Patent Grant
10409206
This application claims the benefit of Japanese Patent Application No. 2017-107780, filed May 31, 2017, which is hereby incorporated by reference herein in its entirety.
The present invention relates to a fixing device for use with an image forming apparatus, such as a copying machine or a laser beam printer, employing an image forming process of an electrophotographic type, an electrostatic recording type, or the like.
As a type of the fixing device, a film fixing type using a ceramic heater has been known. Further, conventionally, a countermeasure against “offset of end portion position due to non-sheet-passing-portion temperature rise” has been considered. That is, when a small sized-paper (recording material) is passed through the fixing device, in an end portion region in which the recording material is not passed through the fixing device, an amount of heat from a heat generating member is accumulated as it is, and the end portion region is very high in temperature in some cases. In such a state, in a case in which a plain paper-sized (large-sized) recording material is passed through the fixing device, such a hot-offset phenomenon occurs in which toner is excessively melted in the end portion region and thus deposits on a fixing film surface, and then adheres to the fixing film surface when the fixing film is rotated through one-full circumference, generates in some instances.
Therefore, in order to reduce a degree of generation of this phenomenon, a constitution in which, between a heat generating member and a holding member for holding the heat generating member, a member having a greater thermal conductivity than a base material of the heat generating member is provided on an entire region of a back surface of the heat generating member has been known (Japanese Laid-Open Patent Application Hei-11-260533). By this constitution, an amount of heat generating at an end portion position is distributed, and a temperature of the heat generating member in the end portion position is decreased, so that a degree of non-sheet-passing-portion temperature rise is alleviated and thus generation of the hot-offset phenomenon can be prevented.
In this constitution, however, as a heat conductive member, a member formed of metal, such as an aluminum plate, is used, and the heat conductive member expands and contracts by heating, and, therefore, there is a need that the heat conductive member is positioned relative to a supporting member for supporting a heater as the heat generating member. For that purpose, when the holding member is provided with a positioning hole separately from a placement window for an electrical power shut-off member, strength of the supporting member weakens from the positioning hole that is a starting point, so that deformation due to a sag of the supporting member generates in the neighborhood of the positioning hole in some cases.
A principal object of the present invention is to provide a fixing device capable of suppressing deformation of a supporting member, for supporting a heat generating member, in order to position a heat conductive member.
According to one aspect, the present invention provides a fixing device comprising an elongated heat generating member extending in a longitudinal direction and having a first region and a second region different in the longitudinal direction, an endless belt rotatable in contact with the heat generating member, an opposing member opposing the endless belt and configured to form a nip in cooperation with the endless belt so that a recording material, on which a toner image is formed, is nipped and fed in the nip, a heat conductive member extending in the longitudinal direction within the first region in which a surface of the heat conductive member contacts the heat generating member, a positioning portion extending from an end portion of the surface of the heat conductive member with respect to the longitudinal direction, in a direction in which the positioning portion is spaced from the heat generating member, an electrical power shut-off member provided at a position corresponding to the second region of the heat generating member and configured to shut-off electrical power supplied to the heat generating member, and a supporting member provided with an opening at a position corresponding to the second region and configured to support the heat generating member through the heat conductive member, wherein the opening is configured to permit insertion of the positioning portion to prevent movement of the heat conductive member.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
In
In
In
In
In
In
Embodiments of the present invention will be described with reference to the drawings.
Fixing Device
In the following description, a longitudinal direction refers to a direction (first direction) perpendicular to a recording material conveyance direction in a recording material conveying path. A short side direction is the same direction as the recording material feeding direction (second direction crossing perpendicular to the first direction).
The fixing device 18 includes a film unit 31 including a cylindrical film (endless belt) 36 having flexibility and includes a pressing roller 32 as a pressing member. The film unit 31 and the pressing roller 32 are provided substantially in parallel to each other between left and right side plates 34 of a device frame 33 so that a heater 37 opposes the pressing roller 32 through the rotatable sheet 36.
