Patent Grant
8588670
The present application is based on and claims priority to Japanese Patent Application No. 2010-106884, filed on May 7, 2010, in the Japan Patent Office, which is hereby incorporated herein by reference in its entirety.
1. Field of the Invention
Exemplary aspects of the present invention 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 including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; 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.
The fixing device used in such image forming apparatuses may employ a fixing belt, formed into a loop, to apply heat to the recording medium bearing the toner image, and a pressing roller, disposed opposite the fixing belt, to apply pressure to the recording medium. A stationary, nip formation pad disposed inside the loop formed by the fixing belt is pressed against the pressing roller disposed outside the loop formed by the fixing belt via the fixing belt to form a nip between the fixing belt and the pressing roller through which the recording medium bearing the toner image passes. As the fixing belt and the pressing roller rotate and convey the recording medium through the nip, they apply heat and pressure to the recording medium to fix the toner image on the recording medium.
As a mechanism that heats the fixing belt, the fixing device may include a substantially tubular metal member disposed inside the loop formed by the fixing belt and a heater disposed inside the metal member to heat the metal member, which in turn heats the fixing belt. In addition, the nip formation pad pressed against the pressing roller may be supported by a pad support disposed inside the metal member. Since the pad support is disposed opposite the heater, it is given a finish that locally or entirely reflects heat emitted by the heater to cause the reflected heat to irradiate an inner circumferential surface of the metal member, thus using the heat striking the pad support for effective heating of the metal member.
The above-described configuration is generally effective, and in part relies on the passage of recording medium through the nip to draw off the heat thus generated. However, a problem arises when relatively small recording media having a smaller width in the axial direction of the fixing belt are conveyed to the nip continuously. In that case, the lateral end portions of the fixing belt in the axial direction thereof may retain an excessive amount of heat because the small recording media do not pass through the lateral end portions of the fixing belt and therefore do not draw heat therefrom, resulting in overheating of the lateral end portions of the fixing belt and the corresponding sections of the metal member disposed opposite the lateral end portions of the fixing belt. Consequently, the fixing belt and the metal member may suffer from thermal damage.
This specification describes below an improved fixing device. In one exemplary embodiment of the present invention, the fixing device fixes a toner image on a recording medium and includes a flexible, endless, belt-shaped fixing rotary body, a pressing rotary body, a nip formation pad, a substantially tubular, metal thermal conductor, a heater, a pad support, a reflector, and a plurality of reflector moving assemblies. The fixing rotary body is formed into a loop. The pressing rotary body is provided outside the loop formed by the fixing rotary body. The nip formation pad is provided inside the loop formed by the fixing rotary body and pressed against the pressing rotary body via the fixing rotary body to form a nip between the pressing rotary body and the fixing rotary body through which the recording medium bearing the toner image passes. The substantially tubular, metal thermal conductor is provided inside the loop formed by the fixing rotary body to heat the fixing rotary body. The heater is provided inside the metal thermal conductor to heat the metal thermal conductor. The pad support is provided inside the metal thermal conductor to support the nip formation pad. The reflector is provided between the heater and the pad support to reflect heat emitted by the heater thereto toward an inner circumferential surface of the metal thermal conductor. The reflector includes a center reflection portion provided at a center of the reflector in a longitudinal direction thereof, and a plurality of end reflection portions provided at respective lateral ends of the reflector in the longitudinal direction thereof, outboard of the center reflection portion. The plurality of reflector moving assemblies is connected to the plurality of end reflection portions of the reflector, respectively, to tilt the plurality of end reflection portions with respect to the center reflection portion.
This specification further describes an improved image forming apparatus. In one exemplary embodiment, the image forming apparatus includes the fixing device described above.
A more complete appreciation of the invention 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
As illustrated in
The toner bottle holder 101 includes four toner bottles 102Y, 102M, 102C, and 102K that contain yellow, magenta, cyan, and black toners, respectively. They are detachably attached to the toner bottle holder 101, thus replaceable with new ones, respectively.
The intermediate transfer unit 85, disposed below the toner bottle holder 101, includes an intermediate transfer belt 78 formed into a loop, four first transfer bias rollers 79Y, 79M, 79C, and 79K, a second transfer backup roller 82, a cleaning backup roller 83, and a tension roller 84 disposed inside the loop formed by the intermediate transfer belt 78, and an intermediate transfer cleaner 80 disposed outside the loop formed by the intermediate transfer belt 78. Specifically, the intermediate transfer belt 78 is supported by and stretched over three rollers, which are the second transfer backup roller 82, the cleaning backup roller 83, and the tension roller 84. A single roller, that is, the second transfer backup roller 82, drives and endlessly moves (e.g., rotates) the intermediate transfer belt 78 in a direction D1.
