Fixing device and image forming apparatus

Abstract

To improve image quality.SOLUTION: A color printer 1 is provided with an image forming unit 14 that forms an image on a recording medium P, and a fixing unit 20. The fixing unit 20 is provided with: a heater 31 that has a plurality of resistors 40 arranged and divided from each other along a main scanning direction Drm, and has an inter-resistor gap GP formed between every pair of resistors 40 adjacent in the main scanning direction Drm; a fixing belt 30 that is heated by the heater 31; a pressure roller 32 that is in contact with an outer peripheral surface of the fixing belt 30; and a thermal diffusion member 36 that is provided between the heater 31 and the fixing belt 30. The thermal diffusion member 36 has projections 49 that are divided from each other for the respective resistors 40 with respect to the main scanning direction Drm, and arranged at positions each corresponding to the center part of the resistor 40 in the main scanning direction Drm.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fixing device and an image forming apparatus, and is suitably applied to a fixing unit mounted in, for example, an electrophotographic image forming apparatus. [Background technology]

[0002] Conventionally, in electrophotographic image forming apparatuses, a device has been widely used in which the surface of a photosensitive drum is charged, the surface of the charged photosensitive drum is exposed to light to form an electrostatic latent image, toner is attached to the electrostatic latent image to form a toner image, and the toner image is transferred to a medium and fixed by a fixing device. Such a fixing device includes a belt heated by a heater and a pressure member that presses the belt to form a nip portion between the belt and the belt.

[0003] There are various sizes of media that image forming apparatuses print on. In response to this, some image forming apparatuses divide the heat generating portion of the heater into multiple portions along the main scanning direction and control the ON / OFF of each heat generating portion independently (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-165076 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in order to ensure insulation between the heat generating parts, a heater composed of multiple heat generating parts needs to provide a space between the heat generating parts and an inter-heating part area between adjacent heat generating parts. The inter-heating part area does not have the heat generating resistance heating wiring that forms the heat generating part, so the amount of heat generated is small. As a result, the temperature of the belt is not constant from one end to the other in the longitudinal direction, and the temperature distribution varies in the longitudinal direction, which can cause gloss unevenness in the fixed image and reduce image quality.

[0006] The present invention has been made in consideration of the above points, and aims to propose a fixing device and an image forming apparatus that can improve image quality. [Means for solving the problem]

[0007] In order to solve such problems, the fixing device of the present invention includes a heater having multiple heat generating sections arranged along the main scanning direction and separated from each other, with an inter-heat generating section area formed between adjacent heat generating sections in the main scanning direction, a belt heated by the heater, a pressure member in contact with the outer peripheral surface of the belt, and a heat diffusion member provided between the heater and the belt, and the heat diffusion member has protrusions that are separated from each other and arranged for each heat generating section in the main scanning direction at positions corresponding to the center of the heat generating section in the main scanning direction.

[0008] The image forming apparatus of the present invention is provided with an image forming unit for forming an image on a medium, and the fixing device described above.

[0009] The present invention dissipates heat generated in the central part of the heat generating portion in the main scanning direction using the protrusions, suppresses the temperature rise in the central part of the heat generating portion in the main scanning direction, and suppresses the temperature difference between the central part of the heat generating portion in the main scanning direction and the gap between the resistors adjacent to the heat generating portion, thereby making the surface temperature of the belt uniform from one end to the other in the main scanning direction. Effect of the Invention

[0010] According to the present invention, heat generated in the central part of the heat generating portion in the main scanning direction is dissipated by the protrusion portion, the temperature rise in the central part of the heat generating portion in the main scanning direction is suppressed, and the temperature difference between the central part of the heat generating portion in the main scanning direction and the gap between the resistors adjacent to the heat generating portion can be suppressed, and the surface temperature of the belt can be made uniform from one end to the other in the main scanning direction, thereby realizing a fixing device and image forming apparatus that can improve image quality. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a right side view showing the configuration of the color printer. [Diagram 2] 1A and 1B show the configuration of the fixing unit, in which FIG. [Diagram 3] 1A is a perspective view of the heat diffusion member, FIG. 1B is a perspective view from the front, and FIG. 1C is a front view. [Figure 4] FIG. 2 is a block diagram showing a control configuration of the color printer. [Diagram 5] 4 is a graph showing a temperature distribution of a fixing belt in a transport width direction. [Figure 6] 1 is a table showing temperature differences between resistors and warm-up times. [Figure 7] 1 is a table showing simulation conditions. [Figure 8] 13 is a graph showing temperature differences between resistors as a function of protrusion width for a number of protrusion heights. [Figure 9] 13 is a graph showing temperature differences between resistors depending on protrusion height for a number of protrusion widths. [Figure 10] 13 is a graph showing the temperature difference between resistors depending on the distance between the resistors with and without a protrusion. [Figure 11] 13 is a graph showing temperature differences between resistors according to distance between resistors for a number of resistor lengths. [Figure 12] FIG. 11 is a diagram illustrating an ON Duty correction. [Figure 13] 11 is a table showing recording medium sizes and ON Duty correction coefficients. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings. [1. Configuration of image forming device] As shown in FIG. 1, the color printer 1 is a color electrophotographic printer that prints a desired color image on a recording medium P, for example, A5 size or A4 size. In the following description, the left end portion in FIG. 1 is the front of the color printer 1, and the up-down direction, left-right direction, and front-rear direction are defined when viewed from the front. In the following description, a position close to the recording medium storage unit 4 as viewed from an arbitrary position on the conveying path 5 along which the recording medium P is conveyed, or a direction toward the recording medium storage unit 4, is referred to as upstream. In the following description, a position close to the discharge stacker unit 22 on which the recording medium P is discharged and stacked, or a direction toward the discharge stacker unit 22, as viewed from an arbitrary position on the conveying path 5, is referred to as downstream. Furthermore, the direction from upstream to downstream is referred to as the conveying direction. In addition, the left-right direction perpendicular to the conveying direction and the thickness direction perpendicular to the paper surface of the conveyed recording medium P is also referred to as the conveying width direction.

[0013] This color printer 1 is composed of a main body 2 and an openable and closable top cover 3. A recording medium storage section 4 capable of storing a plurality of recording media P is provided at the bottom inside the main body 2. A paper feed roller 6 is provided at the upper front end of the recording medium storage section 4, which separates the recording media P stored in a stacked state in the recording medium storage section 4 one by one and feeds the recording media P to a conveying path 5. A first registration roller 7 and a second registration roller 8 are conveying rollers that convey the recording media P fed by the paper feed roller 6 from the recording medium storage section 4 to an image forming section 9. The image forming section 9 is composed of image forming units 14Y, 14M, 14C, and 14K (hereinafter, these are also collectively referred to as image forming units 14).

[0014] The IN1 sensor 10 is disposed upstream of the first registration roller 7 and is a transport system sensor that detects the arrival of the recording medium P. The IN2 sensor 11 is disposed upstream of the second registration roller 8 and is a transport system sensor that detects the arrival of the recording medium P. The WR sensor 12 is disposed downstream of the second registration roller 8 and is a transport system sensor that detects the recording medium P and detects the timing when the recording medium P reaches the image forming unit 9.

