JP2019078820A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the image quality of a printed matter printed on printing paper. SOLUTION: A first heater 5 has a plurality of heat generating resistors 501 to 507 arranged in the longitudinal direction of a ceramic substrate, and individual electrodes 601 to 601 connected to one end of each of the plurality of heat generating resistors 501 to 507. 607, a common electrode 700 connected to the other end of the heat generation resistors 501 to 507 to which the individual electrodes 601 to 607 are not connected, and a power input terminal T provided at one end in the longitudinal direction of the common electrode 700. Has. The common electrode 700 is formed so that the length in the Y-axis direction becomes longer as the distance from the power input terminal T increases. Therefore, even if the length of the common electrode 700 becomes longer in the −Z direction from the power input terminal T, the change in the wiring resistance of the common electrode 700 is small. As a result, the amount of heat generated per unit length of the heat generating resistors 501 to 507 in the Z-axis direction can be made uniform, and the degree of fixing of the toner from the left end to the right end of the printing paper can be made uniform. [Selection diagram] FIG. 5

Description

  The present embodiment relates to a fixing device and an image forming apparatus.

  In a fixing device used in an image forming apparatus, a heater may be used in which a plurality of heating resistors are arranged in the longitudinal direction of a ceramic substrate. Power supply control is performed to each heating resistor from one end of each of the plurality of heating resistors, and the other end of each heating resistor is connected to the common electrode formed in the longitudinal direction, thereby miniaturizing the heater. be able to. In this case, the feed terminal is provided at one end of the common electrode formed in the longitudinal direction.

JP, 2015-219417, A

  However, since the plurality of heat generating resistors are arranged in the longitudinal direction, the wiring resistance for supplying power to the heat generating resistors arranged near the feed terminal and the heat resistance arranged at a position away from the feed terminal When comparing the wiring resistance for supplying power to the body, the latter has higher wiring resistance. Therefore, a difference occurs between the current flowing through the heating resistor disposed near the feeding terminal and the current flowing through the heating resistor disposed away from the feeding terminal, which causes a temperature difference on the surface of the heater. This temperature difference causes a difference between the degree of fixation of the toner on the left side of the printing paper and the degree of fixation of the toner on the right side, which causes deterioration of the image quality.

  The present invention has been made under the above-described circumstances, and an object thereof is to improve the image quality of a printed matter printed on printing paper.

  In order to achieve the above-described problem, the fixing device according to the present embodiment includes a plurality of heating resistors arranged in a first direction and a plurality of heating resistors on a heat-resistant insulating substrate. The individual electrode connected to one end, the common electrode connected to the other end of the heat generating resistor whose longitudinal direction is the first direction and the individual electrode is not connected, and the one end of the common electrode in the longitudinal direction And a power supply input terminal. The common electrode is formed such that the width in the second direction orthogonal to the first direction of the pattern forming the electrode increases as the distance from the power supply input terminal increases, or the thickness of the pattern forming the electrode increases.

FIG. 1 is a diagram showing a configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a view showing the configuration of an image forming unit for black shown in FIG. 1; FIG. 2 is a view showing the configuration of a fixing device shown in FIG. 1; It is XY sectional drawing of the 1st heater shown by FIG. (A) is a Y-Z plan view of a first heater of the fixing device according to the first embodiment, (b) is an X-Z cross-sectional view of a common electrode of the first heater, c) is an X-Z cross-sectional view of the heating resistor of the first heater. It is a figure which shows the structure of the control apparatus shown by FIG. (A) is a Y-Z plan view of the second heater of the fixing device according to Modification 1, (b) is an X-Z cross-sectional view of a common electrode of the second heater, (c) These are XZ sectional drawings of the heating resistor of a 2nd heater. (A) is a Y-Z plan view of the third heater of the fixing device according to Modification 2, (b) is an X-Z cross-sectional view of the common electrode of the third heater, (c) These are XZ sectional drawings of the heating resistor of a 3rd heater. (A) is a Y-Z plan view of the fourth heater of the fixing device according to Modification 3, (b) is an X-Z cross-sectional view of the common electrode of the fourth heater, (c) These are XZ sectional drawings of the heating resistor of a 4th heater. (A) is a Y-Z plan view of the fifth heater of the fixing device according to the second embodiment, (b) is an X-Z cross-sectional view of a branch pattern of the fifth heater, c) is an X-Z cross-sectional view of the heating resistor of the fifth heater. (A) is a Y-Z plan view of the sixth heater of the fixing device according to Modification 4, (b) is an X-Z sectional view of a branch pattern of the sixth heater, (c) These are XZ sectional drawings of the heating resistor of a 6th heater. (A) is a YZ plan view of the seventh heater of the fixing device according to Modification 5, (b) is an XZ sectional view of a branch pattern of the seventh heater, (c) These are XZ sectional drawings of the heating resistor of a 7th heater. (A) is a YZ plan view of the eighth heater of the fixing device according to Modification 6, (b) is an XZ cross section of a branch pattern of the eighth heater, (c) These are XZ sectional drawings of the heating resistor of an 8th heater. (A) is a Y-Z plan view of the ninth heater of the fixing device according to the third embodiment, (b) is an X-Z cross-sectional view of the common electrode of the ninth heater, c) is an X-Z cross-sectional view of a heating resistor of a ninth heater. (A) is a YZ plan view of a tenth heater of the fixing device according to Modification 7, (b) is an XZ cross section of a common electrode of the tenth heater, (c) These are XZ sectional drawings of the heating resistor of a 10th heater. (A), (b), (c) is a figure for demonstrating the other Example of a heater.

