System for collecting an unfixed developer with an airflow

The invention provides a fixing unit including a fixing roller and a pressure roller pressed against the fixing roller inside a housing, for holding and conveying a sheet carrying an image formed by a developer between the fixing roller and the pressure roller thus to fix the image onto the sheet, including a removal section that removes an unfixed developer adhered to the fixing roller or the pressure roller, and an air vent located close to the removal section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2004-243723 filed in Japan on Aug. 24, 2004, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fixing unit including a removal unit that removes unfixed developer adhered to a fixing roller or a pressure roller, and to an image forming apparatus including such a fixing unit.

2. Description of the Related Art

An image forming apparatus based on electrophotography forms a desired toner image on a photoconductive drum, and after transferring the toner image on the photoconductive drum to a paper, fixes the toner image onto the paper by a fixing unit. The fixing unit usually includes a pair of heaters. A typical example of the pair of heaters is a fixing roller and a pressure roller disposed so as to be pressed against each other with a paper feeding path held therebetween. This type of fixing unit holds the paper between the fixing roller and the pressure roller, and applies heat and pressure to the paper to thermocompressively fix the toner image onto the paper, thus completing image forming on the paper.

In such a fixing unit, since at least either of the fixing roller or the pressure roller contacts the toner applied to the paper, the toner may adhere to the fixing roller or the pressure roller during the fixing process. Besides, the toner that has adhered to either of the fixing roller or the pressure roller often adheres to the other, via the contact interface therebetween.

To avoid this, for example Japanese Patent Application Laid-Open No. 05-119661 proposes a fixing unit provided with a brush type cleaner disposed so as to contact the fixing roller, to thereby remove the toner adhere thereto.

FIG. 1is a schematic cross-sectional view showing an internal structure of a conventional fixing unit provided with a cleaner. The fixing unit shown inFIG. 1includes a fixing roller201and a pressure roller202inside a housing200which constitutes a frame of the apparatus. The fixing roller201is a hollow cylindrical-shaped roller including a heater lamp201atherein, which maintains a predetermined temperature of the roller surface. The pressure roller202is a cylindrical-shaped roller pressed against the fixing roller201, so as to provide a fixing nip of a predetermined width with the fixing roller201. When a paper P to which a toner T has adhered is conveyed to the fixing unit, the fixing roller201and the pressure roller202applies heat and pressure to the paper P while feeding the paper P held therebetween, to thereby fix the toner image on the paper.

On the circumferential surface of the pressure roller202, an oil supplier203, a cleaning roller204and a separating blade205are disposed. The oil supplier203applies an oil to the surface of the pressure roller202via an oil applicator203a, for smooth separation of the paper P from the pressure roller202. The cleaning roller204includes a core metal204aand a brush portion204bradially implanted on the core metal204a, to serve to remove the unfixed toner stuck to the pressure roller202. The separating blade205is pressed against the circumferential surface of the pressure roller202, to peel off from the pressure roller202the paper P on which the toner has been fixed. The paper P separated from the pressure roller202passes through a paper guide206and is discharged outward by a discharge roller207.

The conventional fixing unit thus constructed utilizes the brush portion204bof the cleaning roller204to remove the toner stuck to the pressure roller202after the fixing process. However, since a portion of the toner adheres to the brush portion204b, the toner adheres again to the pressure roller via the mutual contact point, when the cleaning roller204has made one rotation.

Besides, the brush204bis generally made of a flexible synthetic resin. Accordingly, when the brush portion204bremoves the unfixed toner, a portion of the toner may be flipped by the tip of the brush portion204b, thus to splash inside the housing200. The toner that has splashed not only contaminates the interior section of the housing200, but also often adheres to the pressure roller202and the paper P being conveyed, which leads to degradation in the printed image quality.

