Fixing device and image forming apparatus

A fixing device includes: a non-contact heating unit configured to heat a recording medium being transported on a transport path in a non-contact manner; a facing member that is disposed along the transport path at a position facing the non-contact heating unit and that is configured to move with respect to the recording medium; and a tension unit configured to tension a facing member in a direction along the transport path.

BACKGROUND

Technical Field

The present invention relates to a fixing device and an image forming apparatus.

Related Art

JP-A-2009-288491 discloses a fixing device configured to heat and fix a toner image formed on paper, the fixing device including: a heating source configured to heat a gist within a heating region by radiation; a transport part configured to transport the paper to the heating region; and a shielding part provided between the heating source and the heating region and configured to shield radiation from the heating source to the heating region, in which a shielding region where the radiation from the heating source to the heating region is shielded by the shielding part is changed in accordance with a position of the paper transported through the heating region.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate to preventing deformation of a facing member in a direction approaching a transport path due to heating, as compared with a fixing device in which a facing member is restrained in a direction along a transport path.

According to an aspect of the present disclosure, there is provided a fixing device including: a non-contact heating unit configured to heat a recording medium being transported on a transport path in a non-contact manner; a facing member that is disposed along the transport path at a position facing the non-contact heating unit and that is configured to move with respect to the recording medium; and a tension unit configured to tension a facing member in a direction along the transport path.

DETAILED DESCRIPTION

Examples of a fixing device and an image forming apparatus according to an exemplary embodiment of the present invention will be described with reference toFIGS.1to13. In the drawings, an arrow H indicates an apparatus upper-lower direction (vertical direction), an arrow W indicates an apparatus width direction (horizontal direction), and an arrow D indicates an apparatus depth direction (horizontal direction).

An image forming apparatus10according to the present exemplary embodiment is an electrophotographic image forming apparatus that forms and fixes a toner image on a sheet member P as an example of a recording medium. As shown inFIG.1, the image forming apparatus10includes accommodating units50, a discharge unit52, an image forming unit12, a transport mechanism60, an inverting mechanism80, a fixing device100, and a cooling unit90.

The accommodating unit50has a function of accommodating the sheet member P. In the image forming apparatus10, plural (for example, two) accommodating units50are provided. The plural accommodating units50are configured such that the sheet member P is selectively fed from the plural accommodating units50.

The discharge unit52is a portion where the sheet member P on which an image is formed is discharged. Specifically, the discharge unit52is configured such that the sheet member P cooled by the cooling unit90is discharged to the discharge unit52after the image is fixed by the fixing device100.

The image forming unit12has a function of forming an image on the sheet member P by an electrophotographic method. Specifically, the image forming unit12includes toner image forming units20that form toner images, and a transfer device30that transfers the toner image formed by the toner image forming unit20to the sheet member P.

Plural toner image forming units20are provided so as to form a toner image for each color. The image forming apparatus10includes the toner image forming units20of a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K). The (Y), (M), (C), and (K) shown inFIG.1indicate constituent portions corresponding to the respective colors.

The toner image forming units20of the respective colors are basically configured in a similar manner except for a toner to be used. Specifically, as shown inFIG.2, the toner image forming unit20of each color includes a photoconductor drum21that rotates in a direction indicated by an arrow A inFIG.2, a charger22that charges the photoconductor drum21, an exposure device23, and a developing device24. The exposure device23exposes the photoconductor drum21charged by the charger22to form an electrostatic latent image on the photoconductor drum21. The developing device24develops the electrostatic latent image formed on the photoconductor drum21by the exposure device23by using toner to form a toner image.

The transfer device30has a function of primarily transferring toner images of the photoconductor drums21of the respective colors onto an intermediate transfer body in a superimposed manner, and secondarily transferring the superimposed toner images onto the sheet member P. Specifically, as shown inFIG.1, the transfer device30includes a transfer belt31serving as the intermediate transfer body, primary transfer rollers33, and a transfer unit35.

The primary transfer roller33has a function of transferring the toner image formed on the photoconductor drum21to the transfer belt31at a primary transfer position T (seeFIG.2) between the photoconductor drum21and the primary transfer roller33.

The transfer belt31has an endless shape and is wound around plural rollers32to determine a posture thereof. When rotationally driven by at least one of the plural rollers32, the transfer belt31rotates in an arrow B direction, and transports the primarily transferred images to a secondary transfer position NT.

The transfer unit35has a function of transferring the toner images transferred to the transfer belt31to the sheet member P. Specifically, the transfer unit35includes a secondary transfer unit34and a facing roller36.

The facing roller36is disposed below the transfer belt31so as to face the transfer belt31. The secondary transfer unit34is disposed on an inner side of the transfer belt31such that the transfer belt31is disposed between the facing roller36and the secondary transfer unit34. The secondary transfer unit34is specifically configured with a corotron. In the transfer unit35, the toner images transferred to the transfer belt31are transferred to the sheet member P that passes through the secondary transfer position NT by electrostatic force generated by discharge of the secondary transfer unit34.

The transport mechanism60has a function of transporting the sheet member P accommodated in the accommodating unit50to the secondary transfer position NT. Further, the transport mechanism60has a function of transporting the sheet member P transported to the secondary transfer position NT from the secondary transfer position NT to a main heating unit120described later.

Specifically, the transport mechanism60includes feed rollers62, plural transport rollers64, and a chain gripper66.

