Fixing device and image forming apparatus

Abstract

To reduce power consumption required for heating a fixing member and sufficiently reduce a voltage change occurring when heating means is turned on and off.SOLUTION: A fixing device is provided with a fixing roller 21 (fixing member) that is heated by heating means and heats a toner image T to fix the image to a surface of a sheet P, and a pressure roller 31 (pressure member) that is in pressure contact with the fixing roller 21 to form a nip part through which the sheet P is conveyed. The heating means is a plurality of spot heaters 26A-26P arranged side by side at an interval in a width direction in a maximum paper feed area X in the fixing roller 21. The plurality of spot heaters 26A-26P are controlled such that they can be individually turned on and off.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fixing device that heats a toner image to fix it on the surface of a sheet, and to an image forming apparatus including the fixing device, such as a copying machine, a printer, a facsimile, or a combination machine thereof. [Background technology]

[0002] Conventionally, in a fixing device of an image forming apparatus such as a copier or printer, a technology has been widely known in which a fixing member (fixing roller) is heated by a heating means to fix a toner image transferred onto the surface of a sheet transported to a nip portion between the fixing member and a pressure member (pressure roller) (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technique for heating a fixing member by using a plurality of rod-shaped heaters that heat a plurality of regions divided in the width direction, for the purpose of satisfying flicker regulations. Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional fixing devices require a large amount of power to heat the fixing member, and the voltage change that occurs when multiple rod-shaped heaters are turned on and off is not small, so flicker and other problems cannot be sufficiently suppressed.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide a fixing device and an image forming apparatus which require little power consumption to heat the fixing member and can sufficiently reduce the voltage change that occurs when the heating means is turned on and off. [Means for solving the problem]

[0006] The fixing device of the present invention includes a fixing member that is heated by a heating means and heats a toner image to fix it on a surface of a sheet, and a pressure member that forms a nip portion through which the sheet is conveyed by being pressed against the fixing member, the heating means being a plurality of spot heaters that are arranged side by side in the width direction with gaps therebetween in a maximum paper passing area of ​​the fixing member, the plurality of spot heaters being: A filament is installed inside a housing having a radiation surface facing in a direction opposite to a direction in which the nip portion is located, These can be controlled to be turned on and off separately. Effect of the Invention

[0007] According to the present invention, it is possible to provide a fixing device and an image forming apparatus which require small power consumption to heat a fixing member and can sufficiently reduce the voltage change that occurs when a heating means is turned on and off. [Brief description of the drawings]

[0008] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a fixing device. [Diagram 3] 1 is a schematic diagram showing an arrangement of multiple spot heaters installed in a fixing roller. [Figure 4] 1A is a timing chart showing an example of control of a plurality of spot heaters, and FIG. 1B is a graph showing voltage changes in a fixing device. [Diagram 5] 1A is a timing chart showing an example of control of a plurality of spot heaters as a comparative example, and FIG. 1B is a graph showing a change in voltage of a fixing device. [Figure 6] 11 is a diagram showing the positional relationship between a plurality of spot heaters and an image formed on the surface of a sheet. FIG. [Figure 7] FIG. 13 is a diagram showing a state in which some spot heaters are removed from the heater unit. [Figure 8] FIG. 11 is a configuration diagram showing a fixing device as a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the duplicated description will be appropriately simplified or omitted.

[0010] First, the overall configuration and operation of an image forming apparatus 1 will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a tandem type color copier as an image forming apparatus, reference numeral 2 denotes a writing unit that emits laser light based on input image information, reference numeral 3 denotes a document transport unit that transports a document D to a document reading unit 4, and reference numeral 4 denotes a document reading unit that reads image information of the document D. Additionally, 7 indicates a paper feed section in which sheets P such as paper are stored, 9 indicates a registration roller (timing roller) that adjusts the timing of transporting sheets P, and 11Y, 11M, 11C, and 11BK indicate photosensitive drums on which toner images of each color (yellow, magenta, cyan, and black) are formed.

