Patent Grant
8811837
The present patent application claims priority pursuant to 35 U.S.C. §119 from Japanese Patent Application No. 2010-048254, filed on Mar. 4, 2010 in the Japan Patent Office, which is incorporated herein by reference in its entirety.
1. Field
Exemplary embodiments of the present disclosure relate to an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunctional device having at least two of the foregoing capabilities, and a fixing device employed in the image forming apparatus.
2. Description of the Background Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction apparatuses 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.
For example, a fixing device like that described in JP-2008-158482-A or JP-2007-334205-A includes a substantially-pipe-shaped metal member (opposed member) to effectively heat an endless fixing belt serving as a fixing member to shorten a warm-up time or a time to first print (hereinafter also “first print time”). Specifically, the metal member is provided inside a loop formed by the endless fixing belt so as to face a portion or the entire of the inner circumferential surface of the fixing belt. The metal member is heated by a built-in or external heater so as to heat the fixing belt. A pressing roller presses against the outer circumferential surface of the fixing belt at a position corresponding to the location of the metal member inside the loop formed by 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 recording medium bearing the toner image passes through the nip, the fixing belt and the pressing roller apply heat and pressure to the recording medium to fix the toner image on the recording medium. For such a fixing device, when the pressing roller is rotated by a driving unit, the fixing belt in pressure contact with the pressing roller at the nip is rotated by friction resistance in accordance with the rotation of the pressing roller.
Alternatively, JP-2004-021079-A proposes an on-demand fixing device employing a ceramic heater to prevent overheating of a fixing belt when the fixing belt slips. The on-demand fixing device includes two temperature detectors to detect the temperature of the ceramic heater and stops heating of the ceramic heater when the difference between temperatures detected by the temperature detectors is equal to or greater than a predetermined threshold.
For the above-described fixing devices like those described in JP-2008-158482-A and JP-2007-334205-A, when a sufficient driving force is not transmitted from the pressing roller to the fixing belt, a slip (rotation failure) of the fixing belt may occur. Such a slip of the fixing belt may cause overheating at a portion of the fixing belt, thermally damaging the fixing belt. In particular, since the fixing device is highly efficient in heating the fixing belt, such a problem is not negligible. Further, the above-described fixing devices like those described in JP-2008-158482-A and JP-2007-334205-A employ a halogen heater as the heating unit. Such a configuration has a limitation in application of a technique of JP-2004-021079-A using the two temperature detectors to detect the temperature of the ceramic heater.
In an aspect of this disclosure, there is provided an improved fixing device including a substantially cylindrical metal member, a heater, an endless, flexible fixing member, a rotary pressing member, a stationary member, a first temperature detector, and a second temperature detector. The heater is positioned to heat the metal member. The fixing member is disposed rotatably around the metal member. An inner circumferential surface of the fixing member is heated by the metal member to heat and fix a toner image. The rotary pressing member is disposed opposite and parallel to the metal member and pressed against an outer circumferential surface of the fixing member to form a nip between the rotary pressing member and the fixing member through which a recording medium bearing the toner image passes. The stationary member is disposed at an inner circumferential surface side of the fixing member and pressed by the rotary pressing member via the fixing member to form the nip. The first temperature detector is disposed upstream from the nip in a rotation direction of the fixing member to detect a surface temperature of the fixing member. The second temperature detector is disposed downstream from the nip in a rotation direction of the rotary pressing member to detect a surface temperature of the rotary pressing member. When a difference between a surface temperature of the fixing member detected by the first temperature detector and a surface temperature of the rotary pressing member detected by the second temperature detector after a predetermined time has elapsed since the first temperature detector detects the surface temperature of the fixing member is greater than a predetermined threshold, the heater stops heating the metal member.
In an aspect of this disclosure, there is provided an improved image forming apparatus including the fixing device described above.
Additional aspects, features, and advantages of the present disclosure will be readily ascertained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The accompanying drawings are intended to depict exemplary embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent 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 similar results.
Although the exemplary embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the invention and all of the components or elements described in the exemplary embodiments of this disclosure are not necessarily indispensable to the present invention.
