Image forming device

Abstract

To provide an image forming device with which it is possible to suppress the occurrence of uneven glossiness of a fixed image when the allocation of inputted electric power to a first and a second heating source is changed in accordance with the size, etc., of a recording medium that is fed through.SOLUTION: Provided is an image forming device comprising image forming means for forming an image on a recording medium and a fixing device that fixes the image to the recording medium, wherein the fixing device includes a fixing member, a first and a second heating source for heating the fixing member and mutually differing in heat allocation characteristic, and allocation change means for changing the allocation of inputted electric power to the first and second heating sources in accordance with an image forming condition. When the allocation change means changes electric power allocation to increase allocated electric power to the first heating source and reduce allocated electric power to the second heating source, the rate of increase of the electric power inputted to the first heating source for the first recording medium after the electric power allocation change, in relation to the electric power inputted to the first heating source for the last recording medium before the electric power allocation change, is 0.5 or less, and a passage time in the fixing unit between the last recording medium and the first recording medium is 3 seconds or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been known an image forming apparatus that includes an image forming unit that forms an image on a recording material and a fixing device that fixes the image on the recording material. Patent Document 1 describes such an image forming apparatus that includes the following fixing device: The fixing device has a main heater that generates heat across the entire width of large-size recording materials, and a sub-heater that generates heat only across the width of small-size recording materials. This fixing device turns off the main heater and turns on the sub-heater when fixing small-size recording materials after fixing large-size recording materials. When the sub-heater is turned on, PID temperature control is initiated according to the difference between the detected temperature of the width of the small-size recording material at that time and the target temperature for fixing the small-size recording material. Summary of the Invention [Problem to be solved by the invention]

[0003] However, when the configuration of the first and second heating sources has different heat distribution characteristics, and the distribution of power input to the first and second heating sources is changed depending on the size of the recording material being passed through, there remains a risk that overshoot will occur and uneven gloss will occur in the fixed image, depending on the configuration of the first and second heating sources. [Means for solving the problem]

[0004] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus including an image forming unit that forms an image on a recording material, and a fixing device that fixes the image on the recording material at a fixing section, the fixing device comprising: a fixing member; The total width of the width direction area of ​​the fixing member corresponding to the maximum width of the recording material that can be passed is each other different Heat distribution characteristics Heating witha first heating source and a second heating source, and a distribution change means for changing the distribution of power input to the first heating source and the second heating source in accordance with image formation conditions; the first heating source has a heat distribution characteristic of uniform heat generation distribution in a width direction of the fixing member, and the second heating source has a heat distribution characteristic of higher heat generation amounts corresponding to both sides in the width direction of the maximum size width than the heat generation amount at the center, When the distribution change means changes the power distribution to increase the power distributed to the first heating source and decrease the power distributed to the second heating source, the increase ratio of the power input to the first heating source for the first recording material after the power distribution change relative to the power input to the first heating source for the last recording material before the power distribution change is 0.5 or less, and the passing time through the fixing section between the last recording material and the first recording material is 3 seconds or less. [Effects of the Invention]

[0005] According to the present invention, it is possible to suppress the occurrence of uneven glossiness in a fixed image when the distribution of power input to the first heating source and the second heating source is changed depending on the size of the recording material being fed. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a printer according to an embodiment. [Figure 2] FIG. [Figure 3] FIG. 2 is a control block diagram relating to lighting control of each heater in the fixing device. [Figure 4] 3A and 3B are diagrams illustrating a heater configuration in the fixing device according to the embodiment. [Figure 5] FIG. [Figure 6] FIG. 10 is a diagram illustrating the temperature rise when switching from a large size lighting mode to a small size lighting mode. [Figure 7] 3 is a flowchart of control according to the first embodiment. [Figure 8] Schematic diagram of the temperature distribution across the width of the first belt surface in the first and second lighting modes. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied. First, the general configuration of the printer will be described. FIG. 1 is a schematic diagram showing the configuration of this printer. Printer 200 is a color printer that uses a tandem system in which image forming units that form multiple color images are arranged side by side along the extension direction of the belt, but the present invention is not limited to this system and can also be applied to not only printers but also copiers, facsimile machines, etc.

[0008] Printer 200 has four image stations as an image forming section each equipped with photosensitive drums 20Y, 20C, 20M, and 20Bk, and an optical writing device 8 as an optical writing device disposed below and facing the four image stations. Printer 200 also has an intermediate transfer belt unit 10 disposed above and facing the four image stations.

