Fixing device and image forming apparatus

Abstract

To reduce a trouble that a good fixing image cannot be formed over the entire area in a width direction and a trouble that local excessive temperature rise occurs in a fixing member.SOLUTION: A fixing device is provided with: a first temperature sensor 40 that moves, during printing, in the entire area M within a width direction range corresponding to the width direction size of a sheet P passing through at least a nip part with a position X in a center part in the width direction as a movement starting position, and detects a surface temperature of a fixing roller 21 over the entire area M within the width direction range; and a second temperature sensor 41 that moves, during printing, in the entire area M within the width direction range with a position at an end in the width direction as a movement starting position, and detects the surface temperature of the fixing roller 21 over the entire area M within the width direction range. Heaters 25, 26 are controlled during printing based on a detection result from the first temperature sensor 40 and a detection result from the second temperature sensor 41.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] 2. Description of the Related Art Conventionally, in fixing devices in image forming apparatuses such as copiers and printers, a technique for moving a temperature sensor that detects the surface temperature of a fixing member (fixing roller) in the width direction has been widely known (see, for example, Patent Documents 1 and 2).

[0003] More specifically, in the fixing device, a pressure member (pressure roller) is pressed against a fixing member (fixing roller), forming a nip portion (fixing nip) through which a sheet (paper) is transported. The fixing member is heated by a heating means such as a heater that is controlled based on the detection result of a temperature sensor that detects the surface temperature of the fixing member. The toner image on the sheet transported to the nip portion is then fixed onto the sheet by the heat received from the fixing member and the pressure of the nip portion.

[0004] On the other hand, Patent Document 1 discloses a technology for controlling on / off of a center heater that heats the center in the width direction of the fixing roller and end heaters that heat both ends in the width direction of the fixing roller, based on the detection results of a temperature sensor that moves between the center in the width direction and one side end in the width direction. Furthermore, Patent Document 2 discloses a technology for controlling the on / off of a heater that heats a fixing roller based on the detection results of a temperature sensor fixed in the center in the width direction and the detection results of a temperature sensor that moves to the end of the paper passing area according to the width direction size of the paper being passed. Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional fixing devices have problems such as being unable to accurately grasp the condition when the surface temperature of the fixing member is uneven across the entire width, making it impossible to form a good fixed image across the entire width, or causing localized overheating of the fixing member.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a fixing device and an image forming apparatus that reduce the problems of not being able to form a good fixed image across the entire width direction and of localized overheating of the fixing member. [Means for solving the problem]

[0007] The fixing device of the invention comprises a fixing member that is heated by a heating means and heats a toner image to fix it on the surface of the sheet, a pressure member that forms a nip portion through which the sheet is transported by pressing it against the fixing member, a first temperature sensor that detects the surface temperature of the fixing member over the entire widthwise range while moving over a widthwise range corresponding to at least the widthwise size of the sheet passing through the nip portion during printing, with the position of the widthwise center as its movement starting position, and a second temperature sensor that detects the surface temperature of the fixing member over the entire widthwise range while moving over the entire widthwise range while starting from the position of the widthwise end portion during printing, and the heating means is controlled based on the detection results of the first temperature sensor and the detection results of the second temperature sensor during printing. Effect of the Invention

[0008] According to the present invention, it is possible to provide a fixing device and an image forming apparatus that reduce the problems of not being able to form a good fixed image across the entire width direction and the problems of localized overheating of the fixing member. [Brief description of the drawings]

[0009] [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] (A) is a schematic diagram showing the widthwise positional relationship between the center heater and the end heater relative to the fixing roller, and (B) is a schematic diagram showing the widthwise positional relationship between the first temperature sensor and the second temperature sensor relative to the fixing roller. [Figure 4] 4 is a graph showing an example of temperature distribution in the width direction of the fixing roller. [Diagram 5] 5 is a flowchart showing an example of heater control. [Figure 6] 10 is a schematic diagram showing a positional relationship in the width direction of a fixing roller between a first temperature sensor and a second temperature sensor in a first modification. FIG. [Figure 7] FIG. 11 is a configuration diagram showing a fixing device in a second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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).

