JP7510109B2 - Heating device, fixing device, drying device, coating device, thermocompression device, image forming device - Google Patents

Description

The present invention relates to a heating device, a fixing device, a drying device, a coating device, a thermocompression device, and an image forming device.

Known devices equipped with a heating device include a fixing device that uses heat to fix toner on paper, and a drying device that dries ink on paper, which are devices installed in image forming devices such as copiers and printers.

For example, some of the fixing devices mentioned above include a cylindrical member such as a fixing belt, an opposing member such as a pressure roller, and a heating element. In this fixing device, the pressure roller and the fixing belt heated by the heating element are pressed together to form a fixing nip, and the image on the recording medium can be fixed by heating and pressurizing the recording medium through the fixing nip.

For example, Patent Document 1 (JP Patent Publication 05-107985 A) discloses an invention in which a nip is formed between the fixing roller and the pressure roller by applying a uniform load to the shaft of the fixing roller from both sides in the axial direction.

In a heating device, for example, when it is necessary to have a deviation in nip pressure, it is sometimes necessary to have a deviation in the pressure applied to the cylindrical member by the opposing member between one side and the other side of the central position in the longitudinal direction.

In order to solve the above problems, the present invention provides a heating device including a heating element having a planar heating element, a cylindrical member heated by the heating element, an opposing member that contacts the cylindrical member to form a nip between the cylindrical member and the first gear, a first gear provided on the opposing member and meshing with a second gear, and a pressurizing mechanism that presses the opposing member toward the cylindrical member, the opposing member being rotated by a driving force transmitted from the second gear to the first gear, and the rotation of the first gear being rotated on a plane perpendicular to the axial direction of the opposing member. If a line that passes through the rotation center and is inclined by the pressure angle of the first gear in the opposite direction to the rotation direction of the opposing member with respect to a straight line that passes through the rotation center and is parallel to the pressure direction of the pressure mechanism against the opposing member, is taken as a reference line, the meshing position of the second gear with respect to the first gear is provided on the same side of the reference line as the exit side of the nip portion , the heat generation amount of the heating element is smaller on one side in the longitudinal direction than on the other side, and in the longitudinal direction, the first gear is provided on the other side of the central position of the heating area of the heating element .

According to the present invention, the pressure applied by the opposing member to the cylindrical member can be made to deviate between one side and the other side with respect to the center position in the longitudinal direction.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a fixing device. FIG. FIG. FIG. FIG. FIG. FIG. FIG. 4 is a perspective view showing a state in which a connector is connected to the heater. FIG. 4 is a diagram showing power supply to a heater. FIG. 2 is a diagram showing a normal current path. FIG. 13 is a diagram showing a current path when unintended current shunting occurs. FIG. 11 is a diagram showing the amount of heat generated by the power supply lines for each block in the heater of FIG. 10 when unintended current shunting occurs. FIG. 11 is a diagram showing the amount of heat generated by the power supply lines for each block when power is supplied to all of the resistance heating elements in the heater of FIG. 10 . FIG. 11 is a plan view showing a heater different from that in FIG. 10 . FIG. 16 is a diagram showing the heat generation amount of the power supply lines for each block of the heater in FIG. 15 . 4A and 4B are diagrams illustrating a driving mechanism including a first gear that drives the pressure roller. FIG. 13 is a diagram showing an engagement position of the second gear with respect to the first gear. FIG. 13 is a diagram showing a driving force transmitted from a second gear to a first gear. FIG. 19 is a diagram showing the meshing position of the second gear with respect to the first gear, which is a diagram showing an arrangement different from that in FIG. 18 . 11A and 11B are diagrams illustrating the relationship between the combination of the configuration of the first gear and the side on which the pressure force of the pressure roller against the fixing belt is larger. FIG. 11 is a diagram showing a preferred range of meshing positions of the second gear with respect to the first gear. FIG. 13 is a side view showing a fixing device having a third gear. FIG. 13 is a diagram showing a case where a convex portion is provided on a stay. FIG. 13 is a diagram showing a case where a convex portion is provided on a heater holder. FIG. 11 is a diagram showing the heat generation amount of each group of power supply lines for a heater having the same configuration as that of FIG. 10 . FIG. 11 is a diagram showing the heat generation amount of each group of power supply lines for a heater having a different configuration from that in FIG. 10 . FIG. 11 is a diagram showing the heat generation amount of each group of power supply lines for a heater having a configuration different from that of FIG. 10 . FIG. 16 is a diagram showing the heat generation amount of each group of power supply lines for a heater having the same configuration as that of FIG. 15 . FIG. 30 is a diagram showing the heat generation amount of each group of power supply lines for heaters having different connection positions from the heater in FIG. 29 . FIG. 30 is a diagram showing the heat generation amount of each group of power supply lines for heaters having different connection positions from the heater in FIG. 29 . 11A to 11C are plan views showing heaters having different shapes of resistive heating elements. FIG. 13 is a plan view showing a heater having a configuration in which power supply lines extending in a direction intersecting the longitudinal direction are inclined. FIG. 13 is a plan view showing a heater in which a part of a power supply line is replaced with a resistance heating element. 11 is a diagram showing a heater configuration in which the arrangement of the electrode parts is different from that in FIG. 10, and power supply to the heater. FIG. 2 is a plan view showing the short-side dimension of a heater and the short-side dimension of a resistance heating element. FIG. 2 is a plan view showing the longitudinal dimension of a heater, the lateral dimension of the heater, and the lateral dimension of a power supply line. FIG. 13 is a diagram showing the configuration of another fixing device. FIG. 13 is a diagram showing the configuration of still another fixing device.

Embodiments of the present invention will be described below with reference to the drawings. In each drawing, the same or corresponding parts are given the same reference numerals, and duplicated explanations will be appropriately simplified or omitted. In the following explanation of each embodiment, a fixing device that fixes toner on paper by heat will be described as an example of a device equipped with a heating device.

The monochrome image forming device 1 shown in FIG. 1 is provided with a photoconductor drum 10. The photoconductor drum 10 is a drum-shaped rotating body capable of carrying toner as a developer on its surface, and rotates in the direction of the arrow in the figure. Around the photoconductor drum 10 are a charging roller 11 that uniformly charges the surface of the photoconductor drum 10, a developing device 12 equipped with a developing roller 7 that supplies toner to the surface of the photoconductor drum 10, and a cleaning blade 13 for cleaning the surface of the photoconductor drum 10.

An exposure unit is disposed above the photoconductor drum 10. Laser light Lb emitted by the exposure unit based on image data is irradiated onto the surface of the photoconductor drum 10 via the mirror 14.

In addition, a transfer means 15 equipped with a transfer charger is disposed opposite the photoreceptor drum 10. The transfer means 15 transfers the image on the surface of the photoreceptor drum 10 onto the paper P.

The paper feed section 4 is located at the bottom of the image forming device 1 and is made up of a paper feed cassette 16 that contains paper P as a recording medium or sheet, and a paper feed roller 17 that conveys the paper P from the paper feed cassette 16 to the conveying path 5. A registration roller 18 is disposed downstream of the paper feed roller 17 in the conveying direction.

The fixing device 9 includes a fixing belt 20 that is heated by a heating member described below, a pressure roller 21 that can apply pressure to the fixing belt 20, and the like.

The basic operation of the image forming device 1 will be described below with reference to FIG. 1.

When the printing operation (image forming operation) starts, the surface of the photoconductor drum 10 is first charged by the charging roller 11. Then, a laser beam Lb is irradiated from the exposure section based on image data, and the potential of the irradiated area is reduced to form an electrostatic latent image. Toner is supplied from the developing device 12 to the surface of the photoconductor drum 10 on which the electrostatic latent image has been formed, and the image is visualized as a toner image (developer image). Any toner remaining on the photoconductor drum 10 after transfer is removed by the cleaning blade 13.

When the printing operation is started, the paper feed roller 17 of the paper feed section 4 rotates at the bottom of the image forming device 1, sending the paper P stored in the paper feed cassette 16 to the transport path 5.

The paper P sent to the transport path 5 is timed by the registration rollers 18 and transported to the transfer section, which is the opposing section between the transfer means 15 and the photosensitive drum 10, at a timing that faces the toner image on the surface of the photosensitive drum 10, and the toner image is transferred by applying a transfer bias by the transfer means 15.

The paper P with the transferred toner image is transported to the fixing device 9, where it is heated and pressurized by the heated fixing belt 20 and pressure roller 21, fixing the toner image to the paper P. The paper P with the fixed toner image is then separated from the fixing belt 20, transported by a pair of transport rollers provided downstream of the fixing device 9, and discharged to a paper output tray provided outside the device.

Next, we will explain the configuration of the fixing device 9 in more detail.

2, the fixing device 9 according to the present embodiment has a heating device 80 including a fixing belt 20 as a cylindrical member or fixing member, a pressure roller 21 as an opposing member or pressure member that contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip N, and a heating unit 19 that heats the fixing belt 20. The heating unit 19 also has a heater 22 as a heating body, a heater holder 23 as a holding member that holds the heater 22, and a stay 24 as a support member that supports the heater holder 23. The fixing belt 20, the pressure roller 21, the heater 22, the heater holder 23, and the stay 24 extend in a direction perpendicular to the paper surface of FIG. 2 (see the direction of the double-headed arrow B in FIG. 3), and hereinafter, this direction is referred to as the longitudinal direction of each member, or the longitudinal direction of the heating unit 19 or the fixing device 9.

The fixing belt 20 is composed of an endless belt member, and has a cylindrical substrate made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of fluorine-based resin such as PFA or PTFE with a thickness of 5 to 50 μm is formed on the outermost layer of the fixing belt 20 to enhance durability and ensure releasability. An elastic layer made of rubber or the like with a thickness of 50 to 500 μm may be provided between the substrate and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

The pressure roller 21 has an outer diameter of, for example, 25 mm and is composed of a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm, which is thicker than the elastic layer of the fixing belt 20. In order to improve the release properties of the surface of the elastic layer 21b, it is desirable to form a release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm.

The pressure roller 21 is pressed against the fixing belt 20 by a pressure mechanism described later, and is pressed against the fixing belt 20. As a result, a fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The pressure roller 21 also functions as a drive roller that is rotated by a driving force transmitted from a drive means provided in the image forming apparatus body. Meanwhile, the fixing belt 20 is configured to rotate in response to the rotation of the pressure roller 21. When the fixing belt 20 rotates, the fixing belt 20 slides against the heater 22, so a lubricant such as oil or grease may be interposed between the heater 22 and the fixing belt 20 to improve the sliding property of the fixing belt 20.

The heater 22 is in contact with the inner surface of the fixing belt 20 at a position corresponding to the pressure roller 21. The heater 22 is a member for heating the fixing belt 20 as a heated member, and for heating the fixing belt 20 to a predetermined fixing temperature.

Unlike this embodiment, the heat generating section 60 may be provided on the opposite side of the substrate 50 from the fixing belt 20 side (the heater holder 23 side). In that case, since the heat from the heat generating section 60 is transferred to the fixing belt 20 via the substrate 50, it is desirable that the substrate 50 be made of a material with high thermal conductivity such as aluminum nitride. Furthermore, in the configuration of the heater 22 according to this embodiment, an insulating layer may be further provided on the surface of the substrate 50 opposite the fixing belt 20 (the heater holder 23 side).

