Fixing device and image forming apparatus

Abstract

To detect, with better responsiveness, a change in the temperature of a fixing belt associated with a fixing operation.SOLUTION: A fixing unit 18 comprises: a fixing belt 120 that heats a developer image transferred to a recording medium to fix the developer image to the recording medium; a heater 121 that is arranged inside the fixing belt 120 and generates heat; a thermal diffusion member 124 that conducts heat from the heater 121 to the fixing belt 120; and temperature sensors 122A-122C that detect the temperature of the thermal diffusion member 124 to specify the temperature of the fixing belt 120.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a fixing device and an image forming apparatus. [Background technology]

[0002] Conventionally, in electrophotographic image forming apparatuses, toner as a developer is heated in a fixing device to fix the toner onto a medium. In the fixing device, a fixing belt is heated by a heater. In order to reliably fix the toner onto the medium, it is necessary to accurately detect the temperature of the fixing belt.

[0003] In the conventional technology, for example, as described in Patent Document 1, a heat storage member for storing heat from the heater is provided on the back side of the heater that is in contact with the fixing belt (in other words, the side opposite to the fixing belt).The temperature is detected from the back side of the heat storage member, in other words, the back side of the heater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-115000 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the temperature is detected on the rear side of the heater, the responsiveness to the temperature change of the fixing belt accompanying the fixing operation is insufficient.

[0006] Therefore, one or more aspects of the present disclosure aim to make it possible to detect temperature changes in a fixing belt accompanying a fixing operation with greater responsiveness. [Means for solving the problem]

[0007] A fixing device according to one aspect of the present disclosure is characterized in that it includes a fixing belt that heats a developer image transferred to a recording medium in order to fix the developer image to the recording medium, a heat source that is disposed inside the fixing belt and generates heat, a heat diffusion member that transfers heat from the heat source to the fixing belt, and a temperature detection unit that detects the temperature of the heat diffusion member in order to identify the temperature of the fixing belt.

[0008] An image forming apparatus according to one aspect of the present disclosure is characterized in that it has a fixing device including a fixing belt that heats a developer image transferred to a recording medium in order to fix the developer image to the recording medium, a heat source that is arranged inside the fixing belt and generates heat, a heat diffusion member that conducts heat from the heat source to the fixing belt, and a temperature detection unit that detects the temperature of the heat diffusion member in order to identify the temperature of the fixing belt. Effect of the Invention

[0009] According to one or more aspects of the present disclosure, it is possible to detect the temperature change of the fixing belt accompanying the fixing operation with improved responsiveness. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional side view showing a schematic configuration of a color printer as an image forming apparatus according to an embodiment; [Diagram 2] 1A and 1B are schematic diagrams illustrating a fixing belt and a heater. [Diagram 3] FIG. 2 is a first schematic diagram showing a pressure roller and a fixing belt as viewed from the side. [Figure 4] 1A and 1B are schematic diagrams illustrating the arrangement of a heat diffusion member, a resistor, a temperature sensor, and a thermostat. [Diagram 5] 11 is a second schematic diagram of the pressure roller and the fixing belt as viewed from the side. FIG. [Figure 6] 13A and 13B are schematic diagrams for explaining how temperature changes with the operation of the fixing unit. [Figure 7]FIG. 2 is a block diagram illustrating the configuration of a control system of a color printer. [Figure 8] FIG. 2 is a schematic diagram for explaining a configuration of a resistor. [Figure 9] 1A and 1B are block diagrams illustrating an example of a hardware configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] FIG. 1 is a cross-sectional side view showing a schematic configuration of a color printer 100 as an image forming apparatus according to an embodiment. The color printer 100 is composed of a main body 1 and a top cover 2 that can be opened and closed relative to the main body 1.

[0012] The recording medium storage unit 3 stores a recording medium 4, which is a medium for recording. The recording medium 4 is paper or the like on which the color printer 100 prints.

[0013] The paper feed roller 5 is a roller for feeding the recording media 4 from the recording medium storage unit 3 one sheet at a time. The first registration roller 7 and the second registration roller 9 are transport rollers that transport the recording medium 4 fed from the recording medium storage unit 3 by the feed roller 5 to the image forming units 13Y, 13M, 13C, and 13K.

