Heating device and image forming apparatus

Abstract

To provide a heating device that can switch a connection configuration of two heating units between serial and parallel and drive only one heating unit, and an image forming apparatus.SOLUTION: A heating device comprises: a first heating unit 51 that, upon supply of power, heats a first area including a center part in a width direction of a sheet on a fixing belt; a second heating unit 52 that, upon supply of power, heats a pair of second areas sandwiching the first area in the width direction on the fixing belt; and a drive circuit 53 that can switch an operation mode among a first mode for supplying power to the first heating unit 51 and not supplying power to the second heating unit 52, a second mode for supplying power to the first heating unit 51 and second heating unit 52 connected in series, and a third mode for supplying power to the first heating unit 51 and second heating unit 52 connected in parallel.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a heating device and an image forming apparatus.

Background Art

[0002] An electrophotographic image forming apparatus includes a fixing member that fixes a toner image transferred onto a sheet to the sheet, and a heating unit that heats the fixing member in response to power supply. Further, an image forming apparatus in which the connection form of a plurality of the heating units can be switched between series and parallel is known as a related art (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the image forming apparatus, both outer sides of a first region including a central portion in the width direction of the sheet on the fixing member may be selectively heated. However, in the image forming apparatus according to the above-described related art, among a first heating unit that heats the first region on the fixing member and a second heating unit that heats a pair of second regions sandwiching the first region in the width direction on the fixing member, only the first heating unit cannot be driven.

[0005] An object of the present invention is to provide a heating device and an image forming apparatus capable of switching the connection form of two heating units between series and parallel and driving only one of the heating units.

Means for Solving the Problems

[0006] A heating device according to one aspect of the present invention is a device that heats a fixing member for fixing a toner image transferred onto a sheet to the sheet, and includes a first heating unit, a second heating unit, and a drive circuit. The first heating unit heats a first region including a central portion in the width direction of the sheet on the fixing member in response to power supply. The second heating unit heats a pair of second regions sandwiching the first region in the width direction on the fixing member in response to power supply. The drive circuit is switchable between a first mode in which power is supplied to the first heating unit and not to the second heating unit, a second mode in which power is supplied to the first heating unit and the second heating unit connected in series, and a third mode in which power is supplied to the first heating unit and the second heating unit connected in parallel.

[0007] An image forming apparatus according to another aspect of the present invention includes the heating device and the fixing member, and forms an image on the sheet using the fixing member.

Advantages of the Invention

[0008] According to the present invention, it is possible to switch the connection form between the two heating units between series and parallel and drive only one of the heating units.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are merely examples of embodying the present invention and do not limit the technical scope of the present invention.

[0011] [Configuration of Image Forming Apparatus 100] First, with reference to FIG. 1, the configuration of the image forming apparatus 100 according to an embodiment of the present invention will be described. Here, FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus 100.

[0012] For convenience of explanation, in the installable state (the state shown in FIG. 1) in which the image forming apparatus 100 can be used, the vertical direction is defined as the up-down direction D1. Also, with the left side surface of the image forming apparatus 100 shown in FIG. 1 as the front (front surface), the front-rear direction D2 is defined. Further, with reference to the front surface of the image forming apparatus 100 in the installable state, the left-right direction D3 is defined.

[0013] The image forming apparatus 100 is a printer having a printing function of forming an image on a sheet based on image data. Note that the present invention can be applied to a facsimile apparatus, a copying machine, a multifunction machine, etc. that form an image by an electrophotographic method.

[0014] As shown in FIG. 1, the image forming apparatus 100 includes an image forming unit 1 and a sheet conveying unit 2. The image forming unit 1 and the sheet conveying unit 2 are housed in the housing 101 of the image forming apparatus 100. The housing 101 is formed in a substantially rectangular parallelepiped shape. At the upper part of the housing 101, a sheet receiving portion 102 for discharging the sheet on which the image is formed by the image forming apparatus 100 is formed.

[0015] The image forming unit 1 can form an image on a sheet by an electrophotographic method based on image data input from an information processing device such as an external personal computer. As shown in FIG. 1, the image forming unit 1 includes a photosensitive drum 11, a charging device 12, an optical scanning device 13, a developing device 14, a transfer roller 15, a cleaning device 16, and a fixing device 17.

[0016] The photosensitive drum 11 is rotatably supported by a housing 101. The photosensitive drum 11 receives a rotational driving force transmitted from a motor (not shown) and rotates in the direction of the arrow shown in FIG. 1.

[0017] The charging device 12 charges the surface of the photosensitive drum 11.

[0018] The optical scanning device 13 irradiates light based on the image data onto the surface of the charged photosensitive drum 11. An electrostatic latent image is formed on the surface of the photosensitive drum 11 by the optical scanning device 13.

[0019] The developing device 14 develops the electrostatic latent image formed on the surface of the photosensitive drum 11 using a developer containing toner. A toner image is formed on the surface of the photosensitive drum 11 by the developing device 14.

[0020] The transfer roller 15 transfers the toner image formed on the surface of the photosensitive drum 11 to a sheet being conveyed by the sheet conveyance unit 2 toward the fixing device 17.

[0021] The cleaning device 16 cleans the surface of the photosensitive drum 11 after the toner image has been transferred by the transfer roller 15.

[0022] The fixing device 17 heats the sheet onto which the toner image has been transferred and fixes the toner image to the sheet.

