Fixing device and image forming apparatus incorporating same

A fixing device includes a first rotator, a second rotator pressed against the first rotator, and a heater to heat the first rotator. The heater includes an elongated substrate extending in an axial direction of the first rotator, a heat generator disposed on a surface of the substrate facing the first rotator, at a position downstream in a rotational direction of the first rotator, a plurality of first conduction paths connected to the heat generator and grounded downstream of the heat generator in the rotational direction of the first rotator, and a second conduction path on which the plurality of first conduction paths are grounded. The heat generator has a heat-generating area divided into a plurality of sub-heat-generating areas in the axial direction of the first rotator. The plurality of sub-heat-generating areas are grounded on the second conduction path via the plurality of first conduction paths.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application Nos. 2013-088663, filed on Apr. 19, 2013, and 2014-072640, filed on Mar. 31, 2014, in the Japan Patent Office, the entire disclosures of which are hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

Embodiments of this disclosure generally relate to a fixing device and to an electrophotographic image forming apparatus incorporating the fixing device.

2. Related Art

Some typical heating devices include a heat-resistant film, a heat generator and a pressure member. The heat generator is fixedly supported at the center in a lateral direction on one side of a heater substrate and divided into six sub-heat generators in a direction perpendicular to a direction in which a recording medium is conveyed. The pressure member is disposed facing the heat generator via the heat-resistant film. The pressure member and the heat generator are pressed against each other via the heat-resistant film to form an area of contact referred to herein as a fixing nip therebetween. The recording medium is conveyed to the fixing nip, between the heat-resistant film and the pressure member, thereby passing through the fixing nip together with the heat-resistant film. Thus, heat energy is transmitted from the heat generator to the recording medium via the heat-resistant film.

Such heating devices are capable of significantly reducing energy consumption by selectively supplying power to the sub-heat generators for individually heating their respective images, thereby reaching a fixing temperature.

In addition, the heating devices include electrical conduction paths to supply power to the heat generator. The electrical conduction paths are provided, e.g., in a substantially symmetrical manner, on both sides of the heater substrate in the lateral direction thereof with the six sub-heat generators interposed therebetween.

Some other typical heating devices, specifically image heating devices, include a heating rotator to heat an image carried by a recording medium, and a heating member to contact and heat the surface of the heating rotator. The heating member includes a heater having a heat generator on a heat-conductive substrate, and a heat-conductive member that contacts the substrate. The heat-conductive member is made of a material having a higher heat conductivity than a material of the substrate. Thus, the typical image heating devices have a heating area allowing both of the heater and the heat-conductive member to heat the surface of the heating rotator.

With such a configuration, the typical image heating devices can shorten warm-up time and lower the temperature of the heater.

Some of them also include substantially one heat generator disposed at a position downstream in a rotational direction of a fixing roller in the heating area.

However, with such a typical wiring pattern, in which electrical conduction paths are disposed on both sides of the heater substrate in the lateral direction thereof, with the heat generator interposed therebetween in a substantially symmetrical manner, a space, that is, a line width of wiring is insufficient to dispose the heat generator having a plurality of heat-generating areas, at a position closer to the fixing nip.

SUMMARY

In one embodiment of this disclosure, an improved fixing device for fixing an unfixed toner image formed on a recording medium onto the recording medium under heat and pressure in a fixing nip includes a first rotator, a second rotator pressed against the first rotator to form the fixing nip, and a heater to heat the first rotator. The heater includes an elongated substrate extending in an axial direction of the first rotator, a heat generator disposed on a surface of the substrate facing the first rotator, at a position downstream in a rotational direction of the first rotator, a plurality of first conduction paths connected to the heat generator and grounded downstream of the heat generator in the rotational direction of the first rotator, and a second conduction path on which the plurality of first conduction paths are grounded. The heat generator has a heat-generating area divided into a plurality of sub-heat-generating areas in the axial direction of the first rotator. The plurality of sub-heat-generating areas are grounded on the second conduction path via the plurality of first conduction paths.

In another embodiment of this disclosure, an improved fixing device for fixing an unfixed toner image formed on a recording medium onto the recording medium under heat and pressure in a fixing nip includes a first rotator, a second rotator pressed against the first rotator to form a fixing nip, and a heater to heat the first rotator. The heater includes an elongated substrate extending in an axial direction of the first rotator, a heat generator disposed on a surface of the substrate facing the first rotator, at a position downstream in a rotational direction of the first rotator, and a plurality of conduction paths connected to the heat generator and grounded downstream of the heat generator in the rotational direction of the first rotator. The elongated substrate has a plurality of through-holes. The heat generator has a heat-generating area divided into a plurality of sub-heat-generating areas in the axial direction of the first rotator. The plurality of conduction paths are wired on a backside of the elongated substrate via the through-holes and grounded.

The accompanying drawings are intended to depict embodiments of this disclosure 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

Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the invention and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable to the present invention.

In a later-described comparative example, embodiment, and exemplary variation, for the sake of simplicity like reference numerals are given to identical or corresponding constituent elements such as parts and materials having the same functions, and redundant descriptions thereof omitted unless otherwise required.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of this disclosure are described below.

Initially with reference toFIG. 1, a description is given of an overall configuration and operation of an image forming apparatus100according to some embodiments of this disclosure.

