt 21 is lower than the initial heating temperatures Tb and Tc. The heating temperatures Tb and Tc at the time t0 are determined so that the region corresponding to the image region X of the fixing belt 21 is equal to or higher than the first target temperature Ttarget that is the target temperature at the time t1, and the heating temperature Tb , Tc, electric power Sb, Sc supplied to the heating elements h2-4 corresponding to the image region X is determined.

  In this case, among the three high-temperature regions heated by the heating elements h2 to h4, the regions at both ends are adjacent to the low-temperature region corresponding to the non-image region Y on each side, and are shown in FIG. Thermal diffusion occurs in a manner similar to the high temperature region. Therefore, the temperature of the high temperature region heated by the heating elements h2 and h4 at both ends is the same as the temperature Tb of the high temperature region shown in FIG. On the other hand, in the middle high temperature region, since both sides are sandwiched between the high temperature regions, there is less thermal diffusion to both sides, and therefore the amount of temperature decrease between time t0 and t1 is also higher than in the high temperature region adjacent to both sides. Get smaller.

  From the above, the heating temperatures Tb and Tc in the high temperature heating region at time t0 can be set lower than the heating temperature Ta in the high temperature heating region shown in FIG. 5 (Tb <Ta, Tc <Ta). The heating temperature Tc (for example, 145 ° C.) in the high temperature heating region can be made smaller than the heating temperature Tb in the high temperature heating region on both sides (Tc <Tb). Correspondingly, the electric power Sb and Sc supplied to the heating elements h2 to h4 are set smaller than the electric power Sa supplied to the heating element h3 in FIG. 6 (Sb <Sa, Sc <Sa), and the middle heating element h3. Is set to be smaller than the power Sb supplied to the heating elements h2 and h4 adjacent to both sides thereof (Sc <Sb). In summary, Tc <Tb <Ta and Sc <Sb <Sa.

  FIG. 8 shows specific heat generation amounts of the heating elements h1 to h5 in the image patterns A, B, and C shown in FIGS. The numerical value in a table | surface is a heating rate in a control period (500 msec). 1.0 means that it is continuously heated (energized) for one control cycle. The numerical value “0.4” in the table corresponds to S1, “0.85” corresponds to Sa, “0.75” corresponds to Sb, and “0.65” corresponds to Sc.

  The specific numerical value of the heating rate shown in FIG. 8 depends on the time t1 until the region of the fixing belt 21 heated by the heater 23 reaches the nip portion N, the thermal conductivity of the fixing belt 28, and the like. It can be changed as appropriate.

  Thus, in the present invention, the heating control means 26 controls the power supplied to each heating element 32 (h1 to h5) to be controlled according to the amount of heat generated by the heating element adjacent to the heating element to be controlled. Yes. Therefore, the power supplied to each heating element 32 (h1 to h5) can be determined in consideration of thermal diffusion to the adjacent heating region. Therefore, a temperature distribution as originally targeted can be formed on the surface of the fixing belt 21, energy loss due to excessive heating can be suppressed, and deterioration in image quality due to poor fixing or abnormal images can be prevented. This effect can be obtained more significantly because the thermal diffusion of the fixing belt 21 increases (for example, the belt becomes thicker) and the thermal diffusion to the adjacent heating region increases. In a full-color type fixing device, which will be described later, an elastic layer made of silicone rubber or the like is formed on the surface of the fixing belt 21 in order to improve the image quality, so that heat diffusion is more likely to occur and the usefulness of the present invention is enhanced.

  Specifically, one of the heating elements adjacent to both sides of the heating element to be controlled (for example, the heating element h2 in FIG. 6 or the heating element h3 in FIG. 7) is in a high temperature state corresponding to the image region X. When the temperature is high (see FIG. 6) or when both are in a high temperature state corresponding to the image area X (see FIG. 7), the heating elements adjacent to both sides of the heating element to be controlled correspond to the non-image area Y. The electric power supplied to the heating element to be controlled can be reduced (Sb <Sa, Sc <Sa) than when the temperature is low (see FIG. 5).

  Further, when the heating elements adjacent to both sides of the heating element to be controlled (for example, the heating element h3 in FIG. 7) are in a high temperature state corresponding to the image area (see FIG. 7), both sides of the heating element to be controlled. Less heat is supplied to the heating element to be controlled than when one of the heating elements adjacent to is in a high temperature state corresponding to the image area and the other is in a low temperature state corresponding to the non-image area (see FIG. 6). (Sc <Sb).

