EP3690550A1 - Fixing device and image forming apparatus incorporating same - Google Patents
Fixing device and image forming apparatus incorporating same Download PDFInfo
- Publication number
- EP3690550A1 EP3690550A1 EP20150101.2A EP20150101A EP3690550A1 EP 3690550 A1 EP3690550 A1 EP 3690550A1 EP 20150101 A EP20150101 A EP 20150101A EP 3690550 A1 EP3690550 A1 EP 3690550A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- fixing belt
- fixing
- heater
- nip
- fixing device
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Images
Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/20—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat
- G03G15/2003—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat
- G03G15/2014—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat using contact heat
- G03G15/2039—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat using contact heat with means for controlling the fixing temperature
- G03G15/2042—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat using contact heat with means for controlling the fixing temperature specially for the axial heat partition
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/20—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat
- G03G15/2003—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat
- G03G15/2014—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat using contact heat
- G03G15/2053—Structural details of heat elements, e.g. structure of roller or belt, eddy current, induction heating
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G2215/00—Apparatus for electrophotographic processes
- G03G2215/20—Details of the fixing device or porcess
- G03G2215/2003—Structural features of the fixing device
- G03G2215/2016—Heating belt
- G03G2215/2035—Heating belt the fixing nip having a stationary belt support member opposing a pressure member
Definitions
- Embodiments of the present disclosure generally relate to a fixing device and an image forming apparatus incorporating the fixing device.
- An image forming apparatus such as a copier, a printer, a facsimile machine, and a multi-functional apparatus including at least two functions of the copier, printer, facsimile machine includes a fixing device to convey a recording medium such as a sheet on which an unfixed image is formed to a fixing nip formed between a fixing belt and a pressing member in the fixing device, heat the recording medium, and fix the unfixed image onto the recording medium.
- a fixing device to convey a recording medium such as a sheet on which an unfixed image is formed to a fixing nip formed between a fixing belt and a pressing member in the fixing device, heat the recording medium, and fix the unfixed image onto the recording medium.
- the fixing device includes a heater disposed inside a loop of the fixing belt to heat the fixing belt and a nip formation member that contacts the pressing member via the fixing belt to form the fixing nip.
- the nip formation member supports an inner circumferential surface of the fixing belt to form the fixing nip between the pressing member and the fixing belt, and, in addition, the heater heats the fixing belt via the nip formation member to suitably heat and press a surface of a recording medium conveyed to the fixing nip.
- the heating distribution of the heater may be ununiform in a width direction of the fixing belt that is a longitudinal direction of the heater.
- the heater exists that generates less heat at end portions than the heat generated at a central portion of the heater.
- Such a heater causes problems such as an extra time for a part of the fixing belt corresponding to a low heat generation area in which the heater generates less heat to reach a temperature for fixing or a fixing failure caused by the part of the fixing belt corresponding to the low heat generation area that does not reach the temperature for fixing.
- the above-described problem is remarkable because the entire image forming apparatus is cooled.
- JP-2017-32633-A discloses the fixing device with a measure to increase the temperature at the end portion of the fixing belt.
- the fixing device includes a first heater 202, second heaters 203, a nip member 204, or the like inside a loop of the film 201.
- the second heaters 203 are disposed upstream from the fixing nip N in a rotation direction of the film 201 and face both end portions of the film 201 in the width direction of the film 201, respectively.
- the nip member 204 has an extended portion 204a extended upstream from the fixing nip N in the rotation direction of the film 201 and protruding portions 204b disposed on both end portions of the extended portion 204a.
- the protruding portions 204b are further extended upstream from a center portion of the extended portion 204a.
- the second heater 203 increases a heat amount to heat the end portion of the film 201 in the width direction, and the film 201 heated by the second heater 203 can enter the nip between the film 201 and the nip member 204 immediately after the second heater 203 heats the film 201. Therefore, the second heater 203 can raise the temperature at the end portion of the film 201 in the width direction in the fixing nip N to a high temperature.
- adding another heater in addition to a main heater and extending the nip formation member to a portion corresponding to the another heater can compensate for the lack of heat amount to heat a portion that the main heater heats with a relatively small heat amount, that is, in the above-described example, the end portion of the fixing belt in the width direction, to sufficiently heat the fixing belt but causes problems such as increase of manufacturing cost of the fixing device due to adding another part and increase of energy consumption of the fixing device.
- an object of the present disclosure is to sufficiently heat a fixing belt facing a low heat generation area of a heater, using a simple structure.
- a fixing device according to claim 1.
- the fixing device includes a rotatable endless fixing belt, a pressing member configured to press the fixing belt, the heater disposed inside a loop of the fixing belt and configured to heat the fixing belt, and a nip formation member disposed inside the loop of the fixing belt and configured to come into contact with the pressing member via the fixing belt to form a fixing nip.
- the heater In a longitudinal direction of the heater, the heater has a low heat generation area that generates a smaller amount of heat than another area of the heater.
- the nip formation member has an elongated portion that extends upstream from the fixing nip in a rotation direction of the fixing belt. The elongated portion has a longest part positioned corresponding to the low heat generation area in the longitudinal direction.
- the length of the elongated portion of the nip formation member is set longest at a position corresponding to the low heat generation area of the heater. That is, a simple structure in which the elongated portion of the nip formation member has a shape corresponding to the heating distribution of the heater enables the fixing belt to be sufficiently heated at the position corresponding to the low heat generation area, which avoids the occurrence of the fixing failure.
- 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.
- the image forming apparatus 1 illustrated in FIG. 1 is a monochrome electrophotographic laser printer.
- the image forming apparatus 1 may be a copier, a facsimile machine, a multifunction peripheral (MFP) having at least two of copying, printing, scanning, facsimile, and plotter functions in addition to the printer.
- the image forming apparatus 1 is not limited to a monochrome image forming apparatus and may be a color image forming apparatus.
- 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 to the image forming device 2, 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.
- 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.
- the photoconductor 7 starts to rotate, and the charging roller 8 uniformly charges the surface of the photoconductor 7 to a high potential.
- 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.
- 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.
- 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.
- the cleaning blade 11 removes residual toner on the photoconductor 7.
- the sheet P bearing the toner image is conveyed to the fixing device 5.
- the fixing device 5 heat and pressure when the sheet P passes through between the fixing belt 21 and the pressure roller 22 fixes the toner image onto the sheet P.
- 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.
- 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
- FIG. 4 is a vertical cross-sectional view of the fixing device 5 viewed from a front side of the fixing device 5.