[0011] Further, reference numeral 12 denotes a charging section which charges the surface of each photoconductor drum 11Y, 11M, 11C, and 11BK, reference numeral 13 denotes a developing section which develops the electrostatic latent image formed on the surface of each photoconductor drum 11Y, 11M, 11C, and 11BK, reference numeral 14 denotes a primary transfer roller which transfers the toner image formed on the surface of each photoconductor drum 11Y, 11M, 11C, and 11BK onto the surface of sheet P, and reference numeral 15 denotes a cleaning section which collects untransferred toner remaining on the surface of each photoconductor drum 11Y, 11M, 11C, and 11BK. In addition, reference numeral 16 denotes an intermediate transfer belt cleaning section that cleans the intermediate transfer belt 17, reference numeral 17 denotes the intermediate transfer belt onto which multiple color toner images are transferred in superimposed order, reference numeral 18 denotes a secondary transfer roller for transferring the color toner image on the intermediate transfer belt 17 onto the sheet P, and reference numeral 20 denotes a fixing device that fixes the toner image (unfixed image) on the sheet P.

[0012] Hereinafter, the operation (printing operation) during normal color image formation in the image forming apparatus will be described. First, the document D is transported from the document table by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the image information of the document D placed on the contact glass 5 is optically read by the document reading unit 4.

[0013] More specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating it with light emitted from an illumination lamp. The light reflected by the document D is then imaged on a color sensor via a group of mirrors and a lens. The color image information of the document D is read by the color sensor for each color separation light of RGB (red, green, blue), and then converted into an electrical image signal. Furthermore, based on the RGB color separation image signal, the image processing unit performs processing such as color conversion processing, color correction processing, and spatial frequency correction processing to obtain color image information of yellow, magenta, cyan, and black.

[0014] Then, the image information for each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, from the writing unit 2, laser light (exposure light) based on the image information for each color is emitted toward the surfaces of the corresponding photoconductor drums 11Y, 11M, 11C, and 11BK.

[0015] Meanwhile, the four photoconductor drums 11Y, 11M, 11C, and 11BK each rotate in the counterclockwise direction in Fig. 1. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at the portions facing the charging unit 12 (charging process). Thus, a charging potential is formed on the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK. Thereafter, the surfaces of the charged photoconductor drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams (exposure process). More specifically, in the writing unit 2, laser beams corresponding to the image signals are emitted from four light sources, one for each color. Each laser beam passes through a separate optical path for each color component of yellow, magenta, cyan, and black.

[0016] The laser light corresponding to the yellow component is irradiated onto the surface of the first photoconductor drum 11Y from the left side of the drawing. At this time, the laser light of the yellow component is scanned in the direction of the rotation axis (main scanning direction, width direction) of the photoconductor drum 11Y by a polygon mirror rotating at high speed. In this way, an electrostatic latent image corresponding to the yellow component is formed on the photoconductor drum 11Y after it has been charged by the charging unit 12.

[0017] Similarly, the laser light corresponding to the magenta component is irradiated onto the surface of the second photoconductor drum 11M from the left on the paper, forming an electrostatic latent image corresponding to the magenta component. The laser light corresponding to the cyan component is irradiated onto the surface of the third photoconductor drum 11C from the left on the paper, forming an electrostatic latent image of the cyan component. The laser light corresponding to the black component is irradiated onto the surface of the fourth photoconductor drum 11BK from the left on the paper, forming an electrostatic latent image of the black component.

[0018] Thereafter, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of each color are formed reach positions facing the developing unit 13. Then, toner of each color is supplied from each developing unit 13 to the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK, and the latent images formed on the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are developed (this is the developing process). Thereafter, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK after the developing process reach the portions facing the intermediate transfer belt 17. Here, primary transfer rollers 14 are provided at each of the facing portions so as to abut against the inner circumferential surface of the intermediate transfer belt 17. Then, at the position of the primary transfer rollers 14, the toner images of each color formed on the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are transferred onto the intermediate transfer belt 17 in order, superimposed on top of each other (this is the primary transfer process).