FIG. 1is a schematic overall view of the image forming apparatus1according to some embodiments of this disclosure.

It is to be noted that, in the following description, suffixes Y, M, C, and K denote colors yellow, magenta, cyan, and black, respectively, and may be omitted where unnecessary.

As illustrated inFIG. 1, the image forming apparatus1of this embodiment is a tandem-type color printer. A bottle container101is disposed in an upper portion of the image forming apparatus1. The bottle container101accommodates four removable toner bottles102Y,102M,102C, and102K. The toner bottles102Y,102M,102C, and102K accommodates toner of yellow, magenta, cyan, and black, respectively. Thus, the four toner bottles102Y,102M,102C, and102K are replaceable.

An intermediate transfer unit85is disposed below the bottle container101. The intermediate transfer unit85includes, e.g., an intermediate transfer belt78, four primary-transfer bias rollers79Y,79M,79C, and79K, a secondary-transfer backup roller82, a cleaning backup roller83, a tension roller84, and an intermediate transfer cleaner80.

Four imaging units4Y,4M,4C, and4K are arranged side by side, facing the intermediate transfer belt78to form toner images of yellow, magenta, cyan, and black, respectively.

The four imaging units4Y,4M,4C, and4K include photoconductive drums5Y,5M,5C, and5K, respectively. The photoconductive drums5Y,5M,5C, and5K serve as image carriers. Each of the photoconductive drums5Y,5M,5C, and5K is surrounded by various pieces of imaging equipment, such as a charging device75, a developing device76, a cleaning device77, and a charge neutralizing device. Imaging processes, namely, charging, exposure, development, transfer, and cleaning processes are performed on each of the photoconductive drums5Y,5M,5C, and5K. Accordingly, the toner images of yellow, magenta, cyan, and black are formed on the photoconductive drums5Y,5M,5C, and5K, respectively.

The photoconductive drums5Y,5M,5C, and5K are rotated in a counterclockwise direction inFIG. 1by a driving motor. Surfaces of the photoconductive drums5Y,5M,5C, and5K are uniformly charged where the surfaces of the photoconductive drums5Y,5M,5C, and5K face the respective charging devices75(charging process). Then, as the photoconductive drums5Y,5M,5C, and5K rotate and reach a position opposite an exposure device3, the surfaces of the photoconductive drums5Y,5M,5C, and5K are scanned with and exposed by laser light L emitted from the exposure device to form electrostatic latent images of yellow, magenta, cyan and black on the photoconductive drums5Y,5M,5C, and5K, respectively (exposure process).

Then, the photoconductive drums5Y,5M,5C, and5K rotate further and reach a position at which the surfaces of the photoconductive drums5Y,5M,5C, and5K face the respective development devices76, where the electrostatic latent images are developed with toner of yellow, magenta, cyan and black into visible images, also known as toner images of yellow, magenta, cyan and black, respectively (development process). Then, the photoconductive drums5Y,5M,5C, and5K rotate further and reach a position at which the surfaces of the photoconductive drums5Y,5M,5C, and5K face primary transfer bias rollers79Y,79M,79C, and79K, respectively, via the intermediate transfer belt78, where the toner images are transferred from the photoconductive drums5Y,5M,5C, and5K onto the intermediate transfer belt78(primary-transfer process). At this time, a small amount of toner may remain untransferred on the surfaces of the photoconductive drums5Y,5M,5C, and5K as residual toner.

Then, the photoconductive drums5Y,5M,5C, and5K rotate further and reach a position at which the surfaces of the photoconductive drums5Y,5M,5C, and5K face the respective cleaning devices77, where the cleaning devices77mechanically collect the residual toner on the surfaces of the photoconductive drums5Y,5M,5C, and5K with cleaning blades incorporated in the cleaning devices77, respectively (cleaning process).

Finally, the photoconductive drums5Y,5M,5C, and5K rotate and reach a position at which the surfaces of the photoconductive drums5Y,5M,5C, and5K face the respective charge neutralizing devices, where residual potential is removed from the surfaces of the photoconductive drums5Y,5M,5C, and5K.

Thus, a series of image forming processes performed on the surfaces of the photoconductive drums5Y,5M,5C, and5K is completed.

After the series of image forming processes, the toner images formed on the surfaces of the photoconductive drums5Y,5M,5C, and5K through the development process are transferred onto the intermediate transfer belt78while being superimposed one atop another to form a multicolor toner image on the intermediate transfer belt78.

The intermediate transfer belt78is stretched over the secondary-transfer backup roller82, the cleaning backup roller83, and the tension roller84, and rotated in a direction indicated by arrow A inFIG. 1by rotation of the secondary-transfer backup roller82.

The four primary transfer bias rollers79Y,79M,79C, and79K and the photoconductive drums5Y,5M,5C, and5K press against each other to form areas of contact via the intermediate transfer belt78herein called primary transfer nips, respectively. Each of the primary transfer bias rollers79Y,79M,79C, and79K is applied with a transfer bias having a polarity opposite a polarity of toner.

The intermediate transfer belt78travels in the direction indicated by arrow A and successively passes through the primary transfer nips formed between the primary transfer bias rollers79Y,79M,79C, and79K, on the one hand, and the photoconductive drums5Y,5M,5C, and5K, respectively, on the other. Thus, the toner images formed on the respective photoconductive drums5Y,5M,5C, and5K are primarily transferred onto the intermediate transfer belt78while being superimposed one atop another.