In this disclosure, the term “width direction” refers to a direction perpendicular to a transport direction of a recording medium in a fixing device or an image forming apparatus.
The term “sheet pass area” refers to an area having a range of the recording medium in the width direction (perpendicular to the transport direction of the recording medium). By contrast, the term “non-sheet-pass area” refers to an area except the sheet pass area in the width direction.
The term “fixedly provided or mounted” state is refers to a state in which a stationary member, a metal member, or a reinforcement member described below is irrotationally held without being driven by, for example, a driving source. Accordingly, for example, even in a case in which the stationary member is urged by an urging member, such as a spring, toward a nip, if the stationary member is irrotationally held, the state of the stationary member is referred to as the “fixedly provided” state.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, exemplary embodiment of the present disclosure are described below.
An exemplary embodiment of the present disclosure is described with reference to
First, configuration and operation of an image forming apparatus 1 according to this exemplary embodiment are described with reference to
In
The image forming devices 4Y, 4M, 4C, and 4K include photoconductive drums 5Y, 5M, 5C, and 5K, respectively. Further, chargers 75Y, 75M, 75C, and 75K, development devices 76Y, 76M, 76C, and 76K, cleaners 77Y, 77M, 77C, and 77K, and dischargers surround the photoconductive drums 5Y, 5M, 5C, and 5K, respectively. Image forming processes including a charging process, an exposure process, a development process, a 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 on the photoconductive drums 5Y, 5M, 5C, and 5K, respectively.
A driving motor drives and rotates the photoconductive drums 5Y, 5M, 5C, and 5K clockwise in
In the exposure process, an exposure device 3 emits laser beams L onto the charged surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K, respectively. 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 transfer process, first transfer bias rollers 5Y, 5M, 5C, and 5K 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.
After the transfer of the yellow, magenta, cyan, and black toner images, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K from which the yellow, magenta, cyan, and black toner images are transferred reach positions at which the cleaners 77Y, 77M, 77C, and 77K are disposed opposite the photoconductive drums 5Y, 5M, 5C, and 5K, respectively.
In the cleaning process, cleaning blades included in the cleaners 77Y, 77M, 77C, and 77K mechanically collect residual toner remaining on the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K from 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.
Accordingly, the yellow, magenta, cyan, and black toner images formed on the photoconductive drums 5Y, 5M, 5C, and 5K, respectively, are transferred and superimposed onto the intermediate transfer belt 78. Thus, a color toner image is formed on the intermediate transfer belt 78.
The intermediate transfer unit 85 includes the intermediate transfer belt 78, the first transfer bias rollers 79Y, 79M, 79C, and 79K, an intermediate transfer cleaner 80, a second transfer backup roller 82, a cleaning backup roller 83, and a tension roller 84. 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 R1.
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 to a polarity of toner forming the yellow, magenta, cyan, and black toner images on the photoconductive drums 5Y, 5M, 5C, and 5K, respectively. Accordingly, the yellow, magenta, cyan, and black toner images formed on the photoconductive drums 5Y, 5M, 5C, and 5K, respectively, are transferred and superimposed onto the intermediate transfer belt 78 rotating in the direction R1 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 color toner image formed, on the intermediate transfer belt 78 reaches the second transfer nip. At the second transfer nip, a second transfer roller 89 and the second transfer backup roller 82 sandwich the intermediate transfer belt 78. The second transfer roller 89 transfers the color toner image formed on the intermediate transfer belt 78 onto the recording medium P fed by a registration roller pair 98 at the second transfer nip formed between the second transfer roller 89 and the intermediate transfer belt 78. 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.
Then, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaner 80. 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 intermediate transfer belt 78, thus completing a single sequence of transfer processes performed on the intermediate transfer belt 78.
A paper tray 12 is provided in a lower portion of the image forming apparatus 1, and loads a plurality of recording media P (e.g., transfer sheets). A 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 a 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. Thus, a color toner image is formed on the recording medium P.
