Patent Description:
As a heating device used in an image forming apparatus such as a printer, there are known, for example, a fixing device that fixes toner on a sheet under heat and a drying device that dries ink on a sheet.

For example, <CIT> or <CIT> (<CIT>) discloses a fixing device including a heater that includes a resistance heat generator on a long base made of ceramic or the like. Such a heater includes electrodes on a base, and connectors as power supply components are connected to the electrodes to supply power to a resistance heat generator.

In the above-described heater including the resistance heat generator, when the resistance heat generator generates heat to heat the base, the base expands due to thermal expansion and contracts due to a subsequent decrease in temperature. The thermal expansion and thermal contraction cause a variation in the position of the electrode on the base. As a result, the electrode repeatedly slides in the connector, and the sliding movement causes abrasion at a contact portion between the electrode and the connector, which may prevent satisfactory power supply to the resistance heat generator. Therefore, a measure to reduce the variation in the position of the electrode due to the thermal expansion and thermal contraction of the base is required.

<CIT> discloses an image heating apparatus comprising, a heating member for heating an image on a recording material, the heating member having a metallic substrate and heat generating resistor, and a supporting member for supporting the heating member, wherein the metallic substrate having a portion for positioning said metallic substrate on said supporting member.

<CIT> discloses a heater unit including a heater in which a heating resistor member and an electrode electrically connected to the heating resistor member are disposed on a board.

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

Advantageously, the heating device includes a heater, a holder configured to hold the heater, a positioner configured to position the heater with respect to the holder in a longitudinal direction of the heater, and a connector including contact portions configured to contact electrodes of the heater. The heater includes a base, a plurality of heat generators disposed on the base, and three or more electrodes disposed on the base and electrically connected to the heat generators. The positioner is closer to the electrodes than a center position of the base in a longitudinal direction of the base.

According to the present disclosure, the variation in the position of the electrode due to the thermal expansion and thermal contraction of the base can be reduced.

The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:.

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

With reference to drawings, a description is given below of the present disclosure. In the drawings illustrating the following embodiments, the same reference numbers are allocated to elements having the same function or shape and redundant descriptions thereof are omitted below.

<FIG> is a schematic diagram illustrating a configuration of an image forming apparatus 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 serving as image forming devices, respectively. The image forming units 1Y, <NUM>, 1C, and 1Bk are removably installed in a body <NUM> of the image forming apparatus <NUM>. The image forming units 1Y, <NUM>, 1C, and 1Bk have a similar construction except that the image forming units 1Y, <NUM>, 1C, and 1Bk contain developers in different colors, that is, yellow, magenta, cyan, and black, respectively, which correspond to color separation components for a color image. Specifically, each of the image forming units 1Y, <NUM>, 1C, and 1Bk includes: a photoconductor <NUM> in a drum-like shape as an image bearer; a charger <NUM> to charge a surface of the photoconductor <NUM>; a developing device <NUM> configured to form a toner image by supplying toner, as a developer, to a surface of the photoconductor <NUM>; and a cleaner <NUM> to clean the surface of the photoconductor <NUM>.

The image forming apparatus <NUM> further includes an exposure device <NUM> to expose the surface of each photoconductor <NUM> to form an electrostatic latent image, a sheet feeder <NUM> to supply a sheet P as a recording medium, a transfer device <NUM> to transfer the toner image formed on each photoconductor <NUM> onto the sheet P, a fixing device <NUM> as a heating device according the present disclosure to fix the transferred toner image onto the sheet P, and an output device <NUM> to eject the sheet P outside the image forming apparatus <NUM>.

The transfer device <NUM> includes: an intermediate transfer belt <NUM> in the form of a rotatable endless belt stretched taut with multiple rollers, as an intermediate transferor; four primary transfer rollers <NUM> each as a primary transferor to transfer the toner image formed on each photoconductor <NUM> onto the intermediate transfer belt <NUM>; and a secondary transfer roller <NUM> as a secondary transferor to transfer the toner image transferred onto the intermediate transfer belt <NUM> onto the sheet P. The primary transfer rollers <NUM> are in contact with the respective photoconductors <NUM> via the intermediate transfer belt <NUM>. Therefore, the intermediate transfer belt <NUM> is in contact with the respective photoconductors <NUM>, thus forming primary transfer nips therebetween. The secondary transfer roller <NUM> contacts, via the intermediate transfer belt <NUM>, one of the plurality of rollers around which the intermediate transfer belt <NUM> is stretched. Thus, a secondary transfer nip is formed between the secondary transfer roller <NUM> and the intermediate transfer belt <NUM>.

The image forming apparatus <NUM> accommodates a sheet conveyance path <NUM> through which the sheet P fed from the sheet feeder <NUM> is conveyed. A timing roller pair <NUM> is disposed in the sheet conveyance path <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> having the construction described above.

When the image forming apparatus <NUM> receives an instruction to start printing, a driver 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. Subsequently, the exposure device <NUM> exposes the surface of each of the photoconductors <NUM> based on image data created by a document scanner that reads an image on a document or print data provided by a terminal, thus decreasing the electric potential of an exposed portion on the photoconductor <NUM> and forming an electrostatic latent image on the photoconductor <NUM>. The developing device <NUM> supplies toner to the electrostatic latent image formed on the photoconductor <NUM>, forming a toner image thereon.

When the toner images formed on the photoconductors <NUM> reach the primary transfer nips defined by the primary transfer rollers <NUM> with the rotation of the photoconductors <NUM>, the toner images formed on the photoconductors <NUM> are transferred 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>, forming a full color toner image thereon. Thereafter, 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> with the rotation of the intermediate transfer belt <NUM> and is transferred onto a sheet P conveyed to the secondary transfer nip. The sheet P is fed from the sheet feeder <NUM>. The timing roller pair <NUM> temporarily stops the sheet P fed from the sheet feeder <NUM> and conveys the sheet P to the secondary transfer nip, timed to coincide with the toner image on the intermediate transfer belt <NUM>. Accordingly, the full color toner image is transferred onto and borne on the sheet P. After the toner image is transferred onto the intermediate transfer belt <NUM>, the cleaner <NUM> removes residual toner remained 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.