First Embodiment
Hereinafter, an image forming apparatus according to the first embodiment will be described with reference to the drawings. The same reference numerals are given to the same parts in the respective drawings, and duplicate explanations are omitted. Moreover, in each figure, the size of each component may differ from the time of implementation, and the ratio of the size of each component is not necessarily constant. Further, in the following drawings, some components may be omitted as appropriate in order to avoid complicating the drawings and clarify them.

[MFP10]
FIG. 1 is a view showing the arrangement of an image forming apparatus according to the first embodiment. In FIG. 1, the image forming apparatus is a multifunction peripheral (MFP (Multi-Function Peripherals)), a printer, a copying machine, etc., and in the following description, the MFP 10 is a specific example. The main body 11 of the MFP 10 includes an operation panel 14 at an upper portion, and the operation panel 14 includes various keys and a touch panel display unit.

[Printer unit 17]
The main body 11 of the MFP 10 includes a control device 36 at the upper portion and a printer unit 17 at the central portion, and a plurality of sheet feeding cassettes 18 for storing any of sheets P (recording media) of a plurality of types of sizes at the lower portion. Prepare. The printer unit 17 is a tandem-type color laser printer, and includes a photosensitive drum and a scanning head 19 including an LED as an exposure device. The printer unit 17 processes image data read by a scanner, image data generated by a personal computer, etc., scans a photosensitive drum with a light beam from the scanning head 19, and obtains an image obtained by processing the image data. On a sheet P.

  The printer unit 17 is an image forming unit 20Y for each color of yellow (Y), magenta (M), cyan (C) and black (K) on the lower side of the intermediate transfer belt 21 and in parallel along the upstream to the downstream side. , 20M, 20C, and 20K. The printer unit 17 also includes a plurality of scanning heads 19 corresponding to the image forming units 20Y, 20M, 20C, and 20K. The image forming units 20Y, 20M, 20C, and 20K have the same configuration.

  FIG. 2 is a diagram showing the configuration of the image forming unit 20K for black shown in FIG. The image forming unit 20K has a photosensitive drum 22K of an image carrier. The image forming unit 20K includes a charger 23K, a developer 24K, a primary transfer roller 25K, a cleaner 26K, and a blade 27K around the photosensitive drum 22K along the rotational direction t. At the exposure position of the photosensitive drum 22K, light is irradiated from the scanning head 19K to form an electrostatic latent image.

  The charger 23K of the image forming unit 20K uniformly charges the surface of the photosensitive drum 22K. The developing device 24K supplies a two-component developer including a black toner and a carrier to the photosensitive drum 22K by the developing roller 24a to which a developing bias is applied, to develop the electrostatic latent image. The cleaner 26K removes residual toner on the surface of the photosensitive drum 22K using a blade 27K.

  Further, as shown in FIG. 1, the intermediate transfer belt 21 is stretched around the driving roller 31 and the driven roller 32 and moves cyclically. Also, the intermediate transfer belt 21 faces and contacts the photosensitive drums 22Y, 22M, 22C, and 22K. A primary transfer voltage is applied by the primary transfer rollers 25Y, 25M, 25d, 25K to the positions facing the photosensitive drums 22Y, 22M, 22C, 22K of the intermediate transfer belt 21, and the photosensitive drums 22Y, 22M, 22C, 22K The upper toner image is primarily transferred to the intermediate transfer belt 21. However, in FIG. 1, reference numerals 25Y, 25M and 25d are not shown, and reference numeral 25K is attached only to the temporary transfer roller on the photosensitive drum 22K.

