Patent Description:
In a belt type or on-demand type fixing device, static electricity may be accumulated on the fixing belt because of its repeated sliding contact with sheets of paper and the heater element of the fixing device. When static electricity accumulates on the fixing belt, an electrostatic offset may occur, thereby deteriorating the quality of an output image formed on the sheet. To prevent the occurrence of such an electrostatic offset, a method has been developed to discharge the accumulated static electricity by connecting the fixing belt to a ground potential (hereinafter, referred to as "GND"). However, since the fixing belt rotates, the connection between the fixing belt and GND tends to be unstable or difficult to maintain continuously.

<CIT> relates to an image processing apparatus according to the preamble of claim <NUM>. <CIT> and <CIT> relate each to an image forming apparatus.

In general, according to one embodiment, an image forming apparatus capable of preventing quality deterioration of an image, and a heating control method are provided.

The invention relates to an image processing apparatus as defined by claim1, and includes a fixing unit. The fixing unit includes a heater and a fixing belt. The fixing belt is electrically connected between a first power source and a ground terminal. A controller is configured to control the heater to heat the fixing belt. The controller is further configured to determine whether a current is flowing through the fixing belt and, upon determining that a current is not flowing through the fixing belt, control the heater not to heat the fixing belt.

Preferably, the image processing apparatus further comprises an insulated detection element connected to the fixing belt and causing a current to flow through the fixing belt when the fixing belt is connected to the ground terminal and not to flow through the fixing belt when the fixing belt is not connected to the ground terminal.

Preferably yet, the insulated detection element includes a photocoupler.

Preferably yet, the insulated detection element includes a light emitting diode and a light receiving element. A cathode of the light emitting diode is connected to the fixing belt, and an anode of the light emitting diode is connected to the first power source. The light receiving element is connected between a second power source and a ground terminal, and the controller determines whether a current is flowing through the fixing belt by detecting a current flowing through the light receiving element.

The controller is further configured to control the heater to alternately switch between an on state and an off state, and determine whether a current is flowing through the fixing belt only when the heater is in the off state.

Preferably, the heater is disposed inside the fixing belt.

Preferably, the fixing unit further includes a microcomputer configured to detect a current flowing through the fixing belt.

Preferably, the heater includes a substrate, a glass layer that contacts an inner surface of the fixing belt, and a heating layer between the substrate and the glass layer.

Preferably, the fixing unit further includes a pressure roller that forms a nip with the fixing belt.

Preferably yet, the heater is disposed inside fixing belt at the nip.

The invention also relates a method as defined by claim <NUM> for controlling an image processing apparatus having a fixing unit, the method comprising:.

Preferably, the method further comprises detecting whether a current is flowing through the fixing belt using an insulated detection element connected between the fixing belt and the ground terminal.

Preferably yet, the insulated detection element includes a light emitting diode and a light receiving element. A cathode of the light emitting diode is connected to the fixing belt, an anode of the light emitting diode is connected to the first power source, and the light receiving element is connected between a second power source and a ground terminal. The method further comprises determining whether a current is flowing through the fixing belt by detecting a current flowing through the light receiving element.

The method further comprises alternately switching the heater between an on state and an off state, wherein whether a current is flowing through the fixing belt is determined only in the off state.

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

<FIG> shows a configuration of an image forming apparatus <NUM> according to an embodiment. The image forming apparatus <NUM> is a multi-function peripheral (MFP) device. The image forming apparatus <NUM> performs an image forming process and an image fixing process. The image forming process is a process of forming an image on a sheet. The image fixing process is a process of fixing the formed image onto the sheet. The sheet is, for example, a piece of paper on which characters, text, images, or the like can be formed. In general, any type of sheet can be used as long as the sheet can be handled by the image forming apparatus <NUM>. The image forming apparatus <NUM> can scan or read images on a sheet or document, generate digital data thereby, and generate an image file corresponding to image on the sheet or document.

The image forming apparatus <NUM> includes an image reading unit <NUM>, a control panel <NUM>, an image forming unit <NUM>, a sheet storage unit <NUM>, a fixing device <NUM>, conveyor rollers 61a and 61b, paper discharge rollers 62a and 62b, and a control device <NUM>.