BRIEF SUMMARY OF THE INVENTION

The present invention has been conceived in view of the foregoing situation, with an object to provide a fixing unit including a removal section that removes unfixed developer adhered to a fixing roller or a pressure roller, and an air vent located close to the removal section, so as to improve the cleaning performance of removing the unfixed toner and thus to execute a high-quality fixing process, and an image forming apparatus including such a fixing unit.

The fixing unit related to the present invention provides a fixing roller and a pressure roller pressed against the fixing roller inside a housing, for holding and conveying a sheet carrying an image formed by a developer between the fixing roller and the pressure roller thus to fix the image onto the sheet, a removal section that removes an unfixed developer adhered to the fixing roller or the pressure roller, and an air vent located close to the removal section.

According to the present invention, the fixing unit includes a removal section that removes an unfixed developer adhered to the fixing roller or the pressure roller and an air vent located close to the removal section, the unfixed developer removed by the removal section is collected into one location by an airflow passing through the air vent.

The fixing unit related to the present invention has the removal section includes a contacting member, which is provided so as to contact with a circumferential surface of the fixing roller or the pressure roller, and a collection member that collects the unfixed developer adhered to the contacting member, and leads the developer to the collection member with an air flow passing through the air vent.

According to the present invention, the removal section includes a contacting member, which is provided so as to contact with a circumferential surface of the fixing roller or the pressure roller, and a collection member that collects the unfixed developer adhered to the contacting member, the developer adhered to the contacting member is collected into the collection member by the airflow passing through the air vent.

The fixing unit related to the present invention provides the collection member located halfway of the vent path through which the airflow passes.

According to the present invention, the collection member is located halfway of the vent path through which the airflow passes, the developer adhered to the contacting member included in the removal section is collected into the collection member by the airflow.

The fixing unit related to the present invention provides the removal section that has a member for removing the developer adhered to the contacting member.

According to the present invention, the removal section further includes a member that removes the developer adhered to the contacting member, the contacting member can remain constantly cleaned. Also, the developer removed from the contacting member is collected into the collector by the airflow passing through the air vent.

The fixing unit related to the present invention provides the contacting member that is a roller brush.

According to the present invention, since the contacting member included in the removal section is a roller brush, the fixing roller and the pressure roller can be prevented from being damaged on the circumferential surface.

The fixing unit related to the present invention further comprises a driving section that rotationally drives the roller brush.

According to the present invention, a driving section that rotationally drives the roller brush allows effectively removing the developer adhered to the fixing roller or the pressure roller.

The fixing unit according to the present invention comprises the roller brush set to rotate in a reverse direction to a rotating direction of the fixing roller or the pressure roller with which the roller brush is in contact.

According to the present invention, Rotating as above the roller brush in a reverse direction to a rotating direction of the fixing roller or the pressure roller with which the roller brush is in contact can further enhance the removing effect of the developer adhered to the fixing roller or the pressure roller.

The image forming apparatus related to the present invention comprising a reception unit that receives image data, a transfer unit that transfers the image formed by a developer based on the received image data, and a fixing unit according to one of the foregoing aspects of the present invention, so as to fix by the fixing unit the image transferred to the sheet by the transfer unit, thus to complete image forming.

According to the present invention, since a fixing unit according to one of the foregoing aspects of the present invention is employed to fix the image on the sheet transferred thereto by the transfer unit and thus to complete image forming, the circumferential surfaces of the fixing roller and the pressure roller can be constantly maintained effectively cleaned, which results in effective prevention of degradation in the print image quality through the fixing process.

In the present invention, a removal unit that removes the unfixed developer adhered to the fixing roller or the pressure roller, and an air vent located close to the removal section. Accordingly, the unfixed developer removed by the removal section is collected into one location by an airflow passing through the air vent, and thus prevented from splashing inside the housing. Consequently, high-quality fixing performance can be executed.

In the present invention, the removal unit includes a contacting member, which is proveded so as to contact with a circumferential surface of the fixing roller or the pressure roller, and a collection member that collects the unfixed developer adhered to the contacting member. Accordingly, the developer adhered to the contacting member is collected into the collection member by the airflow passing through the air vent, and thus prevented from splashing inside the housing. Consequently, high-quality fixing performance can be executed.