Next, a configuration of the fixing device <NUM> is described.

As illustrated in <FIG>, the fixing device <NUM> according to the present embodiment includes a fixing belt <NUM> as a fixing rotator, a pressure roller <NUM> as an opposed rotator to contact an outer circumferential surface of the fixing belt <NUM> and form a nip N, and a heating unit <NUM> to heat the fixing belt <NUM>. The heating unit <NUM> includes a heater <NUM>, a heater holder <NUM>, and a stay <NUM>. The heater <NUM> is a laminated heater and serves as a heater or a heating member. The heater holder <NUM> serves as a holder that holds or supports the heater <NUM>. The stay <NUM> serves as a reinforcement that reinforces the heater holder <NUM> throughout an entire width of the heater holder <NUM> in a longitudinal direction thereof.

The fixing belt <NUM> is formed as an endless belt and includes, for example, a tubular base made of polyimide (PI), the tubular base having an outer diameter of <NUM> and a thickness of from <NUM> to <NUM>. The fixing belt <NUM> further includes a release layer serving as an outermost surface layer. The release layer is made of fluororesin, such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (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>. An elastic layer made of rubber having a thickness of from <NUM> to <NUM> may be provided between the base and the release layer. The base of the fixing belt <NUM> may be made of heat resistant resin such as polyetheretherketone (PEEK) or metal such as nickel (Ni) or stainless steel (Steel Use Stainless, SUS), instead of polyimide. An inner circumferential surface of the fixing belt <NUM> may be coated with polyimide, PTFE, or the like to produce a slide layer.

The pressure roller <NUM> having, for example, an outer diameter of <NUM>, includes a solid iron cored bar 21a, an elastic layer 21b on the surface of the bar 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of <NUM>, for example. Preferably, the release layer 21c is formed by a fluororesin layer having, for example, a thickness of approximately <NUM> on the surface of the elastic layer 21b to improve releasability.

The heater <NUM> extends in a longitudinal direction thereof throughout an entire width of the fixing belt <NUM> in a rotation axis direction of the fixing belt <NUM>, referred to as a longitudinal direction of the fixing belt <NUM> below. The heater <NUM> contacts the inner circumferential surface of the fixing belt <NUM> at a position corresponding to the pressure roller <NUM>. The heater <NUM> includes a planar base <NUM>, a first insulation layer <NUM> disposed on the base <NUM>, a conductor layer <NUM> disposed on the first insulation layer <NUM>, and a second insulation layer <NUM> that covers the conductor layer <NUM>. The conductor layer <NUM> includes a heat generator <NUM>. In the present embodiment, the base <NUM>, the first insulation layer <NUM>, the conductor layer <NUM> including the heat generator <NUM>, and the second insulation layer <NUM> are layered in this order toward the fixing belt <NUM>, that is, the nip N. Heat generated from the heat generator <NUM> is transmitted to the fixing belt <NUM> via the second insulation layer <NUM>.

Alternatively, the heat generator <NUM> may be disposed on a surface of the base <NUM> facing the heater holder <NUM>, that is, the surface opposite to a surface of the base <NUM> facing the fixing belt <NUM>. In that case, since the heat of the heat generator <NUM> is transmitted to the fixing belt <NUM> through the base <NUM>, it is preferable that the base <NUM> be made of a material with high thermal conductivity such as aluminum nitride. In the heater <NUM> according to the present embodiment, another insulation layer may be further disposed on a surface of the base <NUM> facing the heater holder <NUM>, that is, the surface opposite to the surface of the base <NUM> facing the fixing belt <NUM>.

The heater <NUM> may not contact the fixing belt <NUM> or may be disposed opposite the fixing belt <NUM> indirectly via a low friction sheet or the like. However, the heater <NUM> that contacts the fixing belt <NUM> directly as in the present embodiment enhances conduction of heat from the heater <NUM> to the fixing belt <NUM>. The heater <NUM> may contact the outer circumferential surface of the fixing belt <NUM>. However, if the outer circumferential surface of the fixing belt <NUM> is brought into contact with the heater <NUM> and damaged, the fixing belt <NUM> may degrade quality of fixing the toner image on the sheet P. Hence, preferably, the heater <NUM> contacts the inner circumferential surface of the fixing belt <NUM>.

The heater holder <NUM> and the stay <NUM> are disposed inside a loop of the fixing belt <NUM>. The stay <NUM> is configured by a channeled metallic member, and both side plates of the fixing device <NUM> support both end portions of the stay <NUM>. The stay <NUM> supports a stay side face of the heater holder <NUM>, that faces the stay <NUM> and is opposite a heater side face of the heater holder <NUM>, that faces the heater <NUM>. Accordingly, the stay <NUM> retains the heater <NUM> and the heater holder <NUM> to be immune from being bent substantially by pressure from the pressure roller <NUM>, forming the fixing nip N between the fixing belt <NUM> and the pressure roller <NUM>.

The heater holder <NUM> is preferably made of heat-resistant material because heat from the heater <NUM> heats the heater holder <NUM> to a high temperature. The heater holder <NUM> is made of heat-resistant resin having low thermal conduction, such as a liquid crystal polymer (LCP) or polyether ether ketone (PEEK) and reduces heat transfer from the heater <NUM> to the heater holder <NUM> and provides efficient heating of the fixing belt <NUM>.

