JP2014225004A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem of a conventional fixing apparatus which is supplied with electric power depending on whether an image area or a non-image area: a temperature of a fixing roller may not reach a required fixing temperature in fixing a sheet P, due to a temperature of a member constituting the fixing apparatus, that is, a temperature required for fixation cannot be reached when a fixing member constituting the fixing apparatus is low, for example, or heat is excessively supplied when the temperature is high.SOLUTION: A fixing apparatus performs fixation by allowing a recording medium with an unfixed image carried thereon to pass through a nip part. Depending on whether an image area or a non-image area on the recording medium, the fixing apparatus adjusts the quantity of heat to be applied by a heating unit to a fixing member. A fixation control unit adjusts the quantity of heat to be applied by the heating unit to the fixing member on the basis of the temperature of the fixing member.

Description

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

  2. Description of the Related Art Conventionally, there is known a fixing device for fixing a toner image formed on the surface of a recording medium by using a toner made of a heat-meltable resin in an image forming apparatus such as a copying machine, a printer, or a facsimile machine, by heating and pressurizing the toner image. ing.

  Japanese Patent Application Laid-Open No. 2004-133620 discloses control of the fixing temperature when an image area and a non-image area are mixed in the conveyance direction of the paper P. That is, the electric power at which the fixing temperature is obtained is supplied to the halogen heater at the portion of the fixing roller that is in close contact with the image area, and the electric power supply to the halogen heater is stopped or reduced at the portion of the fixing roller that is in close contact with the non-image area. With such a configuration, excessive power supply can be suppressed and energy saving can be improved.

  However, in the technique described in Patent Document 1, since power is supplied based on whether the image area or the non-image area, the paper P is fixed depending on the temperature of the members constituting the fixing device. In some cases, the fixing roller is not at the required fixing temperature. For example, when the temperature of the fixing member constituting the fixing device is low, the temperature required for fixing cannot be reached, or when the temperature of the fixing member is high, excessive heat is supplied. Has occurred.

  In order to solve the above-described problems, in the present invention, a rotating fixing member, a pressure member that forms a nip portion with the fixing member, and a rotation direction of the fixing member for heating the fixing member A heating unit having a plurality of heaters arranged side by side in a direction orthogonal to the temperature, a temperature measuring unit for detecting the temperature of each heating region of the fixing member heated by the plurality of heaters, and the heating unit A fixing device that determines a quantity of heat and controls a temperature of each heater of the heating unit, and performs fixing through a recording medium carrying an unfixed image in the nip portion, and an image on the recording medium In the fixing device that adjusts an amount of heat applied by the heating unit to the fixing member based on a region and a non-image region, the fixing control unit adds the heating unit to the fixing member based on the temperature of the fixing member. And adjusting the amount of heat.

  According to the present invention, the fixing unit includes a fixing member that fixes the recording medium for each part, and a heating unit that heats the fixing member, and the heating unit heats the fixing member based on the temperature of the fixing member. Therefore, heat can be appropriately supplied to the fixing member, and energy can be saved.

1 is a diagram illustrating an overall configuration of an image forming apparatus 1. 2 is a diagram illustrating a configuration of a fixing device 15. FIG. 2 is a perspective view illustrating a configuration of a fixing device 15. FIG. 2 is a diagram illustrating a hardware configuration of a control unit of the image forming apparatus 1. FIG. 2 is a diagram illustrating a functional configuration of a control unit of the image forming apparatus 1. FIG. It is an example of paper P on which an image is transferred. FIG. 6 is a diagram illustrating a relationship between the temperature of the fixing belt 151 and time. 3 is a diagram illustrating a relationship between a temperature of a fixing belt 151 and an amount of heat. FIG. It is a figure showing the relationship between paper basic weight and calorie | heat amount. FIG. 6 is a diagram illustrating a relationship between the smoothness of a sheet P and the amount of heat. FIG. 6 is a diagram illustrating a relationship between a toner adhesion amount and a heat amount. It is a figure showing the relationship between the temperature of the heating part 153, and calorie | heat amount. FIG. 6 is a diagram illustrating a relationship between a fixing facing roller 152 and a heat amount. It is a figure showing the relationship between the space | interval between sheets, and calorie | heat amount. FIG. 3 is a process flow diagram illustrating an overview of a process in which the image forming apparatus 1 forms an image. FIG. 10 is a processing flowchart showing details of fixing processing. FIG. 10 is a diagram illustrating another example of the configuration of the fixing device. It is a figure showing the relationship between the temperature of the pressure roller 156, and calorie | heat amount. 1 is a diagram illustrating an overall configuration of an image forming apparatus including a double-sided printing mechanism. It is a figure which shows the structure of fixing apparatus 15 '. It is a schematic diagram of a thermal heater. FIG. 22A is an example of a sheet P onto which an image has been transferred. FIG. 22A illustrates an image formation pattern in which an image area, a non-image area, and an image area exist in order from the leading edge in the sheet conveyance direction, and FIG. 3 shows an image formation pattern in which an image area and a non-image area exist in order from the leading edge. FIG. 23A shows an example of a sheet P onto which an image has been transferred. FIG. 23A shows an image formation pattern in which an image area and a non-image area exist in the direction orthogonal to the sheet conveyance direction, and FIG. The image forming pattern includes an image area in a part of the orthogonal direction of the image area, and the remaining area includes an image area on the front side and a non-image area on the rear side in the conveyance direction of the paper P. FIG. 6 is a diagram illustrating a relationship between a target temperature of the fixing belt 151 and time. FIG. 25A shows an example of a sheet P on which images are transferred on both sides. FIG. 25A shows an image formation pattern in which an image area, a non-image area, and an image area exist in order from the leading edge in the transport direction of the first side. ) Shows an image forming pattern in which a non-image area and an image area exist in order from the leading edge of the second surface in the conveyance direction. FIG. 6 is a diagram illustrating a relationship between a target temperature of the fixing belt 151 and time. FIG. 6 is a diagram illustrating a relationship between a target temperature of the fixing belt 151 and time.

(First embodiment)
The first embodiment will be described below with reference to FIGS. FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus 1 according to the present embodiment.

<Hardware configuration of image forming apparatus>
The image forming apparatus 1 forms an image on a sheet P that is an example of a recording medium by copying, printing, or the like. In the present embodiment, as shown in FIG. 1, a scanner unit 11 is provided at the top of the image forming apparatus 1. The scanner unit 11 generates RGB image information by optically reading a document placed on the contact glass 111. Specifically, the scanner unit 11 reads the RGB image information by irradiating the paper P with light and receiving the reflected light by a reading sensor 112 such as a charge coupled device (CCD) or a contact image sensor (CIS). The RGB image information is information representing an image formed on the paper P, and includes the brightness of each color of red (R), green (G), and blue (B).

