BACKGROUND
Technical Field
[0001] Embodiments of the present disclosure generally relate to a fixing device and an
image forming apparatus incorporating the fixing device.
Description of the Related Art
[0002] An electrophotographic image forming apparatus such as a copier or a printer includes
a fixing device to convey a recording medium such as a sheet on which an unfixed image
is formed to a nip formed between members such as a roller and a belt facing each
other, heat the recording medium, and fix the unfixed image on the recording medium.
[0003] As such a fixing device, for example,
JP-6164014-B (
JP-2015-69094-A) discloses the fixing device including an endless fixing belt, a heat generator disposed
inside a loop of the fixing belt, a nip member contacting an inner surface of the
fixing belt, a backup member such as a pressure roller that forms a nip between the
fixing belt and the backup member by sandwiching the fixing belt between the backup
member and the nip member, and a stay that supports the nip member.
[0004] In the fixing device including a support member such as the stay arranged around
a heater that is the heat generator, the support member blocks heat radiation from
the heater. Therefore, when the heater continues to generate heat, ambient temperature
around the heater increases, and the high ambient temperature may cause an excessive
rise in temperature of the heater.
SUMMARY
[0005] It is a general object of the present disclosure to provide an improved and useful
fixing device in which the above-mentioned disadvantages are eliminated. In order
to achieve the above-mentioned object, there is provided a fixing device according
to claim 1. Advantageous embodiments are defined by the dependent claims.
[0006] Advantageously, the fixing device includes a fixing member in a cylindrical shape,
an opposite member disposed opposite an outer surface of the fixing member, a nip
formation member disposed inside a loop of the fixing member, a support member disposed
inside the loop of the fixing member and configured to support the nip formation member,
and a heater disposed inside the loop of the fixing member. The nip formation member
sandwiches the fixing member between the nip formation member and the opposite member
and forms a nip between the nip formation member and the opposite member. The heater
includes a tube having a sealing portion at least partially exposed out of the support
member and a heat generator accommodated in the tube.
[0007] According to the present disclosure, an excessive rise in temperature of the heater
can be avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The aforementioned and other aspects, features, and advantages of the present disclosure
would be better understood by reference to the following detailed description when
considered in connection with the accompanying drawings, wherein:
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according
to an embodiment of the present disclosure;
FIG. 2 is a vertical cross-sectional view of a fixing device viewed from a lateral
side of the fixing device;
FIG. 3 is a perspective view of the fixing device with the vertical cross-sectional
view of the fixing device;
FIG. 4 is a vertical cross-sectional view of the fixing device viewed from a front
side of the fixing device;
FIG. 5 is a perspective view of a belt holder;
FIG. 6 is a perspective view of the belt holder according to a variation;
FIG. 7 is a schematic configuration diagram of a halogen heater;
FIG. 8 is a perspective view of a stay and a reflector;
FIG. 9 is a cross-sectional front view illustrating a main configuration in an end
portion of the fixing device according to a first embodiment;
FIG. 10 is a cross-sectional front view illustrating a main configuration in an end
portion of the fixing device according to a second embodiment of the present disclosure;
FIG. 11 is a cross-sectional front view illustrating a main configuration in an end
portion of the fixing device according to a third embodiment of the present disclosure;
FIG. 12 is a graph illustrating a heat generation distribution of a filament that
generates heat larger in a center portion than in end portions in the longitudinal
direction;
FIG. 13 is a graph illustrating a heat generation distribution of a filament that
generates heat larger in the end portions than in the center portion in the longitudinal
direction;
FIG. 14 is a cross-sectional front view illustrating a main configuration in an end
portion of the fixing device according to a fourth embodiment of the present disclosure;
FIG. 15 is a cross-sectional front view illustrating a main configuration in an end
portion of the fixing device according to a fifth embodiment of the present disclosure;
FIG. 16 is a graph illustrating a comparison between the embodiment of the present
disclosure and a comparative example about a temperature rise of the fixing belt outside
a sheet conveyance span;
FIG. 17 is a graph illustrating changes in temperatures of the fixing belt detected
by temperature sensors at a position corresponding to an opening and a position not
corresponding to the opening;
FIG. 18 is a diagram illustrating positions at which the temperature sensors detect
the temperatures of the fixing belt;
FIG. 19 is a diagram illustrating how to arrange wires;
FIG. 20 is a diagram illustrating a specific example of how to arrange wires;
FIG. 21 is a diagram illustrating another specific example of how to arrange wires;
FIG. 22 is a perspective view illustrating a variation of the stay and the reflector;
FIG. 23 is a perspective view illustrating another variation of the stay and the reflector;
FIG. 24 is a schematic diagram illustrating an example of a configuration of the image
forming apparatus including a fixing device which conveys a sheet in a vertical direction;
FIG. 25 is a perspective view of a stay and a reflector according to a comparative
example; and
FIG. 26 is a cross-sectional front view illustrating a main configuration in an end
portion of the fixing device according to the comparative example.
[0009] The accompanying drawings are intended to depict embodiments of the present disclosure
and should not be interpreted to limit the scope thereof. The accompanying drawings
are not to be considered as drawn to scale unless explicitly noted.
DETAILED DESCRIPTION OF EMBODIMENTS
[0010] In describing embodiments illustrated in the drawings, specific terminology is employed
for the sake of clarity. However, the disclosure of this specification is not intended
to be limited to the specific terminology so selected and it is to be understood that
each specific element includes all technical equivalents that have a similar function,
operate in a similar manner, and achieve a similar result.
[0011] Although the embodiments are described with technical limitations with reference
to the attached drawings, such description is not intended to limit the scope of the
disclosure and all of the components or elements described in the embodiments of this
disclosure are not necessarily indispensable.
[0012] With reference to drawings, a description is given below of the present disclosure.
In the drawings to describe following embodiments of the present disclosure, identical
reference numerals are assigned to elements such as members and parts that have an
identical function or an identical shape as long as differentiation is possible and
a description of those elements is omitted once the description is provided.
[0013] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus
according to an embodiment of the present disclosure. Referring to FIG. 1, a configuration
and operation of the image forming apparatus according to the present embodiment are
described below.