[0019] After the transfer process, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK each reach a position facing the cleaning unit 15. Then, the cleaning unit 15 collects untransferred toner remaining on the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK (this is the cleaning process). Thereafter, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK pass through a charge removing section, and a series of image forming processes on the photoconductor drums 11Y, 11M, 11C, and 11BK are completed.

[0020] Meanwhile, the intermediate transfer belt 17, onto which the toner of each color is transferred (carried) in an overlapping manner on the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK, travels in the clockwise direction in FIG. 1 and reaches a position facing the secondary transfer roller 18. Then, at the position facing the secondary transfer roller 18, the color toner images carried on the intermediate transfer belt 17 are transferred onto the sheet P (secondary transfer process). Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhering to the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and the series of transfer processes on the intermediate transfer belt 17 is completed.

[0021] Here, the sheet P conveyed between the intermediate transfer belt 17 and the secondary transfer roller 18 (secondary transfer nip) is conveyed from the paper feed section 7 via the registration rollers 9 and the like. Specifically, the sheet P fed by a feed roller 8 from a feed unit 7 storing the sheet P passes through a transport path and is then guided to a registration roller 9. The sheet P that has reached the registration roller 9 is transported in a timely manner toward the secondary transfer nip.

[0022] Then, the sheet P onto which the full-color image has been transferred is guided by a conveyor belt to the fixing device 20. In the fixing device 20, the color image (toner image) is fixed onto the surface of the sheet P at a nip portion (fixing nip) between a fixing roller and a pressure roller (fixing process). Then, the sheet P after the fixing process is discharged as an output image to the outside of the apparatus main body 1 by a paper discharge roller, and a series of image forming processes (printing operations) is completed.

[0023] Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG. 2 etc. As shown in FIG. 2, the fixing device 20 is composed of a fixing roller 21 as a fixing member, a heater unit 25 (multiple spot heaters 26A to 26P) as a heating means, a pressure roller 31 as a pressure member, and multiple temperature sensors 40A to 40E as temperature detection means.

[0024] Here, the fixing roller 21 (fixing rotor) as the fixing member is a multi-layer roller member in which a coating layer 21b (a laminate of an elastic layer and a release layer) is formed on a hollow core metal 21a made of a metal material such as stainless steel, and is pressed against a pressure roller 31 as a pressure member to form a nip portion (fixing nip). The elastic layer in the covering layer 21b of the fixing roller 21 is made of an elastic material such as fluororubber, silicone rubber, or foamed silicone rubber. The release layer in the covering layer 21b of the fixing roller 21 is made of PFA (tetrafluoroethylene perfluoroalkylvinylether copolymer resin) or the like. By providing a release layer on the surface layer of the fixing roller 21, releasability (peelability) for the toner T (toner image) is ensured. The fixing roller 21 is rotated clockwise in FIG. 2 by a drive motor 51.

[0025] A heater unit 25 serving as a heating means is detachably installed inside the fixing roller 21 (core metal 21a) having a hollow structure. Then, when the main switch of the image forming apparatus main body 1 is turned on (power on), power is supplied from the power supply section 91 to the heater unit 25. Then, the fixing roller 21 is heated by radiant heat from the heater unit 25, and heat is applied to the toner image T on the sheet P from the surface of the heated fixing roller 21. That is, the fixing roller 21 (fixing member) is heated by the heating means, and heats the toner image T to fix it on the surface of the sheet P. In the present embodiment, heater unit 25 functioning as a heating means is made up of a plurality of spot heaters 26A to 26P (see FIG. 3), which will be described in detail later. In addition, the output control of heater unit 25 (multiple spot heaters 26A to 26P) is performed based on the detection results of the roller surface temperature by temperature sensors 40A to 40E as multiple temperature detection means arranged side by side with gaps in the width direction (perpendicular to the paper surface of Figure 2, or left and right direction in Figure 3), which will be described in detail later.