The recording medium P bearing the color toner image is sent to a fixing device 20. In the fixing device 20, a fixing belt 21 and a pressing roller 31 apply heat and pressure to the recording medium P to fix the color toner image on the recording medium P. An output roller pair 99 discharges the recording medium P to an outside of the image forming apparatus 1, that is, a stack portion 100. Thus, the recording media P discharged by the output roller pair 99 are stacked on the stack portion 100 successively to complete a single sequence of image forming processes performed by the image forming apparatus 1.
Referring to
As illustrated in
The fixing belt 21 may be a thin, flexible endless belt that rotates or moves counterclockwise in
The base layer of the fixing belt 21 has a thickness in a range of from approximately 30 μm to approximately 50 μm, and includes a metal material such as nickel and/or stainless steel, and/or a resin material such as polyimide.
The elastic layer of the fixing belt 21 has a thickness in a range of from approximately 100 μm to approximately 300 μm, and includes 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 N 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, suppressing formation of a rough image such as an orange peel image. In this exemplary embodiment, the elastic layer of the fixing belt 21 is made of, for example, silicone rubber of a thickness of approximately 200 μm.
The release layer of the fixing belt 21 has a thickness in a range of from approximately 10 μm to approximately 50 μm, and includes 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 diameter of the fixing belt 21 is set to approximately 15 mm to approximately 120 mm. In this exemplary embodiment, the fixing belt 21 has an inner diameter of, for example, approximately 30 mm. As illustrated in
The stationary member 26 is fixed inside the fixing belt 21 in such a manner that the inner circumferential surface 21a of the fixing belt 21 slides over the stationary member 26. The stationary member 26 is pressed by the pressing roller 31 with the fixing belt 21 sandwiched between the stationary member 26 and the pressing roller 31 to form the nip N between the fixing belt 21 and the pressing roller 31 through which the recording medium P is conveyed. As illustrated in
As illustrated in
The substantially-cylindrical metal member 22 heated by radiation heat generated by the heater 25 heats (e.g., transmits heat to) the fixing belt 21. In other words, the heater 25 heats the metal member 22 directly and heats the fixing belt 21 indirectly via the metal member 22. The metal member 22 may have a thickness not greater than approximately 0.1 mm to maintain desired heating efficiency for heating the fixing belt 21.
The metal member 22 may include a metal thermal conductor, that is, a metal having thermal conductivity, such as stainless steel, nickel, aluminum, and/or iron. Preferably, the metal member 22 may include ferrite stainless steel having a relatively smaller heat capacity per unit volume obtained by multiplying density by specific heat. In this exemplary embodiment, the metal member 22 includes, for example, SUS430 stainless steel as ferrite stainless steel and has a thickness of, for example, 0.1 mm.
The heater 25 may be a halogen heater and/or a carbon heater. As illustrated in
As described above, for the fixing device 20 according to this exemplary embodiment, the metal member 22 does not heat 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
The substantially-cylindrical metal member 22 is fixedly disposed opposite the fixing belt 21 in such a manner that a certain clearance is provided between the inner circumferential surface 21a of the fixing belt 21 and the metal member 22 over an area along the inner surface of the fixing belt 21 except for where the nip N is formed. The clearance δ, that is, a gap between the fixing belt 21 and the metal member 22 at the area along the inner surface of the fixing belt 21 other than the nip N, is not greater than 1 mm, expressed as 0 mm <δ=<1 mm. Accordingly, the fixing belt 21 does not slidably contact the metal member 22 over an increased area, thus suppressing wearing of the fixing belt 21. At the same time, the clearance provided between the metal member 22 and the fixing belt 21 is small enough to prevent any substantial decrease in heating efficiency of the metal member 22 for heating the fixing belt 21. Moreover, the metal member 22 disposed close to the fixing belt 21 supports the fixing belt 21 and maintains the circular loop form of the flexible fixing belt 21, thus limiting degradation of and damage to the fixing belt 21 due to deformation of the fixing belt 21.
A lubricant, such as fluorine grease or silicone oil, is applied between the inner circumferential surface 21a of the fixing belt 21 and the metal member 22, so as to decrease wearing of the fixing belt 21 as the fixing belt 21 slidably contacts the metal member 22.
