Fixing device and image forming apparatus capable of effectively circulating and applying oil for fixing

A fixing device includes a rotatable first nip formation member, a rotatable second nip formation member, and an oil applier. The second nip formation member is provided under the first nip formation member to contact the first nip formation member. The oil applier includes an oil pan, an oil receiver, and an oil filter. The oil pan is provided under the second nip formation member to contain oil in which the second nip formation member is dipped. The oil receiver holds the oil pan. The oil filter is provided between the oil pan and the oil receiver to filter oil overflowing the oil pan.

PRIORITY STATEMENT

The present patent application claims priority from Japanese Patent Application No. 2008-119690, filed on May 1, 2008, in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Example embodiments generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device and an image forming apparatus including the fixing device for fixing a toner image on a recording medium.

2. Description of the Related Art

Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium (e.g., a sheet) according to image data using electrophotography. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner particles to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a sheet or is indirectly transferred from the image carrier onto a sheet via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the sheet; finally, a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image on the sheet, thus forming the image on the sheet.

In such image forming apparatuses, oil is applied to a fixing member of the fixing device, which contacts the toner image on the sheet, to separate toner particles forming the toner image from the fixing member and to maintain fixing property, or the ability of the fixing member to fix the toner image on the sheet. Understanding the way in which the oil is applied requires a detailed discussion of the structure of a typical conventional fixing device.

In order to shorten a warm-up time period of the fixing device, an endless fixing belt is often used as the fixing member.FIG. 1is a sectional view of a fixing device100RA including just such an endless fixing belt.

As can be seen inFIG. 1, the fixing device100RA loops an endless fixing belt92around a fixing roller84and a heating roller83in such a manner that the fixing roller84and the heating roller83apply a reference tension to the fixing belt92. A pressing roller85rotates and presses against the fixing belt92and the fixing roller84to form a fixing nip portion AR between the fixing belt92and the pressing roller85. A heater86is disposed inside the heating roller83, and heats the fixing belt92via the heating roller83. Similarly, a second, separate heater87is disposed inside the pressing roller85, and heats the pressing roller85. The fixing belt92and the pressing roller85apply heat and pressure to a sheet bearing a toner image at the fixing nip portion AR to fix the toner image on the sheet.

An oil application roller R1serves as an oil applier for applying oil to the fixing belt92. For example, the rotating oil application roller R1applies oil supplied from an oil supplier to the fixing belt92at a contact point95at which the oil application roller R1contacts the fixing belt92. The rotating fixing belt92moves an oiled portion of the fixing belt92to which oil is applied to the fixing nip portion AR to separate the sheet bearing the toner image from the fixing belt92. At the fixing nip portion AR, a part of the oil on the fixing belt92moves from the fixing belt92onto a surface of the pressing roller85to separate the sheet bearing the toner image from the pressing roller85. Surplus oil carried on the pressing roller85then flows into an oil pan96provided under the pressing roller85, and is collected by the oil pan96.

The oil collected by the oil pan96is pumped to the oil application roller R1for reuse. However, after repeated circulation and reuse there may not be enough oil left to pump.

On the other hand, when a plurality of sheets continuously passes through the fixing nip portion AR, oil can only move from the fixing belt92onto the pressing roller85during an interval between successive sheets, resulting in a shortage of oil.

Further, simple gravity can easily cause a sheet passing through the fixing nip portion AR to adhere to or wrap around the pressing roller85at an exit side of the fixing nip portion AR.

To address these problems, another related-art fixing device100RB includes an oil applier R3for applying oil to the pressing roller85by directly contacting the pressing roller85, as illustrated inFIG. 2. However, when coated paper is used as a sheet P, the oil applier R3may not apply enough oil to separate the coated paper, which absorbs oil easily, from the pressing roller85. Moreover, it is difficult to locate an oil applier capable of applying a substantial amount of oil to the pressing roller85at a position above the pressing roller85due to limited space.

SUMMARY

At least one embodiment may provide a fixing device that includes a rotatable first nip formation member, a rotatable second nip formation member, and an oil applier. The second nip formation member is provided under the first nip formation member to contact the first nip formation member. The oil applier includes an oil pan, an oil receiver, and an oil filter. The oil pan is provided under the second nip formation member to contain oil in which the second nip formation member is dipped. The oil receiver holds the oil pan. The oil filter is provided between the oil pan and the oil receiver to filter oil overflowing the oil pan.

