Patent Publication Number: US-10310422-B2

Title: Fixing apparatus and image forming apparatus

Description:
The entire disclosure of Japanese patent Application No. 2017-140747, filed on Jul. 20, 2017, is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present invention relates to a fixing apparatus and an image forming apparatus provided with the fixing apparatus, and more particularly to a technique of suppressing a pressurizing member of the fixing apparatus from deviating from an appropriate temperature range. 
     Description of the Related Art 
     In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing and scanning a surface of a photoreceptor on the basis of image data of a document, a toner is supplied to the electrostatic latent image to generate a toner image, and the toner image is thermally fixed by a fixing apparatus after being transferred onto a sheet. 
     Generally, in a fixing apparatus, a sheet is fed through a nip part formed between a heating roller (heating member) and a pressurizing roller (pressurizing member) pressed against the heating roller, and the sheet is conveyed forward while being thermally fixed. In a region where the sheet is fed in an axial direction of each roller (hereinafter referred to as “sheet feeding region”), a large amount of heat is taken away by a sheet, particularly by a toner on the sheet. In a region where the sheet is not fed (hereinafter, referred to as a “non-sheet feeding region”), almost no heat is taken away. Thus, when the heating roller is heated by a heater in order to keep temperature of the nip part in the sheet feeding region at predetermined fixing temperature, temperature in the non-sheet feeding region rises more than necessary. 
     Therefore, as a conventional technique, a fixing apparatus has been proposed in which a sheet of a currently performed print job is cooled by blowing air to the non-sheet feeding region of the heating roller (see, for example, JP 2016-4162 A and JP 2006-119259A). 
     Even though the non-sheet feeding region is cooled by air, from the viewpoint of energy saving, the temperature is conventionally maintained to a degree slightly lower than endurance temperature of components of each part of the fixing apparatus (for example, about 230° C.). 
     In particular, in the conventional method described above, when a sheet width in the print job performed immediately before the current print job is smaller than a sheet width in the current print job, a region that is the non-sheet feeding region with the previous sheet width becomes the sheet feeding region with the current sheet width. Thus, the heating roller contacts with the sheet while the temperature in a difference region (hereinafter, referred to as “difference region”) between the sheet feeding region with the previous sheet width and the sheet feeding region with the current sheet width is maintained at high temperature of 230° C. 
     Normally, the heating roller is designed so as to reduce heat capacity thereof in order to shorten warm-up time and save energy. On the other hand, the pressurizing roller has a larger thickness of an elastic layer on the surface than the heating roller, so that a nip width is increased, and the heat capacity is also increased by that amount. In addition, since the heating roller directly contacts with the toner image, the heat is liable to be taken away. However, since the pressurizing roller contacts with the surface on the back surface of the sheet where the toner image is not formed, the temperature hardly falls. 
     If the difference region described above of the pressurizing roller contacts with the back surface of the sheet at the nip part while being maintained at high temperature, a problem of image noise called a blister (a phenomenon that the gloss of the toner image is degraded and the toner image appears to be clouded) occurs in the fixed image. 
     SUMMARY 
     The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fixing apparatus that suppresses generation of image noise in a difference region when fixing a sheet having a width larger than a width of a previously fixed sheet, and to provide an image forming apparatus provided with the fixing apparatus. 
     To achieve the abovementioned object, according to an aspect of the present invention, there is provided a fixing apparatus for feeding a sheet that is unfixed through a nip formed between a heating member and a pressurizing member to thermally fix the sheet and the fixing apparatus reflecting one aspect of the present invention comprises a cooler that cools the pressurizing member, wherein when a fixing job is performed on a sheet whose sheet width is a second width larger than a first width, after a fixing job is completed on a sheet whose sheet width in an orthogonal direction to a sheet feeding direction is the first width, the cooler cools a difference region in which a first sheet feeding region of the pressurizing member through which the sheet having the first width is fed and a second sheet feeding region through which the sheet having the second width is fed are not overlapped with each other, with a cooling power stronger than that of a region corresponding to the first sheet feeding region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only and thus are not intended as a definition of the limits of the present invention: 
         FIG. 1  is a schematic view for explaining a configuration of a tandem type color copying machine that is an example of an image forming apparatus according to an embodiment of the present invention: 
         FIG. 2  is a view for explaining a configuration of a cooling device provided in the copying machine; 
         FIG. 3A  is a schematic view of when cylindrical first to third shutter members are deployed; 
         FIG. 3B  is an exploded perspective view of the cooling device; 
         FIGS. 4A to 4E  are diagrams for showing examples of shielding states of a plurality of windows by the first to third shutter members; 
         FIGS. 5A and 5B  are schematic diagrams showing a temperature state of a difference region and a non-sheet feeding region of when a large size sheet is fixed after a small size sleet of is fixed; 
         FIG. 6A  is a schematic diagram showing a situation of increasing air volumes in the difference region and the non-sheet feeding region of when the large size sheet is fixed after the small size sheet is fixed in the cooling device; 
         FIG. 6B  is a developed view showing a positional relationship between the first to third shutter members and windows of an air blowing sleeve of when the air volumes are controlled in that way; 
         FIG. 7  is a block diagram showing a configuration of a control part of the copying machine; 
         FIG. 8  is a flowchart showing contents of air blowing volume control of the cooling device by the control part; 
         FIG. 9  is a flowchart showing contents of a first modification of the air blowing volume control of the cooling device; 
         FIGS. 10A and 10B  are diagrams schematically showing an air blowing volume controlled in the first modification; 
         FIG. 11  is a flowchart showing contents of a second modification of the air blowing volume control of the cooling device; 
         FIGS. 12A and 12B  are diagrams schematically showing the air blowing volume controlled in the second modification; 
         FIG. 13  is a flowchart showing contents of a third modification of the air blowing volume control of the cooling device; 
         FIG. 14  is a schematic view showing a modification of the cooling device; 
         FIG. 15  is a schematic view showing a mechanism for adjusting the air blowing volume at each discharge port in the modification of  FIG. 14 ; 
         FIG. 16  is a flowchart showing contents of a fourth modification of the air blowing volume control of the cooling device; 
         FIG. 17  is a schematic diagram showing an example of changing the air blowing volume of the cooling device according to a difference in toner density; 
         FIG. 18  is a perspective view showing another modification of the cooling device; and 
         FIGS. 19A to 19C  are schematic diagrams showing control examples of the air blowing volume of when the pressurizing roller is cooled by the cooling device of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
     Hereinafter, an example in which a fixing apparatus according to the embodiment of the present invention is applied to a fixing part of a tandem type color copying machine (hereinafter, simply referred to as “copying machine”) will be described. 
