Image forming device

Abstract

To prevent an increase in size or a reduction in cost of an image forming apparatus.SOLUTION: An image forming apparatus 100 comprises: a heater 9 having a heating member 22; a developing device 4; and an air current generator 35. In the heating member 22, the maximum total value, of total values of the square of a current flowing in one or more conductive parts at an arbitrary position in a longitudinal direction on one end A in a heating area H, is larger than the maximum total value of total values of the square of a current flowing in one or more conductive parts at an arbitrary position in a longitudinal direction on the other end B in the heating area H. The developing device 4 has a rotating member, and a plurality of slide parts that slide relatively in relation to the rotating member. Of the plurality of slide parts, a slide part reaching the highest temperature is arranged on the one end A in the longitudinal direction of the developing device 4. The air current generator 35 generates an air current 55 on the one end A.SELECTED DRAWING: Figure 13

Description

[Technical Field]

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

[0002] 2. Description of the Related Art In image forming devices such as printers, in order to suppress temperature increases in the various devices installed inside, an airflow generating device such as a blower fan is used to generate airflow within the image forming device body to cool the various devices.

[0003] For example, Patent Document 1 (JP 2007-279263 A) describes an image forming apparatus in which an air flow path for cooling a developing device and an air flow path for cooling a heating device (fixing device) are provided separately. Summary of the Invention [Problem to be solved by the invention]

[0004] In the heating device and developing device installed in the image forming apparatus, the degree of temperature rise may vary from part to part due to variations in the amount of heat generated in the heat source or differences in frictional heat generated in sliding parts, etc. In such cases, it is preferable to effectively cool the parts where the temperature becomes particularly high.

[0005] However, if separate air flow paths are provided for cooling the developing device and the heating device, as in the conventional method (Patent Document 1), the image forming apparatus will become larger and more expensive. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus including a heating device having a heating member, a developing device, and an airflow generating device, wherein the heating member has a base material, a heat generating element, an electrode portion, and a conductive portion connecting the heat generating element and the electrode portion, and the conductive portion is arranged such that the heat generating element is oriented in a direction intersecting the longitudinal direction along a surface of the heating member on which the heat generating element is provided, at one end side that is located on one side of the longitudinal direction relative to the center of the longitudinal direction in a heat generating region of the heating member, and at the other end side that is located on the opposite side of the longitudinal direction relative to the one end side. a plurality of heating devices are arranged one at a time or at intervals in a lateral direction of the heating device, and a temperature of the one end side in the heat generating region is higher than a temperature of the other end side, the developing device has a rotating member and a driving force input unit that inputs a driving force to the rotating member at one end side of the rotating member that is on one side of the longitudinal direction from the center of the longitudinal direction, the one end side of the developing device and the one end side of the heating device are arranged on the same side, and the airflow generating device generates an airflow at the one end side of the developing device and the one end side of the heating device. The temperature of the one end side of the heating device in the heat generating region being higher than the temperature of the other end side of the heating device means that the maximum sum of the squares of the currents flowing through a plurality of or one of the conductive parts at any position in the longitudinal direction of the one end side in the heat generating region is greater than the maximum sum of the squares of the currents flowing through a plurality of or one of the conductive parts at any position in the longitudinal direction of the other end side in the heat generating region. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, it is possible to prevent the image forming apparatus from becoming larger or more expensive. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a fixing device according to the present embodiment. [Figure 3] FIG. 2 is a perspective view of the fixing device. [Figure 4] FIG. 2 is an exploded perspective view of the fixing device. [Figure 5] FIG. 2 is a perspective view of a heating unit included in the fixing device. [Figure 6] FIG. 2 is an exploded perspective view of the heating unit. [Figure 7] FIG. 2 is a plan view of the heater according to the embodiment. [Figure 8] FIG. 2 is an exploded perspective view of the heater. [Figure 9] FIG. 4 is a perspective view showing a state in which a connector is connected to the heater. [Figure 10] FIG. [Figure 11] FIG. 10 is a diagram showing the amount of heat generated by the power supply lines for each block when all the resistance heating elements are made to generate heat. [Figure 12] 10 is a diagram showing the amount of heat generated by the power supply lines for each block when only some of the heat generating portions are made to generate heat. FIG. [Figure 13] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention, viewed from above; [Figure 14] FIG. 2 is a diagram showing the fixing device and each developing device as viewed from the horizontal direction. [Figure 15] 10A and 10B are diagrams showing an example in which a flow path forming member has a plurality of openings from which airflows are blown out. [Figure 16] FIG. 2 is a diagram illustrating an example of the overall configuration of a developing device. [Figure 17] FIG. 2 is a diagram showing each conveying screw and its supporting structure. [Figure 18] 10A and 10B are diagrams illustrating an example in which the diameters of the shaft portions at both ends of each conveying screw are different. [Figure 19] 4A and 4B are diagrams illustrating a drive transmission structure for each conveying screw. [Figure 20] 10A and 10B are diagrams showing an example in which a flow path forming member that blows out an airflow toward a bearing is provided. [Figure 21] 10A and 10B are diagrams showing an example in which a flow path forming member having a plurality of openings that individually blow out airflows toward a plurality of bearings is provided. [Figure 22] 10A and 10B are diagrams illustrating an example in which an airflow is blown onto a bearing from below in the direction of gravity. [Figure 23] FIG. 2 is a diagram showing a circulation path of developer in a developing device. [Figure 24] FIG. 1 is a diagram showing an example in which the present invention is applied to an image forming apparatus dedicated to A4 paper. [Figure 25] FIG. 10 is a plan view illustrating the configuration of a miniaturized heater. [Figure 26] FIG. 10 is a plan view of another heater. [Figure 27]FIG. 10 is a plan view of yet another heater. [Figure 28] FIG. 10 is a diagram illustrating the configuration of another fixing device. [Figure 29] FIG. 10 is a diagram illustrating the configuration of another fixing device. [Figure 30] FIG. 10 is a diagram illustrating the configuration of yet another fixing device. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and descriptions thereof will be omitted once they have been described.

[0010] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

[0011] The image forming apparatus 100 shown in FIG. 1 includes an image forming section 200, a transfer section 300, a fixing section 400, a recording medium supply section 500, and a recording medium discharge section 600.

[0012] The image forming section 200 has four imaging units 1Y, 1M, 1C, and 1Bk and an exposure device 6. Each of the imaging units 1Y, 1M, 1C, and 1Bk is detachable from the image forming apparatus main body. The imaging units 1Y, 1M, 1C, and 1Bk basically have the same configuration, except that they contain toner (developers) of different colors—yellow, magenta, cyan, and black—that correspond to the color separation components of a color image. Specifically, each of the imaging units 1Y, 1M, 1C, and 1Bk includes a photoconductor 2, a charging member 3, a developing device 4, and a cleaning member 5.

[0013] The transfer unit 300 includes a transfer device 8 that transfers an image onto a recording medium, such as paper. The recording medium is not limited to paper, such as plain paper, cardboard, thin paper, coated paper, label paper, or envelopes, but may also be a resin sheet such as an overhead projector. The transfer device 8 includes an intermediate transfer belt 11, four primary transfer rollers 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt member stretched by multiple rollers. Each primary transfer roller 12 contacts a photoconductor 2 via the intermediate transfer belt 11. This forms a primary transfer nip between the intermediate transfer belt 11 and each photoconductor 2, where the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other. Meanwhile, the secondary transfer roller 13 contacts one of the multiple rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11. This forms a secondary transfer nip between the intermediate transfer belt 11 and each photoconductor 2.

[0014] The fixing section 400 has a fixing device 9 that fixes an image on a sheet of paper. The detailed configuration of the fixing device 9 will be described later.

[0015] The recording medium supply unit 500 has a paper feed cassette 14 that stores paper P, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14.

[0016] The recording medium ejection section 600 has a pair of paper ejection rollers 17 that eject paper outside the image forming apparatus, and a paper ejection tray 18 on which the paper ejected by the paper ejection rollers 17 is placed.

[0017] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to FIG.

[0018] When the printing operation is started in the image forming apparatus 100, the photoconductors 2 and intermediate transfer belt 11 of the imaging units 1Y, 1M, 1C, and 1Bk start to rotate. Also, the paper feed rollers 15 start to rotate, causing the paper feed rollers 15 to feed paper P from the paper feed cassette 14. The fed paper P comes into contact with a pair of timing rollers 16 and is temporarily stopped.