At least one embodiment may provide an image forming apparatus that includes an oil circulation system for circulating oil and a fixing device for receiving oil sent from the oil circulation system. The fixing device includes a rotatable first nip formation member, a rotatable second nip formation member, and an oil applier. The rotatable second nip formation member is provided under the first nip formation member to contact the first nip formation member. The oil applier includes an oil pan, an oil receiver, and an oil filter. The oil pan is provided under the second nip formation member to contain oil in which the second nip formation member is dipped. The oil receiver holds the oil pan. The oil filter is provided between the oil pan and the oil receiver to filter oil overflowing the oil pan. The oil circulation system receives oil filtered by the oil filter and resupplies the filtered oil to the oil applier of the fixing device.

Additional features and advantages of example embodiments will be more fully apparent from the following detailed description, the accompanying drawings, and the associated claims.

The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms a “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly toFIG. 3, an image forming apparatus200according to an example embodiment is explained.

As illustrated inFIG. 3, the image forming apparatus200includes an image forming device200A, a sheet supplier200B, a stacker215, and/or a controller260.

The image forming device200A includes optical writers201, chargers202Y,202M,202C, and202K, development devices203Y,203M,203C, and203K, first transfer devices204Y,204M,204C, and204K, photoconductors205Y,205M,205C, and205K, a transfer belt210, a roller211, a transfer roller212, a fixing device100, and/or an oil circulation mechanism250. The sheet supplier200B includes a paper tray220. The oil circulation mechanism250includes an oil tank251and/or an oil pump252.

The image forming apparatus200can be a copier, a facsimile machine, a printer, a plotter, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this example embodiment of the present invention, the image forming apparatus200functions as a tandem type color copier for forming a color image on a recording medium at high speed by electrophotography.

The image forming device200A is provided at a center portion of the image forming apparatus200. The sheet supplier200B is provided under the image forming device200A. An image reader is provided above the image forming device200A.

In the image forming device200A, the transfer belt210includes a transfer surface extending in a horizontal direction. A mechanism for forming an image in a complementary color being complementary to a separation color is provided above the transfer belt210. For example, the photoconductors205Y,205M,205C, and205K, serving as image carriers for carrying toner images in complementary colors (e.g., yellow, magenta, cyan, and black), are arranged along the transfer surface of the transfer belt210.

The photoconductors205Y,205M,205C, and205K are formed of drums which rotate in an identical direction (e.g., counterclockwise inFIG. 3), respectively. The optical writers201, the chargers202Y,202M,202C, and202K, the development devices203Y,203M,203C, and203K, the first transfer devices204Y,204M,204C, and204K, and cleaners surround the photoconductors205Y,205M,205C, and205K, respectively, to perform image forming processes while the photoconductors205Y,205M,205C, and205K rotate. The development devices203Y,203M,203C, and203K contain yellow, magenta, cyan, and black toners, respectively.

The transfer belt210is looped over a driving roller and a driven roller, and opposes the photoconductors205Y,205M,205C, and205K to move in a direction corresponding to the direction of rotation of the photoconductors205Y,205M,205C, and205K. The transfer roller212opposes the roller211serving as a driven roller.

In the sheet supplier200B, the paper tray220loads sheets P serving as a recording medium. A conveyance mechanism feeds the sheets P loaded on the paper tray220one by one toward the transfer roller212. For example, the conveyance mechanism separates an uppermost sheet P from other sheets P loaded on the paper tray220, and conveys the sheet P toward the transfer roller212. A conveyance path provided between the transfer roller212and the fixing device100conveys the sheet P in a horizontal direction. The controller260controls operations of the image forming apparatus200.

The following describes image forming operations performed by the image forming apparatus200. The charger202Y uniformly charges a surface of the photoconductor205Y. The optical writer201forms an electrostatic latent image on the charged surface of the photoconductor205Y according to image data sent by the image reader. The development device203Y for containing the yellow toner makes the electrostatic latent image formed on the photoconductor205Y visible as a yellow toner image. The first transfer device204Y applies a reference bias to the yellow toner image formed on the photoconductor205Y to transfer the yellow toner image onto the transfer belt210. Similarly, magenta, cyan, and black toner images are formed on the photoconductors205M,205C, and205K, respectively, and sequentially transferred onto the transfer belt210by an electrostatic force so that the yellow, magenta, cyan, and black toner images are superimposed on the transfer belt210to form a color toner image on the transfer belt210.