In this exemplary embodiment, the metal member 22 has a cross section of a substantially circular shape. Alternatively, the metal member 22 may have a cross section of a polygonal shape.
As illustrated in
In order to provide the above-described capabilities, the reinforcement member 23 may include metal material having great mechanical strength, such as stainless steel and/or iron. In this exemplary embodiment, the reinforcement member 23 includes, for example, SUS304 (or SUS403) of a thickness of approximately 1.5 mm to approximately 2 mm.
Further, an opposing face of the reinforcement member 23 which faces the heater 25 may include a heat insulation material partially or wholly. Alternatively, the opposing face of the reinforcement member 23 disposed opposite the heater 25 may be mirror-ground. Accordingly, heat radiated by the heater 25 toward the reinforcement member 23 to heat the reinforcement member 23 is used to heat the metal member 22, improving heating efficiency for heating the metal member 22 and the fixing belt 21.
As illustrated in
When the elastic layer 33 of the pressing roller 31 includes a sponge material such as silicon rubber foam, the pressing roller 31 applies decreased pressure to the fixing belt 21 at the nip N to decrease bending of the metal member 22. Further, the pressing roller 31 provides increased heat insulation, and therefore heat is not transmitted from the fixing belt 21 to the pressing roller 31 easily, improving heating efficiency for heating the fixing belt 21.
In this exemplary embodiment, the diameter of the fixing belt 21 is substantially identical to the diameter of the pressing roller 31. Alternatively, the diameter of the fixing belt 21 is may be smaller than the diameter of the pressing roller 31.
The fixing device 20 further includes the second temperature sensor 50, such as a thermistor, to detect the surface temperature of the pressing roller 31. The second temperature sensor 50 is used to detect a slip (rotation failure) of the fixing belt 21 along with the first temperature sensor 40, which is described below in detail.
In this exemplary embodiment, since the two temperature sensors 40 and 50 are used to detect a slip of the fixing belt 21, a heat source directly heating the pressing roller 31 (e.g., a heater within a metal core of the pressing roller 31) is not provided.
As illustrated in
As described above, in this exemplary embodiment, the stationary member 26 forming the nip N has a concave shape. Alternatively, the stationary member 26 may have a flat shape. In other words, the sliding-contact surface of the stationary member 26 that opposes the pressing roller 31 may be formed in flat shape. For such a configuration, the shape of the nip is substantially parallel to an image recorded face of the recording medium P. As a result, the fixing belt 21 comes into closer contact with the recording medium P, thus enhancing fixing performance. In addition, the curvature of the fixing belt 21 is relatively large at the exit side of the nip, thus facilitating smooth separation of the recording medium P from the nip.
The base layer 26a of the stationary member 26 includes a rigid material so that the stationary member 26b is not bent substantially by pressure applied by the pressing roller 31. In this exemplary embodiment, the base layer 26b is made of, for example, aluminum of a thickness of approximately 1.5 mm. In this exemplary embodiment, the base layer 26b is made of, for example, aluminum of a thickness of approximately 1.5 mm.
The substantially pipe-shaped metal member 22 may be formed by bending sheet metal into the desired shape. Sheet metal is used to give the metal member 22 a thin thickness to shorten warm-up time. However, such a thin metal member 22 has little rigidity, and therefore is easily bent or deformed by pressure applied by the pressing roller 31. A deformed metal member 22 does not provide a desired nip length of the nip N, degrading fixing property. To address this problem, in this exemplary embodiment, the rigid stationary member 26 is provided separately from the thin metal member 22 to help form and maintain the proper nip N.
The surface layer 26a of the stationary member 26 is a low friction material such as fluorocarbon rubber. Such a configuration can form a desired nip between the stationary member 26 and the fixing belt 21 while suppressing wear of the fixing belt 21 and the stationary member 26 due to sliding contact of the stationary member 26 with the fixing belt 21. In this exemplary embodiment, the surface layer 26a has a thickness of approximately 1.5 and approximately 2 mm.