[0009] The four image stations are photosensitive drums 20Y, 20C, 20M, and 20Bk, arranged in this order from the upstream side in the A1 direction. Each photosensitive drum 20Y, 20C, 20M, and 20Bk forms a yellow, cyan, magenta, or black image, respectively. Devices for forming images in accordance with the rotation of the photosensitive drum are arranged around each photosensitive drum. Focusing on photosensitive drum 20Bk, which forms a black image, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk are arranged in the rotation direction of photosensitive drum 20Bk, which perform the image formation process.

[0010] The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, and a rotating polygonal mirror as a deflection means. The optical writing device 8 emits writing light Lb corresponding to each color to each of the photoconductor drums 20Y, 20C, 20M, and 20Bk, forming electrostatic latent images on the photoconductor drums 20Y, 20C, 20M, and 20Bk. For convenience, only the image station for the black image is labeled in FIG. 1, but the same applies to the other image stations.

[0011] The intermediate transfer belt unit 10 includes an intermediate transfer belt 11, which is an endless belt serving as an intermediate transfer body, primary transfer rollers 12Y, 12C, 12M, and 12Bk, an elastic roller 72 around which the intermediate transfer belt 11 is wound, and a driven roller 73. The driven roller 73 is provided with a biasing means such as a spring, and also functions as a tension biasing means for the intermediate transfer belt 11.

[0012] The printer 200 also has a secondary transfer roller 5, which is a transfer roller that serves as a transfer member and is arranged opposite the intermediate transfer belt 11, driven by and rotates along with the intermediate transfer belt 11, and an intermediate transfer cleaning device 13 that is arranged opposite the intermediate transfer belt 11 and cleans the surface of the intermediate transfer belt 11.

[0013] The intermediate transfer cleaning device 13 has a cleaning brush and a cleaning blade arranged to contact the intermediate transfer belt 11, and uses these to scrape off and remove foreign matter such as residual toner from the intermediate transfer belt 11, thereby cleaning the intermediate transfer belt 11. The intermediate transfer cleaning device 13 also has a discharge means for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

[0014] The intermediate transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5, and the intermediate transfer cleaning device 13 constitute a transfer device 71.

[0015] The printer 200 is provided at the bottom of the main body with a sheet feeding device 61 on which sheets S are stacked. The sheet feeding device 61 has a feed roller 3 that contacts the upper surface of the uppermost sheet S, and feeds the uppermost sheet S toward the pair of registration rollers 4 by rotating the feed roller 3 counterclockwise.

[0016] The pair of registration rollers 4 feeds the paper S conveyed from the sheet feeding device 61 toward a transfer section between each of the photosensitive drums 20Y, 20C, 20M, and 20Bk and the intermediate transfer belt 11 at a predetermined timing that coincides with the timing of the formation of a toner image by the image station. The printer 200 also includes a sensor that detects when the leading edge of the paper S reaches the pair of registration rollers 4.

[0017] Printer 200 has a contact heating fixing device 100 as a fixing unit for fixing a toner image onto paper S (a fixing target) onto which the toner image has been transferred. Printer 200 also has a paper discharge roller 7 that discharges paper S after the fixing to the outside of the main body of printer 200, and a paper discharge tray 17 that is disposed above the main body of printer 200 and that stacks paper S discharged outside the main body of printer 200 by the paper discharge roller 7. Printer 200 also has toner bottles 9Y, 9C, 9M, and 9Bk below paper discharge tray 17, each containing yellow, cyan, magenta, and black toner.

[0018] The image forming operation of the printer 200 is as follows. Visible images formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk at the four image forming stations are transferred and superimposed on the intermediate transfer belt 11, which moves in the direction of arrow A1 while facing the photosensitive drums 20Y, 20C, 20M, and 20Bk, through a primary transfer process. The superimposed visible images transferred to the intermediate transfer belt 11 are then transferred together onto the paper S through a secondary transfer process using the secondary transfer roller 5. The toner images on the paper S, to which the toner images have been transferred together, are fixed by the fixing device 100, and the fixed paper S is discharged outside the main body of the printer 200 by the paper discharge roller 7.

[0019] FIG. 2 is a schematic diagram of a fixing device 100. The fixing device 100 includes an endless fixing belt 101 as a rotatable fixing member and a pressure roller 103 as a rotatable pressure member disposed opposite the fixing belt 101. The fixing device 100 includes a main heater 102a as a first heat source, a sub-heater 102b as a second heat source, a pad 106 as a nip forming member, and a support member 107 inside the fixing belt 101. The fixing device 100 also includes a reflector 109 as a reflective plate and a sliding member 116 inside the fixing belt 101. The main heater 102a, sub-heater 102b, pad 106, sliding member 116, and support member 107, all of which are disposed inside the fixing belt 101, have lengths equal to or greater than the width of the fixing belt 101. In the figure, paper S is transported from bottom to top, and the direction of movement of the fixing belt 101 is counterclockwise.

