Patent Description:
There is an on-demand heating device referred to as a film fixing unit. As the material used for a heater in such an on-demand heating device, a "TCR" material may be used in some cases. In this context, "TCR" material refers to a material that has a higher electrical resistance value as its temperature increases. Generally, when an on-demand heating device is used, the power available for use by the on-demand heating device may be predetermined. In this case, the heating must be carried out with the available power. Use of a TCR material makes it possible to reduce power consumption and to reduce temperature rise of a non-sheet-passing portion (that is, a portion which is not contacting a sheet during a particular fixing operation) of the heater. Due to characteristics of the TCR material, electric power used by the heater decreases as the temperature rises. However, there is a problem in that time required for starting (beginning heating) of the on-demand heating device becomes longer.

<CIT> relates to a fixing unit according to the preamble of claim <NUM>. <CIT> relates to an image forming apparatus capable of accurately estimating power consumption level. <CIT> relates to an image forming apparatus. <CIT> relates to a fixing device and image forming apparatus. <CIT> relates to a fixing device, an image forming apparatus, and a heater control method. <CIT> relates to a heater controller, a heater control method, and an image forming apparatus. <CIT> relates to an image heating apparatus and image forming apparatus.

An object of the present invention is to reduce the time required for the starting of the heating device while still suppressing power consumption.

The invention is defined by claim <NUM>, and relates to a fixing unit that can be used in an image forming apparatus includes a first heater element that is formed of a material (a "TCR" material) that increases in electrical resistance with increases in temperature. A controller of the fixing unit is configured to vary a duty ratio of electric power applied to the first heater element during a start-up operation in which the temperature of the first heater element is raised to a target operating temperature.

The fixing unit further comprises a second heater element formed of the TCR material, wherein the controller is further configured to vary a duty ratio of electric power applied to the second heater element during the start-up operation.

Preferably, the duty ratio of electric power applied to the first heater element and the duty ratio of electric power applied to the second heater element are the same during the start-up operation.

Preferably, the duty ratio of electric power applied to the first heater element and the duty ratio of electric power applied to the second heater element are different from each other during the start-up operation.

The first heating element is a centrally positioned heating element in the fixing unit and the second heating element is an end positioned heating element in the fixing unit.

Preferably, the controller is configured to increase the duty ratio of electric power applied to the first heater element in increments of a first size and increase the duty ratio of electric power applied to the second heater element in increments of a second size greater than the first size.

The controller is configured to increase the duty ratio of electric power applied to the first heater element at a first fixed time interval during the start-up operation and to increase the duty ratio of electric power applied to the second heater element at a second fixed time interval during the start-up operation, the first and second fixed time intervals being different from each other.

Preferably, the controller is configured to use a first initial duty ratio value for electric power applied to the first heater element during the start-up operation and a second initial duty ratio value for electric power applied to the second heater, the first and second initial duty ratio values being different from each other.

Preferably, the fixing unit further comprises a third heater element formed of the TCR material, wherein the controller is further configured to vary a duty ratio of electric power applied to the third heater element during the start-up operation.

Preferably yet, the first heater element is between the second and third heater elements.

Preferably, the controller is configured to increase the duty ratio of electric power applied to the first heater element during the start-up operation by a fixed duty ratio increment at fixed time intervals.

Preferably, the controller is configured to increase the duty ratio of electric power applied to the first heater element during the start-up operation by a fixed duty ratio increment at varying time intervals.

Preferably, the controller is configured to increase the duty ratio of electric power applied to the first heater element during the start-up operation by varying duty ratio increments at fixed time intervals.

The invention also relates to an image forming apparatus, comprising an image forming unit configured to form an image on a sheet; and a fixing unit as described above configured to receive the sheet from the image forming unit and heat the sheet.

The invention also relates to a heating method for operations in an image forming apparatus as defined by claim <NUM>, the heating method comprising varying a duty ratio of electric power applied to a first heater element of a fixing device during a start-up operation in which the temperature of the first heater element is raised to a target operating temperature, wherein the first heater element is formed of a TCR material that increases in electrical resistance with increases in temperature.

Hereinafter, a fixing unit, an image forming apparatus, and a heating method according to certain example embodiments will be described with reference to the drawings.

<FIG> is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

An image forming apparatus <NUM> according to the first embodiment is, for example, a multi-function peripheral.

The image forming apparatus <NUM> includes a housing <NUM>, a display <NUM>, a scanner unit <NUM>, an image forming unit <NUM>, a sheet supply unit <NUM>, a conveying unit <NUM>, a sheet discharge tray <NUM>, an inversion unit <NUM>, a control panel <NUM>, and a controller <NUM>. Note that the image forming unit <NUM> may be a printing device that produces a toner image, or may be an ink jet device.

The image forming apparatus <NUM> forms an image on sheet S by using a developer such as a toner. The sheet S is, for example, paper or a label paper. In general, the sheet S may be any object or material as long as the image forming apparatus <NUM> can form an image on a surface of the sheet S.

The housing <NUM> forms the outer shape of the image forming apparatus <NUM>.

The display <NUM> is an image display device such as a liquid crystal display, an organic EL (Electro Luminescence) display, or the like. The display <NUM> displays various information about the image forming apparatus <NUM>.

The scanner unit <NUM> reads image information as brightness and darkness of reflected light from a document or the like. The scanner unit <NUM> records the image information as read. The scanner unit <NUM> outputs the generated image information to the image forming unit <NUM>. Note that the recorded image information may instead, or in addition to, be transmitted from another information processing apparatus (e.g., an external device) via a network.

The image forming unit <NUM> forms an output image (hereinafter referred to as a toner image) with a recording agent such as toner on the basis of the image information received from the scanner unit <NUM> or the image information received from an external device. The image forming unit <NUM> transfers the toner image onto the surface of the sheet S. The image forming unit <NUM> heats and presses the toner image on the surface of the sheet S, and thus fixes the toner image to the sheet S. Note that the sheet S may be a sheet supplied by the sheet supply unit <NUM>, or a sheet manually inserted.

The sheet supply unit <NUM> supplies the sheets S one by one to the conveying unit <NUM> in accordance with the timing at which the image forming unit <NUM> forms the toner image. The sheet supply unit <NUM> includes a sheet accommodating portion <NUM> and a pickup roller <NUM>.

The sheet accommodating portion <NUM> accommodates a sheet S having a predetermined size and type.

The pickup roller <NUM> picks up the sheets S, one by one, from the sheet accommodating portion <NUM>. The pickup roller <NUM> supplies the taken-out sheet S to the conveying unit <NUM>.

The conveying unit <NUM> conveys the sheet S from the sheet supply unit <NUM> to the image forming unit <NUM>. The conveying unit <NUM> includes a conveyance roller <NUM> and a registration roller <NUM>.

The conveyance roller <NUM> conveys the sheet S from the pickup roller <NUM> to the registration roller <NUM>. The conveyance roller <NUM> makes a leading end of the sheet S, with respect to the conveyance direction, abut against a nip N of the registration roller <NUM>.

The registration roller <NUM> positions the sheet S at the nip N, thereby adjusting a position of the leading end of the sheet S. The registration roller <NUM> then conveys the sheet S at timing appropriate for transfer of the toner image to the sheet S when the image forming unit <NUM>.

The image forming unit <NUM> includes a plurality of image forming portions <NUM>, a laser scanning unit <NUM>, an intermediate transfer belt <NUM>, a transfer portion <NUM>, and a fixing unit <NUM>.

Each image forming portion <NUM> comprises a photosensitive drum 25d. The image forming portion <NUM> forms, on the photosensitive drum 25d, a toner image corresponding to the image information from the scanner unit <NUM> or an external device. The depicted plurality of image forming portions 25Y, <NUM>, 25C, and <NUM> form toner images of yellow, magenta, cyan, and black toner, respectively.