[0026] The pressure roller 31 as a pressure member is a roller member mainly composed of a core metal 32 and an elastic layer 33 as a coating layer that covers the outer circumferential surface of the core metal 32 . The elastic layer 33 (covering layer) of the pressure roller 31 is made of a material such as silicone rubber, foamed silicone rubber, etc. A thin release layer made of PFA or the like may be provided on the surface of the elastic layer 33, and the cover layer may be formed by the elastic layer 33 and the release layer. Then, the pressure roller 31 is pressed against the fixing roller 21 by a pressure mechanism (not shown). In this way, a desired nip portion is formed between the pressure roller 31 and the fixing roller 21. The pressure roller 31 is rotated counterclockwise in FIG. 2 in accordance with the rotation of the fixing roller 21.

[0027] The fixing device 20 configured as above operates as follows. When the main switch of the apparatus main body 1 is turned on, an AC voltage is applied (power is supplied) from the power supply section 91 to the heater unit 25. Then, when a print command (print request) is input, the fixing roller 21 starts to rotate clockwise by a drive motor (drive mechanism) (not shown), and the pressure roller 31 starts to rotate counterclockwise. After that, the sheet P is fed from the paper feed unit 7, and the toner image on the intermediate transfer belt 17 is carried on the sheet P as an unfixed image at the position of the secondary transfer roller 18. The sheet P carrying the unfixed image T (toner image) is transported in the direction of the arrow in FIG. 2 and is fed into the nip portion between the fixing roller 21 and the pressure roller 31, which are in a pressure-contact state. Then, the toner image T is fixed on the surface of the sheet P by the heating by the fixing roller 21 and the pressing force of the fixing roller 21 and the pressure roller 31. After the fixing process, the sheet P is sent out from the nip portion in the direction of the arrow by the rotating fixing roller 21 and the pressure roller 31.

[0028] The characteristic configuration and operation of the fixing device 20 (image forming apparatus 1) in this embodiment will be described in detail below. As previously described with reference to FIG. 2 etc., the fixing device 20 in this embodiment is provided with a heating means for heating the fixing roller 21 as a fixing member. As shown in Figures 2 and 3, in this embodiment, a heating means for heating the fixing roller 21 is used, which is a plurality of spot heaters 26A to 26P (16 spot heaters in this embodiment) arranged side by side with gaps in the width direction in the maximum paper passing area X (B4 portrait size in this embodiment) of the fixing roller (fixing member).

[0029] More specifically, heater unit 25 is detachably installed inside fixing roller 21 (core metal 21a) having a hollow structure. Heater unit 25 has 16 spot heaters 26A to 26P arranged on substrate 27. These spot heaters 26A-26P are halogen spot heaters configured identically to one another. That is, the 16 spot heaters 26A-26P are configured as common components. This reduces the cost of the heater unit 25 and facilitates maintenance work such as replacing the spot heaters 26A-26P, which will be described later. Furthermore, by using halogen spot heaters as the spot heaters 26A to 26P, the heating efficiency for the fixing roller 21 can be improved without complicating the control thereof.

[0030] Unlike rod-shaped (line-shaped) heaters, spot heaters 26A-26P radiate radiant heat in a substantially fixed direction (the direction of the black arrow in Fig. 2) without spreading out circumferentially. Specifically, spot heaters 26A-26P have a filament installed in a short, substantially cylindrical housing, and radiant heat is radiated from the ceiling surface (the radiation surface, which is made of quartz glass or the like) of the substantially cylindrical housing. In this embodiment, the multiple spot heaters 26A to 26P are arranged so that radiant heat is not emitted in the direction of the nip portion (fixing nip). That is, the multiple spot heaters 26A to 26P are arranged so that radiant heat is emitted in a direction different from the direction of the nip portion (fixing nip). Specifically, in this embodiment, the ceiling surfaces (radiation surfaces) of the 16 spot heaters 26A to 26P are all arranged so that they face the direction of the black arrow in FIG. 2. With this configuration, the portion of the fixing roller 21 corresponding to the nip portion is not directly heated by the spot heaters 26A to 26P. Therefore, even if unevenness in the fixing temperature occurs, the unevenness is smoothed out by the time the directly heated portion reaches the nip portion, as compared to when the nip portion is directly heated, and a good fixed image can be formed.