- the fixing device 5 includes the fixing belt 21, the pressure roller 22, a halogen heater 23 as a heater, a nip formation member 24, a stay 25 as a contact part, a reflector 26, and temperature sensors 28.
- 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.
- SUS nickel and stainless steel
- PFA tetrafluoroethylene-perfluoroalkylvinylether copolymer
- PTFE polytetrafluoroethylene
- 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.
- 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.
- the fixing belt 21 is thin and has a small loop diameter to decrease the thermal capacity of the fixing belt 21.
- the base layer of the fixing belt 21 has a thickness of from 20 ⁇ m to 50 ⁇ m and the release layer has a thickness of from 10 ⁇ m to 50 ⁇ m.
- the fixing belt 21 has a total thickness not greater than 1 mm.
- the thickness of the elastic layer may be set to 100 to 300 ⁇ m.
- the fixing belt 21 may have the total thickness not greater than 0.20 mm and preferably not greater than 0.16 mm.
- the fixing belt 21 may have a loop diameter from 20 to 40 mm and preferably 30 mm or less.
- the pressure roller 22 is a pressing member disposed opposite an outer circumferential 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.
- the pressure roller 22 is a solid roller.
- the pressure roller 22 may be a 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.
- 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.
- a driver disposed inside the image forming apparatus 1 drives and rotates the pressure roller 22 in a direction indicated by 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.
- the sheet P bearing the unfixed toner image T is conveyed to a fixing 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 fixing nip N.
- heat and pressure applied to the sheet P fix the unfixed toner image T onto the sheet P.
- the pressure roller 22 and the fixing belt 21 are configured to be 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 configured to be fixed and the other may be configured to be movable so that the pressure roller 22 and the fixing belt 21 contact and separate each other.
- both the pressure roller 22 and the fixing belt 21 may be configured to move so that the pressure roller 22 and the fixing belt 21 contact and separate each other.
- the halogen heater 23 is a heater disposed inside a loop of the fixing belt 21 and emitting infrared light including far infrared light or near infrared light, and radiant heat from the halogen heater 23 heats the fixing belt 21 from the inside.
- a carbon heater, a ceramic heater or the like may be employed as the heater.
- only one halogen heater 23 is disposed in the loop of the fixing belt 21, but a plurality of halogen heaters 23 having different heat-generating areas may be used according to the width of the sheet.
- the nip formation member 24 sandwiches the fixing belt 21 together with the pressure roller 22, to form the fixing nip N.
- the nip formation member 24 is disposed inside the loop of the fixing belt 21 and has a planar nip formation portion 241 that is in contact with an inner circumferential surface of the fixing belt 21 and an elongated portion 242, which is described in detail below, extending upstream from the nip formation portion 241 (the fixing nip) in the direction B of rotation of the fixing belt 21.
- 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 form the fixing nip N between the pressure roller 22 and the fixing belt 21.
- the nip formation member 24 has a bent portion 243 bent from a downstream end of the nip formation portion 241 in the direction B of rotation of the fixing belt 21 to the side opposite to the pressure roller 22.
- the upstream side of the elongated portion 242 in the direction B of rotation of the fixing belt 21 is configured to have a rounded surface.
- the rounded upstream portion of the elongated portion 242 prevents damage to the inner circumferential surface of the fixing belt 21 caused by sliding between the upstream portion of the elongated portion 242 and the inner circumferential surface of the fixing belt 21.
- the nip formation member 24 has a bent portion 244 continuously bent from an upstream end of the rounded upstream portion of the elongated portion 242 to the opposite side to the pressure roller 22.
- a nip formation surface 241a on the nip formation portion 241 facing the fixing belt 21 directly contacts the inner circumferential surface of the fixing belt 21. Therefore, when the fixing belt 21 rotates, the fixing belt 21 slides along the nip formation surface 241a.
- the nip formation surface 241a may be treated with alumite or coated with fluororesin material. Additionally, a lubricant such as a fluorine-based grease may be applied to the nip formation surface 241a to ensure slidability over time.
- the nip formation surface 241a is planar.
- the nip formation surface 241a may define a recess or other shape.
- the nip formation surface 241a 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.
- the nip formation member 24 is made of a material having a large thermal conductivity such as 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.
- 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.
- 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.
- the stay 25 is attached to a rear side surface of the nip formation member 24 via the reflector 26 and supports the nip formation member 24 against the pressure of the pressure roller 22. Similar to the nip formation member 24, the stay 25 extends in the width direction of the fixing belt 21 inside the loop of the fixing belt 21.
- the stay 25 has a U-shaped cross-section including a pair of vertical wall portions 25a and a bottom wall portion 25b that connects the pair of vertical wall portions 25a.
- the pair of vertical wall portions 25a of the stay 25 supports both ends of the nip formation member 24 in the direction B of rotation of the fixing belt 21.
- the vertical wall portions 25a extending in a direction in which the pressure roller 22 presses against the nip formation member 24 that is a vertical direction in FIG. 2 strengthens the rigidity of the stay 25 in the direction in which the pressure roller 22 presses against the nip formation member 24 and reduces the bend of the nip formation member 24 caused by the pressing force of the pressure roller 22.
- Such a configuration results in a uniform width of the nip 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.
- the reflector 26 is disposed opposite the halogen heater 23 inside the loop of the fixing belt 21 to reflect the radiant heat that is infrared light emitted from the halogen heater 23 to the nip formation member 24.
- 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.
- Each bent portion 26b of the reflector 26 is sandwiched between each vertical wall portion 25a of the stay 25 and the nip formation portion 241 of the nip formation member 24 to hold the reflector 26.
- An opening of an ellipse concave surface of the reflector portion 26a is arranged to face the nip formation member 24 to reflect the radiant heat from the halogen heater 23 toward the nip formation member 24. That is, 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 portion 26a. Therefore, the nip formation member 24 is effectively heated.
- the reflector portion 26a Since the reflector portion 26a is interposed between the halogen heater 23 and the stay 25, the reflector portion 26a functions to block the radiant heat from the halogen heater 23 to the stay 25. This function reduces wasteful energy use to heat the stay 25. In other words, the radiant heat from the halogen heater 23 is applied to the space surrounded by the reflector 26 and the nip formation portion 241 and is blocked from parts disposed outside the space, such as 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 portion 26a blocks heat transfer to the stay 25.