[0014] The first IN sensor 6 is a transport system sensor that detects the arrival of the recording medium 4, and is disposed before the first registration rollers . The second IN sensor 8 is a transport system sensor that detects the arrival of the recording medium 4, and is disposed before the second registration rollers 9.

[0015] The WR sensor 10 is a transport sensor that detects the recording medium 4, and is installed behind the second registration roller 9. The WR sensor 10 can detect the timing when the recording medium 4 reaches the image forming units 13Y, 13M, 13C, and 13K.

[0016] The conveyor belt 11 is an endless belt that conveys the fed recording medium 4 downstream of the image forming units 13Y, 13M, 13C, and 13K.

[0017] Above the conveyor belt 11, LED heads 12Y, 12M, 12C, and 12K and image forming units 13Y, 13M, 13C, and 13K are provided. 1, the configurations related to the colors Yellow, Magenta, Cyan, and black are indicated by the capital letters Y, M, C, and K attached to the end of the reference numerals, respectively. In the following description, when there is no need to specify a color, the capital letters Y, M, C, and K attached to the end of the reference numerals may be omitted.

[0018] Each of the LED heads 12Y, 12M, 12C, and 12K is an exposure unit that emits light in accordance with print data as image formation data. The LED heads 12Y, 12M, 12C, and 12K are supported by holders that can be moved to the openable and closable top cover 2 in accordance with the respective colors. Each of the LED heads 12Y, 12M, 12C, and 12K is capable of exposure when the top cover 2 is closed. Each of the LED heads 12Y, 12M, 12C, and 12K is connected to the main body 1 of the color printer 100 via a cable.

[0019] The image forming units 13Y, 13M, 13C, and 13K each form a toner image, which is a developer image, using toner, which is a developer of the corresponding color. Since the image forming units 13Y, 13M, 13C, and 13K have the same configuration, only the image forming unit 13Y will be described below.

[0020] The image forming unit 13Y forms a toner image by attaching the toner stored inside a toner cartridge 14Y to a photosensitive drum 15Y on which an electrostatic latent image has been formed by an LED head 12Y. The toner cartridge 14Y has a mechanical structure that allows it to be detached from the inside of the color printer 100, since it must be replaced when the toner runs out. The photosensitive drum 15Y is a photosensitive member capable of forming an electrostatic latent image on the drum surface by electrostatic force in accordance with print data.

[0021] The transfer rollers 16Y, 16M, 16C, and 16K are disposed opposite the photosensitive drums 15Y, 15M, 15C, and 15K across the conveyor belt 11. The transfer rollers 16Y, 16M, 16C, and 16K are transfer units that transfer the toner images formed on the surfaces of the photosensitive drums 15Y, 15M, 15C, and 15K onto the recording medium 4.

[0022] A high voltage is applied to the photosensitive drums 15Y, 15M, 15C, and 15K and the transfer rollers 16Y, 16M, 16C, and 16K from a high voltage power supply 22, which will be described later, to enable electrophotographic processes such as electrostatic charging, development, and transfer.

[0023] The FUSER-IN sensor 17 is a transport-system sensor that detects the recording medium 4, and is disposed immediately before the fixing unit .

[0024] The fixing unit 18 is a fixing device that fixes the toner image transferred onto the recording medium 4 by heat and pressure. The fixing unit 18 includes a pressure roller 110 and a fixing belt 120.

[0025] The EXIT sensor 19 is a transport sensor that detects the recording medium 4, and is installed behind the fixing unit 18. The EXIT sensor 19 detects that the recording medium 4 has been discharged from the fixing unit 18.

[0026] The discharge stacker 20 is a stacker to which the recording medium 4 is finally discharged.

[0027] The density sensor 21 is an optical sensor that reads a special pattern formed on the conveyor belt 11 in order to perform operations such as density correction to maintain print quality. The high-voltage power supply 22 is a power supply that generates a high voltage to be applied to the photosensitive drums 15Y, 15M, 15C, and 15K and the transfer rollers 16Y, 16M, 16C, and 16K. The low-voltage power supply 23 is an AC-DC power supply that converts commercial AC power into DC power. The low-voltage power supply 23 supplies DC of 3.3 V, 5 V, 24 V, etc. to each board (not shown). It also supplies AC 100 V to the heat source of the fixing unit 18 via a triac.