[0015] A conveyor belt 13 is provided above the recording medium storage unit 4 within the main body 2, so as to traverse the main body 2 from front to rear. The conveyor belt 13 is stretched so as to go around front and rear rollers each having an elongated cylindrical shape with its central axis oriented in the left-right direction, and is disposed opposite the lower side of the image forming unit 14. The recording medium P is placed on its upper surface and conveyed downstream in the rear direction.

[0016] On the other hand, four image forming units 14Y, 14M, 14C, and 14K are arranged in order from the front to the rear above the conveyor belt 13. That is, the image forming units 14 of each color are arranged in a so-called tandem system. The image forming units 14Y, 14M, 14C, and 14K correspond to the colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The image forming units 14Y, 14M, 14C, and 14K are configured similarly to each other, and only the corresponding toner colors are different. The image forming unit 14 is formed in a box shape that is relatively long in the left-right direction so as to correspond to the left-right width of the recording medium P.

[0017] Further, toner cartridges 15Y, 15M, 15C and 15K (hereinafter collectively referred to as toner cartridges 15) are provided above the image forming units 14Y, 14M, 14C and 14K, respectively. The toner cartridges 15 are hollow containers that are long in the left-right direction, and contain powdered toner of each color, respectively, and have a predetermined stirring mechanism built in. The toner cartridges 15 are configured to be detachable from the image forming units 14.

[0018] Also, LED heads 16Y, 16M, 16C, and 16K (hereinafter, these are also collectively referred to as LED heads 16) are provided in the main body 2 so as to correspond to the image forming units 14Y, 14M, 14C, and 14K, respectively. The LED head 16 is configured as a rectangular parallelepiped elongated in the left-right direction, and a plurality of LEDs (Light Emitting Diodes) are arranged in a row in the left-right direction inside the LED head 16. The LED head 16 is connected to a process control unit 60 (FIG. 4) of the main body 2 via a cable, and causes each LED to emit light in a light emission pattern according to image data supplied from an exposure control unit 62 (FIG. 4). The LED head 16 is supported by the top cover unit 3, and when the top cover unit 3 is closed, the photosensitive drum 17 (photosensitive drums 17Y, 17M, 17C, and 17K) is extremely close to the LED head 16, and exposure processing is performed by light from the LED head 16.

[0019] The image forming units 14Y, 14M, 14C, and 14K are provided with photosensitive drums 17Y, 17M, 17C, and 17K (hereinafter, these are also collectively referred to as photosensitive drums 17). The photosensitive drums 17 can create electrostatic latent images on their surfaces according to print data by electrostatic force, and a toner image is formed by toner supplied from a toner cartridge 15.

[0020] Transfer rollers 18Y, 18M, 18C and 18K (hereinafter collectively referred to as transfer rollers 18) are provided at four locations directly below the image forming units 14Y, 14M, 14C and 14K. That is, the transfer rollers 18 are disposed facing the photosensitive drum 17 with the conveyor belt 13 interposed therebetween. The transfer rollers 18 are configured to be capable of being charged, and transfer the toner image formed on the surface of the photosensitive drum 17 onto the recording medium P. The photosensitive drum 17 and transfer rollers 18 are subjected to a high voltage applied from a high voltage power supply 24, which will be described later, to perform electrophotographic processes such as electrostatic charging, development and transfer.

[0021] In this configuration, the motor control unit 63 (FIG. 4) supplies toner from the toner cartridge 15 to the image forming units 14. At the same time, the exposure control unit 62 (FIG. 4) causes the LED head 16 to emit light so as to form an emission pattern corresponding to the image data supplied from the PC 54 (FIG. 4). In response to this, each image forming unit 14 uses the toner supplied from the toner cartridge 15 to form a toner image corresponding to the emission pattern of the LED head 16, and transfers this toner image onto the recording medium P. As a result, four color toner images corresponding to the image data are sequentially transferred onto the recording medium P being transported by the transport belt 13.

[0022] The FUSER-IN sensor 19 is disposed in the vicinity of the upstream side of the fixing unit 20, and is a transport sensor for detecting the recording medium P.

[0023] The fixing device 20 is provided downstream of the image forming unit 14. The fixing device 20 heats the fixing belt 30 (FIG. 2) and rotates the fixing belt 30 and the pressure roller 32 (FIG. 2) in a predetermined direction under the control of the fixing control unit 64 (FIG. 4). As a result, the fixing device 20 applies heat and pressure to the delivered recording medium P, i.e., the recording medium P on which the four color toner images are superimposed, to fix the toner, and delivers the recording medium P further downstream.

[0024] The EXIT sensor 21 is installed downstream of the fixing unit 20 and is a travel system sensor that detects the recording medium P and detects that the recording medium P has been discharged from the fixing unit 20. The discharge stacker unit 22 is provided outside the main body unit 2 and accumulates the recording medium P on which an image has been formed. The density sensor 23 is an optical sensor that reads a special pattern created on the conveyor belt 13 and is used for print quality maintenance operations such as density correction.

[0025] The high-voltage power supply 24 is a power supply that generates a high voltage to be applied to the photosensitive drum 17 and the transfer roller 18. The low-voltage power supply 25 is an AC-DC power supply that converts a commercial AC power supply into a DC power supply. This low-voltage power supply 25 supplies DC power of 3.3 [V], 5 [V], 24 [V], etc. to each board (not shown). The low-voltage power supply 25 also supplies AC 100 [V] to the heater 31 (FIG. 2) of the fixing unit 20 via triacs 38a and 38b (FIG. 2) described later.

[0026] Here, the above-mentioned transport system sensors (also called paper sensors) (IN1 sensor 10, IN2 sensor 11, WR sensor 12, FUSER-IN sensor 19, and EXIT sensor 21) and density sensor 23 are connected to the process control unit 60 (FIG. 4) via cables. Also, each roller (each roller in the fixing unit 20, the paper feed roller 6, the first registration roller 7, the second registration roller 8, the photosensitive drum 17, and the transfer roller 18) is mechanically driven by an actuator (not shown), and is capable of transporting the recording medium P downstream of the color printer 1.

[0027] Meanwhile, a display unit 26 is provided on the front side of the exterior of the main body 2. The display unit 26 is composed of a liquid crystal display panel and switches, etc., and is capable of displaying the status of the color printer 1 and allowing the user to input operations. This display unit 26 is connected to the process control unit 60 (FIG. 4) via a cable. The liquid crystal display panel is capable of displaying, for example, 24 characters by 2 lines of characters (letters).

[0028] [2. Configuration of the fixing unit] 2, the fixing unit 20 is composed of a fixing belt 30, a heater 31, a pressure roller 32, temperature sensors 33, 34 and 35, thermostats 44 and 45, a heat diffusion member 36, a heat conduction member 46, a heater holder (not shown), and a fixed support member (not shown). Note that FIG. 2(A) is a diagram including a power supply.

[0029] The fixing belt 30 is an endless belt-like body, and the inside is supported by a fixed support member. The fixing belt 30 has a base material, a rubber layer, and a release layer formed from the inner circumference side to the outer circumference side, and for example, the base material is made of a heat-resistant resin such as polyimide or SUS (stainless steel), the rubber layer is made of silicone rubber, and the release layer is made of a material such as fluororesin PFA.

