Patent Grant
8849169
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application Nos. 2011-002890, filed on Jan. 11, 2011 and 2011-266049, filed on Dec. 5, 2011, both in the Japan Patent Office, which are hereby incorporated herein by reference in their entirety.
1. Field of the Invention
Exemplary aspects of the present invention generally relate to a fixing device and an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-function system including a combination thereof, and more particularly, to a fixing device using an electromagnetic induction heating method 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 bearing member; an optical scanner projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device 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 unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
Fixing devices that use an electromagnetic induction heating method to reduce a warm-up time (the time it takes the fixing device to reach a target temperature) of the image forming apparatus, thereby conserving energy, are known, such as JP-2009-14972-A. One example of such a fixing device using the induction heating method is equipped with a support roller (a heating roller) serving as a heat generating body, a fixing auxiliary roller (fixing roller), a fixing belt, an induction heater, and a pressing roller. The fixing belt is formed into a loop and wound around the support roller and the fixing auxiliary roller. The pressing roller contacts the fixing auxiliary roller via the fixing belt. The induction heater is disposed opposite the support roller via the fixing belt, and consists of a coil portion including an excitation coil, a core (excitation coil core) facing the coil portion, and a holder that holds parts such as the coil portion and the core. The excitation coil is wound longitudinally around the induction heater.
As the fixing belt rotates and comes to face the induction heater, the fixing belt is heated by the induction heater. Subsequently, the heated fixing belt heats a toner image on a recording medium at a fixing nip where the fixing auxiliary roller and the pressing roller meet and press against each other and through which the recording medium sheet is conveyed, thereby fixing the toner image onto the recording medium. More specifically, an alternating magnetic field is formed around the coil portion by supplying a high-frequency alternating current thereto. As a result, an eddy current is generated near the surface of the support roller, generating Joule heat through the electrical resistance of the support roller itself, which in turn heats the fixing belt wound around the support roller, accordingly.
In this configuration, the heat generating body is directly heated by electromagnetic induction, hence providing high heat conversion efficiency compared with other known heating methods such as those employing a halogen heater. The electromagnetic induction heating method can heat the surface of the fixing belt to a desired temperature (fixing temperature) quickly with little power.
Another example of a known fixing device using the electromagnetic induction heating method (JP-3519401-B) includes a core (i.e. back surface core) disposed opposite an excitation coil consisting of a C-type core and a center core to enhance heat generating efficiency.
Generally, in the fixing device using the electromagnetic induction heating method, a magnetic circuit needs to be closed to prevent generation of leakage flux from the coil for efficient induction heating. A known technique to close the magnetic circuit includes adding a ferrite core, a shield, or the like. The fixing device using the C-type core and the center core disposed opposite the excitation coil may enhance the heat generating efficiency of the heat generating member. However, the heat generating efficiency may not be sufficient.
In the known fixing devices described above, the heating member and the magnetic core that directs the magnetic flux from the excitation coil to the heat generating member are relatively widely separated, resulting in a longer time to bring the heat generating member to a desired temperature. In other words, the warm-up time of the fixing device is lengthened.
In view of the above, there is demand for an induction heating-type fixing device with good heating efficiency and a short warm-up time.
In view of the foregoing, in an aspect of this disclosure, an induction heating-type fixing device includes a fixing member, an excitation coil, a magnetic core, a holder, and a pressing member. The fixing member includes a heat generating layer to heat and fuse a toner image on a recording medium. The excitation coil wound a predetermined number of times is disposed facing an outer surface of the fixing member, to generate a magnetic flux relative to the fixing member. The magnetic core forms a continuous magnetic path to direct the magnetic flux generated by the excitation coil to the fixing member. The holder holds the excitation coil and the magnetic core. The pressing member is disposed opposite the fixing member to press against the fixing member and form a fixing nip between the fixing member and the pressing member through which the recording medium is conveyed. The magnetic core is exposed from the holder at the fixing member side.
According to another aspect, an induction heating-type fixing device includes a fixing member, an excitation coil, a magnetic core, a holder, and a pressing member. The fixing member includes a heat generating layer to heat and fuse a toner image on a recording medium. The excitation coil wound a predetermined number of times is disposed facing an outer surface of the fixing member, to generate a magnetic flux relative to the fixing member. The magnetic core forms a continuous magnetic path to direct the magnetic flux generated by the excitation coil to the fixing member. The holder holds the excitation coil and the magnetic core. The pressing member is disposed opposite the fixing member to press against the fixing member and form a fixing nip between the fixing member and the pressing member through which the recording medium is conveyed. The magnetic core is embedded in a wall of the holder.
