Patent Description:
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, and multifunction peripherals (MFP) having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data.

For example, an image forming apparatus includes a fixing device including a fixing belt serving as a belt and a heater that heats the fixing belt. The heater includes a base, a resistive heat generator mounted on the base, and an insulating layer. As the resistive heat generator is applied with an alternating current (AC) voltage, the resistive heat generator generates heat, thus heating an inner circumferential face of the fixing belt through the insulating layer and the like.

Since the heater is applied with the alternating current voltage, the insulating layer of the heater and a surface layer of the fixing belt have an equivalence that is common to a condenser. Thus, the alternating current voltage is applied to a fixing nip formed between the fixing belt and an opposed rotator disposed opposite the fixing belt through the fixing belt. The image forming apparatus has a transfer nip where an image is transferred onto a sheet. While the sheet contacts both the transfer nip and the fixing nip, the alternating current voltage is transmitted to the transfer nip through the sheet. Hence, the alternating current voltage may affect a transfer electric field generated at the transfer nip, causing uneven density of the image transferred on the sheet periodically. The uneven density of the image may cause a banding image. For example, if the sheet is used in a high-humidity environment or the sheet is thin, the sheet has low resistance and generation of the banding image becomes more pronounced.

To address the circumstance described above, a fixing device includes a fixing belt and a conductive member that contacts an inner face of the fixing belt. An electric current is released to ground through the conductive member. For example, <CIT> discloses a fixing device that includes a heater holder that includes a projection. The projection is inserted into a hole disposed at one end of the conductive member such that the projection does not move off from the hole. Another end of the conductive member contacts the inner face of the fixing belt (e.g., a heating film).

However, in the fixing device disclosed by <CIT>, the conductive member may pivot in a direction perpendicular to an attachment direction of the conductive member, thus being displaced from a proper position. Accordingly, the fixing device may suffer from an increased number of assembly processes. The conductive member may contact the fixing belt faultily and may not achieve proper discharging.

It is a general object of the present disclosure to provide an improved and useful fixing device in which the above-mentioned problems are eliminated. In order to achieve the above-mentioned object, there is provided the fixing device according to claim <NUM>. Advantageous embodiments are defined by the dependent claims.

Advantageously, the fixing device includes a belt that rotates in a rotation direction and a heater that heats the belt. A conductive member contacts an inner face of the belt and pivots. The conductive member includes one end portion in the rotation direction of the belt, a contact portion that contacts the belt, and an outboard portion that is disposed outboard from the contact portion in the rotation direction of the belt. A holding portion holds the one end portion of the conductive member. A pivot restrictor contacts the outboard portion of the conductive member. The pivot restrictor restricts pivoting of the conductive member about the one end portion of the conductive member.

It is another object of the present disclosure to provide an improved and useful image forming apparatus in which the above-mentioned problems are eliminated.

Advantageously, the image forming apparatus includes the fixing device described above.

Accordingly, the pivot restrictor suppresses pivoting and resultant shifting of the conductive member.

Referring to attached drawings, the following describes embodiments of the present disclosure. In the drawings, identical reference numerals are assigned to elements that are identical or equivalent and redundant descriptions of the elements are simplified or omitted properly.

<FIG> is a schematic cross-sectional view of an image forming apparatus <NUM> according to an embodiment of the present disclosure.

As illustrated in <FIG>, the image forming apparatus <NUM> includes four image forming units 1Y, <NUM>, 1C, and 1Bk that are installed in an apparatus body of the image forming apparatus <NUM> such that the image forming units 1Y, <NUM>, 1C, and 1Bk are attached to and removed from the apparatus body of the image forming apparatus <NUM>. The image forming units 1Y, <NUM>, 1C, and 1Bk have a similar construction. However, the image forming units 1Y, <NUM>, 1C, and 1Bk contain developers in different colors, that is, yellow, magenta, cyan, and black, respectively. The developers correspond to color separation components for a color image. Each of the image forming units 1Y, <NUM>, 1C, and 1Bk includes a photoconductor <NUM>, a charger <NUM>, a developing device <NUM>, and a cleaner <NUM>. The photoconductor <NUM> is drum-shaped and serves as an image bearer. The charger <NUM> charges a surface of the photoconductor <NUM>. The developing device <NUM> supplies toner as the developer to the surface of the photoconductor <NUM> to form a toner image. The cleaner <NUM> cleans the surface of the photoconductor <NUM>.

The image forming apparatus <NUM> further includes an exposure device <NUM>, a sheet feeder <NUM>, a transfer device <NUM>, a fixing device <NUM> serving as a heating device, and an output device <NUM>. The exposure device <NUM> exposes the surface of each of the photoconductors <NUM> and forms an electrostatic latent image thereon. The image forming apparatus <NUM> further includes a sheet conveyance path <NUM>. The sheet feeder <NUM> supplies a sheet P serving as a recording medium to the sheet conveyance path <NUM>. The transfer device <NUM> transfers the toner image formed on each of the photoconductors <NUM> onto the sheet P. The fixing device <NUM> fixes the toner image transferred onto a surface of the sheet P thereon. The output device <NUM> ejects the sheet P onto an outside of the image forming apparatus <NUM>. Each of the image forming units 1Y, <NUM>, 1C, and 1Bk, that includes the photoconductor <NUM> and the charger <NUM>, the exposure device <NUM>, the transfer device <NUM>, and the like construct an image forming device that forms the toner image on the sheet P.

The transfer device <NUM> includes an intermediate transfer belt <NUM>, four primary transfer rollers <NUM>, and a secondary transfer roller <NUM>. The intermediate transfer belt <NUM> is an endless belt serving as an intermediate transferor. The primary transfer rollers <NUM> serve as primary transferors. The secondary transfer roller <NUM> serves as a secondary transferor. The intermediate transfer belt <NUM> is stretched taut across a plurality of rollers. The primary transfer rollers <NUM> transfer yellow, magenta, cyan, and black toner images formed on the photoconductors <NUM> onto the intermediate transfer belt <NUM>, respectively, thus forming a full color toner image on the intermediate transfer belt <NUM>. The secondary transfer roller <NUM> transfers the full color toner image formed on the intermediate transfer belt <NUM> onto the sheet P. The plurality of primary transfer rollers <NUM> is pressed against the photoconductors <NUM>, respectively, via the intermediate transfer belt <NUM>. Accordingly, the intermediate transfer belt <NUM> contacts each of the photoconductors <NUM>, forming a primary transfer nip therebetween. On the other hand, the secondary transfer roller <NUM> is pressed against a secondary transfer opposed roller <NUM>, that is, one of the plurality of rollers across which the intermediate transfer belt <NUM> is stretched taut, via the intermediate transfer belt <NUM>. Thus, a secondary transfer nip is formed between the secondary transfer roller <NUM> and the intermediate transfer belt <NUM>.

The sheet conveyance path <NUM> is provided with a timing roller pair <NUM> at a position between the sheet feeder <NUM> and the secondary transfer nip defined by the secondary transfer roller <NUM>.

Referring to <FIG>, a description is provided of printing processes performed by the image forming apparatus <NUM>.

When the image forming apparatus <NUM> receives an instruction to start printing, a driver disposed inside the apparatus body of the image forming apparatus <NUM> drives and rotates the photoconductor <NUM> clockwise in <FIG> in each of the image forming units 1Y, <NUM>, 1C, and 1Bk. The charger <NUM> charges the surface of the photoconductor <NUM> uniformly at a high electric potential. The exposure device <NUM> exposes the charged surfaces of the photoconductors <NUM>, respectively, according to image data (e.g., print data) sent from a terminal. Alternatively, if the image forming apparatus <NUM> is a copier, the exposure device <NUM> exposes the charged surfaces of the photoconductors <NUM>, respectively, according to image data created by a scanner that reads an image on an original. Accordingly, the electric potential of an exposed portion on the surface of each of the photoconductors <NUM> decreases, forming an electrostatic latent image on the surface of each of the photoconductors <NUM>. The developing device <NUM> of each of the image forming units 1Y, <NUM>, 1C, and 1Bk supplies toner to the electrostatic latent image formed on the photoconductor <NUM>, forming a toner image thereon.

The toner images formed on the photoconductors <NUM> move and reach the primary transfer nips defined by the primary transfer rollers <NUM> in accordance with rotation of the photoconductors <NUM>, respectively. The primary transfer rollers <NUM> transfer the toner images formed on the photoconductors <NUM> onto the intermediate transfer belt <NUM> driven and rotated counterclockwise in <FIG> successively such that the toner images are superimposed on the intermediate transfer belt <NUM>, thus forming a full color toner image thereon. The full color toner image formed on the intermediate transfer belt <NUM> is conveyed to the secondary transfer nip defined by the secondary transfer roller <NUM> in accordance with rotation of the intermediate transfer belt <NUM>. The secondary transfer roller <NUM> transfers the full color toner image onto a sheet P conveyed through the secondary transfer nip. The sheet P is supplied from the sheet feeder <NUM>. The timing roller pair <NUM> temporarily halts the sheet P supplied from the sheet feeder <NUM>. Thereafter, the timing roller pair <NUM> conveys the sheet P to the secondary transfer nip at a time when the full color toner image formed on the intermediate transfer belt <NUM> reaches the secondary transfer nip. The secondary transfer roller <NUM> transfers the full color toner image onto the sheet P. Thus, the sheet P bears the full color toner image. After the toner image is transferred onto the intermediate transfer belt <NUM>, the cleaner <NUM> removes residual toner remaining on the photoconductor <NUM> therefrom.

The sheet P transferred with the full color toner image is conveyed to the fixing device <NUM> that fixes the full color toner image on the sheet P. Thereafter, the output device <NUM> ejects the sheet P onto the outside of the image forming apparatus <NUM>, thus finishing a series of printing processes.

A description is provided of a construction of the fixing device <NUM>.

As illustrated in <FIG>, the fixing device <NUM> according to the embodiment includes a fixing belt <NUM>, a pressure roller <NUM>, a heater <NUM>, a heater holder <NUM>, a stay <NUM>, thermistors <NUM> depicted in <FIG>, a first thermal conductor <NUM>, and a conductive member <NUM>. The fixing belt <NUM> serves as a belt or a fixing rotator. The pressure roller <NUM> serves as an opposed rotator or a pressure rotator. The heater holder <NUM> serves as a holder. The stay <NUM> serves as a support. The thermistors <NUM> serve as temperature detectors. The fixing belt <NUM> is an endless belt. The pressure roller <NUM> contacts an outer circumferential face of the fixing belt <NUM> to form a fixing nip N between the fixing belt <NUM> and the pressure roller <NUM>. The heater <NUM> heats the fixing belt <NUM>. The heater holder <NUM> holds or supports the heater <NUM>. The stay <NUM> supports the heater holder <NUM>. Each of the thermistors <NUM> detects a temperature of the first thermal conductor <NUM>.

The fixing belt <NUM>, the pressure roller <NUM>, the heater <NUM>, the heater holder <NUM>, the stay <NUM>, the first thermal conductor <NUM>, and the like extend in a longitudinal direction that is perpendicular to a paper surface in <FIG>. The longitudinal direction defines a longitudinal direction X that is bidirectional and illustrated in <FIG> and <FIG>, for example. The longitudinal direction X is parallel to a width direction of a sheet P conveyed through the fixing nip N, a belt width direction of the fixing belt <NUM>, and an axial direction of the pressure roller <NUM>. As the fixing belt <NUM> and the pressure roller <NUM> rotate in rotation directions J and K, respectively, the fixing belt <NUM> and the pressure roller <NUM> convey the sheet P in a sheet conveyance direction A. The fixing nip N defines an upstream portion (e.g., a lower portion in <FIG>) of the fixing device <NUM>, that is disposed upstream from the fixing nip N, and a downstream portion (e.g., an upper portion in <FIG>) of the fixing device <NUM>, that is disposed downstream from the fixing nip N, in the sheet conveyance direction A.