[0031] In the present embodiment, the multiple spot heaters 26A to 26P are arranged approximately evenly in the width direction (the left-right direction in FIG. 3). This makes it possible to heat the fixing roller 21 approximately uniformly across the width of the fixing roller 21. In particular, in this embodiment, the multiple spot heaters 26A to 26P are made into common components, so arranging them in this manner is useful. If the gap (spacing) between adjacent spot heaters is too wide, the surface temperature of the fixing roller 21 corresponding to that portion may become low, resulting in temperature unevenness in the width direction. Also, if the gap (spacing) between adjacent spot heaters is too narrow, the number of spot heaters will increase and the task of attaching and detaching the spot heaters, which will be described later, will become difficult. Taking these factors into consideration, the gap (spacing) between adjacent spot heaters is optimized.

[0032] In this embodiment, the plurality of spot heaters 26A to 26P are configured so as to be controlled so as to be able to be turned on and off separately. More specifically, the multiple spot heaters 26A-26P are each connected to a circuit (including a switching circuit 92) formed on the substrate 27. Then, under the control of the control unit 90, the switching circuit 92 switches between supplying power (voltage) from a power supply unit 91 (PSU) to all of the multiple spot heaters 26A-26P to light them all, or supplying power (voltage) to only one or several spot heaters to light them while turning off the other spot heaters. However, no matter what kind of spot heater switching is performed, the circuit is configured so that the magnitude of the power (voltage) of the spot heaters supplied with power is approximately constant (so that the amount of heat when turned on is approximately constant). The control performed by the control unit 90 is sequence control, and a control method such as a contact relay method, a contactless relay method, or a programmable logic controller method is adopted. To enable these controls, the control unit 90 is provided with a storage unit, a calculation unit, an IOB (input output board), an AC control board, and the like.

[0033] In this way, by controlling the multiple spot heaters 26A-26P to be able to be turned on and off separately, the power consumption required to heat the fixing roller 21 is smaller than when multiple rod-shaped heaters are turned on and off, and the voltage change that occurs when the heating means (spot heaters 26A-26P) is turned on and off can be made sufficiently small. As a result, the maintenance cost of the image forming apparatus 1 is reduced, and the occurrence of flicker (a phenomenon in which fluorescent lights flicker in a room where the image forming apparatus 1 connected to a commercial power source is installed) can be reduced.

[0034] Here, referring to FIG. 4(A), in the present embodiment, the multiple spot heaters 26A to 26P are controlled so that when two or more spot heaters are turned on and off, the timings at which they start to turn on and off are shifted from one another. In other words, the sequence control by the control unit 90 causes the plurality of spot heaters 26A to 26P to be turned on and off in succession with overlapping timing.

[0035] As a specific example, as shown in Fig. 4(A), when three spot heaters (first to third spot heaters) are turned on (lit), they are not turned on simultaneously as shown in Fig. 5(A) but are turned on with a slight time difference. Similarly, when three spot heaters (first to third spot heaters) are turned off (exposed), they are not turned off simultaneously as shown in Fig. 5(A) but are turned off with a slight time difference. By controlling in this manner, the voltage (power) supplied from the power supply unit 91 to the fixing device 20 (heater unit 25) does not change suddenly as shown in the area surrounded by the dashed line in Fig. 5(B), but the voltage (power) supplied from the power supply unit 91 to the fixing device 20 (heater unit 25) changes relatively gradually as shown in the area surrounded by the dashed line in Fig. 4(B), thereby reducing the occurrence of flicker.