The feed roller62is a roller that feeds the sheet member P accommodated in the accommodating unit50. The plural transport rollers64are rollers that transport the sheet member P fed by the feed roller62to the chain gripper66. The chain gripper66has a function of holding a tip end portion of the sheet member P and transporting the sheet member P. Specifically, the chain gripper66includes a pair of chains72(seeFIG.4) and grippers76(seeFIG.3) serving as holding portions (=gripping portions).

As shown inFIG.1, the pair of chains72are each formed in an annular shape. The pair of chains72are arranged at an interval in the apparatus depth direction (seeFIG.4). The pair of chains72are respectively wound around a pair of sprockets (not shown) arranged on one end side and the other end side in an axial direction with respect to each of the facing roller36and a pressurizing roller140described later, and a pair of sprockets74arranged at an interval in the apparatus depth direction. When one of the pair of sprockets is rotated, the chain72is configured to rotate in an arrow C direction.

The gripper76that extends in the apparatus depth direction is stretched across the pair of chains72. Plural grippers76are provided, and are fixed to the pair of chains72at predetermined intervals along a circumferential direction (rotation direction) of the chains72.

The gripper76includes a contact member76B that extends in the apparatus depth direction, and plural claws76A attached at predetermined intervals along the apparatus depth direction. The gripper76is configured to hold the sheet member P by sandwiching the tip end portion of the sheet member P between the plural claws76A and the contact member76B.

Then, in the chain gripper66, the chains72are rotated in the arrow C direction in a state where the gripper76holds the tip end portion of the sheet member P, so that the sheet member P is transported. The chain gripper66shown inFIG.1transports the sheet member P transported by the plural transport rollers64to the secondary transfer position NT, and then transports the sheet member P to the main heating unit120described later after passing the sheet member P through a preliminary heating unit102described later. A part of a transport path through which the sheet member P is transported in the transport mechanism60is indicated by a one-dot chain line.

In this configuration, the transport mechanism60transports the sheet member P in the apparatus width direction such that a sheet surface faces an upper-lower direction at least from the secondary transfer position NT to the main heating unit120.

The inverting mechanism80is a mechanism that inverts front and back of the sheet member P. Specifically, as shown inFIG.1, the inverting mechanism80includes plural transport rollers82, an inverting device84, and plural transport rollers86.

The plural transport rollers82are rollers that transport the sheet member P fed from the fixing device100to the inverting device84. As an example, the inverting device84transports the sheet member P while turning the sheet member P plural times such that a transport direction of the sheet member P changes by, for example, 90 degrees. That is, the inverting device84is, for example, a device that twists the sheet member P like a Mobius band to invert the front and back of the sheet member P.

The plural transport rollers86are rollers that transport the sheet member P whose front and back have been inverted by the inverting device84to the chain gripper66.

The fixing device100has a function of fixing the toner image transferred to the sheet member P by the transfer device30to the sheet member P. Details of the fixing device100will be described later.

The cooling unit90has a function of cooling the sheet member P heated by the fixing device100. As shown inFIG.1, the cooling unit90is disposed downstream of the fixing device100in the transport direction of the sheet member P. The sheet member P heated by the fixing device100is transported to the cooling unit90by a transport roller (not shown). The cooling unit90includes two sets of cooling rollers92arranged in the apparatus width direction. Since the two sets of cooling rollers92have similar configurations, one of the cooling rollers92will be described.

As shown inFIG.1, the cooling roller92includes a roller92adisposed on an upper side across the transport path of the sheet member P, and a roller92bdisposed on a lower side across the transport path of the sheet member P. The rollers92aand92bare cylindrical aluminum tubes that extend in the apparatus depth direction, and an air blowing mechanism (not shown) generates an air flow inside the rollers92aand92b. Because of the air flow, a temperature of surfaces of the rollers92aand92bis lower than a temperature in a case where the air flow is not generated. In this configuration, rotational force is transmitted from a driving member (not shown) to the roller92bto rotate the roller92b. Further, the roller92ais rotated following the roller92b. Then, the rollers92aand92btransport the sheet member P while sandwiching the sheet member P therebetween, and cool the sheet member P.

(Operation of Image Forming Apparatus)

In the image forming apparatus10shown inFIG.1, an image is formed as follows.

First, in response to a job input from an outside, the accommodating units50, the discharge unit52, the image forming unit12, the transport mechanism60, the inverting mechanism80, the fixing device100, and the cooling unit90shift to an operation state.

The charger22(seeFIG.2) of each color to which a voltage is applied uniformly negatively charges a surface of the photoconductor drum21of each color at a predetermined potential. Subsequently, based on image data of the job input from the outside, the exposure device23irradiates the charged surface of the photoconductor drum21of each color with exposure light to form an electrostatic latent image.

Accordingly, the electrostatic latent image corresponding to the image data is formed on the surface of each photoconductor drum21. Further, the developing device24of each color develops the electrostatic latent image to visualize the electrostatic latent image as a toner image. Furthermore, the transfer device30transfers the toner image formed on the surface of the photoconductor drum21of each color to the transfer belt31.

Therefore, the sheet member P fed from the accommodating unit50shown inFIG.1to the transport path of the sheet member P by the feed roller62and transported by the chain gripper66is fed to the secondary transfer position NT where the transfer belt31and the facing roller36are in contact with each other. At the secondary transfer position NT, the sheet member P is transported while being sandwiched between the transfer belt31and the facing roller36, so that the toner image on a surface of the transfer belt31is transferred to an upper side surface PA in the apparatus upper-lower direction, which is a surface of the transported sheet member P.