[0014] An image forming apparatus 1 illustrated in FIG. 1 is a monochrome electrophotographic
laser printer. The image forming apparatus 1 according to the embodiments of the present
disclosure may be a printer, a copier, a facsimile machine, a multifunction peripheral
(MFP) having at least two of copying, printing, scanning, facsimile, and plotter functions.
The image forming apparatus 1 is not limited to a monochrome image forming apparatus
and may be a color image forming apparatus.
[0015] As illustrated in FIG. 1, the image forming apparatus 1 includes an image forming
device 2 to form an image, a recording medium feeding device 3 to feed a sheet P as
a recording medium, a transfer device 4 to transfer the image onto the fed sheet P,
a fixing device 5 to fix the image transferred onto the sheet P, and a sheet ejection
device 6 to eject the sheet P with the fixed image to an outside of the image forming
apparatus 1.
[0016] The image forming device 2 includes a drum-shaped photoconductor 7, a charging roller
8 as a charging device to charge a surface of the photoconductor 7, an exposure device
9 as a latent image forming device that exposes the surface of the photoconductor
7 to form an electrostatic latent image on the photoconductor 7, a developing roller
10 as a developing device that supplies toner as a developer to the surface of the
photoconductor 7 to visualize the electrostatic latent image, and a cleaning blade
11 as a cleaner to clean the surface of the photoconductor 7.
[0017] As an image forming operation start is instructed, in the image forming device 2,
the photoconductor 7 starts to rotate, and the charging roller 8 uniformly charges
the surface of the photoconductor 7 to a high potential. Next, based on image data
of an original document read by a scanner or print data instructed by a terminal device,
the exposure device 9 exposes the surface of the photoconductor 7. Potential of an
exposed surface drops, and the electrostatic latent image is formed on the photoconductor
7. The developing roller 10 supplies toner to the electrostatic latent image, thereby
developing the latent image into the toner image on the photoconductor 7.
[0018] The toner image formed on the photoconductor 7 is transferred onto the sheet P in
a transfer nip between the photoconductor 7 and a transfer roller 15 disposed in the
transfer device 4. The sheet P is fed from the recording medium feeding device 3.
In the recording medium feeding device 3, a sheet feeding roller 13 feeds the sheet
P from a sheet tray 12 to a feeding path one by one. A timing roller pair 14 sends
out the sheet P fed from the sheet tray 12 to a transfer nip, timed to coincide with
the toner image on the photoconductor 7. The toner image on the photoconductor 7 is
transferred onto the sheet P at the transfer nip. After the toner image is transferred
from the photoconductors 7 onto the sheet P, the cleaning blade 11 removes residual
toner on the photoconductor 7.
[0019] The sheet P bearing the toner image is conveyed to the fixing device 5. In the fixing
device 5, heat and pressure when the sheet P passes through between a fixing belt
21 and a pressure roller 22 fixes the toner image onto the sheet P. Subsequently,
the sheet P is conveyed to the sheet ejection device 6, and an ejection roller pair
16 ejects the sheet P outside the image forming apparatus 1, and a series of print
operations are completed.
[0020] With reference to FIGS. 2 to 6, a detailed description is provided of a construction
of the fixing device 5 according to embodiments of the present disclosure.
[0021] FIG. 2 is a vertical cross-sectional view of the fixing device 5 viewed from a lateral
side of the fixing device 5, FIG. 3 is a perspective view of the fixing device 5 with
the vertical cross-sectional view of the fixing device 5, and FIG. 4 is a vertical
cross-sectional view of the fixing device 5 viewed from a front side of the fixing
device 5. In addition, FIG. 5 is a perspective view of a belt holder 30 to support
the fixing belt 21, and FIG. 6 is a perspective view of a variation of the belt holder
30.
[0022] As illustrated in FIG. 2, the fixing device 5 includes the fixing belt 21, the pressure
roller 22, a halogen heater 23, a nip formation member 24, a stay 25, a reflector
26, guides 27, and temperature sensors 28.
[0023] The fixing belt 21 is a cylindrical fixing member to fix an unfixed image T to the
sheet P and is disposed on the side of the sheet P on which the unfixed image is held.
The fixing belt 21 in the present embodiment is an endless belt or film, including
a base layer formed on an inner side of the fixing belt 21 and made of a metal such
as nickel and stainless steel (SUS) or a resin such as polyimide, and a release layer
formed on the outer side of the fixing belt 21 and made of tetrafluoroethylene-perfluoroalkylvinylether
copolymer (PFA), polytetrafluoroethylene (PTFE), or the like. Optionally, an elastic
layer made of rubber such as silicone rubber, silicone rubber foam, and fluoro rubber
may be interposed between the base layer and the release layer. While the fixing belt
21 and the pressure roller 22 press the unfixed toner image against the sheet P to
fix the toner image onto the sheet P, the elastic layer having a thickness of about
100 micrometers elastically deforms to absorb slight surface asperities of the fixing
belt 21, preventing variation in gloss of the toner image on the sheet P. Additionally,
in the present embodiment, the fixing belt 21 is thin and has a small loop diameter
to decrease the thermal capacity of the fixing belt 21. For example, the base layer
of the fixing belt 21 has a thickness of from 20 µm to 50 µm and the release layer
has a thickness of from 10 µm to 50 µm. Thus, the fixing belt 21 has a total thickness
not greater than 1 mm. In addition, when the fixing belt 21 includes the elastic layer,
the thickness of the elastic layer may be set to 100 to 300 µm. In order to further
decrease the thermal capacity of the fixing belt 21, the fixing belt 21 may have the
total thickness not greater than 0.20 mm and preferably not greater than 0.16 mm.
In the present embodiment, the fixing belt 21 may have a loop diameter from 20 to
40 mm. Preferably, the loop diameter of the fixing belt 21 may not be greater than
30 mm.
[0024] The pressure roller 22 is an opposite member disposed opposite an outer surface of
the fixing belt 21. The pressure roller 22 includes a cored bar; an elastic layer
coating the cored bar and being made of silicone rubber foam, fluoro rubber, or the
like; and a release layer coating the elastic layer and being made of PFA, PTFE, or
the like. According to the present embodiment, the pressure roller 22 is a solid roller.