A spring serving as a biasing member causes the fixing belt <NUM> and the pressure roller <NUM> to press against each other to form the fixing nip N between the fixing belt <NUM> and the pressure roller <NUM>. As a driving force is transmitted to the pressure roller <NUM> from a driver disposed in the body of the image forming apparatus <NUM>, the pressure roller <NUM> serves as a driving roller that drives and rotates the fixing belt <NUM>. The fixing belt <NUM> is driven and rotated by the pressure roller <NUM> as the pressure roller <NUM> rotates. While the fixing belt <NUM> rotates, the fixing belt <NUM> slides over the heater <NUM>. In order to facilitate sliding performance of the fixing belt <NUM>, a lubricant such as oil or grease may be interposed between the heater <NUM> and the fixing belt <NUM>.

When printing starts, the driver drives and rotates the pressure roller <NUM>, and the fixing belt <NUM> starts rotating with the rotation of the pressure roller <NUM>. As power is supplied to the heater <NUM>, the heat generator <NUM> generates heat to heat the fixing belt <NUM>. When the temperature of the fixing belt <NUM> reaches a predetermined target temperature called a fixing temperature, as illustrated in <FIG>, the sheet P bearing an unfixed toner image is conveyed to the nip N between the fixing belt <NUM> and the pressure roller <NUM>, and the unfixed toner image is heated and pressed onto the sheet P and fixed thereon.

<FIG> is a perspective view of the fixing device <NUM>. <FIG> is an exploded perspective view of the fixing device <NUM>.

As illustrated in <FIG> and <FIG>, the fixing device <NUM> includes a device frame <NUM> that includes a first device frame <NUM> and a second device frame <NUM>. The first device frame <NUM> includes a pair of side walls <NUM> and a front wall <NUM>. The second device frame <NUM> includes a rear wall <NUM>. The side walls <NUM> are disposed at one side and another side of the fixing belt <NUM>, respectively, in the longitudinal direction of the fixing belt <NUM>. The side walls <NUM> support both sides of each of the pressure roller <NUM> and the heating unit <NUM>, respectively. Each of the side walls <NUM> includes a plurality of engaging projections 28a. As the engaging projections 28a engage corresponding engaging holes 29a in the rear wall <NUM>, the first device frame <NUM> is coupled to the second device frame <NUM>.

Each of the side walls <NUM> includes a slot 28b through which a rotation shaft and the like of the pressure roller <NUM> are inserted. The slot 28b opens toward the rear wall <NUM> and closes at a portion opposite the rear wall <NUM>, and the portion of the slot 28b opposite the rear wall <NUM> serves as a contact portion. A bearing <NUM> that supports the rotation shaft of the pressure roller <NUM> is disposed at an end of the contact portion. As both sides of the rotation shaft of the pressure roller <NUM> are attached to the corresponding bearings <NUM>, the side walls <NUM> rotatably support the pressure roller <NUM>.

A driving force transmission gear <NUM> serving as a driving force transmitter is disposed at one side of the rotation shaft of the pressure roller <NUM> in an axial direction thereof. In a state in which the side walls <NUM> support the pressure roller <NUM>, the driving force transmission gear <NUM> is exposed outside the side wall <NUM>. Accordingly, when the fixing device <NUM> is installed in the body of the image forming apparatus <NUM>, the driving force transmission gear <NUM> is coupled to a gear disposed inside the body of the image forming apparatus <NUM> so that the driving force transmission gear <NUM> transmits the driving force from the driver. Alternatively, a driving force transmitter to transmit the driving force to the pressure roller <NUM> may be pulleys over which a driving force transmission belt is stretched taut, a coupler, and the like instead of the driving force transmission gear <NUM>.

A pair of supports <NUM> that supports the fixing belt <NUM>, the heater holder <NUM>, the stay <NUM>, and the like is disposed at both sides of the heating unit <NUM> in a longitudinal direction thereof, respectively. Each support <NUM> has guide grooves 32a. As edges of the slot 28b of the side wall <NUM> enter the guide grooves 32a, respectively, the support <NUM> is attached to the side wall <NUM>.

A pair of springs <NUM> serving as a pair of biasing members is interposed between each of the supports <NUM> and the rear wall <NUM>. As the springs <NUM> bias the supports <NUM> and the stay <NUM> toward the pressure roller <NUM>, respectively, the fixing belt <NUM> is pressed against the pressure roller <NUM> to form the fixing nip between the fixing belt <NUM> and the pressure roller <NUM>.

As illustrated in <FIG>, a hole 29b is disposed near one end of the rear wall <NUM> of the second device frame <NUM>. The hole 29b serves as a positioner of the fixing device <NUM> that positions the body of the fixing device <NUM> with respect to the body of the image forming apparatus <NUM>. Similarly, the body of the image forming apparatus <NUM> includes a projection <NUM> as a positioner fixed on the image forming apparatus <NUM>. The projection <NUM> is inserted into the hole 29b of the fixing device <NUM>. Accordingly, the projection <NUM> engages the hole 29b, positioning the body of the fixing device <NUM> with respect to the body of the image forming apparatus <NUM> in the longitudinal direction of the fixing belt <NUM>. Note that although the hole 29b serving as the positioner is disposed at one side of the rear wall <NUM> in the longitudinal direction of the second device frame <NUM>, a positioner is not disposed at another side of the rear wall <NUM>. Thus, the second device frame <NUM> does not restrict thermal expansion and shrinkage of the body of the fixing device <NUM> in the longitudinal direction of the fixing belt <NUM> due to temperature change.

<FIG> is a perspective view of the heating unit <NUM>. <FIG> is an exploded perspective view of the heating unit <NUM>.

