This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2021-200075, filed on Dec. 9, 2021, and 2022-168319, filed on Oct. 20, 2022, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.
Embodiments of this disclosure relate to a nip forming device and an image forming apparatus, and more specifically, to a nip forming device including a separator for separating a conveyed object having passed through a nip from an endless belt and an image forming apparatus incorporating the nip forming device.
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, and multifunction peripherals (MFP) 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.
Such image forming apparatuses include a fixing device that fixes an image on a recording medium such as a sheet. The fixing device employs a belt fixing method using an endless belt.
This specification describes below an improved nip forming device. In one embodiment, the nip forming device includes an endless belt that is flexible and rotates and a nip former that is disposed opposite an inner circumferential face of the endless belt. A pressure rotator presses against the nip former via the endless belt to form a nip between the endless belt and the pressure rotator, through which a conveyed object is conveyed. A separator is disposed downstream from the nip in a conveyance direction of the conveyed object. The separator separates the conveyed object from the endless belt. The separator includes a non-contact portion separated from the endless belt and a contact portion that contacts the endless belt. The contact portion retains a gap having a predetermined size between the non-contact portion and the endless belt.
This specification further describes an improved image forming apparatus. In one embodiment, the image forming apparatus includes an image forming device that forms an image and the nip forming device described above through which a conveyed object bearing the image is conveyed.
A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:
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. Also, identical or similar reference numerals designate identical or similar components throughout the several views.
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.
Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
Referring to the attached drawings, the following describes embodiments of the present disclosure. In the drawings for explaining the 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.
A description is provided of a construction of an image forming apparatus 100.
The image forming units 1Y, 1M, 1C, and 1Bk have a similar construction. However, the image forming units 1Y, 1M, 1C, and 1Bk contain developers in different colors, that is, yellow, magenta, cyan, and black, respectively, which correspond to color separation components for a color image. For example, each of the image forming units 1Y, 1M, 1C, and 1Bk includes a photoconductor 2, a charger 3, a developing device 4, and a cleaner 5. The photoconductor 2 is drum-shaped and serves as an image bearer. The charger 3 charges a surface of the photoconductor 2. The developing device 4 supplies toner as the developer to the surface of the photoconductor 2 to form a toner image. The cleaner 5 cleans the surface of the photoconductor 2.
The image forming apparatus 100 further includes an exposure device 6, a sheet feeder 7, a transfer device 8, a fixing device 9, and an output device 10. The exposure device 6 exposes the surface of each of the photoconductors 2 and forms an electrostatic latent image thereon. The sheet feeder 7 supplies a sheet P serving as a conveyed object or a recording medium to the transfer device 8. The transfer device 8 transfers the toner image formed on each of the photoconductors 2 onto the sheet P. The fixing device 9 serves as a nip forming unit or a nip forming device that fixes the toner image transferred onto the sheet P thereon. The output device 10 ejects the sheet P onto an outside of the image forming apparatus 100. The recording media include, in addition to plain paper as a sheet P, thick paper, a postcard, an envelope, thin paper, coated paper, art paper, tracing paper, an overhead projector (OHP) transparency, plastic film, prepreg, and copper foil.
The transfer device 8 includes an intermediate transfer belt 11, four primary transfer rollers 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt serving as an intermediate transferor stretched taut across a plurality of rollers. The four primary transfer rollers 12 serve as primary transferors that transfer yellow, magenta, cyan, and black toner images formed on the photoconductors 2 onto the intermediate transfer belt 11, respectively, thus forming a full color toner image on the intermediate transfer belt 11. The secondary transfer roller 13 serves as a secondary transferor that transfers the full color toner image formed on the intermediate transfer belt 11 onto the sheet P. The plurality of primary transfer rollers 12 is pressed against the photoconductors 2, respectively, via the intermediate transfer belt 11.
Accordingly, the intermediate transfer belt 11 contacts each of the photoconductors 2, forming a primary transfer nip therebetween. On the other hand, the secondary transfer roller 13 is pressed against one of the plurality of rollers across which the intermediate transfer belt 11 is stretched taut via the intermediate transfer belt 11. Thus, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.
The image forming apparatus 100 accommodates a sheet conveyance path 14 through which the sheet P fed from the sheet feeder 7 is conveyed. The sheet conveyance path 14 is provided with a timing roller pair 15 at a position between the sheet feeder 7 and the secondary transfer nip defined by the secondary transfer roller 13.
Referring to
When the image forming apparatus 100 receives an instruction to start printing, a driver disposed inside the body of the image forming apparatus 100 drives and rotates the photoconductor 2 clockwise in
When the toner images formed on the photoconductors 2 reach the primary transfer nips defined by the primary transfer rollers 12 in accordance with rotation of the photoconductors 2, the primary transfer rollers 12 transfer the toner images formed on the photoconductors 2 onto the intermediate transfer belt 11 driven and rotated counterclockwise in
The sheet P is supplied from the sheet feeder 7. The timing roller pair 15 temporarily halts the sheet P supplied from the sheet feeder 7. Thereafter, the timing roller pair 15 conveys the sheet P to the secondary transfer nip at a time when the full color toner image formed on the intermediate transfer belt 11 reaches the secondary transfer nip. The secondary transfer roller 13 transfers the full color toner image onto the sheet P. Thus, the sheet P bears the full color toner image. After the toner image is transferred onto the intermediate transfer belt 11, the cleaner 5 removes residual toner remaining on the photoconductor 2 therefrom.
The sheet P transferred with the full color toner image is conveyed to the fixing device 9 that fixes the full color toner image on the sheet P. Thereafter, the output device 10 ejects the sheet P onto the outside of the image forming apparatus 100, thus finishing a series of printing processes.
A description is provided of a construction of the fixing device 9, serving as the nip forming unit or the nip forming device, according to an embodiment of the present disclosure.
As illustrated in
The fixing belt 20 includes a tubular base layer that is made of polyimide (PI) and has an outer diameter of 25 mm and a thickness in a range of from 40 μm to 120 μm, for example. The fixing belt 20 further includes a release layer serving as an outermost surface layer. The release layer is made of fluororesin, such as perfluoroalkoxy alkane (PFA) and polytetrafluoroethylene (PTFE), and has a thickness in a range of from 5 μm to 50 μm to enhance durability of the fixing belt 20 and facilitate separation of the sheet P and a foreign substance from the fixing belt 20.
The fixing belt 20 may further include an elastic layer that is interposed between the base layer and the release layer. The elastic layer is made of rubber or the like and has a thickness in a range of from 50 μm to 500 μm. The base layer of the fixing belt 20 may be made of heat-resistant resin such as polyetheretherketone (PEEK) or metal such as nickel (Ni) and stainless used steel (SUS), instead of polyimide. The fixing belt 20 may include an inner circumferential face 20a that is coated with polyimide, PTFE, or the like to produce a sliding layer.
The pressure roller 21 has an outer diameter of 25 mm, for example. The pressure roller 21 includes a core metal 21a, an elastic layer 21b, and a release layer 21c. The core metal 21a is solid and made of iron. The elastic layer 21b is disposed on a surface of the core metal 21a. The release layer 21c coats an outer surface of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of 3.5 mm, for example. In order to facilitate separation of the sheet P and the foreign substance from the pressure roller 21, the release layer 21c that is made of fluororesin and has a thickness of approximately 40 μm, for example, is preferably disposed on the outer surface of the elastic layer 21b.
The fixing device 9 further includes a biasing member that biases the pressure roller 21 toward the fixing belt 20, pressing the pressure roller 21 against the heater 22 via the fixing belt 20. Thus, the fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The fixing device 9 further includes a driver that drives and rotates the pressure roller 21. As the pressure roller 21 rotates in the rotation direction D21, the fixing belt 20 is driven and rotated by the pressure roller 21.
The heater 22 is a laminated heater that extends in a longitudinal direction thereof throughout an entire span of the fixing belt 20 in a width direction, that is, a longitudinal direction, of the fixing belt 20. The heater 22 includes a base 30 that is platy, resistive heat generators 31 that are disposed on the base 30, and an insulating layer 32 that coats the resistive heat generators 31. The insulating layer 32 of the heater 22 contacts the inner circumferential face 20a of the fixing belt 20. The resistive heat generators 31 generate heat that is conducted to the fixing belt 20 through the insulating layer 32.
According to the embodiment, the base 30 includes a fixing belt opposed face that is disposed opposite the fixing belt 20 and the fixing nip N. The fixing belt opposed face mounts the resistive heat generators 31 and the insulating layer 32. Alternatively, the resistive heat generators 31 and the insulating layer 32 may be mounted on a heater holder opposed face of the base 30, which is disposed opposite the heater holder 23. In this case, heat generated by the resistive heat generators 31 is conducted to the fixing belt 20 through the base 30. Hence, the base 30 is preferably made of a material having an increased thermal conductivity, such as aluminum nitride. The base 30 made of the material having the increased thermal conductivity causes the resistive heat generators 31 to heat the fixing belt 20 sufficiently, even if the resistive heat generators 31 are disposed on the heater holder opposed face of the base 30.