[0030] The heater 31 is disposed on the inner periphery of the fixing belt 30, and is a planar heating element extending in the longitudinal direction. The heater 31 is a heat source in which a front insulating layer, a resistive heating layer, and a protective layer are laminated in this order on a substantially rectangular base material made of, for example, SUS (stainless steel) or ceramic with excellent insulation. The resistive heating layer includes resistors 40 (resistors 40b1, 40a1, 40a2, 40a3, and 40b2) and electrodes. A back insulating layer is laminated on the surface of the base material opposite to the front insulating layer.

[0031] As only the heater 31 is shown below the fixing control unit 64 in Fig. 2(A), the heater 31 has a plurality of resistors 40b1, 40a1, 40a2, 40a3 and 40b2 (hereinafter collectively referred to as resistors 40) arranged at equal intervals in order from left to right along the longitudinal direction of the heater 31 (i.e., the transport width direction or the main scanning direction Drm (hereinafter also referred to as the heater longitudinal direction)) on the base. In other words, the resistors 40 are divided and arranged in the heater longitudinal direction into 40a1, 40a2 and 40a3 (hereinafter collectively referred to as resistors 40a) arranged in the center of the heater longitudinal direction, and 40b1 and 40b2 (hereinafter collectively referred to as resistors 40b) arranged at both ends of the heater longitudinal direction. In this embodiment, all resistors 40b1, 40a1, 40a2, 40a3, and 40b2 have the same length in the heater longitudinal direction. In the following, the heater longitudinal direction (left-right direction) is defined as the main scanning direction Drm (transport width direction), and the front-rear direction perpendicular to the heater longitudinal direction is defined as the sub-scanning direction Drs (transport direction).

[0032] The resistor 40a is disposed over an area including a paper passing area ARpa5, which is an area occupied in the conveying width direction when a narrow-sized (e.g., A5 size) recording medium P, A5 size recording medium Pa5, passes through, and supports the narrow-sized recording medium P. The resistor 40a and resistor 40b are disposed together over an area including a paper passing area ARpa4, which is an area occupied in the conveying width direction when a wide-sized (e.g., A4 size) recording medium P, A4 size recording medium Pa4, passes through, and the resistors 40a and 40b support the wide-sized recording medium P. Hereinafter, the area outside the paper passing area ARpa4 in the conveying width direction, that is, the area at both ends of the conveying width direction of the fixing belt 30 where the recording medium P does not pass through, is also referred to as a non-paper passing area ARnp. The resistor 40a and resistor 40b are controlled to be turned ON / OFF by triacs 38a and 38b (described later), and are supplied with power independently from the AC nominal voltage 37, generating heat.

[0033] Here, in order to arrange a plurality of resistors 40, each of which is supplied with power independently, in series, it is necessary to provide a gap for maintaining insulation between adjacent resistors 40. For this reason, in the heater 31, a gap, that is, an inter-resistor gap GP, is provided between adjacent resistors 40.

[0034] The pressure roller 32 is disposed facing the underside of the fixing belt 30, and forms a nip between the pressure roller 32 and the fixing belt 30. The pressure roller 32 is configured such that the peripheral surface of a cylindrical member made of a metal material is covered with a rubber elastic layer, and the rubber elastic layer is made of a material such as silicone rubber. In this embodiment, in order to form a nip between the fixing belt 30 and the pressure roller 32, when the pressure roller 32 is rotated by the main motor 76 (FIG. 4), the fixing belt 30 also rotates following the pressure roller 32.

[0035] The heat diffusion member 36 is disposed between the heater 31 and the fixing belt 30 along the left-right direction (longitudinal direction) so as to contact the heater 31 and the fixing belt 30. The heat diffusion member 36 uniformly diffuses the temperature in the longitudinal direction and the width direction (the front-rear direction in which the recording medium P is transported). The heat diffusion member 36 is made of a material such as aluminum having high thermal conductivity. Therefore, the color printer 1 detects the temperature of the fixing belt 30, which is heated by the heater 31 or from which heat is absorbed by the recording medium P, etc., with good accuracy and responsiveness using the temperature sensors 33, 34, and 35. In this embodiment, the thickness of the heat diffusion member 36 is set to 0.5 mm as a standard.

[0036] The heat conducting member 46 is disposed along the left-right direction (longitudinal direction) so as to be in contact with the heater 31 on the side of the heater 31 that is separated from the pressure roller 32. This heat conducting member 46 diffuses the temperature uniformly in the longitudinal direction and width direction (the front-rear direction in which the recording medium P is transported) similarly to the heat diffusion member 36. Also, like the heat diffusion member 36, the heat conducting member 46 is made of a material with high thermal conductivity such as aluminum, but if the heat diffusion by the heat diffusion member 36 is sufficient, it may be made of stainless steel or the like, or the heat conducting member 46 itself may not be disposed.

[0037] Between the heater 31 and the heat diffusion member 36 and between the heater 31 and the heat conductive member 46, heat conductive grease (not shown) mainly composed of zinc oxide and silicone oil is applied to improve the heat conductivity between the members. In addition, between the heat diffusion member 36 and the fixing belt 30, sliding grease (not shown) mainly composed of PTFE (perfluoropolyether) is applied.

[0038] The temperature sensor 33 is a contact type thermistor, and is installed so as to be in contact with the heat diffusion member 36 at approximately the center of the paper passing area ARpa5 arranged in the center in the transport width direction of the fixing belt 30, and detects the nip center temperature, which is the temperature of the center in the transport width direction of the fixing belt temperature, which is the surface temperature of the fixing belt 30. The temperature sensors 34 and 35 are contact type thermistors, and are installed so as to be in contact with the heat diffusion member 36 on the right and left sides, respectively, of the paper passing area ARpa5 of the fixing belt 30 in the transport width direction, and detect the fixing belt temperature.

[0039] The thermostat 44 is disposed inside the paper passing area ARpa5 of the fixing belt 30 so as to be in contact with the heat diffusion member 36, similarly to the temperature sensors 33, 34, and 35. The thermostat 45 is disposed on the right side of the paper passing area ARpa5 of the fixing belt 30 in the conveying width direction so as to be in contact with the heat diffusion member 36. The thermostats 44 and 45 detect the fixing belt temperature, and when the fixing belt temperature reaches a predetermined upper limit, cut off the power supply to the resistor 40, thereby functioning as a final safety device. The temperature sensors 33, 34, and 35 and the thermostats 44 and 45 are pressed against the heat diffusion member 36 with a predetermined force by a spring (not shown), thereby reducing errors in the detected temperature and improving responsiveness.

[0040] The AC nominal voltage 37 is, for example, an AC input voltage of AC 100 V. Triacs 38a and 38b (hereinafter, collectively referred to as triacs 38) are semiconductor switching elements used for power control of the heater 31, and are turned on and off by a fixing control unit 64. The fixing control unit 64 will be described in detail later, but it controls the temperature of the fixing belt 30 to be optimal by controlling the heating of a resistor 40 in the heater 31 based on the detection results of the temperature sensors 33, 34, and 35.