As illustrated in <FIG>, the heater holder <NUM> includes an accommodating recess 23a disposed on a belt side face of the heater holder <NUM>, that is a face in front side of <FIG>. The accommodating recess 23a is rectangular and accommodates the heater <NUM>. The accommodating recess 23a has a similar shape and size of the heater <NUM>, but a length L2 of the accommodating recess 23a in the longitudinal direction of the heater holder <NUM> is set slightly longer than a length L1 of the heater <NUM> in the longitudinal direction of the heater <NUM>. The accommodating recess 23a formed slightly longer than the heater <NUM> does not interfere the heater <NUM> even when the heater <NUM> expands in the longitudinal direction due to thermal expansion. The accommodating recess 23a accommodates the heater <NUM>, and a connector as power supplying member described below sandwiches the heater <NUM> and the heater holder <NUM>, thus the heater <NUM> is held in place.

In addition to the guide grooves 32a described above, each of the pair of supports <NUM> includes a belt support 32b, a belt restrictor 32c, and a supporting recess 32d. The belt support 32b is C-shaped and inserted into the loop of the fixing belt <NUM>, thus contacting the inner circumferential surface of the fixing belt <NUM> to support the fixing belt <NUM>. The belt restrictor 32c is a flange that contacts an edge face of the fixing belt <NUM> to restrict motion (e.g., skew) of the fixing belt <NUM> in the longitudinal direction of the fixing belt <NUM>. The supporting recess 32d is inserted with a lateral end of each of the heater holder <NUM> and the stay <NUM> in the longitudinal direction thereof, thus supporting the heater holder <NUM> and the stay <NUM>. The belt supports 32b inserted into the inner periphery of the fixing belt <NUM> in both ends support the fixing belt <NUM> in a state in which the fixing belt <NUM> is not tensioned in a circumferential direction thereof while the fixing belt <NUM> does not rotate, that is, by a free belt system.

As illustrated in <FIG>, the heater holder <NUM> includes a positioning recess 23e as a positioner disposed at one side of the heater holder <NUM> in the longitudinal direction thereof. The support <NUM> further includes an engagement 32e illustrated in a left part in <FIG>. The engagement 32e engages the positioning recess 23e, positioning the heater holder <NUM> with respect to the support <NUM> in the longitudinal direction of the fixing belt <NUM>. The support <NUM> illustrated in a right part in <FIG> does not include the engagement 32e and therefore the heater holder <NUM> is not positioned with respect to the support <NUM> in the longitudinal direction of the fixing belt <NUM>. Positioning the heater holder <NUM> with respect to the support <NUM> at one side of the heater holder <NUM> in the longitudinal direction of the fixing belt <NUM> does not restrict an expansion and contraction of the heater holder <NUM> in the longitudinal direction of the fixing belt <NUM> due to a temperature change.

As illustrated in <FIG>, the stay <NUM> includes step portions 24a at both ends in the longitudinal direction of the stay <NUM> to set the stay <NUM> on the supports <NUM>. Each step portion 24a abuts the support <NUM> to restrict movement of the stay <NUM> in the longitudinal direction with respect to the support <NUM>. However, at least one of the step portions 24a is configured to fit loosely, with a certain amount of play between it and the support <NUM> to enable expansion and contraction of the stay <NUM> in the longitudinal direction of the fixing belt <NUM> due to temperature change.

<FIG> is a plan view of the heater <NUM>. <FIG> is an exploded perspective view of the heater <NUM>.

As illustrated in <FIG>, the heater <NUM> includes a base <NUM>, a first insulation layer <NUM> disposed on the base <NUM>, a conductor layer <NUM> disposed on the first insulation layer <NUM>, and a second insulation layer <NUM> that covers the conductor layer <NUM>.

The base <NUM> is a long plate made of a metal such as stainless steel (Steel Use Stainless, SUS), iron, or aluminum. Alternatively, the base <NUM> may be made of ceramic, glass, etc. If the base <NUM> is made of an insulating material such as ceramic, the first insulation layer <NUM> sandwiched between the base <NUM> and the conductor layer <NUM> may be omitted. Since metal has an excellent durability when it is rapidly heated and is processed readily, metal is preferably used to reduce manufacturing costs. Among metals, aluminum and copper are preferable because aluminum and copper have high thermal conductivity and are less likely to cause uneven temperature. Stainless steel is advantageous because stainless steel is manufactured at reduced costs compared to aluminum and copper.

The first insulation layer <NUM> and the second insulation layer <NUM> are made of material having electrical insulation, such as heat-resistant glass. Alternatively, each of the first insulation layer <NUM> and the second insulation layer <NUM> may be made of ceramic, polyimide (PI), or the like.

The conductor layer <NUM> includes laminated resistive heat generators <NUM>, electrodes <NUM>, and power supply lines <NUM> each of which electrically connects the electrode <NUM> to the heat generators <NUM>. In the present embodiment, six heat generators <NUM> are disposed on the base <NUM>. Each of the heat generators <NUM> is electrically connected to any two of the three electrodes <NUM> via a plurality of power supply lines <NUM> disposed on the base <NUM>.

In <FIG>, the three electrodes <NUM> are referred to as a first electrode 61A, a second electrode 61B, and a third electrode 61C in order from the left side in <FIG>. The first electrode 61A is a common electrode connected to all heat generators <NUM> via a common power supply line 62A. The second electrode 61B is connected in parallel to the heat generators 60A and 60F disposed at both ends of the six heat generators 60A to 60F arranged in the longitudinal direction of the base <NUM> via power supply lines 62B and 62C. The third electrode 61C is connected in parallel to the heat generators 60B to 60E other than the heat generators 60A and 60F disposed at both ends via a power supply line 62D.