[0023] The sheet conveyance unit 2 conveys the sheet on which an image is formed by the image forming unit 1. As shown in FIG. 1, the sheet conveyance unit 2 includes a paper feed cassette 21, a sheet conveyance path 22, a paper feed unit 23, a registration roller pair 24, and a paper discharge roller pair 25.

[0024] The paper feed cassette 21 stores the sheet on which an image is formed by the image forming unit 1. The paper feed cassette 21 is provided at the bottom of the housing 101 as shown in FIG. 1. For example, the paper feed cassette 21 stores sheet members such as paper, coated paper, postcards, envelopes, and OHP sheets. The paper feed cassette 21 has a lift plate for lifting a plurality of sheets stored therein. In the paper feed cassette 21, the posture of the stored sheet is adjusted so that the sheet is arranged at the center in the left - right direction D3 in the paper feed cassette 21.

[0025] The sheet conveyance path 22 is a movement path of the sheet from the paper feed cassette 21, through the transfer roller 15 and the fixing device 17, and to the sheet receiving portion 102. A plurality of roller pairs including the registration roller pair 24 and the paper discharge roller pair 25 are provided in the sheet conveyance path 22. In the sheet conveyance path 22, the sheet carried out from the paper feed cassette 21 by the plurality of roller pairs is conveyed in the conveyance direction D4 (see FIG. 1) toward the sheet receiving portion 102. The sheet conveyance path 22 is formed by a pair of conveyance guide members provided in the housing 101. In the sheet conveyance path 22, the sheet is conveyed so as to move at the center in the left - right direction D3 in the sheet conveyance path 22.

[0026] The sheet feeding unit 23 feeds the sheets accommodated in the sheet feeding cassette 21 one by one to the sheet conveyance path 22. The sheet feeding unit 23 includes a pickup roller, a sheet feeding roller, and a retard roller. The pickup roller rotates in contact with the upper surface of the uppermost sheet among the plurality of sheets lifted by the lift plate of the sheet feeding cassette 21, thereby feeding the sheet to the sheet feeding roller. The sheet feeding roller rotates in contact with the upper surface of the sheet fed by the pickup roller, thereby feeding the sheet to the sheet conveyance path 22. The retard roller is provided so as to be biased from below the sheet feeding roller toward the sheet feeding roller. The retard roller separates the sheets other than the uppermost sheet from the plurality of overlapping sheets when the plurality of sheets are fed out overlapping each other by the pickup roller.

[0027] The registration roller pair 24 conveys the sheet to the transfer position in accordance with the timing at which the toner image formed on the surface of the photosensitive drum 11 is conveyed to the transfer position by the transfer roller 15 due to the rotation of the photosensitive drum 11.

[0028] The discharging roller pair 25 discharges the sheet on which the toner image has been fixed by the fixing device 17 to the sheet receiving portion 102.

[0029] [Configuration of the fixing device 17] Next, the configuration of the fixing device 17 will be described with reference to FIG. 2. Here, FIG. 2 is a cross-sectional view showing the configuration of the fixing device 17.

[0030] As shown in FIG. 2, the fixing device 17 includes a fixing belt 31, a heating device 32, a first support portion 33, a second support portion 34, and a pressure roller 35.

[0031] The fixing belt 31 is heated by a heating device 32. The fixing belt 31 contacts the sheet in a heated state to fix the toner image transferred to the sheet onto the sheet. As shown in FIG. 2, the fixing belt 31 is endless. Further, the fixing belt 31 has flexibility. The fixing belt 31 includes a base material layer, an elastic layer provided on the outer peripheral surface of the base material layer, and a release layer provided on the outer peripheral surface of the elastic layer. The base material layer is formed of a material such as polyimide or a nickel alloy. The elastic layer is formed of a material such as silicone rubber. The release layer is formed of a fluororesin material such as PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin). The fixing belt 31 is long along the left-right direction D3. The size of the fixing belt 31 in the left-right direction D3 is determined according to the maximum size of the sheet on which an image can be formed by the image forming apparatus 100. The fixing belt 31 is an example of the fixing member of the present invention.

[0032] The pressure roller 35 is provided at a position where it can contact the outer peripheral surface 31A (see FIG. 2) of the fixing belt 31. Specifically, as shown in FIG. 2, the pressure roller 35 is provided below the fixing belt 31. The pressure roller 35 is long along the left-right direction D3. The pressure roller 35 includes a shaft portion 35A and an elastic layer 35B. The shaft portion 35A is formed in a cylindrical shape of a metal material. The elastic layer 35B is formed on the outer periphery of the shaft portion 35A of a material having elasticity such as silicone rubber. The surface of the elastic layer 35B is coated with PFA or the like. The shaft portion 35A is rotatably supported by a pair of bearing portions provided inside the housing 101. The pair of bearing portions are movably supported by the housing 101 in a direction orthogonal to the shaft portion 35A and along the direction toward the heating device 32. The pair of bearing portions are biased toward the heating device 32 by a biasing member (not shown). Thereby, the pressure roller 35 rotatably supported by the pair of bearing portions is also biased toward the heating device 32. The pressure roller 35 rotates in the rotation direction D5 (see FIG. 2) by receiving a rotational driving force supplied from a motor (not shown).

