This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application Nos. 2015-141518, filed on Jul. 15, 2015, and 2016-050881, filed on Mar. 15, 2016, in the Japanese Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.
Technical Field
Exemplary aspects of the present disclosure relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus incorporating the fixing device.
Description of the Background
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include a fixing rotator, such as a fixing roller, a fixing belt, and a fixing film, heated by a heater and an opposed rotator, such as a pressure roller and a pressure belt, pressed against the fixing rotator to form a fixing nip therebetween through which a recording medium bearing a toner image is conveyed. As the recording medium bearing the toner image is conveyed through the fixing nip, the fixing rotator and the opposed rotator apply heat and pressure to the recording medium, melting and fixing the toner image on the recording medium.
This specification describes below an improved fixing device. In one exemplary embodiment, the fixing device includes an endless belt rotatable in a predetermined direction of rotation and a nip formation pad disposed opposite an inner circumferential surface of the endless belt. The nip formation pad includes a base and an increased thermal conductivity conductor being interposed between the base and the endless belt and having a thermal conductivity greater than a thermal conductivity of the base. An opposed rotator presses against the nip formation pad via the endless belt to form a fixing nip between the endless belt and the opposed rotator, through which a recording medium bearing a toner image is conveyed. A primary heat generator is disposed opposite the endless belt. A secondary heat generator is disposed opposite the endless belt and disposed outboard from the primary heat generator in an axial direction of the endless belt. A temperature detector, disposed opposite the secondary heat generator, detects a temperature of the endless belt. The temperature detector has a detection span in the axial direction of the endless belt. The secondary heat generator includes an inboard edge and an outboard edge disposed outboard from the inboard edge in the axial direction of the endless belt. The secondary heat generator has an inboard length defined between a center of the detection span of the temperature detector and the inboard edge in the axial direction of the endless belt. The secondary heat generator further has an outboard length defined between the center of the detection span of the temperature detector and the outboard edge in the axial direction of the endless belt. The secondary heat generator defines a ratio of the outboard length to the inboard length that is greater than 7/3.
This specification further describes an improved fixing device. In one exemplary embodiment, the fixing device includes an endless belt rotatable in a predetermined direction of rotation and a nip formation pad disposed opposite an inner circumferential surface of the endless belt. The nip formation pad includes a base and an increased thermal conductivity conductor being interposed between the base and the endless belt and having a thermal conductivity greater than a thermal conductivity of the base. An opposed rotator presses against the nip formation pad via the endless belt to form a fixing nip between the endless belt and the opposed rotator, through which a recording medium bearing a toner image is conveyed. A primary heat generator is disposed opposite the endless belt. A secondary heat generator is disposed opposite the endless belt and disposed outboard from the primary heat generator in an axial direction of the endless belt. A temperature detector, disposed opposite the secondary heat generator, detects a temperature of the endless belt. The secondary heat generator includes an inboard edge and an outboard edge disposed outboard from the inboard edge in the axial direction of the endless belt. The secondary heat generator has an inboard length defined between a center of the temperature detector and the inboard edge in the axial direction of the endless belt. The secondary heat generator further has an outboard length defined between the center of the temperature detector and the outboard edge in the axial direction of the endless belt. The secondary heat generator defines a ratio of the outboard length to the inboard length that is greater than 7/3.
This specification further describes an improved image forming apparatus. In one exemplary embodiment, the image forming apparatus includes an image forming device to form a toner image and a fixing device, disposed downstream from the image forming device in a recording medium conveyance direction, to fix the toner image on a recording medium. The fixing device includes an endless belt rotatable in a predetermined direction of rotation and a nip formation pad disposed opposite an inner circumferential surface of the endless belt. The nip formation pad includes a base and an increased thermal conductivity conductor being interposed between the base and the endless belt and having a thermal conductivity greater than a thermal conductivity of the base. An opposed rotator presses against the nip formation pad via the endless belt to form a fixing nip between the endless belt and the opposed rotator, through which the recording medium bearing the toner image is conveyed. A primary heat generator is disposed opposite the endless belt. A secondary heat generator is disposed opposite the endless belt and disposed outboard from the primary heat generator in an axial direction of the endless belt. A temperature detector, disposed opposite the secondary heat generator, detects a temperature of the endless belt. The temperature detector has a detection span in the axial direction of the endless belt. The secondary heat generator includes an inboard edge and an outboard edge disposed outboard from the inboard edge in the axial direction of the endless belt. The secondary heat generator has an inboard length defined between a center of the detection span of the temperature detector and the inboard edge in the axial direction of the endless belt. The secondary heat generator further has an outboard length defined between the center of the detection span of the temperature detector and the outboard edge in the axial direction of the endless belt. The secondary heat generator defines a ratio of the outboard length to the inboard length that is greater than 7/3.
A more complete appreciation of the disclosure and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing exemplary 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 operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular to
It is to be noted that, in the drawings for explaining exemplary embodiments of this disclosure, identical reference numerals are assigned, as long as discrimination is possible, to components such as members and component parts having an identical function or shape, thus omitting description thereof once it is provided.
It is to be noted that, in the drawings for explaining exemplary embodiments of this disclosure, identical reference numerals are assigned as long as discrimination is possible to components such as members and component parts having an identical function or shape, thus omitting description thereof once it is provided.
Referring to
As illustrated in
For example, each of the image forming devices 4Y, 4M, 4C, and 4K includes a drum-shaped photoconductor 5 serving as an image bearer or a latent image bearer that bears an electrostatic latent image and a resultant toner image; a charger 6 that charges an outer circumferential surface of the photoconductor 5; a developing device 7 that supplies toner to the electrostatic latent image formed on the outer circumferential surface of the photoconductor 5, thus visualizing the electrostatic latent image as a toner image; and a cleaner 8 that cleans the outer circumferential surface of the photoconductor 5. It is to be noted that, in
Below the image forming devices 4Y, 4M, 4C, and 4K is an exposure device 9 that exposes the outer circumferential surface of the respective photoconductors 5 with laser beams. For example, the exposure device 9, constructed of a light source, a polygon mirror, an f-θ lens, reflection mirrors, and the like, emits a laser beam onto the outer circumferential surface of the respective photoconductors 5 according to image data sent from an external device such as a client computer.
Above the image forming devices 4Y, 4M, 4C, and 4K is a transfer device 3. For example, the transfer device 3 includes an intermediate transfer belt 30 serving as an intermediate transferor, four primary transfer rollers 31 serving as primary transferors, a secondary transfer roller 36 serving as a secondary transferor, a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaner 35.
The intermediate transfer belt 30 is an endless belt stretched taut across the secondary transfer backup roller 32, the cleaning backup roller 33, and the tension roller 34. As a driver drives and rotates the secondary transfer backup roller 32 counterclockwise in
The four primary transfer rollers 31 sandwich the intermediate transfer belt 30 together with the four photoconductors 5, forming four primary transfer nips between the intermediate transfer belt 30 and the photoconductors 5, respectively. The primary transfer rollers 31 are coupled to a power supply that applies a predetermined direct current (DC) voltage and/or a predetermined alternating current (AC) voltage thereto.
The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 together with the secondary transfer backup roller 32, forming a secondary transfer nip between the secondary transfer roller 36 and the intermediate transfer belt 30. Similar to the primary transfer rollers 31, the secondary transfer roller 36 is coupled to the power supply that applies a predetermined DC voltage and/or a predetermined AC voltage thereto.
A bottle holder 2 situated in an upper portion of the image forming apparatus 1 accommodates four toner bottles 2Y, 2M, 2C, and 2K detachably attached thereto to contain and supply fresh yellow, magenta, cyan, and black toners to the developing devices 7 of the image forming devices 4Y, 4M, 4C, and 4K, respectively. For example, the fresh yellow, magenta, cyan, and black toners are supplied from the toner bottles 2Y, 2M, 2C, and 2K to the developing devices 7 through toner supply tubes interposed between the toner bottles 2Y, 2M, 2C, and 2K and the developing devices 7, respectively.
In a lower portion of the image forming apparatus 1 are a paper tray 10 that loads a plurality of sheets P serving as recording media and a feed roller 11 that picks up and feeds a sheet P from the paper tray 10 toward the secondary transfer nip formed between the secondary transfer roller 36 and the intermediate transfer belt 30. The sheets P may be thick paper, postcards, envelopes, plain paper, thin paper, coated paper, art paper, tracing paper, overhead projector (OHP) transparencies, and the like. Optionally, a bypass tray that loads thick paper, postcards, envelopes, thin paper, coated paper, art paper, tracing paper, OHP transparencies, and the like may be attached to the image forming apparatus 1.