     (1) Overall Configuration of Copying Machine 
       FIG. 1  is a schematic view for explaining a configuration of a copying machine  1  according to the present embodiment. 
     As shown in the drawing, the copying machine  1  is roughly composed of an image reader part (document reading device) R and a printer part (image forming apparatus) P. 
     &lt;Image Reader Part&gt; 
     An image reader part R includes a scanner part  10  that optically reads a document image and converts the document image into an image signal, and a document conveyance part (ADF unit)  11  provided above the scanner part  10 . 
     The document conveyance part  11  feeds documents one by one from a document bundle set in a document feed tray  11   a , conveys the documents to a reading position R 1  on a platen glass  10   a , and discharges the documents onto a document discharge tray  11   c  after a document image is scanned by the scanner part  10  at the reading position R 1 . 
     In the scanner part  10 , light is emitted from a linear light source  10   b  formed of an LED array or the like, and reflected light from documents passing through the reading position R 1  is focused on a line sensor  10   d  via a condenser lens group  10   c.    
     The line sensor  10   d  is formed by arranging a plurality of charge coupled devices (CCDs) in a straight line in a direction parallel to a main scanning direction, converts reflected light from the document in which light has been incident, into an electrical signal, and outputs the electric signal to the control part  50  of a printer part P. 
     &lt;Printer Part&gt; 
     The printer part P includes an image forming part  20 , a sheet feeding part  30 , a fixing part  40 , a control part  50 , and the like, and forms an image on the sheet based on a document image read by the image reader part R, and image data transmitted from another terminal via a network. 
     The image forming part  20  includes an intermediate transfer belt  26  that is rotatably driven in an arrow direction by a driving source not shown, and process units  20 Y,  20 M,  20 C.  20 K that are provided in an array along a travelling surface of a vertical direction of the intermediate transfer belt  26 . 
     The process units  20 Y,  20 M,  20 C,  20 K form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). 
     Since these process units  20 Y to  20 K have the same configuration except for colors of toners to be used, only the configuration of the process unit  20 Y will be described as a representative. 
     The process unit  20 Y has a charger  22 Y, an exposure device  23 Y, a developing device  24 Y, and the like disposed around the photosensitive drum  21 Y. 
     An outer peripheral surface of the photosensitive drum  21 Y is uniformly charged by the charger  22 Y. 
     The exposure device  23 Y modulates and drives a laser light source based on image data (or image data included in a received print job) acquired by the image reader part R to expose and scan the surface of the charged photosensitive drum  21 Y. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum  21 Y. 
     The electrostatic latent image is developed with a yellow toner by the developing device  24 Y and transferred onto the intermediate transfer belt  26 . 
     A color image is formed by superimposing and transferring the toner images of M, C. and K colors formed on the photosensitive drums in the other process units  20 M.  20 C, and  20 K to the same position on the intermediate transfer belt  26 . 
     The toner image transferred onto the intermediate transfer belt  26  is conveyed to a secondary transfer position opposed to the secondary transfer roller  27  by the circulating motion of the intermediate transfer belt  26 . 
     On the other hand, a sheet feeding part  30  has paper feeding cassettes  31  to  33 , feeds out a sheet from a designated paper feeding cassette, and conveys the sheet to the secondary transfer position at timing by a registration roller  34 , and the toner image on the intermediate transfer belt  26  is secondarily transferred onto the sheet. 
     The sheet to which the toner image has been transferred passes through the nip part formed by the heating roller  41  and the pressurizing roller  42  of the fixing part  40 , is thermally fixed, and thereafter, is discharged onto the discharge tray  29  via the discharge roller  28 . A halogen heater  411  is built in the heating roller  41 . 
     A temperature sensor  412  such as a thermistor is disposed in order to detect surface temperature of a substantially center portion of the heating roller  41  in a longitudinal direction (rotational axis direction). A photoelectric sheet feeding sensor  401  is disposed on an upstream side of a sheet conveyance direction of the nip part of the fixing part  40 . 
     The cooling device  60  is for cooling the pressurizing roller  42  to appropriate temperature. 
     (2) Configuration of Cooling Device  60   
       FIG. 2  is a front view showing a configuration of the cooling device  60 . 
     The cooling device  60  includes a fan device  65 , an air blowing sleeve  66 , first to third shutter members  681  to  683 , drive motors  671  to  673  for rotationally driving the first to third shutter members  681  to  683 , and the like. 
     The air flow generated by the fan device  65  is sent to the cylindrical air blowing sleeve  66  via a duct  651 . The length of the air blowing sleeve  66  is substantially the same as the length of the pressurizing roller  42 , is parallel to the rotation axis of the pressurizing roller  42 , and is disposed in an almost opposite position from the nip part composed of the heating roller  41  and the pressurizing roller  42 , with respect to the pressurizing roller  42  (see  FIG. 1 ). 
     A plurality of rectangular windows  661  are formed at predetermined intervals along the longitudinal direction at positions opposed to the pressurizing roller  42  on the peripheral surface of the air blowing sleeve  66 . Air is blown toward the peripheral surface of the pressurizing roller  42  from each window  661  to cool the pressurizing roller  42 . 
     The opening amount of each window  661  is regulated by the first to third shutter members  681  to  683 , and the air blowing volume is controlled. 
       FIG. 3B  is an exploded perspective view of another part of the cooling device  60  excluding the fan device  65 . 
     In the present embodiment, for the sake of convenience, a configuration of the cooling device  60  in which the sheet widths (the widths in the direction orthogonal to the sheet feeding direction of the sheet) are two widths of a first size L 1  and a second size L 2  (L 1 &lt;L 2 ), will be described. In addition, it is assumed that feeding of the sheet is performed with center reference sheet feeding (feeding of the sheet in a state where the center in the sheet width direction is the same even when the sheet size is different). 
     As shown in  FIG. 3B , the first shutter member  681  is formed by cutting out both end portions  6814 ,  6815  of the peripheral surface of the cylindrical member by approximately half the circumference so that an opening  6813  is formed in a center portion  6812 . 