[0041] [3. Composition of heat diffusion material] 3, the heat diffusion member 36 is formed by bending a single metal plate such as aluminum by sheet metal processing, and has a plate-like portion 47, a side wall portion 48, and a protrusion portion 49. In FIG. 3, the position of the resistor 40 when the heater 31 is accommodated in the heat diffusion member 36 is virtually indicated by a dashed line.

[0042] The plate-like portion 47 is a rectangular thin plate that is thin in the vertical direction, short in the transport direction (front-rear direction), long in the transport width direction (left-right direction), and extends along the left-right direction, with its upper and lower surfaces being flat. The plate-like portion 47 is placed with the lower surface of the heater 31 in contact with its upper surface.

[0043] The side wall portion 48 is a wall portion erected upward at a right angle to the plate-shaped portion 47 from the front end and rear end of the plate-shaped portion 47. The side wall portion 48 is a rectangular thin plate that is short in the up-down direction and thin in the front-rear direction, and is formed continuously from the left end to the right end of the plate-shaped portion 47. The side wall portion 48 has a linear upper end that is the same height from the left end to the right end except for the portion where the protrusion 49 is formed. The heat diffusion member 36 accommodates the heater 31 and the heat conduction member 46 in a space surrounded by the plate-shaped portion 47 and the side wall portion 48.

[0044] The protrusions 49 are walls that extend upward from the upper end of the side wall 48 at right angles to the plate-like portion 47, and all of the protrusions 49 have the same shape. The protrusions 49 are thin plate shapes that are rectangular (rectangular) when viewed from the front-rear direction, have a certain length in the up-down and left-right directions, and are thin in the front-rear direction. The length of the protrusions 49 in the left-right direction is about half that of the resistor 40, and the protrusions 49 are divided from each other in the left-right direction and formed discretely with their centers in the left-right direction at the same position as the center of the resistor 40. Therefore, all of the protrusions 49 have the same left-right distance between adjacent protrusions 49.

[0045] The resistor width W1, which is the width of the resistor 40 in the front-to-back direction, is 7 [mm], the resistor length L1, which is the length of the resistor 40 in the left-to-right direction, is 50 [mm], and the resistor distance G1, which is the length of the left-to-right gap between adjacent resistors 40 (i.e. the left-to-right length of the inter-resistor gap GP), is 5 [mm].

[0046] The heat diffusion member transport direction width W2, which is the width in the front-rear direction of the heat diffusion member 36 (i.e., the distance between the rear surface of the front sidewall portion 48 and the front surface of the rear sidewall portion 48 (in other words, the distance between the inner wall surfaces of the sidewall portions 48 on the plate-like portion 47 side)), is 16 mm, which is the same as the front-rear width of the heater 31. The resistor 40 is disposed at the center in the front-rear direction with respect to the heat diffusion member 36, and a sidewall resistor interval G2, which is the distance from the rear surface of the front sidewall portion 48 of the heat diffusion member 36 to the front end of the resistor 40, and a sidewall resistor interval G2 (not shown), which is the distance from the front surface of the rear sidewall portion 48 of the heat diffusion member 36 to the rear end of the resistor 40, are 4.5 mm.

[0047] The sidewall height H1, which is the height from the top surface of the plate-shaped portion 47 of the heat diffusion member 36 to the top end of the sidewall portion 48, is 3 mm. As a result, the heat diffusion member 36 accommodates the heater 31 and the heat conductive member 46 in the space surrounded by the plate-shaped portion 47 and the sidewall portion 48, and prevents the heat conductive grease applied between the heater 31 and the heat diffusion member 36 from leaking out to the outside. The protrusion height H2, which is the height from the top surface of the plate-shaped portion 47 of the heat diffusion member 36 to the top end of the protrusion 49, is 13 mm. The protrusion width W3, which is the width of the protrusion 49 in the left-right direction, is 25 mm.

[0048] [4. Color printer control configuration] As shown in FIG. 4, the color printer 1 is controlled by a controller control unit 50. The controller control unit 50 has a CPU 51, a ROM (Read Only Memory) 52, and a RAM (Random Access Memory) 53, and the CPU 51, ROM 52, and RAM 53 are connected to each other by an internal bus. The CPU 51 controls the RAM 53 and a process control unit 60 according to a print processing program stored in the ROM 52. The ROM 52 is an area for storing the print processing program, and is a non-volatile memory capable of retaining data even when the color printer 1 is turned off. The RAM 53 is a volatile memory that stores print data input from a PC 54, and the data is erased when the color printer 1 is turned off. The controller control unit 50 is connected to the PC 54 external to the color printer 1.

[0049] The PC 54 is, for example, a personal computer, and has a PC display unit 55 and a PC input unit 56. The PC 54 creates print data and transmits the print data to the color printer 1 via a communication interface consisting of a USB (Universal Serial Bus) or a LAN (Local Area Network), etc. The PC 54 also receives instructions issued by the color printer 1 via the communication interface. The PC display unit 55 is made up of a liquid crystal display or the like, and displays a print image created by an application (not shown) as well as instructions issued by the color printer 1. The PC input unit 56 is made up of a keyboard, mouse, etc., and creates an image of the print data via an application (not shown) as well as inputs responses to instructions issued by the color printer 1.

[0050] The process control unit 60 has a high voltage control unit 61, an exposure control unit 62, a motor control unit 63, and a fixing control unit 64, and controls the printing process such as conveyance of the recording medium P, charging, developing, transferring, and fixing.

[0051] The high voltage control unit 61 has a supply voltage control unit 66, a development voltage control unit 67, a charging voltage control unit 68, and a transfer control unit 69, and appropriately controls the voltages applied to the various rollers in order to transfer the toner to the recording medium P. The supply voltage control unit 66 controls the supply voltage applied to the supply roller 70. The development voltage control unit 67 controls the development voltage applied to the development roller 71. The charging voltage control unit 68 controls the charging voltage applied to the charging roller 72. The transfer control unit 69 controls the transfer voltage applied to the transfer roller 18. The exposure control unit 62 controls the exposure of the LED head 16.

[0052] Motor control unit 63 controls and rotates main motor 76 in color printer 1 to drive the rollers in image forming unit 14, the rollers in fuser 20, paper feed roller 6, first registration roller 7, and second registration roller 8. In this embodiment, only main motor 76 is provided, but motors for driving the rollers in image forming unit 14, the rollers in fuser 20, paper feed roller 6, first registration roller 7, and second registration roller 8 may be provided separately.

[0053] The fixing control unit 64 controls the triacs 38a and 38b of the low voltage power supply 25 to be turned on and off in accordance with the detection results of the temperature sensors 33, 34, and 35 based on the set temperature of the fixing belt, ON Duty parameters, etc., thereby supplying power to the heater 31 from the AC nominal voltage 37 and controlling the surface temperature of the fixing belt 30 to a predetermined appropriate temperature. Here, ON Duty is the ratio of the time voltage is applied to each resistor 40 per given time, and the larger the value, the longer the time voltage is applied to each resistor 40 per given time.