In the present invention, the collection member is located halfway of the vent path through which the airflow passes. Accordingly, the developer adhered to the contacting member included in the removal section is collected into the collection member by the airflow, and thus prevented from splashing inside the housing. Consequently, high-quality image fixing performance can be executed on the sheet.

In the present invention, the removal section further includes a member that removes the developer adhered to the contacting member. Such structure allows maintaining the contacting member constantly cleaned of the developer adhered thereto, and thus preventing the developer from adhering again from the contacting member to the fixing roller or the pressure roller, even when the fixing process is successively executed.

In the present invention, the contacting member included in the removal unit is a roller brush. Such structure allows preventing the fixing roller and the pressure roller from being damaged on the circumferential surface, and hence a stable fixing quality can be maintained.

The fixing unit according to the present invention further comprises a driving unit that rotationally drives the roller brush. Such arrangement allows effectively removing the developer adhered to the fixing roller or the pressure roller.

In the present invention, the roller brush is set to rotate in a reverse direction to a rotating direction of the fixing roller or the pressure roller with which the roller brush is in contact. Such arrangement can further enhance the removing effect of the developer adhered to the fixing roller or the pressure roller.

In the present invention, the image on the sheet transferred thereto by the transfer unit is fixed by the fixing unit according to one of the foregoing aspects of the present invention. Therefore, the circumferential surfaces of the fixing roller and the pressure roller can be constantly maintained effectively cleaned, and the sheet is prevented from being stained by splashing developer. As a result, the present invention effectively prevents the degradation in the print image quality through the fixing process.

DETAILED DESCRIPTION OF THE INVENTION

Hereunder, the present invention will be described in details based on the drawings illustrating the embodiments thereof.

FIRST EMBODIMENT

FIG. 2is a schematic cross-sectional view showing a structure of an image forming apparatus according to the present invention. The image forming apparatus100according to the present invention includes a paper tray10at a lowermost portion thereof, for accommodating therein a sheet such as a paper or an OHP film (hereinafter, simply a paper). The paper tray10is provided with a pickup roller for individually supplying each sheet of paper to a paper feeding path R. The paper forwarded through the paper feeding path R is temporarily retained by a resist roller14. The resist roller14starts to feed the paper adjusting a timing so that an image is formed on a predetermined position on the paper.

The image forming apparatus100includes an image forming unit based on electrophotography, in which a toner image is transferred onto the sheet supplied by the resist roller14, and a fixing unit8A provided posterior to the image forming unit serves to fix the toner image onto the paper, thus completing image forming.

The image forming unit included in the image forming apparatus100is provided with a photoconductive drum3that carries the toner image to be transferred onto the paper, and a charger5, an optical scanning unit11, a developing unit2, a transfer unit6, a cleaning unit4and a discharge lamp12are disposed around the photoconductive drum3.

The charger5charges the surface of the photoconductive drum3to a predetermined potential. The optical scanning unit11scans an optical image over the surface of the photoconductive drum3charged to the predetermined potential, thus to delineate an electrostatic latent image. The developing unit2supplies a toner (developer) in a toner container7to the electrostatic latent image generated on the surface of the photoconductive drum3, to form a toner image. The transfer unit6transfers the toner image on the surface of the photoconductive drum3to the paper forwarded by the resist roller14. The cleaning unit4removes and collects the toner remaining on the surface of the photoconductive drum3, so that a new toner image can be formed on the photoconductive drum3. The discharge lamp12eliminates the charge on the surface of the photoconductive drum3.