In the heater <NUM> according to the present embodiment, the heat generators 60A and 60F disposed at both ends and the other heat generators 60B to 60E disposed therebetween are individually controlled to generate heat. Specifically, a voltage applied to the first electrode 61A and the second electrode 61B causes the heat generators 60A and 60F at both ends to generate heat, and a voltage applied to the first electrode 61A and the third electrode 61C causes heat generators 60B to 60E other than the heat generators 60A and 60F at both ends to generate heat. Further, a voltage applied to all electrodes 61A to 61C causes all heat generators 60A to 60F to generate heat. For example, when the toner image is fixed on the sheet having a small size such as a size equal to or smaller than A4 size in which a sheet conveyance span is <NUM>, the heat generators 60B to 60E other than the heat generators 60A and 60F at both ends generate heat, and when the toner image is fixed on the sheet having a large size such as a size equal to or larger than A3 size in which the sheet conveyance span is <NUM>, all the heat generators 60A to 60F generate heat. As a result, the heater <NUM> can generate heat in a heat generation area corresponding to the sheet conveyance span.

The heat generators <NUM> are produced by mixing silver-palladium (AgPd), glass powder, and the like into a paste. The paste is coated on the base <NUM> by screen printing or the like. Thereafter, the base <NUM> is fired to form the heat generators <NUM>. Alternatively, the heat generator <NUM> may be made of a resistive material such as a silver alloy (AgPt) and ruthenium oxide (RuO2).

The power supply lines <NUM> are made of a conductor having an electrical resistance lower than that of the heat generators <NUM>. Silver (Ag), silver palladium (AgPd) or the like may be used as a material of the power supply lines <NUM> or the electrodes <NUM>. Screen-printing such a material forms the power supply lines <NUM> or the electrodes <NUM>.

In the present embodiments, the heat generators <NUM>, the electrodes <NUM>, and the power supply lines <NUM> are made of an alloy of silver, palladium, or the like to attain a positive temperature coefficient (PTC) property. PTC defines a property in which the resistance value increases as the temperature increases. Therefore, for example, a heater output decreases under a given voltage when the temperature increases. PTC heat generators <NUM> start quickly with an increased output at low temperatures and prevents overheating with a decreased output at high temperatures. For example, if a temperature coefficient of resistance (TCR) of the PTC is in a range of from about <NUM> ppm/°C to about <NUM>,<NUM> ppm/°C, the heater <NUM> is manufactured at reduced costs while retaining a resistance required for the heater <NUM>. The TCR is preferably in a range of from about <NUM> ppm/°C to about <NUM>,<NUM> ppm/°C.

As illustrated in <FIG>, at least a part of each of the electrodes <NUM> is not coated by the second insulation layer <NUM> and is exposed so that the electrodes <NUM> are connected to the connector described below.

<FIG> is a perspective view illustrating the connector <NUM> connected to the heater <NUM>.

As illustrated in <FIG>, the connector <NUM> includes a housing <NUM> made of resin and a plurality of contact terminals <NUM> fixed to the housing <NUM>. Each contact terminal <NUM> is configured by a flat spring and connected to a power supply harness <NUM>.

As illustrated in <FIG>, the connector <NUM> is attached to the heater <NUM> and the heater holder <NUM> such that the connector <NUM> sandwiches the heater <NUM> and the heater holder <NUM> together at the front side and the back side, respectively. Thus, the contact portions 72a disposed at ends of the contact terminals <NUM> elastically contact and press against the electrodes <NUM> each corresponding to the contact terminals <NUM>, and the heat generators <NUM> are electrically connected to the power supply provided in the image forming apparatus via the connector <NUM>. The above-described configuration enables the power supply to supply power to the heat generators <NUM>. In addition, to prevent a positional deviation of the connector <NUM> with respect to the heater holder <NUM>, the connector <NUM> is positioned by a positioner including a recess and a projection that engage each other and are disposed in the connector <NUM> and the heater holder <NUM>.

In the above-described heater including the resistance heat generator, when the resistance heat generator generates heat and heats the base, the base expands due to thermal expansion and contracts due to a subsequent decrease in temperature. The thermal expansion and thermal contraction cause the electrodes to move and slide with respect to the connector, which may cause abrasion at a contact part between the electrode and the connector. Especially, in the image forming apparatus <NUM> according to the present embodiment that can use the sheet having A3 size or more, the length of the heater <NUM> in the longitudinal direction becomes a length corresponding to such a large sheet width. The base of such a long heater has a large amount of the thermal expansion and thermal contraction due to temperature change, which may increase the abrasion in the electrode or the connector.

In addition, as in the present embodiment, using metal that thermally expands larger than ceramic as a material of the base of the heater or using the heat generator having the PTC characteristic increases the amount of the thermal expansion and thermal contraction in the base. When the end portion of the sheet passes over a part of the PTC heat generator in which a current flows in the longitudinal direction of the heater, the resistance value of a part of the PTC heat generator over which the sheet does not pass increases, but the increase in the resistance value does not significantly affect the current flowing through the PTC heat generator. As a result, excessive heat is generated in the part of the PTC heat generator over which the sheet does not pass, and the amount of the thermal expansion and thermal contraction of the base may increase to an undesirable extent.

Therefore, in the present embodiment, the following measures are taken to decrease abrasion at the contact part between the electrode and the connector due to the thermal expansion and thermal contraction in the base.

As illustrated in <FIG>, the heater <NUM> in the present embodiment has a positioner <NUM> to position the heater <NUM> in the longitudinal direction thereof. The positioner <NUM> includes a recess <NUM> disposed at an edge portion <NUM> extending in the longitudinal direction of the base <NUM>. On the other hand, the heater holder <NUM> includes a projection <NUM> as a positioner <NUM> that fits with the recess <NUM>, that is, the positioner <NUM> of the heater <NUM>. The projection <NUM> protrudes from a side wall surface <NUM> extending in the longitudinal direction of the accommodating recess 23a that accommodates the heater <NUM>. When the accommodating recess 23a of the heater holder <NUM> accommodates the heater <NUM>, the projection <NUM> that is the positioner <NUM> of the heater holder <NUM> fits into the recess <NUM> that is the positioner <NUM> of the heater <NUM> to position the heater <NUM> in the longitudinal direction with respect to the heater holder <NUM>.