Then, the intermediate transfer belt78carrying the multicolor toner image reaches a position at which the intermediate transfer belt78faces the secondary transfer roller89, where the secondary transfer backup roller82and the secondary transfer roller89press against each other to form an area of contact via the intermediate transfer belt78, herein called a secondary transfer nip.

The multicolor color toner image formed on the intermediate transfer belt78is transferred onto a recording medium R at the secondary transfer nip. At this time, a small amount of toner may remain untransferred on the intermediate transfer belt78as residual toner. Then, the intermediate transfer belt78reaches a position at which the intermediate transfer belt78faces the intermediate transfer cleaner80. At the position, the residual toner on the intermediate transfer belt78is collected.

Thus, a series of transfer processes performed on the intermediate transfer belt78is completed.

Now, a detailed description is given of movement of the recording medium R. The recording medium R is fed by a sheet tray12disposed in a lower portion of the image forming apparatus1, and conveyed to the secondary transfer nip via a feed roller97and a pair of registration rollers98pressed against each other. Specifically, the sheet tray12accommodates a stack of recording media R, such as transfer sheets, one atop another.

When the feed roller97is rotated in a counterclockwise direction inFIG. 1, an uppermost recording medium R of the plurality of recording media R is fed toward an area of contact of rollers of the pair of registration rollers98.

The recording medium R conveyed to the pair of registration rollers98temporarily stops at a predetermined position as the pair of registration rollers98stops rotating.

The pair of registration rollers98is rotated again to convey the recording medium R to the secondary transfer nip in synchronization with the movement of the intermediate transfer belt78carrying the multicolor toner image. Thus, the multicolor toner image is transferred onto the recording medium R.

Thereafter, the recording medium R carrying the multicolor toner image is conveyed to a fixing device20, described later. In the fixing device20, the multicolor toner image is fixed onto the recording medium R under heat and pressure applied by an endless fixing belt21and a pressing roller25.

Then, the recording medium R passes through rollers of a pair of output rollers99pressed against each other, and is discharged onto an output tray100outside the image forming apparatus1.

Thus, the plurality of recording media R carrying output images rest one atop another on the output tray100. Accordingly, a series of image forming processes performed in the image forming apparatus1is completed.

Referring now toFIGS. 2 to 5, a detailed description is given of the fixing device20according to a first embodiment. Initially with referenceFIG. 2, a description is given of an overall configuration of the fixing device20.

FIG. 2is a schematic sectional view of the fixing device20according to the first embodiment, incorporated in the image forming apparatus1described above. As illustrated inFIG. 2, the fixing device20according to the first embodiment includes the fixing belt21serving as a first rotator, a stationary member22, a base22a, a heater23that directly contacts and heats the fixing belt21, a pressure roller24, and the pressing roller25serving as a second rotator. The fixing belt21and the components disposed inside a loop defined by the fixing belt21, that is, the stationary member22, the base22a, and the heater23may constitute a belt unit121separably coupled with the pressure roller24and the pressing roller25.

The fixing belt21is a thin, flexible, endless belt having a predetermined width, constructed of a base layer, an elastic layer, and a release layer resting in this order from an inner circumferential surface side thereof. The fixing belt21has a total thickness not greater than 1 mm. The base layer of the fixing belt21has a thickness of, e.g., about 30 μm to about 100 μm, and is made of a metal material, such as nickel or stainless steel, or a resin material such as polyimide.

The elastic layer of the fixing belt21has a thickness of, e.g., about 100 μm to about 300 μm, and is made of a rubber material such as silicon rubber, silicon rubber foam, or fluoro rubber. The elastic layer eliminates slight surface asperities of the fixing belt21in an area of contact between the pressing roller25and the fixing belt21, herein called a fixing nip FN. Accordingly, heat is uniformly transmitted to a toner image T on the recording medium R, thereby suppressing formation of a rough image such as an orange peel image.

The release layer of the fixing belt21has a thickness of, e.g., about 10 μm to about 50 μm. The release layer is made of, e.g., tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), polyimide, polyetherimide, or polyether sulfide (PES). The release layer ensures releasability of the toner image T. In other words, the release layer reliably separates the toner image T from the fixing belt21.

The stationary member22is a member having a substantially square bar shape. The stationary member22has a flat surface to form the fixing nip FN in concert with the pressing roller25, described later. The stationary member22is positioned inside the loop defined by the fixing belt21, and both ends of the stationary member22are supported by a frame of the fixing device20. The stationary member22has another flat surface opposite the flat surface for forming the fixing nip FN, on which the base22ais mounted to support the heater23, described later.

Referring now toFIG. 3, a detailed description is given of the heater23.

FIG. 3is a sectional view of the heater23incorporated in the fixing device20described above. The heater23is constructed of at least a substrate231, a heat generator232, and an overcoat layer234. In this embodiment, the heater23also includes a holder235. As illustrated inFIG. 3, the substrate231rests on the holder235. The heat generator232rests on the substrate231. The overcoat layer234coats the substrate231and the heat generator232.

The substrate231has an elongated shape extending in an axial direction, that is, a width direction of the fixing belt21. The substrate231is a glass substrate having print wiring on a surface facing the fixing belt21. Wiring patterns of the print wiring are described later.