Further, the surface layer 26a may be preliminarily impregnated with the lubricant. Thus, the lubricant is retained at the surface of the stationary member 26 contacting the fixing belt 21, thus suppressing wearing of the stationary member 26 and the fixing belt 21.
As illustrated in
In this exemplary embodiment, the metal member 22 is disposed in proximity to the fixing belt 21 throughout substantially the entire circumference thereof. Accordingly, even in a standby mode before printing starts, the metal member 22 heats the fixing belt 21 in the circumferential direction without temperature fluctuation. Consequently, the image forming apparatus 1 starts printing as soon as the image forming apparatus 1 receives a print request. In conventional on-demand fixing devices, when heat is applied to the deformed pressing roller 31 at the nip N in the standby mode, the pressing roller 31 may suffer from thermal degradation due to heating of the rubber included in the pressing roller 31, resulting in a shortened life of the pressing roller 31 or permanent compression strain of the pressing roller 31. Heat applied to the deformed rubber increases permanent compression strain of the rubber. The permanent compression strain of the pressing roller 31 makes a dent in a part of the pressing roller 31, and therefore the pressing roller 31 does not provide the desired nip length of the nip N, generating faulting fixing or noise in accordance with rotation of the pressing roller 31.
To address those problems, according to this exemplary embodiment, the heat insulator 27 is provided between the stationary member 26 and the metal member 22 to reduce heat transmitted from the metal member 22 to the stationary member 26 in the standby mode, suppressing heating of the deformed pressing roller 31 at high temperature in the standby mode.
A lubricant is applied between the stationary member 26 and the fixing belt 21 to reduce sliding resistance between the stationary member 26 and the fixing belt 21. However, the lubricant may deteriorate under high pressure and temperature applied at the nip N, resulting in unstable slippage of the fixing belt 21 over the stationary member 26.
To address this problem, according to this exemplary embodiment, the heat insulator 27 is provided between the stationary member 26 and the metal member 22 to reduce heat transmitted from the metal member 22 to the lubricant at the nip N, thus reducing deterioration of the lubricant due to high temperature.
In this exemplary embodiment, the heat insulator 26 provided between the stationary member 26 and the metal member 22 insulates the stationary member 26 from the metal member 22. Accordingly, the metal member 22 heats the fixing belt 21 with reduced heat at the nip N. Consequently, the recording medium P discharged from the nip N has a decreased temperature compared to when the recording medium P enters the nip N. In other words, at the exit of the nip N, 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. Accordingly, an adhesive force which adheres the fixed toner image T to the fixing belt 21 is decreased and the recording medium P is separated from the fixing belt 21. 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 this exemplary embodiment, a stainless steel sheet having a thickness of about 0.1 mm is bent into the substantially cylindrical metal member 22. However, spring-back of the stainless steel sheet may expand a circumference of the metal member 22, and therefore the stainless steel sheet may maintain the desired pipe shape. As a result, the metal member 22 having an expanded circumference may contact the inner circumferential surface 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 member 22 to the fixing belt 21. To address this problem, according to this exemplary embodiment, the stay 28 supports and holds the concave portion (bent portion) 22a of the metal member 22 provided with an opening so as to prevent deformation of the metal member 22 due to spring-back. For example, the stay 28 is press-fitted to the concave portion 22a of the metal member 22 to contact the inner circumferential surface of the metal member 22 while the shape of the metal member 22 that is bent against spring-back of the stainless steel sheet is maintained.
Preferably, the metal member 22 has a thickness not greater than approximately 0.2 mm to increase heating efficiency of the metal member 22.
As described above, the substantially cylindrical-shaped metal member 22 may be formed by bending sheet metal into the desired shape. Sheet metal is used to give the metal member 22 a thin thickness to shorten warm-up time. However, such a thin metal member 22 has little rigidity, and therefore may be easily bent or deformed by pressure applied by the pressing roller 31. Accordingly, the deformed metal member 22 may not provide a desired nip length of the nip N, resulting in degraded fixing property. To address this problem, according to this exemplary embodiment, the concave portion 22a of the thin metal member 22 into which the stationary member 26 is inserted is spaced away from the nip N to prevent the metal member 22 from receiving pressure from the pressing roller 31 directly.