  The secondary transfer roller 33 is disposed to face the driving roller 31 that stretches the intermediate transfer belt 21. While the sheet P passes between the driving roller 31 and the secondary transfer roller 33, the secondary transfer voltage is applied to the sheet P by the secondary transfer roller 33, and the toner image on the intermediate transfer belt 21 is transferred onto the sheet P Next transferred. Further, a fixing device 4 is provided downstream of the secondary transfer roller 33.

[Fixing device 4]
FIG. 3 is a view showing the configuration of the fixing device 4 shown in FIG. As shown in FIG. 3, the fixing device 4 includes a heating device 400 that is driven to rotate in the S direction, and a pressure roller 440 that rotates according to the rotation of the heating device 400. The pressure roller 440 includes a protective layer 442 made of PFA (copolymer of tetrafluoroethylene (C ₂ F ₄ ) and perfluoroalkoxyethylene), a silicone sponge layer 444 with a thickness of about 5 mm, and a diameter of about 10 mm. And the iron core 446 of

  The heating device 400 includes an endless fixing belt 402. In the fixing belt 402, a heat insulating silicone rubber layer having a thickness of about 200 μm is formed on a base layer such as polyimide (PI) having a thickness of 70 μm, Ni having a thickness of about 70 μm, and SUS (stainless steel) having a thickness of 70 μm. It has a multi-layered structure. The heating device 400 further includes a first heater 5 that is pressed toward the pressure roller 440 together with the fixing belt 402 and forms a fixing nip portion that heats the sheet P. With such a configuration, the heat responsiveness of the fixing nip portion in the fixing device 4 is higher than that of the fixing nip portion heated by the halogen lamp.

[Heater 5]
FIG. 4 is an X-Y cross-sectional view of the first heater 5 shown in FIG. As shown in FIG. 4, the first heater 5 includes a conductor layer 50 formed on a ceramic substrate 514 which is an insulating substrate excellent in heat resistance, and a heat generation resistance layer 52 (heat generation resistance body). A surface protection layer 512 covering the conductor layer 50 and the heating resistance layer 52, and a holder 516 made of a heat-resistant resin are provided for these components. The heat generating resistive layer 52 is formed of, for example, TaSiO. The heat-generating resistive layer 52 is formed by the same method as the thermal head. The heating resistance layer 52 forms heating resistors 501 to 507 that generate heat in response to a supply from a power supply device 800 described later. The conductive layer 50 forms the common electrode 700 and the individual electrodes 601 to 607. Details will be described later.

The surface protective layer 512 is made of Si ₃ N ₄ and protects the conductor layer 50 and the heating resistance layer 52 and the like. The conductor layer 50 is formed on the fixing belt 402 side of the ceramic substrate 514 using silver as a material. When the transported sheet P passes on the surface protective layer 512, the sheet P is heated by the heating resistors 501 to 507 formed by the heating resistor layer 52.

  FIG. 5A is a plan view of the first heater 5 and a diagram showing a peripheral circuit. As shown in FIG. 5A, the first heater 5 includes a plurality of heating resistors 501 to 507 arranged in the longitudinal direction (first direction) of the ceramic substrate 514, and a plurality of heating resistors 501 to 507. The individual electrodes 601 to 607 connected to one end (the lower side in FIG. 5 (the second direction orthogonal to the first direction) of FIG. 5) of each and the heating resistors 501 to which the individual electrodes 601 to 607 are not connected. 50 has a longitudinally extending common electrode 700 connected to the other end side (the upper side in the lateral direction in FIG. 5) and a power input terminal T provided at one end of the common electrode 700 in the longitudinal direction. .

  The length in the Z-axis direction of the heating resistor 504 corresponds to the width of the B5 size printing sheet. The total length in the Z-axis direction of the heat generating resistors 503 to 505 corresponds to the width of A4 size printing paper. The total length in the Z-axis direction of the heat generating resistors 502 to 506 corresponds to the width of B4 size printing paper. The total length in the Z-axis direction of the heat generating resistors 501 to 507 corresponds to the width of A3 size printing paper.

  As shown in FIG. 5A, the common electrode 700 is formed such that the length in the Y-axis direction becomes longer as the distance from the power supply input terminal T increases.

  FIG. 5B is a cross-sectional view of the common electrode 700 of the first heater 5. FIG. 5C is a cross-sectional view of the heating resistors 501 to 507 of the first heater 5. In the first embodiment, the thicknesses of the common electrode 700 and the heating resistors 501 to 507 of the first heater 5 in the X-axis direction are the same. The cross-sectional areas of the heat generating resistors 501 to 507 are S1, S2,.