The image forming devices 4Y, 4M, 4C, and 4K, arranged opposite the intermediate transfer belt 78, form yellow, magenta, cyan, and black toner images, respectively. The image forming devices 4Y, 4M, 4C, and 4K include photoconductive drums 5Y, 5M, 5C, and 5K which are surrounded by chargers 75Y, 75M, 75C, and 75K, development devices 76Y, 76M, 76C, and 76K, cleaners 77Y, 77M, 77C, and 77K, and dischargers, respectively. Image forming processes including a charging process, an exposure process, a development process, a primary transfer process, and a cleaning process are performed on the photoconductive drums 5Y, 5M, 5C, and 5K to form yellow, magenta, cyan, and black toner images thereon, respectively, as a driving motor drives and rotates the photoconductive drums 5Y, 5M, 5C, and 5K clockwise in
Specifically, in the charging process, the chargers 75Y, 75M, 75C, and 75K uniformly charge surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K at charging positions at which the chargers 75Y, 75M, 75C, and 75K are disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K, respectively.
In the exposure process, the exposure device 3 emits laser beams L onto the charged surfaces of the respective photoconductive drums 5Y, 5M, 5C, and 5K according to image data sent from a client computer, for example. In other words, the exposure device 3 scans and exposes the charged surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K at irradiation positions at which the exposure device 3 is disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K to irradiate the charged surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K to form thereon electrostatic latent images corresponding to yellow, magenta, cyan, and black colors, respectively.
In the development process, the development devices 76Y, 76M, 76C, and 76K render the electrostatic latent images formed on the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K visible as yellow, magenta, cyan, and black toner images at development positions at which the development devices 76Y, 76M, 76C, and 76K are disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K, respectively.
In the primary transfer process, the first transfer bias rollers 79Y, 79M, 79C, and 79K transfer and superimpose the yellow, magenta, cyan, and black toner images formed on the photoconductive drums 5Y, 5M, 5C, and 5K onto the intermediate transfer belt 78 at first transfer positions at which the first transfer bias rollers 79Y, 79M, 79C, and 79K are disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K via the intermediate transfer belt 78, respectively. Thus, a color toner image is formed on the intermediate transfer belt 78. After the transfer of the yellow, magenta, cyan, and black toner images, a slight amount of residual toner, which has not been transferred onto the intermediate transfer belt 78, remains on the photoconductive drums 5Y, 5M, 5C, and 5K.
In the cleaning process, cleaning blades included in the cleaners 77Y, 77M, 77C, and 77K mechanically collect the residual toner from the photoconductive drums 5Y, 5M, 5C, and 5K at cleaning positions at which the cleaners 77Y, 77M, 77C, and 77K are disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K, respectively.
Finally, dischargers remove residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K at discharging positions at which the dischargers are disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K, respectively, thus completing a single sequence of image forming processes performed on the photoconductive drums 5Y, 5M, 5C, and 5K.
The following describes the transfer processes, that is, the primary transfer process described above and a secondary transfer process, performed on the intermediate transfer belt 78. The four first transfer bias rollers 79Y, 79M, 79C, and 79K and the photoconductive drums 5Y, 5M, 5C, and 5K sandwich the intermediate transfer belt 78 to form first transfer nips, respectively. The first transfer bias rollers 79Y, 79M, 79C, and 79K are applied with a transfer bias having a polarity opposite a polarity of toner forming the yellow, magenta, cyan, and black toner images on the photoconductive drums 5Y, 5M, 5C, and 5K, respectively. Accordingly, in the primary transfer process, the yellow, magenta, cyan, and black toner images formed on the photoconductive drums 5Y, 5M, 5C, and 5K, respectively, are primarily transferred and superimposed onto the intermediate transfer belt 78 rotating in the direction D1 successively at the first transfer nips formed between the photoconductive drums 5Y, 5M, 5C, and 5K and the intermediate transfer belt 78 as the intermediate transfer belt 78 moves through the first transfer nips. Thus, a color toner image is formed on the intermediate transfer belt 78.
The second transfer roller 89 is pressed against the second transfer backup roller 82 via the intermediate transfer belt 78 in such a manner that the second transfer roller 89 and the second transfer backup roller 82 sandwich the intermediate transfer belt 78 to form a second transfer nip between the second transfer roller 89 and the intermediate transfer belt 78. At the second transfer nip, the second transfer roller 89 secondarily transfers the color toner image formed on the intermediate transfer belt 78 onto a recording medium P sent from the paper tray 12 through the feed roller 97 and the registration roller pair 98 in the secondary transfer process. Thus, the desired color toner image is formed on the recording medium P. After the transfer of the color toner image, residual toner, which has not been transferred onto the recording medium P, remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer cleaner 80 collects the residual toner from the intermediate transfer belt 78 at a cleaning position at which the intermediate transfer cleaner 80 is disposed opposite the cleaning backup roller 83 via the intermediate transfer belt 78, thus completing a single sequence of transfer processes performed on the intermediate transfer belt 78.