  Further, the image forming apparatus 1 is provided with a driving roller 141, a driven roller 142, and a secondary transfer roller 145, and an intermediate transfer belt 143 is bridged between the driving roller 141, the driven roller 142, and the secondary transfer roller 145. Yes. Four photosensitive drums 122C, 122M, 122Y, and 122K are provided so as to be in contact with the intermediate transfer belt 143. Images are formed on the photosensitive drums 122C, 122M, 122Y, and 122K with toners of cyan (C), magenta (M), yellow (Y), and black (K), respectively. The image formed on each photosensitive drum is transferred to the same portion of the surface of the intermediate transfer belt 143, so that a color toner image is formed on the surface of the intermediate transfer belt 143.

  A secondary transfer counter roller 146 is provided at a position facing the secondary transfer roller 145. In order to transfer the toner image formed on the surface of the intermediate transfer belt 143 onto the sheet P (hereinafter referred to as secondary transfer), the secondary transfer roller 145 is interposed between the secondary transfer counter roller 146 and the intermediate transfer belt 143. And apply a secondary transfer bias. A charge opposite to the electrostatic charge charged on the surface of the intermediate transfer belt 143 is applied as the secondary transfer bias.

  A charging unit 123C is provided in the vicinity of the photosensitive drum 122C. The charging unit 123C uniformly charges the surface of the photosensitive drum 122C. An exposure unit 124C is provided in the vicinity of the photosensitive drum 122C. The exposure unit 124 </ b> C forms an electrostatic latent image on the surface of the charged photosensitive drum 122 </ b> C based on the C toner adhesion amount determined by the control unit described later. Further, a developing unit 125C is provided in the vicinity of the photoconductive drum 122C. The developing unit 125C attaches toner to the photoconductive drum 122C on which the electrostatic latent image is formed, and the toner on the surface of the photoconductive drum 122C. Form an image.

  A primary transfer roller 144C is provided to face the photosensitive drum 122C. The primary transfer roller 144C applies a primary transfer bias in order to transfer the toner image on the surface of the photosensitive drum 122C to the intermediate transfer belt 143. A charge opposite to the electrostatic charge charged on the surface of the photosensitive drum 122C is applied as the primary transfer bias.

  In the following description, the one having the photosensitive drum 122C, the charging unit 123C, the exposure unit 124C, and the developing unit 125C is referred to as an image forming unit 12C. The image forming apparatus 1 includes image forming units 12M, 12Y, and 12K. The image forming apparatus 1 is the same as the image forming unit 12C except that images are formed using M, Y, and K color toners, respectively. It has a configuration.

  The paper supply unit 13 supplies the paper P between the secondary transfer roller 145 and the secondary transfer counter roller 146. The paper feed unit 13 includes a paper feed tray 131, a paper feed roller 132, a paper feed belt 133, and a registration roller 134. The paper feed tray 131 contains paper P. The paper feed roller 132 is provided to transport the paper P stored in the paper feed tray 131 toward the paper feed belt 133. The paper feed roller 132 provided in this way takes out the paper P at the top of the stored paper P one by one and places it on the paper feed belt 133.

  The sheet feeding belt 133 conveys the sheet P taken out by the sheet feeding roller 132 toward the secondary transfer roller 145 and the secondary transfer counter roller 146 in the direction of the arrow (A1). A registration roller 134 is provided on the paper feed belt 133 before the paper P reaches the secondary transfer roller 145. The registration roller 134 sends out the paper P at the timing when the portion of the intermediate transfer belt 143 where the toner image is formed reaches the position of the secondary transfer roller 145.

  The fixing device 15 fixes the toner transferred from the intermediate transfer belt 143 to the paper P. Fixing means that the resin component of the toner is welded to the paper P when heat and pressure are simultaneously applied to the toner. In the fixing device 15, a fixing belt 151 as a fixing member that rotates in contact with an unfixed image and a fixing counter roller 152 as a pressure member that forms a nip portion 151 </ b> A between the fixing belt 151 and the fixing belt 151. It is provided facing. The fixing belt 151 presses the paper P while sandwiching the paper P on which the toner has been transferred between the fixing belt 151 and the fixing facing roller 152. Further, the fixing belt 151 rotates in the direction of the arrow (A3) so as to convey the sheet P toward the discharge port together with the fixing counter roller 152. Note that a fixing roller, which is an example of a fixing member, may be used instead of the fixing belt 151.

  As shown in FIG. 2, the fixing belt 151 has an aluminum roller core 151a having an outer diameter of 40 mm and a thickness of 1 mm, and a heat insulating layer 151b covering the surface of the roller core 151a. The heat insulating layer 151b is made of silicon rubber and has a thickness of 3 mm.

  In addition, a good heat conductive layer 151c is formed outside the heat insulating layer 151b. The good heat conductive layer 151c is formed of nickel, stainless steel, aluminum, copper, or a graphite sheet having higher heat conductivity than the heat insulating layer 151b. By forming the good heat conductive layer 151c in this way, it is possible to reduce the temperature unevenness of the fixing belt 151. In addition, a 5 to 30 μm release layer 151d made of a fluorine-based resin such as PFA or PTFE is formed outside the good heat conductive layer 151c. By forming the release layer 151d, the paper P pressed by the fixing belt 151 is easily separated from the release layer 151d.

  The fixing counter roller 152 has an aluminum roller core 152a having an outer diameter of 40 mm and a thickness of 2 mm, and a heat insulating layer 152b covering the surface of the roller core 152a. A nip portion 151A is provided between the fixing counter roller 152 and the fixing belt 151. Form.

  A heating unit 153 that heats the fixing belt 151 with electric power from a power source (not shown) is provided outside the fixing belt 151. FIG. 3 is a perspective view showing the configuration of the fixing device 15. As shown in FIG. 3, the heating unit 153 includes a plurality of heaters 153a to 153g. The heaters 153 a to 153 g are arranged side by side in the width direction of the fixing belt 151, that is, the rotation direction of the fixing member, and each heats a part of the fixing belt 151. Specifically, the heater 153a heats the portion a of the fixing belt 151 shown in FIG. Further, the heater 153a has a shape having a flat surface, and the flat portion is in contact with the portion a of the fixing belt 151 to heat the fixing belt 151 from the outside. Similarly, the heaters 153b to 153g heat the portions b to g of the fixing belt 151, respectively. As a result, a plurality of heating regions are formed on the fixing belt 151.

  Specifically, when the toner adhesion amount adhering to a predetermined portion of the paper P passing through the fixing belt 151 is not zero (hereinafter, this portion is referred to as an image portion), an image is formed on the image portion of the paper P by toner. And the toner needs to be fixed. Therefore, the corresponding heater of the heating unit 153 heats the fixing belt 151 so that the portion of the fixing counter roller 152 that pressurizes the image portion of the paper P is set to 160 ° C. When the amount of toner attached to a predetermined portion of the paper P passing through the fixing belt 151 is 0, the corresponding heater of the heating unit 153 applies the non-image portion of the paper P to the fixing counter roller 152 that pressurizes the non-image portion. The fixing belt 151 is heated so that the portion becomes 110 ° C. Hereinafter, a portion where the toner adhesion amount adhering to the paper P is 0 is referred to as a non-image portion. The temperature at which the heater of the heating unit 153 heats the fixing belt may be any temperature that fixes the toner on the image portion of the paper P, and an appropriate numerical value is set according to various conditions.