The pressing roller 32 includes a metal core 32a, an elastic layer 32b formed outside the metal core 32a, and a parting layer 32c formed outside the elastic layer 32b. This pressing roller 32 is provided as an opposing member opposing the film 36 backed up by the heater 37, and forms a nip N, for nipping and feeding a recording material P, carrying thereon a toner image, in cooperation with the film 36. As a material of the elastic layer 32b of the pressing roller 32, silicone rubber, fluorine-containing rubber, or the like, is used. As a material of the parting layer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or the like, is used.
In this embodiment, the pressing roller 32, prepared by forming an about 3.5 mm-thick silicone rubber elastic layer 32b on a stainless steel-made metal core 32a of 11 mm in outer diameter by injection molding, and then coating an outside of the layer 32b with an about 40 μm-thick PFA resin tube as a parting layer 32c, was used. An outer diameter of the pressing roller 32 is 18 mm. A hardness of the pressing roller 32 may desirably be, from the viewpoints of ensuring a durability of a nip N, in a range of 40 degrees to 70 degrees as measured by an Asker-C hardness meter under a load of 9.8 N. In this embodiment, the hardness is adjusted to 54 degrees.
A length of the elastic layer 32b of the pressing roller 32 measured in a longitudinal direction is 226 mm. The pressing roller 32 is, as shown in
The film unit 31, shown in
The film 36 includes a base layer, an elastic layer formed outside the base layer, and a parting layer formed outside the elastic layer, and is a cylindrical flexible member. The film 36 in this embodiment is 18 mm in inner diameter. In the film 36, as the base layer, a 60 μm-thick polyimide base material is used. As the elastic layer, an about 150 μm-thick silicone rubber layer is used. As the parting layer, a 15 mm-thick PFA resin tube is used.
The supporting member 38 has, as shown in
The heater 37 is, as shown in
The heater 37 has an elongated shape and is provided along a generatrix direction (longitudinal direction, first direction) of the film 36 while opposing a supporting surface of the supporting member 38 so that the longitudinal direction is the first direction. The substrate 37a of the heater 37 has a rectangular parallelopiped shape, which is 270 mm in length measured in the longitudinal direction, 5.8 mm in length measured in the short side direction, and 1.0 mm in thickness, and a material thereof is alumina. The upstream and downstream heat generating resistors 37b have a pattern such that the heat generating resistors 37b are connected with each other by an electrical contact portion at one end portion with respect to the longitudinal direction, and have the same shape, having a longitudinal length of 222 mm and a short-side length of 0.9 mm.
As regards short-side positions of the upstream and downstream heat generating resistors 37b, both the heat generating resistors 37b are disposed at positions of 0.7 mm from longitudinal edges of the ceramic substrate 37a, and the heat generating resistors 37b are printed at symmetrical positions with respect to a short-side center. Incidentally, onto the inner surface of the film 36, a heat-resistant grease is applied, so that a sliding property of the inner surface of the film 36 with the heater 37 and the supporting member 38 are improved.
On the other hand, the thermo switch 44 is supported in direct contact with a back surface of the heater 37 so as to directly sense (detect) heat of the heater 37 through the metal plate 39. A pressing force (pressure) of the thermo switch 44 exerted on the back surface of the heater 37 is imparted by a spring (not shown) provided between the pressing stay 41 and a thermo switch holder (not shown) for holding the thermo switch 44.
The thermistor 42 is prepared by providing a thermistor element in a casing via ceramic paper, or the like, for stabilizing a contact state with the metal plate 39, and then coating the thermistor element with an insulating material, such as a polyimide tape. The thermo switch 44 is a part for detecting abnormal heat generation to shut off electrical power supply to the heater 37 when the heater 37 causes an abnormal temperature rise. The thermo switch 44 is provided with a bimetal portion prepared by firmly bonding two or more kinds of metal or alloy, different in thermal expansion coefficient to each other, and then finishing the bonded material in a plate shape, so that, due to abnormal high temperature of the heater 37, the metal portion having a large thermal expansion coefficient is bent toward the metal portion side having a small thermal expansion coefficient. By using this displacement, an electrical contact is opened and closed, so that a circuit for supplying electrical power (energization) to the heater 37 can be formed.