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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, FIG. 3, etc. As shown in Figures 2 and 3, the fixing device 20 is composed of a fixing roller 21 as a fixing member, heaters 25 and 26 as heating means, a pressure roller 31 as a pressure member, two temperature sensors 40 and 41 for detecting the temperature (surface temperature) of the fixing roller 21, sensor moving mechanisms 55A and 55B for moving the temperature sensors 40 and 41 in the width direction, and photosensors 59A and 59B (position detection means) for detecting the widthwise positions of the temperature sensors 40 and 41.

[0025] 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 (not shown).

[0026] Two heaters (a central heater 25 and an end heater 26) are fixedly provided as heating means inside the hollow fixing roller 21 (metal core 21a). The two heaters 25, 26 are each a rod-shaped halogen heater, and both ends thereof are fixed to the side panels of the fixing device 20. Then, when the main switch of the image forming apparatus main body 1 is turned on (power on), power is supplied to the heaters 25, 26 from power sources 91, 92. Then, the fixing roller 21 is heated by radiant heat from the heaters 25, 26, the output of which is controlled by the control unit 90, and further heat is applied to the toner image T on the sheet P from the surface of the heated fixing roller 21. The output control of the heaters 25 and 26 is performed based on the detection results of the roller surface temperature by two temperature sensors 40 and 41 that face the surface of the fixing roller 21 without making contact with it. By controlling the output of the heaters 25 and 26 in this way, the temperature (fixing temperature) of the fixing roller 21 can be adjusted and controlled to a desired temperature (target control temperature). In this embodiment, the two temperature sensors (first temperature sensor 40 and second temperature sensor 41) are each configured to be movable in the width direction, which will be described in detail later.

[0027] The pressure roller 31 (pressure rotating body) serving as a pressure member is a roller member mainly composed of a core metal 32 and an elastic layer 33 serving 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.

[0028] 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 sources 91 and 92 to the heaters 25 and . 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.

[0029] The characteristic configuration and operation of the fixing device 20 (image forming apparatus 1) in this embodiment will be described in detail below. 2, 3(A), etc., the fixing device 20 in this embodiment is provided with a central heater 25 for heating the central portion of the fixing roller 21 in the width direction, and end heaters 26 for heating both ends of the fixing roller 21 in the width direction, as heating means for heating the fixing roller 21 (fixing member).

[0030] More specifically, the center heater 25 is a halogen heater and is formed so as to be able to heat the center of the fixing roller 21 in the width direction (range N in FIG. 3). The center heater 25 is formed so as to have a width direction length substantially equal to the width direction length of the fixing roller 21, but the portion that functions as a heater (main heater portion) is formed only in the center. The wattage of the center heater 25 is set to 850 W (watts). The center heater 25 has the timing of voltage application supplied from a first power source 91 (see FIG. 2) controlled by the control unit 90. The end heater 26 is a halogen heater and is formed so as to be able to heat both ends in the width direction of the fixing roller 21 (fixing member) (a range slightly wider than the range M in FIG. 3 excluding the range N). The end heater 26 is formed so as to have a width direction length substantially equal to the width direction length of the fixing roller 21, but the portion that functions as a heater (main heater portion) is formed only at both ends. The wattage of the end heater 26 is set to 800 W (watts). The timing of application of the voltage supplied from the second power source 92 to the end heater 26 is controlled by the control unit 90 through the control of the second power source 92 (see FIG. 2).

[0031] In this embodiment, the range N of the "widthwise center" of the fixing roller 21 described above is a range that includes the widthwise center position X (see FIG. 3) and is the paper passing area for the smallest size of sheet P that can be passed through, i.e., the portion that can be the paper passing area for all sizes of sheets P that can be passed through. Moreover, in the range (MN) of the "widthwise ends" of the fixing roller 21 described above, the range M includes a paper passing area for a sheet P of the maximum size that can be passed, and is set to a range slightly larger than that.