Even when the base <NUM> expands due to the thermal expansion caused by the heat generation of the heat generator <NUM> and contracts due to the subsequent decrease in temperature, the positioner <NUM> positions the heater <NUM> in the longitudinal direction. That is, the thermal expansion and thermal contraction in the base <NUM> does not move the positioner <NUM>. Considering the above-described point, in the present embodiment, to reduce the variations in the positions of the electrodes <NUM> due to the thermal expansion and thermal contraction of the base <NUM>, the positioner <NUM> is arranged so that the positioner <NUM> is nearer to all electrodes <NUM> than the center position M of the base <NUM> in the longitudinal direction as illustrated in <FIG>.

In other words, disposing all the electrodes <NUM> on the same side as the positioner <NUM> with respect to the center position M reduces the variation in the position of each electrode <NUM> caused by the expansion and contraction in the base <NUM> due to the temperature change. That is, arranging the electrodes <NUM> near the positioner <NUM> that does not move due to the temperature change can reduce the effect of the variations in the positions of electrodes <NUM> caused by the expansion and contraction of the base <NUM>, that is, reduce the variations in the positions of each electrodes <NUM>. The above-describe configuration in the present embodiment can reduce the slide at the contact part between the electrode <NUM> and the connector <NUM> and the abrasion in the electrode <NUM> or the connector <NUM>.

Although the positioner <NUM> of the heater <NUM> that is the recess <NUM> in the above-described embodiment is outside a range H in which the electrodes <NUM> are aligned in the longitudinal direction as illustrated in <FIG>, as in an example illustrated in <FIG>, it is preferable that at least a part of the positioner <NUM> is inside the range H to efficiently reduce the variations in the positions of the electrodes <NUM> caused by the thermal expansion and the thermal contraction in the base <NUM>. The range H in which the electrodes <NUM> are aligned in the longitudinal direction means a continuous range including all electrodes <NUM> aligning in the longitudinal direction of the base <NUM>, that is, from an outer edge of one of electrodes <NUM> located at one end in the longitudinal direction of the base <NUM> to the other outer edge of the other electrode <NUM> located at the other end in the longitudinal direction of the base <NUM>. Therefore, arranging the positioner <NUM> at the position in the range H in which the electrodes <NUM> are aligned in the longitudinal direction includes arranging the positioner <NUM> at a position corresponding to a position between the electrodes <NUM> adjacent to each other in the longitudinal direction.

A distance between the positioner <NUM> and each of the electrodes <NUM> in the longitudinal direction in the example illustrated in <FIG> is much shorter than a distance between the positioner <NUM> and each of the electrodes <NUM> in the longitudinal direction in the example illustrated in <FIG>. Therefore, the configuration illustrated in <FIG> can further reduce the effect of the variations in the positions of electrodes <NUM> caused by the expansion and contraction of the base <NUM>, that is, effectively reduce the variations in the positions of electrodes <NUM>. Of course, the entire positioner <NUM> may be arranged within a range corresponding to the range H in which the electrodes <NUM> are aligned.

Alternatively, as in the example illustrated in <FIG>, arranging the positioner <NUM> at a position corresponding to a center position J in the range H in which the electrodes <NUM> are aligned in the longitudinal direction can minimize a distance from the positioner <NUM> to the electrode <NUM> furthest away from the positioner <NUM> in the longitudinal direction. The above-described configuration can more effectively reduce the variations in the positions of the electrodes <NUM>.

Preferably, the projection <NUM> of the heater holder <NUM> is formed on the same surface as the surface of the heater holder <NUM> facing the fixing belt so as not to interfere with the contact terminals <NUM>, in particular, the contact portions 72a of the contact terminals <NUM> when the connector <NUM> is attached to and detached from the heater <NUM>. However, as illustrated in <FIG>, the thickness of the projection <NUM> may be made largely so that the projection <NUM> protrudes from the surface of the heater holder <NUM> facing the fixing belt that is the upper surface of the heater holder <NUM> in <FIG> in order to more reliably position the projection <NUM> and improve the workability of assembling the heater <NUM> to the heater holder <NUM>.

In such a case, as illustrated in <FIG>, in order to avoid interference between the projection <NUM> and the contact portions 72a of the contact terminals <NUM>, the projection <NUM> of the heater holder <NUM> is preferably arranged at a position that does not overlap with a passage K on the base <NUM> over which the contact portions 72a of the contact terminals <NUM> pass when the connector <NUM> is attached to or detached from the heater <NUM>. In the above-described configuration, corresponding to the position of the projection <NUM> of the heater holder <NUM> that does not overlap the passage K of the contact portions 72a, the recess <NUM> of the heater <NUM> is arranged at a position that shifts from the passage K of the contact portions 72a in the longitudinal direction of the base <NUM>. The above-described configuration can avoid interference between the contact terminals <NUM> (that is, contact portions 72a) and the projection <NUM> of the heater holder <NUM> when the connector <NUM> is attached to or detached from the heater <NUM>.

As another method for avoiding interference between the projection <NUM> and the contact terminals <NUM>, as illustrated in <FIG>, the recess <NUM> of the heater <NUM> may be formed in an edge portion <NUM>. The edge portion <NUM> is one of a pair of edge portions <NUM>, <NUM> that extend in the longitudinal direction of the base <NUM> to hold the heat generators <NUM> and the electrodes <NUM>, and the contact portions 72a of the contact terminals do not pass over the edge portion <NUM>. In the above-described configuration, corresponding to the recess <NUM> of the heater <NUM>, the projection <NUM> of the heater holder <NUM> is also arranged at a position not overlapping the passage K over which the contact portions 72a pass. Therefore, the above-described configuration can avoid interference between the contact terminals <NUM> (that is, contact portions 72a) and the projection <NUM>. Moreover, the above-described configuration can arrange at least a part of the recess <NUM> of the heater <NUM> at a position within the range corresponding to the range H in which the electrodes <NUM> are aligned in the longitudinal direction, which can effectively reduce the variations in the positions of the electrodes <NUM> caused by the expansion and contraction of the base <NUM>.