[0028] Here, the above-mentioned traveling system sensors such as the first IN sensor 6, the second IN sensor 8, the WR sensor 10, the FUSER-IN sensor 17 and the EXIT sensor 19 are connected to a controller 131 (see FIG. 7) via cables. In addition, rollers such as the paper feed roller 5, the first registration roller 7, the second registration roller 9, the photosensitive drum 15, the transfer roller 16, and the pressure roller 110 are mechanically driven by an actuator (not shown), enabling the recording medium 4 to be transported downstream.

[0029] Display input unit 24 is a printed circuit board composed of a liquid crystal display panel, switches, etc., and functions as a display unit that displays the status of color printer 100 and an input unit that receives input operations by the user. Display input unit 24 is connected to controller 131 via a cable. The liquid crystal display panel is capable of displaying, for example, 24 characters by 2 lines of characters (letters).

[0030] Here, the internal configuration of the fixing unit 18 will be described with reference to FIGS. Fig. 2(A) is a schematic diagram of the fixing belt 120 seen from above, and Fig. 2(B) is a schematic diagram of the heater 121 in the fixing belt 120. Fig. 3 is a schematic diagram of the pressure roller 110 and the fixing belt 120 seen from the side.

[0031] As shown in FIGS. 2A and 3, inside fixing belt 120, heater 121, temperature sensors 122A, 122B, and 122C, thermostats 123A and 123B, a heat diffusion member 124, and a heat conduction member 125 are provided. Although not shown, a heater holder for fixing the heater 121 and a fixing support member for supporting the fixing belt 120 are provided inside the fixing belt 120.

[0032] The pressure roller 110 is disposed opposite the fixing belt 120, and forms a nip portion between the pressure roller 110 and the fixing belt 120. In this way, the pressure roller 110 presses the recording medium 4 from the outside of the fixing belt 120 toward the fixing belt 120.

[0033] Here, the pressure roller 110 is a cylindrical member made of a metal material, the peripheral surface of which is covered with a rubber elastic layer. The rubber elastic layer is made of a material such as silicone rubber. Here, a nip portion is formed between the fixing belt 120 and the pressure roller 110, so that the fixing belt 120 also rotates when the pressure roller 110 is rotated by a main motor 25 (FIG. 7) described later.

[0034] The fixing belt 120 is an endless belt-like body, and is supported from the inside by a fixed support member. The fixing belt 120 heats the toner image transferred onto the recording medium 4 in order to fix the toner image onto the recording medium 4. The fixing belt 120 includes a base material, a rubber layer, and a release layer from the inside. For example, the base material is made of a heat-resistant resin such as polyimide or stainless steel (SUS (Stainless Used Steel)). The rubber layer is made of silicone rubber. The release layer is made of fluorine-based resin such as PFA (Perfluoroalkosy alkane).

[0035] Heater 121 is a heat source disposed inside fixing belt 120. Here, heater 121 is a planar heating element that extends in the longitudinal direction and generates heat. For example, heater 121 is configured such that resistors 126A, 126B, and 126C formed on a substrate configured by laminating an electrical insulating layer, a resistive heating layer, an electrode, and a protective layer in this order on a SUS substrate generate heat upon receiving a voltage from the substrate. Instead of SUS, ceramics with excellent insulating properties may be used.

[0036] As shown in FIG. 2B, within the heater 121, a resistor 126A is formed in the center and resistors 126B and 126C are formed separately at the ends. The resistor 126A in the center has a width that can heat a recording medium of a narrow size (e.g., A5 size). The resistor 126A in the center and the resistors 126B and 126C at both ends together have a width that can heat a recording medium of a wide size (e.g., A4 size). The resistors 126A, 126B, and 126C are heating elements that generate heat when power is independently supplied from an AC commercial power source PW by being controlled to turn on or off by a triac or the like, which will be described later.

[0037] As shown in Fig. 3, the heat diffusion member 124 conducts heat from the heater 121 to the fixing belt 120. Here, the heat diffusion member 124 is disposed between the heater 121 and the fixing belt 120 for the purpose of uniformly diffusing the heat of the heater 121 in the longitudinal direction and the width direction. The width direction is, for example, the direction indicated by the arrow AR in Fig. 3, which is the direction in which the recording medium 4 is transported. The heat diffusion member 124 is in contact with the heater 121 and the fixing belt 120 to conduct heat. Note that even if a lubricant such as sliding grease is applied between the heat diffusion member 124 and either the heater 121 or the fixing belt 120, it is considered that the heat diffusion member 124 is in contact with the heater 121 and the fixing belt 120.

