Patent Description:
As an image forming apparatus such as a copier or a printer, an electrophotographic image forming apparatus is known that forms an image using toner.

In general, the electrophotographic image forming apparatus includes a fixing device that fixes a toner image onto a sheet. The fixing device includes a heating member such as a heater that heats the sheet. When the sheet passes through the fixing device, the heating member heats the sheet so that the toner on the sheet is melted and fixed to the sheet.

For example, <CIT> discloses, as the heating member included in the fixing device, a heater including a planar base, a heat generator, an electrode (an electric contact), and a conductor (a conductor pattern) electrically connecting the heat generator and the electrode. The heat generator, the electrode, and the conductor are disposed on the base.

In the heating member including the above-described conductor disposed on the base, a current flowing through the conductor generates heat in addition to heat generated by the heat generator. As a result, an uneven heat generation distribution of the conductor causes an uneven temperature distribution of the heating member.

The above-described uneven temperature distribution of the heating member affects not only the fixing device including the heating member but also various devices including devices near the fixing device in the image forming apparatus. For example, the temperature distribution of the heating member affects a temperature distribution in an image forming unit that forms an image and causes an uneven temperature distribution of a cleaning blade that cleans the surface of a photoconductor.

Generally, a cleaner requires a suitable contact state between the cleaner and the photoconductor, such as a suitable friction force, a suitable contact pressure, and a suitable impact resilience of the cleaner to maintain a good cleaning performance. When the uneven temperature distribution of the cleaning blade occurs, the influence of heat may prevent the cleaning blade, in particular a high temperature portion of the cleaning blade, from maintaining the suitable contact state. The above-described disadvantage is not limited to the cleaning blade cleaning the surface of the photoconductor and may similarly occur in a blade sliding on another rotator.

<CIT>, <CIT>, <CIT> and <CIT> disclose background art to the invention.

An object of the present disclosure is to provide an image forming apparatus that can solve the above-described disadvantage. In order to achieve this object, there is provided an image forming apparatus according to claim <NUM>. Advantageous embodiments are defined by the dependent claims.

Advantageously, the image forming apparatus configured to form an image on a recording medium includes a heating device, a rotator, and a blade. The heating device heats the recording medium conveyed and includes a heater. The heater includes a heat generator and extends in a direction orthogonal to a conveyance direction of the recording medium. The heater generates a larger amount of heat at one end in the direction orthogonal to the conveyance direction than at a center of the heater in the direction orthogonal to the conveyance direction. The blade includes a rubbing portion. The rubbing portion extends in the direction orthogonal to the conveyance direction. One end of the rubbing portion in the direction orthogonal to the conveyance direction faces the one end of the heater in the direction orthogonal to the conveyance direction. The other end of the rubbing portion in the direction orthogonal to the conveyance direction faces the other end of the heater in the direction orthogonal to the conveyance direction. The rubbing portion rubs a rotator. The rotator and the blade are configured such that a friction force between the rotator and the one end of the rubbing portion is smaller than a friction force between the rotator and the center of the rubbing portion in the direction orthogonal to the conveyance direction.

The above-described image forming apparatus can maintain a suitable contact state between a rotator and a blade.

However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results.

With reference to drawings attached, a description is given below of the present disclosure. In the drawings for illustrating embodiments of the present disclosure, identical reference numerals are assigned to elements such as members and parts that have an identical function or an identical shape as long as differentiation is possible, and descriptions of such elements may be omitted once the description is provided.

<FIG> is a schematic diagram illustrating a configuration of the image forming apparatus according to an embodiment of the present disclosure.

The image forming apparatus <NUM> illustrated in <FIG> includes an image forming section <NUM> as an image forming device, a transfer section <NUM>, a fixing section <NUM>, a recording medium supply section <NUM>, and a recording medium ejection section <NUM>.

The image forming section <NUM> includes four process units 1Y, <NUM>, 1C, and 1Bk and an exposure device <NUM>. Each of the four process units 1Y, <NUM>, 1C, and 1Bk is an image forming unit removably installed in the body of the image forming apparatus <NUM>. The process units 1Y, <NUM>, 1C, and 1Bk have the same configuration except for containing different color toners (developers), i.e., yellow (Y), magenta (M), cyan (C), and black (Bk) toners, respectively, corresponding to decomposed color separation components of full-color images. Each of the process units 1Y, <NUM>, 1C, and 1Bk includes a photoconductor <NUM>, a charger <NUM>, a developing device <NUM>, a cleaning device <NUM>, and a lubricant supply device <NUM>.

The photoconductor <NUM> is an image bearer bearing an image on the surface of the photoconductor <NUM>. The image forming apparatus <NUM> in the present embodiment includes a drum-shaped photoconductor (a photoconductor drum) as the photoconductor <NUM>. Alternatively, the image forming apparatus <NUM> may include a belt-shaped photoconductor (a photoconductor belt) as the photoconductor <NUM>.

The charger <NUM> is a member that charges the surface of the photoconductor <NUM>. The charger <NUM> in the present embodiment is a charging roller that contacts the surface of the photoconductor <NUM>. However, the charger <NUM> is not limited to a contact type and may be a non-contact type such as a corona charger.

The developing device <NUM> supplies the toner as the developer to the surface of the photoconductor <NUM>. For example, the developing device <NUM> includes a developer supply member such as a developing roller in contact with the photoconductor <NUM>. As the developer supply member rotates, the developer (the toner) borne on the developer supply member is supplied to the surface of the photoconductor <NUM>.

The cleaning device <NUM> cleans the surface of the photoconductor <NUM> that is a cleaning target. As illustrated in <FIG>, the cleaning device <NUM> includes a cleaning blade <NUM>, a blade holder <NUM>, and a spring <NUM> serving as a blade biasing member. The cleaning blade <NUM> is a plate made of an elastic material such as urethane rubber and is held in a cantilever manner by a blade holder <NUM>. The spring <NUM> applies a biasing force to the blade holder <NUM>, and the blade holder <NUM> holds the cleaning blade <NUM> to be in contact with the surface of the photoconductor <NUM>. When the photoconductor <NUM> rotates in this state, the cleaning blade <NUM> rubs against the rotating photoconductor <NUM> to remove foreign substances such as residual toner on the photoconductor <NUM>.

The lubricant supply device <NUM> supplies lubricant onto the photoconductor <NUM>. As illustrated in <FIG>, the lubricant supply device <NUM> includes lubricant <NUM>, a brush roller <NUM> as a lubricant applicator, a spring <NUM> as a lubricant biasing member, a coating blade <NUM> as a thin layering member, a coating blade holder <NUM>, and a spring <NUM> as a blade biasing member. The spring <NUM> presses the lubricant <NUM> against the brush roller <NUM>. As the brush roller <NUM> pressed by the lubricant <NUM> rotates, the lubricant <NUM> is scraped off by the brush roller <NUM> and supplied to the surface of the photoconductor <NUM>. The spring <NUM> sets the coating blade <NUM> to be in contact with the surface of the photoconductor <NUM>. The above-described configuration passes the lubricant supplied to the surface of the photoconductor <NUM> through a contact portion between the photoconductor <NUM> and the coating blade <NUM> to form a thin layer having a uniform thickness and apply the lubricant to the surface of the photoconductor <NUM>.

As illustrated in <FIG>, the transfer section <NUM> includes a transfer device <NUM> that transfers the image to a recording medium such as a sheet. The recording medium on which the image is transferred may be a sheet of paper made of plain paper, thick paper, thin paper, coated paper, and label paper, envelopes, or a resin sheet such as an overhead projector (OHP) transparency. The transfer device <NUM> includes an intermediate transfer belt <NUM>, primary transfer rollers <NUM>, a secondary transfer roller <NUM>, and a belt cleaner <NUM>. The intermediate transfer belt <NUM> is an endless belt stretched by a plurality of rollers. The primary transfer rollers <NUM> faces the photoconductor <NUM>. The number of the primary transfer rollers <NUM> are the same as the number of the photoconductors <NUM>. Each of the primary transfer rollers <NUM> is in contact with the corresponding photoconductor <NUM> via the intermediate transfer belt <NUM> to form a primary transfer nip between the intermediate transfer belt <NUM> and each photoconductor <NUM>. Each of the photoconductors <NUM> is in contact with the intermediate transfer belt <NUM> at each of the primary transfer nips. Via the intermediate transfer belt <NUM>, the secondary transfer roller <NUM> is in contact with one of a plurality of rollers around which the intermediate transfer belt <NUM> is stretched. The above-described configuration forms a secondary transfer nip between the intermediate transfer belt <NUM> and the secondary transfer roller <NUM>. The belt cleaner <NUM> includes a cleaning blade <NUM> that contacts the surface of the intermediate transfer belt <NUM>.

The fixing section <NUM> includes a fixing device <NUM> that fixes the image onto the sheet. A detailed configuration of the fixing device <NUM> is described below.

The recording medium supply section <NUM> includes a sheet tray <NUM> to store sheets P as recording media and a feed roller <NUM> to feed the sheet P from the sheet tray <NUM>.

The recording medium ejection section <NUM> includes an output roller pair <NUM> to eject the sheet to the outside of the image forming apparatus and an output tray <NUM> on which the sheet ejected by the output roller pair <NUM> is placed.

Next, a printing operation of the image forming apparatus <NUM> according to the present embodiment is described with reference to <FIG>.

When the image forming apparatus <NUM> starts a print operation, the photoconductors <NUM> of the process units 1Y, <NUM>, 1C, and 1Bk and the intermediate transfer belt <NUM> start rotating. The feed roller <NUM> starts to rotate and feed the sheet P from the sheet tray <NUM>. The sheet P fed from the sheet tray <NUM> is brought into contact with the timing roller pair <NUM> and temporarily stopped.