The image reading unit <NUM> reads an image formed on a sheet as bright and dark signals. For example, the image reading unit <NUM> reads (scans) an image printed on a sheet set on a document reading table or platen of the image forming apparatus <NUM>. The image reading unit <NUM> records the image data that is read/scanned. The recorded image data may be transmitted to another information processing apparatus via a network. The recorded image data may be used to form a corresponding image on another sheet with the image forming unit <NUM>.

The control panel <NUM> includes a display unit and an operation unit. The display unit is a display device, such as a liquid crystal display, an organic electro luminescence (EL) display, or the like. The display unit displays various types of information related to the image forming apparatus <NUM> according to a control signal of the control device <NUM>. The operation unit includes a plurality of buttons, keys, switches, or the like. The operation unit receives an input operation from a user. The operation unit outputs a signal according to an input operation performed by the user to the control device <NUM>. The display unit and the operation unit may be integrated into a touch-enabled display or the like.

The image forming unit <NUM> performs an image forming process. In the image forming process, the image forming unit <NUM> forms an image on a sheet based on image data generated by the image reading unit <NUM> or image data received through a network.

The image forming unit <NUM> includes a transfer belt <NUM>, an exposure unit <NUM>, a plurality of developing devices including developing devices 33Y, <NUM>, 33C, and <NUM>, and a plurality of photoconductive drums including photoconductive drums 34Y, <NUM>, 34C, and <NUM>, and a transfer unit <NUM>.

The transfer belt <NUM> is an intermediate transfer body. The transfer belt <NUM> rotates in a direction indicated by an arrow (depicted as the counterclockwise direction) according to rotation of a roller.

The exposure unit <NUM> is provided below the developing devices 33Y, <NUM>, 33C, and <NUM> facing the photoconductive drums 34Y, <NUM>, 34C, and <NUM>, respectively. The exposure unit <NUM> emits a laser beam toward a photoconductor layer on each of the photoconductive drums 34Y, <NUM>, 34C, and <NUM>. The exposure unit <NUM> is controlled to emit light based on the image data by the control device <NUM>. The exposure unit <NUM> emits the laser beam based on the image data, thereby a static electrical charge on the photoconductive layer of each of the photoconductive drums 34Y, <NUM>, 34C, and <NUM> disappears in areas corresponding to the exposure pattern. As a result, an electrostatic pattern is formed on the photoconductive layers of the photoconductive drums 34Y, <NUM>, 34C, and <NUM>. In other words, by the emission of the laser beam by the exposure unit <NUM>, an electrostatic latent image is formed on the photoconductive layers of the photoconductive drums 34Y, <NUM>, 34C, and <NUM>. In some examples, the exposure unit <NUM> may use light emitting diode (LED) light instead of a laser beam.

The developing devices 33Y, <NUM>, 33C, and <NUM> supply toner to the photoconductive drums 34Y, <NUM>, 34C, and <NUM>. For example, the developing device 33Y develops the electrostatic latent image on the photoconductive layer of the photoconductive drum 34Y with yellow (Y) toner. The developing device <NUM> develops the electrostatic latent image on the photoconductive layer of the photoconductive drum <NUM> with magenta (M) toner. The developing device 33C develops the electrostatic latent image on the photoconductive layer of the photoconductive drum 34C with cyan (C) toner. The developing device <NUM> develops the electrostatic latent image on the photoconductive layer of the photoconductive drum <NUM> with black (K) toner.

The developing devices 33Y, <NUM>, 33C, and <NUM> form toner images on the photoconductive drums 34Y, <NUM>, 34C, and <NUM> as visible images. The toner images formed on the photoconductive drums 34Y, <NUM>, 34C, and <NUM> are transferred onto the transfer belt <NUM> (primary transfer).

The transfer unit <NUM> includes a support roller 35a and a secondary transfer roller 35b. The transfer unit <NUM> transfers the toner image formed on the transfer belt <NUM> to the sheet at a secondary transfer location U. The secondary transfer location U is a location at which the support roller 35a and the secondary transfer roller 35b face each other with the transfer belt <NUM> interposed therebetween. The transfer unit <NUM> provides a transfer bias (controlled by a transfer current) to the transfer belt <NUM>. The transfer unit <NUM> transfers the toner image on the transfer belt <NUM> to the sheet using the transfer bias. The control device <NUM> controls the transfer current used this secondary transfer process.