Alternatively, the pressure roller 22 may be a hollow roller. When the pressure roller
22 is the hollow roller, a heater such as a halogen heater may be disposed inside
the pressure roller 22. The elastic layer of the pressure roller 22 may be made of
solid rubber. Alternatively, if no heater is disposed inside the pressure roller 22,
the elastic layer of the pressure roller 22 is preferably made of sponge rubber to
enhance thermal insulation of the pressure roller 22. Such a configuration reduces
heat conduction from the fixing belt 21 to the pressure roller 22 and improves heating
efficiency of the fixing belt 21.
[0025] A driver inside the image forming apparatus 1 drives and rotates the pressure roller
22 in a direction indicated by an arrow A in FIG. 2. The rotation of the pressure
roller 22 drives the fixing belt 21 to rotate in a direction B in FIG. 2 due to frictional
force therebetween. After the toner image is transferred onto the sheet P, the sheet
P bearing the unfixed toner image is conveyed to a nip N between the fixing belt 21
and the pressure roller 22. The rotating fixing belt 21 and the rotating pressure
roller 22 conveys the sheet P, and the sheet P passes through the nip N. When the
sheet P passes through the nip N, heat and pressure applied to the sheet P fixes the
unfixed image T to the sheet P.
[0026] The pressure roller 22 and the fixing belt 21 are able to contact and separate each
other. If the sheet is jammed in the nip N, separating the pressure roller 22 and
the fixing belt 21 from each other and opening the nip N enables the jammed sheet
to be removed. One of the pressure roller 22 and the fixing belt 21 may be fixed and
the other may be movable so that the pressure roller 22 and the fixing belt 21 contact
and separate each other. Alternatively, both the pressure roller 22 and the fixing
belt 21 may be moved so that the pressure roller 22 and the fixing belt 21 contact
and separate each other.
[0027] The halogen heater 23 is a heating member disposed inside a loop of the fixing belt
21 and emitting infrared light, and radiant heat from the halogen heater 23 heats
the fixing belt 21 via the nip formation member 24. Alternatively, instead of the
halogen heater 23, a carbon heater, a ceramic heater or the like may be employed as
the heater.
[0028] The nip formation member 24 and the pressure roller 22 sandwich the fixing belt 21
to form the nip N. Specifically, the nip formation member 24 extends inside the loop
of the fixing belt 21 in a longitudinal direction that is also a direction of a rotation
axis of the fixing belt 21 (hereinafter called a belt longitudinal direction) and
has a planar nip formation portion 24a that is in contact with an inner circumferential
surface of the fixing belt 21, and a pair of bent portions 24b that are bent from
both end portions of the nip formation portion 24a in a belt rotation direction B
to the opposite side to the pressure roller 22. A pressing member such as a spring
presses the pressure roller 22 against the nip formation member 24, which causes the
pressure roller 22 to contact the fixing belt 21 and forms the nip N therebetween.
[0029] A nip formation surface 24c of the nip formation portion 24a on the fixing belt 21
side may be coated with an alumite treatment or a fluororesin material in order to
improve abrasion resistance and slidability when the fixing belt 21 rotates. Furthermore,
a lubricant such as a fluorine-based grease may be applied to the nip formation surface
24c in order to ensure the slidability over time. In the present embodiment, the nip
formation member 24 has a planar surface. Alternatively, the nip formation member
24 may have another shape. For example, the nip formation member 24 having a concave
shape recessed to the side opposite to the pressure roller 22 leads the outlet of
the sheet in the fixing nip N to be closer to the pressure roller 22, which improves
separation of the sheet from the fixing belt 21.
[0030] The nip formation member 24 is made of a material having a thermal conductivity larger
than that of the stay 25. For example, the material of the nip formation member 24
is preferably copper (thermal conductivity: 398 W / mK) or aluminum (thermal conductivity:
236 W / mK). The nip formation member 24 made of the material having such a large
thermal conductivity absorbs the radiant heat from the halogen heater 23 and effectively
transmits heat to the fixing belt 21. For example, setting the thickness of the nip
formation member 24 to 1 mm or less can shorten a heat transfer time in which the
heat transfers from the nip formation member 24 to the fixing belt 21, which is advantageous
in shortening a warm-up time of the fixing device 5. In contrast, setting the thickness
of the nip formation member 24 to be larger than 1 mm and 5 mm or less can improve
a heat storage capacity of the nip formation member 24.
[0031] The stay 25 is a support member to support the nip formation member 24 against the
pressing force from the pressure roller 22. In the present embodiment, the stay 25
includes a pair of side wall portions 25a extending in a pressing direction of the
pressure roller 22 (the vertical direction in FIG. 2) and arranged in parallel with
each other and a bottom wall portion 25b intersecting the side wall portions 25a and
connecting ends of the side wall portions 25a on the opposite sides with respect to
the pressure roller 22. The side wall portions 25a of stay 25 are in contact with
both ends of the nip formation member 24 in the belt rotation direction B via the
reflector 26, and, as a result, the stay 25 supports the nip formation member 24.
The side wall portions 25a extending in the pressing direction of the pressure roller
22 strengthen the rigidity of the nip formation member 24 in the pressing direction
and reduces the bend of the nip formation member 24 caused by the pressing force of
the pressure roller 22. Such a configuration can form the nip N having a uniform width
in the longitudinal direction and applying a uniform pressure to the sheet P in the
longitudinal direction. The stay 25 is preferably made of an iron-based metal such
as stainless steel (SUS) or steel electrolytic cold commercial (SECC) that is electrogalvanized
sheet steel to ensure rigidity.
[0032] The reflector 26 are disposed opposite the halogen heater 23 inside the loop of the
fixing belt 21 to reflect radiant heat that is infrared light emitted from the halogen
heater 23 to the nip formation member 24. In the present embodiment, the reflector
26 includes a reflector portion 26a formed as an ellipse cross-section and a pair
of bent portions 26b bent from both ends of the reflector portion 26a in a direction
in which the bent portions separate from each other in the belt rotation direction
B. Each bent portion 26b is sandwiched between each side wall portion 25a of the stay
25 and the nip formation portion 24a of the nip formation member 24 to hold the reflector
26.