[0033] The heating device 32 heats the fixing belt 31. As shown in FIG. 2, the heating device 32 is provided inside the inner peripheral surface 31B (see FIG. 2) of the fixing belt 31 and at a position facing the pressure roller 35 with the fixing belt 31 interposed therebetween. The heating device 32 is long in the left-right direction D3 and extends across both outer sides of the fixing belt 31 in the left-right direction D3. The heating device 32 is pressed by the pressure roller 35 biased by the biasing member.

[0034] The first support portion 33 supports the heating device 32 pressed by the pressure roller 35 together with the second support portion 34. As shown in FIG. 2, the first support portion 33 is provided inside the inner peripheral surface 31B of the fixing belt 31. The first support portion 33 is long in the left-right direction D3 and extends across both outer sides of the fixing belt 31 in the left-right direction D3. A recess 33A corresponding to the shape of the heating device 32 is formed at the bottom of the first support portion 33. The heating device 32 is fitted into the recess 33A.

[0035] The second support portion 34 supports the heating device 32 pressed by the pressure roller 35 together with the first support portion 33. As shown in FIG. 2, the second support portion 34 is provided inside the inner peripheral surface 31B of the fixing belt 31 and at a position facing the pressure roller 35 with the first support portion 33 interposed therebetween. The second support portion 34 is long in the left-right direction D3 and extends across both outer sides of the fixing belt 31 in the left-right direction D3. Both end portions of the second support portion 34 in the left-right direction D3 are fixed so as not to be movable in the biasing direction of the biasing member that biases the pressure roller 35. Thereby, the second support portion 34 supports the heating device 32 pressed by the pressure roller 35 and the first support portion 33.

[0036] When the pressure roller 35 is biased by the biasing member, a fixing nip portion 36 (see FIG. 2) for fixing the toner image transferred to the sheet to the sheet is formed between the fixing belt 31 and the pressure roller 35. In this specification, the region where the fixing belt 31 and the pressure roller 35 contact is defined as the fixing nip portion 36. Note that a lubricant such as Si grease and fluorine grease is applied between the heating device 32 and the inner peripheral surface 31B of the fixing belt 31.

[0037] The fixing belt 31 is sandwiched between the heating device 32 and the pressure roller 35. When the pressure roller 35 rotates in the rotation direction D5, the fixing belt 31 rotates along the belt rotation direction D6 (see FIG. 2) following the rotation of the pressure roller 35.

[0038] The first support portion 33 includes a pair of guide portions 33B and 33C (see FIG. 2) that contact the inner peripheral surface 31B of the fixing belt 31 and guide the running of the fixing belt 31. The pair of guide portions 33B and 33C are provided at both ends in the front-rear direction D2 of the first support portion 33. The fixing belt 31 is guided to run along a predetermined running path by the pair of guide portions 33B and 33C.

[0039] Note that the second support portion 34 may be biased toward the pressure roller 35 side. In this case, the pressure roller 35 may not be biased by the biasing member.

[0040] [Configuration of Heating Device 32] Next, the configuration of the heating device 32 will be described with reference to FIGS. 2 to 5. Here, FIG. 3 is a cross-sectional view showing the configuration of the heating device 32. FIG. 4 is a view showing the configuration of the heating device 32 as seen from below. FIG. 5 is a view showing the configurations of the fixing belt 31 and the heating device 32 as seen from below. Note that in FIG. 5, the heating device 32 is shown in a simplified manner.

[0041] The heating device 32 is a resistance heating heater. As shown in FIGS. 3 and 4, the heating device 32 includes a substrate 41, four resistance heating elements 42 (42A to 42D), first electrodes 43A to 43B provided for each of the resistance heating elements 42, four second electrodes 44A to 44D, six conductive paths 45A to 45F, and a protective layer 46.

[0042] The substrate 41 is a flat plate-like member that is long in the left-right direction D3. The substrate 41 is formed of a material having excellent heat resistance, electrical insulation, and low heat capacity. For example, the substrate 41 is formed of a ceramic such as alumina.

[0043] The substrate 41 is larger in size in the left-right direction D3 than the fixing belt 31. The substrate 41 is arranged so as to extend to both outer sides of the fixing belt 31 in the left-right direction D3. Therefore, both end portions of the substrate 41 in the left-right direction D3 protrude outward in the left-right direction D3 from the fixing belt 31 (see FIG. 5).

[0044] As shown in FIGS. 2 and 3, the lower surface of the substrate 41 faces the inner peripheral surface 31B of the fixing belt 31. As shown in FIGS. 3 and 4, four resistance heating elements 42 (42A to 42D), first electrodes 43A to 43B provided for each of the resistance heating elements 42, four second electrodes 44A to 44D, and six conductive paths 45A to 45F are arranged on the lower surface of the substrate 41. Further, a counter region of the lower surface of the substrate 41 that faces the inner peripheral surface 31B of the fixing belt 31 is covered with a protective layer 46 (see FIG. 3). The protective layer 46 is formed of a material having electrical insulation such as glass.

[0045] As shown in FIG. 4, each of the resistance heating elements 42 is formed in a strip shape that is long in the left-right direction D3, which is the longitudinal direction of the substrate 41. Each of the resistance heating elements 42 generates heat in response to power supply from a power source 200 (see FIG. 6). For example, each of the resistance heating elements 42 is formed of a material such as silver palladium (Ag / Pd).