The sheet storage unit <NUM> includes a single paper feed cassette or a plurality of paper feed cassettes. A paper feed cassette stores a sheet <NUM> of a predetermined size and a predetermined type. The paper feed cassette includes a pickup roller. The pickup roller picks up each sheet <NUM> from the paper feed cassette one by one. The pickup roller supplies the picked up sheet <NUM> to a conveyor unit <NUM>.

The fixing device <NUM> performs the image fixing process. In particular, the fixing device <NUM> fixes the toner image on the sheet <NUM> by applying heat and pressure to the sheet <NUM>.

The conveyor rollers 61a and 61b convey the sheet <NUM> fed from the paper feed cassette to the image forming unit <NUM>. The conveyor rollers 61a and 61b face toward each other and form a nip.

The paper discharge rollers 62a and 62b discharge the sheet <NUM> on which the image has been formed by the fixing device <NUM> to a discharging unit. The paper discharge rollers 62a and 62b face toward each other and form a nip.

The control device <NUM> controls each unit of the image forming apparatus <NUM>.

The conveyor unit <NUM> conveys the sheets <NUM>. The conveyor unit <NUM> provides a sheet conveyance path includes a plurality of rollers disposed at various points along the sheet conveyance path. The sheet conveyance path is a path along which the sheet <NUM> is conveyed during image forming processing or the like. The rollers rotate to convey the sheet <NUM> in response to the control of the control device <NUM>.

Hereinafter, a hardware configuration of the image forming apparatus <NUM> will be described.

<FIG> is a hardware block diagram of the image forming apparatus <NUM>. The image forming apparatus <NUM> includes the image reading unit <NUM>, the control panel <NUM>, the image forming unit <NUM>, the sheet storage unit <NUM>, the control device <NUM>, an auxiliary storage device <NUM>, and a network interface <NUM>. The various units are connected to each other via a system bus <NUM> to enable data communication between the units and/or the control device <NUM> as necessary.

The image reading unit <NUM>, the control panel <NUM>, the image forming unit <NUM>, and the sheet storage unit <NUM> operate as described above, and thus repeated descriptions thereof are omitted.

The fixing device <NUM> includes a photocoupler <NUM> and a microcomputer <NUM>. In some examples, the microcomputer <NUM> may be included in or otherwise considered a part of the control device <NUM>. Alternatively, the function of the microcomputer <NUM> may be performed by a dedicated processor <NUM> or the like.

In this example, the control device <NUM> includes the processor <NUM>, a read only memory (ROM) <NUM>, and a random access memory (RAM) <NUM>. The processor <NUM> is, for example, a central processing unit (CPU). The processor <NUM> performs various processes by loading a program from the ROM <NUM> onto the RAM <NUM> and then executing the program.

The ROM <NUM> stores a program to be executed by the processor <NUM>. The RAM <NUM> temporarily stores data used by each unit of the image forming apparatus <NUM>. The RAM <NUM> may also store digital data generated by the image reading unit <NUM>. The RAM <NUM> may temporarily store a print job and a print job log or the like.

The auxiliary storage device <NUM> is, for example, a hard disk or a solid state drive (SSD), and stores various types of data. The various types of data are, for example, digital data, such as image data, a print job, a print job log, and the like.

The network interface <NUM> transmits and receives data to or from another apparatus. Here, in this example, the other apparatus is an information processing apparatus, such as a personal computer, a tablet terminal, a smart phone, or the like. The network interface <NUM> operates as an input interface to receive data or instruction transmitted from the other apparatus. The instruction transmitted from the other apparatus can be a print execution instruction. The network interface <NUM> operates as an output interface to transmit data to the other apparatus as needed.

Hereinafter, a configuration of the fixing device <NUM> will be described.

<FIG> is a front cross-sectional view of the fixing device <NUM>. The fixing device <NUM> includes a pressurizing roller 530p and a film unit <NUM>.

The pressurizing roller 530p forms a nip N with the film unit <NUM>. The pressurizing roller 530p presses the toner image on the sheet when the sheet enters the nip N. The pressurizing roller 530p rotates and conveys the sheet. The pressurizing roller 530p includes a cored bar <NUM>, an elastic layer <NUM>, and a release layer (not separately depicted).

As described above, the pressurizing roller 530p is capable of pressing a surface of a cylindrical film <NUM> and is rotatable.

