Patent Publication Number: US-2009232535-A1

Title: Fixing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from: U.S. provisional application 61/035685, filed on Mar. 11, 2008, and U.S. provisional application 61/039396, filed on Mar. 25, 2008, the entire contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a technique to heat and fix a development agent image on a sheet, and more in particular, to a technique to make uniform a temperature distribution of a sheet heating temperature in a sheet widthwise direction. 
     BACKGROUND 
     Conventionally, a fixing device is known, which includes a fixing roller which is heated, a tension roller, a belt rolled on the fixing roller and the tension roller and a press roller for nipping and carrying a sheet in cooperation with a belt surface of the corresponding belt. 
     In such fixing device, a configuration is known where an induction heating coil is disposed at the outside of a fixing roller, and the induction heating coil heats the fixing roller (for example, see Japanese Patent Application Laid-open No. 2006-267643). 
     In the conventional fixing device, however, uniformity of a temperature distribution in a widthwise direction of a belt surface is not considered upon heating and fixing a small sized sheet in a direction (widthwise direction) orthogonal to a sheet carrying direction. In other words, when a small sized sheet is heated and fixed in a widthwise direction in the conventional fixing device, an area contact with the sheet and an area non-contact with the sheet in the widthwise direction are very different in a heat amount which they take away from the belt surface and thereby a temperature distribution therebetween is not uniform. The un-uniformity of a temperature distribution of the belt surface in the widthwise direction is in danger of causing deterioration (deterioration of image quality of a development agent image formed on a sheet) of a fixing performance of the fixing device. 
     SUMMARY 
     The embodiments of present invention is directed to providing a technique to make uniform a temperature distribution of a sheet heating temperature in a sheet widthwise direction, with no relation to sizes in a direction (sheet widthwise direction) orthogonal to a carrying direction of sheets to be fixed. 
     In order to solve the above-described problems, an aspect of the present invention relates to a fixing device including: a first roller; a second roller configured to rotate with respect to a rotational axis parallel to a rotational axis of the first roller; a belt configured to have a conductive layer and be rolled on the first roller and the second roller; an induction heating coil configured to heat the belt; a heat pipe configured to be disposed inside the second roller and extend toward the rotational axis of the second roller; a third roller configured to press a roller surface of the first roller through the belt, to nip and carry a sheet to be treated in cooperation with a belt surface of the belt; and a temperature sensor configured to sense a temperature of the belt surface of the belt, wherein the temperature sensor, the second roller and the induction heating coil are disposed at different positions in a circumferential direction of the first roller. 
     An aspect of the present invention relates to a fixing method in a fixing device including: a first roller; a second roller configured to rotate with respect to a rotational axis parallel to a rotational axis of the first roller; a belt configured to have a conductive layer and be rolled on the first roller and the second roller; an induction heating coil configured to heat the belt; a heat pipe configured to be disposed inside the second roller and extend toward the rotational axis of the second roller; a third roller configured to press a roller surface of the first roller through the belt, to nip and carry a sheet to be treated in cooperation with a belt surface of the belt; and a temperature sensor configured to sense a temperature of the belt surface of the belt, wherein the temperature sensor sensing a temperature of the belt surface, the second roller giving a tension to the belt and the induction heating coil heating the belt surface are conducted at different positions in a circumferential direction of the first roller. 
     In order to solve the above-described problems, an aspect of the present invention relates to a fixing device including: a first roller; a second roller configured to rotate with respect to a rotational axis parallel to a rotational axis of the first roller; a belt configured to have a conductive layer and be rolled on the first roller and the second roller; an induction heating coil configured to heat the belt; a heat pipe configured to be disposed inside the second roller and extend toward the rotational axis of the second roller; a third roller configured to press a roller surface of the first roller through the belt, to nip and carry a sheet to be treated in cooperation with a belt surface of the belt; and a temperature sensor configured to sense a temperature of the belt surface of the belt, wherein the temperature sensor, the second roller and the induction heating coil are disposed at different positions in a circumferential direction of the first roller, and a size in a direction of a rotational axis of the belt is smaller than any size of the first roller, the second roller and the heat pipe in the direction of the rotational axis. 