The heat generator232is a ceramic heater having an elongated planar shape. As illustrated inFIG. 3and also inFIG. 4referred to later, the heat generator232is disposed on the surface of the substrate231facing the fixing belt21, at a position downstream in a rotational direction of the fixing belt21. The heat generator232has a heat-generating area divided into a plurality of sub-heat-generating areas in the axial direction of the fixing belt21according to the wiring patterns of print wiring, described later.

Referring now toFIG. 4, a detailed description is given of a first example of the wiring patterns of print wiring.

FIG. 4is a plan view of the heater23, with a holder removed therefrom, illustrating the first example of a wiring pattern. The first example of a wiring pattern for supplying power to the heat generator232includes a plurality of first conduction paths (connection terminals) W1, a second conduction path W2, and a plurality of third conduction paths W3.

The plurality of first conduction paths W1are connected to both sides of the heat generator232in a lateral direction thereof, that is, the horizontal direction inFIG. 4, and aligned at a predetermined interval in a longitudinal direction of the heat generator232, that is, the vertical direction inFIG. 4.

A description is now given of power supply to the heat generator232and grounding of the heat generator232.

The substrate231has a planar shape elongated in the axial direction of the fixing belt21. The fixing belt21moves along the overcoat layer234that covers the surface of the substrate231facing the fixing belt21out of two surfaces of the substrate231, namely, front and back surfaces. The heat generator232is disposed in such a manner that the longitudinal direction thereof is along a longitudinal direction of the substrate231. The respective longitudinal directions of the substrate231and the heat generator232correspond to the axial direction of the fixing belt21. The respective lateral directions of the substrate231and the heat generator232correspond to the rotational direction of the fixing belt21.

As illustrated inFIG. 4, the plurality of first conduction paths W1are disposed on both sides of the heat generator232in the lateral direction thereof at a predetermined interval along the longitudinal direction of the heat generator232.

The plurality of first conduction paths W1include a plurality of first conduction paths W1A on one side of the heat generator232in the lateral direction thereof, and the plurality of first conduction paths W1B on the other side of the heat generator232in the lateral direction thereof. More specifically, the plurality of first conduction paths W1A are disposed downstream of the heat generator232in the rotational direction of the fixing belt21while the plurality of first conduction paths W1B are disposed upstream of the heat generator232in the rotational direction of the fixing belt21. Power is supplied to the plurality of first conduction paths W1B, and the plurality of first conduction paths W1A are grounded. Thus, a circuit is configured to supply power to the heat generator232. With such a configuration, the heat-generating area of the heat generator232generates heat.

In this embodiment, power is supplied to each unit of the plurality of first conduction paths W1to heat the corresponding sub-heat-generating area. Each of the plurality of third conduction paths W3is disposed to supply power to the corresponding unit of the plurality of first conduction paths W1. Thus, the plurality of third conduction paths W3are disposed as a wiring pattern for power supply. The plurality of third conduction paths W3are disposed on the surface of the substrate231facing the fixing belt21, on one side of the heat generator232in the lateral direction thereof, and more specifically, upstream of the heat generator232in the rotational direction of the fixing belt21.

The plurality of third conduction paths W3are bidimentionally arranged side by side. Accordingly, the wiring pattern for power supply occupies a considerable area on the substrate231, and more specifically, upstream of the heat generator232in the rotational direction of the fixing belt21.

Thus, according to this embodiment, the plurality of third conduction paths W3are disposed upstream of the heat generator232in the rotational direction of the fixing belt21to ensure a sufficient space, that is, a sufficient line width of wiring to dispose the heat generator232on the substrate231, at a position downstream in the rotational direction of the fixing belt21, that is, closer to the fixing nip FN.

As described above, the plurality of first conduction paths W1A are disposed on the surface of the substrate231facing the fixing belt21, on one side of the heat generator232in the lateral direction thereof, and more specifically, downstream of the heat generator232in the rotational direction of the fixing belt21. The plurality of first conduction paths W1A are grounded on a single elongated conduction path, that is, the second conduction path W2, and thus connected thereto. The second conduction path W2extends in the longitudinal direction of the heat generator232. The second conduction path W2is disposed on the substrate231, downstream of the heat generator232in the rotational direction of the fixing belt21, as a grounding wiring pattern.

As described above, the plurality of first conduction paths W1A are commonly grounded on a single conduction path, that is, the second conduction path W2. Accordingly, the plurality of first conduction paths W1A are not necessarily controlled individually.

In this embodiment, all the plurality of first conduction paths W1A connected to the heat generator232and disposed downstream of the heat generator232in the rotational direction of the fixing belt21are grounded on the second conduction path W2.

Each of the plurality of first conduction paths W1A belongs to any one of the sub-heat-generating areas of the heat generator232. In other words, the sub-heat-generating areas of the heat generator232are grounded via the plurality of first conduction paths W1A. Accordingly, the sub-heat-generating areas of the heat generator232are commonly grounded via the plurality of first conduction paths W1A on the single second conduction path W2.

The above-description is given of power supply to the heat generator232and grounding of the heat generator232.