  As shown in FIG. 5A, the common electrode 700 increases in length in the Y-axis direction as the distance from the power supply input terminal T increases. Therefore, even if the length of the common electrode 700 is increased in the −Z direction from the power supply input terminal T, the change in the wiring resistance of the common electrode 700 is small.

  One end of each of the plurality of heating resistors 501 to 507 (the lower side in the short direction in FIG. 5) is connected to the power supply device 800 via the individual electrodes 601 to 607 and the switches S1 to S4. The power supply input terminal T provided at one end in the longitudinal direction of the common electrode 700 is connected to the other end of the power supply apparatus 800 to which the switches S1 to S4 are not connected. The power supply 800 uses an AC power supply to prevent migration. In FIG. 1, the description of the power supply device 800 is omitted. The switches S1 to S4 are included in a fixing control circuit 372 described later.

[Control unit 36]
FIG. 6 is a diagram showing a configuration of control device 36 shown in FIG. As shown in FIG. 6, control device 36 includes CPU 360 including a CPU and its peripheral circuits, memory 362 including ROM, RAM, flash memory, etc., and operation panel interface (IF) 364 to which operation panel 14 is connected. And

  Further, the control device 36 controls a component between the sheet feeding cassette 18 and the sheet discharge tray of the main body 11 shown in FIG. 1 to perform sheet feeding and sheet conveyance control circuit. 368 is further provided. The control device 36 further includes an image formation control circuit 370 that controls the printer unit 17 and a fixing control circuit 372 that controls the operation of the fixing device 4. The fixing control circuit 372 includes switches S1 to S4 for connecting and disconnecting the heating resistors 501 to 507 and the power supply device 800. The components of control device 36 are connected to one another via a bus 374. Control device 36 controls the operation of each component of MFP 10 according to the user's operation on the operation panel or the like by these components, and realizes image formation on sheet P by MFP 10.

[Operation]
Next, the operation of the fixing device 4 will be described with reference to FIG. Here, the values of the wiring resistances of the individual electrodes 601 to 607 of the first heater 5 and the values of the wiring resistance from the individual electrodes 601 to 607 to the power supply 800 through the switches S1 to S4 are the same. It will be assumed that When the user designates B5 size printing paper, the switch S1 in the control device 36 is turned on. When the user designates A4 size printing paper, the switch S1 and the switch S2 in the control device 36 are turned on. When the user designates printing paper of B4 size, the switches S1 to S3 in the control device 36 are turned on. When the user designates A3 size printing paper, the switches S1 to S4 in the control device 36 are turned on.

A current flowing through the heating resistor 501 is i ₁ , a current flowing through the heating resistor 502 is i ₂ , a current flowing through the heating resistor 503 is i ₃ , and so forth, and a current flowing through the heating resistor 507 is i ₇ . The current i ₁ flowing through the heating resistor 501 reaches the heating resistor 501 through the entire path of the common electrode 700 extending in the longitudinal direction. I ₇ The current flowing through the heating resistor 507, leading to the heating resistor 507 through a short path which is part of the common electrode 700 extending in the longitudinal direction. However, since the length of the common electrode 700 in the Y-axis direction becomes longer as the shape of the common electrode 700 gets farther from the power input terminal T (the width of the common electrode 700 becomes wider), each heating resistor from the power input terminal T The difference in wiring resistance to is small. Therefore, variations in the current density of the current _{i 1} ~ current _{i 7} through the heating resistor 501 to 507 is small. That is, assuming that the cross-sectional areas of the heating resistors 501 to 507 are S1 to S7, the currents i ₁ to i ₇ flowing through the heating resistors are i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S4 ≒ _i 5 / S5 flows so that the _{≒ i 6 / S6 ≒ i 7} / S7.

By thus reduce variations in the current density of the current i _{1 ~} current i _7, it is possible to make uniform the amount of heat generated per unit length of the Z-axis direction of the heating resistor 501 to 507, the printing paper The fixing degree of toner from the left end to the right end can be made uniform. This can improve the quality of the printed image.

  In the above description, the case where the first heater 5 is connected to the switches S1 to S4 and the power supply device 800 has been described, but a switching driver IC may be used instead of the switches S1 to S4. In the above description, the switches S1 to S4 are provided in the control device 36. However, when the switching driver IC is used, the switching driver IC may be provided in the first heater 5, or It may be mounted adjacent to the heater 5 of.