The transfer roller212transfers the color toner image from the transfer belt210onto the sheet P conveyed by the roller211and the transfer roller212. The sheet P bearing the color toner image is further conveyed to the fixing device100. The fixing device100fixes the color toner image on the sheet P. The sheet P bearing the fixed color toner image is sent to the stacker215via an output path.

The oil tank251collects oil used in the fixing device100to improve property for separating the sheet P from the fixing device100. The oil pump252resupplies oil contained in the oil tank251to the fixing device100. The oil tank251and the oil pump252serve as the oil circulation mechanism250provided for the fixing device100.

FIG. 4is a sectional view of the fixing device100. The fixing device100includes a fixing cover100C, a fixing roller11, a fixing belt12, a pressing roller13, a heater13H, a heating roller14, a heat pipe14A, a heater14H, a tension roller15, separation nails16A and16B, a cleaning mechanism17, and/or oil appliers21and22.

The fixing roller11, the fixing belt12, the pressing roller13, the heating roller14, the separation nails16A and16B, and the cleaning mechanism17are provided inside the fixing cover100C. The fixing belt12, serving as a first nip formation member and a fixing member, is looped or stretched over the fixing roller11and the heating roller14with a reference tension. The pressing roller13, serving as a second nip formation member and a pressing member, is provided under the fixing belt12and rotatably presses against the fixing belt12to form a fixing nip portion N between the fixing belt12and the pressing roller13. The fixing belt12and the pressing roller13apply heat and pressure to a sheet P bearing a toner image T at the fixing nip portion N to fix the toner image T on the sheet P. The separation nail16A is provided at an exit side of the fixing nip portion N in such a manner that a head of the separation nail16A contacts or is disposed close to the fixing belt12, so as to prevent a sheet P from wrapping around the fixing belt12. The separation nail16B is provided at the exit side of the fixing nip portion N in such a manner that a head of the separation nail16B contacts the pressing roller13, so as to prevent a sheet P from wrapping around the pressing roller13. The cleaning mechanism17cleans the fixing belt12by pressing a cleaning web against the fixing belt12.

The fixing belt12has an endless belt shape and has a double-layer structure in which an elastic layer, such as a silicon rubber layer, is formed on a base including nickel, stainless steel, and/or polyimide. The fixing roller11includes metal serving as a core metal and silicon rubber. In order to shorten a warm-up time period of the fixing device100, the fixing roller11may include foamed silicon rubber so that the fixing roller11does not absorb heat from the fixing belt12easily. The heating roller14is formed of a hollow roller including aluminum or iron. The heater14H, such as a halogen heater, serves as a heat source and is provided inside the heating roller14. Alternatively, an induction heating (IH) mechanism may serve as the heat source. A plurality of heat pipes14A, which is formed of hollow pipes, is provided in a thick wall of the heating roller14. For example, the heat pipes14A are embedded in the thick wall of the heating roller14in such a manner that the heat pipes14A are evenly spaced in a circumferential direction of the heating roller14and that a longitudinal direction of the heat pipes14A corresponds to a longitudinal direction (e.g., a width direction or an axial direction) of the heating roller14. The heat pipes14A improve heat transmission from the heater14H to a surface of the heating roller14, and thereby the heating roller14uniformly heats the fixing belt12quickly.

When the fixing device100is driven, in a state in which the tension roller15presses against the fixing belt12to apply proper tension to the fixing belt12, the fixing roller11rotates clockwise inFIG. 4in a direction of rotation D1to rotate the fixing belt12clockwise inFIG. 4in a direction of rotation D2in which the fixing belt12feeds a sheet P out of the fixing nip portion N. Thus, the rotating fixing belt12rotates the pressing roller13. Alternatively, instead of the fixing roller11, the pressing roller13or the heating roller14may drive and rotate the fixing belt12. In order to fix a toner image T on a sheet P, the heater14H provided inside the heating roller14generates heat to heat the fixing belt12until a thermistor detects that the fixing belt12is heated up to a reference temperature (e.g., a proper fixing temperature). According to this example embodiment, the fixing belt12, that is, an endless belt, serves as a fixing member. Alternatively, a fixing roller, for example, a hollow cylindrical roller may serve as a fixing member.