The cored bar <NUM> is formed in a cylindrical shape by a metal material such as stainless steel or the like. Both end portions of the cored bar <NUM> in an axial direction are rotatably supported. The cored bar <NUM> is driven by a motor to rotate. The cored bar <NUM> contacts, for example, a cam member. The cam member rotates such that the cored bar <NUM> will approach and be separated from the film unit <NUM> according to the cam member position.

The elastic layer <NUM> is formed of an elastic material such as silicone rubber or the like. The elastic layer <NUM> is formed on an outer peripheral surface of the cored bar <NUM> in a uniform thickness.

The release layer is formed of a resin material such as a poly[tetrafluoroethylene-co-perfluoro (alkyl vinyl ether)] copolymer or the like (referred to as a PFA resin in this context). The release layer is formed on an outer peripheral surface of the elastic layer <NUM>.

Hardness of an outer peripheral surface of the pressurizing roller 530p may be <NUM>° to <NUM>° with respect to a load of <NUM> N measured by an ASKER-C hardness tester. Accordingly, the area of the nip N and the durability of the pressurizing roller 530p are secured.

The pressurizing roller 530p can approach and be separated from the film unit <NUM> via rotation of the cam member. The nip N is formed when the pressurizing roller 530p is brought close to the film unit <NUM> and pressed by a spring element or the like. However, if a sheet jam occurs at the fixing device <NUM>, the jammed sheet may be removed by separating the pressurizing roller 530p from the film unit <NUM> by rotation of the cam member. Plastic deformation of the cylindrical film <NUM> is prevented by separating the pressurizing roller 530p from the film unit <NUM> when the cylindrical film <NUM> is not rotating, e.g., during a sleep state.

The pressurizing roller 530p is rotated by a motor. When the pressurizing roller 530p is rotated while the nip N is formed, the cylindrical film <NUM> of the film unit <NUM> is driven and rotated. The pressurizing roller 530p rotates and conveys a sheet in a conveying direction W through the nip N.

The film unit <NUM> heats a toner image on the sheet that has entered the nip N. The film unit <NUM> includes the cylindrical film <NUM>, a heater <NUM>, a heat transfer member <NUM>, a support member <NUM>, a stay <NUM>, a heater thermometer <NUM>, a thermostat <NUM>, and a thermistor <NUM>.

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

The heater <NUM> includes a substrate 55a and a heating layer 55b. In the present disclosure, an x direction, a y direction, and a z direction are defined as follows. The y direction is a longitudinal direction of the substrate 55a. The y direction is parallel to a width direction and the rotation axis of the cylindrical film <NUM>. The x direction is a lateral direction of the substrate 55a and thus is perpendicular to the y direction. The z direction is a normal direction of the substrate 55a and perpendicular to the x and y directions. A configuration of the heater <NUM> will be described later.

As shown in <FIG>, a straight line CL connecting an axis pc of the pressurizing roller 530p and an axis hc of the film unit <NUM> is defined. A center 541c of the substrate 55a in the x direction is arranged in a +x direction with respect to the straight line CL. Since the substrate 55a extends in the +x direction of the nip N with respect to the substrate 55b, the temperature of the edge in the +x direction of the substate tends to be lower, which helps a sheet passing through the nip N in separating from the film unit <NUM>.

A center 545c of the heating layer 55b in the x direction is located on the straight line CL. The heating layer 55b is entirely included in an area of the nip N and is present at the center of the nip N. Accordingly, heat distribution in the nip N is substantially uniform, and thus the sheet passing through the nip N is uniformly heated.

As shown in <FIG>, the heater <NUM> is arranged inside the cylindrical film <NUM>. A lubricant is applied on an inner peripheral surface of the cylindrical film <NUM>. The heater <NUM> contacts the inner peripheral surface of the cylindrical film <NUM> via the lubricant. When the heater <NUM> generates heat, the viscosity of the lubricant will be decreased. Accordingly, the sliding property between the heater <NUM> and the cylindrical film <NUM> is improved by the heating.

As described above, the cylindrical film <NUM> is a thin film, which slides along a surface of the heater <NUM> while contacting the surface.

The heat transfer member <NUM> is formed of a metal material having high thermal conductivity, such as copper or the like. An outer shape of the heat transfer member <NUM> is similar to an outer shape of the substrate 55a of the heater <NUM>. The heat transfer member <NUM> contacts a surface of the heater <NUM>.

