Fixing apparatus and image forming apparatus

Abstract

To improve image quality. [Solution] The fuser 20 is capable of fixing images to an A5-size recording medium Pa5 having a paper feeding area ARpa5 and an A4-size recording medium Pa4 having a paper feeding area ARpa4 with a wider transport width Dw than the paper feeding area ARpa5. The fuser 20 includes a fuser belt 30, a main resistor 40a which is provided so as to be able to heat the fuser belt 30 and whose end on one side of the transport width Dw is positioned on the other side of the end on one side of the transport width Dw of the A4-size recording medium Pa4, and a sub-resistor 40b which is provided so as to be able to heat the fuser belt 30 and whose end on one side of the transport width Dw is positioned on the other side of the end on one side of the transport width Dw of the A4-size recording medium Pa4. The sub-resistor 40b heats the fuser belt 30 with a greater amount of heat when borderless printing is performed on the A5-size recording medium Pa5 than when bordered printing is performed on the A5-size recording medium Pa5.

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming apparatus, and is suitable for application to a fixing device mounted on, for example, an electrophotographic image forming apparatus.

Background Art

[0002] Conventionally, in an electrophotographic image forming apparatus, the surface of a photosensitive drum is charged, the charged surface of the photosensitive drum is exposed 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, which is widely used. As such a fixing device, there is one having a fixing member heated by a heater and a pressing member that presses the fixing member to form a nip portion therebetween.

[0003] There are various sizes of media printed by such image forming apparatuses. Conventionally, there has been an image forming apparatus that performs heater control according to the media width (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in such an image forming apparatus, when fixing is performed by heater control according to a predetermined media width, image defects may occur when edge-free printing is performed.

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

Means for Solving the Problems

[0007] To solve the above problems, the fixing apparatus of the present invention is a fixing apparatus capable of fixing an image to a first medium having a first width and a second medium having a second width that is wider in the transport width direction than the first width, comprising: a fixing member; a first heater provided to be able to heat the fixing member, with one end in the transport width direction positioned on the other side of the transport width direction than one end in the transport width direction of the second medium; and a second heater provided to be able to heat the fixing member, with one end positioned on the one side of the transport width direction than one end in the transport width direction of the second medium, wherein the second heater heats the fixing member with a greater amount of heat when borderless printing is performed on the first medium than when bordered printing is performed on the first medium.

[0008] Furthermore, the fixing apparatus of the present invention is capable of fixing an image to a first medium having a first width and a second medium having a second width that is wider in the transport width direction than the first width, and comprises a fixing member, a first heater provided to heat the fixing member and having one end on the transport width direction side positioned on the other side of the transport width direction than one end on the second medium, and a second heater provided to heat the fixing member and having one end on the transport width direction side positioned on the one side than one end on the second medium, wherein the first heater heats the fixing member with a greater amount of heat when borderless printing is performed on the first medium than when bordered printing is performed on the first medium.

[0009] Furthermore, the fixing apparatus of the present invention is capable of fixing an image to a first medium having a first width and a second medium having a second width that is wider in the transport width direction than the first width, and comprises a fixing member, a first heater provided to heat the fixing member and heating the central part of the fixing member in the transport width direction more strongly than the edges, and a second heater that heats the edges of the fixing member in the transport width direction more strongly than the central part, wherein the first heater heats the fixing member with a greater amount of heat when borderless printing is performed on the first medium than when bordered printing is performed on the first medium.

[0010] Furthermore, 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.

[0011] The present invention suppresses the temperature drop of the fixing member near the edges in the transport width direction of the toner image when performing borderless printing, and maintains the temperature of the fixing member within a temperature range suitable for fixing from one end to the other in the transport width direction, thereby ensuring a temperature suitable for fixing. Therefore, the present invention can prevent the deterioration of image quality near the edges in the transport width direction of the medium when performing borderless printing. [Effects of the Invention]

[0012] According to the present invention, when performing borderless printing, the temperature drop of the fixing member near the edges in the transport width direction of the toner image is suppressed, and the temperature of the fixing member is maintained within a temperature range suitable for fixing from one end to the other in the transport width direction, thereby ensuring a temperature suitable for fixing. Therefore, the present invention can prevent the deterioration of image quality near the edges in the transport width direction of the medium during borderless printing. Thus, the present invention can realize a fixing device and an image forming device that can improve image quality. [Brief explanation of the drawing]

[0013] [Figure 1] This is a right-side view showing the configuration of a color printer. [Figure 2] The configuration of the fuser according to the first embodiment is shown, where (A) is a front view and (B) is a right side view. [Figure 3] This is a block diagram showing the control configuration of a color printer according to the first embodiment. [Figure 4] This diagram illustrates the ON-Duty correction for the comparative example. [Figure 5] This table shows the ON-Duty correction coefficients for comparative examples according to the recording medium size. [Figure 6] This figure shows the challenges of borderless printing using ON Duty correction in the comparative example and the ON Duty correction according to the first embodiment. [Figure 7]FIG. showing a time chart of ON / OFF control of a resistor according to the first embodiment. [Figure 8] TABLE showing an ON Duty correction factor according to the recording medium size and with or without margin printing in the first embodiment. [Figure 9] FRONT VIEW showing the configuration of a fixing device according to the second embodiment. [Figure 10] FRONT VIEW showing the configuration of a halogen heater. [Figure 11] BLOCK DIAGRAM showing the control configuration of a color printer according to the second embodiment. [Figure 12] FIG. showing a time chart of ON / OFF control of a halogen heater according to the second embodiment. [Figure 13] TABLE showing the ON Duty correction factors of the narrow heater and the wide heater according to the recording medium size and with or without margin printing in the second embodiment. [Figure 14] FIG. showing a time chart of ON / OFF control of a resistor according to another embodiment.

MODE FOR CARRYING OUT THE INVENTION

[0014] Hereinafter, embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings. [1. First Embodiment] [1-1. Configuration of Image Forming Apparatus] As shown in FIG. 1, the color printer 1 is an electrophotographic printer for color, and prints a desired color image on a recording medium P having a size such as A5 size or A4 size. Incidentally, hereinafter, the left end portion in FIG. 1 is regarded as the front of the color printer 1, and the explanation will be made after defining the up-down direction, left-right direction, and front-back direction when viewed facing this front. Also hereinafter, a position close to the recording medium storage unit 4 when viewed from an arbitrary position on the conveyance path 5 on which the recording medium P is conveyed, or the direction toward the recording medium storage unit 4 is called upstream. Further hereinafter, a position close to the discharge stacker unit 22 where the recording medium P is discharged and stacked when viewed from an arbitrary position on the conveyance path 5, or the direction toward the discharge stacker unit 22 is called downstream. Furthermore, the direction from upstream to downstream is called the conveyance direction. Also, the left-right direction orthogonal to the conveyance direction and the thickness direction orthogonal to the paper surface of the recording medium P being conveyed is also called the conveyance width direction.

[0015] This color printer 1 is composed of a main body unit 2 and an openable and closable top cover unit 3. At the lowermost part inside the main body unit 2, a recording medium storage unit 4 capable of accommodating a plurality of recording media P is provided. On the upper side of the front end of the recording medium storage unit 4, a paper feed roller 6 is provided for separating and feeding the recording media P accommodated in an integrated state in the recording medium storage unit 4 one by one to the conveyance path 5. The first registration roller 7 and the second registration roller 8 are conveyance rollers for conveying the recording medium P fed from the recording medium storage unit 4 by the paper feed roller 6 to the image forming unit 9. The image forming unit 9 is composed of image forming units 14Y, 14M, 14C, and 14K (hereinafter, these are also collectively referred to as the image forming unit 14).

[0016] The IN1 sensor 10 is installed on the upstream side of the first registration roller 7 and is a running system sensor for detecting the arrival of the recording medium P. The IN2 sensor 11 is installed on the upstream side of the second registration roller 8 and is a running system sensor for detecting the arrival of the recording medium P. The WR sensor 12 is installed on the downstream side of the second registration roller 8 and is a running system sensor for detecting the recording medium P, and detects the timing when the recording medium P reaches the image forming unit 9.

[0017] Above the recording medium storage section 4 within the main body 2, a transport belt 13 is provided, extending across the main body 2 from front to back. The transport belt 13 is stretched around front and rear rollers, which are elongated cylindrical with their central axis oriented in the left-right direction. It is positioned opposite the lower side of the image forming unit 14 and transports the recording medium P on its upper surface toward the downstream side.

[0018] Meanwhile, above the transport belt 13, four image forming units 14Y, 14M, 14C, and 14K are arranged in order from front to back. That is, the image forming units 14 for each color are arranged in a so-called tandem configuration. These image forming units 14Y, 14M, 14C, and 14K correspond to the colors yellow (Y), magenta (M), cyan (C), and black (K), respectively. Furthermore, the image forming units 14Y, 14M, 14C, and 14K are similarly configured to each other, differing only in the color of the corresponding toner. The image forming units 14 are formed in a roughly box-like shape that is relatively long in the left-right direction to accommodate the left-right width of the recording medium P.