     The length in the longitudinal direction of the opening  6813  is substantially equal to the first size L 1  and the length in a transverse direction of the opening  6813  is set to be the same as or slightly larger than the length in the peripheral direction of the window  661  of the air blowing sleeve  66  (see the developed image of the shutter in  FIG. 3A ). 
     A gear  6816  is formed at a boundary between the first shutter member  681  and the duct  651  so as to be engaged with a pinion gear  6711  mounted on a drive axis of the drive motor  671 . 
     The second and third shutter members  682 ,  683  are symmetrical with respect to the longitudinal direction of the air blowing sleeve  66 , and as shown in the developed view of  FIG. 3A , each of the portions  6821 ,  6831  of the second and third shutter members  682 ,  683  surrounding openings therein openings thereof is composed of a portion orthogonal to an inclined portion with respect to the axis of the air blowing sleeve  66 . 
     Gears  6822 ,  6832  are formed at the end portions of the second and third shutter members  682 ,  683 , respectively, and are engaged with pinion gears  6721 ,  6731  mounted on drive axes of the drive motors  672 ,  673 , respectively. 
     In order to attach the first to third shutter members  681  to  683  to the air blowing sleeve  66  in such cooling device  60 , first, the second and third shutter members  682 ,  683  are inserted from both end portions of the air blowing sleeve  66 , a cap  6817  of the first shutter member  681  is removed, the first shutter member  681  is inserted into the air blowing sleeve  66  and the second and third shutter members  682  and  683 , and finally, the cap  6817  is mounted to the end portion of the first shutter member  681 . 
       FIGS. 4A to 4E  show an example in which an opening area of each window  661  of the air blowing sleeve  66  is variously changed by rotating the first to third shutter members  681  to  683  in the air blowing sleeve  66 . 
       FIGS. 5A and 5B  are schematic diagrams showing a state of temperature distribution in an axial direction of the pressurizing roller  42  of when switching is performed from a fixing job of predetermined pieces of small width sheets (hereinafter, referred to as “small size” sheet) to a fixing job of a large width sheet (hereinafter, referred to as “large size” sheet), and the fixing job is performed, in the fixing part  40 . 
     As shown in  FIG. 5A , in the case of a small size sheet, the cooling device  60  blows air to a sheet feeding region of the width L 1  to temperature T 1  (about 60° C. to 120° C.), and cools the other region (non-sheet feeding region) so that the temperature is temperature T 2  or lower (about 230° C.: T 2 &gt;T 1 ) that is a degree having no problem with durability of the pressurizing roller  42 , since the other region has no influence on a fixed image quality. 
     Then, when a large size sheet of the width L 2  is fed as the next fixing job, target temperature of the sheet feeding region of the pressurizing roller  42  is set to T 1  as shown in  FIG. 5B . However, since a region shown by oblique lines (a difference region between the sheet feeding region for the small size sheet and the sheet feeding region for the large size sheet) A is a non-sheet feeding region in the case of a small size sheet fixing job, the temperature is T 2 , and this portion needs to be quickly lowered to the target temperature T 1 . 
       FIG. 6A  is a diagram schematically showing a magnitude of the air blowing volume from each window  661  by the cooling device  60  at this time. The size of the arrow indicates the magnitude of the air blowing volume (that is, a cooling power). 
     As shown in the drawing, the window  661  that is in a range corresponding to a region where sheet feeding regions of a previous sheet and a next sheet overlap (Hereinafter referred to as “overlapping region”. This overlapping region is equal to the previous small size sheet width) C is shielded by the first shutter member  681  by about half, and the window  661  corresponding to ranges of a difference region A and a non-sheet feeding region B of the large size sheet, are made to have the large cooling power by fully opening the second and third shutter members  682 ,  683 . 
       FIG. 6B  is a schematic diagram showing a relationship between the developed view of the first to third shutter members  681  to  683  and each window  661  of the air blowing sleeve  66 , in this state. 
     The air blowing volume in the difference region A of the cooling device  60  is made larger than the air blowing volume of an overlapping region C in this manner, and thereby, the temperature of the difference region that is the temperature T 2  higher than the temperature T 1  can be quickly lowered to the temperature T 1 , and occurrence of image noise such as blisters in the difference region A is suppressed. 
     Such control of the air blowing volume of the cooling device  60  is performed by the control part  50 . 
     (3) Configuration of Control Part 
       FIG. 7  is a block diagram showing a main configuration of the control part  50  of the copying machine  1 . 
     As shown in the drawing, the control part  50  includes a central processing unit (CPU)  51 , a communication interface (I/F)  52 , a random access memory (RAM)  53 , a read only memory (ROM)  54 , an image processing part  55 , an image memory  56 , and the like. 
     The CPU  51  reads the control program from the ROM  54  at the time of turning on the power to the copying machine  1  and executes the control program with the RAM  53  as a work storage region. 
     The CPU  51  accepts a print job from another external terminal via a communication network such as a LAN by the communication I/F  52 . 
     The data of the print job received from the external terminal and the image data of R, G, and B read by the scanner part  10  is converted into density data of Y, C. M and K that are development colors, by the image processing part  55 , subjected to known image processing such as edge enhancement and smoothing processing, and then stored in the image memory  56 . 
     The CPU  51  controls operation of the image forming part  20 , the sheet feeding part  30 , and the fixing part  40  so as to smoothly perform printing operation, based on the image data of the document read by the scanner part  10  and the image data of the print job accepted from the external terminal via the communication I/F  52 . 
     The temperature sensor  412  detects the surface temperature at the center portion in the axial direction of the heating roller  41 . The control part  50  controls the electric power to be transmitted to the halogen heater  411  based on the temperature detected by the detected temperature so that the heating roller  41  reaches target fixing temperature. 
     The control part  50  monitors the sheet size related to the fixing job and controls the drive motors  671  to  673  of the cooling device  60 , thereby adjusting the opening area of each window  661 , so that temperature in each region of the pressurizing roller  42  is appropriate temperature. 
     (4) Air Blowing Volume Control of Cooling Device 
       FIG. 8  is a flowchart showing the procedure of the air blowing volume control of the cooling device  60  performed by the control part  50  This flowchart is performed as a subroutine of a main flowchart (not shown) for controlling the operation of the entire copying machine  1 . 