The first conduction paths W1B are connected to the plurality of third conduction paths W3. Specifically, each of the plurality of third conduction paths W3is connected to a predetermined number of the first conduction paths W1B, which, in the example shown inFIG. 4, is four first conduction paths W1B. The plurality of third conduction paths W3extend in the longitudinal direction of the heat generator232. In the example shown inFIG. 4, three third conduction paths W3are disposed upward from a center in the longitudinal direction of the heat generator232. Similarly, three other third conduction paths W3are disposed downward from the center in the longitudinal direction of the heat generator232.

When a given third conduction path W3of the plurality of third conduction paths W3is supplied with power, an area of the heat generator232corresponding to the given third conduction paths W3generates heat. Thus, the heat-generating area of the heat generator232is divided into a plurality of sub-heat-generating areas in the axial direction of the fixing belt21.

According to the above-described first embodiment, one heat generator232is illustrated. Alternatively, a plurality of heat generators232may be linearly aligned and connected to the plurality of first conduction paths W1A, respectively. In such a case, the plurality of first conduction paths W1A may be commonly grounded on the conduction path W2. Alternatively, a thermal head may be used.

Referring back toFIG. 3, the overcoat layer234covers the substrate231, the heat generator232, the plurality of first conduction paths W1, the second conduction path W2and the plurality of third conduction paths W3. Preferably, the overcoat layer234is made of a material having good heat conductivity.

As illustrated inFIG. 3, the holder235is a bar-like member having a substantially H-shaped cross-section to hold the substrate231. The holder235is made of, e.g., a resin material having good heat resistance. As illustrated inFIG. 2, the base22aengages a bottom of the holder235. Accordingly, the heater23is coupled to the stationary member22.

The pressure roller24is constructed of a metal core241and an elastic layer242covering the metal core241. The elastic layer242is made of, e.g., silicon rubber foam, silicon rubber, or fluoro rubber.

The pressure roller24is rotatable, and configured to be pressed against the heater23to form an area of contact via the fixing belt21, herein called a nip to transmit heat from the heat generator232to the fixing belt21. Preferably, the elastic layer242is covered by a heat insulation layer made of a flexible, high-heat insulation material.

The heater23has the overcoat layer234, as an outmost layer of the heater23, slidably pressing an inner surface of the fixing belt21. The heater23and associated components are disposed inside the loop defined by the fixing belt21, thereby enhancing effective use of space. The overcoat layer234directly contacts the inner surface of the fixing belt21. The contact area therebetween is a surface-contact area, which is larger than a point-contact area or a line-contact area. Accordingly, heat is transmitted from the heater23to the fixing belt21with relatively high heat conductivity.

The pressing roller25is constructed of a metal core251, and an elastic layer252covering the metal core251. The pressure roller24is rotatable, and configured to be pressed against the stationary member22via the fixing belt21. Thus, a desired fixing nip FN is formed between the pressing roller25and the fixing belt21.

The elastic layer252of the pressing roller25is made of, e.g., silicon rubber foam, silicon rubber, or fluoro rubber. Preferably, the elastic layer252is covered by a thin release layer made of, e.g., PFA or PTFE.

A description is now given of operation and effects of the fixing device20according to the first embodiment.

As described above, the toner image T formed on the recording medium R is fixed onto the recording medium R under heat and pressure applied by the fixing belt21and the pressing roller25. Thus, a multicolor image is formed on the recording medium R. In the image forming apparatus1incorporating the fixing device20according to the first embodiment, the heat generator232has a plurality of sub-heat-generating areas for selectively generating heat. In other words, the image forming apparatus1incorporating the fixing device20according to the first embodiment can divide the recording medium R into an imaged area and a blank area according to image data, and only the imaged area is heated at a fixing temperature when the unfixed toner image T formed on the recording medium R is fixed onto the recording medium R.

A specific example is illustrated inFIGS. 5A and 5B.

FIG. 5Ais a plan view of a recording medium R, illustrating an image formation pattern, with a plurality of sub-heat-generating areas A through F of the heat generator232.FIG. 5Bis a graph of a relationship between the respective fixing temperatures of the sub-heat-generating areas A through F and positions of the recording medium R in a longitudinal direction thereof.

In this example, the unfixed toner image T of an image formation pattern including a blank area carried by the recording medium R illustrated inFIG. 5Ais fixed under heat generated by the heat generator232having the plurality of sub-heat-generating areas A through F. Initially, the image forming apparatus1divides the recording medium R into an imaged area and a blank area according to the image data, and controls the plurality of sub-heat-generating areas A through F to achieve the respective fixing temperatures illustrated inFIG. 5B.

Specifically, an image is formed in an area between a position P1 and a position P2 in the longitudinal direction of the recording medium R across the width of the recording medium R. That is, the area between the position P1 and the position P2 is an imaged area. The image forming apparatus1supplies power to all the sub-heat-generating areas A through F, thereby controlling the respective fixing temperatures to reach a fixing temperature T2, which is a first target temperature. At this time, the power is supplied to the sub-heat-generating areas A through F so that the respective temperatures reach the fixing temperature T2 right before the position P1 of the recording medium R reaches the fixing nip FN.

An image is formed in an area between the position P2 and a position P3 in the longitudinal direction of the recording medium R across the width of the recording medium R, except for a blank area formed at a position corresponding to the sub-heat-generating area D. Accordingly, the image forming apparatus1supplies less power to the sub-heat-generating area D right after the position P2 of the recording medium R passes through the fixing nip FN, thereby lowering the fixing temperature of the sub-heat-generating area D to a preliminary heating temperature T1, which is a second target temperature. Accordingly, the startup time is shortened when the temperature is raised to a predetermined fixing temperature again.