The following describes operation of the fixing device 20 having the above-described structure. When the image forming apparatus 1 is powered on, power is supplied to the heater 25. Further, when a drive force from a drive motor is transmitted to the pressing roller 31, the pressing roller 31 starts rotating in the rotation direction R3. Thus, by friction between the pressing roller 31 and the fixing belt 21, the fixing belt 21 is rotated in the rotation direction R2 in accordance with the 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 N formed between the fixing belt 21 and the pressing roller 31 pressed against each other. At the nip N, the fixing belt 21 heated by the heater 25 via the metal member 22 applies heat to the recording medium P. Simultaneously, the pressing roller 31 and the stationary member 26 reinforced by the reinforcement member 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 N is conveyed in a direction Y11.
Configuration and operation of a fixing device 20 according to an exemplary embodiment of the present disclosure are described below.
As illustrated in
When a difference between a temperature detected by the first temperature sensor 40 (e.g., a temperature of the fixing belt 21 immediately before the fixing belt 21 enters the nip) and a temperature detected by the second temperature sensor 50 (e.g., a temperature of the pressing roller 31 immediately after the pressing roller 31 goes out of the nip) is greater than a predetermined threshold, the controller controls the heater 25 to stop heating the metal member 22. At this time, the second temperature sensor 50 detects the temperature of the pressing roller 31 after a predetermined time has elapsed since the first temperature sensor 40 detects the temperature of the fixing belt 21.
For example, the first temperature sensor 40 detects the surface temperature of the fixing belt 21 rotating in the direction R2 of
To achieve the above-described control, as described below, when the fixing belt 21 normally rotates without slipping, heat from the fixing belt 21 is preferably transferred to the pressing roller 31 at a substantially constant rate (or proportionally), regardless of whether a recording medium is passing through the nip or not.
For example, if the above-described temperature difference greater than the predetermined threshold is detected sequentially more than a predetermined number of times (or over a predetermined time period), the controller determines that the fixing device is out of order, and controls the image forming apparatus 1 to stop image formation and display a message indicating the out-of-order state or prompting servicing. Such a configuration can prevent fixing failure of an output image caused by temperature decrease of the fixing belt 21 at the nip or transport failure of the recording medium P caused by rotation failure of the fixing belt 21.
By contrast, if the above-described temperature difference greater than the predetermined threshold is not detected sequentially more than a predetermined number of times (i.e., the temperature difference returns to a normal value within the predetermined number of times), the power unit starts supplying power to the heater 25 again to heat the metal member 22. Such a configuration can suppress frequent occurrences of downtime of the image forming apparatus 1 while simultaneously preventing overheating of the fixing belt 21.
As illustrated in
Such a configuration can reduce errors in detecting the surface temperature of the fixing belt 21 immediately before the fixing belt 21 enters the nip and the surface temperature of the pressing roller 31 immediately after the pressing roller 31 passes through the nip. Thus, the slip of the fixing belt 21 can be accurately detected.
It is to be noted that, even if the layout of the fixing device 20 and the image forming apparatus 1 prevents the first temperature sensor 40 and/or the second temperature sensor 50 from being disposed within the above-described range, the slip of the fixing belt 21 can be detected if the first temperature sensor 40 and the second temperature sensor 50 are disposed within a range in which the temperature of the fixing belt 21 detected upstream from the nip in the rotation direction R2 of the fixing belt 21 can be associated with the temperature of the pressing roller 31 detected downstream from the nip in the rotation direction R3 of the pressing roller 31.
For example, if the outer diameter and rotation speed of the fixing belt 21 are equivalent to those of the pressing roller 31, the first temperature sensor 40 and the second temperature sensor 50 are disposed so that the circumferential distance from the detection position of the first temperature sensor 40 to the nip (i.e., a central position of the nip) is equivalent to the circumferential distance from the nip (i.e., the central position of the nip) to the detection position of the second temperature sensor 50.