As described above, the recess <NUM> of the heater <NUM> may be disposed at any one of the pair of edge portions <NUM> and <NUM> extending in the longitudinal direction of the base <NUM>. However, preferably, as illustrated in <FIG>, the recess <NUM> is formed at the edge portion <NUM> that is farther from a common power supply line 62A connected to a first electrode 61A as a common electrode to reduce the size of the heater <NUM> in a short-side direction of the heater <NUM>. The above-described power supply line 62A is located along the edge portion of the base <NUM> when components are generally laid out on the base <NUM>. Therefore, as illustrated in <FIG>, when the recess <NUM> is disposed at the edge portion <NUM> that is near the common power supply line 62A, the base <NUM> needs to be designed larger in the short-side direction that is a direction intersecting the longitudinal direction of the base <NUM> and the direction along a surface on which the heat generator <NUM> is disposed because space to locate the recess <NUM> is needed to avoid an interference between the common power supply line 62A and the recess <NUM>. On the other hand, as illustrated in <FIG>, the recess <NUM> disposed at the edge portion <NUM> farther from the common power supply line 62A does not interfere the common power supply line 62A. Therefore, the arrangement of the heat generator <NUM>, the electrodes <NUM>, and power supply lines <NUM> is easy and provides the advantage of reducing the size of the heater <NUM> in the short-side direction.

In the above-described embodiment, as illustrated in <FIG>, the heater <NUM> has six heat generators 60A to 60F, and the heat generators 60A and 60F at both ends are connected to the common second electrode 61B that is different from a common electrode connected to the other heat generators 60B to 60E disposed between the heat generators 60A and 60F. Connecting the heat generators 60A and 60F at both ends to only one of the electrodes (that is, the second electrode 61B) and not to different electrodes can reduce a number of the electrodes and reduce the size of the heater <NUM>.

In the above-described examples, the recess <NUM> and the projection <NUM> as the positioners <NUM> and <NUM> of the heater <NUM> and the heater holder <NUM> are both formed in a rectangular shape including a square shape, but shapes of the positioners <NUM> and <NUM> may be changed as appropriate.

For example, as illustrated in <FIG>, the shapes of the recess <NUM> and the projection <NUM> as the positioners <NUM> and <NUM> may include a curve. Similar to the above-described examples, two facing surfaces 43a facing each other in the recess <NUM> and two side surfaces 64a of the projection <NUM> that fit the two surfaces 43a are surfaces orthogonal to the longitudinal direction of the base <NUM> that can effectively position the heater <NUM> in the longitudinal direction.

Alternatively, as illustrated in <FIG>, the facing surfaces 43a in the recess <NUM> may be projections. In this case, tops of the projections that are the facing surfaces 43a in the recess <NUM> contact the side surfaces 64a in the projection <NUM> of the heater holder <NUM> to position the heater <NUM> in the longitudinal direction.

Alternatively, as illustrated in <FIG>, the positioner <NUM> of the heater <NUM> may be formed as a projection <NUM> instead of the recess <NUM> as described above, and the positioner <NUM> of the heater holder <NUM> may be formed as a recess <NUM> that fits the projection <NUM> of the heater <NUM>.

Alternatively, as illustrated in <FIG>, the positioner <NUM> of the heater <NUM> may be formed as a through hole <NUM> penetrating the base <NUM> in a thickness direction of the base <NUM> that is a direction intersecting the longitudinal direction and the short-side direction. In this case, the projection <NUM> as the positioner <NUM> disposed on the heater holder <NUM> is inserted into the through hole <NUM> of the heater <NUM> to position the heater <NUM> in the longitudinal direction.

In the above-described example, as illustrated in <FIG>, the connector <NUM> can be attached to or detached from, in the short-side direction of the base <NUM>, the electrodes <NUM> aligned in the longitudinal direction of the base <NUM>, but the arrangement of the electrodes <NUM> and a direction in which the connector <NUM> is attached to or detached from the electrodes <NUM> may be changed as appropriate.

For example, as illustrated in <FIG>, the electrodes <NUM> may be aligned in the short-side direction of the base <NUM>, and the connector <NUM> may be detachable in the longitudinal direction of the base <NUM>.

Alternatively, as illustrated in <FIG>, the electrodes <NUM> may be aligned in both the longitudinal direction and the short-side direction of the base <NUM>.

<FIG> illustrates an example of the heater <NUM> including an increased number of electrodes <NUM> and an increased number of groups of the heat generators <NUM> capable of controlling heat generation independently. In this example, the heater <NUM> includes four electrodes <NUM> and three groups of the heat generators <NUM> capable of controlling heat generation independently. When a voltage is applied across the first electrode 61A and the second electrode 61B among the four electrodes 61A to 61D illustrated in <FIG>, only the heat generators 60A and 60F at both ends generate heat. When the voltage is applied across the first electrode 61A and a third electrode 61C among the four electrodes 61A to 61D, only the heat generator 60B and 60E which are located adjacent to the heat generators 60A and 60F at both ends and sandwiched by them generate heat. In addition, when the voltage is applied across the first electrode 61A and the fourth electrode 61D, only the center heat generators 60C and 60D which are located adjacent to each other generate heat. Increasing a number of the electrodes <NUM> and increasing a number of the groups of the heat generators <NUM> capable of controlling the heat generation independently as described above enables various kinds of combination of heat generation areas that can heat the sheets having a lot of widths. Alternatively, the heater <NUM> may include five or more electrodes <NUM> and four or more groups of the heat generators <NUM> capable of controlling heat generation independently.