  In the above description, the values of the wiring resistances of the individual electrodes 601 to 607 of the first heater 5 and the individual electrodes 601 to 607 of the first heater 5 reach the power supply 800 through the switches S1 to S4. It was assumed that the values of the wiring resistance were the same. When the wiring resistances are different, the total value of the wiring resistance from the power input terminal T to each heating resistor, the wiring resistance of the individual electrodes, and the wiring resistance from each individual electrode to the power supply 800 approximate each other. It is desirable to design the shape of the electrode 700.

  In the above description, the power supply input terminal T is provided at one end of the common electrode 700. However, mounting of a component such as a connector as the power input terminal T is not limited. For example, the surface protective layer 512 at one end of the common electrode 700 may be peeled off so as to be electrically connectable to the power supply device 800.

[Modification 1]
In the description of the first embodiment, the case where the length in the short direction (Y-axis direction) of the common electrode 700 is uniformly changed has been described with reference to FIG. However, the shape of the common electrode 700 need not be limited to this. For example, the length of the common electrode 700 in the lateral direction (Y-axis direction) may be changed in an analog manner as a quadratic function or an exponential function. Further, as in the second heater 5 b shown in FIG. 7, the length in the short direction of the common electrode 700 may be changed stepwise. By wiring the common electrode 700 in this manner, the difference in wiring resistance from the power supply input terminal T to each heating resistor is reduced. Thereby, the current density of the current i ₁ to the current i ₇ flowing through the heating resistors 501 to 507 can be expressed as i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ It is assumed that / S6 ≒ i ₇ / S7.

[Modification 2]
In the first embodiment and the first modification, the case where the thickness of the common electrode 700 in the X-axis direction is the same has been described. In the second modification, the third heater 5 c is used instead of the first heater 5. As shown in FIG. 8B, in the third heater 5c, the length in the Y-axis direction of the common electrode 700 is increased as the distance from the power supply input terminal T increases, and the common electrode 700 in the X-axis direction The thickness is increased as the distance from the power supply input terminal T increases. Therefore, even if the length of the common electrode 700 is increased in the −Z direction from the power supply input terminal T, the change in the wiring resistance of the common electrode 700 is small. Thereby, the current density of the current i ₁ to the current i ₇ flowing through the heating resistors 501 to 507 can be expressed as i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ It is assumed that / S6 ≒ i ₇ / S7.

[Modification 3]
In the third modification, instead of the first heater 5, a fourth heater 5d shown in FIG. 9 is used. As shown in FIG. 9, in the fourth heater 5d, the thickness in the X-axis direction of the common electrode 700 is changed stepwise. By wiring the common electrode 700 in this manner, the difference in wiring resistance from the power supply input terminal T to each heating resistor is reduced. Thereby, the current density of the current i ₁ to the current i ₇ flowing through the heating resistors 501 to 507 can be expressed as i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ It is assumed that / S6 ≒ i ₇ / S7.

Second Embodiment
In the first embodiment and the first to third modifications, a technique for reducing the difference in wiring resistance from the power supply input terminal T to the heating resistors 501 to 507 has been described by devising the shape of the common electrode 700. In the second embodiment, the branch patterns 701 to 707 are provided between the common electrode 700 and the heating resistors 501 to 507, and the shape of the branch patterns 701 to 707 is devised to generate the heating resistor 501 from the power supply input terminal T. A technique for reducing the difference in wiring resistance up to .about.507 will be described. The second embodiment will be described below with reference to FIG. About the same or equivalent composition as a 1st embodiment, while using the same numerals, the explanation is omitted or simplified.

[Heater 5]
FIG. 10A is a YZ plan view of the fifth heater 5e replaced with the first heater 5 in the fixing device 4 shown in FIG. 3 and a peripheral circuit. As shown in FIG. 10A, the fifth heater 5e includes a plurality of heating resistors 501 to 507 arranged in the longitudinal direction of the ceramic substrate 514 and one end of each of the plurality of heating resistors 501 to 507 (see FIG. The individual electrodes 601 to 607 connected to the lower side in the Y-axis direction, the common electrode 700 obliquely extending in the longitudinal direction (Z-axis direction), and the other end (Y of the heating resistor not connected to the individual electrodes) A plurality of branch patterns 701 to 707 connecting the upper side in the axial direction and the common electrode 700 and a power input terminal T provided at one end of the common electrode 700 in the longitudinal direction.