Similarly, an image is formed in an area between the position P3 and a position P4 in the longitudinal direction of the recording medium R across the width of the recording medium R, except for a blank area formed at a position corresponding to the sub-heat-generating areas C through F. Accordingly, the image forming apparatus1supplies less power to the sub-heat-generating areas C, E, and F right after the position P3 of the recording medium R passes through the fixing nip FN while continuously supplying the less power to the sub-heat-generating area D, thereby lowering the fixing temperature of the sub-heat-generating areas C, E, and F to the second target temperature, that is, the preliminary heating temperature T1.

At a position P4, an image is formed in an area backward from the position P4 in a direction of conveyance, that is, a longitudinal direction of the recording medium R across the width of the recording medium R. In short, the area backward from the position P4 is an imaged area. The image forming apparatus1supplies power to all the sub-heat-generating areas A through F so that the respective fixing temperatures reach or maintain the first temperature, that is, the fixing temperature T2. At this time, the power is supplied to the sub-heat-generating areas A through F so that the respective temperatures reach or maintain the fixing temperature T2 right before the position P4 of the recording medium R reaches the fixing nip FN.

As described above, the image forming apparatus1incorporating the fixing device20according to the first embodiment supplies power to ensure that a sub-heat-generating area positioned corresponding to an imaged area is maintained at the fixing temperature T2, and that another sub-heat-generating area positioned corresponding to a blank area is maintained at the preliminary heating temperature T1, which is lower than the fixing temperature T2.

In the fixing device20according to the first embodiment, the heat generator232is disposed on the surface of the substrate231facing the fixing belt21, and more specifically, at a position downstream in the rotational direction of the fixing belt21. The elongated second conduction path W2is a single conduction path on which the plurality of first conduction paths W1A are grounded. Such a simple grounding wiring pattern obviates a space necessary for a wiring pattern in which a plurality of conduction paths, such as the plurality of third conduction paths W3, are disposed in the rotational direction of the fixing belt21. Accordingly, the wiring pattern of print wiring for supplying power to the heat generator232is grounded on the second conduction path W2via the plurality of first conduction paths W1A disposed closer to the fixing nip FN.

With this wiring pattern, the distance between an edge of the heat generator232closer to the fixing nip FN and the edge of the substrate231closer to the fixing nip FN is shorter compared to a typical wiring pattern. Accordingly, an amount of heat absorbed from the fixing belt21is decreased during warm-up time.

For example, as illustrated inFIG. 5B, the power supply starts to heat the heat generator232so that the respective temperatures of the sub-heat-generating areas A through F reach the fixing temperature T1 right before the position P1 of the recording medium R reaches the fixing nip FN. Thus, the power supply in the fixing device20starts a time Δt later than the power supply in a fixing device according to a comparative example.

Thus, in the image forming apparatus1incorporating the fixing device20according to the first embodiment, the heat-generating area of the heat generator232is divided into a plurality of sub-heat-generating areas (e.g., sub-heat-generating areas A through F), and the heat generator232is located at a position downstream in the rotational direction of the fixing belt21, that is, closer to the fixing nip FN, in an area of contact between the fixing belt21and the heater23incorporating the heat generator232. Accordingly, the power consumption can be reduced and the warm-up time can be shortened.

Referring now toFIGS. 6 and 7, a description is given of a second example of the wiring patterns of print wiring.

FIG. 6is a sectional view of a heater23′.FIG. 7is a plan view of the heater23′, with the holder235removed therefrom, illustrating a second example of a wiring pattern.

According to the second example of a wiring pattern, a plurality of first conduction paths W1A are connected to the heat generator232and provided closer to the fixing nip FN to be grounded. Each of the plurality of first conduction paths W1A is wired on a backside of the substrate231via a through-hole236. The plurality of first conduction paths W1A thus wired on the backside of the substrate231may be grounded on a single conduction path such as the second conduction path W2, or may be grounded on a plurality of conduction paths such as the plurality of third conduction paths W3.

The above-description is given of the fixing device20and the image forming apparatus1incorporating the fixing device20. The image forming apparatus1incorporates the fixing device20, but is not limited thereto. Alternatively, the image forming apparatus1may incorporate a fixing device20S according to a second embodiment.

Referring now toFIG. 8, a description is given of the fixing device20S according to the second embodiment.

FIG. 8is a schematic sectional view of the fixing device20S according to the second embodiment. The fixing device20S includes a pair of rotatable rollers27and28, an endless fixing belt21stretched over the pair of rotatable rollers27and28, a pressing roller25pressed against the roller27to form an area of contact via the fixing belt21, herein called a fixing nip FN. The fixing device20S also includes a heater23S incorporating a heat generator232. As illustrated inFIG. 8, the heater23S directly contacts and heats the fixing belt21. The fixing belt21and the components disposed inside a loop defined by the fixing belt21, that is, the pair of rotatable rollers27and28, and the heater23S, may constitute a belt unit121S separably coupled with the pressing roller25.

The above-described wiring patterns of print wiring are also applicable to the heater23S incorporated in the fixing device20S.