The aforementioned and other aspects, features and advantages would be more fully apparent from the following detailed description of illustrative embodiments, the accompanying drawings and the associated claims.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be more readily obtained as the same becomes better understood by reference to the following detailed description of illustrative embodiments when considered in connection with the accompanying drawings, wherein:
A description is now given of illustrative embodiments. It should be noted that although such terms as first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that such elements, components, regions, layers and/or sections are not limited thereby because such terms are relative, that is, used only to distinguish one element, component, region, layer or section from another region, layer or section. Thus, for example, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.
In addition, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. Thus, for example, as used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
In describing illustrative 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 a similar result.
In a later-described comparative example, illustrative embodiment, and alternative example, for the sake of simplicity, the same reference numerals will be given to constituent elements such as parts and materials having the same functions, and redundant descriptions thereof omitted.
Typically, but not necessarily, paper is the medium from which is made a sheet on which an image is to be formed. It should be noted, however, that other printable media are available in sheet form, and accordingly their use here is included. Thus, solely for simplicity, although this Detailed Description section refers to paper, sheets thereof, paper feeder, etc., it should be understood that the sheets, etc., are not limited only to paper, but includes other printable media as well.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and initially with reference to
With reference to
As illustrated in
The image forming stations 10Y, 10M, 10C, and 10Bk, one for each of the colors yellow, magenta, cyan, and black are arranged in tandem contacting a conveyance belt 20 for conveying a recording medium such as a sheet of paper. The conveyance belt 20 is disposed below the image forming stations 10. The recording medium adheres electrostatically to the surface of the conveyance belt 20.
It is to be noted that the image forming stations 10Y, 10M, 10C, and 10Bk all have the same configuration as all the others, differing only in the color of toner employed. Thus, a description is provided only of the image forming station 10Y for yellow disposed at the extreme upstream end in a direction of conveyance of the recording medium as a representative example of the image forming stations 10.
The image forming station 10Y includes the photoconductive drum 1Y disposed substantially at the center of the image forming station 10Y. The photoconductive drum 1Y contacts the conveyance belt 20 while rotating. The photoconductive drum 1Y is surrounded by various pieces of imaging equipment, such as a charging device 2Y, an exposure device 3Y, a developing device 4Y, a transfer roller 5Y, a drum cleaner 6Y, and a charge neutralizing device (not illustrated). The charging device 2Y charges the surface of the photoconductive drum 1Y at a certain electric potential. The exposure device 3Y illuminates the charged surface of the photoconductive drum 1Y with light based on an image signal after color separation, thereby forming an electrostatic latent image on the surface of the photoconductive drum 1Y. The developing device 4Y develops the electrostatic latent image on the surface of photoconductive drum 1Y with toner of yellow, thereby forming a visible image, also known as a toner image of yellow. The transfer roller 5Y transfers the developed toner image onto a recording medium conveyed by the conveyance belt 20. The drum cleaner 6Y removes residual toner remaining on the surface of the photoconductive drum 1Y after transfer process. The charge neutralizing device is disposed along the direction of rotation of the photoconductive drum 1Y to remove residual charge on the photoconductive drum 1Y.
In
At the left of the conveyance belt 20, a fixing device 40 according to an illustrative embodiment is provided. A detailed description of the fixing device 40 is provided with reference to
In the fixing device 40, heat and pressure are applied to the recording medium bearing the toner image, thereby fusing and pressing the toner image onto the recording medium. Accordingly, the toner image is fixed on the recording medium. Subsequently, the recording medium is discharged outside the image forming apparatus via sheet discharge rollers disposed downstream from the conveyance path of the fixing device 40. A sequence of imaging cycle is completed.
Next, with reference to
As illustrated in
The metal core 41a is made of a stainless steel, for example, SUS304 or the like formed into a cylinder or a solid tube. The thickness thereof is approximately 1 mm. As the elastic layer 41b, a solid or foam heat-resistant silicone rubber or the like is used to cover the metal core 41a. The thickness of the elastic layer 41b is in a range of from approximately 3 mm to 10 mm. The hardness thereof is in a range from 10° to 50° according to JIS-A.