[0038] Here, the heat diffusion member 124 is made of a material with high thermal conductivity, such as aluminum, in order to detect the temperature of the fixing belt 120, which is heated by the heater 121 and loses heat to the recording medium 4, etc., with high accuracy and good responsiveness.

[0039] The heat conducting member 125 is disposed so as to be in contact with the heater 121. The purpose of providing the heat conducting member 125 is the same as that of the heat diffusion member 124, and the material thereof is, for example, aluminum or the like having high thermal conductivity. If the heat diffusion member 124 provides sufficient heat diffusion, the heat conducting member 125 may be made of stainless steel or the like, and the heat conducting member 125 may not be provided.

[0040] The temperature sensors 122A, 122B, and 122C are temperature detection units that detect the temperature of the heat diffusion member 124 in order to identify the temperature of the fixing belt 120. Here, the temperature sensors 122A, 122B, and 122C are in contact with the heat diffusion member 124. In particular, the temperature sensors 122A, 122B, and 122C detect the temperature of the heat diffusion member 124 in order to identify the temperature of the fixing belt 120 at a nip portion formed between the fixing belt 120 and the pressure roller 110.

[0041] Temperature sensor 122A is disposed at the center of the paper passing area, and temperature sensors 122B and 122C are disposed at the ends of the paper passing area. Here, temperature sensor 122B is provided to measure the temperature heated by resistor 126B on the right side shown in Fig. 2(B), and temperature sensor 122C is provided to measure the temperature heated by resistor 126C on the left side shown in Fig. 2(B). Note that, since resistors 126B and 126C are heated simultaneously, only one of temperature sensors 122B and 122C may be provided.

[0042] Thermostats 123A and 123B as final safety devices are provided so as to be in contact with a heat diffusion member 124 in the fixing belt 120, similar to the temperature sensors 122A, 122B, and 122C. Here, thermostat 123B is provided to detect the temperature heated by resistor 126B on the right side shown in FIG. 2(B), but a thermostat (not shown) may be provided instead of or together with thermostat 123B to detect the temperature heated by resistor 126C on the left side.

[0043] The temperature sensors 122A, 122B, and 122C and the thermostats 123A and 123B are pressed against the heat diffusion member 124 with a predetermined force by a spring (not shown) in order to reduce errors in the detected temperatures and improve responsiveness.

[0044] The AC commercial power source PW supplies an AC input voltage, which is AC 100V in this example.

[0045] Triacs 127A and 127B are semiconductor switching elements used for power control of heater 121. Triacs 127A and 127B are each controlled to be ON or OFF by fixing control unit 148 (see FIG. 7). The details of fixing control unit 148 will be described later, but fixing control unit 148 controls heating using heat-generating resistors 126A, 126B, and 126C in heater 121 based on the detection results of each temperature sensor 122A, 122B, and 122C, and controls so that the temperature of fixing belt 120 is optimal.

[0046] Thermally conductive grease (not shown) is applied between the heater 121 and the heat diffusion member 124, and between the heater 121 and the heat conductive member 125, in order to improve thermal conductivity between the members. The thermally conductive grease is mainly composed of zinc oxide and silicone oil. In addition, sliding grease (not shown) is applied between the heat diffusion member 124 and the fixing belt 120. The sliding grease is mainly composed of PTFE (Perfluoropolyether). Note that since lubricants such as sliding grease are based on the premise that the heat diffusion member 124 and the fixing belt 120 are in contact with each other, even if a lubricant is applied, it is understood that the heat diffusion member 124 and the fixing belt 120 are in contact with each other.

[0047] 4(A) and (B) are schematic diagrams for explaining the arrangement of the heat diffusion member 124, resistors 126A, 126B, and 126C, temperature sensors 122A, 122B, and 122C, and thermostats 123A and 123B. FIG. 4(A) is a perspective view, and FIG. 4(B) is a top view.