[0033] The infrared light reflected by the reflector 26 is emitted to the nip formation
member 24 and heats the nip formation member 24. As described above, the halogen heater
23 directly irradiates the nip formation member 24 with the infrared light, and, additionally,
the nip formation member 24 is also irradiated with the infrared light reflected by
the reflector 26. Therefore, the nip formation member 24 is effectively heated. Since
the reflector 26 is interposed between the halogen heater 23 and the stay 25, the
reflector 26 has a function of blocking the infrared light from the halogen heater
23 to the stay 25. This function reduces wasteful energy use to heat the stay 25.
Additionally, in the present embodiment, thermal insulation of the layer of air in
a gap between the stay 25 and the reflector 26 blocks heat transfer to the stay 25.
[0034] The surface of the reflector 26 facing the halogen heater 23 is treated with mirror
finish or the like to increase reflectance. In the present embodiment, reflectance
is measured using the spectrophotometer that is the ultraviolet visible infrared spectrophotometer
UH4150 manufactured by Hitachi High-Technologies Corporation in which the incident
angle is set 5°. In general, the color temperature of the halogen heater varies depending
on the application. The color temperature of the heater for the fixing device is about
2500 K. The reflectance of the reflector 26 is preferably 70% or more with wavelengths
of high emission intensity in the halogen heater 23, that is, specifically the wavelengths
of 900 to 1600 nm and more preferably 70% or more with the wavelengths of 1000 to
1300 nm.
[0035] Alternatively, the stay 25 may have the function of reflection and thermal insulation
of the reflector 26. For example, performing the thermal insulation treatment or the
mirror finishing on the inner surface of the stay 25 in the halogen heater 23 side
enables the stay 25 to function as the reflector 26. Such a configuration can obviate
the reflector 26 that is a separate component from the stay 25. The reflectance of
the stay 25 subjected to the mirror finishing is preferably similar to the reflectance
of the reflector 26.
[0036] The guides 27 contacts the inner peripheral surface of the fixing belt 21 to guide
the rotating fixing belt 21. In the present embodiment, the guides 27 are disposed
on both the upstream side and the downstream side of the nip N in the belt rotational
direction B. The guide 27 includes an attachment portion 27a fixed to the stay 25
and a curved guide portion 27b in contact with the inner peripheral surface of the
fixing belt 21. As illustrated in FIG. 3, the guide portion 27b includes a plurality
of ribs 27c that are projections provided at equal distances in the belt longitudinal
direction on a guide surface of the guide portion 27b that is the surface of the guide
portion 27b in the fixing belt 21 side. Guiding the fixing belt 21 along the guide
surface having the plurality of ribs 27c enables smooth rotation of the fixing belt
21 without large deformation of the fixing belt 21.
[0037] The temperature sensors 28 face the outer surface of the fixing belt 21 to detect
temperatures of the fixing belt 21. In the present embodiment, the temperature sensors
28 are disposed at two positions, the central position of the fixing belt 21 in the
belt longitudinal direction, and one end position of the fixing belt 21 in the belt
longitudinal direction. The temperature sensor 28 detects the temperature of the outer
circumferential surface of the fixing belt 21, and output of the halogen heater 23
is controlled based on the detected temperatures so that the temperature of the fixing
belt 21 becomes a desired temperature that is a fixing temperature. The temperature
sensor 28 may be either contact type or non-contact type. The temperature sensor 28
may be a known temperature sensor type such as a thermopile, a thermostat, a thermistor,
or a non-contact (NC) sensor.
[0038] As illustrated in FIG. 4, each cylindrical belt holder 30 as a fixing member support
to support a lateral end of the fixing belt 21 is inserted in each of both lateral
ends of the fixing belt 21. As described above, the belt holders 30 inserted into
the both lateral ends of the fixing belt 21 support the fixing belt 21 in a state
in which the fixing belt 21 is not basically applied with tension in a circumferential
direction thereof while the fixing belt 21 does not rotate, that is, by a free belt
system.
[0039] As illustrated in FIGS. 3 to 5, the belt holder 30 includes a C-shaped supporter
30a inserted into the inner periphery of the fixing belt 21 to support the fixing
belt 21 and a flange 30b that contacts an end surface of the fixing belt 21 to stop
a movement of the fixing belt 21 in the longitudinal direction of the fixing belt
21, that is, walking of the fixing belt 21 in the longitudinal direction. As illustrated
in FIG. 6, the supporter 30a may have a cylindrical shape which is continuous over
its entire circumference. As illustrated in FIG. 4, the belt holders 30 are fixed
on a pair of side plates 31 that are frames of the fixing device 5. The belt holder
30 has an opening 30c as illustrated in FIG. 5, and both ends of the halogen heater
23 and the stays 25 are supported by the side plates 31 through the openings 30c.
The halogen heater 23 and the stays 25 may be supported by the belt holders 30.
[0040] Subsequently, with reference to FIG. 7, a description is provided of a configuration
of the halogen heater according to the embodiment of the present disclosure.
[0041] As illustrated in FIG. 7, the halogen heater 23 includes a bulb 40 which is a cylindrical
tube made of quartz glass or the like, a filament 41 as a heating generator accommodated
in the bulb 40, a thin metal foils 42 made of molybdenum or the like, inner leads
43 and outer leads 44.
[0042] The filament 41 includes coils made of a metal wire such as a tungsten wire and is
accommodated in the bulb 40 along the longitudinal direction of the bulb 40. The bulb
40 is filled with an inert gas such as a halogen gas. At both ends in the longitudinal
direction of the bulb 40, sealing portions 40a are formed that are flattened to prevent
the internal gas from leaking out. Each sealing portion 40a accommodates the metal
foil 42. The metal foils 42 are connected to both ends of the filament 41 via the
inner leads 43. Additionally, the outer lead 44 is connected to the metal foil 42
at the side opposite to the side where the inner lead 43 is connected. A part of the
outer lead 44 is out of the sealing portion 40a, and an end of the part is connected
to a power supply via a terminal such as a metal cap or a harness. Since the filament
41 is connected to the power supply via the outer lead 44, the metal foil 42, and
the inner lead 43, power supplied from the power supply causes the filament 41 to
emit infrared light and generate heat. The metal foils 42, the inner leads 43, and
the outer leads 44 hardly generate heat when the power is supplied from the power
supply.