The heat generating layer 41c is constructed of a base layer, a main heat generating layer, an elastic layer and a release layer, in that order from the inner side of the heat generating layer 41c. The base material of the heat generating layer 41c is nickel (Ni) and has a thickness in a range of from approximately 3 μm to 15 μm, thereby enhancing a heat generating efficiency. Alternatively, SUS or a magnetic shunt alloy having a Curie point in a range of from 160° C. to 220° C. may be used as the heat generating layer 41c. An aluminum member may be disposed inside the magnetic shunt alloy, thereby stopping the temperature from rising near the Curie point. Polyimide may be employed for the base layer. With this configuration, the heat capacity of the heat generating layer is less than when using metal in the base material, thereby reducing energy to increase the temperature.
The main heat generating layer of the heat generating layer 41c is made of copper (Cu) and has a thickness equal to or less than 5 μm. For prevention of oxidation, a nickel (Ni) layer may be provided on the surface of the copper (Cu) layer. The elastic layer of the heat generating layer 41c is formed of silicone rubber and has a thickness in a rage of from 100 μm to 500 μm. The elastic layer enhances adhesion of the fixing roller 41 with respect to the recording medium.
The release layer of the heat generating layer 41c is made of a fluorine compound such as perfluoroalkoxy polymer resin (PFA) and has a thickness in a rage of from 10 μm to 100 μm. The release layer enhances releasability of the surface of the fixing roller 41 that contacts directly the toner image T.
According to the first illustrative embodiment, the fixing roller 41 serves as a fixing member that melts the toner image and also serves as a heat generating member that is heated directly by the induction heater 50.
In the present embodiment, the base material of the heat generating layer 41c is a single layer of magnetic metal. The magnetic metal that forms the heat generating layer may include nickel (Ni) having a thickness of approximately 10 μm. Alternatively, iron, cobalt, copper, or alloys thereof may be used.
The pressing roller 42 is constructed of a cylinder member 42a made of metal including, but not limited to, aluminum and copper. An elastic layer 42b is provided on the cylinder member 42a. The elastic layer 42b is formed of rubber material such as fluorocarbon rubber and silicone rubber. The elastic layer 42b of the pressing roller 42 has a thickness in a range of from approximately 0.5 mm to 2 mm and a hardness thereof in a range of from 20° to 50° on the Asker C scale. The pressing roller 42 contacts and presses against the fixing roller 41. The recording medium passes through the fixing nip N between the fixing roller 41 and the pressing roller 42.
With reference to
The excitation coil 51 includes Litz wire consisting of strands of 50 to 500 pieces of wire, each wire having φ in a range of from approximately 0.05 mm to 0.2 mm and insulated electrically from each other. Such Litz wire is wound about 5 times to 15 times. In the holder 53 the excitation coil 51 extends across an entire area of a maximum heating region of the fixing roller 41 and generates an interlinkage magnetic flux relative to the fixing roller 41. On the surface of Litz wire, a fusing layer is provided. The fusing layer is solidified by the Joule heating or when heated in a thermostat chamber so that the shape of the wound coil is maintained. Alternatively, the Litz wire without the fusing layer may be wound and pressure-molded, thereby keeping its shape reliably. The Litz wire needs to be resistant to heat at a temperature equal to or more than the fixing temperature. Hence, the insulating material for a wire strand of the Litz wire includes, but is not limited to, both heat-resistant and insulating resin such as polyamide-imide resin and polyimide resin.
The excitation coil 51 consisting of multiple-wound Litz wire is adhered to the holder 53 using an adhesive agent, for example, a silicone adhesive agent. The holder 53 also needs to be resistant to heat at the temperature equal to or greater than the fixing temperature. Thus, the material for the holder 53 includes, but is not limited to, a highly heat-resistant resin such as polyethylene terephthalate (PET), polyphenylene sulfide (PPS), and liquid crystal polymer (LCP). The excitation coil 51 is held by a surface of the holder 53 facing the fixing roller 41. In order to satisfy product safety standards, insulating properties in accordance with Systems of Insulating Materials UL1446, and moldability of resin, the holder 53 needs to have a certain thickness. In view of this, because liquid crystal polymer is tolerant to heat and has good insulating properties as well as moldability, liquid crystal polymer (LCP) is employed according to the illustrative embodiment of the present invention.