A charger, a developing device, and the like are disposed around the photosensitive drum 25d. The charger charges a surface of the photosensitive drum 25d. The developing device contains a developer. Depending on the color of the image forming portion <NUM>, the developing device contains yellow, magenta, cyan, or black toners. The developing device develops the electrostatic latent image formed on the photosensitive drum 25d. As a result, the toner images formed by the toners of the respective colors are formed on a photosensitive drum 25d.

The laser scanning unit <NUM> scans each photosensitive drum 25d with a laser beam L, and thus selectively exposes the photosensitive drum 25d. The laser scanning unit <NUM> exposes the photosensitive drum 25d of the image forming portions 25Y, <NUM>, 25C, and <NUM> for each color different laser beams LY, LM, LC, and LK. Accordingly, the laser scanning unit <NUM> forms an electrostatic latent image on the photosensitive drum 25d of each component color.

The toner image on the surface of the photosensitive drum 25d is first transferred (the primary transfer) to the intermediate transfer belt <NUM>.

The transfer portion <NUM> then transfers (the secondary transfer) the toner image on the intermediate transfer belt <NUM>, onto the surface of the sheet S at a secondary transfer position.

The fixing unit <NUM> fixes the toner image to the sheet S, by heating and pressing the toner image transferred to the sheet S.

The inversion unit <NUM> inverts the sheet S to permit operations to form an image on a back surface of the sheet S. The inversion unit <NUM> reverses the sheet S discharged from the fixing unit <NUM> by switchback or the like. The inversion unit <NUM> then conveys the inverted sheet S toward the registration roller <NUM>.

The sheet discharge tray <NUM> stores the sheet S (on which an image has been formed) that has been discharged after printing.

The control panel <NUM> includes a plurality of buttons. The control panel <NUM> receives an input operation or operations performed by a user. The control panel <NUM> outputs a signal corresponding to the operation performed by the user to the controller <NUM>. Note that the display <NUM> and the control panel <NUM> may be configured as an integrated touch panel.

The controller <NUM> controls respective components of the image forming apparatus <NUM>.

<FIG> is a hardware configuration diagram of the image forming apparatus <NUM> according to the first embodiment. The image forming apparatus <NUM> includes a central processing unit (CPU) <NUM>, a memory <NUM>, an auxiliary storage device <NUM>, and the like connected by a bus. The image forming apparatus executes a program (more particularly, CPU <NUM> executes program instructions stored in memory <NUM>, auxiliary storage device <NUM>, or otherwise provided). The image forming apparatus <NUM> thus functions as an apparatus having a scanner unit <NUM>, an image forming unit <NUM>, a sheet supply unit <NUM>, a conveying unit <NUM>, an inversion unit <NUM>, a control panel <NUM>, and a communication unit <NUM> by executing a program.

The CPU <NUM> functions as the controller <NUM> by executing a program stored in the memory <NUM> and the auxiliary storage device <NUM>. The controller <NUM> controls the operation of each functional unit of the image forming apparatus <NUM>.

The auxiliary storage device <NUM> is a storage device such as a magnetic hard disk device or a semiconductor storage device. The auxiliary storage device <NUM> stores various types of information related to the image forming apparatus <NUM>.

The communication unit <NUM> includes a communication interface for connecting to an external device. The communication unit <NUM> communicates with the external device via the communication interface.

<FIG> is a front cross-sectional view of a heating device according to the first embodiment. The heating device according to the first embodiment is a fixing unit <NUM>. The fixing unit <NUM> includes a pressing roller 30p and a film unit <NUM>.

The pressing roller 30p forms a nip N with the film unit <NUM>. The pressing roller 30p presses the toner image on the sheet S that has entered the nip N. The pressing roller 30p rotates to convey the sheet S. The pressing roller 30p includes a core metal <NUM>, an elastic layer <NUM>, and a release layer (not separately depicted).

As described above, the pressing roller 30p can press a front surface of a cylindrical film <NUM>, and can be rotationally driven.

The core metal <NUM> is formed into a columnar shape by a metal material such as stainless steel. Both ends of the core metal <NUM> in the axial direction are rotatably supported. The core metal <NUM> is rotationally driven by a motor or the like. The core metal <NUM> abuts against a cam member or the like. The cam member rotates so as to move the core metal <NUM> closer to and away from the film unit <NUM>.

The elastic layer <NUM> is formed of an elastic material such as silicone rubber. The elastic layer <NUM> is formed to have a constant thickness on an outer circumferential surface of the core metal <NUM>.

The release layer is formed of a resin material such as PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer). The release layer is formed on an outer peripheral surface of the elastic layer <NUM>.

Hardness of an outer peripheral surface of the pressing roller 30p is preferably <NUM> to <NUM> at a load of <NUM> N in an ASKER-C hardness meter. Thereby, an area of the nip N and durability of the pressing roller 30p are ensured.

The pressing roller 30p can move closer to and away from the film unit <NUM> by the rotation of the cam member. When the pressing roller 30p is brought close to the film unit <NUM> and pressed by a pressing spring, the nip N is formed. On the other hand, when the sheet jams in the fixing unit <NUM>, the pressing roller 30p is moved away from the film unit <NUM>, so that it is possible to remove the sheet S. Further, when the cylindrical film <NUM> stops rotating during sleep, by the cylindrical film <NUM> being made separating from the film unit <NUM>, the plastic deformation of the cylindrical film <NUM> can be prevented from being deformed.

The pressing roller 30p is driven to rotate by a motor. When the pressing roller 30p rotates in a state where the nip N is formed, the cylindrical film <NUM> of the film unit <NUM> rotates in a driven manner. The pressing roller 30p rotates in a state where the sheet S is disposed at the nip N, thereby conveying the sheet S in the conveyance direction W.

The film unit <NUM> heats the toner image of the sheet S that has entered the nip N. The film unit <NUM> includes a cylindrical film <NUM>, a heater unit <NUM>, a heat conductor <NUM>, a support member <NUM>, a stay <NUM>, a heater temperature sensor <NUM>, a thermostat <NUM>, and a film temperature sensor <NUM>.

The cylindrical film <NUM> is formed in a cylindrical shape. The cylindrical film <NUM> includes, in order from the inner peripheral side, a base layer, an elastic layer, and a release layer. The base layer is formed of a material such as nickel (Ni) in a tubular shape. The elastic layer is laminated on an outer peripheral surface of the base layer. The elastic layer is formed of an elastic material such as silicone rubber. The release layer is laminated on the outer peripheral surface of the elastic layer. The release layer is formed of a material such as a PFA resin.

<FIG> is a front cross-sectional view of the heater unit taken along line IV-IV in <FIG> is a bottom view (a view from the +z direction) of the heater unit. The heater unit <NUM> includes a substrate (heating element substrate) <NUM>, a heating element group <NUM>, and a wiring set <NUM>.

The substrate <NUM> is formed of a metal material such as stainless steel, a ceramic material such as aluminum nitride, or the like. The substrate <NUM> is formed in a plate shape having an elongated rectangular shape. The substrate <NUM> is disposed radially inward of the cylindrical film <NUM>. In the substrate <NUM>, an axial direction of the cylindrical film <NUM> is defined as a longitudinal direction.

In the present application, x direction, y direction, and z direction are defined as follows. The y direction is the longitudinal direction of the substrate <NUM>. The y direction is parallel to the width direction of the cylindrical film <NUM>. As will be described later, the +y direction is a direction from a central heating element 45a toward a first end heating element 45b1.

The x direction is the short direction of the substrate <NUM>, and the +x direction is the conveyance direction (the downstream direction) of the sheet S. The z direction is a normal direction of the substrate <NUM>, and the +z direction is a direction in which the heating element group <NUM> is disposed with respect to the substrate <NUM>. An insulating layer <NUM> is formed of a glass material or the like on a surface in the +z direction of the substrate <NUM>.