The heater holder 23 and the stay 24 are disposed within a loop formed by the fixing belt 20. The stay 24 includes a channel made of metal. The stay 24 have both lateral ends in a longitudinal direction thereof, which are supported by side plates of the fixing device 9, respectively. Since the stay 24 supports the heater holder 23 and the heater 22 supported by the heater holder 23, in a state in which the pressure roller 21 is pressed against the fixing belt 20, the heater 22 receives pressure from the pressure roller 21 precisely to form the fixing nip N stably.
Since the heater holder 23 is subject to high temperatures by heat from the heater 22, the heater holder 23 is preferably made of a heat-resistant material. For example, if the heater holder 23 is made of heat-resistant resin having a decreased thermal conductivity, such as liquid crystal polymer (LCP), the heater holder 23 suppresses conduction of heat thereto from the heater 22, facilitating heating of the fixing belt 20.
In order to decrease a contact area where the heater holder 23 contacts the heater 22 and thereby reduce an amount of heat conducted from the heater 22 to the heater holder 23, the heater holder 23 includes projections 23a that contact the base 30 of the heater 22. According to the embodiment, the projections 23a of the heater holder 23 do not contact a part of the heater holder opposed face of the base 30, which is opposite to the resistive heat generators 31 mounted on the fixing belt opposed face of the base 30, that is, a part of the base 30, which is susceptible to temperature increase, thus decreasing the amount of heat conducted to the heater holder 23 further and causing the heater 22 to heat the fixing belt 20 efficiently.
The heater holder 23 mounts guides 26 that guide the fixing belt 20. The guides 26 are disposed upstream from and below the heater 22 and disposed downstream from and above the heater 22 in
As illustrated in
In the fixing device 9 according to the embodiment, when printing starts, the driver drives and rotates the pressure roller 21 and the fixing belt 20 starts rotation in accordance with rotation of the pressure roller 21. Since the inner circumferential face 20a of the fixing belt 20 is contacted and guided by the fixing belt opposed face 260 of each of the guides 26, the fixing belt 20 rotates stably and smoothly.
Additionally, as power is supplied to the resistive heat generators 31 of the heater 22, the heater 22 heats the fixing belt 20. In a state in which the temperature of the fixing belt 20 reaches a predetermined target temperature (e.g., a fixing temperature), as a sheet P bearing an unfixed toner image is conveyed through the fixing nip N formed between the fixing belt 20 and the pressure roller 21 in a sheet conveyance direction DP as illustrated in
A description is provided of a construction of the heater 22.
The resistive heat generators 31 are electrically connected in parallel to a pair of electrodes 34 through feeders 33. The electrodes 34 are mounted on both lateral ends of the base 30 in a longitudinal direction thereof, respectively. Each of the feeders 33 is made of a conductor having a resistance value smaller than a resistance value of the resistive heat generator 31.
The adjacent resistive heat generators 31 define the gap therebetween, that is 0.2 mm or greater, preferably 0.4 mm or greater, in view of ensuring insulation between the adjacent resistive heat generators 31. If the gap between the adjacent resistive heat generators 31 is excessively great, the fixing belt 20 is subject to temperature decrease at an opposed portion thereon that is disposed opposite the gap. Hence, the gap is 5 mm or smaller, preferably 1 mm or smaller, in view of suppressing uneven temperature of the fixing belt 20 in the longitudinal direction thereof.
The resistive heat generators 31 are made of a material having a positive temperature coefficient (PTC) property that is characterized in that the resistance value increases, that is, a heater output decreases, as the temperature increases. Accordingly, if a sheet P having a decreased width that is smaller than an entire width of the heat generating portion 35 is conveyed through the fixing nip N, for example, since the sheet P does not draw heat from the fixing belt 20 in an outboard span that is outboard from the sheet P in the width direction of the fixing belt 20, the resistive heat generators 31 in the outboard span are subject to temperature increase.
Since a constant voltage is applied to the resistive heat generators 31, when the temperature of the resistive heat generators 31 in the outboard span increases and the resistance value thereof increases, conversely, an output (e.g., a heat generating amount) from the resistive heat generators 31 decreases relatively, suppressing temperature increase of the resistive heat generators 31 that are disposed at both lateral ends of the heat generating portion 35 in a longitudinal direction thereof. Additionally, the plurality of resistive heat generators 31 is electrically connected in parallel, suppressing temperature increase in a non-conveyance span where the sheet P is not conveyed while retaining the printing speed.
Alternatively, the heat generating portion 35 may include heat generators other than the resistive heat generators 31 having the PTC property. The heat generators may be arranged in a plurality of columns in a short direction of the heater 22.
For example, the resistive heat generator 31 is produced as below. Silver-palladium (AgPd), glass powder, and the like are mixed into paste. The paste coats the base 30 by screen printing or the like. Thereafter, the base 30 is subject to firing. According to the embodiment, the resistive heat generator 31 has a resistance value of 80Ω at an ambient temperature.
Alternatively, the resistive heat generators 31 may be made of a resistive material such as a silver alloy (AgPt) and ruthenium oxide (RuO2). The feeders 33 and the electrodes 34 are made of a material prepared with silver (Ag) or silver-palladium (AgPd) by screen printing or the like.
The base 30 is preferably made of ceramic, such as alumina and aluminum nitride, or a nonmetallic material, such as glass and mica, which has an increased heat resistance and an increased insulation. According to the embodiment, the base 30 is made of alumina and has a short width of 8 mm, a longitudinal length of 270 mm, and a thickness of 1.0 mm.
Alternatively, the base 30 may include a conductive layer made of metal or the like and an insulating layer disposed on the conductive layer. The metal is preferably aluminum, stainless steel, or the like that is available at reduced costs. In order to improve evenness of heat generated by the heater 22 so as to enhance quality of an image formed on a sheet P, the base 30 may be made of a material that has an increased thermal conductivity such as copper, graphite, and graphene.
The insulating layer 32 is made of heat-resistant glass and has a thickness of 75 μm, for example. The insulating layer 32 covers the resistive heat generators 31 and the feeders 33 and insulates and protects the resistive heat generators 31 and the feeders 33 while retaining smooth sliding of the fixing belt 20 over the heater 22.
As illustrated in
The power supply circuit further includes a controller 220 that controls the amount of power supplied to the resistive heat generators 31 through the triac 210 based on temperatures of the heater 22, that are detected by the thermistors 25 serving as the temperature detectors, respectively. The controller 220 includes a microcomputer that includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input-output (I/O) interface.
According to the embodiment, the thermistors 25 serving as the temperature detectors are disposed opposite a center span of the heater 22 in the longitudinal direction thereof, that is, a minimum sheet conveyance span where a minimum size sheet P available in the fixing device 9 is conveyed, and one lateral end span of the heater 22 in the longitudinal direction thereof, respectively. The fixing device 9 further includes a thermostat 27 serving as a power interrupter that is disposed opposite one lateral end of the heater 22 in the longitudinal direction thereof. The thermostat 27 interrupts supplying power to the resistive heat generators 31 when a temperature of the resistive heat generator 31 is a predetermined temperature or higher. The thermistors 25 and the thermostat 27 contact a back face of the base 30, which is opposite to a front face of the base 30, which mounts the resistive heat generators 31. The thermistors 25 and the thermostat 27 detect the temperature of the resistive heat generators 31.
Referring to
As illustrated in
Accordingly, the resistive heat generators 31 start generating heat, heating the fixing belt 20. In step S3, the thermistor 25, that is, a center thermistor, disposed opposite the center span of the heater 22 in the longitudinal direction thereof, detects a temperature T4 of the resistive heat generator 31 disposed in the center span of the heater 22 in the longitudinal direction thereof. In step S4, based on the temperature T4 sent from the thermistor 25, that is, the center thermistor, the controller 220 controls the triac 210 to adjust the amount of power supplied to the resistive heat generators 31 so that the resistive heat generators 31 attain a predetermined temperature.
Simultaneously, in step S5, the thermistor 25, that is, a lateral end thermistor, disposed opposite the lateral end span of the heater 22 in the longitudinal direction thereof, also detects a temperature T8 of the resistive heat generator 31 disposed in the lateral end span of the heater 22 in the longitudinal direction thereof. In step S6, the controller 220 determines whether or not the temperature T8 of the resistive heat generator 31, that is detected by the thermistor 25 serving as the lateral end thermistor, is a predetermined temperature TN or higher (T8>TN). If the controller 220 determines that the temperature T8 of the resistive heat generator 31 is lower than the predetermined temperature TN (NO in step S6), the controller 220 determines that an abnormally decreased temperature (e.g., disconnection) generates and interrupts supplying power to the heater 22 in step S7. In step S8, the controller 220 causes a control panel of the image forming apparatus 100 to display an error. Conversely, if the controller 220 determines that the temperature T8 of the resistive heat generator 31, that is detected by the thermistor 25, is the predetermined temperature TN or higher (YES in step S6), the controller 220 determines that no abnormally decreased temperature generates and starts printing in step S9.