The pressing roller13is formed of a cylindrical roller in which an elastic layer including silicon rubber is provided on a core metal including aluminum or iron. A pressure application-release member moves the pressing roller13toward the fixing belt12to cause the pressing roller13to apply pressure to the fixing belt12, and separates the pressing roller13from the fixing belt12to release pressure applied by the pressing roller13to the fixing belt12. When the fixing device100is driven, the pressure application-release member applies constant pressure to the pressing roller13to press the pressing roller13against the fixing belt12. The heater13H is provided inside the pressing roller13, and generates heat to heat the pressing roller13up to a reference temperature as needed, for example, to fix a toner image T on a sheet P.

According to this example embodiment, the pressing roller13having a roller shape serves as a pressing member. Alternatively, an endless belt looped over at least two rollers may serve as a pressing member.

In the fixing device100, a surface of the fixing belt12is heated up to a reference temperature in a state in which the fixing belt12and the pressing roller13are driven and rotated. When a sheet P bearing an unfixed toner image T passes through the fixing nip portion N, that is, when the sheet P moves leftward inFIG. 4, the fixing belt12and the pressing roller13apply heat and pressure to the sheet P at the fixing nip portion N to melt and fix the unfixed toner image T on the sheet P.

When the sheet P bearing the fixed toner image T is discharged from the fixing nip portion N, the sheet P may adhere to or wrap around the fixing belt12or the pressing roller13. To address this, the oil appliers21and22apply oil to the fixing belt12and the pressing roller13to improve property for separating the sheet P from the fixing belt12and the pressing roller13, respectively. The applied oil may be heat-resistant fixed oil, such as silicon oil. When the head of the separation nail16A or16B contacts a leading edge of the sheet P, the separation nail16A or16B separates the sheet P from the fixing belt12or the pressing roller13, respectively. The sheet P discharged from the fixing nip portion N passes through a discharge path and is sent out of the fixing device100.

The oil appliers21and22apply a proper amount of oil to the fixing belt12and the pressing roller13, respectively. The separation nails16A and16B provided at the exit side of the fixing nip portion N operate as needed. Accordingly, the sheet P is discharged out of the fixing nip portion N to the exit side of the fixing nip portion N without adhering to or wrapping around the fixing belt12or the pressing roller13.

FIG. 5is a partially sectional view of the fixing device100. The oil applier22includes an oil pan22A, a blade22B, and/or a cleaning felt22C. The oil pan22A includes a sub oil pan22A1and/or a main oil pan22A2.

In the fixing device100, the rotatable fixing belt12, serving as a first nip formation member and a fixing member, contacts the rotatable pressing roller13, serving as a second nip formation member and a pressing member, provided under the fixing belt12to form the fixing nip portion N between the fixing belt12and the pressing roller13. The sub oil pan22A1is provided under the pressing roller13and contains oil O in which a part of the pressing roller13is dipped. The blade22B is provided downstream from the sub oil pan22A1and upstream from the fixing nip portion N in a direction of rotation of the pressing roller13, and serves as an oil regulating member for regulating an amount of oil O adhering to the pressing roller13.

The oil pan22A is fixed inside the fixing cover100C (depicted inFIG. 4) of the fixing device100, and includes two pans, which are the sub oil pan22A1serving as an oil pan for containing oil O in which a part of the pressing roller13is dipped and the main oil pan22A2serving as an oil receiver for holding the whole sub oil pan22A1. Oil O to be applied to the pressing roller13is supplied from an outside of the oil applier22into the sub oil pan22A1and stored in the sub oil pan22A1. The sub oil pan22A1has a rectangular shape. A long length of the sub oil pan22A1is equal to or longer than at least a long length (e.g., a width) of the pressing roller13, that is, a length in a longitudinal direction (e.g., a width direction or an axial direction) of the pressing roller13.

The pressing roller13is constantly dipped in oil O in the sub oil pan22A1wholly in the width direction (e.g., the axial direction) and partially in a diametrical direction (e.g., a direction perpendicular to the width direction) of the pressing roller13. For example, an oil level of the sub oil pan22A1is higher than a lower end of the pressing roller13even when the pressure application-release member presses the pressing roller13against the fixing belt12. The lower end of the pressing roller13does not touch an inner bottom of the sub oil pan22A1even when pressure applied by the pressure application-release member to the pressing roller13is released. Oil O may be applied to the pressing roller13before a sheet P passes through the fixing nip portion N. Therefore, the pressing roller13needs not be dipped in oil O in the sub oil pan22A1constantly. For example, the pressing roller13may be dipped in oil O in the sub oil pan22A1when the pressing roller13starts rotating.