[0019] Furthermore, each image forming unit 14Y, 14M, 14C, and 14K is equipped with a toner cartridge 15Y, 15M, 15C, and 15K (hereinafter collectively referred to as toner cartridge 15) above it. The toner cartridge 15 is a long, hollow container in the left-right direction, containing powdered toner of each color, and incorporating a predetermined stirring mechanism. This toner cartridge 15 is configured to be detachable from the image forming unit 14.

[0020] Furthermore, within the main body 2, LED heads 16Y, 16M, 16C, and 16K (hereinafter collectively referred to as LED head 16) are provided, corresponding to each image forming unit 14Y, 14M, 14C, and 14K, respectively. This LED head 16 is configured as a long, narrow rectangular parallelepiped, with multiple LEDs (Light Emitting Diodes) arranged inside along the left-right direction. It is connected via a cable to the process control unit 60 (Figure 3) of the main body 2, and causes each LED to emit light in a light emission pattern corresponding to the image data supplied from the exposure control unit 62 (Figure 3). The LED head 16 is supported by the top cover 3, and when the top cover 3 is closed, the photosensitive drum 17 (photosensitive drums 17Y, 17M, 17C, and 17K) comes into very close proximity to the LED head 16, and the exposure process is performed by the light from the LED head 16.

[0021] Each image forming unit 14Y, 14M, 14C, and 14K is equipped with a photosensitive drum 17Y, 17M, 17C, and 17K (hereinafter collectively referred to as the photosensitive drum 17). The photosensitive drum 17 is capable of creating an electrostatic latent image on its surface according to the print data by electrostatic force, and a toner image is formed by the toner supplied from the toner cartridge 15.

[0022] The transfer rollers 18Y, 18M, 18C, and 18K (hereinafter collectively referred to as the transfer roller 18) are provided at four locations directly beneath each image forming unit 14Y, 14M, 14C, and 14K. That is, the transfer rollers 18 are positioned opposite the photosensitive drum 17, with the transport belt 13 in between. The transfer rollers 18 are configured to be electrically 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 the transfer rollers 18 are subjected to electrostatic charging, development, and transfer by applying high voltage from a high-voltage power supply 24, which will be described later.

[0023] In this configuration, the motor control unit 63 (Figure 3) supplies toner from the toner cartridge 15 to the image forming unit 14. Simultaneously, the exposure control unit 62 (Figure 3) causes the LED head 16 to emit light to form a light emission pattern corresponding to the image data supplied from the PC 54 (Figure 3). In response, each image forming unit 14 uses the toner supplied from the toner cartridge 15 to form a toner image corresponding to the light emission pattern of the LED head 16, and transfers this toner image to the recording medium P. As a result, four toner images corresponding to the image data are sequentially transferred onto the recording medium P being transported by the transport belt 13.

[0024] The FUSER-IN sensor 19 is installed near the upstream side of the fuser 20 and is a travel system sensor that detects the recording medium P.

[0025] A fuser 20 is provided downstream of the image forming unit 14. Based on the control of the fuser control unit 64 (Figure 3), the fuser 20 heats the fuser belt 30 (Figure 2) and rotates the fuser belt 30 and the pressure roller 32 (Figure 2) in predetermined directions. As a result, the fuser 20 applies heat and pressure to the received recording medium P, i.e., the recording medium P on which the four-color toner images are superimposed, to fix the toner, and then passes it further downstream.

[0026] The EXIT sensor 21 is installed downstream of the fuser 20 and is a travel system sensor that detects the recording medium P, detecting when the recording medium P has been ejected from the fuser 20. The ejection stacker unit 22 is located outside the main unit 2 and collects the recording medium P on which images have been formed. The density sensor 23 is an optical sensor that reads a special pattern created on the transport belt 13 and is used for print quality maintenance operations such as density correction.

[0027] The high-voltage power supply 24 is a power supply that generates the high voltage 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 commercial AC power to DC power. This low-voltage power supply 25 supplies DC power such as 3.3[V], 5[V], and 24[V] to each circuit board (not shown). The low-voltage power supply 25 also supplies AC100[V] to the heater 31 (Figure 2) of the fuser unit 20 via triacs 38a and 38b (Figure 2), which will be described later.

[0028] Here, each of the aforementioned 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 (Figure 3) via cables. In addition, each roller (each roller in the fuser 20, paper feed roller 6, first register roller 7, second register roller 8, photosensitive drum 17, and transfer roller 18) is mechanically driven by actuators (not shown) and is capable of transporting the recording medium P to the downstream side of the color printer 1.

[0029] On the other hand, a display unit 26 is provided on the front exterior of the main unit 2. The display unit 26 consists of a liquid crystal display panel and switches, etc., and allows for the display of the status of the color printer 1 and input operations by the user. This display unit 26 is connected to the process control unit 60 (Figure 3) via a cable. The liquid crystal display panel can display, for example, 24 characters x 2 lines of characters.

[0030] [1-2. Fuser Unit Configuration] As shown in Figure 2, the fuser 20 consists of a fuser 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 fixing support member (not shown). Figure 2(A) includes the power supply.

[0031] The fixing belt 30 is an endless strip-shaped body, with its interior supported by a fixing support member. The fixing belt 30 has a base material, a rubber layer, and a release layer formed from the inner circumference to the outer circumference. For example, the base material is made of a heat-resistant resin such as polyimide, or stainless steel (SUS), the rubber layer is made of silicone rubber, and the release layer is made of a fluororesin such as PFA (perfluoroalkoxyalkane).

[0032] The heater 31 is positioned on the inner circumference of the fixing belt 30 and is a planar heating element extending in the longitudinal direction. It is a heating source in which an electrical insulation layer, a resistance heating layer, electrodes, and a protective layer are sequentially laminated on a roughly rectangular substrate made of, for example, SUS (stainless steel) or ceramic with excellent insulating properties. The resistance heating layer includes heat-generating resistors 40 (resistors 40b1, 40a1, 40a2, 40a3, and 40b2).

[0033] As shown in Figure 2(A) below the fixing control unit 64, the heater 31 has multiple resistors 40b1, 40a1, 40a2, 40a3, and 40b2 (hereinafter collectively referred to as resistors 40) arranged at equal intervals from left to right along the longitudinal direction of the heater 31 (i.e., the transport width direction Dw or the main scanning direction (hereinafter also referred to as the heater longitudinal direction)) on the substrate. In other words, the resistors 40 are divided with respect to the longitudinal direction of the heater into resistors 40a1, 40a2, and 40a3 (hereinafter collectively referred to as main resistors 40a) located in the center of the heater longitudinal direction, and resistors 40b1 and 40b2 (hereinafter collectively referred to as sub-resistors 40b) located at both ends of the heater longitudinal direction. In this embodiment, the length in the longitudinal direction of the heater is the same for all resistors 40b1, 40a1, 40a2, 40a3, and 40b2. Hereafter, the longitudinal direction of the heater (left-right direction) will be defined as the transport width direction Dw (main scanning direction), and the front-back direction perpendicular to the longitudinal direction of the heater will be defined as the transport direction (sub-scanning direction).

[0034] The main resistor 40a is positioned over an area that includes the paper-passing area ARpa6, which occupies the area in the transport width direction Dw when a narrow-width recording medium P, such as an A6-size recording medium Pa6, passes through, and the paper-passing area ARpa5, which occupies the area in the transport width direction Dw when an intermediate-width recording medium P, such as an A5-size recording medium Pa5, passes through, thus supporting both narrow-width and intermediate-width recording mediums P. When the main resistor 40a and the sub-resistor 40b are combined, they are positioned over an area that includes the paper-passing area ARpa4, which occupies the area in the transport width direction Dw when a wide-width recording medium P, such as an A4-size recording medium Pa4, passes through. Therefore, the main resistor 40a and the sub-resistor 40b support wide-width recording mediums P. In the following, the area outside the paper-feeding area ARpa4 in the transport width direction Dw, that is, the ends of the transport width direction Dw in the fixing belt 30, which are areas through which the recording medium P does not pass, will also be called the non-paper-feeding area ARnp. The main resistor 40a and the sub-resistor 40b are controlled ON / OFF by the triacs 38a and 38b (described later), and power is supplied independently from the AC nominal voltage 37 to each, causing them to generate heat. In the following, the paper-feeding area ARpa5 will also be called the first area AR1, and the area from the left end of the paper-feeding area ARpa4 to the left end of the paper-feeding area ARpa5, and the area from the right end of the paper-feeding area ARpa4 to the right end of the paper-feeding area ARpa5 will also be called the second area AR2.