The heater 22 may be in non-contact with the fixing belt 20 or indirectly contact with the fixing belt 20 via a low-friction sheet or the like, but in order to increase the efficiency of heat transfer to the fixing belt 20, it is preferable to have the heater 22 in direct contact with the fixing belt 20 as in this embodiment. The heater 22 can also be in contact with the outer peripheral surface of the fixing belt 20, but since there is a risk that the fixing quality will decrease if the outer peripheral surface of the fixing belt 20 is damaged by contact with the heater 22, it is preferable that the surface with which the heater 22 contacts is the inner peripheral surface of the fixing belt 20.

The heater holder 23 and the stay 24 are disposed inside the fixing belt 20. The stay 24 is made of a metal channel material, and both ends are supported by both side walls of the fixing device 9. The stay 24 supports the surface of the heater holder 23 opposite the heater 22 side, so that the heater 22 and the heater holder 23 are maintained without being significantly deflected by the pressure force of the pressure roller 21, and a fixing nip N is formed between the fixing belt 20 and the pressure roller 21.

The stay 24 supports the heater holder 23 by abutting a portion extending in the pressure direction of the pressure roller 21 (left and right direction in FIG. 2, see arrow FC) or a portion with thickness against the heater holder 23 from the side opposite the pressure roller 21 (left side in FIG. 2). This makes it possible to suppress bending of the heater holder 23 due to the pressure from the pressure roller 21 (particularly bending in the longitudinal direction in this embodiment).

The heater holder 23 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat of the heater 22. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP, the transfer of heat from the heater 22 to the heater holder 23 is suppressed, and the fixing belt 20 can be heated efficiently.

When the printing operation starts, power is supplied to the heater 22, which causes the heat generating section 60 to generate heat and heat the fixing belt 20. The pressure roller 21 is also rotated and the fixing belt 20 starts to rotate. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 2, the paper P carrying the unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (fixing nip N) (see the direction of arrow A in FIG. 2), and the unfixed toner image is heated and pressurized to be fixed to the paper P. In this way, the paper P is an object to be heated by the fixing device 9 (or the fixing belt 20).

Figure 3 is a perspective view of the fixing device, and Figure 4 is an exploded perspective view of the fixing device.

As shown in Figures 3 and 4, the device frame 40 of the fixing device 9 includes a first device frame 25 consisting of a pair of side walls 28 and a front wall 27, and a second device frame 26 consisting of a rear wall 29. The pair of side walls 28 are arranged at one end side and the other end side in the longitudinal direction, and both end sides of the fixing belt 20, the pressure roller 21, and the heating unit 19 are supported by the side walls 28. Each side wall 28 is provided with a plurality of engagement protrusions 28a, and the first device frame 25 and the second device frame 26 are assembled by each engagement protrusion 28a engaging with an engagement hole 29a provided in the rear wall 29.

Each side wall portion 28 is provided with an insertion groove 28b for inserting the rotating shaft of the pressure roller 21. The insertion groove 28b opens on the rear wall portion 29 side and is a butting portion that does not open on the opposite side. The rotating shaft of the pressure roller 21 is provided with a bearing 30 that supports the shaft portion. Each bearing 30 is inserted into each insertion groove 28b. This allows the pressure roller 21 to be rotatably supported by the side wall portions 28.

A pair of springs 33, which act as a pressure mechanism, contact each bearing 30. Each spring 33 biases the pressure roller 21 toward the fixing belt 20, so that the pressure roller 21 is pressed against the fixing belt 20, forming a fixing nip between the fixing belt 20 and the pressure roller 21.

A first gear 31 is provided on one end of the rotating shaft of the pressure roller 21. The first gear 31 is arranged in a state where it is exposed outside the side wall portions 28 with the pressure roller 21 supported by both side wall portions 28. As a result, when the fixing device 9 is mounted on the image forming apparatus main body, the first gear 31 is connected to a gear provided on the image forming apparatus main body, and is in a state where it can transmit driving force from a driving source described below. The other end of the rotating shaft of the pressure roller 21 is supported by the side wall portions 28 via a bearing 30, and no gear is provided on the other end side.

A pair of flanges 32 are provided at both longitudinal ends of the heating unit 19 to support the fixing belt 20, heater holder 23, stay 24, etc. Each flange 32 is provided with a guide groove 32a. The flanges 32 are assembled to the side wall portion 28 by inserting the guide grooves 32a along the edge of the insertion groove 28b of the side wall portion 28.

As shown in FIG. 4, one end of the rear wall 29 constituting the second device frame 26 in the longitudinal direction is provided with a hole 29b as a positioning portion for positioning the fixing device body relative to the image forming device body. On the other hand, the image forming device body is provided with a protrusion 101 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, and the fixing device body is positioned in the longitudinal direction relative to the image forming device body. Note that no positioning portion is provided on the end side opposite the end side where the hole 29b of the rear wall 29 is provided. This prevents the longitudinal expansion and contraction of the fixing device body due to temperature changes from being restricted.

Figure 5 is a perspective view of the heating unit 19, and Figure 6 is an exploded perspective view of the heating unit 19.

As shown in Figs. 5 and 6, the heater holder 23 has a rectangular storage recess 23a on the fixing belt side (the surface on the near side in Figs. 5 and 6) for storing the heater 22. The storage recess 23a is formed to have approximately the same shape and size as the heater 22, but the longitudinal dimension L2 of the storage recess 23a is set to be slightly longer than the longitudinal dimension L1 of the heater 22. In this way, the storage recess 23a is formed to be slightly longer than the heater 22, so that the heater 22 and the storage recess 23a do not interfere with each other even if the heater 22 expands in the longitudinal direction due to thermal expansion. In addition, the heater 22 is held in the storage recess 23a by being sandwiched together with the heater holder 23 by a connector, which will be described later, as a power supply member.

The pair of flanges 32 have a C-shaped belt support portion 32b that is inserted inside the fixing belt 20 to support the fixing belt 20, a flange-shaped belt regulation portion 32c that contacts the end face of the fixing belt 20 to regulate longitudinal movement (deviation), and support recesses 32d into which both end sides of the heater holder 23 and the stay 24 are inserted to support them. With the belt support portions 32b inserted into both end sides, the fixing belt 20 is supported in a so-called free belt manner in which basically no tension is generated in the circumferential direction (belt rotation direction) when the belt is not rotating.

As shown in Figures 5 and 6, a positioning recess 23e is provided as a positioning portion at one end of the heater holder 23 in the longitudinal direction. The fitting portion 32e of the flange 32 shown on the left side of Figures 5 and 6 fits into this positioning recess 23e, thereby positioning the heater holder 23 and the flange 32 in the longitudinal direction. On the other hand, the flange 32 shown on the right side of Figures 5 and 6 does not have a fitting portion 32e, and is not positioned in the longitudinal direction relative to the heater holder 23. In this way, by positioning the heater holder 23 relative to the flange 32 only on one side in the longitudinal direction, even if the heater holder 23 expands and contracts in the longitudinal direction due to temperature changes, the expansion and contraction is not restricted.

As shown in FIG. 6, steps 24a are provided on both longitudinal ends of the stay 24 to restrict movement of the stay 24 relative to each flange 32. Each step 24a abuts against the flange 32 to restrict longitudinal movement of the stay 24 relative to the flange 32. However, at least one of these step portions 24a is disposed with a gap (backlash) between it and the flange 32. In this way, by disposing at least one step portion 24a with a gap between it and the flange 32, even if the stay 24 expands and contracts in the longitudinal direction due to temperature changes, the expansion and contraction is not restricted.

Figure 7 is a plan view of the heater 22, and Figure 8 is an exploded perspective view of the heater 22.

As shown in FIG. 8, the heater 22 has a substrate 50, a first insulating layer 51 provided on the substrate 50, a conductor layer 52 having a heat generating portion 60 and the like provided on the first insulating layer 51, and a second insulating layer 53 covering the conductor layer 52. In this embodiment, the substrate 50, the first insulating layer 51, the conductor layer 52 (heat generating portion 60), and the second insulating layer 53 are laminated in this order toward the fixing belt 20 side (fixing nip N side), and the heat generated from the heat generating portion 60 is transferred to the fixing belt 20 via the second insulating layer 53 (see FIG. 2).

The substrate 50 is a longitudinal plate made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to metal materials, ceramics, glass, etc. can also be used as the material for the substrate 50. When an insulating material such as ceramics is used for the substrate 50, the first insulating layer 51 between the substrate 50 and the conductor layer 52 can be omitted. On the other hand, metal materials are excellent in durability against rapid heating and are easy to process, making them suitable for reducing costs. Among metal materials, aluminum and copper are particularly preferred because they have high thermal conductivity and are less likely to cause temperature unevenness. Stainless steel also has the advantage of being cheaper to manufacture than these.

Each insulating layer 51, 53 is made of an insulating material such as heat-resistant glass. Alternatively, ceramic or polyimide (PI) may be used as the material.

The conductor layer 52 is composed of a heating section 60 having multiple resistive heating elements (planar heating elements) 59, multiple electrode sections 61, and multiple power supply lines 62 as conductors that electrically connect these. Each resistive heating element 59 is electrically connected in parallel to any two of the three electrode sections 61 via multiple power supply lines 62 provided on the substrate 50. In this embodiment, seven resistive heating elements 59 are arranged in parallel in the longitudinal direction.

The resistance heating element 59 is formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the substrate 50 by screen printing or the like, and then firing the substrate 50. In addition to these, resistance materials such as silver alloy (AgPt) and ruthenium oxide (RuO ₂ ) may also be used as the material for the resistance heating element 59. In this embodiment, each resistance heating element 59 is provided with the same area and is set to generate the same amount of heat.

The power supply line 62 is made of a conductor with a resistance value smaller than that of the resistive heating element 59. The power supply line 62 and the electrode portion 61 can be made of a material such as silver (Ag) or silver palladium (AgPd), and the power supply line 62 and the electrode portion 61 are formed by screen printing or the like of such a material.

Figure 9 is an oblique view showing the connector 70 connected to the heater 22.

As shown in FIG. 9, the connector 70 serving as a power supply member has a resin housing 71 and a number of contact terminals 72 provided on the housing 71. Each contact terminal 72 is made of a leaf spring and is connected to a power supply harness 73.

As shown in FIG. 9, the connector 70 is attached so as to sandwich the heater 22 and heater holder 23 together from the front and back sides. In this state, the contact portions 72a provided at the tip of each contact terminal 72 elastically contact (pressure weld) with the corresponding electrode portions 61, electrically connecting the heat generating portion 60 to the power source provided in the image forming device via the connector 70. This makes it possible to supply power from the power source to the heat generating portion 60. Note that in order to ensure connection with the connector 70, at least a portion of each electrode portion 61 is not covered by the second insulating layer 53 and is exposed (see FIG. 7).

As shown in FIG. 10, the conductor layer 52 of this embodiment includes a plurality of resistive heating elements 59 arranged in the longitudinal direction of the substrate 50, a first electrode portion 61A, a second electrode portion 61B, and a third electrode portion 61C as electrode portions 61, and a first power supply line 62A, a second power supply line 62B, a third power supply line 62C, and a fourth power supply line 62D as power supply lines 62. Each power supply line 62 electrically connects the electrode portions 61 and the resistive heating elements 59.

