Fixing device and image forming apparatus

A fixing device includes a plurality of heating elements, a plurality of first terminals, a second terminal, a movable member, a first conductive circuit and a second conductive circuit. The heating elements are arranged in a main scanning direction and generate heat. The first terminals are electrically connected to the heating elements. The second terminal is electrically connected to a power supply that supplies electric power to the heating elements. The first conductive circuit and the second conductive circuit are provided on a surface of the movable member. The first conductive circuit is configured to electrically connect a first combination of one or more of the first terminals with the second terminal. The second conductive circuit is configured to electrically connect a different, second combination of one or more of the first terminals with the second terminal.

FIELD

Embodiments described herein relate generally to a fixing device and an image forming apparatus.

BACKGROUND

In the related art, in a fixing device of an image forming apparatus, a heating region is divided into a plurality of regions. Heaters are individually arranged in each of the divided subregions, and an independent heating control circuit (for example, a triac) is provided for the heater in each subregion. According to the employment of such a configuration, it is possible to heat a region suitable for each of a plurality of sheet sizes.

However, the number of subregions (i.e., the number of divisions of the heating region) increases according to the sheet size. Therefore, the configuration of the fixing device can become complicated when handling larger sheets, and the number of parts (for example, the number of heating control circuits) may increase accordingly.

DETAILED DESCRIPTION

In general, according to one embodiment, a fixing device includes a plurality of heating elements, a plurality of first terminals, a second terminal, a movable member, a first conductive circuit, a second conductive circuit, a thin film, and a rotating body. The heating elements are arranged in a main scanning direction and generate heat. The first terminals are electrically connected to the heating elements. The second terminal is electrically connected to a power supply that supplies electric power to the heating elements. The first conductive circuit and the second conductive circuit are provided on a surface of the movable member. The thin film is a strip-like thin film that slides on a heating element surface while being in contact with the heating element on one surface thereof. The rotating body is able to press the other surface of the thin film and be rotationally driven. The first conductive circuit is configured to electrically connect a first combination of one or more of the first terminals with the second terminal. The second conductive circuit is configured to electrically connect a second combination of one or more of the first terminals with the second terminal. The first combination is different from the second combination.

Hereinafter, a fixing device and an image forming apparatus of the embodiment will be described with reference to the drawings.FIG. 1is an external view illustrating an overall configuration example of an image forming apparatus100according to the embodiment.FIG. 2is a hardware block diagram of the image forming apparatus100according to the embodiment. The image forming apparatus100is, for example, a multifunction peripheral. The image forming apparatus100includes a display110(e.g., a user interface), a control panel120(e.g., a user interface), an image forming unit130, a sheet containing unit140, and an image reading unit200.

The image forming apparatus100forms an image on a sheet with a developer such as a toner. The developer is heated to be fixed onto the sheet. The sheet is, for example, paper or label paper. Anything can be used as the sheet as long as the image forming apparatus100can form an image on the surface thereof.

The display110is an image display device such as a liquid crystal display or an organic electro luminescence (EL) display. The display110displays various kinds of information relating to the image forming apparatus100.

The image forming unit130forms an image on the sheet based on image information generated by the image reading unit200or image information received via a communication path. The image forming unit130includes, for example, a developing device10, a transfer device20, and a fixing device30. The image forming unit130forms an image, for example, by a process as follows. The developing device10of the image forming unit130forms an electrostatic latent image on a photoconductor drum based on image information. The developing device10of the image forming unit130fixes the developer onto the electrostatic latent image to form a visible image (e.g., a toner image). Specific examples of the developer include a toner. Examples of the toner include a decolorable toner, a non-decolorable toner (e.g., ordinary toner), and a decorative toner.

The transfer device20of the image forming unit130transfers the visible image to the sheet. The fixing device30of the image forming unit130heats and pressurizes the sheet to fix the visible image to the sheet. The sheet on which the image is formed may be a sheet stored in the sheet storage unit140or may be a sheet manually fed.

The sheet storage unit140stores a sheet to be used for forming an image in the image forming unit130.