[0019] In each of the imaging units 1Y, 1M, 1C, and 1Bk, the charging member 3 first charges the surface of the photoconductor 2 to a uniform high potential. Next, the exposure device 6 exposes the surface (charged surface) of each photoconductor 2 based on the image information of the original document read by the document reader or the print image information instructed to be printed from a terminal. This reduces the potential of the exposed area, forming an electrostatic latent image on the surface of each photoconductor 2. The developing device 4 then supplies toner to this electrostatic latent image, forming a toner image on each photoconductor 2. As each photoconductor 2 rotates, the toner image formed on each photoconductor 2 reaches the primary transfer nip (the position of the primary transfer roller 12), where it is transferred sequentially onto the rotating intermediate transfer belt 11 so as to overlap with the original. In this way, a full-color toner image is formed on the intermediate transfer belt 11. The image forming apparatus 100 can form a monochrome image using any one of the imaging units 1Y, 1M, 1C, and 1Bk, or can form a two-color or three-color image using any two or three of the imaging units. After the toner image is transferred from the photoreceptor 2 to the intermediate transfer belt 11, the cleaning member 5 removes any residual toner or foreign matter from each photoreceptor 2, preparing each photoreceptor 2 for the formation of the next electrostatic latent image.

[0020] The toner image transferred onto intermediate transfer belt 11 is transported to the secondary transfer nip (position of secondary transfer roller 13) as intermediate transfer belt 11 rotates, and is transferred onto the transported paper P by timing roller 16. Then, paper P is transported to fixing device 9, which fixes the toner image onto paper P. Thereafter, paper discharge roller 17 discharges paper P onto paper discharge tray 18, completing the series of printing operations.

[0021] Next, the configuration of the fixing device 9 according to this embodiment will be described.

[0022] As shown in FIG. 2, the fixing device 9 according to this embodiment includes a fixing belt 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, and a temperature sensor 19.

[0023] The fixing belt 20 is an endless belt member that contacts the unfixed toner-carrying surface of the paper P to fix the toner image to the paper P. The fixing belt 20 has a substrate made of polyimide. The material of the substrate is not limited to polyimide, but may be a heat-resistant resin such as PEEK, or a metal material such as nickel or SUS. To enhance durability and ensure releasability, a release layer made of a fluororesin such as PFA or PTFE may be provided on the outer peripheral surface of the substrate. An elastic layer made of rubber or the like may be provided between the substrate and the release layer. Furthermore, a sliding layer made of polyimide, PTFE, or the like may be provided on the inner peripheral surface of the substrate.

[0024] The pressure roller 21 is a counter rotating body disposed to face the outer circumferential surface of the fixing belt 20. The pressure roller 21 has a metal core, an elastic layer made of silicone rubber or the like provided on the outer circumferential surface of the core, and a release layer made of fluororesin or the like provided on the outer circumferential surface of the elastic layer.

[0025] The fixing belt 20 and the pressure roller 21 are pressed against each other (pressed together) by a biasing member such as a spring, and a nip N is formed between the fixing belt 20 and the pressure roller 21. When the pressure roller 21 is driven to rotate by a drive source provided in the image forming apparatus main body, the drive force is transmitted to the fixing belt 20 at the nip N, causing the fixing belt 20 to rotate. Then, as shown in FIG. 2 , when a sheet P carrying an unfixed image enters between the rotating fixing belt 20 and the pressure roller 21 (nip N), the sheet P is heated and pressed by the fixing belt 20 and the pressure roller 21 while being transported. As a result, the unfixed image on the sheet P is fixed to the sheet P.

[0026] The heater 22 is a heating member that heats the fixing belt 20. In this embodiment, the heater 22 has a plate-shaped base material 50, a first insulating layer 51 provided on the base material 50, a conductor layer 52 provided on the first insulating layer 51, and a second insulating layer 53 that covers the conductor layer 52. The conductor layer 52 also includes a heat generating portion 60 that generates heat when current is applied.

[0027] The substrate 50 is formed of a metal material such as stainless steel (SUS), iron, or aluminum. The material of the substrate 50 is not limited to a metal material, but may also be ceramic, glass, or the like. When the substrate 50 is formed of an insulating material such as ceramic, the first insulating layer 51 between the substrate 50 and the conductor layer 52 can be omitted. Metal materials, on the other hand, are highly durable against rapid heating and easy to process, making them suitable for reducing the cost of the heater. Among metal materials, aluminum or copper is particularly preferred because it has high thermal conductivity and is less likely to cause temperature unevenness. Furthermore, stainless steel allows the substrate 50 to be manufactured more inexpensively than aluminum or copper.

[0028] Each of the insulating layers 51, 53 is formed of an insulating material such as heat-resistant glass. Specifically, ceramic, polyimide, or the like is used as the material for each of the insulating layers 51, 53. In addition to the surface of the base material 50 on which the first insulating layer 51 and the second insulating layer 53 are provided, an insulating layer may also be provided on the opposite surface.

[0029] In this embodiment, the heat generating section 60 is disposed closer to the nip N than the substrate 50, but conversely, the substrate 50 may be disposed closer to the nip N than the heat generating section 60. In this case, however, the heat from the heat generating section 60 is transferred to the fixing belt 20 via the substrate 50, so it is preferable that the substrate 50 be made of a material with high thermal conductivity, such as aluminum nitride.

[0030] Furthermore, in this embodiment, in order to increase the efficiency of heat transfer from the heater 22 to the fixing belt 20, the heater 22 is arranged so as to be in direct contact with the inner circumferential surface of the fixing belt 20. However, this is not limiting, and the heater 22 may be arranged so as to be in indirect contact with the fixing belt 20 without contact or via a low-friction sheet or the like. Furthermore, the contact point of the heater 22 with the fixing belt 20 may be the outer circumferential surface of the fixing belt 20. However, in order to avoid deterioration of fixing quality caused by scratches on the outer circumferential surface of the fixing belt 20, it is preferable that the contact point of the heater 22 be the inner circumferential surface of the fixing belt 20.

[0031] The heater holder 23 is a heating member holding member that holds the heater 22 inside the fixing belt 20. The heater holder 23 is preferably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 22. In particular, when the heater holder 23 is made of a heat-resistant resin with low thermal conductivity, such as LCP or PEEK, the heat resistance of the heater holder 23 is ensured while heat transfer from the heater 22 to the heater holder 23 is suppressed, so the fixing belt 20 is heated efficiently.

[0032] The stay 24 is a reinforcing member disposed inside the fixing belt 20. The stay 24 supports the surface of the heater holder 23 opposite to the surface on the nip portion N side, thereby suppressing deflection of the heater holder 23 due to the pressure force of the pressure roller 21. This forms the nip portion N of a uniform width between the fixing belt 20 and the pressure roller 21. The stay 24 is preferably made of an iron-based metal material such as SUS or SECC to ensure its rigidity.

[0033] Temperature sensor 19 is a temperature detection unit that detects the temperature of heater 22. A control unit such as a microcomputer provided in the image forming apparatus main body controls the output of heater 22 based on the detection result of temperature sensor 19, thereby controlling the temperature of fixing belt 20 to a desired temperature (fixing temperature). Temperature sensor 19 may be either a contact type or a non-contact type. Known temperature sensors such as a thermopile, thermostat, thermistor, or NC sensor can be used as temperature sensor 19.

[0034] FIG. 3 is a perspective view of the fixing device 9 according to this embodiment, and FIG. 4 is an exploded perspective view thereof.

[0035] 3 and 4, the fixing device 9 according to this embodiment includes a device frame 40 formed in a rectangular frame shape. The device frame 40 includes a first device frame 25 integrally having a pair of side wall portions 28 and a front wall portion 27, and a second device frame 26 having a rear wall portion 29. The first device frame 25 and the second device frame 26 are assembled together by engaging a plurality of engagement protrusions 28a provided on each side wall portion 28 with a plurality of engagement holes 29a provided on the rear wall portion 29.

[0036] The fixing belt 20 and the pressure roller 21 are supported by a pair of side walls 28. Therefore, each side wall 28 has an insertion groove 28b for inserting the rotation shaft of the pressure roller 21. The insertion groove 28b is open at one end (toward the rear wall 29) and has a closed abutment at the opposite end. A bearing 30 is provided at this abutment to rotatably support the rotation shaft of the pressure roller 21. When the pressure roller 21 is supported by each side wall 28, a drive transmission gear 31 provided at one axial end of the pressure roller 21 is positioned in a state where it is exposed outside the side wall 28. Therefore, when the fixing device 9 is installed in the image forming apparatus main body, the drive transmission gear 31 is connected to a gear provided in the image forming apparatus main body. This enables the transmission of driving force from a drive source to the pressure roller 21. Furthermore, the drive transmission member that connects the drive source on the main body side and the pressure roller 21 is not limited to the drive transmission gear 31, but may be a belt mechanism having a belt and pulleys, or a coupling mechanism.

[0037] A pair of support members 32 is provided on both longitudinal ends of the fixing belt 20 to support the fixing belt 20, heater holder 23, stay 24, etc. Each support member 32 is formed with a guide groove 32a. When each support member 32 is inserted into the insertion groove 28b of each side wall portion 28 from the state shown in FIG. 4, the guide groove 32a of each support member 32 engages with the edge of the insertion groove 28b, and each support member 32 is assembled to each side wall portion 28. As a result, the fixing belt 20, heater 22, heater holder 23, and stay 24 are supported by each side wall portion 28 via each support member 32. In addition, a pair of springs 33 serving as urging members are provided between each support member 32 and the rear wall portion 29. The urging force of these springs 33 urges each support member 32 toward the front wall portion 27, thereby pressing the fixing belt 20 against the pressure roller 21 and forming the nip N.