Further, the fixing device100fixes the toner image transferred to the surface of the sheet member P to the sheet member P, and the sheet member P is transported to the cooling unit90. The cooling unit90cools the sheet member P to which the toner image is fixed and discharges the sheet member P to the discharge unit52.

On the other hand, in a case of forming a toner image on a back surface of the sheet member P, the sheet member P that has passed through the fixing device100by being transported by the chain gripper66is transported to the transport rollers82of the inverting mechanism80. The sheet member P transported to the transport rollers82is transported to the inverting device84by the transport rollers82, and the front and back of the sheet member P are inverted by the inverting device84. The sheet member P whose front and back have been inverted is transported from the inverting device84to the transport rollers86, and is transported to the chain gripper66by the transport rollers86. The chain gripper66transports the sheet member P. Then, in order to form a toner image on the back surface, which is the upper side surface PA in the apparatus upper-lower direction of the sheet member P transported by the inversion, the above-described step is performed again.

Next, the fixing device100will be described.

The fixing device100is disposed downstream of the transfer device30in the transport direction of the sheet member P. As shown inFIG.3, the fixing device100includes the preliminary heating unit102as an example of a non-contact heating unit that heats the sheet member P in a non-contact state with the sheet member P being transported. Further, the fixing device100includes the main heating unit120that is in contact with the sheet member P to heat and pressurize the sheet member P, a blowing unit160, a shielding part170, first tension parts210, and second tension parts220. The blowing unit160and the shielding part170are respectively arranged along the transport path of the sheet member P at predetermined positions facing the preliminary heating unit102. Constituent elements of the blowing unit160and the shielding part170do not move from the positions with respect to the transport path. In other words, the blowing unit160and the shielding part170each move with respect to the sheet member P transported along the transport path. The first tension part210and the second tension part220are examples of a tension unit.

As shown inFIG.3, the main heating unit120is disposed downstream of the preliminary heating unit102described later in the transport direction of the sheet member P. The main heating unit120includes a heating roller130that is in contact with the transported sheet member P to heat the sheet member P, a pressurizing roller140that pressurizes the sheet member P toward the heating roller130, and a follower roller150that rotates following the rotating heating roller130.

As shown inFIG.3, the heating roller130is disposed so as to be in contact with an upward surface of the transported sheet member P and extend in the apparatus depth direction with an axial direction as the apparatus depth direction. Further, the heating roller130includes a cylindrical base132, a rubber layer134formed so as to cover an entire periphery of the base132, a release layer136formed so as to cover an entire periphery of the rubber layer134, and a heater138accommodated in the base132. An outer diameter of an outer peripheral surface of the release layer136of the heating roller130is, for example, 80 [mm].

The base132is an aluminum tube and has a thickness of, for example, 20 [mm]. Further, the rubber layer134is formed of silicone rubber and has a thickness of, for example, 6 [mm]. Furthermore, the release layer136is formed of a copolymer of tetrafluoroethylene and perfluoroethylene (PFA resin), and has a thickness of, for example, 50 [μm].

Shaft portions (not shown) that extend in the apparatus depth direction are respectively formed at both end portions of the heating roller130in the apparatus depth direction, and support members (not shown) that respectively support the shaft portions are provided. Accordingly, the heating roller130is rotatably supported by the support members at both end portions of the heating roller130.

As shown inFIG.3, the follower roller150is disposed on a side opposite to the sheet member P transported across the heating roller130so as to extend in the apparatus depth direction with the axial direction as the apparatus depth direction. Further, the follower roller150includes a cylindrical base152and a heater154accommodated in the base152. An outer diameter of an outer peripheral surface of the base152of the follower roller150is, for example, 50 [mm].

The base152is an aluminum tube and has a thickness of, for example, 10 [mm]. Then, the follower roller150is rotatably supported by support members (not shown) at both end portions of the follower roller150.

In this configuration, the follower roller150is rotated following the heating roller130. Then, the follower roller150heats the heating roller130. As described above, since the heating roller130is heated by the follower roller150and the heating roller130itself includes the heater138, a surface temperature of the heating roller130has a predetermined value of 180 [° C.] or higher and 200 [° C.] or lower.

As shown inFIG.3, the pressurizing roller140is disposed on a side opposite to the heating roller130with the transported sheet member P sandwiched therebetween so as to be in contact with a downward surface of the transported sheet member P and extend in the apparatus depth direction with the axial direction as the apparatus depth direction. Further, the pressurizing roller140includes a cylindrical base142, a rubber layer144formed so as to cover the base142, a release layer146formed so as to cover the rubber layer144, and a pair of shaft portions (not shown) formed at both end portions in the apparatus depth direction. An outer diameter of an outer peripheral surface of the release layer146of the pressurizing roller140is, for example, 225 [mm]. As described above, the outer diameter of the pressurizing roller140is larger than the outer diameter of the heating roller.

The base142is an aluminum tube and has a thickness of, for example, 20 [mm]. Further, the rubber layer144is formed of silicone rubber and has a thickness of, for example, 1 [mm]. Furthermore, the release layer146is formed of a copolymer of tetrafluoroethylene and perfluoroethylene (PFA resin), and has a thickness of, for example, 50 [μm].

A recess140athat extends in the apparatus depth direction is formed in an outer peripheral surface of the pressurizing roller140(seeFIG.3). When the sheet member P passes between the pressurizing roller140and the heating roller130, the gripper76that grips the tip end portion of the sheet member P is accommodated in the recess140aso as not to interfere with the pressurizing roller140.