[0020] The fixing belt 101 is composed of a metal belt such as nickel or SUS, or an endless belt or film made of a resin material such as polyimide. The surface of the belt has a release layer such as a PFA or PTFE layer to provide release properties to prevent toner from adhering. An elastic layer made of a silicone rubber layer or the like may be placed between the belt substrate and the PFA or PTFE layer. The deformation of the silicone rubber layer absorbs minute irregularities, improving the orange peel effect of the image.

[0021] The pressure roller 103 has an elastic rubber layer 104 on a core metal 105, and a release layer (PFA or PTFE layer) 103a on its surface to provide releasability. The pressure roller 103 rotates by a driving force transmitted via gears from a driving source such as a motor provided in the image forming apparatus. The pressure roller 103 is pressed against the fixing belt 101 by a spring or the like, and the elastic rubber layer 104 is crushed and deformed to provide a predetermined nip width. The pressure roller 103 may be a hollow roller, and may have a heat source such as a halogen heater.

[0022] Pad 106, which serves as a nip forming member and is disposed inside fixing belt 101, forms fixing nip N, which is a fixing portion, between fixing belt 101 and pressure roller 103. Pad 106 is provided with sliding member 116 that slides against the inner surface of the fixing belt. Pad 106 is supported by support member 107. Support member 107 prevents deflection of pad 106, which receives pressure from pressure roller 103, and ensures that a uniform nip width is obtained in the axial direction.

[0023] The main heater 102a and the sub-heater 102b are halogen heaters, and the fixing belt 101 is directly heated from the inner circumferential side by radiant heat from these heaters 102a and 102b. Each of the heaters 102a and 102b may be an induction heater, a resistance heating element, a carbon heater, or the like, as long as it can heat the fixing belt 101.

[0024] In this embodiment, a reflector 109 is provided between each of the heaters 102a, 102b and the support member 107. Instead of providing the reflector 109, the same effect can be obtained by subjecting the surface of the support member 107 to heat insulation or mirror finishing.

[0025] A temperature detection sensor 110, which is a temperature detection means for detecting the surface temperature of the fixing belt 101, is provided on the outside of the fixing belt 101. A temperature sensor with high temperature responsiveness, such as a thermopile, is used as the temperature detection sensor 110. The temperature detection sensor 110 detects the temperature of the center of the fixing belt 101 in the width direction (see FIG. 4).

[0026] The fixing belt 101 rotates together with the pressure roller 103. In the case of Figure 2, the pressure roller 103 is rotated by a drive source, and the driving force is transmitted to the belt at the fixing nip N, thereby rotating the fixing belt 101. The toner image on the paper is fixed by heat and pressure at the fixing nip N.

[0027] 3 is a control block diagram related to the lighting control of the heaters 102a and 102b in the fixing device. The control unit 150 has a CPU (central processing unit), a read-only memory (ROM) that stores a control program, a random access memory (RAM) that temporarily stores data, a non-volatile flash memory, etc. The control unit 150 is connected to the main heater 102a, the sub-heater 102b, a temperature detection sensor 110, and an operation panel 80. The operation panel 80 has a display unit and an operation unit, and accepts input operations from the user.

[0028] The control unit 150 stores in a nonvolatile flash memory size information of the paper set in the sheet feeding device 61, which information is input by the user through the operation panel 80. The control unit 150 controls the lighting of the heaters 102a and 102b based on the paper size information stored in the nonvolatile flash memory and the temperature of the fixing belt 101 detected by the temperature detection sensor 110.

[0029] FIG. 4 is a diagram illustrating the heater configuration of the fixing device of this embodiment. FIG. 4(a) shows the widthwise distribution of heat generation when both the main heater 102a and the sub-heater 102b are turned on, with the hatched area representing the heat generation distribution by the sub-heater 102B. FIG. 4(b) shows the same heat generation distribution when only the main heater 102a is turned on, with the power supply increased by the amount supplied to the sub-heater 102b in FIG. 4(a). The fixing device of this embodiment is configured to include a main heater 102a with heat distribution characteristics that generate heat uniformly in the widthwise direction, and a sub-heater 102b with heat distribution characteristics that generate more heat at both ends in the widthwise direction than at the center. These heaters correspond to a first heat source and a second heat source for heating the fixing member, which have different heat distribution characteristics.

[0030] The heating area L of each heater 102a, 102b is equal to or larger than the maximum width size that can be passed through this image forming apparatus, and is capable of heating a widthwise area of ​​the fixing belt 101 that is equal to or larger than this maximum width size. The amount of heat generated at the center of the sub-heater 102b is less than the amount of heat generated by the main heater 102a. The maximum width size that can be passed through this image forming apparatus, indicated as "SRA3" in the figure, is a non-standard size, and is a paper size with a width (length perpendicular to the paper passing direction) of 320 mm and a length (length in the paper passing direction) of 450 mm. The width of A3 size paper is 297 mm, and the width of "SRA3" is larger than this.