The fixing unit8A installed posterior to the image forming unit includes a fixing roller81and a pressure roller82. The fixing roller81is controlled to turn heater lamps81c,81d(Ref.FIG. 3) on and off based on a temperature detected by a temperature sensor (not shown), to thereby maintain a predetermined temperature (160 to 200° C., for example). The fixing roller81and the pressure roller82rotate to hold the paper forwarded thereto, to heat up the surface of the paper so as to fix the toner image by thermocompression onto the paper, and to thus complete image forming on the paper. The fixing unit8A also includes, in addition to the fixing roller81and the pressure roller82, a cleaning unit70that removes the unfixed developer stuck to the pressure roller82. The details of the cleaning unit70will be subsequently described.

The paper on which the toner image has been thermocompressively fixed by the fixing unit8A is forwarded along the paper feeding path R by a feed roller25, and discharged to a receiver tray15by a discharge roller26.

The foregoing image forming operation is performed under control of a control unit101including a CPU and so on, which controls the action of the respective components.

FIG. 3is a schematic cross-sectional view showing a structure of the fixing unit according to the first embodiment. The fixing unit8A includes inside a housing80the fixing roller81, the pressure roller82, an external heating roller83and the cleaning unit70. The housing80may be constituted of a thermosetting resin such as PET (polyethylene terephthalate) or PBT (polybutylene terephthalate).

The fixing roller81includes a core metal81aand a separation layer81b, and the core metal81aaccommodates therein heater lamps81c,81dthat serve as a heat source. The core metal81amay be made of a metal such as iron, a stainless steel, aluminum or copper, or an alloy of such metals. In this embodiment, the core metal81ais constituted of an iron (STKM) in a hollow cylindrical shape, in dimensions of 40 mm in diameter and 1.3 mm in thickness. A reason that the thickness of 1.3 mm is adopted in this embodiment is to restrain a thermal capacity at a low level.

The separation layer81bmay be constituted of a fluorine-based resin such as PFA (a copolymer of tetrafluoroethylene and perfluoroalkylvinylether) or PTFE (polytetrafluoroethylene), a silicone rubber, a fluorinated rubber or the like. In this embodiment, a synthetic material composed of PFA and PTFE is applied to the core metal81ain a thickness of 25 μm, to form the separation layer81b.

The heater lamps81c,81dare constituted of halogen heaters, and irradiates an infrared light upon receiving power under control of the control unit101. The infrared light irradiated by the heater lamps81c,81dheats up the inner circumferential surface of the fixing roller81(i.e. the inner circumferential surface of the core metal81a). Also, a temperature sensor (not shown) is disposed close to the fixing roller81, and the control unit101turns the heater lamps81c,81don and off based on the output of the temperature sensor, to thereby maintain the outer circumferential surface of the fixing roller81(i.e. the outer circumferential surface of the separation layer81b) at a predetermined temperature.

The pressure roller82is disposed so as to be pressed against the fixing roller81, at a position opposite thereto across the paper feeding path R. The pressure roller82includes a core metal82a, a heat resistant elastic layer82band a separation layer82c. The core metal82aand the separation layer82care usually made of a similar material to that of the core metal81aand the separation layer81bof the fixing roller81. As the heat resistant elastic layer82ba silicone rubber may be employed, and in this embodiment a silicon rubber (rubber hardness according to JIS-A50°) of 6 mm in thickness is employed.

To the pressure roller82, a biasing force of a predetermined magnitude is applied toward the fixing roller81by a biasing member (not shown) such as a pressure spring, so that a fixing nip of approx. 6 mm in width at the contact interface between the fixing roller81and the pressure roller82.

The external heating roller83is pressed against a portion of the circumferential surface of the pressure roller82. The external heating roller82includes a core metal83aand a separation layer83b, and the core metal83aaccommodates therein a heater lamp83cthat serves as the heat source. The core metal83ais of a hollow cylindrical shape of 15 mm in diameter, and the separation layer83bprovided around the outer circumferential surface of the core metal83ahas a thickness of 25 μm. The core metal83aand the separation layer83cmay be made of a similar material to that of the core metal81aand the separation layer81bof the fixing roller81.