The pressurizing roller140is rotated by rotational force transmitted from a driving member (not shown). Then, the heating roller130rotates following the rotating pressurizing roller140, and the follower roller150rotates following the rotating heating roller130. Further, the heating roller130and the pressurizing roller140sandwich and transport the sheet member P to which the toner image has been transferred, so that the toner image is fixed to the sheet member P.

The preliminary heating unit102is disposed downstream of the secondary transfer position NT where the toner image is transferred to the sheet member P in the transport direction of the sheet member P, and as shown inFIG.3, above the transported sheet member P (=on a side where the toner image is transferred). The preliminary heating unit102includes a reflection plate104and plural infrared heaters106(hereinafter, referred to as “heaters106”). The heater106is an example of a heat source.

The reflection plate104is formed by using an aluminum plate, and is a shallow box-shaped member having an opening on a side of the transported sheet member P. In the present exemplary embodiment, when viewed from above, the reflection plate104covers the transported sheet member P in the apparatus depth direction and the apparatus width direction.

The heater106is a columnar infrared heater that extends in the apparatus depth direction. The plural heaters106are arranged side by side at predetermined intervals in the apparatus width direction along the transport path inside the reflection plate104. In the present exemplary embodiment, when viewed from above, the heaters106cover the transported sheet member P in the apparatus depth direction. Further, the heater106is away from the transported sheet member P by, for example, 30 [mm] in an upper-lower direction.

The heater106emits infrared rays having a maximum spectral radiance at a wavelength of 3 [μm] or more and 5 [μm] or less, and a surface temperature of the heater106becomes a predetermined temperature of 300 [° C.] or higher and 1175 [° C.] or lower.

The preliminary heating unit102heats the sheet member P, which is transported to a lower side of the preliminary heating unit102by the chain gripper66, from a side of an unfixed toner image transferred to the sheet member P in a non-contact state.

As shown inFIG.3, the shielding part170is disposed between the preliminary heating unit102and the transported sheet member P. In the present exemplary embodiment, as shown inFIG.6, the shielding part170includes plural shielding members171arranged in the apparatus width direction along the transport path, and plural support members174that support the shielding members171.

As shown inFIG.3, the plural shielding members171are arranged between the preliminary heating unit102and the transported sheet member P. The shielding member171is an example of a facing member that is disposed along the transport path at a position facing the preliminary heating unit102in the apparatus upper-lower direction and moves with respect to the transported sheet member P, and is an example of a planar body formed of a rectangular plate material that extends in the apparatus depth direction. The plural shielding members171constitute a shielding member group171A by being arranged in the apparatus width direction along the transport path. The shielding member171includes, at both end portions in the apparatus depth direction, cutout portions172having U-shaped edges (seeFIGS.6and8).

As shown inFIG.6, the support members174are members that are arranged at both end portions of the shielding member171in the apparatus depth direction and that extend in the apparatus depth direction. One support member174includes a shaft portion175that extends in the apparatus depth direction, and a flat plate portion176that protrudes in the apparatus depth direction from a tip end of the shaft portion175.

The flat plate portion176has a surface larger than the cutout portion172of the shielding member171, and the shielding member171is placed on the surface such that the cutout portion172is accommodated. Further, an attachment screw177, which is an example of an attachment portion that constitutes the second tension part220described later, is provided on the flat plate portion176so as to protrude from the shielding member171through the cutout portion172. With this configuration, the shielding member171is supported so as not to fall in a gravity direction in a state where the shielding member171has a degree of freedom in the apparatus depth direction (seeFIG.7). Details of the second tension part220will be described later.

In the present exemplary embodiment, an end portion of the shaft portion175on a side opposite to the flat plate portion176is supported by a case (not shown) of the fixing device100via, for example, a bearing so as to be rotatable around the apparatus depth direction. The shaft portion175is configured to be rotationally driven by a motor (not shown). Further, the shaft portion175is restrained in a translation direction by, for example, a stopper around the bearing.

In this configuration, the plural shielding members171may be switched between an open state and a shielded state by the shaft portion175being rotated by the motor (not shown). As shown inFIG.9, the open state in the present exemplary embodiment means a state where, in the plural shielding members171, a gap open in the apparatus upper-lower direction is formed between the adjacent shielding members. When the plural shielding members171are in the open state, the infrared rays emitted from the preliminary heating unit102pass through the gaps formed by the plural shielding members171and heat the sheet member P transported on the transport path. On the other hand, as shown inFIG.10, the shielded state in the present exemplary embodiment means a state where, in the plural shielding members171, the gap between the adjacent shielding members is narrower than that in the open state. When the plural shielding members171are in the shielded state, the infrared rays emitted from the preliminary heating unit102are shielded by the plural shielding members171and are prevented from being emitted below the plural shielding members171. As shown inFIG.10, it is desirable that the plural shielding members171are in contact with each other so as not to form the gap between the adjacent shielding members, but as long as it is possible to shield the infrared rays emitted from the preliminary heating unit102as compared with the open state, the gap may be formed between the adjacent shielding members.

When the fixing device100is in the operation state, the plural shielding members171are in the open state (seeFIG.9). Then, when the job input to the image forming apparatus10is completed, the plural shielding members171shift from the open state to the shielded state (seeFIG.10).