Firstly, in each of the process units 1Y, <NUM>, 1C, and 1Bk, the charger <NUM> uniformly charges the surface of the photoconductor <NUM> to a high potential. Next, the exposure device <NUM> exposes the surface (that is, the charged surface) of each photoconductor <NUM> based on image data of a document read by a document reading device or print image data sent from a terminal that sends a print instruction. As a result, the potential of the exposed portion on the surface of each photoconductor <NUM> decreases, and an electrostatic latent image is formed on the surface of each photoconductor <NUM>. The developing device <NUM> supplies toner to the electrostatic latent image formed on the photoconductor <NUM>, forming a toner image thereon. The image forming apparatus <NUM> according to the present embodiment uses all process units 1Y, <NUM>, 1C, 1Bk to form the full color toner image. Alternatively, the image forming apparatus <NUM> can form a monochrome toner image by using any one of the four process units 1Y, <NUM>, 1C, and 1Bk, or can form a bicolor toner image or a tricolor toner image by using two or three of the process units 1Y, <NUM>, 1C, and 1Bk.

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> 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. After the toner images are transferred onto the intermediate transfer belt <NUM>, the cleaning device <NUM> cleans the surface of each photoconductor <NUM>, the lubricant supply device <NUM> supplies a lubricant to the surface of each photoconductor <NUM>, and the photoconductor <NUM> is prepared for a next image formation.

In accordance with rotation of the intermediate transfer belt <NUM>, the full color toner image transferred onto the intermediate transfer belt <NUM> reaches the secondary transfer nip at the secondary transfer roller <NUM> and is transferred onto the sheet P conveyed by the timing roller pair <NUM> at the secondary transfer nip. Subsequently, the belt cleaner <NUM> cleans the surface of the intermediate transfer belt <NUM> in preparation for subsequent image formation.

After the full color toner image is transferred onto the sheet P, the sheet P is conveyed to the fixing device <NUM>, and the fixing device <NUM> fixes the full color toner image onto the sheet P. The output roller pair <NUM> ejects the sheet P bearing the fixed toner image to the output tray <NUM>. Thus, a series of image forming operations is completed.

Next, a description is given of the configuration of the fixing device <NUM> according to the present embodiment.

As illustrated in <FIG>, the fixing device <NUM> according to the present embodiment includes a fixing belt <NUM>, a pressure roller <NUM>, a heater <NUM>, a heater holder <NUM>, a stay <NUM>, and a temperature sensor <NUM>.

The fixing belt <NUM> is a rotator (a first rotator) that functions as a fixing rotator to fix an unfixed toner image onto the sheet P and is disposed so as to face a side of the sheet P on which the unfixed toner image is borne, that is, an image formed surface of the sheet P. The fixing belt <NUM> includes, for example, a base made of polyimide. 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 (Stainless Used Steel, SUS), in addition to polyimide. A release layer made of fluoroplastic such as perfluoroalkoxy alkane (PFA) or polytetrafluoroethylene (PTFE) may coat an outer circumferential surface of the base to facilitate separation of foreign substances from the fixing belt <NUM> and improve the durability of the fixing belt <NUM>. An elastic layer made of rubber or the like may be interposed between the base and the release layer. Additionally, a sliding layer made of polyimide, polytetrafluoroethylene (PTFE), or the like may be provided on the inner circumferential surface of the base.

The pressure roller <NUM> is an opposed member disposed opposite an outer circumferential surface of the fixing belt <NUM> and is referred to as a second rotator different from the first rotator that is the fixing belt <NUM>. The pressure roller <NUM> includes a cored bar made of metal; an elastic layer coating the cored bar and being made of silicone rubber or the like; and a release layer coating the elastic layer and being made of fluororesin or the like.

The pressure roller <NUM> is pressed against the fixing belt <NUM> by a biasing member such as a spring. Thus, the nip N is formed between the fixing belt <NUM> and the pressure roller <NUM>. A driving force is transmitted to the pressure roller <NUM> from a driver disposed in the body of the image forming apparatus <NUM>. As the driver drives and rotates the pressure roller <NUM>, the driving force of the driver is transmitted from the pressure roller <NUM> to the fixing belt <NUM> at the nip N, thereby rotating the fixing belt <NUM>. As illustrated in <FIG>, the sheet P bearing the unfixed toner image enters the nip N between the rotating fixing belt <NUM> and the rotating pressure roller <NUM>, and the fixing belt <NUM> and the pressure roller <NUM> convey the sheet P and apply heat and pressure to the sheet P. As a result, the unfixed toner image on the sheet P is fixed to the sheet P.

The heater <NUM> is a heating member that heats the fixing belt <NUM>. In the present embodiment, 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 resistive heat generators <NUM> that are energized to generate heat.

In the present embodiment, since the resistive heat generators <NUM> are disposed above a side of the base <NUM> facing the nip N, the heat of the resistive heat generators <NUM> is transmitted to the fixing belt <NUM> without passing through the base <NUM> and can efficiently heat the fixing belt <NUM>. Alternatively, the heat generators <NUM> may be disposed above a side of the base <NUM> opposite the side of the base <NUM> facing the nip N. In this case, since the heat of the heat generators <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 present embodiment, the heater <NUM> directly contacts the inner circumferential surface of the fixing belt <NUM> to efficiently conduct heat from the heater <NUM> to the fixing belt <NUM>. The heater <NUM> is not limited to the heater that directly contacts the fixing belt <NUM> and may not contact the fixing belt <NUM> or may contact the fixing belt <NUM> indirectly via, e.g., a low-friction sheet. 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. Therefore, it is preferable that the heater <NUM> contacts the inner circumferential surface of the fixing belt <NUM> rather than the outer circumferential surface of the fixing belt <NUM>.

The heater holder <NUM> is a heating member holder disposed inside the loop of the fixing belt <NUM> to hold the heater <NUM> contacting the inner circumferential surface of the fixing belt <NUM>. Since the heater holder <NUM> is subject to temperature increase by heat from the heater <NUM>, the heater holder <NUM> is preferably made of a heat resistant material. When 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), the heater holder <NUM> can have a heat-resistant property and reduce heat transfer from the heater <NUM> to the heater holder <NUM>. Therefore, the heater <NUM> can efficiently heats the fixing belt <NUM>.

The stay <NUM> is a reinforcement disposed inside the loop of the fixing belt <NUM> to reinforce the heater <NUM> and the heater holder <NUM>. The stay <NUM> supports a stay side face of the heater holder <NUM>. The stay side face is opposite a nip side face of the heater holder <NUM>. Accordingly, the stay <NUM> prevents the heater holder <NUM> from being bended by a pressing force of the pressure roller <NUM>. Thus, the fixing nip N is formed between the fixing belt <NUM> and the pressure roller <NUM> to be a uniform width. The stay <NUM> is preferably made of an iron-based metal such as stainless steel (SUS) or steel electrolytic cold commercial (SECC) that is electrogalvanized sheet steel to ensure rigidity.

The temperature sensor <NUM> is a temperature detector that detects the temperature of the heater <NUM>. The temperature sensor <NUM> may be a known temperature sensor such as a thermopile, a thermostat, a thermistor, or a non-contact (NC) sensor. The temperature sensor <NUM> may be either a contact type temperature sensor disposed to be in contact with the heater <NUM> or a non-contact type temperature sensor facing and being away from the heater <NUM>. The temperature sensor <NUM> in the present embodiment is disposed so as to be in contact with a surface of the heater <NUM> opposite a surface of the heater <NUM> facing the nip N.

<FIG> is a perspective view of the fixing device <NUM> according to the present embodiment, and <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>. One of the pair of side walls <NUM> is disposed at one end of the fixing belt <NUM> in the longitudinal direction of the fixing belt <NUM>, and the other one of the pair of side walls <NUM> is disposed at the other end of the fixing belt <NUM> in the longitudinal direction. The side walls <NUM> support both ends of the pressure roller <NUM> and both ends of the fixing belt <NUM>. Each side wall <NUM> has a plurality of engagement projections 28a. As the engagement projections 28a engage corresponding coupling 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> has an insertion groove 28b through which a rotation shaft and the like of the pressure roller <NUM> are inserted. The insertion groove 28b opens toward the rear wall <NUM> and closes at a portion opposite the rear wall <NUM>, and the portion of the insertion groove 28b opposite the rear wall <NUM> serves as a contact portion. A bearing <NUM> is disposed at an end of the contact portion to support the rotation shaft of the pressure roller <NUM>. Since both ends of the rotation shaft of the pressure roller <NUM> are attached to the bearings <NUM>, respectively, the side walls <NUM> rotatably support the pressure roller <NUM>.

A driving force transmission gear <NUM> serving as a drive transmitter is disposed at one end of the rotation shaft of the pressure roller <NUM> in an axial direction thereof. When 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 a driver to the pressure roller <NUM>. The drive transmitter to transmit the driving force to the pressure roller <NUM> is not limited to the driving force transmission gear <NUM> and may be pulleys over which a driving force transmission belt is stretched taut, a coupler, or the like.

A pair of supports <NUM> is disposed at both lateral ends of the fixing belt <NUM> in a longitudinal direction thereof, respectively to support the fixing belt <NUM> and the stay <NUM>. The pair of supports <NUM> support the fixing belt <NUM>, the heater holder <NUM>, the stay <NUM>, and the like. Each support <NUM> has guide grooves 32a. The edges of the insertion groove 28b of the side wall <NUM> move along the guide grooves 32a, respectively, to enter the support <NUM> into the insertion groove 28b, and 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> in a longitudinal direction of the second device frame <NUM>. The hole 29b is a positioner to position the body of the fixing device <NUM> with respect to the body of the image forming apparatus <NUM>. On the other hand, the body of the image forming apparatus <NUM> includes a projection <NUM> serving as a positioner. 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>. Although the hole 29b serving as the positioner is disposed near one end of the rear wall <NUM> in the longitudinal direction of the second device frame <NUM>, a positioner is not disposed near another end of the rear wall <NUM>. Such a configuration does not restrict thermal expansion or shrinkage of the body of the fixing device in the longitudinal direction of the fixing belt caused by changes in temperature and prevents the body of the fixing device from deforming.