[0043] The bulb 40 used for the halogen heater 23 is generally made of a heat-resistant
material, but high temperature may cause a crack such as a micro crack in the sealing
portion 40a because of its structure. That is, the filament 41 generates heat, and
the sealing portion 40a becomes high temperature. The high temperature oxidizes the
metal foil 42 and causes a volumetric expansion of the metal foil 42. The volumetric
expansion of the metal foil 42 generates a force to expand the sealing portion 40a
from the inside. When the sealing portion 40a cannot withstand the force, the force
causes the crack in the sealing portion 40a. For example, when the temperature of
the sealing portion 40a exceeds 350°C, the crack may occur in the sealing portion
40a. The temperature when the crack occurs is different depending on the configuration
and specifications of the halogen heater 23.
[0044] When members such as the stay 25 and the reflector 26 are arranged around the sealing
portion 40a, the members prevent heat radiation from the sealing portion 40a and change
the space around the sealing portion 40a to a high-temperature environment. In particular,
for example, as illustrated in FIG. 26, when the halogen heater 23 is arranged inside
the stay 25 and the reflector 26 that are continuously formed in a substantially U-shaped
cross section in the longitudinal direction as illustrated in FIG. 25, the sealing
portion 40a is surrounded by the stay 25 and the reflector 26 on three sides, the
upper side in FIG. 26 and two sides in a direction perpendicular to the paper surface
of FIG. 26. Since the stay 25 and the reflector 26 block the hot air around the sealing
portion 40a and prevent the hot air from flowing outside, the space around the sealing
portion 40a becomes the high-temperature environment.
[0045] To prevent the end of the halogen heater 23 in the longitudinal direction, especially
the sealing portion 40a, from overheating, the embodiments of the present disclosure
employ the following configurations.
[0046] FIG. 8 is a perspective view illustrating the stay 25 and the reflector 26 according
to a first embodiment of the present disclosure.
[0047] As illustrated in FIG. 8, in the embodiment of the present disclosure, the stay 25
has openings 25e that open upward in FIG. 8 and are provided at both end regions of
the stay 25 in the longitudinal direction that is the belt longitudinal direction
E. Like the stay 25, the reflector 26 also has openings 26e that open upward in FIG.
8 at both end regions in the longitudinal direction that is the belt longitudinal
direction E.
[0048] As illustrated in FIG. 9, when the stay 25 and the reflector 26 according to the
present embodiment are arranged inside the loop of the fixing belt 21, the opening
25e of the stay 25 and the opening 26e of the reflector 26 are disposed at an end
region in a belt width direction and are open on the side opposite to the nip formation
member 24 with respect to the halogen heater 23. The above-described arrangement of
the openings 25e and 26e opens the region above the sealing portion 40a and the vicinity
of the sealing portions 40a, which are opposite to the nip formation member 24. Although
FIG. 9 illustrates the configuration of one end of the fixing device, the other end
of the fixing device has the same configuration.
[0049] As described above, in the embodiment of the present disclosure, the openings 25e
and 26e provided at both end regions of the stay 25 and the reflector 26 in the longitudinal
direction open one side of the space around the sealing portions 40a, that is, the
side opposite to the nip formation member 24 with respect to the halogen heater 23.
Specifically, at least a part of the sealing portion 40a (a part at an outer edge
401 side in the belt longitudinal direction) is disposed outside an edge 250 of the
bottom wall portion 25b, which is one of edges of the bottom wall portion 25b and
a pair of side wall portions 25a that constitute the stay 25 in the longitudinal direction
of each of the bottom wall portion 25b and the side wall portions 25a, in the belt
longitudinal direction E (that is, left side in FIG. 9). In the above-described configuration,
a portion of the bottom wall portion 25b of the stay 25 facing at least the part of
the sealing portion 40a is removed to open a portion of the space around the sealing
portion 40a. In the reflector 26, a part of end portion in the longitudinal direction
is cut and removed from the reflector portion 26a having the U-shaped cross section
to form an edge 260 in the longitudinal direction of the reflector 26. In the belt
longitudinal direction E, at least a part of the sealing portion 40a is disposed outside
the edge 260 of the reflector 26. The above-described configuration easily releases
the air around the sealing portion 40a to the outside through the openings 25e and
26e. That is, since at least a part of the sealing portion 40a is exposed out of the
stay 25 and the reflector 26, the stay 25 and the reflector 26 are unlikely to block
heat from the space around the sealing portion 40a of the halogen heater 23. That
is, compared with the comparative example illustrated in FIGS. 25 and 26, the heat
in the space around the sealing portion 40a is easily released, which can prevent
the overheating of the sealing portion 40a.
[0050] Specifically, when the fixing device in the comparative example illustrated in FIGS.
25 and 26 performed the fixing process and continuously passed 500 sheets, the temperature
at the sealing portion 40a exceeded 350°C, a temperature that may cause the crack
in the sealing portion 40a. When the fixing device in the comparative example performed
the fixing process and continuously passed 1000 sheets, the temperature at the sealing
portion 40a reached 380°C. On the other hand, when the fixing device according to
the embodiment of the present disclosure similarly performed the fixing process and
continuously passed 500 sheets or 1000 sheets, the temperature at the sealing portion
40a was maintained at about 320°C and did not reach 350°C as the temperature that
may cause the crack in the sealing portion 40a.
[0051] As described above, since the configuration according to the embodiment of the present
disclosure can prevent the sealing portion 40a from overheating, the configuration
can prevent the occurrence of cracks and disconnections due to an excessive temperature
rise at the sealing portion 40a and improve the reliability of the halogen heater
23. In particular, the configuration according to the embodiment of the present disclosure
is suitable for the fixing device mounted on a small image forming apparatus used
in an office or the like. Generally, since most of the small image forming apparatuses
used in the office or the like are designed on the assumption that the number of output
sheets per one print job is small, the most of the small image forming apparatuses
do not include a blower fan or the like to avoid the temperature rise when the small
image forming apparatuses print a large number of sheets. Therefore, applying the
configuration according to the embodiment of the present disclosure to such a fixing
device can prevent the halogen heater 23 from overheating without providing a blower
fan or the like and provide a small and highly reliable fixing device.