Alternatively, the image forming apparatus1may incorporate a fixing device20T according to a third embodiment, or a fixing device20U according to a fourth embodiment.

Referring now toFIG. 9, a description is given of the fixing device20T according to the third embodiment.

FIG. 9is a schematic view of the fixing device20T according to the third embodiment. The fixing device20T has a configuration similar to that of the fixing device20and that of the fixing device20S as below. Differently from the fixing devices20and20S, the fixing device20T includes a curved-surface member40and an elastic member42. The curved-surface member40is interposed between an endless fixing belt21and a heater23T, thereby serving as an intermediate member. In short, the heater23indirectly contacts the fixing belt21via the curved-surface member40.

The fixing device20T includes the fixing belt21serving as a first rotator, the heater23T to heat the fixing belt21, and a pressing roller25serving as a second rotator pressed against the fixing belt21to form an area of contact herein called a fixing nip FN. The fixing device20T also includes a stationary member22A, a base22B, the curved-surface member40and the elastic member42. The fixing belt21and the components disposed inside a loop defined by the fixing belt21, that is, the stationary member22A, the base22B, the heater23T, the curved-surface member40, and the elastic member42, may constitute a belt unit121T separably coupled with the pressing roller25.

While a recording medium R carrying an unfixed toner image T thereon passes through the fixing nip FN, the toner image T is fixed onto the recording medium R under heat and pressure.

The heater23T includes, e.g., an elongated substrate231extending in an axial direction of the fixing belt21, and a heat generator232.

The heat generator232is disposed on a surface of the substrate231facing the fixing belt21, and more specifically, at a position downstream in a rotational direction of the fixing belt21. The heat generator232has a heat-generating area divided into a plurality of sub-heat-generating areas in the axial direction of the fixing belt21.

The heater23T also includes electrical conduction paths connected to the individual sub-heat-generating areas of the heat generator232and disposed on the surface of the substrate facing the fixing belt21. The sub-heat-generating areas of the heat generator232are commonly grounded on a single electrical conduction path via a plurality of electrical conduction paths disposed downstream of the heat generator232in the rotational direction of the fixing belt21.

The pressing roller25is constructed of a metal core251, and an elastic layer252covering the metal core251.

In this embodiment, a pressure roller such as the pressure roller24incorporated in the fixing device20according to the first embodiment may be omitted. Instead of using the pressure roller24, the curved-surface member40and the elastic member42are used in this embodiment. The curved-surface member40is disposed inside the loop defined by the fixing belt21. The elastic member42presses the curved-surface member40so that the curved-surface member40contacts the inner surface of the fixing belt21.

The curved-surface member40, serving as an intermediate member, has a pillar shape and a length equal to, or substantially equal to the length of the heater23T, extending in the rotational direction of the fixing belt21. The curved-surface member40has a curved surface that conforms to the shape of the inner surface of the fixing belt21, thereby evenly adhering to a curved surface of a cylindrical shape of the fixing belt21.

The curved-surface member40has a contact surface opposite the curved surface. The heater23T is fixed to the contact surface of the curved-surface member40.

The heater23T includes an overcoat layer234in addition to the substrate231and the heat generator232. The overcoat layer234covers one side of the heat generator232. An opposite side of the heat generator232is coupled to the substrate231, as illustrated inFIG. 3orFIG. 6. Thus, the heater23T and the curved-surface member40are coupled to each other via the overcoat layer234.

In this embodiment, the heater23T does not include a holder, such as the holder235. Accordingly, the elastic member42contacts and presses the substrate231as illustrated inFIG. 9. Alternatively, the heater23T may include the holder. In such a case, the substrate232is coupled to the holder, and the elastic member42contacts and presses the holder.

Thus, the curved-surface member40and the heater23T are coupled to each other with the heat generator232enclosed therein at the contact portion of the curved-surface member40and the heater23T. The curved-surface member40is made of metal. Preferably, the curved-surface member40is made of a metal material having good heat conductivity and easy to be heated, such as aluminum having low specific heat.

The stationary member22A is pressed by the pressing roller25via the fixing belt21, thereby forming the fixing nip FN. The stationary member22A has a shape substantially the same as the stationary member22illustrated inFIG. 2. The stationary member22A is positioned inside the loop defined by the fixing belt21, extending in the axial direction of the fixing belt21. Both ends of the stationary member22A are supported by a frame of the fixing device20T.

The base22B is coupled to a surface of the stationary member22A opposite a surface facing the fixing nip FN. The base22B has a rectangular, square-tube shape. The base22B faces the heater23T. The elastic member42is interposed between the base22B and the heater23T to separate the heater23T from the base22B. In this embodiment, an extensible spring is used as the elastic member42.

The elastic member42has an end that presses an outermost part of the heater23T that is, the substrate231in this case. The elastic member42presses the heater23T with its elastic force so that the curved-surface member40closely contacts the fixing belt21. Thus, the overcoat layer234of the heater23T indirectly contacts the fixing belt21via the curved-surface member40.

The fixing belt21is made of a material described above, and has elasticity, rigidity, and tension. The elastic member42applies its force in a direction in which the fixing belt21is extended.

The overcoat layer234is a thin layer that protects the heat generator232. The curved-surface member40interposed between the heater23T and the fixing belt21has a curved-surface that conforms to the curvature of the fixing belt21.