The fixing belt <NUM> includes a base layer, as a tubular base, that is made of polyimide (PI) and has an outer diameter of <NUM> and a thickness in a range of from <NUM> to <NUM>, for example. The fixing belt <NUM> further includes a release layer serving as an outermost surface layer. The release layer is made of fluororesin, such as perfluoroalkoxy alkane (PFA) and polytetrafluoroethylene (PTFE), and has a thickness in a range of from <NUM> to <NUM> to enhance durability of the fixing belt <NUM> and facilitate separation of the sheet P and a foreign substance from the fixing belt <NUM>. Optionally, an elastic layer that is made of rubber or the like and has a thickness in a range of from <NUM> to <NUM> may be interposed between the base layer and the release layer. According to the embodiment, the fixing belt <NUM> is a rubber-less belt that does not include the elastic layer. The base layer of the fixing belt <NUM> may be made of heat-resistant resin such as polyetheretherketone (PEEK) or metal such as nickel (Ni) and stainless used steel (SUS), instead of polyimide. The fixing belt <NUM> may include an inner circumferential face 20a that is coated with polyimide, PTFE, or the like to produce a sliding layer.

The pressure roller <NUM> has an outer diameter of <NUM>, for example. The pressure roller <NUM> includes a core metal 21a, an elastic layer 21b disposed on a surface of the core metal 21a, and a release layer 21c disposed on an outer surface of the elastic layer 21b. The core metal 21a is solid and made of iron. The elastic layer 21b is made of silicone rubber and has a thickness of <NUM>, for example. In order to enhance separation of the sheet P from the pressure roller <NUM>, the elastic layer 21b is preferably coated with the release layer 21c that is made of fluororesin and has a thickness of approximately <NUM>, for example.

The fixing device <NUM> further includes a biasing member that biases and moves the pressure roller <NUM> toward the fixing belt <NUM>, pressing the pressure roller <NUM> against the heater <NUM> via the fixing belt <NUM>. Thus, the fixing nip N serving as a nip is formed between the fixing belt <NUM> and the pressure roller <NUM>. The fixing device <NUM> further includes a driver that drives and rotates the pressure roller <NUM>. As the pressure roller <NUM> rotates in the rotation direction K, the pressure roller <NUM> drives and rotates the fixing belt <NUM> in the rotation direction J.

The heater <NUM> contacts the inner circumferential face 20a of the fixing belt <NUM>. According to the embodiment, the heater <NUM> presses against the pressure roller <NUM> via the fixing belt <NUM>, thus serving as a nip formation pad that forms the fixing nip N between the fixing belt <NUM> and the pressure roller <NUM>. The fixing belt <NUM> also serves as a heated member that is heated by the heater <NUM>. According to the embodiment, the heater <NUM> contacts the inner circumferential face 20a of the fixing belt <NUM> directly. Alternatively, the heater <NUM> may be disposed opposite the fixing belt <NUM> indirectly via an element.

The heater <NUM> is a laminated heater that extends in the longitudinal direction thereof throughout an entire span of the fixing belt <NUM> in the longitudinal direction thereof. The heater <NUM> includes a base <NUM> (e.g., a substrate) that is platy, resistive heat generators <NUM> that are disposed on the base <NUM>, and an insulating layer <NUM> that coats the resistive heat generators <NUM>. The image forming apparatus <NUM> further includes a power supply <NUM> illustrated in <FIG>. As the power supply <NUM> applies an alternating current (AC) voltage to the heater <NUM>, the resistive heat generators <NUM> generate heat mainly, heating the fixing belt <NUM>.

The insulating layer <NUM> of the heater <NUM> contacts the inner circumferential face 20a of the fixing belt <NUM>. The resistive heat generators <NUM> generate heat that is conducted to the fixing belt <NUM> through the insulating layer <NUM>. According to the embodiment, the resistive heat generators <NUM> and the insulating layer <NUM> are mounted on a fixing belt opposed face of the base <NUM>, that is disposed opposite the fixing belt <NUM> and the fixing nip N. Alternatively, the resistive heat generators <NUM> and the insulating layer <NUM> may be mounted on a heater holder opposed face of the base <NUM>, that is disposed opposite the heater holder <NUM>. In this case, heat generated by the resistive heat generators <NUM> is conducted to the fixing belt <NUM> through the base <NUM>. Hence, the base <NUM> is preferably made of a material having an enhanced thermal conductivity, such as aluminum nitride. Since the base <NUM> is made of the material having the enhanced thermal conductivity, even if the resistive heat generators <NUM> are disposed opposite the fixing belt <NUM> via the base <NUM>, the resistive heat generators <NUM> heat the fixing belt <NUM> sufficiently.

The heater holder <NUM> and the stay <NUM> are disposed within a loop formed by the fixing belt <NUM>. The stay <NUM> includes a channel made of metal. The stay <NUM> has both lateral ends in the longitudinal direction thereof, that are supported by side plates of the fixing device <NUM>, respectively. Since the stay <NUM> supports the heater holder <NUM> and the heater <NUM>, in a state in which the pressure roller <NUM> is pressed against the fixing belt <NUM>, the heater <NUM> receives pressure from the pressure roller <NUM> precisely. Thus, the fixing nip N is formed between the fixing belt <NUM> and the pressure roller <NUM> stably. According to the embodiment, the heater holder <NUM> has a thermal conductivity that is smaller than a thermal conductivity of the base <NUM>.

The stay <NUM> includes a base 24b and arms 24a that serve as walls and project from an upstream part and a downstream part of the base 24b, respectively, in the sheet conveyance direction A. The arms 24a are perpendicular to the base 24b. Thus, the stay <NUM> is substantially U-shaped. Each of the arms 24a has an end face that contacts and supports the heater holder <NUM>. The arms 24a extend in a horizontal direction in <FIG>, that is, a pressing direction E in which the pressure roller <NUM> is pressed against the fixing belt <NUM>. The stay <NUM> is grounded through a resistance <NUM>.

According to the embodiment, the arms 24a of the stay <NUM>, that is, extended portions that extend in the pressing direction E of the pressure roller <NUM> (e.g., the horizontal direction in <FIG>) or portions that have an increased thickness, contact the heater holder <NUM> rightward in <FIG> and press against the pressure roller <NUM> via the heater holder <NUM>, the heater <NUM>, and the fixing belt <NUM>. Thus, the stay <NUM> supports the heater holder <NUM>. Accordingly, the stay <NUM> prevents the heater holder <NUM> from being bent by pressure from the pressure roller <NUM>. According to the embodiment, the stay <NUM> prevents bending of the heater holder <NUM> in the longitudinal direction thereof. The stay <NUM> may contact the heater holder <NUM> directly or indirectly via an element. For example, the element is interposed between the stay <NUM> and the heater holder <NUM> in the horizontal direction in <FIG>. At least a part of the element contacts the stay <NUM> and the heater holder <NUM>. The arms 24a of the stay <NUM> may extend in a direction different from the pressing direction E of the pressure roller <NUM>. For example, the arms 24a of the stay <NUM> may extend in an angled direction that is angled with respect to the pressing direction E of the pressure roller <NUM> at an angle within a predetermined range. In this case also, the stay <NUM> prevents the heater holder <NUM> from being bent by pressure from the pressure roller <NUM>.

Since the heater holder <NUM> is subject to high temperatures by heat from the heater <NUM>, the heater holder <NUM> is preferably made of a heat-resistant material. For example, if the heater holder <NUM> is made of heat-resistant resin having a decreased thermal conductivity, such as liquid crystal polymer (LCP) and PEEK, the heater holder <NUM> suppresses conduction of heat thereto from the heater <NUM>. Accordingly, the heater <NUM> heats the fixing belt <NUM> efficiently.

The heater holder <NUM> includes a recess 23e illustrated in <FIG> that holds the first thermal conductor <NUM> and the heater <NUM>.

As illustrated in <FIG>, the heater holder <NUM> includes a guide <NUM> that guides the fixing belt <NUM>. The heater holder <NUM> and the guide <NUM> are molded into a unit. The guide <NUM> is disposed at each of an upstream part and a downstream part of the heater holder <NUM> in the sheet conveyance direction A.

The guide <NUM> includes a plurality of guide ribs <NUM> serving as guides. The guide rib <NUM> is substantially fan-shaped. The guide rib <NUM> includes a guide face 260a that is curved along the inner circumferential face 20a of the fixing belt <NUM>. The guide face 260a defines an arc or a projecting curved face that extends in a circumferential direction of the fixing belt <NUM>.

The first thermal conductor <NUM> is made of a material having a thermal conductivity greater than a thermal conductivity of the base <NUM>. According to the embodiment, the first thermal conductor <NUM> is a plate made of aluminum. Alternatively, the first thermal conductor <NUM> may be made of copper, silver, graphene, or graphite, for example. Since the first thermal conductor <NUM> is platy, the first thermal conductor <NUM> improves accuracy of positioning of the heater <NUM> with respect to the heater holder <NUM> and the first thermal conductor <NUM>.

A description is provided of a method for calculating the thermal conductivity described above.

A thermal diffusivity of a target object was measured and a thermal conductivity was calculated based on the thermal diffusivity.

The thermal diffusivity was measured with a thermal diffusivity-thermal conductivity measurement device, ai-Phase Mobile 1u, manufactured by ai-Phase Co.

The thermal diffusivity was converted into the thermal conductivity based on a density and a specific heat capacity. The density was measured with a dry-process pycnometer, Accupyc <NUM>, manufactured by Shimadzu Corporation. The specific heat capacity was measured with a differential scanning calorimeter, DSC-<NUM>, manufactured by Shimadzu Corporation. Sapphire was used as a reference material having a known specific heat capacity. According to an embodiment, the specific heat capacity was measured five times to obtain an average at <NUM> degrees Celsius. Based on a density ρ, a specific heat capacity S, and a thermal diffusivity α obtained by the above-described measurement of the thermal diffusivity, a thermal conductivity λ is obtained by a formula (<NUM>) below.

In the fixing device <NUM> according to the embodiment, when printing starts, the driver drives and rotates the pressure roller <NUM> and the fixing belt <NUM> starts rotation in accordance with rotation of the pressure roller <NUM>. Since the inner circumferential face 20a of the fixing belt <NUM> is contacted and guided by the guide face 260a of the guide rib <NUM>, the fixing belt <NUM> rotates stably and smoothly. Additionally, as power is supplied to the resistive heat generators <NUM> of the heater <NUM>, the heater <NUM> heats the fixing belt <NUM>. In a state in which the temperature of the fixing belt <NUM> reaches a predetermined target temperature (e.g., a fixing temperature), as a sheet P bearing an unfixed toner image is conveyed through the fixing nip N formed between the fixing belt <NUM> and the pressure roller <NUM> as illustrated in <FIG>, the fixing belt <NUM> and the pressure roller <NUM> fix the unfixed toner image on the sheet P under heat and pressure.

The fixing device <NUM> may cause a banding image. For example, since the fixing device <NUM> incorporates the heater <NUM> that is applied with an alternating current voltage, the insulating layer <NUM> of the heater <NUM> and the release layer as the outermost surface layer of the fixing belt <NUM> have an equivalence that is common to a condenser. As the heater <NUM> contacts the fixing belt <NUM>, the alternating current voltage is applied to the fixing nip N through the fixing belt <NUM>. As illustrated in <FIG>, in a state in which the sheet P contacts both the fixing nip N and a secondary transfer nip NA formed between the secondary transfer roller <NUM> and the secondary transfer opposed roller <NUM>, the alternating current voltage is transmitted to the secondary transfer nip NA in a transmission direction M through the sheet P. The alternating current voltage may affect a transfer electric field, causing periodic, uneven density of a toner image transferred onto the sheet P, that is, a banding image. For example, if the sheet P is used in a high-humidity environment or the sheet P is thin, the sheet P has low resistance and generation of the banding image becomes more pronounced. The secondary transfer nip NA is a nip formed between the secondary transfer roller <NUM> and the secondary transfer opposed roller <NUM>.