- the surface of the reflector portion 26a of the reflector 26 facing the halogen heater 23 is treated with mirror finish or the like to increase reflectance.
- 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°.
- 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 used in the present embodiment 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.
- the stay 25 may have the function of reflection and thermal insulation of the reflector 26.
- 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.
- the temperature sensor 28 is disposed outside the loop of the fixing belt 21 and detects a temperature of the fixing belt 21.
- the temperature sensors 28 are disposed at two positions, the central position in the width direction of the fixing belt 21, and one end position in the belt width direction of the fixing belt 21.
- Output of the halogen heater 23 is controlled based on the temperature of the outer circumferential surface of the fixing belt 21 detected by the temperature sensor 28.
- 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.
- the halogen heater 23, the nip formation member 24, the stay 25, and the reflector 26 are disposed across the fixing belt 21 in a width direction of the fixing belt 21 that is a lateral direction in FIG. 4 , and this direction is hereinafter referred to as a lateral direction of each part, for example, the lateral direction of the halogen heater 23.
- a pair of belt holders 30 is inserted into both lateral ends of the fixing belt 21 in the axial direction of the fixing belt 21 to rotatably support the fixing belt 21.
- the belt holders 30 inserted into the inner periphery 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.
- 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 face of the fixing belt 21 to stop a movement of the fixing belt 21 in the width direction, that is, walking of the fixing belt 21 in the width direction.
- the supporter 30a may have a cylindrical shape which is continuous over its entire circumference. As illustrated in FIG. 4 , each of the belt holders 30 is fixed on a pair of side plates 31 that are frames of the fixing device 5.
- the belt holder 30 has an opening, and both ends of the halogen heater 23 and the reflector 26 are fixed to the side plates 31 through the openings. The halogen heater 23 and the reflector 26 may be fixed to the belt holder 30.
- Part A of FIG. 5 is a graph illustrating the heating distribution in the longitudinal direction of the halogen heater 23, the horizontal axis represents positions in the longitudinal direction of the halogen heater 23, and the vertical axis represents heat generation amounts (light emission amounts) of the halogen heater 23.
- the halogen heater 23 generates a large amount of heat at a central portion in the longitudinal direction and a relatively small amount of heat at end portions and has a low heat generation areas 23a having a low watt density at the end portions.
- the heat generation amount gradually decreases toward the end of the halogen heater 23.
- the low heat generation area 23a partially overlaps a sheet conveyance span of the sheet P having the maximum width H and passed through the fixing device, and the temperature of the fixing belt 21 is unlikely to increase at an end portion corresponding to an end portion of the sheet P having the maximum width H.
- the elongated portion 242 of the nip formation member 24 has longest parts 242a having the maximum length and disposed at both end portions in the longitudinal direction.
- the elongated portion 242 has a flat surface area having a substantially uniform length L1 at a central portion in the longitudinal direction and the longest part 242a having a length L2 at each end portion in the longitudinal direction (L2 > L1).
- a tapered surface area connects between the longest part 242a and the flat surface area at the central portion in the longitudinal direction.
- the longest part 242a partially overlaps the sheet conveyance span of the sheet P having the maximum width H.
- the nip formation member 24 since the nip formation member 24 has the elongated portion 242, the nip formation member 24 can contact the fixing belt 21 at an upstream position from the fixing nip N in the direction B of rotation of the fixing belt. Accordingly, the nip formation member 24 can preheat the fixing belt 21 at the upstream position from the fixing nip N.
- setting the length of the elongated portion 242 based on the heating distribution of the halogen heater 23 enables the halogen heater 23 to efficiently heat the fixing belt 21. That is, since the amount of heat generated at the end portion in the longitudinal direction by the halogen heater 23 is smaller than the amount of heat generated at the central portion, based on the smaller amount of heat, the length of the elongated portion 242 at the end portion in the longitudinal direction is made longer than the length of the elongated portion 242 at the central portion. Specifically, the elongated portion 242 has the longest part 242a at a position corresponding to the low heat generation area 23a in which the heat generation amount of the halogen heater 23 is small.
- the above-described structure can give a long preheating time at the end portion in the width direction of the fixing belt 21 in which raising the temperature of the fixing belt 21 is difficult and sufficiently heat the entire width of the fixing belt 21 to raise the temperature of the fixing belt 21 to a target fixing temperature.
- the above-described structure can reduce temperature unevenness in the fixing nip N of the fixing belt 21 and prevent an occurrence of a fixing failure. Additionally, the above-described structure can shorten the warm-up time when the fixing device 5 starts operation and save energy of the fixing device 5.
- the tapered surface connecting between the central portion of the elongated portion 242 and the end portion of the elongated portion 242 in the longitudinal direction enables the length of the elongated portion 242 to increase based on decrease of the heat generation amount of the halogen heater 23 in the longitudinal direction, which can efficiently reduce the temperature unevenness of the fixing belt 21.
- the longest part 242a arranged outside the sheet conveyance span of the sheet P having the maximum width H and along the longitudinal direction can sufficiently preheat an area of the fixing belt 21 in which the temperature of the fixing belt 21 easily drops.
- the elongated portion 242 may have a curved upstream edge having lengths that increase from a central position indicated by an alternate long and short dash line C in FIGS. 6A to 6C to the longest part 242a at the end portion in the longitudinal direction.
- the upstream edge of the elongated portion 242 may be a tapered shape connecting between the central position in the longitudinal direction of the elongated portion 242 and the longest part 242a at the end portion of the elongated portion 242.
- the elongated portion 242 as illustrated in FIGS. 6A and 6B described above can reduce heating unevenness in the width direction of the fixing belt 21 and efficiently reduce the temperature unevenness of the fixing belt 21.
- the shape of the elongated portion 242 may be appropriately selected in accordance with the heating distribution of the heater in the longitudinal direction.
- the length of the elongated portion 242 may be increased step by step from the central position to the end portion in the longitudinal direction, that is, L2 > L3 > L1.
- the above-described configuration of the elongated portion 242 allows setting the lengths of the elongated portion, for example, corresponding to various widths of the sheets passed through the fixing device 5, in particular, widths of the sheets frequently used in the fixing device 5.
- the longest part 242a may be partially overlapped with the sheet conveyance span of the sheet P having the maximum width H as illustrated in part B of FIG. 5 , or, as illustrated in FIG. 6B , disposed outside the sheet conveyance span of the sheet P having the maximum width H.