A rotational force of the fixing belt21is given by a torque of the pressing roller25, using a frictional force between an elastic layer252of the pressing roller25and the fixing belt21.

For example, the fixing belt21having a perfect round shape without receiving any external force is slightly deformed into an elliptical shape by the elastic member42, thereby keeping its balance with the force of the elastic member42. A pressing force of the curved-surface member40against the fixing belt21can be adjusted to prevent an excessive torque of the pressing roller25from stopping rotation of the fixing belt21. For example, the spring used as the elastic member42may be replaced with another spring having a different elastic modulus.

The curved-surface member40and the heater23are together displaced by an action of the elastic member42. A guide member may be provided to determine a direction of the displacement for a smooth movement.

The curved-surface member40closely contacts and slides on the cylindrical inner surface of the fixing belt21to transmit heat from the heater23to the fixing belt21. The rotatable fixing belt21and the pressing roller25convey the recording medium R through the fixing nip FN, in which the toner image T formed on the recording medium R is fixed onto the recording medium R.

The above-described wiring patterns of print wiring are also applicable to the heater23T incorporated in the fixing device20T.

Referring now toFIG. 10, a description is given of the fixing device20U according to the fourth embodiment.

FIG. 10is a schematic view of the fixing device20U according to the fourth embodiment. In the fixing devices20,20S and20T described above, the heater23,23S and23T are disposed away from the fixing nip FN, respectively. In the fixing device20U, a heater23U is disposed facing a fixing nip FN. The fixing device20U has a configuration similar to those of the fixing devices20,20S and20T described above.

The fixing device20U includes an endless fixing belt21serving as a first rotator, a heater23U that directly contacts and heats the fixing belt21, and a pressing roller25serving as a second rotator pressed against the fixing belt21to form an area of contact herein called a fixing nip FN. The fixing device20U also includes a stationary member22C and a holder240that holds the heater23U. The fixing belt21and the components disposed inside a loop defined by the fixing belt21, that is, the stationary member22C, the heater23U, and the holder240, may constitute a belt unit121U separably coupled with the pressing roller25.

While a recording medium R carrying an unfixed toner image T thereon passes through the fixing nip FN, the toner image T is fixed onto the recording medium R under heat and pressure.

The heater23U has an elongated planner shape and includes, e.g., an elongated substrate231extending in an axial direction of the fixing belt21, a heat generator232, and an overcoat layer234.

The heat generator232is disposed on a surface of the substrate231facing the fixing belt21, and more specifically, at a position downstream in a rotational direction of the fixing belt21. The heat generator232has a heat-generating area divided into a plurality of sub-heat-generating areas in the axial direction of the fixing belt21.

The overcoat layer234covers the substrate231, the heat generator232, and the electrical conduction paths.

The heater23U also includes electrical conduction paths connected to the individual sub-heat-generating areas of the heat generator232and disposed on the surface of the substrate facing the fixing belt21. The sub-heat-generating areas of the heat generator232are commonly grounded on a single electrical conduction path via a plurality of electrical conduction paths disposed downstream of the heat generator232in the rotational direction of the fixing belt21.

The pressing roller25is constructed of a metal core251, and an elastic layer252covering the metal core251.

A stationary member22C is a rigid member having a grooved shape, and disposed inside a loop defined by the fixing belt21, extending in the axial direction of the fixing belt21. Both ends of the stationary member22C are supported by a frame of the fixing device20U. End surfaces of the stationary member22C facing the pressing roller25are coupled to the holder240. The holder240supports the stationary member22C at both ends in the rotational direction of the fixing belt21.

The holder240is coupled to the stationary member22C with a back surface thereof facing the pressing roller25. The back surface of the holder240has a recessed portion50extending in the axial direction of the fixing belt21. The heater23U is disposed in the recessed portion50of the holder240. The heater23U has an elongated planar shape and includes, e.g., the substrate231, the heat generator232, the overcoat layer234, and electric conduction paths as described above.

The pressing roller25is pressed against the overcoat layer234via the fixing belt21to form the fixing nip FN. The stationary member22C supports a pressing force applied by the pressing roller25in the fixing nip FN.

The heater23faces the fixing nip FN and is supported in the recessed portion50of the holder240. Alternatively, the recessed portion50may directly hold the substrate231. The holder240has shoulders51aand51bformed on both sides of the recessed portion50and chamfered along the rotational direction of the fixing belt21to support and smoothly rotate the fixing belt21.

A rotational force of the fixing belt21is given by a torque of the pressing roller25, using a frictional force between the elastic layer252of the pressing roller25and the fixing belt21. An unsupported portion of the fixing belt21may be supported by a support member.

The fixing belt21is heated by heat applied by the heater23in the fixing nip FN. The rotatable fixing belt21and the pressing roller25convey the recording medium R through the fixing nip FN, in which the toner image T formed on the recording medium R is fixed onto the recording medium R.

The above-described wiring patterns of print wiring are also applicable to the heater23U incorporated in the fixing device20U.

The present invention, although it has been described above with reference to specific exemplary embodiments, is not limited to the details of the embodiments described above, and various modifications and enhancements are possible without departing from the scope of the invention. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this invention. The number of constituent elements and their locations, shapes, and so forth are not limited to any of the structure for performing the methodology illustrated in the drawings.