The fixing device <NUM> may form a faulty toner image due to electrostatic offset. For example, while the sheet P is conveyed through the fixing nip N, unfixed toner of the toner image on the sheet P is attracted and adhered to the charged release layer as the outermost surface layer of the fixing belt <NUM>. As the fixing belt <NUM> rotates, the toner adhered to the fixing belt <NUM> moves to the fixing nip N again and adheres to a subsequent sheet P that reaches the fixing nip N subsequently, forming a faulty toner image on the subsequent sheet P.

To address formation of the faulty toner image, according to the embodiment of the present disclosure, the fixing device <NUM> depicted in <FIG> includes the conductive member <NUM> that releases the alternating current voltage to ground from the fixing nip N through the fixing belt <NUM>. Thus, the fixing device <NUM> prevents formation of the banding image. The conductive member <NUM> removes electric charge from a surface of the fixing belt <NUM>, preventing formation of the faulty toner image due to the electrostatic offset.

As illustrated in <FIG>, the conductive member <NUM> is a flexible sheet. The conductive member <NUM> is made of a conductive material. According to the embodiment, the conductive member <NUM> is made of conductive polyimide added with carbon black. The conductive member <NUM> is grounded through the stay <NUM> and the resistance <NUM>. The fixing device <NUM> may incorporate a plurality of conductive members <NUM> arranged in the longitudinal direction of the fixing belt <NUM> or a single conductive member <NUM>. The conductive member <NUM> is interposed between the stay <NUM> and the guide <NUM>.

The conductive member <NUM> includes a fixed end 40a serving as one end and a free end 40b serving as another end. The free end 40b serves as a contact portion that contacts an inner face (e.g., the inner circumferential face 20a) of the fixing belt <NUM>. As the free end 40b contacts the inner circumferential face 20a of the fixing belt <NUM>, the conductive member <NUM> releases the electric charge on the surface of the fixing belt <NUM> to ground through the stay <NUM> and the resistance <NUM>, thus removing the electric charge accumulated on the surface of the fixing belt <NUM>. According to the embodiment, the free end 40b (e.g., another end) of the conductive member <NUM> is opposite to the fixed end 40a (e.g., one end) of the conductive member <NUM>. The free end 40b as another end is opposite to the fixed end 40a as one end via a center position of the conductive member <NUM> in an orthogonal direction perpendicular to a width direction of the conductive member <NUM>. The orthogonal direction extends along a face of the conductive member <NUM>. In other words, in a state in which the conductive member <NUM> is not bent and is substantially sheet-shaped, the free end 40b as another end is opposite to the fixed end 40a as one end via a position equivalent to the center position of the conductive member <NUM> in the orthogonal direction that is perpendicular to the width direction of the conductive member <NUM> and is extended along the face of the conductive member <NUM>.

The conductive member <NUM> includes an opposed portion 40c that is disposed opposite a first opposed face 24d of the stay <NUM> and a second opposed face 26a of the guide <NUM>. The first opposed face 24d and the second opposed face 26a restrict inclination of the conductive member <NUM>. For example, the first opposed face 24d and the second opposed face 26a are disposed at positions where the first opposed face 24d and the second opposed face 26a contact the conductive member <NUM> and restrict inclination of the conductive member <NUM> when the conductive member <NUM> tilts upward or downward in <FIG>.

The conductive member <NUM> includes a bent portion 40d that abuts on the free end 40b. The free end 40b is bent downstream from the bent portion 40d in the rotation direction J of the fixing belt <NUM>.

The fixed end 40a of the conductive member <NUM> abuts on the opposed portion 40c and is bent from the opposed portion 40c. The fixed end 40a that is opposite to the free end 40b via the opposed portion 40c is sandwiched between the arm 24a of the stay <NUM> and the heater holder <NUM> in the horizontal direction in <FIG>. Thus, pressure from the pressure roller <NUM> causes the conductive member <NUM> to be sandwiched between the stay <NUM> and the heater holder <NUM>. Accordingly, the conductive member <NUM> contacts the stay <NUM> precisely and is grounded through the stay <NUM>.

As illustrated in <FIG>, the conductive member <NUM> has an insertion hole 40e that penetrates through the fixed end 40a of the conductive member <NUM>. The conductive member <NUM> is asymmetrical vertically in <FIG>. For example, the insertion hole 40e is disposed above a center <NUM> (e.g., a center line) of the conductive member <NUM> in <FIG>. That is, the insertion hole 40e is shifted from the center <NUM> of the conductive member <NUM> in the width direction that is perpendicular to a longitudinal direction thereof. In other words, the conductive member <NUM> has a length B1 from one lateral end of the conductive member <NUM> to a center 40e1 of the insertion hole 40e in the width direction of the conductive member <NUM>. The conductive member <NUM> has a length B2 from another lateral end of the conductive member <NUM> to the center 40e1 of the insertion hole 40e in the width direction of the conductive member <NUM>. The length B2 is greater than the length B1. The free end 40b of the conductive member <NUM> is tapered to define a tip. The free end 40b as the tip is also disposed above the center <NUM> of the conductive member <NUM> in <FIG>. That is, the free end 40b is shifted from the center <NUM> of the conductive member <NUM> in the width direction thereof.

Referring to <FIG> and <FIG>, a description is provided of a holding construction in which the heater holder <NUM> holds the conductive member <NUM>.

As illustrated in <FIG>, the heater holder <NUM> includes a positioning pin 23a serving as a holding portion and two pivot restricting ribs 23b serving as pivot restrictors that are mounted on a stay opposed face of the heater holder <NUM>, that is disposed opposite the stay <NUM>. The positioning pin 23a is interposed between the two pivot restricting ribs 23b. The positioning pin 23a and the pivot restricting ribs 23b project in a projecting direction (e.g., the horizontal direction in <FIG>) that is parallel to the pressing direction E of the pressure roller <NUM>.

As illustrated in <FIG>, in order to attach the conductive member <NUM> to the heater holder <NUM>, the positioning pin 23a is inserted into the insertion hole 40e of the conductive member <NUM> so that the positioning pin 23a holds the conductive member <NUM>. The free end 40b of the conductive member <NUM> is placed on an end face 260b of the guide rib <NUM>. The free end 40b of the conductive member <NUM> is placed between the two pivot restricting ribs 23b. Thus, the conductive member <NUM> is attached to the heater holder <NUM>. In a state in which the conductive member <NUM> is attached to the heater holder <NUM>, as illustrated in <FIG>, the stay <NUM> comes into contact with the heater holder <NUM>. As illustrated in <FIG>, the stay <NUM> and the heater holder <NUM> sandwich the fixed end 40a of the conductive member <NUM>. Thus, the conductive member <NUM> has a sandwiched portion (e.g., the fixed end 40a) that is sandwiched between the stay <NUM> and the heater holder <NUM> and a non-sandwiched portion (e.g., the opposed portion 40c) that is not sandwiched between the stay <NUM> and the heater holder <NUM> and is disposed closer to the free end 40b than the sandwiched portion is. The non-sandwiched portion projects in a direction that separates from the pressure roller <NUM> and extends leftward in <FIG> along the stay <NUM>. The free end 40b of the conductive member <NUM> is bent from the bent portion 40d toward the stay <NUM>. <FIG> omits illustration of the conductive member <NUM>. <FIG> illustrate the heater holder <NUM> and the stay <NUM> before the fixing belt <NUM> is installed into the fixing device <NUM>.

As described above, the positioning pin 23a is inserted into the insertion hole 40e disposed in the fixed end 40a of the conductive member <NUM>. Hence, as illustrated in <FIG>, the conductive member <NUM> may pivot about the positioning pin 23a. <FIG> illustrates a heater holder 23R that includes the positioning pin 23a and does not include the pivot restricting ribs 23b. Accordingly, as illustrated with a solid line in <FIG> and <FIG>, the free end 40b of the conductive member <NUM> may not contact and discharge the inner circumferential face 20a of the fixing belt <NUM>. <FIG> and <FIG> illustrate the free end 40b that is to contact the inner circumferential face 20a of the fixing belt <NUM> with a broken line. <FIG> illustrates a fixing device 9A in which the free end 40b of the conductive member <NUM> does not contact and discharge the inner circumferential face 20a of the fixing belt <NUM>.

Additionally, when the conductive member <NUM> is attached to the heater holder <NUM>, extra processes for returning the conductive member <NUM> to a proper position and attaching the stay <NUM> to the heater holder <NUM> such that the conductive member <NUM> does not pivot may be added, degrading assembly of the fixing device 9A.

To address the circumstance, according to the embodiment, the heater holder <NUM> incorporates the pivot restricting ribs 23b depicted in <FIG> that prevent pivoting of the conductive member <NUM>. The conductive member <NUM> pivots in a pivot direction V depicted in <FIG> that is parallel to a face perpendicular to the projecting direction of the positioning pin 23a. According to the embodiment, as illustrated in <FIG>, the pivot restricting ribs 23b are disposed opposite both lateral ends of the conductive member <NUM> in the longitudinal direction X of the heater holder <NUM>, respectively, thus preventing the conductive member <NUM> from pivoting bidirectionally in the pivot direction V thereof. Alternatively, the pivot restricting rib 23b may be disposed opposite one of both lateral ends of the conductive member <NUM> in the longitudinal direction X of the heater holder <NUM>.

In order to cause the pivot restricting ribs 23b to restrict a pivot range of the conductive member <NUM> properly, the pivot restricting ribs 23b disposed opposite both lateral ends of the conductive member <NUM>, respectively, in the pivot direction V define an appropriate clearance between the pivot restricting ribs 23b. The following describes an arrangement of the pivot restricting ribs 23b.

As illustrated in <FIG>, if the conductive member <NUM> pivots in one direction at a pivot angle that is greater than a pivot angle C1, the free end 40b of the conductive member <NUM> may not contact the inner circumferential face 20a of the fixing belt <NUM>. If the conductive member <NUM> pivots in another direction at a pivot angle that is greater than a pivot angle C2, the free end 40b of the conductive member <NUM> may not contact the inner circumferential face 20a of the fixing belt <NUM>. Each of the pivot angles C1 and C2 is a limit angle at which the conductive member <NUM> contacts the fixing belt <NUM> precisely. If the conductive member <NUM> pivots at a pivot angle that is greater than the limit angle, as illustrated in <FIG> with a solid line, the conductive member <NUM> may not contact the inner circumferential face 20a of the fixing belt <NUM>. The pivot restricting ribs 23b illustrated in <FIG> restrict the pivot range of the conductive member <NUM> such that the conductive member <NUM> pivots at a pivot angle that is not greater than each of the pivot angles C1 and C2 as the limit angle. In order to cause the conductive member <NUM> to pivot in the pivot range defined by the pivot angle that is not greater than each of the pivot angles C1 and C2, the pivot restricting ribs 23b define a clearance W2 from a center 23a1 of the positioning pin 23a to one of the pivot restricting ribs 23b and a clearance W3 from the center 23a1 of the positioning pin 23a to another one of the pivot restricting ribs 23b in the pivot direction V of the conductive member <NUM>. As one example of the arrangement of the pivot restricting ribs 23b, that attains a restricting angle for restricting pivoting of the conductive member <NUM>, that is not greater than the limit angle, the pivot restricting ribs 23b are preferably arranged to restrict the pivot angle of the conductive member <NUM> such that the conductive member <NUM> pivots in one direction or another direction at a pivot angle not greater than <NUM> degrees. Accordingly, the pivot restricting ribs 23b restrict the pivot range of the conductive member <NUM> properly, causing the conductive member <NUM> to contact the fixing belt <NUM> precisely. Additionally, the conductive member <NUM> contacts the fixing belt <NUM> at an acute angle, decreasing load imposed on the conductive member <NUM> and the fixing belt <NUM> while the fixing belt <NUM> slides over the conductive member <NUM>. The pivot restricting ribs 23b restrict pivoting of the conductive member <NUM> in processes in which the fixing device <NUM> is assembled mainly. The processes include a process in which the conductive member <NUM> is attached to the heater holder <NUM> and a process in which the stay <NUM> is attached to the heater holder <NUM>. Alternatively, the pivot restricting ribs 23b may also restrict pivoting of the conductive member <NUM> even after the fixing device <NUM> is assembled.