[0031] 2, in this embodiment, one temperature detection sensor 110 is provided in the center of the width direction of the fixing belt 101, and the heater is controlled using only this temperature detection sensor 110 so that the temperature of the fixing belt 101 is maintained at a specified temperature (standby temperature or fixing temperature). In this embodiment, the temperature detection sensor 110 is provided in the center of the width direction of the fixing belt 101, but it may be placed within the range of the minimum width size (A6 portrait size: 105 mm in this embodiment) that can pass paper through this image forming apparatus.

[0032] As shown in FIG. 4(a), in this embodiment, the main heater 102a, which is the first heating source, has a heat distribution characteristic that generates a uniform amount of heat across the width, while the sub-heater 102b, which is the second heating source, has a heat distribution characteristic that generates a higher amount of heat across both sides of the maximum size width than across the center. When both the sub-heater 102b and the main heater 102a are turned on, the total amount of heat generated at the ends is greater than the total amount of heat generated at the center. On the other hand, when the sub-heater 102b is turned off and only the main heater 102a is turned on, the amount of heat generated is approximately uniform across the width, as shown in FIG. 4(b). Taking advantage of this characteristic, the following control can be performed.

[0033] For example, when the temperature of an end contact member, such as a guide member that contacts the end of the fixing member, is low, such as when the power is turned on, a large amount of heat transfers from the end of the fixing member to the end contact member. In such a case, by turning on the first and second heating sources and increasing the amount of heat generated at the widthwise ends compared to the center, the temperature of the fixing member can be made almost uniform across the width.

[0034] When the fixing member is heated by the first and second heating sources for a predetermined time, the temperature of the edge contact member becomes approximately the same as that of the fixing member. When the temperature of the edge contact member becomes approximately the same as that of the fixing member, the amount of heat transferred from the edge of the fixing member to the edge contact member decreases. Therefore, even if the heat generated at the edge is not greater than that at the center, the temperature of the fixing member can be made approximately uniform across the width. Therefore, after heating by the first and second heating sources for a predetermined time, the second heating source is turned off, and only the first heating source is controlled based on the detection results of the temperature detection sensor to maintain the temperature of the fixing member at a specified temperature. This allows the temperature of the fixing member to be maintained at approximately the specified temperature across the width.

[0035] Then, during the period when the temperature of the fixing member is maintained based on the detection result of the temperature detection sensor using only the first heat source, the power allocation to the first heat source is increased in order to ensure productivity. Specifically, for example, the allocation is switched from FIG. 4(a) to FIG. 4(b).

[0036] In this way, after heating for a predetermined time with the first and second heating sources, the temperature of the fixing member can be maintained at approximately the specified temperature in the width direction using only the first heating source, so the temperature detection sensor for the second heating source can be eliminated, which reduces the number of temperature sensors and reduces the cost of the device compared to when temperature sensors are provided at both the center and end portions in the width direction.

[0037] In this embodiment, the printer includes an allocation change unit that changes the allocation of power input to the first heating source and the second heating source according to image formation conditions. Image formation conditions include the width of the paper being fed and the duration of continuous printing. For example, the allocation of power input is changed depending on whether the width of the paper being fed exceeds the width X of A3, with paper exceeding X being considered large size and paper equal to or smaller than X being considered small size. Switching from the allocation for large size to the allocation for small size results in a power allocation change that increases the power allocated to the first heating source and decreases the power allocated to the second heating source (including reducing it to zero), as shown in the example of FIG. 4, in order to ensure productivity.

[0038] However, when the power allocation is changed so that the power allocated to the first heating source is increased and the power allocated to the second heating source is decreased, it has been confirmed that the temperature of the fixing member overshoots, resulting in uneven glossiness of the fixed image. This problem is particularly noticeable when a thin fixing belt with a relatively small heat capacity is used as the fixing member of this embodiment.

[0039] After careful research into the cause, the following was discovered: Because temperature control is performed at the center of the fixing belt, approximately the same amount of power is required before and after switching, regardless of paper size, when continuously feeding sheets of the same basis weight and in the same print mode. In other words, regardless of the power allocation before or after switching, it is necessary to supply enough power to compensate for the heat absorbed by the paper at the center of the fixing belt. Therefore, it is necessary to allocate and add approximately the same amount of power to the first heating source after switching as was supplied to the second heating source before the size change.