  In the present embodiment, the amount of heat generated by the heating element 32 (h1 to h5) corresponds to whether the area heated by the heating element corresponds to the image area X or the non-image area Y. , Based on the judgment. This determination is made based on image information input from the image processing means 33 to the heating control means 26. With such a configuration, a sensor or the like for detecting the amount of heat generation is basically unnecessary, so that the cost can be reduced and the layout can be facilitated.

  In the above description, the case where the heating element 32 to be controlled is in a high temperature state corresponding to the image area X is illustrated, but not limited to this, the heating element 32 to be controlled is in a low temperature state corresponding to the non-image area Y. The present invention can also be applied in some cases. For example, in FIG. 6, in the region heated by the low-temperature heating element h2 adjacent to the high-temperature heating element h3, the temperature rises due to thermal diffusion from the region heated by the heating element h3. It is also possible to control the supplied power to be smaller than S1.

[Second Embodiment]
In the first embodiment described above, the power supplied to the heating element to be controlled is controlled by determining the amount of heat generated by the heating element 32 from the image information input to the heating control means 26. In addition, it is also possible to measure the actual temperature of each part of the fixing belt 21 and feed back this temperature information to the heating control means 26 to control the power supplied to each heating element 32.

FIG. 9 is a perspective view showing a specific example of this configuration.
As shown in the figure, the heater 23 of this embodiment includes seven heating elements 32 (h1 to h7). The second sensors 28 (U1 to U7) as belt temperature detecting means for detecting the temperature of the fixing belt 21 are provided for each heating region (partitioned by two-dot chain lines) heated by the heating elements h1 to h7. One by one. The second sensor 28 can be composed of, for example, an infrared radiation thermometer, and the output thereof is input to the heating control means 26, respectively.

  The sensor 28 is disposed upstream of the nip portion N in the rotation direction of the fixing belt 21. In this embodiment, a time is obtained by dividing the distance from the sensor 28 to the heating location of each of the corresponding heating elements h1 to h7 by the rotation speed of the fixing belt 21, and this time is determined as the startup time of the heating elements h1 to h7. (The time from when the heating control means 26 transmits a heating start signal until when heating is actually started).

  For example, when the heating element h4 is a control target, the temperature of the fixing belt 21 heated by the adjacent heating elements h3 and h5 is detected by the sensors U3 and U5, and the adjacent heating elements h3 and h5 are detected based on the temperature information. Determine the calorific value. That is, if this temperature is equal to or higher than a specified temperature (for example, the first target temperature Ttarget), it corresponds to the image area X, and if it is lower than the specified temperature, it is determined to correspond to the non-image area Y, and is described in the first embodiment. The power supplied to the heating element h4 is controlled according to the rules.

  Further, the control of the power supply based on the temperature information described above and the control of the power supply based on the image information described in the first embodiment can be combined. For example, the difference between the temperature measured by the sensor in FIG. 9 (for example, U4) and the heating temperature (Ta in FIG. 5, Tb in FIGS. 6 and 7 and Tc in FIG. 7) set based on the image information. To determine the power supply amount serving as a base for the heating element h4, and when the measured values of the sensors U3 and U5 in the heating region of the adjacent heating elements h3 and h5 are higher than a predetermined value (for example, 130 ° C.) It can be considered that the amount of power supplied to the heating element h4 is less than the base value assuming that there is little heat diffusion to the heating region. On the other hand, if the measured values of the sensors U3 and U5 in the adjacent heating region are lower than the predetermined value, it is determined that the amount of thermal diffusion has increased for some reason, and the power to the heating element h4 is increased. It is also possible to perform control so that the supply amount is larger than the base value.

  In the description of each of the above embodiments, the case where each heating element 32 of the heater 23 has the same length is illustrated, but as shown in FIG. 10, the length of some heating elements 32 a is made longer than the others, Alternatively, it can be shortened. When the length of some of the heating elements 32a is different from the others, the power supplied to each heating element 32 (32a) is based on the power supplied per unit length of each heating element. .