[0038] The rear wall 29 is provided with a hole 29b as a positioning portion. Meanwhile, the image forming apparatus main body is provided with a protrusion 101 (see FIG. 4) as a positioning portion. When the protrusion 101 is inserted into the hole 29b of the fixing device 9, the protrusion 101 and the hole 29b fit together, thereby positioning the fixing device main body relative to the image forming apparatus main body. The position at which the hole 29b is provided is preferably closer to one of the ends of the rear wall 29 than the center in the longitudinal direction. By providing the hole 29b in such a position, the end side where the hole 29b is not provided is allowed to expand and contract in the longitudinal direction due to temperature changes, and distortion of the apparatus frame 40 can be suppressed.

[0039] FIG. 5 is a perspective view of the heating unit, and FIG. 6 is an exploded perspective view of the heating unit.

[0040] 5, the heater 22 and the heater holder 23 are arranged longitudinally in the longitudinal direction of the fixing belt 20 (or the axial direction of the pressure roller 21) when assembled inside the fixing belt 20. Similarly, the stay 24 is also arranged longitudinally in the longitudinal direction of the fixing belt 20.

[0041] 5 and 6, the heater holder 23 is provided with a rectangular accommodating recess 23a for accommodating the heater 22. The accommodating recess 23a is formed to have substantially the same shape and size as the heater 22. However, the longitudinal dimension L2 of the accommodating recess 23a is set to be slightly longer than the longitudinal dimension L1 of the heater 22. This prevents interference between the heater 22 and the accommodating recess 23a even if the heater 22 expands in the longitudinal direction due to thermal expansion, thereby suppressing distortion of the heater 22 and the heater holder 23.

[0042] The pair of support members 32 each have a C-shaped belt support portion 32b, a flange-shaped belt regulating portion 32c, and a support recess 32d. Each belt support portion 32b is inserted inside both longitudinal ends of the fixing belt 20. As a result, the fixing belt 20 is supported by each belt support portion 32b in a so-called free belt manner (no tension is applied to the fixing belt 20 when the fixing belt 20 is not rotating). On the other hand, each belt regulating portion 32c is not inserted inside the fixing belt 20 but is arranged to face the longitudinal end of the fixing belt 20. As a result, even if the fixing belt 20 moves (shifts) in the longitudinal direction, the longitudinal end of the fixing belt 20 comes into contact with the belt regulating portion 32c, thereby regulating the longitudinal movement (shift) of the fixing belt 20. Portions of the heater holder 23 and the stay 24 near their respective longitudinal ends are inserted into each support recess 32d. As a result, the heater holder 23 and the stay 24 are supported by the pair of support members 32.

[0043] 5 and 6, a positioning recess 23e serving as a positioning portion is provided on one end of the heater holder 23 from the center in the longitudinal direction. The fitting portion 32e of the support member 32 on the left side in FIGS. 5 and 6 fits into this positioning recess 23e, thereby positioning the heater holder 23 and the support member 32. On the other hand, the fitting portion 32e is not provided on the support member 32 on the right side in FIGS. 5 and 6. Therefore, the support member 32 is not positioned relative to the heater holder 23 in the longitudinal direction on the right side of the figures. In this way, in this embodiment, the heater holder 23 is positioned relative to the support member 32 only on one side in the longitudinal direction of the heater holder 23, allowing the heater holder 23 to expand and contract due to temperature changes.

[0044] 6, steps 24a that restrict movement of the stay 24 are provided near both ends of the stay 24 in the longitudinal direction. Each step 24a abuts against the support member 32, restricting movement of the stay 24 in the longitudinal direction relative to the support member 32. However, at least one of these steps 24a is disposed with a gap (backlash) between it and the support member 32. In this way, by disposing at least one step 24a with a gap between it and the support member 32, expansion and contraction of the stay 24 due to temperature changes is permitted.

[0045] FIG. 7 is a plan view of the heater 22 according to this embodiment, and FIG. 8 is an exploded perspective view thereof.

[0046] 8, a first insulating layer 51, a conductor layer 52, and a second insulating layer 53 are laminated on a base material 50 of the heater 22. The conductor layer 52 has a plurality of resistance heating elements 59A to 59G, as well as a plurality of electrode portions 61A to 61C and a plurality of power supply lines (conductive portions) 62A to 62D.

[0047] The plurality of resistance heating elements 59A to 59G are provided on the base material 50 via a first insulating layer 51. In FIGS. 7 and 8, if the direction of arrow Z, which is the arrangement direction of the resistance heating elements 59A to 59G, is defined as the "longitudinal direction" of the heater 22 and the base material 50, the resistance heating elements 59A to 59G are arranged in a line across the longitudinal direction Z of the base material 50. A heat generating section 60 is formed on the base material 50 by these resistance heating elements 59. The resistance heating elements 59A to 59G are also arranged at intervals from one another in the longitudinal direction Z. For this reason, an insulating region (second insulating layer 53) is interposed between adjacent resistance heating elements 59A to 59G.

[0048] 7 and 8, if a direction Y that intersects with the longitudinal direction Z along the surface of the base material 50 on which the resistance heating elements 59 are provided is defined as the "short side direction," the power supply lines 62A to 62D are arranged at intervals from one another in the short side direction Y.

[0049] 7, the entire resistance heating elements 59A to 59G and most of the power supply lines 62A to 62D are covered with the second insulating layer 53 to ensure insulation. On the other hand, the electrode portions 61A to 61C are exposed and hardly covered with the second insulating layer 53, because they are connected to connectors (described later) that serve as power supply members.

[0050] Each of the resistance heating elements 59A to 59G is formed by, for example, screen-printing a paste prepared by mixing silver palladium (AgPd) or glass powder onto the substrate 50, and then firing the substrate 50. The material of the resistance heating elements is a resistance material such as silver alloy (AgPt) or ruthenium oxide (RuO2).

[0051] The electrode portions 61A to 61C and the power supply lines 62A to 62D are formed of a conductor having a resistance value smaller than that of the resistance heating element. Specifically, the electrode portions 61A to 61C and the power supply lines 62A to 62D are formed by screen printing a material such as silver (Ag) or silver-palladium (AgPd) on the base material 50.

[0052] FIG. 9 is a perspective view showing a state in which the connector 70 is connected to the heater 22. As shown in FIG.

[0053] As shown in Fig. 9, connector 70 has a resin housing 71 and a plurality of contact terminals 72. Each contact terminal 72 is a conductive elastic member such as a leaf spring. Each contact terminal 72 is provided in housing 71. A power supply harness 73 is connected to each contact terminal 72.

[0054] 9, the connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 together. As a result, the heater 22 and the heater holder 23 are held by the connector 70. In this state, the tip (contact portion 72a) of each contact terminal 72 elastically contacts (pressure-contacts) with the corresponding electrode portion 61, thereby electrically connecting each contact terminal 72 to each electrode portion 61. In this state, power is supplied to each of the resistance heating elements 59A to 59G from a power source provided in the image forming apparatus main body via the connector 70, causing each of the resistance heating elements 59A to 59G to generate heat.

[0055] The configuration of the heater 22 according to this embodiment will be described in more detail below with reference to FIG.

[0056] 10, the heater 22 according to this embodiment is provided with seven resistance heating elements 59A-59G, three electrode portions 61A-61C, and four power supply lines 62A-62D connecting these. Of the three electrode portions 61A-61C, two electrode portions 61A, 61C are arranged on one end side in the longitudinal direction Z of the substrate 50 (the left end side in FIG. 10), and the remaining electrode portion 61B is arranged on the other end side in the longitudinal direction Z of the substrate 50 (the right end side in FIG. 10). Each of the resistance heating elements 59A-59G is arranged between the corresponding electrode portion 61A, 61C on one end side and the electrode portion 61B on the other end side, and is electrically connected to one of the electrode portions 61A, 61C on one end side and the electrode portion 61B on the other end side.

[0057] Specifically, of the seven resistance heating elements 59A-59G, the five resistance heating elements 59B-59F other than those at both ends are connected in parallel to the left-side first electrode 61A via a first power supply line 62A. Meanwhile, the two resistance heating elements 59A and 59G at both ends are connected in parallel to the left-side third electrode 61C via a third power supply line 62C or a fourth power supply line 62D. Furthermore, all seven resistance heating elements 59A-59G are connected in parallel to the right-side second electrode 61B via a second power supply line 62B.