[0040] It was also found that if the power ratio of the second heating source to the first heating source before switching exceeds a predetermined value, the thermal history of the second heating source before switching has a large effect immediately after switching, causing the temperature in the area upstream of the nip to be higher than the target value. The thermal history of the second heating source has two effects. The first is the belt temperature rise caused by the power input to the second heating source in large size lighting mode. The second is the thermal history that continues for a certain period of time due to the influence of radiant heat from the heater's glass tube, which has become hot, even after switching to small size lighting mode, even if the power input to the second heating source is reduced compared to large size lighting mode or becomes zero.

[0041] Figure 5 is an explanatory diagram of the relationship (temperature profile) between the position in front of the nip N and the temperature for each of the power distributions when both heating sources are turned on and when only the first heating source is turned on. The temperature profile schematically shows the temperature of a specific region in the center of the fixing belt's width, tracing the temperature from point P to point Q around the belt circumference marked in Figure 2 while the belt is rotating at the same speed as the belt. Point P corresponds to time t0 on the horizontal axis of Figure 5, and point Q corresponds to time t1 on the horizontal axis of Figure 5.

[0042] Figure 5(a) shows the temperature profile when both the first and second heating sources are on during continuous large-size paper feed, and Figure 5(b) shows the temperature profile when only the first heating source is on during continuous small-size paper feed. The zero point on the temperature vertical axis is the control temperature of 130°C, and the temperature at point Q before nip N is 140°C. Figures 5(a) and 5(b) show schematic diagrams of the temperature in the circumferential direction of the sleeve for different paper sizes when the same number of sheets (20 sheets) are fed from start-up, with the same basis weight of 81.4 g / m2. In the large-size lighting mode in Figure 5(a), the temperature rises gradually in the second heating zone and then rises somewhat more steeply in the first heating zone, resulting in the appropriate temperature TQ being obtained before nip N (upstream of the nip). In the small size lighting mode of FIG. 5(b), the temperature hardly rises in the second heating region, but rises sharply in the first heating region, and an appropriate temperature TQ is obtained before the nip N (upstream of the nip).

[0043] Figure 6 is a diagram illustrating the temperature rise when switching from the large size lighting mode to the small size lighting mode. The dashed line A in Figure 6(a) shows a schematic diagram of the belt temperature rise profile when the power input to the second heating source is allocated to the power input to the first heating source at a predetermined value or less when large size paper is being passed. The dashed line B shows a schematic diagram of the temperature rise profile when the power input to the second heating source is allocated to the power input to the first heating source at a predetermined value or more when large size paper is being passed. The solid line C in Figure 6(a) shows a schematic diagram of the temperature rise profile when switching to the small size lighting mode in Figure 6(b) after large size paper has been passed with the power allocated as shown by dashed line A, and the temperature at point Q before nip N is below the allowable value.

[0044] It was found that by setting the increase ratio of the power input to the first heating source for the first page after switching to the small size lighting mode to 0.5 or less relative to the power input to the first heating source for the last page of this power allocation (lighting mode) when passing large size paper, the influence of the thermal history of the second heating source when passing large size paper can be reduced, the amount of overshoot immediately after switching to the small size lighting mode can be reduced, and the temperature before the nip can be kept below the allowable value.It is practical if the passage time through the nip N between the last recording material before the power allocation switch and the first recording material after the power allocation switch is 3 seconds or less.

[0045] The solid line D in Figure 6(a) shows a schematic diagram of a temperature rise profile in which, after large-size paper has passed through at the input power ratio of the dashed line B, the printer switches to the small-size lighting mode in Figure 6(b) and the temperature at point Q before the nip N exceeds the allowable value. This corresponds to Comparative Examples 1 and 2 described below. When the increase ratio of the power input to the first heating source for the first page after switching to the small-size lighting mode relative to the power input to the first heating source for the last page in the power allocation (lighting mode) when large-size paper is passed exceeds 0.5, the thermal history of the second heating source when large-size paper is passed has a large effect, the amount of overshoot immediately after switching to the small-size lighting mode increases, and the temperature before the nip exceeds the allowable value.

[0046] Example 1 Table 1 shows the experimental results when switching the lighting mode from large size to small size according to Example 1, which will be described later. [Table 1]

[0047] FIG. 7 is a control flowchart for the first embodiment. This flowchart shows the control flow for switching from large size to small size, and does not include the control flow for switching from small size to large size. When the image forming apparatus receives a print command, it turns on both the first and second heating sources in S1. The maximum power consumption at this time is shown in the power consumption in the startup mode in FIG. 3(a).