As described above, the magnetic core 52 consists of the arch core 52a, the side core 52b, and the center core 52c. As illustrated in
As illustrated in
By contrast, in a related-art induction heater as illustrated in
The material for the arch core 52a, the side core 52b, and the center core 52c includes, but is not limited to, soft magnetic material and yet highly electrically resistant such as Mn—Zn ferrites and Ni—Zn ferrites. The magnetic core 52 is made through compression molding in which powder material is compressed in a mold cavity where heat and pressure are applied to sinter. During sinter process, the magnetic core 52 shrinks. Thus, if the shape of the magnetic core 52 is complicated and shrinks during sinter process, the magnetic core 52 deforms or bends in a complicated manner, complicating the resulting shape. For this reason, preferably, the magnetic core 52 has a simple shape.
The arch core 52a, the side core 52b, and the center core 52c are individual parts and assembled together during assembly. Accordingly, each core can have a simple shape, thereby facilitating assembly and hence reducing the manufacturing cost.
Referring now to
As viewed from the fixing roller side, the side cores 52b and the center cores 52c are exposed from the holder 53. The surface of the side cores 52b and the center cores 52c facing the fixing roller 41 is substantially near the fixing roller 41. The center of the holder 53 is curved inward to accommodate the shape of the surface of the fixing roller 41. The width of the exposed portion of the side core 52b and the center core 52c in the longitudinal direction of the holder 53 is not limited to the illustrative embodiment shown in the drawings. As will be later described with reference to
With reference to
A plurality of center cores 52c, here, 6 pieces of center cores 52c, are disposed discontinuously at the center of the holder 53 in the longitudinal direction thereof. The center cores 52c are spaced apart a certain distance and separated by ribs 56 serving as a reinforcing member. The ribs 56 are each disposed between the center cores 52c. The strength of the holder 53 is degraded when the notches 90 are formed in the wall of the holder 53 to insert the side cores 52b and the center cores 52c. In view of this, the ribs 55 and 56 are provided to the holder 53 to reinforce the strength of the holder 53. In
With reference to
According to the illustrative embodiment, the holder 53 includes both the ribs 55 and the ribs 56. Alternatively, the holder 53 may include either the ribs 55 or the ribs 56 to reinforce the holder 53. As illustrated in
As described above, the ribs 55 and 56 provided inside the holder 53 can reinforce the strength of the holder 53 even when the notches 90, from which the side cores 52c and the center cores 52c are inserted, are formed in the holder 53 to expose the side cores 52b and the center cores 52c from the holder 53. It is to be noted that the side cores 52b and the center cores 52c are exposed from the holder 53 as viewed from the fixing roller side. However, other cores are not exposed from the holder 53.
According to the first illustrative embodiment, the side cores 52b and the center cores 52c are adhered to the holder 53 using some form of adhesive. This facilitates assembly and reduces a number of assembly steps and the associated cost. An adhesive agent, for example, a silicone adhesive agent may be used. Alternatively, a heat-resistant adhesive tape may be used to fix the side cores 52b and the center cores 52c to the holder 53.
It is known that separation of the side cores 52b and the center cores 52c from one another does not degrade magnetic coupling and heat generating efficiency as compared with continuously disposing the side cores 52b and the center cores 52c in the longitudinal direction of the holder 53. According to the first illustrative embodiment, the width of the ribs is approximately 2 mm. However, the width is not limited to 2 mm. By increasing the width of the ribs, the number of cores can be reduced, thereby reducing the cost.
Referring back to
As the fixing roller 41 is rotated in a counterclockwise direction by a drive motor, the pressing roller 42 rotates in the clockwise direction. The fixing roller 41 serving as a fixing member is heated by the magnetic flux generated by the induction heater 50 when the fixing roller 41 comes to face the induction heater 50. More specifically, a high-frequency alternating current in a range of from 20 kHz to 1 MHz (preferably, in a range of from 20 kHz to 100 kHz) is supplied to the excitation coil 51 from a power source. Accordingly, a line of magnetic force switches alternately in both directions between the excitation coil 51 and the heat generating layer 41c. The fixing roller 41 is heated inductively by the heat generating layer 41c.