Next, the pressing stay 41, shown in
The left and right flanges 42 hold end portions of the pressing stay 41 with respect to the longitudinal direction, and a vertical groove portion 42a of each of the left and right flanges 42 is engaged with a vertical groove portion 34a of each of the left and right side plates 34 of the device frame 33. In this embodiment, as a material of the flanges 42, a liquid crystal polymer (resin) is used.
Then, as shown in
During an operation of the fixing device, to the driving gear G of the pressing roller 32, a rotational force is transmitted from an unshown driving source, so that the pressing roller 32 is rotationally driven in the clockwise direction in
The film 36 is rotated and the electrical power is supplied to the heater 37, and, in a state in which the temperature of the heater 37 detected by the thermistor 43 reaches the target temperature, the recording material (recording paper) P is introduced. A fixing entrance guide 30 performs the function of guiding the recording material P, on which a toner image tin an unfixed state is formed, so as to be moved toward the nip N.
Into the nip N, the recording material P, having formed thereon the unfixed toner image t, is introduced, and then, a toner image-carrying surface of the recording material P is in close contact with the film 36 at the nip N and the recording material P is nipped and fed (conveyed) through the nip N. In this feeding process, the unfixed toner image t on the recording material P is heated and pressed by heat of the film 36 heated by the heater 37, and thus, is melted and fixed on the recording material P.
The recording material P passing through the nip N is curvature-separated from the surface of the film 36 and then is discharged to an outside of the fixing device by an unshown discharging roller pair. Incidentally, a maximum sheet passable width of the fixing device 18 is 216 mm, so that a LTR (letter)-sized recording material is capable of being subjected to printing at a speed of 20 PPM.
With reference to
As shown in parts (a) and (b) of
As shown in part (a) of
As shown in part (b) of
With reference to part (c) of
The aluminum plate 39 includes a first surface contacting the back surface of the heater 37, and bent portions 39a and 39b, which are second surfaces (surfaces extending from longitudinal ends of the first surface in a direction of being spaced from the heater 37 (opposite direction from the heater 37)) provided at longitudinal end portions thereof, and which are bent at right angle with a length l=3 mm. The bent portions 39a and 39b are inserted in mounting holes 38a and 38b, respectively, provided as openings in the supporting member 38, so that movement of the aluminum plate 39 is prevented. Similarly, the aluminum plate 40 includes bent portions 40a and 40b provided as second surfaces at longitudinal end portions thereof, and the bent portions 40a and 40b are inserted in mounting holes 38b and 38c, respectively.
The mounting holes 38a and 38c have the same size and are provided to have a relatively greater size (error amount Δ of 1 mm or less) than the associated bent portions in order to absorb thermal expansion of the aluminum plates 39 and 40. In this embodiment, a=0.4 mm and b=4.1 mm are set. The mounting hole 38b for mounting the supporting member 38 on a device frame 33 also functions as the placement window 44a in a state in which the supporting member 38 is demounted from the device frame 33, and, in this embodiment, b=4.1 mm and c=15.1 mm are set. Thus, a constitution in which the thermo switch 44 is provided at a position corresponding to a second region of the heater 37 in which the heater 37 does not contact the aluminum plate 39, and the supporting member 38 is provided at a position corresponding to the second region, with the mounting hole 38b for preventing movement of the aluminum plate 39, and supports the heater 37 via the aluminum plate 39, is employed. That is, the supporting member 38 is provided with the placement window 44a at a portion corresponding to the second region, in which the heater 37 does not contact the aluminum plate 39, different from the first region in which the heater 37 contacts the aluminum plate 39, with respect to the longitudinal direction of the heater 37.