[0035] In the color printer 1, the center of the transport width direction Dw in the transport path 5 of the recording medium P is set as the reference position for transporting the recording medium. Therefore, in the color printer 1, the centers of the transport width direction Dw of the main resistor 40a and the sub-resistor 40b coincide with the center of the transport width direction Dw of the transport path 5.

[0036] The pressure roller 32 is positioned opposite the underside of the fixing belt 30, forming a nip section between it and the fixing belt 30. The pressure roller 32 has a cylindrical structure made of metal, with its circumferential surface covered by a rubber elastic layer. For example, the rubber elastic layer is made of a material such as silicone rubber. In this embodiment, since the fixing belt 30 and the pressure roller 32 form a nip section, the main motor 76 (Figure 3) rotates the pressure roller 32, causing the fixing belt 30 to rotate in conjunction with the pressure roller 32.

[0037] The heat diffusion member 36 is positioned between the heater 31 and the fixing belt 30, and is arranged along the left-right direction (longitudinal direction) so as to be in contact with the heater 31 and the fixing belt 30. This heat diffusion member 36 uniformly diffuses heat in the longitudinal direction and the width direction (front-to-back direction in which the recording medium P is transported). The heat diffusion member 36 is made of a material such as aluminum, which has high thermal conductivity. Therefore, the color printer 1 accurately and responsively detects the temperature of the fixing belt 30, which is heated by the heater 31 or has heat removed by the recording medium P, etc., using 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.

[0038] The heat conduction member 46 is arranged along the left-right direction (longitudinal direction) so as to be in contact with the heater 31 on the side away from the pressure roller 32 relative to the heater 31. Similar to the heat diffusion member 36, this heat conduction member 46 uniformly diffuses temperature in the longitudinal direction and the width direction (the front-to-back direction in which the recording medium P is transported). Also, similar to the heat diffusion member 36, the heat conduction 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 conduction member 46 itself may not be provided.

[0039] A thermal conductive grease (not shown) mainly composed of zinc oxide and silicone oil is applied between the heater 31 and the heat diffusion member 36, and between the heater 31 and the heat conduction member 46, improving thermal conductivity between the members. In addition, a sliding grease (not shown) mainly composed of PFPE (perfluoropolyether) is applied between the heat diffusion member 36 and the fixing belt 30.

[0040] The temperature sensor 33 is a contact-type thermistor and is installed so as to contact the heat diffusion member 36 at approximately the center of the paper feed area ARpa6 located in the center of the transport width direction Dw of the fixing belt 30, and detects the nip center temperature, which is the temperature at the center of the transport width direction Dw 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 contact the heat diffusion member 36 to the right and left, respectively, of the paper feed area ARpa5 in the transport width direction Dw of the fixing belt 30, and detect the fixing belt temperature.

[0041] Thermostat 44 is installed inside the paper feeding area ARpa6 of the fixing belt 30 so as to be in contact with the heat diffusion member 36, similar to temperature sensors 33, 34, and 35. Thermostat 45 is installed so as to be in contact with the heat diffusion member 36 to the right of the paper feeding area ARpa5 in the transport width direction Dw of the fixing belt 30. Thermostats 44 and 45 detect the fixing belt temperature and function as final safety devices by shutting off the power supply to the resistor 40 when the fixing belt temperature reaches a predetermined upper limit. Temperature sensors 33, 34, and 35 and thermostats 44 and 45 are pressed against the heat diffusion member 36 with a predetermined force by springs (not shown), thereby reducing errors in detected temperature and improving responsiveness.

[0042] The AC nominal voltage 37 is, for example, an AC input voltage of AC100[V]. The triacs 38a and 38b (hereinafter collectively referred to as triac 38) are semiconductor switching elements used for power control of the heater 31, and their ON / OFF state is controlled by the fixing control unit 64. The details of the fixing control unit 64 will be described later, but it controls the heating of the resistor 40 inside the heater 31 based on the detection results of the temperature sensors 33, 34 and 35, thereby controlling the temperature of the fixing belt 30 to be optimal.

[0043] [1-3. Control Configuration for Color Printers] As shown in Figure 3, the color printer 1 is centrally controlled by the 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 these CPU 51, ROM 52, and RAM 53 are connected to each other by an internal bus. The CPU 51 controls the RAM 53 and the process control unit 60 according to the printing program stored in the ROM 52. The ROM 52 is a non-volatile memory that stores the printing program and can retain data even when the power to the color printer 1 is turned off. The RAM 53 is a volatile memory that stores print data input from the PC 54, and the data is erased when the power to the color printer 1 is turned off. The controller control unit 50 is connected to the PC 54, which is external to the color printer 1.

[0044] PC54 is, for example, a personal computer and has a PC display unit 55 and a PC input unit 56. This PC54 creates print data and transmits the print data to the color printer 1 via a communication interface such as USB (Universal Serial Bus) or LAN (Local Area Network). PC54 also receives instructions issued from the color printer 1 via the communication interface. The PC display unit 55 is composed of a liquid crystal display or the like and displays print images created by an application (not shown) and instructions issued from the color printer 1. The PC input unit 56 is composed of a keyboard and mouse or the like and creates print data images via an application (not shown) and inputs responses to instructions issued from the color printer 1.

[0045] The process control unit 60 includes a high-pressure control unit 61, an exposure control unit 62, a motor control unit 63, and a fixing control unit 64, and controls the printing process, including transport, charging, development, transfer, and fixing of the recording medium P.

[0046] The high-voltage control unit 61 includes 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 voltage applied to various rollers in order to transfer 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.

[0047] The motor control unit 63 controls the main motor 76 in the color printer 1 and rotates it to drive each roller in the image forming unit 14, the pressure roller 32, the paper feed roller 6, the first registration roller 7, and the second registration roller 8 in the fuser 20. In this embodiment, only the main motor 76 is provided, but motors to drive each roller in the image forming unit 14, the pressure roller 32, the paper feed roller 6, the first registration roller 7, and the second registration roller 8 may be provided individually.

[0048] The fixing control unit 64 controls the surface temperature of the fixing belt 30 (fixing belt temperature) to a predetermined appropriate temperature by supplying power from the AC nominal voltage 37 to the heater 31 by switching the triacs 38a and 38b of the low-voltage power supply 25 ON / OFF according to the detection results of each temperature sensor 33, 34, and 35, based on the set temperature of the fixing belt temperature and the ON Duty parameter. Here, ON Duty is the ratio of the voltage application time to each resistor 40 per predetermined time, and the larger the value, the longer the voltage application time to each resistor 40 per predetermined time.

[0049] [1-4. Regarding ON-Duty Correction for Comparative Examples] Figures 4 and 5 illustrate the ON Duty correction of a comparative example of the sub-resistor 40b. Below, the basic operation of the color printer 1 will be omitted, and the fixing operation will be described mainly. The color printer 1 detects the nip center temperature, which is the temperature of the fixing belt at the center of the transport width direction Dw, using a temperature sensor 33 located at the center of the transport width direction Dw of the heat diffusion member 36. The fixing control unit 64 controls the ON / OFF operation of the power supplied from the low-voltage power supply 25 to the main resistor 40a and sub-resistor 40b by controlling the triacs 38a and 38b, thereby controlling the nip center temperature to a predetermined set temperature. This predetermined set temperature is the set temperature determined by each recording medium P, and here it is, for example, 160 [°C].

[0050] The resistor 40 is divided into a main resistor 40a in the center of the transport width direction Dw and sub-resistors 40b at both ends of the transport width direction Dw, and is connected to the AC nominal voltage 37 via triacs 38a and 38b. Triac 38a is connected to the main resistor 40a, and triac 38b is connected to the sub-resistors 40b. Triacs 38a and 38b can be controlled independently of each other. The division position of the resistor 40 is set according to the size of the target recording medium P. In this embodiment, the width of the main resistor 40a in the transport width direction Dw is slightly wider than the paper feeding area ARpa5, and the main resistor 40a supports recording mediums P of A6 size recording medium Pa6 and A5 size recording medium Pa5. Furthermore, the combined width of the main resistor 40a and the sub-resistor 40b in the transport width direction Dw is slightly wider than that of the paper feed area ARpa4, and the combined width of the main resistor 40a and the sub-resistor 40b supports the recording medium P of the A4 size recording medium Pa4.

[0051] In the following, the region that is slightly narrower than the area occupied by the main resistor 40a in the transport width direction Dw and includes the paper feeding region ARpa6 will also be called the narrow region ARn. Furthermore, the region that includes the paper feeding region ARpa4, extending from slightly to the left of the center of the transport width direction Dw in the resistor 40b1 to slightly to the right of the center of the transport width direction Dw in the resistor 40b2, will also be called the wide region ARw. In addition, the region that includes the paper feeding region ARpa5, extending from approximately the center of the transport width direction Dw in the resistor 40b1 to approximately the center of the transport width direction Dw in the resistor 40b2, and is the range between the narrow region ARn and the wide region ARw, will also be called the intermediate region ARm.