  Further, as shown in FIG. 3, a temperature measuring unit 154 for measuring the temperature of the fixing belt 151 is provided in the vicinity of the heating unit 153, and the temperature measuring unit 154 includes a plurality of temperature sensors 154a to 154g. doing. As shown in FIG. 3, the temperature sensor 154a measures the temperature of the portion a of the fixing belt 151 heated by the heater 153a. Similarly, the temperature sensors 154b to 154g measure the temperatures of the portions b to g of the fixing belt 151, respectively. Thereby, the temperatures of the plurality of heating regions of the fixing belt 151 are detected.

  Further, a temperature measuring unit 155 that measures the temperature of the fixing counter roller 152 is provided in the vicinity of the side surface of the fixing counter roller 152, and the temperature measuring unit 155 includes temperature sensors 155a to 155g. Thereby, the temperatures of the plurality of heating regions of the fixing counter roller 152 are detected. Since the fixing belt 151 heated by the heating unit 153 is in contact with the fixing counter roller 152 as described above, the fixing counter roller 152 is heated by the heat from the fixing belt 151 moving. As shown in FIG. 3, the temperature sensor 155a measures the temperature of the portion a 'of the fixing facing roller 152 facing the portion a of the fixing belt 151 heated by the heater 153a. Similarly, the temperature sensors 155b to 155g measure the temperatures of the portions b 'to g' of the fixing counter roller 152, respectively.

  Returning to FIG. 1, on the left side of the image forming apparatus 1 in the drawing, the paper P heated and pressed by the fixing belt 151 and the fixing counter roller 152 to discharge the sheet P on which the image is fixed is discharged to the outside of the image forming apparatus 1. A paper mouth 10 is provided.

  A display / operation unit 18 is provided outside the image forming apparatus 1. The display / operation unit 18 includes a panel display unit 181 and an operation unit 182. The panel display unit 181 is a touch panel or the like on which setting values, selection screens, and the like are displayed and receives input from the user. The operation unit 182 is a numeric keypad for the user to input various information related to image formation, a start key for the user to input a start instruction, and the like.

  Further, the image forming apparatus 1 is provided with a control unit for controlling the above-described units. FIG. 4 is a diagram illustrating a hardware configuration of the control unit of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 4, the control unit includes a CPU (Central Processing Unit) 1011, a main memory (MEM-P) 1012, a north bridge (NB) 1013, and a south bridge (SB) 1014. Further, the control unit includes an AGP (Accelerated Graphics Port) 1015 and an ASIC (Application Specific Integrated Circuit) 1016. The control unit further includes a local memory (MEM-C) 1017, an HD (Hard Disk) 1018, an HDD (Hard Disk Drive) 1019, a PCI bus 1020, and a network I / F 1021.

  The CPU 1011 processes and calculates data according to a program stored in the main memory 1012, and controls the operation of each unit described above. The main memory 1012 is a storage area of the control unit, and includes a ROM (Read Only Memory) 1012a and a RAM (Random Access Memory) 1012b. The ROM 1012a stores programs and data for realizing each function of the control unit. The program stored in the ROM 1012a is recorded in a computer-readable recording medium such as a CD-ROM, FD, CD-R, or DVD as a file in an installable or executable format and provided. May be.

  The RAM 1012b is used as a drawing memory or the like when developing programs and data and printing memory. The NB 1013 is a bridge for connecting the CPU 1011 to the MEM-P 1012, the SB 1014, and the AGP bus 1015. The SB 1014 is a bridge for connecting the NB 1013 and peripheral devices. The AGP bus 1015 is a bus interface for a graphics accelerator card for speeding up graphics processing. The ASIC 1016 includes a memory controller that controls the MEM-C 1017, and a plurality of DMACs (Direct Memory Access Controllers) that rotate image data and the like using hardware logic and the like. The ASIC 1016 is connected to a USB (Universal Serial Bus) interface via a PCI bus 1020. The ASIC 1016 is connected to a network I / F 1021 such as an IEEE 1394 (Institut of Electrical and Electronics Engineers 1394) interface.

  The MEM-C 1017 is a local memory used as a copy image buffer and a code buffer. The HD 1018 is a storage for accumulating image data, accumulating font data used during printing, and accumulating forms. The HDD 1019 controls reading or writing of data with respect to the HD 1018 according to the control of the CPU 1011. A network I / F 1021 transmits / receives information to / from an external device such as an information processing apparatus via a communication network.

<Functional Configuration of Image Forming Apparatus 1>
The functional configuration of the control unit of the image forming apparatus 1 in the present embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating a functional configuration of the control unit of the image forming apparatus 1.

  The control unit controls the operation of the image forming apparatus 1. As shown in FIG. 5, the control unit 191, the input receiving unit 192, the image reading control unit 193, the image formation information generation unit 194, and the image formation control unit 196. A storage / reading processing unit 199 and a storage unit 1900. Each of these units is a function or means realized by operating according to a command from the CPU 1011 according to a program stored in the ROM 1012a shown in FIG. Further, the control unit has a storage unit 1900 constructed by the ROM 1012a or the HD 1018 shown in FIG.

  The transmission / reception unit 191 is realized by the network I / F 1021 illustrated in FIG. 4 and receives RGB image information from an information processing apparatus or the like via the communication network. The RGB image information is information representing an image formed on the paper P, and is indicated using the lightness of each color of red (R), green (G), and blue (B). The input receiving unit 192 receives information input by the user through the display / operation unit 18 shown in FIG. The image reading control unit 193 controls the scanner unit 11 shown in FIG. 1 to optically read an image described in a document and generate RGB image information.

  The image formation information generation unit 194 generates image formation information based on the RGB image information received by the transmission / reception unit 191 or the RGB image information read by the scanner unit 11. Specifically, the image formation information generation unit 194 performs color space conversion processing on the RGB image information, and each of the toner adhesion amounts Vc, Vm, C, M, Y, and K attached to the paper P Vy and Vk are calculated for each pixel. Note that the image formation information generation unit 194 may perform undercolor removal processing, shading correction, position shift correction, color space conversion, gamma correction, and the like in addition to the color space conversion processing. Further, the image formation information is information representing the C, M, Y, and K toner adhesion amounts Vc, Vm, Vy, and Vk attached to each pixel in order to form an image on the paper P. .

  The image forming control unit 196 includes an image forming control unit 1962 that controls the image forming units 12C, 12M, 12Y, and 12K, a paper feed control unit 1963 that controls the paper feeding unit 13, a primary transfer roller 144, a secondary transfer roller 145, The image forming apparatus includes a transfer control unit 1964 that controls the intermediate transfer belt 143 and the like, and a fixing control unit 1965 that controls the fixing device 15.

  Here, the fixing controller 1965 will be described in detail with reference to FIGS. The fixing control unit 1965 includes a heat amount determination unit 19651 and a heating control unit 19652. Based on the image formation information generated by the image formation information generation unit 194, the heat quantity determination unit 19651 determines whether each part of the paper P is an image part or a non-image part. Further, the heat amount determination unit 19651 determines the amount of heat applied to the heating unit 153 based on the temperature of the fixing belt 151, the paper basis weight of the paper P, the smoothness of the paper P, the toner adhesion amount of the paper P, and the temperature of the fixing counter roller 152. decide. The heating control unit 19652 controls the heating unit 153 to heat the fixing belt 151 with the heat amount determined by the heat amount determining unit 19651.