<FIG> is a perspective view of a heating unit incorporated in the fixing device according to the present embodiment; and <FIG> is an exploded perspective view of the heating unit of <FIG>.

As illustrated in <FIG>, the heater holder <NUM> includes an accommodating recess 23a disposed on a fixing belt side face of the heater holder <NUM>. The fixing belt side face of the heater holder <NUM> is a front side face of the heater holder <NUM> in <FIG>. The accommodating recess 23a is rectangular and accommodates the heater <NUM>. The accommodating recess 23a has substantially the same shape and size as the shape and size of the heater <NUM>. Specifically, however, a length L2 of the accommodating recess 23a in the longitudinal direction of the heater holder <NUM> is 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 the heater <NUM> is sandwiched by the heater holder <NUM> and a connector as a power supplying member described below, thus the heater <NUM> is held.

Each of the pair of supports <NUM> includes a C-shaped belt support 32b, a belt restrictor 32c as a flange, and a supporting recess 32d. The belt support 32b is inserted into both openings at both ends of the fixing belt <NUM> in the longitudinal direction of the fixing belt <NUM>. As a result, the belt supports 32b support the fixing belt <NUM> by a free belt system that does not basically apply the fixing belt <NUM> with tension in a circumferential direction thereof while the fixing belt <NUM> does not rotate. On the other hand, the belt restrictor 32c is disposed to contact an end of the fixing belt <NUM> in the longitudinal direction of the fixing belt <NUM> and is not inserted into the loop of the fixing belt <NUM>. The belt restrictor 32c contacts the end of the fixing belt <NUM> and restricts motion (e.g., skew) of the fixing belt <NUM> in the longitudinal direction of the fixing belt <NUM> even if the fixing belt <NUM> moves to one side in the longitudinal direction of the fixing belt <NUM>. One of both ends of the heater holder <NUM> and one of both ends of the stay <NUM> are inserted into one of the supporting recesses 32d, and the other one of both ends of the heater holder <NUM> and the other one of both ends of the stay <NUM> are inserted into the other one of the supporting recesses 32d. Thus, the pair of supports <NUM> supports the heater holder <NUM> and the stay <NUM>.

As illustrated in <FIG>, the heater holder <NUM> includes a positioning recess 23e, serving as a positioner, disposed at one lateral end 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 right parts in <FIG> does not include the engagement 32e. 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> allows 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>. Each step portion 24a abuts the support <NUM> to restrict movement of the stay <NUM> in the longitudinal direction of the stay <NUM> with respect to the support <NUM>. However, at least one of the step portions 24a is arranged to have a gap, that is, loose fit with play between the step portion 24a and the support <NUM>. The above-described arrangement of the gap between the support <NUM> and at least one of the step portions 24a allows an expansion and contraction of the stay <NUM> in the longitudinal direction of the fixing belt <NUM> due to the temperature change.

<FIG> is a plan view of the heater <NUM> according to the present embodiment, and <FIG> is an exploded perspective view of the heater <NUM>.

As illustrated in <FIG>, the heater <NUM> includes a base <NUM> that is a plate. A first insulation layer <NUM>, a conductor layer <NUM>, and a second insulation layer <NUM> are layered on the base <NUM>. The base <NUM> longitudinally extends in a direction indicated by arrow Z in <FIG>, that is, the longitudinal direction of the fixing belt <NUM> and the direction of the rotation axis of the pressure roller <NUM>.

The base <NUM> is made of a metal material such as stainless steel (SUS), iron, or aluminum. The base <NUM> may be made of ceramic, glass, etc. instead of metal. The base <NUM> made of an insulating material such as ceramic allows omitting the first insulation layer <NUM> sandwiched between the base <NUM> and the conductor layer <NUM>. In contrast, 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 the base <NUM> made of 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, ceramic, or polyimide.

The conductor layer <NUM> includes a plurality of electrodes <NUM> and a plurality of power supply lines <NUM> as a plurality of conductors in addition to the plurality of resistive heat generators <NUM>. Each of the resistive heat generators <NUM> is electrically coupled to any two of the three electrodes <NUM> via the plurality of power supply lines <NUM> disposed above the base <NUM>. Thus, the resistive heat generators <NUM> are electrically coupled in parallel to each other.

For example, the resistive heat generators <NUM> are produced as below. Silver-palladium (AgPd), glass powder, and the like are mixed to make paste. The paste is screenprinted on the first insulation layer <NUM> layered on the base <NUM>. Thereafter, the base <NUM> is subject to firing. Then, the resistive heat generators <NUM> are produced. The material of the resistive heat generator <NUM> may contain a resistance material, such as silver alloy (AgPt) or ruthenium oxide (RuO<NUM>), other than the above material.

The electrodes <NUM> and the power supply lines <NUM> are made of conductors having an electrical resistance value smaller than the electrical resistance value of the resistive heat generators <NUM>. Specifically, the electrodes <NUM> and the power supply lines <NUM> may be made of a material prepared with silver (Ag), silver-palladium (AgPd), or the like. Screen-printing such a material on the first insulation layer <NUM> disposed on the base <NUM> forms the electrodes <NUM> and the power supply lines <NUM>.

As illustrated in <FIG>, the heater <NUM> includes the second insulation layer <NUM> covering every resistive heat generators <NUM> and at least a part of the power supply lines <NUM> to ensure the insulation between them. In contrast, the second insulation layer <NUM> does not cover most of the electrodes <NUM> to expose the electrodes <NUM> so as to be connected to the connector.

<FIG> is a perspective view of the connector connected to the heater according to the present embodiment.

As illustrated in <FIG>, the connector <NUM> includes a housing <NUM> made of resin and a plurality of contact terminals <NUM>. Each contact terminal <NUM> is an elastic member having conductivity such as a flat spring. Contact terminals <NUM> are disposed on the housing <NUM>. Contact terminals <NUM> are coupled to harnesses <NUM> that supply power, respectively.

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. Thus, the connector <NUM> holds the heater <NUM> and the heater holder <NUM>. Similarly, another connector <NUM> is connected to the electrode <NUM> located at another end of the heater <NUM> that is different from an end of the heater <NUM> on which the electrodes <NUM> illustrated in <FIG> are located. Contact portions 72a disposed at ends of the contact terminals <NUM> in the connector <NUM> elastically contact and press against the electrodes <NUM> each corresponding to the contact terminals <NUM> to electrically connect electrodes <NUM> and contact terminals <NUM>, respectively. The above-described configuration enables a power supply disposed in the body of the image forming apparatus to supply power to the resistive heat generators <NUM>. In other words, the power is supplied to each resistive heat generator <NUM> via the connectors <NUM>, and each resistive heat generator <NUM> generates heat.

As illustrated in <FIG>, in the present embodiment, the resistive heat generators <NUM> are arranged in the longitudinal direction of the base <NUM> and includes a first resistive heat generator group 60A serving as a first heat generation part and a second resistive heat generator group 60B serving as a second heat generation part. The first resistive heat generator group 60A includes the resistive heat generators <NUM> other than the resistive heat generators <NUM> above both ends of the base <NUM>. The second resistive heat generator group 60B includes the resistive heat generators <NUM> above both ends of the base <NUM>. The first resistive heat generator group 60A and the second resistive heat generator group 60B are separately controllable to generate heat. Specifically, each of the resistive heat generators <NUM> of the first resistive heat generator group 60A (i.e., the resistive heat generators <NUM> other than the resistive heat generators <NUM> above both ends of the base <NUM>) is connected, through a first power supply line 62A, to a first electrode 61A above a first longitudinal end of the base <NUM>. In addition, each of the resistive heat generators <NUM> of the first resistive heat generator group 60A is also connected, through a second power supply line 62B, to a second electrode 61B above a second longitudinal end of the base <NUM> that is the other end of the first longitudinal end of the base <NUM> above which the first electrode 61A is disposed. On the other hand, each of the resistive heat generators <NUM> of the second resistive heat generator group 60B (i.e., the resistive heat generators <NUM> above both ends of the base <NUM>) is connected, through a third power supply line 62C or a fourth power supply line 62D, to a third electrode 61C (that is different from the first electrode 61A) above the first longitudinal end of the base <NUM>. Like each of the resistive heat generators <NUM> of the first resistive heat generator group 60A, each of the second resistive heat generator group 60B is also connected to the second electrode 61B through the second power supply line 62B.

Connecting the connector <NUM> described above to the electrodes 61A to 61C enables a power supply <NUM> to supply power to each resistive heat generator <NUM>. A switch 65A as a switching unit is disposed between the first electrode 61A and the power supply <NUM>, and a switch 65C as a switching unit is disposed between the third electrode 61C and the power supply <NUM>. A control circuit <NUM> controls ON and OFF of these switches 65A and 65C and timing of power supply to the heater <NUM>. For example, the control circuit <NUM> controls ON and OFF of each of the switches 65A and 65C based on detection results of various sensors such as a sheet size sensor in the image forming apparatus <NUM>.