- the length and shape of the elongated portion 242 and the range of the longest part 242a may be appropriately selected in consideration of the heating distribution of the halogen heater 23, the temperature drop of the fixing belt 21, and the like.
- the image forming apparatus is applicable not only to a monochrome image forming apparatus illustrated in FIG. 1 but also to a color image forming apparatus, a copier, a printer, a facsimile machine, or a multifunction peripheral including at least two functions of the copier, printer, and facsimile machine.
- the sheets P serving as recording media may be thick paper, postcards, envelopes, plain paper, thin paper, coated paper, art paper, tracing paper, overhead projector (OHP) transparencies, plastic film, prepreg, copper foil, and the like.
- OHP overhead projector
- the length of the elongated portion at the end portion in the longitudinal direction is set to be longer than the length of the elongated portion at the central portion in the longitudinal direction, but, for example, when increasing the amount of heat added to the central portion of the fixing belt is desired, the length of the elongated portion at the central portion in the longitudinal direction may be set to be longer than the length of the elongated portion at the end portion in the longitudinal direction.
- present disclosure is not limited to the above-described embodiments, and the configuration of the present embodiment can be appropriately modified other than suggested in each of the above embodiments within the scope of the technological concept of the present disclosure.
- positions, the shapes, and the number of components are not limited to the disclosed embodiments, and they may be modified suitably in implementing the present disclosure.
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Abstract
Description
- Embodiments of the present disclosure generally relate to a fixing device and an image forming apparatus incorporating the fixing device.
- An image forming apparatus such as a copier, a printer, a facsimile machine, and a multi-functional apparatus including at least two functions of the copier, printer, facsimile machine includes a fixing device to convey a recording medium such as a sheet on which an unfixed image is formed to a fixing nip formed between a fixing belt and a pressing member in the fixing device, heat the recording medium, and fix the unfixed image onto the recording medium.
- The fixing device includes a heater disposed inside a loop of the fixing belt to heat the fixing belt and a nip formation member that contacts the pressing member via the fixing belt to form the fixing nip. The nip formation member supports an inner circumferential surface of the fixing belt to form the fixing nip between the pressing member and the fixing belt, and, in addition, the heater heats the fixing belt via the nip formation member to suitably heat and press a surface of a recording medium conveyed to the fixing nip.
- However, the heating distribution of the heater may be ununiform in a width direction of the fixing belt that is a longitudinal direction of the heater. For example, the heater exists that generates less heat at end portions than the heat generated at a central portion of the heater. Such a heater causes problems such as an extra time for a part of the fixing belt corresponding to a low heat generation area in which the heater generates less heat to reach a temperature for fixing or a fixing failure caused by the part of the fixing belt corresponding to the low heat generation area that does not reach the temperature for fixing. In particular, when the image forming apparatus is switched on first in the morning, the above-described problem is remarkable because the entire image forming apparatus is cooled.
-
JP-2017-32633-A FIG. 7 , the fixing device includes afirst heater 202,second heaters 203, anip member 204, or the like inside a loop of thefilm 201. Thesecond heaters 203 are disposed upstream from the fixing nip N in a rotation direction of thefilm 201 and face both end portions of thefilm 201 in the width direction of thefilm 201, respectively. Thenip member 204 has an extendedportion 204a extended upstream from the fixing nip N in the rotation direction of thefilm 201 and protrudingportions 204b disposed on both end portions of the extendedportion 204a. Theprotruding portions 204b are further extended upstream from a center portion of the extendedportion 204a. Thesecond heater 203 increases a heat amount to heat the end portion of thefilm 201 in the width direction, and thefilm 201 heated by thesecond heater 203 can enter the nip between thefilm 201 and thenip member 204 immediately after thesecond heater 203 heats thefilm 201. Therefore, thesecond heater 203 can raise the temperature at the end portion of thefilm 201 in the width direction in the fixing nip N to a high temperature. - As described in
JP-2017-32633-A extended portion 204a and theprotruding portion 204b inFIG. 7 ) can compensate for the lack of heat amount to heat a portion that the main heater heats with a relatively small heat amount, that is, in the above-described example, the end portion of the fixing belt in the width direction, to sufficiently heat the fixing belt but causes problems such as increase of manufacturing cost of the fixing device due to adding another part and increase of energy consumption of the fixing device. - Under such circumstances, an object of the present disclosure is to sufficiently heat a fixing belt facing a low heat generation area of a heater, using a simple structure. 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. - Advantageously, the fixing device includes a rotatable endless fixing belt, a pressing member configured to press the fixing belt, the heater disposed inside a loop of the fixing belt and configured to heat the fixing belt, and a nip formation member disposed inside the loop of the fixing belt and configured to come into contact with the pressing member via the fixing belt to form a fixing nip. In a longitudinal direction of the heater, the heater has a low heat generation area that generates a smaller amount of heat than another area of the heater. The nip formation member has an elongated portion that extends upstream from the fixing nip in a rotation direction of the fixing belt. The elongated portion has a longest part positioned corresponding to the low heat generation area in the longitudinal direction.
- According to the present disclosure, the length of the elongated portion of the nip formation member is set longest at a position corresponding to the low heat generation area of the heater. That is, a simple structure in which the elongated portion of the nip formation member has a shape corresponding to the heating distribution of the heater enables the fixing belt to be sufficiently heated at the position corresponding to the low heat generation area, which avoids the occurrence of the fixing failure.
- 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 diagram illustrating a configuration 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 according to the embodiment of the present disclosure 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 includes part A that is a graph illustrating a heating distribution in the longitudinal direction of a halogen heater and part B that is an explanatory diagram illustrating a nip formation member; -
FIGS. 6A to 6C are explanatory diagrams illustrating nip formation members having different shapes; and -
FIG. 7 is a vertical cross-sectional view of a known fixing device viewed from a lateral side of the fixing device. - 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.
- 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.
- 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.
- Referring to the attached drawings, the following describes embodiments 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.