Subsequently, the surface of the fixing roller 41 heated by the induction heater 50 meets the pressing roller 42, forming the fixing nip N between the fixing roller 41 and the pressing roller 42. The recording medium P bearing the toner image T is conveyed to the fixing nip N between the pressing roller 42 and the fixing roller 41 by a guide member, and the toner image T is heated and fused in the fixing nip N, thereby fixing the toner image T onto the recording medium P. More specifically, the recording medium P bearing the toner image T subjected to imaging operation described above is guided by a guide member to the fixing nip N between the fixing roller 41 and the pressing roller 42. The toner image T is heated by both the fixing roller 41 and the pressing roller 42, and fixed reliably onto the recording medium P. After that, the recording medium P is discharged from the fixing nip N.
After the surface of the fixing roller 41 passes through the fixing nip N, the fixing roller 41 arrives at the induction heater 50 again. The sequence of fixing operation as described above is repeated, thereby completing the fixing operation in the image forming process.
With reference to
In the experiment, the fixing device 40 was equipped with the induction heater 50 in which the side cores 52b and the center cores 52c were exposed from the holder 53. In
In the experiment, the temperature change of the surface of the fixing rollers was measured over time where the fixing rollers were rotated simultaneously as the power was supplied. It is to be noted that the configuration of the fixing device 40 was the same as the related-art fixing device except the induction heater. The timing at which the power was supplied at the initial stage of heating was the same for both the fixing device 40 and the related-art fixing device. Here, the warm-up time refers to a time required for the fixing roller 41 to reach a desired temperature for fixing toner (in the first illustrative embodiment, approximately 180° C.). If the warm-up time is short, a user does not have to wait for a long time. Hence it is more convenient to use.
As is understood from
As described above, according to the first illustrative embodiment, both the side cores 52b and the center cores 52c are exposed from the holder 53 so that these cores are near the fixing roller 41. Alternatively, as illustrated in
Next, with reference to
According to the second illustrative embodiment, as illustrated in
Next, with reference to
Similar to the first illustrative embodiment, heat generating efficiency of the fixing roller 41 is enhanced while reducing the warm-up time and saving energy. As compared with the first illustrative embodiment, because the fixing device of the third illustrative embodiment does not include the side core 52b, the cost associated with parts and assembly can be reduced. Furthermore, because the width of the arch core 52a is narrowed, the size of the holder 53 in the width direction can be reduced, hence reducing the size of the image forming apparatus as a whole.
Next, with reference to
According to the fourth illustrative embodiment, the side cores 52b and the center cores 52c, and the holder 53 constitute a single integrated unit by insert molding. Other cores are adhered to the holder 53.
As illustrated in
As illustrated in
In a case in which the side cores 52b and the center cores 52c are adhered to the holder 53 as in the first through third illustrative embodiments, a slight gap may be formed undesirably between the wall of the holder 53 and these cores. In order to reduce or eliminate the gap, preferably, arrangement of these cores may be adjusted, or the shape of these cores may be changed. If there is a gap between the wall of the holder 53 and the cores, air circulating at the back of the holder 53 to prevent overheating of the excitation coil 51 and so forth leaks from the gap into the fixing roller side. Consequently, the cooling effect of the air is reduced, and the leaked air cools down the surface of the fixing roller 41 undesirably, complicating efforts to maintain the temperature of the fixing roller 41 high for fusing the toner.
To address this difficulty, as illustrated in
According to the present embodiment, the side cores 52b and the center cores 52c are molded with the holder 53 by insert molding while the side cores 52b and the center cores 52c are exposed from the holder 53. Alternatively, these cores may be insert molded with the holder 53 such that these cores are embedded in the wall of the holder 53.
The heat generation efficiency depends substantially on the distance between the fixing roller 41, and the side cores 52b and the center cores 52c. Even when the holder 53 made of resin intervenes between the cores and the fixing roller 41, the magnetic flux generated by the excitation coil 51 penetrates through the resin holder 53. Thus, the holder 53 does not affect the heat emission efficiency. In other words, the cores can be brought even closer to the fixing roller 41 if the cores are embedded into the wall of the holder 53. In such a case, similar to exposing the cores from the wall of the holder 53, the heat generating efficiency of the fixing roller 41 can be increased.