The heating element group <NUM> is disposed on the substrate <NUM>. <NUM>, the heating element group <NUM> is formed on a surface in the +z direction of the insulating layer <NUM>. The heating element group <NUM> is formed of a TCR (temperature coefficient of resistance) material. For example, the heating element group <NUM> is formed of a silver-palladium alloy or the like. An outer shape of the heating element group <NUM> is formed in a rectangular shape having the y direction as the longitudinal direction and the x direction as the short direction.

As shown in <FIG>, the heating element group <NUM> includes a first end heating element 45b1, a central heating element 45a, and a second end heating element 45b2 arranged side by side in the y direction. The central heating element 45a is disposed in the center of the heating element group <NUM> in the y direction. The central heating element 45a may be configured by combining a plurality of small heating elements arranged side by side in the y direction. The first end heating element 45b1 is arranged at the +y direction of the central heating element 45a and at the end of the heating element group <NUM> in the y direction. The second end heating element 45b2 is disposed at an end in the - y direction of the central heating element 45a, i.e., at an end in the -y direction of the heating element group <NUM>. The boundary line between the central heating element 45a and the first end heating element 45b1 may be arranged in parallel to the x direction, or may be arranged so as to be angled with respect to the x direction. The same applies to the boundary line between the central heating element 45a and the second end heating element 45b2.

The heating element group <NUM> generates heat when energized. An electric resistance value of the central heating element 45a is smaller than the electric resistance values of the first end heating element 45b1 and the second end heating element 45b2. A sheet S having a small width in the y direction may be passed through the center in the y direction of the fixing unit <NUM> without overlapping the end elements. In such a case, the controller <NUM> causes only the central heating element 45a to generate heat. On the other hand, in the case of a sheet S having a large width in the y direction, the controller <NUM> causes the entirety of the heating element group <NUM> to generate heat. Therefore, heat generation of the central heating element 45a and the first end heating element 45b1 and the second end heating element 45b2 can be controlled independently of each other. Similarly, heat generation of the first end heating element 45b1 and the second end heating element 45b2 can be controlled.

The wiring set <NUM> (also referred to as a wiring group) is formed of a metal material such as silver.

The wiring set <NUM> includes a central junction 52a, a central wiring 53a, an end junction 52b, a first end wiring 53b1, a second end wiring 53b2, a common junction <NUM>, and a common wiring <NUM>.

The central junction 52a is arranged in the -y direction of the heating element group <NUM>. The central routing 53a is arranged in the +x direction of the heating element group <NUM>. The central routing 53a connects the end side in the +x direction of the central heating element 45a and the central junction 52a.

The end junction 52b is arranged in the -y direction of the central junction 52a. The first end holding 53b1 is arranged in the +x direction of the heating element group <NUM> and in the +x direction of the central routing 53a.

The first end holding 53b1 connects an end side of the first end heating element 45b1 in the +x direction and an end of the end junction 52b in the +x direction. The second end holding 53b2 is arranged in the +x direction of the heating element group <NUM> and in the -x direction of the central routing 53a. The second end holding 53b2 connects the end side in the +x direction of the second end heating element 45b2 and the end in the -x direction of the end junction 52b.

The common junction <NUM> is arranged in the +y direction of the heating element group <NUM>. The common wiring <NUM> is arranged in the -x direction of the heating element group <NUM>. The common wiring <NUM> connects the end sides in the -x direction of the central heating element 45a, the first end heating element 45b1, and the second end heating element 45b2 to the common junction <NUM>.

In this way, in the +x direction of the heating element group <NUM>, the second end holding 53b2, the central routing 53a, and the first end holding 53b1 are arranged. On the other hand, only the common wiring <NUM> is disposed in the -x direction of the heating element group <NUM>. Therefore, the center 45c of the heating element group <NUM> in the x direction is offset in the -x direction from the center 41c in the x direction of the substrate <NUM>.

As shown in <FIG>, a straight line CL connecting the center pc of the pressing roller 30p and the center hc of the film unit <NUM> is defined. The center 41c in the x direction of the substrate <NUM> is arranged in the +x direction from the straight line CL. Accordingly, the substrate <NUM> extends in the +x direction of the nip N, and the sheet S that has passed through the nip N is easily peeled off from the film unit <NUM>.

The center 45c of the heating element set <NUM> in the x direction is disposed on the straight line CL. The heating element group <NUM> is entirely contained in the region of the nip N, and is disposed in the center of the nip N. Accordingly, heat distribution of the nip N becomes uniform, and the sheet S passing through the nip N is uniformly heated.

As shown in <FIG>, the heating element group <NUM> and the wiring group <NUM> are formed on the +z direction surface of the insulating layer <NUM>. The protective layer <NUM> is formed of a glass material or the like so as to cover the heating element group <NUM> and the wiring set <NUM>. The protective layer <NUM> improves sliding (reduces friction) between the heater unit <NUM> and the cylindrical film <NUM>.

As shown in <FIG>, the heater unit <NUM> is disposed inside the cylindrical film <NUM>. A lubricant is applied to an inner peripheral surface of the cylindrical film <NUM>. The heater unit <NUM> contacts the inner circumferential surface of the cylindrical film <NUM> via a lubricant. When the heater unit <NUM> generates heat, the viscosity of the lubricant decreases. Accordingly, sliding friction between the heater unit <NUM> and the cylindrical film <NUM> is low.

As described above, the cylindrical film <NUM> is a belt-shaped thin film that slides along a surface of the heater unit <NUM> while being in contact with the heater unit <NUM> on one side.

The heat conductor <NUM> is formed of a metal material having a high thermal conductivity such as copper. An outer shape of the heat conductor <NUM> is equal to an outer shape of the substrate <NUM> of the heater unit <NUM>. The heat conductor <NUM> is disposed in contact with the surface of the heater unit <NUM> in the -z direction.

The support member <NUM> is formed of a resin material such as a liquid crystal polymer. The support member <NUM> is disposed so as to cover the -z direction and both sides in the x direction of the heater unit <NUM>. The support member <NUM> supports the heater unit <NUM> via the heat conductor <NUM>. Rounded chamfers are formed at both ends of the support member <NUM> in the x direction. The support member <NUM> supports the inner peripheral surface of the cylindrical film <NUM> at both ends in the x direction of the heater unit <NUM>.

When the sheet S passing through the fixing unit <NUM> is heated, a temperature distribution is generated in the heater unit <NUM> in accordance with the size of the sheet S. When the heater unit <NUM> locally reaches a high temperature, the temperature may exceed heat resistant temperature of the support member <NUM> formed of a resin material. The heat conductor <NUM> averages the temperature distribution of the heater unit <NUM>. Thereby, the heat resistance of the support member <NUM> is ensured.

<FIG> is a front cross-sectional view of a heat conductor, a heater unit, and a cylindrical belt. The heat conductor <NUM> is disposed on a surface of the heater unit <NUM> that does not come into contact with the cylindrical film <NUM>. Further, the heat conductor <NUM> is configured so as not to come into contact with the heater unit <NUM> at a position where heat generation distribution in the heater unit <NUM> becomes a peak. More specifically, as shown in <FIG>, the heater unit <NUM> and the heat conductor <NUM> are in contact with each other in regions a1 and a2. Then, a non-contact portion forms a groove portion of the heat conductor <NUM>. a width of the groove portion is set to be wider than a width of the heating element group <NUM> of the heater unit <NUM> by length d1 and length d2, respectively. For example, the heating element group <NUM> of the heater unit <NUM> has a width of <NUM> to <NUM>, and the groove portion has a width of about <NUM>.

The stay <NUM> shown in <FIG> is formed of a steel plate material or the like. A cross section perpendicular to the y direction of the stay <NUM> is formed in a U-shape. The stay <NUM> is mounted in the -z direction of the support member <NUM> so as to close an opening portion of the U shape with the support member <NUM>. The stay <NUM> extends in the y direction. Both ends of the stay <NUM> in the y direction are fixed to the housing of the image forming apparatus <NUM>. Thereby, the film unit <NUM> is supported by the image forming apparatus <NUM>. The stay <NUM> improves rigidity of the film unit <NUM>. Flanges that restrict movement of the cylindrical film <NUM> in the y direction can be attached near both ends of the stay <NUM> in the y direction.