     In this flowchart, a case where a mixed job (a job in which printing of the large size sheet and printing of the small size sheet are mixed in a series of jobs) is performed for sheets of two types of sheet widths, will be described. 
     First, whether fixing is to be performed for the next sheet is determined (step S 11 ). In the present embodiment, for example, when a leading end of the sheet to be fixed next is detected by the sheet feeding sensor  401  (see  FIG. 1 ) arranged immediately front of the nip part of the fixing part  40 , in an upstream side of a sheet conveyance direction, it is determined to be “YES”. 
     When it is determined in step S 11  that fixing is to be performed (YES in step S 11 ), the size of the next sheet (the sheet size here is sufficient with only information on sheet width) is acquired (step S 12 ). 
     The sheet size can be acquired by the following method. First, when the job is a print job issued by an external terminal, since information on the sheet size is included in a header portion of the data of the print job, the sheet size can be acquired by reading the information by the control part  50 . 
     In addition, when the job is a copy job, since a document size detection part is generally provided in the document conveyance part  11  or the scanner part  10 , the corresponding sheet size can be obtained by acquiring a detection result of the detection part. 
     When a paper feeding cassette is selected and a print job is performed, the sheet size can be specified by a size detection sensor provided in the paper feeding cassette. 
     Alternatively, a sheet width detection part for detecting the sheet size may be separately provided in the middle of the conveyance path leading to the nip part of the fixing part  40 . 
     When the sheet size of the sheet to be fixed next is acquired in step S 12 , whether this sheet is larger than the sheet width previously fixed, is determined (step S 13 ). 
     The sheet size acquired in step S 12  is temporarily stored in the RAM  53  and is used for comparison with the sheet width of the next sheet in step S 13 . 
     When it is determined to be “YES” in step S 13 , information on the difference region between the sheet related to the previous fixing and the sheet to be fixed next is acquired (step S 14 ). 
     When the sheet widths of the previous time and the next time are specified, the difference region can be easily determined by comparing the sheet widths, and the window  661  corresponding to the difference region is specified. It is preferable that the size and interval of each window  661  are determined such that at least one window  661  is substantially opposed to the difference region of various sheet sizes. 
     Then, from the information on the difference region, the movement amount (rotation amount) of the first to third shutter members  681  to  683  is calculated (step S 15 ). In the case of the present embodiment, as shown in  FIG. 6A , the opening ratios of the window  661  corresponding to the difference region A and the non-sheet feeding region B of the next sheet are equally maximized, and the opening ratio of the overlapping region C (that is, the sheet feeding region of the small size sheet) is set to approximately 50%. 
       FIG. 6B  is a schematic diagram showing the positions of the first to third shutter members  681  to  683  in developed view, of when the opening ratio of each window  661  is set as described above. 
     The drive motors  671  to  673  ( FIG. 2 ) are driven to rotate and move each of the first to third shutter members  681  to  683  by the calculated movement amount (step S 16 ). 
     A well-known technique is applied to the rotation control of each of the drive motors  671  to  673 . 
     For example, when a stepping motor is used as the drive motors  671  to  673 , since a rotation angle can be controlled by the number of drive pulses output to the stepping motor, the reference position (home position) is first determined, a drive pulse of the predetermined count number is output from the reference position to a driver (not shown) of the stepping motor, and thereby, the rotation amount can be controlled. 
     When the drive motors  671  to  673  are DC motors incorporating encoders, the rotation amount can also be controlled by counting the output pulses of the encoder from the reference position. 
     A table related to the opening ratio (or the movement amounts of the first to third shutter members  681  to  683 ) of the window  661  corresponding to the sheet widths of the previous sheet and the next sheet and the difference region A, the non-sheet feeding region B, and the overlapping region C at that time, is stored in the ROM  54 , and the CPU  51  refers to the table and performs step S 16 . 
     In step S 13 , if the sheet width of the next sheet is not larger than the previous sleet (NO in step S 13 ), that is, (a) when the sheet width of the next sheet has the same sheet width as the previous sheet, or (b) when the sheet width of the next sheet is smaller than the sheet width of the previous sheet, step S 14  is skipped, the process moves to step S 15 , and the movement amount of the shutter is calculated. 
     In the case of (a), the air blowing volume from each window  661  is not particularly changed, and in the case of (b), an opening area of each window  661  is set so that the cooling power of the non-sheet feeding region is stronger than the sheet feeding region for the small size sheet. 
     When fixing of the current sheet is completed, the presence or absence of the next sheet is determined (step S 17 ). If there is a next sheet (YES in step S 17 ), steps S 11  to S 16  are repeated. If there is no next sheet, the air blowing volume control is terminated and the process returns to the main flow chart. 
     If the number of continuous fixing sheets of the large size sheet after the small size increases, the temperature in the difference region A may be lower than the lower limit of the appropriate range (60° C. to 120° C.). For such a case, a temperature sensor that detects the surface temperature of the pressurizing roller  42  in the difference region A is provided, the detection result is monitored, and before the temperature in the difference region A reaches the lower limit of the appropriate range, the air blowing volume may be controlled so as to be the same as that of the overlapping region C. 
     As described above, according to the present embodiment, when the large size sheet fixing job is performed after the previous small size sheet fixing job, the air blowing volume in the difference region A of the pressurizing roller  42  is set to larger than the air blowing volume to the overlapping region C where sheet feeding regions for the small size and the large size sheets are superimposed so that the cooling capacity for the difference region A is increased. Thus, the occurrence of image noise such as blisters in the difference region A can be suppressed. 
     &lt;Modification&gt; 
     Although the present invention has been described on the basis of the embodiment, the present invention is of course not limited to the embodiment described above, and the following modifications are conceivable. 
     (1) In the above embodiment, the air blowing volume in the overlapping region C is made constant. However, when the small size sheet fixing job is continuously performed, in the large size sheet fixing job performed thereafter, the temperature of the overlapping region C of the pressurizing roller  42  may be lower than the appropriate range. When only the fixing of a sheet having a low toner density is performed many times, the temperature in the sheet feeding region may be higher than the appropriate range. 
     Therefore, in the present modification, the temperature of the overlapping region C of the pressurizing roller  42  is detected, and the air blowing volume in the overlapping region C is also changed on the basis of the detection. 