As illustrated in <FIG>, according to an embodiment of the present disclosure, the pivot restricting ribs 23b define a clearance therebetween, that has a size equivalent to a width W1 of the conductive member <NUM> in the width direction thereof that is substantially parallel to the pivot direction V. The clearance between the pivot restricting ribs 23b may have a size that is equal to the width W1 precisely. Alternatively, the clearance between the pivot restricting ribs 23b may have a dimension defined by the width W1 added with a dimensional error of the width W1 or a dimension defined by the width W1 added with a position error of the insertion hole 40e.

As the conductive member <NUM> is interposed between the pivot restricting ribs 23b, the pivot restricting ribs 23b restrict pivoting of the conductive member <NUM> bidirectionally in the pivot direction V. According to the embodiment, the pivot restricting ribs 23b position and secure the conductive member <NUM> in the pivot direction V. Accordingly, the pivot restricting ribs 23b cause the conductive member <NUM> to contact the fixing belt <NUM> precisely, preventing failures such as formation of a banding image due to the alternating current voltage. Additionally, the pivot restricting ribs 23b facilitate installation of the conductive member <NUM> into the fixing device <NUM>.

As illustrated in <FIG>, the plurality of pivot restricting rib 23b may be disposed opposite one lateral end of the conductive member <NUM> in the pivot direction V thereof. Accordingly, the pivot restricting ribs 23b restrict the pivot range of the conductive member <NUM> with improved precision. According to the embodiment, the pivot restricting ribs 23b position and secure the conductive member <NUM> in the pivot direction V with improved precision. A number of the pivot restricting ribs 23b is determined arbitrarily. A number and an arrangement of the pivot restricting ribs 23b disposed opposite one lateral end of the conductive member <NUM> in the pivot direction V thereof may be different from a number and an arrangement of the pivot restricting ribs 23b disposed opposite another lateral end of the conductive member <NUM> in the pivot direction V thereof. The plurality of pivot restricting ribs 23b may be disposed opposite one lateral end or another lateral end of the conductive member <NUM> in the pivot direction V.

The embodiment of the present disclosure is preferably applied to the fixing device <NUM> incorporating the fixing belt <NUM> made of polyimide, for example. Since the fixing belt <NUM> is subject to deformation, the conductive member <NUM> is placed inside the fixing device <NUM> precisely. According to the embodiment, the conductive member <NUM> contacts the fixing belt <NUM> precisely. The embodiment of the present disclosure is preferably applied to the fixing device <NUM> incorporating the fixing belt <NUM> that is made of polyimide and does not include the elastic layer. Since the fixing belt <NUM> is also subject to deformation similarly, with application of the embodiment of the present disclosure, the conductive member <NUM> contacts the fixing belt <NUM> precisely.

The above describes examples in which the stay <NUM> and the heater holder <NUM> sandwich the conductive member <NUM>. Alternatively, the stay <NUM> and the heater holder <NUM> may not sandwich the conductive member <NUM>.

Referring to <FIG>, a detailed description is provided of a construction of the heater <NUM> of the fixing device <NUM>.

<FIG> is a plan view of the heater <NUM> according to the embodiment.

As illustrated in <FIG>, the base <NUM> is platy and has a mount face that mounts the plurality of resistive heat generators <NUM> (e.g., the four resistive heat generators <NUM>), feeders 33A and 33B serving as conductors, a first electrode 34A, and a second electrode 34B. The number of the resistive heat generators <NUM> is not limited to four.

<FIG> illustrates the longitudinal direction X of the heater <NUM> and the like, that is perpendicular to the paper surface in <FIG>. The longitudinal direction X also defines an arrangement direction in which the plurality of resistive heat generators <NUM> is arranged. <FIG> illustrates an orthogonal direction Y (e.g., a vertical direction in <FIG>) that is perpendicular to or intersects the arrangement direction of the resistive heat generators <NUM> and is different from a thickness direction of the base <NUM>. The orthogonal direction Y extends along the mount face of the base <NUM>, that mounts the resistive heat generators <NUM>. The orthogonal direction Y is parallel to a short direction of the heater <NUM> or the sheet conveyance direction A in which the sheet P is conveyed through the fixing device <NUM>.

The heater <NUM> includes a heat generation portion <NUM> that is divided into the plurality of resistive heat generators <NUM> arranged in the arrangement direction, that is, the longitudinal direction X of the heater <NUM>. The resistive heat generators <NUM> are electrically connected in parallel to a pair of electrodes, that is, the first electrode 34A and the second electrode 34B, through the feeders 33A and 33B. The first electrode 34A and the second electrode 34B are mounted on one lateral end (e.g., a left end in <FIG>) of the base <NUM> in the longitudinal direction X thereof. Each of the feeders 33A and 33B is made of a conductor having a resistance value smaller than a resistance value of the resistive heat generator <NUM>. The adjacent resistive heat generators <NUM> define a gap therebetween, that is <NUM> or greater, preferably <NUM> or greater, in view of ensuring insulation between the adjacent resistive heat generators <NUM>. If the gap between the adjacent resistive heat generators <NUM> is excessively great, the fixing belt <NUM> is subject to temperature decrease at an opposed portion thereof that is disposed opposite the gap. Hence, the gap is <NUM> or smaller, preferably <NUM> or smaller, in view of suppressing uneven temperature of the fixing belt <NUM> in the longitudinal direction X thereof.

The resistive heat generators <NUM> are made of a material having a positive temperature coefficient (PTC) property that is characterized in that the resistance value increases, that is, a heater output decreases, as the temperature increases.

Since the resistive heat generators <NUM> have the PTC property and the heat generation portion <NUM> is divided into the plurality of resistive heat generators <NUM> in the longitudinal direction X of the heater <NUM>, the heater <NUM> prevents overheating of the fixing belt <NUM> when sheets P having a decreased size are conveyed over the fixing belt <NUM>. For example, if a sheet P having a decreased width that is smaller than an entire length of the heat generation portion <NUM> in the longitudinal direction X of the heater <NUM> is conveyed through the fixing nip N, since the sheet P does not draw heat from the fixing belt <NUM> in an outboard span that is outboard from the sheet P in the longitudinal direction X of the fixing belt <NUM>, the resistive heat generators <NUM> in the outboard span are subject to temperature increase. Since a constant voltage is applied to the resistive heat generators <NUM>, when the temperature of the resistive heat generators <NUM> in the outboard span increases and the resistance value thereof increases, conversely, an output (e.g., a heat generation amount) of the resistive heat generators <NUM> decreases relatively, suppressing temperature increase of the resistive heat generators <NUM> that are disposed in both lateral end spans of the heat generation portion <NUM> in the longitudinal direction X thereof. Additionally, the plurality of resistive heat generators <NUM> is electrically connected in parallel, suppressing temperature increase in a non-conveyance span where the sheet P is not conveyed over the fixing belt <NUM> while the fixing device <NUM> retains a printing speed at which a toner image is fixed on the sheet P. Alternatively, the heat generation portion <NUM> may include heat generators other than the resistive heat generators <NUM> having the PTC property. The resistive heat generators <NUM> may be arranged in a plurality of columns in the orthogonal direction Y of the heater <NUM>.

As described above, the heat generation portion <NUM> is divided into the resistive heat generators <NUM> arranged in the longitudinal direction X of the heater <NUM>. Hence, the heater <NUM> suppresses temperature increase of the resistive heat generators <NUM> that are disposed in both lateral end spans of the heat generation portion <NUM> in the longitudinal direction X thereof, thus suppressing uneven temperature of the fixing belt <NUM> in the longitudinal direction X thereof. The fixing belt <NUM> has rigidity that changes as the temperature of the fixing belt <NUM> changes. Hence, the fixing belt <NUM> that decreases uneven temperature in the longitudinal direction X thereof advantageously contacts the conductive member <NUM> stably. Accordingly, the fixing device <NUM> according to the embodiment of the present disclosure employs the resistive heat generators <NUM> that are separated in the longitudinal direction X of the heater <NUM>. Alternatively, the fixing device <NUM> may employ the first thermal conductor <NUM> and second thermal conductors <NUM> described below with reference to <FIG> and <FIG>. Thus, the conductive member <NUM> preferably contacts the fixing belt <NUM> stably.

For example, the resistive heat generator <NUM> is produced as below. Silver-palladium (AgPd), glass powder, and the like are mixed into paste. The paste coats the base <NUM> by screen printing or the like. Thereafter, the base <NUM> is subject to firing. According to the embodiment, the resistive heat generator <NUM> has a resistance value of <NUM>Ω at an ambient temperature. Alternatively, the resistive heat generator <NUM> may be made of a resistive material such as a silver alloy (AgPt) and ruthenium oxide (RuO<NUM>). The feeders 33A and 33B, the first electrode 34A, and the second electrode 34B are made of a material prepared with silver (Ag) or silver-palladium (AgPd) by screen printing or the like. Each of the feeders 33A and 33B is made of a conductor having a resistance value smaller than a resistance value of the resistive heat generator <NUM>.

The base <NUM> is preferably made of ceramics, such as alumina and aluminum nitride, or a nonmetallic material, such as glass and mica, having an enhanced heat resistance and an enhanced insulation. According to the embodiment, the base <NUM> is made of alumina and has a short width of <NUM> in the orthogonal direction Y, a longitudinal length of <NUM> in the longitudinal direction X, and a thickness of <NUM>. Alternatively, the base <NUM> may include a conductive layer made of metal or the like and an insulating layer disposed on the conductive layer. The metal of the base <NUM> is preferably aluminum, stainless steel, or the like that is available at reduced costs. The base <NUM> made of a stainless steel plate suppresses breakage due to thermal stress. In order to improve evenness of heat conducted from the heater <NUM> so as to enhance quality of an image formed on a sheet P, the base <NUM> may be made of a material that has an increased thermal conductivity such as copper, graphite, and graphene.

The insulating layer <NUM> is made of heat-resistant glass and has a thickness of <NUM>, for example. The insulating layer <NUM> covers the resistive heat generators <NUM> and the feeders 33A and 33B and insulates and protects the resistive heat generators <NUM> and the feeders 33A and 33B. Additionally, the insulating layer <NUM> retains sliding of the fixing belt <NUM> over the heater <NUM>.

<FIG> is a diagram of the heater <NUM> according to the embodiment, illustrating a power supply circuit that supplies power to the heater <NUM>.

As illustrated in <FIG>, according to the embodiment, the power supply circuit for supplying power to the resistive heat generators <NUM> includes the alternating current power supply <NUM> that is electrically connected to the first electrode 34A and the second electrode 34B of the heater <NUM>. The power supply circuit further includes a triac <NUM> that controls an amount of power supplied to the resistive heat generators <NUM>. The power supply circuit further includes a controller <NUM> that controls the amount of power supplied to each of the resistive heat generators <NUM> through the triac <NUM> based on temperatures of the resistive heat generators <NUM>, that are detected by the thermistors <NUM>, respectively. The controller <NUM> includes a microcomputer that includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input-output (I/O) interface.

According to the embodiment, the thermistors <NUM> are disposed opposite a center span of the heater <NUM> in the longitudinal direction X thereof, that is, a minimum sheet conveyance span where a minimum size sheet P available in the fixing device <NUM> is conveyed, and one lateral end span of the heater <NUM> in the longitudinal direction X thereof, respectively. The fixing device <NUM> further includes a thermostat <NUM> that is disposed opposite one lateral end span of the heater <NUM> in the longitudinal direction X thereof. The thermostat <NUM> serves as a power breaker that interrupts supplying power to the resistive heat generators <NUM> when a temperature of the resistive heat generator <NUM> is a predetermined temperature or higher. The thermistors <NUM> and the thermostat <NUM> contact the first thermal conductor <NUM> to detect a temperature of the first thermal conductor <NUM>.