[0052] In the comparative example not having the openings 25e and 26e, to prevent the sealing
portion 40a from overheating, the sealing portion 40a should be arranged at a position
at which the heat is easily released, that is, the position outside an outer edge
301 (see FIG. 26) of the belt holder 30 in the belt longitudinal direction E. Without
such countermeasure, the embodiment of the present disclosure can prevent the sealing
portion 40a from overheating. That is, according to the embodiment of the present
disclosure, without arranging the sealing portion 40a outside the outer edge 301 (see
FIG. 9) of the belt holder 30 in the belt longitudinal direction E, the heat around
the sealing portion 40a can be easily dissipated through the openings 25e and 26e.
Therefore, in the embodiment of the present disclosure, as illustrated in FIG. 9,
the sealing portion 40a can be arranged inside the outer edge 301 of the belt holder
30 in the belt longitudinal direction E, which can reduce the size of the fixing device.
To reduce the size of the fixing device as described above, at least the outer edge
401 of the sealing portion 40a in the belt longitudinal direction E is disposed on
the inner side of the outer edge 301 of the belt holder 30 in the belt longitudinal
direction E. In FIG. 9, a part of the sealing portion 40a is disposed on the inner
side of the inner edge 302 of the belt holder 30 in the belt longitudinal direction
E. However, depending on the configuration and specifications of the fixing device,
the entire sealing portion 40a may be disposed on the inner side of the inner edge
302 of the belt holder 30 to further reduce the size of the fixing device.
[0053] As illustrated in FIG. 9, the openings 25e and 26e are preferably arranged inside
the belt holder 30 in the belt longitudinal direction E so that at least a part of
the openings 25e and 26e do not overlap the belt holder 30 in the belt longitudinal
direction E. That is, the inner edge 250 of the opening 25e and the inner edge 260
of the opening 26e in the belt longitudinal direction E are preferably arranged inside
the inner edge 302 of the belt holder 30 in the belt longitudinal direction E. The
above arrangement in which at least a part of the openings 25e and 26e do not overlap
the belt holder 30 in the belt longitudinal direction E can prevent the belt holder
30 from blocking heat dissipation through the openings 25e and 26e, and the heat is
easily dissipated through the openings 25e and 26e.
[0054] In short, in order to facilitate the heat dissipation from the openings 25e and 26e
and effectively prevent the sealing portion 40a from overheating, the openings 25e
and 26e preferably have a region that corresponds to the sealing portion 40a and does
not overlap the belt holder 30, that is, the region indicated by a reference sign
C in FIG. 9. Additionally, the reflector 26 preferably has an opening 26e at a position
corresponding to the opening 25e of the stay 25 so as not to hinder heat dissipation
from the opening 25e of the stay 25. In the embodiment illustrated in FIGS. 8 and
9, since the opening 26e of the reflector 26 is formed so as not to overlap with the
entire opening 25e of the stay 25, the configuration in the embodiment can effectively
prevent the sealing portion 40a from overheating.
[0055] From the viewpoint of thermal efficiency, the heat dissipated through the openings
25e and 26e is preferably transferred to the fixing belt 21 as much as possible. Therefore,
as illustrated in FIG. 9, the inner edge 250 of the opening 25e and the inner edge
260 of the opening 26e in the belt longitudinal direction E are preferably arranged
within the range of the fixing belt 21 in the belt longitudinal direction E. Arranging
the openings 25e and 26e as described above causes the heat dissipated through the
openings 25e and 26e to easily transfer to the fixing belt 21 and can reduce wasteful
energy consumption caused by heat transfer to members other than the fixing belt 21.
[0056] FIG. 10 is a cross-sectional front view illustrating an end portion of the fixing
device according to a second embodiment in which the openings 25e and 26e are expanded
inward (the right side in FIGS. 9 and 10) in the belt longitudinal direction E as
compared with the first embodiment illustrated in FIG. 9.
[0057] In the second embodiment illustrated in FIG. 10, the inner edge 250 of the opening
25e and the inner edge 260 of the opening 26e in the belt longitudinal direction E
are arranged corresponding to the inner edge 402 of the sealing portion 40a in the
belt longitudinal direction E. The above-described arrangement in which the openings
25e and 26e are arranged corresponding to the entire sealing portion 40a more easily
releases hot air around the sealing portion 40a through the openings 25e and 26e and
can more effectively prevent the sealing portion 40a from overheating.
[0058] FIG. 11 is a cross-sectional front view illustrating the end portion of the fixing
device according to a third embodiment in which the openings 25e and 26e are expanded
inward in the belt longitudinal direction E as compared with the second embodiment
illustrated in FIG. 10.
[0059] In the third embodiment illustrated in FIG. 11, the inner edge 250 of the opening
25e and the inner edge 260 of the opening 26e in the belt longitudinal direction E
are arranged corresponding to an edge 410, which is an outer edge if the filament
41 has the outer edge and an inner edge, of the filament 41 in the belt longitudinal
direction E. Since the infrared light radiated from the filament 41 also spreads outward
in the belt longitudinal direction E, the infrared light radiated from the edge 410
of the filament 41 passes through the openings 25e and 26e and is directly emitted
to the inner peripheral surface of the fixing belt 21. Directly irradiating the inner
peripheral surface of the fixing belt 21 with the infrared light through the openings
25e and 26e as described above can increase a temperature rising speed on an end portion
of the fixing belt 21 in the longitudinal direction E. The above-described configuration
can reduce the heating time (first print time) from a heating standby state to a state
where fixing operation is executable and solve the shortage of heat during high-speed
rotation.