[0046] As shown in FIG. 4, the four resistance heating elements 42 are arranged side by side along the left - right direction D3 on the substrate 41. Each of the resistance heating elements 42 is arranged with a space in the left - right direction D3 from the other adjacent resistance heating elements 42. The row of the four resistance heating elements 42 is smaller in size in the left - right direction D3 than the fixing belt 31. The row of the four resistance heating elements 42 is arranged inside the facing region on the lower surface of the substrate 41. The row of the four resistance heating elements 42 is arranged such that the central part in the left - right direction D3 faces the central part in the left - right direction D3 of the sheet passing through the fixing nip portion 36.

[0047] As shown in FIG. 4, each of the resistance heating elements 42 is sandwiched between the first electrode 43A and the first electrode 43B in the width direction (front - rear direction D2) of the substrate 41.

[0048] The first electrode 43A is electrically connected to the front end portion of the resistance heating element 42 in the front - rear direction D2. As shown in FIG. 4, the first electrode 43A is provided along the front end portion of the resistance heating element 42 in the front - rear direction D2. Also, the first electrode 43A extends across both end portions of the resistance heating element 42 in the left - right direction D3. The first electrode 43A is formed in a strip shape that is long in the left - right direction D3. The first electrode 43A is formed of a conductor such as a metal material having higher conductivity than the resistance heating element 42.

[0049] The first electrode 43B is electrically connected to the rear end portion of the resistance heating element 42 in the front - rear direction D2. As shown in FIG. 4, the first electrode 43B is provided along the rear end portion of the resistance heating element 42 in the front - rear direction D2. Also, the first electrode 43B extends across both end portions of the resistance heating element 42 in the left - right direction D3. The first electrode 43B is formed in the same shape and of the same material as the first electrode 43A.

[0050] The second electrodes 44A to 44B are connected to a power supply 200 (see FIG. 6). As shown in FIG. 4, the conductive path 45A electrically connects the second electrode 44A and the first electrode 43A corresponding to the resistor heating element 42A disposed on the rightmost side among the four resistor heating elements 42. The conductive path 45B electrically connects the first electrode 43B corresponding to the resistor heating element 42A and the first electrode 43B corresponding to the resistor heating element 42D disposed on the leftmost side among the four resistor heating elements 42. The conductive path 45C electrically connects the first electrode 43A corresponding to the resistor heating element 42D and the second electrode 44B. As shown in FIG. 4, an energization path is formed on the substrate 41 from the second electrode 44A through the conductive path 45A, the resistor heating element 42A, the conductive path 45B, the resistor heating element 42D, and the conductive path 45C to the second electrode 44B. The second electrodes 44A to 44B and the conductive paths 45A to 45C are formed of the same material (conductor) as the first electrode 43A. When the second electrodes 44A to 44B are connected to the power supply 200, current flows through the resistor heating element 42A and the resistor heating element 42D, and the resistor heating element 42A and the resistor heating element 42D generate heat.

[0051] The second electrodes 44C to 44D are connected to a power supply 200 (see FIG. 6). As shown in FIG. 4, the conductive path 45D electrically connects the second electrode 44C and the first electrode 43A corresponding to the heating resistor 42B adjacent to the heating resistor 42A on the left side of the heating resistor 42A among the four heating resistors 42. The conductive path 45E electrically connects the first electrode 43B corresponding to the heating resistor 42B and the first electrode 43B corresponding to the heating resistor 42C adjacent to the heating resistor 42B on the left side of the heating resistor 42B among the four heating resistors 42. The conductive path 45F electrically connects the first electrode 43A corresponding to the heating resistor 42C and the second electrode 44D. As shown in FIG. 4, on the substrate 41, an energization path is formed from the second electrode 44C, through the conductive path 45D, the heating resistor 42B, the conductive path 45E, the heating resistor 42C, and the conductive path 45F to the second electrode 44D. The second electrodes 44C to 44D and the conductive paths 45D to 45F are formed of the same material (conductor) as the first electrode 43A. When the second electrodes 44C to 44D are connected to the power supply 200, current flows through the heating resistor 42B and the heating resistor 42C, and the heating resistor 42B and the heating resistor 42C generate heat.

[0052] The heating resistor 42B and the heating resistor 42C constitute a first heating unit 51 (see FIG. 6). The first heating unit 51 heats a first region R1 (see FIG. 5) including a central portion in the sheet width direction (left - right direction D3) of the fixing belt 31 in response to power supply.

[0053] The heating resistor 42A and the heating resistor 42D constitute a second heating unit 52 (see FIG. 6). The second heating unit 52 heats a pair of second regions R2 (see FIG. 5) sandwiching the first region R1 in the sheet width direction (left - right direction D3) of the fixing belt 31 in response to power supply.

[0054] In the image forming apparatus 100, the presence or absence of driving of the second heating unit 52 is switched according to the size in the width direction (left - right direction D3) of the sheet passing through the fixing nip portion 36. Specifically, in the image forming apparatus 100, when an image is formed on a first sheet (an example of the specific sheet of the present invention) whose size in the width direction (left - right direction D3) is larger than the reference size corresponding to the first region R1, the second heating unit 52 is driven. Also, in the image forming apparatus 100, when an image is formed on a second sheet whose size in the width direction (left - right direction D3) is equal to or less than the reference size, the second heating unit 52 is not driven. For example, the reference size is the same size as the size in the left - right direction D3 in the first region R1. Note that the reference size may be a size different from the size in the left - right direction D3 in the first region R1.