A storage unit150(e.g., memory) is configured by using a storage device such as a magnetic hard disk device or a semiconductor storage device. The storage unit150stores data required when the image forming apparatus100operates. The storage unit150may temporarily store data of the image formed in the image forming apparatus100.

A control unit160is configured by using a processor such as a central processing unit (CPU) and a memory. The control unit160reads and executes a program stored in advance in the storage unit150. The control unit160controls the operation of each device included in the image forming apparatus100.

The image reading unit200(e.g., a scanner) reads image information to be read based on brightness and darkness of light. The image reading unit200records the read image information. The recorded image information may be transmitted to another information processing device via a network. The recorded image information may be formed as an image on the sheet by the image forming unit130. The image reading unit200may include automatic document feeding (ADF).

FIG. 3is a front sectional view of the fixing device30according to the embodiment. The fixing device30of the embodiment includes a pressure roller31and a film unit32.

The pressure roller31is configured to be able to press the surface against the film unit32and be rotationally driven. If the surface of the pressure roller31is pressed against the film unit32, the pressure roller31forms a nip33with the film unit32. The pressure roller31pressurizes a visible image of the sheet that enters the nip33. If the pressure roller31is rotationally driven, the sheet is conveyed according to the rotation. The pressure roller31includes, for example, a core metal311(e.g., a metal core) and an elastic layer312.

The core metal311is formed in a columnar shape by a metal material such as stainless steel. Both ends of the core metal311in the axial direction are rotatably supported (e.g., by bearings coupled to housing of the image forming apparatus100). The core metal311is rotationally driven by a first driving unit41(e.g., an electric motor, a driver, an actuator, etc.). The first driving unit41is a device driven by electric power and is configured by using, for example, a motor. The first driving unit41is driven, for example, according to a control signal output from the control unit160.

The elastic layer312is formed of an elastic material such as silicone rubber. The elastic layer312is formed on the outer peripheral surface of the core metal311in a constant thickness. A release layer is formed on the outer peripheral surface of the elastic layer312. The release layer is formed, for example, of a resin material such as PFA (e.g., tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). The hardness of the outer peripheral surface of the pressure roller31is preferably 40° to 70° under a load of 9.8 N with an ASKER-C hardness tester. As a result, the area of the nip33and the durability of the pressure roller31are ensured.

The pressure roller31is rotationally driven by the power of the first driving unit41. If the pressure roller31rotates in a state in which the nip33is formed, a cylindrical film321of the film unit32is driven to rotate. The pressure roller31rotates in a state in which the sheet is disposed at the nip33, so that the sheet is conveyed in the conveyance direction.

The film unit32heats the visible image of the sheet that enters the nip33. The film unit32includes the cylindrical film321(e.g., a cylindrical body), a heater unit322(e.g., a heater), a stay323(e.g., a support, a frame, etc.), and a movable member324.

The cylindrical film321is formed in a cylindrical shape. The cylindrical film321includes a base layer, an elastic layer, and a release layer in this order from the inner peripheral side. The base layer is formed in a cylindrical shape by a material such as nickel (Ni). The elastic layer is laminated on the 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 PFA resin. The cylindrical film321is a strip-like thin film that slides on the surface of the heater unit322while being in contact with the heater unit322on one surface thereof.

FIG. 4is a diagram illustrating a specific example of the heater unit322. The heater unit322includes a substrate51(e.g., a heating element substrate), a plurality of first terminals52, a second terminal53, a plurality of heating elements54, and a heating control circuit55. The heater unit322is connected to a power supply56.

The substrate51is formed of a metal material such as stainless steel or nickel, a ceramic material such as aluminum nitride, or the like. The substrate51is formed, for example, in an elongated rectangular plate shape. The substrate51is disposed on the inner side in the radial direction of the cylindrical film321. The substrate51has the axial direction of the cylindrical film321as the longitudinal direction.

The first terminals52are provided on the substrate51and connected to at least one of the heating elements54(e.g., heaters). The first terminals52are configured to be in contact with third terminals61provided on the movable member324and electrically connected to the third terminals61.