[0048] Next, in S2, when the leading edge of the first sheet of paper enters the nip, the amount of power input is determined in S3 based on the difference between the target temperature and the current temperature detected by temperature detection sensor 110 (hereinafter simply referred to as the current temperature), and in S4 it is determined whether N=1 sheet is wider than the specified width X, which is the specified width. If it is determined in S4 that it is wider than width X, the process proceeds to S8, and in the first lighting mode for large size, the amount of power input determined in S3 is allocated to the first heating source v [W] and the second heating source w [W], and the paper is heated and fixed in S10. As mentioned above, width X in this embodiment is 297 mm, which is the A3 width.

[0049] Next, the control behavior will be explained when the N=20th sheet of paper is SRA3 size (width: 320 mm, length: 450 mm), which is wider than A3 width, and the N=21st sheet and subsequent sheets are A4 portrait size. SRA3 size paper corresponds to the first width recording material, and paper narrower than SRA3 size corresponds to the second width recording material. If N=21st sheet is A4 size in S4, proceed to S5, and because N=20th sheet is SRA3 size, the power is turned on in the first lighting mode for large sizes in S8 until the trailing edge of N=20th sheet of paper leaves nip N in S6, and after the trailing edge of N=20th sheet of paper leaves the nip in S6, the power is corrected from the power determined in S3 by the input power correction in S7.

[0050] The reason for the power correction in S3 is explained below. For the first 20 sheets, the heater is turned on in the large-size heater mode due to the SRA3 size. However, the next page, N=21, is a small-size sheet, resulting in a larger non-paper-passing area. Therefore, switching to the second lighting mode, which reduces the second heating source at the edge height, is necessary to prevent the temperature from rising in the non-paper-passing area. Meanwhile, because the heat required for the central area of ​​the N=20 and N=21 sheets is roughly the same, switching from the first lighting mode to the second lighting mode reduces the heat amount in the area marked by ΔQ in the dotted line, as shown in the heat distribution diagram in Figure 4(b). In S7, the power equivalent to this reduction in ΔQ is corrected for the power determined in S3.

[0051] Next, in S9, the corrected power is allocated to the first heating source by v' [W] and to the second heating source by w' [W] in the second lighting mode for small sizes, and the paper is heated and fixed in S10. If the belt temperature TQ before the nip is within 140°C ± 8°C, gloss unevenness in the full-area red image under the following conditions is no longer visible, so the results for this temperature range are marked with ○ in Table 1.

[0052] Here, the power consumption for the Nth sheet listed in Table 1 is the average power consumption from immediately after the rear edge of the (N-1)th sheet of paper leaves the fixing nip to the rear edge of the Nth sheet of paper. The power consumption for the first sheet is the average power divided by the paper passage time of the first sheet, and the power consumption in start-up mode indicates the maximum power that can be input to the first and second heating sources.

[0053] In this example, the linear velocity was 150 mm / s, the distance between the 20th and 21st sheets was 134 mm, and the time corresponding to the distance between the sheets was 0.9 s. The average power of the first heating source for the 20th sheet was 463 W, and the average power of the first heating source for the 21st sheet was 687 W, with the increase rate being (687 - 463) / 463 = 0.48 ≦ 0.5.

[0054] Using the symbols in the flowchart in Figure 7 to express each average power, the average power of the first heating source for the 20th sheet is Σvi / N = 463 W, and the average power of the first heating source for the 21st sheet is Σvi' / N = 687 W (N is the number of power measurement samples). The belt temperature TQ was within 140 ± 8°C, and the central temperature had a gloss unevenness of O.

[0055] <Condition> The power distribution is switched immediately after SRA3 size paper passes through the fixing nip. Control temperature: 130℃ Belt layer structure: Base layer (Ni) 30um, silicone rubber layer 120um, surface layer 8um PFA coating Power of the first heating source immediately after printing starts at 100V input: 770W Power of the second heating source immediately after printing starts at 100V input: 385W Paper size: After passing 20 SRA3 sheets, 20 A4 portrait size sheets (SRA3 sheets 3 to 19 are not shown) SRA3: 13 CPM / A4 portrait: 20 CPM The image shows a full-surface red image with an adhesion amount of 0.84 mg / cm2, confirming uneven gloss. ·Line speed 150mm / s ·Paper basis weight: 81.4g / m2 Belt temperature measurement: A thermocouple is placed at point Q in the center of the axial direction before the nip. The distance between the rear edge of the 20th sheet and the front edge of the 21st sheet is 134 mm. The time it takes for the sheets to pass through is 0.9 seconds. · Environment: 23℃ / relative humidity: 50%

[0056] Table 2 shows the experimental results of Comparative Example 1 when switching from the large size to the small size lighting mode. [Table 2]

[0057] This is an example in which the distribution of the first and second heat sources at the time of maximum power input is different from that in the first embodiment. <Condition> Control temperature, belt layer configuration, etc. are the same as in Example 1 except for the power distribution before switching. Power of the first heating source immediately after printing starts at 100V input: 700W Power of the second heating source immediately after printing starts at 100V input: 455W

[0058] The average power of the first heating source for the 20th sheet was 422 W, and the average power of the first heating source for the 21st sheet was 685 W. The increase rate was (685-422) / 422=0.62>0.5, at which point the belt temperature TQ exceeded the range of 140±8°C, and the central temperature showed gloss unevenness ×.