[0036] As shown in Figures 2 and 3, in the fixing device 20 of this embodiment, temperature sensors 40A to 40E are arranged side by side with gaps in the width direction as multiple temperature detection means for detecting the temperature (surface temperature) of the fixing roller 21 (fixing member). Specifically, in this embodiment, a total of five temperature sensors 40A to 40E are installed at a central position M in the width direction, both end portions, and positions approximately midway between the central position M and both end portions.

[0037] The plurality of spot heaters 26A to 26P are turned on and off separately based on the detection results of the plurality of temperature sensors 40A to 40E (temperature detection means). Specifically, the control unit 90 controls the on / off of the spot heaters 26A-26P separately so that the temperatures detected by the temperature sensors 40A-40E become the target temperatures. As a specific example, when the temperature detected by the temperature sensor 40A installed at one end becomes lower than the target temperature, the spot heater 26A at one end is turned on, and when the temperature becomes higher than the target temperature, the spot heater 26A at one end is turned off. Also, when an A5 portrait size sheet P is passed, the temperatures detected by the temperature sensors 40B and 40D on both sides of the temperature sensor 40C at the center position M are the target temperature, and when the temperature detected by the temperature sensor 40C at the center position M becomes lower than the target temperature, the spot heaters 26E-26L corresponding to the A5 portrait size are turned on, and when the temperature becomes higher than the target temperature, the spot heaters 26E-26L are turned off. In this manner, by separately controlling on / off of the plurality of spot heaters 26A-26P using the plurality of temperature sensors 40A-40E, it is possible to adjust and control the temperature (fixing temperature) of the fixing roller 21 to a target temperature (target control temperature). In this embodiment, five temperature sensors 40A-40E are provided to reduce costs, but the same number (16) of temperature sensors can be arranged in parallel in the width direction in accordance with the widthwise positions of the 16 spot heaters 26A-26P. In that case, the on / off control of the multiple spot heaters 26A-26P based on the temperatures detected by the temperature sensors is simplified.

[0038] Now, referring to FIG. 3, in the present embodiment, the plurality of spot heaters 26A to 26P are turned on and off separately based on the width direction size of the sheet P passing through the nip portion. 3, when a sheet P of the maximum size B4 portrait size is conveyed, all of the 16 spot heaters 26A to 26P are turned on. In contrast, when a sheet P of the LT portrait size is conveyed, the 14 spot heaters 26B to 26O excluding both ends are turned on, and the other spot heaters 26A and 26P are turned off. When a sheet P of the A4 portrait size is conveyed, the 12 spot heaters 26C to 26N are turned on, and the other spot heaters 26A, 26B, 26O, and 26P are turned off. When a sheet P of the B5 portrait size is conveyed, the 10 spot heaters 26D to 26M are turned on, and the other spot heaters 26A to 26C, 26N to 26P are turned off. When the minimum size A5 portrait size sheet P is conveyed, the eight spot heaters 26E to 26L are turned on, and the other spot heaters 26A to 26D and 26M to 26P are turned off. By carrying out such control, it is possible to prevent the temperature of the non-paper passing area of ​​the fixing roller 21 from excessively increasing. In addition, by controlling the multiple spot heaters 26A-26P on and off according to the sheet size as a base, and also controlling the multiple spot heaters 26A-26P on and off based on the temperatures detected by the multiple temperature sensors 40A-40E described above, the fixing temperature in the paper passing area can be finely adjusted to a target temperature, and excessive heating in the non-paper passing area (a phenomenon that occurs when heat is not removed by the sheet P) can be prevented.