     In this modification, a temperature sensor (not shown) that detects the temperature of the surface of the sheet feeding region (desirably, the axial center portion) for the small size sheet of the pressurizing roller  42  is provided. 
       FIG. 9  is a flowchart showing the procedure of the air blowing volume control performed by the control part  50  in the present modification. 
     What is greatly different from the flowchart in  FIG. 8  is that step S 101  of detecting the pressurizing roller center portion temperature is inserted after the difference region is acquired in step S 14 . 
     In the calculation of the movement amount of the shutter in step S 15 , first, based on the information on the difference region acquired in step S 14 , the movement amounts of the second and third shutter members  682 ,  683  are determined so that the air blowing volumes in the difference region A and the non-sheet feeding region B are increased, and when the detected temperature in step S 101  is lower than predetermined temperature (for example, 60° C.), the movement amount of the first shutter member  681  is determined so that the air blowing volume in the overlapping region C is decreased, and when the detected temperature in step S 101  is higher than predetermined temperature (for example, 120° C.), the movement amount of the first shutter member  681  is determined so that the air blowing volume in the overlapping region C is increased. 
     For example, a table related to the movement amount of the first shutter member  681  is stored in the ROM  54  in association with the temperature of the overlapping region C. and the CPU  51  determines the movement amount of the first shutter member  681  based on the table. 
     Then, the movement of the corresponding shutter member is performed based on the above determined movement amounts of the first to third shutter members  681  to  683  (step S 16 ). 
     Since the other steps are the same as those in  FIG. 8 , the description thereof will be omitted. 
       FIGS. 10A and 10B  are diagrams showing an example of when all windows  661  corresponding to the overlapping region C are shielded by the first shutter member  681 , since the temperature becomes too lower than the predetermined value during cooling of the overlapping region C of the pressurizing roller  42  by a predetermined air blowing volume. 
     That is, in  FIG. 10A , since the temperature of the center portion of the pressurizing roller  42  is in a temperature range not affecting the image quality, the opening ratio of the window  661  in the overlapping region C is set to about 50%. However, when the temperature of the center portion of the pressurizing roller  42  is lower than the appropriate range, the window  661  in the overlapping region C may be shielded by 100% by the first shutter member  681  as shown in  FIG. 10B . 
     Since the air blowing volume of the fan device  65  is constant, as a result of shielding of the window  661  in the overlapping region C, the air blowing volumes to the difference region A and the non-sheet feeding region B further increase, and the cooling effect in this region can be enhanced. 
     The fact that the temperature of the pressurizing roller  42  in the overlapping region C drops down is considered to be one of the reasons that the number of small size sheets to be fixed is large. It is considered that, during that time, the temperature in the difference region A that is the non-sheet feeding region for the small size sleets in which the temperature has not taken away by the sheet, further increases. Thus, it is preferable that the air blowing volume of the difference region A increases as described above. 
     In order to increase the air blowing volume in the difference region A, control may be performed so as to reduce the opening ratio of the window  661  in the overlapping region C as described above, and increase the output of the fan device  65 . 
     (2) In the above embodiment, the air blowing volumes of the difference region A and the non-sheet feeding region B are equalized. However, when the temperature of the difference region A is abnormally high, it is preferable that cooling of the difference region A is prioritized over the non-sheet feeding region B, so that the image noise is prevented. 
     In the present modification, a temperature sensor that detects the surface temperature of the pressurizing roller  42  in the difference region A is provided, and the cooling volume in the difference region A is particularly controlled based on the result. 
       FIG. 11  is a flowchart showing the procedure of the air blowing volume control performed by the control part  50  in the present modification. 
     The difference from the flowchart of  FIG. 8  is that steps S 201  to S 205  are inserted in the middle of the flowchart. 
     When it is determined in step S 13  that the sheet width of the next sheet is larger than the sheet width of the previous sheet (YES in step S 13 ), the difference region A is acquired (step S 14 ) and a flag F is set to “1”. This flag is stored, for example, in the RAM  53 . 
     Then, the surface temperature in the difference region A of the pressurizing roller  42  is detected (step S 202 ). 
     In calculation of the movement amount of the shutter in step S 15 , when the detected temperature in step S 202  described above is higher than predetermined temperature (for example, 150° C.), the movement amount of the first to third shutter members  681  to  683  is determined so that a relationship of “the air blowing volume in the difference region A&gt;the air blowing volume in the non-sheet feeding region B&gt;the air blowing volume in the overlapping region C” is satisfied. 
     In step S 16 , the movement of the corresponding shutter member is performed based on the movement amounts of the first to third shutter members  681  to  683  determined in step S 15  described above. 
     If there is a next sheet (YES in step S 17 ), the flowchart is circulated, and when it is determined that the sheet width of the next sheet is not larger than the sheet width of the previous sheet in step S 13  (NO in step S 13 ), and further, whether the sheet widths of the previous sheet and the next sheet are the same is determined (step S 203 ), and when they are the same (YES in step S 203 ), whether the flag F=1 is satisfied is determined (step S 204 ). If F=1 is satisfied (YES in step S 204 ), temperature detection of the difference region A of winch temperature is already detected, is performed again (step S 202 ), and the movement amount of the shutter is calculated based on the temperature result (step S 15 ). 
     If the detected temperature in step S 202  becomes lower than predetermined temperature (for example, (120°) C), the movement amounts of the first to third shutter members  681  to  683  are calculated so that the air blowing volume of the state shown in  FIG. 6A , or the air blowing volumes of the difference region A and the overlapping region C are equalized with each other. 
     When it is determined in step S 203  that the sheet width of the next sheet is not the same as the sheet width of the previous sheet, that is, the sheet width of the next sheet is smaller (NO in step S 203 ), the difference region A becomes the non-sheet feeding region of the next small size sheet. Thus, the process proceeds to step S 205 , the flag F is set to “0”, step S 202  for detecting the temperature of the difference region is skipped, and calculation of the movement amount of the shutter for the small size sheet is performed (step S 15 ). That is, the movement amount of each shutter is calculated so that the air blowing volume of the non-sheet feeding region is larger than the air blowing volume of the sheet feeding region of the small size sheet, by a predetermined amount. 
     When it is determined in step S 204  that the flag F=1 is not satisfied (NO in step S 204 ), step S 202  for detecting the temperature of the difference region is skipped, and the moving amount of each shutter is calculated so that, with respect to the sheet width of the current sheet, the air blowing volume of the non-sheet feeding region is larger than the air blowing volume of the sheet feeding region, by a predetermined amount (step S 15 ). 