According to the embodiment, the first electrode 34A and the second electrode 34B are disposed in an identical lateral end span of the heater <NUM> in the longitudinal direction X thereof. Alternatively, the first electrode 34A and the second electrode 34B may be disposed in one lateral end span and another lateral end span of the heater <NUM> in the longitudinal direction X thereof, respectively. The resistive heat generator <NUM> may have shapes that are not limited to a shape according to the embodiment. For example, <FIG> illustrates a heater 22A that includes resistive heat generators 31A each of which is rectangular. <FIG> illustrates a heater 22B that includes resistive heat generators 31B each of which includes a linear portion. The linear portion turns to define a parallelogram substantially. As illustrated in <FIG>, the heater 22A includes an extension that extends from the resistive heat generator 31A having a block shape to the feeder 33A or 33B in the orthogonal direction Y. The extension may be a part of the resistive heat generator 31A or may be made of a material equivalent to a material of the feeder 33A or 33B.

<FIG> is a diagram illustrating a temperature profile of the fixing belt <NUM> in the longitudinal direction X thereof. <FIG> illustrates, in a section (a), an arrangement of the resistive heat generators <NUM> of the heater <NUM>. <FIG> illustrates, in a section (b), a vertical axis that represents a temperature T of the fixing belt <NUM> and a horizontal axis that represents the longitudinal direction X of the fixing belt <NUM>.

As illustrated in the sections (a) and (b) in <FIG>, the heater <NUM> includes the plurality of resistive heat generators <NUM> separated and arranged in the longitudinal direction X of the heater <NUM> to produce a gap B (e.g., a dividing region) between the adjacent resistive heat generators <NUM> in the longitudinal direction X of the heater <NUM>. In other words, the plurality of resistive heat generators <NUM> of the heater <NUM> is arranged with the gap B between the adjacent resistive heat generators <NUM>. The gap B defines a dividing region or a dividing span. An opposed portion of the resistive heat generators <NUM>, that is disposed opposite the gap B, occupies an area smaller than an area of other portion of each of the resistive heat generators <NUM>, thus generating a decreased amount of heat. Accordingly, an opposed portion of the fixing belt <NUM>, that is disposed opposite the gap B, has a lower temperature compared to other portion of the fixing belt <NUM>, causing uneven temperature of the fixing belt <NUM> in the longitudinal direction X thereof. The adjacent resistive heat generators <NUM> define an enlarged gap region C (e.g., an enlarged dividing region) encompassing the gap B, serving as the dividing region, and a peripheral region thereof. The heater <NUM> and the fixing belt <NUM> suffer from temperature decrease also in opposed portions thereof, that are disposed opposite the enlarged gap region C, respectively. Similarly, the heater <NUM> suffers from temperature decrease also in an opposed portion thereof, that is disposed opposite the gap B. As illustrated in an enlarged view in the section (a) in <FIG>, the gap B indicates a region encompassing an entirety of the dividing region between the adjacent resistive heat generators <NUM> serving as a main heat generation portion of the heater <NUM> in the longitudinal direction X thereof. The resistive heat generator <NUM> includes a joint <NUM> that is coupled with the feeder 33A or 33B. The enlarged gap region C encompasses the joints <NUM> in addition to the gap B. The joint <NUM> defines a part of the resistive heat generator <NUM>, that extends substantially in the orthogonal direction Y of the heater <NUM> and is coupled with the feeder 33A or 33B.

<FIG> illustrates the heater 22A depicted in <FIG> that includes the resistive heat generators 31A that are rectangular. In the heater 22A also, a temperature of an opposed portion of the heater 22A, that is disposed opposite the gap B, is lower than a temperature of other portion of the heater 22A. <FIG> illustrates a heater 22C that includes a plurality of resistive heat generators 31C that is zigzag. In the heater 22C also, a temperature of an opposed portion of the heater 22C, that is disposed opposite the gap B, is lower than a temperature of other portion of the heater 22C. <FIG> illustrates the heater 22B depicted in <FIG> that includes the resistive heat generators 31B including the linear portion that defines the parallelogram. In the heater 22B also, a temperature of an opposed portion of the heater 22B, that is disposed opposite the gap B, is lower than a temperature of other portion of the heater 22B. As illustrated in <FIG>, <FIG>, the adjacent resistive heat generators <NUM>, 31C, and 31B overlap each other in the longitudinal direction X of the heaters <NUM>, 22C, and 22B, suppressing temperature decrease of the opposed portion of each of the heaters <NUM>, 22C, and 22B, that is disposed opposite the gap B, compared to other portion of each of the heaters <NUM>, 22C, and 22B.

The fixing device <NUM> according to the embodiment incorporates the first thermal conductor <NUM> that suppresses temperature decrease at the gap B and thereby suppresses uneven temperature of the fixing belt <NUM> in the longitudinal direction X thereof.

A description is provided of a configuration of the first thermal conductor <NUM> in detail.

As illustrated in <FIG>, the first thermal conductor <NUM> is interposed between the heater <NUM> and the stay <NUM> in the horizontal direction in <FIG>. Specifically, the first thermal conductor <NUM> is sandwiched between the heater <NUM> and the heater holder <NUM>. For example, the first thermal conductor <NUM> has one face that contacts a back face of the base <NUM> of the heater <NUM> and another face that contacts the heater holder <NUM>.

The stay <NUM> includes the two arms 24a (e.g., perpendicular portions) that extend in a thickness direction of the heater <NUM> and the like. Each of the arms 24a has a contact face that contacts the heater holder <NUM> directly or is disposed opposite the heater holder <NUM> via the conductive member <NUM> indirectly, thus supporting the heater holder <NUM>, the first thermal conductor <NUM>, and the heater <NUM>. The contact faces of the arms 24a are disposed outboard from the resistive heat generators <NUM> in the orthogonal direction Y (e.g., a vertical direction in <FIG>) of the heater <NUM>. Thus, the stay <NUM> suppresses conduction of heat thereto from the heater <NUM>, causing the heater <NUM> to heat the fixing belt <NUM> efficiently.

As illustrated in <FIG>, the first thermal conductor <NUM> is a plate having a thickness of <NUM>, a length of <NUM> in the longitudinal direction X of the first thermal conductor <NUM>, and a width of <NUM> in the orthogonal direction Y. According to the embodiment, the first thermal conductor <NUM> is constructed of a single plate. Alternatively, the first thermal conductor <NUM> may be constructed of a plurality of members. <FIG> omits illustration of the guide <NUM> and the guide rib <NUM> depicted in <FIG>.

The first thermal conductor <NUM> is fitted to the recess 23e of the heater holder <NUM>. The heater <NUM> is attached to the heater holder <NUM> from above the first thermal conductor <NUM>. Thus, the heater holder <NUM> and the heater <NUM> sandwich and hold the first thermal conductor <NUM>. According to the embodiment, the first thermal conductor <NUM> has a length in the longitudinal direction X thereof, which is equivalent to a length of the heater <NUM> in the longitudinal direction X thereof. The heater holder <NUM> includes side walls 23e1, serving as longitudinal direction restrictors, that are disposed at both lateral ends of the heater holder <NUM> in the longitudinal direction X thereof, respectively, and define the recess 23e. The side walls 23e1 restrict motion of the first thermal conductor <NUM> and the heater <NUM> in the longitudinal direction X thereof. Thus, the side walls 23e1 restrict shifting of the first thermal conductor <NUM> in the longitudinal direction X thereof inside the fixing device <NUM>, improving efficiency in thermal conduction in a target span in the longitudinal direction X of the first thermal conductor <NUM>. The heater holder <NUM> further includes side walls 23e2, serving as orthogonal direction restrictors, that are disposed at both ends of the heater holder <NUM> in the orthogonal direction Y thereof, respectively, and define the recess 23e. The side walls 23e2 restrict motion of the first thermal conductor <NUM> and the heater <NUM> in the orthogonal direction Y thereof.

The first thermal conductor <NUM> may extend in a span other than a span in which the first thermal conductor <NUM> extends in the longitudinal direction X thereof as illustrated in <FIG>. For example, <FIG> illustrates a fixing device 9B incorporating a first thermal conductor 28A that extends in a span that is hatched in <FIG> and is defined by the heat generation portion <NUM> in the longitudinal direction X of the heater <NUM>. <FIG> illustrates a fixing device 9C incorporating first thermal conductors 28B. Each of the first thermal conductors 28B is disposed opposite and spans an entire span of the gap B in the longitudinal direction X of the heater 22A in which the resistive heat generators 31A are arranged. <FIG> illustrates the resistive heat generators 31A shifted from the first thermal conductors 28B vertically in <FIG> for convenience. Practically, the resistive heat generators 31A are substantially leveled with the first thermal conductors 28B in the orthogonal direction Y of the heater 22A. Alternatively, the first thermal conductors 28B may be disposed with respect to the resistive heat generators 31A with other arrangement. For example, the first thermal conductor 28B may span or cover a part of the resistive heat generator 31A in the orthogonal direction Y of the heater 22A. <FIG> illustrates a fixing device 9D incorporating a first thermal conductor 28C that spans or covers an entirety of the resistive heat generator 31A in the orthogonal direction Y of the heater 22A.

As illustrated in <FIG>, the first thermal conductor 28C is disposed opposite and spans the gap B in the longitudinal direction X of the heater 22A. Additionally, the first thermal conductor 28C bridges the adjacent resistive heat generators 31A that sandwich the gap B. A state in which the first thermal conductor 28C bridges the adjacent resistive heat generators 31A denotes a state in which the first thermal conductor 28C overlaps the adjacent resistive heat generators 31A at least partially in the longitudinal direction X of the heater 22A. Alternatively, the first thermal conductors 28C may be disposed opposite the gaps B of the heater 22A, respectively. Yet alternatively, for example, as illustrated in <FIG>, the first thermal conductor 28C may be disposed opposite a part of the gaps B, for example, one of the gaps B. A state in which the first thermal conductor 28C spans the gap B in the longitudinal direction X of the heater 22A denotes that at least a part of the first thermal conductor 28C overlaps the gap B in the longitudinal direction X of the heater 22A.

As illustrated in <FIG>, as the pressure roller <NUM> applies pressure to a heater (e.g., the heaters <NUM>, 22A, 22B, and 22C), the heater and the heater holder <NUM> sandwich a first thermal conductor (e.g., the first thermal conductors <NUM>, 28A, 28B, and 28C) such that the first thermal conductor contacts the heater and the heater holder <NUM>. As the first thermal conductor contacts the heater, the first thermal conductor conducts heat generated by the heater in the longitudinal direction X thereof with improved efficiency. The first thermal conductor is disposed opposite at least one gap B between adjacent resistive heat generators (e.g., the resistive heat generators <NUM>, 31A, 31B, and 31C) arranged in the longitudinal direction X of the heater. Thus, the first thermal conductor improves efficiency in conduction of heat at the gaps B, increases an amount of heat conducted to the gaps B, and increases the temperature of the heater at the gaps B arranged in the longitudinal direction X of the heater, thus suppressing uneven temperature of the heater in the longitudinal direction X thereof. Accordingly, the first thermal conductor suppresses uneven temperature of the fixing belt <NUM> in the longitudinal direction X thereof. Consequently, the fixing belt <NUM> suppresses uneven fixing and uneven gloss of a toner image fixed on a sheet P. The heater does not heat the fixing belt <NUM> redundantly to attain sufficient fixing performance at the gaps B, causing a fixing device (e.g., the fixing devices <NUM>, 9B, 9C, and 9D) to save energy. The first thermal conductor extends throughout an entire span of the heat generation portion <NUM> in the longitudinal direction X of the heater. Accordingly, the first thermal conductor improves efficiency in conduction of heat of the heater in an entirety of a main heating span of the heater disposed opposite an imaging span of a toner image formed on a sheet P conveyed through the fixing nip N. Consequently, the first thermal conductor suppresses uneven temperature of the heater and the fixing belt <NUM> in the longitudinal direction X thereof.