[0058] In this way, the resistive heating elements 59B-59F other than those at both ends and the resistive heating elements 59A, 59G at both ends are connected to different electrode portions 61A, 61C, respectively, so that each resistive heating element group can generate heat independently from one another. That is, when a voltage is applied to the first electrode portion 61A and the second electrode portion 61B to generate a potential difference between these electrode portions 61A, 61B, current flows only through the resistive heating elements 59B-59F other than those at both ends. Therefore, only the first heating portion 60A consisting of the resistive heating elements 59B-59F other than those at both ends generates heat. On the other hand, when a voltage is applied to the third electrode portion 61C and the second electrode portion 61B to generate a potential difference between these electrode portions 61C, 61B, current flows only through the resistive heating elements 59A, 59G at both ends. Therefore, in this case, only the second heating portion 60B consisting of the resistive heating elements 59A, 59G at both ends generates heat. Furthermore, when a voltage is applied to all of the electrode portions 61A to 61C to generate a potential difference between the first electrode portion 61A and the second electrode portion 61 and between the third electrode portion 61C and the second electrode portion 61B, a current flows through all of the resistance heating elements 59A to 59G, and therefore, both the first heating portion 60A and the second heating portion 60B generate heat.

[0059] In this manner, in this embodiment, the heat generation range can be changed by changing the electrode part to which voltage is applied. For example, when small-sized paper of A4 size or smaller is conveyed, only the first heat generation part 60A is made to generate heat, and when large-sized paper of A3 size or larger is conveyed, both the first heat generation part 60A and the second heat generation part 60B are made to generate heat, thereby making it possible to set the heat generation range according to the paper width.

[0060] Here, the temperature variation (temperature distribution deviation) occurring in the heater 22 according to this embodiment will be described.

[0061] Generally, in a heater in which a resistance heating element and an electrode are connected via a power supply line, when the resistance heating element is heated, the power supply line also generates a small amount of heat due to the current passing through the power supply line. Therefore, depending on the heat distribution in the power supply line, there is a risk of variation in the temperature distribution of the heater. In particular, when the width of the power supply line is reduced as the heater becomes smaller, or when the current flowing through the heater is increased to accommodate an increase in the speed of an image forming apparatus, the amount of heat generated in the power supply line also increases, and the impact of this increases.

[0062] Fig. 11 shows the amount of heat generated in one or more power feeders in each block divided into sections for the resistance heating elements 59A to 59G and the total amount of heat generated in each block when 20% of the current flows through each of the resistance heating elements 59A to 59G. Fig. 11 shows the current flowing from the first electrode portion 61A to the second electrode portion 61B, but the current flowing through the heater 22 is not limited to direct current and may be alternating current.

[0063] Here, the calorific value (W) is expressed by the following formula (1), and therefore, in the table of FIG. 11, the calorific value is calculated as the square of the current (I) flowing through each power supply line for convenience. Therefore, the calculated calorific value is merely a simplified calculation and differs from the actual calorific value. Furthermore, in this embodiment, the portions of each power supply line 62A, 62B, 62D extending in the short direction Y are short, and the amount of heat generated in these portions extending in the short direction Y is small, so the amount of heat generated in these portions is ignored. Therefore, here, only the amount of heat generated in the portions extending in the longitudinal direction Z is calculated.

[0064]

number

[0065] The calculation method for the calorific value will be described using the first and second blocks in Fig. 11 as examples. In the first block, the current flowing through the first power feed line 62A is 100%, and the current flowing through the fourth power feed line 62D is 20%, so the sum of the squares of these values, 10,400 (10,000 + 400), is the total calorific value of the power feed lines in the first block. In the second block, the current flowing through the first power feed line 62A is 80%, the current flowing through the second power feed line 62B is 20%, and the current flowing through the fourth power feed line 62D is 20%, so the sum of the squares of these values, 7,200 (6,400 + 400 + 400), is the total calorific value of the power feed lines in the second block. In the other blocks, the calorific values are calculated using the same calculation method.

[0066] The graph in FIG. 11 shows the total heat generation amount of each block on the vertical axis. As shown in this graph, in this embodiment, the total heat generation amount of each power supply line is large in the blocks at both ends and conversely is low in the block near the center. Furthermore, the total heat generation amount of each power supply line is different between blocks symmetrical with respect to the center (for example, the first block and the seventh block). Specifically, in the heat generation region H in which the resistance heating elements 59A to 59G are arranged, if one side in the longitudinal direction Z from the center m is defined as "one end side A" and the side opposite the one end side A from the center m is defined as "the other end side B," the one end side A has a higher temperature than the other end side B. As such, the heat generation distribution of the power supply lines varies across the longitudinal direction Z, and this variation also causes variation in the heat generation distribution of the heater.

[0067] Furthermore, such temperature variations due to heat generation from the power supply lines are not limited to cases where all of the resistance heating elements are heated (as in the example shown in FIG. 11 ), but can also occur when only some of the resistance heating elements are heated. For example, if unintended current shunting occurs in the power supply lines, current will flow through paths that previously did not flow, potentially resulting in temperature variations. Unintended current shunting is likely to occur, for example, when the width of the power supply lines is reduced in the short direction of the heater in response to heater miniaturization, resulting in an increased resistance value of the power supply lines. Furthermore, unintended current shunting is also likely to occur when the resistance value of the resistance heating elements is reduced to increase the heat generation amount of the resistance heating elements in response to higher speeds of image forming apparatuses. In other words, when the resistance values of the power supply lines and the resistance values of the resistance heating elements become relatively closer as a result of miniaturization or higher speeds, current can flow through paths that previously did not flow, potentially resulting in temperature variations.

[0068] FIG. 12 shows an example of a case where an unintended current shunt occurs in this embodiment.

[0069] In this example, 20% of the current flows through each of the resistance heating elements 59B-59F (first heat generating portion 60A) other than those at both ends. However, in the second resistance heating element 59B from the left in the figure, a portion (5%) of the current that passed through this resistance heating element 59B flows to the side opposite the second electrode portion 61B (the left side of the figure) at the branch point X of the second power supply line 62B, resulting in unintended shunting. The shunted current passes through the leftmost resistance heating element 59A in FIG. 12, then passes through the third power supply line 62C, the third electrode portion 61C, and the fourth power supply line 62D, passes through the rightmost resistance heating element 59G, and then joins the second power supply line 62B. Note that in this case as well, the current flowing through the heater 22 is not limited to direct current, and may be alternating current.

[0070] The table and graph in Fig. 12 show the heat generation amount and the total amount generated in one or more power feeders for each block when an unintended shunt occurs. The method for calculating the heat generation amount is the same as the method described in the example shown in Fig. 11.

[0071] As shown in the table and graph in Figure 12, in this case too, the total heat generation of the power supply line is large in the blocks at both ends and conversely low in the block in the center, resulting in variation. However, in the case of Figure 12, contrary to Figure 11, the temperature of the block on the left side of the graph (the other end side B) is higher than that of the block on the right side (the one end side A).

[0072] As described above, in the fixing device according to this embodiment, the heater temperature distribution varies depending on the amount of heat generated by the power supply wires in each block. Furthermore, if the heater temperature distribution varies, the surface temperature of the fixing belt heated by the heater also varies, which may result in a decrease in quality, such as uneven gloss on the fixed image. In particular, when all of the resistance heating elements 59A to 59G are turned on (as in the example shown in FIG. 11), the temperature difference between one end and the other end in the longitudinal direction becomes large, so it is necessary to effectively cool the side with the higher temperature.

[0073] Therefore, in the image forming apparatus according to this embodiment, in order to effectively cool the side of the fixing device where the temperature is higher, a cooling airflow 55 is generated on the side of the fixing device 9 where the temperature is higher, as shown in FIG. 13.

[0074] 13 is a schematic diagram of an image forming apparatus 100 according to this embodiment as seen from above, with arrows in the figure indicating airflow 55 and its flow direction. In this case, in the fixing device 9 shown in FIG. 13, the portion to the left of the longitudinal center m of the heat generating region of heater 22 is the side (one end side A) where the temperature is relatively high. That is, the seventh block of resistance heating element 59G (see FIG. 11), which has the highest temperature when all of resistance heating elements 59A to 59G are activated, is disposed on the left side of fixing device 9.

[0075] In this way, by generating an airflow on the side (one end side A) of the fixing device 9 where the temperature is higher, the side where the temperature is higher can be cooled effectively, thereby suppressing temperature variations in the longitudinal direction.

[0076] In this embodiment, a blower fan 35 is provided as an airflow generating device that generates airflow 55. A suction fan may be provided instead of the blower fan 35. Furthermore, a flow path forming member 36 such as a duct or a partition plate that guides the airflow from the blower fan 35 to the fixing device 9 is provided inside the image forming apparatus 100.

[0077] To identify which side of the fixing device 9, one end side A or the other end side B, will have a higher temperature, the sum of the squares of the currents flowing through one or more power feeders at any longitudinal position within the heat generating region H can be calculated and compared. In the example shown in Fig. 11, the largest sum (the sum of the seventh block) of the sums of the squares of the currents flowing through one or more power feeders at any longitudinal position on the one end side A is greater than the largest sum (the sum of the first block) of the sums of the squares of the currents flowing through one or more power feeders at any longitudinal position on the other end side B. Therefore, the one end side A is identified as the side with a higher temperature.