The heater temperature sensor <NUM> is disposed in the -z direction of the heater unit <NUM> with the heat conductor <NUM> interposed therebetween. For example, the heater temperature sensor <NUM> is a thermistor. The heater temperature sensor <NUM> is mounted on and supported by a surface of the support member <NUM> in the -z direction. A temperature sensitive element of the heater temperature sensor <NUM> contacts the heat conductor <NUM> through a hole that passes through the support member <NUM> in the z direction. The heater temperature sensor <NUM> measures the temperature of the heater unit <NUM> through the heat conductor <NUM>.

The thermostat <NUM> is disposed in the same manner as the heater temperature sensor <NUM>. The thermostat <NUM> is incorporated in an electric circuit, which will be described later. When the temperature of the heater unit <NUM> detected through the heat conductor <NUM> exceeds a predetermined temperature, the thermostat <NUM> cuts off the energization of the heating element group <NUM>.

<FIG> is a plan view (a view from the -z direction) of a heater temperature sensor and a thermostat. In <FIG>, description of the support member <NUM> is omitted. Note that the following description of arrangement of the heater temperature sensor, the thermostat, and the film temperature sensor describes arrangement of the respective temperature sensitive elements.

A plurality of heater temperature sensors <NUM> (central heater temperature sensor 62a and end heater temperature sensor 62b) are arranged side by side in the y direction. The plurality of heater temperature sensors <NUM> are disposed near the heating element group <NUM> in the y direction. The plurality of heater temperature sensors <NUM> are disposed in the center of the heating element group <NUM> in the x direction. That is, when viewed in the z direction, the plurality of heater temperature sensors <NUM> and the heating element group <NUM> overlap at least partially.

The plurality of thermostats <NUM> (central thermostat 68a and end thermostat 68b) are also arranged in the same manner as the plurality of heater temperature sensors <NUM> described above.

The plurality of heater temperature sensors <NUM> include the central heater temperature sensor 62a and the end heater temperature sensor 62b.

The central heater temperature sensor 62a measures temperature of the central heating element 45a. The central heater temperature sensor 62a is disposed within the range of the central heating element 45a. That is, when viewed from the z direction, the central heater temperature sensor 62a and the central heating element 45a overlap each other.

The end heater temperature sensor 62b measures the temperature of the second end heating element 45b2. As described above, the heat generation of the first end heating element 45b1 and the second end heating element 45b2 is similarly controlled. Therefore, the temperature of the first end heating element 45b1 and the temperature of the second end heating element 45b2 are equal to each other. The end heater temperature sensor 62b is disposed in the range of the second end heating element 45b2. That is, when viewed in the z direction, the end heater temperature sensor 62b and the second end heating element 45b2 overlap each other.

The plurality of thermostats <NUM> comprise the central thermostat 68a and the end thermostat 68b.

The central thermostat 68a interrupts the energization of the heating element group <NUM> when the temperature of the central heating element 45a exceeds the predetermined temperature. The central thermostat 68a is located within the range of the central heating element 45a. That is, when viewed from the z direction, the central thermostat 68a and the central heating element 45a overlap each other.

When the temperature of the first end heating element 45b1 exceeds the predetermined temperature, the end thermostat 68b cuts off the energization of the heating element group <NUM>. As described above, the heat generation of the first end heating element 45b1 and the second end heating element 45b2 is similarly controlled. Therefore, the temperature of the first end heating element 45b1 and the temperature of the second end heating element 45b2 are equal to each other. The end thermostat 68b is located within the range of the first end heating element 45b1. That is, when viewed from the z direction, the end thermostat 68b and the first end heating element 45b1 overlap each other.

As described above, the central heater temperature sensor 62a and the central thermostat 68a are disposed within the range of the central heating element 45a. As a result, the temperature of the central heating element 45a is measured. In addition, when the temperature of the central heating element 45a exceeds the predetermined temperature, the energization of the heating element group <NUM> is cut off. On the other hand, an end heater temperature sensor 62b and an end thermostat 68b are disposed within the range of the first end heating element 45b1 and the second end heating element 45b2. Accordingly, the temperatures of the first end heating element 45b1 and the second end heating element 45b2 are measured. Further, when the temperature of the first end heating element 45b1 and the second end heating element 45b2 exceeds the predetermined temperature, the energization of the heating element group <NUM> is cut off.

The plurality of heater temperature sensors <NUM> and the plurality of thermostats <NUM> are arranged alternately along the y direction. As described above, the first end heating element 45b1 is disposed in the +y direction of the central heating element 45a. The end thermostat 68b is disposed within the range of the first end heating element 45b1. The central heater temperature sensor 62a is disposed in the +y direction from the center of the central heating element 45a in the y direction. The central thermostat 68a is disposed in the -y direction from the center of the central heating element 45a in the y direction. As described above, the second end heating element 45b2 is disposed in the -y direction of the central heating element 45a. An end heater temperature sensor 62b is disposed within the range of the second end heating element 45b2. Accordingly, from the +y direction, the end thermostat 68b, the central heater temperature sensor 62a, the central thermostat 68a, and the end heater temperature sensor 62b are arranged in this order from the +y direction to the -y direction.

Generally, the thermostat <NUM> connects and disconnects an electrical circuit by utilizing bending deformation of a bimetal with temperature change. The thermostat is formed to be elongated to match the shape of the bimetal. Further, terminals extend outward from both ends in the longitudinal direction of the thermostat <NUM>. The connector of the external sling is connected to the terminal by caulking. Therefore, it is necessary to secure a space on an outer side in the longitudinal direction of the thermostat <NUM>. Since there is no spatial margin in the fixing unit <NUM> in the x-direction, the longitudinal direction of the thermostat <NUM> is arranged along the y-direction.

At this time, when the plurality of thermostats <NUM> are arranged side by side in the y direction, it becomes difficult to secure a connection space for an external routing.

As described above, the plurality of heater temperature sensors <NUM> and the plurality of thermostats <NUM> are alternately arranged along the y direction. Thereby, the heater temperature sensor <NUM> is disposed adjacent to the thermostat <NUM> in the y direction. Therefore, it is possible to secure a connection space for the external routing to the thermostat <NUM>. Further, a degree of freedom in a layout of the thermostat <NUM> and the heater temperature sensor <NUM> in the y direction is increased. Accordingly, the thermostat <NUM> and the heater temperature sensor <NUM> may be disposed at an optimal position, and the temperature of the fixing unit <NUM> may be controlled. Further, an isolation of an AC wiring connected to the plurality of thermostats <NUM> and an DC wiring connected to the plurality of heater temperature sensors <NUM> is facilitated. Accordingly, generation of noise in the electric circuit is suppressed.

The film temperature sensor <NUM> is disposed inside the cylindrical film <NUM> and in the +x direction of the heater unit <NUM>, as shown in <FIG>. The film temperature sensor <NUM> contacts the inner circumferential surface of the cylindrical film <NUM>, and measures temperature of the cylindrical film <NUM>.

Note that the image forming apparatus <NUM> may further include an environment temperature sensor <NUM> in addition to the heater temperature sensor <NUM> and the film temperature sensor <NUM>. The environment temperature sensor <NUM> measures temperature around its mounted position. The environment temperature sensor <NUM> may be attached to any position near the fixing unit <NUM>. The vicinity of the fixing unit <NUM> is a position at which the environment temperature sensor <NUM> can measure temperature of the space in which the fixing unit <NUM> is located (ambient temperature). For example, as shown in <FIG>, the environment temperature sensor <NUM> may be attached to the housing <NUM> located outside of the film unit <NUM>.