Area C shown in FIG. 10 is the heating area in the longitudinal direction of the heater 22. The heating area of the heater 22 is the area where heat is generated by the resistance heating element 59 provided in the heater 22. Position C0 is the longitudinal center position of the heating area C, which coincides with the longitudinal center position of the fourth block described later.

Among the multiple resistive heating elements 59 arranged in the longitudinal direction of the substrate 50, the first heating section 60A consisting of the resistive heating elements 59 other than those at both ends, and the second heating section 60B consisting of the resistive heating elements 59 at both ends are configured to be independently heat-controllable. Specifically, the resistive heating elements 59 other than those at both ends constituting the first heating section 60A are connected to the third electrode section 61C provided at one end of the longitudinal direction of the substrate 50 via the third power supply line 62C. On the other hand, the resistive heating elements 59 at both ends constituting the second heating section 60B are connected to the first electrode section 61A (separate from the third electrode section 61C) provided at one end of the longitudinal direction of the substrate 50 via the first power supply line 62A or the fourth power supply line 62D. In addition, a second electrode section 61B is provided at the end opposite to the first electrode section 61A and the third electrode section 61C. Each resistive heating element 59 is connected to the second electrode portion 61B via a second power supply line 62B. In other words, the power supply lines 62 extending from each resistive heating element 59 join together and are connected to the second electrode portion 61B.

Each of the electrode units 61A to 61C is connected to a power source 64 via the connector 70 described above, and receives power from the power source 64. The first electrode unit 61A is provided with a switch 65A as a switching unit between the power source 64, and the application of voltage can be switched on and off by turning the switch 65A on and off. Similarly, the third electrode unit 61C is provided with a switch 65C as a switching unit between the power source 64, and the application of voltage can be switched on and off by turning the switch 65C on and off. Furthermore, the ON/OFF of these switches 65A and 65C and the timing of the power supply to the heater 22 are controlled by a control circuit 66. The control circuit 66 also performs these controls based on the detection results of various sensors in the image forming apparatus. For example, the timing of passing paper can be determined based on the detection results of sensors provided at the entrance and exit of the fixing nip N, and the supply of power to the heater 22 and the switching of the switches 65A and 65C can be performed. The control circuit 66 may be provided in the image forming device, or in the heating device or fixing device.

When a voltage is applied to the third electrode portion 61C and the second electrode portion 61B, the resistive heating elements 59 other than those at both ends are energized, and only the first heating portion 60A is heated. On the other hand, when a voltage is applied to the first electrode portion 61A and the second electrode portion 61B, the resistive heating elements 59 at both ends are energized, and only the second heating portion 60B is heated. Also, by applying a voltage to all the electrodes 61A to 61C, it is possible to heat both (all) the resistive heating elements 59 of the first heating portion 60A and the second heating portion 60B. For example, when a relatively small width paper of A4 size (paper passing width: 210 mm) or less is passed through, only the first heating portion 60A is heated, and when a relatively large width paper of more than A4 size (paper passing width: 210 mm) is passed through, the second heating portion 60B is also heated in addition to the first heating portion 60A, so that a heating area according to the paper width can be obtained.

Incidentally, in order to further reduce the size of image forming devices and fixing devices, it is important to reduce the size of the heater, which is one of the components arranged inside the fixing belt. That is, by reducing the size of the heater in its short-side direction (the direction of arrow Y in FIG. 10: the direction intersecting the long-side direction along the surface on which the heat generating parts 60A and 60B of the heater 22 are provided, or the direction perpendicular to the long-side direction of the heater 22 and different from the thickness direction of the heater 22, which is the direction perpendicular to the paper surface of FIG. 10), the diameter of the fixing belt can be reduced, which in turn makes it possible to reduce the size of the fixing device and image forming device. Specifically, the following methods can be given as examples of methods for reducing the size of the heater in the short-side direction.

The method is to reduce the size of the power supply line in the short direction. However, when the size of the power supply line is reduced in the short direction, the resistance of the power supply line increases, which may cause unintended current shunting on the heater's conductive path. In particular, when the resistance of the heating element is reduced in order to increase the amount of heat generated by the heating element to meet the increasing speed of 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 to occur. Therefore, in order to reduce the size of the heater in the short direction, it is necessary to reduce the size of the power supply line in the short direction in anticipation of an increase in resistance, and to take separate measures against the unintended current shunting that may occur as a result.

Below, we will explain unintended current diversion and the resulting problems using a heater with the same layout as heater 22 described above as an example.

In the heater 22 shown in FIG. 11, when a voltage is applied to the third electrode portion 61C and the second electrode portion 61B to heat only the resistive heating elements 59 of the first heating portion 60A, a current normally flows through the third power supply line 62C, passes through each resistive heating element 59 other than the two ends, and flows into the second power supply line 62B.

However, when the difference between the resistance of the power supply line and the heating part becomes small due to the increase in resistance of the power supply line caused by the miniaturization described above, or the decrease in resistance of the heating part caused by the increase in the amount of heat generated, an unintended branching of the current occurs, as shown in FIG. 12. That is, part of the current that passed through the second resistive heating element 59 from the left in FIG. 12 flows in the opposite direction to the second electrode part 61B at the branch part X of the second power supply line 62C. The branched current then passes through the resistive heating element 59 at the left end in FIG. 12, and further passes through the first power supply line 62A, the first electrode part 61A, the fourth power supply line 62D, and the resistive heating element 59 at the right end in this order, before joining the second power supply line 62B.

In this way, in the heater 22 shown in FIG. 12, the portion of the second power supply line 62B extending from the branch portion X to the left side of the figure, the resistive heating elements 59 at both ends constituting the second heating portion 60B, the first electrode portion 61A, and the portion including the first power supply line 62A and the fourth power supply line 62D constitute a branched conductive path E3 that allows current to flow through an unintended path.

In addition, such unintended branching can occur when electricity is applied to the first heating portion 60A if the conductive path of the heater 22 has at least a first conductive portion E1 connecting the first heating portion 60A and the third electrode portion 61C, a second conductive portion E2 extending from the first heating portion 60A in a first direction S1 (right side in Figure 12) of the longitudinal direction of the heater 22 and connected to the second electrode portion 61B, and a branch conductive path E3 branching from the second conductive portion E2 in a second direction S2 (left side in Figure 12) opposite to the first direction S1 and connected to the second conductive portion E2 or the second electrode portion 61B without passing through the first conductive portion E1. In other words, the above-mentioned shunting can occur when electricity is applied to the first heat generating part 60A under three conditions: "the first electrode part (first electrode part 61A) is connected to the resistive heating element 59 at both ends in the longitudinal direction," "the second electrode part (third electrode part 61C) is connected to the resistive heating element 59 at the center in the longitudinal direction," and "the power supply lines extending from each resistive heating element 59 join and are connected to the third electrode part (second electrode part 61B)." In this embodiment, the second heat generating part 60B and the first electrode part 61A are provided on the branched conductive path E3, but even in a conductive path that does not have the second heat generating part 60B and the first electrode part 61A or a conductive path that has a conductive member other than these, unintended shunting can occur.

When unintended current shunting occurs, the current flows through a previously unanticipated path, causing variations in the temperature distribution of the heater 22 due to heat generation from the power supply line. For example, in the heater 22 shown in FIG. 13, if 20% of the current flows evenly from the third electrode portion 61C to each resistive heating element 59 of the first heating portion 60A, and if the current passing through the second resistive heating element 59 from the left in the figure is shunted by 5% at the branch point X beyond that, the amount of heat generated in the power supply line within each block divided by the resistive heating elements 59 will be as shown in the table in the figure.

Here, the portion of each power supply line that extends in the short direction of the heater 22 is short, and the amount of heat generated in this portion is small, so this amount of heat is ignored, and only the amount of heat generated in the portion of each power supply line that extends in the longitudinal direction of the heater 22 is calculated. Specifically, the amount of heat generated in the portion of the heater 22 that extends in the longitudinal direction of each of the fourth power supply line 62D, the third power supply line 62C, and the second power supply line 62B that extends in the longitudinal direction is calculated. In addition, since the amount of heat generated (W) is expressed by the following formula (1), the amount of heat generated shown in the table of FIG. 13 is calculated as the square of the current (I) flowing through each power supply line for convenience. Therefore, the values of the amount of heat generated shown in the table of FIG. 13 are merely simply calculated values and differ from the actual amount of heat generated.

The method of calculating the amount of heat generated will be specifically described with reference to FIG. 13. In the first block, the current flowing through the fourth power supply line 62D is 5%, and the current flowing through the third power supply line 62C is 100%, so the sum of the squares of these is 10025 (25 + 10000), which is the total amount of heat generated by the power supply lines in the first block. In the second block, the current flowing through the fourth power supply line 62D is 5%, the current flowing through the third power supply line 62C is 80%, and the current flowing through the second power supply line 62B is 5%, so the sum of the squares of these is 6450 (25 + 6400 + 25), which is the total amount of heat generated by the power supply lines in the second block. In the other blocks, the amount of heat generated is calculated in a similar manner.

The total heat generation amount of each block shown in the table of Figure 13 is graphed below it. Due to the unintended current division described above, the total heat generation amount of each block is asymmetrical with respect to the fourth block in the center of the heat generation area. More specifically, the heat generation amount on one side in the longitudinal direction, which is the side of the first block, is greater than the heat generation amount on the other side in the longitudinal direction, which is the side of the seventh block.

Even when all the heating parts are energized, the amount of heat generated in the longitudinal direction of the heater 22 becomes asymmetric due to the difference in the magnitude of the current flowing through the power supply lines. Specifically, as shown in FIG. 14, when all the heating parts are energized, 20% of the current also flows through the resistance heating elements 59 at both the left and right ends and the power supply lines 62A and 62D connected thereto, which is different from the above case. In contrast, the value of the current flowing through the power supply line 62C is the same as before. In this case, in the first block, the current flowing through the fourth power supply line 62D is 20% and the current flowing through the third power supply line 62C is 100%, so the sum of the squares of each, 10400 (400 + 10000), is the total heat generated by the power supply lines in the first block. In the second block, the current flowing through the fourth power supply line 62D is 20%, the current flowing through the third power supply line 62C is 80%, and the current flowing through the second power supply line 62B is 20%, so the sum of these squares, 7200 (400 + 6400 + 400), is the total heat generation amount of the power supply lines in the second block. The heat generation amount is also calculated in the same way in the other blocks.

As shown in the table and graph of FIG. 14, the total heat generation amount of each block is asymmetrical with respect to the fourth block in the center of the heat generation area. In particular, the current value of the second power supply line 62B connected to all the resistance heating elements 59 is 120% higher downstream, i.e., in the seventh block, resulting in a difference in the heat generation amount between the left and right. More specifically, the heat generation amount on the other longitudinal side, which is the seventh block side, is greater than the heat generation amount on the one longitudinal side, which is the first block side. When actually measuring the heat generation amount of the heater 22, for example, the heat generation amount of the heater 22 alone is measured, and then the heat generation amount of the entire heater 22 including the resistance heating elements 59 and the power supply line 62 is measured.

We will also explain a heater 22 that generates a temperature difference between one side and the other side of the heat generation amount of the longitudinal power supply line, which is different from the heater 22 described above.