[0039] Also, referring to FIG. 6, in this embodiment, the plurality of spot heaters 26A to 26P are turned on and off separately in accordance with the toner image T formed on the surface of the sheet P passing through the nip portion. As a specific example, referring to Fig. 6(A), when a belt-shaped image G (solid image) is formed only on one end of the front surface of an A4 portrait-sized sheet P, among the 14 spot heaters 26C-26N corresponding to that size, the spot heaters 26E and 26F corresponding to the image position are turned on (or the duty is set high), and the other spot heaters 26C, 26D, 26G-26N are turned off (or the duty is set low). Also, referring to Fig. 6(B), when a belt-shaped image G (solid image) is formed only on the other end of the front surface of an A4 portrait-sized sheet P, among the 14 spot heaters 26C-26N corresponding to that size, the spot heaters 26I-26L corresponding to the image position are turned on (or the duty is set high), and the other spot heaters 26C-26H, 26M, 26N are turned off (or the duty is set low). This type of control is performed because the amount of heat required to fix an image (toner image) is greater in areas on the sheet P where an image G is formed (especially areas with high image density such as solid images) than in areas where no image is formed (or areas with low image density). By carrying out such control, it is possible to efficiently form a good fixed image without wasting power. The information of the toner image (image G) formed on the surface of the sheet P can be based on image information acquired by the writing unit 2 (see FIGS. 1 and 2). In this embodiment, the duty (on ratio) of the spot heater corresponding to the width direction position can be controlled to be variable according to the image area ratio (accumulated image density) of the image G formed in the transport direction for each width direction position on the sheet P. Specifically, the duty of the spot heater corresponding to the width direction position where the image area ratio is high is controlled to be high, and the duty of the spot heater corresponding to the width direction position where the image area ratio is low is controlled to be low. By performing such control, the above-mentioned effect is more easily achieved.

[0040] Now, referring to FIG. 7, in the present embodiment, the plurality of spot heaters 26A to 26P are configured to be separately detachable. In detail, the heater unit 25 is fixed to the housing of the fixing device 20 by screw fastening. By releasing the screw fastening, the heater unit 25 can be removed from one end side in the width direction of the fixing roller 21. Then, as shown in FIG. 7, the spot heaters 26F and 26G requiring maintenance (including part replacement) are taken out from the removed heater unit 25 in the direction of the arrow. Then, the spot heaters 26F and 26G after maintenance are attached to the heater unit 25 in the direction opposite to the arrow direction, and the heater unit 25 is attached to the fixing device 20. Note that FIG. 7 shows a state in which the two spot heaters 26F and 26G have been removed, but the other spot heaters are configured to be similarly removable. In addition, in conjunction with the attachment and detachment operations of the spot heaters 26A to 26P, the terminals of the spot heaters 26A to 26P are connected and disconnected to and from the terminals of the circuit of the substrate 27. Such a configuration improves the ease of maintenance of the heater unit 25 and also makes it possible to keep the maintenance costs low.

[0041] <Modification> As shown in FIG. 8, fixing device 20 in the modified example is a belt-type fixing device (a fixing device in which fixing belt 22 is used as a fixing member), and heater unit 25 (multiple spot heaters 26A-26P) is installed as a heating means inside heating roller 24. In detail, fixing belt 22 is stretched and supported by multiple roller members such as fixing auxiliary roller 23, heating roller 24, and tension roller. Furthermore, fixing auxiliary roller 23 is pressed against pressure roller 31 via fixing belt 22 to form a nip portion. Furthermore, heater unit 25 is fixedly installed inside heating roller 24, which has a hollow structure. Also in this modification, the plurality of spot heaters 26A to 26P are controlled so as to be able to be turned on and off separately. This reduces the power consumption required to heat the fixing belt 22, and makes it possible to sufficiently reduce the voltage change that occurs when the heating means is turned on and off.