If the image forming apparatus <NUM> comprises the environment temperature sensor <NUM>, the controller <NUM> may control the energization of the heating element group <NUM> based on the temperatures measured by the heater temperature sensor <NUM>, the film temperature sensor <NUM>, and the environment temperature sensor <NUM>. For example, when the temperature measured by the environment temperature sensor <NUM> is higher than a predetermined value or when the temperature is lower than the predetermined value, the controller <NUM> may stop the energization of the heating element group <NUM>.

<FIG> is an electric circuit diagram of the heating device according to the first embodiment. In <FIG>, a bottom view of <FIG> is arranged above, and a plan view of <FIG> is arranged below, respectively. <FIG> also illustrates the plurality of film temperature sensor meters <NUM>, along with a cross section of the cylindrical film <NUM>, above the plan view below.

The plurality of film temperature sensors <NUM> comprise a central film temperature sensor 64a and an end film temperature sensor 64b.

The central film temperature sensor 64a contacts the center of the cylindrical film <NUM> in the y direction. The central film temperature sensor 64a contacts the cylindrical film <NUM> within the range of the central heating element 45a in the y direction. The central film temperature sensor 64a measures the temperature of the center in the y direction of the cylindrical film <NUM>.

The end film temperature sensor 64b contacts the end of the cylindrical film <NUM> in the -y direction. The end film temperature sensor 64b contacts the cylindrical film <NUM> within the range of the second end heating element 45b2 in the y direction. The end film temperature sensor 64b measures temperature of the end in the -y direction of the cylindrical film <NUM>. As described above, the heat generation of the first end heating element 45b <NUM> and the second end heating element 45b2 is similarly controlled. Therefore, the temperature at the end in the -y direction of the cylindrical film <NUM> and the temperature at the end in the +y direction are equal to each other.

A power source <NUM> is connected to the central junction 52a via a central triac 96a. The power source <NUM> is connected to the end junction 52b via an end triac 96b. The controller <NUM> controls ON/OFF of the central triac 96a and the end triac 96b independently of each other.

When the controller <NUM> turns on the central triac 96a, electric power is supplied from the power source <NUM> to the central heating element 45a. As a result, the central heating element 45a generates heat. When the controller <NUM> turns on the end triac 96b, electric power is supplied from the power source <NUM> to the first end heating element 45b <NUM> and the second end heating element 45b2. Accordingly, the first end heating element 45b <NUM> and the second end heating element 45b2 generate heat. As described above, the central heating element 45a and the first end heating element 45b1 and the second end heating element 45b2 are controlled independently of each other. The central heating element 45a, the first end heating element 45b1, and the second end heating element 45b2 are connected in parallel with respect to the power source <NUM>.

The power source <NUM> is connected to the common junction <NUM> via the central thermostat 68a and the end thermostat 68b. The central thermostat 68a and the end thermostat 68b are connected in series.

When the temperature of the central heating element 45a abnormally rises, detection temperature of the central thermostat 68a exceeds the predetermined temperature. At this time, the central thermostat 68a cuts off the power supply from the power source <NUM> to the entirety of the heating element group <NUM>.

When the temperature of the first end heating element 45b1 abnormally increases, detection temperature of the end thermostat 68b exceeds the predetermined temperature. At this time, the end thermostat 68b cuts off the power supply from the power source <NUM> to the entirety of the heating element group <NUM>. As described above, the heat generation of the first end heating element 45b1 and the second end heating element 45b2 is similarly controlled. Therefore, when the temperature of the second end heating element 45b2 rises abnormally, the temperature of the first end heating element 45b1 increases as well. Therefore, similarly, when the temperature of the second end heating element 45b2 abnormally rises, the end thermostat 68b cuts off the power supply from the power source <NUM> to the entire heating element group <NUM>.

The controller <NUM> measures the temperature of the central heating element 45a by the central heater temperature sensor 62a. The controller <NUM> measures the temperature of the second end heating element 45b2 by the end heater temperature sensor 62b. The temperature of the second end heating element 45b2 is equal to the temperature of the first end heating element 45b1. The controller <NUM> measures the temperature of the heating element group <NUM> by the heater temperature sensor <NUM> at the time of starting of the fixing unit <NUM> (warming-up time) and return from a pause state (sleep state).

When the temperature of at least one of the central heating element 45a and the second end heating element 45b2 is lower than the predetermined temperature during the start of the fixing unit <NUM> and the return from the pause state, the controller <NUM> causes the heating element group <NUM> to generate heat for a short time. Thereafter, the controller <NUM> starts the rotation of the pressing roller 30p. The heating of the heating element group <NUM> causes viscosity of the lubricant applied to the inner surface of the cylindrical film <NUM> to decrease. This improves slidability (reduces sliding friction) between the heater unit <NUM> and the cylindrical film <NUM> at the start of the rotation of the pressing roller 30p.

The controller <NUM> measures the temperature of the central portion of the cylindrical film <NUM> with the central film temperature sensor 64a. The controller <NUM> measures the temperature of the end (in the -y direction) of the cylindrical film <NUM> with the end film temperature sensor 64b. The temperature at the end in the y direction of cylindrical film <NUM> is equal to the temperature at end in the +y direction of cylindrical film <NUM>. The controller <NUM> measures the temperature of the central and end of the cylindrical film <NUM> in the y direction during the operation of the fixing unit <NUM>.

The controller <NUM> performs phase control or wave number control of the power supplied to the heating element group <NUM> with the central triac 96a and the end triac 96b. The controller <NUM> controls energization of the central heating element 45a based on the temperature measurement result of the central portion in the y direction of the cylindrical film <NUM>. The controller <NUM> controls energization of the first end heating element 45b1 and the second end heating element 45b2 based on the temperature measurement result of the end in the y direction of the cylindrical film <NUM>.

In the present embodiment, the heating element group <NUM> (the central heating element 45a, the first end heating element 45b1, and the second end heating element 45b2) uses a TCR material that has a higher resistance value as the temperature increases. In this case, due to the characteristics of the TCR material, the power in the heating element group <NUM> decreases with the temperature rise. More specifically, as the heating element group <NUM> generates heat, a change in power output as shown in the following equation (<NUM>) occurs: <MAT>.

Here, P represents an output [unit : W] at an arbitrary temperature, P0 represents an output [unit : W] at a reference temperature, and T represents the arbitrary temperature [unit: °C], T0 represents the reference temperature [unit: °C], and TCR represents a resistance temperature coefficient [unit: ppm]. In the heating element group <NUM> of the present embodiment, for example, a TCR material having a resistance temperature coefficient of <NUM> ppm is used. When using the heating element group <NUM> in which the TCR material is used, as shown in <FIG>, the power becomes lower as the temperature increases.

In general, during starting of the fixing unit <NUM> and returning from the sleep state (hereinafter, collectively referred to as "start-up time"), heating of the heating element group <NUM> is performed until the cylindrical film reaches a predetermined temperature. That is, at the time of start-up, the heating element group <NUM> is continuously energized. This causes the heating element group <NUM> to be heated continuously. Therefore, the heating element group <NUM> continuously increases in temperature at the time of start-up, and thus the above-described reduction in power becomes significant.

When a start-up processing start condition is satisfied, the controller <NUM> according to the present embodiment energizes the heating element group <NUM> by a start-up time energization method. The energization of the heating element group <NUM> means, in this context, that the central heating element 45a, the first end heating element 45b1, and the second end heating element 45b2 are energized, respectively.

The start-up processing start condition refers to the start-up of the fixing unit <NUM> from an idle or unheated state to a target operation temperature. Note that at least one of a heater temperature range condition, a film temperature sensor range condition, or an ambient temperature range condition may be further added to the start-up processing start condition. The heater temperature range condition is that at least one of the temperatures measured by the heater temperature sensors <NUM> is within a predetermined range. The film temperature sensor range condition is that at least one of the temperatures measured by the film temperature sensors <NUM> is within a predetermined range. The environmental temperature range condition is that the temperature measured by the environment temperature sensor <NUM> is within a predetermined range.