[0054] [5. Temperature difference between resistors and warm-up time] Fig. 5 shows the temperature distribution in the longitudinal direction of the fixing belt when the heater 31 is heated for a predetermined time (e.g., 6 seconds). In Fig. 5, the temperature distribution line LN1 shows the temperature distribution when the heat diffusion member 36 does not have the protrusions 49 (i.e., when the protrusion height H2 of the heat diffusion member 36 (Fig. 3) is 3 mm, which is the same height as the side wall height H1), the temperature distribution line LN2 shows the temperature distribution when the heat diffusion member 36 has the protrusions 49 and has a plate thickness of 0.5 mm, and the temperature distribution line LN3 shows the temperature distribution when the heat diffusion member 36 has the protrusions 49 and has a plate thickness of 0.3 mm.

[0055] 6 shows the temperature difference between resistors and the warm-up time in each of the following configurations: when the heat diffusion member 36 does not have the protrusions 49 (temperature distribution line LN1), when the heat diffusion member 36 has the protrusions 49 and has a plate thickness of 0.5 mm (temperature distribution line LN2), and when the heat diffusion member 36 has the protrusions 49 and has a plate thickness of 0.3 mm (temperature distribution line LN3). Here, the temperature difference between resistors is the temperature difference between the fixing belt temperature at the center of the resistor 40 in the transport width direction (also called the heat generation center position) and the fixing belt temperature at the center of the resistor gap GP adjacent to the resistor 40 in the transport width direction (also called the gap center position).

[0056] As shown in the temperature distribution line LN1 of FIG. 5, the position Pa is the center (heat generating center position) of the resistor 40a1 in the conveying width direction, and therefore the temperature is the highest in the range of the resistor 40a1 in the conveying width direction compared to both ends of the resistor 40a1 adjacent to the resistor gap GP in the conveying width direction. On the other hand, the position Pb in FIG. 5 is the center (gap center position) of the resistor gap GP between the resistor 40a1 and the resistor 40a2 in the conveying width direction, and therefore the position Pb is between the resistor 40a1 and the resistor 40a2 in the conveying width direction, does not generate heat, and is the furthest from the center of the resistor gap GP between the resistor 40a1 and the resistor 40a2 in the conveying width direction, and therefore the temperature is low. The temperature difference between the fixing belt temperature at the position Pa and the fixing belt temperature at the position Pb in the temperature distribution line LN1 (i.e., the temperature difference between the resistors) was 9.0 [°C] as shown in FIG. 6. Furthermore, when the protrusions 49 were not present on the heat diffusion member 36, the warm-up time required for the fixing belt temperature to reach a predetermined temperature was 6.0 seconds, as shown in FIG.

[0057] In this way, the temperature is high in the center of the resistor 40 in the transport width direction, while the temperature is low in the gaps GP between the resistors because they do not generate heat. Heat is diffused from the high temperature areas to the low temperature areas by conductive heat transfer, so when focusing on the range of one resistor 40 in the transport width direction on the temperature distribution line LN1, the temperature distribution has a mountain-like shape.

[0058] As a result, a difference occurs between the temperatures applied from the fixing belt 30 to the toner and recording medium P at positions Pa and Pb, causing gloss unevenness. Here, in the color printer 1 of this embodiment, it has been found that when the temperature difference between the fixing belt temperature at the center heat generating position of the resistor 40 and the fixing belt temperature at the center position of the gap between the resistor 40 and the resistor 40 adjacent to the resistor 40 is 5°C or less, gloss unevenness is improved to a level that is not visually noticeable.

[0059] Next, in the case of the temperature distribution line LN2 of this embodiment, the temperature at the position Pa is about 25 [°C] lower than that of the temperature distribution line LN1, and the temperature at the position Pb is about 15 [°C] lower than that of the temperature distribution line LN1. Therefore, in the case of the temperature distribution line LN2, the temperature difference between the resistors is reduced to 1.6 [°C] as shown in FIG. 6, and the gloss unevenness is greatly improved. In this way, in the case of the temperature distribution line LN2, the temperature can be made much more uniform along the conveying width direction compared to the temperature distribution line LN1.

[0060] However, when the protrusion 49 is present on the heat diffusion member 36, the protrusion 49 acts as a member that dissipates heat near the position Pa. As a side effect of equalizing the temperature in the transport width direction, the warm-up time increases by 1 second, from 6.0 seconds to 7.0 seconds, as shown in FIG. 6, compared to when the protrusion 49 is not present on the heat diffusion member 36.

[0061] In contrast, when the heat diffusion member 36 has the protrusion 49 as in the present embodiment and the plate thickness is reduced from 0.5 [mm] to 0.3 [mm], as shown by the temperature distribution line LN3 in FIG. 5 and by FIG. 6, the temperature difference between the resistors is reduced to some extent from 9.0 [°C] to 3.9 [°C] compared to when the heat diffusion member 36 does not have the protrusion 49, thereby improving gloss unevenness to some extent, while the warm-up time is set to 5.8 seconds to prevent any increase.

[0062] In this way, when the heat diffusion member 36 has the protrusions 49 and the plate thickness is set to 0.3 mm, it is possible to prevent the warm-up time from deteriorating while reducing the temperature difference between the resistors. On the other hand, in the case of an operation mode in which the warm-up time is tolerable, the heat diffusion member 36 may have the protrusions 49 and the plate thickness may be set to 0.5 mm as in this embodiment.

[0063] The above has been described with respect to the position Pa of the center of resistor 40a1 in the transport width direction, and the position Pb, which is the center between resistor 40a1 and resistor 40a2 in the transport width direction, but the same applies to the positions of the centers in the transport width direction of various other resistors 40, and the positions of the centers between resistor 40 and the resistor 40 adjacent to resistor 40.

[0064] 5 and 6 are the results of a simulation using ANSYS Workbench (ANSYS, Inc.). The configuration, material, and dimensions of each member used in the simulation are shown in Fig. 7. The output of the heater 31 was set to 4.4 [W] per 1 [mm] in the conveying width direction, and this output was continued from 0 seconds to 6 seconds.

[0065] [6. Appropriate size of protrusions] First, the appropriate protrusion width W3 and protrusion height H2 will be described with reference to Figs. 8 and 9. Here, the resistor length L1 is 50 mm, and the resistor distance G1 is 5 mm. Fig. 8 shows the temperature difference between resistors according to the protrusion width W3 for three types of protrusion height H2, 3 mm, 8 mm, 10 mm, and 13 mm. Note that the protrusion height H2 of 3 mm means that the protrusion 49 does not exist. Although the characteristics of the temperature difference between resistors change according to the protrusion height H2, in order for the temperature difference between resistors to be 5°C or less, where gloss unevenness is no longer a problem, when the protrusion height H2 is 13 mm, the protrusion width W3 must be 8 mm or more. When the protrusion width W3 is 8 mm, the ratio of the protrusion width W3 to the resistor length L1 of 50 mm is 16%. Furthermore, if the protrusion height H2 is 10 mm, the protrusion width W3 must be 10 mm or more. Furthermore, if the protrusion height H2 is 8 mm, the protrusion width W3 must be 17 mm or more.

[0066] Also, when considering the size variation of the components, it is necessary to select a state in which the change in temperature difference between the resistors is small with respect to the change in the protrusion width W3. In that case, the smaller the gradient of the curve in the graph due to the change in the protrusion width W3, the more stable it becomes, so the protrusion width W3 needs to be about 30 [mm]. When the protrusion width W3 is 30 [mm], the ratio of the protrusion width W3 to the resistor length L1 of 50 [mm] is 60 [%]. Therefore, when the protrusion height H2 is 13 [mm], it is preferable that the protrusion width W3 is about 16 to 60 [%] of the resistor length L1 of 50 [mm].