     An aspect of the present invention relates to a fixing method in a fixing device including: a first roller; a second roller configured to rotate with respect to a rotational axis parallel to a rotational axis of the first roller; a belt configured to have a conductive layer and be rolled on the first roller and the second roller; an induction heating coil configured to heat the belt; a heat pipe configured to be disposed inside the second roller and extend toward the rotational axis of the second roller; a third roller configured to press a roller surface of the first roller through the belt, to nip and carry a sheet to be treated in cooperation with a belt surface of the belt; and a temperature sensor configured to sense a temperature of the belt surface of the belt, a size in a direction of a rotational axis of the belt being smaller than any size of the first roller, the second roller and the heat pipe in the direction of the rotational axis in the device, wherein the temperature sensor sensing a temperature of the belt surface, the second roller giving a tension to the belt and the induction heating coil heating the belt surface are conducted at different positions in a circumferential direction of the first roller. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view to illustrate a schematic configuration of an image forming apparatus (MFP: Multi Function Peripheral) including a fixing device according to a first embodiment of the present invention; 
         FIG. 2  is a longitudinal cross-sectional view to illustrate a schematic configuration of the fixing device according to the first embodiment of the present invention; 
         FIG. 3  is a view to explain an internal configuration of a tension roller; 
         FIG. 4  is a schematic view to illustrate a relation of lengths in a direction of rotational axis of the tension roller, an area heated by an induction heating coil, a belt, and a heat pipe; 
         FIG. 5  is a graph to illustrate a temperature distribution in a direction of rotational axis of a belt surface of the belt when a narrow sheet is fixed in a configuration of not providing the heat pipe to the tension roller; 
         FIG. 6  is a graph to illustrate a temperature distribution in a direction of rotational axis of a belt surface of the belt when a narrow sheet is fixed in a configuration of providing the heat pipe to the tension roller; 
         FIG. 7  is a longitudinal cross-sectional view to illustrate a schematic configuration of a fixing device  7   b  according to a second embodiment of the present invention; and 
         FIG. 8  is a longitudinal cross-sectional view to illustrate a schematic configuration of a fixing device  7   c  according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
     First Embodiment 
     First, a first embodiment of the present invention will now be described. 
       FIG. 1  is a longitudinal cross-sectional view to illustrate a schematic configuration of an image forming apparatus (MFP: Multi Function Peripheral) including a fixing device according to a first embodiment of the present invention. 
     As shown in  FIG. 1 , an image forming apparatus according to the present embodiment includes an image read-out unit R and an image forming unit P. 
     The image read-out unit R reads out images of an original document of a sheet and an original document of a book through scanning. 
     The image forming unit P forms a development agent image on a sheet on the basis of the images read out from an original document by the image read-out unit R or image data transmitted to the image forming apparatus from an external device or the like. 
     The image read-out unit R includes an ADF (Auto Document Feeder)  9  capable of automatically carrying an original document up to a predetermined image read-out position, and reads out images of an original document loaded on a document tray (a predetermined document loading plate) Rt auto-carried by the ADF  9  or an image of an original document mounted on a not-shown document plate, by use of a scan optical system  10 . 
     The image forming unit P includes pickup rollers  51  to  54 , photoconductive members  2 Y to  2 K, development rollers  3 Y to  3 K, mixers  4 Y to  4 K, a middle transcript belt  6 , a fixing device  7   a  and a discharge tray  8 . 
     The image forming apparatus according to the present embodiment includes a CPU  801  and a memory  802  (see  FIG. 1 ). The CPU  801  conducts a variety of processings in the image forming apparatus and also realizes a variety of functions by executing programs stored in the memory  802 . The memory  802  may consist of, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a DRAM (Dynamic Random Access Memory), an SRAM (Static Random Access Memory), a VRAM (Video RAM), or the like and stores lots of information and programs used by the image forming apparatus. 
     A synopsis of a copying operation will now be described as an example of the processings by the image forming apparatus according to the present embodiment. 