According to the embodiment, the first thermal conductor is coupled with the resistive heat generators having the PTC property described above, suppressing overheating of the fixing belt <NUM> in the non-conveyance span where a sheet P having a decreased size is not conveyed effectively. For example, the PTC property suppresses an amount of heat generated by the resistive heat generators in the non-conveyance span. Additionally, the first thermal conductor efficiently conducts heat from the non-conveyance span on the fixing belt <NUM> that suffers from temperature increase to a sheet conveyance span on the fixing belt <NUM>, where the sheet P is conveyed, thus suppressing overheating of the fixing belt <NUM> in the non-conveyance span effectively.

Since the heater generates heat in a decreased amount at the gap B between the adjacent resistive heat generators, the heater has a decreased temperature also in a periphery of the gap B. To address the circumstance, the first thermal conductor is preferably disposed also in the periphery of the gap B. For example, according to the embodiment illustrated in the section (a) of <FIG>, the first thermal conductor <NUM> is disposed opposite the enlarged gap region C. Hence, the first thermal conductor <NUM> improves efficiency in conduction of heat at the gap B and the periphery thereof in the longitudinal direction X of the heater <NUM>, suppressing uneven temperature of the heater <NUM> in the longitudinal direction X thereof. According to the embodiment, the first thermal conductor <NUM> extends throughout the entire span of the heat generation portion <NUM> in the longitudinal direction X of the heater <NUM>. Accordingly, the first thermal conductor <NUM> suppresses uneven temperature of the heater <NUM> and the fixing belt <NUM> in the longitudinal direction X thereof more effectively.

A description is provided of a construction of a fixing device 9E according to an embodiment of the present disclosure.

As illustrated in <FIG>, the fixing device 9E according to the embodiment includes the second thermal conductors <NUM> and a heater holder 23A. The second thermal conductors <NUM> are sandwiched between the heater holder 23A and the first thermal conductor <NUM>. Each of the second thermal conductors <NUM> is disposed at a position different from a position of the first thermal conductor <NUM> in a laminating direction (e.g., a horizontal direction in <FIG>) in which the stay <NUM>, the heater holder 23A, the second thermal conductor <NUM>, the first thermal conductor <NUM>, and the heater <NUM> are arranged. Specifically, the second thermal conductors <NUM> are superimposed on the first thermal conductor <NUM>. Unlike <FIG> illustrating the fixing device <NUM>, <FIG> illustrates a cross section that crosses a longitudinal direction of the fixing device 9E in which the second thermal conductors <NUM> are arranged. For example, <FIG> illustrates the cross section where the second thermal conductor <NUM> is disposed and the thermistor <NUM> is not disposed.

The second thermal conductor <NUM> is made of a material having a thermal conductivity greater than a thermal conductivity of the base <NUM>. For example, the second thermal conductor <NUM> is made of graphene or graphite. According to the embodiment, the second thermal conductor <NUM> is a graphite sheet having a thickness of <NUM>. Alternatively, the second thermal conductor <NUM> may be a plate made of aluminum, copper, silver, or the like.

As illustrated in <FIG>, the plurality of second thermal conductors <NUM> is arranged on a plurality of parts on the heater holder 23A in the longitudinal direction X thereof, respectively. The heater holder 23A includes a recess 23eA that includes cavities placed with the second thermal conductors <NUM>, respectively. The cavities are stepped down by one step from other portion of the recess 23eA. The second thermal conductor <NUM> and the heater holder 23A define a gap therebetween at both lateral ends of the second thermal conductor <NUM> in the longitudinal direction X of the heater holder 23A. Thus, the second thermal conductor <NUM> suppresses conduction of heat to the heater holder 23A from both lateral ends of the second thermal conductor <NUM> in the longitudinal direction X of the heater holder 23A, causing the heater <NUM> to heat the fixing belt <NUM> efficiently. <FIG> omits illustration of the guide <NUM> depicted in <FIG>.

As illustrated in <FIG>, the second thermal conductor <NUM> that is hatched is disposed opposite the gap B between the adjacent resistive heat generators <NUM> and overlaps at least a part of the adjacent resistive heat generators <NUM> in the longitudinal direction X of the heater <NUM>. According to the embodiment, the second thermal conductor <NUM> extends throughout the entire span of the gap B. <FIG> and <FIG> referred to in a description below illustrate the first thermal conductor <NUM> that is disposed opposite and spans the heat generation portion <NUM> in the longitudinal direction X of the heater <NUM>. Alternatively, the first thermal conductor <NUM> may span differently as described above.

The fixing device 9E according to the embodiment includes, in addition to the first thermal conductor <NUM>, the second thermal conductors <NUM> each of which is disposed opposite the gap B and overlaps at least a part of the adjacent resistive heat generators <NUM> in the longitudinal direction X of the heater <NUM>. The second thermal conductors <NUM> improve efficiency in conduction of heat at the gaps B in the longitudinal direction X of the heater <NUM>, suppressing uneven temperature of the heater <NUM> in the longitudinal direction X thereof more effectively.

<FIG> illustrates a fixing device 9F including the first thermal conductors 28B, second thermal conductors 36D, and the heater 22A including the resistive heat generators 31A. The first thermal conductor 28B and the second thermal conductor 36D are preferably disposed opposite the entire span of the gap B in the longitudinal direction X of the heater 22A. Accordingly, the first thermal conductor 28B and the second thermal conductor 36D improve efficiency in conduction of heat at the gap B compared to an outboard region of the heater 22A, which is other than the gap B. <FIG> illustrates the resistive heat generators 31A shifted from the first thermal conductors 28B and the second thermal conductors 36D vertically in <FIG> for convenience. Practically, the resistive heat generators 31A are substantially leveled with the first thermal conductors 28B and the second thermal conductors 36D in the orthogonal direction Y of the heater 22A. Alternatively, the first thermal conductors 28B and the second thermal conductors 36D may be disposed with respect to the resistive heat generators 31A with other arrangement. For example, the first thermal conductor 28B and the second thermal conductor 36D may span a part of the resistive heat generator 31A in the orthogonal direction Y of the heater 22A.

Unlike the embodiment described above, according to an embodiment of the present disclosure, each of a first thermal conductor (e.g., the first thermal conductors <NUM>, 28A, 28B, and 28C) and a second thermal conductor (e.g., the second thermal conductors <NUM> and 36D) is made of a graphene sheet. Hence, each of the first thermal conductor and the second thermal conductor has an enhanced thermal conductivity in a predetermined direction along a surface of the graphene sheet, that is, a longitudinal direction of a heater (e.g., the heaters <NUM>, 22A, 22B, and 22C), not a thickness direction of the first thermal conductor and the second thermal conductor. Accordingly, the first thermal conductor and the second thermal conductor suppress uneven temperature of the heater and the fixing belt <NUM> in the longitudinal direction X thereof effectively.

Graphene is thin powder. As illustrated in <FIG>, graphene is constructed of a plane of carbon atoms arranged in a two-dimensional honeycomb lattice. The graphene sheet is graphene in a sheet form and is usually constructed of a single layer. The graphene sheet may contain impurities in the single layer of carbon atoms. The graphene sheet may have a fullerene structure. The fullerene structure is generally recognized as a polycyclic compound constructed of an identical number of carbon atoms bonded to form a cage with fused rings of five and six atoms. For example, the fullerene structure is a closed cage structure formed of fullerene C<NUM>, C<NUM>, and C<NUM>, <NUM>-coordinated carbon atoms, or the like.

The graphene sheet is artificial and is produced by chemical vapor deposition (CVD), for example.

The graphene sheet is commercially available. A size and a thickness of the graphene sheet and a number of layers and the like of the graphite sheet described below are measured with a transmission electron microscope (TEM), for example.

Graphite is constructed of stacked layers of graphene and is highly anisotropic in thermal conduction. As illustrated in <FIG>, graphite has a plurality of layers, each of which is constructed of hexagonal fused rings of carbon atoms, that are bonded planarly. The plurality of layers defines a crystalline structure. In the crystalline structure, adjacent carbon atoms in the layer are bonded with each other by a covalent bond. Bonding between layers of carbon atoms is established by the van der Waals bond. The covalent bond achieves bonding greater than bonding by the van der Waals bond. Graphite is highly anisotropic with bonding within the layer and bonding between the layers. For example, a first thermal conductor (e.g., the first thermal conductors <NUM>, 28A, 28B, and 28C) or a second thermal conductor (e.g., the second thermal conductors <NUM> and 36D) is made of graphite. Accordingly, the first thermal conductor or the second thermal conductor attains an efficiency in conduction of heat in the longitudinal direction X of a heater (e.g., the heaters <NUM>, 22A, 22B, and 22C), which is greater than an efficiency in conduction of heat in a thickness direction, that is, the laminating direction (e.g., the horizontal direction in <FIG>) in which the stay <NUM>, the heater holder 23A, the second thermal conductor <NUM>, the first thermal conductor <NUM>, and the heater <NUM> are arranged, thus suppressing conduction of heat to the heater holder 23A. Consequently, the first thermal conductor or the second thermal conductor suppresses uneven temperature of the heater in the longitudinal direction X thereof efficiently. Additionally, the first thermal conductor or the second thermal conductor minimizes heat conducted to the heater holder 23A. The first thermal conductor or the second thermal conductor that is made of graphite attains enhanced heat resistance that inhibits oxidation at approximately <NUM> degrees Celsius.

The graphite sheet has a physical property and a dimension that are adjusted properly according to a function of the first thermal conductor or the second thermal conductor. For example, the graphite sheet is made of graphite having enhanced purity or single crystal graphite. The graphite sheet has an increased thickness to enhance anisotropic thermal conduction. In order to perform high speed fixing, a fixing device (e.g., the fixing devices 9E and 9F) employs the graphite sheet having a decreased thickness to decrease thermal capacity of the fixing device. If the fixing nip N and the heater have an increased length in the longitudinal direction X thereof, the first thermal conductor or the second thermal conductor also has an increased length in the longitudinal direction X of the heater.

In view of increasing mechanical strength, the graphite sheet preferably has a number of layers that is not smaller than <NUM> layers. The graphite sheet may include a part constructed of a single layer and another part constructed of a plurality of layers.

The second thermal conductor <NUM> is disposed opposite the gap B between the adjacent resistive heat generators <NUM> and the enlarged gap region C depicted in <FIG> and overlaps at least a part of the adjacent resistive heat generators <NUM> in the longitudinal direction X of the heater <NUM>. Hence, the second thermal conductor <NUM> may be positioned with respect to the resistive heat generators <NUM> differently from the second thermal conductor <NUM> depicted in <FIG>. For example, <FIG> illustrates a fixing device <NUM> including a second thermal conductor 36A that protrudes beyond the base <NUM> bidirectionally in the orthogonal direction Y of the heater <NUM>. The fixing device <NUM> further includes a second thermal conductor 36B that is disposed in a span of the resistive heat generator <NUM> in the orthogonal direction Y of the heater <NUM>. The fixing device <NUM> further includes a second thermal conductor 36C that spans a part of the gap B.

<FIG> illustrates a fixing device <NUM> according to an embodiment of the present disclosure that includes a heater holder 23B including a retracted portion 23c (e.g., a clearance) that is interposed between the first thermal conductor <NUM> and a body of the heater holder 23B in a thickness direction of the heater holder 23B (e.g., a horizontal direction in <FIG>). For example, the retracted portion 23c is disposed in a part of the recess 23eA depicted in <FIG>, which accommodates the heater <NUM>, the first thermal conductor <NUM>, and the second thermal conductors <NUM>. A part of the recess 23eA is stepped down from other part of the recess 23eA, that accommodates the first thermal conductor <NUM>, to produce the retracted portion 23c serving as a thermal insulation layer. The part of the recess 23eA spans a part or an entirety of the heater holder 23B, that is disposed outboard from the second thermal conductor <NUM> in the longitudinal direction X of the heater <NUM>, and spans a part of the heater holder 23B in the orthogonal direction Y of the heater <NUM>. Accordingly, the heater holder 23B contacts the first thermal conductor <NUM> with a decreased contact area, thus suppressing conduction of heat from the first thermal conductor <NUM> to the heater holder 23B and causing the heater <NUM> to heat the fixing belt <NUM> efficiently. On a cross section that intersects a longitudinal direction of the fixing device <NUM> and is provided with the second thermal conductor <NUM>, the second thermal conductor <NUM> contacts the heater holder 23B like the second thermal conductor <NUM> of the fixing device 9E according to the embodiment described above with reference to <FIG>.