[0060] By the way, there is the halogen heater including a filament that ununiformly generates
heat in the longitudinal direction. For example, such a halogen heater generates heat
set to be different between a center portion and end portions in the longitudinal
direction. FIG. 12 is a graph illustrating an example of a heat generation distribution
in a type of the filament that generates heat larger in the end portions than in the
center portion in the longitudinal direction. FIG. 13 is a graph illustrating an example
of a heat generation distribution in a type of the filament that generates heat larger
in the center portion than in the end portions in the longitudinal direction. In FIGS.
12 and 13, a range indicated by a reference sign D means a large heat generation region
in which the filament generates larger heat than another region in the filament, and
a range indicated by a reference sign W means a maximum sheet conveyance span when
a sheet having a maximum width among sheets used in the image forming apparatus passes
through the fixing nip.
[0061] A continuous fixing process when the image forming apparatus 1 continuously prints
many images may accumulate heat in a region of the fixing belt 21 outside a sheet
conveyance span in which heat is not easily taken away by the sheet, which may excessively
raise the temperature in the region of the fixing belt 21 outside the sheet conveyance
span. In such a case, using the halogen heater including the filament that generates
a small amount of heat in the end portions as illustrated in FIG. 12 can reduce heat
accumulation in the region of the fixing belt 21 outside the sheet conveyance span
and prevent the temperature at the region from excessively rising. On the other hand,
using the halogen heater including the filament having the hat generation distribution
as illustrated in FIG. 13 can prevent a temperature drop in the region of the fixing
belt 21 outside the sheet conveyance span when an amount of heat in the region of
the fixing belt 21 outside the sheet conveyance span tends to be insufficient.
[0062] When the fixing device uses the halogen heater having the ununiform heat generation
distribution in the longitudinal direction as described above, ranges of the openings
25e and 26e may be determined based on the heat generation distribution. For example,
in a fourth embodiment in which the fixing device uses the halogen heater including
the filament that generates larger heat in the end portions than in the center portion
as illustrated in FIG. 13, the ranges of the openings 25e and 26e may be expanded
as illustrated in FIG. 14 to a position corresponding to the large heat generation
region D in the end portions of the filament 41. That is, the inner edge 250 of the
opening 25e and the inner edge 260 of the openings 26e in the belt longitudinal direction
E are arranged inside the outer edge d1 of the large heat generation region D in the
belt longitudinal direction E. The above-described arrangement can broaden a range
on the fixing belt 21 which is directly irradiated with the infrared light in the
end portions of the fixing belt 21 in the belt longitudinal direction E and effectively
prevent the temperature drop at the end portion of the fixing belt 21 in the belt
longitudinal direction E. The openings 25e and 26e expanded to the position corresponding
to the large heat generation region D of the filament 41 can reduce the influence
of heat on the sealing portion 40a because the hot air around the sealing portion
40a is easily released through the openings 25e and 26e even when the amount of heat
generated on the end portion of the filament 41 is large. In FIG. 14, the openings
25e and 26e are arranged in the belt longitudinal direction corresponding to the entire
large heat generation region D of the filament 41, that is, the inner edge 250 of
the opening 25e and the inner edge 260 of the opening 26e in the belt longitudinal
direction E are arranged at the same position of the inner edge d2 of the large heat
generation region D or inside the inner edge d2 in the belt longitudinal direction
E. However, the openings 25e and 26e may be arranged corresponding to a part of the
large heat generation region D of the filament 41.
[0063] As in a fifth embodiment illustrated in FIG. 15, the ranges of the openings 25e and
26e may be determined based on the maximum sheet conveyance span W. In the fifth embodiment
illustrated in FIG. 15, the inner edge 250 of the opening 25e and the inner edge 260
of the opening 26e in the belt longitudinal direction E correspond to the edge of
the maximum sheet conveyance span W through which the maximum sheet passes in the
nip N. The openings 25e and 26e expanded to the edge of the maximum sheet conveyance
span W as described above efficiently dissipate heat outside the sheet conveyance
span and can effectively prevent a part of the halogen heater 23 and a part of the
fixing belt 21 which are outside the sheet conveyance span from excessively rising
temperature.
[0064] FIG. 16 is a graph illustrating a comparison between the fifth embodiment of the
present disclosure and the comparative example about the temperature rise of the fixing
belt outside the sheet conveyance span. The temperature of the fixing belt outside
the sheet conveyance span in the fifth embodiment of the present disclosure illustrated
in FIG. 15 is indicated by a reference sign H in FIG. 16. As illustrated in FIG. 16,
the configuration according to the fifth embodiment of the present disclosure can
prevent the temperature of the fixing belt outside the sheet conveyance span from
excessively rising and maintain the temperature of the fixing belt outside the sheet
conveyance span near the target temperature. The temperature of the fixing belt outside
the sheet conveyance span in the comparative example not having the openings 25e and
26e is indicated by a reference sign G in FIG. 16. As illustrated in FIG. 16, the
temperature of the fixing belt outside the sheet conveyance span exceeds the target
temperature after the start of continuous printing and tends to gradually rise. The
ranges of the openings 25e and 26e determined based on the maximum sheet conveyance
span W as described above can prevent the temperature of the fixing belt outside the
sheet conveyance span from excessively rising, similarly prevent the temperature of
the halogen heater outside the sheet conveyance span from excessively rising, therefore,
prevent the temperature of the sealing portion 40a from excessively rising, and prevent
the sealing portion 40a from occurring cracks and breaks.
[0065] Preferably, the position of the temperature sensor 28 is determined based on positions
of the openings 25e and 26e. In FIG. 17, curves indicated by reference signs Tx and
Ty illustrate temperatures of the fixing belt 21 detected by the temperature sensor
28 at different positions. Specifically, the temperature Tx was detected at a position
X in an end portion not corresponding to the openings 25e and 26e illustrated in FIG.
18, and the temperature Ty was detected at a position Y corresponding to the openings
25e and 26e. As illustrated in FIG. 17, the temperature Tx detected at the position
X not corresponding to the openings 25e and 26e stably remained near the target control
temperature. In contrast, the temperature Ty detected at the position Y corresponding
to the openings 25e and 26e fluctuated greatly from the target control temperature.