     In step S 16 , the movement of the corresponding shutter member is performed based on the movement amounts of the first to third shutter members  681  to  683  determined in step S 15  described above. 
     Since the other steps are the same as those in  FIG. 8 , the description thereof will be omitted. 
       FIGS. 12A and 12B  are schematic diagrams showing an example of a case where the air blowing volume of each part is controlled by the first to third shutter members  681  to  683 , since the temperature in the difference region A of the pressurizing roller  42  is higher than a predetermined value. 
     As shown in  FIG. 12A , the window  661  in the difference region A is fully opened by the second and third shutter members  682 ,  683 , and the window  661  in the non-sheet feeding region B is shielded by about half (see a development view of the first to third shutter members  681  to  683  of  FIG. 12B ). 
     At this time, the shielding rate of the window  661  by the first shutter member  681  is set so as to be larger than the shielding rate of the window  661  in the non-sheet feeding region B. This is because the temperature of the non-sheet feeding region B is higher than that of the overlapping region C. and the necessity of cooling is high. 
     Since the air blowing volume from the fan device  65  is constant, by setting the opening state of each window  661  as described above, the air blowing volume in the difference region A becomes the largest, and the cooling effect in this portion can be enhanced. 
     (3) When the job to be performed is a mixed job, in a model capable of selecting a speed priority mode (a mode in which print speed is prioritized) and an image quality priority mode (a mode in which fixing image quality is prioritized over the print speed), the air blowing volume control may be performed as follows. 
     In this modification, a temperature sensor for detecting the surface temperature of the pressurizing roller  42  in at least the difference region A and the overlapping region C is installed. 
       FIG. 13  is a flowchart showing the procedure of the air blowing volume control performed by the control part  50  in the present modification. 
     First, whether fixing is to be performed is determined (step S 11 ). In this modification, a sheet feeding sensor is arranged immediately front of the registration roller  34  in the upstream side in the sheet conveyance direction, and when the leading end of the next sheet is detected by the sheet feeding sensor, it is determined that the fixing of the sheet is performed. 
     When fixing is performed (YES in step S 11 ), whether the current print mode is the image quality priority mode is determined (step S 301 ). 
     Selection between the image quality priority mode and the speed priority mode may be made by the user through the operation panel  70  or may be instructed by the printer driver when a print job is issued from the terminal. Alternatively, the control part  50  may analyze the type (for example, a photo image or a text image) of the image of each page in a print job or a copy job, to set the mode to the image quality priority mode in the case of a photographic image, and set the mode to the speed priority mode in the case of a text image. 
     In step S 301 , when the image quality priority mode is not selected, that is, when the speed priority mode is selected (NO in step S 301 ), the sheet is fed as it is and the fixing job is performed (step S 305 ). 
     When it is determined in step S 301  that the image quality priority mode is selected (YES in step S 301 ), the size of the sheet to be fixed next is acquired (step S 12 ), and when the size is larger than the sheet width of the previously fixed sheet (YES in step S 13 ), the difference region is acquired (step S 14 ), and the surface temperature of the pressurizing roller  42  in each of the difference region A and the overlapping region C is detected (step S 302 ). 
     The movement amounts of the first to third shutter members  681  to  683  are calculated based on the detected temperature (step S 15 ). 
     For example, a table showing the shielding rate of each of the first to third shutter members  681  to  683  is stored in the ROM  54  according to the temperature range of each of the regions A, C, and the CPU  51  calculates the movement amount of each shutter on the basis of the table. 
     Then, each of the first to third shutter members  681  to  683  is moved by the calculated movement amount (step S 16 ). 
     Next, whether the temperature in the difference region A and the overlapping region C is within the appropriate range is determined (step S 303 ). When the temperature is within the appropriate range (YES in step S 303 ), the paper is fed as it is (step S 305 ), and the fixing job is performed. 
     When it is determined in step S 303  that the temperature is not within the appropriate range (NO in step S 303 ), sheet feeding of the next sheet to the fixing part  40  is stopped (step S 304 ), and whether the temperature is within the appropriate range is determined again (step S 303 ). When the temperature is within the appropriate range (YES in step S 303 ), the paper is fed and the fixing job is performed (step S 305 ). 
     The stop of paper feeding to the fixing part  40  in step S 304  is performed by lengthening the stop time of the registration roller  34  and stopping image forming operation in the process units  20 Y to  20 K. 
     When it is determined in step S 303  that the surface temperature of the pressurizing roller  42  in the difference region A and the overlapping region C is within the appropriate range (YES in step S 303 ), the image forming operation in the process units  20 Y to  20 K is started, and the rotation of the registration roller  34  is started in accordance with the timing at which the color image transferred to the intermediate transfer belt  26  reaches the transfer position, so that the next sheet is fed to the fixing part  40  (step S 305 ). 
     In step S 301 , when it is determined that the width of the next sheet is not larger than the width of the previous sheet (NO in step S 301 ), step S 14  is skipped. 
     In this case, since there is no difference region A, in step S 15 , the movement amount of the shutter is calculated only by the temperature of the overlapping region C. 
     After the above processing is performed, the presence of the next sheet is determined (step S 17 ). When there is a next sheet (YES in step S 17 ), the process returns to step S 11  and steps of thereafter are repeated. When it is determined that there is no next sheet in step S 17  (NO in step S 17 ), the process returns to the main flowchart. 
     Since the difference region A of the pressurizing roller  42  having the highest temperature most influences on the image quality, only the surface temperature in the difference region A may be detected in step S 302 , and in step S 303 , whether the temperature in the difference region A is within the appropriate range may be determined. 
     In the present modification, the determination step of whether the mode is the image quality priority mode of step S 301  may be moved so as to be performed next to the shutter movement step of step S 16 . 
     In this case, regardless of whether the mode is the image quality priority mode or not, after steps S 11  to S 14 , S 302 , and S 15  to S 16  are performed first, then, whether the image quality priority mode is set is determined, and steps S 303  and S 304  are performed only when the image quality priority mode is set. When the image quality priority mode is not set, that is, in the case of the speed priority mode, steps S 303  and S 304  are skipped. 