The recording medium P is supplied to the second transfer nip from the paper tray 12 which loads a plurality of recording media P (e.g., transfer sheets). Specifically, the feed roller 97 rotates counterclockwise in
The registration roller pair 98, which stops rotating temporarily, stops the uppermost recording medium P fed by the feed roller 97 and reaching the registration roller pair 98. For example, the roller nip of the registration roller pair 98 contacts and stops a leading edge of the recording medium P. The registration roller pair 98 resumes rotating to feed the recording medium P to the second transfer nip, formed between the second transfer roller 89 and the intermediate transfer belt 78, as the color toner image formed on the intermediate transfer belt 78 reaches the second transfer nip.
After the secondary transfer process described above, the recording medium P bearing the color toner image is sent to the fixing device 20 that includes a fixing belt 21 and a pressing roller 31. The fixing belt 21 and the pressing roller 31 apply heat and pressure to the recording medium P to fix the color toner image on the recording medium P.
Thereafter, the fixing device 20 feeds the recording medium P bearing the fixed color toner image toward the output roller pair 99. The output roller pair 99 discharges the recording medium P to an outside of the image forming apparatus 1, that is, the output tray 100. Thus, the recording media P discharged by the output roller pair 99 are stacked on the output tray 100 successively to complete a single sequence of image forming processes performed by the image forming apparatus 1.
Referring to
As illustrated in
As illustrated in
Specifically, the base layer, having a thickness in a range of from about 30 μm to about 50 μm, constitutes an inner circumferential surface 21a of the fixing belt 21 sliding over the nip formation pad 26, and is made of a metal material such as nickel and/or stainless steel and/or a resin material such as polyimide.
The elastic layer, having a thickness in a range of from about 100 μm to about 300 μm, is made of a rubber material such as silicon rubber, silicon rubber foam, and/or fluorocarbon rubber. The elastic layer eliminates or reduces slight surface asperities of the fixing belt 21 at a nip NP formed between the fixing belt 21 and the pressing roller 31. Accordingly, heat is uniformly transmitted from the fixing belt 21 to a toner image T on a recording medium P, minimizing formation of a rough image such as an orange peel image.
The release layer, having a thickness in a range of from about 10 μm to about 50 μm, is made of tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), polyimide, polyetherimide, and/or polyether sulfide (PES). The release layer releases or separates the toner image T from the fixing belt 21.
The fixing belt 21 has a loop diameter in a range of from about 15 mm to about 120 mm. According to this exemplary embodiment, the fixing belt 21 has an inner diameter of about 30 mm. As illustrated in
The nip formation pad 26 is a stationary member that is fixedly disposed inside the fixing belt 21 in such a manner that the inner circumferential surface 21a of the fixing belt 21 slides over the nip formation pad 26. The nip formation pad 26 presses against the pressing roller 31 via the fixing belt 21 to form the nip NP between the fixing belt 21 and the pressing roller 31 through which the recording medium P bearing the toner image T is conveyed. As illustrated in
As illustrated in
With this configuration, the metal thermal conductor 22 heated by radiation heat generated by the heater 25 serves as a heating member that heats the fixing belt 21 or a heat transmitter that transmits heat received from the heater 25 to the fixing belt 21. That is, the heater 25 heats the metal thermal conductor 22 directly and heats the fixing belt 21 indirectly via the metal thermal conductor 22. Preferably, the metal thermal conductor 22 has a thickness not greater than about 0.1 mm to maintain desired heating efficiency for heating the fixing belt 21.
The metal thermal conductor 22 is made of a metal thermal conductor, that is, a metal having thermal conductivity, such as stainless steel, nickel, aluminum, and/or iron. Preferably, the metal thermal conductor 22 is made of ferrite stainless steel having a relatively smaller heat capacity per unit volume obtained by multiplying density by specific heat. According to this exemplary embodiment, the metal thermal conductor 22, having a thickness of about 0.1 mm, is made of SUS430 stainless steel as ferrite stainless steel.
The heater 25, serving as a heater or a heat source, is a halogen heater or a carbon heater. As illustrated in
As illustrated in
As described above, the fixing device 20 according to this exemplary embodiment includes the two temperature detectors: the first temperature sensor 40A that detects the temperature of a center portion of the fixing belt 21 in the axial direction thereof; and the second temperature sensor 40B that detects the temperature of one of lateral end portions of the fixing belt 21 in the axial direction thereof. The center portion of the fixing belt 21 corresponds to a conveyance region M through which a small recording medium P passes. The lateral end portions of the fixing belt 21 correspond to non-conveyance regions N through which a small recording medium P does not pass. Since small recording media are used more frequently than large recording media, the controller 10 controls the heater 25 based on the temperature of the fixing belt 21 detected by the first temperature sensor 40A that faces the conveyance region M through which small recording media pass.