A conveyance path R extends from the feed roller 11 to an output roller pair 13 to convey the sheet P picked up from the paper tray 10 onto an outside of the image forming apparatus 1 through the secondary transfer nip. The conveyance path R is provided with a registration roller pair 12 located below the secondary transfer nip formed between the secondary transfer roller 36 and the intermediate transfer belt 30, that is, upstream from the secondary transfer nip in a sheet conveyance direction A1. The registration roller pair 12 serving as a timing roller pair conveys the sheet P conveyed from the feed roller 11 toward the secondary transfer nip at a proper time.
The conveyance path R is further provided with a fixing device 20 (e.g., a fuser or a fusing unit) located above the secondary transfer nip, that is, downstream from the secondary transfer nip in the sheet conveyance direction A1. The fixing device 20 fixes an unfixed toner image transferred from the intermediate transfer belt 30 onto the sheet P conveyed from the secondary transfer nip on the sheet P. The conveyance path R is further provided with the output roller pair 13 located above the fixing device 20, that is, downstream from the fixing device 20 in the sheet conveyance direction A1. The output roller pair 13 ejects the sheet P bearing the fixed toner image onto the outside of the image forming apparatus 1, that is, an output tray 14 disposed atop the image forming apparatus 1. The output tray 14 stocks the sheet P ejected by the output roller pair 13.
Referring to
As a print job starts, a driver drives and rotates the photoconductors 5 of the image forming devices 4Y, 4M, 4C, and 4K, respectively, clockwise in
Simultaneously, as the print job starts, the secondary transfer backup roller 32 is driven and rotated counterclockwise in
When the yellow, magenta, cyan, and black toner images formed on the photoconductors 5 reach the primary transfer nips, respectively, in accordance with rotation of the photoconductors 5, the yellow, magenta, cyan, and black toner images are primarily transferred from the photoconductors 5 onto the intermediate transfer belt 30 by the transfer electric field created at the primary transfer nips such that the yellow, magenta, cyan, and black toner images are superimposed successively on a same position on the intermediate transfer belt 30. Thus, a full color toner image is formed on an outer circumferential surface of the intermediate transfer belt 30. After the primary transfer of the yellow, magenta, cyan, and black toner images from the photoconductors 5 onto the intermediate transfer belt 30, the cleaners 8 remove residual toner failed to be transferred onto the intermediate transfer belt 30 and therefore remaining on the photoconductors 5 therefrom, respectively.
On the other hand, the feed roller 11 disposed in the lower portion of the image forming apparatus 1 is driven and rotated to feed a sheet P from the paper tray 10 toward the registration roller pair 12 in the conveyance path R. The registration roller pair 12 halts the sheet P temporarily.
Thereafter, the registration roller pair 12 resumes rotation at a predetermined time to convey the sheet P to the secondary transfer nip at a time when the full color toner image formed on intermediate transfer belt 30 reaches the secondary transfer nip. The secondary transfer roller 36 is applied with a transfer voltage having a polarity opposite a polarity of the charged yellow, magenta, cyan, and black toners constituting the full color toner image formed on the intermediate transfer belt 30, thus creating a transfer electric field at the secondary transfer nip. Thus, the yellow, magenta, cyan, and black toner images constituting the full color toner image are secondarily transferred from the intermediate transfer belt 30 onto the sheet P collectively by the transfer electric field created at the secondary transfer nip. After the secondary transfer of the full color toner image from the intermediate transfer belt 30 onto the sheet P, the belt cleaner 35 removes residual toner failed to be transferred onto the sheet P and therefore remaining on the intermediate transfer belt 30 therefrom.
Thereafter, the sheet P bearing the full color toner image is conveyed to the fixing device 20 that fixes the full color toner image on the sheet P. Then, the sheet P bearing the fixed full color toner image is ejected by the output roller pair 13 onto the outside of the image forming apparatus 1, that is, the output tray 14 that stocks the sheet P.
The above describes the image forming operation of the image forming apparatus 1 to form the full color toner image on the sheet P. Alternatively, the image forming apparatus 1 may form a monochrome toner image by using any one of the four image forming devices 4Y, 4M, 4C, and 4K or may form a bicolor or tricolor toner image by using two or three of the image forming devices 4Y, 4M, 4C, and 4K.
Referring to
A detailed description is now given of a construction of the fixing belt 21.
The fixing belt 21 is a thin, flexible endless belt or film. For example, the fixing belt 21 is constructed of a base layer constituting an inner circumferential surface of the fixing belt 21 and a release layer constituting the outer circumferential surface of the fixing belt 21. The base layer is made of metal such as nickel and SUS stainless steel or resin such as polyimide (PI). The release layer is 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.
A detailed description is now given of a construction of the pressure roller 22.
The pressure roller 22 is constructed of a cored bar 22a; an elastic layer 22b coating the cored bar 22a and made of silicone rubber foam, silicone rubber, fluoro rubber, or the like; and a release layer 22c coating the elastic layer 22b and made of PFA, PTFE, or the like. A pressurization assembly including a spring presses the pressure roller 22 against the nip formation pad 24 via the fixing belt 21. The pressure roller 22 pressingly contacting the fixing belt 21 deforms the elastic layer 22b of the pressure roller 22 at the fixing nip N formed between the pressure roller 22 and the fixing belt 21, thus defining the fixing nip N having a predetermined length in the sheet conveyance direction A1. A driver (e.g., a motor) disposed inside the image forming apparatus 1 depicted in
According to this exemplary embodiment, the pressure roller 22 is a solid roller. Alternatively, the pressure roller 22 may be a hollow roller. In this case, a heater may be disposed inside the hollow roller. If the pressure roller 22 does not incorporate the elastic layer 22b, the pressure roller 22 has a decreased thermal capacity that improves fixing property of being heated quickly to a predetermined fixing temperature at which a toner image T is fixed on a sheet P properly. However, as the pressure roller 22 and the fixing belt 21 sandwich and press the unfixed toner image T on the sheet P passing through the fixing nip N, slight surface asperities of the fixing belt 21 may be transferred onto the toner image T on the sheet P, resulting in variation in gloss of the solid toner image T. To address this circumstance, it is preferable that the pressure roller 22 incorporates the elastic layer 22b having a thickness not smaller than 100 micrometers. The elastic layer 22b having the thickness not smaller than 100 micrometers elastically deforms to absorb slight surface asperities of the fixing belt 21, preventing variation in gloss of the toner image T on the sheet P. The elastic layer 22b may be made of solid rubber. Alternatively, if no heater is situated inside the pressure roller 22, the elastic layer 22b may be made of sponge rubber. The sponge rubber is more preferable than the solid rubber because the sponge rubber has an increased insulation that draws less heat from the fixing belt 21. According to this exemplary embodiment, the pressure roller 22 is pressed against the fixing belt 21. Alternatively, the pressure roller 22 may merely contact the fixing belt 21 with no pressure therebetween.
A detailed description is now given of a configuration of the lateral end heater 23a and the center heater 23b.
The two heaters, that is, the lateral end heater 23a and the center heater 23b, are situated inside the loop formed by the fixing belt 21. Both lateral ends of each of the lateral end heater 23a and the center heater 23b in a longitudinal direction thereof parallel to an axial direction of the fixing belt 21 are mounted on or secured to side plates of the fixing device 20, respectively. For example, the fixing device 20 employs a direct heating method in which the lateral end heater 23a and the center heater 23b heat the fixing belt 21 directly. The direct heating method heats the fixing belt 21 effectively, saving energy and shortening a warm-up time or the like to warm up the fixing belt 21 to a target temperature. A controller 90 (e.g., a processor), that is, a central processing unit (CPU) provided with a random-access memory (RAM) and a read-only memory (ROM), for example, operatively connected to the temperature sensor 27, the lateral end heater 23a, and the center heater 23b controls output of each of the lateral end heater 23a and the center heater 23b based on the temperature of the outer circumferential surface of the fixing belt 21 detected by the temperature sensor 27. The controller 90 may be disposed inside the fixing device 20 or the image forming apparatus 1. Thus, the temperature of the fixing belt 21 is adjusted to a desired fixing temperature. The temperature sensor 27 may be a thermopile, a thermostat, a thermistor, a non-contact (NC) sensor, or the like that detects the temperature.