The second terminal53is provided on the substrate51and is connected to the heating control circuit55. The second terminal53is configured to be in contact with fourth terminals62provided in the movable member324and electrically connected to the fourth terminals62. If the first terminals52and the second terminal53are electrically connected to the third terminals61and the fourth terminals62respectively, an electric circuit including the heating control circuit55, one or a plurality of heating elements54, and the power supply56is formed. In this case, under the control by the heating control circuit55, the electric power is supplied from the power supply56to one or a plurality of heating elements54included in the formed electric circuit.

One end of the heating element54is connected to the first terminal52, and the other end is connected to the power supply56. The plurality of heating elements54are arranged on the substrate51in the main scanning direction. The heating element54generates heat by energization. The heating element54is formed by using a heating resistor such as a silver-palladium alloy. The heating resistor used in the heating element54may be configured by using a material of which a resistance value greatly changes according to the temperature. Specifically, the heating resistor may be configured by using a material having a lower resistance value as the temperature is lower and a higher resistance value as the temperature is higher. For example, the heating element54may be configured, for example, by using a PTC element.

The heating control circuit55is supplied to a part or the entire part of the electric power output from the power supply56to the heating elements54according to the control of the control unit160. The heating control circuit55may be configured by using a semiconductor switching element such as a triac.

The description is made referring back toFIG. 3. The stay323(e.g., a support, a frame member, etc.) is formed by using a steel plate material or the like. The cross section of the stay323may be formed, for example, in a U shape. Both ends of the stay323in the longitudinal direction are fixed to the housing of the image forming apparatus100. As a result, the film unit32is supported by the image forming apparatus100.

The movable member324is configured to be moved by a driving force of a second driving unit42(e.g., an electric motor, a driver, an actuator, etc.) and be able to change the position for contact with the heater unit322.FIG. 5is a diagram illustrating a specific example of the movable member324. A plurality of circuit patterns63(for example,63_1,63_2, and63_3) are formed on the surface of the movable member324. Each of the circuit patterns63includes one or a plurality of third terminals61and the fourth terminal62. In each of the circuit patterns63, one or a plurality of third terminals61and the fourth terminal62are connected by a conducting wire to be electrically connected.

In each of the circuit patterns63, the combination of positions where the third terminals61are provided is different. For example, the circuit pattern63_1(e.g., a first conductive circuit) has six third terminals61arranged at the same interval. For example, the circuit pattern63_2has four third terminals61arranged at the same interval. For example, the circuit pattern63_3(e.g., a second conductive circuit) has two arranged third terminals61. As another specific example of the circuit patterns63, for example, a part of the plurality of third terminals61may be disposed at a different interval. However, if the circuit patterns63are selected, each of the third terminals61of the circuit patterns63is disposed to be in contact with the first terminals52. If the circuit patterns63are selected, each of the fourth terminals62of the circuit patterns63is disposed to be in contact with the second terminal53.

In the specific example ofFIG. 5, the movable member324has a cylindrical shape and each of the circuit patterns63is formed on a curved surface. Since the movable member324rotates according to the driving force of the second driving unit42, the position of the curved surface in contact with the substrate51changes. The heating element54to be activated to generate heat is selected by the control unit160and the circuit pattern63is selected corresponding to the first terminal52of the selected heating element54. The movable member324is moved so that the third terminals61and the fourth terminal62of the selected circuit pattern are in contact with the first terminals52and the second terminal53of the substrate51.

FIG. 6is a diagram illustrating an example of cross sections of the heater unit322and the movable member324. The third terminals61and the fourth terminal62receive a biasing force on the surface of the movable member324in a direction away from the movable member324. This biasing force may be a force generated, for example, according to the materials or shapes of the third terminals61and the fourth terminal62. This biasing force may be a force generated, for example, by an elastic body provided between the third terminals61and the fourth terminal62, and the movable member324.

For example, in the example ofFIG. 6, the height of the third terminal61that is in contact with the first terminal52is h1and the height of the third terminal61that is not in contact with the first terminal52is h2. The third terminal61that is not in contact with the first terminal52maintains the height of h2which is higher than h1according to the biasing force. Meanwhile, the third terminal61that is in contact with the first terminal52receives the force from the first terminal52toward the movable member324to be pressed to the position of the lower height h1. By the generation of the biasing force, the first terminal52and the third terminal61are securely in contact with each other, and electrical connection can be maintained.