If the controller 220 does not perform temperature control based on the temperature detected by the thermistor 25, that is, the center thermistor, due to breakage, disconnection, or the like of the resistive heat generator 31, the resistive heat generator 31 disposed in the lateral end span of the heater 22 in the longitudinal direction thereof and other resistive heat generators 31 may suffer from an abnormally increased temperature. In this case, when the temperature of the resistive heat generator 31 reaches the predetermined temperature TN or higher, the controller 220 activates the thermostat 27 to interrupt supplying power to the resistive heat generators 31, preventing the resistive heat generators 31 from suffering from the abnormally increased temperature.
A description is provided of a construction of a comparative fixing device.
The comparative fixing device includes a fixing belt and a sheet separation plate disposed in proximity to the fixing belt. The sheet separation plate separates a sheet from the fixing belt. If a gap between the fixing belt and the sheet separation plate is excessively small, the sheet separation plate comes into contact with the fixing belt easily, damaging the fixing belt and resulting in formation of a faulty image.
If the gap between the fixing belt and the sheet separation plate is excessively great, the sheet passes through the gap easily and is wound around the fixing belt, causing the sheet to be jammed. Hence, the sheet separation plate is requested to be closer to the fixing belt without contacting the fixing belt.
The comparative fixing device includes a sheet separation plate mover that adjusts and optimizes the gap. However, the sheet separation plate mover includes a driver that drives the sheet separation plate and a plurality of sensors, causing the construction of the comparative fixing device to be complex and increasing costs. To address the circumstances described above of the comparative fixing device, the fixing device 9 according to the embodiments of the present disclosure optimizes a gap between an endless belt (e.g., the fixing belt 20) and a separator with a simple construction, improving separation of a conveyed object (e.g., the sheet P) from the endless belt as described below.
A description is provided of a construction of a sheet separation assembly 300 incorporated in the fixing device 9.
The heater 22 serving as a nip formation pad or a nip former and the heater holder 23 move in a horizontal direction in
The separation plate 310 extends parallel to a longitudinal direction X, that is, an axial direction, of the fixing belt 20. The separation plate 310 includes contact portions 313 disposed at both lateral ends of the separation plate 310 in a longitudinal direction thereof, respectively. The contact portions 313 are disposed outboard from a conveyance span where the sheet P is conveyed over the fixing belt 20 in the longitudinal direction thereof. The contact portions 313 contact the outer circumferential face of the fixing belt 20. As the contact portions 313 contact the outer circumferential face of the fixing belt 20 at both lateral ends of the fixing belt 20 in the axial direction thereof, respectively, the contact portions 313 restrict the gap between the separation plate 310 and the fixing belt 20 to a predetermined size.
The separation plate 310 mounts pivot restricted tabs 312 that project from both lateral ends of the separation plate 310 in the longitudinal direction X thereof, respectively. The pivot restricting hole 321 includes a first restricting portion 321a and a second restricting portion 32 lb. While the contact portions 313 contact the fixing belt 20, the contact portions 313 restrict a position of the separation plate 310 in a pivot direction thereof. Hence, the pivot restricted tab 312 does not contact the first restricting portion 321a basically.
The fixing device 9 further includes flanges 400 serving as guides that support both lateral ends of the fixing belt 20 in the longitudinal direction X thereof, respectively, such that the fixing belt 20 slides over the flanges 400. Each of the flanges 400 is a ring that is inserted into the loop formed by the fixing belt 20 at each lateral end of the fixing belt 20 in the longitudinal direction X thereof such that the inner circumferential face 20a of the fixing belt 20 slides over the flange 400. Thus, the flanges 400 guide the fixing belt 20 that rotates.
As illustrated in
However, if the fixing belt 20 is not parallel to the pressure roller 21, the fixing belt 20 may follow the pressure roller 21 and may be inclined with respect to the flange 400. Accordingly, the fixing belt 20 may rotate unstably, causing the sheet P to be jammed.
According to the embodiment, as illustrated in
For example, as illustrated in
The separation plate 310 further includes an edge portion 311 serving as a non-contact portion that does not contact the fixing belt 20. The edge portion 311 and the outer circumferential face of the fixing belt 20 produce an increased gap G1 that is not appropriate and is greater than a decreased gap G2 that is appropriate. Accordingly, the sheet P may pass through the increased gap G1, may be wound around the fixing belt 20, and may be jammed easily.
To address this circumstance, as illustrated in
As illustrated in
As illustrated in
Referring to
The separation plate 310 is made of heat-resistant metal such as stainless steel. However, since the separation plate 310 has a decreased thickness, the separation plate 310 is subject to deformation. Accordingly, as the separation plate 310 moves toward the fixing belt 20 as illustrated in
Even if the separation plate 310 does not move toward the fixing belt 20 as illustrated in
However, even if the separation plate 310 suffers from deformation (e.g., elastic deformation), the left contact portion 313 and the right contact portion 313 of the separation plate 310 contact the fixing belt 20 as illustrated in
The region T in
In order to enhance separation of the sheet P from the fixing belt 20, the fixing belt 20 has an increased curvature at an exit of the fixing nip N advantageously. For example, as illustrated in
Conversely, as illustrated in
Additionally, if the fixing belt 20 is applied with tension excessively, the fixing device 9B may not be assembled into a fixing unit properly. To address the disadvantages, each of the flanges 400 and the nip formation pad SH has a decreased size in the radial direction of the fixing belt 20 to produce backlash between the inner circumferential face 20a of the fixing belt 20 and each of the flanges 400. As a result, the fixing belt 20 suffers from limitation in increasing a curvature at the exit of the fixing nip N, causing a disadvantage in improving separation of the sheet P from the fixing belt 20. In order to overcome the disadvantages described above, the fixing device 9 according to the embodiment of the present disclosure has a construction described below.
Referring to
As illustrated in
The side plate 320 includes a recess 324 that is U-shaped. The recesses 324 support both lateral ends of a shaft of the pressure roller 21 in an axial direction thereof, respectively, such that the pressure roller 21 rotates. The side plate 320 includes the pivot restricting hole 321 that is disposed above the recess 324 in
As illustrated in
For example, the pivot restricting hole 321 includes the first restricting portion 321a and the second restricting portion 321b. The first restricting portion 321a is disposed at one end (e.g., a left end in
The pivot restricting hole 321 further includes portions other than the first restricting portion 321a and the second restricting portion 321b, that is, arcuate faces that bridge the first restricting portion 321a and the second restricting portion 321b. The pivot restricted tab 312 and each of the arcuate faces define a proper clearance therebetween. The proper clearance prevents the arcuate face from interfering with the pivot restricted tab 312 and degrading pivoting of the separation plate 310.
When the edge portion 311 of the separation plate 310 pivots in the approach direction in which the edge portion 311 moves toward the fixing belt 20, the edge portion 311 and the fixing belt 20 preferably define a gap therebetween in a range of from 0.6 mm to 1.2 mm or a range of from 0.6 mm to 1.3 mm. If the gap between the fixing belt 20 and the edge portion 311 of the separation plate 310 is excessively small, the separation plate 310 comes into contact with the fixing belt 20 easily, damaging the fixing belt 20 and resulting in formation of a faulty image. The gap of 0.6 mm between the edge portion 311 and the fixing belt 20 prevents the separation plate 310 from damaging the fixing belt 20.
If the gap between the fixing belt 20 and the edge portion 311 of the separation plate 310 is excessively great, the sheet P passes through the excessively great gap easily and is wound around the fixing belt 20, causing the sheet P to be jammed. If the gap between the edge portion 311 and the fixing belt 20 is not greater than 1.2 mm or 1.3 mm as described above, the gap prevents the sheet P from being wound around the fixing belt 20 and jammed. Alternatively, a positional relation between the pivot restricted tab 312 and the pivot restricting hole 321 may be reversed. For example, the separation plate 310 may be provided with a pivot restricted hole and the side plate 320 may mount a pivot restricting tab.
The contact portions 313 that are L-shaped are disposed at both lateral ends of the separation plate 310 in the longitudinal direction X thereof, respectively, and lower ends in
The sheet separation assembly 300 further includes spring engagements 314, spring engagements 323, and tension springs 330. The spring engagements 314 are mounted on both lateral ends of the separation plate 310 in the longitudinal direction X thereof, respectively. The spring engagement 323 is mounted on an upper end in
The tension spring 330 biases and pivots the separation plate 310 in the approach direction in which the edge portion 311 moves toward the fixing belt 20. Since the separation plate 310 is subject to deformation as described above, the tension springs 330 are preferably attached to both lateral ends of the separation plate 310 in the longitudinal direction X thereof so as to bias and pivot the separation plate 310 precisely.