The main oil pan22A2serves as an oil receiver for receiving oil O overflowing the sub oil pan22A1. An outlet through which oil O is collected into the oil tank251depicted inFIG. 3is provided under the main oil pan22A2.

The sub oil pan22A1and the main oil pan22A2may include heat-resistant metal or plastic not reacting to oil O.

The blade22B includes an elastic member having a paddle-like shape and has a width equal to or longer than at least the width of the pressing roller13. A long edge of the blade22B constantly contacts a surface of the pressing roller13. In other words, a longitudinal direction of the blade22B corresponds to the longitudinal direction (e.g., the width direction or the axial direction) of the pressing roller13. Thus, the blade22B regulates an amount of oil O adhering to the pressing roller13so that a reference amount of oil O is adhered to the pressing roller13uniformly in the width direction of the pressing roller13. The blade22B includes a material not damaging the surface of the pressing roller13, such as fluorocarbon rubber.

The surface of the pressing roller13includes a material corresponding to oil O. For example, when silicon oil is used as oil O, the surface of the pressing roller13includes silicon rubber. Therefore, when the pressing roller13is dipped in oil O in the sub oil pan22A1, the silicon rubber of the pressing roller13swells and holds oil O. The blade22B contacts a lower surface of the pressing roller13to scrape oil O off the surface of the pressing roller13. For example, an angle θ formed by a head of the blade22B and a tangent line of the head of the blade22B tangent to a curve of the pressing roller13is an acute angle smaller than about 90 degrees. The head of the blade22B opposes the direction of rotation of the pressing roller13to scrape surplus oil O off the surface of the pressing roller13into the oil pan22A. Accordingly, the surface of the pressing roller13carries a sufficient amount of oil O uniformly applied on the surface of the pressing roller13in the width direction of the pressing roller13, which can provide proper property for separating a sheet P bearing a fixed toner image T from the pressing roller13. Surplus oil O on the pressing roller13is collected into the oil pan22A and reused. Namely, surplus oil O is circulated and applied to the pressing roller13again.

The cleaning felt22C may be provided between the oil pan22A, and the blade22B. The cleaning felt22C serves as a cleaner for cleaning the surface of the pressing roller13by contacting the pressing roller13. The cleaning felt22C may be a compressed sheet including heat-resistant fiber not reacting to oil O, such as meta-aramid fiber. While oil O permeates the fiber of the cleaning felt22C, the cleaning felt22C captures fine solid impurities inside. Thus, fine solid impurities (e.g., dust and calcium carbonate originating from a sheet P) contained in oil O can be removed from the surface of the pressing roller13, while the oil O remains on the surface of the pressing roller13.

A support supports the cleaning felt22C in such a manner that the cleaning felt22C contacts the pressing roller13. When the support is formed of a metal material by sheet metal processing to have proper spring property, the support causes the cleaning felt22C to contact the pressing roller13while applying constant pressure to the pressing roller13, so as to adjust an amount of oil O adhering to the pressing roller13.

Referring toFIGS. 5 and 6, the following describes a procedure for applying oil O from the oil applier22to the pressing roller13with the above-described structure.FIG. 6is a flowchart illustrating the procedure for applying oil O from the oil applier22to the pressing roller13.

In step S11, the controller260depicted inFIG. 3starts driving the fixing device100. Accordingly, the fixing belt12starts rotating, and the pressure application-release member causes the pressing roller13to contact the fixing belt12by applying constant pressure to the fixing belt12to form the fixing nip portion N between the fixing belt12and the pressing roller13. Simultaneously, the rotating fixing belt12rotates the pressing roller13. Alternatively, the rotating pressing roller13may drive and rotate the fixing belt12.

In step S12, when the pressing roller13starts rotating, the surface of the pressing roller13dipped in oil O in the sub oil pan22A1is lifted toward the fixing nip portion N in a state in which the oil O is adhered to the surface of the pressing roller13.

In step S13, the oil O adhered to the surface of the pressing roller13permeates the cleaning felt22C, and the cleaning felt22C removes solid impurities from the oil O.