In this exemplary embodiment, as illustrated in
As illustrated in
With such a configuration, even if the recording media P of different sizes pass through the nip, the temperature of the fixing belt 21 detected upstream from the nip can be accurately associated with the temperature of the pressing roller 31 detected downstream from the nip, thus enhancing the accuracy in detecting the slip of the fixing belt 21.
For this exemplary embodiment, the above-described detection of the slip of the fixing belt 21 and control operations involving the detection are performed not only when a recording medium P passes through the nip (i.e., when fixing process is performed at the nip) but also in a warm-up time or a non-sheet-passing period, such as intervals between a plurality of recording media P during sequential sheet feeding, in which, with the heater 25 being powered on, the fixing belt 21 and the pressing roller 31 are rotated without performing fixing process. For this exemplary embodiment, a predetermined threshold for non-sheet-passing period is set smaller than a predetermined threshold for sheet passing period (which is a difference between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50 to determine whether the slip of the fixing belt 21 is in occurrence. As described below in more detail, this is because the amount of heat transferred from the fixing belt 21 to the pressing roller 31 is different between sheet passing period and non-sheet-passing period although the amount of heat is transferred from the fixing belt 21 to the pressing roller 31 at a substantially constant rate (or proportionally) between sheet passing period and non-sheet-passing period. In particular, in the warm-up time, unlike the sheet passing period, the difference between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50 increases proportionally with time from the activation. Therefore, it is preferable to use the elapsed time from the activation as a control parameter. Such configuration and control allows accurate detection of the slip of the fixing belt 21 in both the sheet passing period and the non-sheet-passing period.
With reference to experimental data of
In
A line R0 shows a fluctuation in temperature of a fixing belt in a conventional belt-type fixing device, which is a temperature profile detected by a first temperature sensor in an warm-up time, and a line R1 shows a fluctuation in temperature of a pressing roller in the conventional belt-type fixing device, which is a temperature profile detected by a second temperature sensor in the warm-up time.
As illustrated in
By contrast, since the fixing device 20 according to the fixing device 20 is faster in raising the temperature of the fixing belt 21 than the conventional fixing device, as illustrated in the line S0, the slope of the output of the first temperature sensor 40 is greater. As a result, the amount of heat transferred from the fixing belt 21 to the pressing roller 31 increases over time. Further, since the heater 25 is disposed opposing the fixing belt 21 (and the metal member 22) at an area upstream from the nip N, as illustrated in the line S1, the slope of the output of the second temperature sensor 50 becomes steep, resulting in a shorter delay M (M<N) in starting up.
As described above, for the fixing device 20 according to the fixing device 20, the temperature rising of the fixing belt 21 is steep, the distance from a major heating point of the fixing belt 21 (close to the heater 25) to the nip is short, and the amount of heat transferred from the fixing belt 21 to the pressing roller 31 is relatively great. Such a configuration allows detection of the slip of the fixing belt 21 based on the above-described distance between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50.
As illustrated in
Specifically, in
For this exemplary embodiment, in consideration of the delay M in the output of the second temperature sensor 50 at the start of warm-up operation (which is caused since no heat is transferred from the fixing belt 21 to the pressing roller 31), detection of the slip of the fixing belt 21 is not performed during the time corresponding to the delay M.
In
As illustrated in
As illustrated in
The above-described detection of the slip of the fixing belt 21 may not be performed immediately before and after switching from the non-sheet-passing period to the sheet passing period. This is because fluctuations in the timing at which a leading edge of a recording medium P enters the nip might result in fluctuations in the difference between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50 before and after switching from the non-sheet-passing period to the sheet passing period. The timing of switching between the non-sheet-passing period and the sheet passing period can be calculated from a timing at which the recording medium P starts to be fed from the registration roller pairs 98, a transport distance from the registration roller pairs 98 to the nip of the fixing device 20, and a transport speed (process linear velocity) of the recording medium P.