Applying a voltage to the first electrode 61A and the second electrode 61B generates an electric potential difference between the first electrode 61A and the second electrode 61B, and a current flows the resistive heat generators <NUM> other than the resistive heat generators at both ends. As a result, the first resistive heat generator group 60A generates heat alone. Similarly, applying a voltage to the second electrode 61B and the third electrode 61C generates an electric potential difference between the second electrode 61B and the third electrode 61C, and a current flows the resistive heat generators <NUM> at both ends. As a result, the second resistive heat generator group 60B generates heat alone. When a voltage is applied to all the first to third electrodes 61A to 61C, the resistive heat generators <NUM> of both the first resistive heat generator group 60A and the second resistive heat generator group 60B (i.e., all the resistive heat generators <NUM>) generate heat. For example, the first resistive heat generator group 60A generates heat alone to fix the toner image on a sheet P having a relatively small width conveyed, such as the sheet P of A4 size (sheet width: <NUM>) or a smaller sheet P. By contrast, the second resistive heat generator group 60B generates heat together with the first resistive heat generator group 60A to fix a toner image on a sheet P having a relatively large width conveyed, such as a sheet P of A3 size (sheet width: <NUM>) or a larger sheet P. As a result, the heater <NUM> can generate heat in a heat generation area corresponding to a sheet width.

Generally, the power supply line slightly generates heat when the resistive heat generator generates heat in the heater including the resistive heat generators above the base as described above. The heat generation distribution of the power supply lines may cause the temperature variation in the temperature distribution of the heater. In particular, increasing currents flowing through the resistive heat generators to increase heat generation amount in response to speeding up the image forming apparatus increases the amounts of heat generated in the power supply lines. As a result, affection by the heat generated in the power supply lines cannot be ignored.

With reference to <FIG> and <FIG>, the following describes a temperature distribution variation (a temperature distribution deviation) occurring in the heater <NUM> according to the present embodiment.

<FIG> illustrates blocks separated so as to include each of the resistive heat generators <NUM> and heat generation amounts generated by each of the power supply lines 62A, 62B, and 62D and a total heat generation amount in each block when the current with the same value flows through each of the resistive heat generators <NUM>. The current value is simply referred to as <NUM>%. Based on a relation between a heat generation amount (W) and a current (I) represented by the following equation (<NUM>), each of the heat generation amounts indicated in the table of <FIG> is calculated as the square of the current (I) flowing through each of the power supply lines. Therefore, the numerical values of the heat generation amounts indicated in the table of <FIG> are merely values calculated simply and are different from the actual heat generation amounts. Since a length of each of the power supply lines 62A, 62B, and 62D extending in the short-side direction of the heater <NUM> (that is the direction indicated by arrow Y in <FIG>) is relatively shorter than a length of each of the power supply lines 62A, 62B, and 62D extending in the longitudinal direction of the heater <NUM> (that is the direction indicated by arrow Z in <FIG>), a heat generation amount generated in a portion of each of the power supply lines 62A, 62B, and 62D extending in the short-side direction is relatively small. Therefore, the heat generation amount generated in the portion of each of the power supply lines 62A, 62B, and 62D extending in the short-side direction is eliminated in the table of <FIG>. The table illustrated in <FIG> simply indicates the calculated heat generation amounts generated in a portion of each of power supply lines 62A, 62B, and 62D extending in the longitudinal direction of the heater <NUM>. The short-side direction of the heater <NUM> means a direction (that is, the direction Y) intersecting the longitudinal direction (that is, the direction Z) along the surface of the first insulation layer <NUM> on which the resistive heat generators <NUM> are disposed. Equation <NUM> <MAT> where W represents the heat generation amount, R represents the resistance, and I represents the current.

With continued reference to <FIG>, a description is given of a specific way of calculating the heat generation amount for the first and second blocks, for example. In the first block in <FIG>, a proportion of a current flowing through the fourth power supply line 62D to the current flowing through the first power supply line 62A is <NUM>%, and the proportion of the current flowing through the first power supply line 62A is expressed as <NUM>%. Therefore, the total heat generation amount generated by the power supply lines 62A and 62D in the first block is expressed as <NUM>, which is the total value of the square of the current flowing through the first power supply line 62A that is <NUM> (i.e., the square is <NUM>) and the square of the current flowing through the fourth power supply line 62D that is <NUM> (i.e., the square is <NUM>). In the second block in <FIG>, a proportion of a current flowing through the first power supply line 62A is <NUM>%, a proportion of a current flowing through the second power supply line 62B is <NUM>%, and a proportion of a current flowing through the fourth power supply line 62D is <NUM>%. Therefore, the total heat generation amount generated by the power supply lines 62A, 62B, and 62D in the second block is expressed as <NUM>, which is the total value of the square of the current flowing through the first power supply line 62A that is <NUM> (i.e., the square is <NUM>), the square of the current flowing through the second power supply line 62B that is <NUM> (i.e., the square is <NUM>), and the square of the current flowing through the fourth power supply line 62D that is <NUM> (i.e., the square is <NUM>), that is, <NUM> + <NUM> + <NUM> = <NUM>. The heat generation amounts in other blocks are similarly calculated.

The y-axis in the graph in <FIG> represents the total heat generation amounts described above in the blocks. As can be seen from this graph, the total heat generation amount generated by the power supply lines in each of blocks disposed both ends (i.e., the first block and a seventh block) is larger than the total heat generation amount of each of blocks disposed on a center portion of the heater <NUM> (i.e., a third block and a fourth block). The above-described variation in the heat generation distribution generated by the power supply lines over the longitudinal direction Z of the heater <NUM> causes the variation in the temperature distribution of the heater <NUM>.

The temperature variation caused by the above-described variation in the heat generation distribution generated by the power supply lines may occur not only when all the resistive heat generators generate heat as described in <FIG> but also when a part of the resistive heat generators generate heat. In particular, when downsizing the heater or increasing a print speed of the image forming apparatus causes an unintended shunt in the power supply line, the temperature variation may become significant. The unintended shunt easily occurs when reducing a width of the power supply lines in the short-side direction of the heater to downsize the heater in the short-side direction increases the resistance values of the power supply lines. In addition, the unintended shunt easily occurs when the resistance values of the resistive heat generators are set to be small to increase the heat generation amounts of the resistive heat generators to increase the print speed of the image forming apparatus. That is, when the resistance value of the power supply line and the resistance value of the resistive heat generator are relatively close to each other in accordance with at least one of increasing the resistance values of the power supply lines or small resistance values of the resistive heat generators, a current may flow through a path through which the current did not flow before, that is, the unintended shunt may occur.

For example, as illustrated in <FIG>, unintended shunt occurs when a current flows through the resistive heat generators <NUM> other than the resistive heat generators <NUM> disposed at both ends. Specifically, a proportion of a current flowing through each of the resistive heat generators <NUM> other than the resistive heat generators <NUM> at both ends to a total current is <NUM>% in this example. However, <NUM>% of the current passing through the second resistive heat generator <NUM> from the left in <FIG> flows from a branch X of the second power supply line 62B toward the left side in <FIG> in a direction opposite a direction toward the second electrode 61B. As a result, a shunted current occurs. The shunted current then passes through the resistive heat generator <NUM> on the left end in <FIG> and further passes through the third power supply line 62C, the third electrode 61C, the fourth power supply line 62D, and the resistive heat generator <NUM> on the right end in <FIG> in this order. Finally, the current joins the second power supply line 62B. In the examples in <FIG> and <FIG>, the current flows in one direction, but the present disclosure is not limited to this. The current flowing through the heater <NUM> may be alternating current.

A table and a graph in <FIG> illustrate heat generation amounts generated by each of the first power supply line 62A, the second power supply line 62B, and the fourth power supply line 62D and their total heat generation amounts in each of the blocks of the heater <NUM> flowing the unintended shunt. The method of calculating the heat generation amount is the same as the method described in the example in <FIG>. For the same reason as in the example illustrated in <FIG>, the heat generation amount of the portion extending in the short-side direction (that is the direction indicated by arrow Y) of each of the power supply lines 62A, 62B, and 62D is omitted in the example illustrated in <FIG>.

As can be seen from the table and the graph in <FIG>, the total heat generation amounts generated by the power supply lines in both end blocks (that is, the second block and the sixth block) are also larger than the total heat amount of the center block (that is, the fourth block) in this case, and the variation in the temperature distribution due to the power supply lines occurs. However, contrary to the graph in <FIG>, the total heat generation amount in the left end block is larger than the total heat generation amount in the right end block in the graph in <FIG>. As a result, a temperature in the left end block is higher than a temperature in the right end block.

As described above, the difference between the heat generation amounts generated by the power supply lines in blocks causes an uneven temperature distribution of the heater over the longitudinal direction in the heater according to the present embodiment. The above-described uneven temperature distribution of the heater affects not only the fixing device but also other devices in the image forming apparatus.

Specifically, the image forming apparatus according to the present embodiment includes the process unit 1Y near the fixing device <NUM> as illustrated in <FIG>, and the uneven temperature distribution of the heater affects the process unit 1Y. In addition, since the intermediate transfer belt <NUM> rotates and transmits the heat of the process unit 1Y close to the fixing device <NUM> to the other process units <NUM>, 1C, and 1Bk, the other process units <NUM>, 1C, and 1Bk are influenced to no small degree by the uneven temperature distribution of the heater.

As a result, the temperature distribution of the cleaning blade <NUM> in each of the process units 1Y, <NUM>, 1C, and 1Bk becomes uneven, and the cleaning performance of the cleaning blade <NUM> may be deteriorated particularly at a high temperature portion of the cleaning blade <NUM>. Hereinafter, the principle of deterioration in the cleaning performance of the cleaning blade <NUM> is described.