As viewed from the fixing roller side, the side cores 52b and the center cores 52c are exposed from the holder 53. The surfaces of these cores facing the fixing roller 41 are positioned closer to the fixing roller 41 as compared with the related-art configuration. Furthermore, there is no gap between the wall of the holder 53, and the side cores 52b and the center cores 52c. The width of the exposed portion of the side cores 52b in the longitudinal direction of the holder 53 is narrower than the width of the side cores 52b in the longitudinal direction of the side core 52b itself. However, the width of the exposed portion is not limited thereto, and may be changed, accordingly. In other words, by increasing the wall portion of the holder 53 subjected to insert molding to reduce the width of the exposed portion of the side cores 52b, the strength of the holder 53 is increased. Similarly, the width of the exposed portion of the center core 52c in the longitudinal direction of the holder 53 is slightly narrower than the width of the center core 52c in the longitudinal direction of the center core 52c itself. However, the width of the exposed portion is not limited thereto, and may be changed, accordingly.
A plurality of openings 59, here, 20 pieces of openings 59 are formed in the wall of the holder 53 to correspond to the number of the side cores 52b. The openings 59 are used to fix the position of the side cores 52b in place relative to the holder 53 during insert molding process. More specifically, a positioning member 61 provided to a mold 60 fixes temporarily the side core 52b in place from outside of the holder 53 through the opening 59. As is understood from
As described above, because the side core 52b and the center core 52c are insert molded with the holder 53 as a single integrated unit, the holder 53 and the cores can be assembled simultaneously, thereby reducing the number of manufacturing steps, hence reducing the cost. Furthermore, the undesirable gap between the wall of the holder 53 and the cores is eliminated so that the air for cooling the excitation coil 51 and so forth can be secured at the back of the holder 53. At the front of the holder 53, elimination of the gap can block heat from the fixing roller 41, thereby retaining the temperature of the fixing roller 41. The strength and rigidity of the holder 53 is enhanced as well.
As described above, according to the fourth illustrative embodiment, both the side cores 52b and the center cores 52c are insert molded with the holder 53 to bring the side cores 52b and the center cores 52c close to the fixing roller 41. Alternatively, as illustrated in
In either case, because the magnetic circuit is closed, the heat generating efficiency of the fixing roller 41 is enhanced while reducing the warm-up time and saving energy as in the foregoing embodiments. An amount of thermal contraction of the side cores 52b and the center core 52c, both of which are made of magnetic material, differs from that of the resin. The time for cooling the resin portion of the holder 53 after molding process differs from the time required for cooling the portion of the holder 53 where the side cores 52b and the center cores 52c are insert molded. As a result, deformation occurs easily. By contrast, in a case in which either the side cores 52b or the center cores 52c are insert molded with the holder 53, deformation can be reduced, hence obtaining reliably a desired shape and increasing process yield.
Next, with reference to
According to the fifth illustrative embodiment, the fixing device 40 employs a belt-type fixing member, that is, the fixing belt 43; whereas, in the first and through fourth illustrative embodiments a roller-type fixing member, that is, the fixing roller 41, is employed in the fixing device.
In
According to the fifth illustrative embodiment, the fixing device 40 includes the induction heater 50, the fixing belt 43 serving as a heat generating member and also as a fixing member, a support roller 44 serving as a heat generating member and also as a heating member, a fixing auxiliary roller 45, a pressing roller 42, and so forth.
The support roller 44 includes a metal core made of SUS having a thickness in a range of from approximately 0.2 mm to 1 mm. The surface of the metal core is formed of copper (Cu) and has a thickness in a range of from 3 μm to 15 μm to enhance heat generating efficiency. The surface of the metal core formed of copper (Cu) may be plated with nickel (Ni) to prevent corrosion. Alternatively, a magnetic shunt alloy having the Curie point in a range of from approximately 160° C. to 220° C. may be used. An aluminum member may be disposed inside the magnetic shunt alloy, thereby stopping the temperature from rising near the Curie point.