In step S14, the blade22B regulates the oil O adhered to the surface of the pressing roller13uniformly in the width direction of the pressing roller13. Thereafter, the regulated oil O on the surface of the pressing roller13moves to the fixing nip portion N.

As described above, according to this example embodiment, the oil applier22applies oil O to the pressing roller13provided under the fixing nip portion N in a dip method by utilizing a space under the pressing roller13. Thus, the oil applier22can supply a sufficient amount of oil O to the pressing roller13stably.

FIG. 7is a top view of the oil applier22.FIG. 7does not illustrate the blade22B. The oil applier22further includes an oil spatter prevention member22D.

InFIG. 7, the oil spatter prevention member22D covers an oil surface of oil O contained in the oil pan22A. For example, the oil spatter prevention member22D covers a region of the oil surface of oil O contained in the sub oil pan22A1and the main oil pan22A2of the oil pan22A other than a region of the oil surface of oil O in which the pressing roller13is dipped. The oil spatter prevention member22D may not cover a region of the oil surface of oil O provided under the cleaning felt22C. Thus, the oil spatter prevention member22D can reduce or prevent oil O spattering from the oil surface of oil O contained in the oil pan22A due to rotation of the pressing roller13or other vibration and thereby adhering to and staining a sheet P or a peripheral device.

The oil spatter prevention member22D may be a compressed sheet (e.g., a felt sheet) including heat-resistant fiber not reacting to oil, such as meta-aramid fiber. The oil spatter prevention member22D may float on the oil surface of oil O or may separate from the oil surface of oil O. Alternatively, the oil spatter prevention member22D may include a plurality of spherical members floating on the oil surface of oil O to cover the oil surface of oil O.

In the fixing device100depicted inFIG. 5, the fixing belt12, serving as a first nip formation member and a fixing member, is disposed above the pressing roller13serving as a second nip formation member and a pressing member. Alternatively, a fixing member serving as a first nip formation member having a roller shape may be provided above a pressing member serving as a second nip formation member having a belt shape, as illustrated inFIG. 8.

Referring toFIG. 8, the following describes a fixing device100Z according to another example embodiment.FIG. 8is a sectional view of the fixing device100Z. The fixing device100Z includes a fixing roller12A, a heater12H, rollers R11, R14, and R15, a pressing belt13A, a backup member13B, and/or a heater13H′.

The fixing roller12A, serving as a first nip formation member, is provided above the pressing belt13A serving as a second nip formation member, and rotates clockwise inFIG. 8. The pressing belt13A provided under the fixing roller12A rotates counterclockwise inFIG. 8, and is looped over the rollers R11, R14, and R15. The backup member13B, serving as a pressing pad, faces an inner circumferential surface of the pressing belt13A to cause the pressing belt13A to contact the fixing roller12A and form a fixing nip portion N′ between the fixing roller12A and the pressing belt13A. The heater12H is provided inside the fixing roller12A, and generates heat to heat the fixing roller12A. The heater13H′ is provided inside the roller R14, and generates heat to heat the pressing belt13A.

The oil applier21depicted inFIG. 4applies oil to the fixing roller12A provided above the pressing belt13A. The oil applier22depicted inFIG. 4applies oil to the pressing belt13A provided under the fixing roller12A.

Referring toFIG. 9, the following describes the oil circulation mechanism250, serving as an oil circulation system, included in the image forming apparatus200.FIG. 9is a schematic view of the oil circulation mechanism250. The oil circulation mechanism250further includes a conveyance path253, an oil receiver254, a tube255, and/or a conveyance path256. The oil tank251includes an oil sensor251A.

The oil tank251contains oil to be used in the fixing device100. The oil pump252uses a piezoelectric element. The conveyance path253connects the oil pump252to the oil applier21of the fixing device100. The oil receiver254receives surplus oil sent from the oil applier21. The tube255conveys the oil sent from the oil receiver254to the oil applier22. The conveyance path256connects the oil applier22to the oil tank251. The oil tank251, the oil pump252, and the conveyance paths253and256are disposed outside the fixing device100. The oil receiver254and the tube255are disposed inside the fixing device100. The oil sensor251A detects an amount of oil remaining in the oil tank251.

In the image forming apparatus200, the oil circulation mechanism250circulates oil as described below so that the oil appliers21and22sequentially apply oil to the fixing belt12and the pressing roller13depicted inFIG. 4, respectively.