As illustrated in <FIG>, the cleaning blade <NUM> is generally set to be in contact with the photoconductor <NUM> in a counter direction with respect to a rotation direction A (a surface movement direction) of the photoconductor <NUM>. The blade holder <NUM> holds the cleaning blade <NUM> in a cantilever manner. The counter direction is defined as a direction in which the tip end (that is a free end) of the cleaning blade <NUM> is located upstream from the rear end of the cleaning blade <NUM> (that is an end supported by the blade holder <NUM>) in a rotation direction of the photoconductor <NUM>. As the photoconductor <NUM> rotates, the cleaning blade <NUM> rubs against the surface of the photoconductor <NUM>. Although force in the rotation direction A of the photoconductor <NUM> acts on the tip end as a rubbing portion 77a of the cleaning blade <NUM> as illustrated in <FIG>, the cleaning blade <NUM> is normally held in the counter direction.

However, when the above-described uneven temperature distribution of the heater affects the temperature distribution of the cleaning blade <NUM> to be uneven, the uneven temperature distribution of the cleaning blade <NUM> generates a high temperature portion of the cleaning blade <NUM> having a high rebound resilience with respect to the photoconductor <NUM>. The high rebound resilience increases the friction force between the cleaning blade <NUM> and the photoconductor <NUM>. The high friction force between the cleaning blade <NUM> and the photoconductor <NUM> and the force of the photoconductor <NUM> in the rotation direction A of <FIG> cause so-called curling in which the tip of the cleaning blade <NUM> is reversed as indicated with a dashed line in <FIG>.

As described above, the temperature distribution of the heater affects the temperature distribution of the cleaning blade <NUM> to generate the high temperature portion of the cleaning blade <NUM> that may cause the curling. The occurrence of the curling of the cleaning blade <NUM> prevents maintaining a suitable contact state of the cleaning blade <NUM> with respect to the photoconductor <NUM> and deteriorates the cleaning performance of the cleaning blade <NUM>.

In the present embodiment, the following measures are taken so as to prevent the curling of the cleaning blade <NUM> and maintain the suitable contact state of the cleaning blade <NUM> with respect to the photoconductor <NUM>.

Firstly, the following describes the temperature distribution of the cleaning blade according to the present embodiment with reference to <FIG>.

As illustrated in <FIG>, the cleaning blade <NUM> extends in a longitudinal direction of the photoconductor <NUM> or in a direction of a rotation axis of the photoconductor <NUM>, that is, in a direction indicated by arrow Z in <FIG>. In the above-described configuration, the rubbing portion 77a that is a portion of the cleaning blade <NUM> rubbing the photoconductor <NUM> also extends in the direction indicated by the arrow Z. The longitudinal direction of the cleaning blade <NUM> is the same as the longitudinal direction of the heater <NUM>. In other words, both the cleaning blade <NUM> and the heater <NUM> extend in a sheet width direction (that is the direction indicated by the arrow Z). The above-described term the "sheet width direction (in other words, a recording medium width direction)" means a direction parallel to a sheet surface and orthogonal to the sheet conveyance direction B (a recording medium conveyance direction) in <FIG>. In addition, the "sheet surface" means a surface having the largest area among surfaces of the sheet in three directions intersecting each other.

As described above, since both the cleaning blade <NUM> and the heater <NUM> extend longitudinally in the same direction Z (the direction orthogonal to the sheet conveyance direction), the temperature distribution over the longitudinal direction of the heater <NUM> influences the temperature distribution in the longitudinal direction of the cleaning blade <NUM>. Both the rubbing portion 77a of the cleaning blade <NUM> rubbing the photoconductor <NUM> and a heat generation area H in which the resistive heat generators <NUM> of the heater <NUM> are disposed have substantially the same lengths (lengths in a direction orthogonal to the sheet conveyance direction) and are disposed over a range including the maximum sheet width or the maximum image formation area width. The developing device <NUM> and the like are disposed between the rubbing portion 77a and the heater <NUM>. Accordingly, both ends of the rubbing portion 77a in the longitudinal direction indirectly face both ends of the heater <NUM> in the longitudinal direction. The temperature distribution of the heater <NUM> influences the intermediate transfer belt <NUM>, the developing device <NUM>, and the like near the heater <NUM>, and the influence also affects the cleaning blade <NUM>. The temperature distribution of the heater <NUM> influences the cleaning blade <NUM> such that a temperature of an end of the rubbing portion 77a becomes higher than a temperature of a center portion of the rubbing portion 77a in the longitudinal direction Z (that is the direction orthogonal to the sheet conveyance direction).

Note that "the end of the rubbing portion 77a of the cleaning blade <NUM> faces the end of the heater <NUM>" in the present embodiment means that the end of the rubbing portion 77a is at a position at which the heat of the end of the heater <NUM> affects a function of the end of the rubbing portion 77a. For example, the end of the rubbing portion 77a faces the end of the heater <NUM> when the end of the rubbing portion 77a is substantially at the same position as the end of the heater <NUM> in the longitudinal direction of the heater <NUM>.

The graph in <FIG> illustrates the temperature distribution of the heater <NUM> when all the resistive heat generators <NUM> included in the heater <NUM> generate heat. In this case, the temperatures in the first block and the seventh block of the heater <NUM> on both ends e1 and e2 of the heat generation area H in the longitudinal direction are higher than other temperatures in the heat generation area H in which the resistive heat generators <NUM> are disposed. As a result, temperatures of portions a1 and a2 of the cleaning blade <NUM> facing both ends e1 and e2 in the longitudinal direction of the heat generation area H of the heater <NUM> are higher than a temperature of a portion a5 of the cleaning blade <NUM> facing the longitudinal center c of the heat generation area H of the heater <NUM>, as illustrated in <FIG>.

The graph in <FIG> illustrates the temperature distribution of the heater <NUM> when the first resistive heat generator group (that is, the resistive heat generators <NUM> other than the resistive heat generators at both ends) included in the heater <NUM> generate heat. In this case, the temperatures in the second block and the sixth block of the heater <NUM> near both ends e1 and e2 of the heat generation area H in the longitudinal direction are higher than other temperatures in the heat generation area H of the heater <NUM>. As a result, temperatures of portions a3 and a4 of the cleaning blade <NUM> facing both ends e1 and e2 in the longitudinal direction of the heat generation area H of the heater <NUM> are higher than the temperature of the portion a5 of the cleaning blade <NUM> facing the longitudinal center c of the heat generation area H of the heater <NUM>, as illustrated in <FIG>.

As described above, the cleaning blade <NUM> according to the present embodiment tends to have the temperatures at both ends higher than the temperature at the center portion in the longitudinal direction under the heat generation distributions illustrated in <FIG> and <FIG>. For this reason, the cleaning blade <NUM> according to the present embodiment is designed so that friction forces between photoconductor <NUM> and both ends of the rubbing portion 77a are smaller than a friction force between the photoconductor <NUM> and the center portion of the rubbing portion 77a in the longitudinal direction in order to prevent the curling of the cleaning blade <NUM>. In the above description, the friction force between the photoconductor <NUM> and the portion of the rubbing portion 77a facing the heater <NUM> is set. In other words, the cleaning blade <NUM> in the present embodiment is configured to have a small friction force between photoconductor <NUM> and a portion of the rubbing portion 77a corresponding to a high temperature portion of the heater <NUM>. The high temperature portion of the heater <NUM> is a high heat generation portion of heater <NUM>, in the present embodiment, each of both ends of the heater <NUM>. The heater <NUM> in the above-described embodiment generates a larger heat amount at both ends than another portion. When the heater <NUM> generates a larger heat amount at one end than another portion, the cleaning blade <NUM> is configured to have a smaller friction force at one end of the rubbing portion 77a facing the one end of the heater <NUM> than another portion of the rubbing portion 77a.

In general, the friction force between the cleaning blade and the photoconductor includes a static friction force (a maximum static friction force) generated at the moment when the photoconductor starts rotating and a dynamic friction force generated while the photoconductor rotates after the photoconductor starts rotating. The curling of the cleaning blade may occur both at the moment when the photoconductor starts rotating and thereafter while the photoconductor is rotating. In order to reliably prevent the curling of the cleaning blade in each case, it is preferable to reduce both the static friction force and the dynamic friction force. However, since the image forming apparatus in the present embodiment has an advantage if the configuration in the present embodiment can prevent at least one of the curling occurring when photoconductor starts rotating and the curling occurring while the photoconductor is rotating, the friction force in the present specification means at least one of the static friction force and the dynamic friction force.

As described above, the rubbing portion 77a in which the cleaning blade <NUM> according to the present embodiment rubs the photoconductor <NUM> according to the present embodiment includes longitudinal both ends facing the high temperature portions of the heater <NUM>. The friction forces between the cleaning blade <NUM> and the photoconductor <NUM> on the longitudinal both ends are smaller than the friction force on another portion of the cleaning blade <NUM>. Therefore, the curling of the cleaning blade <NUM> caused by rotation of photoconductor <NUM> can be effectively prevented even if the temperature distribution of the heater <NUM> affects the cleaning blade. As a result, the above-described configuration can maintain an appropriate contact state of the cleaning blade <NUM> with respect to the photoconductor <NUM> and ensure good cleaning performance.

In order to ensure the good cleaning performance, it is preferable to prevent the curling of the cleaning blade <NUM> under the heat generation distributions illustrated in <FIG> and <FIG>. Under the heat generation distributions illustrated in <FIG> and <FIG>, temperatures of the first, seventh, second, and sixth blocks are higher than the temperature of the fourth block at the center of the heater <NUM>. Accordingly, friction forces between the photoconductor <NUM> and portions a1, a2, a3, and a4 of the cleaning blade <NUM> facing the first, seventh, second, and sixth blocks of the heater <NUM>, respectively are designed to be smaller than a friction force between the photoconductor <NUM> and a portion a5 of the cleaning blade <NUM> at the center of the cleaning blade <NUM>.