     A sheet picked up from a cassette by one of the pickup rollers  51  to  54  is sent to a sheet carrying path. The sheet sent to the sheet carrying path is carried in a predetermined carrying direction by plural pairs of rollers. 
     Images of original documents of plural sheets which are successively auto-carried by the ADF  9  are read out at a predetermined image read-out position by the scan optical system  10 . 
     Electrostatic latent images are formed on photoconductive surfaces of the photoconductive members  2 Y,  2 M,  2 C and  2 K to transcribe development agent images of yellow (Y), magenta (M), cyan (C) and black (K) on a sheet, based on image data of images read-out from the original documents by the image read-out unit R. 
     Subsequently, development agents stirred by the mixers  4 Y to  4 K (corresponding to stirring devices) of the development device are supplied to the photoconductive members  2 Y to  2 K on which the electrostatic latent images are formed in such way, by the development rollers (so-called mag-roller)  3 Y to  3 K. Thereby, the electrostatic latent images formed on the photoconductive surfaces of the photoconductive members are developed. 
     The development agent images formed on the photoconductive members in this way are transcribed onto a belt surface of the middle transcript belt  6  (so-called a primary transcript), and the development agent images carried by rotation of the middle transcript belt are transcribed onto sheets which are being carried, at a predetermined secondary transcript position T. 
     The development agent images transcribed onto the sheets are heated and fixed on the sheet by the fixing device  7   a.    
     The sheets on which the development agent images are heated and fixed are carried into the carrying path by the plural pairs of carrying rollers and then are sequentially discharged on the discharge tray  8 . 
     The fixing device according to the first embodiment of the present invention will be described in detail. 
       FIG. 2  is a longitudinal cross-sectional view to illustrate a schematic configuration of the fixing device according to the first embodiment of the present invention. 
     The fixing device  7   a  according to the first embodiment of the present invention includes a fixing roller (a first roller)  701 , a tension roller (a second roller)  702 , a press roller (a third roller)  703 , an induction heating coil  704 , a thermopile (a temperature sensor)  705 , a belt  706  and a heat pipe  707 . 
     The fixing roller (the first roller)  701  rotates with respect to a rotational axis A 1 . The fixing roller  701  contains a core and an elastic layer disposed on the outer circumference of the core. The core is fixed at a predetermined position of the fixing device. The core is made of steel and its outer diameter is set 30 mm. In addition, the elastic layer is made of foamy silicon rubber, which is 10 mm thick and its outer diameter is 50 mm. 
     The tension roller (the second roller)  702  rotates with respect to the rotational axis A 2  parallel to the rotational axis A 1  of the fixing roller  701 . In detail, the tension roller  702  is configured of pipes made of steel, and its outer diameter is 17 mm and inner diameter is about 16 mm. 
     The belt  706  includes a metal layer (conductive layer) and is rolled on the fixing roller  701  and the tension roller  702 . 
     The belt  706  includes a continuously variable belt made of nickel which has an inner diameter of 70 mm and a thickness of about 40 μm, and an elastic layer made of silicon rubber which is about 200 μm thick, disposed on the outer circumference of the continuously variable belt. An exfoliation layer is additionally disposed on (outermost part) the elastic layer, the exfoliation layer being about 30 μm thick and made of fluororesin (PFA (tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer) or PTFE (Poly tetra fluoro ethylene) or a mixture of PFA and PTFE). 
     The induction heating coil  704  heats the belt  706  including the conductive layer by use of electromagnetic induction. 
     The heat pipe  707  is disposed inside the tension roller  702  and seems to have a shape extending in a direction of the rotational axis A 2  of the tension roller  702 .  FIG. 3  is a view to explain an internal configuration of the tension roller  702 . 
     The heat pipe has a structure that a small amount of liquid (working liquid) is sealed in vacuum in a closed container (here, a cylindrical shape extending toward a direction of the rotational axis A 2 ) and the inner wall of the container has a capillary (wick). 