As described above, in the fixing device 20 according to this exemplary embodiment, the metal thermal conductor 22 does not heat only a small part of the fixing belt 21 but heats substantially the entire fixing belt 21 in a circumferential direction of the fixing belt 21. Accordingly, even when the image forming apparatus 1 depicted in
As illustrated in
The inner circumferential surface 21a of the fixing belt 21 is applied with a lubricant, such as fluorine grease, to decrease friction between the fixing belt 21 and the metal thermal conductor 22 and concomitant wear of the fixing belt 21 that may arise as the fixing belt 21 slidably contacts the metal thermal conductor 22.
According to this exemplary embodiment, the metal thermal conductor 22 has a substantially circular shape in cross-section. Alternatively, the metal thermal conductor 22 may have a polygonal shape in cross-section or may include a slit on a circumferential surface thereof.
As illustrated in
In order to provide the above-described effects, the pad support 23 is preferably made of a metal material having great mechanical strength, such as stainless steel and/or iron.
According to this exemplary embodiment, the pad support 23 is a plate that divides the interior of the substantially cylindrical metal thermal conductor 22 into two communicable compartments: an upper compartment disposed downstream from the nip NP in the rotation direction R1 of the fixing belt 21 and a lower compartment disposed upstream from the nip NP in the rotation direction R1 of the fixing belt 21.
The reflector 24 is attached to the pad support 23 and includes heat-reflecting faces disposed opposite the heater 25 and extending in a longitudinal direction of the reflector 24 parallel to the axial direction of the fixing belt 21 so as to reflect heat, emitted by the heater 25 and irradiating the reflector 24, toward an inner circumferential surface of the metal thermal conductor 22. As illustrated in
With the configuration described above, the reflector 24, disposed between the heater 25 and the pad support 23, reflects heat emitted by the heater 25 thereto toward the metal thermal conductor 22 to heat it, improving efficiency of heating of the metal thermal conductor 22 for heating the fixing belt 21.
As illustrated in
As illustrated in
With the elastic layer 33 of the pressing roller 31 made of a sponge material such as silicon rubber foam, the pressing roller 31 applies decreased pressure to the fixing belt 21 at the nip NP to decrease bending of the metal thermal conductor 22. Further, the pressing roller 31 provides increased heat insulation, and thereby preventing easy transmission of heat from the fixing belt 21 to the pressing roller 31 and thus improving heating efficiency of the fixing belt 21.
According to this exemplary embodiment, the fixing belt 21 when formed into its looped shape has a diameter (hereinafter “loop diameter”) identical to that of the pressing roller 31. Alternatively, the loop diameter of the fixing belt 21 may be smaller than that of the pressing roller 31. In this case, the curvature of the fixing belt 21 is smaller than that of the pressing roller 31 at the nip NP, facilitating separation of a recording medium P from the fixing belt 21 when it is discharged from the nip NP.
As illustrated in
As described above, according to this exemplary embodiment, the nip formation pad 26 has a concave shape to form the concave nip NP. Alternatively, however, the nip formation pad 26 may have a flat, planar shape to form a planar nip NP. Specifically, the contact face of the nip formation pad 26 disposed opposite the pressing roller 31 may have a flat, planar shape. Accordingly, the planar nip NP formed by the planar contact face of the nip formation pad 26 is substantially parallel to an imaged side of the recording medium P. Consequently, the fixing belt 21 pressed by the planar contact face of the nip formation pad 26 is precisely adhered to the recording medium P to improve fixing performance. Further, the increased curvature of the fixing belt 21 at an exit of the nip NP facilitates separation of the recording medium P discharged from the nip NP from the fixing belt 21.
The substantially tubular metal thermal conductor 22 is formed by bending a metal sheet into the desired shape. A metal sheet is used to give the metal thermal conductor 22 a thin thickness to shorten a warm-up time. However, such a thin metal thermal conductor 22 has little rigidity, and therefore is easily bent or deformed by pressure applied by the pressing roller 31. A deformed metal thermal conductor 22 does not provide a desired nip length of the nip NP, degrading fixing performance. To address this problem, according to this exemplary embodiment, the rigid nip formation pad 26 is provided separately from the thin metal thermal conductor 22 to help form and maintain the proper nip NP.
As illustrated in
The metal thermal conductor 22 is disposed close to the fixing belt 21 throughout substantially the entire circumference thereof. Accordingly, even in a standby mode before printing starts, the metal thermal conductor 22 heats the fixing belt 21 in the circumferential direction evenly, without temperature fluctuation. Consequently, the image forming apparatus 1 depicted in
Between the nip formation pad 26 and the fixing belt 21 is applied a lubricant that reduces frictional resistance therebetween, but it may deteriorate under high pressure and temperature applied at the nip NP, resulting in unstable slippage of the fixing belt 21 over the nip formation pad 26. To address this problem, according to this exemplary embodiment, the heat insulator 27 is provided between the nip formation pad 26 and the metal thermal conductor 22 to reduce heat transmitted from the metal thermal conductor 22 to the lubricant at the nip NP, thus reducing deterioration of the lubricant due to high temperature.