  The branch patterns 701 to 707 are formed by etching away the conductor layer 50. In the branch patterns 701 to 707, as shown in FIG. 10A, as the heating resistor is farther from the power input terminal T, the wiring length in the Y-axis direction of the branch pattern connecting the heating resistor and the common electrode 700 is greater. It is formed to be short. Specifically, the heating resistor 506 which is farther from the power supply input terminal T than the heating resistor 507 is connected to the common electrode by a branch pattern 706 shorter than the branch pattern 707. The heating resistor 505 which is farther from the power supply input terminal T than the heating resistor 506 is connected to the common electrode 700 by a branch pattern 705 shorter than the branch pattern 706. The same applies to the following.

  FIG. 10B is a cross-sectional view of the branch patterns 701 to 707 of the fifth heater 5 e. FIG. 10C is a cross-sectional view of the heating resistors 501 to 507 of the fifth heater 5e. In the second embodiment, the thicknesses of the branch patterns 701 to 707 of the fifth heater 5 e and the heating resistors 501 to 507 of the fifth heater 5 e in the X-axis direction are the same.

  One end (lower side in the Y-axis direction) of each of the plurality of heating resistors 501 to 507 is connected to the power supply device 800 via the individual electrodes 601 to 607 and the switches S1 to S4. The power supply input terminal T provided at one end in the longitudinal direction of the common electrode 700 is connected to the other end of the power supply apparatus 800 to which the switches S1 to S4 are not connected. The power supply 800 uses an AC power supply to prevent migration.

[Operation]
Next, the operation of the fixing device 4 will be described with reference to FIG. Here, the values of the wiring resistances of the individual electrodes 601 to 607 of the fifth heater 5e and the values of the wiring resistance from the individual electrodes 601 to 607 to the power supply 800 via the switches S1 to S4 are the same. It will be assumed that When the user designates B5 size printing paper, the switch S1 in the control device 36 is turned on. When the user designates A4 size printing paper, the switch S1 and the switch S2 in the control device 36 are turned on. When the user designates printing paper of B4 size, the switches S1 to S3 in the control device 36 are turned on. When the user designates A3 size printing paper, the switches S1 to S4 in the control device 36 are turned on.

A current flowing through the heating resistor 501 is i ₁ , a current flowing through the heating resistor 502 is i ₂ , a current flowing through the heating resistor 503 is i ₃ , and so forth, and a current flowing through the heating resistor 507 is i ₇ . The current i ₁ flowing through the heating resistor 501 reaches the heating resistor 501 through the entire path of the common electrode 700 extending in the longitudinal direction. I ₇ The current flowing through the heating resistor 507, leading to the heating resistor 507 through a short path which is part of the common electrode 700 extending in the longitudinal direction. However, as shown in FIG. 10A, the lengths of the branch patterns 701 to 707 in the Y-axis direction become shorter in the Y-axis direction as they are farther from the power supply input terminal T. Therefore, the difference in wiring resistance from the power supply input terminal T to each heating resistor is small.

Since the power input difference in wiring resistance leading to the heating resistors from the terminal T is small, variations in the current density of the current i _{1 ~} current i ₇ through the heating resistor 501 to 507 is reduced. That is, assuming that the cross-sectional areas of the heating resistors 501 to 507 are S1 to S7, the currents i ₁ to i ₇ flowing through the heating resistors are i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S4 ≒ _i 5 / S5 flows so that the _{≒ i 6 / S6 ≒ i 7} / S7.

By thus reduce variations in the current density of the current i _{1 ~} current i _7, it is possible to make uniform the amount of heat generated per unit length of the Z-axis direction of the heating resistor 501 to 507, the printing paper The fixing degree of toner from the left end to the right end can be made uniform. This can improve the quality of the printed image.

  In the above description, it is assumed that the values of the wiring resistances of the individual electrodes 601 to 607 and the values of the wiring resistance from the individual electrodes 601 to 607 to the power supply 800 through the switches S1 to S4 are the same. explained. When the wiring resistances are different, the total value of the wiring resistance from the power input terminal T to each heating resistor, the wiring resistance of the individual electrodes, and the wiring resistance from each individual electrode to the power supply 800 approximate each other. It is desirable to wire the electrode 700 and the branch patterns 701 to 707.

[Modification 4]
In the description of the second embodiment, the case where the lengths in the short direction (Y-axis direction) of the branch patterns 701 to 707 are changed in an analog manner has been described with reference to FIG. However, it is not necessary to limit the shape of the branch pattern to this. For example, it is also possible to use a sixth heater 5f shown in FIG. 11 instead of the fifth heater 5e. As shown in FIG. 11, in the sixth heater 5f, the length in the short direction of the branch pattern is changed stepwise. By wiring in this manner, the current densities of the currents i ₁ to i ₇ flowing through the heating resistors 501 to 507 can be made equal. That is, i ₁ / S ₁ ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ / S 6 ii ₇ / S ₇ can be obtained.

