This application is based on Japanese Patent Application No. 2010-111844 filed on May 14, 2010, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a fixing device and an image forming apparatus.
2. Description of Related Art
Image forming apparatus employing electrophotographying systems, such as copying machines, printers, facsimiles, and combined machines provided with the functions of the above machines, are well known. In the image forming apparatus, a latent image formed on a photoreceptor is visualized with toner, and the visualized toner image is transferred onto a sheet and fixed on the sheet so that an image is formed on the sheet.
As a fixing device to fix a toner image onto a sheet, there is a roller type fixing device that forms a nip portion with a fixing roller, in which a heat source such as a halogen heater is incorporated, and a pressing roller which contact with the fixing roller, and the roller type fixing device conveys a sheet while pinching the sheet with the nip portion and heats and applies a pressure to the sheet.
Further, as another type fixing device, there is a belt type fixing device. In the belt type fixing device, an endless fixing belt is stretched by a fixing roller, in which a heat source such as a halogen heater is incorporated, and a pressing roller. This fixing device pinches the endless fixing belt between the fixing roller and the pressing roller so as to form a nip portion, and conveys a sheet while pinching the sheet with the nip portion and heats and applies a pressure onto the sheet.
In these fixing devices, toner on a sheet melts by being heated when the sheet passes through the nip portion. Therefore, there is a possibility that the sheet is wound around the surface of the fixing roller or the fixing belt by the adhesive force of the melted toner and is not separated so that a sheet jam is caused. Particularly, in the case where a thin sheet with a small basis weight and a coated sheet used for printing is employed as a sheet, such a sheet tends to wind around the surface of the fixing roller.
In order to prevent the winding of a sheet in the fixing device, a technique relating to an air separating mechanism is proposed to separate a sheet from a fixing roller or a fixing belt by blowing air from a outlet to a sheet conveyed from a nip portion (for example, refer to Patent Document 1). According to the air separating mechanism, since a sheet can be separated without bringing a separating member such as a separating claw in contact with the surface of a fixing roller, there is no fear to damage the surface of the fixing roller.
Further, in order to conduct a fixing action appropriately in such a fixing device, it is required to maintain a temperature at a fixing roller or a fixing belt appropriately. For this purpose, a temperature detecting sensor to detect a temperature at a fixing roller is arranged, and the temperature at the fixing roller is controlled. As the temperature detecting sensor, there are a contact type temperature detecting sensor that is brought in contact with the surface of a fixing roller and a non-contact type temperature detecting sensor that is not brought in contact with the surface of a fixing roller. In the contact type temperature detecting sensor, a trace remains so as to indicate the contact portion of the sensor on the surface of the fixing roller, and streaks take place due to difference in gloss at the remained trace, which results in lowering image quality.
Patent Document 1: Japanese Unexamined Patent Publication No. 2008-3277 Official Report
Patent Document 2: Japanese Unexamined Patent Publication No. 2009-93085 official report
The non-contact type temperature detecting sensor to detect a temperature at a fixing roller or a fixing belt has a large dependency for the surrounding environment. Accordingly, this type temperature detecting sensor is used on the condition that the inside of the fixing device is sealed from the outside. However, as mentioned above, if an air separating mechanism is employed in the fixing device in order to prevent the winding of a sheet, an air current is caused in the sealed inside of the fixing device by air blown from the air separating mechanism. As a result, the air current influences the operation of the non-contact type temperature detecting sensor, so that there is a possibility that a temperature at a fixing roller is erroneously detected.
Then, an object of the present invention is to provide a fixing device and an image forming apparatus which can execute a temperature control appropriately by suppressing erroneous detection in the non-contact type temperature detecting sensor.
To achieve the abovementioned object, a fixing device reflecting one aspect of the present invention, comprises:
a heating member to heat a sheet on which a toner image is supported;
a pressing member to contact with the heating member so as to form a nip portion;
a temperature detecting sensor to detect a temperature of the heating member on a non-contact condition for a surface of the heating member; and
an air separating section to separate the sheet from the heating member by blowing air from a outlet to the sheet conveyed out from the nip portion;
wherein the heating member is arranged to interrupt a straight line which connects the outlet and the temperature detecting sensor.