  In each of the above embodiments, the fixing belt 21 is used as the fixing rotating body, and the heater 23 that is heated from the inner peripheral side of the fixing belt 21 is used as the heating unit. However, the fixing device to which the present invention is applicable is described. Is not limited to this.

  For example, as shown in FIG. 11, the present invention can be applied to a configuration in which a fixing roller 60 is used as a fixing rotating body and a heater 23 that is heated from the outer peripheral side of the fixing roller 60 is used as a heating unit. The fixing roller 60 according to this embodiment covers an aluminum cored bar 60a having an outer diameter of 40 mm and a thickness of 1 mm, a heat insulating layer 60b covering the outer peripheral surface of the cored bar 60a, and an outer peripheral surface of the heat insulating layer 60b. The heat conductive layer 60c and the release layer 60d covering the outer peripheral surface of the heat conductive layer 60c are configured.

  The heat insulation layer 60b is made of silicone rubber and has a thickness of 3 mm. Further, in order to further enhance the heat insulating function of the heat insulating layer 60b, the heat insulating layer 60b may be formed of a foamed silicone rubber with little heat escape.

  The heat conductive layer 60c is made of nickel. However, the material of the heat conductive layer 60c is not limited to nickel, and may be any material having higher heat conductivity than that of the heat insulating layer 60b, such as an iron-based alloy such as stainless steel, a metal-based material such as aluminum or copper, or a graphite sheet. . By providing such a heat conductive layer 60c with good heat conductivity, local temperature variations in the surface temperature of the fixing roller 60 due to uneven heat generation of the heater 23 can be reduced. Further, since the temperature can be raised in a region slightly wider than the region where the heater 23 is provided by the heat conductive layer 60c, there is also an advantage that a deviation from the image can be compensated. Thereby, the freedom degree of setting of the magnitude | size, space | interval, etc. of the several heat generating body 32 which comprises the heater 23 spreads.

  The release layer 60c is made of a fluorine-based resin such as PTF or PTFE, and has a thickness of 5 to 30 μm.

  Further, the fixing device 14 shown in FIG. 11 detects a temperature of the heater 23, a power supply 25 that supplies power to the heater 23, a heating control unit 26 that controls the heater 23 based on information obtained from the image processing unit 33. Although the first sensor 27 and the second sensor 28 for detecting the temperature of the fixing roller 60 are provided, the configuration thereof is basically the same as that of the above-described embodiment, and thus the description thereof is omitted.

  In FIG. 11, the heater 23 is in contact with the surface of the fixing roller 60, but non-contact heating means based on the IH method using a coil and an inverter may be used. In the case of the IH system, a plurality of heating coils are arranged in the axial direction of the fixing roller 60, or a plurality of members for canceling the magnetic flux are arranged in the axial direction of the fixing roller 60. Thus, the heating area and the heating amount can be controlled.

  As shown in FIG. 12, in the fixing device shown in FIG. 2, the heater 23 can be disposed inside the fixing belt 21 and at a site where the nip portion N is formed. In this case, the heating member 23 also functions as the nip forming member 24.

  The image forming apparatus to which the present invention is applicable is not limited to a monochrome image forming apparatus as shown in FIG.

The present invention is also applicable to a fixing device mounted on a color image forming apparatus as shown in FIG.
The color image forming apparatus shown in FIG. 13 includes four process units 20Y, 20M, 20C, and 20K that are detachable from the apparatus main body 1. Each process unit 20Y, 20M, 20C, and 20K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that. Specifically, each of the process units 20Y, 20M, 20C, and 20K includes a photosensitive member 2, a charging roller 3 that charges the surface of the photosensitive member 2, a developing unit 7 that includes a developing roller 6, and a surface of the photosensitive member 5. A cleaning means 10 for cleaning is provided.

  Above each process unit 20Y, 20M, 20C, 20K, an intermediate transfer belt 16, a plurality of primary transfer rollers 17, and a secondary transfer roller 18 are provided as transfer means 8. An exposure device 19 is provided below each process unit 20Y, 20M, 20C, 20K.