The heat insulator 27 disposed between the nip formation pad 26 and the metal thermal conductor 22 insulates the nip formation pad 26 from the metal thermal conductor 22. Accordingly, the metal thermal conductor 22 heats the fixing belt 21 with reduced heat at the nip NP. Consequently, the recording medium P discharged from the nip NP has a decreased temperature compared to when it enters the nip NP. In other words, at the exit of the nip NP, the fixed toner image T on the recording medium P has a decreased temperature, and therefore the toner of the fixed toner image T has a decreased viscosity. That is, with a decreased adhesive force that adheres the fixed toner image T to the fixing belt 21, the recording medium P is separated from the fixing belt 21 easily. Consequently, the recording medium P is not wound around the fixing belt 21 immediately after the fixing process, preventing or reducing jamming of the recording medium P and adhesion of the toner of the toner image T to the fixing belt 21.
As illustrated in
In the present embodiment, a stainless steel sheet having a thickness of about 0.1 mm is bent into the substantially tubular metal thermal conductor 22. However, spring-back of the stainless steel sheet may expand a circumference of the metal thermal conductor 22, and therefore the stainless steel sheet may not maintain the desired pipe shape. As a result, the metal thermal conductor 22 having an expanded circumference may contact the inner circumferential surface 21a of the fixing belt 21, damaging the fixing belt 21 or generating temperature fluctuation of the fixing belt 21 due to uneven contact of the metal thermal conductor 22 to the fixing belt 21.
To address those problems, according to this exemplary embodiment, the stay 28 supports and holds the concave portion (e.g., a bent portion) of the metal thermal conductor 22 provided with an opening so as to prevent deformation of the metal thermal conductor 22 due to spring-back. For example, the stay 28 is press-fitted to the concave portion of the metal thermal conductor 22 to contact the inner circumferential surface of the metal thermal conductor 22 while the shape of the metal thermal conductor 22 that is bent against spring-back of the stainless steel sheet is maintained.
Preferably, the metal thermal conductor 22 has a thickness not greater than about 0.2 mm to increase heating efficiency of the metal thermal conductor 22.
As described above, the metal sheet is bent into the substantially tubular, thin metal thermal conductor 22 to shorten a warm-up time, but lacks the rigidity to withstand deformation due to pressure from the pressing roller 31 and therefore is bent or deformed. Accordingly, the deformed metal thermal conductor 22 may not provide a desired nip length of the nip NP, resulting in degraded fixing performance. To address this problem, according to this exemplary embodiment, the concave portion of the thin metal thermal conductor 22 into which the nip formation pad 26 is inserted is isolated from the nip NP to prevent the metal thermal conductor 22 from receiving pressure from the pressing roller 31 directly.
Referring to
When the image forming apparatus 1 is powered on, power is supplied to the heater 25, and the pressing roller 31 starts rotating in the rotation direction R2. Friction between the pressing roller 31 and the fixing belt 21 at the nip NP rotates the fixing belt 21 in the rotation direction R1 in accordance with rotation of the pressing roller 31.
Thereafter, a recording medium P is sent from the paper tray 12 to the second transfer nip formed between the intermediate transfer belt 78 and the second transfer roller 89. At the second transfer nip, a color toner image is transferred from the intermediate transfer belt 78 onto the recording medium P. A guide plate guides the recording medium P bearing the toner image T in a direction Y10 so that the recording medium P enters the nip NP formed between the fixing belt 21 and the pressing roller 31 pressed against each other.
At the nip NP, the fixing belt 21 heated by the heater 25 via the metal thermal conductor 22 heats the recording medium P. Simultaneously, the pressing roller 31 and the nip formation pad 26 reinforced by the pad support 23 apply pressure to the recording medium P. Thus, the heat applied by the fixing belt 21 and the pressure applied by the pressing roller 31 fix the toner image T on the recording medium P. Thereafter, the recording medium P bearing the fixed toner image T discharged from the nip NP is conveyed in a direction Y11.
Referring to
As illustrated in
For example, the reflector 24 is constructed of two types of reflection plates: the first reflection plate 24a and the pair of second reflection plates 24b. The first reflection plate 24a, that is, a stationary reflection plate serving as a center reflection portion, is fixedly mounted on a center portion of the pad support 23 in the longitudinal direction thereof corresponding to the conveyance region M through which a small recording medium P is conveyed. By contrast, the second reflection plates 24b, that is, movable reflection plates serving as end reflection portions, are disposed at lateral end portions of the pad support 23 in the longitudinal direction thereof corresponding to the non-conveyance regions N through which a small recording medium P is not conveyed, respectively. Each of the second reflection plates 24b is supported by the pad support 23 in such a manner that it is rotatable about the rotation axis 24c attached to the first reflection plate 24a. Specifically, the reflector moving assembly 46 rotates the second reflection plate 24b about the rotation axis 24c as needed from the position of the second reflection plate 24b illustrated in
The reflection face 24r of the reflector 24 is constructed of reflection faces of the first reflection plate 24a and the second reflection plates 24b, each of which is made of aluminum and/or silver having a smaller surface radiation and a greater degree of reflection of heat emitted by the heater 25.