The support member <NUM> is formed of a resin material, such as liquid crystal polymer or the like. The support member <NUM> is arranged to cover the upper (z direction) surface side in <FIG> of the heater <NUM> and both sides in the x direction. The support member <NUM> supports the heater <NUM> through the heat transfer member <NUM>. Round chamfers are formed on both end portions 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 end portions of the heater <NUM> in the x direction.

When the sheet passing through the fixing device <NUM> is heated, a temperature distribution occurs in the heater <NUM> according to a size of the sheet. When the temperature of the heater <NUM> is locally increased, the temperature may exceed a heat-tolerance temperature of the support member <NUM> formed of the resin material. The heat transfer member <NUM> averages (mediates) the temperature distribution along the heater <NUM>. Accordingly, the heat resistance of the support member <NUM> can be secured even if certain local temperatures at points along the length of the heater <NUM> are higher than the heat-tolerance temperature of the support member <NUM>.

The stay <NUM> shown in <FIG> is formed of a bent steel plate material or the like. A cross section of the stay <NUM> perpendicular to the y direction is formed in a U shape. The stay <NUM> is mounted on the above (z direction) the support member <NUM>. The support member <NUM> is positioned at the ends of the U-shaped opening so as to close the U-shaped opening of the stay <NUM>. The stay <NUM> extends in the y direction. Both end portions of the stay <NUM> in the y direction are fixed to a housing or the like of the image forming apparatus <NUM>. Accordingly, the film unit <NUM> is physically supported by the image forming apparatus <NUM>. The stay <NUM> improves rigidity of the film unit <NUM> to limit bending or flexing. A flange (not shown) for restricting movement of the cylindrical film <NUM> in the y direction is mounted near both end portions of the stay <NUM> in the y direction.

The heater thermometer <NUM> is arranged on the upper (z direction) surface side of the heater <NUM> with the heat transfer member <NUM> disposed therebetween. For example, the heater thermometer <NUM> is a thermistor. The heater thermometer <NUM> is mounted on and supported by a surface of the support member <NUM>. A temperature sensitive element of the heater thermometer <NUM> contacts the heat transfer member <NUM> through a hole penetrating the support member <NUM> in the z direction. The heater thermometer <NUM> measures the temperature of the heater <NUM> via the heat transfer member <NUM>.

The thermostat <NUM> is arranged on the heater <NUM> similarly to the heater thermometer <NUM>. The thermostat <NUM> blocks a current flowing to the heating layer 55b when the temperature of the heater <NUM> detected via the heat transfer member <NUM> exceeds a predetermined temperature.

The thermistor <NUM> (also referred to as a film thermometer) is arranged inside the cylindrical film <NUM> as shown in <FIG>. The thermistor <NUM> contacts the inner peripheral surface of the cylindrical film <NUM> and measures the temperature of the cylindrical film <NUM>.

In addition to the heater thermometer <NUM> and the thermistor <NUM>, the image forming apparatus <NUM> may further include an environmental thermometer for measuring surrounding temperatures or the like. In general, the environmental thermometer measures a temperature around the mounted location thereof. The environmental thermometer may be mounted on any location in the vicinity of the fixing device <NUM>. In this context, the vicinity of the fixing device <NUM> is any location where the environmental thermometer is able to measure an environment temperature of the space in which the fixing device <NUM> is located. The environmental thermometer may be mounted on, for example, a housing located outside the film unit <NUM>.

<FIG> is a diagram showing a configuration of the heater <NUM>.

As shown in <FIG>, the heater <NUM> includes four layers including a glass layer 55c, the heating layer 55b, a glass layer 55d, and the substrate 55a stacked in this order on an inner surface of a fixing belt <NUM>.

The substrate 55a is formed of a metal material such as stainless steel or the like, or a ceramic material such as aluminum nitride or the like. The substrate 55a is formed in an elongated rectangular plate shape. The substrate 55a is arranged inside the cylindrical film <NUM>. The substrate 55a extends in a longitudinal direction parallel to an axial direction of the cylindrical film <NUM>.

The heating layer 55b is formed of, for example, a silver palladium alloy or the like. An outer shape of the heating layer 55b has a rectangular shape, the longitudinal direction of which corresponds to the y direction and the lateral direction of which corresponds to the x direction.