[0052] The main resistor 40a is driven with an ON Duty such that the temperature detected by the temperature sensor 33 becomes the set temperature, while the sub-resistor 40b is driven with an ON Duty calculated by multiplying the ON Duty of the main resistor 40a by an ON Duty correction coefficient that varies depending on the size of the recording medium P. In other words, the ON Duty of the sub-resistor 40b is determined by the following formula.

[0053] ON Duty of sub-resistor 40b = Actual ON Duty of main resistor 40a × ON Duty correction coefficient according to recording medium size

[0054] As shown in Figure 5, for example, the ON Duty correction coefficient for an A6 size recording medium Pa6, where the recording medium size fits within the narrow width region ARn, is α1; for an A5 size recording medium Pa5, where the recording medium size fits within the intermediate width region ARm, is α2; and for an A4 size recording medium Pa4, where the recording medium size fits within the wide width region ARw, is α3. The relationship between these coefficients is 0 ≤ α1 ≤ α2 ≤ α3 ≤ 1.

[0055] By controlling the color printer 1 using the ON Duty correction coefficient in this manner, the temperature distribution of the fuser belt 30 in the longitudinal direction can be kept constant even when the size of the recording medium P is different, thereby ensuring stable print quality.

[0056] [1-5. Issues with ON-Duty Correction in Comparative Examples] When color printer 1 performs bordered printing, as shown in Figure 6(A), it forms a toner image TI1 on the recording medium P with margins at the edges in the transport direction (not shown) and the transport width direction Dw on the recording medium P. On the other hand, when color printer 1 performs borderless printing, as shown in Figure 6(B), it forms a toner image TI2 on the recording medium P without margins at the edges in the transport direction (not shown) and the transport width direction Dw on the recording medium P. Furthermore, borderless printing includes not only printing without margins at the edges in the transport direction and the transport width direction Dw, but also printing with a small margin that can be considered substantially borderless printing. For example, printing with a margin width of 1 [mm] or less is substantially borderless printing. However, borderless printing is defined as printing with a narrower margin width on the recording medium P compared to bordered printing, and includes cases where borderless printing is explicitly instructed. For example, if a printed document is ordered to have a border and the margin is 3 mm wide, but an ordered print is ordered to have a borderless margin and the margin is less than 3 mm wide, the latter can be considered borderless printing.

[0057] When the color printer 1 forms a toner image TI1 on an A5-sized recording medium Pa5, as shown in Figure 6(A), which corresponds to the transport width Dw range of the main resistor 40a, and performs bordered printing using the ON Duty correction described in the comparative example above, the ON Duty correction coefficient α2 is set to 0, as shown in Figure 5, and the printer controls the printer so that only the main resistor 40a generates heat, as shown in Figure 6(D). As a result, the color printer 1 maintains the fixing belt temperature in the good fixing temperature range TR from one end to the other in the transport width Dw of the toner image TI1, as shown by the fixing temperature distribution line L1 in Figure 6(C), thereby ensuring a good fixing temperature. Thus, the ON Duty correction coefficient α2 is a correction coefficient necessary when fixing the toner image without generating unnecessary heat in the case of bordered printing.

[0058] Furthermore, when the color printer 1 is controlled in such a way that only the main resistor 40a generates heat in relation to the A5 size recording medium Pa5, as shown in Figure 6(C), the fixing good region ARf1, where the fixing belt temperature is maintained within the fixing good temperature range TR, is slightly wider than the range extending from one end to the other in the transport width direction Dw of the toner image TI1 in bordered printing.

[0059] On the other hand, if the color printer 1 forms a toner image TI2 on an A5-sized recording medium Pa5 as shown in Figure 6(B) and performs borderless printing using the ON Duty correction of the comparative example described above, and controls the printer to generate heat only on the main resistor 40a as shown in Figure 6(D), the good fixing region ARf1 is narrower than the range of the transport width direction Dw in the toner image TI2 (Figure 6(B)). As a result, the fixing belt temperature near the end of the transport width direction Dw in the toner image TI2 falls below the good fixing temperature range TR, making it impossible to secure a temperature suitable for fixing. Therefore, if the color printer 1 controls the energization of the resistor 40 based only on the size of the recording medium P, that is, the media width which is the size of the transport width direction Dw of the recording medium P, then image quality degradation such as gloss unevenness and cold offset will occur, especially near the end of the transport width direction Dw of the recording medium P. Thus, when borderless printing was controlled with the same amount of heat generation as bordered printing using the ON Duty correction of the comparative example, the fixing belt temperature near the edges of the transport width Dw in the toner image TI2 was insufficient, resulting in insufficient heat and sometimes causing gloss unevenness or cold offset.

[0060] [1-6. ON Duty Correction in the First Embodiment] In contrast, the color printer 1 according to this embodiment switches the power supply control of the resistor 40 depending on whether the printing method specified by the print data is bordered printing or borderless printing, even when printing on a recording medium P of the same medium width. Specifically, if the color printer 1 determines, for example, that borderless printing is performed on an A5 size recording medium Pa5 shown in Figure 6(B), it sets the ON Duty correction coefficient α2 to greater than 0 and controls the sub-resistor 40b to generate heat in addition to the main resistor 40a, as shown in Figure 6(E). As a result, the color printer 1 suppresses the decrease in the fuser belt temperature near the end of the transport width direction Dw in the toner image TI2, as shown by the fuser temperature distribution line L2 in Figure 6(C), and maintains the fuser belt temperature in the good fuser temperature range TR from one end to the other in the transport width direction Dw, thereby ensuring a good fuser temperature. For this reason, the color printer 1 can prevent the occurrence of image quality degradation such as gloss unevenness and cold offset near the end of the transport width direction Dw of the recording medium P in borderless printing, and maintain print quality.

[0061] Thus, when the color printer 1 is controlled to generate heat in addition to the main resistor 40a in relation to the A5 size recording medium Pa5, as shown in Figure 6(C), the fixing good region ARf2, where the fixing belt temperature is maintained within the fixing good temperature range TR, is slightly wider than the range extending from one end to the other in the transport width direction Dw of the borderless toner image TI2.

[0062] Figure 7 shows the time chart for ON / OFF control of the main resistor 40a and sub-resistor 40b according to the first embodiment. Note that Figure 7 shows the case where α3 = β3. The ON duty cycle of the sub-resistor 40b is determined by the following formula.

[0063] ON Duty of sub-resistor 40b = Actual ON Duty of main resistor 40a × ON Duty correction coefficient corresponding to the combination of recording medium size and bordered or borderless printing.

[0064] As shown in Figure 8, for example, in the case of an A6 size recording medium Pa6 where the recording medium size fits within the narrow width region ARn, the ON Duty correction coefficient for bordered printing is α1 and the ON Duty correction coefficient for borderless printing is β1. In the case of an A5 size recording medium Pa5 where the recording medium size fits within the intermediate width region ARm, the ON Duty correction coefficient for bordered printing is α2 and the ON Duty correction coefficient for borderless printing is β2. In the case of an A4 size recording medium Pa4 where the recording medium size fits within the wide width region ARw, the ON Duty correction coefficient for bordered printing is α3 and the ON Duty correction coefficient for borderless printing is β3. The relative magnitudes of these coefficients are 0 ≤ α1 ≤ β1 < 1, 0 < α2 < β2 < 1, and 0 < α3 ≤ β3 ≤ 1.

[0065] Furthermore, when comparing bordered prints with borderless prints, the ON Duty correction coefficient increases as the recording medium size increases. For this reason, in the case of bordered prints, α1 < α2 < α3, and in the case of borderless prints, β1 < β2 < β3.

[0066] Here, for a sufficiently narrow recording medium size, the ON Duty correction coefficient may be 0=α1=β1, in which case the ON Duty correction coefficients for bordered and borderless printing may be the same. Also, for a sufficiently wide recording medium size, the ON Duty correction coefficient may be α3=β3=1, in which case the ON Duty correction coefficients for bordered and borderless printing may be the same. However, it is preferable that α1<β1 and α3<β3.

[0067] On the other hand, for recording media with medium widths, α2 and β2 can be set to different values, so the ON Duty correction coefficient for borderless printing should be significantly larger than that for bordered printing.