[0032] 2, 3B, etc., the fixing device 20 in this embodiment is provided with two temperature sensors (a first temperature sensor 40 and a second temperature sensor 41) for detecting the surface temperature of the fixing roller 21 (fixing member). Both of these temperature sensors 40, 41 are non-contact temperature sensors such as a thermopile or a non-contact thermistor that face the surface of the fixing roller 21 without contacting it. The two temperature sensors 40, 41 are configured to be movable in the width direction (the direction perpendicular to the paper surface of FIG. 2, which is perpendicular to the conveying direction of the sheet P, and the left-right direction in FIG. 3B) by sensor moving mechanisms 55A, 55B, respectively.

[0033] In detail, during printing (during the fixing process), the first temperature sensor 40 starts moving (home position) at the widthwise center (in this embodiment, the center position X, shown in Figure 3 (B)) and detects the surface temperature of the fixing roller 21 over the entire widthwise range while moving over at least the entire widthwise range corresponding to the widthwise size of the sheet P passing through the nip portion (fixing nip). In contrast, the second temperature sensor 41 detects the surface temperature of the fixing roller 21 over the entire widthwise range while moving over the entire widthwise range described above, starting from the widthwise end position (in this embodiment, the position shown in Figure 3 (B), which is the widthwise end position in the paper passing area M of the maximum size sheet P that can be passed) as the start of movement (home position) during printing.

[0034] Specifically, in this embodiment, the first temperature sensor 40 and the second temperature sensor 41 each move across the entire widthwise range M corresponding to the paper passage area for a sheet P of the maximum size that can be passed, and detect the surface temperature of the fixing roller 21 (fixing member) across the entire widthwise range.

[0035] More specifically, when the printing operation described above with reference to Figure 1 etc. is started, the first temperature sensor 40 is moved by the first sensor moving mechanism 55A in the direction of the solid arrow (left side of Figure 3(B)) from the central position X shown in Figure 3(B) as the movement start position (home position), and after reaching one end in the width direction, moves in the direction of the dashed arrow (right side of Figure 3(B)), reaches the other end in the width direction, and then returns to the central position X, making one round trip. During this time, the first temperature sensor 40 detects the temperature distribution in the width direction of the fixing roller 21 (see graph S1 in Figure 4). 1 and the like is started, the second temperature sensor 41 is moved by the second sensor moving mechanism 55B in the direction of the solid arrow (left side of FIG. 3B) from the other end side in the width direction shown in FIG. 3B as the movement start position (home position), and after reaching one end side in the width direction, moves in the direction of the dashed arrow (right side of FIG. 3B) and returns to the other end side in the width direction (home position) to make one round trip. During this time, the second temperature sensor 41 detects the temperature distribution in the width direction of the fixing roller 21 (see graph S2 in FIG. 4).

[0036] In this embodiment, when the first temperature sensor 40 and the second temperature sensor 41 each make one round trip across the widthwise range M during printing (a series of jobs, particularly during continuous paper feed), they then move back and forth across the widthwise range M repeatedly until printing is completed. That is, until a series of jobs is completed, the first temperature sensor 40 and the second temperature sensor 41 each repeat the above-described reciprocating movement as much as possible without stopping the movement. Then, the first temperature sensor 40 and the second temperature sensor 41 each constantly detect the surface temperature (fixing temperature) of the fixing roller 21 during the movement. After printing is completed, the first temperature sensor 40 and the second temperature sensor 41 are returned to their respective movement start positions (home positions) shown in FIG. 3(B).

[0037] 3(B) and the like, in this embodiment, a first sensor moving mechanism 55A that moves the first temperature sensor 40 in the width direction is composed of a first motor 56A, a first worm gear 57A, a first feeler 58A, a first guide member (not shown), etc. Similarly, a second sensor moving mechanism 55B that moves the second temperature sensor 41 in the width direction is composed of a second motor 56B, a second worm gear 57B, a second feeler 58B, a second guide member (not shown), etc.