Hereinafter, a mechanism for detecting whether the fixing belt <NUM> included in the fixing device <NUM> of the image forming apparatus <NUM> is connected to GND.

<FIG> is a schematic diagram showing the mechanism for detecting whether the fixing belt <NUM> of the current embodiment is connected to GND.

As shown in <FIG>, the photocoupler <NUM> and the microcomputer <NUM> are used as the mechanism for detecting whether the fixing belt <NUM> is connected to GND. Alternatively, instead of the photocoupler <NUM>, for example, another insulating type detection element, such as a current transformer, may be used as the insulated detection element. In other words, any element may be used instead of the photocoupler <NUM> as long as a current flowing on the primary circuit side is detectable on the secondary circuit side in a non-contact (insulated) manner.

As shown in <FIG>, the photocoupler <NUM> includes a light emitting diode 501a and a light receiving element 501b. An anode of the light emitting diode 501a is connected to a power source of the primary circuit. A cathode of the light emitting diode 501a is connected to the fixing belt <NUM>. The fixing belt <NUM> is connected to GND. An anode of the light receiving element 501b is connected to a power source of the secondary circuit. A cathode of the light receiving element 501b is connected to the microcomputer <NUM> and GND.

According to such a configuration, when the fixing belt <NUM> is connected to GND, the light emitting diode 501a emits light because a current flows from the power source on the primary circuit through the light emitting diode 501a to GND. When light emitted by the light emitting diode 501a is being received by the light receiving element 501b, the light receiving element 501b passes a current from the power source of the secondary circuit to GND. When detecting a current passing through the light receiving element 501b, the microcomputer <NUM> outputs, to the control device <NUM>, a notification indicating normality (a normal state). If current does not pass through the light receiving element 501b (that is, no light is detected from the light emitting diode 501a) a notification indicating abnormality (an abnormal state) is output from the microcomputer <NUM> to the control device <NUM>.

The control device <NUM> obtains the notification output from the microcomputer <NUM>. When the notification indicating the normal state is obtained, the control device <NUM> determines that the fixing belt <NUM> is connected to GND. When it is determined that the fixing belt <NUM> is connected to GND (normal state), the control device <NUM> starts rotation (or maintains rotation) of the fixing belt <NUM> and starts a heating process (or maintains a heating process) by the heater <NUM>.

<FIG> shows a case in which the fixing belt <NUM> is not connected to GND. As shown in <FIG>, when connection between the fixing belt <NUM> and GND is disconnected due to, for example, a wiring disconnection, the current from the power source at the primary circuit does not flow through the light emitting diode 501a. As a result, the light emitting diode 501a does not emit light. When the light is not received from the light emitting diode 501a, a current from the power source of the secondary circuit will not flow through the light receiving element 501b. Upon detecting that the current is not flowing through the light receiving element 501b, the microcomputer <NUM> outputs a notification indicating the abnormal state to the control device <NUM>.

Upon obtaining the notification indicating the abnormal state, the control device <NUM> determines that the fixing belt <NUM> is not connected to GND (abnormal state). When it is determined that the fixing belt <NUM> is not connected to GND, the control device <NUM> stops the rotation (or will not start the rotation) of the fixing belt <NUM> and stops the heating process (or will not start the heating process) by the heater <NUM>.

According to such a configuration, it can be reliably detected whether the fixing belt <NUM> is connected to GND, and when the fixing belt <NUM> is not connected to GND, operations of the fixing belt <NUM> and heater <NUM> are definitely stopped. In the aforementioned embodiments, the microcomputer <NUM> outputs the notification indicating the abnormal state when the current is not flowing through the light receiving element 501b, but the present disclosure not limited thereto. For example, the microcomputer <NUM> may output the notification indicating an abnormal state when the current level of the current flowing through the light receiving element 501b is less than or equal to some predetermined threshold value or the like.

Hereinafter, an operation of the mechanism for detecting whether the fixing belt <NUM> is connected to GND will be described.

<FIG> is a flowchart of operations of the image forming apparatus <NUM>.

The microcomputer <NUM> detects a current state (ACT <NUM>). When detecting that the current is flowing, the microcomputer <NUM> outputs a notification indicating the normal state to the control device <NUM>. On the other hand, when detecting that the current is not flowing, the microcomputer outputs a notification indicating the abnormal state to the control device <NUM>. The control device <NUM> receives the notification output from the microcomputer <NUM>.