[0059] Table 3 shows the experimental results of Example 2 when switching from the large size to the small size lighting mode. [Table 3]

[0060] The average power of the first heating source for the 20th sheet was 475 W, and the average power of the first heating source for the 21st sheet was 707 W, with the increase rate being (707 - 475) / 475 = 0.49, which also reduces gloss unevenness. However, compared to Example 1, by increasing the belt thickness, the total power consumption increased regardless of the number of sheets, making it less energy-efficient than Example 1. <Condition> The belt has a thicker layer. Belt layer structure: Base layer (Ni) 30um, silicone rubber layer 250um, surface layer 15um PFA coating Other conditions were the same as in Example 1.

[0061] Table 4 shows the experimental results for Example 3 when switching from A3 size to A4 size. [Table 4]

[0062] <Condition> Control temperature, belt layer structure, power immediately after printing starts, linear speed, etc. are the same as in Example 1. Paper size: 20 sheets of A3 paper / 20 sheets of A4 portrait paper A3: 14 CPM / A4 portrait: 20 CPM The distance between the rear edge of the 20th sheet and the front edge of the 21st sheet is 134 mm. The time it takes for the sheets to pass through is 0.9 seconds.

[0063] Both A3 and A4 sizes do not exceed the threshold of X=297 in S4 of the flowchart in Figure 7, and are less susceptible to edge droop than SRA3. Figure 8 is a schematic diagram of the temperature distribution across the width of the belt surface for the first sheet in the first and second lighting modes. In this diagram, the solid line represents the first lighting mode, and the dashed line represents the second lighting mode. It can be seen that A3 is less susceptible to edge droop in either mode. Therefore, there is no flow from S4 to S8 or from S5 to S6 in the flowchart in Figure 7. Regardless of the paper size change from N=1 to N=20 and N=21, power is supplied in the second lighting mode at S9. Therefore, the average power fluctuations of each heating source between N=20 and N=21 are small, and the overshoot problem associated with changing paper sizes does not become apparent. Although FIG. 8 shows sizes up to A4, the minimum width is a smaller paper size, for example, a postcard, and the temperature detection sensor 110 is also arranged at a position facing this minimum size width in the width direction.

[0064] Table 5 shows the experimental results for Example 4 when switching from SRA3 size to A4 size. [Table 5]

[0065] <Condition> The distance between the rear edge of the 20th sheet and the front edge of the 21st sheet is 75 mm. The time it takes for the sheets to pass through is 0.5 seconds.

[0066] The paper interval is shorter than in Example 1. The average power of the first heating source on the 20th sheet is 463 W, and the average power of the first heating source on the 21st sheet is 684 W, with an increase rate of (684-463) / 463=0.48≦0.5. Compared to Example 1, the paper is more susceptible to the influence of thermal history and the amount of overshoot is larger, but the central temperature is within 140±8°C, and gloss unevenness can be suppressed.

[0067] Table 6 shows the experimental results of Example 5 when switching from SRA3 size to A4 size. [Table 6]

[0068] <Condition> Control temperature: 145℃ ·Line speed: 250mm / s SRA3: 30 CPM, A4 portrait: 45 CPM The distance between the rear edge of the 40th sheet and the front edge of the 41st sheet is 44 mm. The time it takes for the sheets to pass through the paper is 0.18 seconds divided by the linear speed.

[0069] The paper interval is shorter than in Example 1. The average power of the first heating source on the 20th sheet is 484 W, and the average power of the first heating source on the 21st sheet is 724 W, with the increase ratio being (724 - 484) / 484 = 0.496 ≦ 0.5. If this condition is met, even in this example, which has an increased linear speed compared to Example 3, the amount of overshoot in the central temperature can be kept within 155 ± 8°C, and gloss unevenness can be suppressed.