[0038] The first and second motors 56A and 56B are configured to rotate the first and second worm gears 57A and 57B in both forward and reverse directions. Stepping motors or DC motors can be used as the first and second motors 56A and 56B. When stepping motors are used as the first and second motors 56A and 56B, the first and second temperature sensors 40 and 41 can be moved with high positional accuracy. On the other hand, when DC motors are used as the first and second motors 56A and 56B, it is possible to provide low-cost sensor moving mechanisms 55A and 55B. The first and second temperature sensors 40 and 41 are provided with gear portions that mesh with the first and second worm gears 57A and 57B. Although not shown, the housing of the fixing device 20 is provided with first and second guide members that hold the first and second temperature sensors 40 and 41 non-rotatably and movably in the width direction. With the first and second sensor moving mechanisms 55A, 55B configured in this manner, when the first and second motors 56A, 56B are driven in the forward direction under the control of the control unit 90, the first and second temperature sensors 40, 41 move to the left side (one end in the width direction) in Figure 3(B), and when the first and second motors 56A, 56B are driven in the reverse direction, the first and second temperature sensors 40, 41 move to the right side (the other end in the width direction) in Figure 3(B).

[0039] In order to complete detection of the width-wise temperature distribution by the first and second temperature sensors 40, 41 during any job (to make at least one round trip over the entire width-wise range), it is preferable that the movement speed of the sensor movement mechanisms 55A, 55B is set so that the first and second temperature sensors 40, 41 make one round trip when at least a sheet of the smallest possible conveying direction size is passed through. Furthermore, the sensor moving mechanisms 55A and 55B are not limited to the above configuration, and various configurations can be used.

[0040] Also, referring to FIG. 3(B), the fixing device 20 in this embodiment is provided with a first photosensor 59A as a first position detection means for detecting the widthwise position of the first temperature sensor 40, and a second photosensor 59B as a second position detection means for detecting the widthwise position of the second temperature sensor 41. More specifically, a first filler 58A is provided at a fixed position on the other widthwise end side of the first worm gear 57A of the first sensor moving mechanism 55A. A first photosensor 59A (first position detection means) capable of optically detecting the rotational position of the first filler 58A is provided at a position facing the first filler 58A on the housing of the fixing device 20. The first photosensor 59A thus configured detects the rotational position and the number of rotations in both the forward and reverse directions of the first filler 58A, thereby detecting the absolute position of the first temperature sensor 40 in the widthwise direction. Similarly, a second filler 58B is provided at a fixed position on the other widthwise end side of the second worm gear 57B of the second sensor moving mechanism 55B. A second photosensor 59B (second position detection means) capable of optically detecting the rotational position of the second filler 58B is provided at a position facing the second filler 58B on the housing of the fixing device 20. The second photosensor 59B thus configured detects the rotational position and the number of rotations in both the forward and reverse directions of the second filler 58B, thereby detecting the absolute position of the second temperature sensor 41 in the widthwise direction. Furthermore, the relative positions of the first temperature sensor 40 and the second temperature sensor 41 in the width direction can be ascertained from the detection results of the first photosensor 59A and the detection results of the second photosensor 59B. The first and second position detection means are not limited to the above configuration, and various configurations can be used.

[0041] In this embodiment, the two heaters 25, 26 serving as heating means are controlled based on the detection results of the first temperature sensor 40 and the second temperature sensor 41 during printing. In detail, referring to FIG. 4, in this embodiment, during printing, the heaters 25, 26 (heating means) are controlled so that the temperature distribution S1 across the entire width-wise range M detected by the first temperature sensor 40 and the temperature distribution S2 across the entire width-wise range M detected by the second temperature sensor 41 each approximate a predetermined temperature distribution S0.