Parts (a) and (b) of
The thickness of the aluminum plates 39 and 40 is 0.3 mm, and, therefore, when the above-described error amount Δ is taken into consideration, as regards the gap K between the aluminum plates 39 and 40, the following formula is satisfied:
K+0.3×2+Δ=15.1.
Parts (a) to (c) of
In the comparison example, when the heater back surface temperatures of the heater 37, after a lapse of 3 seconds from the start of energization, are such that the temperature at the portion B is less than the temperature at the portion A by about 17° C., and, on the other hand, in this embodiment, the temperature at the portion B is merely less than the temperature at the portion A by about 2° C. to 3° C. The portions A in this embodiment and the comparison example are unchanged in constitution between this embodiment and the comparison example, and, therefore, the temperature changes at the portions A are substantially the same. When a comparison is made at the portions B, it is understood that the heater back surface temperature in this embodiment greater by about 15° C. than the heater back surface temperature in the comparison example.
As a result of printing of the image in this state, in the comparison example, improper fixing generated at the thermo switch 44 portion in printing of the image on a first sheet. This is because the back surface temperature of the heater 37 locally becomes a low temperature, so that the film surface temperature at this portion also lowers. When the film surface temperature in the comparison example was measured using a radiation thermometer, it turned out that, immediately before the printing of the image on the first sheet, the temperature at the portion B was less by about 5° C. than at the portion A.
The improper fixing remarkably generates immediately after the fixing device 18 is increased in temperature up to a fixing temperature from a state of being sufficiently cooled at normal temperature, and, when the printing is repeated, the heater back surface temperature is uniformized, and, therefore, the improper fixing gradually does not generate. In the comparison example, the improper fixing slightly generates in the printing of the image on a second sheet and disappears in the printing of the image on a third sheet.
On the other hand, in this embodiment, the heater back surface temperature was uniform compared with that in the comparison example, so that the improper fixing did not generate even in the printing of the image on the first sheet and a good image was able to be obtained. This is because, by disposing the aluminum plate on the heater back surface at a position other than the position of the thermo switch 44, the temperature is controlled in a state in which values of thermal capacitance at portions in which the thermo switch 44 is present and absent are added to each other, and thus, a local temperature lowering does not generate at the position of the thermo switch 44.
Strength of the supporting member 38 will be described using
At the arrow α portion, there is no difference in heater surface height between this embodiment and the comparison example, so that a sag of the supporting member 38 does not generate. This would be considered because the thermo switch 44 backs up the sheet 38 in press-contact with the back surface of the heater 37 and thus, suppresses the sag of the supporting member 38.
On the other hand, the heater surface height at the arrow β portion in the comparison example is lower by about 0.03 mm than that in this embodiment. This is because the mounting hole 38d is provided at the arrow β portion in the comparison example and the strength of the supporting member 38 weakens from the mounting hole 38d as a starting point, and thus, deformation of the supporting member 38 occurs due to the sag in the neighborhood of the mounting hole 38d.
As described above, in this embodiment, the metal plate is disposed as a thermal capacitance member on the heater back surface at the position other than the position of the thermo switch 44, and the temperature is controlled in a state in which values of thermal capacity at portions in which the thermo switch 44 is present and absent are added to each other, so that a local temperature lowering at the position of the thermo switch 44 is avoided.
Further, in this embodiment, the supporting member 38 is provided with the opening, corresponding to the thermo switch 44, at the position opposing the second region different in position with respect to the longitudinal direction (first direction) of the heater 37 from the first region in which the heater 37 contacts the aluminum plate 39. By contact between a second surface of the aluminum plate 39 and an end surface of the opening of the supporting member 38 with respect to the first direction, movement of the aluminum plate 39 relative to the supporting member 38 is prevented. Further, the aluminum plate 39 is constituted so that the portion corresponding to the second region of the heater 37 contacts the thermo switch 44. Further, the positioning hole of the metal plate relative to the metal plate is caused to function as the B placement window (opening) of the thermo switch 44, so that the sag caused by the lowering in strength of the supporting member 38 due to the positioning hole is avoided.