The basic image forming operation of the color image forming apparatus shown in FIG. 13 will be described below.
When the image forming operation is started, each photoconductor 2 in each process unit 20Y, 20M, 20C, 20K is rotationally driven, and the surface of each photoconductor 2 is uniformly charged to a predetermined polarity by the charging roller 3. . An electrostatic latent image is formed on the surface of each charged photoreceptor 2 by irradiating laser light from the exposure device 19. At this time, the image information to be exposed on each photoconductor 2 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. The electrostatic latent images formed on the respective photoreceptors 2 in this way are supplied with toner by the developing means 7 so that the electrostatic latent images are visualized (visualized) as toner images. .

  When the image forming operation is started, the intermediate transfer belt 16 is rotationally driven in the direction indicated by the arrow in the drawing. When each toner image of each color on the photoconductor 2 reaches the position of each primary transfer roller 17 with the rotation of each photoconductor 2, the transfer formed between the primary transfer roller 17 and the photoconductor 2. The toner images on the respective photoreceptors 2 are sequentially superimposed and transferred onto the intermediate transfer belt 16 by the electric field. Thus, a full-color toner image is carried on the surface of the intermediate transfer belt 16. Further, the surface of each photoconductor 2 after the transfer is cleaned by the cleaning means 10 and then discharged by a charge removal device (not shown).

  In the lower part of the apparatus main body 1, the paper feed roller 12 starts to rotate, and the paper P is sent from the paper feed tray 11 to the transport path R. The paper P sent to the transport path R is temporarily stopped by the registration roller 13 and then transported between the secondary transfer roller 18 and the intermediate transfer belt 16 at a predetermined timing. The toner images on the intermediate transfer belt 16 are collectively transferred onto the paper P by a transfer electric field formed between the secondary transfer roller 18 and the intermediate transfer belt 16. Thereafter, the paper P is conveyed to the fixing device 14, and after the toner image on the paper P is fixed to the paper P by the fixing device 14, the paper P is discharged out of the device by the paper discharge roller 15.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single-color image is formed using any one of the four process units 20Y, 20M, 20C, and 20K. Two or three image forming units can be used to form a two-color or three-color image.

  The image forming apparatus to which the present invention can be applied is not limited to the above, and may be other printers, copiers, facsimiles, or complex machines thereof.

14 Fixing Device 21 Fixing Belt (Fixing Rotator)
22 Pressure roller (opposing member)
23 Heater (heating member)
24 Nip forming member 25 Power supply 26 Heating control means 30 Pressing member 32 Heating element N Nip part P Paper (recording medium)
X image area Y non-image area

JP-A-6-95540 JP 2001-343860 A JP 2005-181946 A

Claims (8)

A fixing rotator; a counter member that forms a nip portion between the fixing rotator; a heating member that heats the fixing rotator; and a heating control unit that controls the output of the heating member. A plurality of heating elements that can be supplied with power and arranged in the width direction of the recording medium, and the unfixed image of the recording medium supplied to the nip portion has an image area and a non-image area. In the fixing device in which the power supply to each heating element is controlled by the control means so that the heating element corresponding to the image area among the plurality of heating elements becomes high temperature and the heating element corresponding to the non-image area becomes low temperature. ,
A fixing device, wherein the heating control unit controls electric power supplied to a heating element to be controlled in accordance with a heat generation amount of an adjacent heating element.   The fixing device according to claim 1, wherein the heating control unit determines a heat generation amount of an adjacent heating element from image information input to the heating control unit.   Of the fixing rotator, temperature detecting means for measuring the temperature of the fixing rotator is provided for each region heated by each heating element, and temperature information obtained by each temperature detecting means is input to the heating control means, and the temperature information is obtained. The fixing device according to claim 1, wherein the heat generation amount of adjacent heat generating elements is determined based on the above.   4. The fixing device according to claim 2, wherein the heating element to be controlled heats the image area.   5. When at least one of the heating elements adjacent to both sides of the controlled heating element is in a high temperature state, the power supplied to the controlled heating element is reduced as compared to when both are in a low temperature state. The fixing device described.   If both of the heating elements adjacent to both sides of the controlled heating element are in a high temperature state, supply to the controlled heating element than when one of the heating elements adjacent to both sides is in a high temperature state and the other is in a low temperature state The fixing device according to claim 4, wherein electric power to be reduced is reduced.   The fixing device according to claim 1, wherein a pressing member that contacts the fixing rotator is disposed at a position facing the heating member.   An image forming apparatus comprising the fixing device according to claim 1.

Images