[0068] [1-7. Effects, etc.] In the above configuration, the color printer 1 is configured such that the main resistor 40a includes the first region AR1, which is the paper feeding region ARpa5, and the sub-resistors 40b are configured to include the second region AR2, which is the region from the left end of the paper feeding region ARpa4 to the left end of the paper feeding region ARpa5, and the region from the right end of the paper feeding region ARpa4 to the right end of the paper feeding region ARpa5, on both sides of the main resistor 40a in the transport width direction Dw. Here, when considering the left end of the main resistor 40a, the left end, which is the end on one side of the transport width direction Dw, is located to the right, which is the opposite direction to the left end of the A4 size recording medium Pa4, which is the end on one side of the transport width direction Dw. On the other hand, when considering the right end of the main resistor 40a, the right end, which is the end on one side of the transport width direction Dw, is located to the left, which is the opposite direction to the right end of the A4 size recording medium Pa4, which is the end on one side of the transport width direction Dw. Furthermore, when considering the left end of the sub-resistor 40b (i.e., the left end of resistor 40b1), the left end, which is the end on one side of the transport width direction Dw, is positioned to the left, which is one direction away from the left end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. On the other hand, when considering the right end of the sub-resistor 40b (i.e., the right end of resistor 40b2), the right end, which is the end on one side of the transport width direction Dw, is positioned to the right, which is one direction away from the right end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. Also, when considering the main resistor 40a alone, the color printer 1 heats it so that the fixing belt temperature in the first region AR1 is higher than that in the second region AR2, and when considering the sub-resistor 40b alone, the fixing belt temperature in the second region AR2 is higher than that in the first region AR1. Furthermore, the color printer 1 is configured such that the main resistor 40a is driven with an ON Duty such that the temperature detected by the temperature sensor 33 becomes the set temperature, and the sub-resistor 40b is driven with an ON Duty calculated by multiplying the ON Duty of the main resistor 40a by an ON Duty correction coefficient that varies depending on the size of the recording medium P and the combination of bordered or borderless printing.

[0069] As described above, when color printer 1 used the ON Duty correction of the comparative example to control borderless printing with the same amount of heat generation as bordered printing, the fixing belt temperature near the edges of the toner image TI2 in the transport width direction Dw was insufficient, resulting in insufficient heat and sometimes causing fixing defects such as gloss unevenness and cold offset. In particular, since heat is lost to the recording medium P and the toner image, fixing defects tend to occur on the side opposite to the transport direction in the case of the first recording medium P, and even in the case of printing multiple sheets, heat is lost to the recording medium P and the toner image, sometimes causing fixing defects at some point in the transport direction. Thus, if color printer 1 controls the energization of resistor 40 based only on the size of the recording medium P, that is, the media width which is the size of the transport width direction Dw of the recording medium P, image quality degradation such as gloss unevenness and cold offset occurs, especially near the edges of the transport width direction Dw of the recording medium P.

[0070] In contrast, the color printer 1, even when printing on a recording medium P of the same medium width, increases the ON Duty correction coefficient when performing borderless printing on, for example, an A5 size recording medium Pa5, compared to when performing bordered printing. This increases the power (i.e., heat) of the sub-resistor 40b, causing the regions at both ends of the fixing belt 30, which correspond to the toner image positioned near both ends of the transport width direction Dw on the recording medium P, to be heated with a greater amount of heat.

[0071] Therefore, the color printer 1 suppresses the decrease in fuser belt temperature near the ends of the toner image transport width Dw, ​​and maintains the fuser belt temperature in the good fuser temperature range TR from one end to the other of the transport width Dw, ​​thereby ensuring a good fuser temperature. As a result, the color printer 1 can prevent the occurrence of image quality degradation such as gloss unevenness and cold offset near the ends of the transport width Dw of the recording medium P in borderless printing, and can maintain print quality.

[0072] On the other hand, when performing bordered printing, the color printer 1 reduces the ON Duty correction coefficient compared to when performing borderless printing, thereby reducing the power consumption (i.e., heat generation) of the sub-resistor 40b, and reducing or eliminating heating of the areas at both ends of the fuser belt 30. As a result, when performing bordered printing, the color printer 1 prevents the sub-resistor 40b from generating excessive heat, thereby suppressing a decrease in throughput and an increase in power consumption.

[0073] According to the above configuration, the color printer 1 includes an image forming unit 14 for forming an image on a recording medium P, and a fuser 20. The fuser 20 is capable of fixing an image to an A5-size recording medium Pa5 as a first medium having a first width paper feeding area ARpa5, and an A4-size recording medium Pa4 as a second medium having a second width paper feeding area ARpa4 with a width Dw in the transport width direction wider than the paper feeding area ARpa5. The fuser 20 includes a fuser belt 30, and the fuser belt 30 is provided so as to be heatable, with one end on the transport width direction Dw being A4 size. The recording medium Pa4 has a main resistor 40a positioned on the side of the end of the transport width direction Dw that is on the other side, and a sub-resistor 40b that is provided to heat the fixing belt 30 and whose end on the side of the transport width direction Dw is positioned on the side of the end of the A4 size recording medium Pa4 that is on the other side. The sub-resistor 40b heats the fixing belt 30 with a greater amount of heat when borderless printing is performed on the A5 size recording medium Pa5 than when bordered printing is performed on the A5 size recording medium Pa5.

[0074] As a result, when performing borderless printing, the color printer 1 suppresses the decrease in fuser belt temperature near the edges of the toner image in the transport width direction Dw, and maintains the fuser belt temperature in the good fuser temperature range TR from one end to the other in the transport width direction Dw, thereby ensuring a good fuser temperature. Therefore, the color printer 1 can prevent the deterioration of image quality near the edges of the transport width direction Dw of the recording medium P during borderless printing.

[0075] [2. Second Embodiment] [2-1. Configuration of the image forming apparatus] As shown in Figure 1 and Figure 11, which uses the same reference numerals as Figure 3, the color printer 101 according to the second embodiment differs from the color printer 1 according to the first embodiment in that it has a fuser 120 instead of a fuser 20 and a fuser control unit 164 of the process control unit 160 instead of a fuser control unit 64 of the process control unit 60, but is otherwise configured similarly.

[0076] [2-2. Fuser Unit Configuration] As shown in Figure 9, which uses the same reference numerals as Figure 2 for corresponding components, the fuser 120 according to the second embodiment differs from the fuser 20 according to the first embodiment in that it is provided with a heat roller 80 instead of a fuser belt 30, a halogen heater 82 (narrow heater 82n and wide heater 82w) instead of a heater 31, and a thermopile 90 instead of temperature sensors 33, 34, and 35 and thermostats 44 and 45, and the heat diffusion member 36 and heat conduction member 46 are omitted, but otherwise it is configured similarly.

[0077] The heat roller 80 has a hollow cylindrical shape, with a base material, an elastic layer, and a surface layer layered from the inner circumference to the outer circumference. For example, the base material is a cylindrical roller made of aluminum or stainless steel, the elastic layer is silicone rubber, and the surface layer is a fluororesin coating such as PTFE (polytetrafluoroethylene) or PFA, or a tube made from these materials.

[0078] The narrow heater 82n and the wide heater 82w (hereinafter collectively referred to as halogen heater 82) are so-called halogen heaters, positioned on the inner circumference side of the heat roller 80, and are heating elements that extend in the longitudinal direction.

[0079] As shown in Figure 10(A), the narrow heater 82n has halogen gas sealed inside a valve 83, which is a glass tube extending in the transport width direction Dw. Inside the valve 83, a filament 84n and an internal valve lead wire 85n extend along the transport width direction Dw. The internal valve lead wire 85n extends from both ends of the filament 84n in the transport width direction Dw toward the outside in the transport width direction Dw and is connected to a lead wire 86n provided outside the valve 83. The lead wire 86n is connected to the AC nominal voltage 37 and the triac 38a. The narrow heater 82n energizes the internal valve lead wire 85n and the filament 84n from the lead wire 86n without leaking the halogen gas sealed inside the valve 83. The filament 84n is arranged across the area including the paper feeding area ARpa6 and the paper feeding area ARpa5, and supports the A6 size recording medium Pa6 and the A5 size recording medium Pa5.

[0080] On the other hand, as shown in Figure 10(B), the wide heater 82w has halogen gas sealed inside a valve 83, which is a glass tube extending in the transport width direction Dw. Inside the valve 83, a filament 84w extends along the transport width direction Dw from one end to the other inside the valve 83. Therefore, the filament 84w is the same length as the valve 83. The filament 84w is connected to a lead wire 86w provided outside the valve 83. The lead wire 86w is connected to an AC nominal voltage 37 and a triac 38b. The wide heater 82w energizes the filament 84w from the lead wire 86w without leaking the halogen gas sealed inside the valve 83. The filament 84w is arranged over an area including the paper transport area ARpa4 and supports the A4 size recording medium Pa4. The narrow heater 82n and the wide heater 82w are controlled ON / OFF by triacs 38a and 38b, respectively, and power is supplied independently from the AC nominal voltage 37 to generate heat.

[0081] Here, in the color printer 101, similar to the color printer 1, the center of the transport width direction Dw in the transport path 5 of the recording medium P is set as the recording medium transport reference position. For this reason, in the color printer 101, the center of the transport width direction Dw in the narrow heater 82n and the wide heater 82w coincides with the center of the transport width direction Dw in the transport path 5.