A detailed description is now given of a construction of the nip formation pad 24. The nip formation pad 24 is disposed inside the loop formed by the fixing belt 21 and disposed opposite the pressure roller 22 via the fixing belt 21. The nip formation pad 24 is an elongate pad extending continuously in the axial direction of the fixing belt 21. As the pressure roller 22 is pressed against the nip formation pad 24 via the fixing belt 21, the nip formation pad 24 produces the fixing nip N extending continuously in the axial direction of the fixing belt 21. The nip formation pad 24 is secured to and supported by the stay 25. Accordingly, even if the nip formation pad 24 receives pressure from the pressure roller 22, the nip formation pad 24 is not bent by the pressure and therefore produces a uniform nip length in the sheet conveyance direction A1 throughout the entire width of the pressure roller 22 in an axial direction thereof.
The nip formation pad 24 is coated with a low-friction sheet 29 mounted on an opposed face of the nip formation pad 24 that is disposed opposite the fixing belt 21. Thus, the low-friction sheet 29 is sandwiched between the nip formation pad 24 and the fixing belt 21. As the fixing belt 21 rotates in the rotation direction D21, the fixing belt 21 slides over the low-friction sheet 29 that reduces a driving torque developed between the fixing belt 21 and the nip formation pad 24, reducing load exerted to the fixing belt 21 by friction between the fixing belt 21 and the nip formation pad 24. A bulge 45 projects from a downstream end of the nip formation pad 24 that is in proximity to an exit of the fixing nip N toward the pressure roller 22. The bulge 45 does not press against the pressure roller 22 via the fixing belt 21 and therefore is not produced by contact with the pressure roller 22. The bulge 45 lifts the sheet P conveyed through the exit of the fixing nip N from the fixing belt 21, facilitating separation of the sheet P from the fixing belt 21.
The nip formation pad 24 is made of a heat resistant material resistant against temperatures not lower than 200 degrees centigrade. For example, the nip formation pad 24 is made of general heat resistant resin such as polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), and polyether ether ketone (PEEK). Thus, the nip formation pad 24 made of the heat resistant resin is immune from thermal deformation at temperatures in a fixing temperature range desirable to fix the toner image T on the sheet P, retaining the shape of the fixing nip N and quality of the toner image T formed on the sheet P.
A detailed description is now given of a configuration of the stay 25.
The stay 25 is disposed inside the loop formed by the fixing belt 21. Both lateral ends of the stay 25 in a longitudinal direction thereof parallel to the axial direction of the fixing belt 21 are mounted on or secured to the side plates of the fixing device 20, respectively. The stay 25 is made of metal having an increased mechanical strength, such as stainless steel and iron, to prevent bending of the nip formation pad 24. Alternatively, the stay 25 may be made of resin that attains a desired mechanical strength of the stay 25.
A detailed description is now given of a configuration of the reflector 26.
The reflector 26 is interposed between the stay 25 and the two heaters (e.g., the lateral end heater 23a and the center heater 23b). The reflector 26 is secured to or mounted on the stay 25, thus being supported by the stay 25. The reflector 26 interposed between the stay 25 and the two heaters (e.g., the lateral end heater 23a and the center heater 23b) reflects light or heat radiated from the lateral end heater 23a and the center heater 23b to the stay 25 toward the fixing belt 21, heating the fixing belt 21 effectively. The reflector 26 suppresses conduction of heat from the lateral end heater 23a and the center heater 23b to the stay 25 and the like, saving energy. Since the reflector 26 is heated by the lateral end heater 23a and the center heater 23b directly, the reflector 26 is made of metal having an increased melting point or the like. Alternatively, instead of installation of the reflector 26, an opposed face of the stay 25 that is disposed opposite the lateral end heater 23a and the center heater 23b may be treated with polishing or mirror finishing such as coating to produce a reflection face that reflects light or heat radiated from the lateral end heater 23a and the center heater 23b toward the fixing belt 21. For example, the reflector 26 or the reflection face of the stay 25 has a reflection rate of 90 percent or more.
In order to decrease the thermal capacity of the fixing belt 21, the fixing belt 21 is thin and has a decreased loop diameter. For example, the fixing belt 21 is constructed of the base layer having a thickness in a range of from 20 micrometers to 50 micrometers; the elastic layer having a thickness in a range of from 100 micrometers to 300 micrometers; and the release layer having a thickness in a range of from 10 micrometers to 50 micrometers. Thus, the fixing belt 21 has a total thickness not greater than 1 mm. A loop diameter of the fixing belt 21 is in a range of from 20 mm to 40 mm. In order to decrease the thermal capacity of the fixing belt 21 further, the fixing belt 21 may have a total thickness not greater than 0.20 mm and preferably not greater than 0.16 mm. Additionally, the loop diameter of the fixing belt 21 may not be greater than 30 mm.
According to this exemplary embodiment, the pressure roller 22 has a diameter in a range of from 20 mm to 40 mm. Hence, the loop diameter of the fixing belt 21 is equivalent to the diameter of the pressure roller 22. Alternatively, the loop diameter of the fixing belt 21 may be smaller than the diameter of the pressure roller 22. In this case, a curvature of the fixing belt 21 at the fixing nip N is greater than that of the pressure roller 22, facilitating separation of the sheet P ejected from the fixing nip N from the fixing belt 21.
A description is provided of a fixing operation performed by the fixing device 20 having the construction described above.
As the image forming apparatus 1 is powered on, the lateral end heater 23a and the center heater 23b are supplied with power and the driver starts driving and rotating the pressure roller 22 in the rotation direction D22, which in turn rotates the fixing belt 21 in the rotation direction D21. When the fixing belt 21 attains the target temperature, the feed roller 11 depicted in
A description is provided of a construction of the lateral end heater 23a and the center heater 23b in detail.
A portion of each of the lateral end heater 23a and the center heater 23b that is other than the heat generator 231 is a non-heat generator 232 that barely generates heat. The heat generator 231 of the lateral end heater 23a is disposed opposite the non-heat generator 232 of the center heater 23b. The non-heat generator 232 of the lateral end heater 23a is disposed opposite the heat generator 231 of the center heater 23b.
When a small sheet P having a width not greater than a width of the heat generator 231 of the center heater 23b in the longitudinal direction thereof is conveyed through the fixing device 20, the controller 90 depicted in
As illustrated in
For example, the lateral end heater 23a includes a heat generation portion 411 (e.g., a luminous portion) where the filament 41 is coiled helically and densely. The heat generation portion 411 spans the entire width of the heat generator 231 in the longitudinal direction of the lateral end heater 23a. Conversely, the filament 41 is substantially straight in the non-heat generator 232 of the lateral end heater 23a. However, the non-heat generator 232 partially includes a plurality of dense coil portions where the filament 41 is coiled densely. The dense coil portion of the non-heat generator 232 is also called a dead coil and supported by a ring supporter 42 so that the filament 41 retains a desired shape. The supporter 42 is made of tungsten or the like and also situated in the heat generator 231.
Like the lateral end heater 23a, the center heater 23b includes the heat generation portion 411 (e.g., the luminous portion) where the filament 41 is coiled helically and densely. The heat generation portion 411 spans the entire width of the heat generator 231 in the longitudinal direction of the center heater 23b. The heat generation portion 411 is partially supported by the supporters 42. Conversely, the non-heat generator 232 of the center heater 23b is different in construction from the non-heat generator 232 of the lateral end heater 23a. The non-heat generator 232 of the center heater 23b includes a cored bar 43 addressing short circuit that is made of metal such as molybdenum. The filament 41 is coiled around the cored bar 43. The non-heat generator 232 partially includes a plurality of dense coil portions where the filament 41 is coiled densely. The dense coil portions are supported by the supporters 42, respectively.
As described above, the center heater 23b is substantially different from the lateral end heater 23a in that the non-heat generator 232 of the center heater 23b includes the cored bar 43. The cored bar 43 disposed in the non-heat generator 232 suppresses heat generation from the dense coil portions of the filament 41 in the non-heat generator 232. For example, the cored bar 43 decreases the electric resistance of the dense coil portions of the filament 41 in the non-heat generator 232 of the center heater 23b, suppressing heat generation compared to heat generation from the dense coil portions (e.g., the dead coils) of the lateral end heater 23a.
As described above, according to this exemplary embodiment, the cored bar 43 of the center heater 23b suppresses local heat generation from each lateral end span of the center heater 23b in the longitudinal direction thereof. Accordingly, variation in the temperature of the fixing belt 21 is reduced, improving control of the temperature of the fixing belt 21. Additionally, the center heater 23b suppresses redundant heat generation in the non-heat generator 232, decreasing power consumption of the center heater 23b. Even if the center heater 23b shares a common power supply with a lamp, a lighting, or the like, the center heater 23b is immune from flicker. In addition to increased power consumption, a shortened control cycle (e.g., a shortened energization cycle) of the center heater 23b causes the center heater 23b to be susceptible to flicker. According to this exemplary embodiment, decreased power consumption of the center heater 23b shortens the control cycle of the center heater 23b, improving control of the temperature of the fixing belt 21.