[0048] The heat diffusion member 124 has a bottom surface 124a as a plate-like member that contacts the fixing belt 120 in order to provide the fixing belt 120 with heat from the resistor 126A or the resistors 126A and 126B and 126C. In addition, the heat diffusion member 124 includes a wall portion 124b as an extension member extending upward from the bottom surface 124a only at the locations where the temperature sensors 122A, 122B, 122C and the thermostats 123A and 123B are arranged, in order to detect the heat from the resistor 126A or the resistors 126A and 126B and 126C, and the heat cooled by the passage of the recording medium 4, as shown in Figs. 4(A) and (B). In other words, the wall portion 124b is provided at the location where the temperature is detected, and is not provided at the location where the temperature is not detected. As shown in Figs. 4(A) and (B), the wall portion 124b extends in the opposite direction to the fixing belt 120.

[0049] Temperature sensors 122A, 122B, 122C and thermostats 123A, 123B are attached to wall portion 124b. Wall portion 124b only needs to have a size that allows temperature sensors 122A, 122B, 122C and thermostats 123A, 123B to come into contact with each other and detect temperature. This is because if the portions that do not detect temperature are extended upward, the heat capacity increases by the amount of extension, and it becomes necessary to supply heat unnecessarily.

[0050] Next, the temperature characteristics in the fixing unit 18 will be described. 5 is a schematic diagram of the pressure roller 110 and the fixing belt 120 as seen from the side, similar to FIG. 3, but thermostats 123A and 123B are not shown.

[0051] In FIG. 5, the entrance temperature, which is the surface temperature of the fixing belt 120 on the entrance side of the recording medium 4, is designated as H1, the temperature of the heat diffusion member 124 detected by one of the temperature sensors 122A, 122B, or 122C is designated as H2, and the temperature of the back side of the heat conduction member 125 detected by the conventional technology is designated as H3.

[0052] Fig. 6(A) is a time chart showing how the temperatures shown in Fig. 5 change with the operation of the fixing unit 18. Fig. 6(B) is a table summarizing the temperatures in the time chart shown in Fig. 6(A).

[0053] First, at time t1, the fixing control unit 148 gives permission to the heater 121 to heat, and the heater 121 heats up.

[0054] At time t2, the fixing control unit 148 heats the nip portion of the fixing belt 120 until the temperature thereof reaches a predetermined temperature, and when the temperature reaches the predetermined temperature, rotates the main motor 25 shown in Fig. 7. This is because it is necessary to raise the temperature to a temperature at which the sliding agent applied between the heat diffusion member 124 and the fixing belt 120 softens. Here, the predetermined temperature is 80°C, and when the temperature H2 of the heat diffusion member 124 reaches or exceeds 80°C, the main motor 25 rotates.

[0055] At time t3, the fixing control unit 148 heats the fixing belt 120 until the temperature thereof reaches a predetermined temperature, and when the predetermined temperature is reached, starts passing the recording medium 4 to perform printing. Here, the predetermined temperature is 160° C., and when the inlet side temperature H1 of the fixing belt 120 reaches 160° C., the recording medium 4 starts passing.

[0056] Time t4 is the time when 10 sheets of the recording medium 4 have passed.

[0057] Next, the advantages of the method of detecting the temperature of fixing belt 120 using heat diffusion member 124 will be described with reference to FIG. 6(B).

[0058] First, at time t2, the inlet side temperature H1 of the fixing belt 120 is room temperature (25° C.) because the fixing belt 120 is not rotating. Therefore, the temperature of the fixing belt 120 and the nip portion of the fixing belt 120 cannot be detected on the inlet side of the fixing belt 120.

[0059] The temperature H2 of the heat diffusion member 124 can detect the temperature of the nip portion of the fixing belt 120, as shown in FIG. 6(B).

[0060] It should be noted that the temperature H3 on the back side of the heat conductive member 125 can also be detected, but as shown in FIG. 6B, the temperature H3 is higher than the temperature of the nip portion of the fixing belt 120. As shown in FIG. 3, when the heater 121 position is used as a reference, the heat capacity in the direction toward the nip portion is different from the heat capacity in the direction opposite to the nip portion, and the heat capacity in the direction opposite to the nip portion is lighter than the heat capacity in the direction toward the nip portion, so the temperature H3 of the heat conductive member 125 is higher than the temperature of the nip portion of the fixing belt 120. In addition, since the heater 121 uses a SUS substrate, its thermal conductivity is lower than that of the heat diffusion member 124 made of aluminum. This is because the configuration makes it difficult for the temperature change in the nip portion to be transmitted.