-
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present disclosure. Referring toFIG. 1 , a configuration and operation of the image forming apparatus according to the present embodiment are described below. - The
image forming apparatus 1 illustrated inFIG. 1 is a monochrome electrophotographic laser printer. Theimage forming apparatus 1 according to the embodiments of the present disclosure may be a copier, a facsimile machine, a multifunction peripheral (MFP) having at least two of copying, printing, scanning, facsimile, and plotter functions in addition to the printer. Theimage forming apparatus 1 is not limited to a monochrome image forming apparatus and may be a color image forming apparatus. - As illustrated in
FIG. 1 , theimage forming apparatus 1 includes animage forming device 2 to form an image, a recordingmedium feeding device 3 to feed a sheet P as a recording medium to theimage forming device 2, a transfer device 4 to transfer the image onto the fed sheet P, afixing device 5 to fix the image transferred onto the sheet P, and asheet ejection device 6 to eject the sheet P with the fixed image to an outside of theimage forming apparatus 1. - The
image forming device 2 includes a drum-shaped photoconductor 7, acharging roller 8 as a charging device to charge a surface of thephotoconductor 7, anexposure device 9 as a latent image forming device that exposes the surface of thephotoconductor 7 to form an electrostatic latent image on thephotoconductor 7, a developingroller 10 as a developing device that supplies toner as a developer to the surface of thephotoconductor 7 to visualize the electrostatic latent image, and acleaning blade 11 as a cleaner to clean the surface of thephotoconductor 7. - As an image forming operation start is instructed, in the
image forming device 2, thephotoconductor 7 starts to rotate, and thecharging roller 8 uniformly charges the surface of thephotoconductor 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, theexposure device 9 exposes the surface of thephotoconductor 7. Potential of an exposed surface drops, and the electrostatic latent image is formed on thephotoconductor 7. The developingroller 10 supplies toner to the electrostatic latent image, thereby developing the latent image into the toner image on thephotoconductor 7. - The toner image formed on the
photoconductor 7 is transferred onto the sheet P in a transfer nip between thephotoconductor 7 and atransfer roller 15 disposed in the transfer device 4. The sheet P is fed from the recordingmedium feeding device 3. In the recordingmedium feeding device 3, asheet feeding roller 13 feeds the sheet P from asheet tray 12 to a feeding path one by one. Atiming roller pair 14 sends out the sheet P fed from thesheet tray 12 to a transfer nip, timed to coincide with the toner image on thephotoconductor 7. The toner image on thephotoconductor 7 is transferred onto the sheet P at the transfer nip. After the toner image is transferred from thephotoconductors 7 onto the sheet P, thecleaning blade 11 removes residual toner on thephotoconductor 7. - The sheet P bearing the toner image is conveyed to the
fixing device 5. In thefixing device 5, heat and pressure when the sheet P passes through between thefixing belt 21 and thepressure roller 22 fixes the toner image onto the sheet P. Subsequently, the sheet P is conveyed to thesheet ejection device 6, and anejection roller pair 16 ejects the sheet P outside theimage forming apparatus 1, and a series of print operations are completed. - With reference to
FIGS. 2 to 4 , a detailed description is provided of a construction of the fixingdevice 5.FIG. 2 is a vertical cross-sectional view of the fixingdevice 5 viewed from a lateral side of the fixingdevice 5,FIG. 3 is a perspective view of the fixingdevice 5 with the vertical cross-sectional view of the fixingdevice 5, andFIG. 4 is a vertical cross-sectional view of the fixingdevice 5 viewed from a front side of the fixingdevice 5. - As illustrated in
FIG. 2 , the fixingdevice 5 includes the fixingbelt 21, thepressure roller 22, ahalogen heater 23 as a heater, anip formation member 24, astay 25 as a contact part, areflector 26, andtemperature sensors 28. - 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 fixingbelt 21 in the present embodiment is an endless belt or film, including a base layer formed on an inner side of the fixingbelt 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 fixingbelt 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 fixingbelt 21 and thepressure 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 fixingbelt 21, preventing variation in gloss of the toner image on the sheet P. Additionally, in the present embodiment, the fixingbelt 21 is thin and has a small loop diameter to decrease the thermal capacity of the fixingbelt 21. For example, the base layer of the fixingbelt 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 fixingbelt 21 has a total thickness not greater than 1 mm. In addition, when the fixingbelt 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 fixingbelt 21, the fixingbelt 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 fixingbelt 21 may have a loop diameter from 20 to 40 mm and preferably 30 mm or less. - The
pressure roller 22 is a pressing member disposed opposite an outer circumferential surface of the fixingbelt 21. Thepressure 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, thepressure roller 22 is a solid roller. Alternatively, thepressure roller 22 may be a hollow roller. When thepressure roller 22 is the hollow roller, a heater such as a halogen heater may be disposed inside thepressure roller 22. The elastic layer of thepressure roller 22 may be made of solid rubber. Alternatively, if no heater is disposed inside thepressure roller 22, the elastic layer of thepressure roller 22 is preferably made of sponge rubber to enhance thermal insulation of thepressure roller 22. Such a configuration reduces heat conduction from the fixingbelt 21 to thepressure roller 22 and improves heating efficiency of the fixingbelt 21. - A driver disposed inside the
image forming apparatus 1 drives and rotates thepressure roller 22 in a direction indicated by arrow A inFIG. 2 . The rotation of thepressure roller 22 drives the fixingbelt 21 to rotate in a direction B inFIG. 2 due to frictional force therebetween. After the toner image is transferred onto the sheet P, the sheet P bearing the unfixed toner image T is conveyed to a fixing nip N between the fixingbelt 21 and thepressure roller 22. Therotating fixing belt 21 and therotating pressure roller 22 conveys the sheet P, and the sheet P passes through the fixing nip N. When the sheet P passes through the fixing nip N, heat and pressure applied to the sheet P fix the unfixed toner image T onto the sheet P. - The
pressure roller 22 and the fixingbelt 21 are configured to be able to contact and separate each other. If the sheet is jammed in the nip N, separating thepressure roller 22 and the fixingbelt 21 from each other and opening the nip N enables the jammed sheet to be removed. One of thepressure roller 22 and the fixingbelt 21 may be configured to be fixed and the other may be configured to be movable so that thepressure roller 22 and the fixingbelt 21 contact and separate each other. Alternatively, both thepressure roller 22 and the fixingbelt 21 may be configured to move so that thepressure roller 22 and the fixingbelt 21 contact and separate each other. - The
halogen heater 23 is a heater disposed inside a loop of the fixingbelt 21 and emitting infrared light including far infrared light or near infrared light, and radiant heat from thehalogen heater 23 heats the fixingbelt 21 from the inside. Alternatively, instead of thehalogen heater 23, a carbon heater, a ceramic heater or the like may be employed as the heater. In the present embodiment, only onehalogen heater 23 is disposed in the loop of the fixingbelt 21, but a plurality ofhalogen heaters 23 having different heat-generating areas may be used according to the width of the sheet. - The