As illustrated in
Referring to
As illustrated in
Even if the separation plate 310 improves separation of the sheet P, if the fixing device 9 is instructed to fix a toner image bearing toner to a leading edge of the sheet P on the sheet P by an erroneous print setting or the like, the sheet P may enter the gap between the separation plate 310 and the fixing belt 20 and may be wound around the fixing belt 20. If the sheet P is wound around the fixing belt 20 into a plurality of layers or if the sheet P creases substantially, when a user or a service engineer pulls out the sheet P, the sheet P may strike the separation plate 310, deforming the separation plate 310 or damaging the fixing belt 20.
To address this circumstance, according to the embodiment, the tension spring 330 presses the separation plate 310. Accordingly, when the sheet P is pulled out, the separation plate 310 opens against the biasing force of the tension spring 330. Thus, the separation plate 310 is immune from deformation and scratches. Additionally, the user or the service engineer pulls out the sheet P with a decreased pulling force that improves usability of the fixing device 9.
In order to decrease the pulling force, the separation plate 310 opens with an open amount, that is, a clearance between the pivot restricted tab 312 mounted on the separation plate 310 and the pivot restricting hole 321 of the side plate 320, which is greater than a pressure releasing amount with which pressure applied at the fixing nip N is released. As illustrated in
However, if the pivot restricting hole 321 is excessively great, the edge portion 311 of the separation plate 310 may come into contact with the pressure roller 21 and thereby may damage the pressure roller 21. To address this circumstance, the pivot restricting hole 321 preferably has a size that stops the separation plate 310, that pivots, at a position where the edge portion 311 of the separation plate 310 does not come into contact with the pressure roller 21. For example, when the separation plate 310 pivots in a direction in which the gap between the edge portion 311 of the separation plate 310 and the fixing belt 20 increases, the second restricting portion 321b (e.g., the right end in
Alternatively, in order to prevent the edge portion 311 from coming into contact with the pressure roller 21, the position of the support shaft 322 that supports the separation plate 310 may be adjusted to attain a layout that prevents the edge portion 311 from coming into contact with the pressure roller 21. For example, the pressure roller 21 has a diameter that is smaller than a diameter of the fixing belt 20. The pressure roller 21 has a center that is shifted from a center of the fixing belt 20 in a direction in which the pressure roller 21 separates from the separation plate 310 downward in
A description is provided of methods for applying pressure at the fixing nip N and releasing the pressure.
The method for applying pressure at the fixing nip N provides two configurations, that is, a first pressurizing configuration and a second pressurizing configuration. In the first pressurizing configuration, the heater holder 23 disposed within the loop formed by the fixing belt 20 is secured. The pressure roller 21 comes into contact with and separates from the fixing belt 20. The pressure roller 21 is biased toward the fixing belt 20. In the second pressurizing configuration, the pressure roller 21 (e.g., the core metal 21a of the pressure roller 21) is secured. The fixing belt 20 comes into contact with and separates from the pressure roller 21. The fixing belt 20 is biased toward the pressure roller 21.
The second pressurizing configuration is more preferable than the first pressurizing configuration because the user or the service engineer pulls out the jammed sheet P with a smaller pulling force so as to remove the sheet P. For example, in the second pressurizing configuration, the fixing belt 20 separates from the pressure roller 21 to release pressure applied at the fixing nip N. The separation plate 310 also separates from the fixing belt 20. Accordingly, the tension spring 330 displaces with a decreased displacement amount, allowing the user or the service engineer to pull out the sheet P with the smaller pulling force.
Additionally, when the fixing belt 20 is biased toward the pressure roller 21, the separation plate 310 produces a clearance in the pivot restricting hole 321, that is smaller than a clearance in the pivot restricting hole 321, that is produced when the fixing belt 20 releases pressure applied at the fixing nip N. Accordingly, when the fixing belt 20 releases pressure applied at the fixing nip N, the pivot restricting hole 321 restricts clockwise pivoting of the separation plate 310 in
If the user or the service engineer does not see the jammed sheet P through the fixing nip N clearly, the user or the service engineer does not pull out the sheet P readily. If the gap between the fixing belt 20 and the edge portion 311 of the separation plate 310 increases, the user or the service engineer rotates the pressure roller 21 and the fixing belt 20 backward readily to move the sheet P upstream from the fixing nip N and downward in
When the fixing belt 20 rotates backward to move the jammed sheet P, the fixing belt 20 draws a trajectory that is different from a trajectory drawn when the fixing belt 20 rotates forward in the rotation direction D20 depicted in
A description is provided of an inner circumference usage rate.
The fixing belt 20 preferably has an inner circumference usage rate in a range of from 95.0 percent to 99.8 percent (see Japanese Unexamined Patent Application Publication No. 2019-082733). The inner circumference usage rate is calculated as below. As illustrated in
Ur=[(L−W)/L]×100 (1)
In the formula (1), Ur represents an inner circumference usage rate in percent. L represents a circumference of the fixing belt 20. The circumference L of the fixing belt 20 defines an entire length of the cut portion that is shaded in
The inner circumference usage rate defines a rate of a circumference of the flange 400 serving as the guide with respect to the circumference L of the fixing belt 20. The inner circumference usage rate is used as an index for assembly (e.g., engagement). However, the inner circumference usage rate is to be improved as an index for skew of the fixing belt 20 and separation of the sheet P from the fixing belt 20. For example, as illustrated in
To address this circumstance, the slack of the fixing belt 20, which is situated downstream from the fixing nip N in the sheet conveyance direction DP, is measured directly with a height gauge to obtain a slack rate.
Referring to
As illustrated in
The height gauge measures a height coordinate of the top T20 of the fixing belt 20, that is pressed against the flange 400 as illustrated in section (b) in
Sr=[Sa/Di]×100 (2)
In the formula (2), Sr represents the slack rate in percent. Sa represents the slack amount. Di represents the diameter of the fixing belt 20.
If the slack rate is excessively small, the fixing device 9 is not assembled easily. As the fixing belt 20 slides over the flange 400, the fixing belt 20 is subject to abrasion. If the slack rate is excessively great, the fixing belt 20 is subject to inclination. Additionally, the fixing belt 20 has a decreased curvature at the exit of the fixing nip N, degrading separation of the sheet P from the fixing belt 20 and installation of the separation plate 310 in the fixing device 9. To address this circumstance, the slack rate is in a range of from 0.1 percent to 10.0 percent, preferably in a range of from 0.5 percent to 5.0 percent.
Referring to
As illustrated in
The fixing belt 20 is an endless belt. The pressure roller 21 contacts the outer circumferential face of the fixing belt 20 to form the fixing nip N between the fixing belt 20 and the pressure roller 21. The heater 22A heats the fixing belt 20. The heater holder 23 holds or supports the heater 22A. The stay 24 supports the heater holder 23.
The thermistor 25 detects a temperature of the first thermal conductor 28. The fixing belt 20, the pressure roller 21, the heater 22A, the heater holder 23, the stay 24, and the first thermal conductor 28 extend in a longitudinal direction that is perpendicular to a paper surface in
The fixing device 9C according to the embodiment incorporates the first thermal conductor 28 that suppresses temperature decrease at a gap between adjacent resistive heat generators 31A of the heater 22A and thereby suppresses uneven temperature of the fixing belt 20 in the longitudinal direction thereof in which the resistive heat generators 31A are arranged.
A description is provided of a construction of the first thermal conductor 28 in detail.
As illustrated in
The stay 24 includes two perpendicular portions 24a that extend in a thickness direction of the heater 22A and the like. Each of the perpendicular portions 24a has a contact face 24a1 that contacts the heater holder 23, supporting the heater holder 23, the first thermal conductor 28, and the heater 22A. The contact faces 24a1 are disposed outboard from the resistive heat generators 31A in an orthogonal direction (e.g., a vertical direction in
As illustrated in
The heater holder 23 includes a recess 23b into which the first thermal conductor 28 is fitted. The heater 22A is attached to the heater holder 23 from above the first thermal conductor 28. Thus, the heater holder 23 and the heater 22A sandwich and hold the first thermal conductor 28. According to the embodiment, the first thermal conductor 28 has a length in the longitudinal direction thereof, which is equivalent to a length of the heater 22A in the longitudinal direction thereof.