[0061] For these reasons, it is preferable to use the heat diffusion member 124 to detect the temperature when heating occurs while the main motor 25 is stopped.

[0062] Next, from time t3 to time t4 and after time t4, there is a temperature difference between the inlet side temperature H1 of the fixing belt 120 and the temperature H2 of the heat diffusion member 124, but the fluctuation ranges are the same.

[0063] On the other hand, the temperature H3 of the back side of the heat conductive member 125 increases as the number of printed sheets of the recording medium 4 increases. As described above, this is because, when the position of the heater 121 is used as a reference, the heat capacity in the direction toward the nip portion and the heat capacity in the direction away from the nip portion are different, and the heat capacity in the direction away from the nip portion is lighter than the heat capacity in the direction toward the nip portion, so that the temperature H3 of the heat conductive member 125 is higher than the temperature of the nip portion of the fixing belt 120. Also, because the heater 121 uses a SUS substrate, it has a lower thermal conductivity than the heat diffusion member 124 made of aluminum, and is configured in such a way that the temperature change in the nip portion is less likely to be transmitted.

[0064] Therefore, when heating is performed while the main motor 25 is rotating and the recording medium is passing through, it is preferable to detect the temperature using the entrance side of the fixing belt 120 and the heat diffusion member 124.

[0065] Since the temperature of the nip portion of the fixing belt 120 in a stopped state cannot be detected at the inlet side temperature H1 of the fixing belt 120, it is necessary to further detect the temperature H3 of the heat conductive member 125 in order to perform control at the inlet side temperature H1 of the fixing belt 120. For this reason, the number of temperature sensors required increases.

[0066] Furthermore, when printing at a slow printing speed, it takes time for the part of the fixing belt 120 that has nipped the recording medium 4 to reach the entrance side where the temperature is detected. As a result, the heat of that part of the fixing belt 120 is reduced by dissipating heat into the air in the fixing unit 18, and the steep temperature change is flattened out. Thus, when the printing speed is slow, the accuracy of detecting the temperature of the nip part of the fixing belt 120 is low at the entrance side temperature H1 of the fixing belt 120.

[0067] When detecting temperature using the heat diffusion member 124, the temperature of the nip portion of the fixing belt 120 can be detected whether the main motor 25 is stopped or rotating, and the temperature of the fixing belt 120 can be detected accurately regardless of the state without adding any other temperature sensors.

[0068] FIG. 7 is a block diagram showing the schematic configuration of a control system of color printer 100. As shown in FIG. Print data generated by a PC (Personal Computer) (not shown) or the like is received by color printer 100 via communication unit 130 configured with a communication I / F such as a USB (Universal Serial Bus) or a LAN (Local Area Network).

[0069] The controller 131 controls the overall operation of the color printer 100 . The controller 131 includes a central processing unit (CPU) 132, a read only memory (ROM) 133, and a random access memory (RAM) 134, which are connected to each other via an internal bus (not shown).

[0070] The CPU 132 controls the RAM 134 and the process control unit 140 in accordance with a print processing program stored in the ROM 133 .

[0071] ROM 133 is an area for storing the print processing program, and is a non-volatile memory capable of retaining data even when color printer 100 is turned off.

[0072] The RAM 134 is a volatile memory that stores received print data and from which data is erased when the color printer 100 is turned off.

[0073] The process control unit 140 includes a high voltage control unit 141, an exposure control unit 146, a motor control unit 147, and a fixing control unit 148, and controls the printing process, which is an image formation process such as transporting the recording medium 4, charging, developing, transferring, and fixing.

[0074] The high voltage control unit 141 forms a toner image and controls the voltages applied to the various rollers in order to transfer the toner image onto the recording medium 4 . The high voltage control unit 141 includes a supply voltage control unit 142 , a development voltage control unit 143 , a charging voltage control unit 144 , and a transfer control unit 145 .