  The heating unit 153 heats the fixing belt 151 to a temperature necessary for fixing the image portion of the paper P (referred to as a first temperature) so that the toner is properly fixed and energy consumption is saved. To do. Further, when a non-image portion of the paper P that does not need to be fixed passes through the nip portion 151A, the fixing belt 151 that pressurizes the paper P has a predetermined temperature (referred to as a second temperature) lower than the first temperature. Thus, the heating unit 153 heats. The temperature of the fixing belt 151 is measured by the temperature measuring unit 154.

  As an example, it is assumed that the sheet P includes an image part a, a non-image part b, and an image part c as shown in FIG. 6, and passes through the nip part 151A while moving in the direction indicated by the arrow (A4). In that case, the heating unit 153 is controlled by the heating control unit 19652 so as to change the temperature shown in FIG. As shown in FIG. 7, the fixing belt 151 heated by the heating unit 153 becomes the first temperature when the image portion a and the image portion c of the paper P are inserted into the nip portion 151 </ b> A of the fixing device 15. Need to be. Therefore, the heating unit 153 starts heating the fixing belt 151 a predetermined time before the image portion c is inserted into the nip portion 151 </ b> A as shown in FIG. 7 b ′.

  Here, since the temperature of the fixing belt 151 becomes the first temperature, the amount of heat that the heating unit 153 heats the fixing belt is the temperature of the fixing belt, the paper basis weight of the paper P, the smoothness of the paper P, and the toner of the paper P. Based on the adhesion amount and the temperature of the fixing counter roller 152, the heat amount determination unit 19651 determines. Specifically, as the temperature of the fixing belt 151 is higher, the first temperature can be reached even when the heating unit 153 has a smaller amount of heat to heat the fixing belt 151. Therefore, as shown in FIG. 8A, the heat amount determining unit 19651 determines the heat amount so that the heat amount by which the heating unit 153 heats the fixing belt 151 decreases as the temperature of the fixing belt 151 increases.

  Further, when the non-image portion of the paper P passes through the nip portion 151A, the heating unit 153 heats the fixing belt 151 with the temperature of the fixing belt 151 and the amount of heat having the relationship shown in FIG. A calorific value determining unit 19651 determines the calorific value. Further, when the sheet P does not pass through the nip portion 151A, the heat amount is determined so that the heating unit 153 heats the fixing belt 151 with the temperature of the fixing belt 151 and the heat amount having the relationship shown in FIG. Part 19651 determines the amount of heat.

Further, as the paper basis weight, which is the weight per 1 m ^{2 of} the paper P, is larger, heat is more easily transferred to the paper P during the fixing process, and the toner is less likely to be heated. For this reason, as shown in FIG. 9A, the heat amount determining unit 19651 determines the amount of heat so that the heat amount by which the heating unit 153 heats the fixing belt 151 increases as the paper basis weight of the paper P increases.

  Further, as the smoothness of the paper P becomes higher, the toner becomes easier to be fixed on the paper P. Therefore, the fixing process may be performed at a lower temperature than when the smoothness of the paper P is low. Therefore, as shown in FIG. 10A, the heat quantity determining unit 19651 determines the heat quantity so that the heat quantity that the heating part 153 heats the fixing belt 151 decreases as the smoothness of the paper P increases.

  Further, the toner needs to be fixed at a higher temperature as the toner adhesion amount on the paper P is larger. Therefore, as shown in FIG. 11A, the heat amount determining unit 19651 determines the heat amount so that the heat amount by which the heating unit 153 heats the fixing belt 151 increases as the toner adhesion amount increases.

  The heating unit 153 has a larger heat capacity than the fixing belt 151. Therefore, if the heating unit 153 is high temperature, the heating unit 153 can heat the fixing belt 151 to the first temperature with a small amount of heat, but if the heating unit 153 is low temperature, the heating unit 153 causes the fixing belt 151 to heat. It takes time to heat. That is, as shown in FIG. 12 (1), the heat quantity determination unit 19651 determines the heat quantity so that the higher the temperature of the heating part 153, the smaller the heat quantity that the heating part 153 heats the fixing belt 151. The temperature of the heating unit 153 is measured by a temperature sensor as a temperature measuring unit (not shown).

  Similarly, the fixing facing roller 152 has a larger heat capacity than the fixing belt 151. Therefore, if the fixing counter roller 152 is at a low temperature, the heat generated by the heating unit 153 is transmitted to the fixing counter roller 152, and a large amount of heat is required to heat the fixing belt 151. The heating unit 153 can heat the fixing belt 151 to the first temperature with a smaller amount of heat as the fixing counter roller 152 is higher in temperature. That is, as shown in FIG. 13A, the heat amount determination unit 19651 determines the amount of heat so that the heat amount of the heating unit 153 heating the fixing belt 151 decreases as the temperature of the fixing counter roller 152 increases.

  When the non-image portion passes through the nip portion 151A, the paper basis weight of the paper P, the smoothness of the paper P, the toner adhesion amount of the paper P, and the temperature of the fixing facing roller 152 are shown in FIGS. The amount of heat determination unit 19651 determines the amount of heat so as to satisfy the relationship shown in (2).

  When the paper P does not pass through the nip portion 151A, the paper basis weight of the paper P, the smoothness of the paper P, the toner adhesion amount of the paper P, and the temperature of the fixing counter roller 152 are shown in FIGS. The heat quantity determination unit 19651 determines the heat quantity so that the relationship shown in (3) of FIG.

  When the sheet P has not passed through the nip portion 151A, the longer the time from the passage of one sheet P1 through the nip portion to the passage of the next sheet P2 through the nip portion 151A, the higher the temperature of the fixing belt 151. Can be low. Therefore, as shown in FIG. 14A, the heat amount determination unit 19651 determines the heat amount so that the heat amount by which the heating unit 153 heats the fixing belt 151 decreases as the interval between sheets increases.

  The fixing belt 151 is an example of a fixing member, and the smoothness and the paper basis weight of the paper P are examples of characteristics of the recording medium.

<< Processing and Operation of Embodiment >>
Subsequently, processing of the image forming system according to the present embodiment will be described with reference to FIGS. 15 and 16. FIG. 15 is a process flow diagram illustrating an outline of a process in which the image forming apparatus 1 forms an image. FIG. 16 is a process flowchart showing details of the fixing process.

  As shown in FIG. 15, first, the transmission / reception unit 191 receives RGB image information from an external information processing apparatus or the like (step S21). When the transmission / reception unit 191 receives the RGB image information, the image formation information generation unit 194 generates image formation information based on the RGB image information (step S22).