However, the portion or a range of the cleaning blade <NUM> in which the friction force is reduced may be appropriately changed. For example, the friction forces between the photoconductor <NUM> and only the portions a1 and a2 of the cleaning blade <NUM> facing the first and seventh block of the heater <NUM>, respectively may be designed to be smaller than a friction force between the photoconductor <NUM> and another portion of the cleaning blade <NUM> to prevent the curling of the cleaning blade <NUM> under the heat generation distribution illustrated in <FIG> in which the variation in the temperature distribution is particularly significant. The friction force may not be set for each block in which the resistive heat generator <NUM> is disposed. For example, the friction force may be changed continuously or stepwise in one block.

A portion of the cleaning blade <NUM> on which the curling may occur corresponds to the high temperature portion of the heater <NUM>, and the high temperature portion of the heater <NUM> may be identified by comparison between the heat generation amounts of portions of the heater <NUM> in the longitudinal direction of the heater <NUM> (that is the same as the sheet width direction). Note that "the heat generation amounts of portions of the heater <NUM> in the longitudinal direction of the heater <NUM>" include the heat generation amounts generated by the power supply lines <NUM> in addition to the heat generation amounts generated by the resistive heat generators <NUM>.

As illustrated in the above-described equation (<NUM>), since the heat generation amount (W) is proportional to the square of the current (I), a magnitude relation between the heat generation amounts of the heater <NUM> may be identified by using a sum of the square of the currents flowing through the power supply lines 62A, 62B, and 62D. In the above description, since the "currents flowing through the power supply lines 62A, 62B, and 62D" are currents used to specify the magnitude relationship of the heat generation amounts of the heater <NUM>, the above "currents flowing through the power supply lines 62A, 62B, and 62D" do not include the currents flowing through the power supply lines 62A, 62B, and 62D in regions including the resistive heat generators <NUM> at both ends that do not generate heat as in the example illustrated in <FIG>. In other words, the "current flowing through the power supply lines 62A, 62B, and 62D" used to specify the magnitude relationship of the heat generation amounts of the heater <NUM> means currents flowing through the power supply lines 62A, 62B, 62D in a region including the resistive heat generator <NUM> that generates heat. Strictly speaking, the resistive heat generators <NUM> at both ends generate heat in the example illustrated in <FIG> because the unintended shunt that is a little current flows through the resistive heat generators <NUM> at both ends (see <FIG>). However, the above-described "resistive heat generator <NUM> that generates heat" means the resistive heat generators <NUM> that are normally energized to generate heat. Therefore, the region including the resistive heat generator <NUM> through which the unintended shunt flows to slightly generate heat is not considered as the region to specify the magnitude relationship of the heat generation amounts.

Specifically, the following describes structures to reduce the friction force between the cleaning blade <NUM> and the photoconductor <NUM>.

Initially, the friction force is described. As illustrated in the following equation (<NUM>), the friction force (F) between the cleaning blade and the photoconductor is obtained by multiplying a friction coefficient (µ) between the photoconductor and the cleaning blade by the contact pressure (N) of the cleaning blade with respect to the photoconductor. Equation <NUM> <MAT>.

Therefore, according to the equation (<NUM>), the friction force (F) of the cleaning blade can be reduced by reducing the contact pressure (N) of the cleaning blade pressing the photoconductor. The contact pressure (N) of the cleaning blade <NUM> is changed by a free length J (see <FIG>) that is a length of a portion of the cleaning blade <NUM> protruding from the blade holder <NUM> toward the photoconductor <NUM>. That is, as the free length J of the cleaning blade <NUM> is longer, the cleaning blade <NUM> is more easily bent, and thus the contact pressure of the cleaning blade <NUM> with respect to the photoconductor <NUM> becomes smaller.

Therefore, as in the example illustrated in <FIG>, setting free lengths of both ends of the cleaning blade <NUM> in the longitudinal direction (the direction indicated by arrow Z in <FIG>) longer than a free length of the central portion of the cleaning blade <NUM> (J1 <J2) can reduce the friction forces between the photoconductor and both ends of the cleaning blade <NUM> at which the curling is likely to occur.

In the example illustrated in <FIG>, the length of a part of the blade holder <NUM> to hold the cleaning blade <NUM> is continuously changed from the center (the length is R1) to both ends (the length is R2) in the longitudinal direction. In other words, in this case, the length R2 of the part of the blade holder <NUM> holding the cleaning blade <NUM> at both ends is set shorter than the length R1 of the part of the blade holder <NUM> holding the cleaning blade <NUM> at the center (that is, R1 > R2) to set the free lengths of both ends of the cleaning blade <NUM> longer than the free length of the center of the cleaning blade <NUM>.

The shape of the blade holder <NUM> may be appropriately changed. For example, an example as illustrated in <FIG> may be employed. In the example illustrated in <FIG>, the lengths R2 of the parts holding the cleaning blade <NUM> on the blade holder <NUM> in both ends of the blade holder <NUM> having a certain length from both sides of the blade holder <NUM> in the longitudinal direction in which the curling is likely to occur is set shorter than the length R1 of the part holding the cleaning blade <NUM> on the blade holder <NUM> at the center of the blade holder <NUM> (that is, R1 > R2). The above-described structure can reduce a manufacturing cost of the blade holder <NUM> because both ends of the blade holder <NUM> having the certain length from both ends in the longitudinal direction is processed to be short, and another portion is not processed. The tip shape of each of both ends of the blade holder <NUM> having the certain length from both ends in the longitudinal direction may be a shape inclined with respect to the longitudinal direction as in the example illustrated in <FIG> or may be a stepped shape orthogonal to the longitudinal direction as in the example illustrated in <FIG>.

Another structure to reduce the friction force between the cleaning blade <NUM> and the photoconductor <NUM> is the cleaning blade <NUM> having different thicknesses in the longitudinal direction (the direction indicated by arrow Z) as illustrated in <FIG>. The "thickness" of the cleaning blade <NUM> means a dimension in a direction indicated by arrow U in <FIG> intersecting both the longitudinal direction of the cleaning blade <NUM> indicated by arrow Z and a protruding direction indicated by arrow V in which the cleaning blade <NUM> protrudes from the blade holder <NUM>. As the thickness of the cleaning blade <NUM> is thinner, the cleaning blade <NUM> is more easily bent, and thus the contact pressure of the cleaning blade <NUM> with respect to the photoconductor <NUM> becomes smaller. As a result, the friction force becomes small.

Therefore, as illustrated in <FIG>, setting thicknesses of both ends of the cleaning blade <NUM> in the longitudinal direction smaller than a thickness of the central portion of the cleaning blade <NUM> (T1 < T2) can reduce the friction forces between the photoconductor <NUM> and both ends of the cleaning blade <NUM> at which the curling is likely to occur. Similar to the above-described cleaning blade <NUM> having different free lengths, the thickness of the cleaning blade <NUM> may be continuously reduced from the center to both ends in the longitudinal direction or may be reduced only at both ends having a certain length from both ends in the longitudinal direction in which the curling is particularly likely to occur.

Another structure to reduce the friction force between the cleaning blade <NUM> and the photoconductor <NUM> is the cleaning blade <NUM> including portions made of different materials. Since the contact pressure of the cleaning blade <NUM> made of a material having a low rebound resilience with respect to the photoconductor <NUM> is small, the friction force can be reduced.

For example, in the example illustrated in <FIG>, the cleaning blade <NUM> includes both ends (hatched portions in <FIG>) in the longitudinal direction of the cleaning blade <NUM>, and both ends are made of a material having lower rebound resilience than other portions including the central portion. The above-described structure reduces the friction force between the photoconductor <NUM> and both ends of the cleaning blade <NUM> in which the curling is likely to occur and can prevent the curling on both ends.

The end made of different material is not limited to the entire portion in the thickness direction U of the cleaning blade <NUM> as in the example illustrated in <FIG>. As in the example illustrated in <FIG>, a part of the end in the thickness direction U (a hatched portion in <FIG>) may be made of the different material. The part of the end of the cleaning blade <NUM> in the thickness direction U (the hatched portion in <FIG>) made of the material having the lower rebound resilience preferably contacts the photoconductor <NUM>.

Another structure to reduce the friction force between the cleaning blade <NUM> and the photoconductor <NUM> is a structure increasing lubricity between the cleaning blade <NUM> and the photoconductor <NUM> on both ends in which the curling of the cleaning blade <NUM> easily occurs. For example, as illustrated in <FIG>, the lubricant supply device supplies the regions b1 and b2 of the photoconductor <NUM> that are in contact with both ends of the cleaning blade <NUM> in which the curling is likely to occur with the lubricant having higher lubricity than the lubricant supplied to the other regions of the photoconductor <NUM> including the center of the photoconductor <NUM>. The above-described structure reduces the friction forces between the photoconductor <NUM> and both ends of the cleaning blade <NUM> and can prevent the curling. Alternatively, the lubricant supply device may be configured to supply the lubricant to only the region of the photoconductor <NUM> in which the lubricity between the cleaning blade <NUM> and the photoconductor <NUM> is increased.

As the lubricant, for example, a solid lubricant including fatty acid metal salt may be used. The fatty acid metal salt includes, for example, lauroyl lysine, monocetyl phosphate sodium zinc salt, lauroyltaurine calcium, and fatty acid metal salt having a lamellar crystal structure such as fluororesin, zinc stearate, calcium stearate, barium stearate, aluminum stearate, and magnesium stearate. Alternatively, a liquid lubricant such as silicone oil, fluorine-based oil, or natural wax may be used.

The above-described various methods for reducing the friction force between the cleaning blade <NUM> and the photoconductor <NUM> may be used in combination. For example, both ends having the long free lengths and the small thicknesses in the longitudinal direction of the cleaning blade <NUM> can effectively reduce the friction forces between both ends of the cleaning blade <NUM> and the photoconductor <NUM>.