Referring to
A second purpose is that the lateral end sensor 27b detects temperature decrease of the fixing belt 21 in a lateral end span of a conveyance span of the fixing belt 21 where the large sheet P is conveyed. Accordingly, the lateral end sensor 27b is located at a position where the lateral end sensor 27b detects temperature decrease of a lateral end span Jb of a conveyance span Wb of the fixing belt 21 where the large sheet P is conveyed. Hence, the lateral end sensor 27b is positioned relative to the lateral end heater 23a such that the detection span S encompasses the lateral end span Jb where the fixing belt 21 is susceptible to temperature decrease.
Conversely, to address this circumstance, if the lateral end sensor 27b is situated at a position illustrated in
Hence, as the maximum size of the sheets P available in the fixing device 20 increases, the lateral end sensor 27b is requested to detect the temperature of the fixing belt 21 in an increased detection span. Accordingly, the single lateral end sensor 27b may not precisely detect both temperature increase in the lateral end span Ha of the non-conveyance span where the small sheet P is not conveyed over the fixing belt 21 and temperature decrease in the lateral end span Jc of the conveyance span Wc where the large sheet P is conveyed over the fixing belt 21.
A description is provided of a configuration of a comparative fixing device incorporating a plurality of heaters to vary a heating span depending on the width of a sheet conveyed over a fixing rotator (e.g., a fixing roller).
The comparative fixing device includes a center heater and a lateral end heater. The center heater has a center heat generator disposed at a center span of the center heater in a longitudinal direction thereof. The lateral end heater has a lateral end heat generator disposed at each lateral end span of the lateral end heater in a longitudinal direction thereof. A plurality of temperature detectors (e.g., thermistors) is disposed opposite the center heat generator and the lateral end heat generator, respectively, to detect the temperature of the fixing rotator.
If the comparative fixing device is requested to change a maximum heating span in an axial direction of the fixing rotator where the center heat generator and the lateral end heat generator heat the fixing rotator, for example, from a span corresponding to an A3 size sheet to a span corresponding to an A3 extension size sheet greater than the A3 size sheet, the lateral end heat generator is requested to enlarge. Accordingly, location of the temperature detectors is examined. For example, an extra temperature detector is disposed opposite an extension span disposed outboard from the A3 size sheet in the axial direction of the fixing rotator. The extra temperature detector detects the temperature of the extension span of the fixing rotator to prevent cold offset in the extension span. However, the extra temperature detector may increase manufacturing costs. To address this circumstance, instead of installation of the extra temperature detector, a target temperature to which the lateral end heater heats the fixing rotator is increased to prevent cold offset. For example, the number of the temperature detectors is not changed. However, the higher target temperature of the fixing rotator may degrade energy saving. Additionally, the higher target temperature may overheat a non-conveyance span of the fixing rotator where the sheet is not conveyed. To address this circumstance, a movable shield is installed to shield the fixing rotator from the lateral end heater. However, the movable shield may increase manufacturing costs. To address this circumstance, the comparative fixing device is requested to detect the temperature of the extension span of the fixing rotator without installation of the extra temperature detector and the movable shield so as to attain both energy saving and reduced manufacturing costs.
To address those circumstances, the fixing device 20 has a configuration described below.
As illustrated in
A thermal conductivity of the increased thermal conductivity conductor 51 is greater than a thermal conductivity of the base 50. For example, the increased thermal conductivity conductor 51 is made of carbon nanotube having a thermal conductivity in a range of from 3,000 W/mK to 5,500 W/mK, graphite sheet having a thermal conductivity in a range of from 700 W/mK to 1,750 W/mK, silver having a thermal conductivity of 420 W/mK, copper having a thermal conductivity of 398 W/mK, aluminum having a thermal conductivity of 236 W/mK, steel electrolytic cold commercial (SECC), or the like. The increased thermal conductivity conductor 51 has a thermal conductivity not smaller than 236 W/mK. For example, the base 50 is made of heat resistant resin such as PES, PPS, LCP, PEN, PAI, and PEEK.
The conveyance span Wα is a span where the small sheet P, that is, a minimum size sheet, slightly greater than the heat generator 231 of the center heater 23b in the longitudinal direction thereof is conveyed over the fixing belt 21. The conveyance span Wβ is a span where the large sheet P having a width greater than the conveyance span Wα in the longitudinal direction of the lateral end heater 23a is conveyed over the fixing belt 21. For example, an A3 size sheet is conveyed in the conveyance span Wβ. The conveyance span Wγ is a span where the extra-large sheet P, that is, a maximum size sheet, is conveyed over the fixing belt 21. For example, an A3 extension size sheet is conveyed in the conveyance span Wγ. However, the sizes of sheets described above are one example and therefore sheets of other sizes may be used.
In order to encompass the conveyance span Wγ of the A3 extension size sheet as the maximum size sheet, the heat generator 231 of the lateral end heater 23a has an outboard edge 231 out disposed outboard from an outboard edge WγE of the conveyance span Wγ of the A3 extension size sheet in the longitudinal direction of the lateral end heater 23a. Conversely, the heat generator 231 of the lateral end heater 23a has an inboard edge 231 in substantially disposed opposite an outboard edge 231 outb of the heat generator 231 of the center heater 23b.
A center g of the detection span S of the lateral end sensor 27b or a center of the lateral end sensor 27b in the axial direction of the fixing belt 21 is distanced from the center of the fixing belt 21 by 125 mm in the axial direction of the fixing belt 21. Accordingly, the detection span S of the lateral end sensor 27b encompasses a temperature increase span Hα where the fixing belt 21 is susceptible to temperature increase and a temperature decrease span Jβ where the fixing belt 21 is susceptible to temperature decrease. The temperature increase span Hα is in a non-conveyance span disposed outboard from the conveyance span Wα of the small sheet P in the axial direction of the fixing belt 21. The temperature decrease span Jβ is in the conveyance span Wβ of the large sheet P (e.g., the A3 size sheet) in the axial direction of the fixing belt 21. Conversely, the detection span S of the lateral end sensor 27b does not encompass a temperature decrease span Jγ disposed in the conveyance span Wγ of the extra-large sheet P (e.g., the A3 extension size sheet) in the axial direction of the fixing belt 21. That is, the temperature decrease span Jγ where the fixing belt 21 is susceptible to temperature decrease when the extra-large sheet P is conveyed is apparently outside the detection span S where the lateral end sensor 27b detects the temperature of the fixing belt 21 precisely.
To address this circumstance, according to this exemplary embodiment, the increased thermal conductivity conductor 51 extends continuously throughout the entire width of the fixing belt 21 in the axial direction thereof. The increased thermal conductivity conductor 51 conducts heat from the temperature decrease span Jγ to the detection span S, allowing the lateral end sensor 27b to detect temperature decrease of the fixing belt 21 in the temperature decrease span Jγ when the A3 extension size sheet is conveyed. Since the increased thermal conductivity conductor 51 facilitates heat conduction in the fixing belt 21 in the axial direction thereof, heat in the temperature decrease span Jγ when the A3 extension size sheet is conveyed dissipates quickly to a periphery. Accordingly, even if the temperature decrease span Jγ is outside the detection span S, temperature decrease generated in the temperature decrease span Jγ appears in the detection span S quickly, allowing the lateral end sensor 27b to detect temperature decrease of the fixing belt 21.
In order to cause temperature decrease generated at the temperature decrease span Jγ situated at a lateral end of the conveyance span Wγ in the axial direction of the fixing belt 21 to influence the temperature in the detection span S of the lateral end sensor 27b, the increased thermal conductivity conductor 51 extends continuously from the lateral end of the conveyance span Wγ of the A3 extension size sheet to the detection span S of the lateral end sensor 27b in the axial direction of the fixing belt 21. For example, an outboard edge 51 out of the increased thermal conductivity conductor 51 is disposed outboard from the outboard edge WγE of the conveyance span Wγ of the A3 extension size sheet in the axial direction of the fixing belt 21. The increased thermal conductivity conductor 51 extends continuously from the outboard edge 51 out to a center of the increased thermal conductivity conductor 51 in a longitudinal direction thereof parallel to the axial direction of the fixing belt 21 symmetrically via the center of the fixing belt 21 in the axial direction thereof.
The outboard edge 51 out of the increased thermal conductivity conductor 51 does not define an outermost end of the entire increased thermal conductivity conductor 51 in the longitudinal direction thereof but does define an inboard edge of a slot 51a disposed at each lateral end of the increased thermal conductivity conductor 51 in the longitudinal direction thereof.