The varying energization method used during the start-up processing may be any energization method as long as the energization method satisfies the following: the heating element group <NUM> (the central heating element 45a, the first end heating element 45b <NUM>, and the second end heating element 45b2) is energized at a duty ratio of X% at the start of energization, and then is energized at a duty ratio that has been increased by x% at intervals of t<NUM> seconds.

<FIG> is a diagram illustrating a change in the duty ratio according to the energization system during the start-up process. As shown in <FIG>, at the start of energization (t = <NUM>), the heating element group <NUM> starts to be energized at a duty ratio of X%. After that, the duty ratio is changed to (X +x)% when t<NUM> seconds have elapsed. After that, when 2t<NUM> seconds, 3t<NUM> seconds, and 4t<NUM> seconds respectively elapse, the duty ratio is changed to (X + 2x)%, (X + 3x)%, and (X + 4x)% respectively. Note that, when the duty ratio has reached <NUM>%, the duty ratio is not further changed.

When the start-up processing start condition is satisfied, the controller <NUM> controls the central triac 96a and the end triac 96b so that the heating element group <NUM> is energized by the start-up time energization method. Note that the controller <NUM> includes a timing unit capable of measuring times for changing the duty ratio by measuring the elapsed time increments of t<NUM> seconds (for example, issuing a signal).

In addition, when a start-up processing termination condition is satisfied, the controller <NUM> stops the energization of the heating element group <NUM>. The start-up processing termination condition means that at least one of the temperatures measured by heater temperature sensors <NUM> reaches a predetermined temperature (target temperature). The start-up processing termination condition may be that one (or all) of the temperatures measured by the film temperature sensors <NUM> reach a predetermined temperature.

Note that a temperature range deviation condition may be further added to the start-up processing termination condition. The temperature range deviation condition means that at least one of the heater temperature range condition, the film temperature sensor range condition, or the environment temperature range condition is not satisfied.

<FIG> is a flowchart illustrating an example of a process at the time of start-up by the controller <NUM> according to the first embodiment.

The controller <NUM> determines whether or not the start-up processing start condition is satisfied (ACT <NUM>). As described above, the start-up processing start condition refers to the start-up time of the fixing unit <NUM> (for example, the start-up time, the return time from the sleep state, or the like). Note that, the controller <NUM> may determine that the start-up processing start condition is not satisfied if at least one of the temperatures measured by a heater temperature sensor <NUM>, the film temperature sensor <NUM>, or an environment temperature sensor <NUM> is not within a predetermined range.

When it is determined that the start-up processing start condition is satisfied (Yes in ACT <NUM>), the controller <NUM> starts to energize the heating element group <NUM> by the start-up time energization method (ACT <NUM>). As described above, the energization method during start-up processing is an energization method in which the heating element group <NUM> is energized at the duty ratio of X% at the start of energization, and is energized at the duty ratio that has been changed by x% at every time increment t<NUM>.

The controller <NUM> acquires the temperature measured by the film temperature sensor <NUM>. The controller <NUM> checks whether the acquired temperature has reached a predetermined target temperature. When the controller determines that the acquired temperature has reached the target temperature (Yes in ACT <NUM>), the controller stops the energization of the heating element group <NUM> (ACT <NUM>).

On the other hand, when the controller <NUM> determines that the acquired temperature has not reached the target temperature (No in ACT <NUM>), the controller <NUM> waits for a notification (signal) to be output from a timing unit or the like. Note that the timing unit notifies (transmits a signal) every time an increment of t<NUM> seconds has elapsed since the start of the energization to the heating element group <NUM> in ACT <NUM>. As a result, the controller <NUM> can recognize the times at which time increment t<NUM> elapses from the start of the energization.

When it is determined that time increment t<NUM> has elapsed since the reception of the signal (Yes in ACT <NUM>), the controller <NUM> changes the duty ratio of the power in the current supply to the heating element group <NUM> to a value that is higher by x% (ACT <NUM>). Note that, when the duty ratio has already reached <NUM>%, the controller <NUM> does not further change the duty ratio.

Thereafter, the controller <NUM> acquires the temperature measured by the film temperature sensor <NUM> again. The controller <NUM> determines whether the acquired temperature has reached a predetermined target temperature (that is, whether or not the temperature is equal to or higher than the target temperature) (ACT <NUM>).

On the other hand, when it is determined that the start-up processing start condition is not satisfied (ACT <NUM>, No), the controller <NUM> starts to energize the heating element group <NUM> with a normal energization method (ACT <NUM>). The normal energization method is an energization method in which the heating element group <NUM> is energized with a constant duty ratio (that is, without changing the duty ratio until the set temperature is reached). Note that the controller <NUM> may prevent the heating element group <NUM> from being energized if at least one of the temperatures measured by the heater temperature sensor <NUM>, the film temperature sensor <NUM>, or the environment temperature sensor <NUM> is not within a predetermined range.

The controller <NUM> acquires the temperature measured by the film temperature sensor <NUM>. The controller <NUM> checks whether the acquired temperature has reached a predetermined target temperature (that is, whether or not the temperature is equal to or higher than the target temperature). When the controller determines that the acquired temperature has reached the target temperature (Yes in ACT <NUM>), the controller stops the energization of the heating element group <NUM> (ACT <NUM>).

As described above, the processing at the time of start-up by the controller <NUM> shown in the flowchart in <FIG> ends.

Hereinafter, an example of the first embodiment described above will be described.

Experiments were carried out under the following conditions:.

<FIG> is a diagram illustrating an example of an experimental result indicating a relationship between elapsed time from start of energization to the heating element group <NUM> and the temperature of the cylindrical film <NUM>. The horizontal axis in <FIG> represents the elapsed time [unit: seconds] from the start of the energization of the heating element group <NUM>. The vertical axis of <FIG> represents the temperature [unit: °C], and power [unit: W] of the cylindrical film <NUM>.

As shown in <FIG>, when energization is performed on the heating element group <NUM> with the normal energization method (that is, an energization method with a fixed duty ratio), power output decreases as a temperature of the TCR material increases. For example, as shown in <FIG>, the power, which is approximately <NUM> W immediately after the start of energization, is reduced to approximately <NUM> W approximately after <NUM> seconds from the start of energization. This power drop is due to characteristics of the TCR material used in heating element group <NUM>. As a result, when energization is performed by the normal energization method for the heating element group <NUM>, as shown in <FIG>, the rate of rise in the temperature of the cylindrical film <NUM> decreases as time is elapsed from the start of the energization.

On the other hand, as shown in <FIG>, when energization is performed with the heating element group <NUM> in the varying energization method (that is, the energization method with a variable duty ratio) in the start-up processing, the duty ratio of the power is stepped up in increments after a certain period of time (<NUM> seconds in the present experiment). This increases the power being used again for a certain period of time. In the present experiment, the energization to the heating element group <NUM> is started at a duty ratio of <NUM>%, and thereafter, the duty ratio is changed by a total of four times, once after every increment of <NUM> [seconds] at a particular duty ration level, from initially <NUM>%, to <NUM>%, to <NUM>%, to <NUM>%, and then to <NUM>%, respectively. Accordingly, as shown in <FIG>, the power is raised four times. Accordingly, the decrease in power resulting from any increased resistance of TCR-based heating element group <NUM> is suppressed.

As shown in <FIG>, immediately after the start of the energization, approximately <NUM> W of power is being used, and this power level is maintained at approximately <NUM> W even after approximately <NUM> seconds from the start of the energization. Due to this, the decrease in the rate of temperature increase of the temperature of the cylindrical film <NUM> is reduced as compared with the normal energization method.

<FIG> is a diagram illustrating an example of experimental results.

<FIG> shows a comparison result between the start-up time and average power at start-up completion when the energization to the heating element group <NUM> is performed by the normal energization method and the start-up time energization method, respectively.