     In addition, the tension roller  702  has a cylindrical shape in at least a portion thereof, and the outer surface of the heat pipe  707  is disposed in order to contact closely to the inner surface of the tension roller  702 . Disposing the heat pipe  707  as described above improves thermal conductivity, thermal response and uniformity of a temperature distribution of the tension roller  702 . Furthermore, the heat pipe is embedded in the roller in this way and thereby can be used for temperature uniformity of the belt which rotates. 
     The roller surface of the tension roller  702  is coated with a tube  702 p made of fluororesin. 
     Such configuration of the tension roller  702  and the heat pipe  707  can restrict occurrence of a surface temperature variation in a sheet widthwise direction of the tension roller  702 . 
     The press roller (the third roller)  703  rotates with respect to the rotational axis A 3 , presses the roller surface of the fixing roller  701  through the belt  706 , and nips and carries sheets to be treated in cooperation with the belt surface of the belt  706 . Herein, the press roller (the third roller)  703  is assumed to press the fixing roller  701  by, for example, a not-shown elastic member such as a spring or a rubber. 
     In detail, the press roller  703  is configured of a core layer of which outer diameter is 45 mm, an elastic layer made of silicon rubber and 1 mm thick, provided on the outer circumference of the core layer, and an exfoliation layer made of fluororesin and 30 μm thick, provided on the outer circumference of the elastic layer. The core layer, the elastic layer and the exfoliation layer are fixed to each other by adhesive. 
     The thermopile (temperature sensor)  705  senses a belt surface temperature of the belt  706  in a non-contact manner. The CPU  801  controls a heating amount of the induction heating coil  704  on the basis of a temperature sensed by the thermopile  705 . Programs to define a control table or a control algorithm which is referred to upon controlling the heating amount of the induction heating coil  704  are stored in, for example, the memory  802 , and the CPU  801  executes the programs to realize the heating control of the induction heating coil  704 . 
     In addition, as shown in  FIG. 2 , in the fixing device  7   a  of the present embodiment, the thermopile  705 , the tension roller  702  and the induction heating coil  704  are disposed at different positions in the circumferential direction of the fixing roller  701 . 
     Such configuration can lead to a space save and further a simple configuration of the device, thereby, with no relation to sizes in a direction (sheet widthwise direction) orthogonal to a carrying direction of sheets to be fixed, realizing uniformity of a sheet heating temperature in the sheet widthwise direction. 
     The thermopile  705 , the tension roller  702  and the induction heating coil  704  are disposed at different positions in the circumferential direction of the fixing roller  701 , and thereby the thermopile  705  sensing a temperature of the belt surface, the tension roller  702  giving a tension to the belt and the induction heating coil  704  heating the belt surface can be conducted at different positions in the circumferential direction of the fixing roller  701 . Thereby, a space save of the arrangement space can be realized in a rotation radius direction of the fixing roller  701 , and also the thermopile  705  measuring a temperature, the tension roller  702  to include the heat pipe making a temperature of the belt uniform and the induction heating coil heating belt can be realized without interfering each other. 
     In addition, the thermopile  705 , the tension roller  702  and the induction heating coil  704  are arranged in sequence in the circumferential direction of the fixing roller  701 , taking the nip position as a base point, from the upper side to the lower side of moving direction of the roller surface of the fixing roller  701 . 
     Subsequently, a relation of lengths in a direction of rotational axis of the tension roller  702 , an area heated by the induction heating coil  704 , the belt  706  and the heat pipe  707  in the fixing device of the present embodiment will now be described. 
       FIG. 4  is a schematic view to illustrate a relation of lengths in a direction of rotational axis of the tension roller  702 , an area heated by the induction heating coil  704 , the  706  and the heat pipe  707 . 
     As shown in  FIG. 4 , the length L 7  in a direction of the rotational axis A 2  of an effective portion of the heat pipe  707  is configured to be larger than the length L 4  in a direction of the rotational axis of the area heated by the induction heating coil  704 . 
     Here, the “effective portion” refers to a portion where functions of thermal conductivity, thermal response and uniformity of a temperature distribution in the heat pipe  707  effectively work. 
     In addition, the “heated area” here refers to an area of the belt surface of the belt  706  which is substantially heated by the induction heating coil  704 . A flux density may be considered as a method of defining a detailed heated area, for example. 