For the control of the heater 25A, as illustrated in
Graphs S0 and S1 of
As described above, for this exemplary embodiment, the fixing device 20 includes the first temperature sensor 40 serving as a first temperature detector to detect a surface temperature of the fixing belt 21 at a position upstream from the nip in the rotation direction R2 of the fixing belt 21 and the second temperature sensor 50 serving as a second temperature detector to detect a surface temperature of the pressing roller (rotary pressing member) 31 at a position downstream from the nip in the rotation direction R3 of the pressing roller 31. When the difference between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50 is greater than a predetermined threshold, the heater 25 stops heating the metal member 22. Such a configuration can prevent fixing failures, such as uneven fixed image, while achieving a reduced warm-up time and/or first print time. In addition, even if a slip of the fixing belt 21 occurs, overheating of the fixing belt 21 can be prevented.
As described above, in this exemplary embodiment, the first temperature sensor 40 and the second temperature sensor 50 are contact-type thermistors. However, it is to be noted that the first temperature sensor 40 and the second temperature sensor 50 are not limited to such contact-type thermistors. For example, at least one of the first temperature sensor 40 and the second temperature sensor 50 may be a non-contact-type thermistor or temperature sensor (e.g., thermopile). Such a configuration can obtain effects equivalent to the above-described effects.
Next, another exemplary embodiment of the present disclosure is described with reference to
As with the fixing device illustrated in
The fixing device 20 includes an induction heater 60 as a heating unit, instead of the heater 25 illustrated in
The induction heater 60 includes an exciting coil, a core, and a coil guide. The exciting coil includes litz wires formed of a bundle of thin wires, which extend in the axial direction of the fixing belt 21 (e.g., a direction perpendicular to a surface of a sheet on which
Operation of the fixing device 20 having the above-described structure is described below.
The induction heater 60 heats the fixing belt 21 rotating in the rotation direction R2 at a position at which the fixing belt 21 faces the induction heater 60. Specifically, a high-frequency alternating current is applied to the exciting coil to generate magnetic lines of force around the metal member 22 in such a manner that the magnetic lines of force are alternately switched back and forth. Accordingly, an eddy current is generated on the surface of the metal member 22, and electric resistance of the metal member 22 generates Joule heat. The Joule heat heats the metal member 22 by electromagnetic induction, and the heated heating member 22 heats the fixing belt 21.
In order to heat the metal member 22 effectively by electromagnetic induction, the induction heater 60 may face the metal member 22 in an entire circumferential direction of the metal member 22. The metal member 22 may include nickel, stainless steel, iron, copper, cobalt, chrome, aluminum, gold, platinum, silver, tin, palladium, and/or an alloy of a plurality of those metals, or the like.
As described above, the fixing device 20 according to this exemplary embodiment also includes the first temperature sensor 40 serving as a first temperature detector to detect a surface temperature of the fixing belt 21 at a position upstream from the nip in the rotation direction R2 of the fixing belt 21 and the second temperature sensor 50 serving as a second temperature detector to detect a surface temperature of the pressing roller (rotary pressing member) 31 at a position downstream from the nip in the rotation direction R3 of the pressing roller 31. When the difference between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50 is greater than a predetermined threshold, the induction heater 60 stops heating the metal member 22. Such a configuration can prevent fixing failures, such as uneven fixed image, while achieving a reduced warm-up time and/or first print time. In addition, even if a slip of the fixing belt 21 occurs, overheating of the fixing belt 21 can be prevented.
As described above, for the fixing device 20 illustrated in
Even in such a configuration, the controller stops heating the metal member 22 when the difference between temperatures detected by the first temperature sensor 40 and the second temperature sensor 50 at adequate timings adjusted in the same manner as the above-described exemplary embodiment is greater than a predetermined threshold, thus obtaining effects equivalent to those of the above-described exemplary embodiment.
In each of the above-described exemplary embodiments, a fixing belt having the multi-layer structure is used as the fixing belt 21. Alternatively, an endless fixing film including polyimide, polyamide, fluorocarbon resin, and/or metal may be used as a fixing belt to provide effects equivalent to the effects provided by the fixing device 20 described above.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.
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