The image forming apparatus X is constituted with an image forming apparatus main body GH and an image reading apparatus YS. The image forming apparatus main body GH includes a plurality of image forming sections 10Y, 10M, 10C, and 10K, a belt-shaped intermediate transfer belt 5, a sheet conveying section, and a fixing device 8.
On the upper portion of the image forming apparatus main body GH, the image reading apparatus YS constituted with an auto document feeding unit 201 and a document image scanning exposing unit 202 is arranged. A document d placed on a document table of the auto document feeding unit 201 is conveyed by a conveying section, and images on the one side or both sides of the document d are subjected to scanning exposure by an optical system of the document image scanning exposing unit 202 and are read into a line image sensor CCD.
Signals formed via photo-electric conversion by the line image sensor CCD are subjected to analog processing, A/D conversion, shading correction, image compression processing and the like in an image processing section, and then the resultant signals are transmitted to exposing sections 3Y, 3M, 3C, and 3K.
An image forming section 10Y to form an image with a yellow color (Y) includes a charging section 2Y, an exposing section 3Y, a developing section 4Y, and a cleaning section 7Y around a photoreceptor drum 1Y. Image forming sections 10M, 10C, and 10K have the almost same structure as that of the image forming section 10Y. The developing sections 4Y, 4M, 4C, and 4K include therein respectively a two component developer composed of toner being small size particles of yellow (Y), magenta (M), cyan (C), and black (K) and carrier. The toner is composed of pigment or dye used as a colorant, wax that assists the toner so as to be separated from the fixing belt after the fixing, and a binder resin to hold these substances.
Respective color images formed by the image forming sections 10Y, 10M, 10C, and 10K are transferred one after another by transfer sections 6Y, 6M, 6C, and 6K onto the intermediate transfer belt 5 that is supported to be rotatable. With this, a color toner image is formed on the intermediate transfer belt 5. A sheet P accommodated in a sheet feed cassette 20 is fed out from the sheet feed cassette 20 and conveyed to the transfer section 6A via sheet feeding rollers 22A, 22B, 22C, and 22D, and a registration roller 23, and then the color toner image formed on the intermediate transfer belt 5 is transferred onto the sheet P. The sheet P on which the color toner image has been transferred is heated and applied with pressure in the fixing device 8, so that the color toner image is fixed onto the sheet P. Thereafter, the sheet P is pinched and held by a sheet delivery roller 24 and placed on a sheet delivery tray 25.
After the color toner image has been transferred onto the sheet P by the transfer section 6A, toner remaining on the intermediate transfer belt from which the sheet P has been separated is removed by the cleaning section 7A.
The fixing device shown in
The fixing device 8 includes a fixing frame 8F, the fixing belt 81, a heating roller 82, a fixing roller 83, a pressing roller 84, a temperature detecting sensor SE, and an air separating section which is mentioned later. The fixing frame 8F is structured with a plurality of frame members, and forms an outer frame of the fixing device 8. Each of members constituting the fixing device 8 is supported directly or indirectly by the fixing frame 8F. The fixing frame 8F is supported to be able to shift by a guide mechanism such as slide rails, so that the fixing device 8 can be drawn to the outside of the image forming apparatus X in the front side direction (the front side direction on the sheet surface of
The fixing belt 81 is an endless belt and is stretched bythe heating roller 82 and the fixing roller 83. For example, PI (polyimide) with a thickness of 70 μm is employed as the substrate of the fixing belt 81. The outer surface of this substrate is covered with a heat-resistant silicone rubber (hardness: JIS-A30°) with a thickness of 200 μm as an elastic layer. Further, the surface of this elastic layer is coated with PFA (perfluoro alkoxy) being a heat-resistant resin with a thickness of 30 μm.
The heating roller 82 incorporates therein a halogen heater 82 A to heat the fixing belt 81. Further, this heating roller 82 includes a core metal 82B and a resin layer 82C. The core metal 82B is composed of, for example, a cylinder made of aluminum with a thickness of 4 mm. The outer surface of the core metal 82B is covered with a resin layer 82C which is coated with PTFE (poly tetrafluoroethylene) with a thickness of 30 μm. In order to cope with different sheet widths, the halogen heater 82A include, for example, two heater elements with 1200 W, two heater elements with 750 W and one element with 500 W. These heater elements are arranged to form different heat generation distributions in the axial direction corresponding to different sheet width of sheets.