A temperature sensor (not shown) is disposed close to the external heating roller83, and the control unit101turns the heater lamps81c,81don and off based on the output of the temperature sensor, to thereby maintain the outer circumferential surface of the external heating roller83and the pressure roller82at a predetermined temperature (130 to 150° C., for example).

When the paper P to which the toner T has adhered is forwarded to the fixing unit8A configured as above, the paper P is led to the contact interface between the fixing roller81and the pressure roller82by paper feeding guides61,62located at a lower portion of the fixing unit8A. The fixing roller81and the pressure roller82apply heat and pressure to the paper P by holding the paper P therebetween, to thereby fix the toner onto the paper P. The paper P to which the toner has been fixed either spontaneously separates from the fixing roller81and the pressure roller82because of the separation property thereof, or is peeled off by separating blades64,63disposed so as to be pressed against the fixing roller81and the pressure roller82respectively, and forwarded to a downstream side of the paper feeding path R (upward from the fixing unit8A).

When performing the fixing process in this way, a portion of the toner T may adhere to the surface of the fixing roller81. The toner T thus stuck to the surface of the fixing roller81adheres to the pressure roller82via the fixing nip. Therefore, the fixing unit8A according to this embodiment includes a cleaning unit70that removes the toner stuck to the pressure roller82.

The structure of the cleaning unit70is as follows. The cleaning unit70is located in a space delimited by the housing80, a lower cover71and an upper cover72, and includes a cleaning roller84, a projection75and a receiving tray76. The housing80is provided with ventilation ports73,74of an appropriate size. One (73) of the ventilation ports73,74is located at a position higher than the cleaning roller84, and the other (74) is at a lower position than the cleaning roller84.

The cleaning roller84includes a core metal84adisposed parallel to the rotation axis of the pressure roller82, a cylindrical-shaped base material84bfixed over the circumferential surface of the core metal84a, and a brush portion84cmade of a flexible synthetic resin radially implanted on the circumferential surface of the base material84b. The core metal84amay be made of a similar material to that of core metal81aof the fixing roller81. The base material84band the brush portion84cmay be constituted of a conductive nylon for example, and filaments of 200 to 400 deniers may be employed to constitute the brush portion84c.

The cleaning roller84is rotationally driven by a driving unit (not shown) so as to rotate around the core metal84a. The cleaning roller84is set to rotate in a reverse direction to the rotating direction of the pressure roller82, so as to effectively remove the toner stuck to the surface of the pressure roller82. The driving source of the cleaning roller84may be a motor, which may be used in common to also rotate the pressure roller82, or used exclusively for the cleaning roller84.

The projection75is horizontally erected on the housing80, such that a tip portion of the projection75contacts the circumferential surface of the brush portion84c. The projection75, which may be integrally formed with the housing80, is preferably fluorine-coated on the surface. The receiving tray76is located below the projection75, and has an upwardly opened shape.

FIGS. 4A,4B,5A and5B are fragmentary schematic cross-sectional views showing a toner collecting method in the cleaning unit70. As already stated, the toner T stuck to the fixing roller81adheres to the pressure roller82via the fixing nip, and is carried along with the rotation of the pressure roller82, to the contact interface with the cleaning roller84(Ref.FIG. 4A). The brush portion84cof the cleaning roller84removes the toner from the pressure roller82, and the brush portion84ccarries the toner T (Ref.FIG. 4B).

The toner T carried by the brush portion84creaches the contact point with the projection75, by the rotation of the cleaning roller84. The projection75removes the toner T from the brush portion84c. In this embodiment, the ventilation ports73and74are provided at a higher and a lower position than the cleaning roller84respectively. Accordingly, when the cleaning roller84rotates in a direction indicated by the arrow in the drawings, air is caused to flow in a direction indicated by broken lines, inside the housing80. Consequently, the toner T that has been removed does not adhere to the projection75, but falls downward (Ref.FIG. 5A). This effect becomes more prominent, especially when the projection75has a fluorine coating on its surface. The toner T that has fallen down is collected into the receiving tray76located halfway of the air ventilating path (Ref.FIG. 5B).