As shown inFIG.3, the blowing unit160is disposed in a direction along the transport path at a position facing the preliminary heating unit102in the apparatus upper-lower direction. The transported sheet member P passes between the blowing unit160and the preliminary heating unit102. Further, as shown inFIG.4, the blowing unit160includes a fan161, a bottom plate162that is a square plate material, a wall frame163that stands on four sides of the bottom plate162, and a ventilation plate180. The fan161is an example of an air-blowing unit that blows air toward the transport path.

As shown inFIG.3, the fan161and the bottom plate162are arranged so as to face the preliminary heating unit102in the apparatus upper-lower direction. The bottom plate162has an opening that penetrates the bottom plate162in a thickness direction at a central portion and is fitted to an outer peripheral portion of the fan161. The fan161is fitted and disposed so as to be embedded in the opening. A periphery of the fan161embedded in the opening is in an airtight state.

As shown inFIG.4, the wall frame163includes side wall portions163athat stand on two sides of the bottom plate162in the apparatus depth direction, and end wall portions163b(seeFIG.3) that stand on two sides of the bottom plate162in the apparatus width direction. With this configuration, the wall frame163is formed with an opening in an upper portion of the wall frame163.

As shown inFIG.4, the ventilation plate180is an example of a ventilation portion having plural ventilation holes183through which air blown from the fan161toward a lower side surface PB of the sheet member P passes. The ventilation plate180is disposed above the wall frame163so as to cover the opening of the wall frame163in a state where the ventilation plate180has a degree of freedom in the apparatus depth direction and the apparatus width direction with the apparatus upper-lower direction as a thickness direction. Further, the ventilation plate180is disposed at a position facing a lower side of the preliminary heating unit102. The ventilation plate180includes two end portion plates182arranged at both ends of the ventilation plate180in the apparatus width direction along the transport path, and plural plates181arranged between the two end portion plates182at predetermined intervals in the apparatus width direction along the transport path. Further, the ventilation plate180includes plural seal members184. The plural ventilation holes183are formed in the plates181and the end portion plates182.

The plate181and the end portion plate182are examples of a facing member that is disposed along the transport path at a position facing the preliminary heating unit102and moves with respect to the transported sheet member P, and are examples of a planar body formed of a rectangular plate material that extends in the apparatus depth direction. The plates181and the end portion plates182are arranged at positions facing the lower side of the preliminary heating unit102, so that the plates181and the end portion plates182are heated by the preliminary heating unit102.

The plural ventilation holes183penetrate the plates181and the end portion plates182in the thickness direction. As shown inFIG.4, the plural ventilation holes183are arranged two-dimensionally (in a matrix) along the transport direction of the sheet member P and the apparatus front-rear direction. InFIG.4, in order to simplify illustration of the ventilation plate180, some ventilation holes183are omitted.

A gap in the apparatus width direction is formed between the end portion plate182and the plate181adjacent to the end portion plate182in the apparatus width direction. Further, gaps in the apparatus width direction are formed among the plates181arranged in the apparatus width direction. As shown inFIG.3, since the plural seal members184are arranged in these gaps, the air blown from the fan161is prevented from passing through these gaps.

The air blown from the fan161passes through the plural ventilation holes183arranged two-dimensionally (in the matrix) in the plates181and the end portion plates182, so that the air uniformly hits the lower side surface PB of the sheet member P in the apparatus upper-lower direction. Accordingly, a transport posture of the transported sheet member P is stabilized as compared with a configuration in which the blowing unit160is not provided.

Here, “the transport posture of the sheet member P is stabilized” means that a distance from the sheet surface of the sheet member P to the preliminary heating unit102is prevented from varying depending on a position of the sheet surface. In other words, a difference between a longest distance from the sheet surface of the sheet member P to the preliminary heating unit102and a shortest distance is reduced.

The first tension parts210are examples of the tension unit that tensions the ventilation plate180, which is the facing member, in a direction along the transport path. In the present exemplary embodiment, as shown inFIG.4, the first tension part210includes plural pairs of attachment screws164and185in the blowing unit160, and plural tension coil springs188that respectively connect the pairs of attachment screws164and185. The tension coil spring188is an example of a biasing unit that applies tensile force to the ventilation plate180.

The plural attachment screws164are provided on upper portions of the two side wall portions163aat positions that do not interfere with the plates181and the end portion plates182in a state of being arranged at predetermined intervals in the apparatus width direction so as to be paired with the plates181and the end portion plates182. Specifically, in the blowing unit160, the attachment screws164are arranged for each plate181one by one on the upper portions of the side wall portions163aon both sides of one plate181in the apparatus depth direction. Further, the attachment screw164is disposed at a position where the attachment screw164does not interfere with the plate181heated and thermally expanded by the preliminary heating unit102. Further, the attachment screws164are also arranged in the same manner on the upper portions of the side wall portions163aon both sides of the end portion plate182in the apparatus depth direction.

The attachment screws185are provided for each plate181one by one at both end portions of the plate181in the apparatus depth direction in a state of protruding in the same direction as those of the attachment screws164. In this configuration, each attachment screw185forms a pair with the attachment screw164positioned on a side close to each attachment screw185among the plural attachment screws164. The same applies to the end portion plate182.

In this example, the tension coil spring188includes hook portions that is attachable to the attachment screws164and185at both end portions, and the attachment screw164and the attachment screw185are connected by these hook portions.