     In the length L 7  in a direction of the rotational axis A 2  of the effective portion of the heat pipe  707 , a size (sheet width) in the direction of the rotational axis A 2  preset for objects to be fixed by the fixing device  7   a  is set larger than a size (sheet width) Ls in the direction of the rotational axis A 2  of the largest sheet (for example, A3 size). 
     In the length L 4  in the direction of the rotational axis A 2  of the area heated by the induction heating coil  704 , a size in the direction of the rotational axis A 2  preset for objects to be fixed by the fixing device  7   a  is set smaller than a size Ls in the direction of the rotational axis A 2  of the largest sheet. 
     In addition, the size L 6  in the direction of the rotational axis of the belt  706  is smaller than any size of the fixing roller  701 , the tension roller  702  and the heat pipe  707  in the direction of the rotational axis A 2 . 
     The relation of L 1 , L 3 , L 4 , L 6  and L 7  in the present embodiment is as follows: L 7 &gt;L 3 &gt;L 1 &gt;L 6 &gt;Ls&gt;L 4 . 
     In detail, the length L 6  in the sheet widthwise direction of the belt  706  is 330 mm, larger than Ls=316 mm which is the largest sheet-passing width, which thus is a sufficient length for fixing operation. 
     The length L 1  in the direction of the rotational axis A 1  of the fixing roller  701  is set 340 mm, larger than the length L 6  in the direction of the rotational axis of the belt  706 . 
     The length L 3  in the direction of the rotational axis of the press roller  703  is set 350 mm, larger than the length L 1  in the direction of the rotational axis of the fixing roller  701 . 
     In a relation of the heat pipe  707  inside the tension roller  702 , the induction heating coil  704  and the largest sheet-passing width Ls, the length L 7  of the effective portion of the heat pipe  707  is 330 mm, which is larger than the largest sheet-passing width Ls=316 mm. 
     The length L 4  in the direction of the rotational axis A 2  of the area heated by the induction heating coil  704  is 310 mm, which is smaller than the length L 7  in the direction of the rotational axis A 2  of the effective portion of the heat pipe  707  and the largest sheet-passing width Ls. 
     In order to heat the belt  706  such that the entire largest sheet-passing width Ls reaches a temperature in which a fixing is possible, the length L 4  in the direction of the rotational axis A 2  of the area heated by the induction heating coil  704  inherently needs to be equal to or larger than the largest sheet-passing width Ls. However, according to the fixing device  7   a  of the present embodiment, since the heat pipe  707  is embedded in the tension roller  702 , a temperature of the end portion of the largest sheet-passing width Ls can be sufficiently increased due to the thermal conduction of the heat pipe, although the area heated by the induction heating coil  704  is smaller than the largest sheet-passing width Ls. Thereby, cost of overall devices can be reduced by downsizing the induction heating coil and conducting the fixing operation without problems. 
     Like the fixing device  7   a  according to the present embodiment, the thermopile  705  is disposed at the upper side of moving direction of the belt relative to the induction heating coil  704 ; thereby, after detecting a temperature using the thermopile  705  and in turn determining whether or not to heat, the induction heating coil  704  can heat the area if a heating is necessary. 
     Since the induction heating coil  704  is disposed right previously to the nip formed at a position where the press roller  703  and the belt  706  contact with each other and the belt  706  heated by the induction heating coil  704  enters the nip before its temperature is decreased, a high heating efficiency can be realized. 
       FIG. 5  is a graph to illustrate a temperature distribution in the direction of the rotational axis of the belt surface of the belt  706  when a narrow sheet is fixed in a configuration.of not providing the heat pipe  707  to the tension roller  702 .  FIG. 6  is a graph to illustrate a temperature distribution in the direction of rotational axis of the belt surface of the belt  706  when a narrow sheet is fixed in a configuration of providing the heat pipe  707  to the tension roller  702 . 
     As shown in  FIGS. 5 and 6 , it can be known that the configuration according to the present embodiment can restrict occurrence of a temperature variation of the belt surface of the belt  706  in the direction of the rotational axis. 