The heater holder 23 includes side walls 23b1, serving as arrangement direction restrictors, that are disposed at both lateral ends of the heater holder 23 in the longitudinal direction thereof (e.g., an arrangement direction in which the resistive heat generators 31A are arranged), respectively, and define the recess 23b. The side walls 23b1 restrict motion of the first thermal conductor 28 and the heater 22A in the longitudinal direction thereof. Thus, the side walls 23b1 restrict shifting of the first thermal conductor 28 in the arrangement direction in which the resistive heat generators 31A are arranged inside the fixing device 9C, improving efficiency in conduction of heat in a target span in the arrangement direction, that is, the longitudinal direction of the first thermal conductor 28. The heater holder 23 further includes side walls 23b2, serving as orthogonal direction restrictors, that are disposed at both ends of the heater holder 23 in an orthogonal direction perpendicular to the longitudinal direction thereof (e.g., the arrangement direction in which the resistive heat generators 31A are arranged), respectively, and define the recess 23b. The side walls 23b2 restrict motion of the first thermal conductor 28 and the heater 22A in the orthogonal direction.
The first thermal conductor 28 may extend in a span other than a span in which the first thermal conductor 28 extends in the longitudinal direction thereof as illustrated in
As the pressure roller 21 applies pressure to the heater 22A, the heater 22A and the heater holder 23 sandwich a first thermal conductor (e.g., the first thermal conductors 28 and 28A) such that the first thermal conductor contacts the heater 22A and the heater holder 23. As the first thermal conductor contacts the heater 22A, the first thermal conductor conducts heat generated by the heater 22A in the longitudinal direction X thereof with improved efficiency.
The first thermal conductor is disposed opposite gaps B between the adjacent resistive heat generators 31A arranged in the longitudinal direction X of the heater 22A. Thus, the first thermal conductor improves efficiency in conduction of heat at the gaps B, increases an amount of heat conducted to the gaps B in the longitudinal direction X of the heater 22A, and increases the temperature of the heater 22A at the gaps B arranged in the longitudinal direction X of the heater 22A, thus suppressing uneven temperature of the heater 22A in the longitudinal direction X thereof.
Accordingly, the first thermal conductor suppresses uneven temperature of the fixing belt 20 in the longitudinal direction X thereof. Consequently, the fixing belt 20 suppresses uneven fixing and uneven gloss of a toner image fixed on a sheet P.
The heater 22A does not increase an amount of heat generation to attain sufficient fixing performance at the gaps B, causing the fixing device 9C to save energy. The first thermal conductor extends throughout an entire span of the heat generating portion 35S in the longitudinal direction X thereof. Accordingly, the first thermal conductor improves efficiency in conduction of heat of the heater 22A in an entirety of a main heating span of the heater 22A disposed opposite an imaging span of a toner image formed on a sheet P conveyed through the fixing nip N. Consequently, the first thermal conductor suppresses uneven temperature of the heater 22A and the fixing belt 20 in the longitudinal direction X thereof.
According to the embodiment, the first thermal conductor (e.g., the first thermal conductors 28 and 28A) is coupled to the resistive heat generators 31A having the PTC property described above, suppressing overheating of the fixing belt 20 in the non-conveyance span where a sheet P having a decreased size is not conveyed effectively. For example, the PTC property suppresses an amount of heat generated by the resistive heat generators 31A in the non-conveyance span. Additionally, the first thermal conductor efficiently conducts heat from the non-conveyance span on the fixing belt 20 that suffers from temperature increase to the conveyance span on the fixing belt 20 efficiently, suppressing overheating of the fixing belt 20 in the non-conveyance span effectively.
Since the heater 22A generates heat in a decreased amount at the gap B between the adjacent resistive heat generators 31A, the heater 22A has a decreased temperature also in a periphery of the gap B. To address this circumstance, the first thermal conductor is preferably disposed also in the periphery of the gap B. According to the embodiment, the first thermal conductor extends throughout the entire span of the heat generating portion 35S in the longitudinal direction X thereof. Accordingly, the first thermal conductor suppresses uneven temperature of the heater 22A and the fixing belt 20 in the longitudinal direction X thereof more effectively.
A description is provided of a construction of a fixing device 9D according to an embodiment of the present disclosure.
As illustrated in
Specifically, the second thermal conductors 36 are superimposed on the first thermal conductor 28. Unlike
Each of the second thermal conductors 36 is made of a material having a thermal conductivity greater than a thermal conductivity of the base 30. For example, each of the second thermal conductors 36 is made of graphene or graphite. According to the embodiment, the second thermal conductor 36 is a graphite sheet having a thickness of 1 mm. Alternatively, the second thermal conductor 36 may be a plate made of aluminum, copper, silver, or the like.
As illustrated in
The second thermal conductor 36 and the heater holder 23A define a gap therebetween at both lateral ends of the second thermal conductor 36 in the longitudinal direction of the heater holder 23A. Thus, the second thermal conductor 36 suppresses conduction of heat therefrom to the heater holder 23A, causing the heater 22A to heat the fixing belt 20 efficiently.
As illustrated in
The fixing device 9D according to the embodiment includes, in addition to the first thermal conductor 28, the second thermal conductors 36 each of which is disposed opposite the gap B and overlaps at least a part of the adjacent resistive heat generators 31A in the longitudinal direction X of the heater 22A. The second thermal conductors 36 improve efficiency in conduction of heat at the gaps B in the longitudinal direction X of the heater 22A in which the resistive heat generators 31A are arranged, suppressing uneven temperature of the heater 22A in the longitudinal direction X thereof.
Unlike the embodiment described above, according to an embodiment of the present disclosure, each of the first thermal conductor 28 and the second thermal conductors 36 is made of a graphene sheet. Hence, each of the first thermal conductor 28 and the second thermal conductors 36 has an enhanced thermal conductivity in a predetermined direction along a surface of the graphene sheet, that is, the longitudinal direction X, not a thickness direction of the graphene sheet. Accordingly, each of the first thermal conductor 28 and the second thermal conductors 36 suppresses uneven temperature of the heater 22A and the fixing belt 20 in the longitudinal direction X thereof effectively.
For example, the first thermal conductor 28 or the second thermal conductor 36 is made of graphite. Accordingly, the first thermal conductor 28 or the second thermal conductor 36 attains an efficiency in conduction of heat in the longitudinal direction X, which is greater than an efficiency in conduction of heat in a thickness direction, that is, the laminating direction in which the stay 24, the heater holder 23A, the second thermal conductor 36, the first thermal conductor 28, and the heater 22A are arranged, thus suppressing conduction of heat to the heater holder 23A. Consequently, the first thermal conductor 28 or the second thermal conductor 36 suppresses uneven temperature of the heater 22A in the longitudinal direction X thereof efficiently. Additionally, the first thermal conductor 28 or the second thermal conductor 36 minimizes heat conducted to the heater holder 23A. The first thermal conductor 28 or the second thermal conductor 36 that is made of graphite attains enhanced heat resistance that inhibits oxidation at approximately 700 degrees Celsius.
The graphite sheet has a physical property and a dimension that are adjusted properly according to a function of the first thermal conductor 28 or the second thermal conductor 36. For example, the graphite sheet is made of graphite having enhanced purity or single crystal graphite. The graphite sheet has an increased thickness to enhance anisotropic thermal conduction.
In order to perform high speed fixing, the fixing device 9D employs the graphite sheet having a decreased thickness to decrease thermal capacity of the fixing device 9D. If the fixing nip N and the heater 22A have an increased width in the longitudinal direction X thereof, the first thermal conductor 28 or the second thermal conductor 36 also has an increased width in the longitudinal direction X thereof.
In view of increasing mechanical strength, the graphite sheet preferably has a number of layers that is not smaller than 11 layers. The graphite sheet may include a part constructed of a single layer and another part constructed of a plurality of layers.
The second thermal conductor 36 is disposed opposite the gap B between the adjacent resistive heat generators 31A and an enlarged gap region D encompassing the periphery of the gap B depicted in
The heater 22B further includes a second thermal conductor 36B that is disposed within a span of the resistive heat generator 31A in the orthogonal direction Y. The heater 22B further includes a second thermal conductor 36C that spans a part of the gap B.
Accordingly, the heater holder 23A contacts the first thermal conductor 28 with a decreased contact area, thus suppressing conduction of heat from the first thermal conductor 28 to the heater holder 23A and causing the heater 22A to heat the fixing belt 20 efficiently. On a cross section that crosses a longitudinal direction of the fixing device 9E and is provided with the second thermal conductor 36, the second thermal conductor 36 contacts the heater holder 23A as illustrated in
According to the embodiment, the retracted portion 23c spans an entirety of the resistive heat generator 31A in the orthogonal direction (e.g., a vertical direction in
According to the embodiments described above, the second thermal conductor 36 is provided separately from the first thermal conductor 28. Alternatively, the fixing device 9E may have other configuration. For example, the first thermal conductor 28 may include an opposed portion that is disposed opposite the gap B and has a thickness greater than a thickness of an outboard portion of the first thermal conductor 28, which is other than the opposed portion.
As illustrated in
Like the resistive heat generators 31 of a heater 22C described below with reference to
To address this circumstance, according to the embodiment, the first thermal conductor 89 suppresses temperature decrease in the gap region of the fixing belt 61 and therefore suppresses uneven temperature of the fixing belt 61 in the longitudinal direction thereof.