Here, the "start-up time" is a time required for starting the fixing unit <NUM> from an idle or reference state. That is, the start-up time is the time required for the cylindrical film <NUM> to reach the target operating temperature from the start of the energization of the heating element group <NUM>. The "average power at start-up completion" is the average power level used by the fixing unit <NUM> during the starting (start-up) process of the fixing unit <NUM> until completed. That is, the average power level used from the initial start time to start-up completion (i.e., when the cylindrical film <NUM> reaches the target operating temperature).

As shown in <FIG>, the start-up time in the case where the normal energization method (that is, the energization method with the duty ratio fixed) is used was <NUM> [seconds]. On the other hand, the start-up time in the case where the start-up time (varying) energization method (that is, the energization method with the variable duty ratio) was used in the startup processing was <NUM> [seconds]. In this way, when the start-up time varying energization method during the start-up processing is used, the start-up time is shortened by about <NUM>% as compared with the case where the normal energization method is used.

As shown in <FIG>, the average power at start-up completion when the normal energization method was used was <NUM> W. On the other hand, the average power at start-up completion when the start-up time energization method (that is, the duty ratio varying energization method) was <NUM> W. As described above, when the varying energization method during the start-up processing is used, the average power at start-up completion is improved (increased) by about <NUM>% as compared with the case where the normal energization method is used.

As described above, the image forming apparatus <NUM> according to the first embodiment includes the heating element group <NUM>, as a heat generating portion, and the controller <NUM>. The heating element group <NUM> uses a TCR material (that is, a material having a resistance value that increases with an increase in temperature), and generates heat when subjected to energization. The controller <NUM> changes the duty ratio of the supplied electric power during the heating of the heating element group <NUM> as the fixing unit <NUM> is starting up.

With the above-described configuration, the image forming apparatus <NUM> can change the duty ratio of the power supplied to the heating element group <NUM> over time. Generally, for a heating element in which the TCR material is used consumed power decreases as the temperature increases (resistance goes up, current goes down). According to this, there is a problem that the time required for starting (heating) of the fixing unit becomes longer when a TCR material is used. On the other hand, the image forming apparatus <NUM> according to the first embodiment causes the duty ratio of the power to be changed to a higher value, for example, after every increment of a fixed period of time. This allows the image forming apparatus <NUM> to compensate for the reduced power resulting from the temperature increase after every fixed period of time. That is, the image forming apparatus <NUM> can avoid (or limit) a decrease in power. Accordingly, the image forming apparatus <NUM> according to the first embodiment can shorten the time required for the start-up of the fixing unit <NUM> as compared to the related art.

In general, when the image forming apparatus is starting up, the power usable by a fixing unit may be set in advance. In this case, the heating start-up must be carried out with available set power. On the other hand, with the image forming apparatus <NUM> according to the first embodiment, it is possible to perform heating while suppressing power consumption after the start-up time.

Note that, in the above-described embodiment, the controller <NUM> changes the duty ratio of the power to be supplied to the heating element group <NUM> at a constant time increment (at regular intervals), but the present disclosure is not limited to this. For example, the controller <NUM> may change or more specifically lengthen the time interval for changing the duty ratio as the time elapses from the start of the energization. That is, the frequency at which the duty ratio is varied (increased) may be higher closer to the point in time at which the energization is started. In this case, the decrease in utilized power is suppressed at times close to the time when the energization is started.

Further, for example, the controller <NUM> may further reduce or alter the change amount of the duty ratio as the time elapses. That is, the duty ratio may be changed by a greater amount at points in time closer to the initial startup time as compared to later in time.

Generally, during start-up of the fixing unit, the temperature at the ends, in the width direction, of the cylindrical film <NUM> may be lower than the temperature at the center of the cylindrical film <NUM>. This is because the center is sandwiched between both ends that are heated similarly to the center, whereas the end is at a position that is heated on only one side.

In the image forming apparatus <NUM> according to the second embodiment, when the start-up processing start condition is satisfied, the controller <NUM> energizes the central heating element 45a, the first end heating element 45b1, and the second end heating element 45b2 by an energization method different from each other. When the start-up processing start condition is satisfied, the controller <NUM> energizes the central heating element 45a by a specific, central energization method. The controller <NUM> energizes the first end heating element 45b1 and the second end heating element 45b2 by a specific, end energization method.

The central energization method may be any energization method as long as the energization method satisfies the following: the central heating element 45a is energized at a duty ratio of X% at the start of energization, and then is energized at a duty ratio that is changed by x% after every time increment t<NUM>.

The end energization method may be any energization method as long as the energization method satisfies the following: the first end heating element 45b1 and the second end heating element 45b2 are energized at the duty ratio of X% at the start of energization, and then are energized at a duty ratio that has been changed by y% after every time increment t<NUM>. Here, it should be assumed that x < y.

<FIG> is a diagram illustrating a change in the duty ratio according to the central energization method. As shown in <FIG>, at the start of energization (t = <NUM>), the energization of the central heating element 45a is started at a duty ratio of X%. After that, the duty ratio is changed to (X + x)% when t<NUM> seconds have elapsed. After that, the duty ratio is changed to (X + 2x)% and (X + 3x)% after the lapse of 2t<NUM> seconds and the lapse of 3t<NUM> seconds, respectively. Note that, when the duty ratio has reached <NUM>%, the duty ratio is not further changed.

<FIG> is a diagram illustrating a change in the duty ratio according to the end energization method. As shown in <FIG>, at the start of energization (t = <NUM>), the first end heating element 45b1 and the second end heating element 45b2 both start energizing at the duty ratio of X%. After that, the duty ratio is changed to (X + y)% when t<NUM> seconds have elapsed. After that, the duty ratio is changed to (X + 2y)% after the elapse of 2t<NUM> seconds. Note that, when the duty ratio has reached <NUM>%, the duty ratio is not further changed. <FIG> illustrates an example in which the duty ratio reaches <NUM>% once 2t<NUM> seconds have elapsed. Therefore, the duty ratio is not changed when the elapse of 3t<NUM> seconds has elapsed. Note that, as described above, x < y.

As described above, in the image forming apparatus <NUM> of the second embodiment, when the start-up processing start condition is satisfied, the central heating element 45a is energized at a duty ratio that changes by x% after every time increment t<NUM>. On the other hand, the first end heating element 45b1 and the second end heating element 45b2 are energized with a duty ratio that changes by y%, which is greater than x%, after every time increment t<NUM>. Accordingly, the first end heating element 45b <NUM> and the second end heating element 45b2 are relatively more heated/powered than the central heating element 45a, but the power is still increased at regular intervals of t<NUM> seconds.

With the above configuration, the image forming apparatus <NUM> in the second embodiment can suppress possible differences in temperature at the ends of the cylindrical film <NUM> and the temperature at the central portion of the cylindrical film <NUM> when the fixing unit <NUM> is starting up.

The image forming apparatus <NUM> in the second embodiment has a configuration in which the increase amount (x) in the duty ratio for the energization to the central heating element 45a and the increase amount (y) of the duty ratio for the first end heating element 45b <NUM> and the second end heating element 45b2 are different from each other. However, the disclosure is not limited thereto, and for example, the image forming apparatus <NUM> may have a configuration in which the frequency (timer intervals) for changing the duty ratio for energization of the central heating element 45a and the first end heating element 45b <NUM> and the second end heating element 45b2 are different from each other.

Specifically, for example, the duty ratio may be changed every t1 seconds for the central heating element 45a, and the duty ratio may be changed for every t2 seconds for the first end heating element 45b <NUM> and the second end heating element 45b2. Here, it can be assumed that t1 > t2 is satisfied. In such a case as this, the increase amount (change increment) for the duty ratio for the central heating element 45a and the duty ratio for the first end heating element 45b <NUM> and the second end heating element 45b2 may be the same as each other.