As a result, the generation of the improper fixing due to the local temperature lowering of the heater (heat generating member) while maintaining a heat-uniformizing effect by a conventional high heat conductive member, and the sag of the heater supporting member due to the lowering in strength of the supporting member is avoided, so that a good image can be formed.
In the First Embodiment, the constitution in which the thermo switch was directly contacted to the back surface of the heater without via the metal plate, so as to suppress the heat conduction between the heater and the thermo switch during normal use, was employed. In this embodiment, in order to further suppress the heat conduction between the heater and the thermo switch during normal use, a spacer member is used between the heater and the thermo switch. An outline of a fixing device in this embodiment is the same as that of the fixing device in the First Embodiment, and, therefore, is omitted, and only a feature of this embodiment will be described.
Parts (a) to (c) of
The thermo switch 44 has large thermal capacity, and, therefore, the heat of the heater 37 does not readily conduct to the fixing film 36 contacting the (front) surface of the heater 37 compared with other members (the supporting member 38 and the thermistor 43) disposed on the back surface side of the heater 37. As a result, fixing non-uniformity and uneven glossiness of the toner image t on the recording material P can occur. In this embodiment, the spacer 51, formed of a resin material, for the thermo switch 44 is sandwiched between the heater 37 and the thermo switch 44, so that the thermo switch 44 and the back surface of the heater 37 are placed in a non-(direct) contact state.
As a result, a gap between the heater 37 and the thermo switch 44 is fixed while suppressing the heat conduction between the heater 37 and the thermo switch 44, so that the thermo switch 44 can be stably operated while eliminating the fixing non-uniformity and the uneven glossiness of the toner image t on the recording material P. Parts (a) and (b) of
A size of the spacer 51 is J=4 mm in width measured in the longitudinal direction (first direction), G=3 mm in width measured in the recording material feeding direction, and H=0.5 mm in height. Further, via the spacer 51, the thermo switch 44 is supported so as to be pressed toward the back surface of the heater 37. That is, the supporting member 38 is constituted so that the thermo switch 44 and the spacer 51 are in contact with each other at a portion corresponding to the second region different from the first region, in which the heater 37 contacts the aluminum plate 39, with respect to the longitudinal direction of the heater 37. In this embodiment, as a material of the spacer 51, a liquid crystal polymer (LCP) was used.
A comparison example compared with this embodiment is the same as the comparison example compared with the First Embodiment and shown in
As a result of printing of the image in such a state, in the comparison example, improper fixing generated at a position of the thermo switch 44 portion in printing of the image on a first sheet, and slightly generates in the printing of the image on a second sheet and disappears in the printing of the image on a third sheet.
On the other hand, in this embodiment, the heater back surface temperature was uniform compared with that in the comparison example, so that the improper fixing did not generate even in the printing of the image on the first sheet and a good image was able to be obtained. This is because the thermo switch 44 and the back surface of the heater 37 are in a non-contact state by the spacer 51 and thus, the heat conduction between the heater 37 and the thermo switch 44 is suppressed with the result that a local temperature lowering at the position of the thermo switch 44 is suppressed.
Strength of the supporting member 38 will be described using
At the arrow α portion, there is no difference in heater surface height between this embodiment and the comparison example, so that a sag of the supporting member 38 does not generate.
The heater surface height at the arrow β portion in the comparison example is lower by about 0.05 mm than that in this embodiment. This is because, similarly as in the comparison example described in First Embodiment, the mounting hole 38d is provided at the arrow β portion in the comparison example and the strength of the supporting member 38 weakens from the mounting hole 38d as a starting point, and thus, deformation of the supporting member 38 occurs due to the sag in the neighborhood of the mounting hole 38d.