As shown in FIG. 15, the heater 22 of this embodiment includes a plurality of resistive heating elements 59, a first electrode portion 61A and a second electrode portion 61B as electrode portions 61, and a first power supply line 62A and a second power supply line 62B as power supply lines. In this embodiment, five resistive heating elements 59 are arranged in parallel in the longitudinal direction.

The first electrode portion 61A is connected to each resistive heating element 59 via a first power supply line 62A. The second electrode portion 61B is connected to each resistive heating element 59 via a second power supply line 62B. In this embodiment, the connection positions G1, G2 of the first power supply line 62A and the second power supply line 62B to each resistive heating element 59 are located to one side (the left side in the figure) of the longitudinal center position Qa of each resistive heating element 59.

The resistance heating element 59 differs from the heater 22 described above in that it is made of a wire portion that is folded back and forth in the longitudinal direction U of the heater 22 multiple times (three times in this embodiment) via bent portions on both sides in the short direction. In addition, all of the resistance heating elements 59 are connected to the same electrode portion 61A on one side in the longitudinal direction, and are made up of a single heating portion.

As shown in FIG. 16, even in the heater 22 described above, there is a temperature difference in the heat generation amount of the power supply line between one side and the other side in the longitudinal direction. Specifically, the heat generation amount of the first block is 6,800, which is smaller than the heat generation amount of the fifth block, 10,000, and the heat generation amount on the other side in the longitudinal direction is larger.

The above-described asymmetric variation in heat generation in the power supply lines causes temperature variation along the length of the heater 22. When the temperature of the heater 22 varies along the length, temperature unevenness occurs along the length of the fixing belt 20. Since the image fixed on the paper has high gloss in the high temperature areas and low gloss in the low temperature areas, the uneven temperature of the fixing belt 20 can cause uneven gloss on the paper, which can lead to a decrease in image quality. In this embodiment, the length of each block is set to be the same so that small and large size paper can be heated evenly.

The amount of heat generated can be verified by the following experiment. First, the heater itself is placed with both ends supported with the resistive heating element facing upwards. Then, AC voltage (100V) or DC voltage (20-80V) is supplied from an Omron temperature controller "E5EN" to the electrodes on both ends of the heater, operating the heater and generating heat to a specified temperature. The heater temperature is then measured using a FLIR T620 infrared thermography device made by FLIR Systems, which is placed above the heater. Deviations in the measured temperature make it possible to confirm deviations in the amount of heat generated. If deviations occur under any of the above conditions, the effect of the present application can be more pronounced.

Next, we will explain the configuration of this embodiment for suppressing temperature unevenness of the fixing belt 20 caused by longitudinal variations in the heat generation amount of the heater 22.

As shown in FIG. 17, the fixing device 9 is provided with a first gear 31, a second gear 41, and a motor 42 as a drive source.

The first gear 31 is attached to one end of the rotation shaft 21d of the pressure roller 21. In other words, the first gear 31 is provided on one side (the right side in the figure) of the center position C0 (see FIG. 10) of the heating area in the longitudinal direction.

The second gear 41 meshes with the first gear 31. The motor 42 is connected to the second gear 41 and transmits a driving force to the second gear 41. The motor 42 may transmit a driving force directly to the second gear 41, or another driving force transmission member may be provided between the second gear 41 and the motor 42.

In this embodiment, the second gear 41 is rotatably attached to the rear wall portion 29 of the fixing device 9. By attaching the second gear 41 to the frame portion of the fixing device 9, the precision between the first gear 31 and the second gear 41 can be improved. Therefore, the generation of vibration due to poor meshing between the first gear 31 and the second gear 41, and thus poor contact of the connector of the motor 42 can be suppressed. However, the second gear 41 and the motor 42 may be configured to be provided outside the fixing device 9, for example, on the frame of the image forming device.

The pressure roller 21 can move in the direction of approaching and separating from the fixing belt 20 within the fixing device 9. The pressure roller 21 is biased by springs 33 on both sides of the rotation shaft 21d in the direction of approaching the fixing belt 20, and is pressed against the fixing belt 20. The fixing belt 20 may be configured to have some play in the direction of approaching and separating from the fixing device 9, and the fixing belt 20 does not need to be completely fixed to the fixing device 9 in the direction of approaching and separating from the fixing belt 20.

As in this embodiment, the pressure roller 21 is configured to move toward and away from the fixing belt 20, which has the following advantages over a configuration in which the fixing belt 20 is moved:

The first advantage is that the position of the fixing nip N formed by the fixing belt 20 and the pressure roller 21 (the position in the vertical direction in FIG. 17) is less likely to shift, and the positional accuracy of the fixing nip N can be improved. In other words, in the case of a configuration in which the fixing belt 20 is brought into contact with and separated from the pressure roller 21, the position of the fixing nip N changes due to dimensional errors in the outer diameter of the pressure roller 21 and thermal expansion of the pressure roller 21. In particular, the silicone rubber constituting the elastic layer 21b (see FIG. 2) of the pressure roller 21 in this embodiment has a large linear expansion coefficient, and is prone to errors in the position of the fixing nip N. For example, in a fixing device having an outer diameter of the pressure roller 21 of 25 mm and a thickness of the elastic layer 21b of 3.5 mm as in this embodiment, a difference of 0.3 mm occurs in the position of the fixing nip N immediately after the fixing device 9 is started up and during continuous small size paper passing. On the other hand, in the case of the configuration of this embodiment, the pressure roller 21 moves, so the position of the fixing nip N hardly changes due to dimensional errors or thermal expansion of the pressure roller 21. In addition, the position error due to thermal expansion of the fixing belt 20 is slight. As mentioned above, the thickness of the elastic layer provided on the fixing belt 20 is set to 50 to 500 μm, and if the thickness of the elastic layer is 200 μm, the above-mentioned positional deviation of the fixing nip N due to thermal expansion is only about 10 μm. In this way, the configuration of this embodiment can improve the positional accuracy of the fixing nip N, and can prevent wrinkles on the paper due to deviation in the formation position of the fixing nip N and the occurrence of paper jams at the fixing nip N. Note that if the fixing belt 20 is configured without an elastic layer, the positional accuracy of the fixing nip N can be further improved.

The second advantage is that by configuring the side of the pressure roller 21 to come into contact with and separate from the pressure roller 21, rattle of the fixing belt 20 (rattle in the pressure direction of the pressure roller 21) is less likely to occur when the fixing device 9 is driven. In other words, if the side of the fixing belt 20 is configured to come into contact with and separate from the pressure roller 21, the fixing belt 20 vibrates in the pressure direction due to the whirling of the pressure roller 21 during rotation. The configuration of this embodiment suppresses vibration of the fixing belt 20, and prevents the electrical contacts of the heater 22 and connector from sliding and wearing out due to this vibration, which can cause poor connection between the heater 22 and the connector.

The driving force of the motor 42 is transmitted to the pressure roller 21 via the second gear 41 and the first gear 31. This causes the pressure roller 21 to rotate around the rotation shaft 21d. In addition, the fixing belt 20, which is pressed against the pressure roller 21, rotates in response to the pressure roller 21.

Next, the force that the second gear 41 applies to the first gear 31 and the pressure roller 21 will be described with reference to Figures 18 and 19. Note that in Figure 18 and other figures, for convenience, the first gear 31 is shown smaller than the pressure roller 21, but as shown in Figure 17, the diameter of the tooth tip circle of the first gear 31 is larger than the diameter of the pressure roller 21 (more details will be described later).

As shown in FIG. 18, the second gear 41 rotates in the direction of the arrow D2 to transmit the driving force of the motor to the first gear 31 that meshes with the second gear 41. At this time, the teeth of the second gear 41 apply a force F to the teeth of the first gear 31.

The direction of this force F is the direction of the force applied by the tooth surface of the second gear 41 to the tooth surface of the first gear 31, as shown in FIG. 19, and is inclined by the pressure angle α of the first gear 31 with respect to the direction of the tangent L between the first gear 31 and the second gear 41 (more specifically, the tangent L passing through the meshing position of both gears). In this embodiment, the pressure angle α of the first gear 31 is set to 20 degrees. The pressure angle is the angle between the radius line and the tangent to the tooth profile at one point on the tooth surface, and is in accordance with the Japanese Industrial Standards (JIS B 0102).

As shown in FIG. 18, of the force F that the first gear 31 receives from the second gear 41, the component force Fa in the direction in which the pressure roller 21 approaches and separates from the fixing belt 20 (left and right direction in the figure) faces the fixing belt 20. In other words, the first gear 31 in this embodiment receives the driving force of the motor from the second gear 41 and also receives a force in the direction approaching the fixing belt 20. Note that the above-mentioned direction in which the pressure roller 21 approaches and separates from the fixing belt 20 is, in other words, the direction in which the pressure roller 21 applies pressure to the fixing belt 20 and the opposite direction.

In this embodiment, the first gear 31 is provided on one longitudinal side of the rotating shaft 21d, that is, on one longitudinal side of the central position C0 (see FIG. 10) of the heating area. Therefore, on one longitudinal side, the pressure roller 21 receives a component force Fa in addition to the biasing force of the spring 33, and is pressed against the fixing belt 20. On the other longitudinal side, the pressure roller 21 is pressed against the fixing belt 20 only by the biasing force of the spring 33. In this way, due to the component force Fa, the pressure force of the pressure roller 21 on the fixing belt 20 is greater on one longitudinal side than on the other longitudinal side.

The direction of the component force Fa that the first gear 31 receives from the second gear 41 changes depending on the position at which the second gear 41 meshes with the first gear 31. For example, when the second gear 41 is disposed in the position shown in FIG. 20 relative to the first gear 31, the first gear 31 receives a force from the second gear 41 in the direction of arrow F, as shown in FIG. 20, and the component force Fa is in a direction away from the fixing belt 20 (to the right in the figure).

The boundary position where the direction of this component force Fa changes is the reference line H1 shown in FIG. 20. In other words, when the meshing position of the second gear 41 with the first gear 31 is located above the reference line H1 in the figure (the side of the fixing nip N where the paper exits, the exit side of the fixing nip N), the component force Fa is in a direction away from the fixing belt 20 as shown in FIG. 20. On the other hand, when the meshing position of the second gear 41 with the first gear 31 is located below the reference line H1 in the figure (the side of the fixing nip N where the paper enters, the entrance side opposite the exit side of the fixing nip N), the component force Fa is in a direction approaching the fixing belt 20 as shown in FIG. 18.

The reference line H1 will now be described.
The reference line H1 is a line that passes through the rotation center 31a of the first gear 31 on a plane (on the plane of FIG. 20) perpendicular to the axial direction of the pressure roller 21 and is inclined by a pressure angle α in the opposite direction (counterclockwise direction in FIG. 20) to the rotation direction D1 of the pressure roller 21 with respect to a straight line H0 (hereinafter referred to as the horizontal line H0) that is parallel to the pressure direction of the pressure roller 21. When the meshing position of the second gear 41 with the first gear 31 is on the reference line H1, the component force Fa becomes 0, and this position becomes the boundary position of the acting direction of the component force Fa.

A method for determining the reference line H1 will now be described.
If the second gear 41 and the first gear 31 were not gears but circular, the direction F of the force applied by the second gear 41 to the first gear 31 would be tangent to the two, and the boundary line would be the horizontal line H0. However, due to the meshing of the gears, as described above, the direction F of the force applied by the second gear 41 to the first gear 31 will be inclined from the tangent direction by the pressure angle α. Therefore, the reference line H1 will be a line inclined from the horizontal line H0 by the pressure angle α.