[0082] The pressure roller 32 is positioned opposite the lower side of the heat roller 80, forming a nip portion between it and the heat roller 80.

[0083] The thermopile 90 is a non-contact temperature sensor and is installed outside the heat roller 80, facing the surface (outer surface) of the heat roller 80 with a gap between them, near the center of the paper feeding area ARpa6 located in the center of the transport width direction Dw of the heat roller 80. The thermopile 90 detects the nip center temperature, which is the surface temperature of the central part of the heat roller 80 in the transport width direction Dw, by receiving infrared rays emitted from the surface of the heat roller 80 and converting them into temperature.

[0084] The fixing control unit 164 (Figure 11) controls the surface temperature of the heat roller 80 to a predetermined appropriate temperature by switching the triacs 38a and 38b of the low-voltage power supply 25 ON / OFF according to the detection result of the thermopile 90, based on the set temperature of the nip center and the ON Duty parameter.

[0085] [2-3. ON Duty Correction in the Second Embodiment] Figures 12 and 13 illustrate the ON Duty correction according to the second embodiment of the narrow heater 82n and wide heater 82w. Below, the explanation of the basic operation of the color printer 101 will be omitted, and the fixing operation will be explained in detail. The color printer 101 detects the nip center temperature, which is the temperature of the center of the heat roller 80 in the transport width direction Dw, using a thermopile 90 positioned in the center of the heat roller 80 in the transport width direction Dw. The fixing control unit 164 controls the ON / OFF operation of the power supplied from the low-voltage power supply 25 to the narrow heater 82n and wide heater 82w by controlling the triacs 38a and 38b, thereby controlling the nip center temperature to a predetermined set temperature. This predetermined set temperature is a set temperature determined by each recording medium P, and here it is, for example, 160°C.

[0086] The halogen heater 82 has a narrow heater 82n with a filament 84n having a short width in the transport width direction Dw and a wide heater 82w with a filament 84w having a wide width in the transport width direction Dw, and is connected to the AC nominal voltage 37 via triacs 38a and 38b. Triac 38a is connected to the narrow heater 82n, and triac 38b is connected to the wide heater 82w. Triacs 38a and 38b can be controlled independently of each other. The width in the transport width direction Dw of the filament 84n of the narrow heater 82n is set according to the size of the target recording medium P. In this embodiment, the width of the filament 84n of the narrow heater 82n in the transport width direction Dw is slightly wider than the paper feeding area ARpa5, and the narrow heater 82n supports A6 size recording medium Pa6 and A5 size recording medium Pa5. Furthermore, the width of the filament 84w of the wide heater 82w is slightly wider than that of the paper feeding area ARpa4 in the transport width direction Dw, and the wide heater 82w supports the A4 size recording medium Pa4.

[0087] In the following, the region that is slightly narrower than the area occupied by the filament 84n of the narrow heater 82n in the transport width direction Dw, and which includes the paper feeding region ARpa6, will also be called the narrow region ARn. Furthermore, the region that includes the paper feeding region ARpa4, extending from slightly to the right of the left end to slightly to the left of the right end of the filament 84w of the wide heater 82w, will also be called the wide region ARw. In addition, the region that includes the paper feeding region ARpa5 and is located between the narrow region ARn and the wide region ARw will also be called the intermediate width region ARm.

[0088] Figure 12 shows the ON / OFF control time chart for the narrow heater 82n and wide heater 82w according to the second embodiment. Note that Figure 12 shows the case where γ5=γ6 and Δ5=Δ6. The narrow heater 82n and wide heater 82w are driven with an ON Duty calculated by multiplying the calculated ON Duty by an ON Duty correction coefficient that differs depending on the size of the recording medium P and the combination of bordered or borderless printing, so that the temperature detected by the thermopile 90 becomes the set temperature. In other words, the ON Duty of the narrow heater 82n and wide heater 82w is determined by the following formula.

[0089] The ON Duty of the halogen heater 82 = calculated ON Duty × ON Duty correction coefficient corresponding to the combination of recording medium size and bordered or borderless printing.

[0090] As shown in Figure 13, for example, in the case of an A6 size recording medium Pa6 where the recording medium size fits within the narrow region ARn, the ON Duty correction coefficient for bordered printing is γ1 for the narrow heater 82n and Δ1 for the wide heater 82w, and the ON Duty correction coefficient for borderless printing is γ2 for the narrow heater 82n and Δ2 for the wide heater 82w. In the case of an A5 size recording medium Pa5 where the recording medium size fits within the intermediate region ARm, the ON Duty correction coefficient for bordered printing is γ3 for the narrow heater 82n and Δ3 for the wide heater 82w, and the ON Duty correction coefficient for borderless printing is γ4 for the narrow heater 82n and Δ4 for the wide heater 82w. In the case of an A4 size recording medium Pa4 where the recording medium size fits within the wide region ARw, the ON Duty correction coefficient for bordered printing is γ5 for the narrow heater 82n and Δ5 for the wide heater 82w, and the ON Duty correction coefficient for borderless printing is γ4 for the narrow heater 82n and Δ4 for the wide heater 82w. The duty cycle correction coefficient is γ6 for the narrow heater 82n and Δ6 for the wide heater 82w. Furthermore, when comparing the same recording medium size, the ON Duty correction coefficient for the narrow heater 82n is larger for bordered printing than for borderless printing, and the ON Duty correction coefficient for the wide heater 82w is larger for borderless printing than for bordered printing. Therefore, for example, in the case of the A6 size recording medium Pa6, 0≦γ2≦γ1≦1 and 0≦Δ1≦Δ2≦1. The same applies to other recording medium sizes.

[0091] Here, in the case of a sufficiently narrow recording medium size, for example, in the case of an A6 size recording medium Pa6, the ON Duty correction coefficients may be 0=γ1=γ2 and 0=Δ1=Δ2, in which case the ON Duty correction coefficients for bordered printing and borderless printing may be the same. Also, in the case of a sufficiently wide recording medium size, for example, in the case of an A4 size recording medium Pa4, the ON Duty correction coefficients may be γ5=γ6=1 and Δ5=Δ6=1, in which case the ON Duty correction coefficients for bordered printing and borderless printing may be the same. However, it is preferable that γ2<γ1, Δ1<Δ2, γ6<γ5, and Δ5<Δ6. The same applies to other recording medium sizes.

[0092] On the other hand, for recording media with an intermediate media width, γ3 and γ4 can be set to different values, and Δ3 and Δ4 can be set to different values. Therefore, for a wide heater 82w, the ON Duty correction coefficient for borderless printing should be significantly larger than the ON Duty correction coefficient for bordered printing.

[0093] [2-4. Effects, etc.] In the above configuration, the color printer 101 is configured such that the filament 84n of the narrow heater 82n is positioned to include the first region AR1, and the filament 84w of the wide heater 82w is positioned to include the first region AR1 and the second region AR2. Here, when considering the left end of the filament 84n of the narrow heater 82n, the left end, which is the end on one side of the transport width direction Dw, is positioned to the right, which is the opposite direction to the left end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. On the other hand, when considering the right end of the filament 84n of the narrow heater 82n, the right end, which is the end on one side of the transport width direction Dw, is positioned to the left, which is the opposite direction to the right end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. Furthermore, when considering the left end of the wide heater 82w, the left end, which is the end on one side of the transport width direction Dw, is positioned to the left, which is one direction away from the left end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. On the other hand, when considering the right end of the wide heater 82w, the right end, which is the end on one side of the transport width direction Dw, is positioned to the right, which is one direction away from the right end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. The color printer 101 drives the narrow heater 82n and the wide heater 82w with an ON Duty calculated by multiplying the ON Duty by an ON Duty correction coefficient that differs depending on the size of the recording medium P and the combination of bordered or borderless printing, based on the calculated ON Duty, so that the temperature detected by the thermopile 90 becomes the set temperature.

[0094] Furthermore, even when printing on a recording medium P of the same medium width, the color printer 101 increases the ON Duty correction coefficient of the wide heater 82w compared to when performing borderless printing on an A5 size recording medium Pa5. This increases the power consumption (i.e., heat generation) of the filament 84w of the wide heater 82w, thereby heating the areas at both ends of the heat roller 80, which correspond to the toner image positioned near both ends in the transport width direction Dw of the recording medium P, with a greater amount of heat.

[0095] Therefore, the color printer 101 suppresses the temperature drop of the heat roller 80 near the edges of the toner image transport width Dw, ​​and maintains the temperature of the heat roller 80 within a temperature range suitable for fixing from one end to the other of the transport width Dw, ​​thereby ensuring a temperature suitable for fixing. As a result, the color printer 101 can prevent the occurrence of image quality degradation such as gloss unevenness and cold offset near the edges of the transport width Dw of the recording medium P in borderless printing, and maintain print quality.