A description is provided of a construction of a first thermal conductor 89B according to an embodiment of the present disclosure as a variation of the first thermal conductor 89 in detail.
As illustrated in
The stay 65 includes two perpendicular portions 65a that extend in a thickness direction of the heater 63A and the like. Each of the perpendicular portions 65a has a contact face 65a1 that contacts the heater holder 64, supporting the heater holder 64, the first thermal conductor 89B, and the heater 63A. The contact faces 65a1 are disposed outboard from the resistive heat generators 56A in the orthogonal direction Y perpendicular to the longitudinal direction X depicted in
As illustrated in
The first thermal conductor 89B is fitted to a recess 64b of the heater holder 64. The heater 63A is attached to the heater holder 64 from above the first thermal conductor 89B. Thus, the heater holder 64 and the heater 63A sandwich and hold the first thermal conductor 89B. According to the embodiment, the first thermal conductor 89B has a length in the longitudinal direction X thereof, which is equivalent to a length of the heater 63A in the longitudinal direction X thereof.
The recess 64b includes side walls 64b1 that extend in the orthogonal direction Y perpendicular to the longitudinal direction X of the first thermal conductor 89B. The side walls 64b1 serving as longitudinal direction restrictors, respectively, restrict motion of the first thermal conductor 89B and the heater 63A in the longitudinal direction X thereof. Thus, the side walls 64b1 restrict shifting of the first thermal conductor 89B in the longitudinal direction X thereof inside the fixing device 60, improving efficiency in conduction of heat in a target span in the longitudinal direction X of the first thermal conductor 89B. The heater holder 64 further includes side walls 64b2 that extend in the longitudinal direction X of the recess 64b. The side walls 64b2, serving as orthogonal direction restrictors, respectively, restrict motion of the first thermal conductor 89B and the heater 63A in the orthogonal direction Y perpendicular to the longitudinal direction X of the first thermal conductor 89B.
The first thermal conductor 89B may extend in a span other than a span in which the first thermal conductor 89B extends in the longitudinal direction X thereof as illustrated in
Alternatively, as illustrated in
The first thermal conductor 89C may span a part of the resistive heat generator 56A in the orthogonal direction Y. As illustrated in
A state in which the first thermal conductor 89A bridges the adjacent resistive heat generators 56 denotes a state in which the first thermal conductor 89A overlaps the adjacent resistive heat generators 56 at least partially in the longitudinal direction X. As illustrated in
As illustrated in
The first thermal conductor 89B is disposed opposite the gaps B arranged in the longitudinal direction X of the heater 63A. Thus, the first thermal conductor 89B improves efficiency in conduction of heat at the gaps B, increases an amount of heat conducted to the gaps B, and increases the temperature of the heater 63A at the gaps B.
Accordingly, the first thermal conductor 89B suppresses uneven temperature of the heater 63A in the longitudinal direction X thereof, thereby suppressing uneven temperature of the fixing belt 61 in the longitudinal direction X thereof. Consequently, the fixing belt 61 suppresses uneven fixing and uneven gloss of a toner image fixed on a sheet P.
The heater 63A does not increase an amount of heat generation to attain sufficient fixing performance at the gaps B, causing the fixing device 60 to save energy. For example, if the fixing device 60 incorporates the first thermal conductor 89B or 89C that spans an entire region where the resistive heat generators 56A are arranged in the longitudinal direction X, the first thermal conductor 89B or 89C improves efficiency in conduction of heat of the heater 63A in an entirety of a main heating span of the heater 63A disposed opposite the imaging span of a toner image formed on a sheet P conveyed through the fixing nip N. Accordingly, the first thermal conductor 89B or 89C suppresses uneven temperature of the heater 63A and the fixing belt 61 in the longitudinal direction X thereof.
The first thermal conductor 89B or 89C is coupled to the resistive heat generators 56A having the PTC property, suppressing overheating of the fixing belt 61 in the non-conveyance span where the sheet P having the decreased size is not conveyed more effectively. The PTC property defines a property in which the resistance value increases as the temperature increases, for example, a heater output decreases under a given voltage. For example, the resistive heat generator 56 or 56A having the PTC property suppresses an amount of heat generated by the resistive heat generator 56 or 56A in the non-conveyance span effectively. Additionally, the first thermal conductor 89B or 89C conducts heat from the non-conveyance span on the fixing belt 61 that suffers from temperature increase to the conveyance span on the fixing belt 61 efficiently. The PTC property and heat conduction of the resistive heat generator 56 or 56A attain a synergistic effect that suppresses overheating of the fixing belt 61 in the non-conveyance span effectively.
Since the heater 63 or 63A generates heat in a decreased amount at the gap B, the heater 63 or 63A has a decreased temperature also in the periphery of the gap B. To address this circumstance, the first thermal conductor 89A is preferably disposed in the periphery of the gap B. For example, as illustrated in
A description is provided of a construction of the fixing device 60 according to an embodiment of the present disclosure.
As illustrated in
Specifically, the second thermal conductors 90 are superimposed on the first thermal conductor 89B. Like the fixing device 9C depicted in
The second thermal conductors 90 are made of a material having a thermal conductivity greater than a thermal conductivity of the base 55. For example, the second thermal conductors 90 are made of graphene or graphite. According to the embodiment, each of the second thermal conductors 90 is a graphite sheet having a thickness of 1 mm. Alternatively, each of the second thermal conductors 90 may be a plate made of aluminum, copper, silver, or the like.
As illustrated in
The second thermal conductor 90 and the heater holder 64 define clearances therebetween at both lateral ends of the second thermal conductor 90 in the longitudinal direction X. The clearances suppress conduction of heat from the second thermal conductor 90 to the heater holder 64, causing the heater 63A to heat the fixing belt 61 efficiently.
As illustrated in
The fixing device 60 according to the embodiment includes the second thermal conductors 90 in addition to the first thermal conductor 89B. The second thermal conductor 90 is disposed opposite the gap B and overlaps at least a part of the adjacent resistive heat generators 56A in the longitudinal direction X. The second thermal conductor 90 further improves efficiency in conduction of heat at the gap B in the longitudinal direction X, suppressing uneven temperature of the heater 63A in the longitudinal direction X thereof more effectively. As illustrated in
Accordingly, the first thermal conductor 89 and the second thermal conductor 90 improve efficiency in conduction of heat at the gap B compared to an outboard region of the heater 63, which is other than the gap B.
Each of the first thermal conductors 89, 89A, 89B, and 89C and the second thermal conductor 90 may be a graphene sheet. In this case, each of the first thermal conductors 89, 89A, 89B, and 89C and the second thermal conductor 90 has an enhanced thermal conductivity in a predetermined direction along a surface of the graphene sheet, that is, the longitudinal direction X, not a thickness direction of the graphene sheet. Accordingly, each of the first thermal conductors 89, 89A, 89B, and 89C and the second thermal conductor 90 suppresses uneven temperature of the heaters 63 and 63A and the fixing belt 61 in the longitudinal direction X thereof effectively. Each of the first thermal conductors 89, 89A, 89B, and 89C and the second thermal conductor 90 may be a graphite sheet. A description of a configuration of each of the graphene sheet and the graphite sheet is provided below with reference to
The second thermal conductor 90 is disposed opposite the gap B between the adjacent resistive heat generators 56A and the enlarged gap region D depicted in
The second thermal conductor 90B is disposed within a span of the resistive heat generator 56A in the orthogonal direction Y. The second thermal conductor 90C spans a part of the gap B.
A description is provided of a construction of a fixing device 60A according to an embodiment of the present disclosure.
As illustrated in
The retracted portion 64c is disposed at a part of the recess 64b, which is outboard from a portion of the recess 64b, which is placed with the second thermal conductor 90, in the longitudinal direction X of the heater holder 64A.
Accordingly, the heater holder 64A contacts the first thermal conductor 89B with a minimum contact area, suppressing conduction of heat from the first thermal conductor 89B to the heater holder 64A and causing the heater 63A to heat the fixing belt 61 efficiently. On a cross section that crosses a longitudinal direction of the fixing device 60A and is provided with the second thermal conductor 90, the second thermal conductor 90 contacts the heater holder 64A like in the fixing device 60 according to the embodiment depicted in
The fixing device 60A according to the embodiment depicted in
The fixing device 60A according to the embodiment includes the second thermal conductor 90 that is provided separately from the first thermal conductor 89B. Alternatively, the fixing device 60A may have other configuration. For example, the first thermal conductor 89B may include an opposed portion that is disposed opposite the gap B and has a thickness greater than a thickness of an outboard portion of the first thermal conductor 89B, which is other than the opposed portion. Thus, the first thermal conductor 89B also achieves a function of the second thermal conductor 90.