Referring to
Specifically, the driver 47 includes a motor 47a; a pinion 47b rotated by the motor 47a; a rack 47c moved by the rotating pinion 47b; and a lever 47d mounted with the rack 47c and connected to the cam roller 48. When the motor 47a rotates the pinion 47b clockwise in
As described above, the left, reflector moving assembly 46 moves the cam roller 48 in the direction D2 and the right, reflector moving assembly 46 moves the cam roller 48 in the direction D3. Specifically, the driver 47 moves the cam roller 48 in the axial direction of the fixing belt 21 in such a manner that the cam roller 48 contacts a non-reflection face 24b2 of the second reflection plate 24b opposite a reflection face 24b1 that reflects heat emitted by the heater 25, and at the same time biases the second reflection plate 24b, so that the reflection face 24b1 of the second reflection plate 24b is rotated and tilted toward a reflection face 24a1 of the first reflection plate 24a disposed at the center portion of the reflector 24 in the longitudinal direction thereof. The tension spring 49 biases (e.g., pulls and rotates) the second reflection plate 24b to align the reflection face 24b1 of the second reflection plate 24b with the reflection face 24a1 of the first reflection plate 24a.
For example, when the cam roller 48 is at the position illustrated in
By contrast, as shown in
Whether or not the above-described movement of the second reflection plates 24b is performed is determined by the size of the recording medium P in the axial direction of the fixing belt 21, that is, the width of the recording medium P passing through the nip NP formed between the fixing belt 21 and the pressing roller 31 depicted in
Conversely, when the small recording medium P (e.g., an A4 size recording medium P) is conveyed to the nip NP, it passes over the conveyance region M of the fixing belt 21 only. Accordingly, the second reflection plates 24b are tilted toward the center portion of the fixing belt 21 in the axial direction thereof as illustrated in
Accordingly, even when small recording media P are conveyed to the nip NP continuously, the non-conveyance regions N of the fixing belt 21 through which the small recording media P do not pass are not overheated because the non-conveyance regions N are hardly heated by the heater 25. Consequently, even when a large recording medium P is conveyed to the nip NP immediately after the small recording media P, the occurrence of hot offset, which may arise due to an excessively high temperature of the lateral end portions of the fixing belt 21 in the axial direction thereof, can be minimized. Further, for a small recording medium P, the heat L3 emitted by lateral end portions of the heater 25 in the longitudinal direction thereof corresponding to the non-conveyance regions N and then reflected by the second reflection plates 24b is used effectively to heat the center portion of the fixing belt 21 in the axial direction thereof corresponding to the conveyance region M, resulting in effective usage of thermal energy of the heater 25.
It is to be noted that the controller 10 depicted in
Referring to
For example, the multiple pairs of the light emitter 13a and the light receiver 13b are disposed at positions S1, S2, and S3 aligned in a line orthogonal to the conveyance direction of the recording medium P, respectively, as shown in
Specifically, when a small recording medium (e.g., an A5 size recording medium) passes through the sheet size detector 13, only the pair of the light emitter 13a and the light receiver 13b, disposed at the position S3 corresponding to one lateral edge of the small recording medium P outputs an OFF signal. When a medium recording medium (e.g., an A4 size recording medium) passes through the sheet size detector 13, the pair of the light emitter 13a and the light receiver 13b, disposed at the position S2 corresponding to one lateral edge of the medium recording medium P as well as the pair of the light emitter 13a and the light receiver 13b disposed at the position S3 output an OFF signal. When a large recording medium (e.g., an A3 size recording medium) passes through the sheet size detector 13, the pair of the light emitter 13a and the light receiver 13b, disposed at the position S1 corresponding to one lateral edge of the large recording medium P as well as the pairs of the light emitter 13a and the light receiver 13b disposed at the positions S2 and S3 output an OFF signal.