In the present exemplary embodiment, one plate181is applied with tensile force in opposite directions by the respective tension coil springs188via the attachment screws185provided on both end sides in the apparatus depth direction. Further, one plate181is stationary in the apparatus depth direction in a state where the plate181has a degree of freedom in the apparatus depth direction by balancing the tensile force applied from the respective tension coil springs188. In other words, each of the plural plates181is tensioned in a direction that extends in the apparatus depth direction along the transport path by the plural tension coil springs188. The same applies to the end portion plate182.

The “tensioned” state in the exemplary embodiment of the present invention indicates a state where a plate-shaped object having a degree of freedom in a direction along at least one surface is stationary in a state where tensile force is applied in at least one direction of the degree of freedom. In the present exemplary embodiment, the number of degrees of freedom may be two or four. In the present exemplary embodiment, the plate181and the end portion plate182have degrees of freedom in four directions on both sides in the apparatus depth direction and both sides in the apparatus width direction, and tensile force is applied in two directions on both sides in the apparatus depth direction. Further, in the present exemplary embodiment, the shielding member171has degrees of freedom in two directions on both sides in the apparatus depth direction, and tensile force is applied to the shielding member171in two directions on both sides in the apparatus depth direction.

The second tension parts220are examples of the tension unit that tensions the shielding member171, which is the facing member, in a direction along the transport path. In the present exemplary embodiment, as shown inFIG.6, the second tension part220includes plural pairs of attachment screws173and177in the shielding part170, and plural tension coil springs178that respectively connect the pairs of attachment screws173and177. The tension coil spring178is an example of a biasing unit that applies tensile force to the shielding member171.

The attachment screws177are provided one by one on the flat plate portions176of the support members174provided on both sides of the shielding member171in the apparatus depth direction in a state of protruding from the shielding member171through the respective cutout portions172. The plural attachment screws177are arranged at positions that do not interfere with the edges of the cutout portions172of the shielding members171thermally expanded by heating by the preliminary heating unit102.

The attachment screws173are provided for each shielding member171one by one at positions on both end sides of the shielding member171in the apparatus depth direction and on inner sides with respect to the cutout portions172in the apparatus depth direction in a state of protruding in the same direction as those of the attachment screws177. In this configuration, each attachment screw173forms a pair with the attachment screw177positioned on a side close to each attachment screw173among the plural attachment screws177.

In the present exemplary embodiment, the tension coil spring178includes hook portions that is attachable to the attachment screws173and177at both end portions, and the attachment screw173and the attachment screw177are connected by these hook portions.

In the present exemplary embodiment, one shielding member171is applied with tensile force in opposite directions by the respective tension coil springs178via the attachment screws173provided on both end sides in the apparatus depth direction. Further, one shielding member171is stationary in the apparatus depth direction in a state where the shielding member171has a degree of freedom in the apparatus depth direction by balancing the tensile force applied from the respective tension coil springs178. In other words, each of the plural shielding members171is tensioned by the plural tension coil springs178in a direction that extends in the apparatus depth direction along the transport path.

Next, an operation of the present exemplary embodiment will be described. In the following description, the present exemplary embodiment will be compared with a comparative embodiment shown below. In the comparative embodiment, when components and the like used in the image forming apparatus10according to the present exemplary embodiment are used, reference numerals and names of the components and the like are used as they are.

Comparative Embodiment

A fixing device of the comparative embodiment (hereinafter, referred to as “comparative device”) does not include the first tension parts210and the second tension parts220. Specifically, both end portions of the plate181and the end portion plate182in an apparatus depth direction of the ventilation plate180of the comparative device are fastened onto the wall frame163by, for example, screws, and are attached in a state of being restrained in the apparatus depth direction and an apparatus width direction. Further, both end portions of the shielding member171in the apparatus depth direction of the shielding part170of the comparative device are fastened to the flat plate portions176of the support members174by, for example, screws, and are attached in a state of being restrained in the apparatus depth direction and the apparatus width direction.

Except for the above points, the comparative device is configured in the same manner as the fixing device100of the present exemplary embodiment.

When the preliminary heating unit102, which is a non-contact heating unit, heats the transported sheet member P, infrared rays are emitted from the heater106. The infrared rays emitted from the heater106heat the transported sheet member P, and heat the plates181, the end portion plates182, and the shielding members171arranged at positions facing the preliminary heating unit102. The plate181, the end portion plate182, and the shielding member171are thermally expanded by being heated.

In the comparative device, when the plate181, the end portion plate182, and the shielding member171that are facing members are thermally expanded, both end portions in the apparatus depth direction are restrained. Therefore, the plate181, the end portion plate182, and the shielding member171are bent and deformed in a direction approaching a transport path when viewed from a transport direction of the transported sheet member P. Specifically, the plate181and the end portion plate182are in a state where both end portions in the apparatus depth direction are restrained on the wall frame163, upper side surfaces are heated by the heater106, and air is blown from the fan161disposed on a lower side. The air blown from the fan161passes through the ventilation holes183and cools lower side surfaces of the plate181and the end portion plate182. In this state, when the plate181and the end portion plate182are thermally expanded and deformed, the plate181and the end portion plate182are bent and deformed upward in an apparatus upper-lower direction. Then, when the shielding member171is thermally expanded and deformed in a state where both end portions in the apparatus depth direction are restrained, the shielding member171is bent and deformed downward in the apparatus upper-lower direction due to an action of gravity.