In this way, by changing the meshing position of the second gear 41 with respect to the first gear 31, the direction of the component force Fa can be set to be the same as the pressure direction of the pressure roller 21 or the opposite direction.

By combining the above-mentioned meshing position with whether the first gear 31 is provided on one side or the other side in the longitudinal direction with respect to the center position C0 of the heating area (see Figure 10), it is possible to change whether the pressure of the fixing belt 20 against the pressure roller 21 is relatively greater on one side or the other side in the longitudinal direction.

The above combinations are summarized in FIG.
As shown in FIG. 21, the pressure applied by the pressure roller 21 to the fixing belt 20 is increased on one side or the other side in the longitudinal direction depending on whether the first gear 31 is disposed on one side or the other side in the longitudinal direction, and whether the meshing position of the second gear 41 with respect to the first gear 31 is on the upper side or the lower side with respect to the reference line H1. In this manner, in this embodiment, the pressure roller 21 is provided so as to be able to approach and separate from the fixing belt 20, and the component force Fa of the second gear 41 that transmits the driving force to the pressure roller 21 (or the first gear 31) is utilized, so that the pressure applied by the pressure roller 21 to the fixing belt 20 can be relatively increased on any side in the longitudinal direction. In other words, the pressure applied by the pressure roller 21 can be made to have a deviation between one side and the other side in the longitudinal direction without providing a separate mechanism for adjusting the pressure applied by the pressure roller 21. Therefore, the nip pressure and nip width of the fixing nip N can be relatively increased on any side in the longitudinal direction. 20, the side above the reference line H1 in Fig. 21 is the same side as the exit Nb side of the fixing nip N with respect to the reference line H1, and the side below the reference line H1 in Fig. 21 is the opposite side to the exit Nb side of the fixing nip N. The nip width refers to the width of the fixing nip N in the vertical direction in Fig. 20 and the paper transport direction.

As shown in FIG. 13 or FIG. 14, in a configuration in which the temperature of the fixing belt 20 varies between one side and the other side in the longitudinal direction due to a deviation in the amount of heat generated by the power supply wire of the heater 22 in the longitudinal direction, the above-mentioned deviation in pressure can be used to suppress defects caused by this temperature deviation (specifically, uneven image and uneven gloss on the paper). In other words, by adopting a combination configuration in which the "pressure on the other side is large" in FIG. 21, when the amount of heat generated on one side in the longitudinal direction is larger than that on the other side, as in FIG. 13, the nip pressure and nip width of the fixing nip N can be relatively large on the other side in the longitudinal direction. Therefore, defects caused by the temperature deviation of the heater 22 between one side and the other side in the longitudinal direction, specifically, uneven image and uneven gloss on the paper, can be suppressed. Conversely, by adopting a combination configuration in which the "pressure on one side is large" in FIG. 21, when the heat generation amount on the other side in the longitudinal direction is larger than on one side, as in FIG. 14 and FIG. 16, the nip pressure and nip width of the fixing nip N can be relatively increased on one side in the longitudinal direction. This allows the nip pressure and nip width of the fixing nip N to be relatively increased on the side where the heat generation amount of the heater 22 is relatively small. Therefore, problems caused by the temperature deviation of the heater 22 between one side and the other side in the longitudinal direction, specifically, uneven image and uneven gloss of the paper, can be suppressed. In particular, in this embodiment, the pressure deviation is set by using a configuration that moves the pressure roller 21 toward and away from the fixing belt 20 without providing a separate mechanism for adjusting the pressure force as described above, and the effect of suppressing uneven image and uneven gloss of the paper can be obtained with a simple configuration.

In the above explanation, as an example of utilizing the pressure deviation, a case where the amount of heat generated by the heater 22 deviates between the left and right sides has been shown, but the present invention is not limited to this. For example, even if one side of the fixing belt 20 in the longitudinal direction is cooled due to the air flow inside the image forming device, causing a deviation in the temperature of the fixing belt 20 between one side and the other side in the longitudinal direction, by utilizing the configuration of the present embodiment described above, it is possible to suppress problems caused by the temperature deviation of the fixing belt 20, specifically, unevenness in the image and uneven gloss of the paper.

In addition, it is preferable that the meshing position of the second gear 41 with the first gear 31 is located away from the horizontal line H0. For example, as shown in FIG. 22, on a plane perpendicular to the axial direction of the pressure roller 21 (on the paper surface of FIG. 22), a line inclined by an angle β from the horizontal line H0 toward the rotation direction D1 of the pressure roller 21 is set as the second reference line H2, and a line inclined by an angle β in the opposite direction to the rotation direction D1 is set as the third reference line H3. In the circumferential direction of the first gear 31, it is preferable to set the meshing position of the second gear 41 with the first gear 31 in the regions J1 and J2 that do not include the horizontal line H0 among the four regions defined by the second reference line H2 and the third reference line H3.

In other words, if the meshing position of the second gear 41 with the first gear 31 is provided in the regions J3 and J4, the following problems will occur.
First, when the meshing position of the second gear 41 with the first gear 31 is located close to the horizontal line H0 and within the range J3 on the fixing belt 20 side, if the pressure roller 21 is located to the right of the target position when the pressure roller 21 is pressed against the fixing belt 20, for example, if the pressure roller 21 is highly rigid and does not sufficiently bite into the fixing belt 20 side, the first gear 31 and the second gear 41 will separate and will not mesh well with each other. Conversely, when the meshing position of the second gear 41 with the first gear 31 is located close to the horizontal line H0 and within the range J4 on the opposite side to the fixing belt 20 side, if the pressure roller 21 bites into the fixing belt 20 too much, the first gear 31 and the second gear 41 will similarly separate and will not mesh well with each other. In this way, when the first gear 31 and the second gear 41 are engaged at a position close to the horizontal line H0, an error in the positioning of the pressure roller 21 will have a large effect on the engagement between the first gear 31 and the second gear 41. Therefore, it is preferable that the engagement position of the second gear 41 with the first gear 31 is located away from the horizontal line H0, and is preferably located in the range J1 or J2. It is preferable to set β to 30 degrees.

In addition, in order to move the pressure roller 21 toward and away from the fixing belt 20, it is necessary to secure a movement area of the pressure roller 21 in the direction of movement toward and away from the fixing belt 20. However, if the meshing position of the second gear 41 with the first gear 31 is set within range J4, it becomes difficult to secure this movement area. From this perspective, it is preferable to set the meshing position of the second gear 41 with the first gear 31 outside range J4.

The diameter M1 of the tooth tip circle of the first gear 31 shown in FIG. 19 is preferably larger than the diameter M2 of the pressure roller 21 shown in FIG. 2 and smaller than the sum of the diameter M2 of the pressure roller 21 and the diameter M3 of the fixing belt 20. The relationship between the diameter of the first gear 31 and the magnitude of the force that the first gear 31 applies to the fixing belt 20 will be described below.

First, the driving force F applied to the first gear 31 can be expressed by the following formula (2). The driving force F increases in proportion to the driving torque FA of the first gear 31, and decreases as the size of the first gear 31 (the pitch circle diameter in formula 2) increases.

The driving torque FA increases in proportion to the friction force FB and the pressure roller diameter M2, as shown in the following equation (3).

The friction force FB is expressed by the following formula (4). Here, the friction coefficient μ is approximately 0.1 when a lubricant such as grease is present between the fixing belt 20 and the pressure roller 21, so from formula (4), the friction force FB is approximately 10% of the fixing load FC.

Therefore, when the pitch circle diameter M1' of the first gear 31 is larger than the diameter M2 of the pressure roller 21, the following formula (5) is obtained from formulas (2) to (4), and the force F applied by the second gear 41 to the first gear 31 can be set to a value of 10% or less of the fixing load. However, in this embodiment, instead of the pitch circle diameter M1' of the first gear 31, the tooth tip circle diameter M1 of the first gear 31 is made larger than the diameter M2 of the pressure roller 21.

If the force F applied by the second gear 41 to the first gear 31 becomes too large, the longitudinal deviation of the pressure applied from the pressure roller 21 to the fixing belt 20 becomes too large, which may cause the fixing belt 20 to shift to one side and become damaged. In this embodiment, the tooth tip circle diameter M1 of the first gear 31 is made larger than the diameter M2 of the pressure roller 21, thereby preventing damage to the fixing belt 20 due to shifting. In addition, the tooth tip circle diameter M1 of the first gear 31 is made smaller than the sum of the diameter M2 of the pressure roller 21 and the diameter M3 of the fixing belt 20, thereby preventing the fixing device 9 from becoming larger and the first gear 31 from becoming unnecessarily expensive.

The configuration of this embodiment makes it possible to provide a small deviation in the left and right pressure forces of the pressure roller 21 on the fixing belt 20, compared to a method in which deviation is provided only in the biasing forces of the left and right springs 33 (see FIG. 17) to adjust the left and right pressure forces of the pressure roller 21 on the fixing belt 20.

A third gear may be provided between the second gear 41 and the motor 42. For example, as shown in FIG. 23, a third gear 43 is provided that meshes with the second gear 41 and receives the driving force from the motor 42.

By providing the third gear 43, the driving force transmitted to the first gear 31 can be adjusted. That is, the third gear 43 applies a force F' to the second gear 41 by meshing with the second gear 41 and rotating in the direction of the arrow D3. The component force Fa' of this force F' is in the opposite direction to the component force Fa of the force F that the second gear 41 applies to the first gear 31. That is, the component force Fa' acts in a direction to reduce the component force Fa. Therefore, when the component force Fa is designed to be too large, the third gear 43 can be provided to prevent the component force Fa from becoming too large, and damage to the fixing belt 20 can be prevented. Note that the above arrangement is one example, and the meshing position of the third gear 43 with the second gear 41 and the tip circle radius of the third gear 43 can be set appropriately according to the magnitude of the required component force Fa'.

In addition, in this embodiment, when the pressure roller 21 is moved toward or away from the fixing belt 20, the first gear 31 and the second gear 41 rotate around the third gear 43. In other words, the first gear 31 (and the pressure roller 21) rotates in the direction of the double arrow K1 around the rotation center 43a of the third gear 43, and the second gear 41 moves in the direction of the double arrow K2. In other words, the pressure roller 21 can be moved toward or away from the fixing belt 20 without changing the relative positional relationship between the first gear 31, the second gear 41, and the third gear 43. Therefore, the pressure roller 21 can be moved toward or away from the fixing belt 20 while maintaining the positions at which the gears can mesh. Therefore, when the pressure roller 21 is pressed against the fixing belt 20, even if an error occurs in the positioning of the pressure roller 21 due to an error in the rigidity of the pressure roller 21, the gears can be meshed with high precision.

In this embodiment, the third gear 43 is provided, but the present invention is not limited to this. For example, as shown in FIG. 18, in a configuration in which only the first gear 31 and the second gear 41 are provided, the first gear 31 (and the pressure roller 21) may be rotated in the direction of the double arrow K1 around the rotation center 41a of the second gear 41. Even in this case, the pressure roller 21 can be moved toward and away from the fixing belt 20 without changing the relative positional relationship between the first gear 31 and the second gear 41.