[0096] On the other hand, when performing bordered printing, the color printer 101 reduces the ON Duty correction coefficient of the wide heater 82w compared to when performing borderless printing. This reduces the power consumption (i.e., heat generation) of the filament 84w of the wide heater 82w, thereby reducing the amount of heating in the areas at both ends of the heat roller 80, or preventing heating altogether. As a result, when performing bordered printing, the color printer 101 prevents the wide heater 82w from generating more heat than necessary, thus preventing a decrease in throughput and an increase in power consumption.

[0097] According to the above configuration, the color printer 101 includes an image forming unit 14 for forming an image on a recording medium P, and a fuser 120. The fuser 120 is capable of fixing an image to an A5-size recording medium Pa5, which is a first medium having a paper feeding area ARpa5 with a first width, and an A4-size recording medium Pa4, which is a second medium having a paper feeding area ARpa4 with a second width that is wider in the transport width direction Dw than the paper feeding area ARpa5. The fuser 120 includes a heat roller 80, which is provided so as to be able to heat the heat roller 80, and the end on one side of the transport width direction Dw is on the transport width direction of the A4-size recording medium Pa4. The device has a narrow heater 82n with a filament 84n positioned on the side of the end of the transport width direction Dw that is on the other side, and a wide heater 82w with a filament 84w that is provided to heat the heat roller 80 and whose end on the side of the transport width direction Dw is positioned on the side of the end of the transport width direction Dw that is on the other side. The wide heater 82w's filament 84w heats the heat roller 80 with a greater amount of heat when borderless printing is performed on the A5 size recording medium Pa5 than when bordered printing is performed on the A5 size recording medium Pa5.

[0098] In other respects as well, the color printer 101 according to the second embodiment can achieve the same effects and advantages as the color printer 1 according to the first embodiment.

[0099] [3. Other Embodiments] In the first embodiment described above, the color printer 1 changes the power supplied from the AC nominal voltage 37 to the heater 31 by changing the ON Duty, which controls the ON / OFF status of the triacs 38a and 38b. The present invention is not limited to this, and the color printer 1 may also change the power supplied from the AC nominal voltage 37 to the heater 31 by changing the voltage applied to the heater 31 from the AC nominal voltage 37, as shown in Figure 14, where the same reference numerals are used for parts corresponding to Figure 7. Alternatively, the color printer 1 may change the power supplied from the AC nominal voltage 37 to the heater 31 by changing the current flowing from the AC nominal voltage 37 to the heater 31. Furthermore, the color printer 1 may change at least two or more of the ON Duty, voltage, and current in combination. The same applies to the second embodiment.

[0100] Furthermore, in the first embodiment described above, the color printer 1 was configured to generate more heat from the sub-resistor 40b in the case of borderless printing than in the case of bordered printing. The present invention is not limited to this, and the color printer 1 may be configured to have openable and closable heat dissipation slits provided in the housing of the fuser 20 at positions corresponding to both ends of the heater 31, so that the amount of heat generated by the sub-resistor 40b is the same for borderless printing and bordered printing, and in the case of bordered printing, the amount of heat dissipated from the sub-resistor 40b to the outside of the housing of the fuser 20 may be increased by opening the slits, and in the case of borderless printing, the amount of heat dissipated from the sub-resistor 40b to the outside of the housing of the fuser 20 may be decreased by closing the slits. Alternatively, the color printer 1 may be configured to have a fan that blows air for heat dissipation toward the heater 31, so that the amount of heat generated by the sub-resistor 40b is the same for borderless printing and bordered printing, and in the case of bordered printing, the amount of heat dissipated from the sub-resistor 40b may be increased by rotating the fan, and in the case of borderless printing, the amount of heat dissipated from the sub-resistor 40b may be decreased by not rotating the fan. Furthermore, the color printer 1 may be provided with a heat-blocking plate that can be inserted between the heater 31 and the fuser belt 30, and the amount of heat generated by the sub-resistor 40b may be the same for borderless printing and bordered printing. In the case of bordered printing, the heat shield can be inserted between the heater 31 and the fuser belt 30 to suppress the heat transferred from the sub-resistor 40b to the fuser belt 30, while in the case of borderless printing, the heat shield cannot be inserted between the heater 31 and the fuser belt 30 to prevent the heat transferred from the sub-resistor 40b to the fuser belt 30 from being suppressed. The same applies to the second embodiment.

[0101] Furthermore, in the first embodiment described above, the color printer 1 may increase the amount of heat transferred from the heater 31 to the recording medium P by reducing the transport speed of the recording medium P in the case of borderless printing compared to the case of bordered printing. In that case, the color printer 1 should raise the temperature of the fixing belt at both ends of the transport width Dw to such an extent that the temperature of the fixing belt at the center of the transport width Dw does not exceed the good fixing temperature range TR. The same applies to the second embodiment.

[0102] Furthermore, in the first embodiment described above, the color printer 1 may generate more heat from the main resistor 40a in the case of borderless printing than in the case of bordered printing, because the toner image formation area is larger in borderless printing than in the case of bordered printing. The same applies to the second embodiment.

[0103] Furthermore, in the first embodiment described above, the color printer 1 is configured such that the center of the transport width direction Dw in the transport path 5 of the recording medium P is set as the recording medium transport reference position, and the centers of the transport width direction Dw of the main resistor 40a and the sub-resistor 40b are aligned with the center of the transport width direction Dw of the transport path 5. The present invention is not limited to this, but if, for example, the left end of the transport width direction Dw in the transport path 5 of the recording medium P is set as the recording medium transport reference position, the color printer 1 can align the left end of the transport width direction Dw of the main resistor 40a with the left end of the transport width direction Dw of the transport path 5, and place the sub-resistor 40b to the right of the main resistor 40a. In that case, when considering the right end of the main resistor 40a, the right end, which is the end on one side of the transport width direction Dw, is positioned to the left of the right end, which is the end on the other side of the transport width direction Dw of the A4 size recording medium Pa4. Furthermore, when considering the right end of the sub-resistor 40b, the right end, which is the end on one side of the transport width direction Dw, is positioned to the right of the right end, which is the end on one side of the transport width direction Dw of the A4 size recording medium Pa4. In the second embodiment, the left ends of the narrow heater 82n and the wide heater 82w should be aligned with the left end of the transport width direction Dw of the transport path 5.

[0104] Furthermore, in the first embodiment described above, the color printer 1 was described in the case where the length of the transport width direction Dw in all resistors 40b1, 40a1, 40a2, 40a3 and 40b2 (Figure 2) is the same. The present invention is not limited to this, and the color printer 1 may have a different length of the transport width direction Dw in at least one of the resistors 40b1, 40a1, 40a2, 40a3 and 40b2 from the other resistors 40.

[0105] Furthermore, in the first embodiment described above, the color printer 1 controls the power supplied from the nominal AC voltage 37 to the main resistors 40a (resistors 40a1, 40a2, and 40a3) and sub-resistors 40b (resistors 40b1 and 40b2) by controlling the ON / OFF state of two triacs 38a and 38b. The present invention is not limited to this, and the color printer 1 may also be provided with five triacs, and the heat generation of each of the resistors 40b1, 40a1, 40a2, 40a3, and 40b2 may be controlled independently.

[0106] Furthermore, in the first embodiment described above, the color printer 1 was described in which the temperature sensors 34 and 35 are installed at both ends of the conveying width direction Dw on the fixing belt 30. The present invention is not limited to this, and since the resistors 40b1 and 40b2 are heated simultaneously, the color printer 1 may also install the temperature sensors 34 and 35 only at one end of the conveying width direction Dw on the fixing belt 30.

[0107] Furthermore, in the first embodiment described above, the case in which the color printer 1 has the thermostat 45 installed to the right of the paper feeding area ARpa5 on the fixing belt 30 in the transport width direction Dw was described. The present invention is not limited to this, and the color printer 1 may also have the thermostat 45 installed to the left of the paper feeding area ARpa5 on the fixing belt 30 in the transport width direction Dw.

[0108] Furthermore, in the first embodiment described above, the case in which the color printer 1 has temperature sensors 33, 34, and 35 and thermostats 44 and 45 installed in the heat diffusion member 36 was described. The present invention is not limited to this, and the color printer 1 may also have at least one of the temperature sensors 33, 34, and 35 and thermostats 44 and 45 installed in the heater 31 or the heat conduction member 46.

[0109] Furthermore, in the first embodiment described above, the color printer 1 is configured with contact-type temperature sensors 33, 34, and 35 and thermostats 44 and 45, and is installed so as to be in contact with the heat diffusion member 36. The present invention is not limited to this, and the color printer 1 may also be configured with at least one of the temperature sensors 33, 34, and 35 and thermostats 44 and 45 as a non-contact type temperature sensor to detect the fuser belt temperature.