[0075] The supply voltage control unit 142 controls the supply voltages applied to the supply rollers 27Y, 27M, 27C, and 27K in the image forming units 13Y, 13M, 13C, and 13K. The developing voltage control unit 143 controls the developing voltages applied to the developing rollers 28Y, 28M, 28C, and 28K in the image forming units 13Y, 13M, 13C, and 13K. The charging voltage control unit 144 controls the charging voltages applied to the charging rollers 29Y, 29M, 29C, and 29K in the image forming units 13Y, 13M, 13C, and 13K. The transfer control unit 145 controls the transfer voltages applied to the transfer rollers 16Y, 16M, 16C, and 16K.

[0076] The exposure control unit 146 controls the exposure of the LED heads 12Y, 12M, 12C, and 12K. The motor control unit 147 controls and rotates the main motor 25 in the color printer 100. Specifically, the main motor 25 drives the photosensitive drums 15Y, 15M, 15C, and 15K, the pressure roller 110 of the fixing unit 18, the paper feed roller 5, the first registration roller 7, and the second registration roller 9. Here, the only motor is the main motor 25, but multiple motors may be provided.

[0077] The fixing control unit 148 controls the temperature of the nip portion of the fixing belt 120. For example, the fixing control unit 148 controls ON and FF of the heat source driving unit 30 such as a triac of the low voltage power supply 23 based on the detection results of the temperature sensors 122A, 122B, and 122C to supply power to the heater 121 as the heat source 26 from the AC commercial power supply PW, thereby controlling the temperature of the nip portion of the fixing belt 120. The fixing control unit 148 holds a table that stores the set temperature, ON Duty parameters, etc., and performs fixing control based on them. Note that the ON Duty represents the application time ratio of voltage to the resistors 126A, 126B, and 126C per predetermined time.

[0078] Next, the ON duty correction of the resistors 126A, 126B, and 126C will be described with reference to FIG. 2 and FIG. Here, a description of the basic operation of color printer 100 will be omitted, and the fixing operation will be mainly described.

[0079] The fixing unit 18 uses heat and pressure to fix the toner image formed on the recording medium 4. The temperature sensor 122A disposed in the center of the heat diffusion member 124 detects the temperature of the fixing belt 120 at the center of the nip portion.

[0080] The fixing control unit 148 controls the power supplied from the low-voltage power supply 23 to the heat source 26 by turning on and off via the triacs 127A and 127B, so that the temperature is set to a predetermined temperature. The predetermined set temperature is a set temperature determined for each medium.

[0081] Heater 121 as heat source 26 is divided into resistor 126A in the center and resistors 126B, 126C at both ends, and is connected to AC commercial power source PW via triacs 127A, 127B.

[0082] The triac 127A is connected to the resistor 126A in the center, and the triac 127B is connected to the resistors 126B and 126C at both ends, and each can be controlled independently.

[0083] As shown in FIG. 8, the dividing positions of resistors 126A, 126B, and 126C are determined by the size of the target recording medium. Here, the length of resistor 126A in the center is set to the width of A5 size, and by using resistors 126B and 126C at both ends, a maximum width of A4 size can be supported.

[0084] Resistor 126A is driven with an ON duty such that the temperature detected by temperature sensor 122A becomes the set temperature. Meanwhile, resistors 126B and 126C are driven with an ON duty multiplied by a coefficient that differs depending on the size of the recording medium 4, based on the ON duty of resistor 126A in the center.

[0085] Here, the ON duty of resistors 126B and 126C is determined by the following formula (1), where the ON duty of resistors 126B and 126C is OD and the ON duty of resistor 126A is RD. OD=RD × Paper size coefficient CO (1)

[0086] Here, the coefficient CO based on the paper size is, for example, CO1 when the recording medium 4 is A4 size, CO2 when the recording medium 4 is B5 size, and CO3 when the recording medium 4 is A5 size, and the relationship between these is 1≧CO1>CO2>CO3.

[0087] By carrying out the above-described control, the temperature of the nip portion of the fixing belt 120 can be detected with high accuracy even when the size of the recording medium 4 differs, so that stable print quality can be ensured even when there are only a few temperature sensors.