  Specifically, the image formation information generation unit 194 calculates toner adhesion amounts Vc, Vm, Vy, and Vk by performing color space conversion processing on the RGB image information. Note that the image formation information generation unit 194 may execute known image processing such as under color removal processing, color correction processing, and spatial frequency correction processing in addition to color space conversion processing on RGB image information. Further, the image formation information generation unit 194 calculates toner adhesion amounts Vc, Vm, Vy, and Vk for all the pixels on the paper P, and is an image that is information indicating the position on the paper P and the toner adhesion amount corresponding to the position. Generate formation information.

  When the image formation information is generated in step S22, the paper feed unit 13 performs a paper feed process under the control of the paper feed control unit 1963 (step S23). Specifically, the paper feed roller 132 of the paper feed unit 13 takes out the paper P stored in the paper feed tray 131 one by one and places it on the paper feed belt 133. The paper feed belt 133 moves in the direction of the arrow (A1) shown in FIG. When the conveyed paper P reaches the registration roller 134, the registration roller 134 sandwiches the paper P and waits until the toner image formed on the surface of the intermediate transfer belt 143 reaches the secondary transfer roller 145. Then, at the timing when the toner image formed on the surface of the intermediate transfer belt 143 reaches the secondary transfer roller 145, the registration roller 134 feeds the paper P between the secondary transfer roller 145 and the secondary transfer counter roller 146.

  On the other hand, the image forming units 12C, 12M, 12Y, and 12K perform image forming processing for attaching each toner to each photoconductive drum 122 under the control of the image forming control unit 1962 (step S24). Specifically, the charging unit 123C uniformly charges the surface of the photosensitive drum 122C. Then, the exposure unit 124C irradiates the surface of the photosensitive drum 122C with laser light based on the toner adhesion amount Vc of the image formation information generated by the image formation information generation unit 194. As a result, an electrostatic latent image is formed on the surface of the photoconductive drum 122C for adhering the C-color toner having the toner adhesion amount Vc to the paper P.

  When the electrostatic latent image is formed on the surface of the photosensitive drum 122C, the developing unit 125C develops the electrostatic latent image using C-color toner. In this way, a C-color toner image is formed on the surface of the photosensitive drum 122C. Similarly, toner images of M, Y, and K toners are formed on the surfaces of the photosensitive drums 122M, 122Y, and 122K, respectively. Since these image forming processes are the same as the processes for forming a C-color toner image on the surface of the photosensitive drum 122C, the description thereof is omitted.

  When a toner image is formed on the surface of each photosensitive drum 122 with each toner, a transfer process is performed under the control of the transfer control unit 1964 (step S25). Specifically, first, the primary transfer roller 144 applies a primary transfer bias to the intermediate transfer belt 143. Then, the toner image on the surface of each photosensitive drum 122 is transferred to the intermediate transfer belt 143 (hereinafter referred to as primary transfer).

  The intermediate transfer belt 143 onto which the toner image has been transferred moves in the direction of the arrow (A2) as the driving roller 141 and the driven roller 142 rotate. Further, the registration roller 134 sends out the paper P at the timing when the portion of the intermediate transfer belt 143 to which the toner image is transferred reaches the secondary transfer roller 145. When the sheet P is sent out by the registration roller 134 and reaches the secondary transfer roller 145, the secondary transfer roller 145 sandwiches the sheet P and the intermediate transfer belt 143 between the secondary transfer counter roller 146, and the sheet P is subjected to the secondary transfer. Apply transfer bias. As a result, the toner image formed on the surface of the intermediate transfer belt 143 is transferred onto the paper P (hereinafter referred to as secondary transfer).

  As described above, when the toner image is transferred to the paper P, the fixing device 15 performs a fixing process under the control of the fixing control unit 1965 (step S26). Specifically, as shown in FIG. 16, first, the heating unit 153 heats the fixing belt 151 (step S261). Here, the heat amount determination unit 19651 determines the amount of heat with which the heating unit 153 heats the fixing belt 151. Then, the heating control unit 19652 controls the heating unit 153 to heat the fixing belt 151.

  Based on the image formation information generated by the image formation information generation unit 194, the heat quantity determination unit 19651 determines whether each part of the paper P is an image part or a non-image part. Then, the heat amount determination unit 19651 determines the heat amount by which the heating unit 153 heats the fixing belt 151 in contact with the portion determined to be the image portion of the paper P.

  Specifically, as illustrated in FIG. 8A, the heat amount determination unit 19651 determines the heat amount so that the heat amount by which the heating unit 153 heats the fixing belt 151 decreases as the temperature of the fixing belt 151 increases. Further, as shown in FIG. 9A, the heat quantity determination unit 19651 determines the heat quantity so that the heat quantity by which the heating unit 153 heats the fixing belt 151 increases as the paper basis weight of the paper P increases. Further, as shown in FIG. 10A, the heat quantity determination unit 19651 determines the heat quantity so that the heating part 153 reduces the heat quantity for heating the fixing belt 151 as the smoothness of the paper P becomes higher.

  Further, as shown in FIG. 11A, the heat amount determination unit 19651 determines the heat amount so that the heat amount by which the heating unit 153 heats the fixing belt 151 increases as the toner adhesion amount increases. Further, as shown in FIG. 12A, the heat amount determination unit 19651 determines the amount of heat so that the higher the temperature of the heating unit 153, the smaller the amount of heat that the heating unit 153 heats the fixing belt 151. Similarly, as shown in FIG. 13A, as the temperature of the fixing counter roller 152 is higher, the heat amount determination unit 19651 determines the amount of heat so that the heating unit 153 reduces the amount of heat that heats the fixing belt 151.

  The heat amount determining unit 19651 shows the amount of heat that the heating unit 153 heats the fixing belt 151 in contact with the portion determined to be a non-image portion of the paper P, as shown in (2) of FIG. 8 to FIG. The fixing belt 151 is heated with a heat amount having a relationship. The same applies to the paper basis weight of the paper P, the smoothness of the paper P, the toner adhesion amount of the paper P, the temperature of the fixing facing roller, and the temperature of the pressure roller.

  When the amount of heat for heating the fixing belt 151 in the portion in contact with the image portion and the non-image portion of the paper P is determined in this way, the heating unit 153 heats the fixing belt 151 with the determined amount of heat.

  When the conveyed paper P reaches a position where the fixing belt 151 and the fixing opposing roller 152 are in contact with each other, the fixing belt 151 sandwiches the paper P between the fixing belt 151 and the fixing opposing roller 152. At this time, since the fixing belt 151 is heated by the heating unit 153, the fixing belt 151 pressurizes the paper P and simultaneously heats the paper P at a predetermined temperature (step S262). The toner forming the toner image transferred onto the paper P is melted, and the toner is fixed to the paper P when the fixing belt 151 presses the paper P to which the melted toner adheres together with the fixing facing roller 152.

  Here, the process of heating the fixing belt 151 by the heating unit 153 performed in step S261 will be described in detail with reference to FIG. The fixing belt 151 is heated by a heating unit 153 provided inside. At this time, the fixing belt 151 is rotating in the direction of the arrow (A3) in FIG. 1, and the heating unit 153 heats the rotating fixing belt 151, so that the fixing belt 151 becomes high temperature as a whole.