A description is provided of a reason of such definition of the outboard edge 51 out.
Each slot 51a of the increased thermal conductivity conductor 51 positions the increased thermal conductivity conductor 51 to the base 50 of the nip formation pad 24. As a projection serving as a positioner projecting from the base 50 is inserted into each slot 51a of the increased thermal conductivity conductor 51, the increased thermal conductivity conductor 51 is positioned to the base 50 in the longitudinal direction of the increased thermal conductivity conductor 51.
The slot 51a decreases an area where the increased thermal conductivity conductor 51 contacts the fixing belt 21, thus reducing heat conduction from a portion provided with the slot 51a outward in the longitudinal direction of the increased thermal conductivity conductor 51.
Accordingly, an outboard edge of the center span portion Q serving as the thermal conductor of the increased thermal conductivity conductor 51 to conduct heat in the fixing belt 21 in the axial direction thereof, that is, the inboard edge of the slot 51a in the longitudinal direction of the increased thermal conductivity conductor 51, defines the outboard edge 51 out of the increased thermal conductivity conductor 51 in the longitudinal direction thereof. Unlike the increased thermal conductivity conductor 51 according to this exemplary embodiment, if the length L2 of the slot 51a in the sheet conveyance direction A1 is smaller than the half of the length L1 of the increased thermal conductivity conductor 51 in the sheet conveyance direction A1, the outboard span portion Z disposed outboard from the slot 51a in the longitudinal direction of the increased thermal conductivity conductor 51 serves mainly as a thermal conductor. Accordingly, an outboard end of the entire increased thermal conductivity conductor 51 in the longitudinal direction thereof, including the outboard span portion Z disposed outboard from the slot 51a in the longitudinal direction of the increased thermal conductivity conductor 51, defines the outboard edge 51 out of the increased thermal conductivity conductor 51 in the longitudinal direction thereof.
Referring back to
The heat conduction span of the increased thermal conductivity conductor 51 varies depending on the thickness and the material of the increased thermal conductivity conductor 51. According to this exemplary embodiment, since the increased thermal conductivity conductor 51 is made of a material having a thickness of 0.4 mm and a thermal conductivity not smaller than 236 W/mK, the heat conduction span is 20 mm. Alternatively, the heat conduction span of the increased thermal conductivity conductor 51 may vary depending on the thickness and the material of the increased thermal conductivity conductor 51. Additionally, the increased thermal conductivity conductor 51 may not extend throughout the entire width of the nip formation pad 24 in a longitudinal direction thereof parallel to the axial direction of the fixing belt 21.
According to the exemplary embodiments described above, an increased thermal conductivity conductor (e.g., the increased thermal conductivity conductors 51, 51S, and 51T) enlarges the detection span S of the lateral end sensor 27b substantially without increasing the number of the lateral end sensors 27b. For example, even if the lateral end heater 23a is elongated and thereby the lateral end sensor 27b is requested to detect the temperature of the fixing belt 21 in an increased detection span, the single lateral end sensor 27b detects the temperature of the fixing belt 21 precisely. Accordingly, even if the heat generator 231 of the lateral end heater 23a that corresponds to the A3 size sheet as the maximum size sheet available in the fixing device 20 is elongated to correspond to the A3 extension size sheet, the lateral end sensor 27b is not displaced outward in the axial direction of the fixing belt 21. Thus, the lateral end sensor 27b is spaced apart from the lateral edge WγE of the conveyance span Wγ serving as the maximum conveyance span in the axial direction of the fixing belt 21. For example, the lateral end sensor 27b is spaced apart from and disposed inboard from the lateral edge WγE of the conveyance span Wγ in the axial direction of the fixing belt 21 by 25 mm or greater.
Additionally, as illustrated in
However, if the length La is great excessively, the lateral end sensor 27b may be spaced apart excessively from the heat conduction span of the increased thermal conductivity conductor 51. Accordingly, the lateral end sensor 27b may not detect temperature decrease of the fixing belt 21 precisely when the maximum size sheet (e.g., the A3 extension size sheet) is conveyed. To address this circumstance, the ratio of the length La to the length Lb is smaller than 10/3.
Additionally, as illustrated in
However, if the ratio of the length Ld to the length Lc is great excessively, the lateral end sensor 27b may be spaced apart excessively from the heat conduction span of the increased thermal conductivity conductor 51. Accordingly, the lateral end sensor 27b may not detect temperature decrease of the fixing belt 21 precisely when the maximum size sheet (e.g., the A3 extension size sheet) is conveyed. To address this circumstance, the ratio of the length Ld to the length Lc is not greater than 2.50.
The above-described configuration of the lateral end sensor 27b and the increased thermal conductivity conductor 51 is advantageous substantially in a configuration in which the lateral end heater 23a includes the heat generator 231 having an increased width in the axial direction of the fixing belt 21 and the controller 90 controls the lateral end heater 23a precisely to generate heat to be conducted to sheets P including the extra-large sheet (e.g., the A3 extension size sheet) for fixing. For example, the lateral end sensor 27b and the increased thermal conductivity conductor 51 are advantageous substantially if the heat generator 231 of the lateral end heater 23a has a heat generation width greater than 51.5 mm in the longitudinal direction of the lateral end heater 23a. The heat generation width of 51.5 mm of the heat generator 231 of the lateral end heater 23a installed in the fixing device 20 depicted in
Additionally, the above-described configuration of the lateral end sensor 27b and the increased thermal conductivity conductor 51 is also advantageous in a configuration in which the controller 90 controls the lateral end heater 23a precisely to generate heat to be conducted to sheets P including sheets having an increased width in the axial direction of the fixing belt 21. For example, the lateral end sensor 27b and the increased thermal conductivity conductor 51 are also advantageous substantially in a configuration having an increased difference in width between the minimum size sheet and the maximum size sheet among sheets having a width greater than the heat generator 231 of the center heater 23b in the longitudinal direction thereof. For example, a sheet having a width of 217 mm in the axial direction of the fixing belt 21 that is equivalent to the width of the heat generator 231 of the center heater 23b is defined as the minimum size sheet. The A3 extension size sheet having a width of 320 mm in the axial direction of the fixing belt 21 is defined as the maximum size sheet. In this case, if the width of 320 mm of the maximum size sheet is greater than the width of 217 mm of the minimum size sheet by 1.48 times, the lateral end sensor 27b and the increased thermal conductivity conductor 51 are advantageous substantially. Similarly, if the maximum size sheet available in the fixing device 20 is greater the A3 size sheet having the width of 298 mm, the lateral end sensor 27b and the increased thermal conductivity conductor 51 are advantageous substantially.
The fixing device 20 depicted in
A description is provided of reference examples of the fixing device 20 having the construction described above.
According to the exemplary embodiments described above, the cored bar 43 addressing short circuit of the center heater 23b reduces temperature ripple in the non-heat generator 232, allowing the controller 90 to control the temperature of the fixing belt 21 with improved precision. However, the center heater 23b incorporating the cored bar 43 includes the dead coil that barely generates heat. Hence, compared to a heater without the cored bar 43, the cored bar 43 may cause sharp temperature decrease of the fixing belt 21 at a boundary between the heat generator 231 and the non-heat generator 232.
Accordingly, the lateral end heater 23a may deviate from the center heater 23b in the longitudinal direction thereof due to installation error, dimensional tolerance, or the like of the lateral end heater 23a and the center heater 23b. A lateral end of the heat generator 231 of the lateral end heater 23a may overlap a lateral end of the heat generator 231 of the center heater 23b in the longitudinal direction thereof in an overlap span with a decreased overlap amount as indicated by dotted circles in
Referring to
As illustrated in
For example, each of the image forming devices 4Y, 4M, 4C, and 4K includes the drum-shaped photoconductor 5 serving as an image bearer or a latent image bearer that bears an electrostatic latent image and a resultant toner image; the charger 6 that charges the outer circumferential surface of the photoconductor 5; the developing device 7 that supplies toner to the electrostatic latent image formed on the outer circumferential surface of the photoconductor 5, thus visualizing the electrostatic latent image as a toner image; and the cleaner 8 that cleans the outer circumferential surface of the photoconductor 5. It is to be noted that, in
Below the image forming devices 4Y, 4M, 4C, and 4K is the exposure device 9 that exposes the outer circumferential surface of the respective photoconductors 5 with laser beams. For example, the exposure device 9, constructed of the light source, the polygon mirror, the f-θ lens, the reflection mirrors, and the like, emits a laser beam onto the outer circumferential surface of the respective photoconductors 5 according to image data sent from an external device such as a client computer.