[Modification 5]
In the second embodiment and the fourth modification, the case where the thicknesses of the branch patterns 701 to 707 in the X-axis direction are the same has been described. In the fifth modification, instead of the first heater 5, a seventh heater 5g shown in FIG. 12 is used. As shown in FIG. 12B, in the seventh heater 5g, the thickness in the X-axis direction of the branch patterns 701 to 707 increases as the distance from the power supply input terminal T increases. That is, as the distance from the power supply input terminal T increases, the resistance per unit length of the branch patterns 701 to 707 in the Z-axis direction decreases. By wiring the common electrode 700 in this manner, the difference in wiring resistance from the power supply input terminal T to each heating resistor is reduced. Thus, the current densities of the currents i ₁ to i ₇ flowing through the heating resistors 501 to 507 are i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ / S6 ≒ i ₇ / S7.

[Modification 6]
In the sixth modification, an eighth heater 5 h shown in FIG. 13 can be used instead of the first heater 5. As shown in FIG. 13, in the eighth heater 5 h, the thickness in the X-axis direction of the branch patterns 701 to 707 is changed stepwise. By wiring the branch patterns 701 to 707 in this manner, the difference in wiring resistance from the power supply input terminal T to each heating resistor is reduced. Thus, the current densities of the currents i ₁ to i ₇ flowing through the heating resistors 501 to 507 are i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ / S6 ≒ i ₇ / S7.

Third Embodiment
In the third embodiment, a technique for reducing the difference in current density of the currents i ₁ to i ₇ flowing through the heating resistors 501 to 507 by devising the shapes of the heating resistors 501 to 507 will be described. . The third embodiment will be described below. The same reference numerals will be used for configurations that are the same as or equivalent to the first embodiment and the second embodiment, and the description thereof will be omitted or simplified.

  FIG. 14A is a YZ plan view of a ninth heater 5i which is replaced by the first heater 5 in the fixing device 4 shown in FIG. As shown in FIG. 14A, in the ninth heater 5i, the length of the heat generating resistors 501 to 507 in the lateral direction (Y-axis direction) is formed so as to become shorter as the distance from the power supply input terminal T increases. It is done. That is, as the distance from the power supply input terminal T increases, the resistance per unit length of the heating resistor in the Z-axis direction decreases. Further, the common electrodes 700 are directly connected to the heat generating resistors 501 to 507 without providing the branch patterns 701 to 707.

A current flowing through the heating resistor 501 is i ₁ , a current flowing through the heating resistor 502 is i ₂ , a current flowing through the heating resistor 503 is i ₃ , and so forth, and a current flowing through the heating resistor 507 is i ₇ . As the current flowing through the heat generating resistor farther from the power supply input terminal T, the wiring resistance of the common electrode 700 becomes larger. For example, the wiring resistance of the common electrode 700 where the current _{i 1} flows is larger than the wiring resistance of the common electrode 700 current _{i 7} flows. On the other hand, the resistance per unit length in the Z-axis direction decreases as the heating resistors 501 to 507 move away from the power supply input terminal T. That is, the heating resistors 501 to 507 are formed such that the total value of the wiring resistance of the common electrode 700 from the power input terminal T to each heating resistor and the resistance of each heating resistor approximates.

As described above, in the ninth heater 5i of the fixing device 4 according to the third embodiment, the length of the heating resistors 501 to 507 in the Y-axis direction is shortened as the distance from the power input terminal T increases. There is. As a result, i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ / S 6 ii ₇ / S ₇ . By thus reduce variations in the current density of the current i _{1 ~} current i _7, it is possible to make uniform the amount of heat generated per unit length of the Z-axis direction of the heating resistor 501 to 507, the printing paper The fixing degree of toner from the left end to the right end can be made uniform. This can improve the quality of the printed image.

[Modification 7]
In the seventh modification, the tenth heater 5 j shown in FIG. 15 is used instead of the first heater 5. As shown in FIG. 15C, in the tenth heater 5j, the thickness in the X-axis direction of the heating resistors 501 to 507 is increased as the distance from the power supply input terminal T increases. That is, as the distance from the power supply input terminal T increases, the resistance per unit length of the heating resistors 501 to 507 in the Z-axis direction decreases. By thus forming the thickness in the X-axis direction of the heating resistors 501 to 507, the total value of the value of the wiring resistance from the power supply input terminal T to each heating resistor and the value of the resistance of each heating resistor To approximate. Thus, the current densities of the currents i ₁ to i ₇ flowing through the heating resistors 501 to 507 are i ₁ / S 1 ii ₂ / S ₂ ii ₃ / S ₃ ii ₄ / S 4 ii ₅ / S 5 ii ₆ / S6 ≒ i ₇ / S7.