Also, as shown in FIG. 24, the pressure roller 21 can be shaped like a drum, with the diameter at the center of the longitudinal direction being smaller than at the ends. This improves the transportability of the paper P and prevents the paper P from wrinkling when passing through the fixing nip.

However, by forming the pressure roller 21 into a drum shape as described above, the nip pressure between the pressure roller 21 and the fixing belt 20 becomes smaller at the center of the longitudinal direction. In response to this, as shown in FIG. 24, the support surface 24b1 of the support portion 24b of the stay 24 that supports the heater holder 23 is formed into a convex shape in which the center of the longitudinal direction protrudes toward the heater holder 23 side more than the end portion. The support portion 24b is a portion of the stay 24 that abuts against the heater holder 23 (heater 22 in a configuration that directly supports the heater 22) and supports the heater holder 23. This makes it possible to increase the nip pressure between the pressure roller 21 and the fixing belt 20 at the center of the longitudinal direction, and to increase the temperature of the fixing nip N at the center of the longitudinal direction. Therefore, the effect of the decrease in nip pressure caused by forming the pressure roller 21 into a drum shape as described above can be offset, and the temperature unevenness in the longitudinal direction of the fixing belt 20 or the fixing nip N can be suppressed.

In particular, the second moment of area increases in proportion to the cube of the length in the pressure direction, so by increasing the length of the stay 24 in the pressure direction of the pressure roller 21 (the up-down direction in the figure), the rigidity of the stay 24 in the pressure direction of the pressure roller 21 can be effectively increased.

Also, as shown in FIG. 25, the heater holder 23 includes a storage recess 23a serving as a holding portion for holding the heater 22, and the storage recess 23a can be made to have a convex shape with a thickness greater at the longitudinal center than at the ends. More specifically, the bottom surface of the storage recess 23a, which is a surface 23a1 that abuts against the heater 22, is made to have a convex shape with the longitudinal center protruding more toward the heater 22 than the ends. As a result, as in the case of the stay 24 described above, the nip pressure between the pressure roller 21 and the fixing belt 20 at the longitudinal center can be increased, and the temperature of the fixing nip N at the longitudinal center can be increased. This can suppress temperature unevenness in the longitudinal direction of the fixing belt 20.

In particular, by increasing the thickness of the longitudinal center portion of the heater holder 23, which has a low thermal conductivity (compared to the stay 24, etc.), the distance between the heater 22 and the stay 24 can be increased at the longitudinal center. Therefore, the amount of heat flowing from the heater 22 to the stay 24 at the longitudinal center can be reduced, and the temperature of the fixing nip N at the longitudinal center can be increased. This makes it possible to suppress temperature unevenness in the fixing belt 20 or the fixing nip N in the longitudinal center.

In the pressure direction of the pressure roller 21 (the vertical direction in the figure), as shown in FIG. 24, the protrusion amount of the support portion 24b toward the heater 22 side, that is, the protrusion amount of the longitudinal center of the support surface 24b1 toward the heater 22 side relative to the longitudinal end is the protrusion amount R1, or as shown in FIG. 25, the protrusion amount of the bottom surface 23a1 of the accommodating recess 23a of the heater holder 23 toward the heater 22 side of the convex shape, that is, the protrusion amount of the longitudinal center of the bottom surface 23a1 toward the heater 22 side relative to the longitudinal end is the protrusion amount R1, and the difference between the radius of the longitudinal end of the pressure roller 21 and the radius of the center is the squeeze amount R2, it is preferable that the protrusion amount R1 is greater than the squeeze amount R2 and smaller than the thickness R3 of the heater 22. By making the protrusion amount R1 greater than the squeeze amount R2, the nip pressure on the longitudinal center side can be effectively increased, and the temperature of the fixing nip N on the longitudinal center side can be appropriately increased. On the other hand, by making the protrusion amount R1 smaller than the thickness R3 of the heater 22, it is possible to prevent the pressure applied to the heater 22 from becoming too large and damaging the heater 22.

The above-mentioned convex shape may also be provided on both the stay 24 and the heater holder 23. In this case, the above-mentioned protrusion amount R1 is the sum of the protrusion amounts of both components, and it is preferable that this protrusion amount R1 is greater than the pinch amount R2 and smaller than the thickness R3 of the heater 22.

Also, as shown in Figures 24 and 25, from the viewpoint of suppressing temperature unevenness in the longitudinal direction of the fixing belt 20 or the fixing nip N, it is more preferable to provide both a convex shape for the pressure roller 21 and a convex shape for the stay 24 or heater holder 23. However, it is also possible to provide only one of these configurations.

The heater to which the present invention is applicable is not limited to the heater 22 arranged as shown in FIG. 10, FIG. 15, etc. By applying the present invention to a heater 22 in which a difference in heat generation occurs between one side and the other side in the longitudinal direction, it is possible to suppress problems caused by this temperature difference. Therefore, in the following explanation, examples of heaters 22 in which the arrangement of the electrode parts and power supply lines differs from that of FIG. 10 or FIG. 15 and in which a temperature difference occurs between one side and the other side in the longitudinal direction are given in order.

In the following, a simplified explanation will be given of the configuration of the heater 22. As an example, Fig. 26 shows a heater having basically the same configuration as Fig. 10 in terms of the arrangement of the electrodes and the like.
As shown in Fig. 26, a first group of resistive heating elements 69A, a second group of resistive heating elements 69B, and a third group of resistive heating elements 69C are arranged in parallel in the longitudinal direction of the heater 22. Each group of resistive heating elements may be one resistive heating element 59A-59C, or a plurality of resistive heating elements 59 arranged in parallel in the longitudinal direction. For example, when the heater 22 in Fig. 10 is applied to Fig. 26, the first group of resistive heating elements 69A and the third group of resistive heating elements 69C in Fig. 26 are each composed of one resistive heating element 59 at each end in Fig. 10, whereas the second group of resistive heating elements 69B is composed of five resistive heating elements 59 on the central side. In the following description, for the sake of simplicity, the first to third groups of resistive heating elements 69A-69C are each described as being a single resistive heating element 59A-59C (the first heating element 59A-the third heating element 59C).

Hereinafter, the positions corresponding to each of the resistive heating elements 59A to 59C in the longitudinal direction of the heater 22 will be referred to as the first to third groups. It is assumed that a current of 10% flows through each of the resistive heating elements 59A to 59C, and the heat generation amount of the first to third groups is calculated as the square of the current (I) flowing through each power supply line for convenience. For example, when all the resistive heating elements 59 are energized, as shown in FIG. 26, the total heat generation amount of the first group is 200 (100 + 100), the total heat generation amount of the second group is 200 (100 + 100), and the total heat generation amount of the third group is 400, so that the heat generation amount on the other side in the longitudinal direction is larger than that on the other side. In this way, whether the resistive heating element constituting each resistive heating element group is single or multiple, a deviation occurs in the heat generation amount of the power supply line on one side and the other side in the longitudinal direction. In FIG. 26, the first power supply line 62A, the third power supply line 62C, and the fourth power supply line 62D are connected to the corresponding resistance heating element 59 on one side of the longitudinal center position Qa of the resistance heating element 59. The second power supply line 62B is connected to the corresponding resistance heating element 59 on the other side of the longitudinal center position Qa of the resistance heating element 59.

In the following description, the electrode portion where the power supply lines extending from all of the resistive heating elements 59A to 59C join and connect is referred to as the second electrode portion 61B, and the electrode connected to the first resistive heating element 59 on the side different from the second electrode portion 61B is referred to as the first electrode portion 61A. As shown by the arrows in FIG. 26, when a current flows from the second electrode portion 61B to the first electrode portion 61A or the third electrode portion 61C, the third resistive heating element 59C is a resistive heating element that is located upstream of the first resistive heating element 59A or the second resistive heating element 59B in the current direction.

In the heater 22 shown in FIG. 27, the first electrode portion 61A is connected to the first resistive heating element 59A and the second resistive heating element 59B via the first power supply line 62A. The third electrode portion 61C is connected to the third resistive heating element 59C via the third power supply line 62C. The heater 22 of this embodiment can be applied to a fixing device that conveys paper with the left edge of the figure justified, for example. In this case, when small-sized paper is passed through, the first electrode portion 61A and the second electrode portion 61B are energized to cause the first resistive heating element 59A and the second resistive heating element 59B to heat up, and when large-sized paper is passed through, all of the electrodes 61A to 61C are energized to cause all of the resistive heating elements 59A to 59C to heat up.

In this embodiment, as shown in the table at the bottom of FIG. 27, when all the resistive heating elements 59 are energized, the heat generation amount 400 on the other longitudinal side (third group) is greater than the heat generation amount 200 on one side (first group), and a longitudinal deviation occurs in the heat generation amount of the heater 22. Note that in this embodiment, the connection positions of the first power supply line 62A to the first resistive heating element 59A and the second resistive heating element 59B, and the connection position of the third power supply line 62C to the third resistive heating element 59C are located on one side of the longitudinal center position Qa of the corresponding resistive heating element 59. The connection positions of the second power supply line 62B to each resistive heating element 59 are located on the other side of the longitudinal center position Qa of the corresponding resistive heating element 59.

Furthermore, in the heater 22 shown in FIG. 28, the first electrode portion 61A is connected to the first resistive heating element 59A via the first power supply line 62A. The third electrode portion 61C is connected to the second resistive heating element 59B and the third resistive heating element 59C via the third power supply line 62C. The heater 22 of this embodiment can be applied to, for example, a fixing device that conveys paper with the right edge of the figure justified. In this case, when small-sized paper is passed through, the third electrode portion 61C and the second electrode portion 61B are energized to cause the second resistive heating element 59B and the third resistive heating element 59B to heat up, and when large-sized paper is passed through, all of the electrodes 61A to 61C are energized to cause all of the resistive heating elements 59A to 59C to heat up.

In this embodiment, as shown in the table at the bottom of FIG. 28, the heat generation amount 500 on the other side in the longitudinal direction (third group) is larger than the heat generation amount 400 on one side (first group), and a longitudinal deviation occurs in the heat generation amount of the heater 22. In this embodiment, the connection position of the first power supply line 62A to the first resistance heating element 59A is arranged on one side of the longitudinal center position Qa of the first resistance heating element 59A. The connection position of the second power supply line 62B to each resistance heating element 59 is arranged on the other side of the longitudinal center position Qa of the corresponding resistance heating element 59. The connection position of the third power supply line 62C to the second resistance heating element 59B is arranged on one side of the longitudinal center position Qa of the corresponding resistance heating element 59, and the connection position of the third power supply line 62C to the third resistance heating element 59C is arranged on the other side of the longitudinal center position Qa of the corresponding resistance heating element 59.

The above-mentioned connection position patterns of the power supply lines 62 to the resistance heating elements 59 are just examples. The heat generation amount of the power supply lines 62 varies depending on the resistance heating elements 59 to which they are connected, and also varies depending on whether the connection position of the power supply lines 62 to the resistance heating elements 59 is located on one side or the other side of the center position Qa of the resistance heating elements 59. Therefore, the present invention can of course be applied to heaters 22 that have a different connection position from the heaters 22 described above and that have a deviation in the heat generation amount in the longitudinal direction.