FIG. 7is a diagram illustrating a specific example of the selected circuit pattern63. InFIG. 7, the circuit pattern63_1is selected. The six third terminals61of the selected circuit pattern63_1are in contact with the first terminals52, respectively. The fourth terminal62of the selected circuit pattern63_1is in contact with the second terminal53. According to this contact, the six heating elements54are connected to the power supply56via the heating control circuit55. By the formation of the circuit, the electric power is supplied from the power supply56to the six heating elements54and the heat is generated. Therefore, in a heat generating region59_1illustrated with the alternate long and short dash line inFIG. 7, heat for fixing is generated.

FIG. 8is a diagram illustrating a specific example of the selected circuit pattern63. InFIG. 8, the circuit pattern63_3is selected. The two third terminals61of the selected circuit pattern63_3are in contact with the first terminals52, respectively. The fourth terminal62of the selected circuit pattern63_3is in contact with the second terminal53. According to this contact, the two heating elements54are connected to the power supply56via the heating control circuit55. By the formation of the circuit, the electric power is supplied from the power supply56to the two heating elements54and the heat is generated. Therefore, in a heat generating region59_3illustrated with the alternate long and short dash line inFIG. 8, heat for fixing is generated. As illustrated inFIGS. 7 and 8, the heat generating regions59change according to the selected circuit patterns63.

FIG. 9is a flowchart illustrating a specific example of the processing of the control unit160. The control unit160determines a sheet size in accordance with the received image forming data or an operation in the control panel120(ACT101). The control unit160determines the heat generating region59based on the determined sheet size (ACT102). For example, a table in which the heat generating regions59are determined for each sheet size may be registered in the storage unit150in advance. In this case, the control unit160may determine the heat generating region59based on the table registered in the storage unit150.

The control unit160executes a heating position control process corresponding to the determined heat generating region59(ACT103). In the heating position control process, the control unit160drives the second driving unit42to move the movable member324so that the circuit pattern63is in contact with the heater unit322corresponding to the determined heat generating region59. If the movement of the movable member324is completed, the control unit160supplies the electric power to the heating elements54by the control of the heating control circuit55and starts heating (ACT104). If the measured value of the temperature of the heat generating region59exceeds a threshold value determined in advance, the control unit160starts image formation by controlling the developing device10and the transfer device20(ACT105).

In the image forming apparatus100of the embodiment configured in this manner, only one open circuit of one pattern is formed in the heater unit322. According to the selection of the heat generating region59, one circuit pattern63is selected from the plurality of circuit patterns63formed in the movable member324. Also, since each terminal of the selected circuit pattern63comes in contact with each terminal of the heater unit322, a closed circuit is formed in the heater unit322. Also, the electric power from the power supply56is supplied only to the heating element54included in the closed circuit, and the generation of the heat starts. Therefore, the circuit separated into a plurality of parts in the heater unit322becomes unnecessary. As a result, the number of heating control circuits55can be reduced (for example, to one) and the number of parts can be reduced in the configuration of the fixing device. In addition, ON/OFF switching control for each of the circuits divided into plural becomes unnecessary and firmware control can be simplified.

MODIFICATION

FIG. 10is a diagram illustrating a configuration of a modification of the movable member324. In the embodiment described above, the movable member324as illustrated inFIG. 5is configured in a cylindrical shape. However, the shape of the movable member324is not required to be limited to a cylinder. For example, as illustrated inFIG. 10, the movable member324may be configured by using a polygonal columnar object. In the example ofFIG. 10, the movable member324is formed in a hexagonal column shape. Further, the movable member324does not necessarily have to be formed in a columnar shape and may be configured by using, for example, a flat plate. In this case, the surface of the flat plate may be divided into a plurality of regions and the different circuit patterns63may be formed in each region. In this case, the second driving unit42may bring the selected circuit pattern63into contact with the heater unit322by moving the flat plate.