  Returning to FIG. 15, when the toner is fixed on the paper P by the fixing device 15, the paper P is discharged out of the image forming apparatus 1 from the paper discharge port 10 (step S <b> 27).

<< Supplement to the first embodiment >>
In this embodiment, the heating unit 153 is provided outside the fixing belt 151. However, as shown in FIG. 17, the heating unit 153 is provided inside the fixing belt 151, and pressure is applied from the outside of the fixing belt 151. The unit 156 may press the fixing belt 151 against the heating unit 153.

  The pressure unit 156 provided in this way has a larger heat capacity than the fixing belt 151. Therefore, if the pressure unit 156 is at a low temperature, the heat generated by the heating unit 153 is transmitted to the pressure unit 156, and a large amount of heat is required to heat the fixing belt 151. The higher the pressure unit 156 is, the higher the heating unit 153 can heat the fixing belt 151 to the first temperature with a small amount of heat. That is, as shown in FIG. 18A, the heat amount determining unit 19651 determines to decrease the amount of heat applied to the fixing belt 151 as the temperature of the pressure unit 156 (pressure roller) increases. The temperature of the pressure unit 156 (pressure roller) is measured by a temperature sensor (not shown).

  In the present embodiment, the heating unit 153 includes seven heaters 153a to 153g, but the number of heaters may be other than that.

  In this embodiment, the transmission / reception unit 191 receives image information in step S21. However, the reading sensor 112 controlled by the image reading control unit 193 receives an RGB image from a document sheet or the like placed on the contact glass 111. Information may be read.

  In this embodiment, the image forming apparatus 1 forms an image using C, M, Y, and K toners. However, the C, M, Y, and K toners are used. In addition, special toners such as clear toner and white toner may be used.

  In the present embodiment, the image forming apparatus 1 describes a process of forming an image based on RGB image information. However, the image forming apparatus 1 may form an image based on image information representing a monochrome image.

(Second Embodiment)
FIG. 19 is a diagram illustrating an overall configuration of an image forming apparatus including a double-sided printing mechanism according to the second embodiment. The configuration is basically the same as that of the horizontal type image forming apparatus of FIG. 1 except that the paper conveyance direction is different and has a reverse conveyance path. Therefore, the same components are denoted by the same reference numerals. Therefore, explanation is omitted. Here, the configuration and operation of the image forming apparatus according to the present exemplary embodiment are performed only with respect to the reverse conveyance of the fixing device and the sheet and the duplex printing.

  The operation of forming an image on the paper P in the case of single-sided printing is the same as that described with reference to FIG. 1, but in the case of double-sided printing, the operation is as follows. The image forming apparatus 1 forms and fixes an image on one side of the paper P, and guides the paper P to the reversing path 136 by switching the switching claw 138. Next, the switching claw 139 is switched to re-feed the reversed paper P from the re-feed path 137 to the registration roller 134. At this time, a toner image to be a back image is formed and carried on the intermediate transfer belt 143, the toner image is transferred to the back surface of the paper P, and is subjected to a fixing process by the fixing device 15 ′. Paper is ejected up. Henceforth, in the case of double-sided printing, the surface printed first is called a 1st surface, and the back surface is called a 2nd surface.

  FIG. 20 is a diagram illustrating a configuration of a fixing device in the image forming apparatus of the present embodiment. The fixing device 15 ′ in the present embodiment employs an internal heating method of the fixing belt, similarly to the fixing device of FIG. 17. The fixing device 15 ′ has a fixing belt 151 as a fixing member that rotates in contact with an unfixed image, and a pressure roller 152 as a pressure member that forms a nip portion 151 A between the fixing belt 151. doing. The fixing device 15 ′ includes a thermal heater 153 as a heating unit that heats the fixing belt 151 with electric power from a commercial power source. The thermal heater is composed of a thermal head in which a resistance heating element is formed on a plate-like substrate.

  The fixing belt 151 has a PI base 151a having an outer diameter of 40 mm and a thickness of 50 to 100 μm, and an elastic layer 151b coated on the surface of the base 151a. The elastic layer 151b is made of silicon rubber and has a thickness of 50 to 100 μm. On the surface of the fixing belt 151, a release layer 151 c having a thickness of 5 to 50 μm is formed with a fluorine-based resin such as PFA or PTFE in order to enhance durability and ensure release properties. The base 151a of the fixing belt is not limited to polyimide, but may be a metal base such as nickel or SUS.

  There is a support member 161 inside the fixing belt 151, and a pressure roller 160 and a pressure roller 152 are installed at a location of the nip portion 151A, and connected to a side plate external member (not shown) to support the fixing member.

  The pressure roller 152 has an iron cored bar 152a having an outer diameter of 40 mm and a thickness of 2 mm, and an elastic layer 152b covered on the surface of the cored bar 152a. The elastic layer 152b is made of silicon rubber and has a thickness of 5 mm. It is desirable to form a fluororesin layer having a thickness of about 40 μm on the surface of the elastic layer 152b in order to improve releasability. The pressure roller 152 is pressed against the fixing belt 151 by an urging means (not shown).

  FIG. 21 is a schematic diagram of a thermal heater. The thermal heater 153 as a heating unit includes a plurality of heaters 153a to 153g arranged at equal intervals in the width direction of the fixing belt 151 or in the direction orthogonal to the sheet conveyance direction. Each of the heaters 153a to 153g corresponds to a heating region and can be heated independently. A ceramic heater may be used instead of the thermal heater. The thermal heater 153 has seven heaters 153a to 153g, but the number of heaters may be other than that. The thermal heater 153 is pressed against the surface of the fixing belt 151 by an urging means (not shown).

  A pressing roller 160 as a pressing member that presses the fixing belt is disposed at a position facing the heater 153 on the outer peripheral side of the fixing belt 151. The fixing belt 151 comes into contact with the heater 153 by the pressing roller 160.

  A thermistor 154 that detects the surface temperature of the fixing belt 151 is provided downstream of the nip portion 151 </ b> A of the fixing belt 151 and upstream of the heater 153. A thermistor 155 that detects the temperature of the heater 153 is provided on the heater 153. ing. The thermistors 154 and 155 are examples of temperature measuring units.

  Further, the fixing device 15 ′ includes a power source 170 that supplies power to the heater 153, a fixing controller 175 that controls the power source 170 based on detection information of the thermistors 154 and 155, and heating performance of the heating region of each heater 153. A heating performance storage unit 180 that holds information is provided. The fixing control unit 175 changes the heating rate of the thermal heater 153 based on image information for forming an image on the paper P. Here, the fixing control unit 175 means a microcomputer including a CPU, a ROM, a RAM, an I / O interface, and the like. The heating performance storage unit 180 will be described later.

  Next, fixing control will be described. FIG. 22 is a diagram showing a typical pattern of image areas and non-image areas formed on the paper P, and control in the sub-scanning direction is necessary. FIG. 22A shows an image forming pattern in which an image area a, a non-image area b, and an image area a ′ are present in order from the leading end side in the conveyance direction (A4) of the paper P, and corresponds to FIG. To do. The image area a and the image area a ′ where the toner to be fixed exists needs to be fixed, but the non-image area b where no toner exists does not need to be fixed.