The fixing auxiliary roller 45 consists of a metal core 45a and an elastic member 45b provided on the metal core 45a. The metal core 45a is made of metal, for example, stainless steel, carbon steel, and the like. The elastic member 45b is made of heat-resistant solid or foam silicone rubber. The pressing roller 42 presses against the fixing auxiliary roller 45, thereby forming the fixing nip N having a predetermined width between the pressing roller 42 and the fixing auxiliary roller 45. The outer diameter of the fixing auxiliary roller 45 is in a range of from approximately 30 mm to 40 mm. The thickness of the elastic member 45b is in a range of from approximately 3 mm to 10 mm. The stiffness thereof is in a range of from approximately 10° to 50° in accordance with JIS-A.
Next, a detailed description is provided of the fixing belt 43 with reference to
As illustrated in
It is desirable that the base member 43a have sufficient mechanical endurance and flexibility when stretched, and heat resistant properties at the fixing temperature. In view of the above, the base member 43a is made of heat resistant, insulating resin material to inductively heat the support roller 44. The resin material includes, but is not limited to, polyimide, polyimideamide, polyether ether ketone (PEEK), polyethersulfone (PES), polyphenylene sulfide (PPS), and fluorocarbon resin. In light of heat capacity and endurance, it is desirable that the thickness of the base member 43a be in a range of from approximately 30 μm to 200 μm.
In order to obtain an image with even glossiness, the elastic layer 43b is disposed on the belt surface so that the belt surface is substantially soft. The elastic layer 43b is made of rubber. The hardness of the rubber is in a range of from approximately 5° to 50° according to JIS-A, and the thickness thereof is in a range of from approximately 50 μm to 500 μm. The elastic layer 43b needs to be tolerant to heat at the fixing temperature. Hence, the rubber used in the elastic layer 43b includes, but is not limited to silicone rubber and fluorosilicone rubber.
The release layer 43c may include, but is not limited to, fluorocarbon resin such as, polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer resin (PFA), and fluorinated ethylene propylene (FEP), or a mixture of these resins, or fluorocarbon resin dispersed in a heat-resistant resin.
Covering the elastic layer 43b with the release layer 43c can prevent toner and paper dust from sticking to the fixing belt 43. Therefore, no silicone oil needs to be applied to the surface of the fixing belt 43. Generally, the resin having releasing properties is not as elastic as rubber. Thus, if the release layer 43c is too thick, the surface of the fixing belt 43 becomes stiff, causing gloss unevenness. In order to obtain both releasability and softness, the thickness of the release layer 43c is in a range of from approximately 5 μm to 50 μm, preferably, in a range of from 10 μm to 30 μm.
A primer layer may be provided between the layers as needed. Still alternatively, a layer may be provided to the inner surface of the base member 43a to enhance the endurance thereof when moving slidably. Preferably, the base member 43a may include a heat generating layer. For example, as the heat generating layer, a layer made of copper (Cu) having a layer thickness in a range of from approximately 3 μm to 15 μm may be formed on the base layer of polyimide or the like.
The pressing roller 42 employed in the fixing device 40 has the same configuration as the first illustrative embodiment. That is, the pressing roller 42 includes the cylinder member 42a made of metal such as aluminum and copper and the elastic layer 42b provided on the cylinder member 42a. The elastic layer 42b is made of rubber such as fluorocarbon rubber and silicone rubber. The elastic layer 42b of the pressing roller 42 has a thickness in a range of from approximately 0.5 mm to 2 mm and a hardness thereof in a range of from 20° to 50° on the Asker C scale.
The fixing belt 43 rotates in the counterclockwise direction indicated by an arrow A shown in
As illustrated in
Similar to the first illustrative embodiment, a plurality of arch cores 52a is disposed facing the outer circumferential surface of the support roller 44 in a circumference direction via the excitation coil 51 and contacts the side cores 52b. A plurality of side cores 52b and center cores 52c are disposed in the longitudinal direction of the holder 53. The side cores 52b and the center cores 52c may be connected to one another, or may be spaced apart a certain distance. The side cores 52b and the center cores 52c are arranged facing the fixing auxiliary roller 45. The side cores 52b and the center cores 52c are exposed from the holder 53. The side cores 52b and the center cores 52c are fixed to the holder 53 using adhesive such as shown in
Next, a description is provided of operation of the fixing device 40 according to the fifth illustrative embodiment.