[0078] Furthermore, the method of identifying the side where the temperature of the fixing device 9 is higher is not limited to the method of comparing the sum of the squares of the currents flowing through the power supply lines, but may also be performed by a method of detecting the temperature of the fixing device 9 or the heater 22. For example, temperature sensors for detecting the temperature of the heater 22 may be disposed at positions symmetrical to each other on one end side A and the other end side B, and the side where the temperature is higher may be identified by comparing the temperatures detected by these temperature sensors.

[0079] As shown in FIG. 13 , in the image forming apparatus 100 according to this embodiment, the airflow 55 blown by the blower fan 35 is used to cool the fixing device 9 and the multiple developing devices 4. It is generally known that the temperature of a developing device rises due to frictional heat generated between the developer and the conveying screw, or between the conveying screw and a sealing member. When the temperature of a developing device rises, the developer contained therein melts, and the molten developer solidifies, potentially forming aggregates, resulting in abnormal images. Therefore, the developing device must be cooled. However, the degree of temperature rise in a developing device is not uniform throughout the entire developing device but varies depending on the location. Therefore, to effectively prevent abnormal images due to temperature rise, it is necessary to identify the areas of the developing device where temperatures are particularly high and efficiently cool those areas.

[0080] One method for cooling both the fixing device and the developing device is to provide separate air flow paths for each device and generate airflows in the hotter parts of the fixing device and the developing device, as described in the above-mentioned Patent Document 1. However, this method requires a large amount of space to install the air flow paths, which can lead to problems such as an increase in the size and cost of the image forming apparatus.

[0081] 13, the sides of the fixing device 9 and each developing device 4 where the temperatures become higher are arranged on the left side of the figure, and the sides opposite to these higher temperatures are arranged on the right side of the figure. By arranging the sides of the fixing device 9 where the temperatures become higher and the sides of each developing device 4 where the temperatures become higher on the same side (one end side A) in this way, the fixing device 9 and each developing device 4 can be effectively cooled by generating a cooling airflow 55 only on one side (one end side A) of each device. This allows the fixing device 9 and each developing device 4 where the temperatures become higher to be effectively cooled using one air flow path and one airflow generator, so the number of air flow paths and airflow generators can be reduced, enabling a more compact and cost-effective image forming apparatus.

[0082] Generally, the amount of heat generated in the fixing device is greater than the amount of heat generated in the developing devices, so it is preferable to arrange each developing device 4 upstream of the fixing device 9 in the direction of the airflow, as shown in Figure 13. In other words, if the fixing device is located upstream of the developing devices, the airflow heated by the heat of the fixing device will be sent to the developing devices, reducing the cooling effect of the developing devices. In contrast, if each developing device 4 is located upstream of the fixing device 9, the airflow heated by the fixing device 9 will not flow toward each developing device 4, so each developing device 4 can be cooled effectively.

[0083] Furthermore, since heat (hot air) generated from the fixing device basically moves upward in the direction of gravity, the fixing device 9 may be disposed above the developing devices 4 in the direction of gravity, as in the example shown in Fig. 14. In this case, the developing devices 4 are less susceptible to the effects of heat generated from the fixing device 9, and therefore the developing devices 4 can be cooled more effectively.

[0084] 15, a flow path forming member 36 that guides the airflow may be provided with a plurality of openings 360 that blow out part of the airflow toward the fixing device 9 and each developing device 4. In this case, part of the airflow is blown from each opening 360 toward the fixing device 9 and each developing device 4, so that each device can be effectively cooled.

[0085] Hereinafter, specific examples of parts of the developing device that are likely to become hot will be described.

[0086] First, with reference to FIG. 16, an example of the overall configuration of a developing device will be described.

[0087] The developing device 4 shown in FIG. 16 includes a developing roller 41, a supply roller 42, a developing blade 43, and two conveying screws 44 and 45.

[0088] The developing roller 41 is a developer carrier that carries developer on its surface. The developer may be a non-magnetic one-component developer that does not contain carrier and consists only of non-magnetic toner, or a two-component developer that is a mixture of non-magnetic toner and magnetic carrier. The developing roller 41 is disposed opposite the photoreceptor 2. When the developing roller 41 rotates, the developer carried on its surface is transported to a position opposite the photoreceptor 2, and the developer is supplied to the photoreceptor 2.

[0089] The supply roller 42 is a developer supply member that supplies developer to the developing roller 41. The supply roller 42 is provided so as to come into contact with the surface (outer peripheral surface) of the developing roller 41. At the contact portion where the supply roller 42 and the developing roller 41 come into contact with each other, the developer is supplied from the rotating supply roller 42 to the developing roller 41.

[0090] The developing blade 43 is a developer regulating member that regulates the amount of developer on the developing roller 41. The tip of the developing blade 43 is disposed in contact with the surface of the developing roller 41 or with a small gap therebetween. When the developer supplied onto the developing roller 41 passes a position facing the tip of the developing blade 43 as the developing roller 41 rotates, the thickness of the developer is regulated to a uniform thickness. The developer on the developing roller 41 is then supplied to the surface of the photosensitive member 2.

[0091] The two conveying screws 44, 45 are conveying members that convey the developer inside the developing device 4. In the example shown in FIG. 16, the internal space of the developing device 4, in which the developer is accommodated, is divided by a partition wall 46 into an upper first storage space 56 and a lower second storage space 57. One of the conveying screws 44 is disposed in the upper first storage space 56, and the other conveying screw 45 is disposed in the lower second storage space 57. Furthermore, through holes 63a, 63b are provided in the partition wall 46 near both axial ends of each of the conveying screws 44, 45. Therefore, when each of the conveying screws 44, 45 rotates to convey the developer, the developer circulates inside the first storage space 56 and the second storage space 57 via the through holes 63a, 63b.

[0092] Furthermore, a supply port 65 for supplying developer from a toner cartridge (developer storage container) is provided on the top surface of the developing device 4. The developer supplied from the toner cartridge is first accommodated in the first storage space 56 via the supply port 65. The developer is then circulated within the developing device 4 by being transported by the transport screws 44, 45. This allows the supplied new developer to mix with the developer already in the developing device 4, making the state of the developer (the proportion of new developer) uniform and preventing problems such as color unevenness or background scumming.

[0093] FIG. 17 is a diagram showing the conveying screws 44 and 45 and their supporting structures.

[0094] 17, each of the conveying screws 44 and 45 is rotatably supported by a pair of bearings 47a and 47b at both axial ends thereof. Various bearings, such as rolling bearings and plain bearings, can be used as the bearings 47a and 47b. Furthermore, seal members 48a and 48b are provided at both axial ends of each of the conveying screws 44 and 45 to prevent developer from entering the bearings 47a and 47b.

[0095] Here, the seal members 48a, 48b are fixed so as not to rotate, and therefore, when the conveying screws 44, 45 rotate, the seal members 48a, 48b slide relative to the conveying screws 44, 45. At this time, frictional heat is generated at sliding portions 49 between the conveying screws 44, 45 and the seal members 48a, 48b, and the temperature of the developing device 4 rises due to this frictional heat.

[0096] A portion of the frictional heat generated in the sliding portion 49 is dissipated through the bearings 47a, 47b. However, the amount of heat dissipated from each bearing 47a, 47b varies depending on the volume of each bearing 47a, 47b. That is, the smaller the volume of the bearing, the smaller the heat capacity and therefore the amount of heat dissipated. Therefore, if the amount of heat generated in each sliding portion 49 is the same, the smaller the volume of the bearing, the more likely the temperature will rise.

[0097] Furthermore, in developing devices, one of a pair of bearings provided at both ends of the conveying screw may be smaller than the other due to reasons such as component layout. In such cases, the side where the smaller bearing is provided is likely to have a higher temperature. In the example shown in FIG. 17, of the bearings 47a and 47b supporting the conveying screws 44 and 45, the bearing 47a on the left side of the figure is smaller than the bearing 47b on the right side of the figure. Therefore, in the example shown in FIG. 17, the temperature is likely to rise on the left side of the developing device 4.

[0098] 17, the left bearing 47a, which has a smaller volume, should be arranged on the same side as the side where the temperature of the fixing device 9 becomes higher (one end side A). This causes the side where the temperature of the developing device 4 becomes higher and the side where the temperature of the fixing device 9 becomes higher to be on the same side, so that, as described above, it becomes possible to effectively cool the parts of the fixing device 9 and each developing device 4 where the temperature becomes higher using one air flow path and one airflow generating device.

[0099] 17, two types of bearings 47a and 47b with different volumes are used, but three or more types of bearings may be used. In this case, the bearing with the smallest volume among the bearings should be arranged on the side where the temperature of the fixing device 9 becomes high (one end side A).

[0100] Next, the example shown in FIG. 18 is an example in which the diameters d1 and d2 of the shaft portions at both ends of each conveying screw 44, 45 are different.