The image forming apparatus <NUM> is configured so that the friction forces between the photoconductor <NUM> and the both ends of the cleaning blade <NUM> are smaller than the friction force between the photoconductor <NUM> and the center portion of the cleaning blade <NUM> in the above-described embodiments but may be configured so that the friction force between only one end of the cleaning blade <NUM> and the photoconductor <NUM> is smaller than the friction force between the photoconductor <NUM> and the center of the cleaning blade <NUM>. For example, as in the example illustrated in <FIG>, the image forming apparatus including the heater <NUM> having the seventh block in which the temperature is highest may be configured so that the friction force between the photoconductor <NUM> and one end of the cleaning blade <NUM> facing the seventh block is smaller than the friction force between the photoconductor <NUM> and another portion of the cleaning blade <NUM>.

The image forming apparatus according to the present embodiments is configured to have the following relation of the friction forces between photoconductor <NUM> and portions of the rubbing portion 77a in which the cleaning blade <NUM> rubs photoconductor <NUM>. That is, the friction force between the photoconductor <NUM> and a portion of the rubbing portion 77a facing the region of the heater <NUM> generating the largest heat generation amount is smaller than the friction force between the photoconductor <NUM> and a portion of the rubbing portion 77a facing the region of the heater <NUM> generating the smallest heat generation amount. In other words, the above relation is expressed as follows by using currents flowing through the power supply lines 62A, 62B, and 62D instead of the heat generations amounts in the heater <NUM>. That is, the friction force between the photoconductor <NUM> and a portion of the rubbing portion 77a facing the region of the heater <NUM> in which the largest total current flows through the power supply lines 62A, 62B, and 62D is smaller than the friction force between the photoconductor <NUM> and a portion of the rubbing portion 77a facing the region of the heater <NUM> in which the smallest total current flows through the power supply lines 62A, 62B, and 62D.

The application of the present disclosure is not limited to the cleaning blade <NUM> that cleans the surface of the photoconductor <NUM>. The present disclosure may also be applied to a blade that rubs against a rotator other than the photoconductor <NUM>. For example, the present disclosure may be also applicable to the cleaning blade <NUM> that cleans the surface of the intermediate transfer belt <NUM> illustrated in <FIG>.

<FIG> is a schematic diagram illustrating a positional relationship between the cleaning blade <NUM> to clean the surface of the intermediate transfer belt <NUM> and the heater <NUM> included in the fixing device.

As illustrated in <FIG>, since both the cleaning blade <NUM> for the intermediate transfer belt and the heater <NUM> extend longitudinally in the same direction Z (the direction orthogonal to the sheet conveyance direction), the temperature distribution over the longitudinal direction of the heater <NUM> influences the temperature distribution of the cleaning blade <NUM> in the longitudinal direction of the cleaning blade <NUM>. Both the rubbing portion 69a of the cleaning blade <NUM> rubbing the intermediate transfer belt <NUM> and a heat generation area H in which the resistive heat generators <NUM> of the heater <NUM> are disposed have substantially the same lengths (lengths in a direction orthogonal to the sheet conveyance direction) and are disposed over a range including the maximum sheet width or the maximum image formation area width. The housing of the belt cleaner <NUM> and the like are disposed between the rubbing portion 69a and the heater <NUM>. Accordingly, both ends of the rubbing portion 69a of the cleaning blade <NUM> for the intermediate transfer belt and both ends of the heater <NUM> in the longitudinal direction are indirectly facing each other.

Similar to the above-described embodiments, the heater <NUM> has both ends e1 and e2 having the higher temperatures than the center c in the longitudinal direction of the heat generation area H. The temperature distribution of the heater <NUM> influences the cleaning blade <NUM> for the intermediate transfer belt such that a temperature of an end of the rubbing portion 69a becomes higher than a temperature of a center portion of the rubbing portion 69a in the longitudinal direction Z (that is the direction orthogonal to the sheet conveyance direction). Since the cleaning blade <NUM> for the intermediate transfer belt is closer to the heater <NUM> than the cleaning blade <NUM> for the photoconductor, the cleaning blade <NUM> is more likely to be affected by the heat of the heater <NUM> than the cleaning blade <NUM> for the photoconductor.

As described above, since temperatures at both ends of the cleaning blade <NUM> for the intermediate transfer belt in the longitudinal direction is higher than a temperature at the center of the cleaning blade <NUM>, the curling of the cleaning blade <NUM> may occur at both ends. Accordingly, it is preferable to apply the present embodiments to the cleaning blade <NUM> for the intermediate transfer belt. The rubbing portion 69a in which the cleaning blade <NUM> rubs the intermediate transfer belt <NUM> includes longitudinal both ends facing the high temperature portions of the heater <NUM>. The friction forces between the intermediate transfer belt <NUM> and the longitudinal both ends of the cleaning blade <NUM> are preferably set to be smaller than the friction force between the intermediate transfer belt <NUM> and the center of the cleaning blade <NUM> in the longitudinal direction. The above-described structure can effectively prevent the curling of the cleaning blade <NUM> for the intermediate transfer belt <NUM> that is caused by rotation of the intermediate transfer belt <NUM>. A specific structure to reduce the friction force between the cleaning blade <NUM> and the intermediate transfer belt <NUM> may be each structure described in the above embodiments. In the above description, the friction force between the intermediate transfer belt <NUM> and the portion of the rubbing portion 69a facing the heater <NUM> is set. In other words, the cleaning blade <NUM> is configured to have a small friction force between the intermediate transfer belt <NUM> and a portion of the rubbing portion 69a corresponding to the high temperature portion of the heater <NUM>. The high temperature portion of the heater <NUM> is the high heat generation portion, in the present embodiment, each of both ends of the heater <NUM>. The heater <NUM> in the above-described embodiment generates a larger heat amount at both ends than another portion. When the heater <NUM> generates a larger heat amount at one end than another portion, the cleaning blade <NUM> is configured to have a smaller friction force at one end of the rubbing portion 69a facing the one end of the heater <NUM> than another portion of the rubbing portion 69a.

In addition to the cleaning blade <NUM> for the photoconductor and the cleaning blade <NUM> for the intermediate transfer belt, the present embodiments may be applied to the cleaning blade <NUM> to clean the surface of the secondary transfer belt <NUM> as a transferor as in the example illustrated in <FIG>.

As described above, in particular, the present embodiments are preferably applied to the image forming apparatus including a heating member that is likely to occur an uneven temperature distribution because the present embodiments can prevent the curling of the cleaning blade caused by the uneven temperature distribution of the heating member even if the heating member has the uneven temperature distribution.

The heating member that is likely to occur the uneven temperature distribution is the heater <NUM> described above in which the unintended shunt occurs, but a configuration of the heating member included in the image forming apparatus according to the present embodiments is not limited to the above-described configuration. For example, the present embodiments may be applied to the image forming apparatus including the heater <NUM> as illustrated in <FIG>.

The heater <NUM> illustrated in <FIG> is different from the above-described heater <NUM> illustrated in <FIG> in that all the electrodes 61A, 61B, and 61C are disposed on one end of the heater <NUM> (that is, left end in <FIG>) in the longitudinal direction of the heater <NUM>. That is, the position of the second electrode 61B in the heater <NUM> illustrated in <FIG> is opposite to the position of the second electrode 61B in the heater <NUM> illustrated in <FIG> in the lateral direction of <FIG> and <FIG>. In the heater <NUM> illustrated in <FIG>, each of the resistive heat generators <NUM> and the second electrode 61B are coupled to each other via, in addition to the second power supply line 62B, a fifth power supply line 62E disposed so as to be folded back in the longitudinal direction (that is the direction indicated by the arrow Z) from an end of the second power supply line 62B.

However, the following same points of the conductive paths of the heaters <NUM> illustrated in <FIG> and <FIG> generates the unintended shunt similar to the above description when power is supplied to the first resistive heat generator group 60A including the resistive heat generators <NUM> other than the resistive heat generators <NUM> at both ends. That is, the heater <NUM> illustrated in <FIG> and the heater <NUM> illustrated in <FIG> have common conductive paths that are a first conductive path K1, a second conductive path K2, and a third conductive path K3. Specifically, the first conductive path K1 couples the first electrode 61A to each of the resistive heat generators of the first resistive heat generator group 60A other than the resistive heat generators at both ends. The second conductive path K2 extends in the longitudinal direction of the heater <NUM> from each of the resistive heat generators <NUM> other than the resistive heat generators at both ends toward a first direction S1 (that is the right direction in <FIG> or <FIG>) and directly or indirectly couples the second electrode 61B to each of the resistive heat generators <NUM> other than the resistive heat generators at both ends. The third conductive path K3 is a conductive path that branches off from the second conductive path K2, extends toward a second direction S1 (that is the left direction in <FIG> or <FIG>) opposite to the first direction S2, and is coupled to the second conductive path K2 without passing through the first conductive path K1.

<FIG> is a schematic top view of the heater <NUM> of <FIG>, a table, and a graph illustrating heat generation amounts generated by the power supply lines 62A, 62B, 62D, and 62E and total heat generation amounts in each block when the resistive heat generators <NUM> other than the resistive heat generators <NUM> at both ends generate heat. As can be seen from the table and the graph in <FIG>, the total heat generation amounts generated by the power supply lines in both end blocks (that is, the second block and the sixth block) are also larger than the total heat amount of the center block (that is, the fourth block) in this case. As a result, the temperatures of the heater <NUM> at both ends are higher than the temperature at the center portion in the longitudinal direction of the heater <NUM>.