[0088] In this embodiment, since there is a demand for printing on a recording medium 4 of B5 size, and since there are parts of the resistors 126B and 126C through which paper passes and parts that do not pass through, the resistors 126B and 126C are temperature controlled based on the coefficient RD of the ON duty of the resistor 126A, but this embodiment is not limited to such an example. For example, if there is no mixture of parts through which paper passes and parts that do not pass through, the resistors 126B and 126C may be driven with an ON duty so that the temperature detected by the temperature sensor 122B or the temperature sensor 122C becomes the set temperature, similar to the resistor 126A.

[0089] In addition, in this embodiment, the heater 121 is divided in the paper feed direction, but this embodiment is not limited to such an example. For example, even if a heater with heat distribution in the longitudinal direction is used, it can be controlled in the same manner as above.

[0090] 9A, a part or the whole of the process control unit 140 described above can be configured with a memory 31 and a processor 32 such as a CPU (Central Processing Unit) that executes a program stored in the memory 31. Such a program may be provided through a network, or may be provided by being recorded on a recording medium. That is, such a program may be provided as, for example, a program product.

[0091] In addition, a part or all of the process control unit 140 can be configured with a processing circuit 33 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), for example, as shown in FIG. 9(B). As described above, the process control unit 140 can be realized by a processing circuit network.

[0092] As described above, according to this embodiment, the temperature of the nip portion can be detected with high accuracy using the heat diffusion member 124, so print quality can be stabilized. In addition, because the temperature of the nip portion can be detected with high accuracy both when the device is stopped and when the device is rotating, there is no need to detect the temperature at the entrance of the fixing belt, and the number of thermistors can be reduced. This is expected to result in reduced costs and a more compact fixing unit 18.

[0093] The embodiment described above has been explained using color printer 100 as an example, but this embodiment can be applied to image forming devices such as electrophotographic printers, copiers, facsimiles, and multifunction printers that combine multiple of these functions. [Explanation of symbols]

[0094] 100 color printer, 1 main body, 2 top cover, 3 recording medium storage section, 4 recording medium, 5 paper feed roller, 6 first IN sensor, 7 first registration roller, 8 second IN sensor, 9 second registration roller, 10 WR sensor, 11 conveyor belt, 12 LED head, 13 image forming section, 14 toner cartridge, 15 photosensitive drum, 16 transfer roller, 17 FUSER-IN sensor, 18 fixing section, 19 EXIT sensor, 20 discharge stacker, 21 density sensor, 22 high voltage power supply, 23 low voltage power supply, 110 pressure roller, 120 fixing belt, 121 heater, 122 temperature sensor, 123 thermostat, 124 heat diffusion member, 125 heat conduction member, 126 resistor, 127 Triac.

Claims

1. a fixing belt for heating the developer image transferred onto the recording medium in order to fix the developer image onto the recording medium; a heat source disposed inside the fixing belt and generating heat; a heat diffusion member that transfers heat from the heat source to the fixing belt; a temperature detection unit that detects the temperature of the heat diffusion member in order to specify the temperature of the fixing belt; A fixing device comprising:

2. The heat diffusion member is disposed between the heat source and the fixing belt.

2. The fixing device according to claim 1,

3. The heat diffusion member is in contact with the fixing belt.

3. The fixing device according to claim 2, wherein:

4. the heat diffusion member includes a plate-like member in contact with the fixing belt and the heat source, and an extension member extending from the plate-like member in a direction opposite to the fixing belt, The temperature detector is attached to the extension member.

4. The fixing device according to claim 3,

5. The heat diffusion member is made of aluminum. The fixing device according to claim 1 ,

6. The heat source includes a substrate and a heating element that is formed on the substrate and generates heat when a voltage is applied from the substrate. The fixing device according to claim 1 ,

7. Further comprising a pressure roller for applying pressure to the recording medium from the outside of the fixing belt toward the fixing belt. The fixing device according to claim 1 ,

8. The temperature detection unit detects a temperature of the heat diffusion member in order to identify a temperature of the fixing belt at a nip portion formed between the fixing belt and the pressure roller.

8. The fixing device according to claim 7,

9. The fixing device according to any one of claims 1 to 4 is provided. An image forming apparatus comprising:

10. The fixing device according to claim 5 is provided. An image forming apparatus comprising:

11. The fixing device according to claim 6 is provided. An image forming apparatus comprising:

12. The fixing device according to claim 7 is provided. An image forming apparatus comprising:

13. The fixing device according to claim 8 is provided. An image forming apparatus comprising:

Images