[0101] In developing devices, the diameters of the shaft portions at both ends of the conveying screw may be different for reasons such as component layout or to reduce frictional heat at the sliding portions of the seal members. In this case, the larger the diameter of the shaft portion, the longer the circumferential length of the shaft portion, resulting in a faster sliding speed at the sliding portions 49 of the seal members 48a, 48b. Furthermore, as the sliding speed increases, more frictional heat is generated at the sliding portions 49, resulting in a greater temperature rise. Furthermore, by making the shaft diameter at one end of the conveying screw larger than that at the other end, the volume of the bearing supporting the shaft portion at the larger diameter end may be reduced. In this case, the temperature of the bearing with the smaller volume is more likely to rise, further increasing the temperature at one end of the conveying screw. In the example shown in FIG. 18 , of the shaft portions at both ends of each conveying screw 44, 45, the diameter d1 of the shaft portion on the left side of the figure is larger than the diameter d2 of the shaft portion on the right side of the figure. Furthermore, bearing 47a on the left side of the drawing, which supports the shaft portion with a larger diameter, has a smaller volume than bearing 47b on the right side of the drawing. Therefore, in the example shown in Figure 18, a lot of frictional heat is generated in sliding portion 49 on the left side of developing device 4, and the temperature is likely to rise.

[0102] 18, the left sliding portion 49 (the sliding portion that slides against the shaft portion with the large diameter d1) and the left bearing 47a (the bearing with a small volume) should be arranged on the same side (one end side A) where the temperature of the fixing device 9 becomes high. This causes the side where the temperature of the developing device 4 becomes high and the side where the temperature of the fixing device 9 becomes high to be on the same side, so that, as described above, it becomes possible to effectively cool the parts of the fixing device 9 and each developing device 4 where the temperature becomes high using one air flow path and one airflow generating device.

[0103] In the example shown in FIG. 18, each conveying screw 44, 45 has a shaft portion with two different diameters and is provided with bearings 47a, 47b with two different volumes. However, the shaft diameters and bearing volumes may be three or more. In this case, among each shaft portion and each bearing, the sliding portion 49 that slides relative to the shaft portion with the largest diameter and the bearing with the smallest volume may be disposed on the same side as the side where the temperature of the fixing device 9 becomes high (one end side A). Furthermore, when there is only one sliding portion 49, it can be said that this one sliding portion 49 is the sliding portion that slides relative to the shaft portion with the largest diameter. Therefore, in this case, it is sufficient that the one sliding portion 49 is disposed on the same side as the side where the temperature of the fixing device 9 becomes high (one end side A).

[0104] FIG. 19 is a diagram showing the drive transmission structure of each of the conveying screws 44 and 45. As shown in FIG.

[0105] 19, in this example, an input gear 69 serving as a driving force input section is provided at one axial end of the conveying screw 45 shown at the top of the drawing. Further, on the axial opposite side of the input gear 69, transmission gears 67 and 68 serving as driving force transmission sections are provided at the ends of the conveying screws 44 and 45 so as to mesh with each other.

[0106] 19, when the developing device 4 is installed in the image forming apparatus, the input gear 69 is connected to a drive gear provided in the image forming apparatus main body. In this state, when the drive source provided in the image forming apparatus main body is driven, the drive force is input to one of the conveying screws 45 via the input gear 69, and the conveying screw 45 is driven to rotate. The drive force is then transmitted from one of the conveying screws 45 to the other of the conveying screws 44 via the transmission gears 67 and 68, so that the other of the conveying screws 44 is also driven to rotate in conjunction with the one of the conveying screws 45.

[0107] In this configuration in which the input gear 69 is provided on one side of the conveying screw 45, a particularly large load is generally applied to the sliding part 49 on the input gear 69 side or the sliding part 49 closest to the input gear 69. This increases the frictional heat generated in the sliding part 49 on the input gear 69 side, making it easier for the temperature to rise on the input gear 69 side.

[0108] 19, the input gear 69 and the sliding part 49 closest to it should be arranged on the same side (one end side A) where the temperature of the fixing device 9 becomes high. This causes the side where the temperature of the developing device 4 becomes high and the side where the temperature of the fixing device 9 becomes high to be the same side, so that, as described above, it becomes possible to effectively cool the parts of the fixing device 9 and each developing device 4 where the temperature becomes high using one air flow path and one airflow generating device.

[0109] 19, focusing on the conveying screw 44 on the lower side of the drawing, the right side of the drawing, where the transmission gear 68 is provided, can be said to be the driving force input side of this conveying screw 44. However, the driving force input portion in the present invention does not refer to the portion where the driving force is transmitted (input) from one conveying screw to the other conveying screw, but refers to the most upstream portion in a series of transmission paths where the driving force is transmitted via multiple conveying screws.

[0110] 20, a flow path forming member 36 having an opening 360 for blowing out an airflow may be provided on the input gear 69 side (one end side A). In this case, of the two bearings 47a on the input gear 69 side, the bearing 47a supporting the conveying screw 45 on which the input gear 69 is provided (the upper bearing 47a in FIG. 21) is particularly prone to temperature rise. For this reason, it is preferable that the distance g1 between the bearing 47a supporting the conveying screw 45 on which the input gear 69 is provided and the opening 360 be shorter than the distance g2 between the other bearing 47a (the lower bearing 47a in FIG. 20) and the opening 360. In other words, among the distances between multiple bearings and multiple openings, the distance between the bearing with the highest temperature and the opening is preferably shorter than the distance between the other bearings and the same opening. This allows the bearing with the highest temperature to be cooled effectively.

[0111] 21, the flow path forming member 36 may have a plurality of openings 360 that individually blow out airflows toward a plurality of bearings 47a on the input gear 69 side (one end side A). In this case as well, it is preferable that the distance g1 between the bearing 47a with the highest temperature (the upper bearing 47a in FIG. 21) and the opening 360 facing it be shorter than the distance g2 between the other bearing 47a (the lower bearing 47a in FIG. 21) and the opening 360 facing it.

[0112] However, if an airflow is to be blown axially toward the bearing 47a, the input gear 69 may obstruct the blowing of the airflow, making it difficult to blow the airflow effectively. Therefore, as shown in FIG. 22 , the airflow 55 may be blown toward the axial direction of the bearing 47a from a direction inclined with respect to the axial direction of the bearing 47a. In the example shown in FIG. 22 , the opening 360 of the flow path forming member 36 is positioned lower than the bearing 47a in the direction of gravity, and the airflow is blown obliquely upward from below the direction of gravity toward the bearing 47a. This makes it difficult for the input gear 69 to obstruct the airflow 55, allowing the airflow 55 to be blown effectively toward the bearing 47a. The direction in which the airflow is blown may be from above to obliquely downward in the direction of gravity, or any other direction, as long as it is inclined with respect to the axial direction of the bearing.

[0113] FIG. 23 is a diagram showing a circulation path of the developer in the developing device 4. As shown in FIG.

[0114] As shown in FIG. 23 , in this example, a supply port 65 for supplying developer is disposed in the first storage space 56 on the lower left side of the figure. Therefore, in this example, the developer supplied through the supply port 65 is first transported to the right side of the figure by the transport screw 45 disposed in the first storage space 56. Then, when the developer reaches the right end of the first storage space 56 in the figure, it moves to the second storage space 57 on the upper side of the figure through one of the through-holes 63b provided in the partition wall 46. The developer that has moved into the second storage space 57 is transported to the left side of the figure by the transport screw 44 disposed in the second storage space 57. Then, when the developer reaches the left end of the second storage space 57 in the figure, it moves back to the first storage space 56 through the other through-hole 63a provided in the partition wall 46. The lubricant is then transported in the same manner and circulates within the developing device 4.

[0115] As the developer circulates, it is pushed by the transport screws 44 and 45, generating pressure on the developer as it is transported. This pressure is particularly strong at the most downstream position of the developer transport path, where the developer is transported by the transport screws 44 and 45 from the position where the developer is supplied into the developing device 4 (supply port 65). In other words, in the example shown in FIG. 23 , the leftmost position of the second storage space 57 in the drawing is the most downstream position J of the developer transport path, and the pressure on the developer at this position J is particularly strong. The pressure on the developer also acts on the seal members 48 a and 48 b provided on the transport screws 44 and 45. Therefore, a large pressure acts on the seal member 48 a, which is located at or near the most downstream position J, generating particularly large frictional heat at the sliding portion 49 of the seal member 48 a.

[0116] 24, the most downstream position J of the developer transport path and the sliding portion 49 closest to the most downstream position J are arranged on the same side (one end side A) as the side where the temperature of the fixing device 9 becomes high. As a result, the side where the temperature of the developing device 4 becomes high and the side where the temperature of the fixing device 9 becomes high are on the same side, and therefore, as described above, it becomes possible to effectively cool the parts of the fixing device 9 and each developing device 4 where the temperature becomes high using one air flow path and one airflow generating device.