For example, when an image forming operation starts, the oil pump252pumps silicon oil from the oil tank251, which stores a total volume of about 4 liters of silicon oil, and conveys the oil to the oil applier21through the conveyance path253. For example, the oil is put into the oil applier21at a supply speed of about 3 grams per minute.

The oil receiver254collects surplus oil from the oil applier21. The surplus oil is conveyed to the sub oil pan22A1of the oil applier22provided for the pressing roller13(depicted inFIG. 5) through the tube255.

Oil used in the oil applier22is collected into the oil tank251through the conveyance path256.

In the oil circulation mechanism250, solid impurities, such as dust and calcium carbonate originating from a sheet P, are mixed with oil. When oil mixed with solid impurities is circulated, the solid impurities are adhered to devices provided in an oil circulation path, resulting in malfunction of such devices and formation of a faulty image. To address this, a reference oil circulation mechanism (e.g., a reference oil circulation system) may include an oil filter to remove solid impurities, as illustrated inFIG. 10.FIG. 10is a sectional view of a reference oil circulation mechanism250R. The reference oil circulation mechanism250R includes the oil tank251, the oil pump252, and/or an oil filter252A.

The oil filter252A is provided on an oil inlet of the oil pump252. The oil filter252A filters oil O contained in the oil tank251to remove solid impurities from the oil O, and the oil pump252pumps the filtered oil O. Accordingly, the solid impurities do not enter the oil circulation path.

However, when the oil pump252continuously pumps the filtered oil O, the solid impurities may adhere to and clog the oil filter252A. Accordingly, the oil pump252may pump a decreased amount of oil O, resulting in degraded image quality due to shortage of oil O. The oil filter252A provided on the small oil inlet of the oil pump252may be clogged with solid impurities easily.

Referring toFIG. 11, the following describes an image forming apparatus200X according to another example embodiment.FIG. 11is a schematic view of the image forming apparatus200X. The image forming apparatus200X includes a fixing device100X and/or the oil circulation mechanism250. The fixing device100X includes the fixing roller11, the fixing belt12, the pressing roller13, the heating roller14, and/or an oil applier22X. The oil applier22X includes the oil pan22A, the blade22B, the cleaning felt22C, and/or an oil filter22F. The oil pan22A includes the sub oil pan22A1and/or the main oil pan22A2. The oil circulation mechanism250further includes an oil filter256A, a sedimentation tank251B, a supply tank251C, and/or a divider251D.

In the fixing device100X, the rotatable fixing belt12, serving as a first nip formation member and a fixing member, contacts the rotatable pressing roller13, serving as a second nip formation member and a pressing member, provided under the fixing belt12to form the fixing nip portion N between the fixing belt12and the pressing roller13. The sub oil pan22A1, serving as an oil pan, is provided under the pressing roller13and contains oil O in which a part of the pressing roller13is dipped. The main oil pan22A2, serving as an oil receiver, holds the sub oil pan22A1. The oil filter22F is provided between the sub oil pan22A1and the main oil pan22A2. For example, the oil filter22F is provided inside the main oil pan22A2and under the sub oil pan22A1, and filters oil O overflowing the sub oil pan22A1.

The oil circulation mechanism250resupplies oil O filtered by the oil filter22F and sent from the oil applier22X to the oil appliers21and22X.FIG. 11illustrates the fixing device100X and the oil circulation mechanism250partially. However, the fixing device100X is equivalent to the fixing device100depicted inFIGS. 4 and 5except the oil filter22F, and the oil circulation mechanism250is identical to the oil circulation mechanism250depicted inFIG. 9.

The oil filter22F is formed of a sheet having a width equal to or longer than the width of the pressing roller13in the axial direction of the pressing roller13. The oil filter22F may be a compressed sheet including heat-resistant fiber not reacting to oil, such as meta-aramid fiber. While oil O permeates the fiber of the oil filter22F, the oil filter22F captures fine solid impurities inside. Thus, the oil filter22F provided in the oil pan22A can remove fine solid impurities (e.g., dust and calcium carbonate originating from a sheet P) from oil O permeating the oil filter22F. The oil filter22F may include a material equivalent to felt used in other members, such as the oil spatter prevention member22D (depicted inFIG. 7) having a sheet shape. However, the oil filter22F may include a mesh finer than a mesh of such members in a reference range so that the oil filter22F can filter oil O.