nip formation member 24 sandwiches the fixingbelt 21 together with thepressure roller 22, to form the fixing nip N. Specifically, thenip formation member 24 is disposed inside the loop of the fixingbelt 21 and has a planar nipformation portion 241 that is in contact with an inner circumferential surface of the fixingbelt 21 and anelongated portion 242, which is described in detail below, extending upstream from the nip formation portion 241 (the fixing nip) in the direction B of rotation of the fixingbelt 21. A pressing member such as a spring presses thepressure roller 22 against thenip formation member 24, which causes thepressure roller 22 to contact the fixingbelt 21 and form the fixing nip N between thepressure roller 22 and the fixingbelt 21. - The
nip formation member 24 has abent portion 243 bent from a downstream end of thenip formation portion 241 in the direction B of rotation of the fixingbelt 21 to the side opposite to thepressure roller 22. The upstream side of theelongated portion 242 in the direction B of rotation of the fixingbelt 21 is configured to have a rounded surface. The rounded upstream portion of theelongated portion 242 prevents damage to the inner circumferential surface of the fixingbelt 21 caused by sliding between the upstream portion of theelongated portion 242 and the inner circumferential surface of the fixingbelt 21. In addition, thenip formation member 24 has abent portion 244 continuously bent from an upstream end of the rounded upstream portion of theelongated portion 242 to the opposite side to thepressure roller 22. - A
nip formation surface 241a on thenip formation portion 241 facing the fixingbelt 21 directly contacts the inner circumferential surface of the fixingbelt 21. Therefore, when the fixingbelt 21 rotates, the fixingbelt 21 slides along thenip formation surface 241a. In order to improve the abrasion resistance and the slidability of thenip formation surface 241a, thenip formation surface 241a may be treated with alumite or coated with fluororesin material. Additionally, a lubricant such as a fluorine-based grease may be applied to thenip formation surface 241a to ensure slidability over time. In the present embodiment, thenip formation surface 241a is planar. Alternatively, thenip formation surface 241a may define a recess or other shape. For example, thenip formation surface 241a having a concave shape recessed to the side opposite to thepressure roller 22 leads the outlet of the sheet in the fixing nip N to be closer to thepressure roller 22, which improves separation of the sheet from the fixingbelt 21. - The
nip formation member 24 is made of a material having a large thermal conductivity such as copper (thermal conductivity: 398 W/mK) or aluminum (thermal conductivity: 236 W/mK). Thenip formation member 24 made of the material having such a large thermal conductivity absorbs the radiant heat from thehalogen heater 23 and effectively transmits heat to the fixingbelt 21. For example, setting the thickness of thenip formation member 24 to 1 mm or less can shorten a heat transfer time in which the heat transfers from thenip formation member 24 to the fixingbelt 21, which is advantageous in shortening a warm-up time of the fixingdevice 5. In contrast, setting the thickness of thenip formation member 24 to be larger than 1 mm and 5 mm or less can improve a heat storage capacity of thenip formation member 24. - The
stay 25 is attached to a rear side surface of thenip formation member 24 via thereflector 26 and supports thenip formation member 24 against the pressure of thepressure roller 22. Similar to the nipformation member 24, thestay 25 extends in the width direction of the fixingbelt 21 inside the loop of the fixingbelt 21. In the present embodiment, thestay 25 has a U-shaped cross-section including a pair ofvertical wall portions 25a and abottom wall portion 25b that connects the pair ofvertical wall portions 25a. - The pair of
vertical wall portions 25a of thestay 25 supports both ends of thenip formation member 24 in the direction B of rotation of the fixingbelt 21. Thevertical wall portions 25a extending in a direction in which thepressure roller 22 presses against thenip formation member 24 that is a vertical direction inFIG. 2 strengthens the rigidity of thestay 25 in the direction in which thepressure roller 22 presses against thenip formation member 24 and reduces the bend of thenip formation member 24 caused by the pressing force of thepressure roller 22. Such a configuration results in a uniform width of the nip in the longitudinal direction. Thestay 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. - The
reflector 26 is disposed opposite thehalogen heater 23 inside the loop of the fixingbelt 21 to reflect the radiant heat that is infrared light emitted from thehalogen heater 23 to the nipformation member 24. In the present embodiment, thereflector 26 includes areflector portion 26a formed as an ellipse cross-section and a pair ofbent portions 26b bent from both ends of thereflector portion 26a in a direction in which the bent portions separate from each other. Eachbent portion 26b of thereflector 26 is sandwiched between eachvertical wall portion 25a of thestay 25 and thenip formation portion 241 of thenip formation member 24 to hold thereflector 26. - An opening of an ellipse concave surface of the
reflector portion 26a is arranged to face thenip formation member 24 to reflect the radiant heat from thehalogen heater 23 toward thenip formation member 24. That is, thehalogen heater 23 directly irradiates thenip formation member 24 with the infrared light, and, additionally, thenip formation member 24 is also irradiated with the infrared light reflected by thereflector portion 26a. Therefore, thenip formation member 24 is effectively heated. - Since the
reflector portion 26a is interposed between thehalogen heater 23 and thestay 25, thereflector portion 26a functions to block the radiant heat from thehalogen heater 23 to thestay 25. This function reduces wasteful energy use to heat thestay 25. In other words, the radiant heat from thehalogen heater 23 is applied to the space surrounded by thereflector 26 and thenip formation portion 241 and is blocked from parts disposed outside the space, such as thestay 25. Additionally, in the present embodiment, thermal insulation of the layer of air in a gap between thestay 25 and thereflector portion 26a blocks heat transfer to thestay 25. - The surface of the
reflector portion 26a of thereflector 26 facing thehalogen 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 thereflector 26 used in the present embodiment is preferably 70% or more with wavelengths of high emission intensity in thehalogen 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. - Alternatively, the
stay 25 may have the function of reflection and thermal insulation of thereflector 26. For example, performing the thermal insulation treatment or the mirror finishing on the inner surface of thestay 25 in thehalogen heater 23 side enables thestay 25 to function as thereflector 26. Such a configuration can obviate thereflector 26 that is a separate component from thestay 25. The reflectance of thestay 25 subjected to the mirror finishing is preferably similar to the reflectance of thereflector 26. - The
temperature sensor 28 is disposed outside the loop of the fixingbelt 21 and detects a temperature of the fixingbelt 21. In the present embodiment, thetemperature sensors 28 are disposed at two positions, the central position in the width direction of the fixingbelt 21, and one end position in the belt width direction of the fixingbelt 21. Output of thehalogen heater 23 is controlled based on the temperature of the outer circumferential surface of the fixingbelt 21 detected by thetemperature sensor 28. Thus, the temperature of the fixingbelt 21 is adjusted to a desired fixing temperature. Thetemperature sensor 28 may be either contact type or non-contact type. Thetemperature sensor 28 may be a known temperature sensor type such as a thermopile, a thermostat, a thermistor, or a non-contact (NC) sensor. - As illustrated in
FIGS. 3 and4 , thehalogen heater 23, thenip formation member 24, thestay 25, and thereflector 26 are disposed across the fixingbelt 21 in a width direction of the fixingbelt 21 that is a lateral direction inFIG. 4 , and this direction is hereinafter referred to as a lateral direction of each part, for example, the lateral direction of thehalogen heater 23. - A pair of