According to the embodiment, the retracted portion 23c spans an entirety of the resistive heat generator <NUM> in the orthogonal direction Y (e.g., a vertical direction in <FIG>) of the heater <NUM>. Thus, the retracted portion 23c suppresses conduction of heat from the first thermal conductor <NUM> to the heater holder 23B, causing the heater <NUM> to heat the fixing belt <NUM> efficiently. Alternatively, instead of the retracted portion 23c that defines the clearance, the fixing device <NUM> may incorporate a thermal insulator that has a thermal conductivity smaller than a thermal conductivity of the heater holder 23B, as the thermal insulation layer.

According to the embodiments described above, the second thermal conductor <NUM> is provided separately from the first thermal conductor <NUM>. Alternatively, the fixing device <NUM> may have other configuration. For example, the first thermal conductor <NUM> may include an opposed portion that is disposed opposite the gap B and has a thickness greater than a thickness of an outboard portion of the first thermal conductor <NUM>, which is other than the opposed portion. Thus, the opposed portion of the first thermal conductor <NUM> is equivalent to the second thermal conductor <NUM>.

The fixing devices 9E and <NUM> depicted in <FIG> and <FIG>, respectively, also incorporate the pivot restrictor such as the pivot restricting rib 23b that suppresses pivoting and resultant shifting of the conductive member <NUM>.

The above describes the embodiments of the present disclosure. However, the technology of the present disclosure is not limited to the embodiments described above. For example, the embodiments may be modified within the scope of the technology of the present disclosure.

The embodiments of the present disclosure are also applied to fixing devices 9I, 9J, and <NUM> illustrated in <FIG>, and <FIG>, respectively, other than the fixing devices <NUM>, 9B, 9C, 9D, 9E, 9F, <NUM>, and <NUM> described above. Referring to <FIG>, and <FIG>, the following describes a construction of each of the fixing devices 9I, 9J, and <NUM> briefly.

A description is provided of the construction of the fixing device 9I.

As illustrated in <FIG>, the fixing device 9I includes a pressing roller <NUM> that is disposed opposite the pressure roller <NUM> via the fixing belt <NUM>. The pressing roller <NUM> serves as an opposed rotator that is disposed opposite the fixing belt <NUM> serving as a rotator and rotates. The pressing roller <NUM> and the heater <NUM> sandwich the fixing belt <NUM> such that the heater <NUM> heats the fixing belt <NUM>. The fixing device 9I further includes a nip formation pad <NUM> that is disposed opposite the inner circumferential face 20a of the fixing belt <NUM> and is disposed opposite the pressure roller <NUM> via the fixing belt <NUM>. The stay <NUM> supports the nip formation pad <NUM>. The nip formation pad <NUM> and the pressure roller <NUM> sandwich the fixing belt <NUM> to form the fixing nip N between the fixing belt <NUM> and the pressure roller <NUM>.

The guide ribs <NUM> are disposed at an upstream part and a downstream part of the nip formation pad <NUM>, respectively, in the rotation direction J of the fixing belt <NUM>. The conductive member <NUM> is interposed between the upstream, guide rib <NUM> and the stay <NUM>. For example, the upstream, guide rib <NUM> includes a first opposed face 260d serving as a first opposed member. The stay <NUM> includes a second opposed face 24f serving as a second opposed member. The opposed portion 40c of the conductive member <NUM> is disposed opposite the first opposed face 260d and the second opposed face 24f. The opposed portion 40c extends along the first opposed face 260d and the second opposed face 24f. The free end 40b of the conductive member <NUM> contacts the inner circumferential face 20a of the fixing belt <NUM> serving as the rotator.

A description is provided of the construction of the fixing device 9J.

The fixing device 9J illustrated in <FIG> omits the pressing roller <NUM> depicted in <FIG>. In order to attain a contact length with which the heater <NUM> contacts the fixing belt <NUM> in the circumferential direction thereof, the heater <NUM> is an arc having a curvature that is equivalent to a curvature of the fixing belt <NUM>. Other construction of the fixing device 9J is equivalent to the construction of the fixing device 9I depicted in <FIG>.

A description is provided of the construction of the fixing device <NUM>.

As illustrated in <FIG>, the fixing device <NUM> includes a heating assembly <NUM>, a fixing roller <NUM> serving as a fixing rotator, and a pressure assembly <NUM> serving as an opposed pressure assembly. The heating assembly <NUM> includes the heater <NUM>, the first thermal conductor <NUM>, the heater holder <NUM>, and the stay <NUM> that are described in the embodiments above and a heating belt <NUM>. The fixing roller <NUM> presses against the heating belt <NUM> to form a heating nip N1 therebetween. The fixing device <NUM> further includes a pressure belt <NUM> serving as a belt. The fixing roller <NUM> serves as an opposed rotator that is disposed opposite the pressure belt <NUM> and rotates. The fixing roller <NUM> includes a core metal 93a, an elastic layer 93b, and a release layer 93c. The core metal 93a is solid and is made of iron. The elastic layer 93b is disposed on a surface of the core metal 93a. The release layer 93c is disposed on an outer face of the elastic layer 93b. The pressure assembly <NUM> is disposed opposite the heating assembly <NUM> via the fixing roller <NUM>. The pressure assembly <NUM> includes a nip formation pad <NUM>, a stay <NUM>, and the pressure belt <NUM>. The stay <NUM> serves as a support that supports the nip formation pad <NUM>. The pressure belt <NUM> rotates and is formed into a loop within which the nip formation pad <NUM> and the stay <NUM> are disposed. The pressure belt <NUM> and the fixing roller <NUM> define a fixing nip N2 therebetween. As a sheet P is conveyed through the fixing nip N2, the fixing roller <NUM> heated at the heating nip N1 and the pressure belt <NUM> fix a toner image formed on the sheet P thereon under heat and pressure. The pressure belt <NUM> rotates in a rotation direction J97.

The fixing device <NUM> further includes guide ribs <NUM> that are disposed at an upstream part and a downstream part of the nip formation pad <NUM>, respectively, in the rotation direction J97 of the pressure belt <NUM>. A plurality of guide ribs <NUM> is arranged in a longitudinal direction of the pressure belt <NUM>. Each of the guide ribs <NUM> is substantially fan-shaped. The guide rib <NUM> includes a belt opposed face 261a that is disposed opposite an inner circumferential face 97a of the pressure belt <NUM>. The belt opposed face 261a is an arc or a projecting curved face that projects toward the pressure belt <NUM> and extends in a circumferential direction of the pressure belt <NUM>.

The conductive member <NUM> is interposed between the stay <NUM> and the downstream, guide rib <NUM>. The positioning pin 23a holds the fixed end 40a of the conductive member <NUM>. The free end 40b of the conductive member <NUM> contacts the inner circumferential face 97a of the pressure belt <NUM>. If each of the release layer 93c serving as a surface layer of the fixing roller <NUM> and the heating belt <NUM> is made of a conductive material, the conductive member <NUM> may be interposed between the stay <NUM> and the guide rib <NUM> like the conductive member <NUM> of the fixing device <NUM> depicted in <FIG>. In this case, the free end 40b of the conductive member <NUM> contacts an inner circumferential face of the heating belt <NUM> serving as a belt.

The fixing devices 9I, 9J, and <NUM> depicted in <FIG>, and <FIG>, respectively, also incorporate the pivot restrictor such as the pivot restricting rib 23b that suppresses pivoting and resultant shifting of the conductive member <NUM>.

Application of the technology of the present disclosure is not limited to the color image forming apparatus <NUM> depicted in <FIG> that forms a color toner image. The technology of the present disclosure is also applied to a monochrome image forming apparatus that forms a monochrome toner image, a copier, a printer, a facsimile machine, a multifunction peripheral (MFP) having at least two of copying, printing, facsimile, scanning, and plotter functions, or the like.

For example, as illustrated in <FIG>, an image forming apparatus 100A according to an embodiment of the present disclosure includes an image forming device <NUM> including a photoconductive drum, a sheet conveyance device including the timing roller pair <NUM>, the sheet feeder <NUM>, a fixing device <NUM>, the output device <NUM>, and a scanner <NUM>. The sheet feeder <NUM> includes a plurality of sheet trays (e.g., paper trays) that loads a plurality of sheets P having different sizes, respectively.

The scanner <NUM> reads an image on an original Q into image data. The sheet feeder <NUM> loads the plurality of sheets P and feeds the sheets P to a sheet conveyance path one by one. The timing roller pair <NUM> conveys the sheet P conveyed through the sheet conveyance path to the image forming device <NUM>.

The image forming device <NUM> forms a toner image on the sheet P. For example, the image forming device <NUM> includes the photoconductive drum, a charging roller, an exposure device, a developing device, a replenishing device, a transfer roller, a cleaner, and a discharger. The toner image is a reproduction of the image on the original Q, for example. The fixing device <NUM> fixes the toner image on the sheet P under heat and pressure. The sheet P bearing the fixed toner image is conveyed to the output device <NUM> by a conveyance roller and the like. The output device <NUM> ejects the sheet P onto an outside of the image forming apparatus 100A.

A description is provided of a construction of the fixing device <NUM> according to an embodiment of the present disclosure.

A description of elements of the fixing device <NUM>, which are common to the fixing device <NUM> depicted in <FIG>, is omitted properly.

As illustrated in <FIG>, the fixing device <NUM> includes the fixing belt <NUM>, the pressure roller <NUM>, a heater 22D, a heater holder 23B, the stay <NUM>, the thermistors <NUM> depicted in <FIG>, the first thermal conductor <NUM>, and the conductive member <NUM>.

The fixing belt <NUM> and the pressure roller <NUM> define the fixing nip N therebetween. The fixing nip N has a nip width of <NUM> in the sheet conveyance direction A. The fixing belt <NUM> and the pressure roller <NUM> convey the sheet P at a linear velocity of <NUM>/s.

The fixing belt <NUM> includes the base layer made of polyimide and the release layer and does not include an elastic layer. The release layer is heat-resistant film made of fluororesin, for example. The fixing belt <NUM> has an outer diameter of approximately <NUM>.

The pressure roller <NUM> includes the core metal 21a, the elastic layer 21b, and the release layer 21c. The pressure roller <NUM> has an outer diameter in a range of from <NUM> to <NUM>. The elastic layer 21b has a thickness in a range of from <NUM> to <NUM>.

As illustrated in <FIG>, the heater 22D includes the base <NUM>, a thermal insulation layer, a conductor layer including the resistive heat generators 31A, and an insulating layer. The heater 22D has a total thickness of <NUM>. The heater 22D has a width of <NUM> in the orthogonal direction Y thereof.

As illustrated in <FIG>, the conductive member <NUM> is interposed between the stay <NUM> and the downstream, guide rib <NUM>. Like the conductive member <NUM> of the fixing device <NUM> depicted in <FIG>, the fixed end 40a of the conductive member <NUM> is held by the positioning pin 23a. The free end 40b of the conductive member <NUM> contacts the inner circumferential face 20a of the fixing belt <NUM>.