[0117] While specific examples of parts of the developing device that are prone to become hot have been described above, sliding parts that are prone to become hot are not limited to sliding parts of the seal member that slide against the conveying screw, which is a rotating member. The sliding part may also be, for example, a sliding part that slides relative to another rotating member, such as a developing roller or a supply roller. Furthermore, the number of sliding parts is not limited to multiple sliding parts, and may be only one.

[0118] In the above example, as one embodiment of the present invention, an airflow is generated on the side where the temperature is higher (one end side A) when all of the resistance heating elements 59A to 59G generate heat (in the example shown in FIG. 11). However, the present invention is not limited to this embodiment, and it may be possible to cool the side where the temperature is higher when some of the resistance heating elements 59B to 59F generate heat and an unintended shunt occurs (in the example shown in FIG. 12). In other words, if the side where the temperature is higher changes from one end side to the other end depending on the usage mode, etc., it may be possible to selectively or additionally generate an airflow on the side where the temperature is higher (the other end side).

[0119] 12 includes a first conductive portion K1 extending from the first electrode portion 61A, a second conductive portion K2 connected to the second electrode portion 61B, and a third conductive portion (branch path) K3 branching from the second conductive portion K2. In other words, in the example shown in FIG. 12, the first conductive portion K1 corresponds to the first power supply line 62 connecting the first electrode portion 61A to each of the resistance heating elements 59A-59G (first heating portion 60A) other than those at both ends. The second conductive portion K2 is a portion of the second power supply line 62B extending from each of the resistance heating elements 59B-59F other than those at both ends toward the first direction S1 in the longitudinal direction of the heater 22 (to the right in FIG. 12) and connected to the second electrode portion 61B. The third conductive part K3 includes a part extending from the branch part X of the second power supply line 62B in the second direction S2 opposite to the first direction S1, the third power supply line 62C, the third electrode part 61C, the fourth power supply line 62D, and the resistive heating elements 59A and 59G (second heating part 60B) at both ends. That is, the third conductive part K3 is a conductive path connected to the second conductive part K2 or the second electrode part 61B via the resistive heating elements 59A and 59G (second heating part 60B) at both ends and the third electrode part 61C without passing through the first conductive part K1.

[0120] In the above example, the present invention has been described using an example in which heaters are used differently depending on whether small size paper such as A4 size is being conveyed or large size paper such as A3 size is being conveyed. However, the present invention is not limited to image forming apparatuses that use different heaters depending on paper size, and can also be applied to image forming apparatuses that are dedicated to A4 paper or A3 paper and that are equipped with heaters of the same configuration to standardize parts.

[0121] In this case, in an image forming apparatus specifically for A4 paper, basically, only the resistance heating elements 59B-59F (first heating section 60A) other than those at both ends are used to generate heat, as in the example shown in Fig. 12. In this type of use, the temperature of the other end side B of the heater 22 (the side closer to the second direction S2 than the center m in the longitudinal direction) is higher than the temperature of the one end side A (the side closer to the first direction S1 than the center m in the longitudinal direction). Therefore, in this case, as shown in Fig. 24, the side where the temperature of the fixing device 9 is higher and the side where the temperature of each developing device 4 is higher are both located on the other end side B, and airflow 55 is generated on the other end side B.

[0122] On the other hand, in an image forming apparatus dedicated to A3 paper, all of the resistance heating elements 59A to 59G are turned on, and therefore, unlike an image forming apparatus dedicated to A4 paper, the temperature of the heater 22 becomes higher at one end side A (closer to the first direction S1 than the longitudinal center m) as shown in Fig. 11. Therefore, in this case, similar to the example shown in Fig. 13 above, the side where the temperature of the fixing device 9 becomes higher and the side where the temperature of each developing device 4 becomes higher are both located at one end side A, and airflow 55 is generated at one end side A.

[0123] As described above, according to the present invention, it is possible to effectively cool the hot parts of the fixing device and the developing device without providing separate dedicated air flow paths for each, thereby realizing a compact and cost-effective image forming apparatus. Furthermore, according to the present invention, it is possible to improve problems such as deterioration of image quality caused by variations in temperature distribution in the heater's longitudinal direction. Therefore, even if the heater is a small heater in which temperature distribution variations are likely to be significant, or a heater with increased heat output to accommodate higher speeds, such heaters can be actively used.

[0124] Incidentally, there are three methods for reducing the size of the heater in the short direction.

[0125] The first method is to reduce the size of the heat-generating portion (resistance heating element) in the transverse direction. However, this method reduces the size of the heat-generating portion in the transverse direction, thereby reducing the width of the heating area where the fixing belt is heated. This results in a problem of a higher peak temperature rise when attempting to maintain the same amount of heat applied to the fixing belt as before. If the peak temperature rise value increases, the temperature of an overheating detection device, such as a thermostat or fuse, located on the back surface of the heater may exceed its heat resistance temperature or the overheating detection device may malfunction. Furthermore, if the peak temperature rise value increases, the efficiency of heat transfer from the heater to the fixing belt also decreases, which is undesirable from the perspective of energy efficiency. As such, there are circumstances that make it difficult to adopt the method of reducing the heat-generating portion in the transverse direction.

[0126] The second method is to reduce the area in the short direction where the heating element, electrode, and power supply line are not provided. However, this method reduces the gap between the heating element and the power supply line or between the electrode and the power supply line, which may make it difficult to ensure insulation. In view of the current heater structure, it is difficult to further reduce the gap between the heating element and the power supply line or between the electrode and the power supply line.

[0127] The third method is to reduce the width of the power supply line in the transverse direction. This method is more feasible than the previous two methods. However, reducing the width of the power supply line increases its resistance, which can lead to unintended current shunting along the heater's conductive path and result in significant temperature variations. In particular, if the resistance of the heating element is reduced to increase the heat output of the heating element to accommodate faster image forming devices, the resistance of the power supply line and the resistance of the heating element become relatively close, making unintended current shunting more likely. Another possible method to avoid such unintended current shunting is to increase the cross-sectional area of the power supply line by increasing its thickness (the direction intersecting the longitudinal and transverse directions) by the amount of reduction in the width of the power supply line. This, however, makes it difficult to screen-print the power supply line, which would require a change in the power supply line formation method, making it difficult to adopt a solution that involves thickening the power supply line. Therefore, to achieve miniaturization of the heater in the short-side direction, it is necessary to reduce the length of the power supply line in the short-side direction in anticipation of an increase in resistance, and to take separate measures to prevent unintended shunting of current and variations in heat distribution that may occur as a result. Therefore, in the present invention, as described above, an airflow is generated on the side of the fixing device where the temperature is higher, making it possible to effectively suppress variations in temperature distribution.

[0128] Specifically, the present invention is expected to be particularly effective when applied to an image forming apparatus equipped with a small heater as follows.

[0129] Table 1 below shows the variation in heat generation distribution when the heater is miniaturized in the lateral direction. In the test to obtain the results shown in Table 1, the temperature difference between the center and end of the heat generation area in the longitudinal direction of each heater was measured when the ratio (R / Q) of the lateral dimension R of each resistance heating element 59A to 59G to the lateral dimension Q of the base material 50 shown in FIG. 25 was varied. The surface temperature of each heater was also measured using an infrared thermography (FLIR T620) manufactured by FLIR Systems. Note that when the lateral dimension ratio (R / Q) is 80% or more, the ratio of the lateral dimension of each resistance heating element 59A to 59G to the lateral dimension of the base material 50 becomes too large, making it practically difficult to secure space to install power feeders, so measurements were withheld.

[0130] [Table 1]

[0131] As shown in Table 1, the larger the transverse dimension ratio (R / Q), the larger the temperature difference between the center and ends of the heat generating region. Therefore, in heaters with a large transverse dimension ratio (R / Q), i.e., heaters that are compact in the transverse direction, there is a risk of significant temperature variation at both ends. In particular, in heaters with a transverse dimension ratio (R / Q) of 25% or more or 40% or more, the temperature difference between the center and ends of the heat generating region becomes large (5°C or more), and there is a risk of significant temperature variation at both ends. Therefore, the present invention is expected to be particularly effective when applied to image forming apparatuses equipped with heaters with a transverse dimension ratio (R / Q) of 25% or more but less than 80% or 40% or more but less than 80%.

[0132] Furthermore, the heater included in the fixing device according to the present invention is not limited to the heater 22 having block-shaped (quadrilateral) resistance heating elements 59A-59G as shown in FIG. 25. For example, the heater may be the heater 22 having resistance heating elements 59A-59G shaped like a folded straight line as shown in FIG. 26. In the heater 22 shown in FIG. 26, the lateral dimension R of the resistance heating elements 59A-59G does not refer to the thickness of a single linear portion of the folded resistance heating element, but refers to the lateral dimension of the entire resistance heating element. Furthermore, the substrate 50 may have a shape in which the lateral dimension Q varies depending on the position in the longitudinal direction Z. However, in this case, the lateral dimension Q of the substrate 50 is defined as the smallest lateral dimension of the substrate 50 within the longitudinal range (heat generating region) in which the resistance heating elements 59A-59G are arranged.