[0055] In addition, the number of the resistance heating elements 42 arranged along the longitudinal direction of the substrate 41 on the substrate 41 may be three, or may be five or more. Also, the resistance heating element 42 is not limited to a long strip shape (rectangular shape) in the longitudinal direction (left - right direction D3) of the substrate 41, and may be formed in a parallelogram shape.

[0056] By the way, an image forming apparatus capable of switching the connection form of a plurality of heating units between series and parallel is known as a related art.

[0057] However, in the image forming apparatus according to the above - mentioned related art, although the connection form of the plurality of heating units can be switched between series and parallel, only any one of the plurality of heating units cannot be driven.

[0058] On the other hand, in the image forming apparatus 100 according to the embodiment of the present invention, as described below, the connection form of the first heating unit 51 and the second heating unit 52 can be switched between series and parallel, and only the first heating unit 51 can be driven.

[0059] Specifically, the heating device 32 includes a drive circuit 53 shown in FIG. 6. Also, the image forming apparatus 100 includes a drive control unit 54 shown in FIG. 6.

[0060] [Configuration of the drive circuit 53] Hereinafter, with reference to FIG. 6, the configuration of the drive circuit 53 will be described. Here, FIG. 6 is a circuit diagram showing the configuration of the drive circuit 53. In FIG. 6, the control signals SG1 to SG4 output from the drive control unit 54 are shown by broken lines with arrows.

[0061] As shown in FIG. 6, the drive circuit 53 includes a first relay 61, a first triac 62, a second triac 63, a second relay 64, a first energization path 71, a second energization path 72, a third energization path 73, a fourth energization path 74, and a fifth energization path 75.

[0062] As shown in FIG. 6, the first energization path 71 connects the power supply 200 and the second electrode 44C of the first heating unit 51 (see FIG. 4) (an example of the first terminal of the first heating unit of the present invention). The power supply 200 is a commercial power supply outside the image forming apparatus 100 and outputs an alternating voltage with a predetermined frequency and voltage.

[0063] As shown in FIG. 6, the first relay 61 is provided in the first energization path 71. The first relay 61 switches the conduction and interruption of the first energization path 71 according to the presence or absence of the input of the control signal SG1 (see FIG. 6) output from the drive control unit 54. The first relay 61 is an example of the first switch of the present invention. Note that the drive circuit 53 may include a mechanical switch different from a relay and operable by the drive control unit 54 instead of the first relay 61.

[0064] As shown in FIG. 6, the first triac 62 is provided between the first relay 61 and the first heating unit 51 in the first energization path 71. The first triac 62 switches the conduction and interruption of the first energization path 71 according to the presence or absence of the input of the control signal SG2 (see FIG. 6) output from the drive control unit 54. The first triac 62 is an example of the first switching element of the present invention. Note that the drive circuit 53 may include a switching element different from a triac instead of the first triac 62.

[0065] As shown in FIG. 6, the second current path 72 connects the second electrode 44C of the first heating unit 51 and the second electrode 44A of the second heating unit 52 (see FIG. 4) (an example of the first terminal of the second heating unit of the present invention).

[0066] As shown in FIG. 6, the third current path 73 connects the second electrode 44D of the first heating unit 51 (see FIG. 4) (an example of the second terminal of the first heating unit of the present invention) and the second electrode 44B of the second heating unit 52 (see FIG. 4) (an example of the second terminal of the second heating unit of the present invention).

[0067] As shown in FIG. 6, the second triac 63 is provided in the third current path 73. The second triac 63 switches between conduction and interruption of the third current path 73 according to the presence or absence of the input of the control signal SG3 (see FIG. 6) output from the drive control unit 54. The second triac 63 is an example of the second switching element of the present invention. Note that the drive circuit 53 may include a switching element different from the triac instead of the second triac 63.

[0068] As shown in FIG. 6, the fourth current path 74 connects between the first relay 61 and the first triac 62 in the first current path 71 and the second electrode 44B of the second heating unit 52.

[0069] As shown in FIG. 6, the second relay 64 is provided in the fourth current path 74. The second relay 64 switches between conduction and interruption of the fourth current path 74 according to the presence or absence of the input of the control signal SG4 (see FIG. 6) output from the drive control unit 54. The second relay 64 is an example of the second switch of the present invention. Note that the drive circuit 53 may include a mechanical switch different from the relay, which is a mechanical switch operable by the drive control unit 54, instead of the second relay 64.

[0070] As shown in FIG. 6, the fifth current path 75 connects the power supply 200 and the second electrode 44D of the first heating unit 51.

[0071] The drive circuit 53 shown in FIG. 6 can switch the operation mode among a first mode, a second mode, and a third mode. The first mode is an operation mode in which power is supplied to the first heating unit 51 and no power is supplied to the second heating unit 52. The second mode is an operation mode in which power is supplied to the first heating unit 51 and the second heating unit 52 connected in series. The third mode is an operation mode in which power is supplied to the first heating unit 51 and the second heating unit 52 connected in parallel.

[0072] Specifically, in the first mode, the first relay 61 and the first triac 62 are turned on, and the second triac 63 is turned off. In the first mode, the second relay 64 may be either in the on state or the off state.