The above describes the embodiments of the present disclosure applied to a fixing device (e.g., the fixing devices 9, 9A, 9B, 9C, 9D, 9E, 60, and 60A) as one example of a belt type heating device including a nip forming device. However, application of the embodiments of the present disclosure is not limited to the fixing device. Alternatively, the embodiments of the present disclosure may be applied to a dryer that dries liquid such as ink applied on a sheet, a laminator that bonds film as a coating member onto a surface of a sheet by thermocompression, and a heating device such as a heat sealer that bonds sealing portions of a packaging material by thermocompression. The embodiments of the present disclosure are also applied to a nip forming device that does not incorporate a heat source such as a heater.
With reference to
Graphene is thin powder. As illustrated in
The graphene sheet may contain impurities in the single layer of carbon atoms or may have a fullerene structure. The fullerene structure is generally recognized as a polycyclic compound constructed of an identical number of carbon atoms bonded to form a cage with fused rings of five and six atoms. For example, the fullerene structure is other closed cage structure formed of fullerene C60, C70, and C80 or 3-coordinated carbon atoms.
The graphene sheet is artificial and is produced by chemical vapor deposition (CVD), for example. The graphene sheet is commercially available. A size and a thickness of the graphene sheet and a number of layers and the like of the graphite sheet described below are measured with a transmission electron microscope (TEM), for example.
Graphite is constructed of stacked layers of graphene and is highly anisotropic in thermal conduction. As illustrated in
In the crystalline structure, adjacent carbon atoms in the layer are bonded with each other by a covalent bond. Bonding between layers of carbon atoms defines the van der Waals bond. The covalent bond achieves bonding greater than bonding of the van der Waals bond. Graphite is highly anisotropic with bonding within the layer and bonding between the layers. For example, a first thermal conductor (e.g., the first thermal conductors 89, 89A, 89B, and 89C) or a second thermal conductor (e.g., the second thermal conductors 90, 90A, 90B, and 90C) is made of graphite. Accordingly, the first thermal conductor or the second thermal conductor attains an efficiency in conduction of heat in the longitudinal direction X, which is greater than an efficiency in conduction of heat in a thickness direction, that is, a laminating direction (e.g., the horizontal direction in
Consequently, the first thermal conductor or the second thermal conductor suppresses uneven temperature of a heater (e.g., the heaters 63 and 63A) in the longitudinal direction X thereof efficiently. Additionally, the first thermal conductor or the second thermal conductor minimizes heat conducted to the heater holder. The first thermal conductor or the second thermal conductor that is made of graphite attains enhanced heat resistance that inhibits oxidation at approximately 700 degrees Celsius.
The graphite sheet has a physical property and a dimension that are adjusted properly according to a function of the first thermal conductor or the second thermal conductor. For example, the graphite sheet is made of graphite having enhanced purity or single crystal graphite. The graphite sheet has an increased thickness to enhance anisotropic thermal conduction.
In order to perform high speed fixing, the fixing devices 60 and 60A employ the graphite sheet having a decreased thickness to decrease thermal capacity of the fixing devices 60 and 60A. If the fixing nip N and the heater 63A have an increased width in the longitudinal direction X thereof, the first thermal conductor or the second thermal conductor also has an increased width in the longitudinal direction X thereof.
In view of increasing mechanical strength, the graphite sheet preferably has a number of layers that is not smaller than 11 layers. The graphite sheet may include a part constructed of a single layer and another part constructed of a plurality of layers.
Referring to
Referring to
The fixing device 9F includes the thermistors 25 disposed at a position different from a position of the thermistors 25 depicted in
According to the embodiment, the thermistors 25 are disposed upstream from a center NA of the fixing nip N in the rotation direction D20 of the fixing belt 20. In other words, the thermistors 25 are disposed at the entry to the fixing nip N. Since a sheet P draws heat from the fixing belt 20 at the entry to the fixing nip N easily, the thermistors 25 detect a temperature of the heater 22 at the entry to the fixing nip N, thus achieving a fixing property of fixing a toner image on the sheet P properly and suppressing fixing offset effectively.
Referring to
The fixing device 9G includes a pressurization roller 44 disposed opposite the pressure roller 21 via the fixing belt 20. The pressurization roller 44 serves as an opposed rotator disposed opposite the fixing belt 20 serving as a rotator. The pressurization roller 44 rotates in accordance with rotation of the fixing belt 20. The pressurization roller 44 and the heater 22 sandwich the fixing belt 20 so that the heater 22 heats the fixing belt 20.
Within the loop formed by the fixing belt 20 is a nip formation pad 45 that is disposed opposite the pressure roller 21 via the fixing belt 20. The stay 24 supports the nip formation pad 45. The nip formation pad 45 and the pressure roller 21 sandwich the fixing belt 20 and define the fixing nip N.
Referring to
The fixing device 9H does not include the pressurization roller 44. In order to attain a contact length for which the heater 22 contacts the fixing belt 20 in the circumferential direction thereof, the heater 22 is curved into an arc in cross section that corresponds to a curvature of the fixing belt 20. Other construction of the fixing device 9H is equivalent to the construction of the fixing device 9G depicted in
Referring to
The fixing device 9I includes a heating assembly 92, a fixing roller 93 serving as a fixing rotator, and a pressure assembly 94 serving as an opposed rotator.
The heating assembly 92 includes the heater 22, the heater holder 23, and the stay 24 that are described in the embodiments above and a heating belt 120 serving as a rotator. The fixing roller 93 serves as an opposed rotator disposed opposite the heating belt 120 serving as the rotator. The fixing roller 93 rotates in accordance with rotation of the heating belt 120. The fixing roller 93 includes a core metal 93a that is solid and made of iron, an elastic layer 93b that is disposed on a surface of the core metal 93a, and a release layer 93c that coats an outer surface of the elastic layer 93b.
The pressure assembly 94 is disposed opposite the heating assembly 92 via the fixing roller 93. The pressure assembly 94 includes a nip formation pad 95, a stay 96, and a pressure belt 97. The pressure belt 97 rotates and is formed into a loop within which the nip formation pad 95 and the stay 96 are disposed. The heating belt 120 and the fixing roller 93 define a heating nip N1 therebetween. The pressure belt 97 and the fixing roller 93 define a fixing nip N2 therebetween. As a sheet P is conveyed through the fixing nip N2, the fixing roller 93 heated at the heating nip N1 and the pressure belt 97 fix a toner image formed on the sheet P thereon under heat and pressure.
Also in the fixing devices 9G, 9H, and 9I depicted in
Application of the technology of the present disclosure is not limited to the fixing devices (e.g., the fixing devices 9, 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H, 9I, 60, and 60A) according to the embodiments described above. For example, the technology of the present disclosure is also applied to a heater such a dryer that dries ink applied onto a sheet. Further, the technology of the present disclosure is also applied to a heater such as a thermocompression bonding device including a laminator and a heat sealer. The laminator bonds film as a coating member onto a surface of a sheet by thermocompression. The heat sealer bonds sealing portions of a packaging material by thermocompression. Accordingly, the heater heats the opposed portion of the rotator, which is disposed opposite the gap B, sufficiently.
Application of the technology of the present disclosure is not limited to the color image forming apparatus 100 depicted in
The scanner 51 reads an image on an original Q into image data. The sheet feeder 7 loads the plurality of sheets P and feeds the sheets P to a conveyance path one by one. The timing roller pair 15 conveys the sheet P conveyed through the conveyance path to the image forming device 50.
The image forming device 50 forms a toner image on the sheet P. For example, the image forming device 50 includes the photoconductive drum, a charging roller, an exposure device, a developing device, a replenishing device, a transfer roller, a cleaner, and a discharger. The toner image is a reproduction of the image on the original Q, for example.
The fixing device 9J fixes the toner image on the sheet P under heat and pressure. The sheet P bearing the fixed toner image is conveyed to the output device 10 by a conveyance roller and the like. The output device 10 ejects the sheet P onto an outside of the image forming apparatus 100A.
A description is provided of a construction of the fixing device 9J according to an embodiment of the present disclosure.
A description of a construction of the fixing device 9J, which is common to the fixing device 9 depicted in
As illustrated in
The fixing belt 20 includes the base layer made of polyimide and the release layer and does not include the elastic layer. The release layer is heat-resistant film made of fluororesin, for example. The fixing belt 20 has an outer diameter of approximately 24 mm.
The pressure roller 21 includes the core metal 21a, the elastic layer 21b, and the release layer 21c. The pressure roller 21 has an outer diameter in a range of from 24 mm to 30 mm. The elastic layer 21b has a thickness in a range of from 3 mm to 4 mm.