The oil applier22X may include the oil spatter prevention member22D.

Referring toFIGS. 9 and 11, the following describes circulation processes for circulating oil O with the above-described structure.

As illustrated inFIG. 11, the oil filter22F filters oil O used in the oil applier22X, that is, oil O overflowing the sub oil pan22A1into the main oil pan22A2, to remove solid impurities from the oil O. The filtered oil O is sent from the outlet of the main oil pan22A2into the oil tank251through the conveyance path256. The oil pump252pumps oil O stored in the oil tank251to supply the oil O to the oil applier21through the conveyance path253. The oil applier21applies the oil O to the fixing belt12.

As illustrated inFIG. 9, the oil receiver254collects surplus oil O contained in the oil applier21. The oil O is supplied to the sub oil pan22A1of the oil applier22X provided for the pressing roller13(depicted inFIG. 11) through the tube255. The oil applier22X applies the oil O to the pressing roller13. The oil filter22F filters the oil O used in the oil applier22X again. Thereafter, the above-described circulation processes are repeated to reuse the oil O.

According to this example embodiment, no oil filter is provided on the oil inlet of the oil pump252directly. Accordingly, even when the oil pump252is used for a long time period, an amount of oil O pumped by the oil pump252may not decrease. The oil filter22F, which is formed of a large sheet having the width equal to or longer than the width of the pressing roller13in the axial direction of the pressing roller13, filters oil O overflowing the sub oil pan22A1. Accordingly, even when the oil pump252is used for a long time period, the oil pump252may not be clogged with solid impurities. Thus, impurities may not enter the oil circulation path, and a sufficient amount of oil O can be supplied to the oil appliers21and22X. Consequently, the oil appliers21and22X can apply a sufficient amount of oil O not containing impurities to the fixing belt12and the pressing roller13, respectively, so as to provide improved property for separating a sheet P from the fixing belt12and the pressing roller13and maintain improved image quality.

When the oil filter22F is provided, the oil filter256A may be provided secondarily at an end of the conveyance path256provided in the oil tank251to filter oil O to remove impurities from the oil O. Thus, the oil O circulating in the fixing device100X and the oil circulation mechanism250can contain further reduced impurities.

In the oil tank251, the divider251D may be provided to divide the oil tank251into two tanks, which are the sedimentation tank251B and the supply tank251C. Oil O sent from the conveyance path256enters the sedimentation tank251B. After solid impurities are sedimented in the sedimentation tank251B, supernatant oil O overflowing the sedimentation tank251B and crossing over the divider251D is stored in the supply tank251C. The oil pump252pumps oil O from the supply tank251C. Thus, impurities are further removed from oil O in the sedimentation tank251B.

As illustrated inFIG. 11, in a fixing device (e.g., the fixing device100X) according to the above-described example embodiments, an oil filter (e.g., the oil filter22F) is provided in an oil receiver (e.g., the main oil pan22A2) holding an oil pan (e.g., the sub oil pan22A1). Therefore, the oil filter can have a large size. Even when the oil filter filters oil to remove solid impurities from the oil for a long time period, the oil filter may not be clogged with the solid impurities. Further, the oil discharged from the fixing device can be reused. Moreover, the oil filter is provided in the existing oil pan, saving space.

In an image forming apparatus (e.g., the image forming apparatus200X) according to the above-described example embodiments, oil from which the fixing device removes impurities is sent to an oil circulation system (e.g., the oil circulation mechanism250). Accordingly, the oil circulation system may not pump a decreased amount of oil to be circulated. Consequently, a sufficient amount of oil can be applied to members for forming a fixing nip portion (e.g., the fixing nip portion N), which are a first nip formation member (e.g., the fixing belt12) and a second nip formation member (e.g., the pressing roller13), so as to provide improved property for separating a sheet from the first nip formation member and the second nip formation member.

According to the above-described example embodiments, the image forming apparatus including the fixing device can provide improved fixing and separation functions, and therefore can handle various types of paper, such as thin paper and thick paper, and various types of image formation, such as a narrower top margin on a sheet.

The present invention has been described above with reference to specific example embodiments. Nonetheless, the present invention is not limited to the details of example embodiments described above, but various modifications and improvements are possible without departing from the spirit and scope of the present invention. It is therefore to be understood that within the scope of the associated claims, the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative example embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.