[0073] Also, in the second mode, the first relay 61 and the second relay 64 are turned on, and the first triac 62 and the second triac 63 are turned off.

[0074] Also, in the third mode, the first relay 61, the first triac 62, and the second triac 63 are turned on, and the second relay 64 is turned off.

[0075] The drive control unit 54 controls the drive of the heating device 32. The drive control unit 54 includes a CPU, a ROM, and a RAM. The CPU is a processor that executes various arithmetic processes. The ROM is a non-volatile storage device in which information such as control programs for causing the CPU to execute various processes is stored in advance. The RAM is a volatile or non-volatile storage device used as a temporary storage memory (working area) for various processes executed by the CPU. The CPU controls the drive of the heating device 32 by executing various control programs stored in advance in the ROM.

[0076] When an image is formed on the sheet, the drive control unit 54 operates the drive circuit 53 in any one of the operation modes.

[0077] Specifically, when an image is formed on the second sheet, the drive control unit 54 operates the drive circuit 53 in the first mode.

[0078] Also, when an image is formed on the first sheet, the drive control unit 54 operates the drive circuit 53 in the third mode.

[0079] Here, when both the first heating unit 51 and the second heating unit 52 include the resistance heating element 42, since the electrical resistance value of the resistance heating element 42 at normal temperature is low, an excessive current may flow through the drive circuit 53 at the start of power supply to the first heating unit 51 and the second heating unit 52 connected in parallel. If an excessive current flows through the drive circuit 53, there is a risk that the first triac 62 and the second triac 63 will malfunction.

[0080] In contrast, when an image is formed on the first sheet, the drive control unit 54 operates the drive circuit 53 in the second mode until a predetermined switching condition is satisfied, and switches the operation mode of the drive circuit 53 from the second mode to the third mode in response to the satisfaction of the switching condition. Thereby, at the start of power supply to the first heating unit 51 and the second heating unit 52, since the first heating unit 51 and the second heating unit 52 are connected in series, the current flowing through the drive circuit 53 can be suppressed. Also, since the temperature of the first heating unit 51 and the second heating unit 52 rises until the switching condition is satisfied, and thereby the electrical resistance values of the first heating unit 51 and the second heating unit 52 increase, the current flowing through the drive circuit 53 when the operation mode of the drive circuit 53 is switched to the third mode can be suppressed.

[0081] For example, the switching condition is that a predetermined reference time has elapsed since the drive circuit 53 was operated in the second mode. The reference time may be set based on the rising rate of the electrical resistance values of the first heating unit 51 and the second heating unit 52 from the start of power supply to the first heating unit 51 and the second heating unit 52. Note that the switching condition may be that the temperature of the first heating unit 51 and the second heating unit 52 exceeds a predetermined temperature.

[0082] Note that when an image is formed on the first sheet, if the temperatures of the first heating unit 51 and the second heating unit 52 exceed a predetermined temperature, the drive control unit 54 may operate the drive circuit 53 in the third mode from the beginning.

[0083] When the drive circuit 53 is operating in the first mode, the drive control unit 54 controls the drive of the first heating unit 51 based on the temperature of the first region R1 (see FIG. 5) of the fixing belt 31. Specifically, the image forming apparatus 100 is provided with a first sensor (not shown) capable of detecting the temperature of the first region R1 of the fixing belt 31, and a zero-cross detection circuit (not shown) that detects the zero-cross point of the AC voltage output from the power supply 200. Each time a detection signal indicating the detection of the zero-cross point is output from the zero-cross detection circuit, the drive control unit 54 uses the first sensor to determine whether the temperature of the first region R1 of the fixing belt 31 exceeds a predetermined target temperature. Then, when the temperature of the first region R1 of the fixing belt 31 exceeds the target temperature, the drive control unit 54 turns off the first triac 62. Also, when the temperature of the first region R1 of the fixing belt 31 is below the target temperature, the drive control unit 54 turns on the first triac 62.

[0084] Also, when the drive circuit 53 is operating in the third mode, the drive control unit 54 controls the drive of the first heating unit 51 and the second heating unit 52 based on the temperature of the first region R1 of the fixing belt 31. Specifically, each time the detection signal is output from the zero-cross detection circuit, the drive control unit 54 uses the first sensor to determine whether the temperature of the first region R1 of the fixing belt 31 exceeds the target temperature. Then, when the temperature of the first region R1 of the fixing belt 31 exceeds the target temperature, the drive control unit 54 turns off the first triac 62. Also, when the temperature of the first region R1 of the fixing belt 31 is below the target temperature, the drive control unit 54 turns on the first triac 62.

[0085] Also, when the drive circuit 53 is operating in the third mode, the drive control unit 54 controls the drive of the second heating unit 52 based on the temperature of the second region R2 (see FIG. 5) of the fixing belt 31. Specifically, the image forming apparatus 100 is provided with a second sensor (not shown) capable of detecting the temperature of the second region R2 of the fixing belt 31. Each time the detection signal is output from the zero-cross detection circuit, the drive control unit 54 uses the second sensor to determine whether the temperature of the second region R2 of the fixing belt 31 exceeds the target temperature. Then, when the temperature of the second region R2 of the fixing belt 31 exceeds the target temperature, the drive control unit 54 turns off the second triac 63. Also, when the temperature of the second region R2 of the fixing belt 31 is equal to or lower than the target temperature, the drive control unit 54 turns on the second triac 63.