Upon receiving a notification indicating the abnormal state, the control device <NUM> determines that the fixing belt <NUM> is not connected to GND. Upon determining that the fixing belt <NUM> is not connected to GND (No in ACT <NUM>), the control device <NUM> stops (or will not permit the start of) the rotation of the fixing belt <NUM> and the heating process by the heater <NUM> (ACT <NUM>). Thus, the operations of the image forming apparatus <NUM> shown in the flowchart of <FIG> end.

On the other hand, upon determining that the fixing belt <NUM> is connected to GND (Yes in ACT <NUM>), the control device <NUM> starts the rotation of the fixing belt <NUM> and the heating process by the heater <NUM> (ACT <NUM>).

Then, after a predetermined time increment (for example, one second) elapses (Yes in ACT <NUM>), the microcomputer <NUM> detects the current state again (ACT <NUM>). Upon detecting that the current is not flowing, the microcomputer <NUM> outputs a notification indicating the abnormal state to the control device <NUM>. The control device <NUM> receives the notification output from the microcomputer <NUM>.

Upon receiving the notification indicating the abnormal state, the control device <NUM> determines that the fixing belt <NUM> is not connected to GND. Upon determining that the fixing belt <NUM> is not connected to GND (No in ACT <NUM>), the control device <NUM> stops the rotation of the fixing belt <NUM> and the heating process by the heater <NUM> (ACT <NUM>). Then, the operations of the image forming apparatus <NUM> shown in the flowchart of <FIG> end.

On the other hand, when detecting that the current is flowing, the microcomputer <NUM> outputs a notification indicating the normal state to the control device <NUM>. The control device <NUM> receives the notification output from the microcomputer <NUM>. Upon receiving the notification indicating the normal state, the control device <NUM> determines that the fixing belt <NUM> is connected to GND. Upon determining that the fixing belt <NUM> is connected to GND (Yes in ACT <NUM>), the control device <NUM> continues to rotate the fixing belt <NUM> and perform the heating process by the heater <NUM>. Thereafter, after another predetermined time increment (for example, one second) elapses (Yes in ACT <NUM>), the microcomputer <NUM> detects the current state again (ACT <NUM>). The subsequent operations are the same as described above.

In some instances, the fixing belt <NUM> may become an electrically active part due to, for example, malfunction of the heater <NUM> or breakage of the glass layer 55c or 55d. When the fixing belt <NUM> becomes an electrically active part, a current may flow from the power source of the primary circuit into the fixing belt <NUM> even if the intended connection of the fixing belt <NUM> to GND is disconnected. In this case, the light emitting diode 501a of the photocoupler <NUM> may erroneously emit light.

If the light emitting diode 501a erroneously emits light, the light receiving element 501b receives the light emitted by the light emitting diode 501a and will thus still allow a current to flow from the power source on the secondary circuit to GND through the light receiving element 501b. Upon detecting the current, the microcomputer <NUM> could output a notification indicating the normal state to the control device <NUM>. Based upon this notification indicating the normal state, the control device <NUM> would erroneously determine that the fixing belt <NUM> is still properly connected to GND. Accordingly, despite the fixing belt <NUM> not being connected to GND, the rotation of the fixing belt <NUM> and the heating process by the heater <NUM> might still be performed or attempted.

In the present example, it is assumed that the heater <NUM> is a heater that performs a heating process by cycling between an on state and an off state to achieve the desired heating level. In such a case, the microcomputer <NUM> is configured to detect the current state only when the heater <NUM> is in an off state of the heating process. This can prevent the erroneous operation described above since no current is separately being provided to the heater <NUM> during the off state.

Another example of the operation of the mechanism for detecting whether the fixing belt <NUM> is connected to GND will be described.

<FIG> is a flowchart of operations of the image forming apparatus <NUM>. Operations from ACT <NUM> to ACT <NUM> shown in <FIG> are substantially the same as the operations from ACT <NUM> to ACT <NUM> described in conjunction with <FIG>, and thus separate descriptions thereof are omitted.

After the operation of ACT <NUM>, after a predetermined time increment (for example, one second) elapses (Yes in ACT <NUM>), the microcomputer <NUM> (or the control device <NUM>) detects a state of the heating process by the heater <NUM> (ACT <NUM>). When the heater <NUM> is an on state (No in ACT <NUM>), the microcomputer <NUM> does not detect the current application state.