<FIG> is a schematic top view of the heater <NUM> of <FIG>, a table, and a graph illustrating heat generation amounts generated by the power supply lines 62A, 62B, 62D, and 62E and total heat generation amounts in each block when all the resistive heat generators <NUM> generate heat. Also, in this case, since the total heat generation amounts generated by the power supply lines in each of both end blocks (i.e., the first block and the seventh block) is larger than the total heat generation amount in the center block (i.e., the fourth block), the temperatures at both ends of the heater <NUM> is higher than the temperature at the center portion in the longitudinal direction of the heater <NUM>.

As described above, since the heater <NUM> illustrated in <FIG> also has the uneven temperature distribution in which the temperature is higher on both ends than on the center portion in the longitudinal direction of the heater <NUM>, applying the present embodiments can effectively prevent the curling of the blade caused by the uneven temperature distribution.

Since the embodiments of the present disclosure can improve an issue of the blade caused by the uneven temperature distribution of the heating member, that is, the curling of the blade, the embodiments can be applied to a configuration using a small heater or a heater having a large heat generation ability for high-speed printing that are likely to generate the uneven temperature distribution.

Specifically, a particularly large effect can be expected by applying the present embodiments of the present disclosure to the image forming apparatus including the following small heater.

The following Table <NUM> describes results of experiments that examined temperature differences caused by the uneven temperature distribution occurring in the heaters that are downsized in the short-side direction. Specifically, a plurality of heaters are prepared in the experiments. The heaters have different ratios (R / Q) of short-side dimensions R and Q. The short-side dimension R is a dimension of the resistive heat generators <NUM> in the short-side direction of the resistive heat generators <NUM>, and the short-side dimension Q is a dimension of the base <NUM> in the short-side direction of the base <NUM>, as illustrated in <FIG>. In each of experiments, the temperature difference between the center and the end in the longitudinal direction of the heat generation area of each heater was measured. In the experiments, the surface temperatures of the heater were measured using an infrared thermography FLIR T620 manufactured by FLIR Systems. When the ratio (R / Q) of the short-side dimensions R and Q is <NUM>% or more, the ratio of the short-side dimension of the resistive heat generators <NUM> to the short-side dimension of the base <NUM> is too large to design spaces for disposing the power supply lines. Therefore, designing the heater having the ratio (R / Q) <NUM>% or more is difficult. Thus, the measurement about the heater having the ratio (R / Q) <NUM>% or more was suspended.

As illustrated in Table <NUM>, the larger the ratio (R / Q) of the dimensions in the short-side direction is, the larger the temperature difference between the longitudinal center of the heat generation area and the end of the heat generation area is. This means that the temperature difference between both ends of the heater in the longitudinal direction of the heater is likely to be significantly large in the heater having the large ratio (R / Q) of the dimensions in the short-side direction, that is, in the heater miniaturized in the short-side direction. In particular, the heater having the ratio (R / Q) of the dimensions in the short-side direction that is <NUM>% or more or <NUM>% or more has a large temperature difference between the center and the end in the longitudinal direction of the heat generation area, that is, <NUM>. or more, and thus the temperature difference between both ends of the heater in the longitudinal direction is likely to become significantly large. Accordingly, particularly large effect can be expected by applying the present embodiment of the present disclosure to the image forming apparatus including the heater having the ratio (R / Q) of the dimensions in the short-side direction that is equal to or larger than <NUM>% and smaller than <NUM>% or equal to or larger than <NUM>% and smaller than <NUM>%.

The heater disposed in the fixing device is not limited to the heater <NUM> including block-shaped (in other words, square-shaped) resistive heat generators <NUM> as illustrated in <FIG>. The heaters <NUM> may include resistive heat generators <NUM> each having a shape in which a straight line is folded back as illustrated in <FIG>. Note that, in the heater <NUM> illustrated in <FIG>, the short-side dimension R of each of the resistive heat generators <NUM> refers to a short-side dimension of each of the entire resistive heat generators <NUM>, not to a thickness of the straight-line portion of the resistive heat generator <NUM> folded back. By contrast, the short-side dimension Q of the base <NUM> may be changed in accordance with the longitudinal position of the heater <NUM>. In such a case, the short-side dimension Q of the base <NUM> is the smallest dimension of the base <NUM> in the short-side direction within a longitudinal area (the heat generation area) including the resistive heat generators <NUM> arranged in the longitudinal direction of the base <NUM>.

In the embodiments of the present disclosure, the resistive heat generator having a positive temperature coefficient (PTC) characteristic may be used to further prevent the longitudinal unevenness in temperature of the heater <NUM>. The PTC property defines a property in which the resistance value increases as the temperature increases, for example, a heater output decreases under a given voltage. The heat generator having the PTC property starts quickly with an increased output at low temperatures in the heater and prevents overheating of the heater with a decreased output at high temperatures in the heater. For example, if a temperature coefficient of resistance (TCR) of the PTC property 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 value needed for the heater <NUM>. The TCR is preferably in a range of from about <NUM> ppm/°C to about <NUM>,<NUM> ppm/°C.

The TCR can be calculated using the following equation (<NUM>). In the equation (<NUM>), T0 represents a reference temperature, T1 represents a freely selected temperature, R0 represents a resistance value at the reference temperature T0, and R1 represents a resistance value at the selected temperature T1. For example, in the heater <NUM> described above with reference to <FIG>, the TCR is <NUM>,<NUM> ppm/°C from the equation (<NUM>) when the resistance values between the first electrode 61A and the second electrode 61B are 10Ω (i.e., resistance value R0) and 12Ω (i.e., resistance value R1) at <NUM> (i.e., reference temperature T0) and <NUM> (i.e., selected temperature T1), respectively. Equation <NUM>.

Applications of the embodiments of the present disclosure are not limited to the image forming apparatus including the fixing device <NUM> as illustrated in <FIG>. The embodiments of the present disclosure are also applicable to image forming apparatuses including fixing devices as illustrated in <FIG>, respectively, other than the fixing device <NUM> described above.

The fixing device <NUM> illustrated in <FIG> is different from the above-described fixing device in that a fixing nip N1 through which the sheet P passes and a heating nip N2 through which the fixing belt <NUM> is heated by the heater <NUM> are set at different positions. Specifically, the fixing device <NUM> illustrated in <FIG> includes the heater <NUM> and the nip formation pad <NUM> disposed <NUM>° opposite to each other in the rotation direction of the fixing belt <NUM>. The pressure roller <NUM> presses against the fixing belt <NUM> to form the fixing nip N1, and the pressure roller <NUM> presses against the fixing belt <NUM> to form the heating nip N2.

Next, the fixing device <NUM> illustrated in <FIG> omits the above-described pressure roller <NUM> adjacent to the heater <NUM> from the fixing device <NUM> illustrated in <FIG> and includes the heater <NUM> formed to be arc having a curvature of the fixing belt <NUM>. The other configuration is the same as the configuration illustrated in <FIG>. In this case, the arc shaped heater <NUM> surely maintains a length of the contact between the fixing belt <NUM> and the heater <NUM> in the belt rotation direction to efficiently heat the fixing belt <NUM>.

Finally, the fixing device <NUM> illustrated in <FIG> includes belts <NUM> and <NUM> disposed on both sides of the roller <NUM>. Also, in this case, similar to the example illustrated in <FIG>, the fixing nip N1 and the heating nip N2 are set at different positions. On the right side of <FIG>, the nip formation pad <NUM> is pressed against the roller <NUM> via one belt <NUM> to form the nip N1, and on the left side of <FIG>, the heater <NUM> is pressed against the roller <NUM> via the other belt <NUM> to form the nip N2.

Applying the present embodiments of the present disclosure to the image forming apparatus including one of the fixing devices as illustrated in <FIG> described above can prevent the curling of the blade caused by the uneven temperature distribution of the heating member, improve image quality, and is helpful for downsizing the image forming apparatus or increasing the print speed. In this specification, "the end of the rubbing portion directly facing the end of the heater" means that a member does not substantially exist between the rubbing portion and the heater, and "the end of the rubbing portion indirectly facing the end of the heater" means that another member substantially exist between the rubbing portion and the heater. The present embodiments can be applied to both configurations described above without any problem.

Claim 1:
An image forming apparatus (<NUM>) configured to form an image on a recording medium, comprising:
a heating device (<NUM>) being configured to heat the recording medium conveyed and including a heater (<NUM>)
the heater (<NUM>) extending in a direction orthogonal to a conveyance direction of the recording medium and including a heat generator (<NUM>),
the heater (<NUM>) being configured to generate a larger amount of heat at one end in the direction orthogonal to the conveyance direction than at a center of the heater (<NUM>) in the direction orthogonal to the conveyance direction;
a rotator (<NUM>, <NUM>, <NUM>); and
a blade (<NUM>, <NUM>, <NUM>) including a rubbing portion (77a, 69a)
the rubbing portion (77a, 69a) extending in the direction orthogonal to the conveyance direction,
one end of the rubbing portion (77a, 69a) in the direction orthogonal to the conveyance direction facing the one end of the heater (<NUM>) in the direction orthogonal to the conveyance direction,
the other end of the rubbing portion (77a, 69a) in the direction orthogonal to the conveyance direction facing the other end of the heater (<NUM>) in the direction orthogonal to the conveyance direction, and
the rubbing portion (77a, 69a) being configured to rub the rotator (<NUM>, <NUM>, <NUM>),
characterised in that the rotator (<NUM>, <NUM>, <NUM>) and the blade (<NUM>, <NUM>, <NUM>) are configured such that a friction force between the rotator (<NUM>, <NUM>, <NUM>) and the one end of the rubbing portion (77a, 69a) is smaller than a friction force between the rotator (<NUM>, <NUM>, <NUM>) and a center of the rubbing portion (77a, 69a) in the direction orthogonal to the conveyance direction.