[0067] Next, FIG. 9 shows the temperature difference between resistors according to the protrusion height H2 for three types of protrusion width W3, 10 [mm], 20 [mm], and 30 [mm]. Note that FIG. 9 plots the temperature difference between resistors when the protrusion 49 does not exist. Although the characteristics of the temperature difference between resistors change according to the protrusion width W3, in order for the temperature difference between resistors to be 5 [°C] or less, where gloss unevenness is no longer a problem, when the protrusion width W3 is 30 [mm], the protrusion height H2 must be 6 [mm] or more. Furthermore, when the protrusion width W3 is 20 [mm], the protrusion height H2 must be 7.5 [mm] or more. Furthermore, when the protrusion width W3 is 10 [mm], the protrusion height H2 must be 10 [mm] or more.

[0068] Also, when considering the size variation of the components, it is necessary to select a state in which the change in temperature difference between the resistors is small with respect to the change in the protrusion height H2. In that case, the smaller the gradient of the curve in the graph due to the change in the protrusion height H2, the more stable it becomes, so the protrusion height H2 needs to be about 16 [mm]. To summarize the above, it is preferable that the protrusion width W3 is about 16 to 60 [%] of the resistor length L1 of 50 [mm], and the protrusion height H2 is preferably 6 [mm] or more.

[0069] Next, the appropriate size of the protrusion 49 according to the distance G1 between resistors will be described with reference to Fig. 10. Fig. 10 shows the temperature difference between resistors when the distance G1 between resistors is changed to 1 mm, 5 mm, and 10 mm for cases where there is no protrusion 49 and where there is a protrusion 49 with a protrusion width W3 of 25 mm and a protrusion height H2 of 13 mm. Here, the length L1 of the resistor is 50 mm.

[0070] When the distance G1 between resistors is as narrow as 1 mm, the temperature difference between resistors is 5° C. or less even without the protrusion 49, and therefore the protrusion 49 is not necessary. Also, in order to make the temperature difference between resistors 5° C. or less, when the distance G1 between resistors is less than 3 mm, the protrusion 49 is not necessary. Furthermore, when the distance G1 between resistors is less than 3 mm, even if the protrusion 49 is provided, it is not necessary to provide a large-sized protrusion 49 having a protrusion width W3 of 25 mm and a protrusion height H2 of 13 mm as in this embodiment, and the size of the protrusion 49 can be adjusted as described in FIG. 8.

[0071] On the other hand, if the distance G1 between resistors is 7.6 mm or more, even if there is a protrusion 49 with a protrusion width W3 of 25 mm and a protrusion height H2 of 13 mm as in this embodiment, the temperature difference between the resistors will be higher than 5°C. Therefore, in the case of a protrusion 49 with a protrusion width W3 of 25 mm and a protrusion height H2 of 13 mm, the distance G1 between resistors must be less than 7.6 mm.

[0072] Next, the appropriate size of the protrusion 49 according to the inter-resistor distance G1 when the resistor length L1 is short will be described with reference to Fig. 11. Fig. 11 shows the temperature difference between resistors when the inter-resistor distance G1 is changed to 1 mm, 5 mm, and 10 mm for two types of resistor lengths L1 of 30 mm and 50 mm in a state where the protrusion 49 is not present.

[0073] When the resistor length L1 is 50 [mm], the temperature difference between resistors can be kept below 5 [°C] up to the resistor distance G1 of 2.8 [mm]. On the other hand, when the resistor length L1 is 30 [mm], the temperature difference between resistors is greatly reduced compared to when it is 50 [mm]. This is because the distance between the heat generation center position and the gap center position is shorter when the resistor length L1 is 30 [mm] than when it is 50 [mm], so that conductive heat transfer is promoted and the temperature difference between resistors is reduced. For this reason, when the resistor length L1 is 30 [mm], the temperature difference between resistors can be kept below 5 [°C] up to the resistor distance G1 of 7.5 [mm]. Therefore, when the resistor length L1 is 30 [mm] and the resistor distance G1 is less than 7.5 [mm], the protrusion 49 is not necessary. Furthermore, when the resistor length L1 is 30 mm and the resistor distance G1 is less than 7.5 mm, even if a protrusion 49 is provided, there is no need to provide a large-sized protrusion 49 such as the protrusion 49 in this embodiment, which has a protrusion width W3 of 25 mm and a protrusion height H2 of 13 mm.

[0074] [7. Operation, etc.] 12 and 13 are diagrams for explaining ON duty correction of resistor 40b. In the following, explanation of the basic operation of color printer 1 will be omitted, and the fixing operation will be mainly explained. Color printer 1 detects the nip center temperature, which is the temperature of the center of the conveying width direction of the fixing belt temperature, by temperature sensor 33 arranged at the center of the conveying width direction of heat diffusion member 36, and controls triacs 38a and 38b to drive the power supplied from low voltage power source 25 to heater 31 on / off by fixing control unit 64, thereby controlling the nip center temperature to a predetermined set temperature. This predetermined set temperature is a set temperature determined for each recording medium P, and is set to 170° C. here, for example.

[0075] The resistor 40a is driven with an ON duty such that the temperature detected by the temperature sensor 33 becomes the set temperature, while the resistor 40b is driven with an ON duty multiplied by an ON duty correction coefficient that differs depending on the size of the recording medium P, based on the ON duty of the resistor 40a. In other words, the ON duty of the resistor 40b is determined by the following formula.

[0076] ON Duty of resistor 40b=Actual ON Duty of resistor 40a×ON Duty correction coefficient according to recording medium size

[0077] As shown in FIG. 13, for example, the ON Duty correction coefficient for an A4 size recording medium Pa4 where the recording medium P has an A4 size recording medium size is α1, the ON Duty correction coefficient for a B5 size recording medium Pb5 where the recording medium P has a B5 size recording medium size is α2, and the ON Duty correction coefficient for an A5 size recording medium Pa5 where the recording medium P has an A5 size recording medium size is α3, and the magnitude relationship between these is 1≧α1>α2>α3.

[0078] By controlling using the ON Duty correction coefficient in this manner, the color printer 1 can maintain a constant temperature distribution of the fixing belt temperature in the longitudinal direction of the fixing belt 30 even when the size of the recording medium P is different, thereby ensuring stable print quality.

[0079] In this embodiment, color printer 1 is in demand for printing on B5 size recording medium Pb5, and resistor 40b has a mixture of places where recording medium P passes and places where it does not pass in the transport width direction, so resistor 40b is driven with an ON duty obtained by multiplying the ON duty of resistor 40a by an ON duty correction coefficient. However, if color printer 1 does not have a mixture of places where recording medium P passes and places where it does not pass in the transport width direction, resistor 40b may be driven with an ON duty similar to resistor 40a so that the temperature detected by temperature sensor 34 or 35 becomes the set temperature without using the ON duty correction coefficient.