Also, since the lower cover71is located close to the brush portion84cin this embodiment, the toner T stuck to the brush portion84ccan be prevented from being carried toward the pressure roller82even when the toner T has not been completely removed by the projection75, and the toner T is collected into the receiving tray76by the edge portion of the lower cover71.

SECOND EMBODIMENT

While the receiving tray76is located inside the space delimited by the housing80, the lower cover71and the upper cover72in the first embodiment, the receiving tray76does not necessarily have to be located inside the housing80. The second embodiment, accordingly, represents a case where a toner collecting member is provided outside the housing80.

FIG. 6is a schematic cross-sectional view showing a structure of a fixing unit8B according to the second embodiment. Among the constituents of the fixing unit8B shown inFIG. 6, the same constituents as those of the fixing unit8A according to the first embodiment are given the identical numerals, and description thereof will be omitted. The fixing unit8B according to this embodiment includes the fixing roller81, the pressure roller82, the external heating roller83and the cleaning unit70, inside the housing80.

The cleaning unit70includes a cleaning roller84that removes the toner stuck to the pressure roller82, a projection75that removes the toner stuck to the cleaning roller84, and a receiving tray77for collecting the toner removed by the projection75. The cleaning roller84and the projection75are included in a space delimited by the housing80, the lower cover71and the upper cover72, as in the first embodiment. On the other hand, the receiving tray77is located outside the housing80, and below the ventilation port74. The toner removed by the projection75is collected into the receiving tray77, by the air flow generated by the presence of the ventilation ports73and74.

Such configuration makes the receiving tray77accessible from outside the housing80, and hence allows collecting the toner and cleaning the receiving tray77. When adopting such configuration, the receiving tray77may be removably attached to the housing80.

THIRD EMBODIMENT

While the cleaning unit70is installed to remove the toner stuck to the pressure roller82in the first embodiment, the toner may also adhere to the fixing roller81. Accordingly, a cleaning unit for removing the toner on the fixing roller81may be provided.

FIG. 7is a schematic cross-sectional view showing a structure of a fixing unit8C according to the third embodiment. Among the constituents of the fixing unit8C shown inFIG. 7, the same constituents as those of the fixing unit8A according to the first embodiment are given the identical numerals, and description thereof will be omitted. The fixing unit8C according to this embodiment includes the fixing roller81, the pressure roller82, the external heating roller83and a cleaning unit90, inside the housing80.

The cleaning unit90includes a cleaning roller85that removes the toner stuck to the fixing roller81, a projection95that removes the toner stuck to the cleaning roller85, and a receiving tray96for collecting the toner removed by the projection95. The cleaning roller85, the projection95and the receiving tray96are located inside a space delimited by the housing80, a lower cover91and an upper cover92. Also, at appropriate positions on the housing80close to the cleaning roller85, ventilation ports93,94are perforated through the housing80.

The cleaning roller85includes a core metal85adisposed parallel to the rotation axis of the fixing roller81, a cylindrical-shaped base material85bfixed over the circumferential surface of the core metal85a, and a brush portion85cmade of a flexible synthetic resin radially implanted on the circumferential surface of the base material85b.

The cleaning roller85removes the toner stuck to the surface of the fixing roller81. The toner thus stuck to the cleaning roller85is removed by the projection95, and the toner removed from the cleaning roller85is collected into the receiving tray96by an air flow generated by the presence of the ventilation ports93and94.

The first embodiment includes the cleaning unit70that removes the toner stuck to the pressure roller82, while the second embodiment includes the cleaning unit90that removes the toner stuck to the fixing roller81. It is, however, obviously possible to provide a plurality of cleaning units to remove both the toner stuck to the fixing roller81and the toner stuck to the pressure roller82.