Alternatively, the sheet size detector may be provided in the paper tray 12 depicted in
Alternatively, the controller 10 may control movement of the second reflection plates 24b based on a temperature differential between the center portion and the lateral end portions of the fixing belt 21 in the axial direction thereof. For example, when a surface temperature of the lateral end portions of the fixing belt 21 in the axial direction thereof is higher than a surface temperature of the center portion of the fixing belt 21 in the axial direction thereof by a predetermined value, the reflection face 24b1 of each of the second reflection plates 24b may be tilted toward the center portion of the fixing belt 21 in the axial direction thereof as shown in
For example, when the controller 10 identifies that the temperature differential between the center portion and the lateral end portions of the fixing belt 21 in the axial direction thereof is not smaller than the predetermined value based on the surface temperature of the center portion of the fixing belt 21 detected by the first temperature sensor 40A and the surface temperature of one lateral end portion of the fixing belt 21 detected by the second temperature sensor 40B depicted in
It is to be noted that the angle of tilting of the second reflection plates 24b can be adjusted according to the size of the smaller recording medium P: A4 size or A5 size. For example, in the image forming apparatus 1 that accommodates A3 size as the maximum size of recording media P, A4 size and A5 size are identified as the size of smaller recording media P. Therefore, the controller 10 adjusts the position of the cam rollers 48 to cause the angle of tilting of the second reflection plates 24b for A5 size recording media P to be greater than that for A4 size recording media P. Specifically, the controller 10 controls the driver 47 that moves the cam roller 48 in such a manner that, for A5 size recording media P, the cam roller 48 is positioned at a first position provided inward in the longitudinal direction of the reflector 24 from a lateral edge of the second reflection plate 24b toward the first reflection plate 24a, which is closer to the first reflection plate 24a than a second position of the cam roller 48 for A4 size recording media P. With this configuration, even when recording media P of various sizes are conveyed to the nip NP, the second reflection plates 24b can precisely reflect the heat L3 to the conveyance region M.
The above-described configuration of the fixing device 20 includes the reflector 24 in which the second reflection plates 24b are tiltably disposed at the lateral end portions of the pad support 23 in the longitudinal direction thereof on a surface of the pad support 23 facing the heater 25. Thus, even when small recording media P pass through the nip NP continuously, the lateral end portions of the fixing belt 21 and the metal thermal conductor 22 in the longitudinal direction thereof, through which the small recording media P do not pass, are not overheated. Simultaneously, heat emitted from the heater 25 toward the pad support 23 is reflected by the reflector 24 and used for heating the metal thermal conductor 22, further improving efficiency for heating the fixing belt 21 and the metal thermal conductor 22.
According to this exemplary embodiment, although the reflector 24 is made of a relatively thin plate, it is mounted on the rigid pad support 23, and therefore is not deformed by stress exerted thereon. Accordingly, the reflector 24 itself does not require an increased mechanical strength, reducing manufacturing costs, downsizing the reflector 24, and saving space.
As described above, referring to
Since the pressing roller 31 applies a greater tension to an upstream portion of the fixing belt 21 upstream from the nip NP in the rotation direction R1 of the fixing belt 21 than to a downstream portion of the fixing belt 21 downstream from the nip NP, a smaller clearance is provided between the inner circumferential surface 21a of the fixing belt 21 and the outer circumferential surface of the metal thermal conductor 22 in the upstream portion of the fixing belt 21. Generally, the overall clearance between the fixing belt 21 and the metal thermal conductor 22 is small, but in the upstream portion of the fixing belt 21 the clearance becomes even smaller due to tension applied by the pressing roller 31, facilitating heat transmission from the metal thermal conductor 22 to the fixing belt 21. To benefit from this configuration, the heater 25 is disposed in the lower compartment inside the metal thermal conductor 22. Specifically, the heater 25 is disposed at substantially the center position of the lower compartment so that heat emitted by the heater 25 and reflected by the reflector 24 is diffused uniformly throughout the inner circumferential surface of the metal thermal conductor 22 in a circumferential direction thereof.
As described above, according to this exemplary embodiment, with the reflector 24 extending in the axial direction of the fixing belt 21 to reflect heat emitted by the heater 25 thereto toward the inner circumferential surface of the metal thermal conductor 22, the reflection face 24b1 of each of the second reflection plates 24b disposed at the lateral end portions of the reflector 24 in the longitudinal direction thereof is rotated (e.g., tilted) toward the reflection face 24a1 of the first reflection plate 24a disposed at the center portion of the reflector 24 in the longitudinal direction thereof, thus shortening a warm-up time and a first print time of the fixing device 20. Even when the fixing belt 21 of the fixing device 20 is rotated at high speed, the fixing belt 21 is heated to a desired fixing temperature quickly, preventing formation of a faulty toner image due to a low temperature of the fixing belt 21. Further, even when small recording media P are conveyed to the nip NP continuously, the non-conveyance regions N of the fixing belt 21 and the metal thermal conductor 22, through which the small recording media P do not pass, are not overheated.
It is to be noted that, according to this exemplary embodiment, a single second reflection plate 24b, that is, a movable reflection plate, is disposed at each lateral end portion of the reflector 24 in the longitudinal direction thereof. Alternatively, a plurality of second reflection plates 24b may be provided at each lateral end portion of the reflector 24 in the longitudinal direction thereof so that the reflector 24 can accommodate multiple sizes of smaller recording media P. The plurality of second reflection plates 24b at each lateral end portion of the reflector 24 in the longitudinal direction thereof is then selectively tilted according to the size of smaller recording media P. That is, even when smaller recording media P of multiple sizes are conveyed to the nip NP, and therefore the width of the conveyance region M in the axial direction of the fixing belt 21 varies depending on the size of smaller recording media P, the selectively tilted second reflection plates 24b at each lateral end portion of the reflector 24 can precisely reflect heat onto the conveyance region M of various widths.