The shape of the heat generators <NUM> is not limited to a zigzag pattern as illustrated in <FIG> and other drawings and may instead be a straight-line pattern extending in the longitudinal direction of the base <NUM> without the zigzag pattern as illustrated in <FIG>.

The connection of the heat generators <NUM> is not limited to the parallel connection and may instead be a serial connection as illustrated in <FIG>.

The present disclosure is applicable to fixing devices illustrated in <FIG> in addition to the above-described fixing devices. Referring now to <FIG>, a description is given of some variations of the fixing device <NUM>.

First, the fixing device <NUM> illustrated in <FIG> includes a pressurization roller <NUM> opposite the pressure roller <NUM> with respect to the fixing belt <NUM> and heats the fixing belt <NUM> sandwiched by the pressurization roller <NUM> and the heater <NUM>. On the other hand, a nip formation pad <NUM> serving as a nip former is disposed inside the loop formed by the fixing belt <NUM> and disposed opposite the pressure roller <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> and define the fixing nip N.

Next, the fixing device <NUM> illustrated in <FIG> is omitted the above described pressurization roller <NUM> and includes the heater <NUM> formed to be arc having a curvature of the fixing belt <NUM> to keep a circumferential contact length between the fixing belt <NUM> and the heater <NUM>. The rest of the configuration of the fixing device illustrated in <FIG> is the same as the rest of the configuration of the fixing device <NUM> described above.

Lastly, the fixing device <NUM> illustrated in <FIG> includes a pressing belt <NUM> in addition to the fixing belt <NUM> and has a heating nip (a first nip) N1 and the fixing nip (a second nip) N2 separately. That is, the nip formation pad <NUM> and the stay <NUM> are disposed opposite the fixing belt <NUM> with respect to the pressure roller <NUM>, and the pressing belt <NUM> is rotatably arranged to wrap around the nip formation pad <NUM> and the stay <NUM>. The sheet P passes through the fixing nip N2 between the pressing belt <NUM> and the pressure roller <NUM> and is applied to heat and pressure, and the image is fixed on the sheet P. Other construction of the fixing device is equivalent to that of the fixing device <NUM> depicted in <FIG>.

As described above, according to the present disclosure, arranging the positioner nearer to all the electrodes than the center of the base can reduce the variations in the positions of the electrodes caused by the thermal expansion and the thermal contraction in the base and abrasion at the contact part between the electrodes and the connector. As a result, the contact state between the electrodes and the connector can be favorably maintained for a long time, and the reliability is improved.

In particular, a great effect can be expected by applying the present disclosure to the fixing device like the above-described embodiment including the heater formed to be long corresponding to the sheet of A3 size or more, the heater including the base made of metal that thermally expands easily, or the heater including the heat generator having the PTC characteristic because the base of such a heater tends to have the large amount of the thermal expansion and thermal contraction due to temperature change. However, the present disclosure is not limited to the application to such a fixing device. Applying the present disclosure to the fixing device can reduce the variations in the positions of the electrodes caused by the thermal expansion and the thermal contraction in the base and abrasion at the contact part between the electrodes and the connector even when the fixing device includes the short heater corresponding to the sheet having smaller sizes than A3 size, the heater including the base made of ceramic, or the heater not having the PTC characteristic.

In addition to the above-described fixing device, a heating device according to the present disclosure is also applicable to a dryer to dry ink applied to the sheet and a heating device used in a coating device (a laminator) that heats, under pressure, a film serving as a covering member onto the surface of the sheet such as paper. The image forming apparatus <NUM> according to the embodiments of the present disclosure may be a copier, a facsimile machine, a multifunction peripheral (MFP) having at least two of copying, printing, scanning, facsimile, and plotter functions in addition to the printer. Embodiments of the present disclosure may be applied to an ink jet type image forming apparatus in addition to the electrophotographic type image forming apparatus.

Claim 1:
A heating device (<NUM>) comprising:
a heater (<NUM>) including a base (<NUM>), a plurality of heat generators (<NUM>) disposed on the base (<NUM>), and three or more electrodes (<NUM>) disposed on the base (<NUM>) and electrically connected to the heat generators (<NUM>);
a holder (<NUM>) configured to hold the heater (<NUM>);
a positioner (<NUM>, <NUM>) configured to position the heater (<NUM>) with respect to the holder (<NUM>) in a longitudinal direction of the heater (<NUM>), the positioner (<NUM>, <NUM>) disposed closer to the three or more electrodes (<NUM>) than a center position (M) of the base (<NUM>) in a longitudinal direction of the base (<NUM>), the three or more electrodes (<NUM>) and the positioner (<NUM>, <NUM>) all being arranged on the same side with respect to the center position (M);
a connector (<NUM>) including a contact portion (72a) configured to contact the three or more electrodes (<NUM>) for applying a voltage thereto;
a stay (<NUM>) that supports a stay side face of the heater holder (<NUM>) which is opposite to a heater side face that faces the heater (<NUM>); and
a pair of supports (<NUM>) for supporting a fixing belt (<NUM>), the heater holder (<NUM>), and the stay (<NUM>), wherein
a first of the supports includes an engagement portion (32e), and a second of the supports does not include an engagement portion,
the heater holder (<NUM>) includes a further positioner (23e) disposed at one side of the heater holder (<NUM>) in the longitudinal direction thereof, for positioning the heater holder (<NUM>) with respect to one of the supports (<NUM>) at one side of the heater holder (<NUM>) in the longitudinal direction of the fixing belt (<NUM>), and
the engagement portion (32e) engages the further positioner (23e) to position the heater holder (<NUM>) with respect to the support in the longitudinal direction of the fixing belt (<NUM>).