Above the image forming devices 4Y, 4M, 4C, and 4K is the transfer device 3. For example, the transfer device 3 includes the intermediate transfer belt 30 serving as an intermediate transferor, the four primary transfer rollers 31 serving as primary transferors, the secondary transfer roller 36 serving as a secondary transferor, the secondary transfer backup roller 32, the cleaning backup roller 33, the tension roller 34, and the belt cleaner 35.
The intermediate transfer belt 30 is an endless belt stretched taut across the secondary transfer backup roller 32, the cleaning backup roller 33, and the tension roller 34. As the driver drives and rotates the secondary transfer backup roller 32 counterclockwise in
The four primary transfer rollers 31 sandwich the intermediate transfer belt 30 together with the four photoconductors 5, forming the four primary transfer nips between the intermediate transfer belt 30 and the photoconductors 5, respectively. The primary transfer rollers 31 are coupled to the power supply that applies a predetermined DC voltage and/or a predetermined AC voltage thereto.
The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 together with the secondary transfer backup roller 32, forming the secondary transfer nip between the secondary transfer roller 36 and the intermediate transfer belt 30. Similar to the primary transfer rollers 31, the secondary transfer roller 36 is coupled to the power supply that applies a predetermined DC voltage and/or a predetermined AC voltage thereto.
The bottle holder 2 situated in the upper portion of the image forming apparatus 1 accommodates the four toner bottles 2Y, 2M, 2C, and 2K detachably attached thereto to contain and supply fresh yellow, magenta, cyan, and black toners to the developing devices 7 of the image forming devices 4Y, 4M, 4C, and 4K, respectively. For example, the fresh yellow, magenta, cyan, and black toners are supplied from the toner bottles 2Y, 2M, 2C, and 2K to the developing devices 7 through the toner supply tubes interposed between the toner bottles 2Y, 2M, 2C, and 2K and the developing devices 7, respectively.
In the lower portion of the image forming apparatus 1 are the paper tray 10 that loads a plurality of sheets P serving as recording media and the feed roller 11 that picks up and feeds a sheet P from the paper tray 10 toward the secondary transfer nip formed between the secondary transfer roller 36 and the intermediate transfer belt 30. The sheets P may be thick paper, postcards, envelopes, plain paper, thin paper, coated paper, art paper, tracing paper, OHP transparencies, and the like. Optionally, the bypass tray that loads thick paper, postcards, envelopes, thin paper, coated paper, art paper, tracing paper, OHP transparencies, and the like may be attached to the image forming apparatus 1.
The conveyance path R extends from the feed roller 11 to the output roller pair 13 to convey the sheet P picked up from the paper tray 10 onto the outside of the image forming apparatus 1 through the secondary transfer nip. The conveyance path R is provided with the registration roller pair 12 located below the secondary transfer nip formed between the secondary transfer roller 36 and the intermediate transfer belt 30, that is, upstream from the secondary transfer nip in the sheet conveyance direction A1. The registration roller pair 12 serving as a timing roller pair conveys the sheet P conveyed from the feed roller 11 toward the secondary transfer nip at a proper time.
The conveyance path R is further provided with the fixing device 20 located above the secondary transfer nip, that is, downstream from the secondary transfer nip in the sheet conveyance direction A1. The fixing device 20 fixes an unfixed toner image transferred from the intermediate transfer belt 30 onto the sheet P conveyed from the secondary transfer nip on the sheet P. The conveyance path R is further provided with the output roller pair 13 located above the fixing device 20, that is, downstream from the fixing device 20 in the sheet conveyance direction A1. The output roller pair 13 ejects the sheet P bearing the fixed toner image onto the outside of the image forming apparatus 1, that is, the output tray 14 disposed atop the image forming apparatus 1. The output tray 14 stocks the sheet P ejected by the output roller pair 13.
Referring to
As a print job starts, the driver drives and rotates the photoconductors 5 of the image forming devices 4Y, 4M, 4C, and 4K, respectively, clockwise in
Simultaneously, as the print job starts, the secondary transfer backup roller 32 is driven and rotated counterclockwise in
When the yellow, magenta, cyan, and black toner images formed on the photoconductors 5 reach the primary transfer nips, respectively, in accordance with rotation of the photoconductors 5, the yellow, magenta, cyan, and black toner images are primarily transferred from the photoconductors 5 onto the intermediate transfer belt 30 by the transfer electric field created at the primary transfer nips such that the yellow, magenta, cyan, and black toner images are superimposed successively on the same position on the intermediate transfer belt 30. Thus, a full color toner image is formed on the outer circumferential surface of the intermediate transfer belt 30. After the primary transfer of the yellow, magenta, cyan, and black toner images from the photoconductors 5 onto the intermediate transfer belt 30, the cleaners 8 remove residual toner failed to be transferred onto the intermediate transfer belt 30 and therefore remaining on the photoconductors 5 therefrom, respectively.
On the other hand, the feed roller 11 disposed in the lower portion of the image forming apparatus 1 is driven and rotated to feed a sheet P from the paper tray 10 toward the registration roller pair 12 in the conveyance path R. The registration roller pair 12 halts the sheet P temporarily.
Thereafter, the registration roller pair 12 resumes rotation at a predetermined time to convey the sheet P to the secondary transfer nip at a time when the full color toner image formed on intermediate transfer belt 30 reaches the secondary transfer nip. The secondary transfer roller 36 is applied with a transfer voltage having a polarity opposite a polarity of the charged yellow, magenta, cyan, and black toners constituting the full color toner image formed on the intermediate transfer belt 30, thus creating a transfer electric field at the secondary transfer nip. Thus, the yellow, magenta, cyan, and black toner images constituting the full color toner image are secondarily transferred from the intermediate transfer belt 30 onto the sheet P collectively by the transfer electric field created at the secondary transfer nip. After the secondary transfer of the full color toner image from the intermediate transfer belt 30 onto the sheet P, the belt cleaner 35 removes residual toner failed to be transferred onto the sheet P and therefore remaining on the intermediate transfer belt 30 therefrom.
Thereafter, the sheet P bearing the full color toner image is conveyed to the fixing device 20 that fixes the full color toner image on the sheet P. Then, the sheet P bearing the fixed full color toner image is ejected by the output roller pair 13 onto the outside of the image forming apparatus 1, that is, the output tray 14 that stocks the sheet P.
The above describes the image foaming operation of the image forming apparatus 1 to form the full color toner image on the sheet P. Alternatively, the image forming apparatus 1 may form a monochrome toner image by using any one of the four image forming devices 4Y, 4M, 4C, and 4K or may form a bicolor or tricolor toner image by using two or three of the image forming devices 4Y, 4M, 4C, and 4K.
Referring to
A detailed description is now given of a construction of the fixing belt 21.
The fixing belt 21 is a thin, flexible endless belt or film. For example, the fixing belt 21 is constructed of the base layer constituting the inner circumferential surface of the fixing belt 21 and the release layer constituting the outer circumferential surface of the fixing belt 21. The base layer is made of metal such as nickel and SUS stainless steel or resin such as PI. The release layer is made of PFA, PTFE, or the like. Optionally, the 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.
A detailed description is now given of a construction of the pressure roller 22.
The pressure roller 22 is constructed of the cored bar 22a; the elastic layer 22b coating the cored bar 22a and made of silicone rubber foam, silicone rubber, fluoro rubber, or the like; and the release layer 22c coating the elastic layer 22b and made of PFA, PTFE, or the like. The pressurization assembly including the spring presses the pressure roller 22 against the nip formation pad 24 via the fixing belt 21. The pressure roller 22 pressingly contacting the fixing belt 21 deforms the elastic layer 22b of the pressure roller 22 at the fixing nip N formed between the pressure roller 22 and the fixing belt 21, thus defining the fixing nip N having a predetermined length in the sheet conveyance direction A1. The driver (e.g., the motor) disposed inside the image forming apparatus 1 depicted in
According to this reference example, the pressure roller 22 is a solid roller. Alternatively, the pressure roller 22 may be a hollow roller. In this case, a heater may be disposed inside the hollow roller. If the pressure roller 22 does not incorporate the elastic layer 22b, the pressure roller 22 has a decreased thermal capacity that improves fixing property of being heated quickly to a predetermined fixing temperature at which a toner image T is fixed on a sheet P properly. However, as the pressure roller 22 and the fixing belt 21 sandwich and press the unfixed toner image T on the sheet P passing through the fixing nip N, slight surface asperities of the fixing belt 21 may be transferred onto the toner image T on the sheet P, resulting in variation in gloss of the solid toner image T. To address this circumstance, it is preferable that the pressure roller 22 incorporates the elastic layer 22b having a thickness not smaller than 100 micrometers. The elastic layer 22b having the thickness not smaller than 100 micrometers elastically deforms to absorb slight surface asperities of the fixing belt 21, preventing variation in gloss of the toner image T on the sheet P. The elastic layer 22b may be made of solid rubber. Alternatively, if no heater is situated inside the pressure roller 22, the elastic layer 22b may be made of sponge rubber. The sponge rubber is more preferable than the solid rubber because the sponge rubber has an increased insulation that draws less heat from the fixing belt 21. According to this reference example, the pressure roller 22 is pressed against the fixing belt 21. Alternatively, the pressure roller 22 may merely contact the fixing belt 21 with no pressure therebetween.