belt holders 30 is inserted into both lateral ends of the fixingbelt 21 in the axial direction of the fixingbelt 21 to rotatably support the fixingbelt 21. As described above, thebelt holders 30 inserted into the inner periphery of the fixingbelt 21 support the fixingbelt 21 in a state in which the fixingbelt 21 is not basically applied with tension in a circumferential direction thereof while the fixingbelt 21 does not rotate, that is, by a free belt system. - The
belt holder 30 includes a C-shapedsupporter 30a inserted into the inner periphery of the fixingbelt 21 to support the fixingbelt 21 and aflange 30b that contacts an end face of the fixingbelt 21 to stop a movement of the fixingbelt 21 in the width direction, that is, walking of the fixingbelt 21 in the width direction. Thesupporter 30a may have a cylindrical shape which is continuous over its entire circumference. As illustrated inFIG. 4 , each of thebelt holders 30 is fixed on a pair ofside plates 31 that are frames of the fixingdevice 5. Thebelt holder 30 has an opening, and both ends of thehalogen heater 23 and thereflector 26 are fixed to theside plates 31 through the openings. Thehalogen heater 23 and thereflector 26 may be fixed to thebelt holder 30. - Next, descriptions are given of a heating distribution (a light emission amount distribution) of the
halogen heater 23 in the longitudinal direction and a shape of the elongated portion of thenip formation member 24 corresponding to the heating distribution below in detail. - Part A of
FIG. 5 is a graph illustrating the heating distribution in the longitudinal direction of thehalogen heater 23, the horizontal axis represents positions in the longitudinal direction of thehalogen heater 23, and the vertical axis represents heat generation amounts (light emission amounts) of thehalogen heater 23. As illustrated in part A ofFIG. 5 , thehalogen heater 23 generates a large amount of heat at a central portion in the longitudinal direction and a relatively small amount of heat at end portions and has a lowheat generation areas 23a having a low watt density at the end portions. Specifically, at the end portion in the longitudinal direction of thehalogen heater 23, the heat generation amount gradually decreases toward the end of thehalogen heater 23. The lowheat generation area 23a partially overlaps a sheet conveyance span of the sheet P having the maximum width H and passed through the fixing device, and the temperature of the fixingbelt 21 is unlikely to increase at an end portion corresponding to an end portion of the sheet P having the maximum width H. - As illustrated in part B of
FIG. 5 , in the present embodiment, theelongated portion 242 of thenip formation member 24 haslongest parts 242a having the maximum length and disposed at both end portions in the longitudinal direction. Specifically, theelongated portion 242 has a flat surface area having a substantially uniform length L1 at a central portion in the longitudinal direction and thelongest part 242a having a length L2 at each end portion in the longitudinal direction (L2 > L1). A tapered surface area connects between thelongest part 242a and the flat surface area at the central portion in the longitudinal direction. In the longitudinal direction, thelongest part 242a partially overlaps the sheet conveyance span of the sheet P having the maximum width H. - As illustrated in
FIG. 2 , in the present embodiment, since thenip formation member 24 has the elongatedportion 242, thenip formation member 24 can contact the fixingbelt 21 at an upstream position from the fixing nip N in the direction B of rotation of the fixing belt. Accordingly, thenip formation member 24 can preheat the fixingbelt 21 at the upstream position from the fixing nip N. - In particular, in the present embodiment, setting the length of the
elongated portion 242 based on the heating distribution of thehalogen heater 23 enables thehalogen heater 23 to efficiently heat the fixingbelt 21. That is, since the amount of heat generated at the end portion in the longitudinal direction by thehalogen heater 23 is smaller than the amount of heat generated at the central portion, based on the smaller amount of heat, the length of theelongated portion 242 at the end portion in the longitudinal direction is made longer than the length of theelongated portion 242 at the central portion. Specifically, theelongated portion 242 has thelongest part 242a at a position corresponding to the lowheat generation area 23a in which the heat generation amount of thehalogen heater 23 is small. The above-described structure can give a long preheating time at the end portion in the width direction of the fixingbelt 21 in which raising the temperature of the fixingbelt 21 is difficult and sufficiently heat the entire width of the fixingbelt 21 to raise the temperature of the fixingbelt 21 to a target fixing temperature. As a result, the above-described structure can reduce temperature unevenness in the fixing nip N of the fixingbelt 21 and prevent an occurrence of a fixing failure. Additionally, the above-described structure can shorten the warm-up time when the fixingdevice 5 starts operation and save energy of the fixingdevice 5. - In addition, the tapered surface connecting between the central portion of the
elongated portion 242 and the end portion of theelongated portion 242 in the longitudinal direction enables the length of theelongated portion 242 to increase based on decrease of the heat generation amount of thehalogen heater 23 in the longitudinal direction, which can efficiently reduce the temperature unevenness of the fixingbelt 21. - The
longest part 242a arranged outside the sheet conveyance span of the sheet P having the maximum width H and along the longitudinal direction can sufficiently preheat an area of the fixingbelt 21 in which the temperature of the fixingbelt 21 easily drops. - With reference to
FIGS. 6A to 6C , variations of the shape of theelongated portion 242 are described. - As illustrated in
FIG. 6A , theelongated portion 242 may have a curved upstream edge having lengths that increase from a central position indicated by an alternate long and short dash line C inFIGS. 6A to 6C to thelongest part 242a at the end portion in the longitudinal direction. Alternatively, as illustrated inFIG. 6B , the upstream edge of theelongated portion 242 may be a tapered shape connecting between the central position in the longitudinal direction of theelongated portion 242 and thelongest part 242a at the end portion of theelongated portion 242. For example, in a configuration that is different from the above-described embodiment and has a heating distribution of the heater gradually decreasing from the central position to the end portion in the longitudinal direction, theelongated portion 242 as illustrated inFIGS. 6A and 6B described above can reduce heating unevenness in the width direction of the fixingbelt 21 and efficiently reduce the temperature unevenness of the fixingbelt 21. As described above, the shape of theelongated portion 242 may be appropriately selected in accordance with the heating distribution of the heater in the longitudinal direction. - Moreover, as illustrated in
FIG. 6C , the length of theelongated portion 242 may be increased step by step from the central position to the end portion in the longitudinal direction, that is, L2 > L3 > L1. The above-described configuration of theelongated portion 242 allows setting the lengths of the elongated portion, for example, corresponding to various widths of the sheets passed through the fixingdevice 5, in particular, widths of the sheets frequently used in thefixing device 5. - The
longest part 242a may be partially overlapped with the sheet conveyance span of the sheet P having the maximum width H as illustrated in part B ofFIG. 5 , or, as illustrated inFIG. 6B , disposed outside the sheet conveyance span of the sheet P having the maximum width H. As described above, the length and shape of theelongated portion 242 and the range of thelongest part 242a may be appropriately selected in consideration of the heating distribution of thehalogen heater 23, the temperature drop of the fixingbelt 21, and the like. - The present disclosure is not limited to the details of the embodiments described above and various modifications and improvements are possible.