[0080] [8. Effects, etc.] In the color printer 1 having the above-described configuration, a heat diffusion member 36 is provided between the heater 31 and the fixing belt 30, and the heat diffusion member 36 is provided with protrusions 49 which are arranged separately for each resistor 40 in the main scanning direction Drm so that the center of the heat diffusion member 36 is located at the same position in the main scanning direction Drm as the center of the resistor 40 in the main scanning direction Drm.

[0081] Therefore, the color printer 1 can dissipate heat generated from the center portion (heat generating center position) of the resistor 40 in the transport width direction by the protrusions 49, and suppress the temperature rise at the heat generating center position of the resistor 40. Therefore, the color printer 1 can suppress the temperature difference between the resistors, which is the temperature difference between the fixing belt temperature at the heat generating center position of the resistor 40 and the center portion (gap center position) in the transport width direction of the inter-resistor gap GP adjacent to the resistor 40. This allows the color printer 1 to make the fixing belt temperature, which is the surface temperature of the fixing belt 30, uniform from one end to the other end in the longitudinal direction. Thus, the color printer 1 can prevent gloss unevenness, cold offset, etc., and improve print quality.

[0082] According to the above configuration, the color printer 1 includes an image forming unit 14 that forms an image on a recording medium P, and a fixing device 20. The fixing device 20 has a plurality of resistors 40 as heat generating parts arranged along the main scanning direction Drm and separated from one another, a heater 31 in which resistor gaps GP are formed as inter-heating part regions between adjacent resistors 40 in the main scanning direction Drm, a fixing belt 30 heated by the heater 31, a pressure roller 32 that contacts the outer peripheral surface of the fixing belt 30, and a heat diffusion member 36 provided between the heater 31 and the fixing belt 30, and the heat diffusion member 36 has protrusions 49 that are separated from one another and arranged for each resistor 40 in relation to the main scanning direction Drm at positions corresponding to the center of the resistors 40 in the main scanning direction Drm.

[0083] As a result, the color printer 1 can dissipate heat generated at the center of the resistor 40 in the main scanning direction Drm using the protrusion 49, suppressing the temperature rise at the center of the resistor 40 in the main scanning direction Drm, and suppressing the temperature difference in the fixing belt temperature between the center of the resistor 40 in the main scanning direction Drm and the resistor gap GP adjacent to the resistor 40, thereby making the surface temperature of the fixing belt 30 uniform from one end to the other end in the main scanning direction Drm.

[0084] 9. Other Embodiments In the above embodiment, the color printer 1 has been described as having the protrusions 49 of the heat diffusion member 36 (FIG. 3) in a rectangular shape when viewed from the transport direction. The present invention is not limited to this, and the color printer 1 may have the protrusions 49 of the heat diffusion member 36 in various other shapes, such as a semicircular, trapezoidal, or triangular shape when viewed from the transport direction. Furthermore, when the protrusions 49 are semicircular, trapezoidal, or triangular, the height of the protrusions 49 at both ends in the transport width direction is lower than that of the center.

[0085] In the above embodiment, color printer 1 has been described as having protrusions 49 of heat diffusion member 36 (FIG. 3) standing upward at a right angle to plate-shaped portion 47. The present invention is not limited to this, and color printer 1 may have protrusions 49 of heat diffusion member 36 standing in a direction inclined from a right angle to plate-shaped portion 47. Also, color printer 1 may have protrusions 49 standing upward and then bent in various directions.

[0086] Furthermore, in the above-described embodiment, the color printer 1 has been described as having side walls 48 extending from the front and rear ends of the plate-shaped portion 47 of the heat diffusion member 36 (FIG. 3), and protrusions 49 extending from the upper ends of the side walls 48. The present invention is not limited to this, and the color printer 1 may omit the side walls 48 and have protrusions 49 extending from the front and rear ends of the plate-shaped portion 47 of the heat diffusion member 36, provided that leakage of the thermal conductive grease applied between the heater 31 and the heat diffusion member 36 to the outside is not a problem.

[0087] Furthermore, in the above-described embodiment, the color printer 1 has been described as having the heat diffusion member 36 formed by bending a single metal plate through sheet metal processing. However, the present invention is not limited to this, and the color printer 1 may have the protrusions 49 formed by various other manufacturing methods, such as additionally fixing the protrusions 49 onto the side wall 48.

[0088] Furthermore, in the above embodiment, the color printer 1 has been described as being made of aluminum as the heat diffusion member 36. However, the present invention is not limited to this, and the color printer 1 may be configured such that the heat diffusion member 36 is made of various other materials having high thermal conductivity.

[0089] Furthermore, in the above embodiment, the color printer 1 has been described as having resistors 40 arranged at equal intervals in the transport width direction in the heater 31 (FIG. 2). The present invention is not limited to this, and the color printer 1 may have resistors 40 arranged at various other intervals in the transport width direction in the heater 31.

[0090] Furthermore, in the above embodiment, the color printer 1 has been described as having the same length in the transport width direction for all resistors 40b1, 40a1, 40a2, 40a3, and 40b2 (FIG. 2). The present invention is not limited to this, and the color printer 1 may have at least one resistor 40 among resistors 40b1, 40a1, 40a2, 40a3, and 40b2 have a length in the transport width direction that is different from the other resistors 40.

[0091] Furthermore, in the above-described embodiment, the color printer 1 has been described as having the temperature sensors 34 and 35 installed at both ends in the transport width direction of the fixing belt 30. However, the present invention is not limited to this, and since the resistors 40b1 and 40b2 are heated simultaneously, the color printer 1 may have the temperature sensors 34 and 35 installed at only one end of the fixing belt 30 in the transport width direction.

[0092] Furthermore, in the above-described embodiment, the color printer 1 has been described as being installed to the right of the paper passage area ARpa5 of the fixing belt 30 in the transport width direction. However, the present invention is not limited to this, and the color printer 1 may be installed to the left of the paper passage area ARpa5 of the fixing belt 30 in the transport width direction.

[0093] Furthermore, in the above-described embodiment, the color printer 1 has been described as having the temperature sensors 33, 34, and 35 and the thermostats 44 and 45 installed on the heat diffusion member 36. However, the present invention is not limited to this, and the color printer 1 may have at least one of the temperature sensors 33, 34, and 35 and the thermostats 44 and 45 installed on the heater 31 or the heat conductive member 46.

[0094] Furthermore, in the above-described embodiment, color printer 1 has been described as having temperature sensors 33, 34, and 35 and thermostats 44 and 45 configured as contact-type temperature detection sensors and installed so as to be in contact with heat diffusion member 36. However, the present invention is not limited to this, and color printer 1 may have at least one of temperature sensors 33, 34, and 35 and thermostats 44 and 45 configured as a non-contact type temperature detection sensor to detect the fixing belt temperature.

[0095] Furthermore, in the above embodiment, the color printer 1 has been described as adjusting the amount of heat generated by the resistor 40 by controlling the ON duty of the triacs 38a and 38b. However, the present invention is not limited to this, and the color printer 1 may change the amount of heat generated by the resistor 40 by various other methods.

[0096] Furthermore, in the above embodiment, the color printer 1 has been described as using three types of ON duty correction coefficients to heat the resistor 40. However, the present invention is not limited to this, and the color printer 1 may heat the resistor 40 using any other number of types of ON duty correction coefficients.