As illustrated in <FIG>, the conductor layer of the heater 22D includes the plurality of resistive heat generators 31A, a plurality of feeders <NUM>, the first electrode 34A, the second electrode 34B, and a third electrode 34C. According to the embodiment also, as illustrated in an enlarged view in <FIG>, the gap B serving as the dividing region is interposed between the adjacent resistive heat generators 31A arranged in the longitudinal direction X of the heater 22D. <FIG> illustrates the two gaps B in the enlarged view. However, the gap B is disposed at each interval between the adjacent resistive heat generators 31A depicted in <FIG>. The heater 22D further includes three heat generation portions 35A, 35B, and 35C each of which is constructed of the resistive heat generators 31A. As the first electrode 34A and the second electrode 34B are energized, the heat generation portions 35A and 35C generate heat. As the first electrode 34A and the third electrode 34C are energized, the heat generation portion 35B generates heat. Thus, the heat generation portion 35B disposed in a center span of the heater 22D in the longitudinal direction X thereof generates heat separately from the heat generation portions 35A and 35C disposed in both lateral end spans of the heater 22D, respectively, in the longitudinal direction X thereof. For example, in order to fix a toner image on a sheet P having a decreased size not greater than a predetermined size, the heat generation portion 35B generates heat. In order to fix a toner image on a sheet P having an increased size greater than the predetermined size, the heat generation portions 35A, 35B, and 35C generate heat.

As illustrated in <FIG>, the heater holder 23B includes a recess 23d that holds the heater 22D and the first thermal conductor <NUM>. The recess 23d is disposed on a heater opposed face of the heater holder 23B, that is disposed opposite the heater 22D. The recess 23d includes a bottom face 23d1 and walls 23d2 and 23d3. The bottom face 23d1 is substantially parallel to the base <NUM> and recessed with respect to the heater 22D compared to other faces of the heater holder 23B. The wall 23d2 is disposed at at least one of both lateral ends of the heater holder 23B in the longitudinal direction X thereof and serves as an interior wall of the heater holder 23B. The walls 23d3 are disposed at both ends of the heater holder 23B in the orthogonal direction Y thereof and serve as interior walls of the heater holder 23B, respectively. The heater holder 23B includes the guides <NUM>. The heater holder 23B is made of LCP.

As illustrated in <FIG>, the fixing device <NUM> further includes a connector <NUM> that includes a housing made of resin such as LCP and a plurality of contact terminals disposed in the housing.

The connector <NUM> is attached to the heater 22D and the heater holder 23B such that the connector <NUM> sandwiches the heater 22D and the heater holder 23B together at a front face and a back face of the heater 22D and the heater holder 23B. In a state in which the connector <NUM> sandwiches and holds the heater 22D and the heater holder 23B, as the contact terminals of the connector <NUM> contact and press against the first electrode 34A, the second electrode 34B, and the third electrode 34C of the heater 22D depicted in <FIG>, the heat generation portions 35A, 35B, and 35C are electrically connected to a power supply disposed in the image forming apparatus 100A through the connector <NUM>. Thus, the power supply is ready to supply power to the heat generation portions 35A, 35B, and 35C. At least a part of each of the first electrode 34A, the second electrode 34B, and the third electrode 34C is not coated with the insulating layer and is exposed so that each of the first electrode 34A, the second electrode 34B, and the third electrode 34C is coupled with the connector <NUM>.

As illustrated in <FIG>, the fixing device <NUM> further includes a flange <NUM> that is disposed on each lateral end of the fixing belt <NUM> in the longitudinal direction X thereof. The flange <NUM> contacts the inner circumferential face 20a of the fixing belt <NUM> and holds or supports the fixing belt <NUM> at each lateral end of the fixing belt <NUM> in the longitudinal direction X thereof. The flanges <NUM> are secured to a frame of the fixing device <NUM>. The flange <NUM> is inserted into each lateral end of the stay <NUM> in the longitudinal direction X thereof in an insertion direction I53 illustrated in <FIG>.

The connector <NUM> is attached to the heater 22D and the heater holder 23B in an attachment direction A60 illustrated in <FIG> that is parallel to the orthogonal direction Y of the heater 22D. Alternatively, in order to attach the connector <NUM> to the heater holder 23B, one of the connector <NUM> and the heater holder 23B may include a projection that engages a recess disposed in another one of the connector <NUM> and the heater holder 23B such that the projection moves inside the recess relatively. The connector <NUM> is attached to one lateral end of the heater 22D and the heater holder 23B in the longitudinal direction X of the heater 22D. The one lateral end of the heater 22D and the heater holder 23B is opposite to another lateral end of the heater 22D and the heater holder 23B in the longitudinal direction X of the heater 22D, with which the driver (e.g., a motor) that drives the pressure roller <NUM> is coupled.

As illustrated in <FIG>, the thermistors <NUM> are disposed opposite the inner circumferential face 20a of the fixing belt <NUM> at a position in proximity to a center line L and a position in one lateral end span of the fixing belt <NUM> in the longitudinal direction X thereof, respectively. The controller <NUM> depicted in <FIG> controls the heater 22D based on a temperature of the fixing belt <NUM>, that is detected by the thermistor <NUM> disposed at the position in proximity to the center line L, and a temperature of the fixing belt <NUM>, that is detected by the thermistor <NUM> disposed opposite the one lateral end span of the fixing belt <NUM> in the longitudinal direction X thereof, respectively.

The thermostats <NUM> are disposed opposite the inner circumferential face 20a of the fixing belt <NUM> at a position in proximity to the center line L and a position in another lateral end span of the fixing belt <NUM> in the longitudinal direction X thereof, respectively. If the thermostat <NUM> detects a temperature of the fixing belt <NUM>, that is higher than a preset threshold, the thermostat <NUM> breaks power to the heater 22D.

The flanges <NUM> contact and support both lateral ends of the fixing belt <NUM> in the longitudinal direction X thereof, respectively. Each of the flanges <NUM> is made of LCP.

As illustrated in <FIG>, the flange <NUM> includes a slide groove 53a. The slide groove 53a extends in a contact-separation direction in which the fixing belt <NUM> comes into contact with and separates from the pressure roller <NUM>. The slide groove 53a engages an engagement mounted on the frame of the fixing device <NUM>. As the engagement moves relatively inside the slide groove 53a, the fixing belt <NUM> moves in the contact-separation direction with respect to the pressure roller <NUM>.

The fixing device <NUM> also incorporates the pivot restrictor such as the pivot restricting rib 23b that suppresses pivoting and resultant shifting of the conductive member <NUM>.

The recording media include, in addition to plain paper as a sheet P, thick paper, a postcard, an envelope, thin paper, coated paper, art paper, tracing paper, an overhead projector (OHP) transparency, plastic film, prepreg, and copper foil.

A description is provided of aspects of the embodiments of the present disclosure.

A description is provided of a first aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, a fixing device (e.g., the fixing devices <NUM>, 9B, 9C, 9D, 9E, 9F, <NUM>, <NUM>, 9I, 9J, <NUM>, and <NUM>) includes a belt (e.g., the fixing belt <NUM> and the pressure belt <NUM>), a heater (e.g., the heaters <NUM>, 22A, 22B, 22C, and 22D), a conductive member (e.g., the conductive member <NUM>), a holding portion (e.g., the positioning pin 23a), and a pivot restrictor (e.g., the pivot restricting rib 23b).

The belt rotates in a rotation direction (e.g., the rotation directions J and J97). The heater heats the belt. The heater is a laminated heater, for example. The conductive member contacts an inner face (e.g., the inner circumferential faces 20a and 97a) of the belt. As illustrated in <FIG> and <FIG>, the conductive member includes one end portion (e.g., the fixed end 40a) in the rotation direction of the belt, a contact portion (e.g., the free end 40b) that contacts the belt, and an outboard portion (e.g., an outboard portion 40f) that is disposed outboard from the contact portion in the rotation direction of the belt. The outboard portion includes at least one of the opposed portion 40c and the bent portion 40d. The holding portion holds the one end portion of the conductive member. The pivot restrictor contacts the outboard portion of the conductive member to restrict pivoting of the conductive member about the one end portion of the conductive member.

A description is provided of a second aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, in the fixing device according to the first aspect, the pivot restrictor restricts pivoting of the conductive member in a contact range (e.g., the pivot angles C1 and C2) in a pivot direction (e.g., the pivot direction V) of the conductive member. The conductive member contacts the belt in the contact range.

A description is provided of a third aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, in the fixing device according to the first aspect or the second aspect, the pivot restrictors are disposed opposite both ends (e.g., both lateral ends) of the conductive member in the pivot direction thereof, respectively. For example, the fixing device further includes another pivot restrictor (e.g., the pivot restricting rib 23b) that restricts pivoting of the conductive member about the one end portion of the conductive member. The pivot restrictor is disposed opposite one end of the conductive member in the pivot direction thereof and the another pivot restrictor is disposed opposite another end of the conductive member in the pivot direction thereof.

A description is provided of a fourth aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, in the fixing device according to the third aspect, the pivot restrictors disposed opposite both ends of the conductive member, respectively, in the pivot direction thereof define a clearance therebetween, that is equivalent to a width (e.g., the width W1) of the conductive member in the pivot direction of the conductive member.

A description is provided of a fifth aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, in the fixing device according to any one of the first aspect to the fourth aspect, a plurality of pivot restrictors is disposed opposite at least one of one end or another end of the conductive member in the pivot direction thereof.

A description is provided of a sixth aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, in the fixing device according to any one of the first aspect to the fifth aspect, the heater includes a plurality of heat generation portions (e.g., the heat generation portions 35A, 35B, and 35C) that is arranged in a longitudinal direction (e.g., the longitudinal direction X) of the heater and generates heat separately from each other. For example, the heater includes a first heat generation portion (e.g., the heat generation portion 35B) that generates heat and a second heat generation portion (e.g., the heat generation portions 35A and 35C) that is arranged with the first heat generation portion in the longitudinal direction of the heater. The second heat generation portion generates heat separately from the first heat generation portion.

A description is provided of a seventh aspect of the embodiments of the present disclosure.

In the fixing device according to any one of the first aspect to the sixth aspect, the belt is made of polyimide.

A description is provided of an eighth aspect of the embodiments of the present disclosure.

In the fixing device according to the seventh aspect, the belt does not include an elastic layer.

A description is provided of a ninth aspect of the embodiments of the present disclosure.

As illustrated in <FIG> and <FIG>, in the fixing device according to any one of the first aspect to the eighth aspect, the conductive member has an insertion hole (e.g., the insertion hole 40e) that penetrates through the one end portion. The holding portion is inserted into the insertion hole of the conductive member to hold the conductive member. The insertion hole is shifted from a center (e.g., the center <NUM>) of the conductive member in a width direction of the conductive member. The width direction is substantially parallel to the pivot direction of the conductive member.

A description is provided of a tenth aspect of the embodiments of the present disclosure.

As illustrated in <FIG>, an image forming apparatus (e.g., the image forming apparatuses <NUM> and 100A) includes a transfer roller (e.g., the secondary transfer roller <NUM>) that contacts a recording medium (e.g., the sheet P) and the fixing device according to any one of the first aspect to the ninth aspect that is disposed downstream from the transfer roller in a recording medium conveyance direction (e.g., the sheet conveyance direction A).

Claim 1:
A fixing device (<NUM>) comprising:
a belt (<NUM>) to rotate in a rotation direction;
a heater (<NUM>) to heat the belt (<NUM>);
a conductive member (<NUM>) to contact an inner face (20a) of the belt (<NUM>), the conductive member (<NUM>) to pivot,
the conductive member (<NUM>) including:
one end portion (40a) in the rotation direction of the belt (<NUM>);
a contact portion (40b) to contact the belt (<NUM>); and
an outboard portion (40f) disposed outboard from the contact portion (40b) in the rotation direction of the belt (<NUM>);
a holding portion (23a) to hold the one end portion (40a) of the conductive member (<NUM>); characterised by
a pivot restrictor (23b) to contact the outboard portion (40f) of the conductive member (<NUM>), the pivot restrictor (23b) to restrict pivoting of the conductive member (<NUM>) about the one end portion (40a) of the conductive member (<NUM>).