In this case, the duty ratio of the first end heating element 45b1 and the second end heating element 45b2 is changed at a timing relatively quicker than that of the central heating element 45a. Accordingly, the image forming apparatus <NUM> according to the second embodiment can suppress the temperature differences between the ends of the cylindrical film <NUM> the center n of the cylindrical film <NUM> when the fixing unit <NUM> is starting up.

The image forming apparatus <NUM> may also have a configuration in which, for example, the starting duty ratio at the time when energization of the central heating element 45a is started and the starting duty ratio at the start of energization of the first end heating element 45b <NUM> and the second end heating element 45b2 are made different from each other.

More specifically, for example, a configuration may be adopted in which energization is started with a duty ratio of X<NUM>% for energization of the central heating element 45a, and energization is started with a duty ratio of X<NUM>% with respect to energization of the first end heating element 45b1 and the second end heating element 45b2. Here, X<NUM> < X<NUM> would be satisfied. Note that, in this case, the duty ratio change amount increments for the central heating element 45a and for the first end heating element 45b <NUM> and the second end heating element 45b2 may be the same as each other.

In this case, the first end heating element 45b1 and the second end heating element 45b2 start to be energized with relatively higher power (that is, with a higher starting duty ration value) than the central heating element 45a. Accordingly, the image forming apparatus <NUM> according to the second embodiment can suppress the temperature differences along the width direction of the cylindrical film <NUM> when the fixing unit <NUM> is starting up.

As described above, the image forming apparatus <NUM> according to the second embodiment includes the heating element group <NUM> and the controller <NUM>. The heating element group <NUM> includes the central heating element 45a and the first end heating element 45b1 and the second end heating element 45b2 (which may be referred to collectively as "end heating elements"). The central heating element 45a, the first end heating element 45b1, and the second end heating element 45b each use a TCR material, and generate heat with energization. The central heating element 45a is disposed in the center of the heating element group <NUM>. The first end heating element 45b1 and the second end heating element 45b2 are respectively disposed at opposite ends of the heating element group <NUM>. The controller <NUM> changes the duty ratio of the electric power to be supplied to the heating element group <NUM> over time, while the fixing unit <NUM> is starting up. Here, the controller <NUM> makes a duty ratio of the electric power supplied to the central heating element 45a different (a first duty ratio) from a duty ratio of the electric power supplied to each of the first end heating element 45b1 and the second end heating element 45b2 (a second duty ratio).

With the above configuration, the image forming apparatus <NUM> can further increase the duty ratio of the power for energizing the first end heating element 45b <NUM> and the second end heating element 45b2, for example, to be larger than the increasing width of the duty ratio of the power supplied to the central heating element 45a. In this case, more heat is applied to the first end heating element 45b1 and the second end heating element 45b2 than the central heating element 45a. Accordingly, the image forming apparatus <NUM> can suppress the temperature at the end of the cylindrical film <NUM> from being lower than the temperature of the center of the cylindrical film <NUM>.

Note that, in the above-described embodiment, the controller <NUM> makes the duty ratio of the electric power supplied to the central heating element 45a and the duty ratio of the electric power supplied to the first end heating element 45b1 and the second end heating element 45b2 different from each other. However, the present disclosure is not limited to this. For example, the controller <NUM> may cause the duty ratio of the power for energizing the central heating element 45a to be different according to the time interval used for changing the duty ratio of the power for causing the first end heating element 45b <NUM> and the second end heating element 45b2 to be energized.

For example, the controller <NUM> may shorten the time interval for changing the duty ratio of the power for energizing the first end heating element 45b <NUM> and the second end heating element 45b2 to be less the time interval for changing the duty ratio of the power for energizing the central heating element 45a. In this case, more heat is applied to the first end heating element 45b <NUM> and the second end heating element 45b2 than the central heating element 45a. Accordingly, the image forming apparatus <NUM> can prevent the temperature at the end of the cylindrical film <NUM> from being lower than the temperature of the center of the cylindrical film <NUM>.

Further, for example, the controller <NUM> may cause the duty ratio at the start of the energization (that is the initial duty ratio value) to be different for the central heating element 45a and the first end heating element 45b1 and the second end heating element 45b2. For example, the controller <NUM> may set the duty ratio of the electric power for energizing the first end heating element 45b <NUM> and the second end heating element 45b2 at the time of the start of the energization to be higher than the duty ratio of the electric power supplied to the central heating element 45a at the start of the energization. In this case, more heat is applied to the first end heating element 45b <NUM> and the second end heating element 45b2 than the central heating element 45a. Accordingly, the image forming apparatus <NUM> can prevent the temperature at the end of the end of the cylindrical film <NUM> from being lower than the temperature of the center of the cylindrical film <NUM>.

Note that, in the above-described embodiments, the heating element group <NUM> has a configuration in which three heating elements (the central heating elements 45a, the first end heating elements 45b1, and the second end heating elements 45b2) are provided. However, the number of heating elements included in the heating element group <NUM> may be one or two, or may be four or more.

Note that, in each of the above-described embodiments, heater temperature sensors <NUM> are configured to include two heater temperature sensors (the central heater temperature sensor 62a and the end heater temperature sensor 62b). However, the number of the heater temperature sensors <NUM> may be three or more.

Note that in each of the above-described embodiments, the plurality of thermostats <NUM> includes two thermostats (the central thermostat 68a and the end thermostat 68b). However, the number of thermostats <NUM> may be three or more.

Note that the heating element included in the heating element group <NUM> may be considered a heating element having a positive resistance temperature characteristic.

Note that the image forming apparatus <NUM> in each of the above-described embodiments may be a decoloring apparatus. In this case, the heating device is a decoloring unit. A decoloring device performs a process of decoloring (erasing) an image formed on a sheet by a decoloring toner. The decoloring unit decolors a decoloring toner image formed on the sheet passing through a nip by heating the decoloring toner image.

Note that, in each of the above-described embodiments, the cylindrical film <NUM> is an example of a fixing belt. Further, the heating element group <NUM> is an example of a heating unit. Further, the central heating element 45a is an example of a central heat generating part. Further, the first end heating element 45b1 and the second end heating element 45b2 are examples of end heat generating parts.

All or part of the functions of the image forming apparatus <NUM> described as being implemented via software may instead, or in addition to, be realized by using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), and the like. The software program may be recorded in a non-transitory computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM, or a storage device such as a hard disk incorporated in a computer system. The program may be transmitted via a telecommunication line.

In the above-described embodiments, the controller <NUM> is a software-implemented functional unit, but in other examples may be a hardware functional unit such as an LSI or the like.

According to at least one embodiment described above, the image forming apparatus <NUM> changes the duty ratio of the power supplied to the heating element group <NUM> over time, and changes the duty ratio of the power to a higher value after every fixed period, so that the consumed power that is reduced due to the characteristics of the TCR material can be increased again for a certain period of time. That is, the image forming apparatus <NUM> might limit a decrease in power. Accordingly, the image forming apparatus <NUM> can shorten the time required for starting of the heating apparatus as compared with the related art.

Claim 1:
A fixing unit (<NUM>), comprising:
a first heater element formed of a TCR material that increases in electrical resistance with increases in temperature; and
a controller (<NUM>) configured to vary a duty ratio of electric power applied to the first heater element during a start-up operation in which the temperature of the first heater element is raised to a target operating temperature;
a second heater element formed of the TCR material,
wherein the first heater element is a centrally positioned heating element (45a) in the fixing unit and the second heater element is an end positioned heating element (45b1, 45b2) in the fixing unit,
and wherein the controller (<NUM>) is further configured to vary a duty ratio of electric power applied to the second heater element during the start-up operation,
characterized in that the controller (<NUM>) is configured to increase the duty ratio of electric power applied to the first heater element every first fixed time interval during the start-up operation and to increase the duty ratio of electric power applied to the second heater element every second fixed time interval during the start-up operation, the first fixed time interval being greater than the second fixed time interval.