Furthermore, for the heater 22 shown in FIG. 15, which has two electrodes and is connected at different positions, we will list heaters 22 in which the heat generation amount of the power supply line has a deviation in the longitudinal direction.

As an example, the heater 22 shown in FIG. 29 is an example in which the connection positions of the first power supply line 62A to the first resistive heating element 59A and the second heating element 59B are arranged on one side of the longitudinal center position Qa of each resistive heating element 59, the connection position of the first power supply line 62A to the third resistive heating element 59C is arranged on the other side, and the connection positions of the second power supply line 62B to each resistive heating element 59 are arranged on the other side.

Even in this case, as shown in the lower table of FIG. 29, the heat generation amount 500 on the other longitudinal side (third group) is greater than the heat generation amount 400 on one side (first group), resulting in a longitudinal deviation in the heat generation amount of the heater 22.

As shown in Fig. 30(a)-(e), the heat generation amount of the power feeder is greater on the other side in the longitudinal direction than on one side for each connection position. The numerical value at the bottom of each figure indicates the total heat generation amount of the power feeder in each group. As shown in Fig. 31(a)-(f), which is a different connection position from the above, the heat generation amount of the power feeder is greater on one side in the longitudinal direction than on the other side for each connection position. In this way, the heat generation amount of each group of power feeders changes depending on the change in the connection position, and the side on which the heat generation amount is greater also changes. Although not shown, depending on the combination of these connection positions, there are cases where the heat generation amount is equal on one side and the other side in the longitudinal direction. When the left side of Fig. 30 and Fig. 31 is one side and the right side is the other side, the first electrode part is connected to the power feeder extending from one side, and the second electrode part is connected to the power feeder extending to the other side.

To explain the connection positions in each case specifically, in FIG. 30(a), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element (more specifically, one side of the longitudinal center position of the resistive heating element; the same applies below), and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element (more specifically, the other side of the longitudinal center position of the resistive heating element; the same applies below), and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element.

In FIG. 30(b), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element.

In FIG. 30(c), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element.

In FIG. 30(d), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element.

In FIG. 30(e), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element.

In FIG. 31(a), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element.

In FIG. 31(b), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element.

In FIG. 31(c), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element.

In FIG. 31(d), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element.

In FIG. 31(e), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to the other side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element.

In FIG. 31(f), of the power supply lines connected to the resistive heating element at the end on one side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to one side of the resistive heating element, and of the power supply lines connected to the resistive heating element at the end on the other side, the power supply line connected to the first electrode portion is connected to one side of the resistive heating element, and the power supply line connected to the second electrode portion is connected to the other side of the resistive heating element.

In each of the above embodiments shown in Figures 29, 30, and 31, the resistance heating element between the endmost resistance heating element on one side and the endmost resistance heating element on the other side may be connected to the power supply line in any manner.

Furthermore, when each resistance heating element 59 is configured by folding back a line portion as shown in FIG. 15, each resistance heating element 59 may be in the shape of a parallelogram as shown in FIG. 15, or in the shape of a rectangle as shown in FIG. 32. The number of folds can be appropriately selected depending on the required width of the heater 22 in the short direction and the connection position of the power supply line to the resistance heating element. When the resistance heating elements 59 are in the shape of a parallelogram as shown in FIG. 15, that is, when the line portion in the direction intersecting the longitudinal direction U of the heater 22 is inclined with respect to the short direction Y, the gap between the resistance heating elements 59 can be made smaller, and the heat generation amount of the heater 22 can be made more uniform in the longitudinal direction.

Also, as shown in FIG. 33, the portion of each power supply line 62 connected to each resistance heating element 59 may be inclined with respect to the short side direction of the heater 22. Furthermore, as shown in FIG. 34, the portion to which the power supply line 62 is connected may be replaced with a resistance heating element 59.

In addition, for the heater 22 having the configuration shown in FIG. 10, all the electrode parts can be arranged on the same side in the longitudinal direction. For example, the heater 22 shown in FIG. 35 differs from the heater 22 in FIG. 10 in that the second electrode part 61B is arranged on one side in the longitudinal direction. Also, as shown in FIG. 35, since the second electrode part 61B is arranged on one side in the longitudinal direction, the power supply line directly connected to the second electrode part 61B extends to the other side in the longitudinal direction, turns back, and is connected to each resistance heating element 59. In this embodiment, of the power supply lines connecting these second electrode parts 61B and each resistance heating element 59, the part from the part connected to each resistance heating element 59 to the turn-back part on the other side in the longitudinal direction is referred to as the second power supply line 62B, and the part from the part extending to one side in the longitudinal direction that is continuous with the turn-back part to the second electrode part 61B is referred to as the fifth power supply line (conductor) 62E.

Even in such a heater 22, when electricity is applied only to the first heat generating element 60A, and when electricity is applied to both the first heat generating element 60A and the second heat generating element 60B, the longitudinal temperature deviation described above occurs.

The heater configurations described above may also be combined as appropriate. For example, in a configuration in which all electrode parts 61 are arranged on one side in the longitudinal direction as shown in FIG. 35, the resistive heating element 59 may be rectangular as shown in FIG. 32, or the portion of each power supply line 62 connected to each resistive heating element 59 may be inclined with respect to the short side direction of the heater 22 as shown in FIG. 33.

In each of the heaters 22 described above, a combination configuration (see FIG. 21) is adopted in which the pressure is relatively large on the side where the amount of heat generated in the longitudinal direction is relatively small. This makes it possible to increase the nip pressure or nip width in the fixing nip N on the side where the amount of heat generated in the longitudinal direction is small. Therefore, problems caused by deviations in the amount of heat generated in the longitudinal direction, specifically uneven gloss and uneven fixing in the longitudinal direction of the image formed on the paper P, can be suppressed.

The present invention is expected to be more effective when applied to a heater with a small short-side dimension for miniaturization. Specifically, in FIG. 36, if the short-side dimension of the heater 22 (substrate 50) is Wa and the short-side dimension of the resistance heating element 59 is Wb, a great effect can be expected when the present invention is applied to a heater 22 in which the ratio (Wb/Wa) of the short-side dimension Wb of the resistance heating element 59 to the short-side dimension Wa of the heater 22 is 25% or more. Note that the short-side dimension Wb of the resistance heating element 59 does not mean the thickness of one linear portion of the resistance heating element 59 formed to be folded back, but the short-side dimension of the entire resistance heating element 59. Furthermore, if the heater 22 has a short-side dimension ratio (Wb/Wa) of 40% or more, the effect of applying the present invention is even greater.

Next, the experimental results of the temperature deviation occurring between the center side and the end side of the heater 22 in the longitudinal direction when the ratio of the short side dimensions (Wb/Wa) is changed will be described. In the experiment, heaters 22 having the above-mentioned configuration were prepared with the above-mentioned short side dimension ratios (Wb/Wa) of 20% or more and less than 25%, 25% or more and less than 40%, 40% or more and less than 70%, and 70% or more and less than 80%, and a predetermined voltage was applied to all the resistance heating elements of the heater under the condition of the heater alone, and the surface temperatures of the center side and the end side of the heater in the longitudinal direction were measured using an infrared thermography FLIR T620 manufactured by FLIR Systems. The above experimental results are shown in Table 1. In the results of Table 1, the temperature difference between the center side and the end side was less than 2°C as ◯, the temperature difference between 2°C or more and less than 5°C as △, and the temperature difference of 5°C or more as ×. In addition, if the ratio of short side dimensions (Wb/Wa) is 80% or more, there will be no space to place the power supply wires unless the short side dimension of the heater is made extremely large, so this was not included in the experiment.

As shown in Table 1, the temperature difference between the center and ends of the heater increased as the ratio of the short-side dimensions (Wb/Wa) increased. Specifically, the result was ◯ when the ratio was 20% or more and less than 25%, but changed to △ when the ratio was 25% or more and less than 40%, and changed to × when the ratio was 40% or more and less than 70%, and when the ratio was 70% or more and less than 80%. As can be seen from these results, the temperature unevenness in the heater's longitudinal direction becomes noticeable when the ratio of the short-side dimensions (Wb/Wa) is 25% or more, and is particularly noticeable when the ratio is 40% or more. Therefore, it is preferable to apply the above configuration of this embodiment to heaters with such dimensional ratios to suppress problems caused by the temperature deviation.

In the example shown in FIG. 36, the substrate 50 of the heater 22 is rectangular, so the short-side dimension Wa of the heater 22 is the same at any longitudinal position, but if the edge of the substrate 50 is uneven, as in the example shown in FIG. 36, the short-side dimension Lb changes depending on the longitudinal position. In such a case, the short-side dimension Wa of the heater 22 is the smallest dimension in the short-side direction Y of the heater 22 within the heat generating area where all the resistive heating elements 59 are arranged.

The present invention is also applicable to heaters 22 in which the ratio (Wa/La) of the short-side dimension Wa of the heater 22 to the long-side dimension La of the heater 22 is greater than 1.5% and less than 6%, and the ratio (Wc/Wa) of the short-side dimension Wc of the power supply lines 62A and 62B to the short-side dimension Wa of the heater 22 is greater than 2% and less than 20%. In addition, as in the example shown in FIG. 37, when the longitudinal dimension of the substrate 50 varies depending on the portion, the dimension at which the heater 22 is maximum in the longitudinal direction U is defined as the longitudinal dimension La of the heater 22. In addition, the short-side dimension Wc of the power supply lines 62A and 62B means the thickness of the linear portion of the power supply lines 62A and 62B extending in the longitudinal direction U of the heater 22, and does not include the portion bent in the short-side direction Y of the heater 22 to connect to the resistance heating element 59. Also, as shown in FIG. 37, if the thickness of the power supply lines 62A and 62B varies depending on the longitudinal position of the heater 22, the minimum transverse dimension of the first power supply line 62A or the second power supply line 62B within the heat generation region Lb is defined as the transverse dimension Wc of the power supply lines 62A and 62B.

In addition, in the embodiment of the present invention, a resistive heating element having PTC characteristics may be used to further suppress temperature variation along the length of the heater. PTC characteristics are characteristics in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). By using a heating element with PTC characteristics, it is possible to achieve high output at low temperatures and high speed rise in temperature, and low output at high temperatures to suppress overheating. For example, if the TCR coefficient of the PTC characteristics is set to about 300 to 4000 ppm/degree, it is possible to reduce costs while ensuring the resistance value required for the heater. It is more preferable to set the TCR coefficient to 500 to 2000 ppm/degree.

The temperature coefficient of resistance (TCR) can be calculated using the following formula (6). In formula (6), T0 is the 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 the heater 22 described above and shown in FIG. 10, if the resistance value between the first electrode portion 61A and the second electrode portion 61B is 10Ω (resistance value R0) at 25°C (reference temperature T0) and 12Ω (resistance value R1) at 125°C (arbitrary temperature T1), the temperature coefficient of resistance is 2000 ppm/°C according to formula (6).

The layout of the electrodes and other parts arranged on the substrate 50 of the heater 22 is not limited to the above embodiment, and the present invention can be applied to heaters in which the heat generation amount of the power supply line is non-uniform in the longitudinal direction.

In addition to the fixing devices described above, the present invention can also be applied to fixing devices such as those shown in Figures 38 and 39. The configuration of each fixing device shown in Figures 38 and 39 will be briefly described below.