     Second Embodiment 
     A second embodiment of the present invention will now be described. 
     The second embodiment of the present invention is a modification of the above-described first embodiment. Hereinafter, elements having the same functions as those described in the first embodiment are given the same reference numerals, the description of which will be omitted. The present embodiment is different from the first embodiment in arrangement of the thermopile  705 , the tension roller  702  and the induction heating coil  704 . 
       FIG. 7  is a longitudinal cross-sectional view to illustrate a schematic configuration of a fixing device  7   b  according to the second embodiment of the present invention. 
     As shown in  FIG. 7 , in the second embodiment of the present invention, the tension roller  702 , the thermopile  705  and the induction heating coil  704  are arranged in sequence in the circumferential direction of the fixing roller  701 , taking the nip position as a base point, from the upper side to the lower side of moving direction of the roller surface of the fixing roller  701 . 
     The tension roller  702  can be disposed at a position right after the belt  706  passes through the nip, by the configuration according to the present embodiment. Such configuration can largely change a curvature of the belt right after passing through the nip and thus easily remove the sheet from the belt surface after the fixing, in addition to the effect obtained by the configuration according to the first embodiment. 
     Third Embodiment 
     A third embodiment of the present invention will now be described. 
     The third embodiment of the present invention is a modification of the above-described first embodiment. Hereinafter, elements having the same functions as those described in the first embodiment are given the same reference numerals, the description of which will be omitted. The present embodiment is different from the above-described embodiments in arrangement of the thermopile  705 , the tension roller  702  and the induction heating coil  704 . 
       FIG. 8  is a longitudinal cross-sectional view to illustrate a schematic configuration of a fixing device  7   c  according to the third embodiment of the present invention. 
     As shown in  FIG. 8 , in the third embodiment of the present invention, the thermopile  705 , the induction heating coil  704  and the tension roller  702  are arranged in sequence in the circumferential direction of the fixing roller  701 , taking the nip position as a base point, from the upper side to the lower side of moving direction of the roller surface of the fixing roller  701 . 
     According to the configuration according to the present embodiment, the tension roller  702  contacts with the belt right after the belt  706  is heated by the induction heating coil  704  and a temperature of the belt  706  can be made uniform by the heat pipe  707  embedded in the tension roller  702 . Thereby, the belt  706  can enter the nip in a state of uniform temperature by the heat pipe  707 , to realize a fixing leading to images of higher quality. 
     As such, the tension roller  702  including the heat pipe is disposed at the lower side than the induction heating coil and the upper side than the nip in the moving direction of the roller surface of the fixing roller  701 ; thus, a surface temperature of the belt heated by the induction heating coil can be made uniform by the tension roller  702  including the heat pipe before the belt enters the nip. Thereby, the heat added to sheets at the time of the fixing can be made uniform in the sheet widthwise direction to restrict occurrence of bad fixing. 
     Although the respective embodiments described above exemplify the configurations of employing the thermopile as a temperature sensor for sensing a temperature of the belt  706 , the present invention is not necessarily limited thereto. In other words, a sensor which can finally sense a surface temperature of the belt  706 , for example, a contact sensor may be employed. 
     Although the respective embodiments described above exemplify that the metal conductive layer made of nickel is employed as the conductive layer of the belt  706 , not necessarily limited thereto, but a separate thing used for the conductive layer can also obtain the same effect as the present invention. For example, a thing which includes conductor powder and the like in a resin can be employed as the conductive layer of the belt  706 . 
     The angular positions of the tension roller  702 , the thermopile  705  and the induction heating coil  704  in the circumferential direction of the fixing roller  701  with respect to the rotational axis A 1  of the fixing roller  701  are just examples in the respective embodiments described above, and, if an order of arrangement taking the nip as a base point is the same, it is obvious to show the same effect although the above-described angular positions go wrong. 
     Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein. 
     As described above in detail, the present invention can provide a technique to make uniform a temperature distribution of a sheet heating temperature in a sheet widthwise direction, with no relation to sizes in a direction (sheet widthwise direction) orthogonal to a carrying direction of sheets to be fixed.