Referring to
Similar to the fixing device 20 according to the first illustrative embodiment shown in
Referring to
The actuator 50 is disposed at each lateral end of the pad support 23 in the longitudinal direction thereof. It is to be noted that
The first shape-memory alloy 51 and the second shape-memory alloy 52 are connected to respective power sources and electric wiring to receive power from the power sources via the electric wiring.
For example, when power is supplied from the power source to the first shape-memory alloy 51 to heat it by electric resistance, the first shape-memory alloy 51 is bent into a substantially L-shaped form due to its shape-memory function as illustrated in
By contrast, when power is supplied from the power source to the second shape-memory alloy 52 to heat it by electric resistance, the second shape-memory alloy 52 is deformed into a planar shape due to its shape-memory function as illustrated in
Similar to the fixing device 20 according to the first illustrative embodiment depicted in
As described above, similar to the fixing device 20 according to the first illustrative embodiment depicted in
Referring to
Similar to the fixing device 20 according to the first illustrative embodiment shown in
As illustrated in
As described above, similar to the fixing device 20 according to the first illustrative embodiment depicted in
Referring to
Similar to the fixing device 20 according to the first illustrative embodiment shown in
As illustrated in
As described above, similar to the fixing devices 20, 20S, and 20T according to the above-described exemplary embodiments depicted in
Referring to
Similar to the fixing device 20 according to the first illustrative embodiment shown in
As illustrated in
With the configuration described above, the flanged pad support 23V makes the nip-side compartment, which does not receive heat from the heater 25 directly, smaller than the lower compartment inside the metal thermal conductor 22 defined by the pad support 23 shown in
Further, in addition to providing the larger non-nip-side compartment installed with the heater 25, the flanged pad support 23V provides a strength against bending by pressure from the pressing roller 31 by having a certain length in a horizontal direction in
As described above, similar to the fixing devices 20, 20S, 20T, and 20U according to the above-described exemplary embodiments depicted in
Referring to
Similar to the fixing device 20 according to the first illustrative embodiment shown in
As illustrated in
Unlike the substantially tubular metal thermal conductor 22, having the concave portion facing the nip NP, employed in the fixing devices 20, 20S, 20T, 20U, and 20V depicted in
As described above, similar to the fixing devices 20, 20S, 20T, 20U, and 20V according to the above-described exemplary embodiments depicted in
In the fixing devices 20, 20S, 20T, 20U, 20V, and 20W according to the above-described exemplary embodiments, the fixing belt 21 constructed of multiple layers is used as a fixing rotary body. Alternatively, an endless fixing film made of polyimide, polyamide, fluorocarbon resin, and/or metal may be used as a fixing rotary body to provide effects equivalent to those provided by the fixing belt 21 as described above.
Further, the fixing devices 20, 20S, 20T, 20U, 20V, and 20W according to the above-described exemplary embodiments include the two second reflection plates 24b and the two reflector moving assemblies 46 that move the two second reflection plates 24b, respectively, because the recording medium P passing through the nip NP is centered in the axial direction of the fixing belt 21. Alternatively, the above-described exemplary embodiments may be applied to a fixing device in which the recording medium P conveyed through the nip NP is not centered but is aligned on one lateral edge of the fixing belt 21. In that case, the fixing device may include a single second reflection plate 24b and a single reflector moving assembly 46 provided at another lateral end of the fixing belt 21 opposite the lateral edge of the fixing belt 21 on which the recording medium P is aligned. In such fixing device also, the single reflector moving assembly 46 may tilt the single second reflection plate 24b toward the first reflection plate 24a according to the size of the recording medium P, providing the effects of the above-described exemplary embodiments.
According to the above-described exemplary embodiments, a state in which the nip formation pad, the metal thermal conductor, and the pad support are “fixedly disposed” inside the fixing rotary body defines a state in which they are disposed inside the fixing rotary body without being rotated. Therefore, even when a biasing member (e.g., a spring) biases the nip formation pad against the pressing rotary body via the fixing rotary body at the nip, for example, the nip formation pad is “fixedly disposed” inside the fixing rotary body as long as it is not rotated.
Further, according to the above-described exemplary embodiments, the “conveyance region” defines a region corresponding to the width of the recording medium passing through the nip formed between the fixing rotary body and the pressing rotary body of the fixing device in a width direction of the recording medium perpendicular to the conveyance direction of the recording medium. Conversely, the “non-conveyance region” defines a region outside the conveyance region.
Additionally, the “width direction” defines a direction perpendicular to the conveyance direction of the recording medium passing through the nip formed between the fixing rotary body and the pressing rotary body of the fixing device.
The present invention has been described above with reference to specific exemplary embodiments. Note that the present invention 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 invention. It is therefore to be understood that the present invention 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 invention.
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