As the fixing auxiliary roller 45 rotates, the fixing belt 43 is rotated in the direction of arrow A in
More specifically, a high-frequency alternating current in a range of from 20 kHz to 1 MHz (preferably, in a range of from 20 kHz to 100 kHz) is supplied from a power source to the excitation coil 51. Accordingly, a line of magnetic force switches alternately between the excitation coil 51, and the support roller 44 and the fixing belt 43. As the alternating magnetic field is formed, the eddy current is generated on the surface of the support roller 44 and the heat generating layer of the fixing belt 43. Due to an electrical resistance of the support roller 44 and the heat generating layer of the fixing belt 43, the Joule heat is generated, thereby heating the support roller 44 and the heat generating layer of the fixing belt 43. With this configuration, the fixing belt 43 serves as a heat generating member directly heated by the heat generating layer of the fixing belt 43 itself and the support roller 44 which has been heated. The fixing belt 43 also serves as an indirect heat generating member which is heated indirectly by the induction heater 50 via the support roller 44.
Subsequently, the surface of the fixing belt 43 heated by the induction heater 50 comes to face the pressing roller 42 which presses against the fixing auxiliary roller 45 via the fixing belt 43. The recording medium P bearing the toner image T is conveyed to the fixing nip N between the pressing roller 42 and the fixing roller 41 by a guide member, and the toner image T is heated and fused in the fixing nip N, thereby fixing the toner image T onto the recording medium P. The surface of the fixing belt 43 that has passed through the fixing nip comes to the position opposite the induction heater 50 again. This completes a sequence of the fixing operation.
As described above, according to the fifth illustrative embodiment, in addition to the arch cores 52a facing the outer circumferential surface of the fixing belt 43 and the support roller 44 via the excitation coil 51, the plurality of side cores 52b and center cores 52c are arranged in the longitudinal direction of the holder 53 opposite the outer circumferential surface of the fixing belt 43 and the support roller 44. The plurality of side cores 52b and center cores 52 are closer to the fixing belt 43 and the support roller 44 than from the arch cores 52a. Furthermore, the side cores 52b and the center cores 52c are exposed from or embedded to the holder 53 so that the side cores 52b and the center cores 52c can be disposed closer to the fixing belt 43 and the support roller 44 as compared with the related-art fixing device. With this configuration, the heat emission efficiency of the fixing belt 43 and the support roller 44 is enhanced without increasing the number of parts in the induction heater 50. Further, the warm-up time and energy consumption are reduced as is usually desired.
According to the fifth illustrative embodiment, both the fixing belt 43 and the support roller 44 are inductively heated by the induction heater. Alternatively, one of the fixing belt 43 and the support roller 44 is heated by the induction heater 50. For example, if the fixing belt 43 does not include a heat generating layer, the support roller 44 can serve as the heat generating member which is heated inductively by the induction heater 50 to heat the fixing belt 43. With this configuration, the same effect as that of the foregoing embodiments can be achieved.
According to the fifth illustrative embodiment, the induction heater 50 is disposed opposite the outer circumferential surface of the support roller 44 via the fixing belt 43. Alternatively, the induction heater 50 may be disposed directly opposite the outer circumferential surface of the support roller 44. In other words, the induction heater 50 may be disposed directly opposite the support roller 44 without the fixing belt 43 between the induction heater 50 and the support roller 44. In this configuration, the same effect as that of the third illustrative embodiment can be achieved.
According to the fifth illustrative embodiment, the side cores 52b and the center cores 52c are exposed from or embedded in the holder 53 so that the side cores 52b and the center cores 52c are close to the fixing belt 43. Alternatively, either the side cores 52b or the center cores 52c may be exposed from or embedded in the holder 53. In this case, because the magnetic circuit is closed, the heat generating efficiency of the fixing belt 43 is enhanced as in the foregoing embodiments while reducing the warm-up time and hence saving energy.
It is to be noted that the number, the position, and the shape of the side cores and center cores are not limited to the foregoing embodiments.
According to the illustrative embodiment, the teachings of this disclosure are employed in the image forming apparatus. The image forming apparatus includes, but is not limited to, an electrophotographic image forming apparatus, a copier, a printer, a facsimile machine, and a multi-functional system.
Furthermore, it is to be understood that elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. In addition, the number of constituent elements, locations, shapes and so forth of the constituent elements are not limited to any of the structure for performing the methodology illustrated in the drawings.
Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such exemplary variations are not to be regarded as a departure from the scope of the present disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
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| 2011-002890 | Jan 2011 | JP | national |
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