In the comparative device, when the plate181and the end portion plate182of the ventilation plate180are bent and deformed in a direction approaching the transport path, the plate181and the end portion plate182may interfere with the lower side surface PB of the transported sheet member P. Accordingly, a posture of the sheet member P transported above the ventilation plate180may vary. Further, when the transported sheet member P is inverted by the inverting mechanism80, a toner image transferred at the secondary transfer position NT is formed on the lower side surface PB before being inverted by the inverting mechanism80. Therefore, when the deformed plate181and the deformed end portion plate182interfere with the toner image formed on the lower side surface PB of the sheet member P inverted by the inverting mechanism80, an image defect of the image formed on the lower side surface PB may occur.

In the comparative device, when the plate181and the end portion plate182are bent and deformed in a direction approaching the transport path, a two-dimensional property (matrix property) of arrangement of the plural ventilation holes183formed in the plate181and the end portion plate182is impaired. Since the two-dimensional property (matrix property) of the plural ventilation holes183is impaired, the air that is blown from the fan161and passes through the plural ventilation holes183unevenly hits the lower side surface PB of the sheet member P, and the posture of the sheet member P transported above the ventilation plate180may vary.

In the comparative device, when the shielding member171of the shielding part170is bent and deformed in a direction approaching the transport path, the shielding member171may interfere with the upper side surface PA of the transported sheet member P. Accordingly, the posture of the transported sheet member P may vary. Further, the toner image transferred at the secondary transfer position NT is formed on the upper side surface PA of the transported sheet member P. Therefore, when the deformed shielding member171interferes with the upper side surface PA of the transported sheet member P, an image defect of the image formed on the upper side surface PA may occur.

On the other hand, the plate181and the end portion plate182of the present embodiment are tensioned in the apparatus depth direction along the transport path by the first tension parts210in a state where the plate181and the end portion plate182have degrees of freedom in the apparatus depth direction. In this state, when the plate181and the end portion plate182are thermally expanded and deformed, the plate181and the end portion plate182are deformed in a direction in which the plate181and the end portion plate182extend in the apparatus depth direction that is a tension direction, and deformation of bending in a direction approaching the transport path is prevented. Therefore, in the fixing device100according to the present exemplary embodiment, the variation in the posture of the transported sheet member P due to the bending of the plate181, the end portion plate182, and the shielding member171is prevented as compared with the comparative device. Therefore, in the image forming apparatus10according to the present exemplary embodiment, the image defect of the image formed on the sheet member P is prevented as compared with the image forming apparatus including the comparative device.

Since the plate181and the end portion plate182are plate materials that extend in the apparatus depth direction along the transport path, an elongation amount due to thermal expansion in the apparatus depth direction, which is a longitudinal direction, is larger than an elongation amount due to thermal expansion in the apparatus width direction, which is a lateral direction. In the present exemplary embodiment, the first tension parts210tension the plate181and the end portion plate182in the apparatus depth direction that is the longitudinal direction, so that deformation in a direction in which the plate181and the end portion plate182extend in the longitudinal direction is facilitated, and deformation of bending in a direction approaching the transport path is prevented. Therefore, in the present exemplary embodiment, deformation of the plate181and the end portion plate182in a direction approaching the transport path is prevented as compared with a configuration (second configuration) in which the first tension parts210tension the plate181and the end portion plate182in a direction intersecting the longitudinal direction. The same applies to the second tension part220and the shielding member171. The second configuration described above is included in technical ideas of the present invention as a modified example of the present exemplary embodiment.

In the present exemplary embodiment, the ventilation plate180extends in the apparatus depth direction intersecting the transport direction of the transported sheet member P, and includes the plural plates181and the plural end portion plates182arranged side by side in the apparatus width direction along the transport direction. In other words, the ventilation plate180has a configuration divided into the plural plates181and the plural end portion plates182. Therefore, a diagonal length of one plate181or one end portion plate182is shorter than a diagonal length of the ventilation plate180in a configuration (third configuration) in which the ventilation plate180is a single plate material that is not divided. Therefore, in the present exemplary embodiment, a deformation amount of bending of each plate181and a deformation amount of bending of each end portion plate182due to the thermal expansion are smaller than a deformation amount of bending of the third configuration. In other words, in the present exemplary embodiment, deformation of the ventilation plate180in a direction approaching the transport path is prevented as compared with the configuration in which the ventilation plate180is a single plate material having a size equivalent to an overall size of the plural plates181and the two end portion plates182. The same applies to the shielding member group171A and the shielding member171. The third configuration described above is included in the technical ideas of the present invention as a modified example of the present exemplary embodiment (seeFIGS.11and12).

In the present exemplary embodiment, the preliminary heating unit102extends in the apparatus depth direction that is a direction along the transport direction of the transported sheet member P, and includes the plural heaters106arranged at predetermined intervals in the apparatus width direction intersecting the apparatus depth direction. Therefore, deformation amounts of the plate181and the end portion plate182in a direction approaching the transport path by the preliminary heating unit102are larger in the apparatus depth direction, which is a longitudinal direction of the heater106, than in the apparatus width direction in which the plural heaters106are arranged at the predetermined intervals. In the present exemplary embodiment, the first tension parts210tension the plate181and the end portion plate182in the apparatus depth direction that is the longitudinal direction of the heater106, so that deformation in a direction in which the plate181and the end portion plate182extend in the longitudinal direction is facilitated, and deformation in a direction approaching the transport path is prevented. Therefore, in the present exemplary embodiment, deformation of the plate181and the end portion plate182in a direction approaching the transport path is prevented as compared with a configuration (fourth configuration) in which the first tension parts210tension the plate181and the end portion plate182in a direction intersecting the longitudinal direction of the heater106. The same applies to the second tension part220and the shielding member171. The fourth configuration described above is included in the technical idea of the present invention as a modified example of the present exemplary embodiment.