     (4) In addition to the above embodiment or modifications (1) to (3), a temperature sensor that detects the surface temperature of the non-sheet feeding region B of the pressurizing roller  42  is provided, and the air blowing volume of the cooling device  60  may be controlled on the basis of the detection result of this temperature sensor, so that the temperature of the non-sheet feeding region B is within the predetermined appropriate temperature range. 
     (5) In the above embodiment, the air blowing volume of the cooling device  60  can be uniformly changed by the first shutter member  681  for the sheet feeding region for the small size sheet width, and the air blowing volume of the difference region and the non-sheet feeding region for the large size sheet can be changed by the second and third shutter members  682 ,  683 . According to this, in the case of using sheets of two kinds of sheet widths, the control of the air blowing volume is limited. 
     When sheets of three or more kinds of sheet widths are used, it is desirable that the air blowing volume can be controlled in a finer region. 
       FIG. 14  is a schematic view showing the configuration of the cooling device  60  according to the present modification, and the portion of the duct  62  is shown with a side plate on the front side of the drawing removed for easy understanding of the internal structure. 
     As shown in the drawing, the width in the axial direction of the pressurizing roller  42  at a blowing port of the duct  62  of the cooling device  60  according to the present modification is substantially the same as the roller portion of the pressurizing roller  42 , the inside of the duct  62  is divided into three sub ducts  621 ,  622 ,  623  by partition walls  624 ,  625 , and air blowing ports of the fan devices  611  to  613  are connected to the openings  621 A to  623 A of the respective sub ducts. 
     A nozzle portion  63  at the tip of each of the sub ducts  621  to  623  is divided into six small nozzles  631  by a plurality of partition walls  632 , respectively, whereby eighteen small nozzles  631  in total are arranged side by side along the sheet width of the maximum size. 
     Each small nozzle  631  is provided with an opening and closing mechanism for opening and closing the air blowing port. 
       FIG. 15  is a schematic view of when the nozzle portion  63  of the duct  62  is viewed from the right direction in  FIG. 14  in order to explain the configuration of the opening and closing mechanism  64 . 
     As shown in the drawing, the opening and closing mechanism  64  includes a shutter member  646  swingably provided at a tip opening portion of the small nozzle  631 , a swing lever  646   a  attached to the shutter member  646 , and an actuator  647  in which a base end portion is pivotally supported by a support axis  647   a  with respect to the small nozzle  631 , and a tip of the rod portion is connected to an end portion of the swing lever  646   a  by a pin  647   b.    
     The air blowing volume from the small nozzle  631  is controlled by tilting the swing lever  646   a  in the left direction in the drawing by the actuator  647  by a predetermined amount. 
     The type of the actuator  647  is not limited, and any kind of mechanism may be used as long as it is a mechanism for driving the shutter member  646  to open or close, in which, for example, a linear motor, a motor and a cam mechanism, a crank mechanism, a screw feeding mechanism or the like are combined. 
     The air blowing volume can be selectively changed by an instruction from the control part  50  by the fan devices  611  to  613  and the opening and closing mechanism  64  provided at the tip opening portion of each small nozzle  631 . Thus, even when a small size sleet is changed to a large size sheet with respect to sheets of different kinds of sheet widths, an appropriate air blowing volume in the overlapping region, the difference region, and the non-sheet feeding region can be set. 
     As the shutter member  646 , a configuration similar to that of a diaphragm mechanism of a camera can be used. The shutter member  646  may be disposed so as to be slidable in the vertical direction. 
     In the present modification, although three fan devices are used, one fan device may be used as in the embodiment. 
     (6) When the cooling device  60  capable of controlling the air blowing volume for each small nozzle is used as in the modification of above (5), the air blowing volume can be controlled in consideration of the toner amount (toner density) transferred onto the sheet as follows. 
       FIG. 16  is a flow chart showing the procedure of air blowing volume control according to the present modification. 
     What is different from the flowchart of  FIG. 8  in the embodiment is: that density distribution acquisition processing (step S 401 ) in the width direction is provided after the difference region acquiring processing of step S 14 , and the contents of calculating processing of the movement amount of the shutter in step S 15 . 
     That is, when it is determined in step S 13  that the sheet width of the next sheet is larger than the sheet width of the previous sleet (YES in step S 13 ), the difference region between the small size sheet and the large size sheet is acquired (step S 14 ). Further, a distribution (density distribution) in the sheet width direction (main scanning direction) of the toner amount transferred onto the next large size sheet is acquired. 
     With respect to RIP data of the image formed on the sheet, the density distribution is obtained by integrating the density value of each pixel in the sub-scanning direction, creating a density histogram in the main scanning direction, comparing the density histogram with a predetermined threshold, and segmenting the density histogram into some stages from a low density region to a high density region. 
     The density distribution is created by the CPU  51  of the control part  50  based on the image data received from the terminal, the image data read by the scanner, or the image data already stored and filed in the image memory, in the case of a print job. The toner image formed on the intermediate transfer belt  26  ( FIG. 1 ) may be read by a line sensor or the like so that the density data is obtained. 
     In step S 15 , the movement amount of each shutter member is calculated based on the range of the difference region and the density distribution. 
       FIG. 17  is a schematic diagram showing the size relationship between the air blowing volumes from each air blowing port in the case where the density distribution in the main scanning direction is divided into two density regions of a high density region D 1  and a low density region D 2  with reference to a certain threshold, in the present modification. 
     As shown in the drawing, in step S 15 , the movement amount of the shutter is determined according to the following rule. 
     (a) The air blowing volume of the difference region A is larger than the air blowing volume of the overlapping region C. 
     (b) The air blowing volume for the low density region (low density region D 2 ) of the sheet feeding region of the large size sheet (A+C) is larger than the air blowing volume for the high density region (high density region D 1 ). 
     (c) The air blowing volume of the non-sheet feeding region B of the large size sheet is larger than the air blowing volume to the overlapping region C. 
     The reason why the air blowing volume in the low density region D 2  is made larger than the air blowing volume in the high density region D as in above (b) is because a large amount of heat is absorbed by the amount of adhered toner, and thereby, it is not necessary to cool the high density region D 1 , as much as the low density region D 2 . 
     Returning to  FIG. 16 , in step S 16 , each shutter member is moved based on the movement amount calculated in the manner described above in step S 15 , and air blowing is performed. 