[0042] More specifically, the ROM (storage means) of the control unit 90 pre-stores an ideal width-wise temperature distribution S0 according to the type (size, thickness, etc.) of the sheet P being passed and the number of sheets being passed. Also, the ROM (storage means) of the control unit 90 stores in advance data on how the widthwise temperature distribution of the fixing temperature changes depending on a combination of the on / off control of the central heater 25 and the on / off control of the end heater 26. That is, data on the relationship between the temperature distribution S1 detected by the first temperature sensor 40, the temperature distribution S2 detected by the second temperature sensor 41, the on / off control of the central heater 25, and the on / off control of the end heater 26 is stored in advance. Therefore, the control unit 90 controls the on / off of the center heater 25 by the first power source 91 and the on / off of the edge heater 26 by the second power source 92 so as to achieve a uniform target temperature distribution S0 across the width based on the temperature distribution S1 detected by the first temperature sensor 40 and the temperature distribution S2 detected by the second temperature sensor 41. Moreover, these temperature detections and heater controls are performed while being fed back alternately.

[0043] An example of such heater control will be described below with reference to FIG. 5, when the image forming apparatus 1 starts a printing operation from a standby state, the first and second photosensors 59A and 59B determine whether the first and second temperature sensors 40 and 41 are located at their home positions (movement start positions) (steps S1 and S2). When it is confirmed that the first and second temperature sensors 40 and 41 are located at their home positions, the first and second temperature sensors 40 and 41 detect the temperature distributions S1 and S2 while moving the first and second temperature sensors 40 and 41 in the width direction (steps S3 to S5). Then, the detection results S1, S2 from the first and second temperature sensors 40, 41 are compared with the data of the temperature distribution S0 stored in the ROM of the control unit 90 (step S6), and the output of the center heater 25 and the end heater 26 is controlled so as to approach the target temperature distribution S0 (steps S7 to S9). This output control is performed until the series of printing is completed (step S10), and this flow ends when printing is completed.

[0044] In this manner, in the fixing device 20 in this embodiment, the central heater 25 and the end heater 26 are controlled based on the detection result of the first temperature sensor 40, which detects the fixing temperature while moving across the entire width direction from position X at the central part of the width direction as its movement start position, and the detection result of the second temperature sensor 41, which detects the fixing temperature while moving across the entire width direction from a position at an end of the width direction as its movement start position. As a result, even if the surface temperature of the fixing roller 21 is non-uniform across the entire width direction, as shown in graphs S1 and S2 in Fig. 4, it is possible to accurately grasp the state and accurately resolve the state, thereby reducing problems such as not being able to form a good fixed image across the entire width direction and problems such as localized excessive temperature rise of the fixing member. In other words, if the heater is controlled based on the detection result of a temperature sensor installed at a fixed position in the width direction, and if the fixing temperature at the position where the temperature sensor is fixed happens to be too low or too high, the fixing temperature controlled based on the detected temperature will be far from the target temperature when viewed across the entire width direction. In contrast, in this embodiment, the heater is controlled based on the temperature distribution across the entire width direction, so such a problem is less likely to occur.

[0045] In particular, in this embodiment, since the position where the first temperature sensor 40 starts detecting the temperature distribution and the position where the second temperature sensor 41 starts detecting the temperature distribution are different (shifted), it becomes possible to detect the temperature distribution with a time lag by the two temperature sensors 40, 41. That is, when focusing on a predetermined position in the width direction, the two temperature sensors 40, 41 do not detect the temperature simultaneously, but detect the temperature with a time lag. Therefore, the temperature distribution in the width direction, including the change over time, can be detected with high accuracy, and the problem described above is efficiently alleviated. Since the movement start position of the first temperature sensor 40 is the widthwise center where the heater main part of the central heater 25 is located, and the movement start position of the second temperature sensor 41 is the widthwise end where the heater main part of the end heater 26 is located, it becomes possible to control the output of the central heater 25 immediately after the start of printing based on the detection result of the first temperature sensor 40, and to control the output of the end heater 26 immediately after the start of printing based on the detection result of the second temperature sensor 41. By performing such control, the control to approximate the target temperature distribution S0 described above can be performed smoothly.

[0046] In this embodiment, as described above with reference to FIG. 4, the detection results of the first and second temperature sensors 40, 41 are compared with the temperature distribution S0 stored in advance in the control unit 90. On the other hand, the two heaters 25 and 26 can be controlled so that the fixing temperature averaged based on the temperature distributions detected by the first and second temperature sensors 40 and 41 approaches a target fixing temperature.