First, the fixing device 9 shown in FIG. 38 has a pressure roller 90 disposed on the opposite side of the fixing belt 20 from the pressure roller 21 side, and is configured so that the fixing belt 20 is sandwiched and heated by this pressure roller 90 and heater 22. On the other hand, on the pressure roller 21 side, a nip forming member 91 is disposed on the inner circumference of the fixing belt 20. The nip forming member 91 is supported by a stay 24, and the fixing belt 20 is sandwiched between the nip forming member 91 and the pressure roller 21 to form a fixing nip N.

In the fixing device 9 shown in FIG. 38, as described in the above embodiment, a pressure mechanism is provided to press the pressure roller 21 against the fixing belt 20, and the above-mentioned first gear and second gear that transmit driving force to the pressure roller 21 are provided on either side in the longitudinal direction. Then, by setting the longitudinal arrangement of the gears and the combination of the meshing position of the second gear with respect to the first gear as shown in FIG. 21, it is possible to increase the pressure on any side in the longitudinal direction and to cause a deviation in the pressure. In addition, if a deviation occurs in the amount of heat generated in the longitudinal direction of the heater 22 between one side and the other side, the pressure on the side with the smaller amount of heat generated can be relatively increased to relatively increase the nip pressure and nip width on the side with the smaller amount of heat generated in the fixing nip N. Therefore, it is possible to suppress defects caused by the temperature deviation between one side and the other side of the heater 22 in the longitudinal direction. In other words, it is possible to suppress the difference in fixability between one side and the other side in the longitudinal direction, and to suppress the gloss deviation in the longitudinal direction. This helps to reduce unevenness in the image and gloss of the paper.

Next, in the fixing device 9 shown in FIG. 39, the pressure roller 90 described above is omitted, and the heater 22 is formed in an arc shape to match the curvature of the fixing belt 20 in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22. The rest of the configuration is the same as that of the fixing device 9 shown in FIG. 39. By applying the present invention described above to the fixing device 9 of this configuration, the above-mentioned effects can also be obtained.

In addition, examples of devices having the heating device of the present invention are not limited to fixing devices as described in the above embodiments, but may also include drying devices that dry liquids such as ink applied to paper, and further coating devices such as laminators that thermally bond a film as a coating member to the surface of a sheet such as paper, and thermocompression devices such as heat sealers that thermally bond the seal portion of a packaging material as an object to be heated. By applying the present invention to such devices, it is possible to suppress problems caused by deviations in the amount of heat generated in the longitudinal direction of the heater.

Recording media (or objects to be heated or sheets) include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, overhead projector sheets, plastic film, prepreg, copper foil, etc.

In the above explanation, an example of a heating element is a planar heating element, which is a resistive heating element, provided on a substrate, but the present invention is not limited to this. For example, a halogen heater, an induction heater, a carbon heater, etc. can also be used.

In the above explanation, a spring is used as the pressure mechanism for pressing the pressure roller against the fixing belt, but this is not limiting. For example, a pressure lever may be used as the pressure mechanism.

1 Image forming apparatus 9 Fixing device 20 Fixing belt (heated member or cylindrical member or fixing member)
21 Pressure roller (opposing member or pressure member)
21b Elastic layer 21d Rotating shaft 22 Heater (heating body)
23 Heater holder (holding member)
23a Storage recess (holding portion)
24 Stay (support member)
24b Support portion 31 First gear 31a Rotation center 33 Spring (pressure mechanism)
41 Second gear 42 Motor (driving source)
43 Third gear 59 Resistance heating element (surface heating element)
60 Heat generating portion 61 Electrode portion 62 Power supply line (conductor)
70 Connector (power supply member)
80 Heating device A Paper feed direction C Heating area of heater C0 Center position of heating area in the longitudinal direction H0 Horizontal line H1 Reference line H2 Second reference line H3 Third reference line N Fixing nip (nip portion)
P Paper (recording medium or heated object or sheet)
Q: Longitudinal center position of heater Qa: Longitudinal center position of resistance heating element U: Longitudinal direction of heater Y: Shortitudinal direction of heater Wa: Shortitudinal dimension of heater Wb: Shortitudinal dimension of resistance heating element α: Pressure angle of first gear

Japanese Patent Application Laid-Open No. 05-107985

Claims (22)

A heating element having a planar heating element;
A cylindrical member heated by the heating body;
an opposing member that contacts the cylindrical member to form a nip portion between the opposing member and the cylindrical member;
a first gear provided on the opposing member and meshing with a second gear;
a pressure mechanism for pressing the opposing member toward the cylindrical member,
the opposing member is rotated by the driving force transmitted from the second gear to the first gear,
on a plane perpendicular to the axial direction of the opposing member, a line passing through the rotation center of the first gear and inclined by a pressure angle of the first gear in a direction opposite to the rotation direction of the opposing member with respect to a straight line parallel to a pressure direction of the pressure mechanism against the opposing member is defined as a reference line, a meshing position of the second gear with respect to the first gear is provided on the same side as an outlet side of the nip portion with respect to the reference line,
The heat generation amount of the heating body is smaller on one side in the longitudinal direction than on the other side,
A heating device, characterized in that, in the longitudinal direction, the first gear is provided on the other side of a central position of the heating area of the heating body. The heating body is
As heating elements, a first heating element, a second heating element, and a third heating element are arranged in this order in parallel in a longitudinal direction of the heating element;
The electrode portion includes a first electrode portion, a second electrode portion, and a third electrode portion;
a plurality of conductors electrically connecting the heating element and the electrode portion,
the first electrode portion is connected to the first heating element via the conductor;
the third electrode portion is connected to at least one of the second heating element and the third heating element via the conductor;
the conductors extending from the first heating element, the second heating element, and the third heating element are joined together and connected to the second electrode portion;
when a current flows from the second electrode portion to the first electrode portion or the third electrode portion, the third heating element is disposed upstream of the first heating element in a current direction,
2. The heating device according to claim 1, wherein the first gear is provided on the third heating element side with respect to a center position of the heating area of the heating element in the longitudinal direction. The heating body is
As heating elements, a first heating element, a second heating element, and a third heating element are arranged in this order in parallel in a longitudinal direction of the heating element;
The electrode portion includes a first electrode portion, a second electrode portion, and a third electrode portion;
a plurality of conductors electrically connecting the heating element and the electrode portion,
the first electrode portion is connected to the first heating element and the third heating element via the conductor;
the third electrode portion is connected to the second heating element via the conductor;
the conductors extending from the first heating element, the second heating element, and the third heating element are joined together and connected to the second electrode portion;
when a current flows from the second electrode portion side to the first electrode portion side, the third heating element is disposed upstream of the first heating element in a current direction,
2. The heating device according to claim 1, wherein the first gear is provided on the first heating element side with respect to a center position of the heating area of the heating element in the longitudinal direction. The heating body is
As the heating element, a first heating element, a second heating element, and a third heating element are arranged in parallel in a longitudinal direction of the heating element;
As the electrode portion, a first electrode portion and a second electrode portion;
The heat generating element includes a first conductor and a second conductor that electrically connect the heat generating element and the electrode portion,
the first electrode portion is connected to the first heating element, the second heating element, and the third heating element via the first conductor;
the second electrode portion is connected to the first heating element, the second heating element, and the third heating element via the second conductor;
In the longitudinal direction, connection positions of the first conductor and the second conductor to the first heating element, the second heating element, and the third heating element are provided on one side of a center position of the heating element to be connected,
2. The heating device according to claim 1, wherein the first gear is provided on the other side of a center position of the heating region of the heating body in the longitudinal direction. The opposing member has an elastic layer,
5. The heating device according to claim 1, wherein the cylindrical member does not have an elastic layer, or the cylindrical member has an elastic layer, and the thickness of the elastic layer is smaller than the thickness of the elastic layer of the opposing member. An electrode portion;
The heating device according to claim 1 , further comprising a power supply member for supplying power to the electrode portion. On a plane perpendicular to the axial direction of the opposing member, a line passing through the rotation center of the first gear and inclined by 30 degrees in the rotation direction of the opposing member with respect to a straight line parallel to the pressure direction of the pressure mechanism against the opposing member is defined as a second reference line, and a line inclined by 30 degrees in the opposite direction to the rotation direction of the opposing member is defined as a third reference line.
7. The heating device according to claim 1, wherein, in the circumferential direction of the first gear, the meshing position of the second gear with respect to the first gear is located within one of two regions out of four regions defined by the second reference line and the third reference line, on a plane perpendicular to the axial direction of the opposing member, that pass through the center of rotation of the first gear and do not include a straight line parallel to the pressure direction of the pressure mechanism applied to the opposing member. The heating device according to any one of claims 1 to 7, wherein the tip circle diameter of the first gear is larger than the diameter of the opposing member and smaller than the sum of the diameter of the opposing member and the diameter of the cylindrical member. The heating device according to any one of claims 1 to 8, further comprising the second gear. The heating device according to any one of claims 1 to 9, wherein when the opposing member moves toward or away from the cylindrical member, the second gear and the first gear move without changing their relative positional relationship. a third gear meshing with the second gear,
The heating device according to claim 1 , wherein the second gear transmits a driving force transmitted from the third gear to the first gear. The heater further includes a holding member for holding the heater.
The heating device according to claim 1 , wherein the holding member has a holding portion that holds the heating body, the holding portion having a longitudinal center portion that has a convex shape that protrudes toward the heating body more than the longitudinal ends. A holding member for holding the heating body;
The heater further includes a metal support member for supporting the heater or the holding member.
The heating device according to claim 1 , wherein the support member has a longitudinal center portion of a support portion supporting the heating body or the holding member that has a convex shape protruding toward the heating body more than the longitudinal ends. a metal support member for supporting the heating body or the holding member,
The opposing member has a smaller diameter at a center side in a longitudinal direction than at an end side,
The radius of the longitudinal center of the opposing member minus the radius of the longitudinal end of the opposing member is defined as the gripping amount,
If the amount of protrusion of the convex shape of the holding member or the supporting member toward the heating body, or the sum of the amounts of protrusion of the convex shapes of the holding member and the supporting member toward the heating body, is defined as the protrusion amount,
14. The heating device according to claim 12, wherein the protruding amount is greater than the pressing amount and is smaller than a thickness of the heating element. The heating device according to any one of claims 1 to 14, wherein the heating element has a PTC characteristic. If a direction intersecting the longitudinal direction along the surface on which the heating element of the heating element is provided is defined as a short direction,
16. The heating device according to claim 1, wherein a ratio of a widthwise dimension of the heat generating element to a widthwise dimension of the heating element is 25% or more. If a direction intersecting the longitudinal direction along the surface on which the heating element of the heating element is provided is defined as a short direction,
16. The heating device according to claim 1, wherein a ratio of a widthwise dimension of the heat generating element to a widthwise dimension of the heating element is 40% or more. A fixing device that includes the heating device according to any one of claims 1 to 17 and fixes an image on a recording medium. A drying device that includes a heating device according to any one of claims 1 to 17 and dries liquid on a recording medium. A coating device comprising the heating device according to any one of claims 1 to 17, for coating a sheet with a coating material. A thermocompression bonding device comprising the heating device according to any one of claims 1 to 17, for heating and bonding an object to be heated. An image forming apparatus equipped with a heating device according to any one of claims 1 to 17.

Images