[0133] Furthermore, the heater may be a heater 22 as shown in Fig. 27. Unlike the heaters described above, the heater 22 shown in Fig. 27 has one resistance heating element 59 extending in the longitudinal direction Z of the substrate 50. This resistance heating element 59 is connected to a first electrode portion 61A and a second electrode portion 61B via two power supply lines 62A and 62B. In the example shown in Fig. 27, the electrode portions 61A and 61B are arranged on the same end side with respect to the longitudinal center m of the heat generating region H, and the power supply lines 62A and 62B extend in the longitudinal direction Z without being folded back.

[0134] Even in the heater 22 shown in Fig. 27, when a potential difference is generated between the electrode portions 61A, 61B to cause the resistance heating element 59 to generate heat, variations in temperature distribution occur. Specifically, in the example shown in Fig. 27, the currents flowing through the power feed lines 62A, 62B are set to 90%, 50%, and 10% at the center m in the longitudinal direction of the heat generating region H and at arbitrary symmetric positions α1, α2 on both ends e1, e2 of the center m. In this case, the amount of heat generated in each of the power feed lines 62A, 62B will be values as shown in the table in Fig. 27. As in the above example, the amount of heat generated will be expediently calculated as the square of the current flowing through each power feed line (I 2 )

[0135] As shown in the table in Figure 27, in this example, the total heat generation amount of each power supply line 62A, 62B is higher at the other end e2 (left end in the figure) in the longitudinal direction than at one end e1 (right end in the figure), resulting in temperature distribution variations in the longitudinal direction. Therefore, by applying the present invention to a fixing device equipped with such a heater, it is possible to effectively suppress temperature distribution variations. This makes it possible to improve problems such as degradation of image quality caused by temperature distribution variations in the heater.

[0136] Furthermore, a resistance heating element having PTC characteristics may be used to suppress variations in temperature distribution in the longitudinal direction. Here, PTC characteristics refer to a characteristic in which the resistance value increases as the temperature increases (i.e., the heater output decreases when a constant voltage is applied). Using a resistance heating element having PTC characteristics allows the heater to heat up quickly at low temperatures due to high output, and prevents excessive heating at high temperatures due to low output. For example, if the TCR coefficient of the PTC characteristics is approximately 300 to 4000 ppm / °C, costs can be reduced while ensuring the necessary resistance value for the heater. A TCR coefficient of 500 to 2000 ppm / °C is more preferable.

[0137] The temperature coefficient of resistance (TCR) can be calculated using the following formula (2). In formula (2), T0 is a reference temperature, T1 is an arbitrary temperature, R0 is the resistance value at reference temperature T0, and R1 is the resistance value at arbitrary temperature T1. For example, in heater 22 shown in FIG. 10, if the resistance value between first electrode portion 61A and second electrode portion 61B is 10 Ω (resistance value R0) at 25°C (reference temperature T0) and 12 Ω (resistance value R1) at 125°C (arbitrary temperature T1), then formula (2) gives the temperature coefficient of resistance as 2000 ppm / °C.

[0138]

number

[0139] Furthermore, the fixing device cooled by the cooling device according to the present invention is not limited to the fixing device shown in FIG. 2, but may be a fixing device such as those shown in FIGS.

[0140] 2, the fixing device 9 shown in Fig. 28 differs from the fixing device shown in Fig. 2 in that the nip portion N through which the paper P passes and the portion where the heater 22 heats the fixing belt 20 are located at different positions. Specifically, the heater 22 and the nip forming member 90 are located 180° opposite each other in the rotation direction of the fixing belt 20. Pressure rollers 91 and 92 are pressed against the heater 22 and the nip forming member 90 via the fixing belt 20.

[0141] The fixing device 9 shown in Fig. 29 is an example in which the pressure roller 92 on the heater 22 side of the fixing device shown in Fig. 28 is omitted, and furthermore, the heater 22 is formed in an arc shape to match the curvature of the fixing belt 20. In other respects, it is the same as the configuration shown in Fig. 28. In this case, since the heater 22 is formed in an arc shape, the contact length between the fixing belt 20 and the heater 22 in the belt rotation direction is ensured, and the fixing belt 20 can be heated efficiently.

[0142] 30 is an example in which belts 94 and 95 are arranged on either side of roller 93. In this case, as in the examples shown in FIGS. 28 and 29, nip portion N through which paper P passes and the portion heated by heater 22 are located at different positions. That is, nip forming member 90 contacts roller 93 via one belt 94 on the right side of the figure, and heater 22 contacts roller 93 via the other belt 95 on the opposite side.

[0143] By applying the present invention to an image forming apparatus equipped with any of the fixing devices shown in Figures 28 to 30 as described above, the fixing device and developing device can be effectively cooled while reducing the size and cost of the image forming apparatus.

[0144] Furthermore, the fixing device according to the present invention is not limited to a free-belt type fixing device that holds the fixing belt 20 with a pair of belt holding members (for example, a pair of support members 32 shown in FIG. 4). For example, the present invention can also be applied to a fixing device that holds the fixing belt by stretching it using a plurality of rollers or the like.

[0145] In addition, in the above-described embodiments, the present invention has been described as being applied to an electrophotographic image forming apparatus equipped with a fixing device, which is an example of a heating device, but the image forming apparatus according to the present invention is not limited to electrophotographic apparatuses. For example, the present invention can also be applied to an inkjet image forming apparatus equipped with a drying device (heating device) that heats paper to dry ink (liquid) on the paper. [Explanation of symbols]

[0146] 4. Developing device 9 Fixing device (heating device) 22 heater (heating element) 35 Blower fan (airflow generator) 36 Flow path forming member 44 Conveying screw (conveying member, rotating member) 45 Conveying screw (conveying member, rotating member) 49 Sliding part 55 Airflow 59 Resistance heating element (heating element) 60 Heat generating part 60A First heating element 60B Second heating section 61 Electrode section 61A 1st electrode part 61B 2nd electrode part 61C 3rd electrode part 62 Power supply line (conductive part) 69 Input gear (driving force input part) 100 Image forming device 360 opening H Heat generation area K1 First conductive part K2 Second conductive part K3 Third conductive part (branch path) m longitudinal center P Paper (recording medium) S1 1st direction S2 2nd direction Y Short side direction of heater (substrate) Z: Longitudinal direction of heater (substrate) [Prior art documents] [Patent documents]

[0147] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-279263

Claims

1. a heating device having a heating element; A developing device; An airflow generating device; An image forming apparatus comprising: the heating member has a base material, a heating element, an electrode portion, and a conductive portion connecting the heating element and the electrode portion; the conductive portion is disposed one by one at one end side of the heat generating region of the heating member that is closer to the center of the heat generating region in the longitudinal direction than the center of the heat generating region in the longitudinal direction, and the conductive portion is disposed at the other end side of the heat generating region of the heating member that is closer to the center of the heat generating region in the longitudinal direction than ..., and the conductive portion is disposed one by one at one end side of the heat generating region of the heating member that is closer to the center of the heat generating region in the longitudinal direction than the center of the heat generating region in the longitudinal direction. the temperature of the one end side of the heat generating region is higher than the temperature of the other end side, the developing device includes a rotating member and a driving force input portion that inputs a driving force to the rotating member, the driving force input portion being located at one end side of the rotating member that is closer to a center in the longitudinal direction than the center in the longitudinal direction, the one end side of the developing device and the one end side of the heating device are disposed on the same side, the airflow generating device generates airflows at the one end side of the developing device and the one end side of the heating device, An image forming device in which the temperature of one end of the heating device within the heat generation area is higher than the temperature of the other end of the heating device when the maximum sum of the squares of the currents flowing through multiple or one conductive part at any longitudinal position on the one end side within the heat generation area is greater than the maximum sum of the squares of the currents flowing through multiple or one conductive part at any longitudinal position on the other end side within the heat generation area.

2. A heating device having a heating element; A developing device; An airflow generating device; An image forming apparatus comprising: the heating member has a heat generating portion having at least one heat generating element, a first electrode portion, a second electrode portion, a first conductive portion connecting the heat generating portion and the first electrode portion, a second conductive portion extending from the heat generating portion toward a first direction in the longitudinal direction of the heating member and connected to the second electrode portion, and a third conductive portion branching from the second conductive portion, extending toward a second direction opposite to the first direction and connected to the second conductive portion or the second electrode portion without passing through the first conductive portion; the developing device includes a rotating member and a driving force input portion that inputs a driving force to the rotating member, the driving force input portion being located at one end side of the rotating member that is closer to a center in the longitudinal direction than the center in the longitudinal direction, the one end of the developing device and the one end of the heating member that is the second electrode portion side are disposed on the same side, The airflow generating device generates airflows at the one end side of the developing device and the one end side of the heating member in the image forming apparatus.

Images