A detailed description is now given of a configuration of the lateral end heater 23a and the center heater 23b.
The two heaters, that is, the lateral end heater 23a and the center heater 23b, are situated inside the loop formed by the fixing belt 21. Both lateral ends of each of the lateral end heater 23a and the center heater 23b in the longitudinal direction thereof parallel to the axial direction of the fixing belt 21 are mounted on or secured to the side plates of the fixing device 20, respectively. According to this reference example, the fixing device 20 employs the direct heating method in which the lateral end heater 23a and the center heater 23b heat the fixing belt 21 directly. The direct heating method heats the fixing belt 21 effectively, saving energy and shortening the warm-up time or the like to warm up the fixing belt 21 to a target temperature. The controller 90 operatively connected to the temperature sensor 27S, the lateral end heater 23a, and the center heater 23b controls output of each of the lateral end heater 23a and the center heater 23b based on the temperature of the outer circumferential surface of the fixing belt 21 detected by the temperature sensor 27S. Thus, the temperature of the fixing belt 21 is adjusted to a desired fixing temperature.
A detailed description is now given of a construction of the nip formation pad 24.
The nip formation pad 24 is disposed inside the loop formed by the fixing belt 21 and disposed opposite the pressure roller 22 via the fixing belt 21. The nip formation pad 24 is an elongate pad extending continuously in the axial direction of the fixing belt 21. As the pressure roller 22 is pressed against the nip formation pad 24 via the fixing belt 21, the nip formation pad 24 produces the fixing nip N extending continuously in the axial direction of the fixing belt 21. The nip formation pad 24 is secured to and supported by the stay 25. Accordingly, even if the nip formation pad 24 receives pressure from the pressure roller 22, the nip formation pad 24 is not bent by the pressure and therefore produces a uniform nip length in the sheet conveyance direction A1 throughout the entire width of the pressure roller 22 in the axial direction thereof.
The nip formation pad 24 is coated with a low-friction sheet mounted on the opposed face of the nip formation pad 24 that is disposed opposite the fixing belt 21. Thus, the low-friction sheet is sandwiched between the nip formation pad 24 and the fixing belt 21. As the fixing belt 21 rotates in the rotation direction D21, the fixing belt 21 slides over the low-friction sheet that reduces a driving torque developed between the fixing belt 21 and the nip formation pad 24, reducing load exerted to the fixing belt 21 by friction between the fixing belt 21 and the nip formation pad 24. The bulge 45 projects from the downstream end of the nip formation pad 24 that is in proximity to the exit of the fixing nip N toward the pressure roller 22. The bulge 45 does not press against the pressure roller 22 via the fixing belt 21 and therefore is not produced by contact with the pressure roller 22. The bulge 45 lifts the sheet P conveyed through the exit of the fixing nip N from the fixing belt 21, facilitating separation of the sheet P from the fixing belt 21.
The nip formation pad 24 is made of a heat resistant material resistant against temperatures not lower than 200 degrees centigrade. For example, the nip formation pad 24 is made of general heat resistant resin such as PES, PPS, LCP, PEN, PAL and PEEK. Thus, the nip formation pad 24 made of the heat resistant resin is immune from thermal deformation at temperatures in a fixing temperature range desirable to fix the toner image T on the sheet P, retaining the shape of the fixing nip N and quality of the toner image T formed on the sheet P.
A detailed description is now given of a configuration of the stay 25.
The stay 25 is disposed inside the loop formed by the fixing belt 21. Both lateral ends of the stay 25 in the longitudinal direction thereof parallel to the axial direction of the fixing belt 21 are mounted on or secured to the side plates of the fixing device 20, respectively. The stay 25 is made of metal having an increased mechanical strength, such as stainless steel and iron, to prevent bending of the nip formation pad 24. Alternatively, the stay 25 may be made of resin that attains a desired mechanical strength of the stay 25.
A detailed description is now given of a configuration of the reflector 26.
The reflector 26 is interposed between the stay 25 and the two heaters (e.g., the lateral end heater 23a and the center heater 23b). The reflector 26 is secured to or mounted on the stay 25, thus being supported by the stay 25. The reflector 26 interposed between the stay 25 and the two heaters (e.g., the lateral end heater 23a and the center heater 23b) reflects light or heat radiated from the lateral end heater 23a and the center heater 23b to the stay 25 toward the fixing belt 21, heating the fixing belt 21 effectively. The reflector 26 suppresses conduction of heat from the lateral end heater 23a and the center heater 23b to the stay 25 and the like, saving energy. Since the reflector 26 is heated by the lateral end heater 23a and the center heater 23b directly, the reflector 26 is made of metal having an increased melting point or the like. Alternatively, instead of installation of the reflector 26 depicted in
According to this reference example, in order to decrease the thermal capacity of the fixing belt 21, the fixing belt 21 is thin and has a decreased loop diameter. For example, the fixing belt 21 is constructed of the base layer having a thickness in a range of from 20 micrometers to 50 micrometers; the elastic layer having a thickness in a range of from 100 micrometers to 300 micrometers; and the release layer having a thickness in a range of from 10 micrometers to 50 micrometers. Thus, the fixing belt 21 has a total thickness not greater than 1 mm. A loop diameter of the fixing belt 21 is in a range of from 20 mm to 40 mm. In order to decrease the thermal capacity of the fixing belt 21 further, the fixing belt 21 may have a total thickness not greater than 0.20 mm and preferably not greater than 0.16 mm. Additionally, the loop diameter of the fixing belt 21 may not be greater than 30 mm.
According to this reference example, the pressure roller 22 has a diameter in a range of from 20 mm to 40 mm. Hence, the loop diameter of the fixing belt 21 is equivalent to the diameter of the pressure roller 22. Alternatively, the loop diameter of the fixing belt 21 may be smaller than the diameter of the pressure roller 22. In this case, a curvature of the fixing belt 21 at the fixing nip N is greater than that of the pressure roller 22, facilitating separation of the sheet P ejected from the fixing nip N from the fixing belt 21.
A description is provided of a fixing operation performed by the fixing device 20S having the construction described above.
As the image forming apparatus 1 depicted in
A description is provided of a construction of the lateral end heater 23a and the center heater 23b in detail.
Like the lateral end heater 23a and the center heater 23b illustrated in
A portion of each of the lateral end heater 23a and the center heater 23b that is other than the heat generator 231 is the non-heat generator 232 that barely generates heat. The heat generator 231 of the lateral end heater 23a is disposed opposite the non-heat generator 232 of the center heater 23b. The non-heat generator 232 of the lateral end heater 23a is disposed opposite the heat generator 231 of the center heater 23b.
With the fixing device 20S according to this reference example, when a small sheet P having a width not greater than the width of the heat generator 231 of the center heater 23b in the longitudinal direction thereof is conveyed through the fixing device 20S, the controller 90 depicted in
Like the temperature sensor 27 illustrated in
For example, the lateral end heater 23a includes the heat generation portion 411 (e.g., the luminous portion) where the filament 41 is coiled helically and densely. The heat generation portion 411 spans the entire width of the heat generator 231 in the longitudinal direction of the lateral end heater 23a. Conversely, the filament 41 is substantially straight in the non-heat generator 232 of the lateral end heater 23a. However, the non-heat generator 232 partially includes the plurality of dense coil portions where the filament 41 is coiled densely. The dense coil portion of the non-heat generator 232 is also called the dead coil and supported by the ring supporter 42 so that the filament 41 retains a desired shape. The supporter 42 is made of tungsten or the like and also situated in the heat generator 231.
Like the lateral end heater 23a, the center heater 23b includes the heat generation portion 411 (e.g., the luminous portion) where the filament 41 is coiled helically and densely. The heat generation portion 411 spans the entire width of the heat generator 231 in the longitudinal direction of the center heater 23b. The heat generation portion 411 is partially supported by the supporters 42. Conversely, the non-heat generator 232 of the center heater 23b is different in construction from the non-heat generator 232 of the lateral end heater 23a. The non-heat generator 232 of the center heater 23b includes the cored bar 43 addressing short circuit that is made of metal such as molybdenum. The filament 41 is coiled around the cored bar 43. The non-heat generator 232 partially includes the plurality of dense coil portions where the filament 41 is coiled densely. The dense coil portions are supported by the supporters 42, respectively.