[0097] Furthermore, in the above embodiment, the present invention has been described as being applied to a color printer 1 equipped with a heater 31 having a resistor 40 divided into five parts along the main scanning direction Drm. The present invention is not limited to this, and the present invention may be applied to a color printer equipped with a heater 31 having a resistor 40 divided into various numbers of parts, such as four or less or six or more, along the main scanning direction Drm.

[0098] Furthermore, in the above-described embodiment, the present invention has been described as being applied to a so-called direct transfer color printer 1 in which a toner image is directly transferred from the photosensitive drum 17 to the recording medium P. However, the present invention is not limited to this, and the present invention may also be applied to an image forming apparatus of a so-called intermediate transfer type (or secondary transfer type) in which the toner images of each color are transferred from the photosensitive drum 17 to an intermediate transfer belt as a medium so as to be superimposed one on top of the other, and the toner images are then transferred from this intermediate transfer belt to the recording medium P.

[0099] Furthermore, in the above embodiment, the present invention has been described as being applied to a color printer 1 that uses a developer that uses a one-component development method, but the present invention is not limited to this, and may also be applied to an image forming apparatus that uses a developer that uses a two-component development method, in which a carrier and a toner are mixed together and friction between the carrier and the toner is used to impart an appropriate amount of charge to the toner.

[0100] Furthermore, in the above embodiment, the present invention has been described as being applied to a tandem color printer 1 having image forming units 14 of each color arranged in series along the front-to-rear direction. However, the present invention is not limited to this, and may be applied to image forming apparatuses of various other types, such as a four-cycle type.

[0101] Furthermore, in the above-described embodiment, the present invention has been described as being applied to a color printer 1 that has four image forming units 14 corresponding to the colors of yellow, magenta, cyan, and black and forms color images using toner of four colors. However, the present invention is not limited to this, and the present invention may be applied to an image forming device that has three or less image forming units 14 or five or more image forming units 14 depending on the number of colors of toner used in the image forming device, or an image forming device that has one image forming unit and performs monochrome printing.

[0102] Furthermore, in the above-described embodiment, the present invention has been described as being applied to a single-function printer, color printer 1. The present invention is not limited to this, and may be applied to image forming devices having various other functions, such as an MFP (Multi Function Peripheral) having the functions of a copier or facsimile machine. The present invention may also be applied to various electronic devices that have a fixing device that uses a heater divided into multiple units to perform heating and form images on recording media such as paper.

[0103] Furthermore, the present invention is not limited to the above-mentioned embodiment and other embodiments. That is, the scope of application of the present invention extends to an embodiment in which the above-mentioned embodiment and the other embodiments are combined in part or in whole in any manner. The scope of application of the present invention also extends to an embodiment in which a part of the configuration described in any of the above-mentioned embodiment and other embodiments is extracted and replaced or diverted with a part of the configuration of any of the above-mentioned embodiment and other embodiments, or an embodiment in which a part of the extracted configuration is added to any of the embodiments.

[0104] Furthermore, in the above-described embodiment, the color printer 1 as the image forming apparatus is configured by the image forming unit 14 as the image forming unit and the fixing device 20 as the fixing device, and the fixing device has the heater 31 as the heater, the fixing belt 30 as the belt, the pressure roller 32 as the pressure member, and the heat diffusion member 36 as the heat diffusion member. The present invention is not limited to this, and the image forming apparatus may be configured by the image forming unit and the fixing device having various other configurations, and the fixing device may have a heater, a belt, a pressure member, and a heat diffusion member having various other configurations. [Industrial Applicability]

[0105] The present invention can be used, for example, in electrophotographic printers. [Explanation of symbols]

[0106] 1: color printer, 2: main body, 3: top cover, 4: recording medium storage section, 5: transport path, 6: paper feed roller, 7: first registration roller, 8: second registration roller, 9: image forming section, 10: IN1 sensor, 11: IN2 sensor, 12: WR sensor, 13: transport belt, 14: image forming unit, 15: toner cartridge, 16: LED head, 17: photosensitive drum, 18: transfer roller, 19: FUSER-IN sensor, 2 0....fuser, 21....EXIT sensor, 22....output stacker section, 23....density sensor, 24....high voltage power supply, 25....low voltage power supply, 26....display section, 30....fuser belt, 31....heater, 32....pressure roller, 33, 34, 35....temperature sensor, 36....heat diffusion member, 37....AC nominal voltage, 38....triac, 40....resistor, GP....gap between resistors, ARpa5, ARpa4....paper passing area, ARnp....paper non-passing area, 44, 45....thermostat, 46 ......Heat conductive member, 47...Plate-shaped portion, 48...Side wall portion, 49...Protrusion portion, 50...Controller control portion, 51...CPU, 52...ROM, 53...RAM, 54...PC, 55...PC display portion, 56...PC input portion, 60...Process control portion, 61...High voltage control portion, 62...Exposure control portion, 63...Motor control portion, 64...Fuser control portion, 66...Supply voltage control portion, 67...Development voltage control portion, 68...Charge voltage control portion, 69...Transfer control portion, 70...Supply roller, 71... ...developing roller, 72...charging roller, 76...main motor, W1...resistor width, L1...resistor length, G1...distance between resistors, W2...heat diffusion member transport direction width, G2...spacing between resistors in side wall, H1...side wall height, H2...protrusion height, W3...protrusion width, LN1, LN2, LN3...temperature distribution line, Drm...main scanning direction, Drs...sub-scanning direction, Pa5...A5 size recording medium, Pa4...A4 size recording medium, Pb5...B5 size recording medium, P...recording medium.

Claims

1. a heater having a plurality of heat generating portions arranged along a main scanning direction and divided from one another, with an inter-heat generating portion region being formed between the heat generating portions adjacent to each other in the main scanning direction; A belt heated by the heater; a pressure member that contacts the outer circumferential surface of the belt; a heat diffusion member provided between the heater and the belt; having The heat diffusion member has protrusions arranged at positions corresponding to the centers of the heat generating portions in the main scanning direction, the protrusions being separated from one another for each of the heat generating portions in the main scanning direction. Fixing device.

2. The protrusion has a center located at a position in the main scanning direction that is the same as a center of the heat generating portion in the main scanning direction. The fixing device according to claim 1 .

3. The length of the protrusion in the main scanning direction is shorter than the length of the heat generating portion in the main scanning direction. The fixing device according to claim 1 .

4. The length of the protrusion in the main scanning direction is 16 to 60% of the length of the heat generating portion in the main scanning direction. The fixing device according to claim 3 .

5. The protrusion is rectangular. The fixing device according to claim 1 .

6. The height of the central portion of the protrusion in the main scanning direction is greater than the height of both ends in the main scanning direction. The fixing device according to claim 1 .

7. The heat diffusion member is a thin plate-like portion extending in the main scanning direction; sidewall portions extending from one end side and the other end side of the plate-shaped portion in a sub-scanning direction perpendicular to the main scanning direction; The protrusion extending from the side wall portion; The fixing device according to claim 1 , further comprising:

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

9. an image forming unit for forming an image on a medium; The fixing device according to any one of claims 1 to 8, An image forming apparatus comprising:

Images