In the present exemplary embodiment, the plural heaters106extend in the apparatus depth direction intersecting the transport direction of the transported sheet member P, and the plural heaters106are arranged in the apparatus width direction intersecting the apparatus depth direction at the predetermined intervals. Therefore, in the present exemplary embodiment, the transported sheet member P is transported in the apparatus width direction while being uniformly heated in the apparatus depth direction intersecting the transport direction by the plural heaters106. On the other hand, in a configuration (fifth configuration) in which the plural heaters106extend in the apparatus width direction that is a transport direction, and the plural heaters106are arranged in the apparatus depth direction at predetermined intervals, heating spots corresponding to intervals of the plural heaters106occur in the apparatus depth direction intersecting the transport direction on a transport path. Therefore, in the present exemplary embodiment, as compared with the fifth configuration, heating spots in a direction intersecting the transport direction on the transported sheet member P are prevented. The fifth configuration described above is included in the technical idea of the present invention as a modified example of the present exemplary embodiment.

Although a specific embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described exemplary embodiment, and various modifications, changes, and improvements may be made within the scope of the technical idea of the present invention.

For example, in the present exemplary embodiment, the plate181and the end portion plate182having degrees of freedom in the apparatus depth direction are tensioned by the first tension parts210provided on both sides in the apparatus depth direction. However, as a modified example of the present exemplary embodiment, a configuration may be adopted in which, in a state where one end portions of the plate181and the end portion plate182in an apparatus depth direction are restrained in the apparatus depth direction, the other end portions are tensioned by applying tensile force thereto by the first tension parts210. The same applies to the shielding member171and the second tension part220.

In the present exemplary embodiment, in the first tension part210, the tension coil spring188is used as an example of the biasing unit to apply tensile force to the plate181and the end portion plate182. However, the biasing unit is not limited to the tension coil spring188. For example, a configuration may be adopted in which a wire having a weight attached to one end thereof and a fixed pulley provided on the side wall portion163aare used, and tensile force due to gravity of the weight converted in a horizontal direction by the fixed pulley is applied to the plate181and the end portion plate182. The same applies to the shielding member171and the second tension part220.

In the present exemplary embodiment, the plate181and the end portion plate182that extend in the apparatus depth direction are tensioned in the apparatus depth direction. However, the plate181and the end portion plate182may be configured to be tensioned in the apparatus width direction orthogonal to the apparatus depth direction, or may be configured to be tensioned from two directions of the apparatus depth direction and the apparatus width direction. The same applies to the shielding member171and the second tension part220.

In the present exemplary embodiment, the shielding part170is configured to switch between the open state and the shielded state with respect to the preliminary heating unit102by rotating the plural shielding members171around the respective shaft portions175. However, the shielding part170is not limited to the configuration in which the plural shielding members171are rotated around the respective shaft portions175. For example, as shown inFIG.13, the shielding part170may be configured such that the plural shielding members171that extend in an apparatus depth direction slide in an apparatus width direction in a state where the plural shielding members171are densely arranged in the apparatus width direction with plate surfaces facing a direction along a transport path. In the configuration shown inFIG.13, the shaft portion175is supported by a rail (not shown) attached to a case (not shown) of the fixing device100in a state where the shaft portion175has a degree of freedom in the apparatus width direction. As for the configuration in which the plural shielding members171slide, the shielding members171not supported by the shaft portions175may be supported by rails attached to the case of the fixing device100in a state where the shielding members171each have degrees of freedom in the apparatus width direction. Further, the shielding part170may be configured such that one plate material that shields the preliminary heating unit102slides in the apparatus width direction on a rail attached to the case of the fixing device100.

In the present exemplary embodiment, the ventilation plate180has a configuration in which the plural plates181and the plural end portion plates182that extend in the apparatus depth direction are arranged in the apparatus width direction. However, the ventilation plate180may have a configuration in which the plural plates181and the plural end portion plates182that extend in the apparatus width direction are arranged in the apparatus depth direction. The same applies to the shielding part170and the shielding member171.

In the present exemplary embodiment, the tension coil spring188is attached to the attachment screw164provided on the wall frame163. However, an object to which the tension coil spring188is attached is not limited to the attachment screw164. For example, a protrusion formed integrally with the wall frame163may be adopted. The same applies to the attachment screws185for the plate181and the end portion plate182, the attachment screw177for the support member174, and the attachment screw173for the shielding member171.

In the present exemplary embodiment, the transport path of the fixing device100extends in the apparatus width direction. However, the transport path of the fixing device100is not limited to a transport path that extends in the apparatus width direction. For example, the transport path of the fixing device100may extend in the apparatus width direction and extend upward in the apparatus upper-lower direction.

In the present exemplary embodiment, the plates181and the end portion plates182of the ventilation plate180, and the shielding members171of the shielding part170are the facing members that are arranged along the transport path at the positions facing the preliminary heating unit102and move with respect to the transported sheet member P. However, the facing members are not limited thereto. For example, the facing member may be a guide plate disposed along the transport path on a lower side of the transport path in order to contact and support an end portion such that the end portion of the sheet member P transported by the chain gripper66on a side opposite to a side held by the gripper76is positioned at a predetermined height.

In the present exemplary embodiment, the fixing device100includes the shielding part170. However, the fixing device100may not include the shielding part170.