[0042] As described above, the fixing device 20 in this embodiment includes the fixing roller 21 (fixing member) that is heated by the heating means to heat the toner image T and fix it on the surface of the sheet P, and the pressure roller 31 (pressure member) that forms a nip portion through which the sheet P is transported by being pressed against the fixing roller 21. The heating means is a plurality of spot heaters 26A-26P that are arranged side by side with gaps between them in the width direction in the maximum paper passing area X of the fixing roller 21. The plurality of spot heaters 26A-26P are controlled so that they can be turned on and off separately. This reduces the power consumption required to heat the fixing roller 21, and makes it possible to sufficiently reduce the voltage change that occurs when the heating means is turned on and off.

[0043] In this embodiment, the pressure roller 31 is used as the pressure member, but the pressure member is not limited to this, and for example, a pressure belt can also be used as the pressure member. In addition, in the present embodiment, when the pressure roller 31 (pressure member) is configured to be heated, a plurality of spot heaters can be arranged side by side with gaps in the width direction inside the pressure roller 31 (core metal 32) having a hollow structure. In this case, the heating efficiency for the pressure roller 31 can be improved. In these cases, the same effects as those of this embodiment can be obtained.

[0044] It is clear that the present invention is not limited to the present embodiment, and that the present embodiment may be modified as appropriate within the scope of the technical concept of the present invention in addition to the modifications suggested in the present embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and may be any number, position, shape, etc. suitable for implementing the present invention.

[0045] In this specification, the term "width direction" is defined as a direction perpendicular to the sheet conveying direction. In the present specification, the term "sheet" is defined to include not only paper (paper), but also all sheet-like recording media such as coated paper, label paper, OHP sheets, and film sheets. [Explanation of symbols]

[0046] 1 Image forming apparatus (image forming apparatus main body), 20 Fixing device, 21 Fixing roller (fixing member), 25 heater unit (heating means), 26A~26P Spot heater (heating means), 27 boards, 31 pressure roller (pressure member), 40A to 40E temperature sensor (temperature detection means), X Maximum paper passing area, P sheet (recording medium), G image. [Prior art documents] [Patent documents]

[0047] [Patent Document 1] JP 2016-57377 A

Claims

1. a fixing member that is heated by a heating means and heats the toner image to fix it on the surface of the sheet; a pressing member that forms a nip portion through which a sheet is conveyed by being pressed against the fixing member; Equipped with the heating means is a plurality of spot heaters arranged in parallel with gaps in a width direction in a maximum paper passing area of ​​the fixing member, Each of the plurality of spot heaters has A filament is installed inside a housing having a radiation surface facing in a direction opposite to a direction in which the nip portion is located, A fixing device characterized in that it can be controlled to be turned on and off separately.

2. 2. The fixing device according to claim 1, wherein the plurality of spot heaters are a plurality of halogen spot heaters having the same configuration as each other.

3. 3. The fixing device according to claim 1, wherein the plurality of spot heaters are arranged at substantially equal intervals in the width direction.

4. The fixing device according to any one of claims 1 to 3, characterized in that the plurality of spot heaters are controlled such that, when two or more spot heaters are turned on and off, the timings at which the spot heaters start to be turned on and off are shifted from one another.

5. 5. The fixing device according to claim 1, wherein a plurality of temperature detection means for detecting the temperature of the fixing member are arranged side by side with gaps therebetween in the width direction.

6. 6. The fixing device according to claim 5, wherein the plurality of spot heaters are turned on and off separately based on the detection results of the plurality of temperature detection means.

7. 7. The fixing device according to claim 1, wherein the plurality of spot heaters are turned on and off separately based on a width direction size of the sheet passing through the nip portion.

8. 8. The fixing device according to claim 1, wherein the plurality of spot heaters are turned on and off separately in accordance with a toner image formed on the surface of a sheet passing through the nip portion.

9. 9. The fixing device according to claim 1, wherein the plurality of spot heaters are configured to be separately detachable.

10. A fixing device as described in any one of claims 1 to 9, characterized in that the housings of the multiple spot heaters are arranged side by side on a single substrate, on the side on which the radiation surface is not formed and facing the nip portion.

11. An image forming apparatus comprising the fixing device according to any one of claims 1 to 10.

Images