- The image forming apparatus according to the present embodiment of the present disclosure is applicable not only to a monochrome image forming apparatus illustrated in
FIG. 1 but also to a color image forming apparatus, a copier, a printer, a facsimile machine, or a multifunction peripheral including at least two functions of the copier, printer, and facsimile machine. - The sheets P serving as recording media may be thick paper, postcards, envelopes, plain paper, thin paper, coated paper, art paper, tracing paper, overhead projector (OHP) transparencies, plastic film, prepreg, copper foil, and the like.
- In the embodiment described above, the length of the elongated portion at the end portion in the longitudinal direction is set to be longer than the length of the elongated portion at the central portion in the longitudinal direction, but, for example, when increasing the amount of heat added to the central portion of the fixing belt is desired, the length of the elongated portion at the central portion in the longitudinal direction may be set to be longer than the length of the elongated portion at the end portion in the longitudinal direction.
- The present disclosure is not limited to the above-described embodiments, and the configuration of the present embodiment can be appropriately modified other than suggested in each of the above embodiments within the scope of the technological concept of the present disclosure. In addition, the positions, the shapes, and the number of components are not limited to the disclosed embodiments, and they may be modified suitably in implementing the present disclosure.
Claims (5)
- A fixing device (5) comprising:a rotatable endless fixing belt (21);a pressing member (22) configured to press the fixing belt (21);a heater (23) disposed inside a loop of the fixing belt (21) and configured to heat the fixing belt (21), the heater (23) having, in a longitudinal direction of the heater (23), a low heat generation area (23a) that generates a smaller amount of heat than another area of the heater (23); anda nip formation member (24) disposed inside the loop of the fixing belt (21) and configured to come into contact with the pressing member (22) via the fixing belt (21) to form a fixing nip,the nip formation member (24) having an elongated portion (242) that extends upstream from the fixing nip in a rotation direction of the fixing belt (21),the elongated portion (242) having a longest part (242a) positioned corresponding to the low heat generation area in the longitudinal direction.
- The fixing device (5) according to claim 1,
wherein, in a longitudinal direction of the nip formation member (24), a length at an end portion of the elongated portion (242) in the rotation direction is greater than a length at a central portion of the elongated portion (242) in the rotation direction. - The fixing device (5) according to claim 1 or 2,
wherein, in a longitudinal direction of the nip formation member (24), the longest part (242a) is disposed outside a sheet conveyance span of a recording medium having a maximum width among recording media used in the fixing device (5). - The fixing device (5) according to any one of claims 1 to 3,
wherein the elongated portion (242) has a rounded surface at an upstream end in the rotation direction. - An image forming apparatus (1) comprising the fixing device (5) according to any one of claims 1 to 4.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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JP2019015643A JP7223320B2 (en) | 2019-01-31 | 2019-01-31 | Fixing device, image forming device |
Publications (1)
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EP3690550A1 true EP3690550A1 (en) | 2020-08-05 |
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ID=69104323
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EP20150101.2A Withdrawn EP3690550A1 (en) | 2019-01-31 | 2020-01-02 | Fixing device and image forming apparatus incorporating same |
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EP (1) | EP3690550A1 (en) |
JP (1) | JP7223320B2 (en) |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20140341627A1 (en) * | 2013-05-16 | 2014-11-20 | Masaaki Yoshikawa | Fixing device and image forming apparatus |
EP2921911A1 (en) * | 2014-03-17 | 2015-09-23 | Ricoh Company, Ltd. | Fixing device and image forming apparatus |
JP2017032633A (en) | 2015-07-29 | 2017-02-09 | ブラザー工業株式会社 | Fixing device |
JP2018169467A (en) * | 2017-03-29 | 2018-11-01 | 株式会社リコー | Fixing device and image forming apparatus |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP5359790B2 (en) | 2009-10-30 | 2013-12-04 | ブラザー工業株式会社 | Fixing device |
JP5714654B2 (en) | 2013-06-21 | 2015-05-07 | ブラザー工業株式会社 | Fixing device |
JP6888319B2 (en) | 2016-03-11 | 2021-06-16 | 株式会社リコー | Fixing device and image forming device |
-
2019
- 2019-01-31 JP JP2019015643A patent/JP7223320B2/en active Active
-
2020
- 2020-01-02 EP EP20150101.2A patent/EP3690550A1/en not_active Withdrawn
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20140341627A1 (en) * | 2013-05-16 | 2014-11-20 | Masaaki Yoshikawa | Fixing device and image forming apparatus |
EP2921911A1 (en) * | 2014-03-17 | 2015-09-23 | Ricoh Company, Ltd. | Fixing device and image forming apparatus |
JP2017032633A (en) | 2015-07-29 | 2017-02-09 | ブラザー工業株式会社 | Fixing device |
JP2018169467A (en) * | 2017-03-29 | 2018-11-01 | 株式会社リコー | Fixing device and image forming apparatus |
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JP2020122913A (en) | 2020-08-13 |
JP7223320B2 (en) | 2023-02-16 |
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