[0110] Furthermore, in the first embodiment described above, the present invention was applied to a color printer 1 equipped with a heater 31 having resistors 40 divided into five parts along the transport width direction Dw. The present invention is not limited to this, and may also be applied to a color printer equipped with a heater 31 having resistors 40 divided into various numbers, such as four or fewer or six or more, along the transport width direction Dw.

[0111] Furthermore, in the second embodiment described above, the color printer 101 may be provided with a segmented halogen heater instead of the wide heater 82w, such that, like the sub-resistor 40b of the heater 31 in the first embodiment, the filament 84w is not formed in the same transport width direction Dw as the narrow heater 82n, but rather the filament 84w is discretely formed on both sides of the transport width direction Dw compared to the narrow heater 82n.

[0112] Furthermore, in the second embodiment described above, the color printer 101 may be equipped with temperature sensors 33, 34, and 35 and thermostats 44, and 45 instead of the thermopile 90, as in the first embodiment.

[0113] Furthermore, the above-described embodiment described the case in which the present invention is applied to a color printer 1 or 101 that uses a so-called direct transfer method, in which toner images are directly transferred from the photosensitive drum 17 to the recording medium P. The present invention is not limited to this, and may also be applied to an image forming apparatus that uses a so-called intermediate transfer method (or secondary transfer method), in which toner images of each color are sequentially transferred from the photosensitive drum 17 to an intermediate transfer belt used as a medium, and the toner images are transferred from this intermediate transfer belt to the recording medium P.

[0114] Furthermore, the embodiments described above describe the application of the present invention to a color printer 1 or 101 that uses a developer used in a one-component development method. The present invention is not limited to this, and may also be applied to an image forming apparatus that uses a developer in a two-component development method, which is a method of imparting an appropriate amount of charge to the toner by utilizing the friction between the carrier and the toner after mixing the carrier and the toner.

[0115] Furthermore, the above-described embodiment describes the application of the present invention to a tandem-type color printer 1 or 101 having image forming units 14 of each color arranged in series along the front-to-back direction. The present invention is not limited to this, and may be applied to various other types of image forming apparatus, such as a 4-cycle system.

[0116] Furthermore, the above-described embodiment describes the application of the present invention to a color printer 1 having four image forming units 14 corresponding to yellow, magenta, cyan, and black, which form a color image using four toners. The present invention is not limited to this, and may also be applied to an image forming apparatus having three or fewer or five or more image forming units 14 depending on the number of toner colors used in the image forming apparatus, or to an image forming apparatus having one image forming unit that performs monochrome printing.

[0117] Furthermore, the embodiments described above describe the application of the present invention to a single-function printer, such as a color printer 1 or 101. The present invention is not limited to this, and may also be applied to image forming apparatuses with various other functions, such as MFPs (Multi-Function Peripherals) that have the functions of a copier or a facsimile machine.

[0118] Furthermore, the present invention is not limited to the embodiments described above and other embodiments. That is, the scope of the present invention also extends to embodiments obtained by arbitrarily combining some or all of the embodiments described above and other embodiments. In addition, the scope of the present invention also extends to embodiments obtained by extracting a part of the configuration described in any embodiment from the embodiments described above and other embodiments and substituting or adapting it for a part of the configuration of any embodiment from the embodiments described above and other embodiments, or by adding a part of the extracted configuration to any embodiment.

[0119] Furthermore, in the first embodiment described above, a color printer 1 as an image forming device is configured by an image forming unit 14 as an image forming unit and a fuser 20 as a fixing device, and the fixing device has a fixing belt 30 as a fixing member, a main resistor 40a as a first heater and a sub-resistor 40b as a second heater. In the second embodiment described above, a color printer 101 as an image forming device is configured by an image forming unit 14 as an image forming unit and a fuser 120 as a fixing device, and the fixing device has a heat roller 80 as a fixing member, a filament 84n of a narrow heater 82n as a first heater and a filament 84w of a wide heater 82w as a second heater. The present invention is not limited to these, and an image forming device may be configured by an image forming unit and a fixing device having various other configurations, and the fixing device may have a fixing member having various other configurations, a first heater and a second heater. [Industrial applicability]

[0120] This invention can be used, for example, in an electrophotographic printer. [Explanation of Symbols]

[0121] 1, 101...Color printer, 2...Main unit, 3...Top cover, 4...Recording media storage unit, 5...Transport path, 6...Paper feed roller, 7...First registration roller, 8...Second registration roller, 9...Image forming unit, 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, 20, 120...Fuser, 21...EXIT sensor, 2 2...Discharge stacker section, 23...Concentration sensor, 24...High voltage power supply, 25...Low voltage power supply, 26...Display unit, 30...Fixing belt, 31...Heater, 32...Pressure roller, 33, 34, 35...Temperature sensor, 36...Heat diffusion member, 37...AC nominal voltage, 38...Triac, 40...Resistor, 40a...Main resistor, 40b...Sub-resistor, ARpa6, ARpa5, ARpa4...Paper feeding area, ARnp...Non-paper feeding area, ARN...Narrow area, ARw...Wide area, ARm...Intermediate area, AR1...First area, AR2...Second 2 areas, TI1, TI2... toner image, ARf1, ARf2... good fixing area, TR... good fixing temperature range, 44, 45... thermostat, 46... heat conductive material, 50... controller control unit, 51... CPU, 52... ROM, 53... RAM, 54... PC, 55... PC display unit, 56... PC input unit, 60, 160... process control unit, 61... high pressure control unit, 62... exposure control unit, 63... motor control unit, 64, 164... fixing control unit, 66... ​​supply voltage control unit, 67... develop voltage control unit, 68... charging voltage control unit, 69...Transfer control unit, 70...Supply roller, 71...Developing roller, 72...Charging roller, 76...Main motor, 80...Heat roller, 82...Halogen heater, 82n...Narrow heater, 82w...Wide heater, 83...Valve, 84n, 84w...Filament, 85n...Lead wire inside valve, 86n, 86w...Lead wire, 90...Thermopile, L1, L2...Fixing temperature distribution line, Dw...Transport width direction, Pa6...A6 size recording medium, Pa5...A5 size recording medium, Pa4...A4 size recording medium, P...Recording medium.

Claims

1. A fixing device capable of fixing an image onto a first medium having a first width and a second medium having a second width that is wider in the transport width direction than the first width, Fixing member and A first heater is provided so as to be able to heat the fixing member, and the end on one side in the conveying width direction is positioned on the other side in the conveying width direction than the end on the one side of the second medium, The fixing member is provided so as to be heatable, and the end on one side is positioned on the one-side side of the second medium than the end on the one-side side of the second medium, and It has, The second heater heats the fixing member with a greater amount of heat when borderless printing is performed on the first medium than when bordered printing is performed on the first medium. Fixing device.

2. The duty cycle of the second heater when borderless printing is performed on the first medium is higher than the duty cycle of the second heater when bordered printing is performed on the first medium. The fixing device according to claim 1.

3. The power consumption of the second heater when borderless printing is performed on the first medium is greater than the power consumption of the second heater when bordered printing is performed on the first medium. The fixing device according to claim 1.

4. The first width includes a first region, and the second width includes the first region and a second region that is outside the first region in the transport width direction. A fixing device according to any one of claims 1 to 3.

5. The first heater heats the first region, and the second heater heats the second region. The fixing device according to claim 4.

6. The first heater heats the first region, and the second heater heats the first region and the second region. The fixing device according to claim 4.

7. The first heater is heated so that the temperature of the first region is higher than that of the second region. The second heater heats the second region so that its temperature is higher than that of the first region. The fixing device according to claim 5.

8. A fixing device capable of fixing an image onto a first medium having a first width and a second medium having a second width that is wider in the transport width direction than the first width, Fixing member and A first heater is provided so as to be able to heat the fixing member, and the end on one side in the conveying width direction is positioned on the other side in the conveying width direction than the end on the one side of the second medium, The fixing member is provided so as to be heatable, and the end on one side is positioned on the one-side side of the second medium than the end on the one-side side of the second medium, and It has, The first heater heats the fixing member with a greater amount of heat when borderless printing is performed on the first medium than when bordered printing is performed on the first medium. Fixing device.

9. A fixing device capable of fixing an image onto a first medium having a first width and a second medium having a second width that is wider in the transport width direction than the first width, Fixing member and The fixing member is provided with a first heater that can be heated, and which heats the central part of the fixing member in the conveying width direction more strongly than the ends, A second heater that heats the end portion of the fixing member in the conveying width direction more strongly than the central portion, It has, The second heater heats the fixing member with a greater amount of heat when borderless printing is performed on the first medium than when bordered printing is performed on the first medium. Fixing device.

10. An image forming unit that forms an image on a medium, The fixing device according to any one of claims 1 to 3 or claim 8 or 9 An image forming apparatus having

Images