     Since the other steps are the same as those in  FIG. 8 , the description thereof will be omitted. 
     Such air blowing volume control is particularly effective for an image in which a photographic image and a text image are separately displayed in the main scanning direction. 
     (7) In the above embodiment, when the width of the next sheet is wider than the previous sheet, when the leading end of the next sheet is detected by the sheet feeding sensor  401 , the air blowing volume in the difference region A is controlled to be larger than the air blowing volume in the overlapping region C. 
     However, for example, when a print job accepted from another terminal is performed, in what number of sheets the sheet is changed from the small size sheet to the large size sheet can be acquired in advance by the control part  50 . Thus, the portion to be the difference region in the non-sheet feeding region of the small size sheet may be cooled slightly stronger than the other non-sheet feeding regions, from when the fixing job of the small size sheet is performed. 
     (8) In the above embodiment, as shown in  FIG. 1 , the cooling device  60  is disposed at a position to cool an opposite portion from the nip part of the pressurizing roller  42 , but the present invention is not limited thereto. 
     However, when the cooling device  60  is provided in the vicinity of the position where the sheet enters the nip part, air striking the peripheral surface of the pressurizing roller  42  flows upward along the peripheral surface and hits against the leading end of the sheet. Thus, the sheet may flap to damage the leading end of the sheet. Conversely, when the cooling device  60  is provided in the vicinity of the sheet discharge side of the nip part, the sheet after fixing flaps, and when a sheet is still present in the nip part, the sheet may flap, which may cause fixing failure and image disturbance. Thus, it is desirable that the cooling device  60  is disposed at a position that has as little influence on sheet conveyance as possible. 
     However, air is inevitably likely to be pulled along the direction of rotation of the pressurizing roller  42 , and the air from the cooling device  60  may be carried in a direction in which the sheet enters the nip part. 
     Therefore, just before the leading end of the sheet enters the nip part, the air blowing volume may be controlled to be temporarily reduced. The region for reducing the air blowing volume may be the entire region of the pressurizing roller  42  or may be the region where the air blowing volume is relatively large. 
     For example, the air blowing volume of the cooling device  60  may be controlled to be entirely (or partly) reduced during time t (this time t is determined in advance by dividing the conveyance path length from a detection position by the sheet feeding sensor  401  to the nip part by conveyance speed, and is stored in the ROM  54 ) from after the leading end of the sheet is detected by the sheet feeding sensor  401  ( FIG. 1 ) that is before the nip of the fixing part  40 , to when the leading end of the sheet is nipped by the nip part. 
     (9) In the above embodiment, although only one air blowing sleeve  66  is provided in the cooling device  60 , another air blowing sleeve  66 ′ may be disposed parallel to the air blowing sleeve  66  as shown in  FIG. 18 . In the present modification, a movable shutter is not provided over windows  661 ′ in the air blowing sleeve  66 ′, a constant air blowing volume is always maintained over the entire length of the pressurizing roller  42 , and the first to third shutter members  681  to  683  in the air blowing sleeve  66  are moved to change the air blowing volume. 
       FIGS. 19A to 19C  are schematic diagrams showing an example of control of the air blowing volume in the present modification. The air blown from a fan device  65 ′ is split into air blowing sleeves  66 ,  66 ′ via a common duct  651 ′, and cools the surface of the pressurizing roller  42  with the air volume according to the opening area of each window. 
       FIG. 19A  shows an example in which the cooling of the non-sheet feeding region for the large size sheet is made larger than the cooling of the sheet feeding region.  FIG. 19B  corresponds to the air blowing volume control in  FIGS. 6A and 6B .  FIG. 19C  corresponds to the air blowing volume control in  12 A. 
     A movable shutter is provided in the air blowing sleeve  66 ′ as similar to the air blowing sleeve  66 , the shielding ranges of the shutters in the longitudinal direction of the air blowing sleeve  66 ′ are set to be different from the first to third shutter members  681  to  683 , and thereby, the control of the air blowing volume can be more diversified. 
     (10) In the above embodiment, the description has been made mainly on the air blowing volume control at the time of performing the mixed job. However, similar control can be performed even when, after the series of first jobs on the small size sheet are performed, another second job is performed for the large size sheet. 
     (11) In the above embodiment, an example of the fixing apparatus using the heating roller  41  and the pressurizing roller  42  as the heating member and the pressurizing member has been described. However, the fixing apparatus may have a configuration in which a fixing belt and a long pad-like pressurizing member form the nip part. The heat source is not limited to the halogen heater, and may be a method of electromagnetic induction heating the heat generation layer of the fixing belt by using an excitation coil, a method of heating the heating roller with a resistance heating element, or the like. 
     In short, any type of fixing apparatus can be applied as long as the fixing apparatus has a configuration in which a nip part is formed by a heating member and a pressurizing member that are long and disposed in parallel with each other, and a sheet is fed to the nip part and fixed. 
     (12) In the above embodiment, control of the air blowing volume in the fixing job of two kinds of sheet widths has been described. However, even when the kinds of sheet widths are three or more, if the sheet width of the next sheet is larger than the sheet width of the previous sheet, only the ranges of the difference region A, the non-sheet feeding region B, and the overlapping region C differ according to the difference of the sheet widths. Thus, the present invention can be applied. Particularly, when the modifications shown in  FIG. 11  and  FIG. 13  are performed, since the difference region A differs depending on the combination of the sheet widths, there is a case where a plurality of temperature sensors are required to detect the temperature of the different difference regions A. 
     (13) In the above embodiment, a tandem type color copying machine has been described. However, the present invention is not limited thereto, and a facsimile machine or a printer exclusive machine may be used as long as it includes a fixing apparatus. A monochrome image forming apparatus also may be used. 
     (14) Specific values such as an appropriate temperature range, a threshold, a shielding rate of each window described in the above embodiment and modifications can be appropriately determined by those skilled in the art. 
     The above embodiment and modifications may be freely combined as long as they do not depart from the gist of the present invention. For example, in the embodiment and all modifications, steps similar to steps S 303  to S 305  in  FIG. 13  can be provided irrespective of whether or not the image quality priority mode is set, so that the feeding of the next sheet is stopped at least until when the temperature in the difference region A drops to predetermined temperature. 
     The present invention is suitable as a technique for cooling a pressurizing member in a fixing apparatus to prevent generation of image noise. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.