[0086] Also, when the drive circuit 53 is operating in the second mode, the drive control unit 54 does not perform feedback control of the first heating unit 51 and the second heating unit 52 based on the temperature of the fixing belt 31.

[0087] Here, when an image is formed on the first sheet, if the first sheet is thin paper, the heat absorption amount of the fixing belt 31 by the first sheet is small, so that the temperature of the fixing belt 31 may not be controlled near the target temperature by the feedback control of the first heating unit 51 and the second heating unit 52 based on the temperature of the fixing belt 31. That is, the temperature of the fixing belt 31 may rise excessively beyond the target temperature.

[0088] On the other hand, when an image is formed on the first sheet and the thickness of the first sheet is equal to or less than a predetermined reference value, the drive control unit 54 does not switch the operation mode of the drive circuit 53 to the third mode. That is, when an image is formed on the first sheet with a thickness equal to or less than the reference value, the drive control unit 54 operates the drive circuit 53 in the second mode until the image formation is completed. Thereby, since the temperature rise of the first heating unit 51 and the second heating unit 52 due to power supply is suppressed, it is possible to suppress the excessive temperature rise of the fixing belt 31 when an image is formed on the first sheet with a small thickness. The reference value may be set based on the result of an experiment in which the relationship between the thickness of the first sheet and the temperature transition of the fixing belt 31 when feedback control of the first heating unit 51 and the second heating unit 52 based on the temperature of the fixing belt 31 is executed is investigated.

[0089] [Heating control process] Hereinafter, with reference to FIG. 7, an example of the procedure of the heating control process executed by the drive control unit 54 in the image forming apparatus 100 will be described. Here, steps S11, S12,... represent the numbers of the processing steps (steps) executed by the drive control unit 54.

[0090] Note that the drive control unit 54 executes the heating control process when an image forming process for forming an image on a sheet is executed.

[0091] <Step S11> First, in step S11, the drive control unit 54 determines whether the sheet to be image-formed is the first sheet.

[0092] Here, when the drive control unit 54 determines that the sheet to be image-formed is the first sheet (Yes side of S11), the process proceeds to step S12. If the sheet to be image-formed is not the first sheet (No side of S11), the drive control unit 54 proceeds the process to step S21.

[0093] <Step S21> In step S21, the drive control unit 54 operates the drive circuit 53 in the first mode.

[0094] <Step S12> In step S12, the drive control unit 54 determines whether the thickness of the sheet to be image-formed exceeds the reference value.

[0095] Here, when the drive control unit 54 determines that the thickness of the sheet to be image-formed exceeds the reference value (Yes side of S12), the process proceeds to step S13. Also, if the thickness of the sheet to be image-formed is less than or equal to the reference value (No side of S12), the drive control unit 54 proceeds the process to step S22.

[0096] <Step S22> In step S22, the drive control unit 54 operates the drive circuit 53 in the second mode.

[0097] <Step S13> In step S13, the drive control unit 54 operates the drive circuit 53 in the second mode.

[0098] <Step S14> In step S14, the drive control unit 54 determines whether the switching condition is satisfied.

[0099] Here, when the drive control unit 54 determines that the switching condition is satisfied (Yes side of S14), the process proceeds to step S15. Also, if the switching condition is not satisfied (No side of S14), the drive control unit 54 waits for the switching condition to be satisfied in step S14.

[0100] <Step S15> In step S15, the drive control unit 54 switches the operation mode of the drive circuit 53 from the second mode to the third mode.

[0101] Here, the drive control unit 54 switches the operation mode of the drive circuit 53 from the second mode to the third mode according to the following procedure. First, the drive control unit 54 shifts the first triac 62 from the off state to the on state. As a result, the current flowing through the fourth power supply path 74 becomes zero. Next, the drive control unit 54 shifts the second relay 64 from the on state to the off state. Then, the drive control unit 54 shifts the second triac 63 from the off state to the on state. This makes it possible to suppress deterioration of the second relay 64 as compared with a configuration in which the second relay 64 is shifted from the on state to the off state when current is flowing through the fourth power supply path 74.

[0102] <Step S16> In step S16, the drive control unit 54 determines whether or not the image forming process has ended.

[0103] Here, when the drive control unit 54 determines that the image forming process has ended (Yes side of S16), the process proceeds to step S17. If the image forming process has not ended (No side of S16), the drive control unit 54 waits for the end of the image forming process in step S16.

[0104] <Step S17> In step S17, the drive control unit 54 stops the operation of the drive circuit 53. Specifically, the drive control unit 54 turns off the first relay 61.

[0105] In this way, the image forming apparatus 100 is provided with a drive circuit 53 that can switch the operation mode among the first mode, the second mode, and the third mode. As a result, the connection forms of the first heating unit 51 and the second heating unit 52 can be switched between series and parallel, and only the first heating unit 51 can be driven.

[0106] Note that both the first heating unit 51 and the second heating unit 52 do not necessarily include the resistance heating element 42. For example, both the first heating unit 51 and the second heating unit 52 may be a halogen heater or the like. In this case, when an image is formed on the first sheet, the drive control unit 54 may operate the drive circuit 53 in the third mode from the beginning. Further, the drive control unit 54 may operate the drive circuit 53 in either the second mode or the third mode according to the thickness of the first sheet.