[0047] <Variation 1> As shown in FIG. 6, in the fixing device 20 of the first modified example, the widthwise range in which the first temperature sensor 40 moves while detecting the temperature is set to be the entire widthwise range Nx corresponding to the widthwise size of the sheet P passing through the nip portion (fixing nip). Similarly, the width direction range in which the second temperature sensor 41 moves while detecting the temperature is set to be the entire width direction range Nx corresponding to the width direction size of the sheet P passing through the nip portion (fixing nip). However, in the first modification, the movement start position (home position) of the second temperature sensor 41 is set to the position of the width direction end in the sheet passing area M of the maximum size that can be passed, similarly to that in FIG. 3B. That is, in the first modification, when sheets P having different widthwise sizes are passed through, the movement ranges Nx of the first and second temperature sensors 40, 41 change according to the widthwise sizes. In the first variant, similarly to what has been described using Figures 2 to 5 etc., the heaters 25, 26 are controlled during printing based on the detection results of the first temperature sensor 40 and the detection results of the second temperature sensor 41. This reduces problems such as failure to form a good fixed image across the entire width and local overheating of the fixing roller 21. In particular, the first modification enables fine-grained control of the fixing temperature in accordance with the width size of the sheet P being passed. The information regarding the width direction size of the sheet P can be grasped by the control unit 90 based on the sheet information input by the user to the operation panel 100 (see FIGS. 1 and 2). Also, it is possible to provide a size detection sensor in the paper feed unit 7 or the like, directly detect the width direction size of the sheet P using the size detection sensor, and obtain information regarding the width direction size of the sheet P based on the detection result.

[0048] <Variation 2> As shown in FIG. 8, the fixing device 20 in the second modification is a belt-type fixing device (a fixing device using a fixing belt 22 as a fixing member), and heaters 25 and 26 as heating means are installed inside a heating roller 24. More specifically, the fixing belt 22 as a fixing member is stretched and supported by a plurality of roller members such as a fixing auxiliary roller 23, a heating roller 24, and a tension roller. The fixing auxiliary roller 23 is pressed against a pressure roller 31 via the fixing belt 22 to form a nip portion. Furthermore, inside the heating roller 24 having a hollow structure, heaters 25 and 26 are fixed to indirectly heat the fixing belt 22 as a fixing member. Furthermore, two temperature sensors 40 and 41 are configured to detect the temperature distribution in the width direction of the fixing belt 22 while being movable in the width direction. The heaters 25 and 26 are controlled based on the detection results of the two temperature sensors 40 and 41. In the fixing device 20 configured in this manner, problems such as an inability to form a good fixed image across the entire width and problems such as localized excessive temperature rise in the fixing belt 22 are reduced.

[0049] As described above, the fixing device 20 in this embodiment is provided with the fixing roller 21 (fixing member) that is heated by the heaters 25 and 26 (heating means) to heat the toner image and fix it on the surface of the sheet P, and the pressure roller 31 (pressure member) that presses against the fixing roller 21 to form a nip portion through which the sheet P is conveyed. Also provided are a first temperature sensor 40 that detects the surface temperature of the fixing roller 21 over the entire width direction range M while moving over the entire width direction range M corresponding to at least the width direction size of the sheet P passing through the nip portion, with the position X of the width direction center as the movement start position during printing, and a second temperature sensor 41 that detects the surface temperature of the fixing roller 21 over the entire width direction range M while moving over the entire width direction range M with the position of the width direction end as the movement start position during printing. Then, the heaters 25 and 26 are controlled based on the detection results of the first temperature sensor 40 and the detection results of the second temperature sensor 41 during printing. This reduces problems such as a failure to form a good fixed image across the entire width and a localized excessive temperature rise in the fixing roller 21.