As described above, in this embodiment, the metal plate is disposed as a thermal capacitance member on the heater back surface at the position other than the position of the thermo switch 44, and the temperature is controlled in a state in which values of thermal capacity at portions in which the thermo switch 44 is present and absent are added to each other, so that a local temperature lowering at the position of the thermo switch 44 is avoided.
Further, in this embodiment, the spacer member is provided between the heater and the thermo switch, so that the heat conduction between the heater and the thermo switch during normal use can be further suppressed.
Further, the positioning hole of the metal plate relative to the metal plate is caused to function as the B placement window of the thermo switch 44, so that the sag caused by the lowering in strength of the supporting member 38 due to the positioning hole can be avoided.
As a result, the generation of the improper fixing due to the local temperature lowering of the heater (heat generating member) while maintaining a heat-uniformizing effect by a conventional high heat conductive member, and the sag of the heater supporting member due to the lowering in strength of the supporting member is avoided, so that a good image can be formed.
In the above description, preferred embodiments of the present invention were described. The present invention is not limited, however, to these embodiments, and can be variously modified and changed within the scope of the present invention.
In the above-described embodiments, the bent portions 39b and 40b, as the second surfaces of the heat conductive members 39 and 40 including the first surface contacting the heater, were used as the positioning portions positioned relative to the opening 44a of the supporting member 38, but the present invention is not limited thereto.
Positioning members corresponding to the bent portions 39 and 40b as the second surfaces of the heat conductive members 39 and 40 are provided integrally with the heat conductive members 39 and 40, and may also be positioned relative to the opening 44a of the supporting member 38. In this case, the positioning members are not necessarily required to have heat conductivity, and may also be formed of, for example, a resin member, rather than the metal material. Further, as regards the heat conductive members 39 and 40, the first surface contacting the heater and the second surfaces (39a, 40a) as the positioning portions have the same thickness, but the positioning members may also have a thickness different from (for example, greater than) the thickness of the first surface of the heat conductive members contacting the heater.
In the above-described embodiments, a description was made on the presumption that a heat generation distribution of the heat generating resistor with respect to the longitudinal direction (first direction) of the heater, as the heat generating member, was uniform, but the present invention is not limited thereto. The shape of the heat generating resistor may also be changed so that an amount of heat generation is greater at the position of the thermo switch 44 than at another position with respect to the longitudinal direction (first direction). As a result, the generation of the improper fixing due to the local temperature lowering of the heater (heat generating member) can be further suppressed.
In the above-described embodiments, the thermo switch 44, as the electrical power shut-off member for suppressing overheating of the heater, as the heat generating member, was described, but the present invention is not limited thereto, and another element having a large thermal capacity can be used.
In the above-described embodiments, as the opposing member, the pressing roller for pressing the endless belt was used, but the endless belt may also be used as the opposing member. The opposing member is not limited to an opposing member for pressing the endless belt as the rotatable fixing member, but may also be an opposing member to be pressed.
In the above-described embodiments, as the recording material, the recording paper was described, but the recording material in the present invention is not limited to the paper. In general, the recording material is a sheet-like member on which the toner image is formed by the image forming apparatus and includes, for example, regular or irregular materials, such as plain paper, thick paper, thin paper, an envelope, a postcard, a seal, a resin sheet, an overhead projector (OHP) sheet, and glossy paper. In the above-described embodiments, for convenience, handling of the recording material P was described using terms such as the sheet passing or the sheet discharge, but by these terms, the recording material in the present invention is not limited to the paper.
In the above-described embodiments, the fixing device for fixing the unfixed toner image on the sheet was described as an example, but the present invention is not limited thereto. The present invention is also similarly applicable to a device for heating and pressing a toner image temporarily fixed on the sheet in order to improve a gloss (glossiness) of an image (also in this case, the device is referred to as the fixing device).
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
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| Number | Date | Country |
|---|---|---|
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| Number | Date | Country | |
|---|---|---|---|
| 20180348676 A1 | Dec 2018 | US |