The reason is considered as follows. Originally, the thin fixing belt 21 having a
small thermal capacity easily changes its temperature. In addition, a portion of the
fixing belt 21 corresponding to the openings 25e and 26e is directly irradiated with
infrared light through the openings 25e and 26e. Therefore, it is considered that
the temperature change increased with the ON / OFF timing of the halogen heater 23.
According to this result, to avoid misdetection, the temperature sensor 28 used for
controlling the temperature of the fixing belt 21 is preferably arranged to detect
the temperature at the position that gives a relatively stable temperature and does
not correspond to the openings 25e and 26e rather than the position corresponding
to the openings 25e and 26e at which the temperature greatly fluctuates. Furthermore,
it is preferable that the temperature sensor 28 detects the temperature at a portion
of the fixing belt 21 which is not directly irradiated with infrared light. Therefore,
preferably, the temperature sensor 28 detects the temperature at the portion of the
fixing belt 21 inside the inner edges 250 of the openings 25e and the inner edges
260 of the openings 26e in the belt longitudinal direction E. The temperature sensor
28 may be disposed on the nip entrance side or the nip exit side. However, at the
nip exit side, the temperature sensor 28 detects the temperature after the sheet absorbs
the heat of the fixing belt 21. Therefore, preferably, the temperature sensor 28 is
disposed at the nip entrance side in which the temperature sensor 28 can detect the
temperature before the sheet absorbs the heat.
[0066] When the halogen heater 23 directly irradiates the fixing belt 21 with the infrared
light through the openings 25e and 26e, preferably, the halogen heater 23 generates
the heat while the fixing belt 21 rotates. Heat generation of the halogen heater 23
while the fixing belt 21 stops its rotation may cause a large temperature difference
between a portion which is directly irradiated with the infrared light and a portion
other than the portion and distortion in the fixing belt 21 due to thermal expansion.
Therefore, the halogen heater 23 generates the heat during the rotation of the fixing
belt 21, which can disperse areas heated by the direct irradiation of the infrared
light in the belt rotation direction. As a result, the distortion due to the thermal
expansion of the fixing belt 21 is reduced, and deformation and buckling breakage
(kinking) of the fixing belt 21 are less likely to occur.
[0067] Further, as in an example illustrated in FIG. 19, wires 45 such as wire harnesses
connected to both ends of the halogen heater 23 is preferably arranged so that the
wires 45 pass through the openings 25f and 26f that open toward the belt longitudinal
direction E and do not pass through the openings 25e and 26e that open upward in the
stay 25 and the reflector 26 as illustrated in FIG. 19 in order to avoid deterioration
and damage due to heat of the halogen heater 23. One end of each wire 45 is coupled
to the halogen heater 23, and the other end of each wire 45 is coupled to an AC power
supply. To reduce the influence of the heat of the stay 25 which becomes high in temperature,
preferably, the wire 45 passing outside the side wall portion 25a of the stay 25 is
disposed away from the stay 25, that is, at a non-contact position, specifically,
for example, at a position indicated by reference sign 45A or 45B in FIG. 20. Since
the position inside the reflector 26 is affected by the heat from the halogen heater
23 and the reflector 26, preferably, the wire 45 is not arranged in such a position,
that is, the position indicated by the reference sign 45C in FIG. 20. When a resin
cover 50 (or a guide) is disposed outside the stay 25 as in the example illustrated
in FIG. 21, arranging the wire 45 outside the cover 50 can reduce the influence of
heat from the stay 25 to the wire 45. When the cover 50 has a step 50a like this example,
the wire 45 may be arranged on the step 50a. More preferably, to reduce the influence
of the heat of the cover 50, the wire 45 may contact a plurality of ribs 50c disposed
on the cover 50 to decrease a contact area between the wire 45 and the cover 50 rather
than arranging the wire 45 in contact with the flat portion 50b near the step 50a.
[0068] The present disclosure is not limited to the details of the embodiments described
above and various modifications and improvements are possible.
[0069] In the above-described embodiment, to dissipate the heat around the sealing portion
40a, the bottom wall portion 25b of the stay 25 and a part of the reflector 26 corresponding
to the bottom wall portion 25b have the openings 25e and 26e (see FIG. 8), but as
illustrated in FIG. 22, the side wall portion 25a of the stay 25 and a part of the
reflector 26 corresponding to the side wall portion 25a may have the openings 25e
and 26e having the same effect as described above.
[0070] As in the example illustrated in FIG. 23, the side wall portion 25a and the bottom
wall portion 25b of the stay 25 may be shortened in the belt longitudinal direction
to expose at least a part of the sealing portion 40a outside the entire edge 251 of
the stay 25 and the entire edge 261 of the reflector 26 in the belt longitudinal direction
E. The above-described configuration further facilitates the heat dissipation from
the sealing portion 40a and can effectively prevent the sealing portion 40a from overheating.
[0071] In the above-described embodiment, one halogen heater 23 is disposed inside the loop
of the fixing belt 21, but a plurality of heaters may be used. In a configuration
using a plurality of heaters, it is preferable to arrange the openings 25e and 26e
as described above, particularly for a heater having the innermost sealing portion
40a in the belt longitudinal direction E. The shapes of the stay 25 and the reflector
26 are not limited to the above-described embodiment and may be appropriately changed.
[0072] The present disclosure may be applied to a fixing device not including the reflector
26. The fixing device according to the present disclosure is not limited to the fixing
device 5 that conveys the sheet in the horizontal direction as illustrated in FIG.
1. An installation direction of the fixing device 5 may be changed as appropriate,
and the present disclosure is also applicable to the fixing device 5 that conveys
the sheet in the vertical direction as illustrated in FIG. 24.
[0073] The present disclosure is not limited to the application of the fixing device including
the halogen heater having the sealing portion. For example, the present disclosure
may be applied to a carbon heater having a sealing portion.
[0074] Numerous additional modifications and variations are possible in light of the above
teachings. It is therefore to be understood that, within the scope of the above teachings,
the present disclosure may be practiced otherwise than as specifically described herein.
With some embodiments having thus been described, it will be obvious that the same
may be varied in many ways. Such variations are not to be regarded as a departure
from the scope of the present disclosure and appended claims, and all such modifications
are intended to be included within the scope of the present disclosure and appended
claims.