[0070] Table 7 shows the experimental results for Comparative Example 2 when switching from SRA3 size to A4 size. [Table 7]

[0071] <Condition> The rest of the description is the same as in Example 5 except for the power distribution before switching. Power of the first heating source immediately after printing starts at 100V input: 700W Power of the second heating source immediately after printing starts at 100V input: 455W

[0072] The average power of the first heating source for the 40th sheet was 442 W, and the average power of the first heating source for the 41st sheet was 700 W. The increase rate was (700-442) / 442=0.58>0.5, and at this time the belt temperature TQ exceeded the range of 155±8°C, and the central temperature showed gloss unevenness ×. Furthermore, in the same experiment as in Conventional Example 2, when the paper gap between N=40 and N=41 sheets was extended to 750 mm and the paper gap time was extended to 3, the maximum pre-nip temperature on the 41st sheet was 157°C and the gloss unevenness was ○. However, extending the paper gap creates a waiting time, which is an issue that deteriorates usability.

[0073] <Modification> Although a sliding configuration of a sliding sheet on a resin pad is used, a rubbing configuration using a heat conduction auxiliary material such as aluminum may also be used. In this example, the paper width threshold X was set to 297 mm, and the lighting distribution was switched during printing, but the threshold is not limited to this. In this example, the lighting mode was switched on the 21st sheet in Examples 1 to 4 and on the 41st sheet in Example 5, but this number is not limited to this.

[0074] As described above, when the distribution change means changes the power distribution to increase the power distributed to the first heating source and decrease the power distributed to the second heating source, in order to ensure that the increase ratio of the power supplied to the first heating source for the first recording material after the power distribution change relative to the power supplied to the first heating source for the last recording material before the power distribution change is 0.5 or less, for example, the information stored in the power distribution change data table stored in a memory unit such as a ROM of the control unit 150 is set so that the increase ratio is 0.5 or less. [Explanation of symbols]

[0075] 3: Feed roller 4: Registration roller pair 5: Secondary transfer roller 7: Paper ejection roller 8: Optical writing device 8um: surface layer 9Bk: Toner bottle 9C: Toner bottle 9M: Toner bottle 9Y: Toner bottle 10: Intermediate transfer belt unit 11: Intermediate transfer belt 12Bk: Primary transfer roller 12C: Primary transfer roller 12M: Primary transfer roller 12Y: Primary transfer roller 13: Intermediate transfer cleaning device 15um: surface layer 17: Paper output tray 20Bk: Photosensitive drum 20C: Photosensitive drum 20M: Photosensitive drum 20Y: Photosensitive drum 30Bk: Charging device 40Bk:Developing device 50Bk: Cleaning device 61: Sheet feeding device 71: Transfer device 72: Elastic roller 73: Driven roller 80: Operation panel 100: Fixing device 101: Fixing belt 102a: Main heater 102b: Sub-heater 103: Pressure roller 104: Elastic rubber layer 105: Core 106: Pad 107: Support member 109: Reflector 110: Temperature detection sensor 116: Sliding member 150: Control unit 200: Printer L: Heat generation area Lb: Writing light N: Fixing nip S: Paper [Prior art documents] [Patent documents]

[0076] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-148721

Claims

1. An image forming apparatus including an image forming unit for forming an image on a recording material and a fixing device for fixing the image on the recording material at a fixing section, the fixing device includes a fixing member, a first heating source and a second heating source that heat the entire width of a width direction region of the fixing member corresponding to a maximum paper-passable recording material width with heat distribution characteristics different from each other, and an allocation change unit that changes the allocation of input power to the first heating source and the second heating source in accordance with image formation conditions; the first heating source has a heat distribution characteristic of uniform heat generation distribution in a width direction of the fixing member, the second heating source has a heat distribution characteristic in which the heat generation amount corresponding to both sides in the width direction of the maximum size width is higher than the heat generation amount at the center, when the distribution change means changes the power distribution to increase the power distribution to the first heating source and decrease the power distribution to the second heating source, an increase rate of the power input to the first heating source for the first recording material after the power distribution change relative to the power input to the first heating source for the last recording material before the power distribution change is 0.5 or less, an image forming apparatus, characterized in that the time required for the last recording material and the first recording material to pass through the fixing section is 3 seconds or less;

2. In the image forming apparatus according to claim 1, a temperature detecting means for detecting the temperature in a width direction area of ​​the fixing member corresponding to a minimum width of a recording material that can be passed; An image forming apparatus characterized in that at least the first heat source is controlled based on the detection result of the temperature detection means.

3. 3. The image forming apparatus according to claim 1, An image forming apparatus characterized in that, when the fixing target is switched from a recording material of a first width to a recording material of a second width narrower than the first width, a power distribution change is made to increase the power distributed to the first heating source and decrease the power distributed to the second heating source.

4. 4. The image forming apparatus according to claim 1, The fixing device the fixing member is an endless fixing belt, a pressure member that presses the recording material together with the fixing belt, and a forming member that is provided inside the fixing belt and forms a nip that is the fixing portion, The image forming apparatus is characterized in that the second heat source is located upstream of the first heat source in the moving direction of the fixing belt relative to the nip.

Images