As described above, in the first embodiment, by devising the shape of the common electrode 700 have been described techniques for reducing the difference in the current density of the current i _{1 ~} current i ₇ through the heating resistor 501 to 507. In the second embodiment, by devising the shape of the branch patterns 701 to 707, has been described technique for reducing the difference in the current density of the current _{i 1} ~ current _{i 7} through the heating resistor 501 to 507. In the third embodiment, by devising the shape of the heating resistor 501 to 507, it has been described technique for reducing the difference in the current density of the current _{i 1} ~ current _{i 7} through the heating resistors 501 to 507 . In each embodiment, a technique for reducing the difference in current density between the current i ₁ to the current i ₇ flowing through the heating resistors 501 to 507 by devising the length of the pattern and the thickness of the cross section of the pattern Explained. In addition to the embodiments described above, these multiple techniques can be combined and applied, and further variations can be used. For example, in the heater 5k shown in FIG. 16, the length in the short direction (Y-axis direction) of the branch patterns 701 to 707, the thickness in the X axis direction of the branch patterns 701 to 707, the short side of the heating resistors 501 to 507 The length in the direction (Y-axis direction) and the thickness in the X-axis direction of the heating resistors 501 to 507 are changed according to the distance from the power supply input terminal T.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in other various forms, and various omissions, replacements and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 MFP (MFP)
11 main body 14 operation panel 17 printer section 18 paper feed cassette 19 scan head 20 image formation section 21 intermediate transfer belt 22 photosensitive drum 23K charger 24K development unit 25K primary transfer roller 26K cleaner 27K blade 31 drive roller 33 secondary transfer roller 4 Fixing device 400 Heating device 402 Fixing belt 440 Pressure roller 442 Protective layer 444 Silicon sponge layer 446 Iron cores 5, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 5i, 5j, 5k Heaters 50 Conductive layers 501 to 507 Heating resistor 512 Surface protective layer 514 Ceramic substrate 516 Holder 52 Heating resistor layer 601 to 607 Individual electrode 700 Common electrode 701 to 707 Branch pattern 800 Power supply device

Claims (4)

A plurality of heating resistors arranged in a first direction on a heat resistant insulating substrate;
An individual electrode connected to one end of each of the plurality of heating resistors;
A common electrode connected to the other end of the heating resistor whose longitudinal direction is the first direction and the individual electrodes are not connected;
A power input terminal provided at one end of the common electrode in the longitudinal direction;
A fixing device comprising a heater having
The common electrode is formed such that the width of the second direction perpendicular to the first direction of the pattern forming the electrode is wider as the distance from the power supply input terminal increases, or the thickness of the pattern forming the electrode is thicker Being
Fixing device. A plurality of heating resistors arranged in a first direction on a heat resistant insulating substrate;
An individual electrode connected to one end of each of the plurality of heating resistors;
A common electrode whose longitudinal direction is the first direction;
A plurality of branch patterns connecting the common electrode to the other end of the heating resistor not connected to the individual electrodes;
A power input terminal provided at one end of the common electrode in the first direction;
A fixing device comprising a heater having
The wiring length of the branch pattern connecting the heating resistor and the common electrode is formed shorter as the heating resistor is disposed at a position farther from the power supply input terminal, or the thickness of the branch pattern Is thickly formed,
Fixing device. A plurality of heating resistors arranged in a first direction on a heat resistant insulating substrate;
An individual electrode connected to one end of each of the plurality of heating resistors;
A common electrode connected to the other end of the heating resistor whose longitudinal direction is the first direction and the individual electrodes are not connected;
A power input terminal provided at one end of the common electrode in the longitudinal direction;
A fixing device comprising a heater having
The heat generating resistor is formed shorter in the second direction orthogonal to the first direction as the heat generating resistor is disposed at a position farther from the power supply input terminal, or the thickness of the heat generating resistor is Thickly formed,
Fixing device. Photosensitive drum,
A latent image forming unit for forming a latent image on the photosensitive drum;
A developer for the latent image;
A transfer unit for transferring a toner image visualized by the developing unit to a recording medium;
A fixing device according to any one of claims 1 to 3.
An image forming apparatus comprising:

Images