When the state of the heating process by the heater <NUM> is an off state (Yes in ACT <NUM>), the microcomputer <NUM> detects the current application state again (ACT <NUM>). Upon detecting that the current is not flowing, the microcomputer <NUM> outputs the notification indicating the abnormal state to the control device <NUM>. The control device <NUM> receives the notification output from the microcomputer <NUM>.

Upon receiving the notification indicating the abnormal state, the control device <NUM> determines that the fixing belt <NUM> is not connected to GND. Upon determining that the fixing belt <NUM> is not connected to GND (No in ACT <NUM>), the control device <NUM> stops the rotation of the fixing belt <NUM> and the heating process by the heater <NUM> (ACT <NUM>). As such, the operations of the image forming apparatus <NUM> shown in the flowchart of <FIG> end.

On the other hand, upon detecting that the current is flowing, the microcomputer <NUM> outputs the notification indicating the normal state to the control device <NUM>. The control device <NUM> receives the notification output from the microcomputer <NUM>. Upon receiving the notification indicating the normal state, the control device <NUM> determines that the fixing belt <NUM> is connected to GND. Upon determining that the fixing belt <NUM> is connected to GND (Yes in ACT <NUM>), the control device <NUM> continue to rotate the fixing belt <NUM> and perform the heating process by the heater <NUM>. Thereafter, after the predetermined time increment (for example, one second) elapses (Yes in ACT <NUM>), the microcomputer <NUM> again detects the state of the heating process by the heater <NUM> (ACT <NUM>). The subsequent operations are the same as described above.

As described above, the image forming apparatus <NUM> according to the above embodiments includes the fixing device <NUM> and the control device <NUM>. The fixing device <NUM> includes the heater <NUM> and the fixing belt <NUM>. The fixing belt <NUM> contacts each of the heater <NUM> and a member (for example, the thermistor <NUM>) that is not in contact with the heater <NUM>. The fixing belt <NUM> is heated by the heater <NUM>. The control device <NUM> determines whether the fixing belt <NUM> is connected to GND. When it is determined that the fixing belt <NUM> is not connected, the control device <NUM> stops the heating process by the heater <NUM>.

With the above configuration, the image forming apparatus <NUM> may detect whether the fixing belt <NUM> is connected to GND. Accordingly, the image forming apparatus <NUM> may stop the heating by the heater <NUM> when the fixing belt <NUM> is not connected to GND.

As described above, in a belt type or on-demand type fixing device, static electricity may be accumulated on the fixing belt. When the static electricity is accumulated on the fixing belt, an electrostatic offset may occur and the quality of an output image may deteriorate. However, in the image forming apparatus <NUM> according to the aforementioned embodiments, static electricity may be discharged by connecting the fixing belt <NUM> to GND. Furthermore, since the image forming apparatus <NUM> may stop the fixing device <NUM> when it is detected that the fixing belt <NUM> is not connected to GND, accumulation of static electricity on the fixing belt <NUM> can be prevented. As a result, occurrence of an electrostatic offset can be prevented.

As described above, since occurrence of an electrostatic offset is prevented, deterioration of the quality of an output image is prevented.

The image forming apparatus <NUM> stops a current flowing to the heater <NUM> when it is detected that the fixing belt <NUM> is not connected to GND. As a result, an unintended change in the distance between the heater <NUM> and the fixing belt <NUM> can be prevented.

Claim 1:
An image processing apparatus (<NUM>), comprising:
a fixing unit (<NUM>) including:
a heater (<NUM>), and
a fixing belt (<NUM>); and
a controller configured to control the heater (<NUM>) to heat the fixing belt (<NUM>), characterized in that
the fixing belt (<NUM>) is electrically connected between a first power source and a ground terminal, and
the controller is further configured to:
determine whether a current is flowing between the fixing belt (<NUM>) and the ground terminal, and
upon determining that a current is not flowing between the fixing belt (<NUM>) and the ground terminal, control the heater (<NUM>) not to heat the fixing belt (<NUM>)
wherein the controller is further configured to:
control the heater (<NUM>) to alternately switch between an on state and an off state, and
determine whether a current is flowing between the fixing belt (<NUM>) and the ground terminal only when the heater (<NUM>) is in the off state.