As described above, the center heater 23b is substantially different from the lateral end heater 23a in that the non-heat generator 232 of the center heater 23b includes the cored bar 43. The cored bar 43 disposed in the non-heat generator 232 suppresses heat generation from the dense coil portions of the filament 41 in the non-heat generator 232. For example, the cored bar 43 decreases the electric resistance of the dense coil portions of the filament 41 in the non-heat generator 232 of the center heater 23b, suppressing heat generation compared to heat generation from the dense coil portions (e.g., the dead coils) of the lateral end heater 23a.
As described above, according to this reference example, the cored bar 43 of the center heater 23b suppresses local heat generation from each lateral end span of the center heater 23b in the longitudinal direction thereof. Accordingly, variation in the temperature of the fixing belt 21 is reduced, improving control of the temperature of the fixing belt 21. Additionally, the center heater 23b suppresses redundant heat generation in the non-heat generator 232, decreasing power consumption of the center heater 23b. Even if the center heater 23b shares a common power supply with a lamp, a lighting, or the like, the center heater 23b is immune from flicker. In addition to increased power consumption, a shortened control cycle (e.g., a shortened energization cycle) of the center heater 23b causes the center heater 23b to be susceptible to flicker. According to this reference example, decreased power consumption of the center heater 23b shortens the control cycle of the center heater 23b, improving control of the temperature of the fixing belt 21.
When the controller 90 causes both the center heater 23b and the lateral end heater 23a to generate heat, a gap between the heat generator 231 of the center heater 23b and the heat generator 231 of the lateral end heater 23a may suffer from temperature decrease. To address this circumstance, the lateral end of the heat generator 231 of the lateral end heater 23a may overlap the lateral end of the heat generator 231 of the center heater 23b in the longitudinal direction thereof in the overlap span slightly as indicated by the dotted circles in
However, the lateral end heater 23a may deviate from the center heater 23b in the longitudinal direction thereof due to installation error, dimensional tolerance, or the like of the lateral end heater 23a and the center heater 23b. The lateral end of the heat generator 231 of the lateral end heater 23a may overlap the lateral end of the heat generator 231 of the center heater 23b in the longitudinal direction thereof in the overlap span with a decreased overlap amount. Further, the lateral end of the heat generator 231 of the lateral end heater 23a may be spaced apart from the lateral end of the heat generator 231 of the center heater 23b with an interval therebetween in the longitudinal direction thereof. Consequently, the fixing belt 21 may suffer from temperature decrease in the overlap span and the interval between the heat generator 231 of the lateral end heater 23a and the heat generator 231 of the center heater 23b. As illustrated in
A thermal conductivity of the increased thermal conductivity conductor 51U is greater than a thermal conductivity of the base 50. For example, the increased thermal conductivity conductor 51U is made of carbon nanotube, graphite sheet, silver, copper, aluminum, SECC, or the like. Conversely, the base 50 is made of heat resistant resin such as PES, PPS, LCP, PEN, PAI, and PEEK.
A detailed description is now given of a construction of the increased thermal conductivity conductor 51U.
Accordingly, even if the lateral end heater 23a deviates from the center heater 23b in the longitudinal direction thereof, the increased thermal conductivity conductor 51U facilitates heat conduction from an increased temperature portion to a decreased temperature portion of the fixing belt 21 in the axial direction thereof, thus suppressing temperature decrease at an axial span between the lateral ends D and E on the fixing belt 21 in the axial direction thereof. Consequently, it is not requested to increase the target temperature of the fixing belt 21 to which the lateral end heater 23a and the center heater 23b heat the fixing belt 21 and to install another temperature sensor, saving energy and reducing manufacturing costs.
In addition to the increased thermal conductivity conductor 51U incorporated in the nip formation pad 24U, an opposed portion of the fixing belt 21 that is disposed opposite the lateral ends D and E may be made of a material having a thermal conductivity not smaller than 50 W/mK. Thus, the opposed portion of the fixing belt 21 facilitates heat conduction in the axial direction of the fixing belt 21. Accordingly, even if the lateral end heater 23a deviates relative to the center heater 23b, the opposed portion of the fixing belt 21 reduces temperature decrease of the fixing belt 21 effectively.
A description is provided of variations of the increased thermal conductivity conductor 51U.
As illustrated in
A description is provided of variations of the nip formation pad 24V depicted in
The thermal absorber 52 contacts an opposite face of the increased thermal conductivity conductor 51V that is opposite a fixing nip side face disposed opposite the fixing nip N. That is, the thermal absorber 52 is disposed opposite the fixing nip N via the increased thermal conductivity conductor 51V. The thermal absorber 52 is disposed at a part of the nip formation pad 24X in a longitudinal direction thereof parallel to the width direction of the sheet P. The base 50 abuts the thermal absorber 52 in the longitudinal direction of the nip formation pad 24X. For example, the thermal absorber 52 spans an inboard part of the non-conveyance span W2 where the small sheet P is not conveyed over the fixing belt 21. The inboard part abuts the conveyance span W1 because the inboard part is susceptible to the lateral end temperature increase when the small sheet P is conveyed over the fixing belt 21.
The thermal absorber 53 contacts an opposite face of an intermediate layer constructed of the thermal absorber 52 and the base 50 that is opposite a fixing nip side face of the intermediate layer that contacts the increased thermal conductivity conductor 51V. The thermal absorber 53 extends throughout the entire width of the nip formation pad 24X in the longitudinal direction thereof parallel to the width direction of the sheet P.
The thermal absorber 52 spans the inboard part of the non-conveyance span W2 where the fixing belt 21 is susceptible to the lateral end temperature increase when the small sheet P is conveyed over the fixing belt 21. Hence, even if the fixing belt 21 suffers from local temperature increase in the inboard part of the non-conveyance span W2, the thermal absorber 52 absorbs heat from the fixing belt 21, suppressing temperature increase of the fixing belt 21. Heat absorbed by the thermal absorber 52 is conducted to the thermal absorber 53. That is, each of the thermal absorbers 52 and 53 absorbs heat failed to be absorbed by the increased thermal conductivity conductor 51V and facilitates heat conduction in a thickness direction of the nip formation pad 24X. Each of the thermal absorbers 52 and 53 also conducts heat in a direction other than the thickness direction of the nip formation pad 24X. Since each of the thermal absorbers 52 and 53 has a predetermined width in the longitudinal direction of the nip formation pad 24X like the increased thermal conductivity conductor 51V, the thermal absorbers 52 and 53 conduct heat also in the longitudinal direction of the nip formation pad 24X. Similarly, the increased thermal conductivity conductor 51V conducts heat in the thickness direction as well as the longitudinal direction of the nip formation pad 24X.
As illustrated in
To address this circumstance, a resin layer 54 may be sandwiched between the thermal absorber 52 and the increased thermal conductivity conductor 51V as illustrated in
Referring to
As illustrated in
As illustrated in
As illustrated in
In the reference examples illustrated in
A description is provided of a construction of a nip formation pad 24Z as a third variation of the nip formation pad 24V depicted in
As described above, the base 50 serving as a decreased thermal conductivity conductor is interposed between the thermal absorber 52 and the increased thermal conductivity conductor 51V. Accordingly, like the nip formation pad 24Y incorporating the resin layer 54 as illustrated in
The reference examples described above may be modified. For example, according to the reference examples illustrated in
A description is provided of advantages of the fixing devices 20 and 20S.
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
According to the exemplary embodiments described above, the nip formation pad includes the increased thermal conductivity conductor that enlarges the detection span S of the temperature detector substantially. Consequently, the temperature detector is disposed relative to the secondary heat generator such that the secondary heat generator defines the ratio of the outboard length to the inboard length that is greater than 7/3.
According to the exemplary embodiments described above, the fixing belt 21 serves as an endless belt. Alternatively, a fixing film, a fixing sleeve, or the like may be used as an endless belt. Further, the pressure roller 22 serves as an opposed rotator. Alternatively, a pressure belt or the like may be used as an opposed rotator.
The present disclosure has been described above with reference to specific exemplary embodiments. Note that the present disclosure is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the spirit and scope of the disclosure. It is therefore to be understood that the present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present disclosure.
Number | Date | Country | Kind |
---|---|---|---|
2015-141518 | Jul 2015 | JP | national |
2016-050881 | Mar 2016 | JP | national |