The heater 22C includes a base layer, a heat insulation layer, a conductor layer including a resistive heat generator, and an insulating layer. The heater 22C has a total thickness of 1 mm. The heater 22C has a length of 13 mm in the sheet conveyance direction DP, that is, the orthogonal direction Y depicted in
As illustrated in
The heater 22C further includes three heat generating portions 35A, 35B, and 35C each of which is constructed of the resistive heat generators 31. The heat generating portions 35A and 35C serve as lateral end heaters that are disposed opposite and heat both lateral end spans of the fixing belt 20 in the longitudinal direction thereof, respectively. The heat generating portion 35B serves as a center heater that is disposed opposite and heats the center span of the fixing belt 20 in the longitudinal direction thereof. As the electrodes 34A and 34B are energized, the heat generation portions 35A and 35C generate heat. As the electrodes 34A and 34C are energized, the heat generation portion 35B generates heat. For example, in order to fix a toner image on a sheet P having a decreased size, the heat generation portion 35B generates heat. In order to fix a toner image on a sheet P having an increased size, the heat generation portions 35A, 35B, and 35C generate heat.
As illustrated in
The heater holder 23 mounts the guides 26. The heater holder 23 is made of LCP.
As illustrated in
In a state in which the connector 160 sandwiches and holds the heater 22C and the heater holder 23, as the contact terminals of the connector 160 contact and press against the electrodes 34A, 34B, and 34C of the heater 22C, the heat generating portions 35A, 35B, and 35C are electrically connected to a power supply disposed in the image forming apparatus 100A through the connector 160. Thus, the power supply is ready to supply power to the heat generating portions 35A, 35B, and 35C. At least a part of each of the electrodes 34A, 34B, and 34C is not coated with the insulating layer and is exposed so that each of the electrodes 34A, 34B, and 34C is coupled to the connector 160.
The fixing device 9J further includes a flange 53 that is disposed on each lateral end of the fixing belt 20 in the longitudinal direction X thereof. The flange 53 contacts the inner circumferential face 20a of the fixing belt 20 depicted in
The connector 160 is attached to the heater 22C and the heater holder 23 in the orthogonal direction Y perpendicular to the longitudinal direction X of the heater 22C in which the resistive heat generators 31 are arranged. Alternatively, in order to attach the connector 160 to the heater holder 23, one of the connector 160 and the heater holder 23 may include a projection that engages a recess disposed in another one of the connector 160 and the heater holder 23 such that the projection moves inside the recess relatively. The connector 160 is attached to one lateral end of the heater 22C and the heater holder 23 in the longitudinal direction X of the heater 22C in which the resistive heat generators 31 are arranged. The one lateral end of the heater 22C and the heater holder 23 is opposite to another lateral end of the heater 22C and the heater holder 23 to which the driver (e.g., a motor) that drives the pressure roller 21 is coupled.
As illustrated in
The thermostats 27 are disposed opposite the inner circumferential face 20a of the fixing belt 20 at a position in proximity to the center line CL and a position in another lateral end of the fixing belt 20 in the longitudinal direction X thereof, respectively. If the thermostat 27 detects a temperature of the fixing belt 20, that is higher than a preset threshold, the thermostat 27 breaks power to the heater 22C.
The flanges 53 contact and support both lateral ends of the fixing belt 20 in the longitudinal direction X thereof, respectively. Each of the flanges 53 is made of LCP.
As illustrated in
Also in the fixing device 9J depicted in
An image forming apparatus that forms a monochrome toner image with toner in a single color is less susceptible to hot offset compared to an image forming apparatus that forms a color toner image with toners in a plurality of colors. Hence, like in the embodiments of the present disclosure, even if the controller 220 controls the heater 22C based on a detection result provided by the temperature detecting element that is disposed opposite the gap B between the adjacent resistive heat generators 31, the image forming apparatus that uses the toner in the single color is less susceptible to hot offset advantageously.
The above describes the embodiments of the present disclosure. However, the technology of the present disclosure is not limited to the embodiments described above and is modified into variations. For example, the separation plate 310 depicted in
The separation plate 310 may be secured such that the separation plate 310 does not move. For example, the separation plate 310 may be modified as long as the separation plate 310 includes the edge portion 311 and the contact portions 313. The edge portion 311 contacts the sheet P serving as the conveyed object and does not contact the fixing belt 20. As the contact portions 313 contact the fixing belt 20, the contact portions 313 retain the gap having a predetermined size between the edge portion 311 and the fixing belt 20.
According to the embodiments described above, the fixing belt 20 or 61 of the fixing device 9, 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H, 9I, 9J, 60, or 60A is used as an endless belt. Alternatively, the endless belt may be a photoconductor belt. For example, the separation plate 310 may be installed in an image forming apparatus that transfers a toner image borne on the photoconductor belt serving as an image bearer onto a recording medium serving as a conveyed object. The separation plate 310 separates the recording medium from the photoconductor belt.
Yet alternatively, the endless belt may be the intermediate transfer belt 11 serving as an image bearer depicted in
A description is provided of advantages of a nip forming device (e.g., the fixing devices 9, 9A, 9B, 9C, 9D, 9E, 9F, 9G, 9H, 9I, 9J, 60, and 60A).
As illustrated in
The endless belt is flexible and rotates. The nip former (e.g., a nip formation pad) is disposed opposite or contacts an inner circumferential face (e.g., the inner circumferential face 20a) of the endless belt. The pressure rotator presses against the nip former via the endless belt to form a nip (e.g., the fixing nip N) between the endless belt and the pressure rotator. The guide guides each lateral end of the endless belt in a longitudinal direction (e.g., the longitudinal direction X) thereof. A conveyed object (e.g., the sheet P) is conveyed through the nip. The separator separates the conveyed object that is past the nip from the endless belt. The separator includes a non-contact portion (e.g., the edge portion 311) and a contact portion (e.g., the contact portion 313). The non-contact portion is separated from the endless belt. As illustrated in
Accordingly, the contact portion optimizes the gap between the endless belt and the separator, improving separation of the conveyed object from the endless belt.
According to the embodiments described above, the fixing belt 20 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 21 serves as a pressure rotator. Alternatively, a pressure belt or the like may be used as a pressure rotator.
Some aspects of the present disclosure are further described below.
Aspect 1
A nip forming device includes: an endless belt that is rotatable and flexible; a nip former disposed to contact an inner circumferential face of the endless belt; a pressure rotator to press against the nip former via the endless belt to form a nip between the endless belt and the pressure rotator; a guide to guide each lateral end of the endless belt in a longitudinal direction of the endless belt; and a separator to separate the conveyed object from the endless belt, the separator including: a non-contact portion separated from the endless belt; and a contact portion to contact the endless belt to retain a gap having a predetermined size between the non-contact portion and the endless belt.
Aspect 2
The nip forming device according to aspect 1, wherein the separator is disposed to be movable toward the endless belt in an approach direction and away from the endless belt in a separation direction, wherein a motion restrictor is disposed that includes: a first restricting portion to restrict a moving position of the separator in the approach direction; and a second restricting portion to restrict a moving position of the separator in the separation direction.
Aspect 3
The nip forming device according to aspect 2, further comprising a biasing member to bias the separator in the approach direction.
Aspect 4
The nip forming device according to aspect 3, wherein the nip former is disposed to be movable with respect to the pressure rotator between an approach position where the pressure rotator presses against the nip former via the endless belt at the nip and a separation position where the pressure rotator releases pressure applied at the nip, and wherein the nip former is configured to be movable to the separation position in a state in which the first restricting portion restricts motion of the separator.
Aspect 5
The nip forming device according to any one of aspects 2 to 4, wherein, when the separator moves in the separation direction, the second restricting portion restricts motion of the separator in the separation direction at a position where the separator does not come into contact with the pressure rotator.
Aspect 6
The nip forming device according to any one of aspects 2 to 5, wherein the separator includes a separation plate movably supported between a pair of side plates, and wherein the motion restrictor is disposed between the separation plate and each side plate of the pair of side plates.
Aspect 7
The nip forming device according to aspect 6, wherein the motion restrictor includes a motion restricted tab formed on an end of the separation plate and a motion restricting hole formed in each of the side plates, and wherein the first restricting portion is formed by one end of the motion restricting hole, and the second restriction portion is formed by another end of the motion restricting hole the motion restricted tab inserted into the motion restricting hole.
Aspect 8
The nip forming device according to any one of aspects 1 to 7, wherein the contact portion is disposed outboard from a conveyance span of the conveyed object in a longitudinal direction of the endless belt, the conveyance span where the conveyed object is conveyed over the endless belt.
Aspect 9
The nip forming device according to aspect 8, further comprising at least three heaters divided and disposed on the nip format to heat the endless belt, wherein the at least three heaters include: a center heater to heat a center of the endless belt in a longitudinal direction of the endless belt; and end heaters to heat both ends of the endless belt in the longitudinal direction of the endless belt.
Aspect 10
An image forming apparatus, comprising the nip forming device according to any one of aspects 1 to 9.
The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.
Number | Date | Country | Kind |
---|---|---|---|
2021-200075 | Dec 2021 | JP | national |
2022-168319 | Oct 2022 | JP | national |