  FIG. 22B shows an image forming pattern in which an image area a and a non-image area b exist in order from the leading end side in the conveyance direction (A4) of the paper P. The image area a where the toner to be fixed exists needs fixing, but the non-image area b where no toner exists does not need fixing.

  FIG. 23 is a diagram showing another pattern of the image area and the non-image area formed on the paper P, and control in the main scanning direction is necessary. FIG. 23A shows an image forming pattern in which an image area c and a non-image area d exist in a direction orthogonal to the conveyance direction (A4) of the paper P (the width direction of the fixing belt). It is. The image area c where the toner to be fixed exists needs fixing, but the non-image area d where no toner exists does not need fixing.

  FIG. 23B shows an image region e in a part of the direction orthogonal to the transport direction (A4) of the paper P, and the remaining region f has the image region g on the front side in the transport direction (A4) of the paper P and the rear side. An image forming pattern having a non-image area h on the side is shown. The image areas e and g where the toner to be fixed exists need fixing, but the non-image area h where no toner exists does not need fixing.

  In FIG. 22A, image information of the pattern is input to the fixing control unit 175 from an image processing apparatus (not shown). The fixing control unit 175 sets the power supply 170 and the heater 153 so that the temperature of the part of the fixing belt 151 corresponding to the non-image area b is lower than the temperature of the part of the fixing belt 151 corresponding to the image areas a and a ′. Control.

  Here, the portion of the fixing belt 151 corresponding to the image region or the non-image region means a portion of the fixing belt 151 that is in close contact with the image region or the non-image region. That is, power is supplied to the entire area of the heaters 153a to 153g so that the belt portion corresponding to the image area a distributed over the entire sheet width can obtain a predetermined fixing temperature, while the belt corresponding to the non-image area b. The power supply is reduced at the site. Then, power is again supplied to the heaters 153a to 153g so that the belt portion corresponding to the image area a 'at the rear end of the paper reaches the fixing temperature.

  Similarly in FIG. 22B, power is supplied to the entire area of the heaters 153a to 153g so that the belt portion corresponding to the image region a can obtain a predetermined fixing temperature, while the belt corresponding to the non-image region b. The power supply is reduced at the site.

  In FIG. 23A, electric power is supplied to the heaters 153a to 153g so that the belt portion corresponding to the image region c distributed over almost half of the paper width can obtain a predetermined fixing temperature. Specifically, the fixing control unit 175 causes the temperature of the part of the fixing belt 151 corresponding to the non-image area d to be lower than the temperature of the part of the fixing belt 151 corresponding to the image area c. For example, the supply power of the heaters 153e to 153g is made smaller than the supply power of the heaters 153a to 153d.

  In FIG. 23B, electric power is supplied to the entire area of the heaters 153a to 153g so that the belt portion corresponding to the e and fg regions where the image region is distributed over the entire sheet width can obtain a predetermined fixing temperature. To do. Thereafter, for example, the supply power of the heaters 153a to 153d is larger than the supply power of the heaters 153e to 153g so that the belt portion corresponding to the image region e distributed over almost half the width of the sheet can obtain a predetermined fixing temperature. To do.

  The actual supply power in the fixing control is adjusted so that preliminary heating is performed in a portion before the image area enters the nip portion, as indicated by the hatched portion in each drawing. Such a preliminary heating region is a region that mainly takes into account the length of the heater in the circumferential direction and that the heater itself requires a heating time. The preheating region is desirably as small as possible from the viewpoint of energy saving.

  As the fixing control, the power supply may be completely stopped at the portions corresponding to the non-image areas b, d, and h. However, if the temperature is too low, the next image area (the image area in FIG. The rising response to the fixing temperature in a ′) is deteriorated. Therefore, it is desirable to keep the temperature of the fixing belt 151 at a predetermined value or higher by blinking the heater 153 or supplying low power to the heater 153.

  FIG. 24 is a diagram showing the relationship between the target temperature of the fixing belt, which is a fixing member, and time in the case of the image forming pattern of FIG. As indicated by the solid line, the fixing belt temperature is set to the first temperature in the image areas a and a ′, but in the non-image area b, the fixing belt temperature is higher than room temperature and lower than the first temperature. It is controlled to keep the temperature. Also in the case of the image formation patterns of FIGS. 22B, 23A, and 23B, the fixing belt temperature is set to the first temperature in the image area by similarly controlling the heaters 153a to 153g. In the non-image area, the fixing belt temperature can be set to the second temperature.

  As described above, power is supplied to the heater also in the portions corresponding to the non-image areas b, d, and h, but the supplied power is reduced. That is, since the power supply can be made smaller in the region R ′ that does not correspond to the preheating area in the non-image area than the power supply in the area R corresponding to the image area and the preheating area, it is possible to save energy.

  As described above, even in the fixing control during single-sided printing, heating is different depending on the image area and the non-image area in both the sub-scanning direction and the main-scanning direction, but when performing double-sided printing in the image forming apparatus of FIG. There are more points to consider. That is, at the time of printing on the second side (back side), the fixing temperature is changed depending on whether or not there is an image on the first side as well as the image area and non-image area on the second side. This is because if there is a fixed image on the first surface, the heat capacity of the paper P increases at that portion, and it is necessary to supply a larger amount of heat when printing on the second surface. Therefore, in the fixing control during double-sided printing, the fixing temperature on the second surface is changed depending on whether or not there is an image on the first surface.

Specific fixing temperatures at the time of duplex printing are shown in Tables 1 and 2.

  As shown in Table 1, the fixing temperature during the first-side printing is the second temperature for the non-image area and the first temperature for the image area (this is the same as that for single-sided printing). Is). As shown in Table 2, the fixing temperature during the second side printing is divided into four cases depending on the presence / absence of the second side image and the presence / absence of the first side image. For convenience, the overall expression is simply expressed as the first surface and the second surface, but the control is performed for each region divided by a plurality of heaters. The non-image area on the second surface is set to the second temperature regardless of the presence or absence of the image on the first surface. The image area of the second surface is the first temperature if there is no image on the first surface, and the temperature obtained by adding the correction temperature α to the first temperature if there is an image on the first surface.

  The correction temperature α may be a constant value, but can be determined as appropriate based on the image density, image color, etc. formed on the first surface or the second surface. Here, the image density and image color are determined by the fixing control unit 175 based on image information from an image processing apparatus (not shown).

  Next, fixing control during duplex printing will be described. FIG. 25 is a diagram showing an image area and a non-image area formed on both sides of the paper P. FIG. 25A is the first surface of the sheet P, and shows an image formation pattern in which an image area a, a non-image area b, and an image area a ′ are present in order from the leading side in the conveyance direction (A4) of the sheet P. It is shown. FIG. 25B shows an image forming pattern on the second surface of the paper, in which a non-image region b, an image region a, and an image region a ′ are present in order from the leading side in the transport direction (A4) of the paper P. It is a thing. The image area a where the toner to be fixed exists needs fixing, but the non-image area b where no toner exists does not need fixing.