In order to form a nip portion N between the fixing belt 81 and the pressing roller 84, the fixing roller 83 is arranged opposite to the pressing roller. That is, in the first embodiment, the fixing roller 83 corresponds to the first roller in the present invention, and the pressing roller 84 corresponds to a pressing member in the present invention.
The fixing roller 83 includes a core metal 83A, an elastic layer 83B, and a resin layer 83C. The core metal 83A is composed of a solid member made of, for example, metals such as iron. The core metal 83A is covered with a heat-resistant silicone rubber with a thickness of 20 mm as an elastic layer 83B. Further, the elastic layer 83B is covered with a resin layer 83 C coated with PTFE which is a low friction and heat resistant resin with a thickness of 30 μm.
In the vicinity of the heating roller 82, a temperature detecting sensor SE to detect the temperature of the fixing belt 81 on the non-contact condition to the fixing belt 81 is arranged. More concretely, the temperature detecting sensor SE is arranged at the upstream side than the nip portion N in terms of the conveying direction of a sheet. On the basis of the detection result of the temperature detecting sensor SE, the halogen heater 82A is controlled to be ON or OFF, so that the temperature of the fixing belt 81 is maintained at a proper temperature for fixing.
The pressing roller 84 that contact with the fixing belt 81 incorporates therein a halogen heater 84A as a heating means for shortening a temperature raising time right after a power source for the image forming apparatus X has been turned on. Further, the pressing roller 84 includes a core metal 84B, an elastic layer 84C, and a resin layer 84D. The core metal 84B is composed of, for example, a cylinder made of aluminum with a thickness of 4 mm. The outer surface of the core metal 84B is covered with a heat resistant silicone rubber (hardness: JIS-A30°) with a thickness of 1 mm as the elastic layer 84C. Further, the elastic layer 84C is covered with the resin layer 84D which is a PFA tube with a thickness of 30 μm. The pressing roller 84 has an outer diameter of 90 mm. Further, the pressing roller 84 can press the fixing roller 83 via the fixing belt 81 by an pressing mechanism.
In the abovementioned structure, when a toner image is fixed onto a sheet P, the fixing belt 81 is heated by the halogen heater 82A via the heating roller 82, and the pressing roller 84 is also heated by the halogen heater 84A.
Then, when the pressing roller 84 is rotated in an anticlockwise rotating direction (in
The sheet P is conveyed to the fixing device, and, when this sheet P passes through the nip portion between the fixing belt 81 and the pressing roller 84, the sheet P is heated and applied with a pressure. As a result, the toner is fixed onto the sheet P.
In the fixing device, since there is fear that a sheet P on which a toner image has been fixed adheres on and winds around the fixing belt 81 after the sheet has been conveyed out from the nip portion N, there is a need to separate surely the fixed sheet P from the fixing belt 81. The fixing device 8 in the embodiment of the present invention includes an air separating section as an air separating mechanism to separate the sheet P from the fixing belt 81 by blowing air to the sheet P conveyed out from the nip portion N. More concretely, the air separating section is arranged such that a discharging port of the air separating section is positioned at the downstream side than the nip portion N in terms of the conveying direction. The air separating section is constituted with, for example, a fan F, a first duct 121, and a second duet 131.
As shown in
The outlet 131b which is an another opening portion of the second duct 131 is arranged in the vicinity of the nip portion N. The air sent from the fan F flows inside the first duct 121 and the second duct 131 and is discharged from the outlet 131b. With this, air proceeds in between a sheet and the fixing belt 81 and the sheet is separated from the fixing belt 81. Accordingly, it becomes possible to prevent the sheet from winding around the fixing belt 81. Further, since a sheet is separated from the fixing belt 81 by the air separating section constituted by the fan F, the first duct 121, and the second duct 131, the sheet can be separated without bringing a member such as a separating claw in contact with the surface of the fixing belt 81. Accordingly, there is no fear to damage the surface of the fixing belt 81.