[0050] 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 the present embodiment, the second temperature sensor 41 is disposed at the right end with respect to the central position M in FIGS. 3(B) and 6, but the second temperature sensor 41 can also be disposed at the left end with respect to the central position M. In addition, in this embodiment, non-contact type temperature sensors are used as the first and second temperature sensors 40 and 41, but contact type temperature sensors can also be used as the first and second temperature sensors 40 and 41. When non-contact type temperature sensors are used as the first and second temperature sensors 40 and 41, sliding resistance with the fixing roller 21 due to movement is not generated compared to when contact type sensors are used. On the other hand, when contact type temperature sensors are used as the first and second temperature sensors 40 and 41, the accuracy of temperature detection can be improved compared to when non-contact type sensors are used, but black streaks due to scratches and toner adhesion are more likely to occur. However, by moving the temperature sensors 40 and 41 in the width direction, such scratches and toner adhesion are less likely to be formed locally (the occurrence of black streaks is reduced compared to when the contact type temperature sensors 40 and 41 are not moved). In the present embodiment, the two heaters 25 and 26 are used as heating means for heating the fixing member (fixing roller 21), but one heater or three or more heaters may be used as the heating means. In addition, in this embodiment, a thermal heater type heating means is used as the heating means for heating the fixing member (fixing roller 21), but the heating means is not limited to this, and for example, an electromagnetic induction type (IH type) or a resistance heating element type can also be used. In these cases, the same effects as those of this embodiment can be obtained.

[0051] 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.

[0052] 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]

[0053] 1 Image forming apparatus (image forming apparatus main body), 20 Fixing device, 21 Fixing roller (fixing member), 25 central heater (heating means), 26 End heater (heating means), 31 pressure roller (pressure member), 40 first temperature sensor (first temperature detection means), 41 second temperature sensor (second temperature detection means), 55A first sensor moving mechanism, 56A 1st motor, 57A 1st worm gear, 58A 1st filler, 59A first photosensor (first position detection means), 55B second sensor moving mechanism, 56B 2nd motor, 57B 2nd worm gear, 58B 2nd filler, 59B second photosensor (first position detection means), P sheet (paper). [Prior art documents] [Patent documents]

[0054] [Patent Document 1] JP 2000-227732 A [Patent Document 2] Japanese Patent Application Publication No. 9-281845

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; a first temperature sensor that detects a surface temperature of the fixing member over an entire width direction range while moving over an entire width direction range corresponding to at least a width direction size of a sheet passing through the nip portion, the first temperature sensor having a movement start position at a width direction center position during printing; a second temperature sensor that detects a surface temperature of the fixing member over the entire width direction range while moving over the entire width direction range from a position at an end of the width direction as a movement start position during printing; Equipped with 2. A fixing device, comprising: a fixing unit configured to control, during printing, the heating unit based on a detection result of the first temperature sensor and a detection result of the second temperature sensor.

2. 2. The fixing device according to claim 1, wherein the first temperature sensor and the second temperature sensor each detect the surface temperature of the fixing member over the entire widthwise range while moving over the entire widthwise range corresponding to the paper passage area of ​​a sheet of the maximum size that can be passed through.

3. a first position detection means for detecting a position of the first temperature sensor in a width direction; a second position detection means for detecting a position of the second temperature sensor in a width direction; 3. The fixing device according to claim 1, further comprising:

4. A fixing device as described in any one of claims 1 to 3, characterized in that when the first temperature sensor and the second temperature sensor each make one round trip across the widthwise range during printing, they then move back and forth across the widthwise range repeatedly until printing is completed.

5. 5. The fixing device according to claim 1, wherein the movement start position of the second temperature sensor is a position of an end in a width direction in a sheet passing area for a sheet of a maximum size that can be passed.

6. A fixing device as described in any one of claims 1 to 5, characterized in that during printing, the heating means is controlled so that the temperature distribution across the entire width-wise range detected by the first temperature sensor and the temperature distribution across the entire width-wise range detected by the second temperature sensor each approximate a predetermined temperature distribution.

7. The fixing device according to any one of claims 1 to 6, characterized in that the heating means includes a central heater for heating a central portion of the fixing member in the width direction, and end heaters for heating both ends of the fixing member in the width direction.

8. An image forming apparatus comprising the fixing device according to any one of claims 1 to 7.

Images