[0107] [Supplementary Note of the Invention] Hereinafter, the outline of the invention extracted from the above-described embodiment will be appended. Note that each configuration and each processing function described in the following supplementary note can be arbitrarily combined by selection.

[0108] <Supplementary Note 1> A heating device that heats a fixing member that fixes a toner image transferred to a sheet to the sheet, the heating device including: a first heating unit that heats a first region including a central portion in the width direction of the sheet on the fixing member according to power supply; a second heating unit that heats a pair of second regions sandwiching the first region in the width direction on the fixing member according to power supply; a first mode in which power is supplied to the first heating unit and not to the second heating unit; a second mode in which power is supplied to the first heating unit and the second heating unit connected in series; and a drive circuit that can be switched between a third mode in which power is supplied to the first heating unit and the second heating unit connected in parallel.

[0109] <Supplementary Note 2> The drive circuit includes a first energization path connecting a power source and a first terminal of the first heating unit, a mechanical first switch provided in the first energization path, a first switching element provided between the first switch and the first heating unit in the first energization path, a second energization path connecting the first terminal of the first heating unit and the first terminal of the second heating unit, a third energization path connecting the second terminal of the first heating unit and the second terminal of the second heating unit, a second switching element provided in the third energization path, a fourth energization path connecting between the first switch and the first switching element in the first energization path and the second terminal of the second heating unit, a mechanical second switch provided in the fourth energization path, and a fifth energization path connecting the power source and the second terminal of the first heating unit, which is the heating device described in Supplementary Note 1.

[0110] <Supplementary Note 3> An image forming apparatus comprising the heating device described in Supplementary Note 1 or 2 and the fixing member, and forming an image on the sheet using the fixing member.

[0111] <Supplementary Note 4> Both the first heating unit and the second heating unit include a resistance heating element that generates heat in response to power supply. When an image is formed on a specific sheet whose size in the width direction is larger than a reference size corresponding to the first area, the drive control unit operates the drive circuit in the second mode until predetermined switching conditions are satisfied and can switch the operation mode from the second mode to the third mode in response to the satisfaction of the switching conditions. The image forming apparatus described in Supplementary Note 3.

[0112] <Supplementary Note 5> When an image is formed on the specific sheet and the thickness of the specific sheet is equal to or less than a predetermined reference value, the drive control unit does not switch the operation mode to the third mode. The image forming apparatus described in Supplementary Note 4.

Explanation of Reference Numerals

[0113] 1 Image forming unit 2 Sheet conveyance unit 11 Photoconductor drum 12 Charging device 13 Optical scanning device 14 Developing device 15 Transfer roller 16 Cleaning device 17 Fixing device 21 Paper feed cassette 22 Sheet conveyance path 23 Paper feed unit 24 Registration roller pair 25 Discharge roller pair 31 Fixing belt 32 Heating device 33 First support part 34 Second support part 35 Pressing roller 41 Substrate 42 Resistance heating element 43 First electrode 44 Second electrode 45 Conductive path 46 Protective layer 51 First heating part 52 Second heating part 53 Drive circuit 54 Drive control part 61 First relay 62 First triac 63 Second triac 64 Second relay 71 First energization path 72 Second energization path 73 Third energization path 74 Fourth energization path 75 Fifth energization path 100 Image forming apparatus 200 Power supply

Claims

1. A heating device for heating a fixing member that fixes a toner image transferred to a sheet to the sheet, comprising: a first heating unit that heats a first region including a central portion in the width direction of the sheet on the fixing member in response to power supply; a second heating unit that heats a pair of second regions sandwiching the first region in the width direction on the fixing member in response to power supply; a drive circuit capable of switching between a first mode in which power is supplied to the first heating unit and not to the second heating unit, a second mode in which power is supplied to the first heating unit and the second heating unit connected in series, and a third mode in which power is supplied to the first heating unit and the second heating unit connected in parallel; A heating device comprising the above.

2. The drive circuit includes: a first energization path connecting a power source and a first terminal of the first heating unit; a mechanical first switch provided in the first energization path; a first switching element provided between the first switch and the first heating unit in the first energization path; a second energization path connecting the first terminal of the first heating unit and the first terminal of the second heating unit; a third energization path connecting the second terminal of the first heating unit and the second terminal of the second heating unit; a second switching element provided in the third energization path; a fourth energization path connecting between the first switch and the first switching element in the first energization path and the second terminal of the second heating unit; a mechanical second switch provided in the fourth energization path; a fifth energization path connecting the power source and the second terminal of the first heating unit; The heating device according to Claim 1, comprising the above.

3. The heating device according to Claim 1 or 2, and the fixing member, Comprising, An image forming apparatus that forms an image on the sheet using the fixing member.

4. Both the first heating unit and the second heating unit include a resistance heating element that generates heat in response to power supply, The image forming apparatus includes: When an image is formed on a specific sheet whose size in the width direction is larger than a reference size corresponding to the first region, a drive control unit that operates the drive circuit in the second mode until a predetermined switching condition is satisfied and switches the operation mode from the second mode to the third mode in response to satisfaction of the switching condition. The image forming apparatus according to Claim 3.

5. ​ When an image is formed on the specific sheet and the thickness of the specific sheet is equal to or less than a predetermined reference value, the drive control unit does not switch the operation mode to the third mode. The image forming apparatus according to claim 4.

Images