The sheet separated from the fixing belt 81 by the air separating section is guided by an upper guide 211 and low guides 212 and 213, pinched and held by conveying rollers R1 and R2, and conveyed toward a sheet discharging roller 24 (refer to
The temperature detecting sensor SE to detect the temperature of the fixing belt 81 is a non-contact type sensor so that its measurement result tends to change greatly depending on ambient temperature. Accordingly, if the air blown from the outlet 131b of the second duct 131 flows into the periphery of the temperature detecting sensor SE, the surrounding environment of the temperature detecting sensor SE fluctuates, which results in that it becomes difficult to detect accurately the temperature of the fixing belt 81. Then, in the fixing device 8 in the embodiment of the present invention, ingenuity has been made in the arrangement of the outlet 131b and the temperature detecting sensor SE.
As the first ingenuity, as shown in
When the outlet 131b and the temperature detecting sensor SE are arranged in this way, since the fixing belt 81, the heating roller 82, and the fixing roller 83 becomes a wall, it becomes difficult for air blown from the outlet 131b to flow around the periphery of the temperature detecting sensor SE, whereby the fluctuation of the surrounding environment of the temperature detecting sensor SE can be suppressed. As a result, an erroneous detection in the temperature detecting sensor SE can be suppressed so as to control the temperature properly.
The sign M in
As the second ingenuity, the outlet 131b is arranged at an arrow mark “a” side of this virtual plane M, and the temperature detecting sensor SE is arranged at an arrow mark “b” side of this virtual plane M. Namely, the temperature detecting sensor SE is arranged at the opposite side of the outlet 131b in terms of the virtual plane M or across the virtual plane M.
When the temperature detecting sensor SE is arranged at the opposite side of the outlet 131b in terms of the virtual plane M, air blown from the outlet 131b is interrupted by the wall of the fixing belt 81, the heating roller 82, and the fixing roller 83. With this, it becomes difficult for air to flow around the periphery of the temperature detecting sensor SE, whereby the fluctuation of the surrounding environment of the temperature detecting sensor SE can be suppressed. As a result, an erroneous detection in the temperature detecting sensor SE can be suppressed so as to control the temperature properly.
As the third ingenuity, as shown in
The fixing device 8 shown in
In the case of the fixing device 8 of this type, each of the abovementioned first, second and third ingenuity is applied. Namely, as the first ingenuity, as shown in
Further, when the fixing roller 83 closest to the outlet 131b among the abovementioned roller group is made as a standard, a roller having a central axis having a farthest straight line distance from the central axis M1 of the fixing roller 83 being the standard is made as the second roller. For example, in the case shown in
As the second ingenuity, in terms of a virtual plane M which includes the central axis M2 of the heating roller 82 being the second roller and the central axis M1 of the fixing roller 83 being the first roller, the temperature detecting sensor SE is arranged at the opposite side of the outlet 131b.
As the third ingenuity, an exhaust port H to exhaust air is arranged at the arrow mark “a” side of the virtual plane M (which is the side where the outlet 131b is arranged and the opposite side of the arrow mark “b” side where the temperature detecting sensor SE is arranged).
In this way, in the fixing device 8 shown in
Further, as shown in
The fixing device 8 shown in
A sign N1 represents a central line of the nip portion which passes the center of the width “t” of the nip portion N in the lengthwise direction of the heating roller 82, and a sign M represents a virtual plane which includes the central axis M2 of the heating roller and the central line N1 of the nip section N.
In the fixing device 8 shown in
As the second ingenuity, the outlet 131b is arranged at the arrow mark “a” side of the virtual plane M, and the temperature detecting sensor SE is arranged at the arrow mark “b” side of the virtual plane M. That is, the temperature detecting sensor SE is arranged at the opposite side of the outlet 131b in terms of the virtual plane M.
As the third ingenuity, an exhaust port H to exhaust air is arranged at the arrow mark “a” side of the virtual plane M (which is the side where the outlet 131b is arranged and the opposite side of the arrow mark “b” side where the temperature detecting sensor SE is arranged).
In this way, in the roller type fixing device shown in
Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.
Number | Date | Country | Kind |
---|---|---|---|
2010-111844 | May 2010 | JP | national |