  In the case where the image shown in FIG. 25A is formed and fixed on the first surface during duplex printing, when the second surface is fixed, the pattern shown in FIG. Is input to the fixing controller 175. Accordingly, the fixing control unit 175 controls the power supply 170 and the heater 153 so that the temperature of the portion of the fixing belt 151 corresponding to the non-image area b on the second surface becomes the first temperature. Subsequently, the fixing control unit 175 sets the power supply 170 and the heater so that the temperature of the portion of the fixing belt 151 corresponding to the image area a of the second surface where the first surface is the non-image area b becomes the first temperature. 153 is controlled.

  The fixing control unit 175 then adjusts the temperature of the portion of the fixing belt 151 corresponding to the image area a ′ of the second surface whose first surface is the image area a ′ to be the first temperature + correction temperature α. The power source 170 and the heater 153 are controlled. Here, the fixing control unit 175 also calculates the correction temperature α based on the image density and image color in the image area on the second surface and the image density and image color in the image area on the first surface. The supply power is supplied at the shaded portion in the drawing, which is a preheating region for preliminarily heating each heating region of the heaters 153a to 153g.

  FIG. 26 is a diagram showing the relationship between the target temperature of the fixing member and time in the case of the image forming pattern of FIG. As indicated by the solid line, the fixing temperature is set to the first temperature in the image areas a and a ′, but in the non-image area b, the fixing temperature is set to a second temperature higher than room temperature and lower than the first temperature. Control to keep. This is the same as in single-sided printing, and FIG. 26 is the same graph as FIG.

  FIG. 27 is a diagram showing the relationship between the target temperature of the fixing member and time in the case of the image forming pattern of FIG. As indicated by the solid line, the fixing temperature is set to the second temperature in the non-image area b, but the fixing temperature is controlled to be maintained at the first temperature in the image area a. Further, in the image area a ′, the fixing temperature is controlled to be maintained at the first temperature + the correction temperature α.

  For comparison, the relationship between the target temperature and time when the temperature of the fixing member on the second surface does not change depending on the presence or absence of the image on the first surface is indicated by a broken line. In order to steadily fix the image on the second surface, it is necessary to always set the first fixing temperature + the correction temperature β (β ≧ α), which is the maximum fixing temperature assumed. For this reason, depending on the image areas on both sides of the paper P, heat may be supplied between the areas R more than necessary.

  As described above, according to the present embodiment, the fixing temperature can be set low in the region R including no image on the first surface and including the image region and the preheating regions before and after the image region on the second surface. Further, since the correction temperature α is adjusted based on the image density and the image color, the fixing temperature can be appropriately set also in the image area a ′ on the second surface. Thus, energy can be saved without supplying extra heat. Further, since the fixing control unit 175 can supply heat to any location of the heaters 153a to 153g, it is possible to further suppress excessive heat supply.

  In the above description, the case of full-color printing has been described. However, even in the case of monochrome printing with a specific color or black, the operation is the same except that there are unused photoconductors.

  By the way, in the heating region, there may be a case where a variation in the heating region occurs due to an initial or a change over time, and a region where a power density for heating is high or a region where the power density is low is generated. Therefore, when the fixing control unit 175 controls the power supply 170 and the heater 153, the actual power input amount is set by referring to the heating information of the heating area from the heating performance storage unit 180 shown in FIG. For the heating performance storage unit 180, for example, a rewritable nonvolatile memory such as an EEPROM may be used.

  As a result, temperature unevenness on the surface of the fixing member due to variations in the heating performance of each heating region can be suppressed, image quality can be improved, and energy can be further saved without supplying extra heat.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Paper discharge port 11 Scanner part 12 Image forming part 13 Paper feed part 15 Fixing apparatus 15 'Fixing apparatus 18 Display / operation part 134 Registration roller 136 Reverse path 137 Refeed path 138 Switching claw 139 Switching claw 140 Ejection Paper stack unit 143 Intermediate transfer belt 151 Fixing belt 152 Fixing facing roller (pressure roller)
153 Heating part (thermal heater)
154 Temperature measurement unit 155 Temperature measurement unit 156 Pressure unit 175 Fixing control unit 180 Heating performance storage unit 1965 Fixing control unit

JP 2001-343860 A

Claims (13)

A fixing member that rotates, a pressure member that forms a nip portion between the fixing member, and a plurality of members arranged side by side in a direction perpendicular to the rotation direction of the fixing member for heating the fixing member A heating unit having heaters, a temperature measuring unit for detecting a temperature of each heating region of the fixing member heated by the plurality of heaters, a heat amount to be applied to the heating unit, and determining each of the heaters of the heating unit A fixing device for controlling the temperature, and fixing the image through a recording medium carrying an unfixed image in the nip portion, wherein the heating unit is based on an image area and a non-image area on the recording medium. In the fixing device for adjusting the amount of heat applied to the fixing member,
The fixing device, wherein the fixing control unit adjusts an amount of heat applied to the fixing member by the heating unit based on a temperature of the fixing member.   The fixing device according to claim 1, wherein the fixing control unit adjusts an amount of heat applied to the fixing member by the heating unit based on a toner adhesion amount related to an image formed on the recording medium.   The fixing device according to claim 1, wherein the fixing control unit adjusts an amount of heat applied to the fixing member by the heating unit based on characteristics of the recording medium.   The fixing device according to claim 3, wherein the characteristic of the recording medium is a paper basis weight of the recording medium.   The fixing device according to claim 3, wherein the characteristic of the recording medium is smoothness of the recording medium. And a second temperature measuring unit for detecting temperatures of the plurality of heaters of the heating unit,
The fixing control unit adjusts the amount of heat applied to the fixing member by the heating unit based on temperatures of a plurality of heaters of the heating unit detected by the second temperature measurement unit. The fixing device according to claim 5. Furthermore, a third temperature measurement unit that detects the temperature of each heating region of the pressure member heated by the heating region of the fixing member,
The fixing control unit adjusts the amount of heat applied to the fixing member by the heating unit based on the temperature of each heating region of the pressure member detected by the third temperature measurement unit. The fixing device according to any one of 1 to 6.   The fixing device according to claim 1, wherein the fixing control unit adjusts an amount of heat applied to the fixing member by the heating unit based on an interval of the recording medium.   9. The fixing device according to claim 1, wherein the fixing control unit changes a fixing temperature at the time of second-side printing depending on the presence / absence of an image on the first side of the recording medium during duplex printing. Fixing device.   10. The fixing device according to claim 1, wherein the fixing controller changes the fixing temperature at the time of second-side printing according to the image density of the first side of the recording medium during duplex printing. Fixing device.   11. The fixing device according to claim 1, wherein the fixing control unit changes the fixing temperature at the time of the second surface printing according to the image color of the second surface of the recording medium during the duplex printing. Fixing device. Furthermore, a heating performance storage unit that holds heating performance information of a plurality of heaters of the heating unit,
The said fixing control part sets the electric power applied to the several heater of the said heating part by the heating performance information of the several heater of the said heating part, The any one of Claim 1 thru | or 11 characterized by the above-mentioned. Fixing device. An image forming apparatus comprising the fixing device according to claim 1.

Images